C 1sexcitation studies of diamond (111). I. Surface core levels

Abstract

By comparing the C 1s photoemission intensities from a clean diamond {111} surface to those obtained from a fluorine-covered surface, we conclude that a single t, '111) layer of atoms participates in the diamond 2X 1 surface reconstruction. The data interpretation presented does not rely on assuming an electron mean free path, but, in fact provides an independent measurement of its value. For clean diamond (111) a surface core-level peak is observed at 0.80+0.05 eV lower binding energy than the bulk-C 1s peak at 285.0 eV below E~. After fluorine exposure a single chemically shifted carbon peak is observed at 1.85+0.05 eV higher binding energy than the bulk peak, indicating the presence of CF units at the surface.

Work function and electron affinity of the fluorine-terminated (100) diamond surface

“…The solid lines illustrate how the low-energy electron cut-off was determined from the intersection of the baseline with the leading edge of the low energy peak. The presence of adsorbed fluorocarbon has been reported for some F-terminated diamond samples, 19,20 but not for others, 1,10,11,14 and seems to be a peculiarity of the fluorination technique employed here. The deposition of fluorocarbon adlayers from fluorocarbon plasmas has also been described briefly by Schvartzman et al 20 For the case at hand, it is plausible that hydrocarbon molecules in the preparation vacuum chamber are fluorinated along with the sample and adsorb onto its surface as the sample cools.…”

“…A smaller peak with a BE of 286.2 eV that persists even after annealing to 700 C is ascribed to C atoms bonded to one F because the chemical shift of this line with respect to the diamond bulk peak (þ1.6 eV) is similar to that reported for fluorine-terminated (100) and (111) diamond surfaces. 10,11,14,17 Two further peaks are identified at higher binding energies: a strong peak at 289.0 eV (labelled CF I ) and one of lower intensity at 291.1 eV (CF II ). These lines resemble features reported by Smentkowski et al 16 for C 4 F 9 I adsorbed on the (100) diamond surface and are hence attributed to CF 2 and CF 3 species, respectively.…”

“…In contrast, previous reports showed a distinct p-bonded carbon C1s line for samples that were considered to be fluorine-saturated. 10,11,14 We therefore consider the surface after annealing at 350 C to be close to the ideal case, with very little fluorocarbon contamination but an otherwise fully fluorinated (100) diamond surface with one F atom bonded to each surface C atom. For the surface in this state, the work function, electron affinity, and ðE F À E VBM Þ were found to be 7.24 eV, 2.56 eV, and 0.79 eV, respectively.…”

“…9 A variety of techniques have been reported for the preparation of F-terminated diamond surfaces with varying degrees of success. These have been based on the exposure of surfaces to fluorine-containing gases (atomic F, 10-12 F 2 , 2,13 HF, 13 and XeF 2 [14][15][16] ), molecules (fluorocarbons 17 and fluorofullerenes 18 ), and plasmas (CF, 6,19 CHF 3 ,5,20 and C 4 F 8 1,20 ). However, many of these techniques are known to damage or etch the surface and provide unsaturated disordered surfaces with an adsorbed fluorocarbon layer.…”

Bulk and surface thermal stability of ultra nanocrystalline diamond films with 10–30 nm grain size prepared by chemical vapor deposition

“…When recorded as a function of the photon excitation energy, exciting from the C͑1s͒ core level, it has been shown to be a powerful probe of the diamond electronic structure. [43][44][45][46] Unlike Raman spectroscopy, NEXAFS has a similar cross section for different carbon allotropes and it is sensitive to local chemical bonding, which enables analysis of nanosized carbon materials. 47,48 …”