Figure 4
(Color online) (a) SuperSTEM high-resolution BF image of a multiple-walled CNT ion implanted with nitrogen at 100 eV and
. The distance between the graphitic planes is
. Superimposed on the image is the EEL spectrum acquisition grid. Light gray (green) pixels indicate a captured nitrogen signal. The variation in tint of the pixels indicates the integrated intensity in the energy window 400–415 eV of the nitrogen signal of raw, background-subtracted spectra [like in (c) below]: a stronger intensity has a stronger (brighter) tint. (b) Approximate geometry and dimensions of the CNT in (a). (c) Raw EEL intensity in the energy region around the
edge after power-law background subtraction, extracted from the bottom row of pixels in (a), indicated by the black arrow. (d) Same spectra after having undergone principal component analysis and normalization to the same noise bandwidth. (e) Top and middle spectra: DFT (WIEN2K) calculations of the
EEL edge of substitutional N with and without adjacent vacancy in graphene, the structure model is shown in the middle of the figure with carbon atoms in gray (blue) and nitrogen atoms in black, bottom spectrum is of the
edge in hexagonal BN (gray line; green) and nitrogen gas (black line). (f) SuperSTEM high-resolution BF image of a multiple-walled CNT implanted with boron at 100 eV and
. Superimposed on the image is the EEL spectrum acquisition grid. Dark gray (pink) pixels indicate captured boron signals. The variation in tint of the pixels indicates the integrated intensity of the boron signal in the energy window 190–193 eV: a stronger gray (pink) intensity has a stronger tint. (g) Top to bottom: DFT (WIEN2K) calculations of the
EEL edge of substitutional B with and without adjacent vacancy in graphene,
EEL edge of a hexagonal BN standard (Ref.
32) (gray; green) and of nonspatially resolved measurements of a highly boron doped (25%) multiple-walled CNT (black). (h) PCA treated, noise-normalized spectra extracted from the row of pixels in (f), indicated by the black arrow. (i) Signal in the energy region around the
edge in the same spectra as in (h). (j) SuperSTEM high-resolution BF image of five-layered graphene with locations of
signals in the spectra, as in (h), at 190–193 eV, marked as white squares (yellow). (k) SuperSTEM high-resolution BF image of staggered graphene sheets; leftmost is a single layer, followed (toward the right) by a second sheet with a rough edge, which, in turn, is followed by four further graphene sheets with partially straight edges. B-signal positions are marked as white circles (yellow). (l) Top to bottom:
EEL edge of amorphous B, of
and of two typical, overlaid spectra from white (yellow) positions in (k). These signals are significantly above noise level, thus have not been PCA treated. The
peak is missing and comparison with the reference spectra suggests that small few-atom B clusters have formed attached to sheet edges or to monoatomic steps.
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