Monocrystalline films

Simple approach based on the effective mass theory has been developed and successfully applied to simulate electronic properties of monocrystalline and grained nanocrystalline films accounting for the confinement effect and interactions between the grains. Quantum confinement was found to influence band gap values only for the films with the thickness less than 5 nm. The highest gap varied from 0.63 to 0.91 eV depending on the film thickness as well as on the lateral size of the grains. Inclusion of the grains inside the film induces a eonsiderable increase of the gap as compared to the monocrystalline film of the same effective thickness. 

Figure 1. Total band gap (a) and the valence band maximum and conduction band minimum (b) versus monocrystalline film thickness. Dotted lines reproduce the appropriate bulk values.

Energy gap broadening of 0.21 eV or 0.11 and 0.10 eV for the conduction and the valence bands, respectively, takes place. The curves corresponding to the films with larger grains approximately follow the behaviour of Eg versus d for the monocrystalline film with a certain upshift in each case. This upshift can be ascribed to the additional confinement conditions within the plane of the film. Moreover, for the films thicker than 5 nm Eg tends to 0.56 eV that corresponds to experimentally measured value for amorphous CrSia films [9]. 

The electronic properties of monocrystalline and grained nanocrystalline CrSi2 films were estimated within the Effective Mass Theory. Inclusion of the grains inside the film increases the energy gap up to 60% compared to the monocrystalline film of the same effective thickness. 

The term epitaxy is used to describe the growth of a monocrystalline film of one material in a definite crystallographic orientation on a crystal face of another material, the substrate. To promote growth, there must be a correspondence of both lattices at the interface. A misfit between film and substrate results in stresses as the film grows laterally, which may affect the stability of the deposited crystal. The magnetic properties of LPE garnet films can be optimised by varying this misfit. 

Molecular beam epitaxy (MBE). This technique is another class of PVD processes. The main difference from the traditional PVD process resides in the control of the vapor flow, which, for MBE allows the growth of monocrystalline films (epi above and taxis in ordered manner ). To achieve such a highly crystalline film, a crystalline substrate is required, the substrate must be heated to several hundred degree Celsius during deposition, and the precursor vapor must travel through a very high vacuum (10 Pa) at relatively low flow. 

Epitaxial deposition on monocrystalline ceramic substrates such as Sr2Ti03 or MgO is used to prepare monocrystalline films. Investigation on the influence of grain boundaries on the superconducting properties of... 

The essential reason for the much lower 7c of the BSCCO tapes compared to monocrystalline films stems from the existence of grain boundaries, which act as barriers to current flow as discussed above. Considering the importance of grain boundaries in a frame of mechanism of the supercurrent flow in BiPb2223 tapes, two models were proposed, the brick-wall [2.116] and railway-switch [2.117] models, which were combined afterwards within the freeway model [2.118]. 

Insulating EuSe crystals which are transparent in the red, Tsang etal. [1], are green in reflection, Reed, Fahey [2]. Strongly conducting samples have a metallic appearance [1]. Polycrystalline samples look dull (see p. 25), dark brown, Srivastava, Stevenson [3], or dark khaki-colored, Hariharan, Eick [4]. Transparent monocrystalline films on SrO substrate are... 

Films on glass, quartz, sapphire, or MgO substrates are prepared by vapor deposition of Eu and Gd from a Ta crucible at 10" Torr and subsequent reaction with an H2Se stream at about atmospheric pressure and room temperature, Schueler [2]. Epitaxial deposition of monocrystalline films on monocrystalline substrates is achieved by electron beam heating of preformed selenides in a vacuum of 10" Torr. Starting material and film have the same compositions. Mica, quartz, KCl, and NaCl are used as substrates, which must be kept at a temperature of at least 200°C, Holtzberg, Methfessel [3]. 

The dark violet Yb2Se3 crystallizes in the orthorhombic SC2S3 structure type with a = 11.27, b = 8.02, c = 23.98 A. The structure is related to the NaCl type and formed from this by ordered removal of Vs of the cations. The Yb atoms are surrounded by six Se in a slightly distorted octahedron [1]. Epitaxially grown monocrystalline films on the (111) face of CaFg crystallize in the NaCl type with a = 5.654 0.002 A, Suryanarayanan et al. [6], Paparoditis, Suryanarayanan [5]. 

Epitaxy refers to the deposition of monocrystalline films (the epitaxial layers) on a monocryrstalline substrate - homoepitaxy if the grown film material is the same as the substrate (though perhaps more... 

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