Figure 5

Raman measurements of Si nanowires produced by cryogenic dry etching. (a) Two-dimensional (2D) mapping of the dominant Raman peak at around 520.4 cm⁻¹ represented by the triple degenerated optical phonon mode of unstrained planar Si, showing a homogenous distribution within ± 0.1 cm⁻¹. (b) Two different stages of Raman characterization of the Si nanowires (i.e., before and after their detachment from the substrate). (c) Effect of the etch time on the Raman peak shifts. Shifts of 0.2 cm⁻¹ and 0.5 cm⁻¹ towards higher wavenumbers occurred after the planar Si was nanopatterned and etched for 5 and 10 min, respectively, indicating the presence of compressive lattice stress in the nanowires. Raman spectrum of planar Si (black curve) is plotted as a reference. (d) Difference in mechanical property of Si nanowire between top and sidewall, corresponding to compressive and tensile stresses, respectively. This indicates an anisotropy of lattice stress distribution on the surface of Si nanowire.