Argonne National Laboratory

Seminar Series

Date Title

Dec 19, 2017

1:00 pm

Bdlg. 440, Room A105/A106

"Mechanics of Low Dimensional Materials - Plasticity and Fracture",  Horacio D. Espinosa, James and Nancy Farley Professor of Mechanical Engineering, Northwestern University.  Host:  Daniel Lopez

In the past decade, there has been a major thrust to synthesize low dimensional materials exhibiting unique and outstanding physical properties. These nanomaterials are envisioned as building blocks for the next generation of lightweight materials, electronics, sensors, and energy systems. In these applications, identification of size and time dependent mechanical properties is essential. However, such endeavor has proven challenging from both experimental and modeling perspectives. In this presentation, progress in nanoscale mechanical experimentation and modeling, towards accurate identification of plasticity and fracture, will be discussed. Two case studies will be examined. In the first one, the plasticity and time dependent fracture of silver nanowires will be explored by means of in situ electron microscopy testing and molecular modeling. We will show that silver nanowires are very strong and exhibit an unusual Bauschinger effect arising from high surface to volume ratios. Interestingly, we will also show that the same feature can lead to stress-driven atomic surface diffusion, leading to time dependent failure instabilities under constant strain conditions. In a second case study, we will discuss the mechanical properties of graphene oxide, a material presenting functional groups ideal for synthesis of multilayer nanocomposites and membrane filtration films. The effect of chemical functional group type and density on monolayer toughness, stiffness, and strength will be ascertained using a combination of nanomechanics experiments and molecular modeling. Pathways for achieving a several-fold increase in the toughness of graphene oxide monolayers will be examined.

Dec. 11, 2017

11am

Bldg. 440, Room A105/A106

"Intentional Nonlinearity in the Small Scale with Applications to Multi-Frequency Atomic Force Microscopy (AFM) and Mass Sensing", Randi Potekin, Dept of Mechanical Science and Engineering, University of Illinois, Urbana, Host:  Daniel Lopez

In recent decades, micro- and nanomechanical resonators have drawn considerable attention due to their high sensitivity, portability and relatively low-cost. They are currently used in a wide variety of applications including precise frequency generation and timekeeping, nanoscale imaging and sensor technology. This presentation will include results of experimental, numerical and analytical investigations of microscale mechanical resonators with applications in atomic force microscopy (AFM) and mass sensing. The focus of this research effort is to exploit nonlinear phenomena in order to enhance existing measurement techniques in AFM and mass sensing. In the first section of the talk, a summary of my work in the area of AFM will be presented in which I consider a new design of the AFM cantilever. The new probe design utilizes internal resonance to passively amplify higher harmonics for use in multi-harmonic AFM. In contrast to other multifrequency AFM techniques, this approach provides multiple channels with strong signal to noise ratios while maintaining the simplicity of a single excitation frequency. I studied the capability of this cantilever to characterize material properties of polymers, bacteria and viruses and found that the internal resonance-based design results in enhanced sensitivity to Young’s modulus.

In the second section of the talk, I will present results from a study of a new micromechanical mass sensor design that utilizes amplitude shifts within ultra-wide broadband resonances. The sensor consists of a clamped-clamped beam under harmonic base excitation having a concentrated mass at its center. Interestingly, due to geometric nonlinearity, for sufficiently large base excitation amplitudes there is no theoretically predicted jump-down bifurcation point in the primary resonance curve. Further, the critical excitation level above which there is no theoretical jump-down event is significantly lowered by the presence of the concentrated mass, hence its critical role in the beam design. In practice, a jump-down bifurcation point may occur due to the excitation of higher resonances, perturbations in the initial conditions and/or excitation amplitude caused by noise, or the basin of attraction for the upper branch solution may become impractically small. However, I believe it may be possible to physically realize a critical excitation amplitude above which the bandwidth of the resonance increases substantially. By operating at an excitation amplitude above this critical threshold, the ultra-wide resonant bandwidth can be exploited in a mass-sensing technique based on amplitude tracking.
 

Dec. 1, 2017
11am
Bldg. 440, Room A105/A106
"Non-Equilibrium Materials Discovery: Terahertz Light-Quantum-Tuning of Electronic Phases Hidden by Superconductivity", Jigang Wang, Dept. of Physics & Astronomy, Iowa State University - Ames Laboratory.  Host:  Haidan Wen
 
Observation of “sudden” quantum quench of dominant phases without heating of other degrees of freedom in the system can provide transformative opportunities for accessing and controlling new, thermodynamically forbidden, phases of matter. These states are not accessible by traditional adiabatic tuning methods: chemical substitution, temperature, pressure, or magnetic field that reach exotic phases, often with serendipity, via spontaneous coherence. In this talk, I will discuss several examples using terahertz (THz) light-matter coherence for non-adiabatic Hamiltonian design in superconductors which expose new phases and collective modes hidden in equilibrium by the dominant competing SC order. Finally, I will present the outlook for applying the THz quantum control strategy in topological materials and spectroscopy nano-imaging.