Trapping Properties Research Articles

Goal-based testing of semantic web services

Context: Recent years have witnessed growing interests in semantic web and its related technologies. While various frameworks have been proposed for designing semantic web services (SWS), few of them aim at testing.Objective: This paper investigates into the technologies for automatically deriving test cases from semantic web service descriptions based on the Web Service Modeling Ontology (WSMO) framework.Method: WSMO goal specifications were translated into B abstract machines. Test cases were generated via model checking with calculated trap properties from coverage criteria. Furthermore, we employed mutation analysis to evaluate the test suite. In this approach, the model-based test case generation and code-based evaluation techniques are independent of each other, which provides much more accurate measures of the testing results.Results: We applied our approach to a real-world case study of the Amazon E-Commerce Service (ECS). The experimental results have validated the effectiveness of the proposed solution.Conclusion: It is concluded that our approach is capable of automatically generating an effective set of test cases from the WSMO goal descriptions for SWS testing. The quality of test cases was measured in terms of their abilities to discover the injected faults at the code level. We implemented a tool to automate the steps for the mutation-based evaluation.

Superlong and Color-Tunable Red Persistent Luminescence and Photostimulated Luminescence Properties of NaCa2GeO4F:Mn2+,Yb3+ Phosphor.

An excellent persistent luminescence (PersL) phosphor NaCa2GeO4F:Mn2+,Yb3+ has been synthesized by traditional solid-state reaction. By controlling the occupation sites of Mn2+ emitters, the PersL color of this phosphor can be optionally tuned in the red to green-yellow region, and the maximum spectral shift is more than 50 nm. Significantly, the red PersL can be measured for approximately 13 and 3 h (0.32 mcd/m2) and can be observed for more than 20 and 5 h with dark-adapted vision after exposure to ultraviolet irradiation and artificial sunlight, respectively. The crystal/electronic structure and photoluminescence/PersL properties of this phosphor have been investigated in detail. A series of the excitation temperature-dependent thermoluminescence experiments and the initial rising method have been conducted to study the trap properties of this phosphor. It reveals the reasons for the variation of PersL color, excellent red PersL, and degradation of green-yellow PersL. According to the results, the as-prepared NaCa2GeO4F:Mn2+,Yb3+ can be considered as an excellent red PersL phosphor, and it also has potential for application in optical storage.

Titania nanotube photocatalysts for effectively treating waterborne microbial pathogens

Photocatalysts have been identified as a potential material for the efficient decontamination of lethal bacteria from drinking water. Compared to the traditional spherical powders, TiO2 nanotube photocatalysts possess a more efficient structure due to the high-aspect ratio and effective light harvest and improved electron/hole trap properties. The impact of various calcination temperatures and phase content on the antibacterial effect on Escherichia coli, Salmonella typhimurium and Pseudomonas aeruginosa has been investigated. Studies show that high levels (99.9–99.99%) of bacterial inactivation were achieved for all species. Significantly higher levels of bacterial toxicity were achieved with the as prepared nanotubes and nanotubes annealed at 200°C and 400°C. This is explained as the higher percentages of anatase phase present in the sample. Synthesised nanotubes proved more antibacterial than titania P25 commercial nanoparticles. The order of sensitivity from most sensitive to least sensitive was found to be in the following order: E. coli, P. aeruginosa and S. typhimurium. In addition, bacteria were found to be more susceptible to the inactivation while in the stationary (dormant) phase of growth.

Custom-Made Microspheres for Optical Tweezers.

Due to their high position and force sensitivity and the ability to remotely apply forces and torques, optical tweezers are widely used in diverse fields, such as biology, material science, and physics. Often, small dielectric particles are trapped and used as probes, which for experimental convenience are mostly spherical and composed of silica or polystyrene. The optical properties of these materials together with the microsphere size determine the trapping efficiency, and the position and force resolution. However, using only a single, homogeneous, isotropic, and unstructured material limits the range of trapping properties and thereby the applications of optical tweezers. Here, we show how custom-made microspheres composed of coated high-refractive-index materials-titania and nanodiamonds-and birefringent, liquid crystals extend the range and combination of desired trapping properties. These custom-made microspheres either enable the generation of high forces, a high force or time resolution, or the applications of torques. Custom-made probes expand the range of possible experiments and approaches broadening the scope and applicability of optical tweezers.

The Diatom Staurosirella pinnata for Photoactive Material Production.

A native isolate of the colonial benthic diatom Staurosirella pinnata was cultivated for biosilica production. The silicified cell walls (frustules) were used as a source of homogeneous and structurally predictable porous biosilica for dye trapping and random laser applications. This was coupled with the extraction of lipids from biomass showing potential to fabricate photoactive composite materials sustainably. The strain was selected for its ease of growth in culture and harvesting. Biosilica and lipids were obtained at the end of growth in indoor photobioreactors. Frustules were structurally characterized microscopically and their chemistry analyzed with Fourier Transform Infrared Spectroscopy. Frustule capacity of binding laser dyes was evaluated on a set of frustules/Rhodamine B (Rho B) solutions and with respect to silicon dioxide and diatomite by Fluorescence Spectroscopy demonstrating a high affinity for the organic dye. The effect of dye trapping property in conveying Rho B emission to frustules, with enhancement of scattering events, was analyzed on Rho B doped polyacrylamide gels filled or not with frustules. Amplified spontaneous emission was recorded at increasing pump power indicating the onset of a random laser effect in frustule filled gels at lower power threshold compared to unfilled matrices.

Performance of GaAs Nanowire Array Solar Cells for Varying Incidence Angles

Nanowire array solar cells show intrinsic light trapping and absorption enhancement properties due to the diffraction and optical resonances. Here, we report the effect of varying incidence angle on the performance of GaAs nanowire array solar cells. We provide experimental evidence that nanowire array solar cells are highly efficient at gathering diffuse or tilted incident light, even at very high incidence angles; hence, the performance of the nanowire solar cell is retained up to these high incident light angles. Specifically, the measured efficiency at an incidence angle of 60° is 95% of the efficiency at normal incidence. Moreover, our measurements show that a nonzero incidence angle is beneficial for wavelengths above 600 nm, which results in an efficiency improvement by 0.5% absolute points. This increase is so large that we even measure a small increase in absolute output power at 15° tilt, thus, more than fully compensating for the reduced incoming power over the cell with increasing tilt. We show how this gain arises from an enhanced absorption in the part of the nanowire with a high probability of charge extraction. Thus, nanowires show great promise for the delivery of high efficiency in practical nontracking positioning conditions, as well as under diffuse light illumination.

Functionalized TiO2 Nanoparticles Tune the Aggregation Structure and Trapping Property of Polyethylene Nanocomposites

The interfacial region between a nanoparticle and the polymer matrix is considered to have an important effect on the properties of nanocomposites. In this experimental study, the tuning effects of surface-modified TiO2 nanoparticles on the aggregation structure and trapping property of the nanocomposites are investigated. The addition of TiO2 nanoparticles increases the number of spherulites and decreases their sizes. It is also found that TiO2 nanoparticles can suppress the mobility of chain segments in the interfacial region, suppress crystallization, and reduce the crystallinity, depending on the surface modification and loading levels of nanoparticles. On the basis of the conclusions, the model of a spherulite and the interface is established and the trap distribution of the interface is analyzed according to the results of TSC measurements. It is assumed that there is a strong correlation between traps and the charge transport of nanocomposites, and the mechanism of charge transport is discussed wit...

Linking traps to dielectric breakdown through charge dynamics for polymer nanocomposites

Polymer nanocomposites can change the density and/or energy of traps, suppress the accumulation of space charges, and enhance dielectric breakdown strength. It is of interest to reveal the influencing mechanism of trap properties on the dielectric breakdown of polymer nanocomposites. Results of thermally stimulated depolarization current and surface potential decay were reviewed, showing that incorporating a small amount of nanoparticles into a polymer can increase the density and/or energy of deep traps. Then, the relation between traps and dc breakdown field of several polymer nanocomposites were analyzed. It was found that the increase in the density and energy of deep traps contributes to the improved dielectric breakdown performance. The modifications of traps by nanoparticles and surface treatments affect the charge dynamics in the bulk of polymer nanocomposites. Then, the accumulation of space charges, the distortion of electric field, and the energy gain of free carriers are regulated to improve the performance of dielectric breakdown.

Electrical characteristics of multilayered HfO2-Al2O3 charge trapping stacks deposited by ALD

Electrical and charge trapping properties of atomic layer deposited HfO2-Al2O3 multilayer stacks with two different Al2O3 sublayer thicknesses were investigated regarding their implementation in charge trapping non-volatile memories. The effect of post deposition annealing in oxygen at 600°C is also studied. The decreasing Al2O3 thickness increases the stack's dielectric constant and the density of the initial positive oxide charge. The initial oxide charge increases after annealing to ∼6×1012 cm-2 and changes its sign to negative for the stacks with thicker Al2O3. The annealing enhances the dielectric constant of the stacks and reduces their thickness preserving the amorphous status. Nevertheless the annealing is not beneficial for the stacks with thicker Al2O3 as it considerably increases leakage currents. Conduction mechanisms in stacks were considered in terms of hopping conduction at low electric fields, and Fowler- Nordheim tunnelling, Schottky emission and Poole-Frenkel effect at higher ones. Maximum memory windows of about 12 and 16V were obtained for the as-grown structures with higher and lower Al2O3 content, respectively. In latter case additional improvement (the memory window increase up to 23V) is achieved by the annealing.

Correlated trapping of sugar molecules by the trimeric protein channel chitoporin

The protein channel chitoporin (ChiP), which is used by marine bacteria to translocate selected sugar molecules through the outer cell membrane, is studied via single channel current measurements in water and heavy water sugar solutions. The dynamic trapping and escape probabilities of sugar molecules from different monomers in the trimeric channel are characterized, including their dependence on channel orientation and sensitivity to a deuterium isotope effect. A detailed analysis of stochastic current fluctuations reveals that the trapping properties of chitoporin exhibit memory effects: the rate of trapping transitions depends on the previous sequence of transitions; and intermonomer correlations: the average trapping rate of an unblocked monomer is larger when its neighboring monomers are blocked. The latter, likely resulting from rapid re-trapping of recently escaped sugar molecules, is considered as a possible design strategy to enhance sugar transport.

Design and Analysis of Nano-Structured Gratings for Conversion Efficiency Improvement in GaAs Solar Cells

This paper presents the design and analysis of nano-structured gratings to improve the conversion efficiency in GaAs solar cells by reducing the light reflection losses. A finite-difference time domain (FDTD) simulation tool is used to design and simulate the light reflection losses of the subwavelength grating (SWG) structure in GaAs solar cells. The SWG structures perform as an excellent alternative antireflective (AR) coating due to their capacity to reduce the reflection losses in GaAs solar cells. It allows the gradual change in the refractive index that confirms an excellent AR and the light trapping properties, when compared with the planar thin film structures. The nano-rod structure performs as a single layer AR coating, whereas the triangular (i.e., conical or perfect cone) and parabolic (i.e., trapezoidal/truncated cone) shaped nano-grating structures perform as a multilayer AR coating. The simulation results confirm that the reflection loss of triangular-shaped nano-grating structures having a 300-nm grating height and a 830-nm period is about 2%, which is about 28% less than the flat type substrates. It also found that the intermediate (i.e., trapezoidal and parabolic)-shaped structures, the light reflection loss is lower than the rectangular shaped nano-grating structure, but higher than the triangular shaped nano-grating structure. This analysis confirmed that the triangular shaped nano-gratings are an excellent alternative AR coating for conversion efficiency improvement in GaAs solar cells.

Light Trapping by Micro and Nano-hole Texturing of Single-crystalline Silicon Solar Cells

The efficiency of a solar cell strongly depends on the interaction between the incoming light beam and the surface of the device. Any process enhances light-surface interaction increases absorption probability of the light; thus, improves generated current, in turn. Generated current could be improved either by light trapping or by increased device thickness. Considering fabrication costs and recombination losses, mechanically thin optically thick wafers are being focused on in terms of light trapping properties. Surface texturing among the other methods is an effective and more lasting technique in reducing reflections and improving light trapping. In order to maximize the absorption of light and the efficiency of the cell, various light trapping schemes have been proposed so far. In this study, texturing silicon (Si) wafer surface with periodic holes using two top-down fabrication techniques: Metal Assisted Etching (MAE) and Reactive Ion Etching (RIE) was focused on. Following the design of optical masks with patterns of different hole sizes and distributions, hole-textured surfaces with dimensions varying from micron scale to submicron scale were fabricated using both etching techniques. Hole-textured surfaces with desired hole depth values could be successfully fabricated. It was observed that surface having periodic holes with 4μm diameter, 5μm gap between holes and 8μm depth could result in 15.7% efficiency.

The effects of nanoparticles and organic additives with controlled dispersion on dielectric properties of polymers: Charge trapping and impact excitation

This work presents a comprehensive investigation into the effects of nanoparticles and organic additives on the dielectric properties of insulating polymers using reinforced silicone rubber as a model system. TiO2 and ZrO2 nanoparticles (d = 5 nm) were well dispersed into the polymer via a bimodal surface modification approach. Organic molecules with the potential of voltage stabilization were further grafted to the nanoparticle to ensure their dispersion. These extrinsic species were found to provide deep traps for charge carriers and exhibited effective charge trapping properties at a rather small concentration (∼1017 cm−3). The charge trapping is found to have the most significant effect on breakdown strength when the electrical stressing time is long enough that most charges are trapped in the deep states. To establish a quantitative correlation between the trap depth and the molecular properties, the electron affinity and ionization energy of each species were calculated by an ab initio method and were compared with the experimentally measured values. The correlation however remains elusive and is possibly complicated by the field effect and the electronic interactions between different species that are not considered in this computation. At high field, a super-linear increase of current density was observed for TiO2 filled composites and is likely caused by impact excitation due to the low excitation energy of TiO2 compared to ZrO2. It is reasoned that the hot charge carriers with energies greater than the excitation energy of TiO2 may excite an electron-hole pair upon collision with the NP, which later will be dissociated and contribute to free charge carriers. This mechanism can enhance the energy dissipation and may account for the retarded electrical degradation and breakdown of TiO2 composites.

The Effect of Reaction Time on Optical Trapping Nanostructure Formation on the Multi-Crystalline Silicon by Metal-Assisted Chemical Etching

The surface texturing has been considered as an important process for the high-efficiency solar cell fabrication. A two-step metal-assisted chemical etching method was used to produce light trapping nanostructure on multi-crystalline silicon wafers. And the effect of the reaction time on the optical trapping properties of the nanostructures was investigated. Both the density and the size of Ag particles are highly dependent on the deposition time. The etching time instead of the Ag particle deposition time dominates the reflectance of the nanostructures when the etching time is above 30 s. The lowest spectrum-weighted average reflectance obtained in this study is about 9.2%.

Green synthesis of S-doped rod shaped anatase TiO2 microstructures

A simple eco-friendly, direct self assembly process for synthesizing sulphur doped titanium dioxide microrod structures (S-TMS) is presented. Without any specific precursor for sulphur doping, ultrasonicating TiOSO4 in aqueous media followed by refluxing results in the formation of S-TMS. Sulphate ions produced during the reaction act as a source for sulphur doping. In spite of the acidic pH during the reaction, pure anatase phase was favoured due to the increased availability of sulphate ions acting as phase specific directing agent. Pure anatase phase was confirmed using powder X-ray diffraction studies (XRD). Formation of S-TMS with a microrod containing self-assembled nanorods was evidenced from field emission scanning electron microscopy and atomic force microscopy. The obtained S-TMS revealed multiple band light trapping property in visible, near infrared and ultraviolet region which was evidence from UV–vis-NIR spectroscopy.

Optical trapping by Laguerre-Gaussian beams: Far-field matching, equilibria, and dynamics

By using the method of far-field matching we obtain the far-field expressions for the optical (radiation) force exerted by Laguerre-Gaussian (LG) light beams on a spherical (Mie) particle and study the optical-force-induced dynamics of the scatterer near the trapping points represented by the equilibrium (zero-force) positions. The regimes of linearized dynamics are described in terms of the stiffness matrix spectrum and the damping constant of the ambient medium. Numerical analysis is performed for both nonvortex and optical-vortex LG beams. For the purely azimuthal LG beams, the dynamics is found to be locally nonconservative and is characterized by the presence of conditionally stable equilibria (unstable zero-force points that can be stabilized by the ambient damping). We also discuss effects related to the Mie resonances (maxima of the internal field Mie coefficients) that under certain conditions manifest themselves as the points changing the trapping properties of the particles.

Electron trapping properties at HfO2/SiO2 interface, studied by Kelvin probe force microscopy and theoretical analysis**Project supported by the National Natural Science Foundation of China (Grant No. 61176080).

Electron trapping properties at the HfO2/SiO2 interface have been measured through Kelvin Probe force microscopy, between room temperature and 90 °C. The electron diffusion in HfO2 shows a multiple-step process. After injection, electrons diffuse quickly toward the HfO2/SiO2 interface and then diffuse laterally near the interface in two sub-steps: The first is a fast diffusion through shallow trap centers and the second is a slow diffusion through deep trap centers. Evolution of contact potential difference profile in the fast lateral diffusion sub-step was simulated by solving a diffusion equation with a term describing the charge loss. In this way, the diffusion coefficient and the average life time at different temperatures were extracted. A value of 0.57 eV was calculated for the activation energy of the shallow trap centers in HfO2.

Optical trapping force and torque on spheroidal Rayleigh particles with arbitrary spatial orientations.

We investigate the spatial orientation dependence of optical trapping forces and intrinsic torques exerted on spheroidal Rayleigh particles under irradiation of highly focused linearly and circularly polarized beams. It is revealed that the maximal trapping forces and torques strongly depend on the orientation of the spheroid, and the spheroidal particle is driven to be stably trapped at the beam focus with its major axis perpendicular to the optical axis. For a linearly polarized trapping beam, the optical torque is always perpendicular to the plane containing the major axis and the polarization direction of the incident beam. Therefore, the spheroid tends to rotate its major axis along with the polarization direction. However, for a circularly polarized trapping beam, the optical torque is always perpendicular to the plane containing the major axis and the optical axis. What is different from the linear polarization case is that the spheroid tends to have the major axis parallel to the projection of the major axis in the transverse plane. The optical torque in the circular polarization case is half of that in the linear polarization case. These optical trapping properties may be exploited in practical optical manipulation, especially for the nonspherical particle's trapping.

Plasmon Interactions at the (Ag, Al)/InSe Thin-Film Interfaces Designed for Dual Terahertz/Gigahertz Applications

In this article, we investigate the plasmon-dielectric spectral interaction in the Ag/InSe and Al/InSe thin-film interfaces. The mechanism is explored by means of optical absorbance and reflectance at terahertz frequencies and by the impedance spectroscopy at gigahertz frequencies. It was observed that the interfacing of the InSe with Ag and Al metals with a film thickness of 250 nm causes an energy band gap shift that suits the production of thin-film optoelectronic devices. The reflectance and dielectric constant and optical conductivity spectral analysis of these devices displayed the properties of wireless band stop filters at 390 THz. The physical parameters which are computed from the conductivity spectra revealed higher mobility of charge carriers at the Al/InSe interface over that of Ag/InSe. The respective electron-bounded plasmon frequencies are found to be 2.61 and 2.13 GHz. On the other hand, the impedance spectral analysis displayed a microwave resonator feature with series resonance peak position at 1.68 GHz for the Al/InSe/Ag interface. In addition, the temperature-dependent impedance spectra, which were recorded in the temperature range of 300–420 K, revealed no significant effect of temperature on the wave trapping properties of the Al/InSe/Ag interface. The sensitivity of the interfaces to terahertz and gigahertz frequencies nominates it as laser light/microwave traps, which are used in fibers and communications.

Comprehensive study on charge trapping property of Si-containing hafnium-oxide polymorph

The electron-trapping property of Hf oxides with a wide range of Si contents (0–64 at. %) is studied as a charge storage layer of a nonvolatile memory. The largest flatband voltage shift in the MOS capacitor is obtained at a Si content of ∼20 at. %, which corresponds to the formation of a metastable crystalline phase such as a tetragonal or orthorhombic phase. First-principles calculation reveals that metastable phases tend to have a formation energy of oxygen vacancy lower than that of stable monoclinic ones. A schematic picture of traps in crystalline Hf oxides is provided. The metastable phase is also demonstrated to have retention characteristics superior to other phases.