Hop Length Research Articles

Charge transport mechanism in networks of armchair graphene nanoribbons

In graphene nanoribbons (GNRs), the lateral confinement of charge carriers opens a band gap, the key feature that enables novel graphene-based electronics. Despite great progress, reliable and reproducible fabrication of single-ribbon field-effect transistors (FETs) is still a challenge, impeding the understanding of the charge transport. Here, we present reproducible fabrication of armchair GNR-FETs based on networks of nanoribbons and analyze the charge transport mechanism using nine-atom wide and, in particular, five-atom-wide GNRs with large conductivity. We show formation of reliable Ohmic contacts and a yield of functional FETs close to unity by lamination of GNRs to electrodes. Modeling the charge transport in the networks reveals that transport is governed by inter-ribbon hopping mediated by nuclear tunneling, with a hopping length comparable to the physical GNR length. Overcoming the challenge of low-yield single-ribbon transistors by the networks and identifying the corresponding charge transport mechanism is a key step forward for functionalization of GNRs.

Availability and Fade Margin Calculations for 5G Microwave and Millimeter-Wave Anyhaul Links

The deployment of new radio access technologies always provides a good opportunity and timing to optimize the existing mobile front- and backhaul (commonly called “anyhaul”). The legacy systems (Long-Term Evolution (LTE), High-Speed Packet Access (HSPA), third-generation mobile (3G), second-generation mobile (2G)) already extensively utilize the transmission and transport capacities of the mobile anyhaul. With the current launch of 5G (fifth-generation mobile) and recent LTE-A (Advanced Long-Term Evolution), additional new transmission capacities are required again. Depending on the traffic and network topology, additional cell sites are built, and even more locations are connected with fiber optics. The existing microwave and millimeter-wave links are rotated toward those aggregation points that already have optical-fiber access. Due to the increased cell-site density, the average distance of the radio access links can be reduced by network and topology optimization. The reduced hop lengths combined with adaptive modulation and automatic power control bring an opportunity for capacity increase in shortened radio links. Links newly deployed for 5G find a wide spectrum in the millimetric V, E, W, and D frequency bands. This paper discusses the availability and hop-length targets of the anyhaul links that should be carefully kept by proper planning and monitoring.

Charge Transfer in Gap Structures Based on the Chalcogenide System (As2Se3)100 –xBix

The results of investigating charge-transfer processes in thin layers of a vitreous system (As2Se3)100 – xBix are presented. A power-law dependence of the conductivity on the frequency and a decrease in the exponent s with increasing temperature are found. Charge transfer is a thermally activated process with two regions in the temperature dependence of the conductivity with the activation energies E1 = 0.12 ± 0.01 eV and E2 = 0.23 ± 0.01 eV, respectively. The results are explained in terms of the correlated barrier hopping (CBH) model of hopping conductivity in disordered systems. The main microparameters of the system are calculated: the density of localized states (N), the hopping length (Rω), and the largest height of the potential barrier (WM).

Dielectric and electrical characterizations of transition metal ions-doped nanocrystalline nickel ferrites

This paper describes the room temperature dielectric and electrical response of several transition metal ions (Cr3+, Mn2+, Zn2+ and Cd2+)-doped nickel ferrite nanoparticles. The formation of pure cubic spinel phase, microstructural and magnetic properties of these three series of nanocrystalline-doped nickel ferrite samples was reported in previous papers. It is observed that hopping of electrons is the possible charge conduction mechanism for all doped nickel ferrite samples at room temperature. All the doped ferrite samples exhibited increment in ac conductivity with increasing ac field frequency. The hopping length is found to decrease with increasing dopant concentration in Zn–Cd–Ni ferrite and Cr–Ni ferrite. For Mn-doped nickel ferrite, a slight increase in hopping length is observed. All the doped nanoferrites showed good dielectric behavior below 100 Hz along with a rapid decline above 100 Hz and finally attained negligible value. The existence of two semicircles in Nyquist plots indicates that grains and grains boundaries contribute more in dielectric responses.

Dielectric and ferroelectric properties of Gd3+ doped (K0.5Na0.5)0.96Li0.04(Nb0.8Ta0.20)O3 piezoelectric ceramics

We report the structural, dielectric, ferroelectric and piezoelectric properties of Gd3+ doped lead-free (K0.5Na0.5)0.96Li0.04(Nb0.8Ta0.20)O3 (KNLNT) ceramics. The transition temperature (TT-C and TO-T) shifted towards the lower temperature (281 °C and 110 °C) for (K0.5Na0.5)0.92Li0.04Gd0.04(Nb0.8Ta0.20)O3 (KNLGNT) ceramics. Frequency dispersion of TT-C or TO-T suggests that KNLGNT ceramics exhibit a relaxor behavior supported by the Vogel-Fulcher law and modified Curie Weiss law. Temperature-dependent resistivity analysis shows that the conduction mechanism follows Mott’s variable range hopping with an average hopping length of 7.23 nm, hopping energy 0.46 eV and density of states near the Fermi level [N(EF)] = 129 × 1016 eV−1 cm−3 for KNLGNT ceramics. Reduction in leakage current and enhancement in dielectric (εr = 1025, tanδ = 0.061 at 1 MHz), ferroelectric properties (Pr = 23.14 μC/cm2,EC = 8.70 kV/cm at 1 Hz) and piezoelectric properties (kp (53%) and d33 (128 pC/N)) were observed for KNLGNT ceramics, which are promising for high-frequency piezoelectric devices.

Preparation, characterization and photocatalytic activity of nickel-substituted CoFe2O4: exploration of changes in the micro structural parameters and distribution of cations in the lattice

NixCo1−x Fe2O4 (x = 0.0, 0.3, 0.6 and 0.9) samples were prepared by sol-gel combustion method and were characterized by various analytical techniques. The tetrahedral (A) and octahedral (B) radius permits one to calculate the edge length and bond length of M–O at A and B sites. Cation distribution is used to calculate the ionic radius of tetrahedral and octahedral sites and oxygen positional parameter. We investigated the effects of Ni+2 substitutions on structural and electrochemical properties of CoFe2O4. Due to difference in the ionic radius of Ni2+ and Fe3+ for tetrahedral site and Co2+ and Fe3+ for octahedral site the changes are observed in the structural parameter like hopping length at tetrahedral (LA) site and octahedral (LB) and x-ray density. Ni0.6Co0.4 Fe2O4 shows lower charge transfer resistivity compared to other composition. UV-visible spectra of CoFe2O4, Ni0.3Co0.7Fe2O4, Ni0.6Co 0.4Fe2O4 and Ni 0.9Co 0.1Fe2O4 shows wide absorption and the calculated band gap values were found to be 2.59, 2.24, 2.17 and 2.41 eV respectively. The continue absorption implies active d-d transitions involving transition metals present in the composite. The PL spectra show lesser recombination of photogenerated charge carriers for Ni0.6Co 0.4Fe2O4 catalyst compared to other catalysts. Lower intensity peak represents the lower recombination rate. The chemical environment and elemental binding states of Co, Ni, Fe and O were confirmed by XPS analysis. Photocatalytic activity follows in the decreasing order Ni0.6Co0.4Fe2O4 > Ni0.9Co0.1 Fe2O4 > Ni0.3Co0.7 Fe2O4 > CoFe2O4. Superoxide, perhydroxy radical and hydroxyl free radicals are involved in the degradation of Alizarin Red S (ARS).

Structure and Electrical Properties of (ZnO/SiO2)25 Thin Films

(ZnO/SiO2)25 thin-film multilayers consisting of nanocrystalline ZnO layers and amorphous SiO2 spacers with a bilayer thickness from 6 to 10 nm are synthesized in a single deposition process. An analysis of the temperature dependences of the electrical resistivity of (ZnO/SiO2)25 thin films shows that, in the temperature range of 77–300 K, the dominant conductivity mechanism successively changes from hopping conductivity with a variable hopping length in a narrow energy band near the Fermi level at temperatures of 77–250 K to thermally activated impurity conductivity around room temperature. Using the obtained temperature dependences of the electrical resistivity, the effective density of localized states at the Fermi level and the activation energy of impurity levels are estimated. The effect of heat treatment on the structure and electrical properties of the synthesized films is examined. It is established that in (ZnO/SiO2)25 thin-film systems at temperatures of 580–600°C, the ZnO and SiO2 layers chemically interact, which is accompanied by destruction of the multilayer structure and formation of the Zn2SiO4 compound with a tetragonal structure (sp. gr. I-42d).

Routeing Properties in a Gibbsian Model for Highly Dense Multihop Networks

We investigate a probabilistic model for routeing in a multihop ad hoc communication network, where each user sends a message to the base station. Messages travel in hops via other users, used as relays. Their trajectories are chosen at random according to a Gibbs distribution, which favors trajectories with low interference, measured in terms of signal-to-interference ratio. This model was introduced in our earlier paper, where we expressed, in the limit of a high density of users, the typical distribution of the family of trajectories in terms of a law of large numbers. In this paper, we derive its qualitative properties. We analytically identify the emerging typical scenarios in three extreme regimes. We analyze the typical number of hops and the typical length of a hop and the deviation of the trajectory from the straight line, regime 1 in the limit of a large communication area and large distances and regime 2 in the limit of a strong interference weight. In both the regimes, the typical trajectory approaches a straight line quickly, in regime 1 with equal hop lengths. Interestingly, in regime 2, the typical length of a hop diverges logarithmically in the distance of the transmitter to the base station. We further analyze (regime 3) local and global repulsive effects of a densely populated subarea on the trajectories.

Dispersing Content Over Networks in Information-Centric Networking

Information-centric networking (ICN), a new network architecture for efficiently delivering content, has been widely investigated recently. In ICN, cache memory is implemented at each router, and content items are routed in the network by using content name as the locator determining the destination. The caching strategy that determines the content to be cached at each router strongly affects the cache hit ratio and flow hop length, and it is important to efficiently utilize limited cache resources by avoiding duplicated caching of the same content among routers located closely. In this paper, we propose a spatially dispersed caching (SDC), which is a caching strategy dispersing content by assigning a binary ID to each router and limiting the cache targets at each router to content with names whose hash value coincides with the router ID. Through computer simulations using backbone networks of actual ISPs in the United States, we show that the SDC improves the cache hit ratio by about 30%–170% compared with the case when caching content at all routers on the default path, and the SDC reduces the average hop length at cache hit by about 50%–90% compared with the existing caching strategies. Moreover, we show that the SDC improves the sustainable ratio of content acquisition in large-scale failures of routers by about 25%–200% compared with the existing caching strategies.

Bed-load through emergent vegetation

The paper deals with bed-load rates in a mobile bed channel with emerging vegetation. We have adapted the probabilistic/deterministic sediment transport model of Armanini et al.(2015) to account for changes in the flow field induced by vegetation. In addition to the two dimensionless parameters proposed by Einstein (1950), Φ and Ψ, the new adapted model also depends on a third dimensionless parameter representative of vegetation size and density. The adaptation requires two major changes to the original model by Armanini et al.(2015). Firstly, the presence of vegetation reduces the bed area that is active with processes of sediment entrainment and deposition. To account for this, we propose reducing the net unit area useful for the exchange of sediments between bed and flow in proportion to vegetation density. This hypothesis implies redefining Einstein’s parameter Φ, which represents the dimensionless sediment transport rate. Secondly, the presence of vegetation modifies some important parameters that, according to the adopted model, contribute to the formation of the bed load, (i.e. probability distributions of the particle hop length and detachment). Instead of adapting the bed-load formula to account for vegetation, we propose redefining both of Einstein’s dimensionless parameters, Φ and Ψ, so that they are functions of the vegetation characteristics. This formulation is compared with a wide range of experimental data obtained in a laboratory channel, where the plants were represented by rigid emerging cylinders of different sizes and distribution densities within the channel. Under statistically homogenous and stationary conditions, these tests provided solid flow rates and hydrodynamic characteristics for 93 configurations with different values of hydrodynamic, granulometric and stem parameters. The comparison between experimental results and theoretical predictions shows the validity of the approach.

Viscosity decoupled charge transport in surface functionalized ZnS nanoparticle dispersed imidazolium ionanofluids

The mechanism of charge transport in ionic liquid functionalized ZnS nanoparticles dispersed imidazolium-based ionanofluids are investigated combining impedance spectroscopy, viscosity measurement and diff ;erential scanning calorimetry. The viscosity enhances from 76 mPa S to 229 mPa S at room temperature in 0–20 wt% of functionalised nanoparticles addition in the ionic liquid. The conductivity and permittivity spectra are dominated on the low-frequency side by electrode polarization effects. Using the Poisson–Nernst–Planck (PNP) electro-diffusion equations enables us to determine the dc conductivity, ion diffusivity and hopping length of mobile ions and their nature of thermal activation. A decoupling of ion transport with viscosity is observed in the ionanofluids within the entire temperature range and for the 15.0 wt% nanoparticle inserted nanofluid conductivity reaches a maximum value (2.5 mS/cm at 30 °C). The physical explanation regarding the possible origin of the observed remarkable decoupling is proposed.

Observation of impurity band conduction and variable range hopping in heavily doped (010) β-Ga2O3

Temperature-dependent resistivity and Hall measurements were performed on a heavily Sn-doped (010) β-Ga2O3 substrate grown by edge-defined film-fed method. At room temperature, the Hall electron mobility was 77.7 cm2 V−1 s−1. A maximum mobility of 95.2 cm2 V−1 s−1 was achieved at T = 185 K. Because the doping concentration is near the Mott critical value of 2.48 × 1018 cm−3, Hall electron concentration and mobility data were analyzed using the two-band model, which considers transport through both the conduction band and an impurity band. At T > 200 K, charge transport is limited by free carriers in the conduction band. The donor ionization energy was extracted to be ECD = 4 meV. At T ≤ 200 K, the net conductivity is due to electrons in the impurity band, with a concentration 7.6 × 1018 cm−3 and a low mobility of ∼0.09–2.27 cm2 V−1 s−1. Over a very wide temperature range, 1.7–200 K, transport in the impurity band was found to occur via variable range hopping, where the average hopping length increases with decreasing temperature.

On Reasons of the Scatter of Literature Data for Bed‐Load Particle Hops

AbstractThis Report examines two key issues emerging when one deals with high‐resolution data for particle tracks in bed‐load transport. The first relates to how a particle motion/rest state is defined; using different definitions of motion changes the mean values computed for particle hop length and duration, that are key properties for phenomenological analysis of bed‐load transport and quantitative estimation of the associated rates. The second issue refers to the experimental bias due to considering a finite observation area within the channel bed. A conceptual presentation of the problem is here complemented by an analysis of experimental data, from both the literature and new experiments with weak bed‐load transport. Four definitions of motion were employed, together with two different ways (correcting or not the bias due to the observation area) of computing mean values from measured hop data. The results demonstrate that using different definitions and operational methods highly changes the mean values of hop‐related quantities. This may explain the scatter among literature data and challenges future Lagrangian investigation of bed‐load transport.

Temperature and Salt-Dependent Dielectric Properties of Blend Solid Polymer Electrolyte Complexed with LiBOB

In the present paper, the temperature and salt-dependent dielectric properties of poly(ethylene oxide) (PEO) and poly(vinyl pyrrolidone) (PVP) blend matrix complexed with LiBOB are investigated in the frequency range 1 Hz to 1 MHz and temperature range 40 °C to 100 °C (@10 °C). The real and imaginary part of the complex permittivity, complex conductivity have been simulated in the whole frequency window and the various fitted parameters were evaluated respectively. The estimated value of the dielectric constant and the ac conductivity increases with the increase of temperature. The lowering of relaxation time and hopping length is observed with the salt addition that is in correlation with the complex conductivity results. The modulus formalism was used to analyze the recorded dielectric data. The dc conductivity, hopping frequency, and segmental motion are strongly coupled with each other as evidenced by the Debye-Stoke-Einstein (DSE) plot. An interaction mechanism has also been proposed to explore the effect of temperature on the hopping length, relaxation time, hopping potential barrier and the segmental motion of the polymer chain.

Перенос заряда в планарных структурах на основе халькогенидной системы (As-=SUB=-2-=/SUB=-Se-=SUB=-3-=/SUB=-)-=SUB=-100-x-=/SUB=-Bi-=SUB=-x-=/SUB=-

AbstractThe results of investigating charge-transfer processes in thin layers of a vitreous system (As_2Se_3)_100 – _ x Bi_ x are presented. A power-law dependence of the conductivity on the frequency and a decrease in the exponent s with increasing temperature are found. Charge transfer is a thermally activated process with two regions in the temperature dependence of the conductivity with the activation energies E _1 = 0.12 ± 0.01 eV and E _2 = 0.23 ± 0.01 eV, respectively. The results are explained in terms of the correlated barrier hopping (CBH) model of hopping conductivity in disordered systems. The main microparameters of the system are calculated: the density of localized states ( N ), the hopping length ( R _ω), and the largest height of the potential barrier ( W _ M ).

Structural and Magnetic Studies of Zn Doped Nickel Nanoferrites Synthesize by Sol-gel Auto Combustion Method

Abstract A series of nanoferrites with chemical composition Ni1-XZnXFe2O4 (X=0.0 to 1.0) have been prepared by novel microwave assisted sol-gel auto-combustion method. Structural study was performed using XRD technique revealed prepared samples has single spinel phase. Precise value of lattice parameter was determined by plotting lattice parameters versus Nelson-Riley function. The value of lattice parameter shows increasing trend with content of Zn. This behaviour of lattice parameter is due to difference in ionic radii of Zn and Ni. The values of crystallite size, experimental density, theoretical density, porosity, ionic radii, bond length and hopping length at tetrahedral (A) and octahedral (B) sites were measured from XRD data. The crystallite size of nanoparticles form XRD data is in the range 17 - 25 nm. The microstructure was also characterized by scanning electron microscopy. The magnetic behaviour was understood from B-H loop obtained using Vibrating Sample Magnetometer (VSM). It is observed that the magnetic properties change with the increase of Zn content and can be interpreted on the basis of Neel”s two sub lattice model.

Direct evidence for the influence of lithium ion vacancies on polaron transport in nanoscale LiFePO4.

Improving the electronic conductivity in lithium-based compounds can considerably impact the design of rechargeable batteries. Here, we explore the influence of lithium ion vacancies on the electronic conductivity of LiFePO4, an active cathode material, by varying the crystallite sizes. We find that about 17% lithium ion vacancy concentration leads to an enhancement in electronic conductivity of about two orders of magnitude at 313 K with respect to our initial crystallite size. We attribute the enhanced electronic conductivity to the lithium ion vacancy concentration in addition to the reduced hopping length. The lithium ion vacancies are the source of polarons in LiFePO4, which increases with decreasing crystallite size due to the surface energy kinetics. The substantial increase in the polaronic sites (Fe3+) at a lower crystallite size leads to a reduction in lattice parameters including the unit cell volume. The analysis of temperature dependent dc conductivity within the framework of the Mott model of polaron conduction enables us to quantify the various physical parameters associated with polaron hopping in LiFePO4.

Experimental Censorship of Bed Load Particle Motions and Bias Correction of the Associated Frequency Distributions

Knowledge of the statistical distributions of particle hop properties (distances, travel, and rest times) enables a deeper understanding of bed load sediment transport. However, the measurement of particle hops is prone to censorship: Since many hops cross the boundaries of a spatial‐temporal observation window, one knows that they exist but does not know how long they are. An option is to build particle hop samples considering only the hops that are completely observed and excluding (censoring) those observed only partially. Such a choice, however, biases the frequency distributions of the hop properties. Moreover, censorship acts in both space and time, and a hop censored in time will also not contribute to a sample of hop lengths, and vice versa. Time censorship similarly applies to particle rest times. This paper presents a theoretical formulation of censorship that leads to nonparametric bias corrections recovering estimates of values of the underlying distributions of hop distance, travel time, and rest time up to sampling window dimensions. We illustrate the occurrence and consequences of experimental censorship, and the benefit of applying the bias corrections, for both synthetic and laboratory samples of particle hops. The corrections reasonably recover the relative proportions of frequency distributions represented by the data up to the sampling dimensions and improve the estimates of the first two moments of particle hop properties. Recommendations are given regarding how the size of an observation window may be chosen to reduce the bias to below some prescribed value, if the forms of the underlying distributions are known.

Effect of Al substitution on the structural, electric and impedance behavior of cobalt ferrite

Cobalt ferrite nanoparticles doped with Al ions, Co1-x AlxFe2O4 (x = 0, 0.1, 0.3 and 0.5) were prepared by sol-gel method. An attempt is made to understand if and how the Al substitution affect the structural and electrical properties of cobalt ferrite. The X-ray diffractometer (XRD) analysis confirmed the single phase cubic spinel structure of the nanocrystals. Crystallite size, lattice constant and x-ray density were calculated from the XRD data. A reduction in crystallite size and lattice parameter values were found with increased dopant concentration. Tetrahedral and octahedral hopping lengths and other related parameters were also calculated from the XRD data. The effect of doping on morphological features were monitored using Field emission scanning electron microscope (FESEM) images. The Fourier transform infrared spectrometer (FTIR) spectral analysis confirmed the cubic spinel structure of cobalt ferrite nanoparticles with the occurrence of characteristic absorption bands. Improved values of dielectric constant, low dielectric loss and resistivity were displayed by Al doped ferrite samples. Detailed impedance spectroscopy analysis with the help of Cole-Cole plot explored the capability of the Al doped cobalt ferrite to be suitable for high frequency applications and magnetic memory devices.

Dielectric Relaxation and Conductivity of CdGa2S4 Single Crystal Grown by the CTR Method

CdGa2S4 single crystals (a = 5.555 ± 0.002 A, c = 10.190 ± 0.005 A) have been grown by the chemical transport reaction (CTR) method, and their dielectric properties have been analyzed. An experimental study of the frequency dependence of the dielectric coefficients and conductivity of the CdGa2S4 single crystal has made it possible to reveal the nature of dielectric losses, establish the hopping charge-transfer mechanism, and estimate the parameters of localized states (density and energy spread of states near the Fermi level; mean duration and length of hops; and concentration of deep traps, which implement ac conductivity).