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Center for Nanoscale Materials

CNM Seminar Series

The Center for Nanoscale Materials (CNM) hosts a seminar series to enhance multidisciplinary collaboration.

Date Title

October 15, 2019

11:00 am

Bldg. 440, Room A105/A106

Polymer Informatics: Current Status & Critical Next Steps”, Rampi Ramprasad, Materials Science and Engineering, Georgia Institute of Technology, Host:  Subramanian Sankaranarayanan

The Materials Genome Initiative (MGI) has heralded a sea change in the philosophy of materials design. In an increasing number of applications, the successful deployment of novel materials has benefited from the use of computational, experimental and informatics methodologies. Here, we describe the role played by computational and experimental data generation and capture, polymer fingerprinting, machine-learning based property prediction models, and algorithms for designing polymers meeting target property requirements. These efforts have culminated in the creation of an online Polymer Informatics platform (https://​www​.poly​mergenome​.org) to guide ongoing and future polymer discovery and design [1-3]. Challenges that remain will be examined, and systematic steps that may be taken to extend the applicability of such informatics efforts to a wide range of technological domains will be discussed. These include strategies to deal with the data bottleneck, new methods to represent polymer morphology and processing conditions, and the applicability of emerging algorithms for design. 

[1] C. Kim, A. Chandrasekaran, T. D. Huan, D. Das, R. Ramprasad, Polymer Genome: A Data-Powered Polymer Informatics Platform for Property Predictions,” Journal of Physical Chemistry C, J. 122, 31, 17575-17585 (2018).
[2] A. Mannodi-Kanakkithodi, A. Chandrasekaran, C. Kim, T. D. Huan, G. Pilania, V. Botu, R. Ramprasad, Scoping the Polymer Genome: A Roadmap for Rational Polymer Dielectrics Design and Beyond”, Materials Today, 21, 785 (2018).
[3] R. Ramprasad, R. Batra, G. Pilania, A. Mannodi-Kanakkithodi, C. Kim, Machine Learning and Materials Informatics: Recent Applications and Prospects”, npj Computational Materials 3, 54 (2017).

BIO: Prof. Ramprasad is presently the Michael E. Tennenbaum Family Chair and Georgia Research Alliance Eminent Scholar in the School of Materials Science & Engineering at the Georgia Institute of Technology. His expertise is in the virtual design and discovery of application-specific materials using computational and data-driven methods. Among his notable projects are a ONR-sponsored Multi-disciplinary University Research Initiative (MURI) in the past to accelerate the discovery of polymeric capacitor dielectrics for energy storage. He is presently leading another MURI aimed at the understanding and design of dielectrics tolerant to enormous electric fields. Prof. Ramprasad is a Fellow of the American Physical Society, an elected member of the Connecticut Academy of Science and Engineering, and the recipient of the Alexander von Humboldt Fellowship and the Max Planck Society Fellowship for Distinguished Scientists. He has authored or co-authored over 180 peer-reviewed journal articles, 6 book chapters and 4 patents. He has delivered over 150 invited talks at Universities and Conferences worldwide, and has organized several international symposia. Prof. Ramprasad received his B. Tech. in Metallurgical Engineering at the Indian Institute of Technology, Madras, India, an M.S. degree in Materials Science & Engineering at the Washington State University, and a Ph.D. degree also in Materials Science & Engineering at the University of Illinois, Urbana-Champaign.

October 7, 2019

2:00 pm

Bldg. 440, Room A105/A106

Hybrid van der Waals Heterosctuctures Composed of Conventional Semiconductors and Two-Dimensional Materials, Jinkyoung Yoo, Center for Intergrated Nanotechnologies, Los Alamos National Laboratory.  Host: Xuedan Ma

Emerging nanomaterials have attracted much attention due to their novel functionalities, but have also been hindered by lack of scalable synthesis and of ways of controlling characteristics. Atomically thin two-dimensional (2D) materials are good examples of novel materials set promising exotic properties and requiring established manufacturing approaches for practical applications. Heterostructuring is a powerful and general strategy to control physical properties of materials. Moreover, heterostructuring can offer novel characteristics differentiating the heterostructure from individual component in a structure. Recently, 2D/2D heterostructures prepared by stacking are being explored to observe quantum phenomena. However, fabrication of 2D/2D heterostructures has been limited by difficulty in preparation of individual 2D layers in controlled manner. Heterostructuring with 2D and conventional materials in other dimensions (e.g. bulk-like structure for 3D and nanowires for 1D) has shown great potential for multi-dimensional heterostructures.

In this presentation I’ll discuss how to prepare multi-dimensional heterostructures composed of 2D and conventional materials. The experimental approach is epitaxial growth Si, Ge, and ZnO on various 2D materials including graphene, hexagonal boron nitride, transition metal dichalcogenides. Absence of surface dangling bonds on a 2D material provides a unique opportunity to overcome materials compatibility issues. Nucleation strategy and novel characteristics of multi-dimensional heterostructures will be discussed in detail.

September 27, 2019

11:00 am

Bldg. 440, Room A105/A106

Synchrotron X-ray STM Investigation of Nanoscale Materials, Hao Chang, Plasma Science & Fusion Center, Massachusetts Institute of Technology, Host:  Saw Wai Hla and Volker Rose

To date many emerging techniques have been combined with STM to discover and explore new phenomena. On top of the overview of the development of the Synchrotron X-ray STM (SXSTM), this talk explicitly demonstrates novel application of SXSTM which combines synchrotron X-ray and scanning tunneling microscopy to study magnetic, electronic, and structural properties of materials interfaces. A nanofabricated tip is used to capture X-ray magnetic circular dichroism and near edge X-ray absorption fine structure signals, which explain charge transfer and magnetic properties of oxide materials interfaces with chemical and elemental sensitivities. Using X-ray absorption spectroscopy and spectroscopic imaging, the effect of charge transfer at the interfaces formed by transition metals of cobalt and nickel in nanoscale clusters and islands on a Cu (111) surface has been explored. Finally, X-ray standing wave formed by the interference of the incident and diffracted X-ray beams is used to characterize the structural properties of a cobalt thin film grown on a Au (111) surface. These results open novel research directions where material characterizations will be able to perform simultaneous chemical, structural and magnetic contrast potentially down to atomic scale.

September 26, 2019

11:00 am

Bldg. 440, A105/A106

Illuminating the Role of Nanoscale Defects on Diminished Semiconductor Performance by Scanning Probe Microscopy. Sarah Wieghold, Department of Chemistry and Biochemistry, Florida State University.  Host:  Saw Wai Hla and Volder Rose.

Nanomaterials attract great attention in the development of tunable energy conversion and storage systems for renewable energy vectors. Their great potential is related to a high material efficiency and optical/electrical properties that can be tuned by size, shape and interaction with the solid support or solvents. However, while their macroscopic ensemble properties have been extensively studied by e.g. time-resolved optical spectroscopy, X-ray diffraction or efficiency measurements of entire device architectures, the properties on the scale of individual atoms or molecules are still vastly unexplored. One reason is the fundamental mismatch between the spatial extension of optical fields and the electron wave functions in atoms or molecules, which hinders access to the photophysical processes in close proximity to where they occur. As a result, it often remains difficult to trace the origin of the macroscopically measurable properties and identify the root cause of e.g. PCE drop in solar cells, non-emissive losses in LEDs or material degradation and pinpoint whether these mechanisms are determined by the bulk, surface, interlayers or defect properties of the material.

Here I will present an approach to investigate charge carrier mechanisms at the interface of bulk perovskite thin films and create a link to their elemental composition by using synchrotron-based X-ray fluorescence and atomic force microscopy. To further investigate light-matter interactions at the nanoscale for various types of nanomaterials, I utilize single molecule absorption detected by scanning tunneling microscopy. This technique is based on a change in the local density of states upon photon absorption, and thus visualizes the localized excitation. Taking advantage of Stark shifts caused by the applied electric field in the STM, different energy levels can be tuned into resonance with the excitation wavelength.

September 25, 2019

11:00 am

Bldg. 440, Room A105/A106

Time-resolved X-ray Absorption Spectroscopy (TR-XAS): Watching Intermediates Dance, Cunming Liu, XSD/APS, Argonne National Laboratory.  Host:  Saw Wai Hla and Volker Rose 

The introduction of pump-probe techniques to the field of X-ray absorption spectroscopy (XAS) has allowed the monitoring of both electronic and structural evolution between intermediates of photoreaction systems with unprecedented accuracy, both in time and in space. In this talk, I will at first present the TR-XAS technique at APS sector 11-ID-D, which has been developed in the ultrafast laser pump-synchrotron X-ray probe configuration. Then, I will present the application of our TR-XAS technique to measure two representative photoreaction sample systems. In the solution case of spin-crossover (low spin (LS) ↔ high spin (HS)) Fe monomer [1], we have precisely determined the light-induced Fe-N bond length change from LS to HS states in two different solvents. In the suspension example of lead-free perovskite nanocrystals [2], we have found that upon photoexcitation, the electron is delocalized but the hole is localized at Br atom via likely forming Br2 dimer as Vk center. At the same time, the hole localization results in a local structural distorted state, which is long-lived (~ 60 µs) compared to the recombination of charge carriers (~ 20 ns). Additionally, I will present our recent preliminary TR-XAS results of 2D and 3D lead perovskite thin films from our new home-built sample platform [3].

[1] C. Liu, et al.J. Am. Chem. Soc. 139, 17518 (2017).  
[2] C. Liu, et al.J. Am. Chem. Soc. 14113074 (2019).
[3] C. Liu, et al., To be submitted.

September 11, 2019

11:00 am

Bldg. 440, A105/A106

Metasurfaces - Achromatic Polarization Conversion and Efficient Optical Modulation, Hoo-Tong Chen, Center for Integrated Nanotechnologies, Los Alamos National Laboratory. Host:  Xuedan Ma and Haidan Wen.

Two-dimensional plasmonic metamaterials – metasurfaces – offer tremendous opportunities in realizing exotic optical properties and functionalities. Through tailoring the resonant response of basic building blocks as well as their mutual interactions, they enable effective control of the amplitude, phase, and polarization state of optical reflection, transmission, and scattering. In this talk, I will present plasmonic metasurfaces consisting of a few planar layers of subwavelength metallic structures, demonstrating optical functionalities such as antireflection and perfect absorption. By judicious design of anisotropic resonances, the off-resonance phase dispersion can be tailored to achieve achromatic phase retardation, through which we demonstrate ultrabroadband linear polarization rotation and linear-to-circular polarization conversion (i.e., achromatic half and quarter waveplates). In the second topic, I will present hybrid metasurfaces by integrating functional materials such as semiconductors and graphene at critical regions of the resonators, allowing enhanced light-matter interactions and accomplishing dynamic switching, active tuning, and enhanced nonlinearity. In particular, I will show hybrid graphene metasurfaces for efficient optical modulation at mid-infrared wavelengths for imaging applications.  The augmented metasurface functionalities through both structural design and materials integration will provide promising opportunities of metasurfaces for real-world applications.

Bio: Hou-Tong Chen received BS and MS degrees from University of Science and Technology of China in 1997 and 2000, and a Ph.D. degree from Rensselaer Polytechnic Institute in 2004, all in physics. He is currently a Technical Staff Member in the Center for Integrated Nanotechnologies, Los Alamos National Laboratory. His research interests include metamaterials and metasurfaces, terahertz science and technology, ultrafast nanophotonics, and near-field microscopy. He has published over 70 journal papers and delivered nearly 100 invited technical presentations in conferences and accredited research institutions. He is a Topical Editor of Optics Letters (since 2017), and the conference chair of the 8th Optical Terahertz Science and Technology (OTST 2019) to be held at Santa Fe, USA (2019). He won LANL Fellows’ Prize for Outstanding Research (2015), and is a Fellow of American Physical Society (2015).

September 6, 2019

2:00 pm

Bldg. 440, A105/A106

Electrocatalyst for Oxygen Reduction and Evolution Reactions, Hong Yang, Dept. of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, Hosts: Xiao-Min Lin and Chengjun Sun

Chemical transformation processes reply heavily on the catalysts made of carefully designed nanoparticles on supports. Many of these transformations involve oxygen species, which are important in chemical, petrochemical and energy industries, ranging from chemical production, such as epoxidation and automobile exhaust treatment, to the electrocatalysts for hydrogen-powered fuel cells and metal-air batteries. In this presentation, I will present our recent efforts in the following areas related to the catalyst and nanomaterial developments for sustainable technologies: 1) low- and non-platinum group metal (PGM) oxygen reduction catalysts and 2) ternary metal oxide electrocatalysts, such as pyrochlores (A2B2O7), for oxygen evolution reaction. I will focus on illustrating the design principles of high performance catalysts through examining the structure-catalytic property relationship under dynamic, reactive conditions and by developing quantitative analytical models for the synthesis of nanostructured catalyst materials.1-3

References:
1.       Y-T. Pan, J. B. Wu, H Yang, AIChE J, 2016, 62, 399-407.
2.       X. Yin, M. Shi, J. B. Wu, Y.-T. Pan, D. L. Gray, J. A. Bertke, H. Yang, Nano Lett., 2017, 17, 6146-6150.
3.       J. M. Kim, P.-C. Shih, Y. Qin, Z. Al-Bardan, C.-J. Sun, H. Yang, Angew. Chem. Int. Ed., 2018, 57, 13877-13881; P.-C. Shih, J M. Kim, C. J. Sun, H. Yang, ACS Appl. Energy Mater., 2018, 1, 3992-3998; J. M. Kim, P.-C. Shih, K.-C. Tsao, Y.-T. Pan, X. Yin, C.-J. Sun, H. Yang, J. Am. Chem. Soc., 2017, 139, 12076-12083.

BIO: Dr. Hong Yang is the Richard C. Alkire Endowed Chair Professor in Chemical Engineering at the University of Illinois at Urbana-Champaign (UIUC).  He received his B.Sc. degree from Tsinghua University (1989), Ph.D. degree from University of Toronto (1998), and did his postdoctoral research at Harvard University. Among his awards and honors, Dr. Yang received one of the two NSERC Canada Doctoral Prizes in Science, was an NSERC Postdoctoral Fellow, a US National Science Foundation CAREER Award winner, a Visiting Chair Professor with Shanghai Jiaotong University, and is an elected Fellow of American Association for the Advancement of Science (AAAS). He is a Section Editor for Current Opinion in Chemical Engineering, was a Guest Editor for Advanced Materials and Accounts of Chemical Research, and serves on several editorial boards, including Nano TodayChemNanoMat, Science China Materials, and Frontiers in Energy. His research interests include formation of nanocrystals, catalysis, electrocatalysis, and applications of nanomaterials for energy and sustainability. His group currently work in the areas of low-platinum group metal (PGM) and non-PGM catalysts for oxygen reduction, electrode materials for rechargeable battery, electrochemical water splitting, and CO2 utilization.

August 9, 2019

11:00 am

Bldg. 440, A105/A106

Fabrication and Functionality of Molecular Nanosystems at Interfaces, Prof. Dr. Johannes Barth, Molecular Nanoscience & Chemical Physics of Interfaces, Physics Dept., Technical University of Munich. Host:  Saw Wai Hla

The utilization and organization of molecular species is an important issue for advancing nanoscale science and underpins the development of novel functional materials. To this end we explore molecular bonding and assembly at well-defined homogenous surfaces, textured templates, nanoelectrodes and 2D-sheet layers. The developed bottom-up fabrication protocols employ tailored building blocks and exploit both supramolecular engineering and on-surface covalent synthesis. Structure formation, chemical conversions, electronic and other characteristics are addressed by a multitechnique experimental approach, whereby scanning probe microscopy provides molecular-level insights that are frequently rationalized with the help of computational modeling and x-ray spectroscopy investigations. We work toward a rationale for the control of single molecular units and the design of nanoarchitectures with distinct functional properties. 

Bio: The research activities of Prof. Barth centers on the fundamental understanding of phenomena at boundary surfaces and the design of functional molecular nanostructures. His work focuses on the control of complex molecules and highly-organized supramolecular architectures at the atomic scale.  After studying physics at Munich’s Ludwig Maximilian University (LMU), Prof. Barth received his doctorate in physical chemistry under Prof. G. Ertl at the Fritz Haber Institute of the Max Planck Society in Berlin (1992). Following that, he became an IBM Postdoctoral Fellow at the IBM Almaden Research Center in San Jose, USA. He spent over a decade continuing his work at the École Polytechnique Fédérale de Lausanne, Switzerland. It was there that he received his postdoctoral lecture qualification in 1999. Prior to his appointment as a full professor at TUM in 2006, he researched and taught at the Canada Research Chair at the University of British Columbia in Vancouver. He is currently an adjunct professor at that university.

July 30, 2019

2:00 pm

Bldg. 440, A105/A106

Nanotube Electro-Mechanical Resonators, Adrian Bachtold, ICFO, The Barcelona Institute of Science and Technology.  Host:  Daniel Lopez

Mechanical resonators based on carbon nanotubes feature a series of truly exceptional properties. Carbon nanotubes are so small that they make the lightest resonators fabricated thus far. The mechanical vibrations are enormously sensitive to the dynamics of the electrons through the nanotube, and vice versa. Taking advantage of this coupling, we developed a novel detection method that allows us to measure the mechanical vibrations of nanotube resonators with an unprecedented sensitivity [1]. In this talk, I will discuss our efforts to cool the amplitude of the thermal vibrations to a few quanta [2]. Cooling is achieved using a simple yet powerful method, which consists in applying a constant (DC) current of electrons through the suspended nanotube in a dilution fridge. I will also present results where we increase the effect of the electron-phonon interaction to an unprecedented level, enabling the demonstration of polaron physics in an electro-mechanical resonator.

[1] S. L. de Bonis, C. Urgell, W. Yang, C. Samanta, A. Noury, J. Vergara-Cruz, Q. Dong, Y. Jin, A. Bachtold, Ultrasensitive Displacement Noise Measurement of Carbon Nanotube Mechanical Resonators, Nano Letters 18, 5324 (2018)
[2] C. Urgell, W. Yang, S. L. de Bonis, C. Samanta, M. J. Esplandiu, Q. Dong, Y. Jin, A. Bachtold, Cooling and Self-Oscillation in a Nanotube Electro-Mechanical Resonator, arXiv:1903.04892.

July 12, 2019

11:00 am

Bldg. 440, A105/A106

Angstom Scale Chemical Analysis via Scanning Tunneling Microscopy and Tip-Enhanced Raman spectroscopy, Nan Jiang, Department of Chemistry, University of Illinois at Chicago.  Host:  Saw Wai Hla.

My research group is broadly interested in spectroscopically determining how local chemical environments affect single molecule behaviors. We focus on highly heterogeneous systems such as molecular self-assembly and bimetallic catalysis, developing and using new imaging and spectroscopic approaches to probe structure and function on nanometer length scales. This talk will focus on Tip-Enhanced Raman Spectroscopy (TERS), which affords the spatial resolution of traditional Scanning Tunneling Microscopy (STM) while collecting the chemical information provided by Raman spectroscopy. By using a plasmonically-active material for our scanning probe, the Raman signal at the tip-sample junction is incredibly enhanced, allowing for single-molecule probing. This method, further aided by the benefits of ultrahigh vacuum, is uniquely capable of obtaining (1) single molecules chemical identification; (2) the molecular mechanism of chemical bond formation under near-surface conditions using self-assembly concepts; (3)adsorbate-substrate interactions in the ordering of molecular building blocks in supramolecular nanostructures. By investigating substrate structures, superstructures, and the adsorption orientations obtained from vibrational modes, we extract novel surface-chemistry information at an unprecedented spatial (<1nm) and energy (<10 wavenumber) resolution. We are able to interrogate the impact of changes in the chemical environment on the properties of supramolecular nanostructures, and thereby lay the foundation for controlling their size, shape and composition.

June 18, 2019

11:00 am

Bldg. 440, A105/A106

Thermal-emission Engineering: Challenges and Opportunities, Mikhail A. Kats, Department of Electrical and Computer Engineering, University of Wisconsin - Madison.  Host: Daniel Lopez

Thermal emission (thermal radiation) is the phenomenon responsible for most of the light in the universe. Though understanding of thermal emission dates back over a century, recent advances have encouraged the re-examination of this phenomenon and its applications. This talk will describe our group’s advances and outline future work in the measurement and manipulation of thermal emission. First, I will discuss our efforts to improve thermal-emission metrology, especially for low-temperature thermal emitters and/or those with temperature-dependent emissivity. Then, I will describe our use of phase-transition materials including vanadium dioxide and the rare-earth nickelates to demonstrate new phenomena, including negative- and zero-differential thermal emittance, radiative thermal runaway, and thermo-dichroism. I will also discuss our recent demonstration of nanosecond-scale emissivity modulation. The talk will include discussion of exciting opportunities of thermal-emission engineering for infrared camouflage and thermoregulation.

Bio:  Mikhail Kats is an Associate Professor and Dugald C. Jackson Faculty Scholar at the Department of Electrical and Computer Engineering at University of Wisconsin-Madison, with affiliate appointments in the Departments of Physics and Materials Science and Engineering. Mikhail’s research interests include optical properties of engineered materials, novel optical and optoelectronic devices, tailoring of thermal emission and radiative heat transfer, enhancement of human vision, and related topics in optics and photonics. Prior to joining UW-Madison, He received his BS in Engineering Physics from Cornell University in 2008, and his PhD in Applied Physics from Harvard University in 2014. His awards include the ONR Young Investigator Award, the AFOSR Young Investigator Award, and the NSF CAREER award, and selections to the Forbes 30 Under 30” and ASEE Prism’s 20 Under 40” lists.

June 17, 2019

11:00 am

Bldg. 440 - A105/A106

Scalable Nanosystems for Neuromorphic Computing, Vinod K. Sangwan, Department of Materials Science and Engineering, Northwestern University.  Host:  Daniel Lopez

Advances in silicon-based digital electronics and improved understanding of the human brain have spurred tremendous interest in artificial intelligence and neuromorphic computing. Last few decades saw a rapid rise in both computation power and theoretical framework that resulted in a more efficient solution for specialized cognitive tasks. Since logic processing and memory are intimately connected, the neural computation is not burdened by von Neumann bottleneck. However, progress in artificial intelligence has fallen short of initial predictions and inspired the new approach of hardware implementation using a nano-ionic device that mimics biological neuron at a fundamental level. I will discuss an artificial synapse realized in a device called memtransistor that is based on a single layer semiconducting MoS2. The internal resistance of the device is tuned not only by the biasing history but also by a third gate terminal. Furthermore, open architecture channel allows multiple electrodes resulting in elusive heterosynaptic plasticity -a necessary ingredient for hyper-connectivity. In addition, an artificial neuron is needed to integrate signals received via synapses and fires a charge wave along axon causing subsequent synaptic switching. Thus, I will discuss a practical route to design artificial neurons based on films from solution-processed two-dimensional materials that embody two coupled state variables (temperature and charge) needed for action-potential based computation. An alternative artificial neuron based on heterojunctions will also be presented to circumvent the issues of stochasticity. Finally, a new fabrication method and a new memtransistor crossbar architecture will be discussed to achieve the desired scaling. I will conclude with future goals in fundamental research and applications.

Bio: Dr. Vinod K. Sangwan is currently a postdoctoral researcher with Prof. Mark C. Hersam in the Department of Materials Science and Engineering at Northwestern University. He did a B. Tech. in Engineering Physics at Indian Institute of Technology Mumbai and later, a Ph.D. in Physics with Profs. Ellen D. Williams and Michael S. Führer at the University of Maryland College Park. His research at Northwestern spans across several disciplines including applied physics, electrical engineering, materials science, and chemistry. His current interests are defects dynamics in the 2D materials, nanoscale transport, ultrafast optical processes, emerging photovoltaic materials and devices, and quantum materials.

June 11, 2019

11:00 am

Bldg. 440, A105/A106

High Frequency Piezo-optomechanics for Superconducting Microwave and Optical Interface, Xu Han, Yale University, Host: Daniel Lopez

Coherent microwave-optical photon conversion is pivotal in the development of scalable quantum networks, which incorporate powerful local microwave quantum processors, such as superconducting qubits, with long-distance quantum channels through optical fibers. However, due to the dramatic mismatch in frequency and wavelength, establishing effective coupling between microwave and optical photons remains a challenging task. In this talk, I will demonstrate an efficient superconducting piezo-optomechanical interface where the microwave-optical interaction is mediated and significantly enhanced by high frequency phonons. Moreover, the implementation of high frequency mechanics can greatly suppress added thermal noise, paving the way for quantum operation. I will first introduce high frequency piezo-optomechanical resonators above 10 GHz, next demonstrate multimode strong coupling in superconducting electromechanics, and then integrate the two systems together and present our most recent progress on bidirectional coherent microwave-optical photon conversion. At last, two promising future directions will be discussed. One is entanglement-based microwave-optical quantum transduction, which will be able to bypass the stringent requirements for direct conversion. The other one is the exploration of nonlinear micro-electromechanical system (MEMS) in the quantum régime for novel applications such as quantum memory.

May 28, 2019

11:00 am

Bldg. 440, A105/A106

Solid State Quantum Emitters for Quantum Communication and Metrology Applications, Kristiaan De  Greve, Physics Department, Harvard University,  Host:  Daniel Lopez

In this seminar, I will briefly touch upon three different quantum platforms and materials systems that, each in their own way, exemplify different aspects of the overarching theme of my research work thus far: quantum control of solid-state quantum emitters.
In the first half of my talk, I will discuss a series of cryogenic experiments performed on single spins at high magnetic fields in III-V quantum dots. At the single-qubit level, using ultrafast optical pulses, we demonstrated full optical control of both single electron and hole spin qubits, and we identified the dominant dephasing mechanisms in each case [1-2]. We then moved on to two-qubit operation, where we demonstrated, through a novel, ultrafast non-linear measurement technique, the highest to-date solid-state spin-photon entanglement fidelity, as confirmed by full state tomography [3-4]. I will then briefly analyze the fundamental limitations of this materials system in terms of scalability, and potential solutions thereof.
One such solution we recently explored, involves the creation of a fully novel type of quantum device, combining the advantages of an electrostatically controlled quantum dot with the versatile optical access provided by optical quantum dots. For this, we harness the strong optical response and tight excitonic binding energy of monolayer transition metal dichalcogenides (TMDs) [5]. I will show new results demonstrating both the observation of Coulomb blockade in quantum dot transport devices, as well as electrostatic control of the optical emission of rudimentary nanowire-quantum dots [6].
Time permitting, I will also briefly discuss molecular defects in wide-bandgap semiconductors, particularly the nitrogen-vacancy (NV) center in diamond. In a first series of experiments, we used a scanning-NV magnetometer with a scanning magnetic gradient to map out, with sub-nanometer and single-spin resolution, the magnetic and spin environment of shallow NV centers. Such shallow NVs are commonly used for high-resolution magnetometry experiments. We observed a pronounced and dominant spin noise contribution which could be attributed to spin-1/2 defects at the diamond surface [7]. We then developed and studied in detail a novel oxygenation procedure that reduced the surface spin noise by over an order of magnitude – allowing for the observation of the NMR signal of a single, denatured ubiquitin protein [8].

[1]. D. Press, K. De Greve et al., Nature Photonics 4, 367 (2010)
[2] K. De Greve, P. McMahon et al, Nature Physics 7, 872 (2011)
[3] K. De Greve, L. Yu et al, Nature 491, 421 (2012)
[4] K. De Greve*, P. McMahon* et al, Nature Comms. 4, 2228 (2013).
[5] G. Scuri, Y. Zhou et al., PRL 120, 037402 (2018)
[6] K. Wang, K. De Greve et al, Nature Nano. 13, 128 (2018)
[7] M. Grinolds, M. Warner, K. De Greve et al., Nature Nano. 9, 279 (2014)
[8] I. Lovchinsky,.., K. De Greve et al., Science 351, 836 (2016)

May 23, 2019

11:00 am

Bldg. 440, A105/A106

Electronic States in Electron-Doped Rare-Earth Nickelates From First Principles,  Michele Kotiuga, Department of Physics and Astronomy, Rutgers University.  Host:  Pierre Darancet

Correlation effects in transition metal based materials give rise to many interesting and exotic properties. The rare-earth nickelates, with a rich composition-phase diagram, are no exception. Doping rare-earth nickelates can lead to electron localization, introducing defect states that are unlike typical shallow or deep donor states familiar in conventional semiconductors. We present first-principles density-functional-theory-based calculations of rare-earth nickelates, with a focus on lanthanum nickelate and samarium nickelate, in which we add electrons to the material. Here, we investigate doping concentrations on the order of one electron per formula unit with the goal of changing the orbital occupation and triggering a phase transition, akin to the phase control seen with strain modulation. We carry out calculations where a uniform compensating background charge (‘jellium”) has been added to maintain charge neutrality when electrons are added, as well as supercell configurations with defects that electron dope the system, and superlattices where an electron is transferred at interfacial layers. In particular, we explore the effects of intercalated hydrogen and lithium as well as oxygen vacancies in samarium nickelate as well as lanthanum nickelate/strontium iridate superlattices. In comparing these calculations, we find the jellium-background calculations capture the changes to the electronic structure seen with the explicit inclusion of defects and interfaces. The resulting changes to the electronic structure, intimately linked to structural changes, cannot be understood with a rigid shift of the states: the bands are reorganized and the character of the gap is fundamentally altered. This class of doping effects introduces a new knob to turn in the field of materials design.

Bio: Michele Kotiuga is a PostDoc in the group of Prof. Karin Rabe at Rutgers University currently working on complex oxides. She completed her PhD in physics 2015 at UC Berkeley in the group of Prof. Jeffrey Neaton on first-principles calculations of electronic transport in molecular junctions. 

May 22, 2019

12:00 noon

Bldg. 440, A105/A106

An Inside View of the Physical Review Family of Journals, Yan Li, American Physical Society, Host: Maria Chan

Abstract: The Physical Review journals of the American Physical Society (APS) have a long tradition of publishing important physics papers and serving as the bedrock of physics research. In the past decade, the APS has launched several new journals to broaden this collection, including Physical Review X, a highly selective open-access journal;  Physical Review Applied, dedicated to publishing high-quality papers that bridge the gap between engineering and physics; and Physical Review Materials, a new broad-scope journal serving the multidisciplinary community working on materials research. Physical Review Research, the latest fully open access title in the Physical Review family of journals, will be open for submission soon.

In this talk, I will give a brief overview of our journal family and the peer review process, and offer some guidelines on how to communicate effectively with editors and referees to facilitate the review. I will also discuss the current scope and standards for papers on condensed matter and materials physics published in Physical Review B.  

Bio: Yan Li received a B.Sc. from Peking University and a Ph.D. in physics from the University of Illinois at Urbana-Champaign. She joined the American Physical Society in 2015 and is currently an associate editor for Physical Review B.

May 20, 2019

11:00 am

Bldg. 440, A105/A106

Light-matter interactions for optical communications and energy-related applications, Ankun Yang, Department of Materials Science and Engineering, Stanford University.  Host:  Daniel Lopez

Light-matter interactions are closely related to everyday life and are the fundamental basis for optical communications and light microscopy and spectroscopy. In the first part of my talk, I will present my study of small-size lasers toward on-chip optical communications. Plasmon lasers represent a type of small lasers that support ultrasmall mode confinement and ultrafast dynamics with device feature sizes below the diffraction limit. However, plasmon-based lasers show emission with limited far-field directionality. In addition, most plasmon-based lasers rely on solid gain materials, e.g., inorganic semiconducting nanowire or organic dye in a solid matrix, that preclude the possibility of dynamic tuning. I will show that arrays of gold nanoparticles surrounded by liquid dye molecules exhibit directional lasing emission that can be modulated by the dielectric environment. By integrating gold nanoparticle arrays within microfluidic channels and flowing in liquid gain materials with different refractive indices, dynamic tuning of the lasing wavelength has been achieved.

In the second part of the talk, I will present more recent research using in situ light microscopy and spectroscopy approaches to study electrochemical devices. Lithium sulfur (Li-S) batteries are attractive candidates for energy storage with high energy density. Sulfur, the charge product in Li-S batteries, was believed to be solid, while we discovered that sulfur can stay in super-cooled state as liquid sulfur. To reveal the implications of this finding, I use a typical 2D material molybdenum disulfide (MoS2) as a platform to show distinct growth behaviors of sulfur on the basal plane (liquid) and edges (solid). Through correlating the sulfur states (liquid or solid) with the electrochemical performances, liquid sulfur is demonstrated to have much faster kinetics compared to solid sulfur. Using a similar in situ optical set-up, I will also show ion intercalation of 2D materials through electrochemical approach as a promising low-temperature modification strategy to manipulate the material properties for nanoelectronics devices. I will conclude by presenting future prospects for exploiting light-matter interactions in nanostructured materials and systems for applications in both optical communications and energy-related applications.

Bio:  Ankun Yang is a Postdoctoral Research Fellow in the Department of Materials Science and Engineering (MSE) at Stanford University. Ankun received his Bachelor’s and Master’s degrees in MSE at Tsinghua University, China. Ankun then went on to pursue his Ph.D. degree in MSE at Northwestern University under supervision of Professor Teri W. Odom, where he studied light-matter interactions in metallic nanoparticle assemblies and arrays, for plasmon-enhanced sensing and lasing. Ankun joined Professor Yi Cui’s group at Stanford University in July 2016, where he has investigated the interaction of two-dimensional (2D) materials with electrochemical species, including sulfur and alkali ions, through in situ light microscopy and spectroscopy. His research interests broadly lie in light-matter interactions in various low-dimensional material systems including plasmonic materials, 2D materials and energy-related materials for optoelectronics and electrochemical devices. Ankun’s work has earned him the Materials Research Society’s Graduate Student Award, the International Institute for Nanotechnology (IIN) Outstanding Researcher Award, Chinese Government Award for Outstanding Students Abroad, etc.

May 3, 2019

11:00 am

Bldg. 440, A105/A106

Mechanism and New Applications of Large and Persistent Photoconductivity, Rafael Jaramillo, Department of Materials Science and Engineering, Massachusetts Institute of Technology, Host: Gary Wiederrecht 

Large and persistent photoconductivity (LPPC) in semiconductors is due to the trapping of photo-generated minority carriers at crystal defects.  Theory suggests that anion vacancies in II-VI semiconductors are responsible for LPPC due to negative-U behavior, whereby two minority carriers become kinetically trapped by lattice relaxation following photoexcitation [1-2]. By performing a detailed analysis of photoconductivity in CdS, we provide experimental support for this negative-U model of LPPC [3]. We also show that LPPC is correlated with sulfur deficiency.  We use this understanding to vary the photoconductivity of CdS films over nine orders of magnitude, and vary the LPPC characteristic decay time from seconds to 10,000 seconds, by controlling the activities of Cd2+ and S2- ions during chemical bath deposition. We suggest a screening method to identify other materials with long-lived, non-equilibrium, photo-excited states based on the results of ground-state calculations of atomic rearrangements following defect redox reactions, with a conceptual connection to polarons and organic dyes.

We apply our knowledge of defect physics in CdS to propose and design a new type of semiconductor device – the donor level switch (DLS), which operates by switching individual defects between deep-donor and shallow-donor states. We study DLS behavior by making two-terminal devices using hole injection layers to control the charge state of sulfur vacancies. We also apply our knowledge to study the influence of LPPC on the performance of CIGS thin-film solar cells. If time allows we will also cover recent results from our group on infrared optical properties and phase-change functionality in transition metal di-chalcogenides (TMDs), and early results on growth and the opto-electronic performance of sulfide perovskite semiconductors.

[1] S.B. Zhang, S.H Wei & A. Zunger, Phys. Rev B  63, 075205 (2001).
[2] S. Lany & A. Zuner, Phys. Rev B 72, 035215 (2005).
[3] H. Yin, A. Akey & R. Jaramillo, Phys. Rev. Mater. 2, 084602 (2018)

April 3, 2019

11:00 am

Bldg. 440, A105/A106

Band engineering design and demonstration for high performance avalanche photodetector, Jiyuan Zheng, Department of Electrical and Computer Engineering, University of Virginia, Host:  Supratik Guha

If you need to measure incredibly low light signals, you have to make a compromise. If you want the best performance, you must select a photomultiplier tube or superconductor. However, photomultiplier tube is fragile and bulky. Superconductor needs to work under low temperature. The alternative, addressing these weaknesses, is the avalanche photodiode (APD), but it is let down by its poor controllability.

If you need to have a high speed low noise photodetector in long haul telecommunications, APD is the first choice. However, the randomness process in APD limited the noise performance, which restricts the traffic capability.

In order to improve the controllability and noise performance of APD, Band engineering design is deployed in the material lattice structure. Firstly, a high gain, low noise APD has been demonstrated on AlN/GaN periodically stacked material. A record stable high linear gain of over 104 has been realized. Secondly, an extremely low noise APD has been demonstrated on AlInAsSb and InAlAsdigital alloy. A record low excess noise factor of 0.02 has been realized based on these lattice structure in 1550 nm fiber optic window. Both of the two types of devices were verified by experiments and first principle study.

March 28, 2019

11:00 am

Bldg. 440, A105/A106

Accelerating the Discovery of Energy Materials, Linda Hung, Toyota Research Institute, Host:  Maria Chan

The Accelerated Materials Design and Discovery (AMDD) program at the Toyota Research Institute (TRI) is working toward a next-generation platform for materials research. Our team is composed of research scientists and software engineers, together with collaborators at national labs and universities. Our projects focus on automated or high-throughput experiments and computations, as well as the development of software and machine learning tools that enable us to fully leverage the diverse datasets being generated. In this talk, I will give an overview of TRI-AMDD and highlight a few projects: MatScholar, synthesizability networks, and chemical convolutional neural networks.

Biography:  Linda Hung is a senior research scientist at TRI, with a background is in first-principles computations and computational spectroscopy. She obtained her Ph.D. at Princeton University, and has held positions at the Ecole Polytechnique (France), the University of Illinois at Chicago, and the National Institute of Standards and Technology (NIST) before joining TRI.

March 14, 2019

2:00 pm

Bldg. 440, A105/A106

Transition Metal Dichalcogenides Based Vertical Devices for Memory Application, Feng Zhang, Purdue University, Host:  Daniel Lopez

Transition metal dichalcogenides (TMDs) have attracted attention as potential building blocks for various electronic applications due to their atomically thin nature. Innovation in modern storage applications is intimately connected with the development of the entire field of modern information technology. Denser, faster and less power consuming memories are highly sought after by the industry. Resistive random access memory (RRAM) occurs promising as an emerging technology due to its potential scalability, high operation speed, high endurance and ease of process flow. However, reliable and repeatable operation is a potential challenge in future applications since switching involves the uncontrollable motion of individual atoms. In this talk, I will discuss the first experimental demonstration of a vertical MoTe2 based bipolar RRAM device that exhibits a new switching mechanism, i.e. a structural transition from the stable semiconducting 2H phase to a more conductive 2Hd state, which is induced by an electric field. Set and reset voltages are tuned by the MoTe2 flake thickness. 5 ns switching speeds are achieved. This new switch mechanism holds the promise for faster and more reproducible switching if compared with conventional RRAM devices that are based on the migration of ions or the amorphous-to-crystalline transition in phase change memories (PCMs). Moreover, vertical TMD based memory selectors will also be discussed, showing promising characteristics for future application memory applications.

February 22, 2019

2:00 pm

Bldg. 440, A105/A106

Manipulating Exciton Dynamics for Energy Conversion Applications, Mathew Sfeir, City University of New York, Host:  Pierre Darancet

The promise of nanotechnology lies in the emergence of novel electronic and photonic phenomena with the potential for new device technologies. For example, optical transitions at the nanoscale frequently result from strongly absorbing excitons, whose electronic structure and dynamics are shape, size, and morphology dependent. However, since excitons are bound states, device concepts that exploit the unique photophysics of excitons, for example, organic photovoltaics or multiple exciton generation solar cells, depend critically on the ability to direct specific favorable conversion processes and suppress unfavorable ones. Here I will discuss how ultrafast optical spectroscopy is an important tool to understand the success (and failure) of nanoscale device concepts. I will demonstrate how the unique optical signature of excitons allow for dynamical tracking of energy conversion processes on ultrafast time scales. These optical signatures can be used to understand the harvesting of excitons in nanoscale lasers, photocatalytic water splitting devices, and photovoltaics. I will show how the first few picoseconds after light absorption are crucial to understanding the overall performance of a nanomaterial-based energy device.

Bio: Sfeir joined the Graduate Center in January from the U.S. Department of Energy’s Brookhaven National Laboratory.  As part of the laboratory’s Center for Functional Nanomaterials, his work focuses on enabling technologies for next-generation optoelectronic devices.  He has received numerous awards for his work in photophysics, and in 2018 was named an Inventor of the Year” by the global science and technology organization Battelle.  He has served on several committees and advisory boards, including the executive committee for the Energy Subdivision of the American Chemical Society Division of Physical Chemistry; co-authored more than 80 journal articles; and secured five patents.

January 15, 2019

3:00 pm

Bldg. 440, A105/A106

Switchable geometric frustration in an artificial-spin-ice/superconductor hetero-system,  Jing Xu, Department of Physics, Northern Illinois University.  Host: Xufeng Zhang

Superconducting (SC) and ferromagnetic (FM) hybrid systems provide an intriguing combination of two contrasting phenomena and their mutual interaction has been extensively studied to tailor their electromagnetic behavior. Here, a novel FM/SC hybrid structure consisting of a unique artificial spin structure deposited onto a superconducting MoGe film will be presented. The spin structure can produce magnetic charge ice structures mimicking those of a square artificial spin ice with the added value that the long-range ordering can be easily realized and controlled with the application of an in-plane magnetic field [Science 352, 962 (2016)]. The magnetic charge ice can affect the behavior of superconducting vortices present in the underlying MoGe film [Nature Nanotechnology 13(7)]. The novelty of the magnetic spin ice structure and its impact on vortex matching effect and dynamics will be presented including a reconfigurable matching effect and rectification effect in an artificial-spin-ice/superconductor hybrid sample. By controlling the magnetic charge symmetries with an in-plane external magnetic field, those effects can be achieved with in-situ tunable amplitude and polarization.

Bio: Jing Xu is a Ph.D. student in Northern Illinois University is expected to receive his doctoral degree in May 2019. Since 2015 he has been an associate research assistant in material science division at Argonne National Laboratory, His research mainly focused on the magneto-transport on topological materials, vortex dynamic in superconductors and nano-engineering in magnetic materials. He has six (6) publications and being the first author in four (4) of them.

December 17, 2018

11:00 am

Bldg. 440, A105/A106

Chemical and Phase Transformations of Multicomponent Oxides in Batteries, Feng Lin, Department of Chemistry, Virginia Tech.  Host: Xiao-Min Lin

Lithium and sodium layered cathode materials are usually multicomponent transition metal ™ oxides and each TM plays unique roles in operating the cathode chemistry, e.g., redox activity, structural stabilization, surface passivation. Engineering the three-dimensional (3D) distribution of TM cations in individual primary and secondary particles can take advantage of the depth-dependent charging and passivation mechanisms and enable a path towards tuning local TM–O chemical environments and eliminating undesired cathode–electrolyte interfacial reactions that are responsible for capacity fading, voltage decay, and safety hazards. In this presentation, we will highlight our recent progress in understanding and manipulating the cathode chemistry using the unconventional design principle of 3D heterogeneous chemical distribution and advanced diagnostic tools. The presentation will show that  there is plenty of room at the bottom” by tuning nano/meso scale heterogeneities for stabilizing multicomponent transition metal oxides based cathode chemistry in rechargeable batteries.

Bio:  Dr. Feng Lin is currently an Assistant Professor of Chemistry, with a courtesy appointment in the Department of Materials Science and Engineering at Virginia Tech. He holds Bachelor’s degree in Materials Science and Engineering (2009) from Tianjin University, and MSc degree (2011) and Ph.D. degree (2012) in Materials Science from Colorado School of Mines. Prior to Virginia Tech, Feng worked at QuantumScape Corporation as a Senior Member of the Technical Staff (2015-2016), Lawrence Berkeley National Lab as a Postdoctoral Fellow (2013-2015), and National Renewable Energy Lab as a Graduate Research Assistant (2010-2012). Feng is fascinated by energy sciences, materials electrochemistry, and synchrotron X-ray techniques.

December 6, 2018

11:00 am

Bldg. 440, A105/A106

New Strategies in Laser-Based Mass Spectrometry Imaging of Biological, Geological, and Synthetic Samples,  Professor Luke Hanley, Department of Chemistry, University of Illinois at Chicago.  Host: Yuzi Liu

Mass spectrometry (MS) imaging can provide near micron- resolution maps of the elemental and molecular composition of mammalian tissue, microbial biofilms, electronic or medical devices, and other chemically complex structures. Matrix assisted laser desorption ionization is perhaps the leading probe used in MS imaging. Complementing nanosecond laser desorption with laser postionization improves signals, minimizes differential detection, and facilitates analysis of electrically insulating samples. Replacing ns laser desorption with <100 fs laser pulses for sample ablation promises submicron lateral resolution and depth profiling in MS imaging without any need for complex sample preparation schemes. This talk describes several strategies for improving laser-based MS imaging, with examples given in the analysis of microbial biofilms, pancreatic tissue, and geological samples.

December 5, 2018

3:00 pm

Bldg. 440, A105/A106

Topologically Controlled Optoelectronic Properties in Metal-Organic Frameworks.  Pravas Deria,  Department of Chemistry & Biochemistry, Southern Illinois University - Carbondale.  Host Chris Fry

Molecular assemblies in metal-organic frameworks (MOFs) are reminiscent of natural light-harvesting (LH) systems and considered as emerging materials for energy conversion. Such applications require understanding the correlation between their electro-optical properties and underlying topological-net. In this presentation we will discuss how the excited state properties such as energy, dynamics, and wave function in various chemically identical MOFs are controlled by their structures defined by the topological nets. Most of these properties stem from the transition- dipole interactions of the precisely arranged chromophores within the frameworks. Likewise, charge carrier migration plays a critical role in electro/photoelectrochemical process and will be discussed how such properties are impacted by the framework structure.

December 3, 2018

11:00 am

Bldg. 440, A105/A106

Colloidal Semiconductor Nanocrystals: From single objects to 2D materials, Christophe Delerue, Institute of Electronics, Microelectronics and Nanotechnology, Centre National de la Recherché Scientifique.  Host:  Pierre Darancet

Semiconductor nanocrystals prepared by colloidal chemistry have been studied for more than three decades but it is only now that they are employed in mass-market commercial applications. Nowadays, these nano-objects can be fabricated with an excellent control of their composition, size and shape in such manner that their electronic structure and their optical properties can be accurately tuned. In this talk, I will show that semiconductor nanocrystals can be sometimes considered as artificial atoms which can be self-assembled to form new types of two-dimensional crystals in which the electronic structure results from the effect of the periodic scattering of the electrons induced by the nanogeometry. Recent progress in colloidal chemistry enables the fabrication of materials in which each nanocrystal can be considered as a LEGO brick®. Moreover this concept of LEGO® can be extended to the calculation of the electronic band structure of the superlattices. By combining the original band structure of the bulk semiconductor and the effects of the nano-structuring, we show that these new materials are characterized by exotic band structures including Dirac cones, non-trivial flat band bands, and topological bands.

References
[1] Colloidal nanocrystals as LEGO® bricks for building electronic band structure models, Athmane Tadjine, Christophe Delerue, Physical Chemistry Chemical Physics 2018 | DOI: 10.1039/C7CP08400E.

[2] Transport Properties of a Two-Dimensional PbSe Square Superstructure in an Electrolyte- Gated Transistor, M. Alimoradi Jazi, V. A. E. C. Janssen, W. H. Evers, A. Tadjine, C. Delerue, L. D. A. Siebbeles, H. S. J. van der Zant, A. J. Houtepen, D. Vanmaekelbergh, Nano Letters 2017 | DOI: 10.1021/acs.nanolett.7b01348.

[3] From lattice Hamiltonians to tunable band structures by lithographic design, A. Tadjine, G. Allan, C. Delerue, Phys. Rev. B 94, 7 (2016) 075441 | doi: 10.1103/PhysRevB.94.075441.

[4] Topological states in multi-orbital HgTe honeycomb lattices, W. Beugeling et al., Nat. Commun. 6 (2015) 6316 | doi: 10.1038/ncomms7316.

[5] Dirac cones, topological edge states, and nontrivial flat bands in two-dimensional semiconductors with a honeycomb nanogeometry, E. Kalesaki et al, Phys. Rev. X 4, 1 (2014) 011010 | doi: 10.1103/PhysRevX.4.011010.

December 3, 2018

3:00 pm

Bldg. 440, A105/A106

Investigating the Quantum Measurement Process, Humphrey J. Maris, Brown University.  Host:  Dafei Jin

In quantum mechanics the state of a system is described by the wave function. It is remarkable that according to the quantum theory the wave function changes with time in two seemingly distinct ways. There is a change in time which can be calculated from the time-dependent Schrodinger equation, and also the wave function is believed to change discontinuously as a result of measurements. However, despite much effort what constitutes a measurement and how a measurement causes a change in the wave function remains unclear. I will describe a series of experiments in which a part of the wave function of an electron is trapped in a box with walls sufficiently thick to prevent escape by tunneling.

November 27, 2018

2:00 pm

Bldg. 440, A105/A106

Configurable Light-Matter Interactions, Sui Yang, Nanoscale Science and Engineering  Center, University of California, Berkeley.  Host:  Daniel Lopez

Nanophotonics interfaces light and nanoscale matters, usually based on the manipulation of intrinsic physical properties of materials such as surface plasmons, optical bands and exciton physics. The exploration of novel configurable light-matter interactions by self-tailoring structural units (“artificial atoms”) will offer a new route to transform traditional nanophotonic materials and devices. In this talk, I would like to introduce my work on the development of configurable light-matter interactions by artificially structuring optical matters, specifically, exploiting novel soft” metamaterials and optoelectronic devices. Conventional metamaterials are considered as hard” materials whose structural units cannot be tailored after their formation. In contrast, I will present our recently developed soft” exploratory approaches for the synthesis and assembly of nanophotonic metamaterials. Through a feedback driven self-assembly, this new class of metamaterial can self-configure its desired symmetries which are previously unattainable. I will also present our solution-processed sub-diffraction perovskite nanolaser device with unprecedentedly enhanced emission dynamics that holds promise for on-chip optical information processing and communications. In addition to providing new knowledge of nanoscale light-matter interactions, our studies will propel future reconfigurable and self-responsive material applications.

November 9, 2018

11:00 am

Bldg. 440, A105/A106

Directed Self-assembly of Blue Phase Liquid Crystals by Chemically Patterned Surfaces, Xiao Li, Institute for Molecular Engineering, The University of Chicago.  Host:  Daniel Lopez. 

Liquid crystals (LCs) are a state matter intermediate between the solid and liquid phases. The unique properties of LCs, such as inherent ordering as liquid phase, optical anisotropy, the ability to response to an external field, make them be widely used for electronic displays, laser devices, photonics, biosensors, metastructures, etc. Fundamental understanding of the morphology and through-film optical properties of LC system, as well as precisely controlling the orientation of LC molecules towards contacting surfaces, are therefore play the central roles in device design and performance. In this seminar, I will present a generalizable platform based on anchoring contrast from chemically patterned surfaces to directed self-assemble (DSA) LC system. I will concentrate on chiral nematic system to expect more complex liquid crystalline morphologies and behaviors. More specifically, I will focus on blue phase liquid crystals (BPLCs), which exhibit ordered cubic arrangements of topological defects. The highly ordered morphology of BPs gives rise to unusual physical properties, such as Bragg reflection of visible light and fast optical response. However, polycrystalline structures limit their performance in applications. Chemically patterned surfaces are presented for the first time to obtain stable, lattice selective, macroscopic single-crystal BP materials. By studying the chemical pattern assisted heterogeneous crystal nucleation and growth process of BPs, the transformation between BPs is found to be martensitic in nature as the result of the collective behavior of the double- twist-cylinders. I will conclude by discussing some of the potential application of these materials, along with the questions and challenges remaining in the field.

November 2, 2018

11:00 am

Bldg. 440, A105/A106

Bioinspired Micro-Optics and Applications to Imaging Polarimetry, Stanley Pau, University of Arizona, Host: Daniel Lopez

Study of structural colors has led to optical filter designs using liquid crystal polymer that has microscopic structure similar to exoskeleton of many animals. The optical filters are utilized in novel multi-spectral and polarization cameras with applications in medical imaging, remote sensing, surveillance, and metrology.

October 24, 2018

2:00 pm

Bldg. 440, A105/A106

Realizing Resonant Optics with Quantum Electronic Transitions, Zongfu Yu, Department of Electrical and Computer Engineering, University of Wisconsin-Madison, Host:  Dafei Jin

Today’s optical devices are getting smaller and smaller to realize new functionalities and to reduce energy consumption. However, miniaturization becomes more difficult when the size falls below wavelength because of the lack of deep sub-wavelength electromagnetic resonance, an enabling effect for a wide range of applications, from radio-frequency communication, to silicon photonics, metamaterials and metasurfaces.        Quantum electronic transition has the potential to become a new platform to continue the miniaturization of classical optical devices. An electronic transition can resonantly absorb, scatter, and convert photon energy. It has the same scattering matrix as that of classical optical resonators in the single photon régime. Moreover, it has many advantages over classical ones: it is extremely compact, easily tunable by laser, magnetic or electric fields, and can be highly nonlinear.        In this talk, I will start by showing an intriguing function realized by extremely compact resonance. Then, I will discuss how electronic transitions could be used to realize classical functions such as antennas and metasurfaces. Then, I will discuss how electronic transition could rewrite some of the fundamental electromagnetic scattering law when combined with nontrivial topological charge found at Weyl points.

Biography: Zongfu Yu is the Dugald C. Jackson Assistant Professor in the department of electrical and computer engineering at the University of Wisconsin – Madison. His research interests include computational electromagnetics, optics, machine vision and sensing. He is a recipient of Stanford Postdoc Research Awards, DARPA Young Faculty Award (2017), and NSF CAREER Award (2018). He has authored and co-authored over 100 peer-reviewed papers with a total citation over 11,000 and an h-index of 44. He received his Ph.D. in applied physics and M.S. in management science and engineering, both from Stanford University, and a B.S. degree in physics from the University of Science and Technology of China.

October 15, 2018

10:00 am

Bldg. 440, A105/A106

Fine Pitch(<40μm) Integration Platform for Flexible Hybrid Electronics using Fan-Out Wafer-level Packaging, Amir Hanna, University of California Los Angeles

A flexible fan-out wafer-level packaging (FOWLP) process for heterogeneous integration of high performance dies in a flexible and biocompatible elastomeric package (FlexTrateTM) was used to assemble 625 dies with co-planarity and tilt <1µm, average die-shift of 3.28 µm with σ < 2.23 µm. Fine pitch Interconnects (40μm pad pitch) were defined using a novel corrugated topography to mitigate the buckling phenomenon of metal films deposited on elastomeric substrates. Corrugated interconnects were then used to interconnect 200 dies, and then tested for cyclic mechanical bending reliability and have shown less than 7% change in resistance after bending down to 1 mm radius for 1,000 cycles. Two application will be demonstrated: 1) A highly flexible (1 mm bending radius) 7 segment display using 42 high power InGaN LED dies integrated in a 50×40 mm package, and 2) A near field wireless implantable optogenetic implant system on an ultra-flexible (~5mm bending radius) package using commercially available dies showing power transfer efficiency > 15% @ 1cm transmit distance.

October 5, 2018

11:00 am

Bldg. 440, A105/A106

The Birth’, Aging’ and Life-Lengthening of Halide Perovskites, Yuanyuan (Alvin) Zhou, School of Engineering, Brown University.  Host:  Peijun Guo

Halide perovskites have recently emerged as a new family of semiconducting materials that are revolutionizing the field of photovoltaics. The rapid development of perovskite solar cells is being led by the advances in microstructural/compositional engineering of perovskite thin films. In this context, understanding the birth’ (crystallization) and death’ (degradation), and developing new methods for the life-lengthening’ (stabilization) of perovskites are becoming the most significant research directions.

In this talk, first, I will look at fundamental phenomena pertaining to nucleation & grain growth and grain-boundary evolution involved in the thin-film crystallization of perovskites from a materials-science perspective. Established scientific principles that govern these phenomena are invoked in the context of specific examples. Based on these fundamentals, our group have established a set of new synthetic strategies for scalable processing of high-performance large-area perovskite thin films and devices. Second, I will discuss the role of grain boundaries in the degradation processes of perovskites, and show our recent progress in the grain-boundary engineering for enhancing the perovskite stability. Finally, I will discuss the challenges and opportunities in the advanced characterization (e.g. in-situ/operando TEM) of perovskites for not only gaining a deep understanding of defects/microstructures, but also elucidating classical and non-classical phenomena pertaining to the crystallization, degradation, and stabilization of perovskites. The overall goal is to gain a deterministic control over the perovskite thin films with engineered microstructures/compositions for efficient perovskite solar cells that are also highly durable under heat/moisture/light stresses.

Biography: Yuanyuan (Alvin) Zhou is an Assistant Professor (Research) in the School of Engineering at Brown University since June 2016. He received his Ph.D. in Engineering from Brown University in June 2016. He holds a B.S. in Materials Science and Engineering from Xi’an Jiaotong University, and dual M.S. degrees in Materials Science and Engineering from Xi’an Jiaotong University and Chemistry from Korea Research Institute of Chemical Technology. Dr. Zhou’s research focuses on probing the composition-microstructure-property-performance relationships of new-generation functional inorganic materials for energy harvesting, storage and conversion. His research has been funded by NSF, ONR, DURIP and other agencies. He has published 56 journal papers with ~2500 Google citations and 25 H-index.

September 18, 2018

11:00 am

Bldg. 440, A105/A106

Tribochemistry: Shear-Induced Reaction Pathways Explored via Reactive Atomistic Simulation, Ashlie Martini, University of California Merced. Host: Ani Sumant

Low friction in lubricated mechanical components is in part enabled by protective films that form in sliding interfaces during operation. These films, called tribofilms, are formed through chemical reactions between additive molecules in the lubricant and the surfaces, where the reactions are driven by mechanical force exerted by the sliding bodies. Despite the presence of tribofilms in most moving components, the mechanisms of film formation are still poorly understood, primarily because the process occurs inside a moving contact and so cannot be directly interrogated experimentally. Experimental approaches are typically limited to pre- and post-sliding surface analyses. An alternative approach, and one we apply here, is using molecular dynamics simulations to explicitly model the additive molecules and surfaces at the atomic scale. Specifically, we use a reactive force field so the simulation can capture the formation and breaking of covalent bonds that are necessarily part of the tribofilm formation process. We study model systems, including gas phase lubrication of silica surfaces and nanoscale friction at graphene step edges, that can both be explicitly captured in the simulations and for which complementary experiments can be performed to provide partial validation of simulations. Once validated, the atom-scale detail available in the simulations is analyzed to identify the critically important role of shear in the tribofilm formation process. The results indicate that shear not only accelerates reactions but also alters the reaction pathways, enabling the formation of a tribofilm even under relatively low temperature conditions. In general, these findings may form the basis for the design of new boundary lubrication additives based on a better understanding of the tribofilm formation processes.

August 28, 2018

1:30 pm

Bldg. 440, A105/A106

Phonon and Electron Transport Properties of Defected Nanostructured Semiconductors: An Overview, Sanghamitra Neogi, University of Colorado Boulder, Host:  Subramanian Sankaranarayanan

Quantized vibrations in condensed phases, phonons, obey the laws of quantum mechanics in the same way as electrons and photons, that are commonly exploited as energy and/or information carriers. Efforts to control phonons, especially at micro- and nanoscale, have been stimulated by the ever increasing roles that phonons assume via self-interaction and interacting with electrons and photons. Phonon engineering has seen rapid progress through understanding of structure-processing-property relationships that connect nanoscale structures, dictated by methods of fabrication and processing, and vibrational and thermal transport properties. However, a broad range of phonon frequencies needs to be engineered, in contrast with electronic applications, where only energies close to the Fermi level are relevant. The difficulty of working with a broad spectrum of excitations naturally poses major challenges in achieving control over nanoscale phonon transport. Engineered nanoscale features offer remarkable possibilities to manipulate phonons in nanostructures. My research program at CU boulder is focused around the central theme-to tune phonons and their interactions with other quantum particles via engineering of nanostructured materials-in order to enable a broad range of technological applications. However, introduction of structural features impacts the transport of other quantum particles due to increased scattering. Our aim is to devise phonon engineering strategies to produce desired transport of quantum particles in nanostructured materials. In this seminar, I will present an overview of the research activities in my group, in particular, phonon and electron transport in multilayered Si/Ge nanostructures with defected interfaces, electronphonon scattering rates in superlattices, guiding phonons in nanostructured membranes though introduction of local resonances, and statistical/machine learning modeling and prediction of charge transport in multilayered semiconductors.

August 3, 2018

1:30 pm

Bldg. 440, A105/A106

Two-Dimensional Materials under Optical Probes, Shengxi Huang, Host:  Dafei Jin

Two-dimensional (2D) materials have gained increasing attention due to their unique and extraordinary electronic and photonic properties. The realization of the optoelectronic applications of 2D materials still faces several challenges. For example, it is critical to gain clear understandings of (1) the fundamental light-matter interactions in 2D materials, which govern many of the key material properties and are critical for device applications, and (2) the coupling of 2D materials with other nanostructures, which is a required structure for 2D devices and systems. This talk introduces new discoveries and pioneer works using optical spectroscopy techniques on these critical challenges, and novel applications of 2D materials in sensing. The first part of this talk presents the essential properties of 2D materials investigated using spectroscopy, including interlayer coupling of twisted bilayer MoS2 and few-layer black phosphorus, as well as anisotropic light-matter interactions of 2D materials with in-plane anisotropy. The second part of this talk focuses on the interaction of 2D materials with other nanostructures and the related applications. The interactions of 2D materials and selected organic molecules revealed novel enhancement effect of Raman signals for molecules on graphene surface, which offers a new paradigm in chemical and bio sensing. The works presented in this talk are significant in fundamental nanosciences, and offer important guidelines for practical applications of 2D materials in optoelectronics and sensing. The methodologies used here also provide a framework for the future study of many new 2D materials.

July 30, 2018

11:00 am

Bldg. 440, A105/A106

Diffraction and Microscopy with Attosecond Electron Pulses, Yuya Morimoto, Ludwig-Maximillians-Univeristat Munchen-Germany,  Host: Ilke Arslan

Light-matter interaction starts with the motion of charges driven by oscillating light cycles. A full visualization of such electronic motions requires attosecond temporal resolution and nano/atomic-scale spatial resolution. In this presentation, I will introduce attosecond electron microscopy and diffraction [1], which enable the space-time recording of the sub-optical-cycle dynamics. We obtain attosecond electron pulses by temporally modulating a mono-energetic 70 keV electron beam by cycles of a near infrared (1030 nm) laser beam impinged on a dielectric membrane [1,2]. By two proof-of- principle experiments, we show that the attosecond electron pulses are suitable for atomic-scale diffraction and sub-cycle microscopy applications [1]. First, we report Bragg diffraction from a single-crystalline silicon membrane with a signal-to-noise ratio sufficient for time-resolved diffractive imaging. Second, we visualize in real space the oscillating electromagnetic field vectors of an optical wave at a membrane. Our achievements unify the atomic imaging capability of sub-relativistic electron beams with the sub- cycle resolution of attosecond science.

 
References
[1] Y. Morimoto and P. Baum, Nat. Phys. 14, 252 (2018).
[2] Y. Morimoto and P. Baum, Phys. Rev. A 97, 033815 (2018).

July 24, 2018
 
2:00 pm
 
Bldg. 440, A105/A106

Designing and Studying Perovskite Materials for a Renewable Energy Future, Clemens Burda, Department of Chemistry, Case Western Reserve University.  Host:  Tijana Rajh

Over the past decade research in the group of Prof. Burda has focused on the idea to design nanostructured materials with targeted optoelectronic properties. The overarching criterion is that nanoscale materials and interfaces can enhance specific physical properties in ceramics, semiconductors, and metals. In this talk, the synthesis and related excitonic properties of methylammonium lead halide perovskites and their mixed halides are presented with a focus on time-resolved photoluminescence and transient absorption spectroscopy. The substitution of a fraction of bromide with chloride anions leads to a distorted unit cell due to the smaller radius of the chloride anion relative to the bromide ion and thus to decreased symmetry and an increased band gap. Femtosecond laser-induced transient absorption and photoluminescence measurements show that defects contribute to the relaxation processes in photoexcited perovskites. In addition, under two-photon excitation, longer excited state lifetimes could be assigned to the lowest exciton with surprisingly different properties compared to the one-photon created states. Origins and implications of these materials properties will be discussed.

July 23, 2018

11:00 am

Bldg. 440, A105/A106

Engineering of Iron Oxide Nanoparticles for Magnetic Particle Imaging Guided-Hyperthermia (hMPI), Anna C. Samia Department of Chemistry, Case Western Reserve University.  Host:  Tijana Rajh

Iron oxide nanoparticles (IONPs) are investigated due to their chemical tunability and great potential as diagnostic and therapeutic agents. In magnetic particle imaging (MPI), which is an emerging imaging modality that enables the direct mapping of IONP tracers, the signal generation relies heavily on the magnetization reversal of the IONP tracers. As such, it is essential to tune the IONP’s magnetic properties in order to achieve good MPI image resolution. To date, most studies have focused in optimizing spherical magnetite IONPs in MPI applications. In this presentation, a systematic investigation of the effects of chemical doping and shape anisotropy on the MPI performance of IONP tracers will be discussed. Moreover, the demonstration of focused hyperthermia through an MPI-guided approach (hMPI) will be presented. 

July 19, 2018

11:00 am

Bldg. 440, A105/A106

Atomic layer deposition for the synthesis and integration of 2D materials for nanoelectronics and catalysis,  Ageeth Bol, Department of Applied Physics, Eindhoven University of Technology, The Netherlands. Host:  Daniel Lopez
 
Graphene and other layered 2D materials have been the focus of intense research in the last decade due to their unique physical and chemical properties. This presentation will highlight our recent progress on the synthesis and integration of 2D materials for nanoelectronics and catalysis applications using atomic layer deposition (ALD). ALD is a chemical process that is based on self-limiting surface reactions and results in ultrathin films, with sub-nm control over the thickness and wafer-scale uniformity. In the first part of this presentation I will focus on the fabrication of low resistance contacts and ultrathin dielectrics to graphene using atomic layer deposition. In the second part I will show how we use plasma enhanced-ALD to synthesize large-area 2D transition metal dichalcogenides with tuneable functionalities for nanoelectronic and catalysis applications.
 

July 18, 2018

UPDATE: 1:30pm

Bldg. 440, A105/A106

The Nanophone: Sensing Sound with Nanoscale Spider Silk, Jian Zhou, Binghamton University.  Host:  Daniel Lopez

Hundreds of millions of years of evolution resulted in hair-based flow sensors in terrestrial arthropods that stand out among the most sensitive biological sensors known. These tiny sensory hairs can move with a velocity close to that of the surrounding air at frequencies near their mechanical resonance, in spite of the low viscosity and low density of air. No man-made technology to date demonstrates comparable efficiency. Here we show that nanoscale spider silk captures fluctuating airflow with maximum physical efficiency (Vsilk / Vair≈1) from 1 Hz to 50 kHz, providing an effective means for miniaturized flow sensing. Our mathematical model shows excellent agreement with experimental results for silk with various diameters: 500 nm, 1.6 µm, 3 µm. When a fiber is sufficiently thin, it can move with the medium flow perfectly due to the domination of forces applied to it by the medium over those associated with its mechanical properties. While traditional dynamic sensors trade sensitivity for bandwidth – or vice versa, the proposed approach enables the sensitivity of an ideal vibrational sensor without succumbing to the usual bandwidth limitations. By modifying a spider silk to be conductive and transducing its motion using electromagnetic induction, we demonstrate a miniature, directional, broadband, passive, low cost approach to detect fluctuating airflow with almost full fidelity over a frequency bandwidth that easily spans the full range of human hearing, as well as other mammals, birds, amphibians, and reptiles.

July 16, 2018

1:30 pm

Bldg. 440, A105/A106

The Topological Kondo Insulator SmB6: Surface States and Bulk Spin Excitions: Plus…   Laura G. Greene, National MagLab, Florida State University, and Center for Emergent Superconductivity.  Host Daniel Lopez

Samarium hexaboride (SmB6), a well-known Kondo insulator in which the insulating behavior of the bulk arises from strong electron correlations, has recently attracted great attention owing to its possible topological nature. Although there is strong evidence for this, corroborative spectroscopic evidence was lacking; unlike in the weakly correlated counterparts, e.g., Bi2Se3. Our planar tunneling spectroscopy results reveal the linear density of states (DOS) as expected for Dirac cones. The energy and temperature dependence indicate that the topological surface states are not protected above a certain temperature and energy range, and we invoke an inelastic tunneling model involving spin excitons [2.3] that accounts for the observed behavior.

[1] W.K. Park et al., Topological surface states interacting with bulk excitons in the Kondo insulator SmB6 revealed via planar tunneling spectroscopy” PNAS 113, 6599 (2016).
[2] W.T. Fuhrman et al., Interaction driven subgap spin exciton in the Kondo insulator SmB6” Phys. Rev. Lett. 114, 036401 (2015).
[3] G.A. Kapilevich et al. Incomplete protection of the surface Weyl cones of the Kondo insulator SmB6: Spin exciton scattering” Phys. Rev. B 92, 085133 (2015).
 
After this semi-informal talk, we may have informal discussions on any of these topics.
    (PCS = Point Contact Spectroscopy; PTS = Planar Tunneling Spectroscopy)
    Fe-based SCs: PCS detects DoS arising from nematicity, which is explained by orbital fluctuations.
    URu2Si2:        PCS shows hybridization gap is not the hidden order, and more.
    CeCoIn5:       Old PCS work first showing background is a Fano lineshape
 
                Preliminary, undigested PTS work, showing a field-induced pseudogap.

June 21, 2018

1:30pm

Bldg. 440, A105/A106

Engineering the polymer packing structure for intrinsically stretchable electronics, Jie Xu, Stanford University.  Hosts:  Tijana Rajh and Seth Darling.

In the rapidly growing interdisciplinary area of human-integrated and biomimetic electronics, by imparting skin-like mechanical properties (i.e. softness and stretchability) onto electronics, many new functionalities could be achieved. A first step towards this is the development of stretchable electronic materials, especially semiconducting materials. In this talk, I will introduce how we can engineer the polymer packing structure to realize high performance stretchable semiconductors. First, I will talk about the fundamental study of the polymer packing structure and dynamic mobility of nanoconfined soft matter. As an inspiration from this study, I will then move on to the development of a physical approach based on nanoconfinement effect for achieving the first highly stretchable and high-performance semiconductors, which have been further utilized to develop intrinsically stretchable integrated circuits. Further on, I will talk about the unique combination of the nanoconfinement effect and the roll-to-roll printing for simultaneously achieving both enhanced dynamics and multiscale morphological order for conjugated polymers, which are therefore imparted with largely improved stretchability, as well as significantly enhanced electrical performance. At the end, I will talk about how strain deformations influence the polymer packing structures and electrical characteristics in a plasticizer-enabled stretchable semiconducting films.   

June 21, 2018

11:10 am

Bdlg. 402, Room A1100

Quantum Engineering of Superconducting Qubits, William D. Oliver, Department of Physics and Lincoln Laboratory, Massachusetts Institute of Technology.  Host:  Supratik Guha 

Superconducting qubits are coherent artificial atoms assembled from electrical circuit elements. Their lithographic scalability, compatibility with microwave control, and operability at nanosecond time scales all converge to make the superconducting qubit a highly attractive candidate for the constituent logical elements of a quantum information processor. Over the past decade, spectacular improvement in the manufacturing and control of these devices has moved superconducting qubits from the realm of scientific curiosity to the threshold of technical reality. In this talk, we review this progress and our own work at MIT that are creating a future of engineered quantum systems.

June 15, 2018

11:00 am

Bldg. 440, Room A105/A106

The Full Field Diffraction X-ray Microscope on the ID01 beamline ESRF, Tao Zhou, European Synchrotron Radiation Facility (ESRF), Host: Martin Holt.

With the advent of high quality x-ray optics, several techniques have been proposed to exploit the imaging under Bragg conditions at synchrotron sources. Within the framework of the ESRF upgrade, a new dedicated instrument has been implemented on beamline ID01 at The European Synchrotron (ESRF). Since April 2017 this instrument is fully operational and has supplied users with Full Field Diffraction X-ray Microscopy (FFDXM) imaging adapted to various sample environments. Compared to more established scanning diffraction techniques, FFDXM offers fast, spatially resolved images on a large sample area without mechanical motions, perfectly suited for in situ and operando experiments.

The concept of FFDXM will be first demonstrated. A set of objective lens is placed downstream the sample to make a dark field image of the diffracted beam. At 6.5 meters away, the illuminated sample area (Field of View : 200×200 μm^2) is magnified and spatially resolved on a sCMOS camera with a resolution of 100 nm. Essentially an x-ray strain microscope, the FFDXM is capable of probing lattice tilt, strain and grain orientation at surfaces, buried interfaces or inside functioning devices, which is often unreachable for electron microscopy techniques.
Results of several user and in house experiments will be given next, to illustrate the principle of diffraction topography (strained STO), mosaicity (InGaN nano-pyramids) and strain (buried gas cavities in implanted Si wafers) mapping using FFDXM. Typical image acquisition time is around 1 sec; a complete set of measurement takes just a few minutes.
 
Based on these measurement techniques, more complex experiments were conducted. The final part of the talk shall cover preliminary results and outlook from the most recent developments of the microscope, including in situ heating and cryogenic cooling, operando chemistry, sub-ns time resolved and composition sensitive imaging.

June 14, 2018

11:00 am

Bldg. 440, Room A105/A106

Time-Resolved TEM Studies of Nonreversible Processes, Thomas Gage, Chemical Engineering & Materials Science, University of Minnesota.  Host: Ilke Arslan 

Time-resolved in situ TEM studies can offer exclusive insight into dynamic material processes.  High spatial resolution and the ability to perform correlative diffraction and real-space imaging studies make TEM unique as a characterization tool.  While pump-probe techniques can offer picosecond temporal resolution with TEM, they are limited to studying highly reversible processes.  Nonreversible processes, such as crystallization, require all transformation information to be acquired at the rate the phenomenon of interest occurs.  In this talk, I will discuss the unique in situ TEM capabilities we have at the University of Minnesota for studying nonreversible processes. I will focus on the example of laser annealing amorphous yttrium iron garnet films on non-garnet substrates.  The in situ TEM crystallization studies were performed using a high speed camera which is limited to millisecond resolution.  To further push the temporal resolution of in situ TEM studies with our setup, single shot TEM capability in a lightly modified TEM with a small LaB6 cathode was also explored. 

June 11, 2018

1:30 pm

Bldg. 440, Room A105/A106

Fluctuations and nonlinearity in a micromechanical thermal self-oscillator, James Lehto Miller, Kenny Micro Structures & Sensors Lab, Stanford University.  Host:  Daniel Lopez

Microelectromechanical (MEM) resonators are widely used as resonant sensors and oscillators in several areas of science and technology. Present MEM oscillators utilize an external feedback to sustain oscillations. In this presentation, I will discuss a MEM autonomous oscillator whose feedback is mediated by a direct current via the thermal-piezoresistive pumping mechanism. In contrast to traditional oscillators, this self-oscillator operates in its nonlinear régime, where the amplitude is self-limited by nonlinear stiffening and damping. We also study the thermomechanical noise spectrum of our device near the onset for self-oscillations, where we observe non-Lorentzian spectral broadening analogous to the onset of lasing or the ferromagnetic phase transition.

June 8, 2018

11:00 am

Bldg. 440, Room A105/A106

Imaging of Local Structure and Dynamics in Hard and Soft Condensed Matter Systems, Dmitry Karpov, New Mexico State University.  Host:  Martin Holt

With advancement of coherent probes there is a shift from integral studies to highly localized studies in either spatial or temporal domains. Nanostructures and low dimensional phenomena, correlated fluctuations and associated transitions directly benefit from new instrumental capabilities. Studies of ferroelectric and magnetic materials and of their local behavior allow both to test fundamental physics concepts and provide access to technologies with direct practical applications.

Topological phase transitions and topological defects are among the topics that are actively pursued in modern materials science. In recent study [1] conducted by our group we were able to visualize three-dimensional topological vortex structure in a volume of individual ferroelectric nanoparticle of barium titanate under external electric field using Bragg coherent diffractive imaging technique. Among other things we observed: (i) electric field induced structural transition from mixture of tetragonal and monoclinic phases to dominant monoclinic phase; (ii) controllable switching of vortex chirality; (iii) vortex mediated behavior of the nano-domains in the particle; (iv) and that the core of the vortex in the volume behaves as a nanorod of zero ferroelectric polarization which can be rotated by external electric field and can serve as a conducting channel for charge carriers. These findings can be used in the design of novel nanoelectronics devices and for creating artificial states of matter.
 
Better understanding of the materials behavior at the nanoscale requires ways of probing anisotropies of the refractive index. Using polarized laser light, we’ve developed a method [2] termed birefringent coherent diffractive imaging that allows to extract projections of dielectric permittivity tensor in nematic liquid crystal. Further expanding this tool into full-vectorial mode shows that the method can be applied for imaging of magnetic domains, cellular structures, and other samples with different forms of optical anisotropies such as birefringence, depolarization and dichroism. We expect broader impact when the technique is transferred to X-ray régime both from increase in resolution and penetration depth, and from the sensitivity of polarized X-rays to local atomic and ionic displacements and topological chirality.
 
[1] D. Karpov, Z. Liu, T. dos Santos Rolo, R. Harder, P.V. Balachandran, D. Xue, T. Lookman, E. Fohtung, Three-dimensional imaging of vortex structure in a ferroelectric nanoparticle driven by an electric field. Nature Comm. 8 (2017);
 
[2] D. Karpov, T. dos Santos Rolo, H. Rich, Yu. Kryuchkov, B. Kiefer, E. Fohtung, Birefringent coherent diffraction imaging. Proc. of SPIE Vol. 9931 (2016).

June 6, 2018

11:00 am

Bldg. 440, Room A105/A106

Advancing nanoscale materials through the development of coherent x-ray nanobeam scattering techniques, Anastasios Pateras, Department of Materials Science & Engineering, University of Wisconsin-Madison.  Host:  Martin Holt. 

Materials properties dramatically depend on their nanoscale structure. Tightly focused coherent x-ray nanobeams can reveal the atomic structure of crystalline thin films and heterostructures through strain-imaging approaches that solve the phase problem of x-ray crystallography with the use of iterative algorithms. While current modeling approaches are widely based on the kinematical theory of x-ray diffraction are limited to investigating thin layers with thicknesses below the x-ray extinction depth. By considering primary extinction and multiple scattering in the interaction of x-rays with crystals, state-of-the-art strain imaging techniques can be extended to incorporate dynamical diffraction directly inside a phase retrieval algorithm. This opens new opportunities for using coherent x-ray nanobeams for the structural investigation of quantum and energy materials systems that could not be thought before.

April 25, 2018

11:00 am

Bldg. 440, Room A105/A106

Coherent X-ray surface scattering imaging with high-resolution and ptychography, Joon Woo Kim, XSD, ANL, Host:  Martin Holt. 

Lensless coherent diffraction imaging (CDI) has enabled the structure determination of nanomaterials leading to significant scientific discoveries in the field of Materials Science. Coherent surface scattering imaging, which is reflection mode CDI with a grazing incident angle, can image thin nanostructures grown on an opaque substrate, of which the traditional CDI employing transmission or Bragg diffraction geometry is incapable. Since the first demonstration of coherent surface scattering imaging, the efforts have been made to improve spatial resolution with high flux x-ray and to overcome narrow isolated specimen limitations by employing ptychography. I’ll also discuss x-ray radiation pressure effects on nanocrystals during data collection process in Bragg CDI and formation mechanism of five-fold multiply twinned nanoparticle revealed by Bragg CDI.

April 20, 2018

2:00 pm

Bldg. 440, Room A105/A106

Investigating host-guest interactions in two dimensional supramolecular networks, Thomas A. Jung, Paul Scherrer Institute and University of Basel, Switzerland.  Host: Saw Wai Hla

Future quantum technologies, for example, rely on the detailed understanding of the interaction between different well-defined electronic states. Surface supported atomic and molecular systems provide a base for such investigations with the particular advantage of addressability. In our work we establish on-surface architectures which exhibit extraordinary local e.g. electronic, magnetic and quantum properties originating from the reduced dimensionality of the self-assembled and atomically precise architectures. Quantum well arrays, for example, can be produced by the interaction of porous on-surface networks with 2D Shockley-type surface states. Interestingly the periodicity of these (lossy) confinements causes band formation by the coupling between the individual quantum well [1]. In our more recent work the quantum wells have been modified by the adsorption / condensation of Xe atoms [2,3]. Localized and delocalized electronic states can be identified across the 2D array as they lead to new, site-specific physical and chemical behavior.

Sublattices in 2D checkerboard’ architectures of magnetic molecules on magnetic substrates can be selectively switched by chemical ligation [4]. Also we have observed the first example of 2D ferrimagnetic long-range order and remanence for such a 2D architecture on non-magnetic Au(110) [5]. Uniquely, self-assembled 2D architectures contribute to our understanding of fundamental interactions involved in host-guest systems and allow for the specific operation of quantum states with a partial delocalization delocalized by the supramolecular on-surface architecture.
 
[1] Lobo-Checa, J. et al., Science 325:300 (2009)
[2] Nowakowska, S. et al., Nat. Commun. 6:6071 (2015)
[3] Nowakowska, S. et al., Small 12:3757 (2016)
[4] Ballav N., et al., JPCL 4:2303 (2013)
[5] Girovsky, J. et al., Nat. Commun., DOI: 10.1038/ncomms15388 (2017).
 

April 20, 2018

11:00 am

Bldg. 400, Conf. Rm A105/A106

Data Driven 4-D X-ray Imaging of Nanoscale Dynamics, Mathew J. Cherukara, Advanced Photon Source, Argonne National Laboratory.  Host:  Martin Holt

Observing the dynamic behavior of materials following ultra-fast excitation can reveal insights into the response of materials under non-equilibrium conditions of pressure, temperature and deformation. Such insights into materials response under non-equilibrium is essential to design novel materials for catalysis, low-dimensional heat management, piezoelectrics, and other energy applications. However, material response under such conditions is challenging to characterize especially at the nano to mesoscopic spatiotemporal scales. Time-resolved coherent diffraction imaging (CDI) is a unique technique that enables three-dimensional imaging of lattice structure and strain on sub-ns timescales. In such a pump-probe’ technique, stroboscopic x-ray probes’ are used to image the transient response of a sample following its excitation by a laser pump’. In this talk I will present some of our recent work on imaging and modeling of phonon transport and lattice dynamics in nanomaterials. I will also describe my work in the use of deep neural networks in accelerating the analysis of and increasing the robustness of image recovery from 3D X-ray diffraction data. Once trained, our deep neural networks are thousands of times faster than traditional phase retrieval algorithms used for image reconstruction from 3D diffraction data.

April 16, 2018

11:30 am

Bldg. 440, Conf. Rm A105/A106

Geometric Charges and Kirigami,  Michael Moshe, Host:  Daniel Lopez

Kirigami patterns generate non-trivial three dimensional behavior from perforated sheets, and so offer a promising means for developing mechanical metamaterials. To create a generic account of the mechanical behavior of kirigami, we study the unit cell of a typical kirigami structure: an isolated frame. The mechanical behavior of the entire sheet may then be understood in terms of the coupling of many individual frames.

Recent developments in a geometric formulation of elasticity theory paved the way for a mathematical description of such isolated frames using the concept of geometric charges”. In this approach the mechanical problem of Kirigami and coupled frames is transformed to a simpler problem of interacting geometric charges.
 
In this talk I will present experimental and theoretical results on the relation between Kirigami, the geometric approach to elasticity, and geometric charges. I will show how these results provide  simple rules for designing nontrivial Kirigami patterns.

April 2, 2018

11:00 am

Bldg. 440, Conf. Rm A105/A106

X-ray Studies of the Structure and Properties of Materials During Synthesis and Processing, Matt Highland,  Materials Science Division,  Argonne National Laboratory.  Host:  Martin Holt
 
The properties and functionality of a material depends on its structure as well as its interactions with other materials and its environment. Understanding the nature of these interactions will allows use to create new models and define new methodologies for making materials with desired properties. Gaining this understanding requires experimental techniques that allow us to probe the local structure, phase, and strain of a material system during synthesis and processing, within a larger structure, or under excitation. A variety of x-ray techniques are available to address these challenges. I will describe experiments in which we have used a number of these techniques to probe materials during synthesis, high temperature processing, and ultra-fast excitation. I will discuss how this work provides insight into roles that microstructure and local strain fields play in defining the properties of a material and describe a number of projects motivated by these studies.

March 29, 2018

11:00 am

Bldg. 440, Conf. Rm. A105/A106

Quantum Ordering and Mesoscale Dynamics Unraveled by Focused Coherent X-ray Beams, Qingteng Zhang, XSD, ANL. Host: Martin Holt
 
An ongoing scientific thrust is pushing forward a deeper understanding of the rich correlation between electronic, spin, orbital orderings and atomic lattice in quantum materials. A recent study at the Hard X-ray Nanoprobe (HXN) in Center for Nanoscale Materials (CNM) has shown that quantum ordering can be enhanced in patterned nanostructures [1], providing new venues for the manipulation of quantum structures and exciting opportunities for the design and engineering of functional nanomaterials. One of the science cases is ferroelectric nanodomains in thin atomic layers of complex oxides. Ferroelectric polarization in epitaxial nominal atomic layers often forms into striped nanodomains to minimize the total electrostatic energy of the system. Domain walls provide versatile control of thin film properties because domains are easily reconfigurable and intriguing properties arise at domain walls due to the very large atomic strain caused by abrupt change of polarization direction. In a 100 nm thick PbTiO3/SrTiO3 superlattice, the electric coupling between the ferroelectric PbTiO3 layers is tuned by the SrTiO3 layers and results in nm-periodicity domains with serpentine striped patterns commonly observed in spinodal decomposition systems. This seminar will show that the ferroelectric nanodomains can exhibit thermally-driven equilibrium dynamics [2] similar to the Brownian motions [3] and gelation-induced arrested dynamics of colloidal nanoparticles [4], albeit on a much slower timescale of thousands of seconds. The temperature dependence on the time scale of domain fluctuation can be described using Arrhenius equation yielding an activation energy of 0.35 ± 0.21 eV. This energy level corresponds to the average energy barrier height that separates energetically degenerate domain configurations and implies that the formation and fluctuation of nanodomains may be affected by pinning mechanisms such as oxygen ion vacancies.
 
The seminar will also discuss possible prospective areas of research at the HXN, including a systematic investigation on the size-dependence of quantum orderings in patterned nanostructures which plans to leverage the resources of CNM, and speckle analysis using pattern recognition and deep learning which plans to leverage the computing resources at ALCF.
 
References:
[1]. J. Park, J. Mangeri, Q. Zhang et al. Nanoscale 10, 3262 (2018)
[2]. Q. Zhang et al. Phys. Rev. Lett. 118, 097601 (2017)
[3]. Q. Zhang et al. J. Synchrotron. Rad. 63, 679 (2016)
[4]. Q. Zhang et al. Phys. Rev. Lett. 119, 178006 (2017)
 

March 15, 2018

2:00 pm

Bldg. 440, Conf. Rm. A105/A106

Antimicrobial Photodynamic Therapy with Ga-Protoporphyrin Derivatives Against Pathogenic Bacteria, Ana Morales-de-Echegaray, Wei Research Lab, Department of Chemistry, Purdue University.  Host:  Tijana Rajh.

Bacterial pathogens have the ability to acquire hemin through different mechanisms. One mechanism is through cell-surface hemin receptors (CSHRs), which are capable of rapid hemin recognition and make the bacteria vulnerable to antimicrobial photodynamic inactivation (aPDI). The work presented here focuses on gallium protoporphyrin IX (GaPpIX) as a photosensitizer for aPDI against staphylococci. GaPpIX is rapidly uptaken into CSHR-expressing bacteria, and is easily detected within minutes of exposure. Assessment of GaPpIX as a photosensitizer against laboratory strains of Staphylococcus aureus, clinical isolates of methicillin-resistant S. aureus (MRSA), and S. epidermis shows aPDI activity at low micromolar levels, following 15 minutes of exposure to a compact fluorescent light bulb or at nanomolar levels when exposed for 10 seconds with a light emitting diode (LED) light source. Activity also had greater potency when compared against metal-free protoporphyrin (PpIX). These results led to the design of a more potent photosensitizer by incorporating GaPpIX into apohemoglobin (GaPpIXHb) and using the hybrid protein to coat 10-nm silver nanoparticles (AgNPs). The GaPpIXHb-AgNP complexes exhibit remarkable aPDI activity using nanomolar loadings of GaPpIX against clinical MRSA isolates.

March 1, 2018

11:00 am

Bldg. 440, Conf. Rm. A105/A106

Emergent Topology in Artificial Graphenes, Xiao Hu, International Center for Materials Nanoarchitectronics (WPI-MANA), National Institute for Materials Science (NIMS), Tsukuba, Japan.  Host: Ulrich Welp

Honeycomb lattice plays an important role in the course of fostering topology physics as known from the Haldane model and the Kane-Mele model [1]. Recently we formulate a new way to achieve topological states exploiting the C6v symmetry of honeycomb structure, which can be applied to various artificial graphenes with tremendous recent interests. As the first example we show how to realize topological electromagnetic transportations in dielectric photonic crystals, which has been proved by recent experiments [2,3,4]. This idea can also be applied to fermionic systems, and especially we find topological electronic states protected by huge energy gaps in order of eV in graphene with regular nano-hole arrays [5,6,7]. Our approach provides a new facet for exploration of novel topological phenomena and functionalities in terms of advanced nanotechnologies.

 References: [1] H.-M. Weng, R. Yu, X. Hu, X. Dai and Z. Fang: Adv. Phys. vol. 64, 227 (2015).  [2] L.-H. Wu and X. Hu: Phys.  Rev. Lett. vol. 114, 223901 (2015).  [3] Y.-T. Yang, J.-H. Jiang, X. Hu and Z.-H. Hang: arXiv.1610.07780.  [4] Y. Li, H. Chen and X. Hu et al.: arXiv:1801.04395.  [5] L.-H. Wu and X. Hu: Sci. Rep. vol. 6, 24347 (2016).  [6] T. Kariyado and X. Hu: Sci. Rep. vol. 7, 16515 (2017).  [7] T. Kariyado, Y.-C. Jiang, H.-X. Yang and X. Hu: arXiv:1801.03115.

Feb. 21, 2018

2:00 pm

Bldg. 440, Room A105/A106

Deep Learning Applied to Simulation of 2d Materials”, Isaac Tamblyn, Security and Discuptive Technologies, National Research Council of Canada. Host:  Pierre Darancet In this talk,

I’ll show how we are using Artificial intelligence as a new tool to improve computer models of physical and chemical processes at the nanoscale. In particular, I’ll discuss how we show how to rapidly solve the Schrödinger Equation [1], predict phase transitions [2], estimate the strength of chemical bonds [3], provide a confidence level for our predictions [4], and achieve a million times speed up in simulating a nanostructured 2d-material [5].

[1] K. Mills, M. Spanner, I. Tamblyn, Deep learning and the Schrödinger equation Phys. Rev. A 96, 042113 (2017), arXiv:1702.01361
 [2] K. Mills, I. Tamblyn, Deep neural networks for direct, featureless learning through observation: the case of 2d spin models, arXiv:1706.09779
 [3] K. Ryczko, K. Mills, I. Luchak, C. Homenick, I. Tamblyn, Convolutional neural networks for atomistic systems, arXiv:1706.09496 
 [4] K. Mills, I. Tamblyn, Phase space sampling and operator confidence with generative adversarial networks, arXiv:1710.08053
 [5] I. Luchak, K. Mills, K. Ryczko, A. Domurad, I. Tamblyn, Extensive deep neural networks, arXiv:1708.06686

Feb. 20, 2018

11:00 am

Bldg. 440, Room A105/A106

Scattering Studies of a Micron-sized Gold Particle and Average Nanoparticles”, Milan K. Sanyal,Saha Institute of Nuclear Physics Kolkata, West Bengal, India.  Host:  Martin Holt

Availability of intense synchrotron sources delivering nano-sized beam should be able to provide us structure, composition and strain profiles within a nanoparticle from averaged information obtained over only few such particles and finally may be even from an individual particle. We shall discuss here few evolving x-ray scattering techniques with the help of three recently studied systems, namely distribution of non-FCC phase in a micron-sized gold particle, shape-evolution in gold nanoparticles grown in nano-pores and extraction of compositional profile of an average III-V semiconductor quantum-dot - the size-tunable photonic material.

Feb. 13, 2018

10:30 am

Bldg. 440, Room A105/A106

Materials and Processing for Quantum Computing - Ion Traps and Superconductors”, David P. Pappas, National Institute of Standards and Technology, Boulder.  Host:  Ilke Arslan.

A brief description and history of quantum computing will be presented. Materials topics relevant to ion traps and superconductors will be presented. For the ion traps, the influence of anomalous surface noise on gate operations will discussed. Progress at NIST to study and mitigate these effects will be presented. These include cleaning, surface spectroscopy and scanned probe microscopy as well as a novel stylus trap to measure noise from proximal surfaces. In the second part of the talk similar topics on superconducting transmons will be discussed. In particular, the effects and mitigation techniques of spurious two-level systems at surfaces and interfaces as well as new scalable techniques for fabricating junctions will be presented.

Feb. 2, 2018

2:00 pm

Bldg. 440, Room A105/A106

Flexible Electronics Based on Two-Dimensional Materials and Beyond”, Xu Zhang, Massachusetts Instittue of Technology. Host:  Daniel Lopez

The success in creating atomically thin and mechanically robust two-dimensional (2D) materials has unveiled new possibilities for next generation of flexible and ubiquitous electronics. One critical distinction between 2D crystals and 3D crystals is that 2D crystals are all-surface materials. Therefore, it is essential to understand how 2D materials interact with their environments and how this interaction impacts their electronic properties. A suite of X-ray techniques is used to investigate how the functionalizing dopants impact the electronic and chemical states of graphene. Based on this study, we develop an effective and non-invasive doping method for graphene through plasma-based chlorination. In the second part of this talk, I will focus on system-level applications of 2D materials-based flexible electronics with a special focus on wireless energy harvesting and communication. In particular, we developed a 2D material-based GHz flexible rectifier as an enabling component for both wireless energy harvesting and RF frequency mixing. It is the first flexible rectifier operating up to the X-band and it fully covers the Wi-Fi channels. By integrating with an antenna, the MoS2-enabled rectenna successfully demonstrates direct energy harvesting of electromagnetic (EM) radiation in the Wi-Fi band and lights up a commercial light-emitting diode (LED) with zero external bias (battery-free).

Feb. 1, 2018

2:00 pm

Bldg. 440, Room A105/A106

Novel transport characterizations in anisotropic and disordered”, Lintao Peng, Northwestern University, Electrical Engineering and Computer Science.  Host:  Nathan Guisinger

New electrical transport techniques are introduced for characterization of exfoliated black phosphorous devices. First, an all-electrical conformal-5-contact method is proposed to determine the crystal orientation of an exfoliated flake. Second, the disorder-related switching transient conductivity, and a microscopic DOS model thereof, are discussed within the framework of dispersive diffusion transport and continuous time random walk. Finally, the observation of a disorder-scaling behavior in gate-dependent conductivity is presented and modeled.

Jan. 24, 2018

3:30 pm

Bldg. 440, Room A105/A106

Light- and heat-managing nanomaterials for personal health and energy efficience”, Po-Chun Hsu, Department of Mechanical Engineering, Stanford University.  Host:  Supratik Guha

Energy and health are the two vital necessities for humans. While energy is indispensable, it also produces greenhouse gas emission and climate change. In the US, 12% of total energy is used for maintaining indoor temperatures, which is the fundamental need for human health. Therefore, it is crucial to reduce the building energy consumption while maintaining thermal comfort. In this talk, I will present several nanomaterials that can manage photons and heat transfer to enhance building energy efficiency and personal health. The first part is the personal thermal management by controlling radiation heat transfer, which contributes 50% of the human body heat dissipation. I will demonstrate infrared-reflective nanowires textile for heating, infrared-transparent nanoporous polyethylene for cooling, and asymmetrical emitter to achieve both heating and cooling. The second part is transparent electrodes and electrochromic smart windows for solar heat gain modulation. Fabricated by electrospinning, the metal nanofiber transparent electrodes with superior electrical and optical properties and durability can improve the speed and cycle life of electrochromic windows.

Jan. 11, 2018

11:00 am

Bldg. 440, Room A105/A106

There’s Plenty of Room in Higher Dimensions - Internal Resonance and Decision Mechanisms in Mechanical Resonators”, Axel Eriksson, Chalmers University of Technology, Sweden.  Host:  David Czaplewski. 

To understand how adaptive behavior emerges in living and artificial systems is a major challenge for science. In this talk, I consider something simpler – dead vibrating silicon beams and graphene membranes. I will give a short introduction to nonlinear dynamics of vibrational modes in mechanical resonators. An interesting situation occurs when two vibrational modes have a rational relation between their frequencies – a so called internal resonance. The match in frequency allows for efficient transfer of energy between the two modes. Hence, the internal resonance will strongly affect both the dissipation and the driven response of the resonator. The complex response has similarities with other strongly nonlinear systems such as interacting neurons in the brain. Furthermore, the driven response may exhibit choice mechanisms leading to stochastic switching between different long-term behaviors. In future work, we plan to experimentally control this switching as a means to achieve primitive adaptive behavior in mechanical resonators.