Structures of Prismatic and Pyramidal Surfaces of Quartz

The structure of natural growth surfaces of Quartz (10-11) and (10-10)-water interfaces were measured with high resolution X-ray reflectivity. Key observations of this work include:

• The (10-11) growth surface is terminated by a complete SiO₂ layer with a non-bridging oxygen.
• A surface hydration layer is 1.6 Å above the NBO of the surface silicon, with ~1.8 ± 0.15 water per unit mesh (or one water per 19 Ų). This is lower than the expected 2D water density (one water per 10 Ų), but is a dense layer with the NBO.
• The hydration layer is ~3.1 Å above the outermost BO, which is comparable to the expected value of ~2.8 Å for a hydrogen bond.
• Vertical lattice displacements are small

  • Δz_Si < 0.2
  • Δz_O(NBOs) ~ 0.2 Å, 0.4 Å
• No evidence for any longer range ordering of the water (e.g., due to ‘ice-like’ layers) were observed beyond the surface hydration layer.
• Similar results were obtained for the quartz (10-10) surface.