ASEE - Naval Research Laboratory Postdoctoral Fellowship Program

National Defense Science and Engineering Graduate Fellowship

Naval Research Laboratory

THE INSTITUTE FOR NANOSCIENCE

The Naval Research Laboratory has established an Institute for Nanoscience. The Institute’s mission is to carry out interdisciplinary research at the emerging intersection of biology, electronics, chemistry, and condensed matter physics at the nanometer size domain. Those advisors who are currently members of this institute are listed below.

DIRECTOR - Dr. G. Prinz

Magnetic Nanostructures
GA Prinz 64.15.45.B2987

We conduct fundamental and applied magnetic research on reduced dimensionality magnetic films and engineered structures. Studies involve the tailoring of magnetic multilayer and superlattice systems by contact mask deposition, lithographic processing, and ion milling for the generation of dimensionally challenged structures. Facilities include a complete lithographic processing center with sub-micron capabilities for pattern definition of magnetic materials (e.g., CAD mask design, mask manufacture, photoresist application/development, projection printing, and development), atomic/magnetic force microscopy, high resolution (100 Å structure definition) by liquid Ga ion milling, in-plane and perpendicular-to-plane magnetoresistance measurement systems, and extensive magnetic characterization equipment.

Theoretical Studies of the Optical Properties of Nanometer Size Semiconductor Quantum Dots
A Efros 64.15.45.B2868

We have calculated dynamical optical characteristics of II–VI semiconductor nanocrystals, including radiative recombination times, transition oscillator strengths, nonradiative Auger recombination times, thermalization times of nonequilibrium carriers, and spin relaxation times. Competition between these processes is a strong function of crystal radius, and it determines the photoluminescence quantum efficiency. We investigated the polarization properties of the luminescence of an assembly of nonspherical crystals and characterized their shape and orientation distributions. We also study spin-spin contact interactions of electrons and holes as well as their interaction with the spins of nuclei and magnetic ions in different types of quantum dots. Close contact with experiment and collaboration with experimental researchers is maintained.

Bio/Molecular Engineering
BP Gaber 64.15.45.B2690

Our goal is to develop novel devices and processes based on a new fundamental understanding of biological molecules and structures. The projects rely on the potential of molecular and biological self assembly for material applications. Research areas include synthesis of novel monomers, assembly of lipid microstructures by self-organization, gene cloning of novel biomaterials, incorporation of proteins in polymerizable lipid membranes, study of protein function in polymerized matrices, synthesis and characterization of ferroelectric liquid crystal polymers, fabrication of self-assembled films, development of techniques for producing high-resolution patterns of materials on surfaces, and interaction of dye molecules and antibodies with membranes. These materials are characterized by spectroscopic and microscopic techniques. These include Raman spectroscopy, infrared, flourescence, and photon correlation spectroscopies, freeze-fracture electron microscopy, and circular diohroism. Molecular modeling calculations are used to understand structural parameters and stability.

Crystal Engineering
BP Gaber 64.15.45.B2703

Monomolecular films covalently attached to flat surfaces are used as molecular templates for the nucleation and growth of specifically oriented inorganic crystals. Crystal alignment is determined by x-ray diffraction and atomic force microscopy.

Enzyme Machining of Organic Thin Films
BP Gaber 64.15.45.B2704

We are investigating the use of surface immobilized enzymes for chemical modification and patterning of organic films. We have shown that enzymes, which have been immobilized on a solid surface can be used to chemically modify an organic thin film containing the substrate for the enzyme. For example, we have immobilized ?-chymotrypsin to silica beads and used these enzymatically active beads to selectively cleave the AMC fluorophore from an organic thin film of the ?-chymotrypsin substrate peptide (suc-ala-ala-phe-AMC), which was chemisorbed to a silica surface. By controlling the placement of the beads on the surface, we were able to create chemical patterns on the peptide surface, which were visualized with atomic force microscopy and fluorescence microscopy. In future experiments, we expect to study other enzyme/substrate pairs and interaction kinetics, and immobilize the enzymes on other surfaces for rapid preparation of high-resolution chemical patterns.

Protein Patterning and Sensing
BP Gaber 64.15.45.B2705

We are examining methods for patterning proteins on solid surfaces using nonphotolithographic approaches such as direct transfer of the protein from a “donor” surface to a “receiver” surface. Successful approaches will be used to create patterned arrays of antibodies for application as multi-analyte immunosensors. In addition to creating the protein patterns, we will be studying them with atomic force microscopy (AFM) and developing the AFM as a biosensor for sensing the interaction of an antigen with the antibody patterns.

Directed Self-Assembly of Biologically Based Nanostructures
MS Spector 64.15.45.B4594

We are developing novel materials that self-assemble into well defined, hierarchical architectures leading to enhanced properties. The molecular order is controlled by the specific hybridization properties of oligonucleotides. Our goal is to study the structure and properties of such materials and to correlate these with changes in the nucleotide sequence. Research areas include synthesis of novel monomers and their subsequent incorporation into DNA sequences, nucleic acid modification for solid-phase synthesis, formation of films on modified substrates, and characterization of these materials using a variety of physical techniques.

Nano-Spectroscopy and Control of Quantum Dots
DG Gammon 64.15.45.B3991

In this research effort, we are learning to optically probe and control individual semiconductor quantum dots (QDs). By looking at individual QDs with high spatial, spectral, and temporal resolution can measure properties that are completely blurred out in ensemble measurements. In close collaboration with molecular beam epitaxy growth efforts, with theory efforts, and other experimental groups, we are studying the physics of QDs. Emphasis is on unexplored physics and revolutionary technologies such as quantum computation.

Reference
Bonadeo NH, et al: Science 282: 1473, 1998

Nanostructure Science and Technology
ES Snow DG Gammon 64.15.45.B3614

We use scanned probe technology, high spatial and spectral resolution optical techniques, and molecular beam epitaxy growth to investigate a variety of research topics in the area of nanostructure science and technology. Current interest areas include nanolithography, nanoelectronic devices, and quantum dot physics. We have developed scanned probe techniques for fabricating both semiconductor and metallic nanostructures with minimum feature sizes down to atomic dimensions. We are currently using this fabrication approach to investigate a novel class of room-temperature nanometer-scale quantum transistors that operate by using a gate potential to modulate the current flowing through a tunnel barrier. In addition, we have developed novel optical techniques that allow us to explore the detailed physics of single semiconductor quantum dots. We are using these techniques to investigate aspects of quantum computing by using laser pulses to coherently control quantum dot excitons.

Proximal Probe-Based Fabrication of Nanostructures
ES Snow 64.15.45.B2821

We are using scanning probes such as the scanning tunneling microscope (STM) and the atomic force microscope (AFM) to fabricate novel nanometer-scale device structures. Our goal is to approach atomic-scale precision of device fabrication and to study the electrical and optical properties of these structures. Available resources include controlled ambient STM and AFM (used for fabrication and structural characterization), a low-temperature STM, device processing facilities, molecular beam epitaxy growth facilities, and a wide range of electrical and optical probes.

Micro-Acoustics and Structural Acoustics of Complex Systems
BH Houston 64.15.45.B3629

This research focuses on developing an understanding of acoustics for a variety of physical problems over all length scales. This includes thin-film surface acoustic phonon generation and detection, the micro-dynamics of biological systems, and the micro- and macro-acoustics of complex fluid-loaded mechanical systems. These studies are theoretically and experimentally balanced where newly developed measurement and computational tools resident at NRL are employed that include scanning three-dimensional Laser Doppler Vibrometry and advanced finite element, infinite element modeling techniques. Further, the micro-elastic fields in heterogeneous materials are studied with Nearfield Laser Doppler Vibrometry probes. This research leverages ongoing research in the structural acoustics and structural dynamics of complex systems, Elastic Space Holography, and Anderson Localization.

Luminescent Quantum Dots
BL Justus 64.15.45.B3979

The synthesis and characterization of highly luminescent semiconductor nanocrystals (colloidal quantum dots) are being studied. Quantum dots are a mesoscopic state of matter with diameter varying between 15 and 100 Angstroms. The size confinement of the electronic excitation gives rise to optical properties that are not observed in the bulk material. Size dependent optical properties, such as absorption and photoluminescence are being studied. The chemistry of the colloidal dots in solution is carefully investigated since detailed understanding of the solution chemistry is critical if the superior luminescence characteristics of the dots are to be realized and exploited. Capping the surfaces of the dots with appropriate organic molecules protects the dots in solution, enhances their solubility, and prevents agglomeration. The optical properties are fully characterized using laser spectroscopic techniques. Applications for the highly luminescent colloidal quantum dots include detection of biological molecules. Quantum dots are bound to proteins and other biological molecules using appropriate chemical means. The quantum-dot-labeled proteins and antibodies will be used in assays for the detection of chemical and biological molecules of interest. Luminescent quantum dots may also have applications in flat panel display technologies.

Photonic Crystals
A Rosenberg 64.15.45.B4593

This research focuses on producing photonic crystals and understanding their optical properties. These are composite dielectric structures with length scales comparable to a wavelength of light, which allow unprecedented control over the propagation and emission of light. Three general fabrication methods are currently being investigated. (1) Channel glass materials are being modified to obtain novel photonic crystals by the incorporation/growth within the submicron diameter channels of various high-index dielectrics, nonlinear, and luminescent optical materials. (2) New types of photonic crystals are being produced by the growth and patterning of planar waveguides in NRL’s state-of-the-art semiconductor processing facilities. (3) A project to fabricate ordered polymeric composites is also in progress.
Theoretical simulation of light propagation is used to model the experimental results and to predict the properties of new structures. A well-equipped optics laboratory is available, including spectrometers, cw lasers, and a tunable pulsed (ns) laser system. Opportunities exist in the fabrication, theoretical simulation, and/or optical characterization of these fascinating materials.

Surface Chemistry of Electronic Materials
JN Russell, Jr PE Pehrsson 64.15.45.B2737

This research focuses on the surface chemistry of diamonds and other wide bandgap materials (e.g., SiC, AIN, BN, GaN), and post-growth modification of these surfaces for device applications. Specific interests include (1) chemical modification of surfaces in ultrahigh vacuum (UHV) to determine the structure and chemistry of low-index surfaces; (2) the effects of surface chemisorption and processing-based manipulation on electronic properties such as electron affinity and electrical conductivity, for vacuum microelectronics and other applications; (3) the role of surface structure and chemistry in the nucleation and growth of doped epitaxial films; and (4) the surface reaction mechanisms and kinetics of novel precursors for chemical vapor deposition and doping.
Extensive surface science facilities include three UHV systems equipped with a variety of surface analysis tools, including a load-locked UHV analysis and chemical vapor deposition processing system with gas dosing and temperature control. In situ analysis includes high-resolution electron energy loss spectroscopy; Auger electron, ultraviolet photoelectron, and x-ray photoelectron spectroscopies; low-energy electron diffraction; work function measurement using Kelvin probe; collinear four-point probe; infrared reflection absorption spectroscopy; attenuated total internal reflection; and multi-mass temperature programmed desorption.

Atomic-Scale Studies of Semiconductor Surfaces and Interfaces
LJ Whitman 64.15.45.B5083

We investigate the atomic-scale physical and chemical properties of semiconductor surfaces and interfaces using scanning tunneling microscopy and spectroscopy. Current research focuses on (1) the structure and reactivity of highly vicinal Si and Ge surfaces and their potential as new substrates for electronic devices; and (2) the growth, structure, and electronic properties of III–V semiconductor surfaces and interfaces prepared by molecular beam epitaxy. These surfaces are characterized both in situ in plan-view and subsequently in cross-section. Facilities include a number of ultrahigh vacuum systems equipped for scanning tunneling microscopy in addition to other standard surface modification and characterization methods (e.g., film evaporation, gas dosing, sputtering, low-energy electron diffraction, Auger electron spectroscopy, and temperature programmed desorption). Additional information about this research can be obtained on our Web site at http://stm2.nrl.navy.mil/~lwhitman.

References
Laracuente L, Whitman LJ: Surface Science 476: L247, 2001
Barvosa-Carter W, et al: Physical Review Letters 84: 4649, 2000

Surface Nanoscience of Organic and Biomolecular Adsorbates
LJ Whitman 64.15.45.B4294

The goal of this program is to develop methods to immobilize and characterize individual organic molecules or biological nanostructures at predetermined sites on surfaces. By coupling the function of such molecules to external electrical, mechanical, or chemical systems, we hope to develop novel nanometer-scale electronic and mechanical devices. Scanning probe microscopy (SPM) techniques, including scanning tunneling microscopy and atomic force microscopy, are employed to obtain high-resolution images of nanostructures on surfaces in controlled environments, and make spectroscopic measurements of their electrical, chemical, and mechanical properties. The SPM measurements are combined with macroscopic measurements of surface properties made by more conventional analytical techniques. We are particularly interested in developing the methods and infrastructure for combining surface preparation and nanolithography in vacuum with subsequent solution chemistry for biomolecule immobilization. See http://stm2.nrl.navy.mil/.

Revolutionary Biosensors Based on Force Discrimination
LJ Whitman 64.15.45.B4295

We are developing antibody and DNA array biosensors based on the specific binding of magnetic microbeads to receptor-patterned surfaces. A critical component of each assay is the application of a controlled force to remove any beads that are not bound by specific ligand-receptor interactions. Then the remaining beads are counted to determine the concentration of each of the target ligands. In the Force Differentiation Assay (FDA), magnetic force is used to remove the non-specifically bound beads, and those remaining are detected optically. Fluidic forces are used in the Bead ARray Counter (BARC) sensor, and the specifically bound beads are detected by an array of micro-fabricated magnetic field sensors. A prototype FDA system using immobilized antibodies as the receptors has been successfully field tested, demonstrating high sensitivity and specificity for proteins, viruses, and bacteria. In the prototype BARC system, single-stranded DNA probes are arrayed on the sensor chip above the sensor elements. When complementary DNA is present in the sample, it hybridizes with the immobilized probes; labeled microbeads are then introduced that specifically bind to this captured DNA. Because both sensor systems can detect a single microbead, in theory, each could detect a single pathogen or strand of DNA, giving them great potential for a wide range of clinical and pharmaceutical assays. See http://stm2.nrl.navy.mil/.

References
Metzger SW, et al: Journal of Vacuum Science and Technology A17: 2623, 1999
Edelstein RL, et al: Biosensors and Bioelectronics 14: 805, 2000
Lee GU, et al: Analytical Biochemistry 287: 261, 2000

Nanotubes and Nanowires: Surface Chemistry, Interfacial Interactions, Manipulation, and Assembly of Structures
PE Pehrsson 64.15.15.B4860

Future electronic devices will probably include one-dimensional nanofilamentary materials such as carbon nanotubes or nanorods of Si, GaN, and other materials. Their possible uses include electron emitters for switches and displays, MEMS/NEMS, chemical sensors, and connections for molecular electronics. Accordingly, we are examining the fundamental properties of nanofilaments and how those properties are modified by interaction with other nanofilaments, with chemical species such as dopants and functional groups, and with well-characterized surfaces. Specific examples include the effects of nanotube dimensions and chemical functionalization on their electrical conductivity and mechanical properties. Nanofilaments are chemically modified by plasmas, wet chemistry, and locally by probe microscope. The work is done in collaboration with theoretical modeling studies of the electronic structure and its modification by defects, functional groups, and strain.

We study charge transfer between nanofilaments and well-characterized, preferably single-crystal surfaces, with particular emphasis on the role of the surface chemical termination and lattice registry. The interactive forces between nanofilaments and chemically modified surfaces or other filaments are studied in order to develop methods for controllably depositing nanofilaments into useful structures using self-assembly approaches.

The nanofilaments are either grown by chemical vapor deposition (CVD) from ordered metal nanoclusters on surfaces or are obtained from other sources and deposited on surfaces from solution. The suite of available CVD growth techniques includes microwave plasma, inductive heating, and tube furnace. Other growth techniques are available through collaborations with other NRL personnel.

The chemical and physical properties are studied through the use of surface science and scanning probe microscopy techniques. Available techniques include attenuated total reflectance/Fourier-transform infrared, high-resolution electron-energy-loss spectroscopy, Kelvin Probe, Auger, x-ray photoelectron spectroscopy, and low-energy electron diffraction. (See 64.15.15.B2737 “Surface Chemistry of Electronics Materials” for a more complete list). A new multichamber facility under construction will permit in-situ variable temperature scanning probe microscopy (SPM), as well as SPM with independently manipulable scanning transmission microscopy tips for electrical conductivity measurements, nanomanipulation and imaging, scanning electron microscopy, scanning Auger microprobe, and sample processing.

Photoelectron Spectroscopy of Laser-Excited Materials
JP Long 64.15.15.B3602

Photoelectron spectroscopy is employed as the primary tool for investigating the electronic structure of a broad variety of materials subjected to pulsed laser irradiation. Using pulsed synchrotron or up-converted laser sources, the work focuses on the dynamics of transient photoexcited electrons on time scales from 50 ps to 100 ?s. In addition, permanent photochemical transformations are also characterized. In the dynamic pump-probe experiments, a visible or infrared laser pulse promotes electrons into excited states and an ultraviolet (UV) pulse photoemits the excited state distribution after a controllable delay. From the time evolution of the energy distribution, unique information is obtained on phenomena such as surface recombination and surface state occupation, hot electrons, plasma and exciton transport and interaction, and electron transfer. While semiconductors have been most often investigated with these techniques, we have recently expanded the work to include molecular films comprising fullerenes or molecules with promise in new molecularly based optoelectronic technologies. Experiments are undertaken in well-equipped ultrahigh vacuum chambers either at NRL or at the National Synchrotron Light Source.

Micro-Acoustics and Structural Acoustics of Complex Systems
BH Houston 64.15.04.B3629

This research focuses on developing an understanding of acoustics for a number of physical systems over all length scales. This includes thin-film surface acoustic phonon generation and detection, the dynamics of microelectromechanical systems (MEMS) and nanoelectromechanical systems (NEMS), and the acoustics of complex fluid-loaded mechanical systems. With regard to MEMS and NEMS, much of the research is oriented towards understanding and controlling internal friction as a function of scale, frequency and temperature. These studies are theoretically and experimentally balanced where newly developed measurement and computational tools resident at NRL are employed that include optical interferometric probes with sub-wavelength apertures, scanning three-dimensional Laser Doppler Vibrometry microscopes (LDVM) and advanced finite element modeling techniques. This research leverages ongoing research in the structural acoustics and structural dynamics of complex systems, Elastic Space Holography, and Anderson Localization.

Scanning Probe Microscopy and Photoemission Spectroscopy of Organic Nanostructures
ZH Kafafi 64.15.67.B4854

Research is motivated by newly emerging device technologies based on organic electronic and photonic materials. Special emphasis is placed on the study of the surface and interface properties of molecular and polymer organic materials. Our current focus is on ultraviolet (UV) and x-ray photoelectron emission spectroscopies of metal/organic Schottky contacts, and organic/inorganic and organic/organic hetero-interfaces present in electronic, electro-optic and optoelectronic devices such as organic thin-film transistors, organic light-emitting diodes, and organic photovoltaics. Ultrahigh vacuum (UHV) in situ scanning probe microscopy (STM, AFM) is used to image the surface and interface of organic nanostructures.

Instrumentation includes an Omicron multichamber UHV system, which consists of a thin film growth chamber connected by a gate valve to a surface analysis chamber. The surface analysis chamber has a sample heating stage, ultraviolet and x-ray sources, a hemispherical energy analyzer, and AFM and STM probes. The fabrication chamber has resistive heating furnaces for vacuum deposition and ion-sputtering gun, and UV-ozone source for substrate cleaning and pretreatment. A heating/cooling stage is also available for sample preparation at different substrate temperatures.

References
Hill IG, et al: Applied Physics Letters 77: 2003, 2000
Makinen AJ, et al: Applied Physics Letters 79: 557 (2001)
Makinen AJ, et al: Applied Physics Letters 78: 670, 2001

Nanoelectronic Structures, Devices, and Sensors
M Ancona 64.15.25.B4875

We are investigating nanoelectronic structures, devices, and sensors made using self-assembled metal clusters, particularly gold nanoclusters. The clusters can be as small as 10Å across and they exhibit strong Coulomb blockade effects even at room temperature. The goal of our effort is to exploit these effects in order to create new kinds of ultra-small, ultra-low-power electronic devices and sensors. Fabrication techniques (including electron beam and AFM/STM methods), self-assembly chemistry and chemical, structural, and electronic characterization are important to this effort. In addition, work is in progress to model and simulate the clusters, the devices, and potential circuit architectures. A recent interest has focuses on using chemical templates including DNA to guide the assembly of nanocluster devices and structures. We work in close collaboration with a group in NRL’s Chemistry Division (Code 6123) and shared arrangements are possible.

Interfacing Biomolecular Processes with Electronics at the Nanoscale
JM Byers 64.15.85.B4868

The primary objective of our research program is to establish the science and engineering principles behind nanometer-scale integration of electronics and biomolecular structures and processes. We explore issues regarding the assembly and function of high-density addressable electronics at the interface with an aqueous environment for precision control of receptor-ligand binding. Our effort develops and uses prototype devices capable of single biomolecule manipulation and detection in an addressable architecture for the exploration of the biochemical networks for molecular trafficking, synthesis, and gene regulation.

Template-Directed Molecular Imprinting
BP Gaber 64.15.09.B3622

We are uniting the disciplines of template-directed mesoporous synthesis and molecular imprinting in order to make biomimetic materials, which are both highly specific and very rugged. This interdisciplinary program combines materials science with biochemistry, organic synthesis, and molecular design.

NRL Postdoctoral Fellowship Program
American Society for Engineering Education
1818 N Street N.W., Suite 600
Washington, DC 20036

Email: postdocs "at" asee.org
Phone: (202) 331-3525, Fax: (202) 265-8504