Chapter_5_ - CHAPTER 5 Process, Display, Analyze Software...

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Process, Display, Analyze Software CHAPTER 5 97 AFM images are stored in a computer as a three dimensional array of numbers. Te array of numbers can be processed, displayed, analyzed and then reported by specialized image processing software. AFM image processing software is typically just a little di±erent than image display software that is used for traditional microscopes, such as optical and scanning electron microscopes. Te major di±erence is that the AFM images have three dimensional topography content and the traditional microscopes do not; i.e., traditional microscopes do not have height information. De²nitions for the various functions of AFM image processing software are: Process: Changes the data in the image and includes functions like ²ltering and background subtraction. Display: Changes the view of the data on the computer screen and includes the type of colors used and the perspective of the display. Analysis: Achieves the abstraction of quantitative information such as line roughness. Report: Images and analysis dialog boxes may be exported to a clipboard or to Microsoft ³M Office products with the report functions. Te following sections describe the primary functions in each of these steps.
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Chapter 5 • Process, Display, Analyze, Report Software 98 5.1 Process 5.1.1 Leveling AFM images always have some background slope or curvature that must be removed from the image. Sources of the background can be an o±set angle between the probe and surface, or curvature introduced into the image from the xyz scanner. Tere are several algorithms that are used for “leveling” the images. Te primary methods are: Line: Line by line leveling is the most common method for leveling AFM images. In this method each horizontal, or vertical, line in an image is ²t to a polynomial equation, and then the polynomial shape is subtracted from image line. Ten, the average height of each line is set equal to the previous line (see Figure 5-1). Tree point: In the three point method, the AFM operator identi²es 3 points on an image. Te three points de²ne a plane which is then subtracted from an image. Tree point leveling is ideal for samples that have terraces where the background bow associated with the scanner is much less than the height of the terraces. FIGURE 5-1 Line by line leveling is the simplest method for removing unwanted background bow and tilt from AFM images. A line is “±t” to each of the scan lines, and then the “±t” line is subtracted from the scan line. Lowest Point Average Points Highest Point
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99 Chapter 5 • Process, Display, Analyze, Report Software FIGURE 5-2 Areas of an image may be selected and then the background removal, or leveling, does not use these areas in background subtraction calculations. Inclusion/Exclusion: Often AFM images have a few isolated features
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Chapter_5_ - CHAPTER 5 Process, Display, Analyze Software...

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