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Thin Films in Energy Storage and
Conversion Applications
40th Annual Spring Symposium
Michigan Chapter of the American Vacuum Society
Co-Sponsored by
Michigan State University
Monday, August 25, 2014
International Center
427 N. Shaw Lane
Michigan State University
East Lansing, MI 48824
1
Welcome
to the 40th Annual Symposium of
the Michigan Chapter of AVS
A one day conference dedicated to providing an opportunity for
scientists and engineers to meet and discuss recent advances in science and
technology of materials, surface, interfaces, processing and vacuum science and
technology. Cutting-edge technologies of atomic layer deposition, molecular
layer deposition, plasma synthesis, and computation are joining forces to solve
grant challenges in energy storage and conversion applications.
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Meeting Schedule
8:00 Registration, Coffee and Breakfast (Sparty Room)
Keynote Presentations (Room 115) (Chair: Yue Qi)
8:30 Excitonsin OLEDs and OPVs: Can’t live with them, can’t operate without them, Stephen
Forrest, University of Michigan
9:15 Batteries and Battery Materials by Vapor Deposition, Nancy Dudney, Oak Ridge National
Lab
10:00 Coffee Break, Opening of Exhibition (Sparty Room)
Session I: ALD for energy applications (Room 115) (Chair: Donald Morelli)
10:20 Surface modification of silicon anodes for advanced Li-ion batteries Chunmei Ban,
National Renewable Energy Lab
10:50 Atomic layer deposition for energy conversion devices, Neil Dasgupta, University of
Michigan
11:20 Recent advances in the quantum chemistry of semiconductor surface chemistry:
automated precursor screening and alternative surface reaction pathways, Mat Halls,
Schrodinger
11:50 Equipment Exhibit & Lunch (Sparty Room)
Session II: Thin film for energy applications (Room 115) (Chair: Richard Lunt)
1:30 Photoelectrochemical investigation of thin film metal oxide electrodes for solar energy
conversion, Tom Hamann, Michigan State University
2:00 In situ, real time studies of organic semiconductor thin film growth, Jim Engstrom,
Cornell University
2:30 Plasma for controlling the synthesis of semiconductor nanocrystals, Rebecca Anthony,
Michigan State University
3:00 CdTe thin film PV devices: unlocking high performance potential to reality, Zhibo Zhao,
First Solar
Gathering (Sparty Room)
3:45 Poster Session, Equipment Exhibit, and Reception
4:50 Award ceremony for student poster awards
5:00 Symposium ends
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Conference map
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8:30 A.M.
Excitons in OLEDs and OPVs: You can’t live with them and you can’t operate
without them
Stephen R Forrest
Departments of Electrical Engineering and Computer Science, Physics and Materials Science and
Engineering
University of Michigan, Ann Arbor, MI 48109 USA
A persistent challenge with optoelectronic devices based on organic materials is
overcoming their relatively short operational lifetime compared with inorganic semiconductor
devices. This has been a limiting factor in their applications to displays and lighting based on
organic light emitting diodes (OLEDs), and in organic photovoltaic (OPV) cells. We have found
that the intrinsic source of degradation is the presence of high energy excitons1, 2
that often
dissipate their energy by breaking bonds, and hence destroying the active electronic molecular
species. Unfortunately, excitons are also responsible for all of the beneficial optoelectronic
properties of such devices. The question then becomes: can we enhance the benefits of excitons
without leading to device degradation? I will discuss the achievement of long-lived blue
electrophosphorescent OLEDs (PHOLEDs); a problem that has prevented their widespread use
for over a decade in spite of their very high emission efficiencies. We demonstrate a blue
PHOLED that results in a lower exciton density compared to a conventional device without
sacrificing efficiency. A lifetime of 616±10 hrs (time to 80% of the 1000 cd/m2 initial
luminance) is observed, representing a ten-fold lifetime improvement over a conventional blue
PHOLEDs3. Prospects for increasing PHOLED lifetime by another factor of 10 – 100 in view of
our understanding will be discussed. Also, the lifetime of OPVs will be considered using this
same understanding.
1.N. C. Giebink, B. W. D’Andrade, M. S. Weaver, P. B. Mackenzie, J. J. Brown, M. E. Thompson and S. R. Forrest,
J. Appl. Phys. 103, 044509 (2008).
2.X.Tong, N. Wang, M. Slootsky, J. Yu and S. R. Forrest, Solar Energy Materials & Solar Cells 118, 116 (2013).
3.Y. Zhang, J. Lee and S. R. Forrest, Nature Commun., in press (2014).
Stephen R. Forrest,
Education: B. A. Physics, 1972, University of California, MSc and PhD Physics in 1974 and
1979, University of Michigan. At Bell Labs, he investigated photodetectors for optical
communications. In 1985, Prof. Forrest joined the Electrical Engineering and Materials Science
Departments at USC where worked on optoelectronic integrated circuits, and organic
semiconductors. In 1992, Prof. Forrest became the James S. McDonnell Distinguished University
Professor of Electrical Engineering at Princeton University. He served as director of the National
Center for Integrated Photonic Technology, and as Director of Princeton's Center for Photonics
and Optoelectronic Materials (POEM), and from 1997-2001, he chaired Princeton’s Electrical
Engineering Department. In 2006, he rejoined the University of Michigan as Vice President for
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Research, and is the Paul G. Goebel Professor in Electrical Engineering, Materials Science and
Engineering, and Physics. A Fellow of the APS, IEEE and OSA and a member of the National
Academy of Engineering, he received the IEEE/LEOS Distinguished Lecturer Award in 1996-97,
and in 1998 he was co-recipient of the IPO National Distinguished Inventor Award as well as the
Thomas Alva Edison Award for innovations in organic LEDs. In 1999, Prof. Forrest received
the MRS Medal for work on organic thin films. In 2001, he was awarded the IEEE/LEOS
William Streifer Scientific Achievement Award for advances made on photodetectors for optical
communications systems. In 2006 he received the Jan Rajchman Prize from the Society for
Information Display for invention of phosphorescent OLEDs, and is the recipient of the 2007
IEEE Daniel Nobel Award for innovations in OLEDs. Prof. Forrest has been honored by
Princeton University establishing the Stephen R. Forrest Endowed Faculty Chair in Electrical
Engineering in 2012. Prof. Forrest has authored ~550 papers in refereed journals, and has 258
patents. He is co-founder or founding participant in several companies, including Sensors
Unlimited, Epitaxx, Inc., NanoFlex Power Corp. (OTC: OPVS), Universal Display Corp.
(NASDAQ: OLED) and Apogee Photonics, Inc., and is on the Board of Directors of Applied
Materials and PD-LD, Inc. He has also served from 2009-2012 as Chairman of the Board of Ann
Arbor SPARK, the regional economic development organization, and serves on the Board of
Governors of the Technion – Israel Institute of Technology, as well as the Vanderbilt University
School of Engineering Board of Visitors. He is Vice Chairman of the Board of the University
Musical Society and is on the Executive Committee of the Michigan Economic Development
Corp.
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9:15
Batteries and Battery Materials by Vapor Deposition
Nancy Dudney
Oak Ridge National Laboratory
Although most commercial rechargeable batteries are prepared by bulk and powder processing
methods, vapor deposition of materials has led to important advances for fundamental research,
modification of battery materials and interfaces, and also for commercialization of thin film
batteries. Each of these areas will be illustrated with our studies of thin film materials for
electrolyte, anode, and cathode components of rechargeable lithium and lithium-ion batteries
with both planar and 3-dimensional architectures.
Nancy Dudney is a distinguished researcher in the Materials Science and Technology Division
at Oak Ridge National Laboratory. She received her degrees from the College of William and
Mary (BS, Chemistry) and MIT (PhD, Ceramic Materials Science and Engineering) and began
work at Oak Ridge National Laboratory as a Wigner Research Fellow in the Solid State Division.
Dr. Dudney’s research interests include: lithium battery materials and architectures, thin film and
composite electrolytes, thin film materials for batteries, and mixed ionic-electronic conduction in
oxides. She helped pioneer the development of commercial thin-film lithium batteries and
continues to utilize thin film processing and materials in her research toward the stabilization of
battery interfaces. Dr. Dudney is a fellow of the Electrochemical Society. She has won four
R&D 100 awards. Her goal is to promote development of safe and efficient batteries for vehicles
and renewable energy.
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10:20
Surface modification of silicon anodes for advanced Li-ion batteries
Chunmei Ban
National Renewable Energy Laboratory 15013 Denver W Pkwy, Golden, CO 80401
Surface modification, via atomic layer deposition (ALD) and molecular layer
deposition (MLD) techniques, has been applied for stabilization of lithium-ion electrodes.
Greatly improved cycling performance has been demonstrated in the electrodes with these
ultrathin conformally coatings. The electrodes range from already demonstrated commercial
materials to high-energy, high-volume-change materials that could eventually lead to batteries
with higher energy densities. Successfully coated silicon (Si) anodes have exhibited that 5 nm
aluminum alkoxide coatings can enable the durable cycling of Si anodes over a hundred cycles
without major capacity fade. High-resolution microscopy was performed to study the effect of
the conformal coatings on the evolution of Si structure and morphology during
lithiation/delithiation. The findings imply that the good resilience of the elastic coatings provides
sufficient mechanical support to accommodate the major volumetric changes experienced by Si
anodes, as well as to aid in the recovery and preservation of the whole composite network upon
delithiation. Furthermore, this talk will also discuss the importance of ALD and MLD as surface
modifiers and demonstrates their versatility and compatibility with lithium-ion battery
technology.
Dr Chunmei Ban is a Scientist at National Renewable Energy Lab, Golden CO. She received
her Ph.D. in chemistry from State University of New York at Binghamton in 2008 and the
Bachelor and Master of Science degree in chemical engineering (electrochemistry) from Tianjin
University, China in 2000 and 2003. Her research focuses on design and synthesis of
nanostructured, hierarchical materials, and employing electrochemical analytic methods, et-
situ/in-situ structural and morphological characterization for investigation of interfacial
chemistry and electrochemical behavior, structure and chemical properties.
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10:50
Atomic Layer Deposition for Energy Conversion Devices
Neil P. Dasgupta,
Department of Mechanical Engineering, University of Michigan
To address the challenges on environmentally sustainable conversion and storage of
energy in the 21st century, there has been a dramatic increase in research of nanoscale materials
due to several advantageous features such as high surface areas, short transport distances, and
tunable material properties. However, with these benefits come challenges. In particular, the
ability to precisely control the properties of surfaces and heterogeneous interfaces limits the
performance of many of these devices, and requires novel approaches.
One technique that has been increasingly explored for surface and interfacial
engineering of energy conversion and storage devices is Atomic Layer Deposition (ALD). This
is a gas-phase process allowing for highly conformal deposition of a wide variety of materials
with sub-nm precision in material thickness and tunable chemical composition. This
combination of conformality and thickness control facilitate precise tuning of the electronic,
optical, thermal, and chemical properties of these interfaces.
This talk will present a broad overview of the recent developments of ALD for
energy conversion and storage devices, with an emphasis on the unique features afforded by the
ALD process. Examples in fuel cells, solar cells, batteries, and catalysts will be presented. ALD
surface chemistry will be discussed from a theoretical and experimental perspective, and the
importance of synergy between nanocharacterization and modeling will be discussed. The talk
will conclude with a perspective on future directions and challenges for widespread commercial
adaption of these technologies, including a discussion of scalable nanomanufacturing tools and
designs incorporating ALD.
Neil Dasgupta is an Assistant Professor in the Department of Mechanical Engineering at the
University of Michigan. He earned his Ph.D. from Stanford University in 2011. Prior to joining
University of Michigan in 2014, he was a postdoctoral fellow at the University of California,
Berkeley. He is the recipient of a U. S. Department of Energy EERE Postdoctoral Research
Award (SunShot Fellowship), the AVS Student Award for Best Graduate Research in ALD, and
a Stanford Graduate Fellowship. His current research focuses on the application of ALD,
semiconductor nanowires, and quantum confinement structures for energy conversion and
storage devices.
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11:20
Recent advances in the quantum chemistry of semiconductor surface
chemistry: automated precursor screening and alternative surface reaction
pathways
Mathew D. Halls
Schrödinger Inc., Ste. 203, 5820 Oberlin Dr., San Diego, CA 92121
First-principles simulation has been shown to be an invaluable tool for gaining
insight into the atomistic details, energetics and mechanisms for the chemical reactions involved
in thin-film deposition. In the first part of this presentation, a new approach to precursor
discovery is introduced based on the automated simulation of reaction energetics for a library of
candidate precursor structures. This approach is the cornerstone of modern drug discovery, and
presents a powerful new tool to efficiently explore the chemical design space to establish
property limits and identify new reactive precursors for thin film deposition. In the second part of
the presentation, calculations analyzing alternative semiconductor surface reaction pathways are
summarized. Previously unconsidered reaction pathways involving multiple co-reactant species
can give significantly more favorable reaction energetics than single reactant processes. This is
illustrated by an in-depth look at surface reactions involving hydrogen transfer, where a
Grotthuss-type relay mechanism leads to lowered kinetic barriers. Relay reaction mechanisms
may be have general applicability, as illustrated by surface and co-reactant examples involving
heavy-atom transfer.
Mathew D. Halls is the Senior Director of Materials Science at Schrödinger Inc. He was
awarded a PhD in Quantum Chemistry from Wayne State University in 2001 under the direction
of Berny Schlegel. Prior to joining Schrödinger in 2012, his activities focused on advancing and
promoting the adoption of atomic-scale chemical simulation techniques in diverse industries
including aerospace, electronics and specialty chemicals. His research contributions have made
significant impact in areas such as computational spectroscopy, organic optoelectronic materials,
nanocarbon-polymer interfaces, thin-film precursors and deposition processes, and battery
electrolyte additives.
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1:30
Photoelectrochemical investigation of thin film metal oxide electrodes for
solar energy conversion
Thomas Hamann
Chemistry Department, Michigan State University
Hematite has long been considered a potential candidate for photocatalytic water splitting
because of its favourable valence band edge, reasonably low band gap, high stability and low
cost. Unfortunately, only very poor conversion efficiencies have been achieved, which is
generally attributed to a short minority carrier collection length. In principle, the short collection
length can be overcome through nanostructuring the electrode. Thin films represent ideal model
systems of nanostructured electrodes which allow for detailed mechanistic investigations. We
utilize atomic layer deposition (ALD) to make conformal thin film hematite electrodes with
controllable thickness for this purpose. Films less than 20 nm thick, however, are plagued by a
dead layer near the substrate contact. We found that the dead layer can be alleviated by the
incorporation of dopant atoms in the hematite film or by alteration of the contacting substrate. In
both cases significantly improved water oxidation efficiency was observed, however the cause of
the improvement was distinct. A series of photoelectrochemical and spectroscopic measurements
were employed to elucidate the cause of the improved photoactivity of these hematite thin films.
This performance enhancement was determined to be a combination of improved bulk properties
which improved charge separation and surface properties which improved the water oxidation
efficiency. The water oxidation reaction was further found to involve a surface state, which
limits the overall water splitting efficiency. Recent results of the effect of adding water oxidation
catalysts to the hematite surface, as well as alternative metal oxide films, will also be presented.
Thomas Hamann is the inaugural James Dye Professor of Materials Chemistry at Michigan
State University. After completing his graduate work with Nate Lewis at Caltech in 2006, Tom
joined Joseph Hupp’s group as a postdoc at Northwestern University. In 2008, Tom started his
independent academic career at Michigan State University. His research interests include the
synthesis of mesoscopic materials and investigation of interfacial electron-transfer and
photocatalytic reactions at semiconductor surfaces. He was the recipient of a DOE early career
research award, a NSF CAREER award, a Sloan Fellowship and the Camille Dreyfus Teacher-
Scholar Award.
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2:00
In situ, real time studies of organic semiconductor thin film growth
James R. Engstrom
School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, NY 14853 USA
In this presentation we shall review our recent work concerning the examination of
the growth of crystalline small molecule organic thin films, where we make use of both
supersonic molecular beam techniques, and in situ and real time X-ray synchrotron radiation. In
selected cases we also employ ex situ atomic force microscopy, which shall afford a contrast and
comparison between in situ and ex situ techniques. Here we will focus on two sets of studies.
First we have examined the thin film growth of pentacene on three different polymeric
dielectrics, which spanned the range from a low surface energy hydrophobic surface
(polystyrene, PS), to a high surface energy hydrophilic surface [poly(ethylene imine), PEI]. On
all surfaces, pentacene forms a polycrystalline thin film, whose structure is that of the previously
identified “thin film” phase. From in situ real-time x-ray scattering, we find that pentacene
exhibits layer-by-layer (LbL) growth on all surfaces investigated, but the extent of LbL growth
is a strong function of the underlying substrate. In particular, LbL growth is significantly more
prolonged on PEI, and least extended on PS. The roughness and the in-plane feature sizes of
thick, ~ 10 monolayer, pentacene thin films also vary with the surface energy of the substrate—
growth on the high surface energy polymer thin film, PEI, is the smoothest, and is characterized
by the largest features. It appears that interlayer transport is influenced by the underlying
substrate, even for layers that are not in direct contact with the polymer dielectric. In the second
set of work we have examined the nucleation and growth of a series of acceptor-type organic
semiconductors: PTCDI-Cn, where the length of the alkyl tail (Cn) attached to the perylene core
of these molecules has been varied from n = 5, 8 and 13. In addition to examinations of the
growth of these molecules themselves, we have also examined the growth of these molecules on
ultrathin films of the donor-type semiconductor pentacene, and vice-versa, the growth of
pentacene on layers of PTCDI-Cn. Concerning the growth of PTCDI-Cn on 1 monolayer (ML)
of pre-deposited pentacene we find substantial differences between the C5 and C13 variants of
this molecule: X-ray intensity oscillations at the anti-Bragg scattering condition, signifying
layer-by-layer (LbL) growth, are much more extended for the C5 variant. More dramatic
differences emerge as we examine the sequence of deposition. While each perylene variant
grows approximately layer-by-layer on 1 ML of pentacene for several layers of PTCDI-Cn,
when this order is reversed, and pentacene is grown on 1 ML of PTCDI-Cn dramatic changes
occur: growth is immediately 3D, and a very rough morphology is formed. Examination of
multilayer structures, e.g., A/B/A/B… where A is PTCDI-Cn and B is pentacene, shows that the
growth of roughness tends to reflect this asymmetry, where the pentacene cycle tends to roughen
the vacuum|film interface, while the PTCDI-Cn cycle tends to smoothen the interface.
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James R. Engstrom is currently the BP Amoco/H. Laurance Fuller Professor in the School of
Chemical and Biomolecular Engineering at Cornell University. He earned a B.S. degree in
chemical engineering from the University of Minnesota in 1981and a Ph.D. degree in chemical
engineering from the California Institute of Technology in 1987. From 1987-89 he was a
postdoctoral research associate in the Department of Chemistry at the University of Washington.
He joined the faculty at Cornell in 1990 as an Assistant Professor, was appointed to the rank of
Associate Professor in 1996, and to his present position in 2005. Since 2002 he has also been a
member of the Graduate Field of Chemistry and Chemical Biology. Prof. Engstrom is the
recipient of numerous awards, including, in 1991, a NSF Presidential Young Investigator Award.
In 2005 he was made a Fellow of the American Vacuum Society. In 2014 he was appointed
Associate Editor of the Journal of Vacuum Science and Technology A. From 1998 to 2001, he
worked for Symyx Technologies, where he was Vice President of high-throughput screening and
electronic materials. Prof. Engstrom has been conducting research in the area of surface science
and thin film deposition for over 25 years. This work, documented in over 85 publications, 115
contributed and 90 invited presentations, and 11 US patents, includes work in a variety of
technologies ranging from heterogeneous catalysis, to semiconductor device manufacture, to thin
film photovoltaic devices. Much of his work has involved fundamental studies of gas-surface
reactions employing supersonic molecular beams, photoelectron spectroscopy, and X-ray
synchrotron radiation. Presently, Professor Engstrom's research is focusing in three areas:
controlling thin film nucleation in nanoscale electronics using techniques such as atomic layer
deposition; organic thin film electronics, using in situ real time X-ray synchrotron radiation; and
modification and processing of inorganic nanocrystalline materials.
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2:30
Plasma for controlling the synthesis of semiconductor nanocrystals
Rebecca Anthony
Mechanical Engineering Department, Michigan State University
Semiconductor nanocrystals show promise for improving the cost and efficiency of
solid-state lighting technologies, such as light-emitting devices (LEDs). One particularly elegant
tool for nanocrystal synthesis is the nonthermal plasma reactor, which allows rapid growth of
high-quality nanocrystals with tunable structure and surface. Here I present a gas-phase-only
synthesis, processing, and deposition scheme for laying down films of functional nanocrystals
for light-emission applications. The specific example of silicon nanocrystals is discussed, and
some of the possibilities for utilizing this technology in the future are laid out.
Dr. Anthony grew up in Maryland and attended Carleton College where she majored in physics.
She received her Ph.D. in Mechanical Engineering from the University of Minnesota in 2011,
where she studied plasmas for synthesis of light-emitting silicon nanocrystals. Upon finishing,
she stayed at UMN to teach and to do postdoctoral research on diagnostics of dusty plasmas.
Rebecca’s research at MSU is a continuation of plasma synthesis and processing of
semiconductor nanocrystals with an emphasis on gas-phase techniques. Her goals are to develop
new ways to streamline nanomaterial synthesis and surface treatment, followed by direct layer
formation onto substrates – all in avoidance of solution-phase steps.
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3:00
CdTe thin film PV devices: unlocking high performance potential to reality
Zhibo Zhao
Advanced Research, First Solar Inc.
After a long period of stagnancy for record cell efficiency and several years of
significant growth of the industry, CdTe solar-cell efficiency has been increased rapidly in recent
years. Since 2011, Our Advanced Research team at First Solar (FLSR) has been able to steadily
drive up the world record CdTe cell efficiencies (all measured/certified at independent labs) from
17.3% in 2011 to 18.7% in 2012, 20.4% in 2013 and 21.0% in 2014, respectively. While most of
these high performance solar devices were related to increases in short-circuit current (Jsc) and
fill-factor (FF), we have also shown that the open-circuit voltage (Voc) of poly-crystalline thin
film CdTe devices is not fundamentally limited to ~850 mV. Devices with Voc greater than 900
mV (also measured/certified at independent labs) have been demonstrated with great
repeatability. This marks the first substantial increase in Voc of thin film CdTe solar cells in over
a decade of international R&D. In this presentation, I will review these recent advancements,
present device analysis on key third level metrics, and provide a road map on near-term
achievable efficiency target for CdTe based thin film solar devices.
Dr. Zhao joined First Solar in 2008 as a Senior Research Engineer. He was promoted to
Integration Manager on Device and Process in 2011 and to Director of Technology in Advanced
Research recently. His earlier work focused on development of transparent conductive oxides
(TCO) and front contacts for CdTe devices. In last several years Dr. Zhao has been leading First
Solar's Efficiency Team to develop high performance CdTe based devices and to demonstrate its
technology potentials. The team has successfully achieved a number of record-setting CdTe
devices, which were the subject matters of numerous corporate technology news releases in
recent years.
Prior to First Solar, Dr. Zhao worked as a Senior Thin Film Scientist at General Electric in 2006-
2008, where his research focused on advanced optical coatings for light technologies. From
1999 to 2006, Dr. Zhao was a Research Scientist at Delphi Research Labs, where his research
interest was primarily on coating materials and processes for automotive applications. Near the
end of his tenure at Delphi Research, Dr. Zhao also served as the Chief Scientist to Delphi-
Thermal, where he was responsible for development and maintenance of the Research Labs’
technology portfolios for Delphi’s Thermal Systems Division.
Dr. Zhao had BS in Materials Physics from University of Science and Technology Beijing, MS
in Materials Science from Michigan State University, and Ph.D. in Materials Science from
University of Michigan.
15
Equipment Exhibit
Erie Tech Group
16
STUDENT POSTER PRESENTATIONS
#1*
Transparent Luminescent Solar Concentrators Employing UV and NIR
Selective Absorbers
Yimu Zhao
Michigan State University
Luminescent solar concentrators are regaining attention as low-cost solar harvesting systems
around the building envelope. However, the visible absorption and emission of previously
demonstrated chromophores result in highly colored systems that hamper their widespread
adoptability in many applications including solar windows. Here, we demonstrate transparent
luminescent solar concentrators (TLSC) that employ ultraviolet (UV) or near-infrared (NIR)
absorbing luminophores for selective light harvesting that creates an entirely new paradigm for
power-producing transparent surfaces. In the first configuration, we have designed systems
composed of metal halide phosphorescent luminophore blends; these nanoclusters enable
selective harvesting of UV photons with absorption cutoff positioned at the edge of visible
spectrum (430nm) and massive-downconverted emission in the near-infrared (800nm) with
quantum yields for luminescence of 75%. Through experiment and modeling, we show that this
architecture can be scaled up to areas > 1 m2 with a power conversion efficiency of 1-2% due to
the massive luminescent downconversion. We have also developed transparent luminescent solar
concentrators employing fluorescent organic salts with both efficient NIR absorption and
emission that allow for efficiencies > 4-5%. The moderately low Stokes shift of these systems is
overcome by embedding spatially segmented solar cell arrays throughout the waveguide, leading
to minimal reabsorption losses. We will discuss the photophysical properties of both classes of
luminophores, the impact of ligand-host control, and optimization of the TLSC architectures.
*numbered according to submission time
17
#2
Computational Studies of Strain Engineered Lanthanum Strontium Ferrite
Thin Film Oxygen Surface Exchange Coefficients
Tridip Das
Michigan State University
The objective of this research was to understand the role of stress and crystal structure on the
oxygen surface exchange coefficient of SOFC cathode material, Lanthanum Strontium Ferrite
(LSF). The experimental study was performed using MOSS (Multibeam Optical Stress Sensor)
instrument to measure the real-time curvature response induced by the mechano-chemical
coupling on the thin film cathode. The LSF oxygen surface exchange coefficients were extracted
by fitting the curvature relaxation data with a solution to Fick’s Second Law, Stoney’s equation
was used to convert the curvature data into film stress. Different crystal structures of LSF
compositions were studied computationally using VASP. The GGA+U method along with PBE
functional and PAW potentials was utilized for the calculations. After bulk calculations,
structures were converted to a slab for surface calculations. Oxygen vacancy formation energy at
the surface was obtained from DFT calculation was at 0K. Hence, thermodynamic calculations
were then performed to determine the vacancy formation energies at fuel cell operating
temperature and pressure. The details of computational results and the effect of vacancy on
lattice structure, along with effect of lattice strain on the vacancy will be presented in the poster.
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#3
Influence of tetrahedral amorphous carbon thin films on Li intake capacity
for reduced graphene oxide anodes in Li-ion battery
Chananate Uthaisar
Fraunhofer USA
Tetrahedral amorphous carbon (ta-C) thin films were coated on reduced graphene oxides (RGOs)
using Laser-Arc deposition technology, and were used as an anode for Li-ion batteries. RGO
materials were made from expanded graphite, and were synthesized by oxidation followed by
thermal reduction. Our studies show the first reversible capacity of RGOs at low temperature
(250oC) is over 1000 mAh/g with a current density of 500 mA/g (0.33C). In this work, we
studied the electrochemical performance of RGO anodes with/without ta-C coatings. Preliminary
results of ta-C and N-doped ta-C (ta-C:N) coated on RGO anodes show improved cyclability for
over 100 cycles compared to RGOs without a coating. Based on electrochemical impedance
spectroscopy, the charge transfer resistance of RGO coated with ta-C is constant, whereas
uncoated RGOs develop increased resistance. This work indicates that ta-C coatings may be used
to improve the capacity fade and the lifetime of Li-ion batteries.
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#4
Atomic Layer Deposition for Controlled Seeding of Hydrothermally Grown
Zinc Oxide Nanowires
Ashley Bielinski
University of Michigan
Semiconductor nanowires have many beneficial properties for renewable energy technologies.
Solar applications may be improved by their efficient absorption of light, high surface areas, and
short minority carrier transport distances. This enables the use of various earth abundant
materials as light absorbers and current collectors, such as metal oxides and sulfides. Low
temperature hydrothermal methods of growing ZnO nanowires have been consistently reported
in literature. ZnO nanowires can be grown directly on crystalline sapphire wafers due to the
small lattice mismatch, but the more versatile method is to coat alternate substrates with a ZnO
seed layer, which is commonly performed by drop casting However, this process leads to
inhomogeneities and is difficult to reproduce, so large scale manufacturing would be challenging.
Here, we investigate atomic layer deposition (ALD) for the creation of controlled and uniform
ZnO seed layers. We investigated substrate material, seed layer thickness, and ALD process
parameters for their effects on the size, density, and alignment of hydrothermally grown ZnO
nanowires. The nanowires were analyzed using SEM and XRD. ALD coats surfaces conformally,
allowing for the formation of hierarchical 3-D nanostructures. This versatile seeding method can
be performed on various surfaces for the production of heterogeneous material systems.
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#5
Disruption of tethered lipid bilayers by silica-core nanoparticles: effect of
surface functional group
Ying Liu
Michigan State University
Disruption of tethered lipid bilayers by silica-core nanoparticles: effect of surface functional
group Ying Liu, Quanxuan Zhang, Gregory L. Baker, Zhen Zhang, and R. Mark Worden In this
paper, we use present a method that uses a tethered bilayer lipid membrane (tBLM) to study the
interaction of engineered nanomaterials (ENM) with biomembranes. Highly insulating tBLM
were formed on gold electrodes using 1, 2-dipalmitoyl-sn-glycero-phosphothioethanol (DPPTE)
to form the lower leaflet and 1, 2-dioleoyl-sn-glycero-phosphocholine (DOPC) to form the upper
leaflet. The tBLM were then exposed to silica nanoparticles having different surface properties
(unmodified, amine terminated, and carboxylic-acid terminated). Electrochemical impedance
spectroscopy was used to measure time-dependent changes in the tBLM’s impedance following
ENM exposure. The data were fit to an exponential model and then analyzed using a hierarchical
clustering algorithm. The resulting dendrograms confirmed that ENM having different surface
functional groups induced statistically different changes in tBLM impedance. The amine
terminated ENM reduced tBLM impedance considerably faster than did the carboxylic-acid
terminated and unmodified ENM. Based on dynamic light scattering data, exposure to the tBLM
triggered an increase in average particle size for the unmodified ENM but not the amine-
terminated and unmodified ENM. Results of this study could provide insight into fundamental
mechanisms by which ENM interact with biomembranes and may lead to high-throughput
methods to assess the health risk of ENM based on their interactions with biomembranes.
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#6
Colorful, see-through ultra-thin hybrid photovoltaics with high quantum
efficiency
Kyu-Tae Lee
University of Michigan
We demonstrate dual-function photovoltaic (PV) based on ultra-thin dopant-free amorphous
silicon (a-Si) embedded in an optical cavity that not only efficiently extract the photogenerated
electric charges but exhibit distinctive color patterns with the desired angle insensitive
appearances. To create the desired optical effect, the semiconductor layer should be ultra-thin
and the traditional doped regions need to be eliminated. We utilize the charge transport/blocking
layers to meet this demand. A trivial propagation phase shift accumulated in a passage through
the ultra-thin a-Si photoactive layer and an interesting cancellation effect with respect to the
phase of light reflecting from the interface leads to angle-independent color behaviors for an
incidence angle up to ±70° for both s- and p-polarizations. We show that the ultra-thin undoped
a-Si/organic hybrid PV cells can transmit/reflect desired wavelength of light and with high
quantum efficiency benefited by the suppressed electron-hole recombination in the ultra-thin a-Si
layer. A cascaded platform exploiting a tunable spectrum splitting is demonstrated, which
enhances the overall efficiency by absorbing a wide range of spectrum. The scheme could be
applicable to other material systems and open the door to decorative thin-film PV and energy
efficient color display technologies.
22
#7
Angle-Dependent Performance in Thin-Film and Transparent Photovoltaics
Margaret Young
Michigan State University
Understanding the angle dependent performance is an important consideration for building
integrated photovoltaics (PVs), such as transparent PV windows, where illumination angles are
rarely at normal incidence. While the transfer matrix model (TMM) has been widely utilized to
model optical interference and quantum efficiency in thin-film PVs at normal incidence, self-
consistent simulations for PVs under oblique illumination have not yet been demonstrated. We
derive an updated model that is self-consistent for all angles, light polarizations, and electrical /
optical configurations, and experimentally verify the predicted angular quantum efficiency
response of planar heterojunction (PHJ) transparent PVs. We subsequently use this model to
optimize PHJ transparent PVs for maximum short circuit photocurrent density (Jsc) and
transparency as a function of the multivariable landscape under a variety of optical and electrical
configurations, showing that it is possible to greatly reduce the angle-dependent roll-off in
efficiency by moving in this multi-parameter space. We will provide insights into the lesson
learned for designing devices that can reduce this roll-off and increase overall yearly power
output.
23
#8
Efficient Metal Sulfide Buffer Layers for Organic Photovoltaics
Christopher Traverse
Michigan State University
The n-type window layer is a critical component of thin-film and organic photovoltaics (OPVs)
that serves to 1) eliminate Schottky barriers that impede efficient charge collection, 2) block
excitons from becoming quenched at the cathode, and 3) prolong the lifetime by protecting the
active layers of the device during cathode deposition and environmental exposure. While
bathocuproine (BCP) has been widely utilized, it suffers from low conductivity that limits the
optimal thickness and a low glass transition temperature which can result in poor stability. In this
work we demonstrate the structural and electronic control of thermally evaporated zinc sulfide
(ZnS) window layers n-type doped with aluminum sulfide (Al2S3) in OPV devices. We show
through x-ray diffraction, electron spectroscopy, and device characterization that ZnS:Al2S3
window layers offer identical power conversion efficiency and yields to equivalent OPVs with
standard BCP layers. This demonstration adds to the short catalog of high performance
cadmium-free options for n-type window layers that could also prove useful in a range of other
thin film photovoltaics.
24
#9
Investigation of Charge-Storage Mechanisms of Nanostructured Carbides and
Nitrides as Materials for Energy Storage
Abdoulaye Djire
University of Michigan
The need for sustainable high-power and high-energy-density storage devices is of significant
interest in applications such as electronic devices and electric vehicles. In an effort to meet this
need, supercapacitors are being developed. Currently available supercapacitors lack sufficient
energy densities for a number of applications including use in electric vehicles and other load-
leveling applications. The energy stored in supercapacitors depends on the material. The material
currently used in commercial supercapacitors is activated carbon, which is relatively expensive
and has limited capacitance. In this work, we proposed the use of environmental friendly high-
surface-area transition-metal carbides and nitrides as electroactive materials for supercapacitor
applications due to their low cost, high electronic conductivities, high surface areas (can exceed
200 m2/g), good electrochemical stabilities and high capacitances (up to 1340 F/g). Despite
efforts to date, the charge-storage mechanism of early transition-metal carbides and nitrides
remains ill-defined. This presents a challenge to the full exploitation of these materials. Here we
report a detailed investigation of the charge-storage mechanisms in early transition-metal
carbides and nitrides in aqueous media, using a combination of electrochemical techniques
including cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and
electrochemical quartz crystal microbalance (EQCM), x-ray absorption spectroscopy and small
angle neutron scattering.
25
#10
Boron Doped Single Crystal Diamond for High Power Conversion
Applications
Shannon Demlow
Michigan State University
As an electronic material, diamond would be particularly well suited to high-temperature and
high-power conversion devices, such as vertical Schottky Barrier diodes, due to its high
breakdown voltage and carrier mobilities and exceptional thermal conductivity. Fabrication of
high quality vertical diode structures necessitates freestanding, single crystal p-type diamond
substrates, with low resistivity obtained through heavy doping (> 10^20 cm^-3). To achieve
freestanding substrates, the diamond must be mechanically handleable after laser cutting from
the growth substrate, and therefore thick ( > 300 μm). We report on our investigations on the
growth of heavily boron doped SCD. Homoepitaxial diamond is grown in a microwave plasma-
assisted chemical vapor deposition (MPACVD) bell-jar reactor with feedgas mixtures including
hydrogen, methane, and diborane. We summarize strategies for increasing the boron doping
efficiency of SCD while decreasing defects that form during growth, including the effects of
deposition temperature, growth rate and total flow rate of the plasma feedgas.
26
#11
Amphoteric Doping of GaAsBi Alloys with Silicon
Jordan Occena
University of Michigan
Alloys of dilute nitride and dilute bismide semiconductors are of significant interest due to the
fact that their energy bandgaps can be tuned dramatically with minimal change in lattice
parameter. For GaAsN, N-related states are reported to be resonant with the conduction band,
often leading to substantial degradation of electron mobility with increasing N composition. On
the other hand, Bi states are apparently resonant with the valence band, and the electron mobility
of GaAsBi is therefore expected to be only weakly dependent on Bi composition, x. To date, n-
type GaAsBi films have been achieved using Si doping, while p-type films have been achieved
using Be or C. However, for both Be- and C-doped GaAsBi, a decrease in hole mobility with
increasing Bi composition has been reported. Here, we obtain p-type doping of GaAsBi with Si
by varying the growth rate and group V/III beam equivalent pressure (BEP) ratio. For low (high)
group V/III BEP ratios and/or high (low) growth rates, Si doping leads to p-type (n-type)
GaAsBi. In n-type films, we observe electron mobilities as high as 2500 cm^2/V-s, with weak
dependence on x. Interestingly, the hole mobility is essentially independent of Bi composition up
to x = 0.05, suggesting that Si is a promising alternative to Be or C for p-type doping of GaAsBi.
27
#12
Computationally Understanding the Impact of Oxygen Vacancies on Lithium
Removal from Li2MnO3-δ for Lithium-Ion Battery Cathodes
Christine James
Michigan State University
Recent experimental work on xLi2MnO3∙(1-x)LiMO2, where M is a transition metal or
combination of transition metals, has shown that it is a promising high capacity new cathode
material for lithium-ion batteries. The reversible capacity of xLi2MnO3∙(1-x)LiMO2 has been
shown to be above 250 mAh/g reversibly which is high when compared to one of the most
common cathodes LiCoO2 which has a reversible capacity around 160 mAh/g. This capacity is
thought to come from the activation of the Li2MnO3 component which occurs with the loss of
oxygen atoms from the component. The goal of this work is to understand where the oxygen
vacancies are occurring and the effect of these vacancies on the lithium diffusion and removal.
Density functional theory (DFT) and molecular dynamics (MD) are used to study where
vacancies form and how the lithium atoms diffuse, respectively. This work suggests that near
oxygen vacancies the energy for lithium atoms is higher and thus lithium vacancies tend to form
near oxygen vacancies. Thus, the generation of oxygen vacancies also appears to significantly
impact the lithiation and delithiation processes.
28
#13
Solar Water Splitting with Ultrathin Films of Hematite
Omid Zandi
Michigan State University
Hematite (α-Fe2O3) is among the most promising photoanode materials to carry the water oxidation half
of the overall solar water splitting in the photoelectrochemical cells. Atomic layer deposition (ALD) was
utilized to fabricate uniform thin films of hematite on transparent conductive substrates, as model
electrodes to investigate the performance limiting factors. In general, three effective strategies were
utilized to improve the water splitting performance of hematite electrodes, using ALD advantages as the
fabrication tool: Doping (bulk modification), substrate modification, and surface modification. It was
shown that bulk doping with Ti significantly improves the photoelectrochemical performance of the thin
films. Substrate modification with different metal oxide underlayers was also shown to be an effective
alternative performance improvement strategy. The role of bulk doping and substrate modification was
studied in details using a combination of photoelectrochemical, microscopic and spectroscopic techniques.
Lessons learned form these findings, helped us to better understand factors limiting the water splitting
efficiency on the hematite electrodes and develop strategies at mitigating them.
29
#14
Photoelectrochemical Investigation of Solar Water Oxidation on Conditioned
Ni(OH)2-coated α-Fe2O3
Kelley Young
Michigan State University Department of Chemistry
Hematite (α-Fe2O3) is a promising photoanode material for solar water oxidation owing to its
abundance, stability, substantial visible light absorption, and suitable energetics for H2O
oxidation. Efficient water oxidation with hematite, however, has been limited mainly due to a
low minority carrier mobility, which results in the recombination of the photogenerated charge
carries in the bulk and surface recombination of photogenerated holes with the conduction band
electrons. One strategy to mitigate the surface recombination is the addition of a surface coating
such as a water oxidation catalyst in order to reduce recombination of photogenerated holes and
improve water oxidation kinetics. Herein atomic layer deposition (ALD) was employed to
deposit Ni(OH)2 onto thin-film α-Fe2O3, also prepared by ALD. The use of ALD allowed us to
reducibly deposit conformal and uniform coatings of Ni(OH)2 on hematite photoanodes with
tunable thickness. It was found that 10nm of as-deposited Ni(OH)2 is not a remarkable catalyst
as compared to bare-Fe2O3. However, after photoelectrochemical conditioning, an approximate
300 mV cathodic shift was observed in the onset of water oxidation photocurrent compared to
bare α-Fe2O3. The effect of Ni(OH)2 was investigated through photoelectrochemical
measurements.
30
#15
The Function of Lithium Fluoride in Solid Electrolyte Interface for Lithium-
ion Batteries
Jie Pan
University of Kentucky
Engineering a stable solid electrolyte interphase (SEI) is important to improve the performance
and durability of electrodes, such as silicon (Si) which is one of the most promising negative
electrode materials for lithium ion batteries. An ideal stable SEI is expected to be ionicaly
conducting and electronically insulating. Recently, a method to modify the components in SEI
was developed by adding electrolyte additives (e.g., fluoroethylene carbonate for Si electrode). It
has been reported that the fluoroethylene carbonate (FEC) improved the performance of Si
electrodes and increased the presence of lithium fluoride (LiF) in the SEI. To understand this
phenomenon, it is essential to study the properties of LiF as a SEI component. Several defect
formation reactions are examined as a function of μLi of the reservoir in three regions: 1)
intrinsic, 2) transitional , and 3) p-type region. In the intrinsic region (high μLi, typically for the
negative electrode), the main defects are Schottky pairs and in the p-type region (low μLi,
typically for the positive electrode) are Li ion vacancies. The ionic conductivity is calculated to
be approximately 10-31 S/cm when LiF is contacting with a negative electrode but it can
increase to 10-12 S/cm on a positive electrode. Comparing with other SEI components (e.g.,
Li2CO3) on the Si electrode, the ionic conductivity in LiF is about 18 orders magnitude lower
than that in Li2CO3. However, due to the contribution of ionic transport to electronic conduction
in LiF, this low ionic conductivity may help block electron leakage from the electrode and
prevent further electrolyte molecule decomposition. As a result, LiF can be a good component in
the SEI layer because it is a good electronic insulator. In addition, moderate divalent doping of
LiF is suggested to increase the ionic conductivity for improving the beneficial effects of
artificial SEIs.
31
#16
Novel Techniques to Determine Mechanical Properties of Thin Films for
Lithium Ion Batteries
Qinglin Zhang
University of Kentucky
In addition to electrical and ionic conductivities, the mechanical properties of the thin films are
believed important for LIB applications. However, the mechanical properties of thin films may
be different from their bulk counterparts because the differences in synthesis methods, material
structures and the surface area to volume ratio. Understanding the elastic properties of thin films
is, therefore, indispensable for designing the electrode coatings for high energy electrode
materials with large volume change (such as Si, over 300 %) and internal stress during lithiation
and delithiation.
In this work, elastic properties of ALD alumina thin coatings and SEI formed under different
voltages were characterized by laser acoustic wave (LAW) method. LAW is a non-destructive
sonic technique to obtain the mechanical properties of thin films. Surface acoustic waves
(SAWs) propagate parallel to the surface measured with penetration depths as thin as 1/100 of
the wavelength. Hence, SAWs are suitable for determining the elastic properties of very thin
films. We show that the LAW technique, along with other characterization methods, is capable
of measuring the elastic properties of thin ALD films and SEI layers as thin as a few nanometers
in a straightforward manner.
32
#17
Formation of Highly Ordered Organic Molecular Thin Films on Deactivated
Si Surfaces
Sean Wagner
Michigan State University
Control of highly ordered organic molecular thin films with extended π systems is currently of
intense interest for integration into modern electronics due to the tunable nature of organic
molecules. Selection of molecules and substrate can lead to desired transport properties such as
charge transfer, charge injection, exciton diffusion, etc., at the heterointerface, which is crucial to
the development of organic and molecular electronics. However, achieving large-scale molecular
ordering remains a significant challenge. Here, we report our recent discovery of the anisotropic
crystalline step-flow growth of the prototypical metal phthalocyanine molecules on the
deactivated Si(111)-B surface. We also demonstrate that the molecular ordering and molecular
orientation can be effectively modified through selective orbital hybridization between the
molecule and substrate. This growth mode is likely to be generalized for a range of organic
molecules and access to it offers the potential for improved performance in organic field effect
transistors, photovoltaics and nanowire/nanoribbon devices.
33
#18
Nano-fibrillated Cellulose Templated Nano-porous Titania for Photoanodes of
Dye-sensitized Solar Cells
Yan Li
Composite Materials and Structures Center, Michigan State University
Porous metal oxide materials, particularly titanium dioxide, find use in many applications such
as photocatalysts, sensors, paints and photovoltaics. As an attractive way to synthesize varies
metal oxide materials, the sol-gel method is a simple preparation approach utilizing a
precursor/solvent system, resulting in an easy method for coating of large surfaces with variable
thickness and high optical/electrical qualities. Additionally, combining natural templates such as
cellulose nano-fibers offers an approach to build specific 2D or 3D structures and morphology in
a “bottom-up” path based on the fiber properties. To generate porous TiO2 materials, modified
sol-gel routes were studied in this research. We have developed a facile low-temperature sol-gel
method with micro-fibrillated cellulose as templates to synthesize anatase meso/nano porous
TiO2 having a nano-channel structure. Non-hydrolytic and hydrolytic homogeneous cellulose
suspensions were chosen to be the templating systems. Additionally, corresponding coating
techniques such as spin coating, drop casting, or doctor blade and binder assistance were
investigated as alternative processes. Templated TiO2 nanomaterials were synthesized as
photoanodes in dye-sensitized solar cells, and a TTIP-cellulose precursor system showed a ~40%
increase in solar-to-electricity efficiency (1.75%) compared to a commercial paste.
34
#19
Amphoteric Doping of GaAsBi Alloys with Silicon
Richard Field III
University of Michigan
Alloys of dilute nitride and dilute bismide semiconductors are of significant interest due to the
fact that their energy bandgaps can be tuned dramatically with minimal change in lattice
parameter. For GaAsN, N-related states are reported to be resonant with the conduction band,
often leading to substantial degradation of electron mobility with increasing N composition. On
the other hand, Bi states are apparently resonant with the valence band, and the electron mobility
of GaAsBi is therefore expected to be only weakly dependent on Bi composition, x. To date, n-
type GaAsBi films have been achieved using Si doping, while p-type films have been achieved
using Be or C. However, for both Be- and C-doped GaAsBi, a decrease in hole mobility with
increasing Bi composition has been reported. Here, we obtain p-type doping of GaAsBi with Si
by varying the growth rate and group V/III beam equivalent pressure (BEP) ratio. For low (high)
group V/III BEP ratios and/or high (low) growth rates, Si doping leads to p-type (n-type)
GaAsBi. In n-type films, we observe electron mobilities as high as 2500 cm^2/V-s, with weak
dependence on x. Interestingly, the hole mobility is essentially independent of Bi composition up
to x = 0.05, suggesting that Si is a promising alternative to Be or C for p-type doping of GaAsBi.
35
#20
Fabrication of High Surface Area Electrodes for Blood Analysis
James Stambaugh
LNF-Umich/Henry Ford College
Oxidation-reduction (redox) reactions lie at the heart of nearly all human physiologic responses
that occur in times of significant illness or injury. In fact, when the body experiences physiologic
stress (oxidative and metabolic stress), the redox potential can be altered and change over the
course of illness, treatment, and subsequent recovery. Therefore, measuring the redox potential
of whole blood in these patients is a useful tool for analyzing the severity of illness in a patient’s
condition and the effect of therapeutic interventions. Optimally, these redox measurements
should be made in real-time at, or near the patient’s bedside in order to allow for immediate data
reporting of the patient’s condition and subsequent therapeutic intervention as needed. Research
in microfluidic devices has surged in recent years in an effort to create low-cost and efficient
“lab-on-a-chip” devices to offer medical professionals the ability to receive immediate data on a
patient’s health. These devices must be affordable enough to be used on a regular basis and they
must require small sample sizes for measurement, as is the case with redox measurements. Such
a device for redox measurement would also need to be equipped with electrodes that are not only
capable of analyzing redox in whole blood, but also allow for minute sample collection in a
micro-scale device. This work describes methods for the fabrication of suitable microelectrodes
for the above application, as well as testing and characterization of the device using standard
electrochemical methods such as Cyclic Voltammetry and Open Circuit Potential.
36
Organizing Committee
Yue Qi, Symposium Chair
Richard Lunt, Program
Pilar Herrera-Fierro, Treasure & Exhibition
Stephen Gaarenstroom, Registration
Mark Chang and Hiroko Ohtani, Poster Competition
Acknowledgement: The organize committee would like to thank to MSU CHEMS
staff, Ms. Jennifer Keddle, for her hard work and dedication to keep things
organized for this symposium.
We thank the generous support from
We hope you enjoyed the conference!
See you next year!
