Development of STM-TOF mass analyzer and its application for material analysis

在本项目中，我们开发了用于纳米表面分析的高灵敏度和高分辨率的TOF-MS。我们的研究目的是将TOF- ms与UHV-STS/STM相结合，开发一种新的TOF分析系统，可以在原子或分子水平上分析纳米级样品表面的化学成分、化学结构和化学状态。首先，经过多次修改和试验，我们开发了UHV-STS/STM组合的TOF- ms，然后，通过在TOF中引入小尺寸脉冲离子源，我们研究了基于离子束激发解离的TOF- ms。此外，我们还研究并建立了激光辅助电离法测量系统，该系统采用激光脉冲照射样品表面。特别是在这种情况下，在STM测量中，我们通过在大范围内改变偏置电压，得到了电流与针尖与样品之间距离的基本关系。在激光辅助电离法中，我们将波长为355nm的YAG激光激发光束聚焦到STM测量系统的顶端。通过这种处理，我们可以发现样品表面解离离子的强度与激光脉冲强度之间的相关性。在此基础上，以偏置电压和尖端电流为参数，得到了激光脉冲产生的离解离子强度与参数之间的关系，得到了适用于可变材料的有效电离的有用知识。目前，我们正在改进焦点电场，寻找开发高效TOF探测器的最佳条件，并研究通过尖端扫描测量将解吸离子的分布转化为二维图像。

In this project, we developed high sensitive and high resolute TOF-MS for nano-surface analysis. The aim of our study is to develop the new TOF analyzer system that can analyze chemical composition, chemical structure and chemical state of nano-order sample's surface in atomic or molecule size level, by combining TOF-MS with UHV-STS/STM.First, we developd the TOF-MS combined UHV-STS/STM after many revisions and trials, Next, by introducing small size pulse ion source to the TOF, we studied TOF-MS based on ion-beam excited dissociation. In addition, we studied and built up the measurement system that can be used laser assist ionization method in which surface of sample was irradiated with laser pulse. Especially, in these cases, about STM measurement, we got basis date about the relation between the current and the distance between tip and sample, by varying bias voltage in wide range. In the laser assist ionization method, we focused the excitation beam of YAG laser at 355 nm onto the top of tip in the STM measurement system. With this treatment, we could find the correlation between the intensity of dissociated ion from the surface of sample and intensity of laser pulse. More over, based on these results, using bias voltage and current of tip as the parameters, we found the relation between parameters and intensity of dissociated ion originated from laser pulse, and got useful knowledge about effective ionization suitable for variable materials.At present, we are improving the focal electric field and found the optimal condition to develop the efficiency TOF detector, and studying to translate the distribution of desorbed ion into two dimensional picture by tip scanning measurement.