TSF-MOCVD – a novel technique for chemical vapour deposition on oxide thin films and layered heterostructures

A new principle for supplying volatile precursors to MOCVD gas-phase chemical deposition systems is proposed, based on a two-stage evaporation of an organic solution of precursors from a soaked cotton thread, which passes sequentially through the zones of evaporation of the solvent and precursors. The technological capabilities of TSF-MOCVD (Thread-Solution Feed MOCVD) are demonstrated based on examples of obtaining thin epitaxial films of СеО2, h-LuFeO3 and thin-film heterostructures β-Fe2O3/h-LuFeO3. The results of studying the obtained films by X-ray diffraction, energy dispersive X-rayanalysis, and high- and low-resolution transmission microscopy are presented. Using the TSF module, one can finely vary the crystallisation conditions, obtaining coatings of the required degree of crystallinity, as evidenced by the obtained dependences of the integral width of the h-LuFeO3 reflection on the film growth rate. Based on the TEM and XRD data, it was concluded that β-Fe2O3 grows epitaxially over the h-LuFeO3 layer. Thus, using TSF-MOCVD, one can flexibly change the composition of layered heterostructures and obtain highly crystalline epitaxial films with a clear interface in a continuous deposition process

MORPHOLOGICAL MOMENTS OF BINARY IMAGES

The concept of morphological moments of binary images is introduced. Morphological moments can be used as a shape descriptor combining an integral width description of an object with a description of its spatial distribution. The relationship between the proposed descriptor and the disc cover of the figure is discussed and an exact analytical method for descriptor calculation is proposed within the continuous morphology framework. The approach is based on the approximation of the shape by a polygonal figure and the extraction of its medial representation in the form of the continuous skeleton and the radial function. The proposed method for calculation of morphological moments achieves high accuracy and it is computationally efficient. Experimentations have been conducted. Obtained results indicate that the morphological moments are a more informative and rich shape descriptor than the area of the disc cover. Application of morphological moments to the font recognition task improves the recognition quality.

X-ray diffraction broadening analysis

The microstructure is very important in research aimed to the development of new materials. The microstructural parameters, crystallite size, crystallite size distribution, crystallite strain, dislocation density and stacking fault probability, play a major role in physical and chemical properties of the material. These parameters can be determined by a proper analysis of X-ray diffraction line profile broadening. The observed XRD line profile of the studied sample, <em>h</em>(<em>ε</em>), is the convolution of the instrumental profile, <em>g</em>(<em>ε</em>), inherent in diffraction, and pure diffraction profile, <em>f</em>(<em>ε</em>), caused by small crystallite (coherent domain) sizes, by faultings in the sequence of the crystal lattice planes, and by the strains in the crystallites. That is, <em>f</em>(<em>ε</em>) is the convolution of the crystallite size/faulting profile, <em>p</em>(<em>ε</em>), and the strain profile, <em>s</em>(<em>ε</em>). The derivation of <em>f</em>(<em>ε</em>) can be performed from the measured <em>h</em>(<em>ε</em>) and <em>g</em>(<em>ε</em>) by the Fourier transform method, usually referred to as the Stokes method. That method does not require assumptions in the mathematical description of <em>h</em>(<em>ε</em>) and <em>g</em>(<em>ε</em>). The analysis of <em>f</em>(<em>ε</em>) can be done by the Warren-Averbach method, which is applied to the Fourier coefficients obtained by the deconvolution. On the other hand, simplified methods (which may bypass the deconvolution) based on integral widths may be used, especially in studies where a good relative accuracy suffices. In order to obtain the relation among integral widths of <em>f</em>(<em>ε</em>), <em>p</em>(<em>ε</em>) and <em>s</em>(<em>ε</em>), one assumes bell-shaped functions for <em>p</em>(<em>ε</em>) and <em>s</em>(<em>ε</em>). These functions are routinely used in the profile fitting of the XRD pattern and in the Rietveld refinement of the crystal structure. The derived crystallite size and strain parameters depend on the assumptions for the profiles <em>p</em>(<em>ε</em>) and <em>s</em>(<em>ε</em>). Integral width methods overestimate both strain and crystallite size parameters in comparison to the Warren-Averbach-Stokes method. Also, the crystallite size parameter is more dependent on the accuracy, with which the profile tails are measured and how they are truncated, than it is the strain parameter. The integral width also depends on the background level error of the pure diffraction profile. The steps and precautions, which are necessary in order to minimize the errors, are suggested through simple examples. The values of the crystallite size and strain parameters, obtained from integral widths derived by the Stokes deconvolution, are compared with those which followed from the Warren-Averbach treatment of broadening. Recent approaches in derivation of microstructure are also mentioned in short.

Structural, Dielectric Specroscopy and Internal Friction Correlation in 2NB2O9 Ceramics

The research presented in this paper concerns BaBi2Nb2O9 (BBN) which is the member of the Aurivillius family and seems to be interesting from the point of view of its potential applications in storage media. Our investigations focused on temperature dependence crystal structure and mechanical properties of this ceramics as well as on the dielectric properties of samples. Correlation between positions of the maximum of the real part of electric permittivity and the behavior integral width of diffraction lines XRD versus temperature had been discussed based of the presence of polar nano-regions with orthorhombic distortion in macroscopic tetragonal matrix.

Generation and Determination of Compressive Residual Stresses of Short Penetration Depths

Generating compressive residual stress states with high gradients and low penetration depths offers high capability regarding increase of fatigue limit of parts. In this work the determination of such specific residual stress distributions by using X-ray diffraction and a little material removal is introduced. Measurements are compared using two interference peaks of different penetration depths, at which confocal microscopy enables high accuracy in determination of the step sizes in electrochemical machining. Furthermore the realisation of these states by two different peening processes using micro blasting media is described. The suitability of the processes micro peening and ultrasonic wet peening as surface treatment methods to improve fatigue limit are shown. Micro peening is based on the shot peening principle with small shots and ultrasonic wet peening on the acceleration of small blasting particles by cavitation. The investigations were conducted at AISI 4140 in a quenched and tempered state. Besides the residual stresses and the integral width of interference peaks as well as the depth distributions, the surface topography was examined. The beneficial effects of these conditions on the fatigue limit in bending tests are described.

Numerical conversion between the Pearson VII and pseudo-Voigt functions

The shape coefficient of a curve, which is defined as the ratio of its full width at half-maximum intensity to integral width, is a measure of variation in shape. From the definitions of the pseudo-Voigt, Pearson VII and Voigt functions used in X-ray diffractometry, three shape-converting formulae are deduced. Numerical solution helps to establish a numerical model for interconverting the shapes of the pseudo-Voigt, Pearson VII and Voigt functions. Assessment of the error level and some comments on the shape of the pseudo-Voigt and Pearson VII functions are thereby made.

Quantitative phase analysis of iron ore concentrates

The quantification of goethite, magnetite, martite and specularite in iron ores was successfully achieved by a combination of wet chemical analysis and x-ray diffraction. It was found that the intensity of the goethite (111) peak is constant for a certain sample provided that the same sample holder is used. Calibration curves with a linear behavior have been derived using the areas of the above mentioned peak and the amounts of goethite obtained by Mössbauer spectroscopy and optical microscopy. In addition, the integral width of the hematite (012) line broadens linearly as the amount of martite increases, thus allowing an estimation of the amounts of martite and specularite.

Comments onExtinction-corrected mean thickness and integral width used in the program UMWEG98by Rossmanith (2000)

Comments are made on a paper by E. Rossmanith [J. Appl. Cryst.(2000),33, 330–333] concerning the use of asymptotic expressions for the extinction-corrected mean thickness.

Data smoothing and distortion of X-ray diffraction peaks. II. Application

Based on the analysis of geometric relations, it is found that the amplitude of the distortion of the full width at half-maximum (FWHM) of a peak after smoothing is the largest among the distortions of the seven parameters of a peak: maximum intensity, FWHM, shape, asymmetry, integral intensity, peak position and integral width. Hence the FWHM distortion is used as a criterion of smoothing. The 1% and 5% error limits of smoothing are calculated. Quadratic and quartic polynomial Savitzky–Golay filters are compared. Aberrations of an X-ray diffraction (XRD) peak caused by using double, matched, 1.5 and 0.7 FWHM filters are described in more detail by means of the analyses of internal and external factors. It is found that the smoothing-induced distortions of an actual XRD peak trend towards those of ideal curves. The distortions are classified according to three types of peak. A possible method to obtain the actual peak parameters, called `system smoothing refinement', is presented.

Extinction-corrected mean thickness and integral width used in the programUMWEG98

The kinematical upper limit of the extinction-corrected mean thickness as well as the corresponding integral width of the intensity profiles are estimated for spherical crystals. The new expression for the primary-extinction correction is compared with expressions given recently in the literature as well as with those widely used in crystal structure analysis.