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

我们研制了一种超高真空（UHV） STM系统，可以在同步辐射光源的照射下拍摄原子分辨STM图像。为此，我们设计了一个包括隔振台在内的抗振系统，该系统可以安装在狭窄的梁线空间内。由于同步辐射光源中光束线的位置通常具有较大的电气和机械噪声，这完全不适合STM，因此我们需要仔细考虑避免噪声干扰STM的运行，并成功地拍摄了辐照下Si(111)7x7表面的原子分辨STM图像。我们还成功地利用探针尖端作为检测器，获得了样品元素的吸附光谱；当辐照光能大于101eV （Si 2p的吸附边）时，光感应电流增大，表明STM尖端有可能探测到样品核心态发射的光电子。与以前用x射线管所做的工作相比，同步加速器产生的光感应电流要大100倍以上。光的高强度和光能对高吸附截面的可调性是高检出率的主要原因。通过对测量系统的改进，我们也可以定量地测量光感应电流。通过定量测量，我们表征了该元素检测方法的空间分辨率，该方法使用了含有au诱导的5x2和Si7x7表面的混合样品和有2微米大小的铝点排列的Si衬底。我们还开发了一种将检测区域集中在尖端的方法，通过在尖端涂覆绝缘聚合物来提高空间分辨率，并发现成功工作。

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.