Microfabrication and Joining by Field Evaporation Mechanism

本研究的目的是利用扫描隧道显微镜在空气中进行场蒸发和熔融过程，阐明纳米尺度表面改性的机理。实验中使用的针尖是在直流电源的作用下，用电化学蚀刻法生产的。当刻蚀电压为40V时，可制得曲率为33*10nm、纵横比为2.2的尖端。为了防止尖端表面氧化导致分辨率和稳定性下降，采用真空沉积的方法在尖端表面镀上了一层金薄膜。在高分辨率原子尺度（HOPG）的空气中，即使在1周后，尖端也非常稳定。在对样品进行表面修饰的偏压实验中，对样品施加负电压时，观察到样品（Si）的腐蚀。蚀刻区的深度与偏置电压的功率成正比。这一结果表明，表面改性是由电场引起的，而不是由机械接触引起的。当偏置电压为正时，样品没有发生表面修饰，可能是由于Ntype Si的Shottoky效应。从修正区域的I-S（隧道电流间隙距离）特征来看，随着扫描帧数的增加，平均障壁高度psi_m减小。这种效应是由硅的表面氧化引起的。

The purpose of this research is to clarify mechanism of surface modification in nanometer scale by field evaporation and melting process using scanning tunneling microscope in air. The tip used in the experiment was produced by electrochemical etching with DC power supply. The tip with curvature 33*10nm and aspect ratio 2.2 was produced when etching voltage is 40V. In order to prevent tip surface from oxidation whcih causes degradation of resolution and stability, tip was coated with gold thin film by vacuum deposition. The tip was very stable in air with high resolution of atomic scale (HOPG) even after 1 week. In experiment of biasing voltage to sample for surface modification, etching of sample (Si) was observed when negative voltage was applied to the sample. The depth of etching region was proportional to the power of bias voltage. This results mean that surface modification was caused by electric field, not by mechanical contact. With positive bias voltage to sample no surface modification occured, presumably caused by Shottoky effect of Ntype Si. From I-S (tunnel current - gap distance) characteristics of modified region mean barriar height psi_m was decreased as number of scanning frame was increased. This effect was rusulted by surface oxidation of silicon.