原子力显微镜
（Atomic Force Microscope，AFM）
主要用途/ Application：
准确观测样品表面微区(纳米及亚微米尺度)三维形貌；同时可以对样品表面的电场/磁场分布、表面电势等进行扫描。
Mainly applied in high resolution observation of surface morphologies, and simultaneous detection of surface physical characteristics, including EFM，MFM，AM-KPFM and PFM etc.
设备工作原理简介/ Operating principle：
系统以悬臂振幅作为反馈信号，扫描开始时，悬臂的振幅等于阈值，当探针扫描到样品形貌变化时，振幅发生改变， 探测信号偏离了阈值而产生了误差信号。系统通过 PID 控制器消除误差信号，引起扫描管的运动，从而记录下样品形貌。整个 AFM 系统如图 1-2 所示。
图 1. AFM 工作原理示意图。
Most AFMs use optical techniques to detect the position of the cantilever. In the most common scheme, a light beam from a laser diode bounces off the back of the cantilever and onto a quad photo-detector (QPD). As the cantilever bends, the position of the laser beam on the detector changes. The ratio of the path length between the cantilever and the detector to the length of the cantilever itself produces amplification. As a result, the system can detect sub-Ångstrom vertical movement at the free end of the cantilever, where the tip is located.
A QPD typically consists of four segments (segment A, B, C, and D), and each segment is independent of the others. When a laser spot shines on the QPD, each segment generates a voltage signal. Th voltage generated from each segment is proportional to the amount of laser light on that particular segment. The sum of voltage from all four segments is called the SUM signal, SUM=A+B+C+D. The difference between top two segments and the bottom two segments is called the Vertical Deflection signal. This signal is typically normalized by the SUM signal to eliminate effects of laser power fluctuation or Vertical Deflection = [(A+B)-(C+D)]/SUM. Similarly, the amplified differential signal between the sum of the two left photodiodes and the sum of the two right photodiodes, the Lateral Deflection = [(A+C)-(B+D)]/SUM, provides a measure of the torsion in the cantilever.
When the cantilever slightly bends upward because of a tip-sample interaction force change, the cantilever changes slightly its angle. Because of this change, the direction of the reflected laser beam from the back of the cantilever will change; consequently the laser spot position on the QPD will change. When the laser spot move up on the QPD, more light shines on the segments A and B, and less light shines on C and D, so the Vertical Deflection signal increases. So by monitoring the Vertical Deflection, we can know how much the cantilever is bending. Essential to fine control of the distance between tip and sample is a feedback loop which reacts to the bending of the cantilever. Perhaps the simplest implementation of such a feedback loop is that of Contact Mode Imaging, in which the DC deflection signal is monitored to keep the cantilever statically bent at a constant angle (the setpoint) while the surface is scanned. During scanning the z-piezo moves up and down to maintain the setpoint deflection signal. This distance provides the topography information. Other AFM modes, for instance TappingMode AFM, oscillate the cantilever and monitor the amplitude and phase of an AC deflection signal at a specific frequency. Similar to contact mode, a specific tapping amplitude is maintained while scanning.
技术指标/ Specifications：
- XY方向扫描范围90um×90um，Z方向扫描范围10um，XY全范围运动最大高度起伏低于4nm；
- 智能自动进针方式；
- 210mm真空吸附全自动样品台，可程序化控制；
- 配置接触模式、轻敲模式、相位成像模式、压电响应测试模式、智能扫描模式；
- X-Y axis scanning range 90um×90um,Z-axis scanning range 10um, XY scanning maximum height variation is lower than 4nm;
- Auto probe;
- 210mm auto specimen stage with vacuum absorption;
- Scanning mode: Contact mode, Tapping mode, Phaseimaging, Piezo Response Force Modulation (PFM), ScanAsyst mode;
典型使用案例/ Typical scenario：
提供智能扫描模式：要求采用以正弦波驱动压电陶瓷管做力曲线的皮牛级力作反馈进行表面成像，且力曲线频率≥2000Hz。只需要选择扫描范围，系统就能够在扫描过程自动调节“接触力”，“电路增益”，“扫描速度”和“扫描管的量程范围”。
设备类别/Facilities：测试设备/ Characterization
设备编号/No.：ETE3AFM01
设备地点/Location：东区测试III区/ East Testing III Area
工艺工程师/Engineer in response:
姓名：沈贇靓；邮箱：shenyunliang@sjtu.edu.cn；电话：021-34207734-8010
Name: Yunliang Shen；Email：shenyunliang@sjtu.edu.cn; Tel: 021-34207734-8010.
设备照片/Photos：
