Kikuchi Electron Diffraction Patterns Research Articles

Enhancement of several Kikuchi lines in the vicinity of spot reflections

Kikuchi electron diffraction patterns of silicon have been obtained which demonstrate the simultaneous enhancement of several excess Kikuchi lines near different point reflections. This enhancement is explained within the elementary mechanism of the formation of Kikuchi patterns while taking into account the Kikuchi electron double diffraction.

Mechanism of formation of curved Kikuchi lines

The mechanism of formation of curved Kikuchi lines, observed at displacement of point reflections from their normal positions, is proposed. Curving of Kikuchi lines is explained taking into account the participation of diffracted electron beams in the formation of Kikuchi electron diffraction patterns.

Holographic images of Pt(111) using Kikuchi electron diffraction

Three-dimensional atomic images of a Pt(111) surface are obtained by direct inversion of multiple low-energy Kikuchi electron-diffraction patterns. The images are in the backscattering direction, and the positions of the images are consistent with those expected from the atomic structure near the Pt(111) surface. The strong electron scattering of the Pt atoms causes no observable problems in the Kikuchi electron holography.

Holographic inversion of Kikuchi electron diffraction patterns for thin epitaxial NaCl films grown on GaAs(001)

Normal-incidence, multiple-energy Kikuchi electron diffraction patterns (holograms) have been measured for clean GaAs(001) surface and for thin NaCl films epitaxially grown on a GaAs(001) substrate. Three-dimensional atomic images of both structures have been obtained directly by the integral-energy phase-summing method. For the clean semiconductor surface, the superimposed images of Ga and As bulk atoms were well resolved within an accuracy of 0.5 Å. A distinctly different local atomic configuration was found after the deposition of the epitaxial NaCl film. Possible models of the NaCl/GaAs(001) epitaxy are discussed. A detailed analysis of the reconstructed diffraction patterns revealed that an initial formation of the Cl–Ga bond occurred in the system, and after deposition of 5 ML NaCl, the substrate was uniformly covered by a layer at least 3 ML thick.

The potential engineering of grain boundaries through thermomechanical processing

Grain boundary character distribution is a relatively new microstructural feature that describes the proportions of random and special grain boundaries as defined by the coincident site lattice model. The combination of the availability of a new experimental technique based on the automatic indexing of backscatter Kikuchi electron diffraction patterns in the scanning electron microscope (orientation imaging microscopy) and reports in the literature describing the optimization of the grain boundary character distribution through thermomechanical processing are making the potential for enhanced materials properties in commercial metals and alloys a reality. Although the effects of optimizing the grain boundary character distribution in the cost-effective improvement of properties have been documented, the potential for commercialization has limited the disclosure of processing details. In this article, two separate approaches to the optimization of the grain boundary character distribution in oxygen-free electronic copper at Lawrence Livermore National Laboratory are discussed.

New method for rapid determination of crystal orientation via Kikuchi patterns

Kikuchi electron diffraction patterns are used extensively to determine crystal orientations via transmission electron microscopy (TEM) or in the electron backscattering pattern (EBSP) mode of scanning electron microscopy (SEM). A new method is presented that is capable of finding crystal orientations, the camera length, and the projection center from only one pattern per grain using a least-squares technique. This method eliminates the need to perform an alignment with a reference crystal in the backscattering mode. Application to a Σ = 13a silicon bicrystal is presented for TEM patterns and EBSP's. A complete analysis of the propagation of random measurement errors into the disorientation axis/angle pair is carried out. The root mean square deviation from the nominal disorientation angle is found to be 0.3°in the case of TEM and 0.5°in the case of EBSP. The root mean square inclination between the nominal and measured disorientation axis is found to be 1°in the case of TEM and 0.5°in the case of EBSP.

Surface sensitivity of Kikuchi-electron diffraction patterns.

Since the realization by several workers that the electron diffraction from localized sources can be interpreted in a holographic sense, there has been increasing interest in electron holography. Photoelectron and Auger electrons are considered good localized electron sources, but their use experimentally in holography usually requires access to a synchrotron radiation source. We report here the use of our technique to obtain Kikuchi-electron diffraction (KED) patterns using normal low-energy electron-diffraction facilities. This technique improves the KED signal-to-noise ratio and allows us to take KED patterns over a wide range of energies within a short time. Using this method we have shown that Kikuchi electrons can be treated as having come from localized emitters. The results presented here clearly show the surface sensitivity of KED images in the energy range 450--800 eV. This sensitivity is revealed by the subtraction of the bulk contribution to the KED images by acquiring two image sets under exactly the same conditions, one from Si(111)(\ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 )R30\ifmmode^\circ\else\textdegree\fi{}-Pb and one from Si(111)7\ifmmode\times\else\texttimes\fi{}7, and subtracting them. Furthermore, these difference images show intensities which are very strongly dependent on the primary energy, unlike the raw KED images. This energy dependence suggests that a backscattering geometry is dominating the contributions to the intensities in these difference images.

A new approach to obtaining Kikuchi electron diffraction patterns for holographic imaging

A newly developed method is reported here for taking Kikuchi electron diffraction patterns using conventional low-energy electron diffraction facilities. Kikuchi electron forward-scattering diffraction patterns from a single crystal Cu(111) surface have been obtained using a hemispherical rear-view LEED screen and camera interfaced to a computer. The new technique allows us to take a set of Kikuchi electron diffraction images over a wide primary energy range (50–950 eV in steps of 5 eV) within a couple of hours. With this technique we show that the Kikuchi electron, like the photoelectron and Auger electron, can be considered as being emitted from inside the crystal.

Concentric-shell algorithm for Auger and core-level photoelectron diffraction: Theory and applications.

A full multiple-scattering method is described for the calculation of angle-resolved photoelectron, Auger-electron, and Kikuchi-electron diffraction patterns. The method is particularly useful for the range of electron kinetic energies from about 50 eV to a few thousand eV. Approximations that take advantage of the finite experimental angular resolution, and, for the higher electron kinetic energies, the dominant electron forward scattering, are implemented, and may be used to improve computational efficiency. Comparisons of calculations with an experimental LVV Auger dif- fraction pattern from a Cu(001) surface show excellent agreement. The simulated diffraction patterns are also used to investigate the effects of holographic reconstruction in the case of the adsorbate system O/Ni(001), where we examine the influence of multiple scattering. In the case of the Cu(001) diffraction pattern, we examine the effects of the thickness of a film on holographic reconstruction.

Computer-aided prediction and analysis of electron and x-ray diffraction patterns

Using a personal computer, electron and x-ray diffraction patterns are analytically generated and printed to scale. The structure factor equation is used to determine which crystalline planes diffract according to the supplied crystal lattice type, atoms present and their positions in the unit cell, lattice dimension(s), crystal orientation, and radiation wavelength. Single crystal spot and Kikuchi electron diffraction patterns as well as polycrystalline ring patterns can be generated. Powder x-ray diffraction patterns are also generated using this code. Complex composite patterns are generated by overlaying multiple patterns resulting from crystallographic orientation effects. A user friendly program with a direct approach to generate diffraction patterns for any defined crystal aids in the analysis and indexing of these patterns.

Measurement of lattice damage caused by ion-implantation doping of semiconductors†

Discussion of two new techniques used to measure the lattice damage produced in GaAs by the implantation of 60 keV cadmium ions. In the first method, optical reflection spectra of the ion-implanted samples were measured in the wavelength range from 2000 to 4600 A. The decrease in reflectivity resulting from ion-implantation was used to determine the relative amount of lattice damage as a function of ion dose. The second technique employed the scanning electron microscope. Patterns very similar in appearance to Kikuchi electron diffraction patterns are obtained when the secondary and/or backscattered electron intensity is displayed as a function of the angle of incidence of the electron beam on a single crystal surface. The results of measurements made by both methods are compared with each other and with data obtained by the method of measuring lattice damage by Rutherford scattering of 1 MeV helium ions.

ELECTRON BEAM CHANNELING IN SINGLE-CRYSTAL SILICON BY SCANNING ELECTRON MICROSCOPY

An annular semiconductor diode detector was used in a Cambridge Stereoscan electron microscope to resolve beam-orientation-dependent backscattered electron images not only as bands but also as extremely complicated defect and excess line patterns with angular resolution ≤ 5 × 10−4 rad. The resultant patterns are similar in appearance to transmission and reflection Kikuchi electron diffraction patterns.

Further Applications of Kikuchi Diffraction Patterns; Kikuchi Maps

Composite Kikuchi electron diffraction patterns have been obtained which map out reciprocal space for silicon over the 〈001–011–111〉 stereographic triangle. These maps enable unknown diffraction patterns to be quickly solved even when they do not contain any Kikuchi poles. Unlike spot patterns, the Kikuchi patterns and maps uniquely represent the crystal symmetry. Some applications of these maps in crystallographic and electron microscopy investigations are discussed.