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STM设备，并安装在同步辐射装置在筑波。将样品室放置在X-Y-Z台上。X射线束（1 x 0.04 mm）以小入射角照射表面。首先，进行样品位置的调整。当X射线以正确的方式照射样品时，STM尖端电流增加。因此，我们通过监测该STM尖端电流来调整样品位置。然后用旋转泵和涡轮分子泵对样品进行抽真空。最后，停止这些泵并使用离子泵，测量层状样品，如Au（或Ni）-Pt-Si晶片。在真空蒸镀Au时，采用小颗粒作为掩膜，得到了具有小孔的Au层。当X射线照射样品时，可以观察到STM尖端电流。即使施加同步辐射，这个电流也太小了，只有几个pA。对X射线照射前后的STM图像进行比较。然而，未观察到明显差异。隧道电流约为0.5 nA，这是相当大的比X射线诱导的STM尖端电流。我们认识到在同步辐射装置上的实验中应改进的几点。我们打算继续这个实验。

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.