Temperature dependent admittance spectroscopy of GaAs/AlGaAs single-quantum-well laser diodes (SQWLDs)

In this study, the main electrical parameters, such as doping concentration (N_D), barrier height (Φ_CV), depletion layer width (W_D), series resistance (R_s) and Fermi energy level (E_F), of GaAs/Al_xGa_1−xAs single quantum well (SQW) laser diodes were investigated using the admittance spectroscopy (C-V and G/ω-V) method in the temperature range of 80-360 K. The reverse bias C⁻² vs. V plots gives a straight line in a wide voltage region, especially in weak inversion region. The values of Φ_CV at the absolute temperature (T = 0 K) and the temperature coefficient (α) of barrier height were found as 1.22 eV and −8.65 × 10⁻⁴ eV/K, respectively. This value of α is in a close agreement with α of GaAs band gap (−5.45 × 10⁻⁴ eV/K). Experimental results show that the capacitance-voltage (C-V) and conductance-voltage (G/ω-V) characteristics of the diode are affected by not only temperature but also R_s. The capacitance-voltage-temperature (C-V-T) and conductance-voltage-temperature (G/ω-V-T) characteristics confirmed that temperature and R_s of the diode have effects on the electronic parameters in SQW laser diodes.     

Electrical and optical characteristics of Au/PbS/n-6H-SiC structures prepared by electrodeposition of PbS thin film on n-type 6H-SiC substrate

To realize Schottky barrier height (SBH) modification in the Au/n-6H-SiC Schottky diodes, lead sulfide (PbS) thin films were grown on n-6H-SiC by electrodeposition method. At first, XRD experiments were performed to investigate the crystal structure of the PbS film electrodeposited on n-6H-SiC. It has been deduced from the diffraction profile that the PbS thin film has a crystal structure more strongly oriented along the [2 0 0] direction. An optical energy band gap value of 1.42 eV for the PbS film was obtained from its optical absorption spectra. Then, we have prepared Au/PbS/n-6H-SiC Schottky barrier diodes (SBDs) with interface layer and reference Au/n-6H-SiC/Ni SBDs. The SBH enhancement has been succeeded by the PbS interlayer, influencing the space charge region of the SiC. The SBH values of 1.03 and 0.97 eV for the samples with and without the interfacial PbS layer were obtained from the forward bias current-voltage (I-V) characteristics. The SBH increase in the Au/PbS/n-6H-SiC SBD with the interfacial PbS layer has been attributed to the fact that the interface states contain a net negative interface charge in metal/n-type semiconductor contact due to the presence of the interfacial PbS layer.     

Interfacial adhesion characterization of plasma coatings by V(z) inversion technique and comparison to interfacial indentation

This paper presents the development of V(z) inversion technique and its application to quantitative determination of interface adhesion by measuring interface tangential stiffness parameter K_T. The measurement is performed in two steps on an air plasma sprayed bronze-aluminum alloy coating (on a steel substrate) having different adhesion levels: the determination of the coating elastic constants and the determination of the interface tangential stiffness K_T are performed by optimizing the inverted angular-frequency reflectance function R(θ,f). The results obtained by the V(z) inversion are then compared to mechanical testing by interfacial indentation on the same sample. The same behavior (quality of interface adhesion) can be seen by both methods: the coating adhesion decreases as the interfacial stiffness parameter K_T decreases.     

The role of Mg2Si formation in the hydrogenation of Mg film and Mg nanoblade array on Si substrates

In this paper, both an Mg film and an Mg nanoblade array have been first fabricated directly on Si substrates and hydrogenated under 20 bar hydrogen pressure at temperatures ranging from 200 °C to 350 °C. It is found that Mg₂Si alloy starts to form at T = 200 °C in both the Mg samples, which produces a two-layered structure in the hydrogenated films with the bottom dense layer of Mg₂Si. To prevent Mg alloying with Si, a layer of 200 nm thick Ti film was deposited in between the Mg samples and Si substrates as a diffusion barrier, and their hydrogenation results show that Mg₂Si formation is suppressed greatly and even eliminated in nanoblades, though Mg₂Si hillock defects are observed in the hydrogenated films, which could be formed progressively through the pinholes in the Ti film. To improve the diffusion barrier, a unique structure, consisting of layers of Ti nanorod array and Ti film, has been designed for Mg-based nanostructure deposition. The hydrogen cycling study demonstrates that the structure of 450 nm Ti nanorods on 1 μm Ti film can endure enough number of cycles for the hydrogen storage kinetic and thermodynamic study of film-based Mg nanostructures with/without nanocatalyst, and thus one can gain a fundamental understanding of hydrogen interacting with Mg intrinsic nanostructures and nanocatalysts.     

Synthesis and characterization of nanocrystalline ZrNxOy thin films on Si by ion plating

Based on the optimum deposition conditions of ZrN thin film from our previous study, by varying oxygen flow rate ranging from 0 to 8 sccm, nanocrystalline ZrN_xO_y thin films were deposited on p-type (100) Si substrates using hollow cathode discharge ion-plating (HCD-IP) system. The objective of this study was to investigate the effect of oxygen content on the composition, structure and properties of the ZrN_xO_y thin films. The oxygen content of the thin film, determined using X-ray photoelectron spectroscopy (XPS), increased with increasing oxygen flow rate. As the oxygen content increased, the color of the ZrN_xO_y thin film changed from golden yellow to blue and then slate blue, and the microstructure observed by scanning electron microscopy (SEM) varied from columnar structure to finer grains and finally flat and featureless structure. Phase separation of ZrN_xO_y to ZrN and monoclinic ZrO₂ was found from X-ray diffraction (XRD) patterns when the oxygen content was higher than 9.7 at.%. The hardness of the film slightly increased as the oxygen content was less than 9.7% and then decreased to 15.7 GPa, a typical hardness of ZrO₂ phase, as the oxygen content further increased. The total residual stress of the film was measured using an optical method, and the residual stresses of ZrN and ZrO₂ phases were determined separately using modified XRD sin²ψ method. The total stress was close to the stress in ZrN phase as the ZrO₂ fraction was less than 30%, and was close to that in ZrO₂ phase as the ZrO₂ fraction was over 30%. The electrical resistivity of the film increased significantly with the increase of oxygen content. The film properties showed consistent trend with phase separation. As the fraction of ZrO₂ phase was small, the apparent properties of the films were more close to those in ZrN. When ZrO₂ fraction was over 30%, the films mainly exhibited the properties of ZrO₂.     

AC-HVAF制备Cr_3C_2-25CoNiCrAlY和Cr_3C_2-25NiCr涂层的高温氧化及摩擦磨损行为

为提高热作模具的高温氧化和高温耐磨性能,采用活性燃烧高速燃气喷涂(AC-HVAF)技术于H13钢基体上分别制备了Cr_3C_2-25CoNiCrAlY和Cr_3C_2-25Ni Cr涂层,并对比研究两种涂层的高温氧化和摩擦磨损行为,利用SEM、EDS和XRD分析其组织形貌与结构。结果表明:在800℃循环氧化100 h后,Cr_3C_2-25CoNiCrAlY涂层比Cr_3C_2-25Ni Cr涂层表面生成的氧化保护膜更致密,并生成大量高温稳定性好的尖晶石相,前者的氧化增重(0.80 mg/cm2)略小于后者(0.87 mg/cm2),说明Cr_3C_2-25CoNiCrAlY涂层的抗高温氧化能力略优;在700℃下,Cr_3C_2-25CoNiCrAlY涂层也具有更低的摩擦因数和磨损率,这归因于γ-matrix相(Co-Ni-Cr固溶体)具有很好的高温强度和热疲劳性能,对碳化物硬质相起到更强的联结支撑作用,提高了涂层的抗剥落能力。     

锆合金激光熔覆镍基复合层微观组织及界面特征

以Ni35自熔性合金粉末为熔覆材料,采用激光熔覆技术在锆合金表面原位生成了NiZr₂/陶瓷增强镍基涂层.利用金相显微镜、扫描电镜、X射线衍射仪等对熔覆界面附近的微观组织、物相组成及界面结合特征进行分析.结果表明,熔覆层基体组织为NiZr+Ni₁₀Zr₇,增强相NiZr₂以细针状均匀分布在熔覆层上部和底部,块状及棒状的陶瓷相Zr₅（Si_xNi_1-x）₄/Zr（Si_xNi_1-x）分布在熔覆层中部,熔覆层与基体间实现良好的熔焊冶金结合,界面结合区组织不均匀,分布有等轴状NiZr及晶间的α-Zr,熔覆层的显微硬度分布均匀,平均值约为1 100 Hv.     

超声辅助激光沉积原位TiC-TiB2/Al-12Si铝基复合材料微观组织及摩擦磨损行为研究

以Ti、B₄C和Al-12Si粉末为原材料,通过超声辅助激光沉积制备了原位TiC-TiB₂/Al-12Si铝基复合材料。采用XRD、EDS分析了复合材料的物相组成,通过OM、SEM观察了复合材料的微观组织,利用摩擦磨损试验机和三维轮廓仪测试了复合材料的磨损性能。结果表明,随Ti+B₄C含量的增加,α-Al晶粒细化,原位生成的TiB₂呈棒状,且可成为α-Al的异质形核核心;原位生成的TiC为150nm多边形形貌。随Ti+B₄C含量的增加,原位TiC-TiB₂/Al-12Si铝基复合材料的耐磨性提高;未加入Ti+B₄C的Al-12Si合金磨损机制为疲劳磨损;当Ti+B₄C的加入量为8%(质量分数)时,磨损机制为磨粒磨损;当Ti+B₄C的加入量为10%时,其磨损机制转变为疲劳磨损。