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  • 1
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    Liquid-induced damping of mechanical feedback effects in single electron tunneling through a suspended carbon nanotube (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-09-24
    Description: In single electron tunneling through clean, suspended carbon nanotube devices at low temperature, distinct switching phenomena have regularly been observed. These can be explained via strong interaction of single electron tunneling and vibrational motion of the nanotube. We present measurements on a highly stable nanotube device, subsequently recorded in the vacuum chamber of a dilution refrigerator and immersed in the 3 He/  4 He mixture of a second dilution refrigerator. The switching phenomena are absent when the sample is kept in the viscous liquid, additionally supporting the interpretation of dc-driven vibration. Transport measurements in liquid helium can thus be used for finite bias spectroscopy where otherwise the mechanical effects would dominate the current.
    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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    Optimizing the performance of the entropic splitter for particle separation (2014)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2014-08-19
    Description: Recently, it has been shown that entropy can be used to sort Brownian particles according to their size. In particular, a combination of a static and a time-dependent force applied on differently sized particles which are confined in an asymmetric periodic structure can be used to separate them efficiently, by forcing them to move in opposite directions. In this paper, we investigate the optimization of the performance of the “entropic splitter.” Specifically, the splitting mechanism and how it depends on the geometry of the channel, and the frequency and strength of the periodic forcing is analyzed. Using numerical simulations, we demonstrate that a very efficient and fast separation with a practically 100% purity can be achieved by a proper optimization of the control variables. The results of this work could be useful for a more efficient separation of dispersed phases such as DNA fragments or colloids dependent on their size.
    Print ISSN: 0021-9606
    Electronic ISSN: 1089-7690
    Topics: Chemistry and Pharmacology , Physics
    Published by American Institute of Physics (AIP)
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  • 3
    Electronic Resource
    Electronic Resource
    Electrical and optical properties of TiO2 anatase thin films (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 2042-2047 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electrical and optical spectroscopic studies of TiO2 anatase thin films deposited by sputtering show that the metastable phase anatase differs in electronic properties from the well-known, stable phase rutile. Resistivity and Hall-effect measurements reveal an insulator–metal transition in a donor band in anatase thin films with high donor concentrations. Such a transition is not observed in rutile thin films with similar donor concentrations. This indicates a larger effective Bohr radius of donor electrons in anatase than in rutile, which in turn suggests a smaller electron effective mass in anatase. The smaller effective mass in anatase is consistent with the high mobility, bandlike conduction observed in anatase crystals. It is also responsible for the very shallow donor energies in anatase. Luminescence of self-trapped excitons is observed in anatase thin films, which implies a strong lattice relaxation and a small exciton bandwidth in anatase. Optical absorption and photoconductivity spectra show that anatase thin films have a wider optical absorption gap than rutile thin films.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356306
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  • 4
    Electronic Resource
    Electronic Resource
    Raman scattering from PbTiO3 thin films prepared on silicon substrates by radio frequency sputtering and thermal treatment (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 394-399 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Raman scattering has been carried out on PbTiO3 thin films prepared on platinum-coated (100) silicon by radio-frequency (rf)-magnetron sputtering without substrate heating and a post-deposition thermal treatment. The Raman spectra obtained from the thin film are characteristic of powder Raman spectra: In comparison with the single crystal spectra, the intensity of the background is relatively high at low frequencies and the Raman lines are broad. The lattice phonon modes corresponding to the observed lines are identified by comparison with the data on single crystals and powder. The Raman frequencies for the thin film remarkably shift to low frequencies compared with single-crystal data. It is shown that the phenomenon of the frequency shifts is similar with the hydrostatic pressure effect on single crystals of PbTiO3. The result indicates that the thin films are composed of grains that are stressed depending on the grain size by neighboring grains of different orientations when they are split up into ferroelectric domains at the paraelectric-to-ferroelectric transition. This stress effect is significant even for a grain size of ∼0.5 μm. It is found that the lowest frequency E transverse optical (TO) mode in the thin film shows softening with increasing temperature as was reported in previous studies on single crystals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353862
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  • 5
    Electronic Resource
    Electronic Resource
    Raman scattering study of lead zirconate titanate thin films prepared on silicon substrates by radio frequency magnetron sputtering (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 6625-6631 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Raman scattering is used to characterize thin films of PbTi1−xZrxO3. The films have been prepared on platinum-coated (100) silicon by radio-frequency (rf)-magnetron sputtering without substrate heating followed by a post-deposition annealing at 600–650 °C. As the concentration of Zr is increased, the Raman peaks broaden and their intensities decrease more rapidly compared with bulk ceramic or powder samples, while the background intensity increases. The observations show that the crystal structure of the films is locally deformed and significantly disordered. With increasing x, the soft E(TO) mode shifts to lower frequencies. An additional Raman peak appears besides the phonon peaks expected in a perfect crystal. The soft mode strongly couples with the extra mode, similarly with the case of ceramic samples. The results are related to features of the thin films such as a frustrated phase transition, i.e., smaller differences between the lattice parameters a and c in comparison with powder data, and an electrical behavior showing a diffuse ferroelectric-to-paraelectric transition with a broad peak.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355103
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  • 6
    Electronic Resource
    Electronic Resource
    The pseudospectrum of the resistive magnetohydrodynamics operator: Resolving the resistive Alfvén paradox (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 3151-3160 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The "Alfvén paradox'' is that as resistivity decreases, the discrete eigenmodes do not converge to the generalized eigenmodes of the ideal Alfvén continuum. To resolve the paradox, the ε-pseudospectrum of the resistive magnetohydrodynamic (RMHD) operator is considered. It is proven that for any ε, the ε-pseudospectrum contains the Alfvén continuum for sufficiently small resistivity. Formal ε-pseudoeigenmodes are constructed using the formal Wentzel–Kramers–Brillouin–Jeffreys solutions, and it is shown that the entire stable half-annulus of complex frequencies with ρ||ω||2=||k⋅B(x)||2 is resonant to order ε, i.e., belongs to the ε-pseudospectrum. The resistive eigenmodes are exponentially ill-conditioned as a basis and the condition number is proportional to exp(R1/2M), where RM is the magnetic Reynolds number.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870468
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  • 7
    Electronic Resource
    Electronic Resource
    On the collision of rigid spheres in a weakly compressible fluid (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 2683-2689 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Reliable representations for the interparticular collision laws for inertially dominated particulate flows remain elusive due to the complexity of this interaction. In this study, compressibility of both the solid and the containing fluid are considered in the context of pairwise collisions, and the conditions under which these are important are identified in terms of a regime map. To identify the suspension flow conditions under which compressibility effects are important, the map is presented in terms of granular flow quantities, which are derived from the parameters associated with the pairwise collision problem. After demonstrating that there exists a flow regime where the compressibility of the fluid is important, the collision of two rigid spherical particles in a weakly compressible fluid is investigated. Lubrication theory and a perturbation approach for the fluid density are applied to analytically determine the pressure correction due to weak fluid compressibility. It is shown that the first-order dynamical equation describing the collision process does not support rebounding particle trajectories, therefore characterizing rebound as an inherently nonlinear compressibility effect.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858455
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  • 8
    Electronic Resource
    Electronic Resource
    A new mechanism for rapid transition involving a pair of oblique waves (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 1986-1989 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A pair of small but finite-amplitude oblique waves were used as initial condition in numerical simulations of transition to turbulent flow. A rapid energy growth to a transition peak occurred. Although this transition scenario is triggered by a nonlinear interaction, the dominant mechanism yielding substantial disturbance amplitudes was found to be linear. A number of simulations were made that showed that the overall features of this transition scenario remains the same for a range of parameter values.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858367
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  • 9
    Electronic Resource
    Electronic Resource
    Atomic scale study of local TiSi2/Si epitaxies (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 1820-1825 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The TiSi2/Si system is investigated using high-resolution transmission electron microscopy (HRTEM) and electron diffraction in both cross-section and flat-on modes. The results show that the large crystallographic differences between both crystals and the complexity of the reaction path are not obstacles to the formation of flat and well-defined interfaces. (1¯01) TiSi2 proves to be a preferential plane for epitaxial growth on Si (111). In this case, the terminal TiSi2 plane at the interface is composed of single atomic species. It is proposed that the reasons leading to such an epitaxy are related to the small discrepancy of atomic densities and interplanar spacings characteristic of these planes. Observation of local epitaxial relationships are reported and investigated using a lattice matching model. It turns out that they minimize the two-dimensional misfit at the interface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345609
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  • 10
    Electronic Resource
    Electronic Resource
    Oxidation resistance of protective coatings studied by spectroscopic ellipsometry (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 3194-3196 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Spectroscopic ellipsometry is applied to determine the oxidation resistance of TiN and CrN coatings. This technique proves to provide accurate measurements of the oxide layer thickness in a convenient, fast, and nondestructive manner. The magnetron-sputtered thin films were heated in air in the temperature range between 673 and 925 K. The verification with scanning electron microscopy and x-ray reflectometry shows an excellent agreement between these complementary techniques. The rate constant k of the oxidation is directly related to the film morphology in TiN thin films. While understoichiometric films with a dense fine-grained structure exhibit a moderate k of 4 nm2/s at 773 K, overstoichiometric films with a pronounced columnar structure oxidized over seven times faster. The nonstoichiometry in TiNy and CrNy leads to a reduced activation energy for oxidation compared to stoichiometric compounds. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.126626
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