Radiation-assisted formation of microprobes for scanning tunnel microscopes

The formation of tipped tungsten microprobes by ion bombardment in high electric fields with subsequent low-temperature field evaporation is reported. During irradiation, the current density was shown to rise nonmonotonically because of heavy particles present in the bombarding beam due to emitter erosion. It was found that the initially hemispheric working part of the probes turns into the axially symmetric complex-shaped surface. A correlation of these effects with inert gas ionization and tungsten sputtering under the action of super-high-density electron beams is discussed. The atomically smooth microprobes obtained by ion bombardment and field evaporation offer high stability and an atomic-level resolution.