Lishi Wen

Structural, electrical, and optical properties of transparent conductive oxide ZnO:Al films prepared by dc magnetron reactive sputtering

ZnO:Al/(ZaO) films were deposited on quartz substrates by dc magnetron reactive sputtering from a Zn target mixed with Al. The effect of oxygen flow rate, target to substrate distance, substrate temperature, and Al doping content on the structural, electrical and optical properties of ZAO were investigated. It was observed that the (002) peak position of all films shifts to lower angle comparable to that of bulk ZnO due to the residual stress change with deposition parameters. X-ray photoemission spectroscopy was introduced to analyze the chemical state of Al on the film surface and the results show Al enrichment. The dependences of electrical properties such as resistivity, carrier concentration and Hall mobility on substrate temperature, and Al doping content were measured. The visible transmittance of above 80% and infrared reflectance of above 80% were obtained. The minimum resistivity is 4.23×10−4u200aΩu200acm with the carrier concentration of 9.21×1020u200acm−3 and Hall mobility of 16.0 cm2 v1u200as−1. The optical ...

Intrinsic limit of electrical properties of transparent conductive oxide films

Contributions of acoustical deformation scattering, ion impurity scattering and grain boundary potential scattering to the conductivity of TCO films have been calculated in order to deduce the intrinsic limit of conductivity of TCO films regardless of precise details of the preparation procedure. The results indicate that the effective mass of charge carriers has a strong dependence on carrier concentration. Based on the effective mass correction, as well as the carrier concentration ionized impurity centre correction, scattering due to ion impurity has been developed to explain the upper limit of mobility or the lower limit of resistivity of TCO films. Two empirical expressions are introduced to depict the dependence of the upper limit of mobility and the lower limit of resistivity of TCO films on carrier concentration. The dependence of transparency on carrier concentration is also discussed.

Oxidation behaviour of the alloy IC-6 and protective coatings

Abstract In this work, NiCoCrAlY coatings were deposited on a new Ni-base alloy, IC-6. The oxidation kinetic curves of alloy IC-6, K17 and NiCoCrAlY coatings on alloy IC-6 at 900–1100 °C were obtained. The results indicated that the oxide scales consisted of α-Al2O3, NiAl2O4, NiO, as well as a small amount of NiMoO4 and MoO2. These scales occurred after alloy IC-6 exposure at 900 °C for 100 h. The weight loss occurred when alloy IC-6 were exposed at 1050 and 1100 °C due to the formation of volatile MoO3. After the NiCoCrAlY coating was deposited, the scales mainly contained α-Al2O3, when the specimens were oxidized at 900 °C, and α-Al2O3and Cr2O3 at 1050 °C. The formation of α-Al2O3 and Cr2O3 scales on NiCoCrAlY coating was directly responsible for improving oxidation resistance of the alloy IC-6.

A transmission electron microscopy study on Ti–N films deposited by ion plating

The microstructure and interface structure of Ti–N coating deposited by hollow cathode discharge ion plating were investigated with transmission electron microscopy and other methods of microanalysis. A layered structure of the coating was observed, consisting of substrate–FeTi–Ti–Ti2N–TiN. The transition layers FeTi and Ti2N were identified with microbeam electron diffraction. It was also shown that there was a microcrystalline region at the substrate surface. Preferential orientation has been observed and correlated with deposition parameters. The orientation relationships between different layers have been determined. The formation mechanism of transition layers was discussed.

Properties of transparent conducting ZnO : Al oxide thin films and their application for molecular organic light-emitting diodes

ZnO : Al (ZAO) films were deposited on glass substrates by a reactive mid-frequency sputtering system. The microstructural, electrical, and optical properties of ZAO films were investigated. It was observed that the polycrystalline film was (0 0 2n) textured with columnar structure. The minimum resistivity was 1.39×10−4 Ω cm with a carrier concentration of 1.58×1021 cm−3 and a Hall mobility of 28.2 cm2 V−1 s−1, correspondingly with the c-axis nearly equal to the value of ZnO powder and the minimum mechanical stress therein. The average transmittance of 80.8% in the visible range and infrared reflectance of over 86% in the 1600–4400 cm−1 interval were obtained. The ZAO films were used as the transparent anodes to fabricate light-emitting diodes, and a luminance efficiency of 2.09 cd A−1 was measured at a current density of 5.38 A m−2.

Simulation of the influence of the filament arrangement on the gas phase during hot filament chemical vapor deposition of diamond films

The uniform temperature and mass current density of gas in deposition regions of films were very important to obtain uniform diamond films over a large area during hot filament chemical vapor deposition. The simulation showed that the two physical parameters of gas in the chamber varied as a function of space and were influenced by the arrangement of the filaments and the initial rate of the introduced gas. Regions of uniform temperature and mass current density existed in the chamber. The distributions of temperature and mass current density did not vary with the filament diameter. However, the value of the two physical parameters increased and declined with the increment of the diameter, respectively. An optimum distance between filaments was necessary to obtain uniform films over a large area. The mass current density increased with the initial rate of the introduced gas. These results might provide a basis for optimizing the technological parameters to obtain uniform diamond films over a large area.

Effect of Enhanced Plasma Density on the Properties of Aluminium Doped Zinc Oxide Thin Films Produced by DC Magnetron Sputtering

Aluminum doped zinc oxide (AZO) thin films were prepared by DC magnetron sputtering at low substrate temperature. A coaxial solenoid coil was placed near the magnetron target to enhance the plasma density (J(i)). The enhanced plasma density improved significantly the bulk resistivity (p) and its homogeneity in spatial distribution of AZO films. X-ray diffraction (XRD) analysis revealed that the increased J(i) had influenced the crystallinity, stress relaxation and other material properties. The AZO films deposited in low plasma density (LPD) mode showed marked variation in rho (ranging from similar to 6.5x10(-2) to 1.9x10(-3) Omega.cm), whereas those deposited in high plasma density (LPD) mode showed a better homogeneity of films resistivity (ranging from similar to 1.3x10(-3) to 3.3x10(-3) Omega.cm) at different substrate positions. The average visible transmittance in the wavelength range of 500-800 nm was over 80%, irrespective of the deposition conditions. The atomic force microscopy (AFM) surface morphology showed that AZO films deposited in HPD mode were smoother than that in LPD mode. The high plasma density produced by the coaxial solenoid coil improved the electrical property, surface morphology and the homogeneity in spatial distribution of AZO films deposited at low substrate temperature.

Influence of an External Magnetic Field on the Growth of Nanocrystalline Silicon Films Grown by MF Magnetron Sputtering

The effects of an external magnetic field originating from two solenoid coils on the magnetic field configuration, plasma state of a dual unbalanced magnetron sputter system and the structure of nanocrystalline Si films were examined. Numerical simulations of the magnetic field configuration showed that increasing the coil current significantly changed the magnetic field distribution between the substrate and targets. The saturated ion current density J(i) in the substrate position measured by using a circular flat probe increased from 0.18 to 0.55 mA/cm(2) with the coil current ranging from 0 to 6 A. X-ray diffraction and Raman results revealed that increasing the ion density near the substrate would benefit crystallization of films and the preferential growth along [111] orientation. From analysis of the surface morphology and the microstructure of Si films grown under different plasma conditions, it is found that with increasing the J(i), the surface of the film was smoothed and the alteration in the surface roughness was mainly correlated to the localized surface diffusion of the deposited species and the crystallization behavior of the films.