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  • American Institute of Physics (AIP)  (154)
  • Nature Publishing Group  (79)
  • 2015-2019  (20)
  • 1985-1989  (178)
  • 1935-1939  (35)
  • 1
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    The effect of residual gas scattering on Ga ion beam patterning of graphene (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-11-24
    Description: The patterning of graphene by a 30 kV Ga + focused ion beam (FIB) is studied by in-situ and ex-situ Raman spectroscopy. It is found that the graphene surrounding the patterned target area can be damaged at remarkably large distances of more than 10  μ m. We show that scattering of the Ga ions in the residual gas of the vacuum system is the main cause of the large range of lateral damage, as the size and shape of the tail of the ion beam were strongly dependent on the system background pressure. The range of the damage was therefore greatly reduced by working at low pressures and limiting the total amount of ions used. This makes FIB patterning a feasible alternative to electron beam lithography as long as residual gas scattering is taken into account.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 2
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    Wavelet analysis methods for radiography of multidimensional growth of planar mixing layers (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-07-07
    Description: The counter-propagating shear campaign is examining instability growth and its transition to turbulence in the high-energy-density physics regime using a laser-driven counter-propagating flow platform. In these experiments, we observe consistent complex break-up of and structure growth in a tracer layer placed at the shear flow interface during the instability growth phase. We present a wavelet-transform based analysis technique capable of characterizing the scale- and directionality-resolved average intensity perturbations in static radiographs of the experiment. This technique uses the complete spatial information available in each radiograph to describe the structure evolution. We designed this analysis technique to generate a two-dimensional power spectrum for each radiograph from which we can recover information about structure widths, amplitudes, and orientations. The evolution of the distribution of power in the spectra for an experimental series is a potential metric for quantifying the structure size evolution as well as a system’s evolution towards isotropy.
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Published by American Institute of Physics (AIP)
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  • 3
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    A generalization of the Drude-Smith formula for magneto-optical conductivities in Faraday geometry (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-07-01
    Description: In this study, we generalize the impulse response approach and Poisson statistics proposed by Smith [Phys. Rev. B 64 , 155106 (2001)] to evaluate the longitudinal and transverse magneto-optical conductivities in an electron gas system in Faraday geometry. Comparing with the standard Drude model, the coefficients a n are introduced in the Drude-Smith formula to describe the backscattering or localization effect for the n th electronic scattering event. Such a formula can also be applied to study the elements of the dielectric function matrix in the presence of magnetic and radiation fields in electron gas systems. This theoretical work is primely motivated by recent experimental activities in measuring the real and imaginary parts of longitudinal and transverse magneto-optical conductivities in condensed matter materials and electronic devices using terahertz time-domain spectroscopy. We believe that the results obtained from this study can provide an appropriate theoretical tool in reproducing the experimental findings and in fitting with experimental data to determine the important sample and material parameters.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 4
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    The Shock/Shear platform for planar radiation-hydrodynamics experiments on the National Ignition Facilitya) (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-04-18
    Description: An indirectly-driven shock tube experiment fielded on the National Ignition Facility (NIF) was used to create a high-energy-density hydrodynamics platform at unprecedented scale. Scaling up a shear-induced mixing experiment previously fielded at OMEGA, the NIF shear platform drives 130  μ m/ns shocks into a CH foam-filled shock tube (∼ 60 mg/cc) with interior dimensions of 1.5 mm diameter and 5 mm length. The pulse-shaping capabilities of the NIF are used to extend the drive for 〉10 ns, and the large interior tube volumes are used to isolate physics-altering edge effects from the region of interest. The scaling of the experiment to the NIF allows for considerable improvement in maximum driving time of hydrodynamics, in fidelity of physics under examination, and in diagnostic clarity. Details of the experimental platform and post-shot simulations used in the analysis of the platform-qualifying data are presented. Hydrodynamic scaling is used to compare shear data from OMEGA with that from NIF, suggesting a possible change in the dimensionality of the instability at late times from one platform to the other.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 5
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    Modifying mixing and instability growth through the adjustment of initial conditions in a high-energy-density counter-propagating shear experiment on OMEGA (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-06-25
    Description: Counter-propagating shear experiments conducted at the OMEGA Laser Facility have been evaluating the effect of target initial conditions, specifically the characteristics of a tracer foil located at the shear boundary, on Kelvin-Helmholtz instability evolution and experiment transition toward nonlinearity and turbulence in the high-energy-density (HED) regime. Experiments are focused on both identifying and uncoupling the dependence of the model initial turbulent length scale in variable-density turbulence models of k- ϵ type on competing physical instability seed lengths as well as developing a path toward fully developed turbulent HED experiments. We present results from a series of experiments controllably and independently varying two initial types of scale lengths in the experiment: the thickness and surface roughness (surface perturbation scale spectrum) of a tracer layer at the shear interface. We show that decreasing the layer thickness and increasing the surface roughness both have the ability to increase the relative mixing in the system, and thus theoretically decrease the time required to begin transitioning to turbulence in the system. We also show that we can connect a change in observed mix width growth due to increased foil surface roughness to an analytically predicted change in model initial turbulent scale lengths.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 6
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    Combined optical sizing and acoustical characterization of single freely-floating microbubbles (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-12-08
    Description: In this study we present a combined optical sizing and acoustical characterization technique for the study of the dynamics of single freely-floating ultrasound contrast agent microbubbles exposed to long burst ultrasound excitations up to the milliseconds range. A co-axial flow device was used to position individual microbubbles on a streamline within the confocal region of three ultrasound transducers and a high-resolution microscope objective. Bright-field images of microbubbles passing through the confocal region were captured using a high-speed camera synchronized to the acoustical data acquisition to assess the microbubble response to a 1-MHz ultrasound burst. Nonlinear bubble vibrations were identified at a driving pressure as low as 50 kPa. The results demonstrate good agreement with numerical simulations based on the shell-buckling model proposed by Marmottant et al . [J. Acoust. Soc. Am. 118 , 3499–3505 (2005)]. The system demonstrates the potential for a high-throughput in vitro characterization of individual microbubbles.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 7
    Electronic Resource
    Electronic Resource
    Structural and soft-magnetic properties of Fe/CoNbZr and Fe/FeCrB multilayers (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 748-755 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetic and structural properties of ion-beam-sputtered Fe/FeCrB and Fe/CoNbZr multilayers were studied as a function of the FeCrB and CoNbZr layer thicknesses. Good soft-magnetic properties (coercivity 〈60 A/m and permeability 〉1000) are obtained only when Fe grains are small, which requires, on the one hand, multilayers with Fe layer thicknesses below 10 nm and, on the other hand, FeCrB interlayers with thicknesses above 1 nm or CoNbZr interlayers with thicknesses above 3 nm. In this case interlayers are amorphous, which induces repeated nucleation of Fe grains. Only at FeCrB thicknesses of 1 nm are the interlayers crystalline due to interface mixing. This in contrast to CoNbZr interlayers which in addition grow epitaxially in a crystalline structure up to thicknesses of 3 nm. When interlayers are crystalline columnar growth of Fe results. As a consequence coercivity increases and permeability decreases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.343550
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  • 8
    Electronic Resource
    Electronic Resource
    Magnetic and structural properties of MMNi4.15Fe0.85 and its hydride (abstract) (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 3620-3620 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Mischmetal (MM) has been considered as a possible substitute for the rare-earth component in both permanent magnets1,2 and hydrogen storage intermetallics. We have investigated the magnetic and structural properties of a mischmetal-nickel-iron intermetallic and its hydride using magnetization, Mössbauer, x-ray diffraction, and SEM measurements. Magnetic susceptibility measurements were made between room and liquid-nitrogen temperatures. There was a change in the magnetic character of the unhydrided sample at 140 K. Hydriding produced a large increase in the susceptibility with a corresponding change in the magnetization at low temperatures. The 57Fe Mössbauer spectra of the intermetallic yielded a doublet at room temperature and demonstrated a change in magnetic behavior similar to the magnetization results at low temperatures. Experimental data were used to interpret the hydrogen absorption mechanism acting in this intermetallic and the results are discussed with respect to previously proposed models for rare earth-transition metal compounds.3,4
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.340715
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  • 9
    Electronic Resource
    Electronic Resource
    Reduction of stored energy in a heavily irradiated ceramic (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 2062-2064 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The decrease of stored energy that accompanies redamage of a metamict ceramic is compared with the calculated elastic strain energy resulting from the volume misfit between the disordered inclusions and the crystalline matrix. In the case of self-damaged CaPuTi2O7 it is found that the elastic energy contributes no more than 20% to the observed energy decrease. The major part of this decrease must be attributed to rearrangement of atoms by the redamage process into configurations of lower energy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.339550
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  • 10
    Electronic Resource
    Electronic Resource
    Thermal stability of thin-film amorphous W-Ru, W-Re, and Ta-Ir alloys (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 1212-1215 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The crystallization behavior of self-supporting thin-film amorphous W-Ru, W-Re, and Ta-Ir alloys has been studied with transmission electron microscopy. Crystallization temperatures have been observed which are much lower than the temperatures predicted by a semiempirical model: the highest observed temperatures are 775 °C for W-Ru and W-Re alloys, and 900 °C for the Ta-Ir alloys. All three systems show maximum thermal stability at a composition expected using enthalpy considerations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.338171
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