Hello,

Depending on the size I would suggest to use an optical microspe or a SEM and then perform imagen analysis. 

Regards

Hi Marisol,

thank you for your reply. we are working with nanostructured materials and we do already quite a lot of SEM etc. to study morphology, microstructure etc. we have also XRD data, together with Raman, photocurrent measurements and IPCE. I am looking for a technique which can help me to quantify and discriminate between different defects (for examples oxygen vacancies, shallow/deep donor levels etc.),  cheers

Electron spin resonance is one of the option to identify the type and number of the  defects in semiconductor. 

EELS, ELNES in a TEM are powerful. Getting started can be found here

Lim, J., Monllor-Satoca, D., Jang, J.S., Lee, S.b, Choi, W. Visible light photocatalysis of fullerol-complexed TiO2 enhanced by Nb doping, Applied Catalysis B: Environmental, Volume 152-153, Issue 1, 25 June 2014, Pages 233-240

but for details about ELNES you can look in:

Mauchamp, V., Ipicier, T., Le Bossé, J.-C. Application of a fully relativistic theory to the EELS investigation of anisotropy effects at the oxygen K edge in rutile and ZrO2, Physical Review B - Condensed Matter and Materials Physics, Volume 77, Issue 23, 26 June 2008, Article number 235122

Use this links if you have free access:

http://www.sciencedirect.com/science/article/pii/S0926337314000320

http://journals.aps.org/prb/pdf/10.1103/PhysRevB.77.235122

easy is to EIS - follow Warburg impedance -

some really useful suggestions, thanks a lot! some collaborators have actually started some EELS-TEM analysis and so far so good. I may combine it with EIS or IS (i.e. without electrolyte) then, as I have access to those. Many thanks again to all of you for the nice contributions!

best of luck