3. A face center cubic (lattice parameter 0.542 nm) is put into the microscope operating at 200kV and the crystal tilted into the [001] projection. You tilt the crystal into a 2-beam condition for the (020) reflection (extinction distance is 60 nm) and form a phase contrast image using the (000) and (020) reflection. a) What will be the spacing of the fringe pattern obtained? (2) b) Ignoring lens aberrations, what is the visibility of the fringes at sample thicknesses of 5, 10, 15 and 30 nm. (10) 3. A face center cubic (lattice parameter 0.542 nm) is put into the microscope operating at 200kV and the crystal tilted into the [001] projection. You tilt the crystal into a 2-beam condition for the (020) reflection (extinction distance is 60 nm) and form a phase contrast image using the (000) and (020) reflection. a) What will be the spacing of the fringe pattern obtained? (2) b) Ignoring lens aberrations, what is the visibility of the fringes at sample thicknesses of 5, 10, 15 and 30 nm