Tip locking mechanism for STM light Emission Spectroscopy

STM光发射光谱是研究表面微结构特性的有力工具。由于来自STM针尖的电子束直径窄于~ 1 nm，因此可以期望获得单个纳米尺度结构的光发射光谱。STM光发射光谱具有期望的空间分辨率的一个障碍是在光谱测量期间由于环境温度波动等（针尖漂移）而导致的针尖位置的意外变化。由于STM光发射强度弱，因此需要长曝光时间（几百秒或更长）。因此，STM光发射光谱的空间分辨率变得比期望值（光束直径）差。本项目开发了一种新的STM光发射光谱针尖位置锁定机制。锁定的方式如下：让我们假设观察发射光谱所需的总曝光时间为nxT（n乘以T）。拍摄样品表面上的区域的第一形貌图像。然后，在时间段T（光谱的曝光时间为T）内测量来自该区域中的微结构的STM光发射光谱。再次观察与光谱测量之前拍摄的区域相同的区域的地形图像，并且通过比较两个STM图像来计算曝光期间的漂移量。然后将尖端移回微结构上并测量下一个光谱。通过重复上述过程n次并累积光谱，可以以比时间段T期间的漂移量更好的空间分辨率测量对应于曝光时间nxT的STM光发射光谱。如果选择T，则具有高空间分辨率的足够小的STM光发射光谱变得可能。

STM ligth emission spectroscopy is a powerful tool for investigating properties of surface microstructures. Since the beam diameter of electrons from the STM tip is narrower than -1 nm, one can expect to obtain the light emission spectra of individual nanometer-scale structures.One obstruction to STM light emission spectroscopy with the expected spatial resolution is unintended change of tip position due to ambient temperature fluctuation etc. (tip drift) during spectral measurement. Since STM light emission intensity is weak long exposure time (a few hundred seconds or longer) is required. As result spatial resolution of STM light emission spectroscopy becomes worse than the expected value (the beam diameter).In this project a new tip position locking mechanism for STM light emission spectroscopy has been developed. The way of the locking is as follows : Let us assume that the total exposure time required to observe emission spectra is nxT (n times T). First topographic image of an area on the sample surface is taken. Then STM light emission spectrum from a microstructure in the area is measured for the time period of T (the exposure time of the spectrum is T). Again topographic image of the area same as that taken before the spectral measurement is observed and the amount of the drift during the exposure is calculated by comparing the two STM images. Then the tip is moved back on the microstructure and the next spectrum is measured. By repeating the above procedure n times and accumulating the spectra STM light emission spectrum corresponding to the exposure time of nxT can be measured with the spatial resolution better than the amount of drift during the time period T.If T is selected enough small STM light emission spectroscopy with high spatial resolution becomes possible.