AVS 61st International Symposium & Exhibition
    Nanometer-scale Science and Technology Tuesday Sessions
       Session NS+AS+SS-TuA

Invited Paper NS+AS+SS-TuA1
Surface Chemical Choreography of Nanowire Synthesis

Tuesday, November 11, 2014, 2:20 pm, Room 304

Session: Nanowires and Nanotubes: Advances in Growth and Characterization 
Presenter: Michael Filler, Georgia Institute of Technology
Authors: M.A. Filler, Georgia Institute of Technology
S.V. Sivaram, Georgia Institute of Technology
N. Shin, Georgia Institute of Technology
I.R. Musin, Georgia Institute of Technology
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This talk will provide an overview of our recent efforts to understand the chemical phenomena underlying semiconductor nanowire growth. The vapor-liquid-solid technique – where a liquid “catalyst” droplet collects atoms from the vapor and directs crystallization of individual solid layers – is a ubiquitous method for the synthesis of these quintessential nanoscale building blocks, but a lack of atomic-level design rules prevents robust programming of structure. Long-standing challenges in the control of heterostructure, dopant profile, atomic stacking sequence, kinking, and even simple axial growth restrict the accessible property space and highlight the pitfalls of an overreliance on empirical process optimization. We couple in-situ or operando infrared spectroscopy with post-growth high-resolution electron microscopy to connect specific surface chemical bonds present during synthesis with nanowire structure. Studies of Si and Ge nanowires demonstrate the fundamental, and previously unrecognized, role of adsorbed hydrogen atoms. The surface coverage of these precursor (e.g., Si2H6 or Ge2H6) decomposition intermediates, which we quantitatively determine as a function of pressure and temperature, can change over a narrow range and strongly influence growth. Our findings show, for example, that adsorbed hydrogen is essential for stabilizing the catalyst or driving elongation in new crystal directions for Ge and Si nanowires, respectively. We leverage these insights to rationally design precursors that choreograph nanowire structure on multiple length scales, permitting the fabrication of user-defined defect, kinking, and diameter-modulated superstructures.