To discern the anisotropy of silicon nanowires (SiNWs) grown in different directions, the binding energy, heat of formation, and Young's modulus of hydrogen-passivated SiNWs with various diameters and crystallographic orientations were calculated using all-electron density functional theory. In the size range studied, nanowires grown in the [110] direction are most stable while those in the [100] direction are energetically least favorable. Similar trend was observed in the computed Young's modulus. With the same radius, the nanowire along the [110] direction possesses the highest Young's modulus, while the [100] wire has the lowest value. (c) 2007 Elsevier B.V. All rights reserved.