Cage Breaking Threshold in DLPD of C 60
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CAGE BREAKING THRESHOLD IN DLPD OF C60
YUSUF S. HASCICEK*, ALFRED KLEINHAMMES, LOUIS R. TESTARDI Department of Physics, Florida State University, Tallahassee, FL 32306 USA.
ABSTRACT Thin film patterns of desired shape or configuration made of about 15 Am - lines were directly written from a disk of C60 by employing a new laser technique called direct laser patterned deposition (DLPD). DLPD is an ambient technique, needing no special environment or material preparation. Since the ablation and deposition are very localized and deposition and patterning are done in one step this is a very cost efficient process. An energy density threshold was found. Above this density resistance of DLPD films dropped sharply indicating that the C60 cage was broken at least in part of the film. INTRODUCTION The new form of carbon, C60, was first found among other large clusters of carbon by Kroto t et al. in 1985. There have been an avalanche of studies since Kratschmer 2 et al. succeeded in producing large quantities of this material. The discovery of superconductivity over 30K in alkali-metal doped 3 C60 and growth of diamond films4 on C70 made these new forms of carbon even more interesting from both technological and theoretical point of view. Here we report on a new laser technique called direct laser patterned deposition (DLPD), and an energy density threshold. Above this energy density, resistance of DLPD films dropped sharply indicating that the C60 cage was broken at least in part of the film. EXPERIMENTAL Direct laser patterned deposition has been described elsewhere 5 in detail. Briefly
Laser
Computer
Transparent Substrate ---
Bulk a et xy Stage
Fig. 1. Experimental set up of DLPD
Fig. 2. A DLPD pattern (line width is 50 pm)
* presently at: National High Magnetic Field Laboratory, Florida State University, 1800 E. Paul Dirac Dr. Tallahassee, FL32306 USA. Mat. Res. Soc. Symp. Proc. Vol. 285. @1993 Materials Research Society
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as seen in Fig. 1, laser light is directed via a 45 mirror through an adjustable focussing lens towards the substrate target assembly. The laser light is transmitted through the transparent substrate and ablates material off the target. The substrate and target are in contact in most cases. The ablated material deposits onto the side of the substrate facing the target. The target is a polished disk of the material to be patterned onto the substrate; the target needs no special preparation and can be reused repeatedly. In order to generate patterns, the substrate target assembly is moved on a x-y stage under computer control. Several laser transparent substrates and target materials, including high temperature superconductors 6, were used to produce predesigned patterns by DLPD technique. Fig. 2 shows a typical pattern written from a YBa 2 Cu3Ox bulk target onto a polymer transparency substrate. In this study we have deposited thin films of C60 onto freshly cleaved KBr substrates by DLPD under the same conditions except laser energy density. Laser energy output was measured at various outpu
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