A sample preparation method includes disposing a microcrystal on an electrically conductive grid, coating the microcrystal with an electrically conductive material to yield a coated microcrystal, milling the coated microcrystal with a first ion beam to yield a milled microcrystal, and polishing the milled microcrystal with a second ion beam to yield a polished microcrystal. A length of a side of the milled microcrystal is between about 250 nm and about 500 nm, and a length of the corresponding side of the polished microcrystal is between about 150 nm and about 250 nm. Assessing the crystal structure of the polished microcrystal includes rotating the polished microcrystal while accelerating electrons toward the polished microcrystal, diffracting the electrons from the polished microcrystal to yield a multiplicity of diffraction patterns, and assessing, from the multiplicity of diffraction patterns, the crystal structure of the polished microcrystal.