Proposed Undergraduate Research Areas

Microresonator Optics

Prof. Albert T. Rosenberger directs a program in experimental and theoretical optical physics involving investigation into the fundamental properties and technical applications of optical whispering-gallery modes (WGMs).  A fused-silica microresonator (sphere or cylinder), less than one millimeter in diameter, has many WGMs, each with a very high Q (sharp resonance) and an evanescent portion extending outside the microresonator.  Light from a tunable laser is coupled into a WGM by optical tunneling from a tapered fiber and makes many circuits just inside the surface of the microresonator, where it is trapped by total internal reflection.  The WGM frequency can be tuned and locked to the laser by compressing the sphere or stretching the cylinder.  Interaction of the evanescent part of the WGM with the ambient or with a nanocomposite thin-film coating on the microsphere has enabled Dr. Rosenberger’s group to investigate applications such as the following:

These investigations are quite appropriate for the participation of undergraduates, and projects for REU students can be tailored to include experimental work, numerical analysis, or both.

Nanotechnology

Prof. Bret Flanders

Figure 1.Employing spontaneous assembly in the formation of targeted nanostructures holds promise as a revolutionary approach to shrinking the dimensions of electronic components to (as low as) the diameter of the building block (~3nm). The key to understanding spontaneous assembly in nanoparticle populations is knowledge of their interparticle potential. A series of recent studies suggests that dipolar interparticle interactions will play a significant role in the spontaneous behavior of semiconductor nanoparticle populations. For example, the 1999 report of Shim and Guyot-Sionnest predicted that permanent dipole moments are expected in all dielectric nanoparticles. However, a working knowledge of how the experimental parameters can be used to tailor the phase structure in 2D populations of semiconductor nanoparticles is entirely lacking. The objective of this project is to develop ways of reproducibly manipulating nanoparticle populations of metallic and semiconductor nanoparticles in order to fabricate nanoscopic circuitry with targeted properties in a scalable manner. The successful attainment of this objective will enable further characterization of these structures to be performed, which will be necessary in order to identify viable applications for these potential electronic components. Suitable projects for an undergradute student research lie in the following areas.

Fabrication of Interconnects Composed of Gold Nanorods. The idea here is to dielectrophoretically fabricate interconnects composed of gold nanorods, as described in the caption to Figure 1. We will use populations of gold nanorods that are ~50nm in length and ~20nm in width, facilitating characterization via scanning electron, transmission electron, and near-field microscopies. To improve our control over the structural properties of the interconnects, we are in the process of implementing custom circuitry to reproducibly perform the voltage application and termination steps of the dielectrophoretic assembly process. Thus, by employing a highly uniform population of nanorods, lithographic electrodes with negligible sample-to-sample variation in the electrode geometries, and these customized electronics, we expect to assemble single chains of gold nanorods that are electrically interfaced to the electrodes. While this goal is ambitious, it is important to note that we have already demonstrated the dielectrophoretic fabrication of few-particle wide chains of gold nanorods (see the inset to Figure 1A). Here we simply propose to expand upon our skill in order to reproducibly fabricate single chains of nanoparticles.

Raman Scattering Studies on Functionalized Carbon Nanotube Thin Films

Prof. J. P. Wicksted

Dr. Wicksted has been conducting resonant Raman scattering measurements on single-walled carbon nanotubes (SWNT). He is particularly interested in studying changes to the radial breathing Raman modes and the disordered and tangential Raman lineshapes for different types of processed nanotubes, as well as for nanotubes that have been chemically functionalized. In particular, polymer wrapped functionalized SWNTs have indicated some changes in these Raman peaks indicative of debundling of SWNT complexes. We have also noticed a clear difference in the spectral position of the tangential mode (the G-band) of the pristine/polymer spectrum as compared to that of pristine material. In the pristine sample spectrum, the G-band is peaked at ca 1583 cm-1 and is up-shifted to 1592 cm-1 in the presence of polymer. The nature of this G-band resulting from the tangential stretching of the C-C bonds suggests that this band is sensitive to any surface modification of the nanotubes. The fact that this band shifts to higher frequencies in the presence of the polymer can be used as a further indication of the wrapping mode of interaction of the polymer around the nanotubes. Changes to the surface of the nanotubes are further indicated by the increased Raman intensity ratio of the disorder D-band to the G-band in the presence of the polymer. Careful investigation of the different Raman bands of SWNT's in the presence and absence of polymers gives valuable insights about the modes of interactions of polymers with carbon nanotubes.

New Raman measurements will be conducted on functionalized nanotubes both before and after embedding them within polymer matrices Additional work will be conducted on different functionalized and prepared nanotubes, including films. For the Raman measurements, samples of both pristine SWNT's and pristine/polymer mixture will be prepared by drop coating on a clean silicon substrate surface. In brief, a drop (~ 25-35 mL) of each solution will be added on the surface of two separate substrates and dried under 80 oC to yield a solid coating on the surface. This process will be repeated for each sample several times to yield thicken films. Finally, films using functionalized SWNT complexes will be prepared via the Layer-By-Layer technique.

All Raman studies will be conducted using a macro/micro Raman facility located on the fifth floor of the Physical Sciences Building. This facility consists of an Olympus microscope with three objectives (10X, 50X, 100X) providing a spatial resolution down to 20 microns along with a double grating spectrometer with two 1800 grooves/mm holographic gratings, which will allow the bacterial-gold nanoparticle dispersions to be studied. A macro chamber for bulk samples and colloidal solutions is also available. Other equipment includes an Ar+-ion laser operating at 514.5 nm, optics table, PC computer, control system, and a photomultiplier tube with thermoelectric cooling unit. A helium neon laser with line excitation at 633 nm is also available. Measurements will be performed with a laser power varying from 2 to 10 mW at the sample in order to study changes in the surface kinetics as a function of laser heating.

THz Bandwidth Optoelectronics

Prof. Alan Cheville

The spectral region from 300 GHz (l = 1 mm) to 30 THz (l = 10 mm) has been one of the last to see extensive development due to the difficulty of achieving these frequencies by optical or electronic means. Traditionally this spectral region has been accessed by frequency mixing, far infrared gas lasers, and Fourier Transform Spectroscopy. Although both electronics and optics have pushed their boundaries into the far infrared region, recently there is much interest in using a synthesis of ultrafast optical and electronic techniques, THz optoelectronics, to generate sub-picosecond electromagnetic pulses. These pulses, which can be propagated through free space or on micron scale transmission lines, have continuous bandwidths that extend from microwave to far-infrared optical frequencies. Terahertz optoelectronics is an active and rapidly growing area of research which is finding applications across a wide range of disciplines including imaging using raster scanned and single shot electro-optical techniques, fundamental and applied spectroscopy, in situ spectroscopy of combustion, combustion products and high temperature water vapor, noncontact characterization of semiconductors, and fundamental studies on molecular dynamics in liquids. This list of applications spans many disciplines. As such there are opportunities for undergraduates to obtain research experience in a truly integrative environment.

The specific applications of THz optoelectronics in which the REU students will conduct their investigations are electromagnetic scattering measurements and using THz radiation for nondestructive evaluation. THz bandwidth pulses have found application in direct scattering measurements as a potentially simple way to identify complex targets by the late time response. The sub-picosecond temporal resolution permits accurate time gated measurements for fundamental investigations of scattering mechanisms and has enabled the first direct experimental observations of fundamental surface wave velocities, loss mechanisms, and Gouy phase shifts. REU supported students will be incorporated into a research program which is investigating the use of THz impulse ranging techniques for imaging using inverse synthetic aperture radar (ISAR) algorithms. Images of an object are reconstructed by measuring a phase coherent scattered electromagnetic field at many discrete points over an image plane. The optical analog to this is holography in which the interference between scattered and reference optical waves is recorded in film.

Control of Light by Light

Prof. Girish Agarwal

The propagation of light through a medium depends on the optical properties of the medium like its refractive index, absorption and the nonlinear susceptibilities. The latter are especially important if the light field is intense. The coherent fields can be used to manipulate the optical properties of the medium. This therefore results in the control of light by light. In recent times many fundamental contributions to this subject have been made, for example Hau et al demonstrated the ultraslow propagation in a Bose condensate and the groups of Scully and Budker produced ultraslow light in a hot gas. Further Lukin’s group proposed and demonstrated storage and retrieval of light. However much of the previous work relates to the group velocity of the pulses in a coherently prepared linear medium.

The propagation of a pulse of electromagnetic radiation thru a linear medium depends critically on the dispersive properties of the medium. Sommerfeld and Brillouin investigated this problem in great detail. They found that the group velocity had very different values depending on whether one is working in the anomalous region or the normal region. They showed the possibility of superluminal propagation in the anomalous region. This raises an important question-how the information travels thru a medium and in particular they proved that the front of the pulse moves with the velocity of light Recent experiments have established the superluminal propagation which, though counterintuitive, can be understood in terms of the interference of different Fourier components.

We like to focus especially on propagation of light and its control in a nonlinear medium like the system of ultra cold atoms. Some of the pertinent questions of great experimental importance are-the role of relaxations, the effect of pulse width, and the dependence on the driving power.

Optically Stimulated Luminescence Applied to Neutron, Space, Medical, and Accident Dosimetry

Prof. Eduardo Yukihara

Optically Stimulated Luminescence (OSL) is a very versatile technique for dosimetry of ionizing radiation, now used in a large scale for personnel dosimetry. The technique consists is using light to stimulate radiation-induced luminescence in insulating crystals specifically grown for this application, such as carbon-doped aluminum oxide (Al2O3:C). Research is needed to extend the use of this technique to other areas such as neutron, medical, and accident dosimetry. For the detection of neutrons, new materials or combination of materials need to be developed, since Al2O3:C is not sensitive to neutrons. The advantage of OSL is the possibility of using plastic matrices to achieve fast neutron detection. Space dosimetry is one of the challenging situations for radiation dosimetry, since no single detector is capable of providing accurate information on dose equivalent for the very complex radiation field. Research is currently being done to characterize the passive Al2O3:C dosimeters for use in space, and to develop a OSL reader that could be used onboard the International Space Station. In medical dosimetry, new readout procedures and equipments need to be develop to achieve the precision of 1% required for most applications (dose verification, quality assurance, dose mapping). There is also a need for developing 2D and 3D dose mapping systems for application in Intensity Modulated Radiation Therapy (IMRT). Accident dosimetry is another area in which OSL cay play an important role, since there are many natural materials which can be used as dosimeters in case of accident. One of the main concerns is currently on the development of techniques that could be used for triage in case of accidents. In all areas of dosimetry mentioned above, there are important opportunities for REU students. Research involves aspects of physics of radiation, spectroscopy, material sciences, optics and instrumentation, with an interface to other areas such as medicine, biology, and engineering.

Picosecond Laser Spectroscopy of Energy Flow in Protiens

Prof. Aihua Xie

A central problem in the biological physics of proteins is to understand how proteins carry out their functions in view of protein structure, dynamics, and energetics. We study the mechanisms of energy flow in proteins in order to understand functionally important structural transitions in proteins using femtosecond and picosecond mid- to far- infrared free electron lasers. Our major goals are: (1) to investigate the rates and the channels of energy flows in proteins and associated anharmonic vibrational couplings, (2) to identify the vibrational energy donors and acceptors for functionally important structural transitions in proteins and to investigate the functional roles of low frequency collective modes in proteins, and (3) to explore and develop a "quantum inspired" rate theory to characterize the predict the rates of functionally important structural transitions in proteins.

The experimental approaches for our study are challenging. We concentrate on the use of the tunable, intense, picosecond mid- and far-infrared light sources provided by the FELIX free electron laser at the FOM Institute of Plasma Physics in Nieuwegein, the Netherlands. In addition, we will employ cryogenic systems and utilize a second picosecond visible/infrared laser that is based on Ti:sapphire laser pumped system and is synchronized to the infrared free electron laser. We have successfully developed three picosecond pump probe systems: (1) mid-infrared pump probe system, (2) far-infrared pump probe system, and (3) visible pump and infrared probe system. These systems will be further optimized and utilized for studies of picosecond energy flow in proteins.

Computational Materials Simulations

Prof. John Mintmire

The research group of Prof. John Mintmire focuses on computational simulations in materials chemistry and physics, with specific emphasis on large-scale atomistic simulations of the electronic and structural properties of low-dimensional materials. Two specific areas are emphasized in this group: electronic and structural properties of carbon nanotubes (CNTs) and related quasi-one-dimensional nanotube and nanowires systems, as well as empirical molecular dynamics simulations of materials. REU students in this area will have the opportunity to gain experience in several areas such as ab initio and local-density functional electronic structure methods for molecular and solid-state systems, electronic and structural properties of polymer chains, and molecular dynamics simulations of shocked condensed-phase systems.

Laser Cooling and Bose-Einstein Condensation

Prof. Gil Summy

The goal of the Laser Cooling and BEC Laboratory at OSU is to investigate the foundations of quantum mechanics using quantum chaotic systems. Another major component of research involves the development of new atom optical techniques for the construction of devices such as atom interferometers. Both goals are being achieved using laser cooled atoms and Bose-Einstein condensates that are placed in the potential formed by a standing wave of laser light. The REU project will involve students in experiments with cold atoms from a magneto-optic trap. The aim of the project will be to examine an example of quantum chaos called the quantum delta-kicked rotor. Students will investigate quantum resonances and will work on developing a technique which can test for the presence of chaotic behavior in a quantum system.

Experimental Measurement of Neutral Excited-State Species

Prof. Nick Materer

This research focuses on experimental measurements of neutral excited-state species formed during the energetic bombardment of surfaces. Sputtering of material by energetic ions is of practical importance in both material removal and chemical analysis. Despite the obvious importance of this process, experimental information on the production of excited species from well-defined surfaces is lacking. This lack of information has resulted in an incomplete understanding of the underlying processes that lead to both charged and excited neutral particle ejection. The aim is to use well-defined surfaces to investigate experimentally the various excitation mechanisms that give rise to electronically excited neutral species. This understanding of the energy partitioning in excited neutral production will provide insight into the underlying dynamics. Several questions will be addressed. Why are more ions produced than excited neutrals? Are the excited neutrals produced from the ions by electron transfer in the exit channel, or do they result from a non-adiabatic bond breaking process? These questions will be addresses by correlating the emission yields with the surface conditions. These results will enable the relative importance of various excitation mechanisms to be determined, and will aid in the development of a quantitative predictive theory of sputtering.

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