I have stored a material over some time. When I checked its band gap via UV-Vis, it came out to be around 3.8-4 eV rather than 1.2-1.9 eV. Are there any chances that if a material is stored over some time it's particles can become smaller in size or it can change over time resulting in the change in the band gap?
Muhammad Salik Qureshi
Nanoparticles of metals, semiconductors in powder can agglomerate, co-crystallize. This happens as a result of a spontaneous process of decreasing the Gibbs energy of the system (powder). The collective of nanoparticles has too large surface Gibbs energy unfavorable for a steady state. Therefore, the parameters of the electronic structure of semiconductors change. Such a process is more visible in small drops. Over time, they combine into large droplets. But this process is called coalescence.
There seems to be quite strange. Just by thermodynamical reasons, or the sacred rule of minimization of (surface) energy, one should expect the opposite behaviour, i.e. on time passing aggregation may occur under normal storage conditions, not fragmentation. You should show your spectra so one can give you some more meaningful suggestion. Also a knowledge of your material better than simply "material" could help.
Dear Muhammad,
thank you for posting this interesting technical question on RG. As a synthetic inorganic chemist I'm absolutely no expert in this field of research. However, i think you should perhaps be a bit more specific about the "materials" mentioned in your question. You just talk about "materials", but I ssume that you mean "nano materials", right? In addition to the expert answers already provided by Yuri Mirgorod and Giuseppe Curro it might be helpful if you take a look at vthe answers given to the follopwing closely related RG question:
What is Quantum confinement effect?
https://www.researchgate.net/post/What_is_Quantum_confinement_effect
This question from 2021 has received 41 answers.
Good luck with your work!
....before any sophisticated models and books/papers on confinement effects I would CAREFULLY check the experimental data and literature...several times.
- Badges
- Science method
- Similar topics
- Methodology
- Absorption Spectroscopy
- UV-Visible Spectroscopy