Dependence of Negative Substrate Bias on the Optical and Electrical Properties of W-Doped Vanadium Dioxide Thin Films

W-doped VO2 films were prepared by DC reactive magnetron sputtering with various substrate bias. The microstructure, surface morphology, electrical and optical performances of the films were characterized by x-ray diffraction, scanning electron microscope, four-point probe method and spectrophotometer, respectively. The effect of substrate bias on microstructure, electrical and optical properties of sputtered W-doped VO2 films was studied. The XRD results reveal that all samples exhibit preferential VO2 (011) lattice orientation except the as-grown sample in our experiment. All the samples applied substrate bias show some degree optical switching performance in IR range, while the thermochromic phenomena was observed from resistance-temperature dependence plot only for the samples of substrate bias varied from-100V to-200V. This indicate that the optical and electrical properties of W-doped VO2 films have different sensitivity to substrate bias. Optimal substrate bias of-200V sample shows fine semiconductor-metal-transition performance.

Comprehensive Study Of Duckweed Cultivation And Growth Conditions Under Controlled Eutrophication

The paper discussed the issue of eutrophication. The most conspicuous effect of eutrophication is the creation of dense blooms of noxious, foul-smelling phytoplankton that reduce water clarity and harm water quality. Nutrient concentration, temperature and pH of the water largely influence the growth rate and composition of duckweed in general, but it can be said that the temperature and solar irradiation are the most important factors. In order to compare the rate of biomass increase of duckweed biomass in natural conditions and in a laboratory grown sample was analysed by spectrophotometric methods in UV/VIS region (Spectrophotometer GENESYSTM) for the selected nutrients such as ammonium, ammonium nitrogen, nitrite, nitrate, and phosphate.

Synthesis and luminescence properties of a H2annealed Mn-doped Y3Al5O12:Ce3+single crystal for WLEDs

Compared to the blue LED chip and the as-grown sample, upon increasing the annealing temperature, the emission intensity in the yellow-orange region is enhanced and reaches the highest at 1550 °C.

The Room Temperature Ferromagnetism of (N, Co) Co-Doped ZnO Nanopaticles

Co-doped ZnO nanoparticles were fabricated by an electrodeposition method. The XPS results show Co ions have doped into the ZnO crystal lattices successfully. The as-grown sample has no ferromagnetism at room temperature. But after an ammine plasma treatment the room temperature ferromagnetism were detected on Co0.04Zn0.96O nanoparticles. The Hall measurement reveals after the treatment the resistivity increase by three orders of magnitude. Although the aspect conductivity is n type, some holes generated by N doping play an important role to induce the ferromagnetic properties for Co doped ZnO sample.

An Investigation on the Effect of the Catalyst on Physical Properties of Silicon Oxide Nanostructures Prepared by CVD Technique

Here, nano and microstructures of silicon oxide layers grown on p-Si (111) wafer have synthesized by evaporating SnCl2.2H2O powder in a mixture of Ar and O2 gas flow using chemical vapor deposition (CVD) technique. The growth temperature and the vacuum pressure were 950 °C and 10-3 torr, respectively. Through this study, samples have characterized by SEM, XRD, EDS and PL methods. The grown sample while has a combination of porous and layered morphology, it has a polycrystalline nature including a mixture of SiO2-x (002) and SnO2 phases. The EDS elemental analysis confirmed the presence of Si, O and Sn atoms in the composition, which is consistent with the XRD data. The PL spectrum show a strong peak in violet region (424 nm) attributed to the crystal defects at the SiO2-x and SnO2 interfaces.

Effects of Variations in Annealing Temperature and Annealing Time on the Spectral and Solid State Properties of Nickel Oxide (NiO) Thin Films

Chemical bath deposited nickel oxide (NiO) thin film samples were grown at room temperature of 30 °C on glass substrates. Samples k1, k2, and k3 were annealed for one hour at temperatures of 100 °C, 200 °C and 300 °C respectively, while as grown sample k4 served as a reference. A second set of samples k5, k7, and k8 were annealed at a constant temperature of 300 °C for time durations of 1H, 2H and 3H respectively, with as grown sample k6 as a reference. The spectral absorbance, transmittance and reflectance of all the thermally treated thin film samples were measured with a spectrophotmeter (D model Avantes Spec 2048 version 7.0) in the UV-VIS-NIR region of 300-900 nm wavelength. The results show distinctive variations in all the spectral properties for different combinations of annealing time and temperature, each starting at a threshold wavelength of 300 nm and ending with a distinctive minimum or maximum value. Deduced graphical values of the refractive index also show distinctive variations. For annealing time of 3 hours at a temperature of 300 °C, the results produced symmetric reflectance and symmetric refractive index with maximum values of 8% and 0.293 occurring at 500 nm wavelength and photon energy of 2.5 eV respectively. Direct transition band gap energy obtained for all the samples lie between 3.68-3.84 eV. The results reported in this paper clearly indicate that optimum combinations of production parameters of nickel oxide thin films can yield specific values of the properties for specific applications.

Luminescent Properties of As-Grown and Vacuum Annealed LiNbO3 Single Crystals

This paper reports on the luminescent properties of the congruent as-grown and vacuum annealed LiNbO3 single crystals at the UV and X-ray excitations. The shape of excitation spectra is similar for all emission bands in as-grown sample as well as in vacuum annealed sample. The emission spectra (exc=235 nm) observed in the spectral region 250…800 nm at room temperature consist of five elementary bands. Correlation of the relative intensities bands in luminescence spectra under different types of excitation and their temperature dependencies were determined. The most intensitive maxima in as-grown sample are observed at 295 and 691 nm. The main maximum after vacuum annealing is peaked around 295 nm.

Growth of 4H-SiC Epilayers and Z1/2 Center Elimination

Thick and low-doped epilayers with a low Z1/2 center concentration were grown on 8o off-cut 4H-SiC(0001)Si-face substrate. Two post-growth processes, namely, the C+-implantation/annealing process or the thermal oxidation/Ar annealing process, were applied to the thick epilayers. The dependence of the Z1/2 center concentration and the carrier lifetime on process conditions was investigated. Under proper conditions, both processes could eliminate the Z1/2 center to a depth of 100 μm or more, and considerably improved the carrier lifetime while maintaining the surface roughness comparable to that of the as-grown sample. The effect of the post-growth processes applied on C-face is also presented.

Reactive-Ion-Etching Induced Deep Levels Observed in n-Type and p-Type 4H-SiC

In this study, deep levels are investigated, which are introduced by reactive ion etching (RIE) of n-type/p-type 4H-SiC. The capacitance of as-etched p-type SiC is remarkably small due to compensation or deactivation of acceptors. These acceptors can be recovered to the initial concentration of the as-grown sample after annealing at 1000oC. However, various kinds of defects remain at a total density of ~5× 1014 cm-3 in a surface-near region from 0.3 μm to 1.0 μm even after annealing at 1000oC. The following defects are detected by Deep Level Transient Spectroscopy (DLTS): IN2 (EC – 0.35 eV), EN (EC – 1.6 eV), IP1 (EV + 0.35 eV), IP2 (HS1: EV + 0.39 eV), IP4 (HK0: EV + 0.72 eV), IP5 (EV + 0.75 eV), IP7 (EV + 1.3 eV), and EP (EV + 1.4 eV). These defects generated by RIE can be significantly reduced by thermal oxidation and subsequent annealing at 1400oC.

Enhanced UV Photodetector Responsivity in Porous GaN/Si(111) by Metal-Assisted Electroless Etching

This paper presents the structural and optical studies of porous GaN sample compared to the corresponding as grown GaN. The samples were investigated by scanning electron microscopy (SEM), high resolution x-ray diffraction (HRXRD), and photoluminescence (PL). The porous area is very uniform, with pore diameter in the range of 80-110 nm. XRD measurements showed that the (0002) diffraction plane peak width of porous samples was slightly broader than the as-grown sample. PL measurements revealed that the near band edge peak of the porous samples were redshifted. Metal-semiconductor-metal (MSM) photodiode was fabricated on the samples. For as grown GaN sample, this detector shows a sharp cut-off wavelength at 362 nm. A maximum responsivity of 0.258 A/W was achieved at 360 nm. For the porous GaN sample, this detector shows a sharp cut-off wavelength at 364 nm. A maximum responsivity of 0.771 A/W was achieved at 363 nm.