chapter2: Atomic Force Microscopy:Theory,practice,applications

AFM University Introduction to Atomic Force Microscopy by Paul West

2.2.3 Integrating LL-Force Sensors and Scanners

2.2.4 Z Motors-Probe Approach

2.2.5 X-Y Stage

2.2.6 Optic Microscope

2.2.7 Mechanical Loop

2.3 Electronics

2.4 AFM Acquisition Software

2.5 LL-AFM Cantilevers and Probes

2.6.1 Vibrations

2.6.2. Environmental Scanning

2.6.3 Heating/Cooling Stages

2.6.4 Higher Speed AFM Scanning

Chapter 2

There are two primary mechanisms that may be used for the Z motion control, Figure 2-21. In the first, three lead screws are used together with a kinematic mount. All three screws can be turned simultaneously or a single screw may be turned. If only one of the screws is turned, there is a reduction of motion at the center of the three screws. This geometric reduction in motion can be used to get very precise motion. For automated tip approaches, one of the lead screws may be attached to a motor. In the second method, a linear bearing is used to drive the AFM scanner towards the sample. The linear bearing must be very rigid to avoid unwanted vibrations.

FIGURE 2-21 Left: On AFM’s designed for small samples, a kinematic mount is typically used. One of the threaded screws can be motorized for an automated probe approach. Right: A linear bearing can be employed to move the AFM head in the Z axis.

2.2.5 X-Y Stage

Most AFMs include an X-Y position stage for moving the sample relative to the probe. The stage may be manual or automated with motors. The primary function of the X-Y stage is for locating features on a surface for scanning with the AFM. The resolution of the X-Y stage is usually less than 1/10 the range of the x-y scanner that moves the probe.

There are two possible configurations for the X-Y stage. In the first, the sample sits on top of an x and y crossed roller bearing. In the second, the sample is mounted to a block that is directly on the base of the microscope. Typically the base is made from granite. The metal "puck" is then pushed around with the X-Y motors. The advantage of the second design is that there is less chance of the X-Y stage introducing noise into the AFM mechanical loop, (see Figure 2-22).

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