![]() This issue... Wow! Fermilab Confirms the Tau This issue... Wow! Fermilab Confirms the Tau This issue... |
Free-standing Micro-ObjectsThe dimer's high reactivity is the key to creating freestanding diamond objects. Conventionally grown diamond films don't adhere well to silicon-dioxide substrates, says Gruen. But the dimers react readily with silicon dioxide to form a silicon-carbide monolayer a layer one molecule thickwith which dimers can easily react to grow a diamond film. This makes it possible to shape diamond films using photolithographic techniques commonly used in today's computer chip industry, and then chemically separate the film from the substrate, leaving a freestanding diamond object. Gruen worked with the Fraunhofer Institute in Bremen, Germany, which specializes in micro-fabrication, to make a tiny vernier caliperan instrument that tells researchers how much the diamond bends under a given force.
The caliper consists of two arms, one that is fixed and another that moves independently. Each arm has teeth, like the marks on a ruler. Noting where the teeth of the two arms line up provides a precise measurement of strain on the diamond film. Making the gauge requires several steps. First, a silicon wafer is oxidized at high temperature to grow a layer of silicon dioxide. Next, Argonne's dimer-based process grows a diamond film on the silicon dioxide. As described above, the dimers first combine with the silicon dioxide to form a silicon-carbide monolayer, then combine with the silicon carbide to grow the diamond film. Once the film is in place, a photolithographic etching process chemically carves out the gauge's desired shape. Finally, the wafer is exposed to hydrogen fluoride gas, which converts the silicon-dioxide layer to silicon-tetrafluoride gas, leaving the gauge resting loose on the original substrate. Gruen's co-inventor Alan Krauss created the world's smallest diamond tube using a micro-variant of the "lost wax" method that sculptors have used for thousands of years. First, he used the dimer-based process to deposit diamond film on a silicon spike about five micrometers in diameter. When the silicon was etched away, what remained was a freestanding tube with a 5-micrometer-wide channel and uniform walls only 300 nanometers thick.
"Nothing like this has ever been made out of diamond," Krauss says. "On structures this small, conventional CVD doesn't work. Instead of spreading smoothly over the surface, the diamond collects in little balls. It would be totally impossible to make by any other diamond processing method." These demonstrationsthe vernier caliper and the diamond tuberepresent the first significant steps toward building practical microscopic structures and devices out of diamonds. In addition to this experimental work, quantum chemical and molecular dynamics simulations provide continuing insight into the properties of ultra-nanocrystalline diamond films. The technology's success has spawned collaboration with many other research groups at Argonne and in industry. As Argonne's diamond film technology matures, it could point the way to a revolution in tiny machines that improve human health and safety, create new companies and industries, and expand our knowledge of the world and the universe around us. |
![]() ![]() ![]() ![]() ![]() |
||
![]() ![]() | ||||
![]() | ||||
www.pnl.gov/energyscience/ |