Atomic hydrogen treatment of nanodiamond powder studied with photoemission spectroscopy

The effect of atomic hydrogen treatment upon the surface of partially graphitized nanodiamonds has been studied by photoemission spectroscopy. The $\mathrm{C}1s$ core level peak and valence band spectra of a partially graphitized nanodiamond sample were compared with those following hydrogen treatment and following subsequent annealing. We have observed a difference in the binding energy of the $s{p}^3$ component of the $\mathrm{C}1s$ peak and in the valence band which we believe can be assigned to either upward or downward band bending due to surface graphitization and hydrogenation of nanodiamonds, respectively. The data confirms that the graphitic layers which initially cover the nanodiamond particles can be removed through exposure to atomic hydrogen. This method could enable the preparation of hydrogen terminated and separate nanodiamond particles.

Figure 1

$\mathrm{N}1s$ photoemission spectrum of the hydrogenated sample which reveals two peaks at binding energies of 400.7 and $404.0\mathrm{eV}$. The dots represent experimental data and the solid lines are the fitted components from which the spectrum is composed. The background is subtracted by the Shirley method. The resulting fit is superimposed on the data. The spectrum was obtained using a photon energy of $1253.6\mathrm{eV}$.

Figure 2

$\mathrm{C}1s$ photoemission spectrum of ND annealed at $1420\mathrm{K}$. The dots show the experimental data and the solid lines are the fitted components of which the spectrum was composed. The background is subtracted by the Shirley method. The resulting fit is superimposed on the data. The spectrum was obtained using a photon energy of $1253.6\mathrm{eV}$.

Figure 3

$\mathrm{C}1s$ photoemission spectra of (a) the initial ND sample; (b) the same sample after atomic hydrogen treatment; (c) following additional annealing at $1000\mathrm{K}$ after hydrogenation; (d) following additional annealing at $1200\mathrm{K}$ after treatment described in (c). The annealing time was $20\min$ for both temperatures. Dashed lines are used to guide eyes. The binding energies of 284.7 and $286.0\mathrm{eV}$ were taken from the fitted components of Fig. 2. The spectra were obtained using a photon energy of $1253.6\mathrm{eV}$.

Figure 4

(a) $E_{\text{cut}\text{−}\text{off}}$ and (b) $\mathrm{C}1s$ peak position of the sample as a function of applied negative bias voltage after the sample was treated with atomic hydrogen (full squares) and after annealing at $1000\mathrm{K}$ (open triangles).

Figure 5

Valence band spectra of (a) the initial ND sample annealed to $1420\mathrm{K}$, (b) the same sample after atomic hydrogen treatment, (c) the additional annealing at $1000\mathrm{K}$ after hydrogenation, (d) additional annealing at $1200\mathrm{K}$ after treatment described in (c). Dashed lines are used to guide eyes. $E_{\mathrm{F}}$ is the Fermi energy level. The spectra were obtained using a photon energy of $55\mathrm{eV}$.

Figure 6

Valence band spectra of (a) diamond (111) surface from Ref. 60; (b) diamond (100) surface from Ref. 60; (c) hydrogenated ND annealed at $1000\mathrm{K}$ [the same spectrum as in Fig. 5c]. Corresponding excitation energies are presented on the right side of the figure.