Accession Number:

ADP012245

Title:

Optical Characterization and Modeling of Sulfur Incorporated Nanocrystalline Carbon Thin Films Deposited By Hot Filament CVD

Descriptive Note:

Corporate Author:

PUERTO RICO UNIV SAN JUAN DEPT OF PHYSICS

Personal Author(s):

Report Date:

2001-11-01

Pagination or Media Count:

7.0

Abstract:

Sulfur incorporated nanocrystalline carbon n-CS thin films grown on molybdenum substrates by hot-filament chemical vapor deposition HFCVD using gas mixtures of methane, hydrogen and a range of hydrogen sulfide H2S concentrations are optically examined using Raman spectroscopy RS and ex sin spectroscopic phase modulated ellipsometry SPME from near IR to near UV 1.5-5.0 eV obtaining their vibrational frequencies and pseudodielectric function, respectively. The ellipsometry data epsilonsub rE , epsilonsub iE were modeled using Bruggeman effective-medium theory BEMT and five parameters Forouhi and Bloomer FB dispersion Model. A simplified two-layer model consisting of a top layer comprising an aggregate mixture of spsup 3Cspsup 2Cvoid and a bulk layer L2, defined as a dense amorphized FB-modeled material was found to simulate the data reasonably well. Through these simulations, it was possible to estimate the dielectric function of our n-CS material, along with the optical bandgap Esub g, film thickness d, and roughness layer sigma as a function of H2S. The physical interpretations of the modeling parameters obtained were discussed. The Raman and ellipsometry results indicate that the average size of nanocrystallites in the sulfur-incorporated carbon thin films becomes smaller with increasing H2S concentration, consistent with AFM measurements. The bandgap was found to decrease systematically with increasing H2S concentration, indicating the enhancement of midgap states and spsup 2 C network, in agreement with RS results. These results are compared to those obtained for the films grown without sulfur n-C, in order to study the influence of sulfur addition to the CVD process. This analysis led to a correlation between the film microstructure and its electronic properties.

Subject Categories:

  • Solid State Physics

Distribution Statement:

APPROVED FOR PUBLIC RELEASE