Epitaxial films, structure

For ultrathin epitaxial films (less than "100 A), Grazingincidence X-ray Diffraction (GrXD) is the preferred method and has been used to characterize monolayer films. Here the incidence angle is small ("0.5°) and the X rays penetrate only "100-200 A into the specimen (see below). The exit angle of the diffracted X rays is also small and structural information is obtained about (hkl) planes perpendicular to the specimen sur e. Thus, GIXD complements those methods where structural information is obtained about planes parallel to the surface (e.g., Bra -Brentano and DCD). 

K. Kaigawa, T. Kawaguchi, M. Imaeda, H. Sakai, T. Fukuda. Crystal structure of LPE-grown LiNb03 epitaxial films. J Cryst Growth 777 217, 1997. 

This study also reported that films deposited on carbon membranes at temperatures >80°C were of hexagonal (wurtzite) structure, with a high density of planar defects, in contrast to the zincblende obtained from both hydroxide and ion-by-ion mechanisms at lower temperatures and to the epitaxial films on InP at all temperatures. 

Thin epitaxial films (less than 3 nm) of CrAs and CrSb with zinc-blende structure can be grown on GaAs substrates by MBE. Their 7c exceeds 400 K (Akinaga et al. 2000c Zhao et al. 2001b). A zinc-blende structure is confirmed by in-situ RHEED collected during the growth and ex-situ cross-sectional transmission electron microscopy (TEM). The... 

Many other organic materials have been deposited by evaporation in vacuo but usually form either a polycrystalline or an amorphous structure. However, Hoshi et al. [424] have made some progress in depositing epitaxial films of lutetium diphthalocyanine on to single crystals of potassium bromide. Here again the temperature of the substrate is critical but only relatively small areas of continuous crystal have been obtained. 

Growth Procedures. The exact procedures for the growth of devicequality epitaxial films by LPE vary with the deposited material, the design of the growth equipment, and the structure to be fabricated. The general procedure involves preparation of the substrate, loading of the melt constituents and pretreatment of the system, and growth. 

In order to obtain reliable results, magnetostriction should be measured in epitaxial films, free of twins, which are typical for materials of perovskite structure. In the case of films it is not easy, because usually the films are deposited on perovskite substrates, thus presenting difficulties in eliminating twin structures. 

Experimental determinations of barrier heights on oxide semiconductor interfaces using photoelectron spectroscopy are rarely found in literature and no systematic data on interface chemistry and barrier formation on any oxide are available. So far, most of the semiconductor interface studies by photoelectron spectroscopy deal with interfaces with well-defined substrate surfaces and film structures. Mostly single crystal substrates and, in the case of semiconductor heterojunctions, lattice matched interfaces are investigated. Furthermore, highly controllable deposition techniques (typically molecular beam epitaxy) are applied, which lead to films and interfaces with well-known structure and composition. The results described in the following therefore, for the first time, provide information about interfaces with oxide semiconductors and about interfaces with sputter-deposited materials. Despite the rather complex situation, photoelectron spectroscopy studies of sputter-deposited... 

The growth kinetics describes the nucleation processes on the atomic scale. Thermally activated processes as adsorption, desorption, and diffusion at the surface and in the volume, nucleation, and crystallization/ recrystallization determine the film structure and can be controlled by the substrate temperature and the growth rate. Using a diagram ln(J ) over 1/ T, R being the deposition rate and T the growth temperature, three different growth modes (epitaxial, polycrystalline, and amorphous) can be... 

In the absence of good quality single crystal samples, the physical properties of indium nitride have been measured on non-ideal thin films, typically ordered polycrystalline material with crystallites in the 50 nm to 500 nm range. Structural, mechanical and thermal properties have only been reported for epitaxial films on non-lattice-matched substrates. 

XRD and PL are the usual compositional techniques used to determine the alloy composition. These non-destructive methods provide fast feedback to the growth and can be very accurate in the III-arsenide/phosphide alloys systems. However, for the M-nitrides, the epitaxial films are normally grown on a mismatched substrate which results in residual stress being present in the films, ft is also sometimes difficult to identify the band-to-band emission and the magnitude of the bowing parameters is not well established. Therefore, one must be cautious when employing these methods to determine the alloy compositions. In addition, these techniques cannot be used to determine the composition of multilayer structures. 

The limited number of high quality substrates suitable for oxide epitaxy, together with the wide range of structural properties exhibited by oxides, may require the use of a substrate with a different crystal symmetry than the film material. If the crystal symmetries are sufficiently different, antiphase boundaries (ABPs) may result during nucleation of the initial monolayers. Such APBs tend to be very stable and thus typically become permanently ingrained in the film structure. The question we address here is the effect that APBs in the bulk of the film have on the surface structure. 

Perhaps the greatest disadvantage of CSD is the difficulty in depositing ultrathin films (thickness <30 nm). While the possibility has been demonstrated in selected systems, the method is not usually viewed as amenable to that thickness requirement. Another disadvantage of CSD is the fact that three-dimensioanl structures with high aspect ratios cannot be conformally coated. Lastly, while epitaxial films have been prepared by the method, ° generally the films produced are polycrystalline and often not oriented. 

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