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

本研究的目的是开发一种纳米尺度空间分辨率的表面磁性测量仪器。该仪器由扫描隧道显微镜（STM）尖端作为场发射枪和用于测量电子自旋极化的莫特探测器组成。得到了以下结果：(1)建立了偏压在14 ~ 50 V的场致发射条件下尖端的工作原理。发射电流在0.1 ~ 1na范围内稳定。(2)在恒流模式下，改变偏置电压，测量探针与样品之间的距离。结果表明，距离在很大程度上取决于尖端的形状。为了探测到散射的电子，需要一个尖锐的尖端。(3)在偏置电压14 ~ 50 V的场发射条件下工作，使得利用微通道板检测散射电子成为可能。(4)提出了一种尖端屏蔽结构，以改进提取功能。利用仿真程序计算了叶尖屏蔽的影响，并进行了实验验证。散射电子的探测效率变得非常高。(5)证明了利用STM尖端进行纳米级低能电子衍射的可能性。(6)证实了叶尖屏蔽对STM测量的分辨率没有有害影响。利用尖端屏蔽在Si（111）和Si（001）表面上实现了原子分辨率。(7)利用荧光材料研制了一种灵敏度高的小型莫特探测器。由于散射电子的数量非常低，因此该装置的充分开发尚未完成。此外，场发射条件在很大程度上取决于尖端的形状。然而，上述结果为目标仪器的发展指明了道路，并展示了在纳米尺度分辨率下检测表面电子自旋极化的潜力。少

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