TY - JOUR

T1 - (formula presented) hybridization ratio in amorphous carbon from C (formula presented) core-level shifts

T2 - X-ray photoelectron spectroscopy and first-principles calculation

AU - Haerle, Rainer

AU - Riedo, Elisa

AU - Pasquarello, Alfredo

AU - Baldereschi, Alfonso

PY - 2002

Y1 - 2002

N2 - Using a combined experimental and theoretical approach, we address C (formula presented) core-level shifts in amorphous carbon. Experimental results are obtained by x-ray photoelectron spectroscopy (XPS) and electron-energy-loss spectroscopy (EELS) on thin-film samples of different atomic density, obtained by a pulsed-laser deposition growth process. The XPS spectra are deconvoluted into two contributions, which are attributed to (formula presented)- and (formula presented)-hybridized atoms, respectively, separated by 0.9 eV, independent of atomic density. The (formula presented) hybridization content extracted from XPS is consistent with the atomic density derived from the plasmon energy in the EELS spectrum. In our theoretical study, we generate several periodic model structures of amorphous carbon of different densities applying two schemes of increasing accuracy in sequence. We first use a molecular-dynamics approach, based on an environmental-dependent tight-binding Hamiltonian to quench the systems from the liquid phase. The final model structures are then obtained by further atomic relaxation using a first-principles pseudopotential plane-wave approach within density-functional theory. Within the latter framework, we also calculate carbon (formula presented) core-level shifts for our disordered model structures. We find that the shifts associated to threefold- and fourfold- coordinated carbon atoms give rise to two distinct peaks separated by about 1.0 eV, independent of density, in close agreement with experimental observations. This provides strong support for decomposing the XPS spectra into two peaks resulting from (formula presented)- and (formula presented)-hybridized atoms. Core-hole relaxations effects account for about 30% of the calculated shifts.

AB - Using a combined experimental and theoretical approach, we address C (formula presented) core-level shifts in amorphous carbon. Experimental results are obtained by x-ray photoelectron spectroscopy (XPS) and electron-energy-loss spectroscopy (EELS) on thin-film samples of different atomic density, obtained by a pulsed-laser deposition growth process. The XPS spectra are deconvoluted into two contributions, which are attributed to (formula presented)- and (formula presented)-hybridized atoms, respectively, separated by 0.9 eV, independent of atomic density. The (formula presented) hybridization content extracted from XPS is consistent with the atomic density derived from the plasmon energy in the EELS spectrum. In our theoretical study, we generate several periodic model structures of amorphous carbon of different densities applying two schemes of increasing accuracy in sequence. We first use a molecular-dynamics approach, based on an environmental-dependent tight-binding Hamiltonian to quench the systems from the liquid phase. The final model structures are then obtained by further atomic relaxation using a first-principles pseudopotential plane-wave approach within density-functional theory. Within the latter framework, we also calculate carbon (formula presented) core-level shifts for our disordered model structures. We find that the shifts associated to threefold- and fourfold- coordinated carbon atoms give rise to two distinct peaks separated by about 1.0 eV, independent of density, in close agreement with experimental observations. This provides strong support for decomposing the XPS spectra into two peaks resulting from (formula presented)- and (formula presented)-hybridized atoms. Core-hole relaxations effects account for about 30% of the calculated shifts.

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U2 - 10.1103/PhysRevB.65.045101

DO - 10.1103/PhysRevB.65.045101

M3 - Article

AN - SCOPUS:78650598401

SN - 1098-0121

VL - 65

SP - 1

EP - 9

JO - Physical Review B-Condensed Matter

JF - Physical Review B-Condensed Matter

IS - 4

ER -