Electrons In Layer Research Articles

Flexible Janus Textile‐Based Electroosmotic Pump for Large‐Area Unidirectional Positive Water Transport

AbstractMoisture management plays a vital role in enhancing the comfort of smart textiles and has attracted widespread attention. However, passive liquid transportation is the main method for clothes, and exhibits insufficient capacity for moisture transfer. Herein, a novel and flexible Janus textile‐based electroosmotic pump with directional positive water transport is proposed, based on the mechanism of electroosmosis. This Janus structure is assembled with carbon fabric as the anode and nickel‐plated nonwoven as the cathode with a filling of track‐etched polycarbonate membrane. Water flow can be directionally transported, even vertically against gravity, driven by low‐voltage based on the principle of a microfluidic double electron layer in the microchannels of a nanoporous membrane. The maximum water flux of the proposed electroosmotic pump reached 140.94 mg min−1 cm−2 with the driven voltage of 6 V, which is an excellent moisture permeability performance compared with previous membrane‐based electroosmotic pumps. Such innovative wearable devices can actively tune the moisture permeability for various conditions. As a proof of concept, the wearable electroosmotic pump is applied to sports insoles and sportswear to achieve durable, sufficient directional water transport. Such moisture transporting wearable devices have potential in areas such as smart clothing and medical protection.

GaN-on-Si Calorimetric Thermal Conductivity Gas Sensor

Introduction Thermal conductivity gas sensors are used in a multitude of fields where identifying concentrations of certain gasses within mixtures is important, such as in exhaust emission monitoring, chemical process control to name some examples. There is also a growing demand to be able to place sensors in more extreme environments closer to the source of the reaction/emissions. Traditionally, silicon-on-insulator (SOI) is the material of choice for MEMS for use in harsh environments, however SOI has a limit of around 300°C before it can no longer reliably sense [1].In this work, we present a Gallium Nitride-on-Silicon (GaN-on-Si) thermal conductivity calorimetric gas sensor. Depending on the specific process, devices fabricated from GaN can survive temperatures up to 1000°C [2] [3]. As a wide band-gap semiconductor, GaN devices do not suffer the adverse effects of excessive carrier generation that silicon-based devices do [4]. Using GaN, it is possible to fabricate heterogenous devices by growing an alloy layer on top of the GaN layer. In the case of this work, the alloy is Aluminium Gallium Nitride (AlGaN). Just below the interface of the two materials, piezoelectric polarisation induced by the lattice mismatch of the two materials causes a thin layer (angstroms) of electrons to form a 2-dimensional electron gas (2DEG) [5]. Currently several factors limit GaN’s mass market appeal, such as yield and cost, although with more development, GaN is a candidate for the harsh environment sensing domain.This work presents for the first time a thermal conductivity calorimetric gas sensor fabricated in a GaN-on-Silicon process, with 2DEG sensing elements on a membrane structure. Thermal Conductivity Sensing Thermal conductivity gas sensors use heat transfer principles to detect specific gasses or gas concentrations. A heating element used in conjunction with one or more temperature sensing elements can be used to measure the transfer of heat from heater to the gas mixture. Measuring this heat transfer is the basis for this method of gas detection. The Sensor The sensor die is square at 1.6 mm x 1.6 mm. The device consists of a heating element placed in the centre of the membrane with thermopile temperature sensor upstream and downstream of the heater [6][7]. The thermopiles are made up of 5 thermocouples where the junction materials are gold and the AlGaN/GaN 2DEG. The combination of upstream and downstream temperature monitoring along with the heating from the hot wire allow the temperature profile of the gas to be detected and thus the concentration. Figure 1 shows an optical image of the sensor die with the specific devices highlighted. Experiment The experiment was conducted using a custom gas rig consisting of 3 mass flow controllers (MFCs) interfaced with a Raspberry pi. The different MFCs enable the gas concentration to be controlled so that measurements can be conducted to measure the sensitivity of the sensor to various gas concentrations. In this work, zero air is used as a carrier gas with Hydrogen being the gas of interest. Hydrogen was chosen principally due to its high thermal conductivity (185 mW/mK) compared to zero air (28 mW/mK). Flow rate was kept constant at 200 SCCM/Min so that the effect of forced convection due to flow velocity on the temperature profile can be discounted.Initial Results will be presented at the conference. Acknowledgments This work was supported by the Innovate UK project “GaN Sense” (file ref. 103446).

Easily controlled 2D GO film as electronic barrier layer to realize charge transport equilibrium of QLED with greatly enhanced EQE

Abstract An effective Quantum Dot Light Emitting Diodes (QLED) was developed by creatively inserting an easily controlled 2D graphene oxide (GO) film between the luminescent layer and the electron transport layer (ETL) as the electron barrier layer (EBL). As compared with the traditional PMMA and other polymer barrier layers, the GO with particular the lamellar two-dimensional structure was more conducive to the control of film thickness by spin-coating. The introduction of GO increased the conduction band edge and inhibited exciton quenching. Simultaneously, since the electron mobility of the ETL was much higher than the hole mobility of the hole transport layer (HTL), GO with high insulation could be used to inhibit the electron injection effectively and achieve the charge transport balance. The green QLEDs with high performances including a current efficiency of 22.51 cd A−1, a power efficiency of 8. 71 lm W−1 and an EQE of up to 5.98% were successively fabricated. This particular architecture of QLED with GO electron barrier layer and creative method of energy band regulation provided an efficient and feasible strategy for the next generation of QLED displays with high performance and solid-state lighting technologies.

Distribution of Counter Ions in Negatively-charged Lipid/Water/Air Interface: Molecular Dynamics Study

We investigated the distribution of ions around charged membranes at a lipid/water/air interface by using a molecular dynamics (MD) simulation with a sufficiently large cell size for water. It was shown that the thickness of the electronic double layer is different from the classical Debye length, which is a bit longer than the former. It was also found that the distance between the ions in the solution and the membrane charge changes depending on the difference in ionic charge owing to the water molecules around the ions. Detailed analysis of ion distribution near the lipid/water surface was presented.

Dual MAC Based Hierarchical Optical Access Network for Hyperscale Data Centers

A dual media access control (DMAC) based hierarchical optical access network (HOAN) is proposed for data center networks, consisting of passive optical distribution modules (PODMs) at passive optical access layer and top-of-cluster (ToC) switches at electronic access layer. A PODM organizes a group of servers into a computing cluster and forms the intra-cluster channel. Each ToC switch connected with several PODMs forms the inter-cluster channel based on time and wavelength division multiplexing (TWDM). A load-sensing dual-mode (LSDM) protocol is presented for the intra-cluster channel to realize distributed low-load competition and high-load polling operation; the inter-cluster channel applies any polling based TWDM protocol to offer flexible bandwidth allocation. Simulations show that the LSDM can reach 0.95 throughputs at high traffic load, less than 32 μs frame latency, 128 μs frame latency on the 99.9th percentile of the simulated results at 25 Gbps with high priority, verifying the LSDM protocol can realize high throughput, low latency, and the measured latency variation. Compared the performances of DMAC based HOAN with those of passive optical cross-connection network (POXN) and passive optical top-of-rack interconnect (POTORI) architecture, when the normalized intra-rack traffic load reaches 0.8, average frame latencies in one computing cluster are 70.4, 184, and 2480 μs at 10 Gbps, and normalized available bandwidths for inter-cluster channels are 1, 0.2, and 0.2, respectively. Furthermore, the DMAC based HOAN is characterized with the scalability capable of organizing up to 320000 servers with only 500 ToC switches.

Universal three-dimensional crosslinker for all-photopatterned electronics

All-solution processing of large-area organic electronics requires multiple steps of patterning and stacking of various device components. Here, we report the fabrication of highly integrated arrays of polymer thin-film transistors and logic gates entirely through a series of solution processes. The fabrication is done using a three-dimensional crosslinker in tetrahedral geometry containing four photocrosslinkable azide moieties, referred to as 4Bx. 4Bx can be mixed with a variety of solution-processable electronic materials (polymer semiconductors, polymer insulators, and metal nanoparticles) and generate crosslinked network under exposure to UV. Fully crosslinked network film can be formed even at an unprecedentedly small loading, which enables preserving the inherent electrical and structural characteristics of host material. Because the crosslinked electronic component layers are strongly resistant to chemical solvents, micropatterning the layers at high resolution as well as stacking the layers on top of each other by series of solution processing steps is possible.

Flexible field-effect transistors with a high on/off current ratio based on large-area single-crystal graphene

Large-area single-crystal graphene (LSG) over half a millimeter were synthesized via chemical vapor deposition, and a flexible ion gel-gated graphene field-effect transistor (FET) was fabricated to explore the electrical properties of the graphene based on the mechanism of electronic double layers. A procedure of cyclical oxidation/hydrogen-annealing processes by chemical vapor deposition (CVD) was proposed and optimized as a new growth method for the large single-crystal graphene, to facilitate the reconstruction of copper foil surface. To form a flexible FET on the polyethylene terephthalate substrate, LSG was utilized as a channel layer, and a spin-coated ion gel film was used as a gate dielectric. The flexible device demonstrates excellent electrical properties and high degree of bendability. When the device was bent by 8.1%, the on/off current ratio exceeded 400 because the deformation of the graphene crystal lattice widened graphene’s bandgap. This work is a fundamental study on the growth mechanism of LSG and the two-dimensional-material-based ion gel-gated transistor for application in flexible electronic devices.

A2B2O7 (A= La, Pr, Nd, Sm, Gd and B Ti, Zr, Sn) ceramics for mild-temperature NO2 sensing and reduction

Abstract The present work demonstrates the design and synthesis of A2B2O7 (A = La, Pr, Nd, Sm, Gd and B = Ti, Zr, Sn) ceramics to fabricate NO2 sensors for efficient NO2 sensing and reduction at mild temperature. To clarify the sensing mechanism of NO2 sensor, the electron layer mechanism of rare-earth cations at A site and different ionic radius of B-site cations are investigated to discuss the difference from the NO2 sensing and reduction. The unique electronic structure of Pr3+([Xe]4f2) endows the different band structure and the variable valence in nature with +3 and + 4 oxidation states, which would induce different electronic transport, resulting in enhanced NO2 sensing performances and reduction reaction. According to A2B2O7 structure, the activation energy of oxygen hopping is clarified through comparing different ionic radius of B cations, and the surface oxygen species providing a transfer station for oxygen hopping of solid electrolyte are analyzed by various characterization techniques. The results show that high sensitivity obtained over pure Pr2Sn2O7 without any doping at A or B site is as high as 124 nA/ppm towards 25–100 ppm NO2 at 500 °C, which is significantly better than commercial YSZ sensor. This work makes a significant progress in solid electrolytes and gas sensor.

Temperature induced modulation of near-infrared photoluminescence in BaTiO3:Er

Due to the shielding effect of the outermost electronic layer 5s and 5p of rare earth, the near-infrared photoluminescence (PL) of Er3+ can not be easily affected by the external environment. However, we have regulated the near-infrared PL of Er3+ by changing temperature, which is ascribed to the phase transition of BaTiO3 from tetragonal to cubic phase and the presence of impurity. It also found that the redshift of wavelength in samples containing tetragonal phase BaTiO3 can reach 13 nm, which is never observed in other materials. The center wavelength shifts from 1530 nm to 1543 nm as the temperature rises from 20 to 200 °C. Moreover, the full width at half maximum (FWHM) of samples containing cubic phase has a growth of 6 nm (up to 85 nm) with increasing temperature. It indicated that temperature-induced phase transition can be an important method to modulate the PL of Er3+ in BaTiO3 with impurity.

Study on the Transparent Electronic Isolation Layer Material - A Photoresist Composition which is Stable at High Temperature and Humidity

A negative resist composition composed of an acrylic-copolymer-binder resin, a crosslinker, photoinitiators, some agents and solvents has been UV-cured and developed for OverCoat (OC)-Bridge of One Glass Solution (OGS) touch panel (TP) sensor, wherein acrylic-copolymer-binder resin as a key element consisting of N-Phenylmaleimide (N-Pm), Methacrylic acid (MA), Styrene (St) and Isobornyl methacrylate (iBMA) monomers, being designed and synthesized to control the acid value (90-110mgKOH/g), molecular weight (Mw:10,000-20,000) and approximate solubility parameter [10.67-11.05(cal/cm3)1/2]. Here,we demonstrate a OC photoresist applies between two ITO line-films by UV-curing process technology deveoled for OC-Bridge pattern with a kind of acrylic-copolymer-binder resin by ours. Acting as TP sensor, the OC patterns have adequate resistance to solvents, acids and alkalis, good thermal and humid stability, and with excellent transparency and insulation. This OC photoresist, coupled with the acrylic-copolymer-binder resins, provides an unprecedented approach to realize supporting high temperature and humidity OC-Bridge.

Recoil effects on reflection from relativistic mirrors in laser plasmas

Relativistic mirrors can be realized with strongly nonlinear Langmuir waves excited by intense laser pulses in underdense plasma. On reflection from the relativistic mirror, the incident light affects the mirror motion. The corresponding recoil effects are investigated analytically and using particle-in-cell simulations. It is found that if the fluence of the incident electromagnetic wave exceeds a certain threshold, the relativistic mirror undergoes a significant back reaction and splits into multiple electron layers. The reflection coefficient of the relativistic mirror and the factors of electric field amplification and frequency upshift of the electromagnetic wave are obtained.

Collapse of Vapor-Filled Multielectron Bubbles Held Against a Surface

Multielectron bubbles (MEBs) are cavities in liquid helium containing a layer of electrons pinned to the inner surface of the bubbles. Previous experimental work carried out with MEBs in bulk helium-4 above the lambda point showed MEBs can contain vapor, which condenses in a time approximately proportional to the volume of the bubble, and this observation was further confirmed by numerical simulations. In the present work, we describe experiments where the MEBs are held against a solid substrate. We found the rate of vapor condensation and therefore the speed of collapse of the bubble to be orders of magnitude faster compared to MEBs in bulk. We discuss a numerical model and the associated difficulties to explain this difference.

Selective Harmonic Current Rejection for Virtual Oscillator Controlled Grid-Forming Voltage Source Converters

Virtual oscillator control (VOC) is a nonlinear grid-forming controller that simultaneously achieves the functionality of output voltage control and primary control layers in a power electronics interfaced distributed generation (DG) unit. Unlike conventional phasor-based primary control methods such as the droop control and virtual synchronous machine control, VOC is a time-domain controller that can guarantee almost global asymptotic synchronization. However, the high-frequency dynamics has largely been ignored in the analysis of VOC in prior art; as a result, VOC-based DGs fail to suppress harmonic current in the presence of harmonic distortion in the network-side voltage. In this work, we demonstrate that frequency-domain method can be used for oscillator-based converters in the high-frequency range, specifically, for harmonic mitigation in the converter output current. We propose a virtual impedance-based selective harmonic current suppression method, and demonstrate that it is better to use the network-side current feedback rather than that of the converter-side current for VOC implementation with virtual impedance control. Established harmonic rejection strategies for grid-following and conventional grid-forming converters are compared with the proposed method for VOC. Through impedance-based analysis, we demonstrate that the proposed method augments the passivity range of the converter terminal response with a much simpler implementation. The proposed harmonic suppression strategy is validated through hardware experiments using a single-phase inverter prototype.

Electrostabilized homogeneous dispersion of boron nitride nanotubes in wide-range of solvents achieved by surface polarity modulation through pyridine attachment

Boron nitride nanotubes (BNNTs) show exceptional physical properties including high mechanical strength and thermal conductivity; however, their applications have been restricted due to limited dispersibility in processing solvents. Here, a novel BNNT dispersion method with exceptional dispersibility in a wide range of solvents has been demonstrated by surface polarity modulation through short-molecule pyridine attachment. Nitrogen atoms in pyridine are selectively bonded to electron-deficient boron atoms of the BNNT surface through Lewis acid-base reaction, which changes the surface polarity of BNNTs from neutral to negative. Re-dispersing pyridine-attached BNNTs (Py-BNNTs) create a thick and stable electronic double layer (EDL), resulting in uniform dispersion of BNNTs in solvents with an exceptional solubility parameter range of 18.5–48 MPa1/2. The uniform dispersion of BNNTs is maintained even after the mixing with diverse polymers. Finally, composites incorporating uniformly-distributed BNNTs have been realized, and extraordinary property enhancements have been observed. The thermal conductivity of 20 wt.% Py-BNNT/epoxy composite has been significantly improved by 69.6% and the tensile strength of 2 wt.% Py-BNNT/PVA has been dramatically improved by 75.3%. Our work demonstrates a simple and facile route to dispersing BNNTs in diverse solvents, consequently leading to selective utilization of BNNT dispersed solvents in various application fields.

Theory for Influence of the Metal Electrolyte Interface on Heterogeneous Electron Transfer Rate Constant: Fractional Electron Transferred Transition State Approach

We develop a theory for outer sphere heterogeneous electron transfer (ET) rate constant (k0) and exchange current density (i0). The model hypothesizes that the transition state is attained by alignment of Fermi and reactant energy levels through exchange of fractional electronic charge (δ≠). This approach accounts the contributions from: (i) work function and Fermi energy of metal, (ii) solvent polarity and size, (iii) electronic nature and size of electroactive species, and (iv) outer Helmholtz plane (OHP) potential-dependent composition. At the outset, we develop a model for the potential ϕ1 at the inner Helmholtz plane accounting the influence of electronic and inner dipolar layer screening on the metal. The equation for ϕ1 is used to obtain the potential ϕ2 at OHP through a modified Gouy–Chapman–Stern approach. The concentration of electroactive species at OHP (ciOHP) under the influence of the Frumkin effect is obtained by substituting ϕ2 in Kornyshev’s packing density restriction model. Our theory o...

Laser processed semiconductors for integrated photonic devices -INVITED

We report results of laser processing of amorphous silicon and silicon-germanium semiconductor materials for the production of integrated photonic platforms. As the materials are deposited and processed at low temperatures, they are flexible, low cost, and suitable for multi-layer integration with other photonic or electronic layers. We demonstrate the formation of waveguides via crystallization of pre-patterned silicon components and functional microstructures through crystallization and compositional tuning of silicon-germanium alloy films. These results open a route for the fabrication of high density, multi-functional integrated optoelectronic chips.

A Theoretical Study of the Solid Solution Phases of Li<sub>x</sub>FePO<sub>4</sub>

For the next generation Li-battery anode materials LiFePO4, the forming of the solid solution phase LixFePO4 and the related charge/discharge mechanism are the high light topics recently. In the paper, ab-initio calculation was applied to study the formation and electronic structure of the solid solution of LixFePO4, and a Charge/Discharge model of LiFePO4 was set up based on the calculation results. Due to the high formation energy, LixFePO4 separates into FePO4 and LiFePO4 in bulk system under room temperature. The single solid solution phase LixFePO4 could exists in the nanoscale particle, and it is due to that the relative larger lattice mismatch energy. The nanoscale particle materials should have a good rating performance due to the forming of LixFePO4 in solid solution phase, of which the partially occupied state and the small energy gap between the VBM and the defect state could improve the intrinsic electronic conductivity. In bulk materials, the medium region, which is composed of LixFePO4, is very narrow between the two phases FePO4 and LiFePO4. There is a electron potential well in the region, of which the bottom is at the side of LixFePO4 (x<0.5). The number of electron in the well highly affects the lithium insertion and extraction. In order to efficiently transfer the electron between the potential well and the out circuit, an electron conductor network or layer should be coated on the LiFePO4 particle.

Dynamic response of partially spin- and valley-polarised two-dimensional electron liquids

The growing field of valleytronics provides new promising physics. Here, we focus on the collective modes of an infinitely thin electron layer with a binary valley degree of freedom that is unequally occupied. The spin populations are allowed to be imbalanced, too. This system can support four collective modes and two anti-resonances emerge. We study this copious dynamics in the spin- and valley-sensitive random phase approximation (RPA) and explain the uncommon behaviour by building a bridge from the many-fermion system to its bosonic counterpart. For completeness, we also report the RPA exchange and correlation energies for arbitrary spin and valley polarisation. A phase transition occurs at from the four-component to the ferro-magnetic, single-valley-occupation state.

Effect of porous media and its distribution on methane hydrate formation in the presence of surfactant

Hydrates are mainly stored within sediment pores in nature. Therefore, understanding their formation characteristics within the porous space is essential to the transportation of natural gas based on the hydrate-based technology. In this paper, solutions of sodium lauryl sulfate (SDS), sodium dodecyl benzene sulfonate (SDBS), and alcohol ethoxylate (AEO) were used with different-sized porous media to investigate the characteristics (gas storage capacity, formation rate, and formation distribution) of the hydrate formation. The experimental results show that the gas storage capacity was higher in the complex system composed of a small-size porous media. The improvement of hydrate formation in the complex system composed of SDS or SDBS solution was more significant than that in the AEO system which could enhance the hydrate formation. In the three complex systems, the surface of alumina particles was positively charged by hydrolysis, which resulted in a double electron layer consisting of the counter ion in the adjacent liquid phase. The anionic active groups ionized by surfactants (i.e., SDS and SDBS) were aggregated to the surface of particles under Coulomb force. This increased the content of the methane molecules by non-polar adsorption and micellar solubilization. Finally, in the complex system of SDS solution and porous media, the capillary force caused by the pores of porous media could enhance the liquid phase migration in the pores which change the distribution of hydrate formation. This work presents useful insights on the hydrate formation characteristics which are beneficial to the rapid formation of hydrate and its industrial application of both storage and transportation of natural gas in complex porous systems.

Work Function Tunability of Graphene with Thermally Evaporated Rhenium Heptoxide for Transparent Electrode Applications

The possibility of efficient work function tuning of high‐quality graphene, grown on 6H‐SiC(0001), by covering it with thermally evaporated rhenium heptoxide (Re2O7) is presented. Raman spectroscopy, X‐ray photoelectron spectroscopy, and ultraviolet electron spectroscopy are used for structural, chemical, and electronic characterization of Re2O7/graphene heterostructures. The deposited oxide does not induce any defects in the high‐quality graphene lattice and results in a relatively small change in optical transmittance. The observed increase in the work function of the Re2O7/graphene heterostructure (+0.76 eV) emphasizes great potential of modified graphene for use as transparent anode and hole transport layer in organic electronics.