Science.gov

Sample records for charge carrier transport

  1. Analysis of Charge Carrier Transport in Organic Photovoltaic Active Layers

    NASA Astrophysics Data System (ADS)

    Han, Xu; Maroudas, Dimitrios

    2015-03-01

    We present a systematic analysis of charge carrier transport in organic photovoltaic (OPV) devices based on phenomenological, deterministic charge carrier transport models. The models describe free electron and hole transport, trapping, and detrapping, as well as geminate charge-pair dissociation and geminate and bimolecular recombination, self-consistently with Poisson's equation for the electric field in the active layer. We predict photocurrent evolution in devices with active layers of P3HT, P3HT/PMMA, and P3HT/PS, as well as P3HT/PCBM blends, and photocurrent-voltage (I-V) relations in these devices at steady state. Charge generation propensity, zero-field charge mobilities, and trapping, detrapping, and recombination rate coefficients are determined by fitting the modeling predictions to experimental measurements. We have analyzed effects of the active layer morphology for layers consisting of both pristine drop-cast films and of nanoparticle (NP) assemblies, as well as effects on device performance of insulating NP doping in conducting polymers and of specially designed interlayers placed between an electrode and the active layer. The model predictions provide valuable input toward synthesis of active layers with prescribed morphology that optimize OPV device performance.

  2. Dispersive transport of charge carriers in disordered nanostructured materials

    NASA Astrophysics Data System (ADS)

    Sibatov, R. T.; Uchaikin, V. V.

    2015-07-01

    Dispersive transport of charge carriers in disordered nanostructured semiconductors is described in terms of integral diffusion equations nonlocal in time. Transient photocurrent kinetics is analyzed for different situations. Relation to the fractional differential approach is demonstrated. Using this relation provides specifications in interpretation of the time-of-flight data. Joint influence of morphology and energy distribution of localized states is described in frames of the trap-limited advection-diffusion on a comb structure modeling a percolation cluster.

  3. Morphology and charge carrier transport in eumelanin thin films

    NASA Astrophysics Data System (ADS)

    Santato, Clara; Wuensche, Julia; Rosei, Federico

    2012-02-01

    Eumelanin is a biomolecule with important functions in the human body, animals, and plants. However, several fundamental properties of eumelanin, such as the mechanism of charge carrier transport and the supramolecular structure, are still a matter of debate. This work is the first step of a study with the long-term goal to characterize structure and charge carrier transport of eumelanin in thin film form. We compared the most common synthesis routes and processing solvents for eumelanin observing the morphology (AFM) and chemical composition (XPS) of the prepared films. Eumelanin synthesized from tyrosine by oxidation with H2O2 and deposited from dimethyl sulfoxide yielded films with a RMS roughness below 0.4 nm and an elementary composition in agreement with the eumelanin building blocks suggested in literature. A more detailed AFM study revealed a layer-by-layer growth mode for solution-processed eumelanin films. The first electrical characterization of these films in a planar two-electrode configuration and a high-humidity environment demonstrated the high complexity of charge transport in eumelanin films. The planar device geometry permits imaging the changes in the optical or morphological properties of the eumelanin film by optical microscopy and AFM. Our measurements suggest that several processes, including electrochromism and electropolymerization, contribute to determine the electroactivity of eumelanin films, depending on the applied electrical bias. Current transients over several hours support the hypothesis that ions are involved in charge transport.

  4. Charge carrier transport properties in layer structured hexagonal boron nitride

    NASA Astrophysics Data System (ADS)

    Doan, T. C.; Li, J.; Lin, J. Y.; Jiang, H. X.

    2014-10-01

    Due to its large in-plane thermal conductivity, high temperature and chemical stability, large energy band gap (˜ 6.4 eV), hexagonal boron nitride (hBN) has emerged as an important material for applications in deep ultraviolet photonic devices. Among the members of the III-nitride material system, hBN is the least studied and understood. The study of the electrical transport properties of hBN is of utmost importance with a view to realizing practical device applications. Wafer-scale hBN epilayers have been successfully synthesized by metal organic chemical deposition and their electrical transport properties have been probed by variable temperature Hall effect measurements. The results demonstrate that undoped hBN is a semiconductor exhibiting weak p-type at high temperatures (> 700 °K). The measured acceptor energy level is about 0.68 eV above the valence band. In contrast to the electrical transport properties of traditional III-nitride wide bandgap semiconductors, the temperature dependence of the hole mobility in hBN can be described by the form of μ ∝ (T/T0)-α with α = 3.02, satisfying the two-dimensional (2D) carrier transport limit dominated by the polar optical phonon scattering. This behavior is a direct consequence of the fact that hBN is a layer structured material. The optical phonon energy deduced from the temperature dependence of the hole mobility is ħω = 192 meV (or 1546 cm-1), which is consistent with values previously obtained using other techniques. The present results extend our understanding of the charge carrier transport properties beyond the traditional III-nitride semiconductors.

  5. Charge carrier transport in polycrystalline organic thin film based field effect transistors

    NASA Astrophysics Data System (ADS)

    Rani, Varsha; Sharma, Akanksha; Ghosh, Subhasis

    2016-05-01

    The charge carrier transport mechanism in polycrystalline thin film based organic field effect transistors (OFETs) has been explained using two competing models, multiple trapping and releases (MTR) model and percolation model. It has been shown that MTR model is most suitable for explaining charge carrier transport in grainy polycrystalline organic thin films. The energetic distribution of traps determined independently using Mayer-Neldel rule (MNR) is in excellent agreement with the values obtained by MTR model for copper phthalocyanine and pentacene based OFETs.

  6. Determination of charge carrier transport in radio frequency plasma polymerized aniline thin films

    NASA Astrophysics Data System (ADS)

    Sivaraman, Sajeev; Anantharaman, M. R.

    2010-02-01

    The carrier transport mechanism of polyaniline (PA) thin films prepared by radio frequency plasma polymerization is described in this paper. The mechanism of electrical conduction and carrier mobility of PA thin films for different temperatures were examined using the aluminium-PA-aluminium (Al-PA-Al) structure. It is found that the mechanism of carrier transport in these thin films is space charge limited conduction. J-V studies on an asymmetric electrode configuration using indium tin oxide (ITO) as the base electrode and Al as the upper electrode (ITO-PA-Al structure) show a diode-like behaviour with a considerable rectification ratio.

  7. Charge carrier transport and separation in pristine and nitrogen-doped graphene nanowiggle heterostructures

    DOE PAGESBeta

    Lherbier, Aurélien; Liang, Liangbo; Charlier, Jean -Christophe; Meunier, Vincent

    2015-09-03

    Electronic structure methods are combined into a multiscale framework to investigate the electronic transport properties of recently synthesized pristine and nitrogen-doped graphene nanowiggles and their heterojunctions deposited on a substrate. The real-space Kubo-Greenwood transport calculations reveal that charge carrier mobilities reach values up to 1,000 cm2 V–1 s–1 as long as the amount of substrate impurities is sufficiently low. Owing to their type-II band alignment, atomically precise heterostructures between pristine and N-doped graphene nanowiggles are predicted to be excellent candidates for charge carrier separation devices with potential in photoelectric and photocatalytic water splitting applications.

  8. Charge carrier transport and separation in pristine and nitrogen-doped graphene nanowiggle heterostructures

    SciTech Connect

    Lherbier, Aurélien; Liang, Liangbo; Charlier, Jean -Christophe; Meunier, Vincent

    2015-09-03

    Electronic structure methods are combined into a multiscale framework to investigate the electronic transport properties of recently synthesized pristine and nitrogen-doped graphene nanowiggles and their heterojunctions deposited on a substrate. The real-space Kubo-Greenwood transport calculations reveal that charge carrier mobilities reach values up to 1,000 cm2 V–1 s–1 as long as the amount of substrate impurities is sufficiently low. Owing to their type-II band alignment, atomically precise heterostructures between pristine and N-doped graphene nanowiggles are predicted to be excellent candidates for charge carrier separation devices with potential in photoelectric and photocatalytic water splitting applications.

  9. A charge carrier transport model for donor-acceptor blend layers

    NASA Astrophysics Data System (ADS)

    Fischer, Janine; Widmer, Johannes; Kleemann, Hans; Tress, Wolfgang; Koerner, Christian; Riede, Moritz; Vandewal, Koen; Leo, Karl

    2015-01-01

    Highly efficient organic solar cells typically comprise donor-acceptor blend layers facilitating effective splitting of excitons. However, the charge carrier mobility in the blends can be substantially smaller than in neat materials, hampering the device performance. Currently, available mobility models do not describe the transport in blend layers entirely. Here, we investigate hole transport in a model blend system consisting of the small molecule donor zinc phthalocyanine (ZnPc) and the acceptor fullerene C60 in different mixing ratios. The blend layer is sandwiched between p-doped organic injection layers, which prevent minority charge carrier injection and enable exploiting diffusion currents for the characterization of exponential tail states from a thickness variation of the blend layer using numerical drift-diffusion simulations. Trap-assisted recombination must be considered to correctly model the conductivity behavior of the devices, which are influenced by local electron currents in the active layer, even though the active layer is sandwiched in between p-doped contacts. We find that the density of deep tail states is largest in the devices with 1:1 mixing ratio (Et = 0.14 eV, Nt = 1.2 × 1018 cm-3) directing towards lattice disorder as the transport limiting process. A combined field and charge carrier density dependent mobility model are developed for this blend layer.

  10. A charge carrier transport model for donor-acceptor blend layers

    SciTech Connect

    Fischer, Janine Widmer, Johannes; Koerner, Christian; Vandewal, Koen; Leo, Karl; Kleemann, Hans; Tress, Wolfgang; Riede, Moritz

    2015-01-28

    Highly efficient organic solar cells typically comprise donor-acceptor blend layers facilitating effective splitting of excitons. However, the charge carrier mobility in the blends can be substantially smaller than in neat materials, hampering the device performance. Currently, available mobility models do not describe the transport in blend layers entirely. Here, we investigate hole transport in a model blend system consisting of the small molecule donor zinc phthalocyanine (ZnPc) and the acceptor fullerene C{sub 60} in different mixing ratios. The blend layer is sandwiched between p-doped organic injection layers, which prevent minority charge carrier injection and enable exploiting diffusion currents for the characterization of exponential tail states from a thickness variation of the blend layer using numerical drift-diffusion simulations. Trap-assisted recombination must be considered to correctly model the conductivity behavior of the devices, which are influenced by local electron currents in the active layer, even though the active layer is sandwiched in between p-doped contacts. We find that the density of deep tail states is largest in the devices with 1:1 mixing ratio (E{sub t} = 0.14 eV, N{sub t} = 1.2 × 10{sup 18 }cm{sup −3}) directing towards lattice disorder as the transport limiting process. A combined field and charge carrier density dependent mobility model are developed for this blend layer.

  11. Improvement of the charge-carrier transport property of polycrystalline CdTe for digital fluoroscopy

    NASA Astrophysics Data System (ADS)

    Oh, K. M.; Heo, Y. J.; Kim, D. K.; Kim, J. S.; Shin, J. W.; Lee, G. H.; Nam, S. H.

    2014-05-01

    Minimizing the radiation impact to the patient is currently an important issue in medical imaging. Particularly, in case of X-ray fluoroscopy, the patient is exposed to high X-ray dose because a large number of images is required in fluoroscopic procedures. In this regard, a direct-conversion X-ray sensor offers the advantages of high quantum efficiency, X-ray sensitivity, and high spatial resolution. In particular, an X-ray sensor in fluoroscopy operates at high frame rate, in the range from 30 to 60 image frames per second. Therefore, charge-carrier transport properties and signal lag are important factors for the development of X-ray sensors in fluoroscopy. In this study, in order to improve the characteristics of polycrystalline cadmium telluride (CdTe), CdTe films were prepared by thermal evaporation and RF sputtering. The deposition was conducted to form a CdTeO3 layer on top of a CdTe film. The role of CdTeO3 is not only to improve the charge-carrier transport by increasing the life-time but also to reduce the leakage current of CdTe films by acting as a passivation layer. In this paper, to establish the effect of a thin oxide layer on top of a CdTe film, the morphological and electrical properties including charge-carrier transport and signal lag were investigated by means of X-ray diffraction, X-ray photoemission spectroscopy, and resistivity measurements.

  12. Spiro-OMeTAD single crystals: Remarkably enhanced charge-carrier transport via mesoscale ordering.

    PubMed

    Shi, Dong; Qin, Xiang; Li, Yuan; He, Yao; Zhong, Cheng; Pan, Jun; Dong, Huanli; Xu, Wei; Li, Tao; Hu, Wenping; Brédas, Jean-Luc; Bakr, Osman M

    2016-04-01

    We report the crystal structure and hole-transport mechanism in spiro-OMeTAD [2,2',7,7'-tetrakis(N,N-di-p-methoxyphenyl-amine)9,9'-spirobifluorene], the dominant hole-transporting material in perovskite and solid-state dye-sensitized solar cells. Despite spiro-OMeTAD's paramount role in such devices, its crystal structure was unknown because of highly disordered solution-processed films; the hole-transport pathways remained ill-defined and the charge carrier mobilities were low, posing a major bottleneck for advancing cell efficiencies. We devised an antisolvent crystallization strategy to grow single crystals of spiro-OMeTAD, which allowed us to experimentally elucidate its molecular packing and transport properties. Electronic structure calculations enabled us to map spiro-OMeTAD's intermolecular charge-hopping pathways. Promisingly, single-crystal mobilities were found to exceed their thin-film counterparts by three orders of magnitude. Our findings underscore mesoscale ordering as a key strategy to achieving breakthroughs in hole-transport material engineering of solar cells. PMID:27152342

  13. Spiro-OMeTAD single crystals: Remarkably enhanced charge-carrier transport via mesoscale ordering

    PubMed Central

    Shi, Dong; Qin, Xiang; Li, Yuan; He, Yao; Zhong, Cheng; Pan, Jun; Dong, Huanli; Xu, Wei; Li, Tao; Hu, Wenping; Brédas, Jean-Luc; Bakr, Osman M.

    2016-01-01

    We report the crystal structure and hole-transport mechanism in spiro-OMeTAD [2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenyl-amine)9,9′-spirobifluorene], the dominant hole-transporting material in perovskite and solid-state dye-sensitized solar cells. Despite spiro-OMeTAD’s paramount role in such devices, its crystal structure was unknown because of highly disordered solution-processed films; the hole-transport pathways remained ill-defined and the charge carrier mobilities were low, posing a major bottleneck for advancing cell efficiencies. We devised an antisolvent crystallization strategy to grow single crystals of spiro-OMeTAD, which allowed us to experimentally elucidate its molecular packing and transport properties. Electronic structure calculations enabled us to map spiro-OMeTAD’s intermolecular charge-hopping pathways. Promisingly, single-crystal mobilities were found to exceed their thin-film counterparts by three orders of magnitude. Our findings underscore mesoscale ordering as a key strategy to achieving breakthroughs in hole-transport material engineering of solar cells. PMID:27152342

  14. Bulk charge carrier transport in push-pull type organic semiconductor.

    PubMed

    Karak, Supravat; Liu, Feng; Russell, Thomas P; Duzhko, Volodimyr V

    2014-12-10

    Operation of organic electronic and optoelectronic devices relies on charge transport properties of active layer materials. The magnitude of charge carrier mobility, a key efficiency metrics of charge transport properties, is determined by the chemical structure of molecular units and their crystallographic packing motifs, as well as strongly depends on the film fabrication approaches that produce films with different degrees of anisotropy and structural order. Probed by the time-of-flight and grazing incidence X-ray diffraction techniques, bulk charge carrier transport, molecular packing, and film morphology in different structural phases of push-pull type organic semiconductor, 7,7'-(4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b']dithiophene-2,6-diyl)bis(6-fluoro-4-(5'-hexyl-[2,2'-bithiophen]-5yl)benzo[c][1,2,5] thiadiazole), one of the most efficient small-molecule photovoltaic materials to-date, are described herein. In the isotropic phase, the material is ambipolar with high mobilities for a fluid state. The electron and hole mobilities at the phase onset at 210.78 °C are 1.0 × 10(-3) cm(2)/(V s) and 6.5 × 10(-4) cm(2)/(V s), respectively. Analysis of the temperature and electric field dependences of the mobilities in the framework of Gaussian disorder formalism suggests larger energetic and positional disorder for electron transport sites. Below 210 °C, crystallization into a polycrystalline film with a triclinic unit cell symmetry and high degree of anisotropy leads to a 10-fold increase of hole mobility. The mobility is limited by the charge transfer along the direction of branched alkyl side chains. Below 90 °C, faster cooling rates produce even higher hole mobilities up to 2 × 10(-2) cm(2)/(V s) at 25 °C because of the more isotropic orientations of crystalline domains. These properties facilitate in understanding efficient material performance in photovoltaic devices and will guide further development of materials and devices. PMID:25393015

  15. Direct Observation of the Hole Carriers in DNA Photoinduced Charge Transport.

    PubMed

    Harris, Michelle A; Mishra, Ashutosh Kumar; Young, Ryan M; Brown, Kristen E; Wasielewski, Michael R; Lewis, Frederick D

    2016-05-01

    The excited state behavior of DNA hairpins possessing a diphenylacetylenedicarboxamide (DPA) linker separated from a single guanine-cytosine (G-C) base pair by zero-to-six adenine-thymine (A-T) base pairs has been investigated. In the case of hairpins with zero or one A-T separating DPA and G, formation of both DPA anion radical (DPA(-•)) and G cation radical (G(+•)) are directly observed and characterized by their transient absorption and stimulated Raman spectra. For hairpins with two or more intervening A-T, the transient absorption spectra of DPA(-•) and the adenine polaron (An(+•)) are observed. In addition to characterization of the hole carriers, the dynamics of each step in the charge separation and charge recombination process as well as the overall efficiency of charge separation have been determined, thus providing a complete account of the mechanism and dynamics of photoinduced charge transport in these DNA hairpins. PMID:27082662

  16. A new approach to calculate charge carrier transport mobility in organic molecular crystals from imaginary time path integral simulations

    SciTech Connect

    Song, Linze; Shi, Qiang

    2015-05-07

    We present a new non-perturbative method to calculate the charge carrier mobility using the imaginary time path integral approach, which is based on the Kubo formula for the conductivity, and a saddle point approximation to perform the analytic continuation. The new method is first tested using a benchmark calculation from the numerical exact hierarchical equations of motion method. Imaginary time path integral Monte Carlo simulations are then performed to explore the temperature dependence of charge carrier delocalization and mobility in organic molecular crystals (OMCs) within the Holstein and Holstein-Peierls models. The effects of nonlocal electron-phonon interaction on mobility in different charge transport regimes are also investigated.

  17. A new approach to calculate charge carrier transport mobility in organic molecular crystals from imaginary time path integral simulations

    NASA Astrophysics Data System (ADS)

    Song, Linze; Shi, Qiang

    2015-05-01

    We present a new non-perturbative method to calculate the charge carrier mobility using the imaginary time path integral approach, which is based on the Kubo formula for the conductivity, and a saddle point approximation to perform the analytic continuation. The new method is first tested using a benchmark calculation from the numerical exact hierarchical equations of motion method. Imaginary time path integral Monte Carlo simulations are then performed to explore the temperature dependence of charge carrier delocalization and mobility in organic molecular crystals (OMCs) within the Holstein and Holstein-Peierls models. The effects of nonlocal electron-phonon interaction on mobility in different charge transport regimes are also investigated.

  18. Deep localized distortion of alternating bonds and reduced transport of charged carriers in conjugated polymers under photoexcitation

    NASA Astrophysics Data System (ADS)

    Wang, Cong; Jiang, De-Yao; Chen, Ren-Ai; Li, Sheng; George, Thomas F.

    2014-12-01

    In a real bulk heterojunction polymer solar cell, after exciton separation in the heterojunction, the resulting negatively-charged carrier, a polaron, moves along the polymer chain of the acceptor, which is believed to be of significance for the charged carrier transport properties in a polymer solar cell. During the negative polaron transport, due to the external light field, the polaron, which is re-excited and induces deep localization, also forms a new local distortion of the alternating bonds. It is revealed that the excited polaron moves more slowly than the ground-state polaron. Furthermore, the velocity of the polaron moving along the polymer chain is crucially dependent on the photoexcitation. With an increase in the intensity of the optical field, the localization of the excited polaron will be deepened, with a decrease of the polaron's velocity. It is discovered that, for a charged carrier, photoexcitation is a significant factor in reducing the efficiency during the charged carrier transport in polymer solar cells. Mostly, the deep trapping effect of charged carrier in composite conjugated polymer solar cell presents an opportunity for the future application in nanoscale memory and imaging devices.

  19. Relationship between defect density and charge carrier transport in amorphous and microcrystalline silicon

    SciTech Connect

    Astakhov, Oleksandr; Carius, Reinhard; Finger, Friedhelm; Petrusenko, Yuri; Borysenko, Valery; Barankov, Dmytro

    2009-03-01

    The influence of dangling-bond defects and the position of the Fermi level on the charge carrier transport properties in undoped and phosphorous doped thin-film silicon with structure compositions all the way from highly crystalline to amorphous is investigated. The dangling-bond density is varied reproducibly over several orders of magnitude by electron bombardment and subsequent annealing. The defects are investigated by electron-spin-resonance and photoconductivity spectroscopies. Comparing intrinsic amorphous and microcrystalline silicon, it is found that the relationship between defect density and photoconductivity is different in both undoped materials, while a similar strong influence of the position of the Fermi level on photoconductivity via the charge carrier lifetime is found in the doped materials. The latter allows a quantitative determination of the value of the transport gap energy in microcrystalline silicon. The photoconductivity in intrinsic microcrystalline silicon is, on one hand, considerably less affected by the bombardment but, on the other hand, does not generally recover with annealing of the defects and is independent from the spin density which itself can be annealed back to the as-deposited level. For amorphous silicon and material prepared close to the crystalline growth regime, the results for nonequilibrium transport fit perfectly to a recombination model based on direct capture into neutral dangling bonds over a wide range of defect densities. For the heterogeneous microcrystalline silicon, this model fails completely. The application of photoconductivity spectroscopy in the constant photocurrent mode (CPM) is explored for the entire structure composition range over a wide variation in defect densities. For amorphous silicon previously reported linear correlation between the spin density and the subgap absorption is confirmed for defect densities below 10{sup 18} cm{sup -3}. Beyond this defect level, a sublinear relation is found i

  20. Facet-selective charge carrier transport, deactivation mechanism and stabilization of a Cu2O photo-electro-catalyst.

    PubMed

    Li, Yang; Yun, Xiaogang; Chen, Hong; Zhang, Wenqin; Li, Yongdan

    2016-03-14

    A facet-dependent photo-deactivation mechanism of Cu2O was verified and reported, which is caused by the facet-dependent charge carrier transport. During irradiation, the {100} and {110} crystal facets are selectively corroded by the photo-generated holes, while the {111} facets are comparatively stable. PMID:26898270

  1. Insights from transport modeling of unusual charge carrier behavior of PDTSiTzTz:PC71BM bulk heterojunction materials

    NASA Astrophysics Data System (ADS)

    Slobodyan, Oleksiy; Moench, Sarah; Liang, Kelly; Danielson, Eric; Holliday, Bradley; Dodabalapur, Ananth

    2015-03-01

    Development of hole-transporting copolymers for use in bulk heterojunctions (BHJs) has significantly improved organic solar cell performance. Despite advances on the materials side, the physics of charge carrier transport remains unsettled. Intrigued by its ability to maintain high fill factors in thick active layers, we studied the copolymer poly[2-(5-(4,4-dioctyl-4H-silolo[3,2-b:4,5-b’]dithiophen-2-yl)-3-tetradecylthiophen-2-yl)- 5-(3-tetradecylthiophen-2-yl)thiazolo[5,4-d]thiazole] (PDTSiTzTz) blended with PC71BM. Results show mobilities which are carrier-concentration-dependent and characterized by a negative Poole-Frenkel effect. Such behavior is not described by current carrier transport models. Established transport mechanisms like multiple-trap-and-release or variable range hopping yield dependence of mobility on carrier concentration. However, a more basic model like Gaussian distribution model (GDM) is needed to produce the negative Poole-Frenkel effect, though GDM cannot describe carrier-concentration-dependent mobility. We have combined key aspects of existing models to create a unified transport model capable of describing phenomena observed in PDTSiTzTz:PC71BM. This model can be used to address open questions about transport physics of organic BHJ materials. U.S. Department of Energy, Award Number DE-SC0001091.

  2. Electric field dependence of charge carrier hopping transport within the random energy landscape in an organic field effect transistor

    NASA Astrophysics Data System (ADS)

    Fishchuk, I. I.; Kadashchuk, A.; Ullah, Mujeeb; Sitter, H.; Pivrikas, A.; Genoe, J.; Bässler, H.

    2012-07-01

    We extended our analytical effective medium theory [Phys. Rev. BPRBMDO0163-182910.1103/PhysRevB.81.045202 81, 045202 (2010)] to describe the temperature-dependent hopping charge carrier mobility at arbitrary electric fields in the large carrier density regime. Special emphasis was made to analyze the influence of the lateral electric field on the Meyer-Neldel (MN) phenomenon observed when studying the charge mobilities in thin-film organic field-effect transistors (OFET). Our calculations are based on the average hopping transition time approach, generalized for large carrier concentration limit finite fields, and taking into account also spatial energy correlations. The calculated electric field dependences of the hopping mobility at large carrier concentrations are in good agreement with previous computer simulations data. The shift of the MN temperature in an OFET upon applied electric field is shown to be a consequence of the spatial energy correlation in the organic semiconductor film. Our calculations show that the phenomenological Gill equation is clearly inappropriate for describing conventional charge carrier transport at low carrier concentrations. On the other hand a Gill-type behavior has been observed in a temperature range relevant for measurements of the charge carrier mobility in OFET structures. Since the present model is not limited to zero-field mobility, it allows a more accurate evaluation of important material parameters from experimental data measured at a given electric field. In particular, we showed that both the MN and Gill temperature can be used for estimating the width of the density of states distribution.

  3. A new approach to calculate charge carrier transport mobility in organic molecular crystals from imaginary time path integral simulations.

    PubMed

    Song, Linze; Shi, Qiang

    2015-05-01

    We present a new non-perturbative method to calculate the charge carrier mobility using the imaginary time path integral approach, which is based on the Kubo formula for the conductivity, and a saddle point approximation to perform the analytic continuation. The new method is first tested using a benchmark calculation from the numerical exact hierarchical equations of motion method. Imaginary time path integral Monte Carlo simulations are then performed to explore the temperature dependence of charge carrier delocalization and mobility in organic molecular crystals (OMCs) within the Holstein and Holstein-Peierls models. The effects of nonlocal electron-phonon interaction on mobility in different charge transport regimes are also investigated. PMID:25956086

  4. A quantitative model for charge carrier transport, trapping and recombination in nanocrystal-based solar cells

    NASA Astrophysics Data System (ADS)

    Bozyigit, Deniz; Lin, Weyde M. M.; Yazdani, Nuri; Yarema, Olesya; Wood, Vanessa

    2015-01-01

    Improving devices incorporating solution-processed nanocrystal-based semiconductors requires a better understanding of charge transport in these complex, inorganic-organic materials. Here we perform a systematic study on PbS nanocrystal-based diodes using temperature-dependent current-voltage characterization and thermal admittance spectroscopy to develop a model for charge transport that is applicable to different nanocrystal-solids and device architectures. Our analysis confirms that charge transport occurs in states that derive from the quantum-confined electronic levels of the individual nanocrystals and is governed by diffusion-controlled trap-assisted recombination. The current is limited not by the Schottky effect, but by Fermi-level pinning because of trap states that is independent of the electrode-nanocrystal interface. Our model successfully explains the non-trivial trends in charge transport as a function of nanocrystal size and the origins of the trade-offs facing the optimization of nanocrystal-based solar cells. We use the insights from our charge transport model to formulate design guidelines for engineering higher-performance nanocrystal-based devices.

  5. A quantitative model for charge carrier transport, trapping and recombination in nanocrystal-based solar cells

    PubMed Central

    Bozyigit, Deniz; Lin, Weyde M. M.; Yazdani, Nuri; Yarema, Olesya; Wood, Vanessa

    2015-01-01

    Improving devices incorporating solution-processed nanocrystal-based semiconductors requires a better understanding of charge transport in these complex, inorganic–organic materials. Here we perform a systematic study on PbS nanocrystal-based diodes using temperature-dependent current–voltage characterization and thermal admittance spectroscopy to develop a model for charge transport that is applicable to different nanocrystal-solids and device architectures. Our analysis confirms that charge transport occurs in states that derive from the quantum-confined electronic levels of the individual nanocrystals and is governed by diffusion-controlled trap-assisted recombination. The current is limited not by the Schottky effect, but by Fermi-level pinning because of trap states that is independent of the electrode–nanocrystal interface. Our model successfully explains the non-trivial trends in charge transport as a function of nanocrystal size and the origins of the trade-offs facing the optimization of nanocrystal-based solar cells. We use the insights from our charge transport model to formulate design guidelines for engineering higher-performance nanocrystal-based devices. PMID:25625647

  6. FOB-SH: Fragment orbital-based surface hopping for charge carrier transport in organic and biological molecules and materials

    NASA Astrophysics Data System (ADS)

    Spencer, J.; Gajdos, F.; Blumberger, J.

    2016-08-01

    We introduce a fragment orbital-based fewest switches surface hopping method, FOB-SH, designed to efficiently simulate charge carrier transport in strongly fluctuating condensed phase systems such as organic semiconductors and biomolecules. The charge carrier wavefunction is expanded and the electronic Hamiltonian constructed in a set of singly occupied molecular orbitals of the molecular sites that mediate the charge transfer. Diagonal elements of the electronic Hamiltonian (site energies) are obtained from a force field, whereas the off-diagonal or electronic coupling matrix elements are obtained using our recently developed analytic overlap method. We derive a general expression for the exact forces on the adiabatic ground and excited electronic state surfaces from the nuclear gradients of the charge localized electronic states. Applications to electron hole transfer in a model ethylene dimer and through a chain of ten model ethylenes validate our implementation and demonstrate its computational efficiency. On the larger system, we calculate the qualitative behaviour of charge mobility with change in temperature T for different regimes of the intermolecular electronic coupling. For small couplings, FOB-SH predicts a crossover from a thermally activated regime at low temperatures to a band-like transport regime at higher temperatures. For higher electronic couplings, the thermally activated regime disappears and the mobility decreases according to a power law. This is interpreted by a gradual loss in probability for resonance between the sites as the temperature increases. The polaron hopping model solved for the same system gives a qualitatively different result and underestimates the mobility decay at higher temperatures. Taken together, the FOB-SH methodology introduced here shows promise for a realistic investigation of charge carrier transport in complex organic, aqueous, and biological systems.

  7. Photogeneration and transport of charge carriers in hybrid materials of conjugated polymers and dye-sensitized TiO2

    NASA Astrophysics Data System (ADS)

    Däubler, T. K.; Glowacki, I.; Scherf, U.; Ulanski, J.; Hörhold, H.-H.; Neher, D.

    1999-12-01

    Steady state photoconductivity and current-voltage (I-V) experiments are performed on solid films of organic/inorganic composites of dye-sensitized TiO2 in combination with poly(N-vinylcarbazole) (PVK), a ladder-type PPP and a soluble PPV derivative. The I-V characteristics of the composites in the dark are explained by the formation of percolation networks of nanoparticles between the electrodes. Photoaction spectra of the devices prove that the photogeneration of charge carriers is significantly enhanced and spectrally broadened only if electron transfer from the polymer to the dye is possible. Increasing the concentration of the nanoparticles in the hybrid materials changes the spectral shape of the photoresponse. For high TiO2 contents signatures due to the absorption of the Ruthenium dye can be observed. The different electronic properties of anatase/brookite TiO2 and rutile TiO2 have only minor effects on the generation of charge carriers and on the shape of the photoaction spectra. Indeed, photocurrents are more related to the Brunauer—Emmett-Teller surface area of the nanoparticles and thus, to the amount of dye adsorbed. Charge collection efficiencies exceeding 100%, observed for both bias directions, can be explained by photoconductivity gain. It is proposed that recombination is reduced by transport of the oppositely charged carriers in two different phases.

  8. Localized Charge Carrier Transport Properties of Zn1- x Ni x O/NiO Two-Phase Composites

    NASA Astrophysics Data System (ADS)

    Joshi, D. C.; Dasari, K.; Nayak, S.; Palai, R.; Suresh, P.; Thota, S.

    2016-04-01

    We report the localized charge carrier transport of two-phase composite Zn1- x Ni x O/NiO (0 ≤ x ≤ 1) using the temperature dependence of ac-resistivity ρ ac(T) across the Néel temperature T N (= 523 K) of nickel oxide. Our results provide strong evidence to the variable range hopping of charge carriers between the localized states through a mechanism involving spin-dependent activation energies. The temperature variation of carrier hopping energy ɛ h(T) and nearest-neighbor exchange-coupling parameter J ij(T) evaluated from the small poleron model exhibits a well-defined anomaly across T N. For all the composite systems, the average exchange-coupling parameter (J ij)AVG nearly equals to 70 meV which is slightly greater than the 60-meV exciton binding energy of pure zinc oxide. The magnitudes of ɛ h (˜0.17 eV) and J ij (˜11 meV) of pure NiO synthesized under oxygen-rich conditions are consistent with the previously reported theoretical estimation based on Green's function analysis. A systematic correlation between the oxygen stoichiometry and, ɛ h(T) and J ij(T) is discussed.

  9. Thermal influence on charge carrier transport in solar cells based on GaAs PN junctions

    NASA Astrophysics Data System (ADS)

    Osses-Márquez, Juan; Calderón-Muñoz, Williams R.

    2014-10-01

    The electron and hole one-dimensional transport in a solar cell based on a Gallium Arsenide (GaAs) PN junction and its dependency with electron and lattice temperatures are studied here. Electrons and heat transport are treated on an equal footing, and a cell operating at high temperatures using concentrators is considered. The equations of a two-temperature hydrodynamic model are written in terms of asymptotic expansions for the dependent variables with the electron Reynolds number as a perturbation parameter. The dependency of the electron and hole densities through the junction with the temperature is analyzed solving the steady-state model at low Reynolds numbers. Lattice temperature distribution throughout the device is obtained considering the change of kinetic energy of electrons due to interactions with the lattice and heat absorbed from sunlight. In terms of performance, higher values of power output are obtained with low lattice temperature and hot energy carriers. This modeling contributes to improve the design of heat exchange devices and thermal management strategies in photovoltaic technologies.

  10. Thermal influence on charge carrier transport in solar cells based on GaAs PN junctions

    SciTech Connect

    Osses-Márquez, Juan; Calderón-Muñoz, Williams R.

    2014-10-21

    The electron and hole one-dimensional transport in a solar cell based on a Gallium Arsenide (GaAs) PN junction and its dependency with electron and lattice temperatures are studied here. Electrons and heat transport are treated on an equal footing, and a cell operating at high temperatures using concentrators is considered. The equations of a two-temperature hydrodynamic model are written in terms of asymptotic expansions for the dependent variables with the electron Reynolds number as a perturbation parameter. The dependency of the electron and hole densities through the junction with the temperature is analyzed solving the steady-state model at low Reynolds numbers. Lattice temperature distribution throughout the device is obtained considering the change of kinetic energy of electrons due to interactions with the lattice and heat absorbed from sunlight. In terms of performance, higher values of power output are obtained with low lattice temperature and hot energy carriers. This modeling contributes to improve the design of heat exchange devices and thermal management strategies in photovoltaic technologies.

  11. Charge-carrier transport and recombination in heteroepitaxial CdTe

    SciTech Connect

    Kuciauskas, Darius Farrell, Stuart; Dippo, Pat; Moseley, John; Moutinho, Helio; Li, Jian V.; Allende Motz, A. M.; Kanevce, Ana; Zaunbrecher, Katherine; Gessert, Timothy A.; Levi, Dean H.; Metzger, Wyatt K.; Colegrove, Eric; Sivananthan, S.

    2014-09-28

    We analyze charge-carrier dynamics using time-resolved spectroscopy and varying epitaxial CdTe thickness in undoped heteroepitaxial CdTe/ZnTe/Si. By employing one-photon and nonlinear two-photon excitation, we assess surface, interface, and bulk recombination. Two-photon excitation with a focused laser beam enables characterization of recombination velocity at the buried epilayer/substrate interface, 17.5 μm from the sample surface. Measurements with a focused two-photon excitation beam also indicate a fast diffusion component, from which we estimate an electron mobility of 650 cm² (Vs)⁻¹ and diffusion coefficient D of 17 cm² s⁻¹. We find limiting recombination at the epitaxial film surface (surface recombination velocity Ssurface = (2.8 ± 0.3) × 10⁵cm s ⁻¹) and at the heteroepitaxial interface (interface recombination velocity Sinterface = (4.8 ± 0.5) × 10⁵ cm s⁻¹). The results demonstrate that reducing surface and interface recombination velocity is critical for photovoltaic solar cells and electronic devices that employ epitaxial CdTe.

  12. The Effect of Dynamical Image Forces on The Transport Properties of Charge Carriers and Excitons in Metal-Semiconductor Nanostructures

    NASA Astrophysics Data System (ADS)

    Cherqui, Charles

    We examine coupled metal nanoparticle/semiconductor hybrid nano-stuctures and analyze the effect that the surface response metal nanoparticles (MNP) has on the transport properties of the system. This analysis is accomplished by treating surface plasmons as quantum oscillators. We find that charge carriers traveling in the nearby semiconductors experience a repulsion due to the ground state energy of the quantum SP (QSP). This effect is shown to be the quantum analogue of the ponderomotive effect found in plasma physics. We then extend the theory to examine the transport properties of carbon nano-tube excitons in the presence of localized SPs and show that this system maps onto a Fano-Anderson Hamiltonian. Through numerical simulation, we show that the emission patterns of the system are severely modified by the presence of localized surface plasmons.

  13. Carrier separation and charge transport characteristics of reduced graphene oxide supported visible-light active photocatalysts.

    PubMed

    Vinoth, Ramalingam; Karthik, Peramaiah; Muthamizhchelvan, Chellamuthu; Neppolian, Bernaurdshaw; Ashokkumar, Muthupandian

    2016-02-21

    Extending the absorption to the visible region by tuning the optical band-gap of semiconductors and preventing charge carrier recombination are important parameters to achieve a higher efficiency in the field of photocatalysis. The inclusion of reduced graphene oxide (rGO) support in photocatalysts is one of the key strategies to address the above-mentioned issues. In this study, rGO supported AgI-mesoTiO2 photocatalysts were synthesized using a sonochemical approach. The physical effects of ultrasound not only improved the crystallinity of AgI-mesoTiO2 but also increased the surface area and loading of the AgI-mesoTiO2 nanocomposite on rGO sheets. The low intense oxygen functionalities (C-O-C and COOH groups) peak observed in the high resolution C1s spectrum of a hybrid AgI-mesoTiO2-rGO photocatalyst clearly confirmed the successful reduction of graphene oxide (GO) to rGO. The interfacial charge transfer between the rGO and the p-n junction of heterostructured photocatalysts has decreased the band-gap of the photocatalyst from 2.80 to 2.65 eV. Importantly, the integration of rGO into AgI-mesoTiO2 composites serves as a carrier separation centre and provides further insight into the electron transfer pathways of heterostructured nanocomposites. The individual effects of photo-generated electrons and holes over rGO on the photocatalytic degradation efficiency of rhodamine (RhB) and methyl orange (MO) using AgI-mesoTiO2-rGO photocatalysts were also studied. Our experimental results revealed that photo-generated superoxide (O2(-)˙) radicals are the main reactive species for the degradation of MO, whereas photo-generated holes (h(+)) are responsible for the degradation of RhB. As a result, 60% enhancement in MO degradation was observed in the presence of rGO in comparison to that of the pure AgI-mesoTiO2 photocatalyst. This is due to the good electron acceptor and the ultrafast electron transfer properties of rGO that can effectively reduce the molecular oxygen to

  14. Theoretical investigation of fluorination effect on the charge carrier transport properties of fused anthra-tetrathiophene and its derivatives.

    PubMed

    Yin, Jun; Chaitanya, Kadali; Ju, Xue-Hai

    2016-03-01

    The crystal structures of known anthra-tetrathiophene (ATT) and its three fluorinated derivatives (ATT1, ATT2 and ATT3) were predicted by the Monte Carlo-simulated annealing method with the embedded electrostatic potential (ESP) charges. The most stable crystal structures were further optimized by the density functional theory with the dispersion energy (DFT-D) method. In addition, the effect of the electron-withdrawing fluorine atoms on the molecular geometry, molecular stacking, electronic and transport properties of title compounds were investigated by the density functional theory and the incoherent charge-hopping model. The calculated results show that the introduction of fluorine atoms does not affect the molecular planarity but decreases the HOMO-LUMO gap, which is beneficial to electron injection and provides more charge carrier stabilization. The improved electron mobility from ATT to ATT3 is attributed to the favorable molecular packing with strong π-π interaction and the short stacking distance. ATT2 and ATT3 exhibit remarkable angular dependence of mobilities and anisotropic behaviors. The band structures reveal that all the paths with larger transfer integrals are along the directions of large dispersions in the valence band (VB) and conduction band (CB). ATT3 has the largest electron mobility (0.48 cm(2)V(-1)s(-1)) among the four compounds, indicating that fluorination is an effective approach to improve electron transport. PMID:26774641

  15. Charge Carrier Transport Through the Interface Between Hybrid Electrodes and Organic Materials in Flexible Organic Light Emitting Diodes.

    PubMed

    Zhou, Huanyu; Cheong, Hahn-Gil; Park, Jin-Woo

    2016-05-01

    We investigated the electronic properties of composite-type hybrid transparent conductive electrodes (h-TCEs) based on Ag nanowire networks (AgNWs) and indium tin oxide (ITO). These h-TCEs were developed to replace ITO, and their mechanical flexibility is superior to that of ITO. However, the characteristics of charge carriers and the mechanism of charge-carrier transport through the interface between the h-TCE and an organic material are not well understood when the h-TCE is used as the anode in a flexible organic light-emitting diode (f-OLED). AgNWs were spin coated onto polymer substrates, and ITO was sputtered atop the AgNWs. The electronic energy structures of h-TCEs were investigated by ultraviolet photoelectron spectroscopy. f-OLEDs were fabricated on both h-TCEs and ITO for comparison. The chemical bond formation at the interface between the h-TCE and the organic layer in f-OLEDs was investigated by X-ray photoelectron spectroscopy. The performances of f-OLEDs were compared based on the analysis results. PMID:27483896

  16. Charge carrier transport mechanisms in perovskite CdTiO{sub 3} fibers

    SciTech Connect

    Imran, Z.; Rafiq, M. A. Hasan, M. M.

    2014-06-15

    Electrical transport properties of electrospun cadmium titanate (CdTiO{sub 3}) fibers have been investigated using ac and dc measurements. Air annealing of as spun fibers at 1000 °C yielded the single phase perovskite fibers having diameter ∼600 nm - 800 nm. Both the ac and dc electrical measurements were carried out at temperatures from 200 K – 420 K. The complex impedance plane plots revealed a single semicircular arc which indicates the interfacial effect due to grain boundaries of fibers. The dielectric properties obey the Maxwell-Wagner theory of interfacial polarization. In dc transport study at low voltages, data show Ohmic like behavior followed by space charge limited current (SCLC) with traps at higher voltages at all temperatures (200 K – 420 K). Trap density in our fibers system is N{sub t} = 6.27 × 10{sup 17} /cm{sup 3}. Conduction mechanism in the sample is governed by 3-D variable range hopping (VRH) from 200 K – 300 K. The localized density of states were found to be N(E{sub F}) = 5.51 × 10{sup 21} eV{sup −1} cm{sup −3} at 2 V. Other VRH parameters such as hopping distance (R{sub hop}) and hopping energy (W{sub hop}) were also calculated. In the high temperature range of 320 K – 420 K, conductivity follows the Arrhenius law. The activation energy found at 2 V is 0.10 eV. Temperature dependent and higher values of dielectric constant make the perovskite CdTiO{sub 3} fibers efficient material for capacitive energy storage devices.

  17. Anisotropic charge carrier transport in free-standing hexagonal boron nitride thin films

    NASA Astrophysics Data System (ADS)

    Dahal, Rajendra; Ahmed, Kawser; Woei Wu, Jia; Weltz, Adam; Jian-Qiang Lu, James; Danon, Yaron; Bhat, Ishwara B.

    2016-06-01

    The in-plane and out-of-plane mobility–lifetime products of electrons and holes in free-standing hexagonal boron nitride (hBN) films are extracted from current–voltage characteristics of metal–hBN–metal structures measured under external excitations. The in-plane mobility–lifetime products for electrons and holes are ∼2.8 × 10‑5 and ∼4.85 × 10‑6 cm2/V, measured from lateral carrier collection, whereas the out-of-plane mobility–lifetime products for electrons and holes are ∼5.8 × 10‑8 and ∼6.1 × 10‑9 cm2/V, measured from vertical carrier collection, respectively. The mobility–lifetime product is a few orders of magnitude higher along the plane than along the out of plane in hBN films.

  18. Charge carrier transport in thin films of colloidal CdSe quantum rods

    NASA Astrophysics Data System (ADS)

    Persano, A.; Leo, G.; Manna, L.; Cola, A.

    2008-10-01

    Phototransport properties of organically capped colloidal CdSe quantum rod thin films deposited by spin coating are studied in air at room temperature in planar electrode configuration. Under optical excitation, the observed current-voltage characteristics and current transients are well described by a resonant tunneling model. A significant and irreversible current quenching of the photoresponse occurs with either the aging of the samples or the flowing of the current itself when above few picoamperes. The process, which is still interpreted in the frame of the model, can be attributed to the charge trapping by the defect states at the barrier between rods with a consequent increase in the barrier height.

  19. Analysis of carrier transport and carrier trapping in organic diodes with polyimide-6,13-Bis(triisopropylsilylethynyl)pentacene double-layer by charge modulation spectroscopy and optical second harmonic generation measurement

    SciTech Connect

    Lim, Eunju E-mail: taguchi.d.aa@m.titech.ac.jp; Taguchi, Dai E-mail: taguchi.d.aa@m.titech.ac.jp Iwamoto, Mitsumasa E-mail: taguchi.d.aa@m.titech.ac.jp

    2014-08-18

    We studied the carrier transport and carrier trapping in indium tin oxide/polyimide (PI)/6,13-Bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene)/Au diodes by using charge modulation spectroscopy (CMS) and time-resolved electric field induced optical second harmonic generation (TR-EFISHG) measurements. TR-EFISHG directly probes the spatial carrier behaviors in the diodes, and CMS is useful in explaining the carrier motion with respect to energy. The results clearly indicate that the injected carriers move across TIPS-pentacene thorough the molecular energy states of TIPS-pentacene and accumulate at the PI/TIPS-pentacene interface. However, some carriers are trapped in the PI layers. These findings take into account the capacitance-voltage and current-voltage characteristics of the diodes.

  20. Charge-carrier transport mechanisms in composites containing carbon-nanotube inclusions

    SciTech Connect

    Usanov, D. A. Skripal’, A. V.; Romanov, A. V.

    2015-12-15

    From the microwave-radiation transmittance and reflectance spectra, the temperature dependence of the complex permittivity of carbon nanotubes, subjected to high-temperature annealing, and composite materials produced on their basis is determined. The electron transport mechanisms in composites with inclusions of unannealed carbon nanotubes and nanotubes subjected to high-temperature annealing are determined. The influence of the annealing temperature on the parameters that are characteristic of these mechanisms and control the temperature dependence of the conductivity of multiwall carbon nanotubes is established.

  1. Effective Charge Carrier Utilization in Photocatalytic Conversions.

    PubMed

    Zhang, Peng; Wang, Tuo; Chang, Xiaoxia; Gong, Jinlong

    2016-05-17

    Continuous efforts have been devoted to searching for sustainable energy resources to alleviate the upcoming energy crises. Among various types of new energy resources, solar energy has been considered as one of the most promising choices, since it is clean, sustainable, and safe. Moreover, solar energy is the most abundant renewable energy, with a total power of 173 000 terawatts striking Earth continuously. Conversion of solar energy into chemical energy, which could potentially provide continuous and flexible energy supplies, has been investigated extensively. However, the conversion efficiency is still relatively low since complicated physical, electrical, and chemical processes are involved. Therefore, carefully designed photocatalysts with a wide absorption range of solar illumination, a high conductivity for charge carriers, a small number of recombination centers, and fast surface reaction kinetics are required to achieve a high activity. This Account describes our recent efforts to enhance the utilization of charge carriers for semiconductor photocatalysts toward efficient solar-to-chemical energy conversion. During photocatalytic reactions, photogenerated electrons and holes are involved in complex processes to convert solar energy into chemical energy. The initial step is the generation of charge carriers in semiconductor photocatalysts, which could be enhanced by extending the light absorption range. Integration of plasmonic materials and introduction of self-dopants have been proved to be effective methods to improve the light absorption ability of photocatalysts to produce larger amounts of photogenerated charge carriers. Subsequently, the photogenerated electrons and holes migrate to the surface. Therefore, acceleration of the transport process can result in enhanced solar energy conversion efficiency. Different strategies such as morphology control and conductivity improvement have been demonstrated to achieve this goal. Fine-tuning of the

  2. Mean carrier transport properties and charge collection dynamics of single-crystal, natural type IIa diamonds from ion-induced conductivity measurements

    SciTech Connect

    Han, S.S.

    1993-09-01

    Ion-induced conductivity has been used to investigate the detector characteristics of diamond detectors. Both integrated-charge, and time-resolved current measurements were performed to examine the mean carrier transport properties of diamond and the dynamics of charge collection under highly-localized and high-density excitation conditions. The integrated-charge measurements were conducted with a standard pulse-counting system with {sup 241}Am radioactivity as the excitation source for the detectors. The time-resolved current measurements were performed using a 70 GHz random sampling oscilloscope with the detectors incorporated into high-speed microstrip transmission lines and the excitation source for these measurements was an ion beam of either 5-MeV He{sup +} or 10-MeV Si{sup 3+}. The detectors used in both experiments can be described as metal-semiconductor-metal (MSM) devices where a volume of the detector material is sandwiched between two metal plates. A charge collection model was developed to interpret the integrated-charge measurements which enabled estimation of the energy required to produce an electron-hole pair ({epsilon}{sub di}) and the mean carrier transport properties in diamond, such as carrier mobility and lifetime, and the behavior of the electrical contacts to diamond.

  3. Localized charge carriers in graphene nanodevices

    NASA Astrophysics Data System (ADS)

    Bischoff, D.; Varlet, A.; Simonet, P.; Eich, M.; Overweg, H. C.; Ihn, T.; Ensslin, K.

    2015-09-01

    Graphene—two-dimensional carbon—is a material with unique mechanical, optical, chemical, and electronic properties. Its use in a wide range of applications was therefore suggested. From an electronic point of view, nanostructured graphene is of great interest due to the potential opening of a band gap, applications in quantum devices, and investigations of physical phenomena. Narrow graphene stripes called "nanoribbons" show clearly different electronical transport properties than micron-sized graphene devices. The conductivity is generally reduced and around the charge neutrality point, the conductance is nearly completely suppressed. While various mechanisms can lead to this observed suppression of conductance, disordered edges resulting in localized charge carriers are likely the main cause in a large number of experiments. Localized charge carriers manifest themselves in transport experiments by the appearance of Coulomb blockade diamonds. This review focuses on the mechanisms responsible for this charge localization, on interpreting the transport details, and on discussing the consequences for physics and applications. Effects such as multiple coupled sites of localized charge, cotunneling processes, and excited states are discussed. Also, different geometries of quantum devices are compared. Finally, an outlook is provided, where open questions are addressed.

  4. Localized charge carriers in graphene nanodevices

    SciTech Connect

    Bischoff, D. Varlet, A.; Simonet, P.; Eich, M.; Overweg, H. C.; Ihn, T.; Ensslin, K.

    2015-09-15

    Graphene—two-dimensional carbon—is a material with unique mechanical, optical, chemical, and electronic properties. Its use in a wide range of applications was therefore suggested. From an electronic point of view, nanostructured graphene is of great interest due to the potential opening of a band gap, applications in quantum devices, and investigations of physical phenomena. Narrow graphene stripes called “nanoribbons” show clearly different electronical transport properties than micron-sized graphene devices. The conductivity is generally reduced and around the charge neutrality point, the conductance is nearly completely suppressed. While various mechanisms can lead to this observed suppression of conductance, disordered edges resulting in localized charge carriers are likely the main cause in a large number of experiments. Localized charge carriers manifest themselves in transport experiments by the appearance of Coulomb blockade diamonds. This review focuses on the mechanisms responsible for this charge localization, on interpreting the transport details, and on discussing the consequences for physics and applications. Effects such as multiple coupled sites of localized charge, cotunneling processes, and excited states are discussed. Also, different geometries of quantum devices are compared. Finally, an outlook is provided, where open questions are addressed.

  5. Charge-Carrier-Scattering Spectroscopy With BEEM

    NASA Technical Reports Server (NTRS)

    Hecht, Michael H.; Bell, Lloyd D.; Kaiser, William J.

    1992-01-01

    Ballistic-electron-emission microscopy (BEEM) constitutes basis of new spectroscopy of scattering of electrons and holes. Pointed tip electrode scans near surface of metal about 100 angstrom thick on semiconductor. Principle similar to scanning tunneling microscope, except metal acts as third electrode. Used to investigate transport phenomena, scattering phenomena, and creation of hot charge carriers in Au/Si and Au/GaAs metal/semiconductor microstructures.

  6. Self-assembly and charge carrier transport of solution-processed conjugated polymer monolayers on dielectric surfaces with controlled sub-nanometer roughness.

    PubMed

    Li, Mengmeng; Hinkel, Felix; Müllen, Klaus; Pisula, Wojciech

    2016-04-28

    In recent years organic field-effect transistors have received extensive attention, however, it is still a great challenge to fabricate monolayer-based devices of conjugated polymers. In this study, one single layer of poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene) is directly dip-coated, and its self-assembly is precisely tuned from nanofibers to granular aggregates by controlling the dielectric roughness on a sub-nanometer scale. The charge carrier transport of the monolayer transistor exhibits a strong dependence on the dielectric roughness, which is attributed to the roughness-induced effects of higher densities of grain boundaries and charge trapping sites as well as surface scattering. These results mark a great advance in the bottom-up fabrication of organic electronics. PMID:27080325

  7. Role of Sub-Nanometer Dielectric Roughness on Microstructure and Charge Carrier Transport in α,ω-Dihexylsexithiophene Field-Effect Transistors.

    PubMed

    Li, Mengmeng; Marszalek, Tomasz; Müllen, Klaus; Pisula, Wojciech

    2016-06-29

    The effect of dielectric roughness on the microstructure evolution of thermally evaporated α,ω-dihexylsexithiophene (α,ω-DH6T) thin films from a single molecular layer to tens of monolayers (ML) is studied. Thereby, the surface roughness of dielectrics is controlled within a sub-nanometer range. It is found that the grain size of an α,ω-DH6T ML is affected by dielectric roughness, especially for 1.5 ML, whereby the transistor performance is barely influenced. This can be attributed to a domain interconnection in the second layer over a long-range formed on the rough surface. With deposition of more layers, both microstructure and charge carrier transport exhibit a roughness-independent behavior. The structural characterization of α,ω-DH6T 10 ML by grazing-incidence wide-angle X-ray scattering reveals that the interlayer distance is slightly decreased from 3.30 to 3.15 nm due to a higher roughness, while an unchanged π-stacking distance is in excellent agreement with the roughness-independent hole mobility. This study excludes the influence of molecular-solvent interaction and preaggregation taking place during solution deposition, and provides further evidence that the microstructure of the interfacial layer of organic semiconductors has only minor impact on the bulk charge carrier transport in thicker films. PMID:27280702

  8. Self-assembly and charge carrier transport of solution-processed conjugated polymer monolayers on dielectric surfaces with controlled sub-nanometer roughness

    NASA Astrophysics Data System (ADS)

    Li, Mengmeng; Hinkel, Felix; Müllen, Klaus; Pisula, Wojciech

    2016-04-01

    In recent years organic field-effect transistors have received extensive attention, however, it is still a great challenge to fabricate monolayer-based devices of conjugated polymers. In this study, one single layer of poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene) is directly dip-coated, and its self-assembly is precisely tuned from nanofibers to granular aggregates by controlling the dielectric roughness on a sub-nanometer scale. The charge carrier transport of the monolayer transistor exhibits a strong dependence on the dielectric roughness, which is attributed to the roughness-induced effects of higher densities of grain boundaries and charge trapping sites as well as surface scattering. These results mark a great advance in the bottom-up fabrication of organic electronics.In recent years organic field-effect transistors have received extensive attention, however, it is still a great challenge to fabricate monolayer-based devices of conjugated polymers. In this study, one single layer of poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene) is directly dip-coated, and its self-assembly is precisely tuned from nanofibers to granular aggregates by controlling the dielectric roughness on a sub-nanometer scale. The charge carrier transport of the monolayer transistor exhibits a strong dependence on the dielectric roughness, which is attributed to the roughness-induced effects of higher densities of grain boundaries and charge trapping sites as well as surface scattering. These results mark a great advance in the bottom-up fabrication of organic electronics. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr01082b

  9. Electrical transport in a disordered medium: NMR measurement of diffusivity and electrical mobility of ionic charge carriers.

    PubMed

    Heil, S R; Holz, M

    1998-11-01

    Electrical transport in porous media plays an important role in many fields of pure and applied science. The basic microscopic processes of the charge transport have attracted considerable theoretical interest for a long time. However, on a microscopic level there was up to now no experimental access to this problem. In the present paper we demonstrate, by using a suited porous system, that two combined NMR methods can offer such a first experimental access. We apply common PFG NMR methods and the special electrophoretic NMR (ENMR) technique for the measurement of self-diffusion coefficient D+ and electric mobility u+ of a cation ((C4H9)+4) in a disordered gel-like medium (Sephadex LH-20) filled with electrolyte solution. We find a, qualitatively expected, observation time-dependence of D+, but for the first time such a time-dependence is also observed for u+, which means the detection of the phenomenon of "anomalous field assisted diffusion" or "anomalous mobility." For the measurement of the short-time behavior of the mobility a new pulse sequence is presented. The time-dependent mobilities were measured at three different external electrical fields E. From the long-time behavior of D+, u+, and DH2O three independent values for the tortuosity T of the porous system could be derived. We find equality of the tortuosities T(D+) and T(u+), which represents a first experimental proof of the validity of the Einstein relation (D+ approximately u+) in a disordered medium. Finally, we discuss advantages of the possible use of "anomalous field assisted diffusion" over the commonly used "anomalous diffusion" in morphology studies by dynamic imaging in porous media. PMID:9799669

  10. Correlation of film morphology and defect content with the charge-carrier transport in thin-film transistors based on ZnO nanoparticles

    NASA Astrophysics Data System (ADS)

    Polster, S.; Jank, M. P. M.; Frey, L.

    2016-01-01

    The correlation of defect content and film morphology with the charge-carrier transport in field-effect devices based on zinc oxide nanoparticles was investigated. Changes in the defect content and the morphology were realized by annealing and sintering of the nanoparticle thin films. Temperature-dependent electrical measurements reveal that the carrier transport is thermally activated for both the unsintered and sintered thin films. Reduced energetic barrier heights between the particles have been determined after sintering. Additionally, the energetic barrier heights between the particles can be reduced by increasing the drain-to-source voltage and the gate-to-source voltage. The changes in the barrier height are discussed with respect to information obtained by scanning electron microscopy and photoluminescence measurements. It is found that a reduction of surface states and a lower roughness at the interface between the particle layer and the gate dielectric lead to lower barrier heights. Both surface termination and layer morphology at the interface affect the barrier height and thus are the main criteria for mobility improvement and device optimization.

  11. Charge carrier mobility in hybrid halide perovskites

    PubMed Central

    Motta, Carlo; El-Mellouhi, Fedwa; Sanvito, Stefano

    2015-01-01

    The charge transport properties of hybrid halide perovskites are investigated with a combination of density functional theory including van der Waals interaction and the Boltzmann theory for diffusive transport in the relaxation time approximation. We find the mobility of electrons to be in the range 5–10 cm2V−1s−1 and that for holes within 1–5 cm2V−1s−1, where the variations depend on the crystal structure investigated and the level of doping. Such results, in good agreement with recent experiments, set the relaxation time to about 1 ps, which is the time-scale for the molecular rotation at room temperature. For the room temperature tetragonal phase we explore two possible orientations of the organic cations and find that the mobility has a significant asymmetry depending on the direction of the current with respect to the molecular axis. This is due mostly to the way the PbI3 octahedral symmetry is broken. Interestingly we find that substituting I with Cl has minor effects on the mobilities. Our analysis suggests that the carrier mobility is probably not a key factor in determining the high solar-harvesting efficiency of this class of materials. PMID:26235910

  12. Measurement of the Charge Carrier Mobility Distribution in Bulk Heterojunction Solar Cells.

    PubMed

    Seifter, Jason; Sun, Yanming; Choi, Hyosung; Lee, Byoung Hoon; Nguyen, Thanh Luan; Woo, Han Young; Heeger, Alan J

    2015-09-01

    Charge carrier transport through organic solar cells is fundamentally dispersive due to the disordered structure and complex film morphology within the photoactive layer. A novel application of transient photocurrent and short-circuit variable time-delayed collection field measurements is used to reconstruct the complete charge carrier mobility distribution for the photogenerated carriers in optimized organic solar cells. PMID:26199190

  13. Ferroelectric polarization driven optical absorption and charge carrier transport in CH3NH3PbI3/TiO2-based photovoltaic cells

    NASA Astrophysics Data System (ADS)

    Feng, Hong-Jian

    2015-09-01

    Time-dependent density-functional theory(TD-DFT) calculations show that photogenerated electrons accumulate at the interface of CH3NH3PbI3/TiO2. Electrons transport from CH3NH3PbI3 side to TiO2 side, and the recombination of charge carriers is significantly reduced in this heterostructure. This can unambiguously explain why the power conversion efficiency and the open-circuit voltage are so high in the mesoporous TiO2 with an ultrathin layer of the hybrid halide perovskites. The calculated absorption spectrum of CH3NH3PbI3 agrees well with the experimental measurements. Our TD-DFT calculations confirm the connection between the ferroelectric polarization and the optical absorption. The polarization is caused by the combination of stereochemical activity of the lone pair of Pb-6s2 and the distortions of the organic moieties. Ti-3d states play crucial role in the formation of electron-hole pairs and make TiO2 as an electron transport material.

  14. Charge transport in disordered materials

    NASA Astrophysics Data System (ADS)

    Gagorik, Adam Gerald

    This thesis is focused on on using Monte Carlo simulation to extract device relevant properties, such as the current voltage behavior of transistors and the efficiency of photovoltaics, from the hopping transport of molecules. Specifically, simulation is used to study organic field-effect transistors (OFETs) and organic photo-voltaics (OPVs). For OFETs, the current was found to decrease with increasing concentration of traps and barriers in the system. As the barrier/trap concentration approaches 100%, the current recovers as carrier begin to travel through the manifold of connected trap states. Coulomb interactions between like charges are found to play a role in removing carriers from trap states. The equilibrium current in OFETs was found to be independent of charge injection method, however, the finite size of devices leads to an oscillatory current. Fourier transforms of the electrical current show peaks that vary non-linearly with device length, while being independent of device width. This has implications for the mobility of carriers in finite sized devices. Lastly, the presence of defects and high barriers (> 0.4 eV) was found to produce negative differential resistance in the saturation region of OFET curves, unlike traps. While defects and barriers prohibit carriers from reaching the drain at high voltages, the repulsive interaction between like charged carriers pushes charges around the defects. For OPVs, the effects of device morphology and charge delocalization were studied. Fill factors increased with domain size in monolayer isotropic morphologies, but decreased for band morphologies. In single-phase systems without Coulomb interactions, astonishingly high fill factors (. 70%) were found. In multilayer OPVs,a complex interplay of domain size, connectivity, tortuosity, interface trapping, and delocalization determined efficiency.

  15. Transport of charge carriers through the thin base of a heterobipolar transistor under the impact of radiation

    SciTech Connect

    Puzanov, A. S. Obolenskii, S. V. Kozlov, V. A.

    2015-01-15

    The transport of electrons in heterobipolar transistors with radiation defects is studied under conditions where the characteristic sizes of defect clusters and the distances between them can be comparable or can even exceed the sizes of the device base. It is shown that, under some levels of irradiation, neutron radiation can bring about a decrease in the time of flight of hot electrons through the base, which retards the degradation of the transistor parameters.

  16. Charge carrier coherence and Hall effect in organic semiconductors

    PubMed Central

    Yi, H. T.; Gartstein, Y. N.; Podzorov, V.

    2016-01-01

    Hall effect measurements are important for elucidating the fundamental charge transport mechanisms and intrinsic mobility in organic semiconductors. However, Hall effect studies frequently reveal an unconventional behavior that cannot be readily explained with the simple band-semiconductor Hall effect model. Here, we develop an analytical model of Hall effect in organic field-effect transistors in a regime of coexisting band and hopping carriers. The model, which is supported by the experiments, is based on a partial Hall voltage compensation effect, occurring because hopping carriers respond to the transverse Hall electric field and drift in the direction opposite to the Lorentz force acting on band carriers. We show that this can lead in particular to an underdeveloped Hall effect observed in organic semiconductors with substantial off-diagonal thermal disorder. Our model captures the main features of Hall effect in a variety of organic semiconductors and provides an analytical description of Hall mobility, carrier density and carrier coherence factor. PMID:27025354

  17. Charge carrier coherence and Hall effect in organic semiconductors

    NASA Astrophysics Data System (ADS)

    Yi, H. T.; Gartstein, Y. N.; Podzorov, V.

    2016-03-01

    Hall effect measurements are important for elucidating the fundamental charge transport mechanisms and intrinsic mobility in organic semiconductors. However, Hall effect studies frequently reveal an unconventional behavior that cannot be readily explained with the simple band-semiconductor Hall effect model. Here, we develop an analytical model of Hall effect in organic field-effect transistors in a regime of coexisting band and hopping carriers. The model, which is supported by the experiments, is based on a partial Hall voltage compensation effect, occurring because hopping carriers respond to the transverse Hall electric field and drift in the direction opposite to the Lorentz force acting on band carriers. We show that this can lead in particular to an underdeveloped Hall effect observed in organic semiconductors with substantial off-diagonal thermal disorder. Our model captures the main features of Hall effect in a variety of organic semiconductors and provides an analytical description of Hall mobility, carrier density and carrier coherence factor.

  18. Charge carrier coherence and Hall effect in organic semiconductors.

    PubMed

    Yi, H T; Gartstein, Y N; Podzorov, V

    2016-01-01

    Hall effect measurements are important for elucidating the fundamental charge transport mechanisms and intrinsic mobility in organic semiconductors. However, Hall effect studies frequently reveal an unconventional behavior that cannot be readily explained with the simple band-semiconductor Hall effect model. Here, we develop an analytical model of Hall effect in organic field-effect transistors in a regime of coexisting band and hopping carriers. The model, which is supported by the experiments, is based on a partial Hall voltage compensation effect, occurring because hopping carriers respond to the transverse Hall electric field and drift in the direction opposite to the Lorentz force acting on band carriers. We show that this can lead in particular to an underdeveloped Hall effect observed in organic semiconductors with substantial off-diagonal thermal disorder. Our model captures the main features of Hall effect in a variety of organic semiconductors and provides an analytical description of Hall mobility, carrier density and carrier coherence factor. PMID:27025354

  19. On the nature of photo charge carriers in ice

    NASA Astrophysics Data System (ADS)

    Petrenko, V. F.; Khusnatdinov, N. N.

    1994-06-01

    A method of photoelectromotive force (PEMF) was developed to find the charge sign, mobility, and lifetime of photo charge carriers in ice generated by photons with energy hν≳6.5 eV. It was determined that the most mobile photo charge carriers are negative ones, with mobility μ increasing from 2×10-3 cm2/V s at T=-10 °C to 4×10-2 cm2/V s at T=-30 °C, and with their lifetime decreasing from 30 to 10 s in the same temperature range. Activation energies of the mobility and the lifetime are Eμ=-0.77 eV and Eτ=0.32 eV, respectively. In addition to the negative photo charge carriers positive ones arise with mobility μ=2.3×10-4 cm2/V s and lifetime τ=26 min at T=-15 °C. We suggest that the negative photo charge carriers in ice are mobile complexes of an electron, vacancy and D-defect (e-+V+D). To take into account a specific mechanism of charge transport in ice, configurational vector Ω, and the generation of complexes (e-+V+D), a reaction of ``autoionization'' was modified for ice, 2H2O+hν→H3O++OH•int(e-+V+D).

  20. Solid state cloaking for electrical charge carrier mobility control

    DOEpatents

    Zebarjadi, Mona; Liao, Bolin; Esfarjani, Keivan; Chen, Gang

    2015-07-07

    An electrical mobility-controlled material includes a solid state host material having a controllable Fermi energy level and electrical charge carriers with a charge carrier mobility. At least one Fermi level energy at which a peak in charge carrier mobility is to occur is prespecified for the host material. A plurality of particles are distributed in the host material, with at least one particle disposed with an effective mass and a radius that minimize scattering of the electrical charge carriers for the at least one prespecified Fermi level energy of peak charge carrier mobility. The minimized scattering of electrical charge carriers produces the peak charge carrier mobility only at the at least one prespecified Fermi level energy, set by the particle effective mass and radius, the charge carrier mobility being less than the peak charge carrier mobility at Fermi level energies other than the at least one prespecified Fermi level energy.

  1. Selective modulation of charge-carrier transport of a photoanode in a photoelectrochemical cell by a graphitized fullerene interfacial layer.

    PubMed

    Park, Sun-Young; Lim, Dong Chan; Hong, Eun Mi; Lee, Joo-Yeoul; Heo, Jinhee; Lim, Jae Hong; Lee, Chang-Lyoul; Kim, Young Dok; Mul, Guido

    2015-01-01

    We show that a graphitic carbon interfacial layer, derived from C70 by annealing at 500 °C, results in a significant increase in the attainable photocurrent of a photoelectrochemical cell that contains a WO3 -functionalized fluorine-doped tin oxide (FTO) photoanode. Time-resolved photoluminescence spectroscopy, photoconductive atomic force microscopy, Hall measurements, and electrochemical impedance spectroscopy show that the increase in photocurrent is the result of fast and selective electron transport from optically excited WO3 through the graphitic carbon interfacial layer to the FTO-coated glass electrode. Thus the energy efficiency of perspective solar-to-fuel devices can be improved by modification of the interface of semiconductors and conducting substrate electrodes by using graphitized fullerene derivatives. PMID:25410298

  2. Determining charge carrier mobility in Schottky contacted single-carrier organic devices by impedance spectroscopy

    NASA Astrophysics Data System (ADS)

    Tang, Ying; Peng, Yingquan; Sun, Lei; Wei, Yi; Xu, Sunan

    2015-10-01

    Impedance spectroscopy (IS) is one of the most important methods for analyzing transport properties of semiconducting thin films. At present carrier mobility can be determined by IS methods only for Ohmic contacted single-carrier devices, which hinders the use of the IS method for determining the carrier mobility of thin films with high-lying lowest unoccupied molecular orbits or low-lying highest occupied molecular orbits. Based on the theory of space charge limited current conduction and thermionic emission at metal-organic interface, we developed a numerical IS model for single-carrier organic devices with Schottky injection contact. With the help of this model, a concise empirical formula is obtained from which the carrier mobility can be determined from the characteristic frequency of the negative differential susceptance and the Schottky energy barrier height at the injection contact.

  3. Columnar mesophases of hexabenzocoronene derivatives. II. Charge carrier mobility.

    PubMed

    Kirkpatrick, James; Marcon, Valentina; Kremer, Kurt; Nelson, Jenny; Andrienko, Denis

    2008-09-01

    Combining atomistic molecular dynamic simulations, Marcus-Hush theory description of charge transport rates, and master equation description of charge dynamics, we correlate the temperature-driven change of the mesophase structure with the change of charge carrier mobilities in columnar phases of hexabenzocoronene derivatives. The time dependence of fluctuations in transfer integrals shows that static disorder is predominant in determining charge transport characteristics. Both site energies and transfer integrals are distributed because of disorder in the molecular arrangement. It is shown that the contributions to the site energies from polarization and electrostatic effects are of opposite sign for positive charges. We look at three mesophases of hexabenzocoronene: herringbone, discotic, and columnar disordered. All results are compared to time resolved microwave conductivity data and show excellent agreement with no fitting parameters. PMID:19044876

  4. Dynamic Charge Carrier Trapping in Quantum Dot Field Effect Transistors.

    PubMed

    Zhang, Yingjie; Chen, Qian; Alivisatos, A Paul; Salmeron, Miquel

    2015-07-01

    Noncrystalline semiconductor materials often exhibit hysteresis in charge transport measurements whose mechanism is largely unknown. Here we study the dynamics of charge injection and transport in PbS quantum dot (QD) monolayers in a field effect transistor (FET). Using Kelvin probe force microscopy, we measured the temporal response of the QDs as the channel material in a FET following step function changes of gate bias. The measurements reveal an exponential decay of mobile carrier density with time constants of 3-5 s for holes and ∼10 s for electrons. An Ohmic behavior, with uniform carrier density, was observed along the channel during the injection and transport processes. These slow, uniform carrier trapping processes are reversible, with time constants that depend critically on the gas environment. We propose that the underlying mechanism is some reversible electrochemical process involving dissociation and diffusion of water and/or oxygen related species. These trapping processes are dynamically activated by the injected charges, in contrast with static electronic traps whose presence is independent of the charge state. Understanding and controlling these processes is important for improving the performance of electronic, optoelectronic, and memory devices based on disordered semiconductors. PMID:26099508

  5. Charge transport network dynamics in molecular aggregates.

    PubMed

    Jackson, Nicholas E; Chen, Lin X; Ratner, Mark A

    2016-08-01

    Due to the nonperiodic nature of charge transport in disordered systems, generating insight into static charge transport networks, as well as analyzing the network dynamics, can be challenging. Here, we apply time-dependent network analysis to scrutinize the charge transport networks of two representative molecular semiconductors: a rigid n-type molecule, perylenediimide, and a flexible p-type molecule, [Formula: see text] Simulations reveal the relevant timescale for local transfer integral decorrelation to be [Formula: see text]100 fs, which is shown to be faster than that of a crystalline morphology of the same molecule. Using a simple graph metric, global network changes are observed over timescales competitive with charge carrier lifetimes. These insights demonstrate that static charge transport networks are qualitatively inadequate, whereas average networks often overestimate network connectivity. Finally, a simple methodology for tracking dynamic charge transport properties is proposed. PMID:27439871

  6. Non-contact, non-destructive, quantitative probing of interfacial trap sites for charge carrier transport at semiconductor-insulator boundary

    SciTech Connect

    Choi, Wookjin; Miyakai, Tomoyo; Sakurai, Tsuneaki; Saeki, Akinori; Yokoyama, Masaaki; Seki, Shu

    2014-07-21

    The density of traps at semiconductor–insulator interfaces was successfully estimated using microwave dielectric loss spectroscopy with model thin-film organic field-effect transistors. The non-contact, non-destructive analysis technique is referred to as field-induced time-resolved microwave conductivity (FI-TRMC) at interfaces. Kinetic traces of FI-TRMC transients clearly distinguished the mobile charge carriers at the interfaces from the immobile charges trapped at defects, allowing both the mobility of charge carriers and the number density of trap sites to be determined at the semiconductor-insulator interfaces. The number density of defects at the interface between evaporated pentacene on a poly(methylmethacrylate) insulating layer was determined to be 10{sup 12 }cm{sup −2}, and the hole mobility was up to 6.5 cm{sup 2} V{sup −1} s{sup −1} after filling the defects with trapped carriers. The FI-TRMC at interfaces technique has the potential to provide rapid screening for the assessment of interfacial electronic states in a variety of semiconductor devices.

  7. Nanofaceting as a stamp for periodic graphene charge carrier modulations

    PubMed Central

    Vondráček, M.; Kalita, D.; Kučera, M.; Fekete, L.; Kopeček, J.; Lančok, J.; Coraux, J.; Bouchiat, V.; Honolka, J.

    2016-01-01

    The exceptional electronic properties of monatomic thin graphene sheets triggered numerous original transport concepts, pushing quantum physics into the realm of device technology for electronics, optoelectronics and thermoelectrics. At the conceptual pivot point is the particular two-dimensional massless Dirac fermion character of graphene charge carriers and its volitional modification by intrinsic or extrinsic means. Here, interfaces between different electronic and structural graphene modifications promise exciting physics and functionality, in particular when fabricated with atomic precision. In this study we show that quasiperiodic modulations of doping levels can be imprinted down to the nanoscale in monolayer graphene sheets. Vicinal copper surfaces allow to alternate graphene carrier densities by several 1013 carriers per cm2 along a specific copper high-symmetry direction. The process is triggered by a self-assembled copper faceting process during high-temperature graphene chemical vapor deposition, which defines interfaces between different graphene doping levels at the atomic level. PMID:27040365

  8. Nanofaceting as a stamp for periodic graphene charge carrier modulations

    NASA Astrophysics Data System (ADS)

    Vondráček, M.; Kalita, D.; Kučera, M.; Fekete, L.; Kopeček, J.; Lančok, J.; Coraux, J.; Bouchiat, V.; Honolka, J.

    2016-04-01

    The exceptional electronic properties of monatomic thin graphene sheets triggered numerous original transport concepts, pushing quantum physics into the realm of device technology for electronics, optoelectronics and thermoelectrics. At the conceptual pivot point is the particular two-dimensional massless Dirac fermion character of graphene charge carriers and its volitional modification by intrinsic or extrinsic means. Here, interfaces between different electronic and structural graphene modifications promise exciting physics and functionality, in particular when fabricated with atomic precision. In this study we show that quasiperiodic modulations of doping levels can be imprinted down to the nanoscale in monolayer graphene sheets. Vicinal copper surfaces allow to alternate graphene carrier densities by several 1013 carriers per cm2 along a specific copper high-symmetry direction. The process is triggered by a self-assembled copper faceting process during high-temperature graphene chemical vapor deposition, which defines interfaces between different graphene doping levels at the atomic level.

  9. Carrier transport and collection in fully depleted semiconductors by a combined action of the space charge field and the field due to electrode voltages

    DOEpatents

    Rehak, Pavel; Gatti, Emilio

    1987-01-01

    A semiconductor charge transport device and method for making same, characterized by providing a thin semiconductor wafer having rectifying junctions on its opposing major surfaces and including a small capacitance ohmic contact, in combination with bias voltage means and associated circuit means for applying a predetermined voltage to effectively deplete the wafer in regions thereof between the rectifying junctions and the ohmic contact. A charge transport device of the invention is usable as a drift chamber, a low capacitance detector, or a charge coupled device each constructed according to the methods of the invention for making such devices. Detectors constructed according to the principles of the invention are characterized by having significantly higher particle position indicating resolution than is attainable with prior art detectors, while at the same time requiring substantially fewer readout channels to realize such high resolution.

  10. Carrier transport and collection in fully depleted semiconductors by a combined action of the space charge field and the field due to electrode voltages

    DOEpatents

    Rehak, P.; Gatti, E.

    1987-08-18

    A semiconductor charge transport device and method for making same are disclosed, characterized by providing a thin semiconductor wafer having rectifying junctions on its opposing major surfaces and including a small capacitance ohmic contact, in combination with bias voltage means and associated circuit means for applying a predetermined voltage to effectively deplete the wafer in regions thereof between the rectifying junctions and the ohmic contact. A charge transport device of the invention is usable as a drift chamber, a low capacitance detector, or a charge coupled device each constructed according to the methods of the invention for making such devices. Detectors constructed according to the principles of the invention are characterized by having significantly higher particle position indicating resolution than is attainable with prior art detectors, while at the same time requiring substantially fewer readout channels to realize such high resolution. 16 figs.

  11. Carrier transport and collection in fully depleted semiconductors by a combined action of the space charge field and the field due to electrode voltages

    DOEpatents

    Rehak, P.; Gatti, E.

    1984-02-24

    A semiconductor charge transport device and method for making same, characterized by providing a thin semiconductor wafer having rectifying functions on its opposing major surfaces and including a small capacitance ohmic contact, in combination with bias voltage means and associated circuit means for applying a predetermined voltage to effectively deplete the wafer in regions thereof between the rectifying junctions and the ohmic contact. A charge transport device of the invention is usable as a drift chamber, a low capacitance detector, or a charge coupled device each constructed according to the methods of the invention for making such devices. Detectors constructed according to the principles of the invention are characterized by having significantly higher particle position indicating resolution than is attainable with prior art detectors, while at the same time requiring substantially fewer readout channels to realize such high resolution.

  12. Charge carrier coherence and Hall effect in organic semiconductors

    DOE PAGESBeta

    Yi, H. T.; Gartstein, Y. N.; Podzorov, V.

    2016-03-30

    Hall effect measurements are important for elucidating the fundamental charge transport mechanisms and intrinsic mobility in organic semiconductors. However, Hall effect studies frequently reveal an unconventional behavior that cannot be readily explained with the simple band-semiconductor Hall effect model. Here, we develop an analytical model of Hall effect in organic field-effect transistors in a regime of coexisting band and hopping carriers. The model, which is supported by the experiments, is based on a partial Hall voltage compensation effect, occurring because hopping carriers respond to the transverse Hall electric field and drift in the direction opposite to the Lorentz force actingmore » on band carriers. We show that this can lead in particular to an underdeveloped Hall effect observed in organic semiconductors with substantial off-diagonal thermal disorder. Lastly, our model captures the main features of Hall effect in a variety of organic semiconductors and provides an analytical description of Hall mobility, carrier density and carrier coherence factor.« less

  13. Spectroscopy of Charge Carriers and Traps in Field-Doped Single Crystal Organic Semiconductors

    SciTech Connect

    Zhu, Xiaoyang

    2014-12-10

    The proposed research aims to achieve quantitative, molecular level understanding of charge carriers and traps in field-doped crystalline organic semiconductors via in situ linear and nonlinear optical spectroscopy, in conjunction with transport measurements and molecular/crystal engineering. Organic semiconductors are emerging as viable materials for low-cost electronics and optoelectronics, such as organic photovoltaics (OPV), organic field effect transistors (OFETs), and organic light emitting diodes (OLEDs). Despite extensive studies spanning many decades, a clear understanding of the nature of charge carriers in organic semiconductors is still lacking. It is generally appreciated that polaron formation and charge carrier trapping are two hallmarks associated with electrical transport in organic semiconductors; the former results from the low dielectric constants and weak intermolecular electronic overlap while the latter can be attributed to the prevalence of structural disorder. These properties have lead to the common observation of low charge carrier mobilities, e.g., in the range of 10-5 - 10-3 cm2/Vs, particularly at low carrier concentrations. However, there is also growing evidence that charge carrier mobility approaching those of inorganic semiconductors and metals can exist in some crystalline organic semiconductors, such as pentacene, tetracene and rubrene. A particularly striking example is single crystal rubrene (Figure 1), in which hole mobilities well above 10 cm2/Vs have been observed in OFETs operating at room temperature. Temperature dependent transport and spectroscopic measurements both revealed evidence of free carriers in rubrene. Outstanding questions are: what are the structural features and physical properties that make rubrene so unique? How do we establish fundamental design principles for the development of other organic semiconductors of high mobility? These questions are critically important but not comprehensive, as the nature of

  14. NREL Studies Carrier Separation and Transport in Perovskite Solar Cells

    SciTech Connect

    2016-01-01

    NREL scientists studied charge separation and transport in perovskite solar cells by determining the junction structure across the solar device using the nanoelectrical characterization technique of Kelvin probe force microscopy. The distribution of electrical potential across both planar and porous devices demonstrates a p-n junction structure at the interface between titanium dioxide and perovskite. In addition, minority-carrier transport within the devices operates under diffusion/drift. Clarifying the fundamental junction structure provides significant guidance for future research and development. This NREL study points to the fact that improving carrier mobility is a critical factor for continued efficiency gains in perovskite solar cells.

  15. Molecular length dictates the nature of charge carriers in single-molecule junctions of oxidized oligothiophenes.

    PubMed

    Dell, Emma J; Capozzi, Brian; Xia, Jianlong; Venkataraman, Latha; Campos, Luis M

    2015-03-01

    To develop advanced materials for electronic devices, it is of utmost importance to design organic building blocks with tunable functionality and to study their properties at the molecular level. For organic electronic and photovoltaic applications, the ability to vary the nature of charge carriers and so create either electron donors or acceptors is critical. Here we demonstrate that charge carriers in single-molecule junctions can be tuned within a family of molecules that contain electron-deficient thiophene-1,1-dioxide (TDO) building blocks. Oligomers of TDO were designed to increase electron affinity and maintain delocalized frontier orbitals while significantly decreasing the transport gap. Through thermopower measurements we show that the dominant charge carriers change from holes to electrons as the number of TDO units is increased. This results in a unique system in which the charge carrier depends on the backbone length, and provides a new means to tune p- and n-type transport in organic materials. PMID:25698329

  16. Dynamics of charge carriers on hexagonal nanoribbons with vacancy defects

    NASA Astrophysics Data System (ADS)

    Ferreira da Cunha, Wiliam; de Oliveira Neto, Pedro Henrique; Terai, Akira; Magela e Silva, Geraldo

    2016-07-01

    We develop a general model to investigate the dynamics of charge carriers in vacancy endowed honeycomb two-dimensional nanolattices. As a fundamental application, results concerning the influence of vacancies placed on different sites of semiconducting armchair graphene nanoribbons (AGNR) over the transport of polarons are presented. It is observed that the positioning of vacancies plays a major role over the scattering of the charge carriers, in the sense that their overall mobility is determined by where the defect is allocated. By considering different structural configurations of the system, the arising polaron can either move freely or be reflected. Therefore, our work provides a phenomenological understanding of the underlying mechanism responsible for the change of conductivity experienced by systems in which structural defects are present, a fact that has been reported for different nanostructures of the same symmetry. Because vacancies are one of the most common kinds of defects and are, in practice, unavoidable, the kind of description proposed in the present paper is crucial to correctly address transport and electronic properties in more realistic electronic devices based on two-dimensional nanolattices.

  17. Anomalous Charge Transport in Disordered Organic Semiconductors

    SciTech Connect

    Muniandy, S. V.; Woon, K. L.; Choo, K. Y.

    2011-03-30

    Anomalous charge carrier transport in disordered organic semiconductors is studied using fractional differential equations. The connection between index of fractional derivative and dispersion exponent is examined from the perspective of fractional Fokker-Planck equation and its link to the continuous time random walk formalism. The fractional model is used to describe the bi-scaling power-laws observed in the time-of flight photo-current transient data for two different types of organic semiconductors.

  18. Anisotropic charged impurity-limited carrier mobility in monolayer phosphorene

    SciTech Connect

    Ong, Zhun-Yong; Zhang, Gang; Zhang, Yong Wei

    2014-12-07

    The room temperature carrier mobility in atomically thin 2D materials is usually far below the intrinsic limit imposed by phonon scattering as a result of scattering by remote charged impurities in its environment. We simulate the charged impurity-limited carrier mobility μ in bare and encapsulated monolayer phosphorene. We find a significant temperature dependence in the carrier mobilities (μ ∝ T{sup −γ}) that results from the temperature variability of the charge screening and varies with the crystal orientation. The anisotropy in the effective mass leads to an anisotropic carrier mobility, with the mobility in the armchair direction about one order of magnitude larger than in the zigzag direction. In particular, this mobility anisotropy is enhanced at low temperatures and high carrier densities. Under encapsulation with a high-κ overlayer, the mobility increases by up to an order of magnitude although its temperature dependence and its anisotropy are reduced.

  19. Dependence of charge transfer reorganization energy on carrier localisation in organic molecular crystals.

    PubMed

    Bromley, Stefan T; Illas, Francesc; Mas-Torrent, Marta

    2008-01-01

    Taking the organic molecular material dithiophene-tetrathiafulvalene (DT-TTF) as an example of a high mobility organic molecular material, we use density functional calculations to calculate the dependency of the reorganization energy associated with charge carrier transport on: (i) the geometric and electronic responsiveness of the local molecular crystal environment, and, (ii) the local spatial extent of the charge carrier. We find that in our most realistic extended models the charge transfer reorganization energy is strongly dependent on carrier localization. In particular, whereas highly localized carriers are found to be highly susceptible to their charge transfer efficiency being affected by changes in the local crystal environment, more delocalized carriers are better able to maintain their low reorganization energies. Considering that maintaining a relatively small charge transfer reorganization energy magnitude is an important factor in achieving high carrier mobilities, we suggest that those materials better able to sustain carriers with short-range thermally resistant intermolecular delocalisation should be sought for device applications. PMID:18075690

  20. Low-field carrier transport properties in biased bilayer graphene

    NASA Astrophysics Data System (ADS)

    Hu, Bo

    2014-07-01

    Based on a semiclassical Boltzmann transport equation in random phase approximation, we develop a theoretical model to understand low-field carrier transport in biased bilayer graphene, which takes into account the charged impurity scattering, acoustic phonon scattering, and surface polar phonon scattering as three main scattering mechanisms. The surface polar optical phonon scattering of carriers in supported bilayer graphene is thoroughly studied using the Rode iteration method. By considering the metal-BLG contact resistance as the only one free fitting parameter, we find that the carrier density dependence of the calculated total conductivity agrees well with that observed in experiment under different temperatures. The conductivity results also suggest that in high carrier density range, the metal-BLG contact resistance can be a significant factor in determining the BLG conductivity at low temperature, and both acoustic phonon scattering and surface polar phonon scattering play important roles at higher temperature, especially for BLG samples with a low doping concentration, which can compete with charged impurity scattering.

  1. 47 CFR 69.153 - Presubscribed interexchange carrier charge (PICC).

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... (PICC). 69.153 Section 69.153 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) COMMON... § 69.153 Presubscribed interexchange carrier charge (PICC). (a) A charge expressed in dollars and cents... maximum of $4.31 per line per month. In the event the ceilings on the PICC prevent the PICC...

  2. 47 CFR 69.153 - Presubscribed interexchange carrier charge (PICC).

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... (PICC). 69.153 Section 69.153 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) COMMON... § 69.153 Presubscribed interexchange carrier charge (PICC). (a) A charge expressed in dollars and cents... maximum of $4.31 per line per month. In the event the ceilings on the PICC prevent the PICC...

  3. 47 CFR 69.153 - Presubscribed interexchange carrier charge (PICC).

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... (PICC). 69.153 Section 69.153 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) COMMON... § 69.153 Presubscribed interexchange carrier charge (PICC). (a) A charge expressed in dollars and cents... maximum of $4.31 per line per month. In the event the ceilings on the PICC prevent the PICC...

  4. 47 CFR 69.153 - Presubscribed interexchange carrier charge (PICC).

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... (PICC). 69.153 Section 69.153 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) COMMON... § 69.153 Presubscribed interexchange carrier charge (PICC). (a) A charge expressed in dollars and cents... maximum of $4.31 per line per month. In the event the ceilings on the PICC prevent the PICC...

  5. 47 CFR 69.153 - Presubscribed interexchange carrier charge (PICC).

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... (PICC). 69.153 Section 69.153 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) COMMON... § 69.153 Presubscribed interexchange carrier charge (PICC). (a) A charge expressed in dollars and cents... maximum of $4.31 per line per month. In the event the ceilings on the PICC prevent the PICC...

  6. Slower carriers limit charge generation in organic semiconductor light-harvesting systems

    PubMed Central

    Stolterfoht, Martin; Armin, Ardalan; Shoaee, Safa; Kassal, Ivan; Burn, Paul; Meredith, Paul

    2016-01-01

    Blends of electron-donating and -accepting organic semiconductors are widely used as photoactive materials in next-generation solar cells and photodetectors. The yield of free charges in these systems is often determined by the separation of interfacial electron–hole pairs, which is expected to depend on the ability of the faster carrier to escape the Coulomb potential. Here we show, by measuring geminate and non-geminate losses and key transport parameters in a series of bulk-heterojunction solar cells, that the charge-generation yield increases with increasing slower carrier mobility. This is in direct contrast with the well-established Braun model where the dissociation rate is proportional to the mobility sum, and recent models that underscore the importance of fullerene aggregation for coherent electron propagation. The behaviour is attributed to the restriction of opposite charges to different phases, and to an entropic contribution that favours the joint separation of both charge carriers. PMID:27324720

  7. Slower carriers limit charge generation in organic semiconductor light-harvesting systems.

    PubMed

    Stolterfoht, Martin; Armin, Ardalan; Shoaee, Safa; Kassal, Ivan; Burn, Paul; Meredith, Paul

    2016-01-01

    Blends of electron-donating and -accepting organic semiconductors are widely used as photoactive materials in next-generation solar cells and photodetectors. The yield of free charges in these systems is often determined by the separation of interfacial electron-hole pairs, which is expected to depend on the ability of the faster carrier to escape the Coulomb potential. Here we show, by measuring geminate and non-geminate losses and key transport parameters in a series of bulk-heterojunction solar cells, that the charge-generation yield increases with increasing slower carrier mobility. This is in direct contrast with the well-established Braun model where the dissociation rate is proportional to the mobility sum, and recent models that underscore the importance of fullerene aggregation for coherent electron propagation. The behaviour is attributed to the restriction of opposite charges to different phases, and to an entropic contribution that favours the joint separation of both charge carriers. PMID:27324720

  8. Charging up Transportation.

    ERIC Educational Resources Information Center

    Vail, Kathleen R.

    1994-01-01

    In Antelope Valley, California, a regional transportation consortium, cooperatively run by six adjacent school districts, is operating an electric-powered school bus as a pilot project. Although the prototype bus cost nearly six times more than a traditional school bus, lower operating and maintenance expenses and safety factors appeal to many…

  9. Photogeneration of charge carriers in titanium oxides

    NASA Astrophysics Data System (ADS)

    Itoh, Chihiro; Iwahashi, Kuniaki; Kan'no, Ken-ichi

    2002-05-01

    We have measured action spectra of the photoconductivity of rutile crystal at ˜4 K. The photoconductivity spectrum shows a keen rise at 3.0 eV and shows a peak at 3.2 eV and a shoulder around 3.7 eV. The threshold energy of the photoconductivity excitation well agrees with the onset of the fundamental optical absorption. This result indicates that the carriers contributing to the photoconductivity are generated by the fundamental excitation of the crystal. We have found that the photoconductivity shows remarkable field dependence. Below 5 V/mm, the photoconductivity was almost field independent. On the other hand, increasing the field strength in the range from 5 to 25 V/mm strongly enhanced the photoconductivity and varied the shape of the action spectrum. The origin of the field dependence is discussed.

  10. Spatial variation of charge carrier density in graphene under a large bias current

    NASA Astrophysics Data System (ADS)

    Pan, Jie; Zhang, Haijing; Zheng, Yuan; Zhang, Bing; Zhang, Ting; Sheng, Ping

    2016-03-01

    By carrying out the Hall measurements under a large bias current, we have directly observed the spatial variation of the carrier density in graphene. This carrier density variation is found to depend on the bias direction; hence it cannot be caused by the heating effect, which should be independent of the bias current direction. A simple back-gate tuning model, involving a self-consistent calculation on longitudinal transport coupled with carrier density variation, is shown to explain the experimental results very well. Various implications of this phenomenon, including the shift of charge neutrality point under a large bias, are investigated and discussed.

  11. Charge carrier transport and lifetimes in n-type and p-type phosphorene as 2D device active materials: an ab initio study.

    PubMed

    Tea, E; Hin, C

    2016-08-10

    In this work, we provide a detailed analysis of phosphorene's performance as an n-type and p-type active material. This study is based on first principles calculations of the phosphorene electronic structure, and the resulting electron and hole scattering rates and lifetimes. Emphasis is put on extreme regimes commonly found in semiconductor devices, i.e. high electric fields and heavy doping, where impact ionization and Auger recombination can occur. We found that electron-initiated impact ionization is weaker than the hole-initiated process, when compared to carrier-phonon interaction rates, suggesting resilience to impact ionization initiated breakdown. Moreover, calculated minority electron lifetimes are limited by radiative recombination only, not by Auger processes, suggesting that phosphorene could achieve good quantum efficiencies in optoelectronic devices. The provided scattering rates and lifetimes are critical input data for the modeling and understanding of phosphorene-based device physics. PMID:27479904

  12. Assessing charge carrier trapping in silicon nanowires using picosecond conductivity measurements.

    PubMed

    Ulbricht, Ronald; Kurstjens, Rufi; Bonn, Mischa

    2012-07-11

    Free-standing semiconductor nanowires on bulk substrates are increasingly being explored as building blocks for novel optoelectronic devices such as tandem solar cells. Although carrier transport properties, such as mobility and trap densities, are essential for such applications, it has remained challenging to quantify these properties. Here, we report on a method that permits the direct, contact-free quantification of nanowire carrier diffusivity and trap densities in thin (∼25 nm wide) silicon nanowires-without any additional processing steps such as transfer of wires onto a substrate. The approach relies on the very different terahertz (THz) conductivity response of photoinjected carriers within the silicon nanowires from those in the silicon substrate. This allows quantifying both the picosecond dynamics and the efficiency of charge carrier transport from the silicon nanowires into the silicon substrate. Varying the excitation density allows for quantification of nanowire trap densities: for sufficiently low excitation fluences the diffusion process stalls because the majority of charge carriers become trapped at nanowire surface defects. Using a model that includes these effects, we determine both the diffusion constant and the nanowire trap density. The trap density is found to be orders of magnitude larger than the charge carrier density that would be generated by AM1.5 sunlight. PMID:22738182

  13. Charge-carrier relaxation in disordered organic semiconductors studied by dark injection: Experiment and modeling

    NASA Astrophysics Data System (ADS)

    Mesta, M.; Schaefer, C.; de Groot, J.; Cottaar, J.; Coehoorn, R.; Bobbert, P. A.

    2013-11-01

    Understanding of stationary charge transport in disordered organic semiconductors has matured during recent years. However, charge-carrier relaxation in nonstationary situations is still poorly understood. Such relaxation can be studied in dark injection experiments, in which the bias applied over an unilluminated organic semiconductor device is abruptly increased. The resulting transient current reveals both charge-carrier transport and relaxation characteristics. We performed such experiments on hole-only devices of a polyfluorene-based organic semiconductor. Modeling the dark injection by solving a one-dimensional master equation using the equilibrium carrier mobility leads to a too-slow current transient, since this approach does not account for carrier relaxation. Modeling by solving a three-dimensional time-dependent master equation does take into account all carrier transport and relaxation effects. With this modeling, the time scale of the current transient is found to be in agreement with experiment. With a disorder strength somewhat smaller than extracted from the temperature-dependent stationary current-voltage characteristics, also the shape of the experimental transients is well described.

  14. Comprehensive approach to intrinsic charge carrier mobility in conjugated organic molecules, macromolecules, and supramolecular architectures.

    PubMed

    Saeki, Akinori; Koizumi, Yoshiko; Aida, Takuzo; Seki, Shu

    2012-08-21

    Si-based inorganic electronics have long dominated the semiconductor industry. However, in recent years conjugated polymers have attracted increasing attention because such systems are flexible and offer the potential for low-cost, large-area production via roll-to-roll processing. The state-of-the-art organic conjugated molecular crystals can exhibit charge carrier mobilities (μ) that nearly match or even exceed that of amorphous silicon (1-10 cm(2) V(-1) s(-1)). The mean free path of the charge carriers estimated from these mobilities corresponds to the typical intersite (intermolecular) hopping distances in conjugated organic materials, which strongly suggests that the conduction model for the electronic band structure only applies to μ > 1 cm(2) V(-1) s(-1) for the translational motion of the charge carriers. However, to analyze the transport mechanism in organic electronics, researchers conventionally use a disorder formalism, where μ is usually less than 1 cm(2) V(-1) s(-1) and dominated by impurities, disorders, or defects that disturb the long-range translational motion. In this Account, we discuss the relationship between the alternating-current and direct-current mobilities of charge carriers, using time-resolved microwave conductivity (TRMC) and other techniques including field-effect transistor, time-of-flight, and space-charge limited current. TRMC measures the nanometer-scale mobility of charge carriers under an oscillating microwave electric field with no contact between the semiconductors and the metals. This separation allows us to evaluate the intrinsic charge carrier mobility with minimal trapping effects. We review a wide variety of organic electronics in terms of their charge carrier mobilities, and we describe recent studies of macromolecules, molecular crystals, and supramolecular architecture. For example, a rigid poly(phenylene-co-ethynylene) included in permethylated cyclodextrin shows a high intramolecular hole mobility of 0.5 cm(2) V

  15. Charge transport in desolvated DNA

    NASA Astrophysics Data System (ADS)

    Wolter, Mario; Elstner, Marcus; Kubař, Tomáš

    2013-09-01

    The conductivity of DNA in molecular junctions is often probed experimentally under dry conditions, but it is unclear how much of the solvent remains attached to the DNA and how this impacts its structure, electronic states, and conductivity. Classical MD simulations show that DNA is unstable if the solvent is removed completely, while a micro-hydrated system with few water molecules shows similar charge transport properties as fully solvated DNA does. This surprising effect is analyzed in detail by mapping the density functional theory-based electronic structure to a tight-binding Hamiltonian, allowing for an estimate of conductivity of various DNA sequences with snapshot-averaged Landauer's approach. The characteristics of DNA charge transport turn out to be determined by the nearest hydration shell(s), and the removal of bulk solvent has little effect on the transport.

  16. Charge Transport in Synthetic Metals

    SciTech Connect

    Emery, V. J.; Kivelson, S. A.; Muthukumar, V. N.

    1999-01-15

    The phenomenology of charge transport in synthetic metals is reviewed. It is argued that the conventional quasiparticle picture and Boltzmann transport theory do not apply to these materials. The central ideas of Fermi liquid theory are reviewed, and the significant corrections produced by quasiparticle scattering from ferromagnetic spin fluctuations in liquid {sup 3}He are described. It is shown that Sr{sub 2}RuO{sub 4} does not display the symptoms of a nearly-ferromagnetic Fermi liquid, so the source of its odd angular momentum pairing remains to be understood. The solution of an assisted-tunneling model of charge transport in quasi-one dimensional materials is described. This model has a quantum critical point and gives a resistivity that is linear in temperature or frequency, whichever is greater.

  17. Light pulse propagation and charge carrier scattering in semiconductor amplifiers

    SciTech Connect

    Binder, R.; Knorr, A.; Koch, S.W.

    1994-12-31

    The carrier dynamics in inverted semiconductors (optical amplifiers) and light pulse propagations in optical amplifiers have been studied extensively both theoretically and experimentally. Light induced carrier heating processes, which are caused, for example, by two-photon absorption and free carrier absorption, have been studied mainly on the basis of phenomenological models. The full microscopic theory of these processes and their influence on light pulse propagation is still an unsolved problem. Here, the authors present theoretical results on light pulse propagation in inverted semiconductors and semiconductor laser diodes. The theory is based on the semiconductor Maxwell Bloch equations and includes incoherent phenomena due to charge-carrier scattering based on the solution of the appropriate Boltzman equation.

  18. Ab initio charge-carrier mobility model for amorphous molecular semiconductors

    NASA Astrophysics Data System (ADS)

    Massé, Andrea; Friederich, Pascal; Symalla, Franz; Liu, Feilong; Nitsche, Robert; Coehoorn, Reinder; Wenzel, Wolfgang; Bobbert, Peter A.

    2016-05-01

    Accurate charge-carrier mobility models of amorphous organic molecular semiconductors are essential to describe the electrical properties of devices based on these materials. The disordered nature of these semiconductors leads to percolative charge transport with a large characteristic length scale, posing a challenge to the development of such models from ab initio simulations. Here, we develop an ab initio mobility model using a four-step procedure. First, the amorphous morphology together with its energy disorder and intermolecular charge-transfer integrals are obtained from ab initio simulations in a small box. Next, the ab initio information is used to set up a stochastic model for the morphology and transfer integrals. This stochastic model is then employed to generate a large simulation box with modeled morphology and transfer integrals, which can fully capture the percolative charge transport. Finally, the charge-carrier mobility in this simulation box is calculated by solving a master equation, yielding a mobility function depending on temperature, carrier concentration, and electric field. We demonstrate the procedure for hole transport in two important molecular semiconductors, α -NPD and TCTA. In contrast to a previous study, we conclude that spatial correlations in the energy disorder are unimportant for α -NPD. We apply our mobility model to two types of hole-only α -NPD devices and find that the experimental temperature-dependent current density-voltage characteristics of all devices can be well described by only slightly decreasing the simulated energy disorder strength.

  19. Charge transport in disordered semiconducting polymers driven by nuclear tunneling

    NASA Astrophysics Data System (ADS)

    van der Kaap, N. J.; Katsouras, I.; Asadi, K.; Blom, P. W. M.; Koster, L. J. A.; de Leeuw, D. M.

    2016-04-01

    The current density-voltage (J -V ) characteristics of hole-only diodes based on poly(2-methoxy, 5-(2' ethyl-hexyloxy)-p -phenylene vinylene) (MEH-PPV) were measured at a wide temperature and field range. At high electric fields the temperature dependence of the transport vanishes, and all J -V sweeps converge to a power law. Nuclear tunneling theory predicts a power law at high fields that scales with the Kondo parameter. To model the J -V characteristics we have performed master-equation calculations to determine the dependence of charge carrier mobility on electric field, charge carrier density, temperature, and Kondo parameter, using nuclear tunneling transfer rates. We demonstrate that nuclear tunneling, unlike other semiclassical models, provides a consistent description of the charge transport for a large bias, temperature, and carrier density range.

  20. Bipolar Charge Transport Properties of Poly(imide-thienyl(thienylenevinylene))

    NASA Astrophysics Data System (ADS)

    Lafalce, Evan; Jiang, Xiaomei; Zhang, Cheng

    2014-03-01

    The charge transport properties of π-conjugated polymers are of interest from a fundamental perspective and also because they are a limiting factor for many optoelectronic device applications. In this work, we study the charge carrier mobility and recombination in Poly(imide-thienyl(thienylenevinylene)) (imide-PTV), a novel PTV derivative with imide side group. The electron and hole mobility are determined separately through the Space Charge Limited Current (SCLC) analysis of single carrier diodes. These devices are fabricated using interfacial layers that provide carrier selective contacts. A mobility asymmetry factor of approximately 20 that favors hole transport is observed, with the hole mobility of the order of 10-5 [cm2/V*s]. Similar results are obtained from the analysis of the intensity dependence of photoconductivity. Complimentary analysis of the ambipolar carrier mobility through carrier extraction under linearly increasing voltage (CELIV) and double injection transient techniques are also presented. The effects of carrier recombination and trapping are discussed. We conclude that the hole transport is not the limiting factor for power conversion efficiency of photovoltaic device based on imide-PTV and PCBM.

  1. High charge-carrier mobility enables exploitation of carrier multiplication in quantum-dot films

    PubMed Central

    Sandeep, C. S. Suchand; Cate, Sybren ten; Schins, Juleon M.; Savenije, Tom J.; Liu, Yao; Law, Matt; Kinge, Sachin; Houtepen, Arjan J.; Siebbeles, Laurens D. A.

    2013-01-01

    Carrier multiplication, the generation of multiple electron–hole pairs by a single photon, is of great interest for solar cells as it may enhance their photocurrent. This process has been shown to occur efficiently in colloidal quantum dots, however, harvesting of the generated multiple charges has proved difficult. Here we show that by tuning the charge-carrier mobility in quantum-dot films, carrier multiplication can be optimized and may show an efficiency as high as in colloidal dispersion. Our results are explained quantitatively by the competition between dissociation of multiple electron–hole pairs and Auger recombination. Above a mobility of ~1 cm2 V−1 s−1, all charges escape Auger recombination and are quantitatively converted to free charges, offering the prospect of cheap quantum-dot solar cells with efficiencies in excess of the Shockley–Queisser limit. In addition, we show that the threshold energy for carrier multiplication is reduced to twice the band gap of the quantum dots. PMID:23974282

  2. Identification of the Charge Carriers in Cerium Phosphate Ceramics

    SciTech Connect

    Ray, Hannah L.; Jonghe, Lutgard C. De

    2010-06-02

    The total conductivity of Sr-doped cerium orthophosphate changes by nearly two orders of magnitude depending on the oxygen and hydrogen content of the atmosphere. The defect model for the system suggests that this is because the identity of the dominant charge carrier can change from electron holes to protons when the sample is in equilibrium with air vs. humidified hydrogen. In this work are presented some preliminary measurements that can help to clarify this exchange between carriers. The conduction behavior of a 2percent Sr-doped CePO4 sample under symmetric atmospheric conditions is investigated using several techniques, including AC impedance, H/D isotope effects, and chronoamperometry.

  3. Charge transport in semiconductor nanocrystal quantum dots

    NASA Astrophysics Data System (ADS)

    Mentzel, Tamar Shoshana

    In this thesis, we study charge transport in arrays of semiconductor nanocrystal quantum dots. Nanocrystals are synthesized in solution, and an organic ligand on the surface of the nanocrystal creates a potential barrier that confines charges in the nanocrystal. Optical absorption measurements reveal discrete electronic energy levels in the nanocrystals resulting from quantum confinement. When nanocrystals are deposited on a surface, they self-assemble into a close-packed array forming a nanocrystal solid. We report electrical transport measurements of a PbSe nanocrystal solid that serves as the channel of an inverted field-effect transistor. We measure the conductance as a function of temperature, source-drain bias and. gate voltage. The data indicates that holes are the majority carriers; the Fermi energy lies in impurity states in the bandgap of the nanocrystal; and charges hop between the highest occupied valence state in the nanocrystals (the 1S h states). At low source-drain voltages, the activation energy for hopping is given by the energy required to generate holes in the 1Sh state plus activation over barriers resulting from site disorder. The barriers from site disorder are eliminated with a sufficiently high source-drain bias. From the gate effect, we extract the Thomas-Fermi screening length and a density of states that is consistent with the estimated value. We consider variable-range hopping as an alternative model, and find no self-consistent evidence for it. Next, we employ charge sensing as an alternative to current measurements for studying transport in materials with localized sites. A narrow-channel MOSFET serves as a charge sensor because its conductance is sensitive to potential fluctuations in the nearby environment caused by the motion of charge. In particular, it is sensitive to the fluctuation of single electrons at the silicon-oxide interface within the MOSFET. We pattern a strip of amorphous germanium within 100 nm of the transistor. The

  4. Carrier transport in magnesium diboride: Role of nano-inclusions

    NASA Astrophysics Data System (ADS)

    Awasthi, A. M.; Bhardwaj, S.; Awana, V. P. S.; Figini Albisetti, A.; Giunchi, G.; Narlikar, A. V.

    2013-09-01

    Anisotropic-gap and two-band effects smear out the superconducting transition (Tc) in literature reported thermal conductivity of MgB2, where large electronic contributions also suppress anomaly-manifestation in their negligible phononic-parts. Present thermal transport results on scarcely explored specimens featuring nano-inclusions exhibit a small but clear Tc-signature, traced to relatively appreciable phononic conduction, and its dominant electronic-scattering. The self-formed MgO as extended defects strongly scatter the charge carriers and minutely the phonons with their longer-mean-free-path near Tc. Conversely, near room temperature, the shorter-dominant-wavelength phonon's transport is hugely affected by these nanoparticles, undergoing ballistic to diffusive crossover and eventually entering the Ioffe-Regel mobility threshold regime.

  5. Charge carrier recombination dynamics in perovskite and polymer solar cells

    NASA Astrophysics Data System (ADS)

    Paulke, Andreas; Stranks, Samuel D.; Kniepert, Juliane; Kurpiers, Jona; Wolff, Christian M.; Schön, Natalie; Snaith, Henry J.; Brenner, Thomas J. K.; Neher, Dieter

    2016-03-01

    Time-delayed collection field experiments are applied to planar organometal halide perovskite (CH3NH3PbI3) based solar cells to investigate charge carrier recombination in a fully working solar cell at the nanosecond to microsecond time scale. Recombination of mobile (extractable) charges is shown to follow second-order recombination dynamics for all fluences and time scales tested. Most importantly, the bimolecular recombination coefficient is found to be time-dependent, with an initial value of ca. 10-9 cm3/s and a progressive reduction within the first tens of nanoseconds. Comparison to the prototypical organic bulk heterojunction device PTB7:PC71BM yields important differences with regard to the mechanism and time scale of free carrier recombination.

  6. Giant Reduction of Charge Carrier Mobility in Strained Graphene

    NASA Astrophysics Data System (ADS)

    Shah, Raheel; Mohiuddin, Tariq M. G.; Singh, Ram N.

    2013-01-01

    Impact of induced strain on charge carrier mobility is investigated for a monolayer graphene sheet. The unsymmetrical hopping parameters between nearest neighbor atoms which emanate from induced strain are included in the density of states description. Mobility is then computed within the Born approximation by including three scattering mechanisms; charged impurity, surface roughness and lattice phonons interaction. Unlike its strained silicon counterpart, simulations reveal a significant drop in mobility for graphene with increasing strain. Additionally, mobility anisotropy is observed along the zigzag and armchair orientations. The prime reason for the drop in mobility can be attributed to the change in Fermi velocity due to strain induced distortions in the graphene honeycomb lattice.

  7. Spontaneous Charge Carrier Localization in Extended One-Dimensional Systems

    NASA Astrophysics Data System (ADS)

    Vlček, Vojtěch; Eisenberg, Helen R.; Steinle-Neumann, Gerd; Neuhauser, Daniel; Rabani, Eran; Baer, Roi

    2016-05-01

    Charge carrier localization in extended atomic systems has been described previously as being driven by disorder, point defects, or distortions of the ionic lattice. Here we show for the first time by means of first-principles computations that charge carriers can spontaneously localize due to a purely electronic effect in otherwise perfectly ordered structures. Optimally tuned range-separated density functional theory and many-body perturbation calculations within the G W approximation reveal that in trans-polyacetylene and polythiophene the hole density localizes on a length scale of several nanometers. This is due to exchange-induced translational symmetry breaking of the charge density. Ionization potentials, optical absorption peaks, excitonic binding energies, and the optimally tuned range parameter itself all become independent of polymer length as it exceeds the critical localization length. Moreover, we find that lattice disorder and the formation of a polaron result from the charge localization in contrast to the traditional view that lattice distortions precede charge localization. Our results can explain experimental findings that polarons in conjugated polymers form instantaneously after exposure to ultrafast light pulses.

  8. Flexible cobalt-phthalocyanine thin films with high charge carrier mobility

    NASA Astrophysics Data System (ADS)

    Singh, Ajay; Kumar, Arvind; Kumar, Ashwini; Samanta, Soumen; Debnath, Anil K.; Jha, Purushottam; Prasad, Rajeshwar; Salmi, Zakaria; Nowak, Sophie; Chehimi, Mohamed M.; Aswal, Dinesh K.; Gupta, Shiv K.

    2012-11-01

    The structural and charge transport characteristics of cobalt phthalocyanine (CoPc) films deposited on flexible bi-axially oriented polyethylene terephthalate (BOPET) substrates are investigated. CoPc films exhibited a preferential (200) orientation with charge carrier mobility of ˜118 cm2 V-1 s-1 (at 300 K). These films exhibited a reversible resistance changes upon bending them to different radius of curvature. The charge transport in CoPc films is governed by a bias dependent crossover from ohmic (J-V) to trap-free space-charge limited conduction (J-V2). These results demonstrate that CoPc films on flexible BOPET having high mobility and high mechanical flexibility are a potential candidate for flexible electronic devices.

  9. Flexible cobalt-phthalocyanine thin films with high charge carrier mobility

    SciTech Connect

    Singh, Ajay; Kumar, Arvind; Kumar, Ashwini; Samanta, Soumen; Debnath, Anil K.; Jha, Purushottam; Prasad, Rajeshwar; Aswal, Dinesh K.; Gupta, Shiv K.; Salmi, Zakaria; Nowak, Sophie; Chehimi, Mohamed M.

    2012-11-26

    The structural and charge transport characteristics of cobalt phthalocyanine (CoPc) films deposited on flexible bi-axially oriented polyethylene terephthalate (BOPET) substrates are investigated. CoPc films exhibited a preferential (200) orientation with charge carrier mobility of {approx}118 cm{sup 2} V{sup -1} s{sup -1} (at 300 K). These films exhibited a reversible resistance changes upon bending them to different radius of curvature. The charge transport in CoPc films is governed by a bias dependent crossover from ohmic (J-V) to trap-free space-charge limited conduction (J-V{sup 2}). These results demonstrate that CoPc films on flexible BOPET having high mobility and high mechanical flexibility are a potential candidate for flexible electronic devices.

  10. Transport and Structure of Charge Density Waves

    NASA Astrophysics Data System (ADS)

    Dicarlo, David Anthony

    Experimental studies are presented concerning the transport properties and structure of charge-density waves (CDWs) in rm NbSe_3 and rm K_{0.3}MoO_3. Transport measurements were performed to determine how charged impurities affect the CDW and how the narrow -band noise is created in sliding CDWs. Ti-doped rm NbSe_3 is shown to have a weakly pinned CDW even though Ti is incorporated as a charged impurity. The narrow-band-noise amplitude versus sample volume and impurity concentration is consistent with the narrow-band-noise being generated in the bulk by impurities and a weakly pinned CDW. X-ray scattering measurements were performed to determine how impurities, temperature, normal carriers, and electric fields affect the CDW structure. The periodic CDW scatters x-rays and the sharpness of the scattering is a reflection of the CDW structure. The CDW correlation function and its characteristic length are determined through the competition between the disordering impurity forces and the ordering elastic forces. Added impurities and high temperatures decrease the correlations by increasing the disorder forces and decreasing the CDW order parameter Delta , respectively. For rm NbSe_3, the correlation length l was much greater than the average impurity spacing and depends on impurity density n _{i} and temperature as l ~ Delta^2/n_{i}. In addition, the CDW correlation function decays exponentially in real space; ~ e^{-| {bf r}| /l}. These results are consistent with weak pinning. In rm K_{0.3}MoO _3, the CDW exhibits a different structure than that in rm NbSe_3. Changes occur in the correlation function and peak width at low temperatures. These are possibly due to the freeze out of normal carriers in semiconducting rm K _{0.3}MoO_3.. Longitudinal CDW deformations are observed when the CDW was driven by an external electric field. The electric field, temperature, and position dependence of these deformations are consistent with those required for CDW

  11. Scaling properties of charge transport in polycrystalline graphene.

    PubMed

    Van Tuan, Dinh; Kotakoski, Jani; Louvet, Thibaud; Ortmann, Frank; Meyer, Jannik C; Roche, Stephan

    2013-04-10

    Polycrystalline graphene is a patchwork of coalescing graphene grains of varying lattice orientations and size, resulting from the chemical vapor deposition (CVD) growth at random nucleation sites on metallic substrates. The morphology of grain boundaries has become an important topic given its fundamental role in limiting the mobility of charge carriers in polycrystalline graphene, as compared to mechanically exfoliated samples. Here we report new insights to the current understanding of charge transport in polycrystalline geometries. We created realistic models of large CVD-grown graphene samples and then computed the corresponding charge carrier mobilities as a function of the average grain size and the coalescence quality between the grains. Our results reveal a remarkably simple scaling law for the mean free path and conductivity, correlated to atomic-scale charge density fluctuations along grain boundaries. PMID:23448361

  12. Monte Carlo simulations of charge transport in heterogeneous organic semiconductors

    NASA Astrophysics Data System (ADS)

    Aung, Pyie Phyo; Khanal, Kiran; Luettmer-Strathmann, Jutta

    2015-03-01

    The efficiency of organic solar cells depends on the morphology and electronic properties of the active layer. Research teams have been experimenting with different conducting materials to achieve more efficient solar panels. In this work, we perform Monte Carlo simulations to study charge transport in heterogeneous materials. We have developed a coarse-grained lattice model of polymeric photovoltaics and use it to generate active layers with ordered and disordered regions. We determine carrier mobilities for a range of conditions to investigate the effect of the morphology on charge transport.

  13. Niosomal carriers enhance oral bioavailability of carvedilol: effects of bile salt-enriched vesicles and carrier surface charge

    PubMed Central

    Arzani, Gelareh; Haeri, Azadeh; Daeihamed, Marjan; Bakhtiari-Kaboutaraki, Hamid; Dadashzadeh, Simin

    2015-01-01

    Carvedilol (CRV) is an antihypertensive drug with both alpha and beta receptor blocking activity used to preclude angina and cardiac arrhythmias. To overcome the low, variable oral bioavailability of CRV, niosomal formulations were prepared and characterized: plain niosomes (without bile salts), bile salt-enriched niosomes (bilosomes containing various percentages of sodium cholate or sodium taurocholate), and charged niosomes (negative, containing dicetyl phosphate and positive, containing hexadecyl trimethyl ammonium bromide). All formulations were characterized in terms of encapsulation efficiency, size, zeta potential, release profile, stability, and morphology. Various formulations were administered orally to ten groups of Wistar rats (n=6 per group). The plasma levels of CRV were measured by a validated high-performance liquid chromatography (HPLC) method and pharmacokinetic properties of different formulations were characterized. Contribution of lymphatic transport to the oral bioavailability of niosomes was also investigated using a chylomicron flow-blocking approach. Of the bile salt-enriched vesicles examined, bilosomes containing 20% sodium cholate (F2) and 30% sodium taurocholate (F5) appeared to give the greatest enhancement of intestinal absorption. The relative bioavailability of F2 and F5 formulations to the suspension was estimated to be 1.84 and 1.64, respectively. With regard to charged niosomes, the peak plasma concentrations (Cmax) of CRV for positively (F7) and negatively charged formulations (F10) were approximately 2.3- and 1.7-fold higher than after a suspension. Bioavailability studies also revealed a significant increase in extent of drug absorption from charged vesicles. Tissue histology revealed no signs of inflammation or damage. The study proved that the type and concentration of bile salts as well as carrier surface charge had great influences on oral bioavailability of niosomes. Blocking the lymphatic absorption pathway

  14. Correlated charge transport in bilinear tunnel junction arrays

    NASA Astrophysics Data System (ADS)

    Walker, Kelly A.; Cole, Jared H.

    2013-12-01

    We study theoretically the nature of correlations in space and time of the current in a one-dimensional bilinear array of tunnel junctions in the normal conduction limit, using the kinetic Monte Carlo method. The bilinear array consists of two parallel rows of tunnel junctions, capacitively coupled in a ladder configuration. The electrostatic potential landscape and the charge-charge interaction length both depend on the circuit capacitances, which in turn influence transport and charge correlations in the array. We observe the formation of stationary charge states when only one rail is voltage biased. When a symmetric bias is applied to both rails, the site at which the positive and negative charge carriers recombine can drift throughout the array. We also calculate charge densities and auto- and cross-correlation functions.

  15. Spectroscopy of Charge Carriers and Traps in Field-Doped Organic Semiconductors

    SciTech Connect

    Zhu, Xiaoyang; Frisbie, C Daniel

    2012-08-13

    This research project aims to achieve quantitative and molecular level understanding of charge carriers and traps in field-doped organic semiconductors via in situ optical absorption spectroscopy, in conjunction with time-resolved electrical measurements. During the funding period, we have made major progress in three general areas: (1) probed charge injection at the interface between a polymeric semiconductor and a polymer electrolyte dielectric and developed a thermodynamic model to quantitatively describe the transition from electrostatic to electrochemical doping; (2) developed vibrational Stark effect to probe electric field at buried organic semiconductor interfaces; (3) used displacement current measurement (DCM) to study charge transport at organic/dielectric interfaces and charge injection at metal/organic interfaces.

  16. Carrier-mediated transport of peptides by the kidney

    SciTech Connect

    Skopicki, H.A.

    1988-01-01

    Small peptide transport was characterized to determine if: (1) Multiple carriers are present in the luminal membrane of renal proximal tubular cells; (2) Carrier-mediated peptide transport is limited by size; and (3) Gentamicin inhibits carrier-mediated reabsorption of peptides. Uptake of glycyl-({sup 3}H)proline (Gly-Pro) into renal brush border membrane vesicles demonstrated a dual affinity carrier system. Whether multiple carriers are present was further investigated by characterizing the uptake of ({sup 3}H)pyroglutamyl-histidine. To determine if carrier-mediated transport of peptides is limited by size of the molecule, uptake of the hydrolytically resistant tripeptide, ({sup 3}H)pryroglutamyl-histidyl-tryptophan (pGlu-His-Trp), and tetrapeptide, ({sup 3}H)pyroglutamyl-histidyl-tryptophyl-serine (pGlu-His-Trp-Ser) were assessed. These data indicate: multiple carriers exist on the luminal membrane of renal proximal tubular cells for the transport of dipeptides, and tripeptide pGlu-His-Trp and the tetrapeptide pGlu-His-Trp-Ser are not taken up by a carrier-mediated mechanism, suggesting that the carrier may be limited by the size of the substrate.

  17. Charge transport in nanoscale junctions.

    PubMed

    Albrecht, Tim; Kornyshev, Alexei; Bjørnholm, Thomas

    2008-09-01

    Understanding the fundamentals of nanoscale charge transfer is pivotal for designing future nano-electronic devices. Such devices could be based on individual or groups of molecular bridges, nanotubes, nanoparticles, biomolecules and other 'active' components, mimicking wire, diode and transistor functions. These have operated in various environments including vacuum, air and condensed matter, in two- or three-electrode configurations, at ultra-low and room temperatures. Interest in charge transport in ultra-small device components has a long history and can be dated back to Aviram and Ratner's letter in 1974 (Chem. Phys. Lett. 29 277-83). So why is there a necessity for a special issue on this subject? The area has reached some degree of maturity, and even subtle geometric effects in the nanojunction and noise features can now be resolved and rationalized based on existing theoretical concepts. One purpose of this special issue is thus to showcase various aspects of nanoscale and single-molecule charge transport from experimental and theoretical perspectives. The main principles have 'crystallized' in our minds, but there is still a long way to go before true single-molecule electronics can be implemented. Major obstacles include the stability of electronic nanojunctions, reliable operation at room temperature, speed of operation and, last but not least, integration into large networks. A gradual transition from traditional silicon-based electronics to devices involving a single (or a few) molecule(s) therefore appears to be more viable from technologic and economic perspectives than a 'quantum leap'. As research in this area progresses, new applications emerge, e.g. with a view to characterizing interfacial charge transfer at the single-molecule level in general. For example, electrochemical experiments with individual enzyme molecules demonstrate that catalytic processes can be studied with nanometre resolution, offering a route towards optimizing biosensors at

  18. Charge Injection and Transport in Conjugated Polymers.

    NASA Astrophysics Data System (ADS)

    Malliaras, George

    2007-03-01

    We will overview the state-of-the-art in our understanding of charge injection and transport in conjugated polymers. We start by discussing the identifying characteristics of this class of materials, especially in relation with their structure and morphology. We follow by reviewing the advantages and limitations of experimental techniques that are used to probe charge transport. We then embark on a discussion of the fundamentals of charge transport in organics. We follow a didactic approach, where we start from transport in crystalline semiconductors and gradually introduce corrections for space charge effects, for the influence of disorder on mobility, for high charge densities, and for electric field-dependent charge densities. We compare with experimental data from polyfluorenes. We then shift our attention to charge injection. We review some of the recent theories and compared their predictions to experimental data, again from polyfluorenes. We close by proposing directions for future work.

  19. Polaron mass of charge carriers in semiconductor quantum wells

    SciTech Connect

    Maslov, A. Yu. Proshina, O. V.

    2015-10-15

    A theory of the interaction of charge carriers with optical phonons in a quantum well is developed with consideration for interface optical phonons. The dependence of the polaron effective mass on the quantum-well dimensions and dielectric characteristics of barriers is analyzed in detail. It is shown that, in narrow quantum wells, a quasi-two-dimensional polaron can be formed. In this case, however, the interaction parameters are defined by the charge-carrier effective mass in the quantum well and by the frequencies of interface optical phonons. If barriers are made of a nonpolar material, the polaron effective mass depends on the quantum-well width. As the quantum-well width is increased, a new mechanism of enhancement of the electron–phonon interaction develops. The mechanism is implemented, if the optical phonon energy is equal to the energy of one of the electronic transitions. This condition yields an unsteady dependence of the polaron effective mass on the quantum-well width.

  20. Optical detection of charge carriers in multilayer organic light-emitting diodes: Experiment and theory

    NASA Astrophysics Data System (ADS)

    Book, K.; Nikitenko, V. R.; Bässler, H.; Elschner, A.

    2001-03-01

    We have investigated a multilayer organic light-emitting diode with 1,3,5-tris (N,N-bis-(4-methoxyphenyl)aminophenyl)-benzene acting as the hole transporting layer (HTL) and tris (8-hydroxy-quinolinolato) aluminum (Alq3) as the electron transporting layer. Positive charge carriers in the HTL were detected optically as a function of the applied bias. It was found that a hole injecting layer, consisting of 3,4 polyethylene-dioxy-thiophene doped with polystyrenesulfonate, forms an ohmic contact to the HTL by inducing a thin layer of holes in the interfacial region. An analytical model is developed to describe the observed carrier concentrations as well as the current-brightness-voltage characteristics quantitatively.

  1. Charge transport in single crystal organic semiconductors

    NASA Astrophysics Data System (ADS)

    Xie, Wei

    high-quality single crystals and exhibit large ambipolar mobilities. Nevertheless, a gap remains between the theory-predicted properties and this preliminary result, which itself is another fundamental challenge. This is further addressed by appropriate device optimization, and in particular, contact engineering approach to improve the charge injection efficiencies. The outcome is not only the achievement of new record ambipolar mobilities in one of the derivatives, namely, 4.8 cm2V-1s-1 for holes and 4.2 cm2V-1s-1 for electrons, but also provides a comprehensive and rational pathway towards the realization of high-performance organic semiconductors. Efforts to achieve high mobility in other organic single crystals are also presented. The second challenge is tuning the transition of electronic ground states, i.e., semiconducting, metallic and superconducting, in organic single crystals. Despite an active research area since four decades ago, we aim to employ the electrostatic approach instead of chemical doping for reversible and systematic control of charge densities within the same crystal. The key material in this study is the high-capacitance electrolyte, such as ionic liquids (ILs), whose specific capacitance reaches ~ μF/cm2, thus allowing accumulation of charge carrier above 1013 cm-2 when novel transport phenomena, such as insulator-metal transition and superconductivity, are likely to occur. This thesis addresses the electrical characterization, device physics and transport physics in electrolyte-gated single crystals, in the device architecture known as the electrical double layer transistor (EDLT). A detailed characterization scheme is first demonstrated for accurate determination of several key parameters, e.g., carrier mobility and charge density, in organic EDLTs. Further studies, combining both experiments and theories, are devoted to understanding the unusual charge density dependent channel conductivity and gate-to-channel capacitance behaviors. In

  2. Minority carrier transport in GaN and related materials

    NASA Astrophysics Data System (ADS)

    Chernyak, Leonid; Osinsky, Andrei; Schulte, Alfons

    2001-09-01

    Minority carrier transport properties are an indicator of AlGaN quality. This characteristic is particularly of significant importance for AlGaN-based bipolar devices. The goal of this review is to discuss different factors - temperature, doping level, dislocation density, electron current density - which affect minority carrier mobility, lifetime, and diffusion length, and to relate the changes in AlGaN transport properties to the functionality of electronic and optoelectronic devices.

  3. Structural influences on charge carrier dynamics for small-molecule organic photovoltaics

    SciTech Connect

    Wang, Zhiping Shibata, Yosei; Yamanari, Toshihiro; Matsubara, Koji; Yoshida, Yuji; Miyadera, Tetsuhiko; Saeki, Akinori; Seki, Shu; Zhou, Ying

    2014-07-07

    We investigated the structural influences on the charge carrier dynamics in zinc phthalocyanine/fullerene (ZnPc/C{sub 60}) photovoltaic cells by introducing poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and 2,5-bis(4-biphenylyl)-bithiophene (BP2T) between indium tin oxide and ZnPc layers. ZnPc films can be tuned to be round, long fiber-like, and short fiber-like structure, respectively. Time-resolved microwave conductivity measurements reveal that charge carrier lifetime in ZnPc/C{sub 60} bilayer films is considerably affected by the intra-grain properties. Transient photocurrent of ZnPc single films indicated that the charge carriers can transport for a longer distance in the long fiber-like grains than that in the round grains, due to the greatly lessened grain boundaries. By carefully controlling the structure of ZnPc films, the short-circuit current and fill factor of a ZnPc/C{sub 60} heterojunction solar cell with BP2T are significantly improved and the power conversion efficiency is increased to 2.6%, which is 120% larger than the conventional cell without BP2T.

  4. Structural influences on charge carrier dynamics for small-molecule organic photovoltaics

    NASA Astrophysics Data System (ADS)

    Wang, Zhiping; Miyadera, Tetsuhiko; Saeki, Akinori; Zhou, Ying; Seki, Shu; Shibata, Yosei; Yamanari, Toshihiro; Matsubara, Koji; Yoshida, Yuji

    2014-07-01

    We investigated the structural influences on the charge carrier dynamics in zinc phthalocyanine/fullerene (ZnPc/C60) photovoltaic cells by introducing poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and 2,5-bis(4-biphenylyl)-bithiophene (BP2T) between indium tin oxide and ZnPc layers. ZnPc films can be tuned to be round, long fiber-like, and short fiber-like structure, respectively. Time-resolved microwave conductivity measurements reveal that charge carrier lifetime in ZnPc/C60 bilayer films is considerably affected by the intra-grain properties. Transient photocurrent of ZnPc single films indicated that the charge carriers can transport for a longer distance in the long fiber-like grains than that in the round grains, due to the greatly lessened grain boundaries. By carefully controlling the structure of ZnPc films, the short-circuit current and fill factor of a ZnPc/C60 heterojunction solar cell with BP2T are significantly improved and the power conversion efficiency is increased to 2.6%, which is 120% larger than the conventional cell without BP2T.

  5. 14 CFR 382.31 - May carriers impose special charges on passengers with a disability for providing services and...

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 4 2010-01-01 2010-01-01 false May carriers impose special charges on... 382.31 Aeronautics and Space OFFICE OF THE SECRETARY, DEPARTMENT OF TRANSPORTATION (AVIATION PROCEEDINGS) SPECIAL REGULATIONS NONDISCRIMINATION ON THE BASIS OF DISABILITY IN AIR TRAVEL...

  6. 14 CFR 382.31 - May carriers impose special charges on passengers with a disability for providing services and...

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 4 2011-01-01 2011-01-01 false May carriers impose special charges on... 382.31 Aeronautics and Space OFFICE OF THE SECRETARY, DEPARTMENT OF TRANSPORTATION (AVIATION PROCEEDINGS) SPECIAL REGULATIONS NONDISCRIMINATION ON THE BASIS OF DISABILITY IN AIR TRAVEL...

  7. 14 CFR 382.31 - May carriers impose special charges on passengers with a disability for providing services and...

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 14 Aeronautics and Space 4 2012-01-01 2012-01-01 false May carriers impose special charges on... 382.31 Aeronautics and Space OFFICE OF THE SECRETARY, DEPARTMENT OF TRANSPORTATION (AVIATION PROCEEDINGS) SPECIAL REGULATIONS NONDISCRIMINATION ON THE BASIS OF DISABILITY IN AIR TRAVEL...

  8. 14 CFR 382.31 - May carriers impose special charges on passengers with a disability for providing services and...

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 14 Aeronautics and Space 4 2013-01-01 2013-01-01 false May carriers impose special charges on passengers with a disability for providing services and accommodations required by this rule? 382.31 Section 382.31 Aeronautics and Space OFFICE OF THE SECRETARY, DEPARTMENT OF TRANSPORTATION (AVIATION PROCEEDINGS) SPECIAL REGULATIONS...

  9. 14 CFR 382.31 - May carriers impose special charges on passengers with a disability for providing services and...

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 14 Aeronautics and Space 4 2014-01-01 2014-01-01 false May carriers impose special charges on... 382.31 Aeronautics and Space OFFICE OF THE SECRETARY, DEPARTMENT OF TRANSPORTATION (AVIATION PROCEEDINGS) SPECIAL REGULATIONS NONDISCRIMINATION ON THE BASIS OF DISABILITY IN AIR TRAVEL...

  10. Charge Transport across DNA-Based Three-Way Junctions.

    PubMed

    Young, Ryan M; Singh, Arunoday P N; Thazhathveetil, Arun K; Cho, Vincent Y; Zhang, Yuqi; Renaud, Nicolas; Grozema, Ferdinand C; Beratan, David N; Ratner, Mark A; Schatz, George C; Berlin, Yuri A; Lewis, Frederick D; Wasielewski, Michael R

    2015-04-22

    DNA-based molecular electronics will require charges to be transported from one site within a 2D or 3D architecture to another. While this has been shown previously in linear, π-stacked DNA sequences, the dynamics and efficiency of charge transport across DNA three-way junction (3WJ) have yet to be determined. Here, we present an investigation of hole transport and trapping across a DNA-based three-way junction systems by a combination of femtosecond transient absorption spectroscopy and molecular dynamics simulations. Hole transport across the junction is proposed to be gated by conformational fluctuations in the ground state which bring the transiently populated hole carrier nucleobases into better aligned geometries on the nanosecond time scale, thus modulating the π-π electronic coupling along the base pair sequence. PMID:25822073

  11. Order induced charge carrier mobility enhancement in columnar liquid crystal diodes.

    PubMed

    Eccher, Juliana; Faria, Gregório C; Bock, Harald; von Seggern, Heinz; Bechtold, Ivan H

    2013-11-27

    Discotic molecules comprising a rigid aromatic core and flexible side chains have been promisingly applied in OLEDs as self-organizing organic semiconductors. Due to their potentially high charge carrier mobility along the columns, device performance can be readily improved by proper alignment of columns throughout the bulk. In the present work, the charge mobility was increased by 5 orders of magnitude due to homeotropic columnar ordering induced by the boundary interfaces during thermal annealing in the mesophase. State-of-the-art diodes were fabricated using spin-coated films whose homeotropic alignment with formation of hexagonal germs was observed by polarizing optical microscopy. The photophysical properties showed drastic changes at the mesophase-isotropic transition, which is supported by the gain of order observed by X-ray diffraction. The electrical properties were investigated by modeling the current-voltage characteristics by a space-charge-limited current transport with a field dependent mobility. PMID:24191748

  12. Charge carrier rearrangement in spinel crystals irradiated at low temperatures

    NASA Astrophysics Data System (ADS)

    Gritsyna, V. T.; Afanasyev-Charkin, I. V.; Kobyakov, V. A.; Voitsenya, T. I.; Sickafus, K. E.

    2000-05-01

    The results of an investigation of thermoluminescence (TL) in nominally pure MgAl2O4 spinel single crystals in the temperature range between 80-670 K are presented. For a heating rate of 0.21 K/s, TL spectra exhibit glow peaks in three distinct temperature ranges: 100-160, 270-370 and 470-670 K. The most prominent peaks are at 115, 140, 305, 335, 525, 570 and 605 K. The locations of the temperature maxima, as well as the intensity of the peaks, vary depending on the treatment of the crystals, the type of irradiation and the temperature of irradiation. Measurements of the glow peaks at different emission wavelengths and the use of partial bleaching and isothermal decay techniques for TL, allowed us to propose mechanisms for charge carrier rearrangement at lattice defects and impurity ions, during irradiation and subsequent heating.

  13. Intrinsic Charge Carrier Mobility in Single-Layer Black Phosphorus

    NASA Astrophysics Data System (ADS)

    Rudenko, A. N.; Brener, S.; Katsnelson, M. I.

    2016-06-01

    We present a theory for single- and two-phonon charge carrier scattering in anisotropic two-dimensional semiconductors applied to single-layer black phosphorus (BP). We show that in contrast to graphene, where two-phonon processes due to the scattering by flexural phonons dominate at any practically relevant temperatures and are independent of the carrier concentration n , two-phonon scattering in BP is less important and can be considered negligible at n ≳1013 cm-2 . At smaller n , however, phonons enter in the essentially anharmonic regime. Compared to the hole mobility, which does not exhibit strong anisotropy between the principal directions of BP (μx x/μy y˜1.4 at n =1013 cm-2 and T =300 K ), the electron mobility is found to be significantly more anisotropic (μx x/μy y˜6.2 ). Absolute values of μx x do not exceed 250 (700 ) cm2 V-1 s-1 for holes (electrons), which can be considered as an upper limit for the mobility in BP at room temperature.

  14. Intrinsic Charge Carrier Mobility in Single-Layer Black Phosphorus.

    PubMed

    Rudenko, A N; Brener, S; Katsnelson, M I

    2016-06-17

    We present a theory for single- and two-phonon charge carrier scattering in anisotropic two-dimensional semiconductors applied to single-layer black phosphorus (BP). We show that in contrast to graphene, where two-phonon processes due to the scattering by flexural phonons dominate at any practically relevant temperatures and are independent of the carrier concentration n, two-phonon scattering in BP is less important and can be considered negligible at n≳10^{13}  cm^{-2}. At smaller n, however, phonons enter in the essentially anharmonic regime. Compared to the hole mobility, which does not exhibit strong anisotropy between the principal directions of BP (μ_{xx}/μ_{yy}∼1.4 at n=10^{13} cm^{-2} and T=300  K), the electron mobility is found to be significantly more anisotropic (μ_{xx}/μ_{yy}∼6.2). Absolute values of μ_{xx} do not exceed 250 (700)  cm^{2} V^{-1} s^{-1} for holes (electrons), which can be considered as an upper limit for the mobility in BP at room temperature. PMID:27367397

  15. Plasmonic Hot Carrier Transport and Collection in Nanostructures

    NASA Astrophysics Data System (ADS)

    Jermyn, Adam; Sundararaman, Ravishankar; Narang, Prineha; Goddard, William; Atwater, Harry; Joint CenterArtificial Photosynthesis Collaboration

    2015-03-01

    Plasmonic resonances provide a promising pathway for efficiently capturing photons from solar radiation and improving photo-catalytic activity via hot carrier generation. Previous calculations have provided the prompt energy-momentum distributions of hot carriers, but have left open the question of their transport to collection surfaces [Accepted in Nature Communications]. As the overall efficiency of plasmonic devices is dependent not just on how many carriers are collected but also on their energy distribution, a transport model which tracks this distribution is of key importance. Here, we provide a first-principles model of this transport based upon at the linearized Boltzmann equation with the diffusive and ballistic regimes handled separately, and investigate the role of geometry on plasmonic hot carrier collection.

  16. Carrier Transport Mechanism in Single Crystalline Organic Semiconductor Thin Film Elucidated by Visualized Carrier Motion.

    PubMed

    Matsubara, Kohei; Abe, Kentaro; Manaka, Takaaki; Iwamoto, Mitsumasa

    2016-04-01

    Time-resolved microscopic second harmonic generation (TRM-SHG) measurement was conducted to evaluate temperature dependence of the anisotropic carrier transport process in 6,13-Bis(triisopropylsilylethynyl) (TIPS) pentacene single crystalline domains for two orthogonal directions. Enhancement of the electric field induced SHG (EFI-SHG) signal at the electrode edge at low temperature suggests the presence of potential drop in the injection process. We directly evaluated temperature dependence of the carrier mobility by taking into account the potential drop, and concluded that the Marcus theory is appropriate to interpret the carrier transport in anisotropic TIPS pentacene thin film. TRM-SHG method is a facile and effective way to directly visualize transport process in anisotropic materials and to evaluate injection and transport processes simultaneously. PMID:27451638

  17. Thermodynamic picture of ultrafast charge transport in graphene

    NASA Astrophysics Data System (ADS)

    Mics, Zoltán; Tielrooij, Klaas-Jan; Parvez, Khaled; Jensen, Søren A.; Ivanov, Ivan; Feng, Xinliang; Müllen, Klaus; Bonn, Mischa; Turchinovich, Dmitry

    2015-07-01

    The outstanding charge transport properties of graphene enable numerous electronic applications of this remarkable material, many of which are expected to operate at ultrahigh speeds. In the regime of ultrafast, sub-picosecond electric fields, however, the very high conduction properties of graphene are not necessarily preserved, with the physical picture explaining this behaviour remaining unclear. Here we show that in graphene, the charge transport on an ultrafast timescale is determined by a simple thermodynamic balance maintained within the graphene electronic system acting as a thermalized electron gas. The energy of ultrafast electric fields applied to graphene is converted into the thermal energy of its entire charge carrier population, near-instantaneously raising the electronic temperature. The dynamic interplay between heating and cooling of the electron gas ultimately defines the ultrafast conductivity of graphene, which in a highly nonlinear manner depends on the dynamics and the strength of the applied electric fields.

  18. Intrinsic slow charge response in the perovskite solar cells: Electron and ion transport

    SciTech Connect

    Shi, Jiangjian; Xu, Xin; Zhang, Huiyin; Luo, Yanhong; Li, Dongmei; Meng, Qingbo

    2015-10-19

    The intrinsic charge response and hysteresis characteristic in the perovskite solar cell has been investigated by an electrically modulated transient photocurrent technology. An ultraslow charge response process in the timescale of seconds is observed, which can be well explained by the ion migration in the perovskite CH{sub 3}NH{sub 3}PbI{sub 3} film driven by multiple electric fields derived from the heterojunction depletion charge, the external modulation, and the accumulated ion charge. Furthermore, theoretical calculation of charge transport reveals that the hysteresis behavior is also significantly influenced by the interfacial charge extraction velocity and the carrier transport properties inside the cell.

  19. Charge Transport in Hybrid Halide Perovskite Field-Effect Transistors

    NASA Astrophysics Data System (ADS)

    Jurchescu, Oana

    Hybrid organic-inorganic trihalide perovskite (HTP) materials exhibit a strong optical absorption, tunable band gap, long carrier lifetimes and fast charge carrier transport. These remarkable properties, coupled with their reduced complexity processing, make the HTPs promising contenders for large scale, low-cost thin film optoelectronic applications. But in spite of the remarkable demonstrations of high performance solar cells, light-emitting diodes and field-effect transistor devices, all of which took place in a very short time period, numerous questions related to the nature and dynamics of the charge carriers and their relation to device performance, stability and reliability still remain. This presentation describes the electrical properties of HTPs evaluated from field-effect transistor measurements. The electrostatic gating of provides an unique platform for the study of intrinsic charge transport in these materials, and, at the same time, expand the use of HTPs towards switching electronic devices, which have not been explored previously. We fabricated FETs on SiO2 and polymer dielectrics from spin coating, thermal evaporation and spray deposition and compare their properties. CH3NH3PbI3-xClx can reach balanced electron and hole mobilities of 10 cm2/Vs upon tuning the thin-film microstructure, injection and the defect density at the semiconductor/dielectric interface. The work was performed in collaboration with Yaochuan Mei (Wake Forest University), Chuang Zhang, and Z. Valy Vardeny (University of Utah). The work is supported by ONR Grant N00014-15-1-2943.

  20. Bimodal behaviour of charge carriers in graphene induced by electric double layer

    NASA Astrophysics Data System (ADS)

    Tsai, Sing-Jyun; Yang, Ruey-Jen

    2016-07-01

    A theoretical investigation is performed into the electronic properties of graphene in the presence of liquid as a function of the contact area ratio. It is shown that the electric double layer (EDL) formed at the interface of the graphene and the liquid causes an overlap of the conduction bands and valance bands and increases the density of state (DOS) at the Fermi energy (EF). In other words, a greater number of charge carriers are induced for transport and the graphene changes from a semiconductor to a semimetal. In addition, it is shown that the dependence of the DOS at EF on the contact area ratio has a bimodal distribution which responses to the experimental observation, a pinnacle curve. The maximum number of induced carriers is expected to occur at contact area ratios of 40% and 60%. In general, the present results indicate that modulating the EDL provides an effective means of tuning the electronic properties of graphene in the presence of liquid.

  1. Carrier Transport in Epitaxial Multi-layer Graphene

    NASA Astrophysics Data System (ADS)

    Lin, Yu-Ming; Dimitrakopoulos, Christos; Farmer, Damon; Han, Shu-Jen; Wu, Yanqing; Zhu, Wenjuan; Gaskill, D. Kurt; Tedesco, Joseph; Myers-Ward, Rachael; Eddy, Charles, Jr.; Grill, Alfred; Avouris, Phaedon; Ibm Team; Nrl Team

    2011-03-01

    Significant attention has been focused recently on the electrical properties of graphene grown epitaxially on SiC substrates, because it offers an ideal platform for carbon-based electronics using conventional top-down lithography techniques. The transport properties of graphene are usually studied via Hall effect measurements, which provide information on the carrier mobility and density. Hall measurements performed at a single magnetic field yield a weighted average of carrier mobility and density, and are strictly applicable to homogeneous samples. In this study, we performed variable-field Hall and resistivity measurements on epitaxial graphene, and the results were analyzed with a multi-carrier model. Good agreements were obtained between experimental data and the model, providing further evidence of multi-carrier transport in the C-face grown MLG. This work is supported by DARPA under contract FA8650-08-C-7838 through the CERA program and by the Office of Naval Research.

  2. Low temperature carrier transport properties in isotopically controlled germanium

    SciTech Connect

    Itoh, K.

    1994-12-01

    Investigations of electronic and optical properties of semiconductors often require specimens with extremely homogeneous dopant distributions and precisely controlled net-carrier concentrations and compensation ratios. The previous difficulties in fabricating such samples are overcome as reported in this thesis by growing high-purity Ge single crystals of controlled {sup 75}Ge and {sup 70}Ge isotopic compositions, and doping these crystals by the neutron transmutation doping (NTD) technique. The resulting net-impurity concentrations and the compensation ratios are precisely determined by the thermal neutron fluence and the [{sup 74}Ge]/[{sup 70}Ge] ratios of the starting Ge materials, respectively. This method also guarantees unprecedented doping uniformity. Using such samples the authors have conducted four types of electron (hole) transport studies probing the nature of (1) free carrier scattering by neutral impurities, (2) free carrier scattering by ionized impurities, (3) low temperature hopping conduction, and (4) free carrier transport in samples close to the metal-insulator transition.

  3. Mechanisms of Carrier Transport Induced by a Microswimmer Bath

    SciTech Connect

    Kaiser, Andreas; Sokolov, Andrey; Aranson, Igor S.; Lowen, Hartmut

    2015-04-01

    Recently, it was found that a wedgelike microparticle (referred to as ”carrier”) which is only allowed to translate but not to rotate exhibits a directed translational motion along the wedge cusp if it is exposed to a bath of microswimmers. Here we model this effect in detail by resolving the microswimmers explicitly using interaction models with different degrees of mutual alignment. Using computer simulations we study the impact of these interactions on the transport efficiency of V-shaped carrier. We show that the transport mechanisms itself strongly depends on the degree of alignment embodied in the modelling of the individual swimmer dynamics. For weak alignment, optimal carrier transport occurs in the turbulent microswimmer state and is induced by swirl depletion inside the carrier. For strong aligning interactions, optimal transport occurs already in the dilute regime and is mediated by a polar cloud of swimmers in the carrier wake pushing the wedge-particle forward. We also demonstrate that the optimal shape of the carrier leading to maximal transport speed depends on the kind of interaction model used.

  4. Comparison of conventional molecularly doped polymeric photoreceptors and novel liquid-crystalline systems: charge injection and charge transport

    NASA Astrophysics Data System (ADS)

    Adam, Dieter; Swienty, Horst; Pinsler, Heinz; Lutz, Manfred; Bondkowski, Jens; Bleyl, Ingo; Haarer, Dietrich

    1997-10-01

    Charge-carrier transport and charge-carrier injection in mono-layers and two-layer photoreceptors with both "conventional", i. e., molecularly doped polymeric (MDP) transport layers and novel liquid-crystalline (LC) transport systems have been investigated by time-of-flight (TOF) experiments. As compared to the MDP materials, the LC model compounds showed a considerable potential towards high-speed xerographic application due to a charge-carrier mobility as high as 0,1 cm2/V s for the hexa(hexyltho)triphenylene (HHTT). In two-layer systems with MDP CTL, the formation of a sharp and well-defined interface between CGL and TL is impossible, a bulky intermediate layer is inevitable due to the wet-coating process. This results in a delayed charge-carrier injection due to space-charge effects originating from the intermediate layer. Two-layer systems with a LC CTL allow to investigate two novel aspects: (i) Since preparation of a LC CU is feasible in a solvent-free process, the formation of an ideal, i.e., sharp interface between CU and CGL is possible. Hence, charge-carrier injection from a well-defined interface can be studied. The results can be explained (i) by taking into account the different extrinsic charge-generation mechanisms for azo pigments (Azo) and phthalocyanine pigments and (ii) the different HOMO levels of Azo and phthalocyanine as compared to the HOMO-level of HHTT (ii) Due to the high charge carrier mobility, the LC CU is a "fast enough probe" to monitor time resolved injection phenomena.

  5. Ultrafast charge carrier dynamics in Au/semiconductor nanoheterostructures

    NASA Astrophysics Data System (ADS)

    Lambright, Scott

    The charge carrier dynamics in several Au/semiconductor core/shell heterostructures were examined. Firstly, Au/CdS core/shell nanocomposites were synthesized in a four step procedure culminating in a cation exchange performed on the shell. Previous studies of the ultrafast carrier dynamics in Au/CdS nanocomposites with epitaxial boundary regions reported the suppression of plasmon character in transient absorption spectra accompanied by broadband photoinduced absorption. The coupling of electron wavefunctions with lattice defects at the boundary of the two domains has been blamed for these phenomena. In the current study, transmission electron micrographs of Au/CdS synthesized using cation exchange showed no evidence of strain on the lattice of either component, while femtosecond transient absorption data show the retention of bleach regions attributed to CdS's 1S(e)-1S3/2(h) transition and Au's plasmon resonance. Accelerated rates of bleach recovery for both excitations ( tauexiton ≈ 300 ps, tauplasmon ≈ .7 ps) indicated that the interaction of Au and CdS domains leads to faster relaxation to their respective photoexcitations when compared to relaxation times in isolated Au and CdS nanoparticles. It was believed that the Au/CdS boundary was non-epitaxial in the presented core/shell nanocomposites. Secondly, these non-epitaxial Au/CdS core/shells were subsequently used to demonstrate near-field energy transfer from 5 nm diameter Au cores to CdS-encapsulated CdSe quantum dots. To this end, Au/CdS and CdSe/CdS nanocrystals were embedded in semiconductor-matrix-encapsulated-nanocrystal-arrays (SMENA) together. The encapsulation of both domains in the high band-gap semiconductor CdS was a means to suppress charge transfer between the two nanoparticles. The fluorescence intensity in these films was enhanced 6-fold in some cases as a result of the presence of Au domains. It was also demonstrated that the fluorescence enhancement was independent of the potential

  6. Charge and spin transport in mesoscopic superconductors

    PubMed Central

    Wolf, M J; Hübler, F; Kolenda, S

    2014-01-01

    Summary Background: Non-equilibrium charge transport in superconductors has been investigated intensely in the 1970s and 1980s, mostly in the vicinity of the critical temperature. Much less attention has been paid to low temperatures and the role of the quasiparticle spin. Results: We report here on nonlocal transport in superconductor hybrid structures at very low temperatures. By comparing the nonlocal conductance obtained by using ferromagnetic and normal-metal detectors, we discriminate charge and spin degrees of freedom. We observe spin injection and long-range transport of pure, chargeless spin currents in the regime of large Zeeman splitting. We elucidate charge and spin transport by comparison to theoretical models. Conclusion: The observed long-range chargeless spin transport opens a new path to manipulate and utilize the quasiparticle spin in superconductor nanostructures. PMID:24605283

  7. Ambipolar charge transport in microcrystalline silicon thin-film transistors

    SciTech Connect

    Knipp, Dietmar; Marinkovic, M.; Chan, Kah-Yoong; Gordijn, Aad; Stiebig, Helmut

    2011-01-15

    Hydrogenated microcrystalline silicon ({mu}c-Si:H) is a promising candidate for thin-film transistors (TFTs) in large-area electronics due to high electron and hole charge carrier mobilities. We report on ambipolar TFTs based on {mu}c-Si:H prepared by plasma-enhanced chemical vapor deposition at temperatures compatible with flexible substrates. Electrons and holes are directly injected into the {mu}c-Si:H channel via chromium drain and source contacts. The TFTs exhibit electron and hole charge carrier mobilities of 30-50 cm{sup 2}/V s and 10-15 cm{sup 2}/V s, respectively. In this work, the electrical characteristics of the ambipolar {mu}c-Si:H TFTs are described by a simple analytical model that takes the ambipolar charge transport into account. The analytical expressions are used to model the transfer curves, the potential and the net surface charge along the channel of the TFTs. The electrical model provides insights into the electronic transport of ambipolar {mu}c-Si:H TFTs.

  8. Electric Properties of Obsidian: Evidence for Positive Hole Charge Carriers

    NASA Astrophysics Data System (ADS)

    Nordvik, R.; Freund, F. T.

    2012-12-01

    The blackness of obsidian is due to the presence of oxygen anions in the valence state 1-, creating broad energy levels at the upper edge of the valence band, which absorb visible light over a wide spectral range. These energy states are associated with defect electrons in the oxygen anion sublattice, well-known from "smoky quartz", where Al substituting for Si captures a defect electron in the oxygen anion sublattice for charge compensation [1]. Such defect electrons, also known as positive holes, are responsible for the increase in electrical conductivity in igneous rocks when uniaxial stresses are applied, causing the break-up of pre-existing peroxy defects, Si-OO-Si [2]. Peroxy defects in obsidian cannot be so easily activated by mechanical stress because the glassy matrix will break before sufficiently high stress levels can be reached. If peroxy defects do exist, however, they can be studied by activating them thermally [3]. We describe experiments with rectangular slabs of obsidian with Au electrodes at both ends. Upon heating one end, we observe (i) a thermopotential and (ii) a thermocurrent developing at distinct temperatures around 250°C and 450°C, marking the 2-step break-up of peroxy bonds. [1] Schnadt, R., and Schneider, J.: The electronic structure of the trapped-hole center in smoky quartz, Zeitschrift Physik B Condensed Matter 11, 19-42, 1970. [2] Freund, F. T., Takeuchi, A., and Lau, B. W.: Electric currents streaming out of stressed igneous rocks - A step towards understanding pre-earthquake low frequency EM emissions, Physics and Chemistry of the Earth, 31, 389-396, 2006. [3] Freund, F., and Masuda, M. M.: Highly mobile oxygen hole-type charge carriers in fused silica, Journal Material Research, 8, 1619-1622, 1991.

  9. Effects of Disorder on Carrier Transport in Cu2 SnS3

    NASA Astrophysics Data System (ADS)

    Baranowski, Lauryn L.; McLaughlin, Kevin; Zawadzki, Pawel; Lany, Stephan; Norman, Andrew; Hempel, Hannes; Eichberger, Rainer; Unold, Thomas; Toberer, Eric S.; Zakutayev, Andriy

    2015-10-01

    Cu2SnS3 is a promising absorber material that has attracted significant interest in recent years. However, similar to Cu2 ZnSn (S ,Se )4 (CZTS), Cu2 SnS3 displays cation disorder, which complicates the scientific understanding and technological applications of these materials. In this work, we use postdeposition annealing to convert disordered Cu2 SnS3 thin films to the ordered structure. After annealing, we observe crystal structure changes and detect improvements in the majority carrier (hole) transport. However, when the minority carrier (electron) transport is investigated by using optical-pump terahertz-probe spectroscopy, minimal differences are observed in the lifetimes of the photoexcited charge carriers in the ordered and disordered Cu2 SnS3 . By combining the experimental data with theoretical results from first-principles calculations and Monte Carlo simulations, we are able to conclude that even ostensibly "ordered" Cu2 SnS3 displays minority carrier transport properties corresponding to the disordered structure. Transmission electron microscopy investigations reveal only a very low density of planar defects (stacking faults and/or twins) in the annealed film, suggesting that these imperfections can dominate minority carrier transport even at low levels. The results of this study highlight some of the challenges in the development of Cu2 SnS3 -based photovoltaics and have implications for other disordered multinary semiconductors such as CZTS.

  10. The transport mechanism of the mitochondrial ADP/ATP carrier.

    PubMed

    Kunji, Edmund R S; Aleksandrova, Antoniya; King, Martin S; Majd, Homa; Ashton, Valerie L; Cerson, Elizabeth; Springett, Roger; Kibalchenko, Mikhail; Tavoulari, Sotiria; Crichton, Paul G; Ruprecht, Jonathan J

    2016-10-01

    The mitochondrial ADP/ATP carrier imports ADP from the cytosol and exports ATP from the mitochondrial matrix, which are key transport steps for oxidative phosphorylation in eukaryotic organisms. The transport protein belongs to the mitochondrial carrier family, a large transporter family in the inner membrane of mitochondria. It is one of the best studied members of the family and serves as a paradigm for the molecular mechanism of mitochondrial carriers. Structurally, the carrier consists of three homologous domains, each composed of two transmembrane α-helices linked with a loop and short α-helix on the matrix side. The transporter cycles between a cytoplasmic and matrix state in which a central substrate binding site is alternately accessible to these compartments for binding of ADP or ATP. On both the cytoplasmic and matrix side of the carrier are networks consisting of three salt bridges each. In the cytoplasmic state, the matrix salt bridge network is formed and the cytoplasmic network is disrupted, opening the central substrate binding site to the intermembrane space and cytosol, whereas the converse occurs in the matrix state. In the transport cycle, tighter substrate binding in the intermediate states allows the interconversion of conformations by lowering the energy barrier for disruption and formation of these networks, opening and closing the carrier to either side of the membrane in an alternating way. Conversion between cytoplasmic and matrix states might require the simultaneous rotation of three domains around a central translocation pathway, constituting a unique mechanism among transport proteins. This article is part of a Special Issue entitled: Mitochondrial Channels edited by Pierre Sonveaux, Pierre Maechler and Jean-Claude Martinou. PMID:27001633

  11. Charge-Carrier Dynamics in Organic-Inorganic Metal Halide Perovskites.

    PubMed

    Herz, Laura M

    2016-05-27

    Hybrid organic-inorganic metal halide perovskites have recently emerged as exciting new light-harvesting and charge-transporting materials for efficient photovoltaic devices. Yet knowledge of the nature of the photogenerated excitations and their subsequent dynamics is only just emerging. This article reviews the current state of the field, focusing first on a description of the crystal and electronic band structure that give rise to the strong optical transitions that enable light harvesting. An overview is presented of the numerous experimental approaches toward determining values for exciton binding energies, which appear to be small (a few milli-electron volts to a few tens of milli-electron volts) and depend significantly on temperature because of associated changes in the dielectric function. Experimental evidence for charge-carrier relaxation dynamics within the first few picoseconds after excitation is discussed in terms of thermalization, cooling, and many-body effects. Charge-carrier recombination mechanisms are reviewed, encompassing trap-assisted nonradiative recombination that is highly specific to processing conditions, radiative bimolecular (electron-hole) recombination, and nonradiative many-body (Auger) mechanisms. PMID:26980309

  12. Drift of charge carriers in crystalline organic semiconductors

    NASA Astrophysics Data System (ADS)

    Dong, Jingjuan; Si, Wei; Wu, Chang-Qin

    2016-04-01

    We investigate the direct-current response of crystalline organic semiconductors in the presence of finite external electric fields by the quantum-classical Ehrenfest dynamics complemented with instantaneous decoherence corrections (IDC). The IDC is carried out in the real-space representation with the energy-dependent reweighing factors to account for both intermolecular decoherence and energy relaxation by which conduction occurs. In this way, both the diffusion and drift motion of charge carriers are described in a unified framework. Based on an off-diagonal electron-phonon coupling model for pentacene, we find that the drift velocity initially increases with the electric field and then decreases at higher fields due to the Wannier-Stark localization, and a negative electric-field dependence of mobility is observed. The Einstein relation, which is a manifestation of the fluctuation-dissipation theorem, is found to be restored in electric fields up to ˜105 V/cm for a wide temperature region studied. Furthermore, we show that the incorporated decoherence and energy relaxation could explain the large discrepancy between the mobilities calculated by the Ehrenfest dynamics and the full quantum methods, which proves the effectiveness of our approach to take back these missing processes.

  13. Drift of charge carriers in crystalline organic semiconductors.

    PubMed

    Dong, Jingjuan; Si, Wei; Wu, Chang-Qin

    2016-04-14

    We investigate the direct-current response of crystalline organic semiconductors in the presence of finite external electric fields by the quantum-classical Ehrenfest dynamics complemented with instantaneous decoherence corrections (IDC). The IDC is carried out in the real-space representation with the energy-dependent reweighing factors to account for both intermolecular decoherence and energy relaxation by which conduction occurs. In this way, both the diffusion and drift motion of charge carriers are described in a unified framework. Based on an off-diagonal electron-phonon coupling model for pentacene, we find that the drift velocity initially increases with the electric field and then decreases at higher fields due to the Wannier-Stark localization, and a negative electric-field dependence of mobility is observed. The Einstein relation, which is a manifestation of the fluctuation-dissipation theorem, is found to be restored in electric fields up to ∼10(5) V/cm for a wide temperature region studied. Furthermore, we show that the incorporated decoherence and energy relaxation could explain the large discrepancy between the mobilities calculated by the Ehrenfest dynamics and the full quantum methods, which proves the effectiveness of our approach to take back these missing processes. PMID:27083750

  14. Hall effect and band-like carrier transport in high mobility polymer transistors

    NASA Astrophysics Data System (ADS)

    Yamashita, Yu; Hinkel, Felix; Marszalek, Tomasz; Zajaczkowski, Wojciech; Pisula, Wojciech; Baumgarten, Martin; Matsui, Hiroyuki; Müllen, Klaus; Takeya, Jun; Takeya group Team, Prof.; Müllen group Team, Prof.

    A microscopic understanding of charge carrier transport in polymeric semiconductors is essential to improve the state of the art of flexible or printed electronic devices. In particular, thin-film field-effect transistors based on donor-acceptor polymers are in the focus of current literature reaching high charge-carrier mobility. In this work, we demonstrate the Hall effect and the temperature dependence of the charge carrier mobility based on uniaxially ordered CDT-BTZ donor-acceptor copolymer films. Uniaxially ordered films of CDT-BTZ with hexadecyl (C16) and eicosyl (C20) sidechains showed mobility of 5.6 cm2/Vs and 11.4 cm2/Vs respectively. The activation energy of the mobility decreased with the increasing carrier density, and finally the negative temperature dependence of the mobility was observed. Both polymers showed Hall effect, which also indicates the presence of extended electronic states. The temperature and carrier density dependence will be further discussed in the presentation.

  15. Transport-reaction model for defect and carrier behavior within displacement cascades in gallium arsenide

    SciTech Connect

    Wampler, William R.; Myers, Samuel M.

    2014-02-01

    A model is presented for recombination of charge carriers at displacement damage in gallium arsenide, which includes clustering of the defects in atomic displacement cascades produced by neutron or ion irradiation. The carrier recombination model is based on an atomistic description of capture and emission of carriers by the defects with time evolution resulting from the migration and reaction of the defects. The physics and equations on which the model is based are presented, along with details of the numerical methods used for their solution. The model uses a continuum description of diffusion, field-drift and reaction of carriers and defects within a representative spherically symmetric cluster. The initial radial defect profiles within the cluster were chosen through pair-correlation-function analysis of the spatial distribution of defects obtained from the binary-collision code MARLOWE, using recoil energies for fission neutrons. Charging of the defects can produce high electric fields within the cluster which may influence transport and reaction of carriers and defects, and which may enhance carrier recombination through band-to-trap tunneling. Properties of the defects are discussed and values for their parameters are given, many of which were obtained from density functional theory. The model provides a basis for predicting the transient response of III-V heterojunction bipolar transistors to pulsed neutron irradiation.

  16. Charge carrier dynamics in organic semiconductors and their donor-acceptor composites: Numerical modeling of time-resolved photocurrent

    NASA Astrophysics Data System (ADS)

    Johnson, Brian; Kendrick, Mark J.; Ostroverkhova, Oksana

    2013-09-01

    We present a model that describes nanosecond (ns) time-scale photocurrent dynamics in functionalized anthradithiophene (ADT) films and ADT-based donor-acceptor (D/A) composites. By fitting numerically simulated photocurrents to experimental data, we quantify contributions of multiple pathways of charge carrier photogeneration to the photocurrent, as well as extract parameters that characterize charge transport (CT) in organic films including charge carrier mobilities, trap densities, hole trap depth, and trapping and recombination rates. In pristine ADT films, simulations revealed two competing charge photogeneration pathways: fast, occurring on picosecond (ps) or sub-ps time scales with efficiencies below 10%, and slow, which proceeds at the time scale of tens of nanoseconds, with efficiencies of about 11%-12%, at the applied electric fields of 40-80 kV/cm. The relative contribution of these pathways to the photocurrent was electric field dependent, with the contribution of the fast process increasing with applied electric field. However, the total charge photogeneration efficiency was weakly electric field dependent exhibiting values of 14%-20% of the absorbed photons. The remaining 80%-86% of the photoexcitation did not contribute to charge carrier generation at these time scales. In ADT-based D/A composites with 2 wt.% acceptor concentration, an additional pathway of charge photogeneration that proceeds via CT exciton dissociation contributed to the total charge photogeneration. In the composite with the functionalized pentacene (Pn) acceptor, which exhibits strong exciplex emission from a tightly bound D/A CT exciton, the contribution of the CT state to charge generation was small, ˜8%-12% of the total number of photogenerated charge carriers, dependent on the electric field. In contrast, in the composite with PCBM acceptor, the CT state contributed about a half of all photogenerated charge carriers. In both D/A composites, the charge carrier mobilities were

  17. Measuring charge carrier mobility in photovoltaic devices with micron-scale resolution

    SciTech Connect

    Ashraf, A.; Dissanayake, D. M. N. M.; Eisaman, M. D.

    2015-03-16

    We present a charge-extraction technique, micron-scale charge extraction by linearly increasing voltage, which enables simultaneous spatially resolved measurements of charge carrier mobility and photocurrent in thin-film photovoltaic devices with micron-scale resolution. An intensity-modulated laser with beam diameter near the optical diffraction limit is scanned over the device, while a linear voltage ramp in reverse bias is applied at each position of illumination. We calculate the majority carrier mobility, photocurrent, and number of photogenerated charge carriers from the resulting current transient. We demonstrate this technique on an organic photovoltaic device, but it is applicable to a wide range of photovoltaic materials.

  18. The nature of free-carrier transport in organometal halide perovskites

    NASA Astrophysics Data System (ADS)

    Hakamata, Tomoya; Shimamura, Kohei; Shimojo, Fuyuki; Kalia, Rajiv K.; Nakano, Aiichiro; Vashishta, Priya

    2016-01-01

    Organometal halide perovskites are attracting great attention as promising material for solar cells because of their high power conversion efficiency. The high performance has been attributed to the existence of free charge carriers and their large diffusion lengths, but the nature of carrier transport at the atomistic level remains elusive. Here, nonadiabatic quantum molecular dynamics simulations elucidate the mechanisms underlying the excellent free-carrier transport in CH3NH3PbI3. Pb and I sublattices act as disjunct pathways for rapid and balanced transport of photoexcited electrons and holes, respectively, while minimizing efficiency-degrading charge recombination. On the other hand, CH3NH3 sublattice quickly screens out electrostatic electron-hole attraction to generate free carriers within 1 ps. Together this nano-architecture lets photoexcited electrons and holes dissociate instantaneously and travel far away to be harvested before dissipated as heat. This work provides much needed structure-property relationships and time-resolved information that potentially lead to rational design of efficient solar cells.

  19. The nature of free-carrier transport in organometal halide perovskites

    DOE PAGESBeta

    Hakamata, Tomoya; Shimamura, Kohei; Shimojo, Fuyuki; Kalia, Rajiv K.; Nakano, Aiichiro; Vashishta, Priya

    2016-01-19

    Organometal halide perovskites are attracting great attention as promising material for solar cells because of their high power conversion efficiency. The high performance has been attributed to the existence of free charge carriers and their large diffusion lengths, but the nature of carrier transport at the atomistic level remains elusive. Here, nonadiabatic quantum molecular dynamics simulations elucidate the mechanisms underlying the excellent free-carrier transport in CH3NH3PbI3. Pb and I sublattices act as disjunct pathways for rapid and balanced transport of photoexcited electrons and holes, respectively, while minimizing efficiency-degrading charge recombination. On the other hand, CH3NH3 sublattice quickly screens out electrostaticmore » electron-hole attraction to generate free carriers within 1 ps. Together this nano-architecture lets photoexcited electrons and holes dissociate instantaneously and travel far away to be harvested before dissipated as heat. As a result, this work provides much needed structure-property relationships and time-resolved information that potentially lead to rational design of efficient solar cells.« less

  20. The nature of free-carrier transport in organometal halide perovskites.

    PubMed

    Hakamata, Tomoya; Shimamura, Kohei; Shimojo, Fuyuki; Kalia, Rajiv K; Nakano, Aiichiro; Vashishta, Priya

    2016-01-01

    Organometal halide perovskites are attracting great attention as promising material for solar cells because of their high power conversion efficiency. The high performance has been attributed to the existence of free charge carriers and their large diffusion lengths, but the nature of carrier transport at the atomistic level remains elusive. Here, nonadiabatic quantum molecular dynamics simulations elucidate the mechanisms underlying the excellent free-carrier transport in CH3NH3PbI3. Pb and I sublattices act as disjunct pathways for rapid and balanced transport of photoexcited electrons and holes, respectively, while minimizing efficiency-degrading charge recombination. On the other hand, CH3NH3 sublattice quickly screens out electrostatic electron-hole attraction to generate free carriers within 1 ps. Together this nano-architecture lets photoexcited electrons and holes dissociate instantaneously and travel far away to be harvested before dissipated as heat. This work provides much needed structure-property relationships and time-resolved information that potentially lead to rational design of efficient solar cells. PMID:26781627

  1. The nature of free-carrier transport in organometal halide perovskites

    PubMed Central

    Hakamata, Tomoya; Shimamura, Kohei; Shimojo, Fuyuki; Kalia, Rajiv K.; Nakano, Aiichiro; Vashishta, Priya

    2016-01-01

    Organometal halide perovskites are attracting great attention as promising material for solar cells because of their high power conversion efficiency. The high performance has been attributed to the existence of free charge carriers and their large diffusion lengths, but the nature of carrier transport at the atomistic level remains elusive. Here, nonadiabatic quantum molecular dynamics simulations elucidate the mechanisms underlying the excellent free-carrier transport in CH3NH3PbI3. Pb and I sublattices act as disjunct pathways for rapid and balanced transport of photoexcited electrons and holes, respectively, while minimizing efficiency-degrading charge recombination. On the other hand, CH3NH3 sublattice quickly screens out electrostatic electron-hole attraction to generate free carriers within 1 ps. Together this nano-architecture lets photoexcited electrons and holes dissociate instantaneously and travel far away to be harvested before dissipated as heat. This work provides much needed structure-property relationships and time-resolved information that potentially lead to rational design of efficient solar cells. PMID:26781627

  2. Superexchange Charge Transport in Loaded Metal Organic Frameworks.

    PubMed

    Neumann, Tobias; Liu, Jianxi; Wächter, Tobias; Friederich, Pascal; Symalla, Franz; Welle, Alexander; Mugnaini, Veronica; Meded, Velimir; Zharnikov, Michael; Wöll, Christof; Wenzel, Wolfgang

    2016-07-26

    In the past, nanoporous metal-organic frameworks (MOFs) have been mostly studied for their huge potential with regard to gas storage and separation. More recently, the discovery that the electrical conductivity of a widely studied, highly insulating MOF, HKUST-1, improves dramatically when loaded with guest molecules has triggered a huge interest in the charge carrier transport properties of MOFs. The observed high conductivity, however, is difficult to reconcile with conventional transport mechanisms: neither simple hopping nor band transport models are consistent with the available experimental data. Here, we combine theoretical results and new experimental data to demonstrate that the observed conductivity can be explained by an extended hopping transport model including virtual hops through localized MOF states or molecular superexchange. Predictions of this model agree well with precise conductivity measurements, where experimental artifacts and the influence of defects are largely avoided by using well-defined samples and the Hg-drop junction approach. PMID:27359160

  3. Stacking dependence of carrier transport properties in multilayered black phosphorous.

    PubMed

    Sengupta, A; Audiffred, M; Heine, T; Niehaus, T A

    2016-02-24

    We present the effect of different stacking orders on carrier transport properties of multi-layer black phosphorous. We consider three different stacking orders AAA, ABA and ACA, with increasing number of layers (from 2 to 6 layers). We employ a hierarchical approach in density functional theory (DFT), with structural simulations performed with generalized gradient approximation (GGA) and the bandstructure, carrier effective masses and optical properties evaluated with the meta-generalized gradient approximation (MGGA). The carrier transmission in the various black phosphorous sheets was carried out with the non-equilibrium green's function (NEGF) approach. The results show that ACA stacking has the highest electron and hole transmission probabilities. The results show tunability for a wide range of band-gaps, carrier effective masses and transmission with a great promise for lattice engineering (stacking order and layers) in black phosphorous. PMID:26809017

  4. Stacking dependence of carrier transport properties in multilayered black phosphorous

    NASA Astrophysics Data System (ADS)

    Sengupta, A.; Audiffred, M.; Heine, T.; Niehaus, T. A.

    2016-02-01

    We present the effect of different stacking orders on carrier transport properties of multi-layer black phosphorous. We consider three different stacking orders AAA, ABA and ACA, with increasing number of layers (from 2 to 6 layers). We employ a hierarchical approach in density functional theory (DFT), with structural simulations performed with generalized gradient approximation (GGA) and the bandstructure, carrier effective masses and optical properties evaluated with the meta-generalized gradient approximation (MGGA). The carrier transmission in the various black phosphorous sheets was carried out with the non-equilibrium green’s function (NEGF) approach. The results show that ACA stacking has the highest electron and hole transmission probabilities. The results show tunability for a wide range of band-gaps, carrier effective masses and transmission with a great promise for lattice engineering (stacking order and layers) in black phosphorous.

  5. Carrier-mediated ion transport in lipid bilayer membranes.

    PubMed

    Laprade, R; Grenier, F; Pagé-Dansereau, M; Dansereau, J

    1984-08-01

    The electrical properties predicted by a widely accepted model for carrier-mediated ion transport in lipid bilayers are described. The different steps leading to ion transport and their associated rate constants are reaction at the interface between an ion in the aqueous phase and a carrier in the membrane (kRi), followed by translocation of the ion-carrier complex across the membrane interior (kis) and its dissociation at the other interface (kDi) after which the free carrier crosses back the membrane interior (ks). Results on glyceryl monooleate (GMO) membranes for a family of homologue carriers, the macrotetralide actin antibiotics (nonactin, monactin, dinactin, trinactin, and tetranactin) and a variety of ions (Na+, Cs+, Rb+, K+, NH4+, and Tl+) are presented. Internally consistent data obtained from steady-state electrical measurements (zero-current potential and conductance, current-voltage relationship) allow us to obtain the equilibrium permeability ratios for the different ions and show that for a given carrier kRi is relatively invariant from one ion to the other, except for Tl+ (larger), which implies that the ionic selectivity is controlled by the dissociation of the complex. The values of the individual rate constants obtained from current relaxation experiments are also presented and confirm the findings from steady-state measurements, as well as the isostericity concept for complexes of different ions with the same carrier (kis invariant). These also allow us to determine the aqueous phase membrane and torus membrane partition coefficients. Finally, the observed increase in kis from nonactin to tetranactin and, for all homologues, from GMO-decane to solvent-free GMO membranes, together with the concomitant decrease in kDi, can be explained in terms of modifications of electrostatic energy profiles induced by variations in carrier size and membrane thickness. PMID:6498590

  6. An alternative approach to charge transport in semiconducting electrodes

    NASA Technical Reports Server (NTRS)

    Thomchick, J.; Buoncristiani, A. M.

    1980-01-01

    The excess-carrier charge transport through the space-charge region of a semiconducting electrode is analyzed by a technique known as the flux method. In this approach reflection and transmission coefficients appropriate for a sheet of uniform semiconducting material describe its transport properties. A review is presented of the flux method showing that the results for a semiconductor electrode reduce in a limiting case to those previously found by Gaertner if the depletion layer is treated as a perfectly transmitting medium in which scattering and recombination are ignored. Then, in the framework of the flux method the depletion layer is considered more realistically by explicitly taking into account scattering and recombination processes which occur in this region.

  7. Picosecond dynamics of free carrier populations, space- charge fields, and photorefractive nonlinearities in zincblende semiconductors

    NASA Astrophysics Data System (ADS)

    Stark, Thomas Spencer

    Generally, nonlinear optics studies investigate optically-induced changes in refraction or absorption, and their application to spectroscopy or device fabrication. The photorefractive effect is a nonlinear optical effect that occurs in solids, where transport of an optically-induced free-carrier population results in an internal space-charge field, which produces an index change via the linear electrooptic effect. The photorefractive effect has been widely studied for a variety of materials and device applications, mainly because it allows large index changes to be generated with laser beams having only a few milliwatts of average power. Compound semiconductors are important photorefractive materials because they offer a near-infrared optical response, and because their carrier transport properties allow the index change to be generated quickly and efficiently. While many researchers have attempted to measure the fundamental temporal dynamics of the photorefractive effect in semiconductors using continuous-wave, nanosecond- and picosecond-pulsed laser beams, these investigations have been unsuccessful. However, studies with this goal are of clear relevance because they provide information about the fundamental physical processes that produce this effect, as well as the material's speed and efficiency limitations for device applications. In this dissertation, for the first time, we time-resolve the temporal dynamics of the photorefractive nonlinearities in two zincblende semiconductors, semi- insulating GaAs and undoped CdTe. While CdTe offers a lattice-match to the infrared material HgxCd1-xTe, semi-insulating GaAs has been widely used in optoelectronic and high- speed electronic applications. We use a novel transient- grating experimental method that allows picosecond temporal resolution and high sensitivity. Our results provide a clear and detailed picture of the picosecond photorefractive response of both materials, showing nonlinearities due to hot-carrier

  8. Interfacial Study To Suppress Charge Carrier Recombination for High Efficiency Perovskite Solar Cells.

    PubMed

    Adhikari, Nirmal; Dubey, Ashish; Khatiwada, Devendra; Mitul, Abu Farzan; Wang, Qi; Venkatesan, Swaminathan; Iefanova, Anastasiia; Zai, Jiantao; Qian, Xuefeng; Kumar, Mukesh; Qiao, Qiquan

    2015-12-01

    We report effects of an interface between TiO2-perovskite and grain-grain boundaries of perovskite films prepared by single step and sequential deposited technique using different annealing times at optimum temperature. Nanoscale kelvin probe force microscopy (KPFM) measurement shows that charge transport in a perovskite solar cell critically depends upon the annealing conditions. The KPFM results of single step and sequential deposited films show that the increase in potential barrier suppresses the back-recombination between electrons in TiO2 and holes in perovskite. Spatial mapping of the surface potential within perovskite film exhibits higher positive potential at grain boundaries compared to the surface of the grains. The average grain boundary potential of 300-400 mV is obtained upon annealing for sequentially deposited films. X-ray diffraction (XRD) spectra indicate the formation of a PbI2 phase upon annealing which suppresses the recombination. Transient analysis exhibits that the optimum device has higher carrier lifetime and short carrier transport time among all devices. An optimum grain boundary potential and proper band alignment between the TiO2 electron transport layer (ETL) and the perovskite absorber layer help to increase the overall device performance. PMID:26579732

  9. Understanding the dependence of transport parameters on carrier concentration within a Gaussian density of states in molecular organic semiconductors

    NASA Astrophysics Data System (ADS)

    Sharma, A.; Kumar, P.; Rani, V.; Ray, N.; Ghosh, S.

    2016-06-01

    We study charge transport in molecular organic semiconductors using two terminal and three terminal field effect transistor devices. Using phthalocyanines as examples, we achieve unification of carrier mobility between the different configurations in a Gaussian density of states. We find that the current density–voltage characteristics for two terminal devices can be understood by introducing a concentration dependence of the carrier mobility, as described by Oelerich et al (2012 Phys. Rev. Lett. 108 226403, 2010 Appl. Phys. Lett. 97 143302). Studying the evolution of the activation energy with the carrier density, we find results consistent with a percolation picture and a density dependent transport energy.

  10. Understanding the dependence of transport parameters on carrier concentration within a Gaussian density of states in molecular organic semiconductors.

    PubMed

    Sharma, A; Kumar, P; Rani, V; Ray, N; Ghosh, S

    2016-06-15

    We study charge transport in molecular organic semiconductors using two terminal and three terminal field effect transistor devices. Using phthalocyanines as examples, we achieve unification of carrier mobility between the different configurations in a Gaussian density of states. We find that the current density-voltage characteristics for two terminal devices can be understood by introducing a concentration dependence of the carrier mobility, as described by Oelerich et al (2012 Phys. Rev. Lett. 108 226403, 2010 Appl. Phys. Lett. 97 143302). Studying the evolution of the activation energy with the carrier density, we find results consistent with a percolation picture and a density dependent transport energy. PMID:27160656

  11. Theoretical characterization of charge transport in organic molecular crystals

    NASA Astrophysics Data System (ADS)

    Sanchez-Carrera, Roel S.

    The rapid growth in the interest to explore new synthetic crystalline organic semiconductors and their subsequent device characterization has revived the debate on the development of theoretical models to better understand the intrinsic charge transport mechanisms in organic materials. At the moment, several charge-transport theories for organic molecular crystals have been proposed and have observed a comparable agreement with experimental results. However, these models are limited in scope and restricted to specific ranges of microscopic parameters and temperatures. A general description that is applicable in all parameter regimes is still unavailable. The first step towards a complete understanding of the problem associated with the charge transport in organic molecular crystals includes the development of a first-principles theoretical methodology to evaluate with high accuracy the main microscopic charge-transport parameters and their respective couplings with intra- and intermolecular vibrational degrees of freedom. In this thesis, we have developed a first-principles methodology to investigate the impact of electron-phonon interactions on the charge-carrier mobilities in organic molecular crystals. Well-known organic materials such as oligoacene and oligothienoacene derivatives were studied in detail. To predict the charge-transport phenomena in organic materials, we rely on the Marcus theory of electron-transfer reactions. Within this context, the nature of the intramolecular vibronic coupling in oligoacenes was studied using an approach that combines high-resolution gas-phase photo-electron spectroscopy measurements with first-principles quantum-mechanical calculations. This further led to investigation of the electron interactions with optical phonons in oligoacene single crystals. The lattice phonon modes were computed at both density functional theory (DFT) and empirical force field levels. The low-frequency optical modes are found to play a significant

  12. Airline Transport Pilot-Airplane (Air Carrier) Written Test Guide.

    ERIC Educational Resources Information Center

    Federal Aviation Administration (DOT), Washington, DC. Flight Standards Service.

    Presented is information useful to applicants who are preparing for the Airline Transport Pilot-Airplane (Air Carrier) Written Test. The guide describes the basic aeronautical knowledge and associated requirements for certification, as well as information on source material, instructions for taking the official test, and questions that are…

  13. Temperature dependence of charge carrier generation in organic photovoltaics.

    PubMed

    Gao, Feng; Tress, Wolfgang; Wang, Jianpu; Inganäs, Olle

    2015-03-27

    The charge generation mechanism in organic photovoltaics is a fundamental yet heavily debated issue. All the generated charges recombine at the open-circuit voltage (V_{OC}), so that investigation of recombined charges at V_{OC} provides a unique approach to understanding charge generation. At low temperatures, we observe a decrease of V_{OC}, which is attributed to reduced charge separation. Comparison between benchmark polymer:fullerene and polymer:polymer blends highlights the critical role of charge delocalization in charge separation and emphasizes the importance of entropy in charge generation. PMID:25860774

  14. Carrier Transport and Related Effects in Detectors of the Cryogenic Dark Matter Search

    SciTech Connect

    Sundqvist, Kyle Michael

    2012-01-01

    The Cryogenic Dark Matter Search (CDMS) is searching for weakly-interacting massive particles (WIMPS), which could explain the dark matter problem in cosmology and particle physics. By simultaneously measuring signals from deposited charge and the energy in nonequilibrium phonons created by particle interactions in intrinsic germanium crystals at a temperature of 40 mK, a signature response for each event is produced. This response, combined with phonon pulse-shape information, allows CDMS to actively discriminate candidate WIMP interactions with nuclei from electromagnetic radioactive background which interacts with electrons. The challenges associated with these techniques are unique. Carrier scattering is dominated by the spontaneous emission of Luke-Neganov phonons due to zeropoint fluctuations of the lattice ions. Drift fields are maintained at only a few V/cm, else these emitted phonons would dominate the phonons of the original interaction. The dominant systematic issues with CDMS detectors are due to the effects of space charge accumulation. It has been an open question how space charge accrues, and by which of several potential recombination and ionization processes. In this work, we have simulated the transport of electrons and holes in germanium under CDMS conditions. We have implemented both a traditional Monte Carlo technique based on carrier energy, followed later by a novel Monte Carlo algorithm with scattering rates defined and sampled by vector momentum. This vector-based method provides for a full anisotropic simulation of carrier transport including free-fight acceleration with an anisotropic mass, and anisotropic scattering rates. With knowledge of steady state carrier dynamics as a function of applied field, the results of our Monte Carlo simulations allow us to make a wide variety of predictions for energy dependent processes for both electrons and holes. Such processes include carrier capture by charged impurities, neutral impurities, static

  15. Carrier Transport and Related Effects in Detectors of the Cryogenic Dark Matter Search

    NASA Astrophysics Data System (ADS)

    Sundqvist, Kyle Michael

    The Cryogenic Dark Matter Search (CDMS) is searching for weakly-interacting massive particles (WIMPS), which could explain the dark matter problem in cosmology and particle physics. By simultaneously measuring signals from deposited charge and the energy in non-equilibrium phonons created by particle interactions in intrinsic germanium crystals at a temperature of 40 mK, a signature response for each event is produced. This response, combined with phonon pulse-shape information, allows CDMS to actively discriminate candidate WIMP interactions with nuclei from electromagnetic radioactive background which interacts with electrons. The challenges associated with these techniques are unique. Carrier scattering is dominated by the spontaneous emission of Luke-Neganov phonons due to zero-point fluctuations of the lattice ions. Drift fields are maintained at only a few V/cm, else these emitted phonons would dominate the phonons of the original interaction. The dominant systematic issues with CDMS detectors are due to the effects of space charge accumulation. It has been an open question how space charge accrues, and by which of several potential recombination and ionization processes. In this work, we have simulated the transport of electrons and holes in germanium under CDMS conditions. We have implemented both a traditional Monte Carlo technique based on carrier energy, followed later by a novel Monte Carlo algorithm with scattering rates defined and sampled by vector momentum. This vector-based method provides for a full anisotropic simulation of carrier transport including free-flight acceleration with an anisotropic mass, and anisotropic scattering rates. With knowledge of steady state carrier dynamics as a function of applied field, the results of our Monte Carlo simulations allow us to make a wide variety of predictions for energy dependent processes for both electrons and holes. Such processes include carrier capture by charged

  16. Charge carrier identification in tunneling spectroscopy of core-shell nanocrystals

    NASA Astrophysics Data System (ADS)

    Nguyen, T. H.; Habinshuti, J.; Justo, Y.; Gomes, R.; Mahieu, G.; Godey, S.; Nys, J. P.; Carrillo, S.; Hens, Z.; Robbe, O.; Turrell, S.; Grandidier, B.

    2011-11-01

    Semiconductor PbSe/CdSe core-shell nanocrystals (NCs) in a double barrier tunnel junction have been investigated by means of scanning tunneling spectroscopy at low temperature. From the analysis of the differential conductance peak position as a function of the potential distribution in both potential barriers, we demonstrate a unipolar transport regime for a large amount of NCs. The same charge carriers are injected on both sides of the zero-conductance gap, and the peaks observed at higher energy arise from the charging of the NCs. Similar results are obtained for CdSe/CdS dot-in-rod NCs, indicating that the addition of a shell favors transitions between different charge states rather than single particle excited states. Further characterization of the PbSe/CdSe core-shell NCs by x-ray photoemission spectroscopy reveals that the variations in the transport properties from NC to NC are explained by the occurrence of unprotected PbSe facets that have different orientations in the junction.

  17. Carrier transport in dichromatic color-coded semipolar (2021) and (2021) III-N LEDs

    NASA Astrophysics Data System (ADS)

    Kisin, Mikhail V.; Huang, Chih-Li; El-Ghoroury, Hussein S.

    2014-03-01

    Simulation of III-nitride color-coded multiple quantum well (MQW) LED structures was performed using as an experimental benchmark dichromatic semipolar LEDs grown in Ga-polar and N-polar crystallographic orientations (Y. Kawaguchi et.al, APL 100, 231110, 2012). Different QW depths in the color-coded LEDs and opposite interface polarization charges in Ga-polar and N-polar structures provide different conditions for carrier transport across the LED active regions. Combination of several effects was crucial for adequate reproduction of the emission spectra experimentally observed in color-coded structures with violet-aquamarine and aquamarine-violet active region layouts. A standard drift-diffusion transport model wascompleted with rate equations for nonequilibrium QW populations and several high-energy transport features, including the effects of QW carrier overshoot and Auger-assisted QW depopulation. COMSOL-based Optoelectronic Device Modeling Software (ODMS) developed at Ostendo Technologies Inc. was utilized for device simulation.

  18. Conditions for charge transport without recombination in low mobility organic solar cells and photodiodes (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Stolterfoht, Martin; Armin, Ardalan; Philippa, Bronson; White, Ronald D.; Burn, Paul L.; Meredith, Paul; Juška, Gytis; Pivrikas, Almantas

    2015-10-01

    Organic semiconductors typically possess low charge carrier mobilities and Langevin-type recombination dynamics, which both negatively impact the performance of organic solar cells and photodetectors. Charge transport in organic solar cells is usually characterized by the mobility-lifetime product. Using newly developed transient and steady state photocurrent measurement techniques we show that the onset of efficiency limiting photocarrier recombination is determined by the charge that can be stored on the electrodes of the device. It is shown that significant photocarrier recombination can be avoided when the total charge inside the device, defined by the trapped, doping-induced and mobile charge carriers, is less than the electrode charge. Based upon this physics we propose the mobility-recombination coefficient product as an alternative and more convenient figure of merit to minimize the recombination losses. We validate the results in 3 different organic semiconductor-based light harvesting systems with very different charge transport properties. The findings allow the determination of the charge collection efficiency in fully operational devices. In turn, knowing the conditions under which non-geminate recombination is eliminated enables one to quantify the generation efficiency of free charge carriers. The results are relevant to a wide range of light harvesting systems, particularly those based upon disordered semiconductors, and require a rethink of the critical parameters for charge transport.

  19. Symposium GC: Nanoscale Charge Transport in Excitonic Solar Cells

    SciTech Connect

    Bommisetty, Venkat

    2011-06-23

    This paper provides a summary only and table of contents of the sessions. Excitonic solar cells, including all-organic, hybrid organic-inorganic and dye-sensitized solar cells (DSSCs), offer strong potential for inexpensive and large-area solar energy conversion. Unlike traditional inorganic semiconductor solar cells, where all the charge generation and collection processes are well understood, these excitonic solar cells contain extremely disordered structures with complex interfaces which results in large variations in nanoscale electronic properties and has a strong influence on carrier generation, transport, dissociation and collection. Detailed understanding of these processes is important for fabrication of highly efficient solar cells. Efforts to improve efficiency are underway at a large number of research groups throughout the world focused on inorganic and organic semiconductors, photonics, photophysics, charge transport, nanoscience, ultrafast spectroscopy, photonics, semiconductor processing, device physics, device structures, interface structure etc. Rapid progress in this multidisciplinary area requires strong synergetic efforts among researchers from diverse backgrounds. Such effort can lead to novel methods for development of new materials with improved photon harvesting and interfacial treatments for improved carrier transport, process optimization to yield ordered nanoscale morphologies with well defined electronic structures.

  20. Electrostatic Injection of Very Large 2D Charge Carrier Densities to Obtain Metallic Conductivities in Organic Semiconductors

    NASA Astrophysics Data System (ADS)

    Panzer, Matthew; Frisbie, C. Daniel

    2007-03-01

    The traditional choice of SiO2 for the gate dielectric material in organic field-effect transistors (OFETs) limits the amount of charge that one can induce via the field effect due to its relatively weak dielectric strength. In fact, the maximum 2D charge density achievable (near SiO2 breakdown, typically >100 V applied) is only ˜10^13 charges/cm^2, while the 2D molecular packing density of many common organic semiconductors is on the order of 5 x 10^14 molecules/cm^2. In order to achieve a higher fraction of charged semiconductor molecules in the 2D OFET channel, a dielectric layer with a higher capacitance is required. We have used a solid polymer electrolyte as an OFET dielectric in order to obtain 2D charge densities exceeding 10^14 charges/cm2 at operating voltages under 3 V in a variety of organic semiconductors. We have observed metallic conductivity values (˜1000 S/cm) and nearly temperature-independent resistance ratios in poly(3-hexylthiophene) films using a polymer electrolyte-gated OFET. In addition, conductivity maxima at carrier densities approaching 1 charge/molecule were observed in oligomeric, polymeric, and single-crystal organic semiconductors alike. This phenomenon may be caused by carrier correlations or a complete emptying of the semiconductor transport band at very high charge densities.

  1. Charge transport in conjugated materials: insight from quantum chemical calculations

    NASA Astrophysics Data System (ADS)

    Beljonne, David; Cornil, J. P.; Calbert, J. P.; Bredas, Jean-Luc

    2001-06-01

    The electronic structure of neutral and singly charged conjugated molecular clusters is investigated by means of quantum-chemical calculations. We first assess the influence of interchain interactions on the nature of the singly charged species (polarons) in organic conjugated polymers. In a two- chain model aggregate, the polaron is found to be delocalized over the two conjugated chains for short interchain separation. Such a delocalization strongly affects the geometric and electronic relaxation phenomena induced by charge injection, which in turn lead to a dramatic spectral redistribution of the linear absorption cross section. We then consider pentacene clusters built from the experimental crystal structure and compute the HOMO and LUMO bandwidths, which are decisive parameters for charge transport in the limiting case of band-like motion (i.e., complete delocalization of the excess charge over a large number of interacting molecules). Very large bandwidths are obtained, in agreement with the remarkable electron and hole charge-carrier mobilities reported recently for ultrahigh purity pentacene single crystals.

  2. Light-Emitting Quantum Dot Transistors: Emission at High Charge Carrier Densities

    PubMed Central

    2015-01-01

    For the application of colloidal semiconductor quantum dots in optoelectronic devices, for example, solar cells and light-emitting diodes, it is crucial to understand and control their charge transport and recombination dynamics at high carrier densities. Both can be studied in ambipolar, light-emitting field-effect transistors (LEFETs). Here, we report the first quantum dot light-emitting transistor. Electrolyte-gated PbS quantum dot LEFETs exhibit near-infrared electroluminescence from a confined region within the channel, which proves true ambipolar transport in ligand-exchanged quantum dot solids. Unexpectedly, the external quantum efficiencies improve significantly with current density. This effect correlates with the unusual increase of photoluminescence quantum yield and longer average lifetimes at higher electron and hole concentrations in PbS quantum dot thin films. We attribute the initially low emission efficiencies to nonradiative losses through trap states. At higher carrier densities, these trap states are deactivated and emission is dominated by trions. PMID:25652433

  3. Light-emitting quantum dot transistors: emission at high charge carrier densities.

    PubMed

    Schornbaum, Julia; Zakharko, Yuriy; Held, Martin; Thiemann, Stefan; Gannott, Florentina; Zaumseil, Jana

    2015-03-11

    For the application of colloidal semiconductor quantum dots in optoelectronic devices, for example, solar cells and light-emitting diodes, it is crucial to understand and control their charge transport and recombination dynamics at high carrier densities. Both can be studied in ambipolar, light-emitting field-effect transistors (LEFETs). Here, we report the first quantum dot light-emitting transistor. Electrolyte-gated PbS quantum dot LEFETs exhibit near-infrared electroluminescence from a confined region within the channel, which proves true ambipolar transport in ligand-exchanged quantum dot solids. Unexpectedly, the external quantum efficiencies improve significantly with current density. This effect correlates with the unusual increase of photoluminescence quantum yield and longer average lifetimes at higher electron and hole concentrations in PbS quantum dot thin films. We attribute the initially low emission efficiencies to nonradiative losses through trap states. At higher carrier densities, these trap states are deactivated and emission is dominated by trions. PMID:25652433

  4. Charge carrier dynamics in bulk MoS2 crystal studied by transient absorption microscopy

    NASA Astrophysics Data System (ADS)

    Kumar, Nardeep; He, Jiaqi; He, Dawei; Wang, Yongsheng; Zhao, Hui

    2013-04-01

    We report a transient absorption microscopy study of charge carrier dynamics in bulk MoS2 crystals at room temperature. Charge carriers are injected by interband absorption of a 555-nm pulse, and probed by measuring differential reflection of a time-delayed and spatially scanned 660-nm pulse. We find an intervalley transfer time of about 0.35 ps, an energy relaxation time of hot carriers on the order of 50 ps, and a carrier lifetime of 180 ± 20 ps. By monitoring the spatiotemporal dynamics of carriers, we obtained a diffusion coefficient of thermalized electrons of 4.2 ± 0.5 cm2/s, corresponding to a mobility of 170 ± 20 cm2/Vs. We also observed a time-varying diffusion coefficient of hot carriers.

  5. Organic Semiconductors: A Molecular Picture of the Charge-Transport and Energy-Transport Processes.

    NASA Astrophysics Data System (ADS)

    Brédas, Jean-Luc

    2007-03-01

    Conjugated organic oligomer and polymer materials are being increasingly considered for their incorporation as the active semiconductor elements in devices such as photo-voltaic cells, light-emitting diodes, or field-effects transistors. In the operation of these devices, electron-transfer and energy-transfer processes play a key role, for instance in the form of charge transport (in the bulk or across interfaces), energy transport, charge separation, or charge recombination [1]. Here, we provide a theoretical description of electron-transfer phenomena based on electron-transfer theory, which allows us to provide a molecular, chemically-oriented understanding. In this presentation, we focus on the parameters that impact the mobility of charge carriers [2], that is the electronic coupling within chains and between adjacent chains and the reorganization energy of the chains upon ionization. Materials under study include conjugated oligomers such as oligoacenes, oligothiophene-acenes, oligothiophenes, and oligothienacenes. [1] J.L. Br'edas, D. Beljonne, V. Coropceanu, and J. Cornil, ``Charge-Transfer and Energy-Transfer Processes in pi-Conjugated Oligomers and Polymers'', Chemical Reviews, 104, 4971-5004 (2004). [2] V. Coropceanu, J. Cornil, D.A. da Silva Filho, Y. Olivier, R. Silbey, and J.L. Br'edas, ``Charge Transport in Organic Semiconductors'', Chemical Reviews, 107, xxx (2007).

  6. Raman scattering studies and charge transport in polyfluorenes

    NASA Astrophysics Data System (ADS)

    Arif, Mohammad Ali Iftekhar

    Organic semiconductors, such as short-chain oligomers and long-chain polymers, are now a core constituent in numerous organic and organic-inorganic hybrid technologies. Blue-emitting polyfluorenes (PFs) have emerged as especially attractive pi conjugated polymers (CP) due to their high luminescence efficiency and excellent electronic properties and thus great prospects for device applications. The performance of devices based on these polymers depends on side chain conformations, overall crystalline structure, and charge transport processes at the microscopic level. This project entails detailed Raman scattering studies and charge transport properties of two side chain substituted PFs: Poly(2,7-[9,9'-bis(2-ethylhexyl)] fluorene) (PF2/6) and Poly(9,9-(di-n,n-octyl) fluorene) (PF8). The structural properties of PFs are extremely sensitive to the choice of functionalizing side chains. PF8 adopts metastable structures that depend upon the thermal history and choice of solvents used in film forming conditions. Raman scattering techniques as a function of thermal cycling are used to monitor the changes in the backbone and side chain morphology of PF8. These studies establish a correlation between the conformational isomers and the side and main chain morphology. Theoretical modeling of the vibrational spectra of single chain oligomers in conjunction with the experimental results demonstrate the incompatibility of the beta phase, a low energy emitting chromophore, with the overall crystalline phase in PF8. Further, electroluminescence and photoluminescence measurements from PF-based light-emitting diodes (LEDs) are presented and discussed in terms of the crystalline phases and chain morphologies in the PFs. Charge carrier injection and transport properties of PF-based LEDs are presented using current-voltage (I--V) characteristic which is modeled by a space-charge-limited conduction (SCLC) for discrete and continuous traps. PF2/6 with a high level of molecular disorder is

  7. Study on temperature-dependent carrier transport for bilayer graphene

    NASA Astrophysics Data System (ADS)

    Liu, Yali; Li, Weilong; Qi, Mei; Li, Xiaojun; Zhou, Yixuan; Ren, Zhaoyu

    2015-05-01

    In order to investigate the temperature-dependent carrier transport property of the bilayer graphene, graphene films were synthesized on Cu foils by a home-built chemical vapor deposition (CVD) with C2H2. Samples regularity, transmittance (T) and layer number were analyzed by transmission electron microscope (TEM) images, transmittance spectra and Raman spectra. Van Der Pauw method was used for resistivity measurements and Hall measurements at different temperatures. The results indicated that the sheet resistance (Rs), carrier density (n), and mobility (μ) were 1096.20 Ω/sq, 0.75×1012 cm-2, and 7579.66 cm2 V-1 s-1 at room temperature, respectively. When the temperature increased from 0 °C to 240 °C, carrier density (n) increased from 0.66×1012 cm-2 to 1.55×1012 cm-2, sheet resistance (Rs) decreased from 1215.55 Ω/sq to 560.77 Ω/sq, and mobility (μ) oscillated around a constant value 7773.99 cm2 V-1 s-1. The decrease of the sheet resistance (Rs) indicated that the conductive capability of the bilayer graphene film increased with the temperature. The significant cause of the increase of carrier density (n) was the thermal activation of carriers from defects and unconscious doping states. Because the main influence on the carrier mobility (μ) was the lattice defect scattering and a small amount of impurity scattering, the carrier mobility (μ) was temperature-independent for the bilayer graphene.

  8. High energetic excitons in carbon nanotubes directly probe charge-carriers

    PubMed Central

    Soavi, Giancarlo; Scotognella, Francesco; Viola, Daniele; Hefner, Timo; Hertel, Tobias; Cerullo, Giulio; Lanzani, Guglielmo

    2015-01-01

    Theory predicts peculiar features for excited-state dynamics in one dimension (1D) that are difficult to be observed experimentally. Single-walled carbon nanotubes (SWNTs) are an excellent approximation to 1D quantum confinement, due to their very high aspect ratio and low density of defects. Here we use ultrafast optical spectroscopy to probe photogenerated charge-carriers in (6,5) semiconducting SWNTs. We identify the transient energy shift of the highly polarizable S33 transition as a sensitive fingerprint of charge-carriers in SWNTs. By measuring the coherent phonon amplitude profile we obtain a precise estimate of the Stark-shift and discuss the binding energy of the S33 excitonic transition. From this, we infer that charge-carriers are formed instantaneously (<50 fs) even upon pumping the first exciton, S11. The decay of the photogenerated charge-carrier population is well described by a model for geminate recombination in 1D. PMID:25959462

  9. Universal carrier thermoelectric-transport model based on percolation theory in organic semiconductors

    NASA Astrophysics Data System (ADS)

    Lu, Nianduan; Li, Ling; Liu, Ming

    2015-05-01

    Recent measurements conducted over a large range of temperature and carrier density have found that the Seebeck coefficient exhibits an approaching disorder-free transport feature in high-mobility conjugated polymers [D. Venkateshvaran et al., Nature 515, 384 (2014), 10.1038/nature13854]. It is difficult for the current Seebeck coefficient model to interpret the feature of the charge transport approaching disorder-free transport. We present a general analytical model to describe the Seebeck effect for organic semiconductors based on the hopping transport and percolation theory. The proposed model can well explain the Seebeck feature of the polymers with approaching disorder-free transport, as well as that of the organic semiconductors with the general disorder. The simulated results imply that the Seebeck coefficient in the organic semiconductors would happen to transfer from temperature dependence to temperature independence with the decrease of the energetic disorder.

  10. Excited carrier dynamics and transport in plasmonic nanostructures

    NASA Astrophysics Data System (ADS)

    Sundararaman, Ravishankar; Narang, Prineha; Jermyn, Adam; Atwater, Harry; Goddard, William, III

    Surface plasmon resonances provide a pathway to efficiently capture electromagnetic radiation in sub-wavelength structures for energy conversion and photodetection at the nano scale. The complete mechanism involves several microscopic steps spanning length scales from atomic dimensions to tens or hundreds of nanometers, posing challenges for experimental characterization and for first-principles predictions. To provide the basis for predicting and optimizing the complex interplay of materials and geometric effects in plasmon decay-induced excited carrier phenomena, we combined ab initio electronic structure calculations, electromagnetic simulations and Boltzmann transport models. In Au, Ag, Cu and Al nanostructures, we find that initial carrier distributions as well as their subsequent transport, relaxation and thermalization are sensitive to electronic structure, exhibiting strong asymmetries between electrons and holes. We predict energy-dependent spatially-resolved carrier distributions collected in plasmonic nanostructures with strong field inhomogeneities, and explore the possibility of tailoring materials and geometry to collect the carrier distributions needed for such applications as photochemically driven CO2 reduction and water splitting. This material is based upon work performed by JCAP, a DOE Energy Innovation Hub, supported through the Office of Science of the U.S. Department of Energy under Award Number DE-SC0004993.

  11. Temperature dependence of exciton and charge carrier dynamics in organic thin films

    NASA Astrophysics Data System (ADS)

    Platt, A. D.; Kendrick, M. J.; Loth, M.; Anthony, J. E.; Ostroverkhova, O.

    2011-12-01

    -TES-F films. In ADT-TES-F/ADT-TIPS-CN (2%) blends, an additional charge carrier photogeneration component was observed at room temperature at time scales of ˜20 ns due to exciplex dissociation. At ˜0.5-5 ns after photoexcitation, the carriers propagated via thermally and electric-field-activated hopping with an activation energy of ˜0.025 eV. At time scales longer than ˜5 ns, charge transport of carriers that are not frozen in traps proceeded through tunneling via isoenergetic sites.

  12. Understanding Charge Transport in Mixed Networks of Semiconducting Carbon Nanotubes.

    PubMed

    Rother, Marcel; Schießl, Stefan P; Zakharko, Yuriy; Gannott, Florentina; Zaumseil, Jana

    2016-03-01

    The ability to select and enrich semiconducting single-walled carbon nanotubes (SWNT) with high purity has led to a fast rise of solution-processed nanotube network field-effect transistors (FETs) with high carrier mobilities and on/off current ratios. However, it remains an open question whether it is best to use a network of only one nanotube species (monochiral) or whether a mix of purely semiconducting nanotubes but with different bandgaps is sufficient for high performance FETs. For a range of different polymer-sorted semiconducting SWNT networks, we demonstrate that a very small amount of narrow bandgap nanotubes within a dense network of large bandgap nanotubes can dominate the transport and thus severely limit on-currents and effective carrier mobility. Using gate-voltage-dependent electroluminescence, we spatially and spectrally reveal preferential charge transport that does not depend on nominal network density but on the energy level distribution within the network and carrier density. On the basis of these results, we outline rational guidelines for the use of mixed SWNT networks to obtain high performance FETs while reducing the cost for purification. PMID:26867006

  13. Understanding Charge Transport in Mixed Networks of Semiconducting Carbon Nanotubes

    PubMed Central

    2016-01-01

    The ability to select and enrich semiconducting single-walled carbon nanotubes (SWNT) with high purity has led to a fast rise of solution-processed nanotube network field-effect transistors (FETs) with high carrier mobilities and on/off current ratios. However, it remains an open question whether it is best to use a network of only one nanotube species (monochiral) or whether a mix of purely semiconducting nanotubes but with different bandgaps is sufficient for high performance FETs. For a range of different polymer-sorted semiconducting SWNT networks, we demonstrate that a very small amount of narrow bandgap nanotubes within a dense network of large bandgap nanotubes can dominate the transport and thus severely limit on-currents and effective carrier mobility. Using gate-voltage-dependent electroluminescence, we spatially and spectrally reveal preferential charge transport that does not depend on nominal network density but on the energy level distribution within the network and carrier density. On the basis of these results, we outline rational guidelines for the use of mixed SWNT networks to obtain high performance FETs while reducing the cost for purification. PMID:26867006

  14. Charge injection and transport in fluorene-based copolymers.

    NASA Astrophysics Data System (ADS)

    Fong, Hon Hang; Malliaras, George G.; Lu, Tianjian; Dunlap, David

    2007-03-01

    Fluorene-based copolymer is considered to be one of the most promising hole transporting and blue light-emitting conjugated polymers used in polymeric light-emitting diodes (PLEDs). Time-of-flight (TOF) technique has been employed to evaluate the charge drift mobility under a temperature range between 200 - 400 K at the thick film regime (1-10 micron). Meanwhile, contact ohmicity is studied by Dark Current Space Charge Limited Conduction (DISCLC) technique. Charge injection efficiencies from different electrical contacts are also studied and the corresponding injection barriers are independently investigated by photoemission and electroabsorption spectroscopies. Results show that the copolymers exhibit non-dispersive charge transport behavior and possess superior mobilities of up to 0.01cm^2V-1s-1 while single-carrier devices from various electrical contacts such as PEDOT:PSS are varied, depending on the chemical structure of amine component in the fluorene-triarylamine copolymers. Results will shed light on the enhancement of device efficiency and stability in the future polymer electronic devices.

  15. Thermally activated charge transport in microbial protein nanowires

    PubMed Central

    Lampa-Pastirk, Sanela; Veazey, Joshua P.; Walsh, Kathleen A.; Feliciano, Gustavo T.; Steidl, Rebecca J.; Tessmer, Stuart H.; Reguera, Gemma

    2016-01-01

    The bacterium Geobacter sulfurreducens requires the expression of conductive protein filaments or pili to respire extracellular electron acceptors such as iron oxides and uranium and to wire electroactive biofilms, but the contribution of the protein fiber to charge transport has remained elusive. Here we demonstrate efficient long-range charge transport along individual pili purified free of metal and redox organic cofactors at rates high enough to satisfy the respiratory rates of the cell. Carrier characteristics were within the orders reported for organic semiconductors (mobility) and inorganic nanowires (concentration), and resistivity was within the lower ranges reported for moderately doped silicon nanowires. However, the pilus conductance and the carrier mobility decreased when one of the tyrosines of the predicted axial multistep hopping path was replaced with an alanine. Furthermore, low temperature scanning tunneling microscopy demonstrated the thermal dependence of the differential conductance at the low voltages that operate in biological systems. The results thus provide evidence for thermally activated multistep hopping as the mechanism that allows Geobacter pili to function as protein nanowires between the cell and extracellular electron acceptors. PMID:27009596

  16. Thermally activated charge transport in microbial protein nanowires.

    PubMed

    Lampa-Pastirk, Sanela; Veazey, Joshua P; Walsh, Kathleen A; Feliciano, Gustavo T; Steidl, Rebecca J; Tessmer, Stuart H; Reguera, Gemma

    2016-01-01

    The bacterium Geobacter sulfurreducens requires the expression of conductive protein filaments or pili to respire extracellular electron acceptors such as iron oxides and uranium and to wire electroactive biofilms, but the contribution of the protein fiber to charge transport has remained elusive. Here we demonstrate efficient long-range charge transport along individual pili purified free of metal and redox organic cofactors at rates high enough to satisfy the respiratory rates of the cell. Carrier characteristics were within the orders reported for organic semiconductors (mobility) and inorganic nanowires (concentration), and resistivity was within the lower ranges reported for moderately doped silicon nanowires. However, the pilus conductance and the carrier mobility decreased when one of the tyrosines of the predicted axial multistep hopping path was replaced with an alanine. Furthermore, low temperature scanning tunneling microscopy demonstrated the thermal dependence of the differential conductance at the low voltages that operate in biological systems. The results thus provide evidence for thermally activated multistep hopping as the mechanism that allows Geobacter pili to function as protein nanowires between the cell and extracellular electron acceptors. PMID:27009596

  17. Calculation of carrier transport in pseudo-quaternary alloys

    NASA Astrophysics Data System (ADS)

    Weil, T.; Vinter, B.

    1986-08-01

    We present results of a theoretical study of carrier transport in "graded gap superlattices" as employed in heterojunction photodiodes to reduce pile-up. For heavy holes the notion of a graded gap is invalid. Nevertheless, tunnelling and enhanced thermoemission are found to lead to improvements in decay times of current after tum-off of the light pulse of one order of magnitude. Structures with fewer interfaces having the same performances are proposed.

  18. [Is pneumatic sample transport system also a carrier for microorganisms?].

    PubMed

    Alpat, Saygin Nayman; Ozgüneş, Ilhan; Aybey, Aşkin Derya; Ertem, Osman Turgut; Akşit, Filiz

    2009-07-01

    The purpose of this study was to evaluate the possible infection and contamination risk of the pneumatic system used in our hospital and to establish essential infection control measures. The study was conducted in a quaternary health care center with 1.000 bed capacity. A total of 614 specimens were taken 2 times weekly from the pneumatic transport system and its carriers at 22 wards, 5 intensive care units, 3 laboratories, 2 blood taking units, and pharmacy. Samples were also obtained from the fingertips of 33 subjects using the system, before and after contact with the carriers. A questionnaire that consisted of 8 questions was applied to 224 subjects who worked in those units, evaluating the degree of compliance to the obligations for the cleaning of the pneumatic system and carriers and their approach in case of visible pollution at the system. Bacterial growth was observed in 15.2% (45/296) of samples in the 1st week and 7.6% (18/238) of the samples in the 2nd week, making a total of 11.8% (63/534) bacterial growth. No growth was detected from the areas where the carriers were placed. Of these 69.8% were coagulase negative staphylococci, 11.1% diphteroids, 7.9% Acinetobacter Iwoffii, 4.8% Staphylococcus aureus, 4.8% Bacillus spp. and 1.6% Enterococcus durans. Acinetobacter baumannii and Aspergillus were detected at two fingertip samples taken before the contact with carriers, while again A. baumannii and Enterobacter cloacae were detected at the samples following contact. Moreover, 31.3% of the subjects noted that they cleaned the carriers only if any visible contamination was present. In addition, 14.3% reported that they have encountered broken or spilled up material in the system for more than 5 times, 10.3% reported that they followed the instructions in case of presence of infected material inside the carriers, 23.7% reported that they always washed their hands after any contact with the carriers, 9.8% noted that they always used gloves during contact

  19. On the nature of high field charge transport in reinforced silicone dielectrics: Experiment and simulation

    NASA Astrophysics Data System (ADS)

    Huang, Yanhui; Schadler, Linda S.

    2016-08-01

    The high field charge injection and transport properties in reinforced silicone dielectrics were investigated by measuring the time-dependent space charge distribution and the current under dc conditions up to the breakdown field and were compared with the properties of other dielectric polymers. It is argued that the energy and spatial distribution of localized electronic states are crucial in determining these properties for polymer dielectrics. Tunneling to localized states likely dominates the charge injection process. A transient transport regime arises due to the relaxation of charge carriers into deep traps at the energy band tails and is successfully verified by a Monte Carlo simulation using the multiple-hopping model. The charge carrier mobility is found to be highly heterogeneous due to the non-uniform trapping. The slow moving electron packet exhibits a negative field dependent drift velocity possibly due to the spatial disorder of traps.

  20. Electric field assisted charge carrier photogeneration in poly(spirobifluorene-co-benzothiadiazole)

    SciTech Connect

    Devizis, A.; Serbenta, A.; Peckus, D.; Thiessen, A.; Alle, R.; Meerholz, K.; Hertel, D.; Gulbinas, V.

    2010-10-28

    The dynamics of charge carrier generation in poly(spirobifluorene-co-benzothiadiazole) was investigated by electric field-induced fluorescence quenching and differential absorption measurements. Three different time domains of carrier generation have been identified: an ultrafast phase, a subnanosecond phase, and an entire lifetime phase. The charge generation efficiencies during the first and second phases were found to be almost independent of temperature, being about 25% and 10%, respectively, at an applied electric field of 1.3x10{sup 6} V/cm, while the generation efficiency during the third phase increases from 2% at 80 K to 10% at room temperature. The results of transient spectroscopy measurements and quantum chemical calculations suggest an intramolecular charge transfer for about 1 ps from the alkoxy-substituted fluorene side group to the benzothiadiazole subunit of the main chain. The formation and evolution of the resulting charge transfer states determine the way of charge carrier generation.

  1. Earthquake lights and the stress-activation of positive hole charge carriers in rocks

    USGS Publications Warehouse

    St-Laurent, F.; Derr, J.S.; Freund, F.T.

    2006-01-01

    Earthquake-related luminous phenomena (also known as earthquake lights) may arise from (1) the stress-activation of positive hole (p-hole) charge carriers in igneous rocks and (2) the accumulation of high charge carrier concentrations at asperities in the crust where the stress rates increase very rapidly as an earthquake approaches. It is proposed that, when a critical charge carrier concentration is reached, the p-holes form a degenerated solid state plasma that can break out of the confined rock volume and propagate as a rapidly expanding charge cloud. Upon reaching the surface the charge cloud causes dielectric breakdown at the air-rock interface, i.e. corona discharges, accompanied by the emission of light and high frequency electromagnetic radiation. ?? 2006 Elsevier Ltd. All rights reserved.

  2. Temperature Dependent Kinetics DNA Charge Transport

    NASA Astrophysics Data System (ADS)

    Wohlgamuth, Chris; McWilliams, Marc; Slinker, Jason

    2012-10-01

    Charge transport (CT) through DNA has been extensively studied, and yet the mechanism of this process is still not yet fully understood. Besides the benefits of understanding charge transport through this fundamental molecule, further understanding of this process will elucidate the biological implications of DNA CT and advance sensing technology. Therefore, we have investigated the temperature dependence of DNA CT by measuring the electrochemistry of DNA monolayers modified with a redox-active probe. By using multiplexed electrodes on silicon chips, we compare square wave voltammetry of distinct DNA sequences under identical experimental conditions. We vary the probe length within the well matched DNA duplex in order to investigate distance dependent kinetics. This length dependent study is a necessary step to understanding the dominant mechanism behind DNA CT. Using a model put forth by O'Dea and Osteryoung and applying a nonlinear least squares analysis we are able to determine the charge transfer rates (k), transfer coefficients (α), and the total surface concentration (&*circ;) of the DNA monolayer. Arrhenius like behavior is observed for the multiple probe locations, and the results are viewed in light of and compared to the prominent charge transport mechanisms.

  3. 29 CFR 780.155 - Delivery “to carriers for transportation to market.”

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 29 Labor 3 2011-07-01 2011-07-01 false Delivery âto carriers for transportation to market.â 780... “to carriers for transportation to market.” The term “delivery * * * to carriers for transportation to market” includes taking agricultural or horticultural commodities, dairy products, livestock, bees...

  4. 29 CFR 780.155 - Delivery “to carriers for transportation to market.”

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 29 Labor 3 2010-07-01 2010-07-01 false Delivery âto carriers for transportation to market.â 780... “to carriers for transportation to market.” The term “delivery * * * to carriers for transportation to market” includes taking agricultural or horticultural commodities, dairy products, livestock, bees...

  5. Charge Redistribution and Transport in Molecular Contacts

    NASA Astrophysics Data System (ADS)

    Corso, Martina; Ondráček, Martin; Lotze, Christian; Hapala, Prokop; Franke, Katharina J.; Jelínek, Pavel; Pascual, J. Ignacio

    2015-09-01

    The forces between two single molecules brought into contact, and their connection with charge transport through the molecular junction, are studied here using non contact AFM, STM, and density functional theory simulations. A carbon monoxide molecule approaching an acetylene molecule (C2 H2 ) initially feels weak attractive electrostatic forces, partly arising from charge reorganization in the presence of molecular . We find that the molecular contact is chemically passive, and protects the electron tunneling barrier from collapsing, even in the limit of repulsive forces. However, we find subtle conductance and force variations at different contacting sites along the C2 H2 molecule attributed to a weak overlap of their respective frontier orbitals.

  6. Transport in charged colloids driven by thermoelectricity.

    PubMed

    Würger, Alois

    2008-09-01

    We study the thermal diffusion coefficient D{T} of a charged colloid in a temperature gradient, and find that it is to a large extent determined by the thermoelectric response of the electrolyte solution. The thermally induced salinity gradient leads in general to a strong increase with temperature. The difference of the heat of transport of coions and counterions gives rise to a thermoelectric field that drives the colloid to the cold or to the warm, depending on the sign of its charge. Our results provide an explanation for recent experimental findings on thermophoresis in colloidal suspensions. PMID:18851262

  7. Charge transport in strongly coupled quantum dot solids

    NASA Astrophysics Data System (ADS)

    Kagan, Cherie R.; Murray, Christopher B.

    2015-12-01

    The emergence of high-mobility, colloidal semiconductor quantum dot (QD) solids has triggered fundamental studies that map the evolution from carrier hopping through localized quantum-confined states to band-like charge transport in delocalized and hybridized states of strongly coupled QD solids, in analogy with the construction of solids from atoms. Increased coupling in QD solids has led to record-breaking performance in QD devices, such as electronic transistors and circuitry, optoelectronic light-emitting diodes, photovoltaic devices and photodetectors, and thermoelectric devices. Here, we review the advances in synthesis, assembly, ligand treatments and doping that have enabled high-mobility QD solids, as well as the experiments and theory that depict band-like transport in the QD solid state. We also present recent QD devices and discuss future prospects for QD materials and device design.

  8. The influence of negative charged centers on the hole transport in a typical molecularly doped polymer

    NASA Astrophysics Data System (ADS)

    Tyutnev, Andrey P.; Ikhsanov, Renat Sh.; Saenko, Vladimir S.; Pozhidaev, Evgenii D.

    2014-03-01

    We have studied effects of the negative charged centers on the time of flight (TOF) curves measured in a typical hole-conducting molecularly doped polymer. The main effects are the unusual TOF (surface generation) current rise in the preflight region (be it a flat plateau or a cusp) due to the accumulated space charge and the current reduction at all times because of the monomolecular recombination. TOF-2 (bulk generation) transients are less sensitive to charged centers. Analysis of these effects has proved that charged centers do not change the carrier mobility provided that the space charge field and bimolecular recombination are properly accounted for in terms of the proposed two-layer MT model. We have shown that combination of TOF, TOF-1a and TOF-2 variants of the electron-gun based technique allows one to establish definitively the character of the charge carrier transport in MDPs.

  9. Charge transport and injection in amorphous organic electronic materials

    NASA Astrophysics Data System (ADS)

    Tse, Shing Chi

    This thesis presents how we use various measuring techniques to study the charge transport and injection in organic electronic materials. Understanding charge transport and injection properties in organic solids is of vital importance for improving performance characteristics of organic electronic devices, including organic-light-emitting diodes (OLEDs), photovoltaic cells (OPVs), and field effect transistors (OFETs). The charge transport properties of amorphous organic materials, commonly used in organic electronic devices, are investigated by the means of carrier mobility measurements. Transient electroluminescence (EL) technique was used to evaluate the electron mobility of an electron transporting material--- tris(8-hydroxyquinoline) aluminum (Alq3). The results are in excellent agreement with independent time-of-flight (TOF) measurements. Then, the effect of dopants on electron transport was also examined. TOF technique was also used to examine the effects of tertiary-butyl (t-Bu) substitutions on anthracene derivatives (ADN). All ADN compounds were found to be ambipolar. As the degree of t-Bu substitution increases, the carrier mobilities decrease progressively. The reduction of carrier mobilities with increasing t-butylation can be attributed to a decrease in the charge-transfer integral or the wavefunction overlap. In addition, from TOF measurements, two naphthylamine-based hole transporters, namely, N,N'-diphenyl-N,N'-bis(1-naphthyl)(1,1'-biphenyl)-4,4'diamine (NPB) and 4,4',4"-tris(n-(2-naphthyl)-n-phenyl-amino)-triphenylamine (2TNATA) were found to possess electron-transporting (ET) abilities. An organic light-emitting diode that employed NPB as the ET material was demonstrated. The electron conducting mechanism of NPB and 2TNATA in relation to the hopping model will be discussed. Furthermore, the ET property of NPB applied in OLEDs will also be examined. Besides transient EL and TOF techniques, we also use dark-injection space-charge-limited current

  10. Field dependent thermoelectric properties of organic semiconductors—A tool to determine the nature of charge transport in materials exhibiting thermally activated transport

    NASA Astrophysics Data System (ADS)

    Mendels, Dan; Tessler, Nir

    2015-03-01

    By implementing Monte Carlo simulations and employing the concept of effective temperature, we explore the effects of an applied field bias on the charge carrier statistics and Peltier coefficient in hopping systems subject to the parameter range applicable to disordered organic semiconductors. Distinct differences are found between the observed field dependences as obtained from systems in which energetic disorder is spatially correlated and those in which it is not. Considerable differences are also found between the charge carrier statistics and the Peltier coefficient's field dependence in systems in which charge is transported by bare charge carriers and systems in which it is propagated by polarons. Peltier coefficient field dependence investigations are, hence, proposed as a new tool for studying charge transport and thermoelectricity in disordered organic semiconductors and systems which exhibit thermally activated transport in general.

  11. 75 FR 18255 - Passenger Facility Charge Database System for Air Carrier Reporting

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-04-09

    ... Federal Aviation Administration Passenger Facility Charge Database System for Air Carrier Reporting AGENCY... interested parties of the availability of the Passenger Facility Charge (PFC) database system to report PFC... public agency. The FAA has developed a national PFC database system in order to more easily track the...

  12. Bimodal behaviour of charge carriers in graphene induced by electric double layer.

    PubMed

    Tsai, Sing-Jyun; Yang, Ruey-Jen

    2016-01-01

    A theoretical investigation is performed into the electronic properties of graphene in the presence of liquid as a function of the contact area ratio. It is shown that the electric double layer (EDL) formed at the interface of the graphene and the liquid causes an overlap of the conduction bands and valance bands and increases the density of state (DOS) at the Fermi energy (EF). In other words, a greater number of charge carriers are induced for transport and the graphene changes from a semiconductor to a semimetal. In addition, it is shown that the dependence of the DOS at EF on the contact area ratio has a bimodal distribution which responses to the experimental observation, a pinnacle curve. The maximum number of induced carriers is expected to occur at contact area ratios of 40% and 60%. In general, the present results indicate that modulating the EDL provides an effective means of tuning the electronic properties of graphene in the presence of liquid. PMID:27464986

  13. Bimodal behaviour of charge carriers in graphene induced by electric double layer

    PubMed Central

    Tsai, Sing-Jyun; Yang, Ruey-Jen

    2016-01-01

    A theoretical investigation is performed into the electronic properties of graphene in the presence of liquid as a function of the contact area ratio. It is shown that the electric double layer (EDL) formed at the interface of the graphene and the liquid causes an overlap of the conduction bands and valance bands and increases the density of state (DOS) at the Fermi energy (EF). In other words, a greater number of charge carriers are induced for transport and the graphene changes from a semiconductor to a semimetal. In addition, it is shown that the dependence of the DOS at EF on the contact area ratio has a bimodal distribution which responses to the experimental observation, a pinnacle curve. The maximum number of induced carriers is expected to occur at contact area ratios of 40% and 60%. In general, the present results indicate that modulating the EDL provides an effective means of tuning the electronic properties of graphene in the presence of liquid. PMID:27464986

  14. Carrier transport at the metal-MoS2 interface

    NASA Astrophysics Data System (ADS)

    Ahmed, Faisal; Choi, Min Sup; Liu, Xiaochi; Yoo, Won Jong

    2015-05-01

    This study illustrates the nature of electronic transport and its transition from one mechanism to another between a metal electrode and MoS2 channel interface in a field effect transistor (FET) device. Interestingly, measurements of the contact resistance (Rc) as a function of temperature indicate a transition in the carrier transport across the energy barrier from thermionic emission at a high temperature to tunneling at a low temperature. Furthermore, at a low temperature, the nature of the tunneling behavior is ascertained by the current-voltage dependency that helps us feature direct tunneling at a low bias and Fowler-Nordheim tunneling at a high bias for a Pd-MoS2 contact due to the effective barrier shape modulation by biasing. In contrast, only direct tunneling is observed for a Cr-MoS2 contact over the entire applied bias range. In addition, simple analytical calculations were carried out to extract Rc at the gating range, and the results are consistent with the experimental data. Our results describe the transition in carrier transport mechanisms across a metal-MoS2 interface, and this information provides guidance for the design of future flexible, transparent electronic devices based on 2-dimensional materials.This study illustrates the nature of electronic transport and its transition from one mechanism to another between a metal electrode and MoS2 channel interface in a field effect transistor (FET) device. Interestingly, measurements of the contact resistance (Rc) as a function of temperature indicate a transition in the carrier transport across the energy barrier from thermionic emission at a high temperature to tunneling at a low temperature. Furthermore, at a low temperature, the nature of the tunneling behavior is ascertained by the current-voltage dependency that helps us feature direct tunneling at a low bias and Fowler-Nordheim tunneling at a high bias for a Pd-MoS2 contact due to the effective barrier shape modulation by biasing. In contrast

  15. Charge transport in confined ionic liquids

    NASA Astrophysics Data System (ADS)

    Sangoro, Joshua; Iacob, Ciprian; Kipnusu, Wycliffe; Kremer, Friedrich

    2011-03-01

    Charge transport and glassy dynamics in neat and polymerized ionic liquids confined in nanoporous silica are investigated in a wide frequency and temperature ranges by a combination of Broadband Dielectric Spectroscopy and Pulsed Field Gradient Nuclear Magnetic Resonance (PFG NMR). By applying the Einstein-Smoluchowski relations to the dielectric spectra, diffusion coefficients are obtained in quantitative agreement with independent PFG NMR. The impact of geometrical confinement as well as the pore wall-ionic liquid interactions on the overall ionic mobility is explored for diverse categories of ionic liquids. The results are discussed within the framework of dynamic glass transition assisted charge transport in ionic liquids. Financial support from the Deutsche Forschungsgemeinschaft under the DFG SPP 1191 Priority Program on Ionic Liquids is gratefully acknowledged.

  16. Variational multiscale models for charge transport

    PubMed Central

    Wei, Guo-Wei; Zheng, Qiong; Chen, Zhan; Xia, Kelin

    2012-01-01

    This work presents a few variational multiscale models for charge transport in complex physical, chemical and biological systems and engineering devices, such as fuel cells, solar cells, battery cells, nanofluidics, transistors and ion channels. An essential ingredient of the present models, introduced in an earlier paper (Bulletin of Mathematical Biology, 72, 1562-1622, 2010), is the use of differential geometry theory of surfaces as a natural means to geometrically separate the macroscopic domain from the microscopic domain, meanwhile, dynamically couple discrete and continuum descriptions. Our main strategy is to construct the total energy functional of a charge transport system to encompass the polar and nonpolar free energies of solvation, and chemical potential related energy. By using the Euler-Lagrange variation, coupled Laplace-Beltrami and Poisson-Nernst-Planck (LB-PNP) equations are derived. The solution of the LB-PNP equations leads to the minimization of the total free energy, and explicit profiles of electrostatic potential and densities of charge species. To further reduce the computational complexity, the Boltzmann distribution obtained from the Poisson-Boltzmann (PB) equation is utilized to represent the densities of certain charge species so as to avoid the computationally expensive solution of some Nernst-Planck (NP) equations. Consequently, the coupled Laplace-Beltrami and Poisson-Boltzmann-Nernst-Planck (LB-PBNP) equations are proposed for charge transport in heterogeneous systems. A major emphasis of the present formulation is the consistency between equilibrium LB-PB theory and non-equilibrium LB-PNP theory at equilibrium. Another major emphasis is the capability of the reduced LB-PBNP model to fully recover the prediction of the LB-PNP model at non-equilibrium settings. To account for the fluid impact on the charge transport, we derive coupled Laplace-Beltrami, Poisson-Nernst-Planck and Navier-Stokes equations from the variational principle

  17. Charge-reversal nanoparticles: novel targeted drug delivery carriers.

    PubMed

    Chen, Xinli; Liu, Lisha; Jiang, Chen

    2016-07-01

    Spurred by significant progress in materials chemistry and drug delivery, charge-reversal nanocarriers are being developed to deliver anticancer formulations in spatial-, temporal- and dosage-controlled approaches. Charge-reversal nanoparticles can release their drug payload in response to specific stimuli that alter the charge on their surface. They can elude clearance from the circulation and be activated by protonation, enzymatic cleavage, or a molecular conformational change. In this review, we discuss the physiological basis for, and recent advances in the design of charge-reversal nanoparticles that are able to control drug biodistribution in response to specific stimuli, endogenous factors (changes in pH, redox gradients, or enzyme concentration) or exogenous factors (light or thermos-stimulation). PMID:27471667

  18. Understanding charge transport in molecular electronics.

    PubMed

    Kushmerick, J J; Pollack, S K; Yang, J C; Naciri, J; Holt, D B; Ratner, M A; Shashidhar, R

    2003-12-01

    For molecular electronics to become a viable technology the factors that control charge transport across a metal-molecule-metal junction need to be elucidated. We use an experimentally simple crossed-wire tunnel junction to interrogate how factors such as metal-molecule coupling, molecular structure, and the choice of metal electrode influence the current-voltage characteristics of a molecular junction. PMID:14976024

  19. Controlling the screening process of a nanoscaled space charge region by minority carriers

    PubMed Central

    Kloth, Philipp; Kaiser, Katharina; Wenderoth, Martin

    2016-01-01

    The miniaturization of future electronic devices is intimately connected to the ability to control electric fields on the atomic scale. In a nanoscopic system defined by a limited number of charges, the combined dynamics of bound and free charges become important. Here we present a model system based on the electrostatic interaction between a metallic tip of a scanning tunnelling microscope and a GaAs(110) semiconductor surface. The system is driven out of equilibrium by optical excitation, which provides ambipolar free charge carriers, and by an optically induced unipolar tunnel current. This combination enables the active control of the density and spatial distribution of free and bound charge in the space-charge region, that is, modifying the screening processes. Temporal fluctuations of single dopants are modified, meaning we are able to control the noise of the system. It is found that free charge carriers suppress the noise level in field-controlled, nanoscopic systems. PMID:26728867

  20. Controlling the screening process of a nanoscaled space charge region by minority carriers.

    PubMed

    Kloth, Philipp; Kaiser, Katharina; Wenderoth, Martin

    2016-01-01

    The miniaturization of future electronic devices is intimately connected to the ability to control electric fields on the atomic scale. In a nanoscopic system defined by a limited number of charges, the combined dynamics of bound and free charges become important. Here we present a model system based on the electrostatic interaction between a metallic tip of a scanning tunnelling microscope and a GaAs(110) semiconductor surface. The system is driven out of equilibrium by optical excitation, which provides ambipolar free charge carriers, and by an optically induced unipolar tunnel current. This combination enables the active control of the density and spatial distribution of free and bound charge in the space-charge region, that is, modifying the screening processes. Temporal fluctuations of single dopants are modified, meaning we are able to control the noise of the system. It is found that free charge carriers suppress the noise level in field-controlled, nanoscopic systems. PMID:26728867

  1. Controlling the screening process of a nanoscaled space charge region by minority carriers

    NASA Astrophysics Data System (ADS)

    Kloth, Philipp; Kaiser, Katharina; Wenderoth, Martin

    2016-01-01

    The miniaturization of future electronic devices is intimately connected to the ability to control electric fields on the atomic scale. In a nanoscopic system defined by a limited number of charges, the combined dynamics of bound and free charges become important. Here we present a model system based on the electrostatic interaction between a metallic tip of a scanning tunnelling microscope and a GaAs(110) semiconductor surface. The system is driven out of equilibrium by optical excitation, which provides ambipolar free charge carriers, and by an optically induced unipolar tunnel current. This combination enables the active control of the density and spatial distribution of free and bound charge in the space-charge region, that is, modifying the screening processes. Temporal fluctuations of single dopants are modified, meaning we are able to control the noise of the system. It is found that free charge carriers suppress the noise level in field-controlled, nanoscopic systems.

  2. Particle Transport through Hydrogels Is Charge Asymmetric

    PubMed Central

    Zhang, Xiaolu; Hansing, Johann; Netz, Roland R.; DeRouchey, Jason E.

    2015-01-01

    Transport processes within biological polymer networks, including mucus and the extracellular matrix, play an important role in the human body, where they serve as a filter for the exchange of molecules and nanoparticles. Such polymer networks are complex and heterogeneous hydrogel environments that regulate diffusive processes through finely tuned particle-network interactions. In this work, we present experimental and theoretical studies to examine the role of electrostatics on the basic mechanisms governing the diffusion of charged probe molecules inside model polymer networks. Translational diffusion coefficients are determined by fluorescence correlation spectroscopy measurements for probe molecules in uncharged as well as cationic and anionic polymer solutions. We show that particle transport in the charged hydrogels is highly asymmetric, with diffusion slowed down much more by electrostatic attraction than by repulsion, and that the filtering capability of the gel is sensitive to the solution ionic strength. Brownian dynamics simulations of a simple model are used to examine key parameters, including interaction strength and interaction range within the model networks. Simulations, which are in quantitative agreement with our experiments, reveal the charge asymmetry to be due to the sticking of particles at the vertices of the oppositely charged polymer networks. PMID:25650921

  3. Novel macrocyclic carriers for proton-coupled liquid membrane transport

    SciTech Connect

    Lamb, J.D.

    1991-06-10

    The objective of our research program is to elucidate the chemical principles which are responsible for the cation selectivity and permeability of liquid membranes containing macrocyclic carriers. Several new macrocyclic carriers were synthesized during the last three year period, including selenium-containing macrocycles, new crown-4 structures, and several new crown structures containing nitrogen based heterocycles as substituents in the principal macrocyclic ring. The cation binding properties of these macrocycles were investigated by potentiometric titration, calorimetric titration, solvent extraction, and NMR techniques. In addition, hydrophobic macrocycles were incorporated into dual hollow fiber membrane systems to investigate their membrane performance, especially in the proton-coupled transport mode. It was found that the dual hollow fiber system maintains the cation selectivity and permeability of supported liquid membranes, while enhancing membrane stability. The diffusion limited transport model was expanded to account for membrane solvent effects. Furthermore, Eu{sup 2+} transport was found to be similar to that of strontium and much higher than that of the lanthanides, in supported liquid membrane systems.

  4. Carrier transport at the metal-MoS2 interface.

    PubMed

    Ahmed, Faisal; Choi, Min Sup; Liu, Xiaochi; Yoo, Won Jong

    2015-05-28

    This study illustrates the nature of electronic transport and its transition from one mechanism to another between a metal electrode and MoS2 channel interface in a field effect transistor (FET) device. Interestingly, measurements of the contact resistance (Rc) as a function of temperature indicate a transition in the carrier transport across the energy barrier from thermionic emission at a high temperature to tunneling at a low temperature. Furthermore, at a low temperature, the nature of the tunneling behavior is ascertained by the current-voltage dependency that helps us feature direct tunneling at a low bias and Fowler-Nordheim tunneling at a high bias for a Pd-MoS2 contact due to the effective barrier shape modulation by biasing. In contrast, only direct tunneling is observed for a Cr-MoS2 contact over the entire applied bias range. In addition, simple analytical calculations were carried out to extract Rc at the gating range, and the results are consistent with the experimental data. Our results describe the transition in carrier transport mechanisms across a metal-MoS2 interface, and this information provides guidance for the design of future flexible, transparent electronic devices based on 2-dimensional materials. PMID:25927942

  5. Charge carrier mobility and electronic properties of Al(Op)3: impact of excimer formation.

    PubMed

    Magri, Andrea; Friederich, Pascal; Schäfer, Bernhard; Fattori, Valeria; Sun, Xiangnan; Strunk, Timo; Meded, Velimir; Hueso, Luis E; Wenzel, Wolfgang; Ruben, Mario

    2015-01-01

    We have studied the electronic properties and the charge carrier mobility of the organic semiconductor tris(1-oxo-1H-phenalen-9-olate)aluminium(III) (Al(Op)3) both experimentally and theoretically. We experimentally estimated the HOMO and LUMO energy levels to be -5.93 and -3.26 eV, respectively, which were close to the corresponding calculated values. Al(Op)3 was successfully evaporated onto quartz substrates and was clearly identified in the absorption spectra of both the solution and the thin film. A structured steady state fluorescence emission was detected in solution, whereas a broad, red-shifted emission was observed in the thin film. This indicates the formation of excimers in the solid state, which is crucial for the transport properties. The incorporation of Al(Op)3 into organic thin film transistors (TFTs) was performed in order to measure the charge carrier mobility. The experimental setup detected no electron mobility, while a hole mobility between 0.6 × 10(-6) and 2.1 × 10(-6) cm(2)·V(-1)·s(-1) was measured. Theoretical simulations, on the other hand, predicted an electron mobility of 9.5 × 10(-6) cm(2)·V(-1)·s(-1) and a hole mobility of 1.4 × 10(-4) cm(2)·V(-1)·s(-1). The theoretical simulation for the hole mobility predicted an approximately one order of magnitude higher hole mobility than was observed in the experiment, which is considered to be in good agreement. The result for the electron mobility was, on the other hand, unexpected, as both the calculated electron mobility and chemical common sense (based on the capability of extended aromatic structures to efficiently accept and delocalize additional electrons) suggest more robust electron charge transport properties. This discrepancy is explained by the excimer formation, whose inclusion in the multiscale simulation workflow is expected to bring the theoretical simulation and experiment into agreement. PMID:26171287

  6. Charge carrier mobility and electronic properties of Al(Op)3: impact of excimer formation

    PubMed Central

    Friederich, Pascal; Schäfer, Bernhard; Fattori, Valeria; Sun, Xiangnan; Strunk, Timo; Meded, Velimir; Hueso, Luis E; Wenzel, Wolfgang; Ruben, Mario

    2015-01-01

    Summary We have studied the electronic properties and the charge carrier mobility of the organic semiconductor tris(1-oxo-1H-phenalen-9-olate)aluminium(III) (Al(Op)3) both experimentally and theoretically. We experimentally estimated the HOMO and LUMO energy levels to be −5.93 and −3.26 eV, respectively, which were close to the corresponding calculated values. Al(Op)3 was successfully evaporated onto quartz substrates and was clearly identified in the absorption spectra of both the solution and the thin film. A structured steady state fluorescence emission was detected in solution, whereas a broad, red-shifted emission was observed in the thin film. This indicates the formation of excimers in the solid state, which is crucial for the transport properties. The incorporation of Al(Op)3 into organic thin film transistors (TFTs) was performed in order to measure the charge carrier mobility. The experimental setup detected no electron mobility, while a hole mobility between 0.6 × 10−6 and 2.1 × 10−6 cm2·V−1·s−1 was measured. Theoretical simulations, on the other hand, predicted an electron mobility of 9.5 × 10−6 cm2·V−1·s−1 and a hole mobility of 1.4 × 10−4 cm2·V−1·s−1. The theoretical simulation for the hole mobility predicted an approximately one order of magnitude higher hole mobility than was observed in the experiment, which is considered to be in good agreement. The result for the electron mobility was, on the other hand, unexpected, as both the calculated electron mobility and chemical common sense (based on the capability of extended aromatic structures to efficiently accept and delocalize additional electrons) suggest more robust electron charge transport properties. This discrepancy is explained by the excimer formation, whose inclusion in the multiscale simulation workflow is expected to bring the theoretical simulation and experiment into agreement. PMID:26171287

  7. Charge Transport and Glassy Dynamics in Ionic Liquids

    SciTech Connect

    Sangoro, Joshua R; Kremer, Friedrich

    2012-01-01

    Ionic liquids (ILs) exhibit unique features such as low melting points, low vapor pressures, wide liquidus temperature ranges, high thermal stability, high ionic conductivity, and wide electrochemical windows. As a result, they show promise for use in variety of applications: as reaction media, in batteries and supercapacitors, in solar and fuel cells, for electrochemical deposition of metals and semiconductors, for protein extraction and crystallization, and many others. Because of the ease with which they can be supercooled, ionic liquids offer new opportunities to investigate long-standing questions regarding the nature of the dynamic glass transition and its possible link to charge transport. Despite the significant steps achieved from experimental and theoretical studies, no generally accepted quantitative theory of dynamic glass transition to date has been capable of reproducing all the experimentally observed features. In this Account, we discuss recent studies of the interplay between charge transport and glassy dynamics in ionic liquids as investigated by a combination of several experimental techniques including broadband dielectric spectroscopy, pulsed field gradient nuclear magnetic resonance, dynamic mechanical spectroscopy, and differential scanning calorimetry. Based on EinsteinSmoluchowski relations, we use dielectric spectra of ionic liquids to determine diffusion coefficients in quantitative agreement with independent pulsed field gradient nuclear magnetic resonance measurements, but spanning a broader range of more than 10 orders of magnitude. This approach provides a novel opportunity to determine the electrical mobility and effective number density of charge carriers as well as their types of thermal activation from the measured dc conductivity separately. We also unravel the origin of the remarkable universality of charge transport in different classes of glass-forming ionic liquids.

  8. Charge transport and glassy dynamics in ionic liquids.

    PubMed

    Sangoro, Joshua R; Kremer, Friedrich

    2012-04-17

    Ionic liquids (ILs) exhibit unique features such as low melting points, low vapor pressures, wide liquidus temperature ranges, high thermal stability, high ionic conductivity, and wide electrochemical windows. As a result, they show promise for use in variety of applications: as reaction media, in batteries and supercapacitors, in solar and fuel cells, for electrochemical deposition of metals and semiconductors, for protein extraction and crystallization, and many others. Because of the ease with which they can be supercooled, ionic liquids offer new opportunities to investigate long-standing questions regarding the nature of the dynamic glass transition and its possible link to charge transport. Despite the significant steps achieved from experimental and theoretical studies, no generally accepted quantitative theory of dynamic glass transition to date has been capable of reproducing all the experimentally observed features. In this Account, we discuss recent studies of the interplay between charge transport and glassy dynamics in ionic liquids as investigated by a combination of several experimental techniques including broadband dielectric spectroscopy, pulsed field gradient nuclear magnetic resonance, dynamic mechanical spectroscopy, and differential scanning calorimetry. Based on Einstein-Smoluchowski relations, we use dielectric spectra of ionic liquids to determine diffusion coefficients in quantitative agreement with independent pulsed field gradient nuclear magnetic resonance measurements, but spanning a broader range of more than 10 orders of magnitude. This approach provides a novel opportunity to determine the electrical mobility and effective number density of charge carriers as well as their types of thermal activation from the measured dc conductivity separately. We also unravel the origin of the remarkable universality of charge transport in different classes of glass-forming ionic liquids. PMID:22082024

  9. Effects of hole carrier injection and transport in organic light-emitting diodes

    SciTech Connect

    Antoniadis, H.; Miller, J.N.; Roitman, D.B.; Campbell, I.H.

    1997-08-01

    In this paper, the authors examine the effects of hole carrier injection and mobility on both the electroluminescence (EL) quantum efficiency and the operating voltage of bilayer organic light-emitting diodes (OLED`s). They find that hole-injection is limited by the nature of the hole injecting interface and significantly affects the operating voltage, but not the quantum efficiency of the OLED. Hole mobility is found not to affect the device quantum efficiency. They demonstrate the characteristics of an ideal ohmic contact by measuring space-charge-limited currents in a trap-free hole transporting polymer layer.

  10. Dust Charging and Transport on Surfaces

    NASA Astrophysics Data System (ADS)

    Wang, X.; Robertson, S.; Horányi, M.

    2011-11-01

    In this paper, we review laboratory studies of dust transport on surfaces in plasmas, performed for a number of different mechanisms: 1) Dust particles were levitated in plasma sheaths by electrostatic forces balancing the gravitational force. 2) Dust was observed to spread over and lift off a surface that repels electrons in a plasma. 3) Dust was transported on surfaces having different secondary electron yields in plasma with an electron beam as a consequence of differential charging. 4) We also report a mechanism of dust transport by electric fields occurring at electron beam impact/shadow boundaries. These processes are candidates to explain the formation of dust ponds that were recently observed in craters on the asteroid Eros by the NEAR Shoemaker spacecraft.

  11. Tuning the charge carrier density in the thermoelectric colusite

    NASA Astrophysics Data System (ADS)

    Kim, Fiseong S.; Suekuni, Koichiro; Nishiate, Hirotaka; Ohta, Michihiro; Tanaka, Hiromi I.; Takabatake, Toshiro

    2016-05-01

    The colusite Cu26V2Sn6S32 has high potential as a thermoelectric material at medium-high temperatures because of a large Seebeck coefficient (S ≃ 220 μV/K) and rather small electrical resistivity (ρ ≃ 100 μΩm) at 660 K. To improve the thermoelectric performance, we have tuned the hole carrier density p by substituting Zn for Cu in Cu26-xZnxV2Sn6S32 (x = 1-3) and starting with Cu and Sn deficient compositions in Cu26-yV2Sn6S32 (y = 1, 2) and Cu26V2Sn6-zS32 (z = 0.25-1), respectively. Powder x-ray diffraction and electron-probe microanalysis showed that the Zn-substituted samples and Sn-deficient (z ≥ 0.5) samples are formed in a single phase, whereas the Cu26-yV2Sn6S32 samples are composed of two phases with slightly different compositions. Within these samples, the value of p at 300 K varies in the range between 3.6 × 1020 and 2.8 × 1021 cm-3. The relation between p and S led to the effective mass m* of 4-7m0 for the hole carriers. The large S of the colusite is therefore ascribed to the heavy mass carriers of the valence band top. The decreases in p with x and y reduced the dimensionless thermoelectric figure of merit ZT, whereas the increase in p with z raised ZT from 0.56 (z = 0) to 0.62 (z = 0.5) at 660 K.

  12. Temperature dependent performance of Al/ZnCdS Schottky diode and charge transport analysis

    NASA Astrophysics Data System (ADS)

    Das, Mrinmay; Datta, Joydeep; Dey, Arka; Jana, Rajkumar; Ray, Partha Pratim

    2016-05-01

    Here we report the temperature dependent behaviour of Al/ZnCdS interface. In this regard, ZnCdS nanocomposite was synthesized by hydrothermal technique. Detailed study of schottky parameters including rectification ratio, ideality factor, series resistance and barrier height was performed. We explored the underlying charge transport phenomena through the Metal-semiconductor (MS) interface with the help of space charge limited current(SCLC) theory. A compartive analysis of carrier mobility and diffusion length was done.

  13. Stabilization of Charge Carriers in Picket-Fence Polythiophenes Using Dielectric Side Chains.

    PubMed

    Zhao, Chunhui; Sakurai, Tsuneaki; Yoneda, Satoru; Seki, Shu; Sugimoto, Manabu; Oki, Choji; Takeuchi, Masayuki; Sugiyasu, Kazunori

    2016-08-19

    Insulated molecular wires (IMWs) are π-conjugated polymers that are molecularly sheathed with an insulating layer and are structurally analogous to electric power cords at the nanoscale. Such unique architectures are expected in molecular electronics and organic devices. Herein, we propose a new molecular design concept of IMWs, in which the sheaths can be customized, thereby enabling the modulation of the electronic properties of the interior π-conjugated systems. To this end, we focused our attention on the dielectric constant of the sheaths, as it governs the electrostatic interaction between charges. Upon doping, charge carriers, such as polaron and bipolaron, were generated regardless of the dielectric properties of the sheaths. Flash-photolysis time-resolved microwave conductivity measurements revealed that intrawire charge carrier mobility was independent of the sheaths. However, we found that the charge carriers could be stabilized by the sheaths with a high dielectric constant owing to the charge screening effect. We expect that IMWs designed in this way will be useful in a variety of applications, where the nature of charge carriers plays an important role, and particularly when redox switching is required (e.g., electrochromic, magnetic, and memory applications). PMID:27503254

  14. Observation of complete space-charge-limited transport in metal-oxide-graphene heterostructure

    SciTech Connect

    Chen, Wei; Wang, Fei; Fang, Jingyue; Wang, Guang; Qin, Shiqiao; Zhang, Xue-Ao E-mail: xazhang@nudt.edu.cn; Wang, Chaocheng; Wang, Li E-mail: xazhang@nudt.edu.cn

    2015-01-12

    The metal-oxide-graphene heterostructures have abundant physical connotations. As one of the most important physical properties, the electric transport property of the gold-chromium oxide-graphene heterostructure has been studied. The experimental measurement shows that the conductive mechanism is dominated by the space-charge-limited transport, a kind of bulk transport of an insulator with charge traps. Combining the theoretical analysis, some key parameters such as the carrier mobility and trap energy also are obtained. The study of the characteristics of the metal-oxide-graphene heterostructures is helpful to investigate the graphene-based electronic and photoelectric devices.

  15. Probing charge transfer and hot carrier dynamics in organic solar cells with terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Cunningham, Paul D.; Lane, Paul A.; Melinger, Joseph S.; Esenturk, Okan; Heilweil, Edwin J.

    2016-04-01

    Time-resolved terahertz spectroscopy (TRTS) was used to explore charge generation, transfer, and the role of hot carriers in organic solar cell materials. Two model molecular photovoltaic systems were investigated: with zinc phthalocyanine (ZnPc) or alpha-sexathiophene (α-6T) as the electron donors and buckminsterfullerene (C60) as the electron acceptor. TRTS provides charge carrier conductivity dynamics comprised of changes in both population and mobility. By using time-resolved optical spectroscopy in conjunction with TRTS, these two contributions can be disentangled. The sub-picosecond photo-induced conductivity decay dynamics of C60 were revealed to be caused by auto-ionization: the intrinsic process by which charge is generated in molecular solids. In donor-acceptor blends, the long-lived photo-induced conductivity is used for weight fraction optimization of the constituents. In nanoscale multilayer films, the photo-induced conductivity identifies optimal layer thicknesses. In films of ZnPc/C60, electron transfer from ZnPc yields hot charges that localize and become less mobile as they thermalize. Excitation of high-lying Franck Condon states in C60 followed by hole-transfer to ZnPc similarly produces hot charge carriers that self-localize; charge transfer clearly precedes carrier cooling. This picture is contrasted to charge transfer in α-6T/C60, where hole transfer takes place from a thermalized state and produces equilibrium carriers that do not show characteristic signs of cooling and self-localization. These results illustrate the value of terahertz spectroscopic methods for probing charge transfer reactions.

  16. Unraveling Charge Carriers Generation, Diffusion, and Recombination in Formamidinium Lead Triiodide Perovskite Polycrystalline Thin Film.

    PubMed

    Piatkowski, Piotr; Cohen, Boiko; Ponseca, Carlito S; Salado, Manuel; Kazim, Samrana; Ahmad, Shahzada; Sundström, Villy; Douhal, Abderrazzak

    2016-01-01

    We report on studies of the formamidinium lead triiodide (FAPbI3) perovskite film using time-resolved terahertz (THz) spectroscopy (TRTS) and flash photolysis to explore charge carriers generation, migration, and recombination. The TRTS results show that upon femtosecond excitation above the absorption edge, the initial high photoconductivity (∼75 cm(2) V(-1) s(-1)) remains constant at least up to 8 ns, which corresponds to a diffusion length of 25 μm. Pumping below the absorption edge results in a mobility of 40 cm(2) V(-1) s(-1) suggesting lower mobility of charge carriers located at the bottom of the conduction band or shallow sub-bandgap states. Furthermore, analysis of the THz kinetics reveals rising components of <1 and 20 ps, reflecting dissociation of excitons having different binding energies. Flash photolysis experiments indicate that trapped charge carriers persist for milliseconds. PMID:26703885

  17. Charge Redistribution and Transport in Molecular Contacts.

    PubMed

    Corso, Martina; Ondráček, Martin; Lotze, Christian; Hapala, Prokop; Franke, Katharina J; Jelínek, Pavel; Pascual, J Ignacio

    2015-09-25

    The forces between two single molecules brought into contact, and their connection with charge transport through the molecular junction, are studied here using non contact AFM, STM, and density functional theory simulations. A carbon monoxide molecule approaching an acetylene molecule (C_{2}H_{2}) initially feels weak attractive electrostatic forces, partly arising from charge reorganization in the presence of molecular . We find that the molecular contact is chemically passive, and protects the electron tunneling barrier from collapsing, even in the limit of repulsive forces. However, we find subtle conductance and force variations at different contacting sites along the C_{2}H_{2} molecule attributed to a weak overlap of their respective frontier orbitals. PMID:26451568

  18. Importance of Polaronic Effects for Charge Transport in CdSe Quantum Dot Solids.

    PubMed

    Prodanović, Nikola; Vukmirović, Nenad; Ikonić, Zoran; Harrison, Paul; Indjin, Dragan

    2014-04-17

    We developed an accurate model accounting for electron-phonon interaction in colloidal quantum dot supercrystals that allowed us to identify the nature of charge carriers and the electrical transport regime. We find that in experimentally analyzed CdSe nanocrystal solids, the electron-phonon interaction is sufficiently strong that small polarons localized to single dots are formed. Charge-carrier transport occurs by small polaron hopping between the dots, with mobility that decreases with increasing temperature. While such a temperature dependence of mobility is usually considered as a proof of band transport, we show that the same type of dependence occurs in the system where transport is dominated by small polaron hopping. PMID:26269977

  19. Spatially resolved measurements of charge carrier lifetimes in CdTe solar cells

    NASA Astrophysics Data System (ADS)

    Kraft, C.; Hempel, H.; Buschmann, V.; Siebert, T.; Heisler, C.; Wesch, W.; Ronning, C.

    2013-03-01

    The lifetime of the minority charge carriers in polycrystalline Cadmium Telluride (pc-CdTe) for solar cell applications is a crucial material parameter and has been determined by analysis of the decay curves of the luminescence signal. Both the lateral and the transversal distributions of the carrier lifetime on the surface and in the bulk of pc-CdTe material as well as the respective solar cell characteristics were measured as a function of the deposition technique, the activation treatment, and the incorporation of additional group-V elements. The results are compared to prior studies. It was found that an activation process passivates grain boundaries and increases the carrier lifetime, which is then higher at the pn-junction than at the surface. Furthermore, nitrogen and phosphorus doping of the CdTe absorber material influences the charge carrier lifetime. The results show that the spatial resolved measurement of the carrier lifetime in pc-CdTe gives an important insight to the charge carrier dynamics of the material.

  20. Exciton transport, charge extraction, and loss mechanisms in organic photovoltaics

    NASA Astrophysics Data System (ADS)

    Scully, Shawn Ryan

    the primary losses that puts stringent requirements on the charge carrier mobilities in these cells is the recombination losses due to space charge build up at the heterojunction. Because electrons are confined to the acceptor and holes to the donor, net charge density always exists even when mobilities are matched, in contrast to bulk heterojunctions wherein matched mobilities lead to zero net charge. This net charge creates an electric field which opposes the built-in field and limits the current that can be carried away from this heterojunction. Using simulations we show that for relevant current densities charge carrier mobilities must be higher than 10-4 cm2/V.s to avoid significant losses due to space charge formation. In the last part of this work, we will focus on the second class of architectures in which exciton harvesting is efficient. We will present a systematic analysis of one of the leading polymer:fullerene bulk heterojunction cells to show that losses in this architecture are due to charge recombination. Using optical measurements and simulations, exciton harvesting measurements, and device characteristics we will show that the dominant loss is likely due to field-dependent geminate recombination of the electron and hole pair created immediately following exciton dissociation. No losses in this system are seen due to bimolecular recombination or space charge which provides information on charge-carrier mobility targets necessary for the future design of high efficiency organic photovoltaics.

  1. The effect of interfaces on charge transport and recombination in polymeric solar cells

    NASA Astrophysics Data System (ADS)

    Osterbacka, Ronald; Sanden, Simon; Xu, Qian; Sandberg, Oskar; Nyman, Mathias; Smatt, Jan-Henrik; Juska, Gytis

    2013-03-01

    Charge-carrier transport and recombination in hybrid TiO2/P3HT:PCBM bulk-heterojunction solar cells (BHSCs) have been measured using photo-CELIV. We have fabricated hybrid devices in the form of indium tin oxide/titanium dioxide/P3HT:PCBM/Cu) to clarify the impact of the TiO2/P3HT:PCBM interface on the charge transport using the charge extraction by linearly increasing voltage (CELIV) technique. We found that a large equilibrium charge reservoir is accumulated at negative offsets at the TiO2/P3HT:PCBM interface leading to space charge limited extraction current (SCLC) transients. We show analytically the SCLC transient response and compare the experimental data to calculated SCLC in a linearly increasing voltage. The theoretical calculations indicate that the large charge reservoir at negative offset voltages is due to thermally generated charges combined with poor hole extraction at the ITO/TiO2 contact, due to the hole blocking character of TiO2. In this presentation we will discuss how interfaces, both metal-organic but also organic-organic interfaces affect charge carrier transport and recombination measurements. Laboratory of Physical Chemistry

  2. Unified electronic charge transport model for organic solar cells

    NASA Astrophysics Data System (ADS)

    Mottaghian, Seyyed Sadegh; Biesecker, Matt; Bayat, Khadijeh; Farrokh Baroughi, Mahdi

    2013-07-01

    This paper provides a comprehensive modeling approach for simulation of electronic charge transport in excitonic solar cells with organic and organic/inorganic structures. Interaction of energy carrying particles (electrons, holes, singlet excitons, and triplet excitons) with each other and their transformation in the bulk of the donor and acceptor media as well as the donor/acceptor interfaces are incorporated in form of coupling matrices into the continuity equations and interface boundary conditions. As a case study, the model is applied to simulate an organic bilayer photovoltaic (PV) device to quantify the effects of photo generation, recombination coefficient, carrier mobility, and electrode work function on its PV characteristics. The study proves that electron-hole recombination at the donor/acceptor interface is the dominant mechanism that limits open circuit voltage of the device.

  3. Critical Slowing Down of the Charge Carrier Dynamics at the Mott Metal-Insulator Transition

    NASA Astrophysics Data System (ADS)

    Hartmann, Benedikt; Zielke, David; Polzin, Jana; Sasaki, Takahiko; Müller, Jens

    2015-05-01

    We report on the dramatic slowing down of the charge carrier dynamics in a quasi-two-dimensional organic conductor, which can be reversibly tuned through the Mott metal-insulator transition (MIT). At the finite-temperature critical end point, we observe a divergent increase of the resistance fluctuations accompanied by a drastic shift of spectral weight to low frequencies, demonstrating the critical slowing down of the order parameter (doublon density) fluctuations. The slow dynamics is accompanied by non-Gaussian fluctuations, indicative of correlated charge carrier dynamics. A possible explanation is a glassy freezing of the electronic system as a precursor of the Mott MIT.

  4. Charge-Carrier Dynamics and Mobilities in Formamidinium Lead Mixed-Halide Perovskites.

    PubMed

    Rehman, Waqaas; Milot, Rebecca L; Eperon, Giles E; Wehrenfennig, Christian; Boland, Jessica L; Snaith, Henry J; Johnston, Michael B; Herz, Laura M

    2015-12-22

    The mixed-halide perovskite FAPb(Bry I1-y )3 is attractive for color-tunable and tandem solar cells. Bimolecular and Auger charge-carrier recombination rate constants strongly correlate with the Br content, y, suggesting a link with electronic structure. FAPbBr3 and FAPbI3 exhibit charge-carrier mobilities of 14 and 27 cm(2) V(-1) s(-1) and diffusion lengths exceeding 1 μm, while mobilities across the mixed Br/I system depend on crystalline phase disorder. PMID:26402226

  5. Matrix engineering, state filling, and charge transport in PbSe quantum dot solids

    NASA Astrophysics Data System (ADS)

    Law, Matt

    Colloidal semiconductor quantum dots (QDs) are attractive building blocks for solar photovoltaics (PV). In this talk, I will highlight our recent progress in designing PbX (X = S, Se, Te) QD thin film absorbers for next-generation PV. Basic requirements for QD absorber layers include efficient light absorption, charge separation, charge transport, and long-term stability. I begin by discussing QD film fabrication, charge transport physics, insights from theory, and evidence that the carrier diffusion length is short and limited by electronic states in the QD band gap. Studies of carrier mobility as a function of basic film parameters such as inter-QD spacing, QD size, and QD size distribution have led to a better understanding of charge transport within highly disordered QD films. Efforts to improve carrier mobility by enhancing inter-dot electronic coupling, passivating surface states, and implementing surface doping will be highlighted. Engineering the inter-QD matrix to produce QD/inorganic or QD/organic nanocomposites is presented as a powerful way to optimize coupling, remove surface states, eliminate hysteretic charge trapping and ion motion, and achieve long-term environmental stability for high-performance, robust QD films that feature good carrier multiplication efficiency. New results on the use of atomic layer deposition infilling of QD films to yield all-inorganic QD transistors free of the bias-stress effect will be presented, and the likely role of ion transport in QD optoelectronics discussed. The use of infrared transmission spectroscopy to understand state filling and study charge transport in QD thin film transistors will be presented.

  6. Charge Carrier Lifetimes Exceeding 15 μs in Methylammonium Lead Iodide Single Crystals.

    PubMed

    Bi, Yu; Hutter, Eline M; Fang, Yanjun; Dong, Qingfeng; Huang, Jinsong; Savenije, Tom J

    2016-03-01

    The charge carrier lifetime in organic-inorganic perovskites is one of the most important parameters for modeling and design of solar cells and other types of devices. In this work, we use CH3NH3PbI3 single crystal as a model system to study optical absorption, charge carrier generation, and recombination lifetimes. We show that commonly applied photoluminescence lifetime measurements may dramatically underestimate the intrinsic carrier lifetime in CH3NH3PbI3, which could be due to severe charge recombination at the crystal surface and/or fast electron-hole recombination close to the surface. By using the time-resolved microwave conductivity technique, we investigated the lifetime of free mobile charges inside the crystals. Most importantly, we find that for homogeneous excitation throughout the crystal, the charge carrier lifetime exceeds 15 μs. This means that the diffusion length in CH3NH3PbI3 can be as large as 50 μm if it is no longer limited by the dimensions of the crystallites. PMID:26901658

  7. Elimination of charge carrier trapping in diluted semiconductors

    NASA Astrophysics Data System (ADS)

    Abbaszadeh, D.; Kunz, A.; Wetzelaer, G. A. H.; Michels, J. J.; Crăciun, N. I.; Koynov, K.; Lieberwirth, I.; Blom, P. W. M.

    2016-06-01

    In 1962, Mark and Helfrich demonstrated that the current in a semiconductor containing traps is reduced by N/Ntr, with N the amount of transport sites, Nt the amount of traps and r a number that depends on the trap energy distribution. For r > 1, the possibility opens that trapping effects can be nearly eliminated when N and Nt are simultaneously reduced. Solution-processed conjugated polymers are an excellent model system to test this hypothesis, because they can be easily diluted by blending them with a high-bandgap semiconductor. We demonstrate that in conjugated polymer blends with 10% active semiconductor and 90% high-bandgap host, the typical strong electron trapping can be effectively eliminated. As a result we were able to fabricate polymer light-emitting diodes with balanced electron and hole transport and reduced non-radiative trap-assisted recombination, leading to a doubling of their efficiency at nearly ten times lower material costs.

  8. Charge Carrier Dynamics in Transition Metal Oxides Studied by Femtosecond Transient Extreme Ultraviolet Absorption Spectroscopy

    NASA Astrophysics Data System (ADS)

    Jiang, Chang-Ming

    With the ability to disentangle electronic transitions that occur on different elements and local electronic structures, time-resolved extreme ultraviolet (XUV) spectroscopy has emerged as a powerful tool for studying ultrafast dynamics in condensed phase systems. In this dissertation, a visible-pump/XUV-probe transient absorption apparatus with femtosecond resolution was constructed to investigate the carrier relaxation dynamics in semiconductors after photo-excitation. This includes timescales for carrier thermalization by carrier-carrier and carrier-phonon scattering. The 30 -- 72 eV photon energy coverage (17 -- 40 nm wavelength) generated by a table-top XUV light source is suitable for probing the 3p-to-3d core level absorptions of various transition metal oxides (TMOs) with specificities to elements and oxidation states. In Chapter 1, a brief introduction to charge carrier dynamics in semiconductor-based materials is given. In addition, fundamentals of core-level spectroscopy and the high harmonic generation (HHG) process are also addressed in this introductory chapter. Specifications of the experimental apparatus that was constructed are summarized in Chapter 2, including the design concepts and characterization of performance. Chapter 3 presents the spectral tunability of the XUV pulses generated from a semi-infinite gas cell (SIGC), as well as the data acquisition procedures. Charge carrier relaxation dynamics in Co3O4 following the charge transfer excitation pathway at 400 nm are documented in Chapter 4. In Chapter 5, various visible pump wavelengths are used to excite Co3O4 and the differences in the carrier dynamics versus excitation wavelength are considered. After selectively photoexciting a Si/TiO2 heterojunction, the resulted electron transfer process is observed and reported in Chapter 6. The concluding remarks of the dissertation are made in Chapter 7, while several ongoing time-resolved experiments are addressed in the Appendix sections.

  9. Charge transport mechanisms in phthalocyanine thin films

    NASA Astrophysics Data System (ADS)

    Colesniuc, Corneliu; Sharoni, Amos; Schuller, Ivan K.

    2008-03-01

    Devices consisting of phthalocyanine thin films sandwiched between gold electrodes were fabricated by organic molecular beam deposition. Samples with different organic layer thickness were deposited on sapphire substrates in-situ, using a shadow mask and a mobile sample holder controlled manually. The structural asymmetry of the devices determined by the different metal-organic interfaces is reflected in the I-V curves at positive and negative voltages. The logarithmic scale I-V plots can be fitted with linear functions of different slopes corresponding to different conduction regimes. At low temperatures a transition from the ohmic regime to a slope two space charge limited conduction mechanism is followed at higher voltages by a high slope linear dependence that tends to saturate when the voltage reaches maximum values. At higher temperatures the intermediary space charge limited regime disappears and the transition is from ohmic to high slope space charge limited. Traps with different energy and energy distribution determine the different conduction regimes. Shallow traps located at discrete energy levels control the transport at intermediate voltages while exponentially distributed traps determine the high voltage behavior. Work supported by AFOSR-MURI.

  10. Preface: Charge transport in nanoscale junctions

    NASA Astrophysics Data System (ADS)

    Albrecht, Tim; Kornyshev, Alexei; Bjørnholm, Thomas

    2008-09-01

    Understanding the fundamentals of nanoscale charge transfer is pivotal for designing future nano-electronic devices. Such devices could be based on individual or groups of molecular bridges, nanotubes, nanoparticles, biomolecules and other 'active' components, mimicking wire, diode and transistor functions. These have operated in various environments including vacuum, air and condensed matter, in two- or three-electrode configurations, at ultra-low and room temperatures. Interest in charge transport in ultra-small device components has a long history and can be dated back to Aviram and Ratner's letter in 1974 (Chem. Phys. Lett. 29 277-83). So why is there a necessity for a special issue on this subject? The area has reached some degree of maturity, and even subtle geometric effects in the nanojunction and noise features can now be resolved and rationalized based on existing theoretical concepts. One purpose of this special issue is thus to showcase various aspects of nanoscale and single-molecule charge transport from experimental and theoretical perspectives. The main principles have 'crystallized' in our minds, but there is still a long way to go before true single-molecule electronics can be implemented. Major obstacles include the stability of electronic nanojunctions, reliable operation at room temperature, speed of operation and, last but not least, integration into large networks. A gradual transition from traditional silicon-based electronics to devices involving a single (or a few) molecule(s) therefore appears to be more viable from technologic and economic perspectives than a 'quantum leap'. As research in this area progresses, new applications emerge, e.g. with a view to characterizing interfacial charge transfer at the single-molecule level in general. For example, electrochemical experiments with individual enzyme molecules demonstrate that catalytic processes can be studied with nanometre resolution, offering a route towards optimizing biosensors at

  11. Tuning The Optical, Charge Injection, and Charge Transport Properties of Organic Electronic Devices

    NASA Astrophysics Data System (ADS)

    Zalar, Peter

    Since the early 1900's, synthetic insulating polymers (plastics) have slowly taken over the role that traditional materials like wood or metal have had as basic components for construction, manufactured goods, and parts. Plastics allow for high throughput, low temperature processing, and control of bulk properties through molecular modifications. In the same way, pi-conjugated organic molecules are emerging as a possible substitute for inorganic materials due to their electronic properties. The semiconductive nature of pi-conjugated materials make them an attractive candidate to replace inorganic materials, primarily due to their promise for low cost and large-scale production of basic semiconducting devices such as light-emitting diodes, solar cells, and field-effect transistors. Before organic semiconductors can be realized as a commercial product, several hurdles must be cleared. The purpose of this dissertation is to address three distinct properties that dominate the functionality of devices harnessing these materials: (1) optical properties, (2) charge injection, and (3) charge transport. First, it is shown that the electron injection barrier in the emissive layer of polymer light-emitting diodes can be significantly reduced by processing of novel conjugated oligoelectrolytes or deoxyribonucleic acid atop the emissive layer. Next, the charge transport properties of several polymers could be modified by processing them from solvents containing small amounts of additives or by using regioregular and enantiopure chemical structures. It is then demonstrated that the optical and electronic properties of Lewis basic polymer structures can be readily modified by interactions with strongly electron-withdrawing Lewis acids. Through red-shifted absorption, photoluminescence, and electroluminescence, a single pi-conjugated backbone can be polychromatic. In addition, interaction with Lewis acids can remarkably p-dope the hole transport of the parent polymer, leading to a

  12. 14 CFR 206.4 - Exemption of air carriers for military transportation.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 14 Aeronautics and Space 4 2014-01-01 2014-01-01 false Exemption of air carriers for military transportation. 206.4 Section 206.4 Aeronautics and Space OFFICE OF THE SECRETARY, DEPARTMENT OF TRANSPORTATION... AUTHORIZATIONS AND EXEMPTIONS § 206.4 Exemption of air carriers for military transportation. Air...

  13. 14 CFR 206.4 - Exemption of air carriers for military transportation.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 14 Aeronautics and Space 4 2012-01-01 2012-01-01 false Exemption of air carriers for military transportation. 206.4 Section 206.4 Aeronautics and Space OFFICE OF THE SECRETARY, DEPARTMENT OF TRANSPORTATION... AUTHORIZATIONS AND EXEMPTIONS § 206.4 Exemption of air carriers for military transportation. Air...

  14. 14 CFR 206.4 - Exemption of air carriers for military transportation.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 14 Aeronautics and Space 4 2013-01-01 2013-01-01 false Exemption of air carriers for military transportation. 206.4 Section 206.4 Aeronautics and Space OFFICE OF THE SECRETARY, DEPARTMENT OF TRANSPORTATION... AUTHORIZATIONS AND EXEMPTIONS § 206.4 Exemption of air carriers for military transportation. Air...

  15. 14 CFR 206.4 - Exemption of air carriers for military transportation.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 4 2010-01-01 2010-01-01 false Exemption of air carriers for military transportation. 206.4 Section 206.4 Aeronautics and Space OFFICE OF THE SECRETARY, DEPARTMENT OF TRANSPORTATION... AUTHORIZATIONS AND EXEMPTIONS § 206.4 Exemption of air carriers for military transportation. Air...

  16. Imaging charge separation and carrier recombination in nanowire p-i-n junctions using ultrafast microscopy.

    PubMed

    Gabriel, Michelle M; Grumstrup, Erik M; Kirschbrown, Justin R; Pinion, Christopher W; Christesen, Joseph D; Zigler, David F; Cating, Emma E M; Cahoon, James F; Papanikolas, John M

    2014-06-11

    Silicon nanowires incorporating p-type/n-type (p-n) junctions have been introduced as basic building blocks for future nanoscale electronic components. Controlling charge flow through these doped nanostructures is central to their function, yet our understanding of this process is inferred from measurements that average over entire structures or integrate over long times. Here, we have used femtosecond pump-probe microscopy to directly image the dynamics of photogenerated charge carriers in silicon nanowires encoded with p-n junctions along the growth axis. Initially, motion is dictated by carrier-carrier interactions, resulting in diffusive spreading of the neutral electron-hole cloud. Charge separation occurs at longer times as the carrier distribution reaches the edges of the depletion region, leading to a persistent electron population in the n-type region. Time-resolved visualization of the carrier dynamics yields clear, direct information on fundamental drift, diffusion, and recombination processes in these systems, providing a powerful tool for understanding and improving materials for nanotechnology. PMID:24867088

  17. Carrier transport in amorphous silicon utilizing picosecond photoconductivity

    NASA Astrophysics Data System (ADS)

    Johnson, A. M.

    1981-08-01

    The development of a high-speed electronic measurement capability permitted the direct observation of the transient photoresponse of amorphous silicon (a-Si) with a time resolution of approximately 10ps. This technique was used to measure the initial mobility of photogenerated (2.1eV) free carriers in three types of a-Si having widely different densities of structural defects (i.e., as prepared by: (1) RF glow discharge (a-Si:H); (2) chemical vapor deposition; and (3) evaporation in ultra-high vacuum). In all three types of a-Si, the same initial mobility of approximately 1 cu cm/Vs at room temperature was found. This result tends to confirm the often-made suggestion that the free carrier mobility is determined by the influence of shallow states associated with the disorder in the random atomic network, and is an intrinsic property of a-Si which is unaffected by the method of preparation. The rate of decay of the photocurrent correlates with the density of structural defects and varies from 4ps to 200ps for the three types of a-Si investigated. The initial mobility of a-Si:H was found to be thermally activated. The possible application of extended state transport controlled by multiple trapping and small polaron formation is discussed.

  18. Origin and distribution of charge carriers in LaAlO3-SrTiO3 oxide heterostructures in the high carrier density limit

    NASA Astrophysics Data System (ADS)

    Mukherjee, Sumanta; Pal, Banabir; Choudhury, Debraj; Sarkar, Indranil; Drube, Wolfgang; Gorgoi, Mihaela; Karis, Olof; Takagi, H.; Matsuno, Jobu; Sarma, D. D.

    2016-06-01

    Using hard x-ray photoelectron spectroscopy with variable photon energy (2-8 keV), we address the distribution of charge carriers in the prototypical LaAlO3 (LAO) and SrTiO3 (STO) oxide heterostructures with high carrier densities (1017cm-2 ). Our results demonstrate the presence of two distinct charge distributions in this system: one tied to the interface with a ˜1 -nm width and ˜2 -5 × 1014-cm-2 carrier concentration, while the other appears distributed nearly homogeneously through the bulk of STO corresponding to a much larger carrier contribution. Our results also establish bimodal oxygen vacancies, namely on top of LAO and throughout STO, quantitatively establishing these as the origin of the observed bimodal depth distribution of charge carriers in these highly doped sample.

  19. Possibility of contactless measurement of free charge carrier mobility in semiconductors by the uhf resonator method

    SciTech Connect

    Meduedev, Y.V.; Skryl'nikov, A.A.

    1986-01-01

    This paper describes a contact-free uhf resonator method for measurement of charge carrier mobility by means of a quasistatic uhf resonator with externally connected semiconductor specimen. The method obtains simple relationships which allow determination of the magnetoresistive mobility from the change in Q of the external portion of the resonator under the action of a weak magnetic field.

  20. Nonequilibrium population of charge carriers in structures with InGaN deep quantum dots

    SciTech Connect

    Sizov, D. S. Zavarin, E. E.; Ledentsov, N. N.; Lundin, V. V.; Musikhin, Yu. G.; Sizov, V. S.; Suris, R. A.; Tsatsul'nikov, A. F.

    2007-05-15

    Electronic and optical properties of ensembles of quantum dots with various energies of activation from the ground-state level to the continuous-spectrum region were studied theoretically and experimentally with the InGaN quantum dots as an example. It is shown that, depending on the activation energy, both the quasi-equilibrium statistic of charge carriers at the levels of quantum dots and nonequilibrium statistic at room temperature are possible. In the latter case, the position of the maximum in the emission spectrum is governed by the value of the demarcation transition: the quantum dots with the transition energy higher than this value feature the quasi-equilibrium population of charge carriers, while the quantum dots with the transition energy lower than the demarcation-transition energy feature the nonequilibrium population. A model based on kinetic equations was used in the theoretical analysis. The key parameters determining the statistic are the parameters of thermal ejection of charge carriers; these parameters depend exponentially on the activation energy. It is shown experimentally that the use of stimulated phase decomposition makes it possible to appreciably increase the activation energy. In this case, the thermal-activation time is found to be much longer than the recombination time for an electron-hole pair, which suppresses the redistribution of charge carriers between the quantum dots and gives rise to the nonequilibrium population. The effect of nonequilibrium population on the luminescent properties of the structures with quantum dots is studied in detail.

  1. Hybrid Perovskites for Photovoltaics: Charge-Carrier Recombination, Diffusion, and Radiative Efficiencies.

    PubMed

    Johnston, Michael B; Herz, Laura M

    2016-01-19

    Photovoltaic (PV) devices that harvest the energy provided by the sun have great potential as renewable energy sources, yet uptake has been hampered by the increased cost of solar electricity compared with fossil fuels. Hybrid metal halide perovskites have recently emerged as low-cost active materials in PV cells with power conversion efficiencies now exceeding 20%. Rapid progress has been achieved over only a few years through improvements in materials processing and device design. In addition, hybrid perovskites appear to be good light emitters under certain conditions, raising the prospect of applications in low-cost light-emitting diodes and lasers. Further optimization of such hybrid perovskite devices now needs to be supported by a better understanding of how light is converted into electrical currents and vice versa. This Account provides an overview of charge-carrier recombination and mobility mechanisms encountered in such materials. Optical-pump-terahertz-probe (OPTP) photoconductivity spectroscopy is an ideal tool here, because it allows the dynamics of mobile charge carriers inside the perovskite to be monitored following excitation with a short laser pulse whose photon energy falls into the range of the solar spectrum. We first review our insights gained from transient OPTP and photoluminescence spectroscopy on the mechanisms dominating charge-carrier recombination in these materials. We discuss that mono-molecular charge-recombination predominantly originates from trapping of charges, with trap depths being relatively shallow (tens of millielectronvolts) for hybrid lead iodide perovskites. Bimolecular recombination arises from direct band-to-band electron-hole recombination and is found to be in significant violation of the simple Langevin model. Auger recombination exhibits links with electronic band structure, in accordance with its requirement for energy and momentum conservation for all charges involved. We further discuss charge-carrier mobility

  2. Elastic tunneling charge transport mechanisms in silicon quantum dots / Si O 2 thin films and superlattices

    NASA Astrophysics Data System (ADS)

    Illera, S.; Prades, J. D.; Cirera, A.

    2015-05-01

    The role of different charge transport mechanisms in Si / Si O 2 structures has been studied. A theoretical model based on the Transfer Hamiltonian Formalism has been developed to explain experimental current trends in terms of three different elastic tunneling processes: (1) trap assisted tunneling; (2) transport through an intermediate quantum dot; and (3) direct tunneling between leads. In general, at low fields carrier transport is dominated by the quantum dots whereas, for moderate and high fields, transport through deep traps inherent to the SiO2 is the most relevant process. Besides, current trends in Si / Si O 2 superlattice structure have been properly reproduced.

  3. Universal crossover of the charge carrier fluctuation mechanism in different polymer/carbon nanotubes composites

    SciTech Connect

    Barone, C. Mauro, C.; Pagano, S.; Landi, G.; Neitzert, H. C.

    2015-10-05

    Carbon nanotubes added to polymer and epoxy matrices are compounds of interest for applications in electronics and aerospace. The realization of high-performance devices based on these materials can profit from the investigation of their electric noise properties, as this gives a more detailed insight of the basic charge carriers transport mechanisms at work. The dc and electrical noise characteristics of different polymer/carbon nanotubes composites have been analyzed from 10 to 300 K. The results suggest that all these systems can be regarded as random resistive networks of tunnel junctions formed by adjacent carbon nanotubes. However, in the high-temperature regime, contributions deriving from other possible mechanisms cannot be separated using dc information alone. A transition from a fluctuation-induced tunneling process to a thermally activated regime is instead revealed by electric noise spectroscopy. In particular, a crossover is found from a two-level tunneling mechanism, operating at low temperatures, to resistance fluctuations of a percolative network, in the high-temperature region. The observed behavior of 1/f noise seems to be a general feature for highly conductive samples, independent on the type of polymer matrix and on the nanotube density.

  4. Universal crossover of the charge carrier fluctuation mechanism in different polymer/carbon nanotubes composites

    NASA Astrophysics Data System (ADS)

    Barone, C.; Landi, G.; Mauro, C.; Neitzert, H. C.; Pagano, S.

    2015-10-01

    Carbon nanotubes added to polymer and epoxy matrices are compounds of interest for applications in electronics and aerospace. The realization of high-performance devices based on these materials can profit from the investigation of their electric noise properties, as this gives a more detailed insight of the basic charge carriers transport mechanisms at work. The dc and electrical noise characteristics of different polymer/carbon nanotubes composites have been analyzed from 10 to 300 K. The results suggest that all these systems can be regarded as random resistive networks of tunnel junctions formed by adjacent carbon nanotubes. However, in the high-temperature regime, contributions deriving from other possible mechanisms cannot be separated using dc information alone. A transition from a fluctuation-induced tunneling process to a thermally activated regime is instead revealed by electric noise spectroscopy. In particular, a crossover is found from a two-level tunneling mechanism, operating at low temperatures, to resistance fluctuations of a percolative network, in the high-temperature region. The observed behavior of 1/f noise seems to be a general feature for highly conductive samples, independent on the type of polymer matrix and on the nanotube density.

  5. Carrier transport simulation of anomalous temperature dependence in nematic liquid crystals.

    PubMed

    Goto, Masanao; Takezoe, Hideo; Ishikawa, Ken

    2007-10-01

    We investigated the carrier transport phenomena in model liquid crystalline systems, which were constructed on the basis of the Gay-Berne potential and Monte Carlo calculation. The carrier transport was analyzed under the condition that the molecular arrangement in the system was fixed and thermally activated carriers were transported by hopping in the system. The carrier transport simulation was performed by Monte Carlo method using Miller-Abrahams hopping ratio. By these calculations, we reproduced the experimental results of the electronic conduction in nematic liquid crystals. PMID:17994925

  6. Carrier transport simulation of anomalous temperature dependence in nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Goto, Masanao; Takezoe, Hideo; Ishikawa, Ken

    2007-10-01

    We investigated the carrier transport phenomena in model liquid crystalline systems, which were constructed on the basis of the Gay-Berne potential and Monte Carlo calculation. The carrier transport was analyzed under the condition that the molecular arrangement in the system was fixed and thermally activated carriers were transported by hopping in the system. The carrier transport simulation was performed by Monte Carlo method using Miller-Abrahams hopping ratio. By these calculations, we reproduced the experimental results of the electronic conduction in nematic liquid crystals.

  7. Mapping the spatial distribution of charge carriers in quantum-confined heterostructures

    NASA Astrophysics Data System (ADS)

    Smith, Andrew M.; Lane, Lucas A.; Nie, Shuming

    2014-07-01

    Quantum-confined nanostructures are considered ‘artificial atoms’ because the wavefunctions of their charge carriers resemble those of atomic orbitals. For multiple-domain heterostructures, however, carrier wavefunctions are more complex and still not well understood. We have prepared a unique series of cation-exchanged HgxCd1-xTe quantum dots (QDs) and seven epitaxial core-shell QDs and measured their first and second exciton peak oscillator strengths as a function of size and chemical composition. A major finding is that carrier locations can be quantitatively mapped and visualized during shell growth or cation exchange simply using absorption transition strengths. These results reveal that a broad range of quantum heterostructures with different internal structures and band alignments exhibit distinct carrier localization patterns that can be used to further improve the performance of optoelectronic devices and enhance the brightness of QD probes for bioimaging.

  8. Mapping the spatial distribution of charge carriers in quantum-confined heterostructures

    PubMed Central

    Smith, Andrew M.; Lane, Lucas A.; Nie, Shuming

    2014-01-01

    Quantum-confined nanostructures are considered ‘artificial atoms’ because the wavefunctions of their charge carriers resemble those of atomic orbitals. For multiple-domain heterostructures, however, carrier wavefunctions are more complex and still not well understood. We have prepared a unique series of cation-exchanged HgxCd1−xTe quantum dots (QDs) and seven epitaxial core–shell QDs and measured their first and second exciton peak oscillator strengths as a function of size and chemical composition. A major finding is that carrier locations can be quantitatively mapped and visualized during shell growth or cation exchange simply using absorption transition strengths. These results reveal that a broad range of quantum heterostructures with different internal structures and band alignments exhibit distinct carrier localization patterns that can be used to further improve the performance of optoelectronic devices and enhance the brightness of QD probes for bioimaging. PMID:25080298

  9. Investigating and Optimizing Carrier Transport, Carrier Distribution, and Efficiency Droop in GaN-based Light-emitting Diodes

    NASA Astrophysics Data System (ADS)

    Zhu, Di

    2011-12-01

    -current efficiency and reduced efficiency droop. Compared with 4-QB-doped LEDs, 1-QB-doped LEDs show a 37.5% increase in light-output power at high currents. Consistent with the measurements, simulation shows a shift of radiative recombination among the MQWs and a reduced electron leakage current into the p-type GaN when fewer QBs are doped. The results can be attributed to a more symmetric carrier transport and uniform carrier distribution which help to reduce electron leakage and thus reduce the efficiency droop. In this dissertation, artificial evolution is introduced to the LED optimization process which combines a genetic algorithm (GA) and device-simulation software. We show that this approach is capable of generating novel concepts in designing and optimizing LED devices. Application of the GA to the QB-doping in the MQWs yields optimized structures which is consistent with the tailored QB doping experiments. Application of the GA to the EBL region suggests a novel structure with an inverted sheet charge at the spacer-EBL interface. The resulting repulsion of electrons can significantly reduce electron leakage and enhance the efficiency. Finally, dual-wavelength LEDs, which have two types of quantum wells (QWs) emitting at two different wavelengths, are experimentally characterized and compared with numerical simulations. These dual-wavelength LEDs allow us to determine which QW emits most of the light. An experimental observation and a quantitative analysis of the radiative recombination shift within the MQW active region are obtained. In addition, an injection-current dependence of the radiative recombination shift is predicted by numerical simulations and indeed observed in dual-wavelength LEDs. This injection-current dependence of the radiative recombination distribution can be explained very well by incorporating quantum-mechanical tunneling of carriers into and through the QBs into to the classical drift-diffusion model. In summary, using the LEDs with tailored QB

  10. Transportation of pinned charge density waves

    NASA Astrophysics Data System (ADS)

    Koo, Je Huan; Jeong, Jae Yoon; Cho, Guangsup

    2009-01-01

    We investigated the transport of pinned charge density waves (CDWs) that is observed in low dimensional materials. We treated pinned CDWs as moving CDWs that were confined within a typical quantum well amongst the many different types where pinning occurs at the barrier. We calculated the current flowing out of the quantum well by confined CDWs. The calculated conductivity is in good correspondence with experimental data in TTF-TCNQ, where the measured Fröhlich-Peierls temperature is 60 K much higher than the theoretical value of 20 K. The voltage dependence of the conductivity was calculated, where this is easily transformed into the dependence of electric field. The magnetic susceptibility was also calculated with a similar trend of experimental data. The susceptibility is a diamagnetic contribution by CDWs in addition to the constant background Pauli paramagnetic part.

  11. Analysis of electrolyte transport through charged nanopores.

    PubMed

    Peters, P B; van Roij, R; Bazant, M Z; Biesheuvel, P M

    2016-05-01

    We revisit the classical problem of flow of electrolyte solutions through charged capillary nanopores or nanotubes as described by the capillary pore model (also called "space charge" theory). This theory assumes very long and thin pores and uses a one-dimensional flux-force formalism which relates fluxes (electrical current, salt flux, and fluid velocity) and driving forces (difference in electric potential, salt concentration, and pressure). We analyze the general case with overlapping electric double layers in the pore and a nonzero axial salt concentration gradient. The 3×3 matrix relating these quantities exhibits Onsager symmetry and we report a significant new simplification for the diagonal element relating axial salt flux to the gradient in chemical potential. We prove that Onsager symmetry is preserved under changes of variables, which we illustrate by transformation to a different flux-force matrix given by Gross and Osterle [J. Chem. Phys. 49, 228 (1968)JCPSA60021-960610.1063/1.1669814]. The capillary pore model is well suited to describe the nonlinear response of charged membranes or nanofluidic devices for electrokinetic energy conversion and water desalination, as long as the transverse ion profiles remain in local quasiequilibrium. As an example, we evaluate electrical power production from a salt concentration difference by reverse electrodialysis, using an efficiency versus power diagram. We show that since the capillary pore model allows for axial gradients in salt concentration, partial loops in current, salt flux, or fluid flow can develop in the pore. Predictions for macroscopic transport properties using a reduced model, where the potential and concentration are assumed to be invariant with radial coordinate ("uniform potential" or "fine capillary pore" model), are close to results of the full model. PMID:27300979

  12. Analysis of electrolyte transport through charged nanopores

    NASA Astrophysics Data System (ADS)

    Peters, P. B.; van Roij, R.; Bazant, M. Z.; Biesheuvel, P. M.

    2016-05-01

    We revisit the classical problem of flow of electrolyte solutions through charged capillary nanopores or nanotubes as described by the capillary pore model (also called "space charge" theory). This theory assumes very long and thin pores and uses a one-dimensional flux-force formalism which relates fluxes (electrical current, salt flux, and fluid velocity) and driving forces (difference in electric potential, salt concentration, and pressure). We analyze the general case with overlapping electric double layers in the pore and a nonzero axial salt concentration gradient. The 3 ×3 matrix relating these quantities exhibits Onsager symmetry and we report a significant new simplification for the diagonal element relating axial salt flux to the gradient in chemical potential. We prove that Onsager symmetry is preserved under changes of variables, which we illustrate by transformation to a different flux-force matrix given by Gross and Osterle [J. Chem. Phys. 49, 228 (1968), 10.1063/1.1669814]. The capillary pore model is well suited to describe the nonlinear response of charged membranes or nanofluidic devices for electrokinetic energy conversion and water desalination, as long as the transverse ion profiles remain in local quasiequilibrium. As an example, we evaluate electrical power production from a salt concentration difference by reverse electrodialysis, using an efficiency versus power diagram. We show that since the capillary pore model allows for axial gradients in salt concentration, partial loops in current, salt flux, or fluid flow can develop in the pore. Predictions for macroscopic transport properties using a reduced model, where the potential and concentration are assumed to be invariant with radial coordinate ("uniform potential" or "fine capillary pore" model), are close to results of the full model.

  13. Carrier-mediated transport of riboflavin in Ashbya gossypii.

    PubMed

    Förster, C; Revuelta, J L; Krämer, R

    2001-01-01

    The filamentous hemiascomycete Ashbya gossypii is used for industrial riboflavin production. We examined riboflavin uptake and excretion at the plasma membrane using riboflavin auxotrophic and overproducing mutants. The riboflavin uptake system had low activity [Vmax = 20 +/- 4 nmol min(-1) g(-1) mycelial dry weight (dw)] and high affinity (KM = 40 +/- 12 microM). Inhibitor studies with the analogs FMN and FAD revealed high specificity of the uptake system. Excretion of riboflavin was not the consequence of non-specific permeability of the plasma membrane. Excretion rates in the mid-production phase were determined to be 2.5 nmol min(-1) g(-1) dw for wild-type cells and 66.7 nmol min(-1) g(-1) dw for an overproducing mutant, respectively. Inhibition of the reverse reaction, riboflavin uptake, led to an increase in apparent riboflavin efflux in the early production phase, indicating the presence of a separate excretion carrier. Riboflavin accumulation in A. gossypii vacuoles leading to product retention was found to be a secondary transport process. To address the question of whether a flux from the vacuoles back into the cytoplasm is present, we characterized efflux in hyphae in which the plasma membrane was permeabilized with digitonin. Efflux kinetics across the vacuolar membrane were unaffected by the lack of vacuolar H+ATPase activity and ATP, suggesting a passive mechanism. Based on the characterization of riboflavin transport processes in this study, the design of new production strains with improved riboflavin excretion may be possible. PMID:11234964

  14. Microstructure defects mediated charge transport in Nb-doped epitaxial BaTiO3 thin films

    NASA Astrophysics Data System (ADS)

    Zhou, Jian; Jing, Xiaosai; Alexe, Marin; Dai, Jiyan; Qin, Minghui; Wu, Sujuan; Zeng, Min; Gao, Jinwei; Lu, Xubing; Liu, J.-M.

    2016-05-01

    Nb-doped BaTiO3 (BNTO) films were deposited on MgO substrates at different substrate temperatures by pulsed laser deposition. The temperature dependence of their resistivity, carrier mobility and carrier concentration were systematically investigated. It reveals that the BNTO films deposited at lower temperature show higher resistivity and lower carrier mobility, and only show semiconductor characteristics at measurement temperatures ranging from 10 to 400 K. There is a metal-semiconductor transition at about 20 K for the films grown at relatively higher temperature. The intrinsic mechanism responsible for the different charge transport behavior was revealed by microstructure studies. Low crystal quality and high density of microstructure defects, observed for BNTO films grown at low temperatures, are, in particular, massively affecting the charge transport behavior of the BNTO films. The mediated charge transport of the microstructure defects is dominated by the thermal excitation process.

  15. Temperature Dependence of Lateral Charge Transport in Silicon Nanomembranes

    NASA Astrophysics Data System (ADS)

    Hu, Weiwei; Scott, Shelley; Jacobson, Rb; Sookchoo, Pornsatit; Savage, Donald; Eriksson, Mark; Lagally, Max

    2014-03-01

    Thin sheets of single-crystal silicon (nanomembranes), electrically isolated from a bulk substrate by a dielectric layer, are an exceptional tool for studying the electronic transport properties of surfaces in the absence of an extended bulk. Under UHV, we measure the conductivity, and a back gate allows us to look into the depletion region, where we can determine the minimum conductance. For hydrogen-terminated Si(001) NMs, for which the surface has no conductivity, the minimum conductance decreases with decreasing NM thickness (220-42nm), demonstrating the reduction in carriers for thinner NMs. For the clean Si(2 ×1)surface, mobile charge exists in the π* surface band. For thicknesses below 200nm surface conduction dominates, rendering the thickness independence of the minimum. We determine a surface charge mobility of ~50cm2V-1s-1. We have measured the temperature dependence of the conductance of a 42nm thick HF treated SiNM. The results show that the Fermi level is pinned 0.21 +/- 0 . 01 eV below the conduction band minimum, in agreement with XPS results. Supported by DOE.

  16. Valley-symmetry-preserved transport in ballistic graphene layers with gate-defined carrier guiding

    NASA Astrophysics Data System (ADS)

    Kim, Minsoo; Choi, Ji-Hae; Lee, Sang-Hoon; Watanabe, Kenji; Taniguchi, Takashi; Jhi, Seung-Hoon; Lee, Hu-Jong

    Zigzag graphene nanoribbons are predicted to exhibit interesting electronic properties stemming from its Dirac band structure. However, to date, investigation of them is highly limited because of the defects and the roughness at the edges, which mix different valley properties of graphene. Here, we report the signature of conservation of valley symmetry in two types of quasi-1D ballistic graphene transport devices; one is a quantum point contact (QPC) and another is an Aharonov-Bohm (AB) interferometer. In measurements, charge carriers were confined in a potential well formed by the dual gates operation and the four-terminal magnetoconductance (MC) was measured with varying the carrier density, dc bias, and temperature. It exhibits the conductance quantization in steps of ΔG = 4e2/ h starting from G = (2, 6), 10 ×e2 / h in a constricted conducting channel of QPC-type devices. This behavior is similar to the one observed in zigzag graphene nanoribbons having edge localized channels. Our tight-binding calculation shows that quasi-1D charge flow on a graphene plane acts a zigzag-type nanoribbon, unless it is perfectly aligned along the armchair direction. In the AB interferometry, we observed h/ e periodic modulation of MC and the zero-field conductance minimum with a negative MC background.

  17. On the nature of charge carrier scattering in Ag{sub 2}Se at low temperatures

    SciTech Connect

    Jafarov, M. B.

    2010-10-15

    The electric and thermoelectric properties of silver selenide in the temperature range of 4.2-300 K have been studied. The data obtained are interpreted within the theory of one-type carriers and Kane dispersion relation, with allowance for the character of electron-electron interaction. It is established that, for the concentrations n {<=} 7.8 x 10{sup 18} cm{sup -3}, charge carriers are scattered by impurity ions at T {<=} 30 K and by acoustic and optical phonons and point defects at T {>=} 30 K. Electron-electron interactions are found to be elastic at T < 30 K.

  18. The mitochondrial dicarboxylate and 2-oxoglutarate carriers do not transport glutathione

    PubMed Central

    Booty, Lee M.; King, Martin S.; Thangaratnarajah, Chancievan; Majd, Homa; James, Andrew M.; Kunji, Edmund R.S.; Murphy, Michael P.

    2015-01-01

    Glutathione carries out vital protective roles within mitochondria, but is synthesised in the cytosol. Previous studies have suggested that the mitochondrial dicarboxylate and 2-oxoglutarate carriers were responsible for glutathione uptake. We set out to characterise the putative glutathione transport by using fused membrane vesicles of Lactococcus lactis overexpressing the dicarboxylate and 2-oxoglutarate carriers. Although transport of the canonical substrates could be measured readily, an excess of glutathione did not compete for substrate uptake nor could transport of glutathione be measured directly. Thus these mitochondrial carriers do not transport glutathione and the identity of the mitochondrial glutathione transporter remains unknown. PMID:25637873

  19. The mitochondrial dicarboxylate and 2-oxoglutarate carriers do not transport glutathione.

    PubMed

    Booty, Lee M; King, Martin S; Thangaratnarajah, Chancievan; Majd, Homa; James, Andrew M; Kunji, Edmund R S; Murphy, Michael P

    2015-02-27

    Glutathione carries out vital protective roles within mitochondria, but is synthesised in the cytosol. Previous studies have suggested that the mitochondrial dicarboxylate and 2-oxoglutarate carriers were responsible for glutathione uptake. We set out to characterise the putative glutathione transport by using fused membrane vesicles of Lactococcus lactis overexpressing the dicarboxylate and 2-oxoglutarate carriers. Although transport of the canonical substrates could be measured readily, an excess of glutathione did not compete for substrate uptake nor could transport of glutathione be measured directly. Thus these mitochondrial carriers do not transport glutathione and the identity of the mitochondrial glutathione transporter remains unknown. PMID:25637873

  20. Dielectric force microscopy: imaging charge carriers in nanomaterials without electrical contacts.

    PubMed

    Zhang, Jie; Lu, Wei; Li, Yize Stephanie; Cai, Jinhua; Chen, Liwei

    2015-07-21

    Nanomaterials are increasingly used in electronic, optoelectronic, bioelectronic, sensing, and energy nanodevices. Characterization of electrical properties at nanometer scales thus becomes not only a pursuit in basic science but also of widespread practical need. The conventional field-effect transistor (FET) approach involves making electrical contacts to individual nanomaterials. This approach faces serious challenges in routine characterization due to the small size and the intrinsic heterogeneity of nanomaterials, as well as the difficulties in forming Ohmic contact with nanomaterials. Since the charge carrier polarization in semiconducting and metallic materials dominates their dielectric response to external fields, detecting dielectric polarization is an alternative approach in probing the carrier properties and electrical conductivity in nanomaterials. This Account reviews the challenges in the electrical conductivity characterization of nanomaterials and demonstrates that dielectric force microscopy (DFM) is a powerful tool to address the challenges. DFM measures the dielectric polarization via its force interaction with charges on the DFM tip and thus eliminates the need to make electrical contacts with nanomaterials. Furthermore, DFM imaging provides nanometer-scaled spatial resolution. Single-walled carbon nanotubes (SWNTs) and ZnO nanowires are used as model systems. The transverse dielectric permittivity of SWNTs is quantitatively measured to be ∼10, and the differences in longitudinal dielectric polarization are exploited to distinguish metallic SWNTs from semiconducting SWNTs. By application of a gate voltage at the DFM tip, the local carrier concentration underneath the tip can be accumulated or depleted, depending on charge carrier type and the density of states near the Fermi level. This effect is exploited to identify the conductivity type and carrier type in nanomaterials. By making comparison between DFM and FET measurements on the exact

  1. Preface: Charge transport in nanoscale junctions

    NASA Astrophysics Data System (ADS)

    Albrecht, Tim; Kornyshev, Alexei; Bjørnholm, Thomas

    2008-09-01

    Understanding the fundamentals of nanoscale charge transfer is pivotal for designing future nano-electronic devices. Such devices could be based on individual or groups of molecular bridges, nanotubes, nanoparticles, biomolecules and other 'active' components, mimicking wire, diode and transistor functions. These have operated in various environments including vacuum, air and condensed matter, in two- or three-electrode configurations, at ultra-low and room temperatures. Interest in charge transport in ultra-small device components has a long history and can be dated back to Aviram and Ratner's letter in 1974 (Chem. Phys. Lett. 29 277-83). So why is there a necessity for a special issue on this subject? The area has reached some degree of maturity, and even subtle geometric effects in the nanojunction and noise features can now be resolved and rationalized based on existing theoretical concepts. One purpose of this special issue is thus to showcase various aspects of nanoscale and single-molecule charge transport from experimental and theoretical perspectives. The main principles have 'crystallized' in our minds, but there is still a long way to go before true single-molecule electronics can be implemented. Major obstacles include the stability of electronic nanojunctions, reliable operation at room temperature, speed of operation and, last but not least, integration into large networks. A gradual transition from traditional silicon-based electronics to devices involving a single (or a few) molecule(s) therefore appears to be more viable from technologic and economic perspectives than a 'quantum leap'. As research in this area progresses, new applications emerge, e.g. with a view to characterizing interfacial charge transfer at the single-molecule level in general. For example, electrochemical experiments with individual enzyme molecules demonstrate that catalytic processes can be studied with nanometre resolution, offering a route towards optimizing biosensors at

  2. Electrode configuration and signal subtraction technique for single polarity charge carrier sensing in ionization detectors

    DOEpatents

    Luke, Paul

    1996-01-01

    An ionization detector electrode and signal subtraction apparatus and method provides at least one first conductive trace formed onto the first surface of an ionization detector. The first surface opposes a second surface of the ionization detector. At least one second conductive trace is also formed on the first surface of the ionization detector in a substantially interlaced and symmetrical pattern with the at least one first conductive trace. Both of the traces are held at a voltage potential of a first polarity type. By forming the traces in a substantially interlaced and symmetric pattern, signals generated by a charge carrier are substantially of equal strength with respect to both of the traces. The only significant difference in measured signal strength occurs when the charge carrier moves to within close proximity of the traces and is received at the collecting trace. The measured signals are then subtracted and compared to quantitatively measure the magnitude of the charge and to determine the position at which the charge carrier originated within the ionization detector.

  3. Electrode configuration and signal subtraction technique for single polarity charge carrier sensing in ionization detectors

    DOEpatents

    Luke, P.

    1996-06-25

    An ionization detector electrode and signal subtraction apparatus and method provide at least one first conductive trace formed onto the first surface of an ionization detector. The first surface opposes a second surface of the ionization detector. At least one second conductive trace is also formed on the first surface of the ionization detector in a substantially interlaced and symmetrical pattern with the at least one first conductive trace. Both of the traces are held at a voltage potential of a first polarity type. By forming the traces in a substantially interlaced and symmetric pattern, signals generated by a charge carrier are substantially of equal strength with respect to both of the traces. The only significant difference in measured signal strength occurs when the charge carrier moves to within close proximity of the traces and is received at the collecting trace. The measured signals are then subtracted and compared to quantitatively measure the magnitude of the charge and to determine the position at which the charge carrier originated within the ionization detector. 9 figs.

  4. Determination of charge carrier concentration in doped nonpolar liquids by impedance spectroscopy in the presence of charge adsorption.

    PubMed

    Yezer, Benjamin A; Khair, Aditya S; Sides, Paul J; Prieve, Dennis C

    2016-05-01

    The impedance of dodecane doped with sorbitan trioleate (Span 85), sorbitan monooleate (Span 80) and sorbitan monolaurate (Span 20) was measured as a function of frequency using a 10mV amplitude sinusoidal voltage applied across a parallel plate cell with a 10μm spacing. The tested solutions varied in concentration from 1mM to 100mM and the frequency range was 10(-2)-10(4)Hz. Nyquist plots of all three surfactants showed the high frequency semicircle characteristic of parallel resistance and capacitance but often exhibited a second semicircle at low frequencies which was attributed to charge adsorption and desorption. The electrical conductivity of each surfactant was proportional to surfactant concentration for concentrations above 10mM. Fitting the data to models for charge migration, differential capacitance, and adsorption allowed extraction of both charge concentration and two kinetic parameters that characterize the rate of adsorption and desorption. Above 10mM the ratio of charge carriers per surfactant molecule was 22ppm for Span 20, 3ppm for Span 80, and 0.2ppm for Span 85. A higher number of charge carriers per molecule of surfactant was associated with larger micelles. The adsorption rate constants were independent of surfactant concentration while the desorption rate constants were proportional to the surfactant concentration. This dependence indicated that uncharged surfactant, whether in micelles or not, participated in the desorption of charge. Predictions of the adsorption/desorption model for large constant electric fields agreed qualitatively with data from the literature (Karvar et al., 2014). PMID:26905337

  5. 9 CFR 91.18 - Cleaning and disinfection of transport carriers for export.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 9 Animals and Animal Products 1 2010-01-01 2010-01-01 false Cleaning and disinfection of transport carriers for export. 91.18 Section 91.18 Animals and Animal Products ANIMAL AND PLANT HEALTH INSPECTION....18 Cleaning and disinfection of transport carriers for export. All fittings, utensils and...

  6. Efficient charge-carrier extraction from Ag2S quantum dots prepared by the SILAR method for utilization of multiple exciton generation

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaoliang; Liu, Jianhua; Johansson, Erik M. J.

    2015-01-01

    The utilization of electron-hole pairs (EHPs) generated from multiple excitons in quantum dots (QDs) is of great interest toward efficient photovoltaic devices and other optoelectronic devices; however, extraction of charge carriers remains difficult. Herein, we extract photocharges from Ag2S QDs and investigate the dependence of the electric field on the extraction of charges from multiple exciton generation (MEG). Low toxic Ag2S QDs are directly grown on TiO2 mesoporous substrates by employing the successive ionic layer adsorption and reaction (SILAR) method. The contact between QDs is important for the initial charge separation after MEG and for the carrier transport, and the space between neighbor QDs decreases with more SILAR cycles, resulting in better charge extraction. At the optimal electric field for extraction of photocharges, the results suggest that the threshold energy (hνth) for MEG is 2.41Eg. The results reveal that Ag2S QD is a promising material for efficient extraction of charges from MEG and that QDs prepared by SILAR have an advantageous electrical contact facilitating charge separation and extraction.The utilization of electron-hole pairs (EHPs) generated from multiple excitons in quantum dots (QDs) is of great interest toward efficient photovoltaic devices and other optoelectronic devices; however, extraction of charge carriers remains difficult. Herein, we extract photocharges from Ag2S QDs and investigate the dependence of the electric field on the extraction of charges from multiple exciton generation (MEG). Low toxic Ag2S QDs are directly grown on TiO2 mesoporous substrates by employing the successive ionic layer adsorption and reaction (SILAR) method. The contact between QDs is important for the initial charge separation after MEG and for the carrier transport, and the space between neighbor QDs decreases with more SILAR cycles, resulting in better charge extraction. At the optimal electric field for extraction of photocharges, the

  7. Activationless charge transport across 4.5 to 22 nm in molecular electronic junctions

    PubMed Central

    Yan, Haijun; Bergren, Adam Johan; McCreery, Richard; Della Rocca, Maria Luisa; Martin, Pascal; Lafarge, Philippe; Lacroix, Jean Christophe

    2013-01-01

    In this work, we bridge the gap between short-range tunneling in molecular junctions and activated hopping in bulk organic films, and greatly extend the distance range of charge transport in molecular electronic devices. Three distinct transport mechanisms were observed for 4.5–22-nm-thick oligo(thiophene) layers between carbon contacts, with tunneling operative when d < 8 nm, activated hopping when d > 16 nm for high temperatures and low bias, and a third mechanism consistent with field-induced ionization of highest occupied molecular orbitals or interface states to generate charge carriers when d = 8–22 nm. Transport in the 8–22-nm range is weakly temperature dependent, with a field-dependent activation barrier that becomes negligible at moderate bias. We thus report here a unique, activationless transport mechanism, operative over 8–22-nm distances without involving hopping, which severely limits carrier mobility and device lifetime in organic semiconductors. Charge transport in molecular electronic junctions can thus be effective for transport distances significantly greater than the 1–5 nm associated with quantum-mechanical tunneling. PMID:23509271

  8. Activationless charge transport across 4.5 to 22 nm in molecular electronic junctions.

    PubMed

    Yan, Haijun; Bergren, Adam Johan; McCreery, Richard; Della Rocca, Maria Luisa; Martin, Pascal; Lafarge, Philippe; Lacroix, Jean Christophe

    2013-04-01

    In this work, we bridge the gap between short-range tunneling in molecular junctions and activated hopping in bulk organic films, and greatly extend the distance range of charge transport in molecular electronic devices. Three distinct transport mechanisms were observed for 4.5-22-nm-thick oligo(thiophene) layers between carbon contacts, with tunneling operative when d < 8 nm, activated hopping when d > 16 nm for high temperatures and low bias, and a third mechanism consistent with field-induced ionization of highest occupied molecular orbitals or interface states to generate charge carriers when d = 8-22 nm. Transport in the 8-22-nm range is weakly temperature dependent, with a field-dependent activation barrier that becomes negligible at moderate bias. We thus report here a unique, activationless transport mechanism, operative over 8-22-nm distances without involving hopping, which severely limits carrier mobility and device lifetime in organic semiconductors. Charge transport in molecular electronic junctions can thus be effective for transport distances significantly greater than the 1-5 nm associated with quantum-mechanical tunneling. PMID:23509271

  9. Spin Relaxation in Materials Lacking Coherent Charge Transport

    NASA Astrophysics Data System (ADS)

    Harmon, Nicholas

    2015-03-01

    As semiconductor spintronics research extends to materials beyond intrinsic or lightly doped semiconductors (e. g. organic materials, amorphous semiconductors, and impurity bands), the need is readily apparent for new theories of spin relaxation that encompass highly disordered materials, where charge transport is incoherent. We describe a broadly applicable theory of spin relaxation in materials with incoherent charge transport. The theory is based on continuous-time-random-walk theory and can incorporate many different relaxation mechanisms. We focus primarily on spin relaxation caused by spin-orbit and hyperfine effects in conjunction with carrier hopping. Analytic and numerical results from the theory are compared in various regimes with Monte Carlo simulations. Three different systems were examined: a polymer (MEH-PPV), amorphous silicon, and heavily doped n-GaAs. In the organic and amorphous systems, we predict spin relaxation and spin diffusion dependences on temperature and disorder for three different mechanisms (hyperfine, hopping-induced spin-orbit, and intra-site spin relaxation). The resulting unique experimental signatures predicted by the theory for each mechanism in these disordered systems provide a prescription for determining the dominant spin relaxation mechanism. We find our theory to be in agreement with available measurements in these materials. We also predict that large disorder modifies certain mechanisms to be algebraic instead of exponential in time. Our results should assist in evaluating the suitability of various disordered materials for spintronic devices. All work done in collaboration with Michael E. Flatté. Timothy Peterson and Paul Crowell collaborated as well on the n-GaAs study. This work was supported by an ARO MURI and by C-SPIN, one of six centers of STARnet, a Semiconductor Research Corporation program, sponsored by MARCO and DARPA.

  10. Charge transport and structural dynamics in carboxylic-acid-based deep eutectic mixtures.

    PubMed

    Griffin, Philip J; Cosby, Tyler; Holt, Adam P; Benson, Roberto S; Sangoro, Joshua R

    2014-08-01

    Charge transport and structural dynamics in the 1:2 mol ratio mixture of lidocaine and decanoic acid (LID-DA), a model deep eutectic mixture (DEM), have been characterized over a wide temperature range using broad-band dielectric spectroscopy and depolarized dynamic light scattering. Additionally, Fourier transform infrared spectroscopy measurements were performed to assess the degree of proton transfer between the neutral parent molecules. From our detailed analysis of the dielectric spectra, we have determined that this carboxylic-acid-based DEM is approximately 25% ionic at room temperature. Furthermore, we have found that the characteristic diffusion rate of mobile charge carriers is practically identical to the rate of structural relaxation at all measured temperatures, indicating that fast proton transport does not occur in LID-DA. Our results demonstrate that while LID-DA exhibits the thermal characteristics of a DEM, its charge transport properties resemble those of a protic ionic liquid. PMID:25025600

  11. Hybrid organic—inorganic perovskites: low-cost semiconductors with intriguing charge-transport properties

    NASA Astrophysics Data System (ADS)

    Brenner, Thomas M.; Egger, David A.; Kronik, Leeor; Hodes, Gary; Cahen, David

    2016-01-01

    Solution-processed hybrid organic-inorganic perovskites (HOIPs) exhibit long electronic carrier diffusion lengths, high optical absorption coefficients and impressive photovoltaic device performance. Recent results allow us to compare and contrast HOIP charge-transport characteristics to those of III-V semiconductors — benchmarks of photovoltaic (and light-emitting and laser diode) performance. In this Review, we summarize what is known and unknown about charge transport in HOIPs, with particular emphasis on their advantages as photovoltaic materials. Experimental and theoretical findings are integrated into one narrative, in which we highlight the fundamental questions that need to be addressed regarding the charge-transport properties of these materials and suggest future research directions.

  12. Effects of charge carrier concentration in hybrid conjugated polymer/oxide photovoltaic devices

    NASA Astrophysics Data System (ADS)

    White, Matthew Schuette

    2009-12-01

    Organic photovoltaics (OPV) represent an attractive route towards inexpensive, lightweight, and abundant renewable energy. The principal criticisms of OPV are low power conversion efficiency and unstable materials resulting in short device lifetimes. Hybrid OPV (h-OPV) devices with ZnO functioning either as the electron acceptor in the heterojunction, or as an electron transport layer in a polymer/fullerene based heterojunction, present useful device structures for investigating the functional mechanisms within OPV devices and a possible pathway towards air-stable high efficiency devices. Such use allows the vast knowledge surrounding oxide nanostructure morphology, band position, and carrier concentration control to be used in designing bulk-heterojunction OPV devices. The work presented in this thesis explores the effects of carrier concentration modulation in the polymer and/or oxide layers of these devices. Exposure to air is known to induce chemical defects in polymer semiconductors, which act as dopants in OPV devices. This increase in doping density can be used to improve OPV devices, however the low work-function metallic electrodes are often highly air sensitive. Using a silver back electrode and a ZnO interlayer at the transparent front contact in a polymer-based bulk heterojunction device allows for fabrication and testing in air. Relatively efficient devices are fabricated in this manner, but the devices show a characteristic aging time that indicates that air is a requirement to function as a quality diode. Air exposure may be effecting any of the layers in the device, but evidence is presented that shows the increased doping density in the polymer is largely responsible for the change in device quality over this time period. When oxides are used as the electron acceptor material in the device heterojunction, the carrier concentration in both the oxide and the polymer determine the strength of the electric field at the junction. Oxygen related doping

  13. 41 CFR 302-7.103 - How are the charges calculated when a carrier charges a minimum weight, but the actual weight of...

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 41 Public Contracts and Property Management 4 2011-07-01 2011-07-01 false How are the charges calculated when a carrier charges a minimum weight, but the actual weight of HHG, PBP&E and temporary storage is less than the minimum weight charged? 302-7.103 Section 302-7.103 Public Contracts and...

  14. 41 CFR 302-7.103 - How are the charges calculated when a carrier charges a minimum weight, but the actual weight of...

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 41 Public Contracts and Property Management 4 2014-07-01 2014-07-01 false How are the charges calculated when a carrier charges a minimum weight, but the actual weight of HHG, PBP&E and temporary storage is less than the minimum weight charged? 302-7.103 Section 302-7.103 Public Contracts and...

  15. 41 CFR 302-7.103 - How are the charges calculated when a carrier charges a minimum weight, but the actual weight of...

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 41 Public Contracts and Property Management 4 2010-07-01 2010-07-01 false How are the charges calculated when a carrier charges a minimum weight, but the actual weight of HHG, PBP&E and temporary storage is less than the minimum weight charged? 302-7.103 Section 302-7.103 Public Contracts and...

  16. 41 CFR 302-7.103 - How are the charges calculated when a carrier charges a minimum weight, but the actual weight of...

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 41 Public Contracts and Property Management 4 2012-07-01 2012-07-01 false How are the charges calculated when a carrier charges a minimum weight, but the actual weight of HHG, PBP&E and temporary storage is less than the minimum weight charged? 302-7.103 Section 302-7.103 Public Contracts and...

  17. 41 CFR 302-7.103 - How are the charges calculated when a carrier charges a minimum weight, but the actual weight of...

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 41 Public Contracts and Property Management 4 2013-07-01 2012-07-01 true How are the charges calculated when a carrier charges a minimum weight, but the actual weight of HHG, PBP&E and temporary storage is less than the minimum weight charged? 302-7.103 Section 302-7.103 Public Contracts and Property Management Federal Travel Regulation...

  18. Energy Models for One-Carrier Transport in Semiconductor Devices

    NASA Technical Reports Server (NTRS)

    Jerome, Joseph W.; Shu, Chi-Wang

    1991-01-01

    Moment models of carrier transport, derived from the Boltzmann equation, made possible the simulation of certain key effects through such realistic assumptions as energy dependent mobility functions. This type of global dependence permits the observation of velocity overshoot in the vicinity of device junctions, not discerned via classical drift-diffusion models, which are primarily local in nature. It was found that a critical role is played in the hydrodynamic model by the heat conduction term. When ignored, the overshoot is inappropriately damped. When the standard choice of the Wiedemann-Franz law is made for the conductivity, spurious overshoot is observed. Agreement with Monte-Carlo simulation in this regime required empirical modification of this law, or nonstandard choices. Simulations of the hydrodynamic model in one and two dimensions, as well as simulations of a newly developed energy model, the RT model, are presented. The RT model, intermediate between the hydrodynamic and drift-diffusion model, was developed to eliminate the parabolic energy band and Maxwellian distribution assumptions, and to reduce the spurious overshoot with physically consistent assumptions. The algorithms employed for both models are the essentially non-oscillatory shock capturing algorithms. Some mathematical results are presented and contrasted with the highly developed state of the drift-diffusion model.

  19. P type porous silicon resistivity and carrier transport

    SciTech Connect

    Ménard, S.; Fèvre, A.; Billoué, J.; Gautier, G.

    2015-09-14

    The resistivity of p type porous silicon (PS) is reported on a wide range of PS physical properties. Al/PS/Si/Al structures were used and a rigorous experimental protocol was followed. The PS porosity (P{sub %}) was found to be the major contributor to the PS resistivity (ρ{sub PS}). ρ{sub PS} increases exponentially with P{sub %}. Values of ρ{sub PS} as high as 1 × 10{sup 9} Ω cm at room temperature were obtained once P{sub %} exceeds 60%. ρ{sub PS} was found to be thermally activated, in particular, when the temperature increases from 30 to 200 °C, a decrease of three decades is observed on ρ{sub PS}. Based on these results, it was also possible to deduce the carrier transport mechanisms in PS. For P{sub %} lower than 45%, the conduction occurs through band tails and deep levels in the tissue surrounding the crystallites. When P{sub %} overpasses 45%, electrons at energy levels close to the Fermi level allow a hopping conduction from crystallite to crystallite to appear. This study confirms the potential of PS as an insulating material for applications such as power electronic devices.

  20. Molecular ion battery: a rechargeable system without using any elemental ions as a charge carrier

    PubMed Central

    Yao, Masaru; Sano, Hikaru; Ando, Hisanori; Kiyobayashi, Tetsu

    2015-01-01

    Is it possible to exceed the lithium redox potential in electrochemical systems? It seems impossible to exceed the lithium potential because the redox potential of the elemental lithium is the lowest among all the elements, which contributes to the high voltage characteristics of the widely used lithium ion battery. However, it should be possible when we use a molecule-based ion which is not reduced even at the lithium potential in principle. Here we propose a new model system using a molecular electrolyte salt with polymer-based active materials in order to verify whether a molecular ion species serves as a charge carrier. Although the potential of the negative-electrode is not yet lower than that of lithium at present, this study reveals that a molecular ion can work as a charge carrier in a battery and the system is certainly a molecular ion-based “rocking chair” type battery. PMID:26043147

  1. Molecular ion battery: a rechargeable system without using any elemental ions as a charge carrier

    NASA Astrophysics Data System (ADS)

    Yao, Masaru; Sano, Hikaru; Ando, Hisanori; Kiyobayashi, Tetsu

    2015-06-01

    Is it possible to exceed the lithium redox potential in electrochemical systems? It seems impossible to exceed the lithium potential because the redox potential of the elemental lithium is the lowest among all the elements, which contributes to the high voltage characteristics of the widely used lithium ion battery. However, it should be possible when we use a molecule-based ion which is not reduced even at the lithium potential in principle. Here we propose a new model system using a molecular electrolyte salt with polymer-based active materials in order to verify whether a molecular ion species serves as a charge carrier. Although the potential of the negative-electrode is not yet lower than that of lithium at present, this study reveals that a molecular ion can work as a charge carrier in a battery and the system is certainly a molecular ion-based “rocking chair” type battery.

  2. Investigation of optically injected charge carrier dynamics in silicon wafers using terahertz spectroscopic imaging

    NASA Astrophysics Data System (ADS)

    Arnold, Thomas; De Biasio, Martin; Muehleisen, Wolfgang; Leitner, Raimund

    2012-06-01

    Terahertz (THz) time-domain spectroscopy has proven to be a promising technology for a wide range of applications, such as inspection of nished products or materials, quality control, biomedical imaging and diagnostics, counterfeit detection and characterization of semiconductors. This paper investigates the applicability of THz time-domain spectroscopy for the characterization of silicon solar cell properties such as: conductivity, charge carrier mobility and density. Moreover, the possibilities for THz spectroscopy and imaging for the defect analysis in semiconductor and photovoltaic materials are investigated. THz-pump/THz-probe measurements were carried out on silicon wafers which were illuminated by a halogen light source to inject free charge carriers. Initial results indicate that THz time-domain spectroscopy is a promising technique for the characterization of silicon wafers for the photovoltaic industry.

  3. Dynamic charge-carrier-mobility-mediated holography in thin layers of photoconducting polymers

    NASA Astrophysics Data System (ADS)

    Bartkiewicz, S.; Miniewicz, A.; Sahraoui, B.; Kajzar, F.

    2002-11-01

    The dynamic holography technique is proposed for the measurement of the charge-carrier-mobility in thin layers of a photoconducting polymer, used in optically addressed liquid-crystal spatial light modulators. The photorefractive properties of these modulators are studied under short-pulse (20 ps, 532 nm) laser illumination conditions and the charge mobility in the photoconducting polymer (muh=10-7 cm2/V s) is obtained from the temporal evolution of intensity of the first-order diffracted beam. A mechanism responsible for the grating formation is proposed and discussed.

  4. Brownian dynamics determine universality of charge transport in ionic liquids

    SciTech Connect

    Sangoro, Joshua R; Iacob, Ciprian; Mierzwa, Michal; Paluch, Marian; Kremer, Friedrich

    2012-01-01

    Broadband dielectric spectroscopy is employed to investigate charge transport in a variety of glass-forming ionic liquids over wide frequency, temperature and pressure ranges. Using a combination of Einstein, Einstein-Smoluchowski, and Langevin relations, the observed universal scaling of charge transport in ionic liquids is traced back to the dominant role of Brownian dynamics.

  5. Metal oxide charge transport material doped with organic molecules

    DOEpatents

    Forrest, Stephen R.; Lassiter, Brian E.

    2016-08-30

    Doping metal oxide charge transport material with an organic molecule lowers electrical resistance while maintaining transparency and thus is optimal for use as charge transport materials in various organic optoelectronic devices such as organic photovoltaic devices and organic light emitting devices.

  6. Quadrupole transport experiment with space charge dominated cesium ion beam

    SciTech Connect

    Faltens, A.; Keefe, D.; Kim, C.; Rosenblum, S.; Tiefenback, M.; Warwick, A.

    1984-08-01

    The purpose of the experiment is to investigate the beam current transport limit in a long quadrupole-focussed transport channel in the space charge dominated region where the space charge defocussing force is almost as large as the average focussing force of the channel.

  7. 31 CFR 337.2 - Transportation charges and risks.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 31 Money and Finance:Treasury 2 2013-07-01 2013-07-01 false Transportation charges and risks. 337.2 Section 337.2 Money and Finance: Treasury Regulations Relating to Money and Finance (Continued... FEDERAL HOUSING ADMINISTRATION DEBENTURES Certificated Debentures § 337.2 Transportation charges and...

  8. 31 CFR 337.2 - Transportation charges and risks.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 31 Money and Finance:Treasury 2 2012-07-01 2012-07-01 false Transportation charges and risks. 337.2 Section 337.2 Money and Finance: Treasury Regulations Relating to Money and Finance (Continued... FEDERAL HOUSING ADMINISTRATION DEBENTURES Certificated Debentures § 337.2 Transportation charges and...

  9. 31 CFR 337.2 - Transportation charges and risks.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 31 Money and Finance: Treasury 2 2010-07-01 2010-07-01 false Transportation charges and risks. 337.2 Section 337.2 Money and Finance: Treasury Regulations Relating to Money and Finance (Continued... FEDERAL HOUSING ADMINISTRATION DEBENTURES Certificated Debentures § 337.2 Transportation charges and...

  10. 31 CFR 337.2 - Transportation charges and risks.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 31 Money and Finance:Treasury 2 2011-07-01 2011-07-01 false Transportation charges and risks. 337.2 Section 337.2 Money and Finance: Treasury Regulations Relating to Money and Finance (Continued... FEDERAL HOUSING ADMINISTRATION DEBENTURES Certificated Debentures § 337.2 Transportation charges and...

  11. Migration of excited charge carriers in arrays of phosphorus-doped silicon nanocrystals

    SciTech Connect

    Belyakov, V. A. Konakov, A. A.; Burdov, V. A.

    2010-11-15

    The rate of tunnel migration of excited charge carriers (electrons and holes) in the array of silicon nanocrystals doped with phosphorus is calculated. It is shown that, starting from certain phosphorus concentrations dependent on the relation between the dimensions of the emitting and accepting nanocrystals, the rate of tunneling of electrons sharply decreases (by several orders of magnitude) and becomes lower than the rate of interband radiative recombination

  12. Time resolved imaging of carrier and thermal transport in silicon

    SciTech Connect

    D. H. Hurley; O. B. Wright; O. Matsuda; S. L. Shinde

    2010-01-01

    We use ultrashort optical pulses to microscopically image carrier and thermal diffusion in two spatial dimensions in pristine and mechanically polished surfaces of crystalline silicon. By decomposing changes in reflectivity in the latter sample into a transient component that varies with delay time and a steady state component that varies with pump chopping frequency, the influence of thermal diffusion is isolated from that of carrier diffusion and recombination. Additionally, studies using carrier injection density as a parameter are used to clearly identify the carrier recombination pathway.

  13. A review of carrier thermoelectric-transport theory in organic semiconductors.

    PubMed

    Lu, Nianduan; Li, Ling; Liu, Ming

    2016-07-20

    Carrier thermoelectric-transport theory has recently become of growing interest and numerous thermoelectric-transport models have been proposed for organic semiconductors, due to pressing current issues involving energy production and the environment. The purpose of this review is to provide a theoretical description of the thermoelectric Seebeck effect in organic semiconductors. Special attention is devoted to the carrier concentration, temperature, polaron effect and dipole effect dependence of the Seebeck effect and its relationship to hopping transport theory. Furthermore, various theoretical methods are used to discuss carrier thermoelectric transport. Finally, an outlook of the remaining challenges ahead for future theoretical research is provided. PMID:27386952

  14. Collection of photogenerated charge carriers in small-pitched infrared photovoltaic focal plane arrays

    NASA Astrophysics Data System (ADS)

    Chekanova, Galina V.; Drugova, Albina A.; Kholodnov, Viacheslav; Nikitin, Mikhail S.

    2010-10-01

    Technology of infrared (IR) photovoltaic (PV) focal plane arrays (FPA) covering spectral range from 1.6 to 14 μm gradually moves from simple quasi-matrix (linear) arrays like as 4×288 pixels to large format high definition arrays 1280×1024 pixels and more. Major infrared detector materials for PV technology are InSb and its alloys and ternary alloys Hg1-xCdxTe. Progress in IR PV technology was provided in last decade by serious improvement in material growing techniques. Increasing of PV array format is related always to decreasing of pixel size and spacing between neighbor pixels to minimal size reasonable from point of view of infrared physics. So pitch is small (15-25 μm) in large format arrays. Ambipolar diffusion length of photogenerated charge carriers can exceed pitch many times in high quality absorption layers of PV arrays. It means that each pixel can collect excess charge carriers generated far from n+-p junction border. Optimization of resolution, filling factor and cross-talking level of small-pitched PV FPA requires comprehensive estimation of photodiode's (PD) pixel performance depending on pixel and array design, material properties and operating conditions. Objective of the present work was to develop general approach to estimate collection of photogenerated charge carriers in small-pitched arrays.

  15. Crystal structure and charge carrier concentration of W 18O 49

    NASA Astrophysics Data System (ADS)

    Viswanathan, K.; Brandt, K.; Salje, E.

    1981-01-01

    The electrical resistivity of the tungsten oxide, W 18O 49, is 1.75 · 10 -3 Ω cm along the needle axis. The charge carrier density, as determined by reflectivity measurements, is 1.87 · 10 22 cm -3, thereby indicating that most of the charge carriers are delocalized. Hence the smaller conductivity along the needle axis than that expected for such charge carrier concentrations must be found in the structure, which has been refined using the data collected with an automatic diffractometer. The structure consists of WO 6 and WO 7 polyhedra which are linked along edges and/or corners. However, as the linkage parallel to b takes place only by sharing corners, an anisotropy in the electrical conductivity may be expected. Another explanation for the smaller conductivity may be found in the occurrence of defects such as tunnels in the structure, which may scatter the electrons. The refinement shows that the tungsten positions, determined by Magneli ( Arkiv Kemi1, 223 (1950)), are essentially correct; but the positions of the oxygens, especially two of them, differ considerably. This results in one of the tungsten atoms getting an additional coordinating oxygen, the coordination number thereby becoming seven.

  16. Spectroscopic characterization of charge carrier anisotropic motion in twisted few-layer graphene

    NASA Astrophysics Data System (ADS)

    Kandyba, Viktor; Yablonskikh, Mikhail; Barinov, Alexei

    2015-11-01

    Graphene, a layer of carbon atoms in a honeycomb lattice, captures enormous interest as probably the most promising component of future electronics thanks to its mechanical robustness, flexibility, and unique charge carrier quasiparticles propagating like massless high energy Dirac fermions. If several graphene layers form a stack, the interaction between them is, on the one hand, weak, allowing realization of various registries between the layers and, on the other hand, strong enough for a wide range tuning of the electronic properties. Here we grow few layer graphene with various number of layers and twist configurations and address the electronic properties of individual atomic layers in single microscopic domains using angle-resolved photoelectron spectromicroscopy. The dependence of the interlayer coupling on the twist angle is analyzed and, in the domains with tri-layers and more, if different rotations are present, the electrons in weaker coupled adjacent layers are shown to have different properties manifested by coexisting van Hove singularities, moiré superlattices with corresponding superlattice Dirac points, and charge carrier group velocity renormalizations. Moreover, pronounced anisotropy in the charge carrier motion, opening a possibility to transform strongly coupled graphene bilayers into quasi one-dimensional conductors, is observed.

  17. Spectroscopic characterization of charge carrier anisotropic motion in twisted few-layer graphene

    PubMed Central

    Kandyba, Viktor; Yablonskikh, Mikhail; Barinov, Alexei

    2015-01-01

    Graphene, a layer of carbon atoms in a honeycomb lattice, captures enormous interest as probably the most promising component of future electronics thanks to its mechanical robustness, flexibility, and unique charge carrier quasiparticles propagating like massless high energy Dirac fermions. If several graphene layers form a stack, the interaction between them is, on the one hand, weak, allowing realization of various registries between the layers and, on the other hand, strong enough for a wide range tuning of the electronic properties. Here we grow few layer graphene with various number of layers and twist configurations and address the electronic properties of individual atomic layers in single microscopic domains using angle-resolved photoelectron spectromicroscopy. The dependence of the interlayer coupling on the twist angle is analyzed and, in the domains with tri-layers and more, if different rotations are present, the electrons in weaker coupled adjacent layers are shown to have different properties manifested by coexisting van Hove singularities, moiré superlattices with corresponding superlattice Dirac points, and charge carrier group velocity renormalizations. Moreover, pronounced anisotropy in the charge carrier motion, opening a possibility to transform strongly coupled graphene bilayers into quasi one-dimensional conductors, is observed. PMID:26548567

  18. Improved charge carrier separation in barium tantalate composites investigated by laser flash photolysis.

    PubMed

    Schneider, Jenny; Nikitin, Konstantin; Wark, Michael; Bahnemann, Detlef W; Marschall, Roland

    2016-04-20

    Charge carrier dynamics in phase pure Ba5Ta4O15 and in a Ba5Ta4O15-Ba3Ta5O15 composite have been studied by means of diffuse reflectance laser flash photolysis spectroscopy in the presence and absence of an electron donor, in order to reveal the reason for the improved photocatalytic performance of the latter. For the first time the transient absorption of trapped electrons with a maximum at around 650 nm and of trapped holes with a transient absorption maximum at around 310 nm is reported for tantalates. The decay kinetics of the photogenerated charge carriers could be fitted by second order reaction kinetics, and the direct recombination of the trapped electrons with the trapped holes was proven. In the absence of an electron donor, no difference in the decay behavior between the phase pure material and the composite material is found. In the presence of methanol, for the pure phase Ba5Ta4O15 the recombination of the charge carriers could not be prevented and the trapped electrons also recombine with the ˙CH2OH radical formed via the methanol oxidation by the trapped holes. However, in the composite, the electron can be stored in the system, the ˙CH2OH radical injects an electron into the conduction band of the second component of the composite, i.e., Ba3Ta5O15. Thus, the electrons are available for an extended period to induce reduction reactions. PMID:26732364

  19. Optical generation of free charge carriers in thin films of tin oxide

    SciTech Connect

    Zhurbina, I. A. Tsetlin, O. I.; Timoshenko, V. Yu.

    2011-02-15

    The methods of infrared absorption spectroscopy and Raman spectroscopy are used to study nanocrystalline SnO{sub x} films (1 {<=} x {<=} 2) prepared by thermal oxidation of metallic tin layers. A monotonic decrease in the transmittance of films in the infrared region has been observed as a result of exposure of the films to light with the wavelength of 380 nm at room temperature. The effect is at a maximum for the samples with x Almost-Equal-To 2 and is observed for {approx}10 min after switching off of illumination. The mentioned variations in optical properties, similarly to those observed in the case of heating of the samples in the dark, are accounted for by an increase in the concentration of free charge carriers (electrons) in nanocrystals of tin dioxide. The data of infrared spectroscopy and the Drude model are used to calculate the concentrations of photogenerated charge carriers ({approx}10{sup 19} cm{sup -3}); variations in these concentrations in the course of illumination and after switching off of illumination are determined. Mechanisms of observed photogeneration of charge carriers in SnO{sub x} films and possible applications of this effect to gas sensors are discussed.

  20. Charge transport and mobility engineering in two-dimensional transition metal chalcogenide semiconductors.

    PubMed

    Li, Song-Lin; Tsukagoshi, Kazuhito; Orgiu, Emanuele; Samorì, Paolo

    2016-01-01

    Two-dimensional (2D) van der Waals semiconductors represent the thinnest, air stable semiconducting materials known. Their unique optical, electronic and mechanical properties hold great potential for harnessing them as key components in novel applications for electronics and optoelectronics. However, the charge transport behavior in 2D semiconductors is more susceptible to external surroundings (e.g. gaseous adsorbates from air and trapped charges in substrates) and their electronic performance is generally lower than corresponding bulk materials due to the fact that the surface and bulk coincide. In this article, we review recent progress on the charge transport properties and carrier mobility engineering of 2D transition metal chalcogenides, with a particular focus on the markedly high dependence of carrier mobility on thickness. We unveil the origin of this unique thickness dependence and elaborate the devised strategies to master it for carrier mobility optimization. Specifically, physical and chemical methods towards the optimization of the major factors influencing the extrinsic transport such as electrode/semiconductor contacts, interfacial Coulomb impurities and atomic defects are discussed. In particular, the use of ad hoc molecules makes it possible to engineer the interface with the dielectric and heal the vacancies in such materials. By casting fresh light on the theoretical and experimental studies, we provide a guide for improving the electronic performance of 2D semiconductors, with the ultimate goal of achieving technologically viable atomically thin (opto)electronics. PMID:26593874

  1. 75 FR 48409 - Establishment of the Toxic by Inhalation Hazard Common Carrier Transportation Advisory Committee

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-08-10

    ... Surface Transportation Board Establishment of the Toxic by Inhalation Hazard Common Carrier Transportation Advisory Committee AGENCY: Surface Transportation Board. ACTION: Notice of establishment of the Toxic by... the Federal Advisory Committee Act (FACA), 5 U.S.C. app., the Surface Transportation Board...

  2. Charge carrier motion in disordered conjugated polymers: a multiscale ab-initio study

    SciTech Connect

    Vukmirovic, Nenad; Wang, Lin-Wang

    2009-11-10

    We developed an ab-initio multiscale method for simulation of carrier transport in large disordered systems, based on direct calculation of electronic states and electron-phonon coupling constants. It enabled us to obtain the never seen before rich microscopic details of carrier motion in conjugated polymers, which led us to question several assumptions of phenomenological models, widely used in such systems. The macroscopic mobility of disordered poly(3- hexylthiophene) (P3HT) polymer, extracted from our simulation, is in agreement with experimental results from the literature.

  3. Charge Energy Transport in Hopping Systems with Rapidly Decreasing Density of States

    NASA Astrophysics Data System (ADS)

    Mendels, Dan; Organic Electronics Group Technion Team

    2014-03-01

    An accurate description of the carrier hopping topology in the energy domain of hopping systems incorporating a rapidly decreasing density of states and the subsequent energetic position of these systems' so called effective conduction band is crucial for rationalizing and quantifying these systems' thermo-electric properties, doping related phenomena and carrier gradient effects such as the emergence of the General Einstein Relation under degenerate conditions. Additionally, as will be shown, the 'mobile' carriers propagating through the system can have excess energies reaching 0.3eV above the system quasi-Fermi energy. Hence, since these mobile carriers are most prone to reach systems interfaces and interact with oppositely charged carriers, their excess energy should be considered in determining the efficiencies of energy dependent processes such as carrier recombination and exciton dissociation. In light of the stated motivations, a comprehensive numerical and analytical study of the topology of hopping in the energetic density of such systems (i.e. the statistics regarding which energy values carriers visit most and in what manner) was implemented and the main statistical features of the hopping process that determine the position in energy of the system's effective conduction band were distilled. The obtained results also help shed light on yet to be elucidated discrepancies between predictions given by the widely employed transport energy concept and Monte Carlo simulations.

  4. Electrochemical characteristics of ideal polarizable interfaces with limited number of charge carriers

    NASA Astrophysics Data System (ADS)

    Přibyl, Michal; Slouka, Zdeněk

    2015-11-01

    Recent progress in material chemistry and surface engineering has led to emergence of new electrode materials with unique physical and electrochemical properties. Here, we introduce a physical model describing charging of ideal polarizable electrode-electrolyte interface where the electrode is characterized by a limited capacity to store charge. The analytical model treats the electrode and electrolyte phases as independent nonlinear capacitors that are eventually coupled through the condition of equality of the total stored electrical charge opposite in sign. Gouy-Chapman and condensed layer theories applied to a general 1 :n valent electrolyte are used to predict dependencies of differential capacitance of the electrolyte phase and surface concentration of the electrical charge on the applied potential. The model of the nonlinear capacitor for the electrode phase is described by a theory of electron donors and acceptors present in conductive solids as a result of thermal fluctuations. Both the differential capacitance and the surface concentration of the electrical charge in the electrode are evaluated as functions of the applied potential and related to the capacity of the electrode phase to accumulate charge and its ability to form electron donors and acceptors. The knowledge of capacitive properties of both phases allows to predict electrochemical characteristics of ideal polarizable interfaces, e.g., current responses in linear sweep voltammetry. The coupled model also shows significant potential drops in the electrode comparable to those in the electrolyte phase for materials with low charge carrier concentrations.

  5. DNA charge transport within the cell.

    PubMed

    Grodick, Michael A; Muren, Natalie B; Barton, Jacqueline K

    2015-02-01

    The unique characteristics of DNA charge transport (CT) have prompted an examination of roles for this chemistry within a biological context. Not only can DNA CT facilitate long-range oxidative damage of DNA, but redox-active proteins can couple to the DNA base stack and participate in long-range redox reactions using DNA CT. DNA transcription factors with redox-active moieties such as SoxR and p53 can use DNA CT as a form of redox sensing. DNA CT chemistry also provides a means to monitor the integrity of the DNA, given the sensitivity of DNA CT to perturbations in base stacking as arise with mismatches and lesions. Enzymes that utilize this chemistry include an interesting and ever-growing class of DNA-processing enzymes involved in DNA repair, replication, and transcription that have been found to contain 4Fe-4S clusters. DNA repair enzymes containing 4Fe-4S clusters, that include endonuclease III (EndoIII), MutY, and DinG from bacteria, as well as XPD from archaea, have been shown to be redox-active when bound to DNA, share a DNA-bound redox potential, and can be reduced and oxidized at long-range via DNA CT. Interactions between DNA and these proteins in solution, in addition to genetics experiments within Escherichia coli, suggest that DNA-mediated CT can be used as a means of cooperative signaling among DNA repair proteins that contain 4Fe-4S clusters as a first step in finding DNA damage, even within cells. On the basis of these data, we can consider also how DNA-mediated CT may be used as a means of signaling to coordinate DNA processing across the genome. PMID:25606780

  6. In-situ imaging of charge carriers in an electrochemical cell.

    SciTech Connect

    Gerald, R. E. II

    1998-01-30

    A toroid cavity nuclear magnetic resonance (NMR) detector capable of quantitatively recording radial concentration profiles, diffusion constants, displacements of charge carriers, and radial profiles of spin-lattice relaxation time constants was employed to investigate the charge/discharge cycle of a solid-state electrochemical cell. One-dimensional radial concentration profiles (1D-images) of ions solvated in a polyethylene oxide matrix were recorded by {sup 19}F and {sup 7}Li NMR for several cells. A sequence of {sup 19}F NMR images, recorded at different stages of cell polarization, revealed the evolution of a region of the polymer depleted of charge carriers. From these images it is possible to extract the transference number for the Li{sup +} ion. Spatially localized diffusion coefficients and spin-lattice relaxation time constants can be measured simultaneously for the ions in the polymer electrolyte by a spin-labeling method that employs the radial B{sub 1}-field gradient of the toroid cavity. A spatial resolution of 7 {micro}m near the working electrode was achieved with a gradient strength of 800 gauss/cm. With this apparatus, it is also possible to investigate novel intercalation anode materials for lithium ion storage. These materials are coated onto the working electrode in a thin film. The penetration depth of lithium cations in these films can be imaged at different times in the charge/discharge cycle of the battery.

  7. Charge Transport in Conjugated Materials: From Theoretical Models to Experimental Systems

    NASA Astrophysics Data System (ADS)

    Olivier, Yoann; Muccioli, Luca; Zannoni, Claudio; Cornil, Jérôme

    2008-09-01

    Charge carrier mobility is the key quantity to characterize the charge transport properties in devices. Based on earlier work of Bässler and co-workers, we set up a Monte-Carlo approach that allows us to calculate mobility using transfer rates derived from Marcus theory. The parameters entering into the rate expression are evaluated by means of different quantum-chemical techniques. Our approach is applied here to a model one-dimensional system made of pentacene molecules as well as to real systems such as crystalline structures and columnar liquid crystal phases.

  8. Charge Transport in Conjugated Materials: From Theoretical Models to Experimental Systems

    SciTech Connect

    Olivier, Yoann; Cornil, Jerome; Muccioli, Luca; Zannoni, Claudio

    2008-09-17

    Charge carrier mobility is the key quantity to characterize the charge transport properties in devices. Based on earlier work of Baessler and co-workers, we set up a Monte-Carlo approach that allows us to calculate mobility using transfer rates derived from Marcus theory. The parameters entering into the rate expression are evaluated by means of different quantum-chemical techniques. Our approach is applied here to a model one-dimensional system made of pentacene molecules as well as to real systems such as crystalline structures and columnar liquid crystal phases.

  9. Impact of charge transport on current-voltage characteristics and power-conversion efficiency of organic solar cells

    NASA Astrophysics Data System (ADS)

    Würfel, Uli; Neher, Dieter; Spies, Annika; Albrecht, Steve

    2015-04-01

    This work elucidates the impact of charge transport on the photovoltaic properties of organic solar cells. Here we show that the analysis of current-voltage curves of organic solar cells under illumination with the Shockley equation results in values for ideality factor, photocurrent and parallel resistance, which lack physical meaning. Drift-diffusion simulations for a wide range of charge-carrier mobilities and illumination intensities reveal significant carrier accumulation caused by poor transport properties, which is not included in the Shockley equation. As a consequence, the separation of the quasi Fermi levels in the organic photoactive layer (internal voltage) differs substantially from the external voltage for almost all conditions. We present a new analytical model, which considers carrier transport explicitly. The model shows excellent agreement with full drift-diffusion simulations over a wide range of mobilities and illumination intensities, making it suitable for realistic efficiency predictions for organic solar cells.

  10. Impact of charge transport on current–voltage characteristics and power-conversion efficiency of organic solar cells

    PubMed Central

    Würfel, Uli; Neher, Dieter; Spies, Annika; Albrecht, Steve

    2015-01-01

    This work elucidates the impact of charge transport on the photovoltaic properties of organic solar cells. Here we show that the analysis of current–voltage curves of organic solar cells under illumination with the Shockley equation results in values for ideality factor, photocurrent and parallel resistance, which lack physical meaning. Drift-diffusion simulations for a wide range of charge-carrier mobilities and illumination intensities reveal significant carrier accumulation caused by poor transport properties, which is not included in the Shockley equation. As a consequence, the separation of the quasi Fermi levels in the organic photoactive layer (internal voltage) differs substantially from the external voltage for almost all conditions. We present a new analytical model, which considers carrier transport explicitly. The model shows excellent agreement with full drift-diffusion simulations over a wide range of mobilities and illumination intensities, making it suitable for realistic efficiency predictions for organic solar cells. PMID:25907581

  11. Control of charge transport in the perovskite CH3 NH3 PbI3 thin film.

    PubMed

    Shi, Jiangjian; Wei, Huiyun; Lv, Songtao; Xu, Xin; Wu, Huijue; Luo, Yanhong; Li, Dongmei; Meng, Qingbo

    2015-03-16

    Carrier density and transport properties in the CH3 NH3 PbI3 thin film have been investigated. It is found that the carrier density, the depletion field, and the charge collection and transport properties in the CH3 NH3 PbI3 absorber film can be controlled effectively by different concentrations of reactants. That is, the carrier properties and the self-doping characteristics in CH3 NH3 PbI3 films are strongly influenced by the reaction thermodynamic and kinetic processes. Furthermore, by employing mixed solvents with ethanol and isopropanol to deposit the CH3 NH3 PbI3 film, the charge collection and transport efficiencies are improved significantly, thereby yielding an overall enhanced cell performance. PMID:25581504

  12. Revealing the ultrafast charge carrier dynamics in organo metal halide perovskite solar cell materials using time resolved THz spectroscopy

    NASA Astrophysics Data System (ADS)

    Ponseca, C. S., Jr.; Sundström, V.

    2016-03-01

    Ultrafast charge carrier dynamics in organo metal halide perovskite has been probed using time resolved terahertz (THz) spectroscopy (TRTS). Current literature on its early time characteristics is unanimous: sub-ps charge carrier generation, highly mobile charges and very slow recombination rationalizing the exceptionally high power conversion efficiency for a solution processed solar cell material. Electron injection from MAPbI3 to nanoparticles (NP) of TiO2 is found to be sub-ps while Al2O3 NPs do not alter charge dynamics. Charge transfer to organic electrodes, Spiro-OMeTAD and PCBM, is sub-ps and few hundreds of ps respectively, which is influenced by the alignment of energy bands. It is surmised that minimizing defects/trap states is key in optimizing charge carrier extraction from these materials.

  13. Subsurface Imaging and Sensing of Charge Carrier Movements in the Earth’s Crust

    NASA Astrophysics Data System (ADS)

    Dahlgren, R.; Freund, F. T.; Lazarus, M.; Wang, J. S.; Rekenthaler, D.; Peters, R. D.; Duma, G.

    2009-12-01

    The DUSEL facility will enable unique opportunities for field experiments that would otherwise not be possible at surface facilities (Lesko, K.T., TAUP, 2007) and support a host of undergraduate and graduate educational projects. In this presentation, some of the proposed geophysics experiments will be described as part of the subsurface Imaging and Sensing (SIS) project to study charge carrier movement in crustal rock as a function of various perturbations. The electric conductivity of the Earth’s crust is dominated by positive hole charge carriers, e.g. mobile electron vacancy defects (EVD) in the oxygen anion sublattice of minerals that make up the bulk of crustal rocks. We are interested in (i) coupling of fundamental processes linked to the activation of additional EVDs in rocks deep in the crust subjected to tectonic stresses and the outflow of these charge carriers into the surrounding rocks, (ii) their manifestation across the electromagnetic spectrum and other measuands, (iii) induced forces that arise when these charge carriers are subjected to the episodic or daily magnetic field variations coming from geomagnetic storms or from the ionospheric current vortex, and (iv) in the movement of positive holes in the shallow crust when a thunderstorm system drifts overhead, dragging along a charge cloud in the ground. We propose to conduct active rock stressing experiments in situ using expanding grout technique (performing electrical, electromagnetic, and VolksMeter tilt measurements) and to monitor the electric and magnetic field variations penetrating into the Earth’s crust. Additionally optical phenomena will be investigated (anomalous infrared signatures, visible light arising from atomic oxygen and corona discharge, and infrared imaging). If budget permits, measurement of changes of acoustic velocity, evolution of chemical species (H2, O*, Rn, etc) and radar reflectivity as a function of stresses will also be attempted. We propose to study the charge

  14. Nature and the Sign of Stress-Activated Electronic Charge Carriers in Rocks

    NASA Astrophysics Data System (ADS)

    Freund, F.

    2013-12-01

    When rocks are subjected to increasing uniaxial stress, highly mobile charge carriers become activated, which have the remarkable ability to flow out of the stressed rock volume, spreading into and through adjacent less stressed or unstressed rocks. Two basic questions arise: (i) What is the nature - and the sign - of these charge carriers and (ii) How do they exist in the rocks before being activated by stress? A large body of evidence is available that points to a positive sign, consistent with defect electrons, which (in semiconductor parlance) are called 'holes'. Holes that reside in the oxygen anion sublattice, associated with O 2sp-type energy states at the upper edge of the valence band, are called 'positive holes'. The positive holes exist in rocks in form of dormant, electrically inactive peroxy defects. Ever so slight deformation, leading to grain-grain sliding, can break the peroxy bonds and activate positive holes. Electrons that are co-activated by the same process cannot flow out of the stressed rock volume into the unstressed rocks. This leads to charge separation and, hence, to a potential difference similar to a battery voltage. In order to experimentally confirm the positive sign of the positive hole charge carriers flowing out of a given stressed rock volume, certain rules have to be obeyed. If not, unreliable results may be obtained, even negative outflow currents, seemingly inconsistent with the postulated positive sign of the positive hole charge carriers. Such errors can be avoided by taking into account that the charge outflow occurs in response to a 'battery potential', V, rapidly evolving between stressed and unstressed or less stressed parts of the rock. The current I given by Ohm's Law, I=V/R, is then limited by the internal resistance R. A second complicating factor arises from the fact that, as the positive holes are stress-activated and begin to flow out, they simultaneously recombine, returning to the dormant state. The ensuing

  15. Excited state and charge-carrier dynamics in perovskite solar cell materials.

    PubMed

    Ponseca, Carlito S; Tian, Yuxi; Sundström, Villy; Scheblykin, Ivan G

    2016-02-26

    Organo-metal halide perovskites (OMHPs) have attracted enormous interest in recent years as materials for application in optoelectronics and solar energy conversion. These hybrid semiconductors seem to have the potential to challenge traditional silicon technology. In this review we will give an account of the recent development in the understanding of the fundamental light-induced processes in OMHPs from charge-photo generation, migration of charge carries through the materials and finally their recombination. Our and other literature reports on time-resolved conductivity, transient absorption and photoluminescence properties are used to paint a picture of how we currently see the fundamental excited state and charge-carrier dynamics. We will also show that there is still no fully coherent picture of the processes in OMHPs and we will indicate the problems to be solved by future research. PMID:26820442

  16. Excited state and charge-carrier dynamics in perovskite solar cell materials

    NASA Astrophysics Data System (ADS)

    Ponseca, Carlito S., Jr.; Tian, Yuxi; Sundström, Villy; Scheblykin, Ivan G.

    2016-02-01

    Organo-metal halide perovskites (OMHPs) have attracted enormous interest in recent years as materials for application in optoelectronics and solar energy conversion. These hybrid semiconductors seem to have the potential to challenge traditional silicon technology. In this review we will give an account of the recent development in the understanding of the fundamental light-induced processes in OMHPs from charge-photo generation, migration of charge carries through the materials and finally their recombination. Our and other literature reports on time-resolved conductivity, transient absorption and photoluminescence properties are used to paint a picture of how we currently see the fundamental excited state and charge-carrier dynamics. We will also show that there is still no fully coherent picture of the processes in OMHPs and we will indicate the problems to be solved by future research.

  17. Beam transport and space charge compensation strategies (invited).

    PubMed

    Meusel, O; Droba, M; Noll, D; Schulte, K; Schneider, P P; Wiesner, C

    2016-02-01

    The transport of intense ion beams is affected by the collective behavior of this kind of multi-particle and multi-species system. The space charge expressed by the generalized perveance dominates the dynamical process of thermalisation, which leads to emittance growth. To prevent changes of intrinsic beam properties and to reduce the intensity dependent focusing forces, space charge compensation seems to be an adequate solution. In the case of positively charged ion beams, electrons produced by residual gas ionization and secondary electrons provide the space charge compensation. The influence of the compensation particles on the beam transport and the local degree of space charge compensation is given by different beam properties as well as the ion beam optics. Especially for highly charged ion beams, space charge compensation in combination with poor vacuum conditions leads to recombination processes and therefore increased beam losses. Strategies for providing a compensation-electron reservoir at very low residual gas pressures will be discussed. PMID:26932109

  18. Beam transport and space charge compensation strategies (invited)

    NASA Astrophysics Data System (ADS)

    Meusel, O.; Droba, M.; Noll, D.; Schulte, K.; Schneider, P. P.; Wiesner, C.

    2016-02-01

    The transport of intense ion beams is affected by the collective behavior of this kind of multi-particle and multi-species system. The space charge expressed by the generalized perveance dominates the dynamical process of thermalisation, which leads to emittance growth. To prevent changes of intrinsic beam properties and to reduce the intensity dependent focusing forces, space charge compensation seems to be an adequate solution. In the case of positively charged ion beams, electrons produced by residual gas ionization and secondary electrons provide the space charge compensation. The influence of the compensation particles on the beam transport and the local degree of space charge compensation is given by different beam properties as well as the ion beam optics. Especially for highly charged ion beams, space charge compensation in combination with poor vacuum conditions leads to recombination processes and therefore increased beam losses. Strategies for providing a compensation-electron reservoir at very low residual gas pressures will be discussed.

  19. Carrier transport in an InGaAs(P)/InP all-optical switching structure

    SciTech Connect

    Knorr, C.; Wilhelm, U.; Ottenwaelder, D.; Scholz, F.; Hangleiter, A.

    1996-12-31

    All-optical switches play a central role in optical computing and optical data processing. SEEDs (self electro-optic effect devices) are one class of devices, which work at low optical power, but need an external electrical feedback. The authors presented a specially designed SCMQW structure, where hole transport is controlled by an additional large heterobarrier. This barrier gives access to steady state escape times by measuring the charge carrier induced field change in the MWQ region. The authors get a minimum value for the hole extraction time over the barrier of several {micro}s at 77 K. At a temperature of 200 K the measured time constants lie below the values, which their rate equation model and the semi-classical model predict, and show a stronger field dependence. This could be accounted for thermally assisted tunneling and contribution of light hole transport, which both reduce the effective barrier height and show a stronger field dependence. Further investigations of the transport times are currently in progress by changing the thickness of the InP barrier and the barrier height of the quaternary material.

  20. Charge Carrier Conduction Mechanism in PbS Quantum Dot Solar Cells: Electrochemical Impedance Spectroscopy Study.

    PubMed

    Wang, Haowei; Wang, Yishan; He, Bo; Li, Weile; Sulaman, Muhammad; Xu, Junfeng; Yang, Shengyi; Tang, Yi; Zou, Bingsuo

    2016-07-20

    With its properties of bandgap tunability, low cost, and substrate compatibility, colloidal quantum dots (CQDs) are becoming promising materials for optoelectronic applications. Additionally, solution-processed organic, inorganic, and hybrid ligand-exchange technologies have been widely used in PbS CQDs solar cells, and currently the maximum certified power conversion efficiency of 9.9% has been reported by passivation treatment of molecular iodine. Presently, there are still some challenges, and the basic physical mechanism of charge carriers in CQDs-based solar cells is not clear. Electrochemical impedance spectroscopy is a monitoring technology for current by changing the frequency of applied alternating current voltage, and it provides an insight into its electrical properties that cannot be measured by direct current testing facilities. In this work, we used EIS to analyze the recombination resistance, carrier lifetime, capacitance, and conductivity of two typical PbS CQD solar cells Au/PbS-TBAl/ZnO/ITO and Au/PbS-EDT/PbS-TBAl/ZnO/ITO, in this way, to better understand the charge carriers conduction mechanism behind in PbS CQD solar cells, and it provides a guide to design high-performance quantum-dots solar cells. PMID:27176547

  1. Glass transition dynamics and charge carrier mobility in conjugated polyfluorene thin films

    NASA Astrophysics Data System (ADS)

    Qin, Hui; Liu, Dan; Wang, Tao

    Conjugated polymers are commonly used in organic optoelectronic devices, e.g. organic photovoltaics (OPVs), light-emitting diodes (LEDs) and field effect transistors (FETs). In these devices, the conjugated polymers are prepared as thin films with thicknesses in the range of tens to hundreds of nanometers, and are interfaced with different function layers made from organic or inorganic materials. We have studied the glass transition temperature (Tg) of poly(9, 9-dioctylfluorene)-co-N-(1, 4-butylphenyl)diphenylamine) (TFB) thin films supported on different substrates, as well as their SCLC charge carrier mobility in photodiodes. Both Monotonic and non-monotonic Tg deviations are observed in TFB thin films supported on Si/SiOx and PEDOT:PSS, respectively. With low to moderate thermal crosslinking, the thickness dependent Tg deviation still exists, which diminishes in TFB films with a high crosslinking degree. The vertical charge carrier mobility of TFB thin films extracted from the SCLC measurements is found increase with film thickness, a value increases from 1 to 50 x 10-6 cm2 V-1 s-1 in the thickness range from 15 to 180 nm. Crosslinking was found to reduce the carrier mobility in TFB thin films. The Tg deviations are also discussed using the classic layered models in the literature. Our results provide a precise guide for the fabrication and design of high performance optoelectronic devices.

  2. Spatial and temporal imaging of long-range charge transport in perovskite thin films by ultrafast microscopy

    PubMed Central

    Guo, Zhi; Manser, Joseph S.; Wan, Yan; Kamat, Prashant V.; Huang, Libai

    2015-01-01

    Charge carrier diffusion coefficient and length are important physical parameters for semiconducting materials. Long-range carrier diffusion in perovskite thin films has led to remarkable solar cell efficiencies; however, spatial and temporal mechanisms of charge transport remain unclear. Here we present a direct measurement of carrier transport in space and in time by mapping carrier density with simultaneous ultrafast time resolution and ∼50-nm spatial precision in perovskite thin films using transient absorption microscopy. These results directly visualize long-range carrier transport of ∼220 nm in 2 ns for solution-processed polycrystalline CH3NH3PbI3 thin films. Variations of the carrier diffusion coefficient at the μm length scale have been observed with values ranging between 0.05 and 0.08 cm2 s−1. The spatially and temporally resolved measurements reported here underscore the importance of the local morphology and establish an important first step towards discerning the underlying transport properties of perovskite materials. PMID:26101051

  3. Electronic-Structure Theory of Organic Semiconductors: Charge-Transport Parameters and Metal/Organic Interfaces

    NASA Astrophysics Data System (ADS)

    Coropceanu, Veaceslav; Li, Hong; Winget, Paul; Zhu, Lingyun; Brédas, Jean-Luc

    2013-07-01

    We focus this review on the theoretical description, at the density functional theory level, of two key processes that are common to electronic devices based on organic semiconductors (such as organic light-emitting diodes, field-effect transistors, and solar cells), namely charge transport and charge injection from electrodes. By using representative examples of current interest, our main goal is to introduce some of the reliable theoretical methodologies that can best depict these processes. We first discuss the evaluation of the microscopic parameters that determine charge-carrier transport in organic molecular crystals, i.e., electronic couplings and electron-vibration couplings. We then examine the electronic structure at interfaces between an organic layer and a metal or conducting oxide electrode, with an emphasis on the work-function modifications induced by the organic layer and on the interfacial energy-level alignments.

  4. Measurement of charge-carrier concentration in indium phosphide by means of an electrolyte-semiconductor contact

    SciTech Connect

    Asanov, O.M.; Gaman, V.I.; Zorkal'tseva, N.N.; Korableva, T.V.; Petrova, N.G.

    1987-11-01

    An electrolyte-semiconductor contact is used to study the conductivity of epitaxial layers and single crystals of n-type indium phosphide obtained by gas transport. Some of the specimens were alloyed with tin and sulfur. The volt-farad characteristics are used to find the potentials of planar zones, which amount to 0.8-1.3 V for different electrolytes. Values of concentration of charge carriers calculated from measured values of capacitance of the electrolyte-indium-phosphide contact showed good agreement with measurements of the Hall effect on single crystals in the range 10/sup 16/-10/sup 18/ cm/sup -3/. The use of measurements of the capacitance of the electrolyte-semiconductor contact with simultaneous etching of a local region made it possible to study the electron distribution in epitaxial layers of indium phosphide.

  5. Kinetics of photo-activated charge carriers in Sn:CdS

    NASA Astrophysics Data System (ADS)

    Patidar, Manju Mishra; Panda, Richa; Gorli, V. R.; Gangrade, Mohan; Nath, R.; Ganesan, V.

    2016-05-01

    Kinetics of the photo-activated charge carriers has been investigated in Tin substituted Cadmium Sulphide, Cd1-xSnxS (x=0, 0.05, 0.10 and 0.15), thin films prepared by spray pyrolysis. X-Ray Diffraction shows an increase in strain that resulted in the decreased crystallite size upon Sn substitution. At the first sight, the photo current characteristics show a quenching effect on Sn substitution. However, survival of persistent photocurrents is seen even up to 15% of Sn substitution. Transient photo current decay could be explained with a 2τ relaxation model. CdS normally has an n-type character and the Sn doping expected to inject hole carriers. The two fold increase in τ1, increase in activation energy and the decrease in photocurrents upon Sn substitution point towards a band gap cleaning scenario that include compensation and associated carrier injection dynamics. In addition Atomic Force Microscopy shows a drastic change in microstructure that modulates the carrier dynamics as a whole.

  6. Charge transport and device physics of layered-crystalline organic semiconductors (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Hasegawa, Tatsuo

    2015-10-01

    Here we present and discuss our recent investigations into the understanding of microscopic charge transport, novel film processing technologies, and a development of layered-crystalline organic semiconductors for high performance OTFTs. We first discuss the microscopic charge transport in the OTFTs, as investigated by field-induced electron spin resonance spectroscopy. The technique can detect signals due to tiny amount of field-induced carriers, accumulated at the semiconductor-insulator interfaces. Following aspects are presented and discussed; 1) Carrier motion within the crystalline domains can be understood in terms of the trap-and-release transport, 2) charge trap states are spatially extended over several sites depending on the trap levels, and 3) the intra- and inter-domain transport can be discriminated by anisotropic electron spin resonance measurements. Next we discuss novel print production technologies for organic semiconductors showing high layered crystallinity. The concept of "printed electronics" is now regarded as a realistic paradigm to manufacture light-weight, thin, and impact-resistant electronics devices, although production of highly crystalline semiconductor films may be incompatible with conventional printing process. We here present printing techniques for manufacturing high performance OTFTs; 1) double-shot inkjet printing for small-molecule-based semiconductors, and 2) push-coating for semiconducting polymers. We demonstrate that both processes are useful to manufacture high quality semiconductor layers with the high layered crystallinity.

  7. Generating free charges by carrier multiplication in quantum dots for highly efficient photovoltaics.

    PubMed

    Ten Cate, Sybren; Sandeep, C S Suchand; Liu, Yao; Law, Matt; Kinge, Sachin; Houtepen, Arjan J; Schins, Juleon M; Siebbeles, Laurens D A

    2015-02-17

    CONSPECTUS: In a conventional photovoltaic device (solar cell or photodiode) photons are absorbed in a bulk semiconductor layer, leading to excitation of an electron from a valence band to a conduction band. Directly after photoexcitation, the hole in the valence band and the electron in the conduction band have excess energy given by the difference between the photon energy and the semiconductor band gap. In a bulk semiconductor, the initially hot charges rapidly lose their excess energy as heat. This heat loss is the main reason that the theoretical efficiency of a conventional solar cell is limited to the Shockley-Queisser limit of ∼33%. The efficiency of a photovoltaic device can be increased if the excess energy is utilized to excite additional electrons across the band gap. A sufficiently hot charge can produce an electron-hole pair by Coulomb scattering on a valence electron. This process of carrier multiplication (CM) leads to formation of two or more electron-hole pairs for the absorption of one photon. In bulk semiconductors such as silicon, the energetic threshold for CM is too high to be of practical use. However, CM in nanometer sized semiconductor quantum dots (QDs) offers prospects for exploitation in photovoltaics. CM leads to formation of two or more electron-hole pairs that are initially in close proximity. For photovoltaic applications, these charges must escape from recombination. This Account outlines our recent progress in the generation of free mobile charges that result from CM in QDs. Studies of charge carrier photogeneration and mobility were carried out using (ultrafast) time-resolved laser techniques with optical or ac conductivity detection. We found that charges can be extracted from photoexcited PbS QDs by bringing them into contact with organic electron and hole accepting materials. However, charge localization on the QD produces a strong Coulomb attraction to its counter charge in the organic material. This limits the production

  8. Charge carrier mobilities in organic semiconductor crystals based on the spectral overlap.

    PubMed

    Stehr, Vera; Fink, Reinhold F; Deibel, Carsten; Engels, Bernd

    2016-09-01

    The prediction of substance-related charge-transport properties is important for the tayloring of new materials for organic devices, such as organic solar cells. Assuming a hopping process, the Marcus theory is frequently used to model charge transport. Here another approach, which is already widely used for exciton transport, is adapted to charge transport. It is based on the spectral overlap of the vibrational donor and acceptor spectra. As the Marcus theory it is derived from Fermi's Golden rule, however, it contains less approximations, as the molecular vibrations are treated quantum mechanically. In contrast, the Marcus theory reduces all vibrational degrees of freedom to one and treats its influence classically. The approach is tested on different acenes and predicts most of the experimentally available hole mobilities in these materials within a factor of 2. This represents a significant improvement to values obtained from Marcus theory which is qualitatively correct but frequently overestimates the mobilities by factors up to 10. Furthermore, the charge-transport properties of two derivatives of perylene bisimide are investigated. © 2016 Wiley Periodicals, Inc. PMID:27371816

  9. Carriers

    MedlinePlus

    ... for those known to be at risk for genetic diseases. Reproductive Choices For couples who are carriers, reproductive decisions can be sensitive. A number of options are available, such as adoption, prenatal testing, and pre-implantation genetic diagnosis (PGD). PGD screens ...

  10. Analysis of carrier transport in quaterrylene thin film transistors formed by ultraslow vacuum deposition

    NASA Astrophysics Data System (ADS)

    Hayakawa, Ryoma; Petit, Matthieu; Chikyow, Toyohiro; Wakayama, Yutaka

    2008-07-01

    Quaterrylene field-effect transistors (FETs) with top-contact Au electrodes were formed on a SiO2 (200nm )/p-Si (001) substrate by an ultraslow vacuum deposition technique, and their carrier transport was investigated. The quaterrylene FETs showed typical p-channel transistor behavior. The dependence of carrier mobility on grain size, film thickness, and temperature was examined to gain insight into the transport mechanism. Carrier mobility increased with grain size, showing that carrier transport was limited by grain boundaries. Temperature dependence in the range from 300to60K was divided into two distinct behaviors. Above 210K, carrier mobility showed thermally activated behavior, with energies of 100-150meV required to overcome the potential barriers at grain boundaries. In contrast, the conduction mechanism became tunnel-transfer-like below 210K. In the low temperature range, tunnel transfer through potential barriers at grain boundaries predominated over the thermally activated type. The change in carrier mobility was correlated with film thickness. Carrier mobility rose sharply with increasing thickness in the two-dimensional (2D) growth region, followed by saturation at 3 or 4 ML, where the growth process changed from 2D to three-dimensional mode. This result reveals that the first few layers of 2D growth work as an effective transistor channel. Enhancement in 2D growth in the vertical direction is crucial to improving carrier transport.

  11. Field-direction control of the type of charge carriers in nonsymmorphic IrO2

    NASA Astrophysics Data System (ADS)

    Uchida, M.; Sano, W.; Takahashi, K. S.; Koretsune, T.; Kozuka, Y.; Arita, R.; Tokura, Y.; Kawasaki, M.

    2015-06-01

    In the quest for switching of the charge carrier type in conductive materials, we focus on nonsymmorphic crystals, which are expected to have highly anisotropic folded Fermi surfaces due to symmetry requirements. Following a simple tight-binding model simulation, we prepare nonsymmorphic IrO2 single-crystalline films with various growth orientations by molecular beam epitaxy, and systematically quantify their Hall effect for the corresponding field directions. The results clearly demonstrate that the dominant carrier type can be intrinsically controlled by the magnetic field direction, as also evidenced by first-principles calculations revealing nontrivial momentum dependence of the group velocity and mass tensor on the folded Fermi surfaces and its anisotropic nature for the field direction.

  12. Contactless Spectral-dependent Charge Carrier Lifetime Measurements in Silicon Photovoltaic Materials

    NASA Astrophysics Data System (ADS)

    Roller, John; Hamadani, Behrang; Dagenais, Mario

    Charge carrier lifetime measurements in bulk or unfinished photovoltaic (PV) materials allow for a more accurate estimate of power conversion efficiency in completed solar cells. In this work, carrier lifetimes in PV-grade silicon wafers are obtained by way of quasi-steady state photoconductance measurements. These measurements use a contactless RF system coupled with varying narrow spectrum input LEDs, ranging in wavelength from 460 nm to 1030 nm. Spectral dependent lifetime measurements allow for determination of bulk and surface properties of the material, including the intrinsic bulk lifetime and the surface recombination velocity. The effective lifetimes are fit to an analytical physics-based model to determine the desired parameters. Passivated and non-passivated samples are both studied and are shown to have good agreement with the theoretical model.

  13. Temporary Charge Carrier Separation Dominates the Photoluminescence Decay Dynamics of Colloidal CdSe Nanoplatelets.

    PubMed

    Rabouw, Freddy T; van der Bok, Johanna C; Spinicelli, Piernicola; Mahler, Benoît; Nasilowski, Michel; Pedetti, Silvia; Dubertret, Benoît; Vanmaekelbergh, Daniël

    2016-03-01

    Luminescent colloidal CdSe nanoplatelets with atomically defined thicknesses have recently been developed, and their potential for various applications has been shown. To understand their special properties, experiments have until now focused on the relatively short time scales of at most a few nanoseconds. Here, we measure the photoluminescence decay dynamics of colloidal nanoplatelets on time scales up to tens of microseconds. The excited state dynamics are found to be dominated by the slow (∼μs) dynamics of temporary exciton storage in a charge-separated state, previously overlooked. We study the processes of charge carrier separation and exciton recovery in pure CdSe nanoplatelets as well as in core-crown and core-shell CdSe/CdS nanoplatelets with high ensemble quantum yields of 50%, and discuss the implications. Our work highlights the importance of reversible charge carrier trapping and experiments over a wide range of time scales for the understanding of colloidal nanoemitters in general and nanoplatelets in particular. PMID:26863992

  14. Carrier transport in graphite/Si{sub 3}N{sub 4}-nanobelt/PtIr Schottky barrier diodes

    SciTech Connect

    Bi, Jinghui; Wei, Guodong; Shang, Minghui; Gao, Fengmei; Yang, Weiyou E-mail: weiyouyang@tsinghua.org.cn; Tang, Bin E-mail: weiyouyang@tsinghua.org.cn

    2014-11-10

    Understanding the roles of contacts and interfaces between metals and semiconductors is critically important for exploring nanostructure-based nanodevices. The present study shed some light on the dominated mechanism of size-dependent carrier transfer in the Schottky barrier diodes configured by the Pt-Ir/Si{sub 3}N{sub 4}-nanobelt/graphite (metal-semiconductor-metal (MSM)) sandwiched structure via a conductive atomic force microscopy using nanobelts with various thicknesses. The observed I-V behaviors suggested that the charge transports under the low and high biases were dominated by the reverse-biased Schottky barrier and space-charge-limited current (SCLC), respectively. The intermediate region between the low and high biases presented the transition between the Ohmic and SCLC behaviors, in which the ≡Si and =N dangling bonds acted as the defects within the Si{sub 3}N{sub 4} nanobelt surface are predominant in the charge transfer.

  15. Ambipolar charge transport in "traditional" organic hole transport layers.

    PubMed

    Khademi, S; Song, J Y; Wyatt, P B; Kreouzis, T; Gillin, W P

    2012-05-01

    Organic semiconductors are often labeled as electron or hole transport materials due to the primary role they perform in devices. However, despite these labels we have shown using time-of-flight that two of the traditional "hole transport materials" TPD and NPB are actually excellent electron transporters the electron transport properties of which are comparable to those for holes. PMID:22467553

  16. Charge Carrier Dynamics of Quantum Confined Semiconductor Nanoparticles Analyzed via Transient Absorption Spectroscopy

    NASA Astrophysics Data System (ADS)

    Thibert, Arthur Joseph, III

    Semiconductor nanoparticles are tiny crystalline structures (typically range from 1 - 100 nm) whose shape in many cases can be dictated through tailored chemical synthesis with atomic scale precision. The small size of these nanoparticles often results in quantum confinement (spatial confinement of wave functions), which imparts the ability to manipulate band-gap energies thus allowing them to be optimally engineered for different applications (i.e., photovoltaics, photocatalysis, imaging). However, charge carriers excited within these nanoparticles are often involved in many different processes: trapping, trap migration, Auger recombination, non-radiative relaxation, radiative relaxation, oxidation / reduction, or multiple exciton generation. Broadband ultrafast transient absorption laser spectroscopy is used to spectrally resolve the fate of excited charge carriers in both wavelength and time, providing insight as to what synthetic developments or operating conditions will be necessary to optimize their efficiency for certain applications. This thesis outlines the effort of resolving the dynamics of excited charge carriers for several Cd and Si based nanoparticle systems using this experimental technique. The thesis is organized into five chapters and two appendices as indicated below. Chapter 1 provides a brief introduction to the photophysics of semiconductor nanoparticles. It begins by defining what nanoparticles, semiconductors, charge carriers, and quantum confinement are. From there it details how the study of charge carrier dynamics within nanoparticles can lead to increased efficiency in applications such as photocatalysis. Finally, the experimental methodology associated with ultrafast transient absorption spectroscopy is introduced and its power in mapping charge carrier dynamics is established. Chapter 2 (JPCC, 19647, 2011) introduces the first of the studied samples: water-solubilized 2D CdSe nanoribbons (NRs), which were synthesized in the Osterloh

  17. CHARACTERIZING COUPLED CHARGE TRANSPORT WITH MULTISCALE MOLECULAR DYNAMICS

    SciTech Connect

    Swanson, Jessica

    2011-08-31

    This is the final progress report for Award DE-SC0004920, entitled 'Characterizing coupled charge transport with multi scale molecular dynamics'. The technical abstract will be provided in the uploaded report.

  18. Influence of defects on excess charge carrier kinetics studied by transient PC and transient PA

    SciTech Connect

    Feist, H.; Kunst, M.; Swiatkowski, C.

    1997-07-01

    By comparison of transient photoconductivity (TPC) and transient photoinduced absorption (PA) the influence of the density of states in the bandgap on excess charge carrier kinetics is studied for a-Si:H films deposited at different temperatures and for state of the art a-Si:H films in two different states of light soaking. In both series the rising deep defect density leads to an enhancement of electron trapping rather than recombination via deep defects. The samples deposited at temperatures lower than 250 C additionally show a lower effective electron mobility, i.e., a broader conduction band tail.

  19. Evaluation of anisotropic charge carrier mobility of perylene single crystals by time-of-flight method

    NASA Astrophysics Data System (ADS)

    Kougo, Junichi; Ishikawa, Ken

    2016-03-01

    The charge carrier mobilities along the vertical and lateral directions of perylene platelet single crystals were measured by the time-of-flight (TOF) method. In the lateral directional measurement, the entire region between electrodes was irradiated to obtain measurable signals. The transient photocurrent was different from the conventional TOF measurements; hence, we developed an analytic method for lateral directional measurement. The electron mobilities along the thickness and lateral directions were 0.33 and 2.0 cm2·V-1·s-1 and the hole mobilities were 0.12 and 0.6 cm2·V-1·s-1, respectively.

  20. Enhanced charge carrier generation in dye sensitized solar cells by nanoparticle plasmons

    NASA Astrophysics Data System (ADS)

    Hägglund, Carl; Zäch, Michael; Kasemo, Bengt

    2008-01-01

    An interesting possibility to improve the conversion and cost efficiencies of photovoltaic solar cells is to exploit the large optical cross sections of localized (nanoparticle) surface plasmon resonances (LSPRs). We have investigated this prospect for dye sensitized solar cells. Photoconductivity measurements were performed on flat TiO2 films, sensitized by a combination of dye molecules and arrays of nanofabricated elliptical gold disks. An enhanced dye charge carrier generation rate was found and shown to derive from the LSPR contribution by means of the polarization dependent resonance frequency in the anisotropic, aligned gold disks.

  1. Long-lived charge carrier dynamics in polymer/quantum dot blends and organometal halide perovskites

    NASA Astrophysics Data System (ADS)

    Nagaoka, Hirokazu

    Solution-processable semiconductors offer a potential route to deploy solar panels on a wide scale, based on the possibility of reduced manufacturing costs by using earth-abundant materials and inexpensive production technologies, such as inkjet or roll-to-roll printing. Understanding the fundamental physics underlying device operation is important to realize this goal. This dissertation describes studies of two kinds of solar cells: hybrid polymer/PbS quantum dot solar cells and organometal halide perovskite solar cells. Chapter two discusses details of the experimental techniques. Chapter three and four explore the mechanisms of charge transfer and energy transfer spectroscopically, and find that both processes contribute to the device photocurrent. Chapter four investigates the important question of how the energy level alignment of quantum dot acceptors affects the operation of hybrid polymer/quantum dot solar cells, by making use of the size-tunable energy levels of PbS quantum dots. We observe that long-lived charge transfer yield is diminished at larger dot sizes as the energy level offset at the polymer/quantum dot interface is changed through decreasing quantum confinement using a combination of spectroscopy and device studies. Chapter five discusses the effects of TiO2 surface chemistry on the performance of organometal halide perovskite solar cells. Specifically, chapter five studies the effect of replacing the conventional TiO2 electrode with Zr-doped TiO2 (Zr-TiO2). We aim to explore the correlation between charge carrier dynamics and device studies by incorporating zirconium into TiO2. We find that, compared to Zr-free controls, solar cells employing Zr-TiO2 give rise to an increase in overall power conversion efficiency, and a decrease in hysteresis. We also observe longer carrier lifetimes and higher charge carrier densities in devices on Zr-TiO2 electrodes at microsecond times in transient photovoltage experiments, as well as at longer persistent

  2. An acoustic charge transport imager for high definition television applications

    NASA Technical Reports Server (NTRS)

    Hunt, William D.; Brennan, Kevin F.; Summers, Chris J.

    1992-01-01

    In this report we present the progress during the second six month period of the project. This includes both experimental and theoretical work on the acoustic charge transport (ACT) portion of the chip, the theoretical program modelling of both the avalanche photodiode (APD) and the charge transfer and overflow transistor and the materials growth and fabrication part of the program.

  3. DNA Charge Transport for Sensing and Signaling

    PubMed Central

    Sontz, Pamela A.; Muren, Natalie B.; Barton, Jacqueline K.

    2012-01-01

    Conspectus The DNA duplex is an exquisite macromolecular array that stores genetic information to encode proteins and regulate pathways, but its unique structure imparts chemical function that allows it also to mediate charge transport (CT). We have utilized diverse platforms to probe DNA CT, using spectroscopic, electrochemical, and even genetic methods. These studies have established powerful features of DNA CT chemistry. DNA CT can occur over long molecular distances as long as the bases are well stacked; perturbations in base stacking as arise with single base mismatches, DNA lesions, and the binding of some proteins that kink the DNA, all serve to inhibit DNA CT. Significantly, single molecule studies of DNA CT show that ground state CT can occur over 34 nm as long as the duplex is well stacked; one single base mismatch inhibits CT. The DNA duplex is an effective sensor for the integrity of the base pair stack. Moreover the efficiency of DNA CT is what one would expect for a stack of graphite sheets, equivalent to the stack of DNA base pairs, and independent of the sugar-phosphate backbone. Since DNA CT offers a means to carry out redox chemistry from a distance, we have considered how this chemistry might be used for long range signaling in a biological context. We have taken advantage of our chemical probes and platforms to characterize DNA CT also in the context of the cell. CT can occur over long distances, perhaps funneling damage to particular sites and insulating others from oxidative stress. Significantly, transcription factors that activate the genome to respond to oxidative stress can also be activated from a distance through DNA CT. Numerous proteins work to maintain the integrity of the genome and increasingly they have been found to contain [4Fe-4S] clusters that do not appear to carry out either structural or enzymatic roles. Using electrochemical methods, we find that DNA binding shifts the redox potentials of the clusters, activating them

  4. Hot Carrier Transport at the Graphene-Metal Interface Induced by Strong Lateral Photo-Dember Effect

    NASA Astrophysics Data System (ADS)

    Liu, Chang-Hua; Chang, You-Chia; Dissanayake, Nanditha; Zhang, Yaozhong; Zhong, Zhaohui

    2013-03-01

    Ultrafast photo-excitation in a semiconductor can lead to transient spatial charge gradient if electrons and holes have different drift velocities. The charge gradient builds up the transient electric field and causes the subsequent terahertz pulse emission. This phenomenon, known as the photo-Dember effect, was typically considered insignificant in graphene due to its similar electron and hole mobilities. Here, we observe hot carrier transport at the graphene-metal interface driven by the photo-Dember electric field under femtosecond pulse laser excitation. The polarity of hot carrier transport is determined by the asymmetry of electron and hole mobilities of the graphene device and cannot be flipped sign by tuning graphene doping level. This indicates the formation of strong photo-Dember field, dominating over the graphene/metal built-in electric field or thermal electric field. We further analyze the spatial distribution and temporal evolution of the transient electric field near the contact edge by using the drift-diffusion model. The modeling results suggest that strong photo-Dember effect is caused by the low electronic specific heat of graphene and a huge charge gradient near the graphene-metal interface under pulse laser excitation. This work was supported from the Donors of the American Chemical Society Petroleum Research Fund and the U-M/SJTU Collaborative Research Program in Renewable Energy Science and Technology.

  5. The role of charge-transfer integral in determining and engineering the carrier mobilities of 9,10-di(2-naphthyl)anthracene compounds

    NASA Astrophysics Data System (ADS)

    Tse, S. C.; So, S. K.; Yeung, M. Y.; Lo, C. F.; Wen, S. W.; Chen, C. H.

    2006-05-01

    The charge transporting properties of t-butylated 9,10-di(2-naphthyl)anthracene (ADN) compounds have been investigated experimentally and computationally in relation to their molecular structures. The ADN compounds are found to be ambipolar with both electron and hole mobilities in the range of 1-4 × 10 -7 cm 2 V -1 s -1 (electric field 0.5-0.8 MV/cm). As the degree of t-butylation increases, the carrier mobility decreases progressively. The mobility reduction was examined by Marcus theory of reorganization energies. All ADN compounds possess similar reorganization energies of ˜0.3 eV. The reduction of carrier mobilities with increasing t-butylation can be attributed to a decrease in the charge-transfer integral or the wavefunction overlap.

  6. Temperature dependent investigation of carrier transport, injection, and densities in 808 nm AlGaAs multi-quantum-well active layers for VCSELs

    NASA Astrophysics Data System (ADS)

    Engelhardt, Andreas P.; Kolb, Johanna S.; Römer, Friedhard; Weichmann, Ulrich; Moench, Holger; Witzigmann, Bernd

    2014-05-01

    The electro-optical efficiency of semiconductor vertical-cavity surface-emitting lasers (VCSELs) strongly depends on the efficient carrier injection into the quantum wells (QWs) in the laser active region. However, carrier injection degrades with increasing temperature which limits the VCSEL performance particularly in high power applications where self heating imposes high temperatures in operation. By simulation we investigate the transport of charge carriers in 808 nm AlGaAs multi-quantum-well active layers with special attention to the temperature dependence of carrier injection into the QWs. Experimental reference data was extracted from oxide-confined, top-emitting VCSELs. The transport simulations follow a drift-diffusion-model complemented by a customized, energy-resolved, semi-classical carrier capture theory. QW gain was calculated in the screened Hartree-Fock approximation with band structures from 8x8 k.p-theory. Using the gain data and by setting losses and the optical confinement factor according to experimental reference results, the appropriate threshold condition and threshold carrier densities in the QWs for a VCSEL are established in simulation for all transport considerations. With the combination of gain and transport model, we can explain experimental reference data for the injection efficiency and threshold current density. Our simulations show that the decreasing injection efficiency with temperature is not solely due to increased thermionic escape of carriers from the QWs. Carrier injection is also hampered by state filling in the QWs initiated from higher threshold carrier densities with temperature. Consequently, VCSEL properties not directly related to the active layer design like optical out-coupling or internal losses link the temperature dependent carrier injection to VCSEL mirror design.

  7. Carrier Type and Transport Characteristics of a-B4C

    NASA Astrophysics Data System (ADS)

    Sky Driver, Marcus; Janjua, Saad; Karki, Sudarshan; Heum Yeoun, Dae; Caruso, Anthony

    2009-03-01

    Boron carbide has many technological applications, including radiation hard semiconducting applications; the most popular of which is voltaic transduction. Structural defects are known to exist, whose implications in defining the majority carrier type is important, yet unclear. Gaining greater insight into the local physical structure and transport character is crucial toward optimizing the voltaic behavior. Subsequently, gaining information about the majority carrier and carrier concentration from Hall effect and band structure from photoemission spectroscopy gives insight into the electronic structure and transport of boron-rich carbides. Boron carbides are predominately p-type due to their electron deficiency, but it has been suggested that the electron as a majority carrier may also exist. Preliminary studies including Hall effect, photoemission and extended X-ray absorption fine structure will be discussed within the context of amorphous boron carbides with respect to the carrier properties and physical structure for various growth conditions, within the context of local structural defects.

  8. Hyperfine-induced spin relaxation of a diffusively moving carrier in low dimensions: Implications for spin transport in organic semiconductors

    NASA Astrophysics Data System (ADS)

    Mkhitaryan, V. V.; Dobrovitski, V. V.

    2015-08-01

    The hyperfine coupling between the spin of a charge carrier and the nuclear spin bath is a predominant channel for the carrier spin relaxation in many organic semiconductors. We theoretically investigate the hyperfine-induced spin relaxation of a carrier performing a random walk on a d -dimensional regular lattice, in a transport regime typical for organic semiconductors. We show that in d =1 and 2, the time dependence of the space-integrated spin polarization P (t ) is dominated by a superexponential decay, crossing over to a stretched-exponential tail at long times. The faster decay is attributed to multiple self-intersections (returns) of the random-walk trajectories, which occur more often in lower dimensions. We also show, analytically and numerically, that the returns lead to sensitivity of P (t ) to external electric and magnetic fields, and this sensitivity strongly depends on dimensionality of the system (d =1 versus d =3 ). Furthermore, we investigate in detail the coordinate dependence of the time-integrated spin polarization σ (r ) , which can be probed in the spin-transport experiments with spin-polarized electrodes. We demonstrate that, while σ (r ) is essentially exponential, the effect of multiple self-intersections can be identified in transport measurements from the strong dependence of the spin-decay length on the external magnetic and electric fields.

  9. Hyperfine-induced spin relaxation of a diffusively moving carrier in low dimensions: Implications for spin transport in organic semiconductors

    SciTech Connect

    Mkhitaryan, V. V.; Dobrovitski, V. V.

    2015-08-24

    The hyperfine coupling between the spin of a charge carrier and the nuclear spin bath is a predominant channel for the carrier spin relaxation in many organic semiconductors. We theoretically investigate the hyperfine-induced spin relaxation of a carrier performing a random walk on a d-dimensional regular lattice, in a transport regime typical for organic semiconductors. We show that in d=1 and 2, the time dependence of the space-integrated spin polarization P(t) is dominated by a superexponential decay, crossing over to a stretched-exponential tail at long times. The faster decay is attributed to multiple self-intersections (returns) of the random-walk trajectories, which occur more often in lower dimensions. We also show, analytically and numerically, that the returns lead to sensitivity of P(t) to external electric and magnetic fields, and this sensitivity strongly depends on dimensionality of the system (d=1 versus d=3). We investigate in detail the coordinate dependence of the time-integrated spin polarization σ(r), which can be probed in the spin-transport experiments with spin-polarized electrodes. We also demonstrate that, while σ(r) is essentially exponential, the effect of multiple self-intersections can be identified in transport measurements from the strong dependence of the spin-decay length on the external magnetic and electric fields.

  10. Hyperfine-induced spin relaxation of a diffusively moving carrier in low dimensions: Implications for spin transport in organic semiconductors

    DOE PAGESBeta

    Mkhitaryan, V. V.; Dobrovitski, V. V.

    2015-08-24

    The hyperfine coupling between the spin of a charge carrier and the nuclear spin bath is a predominant channel for the carrier spin relaxation in many organic semiconductors. We theoretically investigate the hyperfine-induced spin relaxation of a carrier performing a random walk on a d-dimensional regular lattice, in a transport regime typical for organic semiconductors. We show that in d=1 and 2, the time dependence of the space-integrated spin polarization P(t) is dominated by a superexponential decay, crossing over to a stretched-exponential tail at long times. The faster decay is attributed to multiple self-intersections (returns) of the random-walk trajectories, whichmore » occur more often in lower dimensions. We also show, analytically and numerically, that the returns lead to sensitivity of P(t) to external electric and magnetic fields, and this sensitivity strongly depends on dimensionality of the system (d=1 versus d=3). We investigate in detail the coordinate dependence of the time-integrated spin polarization σ(r), which can be probed in the spin-transport experiments with spin-polarized electrodes. We also demonstrate that, while σ(r) is essentially exponential, the effect of multiple self-intersections can be identified in transport measurements from the strong dependence of the spin-decay length on the external magnetic and electric fields.« less

  11. Interplay between hopping and band transport in high-mobility disordered semiconductors at large carrier concentrations: The case of the amorphous oxide InGaZnO

    NASA Astrophysics Data System (ADS)

    Fishchuk, I. I.; Kadashchuk, A.; Bhoolokam, A.; de Jamblinne de Meux, A.; Pourtois, G.; Gavrilyuk, M. M.; Köhler, A.; Bässler, H.; Heremans, P.; Genoe, J.

    2016-05-01

    We suggest an analytic theory based on the effective medium approximation (EMA) which is able to describe charge-carrier transport in a disordered semiconductor with a significant degree of degeneration realized at high carrier concentrations, especially relevant in some thin-film transistors (TFTs), when the Fermi level is very close to the conduction-band edge. The EMA model is based on special averaging of the Fermi-Dirac carrier distributions using a suitably normalized cumulative density-of-state distribution that includes both delocalized states and the localized states. The principal advantage of the present model is its ability to describe universally effective drift and Hall mobility in heterogeneous materials as a function of disorder, temperature, and carrier concentration within the same theoretical formalism. It also bridges a gap between hopping and bandlike transport in an energetically heterogeneous system. The key assumption of the model is that the charge carriers move through delocalized states and that, in addition to the tail of the localized states, the disorder can give rise to spatial energy variation of the transport-band edge being described by a Gaussian distribution. It can explain a puzzling observation of activated and carrier-concentration-dependent Hall mobility in a disordered system featuring an ideal Hall effect. The present model has been successfully applied to describe experimental results on the charge transport measured in an amorphous oxide semiconductor, In-Ga-Zn-O (a-IGZO). In particular, the model reproduces well both the conventional Meyer-Neldel (MN) compensation behavior for the charge-carrier mobility and inverse-MN effect for the conductivity observed in the same a-IGZO TFT. The model was further supported by ab initio calculations revealing that the amorphization of IGZO gives rise to variation of the conduction-band edge rather than to the creation of localized states. The obtained changes agree with the one we

  12. Charge-transport anisotropy in black phosphorus: critical dependence on the number of layers.

    PubMed

    Banerjee, Swastika; Pati, Swapan K

    2016-06-28

    Phosphorene is a promising candidate for modern electronics because of the anisotropy associated with high electron-hole mobility. Additionally, superior mechanical flexibility allows the strain-engineering of various properties including the transport of charge carriers in phosphorene. In this work, we have shown the criticality of the number of layers to dictate the transport properties of black phosphorus. Trilayer black phosphorus (TBP) has been proposed as an excellent anisotropic material, based on the transport parameters using Boltzmann transport formalisms coupled with density functional theory. The mobilities of both the electron and the hole are found to be higher along the zigzag direction (∼10(4) cm(2) V(-1) s(-1) at 300 K) compared to the armchair direction (∼10(2) cm(2) V(-1) s(-1)), resulting in the intrinsic directional anisotropy. Application of strain leads to additional electron-hole anisotropy with 10(3) fold higher mobility for the electron compared to the hole. Critical strain for maximum anisotropic response has also been determined. Whether the transport anisotropy is due to the spatial or charge-carrier has been determined through analyses of the scattering process of electrons and holes, and their recombination as well as relaxation dynamics. In this context, we have derived two descriptors (S and F(k)), which are general enough for any 2D or quasi-2D systems. Information on the scattering involving purely the carrier states also helps to understand the layer-dependent photoluminescence and electron (hole) relaxation in black phosphorus. Finally, we justify trilayer black phosphorus (TBP) as the material of interest with excellent transport properties. PMID:27257640

  13. One-carrier thermally stimulated currents and space-charge-limited currents in naphthalene crystals

    NASA Astrophysics Data System (ADS)

    Campos, M.; Mergulhão, S.

    1980-03-01

    Electron trapping in naphthalene is studied by analysis of the space-charge-limited and thermally stimulated currents as a function of applied voltage and temperature. The two methods are used on naphthalene single crystals, with continuous electron injection from a silver contact. The use of the two techniques allows a quantitative determination of the characteristics of deep and shallow traps. Three monomolecular current peaks were observed. Activation energies of 0.5, 0.79, and 1.1 eV, and cross sections of 8.8 × 10-20, 6.9 × 10-16, and 1.0 × 10-18 cm2, were calculated for the corresponding discrete trapping levels of the charge carriers. The behavior observed for space-charge-limited current was a current-voltage characteristic of a single set of traps, with an activation energy of 0.71 eV, and a cross section of 7.1 × 10-16 cm2. The results showed that the use of only space-charge-limited current is not good enough for a characterization of the traps of the material.

  14. Charge carrier mobility and concentration as a function of composition in AgPO3-AgI glasses

    NASA Astrophysics Data System (ADS)

    Rodrigues, Ana Candida Martins; Nascimento, Marcio Luis Ferreira; Bragatto, Caio Barca; Souquet, Jean-Louis

    2011-12-01

    Conductivity data of the xAgI(1 - x)AgPO3 system (0 ≤ x ≤ 0.5) were collected in the liquid and glassy states. The difference in the dependence of ionic conductivity on temperature below and above their glass transition temperatures (Tg) is interpreted by a discontinuity in the charge carrier's mobility mechanisms. Charge carrier displacement occurs through an activated mechanism below Tg and through a Vogel-Fulcher-Tammann-Hesse mechanism above this temperature. Fitting conductivity data with the proposed model allows one to determine separately the enthalpies of charge carrier formation and migration. For the five investigated compositions, the enthalpy of charge carrier formation is found to decrease, with x, from 0.86 to 0.2 eV, while the migration enthalpy remains constant at ≈0.14 eV. Based on these values, the charge carrier mobility and concentration in the glassy state can then be calculated. Mobility values at room temperature (≈10-4 cm2 V-1 s-1) do not vary significantly with the AgI content and are in good agreement with those previously measured by the Hall-effect technique. The observed increase in ionic conductivity with x would thus only be due to an increase in the effective charge carrier concentration. Considering AgI as a weak electrolyte, the change in the effective charge carrier concentration is justified and is correlated to the partial free energy of silver iodide forming a regular solution with AgPO3.

  15. Charge carrier concentration dependence of encounter-limited bimolecular recombination in phase-separated organic semiconductor blends

    NASA Astrophysics Data System (ADS)

    Heiber, Michael C.; Nguyen, Thuc-Quyen; Deibel, Carsten

    2016-05-01

    Understanding how the complex intermolecular configurations and nanostructure present in organic semiconductor donor-acceptor blends impacts charge carrier motion, interactions, and recombination behavior is a critical fundamental issue with a particularly major impact on organic photovoltaic applications. In this study, kinetic Monte Carlo (KMC) simulations are used to numerically quantify the complex bimolecular charge carrier recombination behavior in idealized phase-separated blends. Recent KMC simulations have identified how the encounter-limited bimolecular recombination rate in these blends deviates from the often used Langevin model and have been used to construct the new power mean mobility model. Here, we make a challenging but crucial expansion to this work by determining the charge carrier concentration dependence of the encounter-limited bimolecular recombination coefficient. In doing so, we find that an accurate treatment of the long-range electrostatic interactions between charge carriers is critical, and we further argue that many previous KMC simulation studies have used a Coulomb cutoff radius that is too small, which causes a significant overestimation of the recombination rate. To shed more light on this issue, we determine the minimum cutoff radius required to reach an accuracy of less than ±10 % as a function of the domain size and the charge carrier concentration and then use this knowledge to accurately quantify the charge carrier concentration dependence of the recombination rate. Using these rigorous methods, we finally show that the parameters of the power mean mobility model are determined by a newly identified dimensionless ratio of the domain size to the average charge carrier separation distance.

  16. Surface group modification and carrier transport properties of layered transition metal carbides (Ti2CTx, T: -OH, -F and -O)

    NASA Astrophysics Data System (ADS)

    Lai, Shen; Jeon, Jaeho; Jang, Sung Kyu; Xu, Jiao; Choi, Young Jin; Park, Jin-Hong; Hwang, Euyheon; Lee, Sungjoo

    2015-11-01

    In spite of recent significant research into various two-dimensional (2D) materials after the emergence of graphene, the development of a new 2D material that provides both high mobility and an appropriate energy band gap (which are crucial for various device applications) remains elusive. In this report, we demonstrate that the carrier transport behaviour of 2D Ti2CTx, which belongs to the family of 2D transition metal carbides and nitrides, can be tuned by modifying the surface group Tx (-OH, -F, and -O). Our results show that 2D Ti2C(OH)xFy and Ti2COx films can be obtained via simple chemical treatment, thermal annealing, and mechanical exfoliation processes. For the first time, we study the carrier transport properties of 2D Ti2CTx field effect transistors (FETs), obtaining the high field effect carrier mobilities of 104 cm2 V-1 s-1 at room temperature. The temperature dependent resistivity of the Ti2COx film exhibits semiconductor like Arrhenius behaviour at zero gate voltage, from which we estimate the energy gap of 80 meV. One interesting feature of the FETs based on transition metal carbides is that the field effect mobility at room temperature is less sensitive to the measured transport gaps, which may arise from the dominant charge transport of activated carriers over the narrow energy gaps of the transition metal carbides. Our results open up the possibility that new 2D materials with high mobilities and appropriate band gaps can be achieved, and broaden the range of electronic device applications of Ti2CTx films.In spite of recent significant research into various two-dimensional (2D) materials after the emergence of graphene, the development of a new 2D material that provides both high mobility and an appropriate energy band gap (which are crucial for various device applications) remains elusive. In this report, we demonstrate that the carrier transport behaviour of 2D Ti2CTx, which belongs to the family of 2D transition metal carbides and nitrides

  17. An autonomous photosynthetic device in which all charge carriers derive from surface plasmons.

    PubMed

    Mubeen, Syed; Lee, Joun; Singh, Nirala; Krämer, Stephan; Stucky, Galen D; Moskovits, Martin

    2013-04-01

    Solar conversion to electricity or to fuels based on electron-hole pair production in semiconductors is a highly evolved scientific and commercial enterprise. Recently, it has been posited that charge carriers either directly transferred from the plasmonic structure to a neighbouring semiconductor (such as TiO₂) or to a photocatalyst, or induced by energy transfer in a neighbouring medium, could augment photoconversion processes, potentially leading to an entire new paradigm in harvesting photons for practical use. The strong dependence of the wavelength at which the local surface plasmon can be excited on the nanostructure makes it possible, in principle, to design plasmonic devices that can harvest photons over the entire solar spectrum and beyond. So far, however, most such systems show rather small photocatalytic activity in the visible as compared with the ultraviolet. Here, we report an efficient, autonomous solar water-splitting device based on a gold nanorod array in which essentially all charge carriers involved in the oxidation and reduction steps arise from the hot electrons resulting from the excitation of surface plasmons in the nanostructured gold. Each nanorod functions without external wiring, producing 5 × 10(13) H₂ molecules per cm(2) per s under 1 sun illumination (AM 1.5 and 100 mW cm(-2)), with unprecedented long-term operational stability. PMID:23435280

  18. Real-time charge carrier motion in P3HT studied with Kelvin Probe Microscopy

    NASA Astrophysics Data System (ADS)

    Castaneda, Chloe; Zaidi, Alyina; Moscatello, Jason; Aidala, Katherine

    We have developed a technique that uses scanning probe microscopy (SPM) to study the real-time injection and extraction of charge carriers in organic semiconductor devices. We investigate P3HT (full name) in an inverted field effect transistor geometry with gold electrodes. By positioning the SPM tip at an individual location and using Kelvin probe microscopy to record the potential over time, we can record how the charge carriers respond to changing the backgate voltage while the source and drain electrodes are grounded. We see relatively fast screening for negative backgate voltages because holes are quickly injected into the P3HT film. The screening is slower for positive gate voltages, because some of these holes are trapped and therefore less mobile. We compare P3HT transistors with different fabrication procedures that are expected to change the trap distribution: no silanization of the oxide and no annealing, silanization and no annealing, and both silanization and annealing. By incrementally stepping the gate voltage, we probe different trap depths. The recorded change in potential over time is best fit by a double exponential, suggesting two physical mechanisms involved in screening. This work is supported by NSF Grant DMR-0955348, and the Center for Heirarchical Manufacturing at the University of Massachusetts, Amherst (NSF CMMI-1025020).

  19. Doping and charge-carrier density effects in the cuprate superconductors

    SciTech Connect

    Tanner, D.B.; Yoon, Y.D.; Zibold, A.

    1996-12-31

    The undoped phases of the copper-oxide materials are antiferromagnetic insulators, with a gap of 1.5--2 eV. Infrared spectroscopy of these compounds reveals weak absorption, possibly of magnetic origin, in this gap. When the materials are doped, oscillator strength is removed from the charge transfer band. This oscillator strength moves to low frequency, to become midinfrared and free carrier absorption. A systematic study of the electron-doped Nd{sub 2{minus}x}Ce{sub x}CuO{sub 4{minus}y} system reveals that the growth of low-frequency oscillator strength with doping concentration x is twice as rapid as in the case of hole-doped materials, such as La{sub 2{minus}x}Sr{sub x}CuO{sub 4}. This behavior is in accord with electronic structure models based on the 3-band Hubbard model and inconsistent with one-band behavior. However, an anomaly occurs for samples which are doped to the critical concentration for superconductivity; these have a greater than expected free-carrier concentration and weaker charge-transfer bands. 48 refs., 6 figs., 1 tab.

  20. Electrical Conductivity of Rocks and Dominant Charge Carriers. Part 1; Thermally Activated Positive Holes

    NASA Technical Reports Server (NTRS)

    Freund, Friedemann T.; Freund, Minoru M.

    2012-01-01

    The prevailing view in the geophysics community is that the electrical conductivity structure of the Earth's continental crust over the 5-35 km depth range can best be understood by assuming the presence of intergranular fluids and/or of intragranular carbon films. Based on single crystal studies of melt-grown MgO, magma-derived sanidine and anorthosite feldspars and upper mantle olivine, we present evidence for the presence of electronic charge carriers, which derive from peroxy defects that are introduced during cooling, under non-equilibrium conditions, through a redox conversion of pairs of solute hydroxyl arising from dissolution of H2O.The peroxy defects become thermally activated in a 2-step process, leading to the release of defect electrons in the oxygen anion sublattice. Known as positive holes and symbolized by h(dot), these electronic charge carriers are highly mobile. Chemically equivalent to O(-) in a matrix of O(2-) they are highly oxidizing. Being metastable they can exist in the matrix of minerals, which crystallized in highly reduced environments. The h(dot) are highly mobile. They appear to control the electrical conductivity of crustal rocks in much of the 5-35 km depth range.

  1. Simulation of charge transport in pixelated CdTe

    NASA Astrophysics Data System (ADS)

    Kolstein, M.; Ariño, G.; Chmeissani, M.; De Lorenzo, G.

    2014-12-01

    The Voxel Imaging PET (VIP) Pathfinder project intends to show the advantages of using pixelated semiconductor technology for nuclear medicine applications to achieve an improved image reconstruction without efficiency loss. It proposes designs for Positron Emission Tomography (PET), Positron Emission Mammography (PEM) and Compton gamma camera detectors with a large number of signal channels (of the order of 106). The design is based on the use of a pixelated CdTe Schottky detector to have optimal energy and spatial resolution. An individual read-out channel is dedicated for each detector voxel of size 1 × 1 × 2 mm3 using an application-specific integrated circuit (ASIC) which the VIP project has designed, developed and is currently evaluating experimentally. The behaviour of the signal charge carriers in CdTe should be well understood because it has an impact on the performance of the readout channels. For this purpose the Finite Element Method (FEM) Multiphysics COMSOL software package has been used to simulate the behaviour of signal charge carriers in CdTe and extract values for the expected charge sharing depending on the impact point and bias voltage. The results on charge sharing obtained with COMSOL are combined with GAMOS, a Geant based particle tracking Monte Carlo software package, to get a full evaluation of the amount of charge sharing in pixelated CdTe for different gamma impact points.

  2. Charge transport in ion-gated mono-, bi-, and trilayer MoS2 field effect transistors

    PubMed Central

    Chu, Leiqiang; Schmidt, Hennrik; Pu, Jiang; Wang, Shunfeng; Özyilmaz, Barbaros; Takenobu, Taishi; Eda, Goki

    2014-01-01

    Charge transport in MoS2 in the low carrier density regime is dominated by trap states and band edge disorder. The intrinsic transport properties of MoS2 emerge in the high density regime where conduction occurs via extended states. Here, we investigate the transport properties of mechanically exfoliated mono-, bi-, and trilayer MoS2 sheets over a wide range of carrier densities realized by a combination of ion gel top gate and SiO2 back gate, which allows us to achieve high charge carrier (>1013 cm−2) densities. We discuss the gating properties of the devices as a function of layer thickness and demonstrate resistivities as low as 1 kΩ for monolayer and 420 Ω for bilayer devices at 10 K. We show that from the capacitive coupling of the two gates, quantum capacitance can be roughly estimated to be on the order of 1 μF/cm2 for all devices studied. The temperature dependence of the carrier mobility in the high density regime indicates that short-range scatterers limit charge transport at low temperatures. PMID:25465059

  3. 31 CFR 337.2 - Transportation charges and risks.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 31 Money and Finance: Treasury 2 2014-07-01 2014-07-01 false Transportation charges and risks. 337.2 Section 337.2 Money and Finance: Treasury Regulations Relating to Money and Finance (Continued... GOVERNING FEDERAL HOUSING ADMINISTRATION DEBENTURES Certificated Debentures § 337.2 Transportation...

  4. Charge Transport at Ti-Doped Hematite (001)/Aqueous Interfaces

    SciTech Connect

    Chatman, Shawn ME; Pearce, Carolyn I.; Rosso, Kevin M.

    2015-03-10

    Solid-state transport and electrochemical properties of Ti-doped hematite (001) epitaxial thin films (6.0, 8.3, and 16.6 at% Ti) were probed to achieve a better understanding of doped hematite for photoelectrochemical (PEC) applications. Room temperature resistivity measurements predict a resistivity minimum near 10 at% Ti doping, which can be rationalized as maximizing charge compensating Fe2+ concentration and Fe3+ electron accepting percolation pathways simultaneously. Temperature dependent resistivity data are consistent with small polaron hopping, revealing an activation energy that is Ti concentration dependent and commensurate with previously reported values (≈ 0.11 eV). In contact with inert electrolyte, linear Mott-Schottky data at various pH values indicate that there is predominantly a single donor for Ti-doped hematite at 6.0 at% Ti and 16.6 at% Ti concentrations. Two slope Mott-Schottky data at pH extremes indicate the presence of a second donor or surface state in the 8.3 at% Ti-doped film, with an energy level ≈ 0.7 eV below the Fermi level. Mott-Schottky plots indicate pH and Ti concentration dependent flatband potentials of -0.4 to -1.1 V vs. Ag/AgCl, commensurate with previously reported data. Flatband potentials exhibited super-Nernstian pH dependence ranging from -69.1 to -101.0 mV/pH. Carrier concentration data indicate that the Fermi energy of the Ti-doped system is Ti concentration dependent, with a minimum of 0.15 eV near 10 at% Ti. These energy level data allow us to construct an energy band diagram for Ti-doped hematite electrode/electrolyte interfaces, and to determine a Ti-doping concentration t

  5. Charge transport optimization in CZT ring-drift detectors

    NASA Astrophysics Data System (ADS)

    Boothman, V.; Alruhaili, A.; Perumal, V.; Sellin, P.; Lohstroh, A.; Sawhney, K.; Kachanov, S.

    2015-12-01

    Ring-drift design has been applied to large (7.5~\\text{mm}× 7.5~\\text{mm}× 2.3 mm) cadmium zinc telluride (CZT) devices. This low-noise, single-carrier-sensing configuration is the gold standard for spectroscopic silicon x-ray detectors. By combining the advantages of ring-drift with the high quantum efficiency and room-temperature operating capabilities of CZT, a simple and compact device for high-resolution spectroscopy of x-rays in the range 50-500 keV can be created. Quality of CZT crystals has improved greatly in recent years and electron-only sensing overcomes the problem of inherently poor hole transport in II-VI semiconductors. The spatial response of our 3-ring CZT device was studied by microbeam scanning while the voltages applied to all electrodes were systematically varied. Maximum active radius extended to 2.3 mm, beyond the second ring. Resolution was limited by electronic noise. Our results show that the lateral field and its ratio to the bulk field exert a crucial influence on active area, peak position and sensitivity. CZT and the device geometry were modelled in 3D with Sentaurus TCAD. Line scans were simulated and trends in performance with bias conditions matched experimental data, validating the model. We aimed to optimize the resolution, sensitivity and active radius of the device. Fields and charge drift were visualized and the active volume was mapped in 3D to improve understanding of the factors governing performance including number of rings, their widths, positions and bias.

  6. Importance of Depletion Width on Charge Transport and Interfacial Recombination in Extremely Thin Absorber Solar Cells

    NASA Astrophysics Data System (ADS)

    Edley, Michael; Jones, Treavor; Baxter, Jason

    The dynamics of charge carrier transport and recombination and their dependence on physical and electrochemical length scales in extremely thin absorber (ETA) solar cells is vital to cell design. We used J-V characterization, transient photocurrent / photovoltage, and electrochemical impedance spectroscopy to study electron transport and interfacial recombination in ETA cell. ETA cells were composed of ZnO nanowires coated with an ultrathin (5 nm) CdS buffer layer and CdSe absorbers with thicknesses of 10 - 40 nm, with polysulfide electrolyte. In thinner absorbers near short circuit, the depletion region can extend radially into the nanowire, inhibiting interfacial recombination rate. However, depleting the periphery of the nanowire reduces the cross sectional area for charge transport, resulting in longer characteristic collection times. Thicker absorbers suffered more significant bias-dependent collection, and we conclude that slight radial penetration of the depletion region into the nanowires enhances charge collection. This work highlights the importance of considering the impact of depletion width on charge transport and interfacial recombination in the design of liquid junction, semiconductor-sensitized solar cells.

  7. Charge transport studies of polymeric photovoltaic thin films with an electron blocking and trapping layer

    NASA Astrophysics Data System (ADS)

    Lee, Harrison K. H.; Chan, Kevin K. H.; So, S. K.

    2012-06-01

    The transport properties of two photovoltaic polymers, poly(3-hexylthiophene) (P3HT) and poly(2,7-carbazole) derivative (PCDTBT), and their polymer:fullerene bulk heterojunction (BHJ) are studied by space-charge-limited current (SCLC), dark-injection space-charge-limited current (DI-SCLC), and admittance spectroscopy(AS). For a nominally hole-only device, electrons leakage occurs. This results in a current larger than the theoretical SCLC and ill-defined DI-SCLC and AS signals. In order to prevent electron leakage, a hole-transporting but electron blocking/trapping thin layer is added between active layer and Au. The layer composed of copper phthalocyanine (CuPc) doped into an amine-based small molecule. Using this interlayer, well-defined carrier transit time can be obtained for mobility extraction. With a suitable interlayer to suppress undesirable carrier injection and transport, these techniques should find broad applications in the transport characterization of narrow gap photovoltaic polymers and BHJ blends.

  8. Proton intercalated two-dimensional WO3 nano-flakes with enhanced charge-carrier mobility at room temperature

    NASA Astrophysics Data System (ADS)

    Zhuiykov, Serge; Kats, Eugene; Carey, Benjamin; Balendhran, Sivacarendran

    2014-11-01

    Quasi two-dimensional (Q2D) semiconducting metal oxides with enhanced charge carrier mobility hold tremendous promise for nano-electronics, photonics, catalysis, nano-sensors and electrochromic applications. In addition to graphene and metal dichalcogenides MX2 (M = Mo, W; X = S, Se, Te), 2D sub-stoichiometric WO3-x is gaining importance as a promising semiconductor material for field-effect-transistor (FET) based devices. A combination of high permittivity, suppression of the Coulomb effects, and their stratified structure enhances the carrier mobility in such a material. Additionally, the sub-stoichiometry of this semiconductor oxide allows the reduction of the bandgap and increase of the free charge carriers at the same time. Here, we report for the first time H+ intercalated WO3 FETs, made of Q2D nano-flakes, with enhanced charge-carrier mobility exceeding 319 cm2 V-1 s-1 comparable with the charge-carrier mobility of Q2D dichalcogenides MoS2 and WSe2. Analyses indicate that the enhanced electrical properties of the sub-stoichiometric WO3-x depend on the oxygen vacancies in the intercalated nano-flakes. These findings confirmed that Q2D sub-stoichiometric WO3-x is a promising material for various functional FET devices.Quasi two-dimensional (Q2D) semiconducting metal oxides with enhanced charge carrier mobility hold tremendous promise for nano-electronics, photonics, catalysis, nano-sensors and electrochromic applications. In addition to graphene and metal dichalcogenides MX2 (M = Mo, W; X = S, Se, Te), 2D sub-stoichiometric WO3-x is gaining importance as a promising semiconductor material for field-effect-transistor (FET) based devices. A combination of high permittivity, suppression of the Coulomb effects, and their stratified structure enhances the carrier mobility in such a material. Additionally, the sub-stoichiometry of this semiconductor oxide allows the reduction of the bandgap and increase of the free charge carriers at the same time. Here, we report

  9. Thickness dependent charge transport in ferroelectric BaTiO3 heterojunctions

    NASA Astrophysics Data System (ADS)

    Singh, Pooja; Rout, P. K.; Singh, Manju; Rakshit, R. K.; Dogra, Anjana

    2015-09-01

    We have investigated the effect of ferroelectric barium titanate (BaTiO3) film thickness on the charge transport mechanism in pulsed laser deposited epitaxial metal-ferroelectric semiconductor junctions. The current (I)-voltage (V) measurements across the junctions comprising of 20-500 nm thick BaTiO3 and conducting bottom electrode (Nb: SrTiO3 substrate or La2/3Ca1/3MnO3 buffer layer) demonstrate the space charge limited conduction. Further analysis indicates a reduction in the ratio of free to trapped carriers with increasing thickness in spite of decreasing trap density. Such behaviour arises the deepening of the shallow trap levels (<0.65 eV) below conduction band with increasing thickness. Moreover, the observed hysteresis in I-V curves implies a bipolar resistive switching behaviour, which can be explained in terms of charge trapping and de-trapping process.

  10. 14 CFR 382.19 - May carriers refuse to provide transportation on the basis of disability?

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 14 Aeronautics and Space 4 2013-01-01 2013-01-01 false May carriers refuse to provide transportation on the basis of disability? 382.19 Section 382.19 Aeronautics and Space OFFICE OF THE SECRETARY, DEPARTMENT OF TRANSPORTATION (AVIATION PROCEEDINGS) SPECIAL REGULATIONS NONDISCRIMINATION ON THE BASIS OF DISABILITY IN AIR TRAVEL...

  11. Ion and water transport in charge-modified graphene nanopores

    NASA Astrophysics Data System (ADS)

    Qiu, Ying-Hua; Li, Kun; Chen, Wei-Yu; Si, Wei; Tan, Qi-Yan; Chen, Yun-Fei

    2015-10-01

    Porous graphene has a high mechanical strength and an atomic-layer thickness that makes it a promising material for material separation and biomolecule sensing. Electrostatic interactions between charges in aqueous solutions are a type of strong long-range interaction that may greatly influence fluid transport through nanopores. In this study, molecular dynamic simulations were conducted to investigate ion and water transport through 1.05-nm diameter monolayer graphene nanopores, with their edges charge-modified. Our results indicated that these nanopores are selective to counterions when they are charged. As the charge amount increases, the total ionic currents show an increase-decrease profile while the co-ion currents monotonically decrease. The co-ion rejection can reach 76.5% and 90.2% when the nanopores are negatively and positively charged, respectively. The Cl- ion current increases and reaches a plateau, and the Na+ current decreases as the charge amount increases in systems in which Na+ ions act as counterions. In addition, charge modification can enhance water transport through nanopores. This is mainly due to the ion selectivity of the nanopores. Notably, positive charges on the pore edges facilitate water transport much more strongly than negative charges. Project supported by the National Basic Research Program of China (Grant Nos. 2011CB707601 and 2011CB707605), the National Natural Science Foundation of China (Grant No. 50925519), the Fundamental Research Funds for the Central Universities, Funding of Jiangsu Provincial Innovation Program for Graduate Education, China (Grant No. CXZZ13_0087), and the Scientific Research Foundation of Graduate School of Southeast University (Grant No. YBJJ 1322).

  12. First-principles Study on the Charge Transport Mechanism of Lithium Sulfide (Li2 S) in Lithium-Sulfur Batteries.

    PubMed

    Kim, B S Do-Hoon; Lee, M S Byungju; Park, Kyu-Young; Kang, Kisuk

    2016-04-20

    The lithium-sulfur chemistry is regarded as a promising candidate for next-generation battery systems because of its high specific energy (1675 mA h g(-1) ). Although issues such as low cycle stability and power capability of the system remain to be addressed, extensive research has been performed experimentally to resolve these problems. Attaining a fundamental understanding of the reaction mechanism and its reaction product would further spur the development of lithium-sulfur batteries. Here, we investigated the charge transport mechanism of lithium sulfide (Li2 S), a discharge product of conventional lithium-sulfur batteries using first-principles calculations. Our calculations indicate that the major charge transport is governed by the lithium-ion vacancies among various possible charge carriers. Furthermore, the large bandgap and low concentration of electron polarons indicate that the electronic conduction negligibly contributes to the charge transport mechanism in Li2 S. PMID:26928985

  13. Elastic tunneling charge transport mechanisms in silicon quantum dots /SiO{sub 2} thin films and superlattices

    SciTech Connect

    Illera, S. Prades, J. D.; Cirera, A.

    2015-05-07

    The role of different charge transport mechanisms in Si/SiO{sub 2} structures has been studied. A theoretical model based on the Transfer Hamiltonian Formalism has been developed to explain experimental current trends in terms of three different elastic tunneling processes: (1) trap assisted tunneling; (2) transport through an intermediate quantum dot; and (3) direct tunneling between leads. In general, at low fields carrier transport is dominated by the quantum dots whereas, for moderate and high fields, transport through deep traps inherent to the SiO{sub 2} is the most relevant process. Besides, current trends in Si/SiO{sub 2} superlattice structure have been properly reproduced.

  14. Self-Trapping of Charge Carriers in Semiconducting Carbon Nanotubes: Structural Analysis.

    PubMed

    Adamska, Lyudmyla; Nazin, George V; Doorn, Stephen K; Tretiak, Sergei

    2015-10-01

    The spatial extent of charged electronic states in semiconducting carbon nanotubes with indices (6,5) and (7,6) was evaluated using density functional theory. It was observed that electrons and holes self-trap along the nanotube axis on length scales of about 4 and 8 nm, respectively, which localize cations and anions on comparable length scales. Self-trapping is accompanied by local structural distortions showing periodic bond-length alternation. The average lengthening (shortening) of the bonds for anions (cations) is expected to shift the G-mode frequency to lower (higher) values. The smaller-diameter nanotube has reduced structural relaxation due to higher carbon-carbon bond strain. The reorganization energy due to charge-induced deformations in both nanotubes is found to be in the 30-60 meV range. Our results represent the first theoretical simulation of self-trapping of charge carriers in semiconducting nanotubes, and agree with available experimental data. PMID:26722885

  15. Effect of Cooling Rate on Microstructure and Charge Transport in Semiconducting Polymer Thin Films

    NASA Astrophysics Data System (ADS)

    Kang, Evan; Kim, Eunseong; CenterSupersolid; Quantum Matter Research Team

    2011-03-01

    Thermal annealing of polymer thin films often enhances charge carrier mobility which can be attributed to self-healing of the film morphology. We have investigated the effect of cooling rate following the annealing treatment on the thin film microstructure and the charge transport properties using a high performance semiconducting polymer, poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT). The cooling rate plays a key role in determining the microstructure and performance of polymer thin films. Differential scanning calorimeter measurement shows that fast cooling suppresses the crystallization process. The microstructure of thin films is investigated by using 2D X-ray diffraction and atomic force microscopy. Slow cooling results in well-connected large domains with enhanced three dimensional ordering whereas fast cooling leads to misalignment of small domains with relatively rough surface. Transport characteristics at various temperatures show increase in the charge carrier mobility and decrease in the activation energy when the cooling rate is slowed. This change in the mobility and activation energy becomes saturated with cooling rate below 15 °C/min. E. S. H. K. and E. K. gratefully acknowledge financial support from the National Research Foundation of Korea through the Creative Research Initiatives (CSQR).

  16. Charge Transport Properties in Polymer Brushes

    NASA Astrophysics Data System (ADS)

    Moog, Mark; Tsui, Frank; Vonwald, Ian; You, Wei

    Electrical transport properties in poly(3-methyl)thiophene (P3MT) brushes have been studied. The P3MT brushes correspond to a new type of surface-tethered, vertically oriented conjugated molecular wires, sandwiched between two metallic electrodes to form the electrode-molecule-electrode (EME) devices. P3MT is a highly conjugated polymer, a ''workhorse'' material for organic electronics and photonics. The P3MT brushes were grown on ITO surfaces with controlled length (between 2 and 100 nm). The top electrodes were transfer-printed Au films with lateral dimensions between 200 nm and 50 μm. I-V and differential conductance measurements were performed using conductive AFM and 4-terminal techniques. Tunneling and field-emission measurements in EME devices with molecular lengths < 5 nm show HOMO mediated direct hole tunneling with energy barriers of 0.3 and 0.5 eV at the respective interfaces with ITO and Au. The transport properties in longer brushes are indicative of the two quasi-Ohmic interfaces with a characteristic offset in the conductance minimum of 0.12 V biased toward the ITO. Temperature dependent parameters have been examined at various molecular lengths. The drift mobility and the interplay between intra- and intermolecular transport have been investigated.

  17. Behavior of charge carriers and excitons in multilayer organic light-emitting diodes made from a polysilane polymer as monitored with electroluminescence

    NASA Astrophysics Data System (ADS)

    Suzuki, Hiroyuki; Hoshino, Satoshi

    1996-01-01

    Using electroluminescence (EL) as a monitor, we have investigated the behavior of charge carriers injected from electrodes and excitons generated by the recombination of charge carriers in multilayer organic light-emitting diodes (LEDs) using poly(methylphenylsilane) (PMPS) as a hole transporting material. Our multilayer LEDs have two or three functional organic layers including Coumarin 6 [3-(2'-benzothiazolyl)-7-diethylaminocoumarin, abbreviated as C6] and/or tris-(8-hydroxyquinoline) aluminum layers as well as a PMPS layer. When the LEDs were fabricated, two parameters of the C6 layer were changed, the layer thickness (30-120 nm) and the dye concentration (1-100 wt %). We employed a combined analysis of the dependence of the EL spectra on the thickness and dye concentration of the C6 layer, the dye-selective fluorescence spectra and the current-voltage-EL characteristics, to reveal the thickness of the electron-hole capture zone and the behavior of charge carriers and excitons during operation in these LEDs.

  18. Effect of surface charge of immortalized mouse cerebral endothelial cell monolayer on transport of charged solutes.

    PubMed

    Yuan, Wei; Li, Guanglei; Gil, Eun Seok; Lowe, Tao Lu; Fu, Bingmei M

    2010-04-01

    Charge carried by the surface glycocalyx layer (SGL) of the cerebral endothelium has been shown to significantly modulate the permeability of the blood-brain barrier (BBB) to charged solutes in vivo. The cultured monolayer of bEnd3, an immortalized mouse cerebral endothelial cell line, is becoming a popular in vitro BBB model due to its easy growth and maintenance of many BBB characteristics over repeated passages. To test whether the SGL of bEnd3 monolayer carries similar charge as that in the intact BBB and quantify this charge, which can be characterized by the SGL thickness (L(f)) and charge density (C(mf)), we measured the solute permeability of bEnd3 monolayer to neutral solutes and to solutes with similar size but opposite charges: negatively charged alpha-lactalbumin (-11) and positively charged ribonuclease (+3). Combining the measured permeability data with a transport model across the cell monolayer, we predicted the L(f) and the C(mf) of bEnd3 monolayer, which is approximately 160 nm and approximately 25 mEq/L, respectively. We also investigated whether orosomucoid, a plasma glycoprotein modulating the charge of the intact BBB, alters the charge of bEnd3 monolayer. We found that 1 mg/mL orosomucoid would increase SGL charge density of bEnd3 monolayer to approximately 2-fold of its control value. PMID:20087768

  19. Quantum states of charge carriers and longitudinal conductivity in double periodic n-type semiconductor lattice structures in electric field

    SciTech Connect

    Perov, A. A. Penyagin, I. V.

    2015-07-15

    Quantum states of charge carriers in double periodic semiconductor superlattices of n-type quantum dots with Rashba spin–orbit coupling in an electron gas have been calculated in the one-electron approximation in the presence of mutually perpendicular electric and magnetic fields. For these structures in weak constant electric field, the solution to the quasi-classical kinetic Boltzmann equation shows that the states of carriers in magnetic Landau minibands with negative differential conductivity are possible.

  20. Models of long-distance transport: how is carrier-dependent auxin transport regulated in the stem?

    PubMed

    Renton, Michael; Hanan, Jim; Ferguson, Brett J; Beveridge, Christine A

    2012-05-01

    • This paper presents two models of carrier-dependent long-distance auxin transport in stems that represent the process at different scales. • A simple compartment model using a single constant auxin transfer rate produced similar data to those observed in biological experiments. The effects of different underlying biological assumptions were tested in a more detailed model representing cellular and intracellular processes that enabled discussion of different patterns of carrier-dependent auxin transport and signalling. • The output that best fits the biological data is produced by a model where polar auxin transport is not limited by the number of transporters/carriers and hence supports biological data showing that stems have considerable excess capacity to transport auxin. • All results support the conclusion that auxin depletion following apical decapitation in pea (Pisum sativum) occurs too slowly to be the initial cause of bud outgrowth. Consequently, changes in auxin content in the main stem and changes in polar auxin transport/carrier abundance in the main stem are not correlated with axillary bud outgrowth. PMID:22443265

  1. Correlation of Crystalline and Structural Properties of C60 Thin Films Grown at Various Temperature with Charge Carrier Mobility

    SciTech Connect

    Singh,T.; Sarciftci, N.; Yang, H.; Yang, L.; Plochberger, B.; Sitter, H.

    2007-01-01

    Transistors fabricated from C{sub 60} films grown by hot wall epitaxy at higher substrate temperature, showed an order of magnitude increased charge carrier mobility up to 6 cm{sup 2}/V s. In this letter, the authors present an extensive study of morphology and crystallinity of the fullerene films using atomic force microscopy and grazing-incidence x-ray diffraction. A clear correlation of crystalline quality of the C{sub 60} film and charge carrier mobility was found. A higher substrate temperature leads to a single crystal-like faceted fullerene crystals. The high crystalline quality solely brings a drastic improvement in the charge carrier mobility. A gate voltage independent mobility is also observed in these devices which can be attributed to the highly conjugated nature of the C{sub 60} thin film.

  2. Charge carrier mobility in poly[methyl(phenyl)silylene] studied by time-resolved terahertz spectroscopy and molecular modelling.

    PubMed

    Němec, Hynek; Kratochvílová, Irena; Kužel, Petr; Šebera, Jakub; Kochalska, Anna; Nožár, Juraj; Nešpůrek, Stanislav

    2011-02-21

    Time-resolved terahertz spectroscopy and combination of quantum chemistry modeling and molecular dynamics simulations were used for the determination of charge carrier mobility in poly[methyl(phenyl)silylene]. Using time-resolved THz spectroscopy we established the on-chain charge carrier drift mobility in PMPSi as 0.02 cm(2) V(-1) s(-1). This value is low due to the formation of polarons: the hole is self-trapped in a potential formed by local chain distortion and the transient THz conductivity spectra show signatures of its oscillations within this potential well. This view is supported by the agreement between experimental and calculated values of the on-chain charge carrier mobility. PMID:21305068

  3. Ionic charge transport between blockages: Sodium cation conduction in freshly excised bulk brain tissue

    NASA Astrophysics Data System (ADS)

    Emin, David; Akhtari, Massoud; Ellingson, B. M.; Mathern, G. W.

    2015-08-01

    We analyze the transient-dc and frequency-dependent electrical conductivities between blocking electrodes. We extend this analysis to measurements of ions' transport in freshly excised bulk samples of human brain tissue whose complex cellular structure produces blockages. The associated ionic charge-carrier density and diffusivity are consistent with local values for sodium cations determined non-invasively in brain tissue by MRI (NMR) and diffusion-MRI (spin-echo NMR). The characteristic separation between blockages, about 450 microns, is very much shorter than that found for sodium-doped gel proxies for brain tissue, >1 cm.

  4. Ionic charge transport between blockages: Sodium cation conduction in freshly excised bulk brain tissue

    SciTech Connect

    Emin, David; Akhtari, Massoud; Ellingson, B. M.; Mathern, G. W.

    2015-08-15

    We analyze the transient-dc and frequency-dependent electrical conductivities between blocking electrodes. We extend this analysis to measurements of ions’ transport in freshly excised bulk samples of human brain tissue whose complex cellular structure produces blockages. The associated ionic charge-carrier density and diffusivity are consistent with local values for sodium cations determined non-invasively in brain tissue by MRI (NMR) and diffusion-MRI (spin-echo NMR). The characteristic separation between blockages, about 450 microns, is very much shorter than that found for sodium-doped gel proxies for brain tissue, >1 cm.

  5. 2D coherent charge transport in highly ordered conducting polymers doped by solid state diffusion

    NASA Astrophysics Data System (ADS)

    Kang, Keehoon; Watanabe, Shun; Broch, Katharina; Sepe, Alessandro; Brown, Adam; Nasrallah, Iyad; Nikolka, Mark; Fei, Zhuping; Heeney, Martin; Matsumoto, Daisuke; Marumoto, Kazuhiro; Tanaka, Hisaaki; Kuroda, Shin-Ichi; Sirringhaus, Henning

    2016-08-01

    Doping is one of the most important methods to control charge carrier concentration in semiconductors. Ideally, the introduction of dopants should not perturb the ordered microstructure of the semiconducting host. In some systems, such as modulation-doped inorganic semiconductors or molecular charge transfer crystals, this can be achieved by spatially separating the dopants from the charge transport pathways. However, in conducting polymers, dopants tend to be randomly distributed within the conjugated polymer, and as a result the transport properties are strongly affected by the resulting structural and electronic disorder. Here, we show that in the highly ordered lamellar microstructure of a regioregular thiophene-based conjugated polymer, a small-molecule p-type dopant can be incorporated by solid state diffusion into the layers of solubilizing side chains without disrupting the conjugated layers. In contrast to more disordered systems, this allows us to observe coherent, free-electron-like charge transport properties, including a nearly ideal Hall effect in a wide temperature range, a positive magnetoconductance due to weak localization and the Pauli paramagnetic spin susceptibility.

  6. Carrier transport property of truxene discotic liquid crystals with three different ring substituents

    NASA Astrophysics Data System (ADS)

    Monobe, Hirosato; Ni, Hai-Liang; Hu, Ping; Wang, Bi-Qin; Zhao, Ke-Qing; Shimizu, Yo

    2016-03-01

    In this study, the charge carrier transport property of 3,8,13-trioctyloxytruxene [Trx(OC8)3] and its analogues, to which two different ring substituents of hydroxyl [Trx(OH)3(OC8)3] and methoxy [Trx(OMe)3(OC8)3] groups are introduced, has been studied relative to mesomorphism. Three analogues exhibit a hexagonal columnar (Colh) mesophase and their thermal stability increases with the introduction of hydroxyl and methoxy groups. The drift mobility measurements of Trx(OC8)3 and Trx(OH)3(OC8)3 reveal that the drift mobility is on the order of 5 × 10-2 cm2 V-1 s-1 in the Colh phase and it increases to 10-1 cm2 V-1 s-1 at the Colh-metastable phase transition, although Trx(OMe)3(OC8)3 shows a drift mobility of 1 × 10-2 cm2 V-1 s-1 in the Colh phase with temperature dependence. These results indicate that truxene with three alkoxy chains is an interesting molecular core for mesophase semiconductors.

  7. Charge carrier loss mechanisms in CuInS2/ZnO nanocrystal solar cells.

    PubMed

    Scheunemann, Dorothea; Wilken, Sebastian; Parisi, Jürgen; Borchert, Holger

    2016-06-28

    Heterojunction solar cells based on colloidal nanocrystals (NCs) have shown remarkable improvements in performance in the last decade, but this progress is limited to merely two materials, PbS and PbSe. However, solar cells based on other material systems such as copper-based compounds show lower power conversion efficiencies and much less effort has been made to develop a better understanding of factors limiting their performance. Here, we study charge carrier loss mechanisms in solution-processed CuInS2/ZnO NC solar cells by combining steady-state measurements with transient photocurrent and photovoltage measurements. We demonstrate the presence of an extraction barrier at the CuInS2/ZnO interface, which can be reduced upon illumination with UV light. However, trap-assisted recombination in the CuInS2 layer is shown to be the dominant decay process in these devices. PMID:27250665

  8. First measurements of charge carrier density and mobility of in-situ enriched 28Si

    NASA Astrophysics Data System (ADS)

    Ramanayaka, A. N.; Dwyer, K. J.; Kim, Hyun-Soo; Stewart, M. D., Jr.; Pomeroy, J. M.

    Magnetotransport in top gated Hall bar devices is investigated to characterize the electrical properties of in-situ enriched 28Si. Isotopically enriched 28Si is an ideal candidate for quantum information processing devices as the elimination of unpaired nuclear spins improves the fidelity of the quantum information. Using mass filtered ion beam deposition we, in-situ, enrich and deposit epitaxial 28Si, achieving several orders of magnitude better enrichment compared to other techniques. In order to explore the electrical properties and optimize the growth conditions of in-situ enriched 28Si we perform magnetotransport measurements on top gated Hall bar devices at temperatures ranging from 300 K to cryogenic temperatures and at moderate magnetic fields. Here, we report on the charge carrier density and mobility extracted from such experiments, and will be compared among different growth conditions of in-situ enriched 28Si.

  9. Charge carrier dynamics in nanocrystalline Dy substituted ceria based oxygen ion conductors

    NASA Astrophysics Data System (ADS)

    Anirban, Sk.; Dutta, A.

    2016-05-01

    Nano-crystalline Ce1-xDyxO2-δ (x = 0.1-0.5) materials were prepared using the low temperature citrate auto-ignition method. The Rietveld analysis of the XRD data confirmed the single phase cubic fluorite structure. The particle sizes of the sintered samples are in nano range and lattice parameter increases with Dy concentration. Polydispersed and agglomerated particles are observed by SEM. The EDAX spectra show good stoichiometry of the different atoms in the samples. The conductivity is found to have both grain and grain boundary contribution and shows highest value at x= 0.2. The frequency dependence of dielectric permittivity has been analyzed using Havrilliak-Negami formalism. The variation in different electrical properties has been explained by formation defect associates and their interaction with charge carriers.

  10. Internal transmission coefficient in charges carrier generation layer of graphene/Si based solar cell device

    NASA Astrophysics Data System (ADS)

    Rosikhin, Ahmad; Winata, Toto

    2016-04-01

    Internal transmission profile in charges carrier generation layer of graphene/Si based solar cell has been explored theoretically. Photovoltaic device was constructed from graphene/Si heterojunction forming a multilayer stuck with Si as generation layer. The graphene/Si sheet was layered on ITO/glass wafer then coated by Al forming Ohmic contact with Si. Photon incident propagate from glass substrate to metal electrode and assumed that there is no transmission in Al layer. The wavelength range spectra used in this calculation was 200 - 1000 nm. It found that transmission intensity in the generation layer show non-linear behavior and partitioned by few areas which related with excitation process. According to this information, it may to optimize the photons absorption to create more excitation process by inserting appropriate material to enhance optical properties in certain wavelength spectra because of the exciton generation is strongly influenced by photon absorption.

  11. Measurement of carrier transport and recombination parameter in heavily doped silicon

    NASA Technical Reports Server (NTRS)

    Swanson, Richard M.

    1986-01-01

    The minority carrier transport and recombination parameters in heavily doped bulk silicon were measured. Both Si:P and Si:B with bulk dopings from 10 to the 17th and 10 to the 20th power/cu cm were studied. It is shown that three parameters characterize transport in bulk heavily doped Si: the minority carrier lifetime tau, the minority carrier mobility mu, and the equilibrium minority carrier density of n sub 0 and p sub 0 (in p-type and n-type Si respectively.) However, dc current-voltage measurements can never measure all three of these parameters, and some ac or time-transient experiment is required to obtain the values of these parameters as a function of dopant density. Using both dc electrical measurements on bipolar transitors with heavily doped base regions and transients optical measurements on heavily doped bulk and epitaxially grown samples, lifetime, mobility, and bandgap narrowing were measured as a function of both p and n type dopant densities. Best fits of minority carrier mobility, bandgap narrowing and lifetime as a function of doping density (in the heavily doped range) were constructed to allow accurate modeling of minority carrier transport in heavily doped Si.

  12. Proton intercalated two-dimensional WO3 nano-flakes with enhanced charge-carrier mobility at room temperature.

    PubMed

    Zhuiykov, Serge; Kats, Eugene; Carey, Benjamin; Balendhran, Sivacarendran

    2014-12-21

    Quasi two-dimensional (Q2D) semiconducting metal oxides with enhanced charge carrier mobility hold tremendous promise for nano-electronics, photonics, catalysis, nano-sensors and electrochromic applications. In addition to graphene and metal dichalcogenides MX2 (M = Mo, W; X = S, Se, Te), 2D sub-stoichiometric WO(3-x) is gaining importance as a promising semiconductor material for field-effect-transistor (FET) based devices. A combination of high permittivity, suppression of the Coulomb effects, and their stratified structure enhances the carrier mobility in such a material. Additionally, the sub-stoichiometry of this semiconductor oxide allows the reduction of the bandgap and increase of the free charge carriers at the same time. Here, we report for the first time H(+) intercalated WO(3) FETs, made of Q2D nano-flakes, with enhanced charge-carrier mobility exceeding 319 cm(2) V(-1) s(-1) comparable with the charge-carrier mobility of Q2D dichalcogenides MoS(2) and WSe(2). Analyses indicate that the enhanced electrical properties of the sub-stoichiometric WO(3-x) depend on the oxygen vacancies in the intercalated nano-flakes. These findings confirmed that Q2D sub-stoichiometric WO(3-x) is a promising material for various functional FET devices. PMID:25367432

  13. Electrodeless measurement of charge carrier mobility in pentacene by microwave and optical spectroscopy techniques

    NASA Astrophysics Data System (ADS)

    Saeki, Akinori; Seki, Shu; Tagawa, Seiichi

    2006-07-01

    Photoinduced transient conductivity of pentacene thin films prepared by thermal vapor deposition is investigated using time-resolved microwave conductivity (TRMC) measurements, giving intrinsic charge carrier mobility in highly ordered structures without any electrode attached. The real and imaginary conductivity values are analyzed and compared with those predicted by molecular orbital calculations. The effects of substrate surface treatment by hexamethyldisilazane are discussed on the basis of kinetic traces of conductivity and morphology. A mobility of >0.7cm2/Vs was obtained from the TRMC measurements and analysis of transient absorption spectra. The measurement of field-effect-transistor mobility in single-crystal domains requires not only complicated fabrication techniques but also many assumptions on the carrier channels, density, injection, etc. The combination of TRMC and transient optical spectroscopy provides an approach for addressing this issue. The present technique is applicable to a wide variety of organic semiconducting materials. Moreover, it is the only technique revealing the intrinsic potentials of mobility in materials that is supported by complete experimental and quantitative procedures not based on any assumptions.

  14. Quantifying charge carrier concentration in ZnO thin films by Scanning Kelvin Probe Microscopy

    PubMed Central

    Maragliano, C.; Lilliu, S.; Dahlem, M. S.; Chiesa, M.; Souier, T.; Stefancich, M.

    2014-01-01

    In the last years there has been a renewed interest for zinc oxide semiconductor, mainly triggered by its prospects in optoelectronic applications. In particular, zinc oxide thin films are being widely used for photovoltaic applications, in which the determination of the electrical conductivity is of great importance. Being an intrinsically doped material, the quantification of its doping concentration has always been challenging. Here we show how to probe the charge carrier density of zinc oxide thin films by Scanning Kelvin Probe Microscopy, a technique that allows measuring the contact potential difference between the tip and the sample surface with high spatial resolution. A simple electronic energy model is used for correlating the contact potential difference with the doping concentration in the material. Limitations of this technique are discussed in details and some experimental solutions are proposed. Two-dimensional doping concentration images acquired on radio frequency-sputtered intrinsic zinc oxide thin films with different thickness and deposited under different conditions are reported. We show that results inferred with this technique are in accordance with carrier concentration expected for zinc oxide thin films deposited under different conditions and obtained from resistivity and mobility measurements. PMID:24569599

  15. Origin of traps and charge transport mechanism in hafnia

    SciTech Connect

    Islamov, D. R. Gritsenko, V. A.; Cheng, C. H.; Chin, A.

    2014-12-01

    In this study, we demonstrated experimentally and theoretically that oxygen vacancies are responsible for the charge transport in HfO{sub 2}. Basing on the model of phonon-assisted tunneling between traps, and assuming that the electron traps are oxygen vacancies, good quantitative agreement between the experimental and theoretical data of current-voltage characteristics was achieved. The thermal trap energy of 1.25 eV in HfO{sub 2} was determined based on the charge transport experiments.

  16. 41 CFR 302-10.402 - What costs must we pay a commercial carrier for transporting a mobile home?

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... commercial carrier for transporting a mobile home? 302-10.402 Section 302-10.402 Public Contracts and... PROPERTY 10-ALLOWANCES FOR TRANSPORTATION OF MOBILE HOMES AND BOATS USED AS A PRIMARY RESIDENCE Agency Responsibilities § 302-10.402 What costs must we pay a commercial carrier for transporting a mobile home? The...

  17. 41 CFR 302-10.402 - What costs must we pay a commercial carrier for transporting a mobile home?

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... commercial carrier for transporting a mobile home? 302-10.402 Section 302-10.402 Public Contracts and... PROPERTY 10-ALLOWANCES FOR TRANSPORTATION OF MOBILE HOMES AND BOATS USED AS A PRIMARY RESIDENCE Agency Responsibilities § 302-10.402 What costs must we pay a commercial carrier for transporting a mobile home? The...

  18. Carrier transport simulation in a model liquid crystalline system with the biaxial Gay-Berne potential.

    PubMed

    Goto, Masanao; Takezoe, Hideo; Ishikawa, Ken

    2010-02-01

    In this paper, we performed carrier transport simulation to understand the unusual temperature dependence of the carrier mobility observed in nematic liquid crystals. For this purpose, we made a model liquid crystalline system consisting of biaxial Gay-Berne particles, and then we simulated hopping transport between these particles. The hopping rate was formulated suitably for the biaxial Gay-Berne particles based on the investigation of the electronic overlaps between actual aromatic molecules. The carrier transport simulation was performed by master equation method on the model system prepared by N-P-T ensemble Monte Carlo simulation. We reproduced gradual mobility increase in the nematic phase as a result of the change in the short range molecular order. PMID:20136321

  19. Carrier transport simulation in a model liquid crystalline system with the biaxial Gay-Berne potential

    NASA Astrophysics Data System (ADS)

    Goto, Masanao; Takezoe, Hideo; Ishikawa, Ken

    2010-02-01

    In this paper, we performed carrier transport simulation to understand the unusual temperature dependence of the carrier mobility observed in nematic liquid crystals. For this purpose, we made a model liquid crystalline system consisting of biaxial Gay-Berne particles, and then we simulated hopping transport between these particles. The hopping rate was formulated suitably for the biaxial Gay-Berne particles based on the investigation of the electronic overlaps between actual aromatic molecules. The carrier transport simulation was performed by master equation method on the model system prepared by N-P-T ensemble Monte Carlo simulation. We reproduced gradual mobility increase in the nematic phase as a result of the change in the short range molecular order.

  20. Simulation of bipolar charge transport in nanocomposite polymer films

    NASA Astrophysics Data System (ADS)

    Lean, Meng H.; Chu, Wei-Ping L.

    2015-03-01

    This paper describes 3D particle-in-cell simulation of bipolar charge injection and transport through nanocomposite film comprised of ferroelectric ceramic nanofillers in an amorphous polymer matrix. The classical electrical double layer (EDL) model for a monopolar core is extended (eEDL) to represent the nanofiller by replacing it with a dipolar core. Charge injection at the electrodes assumes metal-polymer Schottky emission at low to moderate fields and Fowler-Nordheim tunneling at high fields. Injected particles migrate via field-dependent Poole-Frenkel mobility and recombine with Monte Carlo selection. The simulation algorithm uses a boundary integral equation method for solution of the Poisson equation coupled with a second-order predictor-corrector scheme for robust time integration of the equations of motion. The stability criterion of the explicit algorithm conforms to the Courant-Friedrichs-Levy limit assuring robust and rapid convergence. The model is capable of simulating a wide dynamic range spanning leakage current to pre-breakdown. Simulation results for BaTiO3 nanofiller in amorphous polymer matrix indicate that charge transport behavior depend on nanoparticle polarization with anti-parallel orientation showing the highest leakage conduction and therefore lowest level of charge trapping in the interaction zone. Charge recombination is also highest, at the cost of reduced leakage conduction charge. The eEDL model predicts the meandering pathways of charge particle trajectories.

  1. Theoretical Study on Charge Transport Properties of Intra- and Extra-Ring Substituted Pentacene Derivatives.

    PubMed

    Fan, Jian-Xun; Chen, Xian-Kai; Zhang, Shou-Feng; Ren, Ai-Min

    2016-04-21

    A series of pentacene derivatives, halogen-substituted and thiophene- and pyridine-substituted, have been studied with a focus on the electronic properties and charge transport properties using density functional theory and classical Marcus charge-transfer theory. The transport properties of holes and electrons have been studied to get insight into the effect of halogenation and heteroatom substitution on transport and injection of charge carriers. The calculation results revealed that fluorination and chlorination can effectively lower the lowest unoccupied molecular orbital (LUMO) level, modulate the hole and electron reorganization energy, improve the stacking mode of the crystal structure, and enhance the ambipolar characteristic. Chlorination gives a better ambipolar characteristic. On the basis of halogen substitution, the substitution of terminal benzene ring of triisopropyl-silylethynyl-pentacene (TIPS-PEN) by a thiophene or pyridine will greatly lower the LUMO level and improve the stacking mode, leading to more suitable ambipolar materials. Hence, both intra- and extra-ring substitution are favorable to enhance the ambipolar transport property of TIPS-PEN. PMID:27027319

  2. Disorder Effects in Charge Transport and Spin Response of Topological Insulators

    NASA Astrophysics Data System (ADS)

    Zhao, Lukas Zhonghua

    Topological insulators are a class of solids in which the non-trivial inverted bulk band structure gives rise to metallic surface states that are robust against impurity backscattering. First principle calculations predicted Bi2Te3, Sb2Te3 and Bi2Se3 to be three-dimensional (3D) topological insulators with a single Dirac cone on the surface. The topological surface states were subsequently observed by angle-resolved photoemission (ARPES) and scanning tunneling microscopy (STM). The investigations of charge transport through topological surfaces of 3D topological insulators, however, have faced a major challenge due to large charge carrier densities in the bulk donated by randomly distributed defects such as vacancies and antisites. This bulk disorder intermixes surface and bulk conduction channels, thereby complicating access to the low-energy (Dirac point) charge transport or magnetic response and resulting in the relatively low measured carrier mobilities. Moreover, charge inhomogeneity arising from bulk disorder can result in pronounced nanoscale spatial fluctuations of energy on the surface, leading to the formation of surface `puddles' of different carrier types. Great efforts have been made to combat the undesirable effects of disorder in 3D topological insulators and to reduce bulk carriers through chemical doping, nanostructure fabrication, and electric gating. In this work we have developed a new way to reduce bulk carrier densities using high-energy electron irradiation, thereby allowing us access to the topological surface quantum channels. We also found that disorder in 3D topological insulators can be beneficial. It can play an important part in enabling detection of unusual magnetic response from Dirac fermions and in uncovering new excitations, namely surface superconductivity in Dirac `puddles'. In Chapter 3 we show how by using differential magnetometry we could probe spin rotation in the 3D topological material family (Bi2Se 3, Bi2Te3 and Sb2Te3

  3. A multi-agent quantum Monte Carlo model for charge transport: Application to organic field-effect transistors

    NASA Astrophysics Data System (ADS)

    Bauer, Thilo; Jäger, Christof M.; Jordan, Meredith J. T.; Clark, Timothy

    2015-07-01

    We have developed a multi-agent quantum Monte Carlo model to describe the spatial dynamics of multiple majority charge carriers during conduction of electric current in the channel of organic field-effect transistors. The charge carriers are treated by a neglect of diatomic differential overlap Hamiltonian using a lattice of hydrogen-like basis functions. The local ionization energy and local electron affinity defined previously map the bulk structure of the transistor channel to external potentials for the simulations of electron- and hole-conduction, respectively. The model is designed without a specific charge-transport mechanism like hopping- or band-transport in mind and does not arbitrarily localize charge. An electrode model allows dynamic injection and depletion of charge carriers according to source-drain voltage. The field-effect is modeled by using the source-gate voltage in a Metropolis-like acceptance criterion. Although the current cannot be calculated because the simulations have no time axis, using the number of Monte Carlo moves as pseudo-time gives results that resemble experimental I/V curves.

  4. A multi-agent quantum Monte Carlo model for charge transport: Application to organic field-effect transistors

    SciTech Connect

    Bauer, Thilo; Jäger, Christof M.; Jordan, Meredith J. T.; Clark, Timothy

    2015-07-28

    We have developed a multi-agent quantum Monte Carlo model to describe the spatial dynamics of multiple majority charge carriers during conduction of electric current in the channel of organic field-effect transistors. The charge carriers are treated by a neglect of diatomic differential overlap Hamiltonian using a lattice of hydrogen-like basis functions. The local ionization energy and local electron affinity defined previously map the bulk structure of the transistor channel to external potentials for the simulations of electron- and hole-conduction, respectively. The model is designed without a specific charge-transport mechanism like hopping- or band-transport in mind and does not arbitrarily localize charge. An electrode model allows dynamic injection and depletion of charge carriers according to source-drain voltage. The field-effect is modeled by using the source-gate voltage in a Metropolis-like acceptance criterion. Although the current cannot be calculated because the simulations have no time axis, using the number of Monte Carlo moves as pseudo-time gives results that resemble experimental I/V curves.

  5. A multi-agent quantum Monte Carlo model for charge transport: Application to organic field-effect transistors.

    PubMed

    Bauer, Thilo; Jäger, Christof M; Jordan, Meredith J T; Clark, Timothy

    2015-07-28

    We have developed a multi-agent quantum Monte Carlo model to describe the spatial dynamics of multiple majority charge carriers during conduction of electric current in the channel of organic field-effect transistors. The charge carriers are treated by a neglect of diatomic differential overlap Hamiltonian using a lattice of hydrogen-like basis functions. The local ionization energy and local electron affinity defined previously map the bulk structure of the transistor channel to external potentials for the simulations of electron- and hole-conduction, respectively. The model is designed without a specific charge-transport mechanism like hopping- or band-transport in mind and does not arbitrarily localize charge. An electrode model allows dynamic injection and depletion of charge carriers according to source-drain voltage. The field-effect is modeled by using the source-gate voltage in a Metropolis-like acceptance criterion. Although the current cannot be calculated because the simulations have no time axis, using the number of Monte Carlo moves as pseudo-time gives results that resemble experimental I/V curves. PMID:26233114

  6. Transmembrane auxin carrier systems--dynamic regulators of polar auxin transport.

    PubMed

    Morris, D A

    2000-11-01

    Recent investigations of the biochemistry, physiology and molecular genetics of polar auxin transport have greatly advanced our understanding of the process and of the part it plays in the regulation of development and in the responses of cells, tissues and organs to internal and external stimuli. The molecular and physiological characterization of mutants which exhibit lesions in polar auxin transport has led to the isolation and sequencing of genes which encode putative components of auxin carrier systems, or proteins which directly or indirectly regulate these systems. This work has revealed that specific auxin uptake and efflux carriers are coded not by single genes, but by whole families of genes, the expression of which is tissue or stimulus specific. Furthermore, evidence is accumulating rapidly that at least the auxin efflux carrier is a multi-component system consisting of both catalytic and regulatory subunits, including a separate phytotropin-binding protein. Other genes have been tentatively identified which code proteins that regulate the expression of genes coding auxin carrier components, or which regulate the intracellular traffic or activity of auxin carriers. Investigations of the turn-over and Golgi-mediated trafficking of auxin carrier proteins have revealed that essential components of at least the efflux carrier have a very short half-life in the plasma membrane and are replaced without the need for concurrent protein synthesis, leading to speculation that they might cycle between internal stores and the plasma membrane. The way is now clear for the development of specific molecular probes with which to investigate the intracellular transport and targeting of auxin carrier proteins. PMID:11758564

  7. Long-lived charge carrier generation in ordered films of a covalent perylenediimide–diketopyrrolopyrrole–perylenediimide molecule

    DOE PAGESBeta

    Hartnett, Patrick E.; Dyar, Scott M.; Margulies, Eric A.; Shoer, Leah E.; Cook, Andrew W.; Eaton, Samuel W.; Marks, Tobin J.; Wasielewski, Michael R.

    2015-07-31

    The photophysics of a covalently linked perylenediimide–diketopyrrolopyrrole–perylenediimide acceptor–donor–acceptor molecule (PDI–DPP–PDI, 1) were investigated and found to be markedly different in solution versus in unannealed and solvent annealed films. Photoexcitation of 1 in toluene results in quantitative charge separation in τ = 3.1 ± 0.2 ps, with charge recombination in τ = 340 ± 10 ps, while in unannealed/disordered films of 1, charge separation occurs in τ < 250 fs, while charge recombination displays a multiexponential decay in ~6 ns. The absence of long-lived, charge separation in the disordered film suggests that few free charge carriers are generated. In contrast, uponmore » CH₂Cl₂ vapor annealing films of 1, grazing-incidence X-ray scattering shows that the molecules form a more ordered structure. Photoexcitation of the ordered films results in initial formation of a spin-correlated radical ion pair (electron–hole pair) as indicated by magnetic field effects on the formation of free charge carriers which live for ~4 μs. This result has significant implications for the design of organic solar cells based on covalent donor–acceptor systems and shows that long-lived, charge-separated states can be achieved by controlling intramolecular charge separation dynamics in well-ordered systems.« less

  8. Long-lived charge carrier generation in ordered films of a covalent perylenediimide–diketopyrrolopyrrole–perylenediimide molecule

    SciTech Connect

    Hartnett, Patrick E.; Dyar, Scott M.; Margulies, Eric A.; Shoer, Leah E.; Cook, Andrew W.; Eaton, Samuel W.; Marks, Tobin J.; Wasielewski, Michael R.

    2015-07-31

    The photophysics of a covalently linked perylenediimide–diketopyrrolopyrrole–perylenediimide acceptor–donor–acceptor molecule (PDI–DPP–PDI, 1) were investigated and found to be markedly different in solution versus in unannealed and solvent annealed films. Photoexcitation of 1 in toluene results in quantitative charge separation in τ = 3.1 ± 0.2 ps, with charge recombination in τ = 340 ± 10 ps, while in unannealed/disordered films of 1, charge separation occurs in τ < 250 fs, while charge recombination displays a multiexponential decay in ~6 ns. The absence of long-lived, charge separation in the disordered film suggests that few free charge carriers are generated. In contrast, upon CH₂Cl₂ vapor annealing films of 1, grazing-incidence X-ray scattering shows that the molecules form a more ordered structure. Photoexcitation of the ordered films results in initial formation of a spin-correlated radical ion pair (electron–hole pair) as indicated by magnetic field effects on the formation of free charge carriers which live for ~4 μs. This result has significant implications for the design of organic solar cells based on covalent donor–acceptor systems and shows that long-lived, charge-separated states can be achieved by controlling intramolecular charge separation dynamics in well-ordered systems.

  9. The telegraph equation in charged particle transport

    NASA Technical Reports Server (NTRS)

    Gombosi, T. I.; Jokipii, J. R.; Kota, J.; Lorencz, K.; Williams, L. L.

    1993-01-01

    We present a new derivation of the telegraph equation which modifies its coefficients. First, an infinite order partial differential equation is obtained for the velocity space solid angle-averaged phase-space distribution of particles which underwent at least a few collisions. It is shown that, in the lowest order asymptotic expansion, this equation simplifies to the well-known diffusion equation. The second-order asymptotic expansion for isotropic small-angle scattering results in a modified telegraph equation with a signal propagation speed of v(5/11) exp 1/2 instead of the usual v/3 exp 1/2. Our derivation of a modified telegraph equation follows from an expansion of the Boltzmann equation in the relevant smallness parameters and not from a truncation of an eigenfunction expansion. This equation is consistent with causality. It is shown that, under steady state conditions in a convecting plasma, the telegraph equation may be regarded as a diffusion equation with a modified transport coefficient, which describes a combination of diffusion and cosmic-ray inertia.

  10. Surface charge transport in Silicon (111) nanomembranes

    NASA Astrophysics Data System (ADS)

    Hu, Weiwei; Scott, Shelley; Jacobson, Rb; Savage, Donald; Lagally, Max; The Lagally Group Team

    Using thin sheets (``nanomembranes'') of atomically flat crystalline semiconductors, we are able to investigate surface electronic properties, using back-gated van der Pauw measurement in UHV. The thinness of the sheet diminishes the bulk contribution, and the back gate tunes the conductivity until the surface dominates, enabling experimental determination of surface conductance. We have previously shown that Si(001) surface states interact with the body of the membrane altering the conductivity of the system. Here, we extended our prior measurements to Si(111) in order to probe the electronic transport properties of the Si(111) 7 ×7 reconstruction. Sharp (7 ×7) LEED images attest to the cleanliness of the Si(111) surface. Preliminary results reveal a highly conductive Si(111) 7 ×7 surface with a sheet conductance Rs of order of μS/ □, for 110nm thick membrane, and Rs is a very slowly varying function of the back gate voltage. This is in strong contrast to Si(001) nanomembranes which have a minimum conductance several orders of magnitude lower, and hints to the metallic nature of the Si(111) surface. Research supported by DOE.

  11. Mucus permeating carriers: formulation and characterization of highly densely charged nanoparticles.

    PubMed

    Pereira de Sousa, Irene; Steiner, Corinna; Schmutzler, Matthias; Wilcox, Matthew D; Veldhuis, Gert J; Pearson, Jeffrey P; Huck, Christian W; Salvenmoser, Willi; Bernkop-Schnürch, Andreas

    2015-11-01

    The GI mucus layer represents a significant block to drug carriers absorption. Taking an example from nature, virus-mimicking nanoparticles (NPs) with highly densely charged surface were designed with the aim to improve their mucus permeation ability. NPs were formulated by combining chitosan with chondroitin sulfate and were characterized by particle size, ζ-potential and hydrophobicity. The interaction occurring between NPs and diluted porcine intestinal mucus was investigated by a new method. Furthermore, the rotating tube technique was exploited to evaluate the NPs permeation ability in fresh undiluted porcine intestinal mucus. NPs (400-500 nm) presenting a slightly positive (4.02 mV) and slightly negative (-3.55 mV) ζ-potential resulted to be hydrophobic and hydrophilic, respectively. On the one hand the hydrophobic NPs undergo physico-chemical changes when incubated with mucus, namely the size increased and the ζ-potential decreased. On the other hand, the hydrophilic NPs did not significantly change size and net charge during incubation with mucus. Both types of NPs showed a 3-fold higher diffusion ability compared to the reference 50/50 DL-lactide/glycolide copolymer NPs (136 nm, -23 mV, hydrophilic). Based on these results, this work gives valuable information for the further design of mucus-penetrating NPs. PMID:25576256

  12. Non-Abelian states in Fractional Quantum Hall effect in charge carrier hole systems

    NASA Astrophysics Data System (ADS)

    Simion, George; Lyanda-Geller, Yuli

    Quasiparticle excitations obeying non-Abelian statistics represent the key element of topological quantum computing. Crossing of levels and strong coupling between angular momentum and orbital motion, described by Luttinger Hamiltonian, make properties of charge carrier holes different from those of electrons. Peculiarities of hole spectrum in magnetic field provide an opportunity for controlling Landau level mixing in charge carier hole systems. In order to describe Fractional Quantum Hall effect for holes, we propose a method to map hole spectrum and wavefunctions using a spherical shell. We investigate the experimentally observed ν = 1 / 2 state in spherical geometry. Haldane pseudopotentials are computed and the effect of Landau level mixing is evaluated. Exact diagonalization of Coulomb interaction in systems with eight to fourteen holes is performed. We determine that the ground state superposition with Abelian 331 state is very small and the overlap with Moore-Read state is significant. The quasihole and quasielectron excitations are discussed. Research was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award DE-SC0010544.

  13. Charge carrier dynamics and surface plasmon interaction in gold nanorod-blended organic solar cell

    NASA Astrophysics Data System (ADS)

    Rana, Aniket; Gupta, Neeraj; Lochan, Abhiram; Sharma, G. D.; Chand, Suresh; Kumar, Mahesh; Singh, Rajiv K.

    2016-08-01

    The inclusion of plasmonic nanoparticles into organic solar cell enhances the light harvesting properties that lead to higher power conversion efficiency without altering the device configuration. This work defines the consequences of the nanoparticle overloading amount and energy transfer process between gold nanorod and polymer (active matrix) in organic solar cells. We have studied the hole population decay dynamics coupled with gold nanorods loading amount which provides better understanding about device performance limiting factors. The exciton and plasmon together act as an interacting dipole; however, the energy exchange between these two has been elucidated via plasmon resonance energy transfer (PRET) mechanism. Further, the charge species have been identified specifically with respect to their energy levels appearing in ultrafast time domain. The specific interaction of these charge species with respective surface plasmon resonance mode, i.e., exciton to transverse mode of oscillation and polaron pair to longitudinal mode of oscillations, has been explained. Thus, our analysis reveals that PRET enhances the carrier population density in polymer via non-radiative process beyond the concurrence of a particular plasmon resonance oscillation mode and polymer absorption range. These findings give new insight and reveal specifically the factors that enhance and control the performance of gold nanorods blended organic solar cells. This work would lead in the emergence of future plasmon based efficient organic electronic devices.

  14. Charged carrier spin dynamics in ZnO quantum wells and epilayers

    NASA Astrophysics Data System (ADS)

    Kim, Jungtaek; Puls, J.; Sadofev, S.; Henneberger, F.

    2016-01-01

    Longitudinal charged carrier spin dynamics is studied for ZnO quantum wells and epilayers using the optical transition of the negatively charged exciton X- and the neutral donor bound exciton D0X , respectively. The hole spin relaxation is derived from the optical orientation of X- and D0X photoluminescence, whereas the spin relaxation of the resident electrons and donor electrons is accessed via the bleaching of the spin selective excitation process. Hole spin relaxation times of τ1s ,h of 80 and 140 ps are found for D0X and X-, respectively, which are practically independent of a magnetic field B∥ applied along the ZnO c ⃗ axis. Much longer longitudinal electron spin relaxation times in the 1 μ s range are uncovered if the hyperfine interaction is suppressed by a proper B∥. A field strength of ≈2 mT is large enough proving the extremely small value of the Overhauser field in ZnO. This is related to the very restricted number of magnetic nuclei interacting with the electron inside the volume of the exciton complex.

  15. Nitrogen-doped graphene sheets grown by chemical vapor deposition: synthesis and influence of nitrogen impurities on carrier transport.

    PubMed

    Lu, Yu-Fen; Lo, Shun-Tsung; Lin, Jheng-Cyuan; Zhang, Wenjing; Lu, Jing-Yu; Liu, Fan-Hung; Tseng, Chuan-Ming; Lee, Yi-Hsien; Liang, Chi-Te; Li, Lain-Jong

    2013-08-27

    A significant advance toward achieving practical applications of graphene as a two-dimensional material in nanoelectronics would be provided by successful synthesis of both n-type and p-type doped graphene. However, reliable doping and a thorough understanding of carrier transport in the presence of charged impurities governed by ionized donors or acceptors in the graphene lattice are still lacking. Here we report experimental realization of few-layer nitrogen-doped (N-doped) graphene sheets by chemical vapor deposition of organic molecule 1,3,5-triazine on Cu metal catalyst. When reducing the growth temperature, the atomic percentage of nitrogen doping is raised from 2.1% to 5.6%. With increasing doping concentration, N-doped graphene sheet exhibits a crossover from p-type to n-type behavior accompanied by a strong enhancement of electron-hole transport asymmetry, manifesting the influence of incorporated nitrogen impurities. In addition, by analyzing the data of X-ray photoelectron spectroscopy, Raman spectroscopy, and electrical measurements, we show that pyridinic and pyrrolic N impurities play an important role in determining the transport behavior of carriers in our N-doped graphene sheets. PMID:23879622

  16. Theoretical predictions on the electronic structure and charge carrier mobility in 2D Phosphorus sheets

    PubMed Central

    Xiao, Jin; Long, Mengqiu; Zhang, Xiaojiao; Ouyang, Jun; Xu, Hui; Gao, Yongli

    2015-01-01

    We have investigated the electronic structure and carrier mobility of four types of phosphorous monolayer sheet (α-P, β-P,γ-P and δ-P) using density functional theory combined with Boltzmann transport method and relaxation time approximation. It is shown that α-P, β-P and γ-P are indirect gap semiconductors, while δ-P is a direct one. All four sheets have ultrahigh carrier mobility and show anisotropy in-plane. The highest mobility value is ~3 × 105 cm2V−1s−1, which is comparable to that of graphene. Because of the huge difference between the hole and electron mobilities, α-P, γ-P and δ-P sheets can be considered as n-type semiconductors, and β-P sheet can be considered as a p-type semiconductor. Our results suggest that phosphorous monolayer sheets can be considered as a new type of two dimensional materials for applications in optoelectronics and nanoelectronic devices. PMID:26035176

  17. On the Structure of the Fixed Charge Transportation Problem

    ERIC Educational Resources Information Center

    Kowalski, K.

    2005-01-01

    This work extends the theory of the fixed charge transportation problem (FCTP), currently based mostly on a forty-year-old publication by Hirsch and Danzig. This paper presents novel properties that need to be considered by those using existing, or those developing new methods for optimizing FCTP. It also defines the problem in an easier way,…

  18. Controlled Microdroplet Transport & Charging in an Atmospheric Pressure Microplasma

    NASA Astrophysics Data System (ADS)

    Kelsey, Colin; Maguire, Paul; Mahony, Charles; Hamilton, Neil; Mariotti, Davide; Rutherford, David; McDowell, David; Pérez-Martín, Fátima; Bennet, Euan; Potts, Hugh; Diver, Declan; Ulster University Collaboration; University of Glasgow Collaboration

    2015-09-01

    We have measured charge and evaporation rates of a stream of micron-scale H2O droplets transported through a low-temperature helium-neon rf plasma. Ne and Te, estimated from plasma impedance, were ~ 1013/cm3 and ~5 eV respectively; gas temperature, from N2 spectroscopy, was <400 K. With a log-normal aerosol droplet size distribution, 15 micron CMD and droplet velocity distribution within a parabolic envelope of ~75% of the local gas speed, the plasma induced evaporation caused an average diameter reduction of <2 microns. This is equivalent to an average evaporation rate ~ 2 orders of magnitude higher than reported for similar droplets in a comparable gas flow without plasma. Using charged droplet collection and current amplification, we have measured sub-millisecond charge pulses of up to 107e from a droplet stream with ~ 2 . 5 ×103 droplets/s demonstrating the transport of droplets beyond the plasma and recombination region with negative charge retained. Time averaged measurements using an alternative technique show the mean charge per droplet is ~ 105e. Results from an enhanced resolution charge measurement apparatus, currently being tested and using individual and size selectable droplets will be reported. EPSRC funded

  19. Physical constraints on charge transport through bacterial nanowires

    PubMed Central

    Polizzi, Nicholas F.; Skourtis, Spiros S.

    2012-01-01

    Extracellular appendages of the dissimilatory metal-reducing bacterium Shewanella oneidensis MR-1 were recently shown to sustain currents of 1010 electrons per second over distances of 0.5 microns [El-Naggar et al., Proc. Natl. Acad. Sci. U. S. A., 2010, 107, 18127]. However, the identity of the charge localizing sites and their organization along the “nanowire” remain unknown. We use theory to predict redox cofactor separation distances that would permit charge flow at rates of 1010 electrons per second over 0.5 microns for voltage biases of ≤1V, using a steady-state analysis governed by a non-adiabatic electron transport mechanism. We find the observed currents necessitate a multi-step hopping transport mechanism, with charge localizing sites separated by less than 1 nm and reorganization energies that rival the lowest known in biology. PMID:22470966

  20. Charge transport in thin layer Na x CoO2 (x ∼ 0.63) studied by terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Němec, H.; Knížek, K.; Jirák, Z.; Hejtmánek, J.; Soroka, M.; Buršík, J.

    2016-09-01

    Charge transport in Na0.63CoO2 thin film deposited by a spin-coating method was investigated experimentally by time-domain terahertz spectroscopy and theoretically using Monte Carlo calculations of charge response in nano-structured materials. The dominating type of transport mechanism over the entire investigated range of temperatures (20–300 K) is a metallic-like conductivity of charges partly confined in constituting nano-sized grains. Due to the granular character of our thin film, the scattering time at low temperatures is limited by scattering on grain boundaries and the conductivity is strongly suppressed due to capture of a major fraction of charge carriers in deep traps. Nevertheless, our experimental setup and the applied model allowed us to distinguish the parameters related to the grain interior from those influenced by grain boundaries, and to conclude that the metallic type of conductivity is the intrinsic property relevant to single crystal materials.

  1. Charge transport in thin layer Na x CoO2 (x ∼ 0.63) studied by terahertz spectroscopy.

    PubMed

    Němec, H; Knížek, K; Jirák, Z; Hejtmánek, J; Soroka, M; Buršík, J

    2016-09-01

    Charge transport in Na0.63CoO2 thin film deposited by a spin-coating method was investigated experimentally by time-domain terahertz spectroscopy and theoretically using Monte Carlo calculations of charge response in nano-structured materials. The dominating type of transport mechanism over the entire investigated range of temperatures (20-300 K) is a metallic-like conductivity of charges partly confined in constituting nano-sized grains. Due to the granular character of our thin film, the scattering time at low temperatures is limited by scattering on grain boundaries and the conductivity is strongly suppressed due to capture of a major fraction of charge carriers in deep traps. Nevertheless, our experimental setup and the applied model allowed us to distinguish the parameters related to the grain interior from those influenced by grain boundaries, and to conclude that the metallic type of conductivity is the intrinsic property relevant to single crystal materials. PMID:27365361

  2. Carrier transport in Bi2Se3 topological insulator slab

    NASA Astrophysics Data System (ADS)

    Gupta, Gaurav; Lin, Hsin; Bansil, Arun; Jalil, Mansoor Bin Abdul; Liang, Gengchiau

    2015-11-01

    Electron transport in Bi2Se3 topological insulator slabs is investigated in the thermal activation regime (>50 K) both in the absence (ballistic) and presence of weak and strong acoustic phonon scattering using the non-equilibrium Green function approach. Resistance of the slab is simulated as a function of temperature for a range of slab thicknesses and effective doping in order to gain a handle on how various factors interact and compete to determine the overall resistance of the slab. If the Bi2Se3 slab is biased at the Dirac point, resistance is found to display an insulating trend even for strong electron-phonon coupling strength. However, when the Fermi-level lies close to the bulk conduction band (heavy electron doping), phonon scattering can dominate and result in a metallic behavior, although the insulating trend is retained in the limit of ballistic transport. Depending on values of the operating parameters, the temperature dependence of the slab is found to exhibit a remarkably complex behavior, which ranges from insulating to metallic, and includes cases where the resistance exhibits a local maximum, much like the contradictory behaviors seen experimentally in various experiments.

  3. Charge Density and Molecular Weight of Polyphosphoramidate Gene Carrier Are Key Parameters Influencing Its DNA Compaction Ability and Transfection Efficiency

    PubMed Central

    Ren, Yong; Jiang, Xuan; Pan, Deng; Mao, Hai-Quan

    2011-01-01

    A series of polyphosphoramidates (PPA) with different molecular weights (MWs) and charge densities were synthesized and examined for their DNA compaction ability and transfection efficiency. A strong correlation was observed between the transfection efficiency of PPA/DNA nanoparticles and the MW and net positive charge density of the PPA gene carriers in three different cell lines (HeLa, HEK293 and HepG2 cells). An increase in MW and/or net positive charge density of PPA carrier yielded higher DNA compaction capacity, smaller nanoparticles with higher surface charges and higher complex stability against challenges by salt and polyanions. These favorable physicochemical properties of nanoparticles led to enhanced transfection efficiency. PPA/DNA nanoparticles with the highest complex stability showed comparable transfection efficiency as PEI/DNA nanoparticles likely by compensating the low buffering capacity with higher cellular uptake and affording higher level of protection to DNA in endolysosomal compartment. The differences in transfection efficiency were not attributed by any difference in cytotoxicity among the carriers, as all nanoparticles showed minimal level of cytotoxicity under the transfection conditions. Using PPA as a model system, we demonstrated the structural dependence of transfection efficiency of polymer gene carrier. These results offer more insights into nanoparticle engineering for non-viral gene delivery. PMID:21067136

  4. Isoindigo-based polymer field-effect transistors: effects of selenophene-substitution on high charge carrier mobility.

    PubMed

    Park, Kwang Hun; Cheon, Kwang Hee; Lee, Yun-Ji; Chung, Dae Sung; Kwon, Soon-Ki; Kim, Yun-Hi

    2015-05-11

    We show that selenophene-substitution can be an efficient synthetic strategy toward high charge carrier mobility of isoindigo (IID)-based copolymers when their side chains are optimized. A high mobility of 5.8 cm(2) V(-1) s(-1) is demonstrated by a strategically designed IID-based polymer, with both side-chain adjustment and selenophene-substitution. PMID:25871952

  5. Dielectric spectroscopy for probing the relaxation and charge transport in polypyrrole nanofibers

    NASA Astrophysics Data System (ADS)

    Banerjee, Somik; Kumar, A.

    2011-06-01

    Conductivity relaxation and charge transport mechanisms in polypyrrole (PPy) nanofibers synthesized using a micellar polymerization technique with varying surfactant concentration has been investigated by dielectric relaxation spectroscopy. TEM micrographs depict that the increasing surfactant concentration leads to the reduction of the nanofiber diameter. X-ray diffraction studies show that domain length in the PPy nanofibers decreases with decreasing fiber diameter whereas the strain caused due to dislocations and point defects increases. The permittivity spectra reveal that the relaxation mechanism in PPy nanofibers are dominated by hopping of trapped charges. Two relaxation peaks in the impedance spectra are attributed to the two-phase structure in the PPy nanofibers; the lower frequency peak is ascribed to the phase of oxidized repeat units and the higher frequency peak to the reduced repeat units of PPy nanofibers. The occurrence of relaxation peaks at different frequencies in the impedance and modulus spectra indicates a non-Debye relaxation with a wide distribution of relaxation times. The ac conductivity has been interpreted as a power law of frequency. The decrease of the parameter s with increasing temperature indicates that correlated barrier hopping is the dominant charge transport mechanism. Existence of polarons as major charge carriers has been confirmed by the low values of polaron binding energy.

  6. Charge transport and recombination in P3HT:PbS solar cells

    SciTech Connect

    Firdaus, Yuliar; Khetubol, Adis; Van der Auweraer, Mark; Vandenplas, Erwin; Cheyns, David; Gehlhaar, Robert

    2015-03-07

    The charge carrier transport in thin film hybrid solar cells is analyzed and correlated with device performance and the mechanisms responsible for recombination loss. The hybrid bulk heterojunction consisted of a blend of poly(3-hexylthiophene) (P3HT) and small size (2.4 nm) PbS quantum dots (QDs). The charge transport in the P3HT:PbS blends was determined by measuring the space-charge limited current in hole-only and electron-only devices. When the loading of PbS QDs exceeds the percolation threshold, a significant increase of the electron mobility is observed in the blend with PbS QDs. The hole mobility, on the other hand, only slightly decreased upon increasing the loading of PbS QDs. We also showed that the photocurrent is limited by the low shunt resistance rather than by space-charge effects. The significant reduction of the fill factor at high light intensity suggests that under these conditions the non-geminate recombination dominates. However, at open-circuit conditions, the trap-assisted recombination dominates over non-geminate recombination.

  7. Charge pariticle transport in the non-isotropic turbulences

    NASA Astrophysics Data System (ADS)

    Sun, P.; Jokipii, J. R.

    2015-12-01

    The scattering and diffusion of energetic charged particles is not only important for understanding phenomena such as diffusive shock acceleration but it also is a natural probe of the statistical characteristics of magnetohydrodynamic (MHD) turbulence. Although Parker's transport equation (Parker 1965) allows us to describe the propagation of charged particles, the transport coefficients needed in the equation must be determined. Using Quasi-Linear Theory (QLT, e.g. Jokipii (1966)), one finds that coefficients can be related to the correlation function or power spectrum of homogeneous magnetic turbulence. However, different turbulence models will generally have a different influence on particle's scattering and diffusion. Among those models developed in MHD Turbulence, such as isotropic, Slab plus 2D (Tu & Marsch 1993; Gray et al 1996; Bieber et al 1996), etc. Here, using test-particle orbit simulations to calculate the transport coefficients, we study particle transport in synthesized asymmetric turbulence using the form first proposed by Goldreich & Sridhar (1995). We developed and introduce a systematic method to synthesize scale-dependent non-isotropic magnetic turbulences. We also developed and introduce a method to synthesize the 3d turbulent magnetic field from the observed solar wind time series dataset. We present the comparison of their effects on charge particle transport with previous theories and models.

  8. Mode-selective vibrational modulation of charge transport in organic electronic devices

    NASA Astrophysics Data System (ADS)

    Bakulin, Artem A.; Lovrincic, Robert; Yu, Xi; Selig, Oleg; Bakker, Huib J.; Rezus, Yves L. A.; Nayak, Pabitra K.; Fonari, Alexandr; Coropceanu, Veaceslav; Brédas, Jean-Luc; Cahen, David

    2015-08-01

    The soft character of organic materials leads to strong coupling between molecular, nuclear and electronic dynamics. This coupling opens the way to influence charge transport in organic electronic devices by exciting molecular vibrational motions. However, despite encouraging theoretical predictions, experimental realization of such approach has remained elusive. Here we demonstrate experimentally that photoconductivity in a model organic optoelectronic device can be modulated by the selective excitation of molecular vibrations. Using an ultrafast infrared laser source to create a coherent superposition of vibrational motions in a pentacene/C60 photoresistor, we observe that excitation of certain modes in the 1,500-1,700 cm-1 region leads to photocurrent enhancement. Excited vibrations affect predominantly trapped carriers. The effect depends on the nature of the vibration and its mode-specific character can be well described by the vibrational modulation of intermolecular electronic couplings. This presents a new tool for studying electron-phonon coupling and charge dynamics in (bio)molecular materials.

  9. Versatile Role of Solvent Additive for Tailoring Morphology in Polymer Solar Cells for Efficient Charge Transport.

    PubMed

    Khatiwada, Devendra; Venkatesan, Swaminathan; Ngo, Evan C; Qiao, Qiquan

    2015-09-01

    In this work role of solvent additive namely 1,8 diiodoctane (DIO) on the nanoscale morphology and its relation with the charge transport of poly(diketopyrrolopyrrole-terthiophene) (PDPP3T):PCBM solar cells has been investigated. Addition of DIO led to enhanced structural ordering as observed from optical measurements. Photovoltaic devices processed with DIO additive showed improved efficiencies due to significant enhancement in short circuit current density. Atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM) images showed that DIO led to finer phase segregation that gave rise to better photovoltaic performance in additive processed active layers. Photoinduced current extraction by linearly increasing voltage (P-CELIV) measurements on PDPP3T:PCBM solar cells revealed higher mobility and extracted charge carrier density for DIO processed devices. PMID:26716280

  10. Charge Transport in Thin Organic Semiconducting Films: Seebeck and Field Effect Studies

    NASA Astrophysics Data System (ADS)

    Böhm, W.; Fritz, T.; Leo, K.

    1997-03-01

    We have investigated the charge transport properties of vapor-deposited thin organic films, using the Seebeck effect for determining conduction type and Fermi energy and the field effect to measure mobility and total charge carrier density. We show that the combination of both techniques gives a complete picture of the electrical properties of the films. Wir untersuchen den Ladungsträgertransport in aufgedampften dünnen organischen Schichten, wobei der Seebeck-Effekt zur Bestimmung des Leitfähigkeitstyps und der Lage des Ferminiveaus und der Feldeffekt zur Bestimmung der Leitfähigkeit und der gesamten Ladungsträgerdichte benutzt wird. Es wird gezeigt, daß durch die Kombination beider Methoden ein geschlossenes Bild der elektrischen Eigenschaften erhalten wird.

  11. Charge and spin transport in PEDOT:PSS nanoscale lateral devices.

    PubMed

    de Oliveira, Thales V A G; Gobbi, Marco; Porro, José M; Hueso, Luis E; Bittner, Alexander M

    2013-11-29

    The electrical transport of the highly conductive poly-(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) is investigated with Ohmic and spin-polarized tunnel contacts at nanoscale lateral dimensions. Temperature-dependent charge transport measurements reveal that electrical conductivity scales non-linearly as a function of electrode spacing, which is attributed to the localization of carriers induced by the disorder introduced by the PSS polyelectrolyte. In addition, we demonstrate the integration of this conducting polymer in nanoscale lateral spin-valve devices by increasing the pH of the PEDOT:PSS solution. We present charge and magnetotransport measurement results of NiFe/AlOx/PEDOT:PSS/AlOx/NiFe lateral structures for various thicknesses of the alumina tunnel barriers. We discuss the absence of magnetoresistance of our spin valves within the framework of Valet-Fert theory, and estimate an upper limit for the spin lifetime of carriers in PEDOT:PSS to τsf ≤ 50 ns. PMID:24177495

  12. Ion Transport Dynamics in Acid Variable Charge Subsoils

    SciTech Connect

    Qafoku, Nik; Sumner, Malcolm E.; Toma, Mitsuru

    2005-06-06

    This is a mini-review of the research work conducted by the authors with the objective of studying ion transport in variable charge subsoils collected from different areas around the world. An attempt is made in these studies to relate the unique behavior manifested during ionic transport in these subsoils with their mineralogical, physical and chemical properties, which are markedly different from those in soils from temperate regions. The variable charge subsoils have a relatively high salt sorption capacity and anion exchange capacity (AEC) that retards anions downward movement. The AEC correlates closely with the anion retardation coefficients. Ca2+ applied with gypsum in topsoil may be transported to the subsoil and may improve the subsoil chemical properties. These results may help in developing appropriate management strategies under a range of mineralogical, physical, and chemical conditions.

  13. Charge Transport in Azobenzene-Based Single-Molecule Junctions

    NASA Astrophysics Data System (ADS)

    Garcia-Lekue, Aran; Kim, Youngsang; Sysoiev, Dmytro; Frederiksen, Thomas; Groth, Ulrich; Scheer, Elke

    2013-03-01

    The azobenzene class of molecules has become an archetype of molecular photoswitch research, due to their simple structure and the significant difference of the electronic system between their cis and trans isomers. However, a detailed understanding of the charge transport for the two isomers, when embedded in a junction with electrodes is still lacking. In order to clarify this issue, we investigate charge transport properties through single Azobenzene-ThioMethyl (AzoTM) molecules in a mechanically controlled break junction (MCBJ) system at 4.2 K. Single-molecule conductance, I-V characteristics, and IETS spectra of molecular junctions are measured and compared with first-principles transport calculations. Our studies elucidate the origin of a slightly higher conductance of junctions with cis isomer and demonstrate that IETS spectra of cis and trans forms show distinct vibrational fingerprints that can be used for identifying the isomer.

  14. Charge transport and ac response under light illumination in gate-modulated DNA molecular junctions.

    PubMed

    Zhang, Yan; Zhu, Wen-Huan; Ding, Guo-Hui; Dong, Bing; Wang, Xue-Feng

    2015-05-22

    Using a two-strand tight-binding model and within nonequilibrium Green's function approach, we study charge transport through DNA sequences (GC)NGC and (GC)1(TA)NTA (GC)3 sandwiched between two Pt electrodes. We show that at low temperature DNA sequence (GC)NGC exhibits coherent charge carrier transport at very small bias, since the highest occupied molecular orbital in the GC base pair can be aligned with the Fermi energy of the metallic electrodes by a gate voltage. A weak distance dependent conductance is found in DNA sequence (GC)1(TA)NTA (GC)3 with large NTA. Different from the mechanism of thermally induced hopping of charges proposed by the previous experiments, we find that this phenomenon is dominated by quantum tunnelling through discrete quantum well states in the TA base pairs. In addition, ac response of this DNA junction under light illumination is also investigated. The suppression of ac conductances of the left and right lead of DNA sequences at some particular frequencies is attributed to the excitation of electrons in the DNA to the lead Fermi surface by ac potential, or the excitation of electrons in deep DNA energy levels to partially occupied energy levels in the transport window. Therefore, measuring ac response of DNA junctions can reveal a wealth of information about the intrinsic dynamics of DNA molecules. PMID:25927276

  15. Charge transport and ac response under light illumination in gate-modulated DNA molecular junctions

    NASA Astrophysics Data System (ADS)

    Zhang, Yan; Zhu, Wen-Huan; Ding, Guo-Hui; Dong, Bing; Wang, Xue-Feng

    2015-05-01

    Using a two-strand tight-binding model and within nonequilibrium Green's function approach, we study charge transport through DNA sequences {{(GC)}{{NGC}}} and {{(GC)}1}{{(TA)}{{NTA}}}{{(GC)}3} sandwiched between two Pt electrodes. We show that at low temperature DNA sequence {{(GC)}{{NGC}}} exhibits coherent charge carrier transport at very small bias, since the highest occupied molecular orbital in the GC base pair can be aligned with the Fermi energy of the metallic electrodes by a gate voltage. A weak distance dependent conductance is found in DNA sequence {{(GC)}1}{{(TA)}{{NTA}}}{{(GC)}3} with large NTA. Different from the mechanism of thermally induced hopping of charges proposed by the previous experiments, we find that this phenomenon is dominated by quantum tunnelling through discrete quantum well states in the TA base pairs. In addition, ac response of this DNA junction under light illumination is also investigated. The suppression of ac conductances of the left and right lead of DNA sequences at some particular frequencies is attributed to the excitation of electrons in the DNA to the lead Fermi surface by ac potential, or the excitation of electrons in deep DNA energy levels to partially occupied energy levels in the transport window. Therefore, measuring ac response of DNA junctions can reveal a wealth of information about the intrinsic dynamics of DNA molecules.

  16. 47 CFR 69.111 - Tandem-switched transport and tandem charge.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 3 2014-10-01 2014-10-01 false Tandem-switched transport and tandem charge. 69... SERVICES (CONTINUED) ACCESS CHARGES Computation of Charges § 69.111 Tandem-switched transport and tandem...-switched transport shall consist of two rate elements, a transmission charge and a tandem switching...

  17. 47 CFR 69.111 - Tandem-switched transport and tandem charge.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 3 2010-10-01 2010-10-01 false Tandem-switched transport and tandem charge. 69... SERVICES (CONTINUED) ACCESS CHARGES Computation of Charges § 69.111 Tandem-switched transport and tandem...-switched transport shall consist of two rate elements, a transmission charge and a tandem switching...

  18. Is Bare Band Description of Carrier Transport Appropriate in Pentacene?

    NASA Astrophysics Data System (ADS)

    Andersen, John D.; Giuggioli, Luca; Kenkre, V. M.

    2002-03-01

    Experiments on injected charges in pentacene single crystals reveal mobilities typical of inorganic semiconductors and temperature dependence (for T<430K) suggesting bandlike behavior.(J. H. Schon, C. Kloc, and B. Batlogg, Phys. Rev. Lett. 86, 3843 (2001)) Polaronic bands, particularly their narrowing with increasing temperature, were invoked(V. M. Kenkre, John D. Andersen, D.H. Dunlap, and C.B. Duke, Phys. Rev. Lett. 62, 1165 (1989)) in the related naphthalene problem.(L. B. Schein, C. B. Duke, and A.R. McGhie, Phys. Rev. Lett. 40, 197 (1978); L. B. Schein, W. Warta, and N. Karl, Chem. Phys. Lett. 100, 34 (1983)) Because the low temperature mobility values in pentacene suggest moderately large bandwidths, we address two questions. Does a bare wide (effectively infinite) band description work for pentacene for T<400K? And, is a bare finite band description compatible with those data? These questions are answered by modifications of a theory originally constructed for inorganic materials and a newly developed mobility theory.

  19. 75 FR 7616 - Mitigation of Carrier Fines for Transporting Aliens Without Proper Documents; Modification of...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-02-22

    ... in the Federal Register (63 FR 23643) on April 30, 1998 as an Appendix to the final regulations... screening procedures'' (63 FR 23644). This provision of the MOU gives CBP flexibility to make appropriate... SECURITY U.S. Customs and Border Protection Mitigation of Carrier Fines for Transporting Aliens...

  20. 14 CFR 382.19 - May carriers refuse to provide transportation on the basis of disability?

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... any passenger on the basis of safety, as provided in 49 U.S.C. 44902 or 14 CFR 121.533, or to any... 14 Aeronautics and Space 4 2011-01-01 2011-01-01 false May carriers refuse to provide transportation on the basis of disability? 382.19 Section 382.19 Aeronautics and Space OFFICE OF THE...

  1. 14 CFR 382.19 - May carriers refuse to provide transportation on the basis of disability?

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... any passenger on the basis of safety, as provided in 49 U.S.C. 44902 or 14 CFR 121.533, or to any... 14 Aeronautics and Space 4 2014-01-01 2014-01-01 false May carriers refuse to provide transportation on the basis of disability? 382.19 Section 382.19 Aeronautics and Space OFFICE OF THE...

  2. 14 CFR 382.19 - May carriers refuse to provide transportation on the basis of disability?

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... any passenger on the basis of safety, as provided in 49 U.S.C. 44902 or 14 CFR 121.533, or to any... 14 Aeronautics and Space 4 2012-01-01 2012-01-01 false May carriers refuse to provide transportation on the basis of disability? 382.19 Section 382.19 Aeronautics and Space OFFICE OF THE...

  3. Photogenerated carriers transport behaviors in L-cysteine capped ZnSe core-shell quantum dots

    NASA Astrophysics Data System (ADS)

    Shan, Qingsong; Li, Kuiying; Xue, Zhenjie; Lin, Yingying; Yin, Hua; Zhu, Ruiping

    2016-02-01

    The photoexcited carrier transport behavior of zinc selenide (ZnSe) quantum dots (QDs) with core-shell structure is studied because of their unique photoelectronic characteristics. The surface photovoltaic (SPV) properties of self-assembled ZnSe/ZnS/L-Cys core-shell QDs were probed via electric field induced surface photovoltage and transient photovoltage (TPV) measurements supplemented by Fourier transform infrared, laser Raman, absorption, and photoluminescence spectroscopies. The ZnSe QDs displayed p-type SPV characteristics with a broader stronger SPV response over the whole ultraviolet-to-near-infrared range compared with those of other core-shell QDs in the same group. The relationship between the SPV phase value of the QDs and external bias was revealed in their SPV phase spectrum. The wide transient photovoltage response region from 3.3 × 10-8 to 2 × 10-3 s was closely related to the long diffusion distance of photoexcited free charge carriers in the interfacial space-charge region of the QDs. The strong SPV response corresponding to the ZnSe core mainly originated from an obvious quantum tunneling effect in the QDs.

  4. Charge transport in 4H-SiC detector structures under conditions of a high electric field

    SciTech Connect

    Ivanov, A. M. Mynbaeva, M. G.; Sadokhin, A. V.; Strokan, N. B.; Lebedev, A. A.

    2009-08-15

    Transport of nonequilibrium charge packets in a structure with a Schottky barrier fabricated on a CVD-grown n-4H-SiC film has been studied at the maximum strength of an electric field at 1.1 MV/cm. The charge was introduced by separate {alpha}-particles and recorded by nuclear spectrometric techniques. A superlinear rise in the recorded charge as a function of the reverse bias applied to the structure was observed. Simultaneously, and also superlinearly increased the scatter in the spectrum of the charge amplitude. The observed effect is attributed to the initial stage of impact ionization. The manifestation of the process at unconventionally low fields ({approx}1 MV/cm) is accounted for by specific features of the process of charge generation. Carriers generated by slowing-down {alpha}-particles are 'hot' from the very beginning.

  5. Monte Carlo modeling of the spatially dispersive carrier transport in P3HT and P3HT:PCBM blends

    NASA Astrophysics Data System (ADS)

    Jiang, Xin

    2009-10-01

    The presence of traps, arising from morpohological or chemical defects, can be critical to the performance of organic semiconductor devices. Traps can reduce the charge carrier mobility, disturb the internal electrical field, drive recombination, and reduce the overall device efficiency as well as operational stability. In this work, we investigate the role of traps in determining charge transport properties of organic semiconductors and blends such as P3HT and P3HT:PCBM through Monte-Carlo (MC) simulations in conjunction with time-of-flight (TOF) mobility measurements. We employ a Marcus theory description of individual hopping events based on the molecular reorganization energy (lambda) for the MC simulations. Trap states are modeled as diffuse bands that reside at some energy away from the main transport band. This model is used to simulate TOF transients, and the results are compared to experimental data. As is expected from the Marcus theory equation, the mobility is seen to be maximum for an optimal value of lambda. This optimal value is strongly field dependent, but is found to be independent of the trap density. In comparing MC simulations with TOF data, it is found that inclusion of traps results in a much better fit to the data and provides for a mechanism to simulate dispersive transport with a long tail resulting from trapping and detrapping of carriers before they exit the device. We present results for a range of trap densities and statistical distributions and discuss the implications on the operation of bulk heterojunction organic photovoltaic devices.

  6. Microscopic observation of carrier-transport dynamics in quantum-structure solar cells using a time-of-flight technique

    SciTech Connect

    Toprasertpong, Kasidit; Fujii, Hiromasa; Sugiyama, Masakazu; Nakano, Yoshiaki; Kasamatsu, Naofumi; Kada, Tomoyuki; Asahi, Shigeo; Kita, Takashi; Wang, Yunpeng; Watanabe, Kentaroh

    2015-07-27

    In this study, we propose a carrier time-of-flight technique to evaluate the carrier transport time across a quantum structure in an active region of solar cells. By observing the time-resolved photoluminescence signal with a quantum-well probe inserted under the quantum structure at forward bias, the carrier transport time can be efficiently determined at room temperature. The averaged drift velocity shows linear dependence on the internal field, allowing us to estimate the quantum structure as a quasi-bulk material with low effective mobility containing the information of carrier dynamics. We show that this direct and real-time observation is more sensitive to carrier transport than other conventional techniques, providing better insights into microscopic carrier transport dynamics to overcome a device design difficulty.

  7. 950809 Charged particle transport updated multi-group diffusion

    SciTech Connect

    Corman, E.G.; Perkins, S.T.; Dairiki, N.T.

    1995-09-01

    In 1974, a charged particle transport scheme was introduced which utilized a multi-group diffusion method for the spatial transport and slowing down of energetic ions in a hot plasma. In this treatment a diffusion coefficient was used which was flux-limited to provide, hopefully, some degree of accuracy when the slowing down of an energetic charged particle is dominated by Coulomb collisions with thermal ions and electrons in a plasma medium. An advantage of this method was a very fast, memory-contained program for calculating the behavior of energetic charged particles which resulted in smoothly varying particle number densities and energy depositions. The main limitation of the original multi-group charged particle diffusion scheme is its constraint to a basic ten group structure; the same ten group structure for each of the five energetic ions tracked. This is regarded as a severe limitation, inasmuch as more groups would be desired to simulate more accurately the corresponding Monte Carlo results of energies deposited over spatial zones from a charged particle source. More generally, it seems preferable to have a different group structure for each particle type since they are created at inherently different energies. In this paper, the basic theory and multi-group description will be given. This is followed by the specific techniques that were used to solve the resultant equations. Finally, the modifications that were made to the cross section data as well as the methods used for energy and momentum deposition are described.

  8. Surface-charge-governed electrolyte transport in carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Xue, Jian-Ming; Guo, Peng; Sheng, Qian

    2015-08-01

    The transport behavior of pressure-driven aqueous electrolyte solution through charged carbon nanotubes (CNTs) is studied by using molecular dynamics simulations. The results reveal that the presence of charges around the nanotube can remarkably reduce the flow velocity as well as the slip length of the aqueous solution, and the decreasing of magnitude depends on the number of surface charges and distribution. With 1-M KCl solution inside the carbon nanotube, the slip length decreases from 110 nm to only 14 nm when the number of surface charges increases from 0 to 12 e. This phenomenon is attributed to the increase of the solid-liquid friction force due to the electrostatic interaction between the charges and the electrolyte particles, which can impede the transports of water molecules and electrolyte ions. With the simulation results, we estimate the energy conversion efficiency of nanofluidic battery based on CNTs, and find that the highest efficiency is only around 30% but not 60% as expected in previous work. Project supported by the National Natural Science Foundation of China (Grant Nos. 11375031 and 11335003).

  9. On the generation of charge-carrier recombination centers in the sapphire substrates of silicon-on-sapphire structures

    SciTech Connect

    Aleksandrov, P. A. Belova, N. E.; Demakov, K. D.; Shemardov, S. G.

    2015-08-15

    A method for the production of high-quality radiation-resistant silicon-on-sapphire structures through the fabrication of a layer of nanopores in sapphire by helium ion implantation, i.e., by creating charge-carrier recombination centers, is proposed. In this case, the quality of the silicon layer is simultaneously improved. The problem of the thermal stability of the pores is discussed with the aim of analyzing the possibility of producing a microcircuit on the resultant modified silicon-on-sapphire sample. The layer of pores possesses a large total surface area and, hence, decreases the lifetime of charge carriers generated during irradiation of the operating microcircuit. This effect reduces the charge at the silicon-sapphire interface and improves radiation resistance.

  10. Ion-mediated charge transport in ionomeric electrolytes.

    PubMed

    Lu, Keran; Maranas, Janna K; Milner, Scott T

    2016-05-01

    Ionomers, or single-ion conductors, serve as a model system to study ion transport in polymeric systems. Conductivity is a system property that depends on the net charge transport in the system. The mechanism through which ions are transported can dramatically change the contribution of an ion's self-motion (i.e. diffusion coefficient) to the conductivity of the system. For example, positive and negative ions diffusing as a pair have no net contribution to conductivity. In a coarse-grained molecular dynamics simulation of sodium-neutralized poly(PEO-co-sulfoisophthalate), we show that ion transport is mediated through consecutive coordination with ion pairs and higher order clusters due to the high density of ions. This transport mechanism is highly efficient and shows evidence of cation relaying. We show that larger ion aggregates can serve as ion-conducting paths for positive charges, and demonstrate how a highly ordered ion aggregate network can improve conductivity by enhancing correlated ion transport. PMID:27019986

  11. Intermediate tunnelling-hopping regime in DNA charge transport

    NASA Astrophysics Data System (ADS)

    Xiang, Limin; Palma, Julio L.; Bruot, Christopher; Mujica, Vladimiro; Ratner, Mark A.; Tao, Nongjian

    2015-03-01

    Charge transport in molecular systems, including DNA, is involved in many basic chemical and biological processes, and its understanding is critical if they are to be used in electronic devices. This important phenomenon is often described as either coherent tunnelling over a short distance or incoherent hopping over a long distance. Here, we show evidence of an intermediate regime where coherent and incoherent processes coexist in double-stranded DNA. We measure charge transport in single DNA molecules bridged to two electrodes as a function of DNA sequence and length. In general, the resistance of DNA increases linearly with length, as expected for incoherent hopping. However, for DNA sequences with stacked guanine-cytosine (GC) base pairs, a periodic oscillation is superimposed on the linear length dependence, indicating partial coherent transport. This result is supported by the finding of strong delocalization of the highest occupied molecular orbitals of GC by theoretical simulation and by modelling based on the Büttiker theory of partial coherent charge transport.

  12. Intermediate tunnelling-hopping regime in DNA charge transport.

    PubMed

    Xiang, Limin; Palma, Julio L; Bruot, Christopher; Mujica, Vladimiro; Ratner, Mark A; Tao, Nongjian

    2015-03-01

    Charge transport in molecular systems, including DNA, is involved in many basic chemical and biological processes, and its understanding is critical if they are to be used in electronic devices. This important phenomenon is often described as either coherent tunnelling over a short distance or incoherent hopping over a long distance. Here, we show evidence of an intermediate regime where coherent and incoherent processes coexist in double-stranded DNA. We measure charge transport in single DNA molecules bridged to two electrodes as a function of DNA sequence and length. In general, the resistance of DNA increases linearly with length, as expected for incoherent hopping. However, for DNA sequences with stacked guanine-cytosine (GC) base pairs, a periodic oscillation is superimposed on the linear length dependence, indicating partial coherent transport. This result is supported by the finding of strong delocalization of the highest occupied molecular orbitals of GC by theoretical simulation and by modelling based on the Büttiker theory of partial coherent charge transport. PMID:25698331

  13. 41 CFR 301-72.1 - Why is common carrier presumed to be the most advantageous method of transportation?

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 41 Public Contracts and Property Management 4 2010-07-01 2010-07-01 false Why is common carrier presumed to be the most advantageous method of transportation? 301-72.1 Section 301-72.1 Public Contracts... Transportation § 301-72.1 Why is common carrier presumed to be the most advantageous method of...

  14. 41 CFR 301-72.1 - Why is common carrier presumed to be the most advantageous method of transportation?

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 41 Public Contracts and Property Management 4 2011-07-01 2011-07-01 false Why is common carrier presumed to be the most advantageous method of transportation? 301-72.1 Section 301-72.1 Public Contracts... Transportation § 301-72.1 Why is common carrier presumed to be the most advantageous method of...

  15. 41 CFR 301-72.100 - What must my travel accounting system do in relation to common carrier transportation?

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 41 Public Contracts and Property Management 4 2010-07-01 2010-07-01 false What must my travel accounting system do in relation to common carrier transportation? 301-72.100 Section 301-72.100 Public... for Common Carrier Transportation § 301-72.100 What must my travel accounting system do in relation...

  16. Rational design of charge transport molecules for blue organic light emitting devices

    NASA Astrophysics Data System (ADS)

    Padmaperuma, Asanga; Cosimbescu, Lelia; Koech, Phillip; Polikarpov, Evgueni; Swensen, James; Gaspar, Daniel

    2012-02-01

    The efficiency and stability of blue OLEDs continue to be the primary roadblock to developing organic solid-state white lighting as well as power efficient displays. It is generally accepted that such high quantum efficiency can be achieved with the use of organometallic phosphor doped OLEDs. The transport layers can be designed to increase the carrier density as a way to reduce the drive voltage. We have developed a comprehensive library of charge transporting molecules using combination of theoretical modeling and experimental evidence. Our work focuses on using chemical structure design and computational methods to develop host, transport, emitter, and blocking materials for high efficiency blue OLEDs, along with device architectures to take advantage of these new materials. Through chemical modification of materials we are able to influence both the charge balance and emission efficiency of OLEDs, and understand the influence of the location of photon emission in OLEDs as a function of minor chemical modifications of host and electron transport materials. Design rules, structure-property relationships and results from state of the art OLEDs will be presented.

  17. Spatial localization of excitons and charge carriers in hybrid perovskite thin films

    SciTech Connect

    Simpson, Mary Jane; Doughty, Benjamin; Yang, Bin; Xiao, Kai; Ma, Ying -Zhong

    2015-07-21

    The fundamental photophysics underlying the remarkably high power conversion efficiency of organic-inorganic hybrid perovskite-based solar cells has been increasingly studied using complementary spectroscopic techniques. The spatially heterogeneous polycrystalline morphology of the photoactive layers owing to the presence of distinct crystalline grains has been generally neglected in optical measurements and therefore the reported results are typically averaged over hundreds or even thousands of such grains. Here, we apply femtosecond transient absorption microscopy to spatially and temporally probe ultrafast electronic excited-state dynamics in pristine methylammonium lead tri-iodide (CH3NH3PbI3) thin films and composite structures. We found that the electronic excited-state relaxation kinetics are extremely sensitive to the sample location probed, which was manifested by position-dependent decay timescales and transient signals. As a result, analysis of transient absorption kinetics acquired at distinct spatial positions enabled us to identify contributions of excitons and free charge carriers.

  18. Computational Confirmation of the Carrier for the "XCN" Interstellar Ice Bank: OCN(-) Charge Transfer Complexes

    NASA Technical Reports Server (NTRS)

    Park, J.-Y.; Woon, D. E.

    2004-01-01

    Recent experimental studies provide evidence that carrier for the so-called XCN feature at 2165 cm(exp -1) (4.62 micron) in young stellar objects is an OCN(-)/NH4(+) charge transfer (CT) complex that forms in energetically processed interstellar icy grain mantles. Although other RCN nitriles and RCN iosonitriles have been considered, Greenberg's conjecture that OCN(-) is associated with the XCN feature has persisted for over 15 years. In this work we report a computational investigation that thoroughly confirms the hypothesis that the XCN feature observed in laboratory studies can result from OCN(-)/NH4(+) CT complexes arising from HNCO and NH3, in a water ice environment. Density functional theory calculations with theory calculations with HNCO, NH3, and up to 12 waters reproduce seven spectroscopic measurements associated with XCN: the band origin of the asymmetric stretching mode of OCN(-), shifts due to isotopic substitutions of C, N, O, and H, and two weak features. However, very similar values are also found for the OCN(-)/NH4(+) CT complex arising from HOCN and NH3. In both cases, the complex forms by barrierless proton transfer from HNCO or HOCN to NH3 during the optimization of the solvated system. Scaled B3LYP/6-31+G** harmonic frequencies for HNCO and HOCN cases are 2181 and 2202 cm(exp -1), respectively.

  19. Spatial localization of excitons and charge carriers in hybrid perovskite thin films

    DOE PAGESBeta

    Simpson, Mary Jane; Doughty, Benjamin; Yang, Bin; Xiao, Kai; Ma, Ying -Zhong

    2015-07-21

    The fundamental photophysics underlying the remarkably high power conversion efficiency of organic-inorganic hybrid perovskite-based solar cells has been increasingly studied using complementary spectroscopic techniques. The spatially heterogeneous polycrystalline morphology of the photoactive layers owing to the presence of distinct crystalline grains has been generally neglected in optical measurements and therefore the reported results are typically averaged over hundreds or even thousands of such grains. Here, we apply femtosecond transient absorption microscopy to spatially and temporally probe ultrafast electronic excited-state dynamics in pristine methylammonium lead tri-iodide (CH3NH3PbI3) thin films and composite structures. We found that the electronic excited-state relaxation kinetics aremore » extremely sensitive to the sample location probed, which was manifested by position-dependent decay timescales and transient signals. As a result, analysis of transient absorption kinetics acquired at distinct spatial positions enabled us to identify contributions of excitons and free charge carriers.« less

  20. Heterodimensional charge-carrier confinement in stacked submonolayer InAs in GaAs

    NASA Astrophysics Data System (ADS)

    Harrison, S.; Young, M. P.; Hodgson, P. D.; Young, R. J.; Hayne, M.; Danos, L.; Schliwa, A.; Strittmatter, A.; Lenz, A.; Eisele, H.; Pohl, U. W.; Bimberg, D.

    2016-02-01

    Charge-carrier confinement in nanoscale In-rich agglomerations within a lateral InGaAs quantum well (QW) formed from stacked submonolayers (SMLs) of InAs in GaAs is studied. Low-temperature photoluminescence (PL) and magneto-PL clearly demonstrate strong vertical and weak lateral confinement, yielding two-dimensional (2D) excitons. In contrast, high-temperature (400 K) magneto-PL reveals excited states that fit a Fock-Darwin spectrum, characteristic of a zero-dimensional (0D) system in a magnetic field. This paradox is resolved by concluding that the system is heterodimensional: the light electrons extend over several In-rich agglomerations and see only the lateral InGaAs QW, i.e., are 2D, while the heavier holes are confined within the In-rich agglomerations, i.e., are 0D. This description is supported by single-particle effective-mass and eight-band k .p calculations. We suggest that the heterodimensional nature of nanoscale SML inclusions is fundamental to the ability of respective optoelectronic devices to operate efficiently and at high speed.

  1. Ruthenium cation substitutional doping for efficient charge carrier transfer in organic/inorganic hybrid solar cells

    NASA Astrophysics Data System (ADS)

    Kong, Degui; Jin, Xiao; Sun, Weifu; Du, Jiaxing; Tong, Jifeng; Chen, Changyong; Yang, Xuwei; Cheng, Yuanyuan; Li, Qinghua

    2015-01-01

    Solution-processed organic/inorganic hybrid solar cells have emerged as a new platform for low-cost optoelectronics. At the heart of photovoltaic devices lies the matching of a junction, which requires the suitable energy level alignment of n-type and p-type semiconductors. Incorporating foreign ions into bulk semiconductors has been largely employed for many decades, yet electronically active doping in energy level control of the hybrid bulk heterojunctions has been rarely involved and the demonstration of robust functional optoelectronic devices had thus far been elusive. Herein, we introduce Ru ions into TiO2 to decorate the energy level of the acceptor to gain better energy level alignment between the donor and acceptor. By reducing the 'excess' energy offset between the n-type and p-type semiconductors, the electron transfer becomes faster, thus leading to a notable enhancement in power conversion efficiency, i.e., from 2.20% to 2.89%. The results demonstrate that the energy level can be controlled effectively by the versatile Ru dopants. This work opens an effective route for accelerating the charge carrier transfer at the interface and achieving high-performance organic/inorganic hybrid optoelectronic devices.

  2. Modulation of phase behaviors and charge carrier mobilities by linkage length in discotic liquid crystal dimers.

    PubMed

    Wang, Yi-Fei; Zhang, Chun-Xiu; Wu, Hao; Zhang, Ao; Wang, Jian-Chuang; Zhang, Shuai-Feng; Pu, Jia-Ling

    2015-01-28

    A clear structure-property relationship was revealed in a series of triphenylene-based dimers, which contained two triphenylene nuclei each bearing five β-OC4H9 substituents and are linked through a flexible O(CH2)nO polymethylene chain (n=6-12). Dimers with the linkage close to twice the length of the free side chains (n=8, 9) exhibited a single Colhp phase, while others with the linkage shorter (n=6, 7) or longer (n=10, 11, 12) showed multiphase behaviors with a transition from the Colhp phase to Colh phase; hole mobilities of Colhp phases reached 1.4×10(-2) cm2 V(-1) s(-1) in the dimer for which the linkage is exactly twice the length of the free side chains (n=8), and decreased regularly both with linkage length becoming shorter or longer. This modulation of phase behaviors and charge carrier mobilities was demonstrated to be generated by various steric perturbations introduced by linkages with different lengths, which result in different degrees of lateral fluctuations of discotic moieties in the columns. PMID:25467212

  3. Specific features of intervalley scattering of charge carriers in n-Si at high temperatures

    SciTech Connect

    Fedosov, A. V.; Luniov, S. V.; Fedosov, S. A.

    2010-10-15

    In n-Si, intervalley scattering of electrons can be of two types, f scattering and g scattering. With the purpose of establishing the contributions of f- and g-type transitions to intervalley scattering, the piezoresistance of n-Si crystals is studied in the temperature range T = 295-363 K. The initial concentration of charge carriers in the n-Si samples is 1.1 x 10{sup 14} cm{sup -3}, and the resistivity at 300 K is {rho} = 30 {Omega} cm. As the temperature is increased, the region of leveling-off of the piezoresistance shifts to lower voltages. The characteristic feature of the dependence {rho} = {rho}(T) plotted in the double logarithmic coordinates (log{rho} = f(logT)) is the transition from the slope 1.68 to the slope 1.83 at T > 330 K. This is attributed to the substantial contribution of g transitions to intervalley scattering in the high-temperature region. For verification of the interpretation of the dependence {rho} = {rho}(T), the dependence is calculated on the basis of the theory of anisotropic scattering with consideration for intervalley transitions.

  4. Understanding charge carrier relaxation processes in terbium arsenide nanoparticles using transient absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Vanderhoef, Laura R.

    Erbium arsenide nanoparticles epitaxially grown within III-V semiconductors have been shown to improve the performance of devices for applications ranging from thermoelectrics to THz pulse generation. The small size of rare-earth nanoparticles suggests that interesting electronic properties might emerge as a result of both spatial confinement and surface states. However, ErAs nanoparticles do not exhibit any signs of quantum confinement or an emergent bandgap, and these experimental observations are understood from theory. The incorporation of other rare-earth monopnictide nanoparticles into III-V hosts is a likely path to engineering carrier excitation, relaxation and transport dynamics for optoelectronic device applications. However, the electronic structure of these other rare-earth monopnictide nanoparticles remains poorly understood. The objective of this research is to explore the electronic structure and optical properties of III-V materials containing novel rare-earth monopnictides. We use ultrafast pump-probe spectroscopy to investigate the electronic structure of TbAs nanoparticles in III-V hosts. We start with TbAs:GaAs, which was expected to be similar to ErAs:GaAs. We study the dynamics of carrier relaxation into the TbAs states using optical pump terahertz probe transient absorption spectroscopy. By analyzing how the carrier relaxation rates depend on pump fluence and sample temperature, we conclude that the TbAs states are saturable. Saturable traps suggest the existence of a bandgap for TbAs nanoparticles, in sharp contrast with previous results for ErAs. We then apply the same experimental technique to two samples of TbAs nanoparticles in InGaAs with different concentrations of TbAs. We observe similar relaxation dynamics associated with trap saturation, though the ability to resolve these processes is contingent upon a high enough TbAs concentration in the sample. We have also constructed an optical pump optical probe transient absorption

  5. Efficient, non-toxic anion transport by synthetic carriers in cells and epithelia.

    PubMed

    Li, Hongyu; Valkenier, Hennie; Judd, Luke W; Brotherhood, Peter R; Hussain, Sabir; Cooper, James A; Jurček, Ondřej; Sparkes, Hazel A; Sheppard, David N; Davis, Anthony P

    2016-01-01

    Transmembrane anion transporters (anionophores) have potential for new modes of biological activity, including therapeutic applications. In particular they might replace the activity of defective anion channels in conditions such as cystic fibrosis. However, data on the biological effects of anionophores are scarce, and it remains uncertain whether such molecules are fundamentally toxic. Here, we report a biological study of an extensive series of powerful anion carriers. Fifteen anionophores were assayed in single cells by monitoring anion transport in real time through fluorescence emission from halide-sensitive yellow fluorescent protein. A bis-(p-nitrophenyl)ureidodecalin shows especially promising activity, including deliverability, potency and persistence. Electrophysiological tests show strong effects in epithelia, close to those of natural anion channels. Toxicity assays yield negative results in three cell lines, suggesting that promotion of anion transport may not be deleterious to cells. We therefore conclude that synthetic anion carriers are realistic candidates for further investigation as treatments for cystic fibrosis. PMID:26673261

  6. Efficient, non-toxic anion transport by synthetic carriers in cells and epithelia

    NASA Astrophysics Data System (ADS)

    Li, Hongyu; Valkenier, Hennie; Judd, Luke W.; Brotherhood, Peter R.; Hussain, Sabir; Cooper, James A.; Jurček, Ondřej; Sparkes, Hazel A.; Sheppard, David N.; Davis, Anthony P.

    2016-01-01

    Transmembrane anion transporters (anionophores) have potential for new modes of biological activity, including therapeutic applications. In particular they might replace the activity of defective anion channels in conditions such as cystic fibrosis. However, data on the biological effects of anionophores are scarce, and it remains uncertain whether such molecules are fundamentally toxic. Here, we report a biological study of an extensive series of powerful anion carriers. Fifteen anionophores were assayed in single cells by monitoring anion transport in real time through fluorescence emission from halide-sensitive yellow fluorescent protein. A bis-(p-nitrophenyl)ureidodecalin shows especially promising activity, including deliverability, potency and persistence. Electrophysiological tests show strong effects in epithelia, close to those of natural anion channels. Toxicity assays yield negative results in three cell lines, suggesting that promotion of anion transport may not be deleterious to cells. We therefore conclude that synthetic anion carriers are realistic candidates for further investigation as treatments for cystic fibrosis.

  7. Charge transport in organic multi-layer devices under electric and optical fields

    NASA Astrophysics Data System (ADS)

    Park, June Hyoung

    2007-12-01

    Charge transport in small organic molecules and conjugated conducting polymers under electric or optical fields is studied by using field effect transistors and photo-voltaic cells with multiple thin layers. With these devices, current under electric field, photo-current under optical field, and luminescence of optical materials are measured to characterize organic and polymeric materials. For electric transport studies, poly(3,4-ethylenedioxythiophene) doped by polystyrenesulfonic acid is used, which is conductive with conductivity of approximately 25 S/cm. Despite their high conductance, field effect transistors based on the films are successfully built and characterized by monitoring modulations of drain current by gate voltage and IV characteristic curves. Due to very thin insulating layers of poly(vinylphenol), the transistors are relative fast under small gate voltage variation although heavy ions are involved in charge transport. In IV characteristic curves, saturation effects can be observed. Analysis using conventional field effect transistor model indicates high mobility of charge carriers, 10 cm2/V·sec, which is not consistent with the mobility of the conducting polymer. It is proposed that the effect of a small density of ions injected via polymer dielectric upon application of gate voltage and the ion compensation of key hopping sites accounts for the operation of the field effect transistors. For the studies of transport under optical field, photovoltaic cells with 3 different dendrons, which are efficient to harvest photo-excited electrons, are used. These dendrons consist of two electron-donors (tetraphenylporphyrin) and one electron-accepter (naphthalenediimide). Steady-state fluorescence measurements show that inter-molecular interaction is dominant in solid dendron film, although intra-molecular interaction is still present. Intra-molecular interaction is suggested by different fluorescence lifetimes between solutions of donor and dendrons. This

  8. Charge Transport and Structural Dynamics in Deep Eutectic Mixtures

    NASA Astrophysics Data System (ADS)

    Cosby, Tyler; Holt, Adam; Terheggen, Logan; Griffin, Philip; Benson, Roberto; Sangoro, Joshua

    2015-03-01

    Charge transport and structural dynamics in a series of imidazole and carboxylic acid-based deep eutectic mixtures are investigated by broadband dielectric spectroscopy, dynamic light scattering, 1H nuclear magnetic resonance spectroscopy, calorimetry, and Fourier transform infrared spectroscopy. It is found that the extended hydrogen-bonded networks characteristic of imidazoles are broken down upon addition of carboxylic acids, resulting in an increase in dc conductivity of the mixtures. These results are discussed within the framework of recent theories of hydrogen bonding and proton transport.

  9. Effect of charge trapping on effective carrier lifetime in compound semiconductors: High resistivity CdZnTe

    SciTech Connect

    Kamieniecki, Emil

    2014-11-21

    The dominant problem limiting the energy resolution of compound semiconductor based radiation detectors is the trapping of charge carriers. The charge trapping affects energy resolution through the carrier lifetime more than through the mobility. Conventionally, the effective carrier lifetime is determined using a 2-step process based on measurement of the mobility-lifetime product (μτ) and determining drift mobility using time-of-flight measurements. This approach requires fabrication of contacts on the sample. A new RF-based pulse rise-time method, which replaces this 2-step process with a single non-contact direct measurement, is discussed. The application of the RF method is illustrated with high-resistivity detector-grade CdZnTe crystals. The carrier lifetime in the measured CdZnTe, depending on the quality of the crystals, was between about 5 μs and 8 μs. These values are in good agreement with the results obtained using conventional 2-step approach. While the effective carrier lifetime determined from the initial portion of the photoresponse transient combines both recombination and trapping in a manner similar to the conventional 2-step approach, both the conventional and the non-contact RF methods offer only indirect evaluation of the effect of charge trapping in the semiconductors used in radiation detectors. Since degradation of detector resolution is associated not with trapping but essentially with detrapping of carriers, and, in particular, detrapping of holes in n-type semiconductors, it is concluded that evaluation of recombination and detrapping during photoresponse decay is better suited for evaluation of compound semiconductors used in radiation detectors. Furthermore, based on previously reported data, it is concluded that photoresponse decay in high resistivity CdZnTe at room temperature is dominated by detrapping of carriers from the states associated with one type of point defect and by recombination of carriers at one type of

  10. Charge transport properties of CdMnTe radiation detectors

    SciTech Connect

    Kim K.; Rafiel, R.; Boardman, M.; Reinhard, I.; Sarbutt, A.; Watt, G.; Watt, C.; Uxa, S.; Prokopovich, D.A.; Belas, E.; Bolotnikov, A.E.; James, R.B.

    2012-04-11

    Growth, fabrication and characterization of indium-doped cadmium manganese telluride (CdMnTe)radiation detectors have been described. Alpha-particle spectroscopy measurements and time resolved current transient measurements have yielded an average charge collection efficiency approaching 100 %. Spatially resolved charge collection efficiency maps have been produced for a range of detector bias voltages. Inhomogeneities in the charge transport of the CdMnTe crystals have been associated with chains of tellurium inclusions within the detector bulk. Further, it has been shown that the role of tellurium inclusions in degrading chargecollection is reduced with increasing values of bias voltage. The electron transit time was determined from time of flight measurements. From the dependence of drift velocity on applied electric field the electron mobility was found to be n = (718 55) cm2/Vs at room temperature.

  11. Kinetics of optically excited charge carriers at the GaN surface: Influence of catalytic Pt nanostructures

    NASA Astrophysics Data System (ADS)

    Winnerl, Andrea; Pereira, Rui N.; Stutzmann, Martin

    2015-10-01

    In this work, we use GaN with different deposited Pt nanostructures as a controllable model system to investigate the kinetics of photo-generated charge carriers in hybrid photocatalysts. We combine conductance and contact potential difference measurements to investigate the influence of Pt on the processes involved in the capture and decay of photo-generated charge carriers at and close to the GaN surface. We found that in the presence of Pt nanostructures the photo-excitation processes are similar to those found in Pt free GaN. However, in GaN with Pt nanostructures, photo-generated holes are preferentially trapped in surface states of the GaN covered with Pt and/or in electronic states of the Pt and lead to an accumulation of positive charge there, whereas negative charge is accumulated in localized states in a shallow defect band of the GaN covered with Pt. This preferential accumulation of photo-generated electrons close to the surface is responsible for a dramatic acceleration of the turn-off charge transfer kinetics and a stronger dependence of the surface photovoltage on light intensity when compared to a Pt free GaN surface. Our study shows that in hybrid photocatalysts, the metal nanostructures induce a spatially inhomogeneous surface band bending of the semiconductor that promotes a lateral drift of photogenerated charges towards the catalytic nanostructures.

  12. Kinetics of optically excited charge carriers at the GaN surface: Influence of catalytic Pt nanostructures

    SciTech Connect

    Winnerl, Andrea Pereira, Rui N.; Stutzmann, Martin

    2015-10-21

    In this work, we use GaN with different deposited Pt nanostructures as a controllable model system to investigate the kinetics of photo-generated charge carriers in hybrid photocatalysts. We combine conductance and contact potential difference measurements to investigate the influence of Pt on the processes involved in the capture and decay of photo-generated charge carriers at and close to the GaN surface. We found that in the presence of Pt nanostructures the photo-excitation processes are similar to those found in Pt free GaN. However, in GaN with Pt nanostructures, photo-generated holes are preferentially trapped in surface states of the GaN covered with Pt and/or in electronic states of the Pt and lead to an accumulation of positive charge there, whereas negative charge is accumulated in localized states in a shallow defect band of the GaN covered with Pt. This preferential accumulation of photo-generated electrons close to the surface is responsible for a dramatic acceleration of the turn-off charge transfer kinetics and a stronger dependence of the surface photovoltage on light intensity when compared to a Pt free GaN surface. Our study shows that in hybrid photocatalysts, the metal nanostructures induce a spatially inhomogeneous surface band bending of the semiconductor that promotes a lateral drift of photogenerated charges towards the catalytic nanostructures.

  13. Remarkable enhancement of charge carrier mobility of conjugated polymer field-effect transistors upon incorporating an ionic additive.

    PubMed

    Luo, Hewei; Yu, Chenmin; Liu, Zitong; Zhang, Guanxin; Geng, Hua; Yi, Yuanping; Broch, Katharina; Hu, Yuanyuan; Sadhanala, Aditya; Jiang, Lang; Qi, Penglin; Cai, Zhengxu; Sirringhaus, Henning; Zhang, Deqing

    2016-05-01

    Organic semiconductors with high charge carrier mobilities are crucial for flexible electronic applications. Apart from designing new conjugated frameworks, different strategies have been explored to increase charge carrier mobilities. We report a new and simple approach to enhancing the charge carrier mobility of DPP-thieno[3,2-b]thiophene-conjugated polymer by incorporating an ionic additive, tetramethylammonium iodide, without extra treatments into the polymer. The resulting thin films exhibit a very high hole mobility, which is higher by a factor of 24 than that of thin films without the ionic additive under the same conditions. On the basis of spectroscopic grazing incidence wide-angle x-ray scattering and atomic force microscopy studies as well as theoretical calculations, the remarkable enhancement of charge mobility upon addition of tetramethylammonium iodide is attributed primarily to an inhibition of the torsion of the alkyl side chains by the presence of the ionic species, facilitating a more ordered lamellar packing of the alkyl side chains and interchain π-π interactions. PMID:27386541

  14. Remarkable enhancement of charge carrier mobility of conjugated polymer field-effect transistors upon incorporating an ionic additive

    PubMed Central

    Luo, Hewei; Yu, Chenmin; Liu, Zitong; Zhang, Guanxin; Geng, Hua; Yi, Yuanping; Broch, Katharina; Hu, Yuanyuan; Sadhanala, Aditya; Jiang, Lang; Qi, Penglin; Cai, Zhengxu; Sirringhaus, Henning; Zhang, Deqing

    2016-01-01

    Organic semiconductors with high charge carrier mobilities are crucial for flexible electronic applications. Apart from designing new conjugated frameworks, different strategies have been explored to increase charge carrier mobilities. We report a new and simple approach to enhancing the charge carrier mobility of DPP-thieno[3,2-b]thiophene–conjugated polymer by incorporating an ionic additive, tetramethylammonium iodide, without extra treatments into the polymer. The resulting thin films exhibit a very high hole mobility, which is higher by a factor of 24 than that of thin films without the ionic additive under the same conditions. On the basis of spectroscopic grazing incidence wide-angle x-ray scattering and atomic force microscopy studies as well as theoretical calculations, the remarkable enhancement of charge mobility upon addition of tetramethylammonium iodide is attributed primarily to an inhibition of the torsion of the alkyl side chains by the presence of the ionic species, facilitating a more ordered lamellar packing of the alkyl side chains and interchain π-π interactions. PMID:27386541

  15. Nonlinear charge transport in the helicoidal DNA molecule

    NASA Astrophysics Data System (ADS)

    Dang Koko, A.; Tabi, C. B.; Ekobena Fouda, H. P.; Mohamadou, A.; Kofané, T. C.

    2012-12-01

    Charge transport in the twist-opening model of DNA is explored via the modulational instability of a plane wave. The dynamics of charge is shown to be governed, in the adiabatic approximation, by a modified discrete nonlinear Schrödinger equation with next-nearest neighbor interactions. The linear stability analysis is performed on the latter and manifestations of the modulational instability are discussed according to the value of the parameter α, which measures hopping interaction correction. In so doing, increasing α leads to a reduction of the instability domain and, therefore, increases our chances of choosing appropriate values of parameters that could give rise to pattern formation in the twist-opening model. Our analytical predictions are verified numerically, where the generic equations for the radial and torsional dynamics are directly integrated. The impact of charge migration on the above degrees of freedom is discussed for different values of α. Soliton-like and localized structures are observed and thus confirm our analytical predictions. We also find that polaronic structures, as known in DNA charge transport, are generated through modulational instability, and hence reinforces the robustness of polaron in the model we study.

  16. Nonlinear charge transport in the helicoidal DNA molecule.

    PubMed

    Dang Koko, A; Tabi, C B; Ekobena Fouda, H P; Mohamadou, A; Kofané, T C

    2012-12-01

    Charge transport in the twist-opening model of DNA is explored via the modulational instability of a plane wave. The dynamics of charge is shown to be governed, in the adiabatic approximation, by a modified discrete nonlinear Schrödinger equation with next-nearest neighbor interactions. The linear stability analysis is performed on the latter and manifestations of the modulational instability are discussed according to the value of the parameter α, which measures hopping interaction correction. In so doing, increasing α leads to a reduction of the instability domain and, therefore, increases our chances of choosing appropriate values of parameters that could give rise to pattern formation in the twist-opening model. Our analytical predictions are verified numerically, where the generic equations for the radial and torsional dynamics are directly integrated. The impact of charge migration on the above degrees of freedom is discussed for different values of α. Soliton-like and localized structures are observed and thus confirm our analytical predictions. We also find that polaronic structures, as known in DNA charge transport, are generated through modulational instability, and hence reinforces the robustness of polaron in the model we study. PMID:23278045

  17. Photocurrent microscopy of contact resistance and charge carrier traps in organic field-effect transistors

    NASA Astrophysics Data System (ADS)

    Liewald, C.; Reiser, D.; Westermeier, C.; Nickel, B.

    2016-08-01

    We use a pentacene transistor with asymmetric source drain contacts to test the sensitivity of scanning photocurrent microscopy (SPCM) for contact resistance and charge traps. The drain current of the device strongly depends on the choice of the drain electrode. In one case, more than 94% of the source drain voltage is lost due to contact resistance. Here, SPCM maps show an enhanced photocurrent signal at the hole-injecting contact. For the other bias condition, i.e., for ohmic contacts, the SPCM signal peaks heterogeneously along the channel. We argue from basic transport models that bright areas in SPCM maps indicate areas of large voltage gradients or high electric field strength caused by injection barriers or traps. Thus, SPCM allows us to identify and image the dominant voltage loss mechanism in organic field-effect transistors.

  18. Carrier transport in multilayer organic photodetectors: I. Effects of layer structure on dark current and photoresponse

    NASA Astrophysics Data System (ADS)

    Xue, Jiangeng; Forrest, Stephen R.

    2004-02-01

    In this and the following article (Parts I and II, respectively), we discuss carrier transport in multilayer organic photodetectors. In Part I, we analyze carrier tunneling in multilayer organic photodetectors, both within the organic active region and at the anode/organic interface. The external quantum efficiency of an organic photodetector whose individual layers in the active region are ⩽30 Å thick shows an activation energy of ⩽0.1 eV, suggesting that the photogenerated carriers tunnel through the potential wells formed by the multilayer stack. In such photodetectors, electron tunneling injection from the anode into the organic active region dominates the dark current at T⩾200 K. Fitting of the dark current-voltage characteristics using a semiclassical tunneling model leads to barrier heights in agreement with experimental data. In Part II, the effects of anode preparation on performance of multilayer organic photodetectors are discussed.

  19. Mixed quantum-classical simulations of charge transport in organic materials: Numerical benchmark of the Su-Schrieffer-Heeger model

    SciTech Connect

    Wang Linjun; Beljonne, David; Chen Liping; Shi Qiang

    2011-06-28

    The electron-phonon coupling is critical in determining the intrinsic charge carrier and exciton transport properties in organic materials. In this study, we consider a Su-Schrieffer-Heeger (SSH) model for molecular crystals, and perform numerical benchmark studies for different strategies of simulating the mixed quantum-classical dynamics. These methods, which differ in the selection of initial conditions and the representation used to solve the time evolution of the quantum carriers, are shown to yield similar equilibrium diffusion properties. A hybrid approach combining molecular dynamics simulations of nuclear motion and quantum-chemical calculations of the electronic Hamiltonian at each geometric configuration appears as an attractive strategy to model charge dynamics in large size systems ''on the fly,'' yet it relies on the assumption that the quantum carriers do not impact the nuclear dynamics. We find that such an approximation systematically results in overestimated charge-carrier mobilities, with the associated error being negligible when the room-temperature mobility exceeds {approx}4.8 cm{sup 2}/Vs ({approx}0.14 cm{sup 2}/Vs) in one-dimensional (two-dimensional) crystals.

  20. Anisotropic transport and optical spectroscopy study on antiferromagnetic triangular lattice EuCd2As2 : An interplay between magnetism and charge transport properties

    NASA Astrophysics Data System (ADS)

    Wang, H. P.; Wu, D. S.; Shi, Y. G.; Wang, N. L.

    2016-07-01

    We present anisotropic transport and optical spectroscopy studies on EuCd2As2 . The measurements reveal that EuCd2As2 is a low carrier density semimetal with moderate anisotropic resistivity ratio. The charge carriers experience very strong scattering from Eu magnetic moments, resulting in a Kondo-like increase of resistivity at low temperature. Below the antiferromagnetic transition temperature at TN=9.5 K, the resistivity drops sharply due to the reduced scattering from the ordered Eu moments. Nevertheless, the anisotropic ratio of ρc/ρa b keeps increasing, suggesting that the antiferromagnetic coupling is along the c axis. The optical spectroscopy measurement further reveals, besides an overdamped reflectance plasma edge at low energy, a strong coupling between phonon and electronic continuum. Our study suggests that EuCd2As2 is a promising candidate displaying intriguing interplay among charge, magnetism, and the underlying crystal lattice.