Effects of sample preparation conditions on the formation of Si nano-structures were investigated. The samples were formed by Various deposition methods with various deposition conditions, and subsequent oxidation and/or annealing was carried out. It was found that the film structure as well as the morphology of the thermally treated samples is greatly affected by not only the substrate temperature and the deposition rate but the presence of O-2 during deposition. In particular, O-2 flow during deposition was observed to apparently enhance formation as well as growth of Si grains. It was stated that the enhancement of crystallization is a consequence of formation and subsequent evaporation of SiO. These results were accounted for by formation kinetics of Si nano-structures. Furthermore, it was suggested that an optimized process for Si nano-structure may be obtained through modifications of the kinetics involved by systematic variations of the deposition conditions. In addition, I-V characteristics observed from the multiple junctions showed tunneling behavior implying the feasibility of fabricating novel devices such as single electron transistors.