| AVS 54th International Symposium | |
| Renewable Energy Science & Technology Topical Conference | Wednesday Sessions |
| Session EN+TF+SS-WeA |
| Session: | Photovoltaics, Fuel Cells, and Alternative Energy Materials and Applications |
| Presenter: | H.R. Moutinho, National Renewable Energy Laboratory |
| Authors: | H.R. Moutinho, National Renewable Energy Laboratory R.G. Dhere, National Renewable Energy Laboratory C.-S. Jiang, National Renewable Energy Laboratory B. To, National Renewable Energy Laboratory M.M. Al-Jassim, National Renewable Energy Laboratory |
| Correspondent: | Click to Email |
Electron backscatter diffraction (EBSD) utilizes the electron beam of a scanning electron microscope (SEM) to investigate the crystallographic orientation of materials with high spatial resolution. In EBSD, some of the electrons of the SEM beam are diffracted by the crystalline planes of the sample and collected by a detector, where they form a pattern of Kikuchi lines. These patterns are characteristic of the crystal structure and orientation, and they are collected while the electron beam is being scanned, forming maps of crystallographic orientation. In contrast to X-ray diffraction, which gives the crystallographic orientation of a macroscopic volume of the bulk sample, EBSD provides the individual orientation of volumes with nanometer dimensions. To optimize the EBSD signal, the sample must be inclined by about 70° in relation to the electron beam. Consequently, in rough samples, topographic features shadow some of the diffracted electrons from reaching the detector; thus surface preparation is a common requirement. In this work, we describe the surface processing of CdTe thin films deposited by close-spaced sublimation and physical vapor deposition (PVD). Most of the films studied were too rough to produce good EBSD data. Polishing flattened the sample, but created an amorphous layer on the surface, resulting in no diffraction patterns. Ion-beam milling was not as effective in flattening the surface, but removed rough surface features, resulting in high-quality EBSD data. Etching and light ion milling after polishing also produced good results. After optimizing the sample preparation process, we studied PVD CdTe samples after CdCl2 treatment using dipping or vapor processes, with different parameters. We observed a striking difference in the sample microstructure depending on the CdCl2 process and parameters–with grain sizes varying from a few to several dozen micrometers. Our results showed that maintaining a steady source of CdCl2 during the treatment, compared to a fixed amount, results in completely different recrystallization dynamics. We also studied the grain structure from the substrate to the surface by doing EBSD in cross sections of the samples, as well as analyzing samples after different degrees of polishing.