DEVELOPMENT OF SCANNING TUNNELING MICROSCOPE CAPABLE OF CHEMICAL ANALYSIS

为了开发能够对成像区域中的轻元素进行化学分析的扫描隧道显微镜（STM）系统，已经解决了以下问题。（1）对新设计的光致发光X射线激发电子能谱（PXEEES）的定量考虑表明，如果从非常尖锐的STM尖端获得足够量的场发射电流，则基于用于X射线产生的电子的阈值能量的元素分析是可能的。(2)To为了制造PXEEES测量所需的可再现的尖锐尖端，已经开发了一种尖端制造的新方法，即超快电流关断方法。制造的尖端被证明是稳定的，即使在高偏置电压高达500 V。（3）利用石墨样品的初步实验表明，能量低至100 eV的电子辐照可以引起离子碳的蒸发，这使得我们得出结论，在某些易受这种低能电子辐射损伤的材料中，PXEEES测量是不可能的。(4)As另一种方法，空间分辨光吸收光谱测量在纳米尺度上被发现是可能的，通过使用STM。在GaAs样品上进行了成功的试验。（5）结合STM的电场调制光谱显示出能够测量纳米尺度的半导体（用作测试样品的低温生长GaAs）的能带结构。(6)We提出了一种新的红外吸收光谱方案，该方案利用由于STM隧道结中的非线性电流-电压关系和尖端增强的电磁场而产生的差频产生的红外光。

In order to develop a scanning tunneling microscopic (STM) system that enables chemical analysis of light elements in the imaged regions, the following issues have been addressed.(1)Quantitative considerations on a newly devised photoluminescent X-ray excitation electron energy spectroscopy (PXEEES) revealed that element analysis based on the threshold energy of electrons for X-ray generation is possible if a sufficient amount of field emission current is obtained from very sharp STM tips.(2)To fabricate reproducibly sharp tips necessary for the PXEEES measurements, a novel method of tip fabrication, the ultra-fast current shut-off method, has been developed. The fabricated tips proved to be stable even at high bias voltages up to 500 V.(3)Preliminary experiments using graphite samples revealed that irradiations of electrons in energies as low as 100eV can cause evaporation of ionic carbons, which led us to conclude that the PXEEES measurements are not possible in some materials vulnerable to such low energy electron radiation damage.(4)As an alternative method, spatially-resolved photoabsorption spectroscopic measurements on a nanometer scale were found to be possible by using STM. Tests have been done successfully on GaAs samples.(5)Electric-field modulation spectroscopy coupled with STM revealed to be capable of measuring band structures of semiconductors (low-temperature grown GaAs used as test samples) on nanometer scales.(6)We have proposed a novel scheme of infrared absorption spectroscopy that utilizes infrared light generated by difference frequency generation due to the non-linear current-voltage relation and the tip-enhanced electromagnetic field in the STM tunneling junctions.