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Recently, rhenium (Re) based ohmic contacts to GaN have been studied for their low resistivity, smooth surface morphology, and sharp edge acuity at low annealing temperatures. In this work, we discuss the evolution of surface microstructures for Re‐Al‐Ni‐Au ohmic contacts on n‐GaN as a function of Re layer thickness and annealing temperature. For all Re thicknesses, the Al and Ni segregate into agglomerates that increase in size with increasing annealing temperature. These agglomerates are surrounded by Al‐Au films. Along with the underlying Re layer, they form different crystallographic phases of Re‐Al‐Ni, Al6Re, AlAu2, and Al2Au5. This, along with the formation of Re‐N phases at the metal‐semiconductor interface leads to low resistivity ohmic contacts on n‐GaN. Investigating the evolution of the contact microstructure is an important step in understanding the behavior of the Re‐based ohmic contact system. [ABSTRACT FROM AUTHOR]

While 2D layers of WS2 have been extensively studied, there are very few investigations of WS2 nanotubes. These have usually been grown via a 2-step process involving a WO3-x intermediate. We report a simple process for the synthesis of WS2 nanotubes via the sulfurization of tungsten films under appropriate conditions and present details of their structural and optical properties that help elucidate the formation mechanism. Electron-beam evaporated films of tungsten are sulfurized under flowing N2 gas at 950-1000 °C temperature under atmospheric pressure to obtain WS2 nanotubes. High-resolution scanning and transmission electron microscopy studies show that 2D WS2 flakes curl up and wrap around themselves to form nanotubes. Interlayer spacings in both 'a' and 'c' directions are slightly smaller than the corresponding values in bulk and thin film WS2. Micro-photoluminescence and micro-transmission studies show a resonance that seems intrinsic to the WS2 nanotubes since it cannot be related to the known optical characteristics of WS2 flakes.