The crystal structure and spectral properties of bulk MoS 2 were investigated at high pressures up to 51 GPa using a diamond anvil cell with synchrotron radiation in addition to high temperature X-ray diffraction and high pressure Raman spectroscopic analysis. While the crystal structure of MoS 2 is stable on increasing temperature, results of high pressure experiments show a pressure-induced isostructural hexagonal distortion to a 2H a -hexagonal P6 3 /mmc phase around 26 GPa as predicted by theoretical calculations reported earlier. The 2H a -hexagonal phase coexists with the ambient 2H c phase up to 51 GPa, the highest pressure achieved in our experiments. The Raman data obtained in our high pressure experiments show consistent changes in the vibrational modes. Furthermore, the diffraction data obtained for the shocked MoS 2 to pressures 8 GPa is found to be structurally resilient.

Structural behavior of bulk WS 2 under high pressure was investigated using synchrotron X-ray diffraction and diamond anvil cell up to 52 GPa along with high temperature X-ray diffraction and high pressure Raman spectroscopy analysis. The high pressure results obtained from X-ray diffraction and Raman analysis did not show any pressure induced structural phase transformations up to 52 GPa. The high temperature results show that the WS 2 crystal structure is stable upon heating up to 600 • C. Furthermore, the powder X-ray diffraction obtained on shock subjected WS 2 to high pressures up to 10 GPa also did not reveal any structural changes. Our results suggest that even though WS 2 is less compressible than the isostructural MoS 2 , its crystal structure is stable under static and dynamic compressions up to the experimental limit.

Anodized alumina templates have emerged as an important material system for the low-cost fabrication of semiconductor and metal nanostructure arrays. This material system uses natural self-organization for the creation of periodic arrays of nanoscale structures. In spite of the extensive experimental investigations reported in the literature, the theoretical mechanisms, and their dependence on process parameters such as current density and electrolytes, are not well understood. In this article, we propose a theoretical model based on the rate equation approach in which both the alumina formation and etching are considered. This model employs a minimal number of parameters and yet captures the essence of the experimental observations with sulfuric acid as the electrolyte and can be used as a predictive tool for process selection.

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