Premium
Electronic structure of SP 2 trap states in amorphous carbon
Author(s) -
Fotopoulos N.,
Xanthakis J. P.
Publication year - 2007
Publication title -
surface and interface analysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.52
H-Index - 90
eISSN - 1096-9918
pISSN - 0142-2421
DOI - 10.1002/sia.2475
Subject(s) - amorphous carbon , carbon fibers , chemistry , binding energy , atomic physics , electronic structure , electron , atom (system on chip) , crystallography , molecular physics , chemical physics , amorphous solid , materials science , computational chemistry , physics , composite number , computer science , embedded system , composite material , quantum mechanics
Amorphous carbon, a‐C:H, contains an unusually high number of defect states, typically 10 19 /cm 3 . These states play a major role in the process of field electron emission from a‐C:H since they inhibit (by trapping) the transport of electrons from the cathode to the amorphous carbon film/vacuum interface. In this paper we examine the electronic structure of two of these defects, the pentagon–heptagon pair and a broken carbon double bond (by the addition of one hydrogen at one of the two carbon atoms). These defects are expected to be found in a graphitic environment in a‐C:H. To obtain their electronic structure, we construct large enough graphitic clusters, embed the defects at their center and then use typical semiempirical quantum chemical methods such as the PM3 method—which is a parameterized Hartree–Fock method—to calculate the energy levels in the gap and the binding energies. Both defects produce energy levels just above the highest occupied molecular orbital (HOMO) of the graphite levels, but the pentagon–heptagon pair has a much higher binding energy, making it more stable. From the difference in binding energy, we conclude that the pentagon–heptagon pair is far more stable. Copyright © 2007 John Wiley & Sons, Ltd.