Study Of Charge Transport Properties Research Articles

Theoretical study of charge transport properties of a Si(DPP)2 complex

This article provides a study of the calculations of charge transport, reorganization energy, intermolecular transfer integral and charge mobility for the optimized structure of the new neutral hexacoordinated silicon complex Si(DPP)2. The main calculated and experimental geometric data on the optimized structure are also presented. The complex has a distorted octahedral geometry with short Si-N bond lengths averaging: calculated - 1.958365 Å and experimental - 1.9111 Å. The Si(DPP)2 structure contains two diphenylpyridine (DPP = 2,6-diphenylpyridine ligand) ligands. Optimization and computational calculations of the necessary data of charge transport were performed using a B3LYP functional and a 6-31G* basis set. Geometrical parameters for structure optimization were obtained from recent, known, experimental data. The obtained theoretical data on the charge transport of the Si(DPP)2 structure were compared with the known experimental data. Based on a comparison of the theoretical and experimental values for the charge transport properties of the Si(DPP)2 compound, it was shown that the method we used for calculating the charge mobility gives relatively close values. This work shows that computational methods can help in the further study of future structures, as well as predict the future parameters of as yet unexplored silicon complexes.

Enhanced photocatalytic activity of ZnO hexagonal tube/r-GO composite on degradation of organic aqueous pollutant and study of charge transport properties

ZnO hexagonal tube and ZnO/r-GO nanocomposites were synthesized by hydrothermal method and the nanostructures were characterized by XRD, UV-DRS, PL, FTIR, FESEM, and TEM techniques. The main violet emission peak of the synthesized nanostructures is due to the transition between interstitial zinc and hole (valence band) of ZnO. The potential of ZnO/r-GO nanocomposite was evaluated using methyl orange (MO) and rhodamine-B (RhB), and the results were compared with the activity of synthesized ZnO nanostructures. More than 95% of MO and RhB were by ZnO/r-GO nanocomposite and it was found to be higher than that of ZnO hexagonal tube. The degradation MO and RhB were found to follow first-order kinetics and it has a rate constant of 7.68 × 10−2and 7.83 × 10−2 min−1, respectively. These results are mainly due to the enhanced charge transport property. Trapping experiments show that superoxide radical anion and hydroxide radicals are chief species responsible for the degradation of MO and RhB. The chemical stability of the nanocomposite was evaluated by cycle test experiments and it reveals that the catalyst can be reused up to few cycles without considerable loss of photocatalytic activity. This work affords a simple stratagem to integrate ZnO hexagonal tubes and r-GO nanosheets to construct effective catalysts for the degradation of organic compounds.

Thin films of chlorosubstituted vanadyl phthalocyanine: charge transport properties and optical spectroscopy study of structure

Electrophysics and structure of thin films of chlorosubstituted vanadyl phthalocyanine (VOPcCl16) were studied using complementary experimental and theoretical techniques. To study charge transport properties of the latter films, organic field-effect transistors were fabricated by physical vapor deposition. The device exhibited good air stability without any extent of degradation after a storage in air for two months. The charge carrier mobility was measured to be (2.0 ± 0.1) × 10−3 cm2 V−1 s−1. This value was rationalized by poor ordering of the VOPcCl16 films revealed with the use of polarization dependent Raman and UV–Vis spectroscopies as well as by X-ray diffraction. Apart from this, we performed a detailed assignment of all intense bands in the vibrational spectra of VOPcCl16. To this end, the experimental IR and Raman data were complemented by quantum chemical calculations at the B3LYP/6-311++G(2df,p) level of theory.

DNA assisted regioregular poly (3, 3‴-didodecylquarterthiophene), rr-PQT-12 fiber: Organic bio-electronic devices

Abstract Present work has focused on the development of bio-organic hybrid materials based on hydrophobic DNA-complex incorporated in polymer and the study of charge transport properties across the junction formed by sandwiching it between conducting electrodes (called hetero-structured vertical diode). The inclusion of hydrophilic DNAs, both natural DNA and synthetic DNA (single strand DNA, ss-DNA and double strand DNA, ds-DNA), in organic semiconducting polymer specially regioregular poly (3, 3‴-didodecylquarterthiophene) (rr-PQT-12), have done in chloroform. Prior to DNAs inclusion, hydrophobic DNA-DDAB complexes have formed by reaction of hydrophilic DNA and didodecyldimethylammonium bromide, DDAB in aqueous solvent. Thereafter, as-mixed solution has been aged for 45 min to obtain fibrils' growth and used for the fabrication of devices. Various parameters including rectification ratio, ideality factor, saturation current, barrier height and device stability have been measured to study the nature of charge transport and effect of DNAs on the performance of devices. The device performance has been observed better with the incorporation of G-C rich DNAs. ds-DNA based devices exhibit improved rectification ratio i.e. two times higher than that of ss-DNA and three times higher than that of rr-PQT-12 with least turn-on voltage (0.56 V) or even low ideality factor (3.02), due to hot carrier injection phenomenon by assembled rr-PQT-12 to nearby nucleotide bases.

A theoretical study of charge transport properties of trifluoromethyl (-CF3) substituted naphthalene (TFMNA) molecule

We present a density functional (DFT) study of the charge transport properties of CF3-naphthalene. Nature of charge transport is investigated using parameters such as reorganization energy (X), transfer integral (t), ionization potential (IP), electron affinity (EA), and carrier mobility (μ) computed through electronic structure calculations. We observe a decrease in X and IP from 2,6-DTFMNA to 1,5-DTFMNA, whereas, the EA is found to be enhanced, as a result p-type characteristics, with mild n-type signature, in the organic semiconductor gets increased. In addition, the HOMO-LUMO gap also gets reduced inferring more charge injection through the potential barrier. The maximum hole and electron mobility values for the substituted compound are obtained to be 2.17 cm2/ Vsec & 0.20 cm2/ Vsec, respectively.

Hybrid matrix method for stable numerical analysis of the propagation of Dirac electrons in gapless bilayer graphene superlattices

Gapless bilayer graphene (GBG), like monolayer graphene, is a material system with unique properties, such as anti-Klein tunneling and intrinsic Fano resonances. These properties rely on the gapless parabolic dispersion relation and the chiral nature of bilayer graphene electrons. In addition, propagating and evanescent electron states coexist inherently in this material, giving rise to these exotic properties. In this sense, bilayer graphene is unique, since in most material systems in which Fano resonance phenomena are manifested an external source that provides extended states is required. However, from a numerical standpoint, the presence of evanescent-divergent states in the eigenfunctions linear superposition representing the Dirac spinors, leads to a numerical degradation (the so called Ωd problem) in the practical applications of the standard Coefficient Transfer Matrix (K) method used to study charge transport properties in Bilayer Graphene based multi-barrier systems. We present here a straightforward procedure based in the hybrid compliance-stiffness matrix method (H) that can overcome this numerical degradation. Our results show that in contrast to standard matrix method, the proposed H method is suitable to study the transmission and transport properties of electrons in GBG superlattice since it remains numerically stable regardless the size of the superlattice and the range of values taken by the input parameters: the energy and angle of the incident electrons, the barrier height and the thickness and number of barriers. We show that the matrix determinant can be used as a test of the numerical accuracy in real calculations.

Spectroscopic Analysis and Study of Charge Transport Properties for Pinacyanol Chloride-Organic Acceptor Complex as Potential Optoelectronics Material

Organic photoconductor, pinacyanol chloride, has been studied with infrared spectroscopy because of its thermal activation energy (Ea) and band gap (Eg = 2Ea) lying in the infrared range. Particularly, pinacyanol chloride and its charge transfer (CT) complexes with chloranil, DDQ, TCNQ and TCNE as organic acceptors are studied in details. The CT complexes are having neither two absorption edges like ternary complex having one donor and two acceptors nor binary type with Lorentzian or Gaussian envelopes. The forbidden gap is direct band gap except chloranil complex due to increase in molecular distance and CT interaction. There is imperfect nesting and partial screening determining the mid-IR envelope, which is qualitatively different from the envelopes in binary systems. There is inverted parabola in some range below this envelope. It is explained how infrared absorption is related with the applications of such organic photoconductors in optoelectronic devices.

Conductive preferential paths of hot carriers in amorphous phase-change materials

We study charge transport properties of amorphous phase-change materials (PCM) using a set of balance equations applied to a three-dimensional random network of sites. In the context of trap-limited conduction, model results are checked against experimental data on PCM devices near the limits of scaling (∼10 nm), explaining the main features of the current-voltage characteristics. The stochastic nature of the network also allows us to investigate the statistical variability of the sub-threshold PCM operation. Simulations of batches of similar samples show a standard deviation for the threshold condition of the order of few percent for the threshold voltage and of ten percent for the threshold current. The analysis of the network at the microscopic level near threshold reveals the formation of high-current paths, connecting the two contacts of the device through network nodes hosting the hottest carriers.

Muon-spin-relaxation study of organic semiconductor spiro-linked compound

We report on muon-spin-relaxation (μSR) experiment of organic semiconductor spiro-linked compound 2′,7′-bis(N,N–diphenylamino)-2-(5-(4–tert-butylphenyl)-1,3,4-oxadiazol-2-yl)-9,9-spirobifluorene (Spiro-DPO) measured at temperatures between 8 and 300K and at longitudinal fields up to 395mT in order to study charge transport properties in organic semiconductor. The μSR time spectra were analyzed by using Risch and Kehr (RK) function and it indicates a transition from one-dimensional hopping transport of charge carriers at low temperatures to two- or three-dimensional hopping transport at high temperatures (>75K).

Modeling of charge transport in polycrystalline sexithiophene from quantum charge transfer rate theory beyond the first-order perturbation

Charge mobility in polycrystalline organic semiconductors is often thermally activated, so a semiclassical Marcus charge transfer rate theory has long been used to investigate the charge transport properties of organic semiconductors. However, the classical treatment for the nuclear degrees of freedom and the first-order perturbative nature of electronic coupling in the semiclassical Marcus charge transfer rate theory is often invalid in organic semiconductors. Furthermore, traps in polycrystalline organic semiconductors are not considered during the simulations with the semiclassical Marcus charge transfer rate theory. In the present work, we propose a model to study charge transport properties in polycrystalline organic semiconductors which consist of trap-free crystallitic grains separated by boundaries between them. The charge transfer rate in grains is evaluated with a quantum charge transfer rate theory without weak electronic coupling approximation while the charge transport at grain boundaries is limited by energy barriers there. We find that a thermally activated mobility can be obtained from the quantum charge transfer rate theory when traps at grain boundaries are considered. Meanwhile, a roughly linear dependence of mobility on grain size is shown for large grain size while a rapid variation of mobility with grain size is observed when the grain size is small, which reconciles the discrepancy of the mobility versus grain size in experiments. In addition, the different mobilities for sexithiophene crystal structures in high- and low-temperature phases show that the mobility in polycrystalline organic semiconductors not only depends on the boundary property between grains but also the molecular packing in grains.

Holographic charge transport in Lifshitz black hole backgrounds

We study charge transport properties in a domain-wall geometry, whose near horizon IR geometry is a Lifshitz black hole and whose UV geometry is AdS. The action for the gauge field contains the standard Maxwell term plus the Weyl tensor coupled to Maxwell field strengths. In four dimensions we calculate the conductivity via both the membrane paradigm and Kubo’s formula. Precise agreements between both methods are obtained. Moreover, we perform an analysis of the four-dimensional electro-magnetic duality in our domain-wall background and find that the relation between the longitudinal and transverse components of the current-current correlation functions and those of the ‘dual’ counterparts holds, irrespective of the near horizon IR geometry. Conductivity at extremality is also investigated. Generalizations to higher dimensions are performed.

Modeling graphene-based nanoelectromechanical devices

We report on a theoretical study of charge transport properties of graphene nanoribbons under external mechanical stress. The influence of mechanical forces on the ribbon conductance is shown to be strongly dependent on the ribbon edge symmetry, i.e., zigzag versus armchair. In contrast to zigzag-edge nanoribbons which remain robust against high strain deformations, a stretching-induced metal-semiconductor transition is obtained for armchair-edge configurations. Our results point out that armchair edge ribbons are consequently much better suited for electromechanical applications.

Charge transfer rates in organic semiconductors beyond first-order perturbation: From weak to strong coupling regimes

Semiclassical Marcus electron transfer theory is often employed to investigate the charge transport properties of organic semiconductors. However, quite often the electronic couplings vary several orders of magnitude in organic crystals, which goes beyond the application scope of semiclassical Marcus theory with the first-order perturbative nature. In this work, we employ a generalized nonadiabatic transition state theory (GNTST) [Zhao et al., J. Phys. Chem. A 110, 8204 (2004)], which can evaluate the charge transfer rates from weak to strong couplings, to study charge transport properties in prototypical organic semiconductors: quaterthiophene and sexithiophene single crystals. By comparing with GNTST results, we find that the semiclassical Marcus theory is valid for the case of the coupling <10 meV for quaterthiophene and <5 meV for sexithiophene. It is shown that the present approach can be applied to design organic semiconductors with general electronic coupling terms. Taking oligothiophenes as examples, we find that our GNTST-calculated hole mobility is about three times as large as that from the semiclassical Marcus theory. The difference arises from the quantum nuclear tunneling and the nonperturbative effects.

Studies of Charge Transport Properties in P3HT/ZnO Composites Using Photoinduced Charge Extraction by Linearly Increasing Voltage Technique

AbstractThe charge transport properties in a mixture of regio-regular (poly 3-hexylthiophene) (RR-P3HT) and Zinc Oxide nano particle (ZnO) have been studied using the photoinduced charge extraction by linearly increasing voltage (PhotoCELIV) technique. We have studied the effect of ZnO nanoparticle size (12 nm and 50 nm) on the charge transport properties by fixing the composition ratio of P3HT/ZnO hybrid. The PhotoCELIV mobility in P3HT/50nm-ZnO at room temperature is found to be 7.8×10−5cm2/Vs at an applied electric field of 2.5 × 104 V/cm, which increases to 1.7×10−4cm2/Vs for P3HT/12nm-ZnO composite. The temperature and electric field dependence of charge mobility in these composites have been studied and analysed using Gaussian disorder formalism. The obtained results suggest that the charge transport properties in P3HT/ZnO composite, at low ZnO concentrations, can be tuned by varying the size of the nanoparticle.

Charge Transport in Single Au | Alkanedithiol | Au Junctions: Coordination Geometries and Conformational Degrees of Freedom

Recent STM molecular break-junction experiments have revealed multiple series of peaks in the conductance histograms of alkanedithiols. To resolve a current controversy, we present here an in-depth study of charge transport properties of Au|alkanedithiol|Au junctions. Conductance histograms extracted from our STM measurements unambiguously confirm features showing more than one set of junction configurations. On the basis of quantum chemistry calculations, we propose that certain combinations of different sulfur-gold couplings and trans/gauche conformations act as the driving agents. The present study may have implications for experimental methodology: whenever conductances of different junction conformations are not statistically independent, the conductance histogram technique can exhibit a single series only, even though a much larger abundance of microscopic realizations exists.

ELECTRONIC TRANSPORT AND THERMOPOWER IN APERIODIC DNA SEQUENCES

A detailed study of charge transport properties of synthetic and genomic DNA sequences is reported. Genomic sequences of the Chromosome 22, λ-bacteriophage, and D1s80 genes of Human and Pygmy chimpanzee are considered in this work, and compared with both periodic and quasiperiodic (Fibonacci) sequences of nucleotides. Charge transfer efficiency is compared for all these different sequences, and large variations in charge transfer efficiency, stemming from sequence-dependent effects, are reported. In addition, basic characteristics of tunneling currents, including contact effects, are described. Finally, the thermoelectric power of nucleobases connected in between metallic contacts at different temperatures is presented.

New Phenomena in High Mobility Organic Semiconductors

Field-effect devices on the basis of high-quality molecular single crystals have been used to study charge transport properties of two-dimensional electron and hole systems in organic semiconductor materials. The improvement of crystalline quality and purity leads to the observation of a variety of new phenomena in these materials, such as the quantum Hall effect, ballistic charge transport, or superconductivity, which are summarized in this article.

New developments in IBIC for the study of charge transport properties of radiation detector materials

A study of charge transport properties in various radiation detector materials (Si, Si(Li), CdTe, GaAs, CVD and natural diamond) has become in recent years one of the major applications of the nuclear microprobe technique IBIC. In order to extend the capabilities of IBIC, further developments of the technique were considered. By changing the projectile type and energy, different sample layers in the range between one and several hundreds of microns can be imaged. A trigger signal from simultaneously detected secondary electrons or a transmitted ion enables time-resolved IBIC imaging to be carried out. Furthermore, simultaneous STIM imaging showing areal density distributions, can be essential for the interpretation of IBIC images.