Radial breathing mode in silicon nanowires: An ab initio study

We study by means of first-principles calculations the phonon spectrum of silicon nanowires oriented along the 〈110 〉 direction with a diameter ranging from 1.0 to 2.4 nm. We analyze in particular the evolution of the radial breathing mode frequency as a mean to calibrate experimentally the diameter through Raman analysis. Remarkably, the results of elastic theory analysis are very reliable even in the limit of ultrathin wires with significant deviations from the cylindrical shape.