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第 五 章 STM 仪器及其应用 章海军 张冬仙 （20 12. 02. 27 ）

第 五 章 STM 仪器及其应用 章海军 张冬仙 （20 12. 02. 27 ）. Outline. 5.1 Introduction 5.2 STM System 5.3 STM Applications 5.4 STS 5.5 Build a STM by yourself . 0.2  m. 0.1 nm. 30 8 年. 1674 年. 1982 年. 5.1 Introduction.

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第 五 章 STM 仪器及其应用 章海军 张冬仙 （20 12. 02. 27 ）

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  1. 第 五 章 STM仪器及其应用 章海军 张冬仙 （2012. 02. 27）

  2. Outline • 5.1 Introduction • 5.2 STM System • 5.3 STM Applications • 5.4 STS • 5.5 Build a STM by yourself

  3. 0.2 m 0.1 nm 308年 1674年 1982年 5.1 Introduction The scanning tunneling microscope (STM) is the most powerful type of microscope ever built. 光学 显微镜 扫描隧道 显微镜

  4. 瞧一瞧原子的模样 《钱江晚报》2008年2月20日C8版

  5. The world’s first STM was invented by Gerd K. Binnig and Heinrich Rohrer in 1982 at the IBM Research Laboratories in Zurich, Switzerland. 图5.1 The first STM in the world（1982）

  6. G. Binnig, H. Rohrer Scanning Tunneling Microscopy Helvetica Physica Acta 1982, 55 (6): 726-735. 10/98

  7. The STM acquired the first images of individual surface atoms 图 5.2 The first STM image of silicon atoms

  8. G. Binnig, H. Rohrer. 7×7 Reconstruction on Si(111) resolved in real space Physical Review Letters, 1983, 50: 120–123. G. Binnig. Surface studies by scanning tunneling microscopy Physical Review Letters, 1982, 49: 57.

  9. 5.2 STM 仪器系统(Instruments) For the work of STM, Binnig and Rohrer were awarded a Nobel Prize in Physics in 1986.Since the invention of STM in 1982, a great number of versions of STMs have been developed and used by research groups at universities and industrial laboratories throughout the world.

  10. 5.2.1STM系统的结构 STM之一（第一台STM）

  11. 图 5.3 An STM system operating in air

  12. 图 5.4 An STM system with UHV chamber

  13. Despite of the difference among these STM systems that are designed, built and operated in different ways, the basic concept and the main structure of them are approximately the same.

  14. STM系统的简化示意图 (Binnig & Rohrer) 20/98

  15. STM系统的简化示意图

  16.  Computer  Electronic circuits Image display; Scan control; Feedback control; Positioning; Data storage Scanning; Feedback control; Positioning control  Amplify/Process Measuring tunneling Current; Controls bias voltage  Probe unit  Vibration Isolation  Positioning

  17. 5.2.2 针尖制备 (Tip preparation) The tip is the trickiest part in the STM experiments. It needs a small curvature to resolve coarse structures. For atomic resolution, a nanotip with a one-atomic-end is necessary. STM tips are typically made out of tungsten, platinum or platinum-iridium wires. 图 5.7 Pt-Ir wires for preparing STM tips

  18. Which tip is better or the best ? 5-1

  19. 0.25 mm×1m = 500 元 STM针尖的分类 钨丝针尖 (tungsten , W)：适用于真空 按材料分 铂—铱针尖 (platinum-iridium, Pt-Ir) 多重针尖 (multi-tip or mini-tip) 按结构分 单原子针尖 (nano-tip)

  20. 单原子针尖——针尖只有一个原子

  21. 多重针尖——针尖有多个原子 原子图像？ OK ! ! S

  22. 原子图像？ OK ! ! 30/98

  23. Multi-tip

  24. Multi-tip 30/94

  25. DC etching AC etching STM tip preparation Mechanical cutting and grinding Electrochemical etching Field evaporation: preparing nano-tip

  26. e b Mini-tip a b d Mechanical cutting Mini-tip 图 5.8 Pt-Ir tip made by mechanical cutting

  27. DC etching 形状类似于 光纤探针、毛细管探针 钨丝针尖的制备 不锈钢环 W NaOH 图 5.10 A setup of DC electrochemical tip etching

  28. In DC electrochemical etching, the tungsten (W) wire is put into 2M NaOH (Sodium hydroxide)solution and kept on a positive potential towards a counter electrode. The etching process takes place predominately on the surface of the solution. When the neck is thin enough, the wire fractures due to its weight. 图 5.11 STM tips prepared via DC electrochemical etching

  29. AC etching In AC method, 10% potassium hydroxide solution is used with 10~20V AC bias to etch 0.2~0.5mm diameter tungsten wire. The typical current is 2~3A. The side of the wire will etch more quickly than the bottom, causing the wire to “neck” into a sharp tip shape. The aspect ratio can be controlled by the exposed length of wire to the solution and the time that the applied voltage is shut off. AC Etching is another more elaborate way of constructing a tip for the STM. However, if performed careful, the AC etching method can provide even higher resolution.

  30. 铂铱合金丝针尖的制备 40/98

  31. Field evaporation To further make a nano-tip from mini-tip prepared via cutting or electrochemical etching, the field evaporation method is introduced. The basic principle of this method is to do tip-sharpening during tunneling. We first bring the W tip and the sample into a tunneling state. The bias voltage U is then suddenly increased to about 7V (at the sample) for 2~4 scan lines.

  32. By this treatment some W atoms may walk to the tip apex due to the non-uniform electric field, and finally form a nano-tip. nano-tip Mini-tip U ～1 nm Sample （a） （b） 图 5.13 Preparation of nano-tip via field evaporation method

  33. 5.2.3 样品制备 (Sample preparation) Graphite is a layered material. It is made of large plates of carbon which have weak bonds holding the layers together. These weak bonds are represented by dashed lines in the figures below. In order to expose a layer of graphiteit needs to be cleaved.Cleaving is a very simple process where you stick a piece of scotchtape to the surface of the graphite，and pulls up the top layer of graphite leaving a flat surface below. It also removes any impurities on the surface.

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