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Homework Help: Calculate Elastic Strain Energy in Solid State Physics

  1. Mar 8, 2015 #1
    1. The problem statement, all variables and given/known data
    A think film of ErAs(rock salt structure, a=0.574nm) is grown on top of a thick GaAs (Zn-blend structure, a=0.565nm) substrate. The substrate orientation and the film growth direction are both <001>. For very thin films, the ErAs is tetragonally distorted such that its in-plane lattice constants match that of the substrate. This occurs in order to minimize the interfacial energy. Of course, there is also a price paid in terms of elastic strain energy.

    Assume that the GaAs substrate is perfectly rigid and that the elastic constants (assume isotropic medium) of ErAs are C11=13*10E11[erg/cm^3] and C12=1.6*10E11[erg/cm^3]. Because there is no shear, the elastic energy density of the film is given by:

    2. Relevant equations

    a) what is the elastic strain energy(in eV) per Er atom?

    b) What is te value of the in-plane stress?

    3. The attempt at a solution

    At first, I thought it would be a simple plug-in-and-calculate question, but then I realize that I have no idea how to calculate all the ε's or where and how to find them. Nor do I know the units on those constants. Also, I can't imagine how ErAs "tetragonally distorted" looks like. Would someone help me please?
  2. jcsd
  3. Mar 13, 2015 #2
    Thanks for the post! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?
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