[en] Highlights: •CIGS films showed distinct structures in the observation of cross section. •CIGS films is strongly affected by the choice of preparation of CIG precursors. •CIG alloy precursors resulted in the phase separation in the CIGS thin films. •CuGa/In stacked precursors showed the single phase CIGS at high selenized temperature. •Ga accumulation in large amounts in the films depends on the selenization temperature. -- Abstract: Cu(In_1−x,Ga_x)Se₂ (CIGS) thin films were prepared by the sputtering of CuInGa (CIG) alloy precursors and CuGa/In stacked precursors followed by selenization. The effects of the using CIG precursors prepared by various methods and that of use of various selenization temperatures on the microstructural characteristics of CIGS thin films were investigated and the nature of phase transformation and Ga accumulation are discussed. Observation of the cross section morphologies revealed that the CIGS thin films prepared from CIG alloy precursors show two distinct types of structure. In addition, Ga was found to accumulate in high concentrations in the films. The X-ray diffraction (XRD) patterns of the films indicated the coexistence of CuInSe₂ (CIS) and CIGS phases at low selenization temperatures. However, the CIGS phase seemed to disappear when the selenization temperature was increased to 580 °C. In comparison, the films prepared from CuGa/In stacked precursors also showed Ga accumulation after selenization. Surprisingly, the distinct structure of the films improved when the selenization temperature was increased to 580 °C. The XRD patterns of the films showed that the CIS and Ga-rich CIGS phases coexisted at low selenization temperatures. When the selenization temperature was increased to 580 °C, the positions of the CIS and Ga-rich CIGS peaks seemed to mix and shift to the position of Cu(In_0.7,Ga_0.3)Se₂

[en] Default and deformations are some of issues for Additive manufacturing, as known as the 3D printing. When it processes multilayer thin films stacking, this process will introduce higher residual stress that causes deformation. This phenomenon makes the product faulty such as delamination, crack and blisters. The reason could be included ununiformed casting, temperature, cubical contraction etc. However, it is not easily to seem the difference form the films in the present. For ceramic materials, if deformation was existed at interface between layers, the crack would appear after the sintering was completed. For elastic material, the film will be bended, if the structure of product is unstable or the thickness is not thick enough to resist bending. In order to observe the deformation from material, residual stress and external bending must be considered. The purpose of the present study is to find the best approximation of formula for 3D printing and to predict the residual stress for the products. Later, the producing process could be adjusted until the most deformation is eliminated. The methods for present study are considered for two multilayer formulas. One is derived from Hsueh’s closed-form, the anther is Timoshenko Theory. The results are combined simulation and experimental for two material and their accuracy is examined. Except considering the effect of the thermal stress, the acceptability of assuming for analyses in the 3D printing system is discussed. (author)

[en] In the present study, high-yield W₁₈O₄₉-TiO₂ core–shell nanoparticles were prepared by modified plasma arc gas condensation without any catalysts or substrates. All the as-prepared samples were characterized by FEG-SEM, XRD, FEG-STEM, and HAADF analytic techniques. The results of the structural analysis show that the as-prepared nanoparticles presenting a core–shell morphology with an average diameter of 43.5 ± 8.0 nm were composed of non-stoichiometric tungsten oxide (W₁₈O₄₉ phase) as the core (20–40 nm) and rutile-phase TiO₂ as the shell with non-uniform thickness (10–20 nm). For the optical properties of the as-prepared W₁₈O₄₉-TiO₂ core–shell nanoparticles, Raman spectroscopy and photoluminescence (PL) spectra were used. Compared with pure TiO₂ and W₁₈O₄₉ nanocrystals, the experimental results reveal that the defects in the lattice between the core and shell layers induced the board and shifted peaks in Raman spectra. Also, W₁₈O₄₉-TiO₂ core–shell nanoparticles exhibited green emission at 483 nm wavelength observed in PL spectrum. Thermal gravimetric analyzer (TGA) results indicate that the TiO₂ shell served a stable layer and prevented further oxidation from the atmosphere of the W₁₈O₄₉ core, thereby improving the thermal stability of W₁₈O₄₉ nanoparticles.

[en] With the use of a modified plasma arc gas condensation technique and control of the processing parameters, namely, plasma current and chamber pressure, we synthesized tungsten oxide nanomaterials with aspect ratios ranging from 1.1 (for equiaxed particles with the length and width of 48 nm and 44 nm, respectively) to 12.7 (for rods with the length and width of 266 nm and 21 nm, respectively). The plasma current and chamber pressure, respectively, ranged from 70 to 90 A and from 200 to 600 Torr. We then characterized the tungsten oxide nanomaterials by means of X-ray diffraction, high-resolution transmission electron microscope, UV-visible spectroscope, and photoluminescence (PL) spectroscope. Experimental results show that equiaxed tungsten oxide nanoparticles were produced at a relatively low plasma current of 70 A, whereas nanorods were produced when plasma currents or chamber pressures were increased. All of the as-prepared tungsten oxide nanomaterials exhibited a WO_2.8 phase. Compared to the nanoparticles, the nanorods exhibited unique properties, such as a redshift in the UV-visible spectrum, a blue emission in PL spectrum, and a good performance in field emission. With respect to the field emission, the turn-on voltage for WO_2.8 nanorods was found to be as low as 1.7 V/μm.

[en] Tungsten oxide and titanium-oxide-doped tungsten oxide nanowires were synthesized by using the DC magnetron sputtering and infrared furnace annealing processes. Scanning election microscopy (SEM) and transmission electron microscopy (TEM) were utilized to evaluate the topography and sizes. X-ray diffraction (XRD), grazing incidence X-ray diffraction (GI-XRD), and high-resolution transmission electron microscopy (HRTEM) were used to analyze the composition and structure. From the results of HRTEM, it was discovered that the prepared nanowires have a monoclinic single-crystal phase of W_1_8O_4_9 with lattice growth along the (010) lattice plane, and the lattice spacing is 0.378 nm, which agrees with XRD and GI-XRD results. The prepared tungsten oxide and titanium-oxide-doped tungsten oxide nanowires have turn-on voltage of 3.06 V/μm and 1.46 V/μm respectively. They also possess superior field enhancement factors of 5103 and 10667 respectively. Their behavior thus follows the Fowler-Nordheim expression for tunneling. - Highlights: • A simple method to prepare tungsten oxide nanowires by annealing tungsten film. • High aspect ratio of the 1D titanium-oxide-doped tungsten oxide nanowires. • High field enhancement factor of titanium-oxide-doped tungsten oxide nanowires

[en] In the present study, titania-doped (Ti-doped) W₁₈O₄₉ nanorods have been prepared using a modified plasma arc gas condensation technique. Characterizations by field-emission gun scanning electron microscopy, X-ray powder diffraction, high-resolution transmission electron microscopy and high-resolution X-ray photoelectron spectroscopy indicate that the as-prepared nanorods with a single-crystalline monoclinic W₁₈O₄₉ phase are of 20–100 nm in diameter and several micrometers in length. The Raman peaks of the Ti-doped W₁₈O₄₉ nanorods show a red-shift Raman peaks, and an additional green-emission peak at 497 nm is observed in the photoluminescence (PL) spectrum compared to pure W₁₈O₄₉ nanorods. Field-emission (FE) measurements reveal that the turn-on (E_to) and threshold (E_thr) voltages of the Ti-doped W₁₈O₄₉ nanorods are 2.2 and 3.4 V/μm, respectively. A vapor–solid process that does not involve the use of catalyst is proposed for the nanorod growth mechanism. Experimental results show that the additional defects resulting from titania doping are responsible for the enhancement of the optical and FE properties of the pure W₁₈O₄₉ nanorods.

[en] In this study, we deposited low-resistivity molybdenum (Mo) thin films on soda-lime glass substrates with good adhesion. We adjusted various deposition parameters such as the sputtering power (52–102 W), working distance (5.5–9 cm) and annealing temperature (26–400 °C) to investigate their impact on the sheet resistance. By using a DC magnetron sputtering system, we obtained Mo thin films having the lowest sheet resistance of 0.190 Ω/□ with a sputtering power of 82 W, working distance of 6.5 cm, and annealing temperature of 400 °C; in addition, these films had good adhesivity. These Mo thin films were suitable for use as the Mo back contact in Cu(In,Ga)Se₂-based solar cells. - Highlights: ► Low-resistivity molybdenum (Mo) thin films with good adhesion were prepared. ► The working distance has a great influence on microstructure of Mo films. ► Decrease in working distance can apparently improve the resistivity of Mo films. ► The sheet resistance of 0.19 Ω/□ was obtained under 82 W, 6.5 cm, and 400 °C. ► These Mo films were suitable for use as back contact in Cu(In,Ga)Se₂‐solar cell.

[en] Highlights: • W–10Cu/AlN joint was successfully conducted using a Ni-P/Ti interlayer. • The bond strength depended on interlayer thickness and bonding temperature. • The fracture position of the joints was investigated. • 20% decline in tensile strength of joint after thermal shock test was observed. -- Abstract: Cu/AlN joints are critical for applications in electronic components and high-power electronic devices. To prevent mechanical failures at the interface of the joints resulting from mismatched thermal expansion coefficient (CTE) between Cu and AlN, the W–Cu composite with lower CTE than pure Cu can be used. The choice of interlayers for the W–Cu/AlN joint and their microstructural evolution at the interface during diffusion bonding should be evaluated. In this study, the design and characterization of Ni–P and Ti interlayers for increasing the joint quality between diffusion-bonded W–10Cu (90 wt% W and 10 wt% Cu) and AlN were developed. The effects of the Ni–P interlayer thickness (1.0 and 3.5 µm) and bonding temperature (700 and 800 °C) on the microstructure and corresponding mechanical properties of the joints were investigated. The maximum average tensile strength for the joints reached 26.76 MPa with a Ni–P interlayer thickness of 3.5 µm and bonding temperature of 800 °C. In addition, the phase distribution from the W–10Cu to AlN was determined using X-ray diffraction and electron probe X-ray microanalysis, indicating sufficient diffusion of W–Ni and Ni–Ti in the interfacial zone of the W–10Cu/Ni–P/Ti/AlN joints. Moreover, Cu atoms in W–10Cu diffused into Ni-based layers, forming a solid solution. The fracture location in the joints was influenced by the bonding temperature and thermal shock test. The tensile strength of the joints decreased 20% after thermal shock testing for 100 cycles.

[en] Highlights: ► CuInGa (CIG) ternary targets were prepared by vacuum arc remelting. ► The sputtering energy has a great influence on microstructure of CIG films. ► Increase in sputtering energy resulted in phase transformation and indium loss. ► The surface roughness of CIGS films is determined by the morphology of precursors. ► Rough surface enriched in In lead to poor crystalline CIGS containing InSe phases. - Abstract: CuInGa (CIG) ternary targets were prepared by vacuum arc remelting and used to deposit CIG thin films through direct current (DC) sputtering. We adjusted the sputtering energy (1–2 kWh) by tuning both the sputtering power and the accumulative sputtering time. The impact of the varying sputtering energy on the microstructure of CIG targets and thin films was subsequently investigated. The experimental results indicated that the compositional uniformity of CIG targets is strongly influenced by this parameter. CIG thin films with a flat topography, low porosity, and dense grain boundaries were obtained when targets were accumulatively sputtered at 1 kWh. These films showed good compositional uniformity while the CIG targets were found to maintain their microstructural characteristics as compared to their as-melted counterparts. On the other hand, Cu(In,Ga)Se₂ (CIGS) thin films, obtained by a selenization process, exhibited large faceted grains composed of a single chalcopyrite phase with a preferred orientation along the (1 1 2) plane. Accumulative sputtering of CIG targets at higher energies (e.g., 2 kWh) resulted in phase transformation and loss of In material as a result of an excess of residual heat budget on the surface generated by Ar ions bombardment. The CIG thin films thus showed an In-rich composition ratio, thereby potentially leading to In-rich CIGS thin films containing traces of an InSe compound.

[en] Ti-6Al-4V alloy substrates are diffused with molybdenum (Mo) and nickel (Ni), respectively, using the double glow (DG) plasma surface alloying technique. The crystal structures and surface morphologies of the diffused substrates are investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). In addition, the elemental compositions of the Mo- and Ni-diffusion modified surface layers are examined using an Auger electron spectrometer (AES) and an electron probe X-ray microanalyzer (EPMA). Finally, the hardness and wear resistance properties of the two surface layers are evaluated by means of Knoop hardness tests and pin-on-disk sliding tests, respectively. It is shown that the Mo-diffusion modified layer has a mixed Mo-Ti structure. By contrast, the Ni-diffusion modified layer consists of NiTi phase and Ni₃Ti and NiTi₂ intermetallic phases. Both surface alloying treatments increase the hardness of the Ti-6Al-4V substrate and improve the wear resistance as a result. Notably, the Ni-diffusion modified substrate has a higher friction coefficient than the Mo-diffusion modified substrate, but exhibits a lower wear rate. The improved wear resistance can be attributed to the presence of the NiTi, Ni₃Ti and NiTi₂ phases, which increase the yield strength of the contact surface and therefore reduce the wear mass. - Highlights: • Dense and uniform Mo- and Ni-modified substrates were obtained by DG-PSA on Mo and Ni. • Identify relationships between the microstructure and properties of Mo-and Ni-modified. • The Ni-Ti modified was obviously comprised of two parts. • A model has been made to explain the formation process of the gradient layer. • The Ni-modified substrates show excellent tribological properties.