l*****n
发帖数: 1679 | 1 原子大部分是空的，只有外层电子云和 极小的原子核，
那么SEM看到的规则排列的小球是什么？？？电子云？原子核？
谢谢 | S**********n
发帖数: 264 | 2 SEM couldn't see single atom. It can only see the rough surface of bulk
materials at a resolution larger than 10X atom sizes. All of the
information comes from very shallow surface (2nm?)
Electrons mostly interact with the potential of atoms. For atomic scale
images formed by TEM/STEM, they could be either understood as projections of
potential or complex inteference pattern mostly determined by point spread
function of lens, which could be comparable even smaller than the atom size.
All of these are based on very rigid assumptions which tend to be not that
true.
However, there are still tricks to play. Since all of the works either
involve crystal (atoms are arranged regularly) or isolated heavy atoms
supportd by light base (carbon?). People only care about contrast and can
use imagination.
All of these problems make many research in this field not so convincing.
That is also the reason why diffraction (x ray sees charge, neutron sees
nucles) is more powerful and popular.
Put it simple. If you have an electron eyes, you tend to see potential. If
you have neutron eyes, you tend to see nucleus only. However, what you
really see also depends on instrument blurring function (PSF). | T*M
发帖数: 48 | 3 Imaging single atoms using secondary electrons with an aberration-corrected
electron microscope, Y. Zhu, H. Inada, K. Nakamura & J. Wall1, Nature
Materials 8, 808 - 812 (2009)
of
spread
size.
that
【在 S**********n 的大作中提到】
: SEM couldn't see single atom. It can only see the rough surface of bulk
: materials at a resolution larger than 10X atom sizes. All of the
: information comes from very shallow surface (2nm?)
: Electrons mostly interact with the potential of atoms. For atomic scale
: images formed by TEM/STEM, they could be either understood as projections of
: potential or complex inteference pattern mostly determined by point spread
: function of lens, which could be comparable even smaller than the atom size.
: All of these are based on very rigid assumptions which tend to be not that
: true.
: However, there are still tricks to play. Since all of the works either
| S**********n
发帖数: 264 | 4 Thanks for pointing out some new development and also did a quick reading.
Oh, boy. Didn't follow this field for so many years. Experimentalists are
trying to overrun the (probably old) theories again. Most of their
desciption (except the Cs/Cc corrector) have been clearly discussed in
Williams/Carter books.
Still not totally convinced. Isolated heavy atom and periodic structrue are
powerful when it comes to prove better ideal "resolution". On the other
hand, it is relatively easy to imagine a resolution close to probe size
provided appropriate background and "infinite" signal to noise ratio. Oddly
, I didn't see a simulation of their SEM images plus noise, which should be
fairly easy to do.
As to experiment itself, it is nice. | T****i
发帖数: 2190 | 5 come on
that's not a conventional SEM
corrected
【在 T*M 的大作中提到】
: Imaging single atoms using secondary electrons with an aberration-corrected
: electron microscope, Y. Zhu, H. Inada, K. Nakamura & J. Wall1, Nature
: Materials 8, 808 - 812 (2009)
:
: of
: spread
: size.
: that
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