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

[Lei Wang]

Hi, guys. Did you ever encounter the problem of X-ray disappearing caused by size effect?

 

[Astronuc]

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).

 

[Lei Wang]

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.

 

[Astronuc]

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?

 

[Lei Wang]

It X-ray diffraction.

 

[Bob S]

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.

 

[Dave_H]

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.

 

[Lei Wang]

Thanks, I got that book in our library.

 

[Lei Wang]

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.