Elemental Analysis for Scanning Tunneling Microscope by using X-ray Induced Tunneling Current (Development of Elemental Analysis STM)

我们开发了超高真空扫描隧道显微镜设备，并安装在筑波的同步辐射设施上。在X-Y-Z工作台上放置样品室。X射线束(1×0.04 mm)以小角度照射表面。首先，调整样品的位置。当X射线以正确的方式照射样品时，STM针尖电流增加。因此，我们通过监测这一STM针尖电流来调整样品位置。然后，用旋转泵和涡轮分子泵抽真空样品。最后，停止这些泵并使用离子泵。测量了Au(或Ni)-Pt-Si晶片等层状样品。当真空蒸发Au时，使用小颗粒作为掩模，从而获得具有小孔的Au层。此样品可用于评估横向分辨率。当X射线照射样品时，观察到STM针尖电流。即使使用同步辐射，这个电流也太小了，几帕。比较X射线照射前后的扫描隧道显微镜图像。然而，没有观察到明显的差异。隧道电流约为0.5nA，比X射线诱导的STM尖端电流大得多。我们认识到，在同步辐射设施的实验中，有几点需要改进。我们打算继续这项实验。

We developed ultra-high vacuum STM equipment, and installed to Synchrotron radiation facility in Tsukuba. Sample chamber was placed on X-Y-Z stage. X-Ray beam (1 x 0.04 mm) irradiated the surface at small incident angles. First, adjustment of sample position was performed. When the x-rays irradiated the sample in the correct way, the STM tip current increases. Therefore, we adjusted the sample position by monitoring this STM tip current. Then, sample cumber was evacuated by rotary pump and turbo-molecular pump. Finally, these pumps were stopped and ion pump was used.Layered samples such as Au (or Ni)- Pt-Si wafer were measured. When the vacuum evaporation of Au, small particles were used as mask, as a result, Au layer with small holes was obtained. This sample is useful to evaluate lateral resolution.When X-rays irradiate the sample, the STM tip current is observed. This current was too small even if synchrotron radiation was applied, several pA. The STM images with and without x-ray irradiation were compared each other. However, clear difference was not observed. The tunneling current was about 0.5 nA, which was considerably larger than x-ray induced STM tip current. We recognized several points that should be improved for the experiments at the Synchrotron radiation facility. We intend to continue this experiment.