SEM and transmission electron microscopy (TEM) micrographs of the pristine Si NWs. (a) Top-view SEM micrograph of the Si NWs grown by VLS mechanism showing their random orientation. (b) TEM image of an individual Si NW cross-section representing the continuous native oxide layer of 3 to 4 nm in diameter atop. Regarding the micrographs, the Si core diameter can be estimated as 50 ± 10 nm. The red dotted line insists on the fact that TEM micrograph is taken for a single Si NW among the large ensemble observed through SEM.