Growth of ZnO nanocrystals by pulsed laser deposition on sapphire and silicon and the infrared spectra of the nanocrystals

The ZnO nanorods that comprise highly oriented nanorod structures are grown on sapphire and silicon substrates by laser ablation. The nanostructures grown in different conditions are characterized by means of electron microscopy and Fourier infrared reflectance spectroscopy. The contributions of optical phonons and free charge carriers to the infrared spectra of the layers of ZnO nanorods are identified, and the degree of orientation of the ZnO nanorods with respect to the substrate surface is analyzed in relation to the conditions of growth. Softening of optical phonons of ZnO with decreasing the nanorod diameter is observed.