Trapping Properties Research Articles

Entropic Trapping of DNA with a Nanofiltered Nanopore.

Elucidating the kinetics of DNA passage through a solid-state nanopore is a fertile field of research, and mechanisms for controlling capture, passage, and trapping of biopolymers are likely to find numerous technological applications. Here we present a nanofiltered nanopore device, which forms an entropic cage for DNA following first passage through the nanopore, trapping the translocated DNA and permitting recapture for subsequent reanalysis and investigation of kinetics of passage under confinement. We characterize the trapping properties of this nanodevice by driving individual DNA polymers into the nanoscale gap separating the nanofilter and the pore, forming an entropic cage similar to a "two pores in series" device, leaving polymers to diffuse in the cage for various time lengths, and attempting to recapture the same molecule. We show that the cage results in effectively permanent trapping when the radius of gyration of the target polymer is significantly larger than the radii of the pores in the nanofilter. We also compare translocation dynamics as a function of translocation direction in order to study the effects of confinement on DNA just prior to translocation, providing further insight into the nanopore translocation process. This nanofiltered nanopore device realizes simple fabrication of a femtoliter nanoreactor in which to study fundamental biophysics and biomolecular reactions on the single-molecule level. The device provides an electrically-permeable single-molecule trap with a higher entropic barrier to escape than previous attempts to fabricate similar structures.

Effect of thermal ageing on space charge in ethylene propylene rubber at DC voltage

To understand the space charge characteristics of ethylene propylene rubber (EPR) used in MV/HV power cables under thermal stress, the space charge profile is measured by the pulsed electro-acoustic method under 20 kV/mm at 120 and 160 °C. The complex permittivity and physicochemical properties at the different ageing stages are measured and analyzed for an understanding of the effects of thermal ageing on space charge characteristics. The trap properties of EPR during thermal ageing is calculated and analyzed based on the space charge decay model. The results show that both the ageing time and temperature can affect the space charge characteristics of EPR The space charge characteristics of EPR can be ascribed to the trapping sites caused by the complex chemical and physical structures during thermal ageing. Under the thermal oxygen process, the polar groups and ions increase because of the EPR molecular chain breakages, and the charge injection from the electrodes increases. Based on the decay model of space charge and isothermal decay current theory, the distribution of trap levels in EPR at different ageing stages is obtained. The trap distribution under different ageing process can be explained by the theory of trap filling.

Effect of thermal ageing on space charge in ethylene propylene rubber at DC voltage

To understand the space charge characteristics of ethylene propylene rubber (EPR) used in MV/HV power cables under thermal stress, the space charge profile is measured by the pulsed electro-acoustic method under 20 kV/mm at 120 and 160 °C. The complex permittivity and physicochemical properties at the different ageing stages are measured and analyzed for an understanding of the effects of thermal ageing on space charge characteristics. The trap properties of EPR during thermal ageing is calculated and analyzed based on the space charge decay model. The results show that both the ageing time and temperature can affect the space charge characteristics of EPR The space charge characteristics of EPR can be ascribed to the trapping sites caused by the complex chemical and physical structures during thermal ageing. Under the thermal oxygen process, the polar groups and ions increase because of the EPR molecular chain breakages, and the charge injection from the electrodes increases. Based on the decay model of space charge and isothermal decay current theory, the distribution of trap levels in EPR at different ageing stages is obtained. The trap distribution under different ageing process can be explained by the theory of trap filling.

Structural and light trapping properties of nanoporous silicon micro-pyramid patterns encrusted with silver nanoparticles

Surface modification to improve light trapping properties is one of the choices that can be used to improve the efficiency of silicon (Si)-based solar cells. In this work, a simple combined treatment is used to modify Si surfaces to improve their overall light trapping properties. Silver (Ag) nanoparticles were deposited on porous-Si micro-pyramid structures to investigate the effects of combining the three mechanisms on light trapping properties of the treated-Si surfaces. The surface modifications were introduced for a simple large-scale chemical treatment of the Si surfaces. It was found that the etching current is a limiting factor that controls the size of the etched nanopores. The size of the deposited-Ag nanoparticle depends on both the nanopore sizes of the porous pyramids and on the AgNO3 dipping time. The average Ag particle size increased from 20.5 nm, for samples with smaller nanopores etched with 10 mA/cm2 current, to 24.0 nm for samples with larger nanopores etched with 20 mA/cm2 current. From scanning electron microscopy (SEM) and as verified by X-ray diffraction (XRD), the average Ag particle size increased from 48.25 nm to about 64.09 nm as the AgNO3 dipping time increased from 10 to 40 min. The reflectivity measurements showed a considerable 98.44% reduction in the average reflectance of the treated samples in the wavelength range of 400–840 nm. It is believed that the Ag nanoparticles’ plasmonic behavior and the nanoporous pyramid patterns are responsible for this substantial reflectivity reduction which leads to an increased efficiency of light trapping of the treated-Si samples.

Effect of Functional Groups on Polysulfide Trapping Properties of Complex Framework Materials (CFM) Serving As Effective Sulfur Hosts for Li – S Batteries

Increased demand for efficient portable energy storage systems has promoted researches to focus on identifying better alternatives to the conventional insertion-based lithium-ion battery cathodes. With a theoretical specific capacity of 1672 mAh/g, sulfur has emerged as a promising candidate for high energy density lithium battery cathodes1 , 2. Favorable economics, abundance and ease of availability are additional arguments favoring the use of sulfur cathodes in comparison to transition metal – based cathodes. However, elemental sulfur has poor electronic conductivity (~10-15 S/cm)3 at room temperature which restricts the active material utilization in Li-S batteries. The formation of soluble non-intercalation based polysulfide intermediates (Li2Sn; n=2-8)4 during electrochemical cycling further leads to active material loss by coating onto the anode leading to eventual battery failure. Numerous sulfur encapsulation strategies have been reported in the literature of which, utilizing a mesoporous5 and hollow carbonaceous materials6, 7 as sulfur hosts has shown to reduce polysulfide dissolution by avoiding direct contact with the liquid electrolyte. However the pore size of these materials are in the order on microns and hence the problem of polysulfide dissolution has not been completely addressed. Porous materials with pore sizes comparable or less than the size of polysulfide species (PSS) need to devised in order to completely overcome this problem. In this work, several highly ordered nanoporous complex framework materials (CFM) were synthesized and engineered for use as effective hosts for sulfur. These nanoporous CFM architectures act as effective hosts to bind and trap the polysulfide species (PSS) serving to effectively prevent their dissolution into the electrolyte during cycling. The CFMs with three different functional groups were effectively crafted and synthesized. The resulting materials were then infiltrated with sulfur using vapor-phase infiltration techniques. The surface structure of the CFMs play a major role in efficiently trapping the polysulfide species and controlling their dissolution. The effects of functional groups created on these CFMs specifically on their polysulfide (PS) trapping properties and the corresponding electrochemical cycling performance of the sulfur impregnated CFM based cathodes were studied in detail and the results will be presented and discussed. References J. R. Akridge, Y. V. Mikhaylik and N. White, Solid State Ionics, 2004, 175, 243-245.M. M. Thackeray, C. Wolverton and E. D. Isaacs, Energy & Environmental Science, 2012, 5, 7854-7863.M. Edeling, R. W. Schmutzler and F. Hensel, Philosophical Magazine Part B, 1979, 39, 547-550.S. S. Zhang, Journal of Power Sources, 2013, 231, 153-162.S.-R. Chen, Y.-P. Zhai, G.-L. Xu, Y.-X. Jiang, D.-Y. Zhao, J.-T. Li, L. Huang and S.-G. Sun, Electrochimica Acta, 2011, 56, 9549-9555.W. Ahn, K.-B. Kim, K.-N. Jung, K.-H. Shin and C.-S. Jin, Journal of Power Sources, 2012, 202, 394-399.J. Guo, Y. Xu and C. Wang, Nano Letters, 2011, 11, 4288-4294.

Fabrication of Self-cleaning Antireflective Polymer Surfaces by Mimicking Underside Leaf Hierarchical Surface Structures

In this work, we utilized underside of four different plant leaves with different scale of hierarchical surface roughness to fabricate large area self-cleaning antireflective polymer surfaces. A simple and precise two-step soft-lithography replica molding technique was deployed by using polydimethylsiloxane (PDMS) polymer as a replicating material. In the first step, a negative PDMS replica was fabricated by using the underside of an original leaf as a template material. In the second step, a positive PDMS replica was fabricated through a negative PDMS replica used as a template. In order to study the non-wetting and light trapping properties, as-replicated polymer surfaces were characterized using Scanning Electron Microscopy (SEM), contact angle goniometer, and UV-Vis spectroscopy. SEM images confirmed the successful replication of complex hierarchical structures while contact angle measurement studies established retaining high non-wetting properties in polymer replicas. Optical studies suggest near zero reflection in normal mode and less than 5% diffuse reflection when measured using integrated sphere mode. These results have been correlated and explained with the air-liquid fraction and roughness factor as measured using three-dimensional optical profilometer.

Experimental and simulation studies on temporal evolution of chemically etched Si surface: Tunable light trapping and cold cathode electron emission properties

Anisotropic alkaline etching of single crystalline p-Si(100) substrates is carried out for different times (in the range of 30–2400 s). This leads to the formation of randomly distributed pyramidal structures on Si surfaces, as observed from atomic force microscopy (AFM) and scanning electron microscopy images. During early stages of etching, rough surfaces evolve, but for longer etching times, pyramidally textured surfaces (having dimensions in the range of 0.2–2 μm) are formed. The formation of pyramidal structures is explained in light of simulation studies based on the continuum theory of stress-induced morphological instability. The power spectral density plots extracted from the experimental AFM images and the simulated images show that while the correlation length increases for lower etching times, it gets saturated for higher etching times. These facts corroborate well with our experimental results that reveal increasing pyramidal size with etching time. In addition, we study the temporal evolution of antireflection and field emission properties of such pyramidally textured-silicon substrates in line with their potential use in solar cells and moderate level cold cathode electron emission, respectively. For instance, it is interesting to note that surface reflectance of these pyramidally textured surfaces (formed at higher etching times) can be brought down to as low as 0.4% over a broad spectral range, viz., 300–3000 nm. Likewise, the field emission data show that turn-on potential decreases with increasing etching time (e.g., 2.62 V μm−1 for an etching time of 1200 s).

Numerical interpretation to differentiate hydrogen trapping effects in iron alloys in the Devanathan-Stachurski permeation cell

The Devanathan-Stachurski-cell is the most commonly used electrochemical technique for the investigation of the hydrogen trapping properties of a material. In this set-up, a flux of hydrogen atoms diffuses through a metal membrane under study. The atoms are subjected to the heterogeneities naturally present in the lattice of the metal, acting as traps. This matter influences the diffusion of hydrogen, which is strongly microstructure related. In this paper, we apply a numerical model to different iron-alloys to determine the hydrogen trapping parameters characterizing the materials. We highlight the complexity of the hydrogen trapping mechanism which needs to be further investigated.

Oxygen-impurity charge transfer in NaMgF3:Ln (Ln = Yb, Sm, or Eu): Establishing the lanthanide energy levels in NaMgF3

Abstract Photoluminescence (PL) features arising from intraconfigurational 4f – 4f transitions and also O2− → Ln3+ charge transfer (CT) where Ln3+ = Yb3+, Sm3+ or Eu3+ are observed for Ln-doped NaMgF3 with oxygen impurities. The peak CT stimulation energies are 4.54 eV, >5.1 eV, and 3.65 eV for Yb3+, Sm3+ and Eu3+, respectively. Exciting into the CT bands produces intense 4f – 4f emissions characteristic of the Ln3+ dopant in all cases. The CT peak excitation energies are used to construct a host-referred binding energy (HRBE) diagram for all Ln3+ and Ln2+ dopants, which can then be referenced to understand the luminescence and trapping properties of Ln3+ and Ln2+ ions in all NaMgF3:Ln compounds. We demonstrate that the HRBE accurately describes the electron trapping in NaMgF3:Yb where Yb3+ + e− → Yb2+ after exposure to X-ray irradiation that is stable under UV exposure to stimulation energies up to at least 5 eV. Furthermore, the first 5d levels of the studied Ln2+ dopants are well described within the HRBE diagram. For NaMgF3:Eu, two unique Eu3+ sites are observed where one is highly distorted and is primarily excited by CT, likely due to an adjacent O2− impurity. For the distorted site, the peak intensity of the 5D0 → 7F0 emission is approximately 30 times greater than that of the 5D0 → 7F1 emission. Ultimately, the incorporation of oxygen impurities into the NaMgF3 lattice is shown to enhance Ln3+ luminescence, and the constructed HRBE diagram will be useful for future studies of the compound.

Spatial separation of two blue triplet emitters for improved lifetime in blue phosphorescent organic light-emitting diodes by confining excitons at the interface between two emitting layers

Abstract A device architecture to improve the lifetime of blue phosphorescent organic light-emitting diodes was developed using a double emitting layer structure with different blue triplet emitters in each emitting layer. The two emitters were chosen to have a similar light-emission spectrum, but different carrier trapping properties. An electron trapping type blue triplet emitter was doped in the first emitting layer and a hole trapping type blue triplet emitter was doped in the second emitting layer to control the emission zone of the blue phosphorescent organic light-emitting diodes. The device engineering using the spatially separated two emitters resulted in the lifetime improvement by more than 6 times compared to that of a single emitting layer device.

Stress-induced charge trapping and electrical properties of atomic-layer-deposited HfAlO/Ga2O3 metal–oxide–semiconductor capacitors

Electrical properties and trapping characteristics of an atomic layer deposited Al-rich HfAlO/β-Ga2O3 capacitor were evaluated via constant-voltage stress (CVS), capacitance–voltage (C–V), and current–voltage (I–V) measurements. The magnitude of the stress-induced charge trapping increases with increasing voltage and time. The effective charges (Neff) including the ‘border’ traps located in near-interface oxide, interface traps (Dit) of HfAlO/β-Ga2O3 interface, and fixed charges contribute significantly to the observed charge trapping, and it is found that interface traps contribute more under a large stress bias, compared with ‘border’ traps. In addition, the effective charge density is increased with stress time, implying that the contribution of negative sheet charges during the CVS process might not be negligible. Measurements of oxide permittivity (10.74), interface state density (Dit ~ 1 × 1012 eV−1 cm−2), and gate leakage current (1.18 × 10−5 A cm−2 at +10 V) have been extracted, suggesting the great electrical properties of Al-rich HfAlO/β-Ga2O3 MOSCAP. According to the above analysis, Al-rich HfAlO is an attractive candidate for normally off Ga2O3 transistors.

Quantitative analysis of gradient effective refractive index in silicon nanowires for broadband light trapping and anti-reflective properties

Controlling the light reflection using vertically-aligned nanowires has great importance in fundamental research with interesting applications in photonic devices. Here, we discuss the spatial- and polarization-dependent reflectivity measurements from the cross-sectional as well as from the top surface of vertically-aligned disordered silicon nanowires. The gradient variation in an effective refractive index along the nanowire length is estimated using the cross-sectional reflectivity measurements. We have studied the gradient variation of an effective refractive index profile and its tunability with the nanowire length. The reflectivity is measured to be as low as 5% irrespective of spatial directions and the polarization of incident light in a broad wavelength range. This constitutes the signature of a broadband omnidirectional anti-reflector that is scalable with the nanowire length. The reflectivity measurements are in good agreement with theoretical calculations. Such omnidirectional anti-reflection in a broad wavelength range is useful for applications such as photon management in photovoltaic devices and disorder-induced light scattering.

Gate length effect on trapping properties in AlGaN/GaN high-electron-mobility transistors

A comparative study was performed to assess the gate length effect on trapping properties in AlGaN/GaN metal-oxide-semiconductor channel high-electron-mobility transistors. Deep level transient spectroscopy and electrical simulations were used to investigate the deep levels response in two devices with the same gate surface area but with gate lengths of 15 and 1 μm. Results reveal that the repartition of equipotential lines depends on the gate length and impacts trapping phenomena. We demonstrated that the concentration of the defects localized beneath the gate electrode and associated with etching induced damage is reduced with a short gate length. Furthermore, for a negative gate voltage, the depletion region is less extended toward the buffer layers with a gate length of 1 μm, meaning that the trapping effects are reduced. Finally, this work indicates that it is better to design transistors with a short gate length to moderate the effect of trapping phenomena.

A Photostimulated BaSi2O5:Eu2+,Nd3+ Phosphor‐in‐Glass for Erasable‐Rewritable Optical Storage Medium

AbstractUp‐to‐date optical storage technology calls for large memory capacity, expanded storage dimension, rewritable capability, low cost, and high energy efficiency, which poses stringent requirements on the storage medium. In this study, a novel BaSi2O5:Eu2+,Nd3+ photostimulated luminescence (PSL) phosphor is developed and then made into phosphor‐in‐glass (PiG) storage medium. Upon ultraviolet light irradiation (write‐in), the generated electrons are captured by the traps, which can be further released by thermal or near‐infrared laser stimulation (read‐out). An insightful investigation is carried out to establish the relationship between trap properties and PSL performance. Demonstration application confirmed the intensity‐multiplexing optical information (including the designed bar code, quick response (QR) code, graphic patterns, and binary data) encoding/decoding. Remarkably, BaSi2O5:Eu2+,Nd3+ PSL PiG show excellent erasable‐rewritable capability thanking to the admirable anti‐ultraviolet property in glass host, as well as good optical data retention ability owing to the spatially isolated deep traps. Hopefully, the present work can push forward the research progress of PSL material and its practical application in optical storage.

On the limit of defect doping in transition metal oxides

Transition metal oxides are being increasingly used in many applications like nonvolatile memory, contacts to transition metal dichalcogenide transistors and photovoltaics, and thin-film transistors, to name a few, because the conductivity can be tuned by defect doping. The mechanism of conduction through substoichiometric oxides is however not well understood. Earlier studies attributed the conduction in substoichiometric oxides to Poole–Frenkel emission. But the assumptions underlying the Poole–Frenkel model break down in thin dielectrics and when a broad range of temperature is considered. The authors model the conduction through substoichiometric nickel oxide (NiOx) using a kinetic Monte-Carlo framework based on trap-assisted tunneling (TAT), by studying devices made of metal/NiOx/Si stacks. Modeling the temperature dependence of I–V characteristics enables the extraction of the trap parameters, like trap ionization energy and trap relaxation energy. The authors study the effects of the UV/ozone treatment, which has been shown to reduce the resistivity of NiOx by orders of magnitude, as well as the choice of metal electrode on the trap properties. The high trap relaxation energy (∼1.6 eV) is identified as an important factor in limiting the effectiveness of defect doping in NiOx, because it hinders the carrier emission step of the TAT process. The relaxation energy is another design knob that can be used when screening oxide candidates for various applications.

Numerical study of optical trapping properties of nanoparticle on metallic film with periodic structure**Project supported by the National Natural Science Foundation of China (Grant Nos. 61701382, 61601355, and 61571355), the China Postdoctoral Science Foundation (Grant No. 2016M602770), and the Xi’an Technological University Principal Foundation Key Project, China (Grant No. XAGDXJJ18001).

Based on the three-dimensional dispersive finite difference time domain method and Maxwell stress tensor equation, the optical trapping properties of nanoparticle placed on the gold film with periodic circular holes are investigated numerically. Surface plasmon polaritons are excited on the metal-dielectric interface, with particular emphasis on the crucial role in tailoring the optical force acting on a nearby nanoparticle. Utilizing a first order corrected electromagnetic field components for a fundamental Gaussian beam, the incident beam is added into the calculation model of the proposed method. To obtain the detailed trapping properties of nanoparticle, the selected calculations on the effects of beam waist radius, sizes of nanoparticle and circular holes, distance between incident Gaussian beam and gold film, material of nanoparticle and polarization angles of incident wave are analyzed in detail to demonstrate that the optical-trapping force can be explained as a virtual spring which has a restoring force to perform positive and negative forces as a nanoparticle moves closer to or away from the centers of circular holes. The results of optical trapping properties of nanoparticle in the vicinity of the gold film could provide guidelines for further research on the optical system design and manipulation of arbitrary composite nanoparticles.

Relating Structural Phase Transitions to Mechanoluminescence: The Case of the Ca <sub>1−x</sub>Sr <sub>x</sub>Al <sub>2</sub>Si <sub>2</sub>O <sub>8</sub>:1%Eu <sup>2+</sup>,1%Pr <sup>3+</sup> Anorthite

The phenomenon of mechanoluminescence (ML), where phosphors emit light when pressure is applied, is considered to be closely related to the crystallographic structure of those phosphors. In this work we unravel this connection for the anorthite solid solution Ca1−xSrxAl2Si2O8, which displays two important phase transitions as a function of strontium content x (denoted as xSr), i.e., the nearly second-order P1-I1 transition and the ferroelastic I1-I2/c transition at ambient temperature and pressure. The spontaneous strains reveal that the ferroelastic transition takes place when xSr ∈ (0.70, 0.75), while other optical methods suggest that the second-order P1−I1 transition takes place when xSr is around 0.4. The ML intensity reaches its maximum when the second order transition takes place and drops to zero when the phosphors undergo the ferroelastic transition. The first transition already brings significant changes to electron occupations at traps in this solid solution. The structural phase transitions in the anorthite solid solutions are reflected in specific ML properties, such as the ML intensity and the load threshold. Further analysis suggests this is due to the structural change of the hosts and the trap properties (trap density and electron population function). Analysis of the ML dynamics may therefore serve as a useful tool to investigate phase transitions in ML phosphors.

Direct biocatalysed synthesis of first sulfur-, selenium- and tellurium- containing l-ascorbyl hybrid derivatives with radical trapping and GPx-like properties.

6-O-l-Ascorbyl selenoesters, thioesters and telluroesters can be efficiently and directly prepared from l-ascorbic acid and suitable functionalised chalcogenoesters through lipase-catalysed transesterification reactions. Novel synthesised l-ascorbyl derivatives exhibited remarkable chain breaking and glutathione peroxidase-like activities.

Shape- and size-dependences of gold nanostructures on the electrooxidation of methanol under visible light irradiation.

Plasmonic metal nanocatalysts have excellent light trapping properties and high chemical reactivity. Impressively, Au nanostructures can absorb a wide array of visible light by tuning their morphology. In this work, spherical gold nanoparticles (Au NSs), multi-branched gold nanoparticles (Au NMs) and gold nanorods (Au NRs) were successfully synthesized; the shape- and size-dependences of these gold nanocatalysts on the methanol oxidation reaction (MOR) under light irradiation were studied. It is worth mentioning that Au NRs have the highest anode peak current density under dark conditions due to the exposure of highly active facets. A similar enhancement effect was obtained for Au NSs and Au NMs under visible light irradiation, which is due to the generation of a high concentration of energetic charge carriers on these Au nanostructures. The size dependences of Au NSs on the MOR showed that a larger electrochemically active surface area (ECSA) was obtained for small nanoparticles, which is due to the surface effect. In addition, the catalytic performance, durability and anti-CO stripping of these Au nanocatalysts under visible light irradiation, as well as the effect of light intensity and wavelength were described in detail. This work provides an insight into the mechanism of plasmon enhanced electrocatalysis by Au nanostructures with different sizes and shapes.

Generation of the trapping light structures based on vector fields

The paper discusses the main mechanisms for the formation of arrays of singular beams with non-uniform polarization for capture and particle control. The article considers a new system of vector beams with an ideal dark area, suitable for trapping and manipulating light-absorbing particles in the air. In this case, the trapping properties in the light structure can be controlled. For this purpose, the mechanism of the formation of light structures based on a single-axis crystal scheme was considered in detail. The obtained results provide a new way for creating and controlling the properties of beams suitable for trapping and will expand the possibilities of micromanipulation of absorbing particles. Besides the possibility of generating multidimensional lattices of polaritons are considered.