Hole Density Research Articles

Effective carrier doping and quantum capacitance manipulation of graphene through two-dimensional solid electrolytes of ScI3 and YBr3

Effective carrier doping would be expected to enhance the electrical conductivity and further improve the quantum capacitance (Cq) of graphene. In this work, two-dimensional solid electrolytes of ScI3 and YBr3 as buffer layers have been proposed to modulate the carrier density and improve the Cq. By using first-principles calculations, the effective carrier doping has been examined by building heterostructures of graphene/ScI3 and graphene/YBr3 combined with Li, Na, K, Ca, F dopants. The n-type doping with electron density and p-type doping with hole density of graphene reach up to 1.14 × 1014 cm−2 and 6.66 × 1013 cm−2, respectively. Remarkably, the linear band dispersions of graphene are maintained near the Dirac point. Moreover, the Cq is significantly increased around the zero bias due to the increased density of states near the Fermi level. For Li-, Na-, K-, and Ca-doped systems, the Cq in the negative bias region is effectively enhanced while the Cq is improved in the positive bias region for F-doped system. These results provide an ideal route to implement the effective carrier doping and the Cq manipulation of graphene, facilitating the applications of graphene as electrodes in high-performance optoelectronics and energy storage devices, such as light-emitting diodes, solar cells and supercapacitors.

Propagation of surface plasmons in a quantum collisional semiconductor plasma

In this work, the propagation of surface plasmons in a quantum collisional semiconductor plasma is theoretically investigated using the quantum hydrodynamic model. The general dispersion equation of surface plasmons is deduced and solved in the presence of collisional effects and quantum tunneling of electrons and holes. It is shown that collisions play a significant role in the decay or growth of surface plasmons. Moreover, it is found that the quantum tunneling of electrons and holes increases the phase velocity, the group velocity, and the growth rate of instability. It is also indicated that the growth rate of instability is decreased with the increase of the ratio of hole density to electron density and the ratio of electron effective mass to hole effective mass.

Switching between Mott-Hubbard and Hund Physics in Moiré Quantum Simulators.

Mott-Hubbard and Hund electron correlations have been realized thus far in separate classes of materials. Here, we show that a single moiré homobilayer encompasses both kinds of physics in a controllable manner. We develop a microscopic multiband model that we solve by dynamical mean-field theory to nonperturbatively address the local many-body correlations. We demonstrate how tuning with twist angle, dielectric screening, and hole density allows us to switch between Mott-Hubbard and Hund correlated states in a twisted WSe2 bilayer. The underlying mechanism is based on controlling Coulomb-interaction-driven orbital polarization and the energetics of concomitant local singlet and triplet spin configurations. From a comparison to recent experimental transport data, we find signatures of a filling-controlled transition from a triplet charge-transfer insulator to a Hund-Mott metal. Our finding establishes twisted transition-metal dichalcogenides as a tunable platform for exotic phases of quantum matter emerging from large local spin moments.

Numerical Analysis of Residual Strength in the Perforated Casing of Ultra Deep Wells

A three-dimensional model for the numerical simulation of casing-cement behavior is used to investigate residual strength in the perforated casing of ultra deep wells. The influence of the hole diameter, hole density and phase angle on the residual strength of the casing under non-uniform stress and fracturing conditions is revealed through the consideration of different perforation parameters. It is shown that the residual strength of the casing increases with the hole diameter and periodically changes with the hole density; the phase angle is the main factor that affects the residual strength of the perforated casing, and the perforation should be avoided in the direction of the minimum principal stress to reduce stress concentration at the perforation hole. Moreover, as shown by a companion orthogonal experiment, the descending order of influence of the different influential parameters is: phase angle, hole diameter, hole density and the thickness of casing.

Design, manufacturing and properties of controllable porosity of ceramic filters based on SLA-3D printing technology

The ceramic foam filters are commonly applied in metal casting. However, this kind of filter has a number of drawbacks, such as weak impact resistance, uncontrollable technical parameters, and a long producing cycle. Our work developed a better manufacturing method for ceramic filters based on SLA-3D printing technology in which the structure of filters can be designed according to demands of porosity and hole density. Firstly, it is to propose a ceramic filter model with good mechanical properties under various porosities and hole densities using mechanical simulation and topology optimization. Secondly, SLA-3D printing technology was used to manufacture ceramic filter models with various characteristics. The results demonstrate that the porosity can be achieved with a wide range, and the higher porosity and hole density can approach 90% and 50 PPI, respectively. The preparation error of the internal pillars inside the filters model also can be revised to precisely control the porosity error of filters. Finally, the pore characteristics and compressive performance of the SLA printed ceramic filters were much better than that of the ceramic foam filters.

Molecular engineering of nitrogen-rich helicene based organic semiconductors for stable perovskite solar cells.

Polycyclic heteroaromatics play a pivotal role in advancing the field of high-performance organic semiconductors. In this study, we report the synthesis of a pyrrole-bridged double azahelicene through intramolecular oxidative cyclization. By incorporating bis(4-methoxyphenyl)amine (OMeDPA) and ethylenedioxythiophene-phenyl-OMeDPA (EP-OMeDPA) into the sp3-nitrogen rich double helicene framework, we have successfully constructed two organic semiconductors with ionization potentials suitable for application in perovskite solar cells. The amorphous films of both organic semiconductors exhibit hole density-dependent mobility and conductivity. Notably, the organic semiconductor utilizing EP-OMeDPA as the electron donor demonstrates superior hole mobility at a given hole density, which is attributed to reduced reorganization energy and increased centroid distance. Moreover, this organic semiconductor exhibits a remarkably elevated glass transition temperature of up to 230 °C and lower diffusivity for external small molecules and ions. When employed as the p-doped hole transport layer in perovskite solar cells, TMDAP-EP-OMeDPA achieves an improved average efficiency of 21.7%. Importantly, the solar cell with TMDAP-EP-OMeDPA also demonstrates enhanced long-term operational stability and storage stability at 85 °C. These findings provide valuable insights into the development of high-performance organic semiconductors, contributing to the practical application of perovskite solar cells.

Influence Mechanism of Knowledge Network on Regional Innovation Capability Based on Hydrogen Energy Industry

As an important factor of innovation, knowledge plays a vital role in promoting the growth of innovation ability. In recent years, many scholars have explored the influence of knowledge network structure on innovation. The hydrogen energy industry is highly technical and covers a wide range, which is in urgent need of regional cooperation and easy to form a knowledge network. The function of the knowledge network depends on inter-organizational communication, so traffic development may be a boundary condition. This paper takes the hydrogen energy industry as an example to study the influence mechanism of the knowledge network on regional innovation ability and explore the moderate effect of high-speed rail opening. This paper takes hydrogen patents as samples, uses backward citation data to construct the knowledge network, and conducts regression tests. The results show that the density of the knowledge network has a negative effect on regional innovation ability, while the structural hole and centrality have a positive effect. The opening of high-speed rail will strengthen the influence of density and structural holes, and weaken the influence of centrality. Finally, it is proposed that the development of the hydrogen energy industry should reduce the dependence on the network, and the government should prevent the loss of large enterprises.

Unconventional rate law of water photooxidation at TiO2 electrodes.

Photoelectrochemical oxidation of water over semiconductors is a promising route for the production of sustainable solar fuels. TiO2 water photooxidation has been intensively studied over the past 50 years, but its rate law and mechanism are still undetermined. The main challenges are that there is no appropriate reaction kinetic model currently, and that both the reaction rate constant and reactant photohole concentration/density are not readily quantified with respect to conventional chemical reactions. Here we report that the rate law and photohole transfer mechanism could be determined by a combination of multiple (photo-) electrochemical techniques. We demonstrate that the kinetics of TiO2 water oxidation by photogenerated holes can be well-described by a model of surface state mediating charge transfer and recombination. The rate law, in terms of steady-state photocurrent, is the product of the surface hole density exponential dependent rate constant and the surface hole density, with first order for all the surface hole densities studied. This reactant concentration dependent rate constant is conceptually unexpected for an elementary step in conventional chemical reactions. In addition, we find that hydroxyl ions in bulk solutions are involved in the reaction as indicated by observation of the solution pH dependent apparent rate constant. This study may thus lead to key insights both for strategies to evaluate and/or enhance photoelectrochemical performances and for understanding reaction mechanisms.

Atomically dispersed Ir catalysts exhibit support-dependent water oxidation kinetics during photocatalysis.

Heterogeneous water oxidation catalysis is central to the development of renewable energy technologies. Recent research has suggested that the reaction mechanisms are sensitive to the hole density at the active sites. However, these previous results were obtained on catalysts of different materials featuring distinct active sites, making it difficult to discriminate between competing explanations. Here, a comparison study based on heterogenized dinuclear Ir catalysts (Ir-DHC), which feature the same type of active site on different supports, is reported. The prototypical reaction was water oxidation triggered by pulsed irradiation of suspensions containing a light sensitizer, Ru(bpy)32+, and a sacrificial electron scavenger, S2O82-. It was found that at relatively low temperatures (288-298 K), the water oxidation activities of Ir-DHC on indium tin oxide (ITO) and CeO2 supports were comparable within the studied range of fluences (62-151 mW cm-2). By contrast, at higher temperatures (310-323 K), Ir-DHC on ITO exhibited a ca. 100% higher water oxidation activity than on CeO2. The divergent activities were attributed to the distinct abilities of the supporting substrates in redistributing holes. The differences were only apparent at relatively high temperatures when hole redistribution to the active site became a limiting factor. These findings highlight the critical role of the supporting substrate in determining the turnover at active sites of heterogeneous catalysts.

Magnetic field enhancement of the FeCoSe2 photoanode for the oxygen evolution reaction by adjusting the hole density to reduce competitive adsorption between Fe and Co in a photoelectrochemical water-splitting system

FeCoSe2 has fast oxygen evolution due to polarization electric field and d-band center. However, the large adsorption energy of Fe slows the reaction. Magnetic field reduces Fe's adsorption, enhancing OER performance.

Coupled aerothermal-mechanical analysis in single crystal double wall transpiration cooled gas turbine blades with a large film hole density

• Double wall transpiration cooling protects turbine blades against high heat flux. • A high film hole density can benefit both the aerothermal and mechanical response. • The wall spacing influences the cooling effectiveness and aerothermal response. • The wall thickness ratio influences thermal stresses and the mechanical response. • Stresses tend to apply along secondary crystallographic directions around features. The ambition for increasing gas turbine efficiency beyond current levels through the elevation of gas temperatures demands substantial progress in turbine blade cooling technology. Double wall transpiration cooling (DWTC) is an emerging technology which offers enhanced thermal protection at only modest coolant flows, thanks to a combination of impingement jets and densely packed arrays of film cooling holes. This paper presents a coupled aerothermal-mechanical investigation of a transpiration cooled double wall turbine blade design, by employing Computational Fluid Dynamics (CFD), heat transfer theory as well as stress analysis based on plate theory and Finite Element (FE) analysis. In comparison to previously explored systems with modest outer wall porosity, a system with high porosity is found to display enhanced cooling effectiveness and to reduce the temperature difference across the two walls that drives thermal stresses. This difference can be decreased further by reducing the wall spacing, H , or the inner-outer wall thickness ratio, t c / t h , at the cost of higher overall metal temperatures. A lower bound for H should be used to avoid undesirable poor coolant flow distribution and hot gas ingestion effects, whereas the t c / t h ratio does not impose any aerothermal constraints. Thermal stresses associated with a fixed temperature field are invariant with H but they vary drastically with t c / t h . From a design perspective, the above suggest that H is primarily determined by aerothermal requirements, whereas t c / t h by the mechanical performance. The single crystal orientation and elastic anisotropy of Nickel alloys are shown to have a profound impact on the stress concentration around cooling holes, with secondary crystallographic directions, such as 〈 110 〉 and 〈 111 〉 , playing a prominent role in the local stress state. Our study provides a framework for optimising the aerothermal and mechanical performance in a range of high temperature components and highlights key areas where more elaborate analysis is needed.

Room temperature slot-die coated perovskite layer modified with sulfonyl-γ-AApeptide for high performance perovskite solar devices

Perovskite solar cells (PSCs) exhibited remarkable progress for small aperture area cells, however, the performance of its counterpart, large aperture area cells, lags due to non-uniform and defective perovskite layers. Here, we fabricate reproducible large area homogeneous perovskite films at room temperature and without controlling humidity (up to 40 % RH) with a slot die coater on a c-TiO2 layer deposited using a large area chemical bath. A new artificial peptide – sulfonyl-γ-AApeptide (F-GLU-S) was employed to modify the slot-die coated perovskite surface, grain boundaries and electronic defects. The multi-functional F-GLU-S with carbonyl, carboxyl, sulfonyl, benzene, and chloro groups was capable of strongly interacting with the perovskite layer and repairing the uncoordinated Pb2+ ions and halide vacancies. As a result, both the electron and hole densities of defects were significantly suppressed; consequently, the non-radiative recombination was effectively suppressed for the modified device which can be explicitly seen in the device performance where both Voc and FF of the modified device improved considerably. Therefore, F-GLU-S modified slot-die coated MAPbI3 – based devices demonstrated outstanding performance of 21.44 % PCE with a Voc of 1.13 V, Jsc of 24.64 cm−2, and FF 76.99 %. Moreover, F-GLU-S passivation impeded the infiltration of moisture and oxygen due to its hydrophobic nature and defect repair potential. As a result, the modified device retained above 92 % of its original PCE after 720 h in air (room temperature and 40–60 % RH).

Low-cost preparation of highly-efficient thermoelectric BixSb2-xTe3 nanostructured powders via mechanical alloying

In this paper, a low-cost and facile method for preparing highly-efficient Bi2Te3-based thermoelectric materials is demonstrated. P-type BixSb2-xTe3 (x ​= ​0.2, 0.3, 0.4, 0.5) nanostructured powders were fabricated via mechanical alloying, and consequently consolidated into pellets by hot-press sintering. The effect of Bi/Sb ratio on the thermoelectric properties was investigated. The higher hole density and mobility in samples with lower Bi concentration resulted in higher electrical conductivity and power factor values. The absence of preferred grain orientation and the high density of grain boundaries in these nanostructured materials led to significantly low lattice thermal conductivity. As a result, a peak ZT of 1.13 ​at 355 ​K and an average ZT of 1.01 over the investigated temperature range was achieved for Bi0.3Sb1.7Te3, suggesting that mechanical alloying can be considered as an advantageous technique for single-step synthesis of highly-efficient thermoelectric BixSb2-xTe3 alloys.

Boron Nanotube Structure Explored by Evolutionary Computations

In this work, we explore the structure of single-wall boron nanotubes with large diameters (about 21 Å) and a broad range of surface densities of atoms. The computations are done using an evolutionary approach combined with a nearest-neighbors model Hamiltonian. For the most stable nanotubes, the number of 5-coordinated boron atoms is about 63% of the total number of atoms forming the nanotubes, whereas about 11% are boron vacancies. For hole densities smaller than about 0.22, the boron nanotubes exhibit randomly distributed hexagonal holes and are more stable than a flat stripe structure and a quasi-flat B36 cluster. For larger hole densities (>0.22), the boron nanotubes resemble porous tubular structures with hole sizes that depend on the surface densities of boron atoms.

20%-efficient polycrystalline Cd(Se,Te) thin-film solar cells with compositional gradient near the front junction

Bandgap gradient is a proven approach for improving the open-circuit voltages (VOCs) in Cu(In,Ga)Se2 and Cu(Zn,Sn)Se2 thin-film solar cells, but has not been realized in Cd(Se,Te) thin-film solar cells, a leading thin-film solar cell technology in the photovoltaic market. Here, we demonstrate the realization of a bandgap gradient in Cd(Se,Te) thin-film solar cells by introducing a Cd(O,S,Se,Te) region with the same crystal structure of the absorber near the front junction. The formation of such a region is enabled by incorporating oxygenated CdS and CdSe layers. We show that the introduction of the bandgap gradient reduces the hole density in the front junction region and introduces a small spike in the band alignment between this and the absorber regions, effectively suppressing the nonradiative recombination therein and leading to improved VOCs in Cd(Se,Te) solar cells using commercial SnO2 buffers. A champion device achieves an efficiency of 20.03% with a VOC of 0.863 V.

Interplay of quantum spin Hall effect and spontaneous time-reversal symmetry breaking in electron-hole bilayers. II. Zero-field topological superconductivity

It has been proposed that band-inverted electron-hole bilayers support a phase transition from an insulating phase with spontaneously broken time-reversal symmetry to a quantum spin Hall insulator phase as a function of increasing electron and hole densities. Here we show that in the presence of proximity-induced superconductivity, it is possible to realize Majorana zero modes in the time-reversal symmetry broken phase in the absence of magnetic field. We develop an effective low-energy theory for the system in the presence of a time-reversal symmetry-breaking order parameter to obtain analytically the Majorana zero modes and we find good agreement between the numerical and analytical results in the limit of weakly broken time-reversal symmetry. We show that the Majorana zero modes can be detected in superconductor/time-reversal symmetry broken insulator/superconductor Josephson junctions through the measurement of a $4\ensuremath{\pi}$ Josephson current. Finally, we demonstrate that the Majorana fusion-rule detection is feasible by utilizing the gate voltage dependence of the spontaneous time-reversal symmetry breaking order parameter.

Interplay of quantum spin Hall effect and spontaneous time-reversal symmetry breaking in electron-hole bilayers. I. Transport properties

The band-inverted electron-hole bilayers, such as InAs/GaSb, are an interesting playground for the interplay of quantum spin Hall effect and correlation effects because of the small density of electrons and holes and the relatively small hybridization between the electron and hole bands. It has been proposed that Coulomb interactions lead to a time-reversal symmetry broken phase when the electron and hole densities are tuned from the trivial to the quantum spin Hall insulator regime. We show that the transport properties of the system in the time-reversal symmetry broken phase are consistent with recent experimental observations in InAs/GaSb. Moreover, we carry out a quantum transport study on a Corbino disk where the bulk and edge contributions to the conductance can be separated. We show that the edge becomes smoothly conducting and the bulk is always insulating when one tunes the system from the trivial to the quantum spin Hall insulator phase, providing unambiguous transport signatures of the time-reversal symmetry broken phase.

Regulating Charge Carrier Recombination in the Interconnecting Layer to Boost the Efficiency and Stability of Monolithic Perovskite/Organic Tandem Solar Cells.

The charge carriers of single-junction solar cells can be fluently extracted and then collected by electrodes, leading to weak charge carrier accumulation and low energy loss (Eloss ). However, in tandem solar cells (TSCs), it is a considerable challenge to obtain a balance between the densities of the holes and electrons extracted from the two respective subcells to facilitate an efficient recombination in the interconnecting layer (ICL). Herein, a charge-carrier-dynamic management strategy for inorganic perovskite/organic TSCs is proposed, centered on the simultaneous regulation of the defect states of CsPbI1.9 Br1.1 perovskite in the front subcell and hole transport ability from the perovskite to ICL. The target hole density on the perovskite surface and the hole loss before reaching the ICL are significantly improved. As a result, the hole/electron density offset in the ICL can be effectively narrowed, leading to a balanced charge carrier recombination, which reduces the Eloss in TSCs. The resulting inorganic perovskite/organic 0.062-cm2 TSC exhibits a remarkable power conversion efficiency (PCE) of 23.17% with an ultrahigh open-circuit voltage (Voc ) of 2.15V, and the PCE of the 1.004-cm2 device (21.69%) exhibited a weak size-dependence. This charge-carrier-dynamic management strategy can also effectively enhance the operational and ultraviolet-light stabilities of the TSCs.

Porous-Induced Performance Enhancement of Flat Boron Sheets for Lithium-Ion Batteries

Low-capacity anode materials have been limiting the further take-off of lithium-ion batteries (LIBs), and many researchers are relentlessly pursuing breakthroughs in high-capacity anode materials. Therefore, the properties of materials with a high theoretical capacity and the reasons behind them are worthy of further study. Here, based on the first-principles calculation, we systematically investigate the electrochemical properties of the six flat boron sheets with different hexagonal hole densities η (η = 1/4, 1/5, 1/6, 1/7, 1/8, 1/9), including adsorption, diffusion, theoretical capacity, and open-circuit voltage. We find that due to their own structural and electronic properties, the Li atoms tend to be adsorbed on their hexagonal hole sites, which result in the formation of structures of flat boron sheets with more hexagonal holes that have a higher theoretical capacity for lithium. Besides, their theoretical capacities can be calculated using the empirical equation, with the hexagonal hole densities (η). Finally, we obtain their capacities with increasing hexagonal hole density (η), which are 620, 708, 826, 992, 1240, and 1653 mA h g–1, respectively. Therefore, our results indicate that the porous structure of the anode material is beneficial to improve the storage capacity performance of LIBs.

Evaluation of experimental, computational, molecular docking and dynamic simulation of flucytosine

Flucytosine (5-fluorocytosine), a fluorine derivative of pyrimidine, has been studied both experimentally and quantum chemically. To obtain the optimized structure, vibrational frequencies and other various parameters, the B3LYP method with a 6-311++G(d,p) basis set was used. Atom-in-molecule theory was used to calculate the binding energies, ellipticity and isosurface projection by electron localization of the molecule (AIM). In addition, the computational results from IR and Raman were compared with the experimental spectra. NBO analysis was used to analyze the donor and acceptor interactions. To know the reactive region of the molecule, the molecular electrostatic potential (MEP) and Fukui functions were determined. The UV-Vis spectrum calculated by the TD-DFT/PCM method was also compared with the experimentally determined spectrum. The HOMO-LUMO energy outcomes proved that there was a good charge exchange occurring within the molecule. With DMSO and MeOH as the solvents, maps of the hole and electron density distribution (EDD and HDD) were produced in an excited state. An electrophilicity index parameter was looked at to theoretically test the bioactivity of the compound. To find the best ligand-protein interactions, molecular docking was also carried out with various receptor proteins. In order to verify the inhibitory potency for the receptor protein complex predicted by docking and molecular dynamic simulation studies, the binding free energy of the receptor protein complex was calculated. Using the MM/GBSA technique, we determined the docked complex’s binding free energy. To confirm the molecule’s drug similarity, a biological drug similarity investigation was also executed. Communicated by Ramaswamy H. Sarma