Signal enhancement in nano-Raman spectroscopy by gold caps on silicon nanowiresobtained by vapour–liquid–solid growth

Abstract

Silicon nanowires grown by the vapour–liquid–solid growth mechanism with gold as the catalyst show goldcaps ∼50–400 nm in diameter with an almost ideal hemispherical shape atop a silicon column. These goldcaps are extremely well suited for exploiting the tip or surface enhanced Raman scatteringeffects since they assume the right size on the nanometre scale and a reproducible, almostideal hemispherical shape. On attaching a nanowire with a gold cap to an atomic forcemicroscopy (AFM) tip, the signal enhancement by the gold nanoparticle can be used tospatially resolve a Raman signal. Applications of this novel nanowire based technical tipenhanced Raman scattering solution are widespread and lie in the fields of biomedical andlife sciences as well as security (e.g. detection of bacteria and explosives) and in the field ofsolid state research, e.g. in silicon technology where the material composition, doping,crystal orientation and lattice strain can be probed by Raman spectroscopy. A prerequisitefor obtaining this spatial resolution in nano-Raman spectroscopy is the attachment of ananowire with a gold cap to an AFM tip. This attachment by welding a nanowire ina scanning electron microscope to an AFM tip is demonstrated in this paper.