Hello Guys,
I'm doing the TEM of the nanomicelles. I got two different type of images from same sample and from same grid. One sample haves dark background while other haves bright background. These pictures are from same grid. Can anyone please help me with this. Why it's happening.
I believe the reason that the two images have different brightness levels of backgrounds is a combination of two things - 1 the inherent electron density contrast in the sample, 2 the autobrightness and contrast mechanism of the software. In the first image, with the bright background, the grains in the image appear to be relatively dense and have high electron contrast with respect to the background. (They also display well-formed crystal faces). The autobright/contrast sotware has adjusted so that the full range of bright levels are present in the image. This leads to a 'normal' image where you see dark particles against a bright background. In the second image, with the dark background, the particles are quite different, no clear crystal faces but they appear to be circular aggregates of very small ?equant grains. These have relatively low electron contrast with respect to the background. So when the autobright/contrast adjusts this image in order to give the full range of bright levels it has to increase the contrast in the background, it is this that makes the image relatively dark. The grain of the (presumed) carbon substrate is clear to see, so the density of the material is not far away from that of carbon. This is a common phenomenon in TEM, as you coast around the sample, depending on the density of the particles in the field of view, the brightness levels can vary widely. My conclusion is that the grains in the two samples are not the same.
I suspect you're charging the sample under the electron beam - that gives the bright picture.
I believe the reason that the two images have different brightness levels of backgrounds is a combination of two things - 1 the inherent electron density contrast in the sample, 2 the autobrightness and contrast mechanism of the software. In the first image, with the bright background, the grains in the image appear to be relatively dense and have high electron contrast with respect to the background. (They also display well-formed crystal faces). The autobright/contrast sotware has adjusted so that the full range of bright levels are present in the image. This leads to a 'normal' image where you see dark particles against a bright background. In the second image, with the dark background, the particles are quite different, no clear crystal faces but they appear to be circular aggregates of very small ?equant grains. These have relatively low electron contrast with respect to the background. So when the autobright/contrast adjusts this image in order to give the full range of bright levels it has to increase the contrast in the background, it is this that makes the image relatively dark. The grain of the (presumed) carbon substrate is clear to see, so the density of the material is not far away from that of carbon. This is a common phenomenon in TEM, as you coast around the sample, depending on the density of the particles in the field of view, the brightness levels can vary widely. My conclusion is that the grains in the two samples are not the same.
Thank you Dr. Slipper. What can I do to get the bright background in second sample ??
I suppose that It is also may be result of different image acquisition time. For example, the first picture was taken with 3 second exposure time, while the second one during 0.5 second.
Azat, I am intrigued as to how you read the exposure times.
Sachin, You may try and defeat the autobright and contrast and manually adjust. One other thing I notice is that the beam seems to be converged to quite extent such that the edges are darkening. Presumably this was done in order to get enough signal to allow an exposure? If Azat is correct, and this is the case, then this might be solved by expanding the beam to give a longer exposure. However, I still think it is an inherent problem with the sample.
in the attached file there is "manually corrected AC-AB" - here the vignetting is even more visible... but there is just too much noise in the image to do any serious corrections. sorry
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