- Electronic and
Ionic Conductivity in Oxides with the K2NiF4 Structure
(Prof. A. Jacobson)
Oxides with the perovskite related K2NiF4 structure can be used in applications
that require mixed electron-ion conductivity such as electrodes in solid
oxide fuel cells. The structure of La2NiO4 contains layers of corner-shared
octahedra separated by lanthanum cations that are nine coordinated by oxygen
atoms. An important feature of this structure is that it can accommodate
both oxygen vacancies and excess oxygen atoms in interstitial positions
between the layers, tetrahedrally coordinated by La3+ cations. In La2NiO4+x at ambient temperature, x can be as high as 0.18 and in Pr2NiO4+x, the
maximum value of x is 0.22. Even at ambient temperature, the oxygen interstitials
are mobile enough to permit determination of the oxygen excess phase behavior
by electrochemical oxidation in an aqueous KOH electrolyte. At higher temperature,
the diffusivity increases though this is offset by the decrease in the
concentration of oxygen interstitials.
The objectives of the project are to synthesize examples of this oxide
family and then to characterize the electrical transport behavior at high
temperatures. Compositions such as La2Ni1-xCoxO4+y will be prepared by
solution routes followed by high temperature sintering. Phase purity will
be determined by powder X-ray diffraction and the oxygen content by thermogravimetric
analysis. The total conductivity will be measured as a function of temperature
(25–1000 ºC) by the four-probe dc technique and the ionic conductivity
will be estimated from measurements of electrical conductivity relaxation
behavior. The results will be used to determine the optimum composition
for electrode applications in solid oxide fuel cells.
The student will learn solid state synthesis, diffraction methods for determination
of phase purity and techniques for the measurement of electrical conductivity
at high temperatures. The student will also learn generally about electrochemical
devices and their applications.
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- Synthesis
of Samarium and Gadolinium Alkoxide Complexes and the
Chemical Vapor Deposition of Oxide Films
(Prof. D. Hoffman)
Solid oxide fuel cells are a clean and efficient device for generating
electrical power from natural gas and other fuels. The goal of this project
is to develop a new method to deposit doped cerium oxide for use as an
electrolyte in low temperature solid oxide fuel cells. The student will
synthesize new samarium and gadolinium alkoxide complexes and use them
as dopant precursors in chemical vapor deposition studies to form Sm and
Gd doped cerium oxide films. In the synthetic studies the student will
learn how to handle air sensitive compounds by using classic Schlenk and
glove box techniques. He or she will also learn how to use the departmental
NMR instruments and interpret spectra to characterize the alcohols used
in the syntheses. The student will characterize the paramagnetic alkoxide
complexes by using IR spectroscopy, molecular weight studies, and, where
possible, X-ray crystallography. The film deposition work will provide
experience in using a typical research-scale chemical vapor deposition
apparatus. In these studies, the student will learn how to clean and load
substrates, manipulate gas flow rates using mass flow controllers, load
air sensitive precursors, and characterize the thin films. The hands-on
characterization techniques will include thin film X-ray diffraction, X-ray
photoelectron spectroscopy, and scanning electron microscopy.
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- Synthesis
and Characterization of New Second-Harmonic Generating
Materials
(Prof. S. Halasyamani)
The objective of this research is the synthesis, characterization, and
structure-property measurements of second-harmonic generating (SHG) materials.
One challenge currently faced by the materials community is the synthesis
of compounds with efficient second-order nonlinear optical (NLO) behavior,
i.e. frequency doubling or SHG. Enhancing the SHG capability of materials
relies on understanding the structure-property relationships associated
with the phenomenon. We propose to synthesize new SHG materials by combining
d0 transition metal oxides, e.g., Nb2O5, with oxides containing cations
with stereo-active lone-pairs, e.g., TeO2. The REU researcher will synthesize
the new materials, as powders as well as single crystals, through a variety
of techniques including standard solid-state, supercritical hydrothermal,
and transport reactions. We have all the necessary equipment in our laboratory
for carrying out the syntheses. Once a polycrystalline powder or crystal
is produced diffraction experiments will be undertaken. The student will
be trained on our powder diffractometers and learn to index as well as
refine powder diffraction data. In addition, if a single crystal is grown,
data will be collected on our SMART-CCD system. We have also built in our
laboratory a Kurtz SHG system that permits us to semi-quantitatively determine
the SHG efficiency of polycrystalline materials. Through these measurements
the student will be able to determine the magnitude of the SHG response
and compare the response to known materials. This research is ideally suited
to undergraduate students as it combines synthesis with X-ray diffraction
and detailed physical property measurements.
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- Sputter
Deposition and X-ray Characterization of Thin Metallic
Films
(Prof. W. Donner)
In this project the student will learn basic skills in sputter deposition,
the most relevant industrial method of thin film preparation. Skills in
vacuum and thin film technology as well as X-ray diffraction will be developed.
The results from the student’s work will used to calibrate deposition
rates and to find optimal deposition parameters. The student will clean
the film substrate using established protocols, transfer the substrate
into a UHV magnetron sputter system through a load-lock chamber, and after
a cleaning cycle, deposit a thin (10–50 nm) film. The rate will be
monitored with a quartz oscillator. The thickness, roughness and electron
density of the film and the substrate will be determined by means of X-ray
reflectivity. In this experiment, the sample is mounted on a goniometer
head and the surface normal is aligned with the help of a laser beam. Both
the specular and diffuse reflectivity will be measured with a two-circle
diffractometer equipped with a Cu sealed tube. Windows and LINUX-based
programs will be used for the data reduction and the fitting of a box model to
the data.
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- Extents
of Solid Solutions of Ternary and Quaternary Phases in
Bi-Sr-Ca-Cu-O System
(Dr.
J. Meen)
The system Bi-Sr-Ca-Cu-O (BSCCO) contains a number of ternary and quaternary
phases that have extensive ranges in solid solution chemistry. Although
the broad outlines of the variations have been recognized, the extents
of solid solutions of these phases as functions of temperature and partial
pressure of oxygen are poorly known. This information is vital to developing
optimal processing pathways for BSCCO superconductors and for understanding the
phase chemistry and phase equilibria in this system. Students will perform
experiments on bulk compositions that occur in the known two- and three-phase
fields by melting and crystallization in controlled atmosphere vertical-tube
quench furnaces with samples suspended on gold loops. The students will
identify the phases present using x-ray diffraction and electron backscattered
diffraction (where appropriate) and will determine the compositions of
those phases by electron microprobe analysis. They will be expected to
draw compositional sections showing the variation in compositions of solid
solutions as a function of temperature. Students will learn synthesis techniques, sample
preparation for analysis, and determination of crystal structure by diffraction
techniques, chemical analysis by electron microbeam techniques, basic phase
relations in solid state and melting, and construction of pseudo-binary
phase diagrams.
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- Scanning
Probe Measurements of Oxide Surface Morphology Induced
by High Temperature Treatments
(Prof. S. Perry)
The morphology (topography) of surfaces is known to heavily influence phenomena
such as thin film epitaxial growth, interfacial adhesion, and gas adsorption
and reaction. Atomically flat interfaces are desirable for successful epitaxial
growth in lattice-matched systems and for the control of defect density
in thin film systems. In the proposed undergraduate research project, students
will use the atomic force microscope (AFM) to image the surface of mixed
metal oxide thin films as a function of growth parameters and subsequent
processing. Students will be trained in the fundamentals of scanning probe
microscopy, crystal and surface structure, surface chemistry, data analysis
techniques, and the use of a high temperature furnace. They will explore
the influence of gas composition, annealing temperature, and substrate
induced strain. Experiments with the AFM will provide detailed insight
into the grain structure expressed at the surface, surface roughness, and
the degree of morphological change induced by high temperature processing
in gases of various compositions. Lanthanum aluminate (LaAlO3) will be
used as a model substrate to demonstrate surface crystallinity. Subsequent
experiments will investigate the surface morphological properties of lanthanum
strontium cobalt oxide thin films grown on LaAlO3 and yttria stabilized
zirconia. The results of these measurements will provide insight into the
surface reactivity of these thin films being studied in a correlated research
program.
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- Determination
of the Coverage of Corrosion Inhibitors on Metal Surfaces
by Optical Reflection Techniques
(Prof. S. Baldelli)
In this research project students will study the ability of organic monolayers
on the surface of iron and steel to inhibit corrosion. Since corrosion
causes billions of dollar in material repair/replacement, finding methods
that prevent it are a significant intellectual and practical challenge.
To understand corrosion inhibition, we will be using laser reflectometry
and ellipsometry to determine the surface coverage of the inhibitor as
a function of time, electrode potential, inhibitor molecule and aqueous
environment. Students will use these results in interpreting the spectroscopy
and electrochemistry experiments.
To measure the coverage of a corrosion inhibiting monolayer, the change
in reflection of a laser beam from the surface will be monitored. The reflection
intensity and polarization state will be analyzed and interpreted using
Fresnel equations. The system will be treated as a two-layer model without
the inhibitor or as a three-layer system with the inhibitor. The monolayers
are composed of organic molecules with phosphate end groups that bind to
the metal surface. The remaining portion is a carbon containing hydrocarbon tail
that is composed of various functional groups used to tailor the monolayer
properties. From these experiments students will gain experience in surface
chemistry, optics, electrochemistry and spectroscopy.
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- Theoretical
Study of Solid-State Materials
(Prof. T. A. Albright)
To the theorist and experimentalist, extended solid-state materials present
challenging problems concerning the role of how bonding determines structure.
It is our intention to provide projects in two areas that will introduce
undergraduates to modern bonding concepts related to solid-state chemistry
and electronic structure theory.
A number of transition metal boride structures exist with the formulation
AxM3B2. Here A is an electropositive cation and M can be a large variety
of metals. The electron counts are unusually high, up to 38 electrons per
formula unit. Our interest is derived from a fascinating structural distortion.
For electron counts of 33 to 36, the structure is that of a Kagomè net
with the two boron atoms forming the capping atoms of trigonal bipyramids.
Beyond this electron count there is a successive opening and closing of
the triangular arrays that turns on alternating B-B interactions. We want
to understand the bonding in these compounds and what drives the distortion.
The second project that we wish to pursue is the reconstruction of metal
surfaces as induced by adsorbed atoms and molecules. Our initial investigation
will be to examine the Si surface where there is good experimental and
theoretical data to calibrate our work. We shall then move on to the more
interesting area of alkali induced Si(111) reconstruction where several
geometrical models have been proposed. Our primary focus, however, will
be to look at the Ni(110) surface, which reconstructs very differently
upon oxygen and hydrogen absorption.
The calculations used in these projects are of the tight binding type with
an extended Hückel Hamiltonian. The students will become familiar
with molecular orbital theory, solid-state symmetry along with a variety
of analytical procedures associated with this technique. They shall learn
how to view the structure and stability of materials within the context
of modern bonding arguments.
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- Theoretical
Modeling of Light-Emitting Organic Conjugated Polymer
Materials
(Prof. E. Bittner)
In recent years, there has been tremendous growth the development of electronic
materials based upon organic conjugated polymer materials. However, much
remains to be explored in terms of understanding the fundamental physical
processes that characterize these materials. My research in this area focuses
upon charge-carrier transport in disordered and correlated polymeric materials,
the energetics and dynamics of charge-carrier recombination in LEDs and
light-harvesting materials. The REU student working in my group will learn
about the photophysics of light harvesting and light emitting polymeric
materials and will learn to use some of the theoretical tools developed
by my group for simulating these processes.
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- Crystalline
Thin Films of Functional Organic-Inorganic Hybrid Materials
(Prof.
A. Guloy)
The proposed research represents a serious advance in the study and development
of crystalline organic-inorganic composite materials. The broad goal of
this research is the preparation of new low-dimensional organic-inorganic
molecular composites with tunable electronic and optical properties. Tunability
of these materials arises from the synergism exhibited between polarizable
inorganic layers and polymers and hyperpolarizable organic molecules. This
adds an important handle for tailoring new materials for nonlinear optical
and electronic applications. The REU research will focus on the preparation
of highly crystalline thin films of functional hybrid (organic-inorganic)
compounds materials that will be useful in developing new types of optoelectronic
devices. The utility of hybrid compounds for optoelectronic devices greatly
depends on the ability to synthesize them as single crystals and highly ordered
monolayers or multilayers. Crystal structures of hybrid layered perovskites
reveal significant disorder and/or unresolved lattice structures. Studies
on the absorption spectra of previously prepared thin films of the bilayer
perovskites show weaker peaks due to defects and impurities attributed
to "imperfect" self-assembly. In order to address these problems
in the synthesis of the hybrid perovskites and the preparation of crystalline
thin films of these compounds, we propose to synthesize them by template-directed
nucleation from self-assembled monolayers (SAMs).
Undergraduate students that will work on this project will be uniquely
exposed and trained in the synthesis, characterization (structural and
physical properties) and thin film (from SAMS) processing of organic-inorganic
hybrid materials. They will be required to participate in all aspects of
the project, starting with the generation of highly stable monolayers,
synthesis of hybrid materials, and fabrication and characterization of
the materials. The students will have a unique opportunity to learn a variety
of techniques ranging from inorganic and organic synthetic methods to materials
characterization involving the modern techniques of solid-state chemistry
and UHV surface science. This approach will provide the students with a
broad foundation for future chemical and materials research.
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- Synthesis
of a Polyether-Type Dendron with an Amino group at the
Focal Point
(Prof. C. Cai)
The current research in the Cai laboratory involves design, synthesis,
and processing of novel organic adsorbates based on focally-functionalized
dendron molecules with a surface-active rim. The aim is to develop a new
generation of organic self-assembled monolayers based on these dendrons
with improved stability and control over spacing between the functional
groups than the conventional self-assembled monolayers. The goal of the
summer project for the REU student is to synthesize a dendron compound
with a protected amino group at the focal point. The synthesis (expected
to be completed in four steps) will adopt the methods developed for analogues
dendrons by a graduate student who will provide direct help to the REU
student. Through the work, the student will learn standard techniques for
organic synthesis, such as how to use a vacuum line, rotory evaporator,
and NMR, to interpret the NMR spectra, as well as to separate crude products
with flash chromatography and thin layer chromatography.
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- Nanoscale
Fabrication of a Living Clock Using Soft Lithographic
Patterning
(Prof. T. R. Lee)
This project targets the preparation of a new family of artificial neural
networks that will be used to explore the fundamental mechanisms that underlie
higher brain function. The long-term goals of the proposed research include:
(1) the assembly and characterization of structurally well-defined functional
neural ensembles, (2) an investigation of the activity-dependent features
of neural network performance, and (3) a comprehensive analysis of the
emergent properties of neural network systems. The targeted neural networks
will be fabricated using soft lithographic patterning, which will afford
nanometer-scale control over the structure and composition of the patterned
neural arrays. By drawing from the traditionally distinct fields of organic
chemistry and molecular biology, this integrated research project will
seek to define the fundamental processes by which mammalian clock cells
couple to form a functional circadian clock. Undergraduates who participate
in this project will have the opportunity to learn a variety of modern
research techniques, ranging from organic synthetic methods to analytical
surface science to the rapidly evolving techniques of molecular biology.
Since much of the work in the Lee group is collaborative in nature, undergraduates
often work side-by-side with chemical engineers, physicists, electrical engineers,
biochemists, and biomedical engineers. In this type of environment, students
gain knowledge and skills beyond those typically encountered in traditional
chemistry laboratories.
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- Metal
and Semiconductor Nanocrystals on Conjugated Polymers:
A Precursor Polymer and Surface Initiated Polymerization
Approach
(Prof. R. Advincula)
The student will prepare and investigate metal and semiconductor nanocrystals
that are embedded and grafted on a p-conjugated or conductive polymer matrix.
Unique in-situ and ex-situ protocols that combine processability of conjugated
polymers and nanoparticle formation will be investigated. The goal is to
develop electro-optical nanocomposite polymeric materials with exceptional
mechanical, thermal, and transport properties that can be tailored for
semiconductor applications. The techniques to be investigated will include:
- surface initiated polymerization
- recursor polymer approach
to networks
- reactive chemical blending
Conjugated polymers are a
unique class of electro-optically
active materials that are prepared
by addition, condensation,
and redox methods. The synthesis
of metal and semiconductor
nanoparticles has been demonstrated
using redox methods and micellar
surfactants. Compared to simple
blending, the interfacial properties
and metal-polymer bonding between
the nanocrystal and the conjugated
polymer will be emphasized.
This will have important implications
on coupling electronic and
optical properties of these
two materials that is of fundamental
and practical interest. Emphasis
will be given to investigating
these structure-property relationships
by varying the composition
ratio, nanoparticle size and
distribution, polymer microstructure
and constitution, and processing
conditions. The properties
will be investigated as bulk
and ultrathin films in the
presence of electrical and
optical field effects. Characterization
will include: absorption, photoluminescence,
electrical conductivity, dielectric
constant properties, electrochemical
transport, and charge carrier
mobilities. The ultrathin films
will be used to prepare emissive,
photoconductive, and Schottky
diode devices to demonstrate p–electronic,
emission, photoconductivity,
and charge transport properties.
Students will be trained in
materials synthesis and bulk
(nanocomposite), thin film,
and particle analyses.
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