Firstly, you have to know the phase diagram of silicon. According to the reference: Mujica et al. Reviews of Modern Physics, vol. 75, 863-912 (2003), under pressure there are different polytypes of Si. However with your laser, you must heat the sample. In attach you will found the pressure-temperature phase diagram of Si. At ambient pressure there is not another solid phase until Si melts. At high pressure and high temperature Si transforms to a tetragonal (white tin) structure. You must discard this structure if this is the case. That will be your first step.

With crystalmaker you can produce diffraction pattern of the structure, if you have .cif file of this structure. You can produce diffraction patterns of all known Si-phases, produce their diffraction pattern and compare with experimental pattern. But for comparison you need to determine the orientation (view direction) of your grain. Of course, diffraction pattern will be different for different directions. If you study the metastable state there is a possibility that you have some new structure. 

You could tilt the sample and take a photo of

the new pattern Then with the help of the Int Crystallography

Tables and Laue equations analyze the structure

With a single SAD it is impossible to verify a crystal structure but if you take more SAD from different zones you could do that as "Rolando M. A. Roque-Malherbe" mentioned.

Just be careful because from your diffraction pattern is clear that you picked up signal from either more grains or you might have more than one phase in your SA region. Try to take SADs which contains only one grain (single phase region).

If it is not possible you have to consider another approach.

I have some questions. What is the laser damage region size? What was the SAD aperture size? How does the sample look like? Is it a FIB lamella? Does it contain an unaffected region of single crystalline Si?

Dear, P. Grima Gallardo

Thanks very much for your answer.

Dear Jakub Zalesak, 

the electron pattern I attatched in the question it just for example.  

from your answer it seems that you may know what Im doing.  hope you can help me.

my damage region size is about 1 micrometer, its on the monocrystal-Silicon surface which is covered with 10 micrometer of Silicon Oxide layer ( attatched TEM image below).

I used FIB to make the TEM sample, im not sure what it called, H-bar method or lamella.

the problem to me is that I still cannot realize what to do to. because when the phase transition occur in c-Si, there is a possibility that the crystal structure no longer remain as cubic structer but can change to other phases such as  tetragonal one, ........So How can I know the pattern belong to which crystal structure?

thanks a lots. 

Dear Na Le,

you could take a SAD diffraction image from the whole damaged region. It should be as big as possible but try to avoid the silicon oxide and pure silicon to diffract. The pattern which you will get might contain more grains and therefore it might be something inbetween a spot pattern and a ring pattern. That would be the best. If you know the primary beam position you can azimuthally integrate over a wide range (if there are not many diffracted beams). If you make a calibration you can plot this like an intensity-d spacing plot and than it is easy. You just select the possible candidates (tetragonal-Si, or what could be created) and compare if their HKL fit to your plot. This is like having a 2theta XRD plot. Check my attached example.

If you want I can advice you more in details how to do this.

 Best Regards

    Jakub

Dear Jakub.

I cannot open the image. could you please send me via email.  my email is: [email protected]

if you have time, could you explain me in details. its now impossible to take SAD of the whole region of the damge since now i have no more sample. 

Dear Na Le, recently I read the article: "Researchers find new phase of carbon, make diamond at room temperature". This new phase has been obtained by laser heating. You can read a copy of the article at: http://pedrogrima.blogspot.com/2015/11/researchers-find-new-phase-of-carbon.html. It could be related with your observation of a new phase in silicon.

Best regards,

Pedro