第 五 章  

 STM 仪器及其应用

章海军 张冬仙（ 2012. 02. 27 ）

5.1 Introduction

5.2 STM System

5.3 STM Applications

5.4 STS

5.5 Build a STM by yourself

OutlineOutline

5.1 Introduction

光学显微镜

扫描隧道显微镜

The scanning tunneling microscope (STM) is the most powerful type of microscope ever built.

308年

0.2 m 0.1 nm

1674 年 1982 年

瞧一瞧原子的模样《钱江晚报》 2008 年 2 月 20 日

C8 版

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 ）

G. Binnig, H. Rohrer

Scanning Tunneling Microscopy

Helvetica Physica Acta

1982, 55 (6): 726-735.

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The STM acquired the first images of individual surface atoms

图 5.2 The first STM image of silicon atoms

G. Binnig, H. Rohrer. 7×7 Reconstruction on Si(111) resolved in real spacePhysical Review Letters, 1983, 50: 120–123.

G. Binnig. Surface studies by scanning tunneling microscopyPhysical Review Letters, 1982, 49: 57.

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.

5.2.1 STM 系统的结构

STM 之一（第一台 STM ）

图 5.3 An STM system operating in air

图 5.4 An STM system with UHV chamber

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.

STM 系统的简化示意图 (Binnig & Rohrer)STM 系统的简化示意图 (Binnig & Rohrer)

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STM 系统的简化示意图STM 系统的简化示意图

Probe unit

Positioning Vibration Isolation

Image display;Scan control;Feedback control;Positioning;Data storage

Computer

Measuring tunneling Current;Controls bias voltage

Amplify/Process

Scanning; Feedback control;Positioning control

Electronic circuits

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

Which tip is better or the best ?Which tip is better or the best ?

5-1

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)

0.25 mm×1m= 500 元

单原子针尖——针尖只有一个原子

多重针尖——针尖有多个原子

原子图像？ OK ! !

原子图像？ OK ! !S

原子图像？ OK ! !

原子图像？ OK ! !

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Multi-tip

Multi-tip

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STM tip preparationSTM tip preparation

Mechanical cutting and grinding

Electrochemical etchingDC etching

AC etching

Field evaporation: preparing nano-tip

Mini-tip

图 5.8 Pt-Ir tip made by mechanical cutting

Mini-tip

a

b

b

d

e

Mechanical cutting Mechanical cutting

图 5.10 A setup of DC electrochemical tip etching

NaOH

W 不锈钢环

DC etching DC etching形状类似于

光纤探针、毛细管探针钨丝针尖的制备

图 5.11 STM tips prepared via DC electrochemical etching

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.

AC etching 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.

铂铱合金丝针尖的制备

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Field evaporation 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.

～ 1 nmU

（ a ） （ b ）

图 5.13 Preparation of nano-tip via field evaporation method

Sample

Mini-tip nano-tip

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.

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.

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 graphite it 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.

解理 Cleave

HOPG (Graphite) Graphene

石墨烯（ Graphene）石墨烯（ Graphene）

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康斯坦丁诺沃肖洛夫 (1974－ )

Konstantin Novoselov

安德烈海姆 ( 德、俄、荷 1958－ )

Andre Geim

2010 年诺贝尔物理学奖获得者（英国曼彻斯特大学）

荷兰奈梅亨大学

Left: SEM micrograph of a single-electron transistor based on a graphene quantum dot. Right: Schematic of a hypothetical transistor based on a very small graphene quantum dot.

Andre Geim, 2008, Science 320: 356

1. L. A. Ponomarenko, …S. Novoselov, A. K. Geim. Chaotic Dirac Billiard in Graphene Quantum Dots. Science, 2008, 320: 356-358. 2. R. R. Nair, … K. S. Novoselov, A. K. Geim. Fine Structure Constant Defines Visual Transparency of Graphene. Science, 2008, 320: 1308-1308. 3. K. S. Novoselov, … A.K. Geim. Room-temperature quantum Hall effect in graphene. Science, 2007, 315(1379): 1379-1379. 4. J. C. Meyer, A.K. Geim, K.S. Novoselov. The structure of suspended graphene sheets. Nature, 2007; 446: 60-63. 5. A. N. Grigorenko, A.K. Geim. Nanofabricated media with negative permeability at visible frequencies. Nature, 2005, 438: 335-338. 6. K. S. Novoselov, A.K. Geim. 2D Gas of Massless Dirac Fermions in Graphene. Nature, 2005, 438: 197-200.7. Novoselov, K. S.; Geim, A. K. Subatomic movements of a domain wall in the Peierls potential. Nature, 2003; 426: 812-

1. L. A. Ponomarenko, …S. Novoselov, A. K. Geim. Chaotic Dirac Billiard in Graphene Quantum Dots. Science, 2008, 320: 356-358. 2. R. R. Nair, … K. S. Novoselov, A. K. Geim. Fine Structure Constant Defines Visual Transparency of Graphene. Science, 2008, 320: 1308-1308. 3. K. S. Novoselov, … A.K. Geim. Room-temperature quantum Hall effect in graphene. Science, 2007, 315(1379): 1379-1379. 4. J. C. Meyer, A.K. Geim, K.S. Novoselov. The structure of suspended graphene sheets. Nature, 2007; 446: 60-63. 5. A. N. Grigorenko, A.K. Geim. Nanofabricated media with negative permeability at visible frequencies. Nature, 2005, 438: 335-338. 6. K. S. Novoselov, A.K. Geim. 2D Gas of Massless Dirac Fermions in Graphene. Nature, 2005, 438: 197-200.7. Novoselov, K. S.; Geim, A. K. Subatomic movements of a domain wall in the Peierls potential. Nature, 2003; 426: 812-

中国的石墨烯热 (2011.02)

5.2.4 扫 描 与 反 馈 控 制 器(Scanner)螺旋测微器、电控微动台 ?螺旋测微器、电控微动台 ?

图中所示为一压电陶瓷片， P 为极化方向，当如图中所示加上与极化方向相同的电场方向时，其沿 t 方向会伸长 t=d33V ，沿 l 方向收缩 l=d31V(l/t) ，如果将电场方向颠倒，则在 t 方向上为收缩， l 方向上为伸长，收缩与伸长量不变。

1. PZT ~ Pb(Zr, Ti)O3 ~ Piezoelectric element

P

l

t

收缩

+

－

Stack PZT

＋

—

Tube PZT

—

＋

图 5.14 A tripod scanner and feedback controller

tip

2. Tripod The tip is controlled by three orthogonal piezos, two for XY scanning and one for Z feedback controlling.

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图 5.15 A single tube scanner

3. Single tube scanner A cylinder, made out of piezo elements and covered with metal, serves as the scanner. The outer electrode is divided into four sectors.

5.2.5 进给机构 (Coarse Positioner)

1. Mechanical positioner The tip approaches the sample with the help of springs, de-magnifier and micro-screws ， etc.

2. Louse

图 5.16 Mechanical Positioner 图 5.17 Louse

3. Beetle The Beetle consists of a plate with three piezoelectric tubes, standing on a cylindrical ramp. The sample is mounted in the middle of the ramp whereas the tip with the fine positioner is mounted onthe plate.

图 5.18 Beetle

4. Inchworm actuator To bring the reference unit into tunneling controlled state, an inchworm actuator can be applied to position the probe tip.

Inchworm actuator

5. Impact drive mechanism The movement sequence of impact drive mechanism (IDM) is shown in Fig.5.20.

图 5.20 The principle of impact drive mechanism

前置放大器

Vref

比较放大器

积分器高压放大器

A/D&

D/A

X

Y

放大器高压放大器

Z

VZ

VX

VY

Scan

Feedback

It

Scanner

Tip

Sample

It

5.2.6 控制电路 (Electronic circuits)

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Scheme of pre-amplifier of STMScheme of pre-amplifier of STM

10M

A ＝ 10–9×107 ×10

＝ 0.1 V/nA

R2=9R1

?C

B

金属封装

D

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5.2.7 防震 (Vibration isolation)

图 5.22 Vibration isolation for STM

STM system with UHV chamber at Zhejiang University

50 万欧元 ＝ 550 万元人民币

STM 仪器小结

5.3 STM 在原子图像检测与微纳测试中的应用

STM 适用于STM 适用于

大气环境大气环境

真空中真空中

液体环境液体环境

图 5.26 STM images of Si(111)-7×7 with positive (left) and negative (right) bias.

Before the invention of STM it was known that the surface unit cell of Silicon is constructed of 49 Si(111) original cells.

1. Si(111)-7×7

高温下Si原子晶格的重构

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5-2

When the first Au(111) STM images with atomic resolution were taken ， some features had already been known or assumed by LEED experiments.

图 5.28 Atomic resolution imageof Au(111)

2. Au(111)

3. HOPG Highly oriented pyrolytic graphite or HOPG is not only one of the most commonly used STM substrates, but also an ideal atomic scale.

高定向热解石墨

5-3

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图 5.30 STM images of HOPG and Xe lattices

Z 向尺度的非线性 5-4

STM image of C(4×2) at － 139°C

4. STM image of SO42 on Cu(111)

5.Mica 云母

6. Atomic steps

7. Standard gratings 5-5

8. Carbon nanotube

9. Nano-materials 5-6

10. Biological specimen---DNA

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5.4 扫描隧道谱 (STS)

By measuring the dependence of the

tunneling current on the tip-surface gap or the

bias voltage, spectra containing information

about the work function or density of states on

the surface can be obtained. Furthermore,

because tunneling only occurs over an area

<1nm2 on the surface, such spectra reveal these

properties on an atomic scale.

隧道电流： It Vbexp （ -A

S ） Vb 一定时： It ～ S 的关系—图像

It 一定时： Vb ～ S 的关系曲线

S 一定时： It ～ Vb 的关系曲线

其他关系曲线

Characteristics of STM Characteristics of STM

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Rohrer