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CO2 cluster ions are irradiated at the acceleration voltage of 25 kV to remove hillocks on indium tin oxide (ITO) surfaces and thus to attain highly smooth surfaces. CO2 monomer ions are also bombarded on the ITO surfaces at the same acceleration voltage to compare sputtering phenomena. From the atomic force microscope results, the irradiation of monomer ions makes the hillocks sharper and the surfaces rougher from 1.31 to 1.6 nm in roughness. On the other hand, the irradiation of CO2 cluster ions reduces the height of hillocks and planarize the ITO surfaces as smooth as 0.92 nm in roughness. This discrepancy could be explained by large lateral sputtering yield of the cluster ions and re-deposition of sputtered particles by the impact of the cluster ions on surfaces. [Copyright &y& Elsevier]

The dependence of surface smoothing and sputtering phenomena of Si (1 0 0) solid surfaces irradiated by CO2 cluster ions on cluster-ion dosage was investigated using an atomic force microscope. The flux and total ion dosage of impinging cluster ions at the acceleration voltage of 50 kV were fixed at 109 ions/cm2 s and were scanned from 5×1010 to 5×1013 ions/cm2, respectively. The density of hillocks induced by cluster ion impact was gradually increased with the dosage up to 5×1011 ions/cm2, which caused that the irradiated surface became rough from 0.4 to 1.24 nm in root-mean-square roughness (σrms). At the boundary of the ion dosage of 1012 ions/cm2, the density of the induced hillocks was decreased and σrms was about 1.21 nm, not being deteriorated further. At the dosage of 5×1013 ions/cm2, the induced hillocks completely disappeared and the surface became very flat as much as σrms=0.7 nm. In addition, the irradiated region was sputtered as deep as 5.4 nm. From the experiment of isolated cluster ion impact on the Si surfaces, it was observed that the induced hillocks nm high had the surfaces embossed at the lower ion dosages. The surface roughness was slightly increased with the hillock density and the ion dosage. At higher than a critical ion dosage, the induced hillocks were sputtered and the sputtered particles migrated from the side of the hillocks to the valleys among the hillocks in order to fill. After prolonged irradiation of cluster ions, it was observed that the irradiated region was very flat and etched. A simple phenomenological model in terms of dosage-dependent sequential surface embossment, sputtering, smoothing and etching processes was suggested to explain these cluster-ion impact interactions with the Si surfaces at various dosages. [Copyright &y& Elsevier]