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Seed Projects
(Click here to view Seed Clusters)
Past Seed Projects
Novel Biopolymers for Targeted Drug Delivery: Peptide-Functionalized Polymersomes
This project will attempt to bring biological functionality to polymersomes to facilitate their potential use as
targeted drug delivery vehicles. The target of choice is the £\5£]1 integrin since the interaction with its ligand,
fibronectin (FN), supports numerous adhesive functions and has an important role in health and disease.
Recently the PI has synthesized a novel peptide (called FN-peptide in the remainder of the text) that can support
stronger cell adhesion compared to fibronectin. This is in fact the first time that a peptide has been shown to not
only accurately mimic the cell adhesion domain of the protein, but also to be more adhesive than the natural
ligand. The focus of this exploratory research is on engineering biopolymers and designing nanostructured
interfaces that specifically target the £\5£]1 integrin. For this, the novel FN-peptide will be attached to diblock
copolymers of poly(ethylene oxide)-polybutadiene (PEO-PBD) and functionalized polymersomes will be
designed and characterized.
Novel Magnetic Materials and Nanodevices for Spin Transfer
The recent discovery of spin-polarized current induced magnetization switching (spin transfer) effect has brought great attention to this area given the interest in its physics and great application potentials such as in information storage and processing. So far, all the magnetic thin films in the reported experimental spin transfer devices have in-plane magnetic anisotropy, which has both fundamental and application limits. A fabrication and study of the dynamic properties of magnetic thin films and 100 nm magnetic tunnel junctions (MTJ) devices with perpendicular anisotropy for spin transfer is proposed in this work. Three types of materials for magnetic thin films with perpendicular anisotropy are proposed, [CoFe/Pt]n multilayer films, FeCoGd films and CoCr films. Our preliminary data on [CoFe/Pt]n films support the feasibility of this proposed approach. Magnetic tunnel junctions with perpendicular anisotropy will be fabricated based on a complete fabrication process for 100 nm size devices developed in PI's group. Magnetic thin films and magnetic tunnel junctions with perpendicular anisotropy provide a new platform for the study of spin transfer and spin dynamics. The tunable Gilbert damping constants in [Co/Pt]n multilayer films, FeCoGd rare earth alloys and CoCr films provide extra convenience for the study of fundamental spin dynamics. An essential component is the application of our recently prototyped 100 nm device fabrication method to enable the new materials research for the newly-discovered spin transfer effect. This research may provide a solution for a key issue for magnetic nanodevices, thermal instability, and may enable MRAM for ultra high areal density recording and introduce the first practical spin transistor finally.
Modeling of Dye Sensitized Solar Cells
There is no doubt that harnessing solar energy with inexpensive materials and
manufacturing methods is one of the most important challenges facing humanity. Solarto-
electrical energy conversion methods that make use of photosensitized nanostructures
are emerging as an inexpensive alternative to the p-n junction solar cell. A very recent
example of this approach is the nanowire-based dye sensitized solar cell where a dense
network of wide band gap semiconductor nanowires is sensitized with an organometallic
dye. The dye harvests the incident light and injects an electron into the semiconductor,
where it is transported through the nanowire to reach an electrode connected to the load.
The dye is regenerated by hole injection into an electrolyte. For example, when I-/I3
-
redox couple is used in an electrolyte, I- is oxidized to I3
- at the dye-electrolyte interface
and I3
- is reduced back to I- at the counter electrode to complete the solar electrochemical
cell. The first dye sensitized solar cells were made from TiO2 nanocrystals abutted
against each other to form a mesostructured film which served the same purpose as the
nanowires in Fig. 1. However, there is evidence that the improved electron transport in
the nanowire geometry may be useful. Furthermore, nanowire geometry is much better
defined than the random, mesostructured TiO2 photoelectrodes and, because of its more
regular geometry, will be easier to construct realistic models to describe system behavior
and to aid the design experiments which elucidate the fundamental physical mechanisms
controlling the DSSC operation. Much of the current research focuses on improving the range of spectral
absorbance by modifying the dye, on improving hole transport and cell stability by
replacing the liquid electrolyte with ionic solids or conducting polymers and on
improving electron transport by using alternative wide band gap semiconductor materials
or core-shell structures. The experimental approaches are largely empirical and time
consuming; progress is slow as the fundamental principles of how the dye sensitized solar
Figure 1. Schematic of a nanowire based dye sensitized solar cell (left). Scaning electron micrograph
of ZnO nanowires grown from methenamine and zinc nitrate solution at 60 oC (right). Nanowires are
~8 £gm long and 100 nm in diameter.
cell operates is still being debated. It is certainly fair to say that there is no
comprehensive theoretical and modeling framework that could both guide experiments
and provide a better understanding of experimental observations. Towards this end, we
are proposing to start a modeling and simulation research project aimed at providing such
a framework. Two key areas are targeted; (i) growth mechanism and growth kinetics of
nanowires and (ii) charge transport and kinetics in dye sensitized solar cells.
Growth mechanism and growth kinetics-The quality and microstructure of the
ZnO nanowire array determines the solar cellÕs performance, but we do not understand
quantitatively the effects of key experimental variables on the microstructure. Nanowires,
shown in Fig. 1, are grown from methenamine and zinc nitrate solution at temperatures
less than 100 oC. Anisotropic growth results from different growth rates of the various
crystallographic faces; however, the kinetics of growth are neither understood nor
quantified. Nanowire grow is an example of a special type of solution crystal growth; the
general area of solution crystal growth has received much attention in DerbyÕs prior
research. Models describing the growth of these nanowires will be constructed by
combining simple theories of face growth with analyses of mass transfer through the
liquid phase. These models will rely on experimental data to tune phenomenological
model parameters and will, in turn, provide a mathematical basis to explain how process
changes will affect growth characteristics. We expect the synergy between model and
experiment to enable advances not possible by experimentation alone.
Charge transport and kinetics in dye sensitized solar cells-During the operation of
the cell, electrons are continually generated, injected into and transported in the
nanowires while the hole undergoes a redox reaction at the semiconductor-dye-electrolyte
interface. The ions in the electrolyte penetrate the region between the nanowires and
mediate the positive charge transport between the dye and the counter electrode. The
spatial variation of the electric field is determined by the charge distribution both in the
nanowire and in the electrolyte. The solar cell operation spans 15 and 6 orders of
magnitude in time and length scales, respectively. For example, the electrons are injected
from the dye into the nanowire within several femtoseconds but may take milliseconds to
reach the anode. The nanowire and the electrolyte determine the solar cell thickness
which may be 10-50 £gm; in contrast, the electrical double layer that forms at the
nanowire-dye-electrolyte interface maybe on the order of nanometers. This disparity in
scales presents one of the modeling challenges. We propose to initiate a hierarchical
modeling effort starting from the simplest models of self-consistent electron transport and
kinetics in the nanowires and ion transport and kinetics in the electrolyte. Drift-diffusion
equations for electrons in the solid and for the ions in the electrolyte will be solved
together with the Poisson equation to provide a framework within which experimental
data such as the solar cell current-voltage characteristics can be examined. Such
systematic examinations can be used to infer information about the rate limiting
processes in the solar cell and lead to improved designs. Thus a hierarchy of models,
beginning with analytical, lumped parameter approaches, ranging to 2D, and possibly 3D,
finite element solutions of the governing electrochemical and electromagnetic equations
will be developed and applied to this problem. Derby has had past experience with
modeling electrochemical reactions and the solution of Maxwell equations (see CV), and
we anticipate significant progress can be made in a relatively short time frame.
Oriented Aggregation of Zeolite Nanocrystals: Controlling Twinning and Thin Film Microstructure
At the present time, the fundamental growth mechanisms of zeolites are poorly
understood. Zeolites are ordered framework materials with regular cages and channels of sub-nanometer
size. Their tailored structure, stability, and activity have led to a broad variety of applications in industry
as catalysts, adsorbents, and ion exchangers. Achieving control over crystallite shape and the
microstructure of thin films produced from these materials is a major goal in Materials Science and
Chemistry. A fundamental understanding of zeolite growth mechanisms will lead to improved control
over defect concentrations, size, and morphology of zeolite crystals. There is substantial controversy over
how zeolites crystallize from homogeneous solutions. Hypotheses for growth mechanisms range from the
precipitation of amorphous primary particles followed by crystallization to the diffusion of molecularscale
species to growing, crystalline nuclei to the oriented aggregation of crystalline primary particles.
Published high-resolution transmission electron microscopy (HRTEM) data often show evidence for the
latter mechanism (e.g., Nikolakis, 2000; De Moor, 1999; Shen, 2001; and others). Furthermore, twins,
defects, and stacking faults are often observed in the products of zeolites syntheses, and control over the
presence and concentration of such features is expected to lead to new materials with new properties.
Improved understanding of how zeolites grow and how twinning and stacking faults occur will enable the
production of tailored building blocks for thin film preparation.
Structural Properties of Silicon Nanoparticles -- Theory and Simulation
Unlike bulk, silicon at the nano-size emits light when electrically stimulated. This is because
quantum mechanics, which takes over at this scale, relieves the factors that would normally squander
the energy in ways other than the formation of photons. Thus, the hope of utilizing technologically
important silicon in optoelectronic devices is revived. Biomedical applications are also envisaged.
The synthesis of silicon nanoclusters is nowadays a very active field of research. Recently1,2, an
efficient approach has been developed based on nonthermal plasmas. Depending on the experimental
conditions (mainly particle residence time and gas flow rates), single-crystal particles with sizes in
the 2-8 nm and 20-80 nm range were produced. Further insight was gained by electron microscopy,
which found that the particle shape changes with size: While larger particles have predominantly
cubic shapes, spherical shapes were encountered as size decreases. Particles in the 2-8 nm were
shown to photoluminescence. It was also found that the optical emission correlates very well with
the particle size. However, photoluminescence occurred only in the orange-red range. To diversify the range of applications the next technical challenge is light emission in the blue and
green range. This could be accomplished by a further decrease in particle size and/or coating of
nanoparticles that would prevent unwanted oxygen attachment. To facilitate this goal, further
understanding of the physics of silicon clusters is needed and important questions remain to be
answered. For a given number of silicon atoms N, what cluster shape corresponds to the minimum
energy and is likely to be more stable? What coating shell can favorably seal silicon nanoclusters?
What is the effect of temperature on particle stability? What is the critical size that still preserves the
crystalline silicon ordering? Focusing on these issues we propose a systematic theoretical study
involving ab initio structural optimizationsa and molecular dynamics simulations from a tightbinding
potential, which will emphasize both energetic and kinetic aspects. Since these simulation
methods are quantum mechanical in nature, they will offer information about both the atomic core
and the electronic system (from which optical properties can be extracted). Specifically, the
proposed research will be centered on the following themes: The Energetic, Shape, and Structure of Silicon Nanoclusters; Surface Passivation of Smallest Nanoclusters; and Thermodynamics of Free Clusters.
Past Seed Projects
Computational and Experimental Design of Nucleation Templates for Controlling Crystal Growth and Polymorphis
Designed Heterogeneous Nucleation of Polymeric Foams
Measurement and Synthetic Optimization of Nanomechanical Properties of Three-Dimensionally Ordered Macroporous (3DOM) Solids
Microfabrication of Cell/Material Hybrid Constructs Via Laser-Guided Direct Writing: Application to Artificial Tissue Vascularization
Modeling and Design of Crystals Grown from Solution
Nonlinear Spectroscopic Studies of Nanoscopic Materials Targeted at Phototonic Switching Applications
Organic Semiconductors
Programmable Reconfigurable Integration of Nanowires on Silicon Substrates
Using Biological Structures as Templates for Magnetic Nanostructure Fabrication
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