Reflectance anisotropy spectroscopy of Si(111)-(4 x 1)-In

Conventional surface characterisation techniques have provided compelling evidence that the atomic chains of the Si(111)-(4 x 1)-In structure possess quasi-ID metallic character. The possibility of incorporating such nanowires into practical electronic devices is of considerable technological interest. New reflectance anisotropy spectroscopy results are presented which extend the spectral range of previous studies of this system to lower energy. Enhanced polarisability in the chain direction expected for anisotropic metallic structure in the infrared region is detected for the first time, and low temperature studies reveal anisotropic optical transitions around 1.2 eV, which may be the origin of the enhanced second harmonic signal recently observed for this system using 1.17 eV excitation.