I was trying to determine the best oxide thickness and material for maximising the contrast of one atom thick material layer on top of silicon chip. Using Fresnel equations I was able to do plot the contrast with respect to oxide thickness and wavelength, but alas, contrast seems to be sometimes negative. So first I thought that there is something wrong with my code, but it works perfectly for graphene so that does not seem to be the case. I also checked that you can get negative contrast for graphene when there are enough layers, so maybe my result isn't completely wrong. Thus what does this negative contrast look like? I want to know how easily one can see this one atom thick layer with a microscope, so I need some information on how I can interpret this result. So, any help?