Optical properties of Diamond like Carbon films prepared by DC-PECVD

S Tshomo,R Hussin,M.N Md.Yusuf,S Sholehah Hussein,K Deraman,W.N Wan Shamsuri,A.K Mohsin,B Ismail

doi:10.11113/mjfas.v8n2.129

Abstract

Diamond-like carbon (DLC) thin films were deposited at different substrate temperatures using methane and hydrogen gas in DC-PECVD at 2x10-1Torr. From the light transmission using UV-VIS spectroscopy it was found that the optical transition had changed from allowed indirect transition to allowed direct transition as the substrate temperature increased. The Optical gap increased with temperature, highest of 3.034 eV was observed at 573 K, beyond which it dropped. Colour of the film changed from light brownish to a colourless transparent film in the higher temperature. The Urbach energy decreased from 1.25 eV to 0.75 eV with increasing substrate temperature till 573 K and a slight increase after it. This trend is attributed to change in sp3/sp2 ratio or change in structure. The cluster size decreases with temperature, resulting in larger band gap and the structure more ordered. Similar pattern is also witnessed in the emission spectrum of the photoluminescence.

Highlights

Diamond like Carbon (DLC) usually designates a form of hydrogenated carbon (a-C:H) containing lesser than 50% of sp3hybridisation[1] Commonly, amorphous carbon can have a mixture of sp3,sp2and even sp1 with presence of hydrogen
UV-VISspectrophotometric measurement of light transmission indicated that optical transition changed from allowed indirect to allowed direct as the substrate temperature increased in DLC films
Optical band gap increased with temperature with a maximum observed at 573K of 3.034 eV and a decrease beyond that temperature

Summary

INTRODUCTION

Diamond like Carbon (DLC) usually designates a form of hydrogenated carbon (a-C:H) containing lesser than 50% of sp3hybridisation[1] Commonly, amorphous carbon can have a mixture of sp3,sp2and even sp with presence of hydrogen. As its presence is known to stabilize the sp3bond[3, 4]. It has gained remarkable interest in films and ‘Diamond like’ coating due to desirable properties ranging from low dielectric constant, high band gap, chemical inertness and extreme hardness. In addition optical gap is found to have a significant dependence on deposition parameters which defines the sp and sp2ratio [2, 3] leaving more room to fabricate desired films. The present paper will concentrate on the change in optical properties of films deposited at with different substrate temperature ranging from 373K to 673K while other parameters were fixed at certain value

EXPERIMENTAL

RESULTS & DISCUSSION

Photoluminescence

Conclusion