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Epitaxial Growth of Colloidal Crystals

Why do some materials grow near-perfect crystals with mirror-smooth faces whereas others grow rough, bumpy crystals? Our group has recently gotten a glimpse of crystal growth in real time — not by watching individual atoms, but rather by freezing model atoms that can be observed directly with an optical microscope.

Using a solution of tiny plastic spheres 50 times smaller than a human hair, we have reproduced the conditions that lead to crystallization on the atomic scale. In addition to simply watching the particles crystallize, we were able to move individual particles (atoms) and ask “what if…?” With special laser beams known as “optical tweezers,” we placed an individual particle (atom) on top of a growing crystal island and determined how easy it was for the particle to hop off that island. We discovered that the random darting motions of a particle is a key factor that determines how long it spends on the island. When particles can hop off islands more easily, smooth crystals are grown. If the principles we have uncovered can be applied to the atomic scale, scientists will be able to better control the growth of thin films used to manufacture electronic components for our computers and cell phones.

Below you can see an embedded video of a colloidal crystal freezing onto a square lattice.  To download a higher resolution version of this video, click here.