Nitrogen Doping for Robust Silicon Nanostructures
Presentation for NMSU Postdoctoral Symposium, Sept 20th, based on ExEx work
Sheridan, Thomas Robert↗
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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Physics of Ultra-High Energy Density Relativistic Plasmas from Ordered Nanostructures
This award funded a four-year program at Colorado State University on the physics of ultra-high energy density plasmas generated by focusing femtosecond, >1021 Wcm-2 laser pulses onto ordered nanowire arrays. We used the ALEPH petawatt-class Ti:Sa laser with its high contrast 400 nm second harmonic beamline to irradiate arrays of Ni and TiO2 nanowires made by template assisted electrodeposition and atomic layer deposition over a wide range of average densities. We met two of the three original project goals: radial ion acceleration via doppler shifted K shell emission, and time and spectrally resolved K shell measurements. The main experimental advance was integrating the Lawrence Livermore National Laboratory (LLNL) TREX ultrafast x-ray streak camera with a suite of spherically bent quartz Bragg crystal spectrometers built using Princeton Plasma Physics Laboratory (PPPL) methodology. This is the first TREX-on-bent-quartz setup fielded at a femtosecond, >1021 Wcm-2 facility. It is now a permanent diagnostic at ALEPH and is offered to the LaserNetUS user community. The program produced three peer reviewed journal articles that acknowledge this award. The platform will continue at the upgraded CSU ATLAS facility, where the ALEPH laser is being upgraded to 2 PW.
Hollinger, Reed [Colorado State University]↗
Time-resolved probing of laser-induced nanostructuring processes in liquids
Laser synthesis and processing of colloids (LSPC) in liquids has gained widespread applications in producing nanomaterials of different classes of solids. While the technical processes in different cases of ablation, fragmentation or colloidal fusion may look macroscopically different in each application, the underlying fundamental mechanisms are always the same cascade of laser interaction with matter, non-thermal or thermal energy deposition, phase transitions, and the subsequent structure formation processes. Disentangling these mechanisms represents a veritable challenge, as ultrafast and structurally sensitive experimental methods are required. This review presents a discussion of how state-of-the-art experimental protocols using ultrafast lasers and sensitive structural probes, such as electrons or X-rays are able to address this challenge. In particular, it is possible to investigate LSPC on single objects using single probe pulses and avoid accumulation effects in a heterogeneous sample. The presented results capture structure formation with femtosecond and atomic scale resolution. Ultrafast time-resolved probing approaches are key to revealing the transient states and pathways that govern material transformation in LSPC.
X-ray scattering↗
Raman Study of Uncoated and p-BN/SiC-Coated Hi-Nicalon Fiber-Reinforced Celsian Matrix Composites: Distribution and Nanostructure of Different Phases - Part 1
Hi-Nicalon fiber reinforced celsian matrix composites were characterized by Raman spectroscopy and imaging, using several laser wavelengths. Composite #1 is reinforced by as-received fibers while coatings of p-BN and SiC protect the fibers in composite #2. The matrix contains traces of the hexagonal phase of celsian, which is concentrated in the neighborhood of fibers in composite #1. Some free silicon was evident in the coating of composite #2 which might involve a {BN + SiC yields BNC + Si} "reaction" at the p-BN/SiC interface. Careful analysis of C-C peaks revealed no abnormal degradation of the fiber core in the composites.
Gouadec, Gwenael↗
The Effect of Microgravity on the Growth of Silica Nanostructures
The process of the formation of structures from coagulating ensembles is fundamentally important since the collective behavior of the constituents often results in dramatically improved or unusual mechanical, thermal, chemical, and optical properties. In this study we examine the effect of microgravity on the formation of silica structures, specifically particles and gels.
Smith, D. D.↗
Anisotropic Nanomechanics of Boron Nitride Nanotubes: Nanostructured "Skin" Effect
The stiffness and plasticity of boron nitride nanotubes are investigated using generalized tight-binding molecular dynamics and ab-initio total energy methods. Due to boron-nitride BN bond buckling effects, compressed zigzag BN nanotubes are found to undergo novel anisotropic strain release followed by anisotropic plastic buckling. The strain is preferentially released towards N atoms in the rotated BN bonds. The tubes buckle anisotropically towards only one end when uniaxially compressed from both. A "skin-effect" model of smart nanocomposite materials is proposed which will localize the structural damage towards the 'skin' or surface side of the material.
Srivastava, Deepak↗
Waterproofing Nanostructured Aerogel-Ceramic Fiber Composites
Aerogels are nanoporous materials which can be used to enhance the transport properties of ceramic fiber materials, to exploit their unique properties such as high porosity, large surface area, low density and low thermal conductivity. Numerous applications have been investigated. major obstacle to commercialization is that the structure of aerogels collapses due to the adsorption of water. simple and relatively cheap process has been developed to waterproof silica, alumina and alumina-silica and carbon aerogels and composites incorporating them. Previous waterproofing methods are short lived or expensive and time consuming.
White, Susan↗
Functional Nanostructured Particle Arrays for Nanocrystal Nonvolatile Memories
This presentation outlines the performance characteristics of state-of-the-art nonvolatile memory devices and identifies charge storage mechanisms in nanocrystal floating gate materials.
Atwater, Harry↗
Electric Field-Mediated Processing of Biomaterials: Toward Nanostructured Biomimetic Systems
Significant opportunities exist for the processing of synthetic and biological polymers using electric fields ('electroprocessing'). We review casting of multi-component films and the spinning of fibers in electric fields, and indicate opportunities for the creation of smart polymer systems using these approaches. Applications include 2-D substrates for cell growth and diagnostics, scaffolds for tissue engineering and repair, and electromechanically active biosystems.
Bowlin, Gary L.↗
Nanostructured Composites: Effective Mechanical Property Determination of Nanotube Bundles
Carbon nanotubes naturally tend to form crystals in the form of hexagonally packed bundles or ropes that should exhibit a transversely isotropic constitutive behavior. Although the intratube axial stiffness is on the order of 1 TPa due to a strong network of delocalized bonds, the intertube cohesive strength is orders of magnitude less controlled by weak, nonbonding van der Waals interactions. An accurate determination of the effective mechanical properties of nanotube bundles is important to assess potential structural applications such as reinforcement in future composite material systems. A direct method for calculating effective material constants is developed in the present study. The Lennard-Jones potential is used to model the nonbonding cohesive forces. A complete set of transverse moduli are obtained and compared with existing data.
Saether, E.↗
Competing Classical and Quantum Effects in Shape Relaxation of a Metallic Nanostructure
We demonstrate for the first time that the quantum size effect (QSE) plays a competing role along side the classical thermodynamic effect in the shape relaxation of a small metallic island. Together, these effects transforms a lead(Pb) island grown on Si(111) substrate from its initially flattop faceted morphology to a peculiar ring-shape island, a process catalysed by the tip electric field of a scanning tunnelling microscope (STM). We shall show for the first time how QSE affects the relaxation process dynamically. In particular, it leads to a novel strip-flow growth and double-step growth on selective strips of a plateau inside the ring, defined by the substrate steps more than 60?0?3 below. It appears that atoms diffusing on the plateau can clearly (sub i)(deg)sense(sub i)+/- the quantized energy states inside the island and have preferentially attached to regions that further reduces the surface energy as a result of the QSE, limiting its own growth and stabilizing the ring shape. The mechanism proposed here offers a sound explanation for ring shape metal and semiconductor islands observed in other systems as well.
Chen, Dongmin↗
Soot Nanostructure And Its Impact Upon The O2 Oxidation Rate
Studies of soot oxidation have ranged from in situ flame studies to shock tubes to flow reactors. Each of these systems possesses particular advantages and limitations related to temperature, time and chemical environments. Despite the aforementioned differences, these soot oxidation investigations share three striking features. First and foremost is the wide variation in the rates of oxidation. Reported oxidation rates vary by factors of +6 to - 20 relative to the Nagle Strickland-Constable (NSC) rate for graphite oxidation [3]. Rate variations are not surprising, as the temperatures, residence times, types of oxidants and methods of oxidation differ from study to study. Nevertheless, a valid explanation for rate differences of this magnitude has yet to be presented.
Wal, Randy L. Vander↗
Deposition of Nanostructured Thin Film from Size-Classified Nanoparticles
Materials comprising nanometer-sized grains (approximately 1_50 nm) exhibit properties dramatically different from those of their homogeneous and uniform counterparts. These properties vary with size, shape, and composition of nanoscale grains. Thus, nanoparticles may be used as building blocks to engineer tailor-made artificial materials with desired properties, such as non-linear optical absorption, tunable light emission, charge-storage behavior, selective catalytic activity, and countless other characteristics. This bottom-up engineering approach requires exquisite control over nanoparticle size, shape, and composition. We describe the design and characterization of an aerosol system conceived for the deposition of size classified nanoparticles whose performance is consistent with these strict demands. A nanoparticle aerosol is generated by laser ablation and sorted according to size using a differential mobility analyzer. Nanoparticles within a chosen window of sizes (e.g., (8.0 plus or minus 0.6) nm) are deposited electrostatically on a surface forming a film of the desired material. The system allows the assembly and engineering of thin films using size-classified nanoparticles as building blocks.
Camata, Renato P.↗
Modeling Growth of Nanostructures in Plasmas
As semiconductor circuits shrink to CDs below 0.1 nm, it is becoming increasingly critical to replace and/or enhance existing technology with nanoscale structures, such as nanowires for interconnects. Nanowires grown in plasmas are strongly dependent on processing conditions, such as gas composition and substrate temperature. Growth occurs at specific sites, or step-edges, with the bulk growth rate of the nanowires determined from the equation of motion of the nucleating crystalline steps. Traditional front-tracking algorithms, such as string-based or level set methods, suffer either from numerical complications in higher spatial dimensions, or from difficulties in incorporating surface-intense physical and chemical phenomena. Phase field models have the robustness of the level set method, combined with the ability to implement surface-specific chemistry that is required to model crystal growth, although they do not necessarily directly solve for the advancing front location. We have adopted a phase field approach and will present results of the adatom density and step-growth location in time as a function of processing conditions, such as temperature and plasma gas composition.
Hwang, Helen H.↗
Development of a nanostructured DNA delivery scaffold via electrospinning of PLGA and PLA-PEG block copolymers
The present work utilizes electrospinning to fabricate synthetic polymer/DNA composite scaffolds for therapeutic application in gene delivery for tissue engineering. The scaffolds are non-woven, nano-fibered, membranous structures composed predominantly of poly(lactide-co-glycolide) (PLGA) random copolymer and a poly(D,L-lactide)-poly(ethylene glycol) (PLA-PEG) block copolymer. Release of plasmid DNA from the scaffolds was sustained over a 20-day study period, with maximum release occurring at approximately 2 h. Cumulative release profiles indicated amounts released were approximately 68-80% of the initially loaded DNA. Variations in the PLGA to PLA-PEG block copolymer ratio vastly affected the overall structural morphology, as well as both the rate and efficiency of DNA release. Results indicated that DNA released directly from these electrospun scaffolds was indeed intact, capable of cellular transfection, and successfully encoded the protein beta-galactosidase. When tested under tensile loads, the electrospun polymer/DNA composite scaffolds exhibited tensile moduli of approximately 35 MPa, with approximately 45% strain initially. These values approximate those of skin and cartilage. Taken together, this work represents the first successful demonstration of plasmid DNA incorporation into a polymer scaffold using electrospinning.
Non-NASA Center↗
Novel Biomedical Devices Utilizing Light-Emitting Nanostructures
As part of the NASA project, we are investigating the formation, properties, and performance of QD heterostructures, to be incorporated into a novel biomedical device for detecting bacteria and/or viruses in fluids on board space vehicles. We are presently synthesizing the epitaxial quantum dot structures using molecular beam epitaxy. We recently developed a method for controlling the arrangement of QDs, based upon a combination of buffer layer growth and controlled annealing sequences. This method is promising for producing arrangements of QDs with a locally well-controlled distribution of sizes. In the future, we plan to explore selective pre-patterning of the starting surface using focused ion-beam nanopatterning, which will enable us to precisely tune the compositions, sizes, and placement of the QDs, in order laterally tune the emission and detection wavelengths of QD based devices.
Goldman, Rachel S.↗
Soot Nanostructure: Using Fringe Analysis Software on High Resolution Transmission Electron Microscopy of Carbon Soot
Using high resolution transmission electron images of carbon nanotubes and carbon particles, we are able to use image analysis program to determine several carbon fringe properties, including length, separation, curvature and orientation. Results are shown in the form of histograms for each of those quantities. The combination of those measurements can give a better indication of the graphic structure within nanotubes and particles of carbon and can distinguish carbons based upon fringe properties. Carbon with longer, straighter and closer spaced fringes are considered graphite, while amorphous carbon contain shorter, less structured fringes.
King, James D.↗
The Influence of Tungsten on the Chemical Composition of a Temporally Evolving Nanostructure of a Model Ni-Al-Cr Superalloy
The influence of W on the temporal evolution of gamma' precipitation toward equilibrium in a model Ni-Al-Cr alloy is investigated by three-dimensional atom-probe (3DAP) microscopy and transmission electron microscopy (TEM). We report on the alloys Ni-10 Al-8.5 Cr (at.%) and Ni-10 Al-8.5 Cr-2 W (at.%), which were aged isothermally in the gamma + gamma' two-phase field at 1073 K, for times ranging from 0.25 to 264 h. Spheroidal-shaped gamma' precipitates, 5-15 nm diameter, form during quenching from above the solvus temperature in both alloys at a high number density (approx. 10(exp 23/cu m). As gamma' precipitates grow with aging at 1073 K, a transition from spheriodal- to cuboidal-shaped precipitates is observed in both alloys. The elemental partitioning and spatially resolved concentration profiles across the gamma' precipitates are obtained as a function of aging time from three-dimensional atom-by-atom reconstructions. Proximity histogram concentration profiles of the quaternary alloy demonstrate that W concentration gradients exist in gamma' precipitates in the as-quenched and 0.25-h aging states, which disappear after 1 h of aging. The diffusion coefficient of W in gamma' is estimated to be 6.2 x 10(exp -20) sq m/s at 1073 K. The W addition decreases the coarsening rate constant, and leads to stronger partitioning of Al to gamma' and Cr to gamma.
Sudbrack, Chantal K.↗