Externally-heated Diamond Anvil Cell Research Articles

Pressure-Enhanced Interdiffusion in Amorphous Si/Ge Multilayers: Implications for Defect-Mediated Diffusion

AbstractWe have studied the pressure-dependence of the interdiffusion rate in amorphous Si/Ge multilayers. Samples were annealed in an externally-heated diamond anvil cell at 693 K at pressures ranging from 0 to 3.1 GPa. Interdiffusion rates were determined by ex situ x-ray diffraction measurements of the decay of the artificial Bragg peaks associated with the multilayer periodicity. Scaling experiments were performed to factor out the effects of concentration and time dependence in the diffusivity. All samples showed a consistent increase in diffusivity with applied pressure, characterized by a negative activation volume ranging from −44±3 to −37±2 percent of the atomic volume of Si for films ranging in average Si composition from 25 to 71 percent, respectively. These results are consistent with a model for diffusion in amorphous Si and Ge based on dangling bond migration.

Systematics in the melting behavior of the alkali metals from DAC measurements

The alkali metals K, Rb and Cs undergo a series of phase transitions that are related to a s-to-d electron transfer. These solid-solid transitions strongly affect the melting behavior in the vicinity of the transitions. An externally-heated diamond-anvil cell was used to measure melting temperatures of the alkali metals, Na, K, Rb and Cs at pressures to 150 kbar. Melting was determined visually by changes of the optical properties of the metals. Pressures were obtained from the known pressure and temperature shifts of the ruby line which can be used for accurate measurements to about 650 K. The melting temperature of sodium rises continuously with pressure. The slopes of the melting curves potassium and rubidium change appreciably at the bcc-fcc transitions at 110 and 90 kbar, respectively. An extremely steep melting curve of cesium is observed after the electronic transition at 42 kbar.