Growth of epitaxial TmFeCuO4 thin films by pulsed laser deposition

Epitaxial thin films of TmFeCuO₄ with a two-dimensional triangular lattice structure were successfully grown on yttria-stabilized-zirconia substrates by pulsed laser deposition and ex situ annealing in air. The films as-deposited below 500 °C showed no TmFeCuO₄ phase and the subsequent annealing resulted in the decomposition of film components. On the other hand, as-grown films deposited at 800 °C showed an amorphous nature. Thermal annealing converted the amorphous films into highly (0 0 1)-oriented epitaxial films. The results of scanning electron microscopic analysis suggest that the crystal growth process during thermal annealing is dominated by the regrowth of non-uniformly shaped islands to the distinct uniform islands of hexagonal base.     

Growth control of stoichiometry in LaMnO3 epitaxial thin films by pulsed laser deposition

We have studied structural, magnetic, and optical transport properties of LaMnO₃ (LMO) thin films grown on SrTiO₃. While the stoichiometric LMO is an insulating antiferromagnet, it tends to be a ferromagnetic insulator when grown as thin films. By exploring the majority of growth parameters, we have found that the bulk-like electronic and magnetic phases can be stabilized by growing thin films under reducing atmospheres and by using more energetic laser processes. These conditions are found to reduce the La deficiency in the film resulting in the greatly improved cation stoichiometry. Since oxides are prone to reduce the oxygen content and to alter the cation ratio under such growth conditions, it suggests that the cation and oxygen stoichiometries in complex oxide thin films can be improved by properly optimizing the growth parameters.     

Study of Ge epitaxial growth on Si substrates by cluster beam deposition

Ge epitaxial layers with reasonable quality were grown on Si (1 1 1) substrates by cluster beam deposition (CBD) process. Molecular dynamics study of the low energy Ge clusters deposition process utilizing the Stillinger–Weber two- and three-body interaction potentials was carried out to compare the experimental results. Both experimental and simulation results prove that the substrate temperature plays a dominant role in the epitaxial growth of Ge films in CBD process. The influence mechanisms of temperature are discussed.     

Fabrication and characteristics of CeO2 films on Si(1 0 0) substrates by pulsed laser deposition

A detailed investigation about the dependence of film orientation on deposition temperature and ambient oxygen pressure has been carried out for CeO₂ films on Si(1 0 0) substrates using pulsed laser deposition. It has been found that the CeO₂ film orientation varies with increasing oxygen pressure at 750°C deposition temperature. In addition, the recovery of preferential orientation of CeO₂ films grown at 20 Pa ambient oxygen pressure with increasing deposition temperature has also been found for the first time. X-ray photoelectron spectroscopy (XPS) measurements confirm that stoichiometric CeO₂ films can be grown at lower oxygen pressure (5×10⁻³ Pa). HRTEM result also indicates that the CeO₂ films grown at low oxygen pressure are of high crystallinity.     

High temperature x‐ray diffraction studies of zirconia thin films prepared by reactive pulsed laser deposition

Zirconium oxide thin films have been deposited on Si (100) substrates at room temperature at an optimized oxygen partial pressure of 3x10^‐2 mbar by reactive pulsed laser deposition. High temperature x‐ray diffraction (HTXRD) studies of the film in the temperature range room temperature‐1473 K revealed that the film contained only monoclinic phase at temperatures ≤ 673 K and both monoclinic and tetragonal phases were present at temperatures ≥ 773 K. The tetragonal phase content was significantly dominating over monoclinic phase with the increase of temperature. The phase evolution was accompanied with the increase in the crystallite size from 20 to 40 nm for the tetragonal phase. The mean thermal expansion coefficients for the tetragonal phase have been found to be 10.58x10^‐6 K^‐1 and 20.92x10^‐6K^‐1 along a and c‐axes, respectively. The mean volume thermal expansion coefficient is 42.34x10^‐6 K^‐1 in the temperature range 773‐1473 K. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Properties of InAs co‐doped ZnO thin films prepared by pulsed laser deposition

InAs co‐doped ZnO films were grown on sapphire substrates by pulsed laser deposition. The grown films have been characterized using X‐ray diffraction (XRD), Hall effect measurements, Atomic force microscope (AFM) and Field emission scanning electron microscope (FESEM) in order to investigate the structural, electrical, morphological and elemental properties of the films respectively. XRD analysis showed that all the films were highly orientated along the c‐axis. It was observed from Hall effect measurements that InAs co‐doped ZnO films were of n‐type conductivity. In addition, the presence of In and As has been confirmed by Energy dispersive X‐ray analysis. AFM images revealed that the surface roughness of the films was decreased upon the co‐doping. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical and structural properties of epitaxial GaN films grown by pulsed laser deposition

Epitaxial GaN films have been grown on c-cut sapphire substrates by pulsed laser deposition (PLD) using a KrF laser. The properties of GaN films were improved by increasing the growth temperature to 800°C and the nitrogen pressure during growth to 10 mTorr. Room-temperature photoluminescence exhibits a strong band-edge emission at 3.4 eV. From transmission electron microscopy (TEM), the predominant defects in PLD-GaN observed are stacking faults parallel to the interface and screw dislocations along c-axis, the latter differing from the previously published results where most of the threading dislocation in GaN grown by other techniques are of edge type with Burgers vector of .     

Synchrotron X-ray diffraction studies of heteroepitaxial ZnO films grown by pulsed laser deposition

Heteroepitaxial ZnO films were grown by pulsed laser deposition on various substrates such as GaN-buffered C-Al₂O₃, C-Al₂O₃, A-Al₂O₃, and R-Al₂O₃. The epitaxy nature of the films was investigated mainly by synchrotron X-ray diffraction. The results showed that the GaN interlayer plays a positive role in growing an unstrained, well-aligned epitaxial ZnO film on the basal plane of Al₂O₃. Importantly, the ZnO film grown on R-Al₂O₃ has two differently aligned domains. The dominant (1 1 0) oriented domain has much better alignment in the in-plane direction than the minor portion of (0 0 1) oriented domain, while in the out-of-plane direction the two domains have almost the same mosaic distribution.     

CeO2对CaTiO3陶瓷烧结性能以及微观结构的影响

以CaO和TiO2为原料,采用固相反应烧结法合成钛酸钙陶瓷.以CeO2为添加剂,重点研究CeO2掺杂对合成钛酸钙陶瓷烧结性能及微观结构的影响.利用XRD、SEM、EDS等手段对试样的物相组成、显微形貌以及元素分布进行表征.通过X'pert High score Plus软件研究CeO2添加量和煅烧温度对合成钛酸钙的相组成、晶胞参数、缺陷反应的影响.结果表明:随着CeO2加入量的增大,Ce4+与Ti4+及Ce3+与Ca2+之间发生取代,致使钛酸钙的晶体结构发生畸变,晶格常数以及晶胞体积出现了先增大后减小的趋势.CaTiO3结构中取代位置的改变,是造成晶胞体积呈非线性变化趋势的原因.形成的结构缺陷加速了固相烧结反应,钛酸钙晶粒由发育不完全的台阶状转变为规则的多边形.过量的CeO2会抑制晶粒的生长,减小晶粒尺寸.随着煅烧温度的升高,结构中热缺陷浓度增大,促进了钛酸钙的烧结.     

乙二胺用量对CeO2纳米棒合成的影响

采用水热法,以氯化铈为铈源、乙二胺为络合剂、水合肼为沉淀剂,通过改变乙二胺的用量制备了四种CeO2粉体样品,通过X射线衍射仪(XRD)、紫外可见分光光度计(UV-Vis)、荧光分光光度计(PL)和扫描电镜(SEM)对合成的CeO2样品的结构、形貌和光学性质进行表征。实验结果表明乙二胺剂量对样品的晶格常数、氧空位度、能带间隙、荧光强度等有显著影响。晶格常数随乙二胺剂量的增加先减小后增大,剂量为5 mL时晶格常数最小,氧空位度随乙二胺剂量的增加先增加后减少,剂量为5 mL时氧空位浓度最大、样品能带间隙最小、对紫外线的吸收最强、荧光强度最大。     

样品的形貌对CeO2湿度传感器性能的影响

使用Ce(NO3)3·6H2O为前驱物,采用水热合成法和溶胶凝胶法分别制备了不同形貌的CeO2纳米晶体(纳米带和球形颗粒).通过XRD、SEM和TEM技术表征了材料的相成分、微结构和形貌.将样品制备成湿度传感器后对传感器性能进行了测试,结果表明:具有纳米带形貌的样品所制备的传感器展示了良好的传感性能,其响应-回复时间分别为7 s 和7 s(在15;~95;湿度范围内),最大迟滞为4;,这些性能都要好于球形颗粒所制备的样品.其主要原因是纳米带样品具有较大的比表面积.     

Influence of cooling rate on the liquid-phase epitaxial growth of Zn3P2

We report the liquid-phase epitaxial growth of Zn₃P₂ on InP (1 0 0) substrates by conventional horizontal sliding boat system using 100% In solvent. Different cooling rates of 0.2–1.0 °C/min have been adopted and the influence of supercooling on the properties of the grown epilayers is analyzed. The crystal structure and quality of the grown epilayers have been studied by X-ray diffraction and high-resolution X-ray rocking measurements, which revealed a good lattice matching between the epilayers and the substrate. The supercooling-induced morphologies and composition of the epilayers were studied by scanning electron microscopy and energy dispersive X-ray analysis. The growth rate has been calculated and found that there exists a linear dependence between the growth rate and the cooling rate. Hall measurements showed that the grown layers are unintentionally doped p-type with a carrier mobility as high as 450 cm²/V s and a carrier concentration of 2.81×10¹⁸ cm⁻³ for the layers grown from 6 °C supercooled melt from the cooling rate of 0.4 °C/min.     

静电纺丝法制备CeO2微纳米纤维及其除氟性能

以聚丙烯腈(PAN)为载体,六水合硝酸铈[Ce(NO₃)₃·6H₂O]为原料,采用静电纺丝法制备了Ce(NO₃)₃/PAN纤维,在空气中热处理得到CeO₂微纳米纤维,通过XRD、BET和SEM对CeO₂微纳米纤维进行表征。采用静态吸附实验探讨了CeO₂微纳米纤维去除水溶液中氟离子的性能,考察了溶液pH值、初始氟离子浓度及共存阴离子等对吸附性能的影响。结果表明,pH=3时,CeO₂微纳米纤维对F^-的吸附性能最佳,CeO₂吸附量随着F^-浓度的增大呈上升趋势。CeO₂微纳米纤维对F^-的吸附等温线遵循Langmuir模型,二级动力学模型能很好地描述CeO₂微纳米纤维对F^-的吸附过程。CeO₂微纳米纤维的除氟性能优良,可为其实际应用提供理论参考。     

基于液滴外延法的Al(In)纳米结构在GaAs(001)的形成机制

采用液滴外延法在GaAs(001)衬底上同时沉积In、Al液滴形成纳米结构,利用原子力显微镜(AFM)对实验样品进行形貌表征,并通过X射线光电子能谱(XPS)与扫描电子显微镜分析In、Al组分比样品表面元素分布。实验结果显示,混合沉积后的表面InAlAs纳米结构密度随着In组分的降低而降低,而单个纳米结构的尺寸变大。SEM与XPS测试结果证明表面的In并没有因为衬底温度过高而全部偏析。根据实验结果推测,In&Al液滴同时沉积到表面形成InAl混合液滴。当液滴完全晶化后纳米结构中心出现孔洞,而产生这一现象的主要原因是液滴向下刻蚀。     

Growth and optical absorption spectra of ZnO films grown by pulsed laser deposition

ZnO films on Al₂O₃ substrate were grown by using a pulsed laser deposition method. Through photoluminescence (PL) and X-ray diffraction (XRD) measurements, the optimum growth conditions for the ZnO growth were calculated. The results of the XRD measurement indicate that ZnO film was strongly oriented to the c-axis of hexagonal structure and epitaxially crystallized under constraints created by the substrate. The full-width half-maximum for a theta curve of the (0 0 0 2) peak was 0.201°. Also, from the PL measurement, the grown ZnO film was observed to be a free exciton, which indicates a high quality of epilayer. The Hall mobility and carrier density of the ZnO film at 293 K were estimated to be 299 cm²/V sec and , respectively. The absorption spectra revealed that the temperature dependence of the optical band gap on the ZnO films was − .     

The influence of substrate temperature on the growth of sexiphenyl on mica(001)

Sexiphenyl thin films were grown by Hot Wall Epitaxy on air‐cleaved mica (001) surfaces at substrate temperatures between 293 K and 440 K. For the entire temperature range, organic thin films show nano‐needle like morphology. The nano‐needles grown at low substrate temperature (293 K) are shortest, and their growth is accompanied by a simultaneous formation of flat islands which disturbs the growth of nano‐needles. On the contrary, unusually long nano‐needles with typical lengths up to the mm range evolve during the growth at a substrate temperature close to the material's thermal desorption temperature at about 440 K. X‐ray diffraction reveals two different crystalline orientations for nano‐needles in the entire temperature range. At low substrate temperatures dominantly the (11 ) plane of the β‐phase is formed parallel to the mica (001) surface. At elevated temperatures another strong texture becomes dominant which is close to the (11 ) crystal orientation. In contrast to this, crystallites with the preferred orientation (001) parallel to the surface of the substrate are formed at low substrate temperature (293 K). This crystal orientation can be associated with flat islands observed in the early growth stage. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)