Significant Potential Barrier Research Articles

Dipole-assisted hole injection for efficient blue quantum dot light-emitting diodes

Quantum dot light-emitting diodes (QLEDs) present commercial potential and application prospects in both lighting and display technologies. Blue quantum dots (QDs) possess a substantial bandgap and a profound valence band. The significant potential barrier between blue quantum dots and the hole transport layer leads to an imbalance in charge transfer, thereby adversely impacting the device performance. Self-assembled monolayers are attractive for carrier transport. Here, a dynamic self-assembly method is introduced, doping [2-(9H-carbazol-9-yl)ethyl]phosphonic acid (2PACz) into Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) to form electric dipoles at interfaces, realizing better energy level alignment and hole injection rate. The maximum external quantum efficiency rises from 8.77% to 17.26% with 2PACz: PEDOT:PSS strategy, representing a twofold enhancement. This result demonstrates that small molecules undergo dynamic self-assembled bilateral motions during crystallization process, aligning energy levels and passivating interfacial trap states, thereby endowing blue QLEDs with high brightness and high efficiency. This work offers a viable pathway for broader applications of blue QLEDs.

Gradient tungsten-doped Bi3TiNbO9 ferroelectric photocatalysts with additional built-in electric field for efficient overall water splitting

Bi3TiNbO9, a layered ferroelectric photocatalyst, exhibits great potential for overall water splitting through efficient intralayer separation of photogenerated carriers motivated by a depolarization field along the in-plane a-axis. However, the poor interlayer transport of carriers along the out-of-plane c-axis, caused by the significant potential barrier between layers, leads to a high probability of carrier recombination and consequently results in low photocatalytic activity. Here, we have developed an efficient photocatalyst consisting of Bi3TiNbO9 nanosheets with a gradient tungsten (W) doping along the c-axis. This results in the generation of an additional electric field along the c-axis and simultaneously enhances the magnitude of depolarization field within the layers along the a-axis due to strengthened structural distortion. The combination of the built-in field along the c-axis and polarization along the a-axis can effectively facilitate the anisotropic migration of photogenerated electrons and holes to the basal {001} surface and lateral {110} surface of the nanosheets, respectively, enabling desirable spatial separation of carriers. Hence, the W-doped Bi3TiNbO9 ferroelectric photocatalyst with Rh/Cr2O3 cocatalyst achieves an efficient and durable overall water splitting feature, thereby providing an effective pathway for designing excellent layered ferroelectric photocatalysts.

Australia needs to implement a national health strategy for doctors.

Australia needs to implement a national health strategy for doctors.

Bias‐Triggered Conductivity Switching and High Effective Rectification in Metallocene‐Based Molecular Junctions

AbstractMolecular diodes usually exhibit fixed current values at a specific bias and achieve sizable rectification ratio (RR) at voltages of ≈1.0 V. Here, a series of custom‐designed molecular films of ferrocenyl/ruthenocenyl‐substituted biphenylthiolates and fluorenethiolates on Au (111) is presented, which exhibit a distinctly different behavior. When embedded into two‐terminal junctions, they show two different conduction states, with a high conductivity state at a negative bias and a low conductivity state upon applying a sufficiently high positive bias. Comparing the current values for these two states, an effective RR of more than 1000 is obtained, a value comparable to the best performing molecular diodes but attained already at particularly low voltages. Significantly, the switching between the conduction states is reversible and the initial, high conductivity state can be recovered by the application of a negative bias. The proposed explanation for these observations is the bias‐induced switching of the junction to a metastable state comprising oxidized ferrocenyl/ruthenocenyl entities, which are characterized by less delocalized frontier orbitals and cause the formation of a significant potential barrier within the junction. It is hypothesized that this state can be stabilized by structural changes in the monolayers, affecting also their coupling to the top electrode.

Спектрально-люминесцентные свойства и фотолиз заряженных форм бисфенола А

The spectral luminescent properties and photolysis of the ionic forms (neutral, cationic and anionic) of bisphenol A have been studied experimentally and by methods of quantum chemistry. Calculations and experiment have shown that, in comparison with a neutral form, no new absorption bands appear in the absorption spectra of ionic form in the range 200–600 nm. The polar solvent (water) shifts the absorption spectrum bands of ionic forms towards low energies. In this case, the shift of the absorption spectrum of the cation is insignificant, and the shift of the anion is significant with an increase in the intensity of the absorption bands. The low quantum yield of fluorescence of ionic form is explained by the prevalence of the efficiency of singlet-triplet conversion over the efficiency of the radiation channel of decay of the fluorescent state. The low quantum yield of fluorescence of the anionic form is due not only to the effective singlet-triplet conversion, but also to the low efficiency of the radiative decay of the fluorescent state of the anion caused by a change in its orbital nature. Calculations have shown that the potential curves of the excited states of bisphenol A and its ionic forms have a significant potential barrier to photolysis. The increase in the efficiency of the process of photodissociation of the bisphenol A anion is caused by a noticeable decrease in the potential barrier and an increase in the overlap of the absorption spectra of the bisphenol A anion and solar radiation.

Methods and Cost Estimation for the Synthesis of Nanosized Lithium Sulfide

Lithium sulfide (Li2S) is an alternative cathode material for lithium‐sulfur batteries. It can mitigate the volume expansion problem encountered by the sulfur cathode, in addition, as a fully lithium‐inserted cathode, it can be paired with lithium‐free anodes or be assembled into anode‐free batteries. However, commercially available Li2S powder delivers poor electrochemical performances due to the significant potential barrier during the first charging process, and therefore developing inexpensive synthesis route for nanosized Li2S with small diameter and low charging overpotential becomes the key to the construction of practical Li2S cathode. Herein, the preparation methods for Li2S nanoparticles are summarized, including laboratory synthesis methods and potential large‐scale preparation routes; traditional industrial synthesis methods for commercially available Li2S are also attached as references. In particular, the scalability of these methods is mentioned, and the costs of the resulted Li2S products are also estimated and compared with the currently used cathode materials for Li‐ion batteries. In the end, the commercially worthwhile research pathways for Li2S synthesis as well as the perspective on the practical production of Li2S are discussed. Useful guidance for the selection of practical Li2S synthesis routes is also provided.

Electronic Spectra and Photolysis of Bisphenol A in Water

A quantum chemical study of the spectral and luminescent properties of the BPA + 2H2O complex was carried out. Calculations were performed by the semi-empirical method of intermediate neglect of differential overlap using a program complex and a special parameterization. The spectral behavior of BPA in water was modeled by a complex with water molecules in the ratio 1: 2 forming the hydrogen bond. The calculated data were compared with the results of investigation of the isolated BPA molecule. The nonplanar BPA structure leads to the strong mixing of the π- and σ-type atomic wave functions. The main reason for the low quantum yield of the BPA fluorescence is the efficient process of singlet-triplet conversion in the S1(ππ*) ≳ Tn(πσ*) channel of the BPA molecule and its complex with water. A study of the photolysis of the isolated BPA molecule upon exposure to solar radiation, the short-wavelength boundary of which on the Earth’s surface is located at ~290 nm (~34480 cm–1), showed that the energy of the photodissociative state localized on the O–H bond is much higher than this value for BPA. The binding curve is characteristic of the S1(ππ*) state, while the singlet and triplet states of the πσ* type, localized on the single C–C bonds of the central fragment of the molecule, are repulsion curves with a barrier. From our point of view, the low efficiency of the BPA degradation under the influence of solar radiation is due to the presence of a significant potential barrier to the photolysis in the singlet or triplet state. The mechanisms of bond breaking in the BPA + 2H2O complex are different for the singlet and triplet states, namely, for the S3(πσ*) state, the break occurs by the predissociation mechanism, and for the Tn(πσ*) state, due to its population through the singlet-triplet conversion in the S1(ππ*) → Тn(πσ*) channel.

Resistive switching behavior and improved multiferroic properties of Bi0.9Er0.1Fe0.98Co0.02O3/Co1-xMnxFe2O4 bilayered thin films

Bilayered Bi0.9Er0.1Fe0.98Co0.02O3/Co1-xMnxFe2O4 (BEFCO/CMxFO) thin films were deposited by the sol-gel method. Structural variations between the triclinic-P1 and trigonal-R3c:H (two-phase coexistence) phases in the BEFCO layer were observed owing to the trigonal-R-3m:H phase existing in the CMxFO layer. The oxygen vacancy concentrations of the BEFCO/CMxFO bilayered films are reduced by Mn-doping in the bottom CFO layer. The BEFCO/CFO films showed high oxygen vacancy concentrations with a high leakage current. This induced changes of the significant potential barrier at the interface between the BEFCO and CMxFO layers in the processes of electron capture and release. Thus, the BEFCO/CFO film exhibited obvious resistive switching (RS) effect. The high leakage current also caused a fake polarization phenomenon with a blow up of the P-E loop in the BEFCO/CFO films. However, the real and outstanding ferroelectric properties, which resulted from the fewer oxygen vacancies and the 38% triclinic-P1 structure, were obtained in the BEFCO/CM0.3FO films (Pr~156.3 μC cm−2). In addition, the typical capacitance-voltage curve further confirmed its superior ferroelectric performance. The RS effect almost disappeared in the BEFCO/CM0.3FO bilayered films. Moreover, the enhanced ferromagnetic properties (Ms~100.36 emu cm−3, Mr~55.38 emu cm−3) were obtained for the BEFCO/CM0.1FO films, which was attributed to the magnetic properties of BEFCO (a more triclinic-P1 phase and numerous Fe2+ ions), in addition to the CMxFO layer. The introduction of the doped magnetic layer into the bilayered films thus represented a highly effective method for enhancing the multiferroic properties of BFO.

Homolytic Cleavage of Both Heme-Bound Hydrogen Peroxide and Hydrogen Sulfide Leads to the Formation of Sulfheme.

Many heme-containing proteins with a histidine in the distal E7 (HisE7) position can form sulfheme in the presence of hydrogen sulfide (H2S) and a reactive oxygen species such as hydrogen peroxide. For reasons unknown, sulfheme derivatives are formed specifically on solvent-excluded heme pyrrole B. Sulfhemes severely decrease the oxygen-binding affinity in hemoglobin (Hb) and myoglobin (Mb). Here, use of hybrid quantum mechanical/molecular mechanical methods has permitted characterization of the entire process of sulfheme formation in the HisE7 mutant of hemoglobin I (HbI) from Lucina pectinata. This process includes a mechanism for H2S to enter the solvent-excluded active site through a hydrophobic channel to ultimately form a hydrogen bond with H2O2 bound to Fe(III). Proton transfer from H2O2 to His64 to form compound (Cpd) 0, followed by hydrogen transfer from H2S to the Fe(III)-H2O2 complex, results in homolytic cleavage of the O-O and S-H bonds to form a reactive thiyl radical (HS(•)), ferryl heme Cpd II, and a water molecule. Subsequently, the addition of HS(•) to Cpd II, followed by three proton transfer reactions, results in the formation of a three-membered ring ferric sulfheme that avoids migration of the radical to the protein matrix, in contrast to that in other peroxidative reactions. The transformation of this three-membered episulfide ring structure to the five-membered thiochlorin ring structure occurs through a significant potential energy barrier, although both structures are nearly isoenergetic. Both three- and five-membered ring structures reveal longer NB-Fe(III) bonds compared with other pyrrole nitrogen-Fe(III) bonds, which would lead to decreased oxygen binding. Overall, these results are in agreement with a wide range of experimental data and provide fertile ground for further investigations of sulfheme formation in other heme proteins and additional effects of H2S on cell signaling and reactivity.

Efficient Carrier Separation and Intriguing Switching of Bound Charges in Inorganic-Organic Lead Halide Solar Cells.

We fabricated a mesoporous perovskite solar cell with a ∼14% conversion efficiency, and we investigated its beneficial grain boundary properties of the perovskite solar cells through the use of scanning probe microscopy. The CH3NH3Pb(I0.88,Br0.12)3 showed a significant potential barrier bending at the grain boundary and induced passivation. The potential difference value in the x = 0.00 sample is ∼50 mV, and the distribution of the positive potential is lower than that of the x = 0.12 sample. We also investigated the polarization and hysteretic properties of the perovskite thin films by measuring the local piezoresponse. Specifically, the charged grain boundaries play a beneficial role in electron-hole depairing and in suppressing recombination in order to realize high-efficiency perovskite solar cells.

The diffusion mechanisms of dynamic ridesharing services

Dynamic ridesharing services and platforms need to reach an initial critical mass of users in order to provide desirable levels of matching between drivers and passengers. The objective of this work is to investigate some of the levers that could boost the diffusion of a new ridesharing service, by the means of a system dynamics (SD) model that integrates existing diffusion models with the main outcomes of a project to which the authors contributed. Findings show that a dynamic ridesharing platform should operate mostly in urban areas because higher contact rates turn into increased matching opportunities and therefore support the diffusion process. Moreover, it should focus on the partnering and advertising action, especially toward the population of drivers. Finally, the combination of both high desired matching and short patience expressed by users in waiting for a more effective service provide the most significant potential barrier to the diffusion.

Reluctance of a neutral nanoparticle to enter a charged pore

We consider the translocation of a neutral (uncharged) nanoparticle through a pore in a thin membrane with constant surface charge density. If the concomitant Debye screening layer is sufficiently thin, the resulting forces experienced by the particle on its way through the pore are negligible. But when the Debye length becomes comparable to the pore diameter, the particle encounters a quite significant potential barrier while approaching and entering the pore, and symmetrically upon exiting the pore. The main reason is an increasing pressure, which acts on the particle when it intrudes into the counter ion cloud of the Debye screening layer. In case the polarizability of the particle is different (usually smaller) than that of the ambient fluid, a second, much smaller contribution to the potential barrier is due to self-energy effects. Our numerical treatment of the problem is complemented by analytical approximations for sufficiently long cylindrical particles and pores, which agree very well with the numerics.

Spatially Resolved Mapping of Electrical Conductivity across Individual Domain (Grain) Boundaries in Graphene

All large-scale graphene films contain extended topological defects dividing graphene into domains or grains. Here, we spatially map electronic transport near specific domain and grain boundaries in both epitaxial graphene grown on SiC and CVD graphene on Cu subsequently transferred to a SiO2 substrate, with one-to-one correspondence to boundary structures. Boundaries coinciding with the substrate step on SiC exhibit a significant potential barrier for electron transport of epitaxial graphene due to the reduced charge transfer from the substrate near the step edge. Moreover, monolayer-bilayer boundaries exhibit a high resistance that can change depending on the height of substrate step coinciding at the boundary. In CVD graphene, the resistance of a grain boundary changes with the width of the disordered transition region between adjacent grains. A quantitative modeling of boundary resistance reveals the increased electron Fermi wave vector within the boundary region, possibly due to boundary induced charge density variation. Understanding how resistance change with domain (grain) boundary structure in graphene is a crucial first step for controlled engineering of defects in large-scale graphene films.

Conformational Switching between Protein Substates Studied with 2D IR Vibrational Echo Spectroscopy and Molecular Dynamics Simulations

Myoglobin is an important protein for the study of structure and dynamics. Three conformational substates have been identified for the carbonmonoxy form of myoglobin (MbCO). These are manifested as distinct peaks in the IR absorption spectrum of the CO stretching mode. Ultrafast 2D IR vibrational echo chemical exchange experiments are used to observed switching between two of these substates, A(1) and A(3), on a time scale of <100 ps for two mutants of wild-type Mb. The two mutants are a single mutation of Mb, L29I, and a double mutation, T67R/S92D. Molecular dynamics (MD) simulations are used to model the structural differences between the substates of the two MbCO mutants. The MD simulations are also employed to examine the substate switching in the two mutants as a test of the ability of MD simulations to predict protein dynamics correctly for a system in which there is a well-defined transition over a significant potential barrier between two substates. For one mutant, L29I, the simulations show that translation of the His64 backbone may differentiate the two substates. The simulations accurately reproduce the experimentally observed interconversion time for the L29I mutant. However, MD simulations exploring the same His64 backbone coordinate fail to display substate interconversion for the other mutant, T67R/S92D, thus pointing to the likely complexity of the underlying protein interactions. We anticipate that understanding conformational dynamics in MbCO via ultrafast 2D IR vibrational echo chemical exchange experiments can help to elucidate fast conformational switching processes in other proteins.

Administrators' Perspectives on Ethical Issues in Long-Term Care Research

ETHICAL ISSUES ARE A SIGNIFICANT potential barrier to much-needed research in long-term care settings. LTC stakeholder perspectives are largely absent from the development of regulation and guidelines. Fifteen long-term care administrators were interviewed as part of a study of ethical issues in community-based, long-term care research. Established qualitative procedures for conducting content analysis were used to organize the data. Findings suggest that existing mechanisms to protect human subjects do not take into account important differences between academic and long-term care settings. The full potential of LTC research will not be realized until supportive processes to enhance human subjects protections are developed in a way that is reflective of the LTC environment.

Education delays accelerated decline on a memory test in persons who develop dementia

To test the cognitive reserve hypothesis by examining the effect of education on memory decline during the preclinical course of dementia. Low education is a well known risk factor for Alzheimer disease (AD). Persons destined to develop AD experience an accelerated rate of decline in cognitive ability, particularly in memory. The cognitive reserve hypothesis predicts that persons with greater education begin to experience acceleration in cognitive decline closer to the time of diagnosis than persons with lower reserve, but that their rate of decline is more rapid after the time of acceleration due to increased disease burden. We studied the influence of education on rates of memory decline as measured by the Buschke Selective Reminding Test in 117 participants with incident dementia in the Bronx Aging Study. Subjects had detailed cognitive assessments at entry and at annual follow-up visits. We estimated the time at which the rate of decline begins to accelerate (the change point), and the pre- and post-acceleration rates of decline, from the longitudinal data using a change point model. Each additional year of formal education delayed the time of accelerated decline on the Buschke Selective Reminding Test by 0.21 years. Post-acceleration, the rate of memory decline was increased by 0.10 points per year for each year of additional formal education. As predicted by the cognitive reserve hypothesis, higher education delays the onset of accelerated cognitive decline; once it begins it is more rapid in persons with more education.

Local electrostatic effects of surface structure on field emission

We examined the classical electrostatic effects due to geometric surface structures on conductive field emission needles numerically using the finite element method and compared our results to several commonly applied analytic relations. Analysis of the morphology of electrochemically prepared Mo needles by high-resolution transmission electron microscopy was incorporated in the numerical analysis in the form of small surface protrusions and gross needle shape. We found that the error between the electrostatic potential defined by popular analytic equations and both analytic equations derived in prolate spheroidal coordinates and finite element method results was significant for ellipsoidal needles with and without surface protrusions. The morphology of the surface protrusion was found to introduce a significant nonlinear potential barrier near the needle surface. Finally we numerically analyzed a nonsymmetric, nonhomogeneous experimental needle indicating that even larger errors in the electrostatic potential can be expected relative to analytic equations.

Perceptions of barriers to certification of government forestry in Newfoundland

The Newfoundland Forest Service (NFS) directly manages a substantial portion of the province's forests. The two forest-products companies that manage the remainder have registered their forest management systems to the ISO 14001 Environmental Management System Standard. With an eye to getting all managed forest land in the province registered to ISO 14001, the NFS engaged us to undertake a study of the challenges and opportunities it would face in doing so. To meet the study objective, interviews were conducted with 30 people, most of whom work for the NFS. Upper-management commitment was identified as the most significant potential barrier, in part due to its influence on other possible barriers such as funding and commitment of staff time. Political interference, not previously identified in the literature, also poses a potential barrier. We conclude that no potential barriers pose insurmountable hurdles, and that the NFS should proceed expeditiously with ISO-14001 registration of the forests it manages. Key words: certification, ISO 14001, forest management, Newfoundland, perceptions, barriers

Intra-team boundaries as inhibitors of performance improvement in UK design and build projects: a call for change

The success of the design and build (D&B) procurement route could be undermined by issues arising from the rigid professional cultures of individual participants within project workgroups. These have the potential to inhibit the achievement of a key espoused benefit of D&B procurement, i.e. that it promotes the integration of the design and construction processes for improved project performance. Cultural non-interoperability is identified as a significant potential barrier to effective change management, and to the achievement of innovation within the design and construction processes. This note argues that project responsibilities, which currently are delineated along professional identity lines, produce design and construction solutions that fail to fulfil the potential of D&B procurement. It is suggested that addressing cultural interoperability will require a fundamental and long term reshaping of the industry's structure, beginning with the professional bodies and the higher education system that underpins their future membership.

The Key Event in Force-Induced Unfolding of Titin’s Immunoglobulin Domains

Steered molecular dynamics simulation of force-induced titin immunoglobulin domain I27 unfolding led to the discovery of a significant potential energy barrier at an extension of ∼14 Å on the unfolding pathway that protects the domain against stretching. Previous simulations showed that this barrier is due to the concurrent breaking of six interstrand hydrogen bonds (H-bonds) between β-strands A′ and G that is preceded by the breaking of two to three hydrogen bonds between strands A and B, the latter leading to an unfolding intermediate. The simulation results are supported by Ångstrom-resolution atomic force microscopy data. Here we perform a structural and energetic analysis of the H-bonds breaking. It is confirmed that H-bonds between strands A and B break rapidly. However, the breaking of the H-bond between strands A′ and G needs to be assisted by fluctuations of water molecules. In nanosecond simulations, water molecules are found to repeatedly interact with the protein backbone atoms, weakening individual interstrand H-bonds until all six A′–G H-bonds break simultaneously under the influence of external stretching forces. Only when those bonds are broken can the generic unfolding take place, which involves hydrophobic interactions of the protein core and exerts weaker resistance against stretching than the key event.