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Chapter_6_ - CHAPTER 6 AFM Image Artifacts All measurement...

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AFM Image Artifacts CHAPTER 6 110 All measurement instrumentation used by scientists and engineers for research, development and quality control generates results that may have artifacts. This chapter serves as a guide to identifying common artifacts that occur in AFM images. This guide is organized in sections that are divided by the sources that generate the image artifacts. There are four primary sources of artifacts in images measured with atomic force microscopes. They are: • Probes • Scanners • Image Processing • Vibrations 6.1 Probe Artifacts Images measured with an atomic force microscope are always a convolution of the probe geometry and the shape of the features being imaged. If the probe is much smaller than the features of the images being measured, then the probe-generated artifacts will be minimal and the dimensional measurements derived from the images will be accurate. Avoiding artifacts from probes is achieved by using the optimal probe for the application. For example, if the features that are being imaged have feature sizes of interest in the 100 nanometer range, a probe as large as 10 nanometers in diameter will be adequate for getting good images with no artifacts. In some cases, even if the probe is not as sharp as the object being imaged, it is still possible to get accurate information from the image.

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111 Chapter 6 • AFM Image Artifacts FIGURE 6-1 Motion of an AFM probe as it goes over a sphere that is attached to a surface. In such a measurement the side of the probe will cause a broadening of features in the image. FIGURE 6-2 A-B: 400 × 400 nm AFM image of an 8 nm diameter sphere. A: The line profile of the image shows a diameter of 92 nm and a height of 8 nm. B: The broadening in the image is caused by the shape of the probe used for measuring this AFM image. 6.1.2 Features in an Image Appear Too Small If the probe needs to go into a feature that is below the surface, the size of the feature can appear too small. The line profile in these cases is established by the geometry of the probe and not the geometry of Common artifacts are: Features on a surface appear too large Features in an image appear too small Strangely shaped objects Repeating strange patterns in an image 6.1.1 Features on a Surface Appear Too Large Often the size of features on the surface such as nanotubes or nanospheres look larger than expected. However, the height of the feature when measured by a line profile is correct.
Chapter 6 • AFM Image Artifacts 112 FIGURE 6-3 The motion of an AFM probe as it moves over a hole in a surface. Because of the width of the probe, it does not reach the bottom of the hole. the sample. However, it is still possible to measure the opening of the hole from this type of image. Also, the pitch of repeating patterns can be accurately measured with probes that don’t reach the bottom of the features being imaged.

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