Hi Laura,

XAS gives you two general areas of information. The near-edge (the so called XANES) which gives you chemical info and the extended edge fine structure (EXAFS) which gives you the partial radial distribution function of atomic neighbors.

XANES: this will tell you about the local chemistry, the type of chemical bonds, etc. This information can be gleaned from the edge position (in energy) and the edge shape. However, there are lots of caveats to both of these. The edge position scales with 1/r^2, where r is the nearest neighbor bond distance, and the edge shape will depend in the local (point group) symmetry.

Let's assume you are talking about, say, Pt nano particles. You could do the XANES of the Pt L3 edge. In that case, with sufficiently small nanoparticles, you could get the surface bonding, through information about Pt-organic bonds etc., between the particles, but remember that you will ALSO be getting bonding information from the internal structure of the nanoparticles and so the quality of your significant information (surface of the nano particles) will depend on managing and excluding the insignificant information (the internal structure of the particles).

If you are really focused on the organics, it would be better to do the C K-edge XANES (often called NEXAFS) so that you are only detecting the information about the carbon-specific bonds.

EXAFS: The issue here is the same as that of XANES with the added point that you really will not be able to do good EXAFS fro the C-edge because of two many overlaps the information from all the different types of carbon species.

So, to answer your question broadly, XAS is a designed for bulk-averaged atom-atom correlation information. Trying to use it for speciation of the surface chemistry of nanoparticles would be misuse of the technique unless you are a very sophisticated user of this technique.

You are going to be much better off doing XPS!

The term "internal structure" is somewhat ambiguous..

If you want to 'see' the internal structure then HR-TEM will suffice..

XAS, EXAFS or XANES.are excellent tools to study electronic structure of nano materials..

What I mean about internal structure is what kind of internal binding make the nanoparticles hold together. Is it strong or weak? Is it chemical binding with organic? Can it be as well bridging mechanism with divalent cations and organic matter?

XAS is an element specific technique, you can probe the local structure of a specific element. You can get information about the valence state, bond lengths, coordination numbers and nature of neighboring atoms. There are many review articles available on this technique, which can be useful.

Hi Laura,

XAS gives you two general areas of information. The near-edge (the so called XANES) which gives you chemical info and the extended edge fine structure (EXAFS) which gives you the partial radial distribution function of atomic neighbors.

XANES: this will tell you about the local chemistry, the type of chemical bonds, etc. This information can be gleaned from the edge position (in energy) and the edge shape. However, there are lots of caveats to both of these. The edge position scales with 1/r^2, where r is the nearest neighbor bond distance, and the edge shape will depend in the local (point group) symmetry.

Let's assume you are talking about, say, Pt nano particles. You could do the XANES of the Pt L3 edge. In that case, with sufficiently small nanoparticles, you could get the surface bonding, through information about Pt-organic bonds etc., between the particles, but remember that you will ALSO be getting bonding information from the internal structure of the nanoparticles and so the quality of your significant information (surface of the nano particles) will depend on managing and excluding the insignificant information (the internal structure of the particles).

If you are really focused on the organics, it would be better to do the C K-edge XANES (often called NEXAFS) so that you are only detecting the information about the carbon-specific bonds.

EXAFS: The issue here is the same as that of XANES with the added point that you really will not be able to do good EXAFS fro the C-edge because of two many overlaps the information from all the different types of carbon species.

So, to answer your question broadly, XAS is a designed for bulk-averaged atom-atom correlation information. Trying to use it for speciation of the surface chemistry of nanoparticles would be misuse of the technique unless you are a very sophisticated user of this technique.

You are going to be much better off doing XPS!

Thanks a lot for your detailed and complete answer. I appreciate your help.

As previousyl well explained by several of the participants, XAS is a local, bulk-average technique. In oxides (an other systems) symmetry lowering at surfaces typically allow you to detect surface species (like for example 5-fold Ti in TiO2) by XANES. Changes in such atoms when coordinated to molecules are also visible. Unless your material present a primary particle size below ca. 1 or 1.5 nm (so surface can be a significant contribution to the total signal) the previous method is the only easy application for surface detectetion. Of course, it can not give you a general view of the surface even in these systems (oxides, sulphides,..) and is essentially useless in other systems.

XES (emission spectroscopy) can give you a more comple answer but has not been applied rutinely in nanosystems as far as I an aware due to technical difficulties. I can mention some papers (working in a simple application of "XES"; HR-XAS) concerning, for example, CO adsorption (stop, bridge, etc.) on metal surfaces of nanoparticles ( P. Glatzel, ESRF is one of the main workers in such field). Not sure if this may help you.

I guess that other techinques will provide you a much more complete answer to your problem as far as your particle size is above ca. 1nm.

The question is not clear. What do you mean "internal structure"? Do you mean how NPs are arrranged into "aggregate"? What kind of aggregation for your NPs? What kind of interactions between NPs invovled? XRD might give you some information.

Hi, XAS is element specific so you can know what is valence of element, You can know structure like ferromagnetic, antiferromagnetic, ferimagnetic etc. You can know valence state, bond lengths, coordination numbers and nature of neighboring atoms etc. I have worked on such kind of things. You can read "Ferromagnetic interaction between Cu ions in the bulk region of Cu-doped ZnO nanowires" of my other TiO2 paper.

We recently did some similar EXAFS/XANES experiments on small gold nanoparticles stabilized by some organic stuff and sulfur. In that particular case, XANES and EXAFS were extremely helpful to understand the bond geometry of the gold. Thus, depending of the materials in the NP (besices carbon) I would suggest to do some complimentary XAS measurement if some heavier elements are incorporated. Say, above Si or so!

Good luck, Dirk