Magneto-optical studies of epitaxial EuS films on silicon

An improved simple method for magneto-optical display of ferromagnetic domains by means of laser light is reported. As an example, characteristic domain patterns are presented and discussed, which develop during the magnetization reversal of ferromagnetic EuS-films grown epitaxially on silicon substrates. The critical field strength for domain nucleation, H_K, the coercive field, H_c, the saturation field, H_s, and the direction and width of the domains have been studied as function of angle varied between the magnetical easy and hard axes of (110)- and (111)-EuS films, and as a function of temperature between 6 and 14.5 K. By extrapolating the linear decrease of H²_K,cs vs. T to zero the Curie temperature of the (110)- and (111)-EuS films has been determined to (15.3±0.2) K and (14.5±0.2) K, respectively.     

Determination of strain in epitaxial semiconductor structures by high-resolution X-ray diffraction

High-resolution X-ray diffraction is used to obtain the strain profile of a wide range of epitaxial semiconductor samples. The samples are divided into five categories: Strained layers on a substrate, (partly) relaxed layers on a substrate, strained-layer superlattice structures, multiple relaxed layers and relaxed superlattice structures and ionimplanted samples. For each category a measurement strategy and analysis method is given. Representative examples for each category are shown.     

Measurement of internal stresses via the polarization in epitaxial ferroelectric films

The relations between electrical and mechanical properties of constrained ferroelectric films are analyzed. It is shown that the internal stresses and the elastic constants can be determined through the measurement of the electrical response. The change in the polarization is proportional to internal stresses due to film-substrate misfit, whereas the linear electrical and electromechanical responses to external field do not depend on the misfit and are determined by the film constraint. The theoretical results are successfully applied to PbZr 0.2Ti 0.8O (3) films on (001) LaAlO (3) substrate which exhibit a considerable increase in the saturation polarization due to epitaxial stresses. Significant recovery in the piezoelectric constant and susceptibility is theoretically predicted and experimentally verified for specific film configurations which reduce the degree of constraint. The concept presented in this Letter can be expanded to constrained ferromagnetic and superconductor films.     

Determination of in-plane lattice parameters of InAs/AlAs strained-layer superlattices by X-ray precession camera

A determination of the lattice parametersa andb of InAs/AlAs short-period strained-layer superlattices grown by Atomic Layer Molecular Beam Epitaxy (ALMBE) on GaAs(001) substrates has been performed by means of an X-ray precession camera using copper radiation. Spots belonging to the superlattice are clearly differentiated from those of the substrate, which confirms that they are partly decoupled from each other. It was also possible to resolve the lattice spots of InAs or In_0.8Ga_0.2 As decoupling buffer layers grown between the substrate and the superlattice. This technique proves to be very useful to characterize, in a very short time and with a reasonable resolution, highly mismatched epitaxial systems in which lattice parameters parallel to the interface play a crucial role in the understanding of the growing behaviour.     

Poisson ratio and plasticity of glasses

Analysis of experimental data reveals a regular relation between Poisson’s ratio and plastic characteristics of inorganic glasses.     

High precision studies of lattice parameter changes in lithium intercalation compounds

We present an in situ X-ray diffraction experiment which measures lattice parameter changes resulting from lithium intercalation to a precision of one part in 10⁵. Experiments on 2H-Li_xTaS₂ demonstrate the sensitivity and reproducibility of the method. To our knowledge, these results are the most precise measurments of lattice parameter changes resulting from intercalation. We find that the c-axis of 2H-Li_xTaS₂ exhibits anomalous behaviour near $\text{x=}\text{1}\text{3}$ and $\text{x=}\text{2}\text{3}$ pr esumably because of the order-disorder transitions in the intercalated lithium.     

Terahertz spectroscopy studies on epitaxial vanadium dioxide thin films across the metal-insulator transition

We present results on terahertz (THz) spectroscopy on epitaxial vanadium dioxide (VO(2)) films grown on sapphire across the metal-insulator transition. X-ray diffraction indicates the VO(2) film is highly oriented with the crystallographic relationship: (002)(film)//(0006)(sub) and [010](film)//[2 ?1 ?10](sub). THz studies measuring the change in transmission as a function of temperature demonstrate an 85% reduction in transmission as the thin film completes its phase transition to the conducting phase, which is much greater than the previous observation on polycrystalline films. This indicates the crucial role of microstructure and phase homogeneity in influencing THz properties.     

Periodic lattice distortions in epitaxial films of Fe(110) on W(110)

The epitaxial growth of Fe(110) on W(110) at 500 K is analyzed using LEED and AES. Frank-van der Merwe growth is established by AES. According to LEED, pseudomorphism occurs up to θ = 1.64, where every W atom of two topmost W layers is just covered by exactly one Fe atom. For 2?θ?9, characteristic reflection-multiplets are observed, symmetric about the basic Fe(110) reflections, which are interpreted in terms of periodic lattice distortions. The latter are caused by interaction with the misfitting W substrate.     

Synthesis of epitaxial silicon carbide films through the substitution of atoms in the silicon crystal lattice: A review

A review of recent advances in the field of epitaxial growth of SiC films on Si by means of a new method of epitaxial substitution of film atoms for substrate atoms has been presented. The basic statements of the theory of the new method used for synthesizing SiC on Si have been considered and extensive experimental data have been reported. The elastic energy relaxation mechanism implemented during the growth of epitaxial SiC films on Si by means of the new method of substitution of atoms has been described. This method consists in substituting a part of carbon atoms for silicon matrix atoms with the formation of silicon carbide molecules. It has been found experimentally that the substitution for matrix atoms occurs gradually without destroying the crystalline structure of the matrix. The orientation of the film is determined by the “old” crystalline structure of the initial silicon matrix rather than by the silicon substrate surface only, as is the case where conventional methods are used for growing the films. The new growth method has been compared with the classical mechanisms of thin film growth. The structure and composition of the grown SiC layers have been described in detail. A new mechanism of first-order phase transformations in solids with a chemical reaction through an intermediate state promoting the formation of a new-phase nuclei has been discussed. The mechanism providing the occurrence of a wide class of heterogeneous chemical reactions between the gas phase and a solid has been elucidated using the example of the chemical interaction of the CO gas with the single-crystal Si matrix. It has been shown that this mechanism makes it possible to grow a new type of templates, i.e., substrates with buffer transition layers for growing wide-band-gap semiconductor films on silicon. A number of heteroepitaxial films of wide-band-gap semiconductors, such as SiC, AlN, GaN, and AlGaN on silicon, whose quality is sufficient for the fabrication of a wide class of micro- and optoelectronic devices, have been grown on the SiC/Si substrate grown by solid-phase epitaxy.     

Structural deformation, melting point and lattice parameter studies of size selected silver clusters

Silver clusters have been produced by magnetron sputtering in a gas aggregation nanocluster source. Clusters are size selected using a quadrupole mass filter (3–8 nm) or by varying the aggregation tube length (9–20 nm) of the nanocluster source. Mass selected clusters are deposited on a Si(100) substrate at different bias voltages and are characterized by atomic force microscopy. We observe a significant flattening of clusters on the surface due to the increase of impact energy as a result of increasing substrate bias voltage. The behavior of lattice parameters for size selected clusters are investigated by X-ray diffraction. All measured lattice constants exhibit a tensile strain; it is found that the lattice constant slightly increases with increasing cluster size up to a size of 12 nm and then decreases. The melting temperature of deposited clusters is found to be size-dependent and significantly lower than for bulk material, in agreement with theoretical considerations.     

Temperature dependence of the SmS lattice parameter

The behavior of the lattice parameter of single-crystal SmS with temperature was studied by x-ray diffractometry in the range 100–700 K. The observed features are assigned to a temperature-induced variation in the filling of the Sm²⁺f-shell ground-state multiplet levels. The temperature dependence of the thermal expansion coefficient of SmS was measured. It is shown that the lattice constant behavior in samples that exhibit a pronounced emf generation effect under heating is influenced by the transition of defect samarium ions from the divalent to trivalent state and that the effect itself derives from phase transitions in SmS.     

Interatomic force constants and lattice vibrations of AlP,AlAs and AlSb

The interatomic force constants and the phonon dispersion curves of AlP, AlAs, and AlSb are obtained from the electronic theory of solids by using our presented binding force, which includes mainly covalent interactions in the pseudopotential formalism and partially ionic interactions. The potential-parameter, effective ionic charge and ionic fraction of AlP and AlAs are estimated from those of AlSb and other III–V tetrahedrally- bonded compounds in spite of no experimental information on the band- calculation and the neutron scattering data of AlP and AlAs. Numerical data for the crystal energy of AlP and AlAs are in good agreement with the observed data, and the obtained results for the phonon dispersion curves and bulk modulus are useful to study the lattice dynamics and anharmonic properties of these compounds.     

The Labusch parameter of a driven flux line lattice in YBa Cu O superconducting films

We have investigated the influence of a driving force on the elastic coupling (Labusch parameter) of the field-cooled state of the flux line lattice (FLL) in 400 nm thick YBa₂Cu₃O₇ superconducting films. We found that the FLL of a field-cooled state without driving forces is not in an equilibrium state. Results obtained for magnetic fields applied at and 30 relative to CuO₂ planes, show an enhancement of the elastic coupling of the films at driving current densities several orders of magnitude smaller than the critical one. Our results indicate that the FLL appears to be in a relatively ordered, metastable state after field cooling without driving forces. Received 21 December 1999     

Expansion of the Madelung parameter in terms of multipole moments and as a function of the ratio of two lattice parameters

A method is derived to expand the Madelung parameters of non-cubic crystals as a function of the ratio of two lattice parameters and in terms of multipole moments. Only one expansion of this kind is necessary to evaluate the Madelung constants for a series of compounds of one type of structure either containing polyatomic ions or spherical ions at positions slightly varying from one compound to the other. This method also allows the minimisation of the lattice energy with respect to one particular lattice parameter, leaving invariant all internal distances in the polyatomic ions.     

Duality and the θ parameter in Abelian lattice models

The phase diagrams of abelian lattice gauge theories in four dimensions, and spin models in two dimensions, in the presence of a θ-parameter, are constructed using duality arguments. A rich structure involving an infinite number of phases emerges, together with a mechanism for spontaneous CP violation at θ = π.     

Preparation and properties of epitaxial ZnGeP2 films

Thermodynamic analysis has been applied to the vapor over a ZnGeP₂ crystal when the chlorine source is provided by ZnCl₂. ZnGeP₂ film growth has been examined and the electrophysical and photoluminescence parameters have been measured. All these autoepitaxial films have the chalcopyrite structure, while those parameters are determined by the defects and the substrate orientation.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 74–78, April, 1988.We are indebted to L. G. Lavrent'eva for interest, to A. I. Gribenyukov and T. E. Tkachenko for assistance in growing the single crystal; and to F. Kim for the microprobe analysis.     

Structure and anisotropy of epitaxial fcc FePt films

Pulsed laser deposition (PLD) was used to deposit FePt films onto single crystalline MgO substrates. When deposited at room temperature, films grow epitaxial within the A1 phase. Structure and magnetic properties were examined by X-ray diffraction, Rutherford Backscattering Spectrometry (RBS), magneto-optic Kerr effect, Mössbauer spectroscopy, and Magnetic Orientation Mössbauer Spectroscopy (MOMS). These measurements allow to exclude local ordering and reveal the anisotropic intrinsic and extrinsic magnetic properties. These results are discussed with respect to the texture and microstructure of these films.     

Effect of elastic stresses on the IR spectra of lattice vibrations in epitaxial ZnSe films on (001)GaAs substrates

The lattice IR reflection spectra of epitaxial ZnSe films are studied for different thicknesses on a (001)GaAs substrate. The frequency of the TO mode is found to increase for films with thicknesses of 0.8 and 1.2 μm that exceed the critical value d _cr ≈0.1 μm for ZnSe/GaAs pairs. The effect is explained by the existence of regions with residual stress in the film. Fiz. Tverd. Tela (St. Petersburg) 41, 1948–1952 (November 1999)     

Ellipsometric and reflectance studies of GaAs/AlAs superlattices

Multiple-angle-of-incidence ellipsometry at 632.8 nm and optical reflectance spectra are used to study GaAs/AlAs superlattices on GaAs substrates. The diagnostic potential of the two methods are compared to each other. Precise values of the total film thicknesses are obtained from the ellipsometric data. Significant disagreement between the measured and nominal thicknesses based on RHEED controlled MBE growth conditions is observed. Nonuniformity of a superlattice film is identified with the spatial resolution of about 1 mm². The thickness variations are accompanied by pronounced variations of the optical constants.