Sputter-induced cone and filament formation on InP and AFM tip shape determination

The structures formed on the InP(100) surface by sputtering with fluences of the order of 1021 ions m−2 of 4–8 keV argon are analysed by scanning electron microscopy, atomic force microscopy (AFM) and Auger electron spectroscopy. Well-defined cones are formed if small traces of polymeric coatings are deposited on the surface. However, for clean surfaces at room temperature, the sputtered surface may be cone-free. Surfaces that are sputtered at above ambient temperature exhibit a dense filamentary growth, the heights of which increase in magnitude as the temperature rises. For the conditions used in this work, filaments 200 nm high occur at 260 °C. The mechanism for this growth is thought to arise from stress through capacitative effects arising from charging of an indium cap at the top of the filament by the ion beam. At elevated temperatures, diffusive effects occur to reduce this strain by causing elongation of the filament. Samples may be heated by the power deposited from the ion beam so that filaments occur on samples that would otherwise be at room temperature. By heating the InP in the temperature range 100–180 °C, filaments 30–80 nm high may be grown, which are excellent for imaging the structure at the ends of AFM tips. New software, which averages the images of several individual filaments, allows the tip structure to be monitored, wear effects to be diagnosed and worn tips to be rejected. The samples can be used routinely, in-between other samples, to allow diagnosis directly without the need to use other forms of microscopy.