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02월 28일 19시 이후 : 초록수정 불가능, 일정확인 및 검색만 가능
제111회 대한화학회 학술발표회, 총회 및 기기전시회 안내
Kinetics of semiconductor nanowire nucleation In situ transmission electron microscopy study
2013년 2월 28일 18시 08분 01초
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Recent Advances in Inorganic Material Analysis
, J. Tersoff
, E. A. Stach
, F. M. Ross
광주과학기술원(GIST) 신소재공학부, Korea
IBM T. J. Watson Research Center, Yorktown Heights, NY, USA, United States
Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY, USA, United States
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The effect of size on phase stability and phase transformations is of both fundamental and applied interest. For example, during the nucleation and growth of self-assembled nanowires from nanoscale metal catalysts, the phase of the catalyst determines properties such as the growth rate and the structure of the nanowire. Based on our interest in Si and Ge nanowires catalyzed using Au, we have examined phase stability in the Si-Au and Ge-Au systems. Observations were made
in an ultra high vacuum transmission electron microscope that has gas delivery capabilities. We start with either size-selected aerosol particles or with evaporated and agglomerated Au films on electron transparent SiN membranes. The samples are heated by direct current, and Si or Ge is supplied by flowing the chemical vapor deposition precursor gases, disilane or digermane through a capillary into the polepiece region. For Si-Au, the transformation takes place as Si is added to the particle, and it can be seen that the reaction proceeds from the surface inwards, so that at intermediate times the system consists of a solid Au particle surrounded by liquid AuSi.  Modeling the kinetics of this transformation demonstrates that the Au-AuSi interface energy becomes important in modifying phase stability when the Au size becomes small. Analysis shows a substantial shift in the liquidus line, and a discontinuous change in the liquid composition at the transition. On further addition of Si, the AuSi eutectic liquid droplet becomes supersaturated with Si and eventually Si is precipitated. This nucleation event shows complex kinetics , as the nucleus rapidly jumps to a large volume and then grows more slowly at a rate dependent on the supply of Si. The jump size can be used to determine the supersaturation of Si in AuSi at the moment of nucleation. A comparison of kinetics at a range of temperatures, pressures and droplet sizes shows consistent behavior: supersaturation is not dependent on droplet volume, leading to predictable nucleation kinetics, which may be important in forming Si nanowires controllably. In the Ge-Au system, we find more complex kinetics.  Above the eutectic temperature, the behavior of the system is similar to that of the Au-Si system, with formation of a liquid AuGe phase followed by precipitation of Ge. However, below the eutectic temperature, a liquid phase also forms, and solid Ge precipitates from this liquid. We observed liquid AuGe below the eutectic temperature. The liquid phase persists due to a robust supercooling that is stabilized by the supersaturation of Ge arising from the growth process.
 B. J. Kim, J. Tersoff, C.-Y. Wen, M. C. Reuter, E. A. Stach and F. M. Ross, Physical Review Letters, 103,155701 (2009)
 B. J. Kim, J. Tersoff, S. Kodambaka, M. C. Reuter, E. A. Stach and F. M. Ross, Science, 322, 1070 (2008)
 B.J. Kim, C.-Y. Wen, J. Tersoff, M. C. Reuter, E. A. Stach, F. M. Ross, Nano Letters, 12, 5867 (2012)
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