Research
Nanostructured
Thermoelectrics
Background
In
a typical thermoelectric device, a junction is formed between p-type and n-type
semiconductor materials. The device acts as a Peltier
heat pump when electrical current is passed through the junction or as a Seebeck electrical generator when placed along a
temperature gradient. In either case the device performance is limited by the
non-dimensional thermoelectric figure of merit (ZT) of the material, where T is
the absolute temperature and Z is the thermoelectric figure of merit, Z=sa2/k
(a-thermoelectric
power, s-electrical
conductivity, k-thermal conductivity).
Increasing the thermoelectric figure of merit in conventional solids faces many challenges. For instance, increasing the thermoelectric power usually decreases the electrical conductivity. Moreover, an increase in the electrical conductivity also increases the electronic contribution to thermal conductivity. Therefore, a limit is rapidly approached where a modification to any of the three parameters s, a, k, adversely affects the other transport parameters, and Z does not change significantly.
Motivation
Harvesting medium-grade heat from industrial
stacks alone could generate at least 50 GW of electrical power, which is half
the energy produced by the US nuclear fleet. Current technologies for waste
heat recovery systems employ thermodynamics cycles that work with low-boiling
temperature fluids. At present there are no adequate technologies for
efficiently utilizing abundant sources of waste heat such as low pressure
exhaust gas streams, or non-gas heat sources (e.g., hot surfaces). On another
hand efficient solid-state refrigeration will lead to a revolution in air
conditioning applications from cars to buildings. Advances in solid-state
thermoelectric energy conversion will translate into large scale implementation
of these systems in real world applications. Immediate societal benefits
include a decreased dependence on oil reserves, decreased threat from CO2
environmental damage and creation of a new global market for waste heat
technologies.
Nanostructures and nanostructured materials
are ideal candidates for highly efficient thermoelectric energy conversion. The reasons are rooted in quantum and size
effects of the charge and heat carriers respectively. In suitable nanostructures, quantum
confinement of the charge carriers may enhance the Seebeck
coefficient and electrical conductivity of existing materials due to an
increased density of states at the Fermi level. On the other
hand, enhanced boundary scattering of heat carriers lead to a large reduction
in thermal conductivity of nanostructures. The simultaneous
increase of the power factor and the reduction of thermal conductivity lead to
large figures of merit Z.
Goals
·
Investigate nanoscience
based strategies to achieve high figures of merit in novel materials for solid
state refrigeration and power generation.
·
Develop metrology techniques for thermoelectric properties
characterization of nanostructured thermoelectric materials and their
interfaces with electrodes.
·
Develop fabrication
and testing strategies for nanostructured thermoelectric energy conversion
devices.
Recent contributions and relevant publications
·
Discovery (through a
long-term collaboration with Prof. G. Ramanath’s
group from MSE Dept. at RPI) of a new class of highly scalable, high figure of
merit, nanostructured bulk thermoelectric materials (patent licensed by ThermoAura Inc.). The high ZT results reported were enabled
by reductions in thermal conductivity due to nanopores
and nanograins. There is also a promise for ZT>2
by sulfur doping control facilitated by the new bottom-up synthesis method.
P. Jood,
R. J. Mehta, Y. Zhang, T. Borca-Tasciuc, S. X. Dou,
D. J. Singh, G. Ramanath
“Heavy Element Doping for Enhancing Thermoelectric Properties of
Nanostructured Zinc Oxide,”
RSC Advances, Vol. 4, 6363-6368, 2014 (Link).
R.
J. Mehta, Y. Zhang, H. Zhu, D. S. Parker, M. Belley,
D. J. Singh, R. Ramprasad, T. Borca-Tasciuc,
and G. Ramanath
“Seebeck and Figure of Merit Enhancement in Nanostructured
Antimony Telluride by Antisite Defect Suppression
through Sulfur Doping,”
Nano Letters, Vol. 12, 4523–4529, 2012 (PDF).
Yanliang Zhang, Rutvik J. Mehta, Matthew Belley, Liang Han, Ganpati Ramanath, and Theodorian Borca-Tasciuc
“Lattice
Thermal Conductivity Diminution and High Thermoelectric Power Factor Retention
in Nanoporous Macroassemblies
of Sulfur-Doped Bismuth Telluride Nanocrystals”
Applied Physics Letters, Vol. 100, 1193113 1-4, 2012 (PDF).
Rutvik J. Mehta, Yanliang Zhang, Chinnathambi Karthik, Binay Singh, Richard W. Siegel, Theodorian Borca-Tasciuc & Ganpati Ramanath
“A New Class of Doped Nanobulk High-Figure-of-Merit Thermoelectrics by Scalable Bottom-up Assembly”
Nature Materials, Vol. 11, 233-240, 2012 (PDF).
·
Development of a scanning
thermal microprobe for quantitative characterization of the thermal
conductivity and Seebeck coefficient with microscale resolution. Scanning thermal and thermoelectric
microscopy of nanomaterials.
M.
M. Rojo, J. Martín, S. Grauby,
T. Borca-Tasciuc,
S. Dilhaire and M. Martin-Gonzalez
“Decrease in thermal conductivity in
polymeric P3HT nanowires by size-reduction induced by crystal orientation: new
approaches towards thermal transport engineering of organic materials,”
Nanoscale, Vol. 6,
7858-7865, 
2014 (Link).
T. Borca-Tasciuc
“Scanning Probe Methods for Thermal and Thermoelectric Property Measurements,”
for the volume Experimental Techniques for Micro/Nanoscale Thermal and Thermoelectric Measurements
Annual Reviews of Heat Transfer, Vol.
16, 211-258, Invited paper, 2013 (Link).
Y. Zhang, E. Castillo, R. Mehta, G. Ramanath, and T. Borca-Tasciuc
“A non-contact thermal microprobe for local
thermal conductivity measurement”
Review of Scientific Instruments, Vol. 82, 024902, 2011. (PDF)
Y. Zhang, C. L. Hapenciuc, E. E. Castillo, T. Borca-Tasciuc, R. J. Mehta, C. Karthik, and G. Ramanath
“A microprobe technique for simultaneously
measuring thermal conductivity and Seebeck
coefficient of thin films”
Applied Physics Letters, Vol. 96, 062107, 2010. (PDF)
·
Development of a
transient method for measurement of all thermoelectric properties as well
as electrical and thermal contact resistances in films.
M. M. Rojo, J. J. Romero, D. Ramos, D. Borca-Tasciuc,
T. Borca-Tasciuc and M. Martín-González
“Modeling of transient thermoelectric
transport in Harman method for films and nanowires,”
International Journal of Thermal
Science, Vol. 89, 193-202, 2015 (Link).
E. E. Castillo, C. L. Hapenciuc, and T. Borca-Tasciuc
“Thermoelectric characterization by
transient Harman method under non-ideal contact and boundary conditions”
Review of Scientific instruments, Vol. 81, 044902, 2010. (PDF)
Thermal Transport in
Nanostructures and Nanocomposites
Background
As
nanostructures approach fundamental length scales of the thermal energy
carriers, size and quantum effects may strongly influence their effective thermophysical
properties. A good example is the well-documented reduction of the thermal
conductivity in thin films and superlattices, which is attributed to the
intense surface/interface scattering of heat carriers. Similar effects are
partially responsible for large reductions in the thermal conductivity of
nanowires and quantum dots. This affects the failure rate of devices, which
depends heavily on the operating temperature. Similarly, overheating problems
affect the operation and performance of solid state lasers and LEDs. However,
the reduced thermal conductivity effect may be used to advantage in
thermoelectric applications, in which reduced phonon thermal conductivity and
enhanced electrical conductivity and Seebeck coefficient are required. On the other
hand, novel nanoscale arrangements of atoms could have very high thermal
conductivities, as predicted for single wall carbon nanotubes. This raises new
challenges and also brings new opportunities in heat transfer, energy
conversion, and thermal energy storage using nanomaterials.
Motivation
Structures such as thin films, quantum wells, superlattices, have already numerous applications in microelectronics, optoelectronics, micro-electro-mechanical-systems, solid-state lasers, and most recently in solid-state energy conversion. Moreover, with the emergence of a new era of nanotechnology one-dimensional structures such as nanowires and carbon nanotubes or zero-dimensional structures such as quantum dots may emerge in the next generations of nanoelectronics and optoelectronis devices or nanoelectromechanical systems. New materials and structures bring new opportunities for engineering thermal transport in a variety of applications from thermal management, to thermal energy storage, to thermoelectric energy conversion.
Goals
- Understand thermal transport at nanoscale through measurements and optimize heat transfer by controlling the mechanisms responsible.
- Develop strategies to control the thermal resistance across interfaces and within bulk.
- Develop high thermal conductivity composites for packaging and thermal management applications.
- Develop thermal energy storage materials with enhanced performance.
- Understand the relation between structural and growth parameters and effective thermal properties of nanostructures.
Recent contributions and
relevant publications
·
Development of a photothermoelectric method to determine the anisotropic
thermal conductivity and the interface thermal resistance in thin
film-on-substrate systems.
Borca-Tasciuc, T., Borca-Tasciuc, D.-A., and Chen G.
“A Photothermoelectric
Technique for Anisotropic Thermal Diffusivity Characterization of
Nanowire/Nanotube Composites,”
IEEE
Transactions on Components and Packaging Technologies, Vol. 30,
609-617, 2007. (PDF)
·
Discovery of novel
mechanisms for formation of high thermal conductivity networks in polymer
composites filled with nanoparticles (patent pending). Self assembly of nanoparticles
within the low viscosity phase in high aspect ratio structures, followed
by low temperature sintering (150°C), leads to high thermal conductivity pathways which impart
high thermal conductivity to the nanocomposite.
K. Pashayi, H. R. Fard, F. Lai,
S. Iruvanti,
J. Plawsky and T. Borca-Tasciuc
“Self-Constructed Tree-Shape High Thermal Conductivity Nanosilver Networks in Epoxy,”
Nanoscale, Vol. 6, 4292-4296, 2014 (Link).
Kamyar Pashayi, Hafez Raeisi Fard, Fengyuan Lai, Sushumna Iruvanti, Joel Plawsky, and Theodorian Borca-Tasciuc
“High
Thermal Conductivity Epoxy-Silver Composites Based on Self-Constructed
Nanostructured Metallic Networks”
Journal of Applied Physics, Vol. 111, 104310 1-6, 2012 (PDF).
·
Characterization of
anisotropic thermal properties in aligned carbon nanotube arrays and aligned
carbon-nanotube polymer composites. The findings
reported include the anisotropy of aligned carbon nanotube arrays and the large
thermal conductivity degradation due to defects.
Sunil K. Pal, Youngsuk Son, Theodorian Borca-Tasciuc, Diana-Andra Borca-Tasciuc, Swastik Kar, Robert Vajtai, Pulickel M. Ajayan
”Thermal and electrical transport along
MWCNT arrays grown on Inconel substrates,”
Journal of Materials Research,
Vol. 23, 2099, 2008. (PDF)
Borca-Tasciuc, T., Mazumder,
M., Pal, S. K., Son, Y., L., Schadler, L. S., and Ajayan, P.
“Anisotropic thermal diffusivity characterization of aligned
carbon nanotube-polymer composites”
(Invited) Journal of Nanoscience and Nanotechnology Vol. 7, 1581-1588, 2007. (PDF)
Borca-Tasciuc, T., Vafaei, S., Borca-Tasciuc, D.-A.,
Wei, B. Q, Vajtai, R., and Ajayan,
P.
“Anisotropic Thermal Diffusivity of aligned multiwall carbon
nanotube arrays”
Journal of Applied Physics, Vol.
98, 054309, 2005. (PDF)
·
Characterization of the
interface thermal resistance between novel thermal interface materials (e.g. carbon
nanotube arrays polymer nanocomposites) and the heat
sink or chip substrate. The main findings for CNT arrays is that the native
interface after Chemical Vapor Deposition (CVD) has a high thermal resistivity
due to imperfect substrate-CNT contacts and the low volume fraction of CNTs in
the studied arrays. For polymer nanocomposites the
interface thermal conductance is strongly affected by viscosity.
I. Seshadri, T. Borca-Tasciuc, P. Keblinski and G. Ramanath
“Interfacial thermal conductance-rheology
nexus in metal-contacted nanocomposites,”
Applied Physics Letters, Vol. 103,
173113 1-4, 2013 (Link).
Youngsuk Son, Sunil K. Pal, and Theodorian
Borca-Tasciuc, Pulickel M. Ajayan, and Richard W. Siegel
”Thermal resistance of the native interface between
vertically aligned multiwalled carbon nanotube arrays
and their SiO2/Si substrate,”
Journal of Applied Physics, Vol. 103,
024911, 2008. (PDF).
·
Characterization of
thermal transport in Si/Ge, Si/SiC multilayers and
optical materials. Large thermal conductivity reductions were measured in the
cross-plane direction and were related to the structure and composition of the
films.
H. R. Fard, N. Becker, A. Hess, K. Pashayi1, T. Proslier, M. Pellin and T. Borca-Tasciuc
“Thermal Conductivity of Er+3:Y2O3
films grown by Atomic Layer Deposition,”
Applied Physics Letters, Vol. 103, 193109 1-5, 2013 (Link).
M. Mazumder, T. Borca-Tasciuc, S. Teehan, H. Efstathiadis, E. Stinzianni, and V. Solovyov
“Temperature dependent thermal conductivity of
Si/SiC amorphous multilayer films”
Applied Physics Letters, Vol. 96, 093103, 2010. (PDF)
Micro and
Nano-Electro-Mechanical-Systems
The synergy between microfabrication and nanotechnology may bring tremendous opportunities for the development of novel sensing and actuation concepts. We explore using MEMS fabrication technologies and nanostructured materials with novel properties for the following applications. The microfabrication efforts are facilitated by the class 100 Microfabrication Clean Room (MCR) at Rensselaer Polytechnic Institute.
Research interests in MEMS/NEMS:
· Energy conversion
· Chemical & biological detection
· Fast optical switching
· Flow control
· Inertial sensors
· Test-structures for thermo-fluid and thermoelectric characterization.
