Chapter_2_

Chapter_2_ - CHAPTER 2 AFM Instrumentation An AFM is a...

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CHAPTER 2 AFM Instrumentation 17 An AFM is a deceptively simple instrument that requires a considerable amount of engineering construct such that the AFM is capable of measuring images with nanometer resolution. Te basic components of an AFM are a computer, control electronics, and a stage. FIGURE 2-1 Photograph of a table top AFM illustrating the major components. They are a microscope stage, computer, electronic controller, computer monitor, and optical microscope monitor. The trackball is used for moving the sample stage in the X-Y axis. Most of the AFMs in use in laboratories around the world are table top units such as this. Resolution can often be enhanced by placing the microscope stage on a vibration isolation table. Te functions of each of the microscope’s components is: Computer: Software in the computer is used for acquiring and displaying AFM images. Also, software for processing and analyzing AFM images typically resides in the computer. Control Electronics: Te control electronics generate the electronic signals required for moving stage components such as the Z motors and the XYZ scanner. Te control electronics also digitize the images measured in the stage so that they can be displayed by the computer.
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Chapter 2 • AFM Instrumentation 18 FIGURE 2-2 A piezoelectric disc will expand radially when a voltage potential is applied to the top and bottom electrodes. The disc will change shape such that volume is preserved. Stage: An AFM stage is where the sample is placed when an image is measured. Typically, the AFM stage includes an AFM scanner and an optical microscope, along with motion control systems for moving the scanner relative to a sample in the X-Y-Z axis. An AFM may be constructed for laboratory use and easily ±t on a table top; it may also be constructed to accommodate large samples such as semiconductor wafers. An AFM capable of holding wafers can be large and have a volume of several cubic meters. Regardless of the size of the AFM, they all have the similar components. Often the electronics are separated from the stage because fans used to cool the electronics cause unwanted vibrations in the stage which reduce the resolution of the AFM. 2.1 Basic Concepts ²ere are three basic concepts that you must be familiar with to understand the operation of an AFM. ²ese are piezoelectric transducers, force transducers, and feedback control. Piezoelectric Transducers Piezoelectric materials are electromechanical transducers that convert electrical potential into mechanical motion. Piezoelectric materials are naturally occurring and may be crystalline, amorphous or even polymeric. When a potential is applied across two opposite sides of the piezoelectric, it changes geometry. ²e magnitude of the dimensional changes depends on the material, the geometry of the device, and the magnitude of the applied voltage.
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19 Chapter 2 • AFM Instrumentation Piezoelectric materials are available in a number of sizes and shapes. Typically, the expansion coeffi
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This note was uploaded on 04/09/2009 for the course MSE 111 taught by Professor Giannelis during the Fall '07 term at Cornell.

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Chapter_2_ - CHAPTER 2 AFM Instrumentation An AFM is a...

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