Faculty advisors are active in the study of the structure, reactivity and thermodynamics of materials in addition to the characterization of their electronic and optical properties. Research groups consist of faculty and graduate students from the Chemistry and Physics Departments who guide undergraduate participants in the program.

Nonlinear Optical Spectroscopy of Aqueous Surfaces and Interfaces
Geraldine Richmond, REU Program Director
The undergraduate student who will join my laboratory for the summer will be involved in measuring the vibrational spectroscopy of a solid/liquid interface as surfactants adsorb. We will focus on the CaF2/water interface this summer. Our first experiments will be conducted with fatty acid films where we will monitor both the water structure at the salt surface and the molecular properties of the fatty acid surfactants, such as oleate, as they adsorb at the interface. Fatty acids are very common collectors in calcium mineral flotation with oleate one of the more frequently used collectors in flotation. The student will work closely in training with a graduate student until he/she is familiar with the extensive laser optical instrumentation. The goal is that by mid-summer, the REU student will be able to independently conduct the laser experiments. The project will be a valuable experience for the REU participant in teaching him/her about surface science, laser spectroscopy and nonlinear optics.

Electron Transfer an Nanostructured Semiconductor Interfaces
Mark Lonergan, Chemistry
Our laboratory is currently investigating several semiconductor interfaces characterized by a nanoscale, spatial distribution of barrier heights. These studies are enabled by the unique properties of the n-InP | polypyrole interface including near ideal transport properties and a continuously tunable barrier height. The REU student can be involved in either of two projects. The first involves well-defined nanostructured interfaces fabricated using e-beam lithography to imbed an array of metal dots into the n-InP | polypyrrole interface, and studied using temperature dependent current-voltage, capacitance voltage, and photoresponse measurements as well as current sensing AFM. The second project would involve our current studies a new device architecture involving a three terminal sandwich structure: Si/poly(acetylene)/electrolyte. Alone, the Si/poly(acetylene) interface exhibits diode characteristics with its specific properties determined by the electrochemical potential of poly(acetylene). By adding an electrolyte and a third electrical contact, it is possible to alter the electrochemical properties of poly(acetylene) while observing the properties of the underlying Si/poly(acetylene) interface. Such a structure should yield a variable diode, and permit for the detailed study of precisely how the properties of inorganic semiconductor/conducting polymer interfaces depend on the electrochemical characteristics of conjugated organic polymer. Work on this project will entail the use of synthesis of derivatized poly(acetylene)s using transition metal organometallic catalysts, the fabrication of semiconductor device structures, and the electrical characterization of these structures using electrochemical and capacitance techniques.

Protein local mobility and biological function
Marina Guenza, Chemistry and Physics
We developed a new theoretical-computational approach that aims to bridge the gap between short-time dynamics, as calculated by Molecular Dynamics simulations, and biologically significant long-time dynamics. By means of our approach we calculated the dynamics of biologically active proteins and compared with the dynamics of theirs mutated and biologically not active counterparts. The REU student involved in this new project will learn how to run a Molecular Dynamics simulation of a protein, how to collect and process the data, and how to write a Fortran code to calculate the relevant properties related to the protein dynamics. During the development of this research project the student will have the chance of interacting with other students presently working in the group on related projects.

Interdiffusion and Nucleation at the Interface of Reacting Solids
Dave Johnson, Chemistry
By using elementally modulated reactants in which composition can be controlled on an �ngstrom length scale, we have been able to use slow solid state diffusion rates as a synthetic advantage. Controlled crystallization of elementally modulated reactants results in the rational synthesis of targeted compounds. There are several projects for REU students. These include preparing new thermoelectric materials and measuring their properties, preparing new extended cluster compounds, and preparing crystalline superlattices containing interwoven layers of different compounds. All of these projects involve preparing thermodynamically unstable compounds which cannot be prepared using conventional synthesis techniques. Although the compounds are thermodynamically unstable, they are kinetically stable. The structure of the superlattice compounds is controlled by the structure of the initial modulated elemental reactant. The rational synthesis of superlattice compounds permits the tailoring of physical properties as a function of compositional layer thicknesses and native properties of the parent compounds. The structure of the resulting products is characterized using transmission electron microscopy and x-ray diffraction. The student will measure the properties of the compounds he/she prepares, using electrical conductivity, Seebeck coefficients, Hall measurements and thermal conductivity measurements to correlate properties with structure and composition. We have had an excellent track record (in publications alone) in involving both undergraduate physics and chemistry majors in projects like these and we anticipate that this will continue in the future.

Molecular Approaches To Nanoscale Assemblies of Polypeptides, and Metal Nanoparticles
Jim Hutchison, Chemistry
Research in the Hutchison group focuses on implementing chemical methods, including self assembly and molecular templates, to design and study the electronic properties of new highly ordered, nanoscale assemblies. The REU student will work with a graduate student to prepare, characterize and study the electrical properties of organized polypeptide arrays or assemblies of gold nanoparticles. The highly interdisciplinary nature of this work will provide the student with experience in both chemical and physical methods including: chemical modification of particle/substrate surfaces and nanostructure analysis using an array of physical methods including optical spectroscopy, atomic force microscopy, transmission electron microscopy, x-ray photoelectron microscopy, and thermal gravimetric analysis. Electrical characterization of the individual nanoparticles may be conducted using electrochemical methods.

The Effect of Stress on the Rate of Polymer Photodegradation
David Tyler, Chemistry
An interesting outcome of artificial weathering studies on polymers is the discovery that tensile- and shear-stress can accelerate the rate of photodegradation. REU students will synthesize polymers containing chlorine (a metal-radical trap) along their backbones, and they will study the photochemistry of these polymers.Students working on this project will learn considerable general information about polymers (a topic generally not covered in the undergraduate curriculum), and they will learn about polymer synthesis and characterization techniques (including basic spectroscopic techniques, molecular weight techniques, and thermal analysis methods). In addition, they will be introduced to photochemistry, including general/descriptive material and quantitative methods.

Correlation of Defect Properties of Amorphous Silicon and/or Amorphous Silicon-Germanium Alloys with Photovoltaic Performance
Dave Cohen, Physics
The undergraduate student will attempt to make such a direct comparison between cell performance and the materials electronic properties using a somewhat simplified approach. That is, the Schottky diode device structures we use for our materials characterization studies will also behave as solar cells, albeit less efficient ones than the p-i-n structures preferred. However, most of the key physical properties that control the performance of the p-i-n cells are also present in the simpler Schottky structures. Thus, the student will make use of a variety of Schottky diode test devices that we already have on hand, apply several of the methods used in my laboratory to characterize their electronic properties, and then measure the performance of the same Schottky structures operated as solar cells. If a sufficient number of test devices can be studied in this fashion, and particularly if correlations between materials properties and cell performance can be identified, this summer project will become a valuable, publishable work.

Quantum Information Science
Michael Raymer, Physics
The past decade has seen advances in techniques for manipulating and measuring physical objects at the quantum level, opening a new avenue for research - Quantum Information Science. This includes quantum cryptography and quantum computing, and involves fundamental aspects of quantum optics. During the next decade, research will explore basic questions regarding to what extent such techniques can be used to implement new information technologies. This REU project focuses on control and measurement of the states of individual photons created by photon splitting in nonlinear-optical crystals or fibers. Interferometers are used to measure the quantum states of photons. Crystals and fibers are used to create photons and to change their polarization or energy states. Elementary quantum logic gates are being explored. The REU student may work with diode or titanium-sapphire lasers, single-photon detectors, optical fibers, interferometers, nonlinear optics, and computer interfacing.

Deformed glass microsphere as three dimensional chaotic resonators
Hailin Wang, Physics
Recently, our group has developed a new but very simple experimental approach to fabricate a deformed WGM resonator by fusing two glass microspheres together. The REU student will carry out both experimental and theoretical studies in understanding properties of these deformed resonators. The experimental efforts will involve the measurement of the spatial pattern and Q-factor of the WGMs. The experimental results will be compared with simulations based on an existing ray-tracing program. 1) J.U. Noeckel and A.D. Stone, Nature 385, 45 (1997)

Photonic Crystals - Controlling Light on Wavelength Scale
Miriam Deutsch, Physics
Three-dimensional photonic crystals have been predicted to possess a full photonic band gap - a range of frequencies where no real propagating electromagnetic modes are allowed. In analogy to electronic semiconductors, the existence of a photonic energy gap leads to unique photon-transport properties in these materials. Some of the predictions include inhibition of spontaneous emission, mirror-less lasing, enhancement of optical nonlinear (NLO) effects and optical limiting. Nevertheless, fabrication of such structures on optical length scales remains a serious challenge. A promising approach for making these materials exploits self-assembly of sub-micron sized colloidal spheres into crystalline structures. Recently, colloidal self-assembly has been employed to fabricate 3D photonic crystals from a variety of optical materials. Typically, sub-micron colloidal silica spheres are induced to from ordered crystals on flat substrates. The resulting crystalline materials posses fcc symmetry. These structures, known as artificial opals serve as a 3D template for patterning other materials. Patterning is carried out by infiltration of the opal voids with the appropriate materials, and subsequent removal of the template by selective etching. The result is a 3D photonic crystal, or an "inverted opal". An undergraduate student will have the opportunity to learn novel materials fabrication techniques, as well gain experience in optics experimental research. Once fabricated, the photonic crystals will be characterized to study their compositional, structural and optical properties. The student will become familiar with electron probe and microscopy techniques such as SEM, EDX and TEM. In particular, optical microscopy is used to probe single crystalline domains in the samples. The student will gain experience in setting up combined high-resolution optical microscopy/spectroscopy experiments, and operating standard spectroscopy apparatus.

Membrane-functionalized microparticles
Raghuveer Parthasarathy, Physics
Controlling interactions between microparticles is appealing from both applied and fundamental scientific perspectives. These interactions dictate the material properties of many complex fluids and can guide the formation of new materials with useful optical properties. Microparticle superstructures can serve as visualizable models for atomic and molecular crystals, liquids, glasses, and other states, enhancing our understanding of phase transitions, defect structures, and other collective properties. Despite this broad importance, it remains difficult to control microparticle interactions. The Parthasarathy Lab has adopted a biomimetic approach, coating microspheres with lipid membranes similar to the membranes of cells. We have recently shown that this membrane functionalization can in fact control inter-particle interactions, generating families of attractive and repulsive forces. Moreover, control of interactions sheds light on fundamental mysteries in colloidal physics, such as why like-charges in water can attract rather than repel. An REU student will be involved with particle creation, laser trapping, and image analysis to explore the properties of these biologically inspired materials.

Phenyl-Acetylene Scaffolding as Optoelectric Materials
Michael Haley, Chemistry
Research efforts in the Haley laboratory revolve around the assembly of functional molecules comprised of benzene and acetylene building blocks. Their construction is based extensively on established synthetic methods as well as on reaction sequences developed and/or modified in our lab. These advances now allow us to assemble a tremendous variety of structures that are of a discreet size and of a desired substitution pattern. As each target compound is completed, its chemical and physical properties are extensively investigated, with special attention placed on potential materials applications. Prior work has shown that a particular subset, tetrakis(phenylethynyl)benzenes (TPEBs), are novel 2-D NLO chromophores that possess high two-photon absorption (TPA) cross-sections. An REU student would help construct and study additional scaffolds, thus further refining their design for optimal TPA results. A small set of new TPEBs targets would first be identified and then prepared. Given that our syntheses are modular (think molecular level Legos or Tinkertoys), most of the starting materials are readily available; thus, construction of the compounds would be straightforward. The student would characterize the new molecules by traditional techniques (NMR, IR, UV-vis, MS) as well as more elaborate methods (fluorescence including lifetimes). The TPA values would then be obtained via established collaborations.

Supramolecular Chemistry
Darren Johnson, Chemistry
The Johnson laboratory uses supramolecular chemistry to approach a variety of problems in organic, inorganic and environmental chemistry. Research topics include i) developing a supramolecular design strategy for specific chelation of hazardous metals such as As, Pb and Hg; ii) multi-point molecular recognition of anions and biologically relevant small molecules; iii) elaborating new template strategies for nanoscale, three-dimensional cages. REU students would be introduced to concepts in the field of supramolecular chemistry, and they will specifically apply the principles of self-assembly, symmetry, organic and inorganic synthesis to prepare new molecules. A representative project for an REU student would involve first learning the basics of 3-D computer modeling to design a simple ligand specific for self-assembling Pb-based coordination assemblies. The student would then perform the organic synthesis necessary to prepare the ligand and the inorganic synthesis required to form the complexes. Students will need to draw on their physic backgrounds in using many of the characterization techniques to analyze their new compound - these techniques include NMR spectroscopy, electrospray ionization mass spectrometry, solution molecular weight determination (e.g., using vapor pressure osmometry) and X-ray crystallography. This project will give the student a working knowledge of supramolecular chemistry, expose him/her to molecular modeling, and provide hands-on experience on sophisticated instrumentation.