synthesis-characterization-high-c-axis-zno-thin-film-plasma-enhanced

Synthesis and Characterization of High c-axis ZnO Thin Film by Plasma Enhanced Chemical Vapor Deposition System and its UV Photodetector Application

In this study, zinc oxide (ZnO) thin films with high c-axis (0002) preferential orientation have been successfully and effectively synthesized onto ...

National Taipei University of Technology (TAIPEI TECH)

This paper describes a new low-temperature process underlying the synthesis of highly transparent ultrananocrystalline diamond [UNCD] films by low-pressure and unheated microwave plasma jet-enhanced chemical vapor deposition with Ar-1%CH4-10%H2 gas chemistry. The unique low-pressure/low-temperature [LPLT] plasma jet-enhanced growth even with added H2 and unheated substrates yields UNCD films similar to those prepared by plasma-enhanced growth without addition of H2 and heating procedure. This is due to the focused plasma jet which effectively compensated for the sluggish kinetics associated with LPLT growth. The effects of pressure on UNCD film synthesis from the microwave plasma jet were systematically investigated. The results indicated that the substrate temperature, grain size, surface roughness, and sp3 carbon content in the films decreased with decreasing pressure. The reason is due to the great reduction of Hα emission to lower the etching of sp2 carbon phase, resulting from the increase of mean free path with decreasing pressure. We have demonstrated that the transition from nanocrystalline (80 nm) to ultrananocrystalline (3 to 5 nm) diamond films grown via microwave Ar-1%CH4-10%H2 plasma jets could be controlled by changing the pressure from 100 to 30 Torr. The 250-nm-thick UNCD film was synthesized on glass substrates (glass transition temperature [Tg] 557°C) using the unique LPLT (30 Torr/460°C) microwave plasma jet, which produced UNCD films with a high sp3 carbon content (95.65%) and offered high optical transmittance (approximately 86% at 700 nm).

Synthesis of highly transparent ultrananocrystalline diamond films from a low-pressure, low-temperature focused microwave plasma jet.

Au line nanostructures with different pitch distances from 500 nm to 950 nm on ITO coated glass substrates have been fabricated at room temperature for exploring the color light guide in all kinds of display system. The patterned Au line array is used as a light outcoupling and color-selection component due to the emission wavelength changed by the Au line arrays with different pitch distances that could achieve multi-color selections. The ITO coated glass substrates patterned with periodic Au line arrays with controlled line pitches has been demonstrated and used as a color filter in all display devices. Using a proper pitch distance of Au line nanostructures, the basic third colors of red, green, and blue (RGB) can be simply gained and controlled without a traditional color filter for future optoelectronic display devices.

Light guide of Au nanostructures for color-filterness optoelectronic display devices.

The surfaces of implantable biomaterials improving biocompatibility and bioinertness are critical for new application of bioimplantable devices. Diamond-like carbon (DLC) film is a promising biomaterial with use for coating bioimplantable devices because of its good biocompatibility, bioinertness, and mechanical properties. In this study, concurrent improvement in biocompatibility and bioinertness of DLC films has been achieved using N-incorporation technique. The N doping degree was found to play an important role in affecting the biocompatibility and bioinertness of N-doped DLC films. The results indicated that the N-doped DLC films deposited at N(2) concentration of 5% could help to create suitable condition of surface/structure/adhesion combination of DLC films in the both affinity of the L929 mouse fibroblasts and electrochemical inertness in the Hank's balanced salt solutions (simulating human body fluids). N doping supports the attachment and proliferation of cells and prevents the permeation of electrolyte solutions, thereby simultaneity improved the biocompatibility and bioinertness of DLC films. This finding is useful for the fabrication and encapsulation of in vivo devices without induced immune response in the human body.

Concurrent improvement in biocompatibility and bioinertness of diamond-like carbon films with nitrogen doping.

Gasochromic VO2 thin films were fabricated by the sol-gel spin-coating technique. The results of X-ray absorption spectroscopy and resonant inelastic X-ray scattering spectroscopy reveal that the origin of gasochromic coloration in VO2 is strongly related to the modulation of its structure and the electron-electron correlation. Upon gasochromic coloration, not only does the valence state change with the incorporation of hydrogen, but also the film undergoes the modification of the local atomic structure. The structural distortion varies the strength of hybridization of the O 2p-V 3d states and the bond distance of V-O and V-O varies. In the hydric process, the local atomic structure of VO2 changes from that of an un-symmetric to that of a symmetric V-O framework. The incorporated hydrogen adds electrons into the V 3d t2g orbital, enhancing the electron-electron correlation by reducing the V-V distance. This work presents a new physical insight in which the modulation of the electron-electron correlation is exploited to control the bleached and colored states, giving rise to the gasochromic phenomenon. The strong correlation among atomic spatial rearrangement, electronic structures, and transmittance supports a cooperative mechanism of the VO2 gasochromic transition. These results reveal a clear correlation between the dynamics of the lattice structure and the electronic properties and suggest a possible pathway to gasochromism and elucidation of its mechanism.

Behind the color switching in gasochromic VO2.

Nanotubular TiO2 has attracted considerable attention owing to its unique functional properties, including high surface area and vectorial charge transport along the nanotube, making it a good photocatalytic material. Anodic TiO2-nanotube (TiNT) arrays on a Ti foil substrate were prepared by electrochemical anodic oxidation and SEM/HRTEM/XRD analyses have suggested that the walls of TiO2 tubes are formed from stacked [101] planes (anatase). Both HRTEM and XRD indicate an interplanar spacing of d101 = 0.36 nm in the wall structure. Despite the large amount of work done on nanotube synthesis, a thorough investigation of the electronic and atomic structures of free-standing TiNT arrays has not yet been carried out. X-ray absorption spectroscopy (XAS), resonant inelastic X-ray scattering (RIXS) and scanning photoelectron microscopy (SPEM) are employed herein to examine the electronic and atomic structures at the top and bottom of TiNT arrays. These analyses demonstrate the presence of mixed valence states of the Ti ions (Ti(3+) and Ti(4+)) and a structural distortion at the bottom cap region of the TiNT. Additionally, the results obtained herein suggest the formation of a defective anatase phase at the bottom cap barrier layer between the Ti foil substrate and TiNT during the growth of electrochemically anodized nanotubes.

Da-Hua Wei

Institute of Manufacturing Technology and Department of Mechanical Engineering

National Taipei University of Technology (TAIPEI TECH)

Synthesis and Characterization of High c-axis ZnO Thin Film by Plasma Enhanced Chemical Vapor Deposition System and its UV Photodetector Application