Hi all !:
Does anyone is acquainted with the mechanism of Energy Filtering for Electrons & Phonons (the physics are distinct depending on the particle you are concern about; to be Electrons or Phonons.) in Polycrystalline materials?
This mechanism has been suggested as means to enhance the ZT (Thermoelectric Figure of Merit) of polycrystalline materials with high grain boundaries density, usually conventional TE materials like PbTe, Bi2Te3, Sb2Te3, and other B2Te3-based alloys ...
Is a Quantum Mechanical approach which involves the understanding of concepts like the mean free path, wavelenght and scattering of the carriers.
Where the Grain Boundaries are modified with embedded nanostructures inside them. The Grain Boundaries are treated as a Potential Barriers and the Grains as a Potential Wells, so it requiers a modeling of the Schrödinger Eq. and its solution for a Wave Function. (this is not the Quantum Tunneling mechanism in QM)
This approach (Energy Filtering of Carriers) has been used to try to decouple the inverse relation between the Electrical Conductivity (sigma) and the Thermal Conductivity (k) in the ZT formula:
ZT = (S^2)*sigma/k times T
by allowing just the carriers of given energies to pass through the Grain Boundaries and block others with low energies, lower than a threshold value.
Leaving a couple of references below ! Such interesting topic !
Hope someone else may be familiar with it and we can buil up thread of discussion :)
Best of Regards all !
Hi!
This topic is very interesting!
I am a postgraduate student and currently studying the relation between nano-particle size (of a ceramic sample) and electrical conductivity. based on my readings, smaller particle would give smaller electrical conductivity. However, when the size is reduced to nano regimes, the electrical conductivity would increase. And also, based on my experimental data, i got the same results after analyzing them using 'Brick-layer' model.
But nevertheless, i still couldnt find the 'exact'reason for the increment of the electrical conductivity in nano-regime. I hope to be able to get some reference on this.
Thank you all!
Hello Syafkeena Affandi !
I think I am a little familiar with what you are talking about (based on my literature references too):
What you are trying to study and observe is the so called Quantum size effects (i.e. Quantum Effects due to the reduction in lenght).
Have you read about Quantum Confinement of Excitons in semiconductor nanoparticles ? e.g. Si, Ge, GaAs, etc.. ? meaning Quantum Dots...
I will attach below a very nice review about this whole phenomenon of Quantum Effects due to lenght reduction, ... the main mechanism: Quantum Confinement of Electrons/Excitons.
I hope you can give it a look and let me know some of your comments about it.
I recomend you to go particularly to the sections about Quantum Confinement, the Exciton's Bohr Radius and the clalculation of the total Energy of the Exciton. I'll leave it in the link below...
What you are speaking is about the topics of Quantum Dots and the Quantum size effects when the lenght scales get to the scales of the de Broglie Wavelenght of the electrons, or excitons on these nanoparticles, (this is the phenomenon called Quantum Spatial Confinement of electrons/excitons).
So implicitly, you are talking of Quantum Dots. You will find this definition in function of the Exciton's Bohr Radius, more than using the de Broglie Wavelenght.
I am sure the reading I left below will be very useful, but loosely speaking:
The main explanation it's found in the understanding of how the DOS (Density of States) is modified due to the reduction in lenght of the material. i.e. ; The Density of Satates gets modified and its distribution become to turn discrete again, like an atom, so the nanoparticle starts to show an Energy States distribution like those of individual atoms, with discrete States of Energy.
So these particles (which are called Quantum Dots) start then to show diverse effects related to a spatial confinement of their carriers, since the Energy States are discrete now,
for example: discrete spectra of light emission, an increment in chemcical reactivity, sometimes, an increment on the optical Bandgap, phenomena of Electroluminescense, Fluorescence, etc ...
So, your observation about the increment in the electrical Conductivity likely is related to this phenomenon too.
Review the reference I attached here, if you are pleased:). Also I have a PPT presentation on my 'Research Items', specifically about Quantum Dots, it may be of your interest as well.
I agree with you!, is a very interesting topic of research.
I work more with thin films of semiconductor materials, and no with nanoparticles or QDs...
What materials you work with ? Do you syntethise these nanoparticles yourself (your Lab group) ?
Good Luck ! Regards !:)
It is better to go back to :
Tritt, T.M., 2011. Thermoelectric phenomena, materials, and applications. Annual review of materials research, 41, pp.433-448.
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