Characterization of insulator surfaces after ultra-precision machining by STM/STS with high-frequency pulses

通过高频脉冲 STM/STS 进行超精密加工后绝缘体表面的表征

基本信息

批准号：
13450056
负责人：
ENDO Katsuyoshi
金额：
$ 9.73万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2003
项目状态：
已结题

项目摘要

The purpose of this study is to develop a scanning tunneling microscopy (STM)/ scanning tunneling spectroscopy (STS) system operated by high-frequency pulses in order to observe either atomic distributions or electronic structures of insulator surfaces. Furthermore, we aim at evaluating insulator surfaces after ultra-precision machining processes, and optimizing the condition of the machining process. In order to observe insulator surfaces with STM, we have to apply bias voltages high enough for electrons to tunnel into the conduction band of the insulator surface, and the voltage has to be applied as alternating short pulses (< 1 msec) to avoid the electrification and the destruction of the insulator surface. In addition, we have to develop the feedback circuit of which the source is not a displacement current originated from a stray capacitance but tunneling current between. a probe and a sample. Tunneling current spectroscopy is also necessary to elucidate defect states of insulator … More surfaces.We have developed the RC circuit in which tunneling current can be detected without being hindered by displacement current induced by a rectangular short voltage pulse. The prototype of STM system operated by high-frequency pulses has been constructed in which high-frequency rectangular voltage pulses (frequency : more than 10 kHz, amplitude: up to ±10V) can be applied to the tunneling junction. After the output of the detecting circuit of tunneling current is rectified by a diode, the signal has been controlled by a feedback loop. We have succeeded in obtaining atomic images of highly oriented pyrolytic graphite (HOPG) surfaces by the constructed system. However, atomically resolved images have not been obtained yet of either an intrinsic Si surface or a Si wafer covered with native oxides. In order to observe atomic images of these surfaces, the ratio of signal to noise of a current amplifier must be improved at a high-frequency (>100 kHz) region. At the same time, we have to achieve the higher cut-off frequency of the feedback system. We have designed a new feedback control system for high-frequency STM. The new system equips a current amplifier operated at the high-frequency region, and a lock-in amplifier in order to amplify the component of tunneling current at the specific frequency of applied rectangular pulses. This system does not need a rectifying circuit by a diode, which enhances the ratio of signal to noise. We have confirmed that the cut-off frequency of the new feedback control system is 1.0 kHz. It is expected that insulator surfaces can now be resolved in an atomic scale. Less

这项研究的目的是开发由高频脉冲操作的扫描隧道显微镜（STM）/扫描隧道光谱（STS）系统，以观察原子分布或绝缘体表面的电子结构。此外，我们旨在评估超精确加工过程后的绝缘体表面，并优化加工过程的状况。为了观察使用STM的绝缘体表面，我们必须施加足够高的偏置电压，以使电子隧道隧道进入绝缘体表面的导带中，并且必须将电压应用于改变短脉冲（<1毫秒），以避免电化和绝缘体表面的破坏。另外，我们必须开发反馈电路，该反馈电路不是源的流动电流，起源于散落的电容，而是隧穿电流。探针和样品。对于阐明绝缘子的缺陷状态，隧道电流光谱也是必要的……更多的表面。我们已经开发了RC电路，在该电路中，可以检测到隧穿电流而不会受到矩形短电压脉冲诱导的位移电流的阻碍。已经构建了由高频脉冲操作的STM系统的原型，其中高频矩形电压脉冲（频率：超过10 kHz，放大器：最高±10V）可应用于隧道交界处。在通过二极管纠正隧穿电流的检测电路的输出后，该信号已通过反馈回路控制。我们成功地通过构造系统获得了高度定向的热解石墨表面的原子图像。但是，尚未获得原始分辨的图像，尚未获得固有的Si表面或覆盖有天然氧化物的Si晶片。为了观察这些表面的原子图像，必须在高频（> 100 kHz）区域改善信号与电流放大器的噪声之比。同时，我们必须达到反馈系统的较高截止频率。我们为高频STM设计了一个新的反馈控制系统。新系统等效于在高频区域运行的电流放大器和锁定放大器，以便在应用矩形脉冲的特定频率下放大隧道电流的组件。该系统不需要通过二极管进行整流电路，这可以增强信号与噪声的比率。我们已经确认新反馈控制系统的截止频率为1.0 kHz。预计现在可以以原子量表解决绝缘体表面。较少的