Brian H. Houston

United States Naval Research Laboratory, Washington, Washington, D.C., United States

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Publications (146)263.79 Total impact

  • Physical Review B 05/2015; 91(20). DOI:10.1103/PhysRevB.91.205406 · 3.66 Impact Factor
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    ABSTRACT: Scattering results are presented for the case of cylindrical steel targets buried in elastic sediment with sound incident from the air above. The STARS3D finite element program recently extended to layered, elastic sediments is used to compute the scattering and the resulting normal displacement at the interface since the specific focus here is detection by systems which rely on monitoring the acoustic displacements or displacement-related entities at the fluid-sediment interface. Results are compared for the scattered field produced by the cylinder buried in layered elastic sediment versus in fluid sediment and for the scattered field of a buried cylindrical shell versus a buried solid cylinder. [This work was supported by ONR.].
    The Journal of the Acoustical Society of America 04/2014; 135(4):2349. DOI:10.1121/1.4877722 · 1.56 Impact Factor
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    ABSTRACT: We study the electronic transport properties of graphene with covalently bonded hydrogen impurities. Our measurements reveal low-energy resonant scattering processes within the transport for each charge carrier type. The observed resonances exhibit a strong energy dependence and are accompanied by a sharp increase in the scattering cross section. The ability to observe the scattering resonances was found to depend on the amount of disorder introduced into the graphene through the bonding of hydrogen. The results are shown to be in agreement with a theory regarding low-energy resonant scattering off a short-range impurity in graphene that takes into account both intravalley and intervalley scattering. Theory dictates that the observed resonances are the result of the formation of quasibound states of the Dirac fermions in graphene due to a divergence in one or more of the scattering lengths for the short-range hydrogen impurity potential. We anticipate our experimental results to have implications in graphene valley physics as well as graphene chemical modification, scattering, and localization theories.
    Physical Review B 08/2013; 88(8). DOI:10.1103/PhysRevB.88.085441 · 3.66 Impact Factor
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    ABSTRACT: We report using chemical functionalization to control local carrier type and density in graphene. Low frequency transport measurements demonstrate independent carrier types and densities within adjacent graphene and hydrogenated graphene regions. Measurements of the Hall coefficient confirm that the charge carriers change sign about the charge neutrality point, that the graphene carrier density retains its linear dependence on a back gate voltage, and that the hydrogenated graphene carrier density deviates from a linear relationship. Transport measurements across the bipolar interface reveal an increasing interface resistance for higher hydrogen concentrations and a source of constant resistance for lower hydrogen concentrations.
    Applied Physics Letters 03/2013; 102(10). DOI:10.1063/1.4794990 · 3.52 Impact Factor
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    ABSTRACT: A near-field to far-field projection algorithm is applied to a structure in the free-field case and generalized to a buried scatterer. The method of superposition is applied where the scattered field produced by the target may be approximated by the field produced by a number of point sources placed near the target. The source strengths are determined by requiring the field they produce to satisfy boundary conditions on the measurement surface. In the free-field case, the expression of the Green's function is simple. In the buried case, the two-domain Green's function may be expressed as an integral over special functions. Once the source strengths are determined, the far-field is computed as a superposition of the fields produced by the individual sources. The algorithm is tested on numerically generated data.
    The Journal of the Acoustical Society of America 02/2013; 133(2):912-7. DOI:10.1121/1.4773860 · 1.56 Impact Factor
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    ABSTRACT: Using a finite element-based structural acoustics code, simulations were carried out for the acoustic scattering from an unexploded ordnance rocket buried in the sediment under 3 m of water. The simulation treated 90 rocket burial angles in steps of 2°. The simulations were used to train a generative relevance vector machine (RVM) algorithm for identifying rockets buried at unknown angles in an actual water/sediment environment. The trained RVM algorithm was successfully tested on scattering measurements made in a sediment pool facility for six buried targets including the rocket at 90°, 120°, and 150°, a boulder, a cinderblock, and a cinderblock rolled 45° about its long axis.
    The Journal of the Acoustical Society of America 12/2012; 132(6):3614-7. DOI:10.1121/1.4763997 · 1.56 Impact Factor
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    ABSTRACT: In this article, we review our efforts to continuously tune mechanical and thermal properties in multilayer chemically modified graphene (CMG) films. An alteration of the graphene lattice by functional groups, by defects created during reduction, or by defect re-crystallization is used to control CMG mechanical and thermal properties. We attribute a notable increase in Young's modulus and film strength to an emerging network of sp2–sp3 crosslinks established between graphene layers. Control over the film stress and strength enabled us to dramatically improve the performance of radio frequency CMG resonators by fine tuning the fabrication process.
    Solid State Communications 11/2012; 152(21). DOI:10.1016/j.ssc.2012.04.051 · 1.70 Impact Factor
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    ABSTRACT: We report a method to introduce direct bonding between graphene platelets that enables the transformation of a multilayer chemically modified graphene (CMG) film from a "paper mache-like" structure into a stiff, high strength material. On the basis of chemical/defect manipulation and recrystallization, this technique allows wide-range engineering of mechanical properties (stiffness, strength, density, and built-in stress) in ultrathin CMG films. A dramatic increase in the Young's modulus (up to 800 GPa) and enhanced strength (sustainable stress ≥1 GPa) due to cross-linking, in combination with high tensile stress, produced high-performance (quality factor of 31,000 at room temperature) radio frequency nanomechanical resonators. The ability to fine-tune intraplatelet mechanical properties through chemical modification and to locally activate direct carbon-carbon bonding within carbon-based nanomaterials will transform these systems into true "materials-by-design" for nanomechanics.
    Nano Letters 07/2012; 12(8):4212-8. DOI:10.1021/nl3018059 · 12.94 Impact Factor
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    ABSTRACT: Near-field acoustic holography reconstruction of the acoustic field at the surface of an arbitrarily shaped radiating structure from pressure measurements at a nearby conformal surface is obtained from the solution of a boundary integral equation. This integral equation is discretized using the equivalent source method and transformed into a matrix system that can be solved using iterative regularization methods that counteract the effect of noise on the measurements. This work considers the case when the resultant matrix system is so large that it cannot be explicitly formed and iterative methods of solution cannot be directly implemented. In this case the method of surface decomposition is proposed, where the measurement surface is divided into smaller nonoverlapping subsurfaces. Each subsurface is used to form a smaller matrix system that is solved and the result joined together to generate a global solution to the original matrix system. Numerically generated data are used to study the use of subsurface extensions to increase the continuity of the global solution, and investigate the size of the subsurfaces, as well as the distance between the measurement and the vibrating surface. Finally a vibrating ship hull structure is considered as a physical example to apply and validate the proposed methodology.
    The Journal of the Acoustical Society of America 07/2012; 132(1):186-96. DOI:10.1121/1.4728204 · 1.56 Impact Factor
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    ABSTRACT: A giant negative magnetoresistance of up to 28% at 2.5 T is observed in plasma hydrogenated graphene at the charge neutrality point without any sign of saturation at 2.0 K. A detailed analysis of the gate voltage dependence demonstrates a suppression of the giant negative magnetoresistance, which is accompanied by a crossover from strong localization at low carrier concentrations to weak localization at higher carrier concentrations. Evidence of asymmetry in the electron/hole transport is found in the magnetic field traces at low temperature. The asymmetrical transport is attributed to charge transfer processes at the graphene/metal interface and demonstrates the effect of using invasive contact geometries in hydrogenated graphene devices.
    Physical review. B, Condensed matter 05/2012; 85(19). DOI:10.1103/PhysRevB.85.195437 · 3.66 Impact Factor
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    ABSTRACT: We study the magnetoresistance of hydrogenated graphene devices on a SiO2 substrate. A large negative magnetoresistance of up to 30% in a field of 2.5T is observed at low temperatures and at the film's charge neutrality point without any sign of saturation. A detailed analysis of the gate voltage dependence demonstrates a suppression of the large, negative magnetoresistance, which appears to be driven by a crossover from strong localization at low carrier concentrations to weak localization at higher carrier concentrations. Evidence of electron-hole symmetry breaking is found in the magnetic field traces at low temperature.
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    ABSTRACT: We report shear modulus (G) and internal friction (Q(-1)) measurements of large-area monolayer graphene films grown by chemical vapor deposition on copper foil and transferred onto high-Q silicon mechanical oscillators. The shear modulus, extracted from a resonance frequency shift at 0.4 K where the apparatus is most sensitive, averages 280 GPa. This is five times larger than those of the multilayered graphene-based films measured previously. The internal friction is unmeasurable within the sensitivity of our experiment and thus bounded above by Q(-1) ≤ 3 × 10(-5), which is orders-of-magnitude smaller than that of multilayered graphene-based films. Neither annealing nor interface modification has a measurable effect on G or Q(-1). Our results on G are consistent with recent theoretical evaluations and simulations carried out in this work, showing that the shear restoring force transitions from interlayer to intralayer interactions as the film thickness approaches one monolayer.
    Nano Letters 01/2012; 12(2):1013-7. DOI:10.1021/nl204196v · 12.94 Impact Factor
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    ABSTRACT: We report internal friction and shear modulus measurements of several types of synthesized graphene films. They include reduced graphene oxide, chemical-vapor deposited (CVD) graphene films on thin nickel films and on copper foils. These films were transferred from their host substrate into a water bath, and re-deposited onto to a high-Q single crystal silicon mechanical double-paddle oscillator. A minimal thickness dependence of both internal friction and shear modulus was found for reduced graphene oxide films varying thickness from 4 to 90 nm and CVD graphene films on nickel from 6 to 8 nm. The shear modulus of these multilayered films averages 53 GPa. Their internal friction exhibits a temperature independent plateau below 10K. The values of the plateaus are similar for both the reduced graphene oxide films and CVD graphene films on nickel, and they are as high as the universal "glassy range" where the tunneling states dominated internal friction of amorphous solids lies. In contrast, CVD graphene films on copper foils are 90~95% single layer. The shear modulus of these single layer graphene films are about five times higher, averaging 280 GPa. Their low temperature internal friction is too small to measure within the uncertainty of our experiments. Our results demonstrate the dramatic difference in the elastic properties of multilayer and single layer graphene films.
    Solid State Phenomena 01/2012; 184. DOI:10.4028/www.scientific.net/SSP.184.319
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    ABSTRACT: We report the first observation of the n-type nature of hydrogenated graphene on SiO(2) and demonstrate the conversion of the majority carrier type from electrons to holes using surface doping. Density functional calculations indicate that the carrier type reversal is directly related to the magnitude of the hydrogenated graphene's work function relative to the substrate, which decreases when adsorbates such as water are present. Additionally, we show by temperature-dependent electronic transport measurements that hydrogenating graphene induces a band gap and that in the moderate temperature regime [220-375 K], the band gap has a maximum value at the charge neutrality point, is tunable with an electric field effect, and is higher for higher hydrogen coverage. The ability to control the majority charge carrier in hydrogenated graphene, in addition to opening a band gap, suggests potential for chemically modified graphene p-n junctions.
    ACS Nano 12/2011; 6(1):17-22. DOI:10.1021/nn2034555 · 12.03 Impact Factor
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    ABSTRACT: Graphene films grown by chemical vapor deposition on copper foils were hydrogenated using commercially viable methods. Parameters such as plasma power, plasma frequency, and sample temperature were varied to determine the maximum possible hydrogenation without etching the film. The kinetic energy of the ions inside the plasma is critical, in that higher kinetic energy ions tend to etch the film while lower kinetic energy ions participate in the hydrogenation process. The film sheet resistance was shown to increase, while the hole mobility was shown to decrease with increasing hydrogenation. Variable temperature measurements demonstrate a transition from semi-metallic behavior for graphene to semiconducting behavior for hydrogenated graphene. Sheet resistance measurements as a function of temperature also suggest the emergence of a bandgap in the hydrogenated graphene films.
    Carbon 11/2011; 49(13):4420-4426. DOI:10.1016/j.carbon.2011.06.034 · 6.16 Impact Factor
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    ABSTRACT: A broadband (3-40 kHz) compact range measurement technique has been developed to obtain the acoustic scattering from buried unexploded ordnance and objects simulating natural and man-made clutter. The targets-two 5 in. rockets with 0, 30, and 60 deg pitch angles, a large rock, and cinder blocks with 0 and 45 deg roll-are buried 10 cm beneath the surface of a water-saturated sandy bottom with a mean grain size of 240 μm. A 2D synthetic array is generated at a height of 20 cm above the sediment-water interface with an element spacing of 3 cm (25 kHz Nyquist). Waveforms collected on the synthetic array are processed to extract the structural acoustic response of the buried targets. A Relevance Vector Machine algorithm applied to the scattered data for target identification, which shows that the target features separate even as the receiver array size is considerably decreased. Similar results are presented for numerical simulations of the bistatic returns for the buried 5 in. rocket and a rock of comparable size. [Work supported by ONR and SERDP.].
    The Journal of the Acoustical Society of America 10/2011; 130(4):2341. DOI:10.1121/1.3654366 · 1.56 Impact Factor
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    ABSTRACT: A compact directional acoustic sensor concept is described, which uses an multi-optical fiber probe, a light emitting diode source, a photo-diode detector, and a short, slender cylindrical cantilever to the end of which is attached an optical reflector. A portion of the light exiting one fiber is collected by a second fiber after reflection from the mirror. Acoustically induced transverse displacement of the cantilever tip modulates the light collected by the second fiber, which then conveys the light to a photo-detector. Directional sensitivity is achieved by virtue of the dependence of the collected light on the cosine of the angle between the line connecting the probe fiber centers and the direction of displacement of the cantilever tip (the acoustic wave direction). An analytic model of the acoustic response of the cantilever tip is constructed, which is partially verified using a finite element-based model and experimentally validated using measurements of the acoustic response in air. The model is used to predict its acoustic response versus frequency, how that response depends upon damping near the cantilever resonance frequency, and to what extent and over what frequency band that response depends upon the acoustically generated flow force. [Work supported by ONR.].
    The Journal of the Acoustical Society of America 10/2011; 130(4):2393. DOI:10.1121/1.3654593 · 1.56 Impact Factor
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    ABSTRACT: We present the first nanomechanical resonators microfabricated in single-crystal diamond. Shell-type resonators only 70 nm thick, the thinnest single crystal diamond structures produced to date, demonstrate a high-quality factor (Q approximate to 1000 at room temperature, Q approximate to 20 000 at 10 K) at radio frequencies (50-600 MHz). Quality factor dependence on temperature and frequency suggests an extrinsic origin to the dominant dissipation mechanism and methods to further enhance resonator performance.
    Nano Letters 09/2011; 11(10):4304-8. DOI:10.1021/nl202326e · 12.94 Impact Factor
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    ABSTRACT: We report measurements of energy dissipation in single crystal diamond annular plate resonators for temperatures ranging from 4 to 300 K. An order of magnitude reduction in dissipation is observed as the temperature is lowered from room temperature (1/Q = 5 × 10−4) to 30 K (1/Q = 5 × 10−5).Highlights► Single crystal diamond annular plate resonators; ~ 10 μm diameter, ~ 175 nm thick. ► ~ 50 MHz fundamental and 177 MHz overtone studied. ► Dissipation drops an order of magnitude with temperature from 300 K to 30 K. ► Dissipation up to factor of 5 lower than for ~ 50 MHz NCD or UNCD resonators.
    Diamond and Related Materials 08/2011; 20(8):1204-1207. DOI:10.1016/j.diamond.2011.06.016 · 1.57 Impact Factor
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    ABSTRACT: A zero-power ballast control system that could be used to float and submerge a device solely using a gas source was built and tested. This system could be used to convey sensors, data loggers, and communication devices necessary for water quality monitoring and other applications by periodically maneuvering up and down a water column. Operational parameters for the system such as duration of the submerged and buoyant states can be varied according to its design. The gas source can be of any origin, e.g., compressed air, underwater gas vent, gas produced by microbes, etc. The zero-power ballast system was initially tested using a gas pump and further tested using gas produced by Clostridium acetobutylicum. Using microbial gas production as the only source of gas and no electrical power during operation, the system successfully floated and submerged periodically with a period of 30 min for at least 24 h. Together with microbial fuel cells, this system opens up possibilities for underwater monitoring systems that could function indefinitely.
    The Review of scientific instruments 05/2011; 82(5):055108. DOI:10.1063/1.3587623 · 1.58 Impact Factor

Publication Stats

927 Citations
263.79 Total Impact Points

Institutions

  • 2002–2013
    • United States Naval Research Laboratory
      Washington, Washington, D.C., United States
  • 2011
    • United States Navy
      Monterey, California, United States
  • 2010
    • Louisiana State University
      • Department of Mechanical Engineering
      Baton Rouge, Louisiana, United States
  • 2003
    • Naval Undersea Warfare Center
      Newport, Rhode Island, United States
    • Cornell University
      Ithaca, New York, United States