Phase stability of Crn+ 1GaCn MAX phases from first principles and Cr2GaC thin‐film synthesis using magnetron sputtering from elemental targets

Ab‐initio calculations have been used to investigate the phase stability and magnetic state of Cr_{n+ 1}GaC_n MAX phase. Cr₂GaC (n = 1) was predicted to be stable, with a ground state corresponding to an antiferromagnetic spin configuration. Thin‐film synthesis by magnetron sputtering from elemental targets, including liquid Ga, shows the formation of Cr₂GaC, previously only attained from bulk synthesis methods. The films were deposited at 650 °C on MgO(111) substrates. X‐ray diffraction and high‐resolution transmission electron microscopy show epitaxial growth of (000?) MAX phase. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

MAX相陶瓷的结构、制备及物理性能研究

MAX相陶瓷因具有独特的MX片层与A片层交替堆叠的晶体结构,使其兼具金属和陶瓷的优良特性,如良好的导热导电性、可加工性,同时具有良好的抗氧化性、耐腐蚀性以及耐摩擦磨损等性能,具有非常广泛的应用前景。本文首先介绍了MAX相陶瓷材料的种类与晶体结构,并简述了近几年新发现的MAX相陶瓷材料以及制备手段的发展动态。之后从MAX相物理性能的角度出发,重点综述了几种典型MAX相陶瓷材料的弹性性能、电学性能、热学性能、磁性能以及抗辐照性能的研究进展。此外,进一步介绍了MAX相的二维衍生物MXene的衍生过程、超导性以及其在电化学储能、催化领域的研究进展。最后,本文从探索MAX相材料新结构的多样性、MAX相物理性能及相关理论计算、MXene二维材料以及相应的制备、表征和应用等方面,展望了MAX相陶瓷材料的潜在研究方向及应用前景,为MAX相和MXene材料的深入研究提供了新的思路。     

Theoretical stability,thin film synthesis and transport properties of the Mon +1GaCn MAX phase

The phase stability of Mo_{n +1}GaC_n has been investigated using ab‐initio calculations. The results indicate stability for the Mo₂GaC phase only, with a formation enthalpy of –0.4 meV per atom. Subsequent thin film synthesis of Mo₂GaC was performed through magnetron sputtering from elemental targets onto Al₂O₃ [0001], 6H‐SiC [0001] and MgO [111] substrates within the temperature range of 500 °C and 750 °C. High structural quality films were obtained for synthesis on MgO [111] substrates at 590 ºC. Evaluation of transport properties showed a superconducting behavior with a critical temperature of approximately 7 K, reducing upon the application of an external magnetic field. The results point towards the first superconducting MAX phase in thin film form. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Synthesis, characterization and photoelectrochemical properties of n-CdS thin films

Cadmium sulfide thin films have been deposited on glass substrates by simple and cost effective chemical bath deposition technique. Triethanolamine was used as a complexing agent. The preparative parameters like ion concentration, temperature, pH, speed of substrate rotation and deposition time have been optimized for good quality thin films. The ‘as-grown’ films are characterized for structural, electrical, optical and photoelectrochemical (PEC) properties. The X-ray diffraction (XRD) studies reveal that the films are polycrystalline in nature. Energy-dispersive analysis by X-ray (EDAX) shows that films are cadmium rich. Uniform deposition of CdS thin films on glass substrate is observed from scanning electron microscopy (SEM) and atomic force microscopy (AFM) micrographs. Optical studies reveal a high absorption coefficient (10⁴ cm⁻¹) with a direct type of transition. The band gap is estimated to be 2.47 eV. The film shows n-type conduction mechanism. The photoelectrochemical (PEC) cell with CdS thin film as a photoanode and sulfide/polysulfide (1 M) solution as an electrolyte have been constructed and investigated for various cell parameters. The solar to electrical conversion efficiency (η) and fill factor (ff) are found to be 0.049% and 0.36, respectively.     

Effect of pulsed bias on properties of ZrN/TiZrN films deposited by cathodic vacuum arc

ZrN/TiZrN multilayer are deposited by cathodic vacuum arc method with different substrate bias (from 0 to -800 V), using Ti and Zr plasma flows in residual N₂ atmosphere, combined with ion bombardment of sample surfaces. The effect of pulsed bias on structure and properties of films is investigated. Microstructure of the coating is analyzed by X-ray diffraction (XRD), and scanning electron microscopy (SEM). Meanwhile, the nanohardness, Young's modulus, and scratch tests are performed. The experimental results show that the films exhibit a nanoscale multilayer structure consisting of TiZrN and ZrN phases. Solid solutions are formed for component TiZrN films. The dominant preferred orientation of TiZrN films is (111) and (220). At pulsed bias of -200 V, the nanohardness and the adhesion strength of ZrN/TiZrN multilayer reach a maximum of 38 GPa, and 78 N, respectively. The ZrN/TiZrN multilayer demonstrates an enhanced nanohardness compared with binary TiN and ZrN films deposited under equivalent conditions.     

First‐order Raman scattering of the MAX phases: Ti2AlN,Ti2AlC0.5N0.5, Ti2AlC, (Ti0.5V0.5)2AlC,V2AlC,Ti3AlC2, and Ti3GeC2

Here, we report, for the first time, on the Raman spectra of Ti₂AlN, Ti₂AlC_0.5N_0.5, (Ti_0.5V_0.5)₂AlC, Ti₃AlC₂, and Ti₃GeC₂ and compare the results with those of Ti₂AlC and V₂AlC reported previously. The first‐order mode peaks of the end members are narrower than those of their respective solid‐solution compounds. The Ti₃AlC₂ and Ti₃GeC₂ phases show, in addition to atomic displacements of the ‘M’ and ‘A’ atomic planes, modes that correspond with vibrations of the ‘X’ sublattice relative to itself. We also predict the Raman modes using density functional theory. The agreement between theory and experiment was found to be satisfactory. Copyright © 2011 John Wiley & Sons, Ltd.     

Effect of pulsed bias on the properties of ZrN/TiZrN films deposited by a cathodic vacuum arc

ZrN/TiZrN multilayers are deposited by using the cathodic vacuum arc method with different substrate bias(from 0 to 800 V),using Ti and Zr plasma flows in residual N 2 atmosphere,combined with ion bombardment of sample surfaces.The effect of pulsed bias on the structure and properties of films is investigated.Microstructure of the coating is analyzed by X-ray diffraction(XRD),and scanning electron microscopy(SEM).In addition,nanohardness,Young’s modulus,and scratch tests are performed.The experimental results show that the films exhibit a nanoscale multilayer structure consisting of TiZrN and ZrN phases.Solid solutions are formed for component TiZrN films.The dominant preferred orientation of TiZrN films is(111) and(220).At a pulsed bias of 200 V,the nanohardness and the adhesion strength of the ZrN/TiZrN multilayer reach a maximum of 38 GPa,and 78 N,respectively.The ZrN/TiZrN multilayer demonstrates an enhanced nanohardness compared with binary TiN and ZrN films deposited under equivalent conditions.     

Magnetism of alloyed models of Cr(Mn) V and Mn Cr overlayers on V (001) substrates

The magnetism is calculated for substitutional alloyed of Cr_x(Mn_x)V_1-x monolayers (MLs) and Cr_xMn_1-x on V (001) surface with a variety of concentrations (x = 0.25, 0.50 and 0.75). The substitutional surface alloys were treated by an artificial super cell construction. Parallel magnetic ordering is obtained for all the considered structures. The surface net magnetization increases in terms of Cr (Mn) concentration in Cr_x(Mn_x)V_1-x/V (001) system, while no serious variations occur in Cr_xMn_1-x/V (001). Vanadium atoms at the interfacial layers acquire appreciable magnetic moments antiferromagneticlly (AF) coupled with the surface moments. Received 25 February 2002 / Received in final form 13 May 2002 Published online 14 October 2002 RID="a" ID="a"e-mail: jkalifa@sci.ju.edu.jo     

Structural characterization and magnetoresistance of manganates thin films and Fe-doped manganates thin films

Perovskites thin films with the composition La_0.6Ca_0.4MnO₃ doped with 20% Fe, were prepared by pulsed reactive crossed beam laser ablation, where a synchronized reaction gas pulse interacts with the ablation plume. The films were grown on various substrates and the highest colossal magnetoresistance ratio (CMR) was detected by Hall measurements for films grown on LaAlO₃ (1 0 0), which was selected as substrate for further investigations.Several growth parameters, such as substrate temperature and target to substrate distance were varied to analyze their influence on the film properties.The structure of the deposited thin films was characterized by X-ray diffraction and atomic force microscope, while Rutherford backscattering (RBS) was used to determine the film stoichiometry. The electrical properties were determined by Hall effect measurements in a magnetic field of 0.51 T.These measurements reveal that the amplitude of the CMR ratio depends strongly on the substrate and that the oxygen content influences the temperature where the transition from semiconductor to metal is observed.     

Synthesis of titanium nitride thin films deposited by a new shielded arc ion plating

Thin films of titanium nitride (TiN) were deposited on stainless steel substrates by a modified deposition technique, double-layered shielded arc ion plating with vicarious circular holes (DL-SAIP). The results show that the TiN film with the distance of 10 mm between the double-layered shield plates had the least droplets. The deposition rate of the films prepared with the new technique was more homogeneous than that of all the other shielded arc ion plating. The film/substrate adhesion and microhardness values of the TiN films were higher than 40 N and 18 GPa, respectively. Thus such TiN thin films can be expected in applications.     

Synthesis of MgB2 films by diffusion of magnesium into electrophoretically deposited boron films

The boron films were formed from the optimized stable suspension solution of boron particles using electrophoretic deposition technique. The magnesium film with optimized thickness was deposited onto boron films by vacuum evaporation technique. The heterogeneous structure was given heat treatment in ambient and vacuum atmosphere for diffusion of Mg into the boron films to form MgB₂ phase. XRD studies were carried out on both as deposited and heat treated heterostructure films to investigate their structure and phase. Surface morphological studies of these films were done by SEM.     

Characterization of Ti-Zr-N films deposited by cathodic vacuum arc with different substrate bias

Ti-Zr-N (multi-phase) films were prepared by cathodic vacuum arc technique with different substrate bias (0 to −500 V), using Ti and Zr plasma flows in residual N₂ atmosphere. It was found that the microstructure and mechanical properties of the composite films are strongly dependent on the deposition parameters. All the films studied in this paper are composed of ZrN, TiN, and TiZrN ternary phases. The grains change from equiaxial to columnar and exhibit preferred orientation as a function of substrate bias. With the increase of substrate bias the atomic ratio of Ti to Zr elements keeps almost constant, while the N to (Ti + Zr) ratio increases to about 1.1. The composite films present an enhanced nanohardness compared with the binary TiN and ZrN films deposited under the same condition. The film deposited with bias of −300 V possesses the maximum scratch critical load (L_c).     

Photoconductivity and photoluminescence in chemically deposited films of CdSSe:CdCl2,Ho

Results of the scanning electron microscopy (SEM), X-ray diffraction (XRD), optical absorption, photoconductivity (PC), and photoluminescence (PL) studies for the CdSSe:CdCl₂,Ho films are presented in this paper. The SEM studies of different CdSSe films show a layered growth structure. A crystalline nature of the films is observed in the XRD studies. The regions with stacking fault were also observed in the X-ray diffractograms. The optical absorption spectra of these films show variations corresponding to the band gaps and the grain-sizes obtained under various deposition conditions and also with annealing. The effect of flux, impurities and annealing on the saturated photo to dark current ratio I_pc/I_dc is observed in the PC rise and decay studies. The maximum value of I_pc/I_dc ∼10⁷ is obtained for the impurity doped annealed films. The PL emission spectra of CdSSe films show two emission peaks associated with the annihilation of free excitons and the transitions between shallow donor and deep acceptor states. In CdSSe:CdCl₂,Ho films, two PL emission peaks are observed at 495 nm and 545 nm corresponding to the transitions ⁵S₂→⁵I₈ and ⁵F₃→⁵I₈, respectively, in Ho. The effect of pH on PL and grain size is also included in the present studies.     

First‐order Raman scattering of the MAX phases Ta4AlC3, Nb4AlC3, Ti4AlN3, and Ta2AlC

Herein, we report on the Raman spectra of the following ternary hexagonal carbides and nitrides (MAX phases): Ta₄AlC₃, Ta₂AlC and Ti₄AlN₃. We also present the Raman‐active modes of α‐ and β‐Ta₄AlC₃, Nb₄AlC₃ and Ti₄AlN₃, – also referred to as the 413 MAX phases – as predicted from first principles calculations using density functional theory. We compare the obtained experimental and calculated results with previous studies on Ta₂AlC and Ti₄AlN₃. The vibrational behavior associated with the Raman‐active modes for the 413 phases has been identified for the first time. In general, the agreement is good between theory and experiment. The experimental and calculated results indicate that the modes at low wavenumbers ‐ dominated by the Al atoms ‐ are a weak function of chemistry and the differences in energy can be traced to variations in the reduced mass. The modes at higher wavenumbers are dominated by the C and N atoms and show a strong dependence on the unit cell chemistry, with the Ta–C bond being stiffer than the Nb–C bond, which is in turn stiffer than Ti–N. Copyright © 2011 John Wiley & Sons, Ltd.     

Tribological properties of diamond-like carbon films deposited by pulsed laser arc deposition

A novel method, pulsed laser arc deposition combining the advantages of pulsed laser deposition and cathode vacuum arc techniques, was used to deposit the diamond-like carbon (DLC) nanofilms with different thicknesses. Spectroscopic ellipsometer, Auger electron spectroscopy, x-ray photoelectron spectroscopy, Raman spectroscopy, atomic force microscopy, scanning electron microscopy and multi-functional friction and wear tester were employed to investigate the physical and tribological properties of the deposited films. The results show that the deposited films are amorphous and the sp$^{2}$, sp$^{3}$ and C--O bonds at the top surface of the films are identified. The Raman peak intensity and surface roughness increase with increasing film thickness. Friction coefficients are about 0.1, 0.15, 0.18, when the film thicknesses are in the range of 17--21~nm, 30--57~nm, 67--123~nm, respectively. This is attributed to the united effects of substrate and surface roughness. The wear mechanism of DLC films is mainly abrasive wear when film thickness is in the range of 17--41~nm, while it transforms to abrasive and adhesive wear, when the film thickness lies between 72 and 123~nm.     

Optical and structural characterization of ultrananocrystalline diamond/hydrogenated amorphous carbon composite films deposited via coaxial arc plasma

Ultrananocrystalline diamond/hydrogenated amorphous carbon composite films were deposited in the ambient of hydrogen by coaxial arc plasma deposition. The film compositions and chemical bonding structures were investigated by X-ray diffraction, X-ray photoemission and hydrogen forward scattering spectroscopies. The sp³/(sp²+sp³) ratio and hydrogen content in the film were estimated to be 64% and 35?at.%, respectively. The optical parameters and the optical dispersion profile were determined by using a variable angle spectroscopic ellipsometer at 55°, 65° and 75° angle of incidence in the photon energy range of 0.9–5?eV. Combinations of multiple Gaussian, and Tauc-Lorentz or Cody-Lorentz dispersion functions are used to reproduce the experimental data. Results of ellipsometry showed a refractive index of approximately 2.05 (at 2eV) and optical band gap of 1.63?eV. The imaginary part of dielectric function exhibited a peak at 3.8?eV, which has assigned to π-π* electron transitions. Furthermore, Electron spin resonance measurements implied the existence of dangling bonds, which might have a partial contribution to the optical absorption properties of the deposited films. A correlation between optical parameters and structural profile of the deposited films is discussed.     

脉冲偏压电弧离子镀Cr-O薄膜结构及光学性能研究

采用脉冲偏压电弧离子镀技术在单晶硅基片及石英玻璃上制备了一系列均匀透明的Cr-O薄膜. 用场发射扫描电子显微镜、X射线衍射仪、X射线光电子谱、纳米压痕仪、紫外可见光分光光度计等方法对薄膜的表面形貌、膜厚、相结构、成分、元素的化学价态、硬度和光学性能等进行表征, 主要研究了偏压幅值对薄膜结构和性能的影响. 结果表明, 施加偏压可使薄膜的沉积质量明显提高, 其相结构由非晶态转变为晶体态, 并随着偏压幅值的增加, 由Cr₂O₃相向CrO相转变; 薄膜的硬度先增大后减小, 当偏压为-300 V时, 硬度达到最大值24.4 GPa; 薄膜具有良好的透光率, 最高可达72%; 当偏压为-200 V时, 薄膜的最大光学帯隙为1.88 eV.     

Research on the properties of ZnO thin films deposited by using filtered cathodic arc plasma technique on glass substrate under different flow rate of O2

ZnO thin film has been deposited on the glass substrate at a temperature of 200 °C using the filtered cathodic arc plasma (FCAP) technique with the oxygen flow rate of 1.0, 3.0, 5.0, 7.0, 9.0 and 10.0 sccm. The deposition processes are only held in pure oxygen atmosphere. The as-grown films exhibit a polycrystalline hexagonal wurtzite structure. With the oxygen flow rate increase, the crystallinity of the samples first increases and then decreases as measured by X-ray diffractometry (XRD). And the tensile stress exists in all the as-grown thin films. The small grain with a mean diameter of 13 nm is observed by the field emission scanning electron microscopy (FESEM). The electrical resistivity values of the thin films are very low ranging from 5.42 × 10⁻³ Ω cm to 4.0 × 10⁻² Ω cm. According to the result from room temperature photoluminescence spectra measurement, the luminescent bands also depend on the oxygen supply.