9812051v1 - arXiv:cond-mat/9812051v1 [cond-mat.mtrl-sci] 3...

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Unformatted text preview: arXiv:cond-mat/9812051v1 [cond-mat.mtrl-sci] 3 Dec 1998 IPM-98-17 Jahn-Teller Effect in Diamond-like Carbon M.A. Vesaghi a ∗ and A. Shafiekhani b † a Dept. of Physics, Sharif University of Technology, P.O.Box: 9161,Tehran 11365, Iran b Institute for Studies in Theoretical Physics and Mathematics P.O.Box: 5531, Tehran 19395, Iran Abstract The Jahn-Teller effect used semi-theoretically to analyse UV-visible spec- tra of the diamond like-carbon films on Si substrates. By deconvolution of UV-visible absorption spectra of the typical films, different absorption lines found. For each sample, six lines which were related to V ◦ by Jahn-Teller effect are distinguished. Our theoretical approach based on distortion of the V ◦ as the consequence of the stress in the films, is in agreement with experimental results. The shift of the Jahn-Teller lines toward the zero phonon line of V ◦ were found in accordance to stress decrease in the films. The difference between room temperature and low temperature spectra is discussed. We found that the splitting of the excited state of V ◦ in the films under stress is twice as large as that of the ground state. Typeset using REVT E X ∗ e-mail address: [email protected] † e-mail address: [email protected] 1 I. INTRODUCTION There is a growing interest in vacancies and vacancy related effects in DLC, a-C and a-C:H films from theoretical and experimental points of view. Despite large improvement in the preparation techniques for these type of films, a large number of vacancies is present in such films [1]. This is due to the nature of preparation since practically it is not possible to make films free of vacancies. Different varieties of vacancies exist in these films but the main ones are neutral-single vacancy V ◦ , one carbon with its four valance electrons is missing, and negatively charged- single vacancy V − , one carbon with its three valance electrons is missing. Such vacancies exist in natural diamond or are made in it by neutron, electron or gamma bombardment [2–4]. These vacancies have peculiar absorption, photoluminescence (PL) and cathodlu- minescence (CL) emission . All the PL, CL and absorption spectra show many feature, including different peaks and shoulders [5–8]. The GR1 band with zero phonon line at 1.673 eV and ND1 with zero phonon line at 3.149 eV are associated with V ◦ [9] and V − [10], respectivly. Much work is done on the effect of uniaxial stress in natural diamond to explain lines of GR1 band [9,12–14]. It is reported that for films there is a strong correlation between PL intensity and stress [11] and also, between the line-width of zero phonon line and film strain [15,7] In recent years, considerable attention has been paid to the degenerate electron-lattice in- teraction in molecules and defect centres in solids, called Jahn-Teller effect (JTE) [16,17,10]....
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9812051v1 - arXiv:cond-mat/9812051v1 [cond-mat.mtrl-sci] 3...

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