Structural Study of CIGS2 Thin Film Absorbers using EBSD Technique
- PDF / 225,437 Bytes
- 5 Pages / 432 x 648 pts Page_size
- 89 Downloads / 301 Views
Structural Study of CIGS2 Thin Film Absorbers using EBSD Technique Ashwani Kaul1, Shirish A. Pethe1, Neelkanth G. Dhere1 and Helio R. Moutinho2 1 Florida Solar Energy Center, 1679 Clearlake Road, Cocoa, FL 32922, U.S.A. 2 National Renewable Energy Laboratory, Golden, CO, U.S.A. ABSTRACT In this study electron backscatter diffraction (EBSD) investigation is carried out for CuIn1-xGaXS2 (CIGS2) samples that were prepared by two stage process in which the initial precursor was deposited by DC magnetron sputtering followed by sulfurization in conventional furnace. Due to high surface roughness, low quality EBSD signal was obtained in the samples that were initially polished with ion milling. Polishing with dimpler grinder followed by chemical treatment with bromine/methanol solution improved the quality of EBSD patterns. Efforts are being made to build the database for CIGS2 in the system using high quality EBSD patterns and finally to obtain grain orientation maps. INTRODUCTION Electron backscatter diffraction (EBSD) in scanning electron microscopy (SEM) is a powerful technique that allows crystallographic information such as the grain orientation, grain boundaries and also the grain size to be obtained. In a SEM, the electron beam generates various types of signals such as secondary electrons, X-rays and back scattered electrons. The EBSD technique is based on the diffraction of back scattered electrons at the crystalline planes. This generates orientation maps of the region in the vicinity of the sample surface [1-2]. The diffraction of electrons is governed by Bragg’s law and the electrons are diffracted in all directions forming cones that are termed as Kossel cones [3]. However, when the screen is flat and nearly normal to the incident beam, these cones appear as parabolas which look like parallel lines on a fluorescent screen in the area close to the optic axis. These lines are termed as the Kikuchi lines. Kikuchi pattern consists of sets of two mutually parallel Kikuchi lines as shown in figure 1.
r'
e-
ș
r C z*
Figure 1. Schematic of formation of Kikuchi pattern
163
The Kikuchi lines with higher scattering angles to the incident beam are brighter than the background whereas the lines with smaller angle are less intense than the diffuse background. The distance between the parallel lines corresponds to the total scattering angle 2ș. The Kikuchi pattern is characteristic of the crystal structure and orientation of the sample region from which it is generated. The crystal orientation at each point can be determined when the beam is scanned across a polycrystalline sample. The resulting map reveals the constituent grain boundaries, morphology and orientations. A comprehensive and quantitative representation of the microstructure of a sample can be established with EBSD. The important characteristics of EBSD are [4]: 1) The depth from which the diffracted electrons originate; 2) The angle between the sample surface and the electron beam. The EBSD technique analyzes the material few tens of nanometers beneath
Data Loading...
