R. W. Rendell
United States Naval Research Laboratory
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Featured researches published by R. W. Rendell.
ACS Nano | 2011
Joshua D. Caldwell; Orest J. Glembocki; Francisco J. Bezares; Nabil Bassim; R. W. Rendell; Mariya Feygelson; Maraizu Ukaegbu; Richard Kasica; Loretta Shirey; Charles M. Hosten
Efforts to create reproducible surface-enhanced Raman scattering (SERS)-based chemical and biological sensors has been hindered by difficulties in fabricating large-area SERS-active substrates with a uniform, reproducible SERS response that still provides sufficient enhancement for easy detection. Here we report on periodic arrays of Au-capped, vertically aligned silicon nanopillars that are embedded in a Au plane upon a Si substrate. We illustrate that these arrays are ideal for use as SERS sensor templates, in that they provide large, uniform and reproducible average enhancement factors up to ∼1.2 × 10(8) over the structure surface area. We discuss the impact of the overall geometry of the structures upon the SERS response at 532, 633, and 785 nm incident laser wavelengths. Calculations of the electromagnetic field distributions and intensities within such structures were performed and both the wavelength dependence of the predicted SERS response and the field distribution within the nanopillar structure are discussed and support the experimental results we report.
Journal of Chemical Physics | 1991
K. L. Ngai; R. W. Rendell; Donald J. Plazek
The Adam–Gibbs theory of relaxation for glass‐forming liquids is based on an ensemble of independent and equivalent cooperatively rearranging regions (CRR’s). In this work we extend the Adam–Gibbs theory by incorporating the mutual interactions between the CRR’s. This is done by the method of the coupling scheme in which the transition rate for each independent CRR is slowed down by a time‐dependent factor. The new combined theory predicts a stretched exponential relaxation function and modifies the Adam–Gibbs parameters for the temperature dependence of the relaxation time making them functions of the stretched exponent β. The model is applied to analyze specific heat and dielectric data of supercooled liquids. It is able to explain a previously proposed correlation of the increasing fragility of glass forming liquids with the size of 1−β at Tg and the rapidity of the temperature variation of β. The model also explains, in hydrogen bonded liquids, the correlation of the increasing fragility with the size...
Applied Physics Letters | 2007
S. M. Prokes; O. J. Glembocki; R. W. Rendell; Mario G. Ancona
Surface-enhanced Raman spectroscopy (SERS) was performed on Ga2O3∕Ag and ZnO∕Ag nanowires, which were arranged in either a crossover or noncrossing geometry. Results indicate a high SERS sensitivity (near 0.2pg) for nanowires arranged in a crossing geometry. It is suggested that this is due to the dielectric core/metal shell structure, as well as to the nanowire crossings, which are regions of very high electric fields. Finite element simulations of the electric field near two crossed wires confirm an enhanced plasmon resonance in the vicinity of the crossing, which extends spatially in the crossings and around the nanowires.
Optics Express | 2013
Francisco J. Bezares; James P. Long; Orest J. Glembocki; Junpeng Guo; R. W. Rendell; Richard Kasica; Loretta Shirey; Jeffrey C. Owrutsky; Joshua D. Caldwell
Mie-resonances in vertical, small aspect-ratio and subwavelength silicon nanopillars are investigated using visible bright-field µ-reflection measurements and Raman scattering. Pillar-to-pillar interactions were examined by comparing randomly to periodically arranged arrays with systematic variations in nanopillar diameter and array pitch. First- and second-order Mie resonances are observed in reflectance spectra as pronounced dips with minimum reflectances of several percent, suggesting an alternative approach to fabricating a perfect absorber. The resonant wavelengths shift approximately linearly with nanopillar diameter, which enables a simple empirical description of the resonance condition. In addition, resonances are also significantly affected by array density, with an overall oscillating blue shift as the pitch is reduced. Finite-element method and finite-difference time-domain simulations agree closely with experimental results and provide valuable insight into the nature of the dielectric resonance modes, including a surprisingly small influence of the substrate on resonance wavelength. To probe local fields within the Si nanopillars, µ-Raman scattering measurements were also conducted that confirm enhanced optical fields in the pillars when excited on-resonance.
Rheologica Acta | 1997
Kai L. Ngai; Donald J. Plazek; R. W. Rendell
Thanks to the research efforts of Prof. John D. Ferry and others over the last several decades, the viscoelastic properties of polymers have been extensively determined. From this accumulated wisdom, polymer viscoelasticity has become a mature field of research. This basic knowledge of polymer viscoelasticity has made it possible to discern the deviations from the apparently established general rules that one of us (DJP) have found, continuing the tradition of exhaustive experimental measurement started by Prof. Ferry. From many experimental studies on polymers carried out in different laboratories, it has also become clear that these viscoelastic anomalies are general and not exceptional features. Therefore, they pose significant problems in the quest of a truly satisfactory understanding of polymer viscoelasticity. The Coupling Model (CM) has been used to rationalize a number of deviations from thermorheological simplicity. In the realm of polymer viscoelastic behavior, we consider first the local segmental motion that is responsible for the glass temperature and show that the CM provides a consistent description in either the modulus or the compliance representation. Next, we elucidate several viscoelastic anomalies which originate from the different viscoelastic mechanisms being thermorheologically complex. Finally, we revisit the original formulation of the terminal relaxation of entangled polymer chains using the CM. The neglect of the lateral nature of the constraints imposed on one chain by other chains in the original formulation leads to failure in explaining the shape of the terminal relaxation, although it is successful in other aspects. A new formulation, which includes the lateral nature of the constraints and its subsequent mitigation when the terminal relaxation is reached, has restored consistency of the prediction with the terminal relaxation of a monodisperse polyisoprene melt probed dielectrically. The results can describe also the experimental data of dilute polyisoprene probes in polybutadiene matrices and in networks.
Applied Physics Letters | 2002
N.S. Saks; Mario G. Ancona; R. W. Rendell
A technique is presented for measuring the density of interface traps versus energy DIT(E) using the Hall effect in metal-oxide-semiconductor samples. Good agreement is obtained between this Hall approach and standard C–V techniques in both SiC and silicon test devices. DIT(E) is found to be much higher in 4H–SiC compared to 6H devices oxidized at the same time. DIT(E) in both SiC poly types increases exponentially with energy approaching the conduction bandedge.
Physical Review A | 2002
A. K. Rajagopal; R. W. Rendell
This work is an enquiry into the circumstances under which entropy methods can give an answer to the questions of both quantum separability and classical correlations of a composite state. Several entropy functionals are employed to examine the entanglement and correlation properties guided by the corresponding calculations of concurrence. It is shown that the entropy difference between that of the composite and its marginal density matrices may be of arbitrary sign except under special circumstances when conditional probability can be defined appropriately. This ambiguity is a consequence of the fact that the overlap matrix elements of the eigenstates of the composite density matrix with those of its marginal density matrices also play important roles in the definitions of probabilities and the associated entropies, along with their respective eigenvalues. The general results are illustrated using pure- and mixed-state density matrices of two-qubit systems. Two classes of density matrices are found for which the conditional probability can be defined: (1) density matrices with commuting decompositions and (2) those that are decohered in the representation where the density matrices of the marginals are diagonal. The first class of states encompass those whose separability is currently understood as due to particular symmetries of the states. The second are a class of states that are expected to be useful for understanding separability. Examples of entropy functionals of these decohered states including the crucial isospectral case are discussed.
Applied Physics Letters | 2013
Jake Fontana; John Livenere; Francisco J. Bezares; Joshua D. Caldwell; R. W. Rendell; Banahalli R. Ratna
We demonstrate an average surface-enhanced Raman scattering enhancement on the order of 108 from benzenethiol molecules using self-assembled, macroscopic, and tunable gold nanosphere monolayers on non-templated substrates. The self-assembly of the nanosphere monolayers uses a simple and efficient technique that allows for the creation of a high-density, chemically functionalized gold nanosphere monolayers with enhancement factors comparable to those produced using top-down fabrication techniques. These films may provide an approach for the future development of portable chemical/biological sensors.
Physical Review A | 2010
A. K. Rajagopal; A. R. Usha Devi; R. W. Rendell
It is shown that the fidelity of the dynamically evolved system with its earlier time-density matrix provides a signature of non-Markovian dynamics. Also, the fidelity associated with the initial state and the dynamically evolved state is shown to be larger in the non-Markovian evolution compared to that in the corresponding Markovian case. Starting from the Kraus representation of quantum evolution, the Markovian and non-Markovian features are discerned in its short-time structure. These two features are in concordance with each other and they are illustrated with the help of four models of interaction of the system with its environment. © 2010 The American Physical Society.
IEEE Transactions on Nuclear Science | 1993
N. S. Saks; R.B. Klein; Robert E. Stahlbush; B.J. Mrstik; R. W. Rendell
Changes in interface trap density, D/sub it/, have been determined in MOSFETs as a function of time during hydrogen annealing at 295 K. Large increases in D/sub it/ are observed during H/sub 2/ annealing in MOSFETs previously stressed by either /sup 60/Co irradiation or Fowler-Nordheim electron injection. The annealing behavior is very similar for both types of stress, and this suggests that the D/sub it/ creation mechanism involves similar chemistry for hydrogen reactions. Studies of the time dependence of D/sub it/ creation as a function of MOSFET gate length show that the time dependence is limited primarily by lateral diffusion of molecular hydrogen through the gate oxide. An activation energy of 0.57 eV, which is consistent with H/sub 2/ diffusion, is obtained from the temperature dependence. >