A simple reactor for growth of HgCdTe films using LPE technique

A reactor for growth of Hg_1−x Cd _x Te epilayers by liquid phase epitaxy has been designed and developed. The layers have been successfully grown using this liquid phase epitaxy (LPE) reactor.     

TFA-MOD方法制备YBCO超导薄膜生长研究

TFA-MOD方法是制备YBCO涂层导体的最有应用前景的方法之一.本文采用TFA-MOD方法在LaAlO3单晶基片上生长YBCO薄膜并系统地研究了高温退火不同的停留时间对其影响.XRD分析表明退火时间较短时仍有明显的YBCO(00l)取向,但也有其它杂相峰存在,而延长退火时间可以使杂相峰消失而得到纯的且强度更高的YBCO(00l)取向.SEM分析表明未完全结晶的YBCO薄膜表面晶粒大小不一致,而且气孔较多.而结晶良好的YBCO薄膜表面平整致密,空洞较少.随着退火时间的增加YBCO颗粒尺寸在增大.但是,退火时间太长,会有大的空洞,甚至出现裂纹.超导电性能测试表明,随着退火时间的增加超导临界电流(Ic)在增加,但是退火时间达到60min后,Ic即达到最大值,表明60min就能使前驱膜在该实验条件下完全的结晶形成取向良好的YBCO薄膜,YBCO薄膜的生长速度达到0.16nm/s.     

Site preferences for Nd in YAG films grown by LPE

We have made spin-resonance measurements of the concentration on different, though crystallographically equivalent, sites, of Nd³⁺ dilutely incorporated into thin films of yttrium aluminum garnet (YAG). The films were grown on {001}, {110}, and {111} substrates of pure YAG by liquid phase epitaxy (LPE). Sites which differ only in the orientation of their local axes relative to the growth direction are found to be unequally populated. The site preferences found for {110} films are close to, though larger than, those found previously for {110} facets of bulk crystals grown from the flux. This result supports the view that the growth-induced magnetic anisotropy of LPE films of mixed rare earth iron garnets arises from the same site preference mechanism as the anisotropy found under natural facets of bulk crystals. Very large site preferences, up to 4.5:1, are found in {001} films; but for {111} films they are only slight. Site preferences are not greatly affected by changes in growth temperature (850°C to 1044°C) or in overall concentration (0.1% to 5% atomic). The effective distribution coefficient varies with concentration and substrate orientation.     

原子层沉积低温制备AZO薄膜

采用原子层沉积技术与改进的Al掺杂模式在石英玻璃基体上低温制备AZO薄膜,利用椭圆偏振仪、原子力显微镜、X射线衍射仪、X射线光电子能谱仪、Hall效应测试仪系统地对样品的生长速率、表面形貌、晶体结构、薄膜成分与电学性能进行了表征和分析。结果表明,采用原子层沉积在150℃下制备AZO薄膜,其为六方纤锌矿结构,Al掺杂对Zn O的(002)有明显的抑制作用,Al在基体中弥散分布,其部分替换Zn O晶格中的Zn,以Al—O的形式存在于晶体中,晶体中存在大量的氧空位,最佳铝锌循环比为1∶19,此条件下AZO薄膜电阻率为4.61×10-4Ω·cm。     

LPE growth of Cd doped PbTe

Cd doped PbTe epilayers were grown on Pb_0.8Sn_0.2Te substrates by liquid phase epitaxy (LPE). The Cd behavior in the solution and the solid (substrate and epilayer) was studied. The dependence of the carrier concentration on Cd doping was investigated.     

Thickness and mosaic morphology of InAs films grown by LPE supercooling technique

InAs films with different thicknesses were fabricated on (100)-oriented InAs substrate by liquid phase epitaxy supercooling technique using the sliding graphite boat. The X-ray diffraction measurement shows that films exhibit (100)-preferred crystal orientation. The film thickness dependence on the growth time and cooling rate was investigated by scanning electron microscope and the growth kinetics was analyzed based on one-dimensional diffusion theory. The experimental data were fitted very well by the supercooling equation, and the fitted diffusion coefficient at 520 °C was 6.2 × 10⁻⁵ cm²/s. The newly observed mosaic morphology was probably caused by the shake of the growth solution due to sliding the graphite boat.     

Effect of lanthanum on growth-induced anisotropy in LPE bubble garnet films

Growth-induced anisotropy, Ku, in bubble garnet films containing La and Eu or Sm has been found to be anomalous compared to that produced by Eu or Sm and smaller ions such as Y or Lu. In     

LPE growth of lithium ferrite on spinel substrate crystals

Preliminary results on the growth of lithium ferrite by LPE (liquid phase epitaxy) are described. A PbO-B₂O₃ flux was used with nonmagnetic spinel-structured substrate crystals. Compared with growth of magnetic garnets, the LPE melt was found to be relatively unstable with respect to undercooling. Nevertheless, LPE growth was achieved. All of the epitaxial films grown so far are cracked; however, ferrimagnetic resonance linewidths as low as 7.8 Oe at 9.07 GHz have been measured.     

应力生长FeCoSiB非晶薄膜的磁各向异性研究

采用应力生长方法，制备出受压应力和张应力作用的FeCoSiB非晶磁弹性薄膜，研究了薄膜中的应变大小对FeCoSiB薄膜的磁滞回线、剩磁、应力诱导各向异性场等磁特性的影响．结果表明，无应变薄膜在薄膜面内呈现各向同性，而有应变的薄膜呈现出明显的各向异性。张应力诱导的各向异性与应力方向平行，而压应力形成垂直于应力方向的磁各向异性。各向异性场随应变的增大而线性增大。     

LPE growth reproducibility of garnet bubble materials

The problem of growth reproducibility in liquid phase epitaxy of bubble garnet films is analysed. Deviations of the optimum growth temperature are considered to be the main cause of non-reproducibility of the film properties. An expression is derived for the growth temperature sensitivity of the bubble collapse field of grown films. Evaluation of this expression shows that the sensitivity can be minimized if the growth temperature derivative of the magnetization can be adjusted in a controlled way, preferably in the range of 3 to 6 Gauss/°C. This derivative is determined for several melts of the usual CaGe:YIG-type. It is found to be almost independent of the melt composition and always larger than 5 Gauss/°C. Thus growth reproducibility can be improved to a rather limited extent for such CaGe:YIG-type melts.     

A systematic study of thiophene Langmuir-Blodgett films including new conjugated donor-acceptor molecules

Hemicyanine dyes are an extensively investigated group of materials which show promise for second-order non-linear optical properties; they have also proved to be good materials for deposition by the Langmuir-Blodgett technique. This work concerns a closely related group of materials which contain a thiophene moiety in place of the nitrogen heterocycle of the hemicyanine material. The synthesis of several groups of novel amphiphiles containing the thiophene moiety, and their subsequent screening as materials for deposition by the Langmuir Blodgett technique is described. General trends in the behaviour of the simplest materials are noted, whilst the report of the characterization of the more complex D--A thiophenes is extended to include data relating to the production of heterogeneous monolayer and alternate layer structures.     

A systematic study on group III-nitride thin films with low temperature deposited via MOCVD

Wide bandgap semiconductor materials provide superior electrical, optical, and thermal properties that classical semiconductors, Si and GaAs, are unable to achieve. However, most commercially available substrates have large lattice and thermal expansion mismatches to III-nitrides films. Thus a high quality buffer layer, grown at low temperatures, is essential in growing high quality III-nitride films. This research provides a throughout study on III-nitrides, such as AlN, GaN and AlGaN thin films, which were grown at low temperatures (400–600 °C). Growth rate, stoichiometry and crystal structure of low temperature growth films will be reported by using several advanced post-growth analysis techniques. Temperature, pressure, and V/III molar ratio were also investigated to determine their effect on the film properties. From the study, a better understanding of the relationships between film properties and growth parameters will be achieved.     

Lead incorporation in thin iron garnet films produced by LPE and chemical analysis by the radioactive tracer technique

The mode of incorporation of lead ions into Y₃Fe₅O₁₂ single crystal thin films grown by the LPE technique from lead containing fluxes has been carefully studied using radioactive tracers as the analysis technique. In particular, the variation of lead content with film thickness has been studied. It has confirmed the existence of a lead rich layer at the interface of the substrate and the film. The formation of this layer is connected with the transient period during which stable growth is established. The variation of lead with film growth rate is established. The misfit with the substrate lattice parameter has an influence on the grown film, whereas the species of the substrate does not have an effect. There is evidence that rare-earth ions enter the octahedral sites in the garnet.     

Sulfurization time effects on the growth of Cu2ZnSnS4 thin films by solution method

Cu₂ZnSnS₄ (CZTS) films were obtained by sulfurizing (Cu, Sn) S/ZnS structured precursors prepared by a combination of the successive ionic layer absorption and reaction method and the chemical bath deposition method, respectively. The effect of sulfurization time on structure, composition and optical properties of these CZTS thin films was studied. The results of energy dispersive spectroscopy indicate that the annealed CZTS thin films are of Cu-poor and Zn-rich states. The X-ray diffraction studies reveal that Cu_2?x S phase exists in the annealed CZTS thin film prepared by sulfurization for 20 min, while the Raman spectroscopy analysis shows that there is a small Cu₂SnS₃ phase existing in those by sulfurization for 20 and 40 min. The band gap (E _g ) of the annealed CZTS thin films, which are determined by reflection spectroscopy, varies from 1.49 to 1.56 eV depending on sulfurization time. The best CZTS thin film is the one prepared by sulfurization for 80 min, exhibiting a single kesterite structure, dense morphology, ideal band gap (E _g  = 1.55 eV) and high optical absorption coefficient (>10⁴ cm^?1).     

Automated spatial filtering for rapid characterization of LPE bubble garnet films

An automated spatial filtering apparatus used for characterization of magnetic bubble films with zero field strip widths greater than 1.5μm has been constructed. This apparatus makes measurements of the zero field period and the period in an applied magnetic field. When these two measurements are combined with measured values for the film thickness and the Neél temperature, values for relevant material parameters of the bubble films can be calculated using the Kooy and Enz theory. Details of the spatial filter apparatus, the method used for data analysis, and the accuracy of the method are discussed.     

Adsorbed films of 3He-4He mixtures: A systematic experimental study

The results of a systematic study of helium thin-film adsorption are presented. Measurements are reported, obtained with a 24-MHz crystal adsorptometer, on the adsorbed mass per unit area as a function of the three independent variables temperature, concentration, and pressure of the gas of ³He-⁴He atoms generating the adsorbed film. The investigations span concentrations from zero to unity, all pressures up to the dew point for each mixture, and temperatures from 1.3 to 2.1 K. From the experimental results we display the detailed form of the van der Waals attractive potential holding the helium atoms to the surface. The expected dependence on the cube of the distance from the substrate is confirmed over the range of distances explored. The strength of the van der Waals potential is measured and reported. This attractive potential is demonstrated to be of the same form and of the same strength both for the ³He atoms and for the ⁴He atoms in the mixture at all concentrations. We further deduce, directly from our measurements, the detailed relationship between , the mass per unit area of film absorbed, and d, the thickness of the film.German Academic Exchange Service (DAAD) leave from the Free University of Berlin.     

ZnO nanowire growth by electric current heating method: A study on the effect of substrate temperature

In this study, we report the growth of ZnO nanowire on quartz glass substrates with Au-catalyst assistance by electric current heating of ZnO ceramic bar. The effect of substrate temperature on the properties of ZnO nanostructures has been investigated systematically. Structural analysis indicates that the grown ZnO crystals belong to hexagonal phase with preferential growth along (0 0 2) orientation. Scanning electron microscopic studies reveal the aligned ZnO nanowires were grown at 800 °C. The typical length and diameter of nanowires are in the uniform ranges of 4–20 μm and 20–100 nm, respectively, showing their high aspect ratio of about 1000. We have made an attempt to discuss about the change in ZnO nanostructures with different substrate temperatures and the possible mechanism for the growth of nanowires. Optical reflectance studies show the infrared reflectivity was controlled through the substrate temperature.     

纳米氧化锌掺铝薄膜的微观结构研究

采用溶胶-凝胶(sol-gel)法在玻璃衬底上制备了纳米ZnO掺铝薄膜,利用X射线衍射仪(XRD)和透射电镜(TEM)对薄膜的微观结构进行了系统的研究。结果表明,所有在玻璃衬底上生长的ZnO薄膜均具有c轴择优取向。掺杂量为2%(原子分数)时,Al在ZnO薄膜中达到最高水平。过量Al掺杂明显减弱薄膜的c轴择优取向。随着Al掺杂量的增加,ZnO晶粒进一步细化。其原因是未进入ZnO晶格的Al以非晶Al2O3的形式在ZnO晶界上形成了对晶界运动的钉扎,从而阻碍了ZnO晶粒进一步长大。     

Effect of interface energy on abnormal grain growth in pyrite films prepared by sol-gel method

The pyrite films were prepared on quartz and glass substrates by the sol-gel dip coating process and sulfuration treatment. The film microstructure, chemical composition and morphology dependent on sulfuration temperature were investigated. The sulfuration treatment at 773-923 K for the films prepared by the sol-gel dip coating process can prepare pyrite films. Some grains show abnormal growth during sulfuration treatment. The grain size of abnormal growth increased to a limited value with increasing the sulfuration temperature. The grain size in pyrite films has bimodal distribution. The first peak is of Lognormal distribution and the second peak Gauss distribution. By determination of the abnormal grain growth activation energy, it can be concluded that the reduction in interface energy at the interface between the substrate and film should be responsible for the grain abnormal growth.