6. (a) Sketch separately the plots for "possible solutions function (PSF)" versus aa parameter for Vob corresponding to PSF1 and explain the fundamental differences between the electronic structures of these two cases. Provide the examples of the types of materials corresponding to these two cases.| (b) The graphs below represent the energy of an electron in a 1-dimensional lattice as a function of wave vector k. By sketching over the graph describe the cases you would expect for i) free electrons, ii) moderately bound electrons, and iii) strongly bound electrons. i) E -67/a -47/a -27/a 0 2nt/a 4n/a On/a Kx ii) E Kx iii) E -6it/a -47/a -2nt/a 0 2n/a 4n/a 6n/a Kx