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So in solid state classes we learned about phenomena like band structure and others arising from a periodic potential.

Then we get to doing actual experiment and find out that materials being single crystals are actually fairly rare exceptions rather than the rule: more often, the material is a polycrystal or even amorphous. This kind of upsets my knowledge of what to expect, because all these things I learned were based on perfect crystals.

But, then, I talk to people more knowledgeable than I about things like the band structure of an evaporated film, and they seem to give me the infuriatingly vague answer that we can still kind of expect to see the same properties of the band structure, but maybe not exactly.

I don't even know where to begin theoretically -- it seems like if you have a polycrystal, it's now more like a bunch of quantum wells the width of the grain sizes mashed together, and they can tunnel into each other through their grain boundaries. I guess I could think of something using the knowledge of tunneling I know, but considering the grains are often oriented in random directions, I wouldn't know what to do.

So my question is, is there a way to know what to expect of a polycrystal when you know the properties of the material in bulk? Or is it necessarily the type of thing you'd have to figure out from experiment?

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