Patterned nanostructures and nanodots are attracting increasing interest in the information storage industry. The ultimate recording density of a magnetic medium will have single domain dots aligned in arrays and each dot in such an array acts as a recording bit. The ideal structure is that the dots are magnetic and the surrounding medium is non-magnetic so that each dot can switch magnetization direction freely without the interference from other dots. This paper presents the nanostructure of the nano-dot array investigated by transmission electron microscopy and magnetic force microscopy. The Co:C film was deposited by alternatively sputtering Co target and C target. The as-deposited specimen has an amorphous structure as revealed by electron diffraction in TEM. Such films transform to ferro-magnetic ones after heat treatment [1]. A laser beam of wavelength of 308 nm and a flux of 0.24 J/cm2 was split into two beams of an approximately equal intensity and then recombined, generating an interference pattern and a periodic modulation of the light intensity.