Surface and Bulk Microstructural Modifications in Amorphous Carbon Films after Post-Growth Low Energy Ion Beam Irradiati
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Surface and Bulk Microstructural Modifications in Amorphous Carbon Films after PostGrowth Low Energy Ion Beam Irradiation P. Patsalas and S. Logothetidis Department of Physics, Aristotle University of Thessaloniki, GR-54006 Thessaloniki, Greece. ABSTRACT We present the crystallization effects occurring in sputtered amorphous Carbon (a-C) thin films deposited on Si induced by post-growth low energy (0.5-1.5 keV) Ar+ ion beam irradiation (IBI). The a-C films after IBI have the form of an amorphous matrix with embedded crystalline regions. X-ray diffraction and Electron Microscopy measurements identified the crystalline phases of carbon and SiC. We study in detail the effects of ion energy and fluence on the crystallization process. It was found that low fluence (~2x1016 ions/cm2) of ions with an optimum ion energy (~1.5 keV) promoted the diamond formation. X-Ray Reflectivity (XRR) and Spectroscopic Ellipsometry were used to study the amorphous matrix. XRR discriminated the IBI induced surface and bulk effects through the density and the a-C surface roughness, showing surface smoothing to be more prominent for low energy IBI.
INTRODUCTION Amorphous Carbon (a-C) films have the form of an amorphous network which consists of three- (sp2) or four-fold (sp3) co-ordinated sites and exhibits some exceptional properties, such as ultra high hardness, variable band gap and optical transparency, providing considerable technological importance. Magnetron Sputtering has been used to grow a-C films with controllable amount of sp3 sites [1,2]. We have recently shown [3-5], that post-growth ion beam irradiation (IBI) induces phase transformations in sputtered a-C films. The IBI induced crystallization is a general characteristic of carbon since it has been reported for different kinds of carbon materials such as sputtered a-C films [3-5], tetrahedral a-C (ta-C) films [6] and carbon onions [7,8]. Although a-C has significant scientific interest and technological importance, the ion irradiation induced crystallization of a-C has not been studied extensively as other elements of group IV such as Si [9] and Ge [10]. Post-growth ion irradiation of Carbon [3-5,7,8,11] with low energy ions has lately gained attention, in contrast to ion irradiation of a-C films during deposition where there is a vast literature [12-16]. In this work, we address the structural modifications and the surface morphology of sputtered a-C films after post-growth IBI with varying ion energy (0.5-1.5 keV) and fluence (250x1016 ions/cm2), in order to investigate the appropriate irradiation conditions for diamond nucleation. Combined Transmission Electron Microscopy (TEM) and X-Ray Diffraction (XRD) identified the crystalline phases formed in the films after IBI [3,17]. However, TEM suffers from providing only information about the local structure of the films. XRD was employed to study quantitatively the structural modifications of a-C films due to its large sampling volume taking into account the mean structural characteristics instead of the films’ local structure
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