The material design challenge in thermoelectric materials is to find the materials where the conduction of heat is low and the electrical conductivity is high. It was recently reported, that the thermal conductivity can be strongly reduced in semiconducting Si nanowires that are 20¿300 nm in diameter. Since the thermal conductivity is related to the propagation of phonons, it has been suggested that confinement or unusual behavior of the phonons in low-dimensional structures can be behind this phenomenon. The goal of the proposed work is to study the effect of the confinement on the phonon propagation in Si nanowire using high-intensity spectrometer MERLIN. For this purpose we intent to map phonon excitations in Si nanowires at 5-20meV energy range in the confined and non-confined dimensions. For in-depth data interpretation the experimental studies will be combined with ab-initio model