Identification of Kikuchi lines in electron diffraction patterns collected in small-angle geometry.

It is demonstrated that Kikuchi features become clearly visible if reflection high-energy electron diffraction (RHEED) patterns are filtered using digital image processing software. The results of such pattern transformations are shown for SrTiO3 with mixed surface termination for data collected at different azimuths of the incident electron beam. A simplified analytical approach for the theoretical description of filtered Kikuchi patterns is proposed and discussed. Some examples of raw and filtered patterns for thin films are shown. RHEED patterns may be treated as a result of coherent and incoherent scattering of electron waves. The effects of coherent scattering may be considered as those occurring due to wave diffraction by an idealized crystal and, usually, only effects of this type are analysed to obtain structural information on samples investigated with the use of RHEED. However, some incoherent scattering effects mostly caused by thermal vibrations of atoms, known as Kikuchi effects, may also be a source of valuable information on the arrangements of atoms near the surface. Typically, for the case of RHEED, Kikuchi features are hidden in the intensity background and researchers cannot easily recognize them. In this paper, it is shown that the visibility of features of this type can be substantially enhanced using computer graphics methods.

An Analysis of Kikuchi Lines Observed with a RHEED Apparatus for a TiO2-Terminated SrTiO3 (001) Crystal.

In this study, electron diffraction patterns observed under high vacuum conditions for an SrTiO3 surface were interpreted in detail while paying special attention to the features of inelastic effects. The surface of the SrTiO2 was carefully prepared to enforce its termination with single domains of TiO2 layers at the top. The inelastic patterns were interpreted using analytical models. Two types of Kikuchi lines are recognized in this paper: those which can be described with the Bragg law and those which appear due to surface wave resonance effects. However, we also discuss that there exists a formal connection between the two types of the Kikuchi lines observed.

Simplified Determination of RHEED Patterns and Its Explanation Shown with the Use of 3D Computer Graphics.

The process of preparation of nanostructured thin films in high vacuum can be monitored with the help of reflection high energy diffraction (RHEED). However, RHEED patterns, both observed or recorded, need to be interpreted. The simplest approaches are based on carrying out the Ewald construction for a set of rods perpendicular to the crystal surface. This article describes how the utilization of computer graphics may be useful for realistic reproduction of experimental conditions, and then for carrying out the Ewald construction in a reciprocal 3D space. The computer software was prepared in the Java programing language. The software can be used to interpret real diffractions patterns for relatively flat surfaces, and thus it may be helpful in broad research practice.

Comparison of azimuthal plots for reflection high-energy positron diffraction (RHEPD) and reflection high-energy electron diffraction (RHEED) for Si(111) surface.

Azimuthal plots for RHEPD (reflection high-energy positron diffraction) and RHEED (reflection high-energy electron diffraction) were calculated using dynamical diffraction theory and then compared. It was assumed that RHEPD and RHEED azimuthal plots can be collected practically by recording the intensity while rotating the sample around the axis perpendicular to the surface (for the case of X-ray diffraction, such forms of data are called Renninger scans). It was found that RHEPD plots were similar to RHEED plots if they were compared at Bragg reflections of the same order. RHEPD plots can also be determined in the region of total external reflection and for such conditions multiple scattering effects turned out to be very weak. The findings for azimuthal plots are also discussed in the context of the formation mechanisms of Kikuchi patterns.

Theoretical analysis of reflection high-energy electron diffraction (RHEED) and reflection high-energy positron diffraction (RHEPD) intensity oscillations expected for the perfect layer-by-layer growth.

Predictions from two theoretical models, allowing one to determine the phase of intensity oscillations, are compared for reflected beams of electrons and positrons. Namely, results of the precise dynamical calculations are compared with results obtained using a simplified approach. Within the simplified model, changes in the specularly reflected beam intensity, expected to occur during the deposition of new atoms, are described with the help of interfering waves and the effect of refraction, and respective approximate analytical formulas are employed to determine the phase of the oscillations. It is found that the simplified model is very useful for understanding the physics ruling the appearance of intensity oscillations. However, it seems that the model with the realistic potential is more suitable for carrying out interpretations of experimental data.