Selection Of Dopants Research Articles

Al-, Ga-, Mg-, or Li-doped zinc oxide nanoparticles as electron transport layers for quantum dot light-emitting diodes

Colloidal quantum dots and other semiconductor nanocrystals are essential components of next-generation lighting and display devices. Due to their easily tunable and narrow emission band and near-unity fluorescence quantum yield, they allow cost-efficient fabrication of bright, pure-color and wide-gamut light emitting diodes (LEDs) and displays. A critical improvement in the quantum dot LED (QLED) technology was achieved when zinc oxide nanoparticles (NPs) were first introduced as an electron transport layer (ETL) material, which tremendously enhanced the device brightness and current efficiency due to the high mobility of electrons in ZnO and favorable alignment of its energy bands. During the next decade, the strategy of ZnO NP doping allowed the fabrication of QLEDs with a brightness of about 200 000 cd/m2 and current efficiency over 60 cd/A. On the other hand, the known ZnO doping approaches rely on a very fine tuning of the energy levels of the ZnO NP conduction band minimum; hence, selection of the appropriate dopant that would ensure the best device characteristics is often ambiguous. Here we address this problem via detailed comparison of QLEDs whose ETLs are formed by a set of ZnO NPs doped with Al, Ga, Mg, or Li. Although magnesium-doped ZnO NPs are the most common ETL material used in recently designed QLEDs, our experiments have shown that their aluminum-doped counterparts ensure better device performance in terms of brightness, current efficiency and turn-on voltage. These findings allow us to suggest ZnO NPs doped with Al as the best ETL material to be used in future QLEDs.

Universal In Situ Substitutional Doping of Transition Metal Dichalcogenides by Liquid-Phase Precursor-Assisted Synthesis.

Doping lies at the heart of modern semiconductor technologies. Therefore, for two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs), the significance of controlled doping is no exception. Recent studies have indicated that, by substitutionally doping 2D TMDs with a judicious selection of dopants, their electrical, optical, magnetic, and catalytic properties can be effectively tuned, endowing them with great potential for various practical applications. Herein, and inspired by the sol-gel process, we report a liquid-phase precursor-assisted approach for in situ substitutional doping of monolayered TMDs and their in-plane heterostructures with tunable doping concentration. This highly reproducible route is based on the high-temperature chalcogenation of spin-coated aqueous solutions containing host and dopant precursors. The precursors are mixed homogeneously at the atomic level in the liquid phase prior to the synthesis process, thus allowing for an improved doping uniformity and controllability. We further demonstrate the incorporation of various transition metal atoms, such as iron (Fe), rhenium (Re), and vanadium (V), into the lattice of TMD monolayers to form Fe-doped WS2, Re-doped MoS2, and more complex material systems such as V-doped in-plane WxMo1-xS2-MoxW1-xS2 heterostructures, among others. We envisage that our developed approach is universal and could be extended to incorporate a variety of other elements into 2D TMDs and create in-plane heterointerfaces in a single step, which may enable applications such as electronics and spintronics at the 2D limit.

Designing Multi-Dopant Species in Microporous Architectures to Probe Reaction Pathways in Solid-Acid Catalysis.

The introduction of two distinct dopants in a microporous zeotype framework can lead to the formation of isolated, or complementary catalytically active sites. Careful selection of dopants and framework topology can facilitate enhancements in catalysts efficiency in a range of reaction pathways, leading to the use of sustainable precursors (bioethanol) for plastic production. In this work we describe our unique synthetic design procedure for creating a multi-dopant solid-acid catalyst (MgSiAPO-34), designed to improve and contrast with the performance of SiAPO-34 (mono-dopant analog), for the dehydration of ethanol to ethylene. We employ a range of characterization techniques to explore the influence of magnesium substitution, with specific attention to the acidity of the framework. Through a combined catalysis, kinetic analysis and computational fluid dynamics (CFD) study we explore the reaction pathway of the system, with emphasis on the improvements facilitated by the multi-dopant MgSiAPO-34 species. The experimental data supports the validation of the CFD results across a range of operating conditions; both of which supports our hypothesis that the presence of the multi-dopant solid acid centers enhances the catalytic performance. Furthermore, the development of a robust computational model, capable of exploring chemical catalytic flows within a reactor system, affords further avenues for enhancing reactor engineering and process optimisation, toward improved ethylene yields, under mild conditions.

Study of the effect of chemical composition on the surface wettability of three-dimensional graphene foams

The chemical composition obviously affects the surface wettability of a three-dimensional (3D) graphene material apart from its surface energy and microstructure. In the hydrothermal preparation, the heteroatom doping changes the chemical composition and wettability of the 3D graphene material. To realize the controllable surface wettability of graphene materials, aminobenzene sulfonic acid (ABSA) was selected as a typical doping agent for the preparation of nitrogen and sulfur co-doped 3D graphene foam (SNGF) using a hydrothermal method. Different from using o-ABSA or p-ABSA as the dopant, SNGF with tunable surface wettability is obtained only when m-ABSA is used. This result indicates that the substituent position of -SO3H group in the benzene ring of ABSA is rather important for the tunable wettability. This work provides some theoretical foundations for dopant selection and some new insights in manipulating the properties of 3D graphene foams by adjusting the configuration of dopants.

A novel approach to selection of dopant to immobilize neodymium in uranium-based metallic fuels

Formation of intermetallic compounds of lanthanide fission products within uranium-based metallic fuels with added dopant(s) has been proposed to arrest fission products within the metallic-matrix, before lanthanides chemically react with cladding materials, leading to degradation of the cladding. Unlike previous trial-and-error approach, here we present ab-initio based generic alloy-design principles to identify dopant(s) for a given lanthanide to form dopant-lanthanide intermetallic. Our approach correctly identifies previously known dopants like Pd, as well as predict novel dopants (As and Se) which can bind fission product Nd within U-matrix. Formation of our predicted NdAs intermetallic within the U-matrix has been confirmed experimentally.

Dopant Selection Strategy for High-Quality Factor Localized Surface Plasmon Resonance from Doped Metal Oxide Nanocrystals

Thin films of degenerately doped metal oxides such as those of Sn-doped In2O3 (Sn:In2O3) are commercially significant for their broad utilization as transparent conducting electrodes in optoelectro...

On the doping concentration dependence and dopant selectivity of photogenerated carrier assisted etching of 4H–SiC epilayers

A comprehensive photogenerated carrier assisted etching investigation is carried out on the Si polar surface of high-quality p- and n-type (0001) 4H–SiC epilayers. The epilayers have intentional or unintentional doping densities in the 1014–1018 cm−3 range. Cyclic voltammetry and chronoamperometry studies under a non-focused above bandgap (280–400 nm) light illumination (≤0.66 Wcm−2) in a highly basic etching medium (1 wt% KOH solution, pH ∼12) complemented by Mott-Schottky characterization reveal a dependence of the etch voltage (within ±1 V) and etch rate (∼20–60 nm/min) on doping concentration and type. Our results demonstrate separate mutually exclusive etch voltage windows (∼± 0.3–0.7 V) in the diffusion-limited regime for a pair of doping concentrations with opposite conductivities to establish smooth preferential etching. These results provide insight in the design and fabrication of higher performance three dimensional SiC homo/hetero-junctions for various applications including photonic crystal cavities.

Step-wise transitions of electrons between valence and conduction bands: a tri-doped TiO2 approach

The unwanted structural changes and isolated unoccupied states in the band structure of TiO2 due to doping could be minimized by proper selection of dopants. A good combination of dopants would improve the optical response in visible regime and remove the isolated states from the band gap while keeping minimum structural distortion. Enhanced visible light absorption and effective utilization of photo-generated carriers would improve the photoactivity of TiO2 under solar irradiations. Mono-doped, co-doped and tri-doped models of molybdenum (Mo), carbon (c), and nitrogen (N) are developed in the structure of anatase TiO2 and the corresponding change in the geometrical structure, band structure, and optical response is noted. The Mo and C co-doping produced least structure modification when compared to a reference TiO2 system. The Mo 3d states are mixed with Ti 3d states reducing the band gap of Mo-doped TiO2. While shifting the Fermi level to the middle of the band gap, the C 2p states are introduced around the middle of the gap of C doped TiO2. The impurity states are occupied and maximum reduction in the band gap is found in Mo, C codoped TiO2. The addition of N in the Mo, C codoped TiO2 modified the band structure by creating isolated states in the band gap. The photo-response of Mo, C, N tri-doped TiO2 is prominent among the simulated models attributed to the step wise transition of electrons by the C 2p and N 2p states. The improved optical response allows more visible photons for absorptions but the isolated states may annihilate it. The Mo, C codoped system provided minimum structure changes with clear band structure and reasonable visible light absorption.

Selection of graphene dopants for Na3V2(PO4)3 graphene composite as high rate, ultra long-life sodium-ion battery cathodes

Na3V2(PO4)3 (NVP) is one of the most promising cathode materials for sodium-ion batteries because of its stability, safety, and high reversible capacity. However, the sluggish Na-ion diffusion and poor electronic conductivity of NVP often hinder electrochemical performance, thus requiring compositing with carbon materials, such as graphene to improve the material. In this work, the effect of doping species of graphene on the electrochemical performance of NVP/graphene composites was systematically investigated and vigorously compared. 3D porous NVP fabricated by sol-gel method with 3 nm of carbon coating layers was deposited on graphene sheets with different surface functionalities (GO, N-rGO and P-rGO). NVP/N-rGO composites have low charge transfer resistance and high Na+ diffusion coefficient than that of NVP powder, NVP/P-rGO, and NVP/GO, which delivered a specific capacity of 113.9 mAh g−1 at 0.5C with a capacity retention up to 88.42% after 5000 cycles at 20 C. The superior sodium storage performance derives from the pyridinic and pyrrolic N doping in graphene, which triggers defective and active site numbers but maintains moderate graphitization to accelerate the Na+ and electron transportation.

Photoelectrochemical Properties of p- and n- Type 4H-SiC Epilayers: Doping Concentration Dependence and Dopant Selectivity

Exceptional chemical stability resulting from a large bandgap and low-lying valence band edge narrows the wet-etching based micromachining choices of the covalently bonded electronic and photonic device material, SiC, to mainly photoelectrochemical (PEC) dissolution. The PEC etching process has an anisotropic nature with the accompanying advantages of dopant, bandgap, and spatial selectivity, light intensity dependence, reduced ion damage, and the ability to undercut heterostructures. For the first time, a comprehensive photogenerated minority carrier assisted etching investigation was carried out on Si polar surface of high-quality (micropipe density <1 cm-2) p- and n- type (0001) 4H-SiC epilayers having intentional or unintentional doping densities in the 1014–1018 cm-3 range. Cyclic voltametry and chronoamperometry studies under a parallel supra-bandgap (~320 nm) light illumination with varying intensities (≤0.85 Wcm-2) in a highly basic etching medium (1 wt% KOH solution, pH ~12) revealed the dependence of etch voltage and etch rate (~30–90 nm/min) on type and concentration of doping. In addition, a mutually exclusive etch voltage window (~±0.3–0.5 V versus saturated calomel electrode) was established for both types of conductivities in the diffusion-limited regime. Results to be presented can provide key insight in design and fabrication for higher performance three dimensional SiC homojunctions for various applications including photonic crystal cavities.

Modulation of oxygen vacancies assisted ferroelectric and photovoltaic properties of (Nd, V) co-doped BiFeO3 thin films

We are reporting on the improved ferroelectric and photovoltaic properties of (Nd3+, V5+) co-doped (Bi0.95Nd0.05)(Fe1−xVx)O3 (BNFVO) (x = 0.01, 0.03) thin films grown by PLD. BNFVO thin films showed reduced leakage current, lower optical bandgap, and improved ferroelectricity compared to BFO films, which can be explained by valance change and extinguishing oxygen vacancies due to the doping effect. Piezoresponse force microscopy measurements showed an improved domain back switching in doped thin films indicating that the suppression of oxygen vacancies offset the effect of polarization flipping caused by doping. Further, we found a relatively stable and enhanced photovoltaic effect in BNFVO films with an order of magnitude higher photocurrent and almost doubled photovoltage in comparison to BFO films, which can be explained by less recombination between hopping electrons and oxygen vacancies. Our results demonstrate the significance of dopant selection to suppress the oxygen vacancies for improved ferroelectric and photovoltaic properties of BFO films.

Lewis Acid Doping Induced Synergistic Effects on Electronic and Morphological Structure for Donor and Acceptor in Polymer Solar Cells

AbstractDue to the attraction of optimizing the electronic structure beyond chemical synthesis, molecular doping has recently aroused wide interest in the field of organic solar cells. However, the selection of limited dopants confines its successful application. Inspired by the Lewis base characteristics of the photovoltaic materials, the Lewis acid as novel dopant is introduced in organic solar cells. In both fullerene and nonfullerene based blends, Lewis acid doping leads to increased photovoltaic performance. Detailed experiments reveal that Lewis acid doping has a synergistic effect on modifying the polymer's electronic properties and the acceptor's nanostructure even at low doping concentration, and these are simultaneously responsible for the device improvements. Based on the mechanism studies, it is proposed that the Lewis acid‐doped polymers anions produce induced dipole on the acceptor, this increases the intermolecular interaction and facilitates the morphology optimization. It is believed that the synergistic effect by Lewis acid doping greatly expands the application of doped organic solar cells, in concert with other existing methods to yield higher efficiency values.

An insight into the dopant selection for CeO2-based resistive-switching memory system: a DFT and experimental study

The aim of this study is to figure out better metal dopants for CeO2 for designing highly efficient non-volatile memory (NVM) devices. The present DFT work involves four different metals doped interstitially and substitutionally in CeO2 thin films. First principle calculations involve electron density of states (DOS) and partial density of states (PDOS), and isosurface charge densities are carried out within the plane-wave density functional theory using GGA and GGA + U approach by employing the Vienna ab initio simulation package VASP. Isosurface charge density plots confirmed that interstitial doping of Zr and Ti metals truly assists in generating conduction filaments (CFs), while substitutional doping of these metals cannot do so. Substitutional doping of W may contribute in generating CFs in CeO2 directly, but its interstitial doping improves conductivity of CeO2. However, Ni-dopant is capable of directly generating CFs both as substitutional and interstitial dopants in ceria. Such a capability of Ni appears acting as top electrode in Ni/CeO2/Pt memory devices, but its RS behavior is not so good. On inserting Zr layer to make Ni/Zr:CeO2/Pt memory stacks, Ni does not contribute in RS characteristics, but Zr plays a vital role in forming CFs by creating oxygen vacancies and forming ZrO2 interfacial layer. Therefore, Zr-doped devices exhibit high-resistance ratio of ~ 104 and good endurance as compared to undoped devices suitable for RRAM applications.

Continuous monitoring of pH level in flow aqueous system by using liquid crystal-based sensor device

In this work, we report a liquid crystal (LC)-based sensor to determine pH level of aqueous solutions. This sensor was fabricated by filling the LCs doped with a pH-sensitive molecule into a cupper grid on a glass substrate. Theoretically, the dopants are neutral and disperse freely in the LCs. When the sensor was immersed in the aqueous solution, the increases of pH can lead to the dissociation of the dopants, allowing them to align at the LC/aqueous interface. This phenomenon causes the reorientation of the LC molecules and therefore a bright-to-dark transition of the LC image was observed simply through naked-eye. In our research, we found that the critical pH value for the optical transition of LC sensors can be adjusted from 6.8 to 8.2 through the selection of dopants, while it can be adjusted from 6.2 to 7.0 through the selection of dopant concentrations. By arranging four individual sensors in a device with inlet and out channels, we demonstrated that the pH level of an aqueous flow system can be determined by the number of bright LC sensors shown in the device. Based on this strategy, we developed a device to monitor the pH safety level for drinking water ranging from pH6.5 to 8.5. This device demonstrated fast response (~1s), good stability, reversibility and its capability to measure the pH change in tap water and pond water, which make it suitable for real-time and continuous monitoring the pH change in various flow aqueous systems.

Impact of Doping Concentration on Electronic Properties of Transition Metal-Doped Monolayer Molybdenum Disulfide

Doping engineering has been an emerging topic in monolayer molybdenum disulfide (mMoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ). However, the dopants used for an n- or p-type device and the effect of doping level are of great interests toward next-generation electronic devices. In this paper, we theoretically reveal the work function tunability of mMoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> doped by 3d transition metals. We found that the titanium dopant forms a deep-level trap in the midgap of mMoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> but turning into n-type donor levels in high doping concentration due to the stronger covalent bond and the stable surface morphology, which renders it the widest work function tunability among 3d transition metals. Overall, the n-type behavior is expected by doping with chromium, copper, scandium, and titanium, whereas nickel and zinc dopants lead to the p-type property. The findings feature the selection of dopants for the revolutionary device and highlight the impact of doping levels from the atomistic viewpoint.

Host lattice effects on the design of different metallophilic nanoclusters with novel photonic properties

Abstract Designing nanocluster systems in given host lattices with specific photophysical properties requires the careful selection of dopants and of the host lattice. Nanocluster size and structure, which influence these properties, are dependent on metallophilic interactions between dopant metal complexes as well as metal complex interactions with the specific host. In this study, luminescence spectroscopy and infrared spectroscopy, along with atomistic simulations and DFT calculations are utilized to analyze d8 Pt(CN)42− and d10 Cu(CN)2− complexes doped alone or together in different alkali halide hosts. Nanocluster size and structure are found to be dependent upon the host lattice, which are explained by the interaction energies from atomistic calculations. What we observe in these mixed d10-d8 systems with certain host lattices is electron transfer from the d10 donor to the d8 acceptor ion. This electron transfer is not observed in pure systems. The importance of cluster size and structure is exemplified through laser irradiation experiments which show different photochemical reactions with different alkali halide host lattices.

The Yttrium Effect on Nanoscale Structure, Mechanical Properties, and High-Temperature Oxidation Resistance of (Ti0.6Al0.4)1–x Y x N Multilayer Coatings

As machine tool coating specifications become increasingly stringent, the fabrication of protective titanium aluminum nitride (Ti-Al-N) films by physical vapor deposition (PVD) is progressively more demanding. Nanostructural modification through the incorporation of metal dopants can enhance coating mechanical properties. However, dopant selection and their near-atomic-scale role in performance optimization is limited. Here, yttrium was alloyed in multilayered Ti-Al-N films to tune microstructures, microchemistries, and properties, including mechanical characteristics, adhesion, wear resistance, and resilience to oxidation. By regulating processing parameters, the multilayer period (Λ) and Y content could be adjusted, which, in turn, permitted tailoring of grain nucleation and secondary phase formation. With the composition fixed at x = 0.024 in (Ti0.6Al0.4)1–x Y x N and Λ increased from 5.5 to 24 nm, the microstructure transformed from acicular grains with 〈111〉 preferred orientation to equiaxed grains with 〈200〉 texture, while the hardness (40.8 ± 2.8 GPa to 29.7 ± 4.9 GPa) and Young’s modulus (490 ± 47 GPa to 424 ± 50 GPa) concomitantly deteriorated. Alternately, when Λ = 5.5 nm and x in (Ti0.6Al0.4)1–x Y x N was raised from 0 to 0.024, the hardness was enhanced (28.7 ± 7.3 GPa to 40.8 ± 2.8 GPa) while adhesion and wear resistance were not compromised. The Ti-Al-N adopted a rock-salt type structure with Y displacing either Ti or Al and stabilizing a secondary wurtzite phase. Moreover, Y effectively retarded coating oxidation at 1073 K (800 °C) in air by inhibiting grain boundary oxygen diffusion.

Recent progresses on nickel-rich layered oxide positive electrode materials used in lithium-ion batteries for electric vehicles

High energy density lithium-ion batteries are eagerly required to electric vehicles more competitive. In a variety of circumstances closely associated with the energy density of the battery, positive electrode material is known as a crucial one to be tackled. Among all kinds of materials for lithium-ion batteries, nickel-rich layered oxides have the merit of high specific capacity compared to LiCoO2, LiMn2O4 and LiFePO4. They have already become one of the most attractive candidates for the mainstream batteries in industries. In this work, the recent advances on three commonly concerned nickel-rich layered oxides are presented. The preparation, microstructure, electrochemical performances are focused, the modification including coating design as well as dopant selection is specially discussed in details, which is essential to enhance the durability and energy density of lithium-ion batteries. Additionally, the prospects and challenges are also systematically discussed, as well as the potential applications in the field of energy storage technologies.

Thermoelectric Properties of Indium and Gallium Dually Doped ZnO Thin Films.

We investigated the effect of single and multidopants on the thermoelectrical properties of host ZnO films. Incorporation of the single dopant Ga in the ZnO films improved the conductivity and mobility but lowered the Seebeck coefficient. Dual Ga- and In-doped ZnO thin films show slightly decreased electrical conductivity but improved Seebeck coefficient. The variation of thermoelectric properties is discussed in terms of film crystallinity, which is subject to the dopants' radius. Small amounts of In dopants with a large radius may introduce localized regions in the host film, affecting the thermoelectric properties. Consequently, a 1.5 times increase in power factor, three times reduction in thermal conductivity, and 5-fold enhancement in the figure of merit ZT have been achieved at 110 °C. The results also indicate that the balanced control of both electron and lattice thermal conductivities through dopant selection are necessary to attain low total thermal conductivity.

Effect of cation dopants in zirconia on interfacial properties in nickel/zirconia systems: an atomistic modeling study

Cation doping is often used to stabilize the cubic or tetragonal phase of zirconia for enhanced thermomechanical and electrochemical properties. In the present paper we report a combined density functional theory (DFT) and molecular dynamics study of the effect of Sc, Y, and Ce dopants on properties of Ni/ interfaces and nickel sintering. First, we develop an MD model that is based on DFT data for various nickel/zirconia interfaces. Then, we employ the model to simulate Ni nanoparticles coalescing on a zirconia surface. The results show the possibility of particle migration by means of fast sliding over the surface when the work of separation is small (<). The sliding observed for the O-terminated Ni(1 1 1)/(1 1 1) interface is not affected by dopants in zirconia because the work of separation of the doped interface stays small. The most pronounced effect of the dopants is observed for the Zr-terminated Ni(1 1 1)/(1 1 1) interface, which possesses a large work of separation () and thus restricts the sliding mechanism of Ni nanoparticle migration. DFT calculations for the interface revealed that dopants with a smaller covalent radius result in a larger energy barriers for Ni diffusion. We analyze this effect and discuss how it can be used to suppress nickel sintering by using the dopant selection.