(229n) Exploring Epitaxial Relationships Between Growth Orientations of InAs Nanowires and Au Surfaces

The control in growing large vertical arrays of semiconducting nanowires with specific orientations is imperative to build nanowire based nanoscale devices for commercial logic gate applications.  There has been recent evidence in the literature that the metal particle influences the final structure and orientation of the as-grown nanowires through an epitaxial relationship.  In our experiments on InAs nanowire (NW) growth on shaped Au nanoparticles, we have observed preliminary evidence of preferential growth of <110> nanowires on shaped Au nanoparticles compared to that on spherical nanoparticles.  Since shaped Au nanoparticles have more Au (111) and Au (100) surfaces than the spherical Au nanoparticles, our target is to explore whether an epitaxial relationship can be established between the orientation of the InAs NW growth direction and the surface facets of the gold nanoparticle on which the NW grows.

In this work, we have established the relative binding strengths of ZB and WZ H-terminated InAs NW fragments with particular facets of an Au nanoparticle using density functional theory (DFT) calculations.  In particular, we have first established the binding strengths of (i) an H-terminated [0001], [10-10] and [11-20] oriented wurtzite (WZ) InAs NW fragments with Au(111) and Au(100) surfaces and, (ii) an H-terminated <111> , <100> and <110> oriented zinc blende (ZB) InAs NW fragments with Au(111) and Au(100) surfaces.  The results of the DFT calculations show that the <111> oriented nanowire fragments for both the wurtzite and zinc blende structures are more stable than the <100> and <110> oriented nanowire fragments and particularly, within the size range of the study (< 5 nm), the wurtzite phase is more stable than the zinc blende phase.  Again, the relative stability of the <111> nanowire fragment on the Au(111) surface and that of the <100> and <110> nanowire fragment on the Au(100) surface is demonstrated by calculating the binding energies, excess energies and electronic charge redistribution of various nanowire fragments on the different Au surfaces.  The results of the DFT calculations provide a very exciting prospect of growing certain nanowire orientations by selectively tailoring the metal catalyst surface to have specific surface facets.  This would ultimately allow for catalyst selection and design.