To make this method work, Zuo and company had to measure the angles at which the beams scattered from the crystal with a higher degree of precision than had been done before. They relied on the electron beam to measure small angles, which it did more accurately by avoiding the "extinction effect" that distorts X-ray images. In contrast, the X-ray beam was better at measuring larger angles. And the combination of the two made it possible to flesh out the fine details of the crystal structure. To make a sharp picture of the covalent bonds between copper and oxygen, the group manipulated the charge density map by first moving all ions to the back of the map and then subtracting the background.

CUPRITE-- a crystal of copper and oxygen atoms-- gave researchers their first glimpse at electron orbitals.

Some scientists who are analyzing the pictures have slightly different interpretations. For instance, Roald Hoffmann, the Cornell chemist awarded a Nobel prize in 1981, is skeptical about covalent bonds between copper atoms, believing them to be too far apart. But everyone is convinced of the technique the Arizona researchers developed. Putting ultimate decisions about cuprite's bonds aside, combining convergent beams of electron beam diffraction and X-ray beam diffraction should help researchers better understand a variety of complex materials in the years to come.

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