In addition to advances in understanding of VLS NW growth and ternary phase diagrams for GaAs NW growth in the past years, an understanding of Au catalyzed GaAs NW shape (specifically facets) has also been achieved. The orientation and shape of NW facets determine the heterointerface of GaAs and hence its properties. Facet transformation has been reported as effecting growth rate and composition uniformity of NW shell during synthesis (e.g. shell/core AlGaAs/GaAs NWs).\cite{Zheng_2013} A reuleauxtriangle with three {112}A curved surfaces is determined to be the actual shape at the growth site instead of the previously believed hexagonal surface. GaAs NWs have {112} sidewall facets, but as the NW grows radially the faces transform into mostly {110} planes. Especially when enough energy is supplied to overcome the activation barrier associated with facet change, explaining why during annealing of the NW the facets adopt {110} facets. Jiang and coworkers developed a model based on the VLS nucleation theory to explain these findings.\cite{Jiang_2014}

Various growth parameters may be tuned to achieve specific NW shape. HCl has been used in Au catalyzed GaAs NW growth to suppress wurtzite like crystal growth in favor of zince blende crystal structure growth. The chlorine interacts with the Ga species to prevent Ga from contributing to growth.\cite{Jacobsson_2014}

The growth of wurtzite GaAs NW with diameters on the order of tens of nanometers allows for the suppression of the number of stacking faults within the VLS growth, by exploiting the theoretical result that NWs of small diameter (∼10 nm) adopt purely wurtzite structure and thicken via radial growth once the axial growth exceeds a certain length.\cite{Shtrikman_2009}

Knyazeva and coworkers used a kinetic lattice MonteCarlo model of the growth of GaAs NW by VLS mechanism to simulate the gold catalytic and Ga catalyzed growth of GaAs NW on the GaAs substrate.\cite{Knyazeva_2015} They found that growth depends linearly on As atom flow rates, with more sensitivity being present for the Ga catalyzed growth. It was also found that growth increases with decreasing density of NWs.

I have already discussed how liquid catalyst radius determines NW radius, But I will now discuss how temperature, flow rates and partial pressures of precursors affect NW properties. As temperature is increased the rate of precursor decomposition increases and the rate of available Ga increases as well. With more Ga available the NW grows faster. But if temperature is continued to be increased the radial and axial growth rates compete, with radial growth rates out-competing axial growth rates.\cite{Morral_2011} This increase in radial growth with higher temperature is true generally, including for Au dependent synthesis with no substrate.\cite{Heurlin_2012} But radial growth can be kinetically suppressed by low growth temperatures, and this helps to achieve more uniformly long NW.\cite{Joyce_2007} Axial and radial growth rates increase with increasing As precursors, but at a 40As:1Ga ratio the increase stops. In fact, growth rate decrease and some believe it its because trimers begin to form on the {111}B surface, impeding growth in the axial direction. \cite{Morral_2011}