Open AccessThermal effect in unoccupied molecular orbitals of C 60 molecules adsorbed on a Si(001)‐(2 × 1) surface studied by NEXAFS
Author(s) -
Kondo Daiyu,
Sakamoto Kazuyuki,
Takeda Hideo,
Matsui Fumihiko,
Ohta Toshiaki,
Amemiya Kenta,
Uchida Wakio,
Kasuya Atsuo
Publication year - 2001
Publication title -
journal of synchrotron radiation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.172
H-Index - 99
ISSN - 1600-5775
DOI - 10.1107/s0909049500019695
Subject(s) - homo/lumo , xanes , molecular orbital , van der waals force , chemistry , molecule , valence (chemistry) , monolayer , crystallography , materials science , spectral line , physics , organic chemistry , biochemistry , astronomy
We report here the temperature‐dependent unoccupied molecular orbitals (MO's) of C 60 molecules adsorbed on a Si(001)‐(2 × 1) surface measured using near edge x‐ray absorption fine structure (NEXAFS). At 300 K, the NEXAFS spectrum reveals that the interaction between a 1.0 monolayer (ML) C 60 film and a Si(001) surface is mainly the van der Waals force. After annealing the samples at 500 K, we observe an increment in the full‐width at half‐maximum of unoccupied MO's, which indicates the change of the interaction. Moreover, the lowest unoccupied molecular orbital (LUMO) shifts to the higher photon energy side and the intensity of the LUMO+1 relative to that of the LUMO+3 decreases in the NEXAFS spectrum. These results suggest that the strong interaction induced at 500 K has a covalent character, to which the LUMO+1 contributes.