AVS 46th International Symposium
    Surface Science Division Wednesday Sessions
       Session SS-WeP

Paper SS-WeP22
Direct Absorption of Thermal H Atoms by Crystalline Silicon: A Narrow Substrate Temperature Window

Wednesday, October 27, 1999, 5:30 pm, Room 4C

Session: Poster Session
Presenter: S.K. Jo, Kyung Won University, S. Korea
Authors: J.H. Kang, Kyung Won University, S. Korea
S.K. Jo, Kyung Won University, S. Korea
J. Lee, Seoul National University, S. Korea
B. Gong, University of Texas at Austin
J.M. White, University of Texas at Austin
J.G. Ekerdt, University of Texas at Austin
Correspondent: Click to Email
Si(100) surfaces exposed to gas-phase thermal-energy hydrogen atoms, H(g), were studied by temperature-programmed desorption (TPD) together with H/D isotope exchange experiments. We find that direct absorption of H(g) into crystalline bulk of Si(100) substrates occurs within a narrow substrate temperature window of 400 - 600 K. The bulk-absorbed hydrogen evolved out molecularly from Si(100) at a temperature 70 - 120 K higher than that of surface-adsorbed monohydride phase (@beta@@sub 1@) in TPD. This bul k-phase hydrogen (@alpha@) uptake increased with increasing H(g) exposure without saturation within our experimental limits. While pre-adsorbed hydrogen atoms on the surface, H(a), were readily abstracted and replaced by D(g), the amount of pre-absorbed H in the bulk remained unchanged by subsequent D(g) exposures. Our result of extensive H/D isotope mixing suggests that absorbed H atoms remain trapped atomically, rather than molecularly, at interstitial sites. We propose a model, in which the (2x1) surface dimer structure of Si(100) serves as a two-way barrier for both direct H(g) absorption and thermal evolution of molecular hydrogen.