CVD temperatures are in the order of 1000K or lower, and pressures in the range of 1-5 atm, although some processes use higher pressures. CVD uses a carbon-containing precursor species, which is decomposed over a catalyst yielding C atoms that eventually evolve in carbon nanostructures. Since their discovery, chemical vapor deposition (CVD) methods have become the preferred synthesis method. Single-walled carbon nanotubes (SWCNTs) are among the most promising nanostructures because of their special and unusual physico-chemical properties that make them strong candidates for a variety of applications. Materials Sciences & Engineering Division National Science Foundation (NSF) OSTI Identifier: 1756179 Alternate Identifier(s): OSTI ID: 1865812 Report Number(s): BNL-220767-2020-JAAM Journal ID: ISSN 0957-4484 Grant/Contract Number: SC0012704 SC0019336 AC02-98CH10886 DMR-1419807 SC0019383 Resource Type: Accepted Manuscript Journal Name: Nanotechnology Additional Journal Information: Journal Volume: 32 Journal Issue: 7 Journal ID: ISSN 0957-4484 Publisher: IOP Publishing Country of Publication: United States Language: English Subject: 36 MATERIALS SCIENCE Nanowire, Nanotube, Vapor-Liquid-Solid = , of Technology (MIT), Cambridge, MA (United States) Sponsoring Org.: USDOE Office of Science (SC), Basic Energy Sciences (BES). (BNL), Upton, NY (United States) Massachusetts Inst. Publication Date: Research Org.: Brookhaven National Lab. of Technology (MIT), Cambridge, MA (United States) of Technology, Atlanta, GA (United States) of Technology (MIT), Cambridge, MA (United States) Georgia Inst. Finally, these results indicate that the use of unconventional, nonmetallic catalysts provides opportunities to synthesize unusual oxide nanostructures with potentially useful properties. The twisting rate is consistent with a softening of elastic rigidity. A combination of ex situ and in situ transmission electron microscopy measurements suggest that the hollow core results from a competition between growth and etching at the Ge-ZnO interface during synthesis. The twisted nanotubes show large hollow cores and surprisingly high twisting rates, up to 9°/μm, that cannot be easily explained through the Eshelby twist model. As well as the usual straight nanowires, we describe two other distinct morphologies: twisted nanowires and twisted nanotubes. Here, we show, for the model ZnO system, that unusual nanostructures can be produced via a semiconductor (Ge) catalyst. The exploration of unconventional catalysts for the vapor-liquid-solid synthesis of one-dimensional materials promises to yield new morphologies and functionality.
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