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Therefore, the actual magnifications are different in these three cases. But we see that L m is always changing unless we measure from the microscope PC. L m2, then, is the same image being viewed on a laptop computer, and L m3 would be yet a third length obtained by the image that is projected onto a projection screen, say, if you were giving a PowerPoint presentation.įor these three copies of the same image, we have one value of L s, corresponding to the actual horizontal field of view of the image, for example, in microns. In these three examples, L m1 is supposed to represent the original image being viewed on the microscope PC. Example of the data bar seen in an SEM image. The one shown here has a value of 35,000X, but it would not be accurate if the same image is viewed on any other screen. I say nominal because it only applies to images that are viewed on the microscope PC. Something it nearly always includes is a nominal magnification. In almost all SEM images, you will see a data bar somewhere in the image, like the one shown here. Shorter distances result in higher magnification images. The SEM takes care of this by changing the distance the beam is moved over the sample. If we look at this equation, we see that the monitor length is fixed, so if the magnification, M, is to change, that means that the value of L s must change. The ratio of each length should be the same, that is, they should yield the same magnification. The length measured can be anything from the side of a single pixel all the way up to the entire horizontal or vertical field of view. SEM magnification is defined as the ratio of a length measured from the SEM monitor-L m-to the same length measured on the sample-L s. So to begin this discussion, I will introduce some of the relevant concepts concerning calibration and verification, and I will begin with the concept of magnification.

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It may also be required for accredited laboratories, such as if you have an ISO 17025 accreditation. In an industrial lab, there may be a particular operator appointed to checking the calibrations. Who usually checks the magnification calibration? In academia, it is usually the microscope specialist or lab manager, or an experienced user that is concerned about calibration. You may think that the SEM service engineer has calibrated the instrument so you don’t have to worry about it, but they don’t always use traceable standards for that calibration. Here at MA, for example, we check this annually, or after a major service call. When you ask yourself if the measurements you are making are accurate or not, what you are really asking yourself is, “Has this SEM been properly calibrated?” Some labs have protocols in place where this is checked at regular intervals. In any project I’ve done where measurements are made, this question always gets asked by the client, and it is an important question, so we wanted to address it in some detail here today.

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The topic I would like to discuss today is one of great importance to an SEM operator, and that is how to ensure that measurements made from SEM images are accurate.

Mak Koten (MK): Thanks, Chuck, for that warm introduction, and thank you all for joining us this afternoon for our webinar! We are very pleased to have you. Now, I will hand the program over to Mak.

This webinar is being recorded and will be available on The McCrone Group website under the Webinars tab. Mak will field questions from the audience immediately following today’s presentation. He is also one of the instructors for our Scanning Electron Microscopy course here at Hooke College of Applied Sciences. He designs and conducts experiments that will help clients better understand and solve specific problems such as product contamination, product specifications failure, and unknown manufacturing or processing issues. Mak is part of McCrone Associates’ electron optics group, where he specializes in materials characterization and phase identification via a combination of X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and transmission electron microscopy. Mak is going to talk to us about “SEM Magnification Calibration and Verification: Building Confidence in Your Scale Bar.” Before we get started, I would like to give you a bit of Mak’s background. My name is Charles Zona, and today we welcome Mak Koten. Charles Zona (CZ): Hello, and welcome to another McCrone Group webinar.