Materials Research Science and Engineering Center
Nanoindentation of Colloidal Crystals

Nanoindentation is a common method for studying defect formation in crystalline films. A very small point indents the material, ensuring only a single crystalline region is probed. We study “nano” indentation in thin colloidal crystal films. Each colloidal particle plays the role of an atom; however, the particles can be imaged with a microscope and their individual dynamics can be measured. The nanoindenter is a sewing needle, which has the right scale relative to the colloidal particles. The behavior is visualized using laser-diffraction microscopy, where diffracted laser light is imaged (left). The on-line movie shows nucleation of defects. (http://www.mrsec.harvard.edu/ indentation3.mov). Individual particles are imaged with confocal microscopy (right). The on-line movie shows the thermally-induced nucleation and growth of dislocations. (http://www.mrsec.harvard.edu/indentation14c.mov). Only particles whose order is distorted are displayed. The behavior of the colloidal crystal is remarkably similar to that of atomic films, but allows thermally induced dislocations to be directly visualized.