Cryst. Res. Technol. 41, No. 1, 59 – 63 (2006) / DOI 10.1002/crat.200410530 © 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Transmission electron microscopy and Rutherford backscattering spectrometry studies of Ag 2 Te films formed from Ag-Te thin film couples B. C. Mohanty and S. Kasiviswanathan* Department of Physics, Indian Institute of Technology Madras, Chennai 600 036, India Received 23 November 2004, accepted 9 December 2004 Published online 15 December 2005 Key words thin films, Ag 2 Te, TEM, RBS. PACS 68.55.-a, 68.37.Lp Formation of Ag 2 Te thin films from room temperature (300 K) solid state reaction of Ag and Te thin film couples is investigated. Rutherford Backscattering Spectrometry (RBS) studies confirmed the complete miscibility of the couples and the stoichiometry of the resulting Ag 2 Te. Structural analysis by Transmission Electron Microscopy (TEM) showed a fine-grained structure with monoclinic and orthorhombic phases. Annealing at high temperatures resulted in the growth of giant crystallites with monoclinic phase at random sites. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1 Introduction Silver chalcogenides have long been the subject of experimental and theoretical studies for their ionic conductivity, polymorphism and semiconducting properties [1-2]. The recent discovery of giant magnetoresistance (GMR) [3-5] in silver chalcogenides has deepened the interest, in particular in Ag 2 Te as it has opened up new challenges from theoretical and application points of view. Ag 2 Te undergoes a first order phase transition at ~ 418 K. The high temperature phase is characterized by a cubic phase and enhanced ionic conductivity [6]. Below the transition temperature, Ag 2 Te is a narrow band-gap semiconductor, with band gap in the range 0.04 - 0.17 eV [7]. Monoclinic and orthorhombic structures have been reported for the low temperature phase [8-11]. The structure of off-stoichiometric bulk Ag 2 Te (Ag 2+δ Te) on which the first observation of GMR has been made is reported to be orthorhombic [3]. However, the structure of Ag 2±δ Te thin films that also show similar GMR is found to be monoclinic [4-5]. The present work is aimed at investigating the formation of Ag 2 Te thin films from reaction of Ag and Te thin film couples at 300 K. An important advantage of the growth of Ag 2 Te film from bilayer structure is the possibility to precisely control the composition, which is crucial to the observed GMR [12]. The phase formation of the films has been studied using TEM with emphasis on the microstructure of the films. The composition analysis of the films has been done by RBS. TEM studies have also been made on films annealed at 373 K and 473 K, in order to observe the effect of heat treatment at temperatures below and above the phase transition temperature (418 K). 2 Experimental Ag 2 Te thin films were prepared by solid state reaction of Ag and Te films at 300 K. The Ag-Te bilayers were formed by depositing a thin Ag film followed by a Te film of suitable thickness. The thicknesses of the individual films were so chosen to ensure the stoichoimetry of the final compound. The base pressure during the film growth was about 10 -4 Pa. The rate of deposition and the thickness of the films were monitored in situ by a quartz crystal thickness monitor. The as-deposited samples were vacuum annealed at a pressure of 2×10 -4 Pa for one hour at 373 K and 473 K. The structure and phase purity of the as-deposited and annealed films grown on glass substrates were investigated by a Philips CM-12 transmission electron microscope. The ____________________ * Corresponding author: e-mail: kasi@iitm.ac.in