TEM image simulation of silicon carbide using multislice technique

• Main Author: Saw, Ann Nee.
• Other Authors: Oh Joo Tien
• Format: Final Year Project
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering
• Online Access: http://hdl.handle.net/10356/52653
• Institution: Nanyang Technological University

The objective of this project is to study on the variables that could have an effect on the resolution and phase contrast of a simulated High Resolution Transmission Electron Microscope (HRTEM) image. This project also aims to identify the optimal values of the variables in order to obtain the best resolution simulated image of a Silicon carbide specimen. Artefacts occur in experimental TEM image, which cause image to appear blur and distorted. Computer simulation of HRTEM image is utilised as a reference for experimentally determined TEM image. In addition it provides useful information for researcher to understand materials structure and compositions. The Crystal Maker programme is a crystal visualization programme that enables us to input space group and lattice parameter in order to obtained the atomic positons of atoms in the specimen.With the atomic positions, the projected atomic potential for each layer in a unit cell can be generated via atompot software [1]. The calculated atomic potential for each layer were then inputted into the Multislice software. Multislice is a method which divides the crystal samples into many slices of same thickness and each slice is assume to be a simple phase shift of the electron wave meaning that the thin slice of specimen do not absorb electrons energy [1]. The incident electron beam has high energy and it is capable to propagate and transmit between the slices of specimen without much variation in electron wavelength [1]. The image software is then run to simulate the final image with the effect of spherical aberration taken into account. To obtain optimal HRTEM image we need to consider the variables that will affect the quality of the image i.e. Defocus value, thickness of the sample and accelerating voltage. Contrast transfer function (CTF) graph is plotted to determine the optimal defocus value and accelerating voltage. CTF plot is consider optimal when it remains almost constant close to -1, it indicates broad band of good transmittance. The intensity graph is plotted to determine the optimal thickness of crystal sample for HRTEM image. Accelerating voltage provides energy for electron beam to interact with crystal sample, the higher the accelerating voltage the shorter the electron wave and hence the higher is the resolution of image.