Chiang Mai Journal of Science

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We report scanning tunneling microscope (STM) measurements on the polycrystalline thin films of ZnO prepared by RF-sputtering and sol-gel processes. Our earlier results on these films using various characterization methods such as ellipsometry, optical absorption, band gap measurements, XRD, electron diffraction, transmission and electron microscopy have shown that the films consisted of mainly ZnO. In the present work, STM measurements were done to estimate the lattice constants a_๐ and c_๐ .The ZnO bond length was also measured . These values were found to be in close agreement with the reported values in literature. In addition to ZnO lattice, a square lattice of 0.4 nm X 0.4 nm was also found. This lattice is unknown at the present stage of investigation. The overall lattice structure in the10 nm X 10 nm area of the sol-gel grown film showed a highly uniform distribution of atoms with average roughness of 0.45 nm and standard deviation of 0.07. The surface of the RF - sputtered film scanned over 800 X 800 nm area showed the average roughness of 3.26 nm and standard deviation of 0.98. The lattice constants estimated for the RF-sputtered film were found to be identical with those observed for the films prepared by sol-gel technique. This shows that both the types of films consisted of ZnO. However, in the case of RF-sputtered film the lattice was disturbed with many undulations. This was perhaps due to the fact that the film was not thermally annealed during /after deposition.

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