Laser-induced transformation of a-C:H thin films A. Grigonis a ,Z ˇ . Rutkunien _ e a, * , H. Manikowski b , M. S ˇ ilinskas c a Kaunas University of Technology, Physics Department, Student˛ u street 50, LT-51368, Kaunas, Lithuania b Poznan ´ University of Technology, Institute of Physics, Piotrowo street 3, 60-965 Poznan ´, Poland c Institute of Micro-and Sensor Systems, Otto von Guericke University, Universitatsplatz 2, 39106 Magdeburg, Germany article info Article history: Received 16 June 2008 Received in revised form 12 January 2009 Accepted 30 January 2009 Keywords: Diamond-like carbon Laser irradiation Ion beam deposition Raman spectroscopy IR spectroscopy EPR abstract In this work, we report the laser irradiation effects on the properties of various types of amorphous hydrogenated carbon (a-C:H) films. The influence of the initial carbon film (hydrogen concentration, sp 3 / sp 2 ratio, and sp 2 clustering) is studied. The results show that a loss of hydrogen and an increase of the sp 2 phase are the main processes in the laser power range between 1.8 and 5 MW/cm 2 . Only these processes are stronger for ‘‘more polymer-like’’ and ‘‘graphite-like’’ films than for ‘‘more diamond-like’’ films. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Amorphous carbon films are perspective materials for many applications because of their unique physical and chemical prop- erties [1–3]. It was found that laser treatment is very useful tech- nique for precise patterning of carbon films and the pulsed laser processing has some advantages over mechanical and chemical processing [4,5]. In general, the effect of laser irradiation on carbon films is determined by superposition of three processes, such as graphitization, spallation, and evaporation; they are characterized by different threshold intensities [6]. The laser-induced graphiti- zation of the surface layer has the lowest threshold and causes the changes of material properties. Among these changes, a noticeable reduction of the mass density is the most important for the surface morphology, as it leads to a pronounced surface swelling. Two other processes: spallation and evaporation, cause the material removal and lead to the formation of characteristic surface profiles [4]. On the other hand, the laser influence should depend on the properties of a-C:H films. In our previous works, we had investigated the as-deposited a- C:H films [7,8] and some optical properties of laser-irradiated a-C:H films [9]. In this study, we focus our attention on the influence of the nanosecond laser irradiation on the properties of DLC films. 2. Experimental The a-C:H films were deposited on Si wafers to a thickness up to 300 nm. The films were formed by the direct ion beam deposition using different acetylene–hydrogen mixtures (0–91% of H2). Further details were reported elsewhere [7,8]. Three types of a-C:H films can be separated and used for laser irradiation. The main characteristics of the films are given in Table 1 . The films with the ‘‘higher diamond component’’ are abbreviated in this paper as ‘‘DLC’’, the films with ‘‘higher graphite fraction’’ as ‘‘GLC’’, and the films with ‘‘stronger polymer properties’’ as ‘‘PLC’’. It should be emphasized that all films are diamond-like despite the variation of the film characteristics. In order to reduce the influence of atmosphere during the laser irradiation, the a-C:H films were coated by silica using electron beam evaporation of a SiO 2 target. After that the samples were irradiated in a scanning mode with the step of 25 mm by the second harmonic (wavelength l ¼ 532 nm) of a Q-switched YAG:Nd laser with pulses of duration s ¼ 10 ns and repetition rate of 12.5 Hz. Distribution of intensity in the laser beam was close to that of one mode. Diameter of the laser beam spot was 2.5 mm at height of 1/ e 2 . The intensity of laser pulse was varied in the range of 1.8– 10.2 MW/cm 2 (or the energy of a single pulse 25–145 mJ/cm 2 ). The depth distribution of C and impurities were measured by Rutherford backscattering (RBS) technique using a 2 MeV 4 He 2þ beam at a scattering angle of 160  . The hydrogen concentration was determined by elastic-recoil detection (ERD) experiment using * Corresponding author. Fax: þ370 37 456472. E-mail address: zirut@ktu.lt (Z ˇ . Rutkunien _ e). Contents lists available at ScienceDirect Vacuum journal homepage: www.elsevier.com/locate/vacuum 0042-207X/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.vacuum.2009.01.050 Vacuum 83 (2009) S152–S154