A mathematical evidence-in a statistically significant sense-of a geometric scenario leading to criticality of the Navier-Stokes problem is presented. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4752170]
We investigate electron transport properties in large-area, single-layer graphene embedded in dielectric media, using free-space terahertz (THz) imaging and time-domain spectroscopy. Sandwiched between a thin polymethyl methacrylate (PMMA) layer and a Si substrate, graphene layers of different growth recipes exhibit distinctive spatial inhomogeneity of sheet conductivity. The non-contacting, non-destructive THz...
We demonstrate time-resolved terahertz transmission ellipsometry of vertically aligned multi-walled carbon nanotubes. The angle-resolved transmission measurements reveal anisotropic characteristics of the terahertz electrodynamics in multi-walled carbon nanotubes. The anisotropy is, however, unexpectedly weak: the ratio of the tube-axis conductivity to the transverse conductivity, sigma[subscript z]/sigma[subscript xy] [similar or equal to]...
The growth of YMn₀.₃₅In₀.₆₅O₃ thin films and their optical and magnetic behavior are reported. The YMn₀.₃₅In₀.₆₅O₃ thin film grows along the (0001) orientation with hexagonal structure similar to YMnO₃ on c-plane sapphire. The film shows paramagnetic behavior in the temperature range measured. The film exhibits a blue color due to...
Metal-insulator-insulator-metal tunnel diodes with dissimilar work function electrodes and nanolaminate Al₂O₃-Ta₂O₅ bilayer tunnel barriers deposited by atomic layer deposition are investigated. This combination of high and low electron affinity insulators, each with different dominant conduction mechanisms (tunneling and Frenkel-Poole emission), results in improved low voltage asymmetry and non-linearity of current...
We demonstrate a four-channel on-chip true-time-delay module based on a photonic crystal waveguide array. Using the photonic crystal taper to minimize the coupling loss, the delay lines with 1-3 mm long photonic crystal waveguides can operate up to a group index n(g) similar to ~23 without significant loss. The large...
The piezoelectric fatigue behavior of Pb-free ceramics based on solid solutions of Bi(Zn₀.₅Ti₀.₅)O₃-(Bi₀.5K₀.₅)TiO₃-(Bi₀.₅Na₀.₅)TiO₃ was characterized at 50 kV/cm after 10⁶ bipolar cycles. Ferroelectric compositions containing 2.5% Bi(Zn₀.₅Ti₀.₅)O₃ exhibited only minor losses in maximum strain (~10%). In compositions with 5% Bi(Zn₀.₅Ti₀.₅)O₃ that exhibit large electric field-induced strains, the electromechanical strain actually...
Magnetic nanocomposites, composed of magnetic nanoparticles in an insulating matrix, can have
properties not achievable in bulk, single-phase materials. This work reports on ferromagnetic
resonance (FMR) measurements as a tool to investigate the internal magnetic field in nanocomposite
samples of varying particle packing fractions. The ferromagnetic resonance frequency changes with...
We demonstrate a surface enhanced Raman scattering (SERS) substrate by integrating plasmonic-active SiO₂ nanotubes into Si₃N₄ gratings. First, the dielectric grating that is working under guided mode resonance (GMR) provides enhanced electric field for localized surface plasmon polaritons on the surface of metallic nanoparticles. Second, we use SiO₂ nanotubes with...
SnS is a potential earth-abundant photovoltaic (PV) material. Employing both theory and experiment to assess the PV relevant properties of SnS, we clarify on whether SnS has an indirect or direct band gap and what is the minority carrier effective mass as a function of the film orientation. SnS has...
We develop a classical density functional for water which combines the White Bear fundamental-measure theory (FMT) functional for the hard sphere fluid with attractive interactions based on the statistical associating fluid theory variable range (SAFT-VR). This functional reproduces the properties of water at both long and short length scales over...
Increase in energy demand has led towards considering lignocellulosic feedstocks as potential for ethanol production. Aim of this study was to estimate the potential of grass straws from conservation reserve program (CRP) lands as feedstocks for ethanol production. The CRP was initiated to ensure reduction in soil erosion with a...
Solid solutions ceramics of the Bi(Zn0.5Ti0.5)O-3-(Bi0.5K0.5)TiO3-(Bi0.5Na0.5)TiO3 ternary system for <20 mol. % BZT were created and confirmed to be single phase using x-ray diffraction. The dielectric dispersion showed decreasing T-max of the dielectric spectrum with a broadening of the transition with increasing BZT content. At 2.5BZT-40BKT-57.5BNT, a secondary transition commonly...
This article was originally published online and in print with an incorrect version of Fig. 1. AIP apologizes for this error. All online versions of the article have been corrected.
The defect mechanisms that underpin the high energy density dielectric 0.8BaTiO₃–0.2Bi(Zn₁/₂Ti₁/₂) O₃
were investigated. Characterization of the nominally stoichiometric composition revealed the
presence of a Ti³⁺-related defect center, which is correlated with lower resistivities and an
electrically heterogeneous microstructure. In compositions with 2 mol. % Ba-deficiency, a barium
vacancy-oxygen vacancy...
Full Text:
online 28 September 2012)
[http://dx.doi.org/10.1063/1.4757256]
This article was originally published
Future quantum technologies will require high-efficiency, on-demand sources of entangled photons. A possible route to building such light sources employs two-dimensional (2D) semiconductors interfaced with a source of Cooper pairs. To investigate the possibility of such devices, we are testing methods to make high transparency n-type contacts, p-type contacts, and...
Passively generated lateral motion of fluid during pool boiling on asymmetrically textured mesoscale structures is discussed in this Letter. The surface texture is in the form of 30°–60° mm-scale ratchets with re-entrant cavities located on the 30° face. High speed visualization of growing bubbles from cavities indicates growth and departure...
The energy barrier heights between two recently reported Ta-based amorphous metals (TaWSi and TaNiSi), TaN, and atomic layer deposited Al2O3 and HfO2 insulators are measured in metal/insulator/metal (MIM) structures with Au top electrodes using internal photoemission (IPE) spectroscopy. For Al2O3, the Ta-based metal barrier heights, phi(Bn), increase with increasing metal...
This work investigates the effect of cation substitution on the properties of the lead-free, solid solution (Na₀.₅Bi₀.₅)TiO₃-BaTiO₃ (NBT-BT). Substitution into NBT-BT increases disorder and increases the relaxor ferroelectric properties. These relaxor ferroelectric materials show large piezoelectric strains that can be utilized in actuator applications. Ceramic samples were prepared using standard...
Cobalt germanides have been widely studied as semiconductor contact materials, but recent theoretical studies suggest that they may also be excellent catalysts for methane steam reforming with stabilities and activities comparable to noble metal catalysts. In order to study the catalytic activity of cobalt germanides, it is critical to first...
A novel patterning technique that creates magnetization patterns in a continuous magnetostrictive
film with surface acoustic waves is demonstrated. Patterns of 10 μm wide stripes of alternating
magnetization and a 3 μm dot of reversed magnetization are written using standing and focusing
acoustic waves, respectively. The magnetization pattern is size-tunable,...
3-D printing processes, which use drop-on-demand inkjet printheads, have great potential in
designing and prototyping magnetic materials. Unlike conventional deposition and lithography,
magnetic particles in the printing ink can be aligned by an external magnetic field to achieve both
high permeability and low hysteresis losses, enabling prototyping and development of...
A method for measuring the magnetostriction of thin films using a vibrating sample
magnetometer is described. We describe the design of a custom sample holder to apply an
adjustable bending stress to the sample during measurement and observe the resulting change in
the M-H loop.
We compare characteristics of electron impact ionization (EI) and multiphoton ionization (MPI) of doped super fluid helium droplets using the same droplet source. Selected dopant ion fragments from the two ionization schemes demonstrate different dependence on the doping pressure, which could be attributed to the different ionization mechanisms. While EI...
We investigated the thermal stability of a new ternary amorphous metal thin film, Ta₂.₄Ni₂.₂Si, and assessed its suitability as a Cu diffusion barrier for semiconductor device applications. Transmission electron microscopy was coupled with atom probe tomography to provide a detailed understanding of the atomic-scale evolution of both structure and composition...
Using in-situ synchrotron X-ray scattering, we show that the structural evolution of various bulk metallic glass-forming liquids can be quantitatively connected to their viscosity behavior in the supercooled liquid near T[subscript g]. The structural signature of fragility is identified as the temperature dependence of local dilatation on distinct key atomic...
We examined sub-nanosecond time-scale charge carrier dynamics in crystalline films of a functionalized anthradithiophene (ADT) donor (D) with three different acceptor (A) molecules. A four-fold enhancement in ultrafast charge carrier separation efficiency was observed in D/A blends with a fullerene acceptor added at 7–10 wt. % concentrations, whereas a gradual...
Materials with a strong spin Hall effect and Rashba-Edelstein effect have the potential to improve the efficiency of solid-state magnetic memory technologies and other magnetic logic devices. Heavy metals have been identified as having these properties, including the beta crystal phase of tungsten. In this work, we determine the strength...
The kinetics of laser-induced, liquid-mediated crystallization of amorphousGe thin films were studied using multi-frame dynamic transmission electron microscopy (DTEM), a nanosecond-scale photo-emission transmission electron microscopy technique. In these experiments, high temperature gradients are established in thin amorphousGe films with a 12-ns laser pulse with a Gaussian spatial profile. The hottest...
Full Text:
:10.1063/1.4938751
10.1063/1.4938751
American Institute of Physics
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The need for miniaturization without compromising cost and performance continues to motivate research in advanced capacitor devices. In this report, multilayer ceramic capacitors based on relaxor BaTiO₃-Bi(Zn₁/₂Ti₁/₂)O₃ (BT-BZT) were fabricated and characterized. In bulk ceramic embodiments, BT-BZT has been shown to exhibit relative permittivities greater than 1000, high resistivities (ρ > 1...
Ferromagnetic resonance (FMR) characterization, using a vector network analyzer (VNA), is widely used to determine anisotropy, g-factor, and Gilbert damping parameter of magnetic thin films, but results are typically reported without calculation of the measurement accuracy. We present a method of processing VNA-FMR measurements to determine both the value and...
We show that the transmission of a terahertz (THz) pulse through single-layer graphene is strongly
nonlinear. As the peak electric field of the THz pulse exceeds 50 kV/cm, the graphene becomes
increasingly transparent to the THz radiation. When field strength reaches 800 kV/cm, the increased
transparency corresponds to a two-fold...
We present a modification to our recently published statistical associating fluid theory-based classical
density functional theory for water. We have recently developed and tested a functional for the
averaged radial distribution function at contact of the hard-sphere fluid that is dramatically more accurate
at interfaces than earlier approximations. We now...
We demonstrate active control of plasmonic bandgap on a metallic photonic crystal slab using thermo-optic effects. The Au grating, which is milled by focused-ion beam on a glass substrate, is designed to exhibit an extraordinary optical transmission and a sharp transitional edge for high modulation efficiency. Only a moderate refractive...
This thesis will cover work that I have completed relating to the field of terahertz (THz) science. My work has consisted of generating tunable, narrowband THz pulses in a table-top optical setup and using both narrow- and broadband THz pulses to study various material systems. Broadband THz pulses were used...
The continued development of organic semiconductor materials relies on an understanding of the relationship between optoelectronic properties, molecular structure, and molecular interaction. Several detailed studies of electronic properties in functionalized polyacene materials are presented. A computational model which allows the extraction of charge generation and transport properties from experimental data...
We demonstrate a versatile and efficient setup to perform femtosecond stimulated Raman spectroscopy (FSRS). Technical innovations are implemented to achieve the wavelength tunability for both the picosecond narrowband Raman pump pulse and femtosecond broadband Raman probe pulse. Using a simplified one-grating scheme in a home-built second harmonic bandwidth compressor followed...
Emergence of a terawatt scalable photovoltaic (PV) thin film technology is currently impeded by
the limited supply of relatively rare elements like In or Te, which has spurred active research in
recent years on earth-abundant PV materials. Instead of searching for alternative PV materials,
we approach the problem here by...
All-optical switching has myriad applications in optoelectronics, optical communications, and
quantum information technology. To achieve ultrafast optical switching in a compact yet versatile
setup, we demonstrate distinct sets of two-dimensional (2D) broadband up-converted multicolor
arrays (BUMAs) in a thin type-I β-barium-borate crystal with two noncollinear near-IR
femtosecond pulses at various...
The role of back channel surface chemistry on amorphous zinc tin oxide (ZTO) bottom gate thin film transistors (TFTs) has been characterized by positive bias-stress measurements and x-ray photoelectron spectroscopy. Positive bias-stress turn-on voltage shifts for ZTO-TFTs were significantly reduced by passivation of back channel surfaces with self-assembled monolayers of...
Poly-3-hydroxybutyrate (PHB) is a renewable, biodegradable biopolymer that has
shown great promise to offset the use of hydrocarbon-derived plastics. The genes
encoding the bacterial PHB production pathway have been engineered into several
higher order plant species providing an opportunity to produce PHB as a
co-product on an industrial, agricultural scale....
The diffusion behavior of arsenic (As) and gallium (Ga) atoms from semi-insulating GaAs (SI-GaAs) into ZnO films upon post-growth annealing vis-`a-vis the resulting charge compensation was investigated with the help of x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy. The films, annealed at 600 °C and 700 °C showed...
p-type conducting films of α- BaCu₂S₂ have been deposited onto glass and KBr substrates, yielding a conductivity of 17 S/cm and a Hall mobility of 3.5 cm²/Vs. For a 430-nm-thick film, the optical transparency approaches 90% in the visible portion of the spectrum at 650 nm, and a transparency of...
Spontaneous quasicrystal (QC) formation has not been observed in pure metals either in computation or in experiments (excluding epitaxial growth of thin atomic layers on a QC template). In this thesis work, dodecagonal QC (DDQC) grains are first discovered to spontaneously form during thermal devitrification of pure tantalum (Ta) metallic...
The optical and electronic properties of amorphous oxide thin films depend crucially on chemical composition, and deposition process variations which give rise to sub-gap defect states. Consequently, there is a need for a reliable, high-throughput method to extract sub-gap defect densities of states in amorphous oxide thin films. We present...
We report a facile method of doping cations from an electrospray ionization (ESI) source into superfluid helium droplets. By decelerating and stopping the ion pulse of reserpine and substance P from an ESI source in the path of the droplet beam, about 10⁴ ion-doped droplets (one ion per droplet) can...
A model is developed to describe the reversible nature of gecko dry adhesion. The central aspect of this model is that the seta can be easily peeled away from the contacting surface by a small moment at the contact tip. It is shown that this contact condition is very sensitive,...
We report vibrational information of both the first electronically excited state and the ground
cationic state of jet-cooled triphenylene via the techniques of resonantly enhanced multiphoton
ionization (REMPI) and zero kinetic energy (ZEKE) photoelectron spectroscopy. The first excited
electronic state S₁ of the neutral molecule is of A₁' symmetry and...
Epitaxy of III-V semiconductors on Si gets recent interest for next generation system on
heterogeneous chip on wafer. The understanding of band offset is thus necessary for describing
the charge transport phenomenon in these heterojunctions. In this work, x-ray photoemission
spectroscopy has been used to determine the band offsets in...
Lead-free Bi(Mg₁/₂Ti₁/₂)O₃-(Bi₁/₂K₁/₂)TiO₃-(Bi₁/₂Na₁/₂)TiO₃ (BMT-BKT-BNT) ceramics have
been shown to exhibit large electromechanical strains under high electric fields along with
negligible fatigue under strong electric fields. To investigate the role of point defects on the
fatigue characteristics, the composition 5BMT-40BKT-55BNT was doped to incorporate acceptor and
donor defects on the A and...