Like modern day alchemists, materials scientists often turn unassuming substances into desirable ones. But instead of working metal into gold, they create strange new compounds that could make the electronic components of the future smaller, faster, and more durable. Alexander Goncharov of the Carnegie Institution's Geophysical Laboratory and colleagues have used extreme temperatures and pressures to make two durable compounds called noble metal nitrides; they are the first to succeed in making one of them, and the first to accurately determine the chemical formula of the other. Both nitrides possess a diamond-like hardness, and some compositions might have very low, nearly superconductive electrical resistance--a blend that could prove quite valuable to industry.
The two nitrides--one containing iridium and another containing platinum--could eventually replace the titanium nitrides currently valued by the semiconductor industry as surface coatings because of their strength and durability. The researchers believe iridium and platinum nitrides might be even more durable. The group's work is presented in the March 3, 2006, issue of the journal Science.
Like several other metals such as gold, silver, and palladium, platinum and iridium are noble metals. Such metals are resistant to corrosion and oxidation, and do not easily form compounds with other elements unless coaxed to do so under very high temperatures and pressures. Goncharov and his colleagues used a special tool called a diamond anvil cell to compress the samples to nearly half a million times the atmospheric pressure at sea level. Then they used a focused laser to heat the samples to over 3000 degrees Fahrenheit, or roughly the temperature of a steel mill blast furnace. Under such extreme pressure and temperature the rules of chemistry begin to change, and noble metals can be made to form compounds with other elements such as nitrogen, as in the case of iridium and platinum nitrides.
"We are still attempting to ascertain the electronic properties of these new materials," Goncharov said. "Generally speaking, these nitrides are likely to exhibit several properties that will make them attractive for technological applications. They are potentially important for the electronics industry as durable and reliable coatings, substrates, and conductors. One can also envisage optoelectronic devices, sensitive magnetometers and other metrological equipment that employ these materials."
Though other researchers have previously made platinum nitride, Goncharov's group is the first to discover that for every platinum atom, there are two nitrogen atoms rather than just one. They are also the first to make iridium nitride, which they found has the same basic chemical formula as platinum nitride. In both cases, strong bonds that the dual nitrogen atoms make with the metal atom contribute to the nitrides' hardness and durability. The noble metals, in turn, contribute unusual electronic properties.
So far, Goncharov's group has only created small quantities of iridium and platinum nitrides in the lab. There is much work to do before these compounds can contribute to engineering and manufacturing the technology of tomorrow. But as Goncharov explains, "The present work is useful because it proves that these exotic nitrides exist, even if they were synthesized in a manner that is not practical on an industrial scale."