pillar array polymer template for solar cells travis ... · departments of physics and applied...

Pillar Array Polymer Template for Solar Cells

Travis Rosmus

Chemistry Department, Saint Francis University in Loretto

Heayoung Yoon, Dr. Theresa Mayer

Electrical Engineering Department, Penn State University

Comparing to the conventional planar structure, the geometry of high-aspect-ratio pillar

arrays can offer the potential to achieve a low cost, commercially viable route to the production

of high efficiency solar cells, in that the direction of light absorption is decoupled from that of

carrier collection. This project will explore the design and process to fabricate a pillar array

template using polymers. The REU student will also investigate the properties of the template

including hardness test and FESEM analysis.

I have learned the basics behind the etching process and the creating of a polymer

template for solar cells. I made these templates by spinning a certain thickness of polyimide onto

oxidized silicon pillar arrays followed by the removal of the oxide using BOE, Buffered Oxide

Etchant, to release the polymer template from the substrate. I have used different spinning speeds

and graphed the results in a Thickness vs RPMs graph. From there, I created the protocol that

yielded the appropriate template. This project got me used to working in a real lab environment

with access to equipment I would not have had access to at my small college. It has also allowed

me to work under a graduate student and be a part of a research team on a project that interested

me.

Giant vesicles as model for Red Blood cells Karla M. Santos

Department of Biology, University of Puerto Rico, Cayey, PR 00969 Meghan Andes Koback1, Christine D Keating1 and Jose Stoute2

Department of Chemistry, Penn State University, University Park, PA 168021 MSHMC Infectious Disease, Hershey, PA 17033-0502

Abstract Plasmodium falciparum, a human parasite that causes malaria, is responsible for 1-2

million deaths each year. P. falciparum infects the host by invading and multiplying inside red blood cells. Currently, the mechanism of invasion is unknown. It is hypothesized that glycoproteins on the surface of red blood cells, specifically glycophorin A (GpA) plays a key role. GpA is a 131 amino acid transmembrane protein possessing a tripartite structure: an N-terminal end exposed to the exoplasmic solution, a hydrophobic region inserted into the membrane bilayer, and a C-terminal region facing the cytoplasmic interior. Previous research has focused on examination of red blood cells; however, data is not precise due to the cell structure. The red cell membrane consists of same amounts of lipids and proteins in the surface. Giant vesicles (GVs) provide an alternative means to examining biological problems. GVs are ideal cell models due to their size (>1µm) and composition, and because they provide a simple environment in which biomolecules can be isolated and studied. Reconstitution of GpA into GVs and subsequent incubation with P. falciparum will allow for examination of the role of GpA during invasion.

In order to mimic red blood cells as closely as possible, it is essential that GVs are unilamellar (having only one bilayer), contain GpA in the correct orientation, and are formed in a solution of RPMI/10% albumax (a medium used for parasite growth and survival). Several lipid ratios and compositions containing anionic or cationic lipids, cholesterol, and PEGylated lipids were tested to determine which recipe produced the largest population of GUVs in the desired medium. GVs were formed in all instances, however, the majority of vesicles were multilamellar ((vesicles with more than one bilayer membrane).Flow cytometry was performed in an attempt to separate GUVs from MLVs, however the instrument could not discern between the different vesicle types. Electroformation is an alternative method known to produce large populations of unilamellar vesicles. Preliminary electroformation data shows that anionic GUVS containing DPPC/DPPS/Cholesterol were produced in an aqueous solution. Future electroformation experiments will focus on production of GVs in the culture medium, incorporation of GpA, and determination of GpA orientation via antibodies.

The Electro- and Photochemistry of Self-Assembling Materials Andrew Serino

The Department of Materials Science & Engineering, Penn State University Moonhee Kim, J. Nathan Hohman, Professor Paul S. Weiss Department of Chemistry & Physics, Penn State University

Self-assembled monolayers (SAM) are well-ordered single-molecule-thiol layers whose

head groups bind strongly to a substrate, for example gold. As device structures get smaller and more intricate, spontaneously formed and highly ordered self-assembled monolayers (SAMs) have become appealing for nanofabrication and chemical patterning. Understanding how to tune and to control the chemical and physical properties of SAMs allows us to control the properties of the entire nanoscale system. I have explored the intermolecular interactions within SAMs of m-1-carboranethiol (M1), m-9-carboranethiol (M9), and 3-mercapto-N-nonyl-propionamide (1ATC9) on Au{111} by utilizing cyclic voltammetry. These molecules form stable and highly-ordered SAMs due to strong adsorbate-adsorbate interactions and the strong Au-sulfur bond. The carboranethiols exhibit strong dipole-dipole interactions, which vary depending on the relative positions of the carbon, boron and sulfur. 3-mercapto-N-nonyl-propionamide has an amide group that aligns after assembly to generate hydrogen-bonding interactions within the SAM. The goal of my research was to study the interaction strength of these molecules with electrochemistry. In cyclic voltammetry, a cathodic potential is applied to reductively desorb the alkanethiolate in a one-electron reaction:

RS – Au + 1e- RS- + Au0

This experiment provides information about the relative interaction strengths between molecules that compose SAMs. The stronger the interactions between molecules in a SAM, the higher the voltage to desorb molecules from the gold substrate. Cyclic voltammetry provides the characteristic details such as the intermolecular interaction strength, the number of molecules per unit area, and the degree of molecular ordering.

My work on this project involved measuring reductive potentials of alkanethiolate SAMs using cyclic voltammetry. My work in the Weiss Group helped me to understand and to develop the research skills I need for life as a scientist. I have become well-versed in using cyclic voltammetry to measure novel monolayer. I also learned the importance of using the scientific method for designing experiments and the importance of careful sample preparation and instrument maintenance in order to characterize new nanomaterials.

Imaging Ferroelectric Domains by Nonlinear Optics and Spectroscopy Gabriella Shepard

Department of Physics, Carnegie Mellon University Eftihia Vlahos, Dr. Venkatraman Gopalan

Department of Materials Science and Engineering, Penn State University Ferroelectrics are materials that exhibit spontaneous polarization that can be switched by

the application of external electric field. Such materials consist of areas of uniform polarization, which are called domains, and domain boundaries are known as walls. Room temperature ferroelectrics are important materials to study because of their potential applications in memory devices, such as FRAMs, precision actuators, electro-optic and frequency conversion devices. Optical second harmonic generation (SHG) imaging is one of the techniques used to study the domain structure and symmetry of ferroelectrics. In particular, SHG imaging is a non-linear optical phenomenon, where two incident photons of frequency interact with a non-centrosymmetric material and produce a photon of frequency 2. SHG images are obtained using a confocal microscope equipped with a piezo-scanning stage, which allows precise sample positioning and scanning. In addition, SHG polarization plots, which contain symmetry information, can be simultaneously obtained. My research project focused on studying the ferroelectric domains in barium titanate (BaTiO3), which is a ferroelectric, and bismuth ferrite (BiFeO3), which is a ferroelectric and antiferromagnetic at room temperature. For both materials, SHG images and polar plots were taken to probe their domain structures. Using the 4mm crystal symmetry, we were able to fit the BaTiO3 experimental data, determine the direction of polarization, and verify the presence of 90° domain walls. For BiFeO3 we obtained similar experimental results, with striking images, which are a combination of 71, 109, and 180 domain walls. Theoretical modeling required for the interpretation of the BiFeO3 domain wall structure is presently ongoing. Overall, this research experience was an opportunity to work with useful lab techniques that utilize lasers, which can be applied to many other areas of science. This research program provided a glimpse into the life of a researcher, emphasizing the time and hard work put into understanding and solving each new problem.

Electrochemical Synthesis and Characterization of Bi1-xSbx Nanowires

Nickolas Sneed Department of Physics, Howard University

REU Program, Center for Nanoscale Science, Pennsylvania State University

Meenakshi Singh, Dr, Jian Wang, Dr. Mingliang Tian, Dr. Moses Chan Department of Physics, Pennsylvania State University

Nanotechnology is one of the fastest-growing global industries. In the field of nanotechnology, there has been a heightened interest in the research of nanowires. Nanowires are small structures with a thickness or diameter limited to tens of nanometers or less. There are a number of techniques to fabricate nanowires (eg., metallic, semi-conducting, and insulating), such as chemical vapor deposition (CVD), hydrothermal and template-assisted electrodeposition and so on. Compared with other methods, electrodeposition is the most economically efficient and easy to handle. The high aspect ratio wires are grown into the pores of a porous membrane under a selected electric potential. A better understanding of their physical properties due to the size confinement effect is extremely important for not only the fundamental interest but also the technological application of future generation nanodevices.

Bismuth is a material known for its scientific significance and thermoelectric properties. The most work previously was focused on the bulk materials, less is known for Sb-doped Bi nanowires. The research that is being conducted will attempt to synthesize Bi1-xSbx alloy nanowires using electrodeposition. This project will explore different solutions using varying molarities of salts of bismuth and antimony dissolved in DMSO. The experimental details of the electrodeposition process are as follows. The Bi-Sb solution contains 0.06 M Bi3+ and 0.02 M Sb 3+, and thus the nanowires that were produced consisted of predominantly bismuth. By varying the molar ratio of the electrolyte, we attempt to grow wires with different concentration of Sb.

At the present stage, we have obtained Sb-doped nanowires. The structural characterization, such as XRD and TEM/SEM study, is underway.

Contacts to Germanium and Silicon Nanowires: Phase Formation and Contact Resistance Thomas Swisher

Departments of Physics and Applied Mathematics, Humboldt State University

Nicholas Dellas, Chad Eichfeld, Dr. Suzanne Mohney Department of Materials Science and Engineering, Penn State University

Nanowires (NWs) are tiny metal or semiconducting rods nanometers in diameter. NWs may facilitate the next generation of nanoscale transistors and sensors. Germanium NWs may allow for faster devices than silicon NWs because Ge has higher electron and hole mobilities. Si NWs are usually doped with a gas during VLS growth. In this study we examined the thermal stability of contacts to Ge NWs, and the doping and contact resistance of Si NWs grown using only an Al catalyst. Our Ge NWs were deposited and electrofluidically aligned onto a Si nitride coated Si wafer, which was cleaved into thirds. Each piece was coated with an 80nm film of Cu, Pd, or Ni via electron beam evaporation, then cleaved into three sections and annealed at 400oC, 500oC, or 600oC for two minutes. Field emission scanning electron microscopy revealed that the Cu diffused away from the deposition site most extensively, but we could not confirm if the Cu had diffused axially down the Ge NWs and formed a Cu-germanide segment. Our Si NWs, 5-20 µm long and 75-150 nm wide, were deposited onto a Si nitride coated Si wafer. The Si NWs were overlaid with 80 nm thick Pt contacts via sputter deposition. A backside gate was formed by the deposition of 25 nm of Ti and 50 nm of Au through electron beam evaporation. Electrical measurements were made on the Si NWs using the four point probe technique. The Si NW/platinum contacts showed a linear I-V relationship. The resistance of the Si NWs increased with positive gate voltages and decreased on negative. This behavior is consistent with p-type doping. We conclude that the Si NWs were doped p-type by the Al catalyst, and that Pt can serve as an ohmic contact to these NWs.

Silver Nanoparticle Synthesis and Nanomotive Behavior Under UV-light

Nella Marie Vargas-Barbosa Department of Chemistry, University of Puerto Rico – Rio Piedras Campus

Michael Ibele, Ayusman Sen, Tom E. Mallouk

Department of Chemistry, Penn State University

Perry Edwards, I. C. Khoo Department of Electrical Engineering, Penn State University

Nanomotors are devices that operate on locally supplied fuels and perform different

tasks. These nanodevices may have many applications in the development of nanomachnery, nanomedicine, nanoscale transport and assembly, nanorobotics, fluidic systems and chemical sensing.1 Earlier experiments showed oscillating movement of silver chloride particles in water as UV light was turned on and off.

We investigated the photochemical reaction of H2O2 at silver particles and whether this reaction can drive the movement of silica tracer particles into light-patterned assemblies. The silver nanoparticles were synthesized using silver nitrate as a precursor and citrate as the reducing agent in an aqueous media. The silver colloid solution had a λmax of 454 nm in the UV-Vis spectra. TEM imaging showed that the diameter of the particles ranged from 1 nm thru 50 nm in diameter. A histogram was done and determined that most of the particles diameters ranged from 12 nm thru 24 nm. Using 2 µm silica tracer particles and after aprox. 10 minutes of exposure to UV light the silver particles showed a schooling behavior similar to the AgCl particles. The observed movement of the particles is slow (in comparison to the AgCl which took seconds) because the silver particles are phochemically unstable. When we used 600 nm silica tracer particles some movement is observed but it is mostly brownian. This system shows promising results, I would suggest the optimization of this experiment using more photochemically stable silver nanoparticles in order to continue experiments with smaller silica tracer particles. When this is achieved there could be experiments in which patterns with the silica tracer and silver nanoparticles can be created by patterning the UV light to which the system is exposed.

This summer experience helped me understand the dark side of research: when you do not get the results you expect. Nevertheless, I feel that graduate school is my place to be: overcoming these obstacles and using science to figure out what is going on is definitely what I want. My knowledge in nanotechnology and material science has been greatly broadened. I feel that through this research opportunity I contributed, even in its smallest measure, to the scientific community and the REU Physics Program development of knowledge and prestige.

1. Wang, J. Can Man-Made Nanomachines Compete with Nature Nanomotors?. ACS NANO. 2009, 3, 4-9

Synthesis and Characterization of Au and Ag Triangular Nanoprisms Garrett Wadsworth

Physics Department, Lehigh University

Moonhee Kim, J. Nathan Hohman, Hector Saavedra, Paul S. Weiss Departments of Chemistry and Physics, Penn State University

As technology advances, we are able to create nanoparticles of greater precision with increasingly controlled properties. These are fabricated in many different shapes, including rods, wires, and tubes. Nanoparticles are of great interest due to their tendency to exhibit characteristics that differ from their macroscopic counterparts, in electron confinement, near-field optical effects, and ballistic transport. In nanoparticles, a large fraction of the atoms lie on the surface, and lead the nanoparticles to exhibit properties that differ from both those of molecules and bulk materials. We synthesized and characterized individual metal nanoprisms, triangular nanoparticles that exhibit distinct localized surface plasmon resonance in the ultraviolet-visible/near-infrared region. Nanoprisms have been fabricated and characterized by ensemble measurements, which only represent the averaged properties of the particles in the bulk. Even though several types of nanoprisms have been fabricated, the characteristics that depend on the specific physical and chemical properties of individual nanoprisms have not been determined. By utilizing a scanning tunneling microscope that introduces evanescently-coupled light into the tunneling junction, we will be able to isolate and to image individual nanoprisms at the sub-nanometer scale. The correlations between size, shape, thickness, and their localized surface plasmon resonance will be investigated. This research will provide deeper insight into nanoprisms in order to design and to provide information for tuning the particles for desired applications in nanophotonics, single-cell imaging, and biological diagnostics.

My project this summer was to synthesize gold and silver nanoprisms with consistent size, shape, and thickness. I have fabricated silver nanoprisms. I am continuing to work on the synthesis of gold nanoprisms. The uniformity of the silver nanoprisms has been determined by measuring ultraviolet-visible and near-infrared absorption spectra. We will next use transmission electron microscopy to image the nanoprisms. This research experience has allowed me to see the interaction in a diverse, collaborative research group, and has given me the opportunity to participate in graduate-level research. In addition, being under a faculty mentor who deals mainly in experimental research has given me a stronger grasp on some of the more subtle nuances of conducting experiments. This experience has only strengthened my resolve to continue on to graduate school and a research-focused career.

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Random Close Packing of Colloidal Assemblies Kristi Wegener

Department of Chemical Engineering, The University of Michigan

Cesar Gonzalez Serrano & Professor Darrell Velegol Department of Chemical Engineering, The Pennsylvania State University

Today, it is known how to fabricate colloidal doublets using two colloidal particles easily

using the salting out – quenching – fusing technique. How to separate the colloidal doublets from the single colloidal particles, singlets, on the large scale efficiently is unknown. Without separation, the potential advantages of the colloidal doublets are significantly less. One way to have more information about sorting colloidal doublets from colloidal singlets, is to have more information about the random packing fraction of mixtures of the two. It is known that the random close packing fraction of spheres is known to be close 64%. Similarly the random close packing fraction of spherical doublets is known to be close to 57%. It is unknown what the random close packing fraction of a mixture of singlet and doublet particles is. The random close packing fraction is important not only for the sorting of colloidal doublets from colloidal singlets but also for the general understanding of the behavior of the mixtures. Working on the macro scale the random close packing fraction of mixtures of “singlets” and “doublets” was found. Plastic BBs were found to be extremely uniform in diameter and in mass. The diameter was found to be 5.896 ± 0.024 mm and the mass was found to be 0.1105 ± 0.0032 g. Two BBs super glued together formed “doublets”. The random close packing fraction can easily be found using the mass and diameter of the BBs. The random close packing fractions of the “doublets” alone and “singlets” alone were verified to be 63.83 ± 0.79% and 57.41 ± 0.46% before finding the random close packing fraction of a mixture of “singlets” and “doublets” at different concentration. The ultimate goal of a graph of the random close packing fraction of a concentration of “doublets” in “singlets” ranging from 0 to 100% was found to be linear with doublet concentration.

Fracture at the Nanoscale Denys Zhuo

Department of Material Science and Engineering, Massachusetts Institute of Technology

Sandeep Kumar, Dr. Aman Haque (advisor) Department of Mechanical and Nuclear Engineering, Penn State University

This project aims to develop a micro-electro-mechanical systems (MEMS) device as a tensile testing setup for ultra thin specimens (3-5 nm) of glassy carbon for use in Transmission Electron Microscope (TEM) in order to study fracture mechanisms. In this research, we will use nanofabrication and innovative design principles to miniaturize a mechanical testing device to a 3x5 mm size. The technical contribution of this research is a unique experimental technique that can (i) perform tensile/fracture testing of nanoscale materials with virtually no restriction on specimen thickness/size and (ii) for the first time, provide qualitative (TEM visuals) description of microstructural changes behind the deformation mechanisms at the nanoscale as the quantitative information (stress and strain) is acquired simultaneously. Using this technique, we will study the mechanics of fracture in 3-5 nm thick freestanding glassy carbon specimens. Glassy carbon as a material is interesting because it allows for accurate control of sample thicknesses at the 1-10 nm length-scale. This material is chosen for its exciting applications as a molecular sieve or for use as a catalyst for gas separation. The scientific contribution of this research is that the fundamentals of fracture at extreme (1-10 nm) length-scales will be explored, both qualitatively and quantitatively.

I fabricated tensile testing devices and specimens and worked on integration of the ultra thin glassy carbon samples into the device setup. I will be helping in the testing of the devices in TEM at magnifications of 150,000-200,000x in order to understand how the material fails at very small scales. Through this project, I have gained invaluable experience in the use of cutting edge nanofabrication and electron microscopy tools, an understanding of the realistic aspects in the execution of research principles, and the need for effective communication.

Direction Reconstruction of Cascade-like Events in IceCube Deep Core Michael Prikockis

Department of Physics, Penn State University

Patrick Toale, Tyce DeYoung Department of Physics and Center for Particle Astrophysics, Penn State University

Description of project and the work performed: The IceCube Collaboration (including myself with 250 people world wide) seeks to utilize a particle detector stationed in Antarctica to enhance their understanding of the universe via neutrinos. These low mass particles interact with particles in ice to produce charged leptons that exceed the speed of light in ice. This causes the radiation of a blue light cone, called Cherenkov radiation, often likened to the Mach cone of a sonic boom. Since neutrinos are extremely small and uncharged, they travel through most mediums in straight lines without interaction and therefore make the perfect astronomical messenger. By reconstructing their paths, we can glean new information about the emission sources of these particles. Muon neutrinos will interact and produce muons which have a long track through the detector. As such, we can obtain angular resolution to about one degree. Electron neutrinos, however, produce electrons which causes electromagnetic cascades of many particles. Therefore, angular resolution is not as clear. The present reconstruction techniques for cascades were tested using data from Monte Carlo simulations of events specifically in IceCube Deep Core. This revealed a systematic time shift of the reconstructed time to 160ns later than the true time. Unsure of the cause, we turned to Markov Chains to explore the likelihood space in a series of discrete steps. To do this, we allowed the probability of taking a step to be given by the ratio of the likelihoods. 1,000,000 step Markov Chains were run on a handful of events, and much was learned from the results. First, we discovered that the time offset was not caused by the fitter or minimizer. Second, even though the likelihood for the direction often has strange structure, the minimizer still seems to find the same solution as the Markov Chain. While not too far off, this solution is displaced from the truth value, implying a problem with our model. In our reconstructions, we assume a point source for a finite length cascade, which could distort the likelihood space. There could also be a problem with our model of the ice. We do not yet have much experience with ice at this depth in IceCube. This project reminded me that research often does not go as planned.

Cosmic Ray Electron Synchrotron Telescope (CREST) and

Cosmic Ray Energetics and Mass (CREAM) Daniel Pearson


Tyler Anderson, Matthew Geske, Dr. Stephane Coutu Department of Physics, Penn State University

Description of project and the work performed: The Cosmic Ray Electron Synchrotron Telescope (CREST) project aims to compare the spectral shape of high-energy electrons ( >2 TeV) to the number of nearby sources and their distribution of distances in order to improve our understanding of cosmic ray sources and propagation. The Cosmic Ray Energetics and Mass (CREAM) project will test and improve current models of particle acceleration in supernova shocks which predict a decrease in the proton spectrum at about ~ 100 TeV. By gathering more high-energy proton data than any previous balloon-flown experiment, CREAM will make it possible to distinguish such a feature if it exists. I have soldered components on to circuit boards for CREAM, tested functionality of such boards with an oscilloscope and multimeter, prepared “veto paddles” which allow CREST to differentiate between electron-in duced events and charged cosmic rays, and tested photomultiplier tubes that CREAM uses to detect light emitted when high-energy charged particles pass through scintillator paddles. Working on these projects has made me proficient in various useful skills such as soldering and oscilloscope use. Furthermore, I have made great strides in understanding how research teams divide up work, yet maintain frequent and close collaboration to maximize results.

Amphiphilic Micro/nano-particles for Advanced Oil Recovery

Isamar Ortiz Rivera Department of Chemistry, University of Puerto Rico at Cayey

Samudra Sengupta, Hua Zhang, Dr. Ayusman Sen Department of Chemistry, Penn State University

The oil recovery process has three stages. In the primary and secondary stages only 35% of the oil in the reservoir can be withdrawn. Various new methods to increase oil recovery during the tertiary, or enhanced oil recovery (EOR), have been suggested and practiced. Chemical flooding involves the use of surfactants, which are amphiphilic by nature, to reduce the interfacial tension between oil and water and to increase the wettability of the rock surfaces. The objective of this research is to achieve similar results by using micro/nano-particles. Our preliminary studies involved comparing the effectiveness of gold/polystyrene (Au/PS) Janus particles and a traditional surfactant, sodium dodecyl sulfate (SDS), in displacing an oil column in a glass capillary tube. The Janus particles are prepared by half-coating polystyrene particles with gold. Our preliminary results showed that Au/PS Janus particles and Au/PS-CONH-n-C12H25 particles are qualitatively comparable to a 2 mM SDS solution in their effectiveness at displacing an oil column in a capillary tube. A quantitative analysis of the effectiveness of the particles for advanced oil recovery will be studied by using the Washburn set up. Briefly, the method involves measuring the amount of oil displaced in a column packed with kaolin powder soaked with oil. Monodisperse silica nanoparticles were synthesized. The synthesized nanoparticles will be functionalized and a quantitative analysis of their effectiveness in EOR will also be studied. If the amount of oil recovered using these particles is comparable to that of SDS solution, these particles could be used instead of surfactants in the oil recovery process. The advantage of this modification resides in the reusability of these particles, which will reduce the cost and increase the effectiveness of oil-recovery.

Fabrication of a Single Electron Transistor (SET) Scanning Probe Christopher Olds


Neal Staley, Conor Puls, Dr. Ying Liu Department of Physics, Penn State University

Scanning probe microscopy (SPM), in its various forms, is a primary technique used in

the quantitative analysis of surfaces. The single electron transistor (SET) can serve as the basis for a SPM probe which allows for the characterization of electrochemical potential on the surface of a sample and beneath it. A SET has four basic components: A source and a drain, both of which are metals or semiconductors, separated by a thin region of insulating material which contains a small conducting island, and a gate, which is capacitively coupled to the island. The electrical potential of the island is tuned by the gate voltage. The varying potential of the island determines how large a current can flow between the source and drain, and thus the rest of the circuit. SETs have been created in the past using mainly lithographic techniques, but this process is ill suited to fabricating scanning probes. Therefore a novel method of SET production is required if its unique properties are to be utilized in a measurement device.

The most important part of the scanning SET microscope is a sharp SET tip. In our design, it is made from a borosilicate rod drawn in a micropipette puller. This tip is then coated with two thin gold layers, with an insulating layer of aluminum oxide in between. A focused ion beam (FIB) is used to cut the tip, exposing both gold layers. The gold layers are attached to external voltage sources, forming the source and drain. A gold nanoparticle placed on top of the insulator with 3-Mercaptopropanoic acid (3-MPA) connecting it to the aluminum oxide layer serves as the island. The gate, whose potential modulates the flow of current in the circuit, is the sample being scanned. Variations in the electrochemical potential of the sample in the vicinity of the tip will be accompanied by variations in the current in the circuit, allowing for accurate measurements of the electric properties of a wide variety of solids with greater spatial resolution than is currently possible. This greater resolution is realized because of the extremely small size of the nanoparticle, and the very small (<100nm) size of the tip itself.

The SET tip must first be perfected if it is ever to be implemented as a good scanning device. Dr. Liu's group has previously demonstrated that it is possible to manufacture tips with the pulling method and achieve uniform cuts with the FIB. However, tip quality must be improved to provide the needed resolution, and methods for coating the tip need to be perfected before any attempts can be made to attach the nanoparticle and complete the probe. My work consisted of determining the settings on the micropipette puller which produce the best quality borosilicate tips, finding the most efficient and uniform way to coat the tips with two layers of gold and a layer of aluminum oxide in between, determining the optimum location of the cut to be made with FIB, and finding a way to attach a single gold nanoparticle on the aluminum oxide.

Mololayer, Bilayer and Hybrid Graphene Candice Murray

Department of Physics, Massachusetts Institute of Technology Eric Hao

College of Engineering, University of California at Berkeley Neal Staley, Conor Puls, Greg Harkay, Professor Ying Liu


The recent discovery of graphene, a material composed of a single atomic layer of graphite, has caused a large amount of interest. In addition to being an excellent testing ground for many quantum effects, graphene shows great promise in the area of electronics. Because it is such a young field, many of the properties of graphene have not yet been fully explored. It has been found that the behavior of graphene varies greatly depending on its thickness. Whereas bulk graphite behaves as a semimetal, single layer graphene exhibits Dirac-like properties. Adding a second layer of graphene and applying a voltage allows for the opening of a band gap, which could be useful in transistor applications. Subsequent layers cause comparable changes.

Bilayer graphene was the focus of this project. In order to study it, the graphene was made into four-point tunnel junction devices. This process involved placing a thin (approx. 1 μm) quartz filament across the graphene, allowing for the creation of two sides. Aluminum was then evaporated at an angle of 45 degrees and allowed to oxidize, forming a tunnel barrier. The sample was then rotated by 90 degrees, and gold was evaporated to form an electrode. The filament was then removed and two wires were attached to each of the gold pads (for controlling voltage and current), and a fifth wire was attached to the side of the substrate (for controlling gate voltage). The device was then attached to a liquid helium dip probe, and placed into a dewar of liquid helium. Measurements of resistance vs. temperature and gate voltage and current vs. voltage were taken. However, due to long device production time and high device mortality no conclusive results were achieved. Improvement of method by either decreasing production time or decreasing the device mortality rate is needed.

Reflectivity of Silicon Nanowires for High Aspect Ratio Semiconductor (HARSH) Solar Cells Kelly McCutcheon

Department of Physics, Franklin & Marshall College

Haoting Shen, Dr. Eilzabeth Dickey Department of Materials Science and Engineering, Penn State University

Approximately half of the cost of producing traditional solar cells comes from their

requirement for a relatively thick, high-quality silicon wafer in which the incident photons are absorbed. These wafers must be thick to allow for maximum light absorption, but their thickness demands that quality silicon be used to avoid carrier losses. This project seeks to reduce the cost of solar cell devices by replacing the silicon wafer with an array of silicon nanowires. Because nanowires can be simultaneously thick in the direction of incoming light (along the axis of the wire) and thin in the direction of charge collection (the radial direction of the wire), they reduce the need for high-quality materials and may be a viable way to lower production costs of photovoltaic devices.

In order for nanowires to be effective in efficient solar devices, they must absorb as much of the incident light as possible. My role in this project has been to measure the reflectivity of the nanowire samples, which may allow us to infer their absorptivity. I measured both specular reflection and total reflection, and was able to confirm that the nanowire surfaces are highly specular reflectors. I also modeled the specular reflection from a silicon surface for a given angle of incidence using Fresnel’s equations for complex coefficients of reflection. This project has given me a good introduction to the overall process of research. For example, I learned about how to find procedures for common measurements, how data is shared and presented, and how different research teams cooperate on multifaceted projects. I was also introduced to many methods for materials characterization, and was able to use a few of them. This program also familiarized me with current trends in research, and helped me determine what I should do in the next two years to prepare myself for graduate-level study.

2009 Penn State MRSEC/Physics REU Abstract The Neurochip: An Advanced Nanomaterial for Small-Molecule Capture of Biomolecule Binding

Partners Michelle Martinez-Rivera

Department of Chemistry, University of Puerto Rico- Rio Piedras Campus Mitch Shuster, Department of Physics

Dr. Paul Weiss, Departments of Chemistry and Physics Dr. Anne Andrews, Department of Veterinary and Biomedical Science

Penn State University

Neurotransmitters are chemicals that are used to relay, to amplify, and to modulate signals between a neuron and another cell. This project focuses on studies of the chemical behavior of biofunctionalized monolayers. In order to study this phenomenon, we create self-assembled monolayers (SAM) of oligo (ethylene glycol) with terminal alcohol groups on gold surfaces. These layers are then modified with carboxyl groups that are afterwards exposed to NHS/EDC solution, producing an activated ester that is easily attacked by a primary amine group. The neurotransmitter, which contains a primary amine, is then added to displace the leaving group. After this procedure is done, we have a biofunctionalized surface. Coupling chemistries are verified by grazing angle FT-IR spectroscopy. In this experiment we made serotonin (5-HT) cycling in which we repeat cycles of the NHS/EDC and 5-HT steps until the IR spectra stabilize. After seven NHS/EDC and 5-HT cycles, the surface does not appear to be maximally functionalized. We used the IR to determine day-to-day variations and surface reorganization, tracking how spectral peaks vary when scanned at different times nominally without any chemistry being done in between scans. IR day-to-day intensity variation in serotonin pick is due to the molecules random reorganization in the monolayer surface. We determine the functionalization yield changes with acidification of the carboxyl. Rinsing with acetic acid converts carboxylate to carboxyl functional group which leads to a higher functionalization in the monolayer. These functional surfaces can be used to screen for receptor and transporter proteins for functionally directed proteomics, and for nucleic acid aptamers, which will then be utilized as molecular-recognition elements in the construction of novel nanosensors for in vivo neurotransmitter sensing.

Analysis of Low Energy Flasher Data in IceCube

Michael Larson Department of Physics, Penn State University

Dr. Brendan Fox, Dr. Tyce DeYoung

Department of Physics, Penn State University The IceCube experiment is a ground-breaking, high-energy neutrino telescope currently under construction at the South Pole with the goal of detecting neutrinos from extrasolar sources. The detector is constructed by deploying thousands of optical sensors between 1,450 and 2,450 meters in the deep, clear Antarctic ice. IceCube provides researchers with the opportunity to witness the rare collisions between neutrinos, virtually massless particles traveling at the speed of light, and matter. These neutrinos may contain new information about various astrophysical phenomena. The data that IceCube and its predecessor, the Antarctic Muon and Neutrino Detector Array (AMANDA), gather will contribute to our understanding of various aspects of particle physics and astronomy. To calibrate the detector, the collaboration flashes LEDs located on each optical module within the detector. This summer, I've worked on analyzing the data produced by by these flashes to identify any anomalies in the software reconstructions. My work has raised a few questions about the reconstructions which will eventually help to improve the effectiveness of our software. These improvements will be be used by researchers throughout the collaboration in their efforts to interpret the significance of the scientific conclusions derived from their future analyses of the neutrino data. Identifying and investigating the issues with the software reconstructions this summer has helped me personally as a researcher as well. I've developed my programming abilities and learned about particle physics. It has also given me experience working within a large, worldwide research collaboration that I may not otherwise have recieved.

Metallization for High Temperature Electronics

K. C. Kragh1, Brian Downey2, and Dr. Suzanne E. Mohney2

1Department of Physics and Optical Engineering, Rose-Hulman Institute of Technology 2Department of Materials Science and Engineering, Penn State University

With its wide band gap and large capacity for current and power, silicon carbide can replace silicon as the semiconductor for high temperature and high power electronics. This study investigated metallic capping materials that could withstand elevated temperatures, while maintaining a low sheet resistance. Sputtered gold-ruthenium films were monitored for agglomeration through microscopy and for sheet resistance through the van der Pauw technique. Low resistance pure gold films demonstrated significant agglomeration upon annealing at 600°C. Ruthenium was utilized in alloys to stabilize the gold films with limited increase in resistance. Co-sputtered gold and ruthenium films underwent agglomeration and an increase in sheet resistance after prolonged annealing. Pure ruthenium, however, withstood agglomeration through fifty hours of annealing while sustaining an acceptably low sheet resistance. Ruthenium also demonstrated better adhesion than gold-based films. Despite the popularity of gold, a capping layer of 150nm of ruthenium provides high-quality adhesion and low resistance through continued annealing at 600°C.

Cross-Scale Dynamics of an Acute Infectious Disease in Virtual Hosts Paul Jeffe


Kim Pepin, Igor Volkov, Bryan Grenfell, Department of Biology, Penn State University

Jayanth Banavar Department of Physics, Penn State University

The goal of the project I am working on is to model the spread of acute viral infections, such as the influenza virus. This includes the replication and spread of a virus within a host, and the interactions between hosts in a particular network structure. Differential equations describe growth and competition within hosts, and the virus is transmitted between hosts depending on the rules inherent in a programmed network. In particular, we are looking to assess the effects of the within-host dynamics on the spread of a virus on the population level. The results of this research will help in the development of vaccination programs, as well as to help predict the risk and intensity of outbreaks.

My contribution to this project has been to set up the within-host model. This involves looking for and developing differential equations with biological relevance, and analyzing them in terms of how they would potentially affect the dynamics of the network. In the future, I will also be programming the structure and rules of the network and running simulations of an infection in the network. This research has given me a lot of experience in computer modeling, which is something I have never done before. In addition, I gained a lot of experience doing computer programming, which will be useful in any future research endeavor I might embark on.

Modeling of Guard Cell Closure in Response to Fluctuating Abscisic Acid Signaling Philip Hochendoner


Réka Albert Department of Physics, Penn State University

The hormone Abscisic Acid (ABA) is produced by plants to prevent the loss of water and facilitate the exchange of carbon dioxide for oxygen during a drought. Drought conditions are a serious threat to plant life and subsequently to those who work in the fields of agriculture, biomedicine, and biology. This research concentrated on using a dynamic Boolean model with fluctuating signals of ABA to depict a realistic drought environment. This model benefits those who work with plants in order to know what conditions we can and cannot adjust to prevent plant deterioration and death. In this model, a network of nodes and edges represent ABA, enzymes, proteins, small molecules, ion channels, stomata and their interactions. Each node is in either the state ON or OFF and affects other nodes depending on their interactions and state. The state changes of the nodes are dictated by a list of dynamic rules that represent the propagation of the signal of ABA and are implemented asynchronously (in a random order). This model was generated using a Python library known as Boolean Net which was created for the purpose of Boolean modeling of several different biological systems. While previous work studied constant ABA signaling (Li, Assmann, Albert, 2006), this summer research focused on fluctuating signals and their repercussions. This was done by gradually increasing the probability of the ON state for ABA by 10% every ten time steps. This gradual increase gave us a realistic representation of drought conditions. As the drought continued, we observed the percent of stomata closure increased consistently along with the percentage of ABA. We also witnessed the breakdown of different knockout mutations into two distinct groups. These groups were either indistinguishable from the Wild-Type plant or had nearly 0% closure for all percentages of ABA. This gives a better understanding of how the knockout mutations have an effect on the closure of the stomata. Through this we have opened a new path to further research in the fields of agriculture and biology.

Raman Topography Studies of Graphene Flakes Eric Hao

College of Engineering, University of California, Berkeley Conor Puls, Neal Staley; Ying Liu

Department of Physics, Penn State University It was previously believed that a single 2-dimensional layer of material couldn’t be stable enough to observe and study. Only recently has graphene—the name given to a single layer of

sp2 bonded carbon atoms—been "discovered" experimentally. It is essentially an infinite plane of hexagonal benzene rings. Graphene, in particular, is intriguing for device prospects because it has extremely high electronic mobility at room temperature, can sustain large amounts of current, and has a breaking strength that is two hundred times stronger than steel. There are various methods of creating graphene, one of which is to exfoliate flakes of graphene from bulk graphite, useful for studying fundamental physics. Additionally, it can come in different layers, all of which exhibit different electronic properties. Therefore, it is imperative that we know exactly what we are working with. In essence, we have to use a method to identify and quantify the graphene flakes we work with. The goal of my project is to determine exactly the properties at each region of the graphene. The main technique we used is Raman Spectroscopy, which gives information about a single spot size of about 300 nanometers. A laser light is shot at the sample and scatters the light. Electrons excited by incoming photons interact with the phonons in the material and the energy of the resultant scattered light is shifted. We can measure data from this "Raman shift" and observe different peaks resulting from different Raman active modes. From the position and the shape of the peaks we can determine other characteristics such as charge carrier and strain in the graphene flakes. We used a data analysis program to process the data and determine the graphene properties. The laser spot was scanned over the entire graphene flake and a Raman spectroscopy map of the flake was created.

2009 Physics REU Abstract Form

Self-Assebly of Two Componet Metal Nanowires Pedro J. Gonzalez

Department of Chemistry, University of Puerto Rico Benjamin Smith and Dr. Christine Keating

Department of Chemistry, The Pennsylvania State University Complex and functional particles, such as multicomponet nanowires, have been

synthesized, however, the assembly of these systems has not yet been well studied. Understanding the high-density self-assembly of nanowires could point to improved methods of constructing higher-order structures. Being aware of this assembly is a crucial step in controling the integration of versatile bottom-up assembly methods with the more well established top-down assembly methods, thereby eventually offering superior function and high assembly yields. Unfortunately, complex nanowires assembly approaches often fail due to other interactions between nanowires such as van der Waals interactions and electrostatic forces. Due to the interactions present between the nanowires, however smectic arrangements are observed when wires are allowed to settle out of aqueous suspension. When two component wires (e.g., gold-silver wires) are assembled, ordering within smectic rows is seen (gold sections neighboring gold sections) and can be classified by an ordering parameter called S3. Some work has been done to understand the forces responsible for this phenomenon. With this understanding, better methods of assembly can be developed, so in the future more complex structures can be formed by combining both top-down and bottom-up methods.

Nanowires for this work are created by electrochemical deposition and are subsequently coated with either MESA (2-mercaptoethane sulfonic acid) or DNA. Assemblies are completed on glass cover slips separated by a silicone spacer and viewed using an inverted optical microscope. This research sought to fulfill two goals. Our first goal is to fabricate silver-rhodium nanowires instead of silver-gold ones. The interactions between silver and rhodium are more similar than that between gold and silver. After fabricating the wires, they were coated with MESA and analyze their orientational order, calculating S3 value and comparing them to the silver and gold nanowires to look for less orientational ordering. Second, the MESA coating of wires provides the electrostatic repulsion important for assembly, but does not offer any additional functionality. Therefore, the second goal of the research is to find more functional coatings. The gold-silver nanowires were coated with DNA, which has numerous biological applications, and assembled.

The results from my work that, first, the techniques used to synthesize Ag – Rh have not been effective to develop a homogenous size distribution for this type of wire. Additional work is needed in this area. Second, it was observed that DNA works as a coating material; the same smectic rows observed with MESA coated wires were seen. Selected samples with DNA even show better orientational ordering than samples previously made with MESA coating. Still, new samples must be produced in order to be able to determine the best assembly parameters. These conclusions will serve as a first step to incorporate these nanowires as more useful and functional structures.

Synthesis of silver nanoparticles to apply in the enhancement of the two photon absorption of non-linear liquids

Jaritza Gómez

Chemistry Department, University of Puerto Rico at Cayey

Thomas Mallouk1, Junbin Huang2, Iam-Choon Khoo2

Departments of 1Chemistry, 2Electrical Engineering, The Pennsylvania State University

Optical computing (logic without electrons) requires new materials that can be switched between transparent and opaque states with input of light. The expansion of high power lasers also requires sensory protection devices that can prevent laser damage. The neat liquid 4-propyl 4’-butyl diphenyl acetylene (L34. Figure 1) is of interest for these applications because of its non-linear optical properties. It shows a high transmittance in the visible region, but it shows a two-photon absorption (2PA) and a 2PA-induced singlet and triplet excited state absorption. The 2PA absorbance has been found to depend strongly on the intensity of the incident laser (attenuating of the laser power as it passes through the liquid), but the switching effect is still ineffective for low power or long laser pulses. Electronic structure calculations show that the 2PA triplet should have a maximum absorption at 470nm. A hybrid materials approach is plausible to enhance the absorption in that region and greatly enhance the nonlinear response: silver (Ag) nanoparticles exhibit an absorption peak at different wavelengths near 400nm dependent on the particle size and morphology.

The synthesis of Ag nanoparticles has been achieved through the polyol method using silver nitrate as the source of silver ions, ethylene glycol (EG) as the reducing agent and polyvinylpyrrolidone (PVP) as the capping ligand. TEM imaging confirmed the formation of Ag nanoparticles and UV-VIS confirmed maximum absorption in the expected region: 416nm. With the goal of transferring the particles from EG to non-polar organic solvents, sodium oleate was employed; it proved effective to remove PVP, but not effective as a capping ligand for Ag. Following the removal of PVP with addition of thiols or amines was also ineffective. Future work includes optimizing the synthetic process as well as the phase transfer method and measuring the optical properties of Ag/L34 solutions.

Figure 1: Molecularstructure of L34

Precision RUS Device Measures Elastic Coefficients with Minimal Load Conditions Kurtis Gills

Department of Physics, Westminster College GouXing Liu, Dr. J. D. Maynard


Many bridges and buildings have characteristic natural frequencies which depend upon the elastic constants of the framework’s stainless steel. A strong wind or an earthquake which drives one of the normal modes of the structure will drastically increase the amplitude resulting in structural damage.

The objective of this project was to build a device which could precisely and accurately measure elastic constants using a method that inverts the phenomenon of natural frequencies. That is, a measurement of the natural frequencies is used to determine the elastic constants. This method is known as Resonant Ultrasound Spectroscopy (RUS). The project involved constructing a precision RUS device, with which the elastic constants of exotic solids can be accurately and robustly determined. The design incorporates a delicate balance arm for minimizing load conditions imposed on the solid.

The RUS method uses two acoustic transducers to measure a solid’s natural frequencies. One transducer is a driver and the other is a receiver. The driving transducer sweeps over a range of frequencies while the receiving transducer records peaks at the solid’s natural frequencies. The RUS method compares the measured natural frequencies with natural frequencies calculated numerically. The theoretical data is obtained using assumed elastic constants; by adjusting the assumed constants to match the calculated frequencies with the measured ones, the actual elastic constants of the material are determined. The theoretical calculation of the natural frequencies is accomplished using a finite element method. The equations for the modes of vibration are solved by dividing the structure into a large number of small elements.

Two important features of this RUS device are that it provides both precise and accurate measurements of elastic constants. The precision is determined by a high quality factor Q. With a stainless steel sample, our measured quality factor was 4000, comparable to a tuning fork, an excellent frequency standard. Our high Q indicates that our low loading is successfully preventing energy drain from the resonating sample. The means of obtaining accuracy follows from adding weight to the balance arm; this weight will have two opposing effects: it increases the amplitude of the resonance; yet, it shifts the location of the resonance. The shift in resonance is due to an increase in load conditions. However, by simultaneously removing weight and recording the natural frequencies, the load can be extrapolated to zero; thus, an accurate measurement of elastic constants is achieved.

With minimal load conditions, accurate and precise elastic constants of exotic solids can be determined. The elastic constants obtained through this device and the RUS method enhance our understanding of atomic structures through vibrations; it is these good vibrations that ultimately resonate in our minds.

Morphology Development and Properties of Thin-Film Polymers

Kevin Donaher Department of Physics, Simon’s Rock College

Stephanie A. Petrina, Michael A. Hickner

Department of Materials Science and Engineering, Penn State University In order to function, a proton exchange membrane fuel cell (PEMFC) requires a membrane that selectively allows for the passage of protons, while remaining electrically insulating. One way to accomplish the required proton transport is to use a sulfonated self-assembling block copolymer. The negative charge of the sulfonate groups should cause the desired selective permeability for the positively charged protons and the high density of sulfonate groups in a block copolymer is targeted towards achieving high conductivity.

It is likely that the morphology of the film affects the conductivity, however, before the conductivity-morphology connections can be determined, there must be a reliable way of inducing and monitoring the phase behavior of sulfonated polymers. My work seeks to test ways to control the morphology of the films and to use field emission scanning electron microscopy an atomic force microscopy to characterize the resulting structures. My previous studies have shown that it is possible to anneal unsulfonated films with heat or solvent to achieve more ordered morphologies. With unsulfonated poly(hexyl methacrylate)-b-poly(styrene)-b-poly(hexyl methacrylate) (PHMA-b-PS-b-PHMA) triblock copolymer film, I observed a transition from a disordered morphology in the as-cast state to lamellar and cylindrical morphologies after annealing. For the sulfonated triblock PHMA-PS-PHMA films, thermal annealing and vapor annealing with DMF did not produce a noticeable change in the morphology of the as-cast film. It is hypothesized that the strong ion pairing interactions of the sulfonates and high Tg of the sulfonated phase prevents the block copolymer from forming an ordered morphology. From this project I expect to gain experience with polymers, lab safety, experimental and clean room procedures, and characterization equipment.

Synthesis and Characterization of Bismuth Selenide Nanowires Janie L. De Santos

Department of Physical and Life Sciences, Texas A&M University-Corpus Christi REU Program, Center for Nanoscale Sciences, Pennsylvania State University

Meenakshi Singh, Dr. Mingliang Tian, Dr. Moses H.W Chan


Recent study is motivated by the theoretical prediction that p-type Bi2Se3-based material

is one of the prime candidates for the study of topological surface states. The character and stability of the surface states in Bi2Se3 at room temperature has motivated the suggestion that they may be useful for not only thermoelectronics but quantum-computing applications. The purpose of this project is to produce high quality single-crystal Bi2Se3 nanowires and study their electrical transport properties in low temperatures. An existing method for crystal bismuth selenide nanowires growth involves a complicated protocol therefore this research attempts to develop a method to grow single crystal bismuth selenide nanowires using the simple and inexpensive template-based electro deposition method.

In this research we use DMSO organic solvents versus aqueous solutions and grew the

nanowires under different temperatures. The wire structure using XRD and imaging of the wire morphology using SEM/TEM for characterization were done. The solution preparation was varied from organic to aqueous which does not introduce any new peaks into the wires’ XRD patterns, but depositing at higher temperature gives wider variances in the orientations of the grains. Also, in TEM phase separated Bismuth Selenide

nanowires

were obtained, initial transport measurements and, physical characterization were performed. Future work is to produce a single phase BiSe nanowires by testing organic or aqueous solution with varied volumetric concentration of Bi to Se. Further study will include studying the physics of the nanowires by measuring their electronic transport properties at low temperatures.

Electron spin lifetimes in II-VI and III-V semiconductor epilayers and quantum dots Terence Bretz-Sullivan


Benjamin Cooley, Dr. Nitin Samarth Department of Physics, Penn State University

Description of project and the work performed: This project is designed to investigate electron spin lifetimes in II-VI and III-V semiconductor epilayers and quantum wells. We employ the property of the depolarization of electron spin in a transverse magnetic field, known as the Hanle Effect, to study electron spin lifetime. To do this, we excite electrons into the conduction band of the semiconductor with circularly polarized light. Circularly polarized light carries angular momentum which is imparted to electrons via the conservation of angular momentum upon absorption of photons by sample. Hence, the electrons become polarized along the direction of observation due to circularly polarized light. The presence of an in plane magnetic field causes the polarized electrons to precess. The degree of circular polarization of the photoluminescence, a function of the Larmor frequency and the applied magnetic field, is measured and plotted to form a Lorentzian shaped curve known as the Hanle curve. By measuring the polarization at zero magnetic field and the half width of the curve at half maximum, we can calculate the spin lifetime. We then measured the spin lifetime at decreasing laser pumping powers and plotted a linear fit of the inverse of the spin lifetimes versus the pumping power. The spin lifetime of the sample at zero pumping power was extrapolated via the linear fit. Long electron spin lifetime is critical for applications in spin transport electronics (“spintronics”). These technologies have the potential to revolutionize computing by increasing speed and efficiency and decreasing power usage in semiconductor chips.

For this project, I set up optical instruments, such as linear polarizers, quarter wave plates, a photo elastic modulator, and a diode laser, for carrying out the experiment. I’ve learned how to operate instruments, such as a lock-in amplifier, a photon counter, a spectrometer, and an electromagnet, necessary to take measurements. In addition, I’ve programmed and operated instruments in the Labview programming language and used IGOR graphing and data analysis software. Both setting up equipment and learning measurement techniques are vital tools for the experimental physicist.

How Does Frustration Affect Spin Orientation? Jason Bartell

Department of Physics, Pennsylvania State University

Jie Li1, Sheng Zhang1, Dr. Peter Schiffer1 1Department of Physics, Pennsylvania State University

Frustration is defined as the inability of a system to simultaneously minimize the interaction energies between its components. Normally, the interaction is between neighboring spins in a material. Spin frustration is caused either by competing interactions among the spins or by the geometric arrangement of the spins in the lattice. This latter case is known as geometric frustration and is seen in spin ices. The complex interactions involved in this geometric frustration are the subject of our study. Examining the individual spins in spin ice materials without disturbing the system is difficult. To remove this complication, our group has developed artificially frustrated systems. These systems consist of single domain, ferromagnetic islands. These islands are large enough to be imaged with magnetic force microscopy (MFM) techniques and have stable magnetic moments at room temperature. We have studied several different frustrated arrangements. In all of them we have seen a larger percentage of islands in low energy configurations than would be expected if the arrangements where purely random. This confirms that the interaction energy of the islands affects the dynamics of a frustrated system. To better understand these dynamics, we compare three different systems in a magnetic field. 1) Islands that interact only with the magnetic field. 2) Islands that interact with each other and the magnetic field, but are in a non-frustrated array. 3) Islands that interact with each other and the magnetic field and are in a frustrated array. Ultimately, we hope to be able to predict the island orientations of frustrated systems in a magnetic field.

Ryan Atwater Department of Physics, University of Maryland – Baltimore County

Alejandro Suarez, Dr. Jorge Sofo


A sheet of carbon one atom thick, graphene has fascinated physicists because of its remarkable physical strength as well as its electric and thermal conductivity. Now scientists have discovered a new material called graphane by adding hydrogen atoms to graphene. Graphane, an insulator, could possibly be used as a means of hydrogen-storage to help hydrogen-powered vehicles run more efficiently. More attention, however, has been devoted to using graphane to help make electronic devices. If hydrogen atoms were removed from certain areas of the hydrocarbon, this would form channels of graphene. Once a voltage is applied to the channels, the graphene would function as a semiconductor. Consequently, some researchers believe that graphene could eventually replace silicon as a way to make transistors. This summer, using a simulation program called Materials Studio, I have determined the lattice constant at which the energy is minimized for both graphene and graphane. My results indicate that graphane has a larger lattice constant than graphene. In addition to this, as the graphene sheet becomes less hydrogenated, its lattice constant decreases. Furthermore, I have also determined that the location of the hydrogen atoms on graphene determines the lattice’s minimum energy.

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