Materials Sciences and Engineering

Selected FY 2002 Research Accomplishments:

-   *Giant Magnetoresistance (GMR).* GMR is revolutionizing the magnetic
    recording and data storage industry by enabling major increases in
    data density and ease of read/write processes. GMR is the term
    applied to layered magnetic systems that undergo very large changes
    in resistance in the presence of a magnetic field. The origin of GMR
    and its relationship to layered structure is unknown. New
    experiments in which the GMR is measured with current flowing
    perpendicular to the layer interfaces have yielded insight into the
    factors underlying the effect. Measurements of the GMR in samples
    with quantitatively determined interfacial structure, characterized
    by microscopy and x-ray scattering, have shown a direct relationship
    between the GMR and the interfacial roughness. Since most GMR-based
    devices rely on the magnitude of the effect, these results provide
    guidance for their optimization by interfacial roughness tailoring.

-   *Multifunctional Materials.* For the first time, organic materials
    that exhibit bistability simultaneously in three channels --
    magnetic, optical, and electrical -- have been produced. The new
    materials have many interesting properties. In one state, they are
    paramagnetic (attracted to a magnetic field), infrared transparent,
    and electrically insulating; in the other state, they are
    diamagnetic (repelled by both poles of a magnet), infrared opaque,
    and electrically conducting. The switching between the two states is
    thermally driven, and a switching temperature just above
    technologically useful room temperature has been achieved. These
    multifunctional materials have the potential for use in new types of
    devices for electronics, computers, and data storage where multiple
    channels are used for reading, writing, and transferring
    information.

-   *Transparent Electronic Devices.* Rather than ordinary glass,
    imagine that your window panes at home are a multi-functional wide
    band-gap semiconductor device that might serve as: an energy
    generator, a microprocessor, a detector, and a light modulator. The
    potential of wide-gap semiconductors is enormous, ranging from
    highly efficient solid-state light sources and high-density data
    storage to invisible monitoring devices for national security. The
    key in making this dream a reality is to be able to dope these
    materials with impurities to achieve both the n- and p-type
    mechanisms of electrical conduction. Achieving p-type doping had
    been an insurmountable problem. The root cause was found to be
    twofold: the spontaneous formation of native defects and the
    low-dopant solubility. Suppression of the defect formation was
    achieved by chemical design of the band structure of the
    semiconductor oxides. This approach has led to a family of new
    p-type transparent conducting materials. These studies have
    facilitated the experimental exploration of transparent electronic
    device materials.

-   *World's Smallest Ultraviolet Nanolasers.* The world's smallest
    ultraviolet-emitting lasers, based on "nanowires" of zinc oxide,
    have a broad range of potential applications in fields ranging from
    photonics -- the use of light for superfast data processing and
    transmission -- to the so-called "lab on a chip" technology in which
    a microchip equipped with nano-sized light sources and sensors
    performs instant and detailed analyses for chemistry, biology, and
    medical studies. The nanolasers were fabricated using a new
    processing method that can grow arrays of zinc oxide nanowires
    between 70 and 100 nm in diameter with adjustable lengths between 2
    and 10 microns. This development continues the progress in
    semiconductor laser research, providing new materials that extend
    the availability of these versatile and inexpensive light sources
    from the near infrared and red regions of the spectrum into the
    green-blue and near ultraviolet.

-   *Nanotubes Increase Heat Conduction in Fluids.* Fluids containing 1
    percent carbon nanotubes in oil exhibit a 250 percent increase in
    heat conduction. This addition of nanotubes resulted in the highest
    thermal conductivity enhancement ever achieved in a liquid -- ten
    times higher than predicted by existing theories. This has required
    the development of new heat conduction models for solid/liquid
    suspensions. This research could lead to a major breakthrough in
    solid/liquid composites for numerous engineering applications, such
    as coolants for automobiles, air conditioning, and supercomputers.

-   *Molecular Based Spintronic Material.* For years scientists have
    dreamed of separately controlling the spin and charge of the
    electron to create \"spin electronics\" or spintronics for next
    generation electronic devices. We have advanced one step closer to
    this goal with the fabrication of a new molecular solid integrating
    alternate layers of spin networks with organic metal networks
    through crystal engineering. The close proximity of the spin to the
    metal -- less than one nanometer apart -- promises strong
    communication of spin and charge while allowing each to be
    manipulated separately. The new material is made by relatively
    inexpensively using bottom-up self-assembly as opposed to the
    elaborate and expensive top-down lithography for other semiconductor
    materials.

-   *Deformation at the Nanoscale.* Large-scale atomic-level simulations
    reveal how and why conventional dislocation deformation processes in
    materials break down at the nanoscale. Nanostructures can experience
    very high internal stress levels; thus, mechanical stability and
    compliance represent major obstacles in the development of
    nanodevices. The computer simulations demonstrated that, as the
    grain size becomes ever smaller, a material becomes harder to
    deform. However, at a critical size, dislocations no longer can
    exist, because they are comparable to that of the grains themselves,
    and the material suddenly softens again due to the onset of novel
    deformation mechanisms mediated by the grain boundaries that contain
    the grains. This "strongest size" was shown to be a function of not
    only the material itself but also the stress level to which it is
    subjected. These insights will enable the design of nanodevices with
    tailored mechanical performance, capable of withstanding the very
    high stresses under which they often operate.

-   *Nano-onions.* Carbon "nano-onions," generated by carbon-arc
    discharge in deionized water, are the latest entry in the fullerene
    family. Their structures resemble onions, with a fullerene at the
    core, surrounded by multiple layers of fullerene-like carbon. The
    arc method produces "nano-onions" with diameters from about 10 to
    150 nm. These "Buckyonions" are easily fractionated on the basis of
    diameter by using flow field-flow fractionation, with small
    particles eluting before larger ones. Characterization of these
    "nano-onions" using electron microscopy and light scattering methods
    could lead to new and novel applications for these materials.

-   *A Trillion Elements per Square Inch.* Magnetic storage arrays with
    more than a trillion elements per square inch, ultrahigh resolution
    field emission displays, and high resolution, on-chip macromolecular
    separations devices have been constructed using a new, patented
    technique of self-assembly of polymers. By means of routine chemical
    etching processes, large area arrays of nanopores (4-50 nm in
    diameter) with very high aspect ratios are produced in a simple,
    robust manner. These serve as templates for pattern transfer to
    substrates and as scaffolds to direct surface chemistry or
    electrochemical deposition of metals for the generation of ultrahigh
    density, multilayered nanowire arrays. The simplicity of this
    technique has a broad impact across many disciplines ranging from
    bioactivity to semiconductor devices.

-   *Molecules of Gases and Water Swim Upstream.* A theoretical analysis
    has shown that molecules of hydrogen, oxygen, and even water can
    travel across conducting membranes in opposite directions from what
    would normally be expected. An understanding of these membranes is
    important in the development of advanced materials systems for
    energy storage such as fuel cells. The analysis pertains to a class
    of materials called perovskites that can, under some circumstances,
    conduct charge via both individual electrons and ionized atoms of
    hydrogen and oxygen. Individual chemical species can move in the
    \"wrong\" direction from areas where they are at a lower
    concentration to areas of higher concentration. This is normally
    explained by other driving forces that are taken into account in a
    quantity referred to as the chemical potential. In mixed-conducting
    membranes, however, the new analysis shows that neutral (uncharged)
    molecules can even move contrary to the gradient in the chemical
    potential as a result of the simultaneous, coupled transport of
    multiple species.

-   *Ultra-Sensitive Sensors.* A new principle for chemical sensors with
    ultra-high sensitivity has been developed and successfully
    demonstrated based on computer simulations of the structure and
    properties of particle composites. These sensors are fabricated by
    dispersing electrically conducting magnetic particles into an
    insulating liquid, then organizing the particles into chains with a
    magnetic field while the liquid solidifies by polymerization. These
    materials are referred to as Field-Structured Composites. The
    particle chains conduct electricity quite well. When exposed to
    certain chemical vapors, the polymer absorbs the chemicals and
    swells. The chains are stretched ever so slightly to create gaps
    between the particles, resulting in conductivity decreases of ten
    billion or more. The unprecedented magnitude of this effect makes
    these materials sensitive to even trace amounts of vapors.
    Inexpensive, portable devices for chemical identification can be
    achieved by making an array of sensors, each of which is fabricated
    with a polymer having unique chemical affinities, so that any single
    vapor leaves an identifying signature on the array.

-   *New Analysis Method Enables Prediction of Dendritic Pattern
    Formation.* Just as water freezes into the elaborate patterns of
    snowflakes, so do metals form highly branched patterns called
    dendrites. These dendrites control many aspects of the processing
    and microstructure that determine alloy properties and hence our
    ability to use materials. Dendrite patterns are controlled by minute
    variations of the interface between the material and its melt. While
    simulations have modeled the atomic processes that occur during
    solidification, they have proven inadequate to extract the more
    subtle information about the anisotropy. An entirely new method to
    extract the anisotropy of energy and mobility from supercomputer
    simulations has been devised. The critical step was the
    identification of a related quantity that can be calculated with
    sufficient precision and then used to simulate dendritic growth.
    Additional supercomputer simulations have exploited this new
    information to predict the precise nature of dendritic pattern
    formation in a range of materials from silicon to nickel.

-   *Superconductors Show Their Stripes.* Like tigers and zebras,
    superconductors are distinguished by their stripes. Some physicists
    believe that electricity runs without resistance along "stripes" of
    electric charge in these materials. Stripes have now been observed
    for the first time the most widely studied of the cuprate
    high-temperature superconductors. The material consists of planes of
    copper and oxygen atoms located in a square pattern. Some of the
    electrons are missing in these planes leaving positively charged
    holes that pair together to produce superconductivity. In a standard
    superconductor, these pairs travel through the material without
    hindrance producing the perfect conductivity inherent to a
    superconductor. However, in the cuprate materials, the copper atoms
    have a magnetic moment that makes conductivity in the planes
    difficult. Recent neutron scattering measurements made at the High
    Flux Isotope Reactor show that the holes form lines or stripes in
    the superconductor in which there are no magnetic moments. The holes
    can thus move along the stripe in an unimpeded manner.

-   *Neutron Instrumentation for Nanoscience.* Nanoscience requires the
    study of structures ranging from a few nanometers to a few microns.
    A new neutron scattering technique for study of materials in this
    size range has been developed. The method uses the fact that the
    spin of the neutron has unique behavior in a magnetic field \-- the
    spin precesses like a top in a magnetic field so that the total
    rotation angle of the spin depends on the time the neutron spends in
    the magnetic field. By appropriately designing the magnetic fields,
    the rotation angle can be made to depend on the direction of
    travel of the neutron with respect to some fixed spatial direction,
    effectively \"coding\" the trajectory angle into the value of the
    neutrons spin. This technique can easily be implemented and could be
    perfected in time to impact early measurements at the Spallation
    Neutron Source. 

Selected FY 2002 Facility Accomplishments:

-   The Advanced Light Source

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-   *Superbend Magnets Extend Synchrotron Spectral Range.* Originally
    designed for highest brightness at longer x-ray wavelengths (soft x
    rays), the ALS has been retrofitted with superconducting bend
    magnets (superbends) that dramatically boost the synchrotron
    radiation intensity at shorter x-ray wavelengths (hard x rays)
    without disrupting the soft x-ray performance of the existing
    beamlines, thereby allowing the ALS to service a broader user
    community.

-   *Higher-Order-Mode Dampers Increase Storage Ring Stability.* The
    beam in the ALS storage ring comprises more than 300 discrete
    "bunches" of electrons spaced more or less equally around the ring,
    but interactions between the bunches can cause the beam to become
    unstable. Addition of antennae to the radio-frequency (RF) cavities
    that power the storage ring has substantially improved the
    reliability of the feedback system that combats beam instabilities.

-   *A New Radio-Frequency (RF) Feedback Loop Saves Electrical Power and
    Money.* Driven by the soaring costs that came with the California
    energy crisis, staff at the ALS found a way to reduce the
    electricity bill an estimated 11% by implementing a feedback loop
    that reduced power consumption by a klystron power amplifier without
    interfering with other RF-cavity controls.

-   *Beamline for Ultrahigh-Resolution Chemical Crystallography
    Commissioned.* Based on a novel miniaturized design that is low-cost
    yet robust and high-performance, the ALS has put into operation a
    new beamline that meets the demands of chemists for a tool to
    rapidly determine the atomic structure of molecules with
    sub-angstrom resolution from solid samples (crystals) as small as a
    few micrometers on a side.

-   *An Experimental Station Has Been Designed to Study Magnetic
    Nanostructures.* Consisting of multiple layers of magnetic and
    nonmagnetic materials, each only a few atoms thick, magnetic
    nanostructures are the foundation for advanced magnetic devices. The
    new station at the ALS will allow complete magnetic characterization
    of each layer separately with x rays that are polarized in any
    desired orientation.

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-   The Advanced Photon Source

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-   *Operating in Top-up Mode.* One of the principal operational goals
    has been to run the storage ring in the "constant current" or top-up
    mode. Top-up mode consists of injecting a small amount of charge
    into the storage ring at regular intervals in order to maintain a
    100 mA current. The major benefit of top-up operation is the virtual
    elimination of the beam lifetime (the decay of beam current over
    time) as a factor in further improvements or enhancements of the
    storage ring performance. As an example, the APS can now operate
    efficiently with a lower horizontal emittance, which reduces the
    source size by a factor of two. This reduction in size provides a
    smaller beam spot that can be used to illuminate smaller samples.
    Normally, the decrease in beam lifetime would severely reduce the
    average current available to the users, but with top-up, the
    reduction is non-existent. Top-up operation is now the standard and
    comprises 75 percent of the total operating time of the APS. The APS
    is the first synchrotron facility to have conceived and implemented
    top-up operation.

-   *Canted Undulators for Increased Beamline Capacity.* New
    technologies devised to offset the ever-increasing demand for
    beamline access include the "canted undulator" configuration that
    produces two beamlines originating from one point on the ring.

-   *New Information on High-Pressure Fuel Sprays.* An x-ray imaging
    technique devised at the Basic Energy Sciences-funded Synchrotron
    Radiation Instrumentation Collaborative Access Team (SRI-CAT) has
    produced unprecedented details of the structure of diesel fuel
    sprays, including the first evidence of supersonic shockwaves in
    sprays as they leave high-pressure fuel injectors. This information
    may lead to improvements in fuel injector-engine emissions and
    efficiency, and earned a 2002 National Laboratory Combustion &
    Emissions Control R&D Award from the Department of Energy.

-   *Nanotomography of Integrated Circuit Interconnects.* A
    high-resolution scanning transmission x-ray microscope is providing
    superior 3-D images of the tiny wire interconnects and other
    embedded structures in computer chips without damage to the chips.
    This unique capability makes it possible to more easily identify and
    correct manufacturing problems, and ultimately to build faster,
    smaller, more-efficient, and more-reliable computers.

-   *New Lens for Imaging.* An offshoot of APS expertise in x-ray
    beamline instrumentation is the first full-scale crystal-diffraction
    medical-imaging lens. Resolution with this lens is a factor of three
    better than with most current imaging systems. It can be applied to
    small test animals used by the pharmaceutical industry and to
    imaging small parts of the human body. There are also many
    possibilities for nonmedical applications, including examination of
    nuclear fuel elements and location of radioactive material within a
    larger mass.

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-   The National Synchrotron Light Source

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-   *Source Development Laboratory Laser at 400 nm.* The Deep
    Ultra-Violet Free Electron Laser (DUV-FEL) facility marked an
    important milestone, generating laser light at 400 nm by the process
    of Self Amplified Spontaneous Emission (SASE). Achieving intensity
    20,000 times higher than the spontaneous emission, the result showed
    that the electron beam and the undulator system can support lasing
    down to 88 nm, which has strong user interest in the chemical
    physics community.

-   *Soft X-ray Undulator Beamline Monochromator Upgrade.* A new
    water-cooled, 6-position interferometrically controlled grating
    chamber was installed at beamline X1B. At present, four new gratings
    (300, 600,1200, and 1600 lines/mm) covering the soft x-ray photon
    energy range from 100eV to 1600eV were outfitted. Resolving power of
    more than 10,000 was achieved. The high energy resolution and
    extended energy range provided by the new monochromator will benefit
    greatly all the experimental programs using the beamline, including
    soft x-ray resonant scattering, emission, and imaging.

-   *Ultra-high Vacuum Compatible Soft X-ray Scattering End Station.* A
    novel resonant soft x-ray scattering instrument has become
    operational at the X1B undulator beamline. The instrument combines
    the element and electronic state specificity of soft x-ray
    spectroscopy with x-ray diffraction, which enables the direct
    probing of intrinsic inhomogeneities in strongly correlated electron
    systems and nanoscale magnetic systems. For example, the spatial
    distribution of the doped holes in an epitaxial film of oxygen-doped
    La~2~CuO~4+~ was determined recently using this instrument for the
    first time.

-   *New End Station for Soft X-ray Coherent Scattering and Imaging.* To
    facilitate nanoscience research, imaging techniques with nanometer
    spatial resolution are needed. A new end station for soft x-ray
    coherent scattering and imaging was designed and constructed. It
    will be used to develop two and three dimensional diffraction
    imaging and tomography with tens of nanometer spatial resolution for
    nano-magnetic, organic, and biological systems

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-   The Stanford Synchrotron Radiation Laboratory

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-   *Accelerator Modeling Toolbox Developed.* An interactive accelerator
    modeling software tool called Accelerator Toolbox has been developed
    that greatly increases productivity and flexibility in interactive
    computer modeling. By making the Accelerator Toolbox available to
    other laboratories via the web, a community of users has grown who
    share code and experience in solving similar accelerator modeling
    problems.

-   *High Power X-ray Monochromators Deployed.* X-ray monochromators
    with high-efficiency crystal cooling utilizing liquid nitrogen have
    been designed, fabricated and successfully installed on four
    high-power wiggler beam lines. Their enhanced performance under high
    heat loads has already resulted in significant improvements in the
    stability and throughput of these beam lines. These monochromators
    and others to be implemented will be critical elements in obtaining
    the ultimate performance available from the SPEAR3 accelerator when
    it becomes operational in 2004.

-   *Improved Microfocusing System for X-ray Microspectroscopy.*
    Improved tapered metal capillary focusing optics with a 5 micrometer
    focal spot have been successfully integrated into a new system for
    performing microspectroscopy measurements. These developments, which
    included sample scanning capabilities and software for mapping the
    chemical states of the elemental distributions, will ultimately be
    propagated to a number of beam lines to enable microspectroscopy
    research in biology, materials sciences, and environmental sciences.

-   *Major Progress in SSRL Beamline Upgrade Program.* A beam line
    upgrade program is underway whose goal is to bring all SSRL beam
    lines to optimal performance with SPEAR3 running at 500 mA.
    Improvements to date include high-stability mirror systems for the
    insertion device-based beam lines, new permanent magnet wigglers, a
    high-resolution soft x-ray monochromator, and new liquid
    nitrogen-cooled two-crystal x-ray monochromators. Some upgrades have
    been completed during the current SPEAR2 operations phase, bringing
    higher performance to the ongoing user research programs.

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-   The Intense Pulsed Neutron Source

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-   *Upgrades of IPNS Instruments.* 1) A project was initiated for the
    development of a large-aperture, magnetic bearings-suspension,
    high-resolution chopper system for the HRMECS and LRMECS chopper
    spectrometers at IPNS. 2) A new scattering chamber for the Small
    Angle Diffractometer is being installed. It will improve the data
    quality and collection rates. 3) Through an IPNS/RIKEN collaboration
    a neutron compound refractive lens based on an assembly of MgF2
    single-crystal prism elements was tested on the POSY II beamline for
    focusing cold neutrons.

-   *Operations at IPNS Continues Outstanding.* For the fifth
    consecutive year, IPNS has exceeded its goal of offering at least
    95% reliable operations. This includes delivering the 7 billionth
    pulse to the target. This accomplishment constitutes more pulses
    delivered to target than any other pulsed neutron source in the US.
    In May of 2002, IPNS was designated a Nuclear Historic Landmark by
    the American Nuclear Society.

-   *IPNS Hosts the National Neutron and X-Ray Scattering School.*
    During the two-week period of August 12-23, 2002, Argonne National
    Laboratory once again hosted the National School on Neutron and
    X-Ray Scattering. The school continues to attract outstanding
    graduate students and post-doctoral appointees with 160 applications
    for the 60 positions available in 2001.

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-   The Manuel Lujan Jr. Neutron Scattering Center at the Los Alamos
    Neutron Science Center

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-   *Four Instruments Commissioned.* Four world-class neutron scattering
    instruments completed commissioning and entered the user program.
    These are HIPPO, SMARTS, Protein Crystallography Station, and
    Asterix. New data acquisition systems were completed and installed
    on the new instruments.

-   *Pharos Rebuilt.* Inelastic chopper spectrometer Pharos enjoyed
    substantial upgrades, including detectors on the wide-angle bank,
    commissioning of the new vacuum system, new data acquisition
    electronics and computer system, and a new chopper control system.
    Pharos took its first data and accepted its first users since 1997.

-   *Designed and Installed New Robust Target System, Mark II.* Using a
    simplified Monte Carlo model, the new target improves cooling in
    Mark I moderator and upper target. A beryllium reflector replaced
    the lead reflector, cooling was simplified, and cadmium decoupling
    in the reflector was removed for more robust operation. The target
    received first beam on July 8, 2002, as scheduled.

-   *Completed Basis for Interim Operation for actinide experiments.*
    The new authorization basis enabled over a dozen plutonium and
    uranium studies to be completed and restores an important capability
    to the DOE science complex.

-   *New Shutters and Interlocks.* Greater safety, reliability and
    performance were achieved by replacement of Personnel Access Control
    Systems interlocks on all flight paths, replacement of all mercury
    reservoirs and plumbing, and installation of a new fire detection
    system. Two new mechanical shutters and over 300 tons of shielding
    were installed to enable two new flight paths for new instruments.

-   *Proton Storage Ring Instability Tamed.* A series of successful
    Proton Storage Ring development tests confirmed that the "e-p
    instability" could be controlled at accumulated charge levels
    approaching 10 C, well above the goal of 6.7C.

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-   The High Flux Isotope Reactor

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-   *Major Refurbishment of Reactor Vessel Completed.* The refurbishment
    of the pressure vessel\'s internal components included replacing the
    permanent and semipermanent beryllium reflectors and their support
    structures. This required maintenance was accomplished without
    incident and will support the substantial upgrade in neutron
    scattering research capabilities at HFIR.

-   *HFIR Cooling Tower Replaced.* The original 36-year-old wooden
    cooling tower had significant structural degradation, required
    excessive maintenance, and could no longer reliably support reactor
    operations. The more efficient replacement tower will cost less to
    operate and should last for the remaining life of HFIR.

-   *New Thermal Neutron Beam Tubes Installed at HFIR.* The new beam
    tubes, which replaced existing tubes that had reached their end of
    life, are capable of providing more neutrons to a greater number of
    scientific instruments.

-   *Operational Readiness Review (ORR).* The ORR at HFIR was the first
    to be conducted at any Category 1 DOE facility since the current ORR
    guidance was issued. The ORR included a comprehensive restart plan,
    independent-contractor and DOE reviews, and close coordination with
    DOE headquarters and the site office. Reactor operations were
    resumed on December 18, 2001

-   *Facility Improvements Support Neutron Scattering Instrument
    Upgrades.* New monochromator drums were fabricated for the
    triple-axis spectrometers at HB-1, 2, and 3. A shielding tunnel and
    neutron guide were fabricated for HB-2, where a 20-cm-diameter beam
    tube was installed with beryllium inserts to support four beam
    lines. The resulting beam intensity is expected to be three times
    that of the original design for some of the instruments.

Chemical Sciences, Geosciences, and Energy Biosciences

# Selected FY 2002 Research Accomplishments:

-   *Catalytic Chemistry of Gold Nanoparticles.* Gold spheres of 2.7 nm
    diameter supported on titanium oxide are able to oxidize carbon
    monoxide, and spheres of 2.4 nm diameter are able to activate oxygen
    from air and insert it into propene readily and very selectively.
    Yet bulk gold metal is inert, and particles of slightly smaller or
    larger diameter than those cited are also unreactive or unselective.
    Using a variety of spectroscopic and chemisorption techniques,
    atomic-resolution microscopy, and theoretical electronic structure
    calculations, it was shown that decreasing metal particle size
    provokes changes in the electronic structures of gold and titanium
    oxide such that the particles are able to acquire a partial charge.
    Those variations are shown to decrease the binding energy of gold on
    titanium oxide (and thus alter the morphology of the clusters), as
    well as increase the binding energy of reactants such as oxygen,
    carbon monoxide, and propene to gold. The results explain why gold
    clusters are active and selective oxidation catalysts and provide a
    semiquantitative framework to predict catalytic reactivity on the
    basis of electronic structure of metal clusters.

-   *New Nanoporous Catalysts Developed.* Nanocrystalline materials
    possess unique properties and offer great promise for promoting
    selected physical and chemical processes. Crystalline films of
    magnesium oxide that consist of tilted arrays of filaments attached
    to a flat substrate have been synthesized by impinging a magnesium
    atom beam in an oxygen background toward a surface off-normal by 70°
    to 85°. The individual filaments are thermally stable, highly
    ordered and porous, and contain enormous numbers of binding sites in
    comparison to a magnesium oxide flat surface deposited on a
    substrate. The high surface area (\~1,000 m^2^/g) and high density
    of binding sites potentially render these nanoporous materials
    extraordinary catalysts.

-   *Multidimensional Catalyst Arrays.* Studies of the affects of
    particle spacing on the reactivity of catalysts has been hampered by
    the inability to produce uniform nanoparticles that are regularly
    distributed in a supporting matrix. Recent work shows that two- and
    three-dimensional arrays of platinum nanoparticles are achievable.
    Two-dimensional arrays of platinum supported on 4-inch silicon
    wafers were produced using electron beam lithography and spacer
    photolithography. The latter technique permits variation of particle
    size from 600 nm to 10 nm. More recently, three-dimensional arrays
    of 2-5 nm platinum nanoparticles of vary narrow size distribution
    were prepared, and the resulting x-ray and electron diffraction
    patterns are typical of crystallinity, hence regularity. The results
    significantly enhance enable the production of designer catalysts
    and will answer fundamental questions in catalysis.

-   *Nanostructured Anodes.* There is considerable interest in
    tin/lithium anodes for high-energy electrochemical storage systems
    because, in principle, they can deliver substantially more storage
    capacity than carbon based lithium ion batteries. However, the
    tin-based anode functions by reversibly alloying lithium into the
    tin, and a very large volume expansion occurs when lithium is
    alloyed (as much as 300 percent). As a result, the tin based anode
    system typically has poor cycle life because the volume expansion
    and contraction during cycling causes the anode to self-destruct.
    New research has shown that nanostructured tin/lithium anodes
    prepared via a membrane template method do not suffer from this loss
    of cycle life, even after 1,400 charge discharge cycles. The
    nanostructured electrode gives good cycle life because the absolute
    volume change for a nanofiber is correspondingly small and because
    the brush like configuration of nanofibers provides room to
    accommodate the volume expansion.

-   *Nanometer-Scale Faceting of Metals, a Means to Control Reactivity.*
    Bimetallic catalysts are providing new insights into chemical
    reactivity. Upon annealing at elevated temperatures, the atomically
    rough, "unstable" surfaces were observed to undergo massive
    reconstruction at the nanometer scale, in some instances leading to
    the formation of surface alloys. These structural rearrangements
    were accompanied by corresponding changes in electronic structure,
    morphology, and catalytic activity. Time-dependent, atomically
    resolved images allowed the measurement of the rate of facet growth
    and of their reconstruction in the presence of adsorbates such as
    sulfur and oxygen. Catalytic activity was found to dramatically
    depend on the composition, structure, size, and shape of the facets
    exposed under reaction conditions.

-   *Organic Semiconductors.* Molecular and polymeric semiconductors are
    very important organic compounds that have the potential to replace
    inorganic semiconductors for applications in photoelectrochemical
    and photovoltaic cells for solar energy conversion of sunlight to
    electricity and solar fuels (hydrogen, methane, and alcohols).
    Photoconversion devices based on organic semiconductors could be
    much less expensive and easier to produce and process because of the
    present vast technology available for polymer and molecular
    processing into continuous thin films and sheets. Doping the
    molecular semiconductors to produce the required n-type and p-type
    electrical conductivity to create p-n junctions has been problematic
    as the dopant has not become part of the molecular or atomic
    structure of the compound. Recently, scientists successfully doped
    molecular semiconductors and increased the conductivity by five
    orders of magnitude.

-   *Long-Lived Charge Separation in a Novel Artificial Photosynthetic
    Reaction Center.* Fullerenes and porphyrins have molecular
    architectures that are ideally suited for photochemical conversion
    and storage of solar energy. Their use as three-dimensional electron
    acceptors holds great promise because of their small reorganization
    energy in electron transfer reactions that can significantly improve
    light-induced charge-separation processes. Recent research indicated
    a 24 percent efficient charge-separation within a molecular tetrad.
    In this linear array, a light harvesting antenna assembly composed
    of two porphyrins and a fullerene-ferrocene photosynthetic
    reaction-center mimic were integrated into a single molecule. The
    380 millisecond lifetime of the spatially-separated and high energy
    radical pair, a product of sequential short-range energy and
    electron transfer reactions, enters a time domain that has never
    been achieved in an artificial reaction center.

-   *New Technique for Detection of Impact Ionization in
    Semiconductors.* The thermodynamic conversion efficiency with which
    solar radiant energy can be converted to electricity or to stored
    chemical energy in solar-derived fuels is limited by the energy loss
    of high energy electrons and positive holes created by the
    absorption of high energy solar photons in the photoconversion
    device. The thermodynamic efficiency limit can be more than doubled
    if the high energy photons can be used to create additional
    photogenerated current through a process called impact ionization.
    For the first time, scientists have demonstrated a contactless,
    optical method to detect impact ionization in semiconductors useful
    for solar photoconversion. The method is based on femtosecond
    time-resolved visible pump-infrared probe spectroscopy, and can be
    used to study impact ionization in colloidal semiconductor quantum
    dots where electrical contact to the colloidal particles is not
    possible. Impact ionization in semiconductor quantum dots is
    expected to be greatly enhanced.

-   *Gas-Phase Chemistry of Actinide Ions.* The studies of gas-phase
    reactions of ions provide important insights into fundamental
    chemistry. Such studies have previously been limited to transition
    metal ions and to thorium and uranium in the actinide series;
    however, recent work has expanded this approach to the radioactive
    actinides, which cannot easily be studied by conventional
    techniques. One type of reaction that has been particularly
    enlightening involves the metal- or metal-oxide-catalyzed removal of
    hydrogen from alkene hydrocarbons. In these alkene dehydrogenation
    reactions, the neptunium ion is highly reactive, the plutonium ion
    is significantly less reactive, and the americium ion is essentially
    unreactive. This provides clear evidence that the 5f electrons of
    the actinides beyond neptunium are inert in these organometallic
    reactions. Results for the actinide oxide ions have also been
    illuminating, revealing a decrease in reactivity between uranium
    oxide ions and heavier actinide-oxide ions. The role of 5f electrons
    in bonding is central issue in contemporary actinide science, and
    these results provide experimental evidence for a change in the
    bonding nature of the actinide 5f electrons in molecular compounds,
    ranging from being chemically active for the early members of the
    series to being inert for the actinides beyond neptunium.

-   *Lattice Disorder and f-electrons: Evidence For a New State of
    Matter.* An important question is the nature of the
    non-superconducting high-temperature superconducting (HTSC) ground
    state from which superconductivity arises. Intermetallic alloys
    containing *f*-electron elements, in which superconductivity is
    absent or is easily suppressed, allow one to explore this question.
    Like HTSCs, *f*-electron intermetallic alloys often behave as
    "non-Fermi liquids" (NFL), so named because they are not consistent
    with Fermi liquid theory, which, until recently, has been the basis
    for explaining the properties of metals. Of specific interest is how
    the atoms surrounding an *f*-electron atom, and how disorder in
    their arrangement, affect magnetic and conducting properties. A
    recent study of these arrangements in the NFL compound UCu~4~Pd
    showed that significant lattice disorder exists. Although such
    disorder can produce NFL behavior within a Fermi liquid model, the
    study showed that there is insufficient disorder for the model to
    match the measured magnetic and conductivity data. That is, the
    system acts as though it is more disordered than it actually is.
    These results strongly imply that lattice disorder precipitates NFL
    behavior in this material, perhaps by amplifying the effect of the
    disorder, and thereby the possibility of a new type of metallic
    ground state.

-   *Cellulose Biosynthesis.* The detection and isolation of cellulose
    synthase genes is driving new efforts to understand how cellulose
    acquires its structural characteristics in hopes of eventually
    devising methods of tailoring these characteristics to facilitate
    its use as a renewable resource. Scientists have provided a key
    piece of information in the biochemical dissection of the three
    steps of cellulose synthesis: 1) initiation of the sugar chain; 2)
    adding sugars to the growing chain; and 3) stopping the process at a
    predetermined length. A single copy of a cellulose synthase gene was
    introduced into yeast cells that do not normally make cellulose. The
    result was the formation of a specific lipid-sugar compound that
    serves as a primer for subsequent chain growth. Understanding the
    critical steps in the synthesis of cellulose, the most abundant
    biomolecule, will lead to understanding the function of plant cell
    walls and to engineering modified renewable resources.

-   *Boron in Plant Cell Walls.* Research has confirmed the role of the
    element boron in the growth and development of plant cell walls.
    Over 90 percent of a plant's boron is associated with the cell wall,
    and boron deficiency leads to stunted plants with malformed and
    brittle leaves. Arabidopsis thaliana mutants with a small change in
    the structure of a major type of cell wall carbohydrate show the
    same characteristics but can be rescued by feeding with excess
    borate. This defect was shown to reduce the plant's ability to bind
    the borate that is needed to form and stabilize the cross-linked
    cell wall. Future mechanistic studies relating borate-carbohydrate
    crosslinking to physiological growth could lead to improved
    strategies for the development and production of renewable biomass
    resources.

-   *Naturally Occurring Organochlorine Compounds.* Organochlorine
    molecules are commonly observed in natural soils and have been
    attributed to pollution from manmade sources. Natural organic
    matter, such as humic and fulvic acid, in the shallow subsurface is
    both universal and little understood. It has no fixed stoichiometry
    or structure, cannot be crystallized, and is famously difficult to
    characterize reproducibly. Synchrotron x-ray spectroscopy has been
    used to document changes in the chemical state of chlorine in humic
    materials. This research confirmed the startling conclusion that
    natural organochlorine compounds are common in soil and that there
    is a net transfer of chlorine from inorganic to organic forms with
    common weathering. Abundant catalytic peroxidase facilitates the
    chlorination of natural aromatic organics. These results add strong
    support to the hypothesis that chlorination of organic compounds in
    humic materials is widespread, and may explain the puzzling
    organochlorine concentrations found in otherwise unpolluted
    environments. Accurately understanding natural conditions is
    critical in identifying and taking action to correct man-made
    problems.

-   *Quantum Degenerate Fermi Gases.* A new theoretical formulation
    predicts an unusually high critical temperature for the onset of
    superfluidity in a gas of fermionic potassium atoms. This new form
    of quantum matter, which lies between high-temperature
    superconductors and systems that undergo Bose-Einstein condensation
    should soon be achievable experimentally using optical traps. The
    ultimate goal of these experiments is to achieve Cooper pairing, in
    which pairs of fermionic atoms "condense" and occupy the lowest
    quantum states available to the ensemble of trapped atoms. Such an
    accomplishment would permit studies of the underlying mechanism of
    superconductivity.

Selected FY 2002 Facility Accomplishments:

-   The Combustion Research Facility

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-   *Stagnation-flow Reactor Designed to Probe High-temperature
    Chemistry.* Chemically reacting flows at interfaces are an important
    class of processes occurring in combustion, catalysis, thin film
    formation, and materials synthesis. An innovative stagnation-flow
    reactor with access for optical diagnostics and mass spectrometry is
    nearing completion and will provide a valuable tool for probing
    high-temperature chemistry for a broad range of industrially
    relevant processes.

-   *Fiber-based Laser Systems Developed.* Fiber lasers and amplifiers
    are unique optical sources that provide many advantages for
    detection of chemical and biological compounds. The CRF has
    established the capability to fabricate them in-house. The facility
    will allow the pursuit of new research in optical diagnostics and
    will help DOE remain at the forefront of this field.

-   *New Reactor Allows Investigation of Gasification Processes.* The
    design and facility modifications have been completed for a new
    reactor that will allow unprecedented optical access to pressurized
    combustion and gasification processes. This reactor will give the
    CRF the capability to investigate gas-phase kinetics, materials
    behavior, advanced diagnostic development, and solid and liquid fuel
    combustion chemistry and physics under pressurized conditions.