These "flexible diamond" nanothreads are sp3-bonded and one-dimensional and thus occupy a distinct position in a matrix of hybridization (sp2/sp3) and dimensionality (0D/1D/2D/3D) for carbon nanomaterials.A unifying theme in the Badding group's research is the use of pressure to synthesize, deposit, or probe solid state materials. We are interested in materials that have unusual micro or nano structure or chemical/physical behavior and often apply them to problems of significant technological interest. Photonic materials, energy materials for photovoltaics, and carbon nanomaterials have recently been of particular interest. In the Efree DOE Energy Frontier Research Center we have recently synthesized single crystals of carbon nanothreads (see rotating image above left and nanothread crystal sliding panel above; black spheres are carbons, light pink spheres are hydrogens) through a non-topochemical reaction from solid benzene. These "flexible diamond" nanothreads are sp3-bonded and one-dimensional and thus occupy a distinct position in a matrix of hybridization (sp2/sp3) and dimensionality (0D/1D/2D/3D) for carbon nanomaterials. From the point of view of polymers, nanothreads are very rigid, but from the point of view of bulk solids, they are highly flexible: unique mechanical properties can be anticipated. Much as graphite exfoliates into graphene, nanothread crystals exfoliate into thread bundles along their van der Waals separations. Fully saturated degree-6 nanothreads could exhibit a unique combination of strength, flexibility, and resilience, while partially saturated degree-4 threads with their stiff backbones may form a new class of organic conductors. A new and growing sub-field of chemistry, physics, and materials science has been nucleated; see the Nanothread Bibliography. In IRG3 of the Penn State NSF Materials Research Science and Engineering Center, we have synthesized by high pressure chemical vapor deposition metalattices that are quantum confined yet interconnected to permit the flow of electrons and phonons and magnetic exchange. Single crystal silicon and germanium optical fibers and infrared fiber lasers (in the Air Force Center for Guided Wave Infrared Sources) synthesized by high pressure chemical vapor deposition are another recent focus.
About 1,000,000 kg per year of diamond is produced by high pressure methods, a much larger quantity than is produced by chemical vapor deposition.
Pressure is a thermodynamic variable that is as fundamental as temperature, but is underutilized in materials chemistry research. It can, for example, control interatomic distance (without much variation in other quantities such as the entropy), tune reaction chemical kinetics and thermodynamics (often over a much wider range than is possible with temperature), allow for solvents with hybrid liquid-like and gas-like properties, and infiltrate molecules and materials into near atomic scale voids. Superior materials properties or interesting behavior not possible without the use of pressure for chemical synthesis or tuning can thus be obtained. At the micro and nano scales, high pressure chemistry becomes much more straightforward and practical because pressure is force per unit area and the forces involved become very small as the area decreases. We use a wide range of pressure from just above atmospheric (0.1 megapascals) to tens of gigapascals. Pressure is practical for industrial scale synthesis and is indeed used by industry much more than by academic scientists. About 1,000,000 kg of diamond per year is produced at modest cost at pressures of 5 to 6 GPa, a much larger quantity than is produced by chemical vapor deposition.