How Does Band Gap Influence Lattice Spacing in Materials?

  • Thread starter Thread starter Sr1
  • Start date Start date
  • Tags Tags
    Quantum Solid
Sr1
Messages
4
Reaction score
0
Homework Statement
(a) (10 Points) Diamond has a band gap Eg equal to 5.5eV (at standard temperature and pressure). Use this number to derive a rough estimate of the lattice spacing, a, of the diamond lattice. Do you expect the true lattice spacing to be larger or smaller than your estimate?

(b) (5 Points) What is the minimum wavelength at which a diamond in a jewelry store is opaque? How does this wavelength depend on the size of the diamond?
Relevant Equations
/
How can we link the band gap to lattice spacing?
For (a), if we purely do dimension analysis, then I would guess $$a=\frac{\hbar c}{E_g}$$. But what's the reason behind this answer, and will the true lattice spacing be larger or smaller?
For (b), I guess $$\lambda=\frac{\hbar c}{E_g}$$ due to band gap = photon energy. But I have no idea on the second question.
Also, dose it make sense to have $\lambda=a$?
 
Physics news on Phys.org
ok from dirac comb model, $$\frac{\sqrt{2mE}}{\hbar}a\sim \pi,$$ then $a=0.26nm$. The remaining questions are: Do you expect the true lattice spacing to be larger or smaller than your estimate? How does this wavelength(band gap) depend on the size of the diamond?
 
##|\Psi|^2=\frac{1}{\sqrt{\pi b^2}}\exp(\frac{-(x-x_0)^2}{b^2}).## ##\braket{x}=\frac{1}{\sqrt{\pi b^2}}\int_{-\infty}^{\infty}dx\,x\exp(-\frac{(x-x_0)^2}{b^2}).## ##y=x-x_0 \quad x=y+x_0 \quad dy=dx.## The boundaries remain infinite, I believe. ##\frac{1}{\sqrt{\pi b^2}}\int_{-\infty}^{\infty}dy(y+x_0)\exp(\frac{-y^2}{b^2}).## ##\frac{2}{\sqrt{\pi b^2}}\int_0^{\infty}dy\,y\exp(\frac{-y^2}{b^2})+\frac{2x_0}{\sqrt{\pi b^2}}\int_0^{\infty}dy\,\exp(-\frac{y^2}{b^2}).## I then resolved the two...
It's given a gas of particles all identical which has T fixed and spin S. Let's ##g(\epsilon)## the density of orbital states and ##g(\epsilon) = g_0## for ##\forall \epsilon \in [\epsilon_0, \epsilon_1]##, zero otherwise. How to compute the number of accessible quantum states of one particle? This is my attempt, and I suspect that is not good. Let S=0 and then bosons in a system. Simply, if we have the density of orbitals we have to integrate ##g(\epsilon)## and we have...
Back
Top