Development of an Advanced Low-Energy Electron Diffraction Technique using Field-Emitted Electrons from STM Tips

A prototype instrument has been demonstrated which employs a new technique for determining surface structures. The instrument consists of a STM tip as a field emission gun and a detector for projecting electron scattering patterns. The operation of the tips under a field emission condition with bias voltages of 14 - 30 V made it possible to observe the electron scattering patterns. These experimentally obtained patterns have been compared with calculated results showing close correlation, signifying that the obtained patterns are caused by the electrons scattered on a sample surface after emission from a STM tip. Suitable bias voltages between the tip and the sample for this system are discussed. Although further improvements in the method of extracting electrons are necessary in order to obtain certain diffraction patterns on this instrument, the results demonstrate that the new technique is capable of probing nanometer scale surface structures