Chemistry Reference
In-Depth Information
Figure 6.36. Detail of the
(
T
) curve for
3
showing the Peierls transition. The
dashed line corresponds to a linear interpolation of the higher temperature region.
Reprinted from
Journal of Solid State Chemistry
, Vol. 168, J. Fraxedas, S. Molas,
A. Figueras, I. Jimenez, R. Gago, P. Auban-Senzier and M. Goffman,
Thin films of
molecular metals: TTF-TCNQ
, 384-389, Copyright (2002), with permission from
Elsevier.
ρ
Our next example deals with thin films of TTF[Ni(dmit)
2
]
2
grown by electrode-
position on silicon wafers (de Caro
et al.
, 2004). We recall here that TTF[Ni(dmit)
2
]
2
single crystals exhibit metallic behaviour down to 3 K, with
−
1
cm
−
1
σ
RT
300
and superconductivity is observed at
T
c
6 K under application of a hydrostatic
pressure of 7 kbar (Brossard
et al.
, 1986). The electrodeposited films exhibit metal-
lic character down to
c
. 12 K in spite of their polycrystalline morphology, as will
be shown next. The advantage of the EC technique over vapour-phase deposition
methods is that vapour-phase deposition is limited to sublimation/evaporation of
neutral species. The EC-grown films consist of crystals with sizes ranging from 0.6
to 1
µ
m and the estimated thickness of the films is
c
.1
µ
m.
Figure 6.37 shows the XPS S2
p
line measured
ex situ
for a TTF[Ni(dmit)
2
]
2
thin film. The experimental lineshape can be satisfactorily decomposed into three
contributions. The most intense line, with a binding energy of 163.5 eV, corre-
sponds to C-S-C bonds, and the 161.8 and 165.3 eV lines to C-S-Ni and C
1
.
S
bonds, respectively. In the nominal formula TTF[Ni(dmit)
2
]
2
there are 12 C-S-C, 8
C-S-Ni and 4 C
=
=
S bonds, which results in a ratio 3:2:1. From the fit, the intensity
