Considerable number of efforts have been made to fabricate nanowires in order to exploit their superior structural characteristics suitable for enhancing nano-sized effects. In particular, since the properties of one-dimensional nanostructures could be dramatically changed depending on the dimension of the structures at the size of several tens of nanometer, reliable fabrication methods of precisely controlling the diameter of the nanowires is required.
In a successful effort to produce tens of nanometer-scale nanowires reliably over a large area, we previously introduced repetitive pattern down scaling technology to fabricate the highly compact nanogratings which are used to make nanowires. By applying physical vapor deposition technique on the nanogratings substrate, perfectly aligned nanowires could be simply formed only on the peaks of the nanogratings due to shadowing effect originating from its geometry.
Herein, we fabricate the diameter-controlled nanowires by precisely tuning the pattern size of nanogratings. The size of nanogratings was reduced from 50 nm to sub-10 nm by newly developed wet-chemical digital etching process. We found that a few atomic layers of the silicon surface are naturally oxidized in a nitric acid ($HNO_3$) solution, which enables the surface of the silicon to be etched with 1.0 nm resolution by selectively removing the oxide layers. By applying this high-resolution digital etching technique to silicon nanogratings previously prepared by conventional methods, we successfully controlled the pattern size of silicon nanogratings on an inch-scale wafer. It enables that the fabrication of diameter-controlled nanowires in the region of less than 50 nm in large area.