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Articles you may be interested inField emission induced fabrication of nanostructures on Au thin films using a noncontact mode atomic force microscope J.We have investigated field induced local oxidation of thin Ti films with the tip of an atomic force microscope. Tips, which have been coated with a diamond layer to improve their wear resistance, are shown to have a much longer lifetime than conventional uncoated Si tips. We have studied the oxidation characteristics as a function of the applied tip-sample voltage and scanning speed for both diamond coated and uncoated tips. We find that the diamond coated tips result in a thinner oxide layer for the same voltage and scanning speed. The dependence of the oxidation process on the film thickness was studied for diamond coated tips. Thin films can be completely transformed into an oxide layer for a thickness up to 15 nm. Moreover, for these sufficiently thin films the measured ratio between the oxide height and the Ti film thickness is a constant. It is also possible to completely oxidize Ti films which cover Au islands, opening the way to fabricate more complicated structures.

The local oxidation produced by the tip of an atomic force microscope scanning on a thin metallic film allows to define narrow oxide lines, thus providing a method to fabricate lateral tunnel junctions. In such devices, with rather thick tunnel junction barriers, the electrical transport is governed by thermally activated hopping rather than by direct electron tunneling. In this letter we show that tunneling barriers can also be produced with Ti films covering small gold islands. The gold islands significantly shorten the effective tunneling distance, allowing to observe temperature-independent electron tunneling across the lateral barriers. The mixed Ti/Au tunnel barriers reveal Coulomb blockade effects which may be used for single-electron devices consisting of a single oxide line.

Chemical vapor deposited (CVD) diamond films have a controversial history regarding their surface electronic properties. Hydrogenation is known to induce a p-type conductive surface layer, which is not present on non-hydrogenated samples. The enhanced surface conductance can decrease significantly after annealing under high vacuum conditions at as low as 200 C (a temperature which is sufficiently low to ensure that the hydrogen termination remains intact). Although the hydrogen is necessary for the surface conductance, the surface can be made poorly conductive without removing the hydrogen termination. We have performed scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) to better understand the origin of the enhanced surface conductance. Our STS experiments confirm that hydrogenation induces the appearance of a conductive surface layer, which can change considerably after high vacuum annealing. In this paper, we will discuss the conditions under which the surface conductivity can be restored. In particular we study the conductance changes during plasma hydrogenation and after exposing it to atmospheric conditions. Topographical STM scans confirm that the surface structure is not altered at low annealing temperatures.

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