Diamond and Related Materials 11 (2002) 262–267 0925-9635/02/$ - see front matter  2002 Elsevier Science B.V. All rights reserved. PII: S0925-9635 Ž 01 . 00695-1 Time-dependent in-situ Raman observation of atomic hydrogen etching on diamond-like carbon films C.-L. Cheng *, C.-T. Chia , C.-C. Chiu , I.-N. Lin a, b c d Department of Physics, National Dong Hwa University, Hua-Lien, Taiwan 974, Republic of China a Department of Physics, National Taiwan Normal University, Taipei, Taiwan 117, Republic of China b Institute of Materials Science, National Dong Hwa University, Hua-Lien, Taiwan 974, Republic of China c Material Science Center, National Tsing-Hua University, Hsinchu, Taiwan 300, Republic of China d Received 2 February 2001; received in revised form 12 November 2001; accepted 18 November 2001 Abstract In-situ time-dependent Raman spectra were measured on the thermal annealing of diamond-like carbon films produced by Pulsed Laser Deposition (PLD-DLC), with or without the presence of atomic hydrogen etching. It was found that annealing transformed DLC films into a graphitic structure in both cases and this transformation was completed within 30 min of annealing. Atomic hydrogen etches away the G*s1500 cm band, revealing the existence of the D*s1200 cm band. Both G*- and y1 y1 D*- phases are as stable as graphite during thermal annealing. These observations separate the effects of thermal annealing and annealing with atomic hydrogen etching on diamond-like carbon films.  2002 Elsevier Science B.V. All rights reserved. Keywords: Hydrogen etching; Diamond-like carbon; Raman spectroscopy; Thermal annealing; Field emission 1. Introduction Diamond-like carbon (DLC) thin films have attracted much attention recently due to their unique properties w1,2x. This amorphous form of carbon (a-C) can be produced using various methods, and can contain a significant fraction of sp bonds (a-tC) for various uses 3 including mechanical, electronic, optical and bio-medi- cal applications w3–6x. The properties of the DLC films are directly related to the microscopic structural, ele- mental and carbon bonding structure w7x. One promising application of DLC films is the electron emitter in vacuum microelectronic devices. Impressive field emis- sion characteristics with a low turn-on electric field have been reported w8x and the mechanism of field emission has been proposed w9x. It is now believed that the properties of DLC depend on the structure of the film. Thermal annealing is an effective method to alter the structure of DLC films. Thermal stability, stress and hence film applications can be changed via thermal * Corresponding author. Tel: q886-3-866-2500, ext. 21506; fax: q886-3-866-2303. E-mail address: clcheng@mail.ndhu.edu.tw (C.-L.-L. Cheng). annealing w10–12x. Many results have been observed concerning thermal annealing of DLC films and amor- phous carbons produced from various methods w10–14x. It is now understood that annealing transforms the DLC films from amorphous carbon to a graphitic structure. Among various forms of diamond-like carbon films, hydrogen containing DLC films (a-C:H) show poor thermal stability while excellent temperature stability can be obtained for a-tC with higher sp -bonding car- 3 bons w10x. Raman spectroscopy has been a useful, non-destruc- tive tool in providing the structural information of the films and is now routinely used for the characterization of the DLC films due to its non-destructive nature of the investigation w15,16x. The effect of thermal anneal- ing changes the structure of the film from amorphous form to a graphititic structure as can be seen from the Raman spectra. Atomic hydrogen etching on the DLC film has proven to be an effective method in modifying the film structure, which causes a distinct change of the carbon bonding in the graphitization process w17,18x. As seen from Raman spectra, hydrogen etching of the DLC film results in different changes in the D- and G-bands, both in the band positions evolution and the relative