Thermopower and conductance of single-molecule junctions and atomic contacts
Author
Evangeli, CharalambosEntity
UAM. Departamento de Física de la Materia CondensadaDate
2014-12-11Funded by
This work has been supported by the European Union (FP7) through programs ITN “FUNMOLS” Project Number 212942, ELFOS and by the A.G. Leventis FoundationSubjects
Termoelectricidad - Tesis doctorales; Materiales termoléctricos - Tesis doctorales; Microelectrónica - Tesis doctorales; Calor - Conducción - Tesis doctorales; Electrones - Transportes - Tesis doctorales; FísicaNote
Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física de la Materia Condensada. Fecha de lectura: 11-12-2014Esta obra está bajo una licencia de Creative Commons Reconocimiento-NoComercial-SinObraDerivada 4.0 Internacional.
Abstract
Thermoelectric
fundamental
are
problem of
dissipation problem
materials
difficult
everyday life.
they are light, flexible and potentially
needs to be improved.
the
the most important open problems in nanoscience c
optimization
nanoscale
Single
excellent
interface at a fundamental level.
the electronic conductance is typically the only magnitude measured.
recently
the transport process has been demonstrated
just a few groups
The main
conductance of single
(STM)
new STM head specifically designed for these measurements and the development
of a no
and applied
believed to
waste heat recovery (e.g. from transportation vehicles) or the heat
materials, despite the good performance
to process
Organic thermoelectric materia
introduction of nanostructure
ptimization of thermoelectricity
[Zhang2014
Single-molecule junctions formed using scanning probe techniques constitute an
model system to study the processes occurring at the organic
recently, the possibilit
goal of this thesis has been to
in ambient conditions. An important part of this work is the construction of a
novel powerful technique for measuring
effects in molecular junctions are
point of view
be one of the potential solutions for key energy problems like the
(e.g. in microelectronics).
, (energetically expensive and toxic), heavy and brittle for use in
A strategy for enhanc
ntroduction Zhang2014].
possibility of measuring the thermopower to give further insight into
[Baheti2008
single-molecule junctions using
vel view.
cheap,
nanostructures and multiple interfaces
in organic thermoelectric materials
In most of the experiments in molecular junctions,
y Baheti2008; Widawsky2011
study experimentally the thermo
Indeed, organic thermoelec
Present day inorganic thermoele
performance, are already globally limited, relatively
materials are promising alternatives
although their present efficiency still
enhancing the thermoelectric performance is
concerns the understanding
[Reddy2007
Widawsky2011; Yee2011
a scanning tunneling m
simultaneously
of great interest f
rganic resent ls lthough [See2010
oncerns Reddy2007] and is currently use
Yee2011].
the thermopower
Abstract
thermoelectric materials
since
See2010]. Thus, one of
at the
organic-inorganic
Quite
thermopower and
microscope
5
from
thermoelectric
and
used by
er icroscope
and
conductance of single-molecule junctions, making a complete characterization of
the molecular junction possible. This is detailed in chapter 4.
In chapter 5, this new technique is used to measure the thermopower of C60
molecules and demonstrate the possibility of engineering the thermopower of a
molecular junction by molecular scale manipulation, in particular, the enhancement
of thermopower by forming a C60 dimer is shown.
The thermoelectric properties of atomic nanocontacts of gold and platinum are
explored in chapter 6. As contact size dimensions are reduced, a crossover from
bulk to quantum behaviour involving a change of sign of the thermopower takes
place. Interestingly, quantum oscillations are observed in gold atomic-size contacts,
whereas in platinum they are totally absent. This difference between gold and
platinum is traced back to the different electronic structure of these two metals.
In chapter 7 the effect of lateral chains on the thermopower of OPE derivatives is
examined. The addition of lateral chains is found to increase the thermopower as it
brings the Fermi level closer to molecular resonances. An enhancement of
thermopower with stretching of the molecule is also observed.
Finally, in chapter 8 the use of C60 as a linker in molecular junctions is explored by
forming single-molecule junctions of dumbbell molecules, consisting of two
fullerenes joined by a conjugated backbone.
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