Hopping Rate Research Articles

Quantitative Prediction of Charge Mobilities and Theoretical Insight into the Regulation of Site-Specific Trifluoromethylethynyl Substitution to Electronic and Charge Transport Properties of 9,10-Anthraquinone.

Herein, we systematically studied the electronic and conducting properties of 9,10-anthraquinone (AQ) and its derivatives and discussed the substitute-site effects on their organic field-effect transistor (OFET) properties in detail. Our calculation results show the influence of different substitute sites on the ionization potential (IP), electronic affinity (EA), reorganization energy (λ), electronic couplings (V), and anisotropic mobility (μ) of semiconducting materials, which mainly originates from the variations of the frontier molecular orbital charge distributions, the steric hindrance, and the conjugate degree. Combining quantum-chemical calculations with charge transfer theory, we simulated the intermolecular hopping rate in the organic crystals of AQ derivatives and predicted the fluctuation range of three-dimensional (3D) anisotropic charge carrier mobility for the first time. Our calculation results well reproduced the experimental observations and provided evidence for the determination of the optimal OFET conduction plane and channel direction relative to the crystal axis.

A two-site triplet exciton hopping model: Application to 3P700.

A model is presented describing the effect on spin-polarized transient EPR signals caused by incoherent state hopping between two sites. It is shown that the size of the spin state space can be reduced by half to the subspace described by the site-average Hamiltonian and that the dynamics of the system results in a redistribution of the population between its eigenstates. Analytical expressions for the rates of population redistribution and the line shape are derived for the general case in which the back-and-forth rates are unequal. The EPR signals calculated using these expressions are in very good agreement with those obtained by direct numerical solution of the density matrix rate equations. The model is then used to investigate the influence of exciton hopping on triplet state transient EPR spectra. Using the triplet state of the primary donor of Photosystem I as an example, it is shown that the influence of unequal hopping rates becomes more pronounced in the spectrum at longer delay times after the laser flash.

Steady states and phase transitions in heterogeneous asymmetric exclusion processes

We study nonequilibrium steady states in totally asymmetric exclusion processes (TASEPs) with open boundary conditions having spatially inhomogeneous hopping rates. Considering smoothly varying hopping rates, we show that the steady states are in general classified by the steady state currents in direct analogy with open TASEPs having uniform hopping rates. We calculate the steady state bulk density profiles, which are now spatially nonuniform. We also obtain the phase diagrams in the plane of the control parameters, which, despite having phase boundaries that are in general curved lines, have the same topology as their counterparts for conventional open TASEPs, independent of the form of the hopping rate functions. This reveals a type of universality, not encountered in critical phenomena. Surprisingly and in contrast to the phase transitions in an open TASEP with uniform hopping, our studies on the phase transitions in the model reveal that all three transitions are first order in nature. We also demonstrate that this model admits delocalised domain walls (DDWs) on the phase boundaries, demarcating the generalised low and high density phases in this model. However, in contrast to the DDWs observed in an open TASEP with uniform hopping, the envelopes of the DDWs in the present model are generally curved lines.

Organic Disordered Semiconductors as Networks Embedded in Space and Energy.

Organic disordered semiconductors have a growing importance because of their low cost, mechanical flexibility, and multiple applications in thermoelectric devices, biosensors, and optoelectronic devices. Carrier transport consists of variable-range hopping between localized quantum states, which are disordered in both space and energy within the Gaussian disorder model. In this paper, we model an organic disordered semiconductor system as a network embedded in both space and energy so that a node represents a localized state while a link encodes the probability (or, equivalently, the Miller-Abrahams hopping rate) for carriers to hop between nodes. The associated network Laplacian matrix allows for the study of carrier dynamics using edge-centric random walks, in which links are activated by the corresponding carrier hopping rates. Our simulation work suggests that at room temperature the network exhibits a strong propensity for small-network nature, a beneficial property that in network science is related to the ease of exchanging information, particles, or energy in many different systems. However, this is not the case at low temperature. Our analysis suggests that there could be a parallelism between the well-known dependence of carrier mobility on temperature and the potential emergence of the small-world property with increasing temperature.

Unraveling the complexation effect of electron transporting materials with Liq on the charge transport properties: A theoretical perspective

The effect of coordinated structures of electron transporting materials (ETMs) withlithium quinolate (Liq)on charge transport characteristics was theoretically investigated.Thereorganization energies of holes(λh)and electrons (λe)ofETM-Liqsimultaneously increased compared with those of ETMs, indicating that the charge transporting is retarded. Interestingly,λeofETM-(Liq)n increased, whileλh decreased. Regarding transfer integrals forholes (th) and electrons (te),th‘s ofT2T-LiqandBPyTP2-Liqwere significantly reduced withteofT2T-Liqdecreasing tremendously.Consequently, the hopping rates of holes of Liq-complexes were reduced, while that of electrons ofBPyTP2-Liqincreased and that ofT2T-Liq/TSPO1-Liqwas reduced.

Flocking in one dimension: Asters and reversals.

We study the one-dimensional active Ising model in which aligning particles undergo diffusion biased by the signs of their spins. The phase diagram obtained varying the density of particles, their hopping rate, and the temperature controlling the alignment shows a homogeneous disordered phase but no homogeneous ordered one, as well as two phases with localized dense structures. In the flocking phase, large ordered aggregates move ballistically and stochastically reverse their direction of motion. In what we termed the "aster" phase, dense immobile aggregates of opposite magnetization face each other, exchanging particles, without any net motion of the aggregates. Using a combination of numerical simulations and mean-field theory, we study the evolution of the shapes of the flocks, the statistics of their reversal times, and their coarsening dynamics. Solving exactly for the zero-temperature dynamics of an aster allows us to understand their coarsening, which shows extremal dynamics, while mean-field equationsaccount for their shape.

Analysis and Optimization of Organic Tandem Solar Cells by Full Opto-Electronic Simulation

This paper reports on the analysis and optimization of high-efficiency organic tandem solar cells via full opto-electronic device simulation on continuum level and using a hopping model for the explicit description of the charge recombination junction. Inclusion of the electrical sub-cell interconnection allows for a rigorous assessment of the impact of the internal charge distribution and associated built-in fields as well as quasi-Fermi level profiles on the measured device characteristics. It enables the direct evaluation of the external quantum efficiency in a simulation that follows closely the measurement protocol, and sheds light on complications related to the dependence of the band profile on the illumination conditions. The study also points at fingerprints of insufficient junction quality in the electrical characteristics of the tandem device. After studying the impact of key electrical parameters such as, carrier mobility, lifetime and interface hopping rate, onto the device characteristics, the latter are optimized not only optically, but also electronically, adding in both cases an increasing number of layers to the parameters of the global optimization procedure. An improvement of 2% absolute power conversion efficiency by using the full opto-electronic optimization as compared to optical optimization only is found.

Static Disorder has Dynamic Impact on Energy Transport in Biomimetic Light-Harvesting Complexes.

Despite extensive studies, many questions remain about what structural and energetic factors give rise to the remarkable energy transport efficiency of photosynthetic light-harvesting protein complexes, owing largely to the inability to synthetically control such factors in these natural systems. Herein, we demonstrate energy transfer within a biomimetic light-harvesting complex consisting of identical chromophores attached in a circular array to a protein scaffold derived from the tobacco mosaic virus coat protein. We confirm the capability of energy transport by observing ultrafast depolarization in transient absorption anisotropy measurements and a redshift in time-resolved emission spectra in these complexes. Modeling the system with kinetic Monte Carlo simulations recapitulates the observed anisotropy decays, suggesting an inter-site hopping rate as high as 1.6 ps–1. With these simulations, we identify static disorder in orientation, site energy, and degree of coupling as key remaining factors to control to achieve long-range energy transfer in these systems. We thereby establish this system as a highly promising, bottom-up model for studying long-range energy transfer in light-harvesting protein complexes.

Paramagnetic probes in an organic semiconductor: μSR and DFT calculations of the Mu adducts of Alq3 and 8-hydroxyquinoline.

It has been claimed that longitudinal field muon spin relaxation (LF-μSR) experiments on the organic semiconductor (OSC) tris-(8-hydroxyquinoline)aluminum(III) (Alq3) have measured electron hopping rates of ∼1012s-1, while density functional theory (DFT) calculations suggest that electron hopping between a muoniated radical and a neighboring molecule is energetically unfavorable and that the LF-μSR experiments were probing muoniated radicals with localized spin density. We have performed avoided level crossing muon spin resonance (ALC-μSR) and transverse field muon spin rotation (TF-μSR) measurements on Alq3 and 8-hydroxyquinoline (8hq), which is meant to model the muoniated radicals present in Alq3 when they are not in an OSC. These are supplemented by benchmarked DFT calculations. The ALC-μSR and TF-μSR spectra of 8hq and Alq3 are best explained by Mu adding to all six secondary carbons of the quinolate rings with roughly equal yields and localized spin density. There is no evidence in the TF-μSR spectrum of Alq3 for the formation of radicals with muon hyperfine coupling constants of 23 or 91MHz as reported earlier by others. Our measurements support the view that there is localized spin density on the molecule to which Mu is covalently bound and the muon is not a passive probe in organic systems as it can be incorporated into radicals that have different electronic structures to the parent compounds. The muoniated radicals in Alq3 are more short-lived than in 8hq, which could be due to interactions with mobile electrons in the OSC, but with electron spin flip rates on the order of ∼107s-1.

Fading-free Φ-OTDR evaluation based on the statistical analysis of phase hopping.

In phase-sensitive optical time domain reflectometry (Φ-OTDR), false phase peaks caused by interference fading have been observed experimentally; however, the statistical law has not yet been disclosed. In this work, after clarifying that the false phase peaks originate from the phase hopping of demodulated phase noise during the unwinding process, we define the phase hopping rate (PHR) to evaluate the degree of fading and study the quantitative relationship between the PHR and signal-to-noise ratio (SNR) of the measured signal through theoretical derivation and experimental verification. In addition, a moving rotated-vector-average (MRVA) method is proposed to suppress the fading and eliminate the false phase peaks. In the experiment, after MRVA processing with a 25 ns sliding window, the lowest SNR is pulled from 0.003 to 14.9, and the corresponding PHR is reduced from 0.237 to less than 0.0001, which is consistent with the theoretical analysis.

Generalization on Entropy-Ruled Charge and Energy Transport for Organic Solids and Biomolecular Aggregates.

Herein, a generalized version of the entropy-ruled charge and energy transport mechanism for organic solids and biomolecular aggregates is presented. The effects of thermal disorder and electric field on electronic transport in molecular solids have been quantified by entropy, which eventually varies with respect to the typical disorder (static or dynamic). Based on our previous differential entropy (hs)-driven charge transport method, we explore the nonsteady carrier energy flux principle for soft matter systems from small organic solids to macrobiomolecular aggregates. Through this principle, the synergic nature of charge and energy transport in different organic systems is addressed. In this work, entropy is the key parameter to classify whether the carrier dynamics is in a nonsteady or steady state. Besides that, we also propose the formulation for unifying the hopping and band transport, which provides the relaxation time–hopping rate relation and the relaxation time–effective mass ratio. The calculated disorder drift time (or entropy-weighted carrier drift time) for hole transport in an alkyl-substituted triphenylamine (TPA) molecular device is 9.3 × 10–7 s, which illustrates nuclear dynamics-coupled charge transfer kinetics. The existence of nonequilibrium transport is anticipated while the carrier dynamics is in the nonsteady state, which is further examined from the rate of traversing potential in octupolar molecules. Our entropy-ruled Einstein model connects the adiabatic band and nonadiabatic hopping transport mechanisms. The logarithmic current density at different electric field-assisted site energy differences provides information about the typical transport (whether trap-free diffusion or trap-assisted recombination) in molecular devices, which reflects in the Navamani–Shockley diode equation.

Influence of Al on the structure and ion transport in garnet-type Li7La3-xAlxZr2O12 solid electrolytes for Li-ion batteries

This work reports on the preparation of garnet-type Al-doped Li7La3-xAlxZr2O12 (x = 0, 0.1, and 0.2) electrolytes for solid-state Li-ion batteries. The undoped and Al-doped cubic phase LLZO has been synthesized by conventional solid-state mixing and annealing at 1000 °C for 2 h. The prepared materials have been characterized by X-ray diffraction, scanning electron microscopy, Fourier-transform infrared spectroscopy, and Raman spectroscopy. The electrical properties were evaluated by impedance spectroscopy at varies temperatures. The ionic conductivities of Li7La3Zr2O12, Li7La2.9Al0.1Zr2O12, and Li7La2.8Al0.2Zr2O12 were determined to be 1.8x10−6, 4.1x10−6, and 6.5x10−6 S cm−1 at 100 °C respectively and their activation energy has been derived as 0.70, 0.69 and 0.73 eV from the Arrhenius plot. The DC conductivities were calculated as 1.6x10−4, 3.3x10−4, and 5.7x10−4 S cm−1 for Li7La3Zr2O12, Li7La2.9Al0.1Zr2O12, and Li7La2.8Al0.2Zr2O12 respectively. Furthermore, the hopping rates, charge carrier concentration, ionic mobility, and diffusion coefficient were also calculated and the results show an increasing trend with increasing temperature.

Superfluid–Mott-insulator quantum phase transition in a cavity optomagnonic system

The emerging hybrid cavity optomagnonic system is a very promising quantum information processing platform for its strong or ultrastrong photon-magnon interaction on the scale of micrometers in the experiment. In this paper, the superfluid-Mott insulator quantum phase transition in a two-dimensional cavity optomagnonic array system has been studied based on this characteristic. The analytical solution of the critical hopping rate is obtained by the mean field approach, second perturbation theory and Landau second order phase transition theory. The numerical results show that the increasing coupling strength and the positive detunings of the photon and the magnon favor the coherence and then the stable areas of Mott lobes are compressed correspondingly. Moreover, the analytical results agree with the numerical ones when the total excitation number is lower. Finally, an effective repulsive potential is constructed to exhibit the corresponding mechanism. The results obtained here provide an experimentally feasible scheme for characterizing the quantum phase transitions in a cavity optomagnonic array system, which will offer valuable insight for quantum simulations.

AC conductivity and electrical relaxation of a promising Ag2S-Ge-Te-Se chalcogenide glassy system

In this study, we developed a chalcogenide glassy system comprising (Ag2S)x-(0.4Ge-0.3Te-0.3Se)1-x, where x = 0.05, 0.10, and 0.20. The formation of Ag2S and GeSe2 nanocrystallites with small sizes and the development of GeTe, Ag2GeS3, TeS, and Se5.95Te1.05 phases with high Ag2S contents were confirmed by X-ray diffraction. The Fourier transform-infrared spectra demonstrated the characteristic vibration of Ag–S at 500–600 cm−1. Kinetic analysis of conductivity suggested that the Meyer–Neldel energy was due to polarons hopping from trap to trap induced by multiple phonon excitation. Tunneling of polarons through the grain boundary when x = 0.1 could be interpreted based on the modified non-overlapping small polaron tunneling model. By contrast, the correlated barrier hopping model was more appropriate for explaining the dominant conduction mechanism when x = 0.05 and 0.2. The lower relaxation times when x = 0.05 and 0.2 indicated a higher rate of polaron hopping. The temperature independence of the relaxation process was confirmed based on the scaling process.

Mechanism of length-induced magnetism in polyacene molecules

Within the celebrated Su-Schrieffer-Heeger model including electron-lattice and electron-electron interactions, the electronic ground state of polyacene ($n$-acene) is studied as a function of molecular length $n$. The results demonstrate that the ground state exhibits a phase transition from a nonmagnetic state to an antiferromagnetic state at a critical length of $n=7$. The magnetism is explained by calculating the lattice distortion and the related average hopping rate of the \ensuremath{\pi} electrons. It is revealed that in polyacenes, there exist two competing mechanisms that minimize the molecular energy, namely the lattice dimerization and the formation of an antiferromagnetic spin density. Since the dimerization is restricted to the regions near the ends of the molecules the former mechanism is dominant for short molecules, which therefore assume a nonmagnetic state. When the length is increased beyond the critical value, the lattice dimerization in the middle of the molecule is reduced and a rapid drop of the average hopping rate occurs. This makes the second mechanism dominant and the associated antiferromagnetic state is stabilized. The effect of different interaction strengths and values of hopping integrals on the critical length is discussed. The results are confirmed by first-principles calculations. Suggestions for the design of organic antiferromagnets with a similar ladder structure are also given.

Effects of π‐conjugation on the charge‐transport properties of hole‐transporting materials featuring diphenylamine‐π‐quinacridone for perovskite solar cells: A theoretical study

AbstractDensity functional theory (DFT), time‐dependent DFT, and Marcus theory were used to probe the optoelectronic and charge‐transport properties of compounds obtained by inserting long‐chain aliphatic alkenes or condensed aromatic rings between the planar quinacridone core and the terminal donor diphenylamine moiety of a reference hole‐transporting material (HTM). Compared to the reference HTM, its newly designed derivatives showed lower‐lying highest occupied molecular orbitals that were well matched in energy with the valence band maximum of a representative perovskite absorber. HTMs obtained via the insertion of condensed aromatic rings showed higher hole mobilities than those obtained via the insertion of aliphatic alkenes. Overall, hole mobility was mainly influenced by the charge‐transfer integral, while other factors, such as the hole reorganization energy, hole hopping rate, and centroid distance, had only minor effects.

Combinatorics of a disordered two-species ASEP on a torus

We define a new disordered asymmetric simple exclusion process (ASEP) with two species of particles, first-class particles labelled • and second-class particles labelled □, on a two-dimensional toroidal lattice. The dynamics is controlled by particles labelled •, which only move horizontally, with forward and backward hopping rates pi and qi respectively if the • is on row i. The motion of particles labelled □ depends on the relative position of these with respect to •’s, and can be both horizontal and vertical. We show that the stationary weight of any configuration is proportional to a monomial in the pi’s and qi’s. Our process projects to the disordered ASEP on a ring, and so explains combinatorially the stationary distribution of the latter first derived by Evans (Europhysics Letters, 1996). We compute the partition function, as well as densities and currents of •’s and □’s in the stationary state. We observe a novel mechanism we call the Scott Russell phenomenon: the current of □’s in the vertical direction is the same as that of •’s in the horizontal direction.

Two-lane totally asymmetric simple exclusion process with extended Langmuir kinetics.

Multilane totally asymmetric simple exclusion processes with interactions between the lanes have recently been investigated actively. This paper proposes a two-lane model with extended Langmuir kinetics on a periodic lattice. Both bidirectional and unidirectional flows are investigated. In our model, the hopping, attachment, and detachment rates vary depending on the state of the corresponding site in the other lane. We obtain a theoretical expression for the global density of the system in the steady state from three kinds of mean-field analyses [(1×1)-, (2×1)-, and (2×2)-cluster cases]. We verify that the (2×2)-cluster mean-field analysis reproduces the differences between the two directional flows and approximates well the results of computer simulations for some cases. We observe that (2×1)-cluster mean-field analyses are already good approximations of the simulation results for unidirectional flows; on the other hand, the accuracy of the approximations much improves by (2×2)-cluster one for bidirectional flows. We explain the phenomena in a qualitative manner by a simple analysis of correlations. We expect these findings to give informative suggestions for actual traffic systems.

Fractal and Knot-Free Chromosomes Facilitate Nucleoplasmic Transport

Chromosomes in the nucleus assemble into hierarchies of 3D domains that, during interphase, share essential features with a knot-free condensed polymer known as the fractal globule (FG). The FG-like chromosome likely affects macromolecular transport, yet its characteristics remain poorly understood. Using computer simulations and scaling analysis, we show that the 3D folding and macromolecular size of the chromosomes determine their transport characteristics. Large-scale subdiffusion occurs at a critical particle size where the network of accessible volumes is critically connected. Condensed chromosomes have connectivity networks akin to simple Bernoulli bond percolation clusters, regardless of the polymer models. However, even if the network structures are similar, the tracer's walk dimension varies. It turns out that the walk dimension depends on the network topology of the accessible volume and dynamic heterogeneity of the tracer's hopping rate. We find that the FG structure has a smaller walk dimension than other random geometries, suggesting that the FG-like chromosome structure accelerates macromolecular diffusion and target-search.

Analiza repetitivnog ometanja radija sa sporim frekvencijskim skakanjem

Introduction/purpose: The article presents a model of a slow frequency hopping radio in the case of repeater jamming. The aim is to analyze the effectiveness of repeater jamming to a military tactical slow frequency hopping radio. Methods: It is assumed that the repeater jammer will be successful in detecting signals with slow frequency hopping at each hop and that it will perform successful partial jamming of the intercepted communication. Under partial jamming, it is considered that a certain part of the transmission time of each hop will be jammed. A theoretical analysis of the impact of a repeater jammer on a frequency hopping radio was performed based on the definition of the total probability of error. Various parameters that affect the segment of hop duration under jamming were considered. Results: The obtained results show that high effective jamming is achieved even when a short segment of hop duration is jammed. We discuss the conditions for the repeater jammer to detect the signal during each hop and emit the jamming signal with the required strength. It has been shown that increasing the frequency hopping rate can significantly reduce the effectiveness of the repeater jammer. Conclusion: Repeater jammers are highly effective against slow frequency hopping radio communication systems.