I have a pure Iron oxide nano particle sample(hematite) . I got EDS on my sample in different ages. The EDS result shows the height of Oxygen and Fe picks on EDS result changed after 30 month aging.The change on the height is very obvious. How ever it is still a pure iron oxide. What the height change shows ?? Thank you for your help !
Beam drift. Nanoparticle is too small (much smaller than X-ray generation volume), even slight beam drift is very visible. And why do you want to irradiate the same particle for 30 minutes?
My reserach is about change of hematite Nanoparticle under long term aging. The EDS result shows, both picks Fe and Oxygen got higher under long term aging for all my samples.
I don't know how to explain this and what the hight change shows !? Is that means the amount of oxygen changed in the samples ? I know the size of nano particles increased over age.
I have no experience with Fe2O3 nanoparticles, so I am speaking just about EDS.
Particles cannot increase in size in specimen chamber and still be pure Fe2O3. They have no source of Fe. But there is a well known artifact - carbon contamination under the beam, it increases size of particles. However, it should somewhat decrease intensity of peaks of O and Fe, not to increase them. Can your particles contain something else behind Fe and O, some additional component that can be removed under influence of a beam or/and vacuum?
And again: your particles have no source of Fe, they cannot grow while remaining pure hematite.
My particles are in aqueous media during aging. That's why their size is increased by aging. XRD,BETand DLS result shows the particle size changed over time. I got EDS in different ages as well. The oxegen and fe pickes got higher. So, if the particle change how EDS whould show? So, the increase in the height of the picks can be a reason for the change in particle size ? I know i got more hydroxide bonding during long term age. TGA Curves shows more hydroxylation after 30 month. Can the change in the EDS picks prove this ?
For SEM: Depending on your accelerating voltage, volume of generation of X-rays is 1-2 microns in diameter. Nanoparticle is much smaller, so in your spectra you have not only Fe and O peaks, but X-rays of substrate as well (carbon, I suppose). A bigger particle will occupy larger share of X-ray generation volume and will give peaks of greater intensity.
For TEM we do not have a bulk substrate for electron scattering, so we will not see much of radiation from substrate, but still the rest is true: a bigger particle provides bigger volume for X-ray generation.
If both O and Fe increased in intensity, did they maintain the same ratio? i.e are the quant results the same? (I know that measuring O by EDX is fraught with problems but let's start by just considering this). Did you measure the probe current at each measurement? If this varies by a small amount then the peak heights - all of them - will vary. 30 months is a long time in SEM land, if you are using a W-SEM rather than a FE-SEM then it is likely the filament will have changed, or be in a significantly different state. Unless you are measuring the currents you will not be able to duplicate the electron emission. If you are using FE-SEM then it will still apply; changes in a cold cathode FE-SEM will be greater than a Schottky-FE-SEM, so measuring probe currents becomes more important. If you have a multi-user environment it is vital that all conditions are maintained if you want to do comparisons of peak intensities, for example, was the same aperture size used? was the same spot size used?. Most EDS software can account for these types of changes to provide you with semi-quant information about your material, and is usually sufficient. If you want better quality, non-normalised data then you will need to use standards and control your data acquisition more carefully. However, Vladimir's point about the interaction volume probably overrides all of those considerations...
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