X-Ray Disappearance Due to Size Effect: A Troubleshooting Guide

In summary, when X-ray diffraction is performed on nano-structured materials, the peak width decreases as the size of the material decreases.
  • #1
Lei Wang
5
0
Hi, guys. Did you ever encounter the problem of X-ray disappearing caused by size effect?
 
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  • #2
Lei Wang said:
Hi, guys. Did you ever encounter the problem of X-ray disappearing caused by size effect?
What does one mean by 'X-ray disappearing'? Size of what?

X-rays can be scattered or absorbed (e.g., photo-electric effect).
 
  • #3
Hi, thanks.

I am doing some research about nano porous materials. The bulk materials, I can get a X-ray peak for each element. But when I made it into nano porous material, the peak is gone. The same thing happened to my teammates. In one word, we can't get X ray for a nano-porous material.
 
  • #4
Lei Wang said:
Hi, thanks.

I am doing some research about nano porous materials. The bulk materials, I can get a X-ray peak for each element. But when I made it into nano porous material, the peak is gone. The same thing happened to my teammates. In one word, we can't get X ray for a nano-porous material.
Is one referring to X-ray diffraction? Or is one referring to generating characteristic X-ray by electron bombardment?
 
  • #5
It X-ray diffraction.
 
  • #6
I had a vaguely similar problem when I built a Bragg crystal diffraction spectrometer (Dumond geometry) many years ago. For the quartz 310 crystal (20 cm x 20 cm x 6 mm), the intrinsic angular resolution is of the order of 1 second of arc when it is flat. However, when it is bent (yes, quartz can be bent) to a 7.7 meter radius of curvature, "mosaic domains" in the quartz broadens the intrinsic angular resolution to about 15 seconds of arc. This has been observed in other bent quartz crystals, and also I believe in other crystals, like silicon. I have no idea what happens when the mosaic domains are very small. The reference I have for this is a book by Zachariasen "Theory of X-Ray Diffraction in Crystals" , which was republished by Dover and is available through Amazon.com.
 
  • #7
The width of your peak is a function of several things, including grain size, and residual stress/strain (sample prep, thermal strain...). Are your raw materials nano-structured? Or are you using a insitu grain-refinement technique? If your are losing your peaks due to grain refinement try scanning the angle where you know the peaks should be, but very slowly to try and increase the number of counts, sometimes this will make it easier to distinguish a very low height, high width peak, from the background. I just worked on this today, so I'll attach a figure displaying what I mean.

I hope this helps.
 

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  • #8
Thanks, I got that book in our library.
 
  • #9
Dave_H said:
The width of your peak is a function of several things, including grain size, and residual stress/strain (sample prep, thermal strain...). Are your raw materials nano-structured? Or are you using a insitu grain-refinement technique? If your are losing your peaks due to grain refinement try scanning the angle where you know the peaks should be, but very slowly to try and increase the number of counts, sometimes this will make it easier to distinguish a very low height, high width peak, from the background. I just worked on this today, so I'll attach a figure displaying what I mean.

I hope this helps.

Thanks a lot. I see what you are talking. I will try a small and slow scan.
 

1. What is the "size effect" in X-ray disappearance?

The "size effect" refers to the phenomenon of reduced X-ray intensity or disappearance of X-ray signals when a sample size decreases below a certain threshold. This is due to the fact that smaller sample sizes have a lower number of atoms, resulting in a weaker signal.

2. Why does the size effect occur in X-ray disappearance?

The size effect occurs due to the decrease in the number of atoms present in a smaller sample. X-rays interact with the electrons in the atoms, and when there are fewer atoms, the signal becomes weaker or may disappear completely.

3. How can the size effect be identified in X-ray disappearance?

The size effect can be identified by a sudden decrease or disappearance of X-ray signals when the sample size is reduced. This can be observed through changes in the X-ray diffraction pattern or X-ray fluorescence intensity.

4. What are the common causes of the size effect in X-ray disappearance?

The size effect can be caused by a variety of factors, including changes in sample density, surface roughness, and sample positioning. It can also be influenced by the type of X-ray technique used and the properties of the sample material.

5. How can the size effect in X-ray disappearance be mitigated?

To mitigate the size effect, it is important to carefully consider the sample preparation and measurement techniques. This can include using a larger sample size, adjusting the sample positioning, and optimizing the X-ray technique settings. Additionally, using a reference sample of known size and composition can help to correct for the size effect.

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