Bruce E. Brinson

Nanoshells Made Easy: Improving Au Layer Growth on Nanoparticle Surfaces

The growth of a continuous, uniform Au layer on a dielectric nanoparticle is the critical step in the synthesis of nanoparticles such as nanoshells or nanorice, giving rise to their unique geometry-dependent plasmon resonant properties. Here, we report a novel, streamlined method for Au layer metallization on prepared nanoparticle surfaces using carbon monoxide as the reducing agent. This approach consistently yields plasmonic nanoparticles with highly regular shell layers and is immune to variations in precursor or reagent preparation. Single particle spectroscopy combined with scanning electron microscopy reveal that thinner, more uniform shell layers with correspondingly red-shifted optical resonances are achievable with this approach.

Near-Infrared Excited Raman Optical Activity

Measurements of near-infrared scattered circular polarization Raman optical activity (SCP-ROA) are presented using laser excitation at 780 nm for samples of S-(—)-α-pinene and L-alanyl-L-alanine. These are the first measurements of ROA outside the blue-to-green visible region between 488 and 532 nm. Comparison of Raman and ROA intensities measured with excitation at 532 and 780 nm demonstrate that the expected frequency to the fourth-power dependence for Raman scattering and the corresponding fifth-power dependence for ROA are observed. It can be concluded that, to within this frequency dependence, the same level of efficiency of Raman and ROA measurements using commercial instrumentation with 532 nm excitation is maintained with the change to near-infrared excitation at 780 nm.

A dynamic continuum of nanostructured carbons in the combustion furnace

Abstract The presence of C60, carbon onions and higher fullerenes are confirmed in products from a carbon black combustion furnace. Acetylenic, C2, units participate in the formation and growth phases in the combustion flame. High-resolution TEM data clearly show fullerenes incorporated into the matrix of the carbon; MALDI mass spectral data show C60 and higher fullerenes in the soot itself. The toluene extracts of experimental carbons also contain C60.

Impurity-Induced Plasmon Damping in Individual Cobalt-Doped Hollow Au Nanoshells

The optical properties of plasmonic nanoparticles in the size range corresponding to the electrostatic, or dipole, limit have the potential to reveal effects otherwise masked by phase retardation. Here we examine the optical properties of individual, sub-50 nm hollow Au nanoshells (Co-HGNS), where Co is the initial sacrificial core nanoparticle, using single particle total internal reflection scattering (TIRS) spectroscopy. The residual Co present in the metallic shell induces a substantial broadening of the homogeneous plasmon resonance line width of the Co-HGNS, where the full width at half-maximum (fwhm) broadens proportionately with increasing Co content. This doping-induced line broadening provides a strategy for controlling plasmon line width independent of nanoparticle size, and has the potential to substantially modify the relative decay channels for localized nanoparticle surface plasmons.

Teslaphoresis of Carbon Nanotubes

This paper introduces Teslaphoresis, the directed motion and self-assembly of matter by a Tesla coil, and studies this electrokinetic phenomenon using single-walled carbon nanotubes (CNTs). Conventional directed self-assembly of matter using electric fields has been restricted to small scale structures, but with Teslaphoresis, we exceed this limitation by using the Tesla coils antenna to create a gradient high-voltage force field that projects into free space. CNTs placed within the Teslaphoretic (TEP) field polarize and self-assemble into wires that span from the nanoscale to the macroscale, the longest thus far being 15 cm. We show that the TEP field not only directs the self-assembly of long nanotube wires at remote distances (>30 cm) but can also wirelessly power nanotube-based LED circuits. Furthermore, individualized CNTs self-organize to form long parallel arrays with high fidelity alignment to the TEP field. Thus, Teslaphoresis is effective for directed self-assembly from the bottom-up to the macroscale.

Ring-locking enables selective anhydrosugar synthesis from carbohydrate pyrolysis

The selective production of platform chemicals from thermal conversion of biomass-derived carbohydrates is challenging. As precursors to natural products and drug molecules, anhydrosugars are difficult to synthesize from simple carbohydrates in large quantities without side products, due to various competing pathways during pyrolysis. Here we demonstrate that the nonselective chemistry of carbohydrate pyrolysis is substantially improved by alkoxy or phenoxy substitution at the anomeric carbon of glucose prior to thermal treatment. Through this ring-locking step, we found that the selectivity to 1,6-anhydro-β-D-glucopyranose (levoglucosan, LGA) increased from 2% to greater than 90% after fast pyrolysis of the resulting sugar at 600 °C. DFT analysis indicated that LGA formation becomes the dominant reaction pathway when the substituent group inhibits the pyranose ring from opening and fragmenting into non-anhydrosugar products. LGA forms selectively when the activation barrier for ring-opening is significantly increased over that for 1,6-elimination, with both barriers affected by the substituent type and anomeric position. These findings introduce the ring-locking concept to sugar pyrolysis chemistry and suggest a chemical-thermal treatment approach for upgrading simple and complex carbohydrates.

Structural Characteristics and Properties of a New Graphitic-Based Material.

The hydrogenation of commercial graphite using lithium/ammonia as the reducing agent and tert-butyl alcohol as a proton source was investigated. Characterization of the products after successive reductions of the same material by high-resolution transmission electron microscopy revealed a new material that was replete with edge and circular dislocations. Analysis by solid-state (13)C NMR spectroscopy indicates that after three reductions, the remaining aromatic rings appear to be interior benzene rings. NMR spectroscopy also offers strong evidence for the presence of small amounts of tert-butyl alcohol and ethanol (workup solvent) that could not be removed in vacuo from the samples. These compounds could be observed to move freely between the layers of the hydrographene.

Diatoms at >5000 Meters in the Quelccaya Summit Dome Glacier, Peru

Abstract Diatoms were found in late Holocene age ice-core samples recovered from the Quelccaya Summit Dome in the tropical Andes of Peru and were imaged by environmental scanning electron microscopy and identified. Freshwater diatoms in the genera Hantzschia, Pinnularia, and Aulacoseira were the most common taxa in the samples and indicate a freshwater source for the material, which also is suggested by the presence of the freshwater alga Volvox. The overall species composition of the diatoms suggests that the majority of taxa originated from a high-elevation lake or wetland in the cordillera surrounding the ice cap. The abundant diatom valves, up to 70 µm in size, likely were transported to the ice via wind.

Evaluation of interfaces in narrow InAs/AlSb quantum wells

InAs/AlSb quantum wells may be grown with two types of interfaces: InSb-like and AlAs-like. The interface type refers to the half-monolayer of the well material and half monolayer of barrier which are in contact. The type and quality of the quantum well interface is critical to the ISBT intensity and lineshape and, to a lesser extent, position. In addition to FTIR spectroscopy of the ISBT, we have performed transmission electron microscopy (TEM) to directly evaluate the quality of the interfaces at the atomic level. In order to evaluate the effects of interface type and quality on ISBT intensity, lineshape, and linewidth, we studied the TEM of a 10 nm QW sample with InSb-InSb interfaces and a 3 nm QW sample with InSb-AlAs interfaces.

Structural Studies of Hydrographenes

As a result of the unique physical and electrical properties, graphene continues to attract the interest of a large segment of the scientific community. Since graphene does not occur naturally, the ability to exfoliate and isolate individual layers of graphene from graphite is an important and challenging process. The interlayer cohesive energy of graphite that results from van der Waals attractions has been determined experimentally to be 61 meV per carbon atom (61 meV/C atom). This requires the development of a method to overcome the strong attractive forces associated with graphite. The exfoliation process that we, and others, have investigated involves electron transfer into bulk graphite from intercalated lithium to yield lithium graphenide. The resulting graphenide can be reacted with various reagents to yield functionalized graphene. As a part of our interest in the functionalization of graphene, we have explored the Birch reduction as a route to hydrographenes. The addition of hydrogen transforms graphene into an insulator, leading to the prediction that important applications will emerge. This Account focuses mainly on the characterization of the hydrographenes that are obtained from different types of graphite including synthetic graphite powder, natural flake graphite, and annealed graphite powder. Analysis by solid state 13C NMR spectroscopy proved to be important since it was shown that the hydrographenes are composed of interior, isolated aromatic (predominantly fully substituted benzene) rings surrounded by saturated rings. The expected clusters of benzene rings were not found. NMR spectroscopy also offers strong evidence for the presence of tert-butyl alcohol and ethanol (workup solvent) that could not be removed in vacuo from the samples. These compounds could be observed to move freely within the layers of the hydrographene. High-resolution transmission electron microscopy images revealed a remarkable change in morphology that results when hydrogen is added to the graphenide. The appearance of edge and circular dislocations and increased distances between graphitic layers are most visible in the case of the hydrographenes that are formed from annealed graphite. The repetitive hydrogenation of synthetic graphite powder leads to an increase in the distances between the graphitic layers in the (002) direction from 3.4 Å for the initial graphite to 4.11 Å after the first reduction and to 4.29 Å after a third reduction of the same material. Defect-free graphite is formed when the hydrographenes are heated. The distance between carbon layers decreases from 4.11 to 3.44 Å after heating the samples to 1200 °C. This trend toward the spacing of graphite confirms the reversibility of the functionalization process. The C-H bonds have been broken yielding hydrogen, and the exposed carbon orbitals are in close enough proximity to have reverted to graphite. This Account introduces only a narrow area of materials chemistry, and many applications of graphene and its derivatives can be expected as researchers exploit this burgeoning field.