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Pulsed Laser Melting of Graphite 1

  • G. Braunstein (a1), J. Steinbeck (a1), M. S. Dresselhaus (a1), G. Dresselhaus (a1), B. S. Elman (a2), T. Venkatesan (a3), B. Wilkens (a3) and D. C. Jacobson (a4)...


Experimental evidence for laser melting of graphite, by irradiation with 30ns pulses from a ruby laser, is presented. RBS-channeling analysis, Raman scattering and TEM measurements reveal that the surface of graphite melts at a threshold energy density of about 0.6 J/cm2. For laser pulse energy densities above 0.6 J/cm2, the melt front penetration depth increases nearly linearly with increasing energy density. An intense emission of carbon particles during and after irradiation is observed. The thickness of the carbon layer removed in this process also increases nearly linearly with increasing pulse fluence. A dramatic redistribution of ion implanted impurities is also observed. Furthermore, the crystalline structure of the resolidified material is shown to depend on the energy density of the laser pulse. In order to explain these phenomena, a model for laser melting of graphite at high temperatures to form liquid carbon has been developed in which a free electron gas approximation is used to describe the properties of liquid carbon. The model is solved numerically to give the time and depth dependences of the temperature as a function of the laser pulse energy density. Very good agreement is found between the observed melt depth dependence on laser pulse energy density, as determined by RBS-channeling, and the model calculations. The redistribution of ion implanted impurities and the modification of the crystalline structure, caused by the pulsed laser irradiation, are also consistent with the model and permit the determination, for the first time, of interfacial segregation coefficients for impurities in liquid carbon. The model also predicts that liquid carbon at low pressure (p < 1 kbar) has metallic properties.



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The MIT authors acknowledge NSF Grant #DMR 83-10482 for the support of their portion of the work.



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[1] Bundy, F.P., J. Chem. Phys. 38, 618 (1963).
[2] Venkatesan, T., Jacobson, D.C., Gibson, J.M., Elman, B.S., Braunstein, G., Dresselhaus, M.S. and Dresselhaus, G., Phys. Rev. Lett. 53, 360(1984).
[3] Steinbeck, J., Braunstein, G., Dresselhaus, M.S., Venkatesan, T. and Jacobson, D.C., J. Appl. Phys.(in press).
[4] Braunstein, G., Steinbeck, J., Dresselhaus, M.S., Venkatesan, T., Wilkens, B. and Jacobson, D.C., (to be published).
[5] Reynolds, W.N., Physical Properties of Graphite,(Elsevier, New York 1968).
[6] Kelly, B.T., Physics of Graphite,(Applied Science Publishers, London 1981).
[7] Poate, J.M., Foti, G., Jacobson, D.C. (eds.), Surface Modification and Alloying by Laser,Ion, and Electron Beams, Plenum Press, New York, 1983.
[8] Venkatesan, T., Jacobson, D.C., Steinbeck, J., Braunstein, G., Elman, B. and Dresselhaus, M.S. (submitted to this Symposium).
[9] Elman, B.S., Braunstein, G., Dresselhaus, M.S., Venkatesan, T. and Gibson, J.M., Phys. Rev. B29, 4703 (1984).
[10] Wood, R.F. and Giles, G.E., Phys. Rev. B23, 6 (1981).
[11] Ziman, J.M., Phil. Mag. 12,1013 (1961).
[12] White, C.W. in “Pulsed Laser Processing of Semiconductors”, ed. by Wood, R.F., White, C.W. and Young, R.T., vol. 23 of Semiconductors and Semimetals (Academic Press 1984), p.44.


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