期刊
MICROSCOPY AND MICROANALYSIS
卷 19, 期 5, 页码 1298-1302出版社
CAMBRIDGE UNIV PRESS
DOI: 10.1017/S1431927613001918
关键词
iron carbide; nanowire; forbidden reflections; HRTEM
资金
- South-East Physics Network
- Engineering and Physical Sciences Research Council
Structures comprising single-crystal, iron-carbon-based nanowires encapsulated by multiwall carbon nanotubes self-organize on inert substrates exposed to the products of ferrocene pyrolysis at high temperature. The most commonly observed encapsulated phases are Fe3C, alpha-Fe, and gamma-Fe. The observation of anomalously long-period lattice spacings in these nanowires has caused confusion since reflections from lattice spacings of >= 0.4 nm are kinematically forbidden for Fe3C, most of the rarely observed, less stable carbides, alpha-Fe, and gamma-Fe. Through high-resolution electron microscopy, selective area electron diffraction, and electron energy loss spectroscopy we demonstrate that the observed long-period lattice spacings of 0.49, 0.66, and 0.44 nm correspond to reflections from the (100), (010), and (001) planes of orthorhombic Fe3C (space group Pnma). Observation of these forbidden reflections results from dynamic scattering of the incident beam as first observed in bulk Fe3C crystals. With small amounts of beam tilt these reflections can have significant intensities for crystals containing glide planes such as Fe3C with space groups Pnma or Pbmn.
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