Kinetic Monte Carlo simulation of physical vapor deposition of thin Cu film

A two-dimensional Kinetic Monte Carlo method has been developed for simulating the physical vapor deposition of thin Cu films on Cu substrate. An improved embedded atom method was used to calculate the interatomic potential and determine the diffusion barrier energy and residence time. Parameters, including incident angle,deposition rate and substrate temperature, were investigated and discussed in order to find their influences on the thin film morphology.     

XPS study of BZT thin film deposited on Pt/Ti/SiO2/Si substrate by pulsed laser deposition

Ferroelectric materials were widely applied for actuators and sensors. Barium zirconate titanate Ba（Zr0.25Ti0.75）O3 thin film was grown on Pt/Ti/SiOdSi（100） substrates by pulsed laser deposition. Structure and surface morphology of the thin film were studied by X-ray diffractometry （XRD） and scan electronic microscopy （SEM）. The composition and chemical state near the film surface were obtained by X-ray photoelectron spectroscopy （XPS）. On the sample surface, O 1 s spectra can be assigned to those from the lattice and surface adsorbed oxygen ions, while Cls only result from surface contamination. The result shows that only one chemical state is found for each spectrum of Ba 3d, Zr 3d and Ti 2p photoelectron in the BZT thin film.     

Kinetic Monte Carlo simulation of microalloying effect in Al-Ag alloys

The kinetic Monte Carlo method, which based on the Multi-States Ising Model, was applied to simulate the effect of microelements on the microstructural evolution of Al-Ag alloys during initial aging stage. The simulation results suggest that the microelements In, Sn and Be have a dramatic depression effect on the Ag clustering because of their strong tendency to co-existed with vacancies. There are no significant effects on the process of Ag clustering in Al-Ag alloys containing Li or Cd, because of little interaction between Li/Cd and Ag/vacancies. Microelements can influence the aging by interacting with vacancies and the atoms of precipitated composition, in which the former seems more important. In this model, ＂vacancy-locking＂ and ＂vacancy clusters＂ are two important mechanisms in the aging process.     

焙烧过程晶粒生长的Monte Carlo模拟

基于Monte Carlo（MC）方法,根据晶粒生长机理建立改进的转换概率模型,在不同焙烧温度、焙烧时间和激活能条件下可实现晶粒生长过程结构演化的计算机模拟,对模拟和实验数据进行分析,结果表明：当晶粒生长指数为2.17时,模拟与实验具有较好的一致性,从而得出焙烧过程晶粒的生长动力学模型;该模型能够较好地解释焙烧过程晶粒的生长过程,对晶粒生长动力学研究等具有一定的指导意义。     

Microstructure and grain growth kinetics of nanocrystalline SnO2 thin films prepared by pulsed laser deposition

The isothermal grain growth of SnO₂ thin films prepared by pulsed laser deposition techniques was investigated at Si (100) substrate temperatures between 300 and 450 °C with 50 °C intervals for different annealing times. X-ray diffraction patterns proved that the average grain sizes are in the range of 2.4–27.8 nm. The grain growth data were analyzed using two different models. The first model, assuming normal grain growth as that in conventional polycrystalline materials, yields large grain growth exponent (n) and extremely low activation energy (Q). Although it can describe the evolution of grain sizes, it fails to give satisfactory physical interpretation of n and Q, both beyond the theoretical predictions. The second model is based on the structural relaxation of the interface component in nanocrystalline materials. In this case, the ordering of distorted interfaces by structural relaxation proceeds with grain growth. This structure relaxation model not only describes the evolutions of grain growth well, but also makes reasonable attribution of the low activation energy to the short-range rearrangement of atoms in the interface region as well.     

Growth of HT-LiCoO2 thin films on Pt-metalized silicon substrates

Layered LiCoO2 （HT-LiCoO2） films were grown on Pt-metalized silicon （PMS） substrates and polished bulk nickel （PBN） substrates by pulsed laser deposition. The effects of substrate temperature, oxygen pressure, and substrate surface roughness on the microstructure of LiCoO2 films were investigated. It has been found that a higher substrate temperature and a higher oxygen pressure favor the formation of better crystallized and less lithium-deficient HT-LiCoO2 films. The HT-LiCoO2 film deposited on PBN substrates consists of large randomly orientated equiaxial grains, whereas on PMS substrate, it is made up of loosely packed highly [001] preferential orientated triangular shaped grains with the average grain size less than 100 nm. Electrochemical measurements show that the highly [001] preferentially orientated nanostructured HT-LiCoO2 thin film grown on PMS substrate has good structural stability upon lithium insertion/extraction and can deliver an initial discharge capacity of approximately 45μA·h·cm^-2·μm^-1 with a cycling efficiency of above 99% at the charge/discharge rate of 0.5 C.     

Fabrication of anatase-type TiO2 films by reactive pulsed laser deposition for photocatalyst application

TiO₂ films having anatase crystal structure were prepared on glass substrates by reactive pulsed laser deposition using a metallic Ti target in an O₂ gas ambient. At a fixed substrate temperature of 400 °C, the crystalline structure, surface morphology, optical properties and photocatalytic activity of the TiO₂ films were greatly affected by the O₂ gas pressure. It was found that nearly pure anatase-phase TiO₂ film can be obtained under an O₂ pressure of 15 Pa, which had smallest grain size among the films deposited under various O₂ gas pressure from 5 to 30 Pa. This film also showed good optical transmittance between the wavelength of 200 and 800 nm and high photocatalytic efficiency on the decomposition of methylene blue in aqueous solution. Discussions were given to explain the experimental phenomena.     

Oriented nanocrystals in SrLaMnTiO6 perovskite thin films grown by pulsed laser deposition

We have fabricated SrLaMnTiO₆ thin films by PLD on different substrates (SrTiO₃, LaAlO₃ and Si). Their texture, width, homogeneity and morphology have been evaluated from XRD, SEM and complex impedance spectroscopy. The thickness ranged between 500 and 8800 nm depending on the synthesis conditions. The epitaxial growing could be interpreted in terms of two contributions of microstructural origin: a matrix part and some surface formations (hemi-spheres), with different texture and size distributions. The films were nanostructured and contained vertically aligned nanopores (VANPs) with a pore average size of 30-60 nm, which are very interesting for eventual SOFC anode applications. Magnetization results indicate an improved response respect to nano-sized powder samples.     

Er~(3+)掺杂位置对Er~(3+):BaTiO_3薄膜上转换发光的影响(英文)

采用溶胶-凝胶法在LaNiO3/Si衬底上制备Er3+掺杂BaTiO3薄膜。通过XRD、AFM和PL图谱分别研究薄膜的晶体结构、形貌以及上转换发光性能。结果表明,薄膜的微观结构和发光性能与Er3+掺杂晶格的位置有关。A位掺杂薄膜较B位掺杂薄膜具有较小的晶格常数和较好的结晶。PL光谱表明:A位掺杂的薄膜和B位掺杂的薄膜都于528nm和548nm处获得较强的绿色上转换发光以及在673nm处获得较弱的红光,分别对应Er3+离子的2H11/2→4I15/2,4S3/2→4I15/2和4F9/2→4I15/2能级跃迁。相对于B位掺杂的薄膜,A位掺杂样品有较强的绿光发射积分强度以及较弱的红光发射相对强度。这种差异可以通过薄膜的结晶状况和交叉弛豫机制来进行解释。     

Effect of bias on the As-deposited grain structure of Cr thin film

The film growth of Cr thin film by DC-magnetron sputter deposition was investigated by experimentally measuring the evolution of grain size distribution and by computing the film growth using Monte Carlo simulation. The as-deposited Cr thin film by sputter deposition typically grows in a columnar grain structure at the substrate temperature 260°C, which is far lower than 0.3 T_m. The stagnation of columnar grain structure does not occur in the case of no-bias condition up to the investigated film thickness of about 800 nm. However, the application of a negative bias of 200 V results in a stagnation of columnar grain structure at film thickness of about 50 nm and at the deposition temperature of 260°C. This is believed to arise from the fact that the mobility of ad-atoms is greatly enhanced and the Ar+ ions pin the grain boundary as a result of bias application. This article is based on a presentation made in the 2002 Korea-US symposium on the “Phase Transformation of Nano-Materials,” organized as a special program of the 2002 Annual Meeting of the Korean Institute of Metals and Materials, held at Yonsei University Seoul, Korea on October 25–26, 2002.     

Properties of multilayer gallium and aluminum doped ZnO(GZO/AZO) transparent thin films deposited by pulsed laser deposition process

Multilayer gallium and aluminum doped ZnO (GZO/AZO) films were fabricated by alternative deposition of Ga-doped zinc oxide(GZO) and Al-doped zinc oxide(AZO) thin film by using pulsed laser deposition(PLD) process. The electrical and optical properties of these GZO/AZO thin films were investigated and compared with those of GZO and AZO thin films. The GZO/AZO (1:1) thin film deposited at 400 °C shows the electrical resistivity of 4.18×10-4 Ω·cm, an electron concentration of 7.5×1020 /cm3, and carrier mobility of 25.4 cm2/(V·s). The optical transmittances of GZO/AZO thin films are over 85%. The optical band gap energy of GZO/AZO thin films linearly decreases with increasing the Al ratio.     

线损伤铝合金薄板脉冲激光修复过程的温度场模拟

利用ANSYS有限元分析软件对存在线损伤的铝合金薄板脉冲激光修复过程中的温度场进行了数值模拟。综合考虑了材料热物性参数、边界条件、相变潜热等因素,建立了表面高斯热源+三维锥体热源模型,两个热源功率分配比为1:9,并对模拟结果进行了试验验证。结果表明,数值模拟计算的熔宽和熔池形貌与试验获得结果吻合较好,说明所建立的温度场数值模型和热源模型能够较准确地反映线损伤铝合金薄板脉冲激光修复过程的温度场,可用作此类铝合金薄板脉冲激光修复过程分析及工艺参数优化。     

Epitaxial growth of tin ferrite thin films using pulsed laser deposition technique

Epitaxial thin films of tin ferrite (SnFe₂O₄) were deposited on (0 0 2) oriented strontium titanate (SrTiO₃) substrate using pulsed laser deposition method. The quality and epitaxial nature of the films were investigated by X-ray diffraction technique. The phi scan of the film and the substrate shows four folds symmetry indicating cube-on-cube epitaxial growth of the film on the substrate. The optical bandgap of the film was estimated to be 2.6 eV using optical transmittance data. Magnetic measurements indicate that the coercive field and remnant magnetization of the film decrease with increase in temperature. The presence of hysteresis loop in M vs. H plot at room temperature indicates the ferromagnetic nature of the film.     

Reactive pulsed laser deposition and characterization of niobium nitride thin films

We present a systematic study to explore the effect of important process variables on the composition and structure of niobium nitride thin films synthesized by Reactive Pulsed Laser Deposition (RPLD) technique through ablation of high purity niobium target in the presence of low pressure nitrogen gas. Secondary Ion Mass Spectrometry has been used in a unique way to study and fix gas pressure, substrate temperature and laser fluence, in order to obtain optimized conditions for one variable in single experimental run. The x-ray diffraction and electron microscopic characterization have been complemented by proton elastic backscattering spectroscopy and x-ray photoelectron spectroscopy to understand the incorporation of oxygen and associated non-stoichiometry in the metal to nitrogen ratio. The present study demonstrates that RPLD can be used for obtaining thin film architectures using non-equilibrium processing. Finally the optimized NbN thin films were characterized for their hardness using nano-indentation technique and found to be ~ 30 GPa at the deposition pressure of 8 Pa.     

Pulsed laser deposited Sb2Se3 anode for lithium-ion batteries

Sb₂Se₃ thin film has been successfully fabricated by reactive pulsed laser deposition and was investigated for its electrochemistry with lithium for the first time. The reversible discharge capacities of Sb₂Se₃/Li cells cycled between 0.3 and 2.5 V were found in the range of 530.5–660.7 mAh g⁻¹ during the first 100 cycles. By using ex situ X-ray diffraction, transmission electron microscopy, and selected-area electron diffraction measurements, both classical alloying process and the selenylation/reduction of nanosized metallic antimony were proposed in the lithium electrochemical reaction of Sb₂Se₃. Sb₂Se₃ has high reversible capacity and good cycle performance, which makes it potential anode material for future lithium-ion batteries.     

Pulsed laser deposition of anatase and rutile TiO2 thin films

The investigation deals with the preparation of both anatase and rutile thin films from a sintered rutile target of TiO₂ by pulsed laser ablation technique. Microstructural characterization of the sintered target was carried out using X-ray diffraction and AC impedance spectroscopy. Thin films of titania were deposited on (111) Si substrates at 673 K in the laser energy range 200-600 mJ/pulse at two different conditions: (i) deposition at 3.5 × 10^− 5 mbar of oxygen, and (ii) deposition at an oxygen partial pressure of 0.1 mbar. The influence of laser energy and oxygen addition on the film growth has been studied. X-ray diffraction analysis of the films indicated that the films are single phasic and nano crystalline. Titania films deposited in the energy range 200-600 mJ/pulse at a base pressure of 5 × 10^− 5 mbar are rutile with particle sizes in the range 5-10 nm, whereas the films formed at the oxygen partial pressure 0.1 mbar are anatase with particle sizes in the range 10-24 nm. In addition, at higher energies, a significant amount of particulates of titania are found on the surface of the films. The change in the microstructural features of the films as a function of laser energy and oxygen addition is discussed in relation with the interaction of the ablated species with the background gas.     

脉冲激光沉积WSx/a-C复合薄膜的结构与摩擦学性能

采用脉冲激光烧蚀石墨/WS₂组合靶,在硅基片上沉积不同碳质量分数的WSx/a-C复合膜。用能谱仪、扫描电子显微镜和X射线衍射仪对薄膜的成分、形貌和微观组织进行了表征。采用纳米压痕仪、涂层附着力划痕仪和球-盘式摩擦磨损试验机对薄膜的硬度、结合力和大气中(相对湿度50~55%)的摩擦学性能进行了测试。结果表明,薄膜的S/W比稳定在2.0左右且形成了(002)择优取向的WS₂相。随着薄膜中碳质量分数的增加,薄膜的硬度在36.1%C时出现最高值,结合力随之增大且在52.4%C时达到最高值,摩擦因数先降低后增加,在41.2%C时有最小值0.144。薄膜磨损率在(0.91~1.61)×10_-15 m₃N_-1m_-1范围内变化,36.1%C的WSx/a-C复合膜具有最佳耐磨性能。     

Pulsed laser deposition and characterisation of perovskite-type LaTiO3−xNx thin films

LaTiO_3−xN_x films with high nitrogen contents (x ≈ 0.4–0.8) have been grown on (0 0 1)-oriented MgO and LaAlO₃ substrates by pulsed reactive crossed-beam laser ablation from a La₂Ti₂O₇ target in a one-step process. These films have a perovskite-type structure, similar to bulk polycrystalline LaTiO₂N. The nitrogen content in the films can be changed by selecting the nitriding source, i.e. NH₃ or N₂ gas pulse, and by varying the substrate temperature. Films deposited on MgO show a preferential (0 0 1) and (1 1 2) orientation, whereas films on LaAlO₃ are predominantly (0 0 1) oriented. N(2p) orbitals contribute to the top of the valence band, leading to a considerable decrease in the band gap energy from ∼4.0 eV for the parent LaTiO_3.5 to ∼2.4–2.9 eV for LaTiO_3−xN_x (x ≈ 0.4–0.8) films. This results in a strong visible light absorption at wavelengths below ∼500 nm. The band gap energies in LaTiO_3−xN_x films decrease with increasing nitrogen content. The values of the band gap energies for LaTiO_3−xN_x as a function of the N content agree well with other titanate-based perovskite-type oxynitrides, which confirms the proposed band gap model.     

Structural and dielectric properties of Bi2Zn2/3Nb4/3O7 thin films prepared by pulsed laser deposition at low temperature for embedded capacitor applications

Bi₂Zn_2/3Nb_4/3O₇ thin films were deposited on Pt/TiO₂/SiO₂/Si(1 0 0) substrates at a room temperature under the oxygen pressure of 1-10 Pa by pulsed laser deposition. Bi₂Zn_2/3Nb_4/3O₇ thin films were then post-annealed below 200 °C in a rapid thermal process furnace in air for 20 min. The dielectric and leakage current properties of Bi₂Zn_2/3Nb_4/3O₇ thin films are strongly influenced by the oxygen pressure during deposition and the post-annealing temperature. Bi₂Zn_2/3Nb_4/3O₇ thin films deposited under 1 Pa oxygen pressure and then post-annealed at a temperature of 150 °C show uniform surface morphologies. Dielectric constant and loss tangent are 57 and 0.005 at 10 kHz, respectively. The high resolution TEM image and the electron diffraction pattern show that nano crystallites exist in the amorphous thin film, which may be the origin of high dielectric constant in the Bi₂Zn_2/3Nb_4/3O₇ thin films deposited at low temperatures. Moreover, Bi₂Zn_2/3Nb_4/3O₇ thin film exhibits the excellent leakage current characteristics with a high breakdown strength and the leakage current density is approximately 1 × 10⁻⁷ A/cm² at an applied bias field of 300 kV/cm. Bi₂Zn_2/3Nb_4/3O₇ thin films are potential materials for embedded capacitor applications.     

Three dimensional Monte Carlo simulation of grain growth during GTA welding of titanium

The work reported here represents significant advancement in the modeling of grain structure evolution in metallic systems. Utilizing computed temperature fields from a well tested heat transfer and fluid flow model, the evolution of grain structure was simulated for the first time using a three dimensional (3D) Monte Carlo model of grain growth in the heat affected zone of commercially pure titanium welds. The computed weld geometry and the simulated mean prior β grain size for different heat inputs agreed well with the corresponding experimental results when turbulence in the weld pool was considered. The grain sizes at various locations equidistant from the fusion line were different, indicating that the results of previous 2D calculations need to be reexamined. The computed grain size distribution agreed well with the corresponding experimental data. The agreement indicates significant promise for understanding grain growth in the entire heat-affected zone using a comprehensive phenomenological model.