New imaging techniques .

Optical and electronic properties of small assemblages of atoms called quantum dots depend upon their electronic structure . Not just what's on the surface , but also what's inside . While scientists can calculate the electronic structure , they need to know where the atoms are positioned to do so accurately .

Getting this information , however, has proved to be a challenge for nanocrystals like quantum dots. mapping out positions of atoms requires clues provided by the diffraction alone are not enough .

By combining two sources of information , images and diffraction patterns taken with the same day electron microscope , researchers at the U. of I.can achieve sub-angstrom resolution of structures that were not possible before .

We show that for cadmium - sulfide nanocrystals, the improved image resolution allows a determination of their atomic structures.

Images from electron microscope can resolve individual atoms in a nanocrystal, but the atoms suffer radiation damage . This limits the length of observations . patterns from x-ray diffraction can be used to determine the structure of large crystals, but not for nanocrystals , which are too small and don't diffract well .

To achieve sub-angstrom resolution Zou and colleagues developed a reiterative are algorithm that processes and combines shape information from the lower resolution images and structure information from the high resolution diffraction pattern . Both the image and the pattern are taken with the same transmission - electron microscope .