Search

A rapid microwave (180 s, 100 W) green approach has been demonstrated for the synthesis of TiO2 tripods (TITPs) using Mangifera indica leaf extracts. In this process, mangiferin acts as an efficient reducing agent while microwave radiations control the nucleation and growth of anisotropic TiO2 nanostructure. Surface morphological analyses reveal that synthesized TiO2 nanomaterial has a unique resilient shape of tripods with porosity. The photocatalytic ability of synthesized TITPs has been examined using Methylene blue (MB) as the target contaminant, and ∼75% (under visible light in 75 min) and 96% (under UV in 9 min) dye degradation has been achieved. The TITPs show recyclability for up to three cycles. Moreover, TITPs exhibit good adsorbent property that varies with the change of temperature and pH. The adsorption of the MB by TITPs follows the pseudo-first-order kinetic model and the Langmuir isotherm model. The maximum adsorption capacity of TITPs is found to be 17.54 mg/g based on the Langmuir model. The present multi-facet TITPs prepared via a simple and quick (180 s) microwave method has the potential for application in photocatalytic/adsorption for aqueous contaminant remediation. [ABSTRACT FROM AUTHOR]

This work reports the correlation of changes in structural and optical properties of a-SiNx:H thin films irradiated with 100 MeV Au8+ at various fluences. Cross-sectional TEM studies show the evolution of discontinuous ion tracks with a radius of 3 nm as the nanoscale structural changes in films. Spectroscopic ellipsometry was used for the extraction of different optical parameters, viz., refractive index, extinction coefficient, Urbach tail energy, and bandgap along with thickness and roughness by fitting the experimental data and modeling the dielectric function with the Cody–Lorentz model. An increase in the Si-N phase was evident, with an increase in the bandgap. Change in the Urbach energy and broadening of oscillator parameters suggest an increased disorder and introduction of defect states upon irradiation. The Wemple–Dedomenico dispersion model was used to deduce dispersion energy to establish a change in thin films' density upon irradiation. The change in the density of thin films is further correlated to the increase in the refractive index. The evolution of various parameters reveals the correlation between changes in optical properties with structural properties down to nanoscale upon swift heavy ion irradiation on a-SiNx:H thin films. [ABSTRACT FROM AUTHOR]

Fabrication and optoelectronic applications of graphene based hybrid 2D-1D semiconductor nanostructures have gained tremendous research interest in recent times. Herein, we present a systematic study on the origin and evolution of strong broad band visible and near infrared (NIR) photoluminescence (PL) from vertical ZnO nanorods (NRs) and nanowires (NWs) grown on single layer graphene using both above band gap and sub-band gap optical excitations. High resolution field emission scanning electron microscopy and X-ray diffraction studies are carried out to reveal the morphology and crystalline quality of as-grown and annealed ZnO NRs/NWs on graphene. Room temperature PL studies reveal that besides the UV and visible PL bands, a new near-infrared (NIR) PL emission band appears in the range between 815 nm and 886 nm (1.40–1.52 eV). X-ray photoelectron spectroscopy studies revealed excess oxygen content and unreacted metallic Zn in the as-grown ZnO nanostructures, owing to the low temperature growth by a physical vapor deposition method. Post-growth annealing at 700 °C in the Ar gas ambient results in the enhanced intensity of both visible and NIR PL bands. On the other hand, subsequent high vacuum annealing at 700 °C results in a drastic reduction in the visible PL band and complete suppression of the NIR PL band. PL decay dynamics of green emission in Ar annealed samples show tri-exponential decay on the nanosecond timescale including a very slow decay component (time constant ∼604.5 ns). Based on these results, the NIR PL band comprising two peaks centered at ∼820 nm and ∼860 nm is tentatively assigned to neutral and negatively charged oxygen interstitial (Oi) defects in ZnO, detected experimentally for the first time. The evidence for oxygen induced trap states on the ZnO NW surface is further substantiated by the slow photocurrent response of graphene-ZnO NRs/NWs. These results are important for tunable light emission, photodetection, and other cutting edge applications of graphene-ZnO based 2D-1D hybrid nanostructures. [ABSTRACT FROM AUTHOR]

In this manuscript, we explore diisopropylammonium iodide (DPI) for its ferroelectric properties and phase transitions. DPI showed two phase transitions which were identified by differential scanning calorimetry and dielectric and nonlinear optical measurements. From detailed structural studies it was found that the first transition at 369K is from orthorhombic P212121 to monoclinic P21. The polar P21 phase is ferroelectric as evidenced by the pyroelectric data and has a very high value of spontaneous polarization (Ps=33 µC cm-2), which is probably the highest among other reported bulk organic ferroelectrics. The second transition at 415K is identified as polar monoclinic P21 space group to non-polar monoclinic P21/m. Thus, DPI has a high Curie temperature of 415 K. The large spontaneous polarization and high Curie temperature make DPI technologically important. [ABSTRACT FROM AUTHOR]

Organic photovoltaics (OPVs) can potentially provide a cost-efficient means of harnessing solar energy. However, optimum OPV performance depends on understanding the process–structure–property (PSP) correlation in organic semiconductors. In the working of bulk-heterojunction OPVs, the morphology plays a crucial role in device performance. In order to understand PSP linkage, a theoretical framework has been developed. We first established process–structure correlations by generating a range of morphologies with various blend ratios of donor and acceptor organic semiconductors for various annealing periods. Second, we calculated the effective electronic properties corresponding to the simulated structures using a diffuse interface approach that is numerically more robust and straightforward than the classical sharp interface method. This novel framework, wherein both the process–structure and the structure–property relationship have been established using the diffuse interface approach, completes the theoretical PSP linkage, allowing the optimization of process parameters for device applications. The theoretical PSP linkage is then benchmarked qualitatively with experimental results on a model P3HT:PCBM system. We have been able to identify the morphological characteristics that maximize device performance. This work is carried out in the broad overview of the integrated computational materials engineering framework wherein the processing parameters are optimized by determining the process–structure–property relationships. [ABSTRACT FROM AUTHOR]

The millimeter wave (mm-wave) frequency band provides exciting prospects for quantum science and devices since many high-fidelity quantum emitters, including Rydberg atoms, molecules, and silicon vacancies, exhibit resonances near 100 GHz. High-Q resonators at these frequencies would give access to strong interactions between emitters and single photons, leading to rich and unexplored quantum phenomena at temperatures above 1 K. We report a 3D mm-wave cavity with a measured single-photon internal quality factor of 3 × 10 7 and mode volume of 0.14 × λ 3 at 98.2 GHz, sufficient to reach strong coupling in a Rydberg cavity quantum electrodynamics system. An in situ piezotunability of 18 MHz facilitates coupling to specific atomic transitions. Our unique, seamless, and optically accessible resonator design is enabled by the realization that intersections of 3D waveguides support tightly confined bound states below the waveguide cutoff frequency. Harnessing the features of our cavity design, we realize a hybrid mm-wave and optical cavity, designed for interconversion and entanglement of mm-wave and optical photons using Rydberg atoms. [ABSTRACT FROM AUTHOR]

3D printing technologies are emerging as a disruptive innovation for the treatment of patients in cardiac failure. The ability to create custom devices, at the point of care, will affect both the diagnosis and treatment of cardiac diseases. The introduction of bioinks containing cells and biomaterials and the development of new computer assisted design and computer assisted manufacturing systems have ushered in a new technology known as 3D bioprinting. Small scale 3D bioprinting has successfully created cardiac tissue microphysiological systems. 3D bioprinting provides an opportunity to evaluate the assembly of specific parts of the heart and most notably heart valves. With the continuous development of instrumentation and bioinks and a complete understanding of cardiac tissue development, it is proposed that 3D bioprinting may permit the assembly of a heart described as a total biofabricated heart. [ABSTRACT FROM AUTHOR]

Nonlinear frequency conversion processes depend on the polarization state of the interacting beams. On the other hand, vector vortex beams have space-variant polarization in the transverse beam plane. In light of these two points, is it possible to do nonlinear frequency conversion of the vector vortex beam in single-pass geometry and retain the characteristics of the beam? To address this question, here, we report an experimental scheme for single-pass second harmonic generation (SHG) of vector vortex beams. Using an ultrafast Ti:Sapphire laser of pulse width ∼17 fs and a set of spiral phase plates in a polarization based Mach–Zehnder interferometer (MZI), we have generated vector vortex beams of order as high as lp = 12 at an average power of 860 mW. Using two contiguous bismuth borate crystals with the optic axis orthogonal to each other, we have frequency-doubled the near-IR vector vortex beam into visible vector vortex beam with order as high as lsh = 24. The maximum output power of the vector vortex beam of order, lsh = 2, is measured be as high as 20.5 mW at a single-pass SHG efficiency of 2.4%. Controlling the delay in MZI, we have preserved the vector vortex nature of both the pump and frequency-doubled beams. Measurement on the mode purity confirms the generation of high quality vector vortex beams at pump and SHG wavelengths. This generic scheme can be used to generate vector vortex beams across the electromagnetic spectrum in all time scales, continuous-wave to ultrafast. [ABSTRACT FROM AUTHOR]

Presents information on a study which calculated the range statistics for titanium (Ti) implanted at various energies by analyzing the as-implanted profiles determined by secondary ion-mass spectrometry. Statistical moments of the Ti atom density depth distributions; Experimental results; Conclusions.

Deals with a study which performed high-energy iron and cobalt implantations into InP:Sn at room temperature and in the energy range 0.34-5.0 megaelectron volt. Background to the study; Experimental details; Results and discussion.

Presents a study that examined high energy boron implantations performed into gallium-arsenic (GaAs) and indium-phosphorus (InP). Importance of InP and GaAs in microwave and opto-electronic device applications; Use of Rutherford backscattering analysis; Discussion on the resistivity variation with annealing temperature for different boron fluences in InP.

Variable-fluence 3-MeV Si[SUP+] and 150-keV Ge[SUP+] implants were performed into InP:Fe at 200°C. Lattice damage in the material is greatly reduced over comparable room-temperature (RT) implantations and is rather insensitive to fluence for Si[SUP+] implantation in the range of 8 × 10[SUP14]-5 × 10[SUP15] cm[SUP-2], and no amorphization occurs. For 8 × 10[SUP14]-cm[SUP-2] Si[SUP+] implantation at 200°C, the dopant activation is 82% and carrier mobility is 1200 cm[SUP2]/V s after 875°C/10-s annealing, whereas for the RT implantation the corresponding values are 48% and 765 cm[SUP2]/V s, respectively. The reasons for the improved mobility in the elevated-temperature implants were investigated using Rutherford-backscattering spectrometry. At a dose of 8 × 10[SUP14] cm[SUP-2], the aligned yield after annealing is close to that of a virgin sample, indicating a low concentration of residual damage in the 200°C implant, whereas the lattice remained highly defective in the RT implanted sample. Elevated-temperature implantation of Si[SUP+] and Pi[SUP+] ions was also investigated. Coimplantation did yield an improvement in activation for an implanted fluence of 2 × 10[SUP15] cm[SUP-2] Si[SUP+] , but resulted in an inferior lattice quality which degraded the carrier mobility compared to a Si[SUP+] (only) implant. For a 1 × 10[SUP14]-cm[SUP-2] Ge[SUP+] implant, the maximum dopant activation is 50% (donor) and the material did not turn p type even after 925°C annealing. [ABSTRACT FROM AUTHOR]

Presents a study that performed high energy beryllium implants in the energy range 0.4-3.0 high energy in indium phosphide (InP):iron. Significance of high-energy beryllium implantations into InP; Dose and energy details of coimplantation; Statistical moments of the beryllium atomic density depth distributions.2

Presents information on a study which performed high-energy silicon (Si) implantations into InP:Fe. Use of secondary-ion mass spectrometry to establish the first four moments of the Si implant depth distribution; Statistical moments of the Si atom density depth distributions; Effect of implant dose on the percentage activation and mobility; Results of x-ray rocking curve measurements.

Examines the coimplantation of beryllium[sup+]/phosphorus[sup+], beryllium[sup+]/argon[sup+], and beryllium[sup+]/nitrogen[sup+] into InP:Fe. Details on the experiment; Results of the study; Conclusion.

A representation for collision cross sections of a square-well dilute gas mixture is developed that reduces their computation to the evaluation of one-dimensional integrals with integrands of elementary closed form. Consequently, the computation of collision integrals and Chapman–Enskog and Kihara transport-coefficient approximations, which depend on the collision cross sections, is analytically and numerically simplified. These results are then applied to the limiting case of a Lorentz gas, i.e., a dilute gas of mobile particles diffusing through a bed of scatterers that can be regarded as fixed. In particular, our results are used to evaluate the exact diffusion coefficient DL of a Lorentz gas with square-well potential interactions as a function of both square-well width and temperature, i.e., square-well depth. (We treat here only the case in which the scatterers are dilute enough for the problem to be accurately described by a Boltzmann equation.) The exact DL is compared with its first and second Chapman–Enskog approximations, D1 and DCE2, as well as its second Kihara approximation, DK2. (The first Kihara approximation coincides with the first Chapman–Enskog approximation so that it is unnecessary to attach a superscript to D1 to distinguish between the two approximation schemes.) The DK2 is found to be of high accuracy over the whole range of parameters studied, suggesting that it represents the most accurate of these three approximations available for the binary diffusion coefficient of a dilute square-well gas. Finally, a simple approximation for the collision integrals linear in well depth (i.e., inverse temperature) as well as one that adds to the linear term all contributions from ‘‘soft’’ scattering are used to evaluate D1. For wide wells the latter yields an excellent approximation (which, in turn, is a good approximation to DL for such wells). This approximation is no longer useful for narrow wells... [ABSTRACT FROM AUTHOR]

Successful implementation of multilayer lithography to fabricate three-dimensional structures involves depositing multiple layers of radiation sensitive materials with necessary dose and tone contrast. Resists are radiation sensitive materials (usually polymers dissolved in solvents) used in micro- and nanolithography. Currently, they are deposited on wafers using the spin coating process. Solvent incompatibilities between different resist systems can cause unwanted dissolution and intermixing of adjacent layers. Here, the authors show the use of Hansen solubility parameters to identify compatible solvents and developers. Multiple solubility models have been proposed, and Hansen solubility parameters are the most widely accepted. The Hansen solubility parameters are used to form a three dimensional space in which polymers and their solubility in different solvents can be represented as spheres. This representation makes it convenient to select compatible solvents and developers. It can also provide necessary guidance to synthesize compatible polymer systems for enhancing the lithographic technique. [ABSTRACT FROM AUTHOR]

Three dimensional nanostructures are of great interest in photonics and optical sensor communities. Although there are many theoretical models developed, lithographic reduction to practice is an ongoing challenge. Numerous lithographic techniques have been proposed for fabricating three dimensional structures with applications in photonics. We demonstrate a novel three-dimensional electron beam fabrication method that is precise, fast, intrinsically self-aligned and has the ability to produce large area patterns. [ABSTRACT FROM AUTHOR]

Presents a study that performed silicon implantations into indium phosphide; iron. Method of the study; Results and discussion; Conclusion.

Describes an instrument to study the effects of shearing on the crystallization process in semicrystalline polymers. Process of crystallization in polymer melts; Instrument design; Transient metal flow; Crystallization of a model polymer.

The fully developed turbulent flow in a straight duct of square cross section has been simulated using the large eddy simulation (LES) technique. A mixed spectral-finite difference method has been used in conjunction with the Smagorinsky eddy-viscosity model for the subgrid scales. The simulation was performed for a Reynolds number of 360 based on friction velocity (5810 based on bulk velocity) and duct width. The simulation correctly predicted the existence of secondary flows and their effects on the mean flow and turbulence statistics. The results are in good qualitative agreement with the experimental data available at much higher Reynolds numbers. It is observed that both the Reynolds normal and shear stresses equally contribute to the production of mean streamwise vorticity. [ABSTRACT FROM AUTHOR]

Examines the multiplicity features and the secondary flow structure of the fully developed, laminar flow of a Newtonian fluid in a straight pipe that is rotating about an axis perpendicular to the pipe axis. Governing equations of motion; Dynamical structures involved in the solution structure; Stability of the solutions to two-dimensional perturbations.

The total enthalpy of reaction and heat capacity to 850 °C were measured using differential scanning nanocalorimetry (nano-DSC) for the reaction of a nickel and silicon bilayer at heating rates up to 106 K/s. Exothermic dips in heat capacity attributed to nickel silicide formation were found along with indications of phase changes at 430 and 550 °C. The postreaction phases were identified using electron backscattered diffraction. Samples with a Ni:Si molar ratio of 1.2 heated to 850 °C were a mixture of orthorhombic NiSi and the θ-phase (hexagonal—Ni2Si); samples heated to 790 °C resulted in predominantly NiSi. [ABSTRACT FROM AUTHOR]

We present an experimental demonstration of power gain in quantum-dot cellular automata (QCA) devices. Power gain is necessary in all practical electronic circuits where power dissipation leads to decay of logic levels. In QCA devices, charge configurations in quantum dots are used to encode and process binary information. The energy required to restore logic levels in QCA devices is drawn from the clock signal. We measure the energy flow through a clocked QCA latch and show that power gain is achieved. [ABSTRACT FROM AUTHOR]

We present an experimental demonstration of a latch in a clocked quantum-dot cellular automata (QCA) device. The device consists of three floating micron-size metal dots, connected in series by multiple tunnel junctions and controlled by capacitively coupled gates. The middle dot acts as an adjustable barrier to control single-electron tunneling between end dots. The position of a switching electron in the half cell is detected by a single-electron electrometer. We demonstrate "latching" of a single electron in the end dots controlled by the gate connected to the middle dot. This ability to lock an electron in a controllable way enables pipelining, power gain and reduced power dissipation in QCA arrays. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Investigates the effect of hydrogen ion implantation damage on the resistivity of n-type 4 hydrogen (H)-silicon carbide. Properties of silicon carbide; Need for semi-insulating substrates for the fabrication of high-quality electronic devices; Reasons for performing hydrogen implantation.

The nucleation density and the morphology of diamond crystals and films, synthesized by the combustion flame technique, are shown to be strongly influenced by the nucleation processes at work. Nucleation of diamond on a mechanically abraded molybdenum surface results in well-formed cubo octahedrons with a relatively low nucleation density. Nucleation on an initially formed, diamond-like carbon layer markedly increases the nucleation density and alters the morphology of the diamond crystals and film. The enhancement of nucleation by diamond-like carbon layers is postulated to be a result of the high surface defect density and the high hydrogen concentration of these materials. [ABSTRACT FROM AUTHOR]

Subjecting natural diamond single crystals to the action of atomic hydrogen in a hydrogen plasma is shown to result in the passivation of interband states in the crystal resulting in a marked reduction in the resistivity to about 105 Ω cm from the expected high resistivity of∼1016 Ω cm. When the hydrogenated crystals are heat treated in a neutral ambient, the hydrogen can be expelled from the crystals, restoring the high resistivity. The behavior of natural diamond crystals, with respect to the effects of hydrogen, is shown to be similar to the behavior of diamond thin films synthesized by plasma-enhanced chemical vapor deposition techniques. [ABSTRACT FROM AUTHOR]

Diamond films grown by plasma chemical vapor deposition techniques display a fairly low resistivity (∼106 Ω cm). Heat treating the films causes an increase in the resistivity by up to six orders of magnitude. The low resistivity of the as-grown films is postulated to be due to hydrogen passivation of traps in the films. Annealing causes dehydrogenation resulting in the electrical activation of deep traps with an attendant increase in the resistivity. This mechanism has been confirmed by an observed reduction of the resistivity of the heat-treated films when they are subjected to a plasma hydrogen treatment. [ABSTRACT FROM AUTHOR]

Diamond has many unique physical properties useful as thin-film coatings for laser optics. The calculated value of the laser-induced stress resistance parameter of diamond is orders of magnitude higher than any other material and, therefore, diamond films should have a higher laser damage threshold. This is confirmed by laser damage experiments carried out on free-standing polycrystalline diamond films. Materials susceptible to laser damage can be protected by diamond thin-film coatings to enhance the damage threshold. This is demonstrated in the case of diamond coated silicon substrate. [ABSTRACT FROM AUTHOR]

We have investigated the formation of <110> oriented fivefold diamond microcrystallites on {001} silicon substrates using high-resolution transmission electron microscopy (HRTEM). The HRTEM micrographs clearly show that fivefold symmetry in diamond microcrystallites results from twinning in {111} planes, in agreement with electron diffraction data. The five <110> oriented microcrystallites that provide fivefold symmetry are enclosed by {111} planes. The angles between various planes in these microcrystallites can be directly measured in HRTEM micrographs. The angles between {111} planes are found to vary from 70.5° (ideal) to as much as 74° for some microcrystallites. The boundaries of microcrystallites contain coherent twins with only occasional presence of dislocations to accommodate the misfit. We propose a model for nucleation and formation of fivefold diamond microcrystallites. The proposed model, based upon the presence of a/2<110>{001} edge dislocations, is found to be consistent with HRTEM observations. [ABSTRACT FROM AUTHOR]

We have investigated characteristics of polycrystalline diamond thin films formed by plasma-enhanced chemical vapor deposition method on silicon substrates using Raman spectroscopy, analytical and high-resolution transmission electron microscopy techniques. Grains with average size 1 μm in diameter were observed in these films. The Raman spectra from these films contain the strongest peak at 1335 cm-1, providing the characteristic signature for sp3 (diamond) bonding. The broad peak centered around 1550 cm-1 is believed to be due to some graphitic bonding. From detailed high-resolution images and microdiffraction, films were characterized to be cubic diamond with a lattice parameter of 3.56 Å. Diamond crystallites with fivefold external morphologies were also observed. The large crystallites in the films exhibited preferential texture in <011> type orientations. These crystallites were found to be twinned in {111} planes. The large <011> crystallites exhibited matching in {111} or {200} lattice planes of diamond with {022} planes of silicon. This is in agreement with our previous work on the growth of Ni on MgO, which showed that textured growth can occur by matching a set of lattice planes in the absence of matching of lattice constants. [ABSTRACT FROM AUTHOR]

We study the effect of strain on magnetic tunnel junctions induced by a diamond like carbon (DLC) film. The junction resistance as well as the tunnel magnetoresistance (TMR) reduces with the DLC film. Non-equilibrium Green's function quantum transport calculations show that the application of biaxial strain increases the conductance for both the parallel and anti-parallel configurations. However, the conductance for the minority channel and for the anti-parallel configuration is significantly more sensitive to strain, which drastically increases transmission through a MgO tunnel barrier, therefore, the TMR ratio decreases with biaxial strain. [ABSTRACT FROM AUTHOR]

We present the experimental characterization of a leadless (floating) double-dot system and a leadless quantum-dot cellular automata cell, where aluminum metal islands are connected to the environment only by capacitors. Here, single electron charge transfer can be accomplished only by the exchange of an electron between the dots. The charge state of the dots is monitored using metal islands configured as electrometers. We show improvements in the cell performance relative to leaded dots, and discuss possible implications of our leadless design to the quantum-dot cellular automata logic implementation. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A device representing a basic building block for clocked quantum-dot cellular automata architecture is reported. Our device consists of three floating micron-size metal islands connected in series by two small tunnel junctions where the location of an excess electron is defined by electrostatic potentials on gates capacitively coupled to the islands. In this configuration, the middle dot acts as an adjustable Coulomb barrier allowing clocked control of the charge state of the device. Charging diagrams of the device show the existence of several operational modes, in good agreement with theory. The clocked switching of a single electron is experimentally demonstrated and advantages of this architecture are discussed. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]