I am adding some new entries to the AFM FAQ. Here they are below. To get the answer to your question, contact me with the contact page.Sandhya asks:
Can you please tell me about feed back control. I found it difficult to understand Proportional control, gain and band
and integral gain. From your FAQ AFM, I understand that set point is force
applied on sample by tip.
A: This is a very common question when people start to use AFM. Most AFMs use a PI controller. This is a kind of simplified PID controller. To control the feedback circuits, you change the P and I values. P stands for proportional and I for Integral. However, commonly in the AFM software they are referred to simply as P and I. To understand what these really mean, look at PID controllers on wikipedia, or look at chapter 3. In some instruments, D (derivative) may also be available.
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Chapter 3 is all about the different AFM modes and experiments that can be carried out. The variety of different imaging methods, and the ability to use other modes to detect different properties of the sample, are the real reason for the widespread use of AFM.
In this chapter, the book covers: Topographic modes: contact mode and oscillating modes. Then it moves onto non-topographic modes, including force spectroscopy, Nanoindentation, mechanical property imaging, lateral force microscopy, phase imaging, other dynamic modes, magnetic force microscopy, EFM and SKPM, electrochemical AFM, and thermal modes.Finally, it also covers methods that allow surface modification.
Chapter 3 - AFM modes
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Chapter 5: Processing AFM Images
This chapter covers how to process, display and analyse AFM data. It mostly covers manipulation of topographic data, but some of these techniques apply to other data as well. Since the best data still needs the best treatment to extract desired results, it is important that AFM users are aware of the benefits (and pitfalls), of data processing and analysis techniques.
After reading the chapter, it is advisable to take this test since it will ensure that you are aware of the most important concepts in correct data treatment.
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Measuring AFM Images
This chapter explains how to measure AFM images properly.The topics covered include sample preparation, preparing the microscope for imaging, including optical alignment, optimisation of imaging parameters, and acquiring high-resolution images. There are sections covering contact mode, intermittent contact, lateral force microscopy and acquiring other signals, and measuring force curves.
The quiz will check if you remember important concepts, and avoid common mistakes when acquiring data.
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Chapter 6: AFM Artifacts
In this chapter, common problems in AFM images are discussed. Some of these artifacts are inherent to the technique, and are impossible to avoid. Others depend on the particular instrument used, or the properties of the probe selected. Some are due to imaging parameters, and can be easily avoided. In each section, the artefact is described, the reason for the appearance of the artifact is discussed, and steps that can be taken to avoid it are given. In nearly all cases, there is an illustration of the artefact in a real AFM image.
Take this test to see if you can recognise and understand the reason of, common AFM artifacts, and realise how they can be avoided.
1. Which of these two images was taken with a sharp probe?
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