The physicists at the University of Alabama (UAB) in Birmingham have completed the first step of a five-year effort to create a new compound that can surpass diamond in heat resistance and compete with diamonds in hardness. . They received $20 million in grants from the US National Science Foundation to create new materials and use a fourth material state plasma to improve the technology.
Unlike the other three physical states (solid liquids and gases), the plasma does not exist on Earth, but it can be obtained by heating and ionizing a neutral gas. In the lab, Yogesh Vohra, a professor of physics at the University of Alabama (UAB) in Birmingham, uses plasma to make diamond films. Such films have many potential uses, for example, for the manufacture of artificial joint coatings with long aging or coatings that maintain sharpness of the tool, as well as for the manufacture of sensors for the environment and the synthesis of new superhard materials.
Wola and his colleagues made a diamond film that vents various gases, including carbon-containing gases such as methane, into a vacuum chamber and uses microwave heating to generate a plasma. The low pressure in the vacuum chamber is equivalent to 14 miles above the surface of the Earth. After four hours, the plasma has deposited carbon as a diamond film.
Vohra and colleagues at the University of Alabama (UAB) School of Arts and Sciences in Birmingham explore how to change the properties of diamond materials by adding boron while making diamond films. They reported their findings in a paper on the Materials website.
They have known that a mixture of methane and hydrogen gas can produce a diamond film composed of many microdiamond crystals having an average diameter of about 800 nm. The addition of nitrogen to the mixed gas produces nanostructured diamond (consisting of very small diamond crystals with an average diameter of only 60 nm).
In this study, the Vohra research team added diborane (B 2 H 6) to the hydrogen/methane/nitrogen feed gas, which produced amazing results. The grain size in the diamond film suddenly increased from the 60 nm diameter size grain seen by the hydrogen/methane/nitrogen feed gas to the crystallite diameter size of 800 nm. Moreover, this change occurs only when the amount of diborane added is small, and the plasma is only one hundred and seventy percent.
By changing the amount of diborane in the feed gas and using optical diffraction spectroscopy, Vohra found that diborane reduced the amount of carbon-nitrogen radicals in the plasma. Therefore, Vohra said: "Our research clearly defines the role of carbon and nitrogen in the synthesis of diamond nanostructures, and the addition of boron to the plasma can inhibit carbon and nitrogen."
The addition of boron also allows the diamond film to be changed from a non-conductor to a semiconductor, so the results of the University of Alabama at Birmingham (UAB) provide a new way to control the grain size and electrical properties of the film, which is useful for a variety of practical applications. Very useful.
In the next few years, Vohra and his colleagues plan to explore the use of this plasma chemical vapor microwave deposition process to make films of boron carbide, boron nitride and carbon boron nitride compounds. Their goal is to produce compounds that are more heat resistant than diamond, but still have a diamond-like hardness.
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