If the material is transparent, it should be possible to use light scattering to probe the fluctuations in the sample and so to gain information on the subcritical nuclei. This type of experiment is commonly done close to the critical point of a material. These experiments would be done in situ. I would imagine that it could sometimes be possible to "freeze in" subcritical nuclei, but the quench would have to be very fast to prevent free energy minimization from occurring.

If the material is transparent, it should be possible to use light scattering to probe the fluctuations in the sample and so to gain information on the subcritical nuclei. This type of experiment is commonly done close to the critical point of a material. These experiments would be done in situ. I would imagine that it could sometimes be possible to "freeze in" subcritical nuclei, but the quench would have to be very fast to prevent free energy minimization from occurring.

There is well known methods for observation of such nucleai which forms at decomposition of solid solution (Guinier-Preston zone) by means of X-ray diffraction and TEM. I think thet in your case these methods will appropriate.

Small angle X-ray scattering (SAXS) is fine for glasses. There are old publications by R.J. Kirckpatric.

Hi, you may have a look into the following publication:

"Agglomeration of As antisite in As-rich LT-GaAs: Nucleation without a critical nucleus size" Phys. Rev.Lett. 95 (2005) 125502

In general there is a big difference for nuclei forming in melts and in solids.

SAXS will probably not work in your case since you need nuclei larger than about 1-2 nm and a contrast in the electron density between the precipitates and the matrix.

You could have look at 10.1103/PhysRevLett.109.016101. It is an in situ LEEM study of near critical clusters of some organic molecules (BDA) on copper.

May be you can consider a short order spectroscopic based structural probe such as EXAFS

See an example of pre-oxide nuclei on metal surface demonstrated by in situ TEM. http://pubs.rsc.org/en/content/articlehtml/2013/cc/c3cc46684a

I suggest to have a look to the videos of subcritical clusters of NaClO4 polymorphs recorded in situ and live (no frozen images) by TEM. JACS 136, 1762 (2914).

Small angle x-ray scattering, or small angle neutron scattering are useful for characterizing such structures. Objects with radii as small as 5 Angstrons can be detected routinely and smaller with special set-ups (long sample to detector distances).

To be sure you should perform your experiments in-situ - otherwise there will always be the question of what happens during the quench from the crystallization temperature. Given the preference for in-situ observations, then you would want as much flux as possible (to give the best time resolution) so best to perform the experiments at a Synchrotron (so long as you have enough electronic contrast between the nuclei and the matrix for SAXS).

Hi Manuel,

If using transmission/scattering (TEM/XRD/SAXS/SANS), 'contrast mechanism' is the key concern - will subcritical nuclei produce a chemical/structural mechanism (in sufficient volume fraction, if diffraction) to contrast it from the bulk? Some simple and quite useful calculations can be made on potential chemistries & structures.

Similarly, atom probe microscopy (not transmission/scattering; a point projection microscope) has a signal-to-noise limit. Yes, this is an atomic resolution microscope for structure and chemistry - particles of 2 atoms can be observed - however, it has sources of noise that create information limits; can be determined with appropriate analytical treatment. Quality depends on many factors, like pretty much any other instrument, but is not as simple to theoretically predict - 1 experiment is better than a 1000 guesses.

Hope that helps,

Peter

I think this can be down by TEM and 3DAP for metallic material. Mingwei Chen did similar work on metallic glass to determine the cluster structure. However, the definition of critical, subcritical nucleus in experiment is very important.

look into following publication

DOI:10.1021/cm303522z; Growth kinetics and morphological evolution of ZnO precipitated from solution.

You may find there many useful links related to the early stage of nanopaparticle growth observed by TEM