Surface Review and Letters

A simple and hydrazine-free solution-based approach for depositing Cu₂ZnSnS₄ (CZTS) and Cu₂ZnSn(S,Se)₄ (CZTSSe) absorber layers is reported. The process involves incorporating metal salts (Cu(CH₃COO)₂, Zn(CH₃COO)₂, SnCl₂) and thiourea into a single pyridine-based solution, spin-coating a precursor film, and sulfurizing with sulfur powders or selenizing using Se pellets in an inert atmosphere, to form the desired CZTS or CZTSSe films. X-ray diffraction and Raman spectra studies show that kesterite CZTS and CZTSSe are formed after sulfurization and selenization, respectively. The selenized CZTSSe displays higher crystallinity than the sulfurized CZTS. Photovoltaic devices (glass/Mo/CZTSSe/CdS/i-ZnO/n-ZnO/A) employing the solution precursor selenized at 500°C have yielded power conversion efficiency of 1.44% under AM 1.5 illumination.

The interaction between the H₂ molecule and the PdAg, PdAu, PtAg and PtAu bimetallic dimers deposited on the MgO(100) surface is investigated using density functional theory (DFT). The bimetallic dimers, whose molecular axes are considered to be perpendicular to the support surface, are adsorbed on top of an oxygen atom. Within this adsorption mode, the dimers prefer the orientation in which their Pd or Pt end is closer to the oxygen atom. The Ag and Au ends of the MgO-supported dimers capture the H₂ molecule with small exoenergetic effects. The spontaneous dissociation of H₂ on these ends does not occur. Thus, the MgO support decreases the ability of the dimers to adsorb and dissociate the H₂ molecule. From a catalytic viewpoint, it means that the activity of small bimetallic clusters toward the dissociative adsorption of H₂ is reduced when they are arranged on MgO. On the other hand, the results of our calculations show that the presence of the MgO support strengthens the binding of H atoms inside the PdAu, PtAg and PtAu dimers.

Microarc oxidation (MAO) treatment produces a thick Al₂O₃ coating on the 15SiC_p/2024 aluminum matrix composite. After pretreatment of Ti ion implantation, a thin diamond-like carbon film (DLC) was deposited on the top of polished Al₂O₃ coating by a pulsed filtered cathodic vacuum arc (FCVA) deposition system with a metal vapor vacuum arc (MEVVA) source. The morphology and tribological properties of the duplex Al₂O₃/DLC multiplayer coating were investigated by Raman spectroscopy, scanning electron microscopy (SEM) and SRV ball-on-disk friction tester. It is found that the duplex Al₂O₃/DLC coating had good adhesion and a low friction coefficient of less than 0.07. As compared to a single Al₂O₃ or DLC coating, the duplex Al₂O₃/DLC coating on aluminum matrix composite exhibited a better wear resistance against ZrO₂ ball under dry sliding, because the Al₂O₃ coating as an intermediate layer improved load support for the top DLC coating on 15SiC_p/2024 composite substrate, meanwhile the top DLC coating displayed low friction coefficient.

We report the deposition of Ti and TiN films on Si/SiO₂ (100) substrate using e-beam evaporation technique. The influence of substrate temperature on the structural and morphological properties has been studied. The structure and morphology of the deposited films were analyzed by X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM) measurements, respectively. XRD patterns reveal the FCC symmetry for both the Ti and TiN films. The grain size of the films was found to increase with the increase in substrate temperature. FESEM micrographs showed a smooth morphology of the film with columnar grain structure.

Ceramic coatings have been synthesized on 6063 aluminum alloy by micro-arc oxidation (MAO) technique in the solution of Na₂B₄O₇ electrolyte with and without α-Al₂O₃ nanoadditive. Effects of α-Al₂O₃ nanoadditive on the phase composition, micro-structure, micro-hardness, adhesion and wear resistance of the prepared ceramic coatings have been investigated in this paper. The phase composition and microstructure of the MAO coatings were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDX) analyses, respectively. Micro-hardness, adhesion and tribological and wear tests were also performed. The results showed that the α-Al₂O₃ nanoadditive doped in the electrolyte had great influence on the structural and mechanical properties of the ceramic coatings.

A set of thin tantalum films was prepared by direct current (DC) magnetron sputtering using different substrate temperatures and sputtering power. In order to identify the optimal condition for hillock free thin tantalum (Ta) film deposition, AFM was employed to measure surface morphology of the Ta films and to research the effect of substrate temperatures and sputtering power on the films surface. The relationship between optical constants and film stress of thin Ta films was also investigated. The comparison of AFM results showed that thin Ta films deposited at 500 K with a sputtering power of 56 W produced a hillock free surface as well as minimum surface roughness. All films were also measured by spectroscopic ellipsometry (SE) to characterize their optical properties. Refractive index and extinction coefficient of thin Ta films obtained from SE results by using a 5-layer model increased simultaneously, when sputtering power increased and the substrate temperature remain unchanged. However when the power was a constant, the thin Ta film sputtered at 500 K had a lower refractive index and extinction coefficient than other samples sputtered with other substrate temperatures from 300 to 700 K.

The work functions of (001) and (00-1) surfaces of B₄C are investigated with density functional theory and symmetry slab model. These two surfaces are found to be almost nonpolarized and their work functions are 5.15 eV and 5.46 eV, respectively.

Scanning tunneling microscopy is used to study intercalation of cobalt underneath a graphene layer on Ru(0001). Deposition of cobalt on graphene/Ru(0001) at 873 K leads to the intercalation of cobalt between the graphene layer and the Ru(0001) substrate, and the intercalation is associated with Co diffusion at steps and defects. The morphology of graphene/Co/Ru(0001) shows moiré pattern, as same as that of graphene/Ru(0001). The bright areas where Co islands exist are hcp regions of graphene/Ru(0001). The intercalated Co islands have a pseudomorphic structure superimposed on Ru(0001).

The paper presents research results of the influence of CrN coating on the friction parameters in friction pairs under lubricated friction conditions. The formed CrN homogeneous coating and CrN-steel 46Cr2 "ring" structure coating was matched under test conditions with a counterpart made from SAE-48 and SAE-783 bearing alloys. Tested sliding pairs were lubricated with 5W/40 Lotos synthetic engine oil. The tribological test was conducted on block-on-ring tester. The applied modification technologies of the surface layer of steel allowed for obtaining construction materials with pre-determined tribological characteristics required for the elements of friction pairs in lubricated contact. The results of the tests proved the possibility of implementing CrN coating in friction pairs, which work under mixed friction conditions. The results showed differences in the wear of bearing alloy, as the effect of the interaction between the co-operating surface layers and of the physiochemical changes of their surfaces, induced by external forces. The smallest wear of the bearing alloy occurs during the cooperation with the nitrided layer, whereas the largest wear occurs during the cooperation with the homogenous CrN coating. The CrN coating-46Cr2 steel "ring structure" decreases friction resistance during the start-up of the sliding pair, as well as lowers the level of the friction force and temperature in the friction area during co-operation with SAE-783 bearing alloys.

Characterization and modeling analysis on both ideality factor of the collector current (η_C) and the base current (η_B) have higher than the excepted values of 1.0 and 2.0, respectively, for npn AlGaN/GaN heterojunction bipolar transistors (HBTs) have been reported. We employ the rapid thermal process annealing (RTP-annealing) to modify the base parasitical Schottky diode (called A-HBTs) after the as-deposited Ni/Au bilayers on the base layer for electrode with no annealing (called N-HBTs) to compare with each other. For a HBT operated in Gummel-plot configuration, experimental and modeling results indicate that the base parasitical Schottky diode (BPSD) causes the base current (I_B) and collector current (I_C) with high ideality factor and raise the base-emitter voltage (V_BE) to higher operation point, and therefore lead to more power consumption. Furthermore, the extended Ebers–Moll equivalent-circuit model together with the extracted device parameters provided simulated results that were in a good agreement with experimental ones.

By transferring Mg_xZn_1-xO sol and stearic acid onto a hydrophilic silicon wafer or glass plate, the Langmuir–Blodgett (LB) multilayers of Mg_xZn_1-xO (x:0, 0.2, 0.4) were deposited. After calcinations at 350°C for 0.5 h and at 500°C for 3 h, Mg_xZn_1-xO ultrathin films were fabricated. The optimized parameters for monolayer formation and multilayer deposition were determined by the surface pressure-surface (Π-A) area and the transfer coefficient, respectively. The expended areas of stearic acid with Mg_xZn_1-xO sols under Π-A isotherms inferred the interaction of stearic acid with Mg_xZn_1-xO sols during the formation of monolayer at air–water interface. X-ray diffraction (XRD) was used to determine the crystal structures of Mg_xZn_1-xO nanoparticles and ultrathin films. The surface morphologies of Mg_xZn_1-xO ultrathin films were observed by scanning probe microscopy (AFM). And the optoelectronic properties of Mg_xZn_1-xO were detected and discussed based on photoluminescence (PL) spectra.

Engineering applications of TiB₂ coatings are limited because of the brittle nature of interfacial bonds on the substrate surfaces, although they have many major properties such as high hardness, high wear and high temperature strength. To overcome this drawback, many researchers have studied over many years and their efforts have taken several forms such as the rotation of substrate, heating treatment during deposition or after deposition, application of positive bias voltage to the substrate, the introduction of transition elements as an interlayer, gradient or multilayer or composite strengthening, and the optimization studies performed by changing deposition process types and/or process parameters such as working gas and bias voltage. The purpose of this paper is to discuss these solutions proposed or developed by researchers against the limited use of TiB₂ coatings due to its brittleness and low adhesion. From the results reported in literature, it is concluded that the best solution in order to produce non-brittle TiB₂ based film well adherent to substrate is the use of pulsed-dc deposition technology provided that the process parameters are tuned to give an appropriate composition and/or a coating design. Furthermore, the TiB₂ based coatings with multiphase layers seem to give better results respect to adherence.