DNA nanostructures synthesized in vivo

Like natural diamonds, synthetic diamonds can be produced in a variety of grades, depending on growth conditions. High growth rates can be realized with chemical vapor deposition, but the diamond produced is often not clear because of nitrogen deposits that render the crystals absorptive over the infrared-toultraviolet spectrum, resulting in crystals that appear gray or brown. To reduce absorption, commercial producers anneal natural diamonds at high temperature and pressure. The high pressure is necessary to prevent the diamond from turning into graphite. Yu-fei Meng et al. report that it is possible to anneal single crystals, grown by chemical vapor deposition, at low pressure and greatly improve the optical quality of the diamond. Common industrial annealing pressures are on the order of 50 GPa, or 500,000 times atmospheric pressure; the authors employed half-atmospheric pressure in a hydrogen-rich environment that prevented the diamond’s conversion to graphite. From spectroscopic data, the authors confirmed that the improved optical performance results from a reduced number of defects associated with nitrogen. This technique should provide an easier path to fabricating diamonds for technological applications, the authors say. — K.M.