Analysis of the formation of BaTiO3 island deposited on (111) InSb by metalorganic chemical vapor deposition at low temperature

Islands of BaTiO₃ in a thin film deposited on a (111) InSb substrate by metalorganic chemical vapor deposition at a temperature of 300°C were investigated. Refractive index measured by ellipsometer using a He-Ne laser was 1.95, which is nearly the same value as that of amorphous BaTiO₃ with microcrystals. X-ray diffraction peaks showed the deposit to be mostly amorphous and partly crystalline having the 110BaTiO₃ direction normal to the (111) InSb. Transmission electron microscopy results showed that partially epitaxial BaTiO₃ islands with periodic misfit dislocations had been formed at the interface between amorphous BaTiO₃ thin layer and the (111) InSb substrate. These BaTiO₃ islands on the (111) InSb substrate formed at a low growth temperature were three-dimensional nuclei which were closely associated with surface irregularities of the (111) InSb substrate.     

Epitaxial growth of some II–VI compound films evaporated onto electron-bombarded NaCl substrates

Epitaxial growth of CdS, CdSe, CdTe and ZnSe films, several 10–1000 Å in thickness, evaporated onto (001), (110) and (111)NaCl substrates at 50–400° C, with or without electron bombardment, and almost perpendicularly to the substrate surface, was investigated by RHEED, TEM, TED and XMA. Without electron bombardment, both wurtzite and sphalerite phases generally coexisted in the films. When the substrates were bombarded with electrons (∽10¹² electrons/cm² · sec at 300–500 V) during evaporation at about 150–300° C a single-crystal film of the sphalerite phase was obtained on the (001) and (110)NaCl, and that of the wurtzite phase on the (111)NaCl. Similar effects were observed also when the electron bombardment was applied to the substrate immediately before or in the very early stages of the deposition, or only to the evaporation vapor during the deposition. These results indicate that surface defects and electric charges of the substrate and the vapor play very important roles in the epitaxial process of these compounds.     

Solid phase epitaxial growth of Si through Al film

Uniform epitaxial growth has been obtained by dissolution and transport of an evaporated Si film through an evaporated Al film at temperatures below 500°C. By analyzing the samples made in different ways we show that the presence of a cap on the metal layer, which inhibits the diffusion of the metal through the evaporated Si, plays a fundamental role. The cap consists of a thin oxide layer grown on top of the metal. The cap is made by leaving the sample in vacuum for two days or by heating the sample in vacuum before the Si deposition. The study of the initial growth rate on 〈100〉 and 〈111〉Si substrates reveals that the growth starts as islands which grow until they coalesce to form a continuous layer. Different growth rates have been obtained by using 〈100〉 and 〈111〉Si substrates. Typical growth rates are 50 Å/min at 330°C on 〈100〉 and 100 Å/min at 392°C on 〈111〉. The activation energy of the process is 1.2 eV.     

Ionenstrahlgestäubte GaAs-Schichten auf verschiedenen einkristalline Substraten

Thin GaAs-films have been deposited on spinel, (111)-Si, and (100)-GaAs by ion beam sputtering. The beam system operated with argon ions at a vacuum of 5…︁8 · 10⁻⁶ torr in the chamber. Undoped polycrystalline GaAs was used as target material. The film proporties were investigated by electron optical methods (RHEED respective by C/Pt replica). Substrate temperatures were varied between 180 and 590 °C, and deposition rates were adjusted between 1…︁3 Å/s. Within a relative narrow temperature range epitaxial layers of good quality were obtained; the optimum values being 540 °C in case of GaAs/Si or 400…︁450 °C for GaAs/GaAs. Films deposited at higher temperatures showed extended defects induced by gallium excess because of dissociation.     

Epitaxial Growth of Silver Bromide on Mica from the Melt

It is shown that it is possible to grow silver bromide crystals with definite crystallographic orientation by solidification of liquid silver bromide between mica and quartz plates by cooling the mica side. The orientation is (111). The maximum dimensions were 15mm × 15 mm × 1 mm. The surface is investigated by electron reflection (RHEED). The crystals have a smooth surface and can be used for optical application without surface reconstruction.     

Structure of autoepitaxial diamond films

A reflection high energy electron diffraction (RHEED) method has been used to investigate the structural peculiarities of synthetic diamond autoepitaxial films, deposited from a gaseous phase onto natural diamond seed crystal. The diamond films on the (111) and (110) faces usually have internal stresses, which cause the (111) plane microtwinning process at thicknesses of about 1000 Å. The thickness of twin lamellas is about 0.01?1μm. On the (100) face the diamond films do not undergo twinning and have a high structural perfection.     

Reflection high-energy electron diffraction intensity oscillations during growth of (Al,Ga)As on GaAs(111)A

We have made a reflection high-energy diffraction (RHEED) intensity oscillation study of the growth of (Al,Ga)As on GaAs and (Al,Ga)As (111)A surfaces. The RHEED intensity oscillations during growth of (Al,Ga)As are dependent on both growth temperature and As₄:Ga flux ratio. In addition, the oscillation period decreases as the Al fraction in the (Al,Ga)As is increased. Changes in the oscillation period during growth of the first few monolayers of both GaAs on (Al,Ga)As and (Al,Ga)As on GaAs may indicate the intermixing of Al and Ga near the heterointerface.     

Thermal dissolution of Ag(Cu) in amorphous Ge(Sx Se1 − x)2 system

Thermally induced solid state reaction of Ag(Cu) into thin Ge(S_x Se_1 − x)₂ films with x = 0, 0.1, 0.4 and 1.0 was investigated using a step by step technique in order to design films with exact Ag(Cu) concentrations for applications in integrated IR optical devices. A thin film of Ag(Cu) was deposited on top of the host Ge(S_x Se_1 − x)₂ films followed by annealing in vacuum at constant temperature, which resulted in homogeneous films of good optical quality. The variation in Ag(Cu) concentration in the films ranged between 5 and 35 at.%. The kinetics of the diffusion and dissolution of metal in the host films was measured by optically monitoring the change in thickness of doped chalcogenide during consecutive thermal annealing steps. The kinetics studies revealed that the thermal dissolution rate of the Cu is greater than that of Ag. Optical UV-VIS transmission spectra of chalcogenide glass layers, undoped and thermal doped by Ag(Cu), were measured to establish the optical properties of the films. The spectra were analyzed using the technique proposed by Swanepoel and the results show that the addition of metal increases the absorption coefficient in the power-law regime and consequently the optical gap decreases and the refractive index increases. The amorphous character of the films was checked by X-ray diffraction which confirmed the amorphous structure of all Ag(Cu)GeSSe thin films.     

Structure and growth morphology of RF-sputtered superthin niobium films

Superthin niobium films of 3 to 35 Å thickness prepared by radio-frequency sputtering have been studied by modern X-ray methods, such as reflectometry, fluorescence analysis and grazing beam structure analysis. It has been shown that the films were polycrystalline and consisted of several layers of niobium oxides and solid solution Nb O. Two simple models were used to describe erly stages of film growth. In the stage of island growth the complete oxidation of Nb to Nb₂O₅ is inevitable. Beginning from effective thickness ∼ 5 Å the deposited film becomes continuous, and further, layer-by-layer growth takes place.     

Nanolayer of the A2IIIB3VI (111) phase with ordered cation vacancies on GaAs(111) and InAs(111)

The surface of GaAs(111) and InAs(111) substrates has been investigated by transmission and scanning electron microscopy after thermal treatment in selenium vapor. A pseudomorphic growth of single-crystal phases of indium selenide In₂Se₃(111) and gallium selenide Ga₂Se₃(111) is found; these compounds are crystallized into a sphalerite lattice with ordered stoichiometric cation vacancies. A model of an atomic surface is proposed for the In₂Se₃(111) and Ga₂Se₃(111) structures. The reconstruction of the (√3 × √3)-R30° surface of GaAs(111) and InAs(111) after treatment in Se vapor is considered within this model.     

Dependence of photo-oxidation on Ag(Cu)-content in Ag(Cu)–As2Se3 films

We report the dependence of photo-oxidation (i.e., the formation of As₂O₃ microcrystals) on Ag (or Cu) content in Ag-doped As₂Se₃ and Cu-doped As₂Se₃ films. These chalcogenide films were prepared by thermal evaporation and photodoping, and their film surface was illuminated in air with an Ar laser beam of a wavelength of 0.5145 μm. From viewpoint of applications, we paid attention to the probability and the beginning optical intensity of the As₂O₃ microcrystals formation, and the photodarkening effect as a function of Ag (Cu) content. It has been confirmed that the addition of metals Cu or Ag into As₂Se₃ films is very useful in for suppressing or weakening such a harmful oxidation reaction. It has also been found that there is a distinct difference in these properties between Ag–As₂Se₃ and Cu–As₂Se₃ films, which is attributed to the difference in the coordinate number between Ag and Cu atoms.     

Untersuchungen zum orientierten Aufwachsen von Silberschichten auf Muskovit

In the present paper the effect of an amorphous intermediate carbon layer on the oriented growth of Ag on muscovite is studied. It is proved that the monocrystalline substrate has an orienting effect on the growing silver layer up to a thickness of the intermediate carbon layer of 200 Å.     

MOCVD方法在Ti/Si(111)模板上生长ZnO薄膜的研究

本文采用常压MOCVD方法在Ti/Si（111）模板上生长了氧化锌（ZnO）薄膜，使用二乙基锌为Zn源，去离子水为O源。Si衬底上的Ti薄层采用电子束蒸发台蒸发，然后低温生长缓冲层并在高温下进行重结晶，接着在680％进行ZnO薄膜的生长。采用粉末衍射法、双晶X射线衍射及光致发光技术研究了材料的取向、结晶性能及发光性能。结果表明，本文制备了高度择优取向和良好发光性能的ZnO薄膜。     

Strain relaxation in InGaAs/GaAs quantum wells grown on GaAs (111)A substrates

We have grown In_0.2Ga_0.8As strained quantum wells (SQWs) on GaAs (111)A just and off-angled substrates by molecular beam epitaxy (MBE). The photoluminescence (PL) peak energy of SQWs grown on (111)A related substrates shows a large redshift as compared with the calculated values. The red-shift observed in SQWs grown on a (111)A 5° off toward [001] substrate can be explained by the presence of a built-in electric field E = 154 kV/cm due to piezoelectric effect. The larger red-shift observed in samples grown on the other substrates is partially due to strain relaxation. A strain relaxation mechanism that consists of coherently grown islands when InGaAs growth begins and the generation of misfit dislocations when these islands coalesce, gives a qualitative explanation of the observed results.     

The heteroepitaxial growth of vacuum-deposited GaP thin films on Si substrates

Heteroepitaxial GaP thin films were grown on (100) and (111)Si substrates by vacuum evaporation of the compound GaP and their structural characteristics were compared with homoepitaxial GaP films grown by the same technique on (100)GaP substrates. Nearly monocrystalline GaP thin films were deposited reproducibly on (100)Si substrates at the optimum substrate temperature of about 680–700°C and the deposition rate of 0.1 nms⁻¹. The structure of such films was comparable in quality to homoepitaxial GaP/GaP films. No monocrystalline films could be deposited on (111)Si substrates.     

Electron microscope study of intrinsic and extrinsic stacking faults,and twins in SOS at the early stage of epitaxial growth

Fine structures of the Si films on (1$\text{1}$02) sapphire have been studied by a lattice resolution TEM. The Si was deposited by the pyrolysis of silane in H₂ at 1000°C at a growth rate of 0.1μm/min. The samples for TEM were prepared by peeling off the Si films from the substrates after HF treatment. A film having a mean thickness of 500 Å was composed of (100) and {110} domains. The volume fraction of the {110} domains was more than 50% and about constant as a function of growth time. The {110} domains contained much higher density of microtwins than the (100) domains. These microtwins had various thicknesses including one atomic layer (intrinsic stacking faults) and two atomic layers (extrinsic stacking faults). The density of the intrinsic stacking faults was higher than those of extrinsic stacking faults and other twins. The {110} and (100) islands were nucleated independently and the microtwins were also present in the islands smaller than 500 Å in diameter.     

Misfit Strain Relaxation by Dislocations in InAs Islands and Layers Epitaxially Grown on (001)GaAs Substrates by MOVPE

The misfit dislocation configurations in InAs islands as well as in more or less continuous layers grown on (001) oriented GaAs substrates were studied by weak-beam and high-resolution electron microscopy. The islands are confined by {101} and {111} facets where the aspect ratio (height/lateral extension) can be affected by the growth conditions. It is possible to grow well-defined islands as well as relatively continuous layers by MOVPE under As-stabilized conditions. At constant deposition parameters the growth is characterized by islands of different sizes (but with constant aspect ratio) in various strain states depending on their dislocation content. Coherently strained islands without any dislocation can be observed for heights up to 23 ML InAs, or otherwise, up to a maximal island extension of about 12 nm (for the particular aspect ratio ≈︂0.585). With further increase of island height and lateral extension, the introduction of dislocations becomes favourable. Independent of the island size, the layer thickness and the dislocation density, a residual elastic strain of about ε^r = —0.8% remains after relaxation. This means, about 88% of the total misfit strain of ε = —6.686 × 10^—2 were compensated by Lomer dislocations. These sessile Lomer dislocations lie in the island interior only, where single 60° dislocations were observed exclusively in their near-edge regions. With increasing island size and/or layer thickness some close-spaced 60° dislocations occur additionally within the interfacial region. The Lomer dislocations that are always located 4 monolayers (ML) above the InAs/GaAs interfacial plane result from the well-known fusion of two 60° slip dislocations. These 60° dislocations have been nucleated 7 … 8 ML above the interface at surface steps on the {111} facets confining the islands. Based on our experimental observations a new mechanism is proposed that explains the origin of these 60° dislocations. Their further fusion to sessile Lomer dislocations that compensate the misfit strain most efficiently occurs in the way as commonly accepted.     

Crystal and molecular structure of di(perchlorato)(1,4,8,11-tetraazacyclotetradecane)copper (II). Cu(cyclam) (ClO4)2

The title compound, Cu(C₁₀H₂₄N₄)(ClO₄)₂, crystallizes in the triclinic system with unit cell dimensionsa= 8.744,b= 8.022,c= 8.677 Å, α = 118.7, β = 56.9, γ = 113.5 °,Z= 1, space group P¯1. The structure was solved by Fourier methods and refined by least-squares techniques using the 1545 nonzero three-dimensional counter-diffraction intensity data (CuKα) to give a conventionalR factor of 0.056. The coordination sphere of the copper ion is defined by a planar arrangement of the four nitrogen donors in the macrocyclic ligand with oxygen atoms from the perchlorate groups lying above and below this plane. The resulting tetragonally distorted octahedron of donor atoms gives interatomic distances Cu?N = 2.02(4) Å and 2.02(3) Å, and Cu?N = 2.57(4) Å.     

Crystallographic structure and defects in epitaxial bismuth films grown on mica

Atomic force microscopy is used to image the surface relief of epitaxial Bi films grown on mica substrates. Monatomic terrace steps are readily resolved, which provide detailed information on crystal growth and defect structures. The films grow from the coalescence of isolated three-dimensional islands, however, each island grows layer-by-layer. The islands are triangular in shape and when they coalesce to form a continuous film, their structures are either in-phase, and consequently large crystallites are formed, or they are out-of-phase and defect structures are formed. The most common defects observed are twinning and stacking faults. Images showing the microscopic details of stacking faults, twinning, and grain boundaries are observed as a result of islands coalescing to form a continuous film.     

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)