I have a gold nanoparticles stabilized on hydroxyapatite material. FESEM-EDX revealed around 0.63% of atomic gold but XPS revealed around 13.6 atomic percent of Au4d5? Why is this discrepancy? Isn't it supposed to be the other way round since XPS is only a surface phenomenon ? Can anyone here please explain?
Hi, I think this case combines a number of effects for the understanding of which you need to consider several factors:
i. that XPS is a surface analysis technque while EDS is not, so if the Au particles are on the surface it makes sense that XPS (like UPS and AES) gives a higher apparent gold content;
ii. that the depth from which the X-ray signal comes in EDS depends both on your primary electron energy (Valdimir is right here: try to reduce it) and the absorption path length.
iii. that EDS sensitivity depends on the detector type (SDD vs Si:Li vs. Ge), window type (windowlss vs. ultrathin vs thin vs Be) and the line type chosen for quantification (for Au you can select L lines @ around 9-11keV or M lines @2keV: whcih did you choose?);
iv. that most software packages have real issues quantifying very light elements, of which your hydroxy-apatite {Ca10(PO4)6(OH)2} almost exclusively consists of, and if you quantify light vs very heavy elements no commercial software will get this right. Mind you, it's not much different for XPS .
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