Chemistry Reference
In-Depth Information
Figure 6.4. (a) Band structure calculated for the RT structure of TTF-TCNQ where
=
(0 0 1/2) in units of the monoclinic
reciprocal lattice vectors. (b) Total DOS calculated for TTF-TCNQ and PDOS
for the sulfur, carbon and nitrogen atoms (black lines). The S2
p
,N1
s
and C1
s
NEXAFS spectra of TTF-TCNQ (grey lines) are superposed to the PDOS of S,
N and C, respectively. Energy is given relative to
E
F
. Reprinted with permission
from J. Fraxedas, Y. J. Lee, I. Jimenez, R. Gago, R. M. Nieminen, P. Ordejon
and E. Canadell,
Physical Review B
,
68
, 195115 (2003). Copyright (2003) by the
American Physical Society.
(0 0 0), X
=
(1/2 0 0), Y
=
(0 1
/
2 0) and Z
=
Electronic structure of occupied states
The electronic structure of the occupied states of TTF-TCNQ has been experimen-
tally determined in UHV by means of ARUPS for
in situ
cleaved single crystals
(Zwick
et al.
, 1998; Claessen
et al.
, 2002) as well as for thin films prepared
ex situ
with PVD (Rojas
et al.
, 2001). Let us start with the ARUPS spectra measured on
high-quality single crystals of TTF-TCNQ along the
b
-axis (
-Y direction) taken
at 150 K with 20 eV monochromatic radiation shown in Fig. 6.6 (Zwick
et al.
,
1998). A prominent feature dispersing symmetrically about the
0) is
observed in Fig. 6.6(a), and it approaches
E
F
. At larger wave vectors, it disperses
away from
E
F
, to a maximum binding energy of 0.75 eV at the Y-point. The spectra
measured perpendicular to the chains, along the
a
-axis (Fig. 6.6(b)), do not exhibit
any dispersion, evidencing the 1D character. Figure 6.6(c) reproduces spectra from
Fig. 6.6(a), at the
-point (
k
=
- and Y-points. According to the spectra the band crossing at
E
F
