Number Of Effective Charge Carriers Research Articles

Nanoscale Confinement Effects on Ionic Conductivity of Solid Polymer Electrolytes: The Interplay between Diffusion and Dissociation.

Solid polymer electrolytes (SPEs) are attractive for next-generation lithium metal batteries but still suffer from low ionic conductivity. Nanostructured materials offer design concepts for SPEs with better performance. Using molecular dynamics simulation, we examine SPEs under nanoscale confinement, which has been demonstrated to accelerate the transport of neutral molecules such as water. Our results show that while ion diffusion indeed accelerates by more than 2 orders of magnitude as the channel diameter decreases from 15 to 2 nm, the ionic conductivity does not increase significantly in parallel. Instead, the ionic conductivity shows a nonmonotonic variation, with an optimal value above, but on the same order as, its bulk counterparts. This trend is due to enhanced ion association with decreasing channel size, which reduces the number of effective charge carriers. This effect competes with accelerated ion diffusion, leading to the nonmonotonicity in ion conductivity.

Effect of Nanoscale Confinement on Ultrafast Dynamics of Singlet Fission in TIPS-Pentacene.

Singlet fission (SF) is a phenomenon for the generation of a pair of triplet excitons from anexcited molecule in singlet electronic state interacting with another adjacent molecule in its ground electronic state. By increasing the effective number of charge carriers and reducing thermal dissipation of excess energy, SF is promised to enhance light-harvesting efficiency for photovoltaic applications. While SF has been extensively studied in thin films and crystals, the same has not been explored much within a confined medium. Here, we report the ultrafast SF dynamics of triisopropylsilylethynyl pentacene (TIPS-Pn) in micellar nanocavity of varying sizes (prepared from TX-100, CTAB, and SDS surfactants). The nanoparticles with a smaller size contain weakly coupled chromophores which are shown to be more efficient for SF followed by triplet generation as compared to the nanoparticles of larger size which contain strongly coupled chromophores which are less efficient due to the presence of singlet exciton traps. Through these studies, we delineate how a subtle interplay between short-range and long-range interaction among chromophores confined within nanoparticles, fine-tuned by the curvature of the micellar interface but irrespective of the nature of the micelle (cationic or anionic or neutral), play a crucial role in SF through and generation of triplets.

Physical properties of rhodium retrieved from modeling its dielectric function by a simulated annealing approach

Optical, charge carriers transport, quantum mechanics, magnetic, thermal, and plasmonic properties of the transition metal rhodium are considered. An extended Drude-Lorentz (DL) model is applied to describe the dielectric function (DF) of rhodium in a spectral range going from the mid-infrared (12.4 μm) to the vacuum ultraviolet (32 nm). The Drude term of the DF includes, as optimization parameters, the inverse of the high frequency dielectric constant, the volume plasma frequency and scattering frequency of the electrons, the scattering frequency of holes relative to that of electrons, the ratio between the effective masses of electrons and holes, the number of holes per atom relative to that of electrons, and the renormalized times between grain boundary scattering events for electrons and holes. The Lorentz contribution to the DF includes the number of conduction electrons per atom, the oscillator strengths, the resonance energies, and the Lorentzian widths. Values of the parameters involved in the DF are optimized by an acceptance-probability-controlled simulated annealing method that minimizes spectral differences between the real and imaginary parts of the DF values obtained from the literature and those evaluated from the DL parametric formulation, accounting for the presence of electrons and holes as charge carriers. Once an optimized spectral description of the DF of rhodium is obtained, a large set of charge-transport, magnetic, thermal, plasmonic, and quantum mechanics derived quantities are evaluated: mobilities, relaxation times, Fermi velocities, effective masses, electrical and thermal conductivities, heat capacity coefficients, Hall coefficient, diamagnetic and paramagnetic susceptibilities, effective number of Bohr magnetons, Fermi energies and corresponding densities of states, energy loss functions, effective number of charge carriers participating in conduction, and effective number of electrons involved in inter-band transitions.

Decoupling mobility and charge carrier concentration in AgR-AgPO3 glasses (R = Cl, Br, I)

Halide-containing silver phosphate glasses have been used as model systems for the study of the ionic conductivity of oxide glasses for the past 50 years, mostly due to the massive increase in conductivity observed as the halide concentration is increased, even if the molar ratio of silver is kept constant. Furthermore there is still no consensus if the increased conductivity is due to an enhancement of the number of effective charge carriers (glass as a weak electrolyte) or a higher charge carrier mobility (glass as a strong electrolyte). In this work we investigate the electrical properties of silver-halide-containing silver metaphosphate glasses through Impedance Spectroscopy. We find the glasses to follow the “canonical scaling”, which coupled with the diffusional nature of the conductivity allows us to show that the number of effective charge carriers remains constant with increasing halide concentration, and that the conductivity follows the same scaling as the ionic mobility.

In situ synthesis and characterization of polyaniline/prussian blue/zinc oxide nanocomposite

A new ternary nanocomposite of polyaniline (PANI), prussian blue (PB) and zinc oxide (ZnO), i.e., PANI–PB–ZnO was successfully synthesized in one pot process through chemical oxidative polymerization of aniline using ammonium persulfate as oxidizing agent. The morphological studies showed the formation of PB nanocubes and agglomerated quasi-spherical ZnO nanoparticles over PANI matrix, and the elemental composition of PANI–PB–ZnO was analyzed with energy-dispersive X-ray spectroscopy. The XRD measurements reveal the semicrystalline structure of the PANI–PB–ZnO nanocomposite after the polymerization reaction. The various functional groups present in PANI–PB–ZnO were identified using FTIR spectroscopy which confirms the presence of ZnO, PB and PANI in the synthesized ternary nanocomposite. From thermogravimetric analysis, the thermal degradation mechanism of PANI–PB–ZnO nanocomposite was explored and the activation energy (EA) was calculated from Coats–Redfern plot and was found to be 14.33 kJ/mol. 38 wt% of PANI–PB–ZnO nanocomposite was obtained as a residue at 800 °C indicating the high thermal stability. The bulk ionic conductivity value of the synthesized nanocomposite was found to be 8.509 × 10−5 Ω−1 cm−1 at 30 °C and 1.22 × 10−4 Ω−1 cm−1 at 100 °C. The ionic conductivity was found to increase with temperature for the synthesized material which showed an increase in the number of effective charge carriers. The characteristic absorption bands were detected using UV–Vis spectroscopy that confirms the formation of PANI–PB–ZnO nanocomposite. X-ray photoelectron spectroscopy measurements confirmed the valence states of constituent elements in ZnO nanoparticles and ternary PANI–PB–ZnO nanocomposite. I–V studies revealed that hybrid PANI–PB–ZnO nanocomposite has higher conductivity (2.4 × 10−4 S cm−1) than ZnO nanoparticles (3.5 × 10−10 S cm−1).

Exploration of channel width scaling and edge states in transition metal dichalcogenides

We explore the impact of edge states in three types of transition metal dichalcogenides (TMDs), namely metallic Td-phase WTe2 and semiconducting 2H-phase MoTe2 and MoS2, by patterning thin flakes into ribbons with varying channel widths. No obvious charge depletion at the edges is observed for any of these three materials, in contrast to observations made for graphene nanoribbon devices. The semiconducting ribbons are characterized in a three-terminal field-effect transistor (FET) geometry. In addition, two ribbon array designs have been carefully investigated and found to exhibit current levels higher than those observed for conventional one-channel devices. Our results suggest that device structures incorporating a high number of edges can improve the performance of TMD FETs. This improvement is attributed to a higher local electric field, resulting from the edges, increasing the effective number of charge carriers, and the absence of any detrimental edge-related scattering.

Violation of an f -sum rule with generalized kinetic energy

Motivated by the normal state of the cuprates in which the f-sum rule increases faster than a linear function of the particle density, we derive a conductivity sum rule for a system in which the kinetic energy operator in the Hamiltonian is a general function of the momentum squared. Such a kinetic energy arises in scale invariant theories and can be derived within the context of holography. Our derivation of the f-sum rule is based on the gauge couplings of a non-local Lagrangian in which the kinetic operator is a fractional Laplacian of order $\alpha$. We find that the f-sum rule in this case deviates from the standard linear dependence on the particle density. We find two regimes. At high temperatures and low densities, the sum rule is proportional to $nT^{\frac{\alpha-1}{\alpha}}$ where $T$ is the temperature. At low temperatures and high densities, the sum rule is proportional to $n^{1+\frac{2(\alpha-1)}{d}}$ with $d$ being the number of spatial dimensions. The result in the low temperature and high density limit, when $\alpha < 1$, can be used to qualitatively explain the behavior of the effective number of charge carriers in the cuprates at various doping concentrations.

An Investigation of Ac Impedance and Dielectric Spectroscopic Properties of Conducting Chitosan-silane Crosslinked-poly (Vinyl Alcohol) Blended Films

The films of chitosan (CS)-silane crosslinked-poly(vinyl alcohol) (PVA) with different weight % were prepared. The effect on conductivity of CS/PVA blended films due to change in the concentration of PVA and temperature was investigated by impedance spectroscopy and showed good conductance properties. The complex impedance plots revealed single semicircular arcs indicating the bulk contribution to overall electrical behavior of all synthesized samples. The ac conductivity obeyed the Jonscher's power law for all samples in the frequency range of 2 kHz to 2 MHz. The ionic conductivity of the films was increased with the increase in temperature for all synthesized samples which showed an increase in the number of effective charge carriers while it was decreased at a specific higher temperature for each film. The observed activation energy for CP4, CP8 and CP10 were 0.431, 0.610 and 0.425 eV, respectively. These properties showed that the films were promising materials to be employed for conducting properties.

Spectroscopic studies on ion dynamics of PVP–NH4SCN polymer electrolytes

Proton-conducting polymer electrolyte comprising of poly(N-vinyl pyrrolidone) (PVP) and ammonium thiocyanate (NH4SCN) are prepared by solvent casting method with different polymer–salt concentrations. The changes in the Raman spectra with increasing NH4SCN concentration state that the free ion concentration is maximum for 20 mol% NH4SCN concentrated system. At higher salt concentrations (25 mol%), the effective number of charge carriers decreases due to the formation of ion aggregates as confirmed by the Raman analysis. Solid-state NMR and MAS NMR studies are performed to obtain the information about the ionic structure, mobility of the charge carriers, and also to gain insight into the polymer–salt interactions in the polymer electrolytes. The results of ionic transference number show that the charge transport in these polymer electrolytes is mainly due to ions.

Charge carrier concentration and mobility in alkali silicates

The respective contributions of the charge carrier concentration and mobility to the ionic conductivity in glasses remain an open question. In the present work we calculate these two parameters from conductivity data as a function of temperature below and above the glass transition temperature, T(g). The basic hypothesis assumes that ionic displacement results from the migration of cationic pairs formed by a partial dissociation, which is a temperature-activated process. Below T(g) their migration would follow a temperature-activated mechanism, while a free volume mechanism prevails above this temperature, leading to a deviation from the Arrhenius behavior. Expressions are formulated for the variation in ionic conductivity as a function of temperature in the supercooled and glassy states. Fitting the experimental data with the proposed expressions allows for the determination of characteristic parameters such as the charge carrier formation and migration enthalpies. Based on these values, it is then possible to calculate the charge carrier concentration and mobility in the entire temperature range. At room temperature, the mobility of effective charge carriers is estimated close to 10(-4) cm(2) s(-1) V(-1) for alkali disilicates glasses under study, while the ratio between the number of effective charge carriers and the total number of alkali cations is estimated to be from 10(-8) to 10(-10), comparable to the concentration of intrinsic defects in an ionic crystal or dissociated species from a weak electrolyte solution.

Ionic properties of non-aqueous liquid and PVDF-based gel electrolytes containing a cesium thiolate/disulfide redox couple

Liquid electrolytes containing a cesium thiolate/disulfide redox couple, prepared from 5-mercapto-1-methyltetrazole cesium salt (CsT) and di-5-(1-methyltetrazole)disulfide (T 2) dissolved in several aprotic solvents and solvent mixtures, have been studied using various techniques. FTIR spectroscopy reveals that relatively strong interactions occur between the reduced species T − and DMSO or DMF while Cs + ions are very weakly coordinated to the SO or CO bond. It is shown that the electrolyte consisting of 1.55 mol kg −1 CsT in the solvent mixture DMSO/DMF (40/60%) exhibits the highest conductivity (1.1×10 −2 and 2.3×10 −2 S cm −1 at 23 and 80 °C, respectively), and that the presence of the oxidized species T 2 does not affect significantly its electrical properties up to a CsT:T 2 molar ratio of 5:1. Conductivity values as a function of salt concentration are discussed in terms of the effective number of charge carriers, taking into account the level of ionic association, and of the ionic mobility. Optically transparent gel electrolytes have been prepared by incorporation of the optimal liquid electrolyte into various amounts of poly(vinylidene fluoride) (PVDF). It is shown that ionic mobility is not much affected by the polymer concentration, suggesting that migration of ions occurs mainly through the solvent mixture surrounded by the PVDF matrix.

FTIR spectroscopic study and thermal and electrical properties of polymer electrolytes containing a cesium thiolate/disulfide redox couple

High molecular weight (HMW) PEO-based copolymer (modified PEO) complexed with a cesium thiolate/disulfide redox couple, prepared from 5-mercapto-1-methyltetrazole cesium salt (CsT) and di-5-(1-methyltetrazole) disulfide (T 2), has been studied using various techniques. Phase diagrams of the modified PEO x –CsT and modified PEO x –CsT/0.1T 2 systems, developed using polarized light optical microscopy and differential scanning calorimetry, are discussed. It is shown that an intermediate compound and an eutectic of composition corresponding to a (CH 2–CH 2–O)/Cs molar ratio (O/Cs) of 12/1, which melts at 29°C, are formed. At high salt concentration (O/Cs≤8/1), non-spherulitic crystallites observed over the homogeneous amorphous phase are attributed to undissolved CsT. Ionic conductivity measurements show that the polymer electrolytes investigated in this work exhibit a conductivity maximum that occurs at the eutectic composition. Conductivity values as a function of salt concentration are discussed in terms of the effective number of charge carriers and of the stiffening of the polymer chains. The valuable role of the disulfide (T 2) for increasing the electrolyte conductivity is reported. The slight higher conductivity of the fully amorphous electrolyte containing CsT instead of KT may be correlated to the lower polyether–Cs + interaction, as revealed by FTIR spectroscopy.

Avoiding Transient Diffusion of Boron in Si(100)

ABSTRACTThe diffusion of boron ions implanted in Si(100) during high temperature treatment has been studied by means of Secondary Ion Mass Spectrometry. The boron ions were implanted at energies of 5 and 10 keV along random direction and along [100]. The implantation dose amounted to 1×1013/cm2. During annealing an enhanced diffusion of boron is observed in the tail region of the implantation profiles. In all cases the enhanced diffusion is completed after Rapid Thermal Annealing at 900°Cfor 10”. The enhanced diffusion is largest for the channeled ion implantations. Channeling analysis shows that the transient diffusion is not correlated with the annihilation of defects near the projected range. Therefore, the observed diffusion tail is attributed to rapidly diffusing interstitial boron. Post-amorphization of boron implanted silicon with Si+ ions is used to prevent transient diffusion. Thus a very sharp pn-junction is obtained at a depth of 03 jim and the effective number of charge carriers equals the implanted dose after annealing at 550°Cfor 5hrs and 1000°Cfor 10”.

Injection and migration of protons in single crystals of lithium sulphate monohydrate

By employing a palladium-hydrogen electrode it is possible to inject protons into single crystals of Li2SO4H2O. As predicted by Maricic et al. migration of protons is much preferred along the b axis of the monoclinic crystal. The current-voltage characteristics for this direction, and for the other two major directions, are interpretable in terms of space-charge-limited-currents, and, using the equations valid under such conditions the effective mobility (assumed to be field-independent) is estimated to be ca 10–7 to 10–8 cm2 V–1 s–1. Lower limits for the trap concentration are in the range 1012–1013 cm–3, and the number of effective charge carriers is about 1011 cm–3. From an examination of the structure of the solid, it is possible to formulate a plausible mechanism, based on Grotthuss conduction, for the preferred migration of the protons.