With the runaway success of the slogan—"a diamond is forever"—diamonds have come to symbolize everlasting love and secured their place in engagement rings worldwide. Now, the more affordable, man-made version of this super-strong material is aiming for much more than the jewelry market. Already used as heat sinks for electronics, in saw blades for cutting asphalt and marble, in drill bits for oil and gas drilling and as an exfoliant in cosmetics, synthetic diamond is also showing potential for applications such as high-powered electronics.

Companies have been synthesizing diamond for about 50 years. Today, firms around the world like Diamond Innovations (formerly part of General Electric), Sumitomo Electric and De Beers grow more than 100 tons of diamond a year. Diamond is attractive for a variety of materials applications because it possesses a remarkable range of properties. Of all known materials, it's the hardest, stiffest and most thermally conductive, yet it hardly expands when heated. It is also chemically impervious to virtually all acids and bases. Moreover, it is a superb electrical insulator and is transparent to UV, visible and infrared light.

While impurities in naturally occurring diamond produce distinctive colors, impurities in synthetic diamond provide a way for gem makers to control material properties. For example, companies can replace some of the carbon atoms in the diamond lattice with boron and turn the diamond into a p-type semiconductor, or one that can conduct positive charge. (Transforming a diamond into an n-type semiconductor is also possible but more problematic). Such boron-doped semiconducting diamonds could be used to manufacture diamond-based electronic devices that could withstand heat and harsh chemicals.

According to James E. Butler, who is leading efforts to analyze, grow and use diamond at the U.S. Naval Research Laboratory, high-pressure, high-temperature methods of producing diamond are not capable of finely controlling impurities and creating big gems. Instead, a low-pressure technique called chemical vapor deposition (CVD) may be the solution, he believes. With this method, impurities can be tightly controlled and larger diamonds can be grown.

Using this technique, Boston start-up company Apollo Diamond can now produce single-crystal diamonds—just like in nature—as opposed to polycrystalline ones, which until recently accounted for most of the diamonds grown by CVD methods. Single-crystal diamonds are even stronger, more thermally conductive and more optically transparent than polycrystalline ones. And some applications, especially those such as electronics that call for the maximum carrier mobility, can employ only single-crystal—not polycrystalline—diamonds, Robert C. Linares, Apollo's founder and chairman, tells Chemical & Engineering News. In fact, in order for the synthetic material to fulfill its potential as an alternative to silicon for crafting electronic devices, "what's required is high-quality, single-crystal CVD diamond in usable sizes," asserts Steven E. Coe, R&D manager at U.K.-based Element Six, formerly called De Beers Industrial Diamonds.

Nevertheless, polycrystalline diamond still preserves many of the remarkable properties of naturally occurring single-crystal diamond and has thus rounded up several applications, such as in biosensing methods and in electrodes to study redox reactions. In addition, many scientists are synthesizing polycrystalline boron-doped diamond electrodes to identify—and in some cases, break down—redox-reactive organic contaminants in water supplies. Moreover, Element Six is using its polycrystalline diamond in surgical blades that resist dulling and as optical windows for high-powered CO2 lasers. It's also selling its diamond for use as heat spreaders in high-powered electronic devices.

Still, developing single-crystal diamond for electronic devices may offer the biggest payoff, as microchips operate at higher and higher temperatures and threaten to expose silicon to too much heat. Diamond, in contrast, could handle the heat. While some say two reasons will prevent the material from ever completely replacing silicon—the fact that silicon is economical and the fact that it's well established in the computer industry—diamond is ideal for "certain specialized applications, such as devices that run at high power or high temperature," says Reza Abbaschian, a professor of materials science and engineering at the University of Florida.

In short, with its extraordinary optical, thermal, chemical and electronic properties, synthetic diamond is proving that it's more than just pretty; it's practical.

Source:

The Many Facets of Man-Made Diamonds
Amanda Yarnell
Chemical & Engineering News, February 2, 2004
pubs.acs.org/cen/coverstory/8205/8205diamonds.html