Well-defined uniform octahedral WO₃ are prepared via a simple one-step thermal plasma technique. The detailed structures of the synthesized materials are characterized by XRD, EDX, FESEM, SAED and HRTEM. Each octahedron is nearly perfect with a highly symmetric, regular shape containing 8 facets, 6 vertices, and 12 edges, which exhibit sharp edges and corners as well as smooth surfaces. Processing parameters dependent experiments are performed to control its shape and size distribution. The regular octahedral WO₃ shows good sensing properties to benzene gas, which might mainly be due to its highly exposed {111} faces and the regular octahedral shape.

High power impulse magnetron sputtering (HiPIMS) is well known in modern physical vapor deposition (PVD) owing to its high peak power density, high degree of ionization, high plasma density and hence high ion flux towards the substrate that allows ones to deposit high quality thin films in comparison with conventional magnetron sputtering technology. The present short review on HiPIMS intends to provide readers with a summary of the current status of this emerging PVD technique: the developmental history, the plasma characterization, and the applications in hardness and functional thin film fabrications. Several items on the distinctive feature of HiPIMS, including self-sputtering mechanism, low deposition rate, arcing phenomenon and key factors of deposition process are reviewed in detail. To limit the scope, the emphasis is put on thermo-chromic VO₂ thin film deposited by HiPIMS. Based on this typical issue, some classical ideas and approaches on fabrication of the functional thin films through HiPIMS technique are demonstrated.

Blue core (BC) is a special spectral phenomenon in argon helicon plasma, with intense blue lights from ion emission around the radial center of discharge tube. In this paper, the characteristics of BC in argon (Ar) helicon plasma were investigated experimentally from aspects of discharge mode transitions, plasma spatial distributions, and spectral features. It is found that the BC generally appears at strong magnetic field (480 G or above in this work) with high plasma density in wave mode, accompanied by exponentially rising of ion line intensity. The electron density and temperature, the neutral density and temperature, and the line emission intensity show a radial profile with a central peak in BC mode. The steep gradient of ion line intensity (corresponding to the ion density) defines a clear boundary of the core. Further, a pressure balance model was developed to investigate the influence of neutral depletion on BC formation. The neutral density is depleted significantly from $7.24\times {10}^{13}$ to 0.38 × 10¹³ cm⁻³ at magnetic field of 600 G in BC mode, while to 3.13 × 10¹³ cm⁻³ at magnetic field of 250 G in normal wave (NW) mode. The ionization rate in BC reaches as high as 70% compared with 9.6% of that in NW mode. The ionization rate and the ion line intensity show similar radial profiles, indicating the BC phenomenon is closely related to the distribution of peaked ion density and hollowed neutral density. Fundamentally, the central electron heating and strong magnetic field contribute to the centrally local high ionization rate and strong neutral heating. The severe neutral depletion with prominent central heating is considered to be the immediate cause of appearance of blue core.