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  • 1
    Online Resource
    Online Resource
    Field-structured magnetic platelets as a route to improved thermal interface materials
    AIP Publishing ; 2012
    In:  Journal of Applied Physics Vol. 111, No. 7 ( 2012-04-01)
    Details
    In: Journal of Applied Physics, AIP Publishing, Vol. 111, No. 7 ( 2012-04-01)
    Abstract: The development of high-performance thermal interface materials (TIMs) is crucial to enabling future generations of microelectronics because the TIM is usually the limiting thermal resistance in the heat removal path. Typical TIMs achieve modest thermal conductivities by including large volume fractions of randomly-dispersed, highly-conductive, spherical particles in a polymer resin. This paper explores field-structured magnetic platelet composites as a new approach to more effective TIMs. The motivation for this approach is rooted in shape functional theory, which shows that when the particle material has a significantly higher thermal conductivity than that of the polymer, the particle shape and orientation are the factors that limit conductivity enhancement. Oriented platelets are highly effective for heat transfer and if these are magnetic, then magnetic fields can be used to both orient and agglomerate these into structures that efficiently direct heat flow. In this paper we show that such field-structured composites have a thermal conductivity anisotropy of ∼3, and at the highest particle loading of 16 vol.% we have achieved a 23-fold conductivity enhancement, which is 3-times larger than that achieved in unstructured platelet composites and 8-times greater than unstructured spherical particle composites.
    Type of Medium: Online Resource
    ISSN: 0021-8979 , 1089-7550
    URL: Article
    DOI: 10.1063/1.3699013
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2012
    detail.hit.zdb_id: 220641-9
    detail.hit.zdb_id: 3112-4
    detail.hit.zdb_id: 1476463-5
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  • 2
    Online Resource
    Online Resource
    Atom–matrix interactions: An MCD study of copper atoms in argon
    AIP Publishing ; 1983
    In:  The Journal of Chemical Physics Vol. 78, No. 5 ( 1983-03-01), p. 2231-2239
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 78, No. 5 ( 1983-03-01), p. 2231-2239
    Abstract: The absorption and MCD spectra of the 2P ← 2S transition of Cu atoms isolated in argon matrices have been measured over the temperature range 13–25 K. Spectral band moments (up to third order in MCD) have been determined and parameters of interest extracted from them. The observed triplet bands’ separation and MCD 𝒞 term signs are analyzed assuming a static trigonal site distortion. It is shown that a static site distortion model is incapable of reproducing the experimental results. Simultaneous spin orbit and noncubic lattice vibrational couplings (Jahn–Teller effect) are shown to be active in the Cu excited 2P state. The observed triplet of bands and its MCD 𝒞 terms are satisfactorily described by an adiabatic model developed by Moran. Comparison of the observed band shape to ones calculated by Cho using Monte Carlo methods show that simultaneous spin-orbit and e and t2 lattice mode interactions are operative. The observed reduction of 25% in the excited state spin-orbit coupling constant is attributed to the overlap of Cu 4p orbitals with the Ar 3p orbitals. A new method for the determination of the temperature of matrix-isolated samples is described. The temperature dependence of the MCD first moment and absorption zeroth moment of a matrix-isolated paramagnetic species is determined once to find the lowest temperature attainable.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.445068
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1983
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 3
    Online Resource
    Online Resource
    Isothermal Magnetic Advection: Creating functional fluid flows for heat and mass transfer
    AIP Publishing ; 2010
    In:  Applied Physics Letters Vol. 97, No. 3 ( 2010-07-19)
    Details
    In: Applied Physics Letters, AIP Publishing, Vol. 97, No. 3 ( 2010-07-19)
    Abstract: Natural convection has been of interest for over a century due to its rich nonlinear dynamics and applications to heat transfer. However, convection occurs only when both gravity and a destabilizing thermal gradient exist. We have discovered a unique class of vigorous, emergent fluid flows that have the full functionality of natural convection but can be stimulated regardless of gravity or thermal gradients, simply by subjecting a platelet suspension to certain time-dependent biaxial magnetic fields of modest strength. This enigmatic phenomenon may facilitate cooling in microgravity environments and in other circumstances where convection fails.
    Type of Medium: Online Resource
    ISSN: 0003-6951 , 1077-3118
    URL: Article
    URL: Article
    URL: Article
    URL: Article
    DOI: 10.1063/1.3462310
    DOI: 10.1063/1.3462310.1
    DOI: 10.1063/1.3462310.2
    DOI: 10.1063/1.3462310.3
    RVK:
    UA 1000
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2010
    detail.hit.zdb_id: 211245-0
    detail.hit.zdb_id: 1469436-0
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  • 4
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    Online Resource
    Ultrafast electron diffraction from transiently aligned asymmetric top molecules: Rotational dynamics and structure retrieval
    AIP Publishing ; 2022
    In:  Structural Dynamics Vol. 9, No. 5 ( 2022-09-01)
    Details
    In: Structural Dynamics, AIP Publishing, Vol. 9, No. 5 ( 2022-09-01)
    Abstract: Ultrafast electron diffraction (UED) from aligned molecules in the gas phase has successfully retrieved structures of both linear and symmetric top molecules. Alignment of asymmetric tops has been recorded with UED but no structural information was retrieved. We present here the extraction of two-dimensional structural information from simple transformations of experimental diffraction patterns of aligned molecules as a proof-of-principle for the recovery of the full structure. We align 4-fluorobenzotrifluoride with a linearly polarized laser and show that we can distinguish between atomic pairs with equal distances that are parallel and perpendicular to the aligned axis. We additionally show with numerical simulations that by cooling the molecules to a rotational temperature of 1 K, more distances and angles can be resolved through direct transformations.
    Type of Medium: Online Resource
    ISSN: 2329-7778
    URL: Article
    DOI: 10.1063/4.0000163
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2022
    detail.hit.zdb_id: 2758684-4
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  • 5
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    Mesmerizing magnetic fields
    AIP Publishing ; 2015
    In:  Physics Today Vol. 68, No. 8 ( 2015-08-01), p. 66-67
    Details
    In: Physics Today, AIP Publishing, Vol. 68, No. 8 ( 2015-08-01), p. 66-67
    Abstract: The behavior displayed by a suspension of magnetic particles exposed to a rapidly varying multiaxial magnetic field is both dazzling and practically applicable.
    Type of Medium: Online Resource
    ISSN: 0031-9228 , 1945-0699
    URL: Article
    DOI: 10.1063/PT.3.2892
    RVK:
    UA 1000
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2015
    detail.hit.zdb_id: 2031187-4
    detail.hit.zdb_id: 208863-0
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  • 6
    Online Resource
    Online Resource
    Field-structured, multilayered platelets enable high performance, dielectric thermal composites
    AIP Publishing ; 2012
    In:  Journal of Applied Physics Vol. 112, No. 5 ( 2012-09-01)
    Details
    In: Journal of Applied Physics, AIP Publishing, Vol. 112, No. 5 ( 2012-09-01)
    Abstract: Moldable, thermally conductive polymer composites have broad applications as thermal interface materials and encapsulants. These thermal composites are generally comprised of single-phase particles that are randomly oriented and dispersed. Magnetic platelets have been shown to give exceptionally high thermal conductivities when magnetically aligned along the intended direction of heat flow, but produce composites that are electrically conductive. We have designed precision multilayered platelets that enable the development of high performance thermal composites that are electrically insulating. These platelets consist of a thin Ni core that permits field alignment, Al or Cu coatings that facilitate heat transport, and dielectric layers of MgF2 or SiO2 that ensure that the final composite is electrically insulating. These platelets can be made flat or corrugated, square or irregular, and the thickness of the various layers can be varied over a wide range. Thermal conductivity data for a variety of platelet compositions, layer thicknesses, and geometries demonstrate that these platelets are highly effective at producing composites with thermal conductivities much greater than that of the resin. Simulation data are presented that show that multilayer platelets have surprising dependencies of their efficiency for heat transfer on the relative thermal conductivities of the various layers. In fact, analysis shows that if the thermal conductivity of the particle phase is much greater than that of the resin, then the thermal conductivity of the composite, at fixed number density of particles, is insensitive to the platelet thickness. These electrically insulating composites would be especially useful as thermally conductive encapsulants for electronic devices.
    Type of Medium: Online Resource
    ISSN: 0021-8979 , 1089-7550
    URL: Article
    DOI: 10.1063/1.4747833
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2012
    detail.hit.zdb_id: 220641-9
    detail.hit.zdb_id: 3112-4
    detail.hit.zdb_id: 1476463-5
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  • 7
    Online Resource
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    Controlling the column spacing in isothermal magnetic advection to enable tunable heat and mass transfer
    AIP Publishing ; 2012
    In:  Journal of Applied Physics Vol. 112, No. 9 ( 2012-11-01)
    Details
    In: Journal of Applied Physics, AIP Publishing, Vol. 112, No. 9 ( 2012-11-01)
    Abstract: Isothermal magnetic advection (IMA) is a recently discovered method of inducing highly organized, non-contact flow lattices in suspensions of magnetic particles, using only uniform ac magnetic fields of modest strength. The initiation of these vigorous flows requires neither a thermal gradient nor a gravitational field, and so can be used to transfer heat and mass in circumstances where natural convection does not occur. These advection lattices are comprised of a square lattice of antiparallel flow columns. If the column spacing is sufficiently large compared to the column length and the flow rate within the columns is sufficiently large, then one would expect efficient transfer of both heat and mass. Otherwise, the flow lattice could act as a countercurrent heat exchanger and only mass will be efficiently transferred. Although this latter case might be useful for feeding a reaction front without extracting heat, it is likely that most interest will be focused on using IMA for heat transfer. In this paper, we explore the various experimental parameters of IMA to determine which of these can be used to control the column spacing. These parameters include the field frequency, strength, and phase relation between the two field components, the liquid viscosity, and particle volume fraction. We find that the column spacing can easily be tuned over a wide range to enable the careful control of heat and mass transfer.
    Type of Medium: Online Resource
    ISSN: 0021-8979 , 1089-7550
    URL: Article
    DOI: 10.1063/1.4764308
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2012
    detail.hit.zdb_id: 220641-9
    detail.hit.zdb_id: 3112-4
    detail.hit.zdb_id: 1476463-5
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  • 8
    Online Resource
    Online Resource
    Vortex magnetic field mixing with anisometric particles
    AIP Publishing ; 2010
    In:  Journal of Applied Physics Vol. 107, No. 11 ( 2010-06-01)
    Details
    In: Journal of Applied Physics, AIP Publishing, Vol. 107, No. 11 ( 2010-06-01)
    Abstract: Recently, we reported a vigorous, scale-adaptive mixing technique suitable for microfluidic applications, wherein a suspension of spherical magnetic particles is subjected to a vortex magnetic field, which induces the formation of dynamic particle chains that efficiently stir the solution. Here we explore the dependence of the mixing torque on particle shape, and show that increasing degrees of shape anisometry (i.e., spheres, platelets, rods) give increased mixing torque at the same particle volume fraction. Moreover, all particles, regardless of shape, exhibit similar dependencies of the mixing torque on the vortex field parameters: the torque is maximized in a balanced vortex magnetic field, is proportional to the square of the field strength, and is independent of the field frequency. However, the torque advantage of anisometric particles is somewhat offset by their increased packing volume, which can make the removal of trapped fluid difficult.
    Type of Medium: Online Resource
    ISSN: 0021-8979 , 1089-7550
    URL: Article
    DOI: 10.1063/1.3394000
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2010
    detail.hit.zdb_id: 220641-9
    detail.hit.zdb_id: 3112-4
    detail.hit.zdb_id: 1476463-5
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  • 9
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    Online Resource
    High current table-top setup for femtosecond gas electron diffraction
    AIP Publishing ; 2017
    In:  Structural Dynamics Vol. 4, No. 4 ( 2017-07-01)
    Details
    In: Structural Dynamics, AIP Publishing, Vol. 4, No. 4 ( 2017-07-01)
    Abstract: We have constructed an experimental setup for gas phase electron diffraction with femtosecond resolution and a high average beam current. While gas electron diffraction has been successful at determining molecular structures, it has been a challenge to reach femtosecond resolution while maintaining sufficient beam current to retrieve structures with high spatial resolution. The main challenges are the Coulomb force that leads to broadening of the electron pulses and the temporal blurring that results from the velocity mismatch between the laser and electron pulses as they traverse the sample. We present here a device that uses pulse compression to overcome the Coulomb broadening and deliver femtosecond electron pulses on a gas target. The velocity mismatch can be compensated using laser pulses with a tilted intensity front to excite the sample. The temporal resolution of the setup was determined with a streak camera to be better than 400 fs for pulses with up to half a million electrons and a kinetic energy of 90 keV. The high charge per pulse, combined with a repetition rate of 5 kHz, results in an average beam current that is between one and two orders of magnitude higher than previously demonstrated.
    Type of Medium: Online Resource
    ISSN: 2329-7778
    URL: Article
    DOI: 10.1063/1.4983225
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2017
    detail.hit.zdb_id: 2758684-4
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  • 10
    Online Resource
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    Micro-fabricated stylus ion trap
    AIP Publishing ; 2013
    In:  Review of Scientific Instruments Vol. 84, No. 8 ( 2013-08-01)
    Details
    In: Review of Scientific Instruments, AIP Publishing, Vol. 84, No. 8 ( 2013-08-01)
    Abstract: An electroformed, three-dimensional stylus Paul trap was designed to confine a single atomic ion for use as a sensor to probe the electric-field noise of proximate surfaces. The trap was microfabricated with the UV-LIGA technique to reduce the distance of the ion from the surface of interest. We detail the fabrication process used to produce a 150 μm tall stylus trap with feature sizes of 40 μm. We confined single, laser-cooled, 25Mg+ ions with lifetimes greater than 2 h above the stylus trap in an ultra-high-vacuum environment. After cooling a motional mode of the ion at 4 MHz close to its ground state (⟨n⟩ = 0.34 ± 0.07), the heating rate of the trap was measured with Raman sideband spectroscopy to be 387 ± 15 quanta/s at an ion height of 62 μm above the stylus electrodes.
    Type of Medium: Online Resource
    ISSN: 0034-6748 , 1089-7623
    URL: Article
    DOI: 10.1063/1.4817304
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2013
    detail.hit.zdb_id: 209865-9
    detail.hit.zdb_id: 1472905-2
    SSG: 11
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