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12th January 2022 | Author: Hui Jiang
In the past, when I used SEM for composition analysis, the usual workflow was to scan an electron image first, find a position and stay, adjusting the focus, brightness and contrast and other parameters, and then perform EDS point analysis or mapping. If the location is not ideal, the above process needs to be repeated several times to find a suitable collection area for further detailed analysis. I believe many practitioners have a similar experience to mine and agree this repeated search and repetitive work is time consuming and exhausting . When I work on unfamiliar samples, I also worry about missing anything interesting and important.
Since Oxford Instruments launched the AZtecLive Chemical Imaging system, I have changed my working habits and browsed samples directly in real-time through AZtecLive, looking for representative areas in live EDS element distribution maps overlayed on the electron image by continuously driving stage around. It has greatly improved work efficiency.
Let’s now have a look at a sample for particle analysis. In this case, we are determining technical cleanliness in component manufacture: a ball bearing, which is a key component in many types of vehicles. This sample was prepared by washing a known volume of finished product. These particles were captured on a membrane filter, which was then attached to a sample stub and coated with carbon to minimise charging of the non-conductive filter material under the electron beam of the SEM.
This particle data gives an overall assessment of the particle population, indicating the types of particles present and their abundances. From this, the cleanliness level of components can also be determined. Before setting up for automated particle analysis, we use Live Chemical Imaging to rapidly understand what elements and types of particles there are and see if there are different types of particles joined together which need to be separated using our advanced mapping function working along with particle analysis. While navigating the sample, I am also looking for a representative area for the particle analysis experiment I intend to do later.
As you can see from the video, when we start scanning an electron image, we get auto ID and maps for the elements that are present. Instantly, we know there are some steel particles which could be coming from the inner ring and outer cage. There are also Si oxides, calcium carbonates and calcium silicates. I very quickly start to have a good idea of what type of particles we have in the sample.
The video also shows a case where particles are touching each other. Ideally, when samples of this sort are prepared, particles will be evenly distributed over the whole surface of the filter without touching or overlapping. However, in practice, it is often difficult to avoid having any touching or overlapping particles. Multiple phases may have similar grey levels, meaning that when they overlap, it is impossible to separate them from one another using grey level thresholds. However, it can be clearly distinguished through the element distribution map obtained in real time. Live Chemical Imaging maps them and indicates there are two phases, and if we change to spot mode and collect spectra from them, one of them is steel and the other is silicate, so we understand there are two phases within the particle. This information would have been lost without using Live Chemical Imaging. Being aware of this problem at earlier stage helps us optimise settings in AZtecFeature to solve this problem when carrying out particle analysis later.
Live Chemical Imaging helps me review the sample quickly and determine optimised settings to use.
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