Influence of Hydrogen Content and Carbon Hybridizations on Optical Properties of A-C:H Thin Films Obtained by PECVD

摘要

Hydrogenated amorphous carbon (a-C:H) have recently received considerable attention because they posses interesting properties like extreme hardness, chemical inertness and optical transparency. In this work, the optical properties of a-C:H thin films prepared by r.f. plasma enhanced vapor deposition from a CH_4/Ar or CH_4/He gas mixtures are investigated. The optical gap E and the Urbach gap parameter E_u have been determined by optical-ultraviolet absorption characteristics. The Urbach disorder parameter and the optical gap are important parameters to characterize a-C:H. These parameters depend on initial disorder, hydrogen content and sp~3/sp~2 ratio. Elastic Recoil Detection Analysis, Infrared and Raman spectroscopies have been respectively used to quantify hydrogen content, the bonding and sp~2 carbon proportion of thin films. We have found that optical band gap E of these films decrease with the loss of hydrogen (bonded and unbonded) and increasing sp~2 content with E_u gap increase indicating a structural disorder increase with the loss of hydrogen. Moreover, sp~2 clusters sizes obtained from Raman scattering decrease with decreasing hydrogen content.