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Analysis of the ellipsometric spectra of amorphous carbon thin films for evaluation of the sp<sup>3</sup>-bonded carbon content

Lee, J and Collins, RW and Veerasamy, VS and Robertson, J (1998) Analysis of the ellipsometric spectra of amorphous carbon thin films for evaluation of the sp<sup>3</sup>-bonded carbon content. Diamond and Related Materials, 7. pp. 999-1009. ISSN 0925-9635

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Abstract

Using spcctroscopic ellipsometry (SE), we have measured the optical properties and optical gaps of a series of amorphous carbon (a-C) films ∼ 100-300 Å thick, prepared using a filtered beam of C+ions from a cathodic arc. Such films exhibit a wide range of sp3-bonded carbon contents from 20 to 76 at.%, as measured by electron energy loss spectroscopy (EELS). The Taue optical gaps of the a-C films increase monotonically from 0.65 eV for 20 at.% sp3C to 2.25 eV for 76 at.% sp3C. 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 sp2C and sp3C components. The most widely used EMT, namely that of Bruggeman (with three-dimensionally isotropic screening), yields atomic fractions of sp3C 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 sp3C from SE using the Bruggeman EMT shows good numerical agreement with the atomic percent sp3C 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 sp2C and sp3C components. © 1998 Elsevier Science S.A.

Item Type: Article
Subjects: UNSPECIFIED
Divisions: Div B > Solid State Electronics and Nanoscale Science
Depositing User: Cron Job
Date Deposited: 17 Jul 2017 19:22
Last Modified: 21 Jun 2018 02:17
DOI: