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Transformation of nanodiamond into carbon onions: A comparative study by high-resolution transmission electron microscopy, electron energy-loss spectroscopy, x-ray diffraction, small-angle x-ray scattering, and ultraviolet Raman spectroscopy
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10.1063/1.1868054
/content/aip/journal/jap/97/7/10.1063/1.1868054
http://aip.metastore.ingenta.com/content/aip/journal/jap/97/7/10.1063/1.1868054

Figures

Image of FIG. 1.
FIG. 1.

HRTEM image of the nanodiamond recorded at the Scherzer defocus. The two white parallel lines show an interplanar distance of , corresponding to {111} of the diamond crystal structure.

Image of FIG. 2.
FIG. 2.

EELS spectra of a general area of the nanodiamond (a), carbon onions found in the partially transformed nanodiamond shown in Fig. 3(b) (b), and carbon onions∕polyhedrons found in the fully transformed nanodiamond (c).

Image of FIG. 3.
FIG. 3.

HRTEM images of the nanodiamond annealed in vacuum at for (a) and (b) and (c) and (d) recorded at the Scherzer defocus. Two white parallel lines in part (c) of the figure show an intershell spacing of .

Image of FIG. 4.
FIG. 4.

XRD patterns (Cu radiation) of a diamond powder, grain size , used for measurements of an instrumental broadening of the diffractometer (a), the nanodiamond (b), and the nanodiamond annealed in vacuum at for (c) and (d). Positions of diamond (space group , ) and graphite (space group , and ) reflections assigned by Miller indices are shown for reference at the bottom and the top of the figure respectively (wavelength of x-ray radiation has been used in the calculations).

Image of FIG. 5.
FIG. 5.

The physical broadening of the diamond diffraction peaks (assigned by Miller indices) in the nanodiamond plotted vs . The solid line is a linear fit to the data used in the Williamson–Hall analysis.

Image of FIG. 6.
FIG. 6.

Calculated curves of apparent physical broadening of the diamond diffraction peaks caused by a hexagonal distortion of the diamond cubic cell ( is used as a distortion parameter). The curves are assigned by the Miller indices of the diamond diffraction peaks (Miller indices corresponding to superimposed hexagonal peaks are given in brackets). It has been accepted in the calculations that the nanodiamond crystallites are spherical (average diameter ), the shape of the diffraction peaks is Lorentzian, , where and are volumes of hexagonal unit cells corresponding to the perfect (cubic) diamond crystal structure and to a diamond structure with hexagonal distortion , respectively. The calculations have been made only within a range of values where hexagonal 110 and 104 peaks corresponding to a cubic 022 cannot be resolved experimentally (, where is a full width at half maximum of a Lorentzian).

Image of FIG. 7.
FIG. 7.

A plot of the spacing derived from the angle position of the 002 carbon onion reflection measured in this work (open circle) and another work (see Ref. 10) (closed squares) vs the annealing temperature used for a transformation of nanodiamond into carbon onions. The solid curve represents the thermal dependence of the spacing in a perfect graphite structure [the linear thermal expansion coefficient along the direction of graphene layers stacking, axis, for the calculation was taken from a Handbook (see Ref. 58).

Image of FIG. 8.
FIG. 8.

Porod plot of SAXS patterns for the nanodiamond (diamonds) and the nanodiamond after annealing in vacuum at for (squares) and (circles).

Image of FIG. 9.
FIG. 9.

The Porod region of SAXS patterns plotted on a logarithmic scale (log–log plot) for the nanodiamond (a), the nanodiamond annealed in vacuum at for (b), and (c). The patterns are fitted by the classical Porod law [dashed lines in (a), (b), and (c)] and by Porod’s law corrected by the sigmoidal-gradient model [solid curves in (a) and (b)].

Image of FIG. 10.
FIG. 10.

A schematic illustration of the relationship between core-shell structure of a nanodiamond spherical particle with a two-step boundary (a) and electron density variation in the radial direction of the sphere: the sigmoidal gradient model (see Refs. 63 and 79) (b) and a nanodianond particle with a two-step boundary (c). The following parameters , , , , , ), and have been used to plot the scheme.

Image of FIG. 11.
FIG. 11.

Representative multiwavelength Raman spectra of the nanodiamond. Each curve is identified by the wavelength (and photon energy) of exciting laser radiation. The sharp band at of the Raman spectrum excited by originates from vibrational states of oxygen molecules present in a surrounding air. The Raman spectrum excited by is plotted after subtraction of luminescence background approximated by a cubic polynomial.

Image of FIG. 12.
FIG. 12.

A comparison of experimental Raman spectrum of the nanodiamond (open circles) recorded within a region of the diamond optical modes frequency of with Raman scattering patterns (lines) simulated for nanodiamond crystallites (diameter 30, 35, 45, and ) using the phonon confinement model with Ager et al. parameters (see Ref. 26) for an approximation of the diamond dispersion curves. Similar patterns could be achieved with Yoshikawa et al. parameters (see Ref. 73) for crystallites of diameter 36, 41, 53, and , respectively. The inset compares the one-dimensional approximation of the diamond dispersion curves at vicinity of the point using both the Ager et al. (see Ref. 26) and Yoshikawa et al. (see Ref. 73) parameters.

Image of FIG. 13.
FIG. 13.

Representative UV Raman spectra (excited by laser radiation with ) of the nanodiamond (a) and the nanodiamond annealed in vacuum at for (b) and (c). Positions of diamond optical mode band at and graphite mode band at are marked, respectively, by the dashed and dotted lines crossing the figure. The inset shows the phonon density of states of diamond. (see Ref. 74). Sharp bands located at and correspond to Raman bands of oxygen and nitrogen molecules, respectively, present in the surrounding air.

Tables

Generic image for table
Table I.

Relation of the Miller indices of the diamond diffraction peaks assigned either in a cubic unit cell (, space group ) or in a hexagonal unit cell ( and , space group ).

Generic image for table
Table II.

Characteristics of samples used in the SAXS measurements (the density of the carbon material , the mean density of the powder sample , and the volume fraction of the carbon material in the sample ) and parameters of the samples determined from the SAXS measurements (the Porod constant , the Porod invariant determined from the curve by the numerical integration, the specific surface area , the range of “inhomogeneity” (see Ref. 59), the mean particle core radius (see Ref. 59), the transition-layer width , and the mean diameter of carbon particles ). The results of fitting by two models (the classical Porod law and the Porod law modified by the sigmoidal electron-density gradient model) are presented for the nanodiamond and for the partially transformed nanodiamond. All values have been rounded to significant figures after calculations.

Generic image for table
Table III.

Diamond crystallite size (Å) obtained by different methods.

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/content/aip/journal/jap/97/7/10.1063/1.1868054
2005-03-21
2014-04-19
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Transformation of nanodiamond into carbon onions: A comparative study by high-resolution transmission electron microscopy, electron energy-loss spectroscopy, x-ray diffraction, small-angle x-ray scattering, and ultraviolet Raman spectroscopy
http://aip.metastore.ingenta.com/content/aip/journal/jap/97/7/10.1063/1.1868054
10.1063/1.1868054
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