Toward catalyst-mediated growth of diamond and cubic boron nitride wires

Abstract

Sustained catalyst-mediated growth of diamond and cubic boron nitride (cBN) wires has yet to be established reproducibly, although related methods produce carbon and BN nanotubes and many elemental and compound nanowires. I hypothesize that a retained contact between a catalyst and an existing tetrahedral crystal can sustain wire extension under conditions that do not nucleate that crystal on an otherwise comparable unseeded catalyst. The prediction is repeated, vapor-derived target-phase extension during an interval in which matched unseeded contacts do not nucleate that phase. I develop tests using diamond seeds, SiC starter wires and cBN seeds, separating the conditions used to establish the contact from those used for continuation. Worked estimates distinguish bulk precipitation driving forces from sidewall costs and show why increased carbon activity alone cannot select diamond over graphite. Comparisons with established synthesis identify the roles of pressure, hydrogen and activated nitrogen that must be retained or replaced. Isotope tracing, local structural measurements and time-dependent growth distinguish continued incorporation from seed consumption, conversion and etching. Nanometer, micrometer and larger wires could provide electrically insulating thermal connections, mechanical probes and reinforcing filaments.

arXiv commentRevised Perspective with quantitative thermodynamic estimates and proposed tests of sustained wire growth; 39 pages, including 14 pages of Supporting Information; 6 figures