Thin epitaxial

Significant improvements in ECALE deposit morphology and quality were reported as achieved by switching from a thin layer cell to a thick layer H-form cell, integrated in an automated deposition system [46]. Thin epitaxial films of zinc blende CdTe, CdSe, and CdS with predominate (111) orientations were grown. 

From a practical point of view, the optical detection of possible X—H bonds in hydrogenated samples is performed at LHeT as a better sensitivity is obtained at this temperature because the features are sharper than the ones observed at ambient. The sensitivity of Fourier Transform Spectroscopy (FTS) allows usually a normal incidence geometry of the optical beam. Two kinds of samples are generally used in the hydrogenation studies. The first are thin epitaxial layers (1 to 5 in thickness) with dopant concentrations in the 1017-102° at/cm3 range on a semi-insulating... 

The scattered intensity is proportional to the volume of the crystal. This implies that the scattering from a thin epitaxial layer, large in area compared with the beam diameter, will be proportional to the layer thickness. 

Thin epitaxial layers display a rich variety of X-ray optical phenomena which can be exploited for materials characterisation. Superlattice structures in... 

Submonolayer of Ni deposited in the temperature range of 130-180 K on the missing-row reconstructed Au(llO)-(1 X 2) surface has been analyzed using STM [465]. An order within the thin epitaxial AuNi film deposited on an Au(lOO) surface, accompanying temperature changes, has been investigated by applying X-ray diffraction [466]. 

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... 

A primary focus of our work has been to understand the ferroelectric phase transition in thin epitaxial films of PbTiOs. It is expected that epitaxial strain effects are important in such films because of the large, anisotropic strain associated with the phase transition. Figure 8.3 shows the phase diagram for PbTiOs as a function of epitaxial strain and temperature calculated using Landau-Ginzburg-Devonshire (lgd) theory [9], Here epitaxial strain is defined as the in-plane strain imposed by the substrate, experienced by the cubic (paraelectric) phase of PbTiOs. The dashed line shows that a coherent PbTiOs film on a SrTiOs substrate experiences somewhat more than 1 % compressive epitaxial strain. Such compressive strain favors the ferroelectric PbTiOs phase having the c domain orientation, i.e. with the c (polar) axis normal to the film. From Figure 8.3 one can see that the paraelectric-ferroelectric transition temperature Tc for coherently-strained PbTiOs films on SrTiOs is predicted to be elevated by 260°C above that of... 

Originated in the late 1970 s, ALE has become a widely used synthesis route for thin epitaxial layers. Many ALE coated materials are produced commercially today. 

F. Besenbacher, L. Pleth Nielsen and P. T. Sprunger, Surface alloying in heteroepitaxial metal-on-metal growth, in Growth and Properties of Ultra-thin Epitaxial Layers, Vol. 8 of The Chemical Physics of Solid, Surfaces and Heterogeneous Catalysis, eds. D. A. King and D. P. Woodruff (Elsevier Science, Amsterdam, 1997), p. 207. 

Commercial n-type 6H-SiC wafers with a concentration of uncompensated donors Nd - Na = 3x lO cm were used as substrates. These substrates were covered with a thin epitaxial n-GaN buffer layer grown by hybrid vapor phase epitaxy (HVPE). This buffer layer had a thickness of 0.2 pm and a donor concentration of Nd-Na = (2-3)xl0 cm . On top. Mg doped / -type AlGaN epitaxial layers with thickness of 0.8 pm and an Al content of 12 at.% were also grown by HVPE with an acceptor concentration of Na-Nd = (5-8)xl0 cm. Then, Ga doped n-ZnO epitaxial layers were deposited using chemical vapor deposition (CVD) with a thickness of 0.8 pm and a donor concentration ofNd - Na = 7xl0 cm. The growth process was stimulated by a discharge plasma, that allowed to reduce the substrate temperature by up to 400 °C and thus improve the structural quality of the ZnO layers. ... 

Structure of thin epitaxial oxide films and their surfaces... 

Pure bulk iron in the fee crystal structure (7-Fe) only exists at very high temperatures (between 1183 and 1667K). However, 7-Fe may be stabilized at low temperatures as small coherent precipitates in copper or copper-alloy matrices or as thin epitaxial films on a Cu or Cu-based alloy substrate [113], (114). Recently the interest in 7-Fe has been revived due to the existence of multiple magnetic states revealed by band-structure calculations [115], which is believed to be related to INVAR phenomena in 7-Fe-based alloys [116]. 

Comparative studies in an electrochemical environment and under UHV conditions gain detailed information on die mechanistic role on anions and solvent molecules. This is demonstrated for nucleation and growth of thin epitaxial Ni films on Au(l 11). In contrast to Cu, no UPD or anion effects were found for Ni on Au [25]. In addition, due to the negative deposition potential of Ni the Au(l 11) electrode can be kept in a potential regime in vdiich Ihe surface exhibits the herringbone reconstruction, well known fiom UHV studies [26]. In Fig. 4(a), recorded in a modified Watts electrolyte [25], the zigzag pattern of die herringbone reconstruction is clearly visible on the electrode surface. 

II-VI semiconductor layers and bulk semiconductors like Si, GaAs, InP, etc. In particular, quantum wells are formed by thin epitaxial multilayered structures like (Zn, Cd)Se/ZnS. Nevertheless, the choice between bulk semiconductors and the layers deposited or between the multilayers is governed by the lattice mismatch between the two components as the lattice mismatch causes the formation of misfit dislocations. In the optical devices these defects are potential non-radiative centres and at worst they can cause the failure of injection lasers. Figure 29 is a map of energy gap versus lattice constants for a variety of semiconductors it can be used to select different heterostructures, not only for optoelectronics applications but also for photovoltaic cells. In the latter application the deposited films are generally polycrystalline and the growth of high-quality epitaxial layers has received little applications. 

An alternative technique for producing clean surfaces of any orientation of III—V compounds and alloys is to grow a thin epitaxial film (> 2000 A) in situ from molecular beams of the elements generated from Knudsen sources inside the UHV system. The growth process has become known as molecular beam epitaxy or MBE [111]. Any impurities remain at the film—substrate interface and the freshly created surface is very clean. A more detailed account of this process will be given in Sect. 5. 

Pd particles (1-15 nm) were prepared by ultra high vacuum (UHV) condensation of the metal on clean MgO or ZnO microcrystals, on ZnO (00.1) thin epitaxial layers synthesized in situ and on clean (001) MgO single crystals, air cleaved and in situ cleaned. The metal was evaporated from a Knudsen cell at a calibrated flux b The temperatures of the substrates were between 400 °C... 

Pd and bimetallic PdCu and PdCu3 particles have been prepared, both under UHV conditions and by decomposition of organometallic compounds, on MgO and ZnO micro-crystals, single crystals or thin epitaxial layers. The shapes and structures of the particles and the structures of the interfaces, and the dependence of these on particle size and annealing conditions, were determined by HRTEM and WBDF imaging. 

Figure 15.4. (a) Visual appearance of thin epitaxial polygermanosilyne layers as a function of the Ge content x. (b) Comparison of the photoluminescence spectra of the different sheet polymers as a function of the Ge content x. All spectra have been measured at room temperature and have been normalized, (c) Comparison of the dependences of the photoluminescence energies and the absorption edges of several Sii.xGex compounds on the Ge content x. 

In this sechon we consider evolution of a thin epitaxial him in the case when the him instability is caused by the epitaxial stress, the him surface energy is isotropic, and the him is thin enough so that wetting interachons between the him and the substrate are important. In more detail, the material discussed in this sechon can be found in [11]. (The hgures are reprinted with permission from [11], (5)2003 by the American Physical Society). 

Eq.(5) describes the nonlinear evolution of a thin, epitaxially-strained film in the presence of wetting interactions with the substrate. Without wetting interactions g = 0), the dispersion relation for the growth rate of infinitesimal perturbations of the film surface h isa = k —k, see Fig.2a (in the... 

The increase of the substrate temperature up to 100 °C results in an appearance of the new surface phase ((2/3) 3x(2/3) 3)-R30° (Fig. lb). This surface phase looks to be a thin epitaxial magnesium silicide film with the misfit 1.9 % with a silicon lattice [5]. According to our EELS data this surface phase is characterized by surface (hux = 9.8 eV) and bulk (hux, = 13.6 eV) plasmons, while for thick magnesium silicide films the surface (hoy = 10.3 eV) and bulk (htav= 14.6 eV) plasmons are typical [8]. The observed difference could be caused by tension of surface phase lattice. At further adsorption the metallic magnesium grows atop the silicide surface phase. 

The high sensitivity of CBED patterns to small changes in lattice parameter is illustrated in Figure 3. These two CBED patterns compare the central bright-held CBED disk for a thin GaN him oriented close to [10-10], with the corresponding disk from a thin epitaxial Gao.96lno.04N quantum well layer. The fractional difference in lattice parameter due to the difference in composition is considerably less than 0.5%, but the relative positions of the dark... 

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