Low-temperature growth of stoichiometric aluminum nitride films prepared by magnetic-filtered cathodic arc ion plating

AlN films were prepared on Si(100) and quartz glass substrates with high deposition rate of 30 nm·min~(-1) at the temperature of below 85℃ by the magnetic-filtered cathodic arc ion plating(FCAIP) method. The as-deposited AlN films show very smooth surface and almost no macrodroplets. The films are in amorphous state, and the formation of AlN is confirmed by N1s and Al2p X-ray photoelectron spectroscopy(XPS). The XPS depth profile analysis shows that oxygen is mainly absorbed on the AlN surface. The AlN film has Al and N concentrations close to the stoichiometric ratio with a small amount of Al_2O_3. The prepared AlN films are highly transparent over the wave-length range of 210–990 nm. The optical transmission spectrum reveals the bandgap of 6.1 eV. The present technique provides a good approach to prepare large-scale AlN films with controlled structure and good optical properties at low temperature.     

Protective Properties of Aluminum Nitride Coatings by DC-PVD Sputtering on Cu-10Al-13Mn Shape Memory Alloy

The AlN coating was applied on the surface of a Cu-10Al-13Mn alloy using the DC-PVD sputtering method. The substrate was set at three different temperatures which were ambient, 100 and 200 °C. The effect of the substrate temperature on the quality of AlN coating was modeled by simulating stress on the coating and substrate. The preparation, microstructure, and corrosion resistance of the coating were studied. The surface morphology and element distribution of the coating were investigated by scanning electron microscopy (SEM) and energy distribution spectroscopy (EDS), respectively. In addition, the corrosion resistance of coating was measured using electrochemical impedance spectroscopy (EIS) method in 1 M NaCl solution. The results showed that the AlN coating was formed on the Cu-10Al-13Mn alloy by DC-PVD sputtering method and the AlN coating considerably improved the corrosion resistance of Cu-10Al-13Mn alloy in the given corrosive media. According to EIS test, polarization resistance increased from approximately 1.6 to 115 KΩ, at 200 °C for uncoated and coated samples, respectively. Thus, corrosion resistance of AlN coating improved with the increase in the substrate temperature during the DC-PVD sputtering process.     

Experimental and Modeling Studies on the Microstructures and Properties of Oxidized Aluminum Nitride Ceramic Substrates

Oxidation of aluminum nitride (AlN) ceramic substrates doped with 2 wt.% Y₂O₃ was performed in air at temperatures ranging from 1000 to 1300 °C for various lengths of time. Microstructure, bending strength, and thermal conductivity of the oxidized AlN substrates were studied experimentally and also via mathematical models. The results show that the oxide layer formed on the AlN substrates is composed of α-Al₂O₃ nanocrystallines and interconnected micropores. Longitudinal and transverse cracks are induced in the oxide layer under tensile and shear stresses, respectively. Intergranular oxidation of the AlN grains close to the oxide layer/AlN interface also occurs, leading to widening and cracking of the AlN grain boundaries. These processes result in the monotonous degradation of bending strength and thermal conductivity of the oxidized AlN substrates. Two mathematic models concerning these properties of the oxidized AlN substrates versus the oxide layer thickness were put forward. They fit well with the experimental results.     

AlN-based surface acoustic wave resonators on platinum bottom electrodes for high-temperature sensing applications

Surface acoustic wave(SAW) resonators with Pt/AlN/Si and Pt/AlN/Pt/Si configurations were fabricated by lift-off photolithography techniques. High-temperature performances of both configurations were investigated for temperature sensor applications. AlN films grown on Ptcoated Si substrates exhibit a lower(002) preferred orientation than those grown on Si substrates. The center frequencies of Pt/AlN/Si and Pt/AlN/Pt/Si configurations at room temperature are 424.1 and 456.4 MHz, respectively.The SAW was limited by Pt bottom electrodes to propagate in AlN layer. The temperature coefficient of frequency(TCF) values of Pt/AlN/Si and Pt/AlN/Pt/Si configurations are-51.6 9 10~(-6) and-69.2 9 10~(-6)°C~(-1), respectively.Compared with that of Pt/AlN/Si configuration, the TCF value of Pt/AlN/Pt/Si configuration decreases by 34.1 %.AlN resonator with the Pt floating bottom electrodes provides a large, quasi-constant temperature sensitivity which is suitable for temperature sensor applications.     

Spin polarization in Cu2MnSn Heusler alloy produced by melt-spinning

We report on magnetism, transport and spin polarization characteristics of the melt-spun Cu₂MnSn alloy prepared by the rapid quenching technique. The as- cast ribbons showed a relatively well ordered chemical composition (Cu = 50.4%, Mn = 27.1%, Sn = 22.5%). The structural characterization by using X-ray diffraction shows L2₁/B2 crystalline structure with the lattice parameter a = 6.196 Å. The magnetic and transport measurements show a metallic behavior with the Curie temperature of 530 K and reveal anisotropic character with the easy magnetization plane parallel with respect to the ribbon plane. As-cast Cu₂MnSn ribbons show the spin polarization measured by using Andreev reflection technique within the range 68–75%.     

Experimental and DFT Study of Structural and Optical Properties of Kesterite-Type Cu<Subscript>2</Subscript>ZnSnS<Subscript>4</Subscript> Compound for Solar Cell Applications

In this work, Cu₂ZnSnS₄ (CZTS) thin films were prepared by thermal evaporation from Cu₂SnS₃ and ZnS initially mixed by a mechanical alloying process. Structural and optical properties of CZTS films have been studied. X-ray diffraction results showed that the semiconductor has the Kesterite structure, and the optical absorption coefficient and band gap energy of the thin films were about 10⁴ cm^?1 and 1.46 eV, respectively. The structural and optical properties of Kesterite CZTS, studied by using the full potential linearized augmented plane wave method within the density functional theory, showed good agreement with our experimental results. The surface morphological studies revealed the formation of a smooth, compact and uniform CZTS surface.     

Influence of NH4Cl Powder Addition for Fabrication of Aluminum Nitride Coating in Reactive Atmospheric Plasma Spray Process

Reactive plasma spray is the key to fabricating aluminum nitride (AlN) thermally sprayed coatings. It was possible to fabricate AlN/Al composite coatings using atmospheric plasma spray process through plasma nitriding of Al powders (Al 30 ??m). The nitriding reaction and the AlN content could be improved by controlling the spray distance and the feedstock powder particle size. Increasing the spray distance and/or using smaller particle size of Al powders improved the in-flight nitriding reaction. However, it was difficult to fabricate thick and dense AlN coatings with an increase in the spray distance and/or when using fine particles. Thus, the coatings thickness was suppressed because of the complete nitriding of some particles (formation of AlN particles) during flight, which prevents the particle deposition. Furthermore, the excessive vaporization of Al fine particles (due to increased particle temperature) decreased the deposition efficiency. To fabricate thick AlN coatings in the reactive plasma spray process, improving the nitriding reaction of the large Al particles at short spray distance is required to decrease the vaporization of Al particles during flight. This study investigated the influence of adding ammonium chloride (NH₄Cl) powders on the nitriding process of large Al powders and on the microstructure of the fabricated coatings. It was possible to fabricate thick AlN coatings at 100 mm spray distance with small addition of NH₄Cl powders to the Al feedstock powders (30 ??m). Addition of NH₄Cl to the starting Al powders promoted the formation of AlN through changing the reaction path to vapor-phase nitridation chlorination-nitridation sequences as confirmed by the thermodynamic analysis of possible intermediate reactions. This changes the nitriding reaction to a mild way, so it is more controlled with no explosive mode and with relatively low heating rates. Thus, NH₄Cl acts as a catalyst, nitrogen source, and diluent agent. Furthermore, the evolved gases from the sublimation or decomposition of NH₄Cl can prevent the Al particles coalescing after melting.     

Quantum-mechanical study of effect of lattice defects on surface properties and copper activation of sphalerite surface

The electronic properties of sphalerite (110) surface bearing Fe, Mn and Cd impurities were calculated using density-functional theory, and the effects of impurities on the copper activation of sphalerite were investigated. Calculated results indicate that both Fe and Mn impurities narrow the band gap of sphalerite surface and lead to the Fermi level shifting to conduction band. Impurity levels composed of Fe 3d and Mn 3d orbital appearing in band gap are beneficial to electrons transfer from the valence band to the conduction band and promote the surface conductivity and the electrochemical activity. The results show that Fe and Mn impurities cannot be replaced by Cu atom, which reduces the exchange sites (Zn) for Cu atom, hence Fe- and Mn-bearing sphalerites are hard to be activated by copper. Cd impurity has little effect on electronic structure of sphalerite surface; however, Cd atom is easily replaced by Cu atom, and this is the reason why the Cd-bearing sphalerite can be easily floated.     

Electronic structure and optical properties of plutonium dioxide from first-principles calculations

The electronic structure and optical properties of plutonium dioxide were calculated using the generalized gradient approximation with a Hubbard parameter U(GGA+U) for considering the strong coulomb correlation between localized Pu 5f electrons based on the first-principles density functional theory. The calculated results show that PuO_2 is a semiconductor material with the band gap of 1.8 eV, which is in good agreement with the corresponding experimental data. Furthermore, the dielectric function, reflectivity, refractive index, and extinction coefficient were calculated and analyzed using the Kramers–Kronig relationship for PuO_2. The calculated results were compared with the experimental data from the published literature.     

Bias Voltage-Dependent Impedance Spectroscopy Analysis of Hydrothermally Synthesized ZnS Nanoparticles

In this report, bias voltage-dependent dielectric and electron transport properties of ZnS nanoparticles were discussed. ZnS nanoparticles were synthesized by introducing a modified hydrothermal process. The powder XRD pattern indicates the phase purity, and field emission scanning electron microscope image demonstrates the morphology of the synthesized sample. The optical band gap energy (E_g?=?4.2 eV) from UV measurement explores semiconductor behavior of the synthesized material. The electrical properties were performed at room temperature using complex impedance spectroscopy (CIS) technique as a function of frequency (40 Hz-10 MHz) under different forward dc bias voltages (0-1 V). The CIS analysis demonstrates the contribution of bulk resistance in conduction mechanism and its dependency on forward dc bias voltages. The imaginary part of the impedance versus frequency curve exhibits the existence of relaxation peak which shifts with increasing dc forward bias voltages. The dc bias voltage-dependent ac and dc conductivity of the synthesized ZnS was studied on thin film structure. A possible hopping mechanism for electrical transport processes in the system was investigated. Finally, it is worth to mention that this analysis of bias voltage-dependent dielectric and transport properties of as-synthesized ZnS showed excellent properties for emerging energy applications.     

Advanced Mechanical Properties of a Powder Metallurgy Ti-Al-N Alloy Doped with Ultrahigh Nitrogen Concentration

Titanium and its alloys are recognized for their attractive properties. However, high-performance Ti alloys are often alloyed with rare or noble-metal elements. In the present study, Ti alloys doped with only ubiquitous elements were produced via powder metallurgy. The experimental results showed that pure Ti with 1.5 wt.% AlN incorporated exhibited excellent tensile properties, superior to similarly extruded Ti-6Al-4V. Further analysis revealed that its remarkably advanced strength could primarily be attributed to nitrogen solid-solution strengthening, accounting for nearly 80% of the strength increase of the material. In addition, despite the ultrahigh nitrogen concentration up to 0.809 wt.%, the Ti-1.5AlN sample showed elongation to failure of ~ 10%. This result exceeds the well-known limitation for nitrogen (over 0.45 wt.%) that causes embrittlement of Ti alloys.     

Advances in Characterization of Non-Rare-Earth Permanent Magnets: Exploring Commercial Alnico Grades 5–7 and 9

The magnetic domain structure of commercial alnico grades 5–7 and 9 was investigated using a magneto-optical Kerr effect (MOKE) to gain an understanding of their coercivity mechanisms at the micron to millimeter scale. In alnico 5–7, the magnetic domain structure exhibits stripes of alternating high and low induction. Magnetic domains easily cross grain boundaries if neighboring grains have a similar tilt and rotation of their crystallographic axes relative to the magnet body. In contrast for alnico 9, stripe-like magnetic domains are not observed regularly throughout the transverse section; rather, discrete localization of high- and low-induction stripe features are observed. In higher magnification MOKE experiments, i.e., ~100 μm, a zigzag-shaped magnetic domain structure was observed in both alnico 5–7 and 9. The zigzag features are four to five times smaller in size than an average grain of alnico 5–7, implying a pinning mechanism that is caused by structural elements within the grains. Discontinuous and reversible motion on a length scale of a few microns was observed for the zigzag-shaped domains for incremental changes in the applied field of ~10 Oe. Complimentary magnetic force microscopy measurements show that there are domain structures on an even smaller scale, i.e., 2 μm to 100 μm.     

Experimental Investigation of Spray-Deposited Fe-Doped ZnO Nanoparticle Thin Films: Structural, Microstructural, and Optical Properties

Structural, microstructural, and optical properties of the undoped and Fe-doped zinc oxide (ZnO) thin films grown by spray pyrolysis technique using zinc nitrate as a host precursor have been reported here. X-ray diffraction spectra confirm that all the films have stable wurtzite structure and the effects of Fe dopants on the diffraction patterns have been found to be in agreement with the Vegard’s law. Scanning electron microscopy results show good uniformity and dense surface having spherical-shaped grains. Energy dispersive x-ray analyses with elemental mapping of the Fe-doped films show that the Fe dopants are incorporated homogeneously into the ZnO film matrix. The x-ray photoelectron spectroscopy spectra confirm the presence of 3+ oxidation state of Fe in the doped films. Atomic force microscopy analyses clearly show that the average surface roughness and the grain size decrease with the addition of Fe dopants. Optical studies reveal that the optical band gap value decreases on Fe doping. The 1 at.% Fe-doped film shows normal dispersion for the wavelength range 450-700 nm. The PL spectra of the films show a strong ultraviolet emission centered at ~388 nm in the case of 1 at.% Fe-doped film. A slow photo current response in the films has been observed in the transient photoconductivity measurement.     

Microstructure and Mechanical Properties of AlN/Cu Brazed Joints

In this study, the AlN/Cu bonding was explored using the brazing technique. During AlN/Cu brazing, the temperature was set at 800, 850, and 900 °C for 10, 20, 30, and 60 min, respectively. We studied the bonding mechanism, microstructure formation, and the mechanical characteristics of the bond. The reaction layer developed at the interface of AlN/Cu is observed to be TiN. The activation energy of TiN is about 149.91 kJ/mol. The reaction layer thickness is linearly dependent on the temperature and duration at 800 and 850 °C for 60 min and 900 °C for 30 min. However, the growth of the reactive layers decreases gradually at 900 °C when the duration changed from 30 to 60 min. The strength of the specimens with thickness ranging between 1 and 1.5 μm is 40-51 MPa.     

AlN粉体表面抗水解涂层的制备及其对AlN陶瓷热导率的影响

提升AlN陶瓷粉体的抗水解性能对于其储存和成型加工至关重要。使用一种抗水解涂层作为阻止水分与AlN表面接触的屏障,以提升AlN粉体的抗水解性能。采用化学沉淀工艺在AlN粉体表面制备均匀、全包覆的非晶Y₂O₃涂层。利用TEM、XPS和Zeta电位测试详细研究了包覆层的有效性和完整性。通过测试室温下水基AlN悬浮液的pH-时间曲线以研究AlN粉体的水解性能。结果表明,经包覆处理的AlN粉体能够在水中保持稳定至48 h,这说明Y₂O₃表面包覆处理可以有效钝化AlN粉体,从而避免了其水解反应的发生。此外,与球磨工艺引入烧结助剂相比,化学沉淀工艺有利于提升AlN陶瓷的热导率。     

采用两种银基活性钎料钎焊AlN陶瓷与可伐合金的接头组织与性能

采用Ag-Cu-Ti和Ag-Cu-In-Ti两种活性钎料箔带,分别在860℃/10 min和760℃/10 min两种规范下对AlN与可伐合金(4J29)进行了真空钎焊连接,获得了冶金质量良好的接头. 对接头室温抗剪强度进行了测试,AlN/Ag-Cu-Ti/4J29和AlN/Ag-Cu-In-Ti/4J29两种接头强度分别为126和113 MPa. 微观分析结果表明,两种接头中靠近陶瓷母材附近生成了连续的扩散反应层,结合XRD结果,该层主要由TiN相组成,反应层的厚度对接头强度有影响;钎缝基体区由铜基固溶体、银基固溶体和复杂的Ni(Fe,Co)-Ti化合物组成.     

Room temperature ferromagnetism of Si-doped ZnO thin films prepared by sol–gel method

Pure ZnO and Si-doped ZnO thin films were deposited on quartz substrate by using sol-gel spin coating process. X-ray diffraction analysis shows that all the thin films have hexagonal wurtzite structure and preferred c-axis orientation. Si-doped ZnO films show room temperature ferromagnetism (RTFM) and reach the maximum saturation magnetization value of 1.54 kAm-1 at 3% Siconcentration. RTFM of Si-doped ZnO decreases with the increasing annealing temperature because of the formation of SiO 2 . Photoluminescence measurements suggest that the RTFM in Si-doped ZnO can be attributed to the defect complex related to zinc vacancies V Zn and oxygen interstitials Oi .     

Influence of High Pulsed Magnetic Field on the Dislocations and Mechanical Properties of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Al Composites

At T6 state, Al–Zn–Mg–Cu aluminum matrix composites reinforced with Al₂O₃ particles generated in situ were subjected to high pulsed magnetic fields at different magnetic induction intensities (B = 2, 3 and 4 T). The results show that the dislocation densities in the treated samples increased with increasing B, and the magnetoplastic effect was determined to be the primary cause. The effect of the magnetic field is believed to alter the spin state of free electrons between dislocations and obstacles from the singlet state (associated with high bonding energy) to the triplet state (low bonding energy). The maximum ultimate tensile strength of 532 MPa was obtained at B = 4 T with 30 pulses, which was 20.7% higher than that of the initial sample, primarily because of dislocation strengthening. At B = 2 T, the elongation was at its maximum of 9.3%, representing an increase of 12% compared with the initial sample, while the associated ultimate tensile strength (447 MPa) was still higher than that of the untreated sample (440 MPa). The relationship between mechanical properties and microstructure was analyzed, and the improved properties observed in this work are explained by the transition of the electron spin state and the piling up of dislocations.     

Optical and structural properties of highly porous shell structured Fe doped TiO2 thin films

TiO2thin films with 0.2 wt%, 0.4 wt%, 0.6wt%, and 0.8 wt% Fe were prepared on glass and silicon substrates using sol–gel spin coating technique. The optical cut-off points are increasingly red-shifted and the absorption edge is shifted over the higher wavelength region with Fe content increasing. As Fe content increases, the optical band gap decreases from 3.03 to 2.48 eV whereas the tail width increases from 0.26 to 1.43 eV. The X-ray diffraction（XRD） patterns for doped films at 0.2 wt% and0.8 wt% Fe reveal no characteristic peaks, indicating that the film is amorphous whereas undoped TiO2exhibits（101） orientation with anatase phase. Thin films of higher Fe content exhibit a homogeneous, uniform, and nanostructured highly porous shell morphology.     

Synthesis of high-purity Ti2AlN ceramic by hot pressing

High-purity Ti2AIN ceramic was prepared at 1300℃ by hot pressing（HP） of Ti/Ai/TiN powders in stoichiometric proportion. The sintered product was characterized using X-ray diffraction（XRD） and MDI Jade 5.0 software （Materials Data Inc, Liverpool, CA）. Scanning electron microscopy（SEM） and electron probe micro-analysis（EPMA） coupled with energy-dispersive spectroscopy（EDS） were utilized to investigate the morphology characteristics. The results show that Ti2AIN phase is well-developed with a close and lamellar structure. The grains are plate-like with the size of 3-5 μm, thickness of 8-10 μm and elongated dimension. The density of Ti2AlN is measured to be 4.22 g/cm^3, which reaches 97.9% of its theory value. The distribution of Ti2AlN grains is homogeneous.