I cannot open images, but probably your "selected area" aperture covered more than one crystallite - if they are in random orientation, diffraction will result in circles instead of set of sharp dots. From small images that I can see I would say you got one big crystallite (to whom sharp dots correspond) with a small fraction of randomly oriented crystallites of the same material (basically you have a combination of single-crystal difraction and poly-crystalline in one image). I suggest you use smaller aperture to collect only from single crystal or larger to get "circles".

I attached one TEM image with separate SAED patterns of the same material for comparison. In your case you got both in one SAED pattern. Hope it helps.

I cannot open images, but probably your "selected area" aperture covered more than one crystallite - if they are in random orientation, diffraction will result in circles instead of set of sharp dots. From small images that I can see I would say you got one big crystallite (to whom sharp dots correspond) with a small fraction of randomly oriented crystallites of the same material (basically you have a combination of single-crystal difraction and poly-crystalline in one image). I suggest you use smaller aperture to collect only from single crystal or larger to get "circles".

I attached one TEM image with separate SAED patterns of the same material for comparison. In your case you got both in one SAED pattern. Hope it helps.

It is quite possible that you had two crystals in focus, as Janez said.

It is also possible that your crystal has more than one lattice by itself which could lead to partially overlapping diffraction patterns of two or more lattices in the case of non-zero twin obliquity. You would expect split reflections in the higher resolution and overlaps in the lower resolution.

Another possible explanation would be the presence of a superstructure in the crystal phase which could be either commensurate (good for you) or incommensurate (bad for you). Both would lead to satellite reflections along the main reflection.

In principle you should be able to solve a structure with the aforementioned phenotypes, but that also depends a lot on your sample and the quality of your data.

Another possibility is that you damaged your sample during preparation, typically during cryo-protection. That case is pretty much the same as having two crystals in focus. You might be able to avoid that and to improve your data by working out a better sample preparation strategy.

Thanks Janez Zavašnik  and Stefan Gajewski,

Im now clear about the problem.  I have one more question. initially the crystal structure is diamond cubic Silicon (dc-Si), I took SADPs after the sample is damaged by laser. Then if the SADP have more than one crystals in focus.,how can I REFINE the dc-Si reflections. I mean how can I defined which spot belongs to dc-Si?

 2. And for twinning, any has some explanation how it is formed from diamond cubic structure by using laser?. I guess it because of the shear generted by laser shock wave, but Im not understand deeply it. 

can anyone help me to explain it. thanks

Dear Na Le, if you want to be sure, then you need to index your pattern. For this, firstly you need to find a basic unit which represent one whole set of pattern. Measure distance of two non co-linear directions in the chosen unit, in 1/nm. Calculate their reciprocal, then you have the d-spacing. Compare your measurements with the standard database of , Si as you expected. Then you have the (h1 k1 l1) (h2 k2 l2). Calculate the inter-plane angle between the two and compare with the one you measured in your SAD pattern. If you find both of them are consistent, then your indexing should be right.

Regarding how many crystals you have for your SAD pattern, why not you showing your corresponding bright field image? This sometimes helps. Also, maybe when next time you are with the TEM, it is better to choose one of those extra tiny spots and form a dark field image so than you can from which phase/crystal it is from. 

I also saw streaks in your SAD, either one direction (the top image) or two directions(bottom image), do you also expect precipitation in your specimen or lattice strains?   

Hope this helps you somehow.

Regards

Jun

Dear Na,

You can use the dark field technique to determine whether the extra diffraction spots are generated by multiple grains or phases. It seems that the extra spots in the first figure make a triple modulations on the (111). If they are generated by multiple grains/phases, you may use the nano diffraction. 

Can anyone help me to analyze this SAED image. why am i getting many spots and what does it mean

Dear Sangeetha Ramamoorthy your attached SAD pattern shows that the area within the selected area, by the aperture you used to form the diffraction pattern, contains multiple grains and without preferred grain orientation (micro-texture). The distance between the central spot to any spot corresponds to the reciprocal of one specific inter-planar distance, namely the crystal plane. The indexing will be huge amount of work since your pattern has randomly distributed spots.

To be honest, this is the first time that i see such kind of diffraction pattern and i think more detailed context can help. For example, a bright field image including the area where the SAD was formed, the aperture u used, the material (the crystal structure. Moreover, your SAD image has no scale bar.

Kind regards,

Jun

Dear Jun Wu, Thank you so much. I don't know about the details you have asked. I will ask the operator and reply to you. The material I used is ZrO2 (monoclinic phase).

Please email to Prof Osamu Terasaki. He is the Number 1 Prof in the World. I beleive he give you feed back to you.