Cottrell Scholar Awards - 2016
Interactions between Impurities and Dislocations in Small Colloidal Crystals
There are no perfect crystals in nature – that’s because the rigidly repeating lattice patterns of atoms that compose any crystalline material invariably have imperfections here and there. That’s not a bad thing – crystals would be quite boring without their imperfections. In fact it’s the artificially added impurities, in a process called doping, that enable scientists to manipulate the characteristics of semiconductors, which can then be used to make electronic devices like computer chips.
Another kind of imperfection, which occurs in the otherwise perfectly ordered atomic rows of crystals, happens when atoms become dislocated, causing atomic-scale lattices to twist and distort. What’s more, within atomic or molecular crystalline lattices, some dislocations can move about. That’s because these tiny defects are subject to various atomic and mechanical forces.
Sharon Gerbode, assistant professor of physics, Harvey Mudd College plans to measure the interactions between dislocations and impurities, and by perturbing crystals of various sizes, ultimately discover how these interactions change the properties of crystals.
According to Gerbode, while existing theories of dislocation and impurity motion are accurate for very large, effectively continuum crystals, these theories sometimes fail for smaller, but technologically important systems such as nanocrystals. Also called quantum dots, nanocrystals are exceptionally tiny bits of matter – a nanometer is one-billionth of a meter. In fact, they are so small their impurities and dislocations cannot be studied directly very easily.
Thus, Gerbode and her research associates will attempt to draw analogies to lattice defects and dislocations by inducing disorder in a more manageable system – a “colloidal suspension” – which is a system of micron-sized silica particles suspended in a “solvent” of even smaller silica particles.
“The colloidal particles can be large [relative to quantum dots] – on the scale of one micron – making them big and slow enough to observe with an optical microscope,” Gerbode says, adding, “Colloids offer a truly unique opportunity to actually watch the time evolution of a crystalline system, particle by particle. Results obtained from experiments on colloidal systems have been used to probe unanswered questions in analogous atomic or molecular systems whose constituents are made inaccessible by both size and speed.”
Her research could have important implications for improving the performance of electronic devices, for example, increasing the efficiency of solar panels that produce electricity directly from sunlight.
For the education component of the Cottrell Scholar Award, Gerbode will work with the creators of “CS5,” Harvey Mudd’s highly praised introductory computer science programming course. With their assistance she will develop a broadly appealing mechanics animations course designed to encourage students to encode interactive animations of challenging physics topics.