Development of a nanometer scale spin polarized scanning electron microscope for surface magnetism

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The goal of this research is to develop an apparatus for measurement of surface magnetism at nanometer-scale spatial resolution. The instrument consists of a scanning tunneling microscopy (STM) tip as a field emission gun, and a Mott detector for measuring the electron spin polarization.The following results have been obtained. (1) The operation of the tips under a field emission condition with bias voltages of 14 - 50 V has been established. The emission current was stable in the region from 0.1 nA to 1 nA. (2) The distances between the tip and the sample were measured while the bias voltage was changed, under a constant current mode. The results show that the distances strongly depend on the shape of the tip apex. A sharp tip apex is necessary to detect the scattered electrons. (3) The operation of the tips under a field emission condition with bias voltages of 14 - 50 V made it possible to detect the scattered electrons using a micro-channel plate. (4) A tip-shield has been proposed … More to improve extraction functions. The influence of the tip-shield was calculated using a simulation program and confirmed experimentally. The detection efficiency of the scattered electrons became remarkably large. (5) The possibility of nanometer-scale low-energy electron diffraction using STM tips has been demonstrated. (6) It has been confirmed that the tip-shield exerts no harmful influences on the resolution of the STM measurements. Atomic resolution has been achieved with the tip-shield on Si(111) and Si(001) surfaces. (7) A small-size Mott detector of good sensitivity has been developed using a fluorescent material.The full development of the apparatus has not been completed because the amount of scattered electrons is very low. Moreover, the field emission condition depends very strongly on the shape of the tip apex. However, the above results show the path for the development of the target instrument, and demonstrate a potential for the detection of the surface electron spin polarization at nanometer-scale resolution. Less