We report here the first study of formation kinetics of vertically-aligned periodic Si nanorod arrays on (001) Si substrates in H(2)O(2)/HF/EtOH etching solutions. The diameter, length, location, and crystallographic orientation of the Si nanorods produced were well-controlled using the colloidal nanosphere lithography combined with the Au-assisted selective chemical etching process. The as-synthesized Si nanorods were determined to be single crystals and the axial orientation of the Si nanorods was identified to be parallel to the [001] direction, which was identical to the orientation of the (001)Si wafers used. The lengths of Si nanorods could be tuned from sub-micrometer to several micrometers by adjusting the etching temperatures and time. The activation energy for the formation of Si nanorods array on blank-(001)Si was about 76.7 kJ/mole, which was calculated according to the Arrhenius plot. From water contact angle measurements, it is found that the Si substrate with Si nanorod arrays exhibited a more hydrophobic behavior compared to the blank-(001)Si sample. The hydrophobic behavior of the HF-treated Si nanorod arrays could be explained by the Cassie-Baxter model. (C) 2009 Elsevier B.V. All rights reserved.