Chemistry Reference
In-Depth Information
Figure 6.35.
ρ
(
T
) curves of thin TTF-TCNQ films grown at (
1a
and
1b
)
T
sub
=
RT
and
T
ann
350 K. The measurements were
performed using the four contacts low-frequency lock-in technique with 10
350 K and (
3
)
T
sub
325 K and
T
ann
A for
µ
1a
and 0.1
A for
1b
and
3
. 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.
µ
350 K (
3
). The conduction barrier energy
E
a
can be obtained from the
Arrhenius plot:
E
a
T
ann
8 and 295.4 K for the nominally identical samples
1a
and
1b
(grown in different experiments) and 273.7 K for sample
3
. Earlier reported
E
a
values for oriented thin TTF-TCNQ films lie between 170 and 580 K (Reinhardt
et al.
, 1980; de Caro
et al.
, 2000a). The decrease of
E
a
upon increase of
T
sub
is in line
with the increase in size of the microcrystals, which reduces the number of grain
boundaries. The obtained
296
.
−
1
cm
−
1
) are comparable
σ
RT
values (2
<σ
RT
<
10
−
1
cm
−
1
)
(Reinhardt
et al.
, 1980; Sumimoto
et al.
, 1995; Figueras
et al.
, 1999; de Caro
et al.
, 2000a), the conductivity of the films resulting from a random contribution of
σ
a
and
with earlier determinations on thin TTF-TCNQ films (1
<σ
RT
<
30
σ
b
values.
A detail of the
(
T
) curve is displayed for sample
3
in Fig. 6.36. The non-linear
increase of resistivity below
c
. 50 K corresponds to the metal-insulator Peierls
transition. The Peierls transition is more readily observed for the
E
a
ρ
273
.
7K
sample because of its lower activation energy as compared to the
c
.
E
a
296 K
samples.
