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Sample records for charge carrier transport

  1. Charge carrier transport in indium oxide nanocrystals

    SciTech Connect

    Forsh, E. A.; Marikutsa, A. V.; Martyshov, M. N.; Forsh, P. A. Rumyantseva, M. N.; Gas'kov, A. M.; Kashkarov, P. K.

    2010-10-15

    Nanocrystalline indium oxide samples with various sizes of nanocrystals are synthesized by the sol-gel method. The minimal and maximal average sizes of nanocrystals are 7-8 and 18-20 nm, respectively. An analysis of conductivity measured at dc and ac signals in a wide temperature range (T = 50-300 K) shows that the transport of charge carriers at high temperatures takes place over the conduction band, while in the low-temperature range, the hopping mechanism with a varying jump length over localized states is observed.

  2. Charge carrier transport in indium oxide nanocrystals

    NASA Astrophysics Data System (ADS)

    Forsh, E. A.; Marikutsa, A. V.; Martyshov, M. N.; Forsh, P. A.; Rumyantseva, M. N.; Gas'kov, A. M.; Kashkarov, P. K.

    2010-10-01

    Nanocrystalline indium oxide samples with various sizes of nanocrystals are synthesized by the sol-gel method. The minimal and maximal average sizes of nanocrystals are 7-8 and 18-20 nm, respectively. An analysis of conductivity measured at dc and ac signals in a wide temperature range ( T = 50-300 K) shows that the transport of charge carriers at high temperatures takes place over the conduction band, while in the low-temperature range, the hopping mechanism with a varying jump length over localized states is observed.

  3. 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.

  4. 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.

  5. Charge carrier transport and injection across organic heterojunctions

    NASA Astrophysics Data System (ADS)

    Tsang, Sai Wing

    The discovery of highly efficient organic light-emitting diodes (OLEDs) in the 1980s has stimulated extensive research on organic semiconductors and devices. Underlying this breakthrough is the realization of the organic heterojunction (OH). Besides OLEDs, the implementation of the OH also significantly improves the power conversion efficiency in organic photovoltaic cells (OPVs). The continued technological advancements in organic electronic devices depend on the accumulation of knowledge of the intrinsic properties of organic materials and related interfaces. Among them, charge-carrier transport and carrier injection are two key factors that govern the performance of a device. This thesis mainly focuses on the charge carrier injection and transport at organic heterojunctions. The carrier transport properties of different organic materials used in this study are characterized by time-of-flight (TOF) and admittance spectroscopy (AS). An injection model is formulated by considering the carrier distribution at both sides of the interface. Using a steady-state simulation approach, the effect of accumulated charges on energy level alignment at OH is revealed. Instead of a constant injection barrier, it is found that the barrier varies with applied voltage. Moreover, an escape probability function in the injection model is modified by taking into account the total hopping rate and available hopping sites at the interface. The model predicts that the injection current at low temperature can be dramatically modified by an extremely small density of deep trap states. More importantly, the temperature dependence of the injection current is found to decrease with increasing barrier height. This suggests that extracting the barrier height from the J vs 1/T plot, as commonly employed in the literature, is problematic. These theoretical predictions are confirmed by a series of experiments on heterojunction devices with various barrier heights. In addition, the presence of deep trap states is also consistent with carrier mobility measurements at low temperature. From the point of view of application, an interface chemical doping method is proposed to engineer the carrier injection at an organic heterojunction. It is found that the injection current can be effectively increased or suppressed by introducing a thin (2 nm) doped organic layer at the interface. This technique is further extended to study the impact of an injection barrier at the OH, in OLEDs, on device performance. It is shown that a 0.3 eV injection barrier at the OH, that is normally negligible at metal/organic interface, can reduce the device efficiency by 25%. This is explained by the carrier distribution in the density-of-states at the OH. Furthermore, the carrier transport properties in a bulk heterojunction system are investigated. The bulk heterojunction consists of an interpenetrating network of a polymeric electron donor and a molecular electron acceptor. This material system has been studied in the last few years as an attractive power conversion efficiency (5% under AM 1.5) of OPV cells has been demonstrated. It is found that the electron mobility is greatly dependent on the thermal treatment of the film. Interfacial dipole effect at the heterojunction between the donor and the acceptor is proposed to be the determining factor that alters the carrier mobility in different nanoscale structures.

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

    SciTech Connect

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

    2014-10-15

    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 ? ? (T/T{sub 0}){sup ??} with ? = 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 ?? = 192 meV (or 1546 cm{sup -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.

  7. Vertical charge-carrier transport in Si nanocrystal/SiO2 multilayer structures.

    PubMed

    Osinniy, V; Lysgaard, S; Kolkovsky, Vl; Pankratov, V; Nylandsted Larsen, A

    2009-05-13

    Charge-carrier transport in multilayer structures of Si nanocrystals (NCs) embedded in a SiO(2) matrix grown by magnetron sputtering has been investigated. The presence of two types of Si NCs with different diameters after post-growth annealing is concluded from transmission-electron microscopy and photoluminescence measurements. Based on the electric field and temperature dependences of capacitance and resistivity, it is established that the carrier transport is best described by a combination of phonon-assisted and direct tunneling mechanisms. Poole-Frenkel tunneling seems to be a less suitable mechanism to explain the vertical carrier transport due to the very high values of refractive indices obtained within this model. The possibility to more effectively collect charge carriers generated by light in structures having Si NCs of different size is discussed. PMID:19420632

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. Charge carrier transport and photogeneration in P3HT:PCBM photovoltaic blends.

    PubMed

    Laquai, Frdric; Andrienko, Denis; Mauer, Ralf; Blom, Paul W M

    2015-06-01

    This article reviews the charge transport and photogeneration in bulk-heterojunction solar cells made from blend films of regioregular poly(3-hexylthiophene) (RR-P3HT) and methano-fullerene (PCBM). The charge transport, specifically the hole mobility in the RR-P3HT phase of the polymer:fullerene photovoltaic blend, is dramatically affected by thermal annealing. The hole mobility increases more than three orders of magnitude and reaches a value of up to 2 10(-4) cm(2) V(-1) s(-1) after the thermal annealing process as a result of an improved semi-crystallinity of the film. This significant increase of the hole mobility balances the electron and hole mobilities in a photovoltaic blend in turn reducing space-charge formation, and this is the most important factor for the strong enhancement of the photovoltaic efficiency compared to an as cast, that is, non-annealed device. In fact, the balanced charge carrier mobility in RR-P3HT:PCBM blends in combination with a field- and temperature-independent charge carrier generation and greatly reduced non-geminate recombination explains the large quantum efficiencies mea-sured in P3HT:PCBM photovoltaic devices. PMID:25940132

  13. Charge carrier hopping transport based on Marcus theory and variable-range hopping theory in organic semiconductors

    NASA Astrophysics Data System (ADS)

    Lu, Nianduan; Li, Ling; Banerjee, Writam; Sun, Pengxiao; Gao, Nan; Liu, Ming

    2015-07-01

    Charge carrier hopping transport is generally taken from Miller-Abrahams and Marcus transition rates. Based on the Miller-Abrahams theory and nearest-neighbour range hopping theory, Apsley and Hughes developed a concise calculation method (A-H method) to study the hopping conduction in disordered systems. Here, we improve the A-H method to investigate the charge carrier hopping transport by introducing polaron effect and electric field based on Marcus theory and variable-range hopping theory. This improved method can well describe the contribution of polaron effect, energetic disorder, carrier density, and electric field to the charge carrier transport in disordered organic semiconductor. In addition, the calculated results clearly show that the charge carrier mobility represents different polaron effect dependence with the polaron activation energy and decreases with increasing electric field strength for large fields.

  14. 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.

  15. Application of admittance spectroscopy to evaluate carrier mobility in organic charge transport materials

    NASA Astrophysics Data System (ADS)

    Tsang, S. W.; So, S. K.; Xu, J. B.

    2006-01-01

    We examine the feasibility of admittance spectroscopy (AS) and susceptance analysis in the determination of the charge-carrier mobility in an organic material. The complex admittance of the material is analyzed as a function of frequency in AS. We found that the susceptance, which is the imaginary part of the complex admittance, is related to the carrier transport properties of the materials. A plot of the computer-simulated negative differential susceptance versus frequency yields a maximum at a frequency τr-1. The position of the maximum τr-1 is related to the average carrier transit time τdc by τdc=0.56τr. Thus, knowledge of τr can be used to determine the carrier mobility in the material. Devices with the structure ITO/4,4',4'' -tris[N, -(3-methylphenyl)-N-phenylamino] triphenylamine/Ag have been designed to investigate the validity of the susceptance analysis in the hole mobility determination. The hole mobilities were measured both as functions of the electric field and the temperature. The hole mobility data extracted by susceptance analysis were in excellent agreement with those independently obtained from time-of-flight (TOF) measurements. Using the temperature dependence results, we further analyzed the mobility data by the Gaussian disorder model (GDM). The GDM disorder parameters are also in good agreement with those determined from TOF.

  16. A study of the transport of charge carriers in coupled quantum regions

    SciTech Connect

    Konoplev, B. G.; Ryndin, E. A.

    2008-12-15

    Specific features of controlled relocation of charge carriers in nanostructures based on tunnelingcoupled quantum regions formed by GaAs/AlGaAs heterojunctions are considered. The results of numerical simulation of dynamics of controlled tunneling relocation of the maximum in the amplitudes of wave functions of charge carriers are discussed.

  17. 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

  18. 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.

  19. 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.

  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. Charged droplet transportation under direct current electric fields as a cell carrier

    NASA Astrophysics Data System (ADS)

    Lee, Chiun-Peng; Chang, Hsien-Chih; Wei, Zung-Hang

    2012-07-01

    This study verifies the reliability of the cell transport through charged droplets under DC electrical fields. Over 90% cell viability can be obtained after charging and discharging for thousands of times. The high cell viability indicates that the electrical charging of a droplet barely influences the cells inside over a long working period. DC field induced AC electrical signals via droplet motion are also observed and analyzed quantitatively. The measured AC signals help us understand the charge transfer of a droplet during charging and discharging processes.

  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

    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

  5. Charge carrier transport and collection enhancement of copper indium diselenide photoactive nanoparticle-ink by laser crystallization

    SciTech Connect

    Nian, Qiong; Cheng, Gary J.; Zhang, Martin Y.; Wang, Yuefeng; Das, Suprem R.; Bhat, Venkataprasad S.; Huang, Fuqiang

    2014-09-15

    There has been increasing needs for cost-effective and high performance thin film deposition techniques for photovoltaics. Among all deposition techniques, roll-to-roll printing of nanomaterials has been a promising method. However, the printed thin film contains many internal imperfections, which reduce the charge-collection performance. Here, direct pulse laser crystallization (DPLC) of photoactive nanoparticles-inks is studied to meet this challenge. In this study, copper indium selenite (CIS) nanoparticle-inks is applied as an example. Enhanced crystallinity, densified structure in the thin film is resulted after DLPC under optimal conditions. It is found that the decreased film internal imperfections after DPLC results in reducing scattering and multi-trapping effects. Both of them contribute to better charge-collection performance of CIS absorber material by increasing extended state mobility and carrier lifetime, when carrier transport and kinetics are coupled. Charge carrier transport was characterized after DPLC, showing mobility increased by 2 orders of magnitude. Photocurrent under AM1.5 illumination was measured and shown 10 times enhancement of integrated power density after DPLC, which may lead to higher efficiency in photo-electric energy conversion.

  6. Experimental investigation of charge carrier transport in organic thin-film transistors with "buried surface layers".

    PubMed

    Wei, Qingshuo; Hashimoto, Kazuhito; Tajima, Keisuke

    2011-02-01

    We studied how the layers with different transport properties buried inside a semiconductor material affect the characteristics of organic thin film transistors (OTFT) using a well-defined multilayered structure fabricated by a contact film transfer method that we recently developed (ACS Appl. Mater. Interfaces 1, 2660 (2009)). A simple model with the charge distribution in the organic semiconductor film, the mobility dependence on the charge density, and the buried surface layers with a high mobility successfully reproduced the experimental mobility dependence on the thickness of the spin-coated films and the gate voltage. These results demonstrated that charge transport layers located far from the dielectric interface could contribute significantly to the total current in OTFTs. PMID:21271745

  7. Charge carrier generation and transport in different stoichiometry APFO3:PC61BM solar cells.

    PubMed

    Pranculis, Vytenis; Infahsaeng, Yingyot; Tang, Zheng; Deviis, Andrius; Vithanage, Dimali A; Ponseca, Carlito S; Ingans, Olle; Yartsev, Arkady P; Gulbinas, Vidmantas; Sundstrm, Villy

    2014-08-13

    In this paper we studied carrier drift dynamics in APFO3:PC61BM solar cells of varied stoichiometry (2:1, 1:1, and 1:4 APFO3:PC61BM) over a wide time range, from subpicoseconds to microseconds with a combination of ultrafast optical electric field probing and conventional transient integrated photocurrent techniques. Carrier drift and extraction dynamics are strongly stoichiometry dependent: the speed of electron or hole drift increases with higher concentration of PC61BM or polymer, respectively. The electron extraction from a sample with 80% PC61BM takes place during hundreds of picoseconds, but slows down to sub-microseconds in a sample with 33% PC61BM. The hole extraction is less stoichiometry dependent: it varies form sub-nanoseconds to tens of nanoseconds when the PC61BM concentration changes from 33% to 80%. The electron extraction rate correlates with the conversion efficiency of solar cells, leading to the conclusion that fast electron motion is essential for efficient charge carrier separation preventing their geminate recombination. PMID:25025885

  8. Investigation of charge carrier transport and charge sharing in X-ray semiconductor pixel detectors such as Medipix2

    NASA Astrophysics Data System (ADS)

    Korn, Alexander; Firsching, Markus; Anton, Gisela; Hoheisel, Martin; Michel, Thilo

    2007-06-01

    The output of X-ray semiconductor pixel detectors such as Medipix2 depends on various effects, such as the primary energy distribution inside the sensor layer, the diffusion of the generated charge carriers during the drift, the discrimination of the input signal by a threshold, and detection of scattered quanta originating from the detector parts behind the sensor layer. In this study we introduce an advanced Monte Carlo simulation including all these effects. The simulation was verified for energy distribution functions by performing threshold scans of monoenergetic radiation with the Medipix2.

  9. Effects of Te inclusions on charge-carrier transport properties in CdZnTe radiation detectors

    NASA Astrophysics Data System (ADS)

    Gu, Yaxu; Rong, Caicai; Xu, Yadong; Shen, Hao; Zha, Gangqiang; Wang, Ning; Lv, Haoyan; Li, Xinyi; Wei, Dengke; Jie, Wanqi

    2015-01-01

    The influence of tellurium (Te) inclusions on the charge collection efficiency in cadmium zinc telluride (CdZnTe or CZT) detectors has been investigated using ion beam induced charge (IBIC) technique. Combining the analysis of infrared transmittance image, most of the low charge collection areas in the IBIC images prove the existence of Te inclusions. To further clarify the role of Te inclusions on charge transport properties, bias dependent local IBIC scan was performed on Te inclusion related regions from 20 V to 500 V. The result shows that charge collection efficiencies in Te inclusion degraded regions experience fast ascent under low biases and slow descent at high applied biases, which deviates from Hecht rule. This behavior is attributed to the competitive influence of two mechanisms under different biases, namely charge carrier trapping due to uniformly distributed point defects and Te inclusion induced transient charge loss. A modified Hecht equation is further proposed to explain the effects of high-density localized defects, say Te inclusions, on the charge collection efficiency.

  10. Charge carrier thermalization in organic diodes

    PubMed Central

    van der Kaap, N. J.; Koster, L. J. A.

    2016-01-01

    Charge carrier mobilities of organic semiconductors are often characterized using steady-state measurements of space charge limited diodes. These measurements assume that charge carriers are in a steady-state equilibrium. In reality, however, energetically hot carriers are introduces by photo-excitation and injection into highly energetic sites from the electrodes. These carriers perturb the equilibrium density of occupied states, and therefore change the overall charge transport properties. In this paper, we look into the effect of energetically hot carriers on the charge transport in organic semiconductors using steady state kinetic Monte Carlo simulations. For injected hot carriers in a typical organic semiconductor, rapid energetic relaxation occurs in the order of tens of nanoseconds, which is much faster than the typical transit time of a charge carrier throught the device. Furthermore, we investigate the impact of photo-generated carriers on the steady-state mobility. For a typical organic voltaic material, an increase in mobility of a factor of 1.1 is found. Therefore, we conclude that the impact of energetically hot carriers on normal device operation is limited. PMID:26791095

  11. Charge carrier thermalization in organic diodes

    NASA Astrophysics Data System (ADS)

    van der Kaap, N. J.; Koster, L. J. A.

    2016-01-01

    Charge carrier mobilities of organic semiconductors are often characterized using steady-state measurements of space charge limited diodes. These measurements assume that charge carriers are in a steady-state equilibrium. In reality, however, energetically hot carriers are introduces by photo-excitation and injection into highly energetic sites from the electrodes. These carriers perturb the equilibrium density of occupied states, and therefore change the overall charge transport properties. In this paper, we look into the effect of energetically hot carriers on the charge transport in organic semiconductors using steady state kinetic Monte Carlo simulations. For injected hot carriers in a typical organic semiconductor, rapid energetic relaxation occurs in the order of tens of nanoseconds, which is much faster than the typical transit time of a charge carrier throught the device. Furthermore, we investigate the impact of photo-generated carriers on the steady-state mobility. For a typical organic voltaic material, an increase in mobility of a factor of 1.1 is found. Therefore, we conclude that the impact of energetically hot carriers on normal device operation is limited.

  12. Charge carrier thermalization in organic diodes.

    PubMed

    van der Kaap, N J; Koster, L J A

    2016-01-01

    Charge carrier mobilities of organic semiconductors are often characterized using steady-state measurements of space charge limited diodes. These measurements assume that charge carriers are in a steady-state equilibrium. In reality, however, energetically hot carriers are introduces by photo-excitation and injection into highly energetic sites from the electrodes. These carriers perturb the equilibrium density of occupied states, and therefore change the overall charge transport properties. In this paper, we look into the effect of energetically hot carriers on the charge transport in organic semiconductors using steady state kinetic Monte Carlo simulations. For injected hot carriers in a typical organic semiconductor, rapid energetic relaxation occurs in the order of tens of nanoseconds, which is much faster than the typical transit time of a charge carrier throught the device. Furthermore, we investigate the impact of photo-generated carriers on the steady-state mobility. For a typical organic voltaic material, an increase in mobility of a factor of 1.1 is found. Therefore, we conclude that the impact of energetically hot carriers on normal device operation is limited. PMID:26791095

  13. Massively parallel kinetic Monte Carlo simulations of charge carrier transport in organic semiconductors

    NASA Astrophysics Data System (ADS)

    van der Kaap, N. J.; Koster, L. J. A.

    2016-02-01

    A parallel, lattice based Kinetic Monte Carlo simulation is developed that runs on a GPGPU board and includes Coulomb like particle-particle interactions. The performance of this computationally expensive problem is improved by modifying the interaction potential due to nearby particle moves, instead of fully recalculating it. This modification is achieved by adding dipole correction terms that represent the particle move. Exact evaluation of these terms is guaranteed by representing all interactions as 32-bit floating numbers, where only the integers between -222 and 222 are used. We validate our method by modelling the charge transport in disordered organic semiconductors, including Coulomb interactions between charges. Performance is mainly governed by the particle density in the simulation volume, and improves for increasing densities. Our method allows calculations on large volumes including particle-particle interactions, which is important in the field of organic semiconductors.

  14. 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.

    2015-12-01

    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 ? ac(T) across the Nel 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 ? 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 ? 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, ? h(T) and J ij(T) is discussed.

  15. 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.

  16. 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 ?m 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 cm (Vs)? and diffusion coefficient D of 17 cm s?. We find limiting recombination at the epitaxial film surface (surface recombination velocity Ssurface = (2.8 0.3) 10?cm s ?) and at the heteroepitaxial interface (interface recombination velocity Sinterface = (4.8 0.5) 10? cm s?). The results demonstrate that reducing surface and interface recombination velocity is critical for photovoltaic solar cells and electronic devices that employ epitaxial CdTe.

  17. 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 produce a large amount of reactive O2(-)? radicals. However, in the case of RhB degradation, h(+) is the main reactive species which showed a slightly increased photocatalytic activity (12%) in the presence of rGO support where the role of rGO is almost negligible. This study suggests the effective roles of rGO for the degradation of organics, i.e., the rate of photocatalytic degradation also depends on the nature of compound rather than rGO support. PMID:26806337

  18. Charge carrier transport mechanisms in perovskite CdTiO3 fibers

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

    Electrical transport properties of electrospun cadmium titanate (CdTiO3) 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 Nt = 6.27 1017 /cm3. 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(EF) = 5.51 1021 eV-1 cm-3 at 2 V. Other VRH parameters such as hopping distance (Rhop) and hopping energy (Whop) 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 CdTiO3 fibers efficient material for capacitive energy storage devices.

  19. 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

  20. 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.

  1. 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.

  2. Charge carriers and excitons transport in an organic solar cell-theory and simulation

    NASA Astrophysics Data System (ADS)

    Shahini, Ali.; Abbasian, Karim.

    2012-08-01

    An organic solar cell model is developed that consists of both excitonic and classical bipolar aspects of solar cells. In order to achieve this goal, the photon recycling term is imported into the equations to connect the Shockley-Queisser theory and the classical diode theory. This model for excitonic and classical bipolar solar cells can describe the combined transport and interaction of electrons, holes and excitons. For high mobilities this model reproduces the Shockley Queisser efficiency limit. We show how varying the respective mobilities of the different species changes the operation mode of the solar cell path between excitonic and bipolar. Then, the effect of conduction band offset on transport will be described in this paper. Finally, validity of reciprocity theorem between quantum efficiency and electroluminescence in this model will be discussed.

  3. 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.

  4. 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

    Graphenetwo-dimensional carbonis 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. Generation-dependent charge carrier transport in Cu(In,Ga)Se2/CdS/ZnO thin-film solar-cells

    NASA Astrophysics Data System (ADS)

    Nichterwitz, Melanie; Caballero, Raquel; Kaufmann, Christian A.; Schock, Hans-Werner; Unold, Thomas

    2013-01-01

    Cross section electron-beam induced current (EBIC) and illumination-dependent current voltage (IV) measurements show that charge carrier transport in Cu(In,Ga)Se2 (CIGSe)/CdS/ZnO solar-cells is generation-dependent. We perform a detailed analysis of CIGSe solar cells with different CdS layer thicknesses and varying Ga-content in the absorber layer. In conjunction with numerical simulations, EBIC and IV data are used to develop a consistent model for charge and defect distributions with a focus on the heterojunction region. The best model to explain our experimental data is based on a p+ layer at the CIGSe/CdS interface leading to generation-dependent transport in EBIC at room temperature. Acceptor-type defect states at the CdS/ZnO interface cause a significant reduction of the photocurrent in the red-light illuminated IV characteristics at low temperatures (red kink effect). Shallow donor-type defect states at the p+ layer/CdS interface of some grains of the absorber layer are responsible for grain specific, i.e., spatially inhomogeneous, charge carrier transport observed in EBIC.

  7. Charge carrier scattering by defects in semiconductors

    NASA Astrophysics Data System (ADS)

    Lordi, Vincenzo; Erhart, Paul; berg, Daniel

    2010-06-01

    A first-principles framework for calculating the rates of charge carrier scattering by defects in semiconductors is presented. First a quantitative formalism is outlined, followed by the development of an approximate relative formalism that allows rapid assessment of the effects of different defects on carrier transport in given materials. Representative results are presented that demonstrate the applicability of the relative formalism, which achieves a three to four orders of magnitude reduction in computational cost compared to the full quantitative calculation. The differences between the two formalisms are discussed in light of average carrier scattering by a defect, differences between electron and hole scattering, and variations of the scattering matrix elements throughout the Brillouin zone. Results and analysis are presented within the Born approximation for carrier scattering, which is applicable in the absence of strong interactions between scattering centers (i.e., the dilute limit). The theory as presented can be extended to interacting defects without modification if they can be represented as a set of unit defect clusters/complexes without long-range correlated interactions between them.

  8. Optimization of charge carrier transport balance for performance improvement of PDPP3T-based polymer solar cells prepared using a hot solution.

    PubMed

    Wang, Jian; Zhang, Fujun; Zhang, Miao; Wang, Wenbin; An, Qiaoshi; Li, Lingliang; Sun, Qianqian; Tang, Weihua; Zhang, Jian

    2015-04-21

    Polymer solar cells (PSCs), with poly(diketopyrrolopyrrole-terthiophene) (PDPP3T):[6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as the active layers, were fabricated using solutions of different temperatures. The best power conversion efficiency (PCE) of the PSCs prepared using a hot solution was about 6.22%, which is better than 5.54% for PSCs prepared using cool (room temperature) solutions and 5.85% for PSCs prepared using cool solutions with a 1,8-diiodooctane (DIO) solvent additive. The underlying reasons for the improved PCE of the PSCs prepared using a hot solution could be attributed to the more dispersive donor and acceptor distribution in the active layer, resulting in a better bi-continuous interpenetrating network for exciton dissociation and charge carrier transport. An enhanced and more balanced charge carrier transport in the active layer is obtained for the PSCs prepared using a hot solution, which can be determined from the J-V curves of the related hole-only and electron-only devices. PMID:25777139

  9. Role of dopants in long-range charge carrier transport for p-type and n-type graphene transparent conducting thin films.

    PubMed

    Bult, Justin B; Crisp, Ryan; Perkins, Craig L; Blackburn, Jeffrey L

    2013-08-27

    Monolayer to few-layer graphene thin films have several attractive properties such as high transparency, exceptional electronic transport, mechanical durability, and environmental stability, which are required in transparent conducting electrodes (TCs). The successful incorporation of graphene TCs into demanding applications such as thin film photovoltaics requires a detailed understanding of the factors controlling long-range charge transport. In this study, we use spectroscopic and electrical transport measurements to provide a self-consistent understanding of the macroscopic (centimeter, many-grain scale) transport properties of chemically doped p-type and n-type graphene TCs. We demonstrate the first large-area n-type graphene TCs through the use of hydrazine or polyethyleneimine as dopants. The n-type graphene TCs utilizing PEI, either as the sole dopant or as an overcoat, have good stability in air compared to TCs only doped with hydrazine. We demonstrate a shift in Fermi energy of well over 1 V between the n- and p-type graphene TCs and a sheet resistance of ~50 ?/sq at 89% visible transmittance. The carrier density is increased by 2 orders of magnitude in heavily doped graphene TCs, while the mobility is reduced by a factor of ~7 due to charged impurity scattering. Temperature-dependent measurements demonstrate that the molecular dopants also help to suppress processes associated with carrier localization that may limit the potential of intrinsic graphene TCs. These results suggest that properly doped graphene TCs may be well-suited as anodes or cathodes for a variety of opto-electronic applications. PMID:23859709

  10. Dynamics of spin charge carriers in polyaniline

    NASA Astrophysics Data System (ADS)

    Krinichnyi, V. I.

    2014-06-01

    The review summarizes the results of the study of emeraldine forms of polyaniline by multifrequency (9.7-140 GHz, 3-cm and 2-mm) wavebands Electron Paramagnetic Resonance (EPR) spectroscopy combined with the spin label and probe, steady-state saturation of spin-packets, and saturation transfer methods. Spin excitations formed in emeraldine form of polyaniline govern structure, magnetic resonance, and electronic properties of the polymer. Conductivity in neutral or weakly doped samples is defined mainly by interchain charge tunneling in the frames of the Kivelson theory. As the doping level increases, this process is replaced by a charge thermal activation transport by molecular-lattice polarons. In heavily doped polyaniline, the dominating is the Mott charge hopping between well-conducting crystalline ravels embedded into amorphous polymer matrix. The main properties of polyaniline are described in the first part. The theoretical background of the magnetic, relaxation, and dynamics study of nonlinear spin carriers transferring a charge in polyaniline is briefly explicated in the second part. An original data obtained in the EPR study of the nature, relaxation, and dynamics of polarons as well as the mechanism of their transfer in polyaniline chemically modified by sulfuric, hydrochloric, camphorsulfonic, 2-acrylamido-2-methyl-1-propanesulfonic, and para-toluenesulfonic acids up to different doping levels are analyzed in the third part. Some examples of utilization of polyaniline in molecular electronics and spintronics are described.

  11. 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.

  12. Charge carrier dynamics and interactions in electric force microscopy.

    PubMed

    Lekkala, Swapna; Hoepker, Nikolas; Marohn, John A; Loring, Roger F

    2012-09-28

    In electric force microscopy, a charged atomic force microscope tip in vacuum senses a fluctuating electrical force generated by the sample. Such measurements can in principle probe electrical noise generated by moving charge carriers in an organic semiconductor. We present a theory of cantilever frequency fluctuations in electric force microscopy, driven by coupled charge carrier dynamics and dielectric fluctuations. The connection between observable frequency fluctuations in electric force microscopy and the Casimir-Lifshitz force is described. This classical electrodynamic calculation is based on Maxwell's equations coupled to diffusive carrier transport. The effects of carrier transport and inter-carrier interactions on the spectrum of cantilever frequency noise are elucidated. We find that a simplified model of freely diffusing carriers can overestimate cantilever frequency noise by several orders of magnitude because of the neglect of interactions. Electric force microscopy measurements on an organic field effect transistor are reported and qualitatively interpreted in terms of the suppression of electrical noise from charge carriers by Coulomb interactions. PMID:23020344

  13. Probing surface states in PbS nanocrystal films using pentacene field effect transistors: controlling carrier concentration and charge transport in pentacene.

    PubMed

    Park, Byoungnam; Whitham, Kevin; Bian, Kaifu; Lim, Yee-Fun; Hanrath, Tobias

    2014-12-21

    We used a bilayer field effect transistor (FET) consisting of a thin PbS nanocrystals (NCs) film interfaced with vacuum-deposited pentacene to probe trap states in NCs. We interpret the observed threshold voltage shift in context of charge carrier trapping by PbS NCs and relate the magnitude of the threshold voltage shift to the number of trapped carriers. We explored a series of NC surface ligands to modify the interface between PbS NCs and pentacene and demonstrate the impact of interface chemistry on charge carrier density and the FET mobility in a pentacene FET. PMID:25017003

  14. Screening-induced carrier transport in silicene

    NASA Astrophysics Data System (ADS)

    Hu, Bo

    2015-06-01

    Based on the Boltzmann transport equation in the MRT approximation, we present a theory to investigate low-field carrier transport in dual-gated silicene FETs by taking into account screened charged impurity scattering, which is the most likely scattering mechanism limiting the conductivity. Static RPA dielectric screening is also included in the conductivity calculation to study temperature-dependent silicene transport. It is found that both calculated conductivity and band gap not only depend strongly on carrier sheet density, but also depend strongly on effective offset density. More importantly, screening-induced metal-insulator-transition phenomena in buckled silicene can be observed theoretically, which is similar to that obtained in monolayer graphene.

  15. Screening-induced carrier transport in silicene.

    PubMed

    Hu, Bo

    2015-06-24

    Based on the Boltzmann transport equation in the MRT approximation, we present a theory to investigate low-field carrier transport in dual-gated silicene FETs by taking into account screened charged impurity scattering, which is the most likely scattering mechanism limiting the conductivity. Static RPA dielectric screening is also included in the conductivity calculation to study temperature-dependent silicene transport. It is found that both calculated conductivity and band gap not only depend strongly on carrier sheet density, but also depend strongly on effective offset density. More importantly, screening-induced metal-insulator-transition phenomena in buckled silicene can be observed theoretically, which is similar to that obtained in monolayer graphene. PMID:26030373

  16. Delayed emission of surface-generated trapped carriers in transient charge transport of single-crystal and polycrystalline HgI2

    NASA Astrophysics Data System (ADS)

    Zuck, Asaf; Schieber, Michael M.; Khakhan, Oleg; Burshtein, Zeev

    2003-01-01

    Transient charge transport (TCT) measurements were used to evaluate the electrical conduction properties of HgI2 single crystals. Some comparative preliminary results for polycrystalline mercuric iodide (poly-HgI2) thick-film X-ray detectors are also reported. The latter were prepared by physical vapor deposition (PVD). The mobility , trapping time 2, and surface recombination velocity s of electrons or holes were determined by analyses of transient voltages developed across the sample in response to a drift of the corresponding charge carriers created by alpha particle absorption near one of the electrodes. Electron-, and hole mobilities of single crystal HgI2 were n = 80 cm2/Vs and p = 4.8 cm2/Vs, respectively. Trapping times were 2n ? 22 V and 2p ? 8 V, and surface recombination velocities sn ? 1.1 105 cm/s and sp ? 3.6 103 cm/s . Those of the polycrystalline material depend on the deposition technology, and vary between 65 and 88 cm2/Vs for electrons, and between 4.3 and 4.1 cm2/Vs for holes. Bulk trapping-times and surface recombination velocities appear of the same order of magnitude as in the single crystal. An effect of carriers being first generated in near-surface traps and then gradually released is observed for both the single crystal and the polycrystalline material. It is stronger for electrons as compared to holes, and stronger in the polycrystalline material as compared to the single crystal.

  17. Charge carrier mobility in hybrid halide perovskites.

    PubMed

    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 cm(2)V(-1)s(-1) and that for holes within 1-5 cm(2)V(-1)s(-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

  18. 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 510?cm2V?1s?1 and that for holes within 15?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

  19. Charge transport in guanine crystals

    NASA Astrophysics Data System (ADS)

    Ortmann, Frank; Hannewald, Karsten; Bechstedt, Friedhelm

    2008-03-01

    Charge-transport processes in organic molecular crystals exhibit similarities and differences to those in ?-conjugated polymers. For both types of condensed matter the polaronic effects are of high importance. These effects can cause a transition from bandlike transport to themally activated hopping. While the hopping regime is prevalent for DNA polymers, it is not clear if the same holds also for crystalline guanine or if band transport dominates. Also the influence of the temperature is rarely discussed in literature. In our approach to the problem of charge-carrier transport in these systems [1], we discuss the temperature dependence of the polaron bandwidth and the mobility in guanine crystals [2]. [1] K. Hannewald et al., Phys. Rev. B 69, 075211 (2004); 075212 (2004). [2] F. Ortmann et al., J. Phys. Chem. B (to be published).

  20. The Impact of the Dielectric/Semiconductor Interface on Microstructure and Charge Carrier Transport in High-Performance Polythiophene Transistors

    SciTech Connect

    Jung, Y.; Kline, R; Lin, E; Fischer, D; Toney, M; Heeney, M; McCulloch, I; DeLongchamp, D

    2008-01-01

    The performance of organic field-effect transistors (OFETs) significantly depends on the properties of the interface between the semiconductor and gate dielectric. Here, we study the impact of chemically modified and morphologically controlled dielectrics on the performance of poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene) (pBTTT) semiconductors. We find that the molecular packing, domain size, and carrier mobility of pBTTT are highly sensitive to dielectric chemistry and dielectric roughness. The large and well-oriented terraced domains that are the origin of pBTTT's high performance can develop well on certain dielectrics, but can be disrupted on others.

  1. Charge carrier relaxation model in disordered organic semiconductors

    SciTech Connect

    Lu, Nianduan; Li, Ling Sun, Pengxiao; Liu, Ming

    2013-11-15

    The relaxation phenomena of charge carrier in disordered organic semiconductors have been demonstrated and investigated theoretically. An analytical model describing the charge carrier relaxation is proposed based on the pure hopping transport theory. The relation between the material disorder, electric field and temperature and the relaxation phenomena has been discussed in detail, respectively. The calculated results reveal that the increase of electric field and temperature can promote the relaxation effect in disordered organic semiconductors, while the increase of material disorder will weaken the relaxation. The proposed model can explain well the stretched-exponential law by adopting the appropriate parameters. The calculation shows a good agreement with the experimental data for organic semiconductors.

  2. 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.

  3. Evaluation of Intrinsic Charge Carrier Transport at Insulator-Semiconductor Interfaces Probed by a Non-Contact Microwave-Based Technique

    PubMed Central

    Honsho, Yoshihito; Miyakai, Tomoyo; Sakurai, Tsuneaki; Saeki, Akinori; Seki, Shu

    2013-01-01

    We have successfully designed the geometry of the microwave cavity and the thin metal electrode, achieving resonance of the microwave cavity with the metal-insulator-semiconductor (MIS) device structure. This very simple MIS device operates in the cavity, where charge carriers are injected quantitatively by an applied bias at the insulator-semiconductor interface. The local motion of the charge carriers was clearly probed through the applied external microwave field, also giving the quantitative responses to the injected charge carrier density and charge/discharge characteristics. By means of the present measurement system named field-induced time-resolved microwave conductivity (FI-TRMC), the pentacene thin film in the MIS device allowed the evaluation of the hole and electron mobility at the insulator-semiconductor interface of 6.3 and 0.34 cm2 V−1 s−1, respectively. This is the first report on the direct, intrinsic, non-contact measurement of charge carrier mobility at interfaces that has been fully experimentally verified. PMID:24212382

  4. 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).

  5. 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.

  6. 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

  7. 47 CFR 69.153 - Presubscribed interexchange carrier charge (PICC).

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... CARRIER SERVICES (CONTINUED) ACCESS CHARGES Computation of Charges for Price Cap Local Exchange Carriers... to recover revenues totaling Average Price Cap CMT Revenues per Line month times the number of...

  8. Transistors: Impact of Interfacial Microstructure on Charge Carrier Transport in Solution-Processed Conjugated Polymer Field-Effect Transistors (Adv. Mater. 11/2016).

    PubMed

    Li, Mengmeng; An, Cunbin; Marszalek, Tomasz; Baumgarten, Martin; Müllen, Klaus; Pisula, Wojciech

    2016-03-01

    The interfacial microstructure of a semicrystalline semiconductor polymer film is precisely modulated by the dielectric with surface roughness ranging from 0.15 to 0.39 nm, without affecting the morphology in the upper layers, as described by K. Müllen, W. Pisula, and co-workers. On page 2245, they demonstrate that the interfacial microstructure has only a minor impact on transistor performance because charge carriers can bypass the interfacial defects. PMID:26970067

  9. 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 semiconductorinsulator 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.

  10. The impact of hot charge carrier mobility on photocurrent losses in polymer-based solar cells

    PubMed Central

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

    2014-01-01

    A typical signature of charge extraction in disordered organic systems is dispersive transport, which implies a distribution of charge carrier mobilities that negatively impact on device performance. Dispersive transport has been commonly understood to originate from a time-dependent mobility of hot charge carriers that reduces as excess energy is lost during relaxation in the density of states. In contrast, we show via photon energy, electric field and film thickness independence of carrier mobilities that the dispersive photocurrent in organic solar cells originates not from the loss of excess energy during hot carrier thermalization, but rather from the loss of carrier density to trap states during transport. Our results emphasize that further efforts should be directed to minimizing the density of trap states, rather than controlling energetic relaxation of hot carriers within the density of states. PMID:25047086

  11. The impact of hot charge carrier mobility on photocurrent losses in polymer-based solar cells.

    PubMed

    Philippa, Bronson; Stolterfoht, Martin; Burn, Paul L; Juka, Gytis; Meredith, Paul; White, Ronald D; Pivrikas, Almantas

    2014-01-01

    A typical signature of charge extraction in disordered organic systems is dispersive transport, which implies a distribution of charge carrier mobilities that negatively impact on device performance. Dispersive transport has been commonly understood to originate from a time-dependent mobility of hot charge carriers that reduces as excess energy is lost during relaxation in the density of states. In contrast, we show via photon energy, electric field and film thickness independence of carrier mobilities that the dispersive photocurrent in organic solar cells originates not from the loss of excess energy during hot carrier thermalization, but rather from the loss of carrier density to trap states during transport. Our results emphasize that further efforts should be directed to minimizing the density of trap states, rather than controlling energetic relaxation of hot carriers within the density of states. PMID:25047086

  12. 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.

  13. 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.

  14. 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.

  15. Organic (opto)electronic materials: understanding charge carrier dynamics

    NASA Astrophysics Data System (ADS)

    Ostroverkhova, Oksana

    2008-05-01

    There is growing interest in using organic (opto)electronic materials for applications in electronics and photonics. In particular, organic semiconductor thin films offer several advantages over traditional silicon technology, including low-cost processing, the potential for large-area flexible devices, high-efficiency light emission, and widely tunable properties through functionalization of the molecules. Over the past decade, remarkable progress in materials design and purification has been made, which led to applications of organic semiconductors in light-emitting diodes, polymer lasers, photovoltaic cells, high-speed photodetectors, organic thin-film transistors, and many others. Most of the applications envisioned for organic semiconductors rely on their conductive or photoconductive properties. However, despite remarkable progress in organic electronics and photonics, the nature of charge carrier photogeneration and transport in organic semiconductors is not completely understood and remains controversial, partly due to difficulties in assessing intrinsic properties that are often masked by impurities, grain boundaries, etc. Measurements of charge carrier dynamics at picosecond time scales after excitation reveal the intrinsic nature of mobile charge carriers before they are trapped at defect sites. In this presentation, I will review the current state of the field and summarize our recent results on photoconductivity of novel high-performance organic semiconductors (such as functionalized pentacene and anthradithiophene thin films) from picoseconds to seconds after photoexcitation. Photoluminescent properties of these novel materials will also be discussed.

  16. 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.

  17. 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 charge carriers is known to evolve as the carrier concentration increases, due to the presence of intrinsic disorder in organic semiconductors. Thus, a complementary question is: how does the nature of charge transport change as a function of carrier concentration?

  18. Organic Charge Carriers for Perovskite Solar Cells.

    PubMed

    Vlker, Sebastian F; Collavini, Silvia; Delgado, Juan Luis

    2015-09-21

    The photovoltaic field is currently experiencing the "perovskite revolution". These materials have been known for decades, but only recently have they been applied in solid-state solar cells to obtain outstanding power conversion efficiencies. Given that the variety of perovskites used so far is limited, a lot of attention has been devoted to the development of suitable organic charge-transport materials to improve device performance. In this article, we will focus on the most promising materials able to transport electrons or holes from a structural point of view. Thereby, we focus on organic materials owing to their ease of preparation and manipulation, and this is nicely combined with the potential tuning of their properties through chemical synthesis. PMID:26311591

  19. 47 CFR 69.153 - Presubscribed interexchange carrier charge (PICC).

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... period lines less revenues recovered through the End User Common Line charge established under 69.152... charge revenues. (b) If an end-user customer does not have a presubscribed interexchange carrier, the local exchange carrier may collect the PICC directly from the end user. (c) (d) Local exchange...

  20. 47 CFR 69.153 - Presubscribed interexchange carrier charge (PICC).

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... period lines less revenues recovered through the End User Common Line charge established under 69.152... charge revenues. (b) If an end-user customer does not have a presubscribed interexchange carrier, the local exchange carrier may collect the PICC directly from the end user. (c) (d) Local exchange...

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

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... period lines less revenues recovered through the End User Common Line charge established under 69.152... charge revenues. (b) If an end-user customer does not have a presubscribed interexchange carrier, the local exchange carrier may collect the PICC directly from the end user. (c) (d) Local exchange...

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

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... period lines less revenues recovered through the End User Common Line charge established under 69.152... charge revenues. (b) If an end-user customer does not have a presubscribed interexchange carrier, the local exchange carrier may collect the PICC directly from the end user. (c) (d) Local exchange...

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

    NASA Astrophysics Data System (ADS)

    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.

  4. Forth-back oscillated charge carrier motion in dynamically disordered hexathienocoronene molecules: a theoretical study.

    PubMed

    Navamani, K; Senthilkumar, K

    2015-07-21

    Electronic structure calculations were performed to investigate the charge transport properties of hexathienocoronene (HTC) based molecules. The effective displacement of the charge carrier along the ?-orbital of nearby molecules is calculated by monitoring the forth and back oscillations of the charge carrier through kinetic Monte Carlo simulation. The charge transport parameters such as charge transfer rate, mobility, hopping conductivity, localized charge density, time average effective mass and degeneracy pressure are calculated and used to study the charge transport mechanism in the studied molecules. The existence of degeneracy levels facilitates the charge transfer and is analyzed through degeneracy pressure. Theoretical results show that the site energy difference in the dynamically disordered system controls the forth-back oscillation of charge carrier and facilitates the unidirectional charge transport mechanism along the sequential localized sites. The ethyl substituted HTC has good hole and electron hopping conductivity of 415 and 894 S cm(-1), respectively, whereas unsubstituted HTC has the small hole mobility of 0.06 cm(2) V(-1) s(-1) which is due to large average effective mass of 1.42 10(-28) kg. PMID:26080732

  5. Robust tris-cyclometalated iridium(III) phosphors with ligands for effective charge carrier injection/transport: synthesis, redox, photophysical, and electrophosphorescent behavior.

    PubMed

    Zhou, Guijiang; Wang, Qi; Ho, Cheuk-Lam; Wong, Wai-Yeung; Ma, Dongge; Wang, Lixiang; Lin, Zhenyang

    2008-10-01

    With the target to design and develop new functionalized green triplet light emitters that possess distinctive electronic properties for robust and highly efficient phosphorescent organic light-emitting diodes (PHOLEDs), a series of bluish-green to yellow-green phosphorescent tris-cyclometalated homoleptic iridium(III) complexes [Ir(ppy-X)(3)] (X=SiPh(3), GePh(3), NPh(2), POPh(2), OPh, SPh, SO(2)Ph, Hppy=2-phenylpyridine) have been synthesized and fully characterized by spectroscopic, redox, and photophysical methods. By chemically manipulating the lowest triplet-state character of Ir(ppy)(3) with some functional main-group 14-16 moieties on the phenyl ring of ppy, a new family of metallophosphors with high-emission quantum yields, short triplet-state lifetimes, and good hole-injection/hole-transporting or electron-injection/electron-transporting properties can be obtained. Remarkably, all of these Ir(III) complexes show outstanding electrophosphorescent performance in multilayer doped devices that surpass that of the state-of-the-art green-emitting dopant Ir(ppy)(3). The devices described herein can reach the maximum external quantum efficiency (eta(ext)) of 12.3 %, luminance efficiency (eta(L)) of 50.8 cd A(-1), power efficiency (eta(p)) of 36.9 Lm W(-1) for [Ir(ppy-SiPh(3))(3)], 13.9 %, 60.8 cd A(-1), 49.1 Lm W(-1) for [Ir(ppy-NPh(2))(3)], and 10.1 %, 37.6 cd A(-1), 26.1 Lm W(-1) for [Ir(ppy-SO(2)Ph)(3)]. These results provide a completely new and effective strategy for carrier injection into the electrophosphor to afford high-performance PHOLEDs suitable for various display applications. PMID:18615423

  6. Surface-acoustic-wave-induced carrier transport in quantum wires

    NASA Astrophysics Data System (ADS)

    Alsina, F.; Santos, P. V.; Schnherr, H.-P.; Seidel, W.; Ploog, K. H.; Ntzel, R.

    2002-10-01

    The ambipolar transport of photogenerated electron-hole pairs by surface acoustic waves (SAW's) in coupled GaAs quantum wells (QW's) and quantum wires (QWR's) is investigated by spatially and time-resolved photoluminescence. Experimental configurations for SAW propagation direction parallel or perpendicular to the QWR's have been studied. In the first configuration, the QWR confinement potential inhibits lateral carrier diffusion. The carriers are then efficiently transported along the wire as well-defined charge packages with a repetition rate corresponding to the SAW frequency. In the second configuration, we demonstrate that the SAW can be used to transfer electron-hole pairs generated in the QW into the QWR. We also provide clear evidence for the extraction of carriers from the QWR into the QW, when the SAW piezoelectric field is sufficiently strong to overcome the QWR confinement potential.

  7. Microscopic charge carrier lifetime in silicon from a transient approach

    NASA Astrophysics Data System (ADS)

    Heinz, Friedemann D.; Kasemann, Martin; Warta, Wilhelm; Schubert, Martin C.

    2015-09-01

    We present an experimental approach to determine the charge carrier lifetime in silicon based on the measured transient decay of the emitted photoluminescence intensity, requiring only a crystal volume of 50 μm in diameter. This becomes feasible by a combination of the time correlated single photon counting technique and confocal microscopy. Using combined pulsed and pulse train laser excitation, we obtain a self-consistent charge carrier lifetime in a high dynamic range from 100 ns to ms and an injection range from 1010 cm-3 to high injection densities. An iterative data evaluation routine incorporates all effects induced by the spatially non-homogeneous charge carrier generation.

  8. 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 ? in bare and encapsulated monolayer phosphorene. We find a significant temperature dependence in the carrier mobilities (? ? T{sup ??}) 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-? overlayer, the mobility increases by up to an order of magnitude although its temperature dependence and its anisotropy are reduced.

  9. Carrier transport in unipolar barrier infrared detectors

    NASA Astrophysics Data System (ADS)

    Ting, David Z.; Soibel, Alexander; Hglund, Linda; Hill, Cory J.; Khoshakhlagh, Arezou; Keo, Sam A.; Fisher, Anita M.; Luong, Edward M.; Liu, John K.; Mumolo, Jason M.; Rafol, B., , Sir; Gunapala, Sarath D.

    2015-06-01

    We examine carrier transport in unipolar barrier infrared photodetectors and discuss aspects of barrier, contact, and absorber properties that can affect minority carrier collection. In a barrier infrared detector the unipolar barrier should block only the majority carriers while allowing the un-impeded flow of the minority carriers. Under the right conditions, unipolar barrier doping can reduce generation-recombination dark current without affecting minority carrier extraction. In an nBn structure, ideally with an electron unipolar barrier, improper barrier doping or barrier-absorber valence band offset could also block minority carriers and result in higher turn-on bias. We also examined the temperature-dependent turn-on bias in an n+Bn device and showed that observed behavior may be attributed to contact doping. Hole mobility in n-doped type-II superlattice (T2SL) is believed to be very low because of the extremely large effective mass along the growth direction. In practice MWIR and LWIR barrier infrared detectors with n-type T2SL absorbers have demonstrated good optical response. A closer inspection of the T2SL band structure offers a possible explanation as to why the hole mobility may not be as poor as suggested by the simple effective mass picture.

  10. The solute carrier 6 family of transporters

    PubMed Central

    Bröer, Stefan; Gether, Ulrik

    2012-01-01

    The solute carrier 6 (SLC6) family of the human genome comprises transporters for neurotransmitters, amino acids, osmolytes and energy metabolites. Members of this family play critical roles in neurotransmission, cellular and whole body homeostasis. Malfunction or altered expression of these transporters is associated with a variety of diseases. Pharmacological inhibition of the neurotransmitter transporters in this family is an important strategy in the management of neurological and psychiatric disorders. This review provides an overview of the biochemical and pharmacological properties of the SLC6 family transporters. LINKED ARTICLES BJP published a themed section on Transporters in 2011. To view articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.2011.164.issue-7/issuetoc PMID:22519513

  11. Ballistic carrier transport in semiconductors studied by ultrafast laser techniques

    NASA Astrophysics Data System (ADS)

    Werake, Lalani K.

    Exploring the spin degree of freedom of electrons has been recognized as a promising solution to several limitations in semiconductor device industry. Injection, transport, detection and manipulation of "spin" in materials are the key elements of this new electronic technology, known as spintronics. Despite the extensive efforts in recent years, there are still significant challenges and spintronics is still in the research phase. This dissertation is devoted to study one of these key processes: spin transport. We used quantum interference and control technique to inject spin currents. Two techniques are developed to detect the spin transport, namely a pump probe technique and a second-harmonic generation technique. Spin transport in several materials and structures are studied, including GaAs bulk, quantum wells, and germanium wafers. We observed the intrinsic inverse spin-Hall effect by time-resolving the ballistic spin and charge transport. We found that the Hall current appeared before the first scattering event. We discovered a new nonlinear optical effect, second-harmonic generation, induced by the pure spin current, and demonstrated that it can be used to directly detect pure spin currents. We have also discovered a charge-current-induced second-harmonic generation process, and used it to study plasma oscillation in GaAs. Finally, we also attempted to observe the second harmonic generation induced by spin polarized and spin unpolarized carrier populations. We did not observe a significant change in the observed second harmonic generation induced by spin polarized and spin unpolarized carrier populations.

  12. On the role of local charge carrier mobility in the charge separation mechanism of organic photovoltaics.

    PubMed

    Yoshikawa, Saya; Saeki, Akinori; Saito, Masahiko; Osaka, Itaru; Seki, Shu

    2015-07-21

    Although the charge separation (CS) and transport processes that compete with geminate and non-geminate recombination are commonly regarded as the governing factors of organic photovoltaic (OPV) efficiency, the details of the CS mechanism remain largely unexplored. Here we provide a systematic investigation on the role of local charge carrier mobility in bulk heterojunction films of ten different low-bandgap polymers and polythiophene analogues blended with methanofullerene (PCBM). By correlating with the OPV performances, we demonstrated that the local mobility of the blend measured by time-resolved microwave conductivity is more important for the OPV output than those of the pure polymers. Furthermore, the results revealed two separate trends for crystalline and semi-crystalline polymers. This work offers guidance in the design of high-performance organic solar cells. PMID:26084482

  13. Charge carrier generation mechanism operative under electron bombardment in orthorhombic benzophenone single crystals

    NASA Astrophysics Data System (ADS)

    Saleh, M.

    1987-12-01

    The charge carrier generation mechanism operative under electron bombardment in orthorhombic benzophenone single crystals has been studied and the results are explained on the basis of a combined Warter-Weiz Cobas model. The minimum quantum efficiency for charge carrier pair production is ~ 2% and since it is field dependent, greater quantum efficiency for charge carrier pair production may be possible for very thin vapour grown crystals. The magnitude of the room temperature drift mobilities in the a, b, and c directions of orthorhombic benzophenone single crystals were (0.016 0.02), (0.049 0.02), and (0.055 0.002) cm2 s-1 V-1 respectively, and were consistent with small polaron charge transport as has been reported earlier.

  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, 2011 CFR

    2011-07-01

    ...-TRANSPORTATION AND TEMPORARY STORAGE OF HOUSEHOLD GOODS AND PROFESSIONAL BOOKS, PAPERS, AND EQUIPMENT (PBP&E... calculated when a carrier charges a minimum weight, but the actual weight of HHG, PBP&E and temporary storage... actual weight of HHG, PBP&E and temporary storage is less than the minimum weight charged? Charges...

  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

    ...-TRANSPORTATION AND TEMPORARY STORAGE OF HOUSEHOLD GOODS AND PROFESSIONAL BOOKS, PAPERS, AND EQUIPMENT (PBP&E... calculated when a carrier charges a minimum weight, but the actual weight of HHG, PBP&E and temporary storage... actual weight of HHG, PBP&E and temporary storage is less than the minimum weight charged? Charges...

  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, 2013 CFR

    2013-07-01

    ...-TRANSPORTATION AND TEMPORARY STORAGE OF HOUSEHOLD GOODS AND PROFESSIONAL BOOKS, PAPERS, AND EQUIPMENT (PBP&E... calculated when a carrier charges a minimum weight, but the actual weight of HHG, PBP&E and temporary storage... actual weight of HHG, PBP&E and temporary storage is less than the minimum weight charged? Charges...

  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, 2012 CFR

    2012-07-01

    ...-TRANSPORTATION AND TEMPORARY STORAGE OF HOUSEHOLD GOODS AND PROFESSIONAL BOOKS, PAPERS, AND EQUIPMENT (PBP&E... calculated when a carrier charges a minimum weight, but the actual weight of HHG, PBP&E and temporary storage... actual weight of HHG, PBP&E and temporary storage is less than the minimum weight charged? Charges...

  18. 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

  19. 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…

  20. Electronic carrier transport at epitaxial oxide-semiconductor interfaces

    NASA Astrophysics Data System (ADS)

    Kornblum, Lior; Jin, Eric; Ahn, Charles; Walker, Fred

    2015-03-01

    The epitaxial growth of transition metal perovskite oxides on conventional semiconductors is a promising approach for integrating the wealth of electronic phenomena found in these oxides with existing devices and technologies. Some oxide functionalities require charge transport to and from the semiconductor, making the semiconductor-oxide interface an important focal point in the utilization of epitaxial oxides in electronic devices. We present our findings on electronic carrier transport in the conduction band of titanate perovskites (RTiO3) epitaxially grown on silicon and on germanium. Metal oxide semiconductor devices were fabricated by evaporation of metal contacts on top of epitaxially-grown oxides on semiconductors. Transport measurements show diode-like transport across the interface of some of the structures, whereas only leakage currents are observed in others. These results are discussed in light of the physical and electronic structure at the oxide-semiconductor interface.

  1. Conformation sensitive charge transport in conjugated polymers

    SciTech Connect

    Mattias Andersson, L.; Hedstrm, Svante; Persson, Petter

    2013-11-18

    Temperature dependent charge carrier mobility measurements using field effect transistors and density functional theory calculations are combined to show how the conformation dependent frontier orbital delocalization influences the hole- and electron mobilities in a donor-acceptor based polymer. A conformationally sensitive lowest unoccupied molecular orbital results in an electron mobility that decreases with increasing temperature above room temperature, while a conformationally stable highest occupied molecular orbital is consistent with a conventional hole mobility behavior and also proposed to be one of the reasons for why the material works well as a hole transporter in amorphous bulk heterojunction solar cells.

  2. 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

  3. Charge transport along proton wires.

    PubMed

    Karahka, Markus Leopold; Kreuzer, Hans Jürgen

    2013-12-01

    Using density functional theory we look at the quantum mechanics of charge transport along water wires both with free ends and donor/acceptor terminated. With the intermediate geometries in the DFT iterations we can follow the charge transfer mechanism and also construct the energy landscape explicitly. It shows activation barriers when a proton is transferred from one water molecule to the next. This, together with snapshots of intermediate geometries, leads to a justification and further elucidation of the Grotthuss mechanism and the Bjerrum effect. The charge transfer times and the conductivity of the proton wire are obtained in agreement with experimental results. PMID:24706126

  4. 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 (?) 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 ? > 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 ? 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(-1) s(-1), based on a combination of flash-photolysis TRMC and transient absorption spectroscopy (TAS) measurements. Single-crystal rubrene showed an ambipolarity with anisotropic charge carrier transport along each crystal axis on the nanometer scale. Finally, we describe the charge carrier mobility of a self-assembled nanotube consisting of a large ?-plane of hexabenzocoronene (HBC) partially appended with an electron acceptor. The local (intratubular) charge carrier mobility reached 3 cm(2) V(-1) s(-1) for the nanotubes that possessed well-ordered ?-stacking, but it dropped to 0.7 cm(2) V(-1) s(-1) in regions that contained greater amounts of the electron acceptor because those molecules reduced the structural integrity of ?-stacked HBC arrays. Interestingly, the long-range (intertubular) charge carrier mobility was on the order of 10(-4) cm(2) V(-1) s(-1) and monotonically decreased when the acceptor content was increased. These results suggest the importance of investigating charge carrier mobilities by frequency-dependent charge carrier motion for the development of more efficient organic electronic devices. PMID:22676381

  5. Spatial Imaging of Charge Transport in Germanium at Low Temperature

    NASA Astrophysics Data System (ADS)

    Moffatt, R. A.; Cabrera, B.; Kadribasic, F.; Redl, P.; Shank, B.; Young, B. A.; Brandt, D.; Brink, P.; Cherry, M.; Tomada, A.

    2014-09-01

    The purpose of this experiment is to observe the oblique propagation of electrons through germanium by exciting a point source of charge carriers with a focused laser pulse on one face of a germanium crystal. After the electrons are drifted through the crystal by a uniform electric field, the pattern of charge density arriving on the opposite face is mapped and used to reconstruct the trajectories of the electrons. These measurements will verify in detail the Monte Carlo analysis utilized in the Cryogenic Dark Matter Search to model the transport of charge carriers in high-purity germanium detectors, including both oblique electron propagation and inter-valley scattering.

  6. Combined charge carrier transport and photoelectrochemical characterization of BiVO4 single crystals: intrinsic behavior of a complex metal oxide.

    PubMed

    Rettie, Alexander J E; Lee, Heung Chan; Marshall, Luke G; Lin, Jung-Fu; Capan, Cigdem; Lindemuth, Jeffrey; McCloy, John S; Zhou, Jianshi; Bard, Allen J; Mullins, C Buddie

    2013-07-31

    Bismuth vanadate (BiVO4) is a promising photoelectrode material for the oxidation of water, but fundamental studies of this material are lacking. To address this, we report electrical and photoelectrochemical (PEC) properties of BiVO4 single crystals (undoped, 0.6% Mo, and 0.3% W:BiVO4) grown using the floating zone technique. We demonstrate that a small polaron hopping conduction mechanism dominates from 250 to 400 K, undergoing a transition to a variable-range hopping mechanism at lower temperatures. An anisotropy ratio of ~3 was observed along the c axis, attributed to the layered structure of BiVO4. Measurements of the ac field Hall effect yielded an electron mobility of ~0.2 cm(2) V(-1) s(-1) for Mo and W:BiVO4 at 300 K. By application of the Gärtner model, a hole diffusion length of ~100 nm was estimated. As a result of low carrier mobility, attempts to measure the dc Hall effect were unsuccessful. Analyses of the Raman spectra showed that Mo and W substituted for V and acted as donor impurities. Mott-Schottky analysis of electrodes with the (001) face exposed yielded a flat band potential of 0.03-0.08 V versus the reversible H2 electrode, while incident photon conversion efficiency tests showed that the dark coloration of the doped single crystals did not result in additional photocurrent. Comparison of these intrinsic properties to those of other metal oxides for PEC applications gives valuable insight into this material as a photoanode. PMID:23869474

  7. Combined Charge Carrier Transport and Photoelectrochemical Characterization of BiVO4 Single Crystals: Intrinsic Behavior of a Complex Metal Oxide

    SciTech Connect

    Rettie, Alexander J.; Lee, Heung Chan; Marshall, Luke G.; Lin, Jung-Fu; Capen, Cigdem; Lindemuth, Jeffrey; McCloy, John S.; Zhou, Jianshi; Bard, Allen J.; Mullins, C. Buddie

    2013-07-08

    ABSTRACT: Bismuth vanadate (BiVO4) is a promising photoelectrode material for the oxidation of water, but fundamental studies of this material are lacking. To address this, we report electrical and photoelectrochemical (PEC) properties of BiVO4 single crystals (undoped, 0.6% Mo and 0.3% W:BiVO4) grown using the floating zone technique. We demonstrate that a small polaron hopping conduction mechanism dominates from 250-400 K, transitioning to a variable range hopping mechanism at lower temperatures. An anisotropy ratio of ~3 was observed along the c-axis, attributed to the layered structure of BiVO4. Measurements of the AC field Hall effect yielded an electron mobility of ~0.2 cm2 V-1 s-1 for Mo and W:BiVO4 at 300 K. By application of the Gärtner model, a hole diffusion length of ~140 nm was estimated. As a result of low carrier mobility, attempts to measure the DC Hall effect were unsuccessful. Analyses of the Raman spectra showed that Mo and W substituted for V and acted as donor impurities. Mott-Schottky analysis of electrodes with the (001) face exposed yielded a flat band potential of 0.03-0.08 V vs. RHE, while incident photon conversion efficiency tests showed that the dark coloration of the doped single crystals did not result in additional photocurrent. Comparison of these intrinsic properties to other metal oxides for PEC applications gives valuable insight into this material as a photoanode.

  8. Charge transport in desolvated DNA

    NASA Astrophysics Data System (ADS)

    Wolter, Mario; Elstner, Marcus; Kuba?, Tom

    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.

  9. Measurement of the Charge Carrier Mobility in MEH-PPV and MEH-PPV-POSS Organic Semiconductor Films

    NASA Astrophysics Data System (ADS)

    Romanov, I. V.; Voitsekhovskii, A. V.; Dyagterenko, K. M.; Kopylova, T. N.; Kokhanenko, A. P.; Nikonova, E. N.

    2015-03-01

    The values of the charge carrier mobility in organic semiconductor materials (MEH-PPV, MEH-PPV-POSS) are obtained on the basis of an analysis of the relaxation curves of transient electroluminescence in organic light-emitting diodes (OLEDs). The data on the mobility of charge carriers are analyzed according to the Poole-Frenkel model using the dependences of the charge carrier mobility on the electric field. Physical interpretation of the transport phenomena in OLED structures based on MEH-PPV and MEH-PPV-POSS is given.

  10. Charge transport in ion-gel gated IDTBT transistors

    NASA Astrophysics Data System (ADS)

    Wang, Shun; Bao, Bei; Shao, Xianyi; Tan, Lu; Wu, Yueshen; Wen, Libin; Bai, Xuxu; Guo, Xiaojun; Liu, Ying

    2015-03-01

    Ionic liquids (ion gels) have been employed as the gate dielectric for polymer transistors due to its ultra-high capacitance. At high charge carrier density provided by ionic liquid gating, polymers like P3HT and PBTTT can exhibit very high mobility. We have fabricated ion-gel gated IDTBT transistors and measured its charge transport properties. We found that the mobility of ion-gel gated IDTBT transistors is greatly suppressed compared to the Cytop gated devices. At carrier density on the order of 1021/cm3, IDTBT shows mobility of about 0.05 cm2/V/s. Detailed analysis of the temperature dependence of resistivity shows 3D Mott variable range hopping in IDTBT at such carrier density, indicating a different charge transport mechanism from Cytop gated device.

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

    NASA Astrophysics Data System (ADS)

    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.

    2013-08-01

    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.

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

    PubMed

    Sandeep, C S Suchand; ten Cate, Sybren; 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 cm(2) 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

  13. 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 electronhole 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 electronhole 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 ShockleyQueisser 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

  14. 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.

  15. Decoupling Charge Transfer and Transport at Polymeric Hole Transport Layer in Perovskite Solar Cells.

    PubMed

    Sin, Dong Hun; Ko, Hyomin; Jo, Sae Byeok; Kim, Min; Bae, Geun Yeol; Cho, Kilwon

    2016-03-16

    Tailoring charge extraction interfaces in perovskite solar cells (PeSCs) critically determines the photovoltaic performance of PeSCs. Here, we investigated the decoupling of two major determinants of the efficient charge extraction, the charge transport and interfacial charge transfer properties at hole transport layers (HTLs). A simple physical tuning of a representative polymeric HTL, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate), provided a wide range of charge conductivities from 10(-4) to 10(3) S cm(-1) without significant modulations in their energy levels, thereby enabling the decoupling of charge transport and transfer properties at HTLs. The transient photovoltaic response measurement revealed that the facilitation of hole transport through the highly conductive HTL promoted the elongation of charge carrier lifetimes within the PeSCs up to 3 times, leading to enhanced photocurrent extraction and finally 25% higher power conversion efficiency. PMID:26887635

  16. 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

    ... occupy the space of more than one seat. This is not considered a special charge under this section. (c... 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...

  17. 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

    ... occupy the space of more than one seat. This is not considered a special charge under this section. (c... 14 Aeronautics and Space 4 2013-01-01 2013-01-01 false May carriers impose special charges on... 382.31 Aeronautics and Space OFFICE OF THE SECRETARY, DEPARTMENT OF TRANSPORTATION...

  18. Carrier Transport and Sensing in Compound Semiconductor Nanowires

    NASA Astrophysics Data System (ADS)

    Salfi, Joseph R.

    Experiments and analysis in this thesis advance the understanding of critical issues in the carrier transport properties of InAs and InAs/GaAs core/shell heterostructure nanowires (diameter 30-60 nm) grown by molecular beam epitaxy. Effects of robust sub-band quantization structure on the gate-voltage dependence of conductance are observed up to 77 K in a single InAs nanowire with diameter 34+/-2 nm. Electronic field effect mobility at 300 K and 30 K are typically 2000-4000 cm2V-1s -1 and 10000-20000 cm2V-1s-1 . Strain induced by lattice mismatch in epitaxial core/shell InAs/GaAs heterostructure nanowires is found to relax by formation of dislocations, correlated with nearly one order of magnitude suppression of room temperature field effect mobility compared with bare InAs nanowires. The carrier transport properties of Mn-doped ZnO nanowires were also investigated, where despite the large bandgap, conductivity is not thermally activated, and carrier mobility is consistent with strong degeneracy of the electron gas at 10 K. A novel method was developed providing the first experimental characterization of the quasi-equilibrium gate-voltage dependent surface potential in nanowire field-effect transistors, based on statistics of charging/discharging of a single Coulomb impurity evident in a random telegraph signal, which succeeds in nanostructures with tiny (attofarad) gate capacitance, where similar capacitance-voltage methods are challenging or impossible. We find that the evolution of channel potential with gate voltage is suppressed in the transistor's accumulation regime due to the screening effects of surface states with D ss = 1-- 2 x 1012 cm-2 eV-1. The gate voltage dependence of the random telegraph signals were used as a novel probe to spectroscopically study strong carrier reflection by single Coulomb impurities in nanowires. Reflection probabilities R = 0.98 -- 0.999 approach unity for an electron gas with density n = 30 -- 10 /mum in 30 nm diameter, 1 mum long InAs nanowires at 30 K. Results were compared with microscopic theory of electron scattering by Coulomb impurities in nanowires with dielectric confinement, i.e low dielectric constant surroundings. The latter, which is known to enhance the bare Coulomb interaction and excitonic binding energy, is an essential ingredient for the strong scattering in this regime, and in small diameter nanowires causes a breakdown in linear screening. Extending this, we show that InAs nanowires can operate is extremely sensitive charge sensors with sensitivity 60 mueHz-1/2 at high temperatures (200 K), a combination of characteristics that is not achieved by existing technology. Strong electrostatic coupling of a single charge to the conducting electron gas in the nanowire is enabled by miniaturization of nanowire diameter, operation in a regime of carrier density where the electronic screening length exceeds the nanowire diameter, and dielectric confinement. Finally, single ZnSe nanowire photodetectors are fabricated and studied. Peak responsivity at 2.0 V bias is 20 A/W at room temperature, similar to that of the best epitaxial ZnSe photodetectors. The high responsivity is due to a photoconductive gain g ? 500, the ratio of carrier lifetime to carrier transit time. The former is enhanced at room temperature due to rapid selective trapping of one species of excited carriers by surface states.

  19. 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.

  20. Subpicosecond to Second Time-Scale Charge Carrier Kinetics in Hematite-Titania Nanocomposite Photoanodes.

    PubMed

    Ruoko, Tero-Petri; Kaunisto, Kimmo; Brtsch, Mario; Pohjola, Juuso; Hiltunen, Arto; Niederberger, Markus; Tkachenko, Nikolai V; Lemmetyinen, Helge

    2015-08-01

    Water splitting with hematite is negatively affected by poor intrinsic charge transport properties. However, they can be modified by forming heterojunctions to improve charge separation. For this purpose, charge dynamics of TiO2:?-Fe2O3 nanocomposite photoanodes are studied using transient absorption spectroscopy to monitor the evolution of photogenerated charge carriers as a function of applied bias voltage. The bias affects the charge carrier dynamics, leading to trapped electrons in the submillisecond time scale and an accumulation of holes with a lifetime of 0.4 0.1 s. By contrast, slower electron trapping and only few long-lived holes are observed in a bare hematite photoanode. The decay of the long-lived holes is 1 order of magnitude faster for the composite photoanodes than previously published for doped hematite, indicative of higher catalytic efficiency. These results illustrate the advantages of using composite materials to overcome poor charge carrier dynamics, leading to a 30-fold enhancement in photocurrent. PMID:26267170

  1. Charge transport in nanoscale junctions.

    PubMed

    Albrecht, Tim; Kornyshev, Alexei; Bjrnholm, 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 the molecular level. Nanoscale charge transport experiments in ionic liquids extend the field to high temperatures and to systems with intriguing interfacial potential distributions. Other directions may include dye-sensitized solar cells, new sensor applications and diagnostic tools for the study of surface-bound single molecules. Another motivation for this special issue is thus to highlight activities across different research communities with nanoscale charge transport as a common denominator. This special issue gathers 27 articles by scientists from the United States, Germany, the UK, Denmark, Russia, France, Israel, Canada, Australia, Sweden, Switzerland, the Netherlands, Belgium and Singapore; it gives us a flavour of the current state-of-the-art of this diverse research area. While based on contributions from many renowned groups and institutions, it obviously cannot claim to represent all groups active in this very broad area. Moreover, a number of world-leading groups were unable to take part in this project within the allocated time limit. Nevertheless, we regard the current selection of papers to be representative enough for the reader to draw their own conclusions about the current status of the field. Each paper is original and has its own merit, as all papers in Journal of Physics: Condensed Matter special issues are subjected to the same scrutiny as regular contributions. The Guest Editors have deliberately not defined the specific subjects covered in this issue. These came out logically from the development of this area, for example: 'Traditional' solid state nanojunctions based on adsorbed layers, oxide films or nanowires sandwiched between two electrodes: effects of molecular structure (aromaticity, anchoring groups), symmetry, orientation, dynamics (noise patterns) and current-induced heating. Various 'physical effects': inelastic tunnelling and Coulomb blockade, polaron effects, switching modes, and negative differential resistance; the role of many particle excitations, new surface states in semiconductor electrodes, various mechanisms for

  2. 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 significantly reduced oral bioavailability of CRV niosomes. Overall twofold enhancement in bioavailability in comparison with drug suspension confers the potential of niosomes as suitable carriers for improved oral delivery of CRV. PMID:26251598

  3. Charge transport in single crystal organic semiconductors

    NASA Astrophysics Data System (ADS)

    Xie, Wei

    Organic electronics have engendered substantial interest in printable, flexible and large-area applications thanks to their low fabrication cost per unit area, chemical versatility and solution processability. Nevertheless, fundamental understanding of device physics and charge transport in organic semiconductors lag somewhat behind, partially due to ubiquitous defects and impurities in technologically useful organic thin films, formed either by vacuum deposition or solution process. In this context, single-crystalline organic semiconductors, or organic single crystals, have therefore provided the ideal system for transport studies. Organic single crystals are characterized by their high chemical purity and outstanding structural perfection, leading to significantly improved electrical properties compared with their thin-film counterparts. Importantly, the surfaces of the crystals are molecularly flat, an ideal condition for building field-effect transistors (FETs). Progress in organic single crystal FETs (SC-FETs) is tremendous during the past decade. Large mobilities ~ 1 - 10 cm2V-1s-1 have been achieved in several crystals, allowing a wide range of electrical, optical, mechanical, structural, and theoretical studies. Several challenges still remain, however, which are the motivation of this thesis. The first challenge is to delineate the crystal structure/electrical property relationship for development of high-performance organic semiconductors. This thesis demonstrates a full spectrum of studies spanning from chemical synthesis, single crystal structure determination, quantum-chemical calculation, SC-OFET fabrication, electrical measurement, photoelectron spectroscopy characterization and extensive device optimization in a series of new rubrene derivatives, motivated by the fact that rubrene is a benchmark semiconductor with record hole mobility ~ 20 cm2V-1s-1. With successful preservation of beneficial pi-stacking structures, these rubrene derivatives form 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 ~ ?F/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 addition, Hall effect and temperature-dependent measurements are employed for more in-depth unders

  4. 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.

  5. 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.

  6. Interaction of yeast 3-phosphoglycerate kinase with negatively charged carriers.

    PubMed

    Roustan, C; Fattoum, A; Jeanneau, R; Pradel, L A; Schuhmann, D; Vanel, P

    1982-05-01

    The aim of this study was to investigate the possibility of an interaction of yeast 3-phosphoglycerate kinase with negatively charged carriers such as polyanionic agents or a polarized electrode. Various polyanions were found to promote enzyme aggregation as judged by ultracentrifugation measurements and chemical modification. The data obtained suggest that these interactions are mediated through the N-terminal domain of the protein. However, the most striking property of 3-phosphoglycerate kinase described here is concerned with its significant dipolar moment as evidenced by electrocapillary measurements, which allows an orientation of the macromolecule in an electric field. Further, the enzyme could be absorbed by a negatively charged surface, first by hydrophobic links and then oriented perpendicularly to the surface. Therefore, the intrinsic properties of yeast 3-phosphoglycerate kinase agree with the formation of an enzyme-membrane complex and afford the ability for a specific orientation of the molecule at the lipid bilayer surface or in the cytoplasm. PMID:6178443

  7. Acoustic carrier transportation induced by surface acoustic waves in graphene in solution

    NASA Astrophysics Data System (ADS)

    Okuda, Satoshi; Ikuta, Takashi; Kanai, Yasushi; Ono, Takao; Ogawa, Shinpei; Fujisawa, Daisuke; Shimatani, Masaaki; Inoue, Koichi; Maehashi, Kenzo; Matsumoto, Kazuhiko

    2016-04-01

    The acoustic charge transportation induced by surface acoustic wave (SAW) propagation in graphene in solution was investigated. The sign of acoustic current (I A) was found to switch when crossing the Dirac point because the major carrier was transitioned from holes to electrons by the change in electrolyte-gate voltage. I A also exhibited a peak value under conditions of both hole and electron conduction. These results can be explained on the basis of a change in the type of major carrier in graphene, as well as a change in the carrier mobility of graphene.

  8. Charge Transport in Polypyrrole Nanotubes.

    PubMed

    Majumdar, Dipanwita; Saha, Shyamal Kumar

    2015-12-01

    True metallic conductivity in conjugated polymers has been major challenge for the last few years. Heeger and co-workers have reported metallic conductivity in bulk polyaniline film, but the problem of metallic transport in their nanophase still remains unexplored. In the recent past, our group had observed metallic conductivity in single nanotube by studying I-V characteristics using Atomic Force Microscopy. In the present work, Polypyrrole (PPy) nanotubes with variable wall thickness have been synthesized by chemical route. Electrical measurements--current-voltage characteristics as well as variation of resistance over the temperature range from 12 K to 300 K for these nanotubes with variable wall thickness, have also been carried out. The conductivity varies widely from semiconductor to metallic as the wall thickness decreases. Transmission Electron Microscopic study, further, confirms that very aligned and ordered polymer chains are formed due to directional growth in thin walled polypyrrole nanotubes, results in true metallic conductivity with a positive temperature coefficient of resistance over the whole temperature range. To the best of our knowledge, there is no such systematic study reported so far which embraces variation of charge transport characteristics with varying wall thickness of conjugated polymer nanotubes involving both I-V and R-T measurements supplementing each other, which being the main focus of this communication. PMID:26682442

  9. Measuring charge carrier diffusion in coupled colloidal quantum dot solids.

    PubMed

    Zhitomirsky, David; Voznyy, Oleksandr; Hoogland, Sjoerd; Sargent, Edward H

    2013-06-25

    Colloidal quantum dots (CQDs) are attractive materials for inexpensive, room-temperature-, and solution-processed optoelectronic devices. A high carrier diffusion length is desirable for many CQD device applications. In this work we develop two new experimental methods to investigate charge carrier diffusion in coupled CQD solids under charge-neutral, i.e., undepleted, conditions. The methods take advantage of the quantum-size-effect tunability of our materials, utilizing a smaller-bandgap population of quantum dots as a reporter system. We develop analytical models of diffusion in 1D and 3D structures that allow direct extraction of diffusion length from convenient parametric plots and purely optical measurements. We measure several CQD solids fabricated using a number of distinct methods and having significantly different doping and surface ligand treatments. We find that CQD materials recently reported to achieve a certified power conversion efficiency of 7% with hybrid organic-inorganic passivation have a diffusion length of 80 10 nm. The model further allows us to extract the lifetime, trap density, mobility, and diffusion coefficient independently in each material system. This work will facilitate further progress in extending the diffusion length, ultimately leading to high-quality CQD solid semiconducting materials and improved CQD optoelectronic devices, including CQD solar cells. PMID:23701285

  10. The charge bag mechanism of superconductivity in carrier injected charge density wave systems

    NASA Astrophysics Data System (ADS)

    Gaitonde, D. M.; Behera, S. N.

    1991-02-01

    A new mechanism is proposed for superconductivity (SC) arising in carrier injected charge density wave (CDW) insulators. It is demonstrated that an attractive interaction between the injected charge carriers is predominantly generated by the exchange of the CDW-amplitude mode, which is a high frequency optic phonon of the lattice distorted CDW state. This attractive interaction then produces pairing and hence superconductivity, whose transition temperature ( Tc) is enhanced due to an increase in the cutoff frequency as well as the density of states at the Fermi level. It is argued that the model can successfully explain the high temperature superconductivity observed in the perovskite compound Ba 1- xK xBiO 3. An understanding of the enhancement of Tc on intercalation in certain layered transition metal dichalchogenides can also be achieved in terms of this charge bag model.

  11. Microscopic Simulations of Charge Transport in Disordered Organic Semiconductors

    PubMed Central

    2011-01-01

    Charge carrier dynamics in an organic semiconductor can often be described in terms of charge hopping between localized states. The hopping rates depend on electronic coupling elements, reorganization energies, and driving forces, which vary as a function of position and orientation of the molecules. The exact evaluation of these contributions in a molecular assembly is computationally prohibitive. Various, often semiempirical, approximations are employed instead. In this work, we review some of these approaches and introduce a software toolkit which implements them. The purpose of the toolkit is to simplify the workflow for charge transport simulations, provide a uniform error control for the methods and a flexible platform for their development, and eventually allow in silico prescreening of organic semiconductors for specific applications. All implemented methods are illustrated by studying charge transport in amorphous films of tris-(8-hydroxyquinoline)aluminum, a common organic semiconductor. PMID:22076120

  12. Surface states of charge carriers in epitaxial films of the topological insulator Bi2Te3

    NASA Astrophysics Data System (ADS)

    Luk'yanova, L. N.; Boikov, Yu. A.; Danilov, V. A.; Usov, O. A.; Volkov, M. P.; Kutasov, V. A.

    2014-05-01

    The galvanomagnetic properties of p-type bismuth telluride heteroepitaxial films grown by the hot wall epitaxy method on oriented muscovite mica substrates have been investigated. Quantum oscillations of the magnetoresistance associated with surface electronic states in three-dimensional topological insulators have been studied in strong magnetic fields ranging from 6 to 14 T at low temperatures. The cyclotron effective mass, charge carrier mobility, and parameters of the Fermi surface have been determined based on the results of analyzing the magnetoresistance oscillations. The dependences of the cross-sectional area of the Fermi surface S( k F), the wave vector k F, and the surface concentration of charge carriers n s on the frequency of magnetoresistance oscillations in p-type Bi2Te3 heteroepitaxial films have been obtained. The experimentally observed shift of the Landau level index is consistent with the value of the Berry phase, which is characteristic of topological surface states of Dirac fermions in the films. The properties of topological surface states of charge carriers in p-type Bi2Te3 films obtained by analyzing the magnetoresistance oscillations significantly expand fields of practical application and stimulate the investigation of transport properties of chalcogenide films.

  13. 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.

  14. 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.

  15. Control of carrier transport in organic semiconductors by aluminum doping

    NASA Astrophysics Data System (ADS)

    Wang, Z. J.; Wu, Y.; Zhou, Y. C.; Zhou, J.; Zhang, S. T.; Ding, X. M.; Hou, X. Y.; Zhu, Z. Q.

    2006-05-01

    Control of carrier transport in organic semiconductors by aluminum doping is realized in organic light-emitting devices (OLEDs) for which electroluminescence can sensitively reflect the status of carrier transport. It is found that an Al-doped layer with proper thickness (1-10nm) may block hole transport completely and enhance electron transport to some extent regardless of its location in the organic carrier transport layers. Improvement in the efficiency of OLEDs with an aluminum cathode is achieved upon the introduction of a very thin (3nm) Al-doped region near the light-emitting area. The current efficiency obtained with such Al-doped devices is about 30% higher than that with undoped devices.

  16. 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 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...

  17. Mechanisms of carrier transport induced by a microswimmer bath.

    PubMed

    Kaiser, Andreas; Sokolov, Andrey; Aranson, Igor S; Löwen, Hartmut

    2015-04-01

    It was shown that a wedgelike microparticle (referred to as "carrier") 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 a V-shaped carrier. We show that the transport mechanism itself strongly depends on the degree of alignment embodied in the modeling 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. PMID:25347885

  18. Layered Distribution of Charge Carriers in Organic Thin Film Transistors

    NASA Astrophysics Data System (ADS)

    Shehu, Arian; Quiroga, Santiago D.; D'Angelo, Pasquale; Albonetti, Cristiano; Borgatti, Francesco; Murgia, Mauro; Scorzoni, Andrea; Stoliar, Pablo; Biscarini, Fabio

    2010-06-01

    Drain-source current in organic thin-film transistors has been monitored in situ and in real time during the deposition of pentacene. The current starts to flow when percolation of the first monolayer (ML) occurs and, depending on the deposition rate, saturates at a coverage in the range 2-7 MLs. The number of active layers contributing to the current and the spatial distribution of charge carriers are modulated by the growth mode. The thickness of the accumulation layer, represented by an effective Debye length, scales as the morphological correlation length. These results show that the effective Debye length is not just a material parameter, but depends on the multiscale morphology. Earlier controversial results can be unified within this framework.

  19. Stress-Activated Electronic Charge Carriers in Igneous Rocks

    NASA Astrophysics Data System (ADS)

    Pan, C. T.; Jones, H. H.; Freund, F. T.

    2006-12-01

    Igneous rocks, when subjected to deviatory stress, turn into a battery. We report on gabbro (Shanxi, China) and anorthosite (Larvik, Norway). We use tiles, 30 x 30 x 0.9 cm3, and a pair of steel pistons, 4.4 cm diameter to subject a small off-center volume of ~10 cm3 to 10 MPa, about 5% failure strength. Instantly upon loading, two types of electronic charge carriers are activated in the stressed rock volume and a current begins to flow. One current leg is carried by holes, which flow from the stressed through the unstressed rock to the edges of the tile. The other current leg is carried by electrons, which flow from the stressed rock into the steel pistons and through the external wire to the edge, where they meet the holes. We have measured the impedance of the gabbro and anorthosite over the frequency range from <1 Hz to 10 MHz. We measured the impedence across the 10 cm3 volume between the two pistons and a similar volume outside the pistons in the path of the holes flowing to the edges of the tile: (1) before loading, (2) during loading. We obtain thus information about both types of charge carriers, electrons and holes. Both are associated with oxygen anions that changed their valence from 2- to 1- (peroxy). An O- among O2- represents a defect electron in the O2- sublattice, known as positive hole or p-hole for short. In unstressed rocks the O- exist in an electrically inactive form as O- pairs, chemically equivalent to peroxy links, O3X-OO-XO3 with X = Si4+, Al3+ etc. Stresses cause the peroxy links to break, allowing electrons from neighboring O2- to jump in and p-holes to jump out. The p-holes can spread through unstressed rocks using energy levels at the upper edge of the valence band.

  20. Top-gate dielectric induced doping and scattering of charge carriers in epitaxial graphene

    NASA Astrophysics Data System (ADS)

    Puls, Conor P.; Staley, Neal E.; Moon, Jeong-Sun; Robinson, Joshua A.; Campbell, Paul M.; Tedesco, Joseph L.; Myers-Ward, Rachael L.; Eddy, Charles R.; Gaskill, D. Kurt; Liu, Ying

    2011-07-01

    We show that an e-gun deposited dielectric impose severe limits on epitaxial graphene-based device performance based on Raman spectroscopy and low-temperature transport measurements. Specifically, we show from studies of epitaxial graphene Hall bars covered by SiO2 that the measured carrier density is strongly inhomogenous and predominantly induced by charged impurities at the grapheme/dielectric interface that limit mobility via Coulomb interactions. Our work emphasizes that material integration of epitaxial graphene and a gate dielectric is the next major road block towards the realization of graphene-based electronics.

  1. Charge carrier trapping into mobile, ionic defects in nanoporous ultra-low-k dielectric materials

    NASA Astrophysics Data System (ADS)

    Plawsky, Joel; Borja, Juan; Lu, Toh-Ming; Gill, William

    2014-03-01

    Reliability and robustness of low-k materials for advanced interconnects has become a major challenge for the continuous down-scaling of silicon semiconductor devices. Metal catalyzed time dependent breakdown (TDDB) is a major force preventing the integration of sub-32nm process technology nodes. We investigate how ionic species can become trapping centers (mobile defects) for charge carriers. A mechanism for describing and quantifying the trapping of charge carriers into mobile ions under bias and temperature stress is presented and experimentally investigated. The dynamics of trapping into ionic centers are severely impacted by temperature and species mass transport. After extended bias and temperature stress, the magnitude of charge trapping into ionic centers decreases asymptotically. Various processes such as the reduction of ionic species, moisture outgassing, and the inhibition of ionic drift via the distortion of local fields were investigated as possible cause for the reduction in charge trapping. Simulations suggest that built-in fields reduce the effect of an externally applied field in directing ionic drift, which can lead to the inhibition of the trapping mechanism. In addition, conduction mechanisms are investigated for reactive and inert electrodes. Seimconductor Research Corporation.

  2. Proton-irradiation effects on the charge transport in highly oriented pyrolytic graphite

    NASA Astrophysics Data System (ADS)

    Kim, Jinsoo; Kim, Dowan; Lee, Kyu Won; Choi, E. H.; Noh, S. J.; Kim, H. S.; Lee, Cheol Eui

    2014-05-01

    We have investigated the proton-irradiation effects on the electrical resistivity and magnetoresistance of highly oriented pyrolytic graphite (HOPG). The temperature- and magnetic field-dependent measurements indicate that the carrier mobility rather than the carrier density dictates the charge transport in the HOPG systems.

  3. Transmission line model for strained quantum well lasers including carrier transport and carrier heating effects.

    PubMed

    Xia, Mingjun; Ghafouri-Shiraz, H

    2016-03-01

    This paper reports a new model for strained quantum well lasers, which are based on the quantum well transmission line modeling method where effects of both carrier transport and carrier heating have been included. We have applied this new model and studied the effect of carrier transport on the output waveform of a strained quantum well laser both in time and frequency domains. It has been found that the carrier transport increases the turn-on, turn-off delay times and damping of the quantum well laser transient response. Also, analysis in the frequency domain indicates that the carrier transport causes the output spectrum of the quantum well laser in steady state to exhibit a redshift which has a narrower bandwidth and lower magnitude. The simulation results of turning-on transients obtained by the proposed model are compared with those obtained by the rate equation laser model. The new model has also been used to study the effects of pump current spikes on the laser output waveforms properties, and it was found that the presence of current spikes causes (i) wavelength blueshift, (ii) larger bandwidth, and (iii) reduces the magnitude and decreases the side-lobe suppression ratio of the laser output spectrum. Analysis in both frequency and time domains confirms that the new proposed model can accurately predict the temporal and spectral behaviors of strained quantum well lasers. PMID:26974607

  4. 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.

  5. 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.

  6. Realization of Room-Temperature Phonon-Limited Carrier Transport in Monolayer MoS2 by Dielectric and Carrier Screening.

    PubMed

    Yu, Zhihao; Ong, Zhun-Yong; Pan, Yiming; Cui, Yang; Xin, Run; Shi, Yi; Wang, Baigeng; Wu, Yun; Chen, Tangsheng; Zhang, Yong-Wei; Zhang, Gang; Wang, Xinran

    2016-01-01

    By combining a high-? dielectric substrate and a high density of charge carriers, Coulomb impurities in MoS2 can be effectively screened, leading to an unprecedented room-temperature mobility of ?150 cm(2) V(-1) s(-1) and room-temperature phonon-limited transport in a monolayer MoS2 transistor for the first time. PMID:26603698

  7. Thermodynamic picture of ultrafast charge transport in graphene

    PubMed Central

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

    2015-01-01

    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. PMID:26179498

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

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

    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 CH3NH3PbI3 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.

  9. Quantum control of charge carrier dynamics in layered semiconductor heterostructures

    NASA Astrophysics Data System (ADS)

    Shuford, Kevin Lee

    This dissertation presents theoretical studies of charge carrier dynamics in layered semiconductor heterostructures. Carrier dynamics are investigated by solving the Schrodinger equation numerically on a grid. Control methods are used to discover laser pulses that actively manipulate and control dynamics in quantum well systems. Results indicate that a wide array of possible target objectives can be achieved successfully using simple, experimentally feasible electric fields. A tailored laser pulse can drive an electronic wave packet to maximum overlap with a target distribution at a specified time. A genetic algorithm is used to determine the optimal parameters of the excitation pulse. The robustness of the results is analyzed by considering fluctuations in the do field, two types of sample defects, and environmental coupling. In all cases studied, the genetic algorithm can re-optimize the laser field to achieve the control objective. The effects of Coulomb interactions with regard to controlling wave packets in quantum wells are investigated. The goal is to clarify the extent that the attraction between electrons and holes affects control. The primary effect is to modify the energy splittings, which induces small changes in oscillation period and frequency of the wave packet. The results show that the interaction does not substantially affect the control, yet can alter dynamics in some cases. Quantum wells are sources of controllable radiation. Oscillating wave packets in the conduction band typically radiate in the Terahertz frequency regime. The frequency and amplitude of the radiation is tunable by altering excitation conditions. Terahertz fields can be designed by controlling the characteristics of the emission, and used as excitation sources for other applications. Electronic population can be switched adiabatically between quantum wells. A time-dependent do field guides an initial state along a smooth path to a target state. The general requirements for adiabaticity are determined. Successfully meeting the requirements produces a pure state that evolves adiabatically to the final state. This procedure provides an effective method for adiabatic passage with smooth transitions, selectivity, and reversibility.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. Electron and molecular dynamics: Penning ionization and molecular charge transport

    NASA Astrophysics Data System (ADS)

    Madison, Tamika Arlene

    An understanding of fundamental reaction dynamics is an important problem in chemistry. In this work, experimental and theoretical methods are combined to study the dynamics of fundamental chemical reactions. Molecular collision and dissociation dynamics are explored with the Penning ionization of amides, while charge transfer reactions are examined with charge transport in organic thin film devices. Mass spectra from the Penning ionization of formamide by He*, Ne*, and Ar* were measured using molecular beam experiments. When compared to 70eV electron ionization spectra, the He* and Ne* spectra show higher yields of fragments resulting from C--N and C--H bond cleavage, while the Ar* spectrum only shows the molecular ion, H-atom elimination, and decarbonylation. The differences in yields and observed fragments are attributed to the differences in the dynamics of the two ionization methods. Fragmentation in the Ar* spectrum was analyzed using quantum chemistry and RRKM calculations. Calculated yields for the Ar* spectrum are in excellent agreement with experiment and show that 15% and 50% of the yields for decarbonylation and H-atom elimination respectively are attributed to tunneling. The effects of defects, traps, and electrostatic interactions on charge transport in imperfect organic field effect transistors were studied using course-grained Monte Carlo simulations with explicit introduction of defect and traps. The simulations show that electrostatic interactions dramatically affect the field and carrier concentration dependence of charge transport in the presence of a significant number of defects. The simulations also show that while charge transport decreases linearly as a function of neutral defect concentration, it is roughly unaffected by charged defect concentration. In addition, the trap concentration dependence on charge transport is shown to be sensitive to the distribution of trap sites. Finally, density functional theory calculations were used to study how charge localization affects the orbital energies of positively charged bithiophene clusters. These calculations show that the charge delocalizes over at least seven molecules, is more likely to localize on "tilted" molecules due to polarization effects, and affects molecules anisotropically. These results suggest that models for charge transport in organic semiconductors should be modified to account for charge delocalization and intermolecular interactions.

  15. 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

  16. 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 (?) were 1096.20 ?/sq, 0.751012 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 0.661012 cm-2 to 1.551012 cm-2, sheet resistance (Rs) decreased from 1215.55 ?/sq to 560.77 ?/sq, and mobility (?) 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 (?) was the lattice defect scattering and a small amount of impurity scattering, the carrier mobility (?) was temperature-independent for the bilayer graphene.

  17. 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

  18. 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.

  19. 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.

  20. 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

  1. 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

  2. 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

  3. 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 reduced and trap densities and average trap depths were increased, as compared to a pristine ADT donor film. A considerably slower recombination of free holes with trapped electrons was found in the composite with the PCBM acceptor, which led to slower decays of the transient photocurrent and considerably higher charge retention, as compared to a pristine ADT donor film and the composite with the functionalized Pn acceptor.

  4. Where are the charge carriers along a closed circuit? A relativistic description

    NASA Astrophysics Data System (ADS)

    Fautrat, Sylvain

    2016-03-01

    We present relativistic transformations of charge densities for a closed electric circuit consisting of straight sections of finite length wires. The study of charge carrier movement is made in the rest frame of carriers, and with only basic relativistic kinematics, we follow a group of charge carriers along the different segments of the circuit. From the change in inter-particle distances when moving from one wire segment to another, expressions for the charge densities are deduced. This approach aims to provide a deeper understanding of the relativistic motion of objects around a closed loop.

  5. 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.

  6. 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…

  7. Magnetoresistance and charge transport in graphene governed by nitrogen dopants.

    PubMed

    Rein, Markus; Richter, Nils; Parvez, Khaled; Feng, Xinliang; Sachdev, Hermann; Klui, Mathias; Mllen, Klaus

    2015-02-24

    We identify the influence of nitrogen-doping on charge- and magnetotransport of single layer graphene by comparing doped and undoped samples. Both sample types are grown by chemical vapor deposition (CVD) and transferred in an identical process onto Si/SiO2 wafers. We characterize the samples by Raman spectroscopy as well as by variable temperature magnetotransport measurements. Over the entire temperature range, the charge transport properties of all undoped samples are in line with literature values. The nitrogen doping instead leads to a 6-fold increase in the charge carrier concentration up to 4 10(13) cm(-2) at room temperature, indicating highly effective doping. Additionally it results in the opening of a charge transport gap as revealed by the temperature dependence of the resistance. The magnetotransport exhibits a conspicuous sign change from positive Lorentz magnetoresistance (MR) in undoped to large negative MR that we can attribute to the doping induced disorder. At low magnetic fields, we use quantum transport signals to quantify the transport properties. Analyses based on weak localization models allow us to determine an orders of magnitude decrease in the phase coherence and scattering times for doped samples, since the dopants act as effective scattering centers. PMID:25548883

  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. 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 impurities, neutral impurities, static dipoles, and capture forming anion ( D-/A+) states. We also generate predictions for impact ionization of shallow impurities and of impact neutralization of D- /A+ states. We use measurements of carrier capture performed on CDMS detectors to validate a plausible model for electron and hole capture due to neutral shallow impurities and their charged D-/A + states. This model, along with carrier drift and diffusion parameters from Monte Carlo simulation, can be used as the foundation for simulations of space charge evolution in CDMS detectors, simultaneously solving continuity equations with Poisson's equation.

  10. Disrupted Attosecond Charge Carrier Delocalization at a Hybrid Organic/Inorganic Semiconductor Interface.

    PubMed

    Racke, David A; Kelly, Leah L; Kim, Hyungchul; Schulz, Philip; Sigdel, Ajaya; Berry, Joseph J; Graham, Samuel; Nordlund, Dennis; Monti, Oliver L A

    2015-05-21

    Despite significant interest in hybrid organic/inorganic semiconductor interfaces, little is known regarding the fate of charge carriers at metal oxide interfaces, particularly on ultrafast time scales. Using core-hole clock spectroscopy, we investigate the ultrafast charge carrier dynamics of conductive ZnO films at a hybrid interface with an organic semiconductor. The adsorption of C60 on the ZnO surface strongly suppresses the ultrafast carrier delocalization and increases the charge carrier residence time from 400 attoseconds to nearly 30 fs. Here, we show that a new hybridized interfacial density of states with substantial molecular character is formed, fundamentally altering the observed carrier dynamics. The remarkable change in the dynamics sheds light on the fate of carriers at hybrid organic/inorganic semiconductor interfaces relevant to organic optoelectronics and provides for the first time an atomistic picture of the electronically perturbed near-interface region of a metal oxide. PMID:26263273

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

    PubMed

    Gao, Feng; Tress, Wolfgang; Wang, Jianpu; Ingans, 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

  12. 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.

  13. Clarification of Charge Separation and Transport Behavior at Two-dimensional Charge Sheet of Organic Donor/Acceptor Heterointerfaces

    NASA Astrophysics Data System (ADS)

    Irie, Toru; Sakanoue, Tomo; Adachi, Chihaya

    Organic donor/acceptor bilayers form a two-dimensional charge sheet composed of electron-hole pairs at their heterointerfaces due to formation of charge-transfer (CT) complexes. The CT induces electron-hole pairs which are useful for carrier transport in both vertical and lateral direction, providing novel electronic device applications. Here, we fabricated a two-dimensional charge sheet using organic donor/acceptor heterointerfaces and investigated its electrical behavior. Further, we revealed that conductive CT interfaces are generated by stacking almost monolayer of donor and acceptor thin films. These novel charge induction mechanisms will provide a new principle for designing organic devices.

  14. 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.

  15. Electron spin resonance observation of charge carrier concentration in organic field-effect transistors during device operation

    NASA Astrophysics Data System (ADS)

    Tanaka, Hisaaki; Hirate, Masataka; Watanabe, Shun-ichiro; Kaneko, Kazuaki; Marumoto, Kazuhiro; Takenobu, Taishi; Iwasa, Yoshihiro; Kuroda, Shin-ichi

    2013-01-01

    Charge carrier concentration in operating organic field-effect transistors (OFETs) reflects the electric potential within the channel, acting as a key quantity to clarify the operation mechanism of the device. Here, we demonstrate a direct determination of charge carrier concentration in the operating devices of pentacene and poly(3-hexylthiophene) (P3HT) by field-induced electron spin resonance (FI-ESR) spectroscopy. This method sensitively detects polarons induced by applying gate voltage, giving a clear FI-ESR signal around g=2.003 in both devices. Upon applying drain-source voltage, carrier concentration decreases monotonically in the FET linear region, reaching about 70% of the initial value at the pinch-off point, and stayed constant in the saturation region. The observed results are reproduced well from the theoretical potential profile based on the gradual channel model. In particular, the carrier concentration at the pinch-off point is calculated to be ?/(?+1) of the initial value, where ? is the power exponent in the gate voltage (Vgs) dependence of the mobility (?), expressed as ??Vgs?-2, providing detailed information of charge transport. The present devices show ?=2.6 for the pentacene and ?=2.3 for the P3HT cases, consistent with those determined by transfer characteristics. The gate voltage dependence of the mobility, originating from the charge trapping at the device interface, is confirmed microscopically by the motional narrowing of the FI-ESR spectra.

  16. 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.

  17. Nanocone Tip-Film Solar Cells with Efficient Charge Transport

    SciTech Connect

    Lee, Sang Hyun; Zhang, Xiaoguang; Parish, Chad M; Smith, Barton; Xu, Jun; Lee, Ho Nyung

    2011-01-01

    Nanojunctions promise to provide higher charge transport efficiencies and less costly solar cell fabrication methods. We report a three-dimensional (3D) solar cell structure based on interdigitated nanojunctions formed with the tips of n-type ZnO nanocones embedded in a p-type polycrystalline (PX) CdTe film. This 3D nanocone tip-film cell, without optimization, enabled 3.2% power conversion efficiency, higher than that produced by a planar solar cell fabricated using the same materials. Reducing CdTe grain size and enriching the grain boundaries with chlorine improved the conversion efficiency for the tip-film structure. This higher conversion efficiency is attributable to improved charge transport in the nanojunction due to a combination of the high electric field generated in the CdTe and the utilization of the small junction area. The high field facilitates the extraction of minority carriers from the photoactive layer to the small junction region, while the use of the small junction area reduces the total electron recombination loss. The improved carrier transport in the nanocone tip-film junction implies that nanocone-based photovoltaic solar cells are capable of tolerating the imperfect materials produced using low-cost fabrication methods.

  18. Influence of Lifshitz transitions and correlation effects on the scattering rates of the charge carriers in iron-based superconductors

    NASA Astrophysics Data System (ADS)

    Fink, J.

    2016-01-01

    Minimum model calculations on the co-action of hole vanishing Lifshitz transitions and correlation effects in ferropnictides are presented. The calculations predict non-Fermi-liquid behaviour and huge mass enhancements of the charge carriers at the Fermi level. The findings are compared with recent ARPES experiments and with measurements of transport and thermal properties of ferropnictides. The results from the calculation can be also applied to other unconventional superconductors and question the traditional view of quantum-critical points.

  19. 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

  20. 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

  1. 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.

  2. Minority-charge-carrier mobility at low injection level in semiconductors

    SciTech Connect

    Pomortseva, L. I.

    2011-04-15

    From the kinetic equations, the distribution functions for majority and minority charge carriers are obtained at a low injection level. For describing the electron-hole collisions, the Landau collision integral is used. The carrier scattering at ionized or neutral impurity and at acoustic phonons is taken into account. The majority-carrier distribution function is presented in the analytical form. The minority-carrier mobility is calculated and analyzed, and the features of its behavior at low temperatures are revealed. It follows from the developed theory that the hole mobility in an n-type material increases with doping and neutral-impurity concentration. This effect is attributed to mutual charge-carrier collisions and different effective masses of different-sign carriers.

  3. Ultrafast charge carrier relaxation and charge transfer processes in CdS/CdTe thin films.

    PubMed

    Pandit, Bill; Dharmadasa, Ruvini; Dharmadasa, I M; Druffel, Thad; Liu, Jinjun

    2015-07-14

    Ultrafast transient absorption pump-probe spectroscopy (TAPPS) has been employed to investigate charge carrier relaxation in cadmium sulfide/cadmium telluride (CdS/CdTe) nanoparticle (NP)-based thin films and electron transfer (ET) processes between CdTe and CdS. Effects of post-growth annealing treatments to ET processes have been investigated by carrying out TAPPS experiments on three CdS/CdTe samples: as deposited, heat treated, and CdCl2 treated. Clear evidence of ET process in the treated thin films has been observed by comparing transient absorption (TA) spectra of CdS/CdTe thin films to those of CdS and CdTe. Quantitative comparison between ultrafast kinetics at different probe wavelengths unravels the ET processes and enables determination of its rate constants. Implication of the photoinduced dynamics to photovoltaic devices is discussed. PMID:26033446

  4. Temperature-dependent effects of cholesterol on sodium transport through lipid membranes by an ionizable mobile carrier.

    PubMed

    Wehrli, S; Ramirez, C; Kraus, J L; Castaing, M

    1992-06-30

    Temperature-jump relaxation experiments on Na+ transport by (221)C10-cryptand were carried out in order to study the influence of cholesterol and its temperature-dependence on ion transport through thin lipid membranes. The experiments were performed on large, negatively charged unilamellar vesicles (LUV) prepared from mixtures of dioleoylphosphatidylcholine, phosphatidic acid and cholesterol (mole fractions 0-0.43), at various temperatures and carrier concentrations. The initial rates of Na+ transport and the apparent rate constants of its translocation by (221)C10 increased with the carrier concentration and the temperature. The incorporation of cholesterol into the membranes significantly reduced the carrier concentration- and temperature-dependence of these two parameters. The apparent energy required to activate the transport decreased significantly with increasing carrier concentrations at any given cholesterol molar fraction, and increased significantly with the cholesterol molar fraction at any given carrier concentration. Our interpretation of the action of cholesterol on this transport system is based on the assumption that the binding cavity of cryptands is likely to be located towards the aqueous side of the dipole layer. The results are discussed in terms of the structural, physico-chemical and electrical characteristics of carriers and complexes, and of the interactions occurring between an ionizable mobile carrier and the membrane. PMID:1504075

  5. 47 CFR 69.154 - Per-minute carrier common line charge.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... weighting method set forth in paragraph (c) of this section. The maximum such charge shall be the lower of... the weighting method set forth in paragraph (c) of this section. (c) For each Carrier Common...

  6. 47 CFR 69.154 - Per-minute carrier common line charge.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... weighting method set forth in paragraph (c) of this section. The maximum such charge shall be the lower of... the weighting method set forth in paragraph (c) of this section. (c) For each Carrier Common...

  7. 47 CFR 69.154 - Per-minute carrier common line charge.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... weighting method set forth in paragraph (c) of this section. The maximum such charge shall be the lower of... the weighting method set forth in paragraph (c) of this section. (c) For each Carrier Common...

  8. 47 CFR 69.154 - Per-minute carrier common line charge.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... weighting method set forth in paragraph (c) of this section. The maximum such charge shall be the lower of... the weighting method set forth in paragraph (c) of this section. (c) For each Carrier Common...

  9. 47 CFR 69.154 - Per-minute carrier common line charge.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... weighting method set forth in paragraph (c) of this section. The maximum such charge shall be the lower of... the weighting method set forth in paragraph (c) of this section. (c) For each Carrier Common...

  10. 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

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

    PubMed

    Alpat, Saygin Nayman; Ozgne?, Ilhan; Aybey, A?kin Derya; Ertem, Osman Turgut; Ak?it, 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 with the system. Of the subjects 73.7% declared that they had no information about cleaning and decontamination procedures related to the system. These data revealed that the pneumatic system used in our hospital carried contamination risk and the rules for hygiene and disinfection regarding the pneumatic transport system has to be determined, implemented and checked in order to establish appropriate infection control measures. PMID:19795620

  12. 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

    We report on physical mechanisms behind the temperature-dependent optical absorption, photoluminescence (PL), and photoconductivity in spin-coated films of a functionalized anthradithiophene (ADT) derivative, ADT-triethylsilylethynyl (TES)-F, and its composites with C60 and another ADT derivative, ADT-TIPS-CN. Measurements of absorption and PL spectra, PL lifetimes, and transient photocurrent were performed at temperatures between 98 and 300 K as a function of applied electric field. In pristine ADT-TES-F films, absorptive and emissive species were identified to be disordered H aggregates whose properties are affected by static and dynamic disorder. The exciton bandwidths were ≤0.06 and ˜0.115 eV for absorptive and emissive aggregates, respectively, indicative of higher disorder in the emissive species. The exciton in the latter was found to be delocalized over approximately four to five molecules. The PL properties were significantly modified upon adding a guest molecule to the ADT-TES-F host. In ADT-TES-F/C60 composites, the PL was considerably quenched due to photoinduced electron transfer from ADT-TES-F to C60, while in ADT-TES-F/ADT-TIPS-CN blends, the PL was dominated by emission from an exciplex formed between ADT-TES-F and ADT-TIPS-CN molecules. In all materials, the PL quantum yield dramatically decreased as the temperature increased due to thermally activated nonradiative recombination. Considerable electric-field-induced PL quenching was observed at low temperatures at electric fields above ˜105 V/cm due to tunneling into dark states. No significant contribution of ADT-TES-F emissive exciton dissociation to transient photocurrent was observed. In all materials, charge carriers were photogenerated at sub-500-ps time scales, limited by the laser pulse width, with temperature- and electric-field-independent photogeneration efficiency. In ADT-TES-F/C60 (2%) composites, the photogeneration efficiency was a factor of 2-3 higher than that in pristine ADT-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.

  13. 25th anniversary article: charge transport and recombination in polymer light-emitting diodes.

    PubMed

    Kuik, Martijn; Wetzelaer, Gert-Jan A H; Nicolai, Herman T; Craciun, N Irina; De Leeuw, Dago M; Blom, Paul W M

    2014-01-01

    This article reviews the basic physical processes of charge transport and recombination in organic semiconductors. As a workhorse, LEDs based on a single layer of poly(p-phenylene vinylene) (PPV) derivatives are used. The hole transport in these PPV derivatives is governed by trap-free space-charge-limited conduction, with the mobility depending on the electric field and charge-carrier density. These dependencies are generally described in the framework of hopping transport in a Gaussian density of states distribution. The electron transport on the other hand is orders of magnitude lower than the hole transport. The reason is that electron transport is hindered by the presence of a universal electron trap, located at 3.6 eV below vacuum with a typical density of ca. 3 × 10¹⁷ cm⁻³. The trapped electrons recombine with free holes via a non-radiative trap-assisted recombination process, which is a competing loss process with respect to the emissive bimolecular Langevin recombination. The trap-assisted recombination in disordered organic semiconductors is governed by the diffusion of the free carrier (hole) towards the trapped carrier (electron), similar to the Langevin recombination of free carriers where both carriers are mobile. As a result, with the charge-carrier mobilities and amount of trapping centers known from charge-transport measurements, the radiative recombination as well as loss processes in disordered organic semiconductors can be fully predicted. Evidently, future work should focus on the identification and removing of electron traps. This will not only eliminate the non-radiative trap-assisted recombination, but, in addition, will shift the recombination zone towards the center of the device, leading to an efficiency improvement of more than a factor of two in single-layer polymer LEDs. PMID:24458577

  14. 47 CFR 51.909 - Transition of rate-of-return carrier access charges.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 3 2013-10-01 2013-10-01 false Transition of rate-of-return carrier access charges. 51.909 Section 51.909 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) COMMON CARRIER SERVICES (CONTINUED) INTERCONNECTION Transitional Access Service Pricing 51.909 Transition...

  15. 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 an exemplary system for the SCLC model with discrete single level shallow traps. Charge transport as a function of sample thickness uncovers the origin of these traps. The thickness dependent SCLC measurements show the influence of both surface and bulk traps on charge transport. Temperature dependence of I--V and dc conductivity measurements suggest thermal assisted variable-range hopping transport instead of band transport in these materials. Charge carrier injection and doping in CPs induce structural deformation with the formation of self-localized excitation states, such as polarons or bipolarons inside the band gap. Raman scattering studies of PF2/6-based LEDs with doping and in the presence of injected and photo-generated charge carriers show increasing backgrounds with asymmetric Briet-Wigner Fano (BWF) line shapes, indicating strong electron-phonon interactions.

  16. Molecular Level Manipulation of Interfacial Charge Transport

    NASA Astrophysics Data System (ADS)

    Song, Charles Kiseok

    The bulk-heterojunction organic (BHJ) photovoltaics (OPVs) and lithium ion battery (LiB) have been extensively studied. Power conversion efficiency (PCE) of an OPV greater than 10% and utilizing group 4 elements as the anode to accommodate high capacity for LiBs are the goals of many studies. However, the currently ubiquitous hole-collecting layer of OPVs limit device performance and durability, and group 4 elements are unstable and brittle to be commercially produced. Thus, my thesis has focused on developing functional and durable interfacial layers (IFLs) for OPVs and characterizing flexible artificial solid-electrolyte interphase (SEI) for LiBs. In Chapter 2, a series of robust organosilane-based dipolar self-assembled monolayer (SAM) IFLs on the tin-doped indium oxide (ITO) anodes of OPVs are developed. These hydrophobic and amorphous IFLs modify anode work functions from 4.66 to 5.27 eV. Two series of Glass/ITO/SAM IFL/Active Layer/LiF/Al BHJ OPVs are fabricated, and a strong positive correlation between the electrochemically-derived heterogeneous electron transport rate constants (ks) and OPV PCEs are observed due to enhanced anode carrier extraction. In Chapter 3, a series of unusually denser organosilane-based SAM IFLs on ITO anodes of OPVs are developed. Precursor mixtures having short and long tail groups were simultaneously deposited to minimize sterical encumbrance and denser SAM IFLs are achieved. These heterogeneous supersaturated SAMs (SHSAMs), with PCE (7.62%) exceeding that of PEDOT:PSS IFL, are found to be 17% denser and enhances PCE by 54% versus comparable devices with homogeneous SAM IFLs due to enhanced charge selectivity and collection. In Chapter 4, libraries of electron affinities (EAs) of widely used conductive polymers are constructed by cyclic voltammetry (CV) in conventional and LiB media. The EAs of the conductive polymer films measured via CV in conventional (EAC) and Li+ battery (EAB) media could be linearly correlated by EAB = (1.07 +/- 0.13) x EAC + (2.84 +/- 0.22)V. The slope and the intercept are correlated to the dielectric constants encompassing the polymer film and the redox potential of the reference electrode affected by the surrounding electrolyte, respectively.

  17. Charged-particle transport in one dimension

    NASA Technical Reports Server (NTRS)

    Wilson, J. W.; Townsend, L. W.; Ganapol, B.; Chun, S. Y.; Buck, W. W.

    1988-01-01

    A numerical solution to high-energy charged-particle transport is found by evaluation of the integral equations obtained by inverting the Boltzmann differential operator. An algorithm has been written for either continuous or discrete spectra at the boundary, which allows efficient and accurate evaluation of this rather complicated problem. Present results are compared with analytic solutions based on the perturbation theory.

  18. 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

  19. 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

  20. Transistors: Realization of Room-Temperature Phonon-Limited Carrier Transport in Monolayer MoS2 by Dielectric and Carrier Screening (Adv. Mater. 3/2016).

    PubMed

    Yu, Zhihao; Ong, Zhun-Yong; Pan, Yiming; Cui, Yang; Xin, Run; Shi, Yi; Wang, Baigeng; Wu, Yun; Chen, Tangsheng; Zhang, Yong-Wei; Zhang, Gang; Wang, Xinran

    2016-01-01

    On page 547, charged impurities in monolayer MoS2 are effectively screened by combining a high-? dielectric substrate and a high density of carriers, leading to an unprecedented room-temperature electron mobility of ?150 cm(2) V(-1) s(-1) . Y. Shi, G. Zhang, X. Wang and co-workers also demonstrate phonon-limited transport in monolayer MoS2 for the first time, an important milestone for electronic device applications. PMID:26765676

  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. 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

  3. 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

  4. Low Temperature Charge Transport Study in Polypyrrole

    NASA Astrophysics Data System (ADS)

    Taunk, Manish; Chand, Subhash

    2011-12-01

    Organic polymers were usually considered as electrical insulators but due to the extended ?-backbone system a new class of electrically conductive organic polymers is possible. These ? conjugated polymers have various remarkable properties which leads to their probable use in variety of applications like electronic devices, rechargeable batteries, sensors, corrosion protecting coating etc. Among other conducting polymers polypyrrole has attracted great attension due to high electrical conductivity and good environmental stability. In this study pelletized samples of chemically synthesized polypyrrole using ferric chloride and ammonium peroxydisulphate as oxidizing agents were electrically characterized over wide temperature range of 10-300 K. An effort has been made to explore the charge transport in these doped samples using charge transport models. The analysis of experimental data predicts that hopping and tunneling transports are the dominant mechanism in their respective temperature range.

  5. 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, 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. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr01044f

  6. 34 nm Charge Transport through DNA

    NASA Astrophysics Data System (ADS)

    Slinker, Jason; Muren, Natalie; Renfrew, Sara; Barton, Jacqueline

    2011-03-01

    Long-range charge transport through DNA has broad-reaching implications due to its inherent biological recognition capabilities and unmatched capacity to be patterned into precise, nanoscale shapes. We have observed charge transport through 34 nm DNA monolayers (100 base pairs) using DNA-mediated electrochemistry. Cyclic voltammetry of multiplexed gold electrodes modified with 100mer DNAs reveal sizable peaks from distally-bound Nile Blue redox probes for well matched duplexes but highly attenuated redox peaks from 100mer monolayers containing a single base pair mismatch, demonstrating that the charge transfer is DNA-mediated. The 100mers on the gold surface are efficiently cleaved by the restriction enzyme RsaI. The 100mers in the DNA film thus adopt conformations that are readily accessible to protein binding and restriction. The ability to assemble well-characterized DNA films with these 100mers permits the demonstration of charge transport over distances surpassing most reports of molecular wires. Supported by funding from the NIH/NIBIB.

  7. Strong Asymmetric Charge Carrier Dependence in Inelastic Electron Tunneling Spectroscopy of Graphene Phonons

    NASA Astrophysics Data System (ADS)

    Natterer, Fabian D.; Zhao, Yue; Wyrick, Jonathan; Chan, Yang-Hao; Ruan, Wen-Ying; Chou, Mei-Yin; Watanabe, Kenji; Taniguchi, Takashi; Zhitenev, Nikolai B.; Stroscio, Joseph A.

    2015-06-01

    The observation of phonons in graphene by inelastic electron tunneling spectroscopy has been met with limited success in previous measurements arising from weak signals and other spectral features which inhibit a clear distinction between phonons and miscellaneous excitations. Utilizing a back-gated graphene device that allows adjusting the global charge carrier density, we introduce an averaging method where individual tunneling spectra at varying charge carrier density are combined into one representative spectrum. This method improves the signal for inelastic transitions while it suppresses dispersive spectral features. We thereby map the total graphene phonon density of states, in good agreement with density functional calculations. Unexpectedly, an abrupt change in the phonon intensity is observed when the graphene charge carrier type is switched through a variation of the back-gate electrode potential. This sudden variation in phonon intensity is asymmetric in the carrier type, depending on the sign of the tunneling bias.

  8. Charge transport in strongly coupled quantum dot solids.

    PubMed

    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. PMID:26551016

  9. 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.

  10. Carrier transport in graphite/Si3N4-nanobelt/PtIr Schottky barrier diodes

    NASA Astrophysics Data System (ADS)

    Bi, Jinghui; Wei, Guodong; Shang, Minghui; Gao, Fengmei; Tang, Bin; Yang, Weiyou

    2014-11-01

    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/Si3N4-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 Si3N4 nanobelt surface are predominant in the charge transfer.

  11. Charge carrier mobility and photorefractive grating buildup in bipolar organic glasses

    NASA Astrophysics Data System (ADS)

    Sohn, Jiwon; Hwang, Jaehoon; Park, Soo Young; Noh, Yong-Young; Kim, Jang-Joo

    2002-07-01

    Two-component organic glasses consisting of photoconductive molecule, N')-9-(2-ethylhexyl-9H-carbazol-3-ylmethylene-N,N-diphenyl- hydrazine (EHCzHy), and multifunctional photorefractive molecules, 9-(2-ethyl-hexyl)-3-2-(4-methanesulfonyl-phenyl)-vinyl-9H-carbazole (EHCS) [J. Sohn [et al.], Appl. Phys. Lett. 77, 1422 (2000)] and 9-(2-ethylhexyl)-3-2-(4-nitro-phenyl)-vinyl-9H-carbazole (EHCN), were prepared, and their charge carrier mobility and photorefractive grating buildup were investigated. EHCzHy is a unipolar hole-transporting (muh=4.16 x10-6 cm2/V s) molecule with no electro-optic property. EHCS and EHCN are nonlinear optical molecules with unipolar (muh=2.42 x10-6 cm2/V s) and bipolar (muh=2.30 x10-6 cm2/V s,mue=2.86 x10-6 cm2/V s) carrier mobilities, respectively. Different behaviors of the photorefractive grating buildup in two-component organic glasses were investigated as a function of EHCN or EHCS content.

  12. 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...

  13. Electron transport model of dielectric charging

    NASA Technical Reports Server (NTRS)

    Beers, B. L.; Hwang, H. C.; Lin, D. L.; Pine, V. W.

    1979-01-01

    A computer code (SCCPOEM) was assembled to describe the charging of dielectrics due to irradiation by electrons. The primary purpose for developing the code was to make available a convenient tool for studying the internal fields and charge densities in electron-irradiated dielectrics. The code, which is based on the primary electron transport code POEM, is applicable to arbitrary dielectrics, source spectra, and current time histories. The code calculations are illustrated by a series of semianalytical solutions. Calculations to date suggest that the front face electric field is insufficient to cause breakdown, but that bulk breakdown fields can easily be exceeded.

  14. 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.

  15. Field dependent thermoelectric properties of organic semiconductorsA 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.

  16. 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 (DISCLC) to study the charge injection properties of three phenylamine-based (PA) compounds, MTDATA (4,4',4''-Tris(N-3-methylphenyl-N-phenyl-amino)triphenylamine), NPB, and TPD (N,N'-diphenyl-N,N'-bis(3-methyl phenyl) (1,1'-biphenyl)-4,4'diamine).Poly(3,4-ethylenedioxythiophene) doped with polystyrenesulphonic acid (PEDOT:PSS) was used as a hole-injecting anode in current-voltage (JV) and DISCLC. Clear DISCLC transient peaks were observed over a wide range of electric fields in all cases. For MTDATA and NPB, hole mobilities evaluated by DI experiments are in excellent agreement with mobilties deduced from TOF technique. It can be concluded that, for the purpose of JV and DI experiments, PEDOT:PSS forms an Ohmic contact with MTDATA and a quasi-Ohmic contact with NPB despite the relatively low-lying highest occupied molecular orbital of the later. In the case of TPD, hole injection from PEDOT:PSS deviates substantially from Ohmic injection, leading to a lower than expected DI-extracted hole mobility. Finally, a composite anode will be demonstrated to improve the hole injection efficiency.

  17. Negative correlation between charge carrier density and mobility fluctuations in graphene

    NASA Astrophysics Data System (ADS)

    Lu, Jianming; Pan, Jie; Yeh, Sheng-Shiuan; Zhang, Haijing; Zheng, Yuan; Chen, Qihong; Wang, Zhe; Zhang, Bing; Lin, Juhn-Jong; Sheng, Ping

    2014-08-01

    By carrying out simultaneous longitudinal and Hall measurements in graphene, we find that the 1/f noise for the charge carrier density is negatively correlated to that of mobility, with a governing behavior that differs significantly from the relation between their mean values. The correlation in the noise data can be quantitatively explained by a single-parameter theory whose underlying physics is the trapping and detrapping of the fluctuating charge carriers by the oppositely charged Coulomb scattering centers. This can alter the effective density of long-range scattering centers in a transient manner, with the consequent fluctuating effect on the mobility.

  18. 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

  19. 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

  20. 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.

  1. Negative correlation between charge carrier density and mobility fluctuations in graphene

    NASA Astrophysics Data System (ADS)

    Pan, Jie; Lu, Jianming; Sheng, Ping; Institute of Physics and Department of Electrophysics, National Chiao Tung University, Taiwan Collaboration

    2014-03-01

    By carrying out simultaneous longitudinal and Hall measurements in graphene, we find that the 1/f noise for the charge carrier density is negatively correlated to that of mobility, with a governing behavior that differs significantly from the relation between their mean values. The correlation in the noise data can be quantitatively explained by a single parameter theory whose underlying physics is the trapping and de-trapping of the fluctuating charge carriers by the oppositely charged Coulomb scattering centers. This can alter the effective density of long-range scattering centers in a transient manner, with the consequent fluctuating effect on the mobility. The longitudinal noise turns out to be dominated by the remaining component of the mobility fluctuations, and display no correlation to the Hall noise. Due to the negative correlation between charge carrier density and mobility fluctuations, the normalized PSD is smaller than that of the Hall noise. Research Grants Council of Hong Kong Grant HKUST9/CRF/08.

  2. 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

  3. 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 for chemo-electro-fluid systems. A number of computational algorithms is developed to implement the proposed new variational multiscale models in an efficient manner. A set of ten protein molecules and a realistic ion channel, Gramicidin A, are employed to confirm the consistency and verify the capability. Extensive numerical experiment is designed to validate the proposed variational multiscale models. A good quantitative agreement between our model prediction and the experimental measurement of current-voltage curves is observed for the Gramicidin A channel transport. This paper also provides a brief review of the field. PMID:23172978

  4. 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.

  5. Particle Transport through Hydrogels Is Charge Asymmetric

    PubMed Central

    Zhang, Xiaolu; Hansing, Johann; Netz, RolandR.; DeRouchey, JasonE.

    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

  6. Particle transport through hydrogels is charge asymmetric.

    PubMed

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

    2015-02-01

    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

  7. 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

  8. 78 FR 59082 - Privacy Act of 1974; Department of Transportation, Federal Motor Carrier Safety Administration...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-09-25

    ...In accordance with the Privacy Act of 1974, the Department of Transportation proposes to update and reissue a current Department of Transportation system of records titled, ``Department of Transportation Federal Motor Carrier Safety Administration DOT/FMCSA 001 Motor Carrier Management Information System System of Records.'' This system of records will allow the Department of Transportation......

  9. 41 CFR 301-10.105 - What are the basic requirements for using common carrier transportation?

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... mandatory user of GSA's city-pair contracts for air passenger transportation services, unless you have an... requirements for using common carrier transportation? 301-10.105 Section 301-10.105 Public Contracts and... TRAVEL EXPENSES 10-TRANSPORTATION EXPENSES Common Carrier Transportation 301-10.105 What are the...

  10. 41 CFR 301-10.105 - What are the basic requirements for using common carrier transportation?

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... mandatory user of GSA's city-pair contracts for air passenger transportation services, unless you have an... requirements for using common carrier transportation? 301-10.105 Section 301-10.105 Public Contracts and... TRAVEL EXPENSES 10-TRANSPORTATION EXPENSES Common Carrier Transportation 301-10.105 What are the...

  11. 41 CFR 301-10.105 - What are the basic requirements for using common carrier transportation?

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... mandatory user of GSA's city-pair contracts for air passenger transportation services, unless you have an... requirements for using common carrier transportation? 301-10.105 Section 301-10.105 Public Contracts and... TRAVEL EXPENSES 10-TRANSPORTATION EXPENSES Common Carrier Transportation 301-10.105 What are the...

  12. 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

  13. Dust Charging and Transport on Surfaces

    SciTech Connect

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

    2011-11-29

    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.

  14. Carrier transport properties of nanocrystalline Er{sub 3}N@C{sub 80}

    SciTech Connect

    Sun, Yong Maeda, Yuki; Sezaimaru, Hiroki; Sakaino, Masamichi; Kirimoto, Kenta

    2014-07-21

    Electrical transport properties of the nanocrystalline Er{sub 3}N@C{sub 80} with fcc crystal structure were characterized by measuring both temperature-dependent d.c. conductance and a.c. impedance. The results showed that the Er{sub 3}N@C{sub 80} sample has characteristics of n-type semiconductor and an electron affinity larger than work function of gold metal. The Er{sub 3}N@C{sub 80}/Au interface has an ohmic contact behavior and the contact resistance was very small as compared with bulk resistance of the Er{sub 3}N@C{sub 80} sample. The charge carriers in the sample were thermally excited from various trapped levels and both acoustic phonon and ionic scatterings become a dominant process in different temperature regions, respectively. At temperatures below 250 K, the activation energy of the trapped carrier was estimated to be 35.5 meV, and the ionic scattering was a dominant mechanism. On the other hand, at temperatures above 350 K, the activation energy was reduced to 15.9 meV, and the acoustic phonon scattering was a dominant mechanism. In addition, a polarization effect from the charge carrier was observed at low frequencies below 2.0 MHz, and the relative intrinsic permittivity of the Er{sub 3}N@C{sub 80} nanocrystalline lattice was estimated to be 4.6 at frequency of 5.0 MHz.

  15. Tuning the polarity of charge transport in InSb nanowires via heat treatment.

    PubMed

    Hnida, Katarzyna E; B?ler, Svenja; Akinsinde, Lewis; Gooth, Johannes; Nielsch, Kornelius; Socha, Robert P; ?aszcz, Adam; Czerwinski, Andrzej; Sulka, Grzegorz D

    2015-07-17

    InSb nanowire (NW) arrays were prepared by pulsed electrodeposition combined with a porous template technique. The resulting polycrystalline material has a stoichiometric composition (In:Sb = 1:1) and a high length-to-diameter ratio. Based on a combination of Fourier transform infrared spectroscopy (FTIR) analysis and field-effect measurements, the band gap, the charge carrier polarity, the carrier concentration, the mobility and the effective mass for the InSb NWs was investigated. In this preliminary work, a transition from p-type to n-type charge transport was observed when the InSb NWs were subjected to annealing. PMID:26112309

  16. Tuning the polarity of charge transport in InSb nanowires via heat treatment

    NASA Astrophysics Data System (ADS)

    Hnida, Katarzyna E.; B?ler, Svenja; Akinsinde, Lewis; Gooth, Johannes; Nielsch, Kornelius; Socha, Robert P.; ?aszcz, Adam; Czerwinski, Andrzej; Sulka, Grzegorz D.

    2015-07-01

    InSb nanowire (NW) arrays were prepared by pulsed electrodeposition combined with a porous template technique. The resulting polycrystalline material has a stoichiometric composition (In:Sb = 1:1) and a high length-to-diameter ratio. Based on a combination of Fourier transform infrared spectroscopy (FTIR) analysis and field-effect measurements, the band gap, the charge carrier polarity, the carrier concentration, the mobility and the effective mass for the InSb NWs was investigated. In this preliminary work, a transition from p-type to n-type charge transport was observed when the InSb NWs were subjected to annealing.

  17. 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

  18. Charge carrier dynamics of the heavy-fermion metal CeCoIn5 probed by THz spectroscopy

    NASA Astrophysics Data System (ADS)

    Pracht, Uwe S.; Simmendinger, Julian; Dressel, Martin; Endo, Ryota; Watashige, Tatsuya; Hanaoka, Yousuke; Shimozawa, Masaaki; Terashima, Takahito; Shibauchi, Takasada; Matsuda, Yuji; Scheffler, Marc

    2016-02-01

    We discuss the charge carrier dynamics of the heavy-fermion compound CeCoIn5 in the metallic regime measured by means of quasi-optical THz spectroscopy. The transmittance of electromagnetic radiation through a CeCoIn5 thin film on a dielectric substrate is analyzed in the single-particle Drude framework. We discuss the temperature dependence of the electronic properties, such as the scattering time and dc-conductivity and compare with transport measurements of the sheet resistance. Towards low temperatures, we find an increasing mismatch between the results from transport and Drude-analyzed optical measurements and a growing incapability of the simple single-particle picture describing the charge dynamics, likely caused by the evolving heavy-fermion nature of the correlated electron system.

  19. 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.

  20. Nonequilibrium properties of charge carriers in cadmium iodide crystals

    SciTech Connect

    Lyskovich, A.B.; Piroga, S.A; Bondar', V.D.; Gal'chinskii, A.V.

    1988-03-01

    Detection and measurement of the photomagnetic effect (PME) in layered crystals of cadmium iodide are discussed. The basic behavior of the PME at room temperature, as well as its dependence on wavelength and intensity of illumination, the magnetic field, and the photoconductivity, are presented. These dependencies were obtained to calculate the diffusion length, bipolar diffusion coefficient, the surface recombination velocity, and the lifetime. The intrinsic behavior of the odd-function PME in highly conducting cadmium iodide crystals at room temperature and fields up to 6.8 /times/ 10/sup 5/ A/m may be qualitatively explained in the context of the theory developed for the case of thick specimens in a weak magnetic field and high injection level. The observed odd-function PME and photoconductivity have yielded, for the first time, values for the parameters associated with nonequilibrium carriers in highly conducting cadmium iodide crystals.

  1. Near-field control and imaging of free charge carrier variations in GaN nanowires

    NASA Astrophysics Data System (ADS)

    Berweger, Samuel; Blanchard, Paul T.; Brubaker, Matt D.; Coakley, Kevin J.; Sanford, Norman A.; Wallis, Thomas M.; Bertness, Kris A.; Kabos, Pavel

    2016-02-01

    Despite their uniform crystallinity, the shape and faceting of semiconducting nanowires (NWs) can give rise to variations in structure and associated electronic properties. Here, we develop a hybrid scanning probe-based methodology to investigate local variations in electronic structure across individual n-doped GaN NWs integrated into a transistor device. We perform scanning microwave microscopy (SMM), which we combine with scanning gate microscopy to determine the free-carrier SMM signal contribution and image local charge carrier density variations. In particular, we find significant variations in free carriers across NWs, with a higher carrier density at the wire facets. By increasing the local carrier density through tip-gating, we find that the tip injects current into the NW with strongly localized current when positioned over the wire vertices. These results suggest that the strong variations in electronic properties observed within NWs have significant implications for device design and may lead to new paths to optimization.

  2. 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.

  3. The Effect of Inelastic Scattering of Charge Carriers on the Reliability of the Value of the Spin Polarization as Determined from Superconductor/Ferromagnet Point Contact Conductance Data

    NASA Astrophysics Data System (ADS)

    Dolan, Paul J., Jr.; Smith, Charles W.

    2014-03-01

    An extended BTK model for charge transport in a superconductor/ferromagnet point contact can be used to determine the value of the spin polarization of the ferromagnet. We estimate the effect of inelastic scattering of charge carriers in the active region of the contact on the reliability of the value of the polarization as determined from conductance data. The effect can be substantial and depends upon contact transparency.

  4. Semiconductor nanoparticles with spatial separation of charge carriers: synthesis and optical properties

    NASA Astrophysics Data System (ADS)

    Vasiliev, Roman B.; Dirin, Dmitry N.; Gaskov, Alexander M.

    2011-12-01

    The results of studies on core/shell semiconductor nanoparticles with spatial separation of photoexcited charge carriers are analyzed and generalized. Peculiarities of the electronic properties of semiconductor/semiconductor heterojunctions formed inside such particles are considered. Data on the effect of spatial separation of charge carriers on the optical properties of nanoparticles including spectral shifts of the exciton bands, absorption coefficients and electron-hole pair recombination times are presented. Methods of synthesis of core/shell semiconductor nanoparticles in solutions are discussed. Specific features of the optical properties of anisotropic semiconductor nanoparticles with the semiconductor/semiconductor junctions are noted. The bibliography includes 165 references.

  5. 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

    2015-12-01

    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 ?m, while mobilities across the mixed Br/I system depend on crystalline phase disorder. PMID:26402226

  6. 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; Mller, 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.

  7. Tuning nitrogen species to control the charge carrier concentration in highly doped graphene

    NASA Astrophysics Data System (ADS)

    Scardamaglia, Mattia; Struzzi, Claudia; Osella, Silvio; Reckinger, Nicolas; Colomer, Jean-François; Petaccia, Luca; Snyders, Rony; Beljonne, David; Bittencourt, Carla

    2016-03-01

    Highly nitrogen-doped graphene on copper has been obtained by post-synthesis low-energy ion implantation. Core level and angle resolved photoemission spectroscopies are correlated to link the actual charge carrier doping to the different nitrogen species implanted in the nanostructure. Indeed, we exploit the possibility of controlling the graphitic/pyridinic ratio through thermal heating to tune the charge carrier density; this implicates Dirac cone shifts that are directly correlated to the different doping contribution of the nitrogen species. Supported by density functional theory calculations, we identify graphitic nitrogen as being responsible for n-doping when the amount of counterbalancing pyridinic nitrogen species is reduced upon thermal heating.

  8. Charge Redistribution and Transport in Molecular Contacts.

    PubMed

    Corso, Martina; Ondr?ek, Martin; Lotze, Christian; Hapala, Prokop; Franke, Katharina J; Jelnek, 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

  9. 41 CFR 301-72.3 - What method of payment must we authorize for common carrier transportation?

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... must we authorize for common carrier transportation? 301-72.3 Section 301-72.3 Public Contracts and... RESPONSIBILITIES 72-AGENCY RESPONSIBILITIES RELATED TO COMMON CARRIER TRANSPORTATION Procurement of Common Carrier Transportation 301-72.3 What method of payment must we authorize for common carrier transportation? You...

  10. 41 CFR 301-72.3 - What method of payment must we authorize for common carrier transportation?

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... must we authorize for common carrier transportation? 301-72.3 Section 301-72.3 Public Contracts and... RESPONSIBILITIES 72-AGENCY RESPONSIBILITIES RELATED TO COMMON CARRIER TRANSPORTATION Procurement of Common Carrier Transportation 301-72.3 What method of payment must we authorize for common carrier transportation? You...

  11. 41 CFR 301-72.3 - What method of payment must we authorize for common carrier transportation?

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... must we authorize for common carrier transportation? 301-72.3 Section 301-72.3 Public Contracts and... RESPONSIBILITIES 72-AGENCY RESPONSIBILITIES RELATED TO COMMON CARRIER TRANSPORTATION Procurement of Common Carrier Transportation 301-72.3 What method of payment must we authorize for common carrier transportation? You...

  12. 41 CFR 301-72.3 - What method of payment must we authorize for common carrier transportation?

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... must we authorize for common carrier transportation? 301-72.3 Section 301-72.3 Public Contracts and... RESPONSIBILITIES 72-AGENCY RESPONSIBILITIES RELATED TO COMMON CARRIER TRANSPORTATION Procurement of Common Carrier Transportation 301-72.3 What method of payment must we authorize for common carrier transportation? You...

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

    NASA Astrophysics Data System (ADS)

    Scully, Shawn Ryan

    Organic photovoltaics have attracted significant interest over the last decade due to their promise as clean low-cost alternatives to large-scale electric power generation such as coal-fired power, natural gas, and nuclear power. Many believe power conversion efficiency targets of 10-15% must be reached before commercialization is possible. Consequently, understanding the loss mechanisms which currently limit efficiencies to 4-5% is crucial to identify paths to reach higher efficiencies. In this work, we investigate the dominant loss mechanisms in some of the leading organic photovoltaic architectures. In the first class of architectures, which include planar heterojunctions and bulk heterojunctions with large domains, efficiencies are primarily limited by the distance photogenerated excitations (excitons) can be transported (termed the exciton diffusion length) to a heterojunction where the excitons may dissociate. We will discuss how to properly measure the exciton diffusion length focusing on the effects of optical interference and of energy transfer when using fullerenes as quenching layers and show how this explains the variety of diffusion lengths reported for the same material. After understanding that disorder and defects limit exciton diffusion lengths, we suggest some approaches to overcome this. We then extensively investigate the use of long-range resonant energy transfer to increase exciton harvesting. Using simulations and experiments as support, we discuss how energy transfer can be engineered into architectures to increase the distance excitons can be harvested. In an experimental model system, DOW Red/PTPTB, we will show how the distance excitons are harvested can be increased by almost an order of magnitude up to 27 nm from a heterojunction and give design rules and extensions of this concept for future architectures. After understanding exciton harvesting limitations we will look at other losses that are present in planar heterojunctions. One of 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.

  14. 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.

  15. 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

  16. High-temperature thermoelectric transport at small scales: Thermal generation, transport and recombination of minority carriers

    PubMed Central

    Bakan, Gokhan; Khan, Niaz; Silva, Helena; Gokirmak, Ali

    2013-01-01

    Thermoelectric transport in semiconductors is usually considered under small thermal gradients and when it is dominated by the role of the majority carriers. Not much is known about effects that arise under the large thermal gradients that can be established in high-temperature, small-scale electronic devices. Here, we report a surprisingly large asymmetry in self-heating of symmetric highly doped silicon microwires with the hottest region shifted along the direction of minority carrier flow. We show that at sufficiently high temperatures and strong thermal gradients (~1?K/nm), energy transport by generation, transport and recombination of minority carriers along these structures becomes very significant and overcomes convective energy transport by majority carriers in the opposite direction. These results are important for high-temperature nanoelectronics such as emerging phase-change memory devices which also employ highly doped semiconducting materials and in which local temperatures reach ~1000?K and thermal gradients reach ~10100?K/nm. PMID:24056703

  17. Charge transfer polarisation wave and carrier pairing in the high T(sub c) copper oxides

    NASA Technical Reports Server (NTRS)

    Chakraverty, B. K.

    1990-01-01

    The High T(sub c) oxides are highly polarizable materials and are charge transfer insulators. The charge transfer polarization wave formalism is developed in these oxides. The dispersion relationships due to long range dipole-dipole interaction of a charge transfer dipole lattice are obtained in 3-D and 2-D. These are high frequency bosons and their coupling with carriers is weak and antiadiabatic in nature. As a result, the mass renormalization of the carriers is negligible in complete contrast to conventional electron-phonon interaction, that give polarons and bipolarons. Both bound and superconducting pairing is discussed for a model Hamiltonian valid in the antiadiabatic regime, both in 3-D and 2-D. The stability of the charge transfer dipole lattice has interesting consequences that are discussed.

  18. Charge and Spin Transport in Dilute Magnetic Semiconductors

    SciTech Connect

    Ullrich, Carsten A.

    2009-07-23

    This proposal to the DOE outlines a three-year plan of research in theoretical and computational condensed-matter physics, with the aim of developing a microscopic theory for charge and spin dynamics in disordered materials with magnetic impurities. Important representatives of this class of materials are the dilute magnetic semiconductors (DMS), which have attracted great attention as a promising basis for spintronics devices. There is an intense experimental effort underway to study the transport properties of ferromagnetic DMS such as (Ga,Mn)As, and a number of interesting features have emerged: negative magnetoresistance, anomalous Hall effect, non-Drude dynamical conductivity, and resistivity maxima at the Curie temperature. Available theories have been able to account for some of these features, but at present we are still far away from a systematic microscopic understanding of transport in DMS. We propose to address this challenge by developing a theory of charge and spin dynamics based on a combination of the memory-function formalism and time-dependent density functional theory. This approach will be capable of dealing with two important issues: (a) the strong degree of correlated disorder in DMS, close to the localization transition (which invalidates the usual relaxation-time approximation to the Boltzmann equation), (b) the essentially unknown role of dynamical many-body effects such as spin Coulomb drag. We will calculate static and dynamical conductivities in DMS as functions of magnetic order and carrier density, which will advance our understanding of recent transport and infrared absorption measurements. Furthermore, we will study collective plasmon excitations in DMS (3D, 2D and quantum wells), whose linewidths could constitute a new experimental probe of the correlation of disorder, many-body effects and charge and spin dynamics in these materials.

  19. 14 CFR 234.13 - Reports by air carriers on incidents involving animals during air transport.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... involving animals during air transport. 234.13 Section 234.13 Aeronautics and Space OFFICE OF THE SECRETARY... REPORTS § 234.13 Reports by air carriers on incidents involving animals during air transport. (a) Any air... during air transport provided by the air carrier. (b) The report shall be made in the form and manner...

  20. 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...

  1. 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...

  2. 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...

  3. 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...

  4. Light-induced charge transport within a single asymmetric nanowire.

    PubMed

    Liu, Chong; Hwang, Yun Jeong; Jeong, Hoon Eui; Yang, Peidong

    2011-09-14

    Artificial photosynthetic systems using semiconductor materials have been explored for more than three decades in order to store solar energy in chemical fuels such as hydrogen. By mimicking biological photosynthesis with two light-absorbing centers that relay excited electrons in a nanoscopic space, a dual-band gap photoelectrochemical (PEC) system is expected to have higher theoretical energy conversion efficiency than a single band gap system. This work demonstrates the vectorial charge transport of photogenerated electrons and holes within a single asymmetric Si/TiO(2) nanowire using Kelvin probe force microscopy. Under UV illumination, higher surface potential was observed on the n-TiO(2) side, relative to the potential of the p-Si side, as a result of majority carriers' recombination at the Si/TiO(2) interface. These results demonstrate a new approach to investigate charge separation and transport in a PEC system. This asymmetric nanowire heterostructure with a dual band gap configuration and simultaneously exposed anode and cathode surfaces represents an ideal platform for the development of technologies for the generation of solar fuels, although better photoanode materials remain to be discovered. PMID:21766837

  5. Photoinduced Dedoping of Conducting Polymers: An Approach to Precise Control of the Carrier Concentration and Understanding Transport Properties.

    PubMed

    Wei, Qingshuo; Mukaida, Masakazu; Kirihara, Kazuhiro; Naitoh, Yasuhisa; Ishida, Takao

    2016-01-27

    Exploring the various applications of conjugated polymers requires systematic studies of their physical properties as a function of the doping density, which, consequently, calls for precise control of their doping density. In this study, we report a novel solid-state photoinduced charge-transfer reaction that dedopes highly conductive polyelectrolyte complexes such as poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate). Varying the UV-irradiation time of this material allows the carrier density inside the film to be precisely controlled over more than 3 orders of magnitude. We extract the carrier density, carrier mobility, and Seebeck coefficient at different doping levels to obtain a clear image of carrier-transport mechanisms. This approach not only leads to a better understanding of the physical properties of the conducting polymer but also is useful for developing applications requiring patterned, large-area conducting polymers. PMID:26734776

  6. Spatially mapping charge carrier density and defects in organic electronics using modulation-amplified reflectance spectroscopy.

    PubMed

    Davis, Andrew R; Pye, Lorelle N; Katz, Noam; Hudgings, Janice A; Carter, Kenneth R

    2014-07-01

    Charge-modulated optical spectroscopy is used to achieve dynamic two-dimensional mapping of the charge-carrier distribution in poly(3-hexylthiophene) thin-film transistors. The resulting in-channel distributions evolve from uniformly symmetric to asymmetrically saturated as the devices are increasingly biased. Furthermore, physical, chemical, and electrical defects are spatially resolved in cases where their presence is not obvious from the device performance. PMID:24889350

  7. Sodium transport by an ionizable and a neutral mobile carrier: effects of membrane structure on the apparent activation energy.

    PubMed

    Vareille, G; Marion, P; Kraus, J L; Castaing, M

    1993-02-23

    Temperature-jump relaxation experiments on Na+ transport by (221)C10-cryptand (ionizable mobile carrier) and nonactin (neutral mobile carrier) were carried out in order to study the effects of cholesterol and the degree of acyl chain unsaturation, and their temperature-dependence on ion transport through thin lipid membranes. The experiments were performed on large, negatively charged unilamellar vesicles (LUV) prepared from mixtures of phosphatidylcholine (egg phosphatidylcholine, dioleoylphosphatidylcholine and dilinoleolylphosphatidylcholine), phosphatidic acid and cholesterol (mole fractions 0-0.43), at various temperatures and carrier concentrations. The apparent rate constants of Na+ translocation by (221)C10 and nonactin increased with the carrier concentration, the degree of acyl chain unsaturation and the temperature. The incorporation of cholesterol into the membranes significantly reduced the carrier concentration-, acyl chain unsaturation- and temperature-dependence of this parameter. The apparent energy required to activate the transport decreased significantly with increasing (221)C10 concentrations and remained constant with increasing those of nonactin at any given cholesterol molar fraction and degree of acyl chain unsaturation. It increased significantly with increasing the cholesterol molar fraction at any given carrier concentration to an extent depending on the degree of acyl chain unsaturation. Our interpretation of the action of cholesterol on these transport systems is based on the assumption that the adsorption plane of Na(+)-(221)C10 and Na(+)-nonactin complexes is likely to be located towards the aqueous and the hydrocarbon side of the dipole layer, respectively. The results are discussed in terms of the structural, physico-chemical and electrical characteristics of carriers and complexes, and of the interactions occurring between an ionizable or a neutral mobile carrier and the membrane. PMID:8443224

  8. Electrical currents associated with nucleotide transport by the reconstituted mitochondrial ADP/ATP carrier.

    PubMed

    Brustovetsky, N; Becker, A; Klingenberg, M; Bamberg, E

    1996-01-23

    The electrophoretic export of ATP against the import of ADP in mitochondria bridges the intra- versus extramitochondrial ATP potential gap. Here we report that the electrical nature of the ADP/ATP exchange by the mitochondrial ADP/ATP carrier (AAC) can be directly studied by measuring the electrical currents via capacitive coupling of AAC-containing vesicles on a planar lipid membrane. The currents were induced by the rapid liberation of ATP or ADP with UV flash photolysis from caged nucleotides. Six different transport modes of the AAC were studied: heteroexchange with either ADP or ATP inside the vesicles, initiated by photolysis of caged ATP or ADP; homoexchange with ADPex/ADPin or ATPex/ATPin; and caged ADP or ATP with unloaded vesicles. The heteroexchange produced the largest currents with the longest duration in line with the electrical charge difference ATP4- versus ADP3-. Surprisingly, also in the homoexchange and with unloaded vesicles, small currents were measured with shorter duration. In all three modes with caged ATP, a negative charge moved into the vesicles and with caged ADP it moved out of the vesicles. All currents were completely inhibited by a mixture of the inhibitors of the AAC, carboxyatractyloside and hongkrekate, which proves that the currents are exclusively due to AAC function. The observed charge movements in the heteroexchange system agree with the prediction from transport studies in mitochondria and reconstituted vesicles. The unexpected charge movements in the homoexchange or unloaded systems are interpreted to reveal transmembrane rearrangements of charged sites in the AAC when occupied with ADP or ATP. The results also indicate that not only ATP4- but also ADP3- contribute, albeit in opposite direction, to the electrical nature of the ADP/ATP exchange, which is at variance with former conclusions from biochemical transport studies. These measurements open up new avenues of studying the electrical interactions of ADP and ATP with the AAC. PMID:8570612

  9. 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.

  10. 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.

  11. 47 CFR 51.907 - Transition of price cap carrier access charges.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... trunking basket as described in 47 CFR 61.42(d)(2) and (3) to the extent that such rate elements are not... 47 Telecommunication 3 2013-10-01 2013-10-01 false Transition of price cap carrier access charges. 51.907 Section 51.907 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) COMMON...

  12. 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 two-orders of magnitude increase in the hole mobility. Finally, the hole, electron, and double carrier transport in solar cell devices are studied in a bid to examine the correlations between bulk morphologies and free carrier recombination. The sum of these works help to create new pathways for the synthesis and design of new pi-conjugated materials and device architectures. All of this is in hopes of achieving higher performance and more stable devices to rival inorganic systems.

  13. 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 values extracted from OPTP measurements and their dependence on perovskite composition and morphology. The significance of the reviewed charge-carrier recombination and mobility parameters is subsequently evaluated in terms of the charge-carrier diffusion lengths and radiative efficiencies that may be obtained for such hybrid perovskites. We particularly focus on calculating such quantities in the limit of ultra-low trap-related recombination, which has not yet been demonstrated but could be reached through further advances in material processing. We find that for thin films of hybrid lead iodide perovskites with typical charge-carrier mobilities of ∼30cm(2)/(V s), charge-carrier diffusion lengths at solar (AM1.5) irradiation are unlikely to exceed ∼10 μm even if all trap-related recombination is eliminated. We further examine the radiative efficiency for hybrid lead halide perovskite films and show that if high efficiencies are to be obtained for intermediate charge-carrier densities (n ≈ 10(14) cm(-3)) trap-related recombination lifetimes will have to be enhanced well into the microsecond range. PMID:26653572

  14. 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

    The recent tremendous boost in the number and diversity of applications for light-emitting diodes (LEDs) indicates the emergence of the next-generation lighting and illumination technology. The rapidly improving LED technology is becoming increasingly viable especially for high-power applications. However, the greatest roadblock before finally breaching the main defensive position of conventional fluorescent and incandescent lamps still remains: GaN-based LEDs encounter a significant decrease in efficiency as the drive current increases, and this phenomenon is known as the efficiency droop. This dissertation focuses on uncovering the physical cause of efficiency droop in GaN-based LEDs and looks for solutions to it. GaN-based multiple-quantum-well (MQW) LEDs usually have abnormally high diode-ideality factors. Investigating the origin of the high diode-ideality factors could help to better understand the carrier transport in the LED MQW active region. We investigate the ideality factors of GaInN LEDs with different numbers of doped quantum barriers (QBs). Consistent with the theory, a decrease of the ideality factor as well as a reduction in forward voltage is found with increasing number of doped QBs. Experimental and simulation results indicate that the band profiles of QBs in the active region have a significant impact on the carrier transport mechanism, and the unipolar heterojunctions inside the active region play an important role in determining the diode-ideality factor. This dissertation will discuss several mechanisms leading to electron leakage which could be responsible for the efficiency droop. We show that the inefficient electron capture, the electron-attracting properties of polarized EBL, the inherent asymmetry in electron and hole transport and the inefficient EBL p-doping at high Al contents severely limit the ability to confine electrons to the MQWs. We demonstrate GaInN LEDs employing tailored Si doping in the QBs with strongly enhanced high-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 doping and dual-wavelength LEDs, we investigate the origin of the high diode-ideality factor of LEDs and gain insight on the control of carrier transport, carrier distribution, and radiative recombination in the LED MQW active region. Our results provide solid evidence on the effectiveness of the GA in the LED device optimization process. In addition, the innovative EBL structure optimized by the GA sheds light on further paths for the optimization of LED design. Our results are the starting point of applying artificial evolution to practical semiconductor devices, opening new perspectives for complex semiconductor device optimization and enabling breakthroughs in high-performance LED design.

  15. 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.

  16. 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 coreshell 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

  17. 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.

  18. 49 CFR 385.13 - Unsatisfactory rated motor carriers; prohibition on transportation; ineligibility for Federal...

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ..., a motor carrier rated “unsatisfactory” is prohibited from operating a CMV. Information on motor... materials in quantities requiring placarding, and motor carriers transporting passengers in a CMV, are prohibited from operating a CMV in motor carrier operations in commerce beginning on the 46th day after...

  19. 49 CFR 385.13 - Unsatisfactory rated motor carriers; prohibition on transportation; ineligibility for Federal...

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ..., a motor carrier rated “unsatisfactory” is prohibited from operating a CMV. Information on motor... materials in quantities requiring placarding, and motor carriers transporting passengers in a CMV, are prohibited from operating a CMV in motor carrier operations in commerce beginning on the 46th day after...

  20. 49 CFR 385.13 - Unsatisfactory rated motor carriers; prohibition on transportation; ineligibility for Federal...

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ..., a motor carrier rated “unsatisfactory” is prohibited from operating a CMV. Information on motor... materials in quantities requiring placarding, and motor carriers transporting passengers in a CMV, are prohibited from operating a CMV in motor carrier operations in commerce beginning on the 46th day after...

  1. 49 CFR 385.13 - Unsatisfactory rated motor carriers; prohibition on transportation; ineligibility for Federal...

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ..., a motor carrier rated “unsatisfactory” is prohibited from operating a CMV. Information on motor... materials in quantities requiring placarding, and motor carriers transporting passengers in a CMV, are prohibited from operating a CMV in motor carrier operations in commerce beginning on the 46th day after...

  2. 49 CFR 385.13 - Unsatisfactory rated motor carriers; prohibition on transportation; ineligibility for Federal...

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ..., a motor carrier rated “unsatisfactory” is prohibited from operating a CMV. Information on motor... materials in quantities requiring placarding, and motor carriers transporting passengers in a CMV, are prohibited from operating a CMV in motor carrier operations in commerce beginning on the 46th day after...

  3. Tunable spin and charge transport in silicene nanoribbons

    NASA Astrophysics Data System (ADS)

    Shakouri, Kh.; Simchi, H.; Esmaeilzadeh, M.; Mazidabadi, H.; Peeters, F. M.

    2015-07-01

    Using the tight-binding formalism, we study spin and charge transport through a zigzag silicene ribbon subject to an external electric field Ez. The effect of an exchange field Mz is also taken into account and its consequences on the band structure as well as spin transport are evaluated. We show that the band structure lacks spin inversion symmetry in the presence of intrinsic spin-orbit interaction in combination of Ez and Mz fields. Our quantum transport calculations indicate that for certain energy ranges of the incoming electrons the silicene ribbon can act as a controllable high-efficiency spin polarizer. The polarization maxima occur simultaneously with the van Hove singularities of the local density of states. In this case, the combination of electric and exchange fields is the key to achieving nearly perfect spin polarization, which also leads to the appearance of additional narrow plateaus in the quantum conductance. Moreover, we demonstrate that the output current still remains completely spin-polarized for low-energy carriers even when a few edge vacancies are present.

  4. Strain engineering the charged-impurity-limited carrier mobility in phosphorene

    NASA Astrophysics Data System (ADS)

    Mohammadi, Yawar; Nia, Borhan Arghavani

    2016-01-01

    We investigate, based on the tight-binding model and in the linear deformation regime, the strain dependence of the electronic band structure of phosphorene, exposed to a uniaxial strain in one of its principle directions, the normal, the armchair and the zigzag directions. We show that the electronic band structure of strained phosphorene, for the experimentally accessible carrier densities and the uniaxial strains, is well described by a strain-dependent decoupled electron-hole Hamiltonian. Then, employing the decoupled Hamiltonian, we consider the strain dependence of the charged-impurity-limited carrier mobility in phosphorene, for both types of carriers, arbitrary carrier densities and in both armchair and zigzag directions. We show that a uniaxial tensile (compressive) strain in the normal direction enhances (weakens) the anisotropy of the carrier mobility, while a uniaxial strain in the zigzag direction acts inversely. Moreover applying a uniaxial strain in the armchair direction is shown to be ineffective on the anisotropy of the carrier mobility. These will be explained based on the effects of the strains on the carrier effective masses.

  5. Exciton shelves for charge and energy transport in third-generation quantum-dot devices

    NASA Astrophysics Data System (ADS)

    Goodman, Samuel; Singh, Vivek; Noh, Hyunwoo; Casamada, Josep; Chatterjee, Anushree; Cha, Jennifer; Nagpal, Prashant

    2014-03-01

    Quantum dots are semiconductor nanocrystallites with size-dependent quantum-confined energy levels. While they have been intensively investigated to utilize hot-carriers for photovoltaic applications, to bridge the mismatch between incident solar photons and finite bandgap of semiconductor photocells, efficient charge or exciton transport in quantum-dot films has proven challenging. Here we show development of new coupled conjugated molecular wires with ``exciton shelves'', or different energy levels, matched with the multiple energy levels of quantum dots. Using single nanoparticle and ensemble device measurements we show successful extraction and transport of both bandedge and high-energy charge carriers, and energy transport of excitons. We demonstrate using measurements of electronic density of states, that careful matching of energy states of quantum-dot with molecular wires is important, and any mismatch can generate midgap states leading to charge recombination and reduced efficiency. Therefore, these exciton-shelves and quantum dots can lead to development of next-generation photovoltaic and photodetection devices using simultaneous transport of bandedge and hot-carriers or energy transport of excitons in these nanostructured solution-processed films.

  6. 47 CFR 1.1154 - Schedule of annual regulatory charges and filing locations for common carrier services.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 1 2011-10-01 2011-10-01 false Schedule of annual regulatory charges and filing locations for common carrier services. 1.1154 Section 1.1154 Telecommunication FEDERAL... 1.1154 Schedule of annual regulatory charges and filing locations for common carrier services....

  7. Studies of the mobility of charge carriers in low-dimensional systems in a transverse DC electric field

    SciTech Connect

    Sinyavskii, E. P.; Karapetyan, S. A.

    2011-08-15

    The mobility of charge carriers {mu} in a parabolic quantum well in an electric field E directed along the size-confinement axis is calculated. With consideration for scattering of charge carriers at a rough surface, the mobility {mu} is shown to decrease with increasing E. A physical interpretation of this effect is proposed.

  8. Charge compensation mechanism of a Na+-coupled, secondary active glutamate transporter.

    PubMed

    Grewer, Christof; Zhang, Zhou; Mwaura, Juddy; Albers, Thomas; Schwartz, Alexander; Gameiro, Armanda

    2012-08-01

    Forward glutamate transport by the excitatory amino acid carrier EAAC1 is coupled to the inward movement of three Na(+) and one proton and the subsequent outward movement of one K(+) in a separate step. Based on indirect evidence, it was speculated that the cation binding sites bear a negative charge. However, little is known about the electrostatics of the transport process. Valences calculated using the Poisson-Boltzmann equation indicate that negative charge is transferred across the membrane when only one cation is bound. Consistently, transient currents were observed in response to voltage jumps when K(+) was the only cation on both sides of the membrane. Furthermore, rapid extracellular K(+) application to EAAC1 under single turnover conditions (K(+) inside) resulted in outward transient current. We propose a charge compensation mechanism, in which the C-terminal transport domain bears an overall negative charge of -1.23. Charge compensation, together with distribution of charge movement over many steps in the transport cycle, as well as defocusing of the membrane electric field, may be combined strategies used by Na(+)-coupled transporters to avoid prohibitive activation barriers for charge translocation. PMID:22707712

  9. Charge Compensation Mechanism of a Na+-coupled, Secondary Active Glutamate Transporter*

    PubMed Central

    Grewer, Christof; Zhang, Zhou; Mwaura, Juddy; Albers, Thomas; Schwartz, Alexander; Gameiro, Armanda

    2012-01-01

    Forward glutamate transport by the excitatory amino acid carrier EAAC1 is coupled to the inward movement of three Na+ and one proton and the subsequent outward movement of one K+ in a separate step. Based on indirect evidence, it was speculated that the cation binding sites bear a negative charge. However, little is known about the electrostatics of the transport process. Valences calculated using the Poisson-Boltzmann equation indicate that negative charge is transferred across the membrane when only one cation is bound. Consistently, transient currents were observed in response to voltage jumps when K+ was the only cation on both sides of the membrane. Furthermore, rapid extracellular K+ application to EAAC1 under single turnover conditions (K+ inside) resulted in outward transient current. We propose a charge compensation mechanism, in which the C-terminal transport domain bears an overall negative charge of ?1.23. Charge compensation, together with distribution of charge movement over many steps in the transport cycle, as well as defocusing of the membrane electric field, may be combined strategies used by Na+-coupled transporters to avoid prohibitive activation barriers for charge translocation. PMID:22707712

  10. Charge Transport in Trehalose-Derived Sugar Glasses

    NASA Astrophysics Data System (ADS)

    Nemzer, Louis; Navati, Mahantesh; Friedman, Joel; Epstein, Arthur

    2013-03-01

    Trehalose is a naturally occurring disaccharide with a well-known ability to preserve the biological function of proteins and cell membranes during periods of stress, including dehydration, by stabilizing the conformations of the macromolecules within a glassy matrix. This phenomenon makes use of the propensity of trehalose to interact strongly with protein functional groups and solvating water molecules via hydrogen bonding. Recently, it has been shown that trehalose sugar glasses also support long range charge transport in the form of oxidation-reduction reactions occurring between spatially separated donors and acceptors. Based on an Arrhenius conductivity analysis, along with IR-absorption and dielectric spectroscopy data, we propose that a Grotthuss-like proton hopping mechanism is responsible for the high charge carrier mobility and observed bias-dependent apparent activation energy. The possibility is raised for novel redox reactions to be performed on proteins constrained to specific 3D conformations. This could lead to a deeper understanding of biological processes, such as anhydrobiosis, as well as the development of new biomimetic photovoltaic devices.

  11. 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.

  12. 9 CFR 91.18 - Cleaning and disinfection of transport carriers for export.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 9 Animals and Animal Products 1 2011-01-01 2011-01-01 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...

  13. 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...

  14. 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 same SWNTs, it is found that the DFM gate modulation ratio, which is the ratio of DFM signal strengths at different gate voltage, is linearly proportional to the logarithm of FET device on/off ratio. A Drude-level model is established to explain the semilogarithmic correlation between DFM gate modulation ration and FET device on/off ratio and simulate the dependence of DFM force on charge carrier concentration and mobility. Future developments towards DFM imaging of charge carrier concentration or mobility in nanomaterials and nanodevices can thus be expected. PMID:26061707

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

    DOEpatents

    Luke, Paul (Castro Valley, CA)

    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.

  16. 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.

  17. Charge Transport Characterization of Novel Electronic Materials.

    NASA Astrophysics Data System (ADS)

    Marcy, Henry Orlando, 5th.

    1990-01-01

    The work presented includes analysis of electronic transport data and related measurements for the following types of materials: molecular metals and conducting polymers based upon phthalocyanine (Pc) building blocks, new composites of conducting polymers with inorganic polymeric and layered materials, and both bulk and thin film samples of the high -T_{rm c} ceramic superconductors. To successfully study such a wide spectrum of materials, the charge transport instrumentation has evolved into multiple computer-controlled experimental arrangements which process data for temperature dependent ac and dc conductivity, thermoelectric power, critical current density, and other measurements, over the temperature range of 1.5 K to 400 K. The phthalocyanine-based molecular metals and conducting polymers exhibit some of the highest reported conductivities for environmentally stable organic conductors, and possess a unique structure which is inherently resistant to large structural transformations upon donor/acceptor doping. These properties are demonstrated primarily by results for Ni(Pc)(ClO_4) _{rm y} and { (Si(Pc)O) X_{rm y}}_{rm n}. The rigidly-enforced structure of the latter system of materials allows for controllable tuning of the band-filling and hence, the charge transport properties of an organic conductor, from insulating to metal-like behavior, without any major structural alterations of the polymeric backbone. Other types of polymeric samples for which results are presented consist of composite fibers formed from the rigid rod polymers, Kevlar and PBT, "alloyed" with the (Pc)-based conducting polymers, and new microlaminates formed by intercalating various conducting polymers into the van der Waals gap of inorganic, layered host materials. Significant success has been achieved in the fabrication of superconducting films of Y-Ba-Cu-O, Bi-Sr(Pb)-Ca-Cu -O, and Tl-Ba-Ca-Cu-O by organometallic chemical vapor deposition. Results are also presented for films prepared by excimer laser ablation. Correlation of the processing parameters with the observed normal state and superconducting properties of films produced by both methods, has pointed the way to improvements in the deposition methodology and led to the reproducible fabrication of high quality films.

  18. 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

  19. 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.

  20. P type porous silicon resistivity and carrier transport

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

    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%) was found to be the major contributor to the PS resistivity (ρPS). ρPS increases exponentially with P%. Values of ρPS as high as 1 × 109 Ω cm at room temperature were obtained once P% exceeds 60%. ρPS 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 ρPS. Based on these results, it was also possible to deduce the carrier transport mechanisms in PS. For P% lower than 45%, the conduction occurs through band tails and deep levels in the tissue surrounding the crystallites. When P% 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.

  1. 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 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. Electronic supplementary information (ESI) available: Experimental details, XRD analysis, EDX analysis, PIA spectra, J-V curves, differential resistance and static resistance, photon energy dependent carrier extraction measurement. See DOI: 10.1039/c4nr04463k

  2. 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 the molecular level. Nanoscale charge transport experiments in ionic liquids extend the field to high temperatures and to systems with intriguing interfacial potential distributions. Other directions may include dye-sensitized solar cells, new sensor applications and diagnostic tools for the study of surface-bound single molecules. Another motivation for this special issue is thus to highlight activities across different research communities with nanoscale charge transport as a common denominator. This special issue gathers 27 articles by scientists from the United States, Germany, the UK, Denmark, Russia, France, Israel, Canada, Australia, Sweden, Switzerland, the Netherlands, Belgium and Singapore; it gives us a flavour of the current state-of-the-art of this diverse research area. While based on contributions from many renowned groups and institutions, it obviously cannot claim to represent all groups active in this very broad area. Moreover, a number of world-leading groups were unable to take part in this project within the allocated time limit. Nevertheless, we regard the current selection of papers to be representative enough for the reader to draw their own conclusions about the current status of the field. Each paper is original and has its own merit, as all papers in Journal of Physics: Condensed Matter special issues are subjected to the same scrutiny as regular contributions. The Guest Editors have deliberately not defined the specific subjects covered in this issue. These came out logically from the development of this area, for example: 'Traditional' solid state nanojunctions based on adsorbed layers, oxide films or nanowires sandwiched between two electrodes: effects of molecular structure (aromaticity, anchoring groups), symmetry, orientation, dynamics (noise patterns) and current-induced heating. Various 'physical effects': inelastic tunnelling and Coulomb blockade, polaron effects, switching modes, and negative differential resistance; the role of many particle excitations, new surface states in semiconductor electrodes, various mechanisms for single molecule rectification of the current, inelastic electron spectra and SERS spectroscopy. Three terminal architectures allowing (electrochemical) gating and transistor effects. Electrochemical nanojunctions and gating: intermolecular electron transfer in multi-redox metalloproteins, contact force modulation, characteristic current-noise patterns due to conformational fluctuations, resonance effects and electrocatalysis. Novel architectures: linear coupled quantum-dot-bridged junctions, electrochemical redox mediated transfer in two center systems leading to double maxima current-voltage plots and negative differential resistance, molecular-nanoparticle hybrid junctions and unexpected mesoscopic effects in polymeric wires. Device integration: techniques for creating stable metal/molecule/metal junctions using 'nano-alligator clips' and integration with 'traditional' silicon-based technology. The Guest Editors would like to thank all of the authors and referees of this special issue for their meticulous work in making each paper a valuable contribution to this research area, the early-bird authors for their patience, and Journal of Physics: Condensed Matter editorial staff in Bristol for their continuous support.

  3. The non-random walk of chiral magnetic charge carriers in artificial spin ice

    PubMed Central

    Zeissler, K.; Walton, S. K.; Ladak, S.; Read, D. E.; Tyliszczak, T.; Cohen, L. F.; Branford, W. R.

    2013-01-01

    The flow of magnetic charge carriers (dubbed magnetic monopoles) through frustrated spin ice lattices, governed simply by Coulombic forces, represents a new direction in electromagnetism. Artificial spin ice nanoarrays realise this effect at room temperature, where the magnetic charge is carried by domain walls. Control of domain wall path is one important element of utilizing this new medium. By imaging the transit of domain walls across different connected 2D honeycomb structures we contribute an important aspect which will enable that control to be realized. Although apparently equivalent paths are presented to a domain wall as it approaches a Y-shaped vertex from a bar parallel to the field, we observe a stark non-random path distribution, which we attribute to the chirality of the magnetic charges. These observations are supported by detailed statistical modelling and micromagnetic simulations. The identification of chiral control to magnetic charge path selectivity invites analogy with spintronics. PMID:23409243

  4. 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

  5. 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

  6. Thickness dependence of surface morphology and charge carrier mobility in organic field-effect transistors

    NASA Astrophysics Data System (ADS)

    Tian, Xue-Yan; Xu, Zheng; Zhao, Su-Ling; Zhang, Fu-Jun; Yuan, Guang-Cai; Li, Jing; Sun, Qin-Jun; Wang, Yun; Xu, Xu-Rong

    2010-01-01

    With the aim of understanding the relationships between organic small molecule field-effect transistors (FETs) and organic conjugated polymer FETs, we investigate the thickness dependence of surface morphology and charge carrier mobility in pentacene and regioregular poly (3-hexylthiophene) (RR-P3HT) field-effect transistors. On the basis of the results of surface morphologies and electrical properties, we presume that the charge carrier mobility is largely related to the morphology of the organic active layer. We observe that the change trends of the surface morphologies (average size and average roughness) of pentacene and RR-P3HT thin films are mutually opposite, as the thickness of the organic layer increases. Further, we demonstrate that the change trends of the field-effect mobilities of pentacene and RR-P3HT FETs are also opposite to each other, as the thickness of the organic layer increases within its limit.

  7. Effective mass of a charged carrier in a nonpolar liquid: Snowball effect in superfluid helium

    SciTech Connect

    Chikina, I.; Varlamov, A. A.

    2007-05-01

    The problem of a correct definition of the charged carrier effective mass in superfluid helium is revised. It is shown that the effective mass of such a quasiparticle can be introduced without Atkins's idea about the solidification of liquid He{sup 4} in the close vicinity of an ion (the so-called ''snowball'' model). Moreover, in addition to the generalization of Atkins's model, the charged carrier effective mass formation is considered within the framework of the two-fluid scenario. The physical reasons of the normal-fluid contribution divergency and the way of the corresponding regularization procedure are discussed. Agreement between the theory and the available experimental data is found in a wide range of temperatures.

  8. 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

  9. 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

  10. Hybrid organicinorganic 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 organicinorganic 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 IIIV 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.

  11. 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. Flatt. 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.

  12. 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

  13. 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, moir 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.

  14. 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.

  15. 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, moir 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

  16. DNA charge transport over 34 nm

    NASA Astrophysics Data System (ADS)

    Slinker, Jason D.; Muren, Natalie B.; Renfrew, Sara E.; Barton, Jacqueline K.

    2011-03-01

    Molecular wires show promise in nanoscale electronics, but the synthesis of uniform, long conductive molecules is a significant challenge. Deoxyribonucleic acid (DNA) of precise length, by contrast, is synthesized easily, but its conductivity over the distances required for nanoscale devices has not been explored. Here we demonstrate DNA charge transport (CT) over 34 nm in 100-mer monolayers on gold. Multiplexed gold electrodes modified with 100-mer DNA yield sizable electrochemical signals from a distal, covalent Nile Blue redox probe. Significant signal attenuation upon incorporation of a single base-pair mismatch demonstrates that CT is DNA-mediated. Efficient cleavage of these 100-mers by a restriction enzyme indicates that the DNA adopts a native conformation accessible to protein binding. Similar electron-transfer rates measured through 100-mer and 17-mer monolayers are consistent with rate-limiting electron tunnelling through the saturated carbon linker. This DNA-mediated CT distance of 34 nm surpasses that of most reports of molecular wires.

  17. 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...

  18. 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...

  19. 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...

  20. Fullerene-Free Polymer Solar Cells with Highly Reduced Bimolecular Recombination and Field-Independent Charge Carrier Generation.

    PubMed

    Roland, Steffen; Schubert, Marcel; Collins, Brian A; Kurpiers, Jona; Chen, Zhihua; Facchetti, Antonio; Ade, Harald; Neher, Dieter

    2014-08-21

    Photogeneration, recombination, and transport of free charge carriers in all-polymer bulk heterojunction solar cells incorporating poly(3-hexylthiophene) (P3HT) as donor and poly([N,N'-bis(2-octyldodecyl)-naphthelene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)) (P(NDI2OD-T2)) as acceptor polymer have been investigated by the use of time delayed collection field (TDCF) and time-of-flight (TOF) measurements. Depending on the preparation procedure used to dry the active layers, these solar cells comprise high fill factors (FFs) of up to 67%. A strongly reduced bimolecular recombination (BMR), as well as a field-independent free charge carrier generation are observed, features that are common to high performance fullerene-based solar cells. Resonant soft X-ray measurements (R-SoXS) and photoluminescence quenching experiments (PQE) reveal that the BMR is related to domain purity. Our results elucidate the similarities of this polymeric acceptor with the superior recombination properties of fullerene acceptors. PMID:26278084

  1. Bi(1)-(x)Sb(x) alloy nanocrystals: colloidal synthesis, charge transport, and thermoelectric properties.

    PubMed

    Zhang, Hao; Son, Jae Sung; Jang, Jaeyoung; Lee, Jong-Soo; Ong, Wee-Liat; Malen, Jonathan A; Talapin, Dmitri V

    2013-11-26

    Nanostructured Bi1-xSbx alloys constitute a convenient system to study charge transport in a nanostructured narrow-gap semiconductor with promising thermoelectric properties. In this work, we developed the colloidal synthesis of monodisperse sub-10 nm Bi1-xSbx alloy nanocrystals (NCs) with controllable size and compositions. The surface chemistry of Bi1-xSbx NCs was tailored with inorganic ligands to improve the interparticle charge transport as well as to control the carrier concentration. Temperature-dependent (10-300 K) electrical measurements were performed on the Bi1-xSbx NC based pellets to investigate the effect of surface chemistry and grain size (?10-40 nm) on their charge transport properties. The Hall effect measurements revealed that the temperature dependence of carrier mobility and concentration strongly depended on the grain size and the surface chemistry, which was different from the reported bulk behavior. At low temperatures, electron mobility in nanostructured Bi1-xSbx was directly proportional to the average grain size, while the concentration of free carriers was inversely proportional to the grain size. We propose a model explaining such behavior. Preliminary measurements of thermoelectric properties showed a ZT value comparable to those of bulk Bi1-xSbx alloys at 300 K, suggesting a potential of Bi1-xSbx NCs for low-temperature thermoelectric applications. PMID:24134215

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

    PubMed

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

    2015-12-22

    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

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

    NASA Astrophysics Data System (ADS)

    P?ibyl, Michal; Slouka, Zden?k

    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.

  4. 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.

  5. Overall current-voltage characteristics of space charge controlled currents for thin films by a single carrier species

    NASA Astrophysics Data System (ADS)

    Seki, Kazuhiko

    2014-08-01

    The Mott-Gurney equation (Child's law) has been frequently applied to measure the mobility of carrier transport layers. One of the main assumption in the Mott-Gurney theory is ignoring the diffusive currents. It was not obvious, however, whether the diffusive currents can be ignored for thin carrier transport layers. We obtained the current-voltage relation using analytical solutions of drift-diffusion equation coupled with the Poisson's equation. The integration constants were numerically determined using nonlinear equations obtained from boundary conditions. A simple analytical relation between the voltage and current was also derived. The analytical equation improved over the Mott-Gurney equation when the voltage is between 0.1 and 2 (V) at room temperature. By using published data, we show that both the mobility and the layer thickness can be simultaneously obtained by applying the analytical expression. The effect of diffusion on the current-voltage relation is explained by the movement of the virtual electrode formed by space charge accumulation.

  6. Single-step Charge Transport through DNA over Long Distances

    PubMed Central

    Genereux, Joseph C.; Wuerth, Stephanie M.; Barton, Jacqueline K.

    2011-01-01

    Quantum yields for charge transport across adenine tracts of increasing length have been measured by monitoring hole transport in synthetic oligonucleotides between photoexcited 2-aminopurine, a fluorescent analogue of adenine, and N2-cyclopropyl guanine. Using fluorescence quenching, a measure of hole injection, and hole trapping by the cyclopropyl guanine derivative, we separate the individual contributions of single- and multi-step channels to DNA charge transport, and find that with 7 or 8 intervening adenines the charge transport is a coherent, single-step process. Moreover, a transition occurs from multi-step to single-step charge transport with increasing donor/acceptor separation, opposite to that generally observed in molecular wires. These results establish that coherent transport through DNA occurs preferentially across 10 base pairs, favored by delocalization over a full turn of the helix. PMID:21348520

  7. 41 CFR 302-10.200 - What costs are allowable when a commercial carrier transports my mobile home overland or over water?

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 41 Public Contracts and Property Management 4 2010-07-01 2010-07-01 false What costs are allowable....200 Public Contracts and Property Management Federal Travel Regulation System RELOCATION ALLOWANCES... permits to transport mobile homes in or through its jurisdiction; (4) Carrier's service charges...

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

    PubMed

    Ponseca, C S; Sundström, V

    2016-03-17

    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. PMID:26763720

  9. Comparison between charge and spin transport in few-layer graphene

    NASA Astrophysics Data System (ADS)

    Maassen, T.; Dejene, F. K.; Guimarães, M. H. D.; Józsa, C.; van Wees, B. J.

    2011-03-01

    Transport measurements on few-layer graphene (FLG) are important because they interpolate between the properties of single-layer graphene (SLG) as a true two-dimensional material and the three-dimensional bulk properties of graphite. In this article we present four-probe local charge transport and nonlocal spin-valve and spin-precession measurements on lateral spin field-effect transistors on FLG. We study systematically the charge- and spin-transport properties depending on the number of layers and the electrical back gating of the device. We explain the charge-transport measurements by taking the screening of scattering potentials into account and use the results to understand the spin data. The measured samples are between 3 and 20 layers thick, and we include in our analysis our earlier results of the measurements on SLG for comparison. In our room-temperature spin-transport measurements we manage to observe spin signals over distances up to 10 μm and measure enhanced spin-relaxation times with an increasing number of layers, reaching τs~500 ps as a maximum, about 4 times higher than in SLG. The increase of τs can result from the screening of scattering potentials due to additional intrinsic charge carriers in FLG. We calculate the density of states of FLG using a zone-folding scheme to determine the charge-diffusion coefficient DC from the square resistance RS. The resulting DC and the spin-diffusion coefficient DS show similar values and depend only weakly on the number of layers and gate-induced charge carriers. We discuss the implications of this on the identification of the spin-relaxation mechanism.

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

    PubMed Central

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

    NASA Astrophysics Data System (ADS)

    Wrfel, 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.

  12. 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

  13. 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.

  14. Initial spatial distribution of geminate charge carriers photogenerated in doped conjugated polymers

    NASA Astrophysics Data System (ADS)

    Lukin, L. V.

    2015-12-01

    A diffusion model of the charge carrier photogeneration in doped conjugated polymers is suggested. A dissociation of a vibrationally relaxed exciton into a Coulombically bound geminate pair of charges occurs at a charge transfer center which consists of a conjugated segment of a polymer chain and a nearby dopant molecule. A photogenerated hole executes one-dimensional diffusion motion along the conjugated segment in the on-chain potential well formed by the Coulomb and external electric fields. Holes are assumed to become localized in trapping sites. It is shown that the spatial distribution of trapped holes is determined mainly by effective temperature of pretrapped holes and external electric field. The model is consistent with experimental data on photoconduction of a copolymer of a phenyl-substituted poly-phenylenevinylene doped with trinitrofluorenone, which have been reported by Weiter et al. (2004). Effective temperature of holes is evaluated at about 1200 K.

  15. 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.

  16. DNA Charge Transport within the Cell

    PubMed Central

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

    2015-01-01

    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 E. 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. Based on 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

  17. Carriers

    MedlinePLUS

    ... a recessive disease, which means that, generally, a child will only have SMA if both parents pass on the ... chance that their child will have SMA If only one parent is a carrier, the child is usually not at risk for SMA (though ...

  18. Charge transport in tri-p-tolylamine doped trinaphthalylbenzene glass

    NASA Astrophysics Data System (ADS)

    Lin, Liang-Bih; O'Reilly, James M.; Magin, Edward H.; Weiss, David S.; Jenekhe, Samson A.

    2000-09-01

    The charge transport properties of tri-p-tolylamine (TTA) doped trinaphthalylbenzene have been measured as a function of electric field and temperature. The charge mobilities of the composite are comparable to but somewhat lower than that of TTA doped polystyrene, a nonpolar polymeric host, at similar weight fractions. We suggest that the difference is due to inhomogeneity between the host and the dopant. The results suggest that, similar to polymer hosts in molecularly doped polymers, the molecular host only functions as an inert diluter and does not directly participate in the charge transport manifold. The results also substantiate the importance of molecular packing to charge hopping in disordered organic materials. The charge mobility data are analyzed with a disorder model due to Bässler and coworkers and a recently modified expression due to Novikov and coworkers [Phys. Rev. Lett. 81, 4472 (1998)]. Both models provide adequate descriptions of charge transport in organic amorphous materials.

  19. Electron transport and charge induction in cadmium zinc telluride detectors with space charge build up under intense x-ray irradiation

    SciTech Connect

    Bale, Derek S.; Szeles, Csaba

    2010-06-15

    Under intense x-ray irradiation, wide band gap semiconductor radiation detectors fabricated from crystals with low hole transport properties develop a steady-state space charge distribution that results from a dynamic equilibrium between charge carrier dynamics and the incident photon field. At a high enough x-ray flux, this space charge can collapse the electric field within the detector, resulting in the paralyzation of photon counting (i.e., high-flux polarization). However, well before polarization causes a catastrophic device failure, there can be enough space charge present to significantly modify the electric field. A modified field affects the electron transport and, therefore, signal generation within the sensor, which can ultimately degrade the performance of high-rate photon counting electronics. In this study, we analytically solve the fundamental equation of charge conservation to derive the modified electron transport in the presence of an exponential space charge distribution that results from the incident x-rays. We use these space-time solutions to calculate and study the time dependence of the resulting charge-induced signals. The predicted induced signals are compared throughout with numerical solutions of the full charge transport equation. In addition, we present analogous closed-form signals for a uniform distribution relevant to a broader class of {gamma}-ray applications. Finally, we use these solutions to derive a two-parameter family of modified Hecht curves that naturally predict a voltage offset that appears due to the space charge.

  20. 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

  1. 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 of free charges that can contribute to the photocurrent in a device. We show that free mobile charges can be efficiently produced via CM in solids of strongly coupled PbSe QDs. Strong electronic coupling between the QDs resulted in a charge carrier mobility of the order of 1 cm(2) V(-1) s(-1). This mobility is sufficiently high so that virtually all electron-hole pairs escape from recombination. The impact of temperature on the CM efficiency in PbSe QD solids was also studied. We inferred that temperature has no observable effect on the rate of cooling of hot charges nor on the CM rate. We conclude that exploitation of CM requires that charges have sufficiently high mobility to escape from recombination. The contribution of CM to the efficiency of photovoltaic devices can be further enhanced by an increase of the CM efficiency above the energetic threshold of twice the band gap. For large-scale applications in photovoltaic devices, it is important to develop abundant and nontoxic materials that exhibit efficient CM. PMID:25607377

  2. 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.

  3. Enhanced charge transport kinetics in anisotropic, stratified photoanodes.

    PubMed

    Yazdani, Nuri; Bozyigit, Deniz; Utke, Ivo; Buchheim, Jakob; Youn, Seul Ki; Patscheider, Jrg; Wood, Vanessa; Park, Hyung Gyu

    2014-02-12

    The kinetics of charge transport in mesoporous photoanodes strongly constrains the design and power conversion efficiencies of dye sensitized solar cells (DSSCs). Here, we report a stratified photoanode design with enhanced kinetics achieved through the incorporation of a fast charge transport intermediary between the titania and charge collector. Proof of concept photoanodes demonstrate that the inclusion of the intermediary not only enhances effective diffusion coefficients but also significantly suppresses charge recombination, leading to diffusion lengths two orders of magnitude greater than in standard mesoporous titania photoanodes. The intermediary concept holds promise for higher-efficiency DSSCs. PMID:24467298

  4. 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.

  5. 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.

  6. High field carrier transport in graphene: Insights from fast current transient

    NASA Astrophysics Data System (ADS)

    Majumdar, Kausik; Kallatt, Sangeeth; Bhat, Navakanta

    2012-09-01

    In this work, we observe gate tunable negative differential conductance (NDC) and current saturation in single layer and bilayer graphene transistor at high source-drain field, which arise due to the interplay among (1) self-heating, (2) hot carrier injection, and (3) drain induced minority carrier injection. The magnitude of the NDC is found to be reduced for a bilayer, in agreement with its weaker carrier-optical phonon coupling and less efficient hot carrier injection. The contributions of different mechanisms to the observed results are decoupled through fast transient measurements with nanosecond resolution. The findings provide insights into high field transport in graphene.

  7. 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 laboratory (UCD). The measured signals were decomposed into the constituent dynamics of three transient populations: hot tightly bound excitons, relaxed tightly bound excitons, and separated trapped carriers (holes and electrons). The influenes of three external factors affecting the observed dynamics were explored: (1) excitation wavelength, (2) excitation fluence, and (3) presence of the hole scavenger HS -. Both higher-energy excitation photons and higher-intensity excitation induce slower relaxation of charge carriers to the band edge due to the need to dissipate excess excitation energy. Nonlinear decay kinetics of the relaxed exciton population is observed and demonstrated to arise from bimolecular trapping of excitons with low-density trap sites located at CdSe NR surface sites instead of the commonly resolved multiparticle Auger recombination mechanism. This is supported by the observed linear excitation-fluence dependence of the trapped-carrier population that is n umerically simulated and found to deviate from the excitation fluence dependence expected of Auger recombination kinetics. Introducing hole scavenging HS- has a negligible effect on the exciton kinetics, including migration and dissociation, and instead passivates surface trap states to induce the rapid elimination of holes after exciton dissociation. This increases the lifetime of the reactive electron population and increases measured photocatalytic H2 generation activity. A broad (200 nm) and persistent (20 ps) stimulated emission observed in the tightly bound excitons suggests their potential use as broadband microlasers. In chapter 3 (JPCL, 2688, 2011), the photocatalytic H2O splitting activities of CdSe and CdSe/CdS core/shell quantum dots, which were also synthesized in the Osterloh laboratory (UCD) are contrasted. CdSe/CdS core/shell quantum dots constructed from 4.0 nm CdSe quantum dots are shown to be strongly active for visible-light-driven photocatalytic H2 evolution in 0.1M Na 2S/Na2SO3 solution with a turnover number of 9.94 after 5 h at 103.9 ?mol/h. CdSe quantum dots themselves are only marginally active in 0.1 M Na2S/Na2SO3 solution with a turnover number of 1.10 after 5 h at 11.53 ?mol/h, while CdSe quantum dots in pure H2O are found to be completely inactive. Broad-band transient absorption spectroscopy is used to elucidate the mechanisms that facilitate the enhancement in the CdSe core/shell quantum dots, which is attributed to passivation of surface-deep trap states with energies lying below the reduction potential necessary for H2O reduction. Thus, it is shown that surface trapping dynamics and energetics can be manipulated to dictate the photocatalytic activities of novel CdSe quantum dot based photocatalytic materials. Chapter 4 builds upon this work examining the differences in dynamics that occur upon passivation of water soluble CdZnS alloy cores with ZnS shells, which were produced in the Snee laboratory (UI Chicago), via 400 nm pump broadband probe ultrafast transient absorption spectroscopy, and global analysis modeling. We also examine the perturbation invoked on charge carrier dynamics caused by growing Pd nanoparticles on the CdZnS/ZnS shell surface in-situ and note the cyclical charge carrier transfer that takes place. Both the CdZnS core and CdZnS/ZnS core/shell quantum dots exhibit unusually long lived excited states (much > 8 ns) while the CdZnS/ZnS.Pd tandem core/shell quantum dots recover much quicker (~3 ns). Additionally, ultrafast excitation fluence dependencies are used to characterize Auger recombination and the presence of two different trap state populations observable in the visible spectrum. In chapter 5 (JACS, 20664, 2011), we switch from examining direct band-gap chalcogenide based quantum dots to Si quantum dots synthesized in the Kauzlarich laboratory (UCD), which exhibit an indirect band-gap. Here a microwave-assisted reaction to produce hydrogen-terminated silicon quantum dots is discussed. The Si quantum dots were passivated for water solubility via two different methods: hydrosilylation produced 3-aminopropenyl-terminated Si quantum dots, and a modified Stber process produced silica-encapsulated Si quantum dots. Both methods produce water-soluble quantum dots with maximum emission at 414 nm, and after purification, the quantum dots exhibit intrinsic fluorescence quantum yield efficiencies of 15 and 23%, respectively. Even though the quantum dots have different surfaces, they exhibit nearly identical absorption and fluorescence spectra. Femtosecond transient absorption spectroscopy was used for temporal resolution of the photoexcited carrier dynamics between the quantum dots and ligand. The transient dynamics of the 3-aminopropenyl-terminated Si quantum dots is interpreted as a formation and decay of a charge-transfer excited state between the delocalized ? electrons of the carbon linker and the Si core excitons. This charge transfer state is stable for ~4 ns before reverting back to a more stable, long-living species. The silica-encapsulated Si QDs show a simpler spectrum without charge transfer dynamics. Appendix I (Chem. Mat., 1220, 2010), addresses the long-time (?s) transient kinetics associated with TiO2 and layered titanates (TBA2 2Ti4O9), which were synthesized in the Osterloh laboratory (UCD). Transient absorption data reveal that photogenerated electrons become trapped in mid band-gap states, from which they decay exponentially with a time-constant of 43.67 + 0.28 ms in titanates, which is much slower than the 68 + 1 ns observed for TiO2 nanocrystals. The slower kinetics observed for the TBA 2Ti4O9 nanosheets originates either from the presence of deeper trap sites on the sheets vs. the nanoparticles, more trap sites, or from more effective electron-hole separation because of the micrometer dimensions of the 2D lattice. Appendix II, depicts the visible solar spectrum at sea level detailing the percentage of photons and energy that exist within certain wavelength ranges.

  8. Experimental measurements of charge carrier mobility: lifetime products for large sample of pixilated CZT detectors

    NASA Astrophysics Data System (ADS)

    Vadawale, S. V.; Shanmugam, M.; Purohit, Shishir; Acharya, Y. B.; Sudhakar, Manju

    2012-07-01

    Cadmium-Zinc-Telluride (CZT) is thought to be a primary work horse for hard X-ray astronomy in future. Due to the relatively large band-gap, it offers near room temperature operation while maintaining much better energy resolution then scintillator detectors operating in similar energy range. Further, CZT detectors are available in the form of pixilated detectors with area up to few cm2 and hence it is possible to realize very large detector area by having an array of such pixilated CZT detectors. However, it is well known that the energy spectrum of mono-energetic X-ray measured by CZT detectors does not have a Gaussian shape but has significant low-energy tail. This is mainly due to relatively poor mobility and small life time of the charge carriers, particularly of holes, in the CZT crystals. Thus, in order to understand spectral response for a large array of CZT detectors consisting of multiple elements / pixels, it is essential to characterize the mobility-lifetime products of charge carriers for each individual elements / pixels. Here we present experimental measurements of charge carrier mobility-lifetime products for large sample of multi-pixel CZT detectors. The mobility-lifetime products are measured by simultaneously fitting a CZT line model to pixel wise spectra of 122 keV X-rays from 57Co at three different bias voltages. These were carried out as a part of selection of CZT detector modules for the High Energy X-ray spectrometer (HEX) onboard Indian moon mission - Chandrayaan-1.

  9. 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.

  10. 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 photovoltages extending from ~millisecond to tens of sec. Finally, we characterize the combined effects of pyridine treatment and Zr-TiO2 on device performance and carrier lifetimes.

  11. 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.

  12. Influence of Exciton Lifetime on Charge Carrier Dynamics in an Organic Heterostructure

    SciTech Connect

    Agrawal, Kanika L.; Sykes, Matthew E.; An, Kwang Hyup; Frieberg, Bradley; Green, P. F.; Shtein, Max

    2013-03-18

    Interactions between charge carriers and excitons, as well as between excitons and optical cavity modes in organic optoelectronic devices are fundamental to their operational limits and chief in preventing the realization of certain phenomena, such as electrically pumped organic lasing. We uncovered a previously unreported phenomenon, wherein optical cavity-modulated exciton decay rate leads to a concomitant modulation in the electrical current of an archetypal NPD/Alq₃ organic light emitting device operated in forward bias. The magnitude of this variation is sensitive to the local dielectric environment of the device and is found to be as large as 15%.

  13. Recombination of charge carriers in the GaAs-based p-i-n diode

    SciTech Connect

    Ayzenshtat, G. I.; Yushenko, A. Y.; Gushchin, S. M.; Dmitriev, D. V.; Zhuravlev, K. S.; Toropov, A. I.

    2010-10-15

    It is established that the radiative recombination of charge carriers plays a substantial role in the GaAs-based p-i-n diodes at high densities of the forward current. It is shown experimentally that the diodes operating in microwave integrated circuits intensely emit light in the IR range with wavelengths from 890 to 910 nm. The obtained results indicate the necessity of taking into account the features of recombination processes in the GaAs-based microwave p-i-n diodes.

  14. Charge Transport Asymmetry in Cryogenic High Purity Germanium

    NASA Astrophysics Data System (ADS)

    Shank, B.; Nagasawa, D. Q.; Cabrera, B.; Cherry, M.; Young, B. A.

    2014-08-01

    The SuperCDMS experiment relies on detection of free charges generated in high purity germanium (HPGe) crystals by particle interactions. To better understand long-term trapping effects which make carriers unavailable for such rapid ionization measurements, we used infrared LEDs ( = 940 nm) to create electron-hole pairs near each face of a HPGe SuperCDMS detector operated under applied electric field at 400 mK. By alternating the polarity of an applied electric field, we were able to study propagation of each carrier through the crystal separately. Asymmetry in the resulting current transients revealed differences in trapping characteristics between electrons and holes at these low temperatures.

  15. Perturbation theory for charged-particle transport in one dimension

    NASA Technical Reports Server (NTRS)

    Wilson, J. W.; Lamkin, S. L.

    1975-01-01

    Perturbation theory, when applied to charged-particle transport, generates a series solution that requires a double quadrature per term. The continuity of higher-order terms leads to numerical evaluation of the series. The high rate of convergence of the series makes the method a practical tool for charged-particle transport problems. The coupling of the neutron component in the case of proton transport in tissue does not greatly alter the rate of convergence. The method holds promise for a practical high-energy proton transport theory.

  16. 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.

  17. 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

  18. 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.

  19. Correlation between thermal fluctuation effects and phase coherence factor in carrier transport of single-crystal organic semiconductors

    NASA Astrophysics Data System (ADS)

    Fukami, Tatsuya; Ishii, Hiroyuki; Kobayashi, Nobuhiko; Uemura, Takafumi; Sakai, Kenichi; Okada, Yugo; Takeya, Jun; Hirose, Kenji

    2015-04-01

    We find that the phase coherence factor derived from Hall effect measurements of single-crystal thin-film field-effect transistors of pentacene, which relates the intrinsic charge transport with the phase coherence, has a strong correlation with the thermal fluctuations of transfer energies between neighboring molecules. This observation also holds true for other organic semiconductors such as tetracene, dianthrathiophene (DAT)-V, and dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT). This gives us clues for constructing flexible molecular systems with high carrier mobility.

  20. 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.

  1. 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, 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. Electronic supplementary information (ESI) available: SEM images and elemental mapping of Ti2CTx, thickness dependence of the Raman spectrum, and morphologies of Ti2CTx with different thicknesses. See DOI: 10.1039/c5nr06513e

  2. Optimizing charge transport in Fe IIO 3 films deposited on nanowire arrays

    NASA Astrophysics Data System (ADS)

    Barnes, Piers R. F.; Blake, David; Glasscock, Julie A.; Plumb, Ian C.; Vohralik, Peter F.; Bendavid, Avi; Martin, Philip J.

    2006-08-01

    The short diffusion length of photo-excited charge carriers in Fe IIO 3 is one of the factors limiting the water splitting efficiency of iron oxide based materials. To overcome this problem we are engineering transparent arrays of nanowires to act as conducting substrates for the Fe IIO 3. To help understand the charge transport characteristics of the Fe IIO 3 component we report transient photocurrent measurements performed on an absorbing thin film of Fe IIO 3 deposited by filtered arc deposition on conducting glass with a semi-transparent silver Schottky top contact. Ultraviolet laser pulses were used to generate charge carriers near the surface and the resulting current transients were measured. A simulation of this charge transport has also been developed. The sign of the observed transients was independent of applied bias, consistent with a fully depleted film. The measurements also suggest that recombination may play a significant factor in determining the transient shape. Further investigation is required to confidently predict mobilities.

  3. 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 (?-P, ?-P,?-P and ?-P) using density functional theory combined with Boltzmann transport method and relaxation time approximation. It is shown that ?-P, ?-P and ?-P are indirect gap semiconductors, while ?-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, ?-P, ?-P and ?-P sheets can be considered as n-type semiconductors, and ?-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

  4. Theoretical predictions on the electronic structure and charge carrier mobility in 2D phosphorus sheets.

    PubMed

    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 (?-P, ?-P,?-P and ?-P) using density functional theory combined with Boltzmann transport method and relaxation time approximation. It is shown that ?-P, ?-P and ?-P are indirect gap semiconductors, while ?-P is a direct one. All four sheets have ultrahigh carrier mobility and show anisotropy in-plane. The highest mobility value is ~3 10(5) cm(2)V(-1)s(-1), which is comparable to that of graphene. Because of the huge difference between the hole and electron mobilities, ?-P, ?-P and ?-P sheets can be considered as n-type semiconductors, and ?-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

  5. Nanoscale Imaging of Charge Carrier and Exciton Trapping at Structural Defects in Organic Semiconductors.

    PubMed

    Große, Christoph; Gunnarsson, Olle; Merino, Pablo; Kuhnke, Klaus; Kern, Klaus

    2016-03-01

    Charge carrier and exciton trapping in organic semiconductors crucially determine the performance of organic (opto-)electronic devices such as organic field-effect transistors, light-emitting diodes, or solar cells. However, the microscopic origin of the relevant traps generally remains unclear, as most spectroscopic techniques are unable to simultaneously probe the electronic and morphological structure of individual traps. Here, we employ low-temperature scanning tunneling microscopy (STM) and spectroscopy (STS) as well as tight-binding calculations derived from ab initio calculations to image the localized electronic states arising at structural defects in thin C60 films (<10 ML). The spatially and spectrally resolved STM-induced luminescence at these states reveals an enhanced radiative decay of excitons, which is interpreted in terms of the local symmetry lowering and the trapping of excitons by an X-trap. The combined mapping of the STM-induced luminescence, electronic structure, and morphology thus provides new insights into the origin and characteristics of individual exciton traps in organic semiconductors and offers new avenues to study charge carrier and exciton dynamics on molecular scales. PMID:26871739

  6. Doped GaN nanowires on diamond: Structural properties and charge carrier distribution

    NASA Astrophysics Data System (ADS)

    Schuster, Fabian; Winnerl, Andrea; Weiszer, Saskia; Hetzl, Martin; Garrido, Jose A.; Stutzmann, Martin

    2015-01-01

    In this work, we present a detailed study on GaN nanowire doping, which is vital for device fabrication. The nanowires (NWs) are grown by means of molecular beam epitaxy on diamond (111) substrates. Dopant atoms are found to facilitate nucleation, thus an increasing NW density is observed for increasing dopant fluxes. While maintaining nanowire morphology, we demonstrate the incorporation of Si and Mg up to concentrations of 9 1020cm-3 and 1 1020cm-3 , respectively. The dopant concentration in the nanowire cores is determined by the thermodynamic solubility limit, whereas excess dopants are found to segregate to the nanowire surface. The strain state of the NWs is investigated by X-ray diffraction, which confirms a negligible strain compared to planar thin films. Doping-related emissions are identified in low-temperature photoluminescence spectroscopy and the temperature quenching yields ionization energies of Si donors and Mg acceptors of 17 meV and 167 meV, respectively. At room temperature, luminescence and absorption spectra are found to coincide and the sub-band gap absorption is suppressed in n-type NWs. The charge carrier distribution in doped GaN nanowires is simulated under consideration of surface states at the non-polar side facets. For doping concentrations below 1017cm-3 , the nanowires are depleted of charge carriers, whereas they become highly conductive above 1019cm-3 .

  7. An autonomous photosynthetic device in which all charge carriers derive from surface plasmons.

    PubMed

    Mubeen, Syed; Lee, Joun; Singh, Nirala; Krmer, 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 TiO?) 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) H? 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

  8. An autonomous photosynthetic device in which all charge carriers derive from surface plasmons

    NASA Astrophysics Data System (ADS)

    Mubeen, Syed; Lee, Joun; Singh, Nirala; Krmer, 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 1013 H2 molecules per cm2 per s under 1 sun illumination (AM 1.5 and 100 mW cm-2), with unprecedented long-term operational stability.

  9. 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.

  10. Enhanced Visible Light-Induced Charge Separation and Charge Transport in Cu2O-Based Photocathodes by Urea Treatment.

    PubMed

    Wang, Peng; Tang, Yiming; Wen, Xiaoming; Amal, Rose; Ng, Yun Hau

    2015-09-16

    Carrier density, photocharge transfer kinetics, and charge transfer resistance of the anodized Cu-Cu2O-CuO photocathode were greatly improved using thermal treatment with urea. Time-correlated single-photon counting (TCSPC) results revealed the faster electron transfer kinetics from Cu2O to CuO in the urea-treated Cu-Cu2O-CuO composite photoelectrodes. Preservation of the metallic copper component via the intermediate Cu3N during the treatment facilitated higher bulk conductance of the Cu-Cu2O-CuO photocathode for improved charge transport. Higher carrier density was also observed in the urea-treated photoelectrode, which was possibly attributed to the presence of nitrogen as a dopant. Furthermore, the compact outer layer of CuO protected the underlayer Cu2O from being in direct contact with the aqueous solution. This suppressed the photocorrosion of Cu2O and resulted in the higher photostability of the Cu-Cu2O-CuO film. When these advantages were combined, the urea-treated Cu-Cu2O-CuO film showed a higher photocurrent of 2.2 mA/cm2 and improved stability versus that of the conventional Cu-Cu2O-CuO film (1.2 mA/cm2). To improve the charge transfer kinetics and carrier density, this paper provides a new strategy for synthesizing effective and stable Cu2O-based photoelectrodes by using urea treatment. PMID:26305707

  11. 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

  12. 14 CFR 234.13 - Reports by air carriers on incidents involving animals during air transport.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 4 2011-01-01 2011-01-01 false Reports by air carriers on incidents involving animals during air transport. 234.13 Section 234.13 Aeronautics and Space OFFICE OF THE SECRETARY, DEPARTMENT OF TRANSPORTATION (AVIATION PROCEEDINGS) ECONOMIC REGULATIONS AIRLINE SERVICE QUALITY...

  13. 41 CFR 301-10.105 - What are the basic requirements for using common carrier transportation?

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 41 Public Contracts and Property Management 4 2011-07-01 2011-07-01 false What are the basic requirements for using common carrier transportation? 301-10.105 Section 301-10.105 Public Contracts and Property Management Federal Travel Regulation System TEMPORARY DUTY (TDY) TRAVEL ALLOWANCES ALLOWABLE TRAVEL EXPENSES 10-TRANSPORTATION...

  14. Simulation of charge transport in pixelated CdTe

    PubMed Central

    Kolstein, M.; Ario, G.; Chmeissani, M.; De Lorenzo, G.

    2014-01-01

    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. PMID:25729404

  15. Simulation of charge transport in pixelated CdTe

    NASA Astrophysics Data System (ADS)

    Kolstein, M.; Ario, 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.

  16. Coupled simulation of carrier transport and electrodynamics: the EMC/FDTD/MD technique

    NASA Astrophysics Data System (ADS)

    Willis, K. J.; Sule, N.; Hagness, S. C.; Knezevic, I.

    2015-03-01

    In order to understand the response of conductive materials to high-frequency electrical or optical excitations, the interplay between carrier transport and electrodynamics must be captured. We present our recent work on developing EMC/FDTD/MD, a self-consistent coupled simulation of semiclassical carrier transport, described by ensemble Monte Carlo (EMC), with full-wave electrodynamics, described by the finite-difference time-domain (FDTD) technique and molecular dynamics (MD) for sub-grid-cell interactions. Examples of room-temperature terahertz-frequency transport simulation of doped silicon and back-gated graphene are shown.

  17. 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 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. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr05008h

  18. 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...

  19. Verification of three dimensional charge transport simulations using ion microbeams

    SciTech Connect

    Horn, K.M.; Dodd, P.E.; Breese, M.B.H.; Doyle, B.L.

    1996-12-31

    Optically targeted, ion microbeams provide a useful means of exposing individual structures within an integrated circuit to ionizing radiation. With this tool, calibrated, low damage, charge collection spectra can be measured from specific circuit structures without preceding ion damage to the structure or surrounding circuitry. This paper presents comparisons of calibrated, low damage, ion microbeam- based charge collection measurements and three-dimensional, charge transport simulations of charge collection for isolated n- and p- channel field effect transistors under conducting and non-conducting bias conditions.

  20. 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.

  1. 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

  2. Collective charge transport in semiconductor-metal hybrid nanocomposite

    NASA Astrophysics Data System (ADS)

    Shuvra Basu, Tuhin; Ghosh, Siddhartha; Gierlotka, Stanislaw; Ray, Mallar

    2013-02-01

    Collective charge transport through a hybrid nanocomposite made of Ag nanoparticles (NPs) embedded in ultra-small Si quantum dot (QD) matrix exhibits unexpected and fascinating characteristics. Metallic inclusion (10 wt. % of Ag NPs) in the Si QD matrix affects six orders of magnitude increase in current. In the semiconductor-metal hybrid, three different charge transport mechanismsquantum tunneling through insulating barriers, variable range hoping, and simple thermally activated conduction dominate in three different temperature regimes that are influenced by bias voltage. We show that there is a cross-over from one transport mechanism to the other and determine the voltage dependent cross-over temperatures.

  3. Charged particles time-dependent transverse transport

    NASA Astrophysics Data System (ADS)

    Fraschetti, F.; Jokipii, J. R.

    2010-12-01

    We discuss an analytical derivation for the temporal dependence of the transverse transport coefficient for times smaller than the correlation time of the magnetic turbulence, as seen by the particle, where the quasi-linear theory is not valid. The transverse transport is assumed to be dominated by the guiding center motion. Contributions of wavelengths shorter and longer than the coherence length to particle drift from the local magnetic field lines and to the magnetic field lines random walk are assessed for slab and 3D isotropic turbulence. Extensions of this model will allow for a study of solar wind physically motivated anisotropy.

  4. Corona charged polychlorotrifluorotylene film electrets, and its charge storage and transport

    NASA Astrophysics Data System (ADS)

    Xia, Zhong F.; Jiang, Jian

    1991-11-01

    In this paper, the electret properties of negative and positive charging at room and elevated temperatures for polychlorotrifluorothylene (Aclar PCTFE) were studied by means of corona charging, electron beam bombardment, and thermally stimulated discharge (TSD). The shift of mean charge depth with the prolongation of time during aging at 150 degree(s)C after corona charging at RT was investigated. The transport model of detrapped charge in an Aclar PCTFE sample was discussed by means of laser induced pressure pulse (LIPP) method. The geometric distribution of traps with different activation energies along thickness was studied by means of electron beam discharge and TSD currents in combination with heat pulse method. At the same time, the comparison of the charge storage ability between positive and negative corona charged sample was carried out.

  5. 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.

  6. Polaron effects and electric field dependence of the charge carrier mobility in conjugated polymers

    NASA Astrophysics Data System (ADS)

    Jakobsson, Mattias; Stafström, Sven

    2011-10-01

    Charge transport in conjugated polymers has been investigated using Monte Carlo simulations implemented on top of the Marcus theory for donor-acceptor transition rates. In particular, polaron effects and the dependency of the mobility on the temperature and the applied electric field have been studied. The conclusions are that while the qualitative temperature dependence is similar to that predicted by Miller-Abrahams theory in the Gaussian disorder model (GDM), the electric field dependence is characterized by a crossover into the Marcus inverted region, not present in the GDM. Furthermore, available analytical approximations to describe the electric field dependence of the mobility in Marcus theory fail to fit the simulation data and hence cannot be used to directly draw conclusions about the importance of polaron effects for charge transport in conjugated polymers.

  7. 49 CFR 377.209 - Additional charges.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 49 Transportation 5 2011-10-01 2011-10-01 false Additional charges. 377.209 Section 377.209... CHARGES Extension of Credit to Shippers by Motor Common Carriers, Water Common Carriers, and Household Goods Freight Forwarders 377.209 Additional charges. When a carrier (a) Has collected the amount...

  8. 49 CFR 377.209 - Additional charges.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 49 Transportation 5 2010-10-01 2010-10-01 false Additional charges. 377.209 Section 377.209... CHARGES Extension of Credit to Shippers by Motor Common Carriers, Water Common Carriers, and Household Goods Freight Forwarders 377.209 Additional charges. When a carrier (a) Has collected the amount...

  9. 49 CFR 377.209 - Additional charges.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 49 Transportation 5 2013-10-01 2013-10-01 false Additional charges. 377.209 Section 377.209... CHARGES Extension of Credit to Shippers by Motor Common Carriers, Water Common Carriers, and Household Goods Freight Forwarders 377.209 Additional charges. When a carrier (a) Has collected the amount...

  10. 49 CFR 377.209 - Additional charges.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 49 Transportation 5 2014-10-01 2014-10-01 false Additional charges. 377.209 Section 377.209... CHARGES Extension of Credit to Shippers by Motor Common Carriers, Water Common Carriers, and Household Goods Freight Forwarders 377.209 Additional charges. When a carrier (a) Has collected the amount...

  11. 49 CFR 377.209 - Additional charges.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 49 Transportation 5 2012-10-01 2012-10-01 false Additional charges. 377.209 Section 377.209... CHARGES Extension of Credit to Shippers by Motor Common Carriers, Water Common Carriers, and Household Goods Freight Forwarders 377.209 Additional charges. When a carrier (a) Has collected the amount...

  12. Negative differential resistance and carrier transport of electrically bistable devices based on poly(N-vinylcarbazole)-silver sulfide composites

    PubMed Central

    2014-01-01

    An electrically bistable device has been fabricated based on poly(N-vinylcarbazole) (PVK)-silver sulfide (Ag2S) composite films using a simple spin-coating method. Currentvoltage (I-V) characteristics of the as-fabricated devices exhibit a typical electrical bistability and negative differential resistance (NDR) effect. The NDR effect can be tuned by varying the positive charging voltage and the charging time. The maximum current ratio between the high-conducting state (ON state) and low-conducting state (OFF state) can reach up to 104. The carrier transport mechanisms in the OFF and ON states are described by using different models on the basis of the experimental result. PMID:24641989

  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. 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.

  15. 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).

  16. Heating of charge carriers and rectification of current in asymmetrical p-n junction in a microwave field

    SciTech Connect

    Dadamirzayev, M. G.

    2011-03-15

    The emf U{sub oc} of hot charge carriers generated in an asymmetrical p-n junction in a microwave electromagnetic field is determined by hot holes despite the fact that the temperature of electrons is much higher than that of holes. It is established that the open-circuit voltage depends on the temperature of the carriers, which determine the total current through p-n junction.

  17. Electron spin resonance of charge carriers and antiferromagnetic clusters in Ge0.99Cr0.01 nanowires

    NASA Astrophysics Data System (ADS)

    Morgunov, R. B.; Dmitriev, A. I.; Tanimoto, Y.; Kazakova, O.

    2009-05-01

    We report an electron spin resonance study of Ge nanowires doped with chromium. The Ge0.99Cr0.01 nanowires contain both diluted ?r3+ and ?r2+ ions and a large amount of Cr-based nanoclusters revealing spin-glass properties at T <60 K. The observed antiferromagnetic resonance at low temperatures is attributed to Ge-Cr nanoclusters. Additionally, we detect an asymmetric, isotropic resonant line clearly distinguished in the whole temperature range, T =4-300 K, which corresponds to a paramagnetic resonance of the charge carriers in the Ge0.99Cr0.01 nanowires. On the base of our previous studies, we compare properties of the charge carriers in germanium nanowires doped with different transition metals. We demonstrate that the effective g-factor related to charge carriers is reduced with an increase in the spin-orbital interaction in the row: Mn2+, Cr2+, Fe3+, and Co2+.

  18. Numerical Simulation on the Charge Transport in Tris(8-hydroxyquinolinato)aluminum-Based Organic Light-Emitting Diode Structure

    NASA Astrophysics Data System (ADS)

    Kim, Kwangsik; Won, Taeyoung

    2013-10-01

    In this paper, we report on our theoretical study on the charge transport of a multilayer structure for organic light-emitting diodes (OLEDs). Our simulation structure comprises a hole transport layer (HTL), an emission layer (EML), and an electron transport layer (ETL) between two electrodes wherein the HTL is N,N '-bis(3-methylphenyl)-N,N '-bis(phenyl)benzidine (TPD) and the ETL includes tris(8-hydroxyquinolinato)aluminum (Alq3). We discuss the carrier transport mechanism of the Alq3-based two-layer structure and thereby propose a high-efficiency device structure. We also report our investigation on the transient response during the turn-on/off period and the carrier transport in response to the variation of the injection barrier and applied voltage. This paper also reports the effect of the insertion of the EML layer and the efficiency dependence on the difference in the internal barrier height.

  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. 41 CFR 301-10.100 - What types of common carrier transportation may I be authorized to use?

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 41 Public Contracts and Property Management 4 2011-07-01 2011-07-01 false What types of common... TRAVEL EXPENSES 10-TRANSPORTATION EXPENSES Common Carrier Transportation 301-10.100 What types of common carrier transportation may I be authorized to use? You may be authorized to use airline,...

  1. 41 CFR 301-10.100 - What types of common carrier transportation may I be authorized to use?

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 41 Public Contracts and Property Management 4 2010-07-01 2010-07-01 false What types of common... TRAVEL EXPENSES 10-TRANSPORTATION EXPENSES Common Carrier Transportation 301-10.100 What types of common carrier transportation may I be authorized to use? You may be authorized to use airline,...

  2. 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...

  3. 41 CFR 302-10.402 - What costs must we pay a commercial carrier for transporting a mobile home?

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 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...

  4. 41 CFR 302-10.402 - What costs must we pay a commercial carrier for transporting a mobile home?

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 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...

  5. 41 CFR 302-10.402 - What costs must we pay a commercial carrier for transporting a mobile home?

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 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...

  6. Effect of charge carrier trapping on germanium coaxial detector line shapes

    NASA Astrophysics Data System (ADS)

    Raudorf, Thomas W.; Pehl, Richard H.

    1987-04-01

    A theoretical method to predict and quantify the effects of charge carrier trapping on germanium coaxial detector line shapes has been developed. This model was used to calculate line shapes which closely matched the measured line shapes of both conventional and reverse electrode high-purity germanium coaxial detectors that had suffered fast neutron damage. In accordance with experimentally established behavior, the theory predicts that reverse electrode detectors are vastly more resistent to the effects of neutron damage than conventional electrode detectors. The theory also predicts that the energy resolution and line shape of neutron-damaged conventional electrode detectors are far more dependent on detector diameter than are detectors of the reverse electrode configuration. The generally observed variation of the energy resolution and line shape as a function of bias voltage is shown to arise from an E -1 dependence of the trap cross section on electric field.

  7. Spatial Localization of Excitons and Charge Carriers in Hybrid Perovskite Thin Films.

    PubMed

    Simpson, Mary Jane; Doughty, Benjamin; Yang, Bin; Xiao, Kai; Ma, Ying-Zhong

    2015-08-01

    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. However, the spatially heterogeneous polycrystalline morphology of the photoactive layers owing to the presence of distinct crystalline grains has been generally neglected in optical measurements; 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 time scales and transient signals. Analysis of transient absorption kinetics acquired at distinct spatial positions enabled us to identify contributions of excitons and free charge carriers. PMID:26267200

  8. The interaction of charge carriers with excitons and plasmons within colloidal and epitaxial semiconductor nanostructures

    NASA Astrophysics Data System (ADS)

    Tice, Daniel Boitnott

    This dissertation describes the influence of the presence of charges--both bound electron and hole charge pairs (excitons) as well as free carriers--on the optical properties of semiconductor nanostructures. In a characterization of the evolution of the electronic structure of semiconductor nanostructures with increasing shape anisotropy, transient absorption (TA) and photoluminescence excitation (PLE) anisotropy measurements revealed that the band-edge absorptive and emissive transitions of CdSe nanorods contain both linear (z) and planar (xy) polarization character. The degree of planar character at the band-edge, modulated by classical local field effects arising from the dielectric contrast between the nanorod and the solvent, limits the degree of photoselection at this wavelength, while variation in the magnitude of the xy projection of the absorptive transitions within states above the band-edge is responsible for the observed wavelength-dependence of the absorption and emission anisotropies. The interaction of excess charge with the excitonic states of CdSe quantum dots (QDs) was probed with steady-state photoluminescence (PL) and ultrafast transient absorption measurements. The results of these experiments were utilized to construct a model for photobrightening (PB) - an increase in PL quantum yield with photoexcitation - based on migration of photoexcited electrons within the film. The basis for this model is that PB is limited by the rate of migration of electrons among surface-localized energetically shallow traps in the film, and not by the rate of creation of surface-trapped charge carriers. Finally, TA and transient third harmonic generation probe (THG-probe) spectroscopies were used to investigate the response of the localized surface plasmon resonances (LSPRs) of vertically aligned ITO nanowires (NWs) upon UV excitation. Both TA and THG-probe experiments show an increase in the frequency of the LSPR upon population of the conduction band of the ITO. The LSPR shifts back to its original energy on the single-picosecond lifetime of the photoexcited electrons. These results indicate that UV excitation modulates the plasma frequency of ITO on the ultrafast timescale by the injection of electrons into, and their subsequent decay from, the conduction band of the NWs, with ~13% changes to the electron concentration in the conduction band achievable in these experiments.

  9. Quantifying charge carrier concentration in ZnO thin films by Scanning Kelvin Probe Microscopy.

    PubMed

    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

  10. 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

  11. 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.

  12. Ionic charge transport between blockages: Sodium cation conduction in freshly excised bulk brain tissue

    PubMed Central

    Emin, David; Akhtari, Massoud; Ellingson, B. M.; Mathern, G. W.

    2015-01-01

    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. PMID:26339528

  13. 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

  14. Doped GaN nanowires on diamond: Structural properties and charge carrier distribution

    SciTech Connect

    Schuster, Fabian Winnerl, Andrea; Weiszer, Saskia; Hetzl, Martin; Garrido, Jose A.; Stutzmann, Martin

    2015-01-28

    In this work, we present a detailed study on GaN nanowire doping, which is vital for device fabrication. The nanowires (NWs) are grown by means of molecular beam epitaxy on diamond (111) substrates. Dopant atoms are found to facilitate nucleation, thus an increasing NW density is observed for increasing dopant fluxes. While maintaining nanowire morphology, we demonstrate the incorporation of Si and Mg up to concentrations of 9× 10{sup 20}cm{sup −3} and 1 × 10{sup 20}cm{sup −3}, respectively. The dopant concentration in the nanowire cores is determined by the thermodynamic solubility limit, whereas excess dopants are found to segregate to the nanowire surface. The strain state of the NWs is investigated by X-ray diffraction, which confirms a negligible strain compared to planar thin films. Doping-related emissions are identified in low-temperature photoluminescence spectroscopy and the temperature quenching yields ionization energies of Si donors and Mg acceptors of 17 meV and 167 meV, respectively. At room temperature, luminescence and absorption spectra are found to coincide and the sub-band gap absorption is suppressed in n-type NWs. The charge carrier distribution in doped GaN nanowires is simulated under consideration of surface states at the non-polar side facets. For doping concentrations below 10{sup 17}cm{sup −3}, the nanowires are depleted of charge carriers, whereas they become highly conductive above 10{sup 19}cm{sup −3}.

  15. Tuning optoelectronic properties and understanding charge transport in nanocrystal thin films of earth abundant semiconducting materials

    NASA Astrophysics Data System (ADS)

    Riha, Shannon C.

    2011-12-01

    With the capability of producing nearly 600 TW annually, solar power is one renewable energy source with the potential to meet a large fraction of the world's burgeoning energy demand. To make solar technology cost-competitive with carbon-based fuels, cheaper devices need to be realized. Solution-processed solar cells from nanocrystal inks of earth abundant materials satisfy this requirement. Nonetheless, a major hurdle in commercializing such devices is poor charge transport through nanocrystal thin films. The efficiency of charge transport through nanocrystal thin films is strongly dependent on the quality of the nanocrystals, as well as their optoelectronic properties. Therefore, the first part of this dissertation is focused on synthesizing high quality nanocrystals of Cu2ZnSnS4, a promising earth abundant photovoltaic absorber material. The optoelectronic properties of the nanocrystals were tuned by altering the copper to zinc ratio, as well as by introducing selenium to create Cu2ZnSn(S1-xSe x)4 solid solutions. Photoelectrochemical characterization was used to test the Cu2ZnSnS4 and Cu2ZnSn(S 1-xSex)4 nanocrystal thin films. The results identify minority carrier diffusion and recombination via the redox shuttle as the major loss mechanisms hindering efficient charge transport through the nanocrystal thin films. One way to solve this issue is to sinter the nanocrystals together, creating large grains for efficient charge transport. Although this may be quick and effective, it can lead to the formation of structural defects, among other issues. To this end, using a different copper-based material, namely Cu2Se, and simple surface chemistry treatments, an alternative route to enhance charge transport through nanocrystals thin films is proposed.

  16. A Simple Index for Characterizing Charge Transport in Molecular Materials.

    PubMed

    Jackson, Nicholas E; Savoie, Brett M; Chen, Lin X; Ratner, Mark A

    2015-03-19

    While advances in quantum chemistry have rendered the accurate prediction of band alignment relatively straightforward, the ability to forecast a noncrystalline, multimolecule system's conductivity possesses no simple computational form. Adapting the theory of classical resistor networks, we develop an index for quantifying charge transport in bulk molecular materials, without the requirement of crystallinity. The basic behavior of this index is illustrated through its application to simple lattices and clusters of common organic photovoltaic molecules, where it is shown to reproduce experimentally known performances for these materials. This development provides a quantitative computational means for determining a priori the bulk charge transport properties of molecular materials. PMID:26262862

  17. 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.

  18. Experimental investigation of the excess charge and time constant of minority carriers in the thin diffused layer of 0.1 Ohm-cm silicon solar cells

    NASA Technical Reports Server (NTRS)

    Godlewski, M. P.; Brandhorst, H. W., Jr.; Lindholm, F. A.; Sah, C. T.

    1976-01-01

    The observed low open-circuit voltage in 0.1 Ohm-cm solar cells is probably related to an excessively high diode saturation current. Theoretical studies conducted by Lindholm et al. (1975) and by Godlewski et al. (1975) have shown that a high saturation current could be produced by either high recombination rates or bandgap narrowing effects. A description is given of an investigation which shows that bandgap narrowing effects have a first order significance in determining the charge carrier transport controlling the open-circuit voltage of 0.1 Ohm-cm silicon solar cells.

  19. A multi-agent quantum Monte Carlo model for charge transport: Application to organic field-effect transistors

    NASA Astrophysics Data System (ADS)

    Bauer, Thilo; Jger, 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.

  20. 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

  1. 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

  2. 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.

  3. Simulation of carrier-facilitated transport of phenanthrene in a layered soil profile.

    PubMed

    Prechtel, Alexander; Knabner, Peter; Schneid, Eckhard; Totsche, Kai Uwe

    2002-06-01

    The appropriate prediction of the fate of the contaminant is an essential step when evaluating the risk of severe groundwater pollutions-in particular in the context of natural attenuation. We numerically study the reactive transport of phenanthrene at the field scale in a multilayer soil profile based on experimental data. The effect of carrier facilitation by dissolved organic carbon is emphasized and incorporated in the model. Previously published simulations are restricted to the saturated zone and/or to homogeneous soil columns at the laboratory scale. A numerical flow and transport model is extended and applied to understand and quantify the relevant processes in the case of a strongly sorbing hydrophobic organic compound that is subject to carrier facilitation in the unsaturated zone. The contaminant migration is investigated on long- and short-term time scales and compared to predictions without carrier facilitation. The simulations demonstrate the importance of carrier facilitation and suggest strongly to take this aspect into account. By carrier facilitation breakthrough times at the groundwater level decreased from 500 to approximately 8 years and concentration peaks increased by two orders of magnitude in the long-term simulation assuming a temporary spill in an initially unpolluted soil with a non-sorbing carrier. PMID:12102319

  4. 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.

  5. 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.

  6. 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

  7. 14 CFR 221.2 - Carrier's duty.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 4 2011-01-01 2011-01-01 false Carrier's duty. 221.2 Section 221.2 Aeronautics and Space OFFICE OF THE SECRETARY, DEPARTMENT OF TRANSPORTATION (AVIATION PROCEEDINGS) ECONOMIC... be used. (b) Must observe tariffs. No air carrier or foreign air carrier shall charge or demand...

  8. 14 CFR 221.2 - Carrier's duty.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 4 2010-01-01 2010-01-01 false Carrier's duty. 221.2 Section 221.2 Aeronautics and Space OFFICE OF THE SECRETARY, DEPARTMENT OF TRANSPORTATION (AVIATION PROCEEDINGS) ECONOMIC... be used. (b) Must observe tariffs. No air carrier or foreign air carrier shall charge or demand...

  9. 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.

  10. 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.

  11. Collective charge transport processes in condensed matter and biological systems

    NASA Astrophysics Data System (ADS)

    Cardenas, Gustavo

    Collective charge transport processes occur in inanimate condensed matter systems as well as biological macro-molecules. Physical models can provide insight into both types of systems when there is transport of charges. A large body of experimental evidence suggests that the decay of the false vacuum, accompanied by quantum pair creation of soliton domain walls, can occur in a variety of condensed matter systems. A macroscopic quantum charge transport of density waves by pair creation of soliton domain walls is studied. It is discussed under theoretical arguments for the existence of high-temperature collective quantum phenomena. Here a macroscopic Coulomb blockade model is utilized to develop and study a novel soliton tunneling transistor, which represents a macroscopic version of the single electron transistor. The electron transport is reviewed via quantum tunneling in proteins and a theoretical junction model of the mitochondrial electron transport chain is proposed. The interaction of the mitochondrial electron transport with oscillatory electric field is considered; therefore, the numerical predictions are compared with the results obtained by experimental measurements of the harmonics induced in the mitochondria of yeast cells.

  12. Charge transfer vs. dimensionality: what affects the transport properties of ferecrystals?

    NASA Astrophysics Data System (ADS)

    Alemayehu, Matti B.; Ta, Kim; Falmbigl, Matthias; Johnson, David C.

    2015-04-01

    A series of ([SnSe]1+?)m(NbSe2)2 compounds with two layers of NbSe2 separated by m bilayers of SnSe, where 1 <= m <= 20, were prepared from modulated precursors by systematically changing the number of SnSe layers in the repeating unit. A change in the c-lattice parameter of 0.579(3) nm per SnSe bilayer was observed. The thickness of the NbSe2 layer was determined to be 1.281(4) nm: twice the value of a single NbSe2 layer. HAADF-STEM images revealed the presence of extensive rotational disorder and the lack of any epitaxial relationship among the constituent layers. Two different coordination environments for the Nb in NbSe2 (trigonal prismatic and octahedral) were observed. The electrical resistivity increases and the carrier concentration decreases in the ([SnSe]1+?)m(NbSe2)2 compounds with increasing number of SnSe bilayers. The temperature dependence of the resistivity suggests localization of carriers for higher m values. The decline in carrier concentration as a function of m implies the presence of charge transfer from SnSe to NbSe2. The transport properties of the ([SnSe]1+?)m(NbSe2)2 compounds and the previously reported ([SnSe]1+?)m(NbSe2)1 compounds both have unusually temperature independent resistivity compared to bulk NbSe2. Compounds with similar m/n ratios exhibit similar transport properties. Consequently, the dominant effect on the transport properties of ([SnSe]1+?)m(NbSe2)2 is charge transfer, and there are only subtle differences between a monolayer and a bilayer of NbSe2.A series of ([SnSe]1+?)m(NbSe2)2 compounds with two layers of NbSe2 separated by m bilayers of SnSe, where 1 <= m <= 20, were prepared from modulated precursors by systematically changing the number of SnSe layers in the repeating unit. A change in the c-lattice parameter of 0.579(3) nm per SnSe bilayer was observed. The thickness of the NbSe2 layer was determined to be 1.281(4) nm: twice the value of a single NbSe2 layer. HAADF-STEM images revealed the presence of extensive rotational disorder and the lack of any epitaxial relationship among the constituent layers. Two different coordination environments for the Nb in NbSe2 (trigonal prismatic and octahedral) were observed. The electrical resistivity increases and the carrier concentration decreases in the ([SnSe]1+?)m(NbSe2)2 compounds with increasing number of SnSe bilayers. The temperature dependence of the resistivity suggests localization of carriers for higher m values. The decline in carrier concentration as a function of m implies the presence of charge transfer from SnSe to NbSe2. The transport properties of the ([SnSe]1+?)m(NbSe2)2 compounds and the previously reported ([SnSe]1+?)m(NbSe2)1 compounds both have unusually temperature independent resistivity compared to bulk NbSe2. Compounds with similar m/n ratios exhibit similar transport properties. Consequently, the dominant effect on the transport properties of ([SnSe]1+?)m(NbSe2)2 is charge transfer, and there are only subtle differences between a monolayer and a bilayer of NbSe2. Electronic supplementary information (ESI) available: Detailed results of the Rietveld refinement including a table of parameters and the refinement patterns are available. See DOI: 10.1039/c4nr07338j

  13. 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.

  14. Carrier-mediated transport of actinide ions using supported liquid membranes containing TODGA as the carrier extractant

    SciTech Connect

    Panja, S.; Dakshinamoorthy, A.; Munshi, S.K.; Dey, P.K.; Mohapatra, P.K.; Manchanda, V.K.

    2008-07-01

    The transport behavior of Pu{sup 3+} under varying reducing conditions was investigated from a feed containing 3.0 M HNO{sub 3} into a receiver phase containing 0.1 M HNO{sub 3} using TODGA (N,N,N',N' - tetraoctyl-diglycolamide) as the carrier ligand. A mixture of 0.2 M hydroxyl ammonium nitrate and 0.2 M hydrazinium nitrate (used in the feed as the reducing agent) has been found to be effective for quantitative (>99%) transport of the trivalent Pu in about 3 h. Transport of trivalent plutonium in 3 h (>99%) was higher as compared to that of the tetravalent plutonium (94%), though their D values followed an opposite trend. The permeability coefficient (P) of Pu{sup 3+} was (4.63 {+-} 0.26) x 10{sup -3} cm/s as compared to (2.10 {+-} 0.14) x 10{sup -3} cm/s for Pu{sup 4+} and (3.67 {+-} 0.06) x 10{sup -3} cm/s Am{sup 3+}. P values of trivalent actinide ions such as Am{sup 3+}, Pu{sup 3+}, and Cm{sup 3+} are compared with their distribution data. (authors)

  15. Dislocation-assisted tunnelling of charge carriers across the Schottky barrier on the hydride vapour phase epitaxy grown GaN

    NASA Astrophysics Data System (ADS)

    Chatterjee, Abhishek; Khamari, Shailesh K.; Dixit, V. K.; Oak, S. M.; Sharma, T. K.

    2015-11-01

    Barrier height and Ideality factor of Ni/n-GaN Schottky diodes are measured by performing temperature dependent current-voltage measurements. The measured value of barrier height is found to be much smaller than the theoretically calculated Schottky-Mott barrier height for the Ni/n-GaN diodes. Furthermore, a high value of ideality factor (>2) is measured at low temperatures. In order to understand these results, we need to consider a double Gaussian distribution of barrier height where the two components are related to the thermionic emission and thermionic filed emission mediated by dislocation-assisted tunnelling of carriers across the Schottky barrier. Thermionic emission is seen to dominate at temperatures higher than 170 K while the dislocation-assisted tunnelling dominates at low temperatures. The value of characteristic tunnelling energy measured from the forward bias current-voltage curves also confirms the dominance of dislocation-assisted tunnelling at low temperatures which is strongly corroborated by the Hall measurements. However, the value of characteristic tunnelling energy for high temperature range cannot be supported by the Hall results. This discrepancy can be eliminated by invoking a two layer model to analyse the Hall data which confirms that the charged dislocations, which reach the sample surface from the layer-substrate interface, provide an alternate path for the transport of carriers. The dislocation-assisted tunnelling of carriers governs the values of Schottky diode parameters at low temperature and the same is responsible for the observed inhomogeneity in the values of barrier height. The present analysis is applicable wherever the charge transport characteristics are severely affected by the presence of a degenerate layer at GaN-Sapphire interface and dislocations lines pierce the Schottky junction to facilitate the tunnelling of carriers.

  16. 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...

  17. 29 CFR 780.155 - Delivery “to carriers for transportation to market.”

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 29 Labor 3 2012-07-01 2012-07-01 false Delivery âto carriers for transportation to market.â 780.155 Section 780.155 Labor Regulations Relating to Labor (Continued) WAGE AND HOUR DIVISION, DEPARTMENT OF LABOR STATEMENTS OF GENERAL POLICY OR INTERPRETATION NOT DIRECTLY RELATED TO REGULATIONS EXEMPTIONS APPLICABLE TO AGRICULTURE, PROCESSING...

  18. 29 CFR 780.155 - Delivery “to carriers for transportation to market.”

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 29 Labor 3 2013-07-01 2013-07-01 false Delivery âto carriers for transportation to market.â 780.155 Section 780.155 Labor Regulations Relating to Labor (Continued) WAGE AND HOUR DIVISION, DEPARTMENT OF LABOR STATEMENTS OF GENERAL POLICY OR INTERPRETATION NOT DIRECTLY RELATED TO REGULATIONS EXEMPTIONS APPLICABLE TO AGRICULTURE, PROCESSING...

  19. 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

    ... passengers with a disability for providing services and accommodations required by this rule? 382.31 Section... and Access to Services and Information 382.31 May carriers impose special charges on passengers with a disability for providing services and accommodations required by this rule? (a) Except...

  20. 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,

  1. 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.

  2. Charge transport properties of bulk Ta3N5 from first principles

    NASA Astrophysics Data System (ADS)

    Morbec, Juliana M.; Galli, Giulia

    2016-01-01

    Tantalum nitride is considered a promising material for photoelectrochemical water splitting, however, its charge transport properties remain poorly understood. We investigated polaronic and band transport in Ta3N5 using first-principles calculations. We first studied the formation of small polarons using density-functional theory (DFT) including DFT +U and hybrid functionals. We found that electron small polarons may occur but hole polarons are not energetically favorable. The estimated polaronic mobility for electrons is at least three orders of magnitude smaller than that measured in Ta3N5 films, suggesting that the main transport mechanism for both electrons and holes is bandlike. Since band transport is strongly affected by the carrier effective masses, and Ta3N5 is known to have large electron and hole effective masses, we also investigated whether substitutional impurities or strain may help lower the effective masses. We found a significant reduction in both electron and hole effective masses (up to 17% for electrons and 39% for holes) under applied strain, which may lead to a substantial improvement (up to 30% for electrons and 15% for holes) in the carrier mobilities.

  3. Direct observation of ballistic and drift carrier transport regimes in InAs nanowires

    NASA Astrophysics Data System (ADS)

    Zhou, X.; Dayeh, S. A.; Aplin, D.; Wang, D.; Yu, E. T.

    2006-07-01

    Conductive atomic force microscopy has been used to characterize distance-dependent electron transport behavior in InAs nanowires grown by metal-organic chemical vapor deposition. Using a conducting diamond-coated tip as a local electrical probe in an atomic force microscope, the resistance of the InAs nanowire has been measured as a function of electron transport distance within the nanowire. Two regimes of transport behavior are observed: for distances of 200nm or less, resistance independent of electron transport distance, indicative of ballistic electron transport, is observed; for greater distances, the resistance is observed to increase linearly with distance, as expected for conventional drift transport. These observations are in very good qualitative accord with the Landauer formalism for mesoscopic carrier transport, and the resistance values derived from these measurements are in good quantitative agreement with carrier concentrations and mobilities determined in separate experiments. These results provide direct information concerning distances over which ballistic transport occurs in InAs nanowires as well as demonstrating the ability of the scanning probe techniques employed to characterize nanoscale transport characteristics in semiconductor nanowire structures.

  4. Homoleptic copper(I) arylthiolates as a new class of p-type charge carriers: structures and charge mobility studies.

    PubMed

    Che, Chi-Ming; Li, Cheng-Hui; Chui, Stephen Sin-Yin; Roy, V A L; Low, Kam-Hung

    2008-01-01

    Polymeric homoleptic copper(I) arylthiolates [Cu(p-SC(6)H(4)-X)](infinity) (X=CH(3) (1), H (2), CH(3)O (3), tBu (4), CF(3) (5), NO(2) (6), and COOH (7)) have been prepared as insoluble crystalline solids in good yields (75-95 %). Structure determinations by powder X-ray diffraction analysis have revealed that 1-3 and 6 form polymers of infinite chain length, with the copper atoms bridged by arylthiolate ligands. Weak intra-chain pi***pi stacking interactions are present in 1-3, as evidenced by the distances (3.210 A in 1, 3.016 A in 2, 3.401 A in 3) between the mean planes of neighboring phenyl rings. In the structure of 6, the intra-chain pi***pi interactions (d=3.711 A) are insignificant and the chain polymers are associated through weak, non-covalent C-H...O hydrogen-bonding interactions (d=2.586 A). Samples of 1-7 in their polycrystalline forms proved to be thermally stable at 200-300 degrees C; their respective decomposition temperatures are around 100 degrees C higher than that of the aliphatic analogue [Cu(SCH(3))](infinity). Data from in situ variable-temperature X-ray diffractometry measurements indicated that the structures of both 1 and 7 are thermally more robust than that of [Cu(SCH(3))](infinity). TEM analysis revealed that the solid samples of 1-5 and [Cu(SCH(3))](infinity) contained homogeneously dispersed crystalline nanorods with widths of 20-250 nm, whereas smaller plate-like nanocrystals were found for 6 and 7. SAED data showed that the chain polymers of 1-3 and [Cu(SCH(3))](infinity) similarly extend along the long axes of their nanorods. The nanorods of 1-5 and [Cu(SCH(3))](infinity) have been found to exhibit p-type field-effect transistor behavior, with charge mobility (micro) values of 10(-2)-10(-5) cm(2) V(-1) s(-1). Polycrystalline solid samples of 6 and 7 each showed a low charge mobility (<10(-6) cm(2) V(-1) s(-1)). The charge mobility values of field-effect transistors made from crystalline nanorods of 1-3 and [Cu(SCH(3))](infinity) could be correlated with their unique chain-like copper-sulfur networks, with the para-substituent of the arylthiolate ligand influencing the charge-transport properties. PMID:18350558

  5. 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.

  6. Effect of dielectric/organic interface properties on charge transport in organic thin film transistors

    NASA Astrophysics Data System (ADS)

    Rahimi, Ronak; Kuchibhatla, S.; Korakakis, D.

    2013-04-01

    Charge carrier transport within the organic thin films as well as charge carrier injection between organic layers and organic/inorganic materials such as metal or dielectric layers are crucial factors in determining the efficiency of organic electronic devices. These parameters rely largely on the molecular structure, morphology, and ordering of the organic thin films. Therefore, a profound understanding of the structure of organic materials as well as the properties of the interfacial layers is crucial to enhance the performance of the device. To achieve this fact, structure and morphology of PTCDI-C8 and pentacene thin films on Lithium Fluoride (LiF) have been studied using X-ray reflectivity technique. These films have been integrated into organic thin film transistors (OTFTs) to investigate their transport properties. The structural characterization revealed that the PTCDI-C8 films form an ordered structure on the LiF dielectric layer. Devices with LiF/PTCDI-C8 bilayer exhibit about one order of magnitude higher output current (Ids) at a constant drain-source voltage (Vds) compared to the devices with LiF/pentacene bilayer. The observed differences in the electrical characteristics of these devices can be attributed to the effects of the dielectric/organic interface and the molecular structure of the organic layers. The results of this study present the importance of the dielectric/organic interfaces in the performance of OTFTs.

  7. Dynamical- and static-disorder effects on charge transport property of organic semiconductors

    NASA Astrophysics Data System (ADS)

    Ishii, Hiroyuki; Kobayashi, Nobuhiko; Hirose, Kenji

    2014-03-01

    In comparison with inorganic materials, electron transfer energy of typical organic semiconductors is small in the range of 10 - 100meV, which is comparable to the magnitude of dynamical disorder of transfer energy originating from the thermal fluctuations of molecular motions. Furthermore, the static disorder inevitably exists in realistic organic devices and disturbs the transport of charge carrier. To clarify the influence of the dynamical and static disorders on the mobility, we employ a realistic static-disorder potential, which is deduced from the data obtained by electron-spin-resonance spectroscopy. We evaluate the carrier mobilities of pentacene and rubrene semiconductors under the realistic situation, using our time-dependent wave-packet diffusion method. In this methodology, we carry out the quantum-mechanical time-evolution calculations of wave packets and the classical molecular dynamics simulations simultaneously. We clarify the relation between the charge transport property and these disorders. We will talk about these results in my presentation. This work was supported by JST, PRESTO, and a Grant-in-Aid for Scientific Research from the JSPS.

  8. 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

  9. Unity quantum yield of photogenerated charges and band-like transport in quantum-dot solids.

    PubMed

    Talgorn, Elise; Gao, Yunan; Aerts, Michiel; Kunneman, Lucas T; Schins, Juleon M; Savenije, T J; van Huis, Marijn A; van der Zant, Herre S J; Houtepen, Arjan J; Siebbeles, Laurens D A

    2011-11-01

    Solid films of colloidal quantum dots show promise in the manufacture of photodetectors and solar cells. These devices require high yields of photogenerated charges and high carrier mobilities, which are difficult to achieve in quantum-dot films owing to a strong electron-hole interaction and quantum confinement. Here, we show that the quantum yield of photogenerated charges in strongly coupled PbSe quantum-dot films is unity over a large temperature range. At high photoexcitation density, a transition takes place from hopping between localized states to band-like transport. These strongly coupled quantum-dot films have electrical properties that approach those of crystalline bulk semiconductors, while retaining the size tunability and cheap processing properties of colloidal quantum dots. PMID:21946709

  10. 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.

  11. Elastomeric transistor stamps: reversible probing of charge transport in organic crystals.

    PubMed

    Sundar, Vikram C; Zaumseil, Jana; Podzorov, Vitaly; Menard, Etienne; Willett, Robert L; Someya, Takao; Gershenson, Michael E; Rogers, John A

    2004-03-12

    We introduce a method to fabricate high-performance field-effect transistors on the surface of freestanding organic single crystals. The transistors are constructed by laminating a monolithic elastomeric transistor stamp against the surface of a crystal. This method, which eliminates exposure of the fragile organic surface to the hazards of conventional processing, enables fabrication of rubrene transistors with charge carrier mobilities as high as approximately 15 cm2/V.s and subthreshold slopes as low as 2nF.V/decade.cm2. Multiple relamination of the transistor stamp against the same crystal does not affect the transistor characteristics; we exploit this reversibility to reveal anisotropic charge transport at the basal plane of rubrene. PMID:15016993

  12. 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.

  13. 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

  14. Quadrimolecular recombination kinetics of photogenerated charge carriers in the composites of regioregular polythiophene derivatives and soluble fullerene

    NASA Astrophysics Data System (ADS)

    Tanaka, Hisaaki; Yokoi, Yuki; Hasegawa, Naoki; Kuroda, Shin-ichi; Iijima, Takayuki; Sato, Takao; Yamamoto, Takakazu

    2010-04-01

    Light-induced electron spin resonance (LESR) measurements have been performed on the composites of regioregular polythiophene derivatives and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) in order to study the recombination kinetics of photogenerated charge carriers. We adopt two regioregular polymers with different side chains; head-to-tail poly(3-hexylthiophene) (RR-P3HT) and head-to-head poly(3-dodecynylthiophene-2,5-diyl) [HH-P3(C≡CDec)Th]. In both systems, two LESR signals due to positive polarons on the polymer (g ˜2.002) and fullerene radical anions (g ˜2.000) have been observed. Quadrimolecular recombination (QR) kinetics, previously reported for RR-P3HT/C60 composites, where two positive polarons and two radical anions recombine simultaneously, has been confirmed in both systems by the observation of Iex0.25 dependence of the LESR intensity on the excitation light intensity (Iex) and the decay curve of the LESR intensity. This process implies the formation of doubly-charged states such as bipolarons or polaron pairs on the polymer to attract two radical anions. Temperature dependence of the QR rate constant, γ, in both systems has exhibited a crossover of the transport mechanism from low temperature tunneling to high temperature hopping process, as in the case of RR-P3HT/C60 composites. In the RR-P3HT/PCBM composites, γ has exhibited marked dependencies on the PCBM concentration or annealing, which may be related to the change of the crystallinity of the phase-separated polymer and fullerene domains as well as their interface structures, affecting the carrier mobilities or the trap states at the interface. Associated change of the molecular orientation of RR-P3HT crystalline domains with the lamellar structure has been further confirmed from the anisotropic LESR signals of the cast films on the substrates, exhibiting a qualitative agreement with the reported x-ray or optical analyses. In the HH-P3(C≡CDec)Th/PCBM composite, γ has been smaller than those in the RR-P3HT/PCBM composites, reflecting the difference of local structures due to the different molecular structure. Furthermore, the hyperfine-determined LESR linewidth of the positive polaron has exhibited a smaller value than those in the RR-P3HT composite, implying the larger extension of the polaron wave function on the polymer chain, which is consistent with the highly coplanar structure of this polymer.

  15. 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.

  16. Electrolyte transport in neutral polymer gels embedded with charged inclusions

    NASA Astrophysics Data System (ADS)

    Hill, Reghan

    2005-11-01

    Ion permeable membranes are the basis of a variety of molecular separation technologies, including ion exchange, gel electrophoresis and dialysis. This work presents a theoretical model of electrolyte transport in membranes comprised of a continuous polymer gel embedded with charged spherical inclusions, e.g., biological cells and synthetic colloids. The microstructure mimics immobilized cell cultures, where electric fields have been used to promote nutrient transport. Because several important characteristics can, in principle, be carefully controlled, the theory provides a quantitative framework to help tailor the bulk properties for enhanced molecular transport, microfluidic pumping, and physicochemical sensing applications. This talk focuses on the electroosmotic flow driven by weak electric fields and electrolyte concentration gradients. Also of importance is the influence of charge on the effective ion diffusion coefficients, bulk electrical conductivity, and membrane diffusion potential.

  17. 47 CFR 69.111 - Tandem-switched transport and tandem charge.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 3 2011-10-01 2011-10-01 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. 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.

  19. Polarized recombination of acoustically transported carriers in GaAs nanowires

    PubMed Central

    2012-01-01

    The oscillating piezoelectric field of a surface acoustic wave (SAW) is employed to transport photoexcited electrons and holes in GaAs nanowires deposited on a SAW delay line on a LiNbO3 crystal. The carriers generated in the nanowire by a focused light spot are acoustically transferred to a second location where they recombine. We show that the recombination of the transported carriers occurs in a zinc blende section on top of the predominant wurtzite nanowire. This allows contactless control of the linear polarized emission by SAWs which is governed by the crystal structure. Additional polarization-resolved photoluminescence measurements were performed to investigate spin conservation during transport. PMID:22583747

  20. 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

  1. Polarized recombination of acoustically transported carriers in GaAs nanowires.

    PubMed

    Mller, Michael; Hernndez-Mnguez, Alberto; Breuer, Steffen; Pfller, Carsten; Brandt, Oliver; de Lima, Mauricio M; Cantarero, Andrs; Geelhaar, Lutz; Riechert, Henning; Santos, Paulo V

    2012-01-01

    : The oscillating piezoelectric field of a surface acoustic wave (SAW) is employed to transport photoexcited electrons and holes in GaAs nanowires deposited on a SAW delay line on a LiNbO3 crystal. The carriers generated in the nanowire by a focused light spot are acoustically transferred to a second location where they recombine. We show that the recombination of the transported carriers occurs in a zinc blende section on top of the predominant wurtzite nanowire. This allows contactless control of the linear polarized emission by SAWs which is governed by the crystal structure. Additional polarization-resolved photoluminescence measurements were performed to investigate spin conservation during transport. PMID:22583747

  2. The mimivirus genome encodes a mitochondrial carrier that transports dATP and dTTP.

    PubMed

    Monn, Magnus; Robinson, Alan J; Boes, Christoph; Harbour, Michael E; Fearnley, Ian M; Kunji, Edmund R S

    2007-04-01

    Members of the mitochondrial carrier family have been reported in eukaryotes only, where they transport metabolites and cofactors across the mitochondrial inner membrane to link the metabolic pathways of the cytosol and the matrix. The genome of the giant virus Mimiviridae mimivirus encodes a member of the mitochondrial carrier family of transport proteins. This viral protein has been expressed in Lactococcus lactis and is shown to transport dATP and dTTP. As the 1.2-Mb double-stranded DNA mimivirus genome is rich in A and T residues, we speculate that the virus is using this protein to target the host mitochondria as a source of deoxynucleotides for its replication. PMID:17229695

  3. The Mimivirus Genome Encodes a Mitochondrial Carrier That Transports dATP and dTTP?

    PubMed Central

    Monn, Magnus; Robinson, Alan J.; Boes, Christoph; Harbour, Michael E.; Fearnley, Ian M.; Kunji, Edmund R. S.

    2007-01-01

    Members of the mitochondrial carrier family have been reported in eukaryotes only, where they transport metabolites and cofactors across the mitochondrial inner membrane to link the metabolic pathways of the cytosol and the matrix. The genome of the giant virus Mimiviridae mimivirus encodes a member of the mitochondrial carrier family of transport proteins. This viral protein has been expressed in Lactococcus lactis and is shown to transport dATP and dTTP. As the 1.2-Mb double-stranded DNA mimivirus genome is rich in A and T residues, we speculate that the virus is using this protein to target the host mitochondria as a source of deoxynucleotides for its replication. PMID:17229695

  4. 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.

  5. Switching and memory effects governed by the hopping mechanism of charge carrier transfer in composite films based on conducting polymers and inorganic nanoparticles

    NASA Astrophysics Data System (ADS)

    Aleshin, A. N.; Alexandrova, E. L.

    2008-10-01

    The switching and memory effects in composite films based on conducting polymers [poly(phenylenevinylene), thiophene, and carbazole derivatives] and inorganic nanoparticles (ZnO, Si) are investigated. It is established that the introduction of inorganic nanoparticles (ZnO, Si) exhibiting strong acceptor properties into polymer materials leads to the appearance of memory effects, which manifest themselves in the transition of the polymer from a low-conductivity state to a high-conductivity state. For a number of composites, this transition is accompanied by the formation of a region with a negative differential resistance and a hysteresis in the current-voltage characteristics. It is demonstrated that the observed effects are determined by the mechanism of charge carrier transfer in the composite. In particular, the main mechanism of transport in films based on thiophene derivatives is associated with electrical conduction due to the tunneling of charge carriers between conducting regions embedded in a nonconducting matrix, whereas the dominant mechanism of transport in “polymer-semiconductor nanoparticle” composite films is hopping conduction, which is responsible for the effects observed in these objects.

  6. Pore network model of electrokinetic transport through charged porous media.

    PubMed

    Obliger, Amal; Jardat, Marie; Coelho, Daniel; Bekri, Samir; Rotenberg, Benjamin

    2014-04-01

    We introduce a method for the numerical determination of the steady-state response of complex charged porous media to pressure, salt concentration, and electric potential gradients. The macroscopic fluxes of solvent, salt, and charge are computed within the framework of the Pore Network Model (PNM), which describes the pore structure of the samples as networks of pores connected to each other by channels. The PNM approach is used to capture the couplings between solvent and ionic flows which arise from the charge of the solid surfaces. For the microscopic transport coefficients on the channel scale, we take a simple analytical form obtained previously by solving the Poisson-Nernst-Planck and Stokes equations in a cylindrical channel. These transport coefficients are upscaled for a given network by imposing conservation laws for each pores, in the presence of macroscopic gradients across the sample. The complex pore structure of the material is captured by the distribution of channel diameters. We investigate the combined effects of this complex geometry, the surface charge, and the salt concentration on the macroscopic transport coefficients. The upscaled numerical model preserves the Onsager relations between the latter, as expected. The calculated macroscopic coefficients behave qualitatively as their microscopic counterparts, except for the permeability and the electro-osmotic coupling coefficient when the electrokinetic effects are strong. Quantitatively, the electrokinetic couplings increase the difference between the macroscopic coefficients and the corresponding ones for a single channel of average diameter. PMID:24827338

  7. Lightning charge-transport measured by field-changes aloft

    NASA Astrophysics Data System (ADS)

    Sonnenfeld, R.; Winn, W. P.; Battles, J.; Lu, G.; Peischl, J.; Walden-Newman, W.

    2005-12-01

    Analysis of vector ?c{E} field-changes aloft is beginning to yield information about the amount of charge transported in lightning flashes. A single field-change device obtained data from 6 storms in the Magdalena mountains of New Mexico. Field-change data were correlated with lightning-mapping array (LMA) data. The first finding is that the two types of data correspond in a sensible way on a time scales of 100 ? s (The time-resolution of the field-change instrument.). The second finding is the direction and magnitude of observed field-changes for intra-cloud flashes can be generally predicted by placing negative charges along the lightning channel at the locations given by the LMA data points. The third finding is that the minimum charge that needs to be transported to produce the observed changes in Flash "A" (Centered at 33.982N, 107.091W on 8/18/2004 at 20:12:41Z) is 5 Coulombs. The fourth finding is that Flash "A" can be initially modeled as simply transporting a lumped charge from the initial to the terminal point of the LMA-visible channel, and that the direction of the horizontal ?c{E} field changes in such a way as to point directly at the terminal point of the channel. Details of the instrument, its calibration, and the methodology for correlating field-change with LMA data will be discussed.

  8. 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.

  9. 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).

  10. Organic n-type materials for charge transport and charge storage applications.

    PubMed

    Stolar, Monika; Baumgartner, Thomas

    2013-06-21

    Conjugated materials have attracted much attention toward applications in organic electronics in recent years. These organic species offer many advantages as potential replacement for conventional materials (i.e., silicon and metals) in terms of cheap fabrication and environmentally benign devices. While p-type (electron-donating or hole-conducting) materials have been extensively reviewed and researched, their counterpart n-type (electron-accepting or electron-conducting) materials have seen much less popularity despite the greater need for improvement. In addition to developing efficient charge transport materials, it is equally important to provide a means of charge storage, where energy can be used on an on-demand basis. This perspective is focused on discussing a selection of representative n-type materials and the efforts toward improving their charge-transport efficiencies. Additionally, this perspective will also highlight recent organic materials for battery components and the efforts that have been made to improve their environmental appeal. PMID:23674178

  11. Electronic structure and charge carriers in metallic DNA investigated by soft x-ray spectroscopy

    NASA Astrophysics Data System (ADS)

    MacNaughton, J. B.; Kurmaev, E. Z.; Finkelstein, L. D.; Lee, J. S.; Wettig, S. D.; Moewes, A.

    2006-05-01

    Resonant inelastic x-ray scattering (RIXS) measurements of dried metallic DNA with metal ions incorporated inside the helix [(X)M-DNA, X=Co,Ni ], dried DNA with metal ions attached to the outside of the helix [(X)B-DNA, X=Co,Ni ], and dried double-strand DNA (B-DNA) are presented. The metal L edge RIXS spectra show that the I(L2)/I(L3) intensity ratio can be used as a probe of metallicity in 3d metal-containing systems because of the influence of nonradiative Coster-Kronig transitions. Using this technique it is found that (X)B-DNA has fewer mobile charge carriers than (X)M-DNA. X-ray absorption measurements at the L edge of the 3d metals are compared to density functional calculations to confirm that spectral features are not simply results of residual metal impurities. Nitrogen RIXS measurements reveal that the occupied electronic states are more localized in B-DNA than in (X)M-DNA systems.

  12. 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.

  13. 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.

  14. Storage of charge carriers on emitter molecules in organic light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Weichsel, Caroline; Burtone, Lorenzo; Reineke, Sebastian; Hintschich, Susanne I.; Gather, Malte C.; Leo, Karl; Lssem, Bjrn

    2012-08-01

    Organic light-emitting diodes (OLEDs) using the red phosphorescent emitter iridium(III)bis(2-methyldibenzo[f,h]quinoxaline) (acetylacetonate) [Ir(MDQ)2(acac)] are studied by time-resolved electroluminescence measurements. A transient overshoot after voltage turn-off is found, which is attributed to electron accumulation on Ir(MDQ)2(acac) molecules. The mechanism is verified via impedance spectroscopy and by application of positive and negative off-voltages. We calculate the density of accumulated electrons and find that it scales linearly with the doping concentration of the emitter. Using thin quenching layers, we locate the position of the emission zone during normal OLED operation and after voltage turn-off. In addition, the transient overshoot is also observed in three-color white-emitting OLEDs. By time- and spectrally resolved measurements using a streak camera, we directly attribute the overshoot to electron accumulation on Ir(MDQ)2(acac). We propose that similar processes are present in many state-of-the-art OLEDs and believe that the quantification of charge carrier storage will help to improve the efficiency of OLEDs.

  15. Charge carriers' trapping states in pentacene films studied by modulated photocurrent

    NASA Astrophysics Data System (ADS)

    Gorgolis, S.; Giannopoulou, A.; Kounavis, P.

    2013-03-01

    The modulated photocurrent (MPC) technique is employed to study the charge carriers' trapping states of pentacene films. The characteristics of the experimental MPC spectra were found to be compatible with trapping-detrapping process of holes in gap states in which their occupancy can be modified by the bias illumination. A demarcation energy level separating empty from partially occupied traps was deduced from the MPC spectra, which can be used to monitor bias-light induced changes in the quasi Fermi level. An exponential trap distribution from structural disorder and a deep metastable gaussian trap distribution from adsorbed environmental impurities were extracted by means of the MPC spectroscopy. An attempt to escape frequency of the order of 1010s-1 was deduced for the gap sates. The derived trap distributions agree with those found before by means of other techniques. The present results indicate that the MPC technique can be used as a valuable tool for pentacene films characterization since it can be also applied to field effect samples.

  16. 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.

  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. 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

  19. Trap-assisted charge transport at conjugated polymer interfaces

    NASA Astrophysics Data System (ADS)

    Ribeiro Junior, Luiz Antonio; de Brito, Sara Santiago; de Oliveira Neto, Pedro Henrique

    2016-01-01

    The trap-assisted charge transport in conjugated polymers is numerically investigated in the framework of a one-dimensional tight-binding model. Our findings show that a polaron trapped within an interchain region can be released migrating between the chains at low temperature regimes. Conversely, a trapped bipolaron cannot be released even considering high temperature values. Interestingly, for systems containing more than one polaron, the formation of trapped states is avoided and there is no charge transfer between the chains. Considering more than one bipolaron, the generation of trapped states occurs and a bipolaron can migrates between the chains.

  20. 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 Bttiker theory of partial coherent charge transport.

  1. 14 CFR 158.23 - Consultation with air carriers and foreign air carriers.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 14 Aeronautics and Space 3 2014-01-01 2014-01-01 false Consultation with air carriers and foreign air carriers. 158.23 Section 158.23 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION (CONTINUED) AIRPORTS PASSENGER FACILITY CHARGES (PFC'S) Application and Approval 158.23 Consultation with air carriers...

  2. On the advancement of quantum dot solar cell performance through enhanced charge carrier dynamics

    NASA Astrophysics Data System (ADS)

    Baker, David R.

    The quantum dot solar cell is one of the few solar technologies which promises to compete with fossil fuels, but work is still needed to increase its performance. Electron transfer kinetics at interfaces and limitations of the redox couple within the cell, are responsible for lowering power conversion efficiency. Several techniques which are able to increase electron transfer within the working electrode and at the counter electrode/electrolyte interface are discussed in this dissertation. Trap sites on the surface of CdSe quantum dots are created when mercaptopropionic acid (MPA) is added to the suspension. The trap sites are emissive creating a loss pathway for photogenerated charges which will manifest as reduced photocurrent. MPA displaces amines on the surface of CdSe creating Se vacancies. Emission properties are controlled by the concentration of MPA. Because trap sites are generated, a more successful method to sensitize TiO2 films is the SILAR technique which directly grows quantum dots on the desired surface. Anodically etched TiO2 nanotubes yield photocurrents 20% greater than TiO2 nanoparticles because of longer electron diffusion lengths. Peak incident photon to charge carrier efficiencies of TiO2 nanotube samples show a doubling of photocurrent in the visible region compared to nanoparticles. The TiO2 substrates are sensitized with CdS by the SILAR process which is found to utilize both the inside and outside surfaces of the TiO2 nanotubes. Etched TiO2 nanotubes are removed from the underlying titanium foil in order to use spectroscopic techniques. Ultrafast transient absorption shows the extremely fast nature of charge injection from SILAR CdS into TiO 2 nanotubes. Surface area analysis of TiO2 nanotube powder gives an area of 77m2/g, a value 1.5 times larger than traditional TiO2 nanoparticles. By isolating the counter electrode with a salt bridge the effect of the polysulfide electrolyte is found to act as an electron scavenger on the working electrode. Though activity at the platinum counter electrode increases with the presence of polysulfides, the activity is too low to counteract scavenging at the working electrode. Cu2S, CoS and PbS electrochemically show promise as alternatives to platinum. Cu2S and CoS produce higher photocurrents and fill factors, greatly improving cell performance.

  3. Carrier-mediated system for transport of biotin in rat intestine in vitro

    SciTech Connect

    Said, H.M.; Redha, R.

    1987-01-01

    Transport of biotin was examined in rat intestine using the everted sac technique. Transport of 0.1 ..mu..M biotin was linear with time for at least 30 min of incubation and occurred at a rate 3.7 pmol g initial tissue wet wt/sup -1/ min/sup -1/. Transport of biotin was higher in the jejunum than the ileum and was minimum in the colon (85 +/- 6, 36 +/- 6, and 2.8 +/- 0.6 pmol x g initial tissue wet wt/sup -1/ x 25 min/sup -1/, respectively). In the jejunum, transport of biotin was saturable at low concentrations but linear at higher concentrations. The transport of low concentrations of biotin was 1) inhibited by structural analogues (desthiobiotin, biotin methyl ester, diaminobiotin, and biocytin), 2) Na/sup +/ dependent, 3) energy dependent, 4) temperature dependent, and 5) proceeded against a concentration gradient in the serosal compartment. No metabolic alteration occurs to the biotin molecule during transport. This study demonstrates that biotin transport in rat intestine occurs by a carrier-mediated process at low concentrations and by simple diffusion at high concentrations. Furthermore, the carrier-mediated process is Na/sup +/, energy, and temperature dependent.

  4. 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 extended defects. The recombination at the extended defects produces long, logarithmic decay limiting substantially performance of CdZnTe detectors. This decay is associated with the “electrostatic trapping” of excess holes by the Schottky-type depletion space-charge regions formed around the defects.

  5. Electronic transport characterization of silicon wafers by combination of modulated free carrier absorption and photocarrier radiometry

    NASA Astrophysics Data System (ADS)

    Huang, Qiuping; Li, Bincheng

    2011-01-01

    A combined modulated free carrier absorption (MFCA) and photocarrier radiometry (PCR) technique is developed to determine simultaneously the electronic transport properties (carrier diffusion coefficient, carrier lifetime, and front surface recombination velocity) of silicon wafers. Comparative computer simulations are carried out to investigate how the experimental measurement errors affect the simultaneous determination of the electronic transport parameters by introducing random or systematic errors into the simulated MFCA and PCR data and statistically analyzing the fitted results, by means of separate MFCA and PCR, as well as the combined MFCA and PCR through fitting the experimental dependences of signal amplitudes and phases to the corresponding theoretical models via a multiparameter fitting procedure, respectively. The simulation results show that with the combined MFCA and PCR the effect of experimental errors on the simultaneous determination of the transport parameters is significantly reduced and therefore the accuracy of the fitted results is greatly improved. Experiments with two c-Si wafers with the three methods were performed and the results were compared. The experimental results showed that the combined MFCA and PCR provided the most accurate fitted transport parameters, in agreement with the simulation results.

  6. 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.

  7. DNA-mediated charge transport for DNA repair

    NASA Astrophysics Data System (ADS)

    Boon, Elizabeth M.; Livingston, Alison L.; Chmiel, Nikolas H.; David, Sheila S.; Barton, Jacqueline K.

    2003-10-01

    MutY, like many DNA base excision repair enzymes, contains a [4Fe4S]2+ cluster of undetermined function. Electrochemical studies of MutY bound to a DNA-modified gold electrode demonstrate that the [4Fe4S] cluster of MutY can be accessed in a DNA-mediated redox reaction. Although not detectable without DNA, the redox potential of DNA-bound MutY is 275 mV versus NHE, which is characteristic of HiPiP iron proteins. Binding to DNA is thus associated with a change in [4Fe4S]3+/2+ potential, activating the cluster toward oxidation. Given that DNA charge transport chemistry is exquisitely sensitive to perturbations in base pair structure, such as mismatches, we propose that this redox process of MutY bound to DNA exploits DNA charge transport and provides a DNA signaling mechanism to scan for mismatches and lesions in vivo.

  8. 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.

  9. Influence of Carrier Transport on Diffraction Efficiency of Steady-State Photocarrier Grating

    NASA Astrophysics Data System (ADS)

    Sun, Q. M.; Wang, Y. F.; Gao, C. M.; Cui, H.

    2015-06-01

    A two-dimensional theoretical model of a diffractive steady-state photocarrier grating (SSPCG) has been developed. The carrier diffusion equation with a spatially periodic excitation source was solved, and an analytical expression of the carrier density distribution was obtained. Based on the band-filling theory and the Kramers-Kronig relation, the carrier-induced refractive index change of SSPCG was estimated, and the refractive index profile was determined. The diffraction efficiency of the SSPCG was calculated by multilevel rigorous coupled-wave analysis. Simulations were carried out to investigate the influence of the carrier transport properties on the diffraction efficiency of the SSPCG. The results show that a semiconductor material with a longer lifetime and a smaller diffusivity will have a higher diffraction efficiency. The spatial amplitude of the carrier density and the grating strength of the SSPCG are closely related to the grating period. For an InP-based SSPCG, the diffraction efficiency of the transmitted wave reaches its maximum value (25 %) when the grating provides a phase shift. The theoretical analysis and conclusions are helpful for material selection and experimental parameter determination of a diffractive SSPCG.

  10. Effects of hydrostatic pressure on lipid bilayer membranes. II. Activation and reaction volumes of carrier mediated ion transport.

    PubMed Central

    Benz, R.; Conti, F.

    1986-01-01

    Measurements of voltage relaxations following brief charge-pulses applied to lipid bilayers have been performed at different hydrostatic pressures in the presence of the neutral carriers cyclo (D-Val-L-Pro-L-Val-D-Pro)3(PV) and valinomycin. From double-exponential relaxations observed in membranes containing PV-K+ complexes estimates were obtained of the amount of membrane absorbed complexes, NMS, and of the rate of complex translocation, kMS. The pressure dependence of kMS corresponded to an activation volume for translocation of approximately 12 cm3/mol independent of ionic strength and K+ concentration. The pressure dependence of NMS strongly varied with K+-concentration suggesting a major role of ion-complexation in solution which is estimated to involve a reaction volume of 25.5 cm3/mol, while the volume of absorption of a PV-K+ complex by the membrane was estimated -7.5 cm3/mol. The relaxations observed in the presence of valinomycin contained three exponentials and could be used to estimate four rate constants and one absorption parameter which characterize the valinomycin-mediated transport. When the transport of Rb+ was tested, the rate constant for the complex dissociation, kD, and the total concentration of free and complexed carriers in the membrane, No, were found to be pressure insensitive. The translocation rates for the complex, kMS and for the free carrier, kS, were instead markedly pressure dependent according to estimated activation volumes in the range of 11 to 18 cm3/mol. The recombination rate constant kR was also pressure dependent according to an activation volume of 12-14 cm3/mol. The study of the valinomycin-K+ transport yielded similar results as far as N.,ks, and kms are concerned, but in this case kR was pressure independent, while kD was increased by pressure. The net volume change associated with the transfer of a free ion to the membrane in the form of a valinomycin-ion complex was nevertheless very similar for K+ and Rb+. It is concluded that pressure affects the transmembrane mobility of liposoluble molecules, whether charged or not, mostly by increasing the effective viscosity of the hydrocarbon core of the bilayer. The pressure dependence of the membrane uptake of amphipathic compounds seems also to obey the general rule: that of involving a negative volume change. However, when the compounds arise from a complexation reaction in solution or at the membrane solution interface possible positive volumes of complexation may make effective uptake to be reversed rather than increased by pressure. PMID:3730510

  11. Mesoporous perovskite solar cells: material composition, charge-carrier dynamics, and device characteristics.

    PubMed

    Zhao, Yixin; Nardes, Alexandre M; Zhu, Kai

    2014-01-01

    We report on our investigations on charge transport and recombination in TiO(2)-based mesoporous solar cells using PbI(2) and various perovskite compositions, including CH(3)NH(3)PbI(3), CH(3)NH(3)PbI(2)Br, CH(3)NH(3)PbIBr(2), and CH(3)NH(3)PbBr(3). The mesoporous TiO(2) film is about 650 nm thick. Electron microscopy measurements show that no perovskite capping layer is formed on the top surface of the TiO(2) film. Intensity-modulated photocurrent/photovoltage spectroscopies show that the electron diffusion coefficient and recombination lifetime are governed by the underlying mesoporous TiO(2) film and thus do not depend on the perovskite composition. However, replacing the perovskite absorber with PbI(2) leads to a diffusion coefficient that is about a factor of 5 slower than that in perovskite-based devices. We also find that TiCl(4) treatment of the mesoporous TiO(2) film prior to device fabrication substantially reduces the charge recombination kinetics in mesoporous perovskite solar cells. PMID:25407110

  12. 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.; Kofan, 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 Schrdinger 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 ?, which measures hopping interaction correction. In so doing, increasing ? 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 ?. 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.

  13. Nonlinear charge transport in the helicoidal DNA molecule.

    PubMed

    Dang Koko, A; Tabi, C B; Ekobena Fouda, H P; Mohamadou, A; Kofan, 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 Schro?dinger 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 ?, which measures hopping interaction correction. In so doing, increasing ? 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 ?. 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

  14. Charge Transport Characteristics Of Cobalt Phthalocyanine Thin Films Grown By Molecular Beam Epitaxy

    SciTech Connect

    Gupta, S. K.; Singh, Ajay; Samanta, Soumen; Kumar, Arvind; Debnath, A. K.; Aswal, D. K.

    2010-12-01

    In the recent times organic semiconductors (OSC) have received attention because of their application in low-cost, flexible, and large area electronics devices. The application of OSC thin films has been limited due to their low charge carrier mobility ({approx}0.1 cm{sup 2}/V-s). We have investigated the effect of substrate on structure and charge transport characteristics of cobalt phthalocyanine (CoPc) films. Thin films have been grown on both single crystal (sapphire and LaAlO{sub 3}) and amorphous (quartz) substrates using molecular beam epitaxy system. The films grown on LaAlO{sub 3} substrates exhibited a higher value of mobility ({approx}4 cm{sup 2}/V-s) while those grown on Al{sub 2}O{sub 3} and quartz showed mobility value of {approx}1 cm{sup 2}/V-s. High mobility for LaAlO{sub 3} substrates has been attributed to the enhanced ordering of the molecules due to natural twin boundaries of substrates. In order to further confirm role of grain boundaries in aligning the CoPc molecules, we measured the charge transport on films deposited at bi-crystal SrTiO{sub 3} substrates. The results showed that current along bi-crystal grain boundary is three orders of magnitude higher than for films on SrTiO{sub 3} substrate without grain boundary, which confirms our hypothesis of ordering of molecules along grain boundaries.

  15. Carrier-mediated placental transport of cimetidine and valproic acid across differentiating JEG-3 cell layers.

    PubMed

    Ikeda, K; Ueda, C; Yamada, K; Nakamura, A; Hatsuda, Y; Kawanishi, S; Nishii, S; Ogawa, M

    2015-07-01

    Human choriocarcinoma has been used as a model to study trophoblast transcellular drug transport in the placenta. Previous models had limitations regarding low molecular weight drug transport through the intracellular gap junction. The purpose of this study was to evaluate placental carrier-mediated transport across a differentiating JEG-3 choriocarcinoma cell (DJEGs) layer model in which the intracellular gap junction was restricted. Cimetidine is the substrate of an efflux transporter, breast cancer resistance protein (BCRP). BCRP highly expressed in the placenta, and its function in the DJEGs model was investigated. In addition, the placental drug transport of another efflux transporter, multidrug resistance-associated proteins (MRPs), and an influx transporter, monocarboxylate transporter (MCT), were examined with various substrates. Cimetidine permeated from the fetal side to the maternal side at significantly high levels and saturated in a dose-dependent manner. The permeability coefficient of a MRP substrate, fluorescein, across the DJEGs model was significantly increased by inhibiting MRP function with probenecid. On the other hand, permeation in the influx direction to the fetal side with a substrate of MCT, valproic acid, had a gentle dose-dependent saturation. These findings suggest that the DJEGs model could be used to evaluate transcellular placental drug transport mediated by major placental transporters. PMID:26373208

  16. Mixed quantum-classical simulations of charge transport in organic materials: numerical benchmark of the Su-Schrieffer-Heeger model.

    PubMed

    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 ?4.8 cm(2)?Vs (?0.14 cm(2)/Vs) in one-dimensional (two-dimensional) crystals. PMID:21721621

  17. 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.

  18. Study of the effect of the charge transport layer in the electrical characteristics of the organic photovoltaics

    NASA Astrophysics Data System (ADS)

    Rahimi, Ronak; Roberts, Alex; Narang, V.; Kumbham, Vamsi Krishna; Korakakis, D.

    2013-09-01

    Significant progress in fabrication and optimization of organic photovoltaics (OPVs) has been made during the last decade. The main reason for popularity of OPVs is due to their low production cost, large area devices and compatibility with flexible substrates 1-3. Various approaches including optimizing morphology of the active layers 1, 2, introducing new materials as the donor and acceptor 3,4, new device structures such as tandem structure 5, 6 have been adapted to improve the efficiency of the organic photovoltaics. However, electrical characteristics of the OPVs do not only depend on the active layer materials or device structure. They can also be defined by the interface properties between active layers and the charge transport layers or the metal contacts. Within this paper, the effect of the thickness variation of the charge transport layer in the electrical properties of the bilayer heterojunction OPVs has been studied. Several devices with CuPc/PTCDI-C8 as the donor/acceptor layers have been fabricated with different thicknesses of electron transport layer. MoO3 and Alq3 have been used respectively as the hole transport layer (HTL) and the electron transport layer (ETL). It has been shown that the S-shape effect in the current-voltage curve is attributed to the accumulation of the charge carriers at the interface between the active layer and the charge transport layer 5, 7.

  19. Study of the effect of the charge transport layer in the electrical characteristics of the organic photovoltaics

    NASA Astrophysics Data System (ADS)

    Rahimi, Ronak; Roberts, Alex; Narang, V.; Kumbham, Vamsi Krishna; Korakakis, D.

    2013-03-01

    Significant progress in fabrication and optimization of organic photovoltaics (OPVs) has been made during the last decade. The main reason for popularity of OPVs is due to their low production cost, large area devices and compatibility with flexible substrates [1-3]. Various approaches including optimizing morphology of the active layers [1,2], introducing new materials as the donor and acceptor [3,4], new device structures such as tandem structure [5,6] have been adapted to improve the efficiency of the organic photovoltaics. However, electrical characteristics of the OPVs do not only depend on the active layer materials or device structure. They can also be defined by the interface properties between active layers and the charge transport layers or the metal contacts. Within this paper, the effect of the thickness variation of the charge transport layer in the electrical properties of the bilayer heterojunction OPVs has been studied. Several devices with CuPc/PTCDI-C8 as the donor/acceptor layers have been fabricated with different thicknesses of electron transport layer. MoO3 and Alq3 have been used respectively as the hole transport layer (HTL) and the electron transport layer (ETL). It has been shown that the S-shape effect in the current-voltage curve is attributed to the accumulation of the charge carriers at the interface between the active layer and the charge transport layer [5,7].

  20. Charge Transport Phenomena in Detectors of the Cryogenic Dark Matter Search

    NASA Astrophysics Data System (ADS)

    Sundqvist, Kyle

    2008-03-01

    The Cryogenic Dark Matter Search (CDMS) seeks to detect putative weakly-interacting massive particles (WIMPS), which could explain the dark matter problem in cosmology and particle physics. By simultaneously measuring the number of charge carriers and the energy in athermal phonons created by particle interactions in intrinsic Ge and Si 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 apart from electromagnetic radioactive background which interacts with electrons. The challenges associated with these techniques are unique. Carrier drift-fields are maintained at only a few V/cm, else drift-emitted Luke-Neganov phonons would dominate the phonons of the original interaction. Under such conditions, carrier scattering is dominated by zero-point fluctuations of the lattice ions. It has been an open question how well the 8 Kelvin data prominent in the literature depicts this case. We compare the simulated transport properties of electrons and holes in <100> Ge at 40 mK and at 8 K, and apply this understanding to our detectors.