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Ab initio thermodynamics study of ambient gases reacting with amorphous carbon

: Held, A.; Moseler, M.

Volltext urn:nbn:de:0011-n-5380482 (639 KByte PDF)
MD5 Fingerprint: 39e33bd0acc9b137a66db560a312832b
Erstellt am: 18.4.2019

Physical Review. B 99 (2019), Nr.5, Art. 054207, 16 S.
ISSN: 0163-1829
ISSN: 1098-0121
ISSN: 0556-2805
ISSN: 2469-9950
Deutsche Forschungsgemeinschaft DFG
MO 879/17-1
Zeitschriftenaufsatz, Elektronische Publikation
Fraunhofer IWM ()
amorphous carbon; Atom; chemical analysis; dangling bonds; gases; pore size; thermodynamic; tribology

Amorphous carbon (a-C) occurs as a tribologically induced phase in diamond or diamond-like carbon coatings. The interaction of ambient gases (H2, N2, O2, H2O, CO2) with a-C of varying mass density is studied by means of ab initio thermodynamics simulations. Different scenarios such as moist air or pure gases are investigated under different pressure and temperature conditions. Equilibrium concentrations of chemisorbed and fragmented final states are found to only exhibit a minor dependence on the specific conditions of the gas phase reservoir. The differences in local structure of the a-C samples with varying mass density such as pore size and coordination and dangling bonds, as well as the competition among different gas molecules for a-C atoms as reactants, affect the equilibrium concent rations to a greater degree. The availability and reactivity of a-C atoms are thus found to mainly control the chemical composition of a-C interacting with ambient gases in thermodynamic equilibrium. Trends found in the analysis of chemical groups occurring in equilibrium can possibly be transferred to a more realistic nonequilibrium tribological scenario.