Electron microscopy study of thermoelectric n-type Bi2(Te0.9Se0.1)3 film deposited by dc sputtering

Abstract

Thermoelectric +90 film of the ternary compound was deposited by dc. sputtering from n-type Bi2Te2.7Se0.3 target on polyimide foil substrate at 200 degrees C. The surface morphology and elemental composition of the deposited film was characterised by scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDX). SEM images and EDX spectra showed that the surface morphology of thermoelectric film exists in the form of big grains with small grains, rough surface and expected structure. The percentage of deviation from stoichiometry was calculated as +/- 3.599% for Bi-2(Te0.9Se0.1)(3). Therefore, it was found that the composition of the film stoichiometry was close to the sputtering target stoichiometry. It was seen from transmission electron microscopy (TEM) images and selected area diffraction (SAD) patterns that the thermoelectric film has poly crystalline structures with nano-sized and different orientations. It was also observed that the film have no second phase, precipitate and separation between the layers. Study of lattice images for the sample was done by high-resolution TEM. d(hkl) values of grains with different orientations were measured and some deformed areas were observed. In addition to, a structural modulation structure was monitorized in the sample. These modulations have a periodicity of approximate 1 nm. (C) 2013 Elsevier Ltd. All rights reserved.