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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. 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.

  4. Charge carrier and phonon transport in nanostructured thermoelectrics

    NASA Astrophysics Data System (ADS)

    Norouzzadeh, Payam

    There is currently no quantum mechanical transport model for charge (or phonon) transport in multiphase nano-crystalline structures. Due to absence of periodicity, one cannot apply any of the elegant theorems, such as Bloch's theorem, which are implicit in the basic theory of crystalline solids. Atomistic models such as Kubo and NEGF may assume an accurate knowledge of the interatomic potentials; however, calculations for real 3D random multi-phase systems require so large computational times that makes them practically impossible. In a multi-phase nano-crystalline material, grains and interfacial microstructures may have three distinct types as depicted in figure. In such a material, the physical processes in each individual grain no longer follow the well described classical continuum linear transport theory. Therefore, a proper model for coupled transport of charge carriers and phonons that takes into account the effect of their non-equilibrium energy distribution is highly desirable. Two new theories and associated codes based on Coherent Potential Approximation (CPA) one for electron transport and one for phonon transport are developed. The codes calculate the charge and phonon transport parameters in nanocomposite structures. These can be nano-crystalline (symmetric case) or the material with embedded nano-particles (dispersion case). CPA specifically considers multi-scattering effect that cannot be explained with other semi-classical methods such as Partial Wave or Fermi's golden rule. To our knowledge this is the first CPA code developed to study both charge and phonon transport in nanocomposite structures. The codes can be extend to different types of nano-crystalline materials taking into account the average grain size, as well as the grain size distribution, and volume fraction of the different constituents in the materials. This is a strong tool that can describe more complex systems such as nano-crystals with randomly oriented grains with predictive power for the properties of electrical and thermal properties of disordered nano-crystalline electronic materials.

  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. Optical Profile and Nanostructure Effects in the Charge Carrier Transport and Performance of Photovoltaic Devices

    NASA Astrophysics Data System (ADS)

    Liu, Yingchi

    Charge carrier plays a significant role in energy harvesting in photovoltaic devices. Due to recombination, the inadequate charge carrier transport length prevents the devices from achieving efficient absorption by increasing active layer thickness. Fundamental research on the charge transport is important as it is a critical factor to determine the optimal device structures. In this thesis, the charge carrier transport process is studied in photovoltaic devices by linking local characteristic light absorption profiles to photocurrent measurements. Local light absorption profile can be approximated as the free charge generation profile, which determines the average charge transport distance. Together with incident light wavelength, illumination direction effectively controls the generation profile and hence the charge transport distance. And this charge transport distance is demonstrated to relate to recombination that can be measured from photocurrent. Therefore, the charge carrier transport length can be estimated. On the other hand, the potential of the nanostructured solar cells as a key to solve the problem lies between adequate light absorption and efficient charge carrier collection. In this thesis, the discussion focuses on the nanostructured bulk heterojunction (BHJ) organic photovoltaics (OPVs). As photonic crystal nanostructures have been proposed to increase the light trapping effects without increasing the volumes of the active materials, intuitively, it is believed that the nanostructure will affect only the optical absorption. However, in this thesis it is demonstrated that there is a tradeoff between light trapping enhancement and charge carrier collection deterioration due to the nanopatterning effects. Furthermore, the nanopatterning process is shown to affect the material composition in BHJ OPVs as well. Improvement of BHJ OPVs' performance by nanostructures is not a simple task of increasing light absorption. Comprehensive considerations are demonstrated necessary for design of optimal device structures.

  8. 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

  9. Exciton harvesting, charge transfer, and charge-carrier transport in amorphous-silicon nanopillar/polymer hybrid solar cells

    E-print Network

    McGehee, Michael

    Exciton harvesting, charge transfer, and charge-carrier transport in amorphous-silicon nanopillar/polymer report on the device physics of nanostructured amorphous-silicon a-Si:H /polymer hybrid solar cells. Using two different polymers, poly 3-hexylthiophene P3HT and poly 2-methoxy-5- 2 -ethyl-hexyloxy -1

  10. 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.

  11. Thermal generation and mobility of charge carriers in collective proton transport in hydrogen-bonded chains

    SciTech Connect

    Peyrard, M.; Boesch, R.; Kourakis, I. . Faculte des Sciences)

    1991-01-01

    The transport of protons in hydrogen-bonded systems is a long standing problem which has not yet obtained a satisfactorily theoretical description. Although this problem was examined first for ice, it is relevant in many systems and in particular in biology for the transport along proteins or for proton conductance across membranes, an essential process in cell life. The broad relevance makes the study of proton conduction very appealing. Since the original work of Bernal and Fowler on ice, the idea that the transport occurs through chains of hydrogen bonds has been well accepted. Such proton wires'' were invoked by Nagle and Morowitz for proton transport across membranes proteins and more recently across lipid bilayers. In this report, we assume the existence of such an hydrogen-bonded chain and discuss its consequences on the dynamics of the charge carriers. We show that this assumption leads naturally to the idea of soliton transport and we put a special emphasis on the role of the coupling between the protons and heavy ions motions. The model is presented. We show how the coupling affects strongly the dynamics of the charge carriers and we discuss the role it plays in the thermal generation of carriers. The work presented has been performed in 1986 and 87 with St. Pnevmatikos and N. Flyzanis and was then completed in collaboration with D. Hochstrasser and H. Buettner. Therefore the results presented in this part are not new but we think that they are appropriate in the context of this multidisciplinary workshop because they provide a rather complete example of the soliton picture for proton conduction. This paper discusses the thermal generation of the charge carriers when the coupling between the protons and heavy ions dynamics is taken into account. The results presented in this part are very recent and will deserve further analysis but they already show that the coupling can assist for the formation of the charge carriers.

  12. Ambipolar charge carrier transport in mixed organic layers of phthalocyanine and fullerene

    E-print Network

    A. Opitz; M. Bronner; W. Bruetting

    2006-12-21

    Mixed layers of copper-phthalocyanine (p-conductive) and fullerene (n-conductive) are used for the fabrication of organic field-effect transistors (OFETs) and inverters. Regarding the electrical characteristics of these donor-acceptor blends they show ambipolar charge carrier transport, whereas devices made from only one of the materials show unipolar behavior. Such mixed films are model systems for ambipolar transport with adjustable field-effect mobilities for electrons and holes. By variation of the mixing ratio it is possible to balance the transport of both charge-carrier types. In this paper we discuss the variation of mobility and threshold voltage with the mixing ratio and demonstrate ambipolar inverters as a leadoff application. The gained results were analyzed by simulations using an analytical model for ambipolar transistors and subsequently compared to complementary inverters.

  13. Molecular semiconductor blends: Microstructure, charge carrier transport, and application in

    E-print Network

    Schreiber, Frank

    -complementary organic field- effect transistors and organic photovoltaic cells. Many inves- tigations in the latter transport properties in diodes and field-effect transistors. Furthermore, we compare the photovoltaic in photovoltaic cells Andreas Opitz*,1 , Julia Wagner 1 , Wolfgang Bru¨ tting 1 , Alexander Hinderhofer 2

  14. 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.

  15. Study of the charge carrier transport through a metal-poly(arylenephthalide)-class polymer interface

    NASA Astrophysics Data System (ADS)

    Yusupov, A. R.; Rakhmeev, R. G.; Lachinov, A. N.; Kalimullina, L. R.; Nakaryakov, A. S.; Bunakov, A. A.

    2013-07-01

    The influence of the chemical structure of the poly(arylenephthalide)-class polymers on the charge carrier transport through a metal/polymer interface has been discussed. On the basis of the results obtained by physical and optical methods and quantum chemical modeling, the conclusion is made that a change in the skeleton part of the polymer molecule leads to a substantial change in the value of the potential barrier.

  16. 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.

  17. 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.

  18. 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.

  19. Distribution of charge carrier transport properties in organic semiconductors with Gaussian disorder

    NASA Astrophysics Data System (ADS)

    Lorrmann, Jens; Ruf, Manuel; Vocke, David; Dyakonov, Vladimir; Deibel, Carsten

    2014-05-01

    The charge carrier drift mobility in disordered semiconductors is commonly graphically extracted from time-of-flight (TOF) photocurrent transients yielding a single transit time. However, the term transit time is ambiguously defined and fails to deliver a mobility in terms of a statistical average. Here, we introduce an advanced computational procedure to evaluate TOF transients, which allows to extract the whole distribution of transit times and mobilities from the photocurrent transient, instead of a single value. This method, extending the work of Scott et al. (Phys. Rev. B 46, 8603 (1992)), is applicable to disordered systems with a Gaussian density of states and its accuracy is validated using one-dimensional Monte Carlo simulations. We demonstrate the superiority of this new approach by comparing it to the common geometrical analysis of hole TOF transients measured on poly(3-hexyl thiophene-2,5-diyl). The extracted distributions provide access to a very detailed and accurate analysis of the charge carrier transport. For instance, not only the mobility given by the mean transit time but also the mean mobility can be calculated. Whereas the latter determines the macroscopic photocurrent, the former is relevant for an accurate determination of the energetic disorder parameter ? within the Gaussian disorder model. ? derived by using the common geometrical method is, as we show, underestimated instead.

  20. 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.

  1. 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

  2. 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.

  3. 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.

  4. 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 cm² (Vs)?¹ and diffusion coefficient D of 17 cm² s?¹. We find limiting recombination at the epitaxial film surface (surface recombination velocity Ssurface = (2.8 ± 0.3) × 10?cm s ?¹) and at the heteroepitaxial interface (interface recombination velocity Sinterface = (4.8 ± 0.5) × 10? cm s?¹). The results demonstrate that reducing surface and interface recombination velocity is critical for photovoltaic solar cells and electronic devices that employ epitaxial CdTe.

  5. 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.

  6. 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.

  7. 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.

  8. Morphology and Charge Transport in Conjugated Polymers

    E-print Network

    McGehee, Michael

    Morphology and Charge Transport in Conjugated Polymers R. J. KLINE AND M. D. McGEHEE Department charge transport and morphology is key to increasing the charge carrier mobility of conjugated polymers to provide insight into how the charge carriers move through a conjugated polymer film and provide a model

  9. 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.

  10. All-optical measurement of vertical charge carrier transport in mid-wave infrared InAs/GaSb type-II superlattices

    E-print Network

    Flatte, Michael E.

    charge carrier transport in mid-wave infrared InAs/GaSb type-II superlattices (T2SLs). By optically investigation of both unintentionally doped and p-type T2SLs, the vertical hole and electron diffusionAs/Ga(In)Sb type-II superlattices (T2SLs), as well as the recent demonstration of Ga-free T2SLs with microsecond

  11. Localized charge carriers in graphene nanodevices

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

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

  12. Charge carrier scattering by defects in semiconductors

    NASA Astrophysics Data System (ADS)

    Lordi, Vincenzo; Erhart, Paul; Åberg, 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.

  13. 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

  14. 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.

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

    PubMed

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

    2015-09-01

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

  16. Combined Charge Carrier Transport and Photoelectrochemical Characterization of BiVO4 Single Crystals: Intrinsic Behavior of a

    E-print Network

    Lin, Jung-Fu "Afu"

    , attributed to the layered structure of BiVO4. Measurements of the ac field Hall effect yielded an electron diffusion length of 100 nm was estimated. As a result of low carrier mobility, attempts to measure the dc a flat band potential of 0.03-0.08 V versus the reversible H2 electrode, while incident photon conversion

  17. 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.

  18. Charge carrier mobility in hybrid halide perovskites

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

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

  19. Charge carrier mobility in hybrid halide perovskites

    PubMed Central

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

    2015-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

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

  1. 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

  2. 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.

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

    PubMed

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

    2008-09-01

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

  4. Balanced charge carrier mobilities in bulk heterojunction organic solar cells

    NASA Astrophysics Data System (ADS)

    Abbas, Mamatimin; Tekin, Nalan

    2012-08-01

    All solution processed ambipolar bulk heterojunction organic field effect transistors were fabricated using Au and Al as hole and electron injection contacts to study both types of charge carrier mobilities in a single device. Poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) were mixed with different ratios. Well balanced electron and hole mobilities were obtained at 1:0.3 ratio. Organic solar cells with the same ratio yielded draft enhancement in device performance parameters, indicating optimized carrier transport in the bulk of solar cell devices.

  5. Observation of defect-induced Photoresponse and charge carrier transport in single GeSe2 nanobelt devices

    NASA Astrophysics Data System (ADS)

    Mukherjee, Bablu; Tok, Eng Soon; Haur Sow, Chorng

    2013-03-01

    Single crystal GeSe2 nanobelts were grown using chemical vapor deposition techniques. Morphology of the nanostructures was characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffractometry (XRD) and Raman spectroscopy. Electronic transport properties, impedance spectroscopy, photoconductive characteristics and temperature-dependent electrical resistivity measurements were carried out on individual GeSe2 nanobelt devices. The photosensitivity of single GeSe2 nanobelt (NB) devices was examined with two different excitation wavelengths of laser beams with photon energies above band gap and at sub-band gap of the NB. A maximum photoconductive gain 106 % was achieved at a wavelength of 808 nm. The magnitude of the photocurrent and response time of the individual GeSe2 NB device indicate that the photoresponse could be attributed to the presence of isolated mid band gap defect levels. Temperature dependent photocurrent measurements indicate the rough estimation of the energy levels for the defect states. Localized photostudy shows that the large photoresponse of the device primarily occurs at the metal-NB contact regions. Department of Physics, 2 Science Drive 3, National University of Singapore (NUS), Singapore 117542

  6. 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

  7. Degradation effects on charge carrier transport in P3HT:PCBM solar cells studied by Photo-CELIV and ToF

    NASA Astrophysics Data System (ADS)

    Stephen, M.; Karuthedath, S.; Sauermann, T.; Genevi?ius, K.; Juška, G.

    2014-10-01

    Oxygen induced degradation is one of the major problems in the field of organic photovoltaics. Photo-degradation impacts on performance of inverted bulk hetero junction poly(3-hexylthiophene) : phenyl-C61-butyric acid methyl ester (P3HT:PCBM) solar cells has been investigated by means of charge extraction by linearly increasing voltage (CELIV) and time of flight (ToF) methods. The irreversible loss in short circuit current (Jsc) can be attributed to a combination of adverse effects such as loss in mobility of the charge carrires, increase in trapping effect and sheilding of electric field by equilibrium carriers upon degradation.

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

    SciTech Connect

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

    2014-07-21

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

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

    DOEpatents

    Rehak, 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.

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

    DOEpatents

    Rehak, Pavel (Patchogue, NY); Gatti, Emilio (Lesmo, IT)

    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.

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

    DOEpatents

    Rehak, P.; Gatti, E.

    1984-02-24

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

  12. 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?

  13. 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.

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

    NASA Astrophysics Data System (ADS)

    Alsina, F.; Santos, P. V.; Schönherr, H.-P.; Seidel, W.; Ploog, K. H.; Nötzel, 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.

  15. Organic Charge Carriers for Perovskite Solar Cells.

    PubMed

    Völker, 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

  16. 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.

  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, 2010 CFR

    2010-07-01

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

  18. 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

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

  19. 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

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

  20. 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

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

  1. Modeling Carrier Behavior in Sequential Auction Transportation Markets

    E-print Network

    Bertini, Robert L.

    Modeling Carrier Behavior in Sequential Auction Transportation Markets M. A. Figliozzi, University ______________________________________________________________________________ August 10-15, 2003 2 Title: Modeling Carrier Behavior in Sequential Auction Transportation Markets Miguel Phone: 301-405-0752 Fax: 301-405-2585 eMail: masmah@umd.edu Abstract Online markets for transportation

  2. 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

  3. Resolving the ultrafast dynamics of charge carriers in nanocomposites

    E-print Network

    Barreto, J; Kaplan, A

    2012-01-01

    Here we describe an optical method to determine the dynamics of optically excited carriers in nanostructured composite samples. By combining pump-probe time-resolved reflectivity with scattering measurements, we extract the characteristic times for charge carrier evolution. We use the 3D Maxwell-Garnett formulae, modified to include the Drude optical response, to model the results. The method, applied to hydrogenated amorphous silicon containing crystalline silicon nanoparticles, showed that the recombination times in the nanocrystals and in the matrix were ~4.9 ps and ~22 ps, respectively. The charge transfer time between the crystals and the matrix was ~4 ps.

  4. 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.

  5. 41 CFR 301-10.105 - What are the basic requirements for using common carrier transportation?

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ...basic requirements for using common carrier transportation? 301-10... Federal Travel Regulation System TEMPORARY DUTY (TDY) TRAVEL...10-TRANSPORTATION EXPENSES Common Carrier Transportation § 301-10...basic requirements for using common carrier transportation?...

  6. 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.

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

    PubMed Central

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

    2013-01-01

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

  8. 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.

  9. 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

  10. Visualization of charge transport through Landau levels in graphene

    NASA Astrophysics Data System (ADS)

    Nazin, G.; Zhang, Y.; Zhang, L.; Sutter, E.; Sutter, P.

    2010-11-01

    Band bending and the associated spatially inhomogeneous population of Landau levels play a central role in the physics of the quantum Hall effect (QHE) by constraining the pathways for charge-carrier transport and scattering. Recent progress in understanding such effects in low-dimensional carrier gases in conventional semiconductors has been achieved by real-space mapping using local probes. Here, we use spatially resolved photocurrent measurements in the QHE regime to study the correlation between the distribution of Landau levels and the macroscopic transport characteristics in graphene. Spatial maps show that the net photocurrent is determined by hot carriers transported to the periphery of the graphene channel, where QHE edge states provide efficient pathways for their extraction to the contacts. The photocurrent is sensitive to the local filling factor, which allows us to reconstruct the local charge density in the entire conducting channel of a graphene device.

  11. 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.

  12. Ultrafast Charge-Carrier Dynamics in Low-Dimensional Solids

    NASA Astrophysics Data System (ADS)

    Perfetti, Luca; Kampfrath, Tobias; Wolf, Martin; Frischkorn, Christian

    Ultrashort broadband THz pulses are applied to probe the femtosecond charge-carrier dynamics of laser-excited graphite and carbon nanotubes. In graphite, the electrons lose more than 90% of their excess energy which selectively heat up a very small subset of strongly coupled optical phonons. In the nanotube sample, the absence of a free-carrier response is due to the photogeneration of strongly bound excitons in the semiconducting tubes. A pronounced dichroism of a spectral feature of increased absorption gives direct evidence of excitations which are localized on a 100-nm length scale.

  13. Charge-carrier properties in synthetic single-crystal diamond measured with the transient-current technique

    E-print Network

    Pernegger, H; Frais-Kölbl, H; Griesmayer, E; Kagan, H; Roe, S; Schnetzer, S; Stone, R; Trischuk, W; Twitchen, D; Weilhammer, Peter; Whitehead, A; 10.1063/1.1863417

    2005-01-01

    For optimal operation of chemical-vapor deposition (CVD) diamonds as charged particle detectors it is important to have a detailed understanding of the charge-carrier transport mechanism. This includes the determination of electron and hole drift velocities as a function of electric field, charge carrier lifetimes, as well as effective concentration of space charge in the detector bulk. We use the transient-current technique, which allows a direct determination of these parameters in a single measurement, to investigate the charge-carrier properties in a sample of single-crystal CVD diamond. The method is based on the injection of charge using an alpha source close to the surface and measuring the induced current in the detector electrodes as a function of time.

  14. Bipolar carrier transport in tris(8-hydroxy-quinolinato) aluminum observed by impedance spectroscopy measurements

    NASA Astrophysics Data System (ADS)

    Ishihara, Shingo; Hase, Hiroyuki; Okachi, Takayuki; Naito, Hiroyoshi

    2011-08-01

    We studied bipolar carrier transport in tris(8-hydroxy-quinolinato) aluminum (Alq3) thin films using impedance spectroscopy (IS). Two transit times were observed in the impedance spectra of the Alq3 double-injection diodes. The mobilities determined from the transit times are in good agreement with the electron and the hole mobilities in Alq3 measured by IS using single injection diodes and by the time-of-flight transient photocurrent technique. The bipolar carrier transport observed in Alq3 shows that the carrier recombination of Alq3 is weak on the basis of the simulation [M. Schmeits, J. Appl. Phys. 101, 084508 (2007)]. Simultaneous measurements of electron and hole mobilities are useful in the study of charge-carrier transport in active layers in organic light-emitting diodes and organic solar cells.

  15. 41 CFR 301-72.3 - What method of payment must we authorize for common carrier transportation?

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ...payment must we authorize for common carrier transportation? ...Federal Travel Regulation System TEMPORARY DUTY (TDY) TRAVEL...RESPONSIBILITIES RELATED TO COMMON CARRIER TRANSPORTATION Procurement of Common Carrier Transportation...

  16. 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

    ...payment must we authorize for common carrier transportation? ...Federal Travel Regulation System TEMPORARY DUTY (TDY) TRAVEL...RESPONSIBILITIES RELATED TO COMMON CARRIER TRANSPORTATION Procurement of Common Carrier Transportation...

  17. 49 CFR 385.13 - Unsatisfactory rated motor carriers; prohibition on transportation; ineligibility for Federal...

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ...2012-10-01 false Unsatisfactory rated motor carriers; prohibition on transportation...Transportation (Continued) FEDERAL MOTOR CARRIER SAFETY ADMINISTRATION, DEPARTMENT OF TRANSPORTATION FEDERAL MOTOR CARRIER SAFETY REGULATIONS SAFETY...

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

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ...2010-10-01 false Unsatisfactory rated motor carriers; prohibition on transportation...Transportation (Continued) FEDERAL MOTOR CARRIER SAFETY ADMINISTRATION, DEPARTMENT OF TRANSPORTATION FEDERAL MOTOR CARRIER SAFETY REGULATIONS SAFETY...

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

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ...2014-10-01 false Unsatisfactory rated motor carriers; prohibition on transportation...Transportation (Continued) FEDERAL MOTOR CARRIER SAFETY ADMINISTRATION, DEPARTMENT OF TRANSPORTATION FEDERAL MOTOR CARRIER SAFETY REGULATIONS SAFETY...

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

    SciTech Connect

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

    2012-11-26

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

  1. Carrier-mediated transport of peptides by the kidney

    SciTech Connect

    Skopicki, H.A.

    1988-01-01

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

  2. Band filling with free charge carriers in organometal halide perovskites

    NASA Astrophysics Data System (ADS)

    Manser, Joseph S.; Kamat, Prashant V.

    2014-09-01

    The unique and promising properties of semiconducting organometal halide perovskites have brought these materials to the forefront of solar energy research. Here, we present new insights into the excited-state properties of CH3NH3PbI3 thin films through femtosecond transient absorption spectroscopy measurements. The photoinduced bleach recovery at 760?nm reveals that band-edge recombination follows second-order kinetics, indicating that the dominant relaxation pathway is via recombination of free electrons and holes. Additionally, charge accumulation in the perovskite films leads to an increase in the intrinsic bandgap that follows the Burstein-Moss band filling model. Both the recombination mechanism and the band-edge shift are studied as a function of the photogenerated carrier density and serve to elucidate the behaviour of charge carriers in hybrid perovskites. These results offer insights into the intrinsic photophysics of semiconducting organometal halide perovskites with direct implications for photovoltaic and optoelectronic applications.

  3. Mobility of Charge Carriers in Polymer and Mica Electrets

    NASA Astrophysics Data System (ADS)

    Novikov, G. K.; Fedchishin, V. V.

    2015-04-01

    Ionizing radiation of an electric corona gas discharge (ECGD) and electric barrier gas discharge (EBGD) creates a radiation thickness gradient of recombination center concentration N rec = f(h) near the surface of polymer and mica electrets. The mobility of charge carriers in polymer and mica electrets and the stability of the electret potential difference U el = f(t) are obtained by the method of experimental measurements of the x-ray radiation half-absorption depth ? 1/2ECGD, EBGD .

  4. 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

  5. Spontaneous charge carrier localization in extended one-dimensional systems

    E-print Network

    Vl?ek, Vojt?ch; Steinle-Neumann, Gerd; Baer, Roi

    2015-01-01

    Charge carrier localization in extended atomic systems can be driven by disorder, point defects or distortions of the ionic lattice. Herein we give first-principles theoretical computational evidence that it can also appear as a purely electronic effect in otherwise perfectly ordered periodic structures. Optimally-tuned range separated density functional calculations reveal that in trans-polyacetylene and polythiophene the hole density localizes on a length scale of several nanometers. This is due to exchange induced translational symmetry breaking of the charge density. Ionization potentials, optical absorption peaks, excitonic binding energies and the optimally-tuned range parameter itself all become independent of polymer length when it exceeds the critical localization length scale. These first-principles findings show, for the first time, that charge localization is not caused by lattice distortion but it is rather its cause. This helps to explain experimental findings that polarons in conjugated polymer...

  6. 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.

  7. 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

  8. 14 CFR 206.4 - Exemption of air carriers for military transportation.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ...false Exemption of air carriers for military transportation. 206.4 Section...CERTIFICATES OF PUBLIC CONVENIENCE AND NECESSITY: SPECIAL AUTHORIZATIONS AND EXEMPTIONS...206.4 Exemption of air carriers for military transportation. Air carriers...

  9. 14 CFR 206.4 - Exemption of air carriers for military transportation.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ...false Exemption of air carriers for military transportation. 206.4 Section...CERTIFICATES OF PUBLIC CONVENIENCE AND NECESSITY: SPECIAL AUTHORIZATIONS AND EXEMPTIONS...206.4 Exemption of air carriers for military transportation. Air carriers...

  10. 14 CFR 206.4 - Exemption of air carriers for military transportation.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ...false Exemption of air carriers for military transportation. 206.4 Section...CERTIFICATES OF PUBLIC CONVENIENCE AND NECESSITY: SPECIAL AUTHORIZATIONS AND EXEMPTIONS...206.4 Exemption of air carriers for military transportation. Air carriers...

  11. 14 CFR 206.4 - Exemption of air carriers for military transportation.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ...false Exemption of air carriers for military transportation. 206.4 Section...CERTIFICATES OF PUBLIC CONVENIENCE AND NECESSITY: SPECIAL AUTHORIZATIONS AND EXEMPTIONS...206.4 Exemption of air carriers for military transportation. Air carriers...

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

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ...false Exemption of air carriers for military transportation. 206.4 Section...CERTIFICATES OF PUBLIC CONVENIENCE AND NECESSITY: SPECIAL AUTHORIZATIONS AND EXEMPTIONS...206.4 Exemption of air carriers for military transportation. Air carriers...

  13. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2001-03-01

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

  15. Scaling Properties of Charge Transport in Polycrystalline Graphene

    PubMed Central

    2013-01-01

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

  16. 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.

  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, 2014 CFR

    2014-07-01

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

  18. 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.

  19. 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

  20. 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.

  1. 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.

  2. 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.

  3. Charge transport through a single tetracene grain boundary

    SciTech Connect

    Schon, Jan Hendrik; Kloc, Christian

    2001-06-11

    The hole transport through a single grain boundary is investigated in the temperature range from 4 to 300 K using a tetracene bicrystal. The carrier concentration is varied by the field effect. The results can be explained using the grain-boundary-trapping model. A potential barrier is formed at the grain boundary due to charged traps at the grain boundary. The barrier height depends significantly on the carrier density within the grain. At low temperatures, tunneling through the grain boundary dominates over thermionic emission over the barrier. {copyright} 2001 American Institute of Physics.

  4. 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.

  5. Transport of elliptic intense charged -particle beams

    E-print Network

    Zhou, J. (Jing), 1978-

    2006-01-01

    The transport theory of high-intensity elliptic charged-particle beams is presented. In particular, the halo formation and beam loss problem associated with the high space charge and small-aperture structure is addressed, ...

  6. 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.

  7. Effect of charge carrier doping in YbRh2Si2

    NASA Astrophysics Data System (ADS)

    Gegenwart, Philipp

    2013-03-01

    We investigate the effect of non-isovalent partial substitution of Rh by either Fe or Ni in single crystalline YbRh2Si2. This material is a prototype quantum critical heavy-fermion metal. It displays an interesting low-temperature vs magnetic field phase diagram with an antiferromagnetic quantum critical point and an additional low-energy scale T* (H) , which has been associated with the Kondo breakdown. We study the evolution of quantum criticality and the T* scale with charge carrier doping by thermodynamic and transport experiments down to mK temperatures. Work in collaboration with H.S. Jeevan, Y. Tokiwa, M. Schubert, E. Blumenroether

  8. 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

    ...false What types of common carrier transportation...Federal Travel Regulation System TEMPORARY DUTY (TDY...10-TRANSPORTATION EXPENSES Common Carrier Transportation...100 What types of common carrier transportation...bus, or other transit system. [FTR Amdt....

  9. 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

    ...false What types of common carrier transportation...Federal Travel Regulation System TEMPORARY DUTY (TDY...10-TRANSPORTATION EXPENSES Common Carrier Transportation...100 What types of common carrier transportation...bus, or other transit system. [FTR Amdt....

  10. Charge carrier photogeneration, trapping, and space-charge field formation in PVK-based photorefractive materials

    NASA Astrophysics Data System (ADS)

    Däubler, T. K.; Bittner, R.; Meerholz, K.; Cimrová, V.; Neher, D.

    2000-05-01

    We studied the dark conductivity (jdark), the photoconductivity (jphoto), and the charge carrier photogeneration efficiency ? of poly(N-vinylcarbazole)-based photorefractive (PR) materials with different glass-transition temperatures (Tg) and chromophore content (?CHR). Measurements were carried out at wavelengths similar to those used in degenerate four-wave mixing (DFWM) and two-beam coupling (2BC) experiments. Both thick (37 ?m) and thin samples (~1 ?m) were analyzed. Photoconductivity experiments at different temperatures show that both jdark and jphoto are thermally activated. For jdark the activation is not related to the glass-transition temperature of the blends, whereas photocurrents exhibit a universal behavior with respect to Tr=Tg-T. The charge carrier photogeneration efficiency ? was measured by xerographic discharge experiments. ? was found to be independent of both Tg and of ?CHR. The photoconductivity gain factor G defined as the number of charge carriers measured in photoconductivity in relation to the number of carriers initially photogenerated as determined by the xerographic experiments is used to compare the results of photoconductivity and xerographic discharge experiments. G is found to be much smaller than unity even for thin samples, which indicates that the mean free path of the photogenerated charge carriers is less than 1 ?m at photoelectrical equilibrium. Using Schildkraut's model for the space-charge field formation in organic PR materials, trap densities Ti of approximately 1017 cm-3 could be derived from G. The field and temperature dependence of Ti is independent of ?CHR and might account for the universal Tr dependence of jphoto. The estimated trap densities are used to calculate the first-order Fourier component of the space-charge field in the PR materials illuminated with a sinusoidal intensity pattern. Modifying Schildkraut's model so that the tilt between the applied electric field and the index of refraction grating is taken into account yields saturation fields of approximately 100 V/?m in agreement with findings from PR experiments. The dramatic decrease of the space-charge field when the temperature exceeds the glass-transition temperature of the blend is fully explained by a decrease in trap density. The fact that the trap density depends on the temperature with respect to Tg and not on the absolute temperature suggests that the relevant traps are most likely of conformational nature.

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

    E-print Network

    Rudenko, A N; Katsnelson, M I

    2015-01-01

    We present a theory for single- and two-phonon charge carrier scattering in anisotropic semiconductors, which is applied to a single-layer black phosphorus (BP). We show that in contrast to graphene, where two-phonon processes due to the scattering by flexural phonons dominate at any practically relevant temperatures and are independent on the carrier concentration $n$, two-phonon scattering in BP is less important and can be considered negligible at $n>10^{13}$ cm$^{-2}$. At smaller $n$, however, phonons enter in the essentially anharmonic regime. Compared to the hole mobility, which does not exhibit strong anisotropy between the principal directions of BP ($\\mu_{xx}/\\mu_{yy}\\sim1.4$ at $n=10^{13}$ cm$^{-2}$ and $T=300$K), the electron mobility is found to be significantly more anisotropic ($\\mu_{xx}/\\mu_{yy}\\sim6.2$). Absolute values of $\\mu_{xx}$ do not exceed 250 (700) cm$^2$V$^{-1}$s$^{-1}$ for holes (electrons), which can be considered as an upper limit for the mobility in single-layer BP samples at roo...

  12. 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.

  13. 75 FR 18255 - Passenger Facility Charge Database System for Air Carrier Reporting

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-04-09

    ...FAA-2010] Passenger Facility Charge Database System for Air Carrier Reporting AGENCY...the Passenger Facility Charge (PFC) database system to report PFC quarterly report...The FAA has developed a national PFC database system in order to more easily...

  14. 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…

  15. 49 CFR 385.13 - Unsatisfactory rated motor carriers; prohibition on transportation; ineligibility for Federal...

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ...TRANSPORTATION FEDERAL MOTOR CARRIER SAFETY REGULATIONS SAFETY FITNESS PROCEDURES General § 385.13 Unsatisfactory rated...carrier is making a good-faith effort to improve its safety fitness, FMCSA may allow the motor carrier to operate for up to...

  16. 49 CFR 385.13 - Unsatisfactory rated motor carriers; prohibition on transportation; ineligibility for Federal...

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ...TRANSPORTATION FEDERAL MOTOR CARRIER SAFETY REGULATIONS SAFETY FITNESS PROCEDURES General § 385.13 Unsatisfactory rated...carrier is making a good-faith effort to improve its safety fitness, FMCSA may allow the motor carrier to operate for up to...

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

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ...carriers for transportation to market” includes taking agricultural or horticultural commodities, dairy products, livestock, bees or their honey, fur-bearing animals or their pelts, and poultry to any carrier (including carriers by truck,...

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

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ...carriers for transportation to market” includes taking agricultural or horticultural commodities, dairy products, livestock, bees or their honey, fur-bearing animals or their pelts, and poultry to any carrier (including carriers by truck,...

  19. 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.

  20. 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

  1. Thermodynamic picture of ultrafast charge transport in graphene

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

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

  2. 9 CFR 91.18 - Cleaning and disinfection of transport carriers for export.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ...Animal Products 1 2012-01-01 2012-01-01 false Cleaning and disinfection of transport carriers for export. 91...EXPORTATION Inspection of Vessels and Accommodations § 91.18 Cleaning and disinfection of transport carriers for...

  3. 9 CFR 91.18 - Cleaning and disinfection of transport carriers for export.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ...Animal Products 1 2013-01-01 2013-01-01 false Cleaning and disinfection of transport carriers for export. 91...EXPORTATION Inspection of Vessels and Accommodations § 91.18 Cleaning and disinfection of transport carriers for...

  4. 9 CFR 91.18 - Cleaning and disinfection of transport carriers for export.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ...Animal Products 1 2014-01-01 2014-01-01 false Cleaning and disinfection of transport carriers for export. 91...EXPORTATION Inspection of Vessels and Accommodations § 91.18 Cleaning and disinfection of transport carriers for...

  5. 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

  6. 41 CFR 301-72.200 - Under what conditions may we authorize cash payments for procuring common carrier transportation...

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ...cash payments for procuring common carrier transportation services...Federal Travel Regulation System TEMPORARY DUTY (TDY...RESPONSIBILITIES RELATED TO COMMON CARRIER TRANSPORTATION Cash Payments for Procuring Common Carrier Transportation...

  7. 41 CFR 301-72.200 - Under what conditions may we authorize cash payments for procuring common carrier transportation...

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ...cash payments for procuring common carrier transportation services...Federal Travel Regulation System TEMPORARY DUTY (TDY...RESPONSIBILITIES RELATED TO COMMON CARRIER TRANSPORTATION Cash Payments for Procuring Common Carrier Transportation...

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

    NASA Astrophysics Data System (ADS)

    Nordvik, R.; Freund, F. T.

    2012-12-01

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

  9. Nanotubes in polar environments: Solvated charge carriers and their dynamics

    NASA Astrophysics Data System (ADS)

    Ussery, Geoffrey; Gartstein, Yuri

    2008-03-01

    Excess charge carriers on semiconducting nanotubes immersed in sluggish polar environments (such as common solvents) can undergo self-localization into polaronic states whose properties are profoundly different from the free band states. We explore such solvated states within the adiabatic continuum framework using a simplified picture of an electron or a hole confined to a cylindrical surface in the 3D polar medium. At the static level, the binding energy of a polaron is evaluated and found to be a sizable fraction (˜ 0.3) of the corresponding Wannier- Mott exciton binding energy, which is expected to substantially decrease the thermal activation energy for the exciton dissociation. We discuss the diffusion and mobility of polarons caused by the dielectric fluctuations of the medium and applied electric fields, as well as the local dielectric relaxation modes in the vicinity of the polaron. We also discuss the electronic (optical) transitions between the localized electronic states within a self-consistent potential well due to the orientational polarization pattern. [1] Yu.N. Gartstein, Phys. Lett. A 349, 377 (2006). [2] Yu.N. Gartstein, T.D. Bustamante, S. Ortega Castillo, J. Phys.: Cond. Matter 17, 156210 (2007).

  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. 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

  12. Identifying the charge carriers of the quark-gluon plasma.

    PubMed

    Pratt, Scott

    2012-05-25

    Charge correlations in lattice gauge calculations suggest that up, down, and strange charges move independently in the quark-gluon plasma, and that the density of such charges is similar to what is expected from simple thermal arguments. Here, we show how specific elements of the charge-charge correlation matrix in the quark-gluon plasma survive hadronization and become manifest in final-state charge-charge correlation measurements. PMID:23003245

  13. Identifying the Charge Carriers of the Quark-Gluon Plasma

    E-print Network

    Scott Pratt

    2012-03-20

    Charge correlations in lattice gauge calculations suggest that up, down and strange charges move independently in the QGP (quark-gluon plasma), and that the density of such charges is similar to what is expected from simple thermal arguments. Here, we show how specific elements of the charge-charge correlation matrix in the QGP survive hadronization and become manifest in final-state charge-charge correlation measurements.

  14. 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

  15. 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.

  16. 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

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

    PubMed

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

    2015-03-27

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

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. Effect of film nanostructure on in-plane charge transport in organic bulk heterojunction materials

    NASA Astrophysics Data System (ADS)

    Danielson, Eric; Ooi, Zi-En; Dodabalapur, Ananth

    2013-09-01

    Bulk heterojunction (BHJ) organic solar cells are a promising alternative energy technology, but a thorough understanding of charge transport behavior in BHJ materials is necessary in order to design devices with high power conversion efficiencies. Parameters such as carrier mobilities, carrier concentrations, and the recombination coefficient have traditionally been successfully measured using vertical structures similar to organic photovoltaic (OPV) cells. We have developed a lateral BHJ device which complements these vertical techniques by allowing spatially resolved measurement along the transport direction of charge carriers. This is essential for evaluating the effect of nanoscale structure and morphology on these important charge transport parameters. Nanomorphology in organic BHJ films has been controlled using a variety of methods, but the effect of these procedures has been infrequently correlated with the charge transport parameter of the BHJ material. Electron beam lithography has been used to create lateral device structures with many voltage probes at a sub-micron resolution throughout the device channel. By performing in-situ potentiometry, we can calculate both carrier mobilities and determine the effect of solvent choice and annealing procedure on the charge transport in BHJ system. Spin coated P3HT:PCBM films prepared from solutions in chloroform and o-xylene are characterized using this technique.

  3. Quantum dynamics in condensed phases : charge carrier mobility, decoherence, and excitation energy transfer

    E-print Network

    Cheng, Yuan-Chung, Ph. D. Massachusetts Institute of Technology

    2006-01-01

    In this thesis, we develop analytical models for quantum systems and perform theoretical investigations on several dynamical processes in condensed phases. First, we study charge-carrier mobilities in organic molecular ...

  4. 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

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

    PubMed

    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

  6. 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...

  7. 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.

  8. 41 CFR 301-72.1 - Why is common carrier presumed to be the most advantageous method of transportation?

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ...2010-07-01 false Why is common carrier presumed to be the... Federal Travel Regulation System TEMPORARY DUTY (TDY) TRAVEL...RESPONSIBILITIES RELATED TO COMMON CARRIER TRANSPORTATION Procurement of Common Carrier Transportation...

  9. 41 CFR 301-72.100 - What must my travel accounting system do in relation to common carrier transportation?

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ...must my travel accounting system do in relation to common carrier transportation...must my travel accounting system do in relation to common carrier transportation...authorization and claims accounting systems with common carrier...

  10. 41 CFR 301-72.100 - What must my travel accounting system do in relation to common carrier transportation?

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ...must my travel accounting system do in relation to common carrier transportation...must my travel accounting system do in relation to common carrier transportation...authorization and claims accounting systems with common carrier...

  11. 41 CFR 301-51.100 - What method of payment must I use to procure common carrier transportation?

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ...payment must I use to procure common carrier transportation? 301-51... Federal Travel Regulation System TEMPORARY DUTY (TDY) TRAVEL...TRAVEL EXPENSES Paying for Common Carrier Transportation § 301-51...payment must I use to procure common carrier...

  12. 41 CFR 301-51.100 - What method of payment must I use to procure common carrier transportation?

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ...payment must I use to procure common carrier transportation? 301-51... Federal Travel Regulation System TEMPORARY DUTY (TDY) TRAVEL...TRAVEL EXPENSES Paying for Common Carrier Transportation § 301-51...payment must I use to procure common carrier...

  13. 41 CFR 301-72.1 - Why is common carrier presumed to be the most advantageous method of transportation?

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ...2011-07-01 false Why is common carrier presumed to be the... Federal Travel Regulation System TEMPORARY DUTY (TDY) TRAVEL...RESPONSIBILITIES RELATED TO COMMON CARRIER TRANSPORTATION Procurement of Common Carrier Transportation...

  14. 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.

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

    NASA Astrophysics Data System (ADS)

    Brédas, Jean-Luc

    2007-03-01

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

  16. 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

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

    NASA Astrophysics Data System (ADS)

    Mendels, Dan; Tessler, Nir

    2015-03-01

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

  18. 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.

  19. Charge-carrier dynamics in benzoporphyrin films investigated by time-resolved terahertz spectroscopy

    NASA Astrophysics Data System (ADS)

    Ohta, Kaoru; Hiraoka, Sho; Tamura, Yuto; Yamada, Hiroko; Tominaga, Keisuke

    2015-11-01

    We investigated charge-carrier dynamics in benzoporphyrin (BP) and BP-based bulk heterojunction (BHJ) films with optical pump-broadband terahertz (THz) probe spectroscopy. In both samples, we observed instantaneous appearance of transient THz signals, which are attributed to mobile charge carriers that are much lower in transition energy than excitons. These carriers recombine and/or trap at defect sites within a few ps. In the BP-based BHJ films, the decay dynamics of transient THz signals was faster relative to that in the BP films. In contrast to the BP films, approximately 10% of the transient signal does not decay within 35 ps, indicating survival of free charge carriers.

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

    PubMed

    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

    2015-06-19

    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. PMID:26196985

  1. PUBLISHED ONLINE: 22 AUGUST 2010 | DOI: 10.1038/NPHYS1745 Visualization of charge transport through Landau

    E-print Network

    Loss, Daniel

    and scattering1 . Recent progress in understanding such effects in low-dimensional carrier gases in conventional in the physics of the quantum Hall effect (QHE) by constraining the pathways for charge-carrier transport semiconductors has been achieved by real- space mapping using local probes2,3 . Here, we use spatially resolved

  2. Carrier injection and transport in organic field-effect transistors

    NASA Astrophysics Data System (ADS)

    Moon, Hyunsik

    2005-07-01

    The performance of organic field-effect transistors (OFETs) is determined by both carrier injection and transport in organic semiconductors. To improve injection in bottom contact OFET devices, self-assembled monolayers (SAMs) of octadecanethiol (ODT), 2-mercapto-benzothiazole (BZT), or 5-mercapto-2,2 '-bithienyl (BTT) were made on Au electrodes, followed by evaporation of pentacene. The devices with the SAMs showed better transistor performance, and apparent carrier mobility in the devices with electron-rich BTT SAMs was 10 times higher than in the devices without SAMs. BTT SAM devices were also better than ODT and BZT SAM devices. This increased performance is attributed to a combination of better adhesion between pentacene and the electrodes and to matching the energy levels of the BTT SAMs to the semiconducting pentacene. Novel organic semiconductors with a pi-stacked structure were synthesized to understand structural and transport properties of pi-stacked materials. Variable-temperature X-ray diffraction patterns showed that a cooligomer of 4,4'-dinonyl-2,2'-bithiazole and 3,4-ethylenedioxythiophene (NTZN) had a crystal-crystal transition at 110°C. Variable-temperature UV-Vis spectra showed that NTZN had less exciton coupling in the high temperature phase as shown by loss of fine structure. A mobility of 5,11-dichlorotetracene was measured to be as high as 1.6 cm2/V·s in single-crystal transistors. The pi-stacked structure, which provides more efficient orbital overlap and thereby facilitates carrier transport, is responsible for this high mobility. On the other hand, the mobility in thin-film devices is affected by film morphology. Oligofluorene-thiophene derivatives with dodecyl side chains were prepared to study the effect of the side chains on the film morphology. The interactions between the side chains promote two-dimensional crystal growth, leading to large and well-interconnected grains. Poly(phenyleneethynylene) with end-capping thiol groups (PPE-SH) was synthesized to explore 'intra'molecular transport in one molecular wire, which is connected between two electrodes. PPE-SH was self-assembled onto a device with nano-gap Au structures. SEM images of the device before and after the self assembly showed that polymer chains lay flat on the Au electrodes. This may be due to highly polarizable pi electron clouds of conjugated cores, which substantially induce dispersion force attraction towards polarizable Au surfaces.

  3. 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.

  4. 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 ~10–100?K/nm. PMID:24056703

  5. Carriers

    MedlinePLUS

    ... has been caused by a single carrier. Carrier Testing A DNA test is the only way to detect carrier status. The DNA test is simple procedure, based on a small blood draw. In the ... genetic testing is highly personal, and we strongly recommend discussing ...

  6. 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.

  7. 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

  8. 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.

  9. Effect of Molecular Orientation, on Photovoltaic Efficiency and Carrier Transport, in a New Semiconducting Polymer

    NASA Astrophysics Data System (ADS)

    Kažukauskas, V.; Pranaitis, M.; Sentein, C.; Rocha, L.; Raimond, P.; Duyssens, I.; van, I.; Severen; Lutsen, L.; Cleij, T.; Vanderzande, D.

    2008-03-01

    New functionalized soluble poly(p-phenylene vinylene) derivative bearing polar molecules was designed and synthesized in order to investigate effects of molecular orientation in polymer photovoltaic devices. The active polar molecule is the 4-(N-butyl-N-2-hydroxyethyl)-1- nitro-benzene group. The grafting of the push-pull molecule with a donor/transmitter/acceptor structure, possessing a large ground state dipole moment, enables the molecular orientation by a dc electric field. An internal electric field stored in such system facilitates exciton dissociation and improves charge transport in single-layer devices. In our systems an increase in the external quantum efficiency by a factor of about 1.5 to 2 is estimated. The associated effects of orientation on the carrier injection and transport properties were evidenced.

  10. 77 FR 42548 - Privacy Act of 1974; Department of Transportation, Federal Motor Carrier Safety Administration...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-07-19

    ...DEPARTMENT OF TRANSPORTATION Federal Motor Carrier Safety Administration...industry service providers and motor carriers as part of the operator-applicant's...industry service providers and motor carriers may use PSP records...Electronic records may be stored on magnetic disc, tape, digital...

  11. 49 CFR 385.13 - Unsatisfactory rated motor carriers; prohibition on transportation; ineligibility for Federal...

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... carriers, including their most current safety rating, is available from the FMCSA on the Internet at http...” safety rating becomes final, FMCSA will issue an order placing out of service the motor carrier's... Regulations Relating to Transportation (Continued) FEDERAL MOTOR CARRIER SAFETY ADMINISTRATION, DEPARTMENT...

  12. Measurement of charge transport through organic semiconducting devices

    NASA Astrophysics Data System (ADS)

    Klenkler, Richard A.

    2007-12-01

    In this thesis, two important and unexplored areas of organic semiconductor device physics are investigated: The first area involves determining the effect of energy barriers and intermixing at the interfaces between hole transport layers (HTLs). This effect was discerned by first establishing a method of pressure-laminating successive solution coated HTLs to gether. It was found that in the range of 0.8--3.0 MPa a pressure-laminated interface between two identical HTLs causes no measurable perturbation to charge transport. By this method, 2 different HTLs can be sandwiched together to create a discrete interface, and by inserting a mixed HTL in the middle an intermixed interface between the 2 HTLs can be simulated. With these sandwiched devices, charge injection across discrete versus intermixed interfaces were compared using time-of-flight measurements. For the hole transport materials investigated, no perturbation to the overall charge transport was observed with the discrete interface, however in contrast the rate of charge transport was clearly reduced through the intermixed interface. The second area that was investigated pertains to the development of a bulk mobility measurement technique that has a higher resolution than existing methods. The approach that was used involved decoupling the charge carrier transient signal from the device charging circuit. With this approach, the RC time constant constraint that limits the resolution of existing methods is eliminated. The resulting method, termed the photoinduced electroluminescence (EL) mobility measurement technique, was then used to compare the electron mobility of the metal chelate, AlQ3 to that of the novel triazine material, BTB. Results showed that BTB demonstrated an order of magnitude higher mobility than AlQ3. Overall, these findings have broad implications regarding device design. The pressure-lamination method could be used, e.g., as a diagnostic tool to help in the design of multilayer xerographic photoreceptors, such as those that include an abrasion resistant overcoat. Further, the photoinduced EL technique could be use as a tool to help characterize charge flow and balance in organic light emitting devices amongst others.

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

    PubMed

    Hnida, Katarzyna E; Bä?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

  14. 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 ?m. 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

  15. 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.

  16. 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.

  17. Coupling of carriers injection and charges distribution in Schottky barrier charge-trapping memories using source-side electrons programming

    NASA Astrophysics Data System (ADS)

    Luo, Yan-Xiang; Shih, Chun-Hsing

    2014-11-01

    This study elucidates the coupling of Schottky barriers and trapped charges involved in the source-side electrons programming and two-bit/cell reading of the Schottky barrier charge-trapping cells. Two-dimensional numerical iterations were employed to examine the distribution of electron injections and trapped charges, and to discuss the differences of physical mechanisms between the Schottky barrier and conventional cells. In the Schottky barrier cells, both the conduction and injection of electron carriers depend on the Schottky source barrier lowering. The source-side trapped charges alter the source-side lateral field distribution, reducing the maximum of the lateral electric field, and moving the subsequent injections away from the source edge. The distribution of total trapped-charges is considerably wider than that of the initial injection. However, because of source-side conduction, the excellent screening of second-bit effect is beneficial to operate the NOR-type multibit/cell charge-trapping memories.

  18. 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...

  19. Transport in charged colloids driven by thermoelectricity.

    PubMed

    Würger, Alois

    2008-09-01

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

  20. Transport in Charged Colloids Driven by Thermoelectricity

    E-print Network

    Alois Würger

    2014-01-29

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

  1. 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.

  2. 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

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

    PubMed

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

    2014-06-11

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

  4. Recombination in liquid filled ionisation chambers with multiple charge carrier species: Theoretical and numerical results

    NASA Astrophysics Data System (ADS)

    Aguiar, P.; González-Castaño, D. M.; Gómez, F.; Pardo-Montero, J.

    2014-10-01

    Liquid-filled ionisation chambers (LICs) are used in radiotherapy for dosimetry and quality assurance. Volume recombination can be quite important in LICs for moderate dose rates, causing non-linearities in the dose rate response of these detectors, and needs to be corrected for. This effect is usually described with Greening and Boag models for continuous and pulsed radiation respectively. Such models assume that the charge is carried by two different species, positive and negative ions, each of those species with a given mobility. However, LICs operating in non-ultrapure mode can contain different types of electronegative impurities with different mobilities, thus increasing the number of different charge carriers. If this is the case, Greening and Boag models can be no longer valid and need to be reformulated. In this work we present a theoretical and numerical study of volume recombination in parallel-plate LICs with multiple charge carrier species, extending Boag and Greening models. Results from a recent publication that reported three different mobilities in an isooctane-filled LIC have been used to study the effect of extra carrier species on recombination. We have found that in pulsed beams the inclusion of extra mobilities does not affect volume recombination much, a behaviour that was expected because Boag formula for charge collection efficiency does not depend on the mobilities of the charge carriers if the Debye relationship between mobilities and recombination constant holds. This is not the case in continuous radiation, where the presence of extra charge carrier species significantly affects the amount of volume recombination.

  5. 49 CFR 1139.21 - Study carriers.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 49 Transportation 8 2010-10-01 2010-10-01 false Study carriers. 1139.21 Section 1139.21... Industry § 1139.21 Study carriers. (a) For the purposes of this proceeding the “study carriers” shall... and/or charges. (b) To corroborate the selection of the above study carriers, and to provide a...

  6. 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.

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

    PubMed Central

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

    2014-01-01

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

  8. 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...

  9. Proton Conduction in Bio-macromolecules The Search for the Dominant Charge Carrier within Melanin

    E-print Network

    Powell, Ben

    Proton Conduction in Bio-macromolecules The Search for the Dominant Charge Carrier within Melanin A electro-polymerized melanin and teaching me the ropes in obtaining conductivity data. When I was running out of melanin sample, Dr.Indu Mahadevan provided me with auto- oxidised melanin samples, she also

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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 (?PS). ?PS increases exponentially with P%. Values of ?PS as high as 1 × 109 ? cm at room temperature were obtained once P% exceeds 60%. ?PS was found to be thermally activated, in particular, when the temperature increases from 30 to 200 °C, a decrease of three decades is observed on ?PS. 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.

  15. 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.

  16. Light-Induced Charge Transport within a Single Asymmetric Nanowire

    SciTech Connect

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

    2011-01-21

    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 photo-generated electrons and holes within a single asymmetric Si/TiO2 nanowire using Kelvin probe force microscopy (KPFM). Under UV illumination, higher surface potential was observed on the n-TiO? side, relative to the potential of the p-Si side, as a result of majority carriers’ recombination at the Si/TiO? 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.

  17. 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.

  18. 41 CFR 301-72.2 - May we utilize methods of transportation other than common carrier (e.g., POVs, chartered...

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ...of transportation other than common carrier (e.g., POVs... Federal Travel Regulation System TEMPORARY DUTY (TDY) TRAVEL...RESPONSIBILITIES RELATED TO COMMON CARRIER TRANSPORTATION Procurement of Common Carrier Transportation...

  19. 41 CFR 301-72.2 - May we utilize methods of transportation other than common carrier (e.g., POVs, chartered...

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ...of transportation other than common carrier (e.g., POVs... Federal Travel Regulation System TEMPORARY DUTY (TDY) TRAVEL...RESPONSIBILITIES RELATED TO COMMON CARRIER TRANSPORTATION Procurement of Common Carrier Transportation...

  20. 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 fa

  1. 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.

  2. 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.

  3. 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

  4. 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

  5. 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.

  6. 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

    ...Mitigation of Carrier Fines for Transporting Aliens Without Proper Documents; Modification...that transports to the United States an alien who does not have a valid passport and...applicable law, is subject to a fine for each alien transported lacking the required...

  7. Ambipolar blends of CuPc and C60: charge carrier mobility, electronic structure and its implications for solar cell applications

    E-print Network

    W. Bruetting; M. Bronner; M. Goetzenbrugger; A. Opitz

    2007-09-25

    Ambipolar transport has been realised in blends of the molecular hole conductor Cu-phthalocyanine (CuPc) and the electron conducting fullerene C60. Charge carrier mobilities and the occupied electronic levels have been analyzed as a function of the mixing ratio using field-effect transistor measurements and photoelectron spectroscopy. These results are discussed in the context of photovoltaic cells based on these materials.

  8. 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

  9. 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 themselv

  10. Hot Carrier Transport and Photocurrent Response in Graphene

    E-print Network

    Song, Justin Chien Wen

    Strong electron–electron interactions in graphene are expected to result in multiple-excitation generation by the absorption of a single photon. We show that the impact of carrier multiplication on photocurrent response ...

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

    SciTech Connect

    Vukmirovic, Nenad; Wang, Lin-Wang

    2009-11-10

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

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

    PubMed

    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

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

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

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

  14. 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

  15. 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

  16. 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.

  17. 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

  18. 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.

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

    NASA Astrophysics Data System (ADS)

    Kandyba, Viktor; Yablonskikh, Mikhail; Barinov, Alexei

    2015-11-01

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

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

    PubMed

    Kandyba, Viktor; Yablonskikh, Mikhail; Barinov, Alexei

    2015-01-01

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

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

    PubMed Central

    Kandyba, Viktor; Yablonskikh, Mikhail; Barinov, Alexei

    2015-01-01

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

  2. 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.

  3. Electrical detection of ambipolar acoustic carrier transport by surface acoustic waves

    NASA Astrophysics Data System (ADS)

    Jiao, S. J.; Batista, P. D.; Biermann, K.; Hey, R.; Santos, P. V.

    2009-09-01

    We have investigated the efficiency of the ambipolar transport of photogenerated electrons and holes in (Al,Ga)As structures by surface acoustic waves (SAWs). In the experiments, the photogenerated electrons and holes transported by the SAW are collected by a lateral p-i-n junction and detected by electrometers. Carrier recombination during transport was also studied by detecting the photoluminescence emitted along the SAW path by the transported carriers. We show that the acoustic transport efficiency improves by using biased metallic guides along the SAW beam to create independent transport channels for electrons and holes. By optimizing the photon absorption efficiency and the amplitude of the acoustic fields, we demonstrated overall transport efficiencies above 85% for transport lengths on the order of 300 ?m.

  4. Hot carrier diffusion in graphene

    E-print Network

    Ruzicka, Brian Andrew; Wang, Shuai; Werake, Lalani Kumari; Weintrub, Ben; Loh, Kian Ping; Zhao, Hui

    2010-11-01

    We report an optical study of charge transport in graphene. Diffusion of hot carriers in epitaxial graphene and reduced graphene oxide samples are studied using an ultrafast pump-probe technique with a high spatial resolution. ...

  5. 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 ?(r), which can be probed in the spin-transport experiments with spin-polarized electrodes. We also demonstrate that, while ?(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

  6. 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 ?(r), which can be probed in the spin-transport experiments with spin-polarized electrodes. We also demonstrate that, while ?(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.

  7. Hyperfine-induced spin relaxation of a diffusively moving carrier in low dimensions: Implications for spin transport in organic semiconductors

    NASA Astrophysics Data System (ADS)

    Mkhitaryan, V. V.; Dobrovitski, V. V.

    2015-08-01

    The hyperfine coupling between the spin of a charge carrier and the nuclear spin bath is a predominant channel for the carrier spin relaxation in many organic semiconductors. We theoretically investigate the hyperfine-induced spin relaxation of a carrier performing a random walk on a d -dimensional regular lattice, in a transport regime typical for organic semiconductors. We show that in d =1 and 2, the time dependence of the space-integrated spin polarization P (t ) is dominated by a superexponential decay, crossing over to a stretched-exponential tail at long times. The faster decay is attributed to multiple self-intersections (returns) of the random-walk trajectories, which occur more often in lower dimensions. We also show, analytically and numerically, that the returns lead to sensitivity of P (t ) to external electric and magnetic fields, and this sensitivity strongly depends on dimensionality of the system (d =1 versus d =3 ). Furthermore, we investigate in detail the coordinate dependence of the time-integrated spin polarization ? (r ) , which can be probed in the spin-transport experiments with spin-polarized electrodes. We demonstrate that, while ? (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.

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

    PubMed

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

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

    PubMed Central

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

    2015-01-01

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

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

    PubMed

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

    2015-03-16

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

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

    PubMed

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

    2015-01-01

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

  13. Charge transport gap in graphene antidot lattices

    NASA Astrophysics Data System (ADS)

    Giesbers, A. J. M.; Peters, E. C.; Burghard, M.; Kern, K.

    2012-07-01

    Graphene antidot lattices (GALs) offer an attractive approach to band-gap engineering in graphene. Theoretical studies indicate that the size of the opened gap is sensitive to the shape, size, and architecture of the nanoholes introduced into the graphene sheet. We have investigated the temperature-dependent electrical conductivity of GALs comprising 50-nm-diameter nanoholes with a pitch of 80, 100, and 200 nm, respectively. The data reveal the presence of localized states within a transport gap, whose interactions lead to a soft Coulomb gap and associated Efros-Shklovskii variable range hopping (ES-VRH). This conduction type is preserved upon application of magnetic fields up to 1 Tesla, above which a transition to Mott variable range hopping occurs. Such a crossover can alternatively be introduced at zero magnetic fields by increasing either the nanohole spacing or the gate-controlled carrier concentration. Furthermore, at intermediate magnetic fields, the hopping exponent assumes a value of 2/3, as predicted by percolation theory for ES-VRH under this condition.

  14. Charge-carrier transport in amorphous organic semiconductors

    E-print Network

    Limketkai, Benjie, 1982-

    2008-01-01

    Since the first reports of efficient luminescence and absorption in organic semiconductors, organic light-emitting devices (OLEDs) and photovoltaics (OPVs) have attracted increasing interest. Organic semiconductors have ...

  15. 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 ?m 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

  16. Spatial and temporal imaging of long-range charge transport in perovskite thin films by ultrafast microscopy

    NASA Astrophysics Data System (ADS)

    Guo, Zhi; Manser, Joseph S.; Wan, Yan; Kamat, Prashant V.; Huang, Libai

    2015-06-01

    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 ?m 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.

  17. Surface group modification and carrier transport properties of layered transition metal carbides (Ti2CTx, T: -OH, -F and -O).

    PubMed

    Lai, Shen; Jeon, Jaeho; Jang, Sung Kyu; Xu, Jiao; Choi, Young Jin; Park, Jin-Hong; Hwang, Euyheon; Lee, Sungjoo

    2015-12-14

    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 10(4) cm(2) 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. PMID:26535782

  18. 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.

  19. Aspects of charge recombination and charge transport in organic solar cells and light-emitting devices

    E-print Network

    Difley, Seth

    2010-01-01

    In this thesis, aspects of charge reconbination and charge transport in organic solar cells and light-emitting devices are presented. These devices show promise relative to traditional inorganic semiconductors. We show ...

  20. Selective Monosaccharide Transport through Lipid Bilayers Using Boronic Acid Carriers

    E-print Network

    Smith, Bradley D.

    potential, and temperature. Overall, the evidence is strongly in favor of a membrane carrier mechanism, such as glucose, across cell membranes is a ubiquitous cellular activity. A typical human red cell, for example, as well as systematic investigations of various environmental changes such as pH, added salt, membrane

  1. Molecular ferries: membrane carriers that promote phospholipid flip-flop and chloride transport

    E-print Network

    Smith, Bradley D.

    Molecular ferries: membrane carriers that promote phospholipid flip-flop and chloride transport with affinities for anions are shown to act as molecular ferries and facilitate the movement of chloride ions and salts across vesicle and cell membranes. A process that competes with chloride transport is phospholipid

  2. 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.

  3. 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...

  4. 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...

  5. 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.

  6. 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

  7. 41 CFR 302-10.402 - What costs must we pay a commercial carrier for transporting a mobile home?

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ...a commercial carrier for transporting a mobile home? 302-10.402 Section 302-10... 10-ALLOWANCES FOR TRANSPORTATION OF MOBILE HOMES AND BOATS USED AS A PRIMARY RESIDENCE...a commercial carrier for transporting a mobile home? The costs you must pay a...

  8. 41 CFR 302-10.402 - What costs must we pay a commercial carrier for transporting a mobile home?

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... commercial carrier for transporting a mobile home? 302-10.402 Section 302-10.402 Public Contracts and... PROPERTY 10-ALLOWANCES FOR TRANSPORTATION OF MOBILE HOMES AND BOATS USED AS A PRIMARY RESIDENCE Agency Responsibilities § 302-10.402 What costs must we pay a commercial carrier for transporting a mobile home? The...

  9. 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.

  10. Models of long-distance transport: how is carrier-dependent auxin transport regulated in the stem?

    PubMed

    Renton, Michael; Hanan, Jim; Ferguson, Brett J; Beveridge, Christine A

    2012-05-01

    • This paper presents two models of carrier-dependent long-distance auxin transport in stems that represent the process at different scales. • A simple compartment model using a single constant auxin transfer rate produced similar data to those observed in biological experiments. The effects of different underlying biological assumptions were tested in a more detailed model representing cellular and intracellular processes that enabled discussion of different patterns of carrier-dependent auxin transport and signalling. • The output that best fits the biological data is produced by a model where polar auxin transport is not limited by the number of transporters/carriers and hence supports biological data showing that stems have considerable excess capacity to transport auxin. • All results support the conclusion that auxin depletion following apical decapitation in pea (Pisum sativum) occurs too slowly to be the initial cause of bud outgrowth. Consequently, changes in auxin content in the main stem and changes in polar auxin transport/carrier abundance in the main stem are not correlated with axillary bud outgrowth. PMID:22443265

  11. 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

  12. 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.

  13. 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.

  14. 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.

  15. Ultrafast Carrier Relaxation in InN Nanowires Grown by Reactive Vapor Transport

    PubMed Central

    2009-01-01

    We have studied femtosecond carrier dynamics in InN nanowires grown by reactive vapor transport. Transient differential absorption measurements have been employed to investigate the relaxation dynamics of photogenerated carriers near and above the optical absorption edge of InN NWs where an interplay of state filling, photoinduced absorption, and band-gap renormalization have been observed. The interface between states filled by free carriers intrinsic to the InN NWs and empty states has been determined to be at 1.35 eV using CW optical transmission measurements. Transient absorption measurements determined the absorption edge at higher energy due to the additional injected photogenerated carriers following femtosecond pulse excitation. The non-degenerate white light pump-probe measurements revealed that relaxation of the photogenerated carriers occurs on a single picosecond timescale which appears to be carrier density dependent. This fast relaxation is attributed to the capture of the photogenerated carriers by defect/surface related states. Furthermore, intensity dependent measurements revealed fast energy transfer from the hot photogenerated carriers to the lattice with the onset of increased temperature occurring at approximately 2 ps after pulse excitation.

  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. 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. Current–voltage (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

  18. 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.

  19. 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

  20. Photon-induced carrier transport in high efficiency midinfrared quantum cascade lasers

    E-print Network

    Mátyás, Alpár; Jirauschek, Christian; 10.1063/1.3608116

    2011-01-01

    A midinfrared quantum cascade laser with high wall-plug efficiency is analyzed by means of an ensemble Monte Carlo method. Both the carrier transport and the cavity field dynamics are included in the simulation, offering a self-consistent approach for analyzing and optimizing the laser operation. It is shown that at low temperatures, photon emission and absorption can govern the carrier transport in such devices. Furthermore, we find that photon-induced scattering can strongly affect the kinetic electron distributions within the subbands. Our results are validated against available experimental data.

  1. 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?k? for monolayer and 420 ? 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??F/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

  2. Charge transport in ion-gated mono-, bi-, and trilayer MoS2 field effect transistors

    NASA Astrophysics Data System (ADS)

    Chu, Leiqiang; Schmidt, Hennrik; Pu, Jiang; Wang, Shunfeng; Özyilmaz, Barbaros; Takenobu, Taishi; Eda, Goki

    2014-12-01

    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 k? for monolayer and 420 ? 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 ?F/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.

  3. Charge transport in ion-gated mono-, bi-, and trilayer MoS2 field effect transistors.

    PubMed

    Chu, Leiqiang; Schmidt, Hennrik; Pu, Jiang; Wang, Shunfeng; Ozyilmaz, 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 (>10(13) cm(-2)) densities. We discuss the gating properties of the devices as a function of layer thickness and demonstrate resistivities as low as 1 k? for monolayer and 420 ? 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 ?F/cm(2) 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

  4. BALLISTIC CARRIER TRANSPORT IN SEMICONDUCTORS STUDIED BY ULTRAFAST LASER TECHNIQUES

    E-print Network

    Werake, Lalani Kumari

    2011-08-31

    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...

  5. Survey of microwave surface impedance data of high-Tc superconductors - Evidence for nonpairing charge carriers

    NASA Astrophysics Data System (ADS)

    Mueller, G.; Klein, N.; Brust, A.; Chaloupka, H.; Hein, M.

    1990-09-01

    The microwave surface impedance of the high-Tc oxide superconductors has been measured at many laboratories around the world. A survey of their data between 100 MHz and 150 GHz for polycrystalline as well as single crystalline samples is given, focusing on YBa2Cu3O(7-delta). In comparison to the classical superconductors, these results reveal a very similar temperature dependence of the surface impedance close to Tc but an anomalous high residual surface resistance at lower temperatures. Both features can be explained by the assumption that oxide superconductors contain a significant number of nonpairing charge carriers. Within the framework of a properly extended two-fluid model, this is shown by analysis of best thin-film data. Moreover, the enhanced losses in polycrystalline material, especially for superposed magnetostatic field, result, to a large extent, from the deeper penetration depth. The possible origin of the nonpairing charge carriers and their impact on the applicability of the oxide superconductors is briefly discussed.

  6. 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.

  7. 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 .

  8. 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}.

  9. 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

  10. Measurement and modeling of ultrafast carrier dynamics and transport in germanium/silicon-

    E-print Network

    Miller, David A. B.

    Measurement and modeling of ultrafast carrier dynamics and transport in germanium/silicon- germanium quantum wells Stephanie A. Claussen,1,3,* Emel Tasyurek,1,3 Jonathan E. Roth, 1,2 and David A. B. S. Harris, and D. A. B. Miller, Optical modulator on silicon employing germanium quantum wells, Opt

  11. 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...

  12. Carrier Transport and Related Effects in Detectors of the Cryogenic Dark Matter Kyle Michael Sundqvist

    E-print Network

    California at Berkeley, University of

    Carrier Transport and Related Effects in Detectors of the Cryogenic Dark Matter Search by Kyle of Doctor of Philosophy in Physics and the Designated Emphasis in Nanoscale Science and Engineering Effects in Detectors of the Cryogenic Dark Matter Search Copyright 2012 by Kyle Michael Sundqvist #12

  13. 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.

  14. 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.

  15. Electron spin resonance of charge carriers in chlorophyll a/water micelles

    SciTech Connect

    Bowman, M.K.; Michalski, T.J.; Tyson, R.L.; Worcester, D.L.; Katz, J.J.

    1988-03-01

    Chlorophyll a/water micelles (P740) prepared in hydrocarbon media have been shown by small-angle neutron scattering to consist of hollow cylinders whose surface is formed of a monolayer of chlorophyll crosslinked by water. The micelles can be reversibly oxidized or reduced to generate highly mobile holes or electrons that undergo rapid, one-dimensional transport along the chains of chlorophyll macrocycles comprising the surface of the micelles. Large ..pi..-..pi.. overlap within the chains facilitates the one-dimensional charge transport and is expected to do the same for energy transport. Structural defects in the micelle surface act as boundaries for charge transport, confining the spins to one-dimensional domains of approximately 200 macrocycles. The one-dimensional transport within the limited domains results in motionally narrowed electron spin resonance lines with some residual inhomogeneous broadening. Although the chlorophyll a incorporated in micelles is more easily oxidized than is monomeric chlorophyll a, it is much more resistant to chemical alteration.

  16. Frequency dependent magneto-transport in charge transfer Co(II) complex

    NASA Astrophysics Data System (ADS)

    Shaw, Bikash Kumar; Saha, Shyamal K.

    2014-09-01

    A charge transfer chelated system containing ferromagnetic metal centers is the ideal system to investigate the magneto-transport and magneto-dielectric effects due to the presence of both electronic as well as magnetic properties and their coupling. Magneto-transport properties in materials are usually studied through dc charge transport under magnetic field. As frequency dependent conductivity is an essential tool to understand the nature of carrier wave, its spatial extension and their mutual interaction, in the present work, we have investigated frequency dependent magneto-transport along with magnetization behavior in [Co2(II)-(5-(4-PhMe)-1,3,4-oxadiazole-H+-2-thiolate)5](OAc)4 metal complex to elucidate the nature of above quantities and their response under magnetic field in the transport property. We have used the existing model for ac conduction incorporating the field dependence to explain the frequency dependent magneto-transport. It is seen that the frequency dependent magneto-transport could be well explained using the existing model for ac conduction.

  17. 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.

  18. Charge Transport in Proteins Probed by Resonant Photoemission

    NASA Astrophysics Data System (ADS)

    Vyalikh, D. V.; Maslyuk, V. V.; Blüher, A.; Kade, A.; Kummer, K.; Dedkov, Yu. S.; Bredow, T.; Mertig, I.; Mertig, M.; Molodtsov, S. L.

    2009-03-01

    The degrees of charge localization in the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) of the bacterial surface layer protein of Bacillus sphaericus NCTC 9602 were studied by resonant photoemission. In agreement with a charge transport hopping mechanism that involves torsional motions of the peptide backbone, the lifetime of electrons excited into the LUMO was found to be ˜100fs.

  19. Field-modulated carrier transport in carbon nanotube transistors.

    PubMed

    Appenzeller, J; Knoch, J; Derycke, V; Martel, R; Wind, S; Avouris, Ph

    2002-09-16

    We have investigated the electrical transport properties of carbon nanotube field-effect transistors as a function of channel length, gate dielectric film thickness, and dielectric material. Our experiments show that the bulk properties of the semiconducting carbon nanotubes do not limit the current flow through the metal/nanotube/metal system. Instead, our results can be understood in the framework of gate and source-drain field induced modulation of the nanotube band structure at the source contact. The existence of one-dimensional Schottky barriers at the metal/nanotube interface determines the device performance and results in an unexpected scaling behavior. PMID:12225112

  20. 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.

  1. Effect of atmospheric-air pressure on charge transport in structures with oxidized porous silicon

    SciTech Connect

    Bilenko, D. I. Belobrovaya, O. Ya.; Zharkova, E. A.; Terin, D. V.; Khasina, E. I.

    2007-08-15

    The electron-transport processes in structures with oxidized porous silicon (OPS) are investigated during adsorption and desorption of polar molecules from atmosphere when the air pressure varies. It is shown that the cause of the existence of the open-circuit voltage in Pd-OPS-p{sup +}-Si-Al structures in the initial state is the surface-charge change on the Pd-OPS interface due to the polar-molecule adsorption from atmospheric air. The desorption of atmospheric-air molecules leads to a change in the current-voltage characteristics of structures, growth of the metal-OPS barrier in samples with the Schottky barrier, and initiation of current instabilities. The nanocrystalline nature of OPS manifests itself in the charge-carrier localization in quantum dots (QDs) during desorption in samples with space-charge-limited currents.

  2. Carrier transport in Bi2Se3 topological insulator slab

    NASA Astrophysics Data System (ADS)

    Gupta, Gaurav; Lin, Hsin; Bansil, Arun; Jalil, Mansoor Bin Abdul; Liang, Gengchiau

    2015-11-01

    Electron transport in Bi2Se3 topological insulator slabs is investigated in the thermal activation regime (>50 K) both in the absence (ballistic) and presence of weak and strong acoustic phonon scattering using the non-equilibrium Green function approach. Resistance of the slab is simulated as a function of temperature for a range of slab thicknesses and effective doping in order to gain a handle on how various factors interact and compete to determine the overall resistance of the slab. If the Bi2Se3 slab is biased at the Dirac point, resistance is found to display an insulating trend even for strong electron-phonon coupling strength. However, when the Fermi-level lies close to the bulk conduction band (heavy electron doping), phonon scattering can dominate and result in a metallic behavior, although the insulating trend is retained in the limit of ballistic transport. Depending on values of the operating parameters, the temperature dependence of the slab is found to exhibit a remarkably complex behavior, which ranges from insulating to metallic, and includes cases where the resistance exhibits a local maximum, much like the contradictory behaviors seen experimentally in various experiments.

  3. 49 CFR 369.2 - Classification of carriers-motor carriers of property, household goods carriers, and dual...

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... false Classification of carriers-motor carriers of property, household goods...Transportation (Continued) FEDERAL MOTOR CARRIER SAFETY ADMINISTRATION, DEPARTMENT OF TRANSPORTATION FEDERAL MOTOR CARRIER SAFETY REGULATIONS...

  4. 49 CFR 369.2 - Classification of carriers-motor carriers of property, household goods carriers, and dual...

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... false Classification of carriers-motor carriers of property, household goods...Transportation (Continued) FEDERAL MOTOR CARRIER SAFETY ADMINISTRATION, DEPARTMENT OF TRANSPORTATION FEDERAL MOTOR CARRIER SAFETY REGULATIONS...

  5. 49 CFR 369.2 - Classification of carriers-motor carriers of property, household goods carriers, and dual...

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... false Classification of carriers-motor carriers of property, household goods...Transportation (Continued) FEDERAL MOTOR CARRIER SAFETY ADMINISTRATION, DEPARTMENT OF TRANSPORTATION FEDERAL MOTOR CARRIER SAFETY REGULATIONS...

  6. 49 CFR 369.2 - Classification of carriers-motor carriers of property, household goods carriers, and dual...

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... false Classification of carriers-motor carriers of property, household goods...Transportation (Continued) FEDERAL MOTOR CARRIER SAFETY ADMINISTRATION, DEPARTMENT OF TRANSPORTATION FEDERAL MOTOR CARRIER SAFETY REGULATIONS...

  7. Charge transport by holographic Fermi surfaces

    E-print Network

    Faulkner, Thomas

    We compute the contribution to the conductivity from holographic Fermi surfaces obtained from probe fermions in an AdS charged black hole. This requires calculating a certain part of the one-loop correction to a vector ...

  8. High-pressure thermoelectric characteristics of Bi2Te3 semiconductor with different charge carrier densities

    NASA Astrophysics Data System (ADS)

    Brazhkin, V. V.; Orlov, A. I.

    2014-05-01

    The measurements of the absolute values of the thermopower and of the relative electrical resistance have been performed for n type Bi2Te3 under hydrostatic pressure up to 9 GPa at room temperature. Under pressures exceeding 5 GPa and up to the phase transition (at 7 GPa), the samples with the charge carrier density below 10-19 cm-3 exhibit an anomalous growth of the thermopower. For the purest sample ( n = 10-18 cm-3), the thermopower is as high as +150 ?V/K. The pressure dependence of the electrical resistance for n-Bi2Te3 does not exhibit any anomalies up to the pressure corresponding to the phase transition (7 GPa). Thus, the state with the giant thermoelectric efficiency is found in Bi2Te3 under pressure before the phase transition.

  9. 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

  10. 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.

  11. 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

  12. 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

  13. 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...

  14. Analysis of Carrier Transport of Organic Devices by Using Nonlinear Optical Polarization.

    PubMed

    Lim, Eunju; Iwamoto, Mitsumasa

    2015-03-01

    In this review, we discuss the Maxwell-Wagner (MW) effect model analysis of organic devices and time-resolved optical second harmonic generation (TR-EFISHG) measurement that is available for directly probing carrier motion in organic semiconductor devices. Using these, we show that organic field effect transistor as well organic double-layer device operation is analyzed well, and we can make clear the mechanism of these organic devices' operation. Finally, we conclude that the dielectric physics approach using the MW model analysis and the TR-EFISHG experiment is useful to study carrier transport mechanism of organic devices. PMID:26413610

  15. 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

  16. 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.

  17. Simulation of charge transport in pixelated CdTe

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    The Voxel Imaging PET (VIP) Pathfinder project intends to show the advantages of using pixelated semiconductor technology for nuclear medicine applications to achieve an improved image reconstruction without efficiency loss. It proposes designs for Positron Emission Tomography (PET), Positron Emission Mammography (PEM) and Compton gamma camera detectors with a large number of signal channels (of the order of 106). The design is based on the use of a pixelated CdTe Schottky detector to have optimal energy and spatial resolution. An individual read-out channel is dedicated for each detector voxel of size 1 × 1 × 2 mm3 using an application-specific integrated circuit (ASIC) which the VIP project has designed, developed and is currently evaluating experimentally. The behaviour of the signal charge carriers in CdTe should be well understood because it has an impact on the performance of the readout channels. For this purpose the Finite Element Method (FEM) Multiphysics COMSOL software package has been used to simulate the behaviour of signal charge carriers in CdTe and extract values for the expected charge sharing depending on the impact point and bias voltage. The results on charge sharing obtained with COMSOL are combined with GAMOS, a Geant based particle tracking Monte Carlo software package, to get a full evaluation of the amount of charge sharing in pixelated CdTe for different gamma impact points.

  18. 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.

  19. 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.

  20. Space-charge dynamics in photorefractive polymers Oksana Ostroverkhovaa)

    E-print Network

    Ostroverkhova, Oksana

    to both photoconductivity and PR dynamics. Effects of plasticizer components are also discussed. © 2002 of charge carriers created under the influ- ence of optical beams. This mechanism results in a process- generation of charge carriers, transport of mobile carriers, trapping of these carriers in the regions

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

    NASA Astrophysics Data System (ADS)

    Bauer, Thilo; Jäger, Christof M.; Jordan, Meredith J. T.; Clark, Timothy

    2015-07-01

    We have developed a multi-agent quantum Monte Carlo model to describe the spatial dynamics of multiple majority charge carriers during conduction of electric current in the channel of organic field-effect transistors. The charge carriers are treated by a neglect of diatomic differential overlap Hamiltonian using a lattice of hydrogen-like basis functions. The local ionization energy and local electron affinity defined previously map the bulk structure of the transistor channel to external potentials for the simulations of electron- and hole-conduction, respectively. The model is designed without a specific charge-transport mechanism like hopping- or band-transport in mind and does not arbitrarily localize charge. An electrode model allows dynamic injection and depletion of charge carriers according to source-drain voltage. The field-effect is modeled by using the source-gate voltage in a Metropolis-like acceptance criterion. Although the current cannot be calculated because the simulations have no time axis, using the number of Monte Carlo moves as pseudo-time gives results that resemble experimental I/V curves.

  2. 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

  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. 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 ? = 3.1 ± 0.2 ps, with charge recombination in ? = 340 ± 10 ps, while in unannealed/disordered films of 1, charge separation occurs in ? < 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 CH?Cl? 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 ?s. 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.

  5. Influence of radiative recombination on the minority-carrier transport in direct band-gap semiconductors

    NASA Technical Reports Server (NTRS)

    Von Roos, O.

    1983-01-01

    When a semiconductor sample is irradiated by means of an external source, emitting photons or electrons, excess carriers are produced which distribute themselves throughout the sample. One of the parameters which determine the distribution of the carriers is the surface recombination velocity. The present investigation is concerned with the recombination lifetime tau. The predominant mechanism for recombination in wide band-gap semiconductors is described by the Shockley-Read-Hall (SRH) theory. The transport equations are derived for free carriers and the radiation field. The considered theory is applied to a semiinfinite, one-dimensional semiconductor slab irradiated by light of a given frequency. Some numerical considerations based on n-type GaAs are presented. Attention is given to a determination of the radiation transmitted through the surface of the sample.

  6. Disorder Effects in Charge Transport and Spin Response of Topological Insulators

    NASA Astrophysics Data System (ADS)

    Zhao, Lukas Zhonghua

    Topological insulators are a class of solids in which the non-trivial inverted bulk band structure gives rise to metallic surface states that are robust against impurity backscattering. First principle calculations predicted Bi2Te3, Sb2Te3 and Bi2Se3 to be three-dimensional (3D) topological insulators with a single Dirac cone on the surface. The topological surface states were subsequently observed by angle-resolved photoemission (ARPES) and scanning tunneling microscopy (STM). The investigations of charge transport through topological surfaces of 3D topological insulators, however, have faced a major challenge due to large charge carrier densities in the bulk donated by randomly distributed defects such as vacancies and antisites. This bulk disorder intermixes surface and bulk conduction channels, thereby complicating access to the low-energy (Dirac point) charge transport or magnetic response and resulting in the relatively low measured carrier mobilities. Moreover, charge inhomogeneity arising from bulk disorder can result in pronounced nanoscale spatial fluctuations of energy on the surface, leading to the formation of surface `puddles' of different carrier types. Great efforts have been made to combat the undesirable effects of disorder in 3D topological insulators and to reduce bulk carriers through chemical doping, nanostructure fabrication, and electric gating. In this work we have developed a new way to reduce bulk carrier densities using high-energy electron irradiation, thereby allowing us access to the topological surface quantum channels. We also found that disorder in 3D topological insulators can be beneficial. It can play an important part in enabling detection of unusual magnetic response from Dirac fermions and in uncovering new excitations, namely surface superconductivity in Dirac `puddles'. In Chapter 3 we show how by using differential magnetometry we could probe spin rotation in the 3D topological material family (Bi2Se 3, Bi2Te3 and Sb2Te3), and describe our detection of paramagnetic singularity in the magnetic susceptibility at low magnetic fields that persists up to room temperature, and which we have demonstrated to arise from the surfaces of the samples. The singularity is universal to the entire family, largely independent of the bulk carrier density, and consistent with the existence of electronic states near the spin-degenerate Dirac point of the 2D helical metal. The exceptional thermal stability of the signal points to an intrinsic surface cooling process, probably of thermoelectric organ, and establishes a sustainable platform for the singular field-tunable Dirac spin response. In Chapter 4 we describe our discovery of surface superconductivity in a hole-conducting topological insulator Sb2Te3 with transition to zero resistance induced through a minor tuning of growth chemistry that depletes bulk conduction channels. The depletion shifts Fermi energy towards the Dirac point as witnessed by over two orders of magnitude reduced bulk hole density and by the largest carrier mobility (~ 25,000 cm 2 V-1 s-1) found in any topological material. Direct evidence from transport, the unprecedentedly large diamagnetic screening, and the presence of up to ~ 25 meV gaps in differential conductance detected by scanning tunneling spectroscopy (STM) reveal the superconducting condensate to emerge first in surface puddles at unexpectedly high temperature, near 50 K. Percolative Josephson paths mediated by diffusing quasiparticles establish global phase coherence around 9 K. Rich structure of this state lends itself to manipulation and tuning via growth conditions and the topological material's parameters such as Fermi velocity and mean free path. In Chapter 5 we describe a new approach we have developed to reaching stable charge neutrality in 3D topological materials. The technique uses swift (~ 2.5 MeV energy) electron beams to compensate charged bulk defects and bring the Fermi level back into the bulk gap. By controlling the beam fluence we could tune bulk conductivity from p- (hole-like) to n-type (ele

  7. 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, ?-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 (400-500nm) presenting a slightly positive (4.02mV) and slightly negative (-3.55mV) ?-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 ?-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 (136nm, -23mV, hydrophilic). Based on these results, this work gives valuable information for the further design of mucus-penetrating NPs. PMID:25576256

  8. Charge carrier and exciton dynamics in LaBr{sub 3}:Ce{sup 3+} scintillators: Experiment and model

    SciTech Connect

    Bizarri, G.; Dorenbos, P.

    2007-05-01

    The scintillation yield and decay time of LaBr{sub 3} doped with 0.2%, 0.5%, and 5% cerium were studied between 80 K and 600 K. LaBr{sub 3}:5%Ce{sup 3+} on a photomultiplier tube shows at 300 K a very high scintillation yield of 22 800 photoelectrons per MeV (64 000 photons per MeV) with a decay time of 16 ns. At 600 K the yield decreases by {approx_equal}15%. The scintillation yield of LaBr{sub 3}:0.2%Ce{sup 3+} is 19 800 photoelectrons per MeV (56 000 photons per MeV) at 300 K with a decrease by {approx_equal}50% at 600 K and a main scintillation decay time around 30 ns. The appearance of slow components in the Ce emission indicates a relatively slow energy transfer from the host crystal to Ce. The presence or absence of slow components depends on both concentration and temperature. The results are analyzed and interpreted with a model that comprises prompt charge carrier trapping by Ce and delayed excitation of Ce by means of thermally activated transport of self-trapped exciton defects. The results of the study provide detailed information on the scintillation mechanism. Besides presenting experimental data, the different energy transfer processes are quantified.

  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. The Major Facilitative Folate Transporters Solute Carrier 19A1 and Solute Carrier 46A1: Biology and Role in Antifolate Chemotherapy of Cancer

    PubMed Central

    Wilson, Mike R.; Hou, Zhanjun

    2014-01-01

    This review summarizes the biology of the major facilitative membrane transporters, the reduced folate carrier (RFC) (Solute Carrier 19A1) and the proton-coupled folate transporter (PCFT) (Solute Carrier 46A1). Folates are essential vitamins, and folate deficiency contributes to a variety of health disorders. RFC is ubiquitously expressed and is the major folate transporter in mammalian cells and tissues. PCFT mediates the intestinal absorption of dietary folates and appears to be important for transport of folates into the central nervous system. Clinically relevant antifolates for cancer, such as methotrexate and pralatrexate, are transported by RFC, and loss of RFC transport is an important mechanism of methotrexate resistance in cancer cell lines and in patients. PCFT is expressed in human tumors, and is active at pH conditions associated with the tumor microenvironment. Pemetrexed is an excellent substrate for both RFC and PCFT. Novel tumor-targeted antifolates related to pemetrexed with selective membrane transport by PCFT over RFC are being developed. In recent years, there have been major advances in understanding the structural and functional properties and the regulation of RFC and PCFT. The molecular bases for methotrexate resistance associated with loss of RFC transport and for hereditary folate malabsorption, attributable to mutant PCFT, were determined. Future studies should continue to translate molecular insights from basic studies of RFC and PCFT biology into new therapeutic strategies for cancer and other diseases. PMID:24396145

  11. Ion and water transport in charge-modified graphene nanopores

    NASA Astrophysics Data System (ADS)

    Qiu, Ying-Hua; Li, Kun; Chen, Wei-Yu; Si, Wei; Tan, Qi-Yan; Chen, Yun-Fei

    2015-10-01

    Porous graphene has a high mechanical strength and an atomic-layer thickness that makes it a promising material for material separation and biomolecule sensing. Electrostatic interactions between charges in aqueous solutions are a type of strong long-range interaction that may greatly influence fluid transport through nanopores. In this study, molecular dynamic simulations were conducted to investigate ion and water transport through 1.05-nm diameter monolayer graphene nanopores, with their edges charge-modified. Our results indicated that these nanopores are selective to counterions when they are charged. As the charge amount increases, the total ionic currents show an increase-decrease profile while the co-ion currents monotonically decrease. The co-ion rejection can reach 76.5% and 90.2% when the nanopores are negatively and positively charged, respectively. The Cl- ion current increases and reaches a plateau, and the Na+ current decreases as the charge amount increases in systems in which Na+ ions act as counterions. In addition, charge modification can enhance water transport through nanopores. This is mainly due to the ion selectivity of the nanopores. Notably, positive charges on the pore edges facilitate water transport much more strongly than negative charges. Project supported by the National Basic Research Program of China (Grant Nos. 2011CB707601 and 2011CB707605), the National Natural Science Foundation of China (Grant No. 50925519), the Fundamental Research Funds for the Central Universities, Funding of Jiangsu Provincial Innovation Program for Graduate Education, China (Grant No. CXZZ13_0087), and the Scientific Research Foundation of Graduate School of Southeast University (Grant No. YBJJ 1322).

  12. Temperature-dependent investigation of carrier transport, injection, and densities in AlGaAs-based multi-quantum-well active layers for vertical-cavity surface-emitting lasers

    NASA Astrophysics Data System (ADS)

    Engelhardt, Andreas P.; Kolb, Johanna S.; Roemer, Friedhard; Weichmann, Ulrich; Moench, Holger; Witzigmann, Bernd

    2015-01-01

    The electro-optical efficiency of vertical-cavity surface-emitting lasers (VCSELs) strongly depends on the efficient carrier injection into the quantum wells (QWs) in the laser active region. Carrier injection degrades with increasing temperature, which limits VCSEL performance in high-power applications where self-heating imposes high-operating temperatures. In a numerical model, we investigate the transport of charge carriers in an 808-nm AlGaAs multi-quantum-well structure with special attention to the temperature dependence of carrier injection into the QWs. Experimental reference data were extracted from oxide-confined, top-emitting VCSELs. The transport simulations follow a drift-diffusion-model complemented by an energy-resolved carrier-capture model. The QW gain was calculated in the screened Hartree-Fock approximation. With the combination of the gain and transport model, we explain experimental reference data for the injection efficiency and threshold current. The degradation of the injection efficiency with increasing temperature is not only due to increased thermionic escape of carriers from the QWs, but also to state filling in the QWs initiated from higher threshold carrier densities. With a full opto-electro-thermal VCSEL model, we demonstrate how changes in VCSEL properties affecting the threshold carrier density, like mirror design or optical confinement, have consequences on the thermal behavior of the injection and the VCSEL performance.

  13. Subsurface imaging of coupled carrier transport in GaAs/AlGaAs core-shell nanowires.

    PubMed

    Chen, Guannan; McGuckin, Terrence; Hawley, Christopher J; Gallo, Eric M; Prete, Paola; Miccoli, Ilio; Lovergine, Nico; Spanier, Jonathan E

    2015-01-14

    We demonstrate spatial probing of carrier transport within GaAs/AlGaAs core-shell nanowires with nanometer lateral resolution and subsurface sensitivity by energy-variable electron beam induced current imaging. Carrier drift that evolves with applied electric field is distinguished from a coupled drift-diffusion length. Along with simulation of injected electron trajectories, combining beam energy tuning with precise positioning for selective probing of core and shell reveals axial position- and bias-dependent differences in carrier type and transport along parallel conduction channels. These results indicate how analysis of transport within heterostructured nanomaterials is no longer limited to nonlocal or surface measurements. PMID:25545191

  14. Borehole model for simulation transport geothermal heat with heat pipe system and with forced circulation of heat carrier

    NASA Astrophysics Data System (ADS)

    Jakubský, Michal; Lenhard, Richard; Vantúch, Martin; Malcho, Milan

    2012-04-01

    In the call OPVaV-2008/2.2/01-SORO Operational Programme Research and Development - knowledge and technology transfer from research and development into practice (ITMS-26220220057), whose strategic goal is "Device to use low-potential geothermal heat without forced circulation of heat carrier deep in the well "in the Department of Energy laboratory techniques to construct a simulator of transport low potential of geothermal energy in comparative test-drilling in the laboratory. The article describes a device that was designed as a scale model of two deep boreholes each of which withdraws the earth's heat by heat transfer technology and heat carrier. Device using forced circulation of heat carrier will respond in the construction of equipment currently used to transport heat from deep borehole. As the heat carrier will be used CO2. Facilities without using forced circulation of heat carrier, the new technology, which will be used as heat carrier ammonia (NH3).

  15. Dynamic disorder in molecular semiconductors: charge transport in two dimensions.

    PubMed

    Troisi, Alessandro

    2011-01-21

    A semiclassical model to study charge transport in molecular semiconductors is extended from one to an arbitrary number of dimensions. The model is applied to the calculation of the charge mobility of the holes in the two dimensional plane of rubrene with the largest charge mobility. The absolute values of the computed mobility tensor, evaluated without adjustable parameters, are in excellent agreement with the experimental results of Podzorov et al. [Phys. Rev. Lett. 95, 226601 (2005)] and have the correct temperature dependence. The localization length and density of states determined by dynamic disorder are analyzed in detail and provide a global description of the charge transport process in agreement with the spectroscopic experiments. The effect of correlation in the modeling of dynamic disorder is also investigated. PMID:21261379

  16. 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.

  17. Model for transport and reaction of defects and carriers within displacement cascades in gallium arsenide

    SciTech Connect

    Wampler, William R. Myers, Samuel M.

    2015-01-28

    A model is presented for recombination of charge carriers at evolving 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 the 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 of defects. The initial radial defect profiles within the cluster were determined through pair-correlation-function analysis of the spatial distribution of defects obtained from the binary-collision code MARLOWE, using recoil energies for fission neutrons. 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 displacement damage from energetic particle irradiation.

  18. 49 CFR 369.3 - Classification of carriers-motor carriers of passengers.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... false Classification of carriers-motor carriers of passengers. 369.3 ...Transportation (Continued) FEDERAL MOTOR CARRIER SAFETY ADMINISTRATION, DEPARTMENT OF TRANSPORTATION FEDERAL MOTOR CARRIER SAFETY REGULATIONS...

  19. 49 CFR 369.3 - Classification of carriers-motor carriers of passengers.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... false Classification of carriers-motor carriers of passengers. 369.3 ...Transportation (Continued) FEDERAL MOTOR CARRIER SAFETY ADMINISTRATION, DEPARTMENT OF TRANSPORTATION FEDERAL MOTOR CARRIER SAFETY REGULATIONS...

  20. 49 CFR 369.3 - Classification of carriers-motor carriers of passengers.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... false Classification of carriers-motor carriers of passengers. 369.3 ...Transportation (Continued) FEDERAL MOTOR CARRIER SAFETY ADMINISTRATION, DEPARTMENT OF TRANSPORTATION FEDERAL MOTOR CARRIER SAFETY REGULATIONS...

  1. 49 CFR 369.3 - Classification of carriers-motor carriers of passengers.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... false Classification of carriers-motor carriers of passengers. 369.3 ...Transportation (Continued) FEDERAL MOTOR CARRIER SAFETY ADMINISTRATION, DEPARTMENT OF TRANSPORTATION FEDERAL MOTOR CARRIER SAFETY REGULATIONS...

  2. Charge transport through chains of nanoparticles

    NASA Astrophysics Data System (ADS)

    Lüdtke, T.; Mirovsky, P.; Hüther, R.; Govor, L.; Bauer, G. H.; Parisi, J.; Haug, R. J.

    2010-09-01

    We present transport measurements through nanoparticles as well as preparation techniques to contact short chains of nanoparticles. The nanoparticles are deposited onto a mica substrate in a dewetting process of hexane solution containing the nanoparticles. The measurements were done in a self-developed probing tip setup inside a SEM, where the probing tips were driven by piezoelectric motors. The platinum iridium tips were fabricated by anodic dissolving in a drop-off method which results in sharp tip diameters. With this setup it was possible to contact and measure the nanoparticles under vacuum conditions. The I- V characteristics show a power law behavior as expected for low dimensional cluster systems. Transport in the device is expected to be influenced by Coulomb blockade effects and disorder.

  3. Alternating carrier models of asymmetric glucose transport violate the energy conservation laws.

    PubMed

    Naftalin, Richard J

    2008-11-01

    Alternating access transporters with high-affinity externally facing sites and low-affinity internal sites relate substrate transit directly to the unliganded asymmetric "carrier" (Ci) distribution. When both bathing solutions contain equimolar concentrations of ligand, zero net flow of the substrate-carrier complex requires a higher proportion of unliganded low-affinity inside sites (proportional, variant 1/KD(in)) and slower unliganded "free" carrier transit from inside to outside than in the reverse direction. However, asymmetric rates of unliganded carrier movement, kij, imply that an energy source, DeltaGcarrier = RT ln (koi/kio) = RT ln (Cin/Cout) = RT ln (KD(in)/KD(out)), where R is the universal gas constant (8.314 Joules/M/K degrees), and T is the temperature, assumed here to be 300 K degrees , sustains the asymmetry. Without this invalid assumption, the constraints of carrier path cyclicity, combined with asymmetric ligand affinities and equimolarity at equilibrium, are irreconcilable, and any passive asymmetric uniporter or cotransporter model system, e.g., Na-glucose cotransporters, espousing this fundamental error is untenable. With glucose transport via GLUT1, the higher maximal rate and Km of net ligand exit compared to net ligand entry is only properly simulated if ligand transit occurs by serial dissociation-association reactions between external high-affinity and internal low-affinity immobile sites. Faster intersite transit rates occur from lower-affinity sites than from higher-affinity sites and require no other energy source to maintain equilibrium. Similar constraints must apply to cotransport. PMID:18658227

  4. Carrier separation and transport in perovskite solar cells studied by nanometre-scale profiling of electrical potential.

    PubMed

    Jiang, Chun-Sheng; Yang, Mengjin; Zhou, Yuanyuan; To, Bobby; Nanayakkara, Sanjini U; Luther, Joseph M; Zhou, Weilie; Berry, Joseph J; van de Lagemaat, Jao; Padture, Nitin P; Zhu, Kai; Al-Jassim, Mowafak M

    2015-01-01

    Organometal-halide perovskite solar cells have greatly improved in just a few years to a power conversion efficiency exceeding 20%. This technology shows unprecedented promise for terawatt-scale deployment of solar energy because of its low-cost, solution-based processing and earth-abundant materials. We have studied charge separation and transport in perovskite solar cells-which are the fundamental mechanisms of device operation and critical factors for power output-by determining the junction structure across the device using the nanoelectrical characterization technique of Kelvin probe force microscopy. The distribution of electrical potential across both planar and porous devices demonstrates p-n junction structure at the TiO2/perovskite interfaces and minority-carrier diffusion/drift operation of the devices, rather than the operation mechanism of either an excitonic cell or a p-i-n structure. Combining the potential profiling results with solar cell performance parameters measured on optimized and thickened devices, we find that carrier mobility is a main factor that needs to be improved for further gains in efficiency of the perovskite solar cells. PMID:26411597

  5. Carrier separation and transport in perovskite solar cells studied by nanometre-scale profiling of electrical potential

    NASA Astrophysics Data System (ADS)

    Jiang, Chun-Sheng; Yang, Mengjin; Zhou, Yuanyuan; To, Bobby; Nanayakkara, Sanjini U.; Luther, Joseph M.; Zhou, Weilie; Berry, Joseph J.; van de Lagemaat, Jao; Padture, Nitin P.; Zhu, Kai; Al-Jassim, Mowafak M.

    2015-09-01

    Organometal-halide perovskite solar cells have greatly improved in just a few years to a power conversion efficiency exceeding 20%. This technology shows unprecedented promise for terawatt-scale deployment of solar energy because of its low-cost, solution-based processing and earth-abundant materials. We have studied charge separation and transport in perovskite solar cells--which are the fundamental mechanisms of device operation and critical factors for power output--by determining the junction structure across the device using the nanoelectrical characterization technique of Kelvin probe force microscopy. The distribution of electrical potential across both planar and porous devices demonstrates p-n junction structure at the TiO2/perovskite interfaces and minority-carrier diffusion/drift operation of the devices, rather than the operation mechanism of either an excitonic cell or a p-i-n structure. Combining the potential profiling results with solar cell performance parameters measured on optimized and thickened devices, we find that carrier mobility is a main factor that needs to be improved for further gains in efficiency of the perovskite solar cells.

  6. Carrier separation and transport in perovskite solar cells studied by nanometre-scale profiling of electrical potential

    PubMed Central

    Jiang, Chun-Sheng; Yang, Mengjin; Zhou, Yuanyuan; To, Bobby; Nanayakkara, Sanjini U.; Luther, Joseph M.; Zhou, Weilie; Berry, Joseph J.; van de Lagemaat, Jao; Padture, Nitin P.; Zhu, Kai; Al-Jassim, Mowafak M.

    2015-01-01

    Organometal–halide perovskite solar cells have greatly improved in just a few years to a power conversion efficiency exceeding 20%. This technology shows unprecedented promise for terawatt-scale deployment of solar energy because of its low-cost, solution-based processing and earth-abundant materials. We have studied charge separation and transport in perovskite solar cells—which are the fundamental mechanisms of device operation and critical factors for power output—by determining the junction structure across the device using the nanoelectrical characterization technique of Kelvin probe force microscopy. The distribution of electrical potential across both planar and porous devices demonstrates p–n junction structure at the TiO2/perovskite interfaces and minority-carrier diffusion/drift operation of the devices, rather than the operation mechanism of either an excitonic cell or a p-i-n structure. Combining the potential profiling results with solar cell performance parameters measured on optimized and thickened devices, we find that carrier mobility is a main factor that needs to be improved for further gains in efficiency of the perovskite solar cells. PMID:26411597

  7. 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.

  8. Charge Transport Behavior in Microfluidic Microbial Energy Conversion Devices

    NASA Astrophysics Data System (ADS)

    Kumar, Aloke; Mukherjee, Partha; Borole, Abhijeet; Doktycz, Mitchel

    2010-11-01

    Microbial energy harvesting devices utilize anode-respiring bacteria (ARB), present as a biofilm matrix, to generate electrical current from organic matter. The conductive biofilm matrix in the anode compartment plays a key role in the overall charge transport behavior. Especially, biofilm kinetics and ARB community dynamics are of paramount importance influencing the anode overpotential, which is further dependent on the pH variation. In this work, we present a theoretical framework to study the charge transport characteristics with concomitant biofilm kinetics, substrate utilization, diffusion and migration in a microfluidic device with microbial energy generation.

  9. 49 CFR 1572.203 - Transportation of explosives from Canada to the United States via railroad carrier.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... Safety, Research and Special Programs Administration, in accordance with 49 CFR 173.56, and determined to meet the definition for a Class 1 material in 49 CFR 173.50. Known railroad carrier means a person that... railroad carrier may transport in commerce any explosive into the United States from Canada, via a...

  10. 49 CFR 1572.203 - Transportation of explosives from Canada to the United States via railroad carrier.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... Safety, Research and Special Programs Administration, in accordance with 49 CFR 173.56, and determined to meet the definition for a Class 1 material in 49 CFR 173.50. Known railroad carrier means a person that... railroad carrier may transport in commerce any explosive into the United States from Canada, via a...

  11. 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

  12. Mode-selective vibrational control of charge transport in $?$-conjugated molecular materials

    E-print Network

    Artem A. Bakulin; Robert Lovrin?i?; Yu Xi; Oleg Selig; Huib J. Bakker; Yves L. A. Rezus; Pabitra K. Nayak; Alexandr Fonari; Veaceslav Coropceanu; Jean-Luc Brédas; David Cahen

    2015-03-02

    The soft character of organic materials leads to strong coupling between molecular nuclear and electronic dynamics. This coupling opens the way to control charge transport in organic electronic devices by inducing molecular vibrational motions. However, despite encouraging theoretical predictions, experimental realization of such control has remained elusive. Here we demonstrate experimentally that photoconductivity in a model organic optoelectronic device can be controlled 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 1500-1700 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. Vibrational control thus presents a new tool for studying electron-phonon coupling and charge dynamics in (bio)molecular materials.

  13. 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.

  14. 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.

  15. Analysis of electrolyte transport through charged nanopores

    E-print Network

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

    2015-12-14

    We revisit the classical problem of the flow of an electrolyte solution through charged capillaries (nanopores). In the limit where the length of the capillary is much larger than its radius, the problem can be simplified to a one-dimensional averaged flux-force formalism that relates the relevant fluxes (electrical current, salt flux, fluid velocity) to their respective driving forces (difference in electric potential, salt concentration, pressure). Calculations in literature mainly consider the limit of non-overlapping electrical double layers (EDLs) in the pores and the absence of salt concentration gradients in the axial direction. In the present work these simplifications are relaxed and we discuss the general case with overlapping EDLs and nonzero axial salt concentration gradients. The 3x3 matrix that relates these quantities exhibits Onsager symmetry and for one of the cross coefficients we report a new significant simplification. We describe how Onsager symmetry is preserved under change of variables which we illustrate by one example of a different flux-force matrix given by Gross and Osterle (1968). The model is well-suited to physically represent membranes consisting of charged nanopores for electrokinetic energy conversion and water desalination. We analyse the energy conversion of a salt concentration difference into electrical power using an efficiency vs. power diagram. Because of the non-zero axial gradient in salt concentration that we allow in our calculations, under wide ranges of conditions, partial loops in current, salt flux or fluid flow are predicted in the pore.

  16. 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.

  17. 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 (??) 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??s and 8??s. 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.

  18. 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.

  19. Analysis of electrolyte transport through charged nanopores

    E-print Network

    Peters, P B; Bazant, M Z; Biesheuvel, P M

    2015-01-01

    We revisit the classical problem of the flow of an electrolyte solution through charged capillaries (nanopores). In the limit where the length of the capillary is much larger than its radius, the problem can be simplified to a one-dimensional averaged flux-force formalism that relates the relevant fluxes (electrical current, salt flux, fluid velocity) to their respective driving forces (difference in electric potential, salt concentration, pressure). Calculations in literature mainly consider the limit of non-overlapping electrical double layers (EDLs) in the pores and the absence of salt concentration gradients in the axial direction. In the present work these simplifications are relaxed and we discuss the general case with overlapping EDLs and nonzero axial salt concentration gradients. The 3x3 matrix that relates these quantities exhibits Onsager symmetry and for one of the cross coefficients we report a new significant simplification. We describe how Onsager symmetry is preserved under change of variables...

  20. Charge transport in gapless electron-hole systems with arbitrary band dispersion

    NASA Astrophysics Data System (ADS)

    Das Sarma, S.; Hwang, E. H.

    2015-05-01

    Using the semiclassical Boltzmann transport theory, we analytically consider dc charge transport in gapless electron-hole (both chiral and nonchiral) systems in the presence of resistive scattering due to static disorder arising from random quenched impurities in the background. We obtain the dependence of the Boltzmann conductivity on carrier density and temperature for arbitrary band dispersion in arbitrary dimensionality assuming long-range (˜1 /r ) Coulomb disorder and zero-range white-noise disorder [˜? (r ) ]. We establish that the temperature and the density dependence of the Boltzmann conductivity manifests scaling behaviors determining, respectively, the intrinsic semimetallic or the extrinsic metallic property of the gapless system. Our results apply equally well to both chiral and nonchiral gapless systems, and provide a qualitative understanding of the dependence of the Boltzmann conductivity on the band dispersion in arbitrary dimensionality.

  1. Charge carrier mobility through vacuumsublimed glassy films of s-triazine-and carbazole-based bipolar hybrid and unipolar

    E-print Network

    Chen, Shaw H.

    as bipolar charge transport media for organic electronics, chemical hybrids comprising non-conjugated spacers Organic Electronics 14 (2013) 2925­2931 Contents lists available at ScienceDirect Organic Electronics

  2. 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.

  3. Charge transport properties of spin crossover systems.

    PubMed

    Ruiz, Eliseo

    2014-01-01

    The study of spin crossover compounds by means of theoretical or experimental approaches has provided interesting results in recent decades. The main feature of such compounds is the change in the spin state induced by many different external stimuli, i.e. temperature, light, pressure, solvent coordination and the electric field. Spin crossover systems are potentially more useful than other magnetic molecules because their switching behaviour can occur closer to room temperature, and they are thus candidates for use in spintronic devices. Here, I review the state of the art in quantum chemical approaches to the study of such systems and discuss experiments that have focused on transport properties in single-molecule, nano-objects or thin-film spin crossover systems. PMID:24217339

  4. 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,…

  5. Charge transport in highly aligned conjugated polymers (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    O'Connor, Brendan; Xue, Xiao; Sun, Tianlei

    2015-10-01

    Charge transport in conjugated polymers has a complex dependence on film morphology. Aligning the polymer chains in the plane of the film simplifies the morphology of the system allowing for insight into the morphological dependence of charge transport. Highly aligned conjugated polymers have also been shown to lead to among the highest reported field effect mobilities in these materials to date. In this talk, a comparison will be made between aligned polymer films processed using two primary methods, nanostructured substrate assisted growth and mechanical strain. A number of polymer systems including P3HT, pBTTT, N2200, and PCDTPT are considered, and the processed films are analyzed in detail with optical spectroscopy, AFM, TEM, and X-ray scattering providing insight into the molecular features that allow for effective alignment. By contrasting the morphology of these films, several insights into underlying charge transport limitations can be made. A number of key morphological features that lead to high field effect mobility and charge transport anisotropy in these films will be discussed. In addition, several unique features of organic thin film transistor device behavior in these systems will be examined including the commonly observed gate voltage dependence of saturated field effect mobility.

  6. 31 CFR 337.2 - Transportation charges and risks.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... FEDERAL HOUSING ADMINISTRATION DEBENTURES Certificated Debentures § 337.2 Transportation charges and risks. Debentures presented for redemption at call or maturity, or for authorized prior purchase, or for conversion to book-entry form, must be delivered at the expense and risk of the holder. Debentures...

  7. Two-dimensional mineral [Pb2BiS3][AuTe2]: high-mobility charge carriers in single-atom-thick layers.

    PubMed

    Fang, Lei; Im, Jino; Stoumpos, Constantinos C; Shi, Fengyuan; Dravid, Vinayak; Leroux, Maxime; Freeman, Arthur J; Kwok, Wai-Kwong; Chung, Duck Young; Kanatzidis, Mercouri

    2015-02-18

    Two-dimensional (2D) electronic systems are of wide interest due to their richness in chemical and physical phenomena and potential for technological applications. Here we report that [Pb2BiS3][AuTe2], known as the naturally occurring mineral buckhornite, hosts 2D carriers in single-atom-thick layers. The structure is composed of stacking layers of weakly coupled [Pb2BiS3] and [AuTe2] sheets. The insulating [Pb2BiS3] sheet inhibits interlayer charge hopping and confines the carriers in the basal plane of the single-atom-thick [AuTe2] layer. Magneto-transport measurements on synthesized samples and theoretical calculations show that [Pb2BiS3][AuTe2] is a multiband semimetal with a compensated density of electrons and holes, which exhibits a high hole carrier mobility of ?1360 cm(2)/(V s). This material possesses an extremely large anisotropy, ? = ?(c)/?(ab) ? 10(4), comparable to those of the benchmark 2D materials graphite and Bi2Sr2CaCu2O(6+?). The electronic structure features linear band dispersion at the Fermi level and ultrahigh Fermi velocities of 10(6) m/s, which are virtually identical to those of graphene. The weak interlayer coupling gives rise to the highly cleavable property of the single crystal specimens. Our results provide a novel candidate for a monolayer platform to investigate emerging electronic properties. PMID:25612093

  8. Physical constraints on charge transport through bacterial nanowires

    PubMed Central

    Polizzi, Nicholas F.; Skourtis, Spiros S.

    2012-01-01

    Extracellular appendages of the dissimilatory metal-reducing bacterium Shewanella oneidensis MR-1 were recently shown to sustain currents of 1010 electrons per second over distances of 0.5 microns [El-Naggar et al., Proc. Natl. Acad. Sci. U. S. A., 2010, 107, 18127]. However, the identity of the charge localizing sites and their organization along the “nanowire” remain unknown. We use theory to predict redox cofactor separation distances that would permit charge flow at rates of 1010 electrons per second over 0.5 microns for voltage biases of ?1V, using a steady-state analysis governed by a non-adiabatic electron transport mechanism. We find the observed currents necessitate a multi-step hopping transport mechanism, with charge localizing sites separated by less than 1 nm and reorganization energies that rival the lowest known in biology. PMID:22470966

  9. Carrier of Wingless (Cow), a Secreted Heparan Sulfate Proteoglycan, Promotes Extracellular Transport of Wingless

    PubMed Central

    Chang, Yung-Heng; Sun, Yi Henry

    2014-01-01

    Morphogens are signaling molecules that regulate growth and patterning during development by forming a gradient and activating different target genes at different concentrations. The extracellular distribution of morphogens is tightly regulated, with the Drosophila morphogen Wingless (Wg) relying on Dally-like (Dlp) and transcytosis for its distribution. However, in the absence of Dlp or endocytic activity, Wg can still move across cells along the apical (Ap) surface. We identified a novel secreted heparan sulfate proteoglycan (HSPG) that binds to Wg and promotes its extracellular distribution by increasing Wg mobility, which was thus named Carrier of Wg (Cow). Cow promotes the Ap transport of Wg, independent of Dlp and endocytosis, and this function addresses a previous gap in the understanding of Wg movement. This is the first example of a diffusible HSPG acting as a carrier to promote the extracellular movement of a morphogen. PMID:25360738

  10. 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

    ... when a commercial carrier transports my mobile home overland or over water? 302-10.200 Section 302-10... TRANSPORTATION AND STORAGE OF PROPERTY 10-ALLOWANCES FOR TRANSPORTATION OF MOBILE HOMES AND BOATS USED AS A... carrier transports my mobile home overland or over water? Your agency will allow the following costs...

  11. Retrieval of Electronic Spectra of Charge Carriers in Organic Field-Effect Transistors from Charge Modulation Reflectance Spectra Distorted by Optical Interference

    NASA Astrophysics Data System (ADS)

    Miyata, Kiyoshi; Ishino, Yuta; Watanabe, Kazuya; Miwa, Kazumoto; Uemura, Takafumi; Takeya, Jun; Matsumoto, Yoshiyasu

    2013-06-01

    Charge modulation (CM) spectroscopy is useful for detecting and characterizing the electronic structure of charge carriers accumulated in organic field-effect transistors (OFETs). However, CM spectra are distorted by optical interference due to multiple reflections in OFETs particularly when reflection configurations are used. In this study, we demonstrated a method for retrieving the spectra of complex refractive indices of carriers from the distorted CM spectra by using a 4×4 matrix algorithm with general transition matrices. We tested this method by applying it to the CM spectra of a rubrene single-crystal FET measured at several incident angles of light. In spite of the strong distortion of the CM spectra, we could retrieve the spectrum of the imaginary part of refractive indices, which is similar to that observed in the transmission configuration. This method extends the applicability of CM spectroscopy to OFETs with opaque electrodes, where transmission configurations cannot possibly be applied.

  12. Ion Transport Dynamics in Acid Variable Charge Subsoils

    SciTech Connect

    Qafoku, Nik; Sumner, Malcolm E.; Toma, Mitsuru

    2005-06-06

    This is a mini-review of the research work conducted by the authors with the objective of studying ion transport in variable charge subsoils collected from different areas around the world. An attempt is made in these studies to relate the unique behavior manifested during ionic transport in these subsoils with their mineralogical, physical and chemical properties, which are markedly different from those in soils from temperate regions. The variable charge subsoils have a relatively high salt sorption capacity and anion exchange capacity (AEC) that retards anions downward movement. The AEC correlates closely with the anion retardation coefficients. Ca2+ applied with gypsum in topsoil may be transported to the subsoil and may improve the subsoil chemical properties. These results may help in developing appropriate management strategies under a range of mineralogical, physical, and chemical conditions.

  13. Sign of the dominant charge carriers in photorefractive crystals determined by a phase-locked holographic technique

    NASA Astrophysics Data System (ADS)

    Freschi, A. A.; Callegari, F. A.; De Vicente, F. S.; Gesualdi, M. R. R.

    2015-10-01

    This work presents a holographic method based on active feedback techniques for determining the sign of the dominant charge carriers in photorefractive materials. A two-step procedure is proposed: first off a stationary phase-locked hologram is recorded; an electric field normal to the grating layers is then applied to the material, thus producing a running hologram. The sign of the charge carriers is determined by comparing the direction of the applied field with the direction of the hologram movement, which is known through the automatically attached light pattern. The method can be applied from highly photoconductive to highly insulating materials. Furthermore, no information on any material parameter is required. The method is validated by a set of holographic experiments using a Bi12TiO20 crystal that has electrons as the majority photocarriers.

  14. Effect of temperature and rare-earth doping on charge-carrier mobility in indium-monoselenide crystals

    SciTech Connect

    Abdinov, A. Sh.; Babayeva, R. F.; Amirova, S. I.; Rzayev, R. M.

    2013-08-15

    In the temperature range T = 77-600 K, the dependence of the charge-carrier mobility ({mu}) on the initial dark resistivity is experimentally investigated at 77 K ({rho}d{sub 0}), as well as on the temperature and the level (N) of rare-earth doping with such elements as gadolinium (Gd), holmium (Ho), and dysprosium (Dy) in n-type indium-monoselenide (InSe) crystals. It is established that the anomalous behavior of the dependences {mu}(T), {mu}({rho}d{sub 0}), and {mu}(N) found from the viewpoint of the theory of charge-carrier mobility in crystalline semiconductors is related, first of all, to partial disorder in indium-monoselenide crystals and can be attributed to the presence of random drift barriers in the free energy bands.

  15. Influence of Surface Recombination on Charge-Carrier Kinetics in Organic Bulk Heterojunction Solar Cells with Nickel Oxide Interlayers

    NASA Astrophysics Data System (ADS)

    Wheeler, Scot; Deledalle, Florent; Tokmoldin, Nurlan; Kirchartz, Thomas; Nelson, Jenny; Durrant, James R.

    2015-08-01

    The choice of electrode for organic photovoltaics is known to be of importance to both device stability and performance, especially regarding the open-circuit voltage (VOC ). Here we show that the work function of a nickel oxide anode, varied using an O2 plasma treatment, has a considerable influence on the open-circuit voltage VOC of an organic solar cell. We probe recombination in the devices using transient photovoltage and charge extraction to determine the lifetime as a function of charge-carrier concentration and compare the experimental results with numerical drift-diffusion simulations. This combination of experiment and simulations allows us to conclude that the variations in VOC are due to a change in surface recombination, localized at the NiO anode, although only a small change in carrier lifetime is observed.

  16. Comparison of majority carrier charge transfer velocities at Si/polymer and Si/metal photovoltaic heterojunctions

    SciTech Connect

    Price, Michelle J.; Foley, Justin M.; May, Robert A.; Maldonado, Stephen

    2010-08-23

    Two sets of silicon (Si) heterojunctions with either Au or PEDOT:PSS contacts have been prepared to compare interfacial majority carrier charge transfer processes at Si/metal and Si/polymer heterojunctions. Current-voltage (J-V) responses at a range of temperatures, wavelength-dependent internal quantum yields, and steady-state J-V responses under illumination for these devices are reported. The cumulative data suggest that the velocity of majority carrier charge transfer, v{sub n}, is several orders of magnitude smaller at n-Si/PEDOT:PSS contacts than at n-Si/Au junctions, resulting in superior photoresponse characteristics for these inorganic/organic heterojunctions.

  17. Relationship between composition and charge carrier concentration in Eu8Ga16-xGe30+x clathrates

    NASA Astrophysics Data System (ADS)

    Pacheco, V.; Bentien, A.; Carrillo-Cabrera, W.; Paschen, S.; Steglich, F.; Grin, Yu.

    2005-04-01

    The charge carrier concentratioin is an important parameter in the search for intermetallic clathrates adequate for thermoelectric applications. This work reveals the influence of the exact composition of Eu8Ga16-xGe30+x on the charge carrier concentration. The samples with initial composition Eu8Ga16Ge30 were processed according to two different heat treatments. Slow cooling of the melt and subsequent annealing produced the ? phase with clathrate I structure (space group Pm3¯n ). In contrast, samples quenched from 1040 °C and then annealed showed the clathrate-VIII structure ( ? phase, space group I4¯3m ). Lattice parameter investigations and energy dispersive x-ray spectroscopy analysis show that the ? phase possesses a narrow homogeneity range Eu8Ga16-xGe30+x(0.49?x?1.01) . The charge carrier concentration (n) at 2 K, as determined from Hall-effect measurements, correlates with x ( 0.15e- /unit cell ?n?0.50e- /unit cell). The ? phase has a homogeneity range with 0.28?x?0.48 at 650 °C. The ideal Zintl composition (x=0) was not achieved for either modification using the applied preparation conditions. From x-ray absorption spectroscopy and the temperature and magnetic field dependence of the magnetization we find that the electronic configuration of the cations in both phases is 4f7(Eu2+) . It is believed that the Rudermann-Kittel-Kasuya-Yosida interaction is responsible for the observed ferromagnetic ordering. This agrees well with the observation made in this and another paper [A. Bentien, V. Pacheco, S. Paschen, Yu. Grin, and F. Steglich, Phys. Rev. B 71, 165206 (2005)] on this work that the large difference in ordering temperature between the two phases scales with the effective masses of the charge carriers.

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

    PubMed

    Obliger, Amaël; 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

  19. The solute carrier family 10 (SLC10): beyond bile acid transport

    PubMed Central

    da Silva, Tatiana Claro; Polli, James E.; Swaan, Peter W.

    2012-01-01

    The solute carrier (SLC) family 10 (SLC10) comprises influx transporters of bile acids, steroidal hormones, various drugs, and several other substrates. Because the seminal transporters of this family, namely, sodium/taurocholate cotransporting polypeptide (NTCP; SLC10A1) and the apical sodium-dependent bile acid transporter (ASBT; SLC10A2), were primarily bile acid transporters, the term “sodium bile salt cotransporting family” was used for the SLC10 family. However, this notion became obsolete with the finding of other SLC10 members that do not transport bile acids. For example, the sodium-dependent organic anion transporter (SOAT; SLC10A6) transports primarily sulfated steroids. Moreover, NTCP was shown to also transport steroids and xenobiotics, including HMG-CoA inhibitors (statins). The SLC10 family contains four additional members, namely, P3 (SLC10A3; SLC10A3), P4 (SLC10A4; SLC10A4), P5 (SLC10A5; SLC10A5) and SLC10A7 (SLC10A7), several of which were unknown or considered hypothetical until approximately a decade ago. While their substrate specificity remains undetermined, great progress has been made towards their characterization in recent years. SLC10A4 may participate in vesicular storage or exocytosis of neurotransmitters or mastocyte mediators, whereas SLC10A5 and SLC10A7 may be involved in solute transport and SLC10A3 may have a role as a housekeeping protein. Finally, the newly found role of bile acids in glucose and energy homeostasis, via the TGR5 receptor, sheds new light on the clinical relevance of ASBT and NTCP. The present mini-review provides a brief summary of recent progress on members of the SLC10 family. PMID:23506869

  20. 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).

  1. Intermediate tunnelling-hopping regime in DNA charge transport

    NASA Astrophysics Data System (ADS)

    Xiang, Limin; Palma, Julio L.; Bruot, Christopher; Mujica, Vladimiro; Ratner, Mark A.; Tao, Nongjian

    2015-03-01

    Charge transport in molecular systems, including DNA, is involved in many basic chemical and biological processes, and its understanding is critical if they are to be used in electronic devices. This important phenomenon is often described as either coherent tunnelling over a short distance or incoherent hopping over a long distance. Here, we show evidence of an intermediate regime where coherent and incoherent processes coexist in double-stranded DNA. We measure charge transport in single DNA molecules bridged to two electrodes as a function of DNA sequence and length. In general, the resistance of DNA increases linearly with length, as expected for incoherent hopping. However, for DNA sequences with stacked guanine-cytosine (GC) base pairs, a periodic oscillation is superimposed on the linear length dependence, indicating partial coherent transport. This result is supported by the finding of strong delocalization of the highest occupied molecular orbitals of GC by theoretical simulation and by modelling based on the Büttiker theory of partial coherent charge transport.

  2. Charge transport through exciton shelves in cadmium chalcogenide quantum dot-DNA nano-bioelectronic thin films

    SciTech Connect

    Goodman, Samuel M.; Singh, Vivek; Noh, Hyunwoo; Cha, Jennifer N.; Nagpal, Prashant

    2015-02-23

    Quantum dot (QD), or semiconductor nanocrystal, thin films are being explored for making solution-processable devices due to their size- and shape-tunable bandgap and discrete higher energy electronic states. While DNA has been extensively used for the self-assembly of nanocrystals, it has not been investigated for the simultaneous conduction of multiple energy charges or excitons via exciton shelves (ES) formed in QD-DNA nano-bioelectronic thin films. Here, we present studies on charge conduction through exciton shelves, which are formed via chemically coupled QDs and DNA, between electronic states of the QDs and the HOMO-LUMO levels in the complementary DNA nucleobases. While several challenges need to be addressed in optimizing the formation of devices using QD-DNA thin films, a higher charge collection efficiency for hot-carriers and our detailed investigations of charge transport mechanism in these thin films highlight their potential for applications in nano-bioelectronic devices and biological transducers.

  3. Charge Transport and Transfer at the Nanoscale Between Metals and Novel Conjugated Materials

    NASA Astrophysics Data System (ADS)

    Worne, Jeffrey Howard

    Organic semiconductors (OSCs) and graphene are two classes of conjugated materials that hold promise to create flexible electronic displays, high speed transistors, and low-cost solar cells. Crucial to understanding the behavior of these materials is understanding the effects metallic contacts have on the local charge environment. Additionally, characterizing the charge carrier transport behavior within these materials sheds light on the physical mechanisms behind transport. The first part of this thesis examines the origin of the low-temperature, high electric field transport behavior of OSCs. Two chemically distinct OSCs are used, poly-3(hexylthiophene) (P3HT) and 6,13-bis(triisopropyl-silylethynyl) (TIPS) pentacene. Several models explaining the low-temperature behavior are presented, with one using the Tomonaga-Luttinger liquid (TLL) insulator-to-metal transition model and one using a field-emission hopping model. While the TLL model is only valid for 1-dimensional systems, it is shown to work for both P3HT (1D) and TIPS-pentacene (2D), suggesting the TLL model is not an appropriate description of these systems. Instead, a cross-over from thermally-activated hopping to field-emission hopping is shown to explain the data well. The second part of this thesis focuses on the interaction between gold and platinum contacts and graphene using suspended graphene over sub-100 nanometer channels. Contacts to graphene can strongly dominate charge transport and mobility as well as significantly modify the charge environment local to the contacts. Platinum electrodes are discovered to be strong dopants to graphene at short length scales while gold electrodes do not have the same effect. By increasing the separation distance between the electrodes, this discrepancy is shown to disappear, suggesting an upper limit on charge diffusion from the contacts. Finally, this thesis will discuss a novel technique to observe the high-frequency behavior in OSCs using two microwave sources and an organic transistor as a mixer. A theoretical model motivating this technique is presented which suggests the possibility of retrieving gigahertz charge transport phenomena at kilohertz detection frequencies. The current state of the project is presented and discrepancies between devices made with gold and platinum electrodes measured in the GHz regime are discussed.

  4. 47 CFR 51.909 - Transition of rate-of-return carrier access charges.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 2013-10-01 false Transition of rate-of-return carrier...Service Pricing § 51.909 Transition of rate-of-return carrier...Cap the rates for all rate elements for services contained...interstate switched access rate elements, in its interstate...

  5. 47 CFR 51.907 - Transition of price cap carrier access charges.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 2014-10-01 false Transition of price cap carrier access...Service Pricing § 51.907 Transition of price cap carrier access...interstate and intrastate rate elements for services contained...interstate and intrastate rate elements in the traffic sensitive...

  6. 47 CFR 51.907 - Transition of price cap carrier access charges.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 2012-10-01 false Transition of price cap carrier access...Service Pricing § 51.907 Transition of price cap carrier access...interstate and intrastate rate elements for services contained...interstate and intrastate rate elements in the traffic sensitive...

  7. 47 CFR 51.909 - Transition of rate-of-return carrier access charges.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 2012-10-01 false Transition of rate-of-return carrier...Service Pricing § 51.909 Transition of rate-of-return carrier...Cap the rates for all rate elements for services contained...interstate switched access rate elements, in its interstate...

  8. 47 CFR 51.907 - Transition of price cap carrier access charges.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 2013-10-01 false Transition of price cap carrier access...Service Pricing § 51.907 Transition of price cap carrier access...interstate and intrastate rate elements for services contained...interstate and intrastate rate elements in the traffic sensitive...

  9. 47 CFR 51.909 - Transition of rate-of-return carrier access charges.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 2014-10-01 false Transition of rate-of-return carrier...Service Pricing § 51.909 Transition of rate-of-return carrier...Cap the rates for all rate elements for services contained...interstate switched access rate elements, in its interstate...

  10. Utilizing carbon nanotube electrodes to improve charge injection and transport in bis(trifluoromethyl)-dimethyl-rubrene ambipolar single crystal transistors.

    PubMed

    Xie, Wei; Prabhumirashi, Pradyumna L; Nakayama, Yasuo; McGarry, Kathryn A; Geier, Michael L; Uragami, Yuki; Mase, Kazuhiko; Douglas, Christopher J; Ishii, Hisao; Hersam, Mark C; Frisbie, C Daniel

    2013-11-26

    We have examined the significant enhancement of ambipolar charge injection and transport properties of bottom-contact single crystal field-effect transistors (SC-FETs) based on a new rubrene derivative, bis(trifluoromethyl)-dimethyl-rubrene (fm-rubrene), by employing carbon nanotube (CNT) electrodes. The fundamental challenge associated with fm-rubrene crystals is their deep-lying HOMO and LUMO energy levels, resulting in inefficient hole injection and suboptimal electron injection from conventional Au electrodes due to large Schottky barriers. Applying thin layers of CNT network at the charge injection interface of fm-rubrene crystals substantially reduces the contact resistance for both holes and electrons; consequently, benchmark ambipolar mobilities have been achieved, reaching 4.8 cm(2) V(-1) s(-1) for hole transport and 4.2 cm(2) V(-1) s(-1) for electron transport. We find that such improved injection efficiency in fm-rubrene is beneficial for ultimately unveiling its intrinsic charge transport properties so as to exceed those of its parent molecule, rubrene, in the current device architecture. Our studies suggest that CNT electrodes may provide a universal approach to ameliorate the charge injection obstacles in organic electronic devices regardless of charge carrier type, likely due to the electric field enhancement along the nanotube located at the crystal/electrode interface. PMID:24175573

  11. Carrier Transport Behaviour of Molecular Doped Poly(N-Vinylcarbozole) in Polymer Light-Emitting Diodes

    NASA Astrophysics Data System (ADS)

    Chen, Xiao-Hong; Xu, Zheng; Hou, Yan-Bing; Liu, Shu-Man; Teng, Feng; Xu, Xu-Rong

    2002-11-01

    Single-layer polymer light-emitting diodes are prepared from blends of poly(N-vinylcarbozole) (PVK) doped with tris(8-hydroxy-quinoline) aluminium (Alq3) of 2 wt% (sample a) and 0.2 wt% (sample b). The onset of PVK transient electroluminescence (EL) is delayed with respect to that of Alq3 in sample a under pulsed excitation, while the EL onsets of Alq3 and PVK in sample b are simultaneous. The total carrier mobility of the Alq3-rich regions in sample a is larger than that of the PVK-rich regions. However, the total carrier mobility is homogeneous in sample b. The phase image of atomic force microscopy and photoluminescence spectra of samples a and b indicate that the separated phase of samples a and b exists in the PVK-rich and Alq3-rich regions. The variance of the doping concentration and separated phase in blends results in the different carrier transport mobility of Alq3-rich and PVK-rich regions.

  12. Optical absorption and DFT calculations in L-aspartic acid anhydrous crystals: Charge carrier effective masses point to semiconducting behavior

    NASA Astrophysics Data System (ADS)

    Silva, A. M.; Silva, B. P.; Sales, F. A. M.; Freire, V. N.; Moreira, E.; Fulco, U. L.; Albuquerque, E. L.; Maia, F. F., Jr.; Caetano, E. W. S.

    2012-11-01

    Density functional theory (DFT) computations within the local-density approximation and generalized gradient approximation in pure form and with dispersion correction (GGA+D) were carried out to investigate the structural, electronic, and optical properties of L-aspartic acid anhydrous crystals. The electronic (band structure and density of states) and optical absorption properties were used to interpret the light absorption measurements we have performed in L-aspartic acid anhydrous crystalline powder at room temperature. We show the important role of the layered spatial disposition of L-aspartic acid molecules in anhydrous L-aspartic crystals to explain the observed electronic and optical properties. There is good agreement between the GGA+D calculated and experimental lattice parameters, with (?a, ?b, ?c) deviations of (0.029,-0.023,-0.024) (units in Å). Mulliken [J. Chem. Phys.JCPSA60021-960610.1063/1.1740588 23, 1833 (1955)] and Hirshfeld [Theor. Chim. ActaTCHAAM0040-574410.1007/BF00549096 44, 129 (1977)] population analyses were also performed to assess the degree of charge polarization in the zwitterion state of the L-aspartic acid molecules in the DFT converged crystal. The lowest-energy optical absorption peaks related to transitions between the top of the valence band and the bottom of the conduction band involve O 2p valence states and C 1p and O 2p conduction states, with the carboxyl and COOH lateral chain group contributing significantly to the energy band gap. Among the calculated band gaps, the lowest GGA+D (4.49-eV) gap is smaller than the experimental estimate of 5.02 eV, as obtained by optical absorption. Such a wide-band-gap energy together with the small carrier effective masses estimated from band curvatures allows us to suggest that an L-aspartic acid anhydrous crystal can behave as a wide-gap semiconductor. A comparison of effective masses among directions parallel and perpendicular to the L-aspartic molecules layers reveals that charge transport must be favored in the former case. Finally, we also show that there is a strong optical anisotropy in the dielectric function of L-aspartic acid anhydrous crystals.

  13. Secondary electron emission and self-consistent charge transport in semi-insulating samples

    SciTech Connect

    Fitting, H.-J.; Touzin, M.

    2011-08-15

    Electron beam induced self-consistent charge transport and secondary electron emission (SEE) in insulators are described by means of an electron-hole flight-drift model (FDM) now extended by a certain intrinsic conductivity (c) and are implemented by an iterative computer simulation. Ballistic secondary electrons (SE) and holes, their attenuation to drifting charge carriers, and their recombination, trapping, and field- and temperature-dependent detrapping are included. As a main result the time dependent ''true'' secondary electron emission rate {delta}(t) released from the target material and based on ballistic electrons and the spatial distributions of currents j(x,t), charges {rho}(x,t), field F(x,t), and potential V(x,t) are obtained where V{sub 0} = V(0,t) presents the surface potential. The intrinsic electronic conductivity limits the charging process and leads to a conduction sample current to the support. In that case the steady-state total SE yield will be fixed below the unit: i.e., {sigma} {eta} + {delta} < 1.

  14. Optical conductivity and optical effective mass in a high-mobility organic semiconductor: Implications for the nature of charge transport

    NASA Astrophysics Data System (ADS)

    Li, Yuan; Yi, Yuanping; Coropceanu, Veaceslav; Brédas, Jean-Luc

    2014-12-01

    We present a multiscale modeling of the infrared optical properties of the rubrene crystal. The results are in very good agreement with the experimental data that point to nonmonotonic features in the optical conductivity spectrum and small optical effective masses. We find that, in the static-disorder approximation, the nonlocal electron-phonon interactions stemming from low-frequency lattice vibrations can decrease the optical effective masses and lead to lighter quasiparticles. On the other hand, the charge-transport and infrared optical properties of the rubrene crystal at room temperature are demonstrated to be governed by localized carriers driven by inherent thermal disorders. Our findings underline that the presence of apparently light carriers in high-mobility organic semiconductors does not necessarily imply bandlike transport.

  15. Human Transport Protein Carrier for Controlled Photoactivation of Antitumor Prodrug and Real-Time Intracellular Tumor Imaging

    E-print Network

    Xing, Bengang

    Human Transport Protein Carrier for Controlled Photoactivation of Antitumor Prodrug and Real indicates great potential for clinical practice in the future.6-9 Over various types of nanostructures transport protein in human blood, could serve as an ideal platform for effective delivery of therapeutic

  16. Dopant effects on charge transport to enhance performance of phosphorescent white organic light emitting diodes

    NASA Astrophysics Data System (ADS)

    Zhu, Liping; Chen, Jiangshan; Ma, Dongge

    2015-11-01

    We compared the performance of phosphorescent white organic light emitting diodes (WOLEDs) with red-blue-green and green-blue-red sequent emissive layers. It was found that the influence of red and green dopants on electron and hole transport in emissive layers leads to the large difference in the efficiency of fabricated WOLEDs. This improvement mechanism is well investigated by the current density-voltage characteristics of single-carrier devices based on dopant doped emissive layers and the comparison of electroluminescent and photoluminescence spectra, and attributed to the different change of charge carrier transport by the dopants. The optimized device achieves a maximum power efficiency, current efficiency, and external quantum efficiency of 37.0 lm/W, 38.7 cd/A, and 17.7%, respectively, which are only reduced to 32.8 lm/W, 38.5 cd/A, and 17.3% at 1000 cd/m2 luminance. The critical current density is as high as 210 mA/cm2. It can be seen that the efficiency roll-off in phosphorescent WOLEDs can be well improved by effectively designing the structure of emissive layers.

  17. Relationship between structural coherence and intrinsic carrier transport in an isolated poly(3-hexylthiophene) nanofiber

    NASA Astrophysics Data System (ADS)

    Shimomura, Takeshi; Takahashi, Tomoyuki; Ichimura, Yasutaka; Nakagawa, Shino; Noguchi, Keiichi; Heike, Seiji; Hashizume, Tomihiro

    2011-03-01

    Our study is focused on the relationship between the structural coherence and intrinsic carrier transport in a regioregular poly(3-hexylthiophene-2,5-diyl) (P3HT) nanofiber, particularly in an isolated nanofiber, formed in various ratios of good and poor solvent mixtures. The P3HT nanofiber, which is formed in solvent mixtures, had a whisker structure with the length of several ?m, the height decreased from 9 to 2 nm as estimated by scanning force microscope observation, and the structural coherent length along the longitudinal axis increased from 40 to 59 Å as determined by x-ray-diffraction measurement, with increasing ratio of the good solvent. The I-V characteristics measured by the four-probe method showed that the activation energy of hopping conduction, which was considerably related with the structural disorder, decreased with increasing ratio of the good solvent. Moreover, the field-effect-transistor characteristics of the nanofiber showed that the carrier mobility increased with increasing ratio of the good solvent, and the nanofiber formed under the good-solvent-rich condition showed the mobility from 3.8×10-2 to 5.6×10-2 cm2 V-1 s-1. The tendency of the mobility to increase has been explained on the basis of the change in the structural coherent length and thermal activation energy, assuming the model that regarded the nanofiber as a one-dimensional array of electronically coherent regions and incoherent defects, and hence the relationship between the structural coherence and carrier transport has been clarified.

  18. Dioxin mediates downregulation of the reduced folate carrier transport activity via the arylhydrocarbon receptor signalling pathway

    SciTech Connect

    Halwachs, Sandra; Lakoma, Cathleen; Gebhardt, Rolf; Schaefer, Ingo; Seibel, Peter; Honscha, Walther

    2010-07-15

    Dioxins such as 2,3,7,8-tetrachlordibenzo-p-dioxin (TCDD) are common environmental contaminants known to regulate several genes via activation of the transcription factor aryl hydrocarbon receptor (AhR) associated with the development of numerous adverse biological effects. However, comparatively little is known about the molecular mechanisms by which dioxins display their toxic effects in vertebrates. The 5' untranslated region of the hepatocellular Reduced folate carrier (Rfc1; Slc19a1) exhibits AhR binding sites termed dioxin responsive elements (DRE) that have as yet only been found in the promoter region of prototypical TCDD target genes. Rfc1 mediated transport of reduced folates and antifolate drugs such as methotrexate (MTX) plays an essential role in physiological folate homeostasis and MTX cancer chemotherapy. In order to determine whether this carrier represents a target gene of dioxins we have investigated the influence of TCDD on functional Rfc1 activity in rat liver. Pre-treatment of rats with TCDD significantly diminished hepatocellular Rfc1 uptake activity in a time- and dose-dependent manner. In further mechanistic studies we demonstrated that this reduction was due to TCDD-dependent activation of the AhR signalling pathway. We additionally showed that binding of the activated receptor to DRE motifs in the Rfc1 promoter resulted in downregulation of Rfc1 gene expression and reduced carrier protein levels. As downregulation of pivotal Rfc1 activity results in functional folate deficiency associated with an elevated risk of cardiovascular diseases or carcinogenesis, our results indicate that deregulation of this essential transport pathway represents a novel regulatory mechanism how dioxins display their toxic effects through the Ah receptor.

  19. Transportable cavity-stabilized laser system for optical carrier frequency transmission experiments.

    PubMed

    Parker, B; Marra, G; Johnson, L A M; Margolis, H S; Webster, S A; Wright, L; Lea, S N; Gill, P; Bayvel, P

    2014-12-10

    We report the design and performance of a transportable laser system at 1543 nm, together with its application as the source for a demonstration of optical carrier frequency transmission over 118 km of an installed dark fiber network. The laser system is based around an optical reference cavity featuring an elastic mounting that bonds the cavity to its support, enabling the cavity to be transported without additional clamping. The cavity exhibits passive fractional frequency insensitivity to vibration along the optical axis of 2.0×10(-11)??m(-1)?s(2). With active fiber noise cancellation, the optical carrier frequency transmission achieves a fractional frequency instability, measured at the user end, of 2.6×10(-16) at 1 s, averaging down to below 3×10(-18) after 20,000 s. The fractional frequency accuracy of the transfer is better than 3×10(-18). This level of performance is sufficient for comparison of state-of-the-art optical frequency standards and is achieved in an urban fiber environment. PMID:25608055

  20. Charge Transport through Organized Organic Assemblies in Confined Geometries 

    E-print Network

    Schuckman, Amanda Eileen

    2012-07-16

    of Department, David H. Russell May 2011 Major Subject: Chemistry iii ABSTRACT Charge Transport through Organized Organic Assemblies in Confined Geometries. (May 2011) Amanda Eileen Schuckman, B.S., Texas Lutheran University Chair of Advisory.... ........................... 9 1.2 (A) Structure of the porphyrin macrocycles with a cadre of common meso (5,10,15,20) aryl derivatives. Note the meso alkane compounds are also readily accessible synthetically. (B) Much of the supramolecular chemistry of porphyrins uses...

  1. 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.

  2. 19 CFR 351.515 - Internal transport and freight charges for export shipments.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 19 Customs Duties 3 2010-04-01 2010-04-01 false Internal transport and freight charges for export... Internal transport and freight charges for export shipments. (a) Benefit—(1) In general. In the case of internal transport and freight charges on export shipments, a benefit exists to the extent that the...

  3. 47 CFR 69.111 - Tandem-switched transport and tandem charge.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 3 2013-10-01 2013-10-01 false Tandem-switched transport and tandem charge. 69... 69.123, per-minute common transport charges described in paragraph (a)(1) of this section shall be... pricing zones as described in section 69.123, per-minute common transport charges described in...

  4. 47 CFR 69.111 - Tandem-switched transport and tandem charge.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 3 2012-10-01 2012-10-01 false Tandem-switched transport and tandem charge. 69... 69.123, per-minute common transport charges described in paragraph (a)(1) of this section shall be... pricing zones as described in section 69.123, per-minute common transport charges described in...

  5. 47 CFR 69.111 - Tandem-switched transport and tandem charge.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 3 2010-10-01 2010-10-01 false Tandem-switched transport and tandem charge. 69... 69.123, per-minute common transport charges described in paragraph (a)(1) of this section shall be... pricing zones as described in section 69.123, per-minute common transport charges described in...

  6. 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... 69.123, per-minute common transport charges described in paragraph (a)(1) of this section shall be... pricing zones as described in section 69.123, per-minute common transport charges described in...

  7. 47 CFR 69.111 - Tandem-switched transport and tandem charge.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 3 2014-10-01 2014-10-01 false Tandem-switched transport and tandem charge. 69... 69.123, per-minute common transport charges described in paragraph (a)(1) of this section shall be... pricing zones as described in section 69.123, per-minute common transport charges described in...

  8. Improved understanding of the electronic and energetic landscapes of perovskite solar cells: high local charge carrier mobility, reduced recombination, and extremely shallow traps.

    PubMed

    Oga, Hikaru; Saeki, Akinori; Ogomi, Yuhei; Hayase, Shuzi; Seki, Shu

    2014-10-01

    The intriguing photoactive features of organic-inorganic hybrid perovskites have enabled the preparation of a new class of highly efficient solar cells. However, the fundamental properties, upon which the performance of these devices is based, are currently under-explored, making their elucidation a vital issue. Herein, we have investigated the local mobility, recombination, and energetic landscape of charge carriers in a prototype CH3NH3PbI3 perovskite (PVK) using a laser-flash time-resolved microwave conductivity (TRMC) technique. PVK was prepared on mesoporous TiO2 and Al2O3 by one or two-step sequential deposition. PVK on mesoporous TiO2 exhibited a charge carrier mobility of 20 cm(2) V(-1) s(-1), which was predominantly attributed to holes. PVK on mesoporous Al2O3, on the other hand, exhibited a 50% lower mobility, which was resolved into balanced contributions from both holes and electrons. A general correlation between crystal size and mobility was revealed irrespective of the fabrication process and underlying layer. Modulating the microwave frequency from 9 toward 23 GHz allowed us to determine the intrinsic mobilities of each PVK sample (60-75 cm(2) V(-1) s(-1)), which were mostly independent of the mesoporous scaffold. Kinetic and frequency analysis of the transient complex conductivity strongly support the superiority of the perovskite, based on a significant suppression of charge recombination, an extremely shallow trap depth (10 meV), and a low concentration of these trapped states (less than 10%). The transport mechanism was further investigated by examining the temperature dependence of the TRMC maxima. Our study provides a basis for understanding perovskite solar cell operation, while highlighting the importance of the mesoporous layer and the perovskite fabrication process. PMID:25188538

  9. 41 CFR 302-10.300 - May I receive an advance of funds when a commercial carrier transports the mobile home?

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ...when a commercial carrier transports the mobile home? 302-10.300 Section 302-10... 10-ALLOWANCES FOR TRANSPORTATION OF MOBILE HOMES AND BOATS USED AS A PRIMARY RESIDENCE...when a commercial carrier transports the mobile home? Yes, you may receive an...

  10. 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, 2014 CFR

    2014-07-01

    ... State or local law. (b) When transporting over water cost must include, but not limited to the cost of... when a commercial carrier transports my mobile home overland or over water? 302-10.200 Section 302-10... carrier transports my mobile home overland or over water? Your agency will allow the following costs...

  11. 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, 2012 CFR

    2012-07-01

    ... State or local law. (b) When transporting over water cost must include, but not limited to the cost of... when a commercial carrier transports my mobile home overland or over water? 302-10.200 Section 302-10... carrier transports my mobile home overland or over water? Your agency will allow the following costs...

  12. 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, 2013 CFR

    2013-07-01

    ... State or local law. (b) When transporting over water cost must include, but not limited to the cost of... when a commercial carrier transports my mobile home overland or over water? 302-10.200 Section 302-10... carrier transports my mobile home overland or over water? Your agency will allow the following costs...

  13. 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, 2011 CFR

    2011-07-01

    ... State or local law. (b) When transporting over water cost must include, but not limited to the cost of... when a commercial carrier transports my mobile home overland or over water? 302-10.200 Section 302-10... carrier transports my mobile home overland or over water? Your agency will allow the following costs...

  14. Nanostructural analysis of ZnO:Al thin films for carrier-transport Seung-Yoon Lee a,b

    E-print Network

    Park, Byungwoo

    . Introduction In Si thin-film solar cells, the polycrystalline ZnO:Al transparent conducting oxide (TCO) frontNanostructural analysis of ZnO:Al thin films for carrier-transport mechanisms Seung-Yoon Lee a-doped ZnO Sputtering a b s t r a c t The carrier mobility of sputter-deposited Al-doped ZnO transparent

  15. Real-time dynamics of the acoustically induced carrier transport in GaAs quantum wires

    NASA Astrophysics Data System (ADS)

    Alsina, F.; Santos, P. V.; Schönherr, H.-P.; Nötzel, R.; Ploog, K. H.

    2003-04-01

    We have investigated the dynamics of the ambipolar transport of photogenerated electrons and holes induced by surface acoustic waves in GaAs quantum wires by using photoluminescence measurements with spatial and temporal resolutions. This technique allows us to trace the trajectory of charge packages in real time and to access the dynamics of radiative trapping centers. We identify two different kinds of trapping defects, which capture preferentially either holes or electrons.

  16. Investigation of free charge carrier dynamics in single-crystalline CVD diamond by two-photon absorption

    SciTech Connect

    Ivakin, E V; Kisialiou, I G; Ralchenko, V G; Bolshakov, A P; Ashkinazi, E E; Sharonov, G V

    2014-11-30

    By using the methods of transient gratings (TGs) and induced absorption, we have studied the kinetics of plasma of free charge carriers (FCCs) created by the action of a picosecond laser pulse in two high-purity diamond single crystals synthesised from the gas phase. The gratings with different spatial periods have been excited at the wavelengths of 266 or 213 nm (above and below the fundamental absorption edge in diamond) and probed with continuous-wave radiation in the visible region. At the moderate FCC concentrations (?7 × 10{sup 17} cm{sup -3}), the coefficient of ambipolar diffusion and the carrier recombination time of two crystals are 20.3 and 18.9 cm{sup 2} s{sup -1} and 30 and 190 ns, respectively. The increase in the carrier concentration up to 5 × 10{sup 19} cm{sup -3} reduces the TG lifetime. We have determined the conditions under which the relaxation of the grating of carriers leads to the formation of a thermal grating, with the amplitude sufficient for its experimental observation. (interaction of laser radiation with matter. laser plasma)

  17. Electron spin resonance study of Er-concentration effect in GaAs;Er,O containing charge carriers

    SciTech Connect

    Elmasry, F.; Okubo, S.; Ohta, H.; Fujiwara, Y.

    2014-05-21

    Er-concentration effect in GaAs;Er,O containing charge carriers (n-type, high resistance, p-type) has been studied by X-band Electron spin resonance (ESR) at low temperature (4.7?K?carrier. The local structure around Er-2O centers is not affected by carriers because similar angular dependence of g-values was observed in both cases (with/without carrier). For temperature dependence, linewidth and lineshape analysis suggested the existence of Er dimers with antiferromagnetic exchange interaction of about 7?K. Moreover, drastic decrease of ESR intensity for C signal in p-type sample was observed and it correlates with the decrease of photoluminescence (PL) intensity. Possible model for the Er-2O trap level in GaAs:Er,O is discussed from the ESR and PL experimental results.

  18. Space-Charge Transport Limits in Periodic Channels

    SciTech Connect

    Lund, S M; Chawla, S R

    2005-05-16

    It has been empirically observed in both experiments and particle-in-cell simulations that space-charge-dominated beams suffer strong emittance growth and particle losses in alternating gradient quadrupole transport channels when the undepressed phase advance {sigma}{sub 0} increases beyond about 85{sup o} per lattice period. Although this criteria has been used extensively in practical designs of intense beam transport lattices, no theory exists that explains the limit. We propose a mechanism for the transport limit resulting from classes of halo particle resonances near the core of the beam that allow near-edge particles to rapidly increase in oscillation amplitude when the space-charge intensity and the flutter of the matched beam envelope are both sufficiently large. Due to a finite beam edge and/or perturbations, this mechanism can result in dramatic halo-driven increases in statistical beam phase space area, lost particles, and degraded transport. A core-particle model for a uniform density elliptical beam in a periodic focusing lattice is applied to parametrically analyze this process.

  19. Dissociation of Charge Transfer States and Carrier Separation in Bilayer Organic Solar Cells: A Time-Resolved Electroabsorption Spectroscopy Study.

    PubMed

    Devižis, Andrius; De Jonghe-Risse, Jelissa; Hany, Roland; Nüesch, Frank; Jenatsch, Sandra; Gulbinas, Vidmantas; Moser, Jacques-E

    2015-07-01

    Ultrafast optical probing of the electric field by means of Stark effect in planar heterojunction cyanine dye/fullerene organic solar cells enables one to directly monitor the dynamics of free electron formation during the dissociation of interfacial charge transfer (CT) states. Motions of electrons and holes is scrutinized separately by selectively probing the Stark shift dynamics at selected wavelengths. It is shown that only charge pairs with an effective electron-hole separation distance of less than 4 nm are created during the dissociation of Frenkel excitons. Dissociation of the coulombically bound charge pairs is identified as the major rate-limiting step for charge carriers' generation. Interfacial CT states split into free charges on the time-scale of tens to hundreds of picoseconds, mainly by electron escape from the Coulomb potential over a barrier that is lowered by the electric field. The motion of holes in the small molecule donor material during the charge separation time is found to be insignificant. PMID:26037526

  20. 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 ? = 3.1 ± 0.2 ps, with charge recombination in ? = 340 ± 10 ps, while in unannealed/disordered films of 1, charge separation occurs in ? more »CH?Cl? 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 ?s. 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

  1. An acoustic charge transport imager for high definition television applications

    NASA Technical Reports Server (NTRS)

    Hunt, W. D.; Brennan, K. F.; Summers, C. J.

    1994-01-01

    The primary goal of this research is to develop a solid-state television (HDTV) imager chip operating at a frame rate of about 170 frames/sec at 2 Megapixels/frame. This imager will offer an order of magnitude improvements in speed over CCD designs and will allow for monolithic imagers operating from the IR to UV. The technical approach of the project focuses on the development of the three basic components of the imager and their subsequent integration. The camera chip can be divided into three distinct functions: (1) image capture via an array of avalanche photodiodes (APD's); (2) charge collection, storage, and overflow control via a charge transfer transistor device (CTD); and (3) charge readout via an array of acoustic charge transport (ACT) channels. The use of APD's allows for front end gain at low noise and low operating voltages while the ACT readout enables concomitant high speed and high charge transfer efficiency. Currently work is progressing towards the optimization of each of these component devices. In addition to the development of each of the three distinct components, work towards their integration and manufacturability is also progressing. The component designs are considered not only to meet individual specifications but to provide overall system level performance suitable for HDTV operation upon integration. The ultimate manufacturability and reliability of the chip constrains the design as well. The progress made during this period is described in detail.

  2. An acoustic charge transport imager for high definition television applications

    NASA Technical Reports Server (NTRS)

    Hunt, W. D.; Brennan, Kevin F.

    1994-01-01

    The primary goal of this research is to develop a solid-state high definition television (HDTV) imager chip operating at a frame rate of about 170 frames/sec at 2 Megapixels per frame. This imager offers an order of magnitude improvement in speed over CCD designs and will allow for monolithic imagers operating from the IR to the UV. The technical approach of the project focuses on the development of the three basic components of the imager and their integration. The imager chip can be divided into three distinct components: (1) image capture via an array of avalanche photodiodes (APD's), (2) charge collection, storage and overflow control via a charge transfer transistor device (CTD), and (3) charge readout via an array of acoustic charge transport (ACT) channels. The use of APD's allows for front end gain at low noise and low operating voltages while the ACT readout enables concomitant high speed and high charge transfer efficiency. Currently work is progressing towards the development of manufacturable designs for each of these component devices. In addition to the development of each of the three distinct components, work towards their integration is also progressing. The component designs are considered not only to meet individual specifications but to provide overall system level performance suitable for HDTV operation upon integration. The ultimate manufacturability and reliability of the chip constrains the design as well. The progress made during this period is described in detail in Sections 2-4.

  3. The Carrier's Liability for Damage Caused by Delay in International Air Transport

    NASA Technical Reports Server (NTRS)

    Lee, Kang Bin

    2003-01-01

    Delay in the air transport occurs when passengers, baggage or cargo do not arrive at their destination at the time indicated in the contract of carriage. The causes of delay in the carriage of passengers are booking errors or double booking, delayed departure of aircraft, incorrect information regarding the time of departure, failure to land at the scheduled destination and changes in flight schedule or addition of extra landing stops. Delay in the carriage of baggage or cargo may have different causes: no reservation, lack of space, failure to load the baggage or cargo at the right place, or to deliver the covering documents at the right place. The Montreal Convention of 1999 Article 19 provides that 'The carrier is liable for damage occasioned by delay in the carriage by air of passengers, baggage or cargo. Nevertheless, the carder shall not be liable for damage occasioned by delay if it proves that it and its servants and agents took all measures that could reasonably be required to avoid the damage or that it was impossible for it or them to take such measures'. The Montreal Convention Article 22 provides liability limits of the carrier in case of delay for passengers and their baggage and for cargo. In the carriage of persons, the liability of the carrier for each passenger is limited to 4,150 SDR. In the carriage of baggage, the liability of the carrier is limited to 1,000 SDR for each passenger unless a special declaration as to the value of the baggage has been made. In the carriage of cargo, the liability of the carrier is limited to 17 SDR per kilogram unless a special declaration as to the value of the cargo has been made. The Montreal Convention Article 19 has shortcomings: it is silent on the duration of the liability for carriage,andit does not make any distinction between persons and good. It does not give any indication concerning the circumstances to be taken into account in cases of delay, and about the length of delay. In conclusion, it is desirable to define the period of carriage with accuracy, and to insert the word 'unreasonable' in Article 19.

  4. Charge transport in dye-sensitized solar cell

    NASA Astrophysics Data System (ADS)

    Yanagida, Masatoshi

    2015-03-01

    The effect of charge transport on the photovoltaic properties of dye-sensitized solar cells (DSCs) was investigated by the experimental results and the ion transport. The short current photocurrent density (Jsc) is determined by the electron transport in porous TiO2 when the diffusion limited current (Jdif) due to the {{I}3}- transport is larger than the photo-generated electron flux (Jg) estimated from the light harvesting efficiency of dye-sensitized porous TiO2 and the solar spectrum. However, the Jsc value is determined by the ion transport in the electrolyte solution at Jdif < Jg. The J value becomes constant against light intensity, and is expressed as the saturated current (Jscs). The {{J}s} value depends on the thickness (d) of the TiO2 layer, the initial concentration (COX0), and the diffusion coefficient (DOXb) of {{I}3}-. These suitable parameters were determined by using the ion transport. Invited talk at the 7th International Workshop on Advanced Materials Science and Nanotechnology IWAMSN2014, 2-6 November, 2014, Ha Long, Vietnam.

  5. Normal and impaired charge transport in biological systems

    NASA Astrophysics Data System (ADS)

    Miller, John H.; Villagrán, Martha Y. Suárez; Maric, Sladjana; Briggs, James M.

    2015-03-01

    We examine the physics behind some of the causes (e.g., hole migration and localization that cause incorrect base pairing in DNA) and effects (due to amino acid replacements affecting mitochondrial charge transport) of disease-implicated point mutations, with emphasis on mutations affecting mitochondrial DNA (mtDNA). First we discuss hole transport and localization in DNA, including some of our quantum mechanical modeling results, as they relate to certain mutations in cancer. Next, we give an overview of electron and proton transport in the mitochondrial electron transport chain, and how such transport can become impaired by mutations implicated in neurodegenerative diseases, cancer, and other major illnesses. In particular, we report on our molecular dynamics (MD) studies of a leucine?arginine amino acid replacement in ATP synthase, encoded by the T?G point mutation at locus 8993 of mtDNA. This mutation causes Leigh syndrome, a devastating maternally inherited neuromuscular disorder, and has been found to trigger rapid tumor growth in prostate cancer cell lines. Our MD results suggest, for the first time, that this mutation adversely affects water channels that transport protons to and from the c-ring of the rotary motor ATP synthase, thus impairing the ability of the motor to produce ATP. Finally, we discuss possible future research topics for biological physics, such as mitochondrial complex I, a large proton-pumping machine whose physics remains poorly understood.

  6. Origin of stress and enhanced carrier transport in solution-cast organic semiconductor films

    NASA Astrophysics Data System (ADS)

    Cour, Ishviene; Chinta, Priya V.; Schlepütz, Christian M.; Yang, Yongsoo; Clarke, Roy; Pindak, Ron; Headrick, Randall L.

    2013-09-01

    Molecular packing in laterally directed solution deposition is a strong function of variables such as printing speed, substrate temperature, and solution concentration. Knowledge of the ordering mechanisms impacts on the development of new processes and materials for improved electronic devices. Here, we present real-time synchrotron x-ray scattering results combined with optical video microscopy, revealing the stages of ordering during the deposition of organic thin films via hollow capillary writing. Limited long range ordering is observed during the initial crystallization, but it gradually develops over 3-4 s for a range of deposition conditions. Buckling of thin films is typically observed for deposition above room temperature. We infer that compressive stress originates from thermal transients related to solvent evaporation on timescales similar to the development of long range ordering. Under optimized conditions, elimination of cracks and other structural defects significantly improves the average charge carrier mobility in organic field-effect transistors.

  7. Simultaneous enhancements in photon absorption and charge transport of bismuth vanadate photoanodes for solar water splitting

    NASA Astrophysics Data System (ADS)

    Kim, Tae Woo; Ping, Yuan; Galli, Giulia A.; Choi, Kyoung-Shin

    2015-10-01

    n-Type bismuth vanadate has been identified as one of the most promising photoanodes for use in a water-splitting photoelectrochemical cell. The major limitation of BiVO4 is its relatively wide bandgap (~2.5 eV), which fundamentally limits its solar-to-hydrogen conversion efficiency. Here we show that annealing nanoporous bismuth vanadate electrodes at 350 °C under nitrogen flow can result in nitrogen doping and generation of oxygen vacancies. This gentle nitrogen treatment not only effectively reduces the bandgap by ~0.2 eV but also increases the majority carrier density and mobility, enhancing electron-hole separation. The effect of nitrogen incorporation and oxygen vacancies on the electronic band structure and charge transport of bismuth vanadate are systematically elucidated by ab initio calculations. Owing to simultaneous enhancements in photon absorption and charge transport, the applied bias photon-to-current efficiency of nitrogen-treated BiVO4 for solar water splitting exceeds 2%, a record for a single oxide photon absorber, to the best of our knowledge.

  8. Simultaneous enhancements in photon absorption and charge transport of bismuth vanadate photoanodes for solar water splitting

    PubMed Central

    Kim, Tae Woo; Ping, Yuan; Galli, Giulia A.; Choi, Kyoung-Shin

    2015-01-01

    n-Type bismuth vanadate has been identified as one of the most promising photoanodes for use in a water-splitting photoelectrochemical cell. The major limitation of BiVO4 is its relatively wide bandgap (?2.5?eV), which fundamentally limits its solar-to-hydrogen conversion efficiency. Here we show that annealing nanoporous bismuth vanadate electrodes at 350?°C under nitrogen flow can result in nitrogen doping and generation of oxygen vacancies. This gentle nitrogen treatment not only effectively reduces the bandgap by ?0.2?eV but also increases the majority carrier density and mobility, enhancing electron–hole separation. The effect of nitrogen incorporation and oxygen vacancies on the electronic band structure and charge transport of bismuth vanadate are systematically elucidated by ab initio calculations. Owing to simultaneous enhancements in photon absorption and charge transport, the applied bias photon-to-current efficiency of nitrogen-treated BiVO4 for solar water splitting exceeds 2%, a record for a single oxide photon absorber, to the best of our knowledge. PMID:26498984

  9. Simultaneous enhancements in photon absorption and charge transport of bismuth vanadate photoanodes for solar water splitting.

    PubMed

    Kim, Tae Woo; Ping, Yuan; Galli, Giulia A; Choi, Kyoung-Shin

    2015-01-01

    n-Type bismuth vanadate has been identified as one of the most promising photoanodes for use in a water-splitting photoelectrochemical cell. The major limitation of BiVO4 is its relatively wide bandgap (?2.5?eV), which fundamentally limits its solar-to-hydrogen conversion efficiency. Here we show that annealing nanoporous bismuth vanadate electrodes at 350?°C under nitrogen flow can result in nitrogen doping and generation of oxygen vacancies. This gentle nitrogen treatment not only effectively reduces the bandgap by ?0.2?eV but also increases the majority carrier density and mobility, enhancing electron-hole separation. The effect of nitrogen incorporation and oxygen vacancies on the electronic band structure and charge transport of bismuth vanadate are systematically elucidated by ab initio calculations. Owing to simultaneous enhancements in photon absorption and charge transport, the applied bias photon-to-current efficiency of nitrogen-treated BiVO4 for solar water splitting exceeds 2%, a record for a single oxide photon absorber, to the best of our knowledge. PMID:26498984

  10. The influence of Morphology on Charge Transport Properties in P3HT

    NASA Astrophysics Data System (ADS)

    Dixon, Alex; Kopidakis, Nikos; Shaheen, Sean

    2014-03-01

    The field of Organic Photovoltaic (OPV) has been growing quickly, yet there are still several questions about the underlying physics that remain poorly understood. One question is the nature of the relationship between active layer microstructure and charge transport. To investigate this, we fabricated devices using a range of molecular weights (from 13kDa to 331kDa) of poly 3-hexothyophene (P3HT). Varying the molecular weight of P3HT causes the films to exhibit changes in microstructure, with low molecular weights forming a paraffinic-like structure and higher molecular weights forming a semi-crystalline structure. Using the Charge Extraction by Linearly Increasing Voltage (CELIV) technique, we determined the hole mobility and recombination factor for theses devices. We found that the mobility in the devices peaked at 47kDa and the recombination rate decreased with increasing molecular weight. We hypothesize that the decrease in recombination is due to spacial separation of charge carrier in the semi-crystalline regions, with the holes populating the crystalline regions and the electrons populating the amorphous areas. This improves mobility for mid rage molecular weights but defects cause it to dip at higher molecular weights.

  11. Effect of Mg doping on the structural and free-charge carrier properties of InN films

    SciTech Connect

    Xie, M.-Y.; Ben Sedrine, N.; Hung, L.; Monemar, B.; Darakchieva, V.; Schöche, S.; Hofmann, T.; Schubert, M.; Wang, X.; Yoshikawa, A.; Wang, K.; Araki, T.; Nanishi, Y.

    2014-04-28

    We present a comprehensive study of free-charge carrier and structural properties of two sets of InN films grown by molecular beam epitaxy and systematically doped with Mg from 1.0?×?10{sup 18}?cm{sup ?3} to 3.9?×?10{sup 21}?cm{sup ?3}. The free electron and hole concentration, mobility, and plasmon broadening parameters are determined by infrared spectroscopic ellipsometry. The lattice parameters, microstructure, and surface morphology are determined by high-resolution X-ray diffraction and atomic force microscopy. Consistent results on the free-charge carrier type are found in the two sets of InN films and it is inferred that p-type conductivity could be achieved for 1.0?×?10{sup 18}?cm{sup ?3}???[Mg]???9.0?×?10{sup 19}?cm{sup ?3}. The systematic change of free-charge carrier properties with Mg concentration is discussed in relation to the evolution of extended defect density and growth mode. A comparison between the structural characteristics and free electron concentrations in the films provides insights in the role of extended and point defects for the n-type conductivity in InN. It further allows to suggest pathways for achieving compensated InN material with relatively high electron mobility and low defect densities. The critical values of Mg concentration for which polarity inversion and formation of zinc-blende InN occurred are determined. Finally, the effect of Mg doping on the lattice parameters is established and different contributions to the strain in the films are discussed.

  12. Positively and negatively surface-charged chondroitin sulfate-trimethylchitosan nanoparticles as protein carriers.

    PubMed

    Young, Jenn-Jong; Chen, Cheng-Cheung; Chen, Ying-Chuan; Cheng, Kuang-Ming; Yen, Hui-Ju; Huang, Yu-Chuan; Tsai, Tsung-Neng

    2016-02-10

    Positively and negatively surface-charged nanoparticles (NPs) were prepared with chondroitin sulfate (ChS) and trimethylchitosan (TMC). NP size, surface charge, formation yield, and water content were investigated as a function of weight ratio and concentration. Size and zeta potential were controlled by varying the ChS/TMC mass ratio. FTIR spectra revealed interactions among composite NP constituents. TEM images showed that the NPs were nearly spherical, with an average size of ?300nm. Encapsulation efficiency increased in positively charged NPs with increases in fluorescein isothiocyanate-bovine serum albumin concentration. Negatively charged NPs had only 10-20% encapsulation efficiency. The release profile, release kinetics and mechanism of positively charged ChS-TMC NPs were studied in vitro. NP cytocompatibility and uptake were verified ex vivo. Both types of NPs were taken up and retained in cells. A549 cells took up more positively charged (49.4%) than negatively charged (35.5%) NPs. PMID:26686160

  13. Excellent spin transport in spin valves based on the conjugated polymer with high carrier mobility

    PubMed Central

    Li, Feng; Li, Tian; Chen, Feng; Zhang, Fapei

    2015-01-01

    Organic semiconductors (OSCs) are characteristic of long spin-relaxation lifetime due to weak spin-orbit interaction and hyperfine interaction. However, short spin diffusion length and weak magnetoresistance (MR) effect at room temperature (RT) was commonly found on spin valves (SVs) using an organic spacer, which should be correlated with low carrier mobility of the OSCs. Here, N-type semiconducting polymer P(NDI2OD-T2) with high carrier mobility is employed as the spacer in the SV devices. Exceedingly high MR ratio of 90.0% at 4.2?K and of 6.8% at RT are achieved, respectively, via improving the interface structure between the polymer interlayer and top cobalt electrode as well as optimal annealing of manganite bottom electrode. Furthermore, we observe spin dependent transport through the polymeric interlayer and a large spin diffusion length with a weak temperature dependence. The results indicate that this polymer material can be used as a good medium for spintronic devices. PMID:25797862

  14. Excellent spin transport in spin valves based on the conjugated polymer with high carrier mobility

    NASA Astrophysics Data System (ADS)

    Li, Feng; Li, Tian; Chen, Feng; Zhang, Fapei

    2015-03-01

    Organic semiconductors (OSCs) are characteristic of long spin-relaxation lifetime due to weak spin-orbit interaction and hyperfine interaction. However, short spin diffusion length and weak magnetoresistance (MR) effect at room temperature (RT) was commonly found on spin valves (SVs) using an organic spacer, which should be correlated with low carrier mobility of the OSCs. Here, N-type semiconducting polymer P(NDI2OD-T2) with high carrier mobility is employed as the spacer in the SV devices. Exceedingly high MR ratio of 90.0% at 4.2 K and of 6.8% at RT are achieved, respectively, via improving the interface structure between the polymer interlayer and top cobalt electrode as well as optimal annealing of manganite bottom electrode. Furthermore, we observe spin dependent transport through the polymeric interlayer and a large spin diffusion length with a weak temperature dependence. The results indicate that this polymer material can be used as a good medium for spintronic devices.

  15. Excellent spin transport in spin valves based on the conjugated polymer with high carrier mobility.

    PubMed

    Li, Feng; Li, Tian; Chen, Feng; Zhang, Fapei

    2015-01-01

    Organic semiconductors (OSCs) are characteristic of long spin-relaxation lifetime due to weak spin-orbit interaction and hyperfine interaction. However, short spin diffusion length and weak magnetoresistance (MR) effect at room temperature (RT) was commonly found on spin valves (SVs) using an organic spacer, which should be correlated with low carrier mobility of the OSCs. Here, N-type semiconducting polymer P(NDI2OD-T2) with high carrier mobility is employed as the spacer in the SV devices. Exceedingly high MR ratio of 90.0% at 4.2 K and of 6.8% at RT are achieved, respectively, via improving the interface structure between the polymer interlayer and top cobalt electrode as well as optimal annealing of manganite bottom electrode. Furthermore, we observe spin dependent transport through the polymeric interlayer and a large spin diffusion length with a weak temperature dependence. The results indicate that this polymer material can be used as a good medium for spintronic devices. PMID:25797862

  16. Enhancing light absorption within the carrier transport length in quantum junction solar cells.

    PubMed

    Fu, Yulan; Hara, Yukihiro; Miller, Christopher W; Lopez, Rene

    2015-09-10

    Colloidal quantum dot (CQD) solar cells have attracted tremendous attention because of their tunable absorption spectrum window and potentially low processing cost. Recently reported quantum junction solar cells represent a promising approach to building a rectifying photovoltaic device that employs CQD layers on each side of the p-n junction. However, the ultimate efficiency of CQD solar cells is still highly limited by their high trap state density in both p- and n-type CQDs. By modeling photonic structures to enhance the light absorption within the carrier transport length and by ensuring that the carrier generation and collection efficiencies were both augmented, our work shows that overall device current density could be improved. We utilized a two-dimensional numerical model to calculate the characteristics of patterned CQD solar cells based on a simple grating structure. Our calculation predicts a short circuit current density as high as 31??mA/cm2, a value nearly 1.5 times larger than that of the conventional flat design, showing the great potential value of patterned quantum junction solar cells. PMID:26368966

  17. Two-dimensional semimetal in wide HgTe quantum wells: Charge-carrier energy spectrum and magnetotransport

    SciTech Connect

    Germanenko, A. V.; Minkov, G. M.; Rut, O. E.; Sherstobitov, A. A.; Dvoretsky, S. A.; Mikhailov, N. N.

    2013-12-15

    The magnetoresistivity and the Hall and Shubnikov-de Haas effects in heterostructures with a single 20.2-nm-wide quantum well made from the gapless semiconductor HgTe are studied experimentally. The measurements are performed on gated samples over a wide range of electron and hole densities. The data obtained are used to reconstruct the energy spectrum of electrons and holes in the vicinity of the extrema of the quantum-confinement subbands. It is shown that the charge-carrier dispersion relation in the investigated systems differs from that calculated within the framework of the conventional kp model.

  18. The mechanism of transport by mitochondrial carriers based on analysis of symmetry.

    PubMed

    Robinson, Alan J; Overy, Catherine; Kunji, Edmund R S

    2008-11-18

    The structures of mitochondrial transporters and uncoupling proteins are 3-fold pseudosymmetrical, but their substrates and coupling ions are not. Thus, deviations from symmetry are to be expected in the substrate and ion-binding sites in the central aqueous cavity. By analyzing the 3-fold pseudosymmetrical repeats from which their sequences are made, conserved asymmetric residues were found to cluster in a region of the central cavity identified previously as the common substrate-binding site. Conserved symmetrical residues required for the transport mechanism were found at the water-membrane interfaces, and they include the three PX[DE]XX[RK] motifs, which form a salt bridge network on the matrix side of the cavity when the substrate-binding site is open to the mitochondrial intermembrane space. Symmetrical residues in three [FY][DE]XX[RK] motifs are on the cytoplasmic side of the cavity and could form a salt bridge network when the substrate-binding site is accessible from the mitochondrial matrix. It is proposed that the opening and closing of the carrier may be coupled to the disruption and formation of the 2 salt bridge networks via a 3-fold rotary twist induced by substrate binding. The interaction energies of the networks allow members of the transporter family to be classified as strict exchangers or uniporters. PMID:19001266

  19. Electrical characteristics and carrier transport mechanism for Ti/ p-GaN Schottky diodes

    NASA Astrophysics Data System (ADS)

    Jang, Seon-Ho; Jang, Ja-Soon

    2013-03-01

    The temperature dependence of the electrical characteristics of non-alloyed Ti/ p-GaN Schottky diodes was examined using current-voltage-temperature, turn-on voltage-temperature, and series resistance-temperature measurements. The thermal coefficient ( K j ) and characteristic temperature ( T 0 ) at T ? 293 K were determined to be -4.1 mV/K and 65.06 K, respectively. The effective Schottky barrier height (SBH) was also determined to be 2.1 (±0.03) eV, which was in good agreement with the theoretical value. The possible carrier transport mechanisms at the interface are described in terms of the thermally decreased energy-band gap of p-GaN layers, thermally increased deep-level acceptor and increased further-activated-shallow-level acceptor. These were confirmed by the thermally increased ideality factor and high tunnelling parameter.

  20. Enhanced charge-carrier transfer by CdS and Ag2S quantum dots co-sensitization for TiO2 nanotube arrays.

    PubMed

    Liu, Zhongqing; Ji, Gangqiang; Guan, Debin; Wang, Bin; Wu, Xueliang

    2015-11-01

    Thioglycollic acid was employed as a molecular linker to prepare CdS and/or Ag2S quantum dots (QDs) for the co-sensitization of TiO2 nanotube arrays through the successive ionic layer adsorption and reaction (SILAR) method. The microstructure, chemical composition, and photoabsorption of the prepared samples were analyzed by using field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), X-ray diffraction (XRD), and UV-Vis diffuse reflectance spectroscopy (UV-Vis DAS). The interfacial separation and transport of photoinduced charge carries were also examined by applying current-voltage characteristics (J-V), electrochemical impedance spectroscopy (EIS), transient open circuit potential plots, and Mott-Schottky techniques. The sizes of the CdS and Ag2S QDs were found to be 6 and 4 nm, respectively. The co-sensitized samples demonstrate significantly enhanced photo absorption, greatly reduced charge transfer resistance at the semiconductor interfaces, positive shift of the flat band, elongated electron lifetimes, and accelerated interfacial separation and transport of the photoinduced charge carriers. A critical operation sequence is to first carry out the deposition of the CdS QDs that are less mismatched with TiO2 crystal lattice, followed by the deposition of Ag2S QDs. The samples prepared in this manner presented the best optoelectronic characteristics with a short photocurrent density of 9.5 mA·cm(-2). This value is 7.6% higher than 8.83 mA·cm(-2) of the sample prepared by depositing the more mismatched Ag2S QDs followed by deposition of CdS. This value is 18.8% higher than 8 mA·cm(-2) of the Ag2S-only sensitized sample, and 22.6% higher than 7.75 mA·cm(-2) of the CdS-only sensitized sample. PMID:26142959

  1. Theoretical Prediction of Isotope Effects on Charge Transport in Organic Semiconductors.

    PubMed

    Jiang, Yuqian; Geng, Hua; Shi, Wen; Peng, Qian; Zheng, Xiaoyan; Shuai, Zhigang

    2014-07-01

    We suggest that the nuclear tunneling effect is important in organic semiconductors, which we showed is absent in both the widely employed Marcus theory and the band-like transport as described by the deformation potential theory. Because the quantum nuclear tunneling tends to favor electron transfer while heavier nuclei decrease the quantum effect, there should occur an isotope effect for carrier mobility. For N,N'-n-bis(n-hexyl)-naphthalene diimide, electron mobility of all-deuteration on alkyls and all (13)C-substitution on the backbone decrease ?18 and 7%, respectively. Similar isotope effects are found in the N,N'-n-bis(n-octyl)-perylene diimide. However, there is nearly no isotope effect for all-deuterated rubrene or tetracene. We have found that the isotopic effect only occurs when the substituted nuclei contribute actively to vibrations with appreciable charge reorganization energy and coupling with carrier motion. Thus, this prediction can shed light on the current dispute over the hopping versus band-like mechanisms in organic semiconductors. PMID:26279545

  2. Charge and energy transport in one-dimensional nanomaterials

    NASA Astrophysics Data System (ADS)

    Blaustein, Gail S.

    This dissertation is comprised of two parts: Charge transport in DNA hair-pins and light transport in linear arrays of dielectric spherical particles. Experimental results suggest specific charge (hole) migration kinetics for stilbene-capped DNA hair-pins of the form Sa(AT)nSd, where Sa and Sd denote the acceptor and donor stilbene respectively and (AT) n a bridge of adenine-thymine base pairs of length n = 1 -- 7. Kinetics equations are derived from experimental data for both charge separation and recombination. Counterion binding to the radicalized stilbene ions is considered a significant contributor to charge migration kinetics. In the second part, bound modes infinite linear chains of dielectric particles of various lengths and particle materials are investigated. Through a unique application of the multisphere Mie scattering formalism, numerical methods are developed to calculate eigen-optical modes for various arrays of particles. Eigenmodes with the highest quality factor are identified by the application of a modified version of the Newton-Raphson algorithm. Convergence is strong using this algorithm for linear chains of up to several hundred particles. By comparing the dipolar approach with the more complex approach utilizing a combination of both dipolar and quadrupolar approaches, the dipolar approach is shown to have an accuracy of approximately 99%. The quality factor increases with the cubed value of the number of particles in agreement with previously developed theory. The effects of disordering of particle sizes and inter-particle distances as well as interference of guiding modes in "traffic circle" waveguide configurations will be discussed.

  3. Charge transport model to predict intrinsic reliability for dielectric materials

    NASA Astrophysics Data System (ADS)

    Ogden, Sean P.; Borja, Juan; Plawsky, Joel L.; Lu, T.-M.; Yeap, Kong Boon; Gill, William N.

    2015-09-01

    Several lifetime models, mostly empirical in nature, are used to predict reliability for low-k dielectrics used in integrated circuits. There is a dispute over which model provides the most accurate prediction for device lifetime at operating conditions. As a result, there is a need to transition from the use of these largely empirical models to one built entirely on theory. Therefore, a charge transport model was developed to predict the device lifetime of low-k interconnect systems. The model is based on electron transport and donor-type defect formation. Breakdown occurs when a critical defect concentration accumulates, resulting in electron tunneling and the emptying of positively charged traps. The enhanced local electric field lowers the barrier for electron injection into the dielectric, causing a positive feedforward failure. The charge transport model is able to replicate experimental I-V and I-t curves, capturing the current decay at early stress times and the rapid current increase at failure. The model is based on field-driven and current-driven failure mechanisms and uses a minimal number of parameters. All the parameters have some theoretical basis or have been measured experimentally and are not directly used to fit the slope of the time-to-failure versus applied field curve. Despite this simplicity, the model is able to accurately predict device lifetime for three different sources of experimental data. The simulation's predictions at low fields and very long lifetimes show that the use of a single empirical model can lead to inaccuracies in device reliability.

  4. Morphology and charge transport in ammonium based polymerized ionic liquids

    NASA Astrophysics Data System (ADS)

    Heres, Maximilian; Minutolo, Joseph; Shamblin, Jacob; Long, Maik; Berdzinski, Stefan; Stremel, Veronika; Sangoro, Joshua

    2015-03-01

    Ionic conduction, structural dynamics and morphology in a series of ammonium based polymerized ionic liquids are investigated using broadband dielectric spectroscopy, temperature-modulated differential scanning calorimetry, and neutron as well as x-ray scattering techniques. The dielectric spectra are dominated on the low frequency regime by electrode polarization while hopping conduction is the underlying mechanism at higher frequencies. At their respective calorimetric glass transition temperatures, a strong correlation between the morphology and ionic conductivity is found. These results are discussed within the recent approaches proposed to explain the decoupling of charge transport from structural dynamics. UT/ORNL Science Alliance.

  5. Acoustic charge transport technology investigation for advanced development transponder

    NASA Technical Reports Server (NTRS)

    Kayalar, S.

    1993-01-01

    Acoustic charge transport (ACT) technology has provided a basis for a new family of analog signal processors, including a programmable transversal filter (PTF). Through monolithic integration of ACT delay lines with GaAs metal semiconductor field effect transistor (MESFET) digital memory and controllers, these devices significantly extend the performance of PTF's. This article introduces the basic operation of these devices and summarizes their present and future specifications. The production and testing of these devices indicate that this new technology is a promising one for future space applications.

  6. Unusual charge transport and reduced bimolecular recombination in PDTSiTzTz:PC71BM bulk heterojunction blend

    NASA Astrophysics Data System (ADS)

    Slobodyan, O. V.; Danielson, E. L.; Moench, S. J.; Dinser, J. A.; Gutierrez, M.; Vanden Bout, D. A.; Holliday, B. J.; Dodabalapur, A.

    2015-06-01

    Solar cells with bulk heterojunction active layers containing donor-acceptor copolymer PDTSiTzTz exhibit persistent high fill factors with thicknesses up to 400 nm. Transport and recombination in a blend of PDTSiTzTz and fullerene derivative PC71BM is studied using lateral organic photovoltaic structures. This material system is characterized by carrier-concentration-dependent charge carrier mobilities, a strongly reduced bimolecular recombination factor, and a negative Poole-Frenkel coefficient. The analysis provides an explanation for the relatively thickness-independent fill factor behaviour seen in solar cells using the copolymer PDTSiTzTz. Cumulative insights from this copolymer can be employed for future organic photovoltaic material development, study of existing high performance bulk heterojunciton blends, and improved solar cell design.

  7. Transport of 3D space charge dominated beams

    NASA Astrophysics Data System (ADS)

    Lü, Jian-Qin

    2013-10-01

    In this paper we present the theoretical analysis and the computer code design for the intense pulsed beam transport. Intense beam dynamics is a very important issue in low-energy high-current accelerators and beam transport systems. This problem affects beam transmission and beam qualities. Therefore, it attracts the attention of the accelerator physicists worldwide. The analysis and calculation for the intense beam dynamics are very complicated, because the state of particle motion is dominated not only by the applied electromagnetic fields, but also by the beam-induced electromagnetic fields (self-fields). Moreover, the self fields are related to the beam dimensions and particle distributions. So, it is very difficult to get the self-consistent solutions of particle motion analytically. For this reason, we combine the Lie algebraic method and the particle in cell (PIC) scheme together to simulate intense 3D beam transport. With the Lie algebraic method we analyze the particle nonlinear trajectories in the applied electromagnetic fields up to third order approximation, and with the PIC algorithm we calculate the space charge effects to the particle motion. Based on the theoretical analysis, we have developed a computer code, which calculates beam transport systems consisting of electrostatic lenses, electrostatic accelerating columns, solenoid lenses, magnetic and electric quadruples, magnetic sextupoles, octopuses and different kinds of electromagnetic analyzers. The optimization calculations and the graphic display for the calculated results are provided by the code.

  8. Transport in Halobacterium Halobium: Light-Induced Cation-Gradients, Amino Acid Transport Kinetics, and Properties of Transport Carriers

    NASA Technical Reports Server (NTRS)

    Lanyi, Janos K.

    1977-01-01

    Cell envelope vesicles prepared from H. halobium contain bacteriorhodopsin and upon illumination protons are ejected. Coupled to the proton motive force is the efflux of Na(+). Measurements of Na-22 flux, exterior pH change, and membrane potential, Delta(psi) (with the dye 3,3'-dipentyloxadicarbocyanine) indicate that the means of Na(+) transport is sodium/proton exchange. The kinetics of the pH changes and other evidence suggests that the antiport is electrogenic (H(+)/Na(++ greater than 1). The resulting large chemical gradient for Na(+) (outside much greater than inside), as well as the membrane potential, will drive the transport of 18 amino acids. The I9th, glutamate, is unique in that its accumulation is indifferent to Delta(psi): this amino acid is transported only when a chemical gradient for Na(+) is present. Thus, when more and more NaCl is included in the vesicles glutamate transport proceeds with longer and longer lags. After illumination the gradient of H+() collapses within 1 min, while the large Na(+) gradient and glutamate transporting activity persists for 10- 15 min, indicating that proton motive force is not necessary for transport. A chemical gradient of Na(+), arranged by suspending vesicles loaded with KCl in NaCl, drives glutamate transport in the dark without other sources of energy, with V(sub max) and K(sub m) comparable to light-induced transport. These and other lines of evidence suggest that the transport of glutamate is facilitated by symport with Na(+), in an electrically neutral fashion, so that only the chemical component of the Na(+) gradient is a driving force.

  9. Towards a unified description of the charge transport mechanisms in conductive atomic force microscopy studies of semiconducting polymers

    NASA Astrophysics Data System (ADS)

    Moerman, D.; Sebaihi, N.; Kaviyil, S. E.; Leclère, P.; Lazzaroni, R.; Douhéret, O.

    2014-08-01

    In this work, conductive atomic force microscopy (C-AFM) is used to study the local electrical properties in thin films of self-organized fibrillate poly(3-hexylthiophene) (P3HT), as a reference polymer semiconductor. Depending on the geometrical confinement in the transport channel, the C-AFM current is shown to be governed either by the charge transport in the film or by the carrier injection at the tip-sample contact, leading to either bulk or local electrical characterization of the semiconducting polymer, respectively. Local I-V profiles allow discrimination of the different dominating electrical mechanisms, i.e., resistive in the transport regime and space charge limited current (SCLC) in the local regime. A modified Mott-Gurney law is analytically derived for the contact regime, taking into account the point-probe geometry of the contact and the radial injection of carriers. Within the SCLC regime, the probed depth is shown to remain below 12 nm with a lateral electrical resolution below 5 nm. This confirms that high resolution is reached in those C-AFM measurements, which therefore allows for the analysis of single organic semiconducting nanostructures. The carrier density and mobility in the volume probed under the tip under steady-state conditions are also determined in the SCLC regime.In this work, conductive atomic force microscopy (C-AFM) is used to study the local electrical properties in thin films of self-organized fibrillate poly(3-hexylthiophene) (P3HT), as a reference polymer semiconductor. Depending on the geometrical confinement in the transport channel, the C-AFM current is shown to be governed either by the charge transport in the film or by the carrier injection at the tip-sample contact, leading to either bulk or local electrical characterization of the semiconducting polymer, respectively. Local I-V profiles allow discrimination of the different dominating electrical mechanisms, i.e., resistive in the transport regime and space charge limited current (SCLC) in the local regime. A modified Mott-Gurney law is analytically derived for the contact regime, taking into account the point-probe geometry of the contact and the radial injection of carriers. Within the SCLC regime, the probed depth is shown to remain below 12 nm with a lateral electrical resolution below 5 nm. This confirms that high resolution is reached in those C-AFM measurements, which therefore allows for the analysis of single organic semiconducting nanostructures. The carrier density and mobility in the volume probed under the tip under steady-state conditions are also determined in the SCLC regime. Electronic supplementary information (ESI) available: SI-1: tapping mode AFM image of fibrillar P3HT. SI-2: current-distance profile of a high aspect ratio channel exhibiting both the contact and transport resistance dominating regimes. SI-3: full analytical derivation of the Mott-Gurney law, describing the SCLC regime in a point probe geometrical configuration for C-AFM measurements. See DOI: 10.1039/c4nr02577f

  10. The Effect of Diiodooctane on the Charge Carrier Generation in Organic Solar Cells Based on the Copolymer PBDTTT-C

    PubMed Central

    Zusan, Andreas; Gieseking, Björn; Zerson, Mario; Dyakonov, Vladimir; Magerle, Robert; Deibel, Carsten

    2015-01-01

    Microstructural changes and the understanding of their effect on photocurrent generation are key aspects for improving the efficiency of organic photovoltaic devices. We analyze the impact of a systematically increased amount of the solvent additive diiodooctane (DIO) on the morphology of PBDTTT-C:PC71BM blends and related changes in free carrier formation and recombination by combining surface imaging, photophysical and charge extraction techniques. We identify agglomerates visible in AFM images of the 0% DIO blend as PC71BM domains embedded in an intermixed matrix phase. With the addition of DIO, a decrease in the size of fullerene domains along with a demixing of the matrix phase appears for 0.6% and 1% DIO. Surprisingly, transient absorption spectroscopy reveals an efficient photogeneration already for the smallest amount of DIO, although the largest efficiency is found for 3% DIO. It is ascribed to a fine-tuning of the blend morphology in terms of the formation of interpenetrating donor and acceptor phases minimizing geminate and nongeminate recombination as indicated by charge extraction experiments. An increase in the DIO content to 10% adversely affects the photovoltaic performance, most probably due to an inefficient free carrier formation and trapping in a less interconnected donor-acceptor network. PMID:25655785

  11. Nonquenching of charge carriers by Fe3O4 core in Fe3O4/ZnO nanosheet photocatalyst.

    PubMed

    Karunakaran, Chockalingam; Vinayagamoorthy, Pazhamalai; Jayabharathi, Jayaraman

    2014-12-16

    Fe3O4-implanted ZnO and pristine ZnO nanosheets have been synthesized hydrothermally. High-resolution scanning electron microscopy, high-resolution transmission electron microscopy, energy dispersive X-ray spectroscopy, elemental mapping, selected area electron diffractometry, powder X-ray diffractometry, Raman spectroscopy, vibrating sample magnetometry, solid state impedance spectroscopy, UV-visible diffuse reflectance spectroscopy, and photoluminescence spectroscopy show implantation of Fe3O4 in ZnO nanosheets. Fe3O4 core with ZnO shell is of type I core/shell heterostructure which is to quench charge carriers and suppress photocatalysis. But the photocatalytic activity is not suppressed on implantation of Fe3O4 in ZnO nanosheets, and time controlled single photon counting lifetime spectroscopy shows that the photogenerated charge carriers are not quenched by the Fe3O4 core in the ZnO nanosheets. The composite nanosheets are photostable, reusable, and magnetically recoverable, revealing potential application in mineralization of organic pollutants. PMID:25425261

  12. Tungsten-based nanomaterials (WO3 & Bi2WO6): Modifications related to charge carrier transfer mechanisms and photocatalytic applications

    NASA Astrophysics Data System (ADS)

    Girish Kumar, S.; Koteswara Rao, K. S. R.

    2015-11-01

    Heterogeneous photocatalysis is an ideal green energy technology for the purification of wastewater. Although titania dominates as the reference photocatalyst, its wide band gap is a bottleneck for extended utility. Thus, search for non-TiO2 based nanomaterials has become an active area of research in recent years. In this regard, visible light absorbing polycrystalline WO3 (2.4-2.8 eV) and Bi2WO6 (2.8 eV) with versatile structure-electronic properties has gained considerable interest to promote the photocatalytic reactions. These materials are also explored in selective functional group transformation in organic reactions, because of low reduction and oxidation potential of WO3 CB and Bi2WO6 VB, respectively. In this focused review, various strategies such as foreign ion doping, noble metal deposition and heterostructuring with other semiconductors designed for efficient photocatalysis is discussed. These modifications not only extend the optical response to longer wavelengths, but also prolong the life-time of the charge carriers and strengthen the photocatalyst stability. The changes in the surface-bulk properties and the charge carrier transfer dynamics associated with each modification correlating to the high activity are emphasized. The presence of oxidizing agents, surface modification with Cu2+ ions and synthesis of exposed facets to promote the degradation rate is highlighted. In depth study on these nanomaterials is likely to sustain interest in wastewater remediation and envisaged to signify in various green energy applications.

  13. 41 CFR 301-72.100 - What must my travel accounting system do in relation to common carrier transportation?

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 41 Public Contracts and Property Management 4 2010-07-01 2010-07-01 false What must my travel accounting system do in relation to common carrier transportation? 301-72.100 Section 301-72.100 Public Contracts and Property Management Federal Travel Regulation System TEMPORARY DUTY (TDY) TRAVEL...

  14. 41 CFR 301-72.100 - What must my travel accounting system do in relation to 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 must my travel accounting system do in relation to common carrier transportation? 301-72.100 Section 301-72.100 Public Contracts and Property Management Federal Travel Regulation System TEMPORARY DUTY (TDY) TRAVEL...

  15. 41 CFR 301-72.100 - What must my travel accounting system do in relation to common carrier transportation?

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 41 Public Contracts and Property Management 4 2014-07-01 2014-07-01 false What must my travel accounting system do in relation to common carrier transportation? 301-72.100 Section 301-72.100 Public Contracts and Property Management Federal Travel Regulation System TEMPORARY DUTY (TDY) TRAVEL...

  16. 41 CFR 301-72.100 - What must my travel accounting system do in relation to common carrier transportation?

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 41 Public Contracts and Property Management 4 2013-07-01 2012-07-01 true What must my travel accounting system do in relation to common carrier transportation? 301-72.100 Section 301-72.100 Public Contracts and Property Management Federal Travel Regulation System TEMPORARY DUTY (TDY) TRAVEL...

  17. 41 CFR 301-72.100 - What must my travel accounting system do in relation to common carrier transportation?

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 41 Public Contracts and Property Management 4 2012-07-01 2012-07-01 false What must my travel accounting system do in relation to common carrier transportation? 301-72.100 Section 301-72.100 Public Contracts and Property Management Federal Travel Regulation System TEMPORARY DUTY (TDY) TRAVEL...

  18. Electron carrier concentration dependent magnetization and transport properties in ZnO:Co diluted magnetic semiconductor thin films

    E-print Network

    Yang, Zheng

    Electron carrier concentration dependent magnetization and transport properties in ZnO:Co diluted for ferromagnetic exchange in ZnO:Co diluted magnetic semiconductor materials. © 2008 American Institute of Physics hinders their applications in commercial prod- ucts. In recent years, magnetically doped ZnO has emerged

  19. Dielectric and carrier transport properties of vanadium dioxide thin films across the phase transition utilizing gated capacitor devices

    E-print Network

    Yang, Zheng

    Dielectric and carrier transport properties of vanadium dioxide thin films across the phase; published 1 November 2010 Vanadium dioxide VO2 is a strongly correlated oxide that undergoes a sharp metal.22.Ch I. INTRODUCTION Vanadium dioxide VO2 is a material of great interest in condensed-matter physics

  20. 76 FR 2744 - Disclosure of Code-Share Service by Air Carriers and Sellers of Air Transportation

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-01-14

    ... Office of the Secretary Disclosure of Code-Share Service by Air Carriers and Sellers of Air... Department is publishing the following notice on the enforcement of its rules relating to disclosure of code... Transportation, Office of the Secretary, Washington, DC Guidance on Disclosure of Code-Share Service Under...

  1. 76 FR 2744 - Disclosure of Code-Share Service by Air Carriers and Sellers of Air Transportation

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-01-14

    ...TRANSPORTATION Office of the Secretary Disclosure of Code-Share Service by Air Carriers and Sellers...of its rules relating to disclosure of code-share service on Internet Web sites and...Washington, DC Guidance on Disclosure of Code-Share Service Under Recent...

  2. Mixed quantum-classical dynamics for charge transport in organics.

    PubMed

    Wang, Linjun; Prezhdo, Oleg V; Beljonne, David

    2015-05-21

    Charge transport plays a crucial role in the working principle of most opto-electronic and energy devices. This is especially true for organic materials where the first theoretical models date back to the 1950s and have continuously evolved ever since. Most of these descriptions rely on perturbation theory to treat small interactions in the Hamiltonian. In particular, applying a perturbative treatment to the electron-phonon and electron-electron coupling results in the band and hopping models, respectively, the signature of which is conveyed by a characteristic temperature dependence of mobility. This perspective describes recent progress of studying charge transport in organics using mixed quantum-classical dynamics techniques, including mean field and surface hopping theories. The studies go beyond the perturbation treatments and represent the processes explicitly in the time-domain, as they occur in real life. The challenges, advantages, and disadvantages of both approaches are systematically discussed. Special focus is dedicated to the temperature dependence of mobility, the role of local and nonlocal electron-phonon couplings, as well as the interplay between electronic and electron-phonon interactions. PMID:25772795

  3. Effects of cytosine methylation on DNA charge transport

    NASA Astrophysics Data System (ADS)

    Hihath, Joshua; Guo, Shaoyin; Zhang, Peiming; Tao, Nongjian

    2012-04-01

    The methylation of cytosine bases in DNA commonly takes place in the human genome and its abnormality can be used as a biomarker in the diagnosis of genetic diseases. In this paper we explore the effects of cytosine methylation on the conductance of DNA. Although the methyl group is a small chemical modification, and has a van der Waals radius of only 2 Å, its presence significantly changes the duplex stability, and as such may also affect the conductance properties of DNA. To determine if charge transport through the DNA stack is sensitive to this important biological modification we perform multiple conductance measurements on a methylated DNA molecule with an alternating G:C sequence and its non-methylated counterpart. From these studies we find a measurable difference in the conductance between the two types of molecules, and demonstrate that this difference is statistically significant. The conductance values of these molecules are also compared with a similar sequence that has been previously studied to help elucidate the charge transport mechanisms involved in direct DNA conductance measurements.

  4. 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

    ... New Application Screening (NAS)--NAS is an application, which is populated by A&I, that identifies potential ``chameleon carriers'' within the FMCSA past and present carrier population. This tool provides you with the ability to search...

  5. Simulating charge transport to understand the spectral response of Swept Charge Devices

    E-print Network

    Athiray, P S; Narendranath, S; Gow, J P D

    2015-01-01

    Swept Charge Devices (SCD) are novel X-ray detectors optimized for improved spectral performance without any demand for active cooling. The Chandrayaan-1 X-ray Spectrometer (C1XS) experiment onboard the Chandrayaan-1 spacecraft used an array of SCDs to map the global surface elemental abundances on the Moon using the X-ray fluorescence (XRF) technique. The successful demonstration of SCDs in C1XS spurred an enhanced version of the spectrometer on Chandrayaan-2 using the next-generation SCD sensors. The objective of this paper is to demonstrate validation of a physical model developed to simulate X-ray photon interaction and charge transportation in a SCD. The model helps to understand and identify the origin of individual components that collectively contribute to the energy-dependent spectral response of the SCD. Furthermore, the model provides completeness to various calibration tasks, such as generating spectral response matrices (RMFs - redistribution matrix files), estimating efficiency, optimizing event...

  6. Incipient localization of charge carriers in the two-dimensional electron system in LaAl O3 /SrTi O3 under hydrostatic pressure

    NASA Astrophysics Data System (ADS)

    Fuchs, D.; Sleem, A.; Schäfer, R.; Zaitsev, A. G.; Meffert, M.; Gerthsen, D.; Schneider, R.; v. Löhneysen, H.

    2015-10-01

    The two-dimensional electron system (2DES) in LaAl O3 /SrTi O3 (LAO/STO) heterostructures, showing superconductivity below 200 mK at ambient pressure, displays incipient localization under hydrostatic pressure p . Even small p significantly affects the transport properties for 10 K charge carriers with increasing hydrostatic pressure. For T <10 K negative logarithmic corrections to the conductance are attributed to electron-electron interaction. Weak localization and antilocalization, if present, are dominated by the pivotal role of impurity scattering by, e.g., oxygen vacancies, for the transport properties of the 2DES in LAO/STO heterostructures. This interpretation is favorited by exploiting the strong dependence of the dielectric permittivity of STO on pressure. Measurements of the magnetoresistance corroborate this interpretation.

  7. 49 CFR 385.13 - Unsatisfactory rated motor carriers; prohibition on transportation; ineligibility for Federal...

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... prohibited from operating a CMV in motor carrier operations in commerce beginning on the 46th day after the... carrier operations in commerce beginning on the 61st day after the date of the FMCSA notice of proposed... operations in commerce. The out-of-service order shall apply both to the motor carrier's operations...

  8. 49 CFR 385.13 - Unsatisfactory rated motor carriers; prohibition on transportation; ineligibility for Federal...

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... prohibited from operating a CMV in motor carrier operations in commerce beginning on the 46th day after the... carrier operations in commerce beginning on the 61st day after the date of the FMCSA notice of proposed... operations in commerce. The out-of-service order shall apply both to the motor carrier's operations...

  9. 77 FR 42548 - Privacy Act of 1974; Department of Transportation, Federal Motor Carrier Safety Administration...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-07-19

    ... vehicle (CMV) drivers on behalf of motor carriers and/or CMV drivers. This change reflects motor carrier... Screening program to provide commercial drivers and persons conducting pre-employment screening services for the motor carrier industry electronic access to driver history reports extracted from the...

  10. Charge transport properties in CdZnTe detectors grown by the vertical Bridgman technique

    SciTech Connect

    Auricchio, N.; Caroli, E.; Abbene, L.; Honkimaki, V.

    2011-12-15

    Presently, a great amount of effort is being devoted to the development of CdTe and CdZnTe (CZT) detectors for a large variety of applications such as medical, industrial, and space research. We present the spectroscopic properties of some CZT crystals grown by the standard vertical Bridgman method and by the boron oxide encapsulated vertical Bridgman method, which has been recently implemented at IMEM-CNR (Parma, Italy). In this technique, the crystal is grown in an open quartz crucible fully encapsulated by a thin layer of liquid boron oxide. This method prevents contact between the crystal and the crucible, thereby allowing larger single grains with a lower dislocation density to be obtained. Several mono-electrode detectors were realized, with each having two planar gold contacts. The samples are characterized by an active area of about 7 mm x 7 mm and thicknesses ranging from 1 to 2 mm. The charge transport properties of the detectors have been studied by mobility-lifetime ({mu} x {tau}) product measurements, carried out at the European Synchrotron Radiation Facility (Grenoble, France) in the planar transverse field configuration, where the impinging beam direction is orthogonal to the collecting electric field. We have performed several fine scans between the electrodes with a beam spot of 10 {mu}m x 10 {mu}m at various energies from 60 to 400 keV. In this work, we present the test results in terms of the ({mu} x {tau}) product of both charge carriers.

  11. Charge transport properties in CdZnTe detectors grown by the vertical Bridgman technique

    NASA Astrophysics Data System (ADS)

    Auricchio, N.; Marchini, L.; Caroli, E.; Zappettini, A.; Abbene, L.; Honkimaki, V.

    2011-12-01

    Presently, a great amount of effort is being devoted to the development of CdTe and CdZnTe (CZT) detectors for a large variety of applications such as medical, industrial, and space research. We present the spectroscopic properties of some CZT crystals grown by the standard vertical Bridgman method and by the boron oxide encapsulated vertical Bridgman method, which has been recently implemented at IMEM-CNR (Parma, Italy). In this technique, the crystal is grown in an open quartz crucible fully encapsulated by a thin layer of liquid boron oxide. This method prevents contact between the crystal and the crucible, thereby allowing larger single grains with a lower dislocation density to be obtained. Several mono-electrode detectors were realized, with each having two planar gold contacts. The samples are characterized by an active area of about 7 mm × 7 mm and thicknesses ranging from 1 to 2 mm. The charge transport properties of the detectors have been studied by mobility-lifetime (? × ?) product measurements, carried out at the European Synchrotron Radiation Facility (Grenoble, France) in the planar transverse field configuration, where the impinging beam direction is orthogonal to the collecting electric field. We have performed several fine scans between the electrodes with a beam spot of 10 ?m × 10 ?m at various energies from 60 to 400 keV. In this work, we present the test results in terms of the (? × ?) product of both charge carriers.

  12. Device and morphological engineering of organic solar cells for enhanced charge transport and photovoltaic performance

    NASA Astrophysics Data System (ADS)

    Adhikari, Nirmal; Khatiwada, Devendra; Dubey, Ashish; Qiao, Qiquan

    2015-01-01

    Conjugated polymers are potential materials for photovoltaic applications due to their high absorption coefficient, mechanical flexibility, and solution-based processing for low-cost solar cells. A bulk heterojunction (BHJ) structure made of donor-acceptor composite can lead to high charge transfer and power conversion efficiency. Active layer morphology is a key factor for device performance. Film formation processes (e.g., spray-coating, spin-coating, and dip-coating), post-treatment (e.g., annealing and UV ozone treatment), and use of additives are typically used to engineer the morphology, which optimizes physical properties, such as molecular configuration, miscibility, lateral and vertical phase separation. We will review electronic donor-acceptor interactions in conjugated polymer composites, the effect of processing parameters and morphology on solar cell performance, and charge carrier transport in polymer solar cells. This review provides the basis for selection of different processing conditions for optimized nanomorphology of active layers and reduced bimolecular recombination to enhance open-circuit voltage, short-circuit current density, and fill factor of BHJ solar cells.

  13. Mode-selective vibrational modulation of charge transport in organic electronic devices.

    PubMed

    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

    2015-01-01

    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. PMID:26246039

  14. Charge transport in nanopatterned PbS colloidal quantum dot arrays

    E-print Network

    Ray, Nirat

    2015-01-01

    In this thesis, we study charge transport in nanopatterned arrays of PbS colloidal quantum dots using conventional two-probe measurements and an integrated charge sensor. PbS dots are synthesized in solution with an organic ...

  15. Simulating charge transport to understand the spectral response of Swept Charge Devices

    NASA Astrophysics Data System (ADS)

    Athiray, P. S.; Sreekumar, P.; Narendranath, S.; Gow, J. P. D.

    2015-11-01

    Context. Swept Charge Devices (SCD) are novel X-ray detectors optimized for improved spectral performance without any demand for active cooling. The Chandrayaan-1 X-ray Spectrometer (C1XS) experiment onboard the Chandrayaan-1 spacecraft used an array of SCDs to map the global surface elemental abundances on the Moon using the X-ray fluorescence (XRF) technique. The successful demonstration of SCDs in C1XS spurred an enhanced version of the spectrometer on Chandrayaan-2 using the next-generation SCD sensors. Aims: The objective of this paper is to demonstrate validation of a physical model developed to simulate X-ray photon interaction and charge transportation in a SCD. The model helps to understand and identify the origin of individual components that collectively contribute to the energy-dependent spectral response of the SCD. Furthermore, the model provides completeness to various calibration tasks, such as generating spectral matrices (RMFs - redistribution matrix files), estimating efficiency, optimizing event selection logic, and maximizing event recovery to improve photon-collection efficiency in SCDs. Methods: Charge generation and transportation in the SCD at different layers related to channel stops, field zones, and field-free zones due to photon interaction were computed using standard drift and diffusion equations. Charge collected in the buried channel due to photon interaction in different volumes of the detector was computed by assuming a Gaussian radial profile of the charge cloud. The collected charge was processed further to simulate both diagonal clocking read-out, which is a novel design exclusive for SCDs, and event selection logic to construct the energy spectrum. Results: We compare simulation results of the SCD CCD54 with measurements obtained during the ground calibration of C1XS and clearly demonstrate that our model reproduces all the major spectral features seen in calibration data. We also describe our understanding of interactions at different layers of SCD that contribute to the observed spectrum. Using simulation results, we identify the origin of different spectral features and quantify their contributions.

  16. Charge Recombination, Transport Dynamics, and Interfacial Effects in Organic Solar Cells

    SciTech Connect

    Heeger, Alan; Bazan, Guillermo; Nguyen, Thuc-Quyen; Wudl, Fred

    2015-02-27

    The need for renewable sources of energy is well known. Conversion of sunlight to electricity using solar cells is one of the most important opportunities for creating renewable energy sources. The research carried out under DE-FG02-08ER46535 focused on the science and technology of “Plastic” solar cells comprised of organic (i.e. carbon based) semiconductors. The Bulk Heterojunction concept involves a phase separated blend of two organic semiconductors each with dimensions in the nano-meter length scale --- one a material that functions as a donor for electrons and the other a material that functions as an acceptor for electrons. The nano-scale inter-penetrating network concept for “Plastic” solar cells was created at UC Santa Barbara. A simple measure of the impact of this concept can be obtained from a Google search which gives 244,000 “hits” for the Bulk Heterojunction solar cell. Research funded through this program focused on four major areas: 1. Interfacial effects in organic photovoltaics, 2. Charge transfer and photogeneration of mobile charge carriers in organic photovoltaics, 3. Transport and recombination of the photogenerated charge carriers in organic photovoltaics, 4. Synthesis of novel organic semiconducting polymers and semiconducting small molecules, including conjugated polyelectrolytes. Following the discovery of ultrafast charge transfer at UC Santa Barbara in 1992, the nano-organic (Bulk Heterojunction) concept was formulated. The need for a morphology comprising two interpenetrating bicontinuous networks was clear: one network to carry the photogenerated electrons (negative charge) to the cathode and one network to carry the photo-generated holes (positive charge) to the anode. This remarkable self-assembled network morphology has now been established using Transmission electron Microscopy (TEM) either in the Phase Contrast mode or via TEM-Tomography. The steps involved in delivering power from a solar cell to an external circuit are the following: • Photo-excitation of the donor (or the acceptor). • Charge transfer with holes in the donor domain and electrons in the acceptor domain. • Sweep-out to electrodes prior to recombination by the internal electric field. • Energy delivered to the external circuit. Each of these four steps was studied in detail using a wide variety of organic semiconductors with different molecular structures. This UC Santa Barbara group was the first to clarify the origin and the mechanism involved in the ultrafast charge transfer process. The ultrafast charge transfer (time scale approximately 100 times faster than the first step in the photo-synthesis of green plants) is the fundamental reason for the potential for high power conversion efficiency of sunlight to electricity from plastic solar cells. The UCSB group was the first to emphasize, clarify and demonstrate the need for sweep-out to electrodes prior to recombination by the internal electric field. The UCSB group was the first to synthesize small molecule organic semiconductors capable of high power conversion efficiencies. The results of this research were published in high impact peer-reviewed journals. Our published papers (40 in number) provide answers to fundamental questions that have been heavily discussed and debated in the field of Bulk Heterojunction Solar Cells; scientific questions that must be resolved before this technology can be ready for commercialization in large scale for production of renewable energy. Of the forty publications listed, nineteen were co-authored by two or more of the PIs, consistent with the multi-investigator approach described in the original proposal. The specific advantages of this “plastic” solar cell technology are the following: a. Manufacturing by low-cost printing technology using soluble organic semiconductors; this approach can be implemented in large scale by roll-to-roll printing on plastic substrates. b. Low energy cost in manufacturing; all steps carried out at room temperature (approx. a factor of ten less than the use of Silicon which req

  17. Carrier transport in quantum dot quantum well microstructures of the self-assembled CdTe/CdS/ligand core-shell system

    NASA Astrophysics Data System (ADS)

    Li, K. Y.; Shan, Q. S.; Zhu, R. P.; Yin, H.; Lin, Y. Y.; Wang, L. Q.

    2015-04-01

    The study on the quantum dot quantum well (QDQW) microstructure modified by choosing different ligands containing a sulfhydryl group is of significance because it enables one to regulate photoexcited free charge carriers' (FCCs') transport behaviours in high-quality CdTe/ligand QDs via a self-assembled way. The photoelectron characteristics of ligand-capped CdTe nanoparticles were probed by a combination of surface photovoltaic (SPV) and photoacoustic technologies, supplemented by a computer simulation method of the CASTEP module. The experiment reveals that the D-value ?EWi obtained by the associated two parameters of the SPV spectroscopy was closely related to the quantum confinement energy in the self-assembled CdTe/CdS/ligand core-shell system. In the paper the D-value was termed the depth of QWs, which were buried in the space charge regions located in the graded-band-gap and on either side of the shell-CdS. Obvious resonance quantum tunnelling may occur in the energy band structure with deep QWs on using certain ligands, resulting in an extended diffusion length of the FCCs on illumination of the photon energy h? >= Eg, core-CdTe, and in a strong SPV response at a specific wavelength region. In addition, the carrier-longitudinal optical phonon interaction is the reciprocal of the carriers' lifetime. The d-frontier orbital in the graded-band-gap plays an important role in both the microstructure and the resonance quantum tunnelling of the QDQW system according to the CASTEP calculations.The study on the quantum dot quantum well (QDQW) microstructure modified by choosing different ligands containing a sulfhydryl group is of significance because it enables one to regulate photoexcited free charge carriers' (FCCs') transport behaviours in high-quality CdTe/ligand QDs via a self-assembled way. The photoelectron characteristics of ligand-capped CdTe nanoparticles were probed by a combination of surface photovoltaic (SPV) and photoacoustic technologies, supplemented by a computer simulation method of the CASTEP module. The experiment reveals that the D-value ?EWi obtained by the associated two parameters of the SPV spectroscopy was closely related to the quantum confinement energy in the self-assembled CdTe/CdS/ligand core-shell system. In the paper the D-value was termed the depth of QWs, which were buried in the space charge regions located in the graded-band-gap and on either side of the shell-CdS. Obvious resonance quantum tunnelling may occur in the energy band structure with deep QWs on using certain ligands, resulting in an extended diffusion length of the FCCs on illumination of the photon energy h? >= Eg, core-CdTe, and in a strong SPV response at a specific wavelength region. In addition, the carrier-longitudinal optical phonon interaction is the reciprocal of the carriers' lifetime. The d-frontier orbital in the graded-band-gap plays an important role in both the microstructure and the resonance quantum tunnelling of the QDQW system according to the CASTEP calculations. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr00494b

  18. Calculation of the charge-carrier mobility in diamond at low temperatures

    SciTech Connect

    Baturin, A. S.; Gorelkin, V. N.; Soloviev, V. R.; Chernousov, I. V.

    2010-07-15

    The discrepancies between the quasi-elastic and inelastic approaches to the calculation of the electron and hole mobilities in diamond at low temperatures when the carrier scattering from acoustic phonons becomes significantly inelastic have been numerically estimated. The calculations showed that the mobility described by a close-to-equilibrium distribution function differs several times from that obtained within the quasi-elastic approach even at 20 K. The results obtained are important for interpreting the low-temperature electrical experiments on high-purity diamond single crystals.

  19. Transient luminescence induced by electrical refilling of charge carrier traps of dislocation network at hydrophilically bonded Si wafers interface

    SciTech Connect

    Bondarenko, Anton; Vyvenko, Oleg

    2014-02-21

    Dislocation network (DN) at hydrophilically bonded Si wafers interface is placed in space charge region (SCR) of a Schottky diode at a depth of about 150 nm from Schottky electrode for simultaneous investigation of its electrical and luminescent properties. Our recently proposed pulsed traps refilling enhanced luminescence (Pulsed-TREL) technique based on the effect of transient luminescence induced by refilling of charge carrier traps with electrical pulses is further developed and used as a tool to establish DN energy levels responsible for D1 band of dislocation-related luminescence in Si (DRL). In present work we do theoretical analysis and simulation of traps refilling kinetics dependence on refilling pulse magnitude (Vp) in two levels model: shallow and deep. The influence of initial charge state of deep level on shallow level occupation-Vp dependence is discussed. Characteristic features predicted by simulations are used for Pulsed-TREL experimental results interpretation. We conclude that only shallow (?0.1 eV from conduction and valence band) energetic levels in the band gap participate in D1 DRL.

  20. Molecular structure of the discotic liquid crystalline phase of hexa-peri-hexabenzocoronene/oligothiophene hybrid and their charge transport properties

    NASA Astrophysics Data System (ADS)

    Bag, Saientan; Maingi, Vishal; Maiti, Prabal K.; Yelk, Joe; Glaser, Matthew A.; Walba, David M.; Clark, Noel A.

    2015-10-01

    Using atomistic molecular dynamics simulation, we study the discotic columnar liquid crystalline (LC) phases formed by a new organic compound having hexa-peri-Hexabenzocoronene (HBC) core with six pendant oligothiophene units recently synthesized by Nan Hu et al. [Adv. Mater. 26, 2066 (2014)]. This HBC core based LC phase was shown to have electric field responsive behavior and has important applications in organic electronics. Our simulation results confirm the hexagonal arrangement of columnar LC phase with a lattice spacing consistent with that obtained from small angle X-ray diffraction data. We have also calculated various positional and orientational correlation functions to characterize the ordering of the molecules in the columnar arrangement. The molecules in a column are arranged with an average twist of 25° having an average inter-molecular separation of ˜5 Å. Interestingly, we find an overall tilt angle of 43° between the columnar axis and HBC core. We also simulate the charge transport through this columnar phase and report the numerical value of charge carrier mobility for this liquid crystal phase. The charge carrier mobility is strongly influenced by the twist angle and average spacing of the molecules in the column.

  1. Molecular structure of the Discotic Liquid Crystalline Phase of Hexa-peri-Hexabenzocoronene/Oligothiophene Hybrid and their Charge Transport properties

    E-print Network

    Saientan Bag; Vishal Maingi; Prabal K Maiti; Joseph Yelk; Matthew A. Glaser; David M. Walba; Noel A. Clark

    2015-10-10

    Using atomistic molecular dynamics simulation we study the discotic columnar liquid crystalline (LC) phases formed by a new organic compound having Hexa-peri-Hexabenzocoronene (HBC) core with six pendant oligothiophene units recently synthesized by Nan Hu et al. (N. Hu, R. Shao, Y. Shen, D. Chen, N. A. Clark and D. M. Walba, Adv. Mater. 26, 2066, 2014). This HBC core based LC phase was shown to have electric field responsive behavior and has important application in organic electronics. Our simulation results confirm the hexagonal arrangement of columnar LC phase with a lattice spacing consistent with that obtained from small angle X-ray diffraction data. We have also calculated various positional and orientational correlation functions to characterize the ordering of the molecules in the columnar arrangement. The molecules in a column are arranged with an average twist of 25 degrees having an average inter-molecular separation of ~5 {\\AA}. Interestingly, we find an overall tilt angle of 43 degrees between the columnar axis and HBC core. We also simulate the charge transport through this columnar phase and report the numerical value of charge carrier mobility for this liquid crystal phase. The charge carrier mobility is strongly influenced by the twist angle and average spacing of the molecules in the column.

  2. Molecular structure of the discotic liquid crystalline phase of hexa-peri-hexabenzocoronene/oligothiophene hybrid and their charge transport properties.

    PubMed

    Bag, Saientan; Maingi, Vishal; Maiti, Prabal K; Yelk, Joe; Glaser, Matthew A; Walba, David M; Clark, Noel A

    2015-10-14

    Using atomistic molecular dynamics simulation, we study the discotic columnar liquid crystalline (LC) phases formed by a new organic compound having hexa-peri-Hexabenzocoronene (HBC) core with six pendant oligothiophene units recently synthesized by Nan Hu et al. [Adv. Mater. 26, 2066 (2014)]. This HBC core based LC phase was shown to have electric field responsive behavior and has important applications in organic electronics. Our simulation results confirm the hexagonal arrangement of columnar LC phase with a lattice spacing consistent with that obtained from small angle X-ray diffraction data. We have also calculated various positional and orientational correlation functions to characterize the ordering of the molecules in the columnar arrangement. The molecules in a column are arranged with an average twist of 25° having an average inter-molecular separation of ?5 Å. Interestingly, we find an overall tilt angle of 43° between the columnar axis and HBC core. We also simulate the charge transport through this columnar phase and report the numerical value of charge carrier mobility for this liquid crystal phase. The charge carrier mobility is strongly influenced by the twist angle and average spacing of the molecules in the column. PMID:26472387

  3. Charge transport in hybrid nanorod-polymer composite photovoltaiccells

    SciTech Connect

    Huynh, Wendy U.; Dittmer, Janke J.; Teclemariam, Nerayo; Milliron, Delia; Alivisatos, A. Paul; Barnham, Keith W.J.

    2002-06-21

    Charge transport in composites of inorganic nanorods and aconjugated polymer is investigated using a photovoltaic device structure.We show that the current-voltage (I-V) curves in the dark can be modelledusing the Shockley equation modified to include series and shuntresistance at low current levels, and using an improved model thatincorporates both the Shockley equation and the presence of a spacecharge limited region at high currents. Under illumination, theefficiency of photocurrent generation is found to be dependent on appliedbias. Furthermore, the photocurrent-light intensity dependence was foundto be sublinear. An analysis of the shunt resistance as a function oflight intensity suggests that the photocurrent as well as the fill factoris diminished as a result of increased photoconductivity of the activelayer at high light intensity. By studying the intensity dependence ofthe open circuit voltage for nanocrystals with different diameters andthus ! band gaps, it was inferred that Fermi-level pinning occurs at theinterface between the aluminum electrode and the nanocrystal.

  4. Short chain molecular junctions: Charge transport versus dipole moment

    NASA Astrophysics Data System (ADS)

    Ikram, I. Mohamed; Rabinal, M. K.

    2015-03-01

    The investigation of the influence of dipole moment of short chain organic molecules having three carbon atoms varying in end group on silicon surface was carried on. Here, we use three different molecules of propargyl series varying in dipole moment and its orientation to constitute molecular junctions. The charge transport mechanism in metal-molecules-semiconductor (MMS) junction obtained from current-voltage (I-V) characteristics shows the rectification behavior for two junctions whereas the other junction shows a weak rectification. The electronic properties of the molecules were calculated using Gaussian software package. The observed rectification behavior of these junctions is examined and found to be accounted to the orientation of dipole moment and electron cloud density distribution inside the molecules.

  5. Lunar dust transport by photoelectric charging at sunset

    NASA Technical Reports Server (NTRS)

    Pelizzari, M. A.; Criswell, D. R.

    1978-01-01

    The motion of dust grains from a photoelectrically charged object at the moon's sunset terminator is studied with the aid of a simple model. It is shown that sunlit objects ranging in size from less than 0.01 cm to 5 cm in radius are responsible for the levitation of dust grains to heights of observed horizon glow. The transverse displacement of these grains is observed to be at least twice their maximum altitude, so that fitting the latter to horizon glow implies horizontal particle ranges typically 6 to 60 cm. Detachment of these grains from the sunlit areas takes place mainly along the contracting sunlight boundaries as the areas shrink during sunset. A high ratio of intergrain adhesion force to dust-grain weight is essential for the occurrence of horizon glow and significant dust transport from the subcentimeter sized sunlit areas.

  6. Perovskite solar cells employing organic charge-transport layers

    NASA Astrophysics Data System (ADS)

    Malinkiewicz, Olga; Yella, Aswani; Lee, Yong Hui; Espallargas, Guillermo Mínguez; Graetzel, Michael; Nazeeruddin, Mohammad K.; Bolink, Henk J.

    2014-02-01

    Thin-film photovoltaics play an important role in the quest for clean renewable energy. Recently, methylammonium lead halide perovskites were identified as promising absorbers for solar cells. In the three years since, the performance of perovskite-based solar cells has improved rapidly to reach efficiencies as high as 15%. To date, all high-efficiency perovskite solar cells reported make use of a (mesoscopic) metal oxide, such as Al2O3, TiO2 or ZrO2, which requires a high-temperature sintering process. Here, we show that methylammonium lead iodide perovskite layers, when sandwiched between two thin organic charge-transporting layers, also lead to solar cells with high power-conversion efficiencies (12%). To ensure a high purity, the perovskite layers were prepared by sublimation in a high-vacuum chamber. This simple planar device structure and the room-temperature deposition processes are suitable for many conducting substrates, including plastic and textiles.

  7. Symmetric and asymmetric charge transport in interacting asymmetric quantum impurities

    NASA Astrophysics Data System (ADS)

    Roy, Dibyendu

    2010-02-01

    We study steady-state charge transfer across an interacting resonance-level model connected asymmetrically to two leads. For a linear energy dispersion relation of the leads, we calculate current-voltage characteristics of the model exactly employing the scattering Bethe ansatz of Mehta-Andrei and find symmetric transport showing the absence of diode effect. Next we study a lattice version of this model with a nonlinear dispersion for the leads using the Lippmann-Schwinger scattering theory. We find that the inclusion of nonlinearity in the leads’ dispersion causes rectification for asymmetric junctions but does not rectify for asymmetric interactions and perfect junctions. The model in the latter case can be mapped into a model of a single noninteracting electron in higher dimensions.

  8. Charge transport in cancer-related genes and early carcinogenesis

    NASA Astrophysics Data System (ADS)

    Shih, Chi-Tin; Cheng, Yun-Yin; Wells, Stephen A.; Hsu, Ching-Ling; Römer, Rudolf A.

    2011-01-01

    The electronic transmission properties of DNA molecules are believed to play a significant role in many physical phenomena taking place in living organisms (Chakraborty, 2007) [1]. Here we study the charge transport (CT) properties of cancer-related genes, including some of the most important tumor suppressors. We find that the changes in averaged CT around the sites of pathogenic and cancerous mutations are statistically smaller than those on sites where pathogenic mutations have not been observed. The results suggest that CT might be an indicator to discriminate between pathogenic and non-pathogenic mutations at an early stage. Mutations which cause little change in CT may be more likely to occur, or more likely to be missed by damage-repair enzymes which probe CT, and are therefore more likely to persist and cause disease.

  9. EPR, charge transport, and spin dynamics in doped polyanilines

    NASA Astrophysics Data System (ADS)

    Kon'kin, A. L.; Shtyrlin, V. G.; Garipov, R. R.; Aganov, A. V.; Zakharov, A. V.; Krinichnyi, V. I.; Adams, P. N.; Monkman, A. P.

    2002-08-01

    Charge transport and magnetic properties of films of polyaniline (PAN) doped with 10-camphorsulfonic acid and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) have been studied by conductivity, magnetic-susceptibility superconducting quantum interference device measurements, and 3-cm and 8-mm electron paramagnetic resonance (EPR) spectroscopy at doping levels (x) from 0.3 to 0.9 over a temperature range from 15 to 300 K. The temperature dependences of conductivities were explained in terms of the advanced multiphase heterogeneous granular metallic (HGM) model with percolation including disordered metallic (DM) and nonmetallic (NM) phases. The anomalous conductivity change in the PAN-AMPSAx system at T>240 K was accounted quantitatively for a solid-phase equilibrium with the occurrence of the disordered anion phase from the metallic islands. A means for analysis of the EPR line shape in conducting media has been developed and, with this, conductivity and microwave dielectric constants were estimated and two EPR signals, R1 and R2, were detected in both systems. It was shown that R1 signal belongs to pinned radicals of isolated polymer chains, whereas R2 is the weight-averaged signal, resulting from three types of paramagnetic centers, localized and mobile spins in the NM and DM phases, which interact via exchange. From the temperature and frequency dependences of the R2 linewidth the spin-diffusion parameters for the NM phase in both systems were determined. It was found that the HGM model allows good explanation of both charge transport and spin diffusion in the doped polyaniline films.

  10. Carrier transport in the V[TCNE]x (TCNE = tetracyanoethylene; x ~ 2) organic-based magnet.

    PubMed

    Pokhodnya, Konstantin; Bonner, Michael; Prigodin, Vladimir; Epstein, Arthur J; Miller, Joel S

    2013-05-15

    The carrier transport of chemical vapor deposition (CVD) prepared films of the room temperature organic-based magnet V[TCNE]x (TCNE = tetracyanoethylene; x ~ 2) over a broad temperature and magnetic field range is reported. Due to disorder the [TCNE](·-) sites are located in statistically different environments, and their energies vary from site-to-site, which leads to tailing the density of states into the energy gap, creating electronic traps and suppressing the electron mobility. Conversely, these variations have little effect on the valence band derived from the octahedral V(II)3d(t(2g)) levels, and, hence, on the hole mobility. Presuming a Gaussian distribution of the energies of the localized states in the gap, a model that adequately describes the experimental data is proposed. In this model the T(-1) temperature dependent term was added to the Arrhenius activation energy, Ea, which effectively describes its decrease on cooling. The linear increase of positive magnetoresistance with magnetic field, as well as its weak temperature dependence [ is proportional to (1-T/Tc)(-1/2)] is discussed in terms of a small contribution to Ea associated with the change of magnetic energy. PMID:23604366

  11. Carrier Transport at Metal/Amorphous Hafnium-Indium-Zinc Oxide Interfaces.

    PubMed

    Kim, Seoungjun; Gil, Youngun; Choi, Youngran; Kim, Kyoung-Kook; Yun, Hyung Joong; Son, Byoungchul; Choi, Chel-Jong; Kim, Hyunsoo

    2015-10-14

    In this paper, the carrier transport mechanism at the metal/amorphous hafnium-indium-zinc oxide (a-HIZO) interface was investigated. The contact properties were found to be predominantly affected by the degree of interfacial reaction between the metals and a-HIZO; that is, a higher tendency to form metal oxide phases leads to excellent Ohmic contact via tunneling, which is associated with the generated donor-like oxygen vacancies. In this case, the Schottky-Mott theory is not applicable. Meanwhile, metals that do not form interfacial metal oxide, such as Pd, follow the Schottky-Mott theory, which results in rectifying Schottky behavior. The Schottky characteristics of the Pd contact to a-HIZO can be explained in terms of the barrier inhomogeneity model, which yields a mean barrier height of 1.40 eV and a standard deviation of 0.14 eV. The work function of a-HIZO could therefore be estimated as 3.7 eV, which is in good agreement with the ultraviolet photoelectron spectroscopy (3.68 eV). Our findings will be useful for establishing a strategy to form Ohmic or Schottky contacts to a-HIZO films, which will be essential for fabricating reliable high-performance electronic devices. PMID:26411354

  12. Solar-induced direct biomass-to-electricity hybrid fuel cell using polyoxometalates as photocatalyst and charge carrier

    NASA Astrophysics Data System (ADS)

    Liu, Wei; Mu, Wei; Liu, Mengjie; Zhang, Xiaodan; Cai, Hongli; Deng, Yulin

    2014-02-01

    The current polymer-exchange membrane fuel cell technology cannot directly use biomass as fuel. Here we present a solar-induced hybrid fuel cell that is directly powered with natural polymeric biomasses, such as starch, cellulose, lignin, and even switchgrass and wood powders. The fuel cell uses polyoxometalates as the photocatalyst and charge carrier to generate electricity at low temperature. This solar-induced hybrid fuel cell combines some features of solar cells, fuel cells and redox flow batteries. The power density of the solar-induced hybrid fuel cell powered by cellulose reaches 0.72?mW?cm-2, which is almost 100 times higher than cellulose-based microbial fuel cells and is close to that of the best microbial fuel cells reported in literature. Unlike most cell technologies that are sensitive to impurities, the cell reported in this study is inert to most organic and inorganic contaminants present in the fuels.

  13. Dynamics of charge carriers at the place of the formation of a muonic atom in diamond and silicon

    SciTech Connect

    Antipov, S. A.; Belousov, Yu. M.; Solov'ev, V. R.

    2012-11-15

    The space-time distribution of charge carriers at the place of the location of a muonic atom formed when a negative muon is captured by an atom of the lattice has been numerically simulated taking into account the self-consistent electric field. The results of {mu}SR experiments with negative muons in diamond crystals have been explained and reasons for the difference in the behavior of the spin polarization of the negative muon in boron-doped diamond and in silicon have been revealed. The condition of the validity of the analytical solution of this problem has been obtained. It has been shown that the muonic atom in diamond, in contrast to silicon, does not form a neutral acceptor center in the paramagnetic state during the muon experiment and remains in the diamagnetic state of a positive ion.

  14. Charge carrier trapping in highly-ordered lyotropic chromonic liquid crystal films based on ionic perylene diimide derivatives

    NASA Astrophysics Data System (ADS)

    Soroka, Pavlo V.; Vakhnin, Alexander Yu.; Skryshevskiy, Yuriy A.; Boiko, Oleksandr P.; Anisimov, Maksim I.; Slominskiy, Yuriy L.; Nazarenko, Vassili G.; Genoe, Jan; Kadashchuk, Andrey

    2014-12-01

    Charge carrier trapping in thin films of lyotropic chromonic liquid crystals (LCLCs) based on ionic perylene diimide derivative and in chemically-similar neutral N,N'-dipentyl-3,4,9,10-perylene-dicarboximide (PTCDI-C5) films is investigated by thermally-stimulated luminescence (TSL) technique. The LCLC films comprise elongated molecular aggregates featuring a long-range orientational order. The obtained results provide direct evidence for the improved energetic ordering (smaller effective energetic disorder) in aggregated LCLC films as compared to conventional PTCDI-C5 films. The width of the density-of-state distribution of 0.09 eV and 0.13 eV was estimated for the LCLC and PTCDI-C5 films, respectively. Relatively small effective energetic disorder in LCLC films is ascribed to formation of macroscopically larger LCLC aggregates.

  15. Hot Electrons Generated from Doped Quantum Dots via Upconversion of Excitons to Hot Charge Carriers for Enhanced Photocatalysis.

    PubMed

    Dong, Yitong; Choi, Julius; Jeong, Hae-Kwon; Son, Dong Hee

    2015-04-29

    We show that hot electrons exhibiting the enhanced photocatalytic activity in H2 production reaction can be efficiently generated in Mn-doped quantum dots via the "upconversion" of the energy of two excitons into the hot charge carriers. The sequential two-photon-induced process with the long-lived Mn excited state serving as the intermediate state is considered as the pathway generating hot electrons. H2 production rate from doped quantum dots is significantly higher than that from undoped quantum dots and also exhibited the quadratic increase with the light intensity, demonstrating the effectiveness of the hot electrons produced in doped quantum dots in photocatalytic reaction. Due to the very long lifetime of Mn excited state (?6 ms) in the doped quantum dots, the sequential two-photon excitation requires relatively low excitation rates readily achievable with a moderately concentrated solar radiation, demonstrating their potential as an efficient source of hot electrons operating at low excitation intensities. PMID:25860231

  16. The role of electron-electron interaction in the process of charge-carrier capture in deep quantum wells

    SciTech Connect

    Danilov, L. V. Zegrya, G. G.

    2013-10-15

    The role of electron-electron interaction in the process of electron capture to a deep quantum well is investigated. Using two-level and three-level quantum wells as examples, the basic electron-capture mechanisms, i.e., the interaction with optical phonons and the Coulomb electron-electron interaction, are considered, and the corresponding capture probabilities and electron lifetimes are calculated. The effect of Auger recombination on the charge-carrier distribution in a quantum well is also taken into account. With this taken into consideration, a set of rate equations is solved for a nonsteady-state mode, and the time dependences of the electron concentration at the ground energy level in the quantum well are found. The contributions of each of the recombination processes under consideration are shown.

  17. Solar-induced direct biomass-to-electricity hybrid fuel cell using polyoxometalates as photocatalyst and charge carrier.

    PubMed

    Liu, Wei; Mu, Wei; Liu, Mengjie; Zhang, Xiaodan; Cai, Hongli; Deng, Yulin

    2014-01-01

    The current polymer-exchange membrane fuel cell technology cannot directly use biomass as fuel. Here we present a solar-induced hybrid fuel cell that is directly powered with natural polymeric biomasses, such as starch, cellulose, lignin, and even switchgrass and wood powders. The fuel cell uses polyoxometalates as the photocatalyst and charge carrier to generate electricity at low temperature. This solar-induced hybrid fuel cell combines some features of solar cells, fuel cells and redox flow batteries. The power density of the solar-induced hybrid fuel cell powered by cellulose reaches 0.72?mW?cm(-2), which is almost 100 times higher than cellulose-based microbial fuel cells and is close to that of the best microbial fuel cells reported in literature. Unlike most cell technologies that are sensitive to impurities, the cell reported in this study is inert to most organic and inorganic contaminants present in the fuels. PMID:24504242

  18. Molecular weight dependent charge carrier mobility in poly(3,3' '-dioctyl-2,2':5',2' '-terthiophene).

    PubMed

    Verilhac, Jean-Marie; Pokrop, Rafal; LeBlevennec, Gilles; Kulszewicz-Bajer, Irena; Buga, Katarzyna; Zagorska, Malgorzata; Sadki, Said; Pron, Adam

    2006-07-13

    Poly(3,3' '-dioctyl-2,2':5',2' '-terthiophene), a polymer recently used for the fabrication of organic field effect transistors, has been fractionated into five fractions distinctly differing in their molecular weights (Mn), with the goal of determining the influence of the degree of polymerization (DPn) on its principal physicochemical parameters. It has been demonstrated that within the Mn range studied (from 1.5 kDa to 10.5 kDa by SEC), corresponding to DPn from 10 to 38, the polymer band gap steadily decreases with growing molecular weight, which is clearly manifested by an increasing bathochromic shift of the band originating from the pi-pi* transition. The same trend is observed for the HOMO level, determined from the onset of the p-doping in cyclic voltammetry, which shifts from -5.10 eV to -4.90 eV for the lowest and the highest molecular weight fractions, respectively. The most pronounced influence of DPn has been found for the charge carriers' mobility-one of the most important parameters of field effect transistors (FETs) fabricated from this polymer. A fourfold increase in DPn results in an increase of the carriers' mobility by more than 3 orders of magnitude. Comparison of these results with those obtained for fractionated regioregular poly(3-hexylthiophene) shows a strikingly similar behavior of both polymers with respect to the molecular weight. PMID:16821847

  19. Structural features of the photogeneration mechanism of free charge carriers in element-containing polydisalicylidene azomethine series

    SciTech Connect

    Aleksandrova, E. L.; Ivanov, A. G. Geller, N. M. Shamanin, V. V.

    2010-05-15

    Photophysical properties of new polytetra- and polydisalicylidene azomethines (PSAMs) with chains containing Si, Ge, Sn, or transition metal atoms and atoms of a number of other divalent metals are studied. Based on data on ultraviolet and infrared spectra, it was found that the noncovalent transannular donor-acceptor interaction N M (M is semimetal or metal) occurs in polymers, which leads to the formation of a polymer chain of six-membered cycles. As a result, polyconjugations arise in PSAMs by a 'non-classical' mechanism. Due to multiple donor-acceptor interactions of unshared electron pairs of azomethine groups with vacant d-orbitals in metals, polymers feature conductive, photosensitive, and photoconductive properties. The photosensitivity and quantum yield of photogeneration of free charge carriers for PSAMs are close to the values characteristic of classical conducting polymers. It was shown that the PSAM properties are controlled by the azomethine fragment structure and acceptor properties of metal. A mechanism of free carrier photogeneration was suggested.

  20. Magnetic Fields Facilitate DNA-Mediated Charge Transport.

    PubMed

    Wong, Jiun Ru; Lee, Kee Jin; Shu, Jian-Jun; Shao, Fangwei

    2015-06-01

    Exaggerated radical-induced DNA damage under magnetic fields is of great concern to medical biosafety and biomolecular electronic devices. In this report, the effects of an external magnetic field (MF) on DNA electronic conductivity were investigated by studying the efficiencies of photoinduced DNA-mediated charge transport (CT) via guanine damage. Under a static MF of 300 mT, positive enhancements in the decomposition of 8-cyclopropyldeoxyguanosine ((8CP)G) were observed at both the proximal and distal guanine doublets, indicating a more efficient propagation of radical cations and higher electronic conductivity of duplex DNA. MF-assisted CT has shown sensitivity to magnetic field strength, duplex structures, and the integrity of base pair stacking. Spin evolution of charge injection and the alignment of base pairs to the CT-active conformation during radical propagation were proposed to be the two major factors that MF contributes to facilitate DNA-mediated CT. Herein, MF-assisted CT may offer a new avenue for designing DNA-based electronic devices and unraveling MF effects on redox and radical relevant biological processes. PMID:25946473

  1. Charge transport in single CuO nanowires

    SciTech Connect

    Wu, Junnan; Yin, Bo; Wu, Fei; Myung, Yoon; Banerjee, Parag

    2014-11-03

    Charge transport in single crystal, p-type cupric oxide (CuO) nanowire (NW) was studied through temperature based (120?K–400?K) current-voltage measurements. CuO NW with a diameter of 85?nm was attached to Au electrodes 2.25??m apart, using dielectrophoresis. At low electrical field (<0.89?×?10{sup 3?}V/cm), an ohmic conduction is observed with an activation energy of 272?meV. The injected electrons fill traps with an average energy, E{sub T}?=?26.6?meV and trap density, N{sub T}?=?3.4?×?10{sup 15?}cm{sup ?3}. After the traps are saturated, space charge limited current mechanism becomes dominant. For 120?K???T???210?K phonon scattering limits mobility. For T???220?K, a thermally activated mobility is observed and is attributed to small polaron hopping with an activation energy of 44?meV. This mechanism yields a hole mobility of 0.0015?cm{sup 2}/V s and an effective hole concentration of 4?×?10{sup 18?}cm{sup ?3} at 250?K.

  2. Magnetic fields facilitate DNA-mediated charge transport

    E-print Network

    Wong, Jiun Ru; Shu, Jian-Jun; Shao, Fangwei

    2015-01-01

    Exaggerate radical-induced DNA damage under magnetic fields is of great concerns to medical biosafety and to bio-molecular device based upon DNA electronic conductivity. In this report, the effect of applying an external magnetic field (MF) on DNA-mediated charge transport (CT) was investigated by studying guanine oxidation by a kinetics trap (8CPG) via photoirradiation of anthraquinone (AQ) in the presence of an external MF. Positive enhancement in CT efficiencies was observed in both the proximal and distal 8CPG after applying a static MF of 300 mT. MF assisted CT has shown sensitivities to magnetic field strength, duplex structures, and the integrity of base pair stacking. MF effects on spin evolution of charge injection upon AQ irradiation and alignment of base pairs to CT-active conformation during radical propagation were proposed to be the two major factors that MF attributed to facilitate DNA-mediated CT. Herein, our results suggested that the electronic conductivity of duplex DNA can be enhanced by a...

  3. Glutamate, water and ion transport through a charged nanosize pore.

    PubMed

    De Luca, G; Glavinovi?, M I

    2007-02-01

    The transport of transmitter, ions and water through a positively-charged nanopore was investigated through computer simulations. The physics of the problem is described by a coupled set of Poisson-Nernst-Planck and Navier-Stokes equations in a computational domain consisting a cylindrical pore, whose radius ranged from 1 to 8 nm and which was flanked by two compartments representing the vesicular interior and extra-cellular space. The concentration of co-ions is suppressed and of counter-ions enhanced, especially near the pore wall owing to electrostatic interactions. Glutamate (i.e. the transmitter considered) is negatively charged and is simulated as a counter-ion. The electro-kinetically induced pressure due to the movement of ions is negative and very pronounced near the pore wall where the concentration and flux of counter-ions is very high. The water velocity peaks in the pore center, diminishes to zero at the pore wall, but is constant along the pore axis. The mean velocity of the water/fluid is proportional to the vesicular pressure and pore cross-sectional area. Interestingly it is inversely related to the vesicular glutamate concentration. The factors determining the glutamate flux are complex. The diffusive flux generally predominates for narrow pore, and convective flux may dominate for wide pore if the vesicular pressure is high. Surprisingly at low vesicular pressure the mean total glutamate flux per unit cross-sectional pore area is higher for narrow pores. Higher flux is probably due to the rise of glutamate concentration in the nanopore, which is much more pronounced for narrow nanopores, due to the maintenance of approximate neutrality of charges in the pore and on the pore wall. In conclusion intra-vesicular pressure helps 'flushing-out' the transmitter, but the induced pressure 'drags-out' the water into the extra-cellular space. PMID:17014822

  4. Salicylic Acid Transport in Ricinus communis Involves a pH-Dependent Carrier System in Addition to Diffusion1[OA

    PubMed Central

    Rocher, Françoise; Chollet, Jean-François; Legros, Sandrine; Jousse, Cyril; Lemoine, Rémi; Faucher, Mireille; Bush, Daniel R.; Bonnemain, Jean-Louis

    2009-01-01

    Despite its important functions in plant physiology and defense, the membrane transport mechanism of salicylic acid (SA) is poorly documented due to the general assumption that SA is taken up by plant cells via the ion trap mechanism. Using Ricinus communis seedlings and modeling tools (ACD LogD and Vega ZZ softwares), we show that phloem accumulation of SA and hydroxylated analogs is completely uncorrelated with the physicochemical parameters suitable for diffusion (number of hydrogen bond donors, polar surface area, and, especially, LogD values at apoplastic pHs and ? LogD between apoplast and phloem sap pH values). These and other data (such as accumulation in phloem sap of the poorly permeant dissociated form of monohalogen derivatives from apoplast and inhibition of SA transport by the thiol reagent p-chloromercuribenzenesulfonic acid [pCMBS]) lead to the following conclusions. As in intestinal cells, SA transport in Ricinus involves a pH-dependent carrier system sensitive to pCMBS; this carrier can translocate monohalogen analogs in the anionic form; the efficiency of phloem transport of hydroxylated benzoic acid derivatives is tightly dependent on the position of the hydroxyl group on the aromatic ring (SA corresponds to the optimal position) but moderately affected by halogen addition in position 5, which is known to increase plant defense. Furthermore, combining time-course experiments and pCMBS used as a tool, we give information about the localization of the SA carrier. SA uptake by epidermal cells (i.e. the step preceding the symplastic transport to veins) insensitive to pCMBS occurs via the ion-trap mechanism, whereas apoplastic vein loading involves a carrier-mediated mechanism (which is targeted by pCMBS) in addition to diffusion. PMID:19493970

  5. Photoinduced Charge Carrier Generation and Decay in Sequentially Deposited Polymer/Fullerene Layers: Bulk Heterojunction vs. Planar Interface

    SciTech Connect

    Nardes, A.; Ayzner, A.; Hammond, S.; Ferguson, A.; Schwartz, B.; Kopidakis, N.

    2012-04-05

    In this work, we use the time-resolved microwave conductivity (TRMC) technique to study the dynamics of charge carrier generation in sequentially deposited conjugated polymer/fullerene layers. These layers are either fully solution-processed, using orthogonal solvents for the layers of the polymer poly(3-hexylthiophene) (P3HT) and the fullerene phenyl-C{sup 61}-butyric acid methyl ester (PCBM), or prepared by thermally evaporating a C{sup 60} layer onto P3HT films. Our work is motivated by the remarkable efficiency of organic photovoltaic (OPV) devices using a sequentially processed P3HT/PCBM active layer. Here we use an electrodeless photoconductivity probe, so we can photoexcite the sample either through the polymer or the fullerene layer. We use samples with extremely thick P3HT films (2.4 {micro}m) and show that excitation from either side of both as-cast and thermally annealed sample yields virtually identical results, consistent with mixing of the PCBM into the polymer film. We also compare solution-deposited samples to samples made by thermally evaporating C{sup 60} on P3HT, and find that we can distinguish between charge generation in bulk-P3HT and at the polymer/fullerene interface. We show that, despite their morphological differences, the carrier dynamics in the sequentially processed samples resemble those of mixed, bulk heterojunction (BHJ) systems. All of this is consistent with the idea that PCBM readily mixes into the P3HT film in sequentially deposited P3HT/PCBM samples, although the total amount of fullerene mixed into the P3HT appears to be less than that typically used in an optimized BHJ. Finally, we discuss the implications for OPV device architectures prepared by sequential deposition from solution.

  6. The image charge effect and vibron-assisted processes in Coulomb blockade transport: a first principles approach

    NASA Astrophysics Data System (ADS)

    Souza, A. M.; Rungger, I.; Schwingenschlögl, U.; Sanvito, S.

    2015-11-01

    We present a combination of density functional theory and of both non-equilibrium Green's function formalism and a Master equation approach to accurately describe quantum transport in molecular junctions in the Coulomb blockade regime. We apply this effective first-principles approach to reproduce the experimental results of Perrin et al., [Nat. Nanotechnol., 2013, 8, 282] for the transport properties of a Au-(Zn)porphyrin-Au molecular junction. We demonstrate that energy level renormalization due to the image charge effect is crucial to the prediction of the current onset in the current-voltage, I-V, curves as a function of electrode separation. Furthermore, we show that for voltages beyond that setting the current onset, the slope of the I-V characteristics is determined by the interaction of the charge carriers with molecular vibrations. This corresponds to current-induced local heating, which may also lead to an effective reduced electronic coupling. Overall our scheme provides a fully ab initio description of quantum transport in the Coulomb blockade regime in the presence of electron-vibron coupling.We present a combination of density functional theory and of both non-equilibrium Green's function formalism and a Master equation approach to accurately describe quantum transport in molecular junctions in the Coulomb blockade regime. We apply this effective first-principles approach to reproduce the experimental results of Perrin et al., [Nat. Nanotechnol., 2013, 8, 282] for the transport properties of a Au-(Zn)porphyrin-Au molecular junction. We demonstrate that energy level renormalization due to the image charge effect is crucial to the prediction of the current onset in the current-voltage, I-V, curves as a function of electrode separation. Furthermore, we show that for voltages beyond that setting the current onset, the slope of the I-V characteristics is determined by the interaction of the charge carriers with molecular vibrations. This corresponds to current-induced local heating, which may also lead to an effective reduced electronic coupling. Overall our scheme provides a fully ab initio description of quantum transport in the Coulomb blockade regime in the presence of electron-vibron coupling. Electronic supplementary information (ESI) available: Details of the master equation approach, the scissor operator method and the procedure used to extract the electronic couplings. See DOI: 10.1039/C5NR04245C

  7. Interaction of charge carriers with lattice and molecular phonons in crystalline pentacene.

    PubMed

    Girlando, Alberto; Grisanti, Luca; Masino, Matteo; Brillante, Aldo; Della Valle, Raffaele G; Venuti, Elisabetta

    2011-08-28

    The computational protocol we have developed for the calculation of local (Holstein) and non-local (Peierls) carrier-phonon coupling in molecular organic semiconductors is applied to both the low temperature and high temperature bulk crystalline phases of pentacene. The electronic structure is calculated by the semimpirical INDO/S (Intermediate Neglect of Differential Overlap with Spectroscopic parametrization) method. In the phonon description, the rigid molecule approximation is removed, allowing mixing of low-frequency intra-molecular modes with inter-molecular (lattice) phonons. A clear distinction remains between the low-frequency phonons, which essentially modulate the transfer integral from a molecule to another (Peierls coupling), and the high-frequency intra-molecular phonons, which modulate the on-site energy (Holstein coupling). The results of calculation agree well with the values extracted from experiment. The comparison with similar calculations made for rubrene allows us to discuss the implications for the current models of mobility. PMID:21895208

  8. Expression of human solute carrier family transporters in skin: possible contributor to drug-induced skin disorders

    PubMed Central

    Fujiwara, Ryoichi; Takenaka, Saya; Hashimoto, Mitsuhiro; Narawa, Tomoya; Itoh, Tomoo

    2014-01-01

    Solute carrier (SLC) transporters play important roles in absorption and disposition of drugs in cells; however, the expression pattern of human SLC transporters in the skin has not been determined. In the present study, the expression patterns of 28 human SLC transporters were determined in the human skin. Most of the SLC transporter family members were either highly or moderately expressed in the liver, while their expression was limited in the skin and small intestine. Treatment of human keratinocytes with a reactive metabolite of ibuprofen significantly reduced cell viability. Expression array analysis revealed that S100 calcium binding protein A7A (S100A7A) was induced nearly 50-fold in dermal cells treated with ibuprofen acyl-glucuronide. Determination of the expression of drug-metabolizing enzymes as well as drug transporters prior to the administration of drugs would make it possible to avoid the development of idiosyncratic skin diseases in individuals. PMID:24918694

  9. Electrical and thermal transport properties of Y bxCo4Sb12 filled skutterudites with ultrahigh carrier concentrations

    NASA Astrophysics Data System (ADS)

    Li, Yulong; Qiu, Pengfei; Xiong, Zhen; Chen, Jikun; Nunna, Raghavendra; Shi, Xun; Chen, Lidong

    2015-11-01

    For filled skutterudites, element Yb is one of the most common and important fillers. However, the optimal carrier concentration range in Y bxCo4Sb12 filled skutterudites has not been determined as a result of the low Yb filling fraction limit. In this study, a non-equilibrium fabrication process (MS-SPS process), consisting of a melt-spinning method and a spark plasma sintering technique, has been applied to prepare Y bxCo4Sb12 samples. The Yb filling fraction is successfully extended to 0.35, which provides the possibility to clarify the optimal carrier concentration range for Yb-filled skutterudites. High carrier concentrations, with a maximum of around 1 × 1021 cm-3, were achieved in the MS-SPS Y bxCo4Sb12 samples due to the significantly enhanced Yb filling fractions. The phase compositions, lattice parameters, electrical and thermal transport properties of the MS-SPS Y bxCo4Sb12 samples with high carrier concentrations were systematically investigated. An optimal carrier concentration range of around 5 ˜ 6 × 1020 cm-3, corresponding to the actual Yb filling fraction of around 0.21˜0.26, has been determined, which displays the highest thermoelectric performance in Y bxCo4Sb12 thermoelectric materials.

  10. Improved charge transport and injection in a meso-superstructured solar cell by a tractable pre-spin-coating process.

    PubMed

    Li, Nan; Li, Haoyuan; Li, Yu; Wang, Shufeng; Wang, Liduo

    2015-10-01

    In meso-superstructured solar cells (MSSCs), the state-of-the-art perovskite acts as both the light harvester and electron transporter due to its ambipolar properties. The inefficient pore filling and infiltration of perovskite directly affect the continuous distribution of perovskite in mesoporous Al2O3, resulting in discontinuous carrier transport in the mesoporous structure and insufficient electron injection to the compact TiO2 layer. Herein, we introduce a simple pre-spin-coating process to improve the infiltration and pore filling of perovskite, which results in higher light absorption and enhanced electron injection, as seen in UV-vis spectra and photoluminescence (PL) spectra, respectively. We first apply time of flight (TOF) experiments to characterize charge transport in MSSCs, and the results reveal that more continuous charge transport pathways are formed with the pre-spin-coating process. This effective method, with ease of processing, demonstrates obviously improved photocurrents, reaching an efficiency as high as 14%, and promotes the application of lead halide perovskite materials in the photovoltaics field. PMID:26315559

  11. Carrier-mediated transport of thyroid hormones into rat glial cells in primary culture.

    PubMed

    Francon, J; Chantoux, F; Blondeau, J P

    1989-11-01

    The uptake of 3,3',5-[3'-125I]triiodo-L-thyronine ([125I]L-T3) and of L-[3',5'-125I]thyroxine ([125I]L-T4) by cultured rat glial cells was studied under initial velocity (Vi) conditions. Uptake of both hormones was carrier mediated and obeyed simple Michaelis-Menten kinetics. The following respective values of Km (microM) and Vmax (fmol/min/microgram of DNA) were obtained at 25 degrees C: 0.52 +/- 0.09 and 727 +/- 55 for L-T3 and 1.02 +/- 0.21 and 690 +/- 85 for L-T4. Ki values (microM) for the inhibition of [125I]L-T3 uptake by unlabeled analogues were as follows: L-T4, 0.88; 3,3',5'-triiodo-L-thyronine, 1.4; 3,3'-diiodo-L-thyronine, 2.9; 3,3',5-triiodo-D-thyronine, 4.8; and triiodothyroacetic acid, 5.3. These values indicate that the uptake system is stereospecific. Unlabeled L-T3 was a better competitor than unlabeled L-T4 for the uptake of [125I]L-T4, an observation suggesting that both hormones were taken up by a common carrier system. L-T3, and L-T4 uptake was pH dependent, a finding suggesting that the phenolic unionized form of the hormones was preferentially taken up. L-T3 uptake was studied in the presence of various inhibitors; the results suggest that uptake was independent of the transmembrane Na+ gradient and of the cellular energy. Compounds that inhibited cellular uptake but were without effect on L-T3 binding to isolated nuclei also inhibited L-T3 nuclear binding in intact cells, an observation suggesting that uptake could be rate limiting for the access of L-T3 to nuclear receptors when transport is severely inhibited. PMID:2795012

  12. Effect of band offset on carrier transport and infrared detection in InP quantum dots/Si nano-heterojunction grown by metalorganic chemical vapor deposition technique

    SciTech Connect

    Halder, Nripendra N.; Biswas, Pranab; Nagabhushan, B.; Banerji, P.; Kundu, Souvik; Biswas, D.

    2014-05-28

    Epitaxy of III-V semiconductors on Si gets recent interest for next generation system on heterogeneous chip on wafer. The understanding of band offset is thus necessary for describing the charge transport phenomenon in these heterojunctions. In this work, x-ray photoemission spectroscopy has been used to determine the band offsets in a heterojunction made of InP quantum dots on Si. The valence and conduction band offset was found to be 0.12?eV and 0.35?eV, respectively, with a type-II band lineup. Deviation from theoretical prediction and previously published reports on quasi similar systems have been found and analyzed on the basis of the effect of strain, surface energy, shift in the electrostatic dipole and charge transfer at the interface. The carrier transport mechanisms along with different device parameters in the heterojunction have been studied for a temperature range of 180–300?K. This heterojunction is found to behave as an efficient infrared photodetector with an ON/OFF ratio of 21 at a reverse bias of 2?V. The corresponding rise and decay time was found to be 132?ms and 147?ms, respectively.

  13. Ultrafast carriers dynamics in filled-skutterudites

    NASA Astrophysics Data System (ADS)

    Guo, Liang; Xu, Xianfan; Salvador, James R.

    2015-06-01

    Carrier dynamics of filled-skutterudites, an important class of thermoelectric materials, is investigated using ultrafast optical spectroscopy. By tuning the wavelength of the probe laser, charge transfers at different electronic energy levels are interrogated. Analysis based on the Kramers-Kronig relation explains the complex spectroscopy data, which is mainly due to band filling caused by photo-excited carriers and free carrier absorption. The relaxation time of hot carriers is found to be about 0.4-0.6 ps, depending on the electronic energy level, and the characteristic time for carrier-phonon equilibrium is about 0.95 ps. These studies of carrier dynamics, which fundamentally determines the transport properties of thermoelectric material, can provide guidance for the design of materials.

  14. Photoinduced Charge Transport in a BHJ Solar Cell Controlled by an External Electric Field

    PubMed Central

    Li, Yongqing; Feng, Yanting; Sun, Mengtao

    2015-01-01

    This study investigated theoretical photoinduced charge transport in a bulk heterojunction (BHJ) solar cell controlled by an external electric field. Our method for visualizing charge difference density identified the excited state properties of photoinduced charge transfer, and the charge transfer excited states were distinguished from local excited states during electronic transitions. Furthermore, the calculated rates for the charge transfer revealed that the charge transfer was strongly influenced by the external electric field. The external electric field accelerated the rate of charge transfer by up to one order when charge recombination was significantly restrained. Our research demonstrated that photoinduced charge transport controlled by an external electric field in a BHJ solar cell is efficient, and the exciton dissociation is not the limiting factor in organic solar cells.Our research should aid in the rational design of a novel conjugated system of organic solar cells. PMID:26353997

  15. 77 FR 38747 - Reports by Air Carriers on Incidents Involving Animals During Air Transport

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-06-29

    ... Privacy Act statement in the Federal Register published on April 11, 2000 (65 FR 19477-78), or you may... implementing section 710 of AIR-21. See 68 FR 47798. The rule required air carriers that provide scheduled... regulations. See 70 FR 7392. The rule is codified at 14 CFR 234.13. Section 234.13 requires air carriers...

  16. Probing Neutral Majorana Fermion Edge Modes with Charge Transport Liang Fu and C. L. Kane

    E-print Network

    Kane, Charles

    Probing Neutral Majorana Fermion Edge Modes with Charge Transport Liang Fu and C. L. Kane allows the neutral Majorana fermions to be probed with charge transport. We will discuss a novel of neutral Majorana fermions through a point contact to be measured. We introduce a point contact formed

  17. Charge Transport Measurements at the Nanoscale using a Multi-Tip STM

    E-print Network

    Ku?el, Petr

    Charge Transport Measurements at the Nanoscale using a Multi-Tip STM Seminá odd. 26 Tenkých vrstev an ultra-compact, ultra-stable four-tip STM for charge transport measurements at the nanoscale for novel semiconductor devices in future electronic and opto-electronic applications such as solar cells

  18. Reversible chemical tuning of charge carriers for enhanced photoelectrochemical conversion and probing of living cells.

    PubMed

    Wang, Yongcheng; Tang, Jing; Zhou, Tong; Da, Peimei; Li, Jun; Kong, Biao; Yang, Zhongqin; Zheng, Gengfeng

    2014-12-10

    A facile, solution method for reversible tuning of oxygen vacancies inside TiO2 nanowires, in which the reducing treatment of TiO2 by NaBH4 leads to 2.4-fold increase of photocurrent density, compared to pristine TiO2 nanowires, is reported. Subsequent oxidizing treatment using KMnO4 or annealing in air can reset the photocurrent density to the original values. The incident photo-to-current conversion efficiency measurement exhibits that the reduced TiO2 nanowires present both enhanced photoactivity in both UV and visible regions. Density functional theory calculations reveal that the oxygen vacancies in the reduced TiO2 cause defect states in the band structure and result in enhanced carrier density and conductivity. In addition, the enhanced solar energy-driven photoelectrochemical conversion allows real-time, sensitive chemical probing of living cells that are directly grown on the TiO2 nanowire photoanodes. As proofs-of-concept, after functionalized with horseradish peroxidase (HRP) on the surface, the reduced TiO2 NWs demonstrate sensitive, real-time monitoring of the H2O2 levels in several distinctive living cell lines, with the lowest detectable H2O2 concentration of 7.7 nM. This reversible tuning of oxygen vacancies suggests a facile means for transition metal oxides, with enhanced photoconversion activity and electrochemical sensitivity. PMID:25044916

  19. Organic thin-film transistors for circuits in a foundry: process, charge transport phenomena and device library

    NASA Astrophysics Data System (ADS)

    Pankalla, Sebastian; Ganz, Simone; Spiehl, Dieter; Dörsam, Edgar; Glesner, Manfred

    2013-09-01

    For the development of circuits consisting of organic thin film transistors (OTFT) with satisfying yield, a stable and reliable process is necessary. This can be achieved by eliminating failure mechanisms and understanding the charge transport phenomena in the individual device. Following the way of a charge through the device, we start with the investigation of the influence of the Schottky barrier height and contact morphology on the device performance by finite-elements simulations. It could be verified that the charge injection limiting contact resistance can be decreased by two orders of magnitude by reducing the thin oxide layer at the source and drain contacts and improving the semiconductor layer morphology at their vicinity. Second, we present an analytical closed-form solution of the OTFT channel potential used for Monte-Carlo charge transport simulations and compute current-voltage and transient response characteristics out of it. In a next step, the influence of the deposition process on the layer interface is investigated. Therefore, velocity distribution measurements of the charge carriers lead to a simulation model with varying disorder, depending on the layer surfaces and deposition techniques. Afterwards, leakage currents through the gate dielectric can be described by a poor conducting semiconductor model in the finite-elements framework. Leakage currents increase power consumption in circuits and, what is more critical, can lead to a total failure of the OTFT. However, they can be influenced by the number of deposited dielectric layers and charge injection supporting self-assembled monolayers at the source and drain contacts. These findings lead to circuit building blocks for an organic device library whereupon still existing performance fluctuations can be coped with Monte-Carlo circuit simulations.

  20. Microscopic model for d-wave charge-carrier pairing and non-Fermi-liquid behavior in a purely repulsive two-dimensional electron system

    E-print Network

    John, Sajeev

    manuscript received 28 March 2000 We investigate a microscopic model for strongly correlated electronsMicroscopic model for d-wave charge-carrier pairing and non-Fermi-liquid behavior in a purely repulsive two-dimensional electron system Mona Berciu and Sajeev John Department of Physics, University