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  • 1
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    Localised polymer networks in chiral nematic liquid crystals for high speed photonic switching (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-05-14
    Description: Self-assembled periodic structures based upon chiral liquid crystalline materials have significant potential in the field of photonics ranging from fast-switching optoelectronic devices to low-threshold lasers. The flexoelectro-optic effect, which is observed in chiral nematic liquid crystals (LCs) when an electric field is applied perpendicular to the helical axis, has significant potential as it exhibits analogue switching in 10–100  μ s. However, the major technological barrier that prohibits the commercial realisation of this electro-optic effect is the requirement of a uniform, in-plane alignment of the helix axis between glass substrates. Here, it is shown that periodic polymer structures engineered in the nematic phase of a chiral nematic LC device using direct laser writing can result in the spontaneous formation of the necessary uniform lying helix (ULH) state. Specifically, two-photon polymerization is used in conjunction with a spatial light modulator so as to correct for aberrations introduced by the bounding glass substrates enabling the polymer structures to be fabricated directly into the device. The ULH state appears to be stable in the absence of an externally applied electric field, and the optimum contrast between the bright and dark states is obtained using polymer structures that have periodicities of the order of the device thickness.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 2
    Electronic Resource
    Electronic Resource
    Field-induced intensity and Stark shift measurements of the electric dipole moment of ICl in the B 3Π0+ state (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 5464-5472 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The laser-induced fluorescence spectrum in ICl of the (2'–0‘) vibrational band in the B 3Π0+–X 1Σ+ electronic system has been measured as a function of the electric field strength up to 32.5 kV/cm. Field-induced intensity measurements on I35Cl have been used to determine the magnitude and sign of the electric dipole moment μB in the B state relative to the magnitude and sign of the moment μX in the X state. From the intensity ratio of the field-induced line Q(0) to the allowed Stark component P(1,0), which has the same upper state, it was found that μB/μX=+(0.888±0.051). The positive sign indicates that the polarity is the same in the B and the X states. Intensity ratio measurements for Q(0) to R(5) and for Q(1) to R(5) yield similar (but less precise) results. In order to test this first application of the method to excited electronic states, Stark shift measurements were carried out on a number of P-branch Stark components. It was found for I35Cl that ||μB/μX||=(0.8984±0.0036), in good agreement with the intensity measurements. The corresponding determination for I37Cl is that ||μB/μX||=(0.900±0.014). The present results are in agreement with those obtained earlier from studies of the absorption spectrum by Watanabe et al. [Jpn. J. Appl. Phys. 31, 901 (1992)].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467335
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  • 3
    Electronic Resource
    Electronic Resource
    Light-scattering observation of anomalous parametric spin-wave character in subsidiary absorption (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 5477-5479 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The technique of Brillouin light scattering has been used for the characterization, in terms of wave number and direction of propagation, of parametric spin waves associated with subsidiary absorption in thin films of yttrium iron garnet. Measurements at 7.99, 8.47, and 9.90 GHz have revealed a spin-wave character consistent with theory, with two notable exceptions. First, the data show no evidence for a predicted flip in the azimuthal propagation angle. Second, the measured magnon wave numbers at high fields are inconsistent with the theoretical values. The wave number and polar angle results imply that the change to low-k spin waves is not a discontinuous transition as indicated by the model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342524
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  • 4
    Electronic Resource
    Electronic Resource
    Measurements of characteristic transients of planar electrostatic probes in cold plasmas (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2722-2727 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: This article describes how to extract accurate information about a plasma from a capacitively coupled planar probe that is biased using pulsed radio-frequency excitation. The conditions necessary to observe correct saturation of the probe current are investigated, particularly the use of correct geometry and biasing for the guard ring. With these precautions the probe is an effective diagnostic for electron tail temperature at energies beyond those probed by conventional cylindrical probes. The dynamic response of the probe is investigated using conventional sweep voltages and shows the onset of displacement current and inertial effects associated with ions and electrons. In addition the effect of insulating films on the probe surface is examined, showing how the probe continues to operate even when it is coated. Characteristic changes caused by the presence of an insulating film give information about its electrical properties and its thickness. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150681
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  • 5
    Electronic Resource
    Electronic Resource
    Self-channeling of magnetostatic waves in ferromagnetic film (abstract) : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 5630-5630 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Low power magnetostatic wave (MSW) experiments reporting beam formation and propagation inside ferromagnetic films have been carried out .1,2 In this work, we report the first observation of self channeling of MSW and the formation of the spatial solitons of MSW for an in-plane magnetized YIG film and waves propagating perpendicularly to the direction of magnetization. The experiments were conducted using YIG film of 4.9 μm thickness magnetized in-plane by a permanent magnetic field of 1094 Oe. A cw signal was launched into the film through a microstrip antenna. A Brillouin scattering system consisting of a tandem Fabry–Perot interferometer has been used to observe the profile of a MSW beam. Self-channeling MSW beam propagation occurring as a result of an interplay between diffraction of the beam and self-modulation was observed for various magnitudes of input power and initial frequency. At low power levels the formed MSW beam broadens and weakens during the propagation. As the input power increases, the intensity of the peak power of the beam also increases and a narrow channel of the MSW beam is formed. The power threshold depends on the wavelength of MSW and the width of the excitation microstrip. A theory describing the spatial MSW self-channeling is developed. The necessary and sufficient conditions are analyzed and numerical calculations are provided. The experimental data are in a semi-quantitative agreement with theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355665
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  • 6
    Electronic Resource
    Electronic Resource
    CF2 kinetics and related mechanisms in the presence of polymers in fluorocarbon plasmas (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 2124-2130 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Laser-induced fluorescence was used to characterize the fluorocarbon plasma that was used to modify the wettability of hexatriacontane (HTC), a polymer model. The plasma volume downstream from a microwave plasma source was examined by monitoring the CF2 concentration as well as the CF2 decay rate (in the afterglow of a pulsed discharge) during treatment of the polymer surface (in 20–100 mTorr CF4). In parallel, the behavior of F atoms was monitored by means of actinometric optical emission. Pulsed modulation of the discharge allowed the effects of variations in the loss and production rates for CF2 to be distinguished, in the presence of hexatriacontane. Our observations are consistent with enhanced production of CF2, possibly by an ion-assisted surface mechanism, in the presence of HTC. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.364255
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  • 7
    Electronic Resource
    Electronic Resource
    On the formation and loss of S2 molecules in a reactive ion etching reactor operating with SF6 (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 6957-6966 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Laser-induced-fluorescence (LIF) spectroscopy was used to study, with spatial and temporal resolution, the processes by which diatomic sulfur S2 is formed and lost in SF6 plasmas. We present results concerning the relative S2 number density in steady-state or pulsed discharges in a reactive ion etching (RIE) reactor operated at different SF6 gas pressures and RF powers, in the presence or absence of a silicon wafer. It is found that S2 is formed mainly on surfaces under conditions when the F-atom density is high, but that volume formation can also occur when the F-atom population is depleted (namely, when Si is present). It is also shown that loss of S2 is mainly due to diffusion out of the inter-electrode space to the main reactor volume, excluding electron-impact dissociation processes. It is apparent that, in a RIE reactor, the only electron process pertinent to the balance of S2 density is the formation of its precursors (probably S atoms and SF molecules) by fragmentation of the SF6 gas. The remaining reactions controlling the density of S2 are neutral-neutral interactions in the volume and on surfaces. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360463
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  • 8
    Electronic Resource
    Electronic Resource
    Magnetic transitions at high fields in (Fe,Mn)3Si alloys : The 6th joint magnetism and magnetic materials (MMM)-intermag conference (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 6359-6361 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In the series of ordered DO3 solid solutions Fe3−xMnxSi, field-induced transitions have previously been found to occur for antiferromagnetic alloys with values of x near 1.70. The present work has determined a region of composition in which antiferromagnetism is the low-field, low-temperature state and gives the variation of the critical field as a function of temperature and composition. The critical field decreases approximately quadratically with temperature and rises to beyond 6 T in the range of composition from 1.6≤x≤1.8. Neutron diffraction indicates that the antiferromagnetic axis is shifted from the [111] direction and that in a 5 T field the antiferromagnetic component of the scattering is reduced considerably from that in zero field. However, no corresponding increase in ferromagnetic component is observed within experimental error and Arrott plots suggest the high-field state is still largely antiferromagnetic.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358266
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  • 9
    Electronic Resource
    Electronic Resource
    High field transitions in (FeMn)3Si alloys : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5671-5673 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetic ordering in the series of solid solutions Fe3−xMnxSi having the D03 structure has been extensively studied at low fields over a wide range of temperatures. The present study reports observations of high-field-induced transitions in the low temperature range below the reordering temperature TR for members of the series falling within the concentration range 1.6≤x≤1.8. These alloys appear antiferromagnetic in low fields below TR but application of a field within the range up to 12 T results in a transition to an apparently ferromagnetic state. The transition occurs at all temperatures below TR and occurs reversibly except at the lowest temperatures where the hysteresis may be ∼0.5 T. The variation of the critical field with temperature follows an approximately quadratic form. Above TR Arrott plots suggest for the alloy with x=1.70 that a narrow ferromagnetic regime exists over the range 65≤T≤85 K above which the material is paramagnetic. For the alloy with x=1.75 however the Arrott plots suggest a direct conversion to paramagnetism at the reordering temperature TR indicating a possible phase diagram similar to that of Au2Mn. A discussion is given in terms of a model previously proposed to explain the low-field behavior.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353586
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  • 10
    Electronic Resource
    Electronic Resource
    Structural and magnetic properties of Co(AlV) alloys (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 5271-5273 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetization and magnetic susceptibility measurements have been made over a wide range of temperature for the alloy series CoAl1−xVx for 0≤x≤0.5. Neutron diffraction measurements have also been made at room temperature using the Rutherford Appleton Laboratory spallation source (ISIS). The observed intensities suggest that for x≤0.25 the structure is the singly ordered B2 (CsCl) structure with the V atoms occupying Al sites. Beyond this concentration a model in which double ordering of the L21 (Heusler) type with the V atoms favoring one of the two equivalent Al sites seems consistent with the results. The magnetization measurements indicate that the series becomes ferromagnetic for x〉∼0.1 with the intrinsic magnetization σ rising to a maximum of ∼50 emu. g−1 at x=0.5 for which the Curie temperature TC is ∼320 K. The inverse susceptibilities are generally linear with temperature and almost independent of concentration for x〉0.2, suggesting an itinerant interpretation. The maximum values of TC and σ reached are less than half those achieved in the corresponding CoAl1−xMnx system but comparable with those seen in the CoAl1−xCrx system. Comparisons with the isoelectronic CoGa system are drawn. The results have relevance to theoretical estimates of impurity moments in CoAl and CoGa.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344634
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