NER: Chemical Vapor Deposition of Carbon Nanotube/Diamond Composites

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PROJECT SUMMARY The objectives of this nanoscale exploratory research project are the growth of composite films of carbon nanotubes and diamond using chemical-vapor deposition, to extensively characterize these films, and to understand the film-growth process at the atomistic level through detailed simulations of the molecular processes. Carbon nanotubes (CNT) and diamond have properties that are individually exceptional but also complementary in a fashion such that a composite material made of these components should have truly unique properties. CNT are predicted to have extremely high values of Young's modulus while also being able to sustain large strain in the axial direction. It has been demonstrated that, using the tip of an AFM, multiwalled CNT can be bent repeatedly through large angles without causing any apparent fracture. On the other hand, diamond is the hardest known material and has the highest room-temperature thermal conductivity. Other properties include a very low coefficient of friction, good resistivity and optical transparency, and some superior semiconducting properties when appropriately doped. Recent research has shown that polycrystalline diamond can be readily deposited as a film on various substrates. Such diamond films have found applications primarily as wear-resistant coatings and heat-spreading devices, though film brittleness significantly limits the use of pure diamond films. In order to capitalize on the favorable properties of diamond while addressing the brittleness problem, a CNT/diamond composite material is manufactured that should have extreme hardness combined with outstanding toughness. The synthesis method is chemical vapor deposition (CVD) which is currently used to deposit both diamond and CNT under similar conditions. By careful selection of process conditions, a dense CNT/diamond film with a strong interface is produced that can be controlled and optimized by variation of reactor parameters. Deposition experiments are conducted in an existing CVD reactor, which is slightly modified to allow for CNT and diamond deposition on the same wafer. After the initial CNT film is generated, diamond is deposited using hot-filament CVD (HF-CVD). The structural properties of the composite films are characterized by high-resolution transmission electron microscopy. The roles of the substrate and catalyst on the growth of CNT and diamond, and the interface and internal film stresses are investigated. The mechanical properties of the composite are studied with atomic-force microscopy using a diamond-tipped probe. A complementary modeling and simulation effort provides understanding of the fundamental phenomena offers insight into remedial measures and potential process improvement.Broader impactThis work provides education and experience for university students in nanotechnology. Results obtained in this study are widely disseminated through conferences and archival journal publications. Should this effort at film synthesis be successful, a great potential for technology transfer with the emerging nanotechnology industry will be present. The involvement of students from under-represented groups is promoted through recruiting efforts, as well as through the university's formal SURGE program. Facility upgrades required for this project improve the infrastructure and enhance the ability to conduct research in the area of nanomaterials .