Advanced Materials Research Vols. 415-417

Abstract: A novel TiO₂/Cu composite photocatalyst thin film was successfully fabricated by 2-step Mechanical Coating Technique (2-step MCT). The composite photocatalyst thin film was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), among others. The formation process of Cu thin film and TiO₂/Cu composite photocatalyst thin film were also examined. The results revealed that the formation of Cu thin film can fall into the following stages: nucleation, growth of nuclei and connection, formation and thickening of continuous thin film, and the exfoliation of thin film. In addition, TiO₂/Cu composite thin film had a composite microstructure of TiO₂ islands coated on Cu thin film. Furthermore, the photocatalytic activity of TiO₂/Cu composite photocatalyst thin film was evaluated by measuring the degradation rate of methylene blue (MB). Enhancement on the photocatalytic activity of TiO₂ was confirmed. The improvement of the photocatalytic activity of TiO₂/Cu composite photocatalyst thin film should result from the increase of the charge separation efficiency and the mass increase of TiO₂ in the composite thin film.

Abstract: Magnetic materials have long been used for signal processing structures in the microwave range. High-frequency signal processing as for band-stop or notch filters, ferromagnetic resonance frequency can be adjusted or set by magnetic properties, such as saturation magnetization M_s. In this work, Fe-Co-N thin films have been synthesized using an improved facing-target magnetron sputtering system, where the sputtering current on Co and Fe targets can be regulated independently. During deposition of Fe-Co-N thin film, parameters on Fe target followed the one for synthesis of ε-Fe₃N, while changing the input current on Co target. It was found that on an unheated substrate, with the Co content of about 7 at.%, high value of M_s (265.08Am²kg^-1) could be obtained in the Fe-Co-N film, which contained α"-(Fe,Co)₁₆N₂ nanoparticles with the average size of 7 nm.

Abstract: Abstract. Using the radio frequency reactive magnetron sputtering technique, ZnO and Al-dopped ZnO thin films were fabricated on glass substrate by changing the Ar/O₂ ratio and substrate temperature. The film crystallinity、optical properties and surface morphology were investigated by X-ray diffraction、 UV - visible spectrophotometer and scanning electron microscopy (SEM). The XRD results showed that by changing the argon oxygen ratio, Al-dopped ZnO films deposited at sputtering power of 40W and room temperature for 1 hour sputtering time showed no significant peaks, suggesting that the film growth was amorphous. UV-Vis spectrophotometer at 400nm wavelength test showed less than 90% light transmission rate. When substrate temperature was increased to 200 ° C, significant (002) diffraction peak and transmittance of 88% or more in the 400 ~ 800nm wavelength range appeared. A minimum XRD diffraction peak FWHM was found at substrate temperature of 300 ° C. TEM showed well crystal growth with maximum grain size at 300 ° C, XRD showed that there are only (101) peaks ,no (002) peaks in Al- doped ZnO.

Abstract: Unintentionally doped GaN were grown on Si (111) substrates by metal organic chemical vapor deposition (MOCVD). The high-resolution X-ray diffraction (HRXRD) and Lehighton contactless sheet resistance measuring systems were employed to characterize the quality and sheet resistance (R_s) of GaN epilayer. The threading dislocation density (TDD) was estimated by calculating the full width at half maximum (FWHM) of GaN (0002) and (10-12) diffractions measured by HRXRD. The relationship between R_s and TDD in GaN epilayer was investigated. The influence of growth conditions of bottom GaN initial layer including carrier gas category (H₂ or N₂), growth temperatures, and growth pressures on the quality or resistivity of top GaN epilayer was discussed and analyzed. As a result, the improved resistivity was achieved in top GaN epilayer with low TDD by using H2 carrier, low growth temperature of 1050°C, and high growth pressure of 400mbar during the growth of bottom GaN initial layer.

Abstract: _{Subscript text}Reactive ion etching of barium strontium titanate (BST) thin films using an SF₆/Ar plasma has been studied. BST surfaces before and after etching were analyzed by X-ray photoelectron spectroscopy to investigate the reaction ion etching mechanism, and chemical reactions had occurred between the F plasma and the Ba, Sr and Ti metal species. Fluorides of these metals were formed and some remained on the surface during the etching process. Ti can be removed completely by chemical reaction because the TiF₄ by-product is volatile. Minor quantities of Ti-F could still be detected by narrow scan X-ray photoelectron spectra, which was thought to be present in metal-oxy-fluoride(Metal-O-F). These species were investigated from O_1s spectra, and a fluoride-rich surface was formed during etching because the high boiling point BaF₂ and SrF₂ residues are hard to remove. The etching rate was limited to 14.28nm/min. A 1-minute Ar/10 plasma physical sputtering was carried out for every 4 minutes of surface etching, which effectively removed remaining surface residue. Sequential chemical reaction and sputtered etching is an effective etching method for BST films.

Abstract: Diamond-like carbon (DLC) films with different sp³/sp² ratios were deposited using middle frequency magnetron sputtering. The sp³/sp² ratio of the films can be tailored by codoping of Ti and Si elements under different CH₄ flow rate. The films were characterized by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and Fourier transform infrared (FTIR) spectroscopy. The results show that the sp³/sp² ratio ranges from 0.18 to 0.63 with increasing of CH₄ flow rate. Hydrogen atoms in the films are mainly bonded to sp³ carbon atoms. The film deposited at 60 sccm CH₄ flow rate exhibits the highest bonded hydrogen content.

Abstract: We study the tunneling properties in GaAs/Al_0.33Ga_0.67As/In_xGa_1-xAs (x=0~0.05) double-barrier resonant tunneling structures. On increasing bias voltage, the behavior of current density for x=0 can be explained by the interplay between the increase of the supply function of available electrons and the decrease of transmission coefficient through device area. On increasing the Indium content from 0, the peak current density decreases, and the reason is that both the supply function and the transmission coefficient decreases. At zero bias, the structure is on resonance with the lowest x value of 0.02.

Abstract: Electro Dynamic Gradient (EDG) method was utilized for TlBr crystal growth in this paper. The influence of crystal growth conditions such as temperature gradient and growth rate on optical and electrical properties of grown TlBr crystals was investigated. The quality of TlBr crystals was characterized by infrared (IR) transmittance spectrum, X-ray diffraction, and I-V measurements.

Abstract: We reported that Bi(Mg_1/2Ti_1/2)O₃–PbTiO₃ (BMT-PT) systems had high piezoelectric, dielectric performances and high Curie temperature. The phase structure of the system was identified by X-ray diffraction analysis. The piezoelectric and dielectric properties were also investigated. The results showed that 0.6BMT–0.4PT (Mg/Ti = 0.5:0.5) with 1mol% MnO₂ was the optimum composition which exhibited the highest curie temperature Tc = 511 °C and the stable temperature of dielectric loss reached to 500 °C. Further, the dielectric and piezoelectric properties of this composition were given as follows:kp = 22.5%;εr= 734; room temperature d₃₃ = 131.3 pC/N; tanδ = 1.96%.

Abstract: We investigate the values of the Rashba spin-orbit coupling parameter α in a gated In_0.53Ga_0.47As/InP quantum well structure using the k•p formalism. With more positive gate voltage applied, the quantum well potential profile becomes more symmetric and the value of α decreases. The theoretical values of α are much smaller than experimental ones. The discrepancy can be reasonably explained by the neglect of the interface contribution in the k•p formalism and the formation of additional InAs_xP_1-x and Ga_xIn_1-xAs_yP_1-y interfacial layers in our sample.