Development of STM combined with synchrotron-radiation light source and its application to elemental analysis and spin observation

我们研制了一套超高真空扫描隧道显微镜系统，利用该系统可以在同步辐射光源的照射下拍摄原子分辨的扫描隧道显微镜图像。为此，我们设计了一种包括隔振台在内的减振系统，该隔振台可以安装在狭窄的光束线空间中。由于同步辐射光源中的光束线位置通常存在相当大的电学和机械噪声，这是完全不适合扫描隧道显微镜的，我们需要仔细考虑避免噪声干扰扫描隧道显微镜的运行，成功地拍摄了辐照下Si(111)7x7表面的原子分辨扫描隧道显微镜图像，并成功地利用探针尖端作为探测器拍摄了样品元素的吸收光谱，发现当辐照光能超过101 eV时，光生电流增加，这表明扫描隧道显微镜针尖可以检测到样品芯态发出的光电子。与以前用X射线管所做的工作相比，同步加速器的光感应电流要大100倍以上。较高的光强和光能与高吸收截面的可调性是产生高检测的主要原因，对测量系统进行改进后，还可以对光生电流进行定量测量。通过定量测量，我们用一个由Au诱导的5x2和Si7x7表面和规则排列着2微米大小的铝点的硅衬底组成的样品来表征这种元素检测方法的空间分辨率。我们还开发了一种通过在尖端涂上绝缘聚合物来提高空间分辨率的方法，并成功地将探测区域聚焦在尖端。

We have developed an ultrahigh vacuum (UHV) STM system with which we can take atomically resolved STM images under an Iiradiation of synchrotron radiation light source. In order to do that, we designed an anti-vibration system including a vibration-isolation table which can be fitted in a narrow space of beamline. Since sites of beamlines in synchrotron-radiation light source are usually quite noisy electrically and mechanically, which is completely inappropriate for STM, we needed to consider carefully to avoid the noises to disturb the operation of STM, and successfully took atomically resolved STM images of the Si(111)7x7 surface under the irradiation.We also succeeded in taking adsorption spectra of the sample element by using the probe tip as a detector; it was found that the photoinduced current increases when the irradiated light energy is above 101eV, an adsorption edge of Si 2p, demonstrating a possibility that the STM tip can detect photoelectron emitted from core states of sample. Compared with the previous work done with a X-ray tube, the photoinduced current by the synchrotron is larger by a factor of more than 100. High intensity of the light and tunability of a light energy to that of a high adsorption crosssection are the main reasons for the high detection.After an modificatIon of the measurement system, we could also measure the photoinduced current quantitatively. From the quantitative measurement we characterized a spatial resolution of this elemental detection method by using a sample with a mixture of Au-induced 5x2 and Si7x7 surfaces and a Si substrate on which 2-micron size aluminum dots are regularly arranged. We also developed a method to focus the detection area on the tip for improving the spatial resolution by coating the tip with an insulating polymer and found successfully working.