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At least 1,801 records · Page 100

Trap assisted space charge conduction in p-NiO/n-ZnO heterojunction diode

Highlights: • p-NiO/n-ZnO heterojunction diode with enhanced junction parameters has been prepared. • Temperature dependent I–V throw insight into the involved conduction mechanism. • SCLC with exponential trap distribution was found to be the dominant mechanism. • C–V measurement at different frequencies support the presence of traps. - Abstract: The development of short-wavelength p–n junction is essentially important for the realization of transparent electronics for next-generation optoelectronic devices. In the present work, a p–n heterojunction diode based on p-NiO/n-ZnO has been prepared under the optimised growth conditions exhibiting improved electrical and junction parameters. The fabricated heterojunction gives typical current–voltage (I–V) characteristics with good rectifying behaviour (rectification ratio ≈ 10{sup 4} at 2 V). The temperature dependent current–voltage characteristics of heterojunction diode have been studied and origin of conduction mechanism is identified. The space-charge limited conduction with exponential trap distribution having deep level trap is found to be the dominant conduction mechanism in the fabricated p–n heterojunction diode. The conduction and valence band discontinuities for NiO/ZnO heterostructure have been determined from the capacitance–voltage (C–V) measurements.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Low operating voltage n-channel organic field effect transistors using lithium fluoride/PMMA bilayer gate dielectric

Highlights: • Alternative to chemically crosslinking of PMMA to achieve low leakage in provided. • Effect of LiF in reducing gate leakage through the OFET device is studied. • Effect of gate leakage on transistor performance has been investigated. • Low voltage operable and low temperature processed n-channel OFETs were fabricated. - Abstract: We report low temperature processed, low voltage operable n-channel organic field effect transistors (OFETs) using N,N′-Dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C{sub 8}) organic semiconductor and poly(methylmethacrylate) (PMMA)/lithium fluoride (LiF) bilayer gate dielectric. We have studied the role of LiF buffer dielectric in effectively reducing the gate leakage through the device and thus obtaining superior performance in contrast to the single layer PMMA dielectric devices. The bilayer OFET devices had a low threshold voltage (V{sub t}) of the order of 5.3 V. The typical values of saturation electron mobility (μ{sub s}), on/off ratio and inverse sub-threshold slope (S) for the range of devices made were estimated to be 2.8 × 10{sup −3} cm{sup 2}/V s, 385, and 3.8 V/decade respectively. Our work thus provides a potential substitution for much complicated process of chemically crosslinking PMMA to achieve low leakage, high capacitance, and thus low operating voltage OFETs.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Deposition temperature dependent optical and electrical properties of ALD HfO{sub 2} gate dielectrics pretreated with tetrakisethylmethylamino hafnium

Highlights: • ALD-derived HfO{sub 2} gate dielectrics have been deposited on Si substrates. • The leakage current mechanism for different deposition temperature was discussed. • Different emission at different field region has been determined precisely. - Abstract: The effect of deposition temperature on the growth rate, band gap energy and electrical properties of HfO{sub 2} thin film deposited by atomic layer deposition (ALD) has been investigated. By means of characterization of spectroscopy ellipsometry and ultraviolet–visible spectroscopy, the growth rate and optical constant of ALD-derived HfO{sub 2} gate dielectrics are determined precisely. The deposition temperature dependent electrical properties of HfO{sub 2} films were determined by capacitance–voltage (C–V) and leakage current density–voltage (J–V) measurements. The leakage current mechanism for different deposition temperature has been discussed systematically. As a result, the optimized deposition temperature has been obtained to achieve HfO{sub 2} thin film with high quality.

36 MATERIALS SCIENCE↗

Origin of giant dielectric constant and conductivity behavior in Zn{sub 1−x}Mg{sub x}O (0 ≤ x ≤ 0.1) ceramics

Highlights: • Mg doped zinc oxide ceramics were fabricated by co-precipitation/solid state reaction. • MZO ceramics shown a Debye type and colossal dielectric response. • Physical absorption of atmospheric water vapor contributes these high permittivity. • The fabricated ceramic shows Maxwell–Wagner type of relaxation. - Abstract: Zn{sub 1−x}Mg{sub x}O ( ≤ x ≤ 0.1) ceramics were fabricated by conventional solid-state reaction of co-precipitated zinc oxide and magnesium hydroxide nanoparticles. Structural and morphological properties of the fabricated ceramics were studied using X-ray diffraction and scanning electron microscopic analysis. The dielectric measurements of the ceramics were carried out as a function of frequency and temperature respectively. Interestingly, Mg doped ZnO (MZO) samples exhibited colossal dielectric response (∼1 × 10{sup 4} at 1 kHz) with Debye like relaxation. The detailed dielectric studies and thermal analyses showed that the unusual dielectric response of the samples were originated from the defected grain and grain boundary (GB) conductivity relaxations due to the absorbed atmospheric water vapor (moisture). Impedance spectroscopy was employed to determine the defected grain and GB resistances, capacitances and which supported Maxwell–Wagner type relaxation phenomena.

36 MATERIALS SCIENCE↗

Characterization of electronic structures from CdS/Si nanoheterostructure array based on silicon nanoporous pillar array

Highlights: • CdS/Si nanoheterostructure array has been fabricated through a CBD method. • The electronic properties have been investigated by the I–V and C–V techniques. • The onset voltages, characteristic frequency and built-in potential are investigated. • The electronic structures can be tuned through the annealing treatments. - Abstract: The electronic properties of heterostructures are very important to its applications in the field of optoelectronic devices. Understanding and control of electronic properties are very necessary. CdS/Si nanoheterostructure array have been fabricated through growing CdS nanocrystals on the silicon nanoporous pillar array using a chemical bath deposition method. The electronic properties of CdS nanoheterostructure array have been investigated by the current–voltage, complex impedance spectroscopy and capacitance–voltage techniques. The onset voltages, characteristic frequency and built-in potential are gradually increased with increasing the annealing temperature. It is indicated that the electronic structures of CdS/Si nanoheterostructure array can be tuned through the annealing treatments.

36 MATERIALS SCIENCE↗

From graphite-clay composites to graphene electrode materials: In-situ electrochemical oxidation and functionalization

Highlights: • Graphene was synthesized by electrochemical exfoliation of graphite-clay rods with different clay:graphite ratios. • In-situ electrochemical oxidation and functionalization were used in the exfoliated process. • Graphene thin-film electrodes were constructed for supercapacitors and lithium ion batteries. • This work provided a value-added way that can transform the low-purity graphite resources to graphene electrode materials. - Abstract: The development of cost- and time-effective methods to synthesize graphene materials is very urgent in order to promote its large-scale application in electrochemical energy storage devices. Herein, graphene materials were synthesized by the electrochemical exfoliation (electrochemical oxidation) of graphite-clay rods with different clay:graphite ratios in aqueous solution and in short reaction time (1 h). The dual role of electrochemical oxidation reaction was presented: (1) the electrochemical oxidation reaction facilitates the exfoliation of pencil graphite leads and in-situ forms functional groups on graphene; (2) the electrochemical oxidation reaction enhances the Faradaic reaction in supercapacitor. The in-situ electrochemical oxidation and functionalization methods can transform low purity graphite to high-value graphene electrode materials for supercapacitors and lithium ion batteries. The specific capacitances of exfoliated graphene are 20-time larger than that of graphite-clay composites. This work provided a value-added way that can transform the low-purity graphite resources to high performance graphene electrode materials.

36 MATERIALS SCIENCE↗

Surfactant-free synthesis, photocatalytic and electrochemical property study of Co3O4 nanoparticles

Highlights: • Surfactant-free Co{sub 3}O{sub 4} nanoparticles were synthesized in aqueous solution. • The size of Co{sub 3}O{sub 4} nanoparticles can be controlled by changing the NaOH concentration. • The Co{sub 3}O{sub 4} nanoparticles size bears a linear relationship to the NaOH concentration. • The photocatalytic and electrochemical properties of Co{sub 3}O{sub 4} nanoparticles are size dependent. - Abstract: A facile surfactant-free route for size-control preparation of Co{sub 3}O{sub 4} nanoparticles in aqueous solution was reported. The feeding ratio of OH{sup −} to Co{sup 2+} influences the conversion of Co{sup 2+} to Co{sub 3}O{sub 4} crystals, and affects the crystallinity of the final Co{sub 3}O{sub 4} products. The size of Co{sub 3}O{sub 4} nanoparticles can be controlled to be 15, 18, 27 and 30 nm by simply regulating the concentration of NaOH solution through a β-Co(OH){sub 2} → Co{sub 3}O{sub 4} process. A linear relationship between Co{sub 3}O{sub 4} size and NaOH concentration was found. The photocatalytic property for rhodamine B (RhB) degradation and electrochemical property for supercapacitor of the Co{sub 3}O{sub 4} nanoparticles are size dependent. Co{sub 3}O{sub 4} nanoparticles in the size of 15 nm showed the highest photocatalytic efficiency of 70% in pH 3 under visible-light irradiation for 3 h, and behaved the highest specific capacitance of 177 F g{sup −1}.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

Origin of relaxor behavior in 0.78(Na0.5Bi0.5)TiO3-0.2SrTiO3-0.02BaTiO3 ceramic: An electrical modulus study

Highlights: • Implementation of IS technique to study thermal evolution of polar nano regions. • Indirect evidence of the existence of polar nano regions well above T{sub B} and below T{sub f}. • Visualization of relaxation dynamics of PNRs on cooling by a schematic diagram. - Abstract: The relaxation dynamics of the polar nano-regions (PNRs) in the 0.78Na{sub 0.5}Bi{sub 0.5}TiO{sub 3}-0.2SrTiO{sub 3}-0.02BaTiO{sub 3} lead free ternary system over a wide temperature range (50–650 °C) is investigated using complex electric modulus formalism. The modulus spectra are analyzed across three characteristic temperatures T{sub B}, T{sub m}, and T{sub f} with a special focus on the evolution of dynamics of PNRs. Portraying high capacitance of shoulder response as compared to the bulk response in M{sup (}f) spectra shows indirectly the presence of highly polarisable entities that persist even above T{sub B} and below T{sub f}. The activation energies extracted from an Arrhenius fit to the relaxation time of both bulk and shoulder response signify different relaxation mechanisms. Further, the value of the stretched exponent β and the scaling behavior study of the M{sup (}f) spectra envisage temperature sensitive dipolar relaxation.

36 MATERIALS SCIENCE↗

Solvent free solid-state synthesis of Pr6O11/g-C3N4 visible light active photocatalyst for degradation of AV7 dye

Highlights: • A new combination of Pr{sub 6}O{sub 11}/g-C{sub 3}N{sub 4} photocatalyst is synthesized by simple solvent free solid state method. • The photocatalytic activity of Pr{sub 6}O{sub 11}/g-C{sub 3}N{sub 4} is investigated by degradation of AV7 dye under visible light. • Improved performance is attributed to enhanced visible light absorption and efficient charge separation as evidenced by photoelectrochemical study. • Pr{sub 6}O{sub 11}/g-C{sub 3}N{sub 4} also exhibit super capacitance behavior. - Abstract: A new Pr{sub 6}O{sub 11}/g-C{sub 3}N{sub 4} heterostructure material has been prepared by single step solvent free solid state method for photocatalytic environmental cleaning application using visible light. The Pr{sub 6}O{sub 11}/g-C{sub 3}N{sub 4} heterostructure exhibits enhanced visible light absorption, resulting in improved photoelectrochemical properties and photocatalytic performance. The optimized composition of Pr{sub 6}O{sub 11}/g-C{sub 3}N{sub 4} composite shows improved degradation kinetics and completely degrades AV7 dye within 20 min of visible light irradiation. Photoluminescence and electrochemical studies suggest better separation of photogenerated charge carriers in the composite compared to single phase materials. This is further substantiated by the improved photocurrent response of the composite. The notable increase of photocatalytic activity of Pr{sub 6}O{sub 11}/g-C{sub 3}N{sub 4} heterostructure is ascribed to the improved visible light absorption, reduced band gap and better separation of photogenerated electrons and holes. To the best of our knowledge, this new heterostructure photocatalyst is found to be more efficient for the degradation of AV7 dye compared to the systems reported so far.

36 MATERIALS SCIENCE↗

Probing lead acetate in solution using X-ray diffraction

Here, for the purpose of water purification involving toxic metal sensing and removal, high energy X-ray diffraction experiments have been performed on lead acetate Pb(Ac) 2 solutions, liquid and amorphous glutathione disulfide (GSSG), and their mixtures. The data have been interpreted using Empirical Potential Structure Refinement and pair distribution function analysis. At the highest concentration of 1 M Pb(Ac) 2 in water, the lead molecules are found to cluster and the second shell in the water structure becomes slightly more ordered as the water molecules become compressed. Liquid and amorphous GSSG are found to hydrogen bond primarily via OH-O interactions, while NH-O bonds are much more distorted. Aqueous solutions of Pb(Ac) 2 + GSSG show the closest Pb-O (carboxyl) and Pb-N (amine) bonds both at a distance of 2.5 ± 0.1 Å at a concentration of 1 M Pb(Ac) 2 in water. At 0.75 M Pb(Ac) 2 in water, strong Pb-S bonds are found at a distance of 2.8 ± 0.1 Å. The implications for lead removal using capacitive deionization are discussed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Patterned anodes with sub-millimeter spatial resolution for large-area MCP-based photodetector systems

Micro-channel-plate-based photo-detectors are unique in being capable of covering very large areas such as those required in elementary particle and nuclear physics, while providing sub-millimeter space resolution, time resolutions of less than 10 picoseconds for charged particles, and time resolutions of 30 psec–50 psec for single photons. In such systems the electronic channel count is a major cost driver. Incorporating a capacitively-coupled anode allows the use of external pickup electrodes with patterns of individual channels optimized for occupancy, rate, and time/space resolution. The signal pickup antenna can be economically implemented as a printed circuit card with a 2-dimensional array of pads for high-occupancy/high-rate applications such as in particle colliders and medical imaging, or a 1-dimensional array of strips for a lower channel count in low-occupancy/low-rate applications such as large neutrino detectors. In this paper we present pad patterns that enhance signal-sharing between pads to lower the channel count per unit area in large-area systems by factors up to 4, while maintaining spatial resolutions of approximately 100 to 200 μ m for charged particles and 400 to 1000 μ m for single photons. Patterns that use multiple signal layers in the signal-pickup board can lower the channel count even further, moving the scaling behavior in the number of pads versus total area from quadratic to linear.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

Electrosorption of organic acids from aqueous bio-oil and conversion into hydrogen via microbial electrolysis cells

Neutralization of the bio-oil pH has been shown to generate a neutralized bio-oil aqueous phase (NBOAP) that includes most of the acidic components and a neutralized bio-oil organic phase (NBOOP) that includes hydrophobic organics, such as phenols. NBOOP can be used for fuel production, while NBOAP can be fed to microbial electrolysis cells (MECs) for hydrogen production. After pH neutralization, some organic acidic components remain in NBOOP. This work is focused on capturing acidic compounds from NBOOP through water extraction and electrosorption, and demonstrating hydrogen production via MECs. Capacitive deionization (CDI) is proven effective in capturing ions from NBOOP-contacted water and NBOAP via electrosorption. Captured acidic compounds enable the MEC application to effectively produce renewable hydrogen. Chemical oxygen demand (COD) removal of 49.2%, 61.5%, and 60.8% for 2, 4, and 10 g/L-anode/day loading were observed, corresponding to a total COD degradation of 0.19 g/L, 0.79 g/L, and 1.3 g/L, respectively. A maximum hydrogen productivity of 4.3 L-H 2 /L-anode/day was obtained. Major compounds in the water phase such as fatty acids, sugar derivatives, furanic and phenolic compounds were converted to hydrogen with an efficiency of 80–90%. Lastly, this approach may lead the entire biomass pyrolysis process to be an overall carbon-neutral process.

09 BIOMASS FUELS↗

Pathway for recovery of photo-degraded polymer solar cells by post degradation thermal anneal

The photo-degradation of polymer solar cells is a critical challenge preventing its commercial deployment. We experimentally fabricate organic solar cells and characterize their degradation under solar simulators in an environmental chamber under nitrogen flow, without exposure to oxygen and moisture. We have developed a thermally stable inverted organic solar cell architecture in which light induced degradation of device characteristics can be reversibly annealed to the pristine values. The stable inverted cells utilized MoO x layers that are thermally treated immediately after their deposition on the organic layer, and before metal cathode deposition. Organic solar cells that are photo-degraded in the presence of oxygen, however show irreversible degradation that cannot be thermally recovered. The decrease of organic solar cell characteristics correlates with increases in mid-gap electronic states, measured using capacitance spectroscopy and dark current. It is likely the photo-induced defect states caused by local H motion from the alkyl chains to the aromatic backbone, can be reversibly annealed at elevated temperatures after photo-degradation. Finally, our results provide a pathway for improving the stability of organic photovoltaics.

14 SOLAR ENERGY↗

Characterizing Structure-Dependent TiS 2 /Water Interfaces Using Deep-Neural-Network-Assisted Molecular Dynamics

As a promising layered electrode material, TiS 2 -based capacitive deionization (CDI) devices for water desalination have attracted significant attention. However, TiS 2 /H 2 O interfacial features, potentially important for device optimization, remain unidentified. Using Deep Potential Molecular Dynamics (DPMD), we characterized distinct aqueous interfaces introduced by four TiS 2 terminations expected to be present as water intercalates into TiS 2 , namely, Armchair, Zigzag, Zigzag-L, and Zigzag-R. First, we assessed important representative physical properties of the system to validate the deep potentials (DPs). DPMD simulations agree well with experiments and first-principles simulations, suggesting the DPs are accurate and reliable. Subsequent simulations of these TiS 2 /water interfaces revealed how TiS 2 surface termination influences the structure of interfacial water. This effect is most evident in the first and second water layers close to the TiS 2 surface, and more pronounced when spontaneous dissociative adsorption of water occurs. The extent of water dissociation on each surface was evaluated using enhanced sampling. Zigzag-L is the only interface where proton transfer from adsorbed water to TiS 2 surface S atoms is thermodynamically and kinetically favored. The coexistence of surface four-fold-coordinated Ti (Ti 4c ) and one-fold-coordinated S (S 1c ) is found to be essential to making proton transfer feasible on the Zigzag-L surface. Furthermore, remaining unprotonated S 1c atoms can act as good proton acceptors after water dissociation. Thus, TiS 2 with Zigzag-L termination may be a surface to avoid in CDI device construction, given that pH fluctuations adversely affect performance. Furthermore, this work provides new understanding of TiS 2 /H 2 O interfacial features that could aid future design and optimization of TiS 2 -based CDI devices for water desalination.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Unraveling the Ion Adsorption Kinetics in Microporous Carbon Electrodes: A Multiscale Quantum-Continuum Simulation and Experimental Approach

With the understanding that sorption in porous carbon electrodes is crucial to many environmental and energy technologies, such as capacitive deionization (CDI), supercapacitor energy storage, and activated carbon filters. In each of these examples, a practical model that can describe ion electrosorption kinetics is highly desirable for accelerating material design. Here, we proposed a multiscale model to study the ion electrosorption kinetics in porous carbon electrodes by combining quantum mechanical simulations with continuum approaches. Our model integrates the Butler-Volmer (BV) equation for sorption kinetics and a continuously stirred tank reactor (CSTR) formulation with atomistic calculations of ion hydration and ion-pore interactions based on density functional theory (DFT). We validated our model experimentally by using ion mixtures in a flow-through electrode CDI device and developed an in-line UV absorption system to provide unprecedented resolution of individual ions in the separation process. We showed that the multiscale model captures unexpected experimental phenomena that cannot be explained by the traditional ion electrosorption theory. The proposed multiscale framework provides a viable approach for modeling separation processes in systems where pore sizes and ion hydration effects strongly influence the sorption kinetics, which can be leveraged to explore possible strategies for improving carbon-based and, more broadly, pore-based technologies

36 MATERIALS SCIENCE↗

Characterizing Density and Spatial Distribution of Trap States in Ta 3 N 5 Thin Films for Rational Defect Passivation

Tantalum nitride (Ta 3 N 5 ) has gained significant attention as a potential photoanode material, yet it has been challenged by material quality issues. Defect-induced trap states are detrimental to the performance of any semiconductor material. Beyond influencing the performance of Ta 3 N 5 films, defects can also accelerate the degradation in water during desired electrochemical applications. Defect passivation has provided an enormous boost to the development of many semiconductor materials but is currently in its infancy for Ta 3 N 5 . This is in part due to a lack of experimental understanding regarding the spatial and energetic distribution of trap states throughout Ta 3 N 5 thin films. Here, we employ drive-level capacitance profiling (DLCP) to experimentally resolve the spatial and energetic distribution of trap states throughout Ta 3 N 5 thin films. The density of deeper energetic traps is found to reach ∼2.5 to 6 × 10 22 cm –3 at the interfaces of neat Ta 3 N 5 thin films, over an order of magnitude greater than the bulk. In addition to the spatial profile of deep trap states, we report neat Ta 3 N 5 thin films to be highly n-type in nature, owning a free carrier density of ∼9.74 × 10 17 cm –3 . This information, coupled with the present understanding of native oxide layers on Ta 3 N 5 , has facilitated the rational design of a targeted passivation strategy that simultaneously provides a means for catalyst immobilization. Loading catalyst via silatrane moieties suppresses the density of defects at the surface of Ta 3 N 5 thin films by two orders of magnitude, while also reducing the free carrier density of films by over one order of magnitude, effectively dedoping the films to ∼2.40 × 10 16 cm –3 . The surface passivation of Ta 3 N 5 films translates to suppressed defect-induced trapping and recombination of photoexcited carriers, as determined through absorption, photoluminescence, and transient photovoltage. Here, this illustrates how developing a deeper understanding of the distribution and influence of defects in Ta 3 N 5 thin films has the potential to guide future works and ultimately accelerate the integration and development of high-performance Ta 3 N 5 thin film devices.

defect passivation↗

Bisphenol-A sensors on polyimide fabricated by laser direct writing for on-site river water monitoring at attomolar concentration

This work presents an aptamer-based, highly sensitive and specific sensor for atto- to femtomolar level detection of bisphenol A (BPA). Because of its widespread use in numerous products, BPA enters surface water from effluent discharges during its manufacture, use, and from waste landfill sites throughout the world. On-site measurement of BPA concentrations in water is important for evaluating compliance with water quality standards or environmental risk levels of the harmful compound in the environment. The sensor in this work is porous, conducting, interdigitated electrodes that are formed by laser-induced carbonization of flexible polyimide sheets. BPA-specific aptamer is immobilized on the electrodes as the probe, and its binding with BPA at the electrode surface is detected by capacitive sensing. The binding process is aided by ac electroosmotic effect that accelerates the transport of BPA molecules to the nanoporous graphene-like structured electrodes. The sensor achieved a limit of detection of 58.28 aM with a response time of 20 s. The sensor is further applied for recovery analysis of BPA spiked in surface water. In conclusion, this work provides an affordable platform for highly sensitive, real time, and field-deployable BPA surveillance critical to the evaluation of the ecological impact of BPA exposure.

36 MATERIALS SCIENCE↗

Electric Double-Layer Structure in Primitive Model Electrolytes. Comparing Molecular Dynamics with Local-Density Approximations

We evaluate the accuracy of local-density approximations (LDAs) using explicit molecular dynamics simulations of binary electrolytes comprised of equisized ions in an implicit solvent. The Bikerman LDA, which considers ions to occupy a lattice, poorly captures excluded volume interactions between primitive model ions. Instead, LDAs based on the Carnahan–Starling (CS) hard-sphere equation of state capture simulated values of ideal and excess chemical potential profiles extremely well, as is the relationship between surface charge density and electrostatic potential. Excellent agreement between the EDL capacitances predicted by CS-LDAs and computed in molecular simulations is found even in systems where ion correlations drive strong density and free charge oscillations within the EDL, despite the inability of LDAs to capture the oscillations in the detailed EDL profiles.

25 ENERGY STORAGE↗

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