Silicon nanowires are grown epitaxially on Si (100) surfaces using thermal (a) and rf plasma excitation (b) for vapor-liquid-solid (VLS) growth. Plasma excitation at low growth temperatures promotes the nucleation of smaller diameter [110] oriented Si nanowires and is attributed to a plasma-induced increase in silicon chemical potential; it also increases low temperature nanowire growth rates (see figure). The rate limiting step in VLS growth here is due to silicon incorporation at the vapor-liquid interface. Plasma excitation enables additional control over nanowire orientation.