부산대학교 도서관

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/S0925-9635(97)00341-5 Byline: Joungchel Lee (a), R.W. Collins (a), V.S. Veerasamy (b), J. Robertson (b) Abstract: Using spectroscopic ellipsometry (SE), we have measured the optical properties and optical gaps of a series of amorphous carbon (a-C) films [approximately equal to] 100-300 A thick, prepared using a filtered beam of C.sup.+ ions from a cathodic arc. Such films exhibit a wide range of sp.sup.3-bonded carbon contents from 20 to 76 at.%, as measured by electron energy loss spectroscopy (EELS). The Tauc optical gaps of the a-C films increase monotonically from 0.65 eV for 20 at.% sp.sup.3 C to 2.25 eV for 76 at.% sp.sup.3 C. Spectra in the ellipsometric angles (1.5-5 eV) have been analyzed using different effective medium theories (EMTs) applying a simplified optical model for the dielectric function of a-C, assuming a composite material with sp.sup.2 C and sp.sup.3 C components. The most widely used EMT, namely that of Bruggeman (with three-dimensionally isotropic screening), yields atomic fractions of sp.sup.3 C that correlate monotonically with those obtained from EELS. The results of the SE analysis, however, range from 10 to 25 at.% higher than those from EELS. In fact, we have found that the volume percent sp.sup.3 C from SE using the Bruggeman EMT shows good numerical agreement with the atomic percent sp.sup.3 C from EELS. The SE-EELS discrepancy has been reduced by using an optical model in which the dielectric function of the a-C is determined as a volume-fraction-weighted average of the dielectric functions of the sp.sup.2 C and sp.sup.3 C components. Author Affiliation: (a) Materials Research Laboratory and Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA (b) Department of Engineering, University of Cambridge, Trumpington Street, Cambridge, CB2 1PZ, UK Article History: Received 22 April 1997; Accepted 28 November 1997