Development of a field electron emission-scanning probe microscope with a build-up tip

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We have developed a new instrument combined with a field electron emission-scanning probe microscope (FEE-SPM) and an electron energy analyzer to acquire energy spectra of electrons backscattered from a sample surface. The sample was irradiated with electrons field-emitted from a build-up [111]-oriented W tip. The area irradiated with the electrons can be imaged by STM with the same tip.In this instrument, the tip fabrication is crucial to draw a stable electron beam. We applied a build-up technique to fabricate it, which is called a thermal-field (T-F) treatment : we apply a positive high voltage to the tip while heating it. The surface atoms on the tip are polarized and pulled toward its apex with a higher electric field, resulting in expansion of some facets with specific plane indices. Consequently, the tip apex is surrounded by a set of facets with vertices and ridges. By choosing the tip axis to a vertex direction, the tip is sharpened : it is the [111] direction for W.An elastic peak with plasmon losses and Auger electron peaks were found for a Si (111) and a Si (111) covered with Ge, and other samples. The Ge islands with 5x5 and 7x7 reconstructions grown on the step and the domain boundaries of the substrate are imaged with the STM.After STM imaging, the tip is retracted slightly and the electron beam is field-emitted from the tip. Several energy peaks are found, which are attributed to plasmons and to Auger electrons of Si LVV and Ge MVV.The Auger peaks shifted toward lower energies as the separation between tip and sample decreases. The electron trajectoriey are possibly deflected in the electric field between tip and sample. A metal plate with a small hole to reduce the electric field was inserted between tip and sample : the peaks became prominent.