RBS, XRD, Raman and AFM Studies of Microwave Synthesized Ge Nanocrystals
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RBS, XRD, Raman and AFM Studies of Microwave Synthesized Ge Nanocrystals N Srinivasa Rao, A P Pathak*, G Devaraju, V Saikiran and S V S Nageswara Rao School of Physics, University of Hyderabad, Central University (P.O), Hyderabad 500 046, India.
ABSTRACT Ge nanocrystals embedded in silica matrix have been synthesized on Si substrate by cosputtering of SiO2 and Ge using RF magnetron sputtering technique. The as-deposited films were subjected to microwave annealing at 800 and 9000C. Rutherford backscattering spectrometry (RBS) has been used to measure the Ge composition and film thickness. The structural characterization was performed by using X-ray diffraction (XRD) and Raman spectrometry. XRD measurements confirmed the formation of Ge nanocrystals. Raman scattering spectra showed a peak of Ge-Ge vibrational mode around 299 cmí1, which was caused by quantum confinement of phonons in the Ge nanocrystals. Surface morphology of the samples was studied by atomic force microscopy (AFM). Variation of nanocrystal size with annealing temperature has been discussed. Advantages of microwave annealing are explained in detail. Keywords: microwave heating, nanostructure, Ge *Corresponding author E-mail: [email protected] Tel: +91-40-23010181/23134316, Fax: +91-40-23010181 / 23010227. INTRODUCTION Quantum confinement effects are known to play an essential role in optical absorption and emission processes in semiconductor nanocrystals since the energy band gap increases with decreasing particle size and electronic states become discrete with higher oscillator strength. In semiconductor nanocrystals the excitons are confined in all three spatial dimensions. As a result, they have different properties than those of bulk semiconductors. Besides, the surface electronic states also affect both electronic and optical properties of semiconductor nanocrystals due to large surface-to-volume ratios [1–3]. For these reasons, enormous amount of research effort has been made worldwide, to synthesize and study these materials. Particularly Si and Ge nanocrystals embedded in a dielectric matrix have been demonstrated as potential candidates for the fabrication of optoelectronic, photovoltaic and nonvolatile memory devices [4–6]. Different annealing techniques have been used for synthesis of Ge nanocrystals such as furnace annealing [7] and rapid thermal annealing [8]. In addition to above annealing methods, microwave annealing has been recognized to be a good technique for synthesizing nanocrystals, having its own advantages. Here, we present a brief report on the principal features and conclusions from our recently published paper [9] “Growth and characterization of nc-Ge prepared by microwave annealing” which was presented as a poster in the Spring, 2011 MRS meeting. Structure of the synthesized films has been evaluated by XRD and Raman spectroscopy. Surface
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morphology of the films was studied by AFM. RBS was used to estimate composition of Ge in as-deposited samples. EXPERIMENTAL DETAILS The composite thin films of Ge and SiO2 were
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