A simple process enables to synthesize tungsten oxide with various nanomorphologies, i.e. nanorods, nanowires, and nanosheets. The tungsten hexachloride (WCl6) was used as a raw material and the tungsten oxide nanoparticles were obtained by solvothermal treatment with solvents, i.e., ethanol, mixed solvent (ethanol+water), and water, at 200°C for 10 h. The various crystalline phases of tungsten oxide, such as monoclinic W18O49 nanorods, hexagonal WO3 platelets, and monoclinic WO3 nanosheets, were synthesized by simply changing the composition of the solvent. The oxygen, which was contained in water, played an important role in the final tungsten oxide phase. Especially, W18O49 nanorods grew to nanowires as the concentration of WCl6 was decreased. Using this simple process, it will be possible to control the crystalline phase and morphologies of nanostructured tungsten oxide system.

The authors prepared uniformly shaped WO 2.72 nanowire bundles using the solvothermal synthesis method. They investigated the potential of the WO 2.72 nanowire bundles to be used as a cathode electrode for electrochromic devices and the effect of the Li + insertion ͑or extraction͒ kinetics and diffusion of Li +. An electrode consisting of arrays of WO 2.72 nanowire bundles was formed and used in an experiment using the Langmuir-Blodgett technique. The one-dimensional nanostructure of WO 2.72 has a high Li-ion diffusion coefficient ͑ϳ5.2ϫ 10 −11 cm 2 /s͒ and low charge transfer resistance ͑ϳ28.6 ⍀͒, which result in its having a fast electrochromic response time ͑coloring time Ͻ3.5 s, bleaching time Ͻ1.1 s͒, and outstanding high coloration efficiency ͑Ͼ55 cm 2 /C͒.

We have investigated the effects of surface passivation on off-state leakage current and current collapse effects of high-voltage GaN-on-Si heterojunction field effect transistors (HFETs) by using low pressure chemical vapor deposition (LPCVD) of silicon nitride (SiN x ). In this work, the metaloxide-semiconductor (MOS) structure-based HFETs are realized on AlGaN/GaN epitaxy grown silicon substrates by metal-organic chemical vapor deposition (MOCVD). For a comparative study, we have fabricated two types of HFETs, standard and modified MOS-HFETs. In the modified MOS-HFETs process, the surface passivation layer of SiN x is deposited by LPCVD after the mesa isolation step, while the gate is deposited and self-aligned in the trench etched in LPCVD-SiN x layer using inductively coupled plasma reactive ion etching (ICP-RIE). The high temperature deposition of LPCVD-SiN x prevents the degradation caused by the ohmic annealing and other process-induced surface damage. Compared to the standard MOS structure, the modified MOS-HFET devices exhibit 10 times lower off-state leakage currents within high voltage range (0-800 V) and significantly alleviated current collapse effects simultaneously.

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