A study of structure properties of ZnS nano-crystals using electron crystallography

Abstract

Poster Sessions depending on the experimental condition [1][2][3][4]. The deficient line is black and the excess line white on photograph. The deficient-excess unindexed line is black on one side and white on the other side of the line. In the present work for the first time the contrast reversal along the unindexed line is obtained. The specimens were single crystalline silicon films prepared by chemical etching of bulky crystals. The transmission electron diffraction patterns were obtained in an EG-100M electron diffraction camera at an accelerating voltage of 100kV with the primary electron beam almost parallel to [111] axis. In the obtained Kikuchi patterns the unindexed line runs along the middle line of the Kikuchi band. The deficient unindexed line in the vicinity of the strong and spot reflections changes the contrast and transforms into excess line. The experimental conditions of unindexed line contrast reversal are founded. It is shown that the contrast is reversed when unindexed line passes through or in vicinity of an intense spot reflection. The contrast reversal of unindexed line is explained within the framework of the Kikuchi patterns formation mechanism with due regard for the double Kikuchi diffraction [5] The synthesis of new nanocrystalline structures demands new rapid methods of solving their crystal structures. Our goal is real-time structure solution at the electron microscope, based on automated acquisition of three-dimensional electron diffraction data with subsequent phasing of the data set and presentation of a unit-cell potential map that displays atomic positions and even species. To achieve this we must consider: 1) translation of the specimen during automated tilting; 2) automated recognition of zone-axis orientations; 3) multiple-scattering artifacts; 4) indexing methods; 5) absolute intensity scaling of the data; 6) scaling of data collected at different orientations; and 7) the phase problem. Initially, we have focused on issues 3) through 7) following manual acquisition of three-dimensional diffraction data from a known test crystal (the MgAl2O4 spinel structure). Data was collected by two techniques, both of which minimize multiple-scattering artifacts: precession electron diffraction (PED) and kinematic convergent beam electron diffraction (CBED) using an in-column Omega energy filter. After indexing and scaling, experimental structure-factor magnitudes were obtained from the patterns. These provide input to the charge-flipping algorithm [1], which works well with relatively poor-quality electron diffraction data or powder diffraction data [2], to solve the phase problem and obtain the correct crystal structure. Solutions for PED and kinematic CBED data are presented for comparison with each other and with simulations. Further development requires automated, scripted control of specimen tilt and data acquisition.[1] G. Oszlanyi and A. Suto. Acta Cryst., A60, 134 (2004).[2] J.S. Wu, J. Spence, M. O'Keeffe, and K. Leinenweber. Nat. Mater., 5, 647 (2006 A new metastable zirconi...