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Please who can help explain the contrast difference in these two images?

透射电镜(TEM)

  • Sorry not be able to type Chinese on this computer!
    Attached are two ADF images, image 1 is taken at higher collection angle than image 2, so i would expect diffraction contrast in image 2, and mostly Z contrast in image 1. You can notice that there are areas (arrowed in the images) that appear dark in image 1 but bright in image 2. Initially, I thought the bright area in image 1 indicates a heavier material, but actually both brighter and darker areas in image 1 has the same composition suggested by EDX. So I am confused why I see the contrast in image 1 for same material? if it is still a diffraction contrast, then why it is reversed compared to that in image 2?
    Anybody has some idea about this? Any suggestions would be appreciated!
    Thank you!
    Image 1:

    Image 2:
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  • m3033883

    第1楼2016/04/03

    应助达人

    由于在不同的角度收集信号。可能该区的强衍射正好落在你收集的范围内。例如图1的亮区。当换到图2时,这些衍射就不在收集的范围内,该区就变暗了。基本原理估计就是这样。个人意见,仅供参考。

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  • Jin

    第2楼2016/04/03

    确认一下你的带轴
    图1亮区域是否更靠近晶带轴?

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  • alcestis

    第3楼2016/04/03

    谢谢楼上两位回复。我的问题是什么散射信号会在低角的STEM 暗场图像上是暗的,而在较高角的暗场图像上是亮的。已经排除不是化学成分不同引起。按照Jin的建议,如果图一亮区是因为靠近晶带轴,那么在图二也应该会亮,因为图二的scattering angle更低,基本就是衍射衬度。

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  • 洪星二锅头

    第4楼2016/04/08

    可能是局部应力造成的衍射衬度,做一下暗场应该就能区分了

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