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1

Charge carrier transport properties in layer structured hexagonal boron nitride  

NASA Astrophysics Data System (ADS)

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/T0)-? 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-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.

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

2014-10-01

2

Charge carrier transport properties in layer structured hexagonal boron nitride  

SciTech Connect

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.

Doan, T. C.; Li, J.; Lin, J. Y.; Jiang, H. X., E-mail: hx.jiang@ttu.edu [Department of Electrical and Computer Engineering, Texas Tech University, Lubbock, Texas 79409 (United States)

2014-10-15

3

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

E-print Network

of high efficiency organic light-emitting diodes OLEDs in 1980s has triggered extensive researchApplication of admittance spectroscopy to evaluate carrier mobility in organic charge transport AS and susceptance analysis in the determination of the charge-carrier mobility in an organic material. The complex

So, Shu K.

4

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

PubMed

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

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

2009-05-13

5

Fundamentals of Carrier Transport  

Microsoft Academic Search

Fundamentals of Carrier Transport explores the behavior of charged carriers in semiconductors and semiconductor devices for readers without an extensive background in quantum mechanics and solid-state physics. This second edition contains many new and updated sections, including a completely new chapter on transport in ultrasmall devices and coverage of \\

Mark Lundstrom

2000-01-01

6

Quantitative description of charge-carrier transport in a white organic light-emitting diode  

NASA Astrophysics Data System (ADS)

We present a simulation model for the analysis of charge-carrier transport in organic thin-film devices, and apply it to a three-color white hybrid organic light-emitting diode (OLED) with fluorescent blue and phosphorescent red and green emission. We simulate a series of single-carrier devices, which reconstruct the OLED layer sequence step by step. Thereby, we determine the energy profiles for hole and electron transport, show how to discern bulk from interface limitation, and identify trap states.

Schober, M.; Anderson, M.; Thomschke, M.; Widmer, J.; Furno, M.; Scholz, R.; Lüssem, B.; Leo, K.

2011-10-01

7

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

SciTech Connect

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.

Peyrard, M.; Boesch, R.; Kourakis, I. (Dijon Univ., 21 (France). Faculte des Sciences)

1991-01-01

8

A charge carrier transport model for donor-acceptor blend layers  

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

9

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

NASA Astrophysics Data System (ADS)

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.

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

2014-05-01

10

Physical mechanisms in double-carrier trap-charge limited transport processes in organic electroluminescent devices: A numerical study  

NASA Astrophysics Data System (ADS)

We have developed a numerical model to simulate the double-carrier injection trap-charge limited (TCL) transport processes in organic electroluminescent devices (OEDs). Current-voltage characteristics, energy and charge profiles are obtained and analyzed to understand the mechanisms governing the OED performance under TCL conditions. Good agreement with general experimental trends and previous analytical predictions are achieved. Dependencies on several important parameters (carrier injection level, device thickness, recombination constant, temperature, etc.) are also studied.

Shen, Jun; Yang, Jie

1998-06-01

11

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

NASA Astrophysics Data System (ADS)

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.

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

2014-05-01

12

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

NASA Astrophysics Data System (ADS)

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.

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

2014-12-01

13

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

SciTech Connect

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

Astakhov, Oleksandr; Carius, Reinhard; Finger, Friedhelm; Petrusenko, Yuri; Borysenko, Valery; Barankov, Dmytro [Forschungszentrum Juelich, Institute of Energy Research-Photovoltaic, 52425 Juelich, Germany and National Science Center-Kharkov Institute of Physics and Technology, Cyclotron Science and Research Establishment, 61108 Kharkov (Ukraine); Forschungszentrum Juelich, Institute of Energy Research-Photovoltaic, 52425 Juelich (Germany); National Science Center-Kharkov Institute of Physics and Technology, Cyclotron Science and Research Establishment, 61108 Kharkov (Ukraine)

2009-03-01

14

Temperature dependent charge transport in organic field-effect transistors with the variation of both carrier concentration and electric field  

NASA Astrophysics Data System (ADS)

We present experimental evidence of combined effects of temperature, carrier concentration, electric field as well as disorder on charge transport in an organic field-effect transistor (OFET). Transfer characteristics of an OFET based on sexithiophene active layer were measured from 80 to 300 K. Thermally activated carrier mobility followed Arrhenius law with two activation energies. Carrier density variation led to finite extrapolated Meyer-Neldel (MN) temperature (780 K) at low fields. Negative electric field-dependent mobility was observed in available field range. MN temperature shifted towards higher temperature when the electric field increased, and did not retain its finite character above the field of 4 × 103 V cm-1.

Abbas, Mamatimin; Pivrikas, Almantas; Arici, Elif; Tekin, Nalan; Ullah, Mujeeb; Sitter, Helmut; Sariciftci, Niyazi Serdar

2013-12-01

15

Charge Carrier Transport Properties of Semiconductor Materials Suitable for Nuclear Radiation Detectors  

Microsoft Academic Search

Charge carrier drift velocities in semiconductor materials suitable for solid state detectors has been reviewed. Si, Ge, CdTe and GaAs are considered. New data for HgI2 recently obtained are also reported. The data cover a large range of temperatures (6-430 K) and electric fields up to 50 KV\\/cm. An anisotropy effect in the drift velocity obtained by applying the electric

G. Ottaviani; C. Canali; A. Alberigi Quaranta

1975-01-01

16

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

NASA Astrophysics Data System (ADS)

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.

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

2015-01-01

17

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

PubMed

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

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

2015-01-01

18

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

PubMed Central

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

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

2015-01-01

19

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

SciTech Connect

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.

Nian, Qiong; Cheng, Gary J., E-mail: gjcheng@purdue.edu [Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47906 (United States); School of Industrial Engineering, Purdue University, West Lafayette, Indiana 47906 (United States); Zhang, Martin Y. [School of Industrial Engineering, Purdue University, West Lafayette, Indiana 47906 (United States); Wang, Yuefeng [Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47906 (United States); School of Materials Engineering, Purdue University, West Lafayette, Indiana 47906 (United States); Das, Suprem R.; Bhat, Venkataprasad S. [Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47906 (United States); Huang, Fuqiang [Shanghai Institute of Ceramics, Chinese Academy of Science, Shanghai 200050 (China)

2014-09-15

20

Charge Carrier Mobilities in Amorphous Triphenylamine-Fluorene Copolymers: Role of Triphenylamine Unit in Intra- and Intermolecular Charge Transport  

NASA Astrophysics Data System (ADS)

We investigated the effect of the triphenylamine (TPA) content of TPA-fluorene copolymers on their charge carrier mobilities. Intramolecular mobilities were measured by flash-photolysis time-resolved microwave conductivity (TRMC), while intermolecular hole mobilities were determined on the basis of space-charge limited current (SCLC) and field-effect transistor (FET). TRMC and SCLC except for FET showed an analogous dependence on the TPA content. The results are discussed from the viewpoints of delocalization of singly-occupied molecular orbital of radical cation, conformation of polymer chain, and trap effect. This study highlights the importance of optimizing the TPA content in the polyfluorene backbone for electronic device application.

Fukumatsu, Takahiro; Saeki, Akinori; Seki, Shu

2012-06-01

21

Charge carrier transport properties in thallium bromide crystals used as radiation detectors  

Microsoft Academic Search

The authors report on measurements of the two most important transport parameters, the mobility ? and the mean trapping time ? for electrons and holes, in TlBr crystals prepared in the laboratory. The results using the transient charge technique are presented along with the data obtained by the pulse height spectrum analysis. The values of (??)e and (??)h measured for

F. Olschner; M. Toledo-Quinones; K. S. Shah; J. C. Lund

1990-01-01

22

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

23

Enhanced charge-carrier transport through shorter carbon nanotubes in organic photovoltaics.  

PubMed

We demonstrate for the first time the efficiency improvement of organic photovoltaics by the addition of shorter multiwalled carbon nanotubes (MWNTs) generated by size sorting. The different size MWNTs were generated by size sorting a batch of carboxylated MWNTs and were introduced as charge carriers in poly(3-hexylthiophene) (P3HT):phenyl-C61-butyric acid methyl ester (PCBM) bulk heterojunction photovoltaic cells. As compared to a control with only PCBM, the addition of the long and short MWNT resulted in 12 and 34% improvement in short circuit current density (Jsc) respectively. The results indicate that length of carbon nanotubes is an important consideration in photovoltaic and possibly other nanoelectronic devices. PMID:24410974

Lau, Xinbo C; Wu, Zheqiong; Mitra, Somenath

2014-02-12

24

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

NASA Astrophysics Data System (ADS)

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.

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

2014-10-01

25

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

SciTech Connect

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.

Osses-Márquez, Juan; Calderón-Muñoz, Williams R., E-mail: wicalder@ing.uchile.cl [Department of Mechanical Engineering, University of Chile, Beauchef 850, Santiago (Chile)

2014-10-21

26

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

NASA Astrophysics Data System (ADS)

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

Cherqui, Charles

27

Charge-carrier transport and recombination in heteroepitaxial CdTe  

SciTech Connect

We analyze charge-carrier dynamics using time-resolved spectroscopy and varying epitaxial CdTe thickness in undoped heteroepitaxial CdTe/ZnTe/Si. By employing one-photon and nonlinear two-photon excitation, we assess surface, interface, and bulk recombination. Two-photon excitation with a focused laser beam enables characterization of recombination velocity at the buried epilayer/substrate interface, 17.5??m from the sample surface. Measurements with a focused two-photon excitation beam also indicate a fast diffusion component, from which we estimate an electron mobility of 650?cm{sup 2} (Vs){sup ?1} and diffusion coefficient D of 17?cm{sup 2}?s{sup ?1}. We find limiting recombination at the epitaxial film surface (surface recombination velocity S{sub surface}?=?(2.8?±?0.3)?×?10{sup 5?}cm?s{sup ?1}) and at the heteroepitaxial interface (interface recombination velocity S{sub interface}?=?(4.8?±?0.5)?×?10{sup 5?}cm?s{sup ?1}). The results demonstrate that reducing surface and interface recombination velocity is critical for photovoltaic solar cells and electronic devices that employ epitaxial CdTe.

Kuciauskas, Darius, E-mail: Darius.Kuciauskas@nrel.gov; 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. [National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401-3305 (United States); Colegrove, Eric; Sivananthan, S. [Microphysics Laboratory, Physics Department, University of Illinois at Chicago, Chicago, Illinois 60612 (United States)

2014-09-28

28

Charge carrier transport mechanisms in perovskite CdTiO3 fibers  

NASA Astrophysics Data System (ADS)

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.

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

2014-06-01

29

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

SciTech Connect

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.

Imran, Z.; Rafiq, M. A., E-mail: aftab@cantab.net; Hasan, M. M. [Micro and Nano Devices Group, Department of Metallurgy and Materials Engineering, Pakistan Institute of Engineering and Applied Sciences (PIEAS), P.O. Nilore, Islamabad, 45650 (Pakistan)

2014-06-15

30

Charge transport  

NASA Astrophysics Data System (ADS)

We report results from theoretical studies of charge and energy dynamics in organic molecular and polymeric systems. The studies were performed by employing an extended three-dimensional version of the Su-Schrieffer-Heeger model. The equation of motion for the lattice as well as the time dependent Schrodinger equation were solved simultaneously. The dynamics of charge transport and charge separation in conjugated polymeric systems have been investigated as well as the time evolution following the injection of hot electrons and excitons. The results of such studies will contribute to the understanding and the development of organic electronic and photovoltaic devices as well as artificial photosynthesis.

Stafstrãm, Sven; Boman, Magnus; Hultell Andersson, Magnus

2004-03-01

31

Carrier-Phonon Scattering Rate and Charge Transport in Spherical and TMV Viruses  

E-print Network

The present paper presents the carrier-acoustic phonon scattering in the spherical and TMV viruses. We demonstrate theoretically that the absorption rate changes in spherical and TMV viruses according to the phonon energy while emission of phonon is limited by the hole energy. The obtained relaxation rate is then used to calculate the conductivity and mobility of viruses. The obtained conductivity for spherical and TMV viruses suggest that the TMV virus is more conducting and therefore may be a good candidate for the connector or wire to be used in the nanoelectronics. The value of resistance obtained for TMV virus is lower than the earlier reported resistance of DNA.

Sanjeev K. Gupta; Prafulla K. Jha

2009-04-15

32

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

SciTech Connect

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.

Han, S.S.

1993-09-01

33

Charge-Carrier-Scattering Spectroscopy With BEEM  

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

34

Transport Properties of Charge Carriers in Single-Walled Carbon Nanotubes by Flash-Photolysis Time-Resolved Microwave Conductivity Technique  

NASA Astrophysics Data System (ADS)

Transport properties of charge carriers in single-walled carbon nanotubes (SWNTs) were investigated by flash-photolysis time-resolved microwave conductivity (FP-TRMC) technique. With this technique, it is possible to monitor the change in conductivity on pulsed laser excitation on a nanosecond timescale, without contacting layer with electrode. The FP-TRMC signals obtained by SWNT sample is drastically larger than that of only catalyst. The dependence of excitation wavelength on ???, which is a product of a quantum yield and sum of mobility, was obtained, indicating variety in transport property of size-distributed SWNTs.

Ohno, Yasuhide; Maehashi, Kenzo; Inoue, Koichi; Matsumoto, Kazuhiko; Saeki, Akinori; Seki, Shu; Tagawa, Seiichi

2005-06-01

35

Effect of charging on electronic structure of the Alq 3 molecule: the identification of carrier transport properties  

NASA Astrophysics Data System (ADS)

The effects of electrical charging on the electronic structure of tris(8-hydroxy-quinoline) aluminum (Alq 3) have been studied theoretically using density functional theory, and semi-empirical and ab initio molecular orbital theories. All three methods show that negatively charged Alq 3 molecules have rather delocalized electronic structures suitable for electron transport. On the other hand, the distribution of the highest occupied molecular orbital in the Alq 3 molecule becomes highly localized upon positive charging. This localization of the frontier molecular orbital restrains movement of the residing electrons and thus inhibits the electron transport. The success of the current approach in explaining the electron transport properties of the Alq 3 molecule suggests it may be useful for the design of organic molecules for electronic applications.

Zhang, R. Q.; Lee, C. S.; Lee, S. T.

2000-08-01

36

Carrier-mediated auxin transport  

Microsoft Academic Search

1.Auxin (IAA) transport was investigated using crown gall suspension tissue culture cells. We have shown that auxin can cross the plasmalemma both by transport of IAA anions on a saturable carrier and by passive (not carriermediated) diffusion of the lipid-soluble undissociated IAA molecules (pK=4.7). The pH optimum of the carrier for auxin influx is about pH 6 and it is

P. H. Rubery; A. R. Sheldrake

1974-01-01

37

Hopping Transport of Charge Carriers in LEDs Based on Multiple InGaN/GaN Quantum Wells  

NASA Astrophysics Data System (ADS)

The results of experimental studies of forward current-voltage characteristics of blue LEDs with an active region consisting of the multiple InGaN/GaN quantum wells are presented. A model explaining the limitation of the forward current at decreasing temperature is proposed. The model is based on the concept of current limited by the space charge and caused by hopping transport of electrons in the region of multiple quantum wells. It is shown that the most probable mechanism of charge accumulation is the electron capture by shallow traps. According to the results of different measurements, the activation energy of traps decreases with decreasing temperature, which is consistent with the concept of hopping conductance mechanism in materials with an exponential distribution of the defect state density in the band gap.

Prudaev, I. ?.; Zubrilkina, Yu. L.; Baktybaev, ?. ?.; Romanov, I. S.

2015-01-01

38

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

PubMed

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

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

2015-04-01

39

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

PubMed

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

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

2013-08-27

40

Carrier-mediated auxin transport.  

PubMed

1. Auxin (IAA) transport was investigated using crown gall suspension tissue culture cells. We have shown that auxin can cross the plasmalemma both by transport of IAA anions on a saturable carrier and by passive (not carriermediated) diffusion of the lipid-soluble undissociated IAA molecules (pK=4.7). The pH optimum of the carrier for auxin influx is about pH 6 and it is half-saturated by auxin concentrations in the region of 1-5 ?M. We found that the synthetic auxin 2,4D specifically inhibited carrier-mediated IAA anion influx, and possibly also efflux. Other lipid-soluble weak acids which are not auxins, such as 3,4-dichlorobenzoic acid, had no effect on auxin transport. By contrast, we found that TIBA, an inhibitor of polar auxin transport in intact tissues inhibited only the carrier-mediated efflux of IAA. 2. When the pH outside the cells is maintained below that of the cytoplasm (pH 7), auxin can be accumulated by the cells: In the initial phase of uptake, the direction of the auxin concentration gradient allows both passive carrier-mediated anion influx (inhibited by 2,4D) and a passive diffusion of undissociated acid molecules into the cells. Once inside the cytoplasm, the undissociated molecules ionise, producing IAA anions, to a greater extent than in the more acidic extracellular environment. Uptake by passive diffusion continues as long as the extracellular concentration of undissociated acid remains higher than its intra-cellular concentration. Thus, the direction of the auxin anion concentration gradient is reversed after a short period of uptake and auxin accumulates within the cells. The carrier is now able to mediate passive IAA anion efflux (inhibited by TIBA) down this concentration gradient even though net uptake still proceeds because the carrier is saturable whereas passive diffusion is not. 3. Auxin "secretion" from cells is regarded as a critical step in polar auxin transport. The evidence which we present is consistent with the view that auxin "secretion" depends on a passive carrier-mediated efflux of auxin anions which accumulate within the cells when the extra-cellular pH is below that of the cytoplasm. The implications of this view for theories of polar auxin transport are discussed. PMID:24442257

Rubery, P H; Sheldrake, A R

1974-06-01

41

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

Code of Federal Regulations, 2010 CFR

...2010-10-01 false Presubscribed interexchange carrier charge (PICC). 69.153 Section 69.153 Telecommunication... COMMON CARRIER SERVICES (CONTINUED) ACCESS CHARGES Computation of Charges for Price Cap Local Exchange Carriers §...

2010-10-01

42

Dynamics of spin charge carriers in polyaniline  

NASA Astrophysics Data System (ADS)

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.

Krinichnyi, V. I.

2014-06-01

43

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

PubMed

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

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

2014-12-21

44

Tuning Carrier Mobilities and Polarity of Charge Transport in Films of CuInSex S2-x Quantum Dots.  

PubMed

CuInSex S2--x quantum dot field-effect transistors show p-type, n-type, and ambipolar behaviors with carrier mobilities up to 0.03 cm(2) V-(-1) s(-1) . Although some design rules from studies of cadmium and lead containing quantum dots can be applied, remarkable differences are observed including a strong gating effect in as-synthesized nanocyrstals with long ligands. PMID:25613726

Draguta, Sergiu; McDaniel, Hunter; Klimov, Victor I

2015-03-01

45

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

Code of Federal Regulations, 2014 CFR

...Presubscribed interexchange carrier charge (PICC). 69.153 Section 69.153 Telecommunication...Presubscribed interexchange carrier charge (PICC). (a) A charge expressed...month. In the event the ceilings on the PICC prevent the PICC from recovering all...

2014-10-01

46

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

Code of Federal Regulations, 2013 CFR

...Presubscribed interexchange carrier charge (PICC). 69.153 Section 69.153 Telecommunication...Presubscribed interexchange carrier charge (PICC). (a) A charge expressed...month. In the event the ceilings on the PICC prevent the PICC from recovering all...

2013-10-01

47

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

Code of Federal Regulations, 2011 CFR

...Presubscribed interexchange carrier charge (PICC). 69.153 Section 69.153 Telecommunication...Presubscribed interexchange carrier charge (PICC). (a) A charge expressed...month. In the event the ceilings on the PICC prevent the PICC from recovering all...

2011-10-01

48

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

Code of Federal Regulations, 2012 CFR

...Presubscribed interexchange carrier charge (PICC). 69.153 Section 69.153 Telecommunication...Presubscribed interexchange carrier charge (PICC). (a) A charge expressed...month. In the event the ceilings on the PICC prevent the PICC from recovering all...

2012-10-01

49

Evaluation of intrinsic charge carrier transport at insulator-semiconductor interfaces probed by a non-contact microwave-based technique.  

PubMed

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

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

2013-01-01

50

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

NASA Astrophysics Data System (ADS)

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.

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

2013-11-01

51

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

PubMed Central

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

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

2013-01-01

52

Terahertz microscopy of charge carriers in semiconductors  

NASA Astrophysics Data System (ADS)

We report on the application of apertureless THz near-field microscopy for sensing charge carriers in semiconductors. This technique allows for contactless probing of electron concentrations on a micrometer scale. Experimental data and model calculations indicate that as few as about 5000 electrons can be detected in a GaAs structure.

Buersgens, F.; Kersting, R.; Chen, H.-T.

2006-03-01

53

Evaluation of the intrinsic charge carrier transporting properties of linear- and bent-shaped ?-extended benzo-fused thieno[3,2-b]thiophenes.  

PubMed

The intrinsic charge carrier transporting properties of two isomeric linear- and bent-shaped 7-ring benzo-fused thieno[3,2-b] thiophenes and their octyl-substituted analogues were newly investigated using flash-photolysis (FP-) and field-induced (FI-) time-resolved microwave conductivity (TRMC) techniques. FP-TRMC study in the solid state revealed that octyl-substitution potentially improved the photoconductivity due to the enhanced crystalline lamellar packing. After this screening process, local-scale hole mobilities at the thienoacene-poly(methylmethacrylate) insulator interfaces were precisely recorded using FI-TRMC, reaching up to 4.5 cm(2) V(-1) s(-1) for the linear-shaped non-alkylated thienoacene. The combination of FP- and FI-TRMC measurements provides a rapid and quantitative evaluation scheme even for a variety of compounds with some issues in the processing conditions, leading to the optimized structure of the compounds used as active (interfacial) layers in practical electronic devices. PMID:25786070

Tsutsui, Yusuke; Sakurai, Tsuneaki; Minami, Sojiro; Hirano, Koji; Satoh, Tetsuya; Matsuda, Wakana; Kato, Kenichi; Takata, Masaki; Miura, Masahiro; Seki, Shu

2015-04-01

54

Closed-form expressions correlating exciton transport and interfacial charge carrier generation with the donor/acceptor morphology in organic bulk heterojunction solar cells  

NASA Astrophysics Data System (ADS)

Organic bulk heterojunction (BHJ) solar cells are frequently modeled with effective-medium device models; these models, however, do not resolve the relation between excitonic processes in the donor/acceptor (D/A) blend and the D/A morphology. In this context, we derive a simple analytical model to relate the interfacial exciton flux and the volumetric generation rate of interfacial electron-hole pairs with the morphological characteristics of a D/A blend. Our approach does not require explicit morphological information of the D/A blend, except for the specific interfacial area and the blending ratio between donor and acceptor materials, both of which can be assessed experimentally. The expressions are verified with numerical simulations based on randomly generated three-dimensional D/A morphologies - overall, good agreement is found. The analytical expressions developed in this paper can easily be integrated into existing effective-medium device models, allowing them to capture the effect of exciton transport and morphology on free charge carrier generation in more detail. These expressions potentially allow morphological features in a D/A blend to be optimized within a fast, 1D computational framework.

Zhang, Teng; Birgersson, Erik; Luther, Joachim

2015-01-01

55

ccsd-00016692,version2-20Jul2006 Phys. Rev. Lett. 97, 026601 (2006) Quantum transport of slow charge carriers in quasicrystals and correlated systems  

E-print Network

to a transition from a metallic like to an insulating like regime when scattering by defects increases properties of some heavy fermions or polaronic systems, where charge carriers are also slow, present a deep a metallic regime for V > Lwp and an insulating like regime for V

Boyer, Edmond

2006-01-01

56

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

PubMed

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

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

2015-01-01

57

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

PubMed Central

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

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

2014-01-01

58

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

NASA Astrophysics Data System (ADS)

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.

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

2014-07-01

59

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

NASA Astrophysics Data System (ADS)

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.

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

2014-10-01

60

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

NASA Astrophysics Data System (ADS)

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 1012 cm-2, and the hole mobility was up to 6.5 cm2 V-1 s-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.

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

2014-07-01

61

Charge-Carrier Screening in Single-Layer Graphene  

NASA Astrophysics Data System (ADS)

Unlike normal metals that have a true Fermi surface, the pointlike Fermi surface of undoped graphene allows for long-ranged coulomb interactions to be unscreened by free charges, leading to singular behaviors. Therefore, the introduction of charge to a neutral graphene sheet can have a profound effect on transport properties and device performance. In this talk I will demonstrate the effects of charge-carrier screening of the electron-electron and electron-impurity interactions on the electronic properties of graphene, as we have observed through angle-resolved photoemission spectroscopy (ARPES). These observations help us to understand the basis for the transport properties of graphene, and shed light on the fundamental physics in the vicinity of the Dirac point crossing.

Siegel, David; Regan, William; Fedorov, Alexei; Zettl, Alex; Lanzara, Alessandra

2013-03-01

62

Criticality of surface topology for charge-carrier transport characteristics in two-dimensional borocarbonitrides: design principles for an efficient electronic material  

NASA Astrophysics Data System (ADS)

We have studied the effect of the spatial distribution of B, N and C domains in 2-dimensional borocarbonitrides and its influence on carrier mobility, based on density functional theory coupled with the Boltzmann transport equation. Two extreme features of C-domains in BN-rich B2.5CN2.5, namely, BCN-I (random) and BCN-II (localized), have been found to exhibit an electron (hole) mobility of ~106 cm2 V-1 s-1 (~104 cm2 V-1 s-1) and ~103 cm2 V-1 s-1 (~106 cm2 V-1 s-1), respectively. We have ascertained the underlying microscopic mechanisms behind such an extraordinarily large carrier mobility and the reversal of conduction polarity. Finally, we have derived the principle underlying the maximization of mobility and for obtaining a particular (electron/hole) conduction polarity of this nanohybrid in any stoichiometric proportion.We have studied the effect of the spatial distribution of B, N and C domains in 2-dimensional borocarbonitrides and its influence on carrier mobility, based on density functional theory coupled with the Boltzmann transport equation. Two extreme features of C-domains in BN-rich B2.5CN2.5, namely, BCN-I (random) and BCN-II (localized), have been found to exhibit an electron (hole) mobility of ~106 cm2 V-1 s-1 (~104 cm2 V-1 s-1) and ~103 cm2 V-1 s-1 (~106 cm2 V-1 s-1), respectively. We have ascertained the underlying microscopic mechanisms behind such an extraordinarily large carrier mobility and the reversal of conduction polarity. Finally, we have derived the principle underlying the maximization of mobility and for obtaining a particular (electron/hole) conduction polarity of this nanohybrid in any stoichiometric proportion. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr04198d

Banerjee, Swastika; Pati, Swapan K.

2014-10-01

63

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

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.

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

1987-01-01

64

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

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.

Rehak, P.; Gatti, E.

1984-02-24

65

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

SciTech Connect

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?

Zhu, Xiaoyang

2014-12-10

66

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

NASA Astrophysics Data System (ADS)

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.

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

2015-03-01

67

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

PubMed

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

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

2015-03-01

68

Charge carrier trapping effect by luminescent dopant molecules in single-layer organic light emitting diodes  

Microsoft Academic Search

We investigated electroluminescent (EL) characteristics of single-layer organic light emitting diodes (SOLEDs). Our SOLED devices are composed of an inert polymer as a binder, in which hole transport molecules, emissive electron transport molecules (ETMs), and highly fluorescent dopants as luminescent centers are dispersed. We examined two typical dopants: rubrene and coumarin 6. These exhibited different charge carrier recombination and emission

Masahiro Uchida; Chihaya Adachi; Toshiki Koyama; Yoshio Taniguchi

1999-01-01

69

Performance of Acoustic Charge Transport Programmable Tapped Delay Line  

Microsoft Academic Search

An Acoustic Charge Transport (ACT) based Programmable Tapped Delay Line (PTDL) with monolithic tap weight control circuitry has been designed and developed. The ACT device is a new type of high frequency monolithic charge transfer device (CTD), where carriers are gathered by and transported within the traveling wave electric field of a powerful Surface Acoustic Wave (SAW), propagating in a

F. Guediri; R. L. Martin; B. J. Hunsinger; F. M. Fliegel

1987-01-01

70

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

Code of Federal Regulations, 2010 CFR

...2010-10-01 false Per-minute carrier common line charge. 69.154 Section 69.154 Telecommunication... COMMON CARRIER SERVICES (CONTINUED) ACCESS CHARGES Computation of Charges for Price Cap Local Exchange Carriers §...

2010-10-01

71

The solute carrier 6 family of transporters  

PubMed Central

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

Bröer, Stefan; Gether, Ulrik

2012-01-01

72

Anisotropic charged impurity-limited carrier mobility in monolayer phosphorene  

NASA Astrophysics Data System (ADS)

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-?) 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.

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

2014-12-01

73

Carrier transport at grain boundaries in silicon  

NASA Astrophysics Data System (ADS)

A series of experimental measurements is presented of electron and hole transport at grain boundaries (and dislocations) in cast silicon. These experiments include four-probe measurements on individual grain boundaries, the effects of grain-boundary proximity on Schottky barrier characteristics and spectral/photovoltaic behaviour of 1 sq cm grating solar cells (both minMIS and majority-carrier types). In addition, the results of theoretical studies are described, which employ numerical finite-element methods with the Newton-Raphson-Kantorovitch algorithm. In these calculations, the quasi-Fermi potentials and the electrostatic potential across the grain boundary are solved self-consistently, without the need for a priori assumptions of particular carrier transport mechanisms.

Card, H. C.; Shaw, J. G.; McGonigal, G. C.; Thomson, D. J.; de Groot, A. W.; Kao, K. C.

74

A review of some charge transport properties of silicon  

Microsoft Academic Search

Basic bulk transport properties of charge carriers in silicon are reviewed, with particular reference to their use in designing solid-state components. The current theoretical model for transport in silicon is outlined, along with experimental techniques for determining most important transport parameters such as the drift velocity and diffusion coefficient. Phenomenological expressions are presented, which are in good agreement with experimental

C. Jacoboni; C. Canali; G. Ottaviani; A. Alberigi Quaranta

1977-01-01

75

Signals Induced by Charge Carrier Trapping  

NASA Astrophysics Data System (ADS)

Cryogenic germanium detectors used in dark matter searches operate at ranges of low temperature 100 and electric field 1 such that charge trapping in the bulk of the detector plays a significant role in the net charge collected following a particle interaction. It is shown that in EDELWEISS FID800 detectors, these trapped charges induce residual charge signals that perturb the measurement of the total charge, significantly degrading the energy resolution at high energy. It is also shown that, by reading out the signal on all the electrodes, it is possible to clearly identify these effects and correct the total charge measurement accordingly, resulting in a 30 % improvement of the resolution at high energy. This effect is demonstrated with data. A simple analytical model based on Shockley-Ramo's theorem is presented, whereby this effect is due to the position dependence of signals induced by trapped charges.

Arnaud, Q.

2014-09-01

76

Channel hot-carrier induced oxide charge trapping in NMOSFET'S  

Microsoft Academic Search

Localized oxide charge trapping in N-channel MOSFETs caused by channel-hot-carrier (CHC) injection has been studied by the use of a modified charge-pumping technique. Depending on the CHC injection conditions, trapping of either positive or negative oxide charge, along with an increase in the interface-trap density, has been measured by this technique with excellent sensitivity. Evidence for the dynamic evolution of

W. Chen; T.-P. Ma

1991-01-01

77

Modeling Carrier Behavior in Sequential Auction Transportation Markets  

E-print Network

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

Bertini, Robert L.

78

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

PubMed

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

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

2012-08-21

79

Resolving the ultrafast dynamics of charge carriers in nanocomposites  

NASA Astrophysics Data System (ADS)

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.

Barreto, J.; Roger, T.; Kaplan, A.

2012-06-01

80

Charge transport in organic semiconductors.  

PubMed

Modern optoelectronic devices, such as light-emitting diodes, field-effect transistors and organic solar cells require well controlled motion of charges for their efficient operation. The understanding of the processes that determine charge transport is therefore of paramount importance for designing materials with improved structure-property relationships. Before discussing different regimes of charge transport in organic semiconductors, we present a brief introduction into the conceptual framework in which we interpret the relevant photophysical processes. That is, we compare a molecular picture of electronic excitations against the Su-Schrieffer-Heeger semiconductor band model. After a brief description of experimental techniques needed to measure charge mobilities, we then elaborate on the parameters controlling charge transport in technologically relevant materials. Thus, we consider the influences of electronic coupling between molecular units, disorder, polaronic effects and space charge. A particular focus is given to the recent progress made in understanding charge transport on short time scales and short length scales. The mechanism for charge injection is briefly addressed towards the end of this chapter. PMID:21972021

Bässler, Heinz; Köhler, Anna

2012-01-01

81

Conformation sensitive charge transport in conjugated polymers  

SciTech Connect

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

Mattias Andersson, L., E-mail: matan@ifm.liu.se [Department of Physics, Chemistry and Biology (IFM), Linköping University, Linköping SE-581 83 (Sweden); Hedström, Svante; Persson, Petter [Division of Theoretical Chemistry, Lund University, P.O. Box 124, SE-221 00 Lund (Sweden)] [Division of Theoretical Chemistry, Lund University, P.O. Box 124, SE-221 00 Lund (Sweden)

2013-11-18

82

Nanoscale Charge Transport in Excitonic Solar Cells  

SciTech Connect

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.

Venkat Bommisetty, South Dakota State University

2011-06-23

83

Highly mobile oxygen hole-type charge carriers in fused silica  

Microsoft Academic Search

Some peculiar positive charge carriers are thermally generated in fused silica above 500 C. These charge carriers appear to be positive holes, chemically O-states, probably arising from dissociation of peroxy defects. The charge carriers give rise to a pronounced positive surface charge which disappears upon cooling but can be quenched by rapid quenching from about 800 C. Reheating to 200

Friedemann Freund; Michael M. Masuda; Minoru M. Freund

1991-01-01

84

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

PubMed Central

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

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

85

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

SciTech Connect

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.

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

86

Charging up Transportation.  

ERIC Educational Resources Information Center

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

Vail, Kathleen R.

1994-01-01

87

Identification of the Charge Carriers in Cerium Phosphate Ceramics  

SciTech Connect

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.

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

2010-06-02

88

Efficient charge transport along phenylene-vinylene molecular wires.  

PubMed

We have studied the motion of charge carriers along isolated phenylene-vinylene (PV) chains using a combination of experimental and theoretical methods. The conductive properties of positive charges along PV chains in dilute solution were studied by using the pulse-radiolysis time-resolved microwave conductivity (TRMC) technique. This technique enables the measurement of high-frequency (tens of GHz) charge carrier mobilities along isolated PV chains without the use of electrodes. The charge carrier mobility along PV chains with finite and infinite length was studied theoretically by charge transport simulations with parameters from density functional theory (DFT) calculations. The high-frequency charge carrier mobility is found to depend strongly on the conjugation length of the PV chains and is found to increase both with increasing length of the PV chain and with increasing conjugation fraction. The experimental results are in good agreement with the calculated results. On the basis of this combined experimental and theoretical study an intrachain charge carrier mobility of a few tens of cm2/Vs is expected for an infinitely long PV chain without conjugation breaks. PMID:16869569

Prins, Paulette; Grozema, Ferdinand C; Siebbeles, Laurens D A

2006-08-01

89

Photochemical etching of silicon: The influence of photogenerated charge carriers  

NASA Astrophysics Data System (ADS)

Low-intensity cw band-gap excitation enhances the etch rate of silicon by XeF2. It has been proposed that the enhancement mechanism involves participation of photogenerated charge carriers in the fluorination reaction itself. A new study has been made of this system by molecular beam mass spectrometry. The results show that for both n- and p-type silicon the SiF3 free radical is the primary etch product at Ar-ion laser powers exceeding 40 W/cm2. SiF4 is also observed, but its formation is independent of light intensity. The data, including measurements of most probable translational energies, are consistent with a photochemical process being responsible for SiF3 formation. Surface heating, which is minimal, cannot account for the experimental results. Since SiF3 is the principal adsorbate on the surface, it is argued that etching is a result of desorption of SiF3 stimulated by a chemical reaction involving two charge carriers. This is distinct from the photodesorption mechanism usually invoked for semiconductor surfaces, which involves single charge capture by a surface adsorbate. Evidence pertaining to participation of charge carriers in other stages of the fluorination reaction-adsorption of XeF2 and diffusion of F--has also been obtained. The data indicate that photogenerated charge carriers inhibit chemisorption of XeF2. Field-assisted diffusion, which has been invoked as a rate-determining process in photoassisted etching of semiconductors, is not found to be so for this system.

Houle, F. A.

1989-05-01

90

Flexible cobalt-phthalocyanine thin films with high charge carrier mobility  

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

91

Charge carrier trapping and thermoluminescence in calcium fluoride based phosphors  

NASA Astrophysics Data System (ADS)

This paper reviews recent progress in the understanding and applications of the phenomenon of thermoluminescence (TL) in calcium fluoride based phosphors. The formation of charge carrier traps in rare earth and Mn doped CaF 2 and the effects of dose and the LET of radiation on the glow curve are discussed. The dosimetric properties and applications of the popular materials like CaF 2:Tm, CaF 2:Mn and CaF 2:Dy are also described. The various explanations for the TL phenomenon in these materials are given to highlight the complications and difficulties in completely understanding the mechanisms involved. Optical absorption, ESR, electrical relaxation studies and detailed analysis of the TL emission spectrum lead to the identification of some charge carrier traps and luminescent centres, but one-to-one trap/luminescent centre correlation is very difficult.

Jain, V. K.

92

Band filling with free charge carriers in organometal halide perovskites  

NASA Astrophysics Data System (ADS)

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.

Manser, Joseph S.; Kamat, Prashant V.

2014-09-01

93

Highly mobile oxygen hole-type charge carriers in fused silica  

NASA Technical Reports Server (NTRS)

Some peculiar positive charge carriers are thermally generated in fused silica above 500 C. These charge carriers appear to be positive holes, chemically O-states, probably arising from dissociation of peroxy defects. The charge carriers give rise to a pronounced positive surface charge which disappears upon cooling but can be quenched by rapid quenching from about 800 C. Reheating to 200 C remobilizes these charge carriers and causes them to anneal below 400 C. The generation of positive holes charge carriers may be important to understand failure mechanisms of SiO2 insulators.

Freund, Friedemann; Masuda, Michael M.; Freund, Minoru M.

1991-01-01

94

Photochemical etching of silicon: The influence of photogenerated charge carriers  

Microsoft Academic Search

Low-intensity cw band-gap excitation enhances the etch rate of silicon by XeF2. It has been proposed that the enhancement mechanism involves participation of photogenerated charge carriers in the fluorination reaction itself. A new study has been made of this system by molecular beam mass spectrometry. The results show that for both n- and p-type silicon the SiF3 free radical is

F. A. Houle

1989-01-01

95

Giant Reduction of Charge Carrier Mobility in Strained Graphene  

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

96

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

SciTech Connect

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.

Zhu, Xiaoyang; Frisbie, C Daniel

2012-08-13

97

Fractal like charge transport in polyaniline nanostructures  

NASA Astrophysics Data System (ADS)

The structural and electrical properties of camphorsulfonic acid (CSA) doped nanotubes, and hydrochloric acid (HCl) doped nanofibers and nanoparticles of polyaniline have been studied as a function of doping level. The crystallinity increases with doping for all the nanostructures. Electrical transport measurements in the temperature range of 5-300 K show an increase in conductivity with doping for the nanostructures. All the nanostructures exhibit metal to insulator (MIT) transition below 40 K. The metallic behavior is ascribed to the electron-electron interaction effects. In the insulating regime of the nanotubes conduction follows the Mott quasi-1D variable range hopping model, whereas the conduction in the nanofibers and nanoparticles occur by variable range hopping of charge carriers among superlocalized states without and with Coulomb interaction, respectively. The smaller dopant size in case of HCl makes the polymer fractal resulting in superlocalization of electronic wave-functions. The confined morphology of the nanoparticles results in effective Coulomb interaction dominating the intersite hopping.

Nath, Chandrani; Kumar, A.

2013-10-01

98

Mechanisms of carrier transport induced by a microswimmer bath  

E-print Network

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

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

2014-08-08

99

Exceptional charge transport properties of graphene on germanium.  

PubMed

The excellent charge transport properties of graphene suggest a wide range of application in analog electronics. While most practical devices will require that graphene be bonded to a substrate, such bonding generally degrades these transport properties. In contrast, when graphene is transferred to Ge(001) its conductivity is extremely high and the charge carrier mobility derived from the relevant transport measurements is, under some circumstances, higher than that of freestanding, edge-supported graphene. We measure a mobility of ? 5 × 10(5) cm(2) V(-1) s(-1) at 20 K, and ? 10(3) cm(2) V(-1) s(-1) at 300 K. These values are close to the theoretical limit for doped graphene. Carrier densities in the graphene are as high as 10(14) cm(-2) at 300 K. PMID:25203974

Cavallo, Francesca; Rojas Delgado, Richard; Kelly, Michelle M; Sánchez Pérez, José R; Schroeder, Daniel P; Xing, Huili Grace; Eriksson, Mark A; Lagally, Max G

2014-10-28

100

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

Federal Register 2010, 2011, 2012, 2013, 2014

...Docket No. FAA-2010] Passenger Facility Charge Database System for Air Carrier Reporting...availability of the Passenger Facility Charge (PFC) database system to report PFC...Financial Analysis and Passenger Facility Charge Branch (APP-510), Room 619,...

2010-04-09

101

Scaling properties of charge transport in polycrystalline graphene.  

PubMed

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

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

2013-04-10

102

Scaling Properties of Charge Transport in Polycrystalline Graphene  

PubMed Central

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

2013-01-01

103

Collective bulk carrier delocalization driven by electrostatic surface charge accumulation.  

PubMed

In the classic transistor, the number of electric charge carriers--and thus the electrical conductivity--is precisely controlled by external voltage, providing electrical switching capability. This simple but powerful feature is essential for information processing technology, and also provides a platform for fundamental physics research. As the number of charges essentially determines the electronic phase of a condensed-matter system, transistor operation enables reversible and isothermal changes in the system's state, as successfully demonstrated in electric-field-induced ferromagnetism and superconductivity. However, this effect of the electric field is limited to a channel thickness of nanometres or less, owing to the presence of Thomas-Fermi screening. Here we show that this conventional picture does not apply to a class of materials characterized by inherent collective interactions between electrons and the crystal lattice. We prepared metal-insulator-semiconductor field-effect transistors based on vanadium dioxide--a strongly correlated material with a thermally driven, first-order metal-insulator transition well above room temperature--and found that electrostatic charging at a surface drives all the previously localized charge carriers in the bulk material into motion, leading to the emergence of a three-dimensional metallic ground state. This non-local switching of the electronic state is achieved by applying a voltage of only about one volt. In a voltage-sweep measurement, the first-order nature of the metal-insulator transition provides a non-volatile memory effect, which is operable at room temperature. Our results demonstrate a conceptually new field-effect device, extending the concept of electric-field control to macroscopic phase control. PMID:22837001

Nakano, M; Shibuya, K; Okuyama, D; Hatano, T; Ono, S; Kawasaki, M; Iwasa, Y; Tokura, Y

2012-07-26

104

Imaging ultrafast carrier transport in nanoscale field-effect transistors.  

PubMed

In the present study, we visualize ultrafast carrier dynamics in one-dimensional nanoscale devices, such as Si nanowire and carbon nanotube transistors using femtosecond photocurrent microscopy. We investigate transit times of ultrashort carriers that are generated near one metallic electrode and subsequently transported toward the opposite electrode based on drift and diffusion motions. Conversely, pure diffusion motion is observed when the pump pulse is located in the middle of the nanowires. Carrier dynamics have been addressed for various working conditions, in which we found that the carrier velocity and pulse width can be manipulated by the external electrodes. In particular, the carrier velocities extracted from transit times increase for a larger negative gate bias because of the increased field strength at the Schottky barrier. PMID:25338294

Son, Byung Hee; Park, Jae-Ku; Hong, Jung Taek; Park, Ji-Yong; Lee, Soonil; Ahn, Yeong Hwan

2014-11-25

105

Low temperature carrier transport properties in isotopically controlled germanium  

SciTech Connect

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.

Itoh, K.

1994-12-01

106

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

107

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

SciTech Connect

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.

Wang, Zhiping, E-mail: wang-zhiping@aist.go.jp; Shibata, Yosei; Yamanari, Toshihiro; Matsubara, Koji; Yoshida, Yuji [Research Center for Photovoltaic Technologies, National Institute of Advanced Industrial Science and Technology (AIST), AIST Tsukuba Central 5, 1-1-1 Higashi, 305-8565 Tsukuba (Japan); Miyadera, Tetsuhiko, E-mail: tetsuhiko-miyadera@aist.go.jp [Research Center for Photovoltaic Technologies, National Institute of Advanced Industrial Science and Technology (AIST), AIST Tsukuba Central 5, 1-1-1 Higashi, 305-8565 Tsukuba (Japan); JST-PRESTO, Japan Science and Technology Agency (JST), 4-1-8 Honcho Kawaguchi, 332-0012 Saitama (Japan); Saeki, Akinori; Seki, Shu [Department of Applied Chemistry, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, 565-0871 Suita, Osaka (Japan); Zhou, Ying [Electronics and Photonics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), AIST Tsukuba Central 5, 1-1-1 Higashi, 305-8565 Tsukuba (Japan)

2014-07-07

108

Charge transport in single crystal organic semiconductors  

NASA Astrophysics Data System (ADS)

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

Xie, Wei

109

Charge transport in nanoscale junctions.  

PubMed

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

Albrecht, Tim; Kornyshev, Alexei; Bjørnholm, Thomas

2008-09-01

110

Correlating domain purity with charge carrier mobility in bulk heterojunction polymer solar cells  

NASA Astrophysics Data System (ADS)

We report on the impact of morphology onto charge carrier transport and photovoltaic properties in bulk heterojunction solar cells. The study is based on ternary blends of amorphous and semi-crystalline anthracene-containing poly(p-phenylene- ethynylene)-alt-poly(p-phenylene-vinylene) (PPE-PPV) copolymers, with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). Both copolymers exhibit the identical backbone, but bear different side-chain substitutions, which in turn yield changes in the conformation from semi-crystalline (AnE-PVab) to amorphous (AnE-PVba). Strongly phase separated domains are observed for binary AnE-PVab:PCBM blends, presumably dueto strong stacking tendency of AnE-PVab. On the other hand and due to good miscibility a fine-scaled homogeneously intermixed amorphous phase is obtained for binary AnE-PVba:PCBM blends. Upon ternary blending the phase separation between the polymers can readily be continuously tuned between coarse grained and fine-scaled. For each photoactive layer composition the dominant domain spacing was evaluated by resonant soft x-ray scattering (R-SoXS) and related to photovoltaic properties and charge carrier mobility. A with the AnE-PVba steadily decaying domain size and a strong correlation between phase separation and charge transport is demonstrated.

Kästner, Christian; Jiao, Xuechen; Egbe, Daniel A. M.; Ade, Harald; Hoppe, Harald

2014-10-01

111

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

Microsoft Academic Search

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,

France St-Laurent; John S. Derr; Friedemann T. Freund

2006-01-01

112

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

NASA Astrophysics Data System (ADS)

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.

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

113

Ballistic charge carrier transmission through graphene multi-barrier structures in uniform magnetic field  

NASA Astrophysics Data System (ADS)

We investigate charge carrier transport in graphene multi-barrier structures placed in a uniform magnetic field. The transmission coefficient is found analytically by generalizing the transfer matrix method for the case of graphene regions subjected to a uniform magnetic field. The transmission coefficient through the structure can be modulated by varying the gate voltages, the magnetic field and/or the width of the gated regions. Such a configuration could be used in multiple-valued logic circuits, since it has several output states with discrete and easily selectable transmission/current values.

Zubarev, A.; Dragoman, D.

2014-10-01

114

Transport of elliptic intense charged -particle beams  

E-print Network

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, ...

Zhou, J. (Jing), 1978-

2006-01-01

115

Nonlinear charge transport mechanism in periodic and disordered DNA  

NASA Astrophysics Data System (ADS)

We study a model for polaron-like charge transport mechanism along DNA molecules with emphasis on the impact of parametrical and structural disorder. Our model Hamiltonian takes into account the coupling of the charge carrier to two different kinds of modes representing fluctuating twist motions of the base pairs and H-bond distortions within the double helix structure of ?-DNA. Localized stationary states are constructed with the help of a nonlinear map approach for a periodic double helix and in the presence of intrinsic static parametrical and/or structural disorder reflecting the impact of ambient solvent coordinates. It is demonstrated that charge transport is mediated by moving polarons and breather compounds carrying not only the charge but also causing local temporal deformations of the helix structure through the traveling torsion and bond breather components illustrating the interplay of structure and function in biomolecules.

Hennig, D.; Archilla, J. F. R.; Agarwal, J.

2003-06-01

116

Microscopic Simulations of Charge Transport in Disordered Organic Semiconductors  

PubMed Central

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

2011-01-01

117

Fractal spectrum of charge carriers in quasiperiodic graphene structures.  

PubMed

In this work we investigate the interaction of charge carriers in graphene with a series of p-n-p junctions arranged according to a deterministic quasiperiodic substitutional Fibonacci sequence. The junctions create a potential landscape with quantum wells and barriers of different widths, allowing the existence of quasi-confined states. Spectra of quasi-confined states are calculated for several generations of the Fibonacci sequence as a function of the wavevector component parallel to the barrier interfaces. The results show that, as the Fibonacci generation is increased, the dispersion branches form energy bands distributed as a Cantor-like set. Besides, for a quasiperiodic set of potential barriers, we obtain the electronic tunneling probability as a function of energy, which shows a striking self-similar behavior for different generation numbers. PMID:21403366

Sena, S H R; Pereira, J M; Farias, G A; Vasconcelos, M S; Albuquerque, E L

2010-11-24

118

Charge Transport across DNA-Based Three-Way Junctions.  

PubMed

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

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

2015-04-22

119

Kinetics of electrogenic transport by the ADP/ATP carrier.  

PubMed Central

The electrogenic transport of ATP and ADP by the mitochondrial ADP/ATP carrier (AAC) was investigated by recording transient currents with two different techniques for performing concentration jump experiments: 1) the fast fluid injection method: AAC-containing proteoliposomes were adsorbed to a solid supported membrane (SSM), and the carrier was activated via ATP or ADP concentration jumps. 2) BLM (black lipid membrane) technique: proteoliposomes were adsorbed to a planar lipid bilayer, while the carrier was activated via the photolysis of caged ATP or caged ADP with a UV laser pulse. Two transport modes of the AAC were investigated, ATP(ex)-0(in) and ADP(ex)-0(in). Liposomes not loaded with nucleotides allowed half-cycles of the ADP/ATP exchange to be studied. Under these conditions the AAC transports ADP and ATP electrogenically. Mg(2+) inhibits the nucleotide transport, and the specific inhibitors carboxyatractylate (CAT) and bongkrekate (BKA) prevent the binding of the substrate. The evaluation of the transient currents yielded rate constants of 160 s(-1) for ATP and >/=400 s(-1) for ADP translocation. The function of the carrier is approximately symmetrical, i.e., the kinetic properties are similar in the inside-out and right-side-out orientations. The assumption from previous investigations, that the deprotonated nucleotides are exclusively transported by the AAC, is supported by further experimental evidence. In addition, caged ATP and caged ADP bind to the carrier with similar affinities as the free nucleotides. An inhibitory effect of anions (200-300 mM) was observed, which can be explained as a competitive effect at the binding site. The results are summarized in a transport model. PMID:10423420

Gropp, T; Brustovetsky, N; Klingenberg, M; Müller, V; Fendler, K; Bamberg, E

1999-01-01

120

Energy resolution and related charge carrier mobility in LaBr{sub 3}:Ce scintillators  

SciTech Connect

The scintillation response of LaBr{sub 3}:Ce scintillation crystals was studied as function of temperature and Ce concentration with synchrotron X-rays between 9 keV and 100 keV. The results were analyzed using the theory of carrier transport in wide band gap semiconductors to gain new insights into charge carrier generation, diffusion, and capture mechanisms. Their influence on the efficiency of energy transfer and conversion from X-ray or ?-ray photon to optical photons and therefore on the energy resolution of lanthanum halide scintillators was studied. From this, we will propose that scattering of carriers by both the lattice phonons and by ionized impurities are key processes determining the temperature dependence of carrier mobility and ultimately the scintillation efficiency and energy resolution. When assuming about 100 ppm ionized impurity concentration in 0.2% Ce{sup 3+} doped LaBr{sub 3,} mobilities are such that we can reproduce the observed temperature dependence of the energy resolution, and in particular, the minimum in resolution near room temperature is reproduced.

Khodyuk, I. V.; Quarati, F. G. A.; Alekhin, M. S.; Dorenbos, P. [Luminescence Materials Research Group, Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, Delft, 2629JB (Netherlands)] [Luminescence Materials Research Group, Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, Delft, 2629JB (Netherlands)

2013-09-28

121

The effect of carrier gas contaminants on the charging probability of aerosols under bipolar charging conditions  

PubMed Central

This work concentrates on the experimental determination of the properties of ionic molecular clusters that are produced in the bipolar ionic atmosphere of a radioactivity based 241Am charger. The main scope of this study was to investigate the dependency of the ions' properties on carrier gas contaminants caused by the evaporation of trace gases from different kinds of frequently encountered tubing materials. A recently developed high resolution mobility spectrometer allows the precise determination of the ions' electrical mobility; an empirical mass-mobility relationship was used to approximate the corresponding ion masses. It was found that impurities in the carrier gas dramatically change the pattern of the ion mobility/size distribution, resulting in very different ion properties that strongly depend on the carrier gas composition. Since the ion properties control the charging process of aerosols, it was further investigated how the different ion properties affect the calculation of the charging probabilities of aerosols. The results show that despite large variations of the ions' properties, only a minor effect on the calculated charging probabilities can be found. PMID:23209330

Steiner, Gerhard; Reischl, Georg P.

2012-01-01

122

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

ERIC Educational Resources Information Center

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…

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

123

Topological aspects of charge-carrier transmission across grain boundaries in graphene.  

PubMed

Dislocations and grain boundaries are intrinsic topological defects of large-scale polycrystalline samples of graphene. These structural irregularities have been shown to strongly affect electronic transport in this material. Here, we report a systematic investigation of the transmission of charge carriers across the grain-boundary defects in polycrystalline graphene by means of the Landauer-Büttiker formalism within the tight-binding approximation. Calculations reveal a strong suppression of transmission at low energies upon decreasing the density of dislocations with the smallest Burgers vector b = (1,0). The observed transport anomaly is explained from the point of view of resonant backscattering due to localized states of topological origin. These states are related to the gauge field associated with all dislocations characterized by b = (n,m) with n - m ? 3q (q ? Z). Our work identifies an important source of charge-carrier scattering caused by the topological defects present in large-area graphene samples produced by chemical vapor deposition. PMID:24295423

Gargiulo, Fernando; Yazyev, Oleg V

2014-01-01

124

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

125

BALLISTIC CARRIER TRANSPORT IN SEMICONDUCTORS STUDIED BY ULTRAFAST LASER TECHNIQUES  

E-print Network

generation …………………………………… 72 6.3.1 Current induced second harmonic generation …………………… 72 6.3.2 Spin-current-induced second harmonic generation …………...… 73 6.3.3 DC electric field induced second harmonic generation ………….. 76 Chapter 7: Carrier... transport studied by second harmonic generation technique ……… 78 7.1 Coherent detection …………………………………………………….…. 78 7.2 Pure spin current induced second harmonic generation ………………..... 80 7.2.1 Experimental setup ………………………………………………. 81...

Werake, Lalani Kumari

2011-08-31

126

CLASSIFICATION OF THE MGR CARRIER/CASK TRANSPORT SYSTEM  

SciTech Connect

The purpose of this analysis is to document the Quality Assurance (QA) classification of the Monitored Geologic Repository (MGR) carrier/cask transport system structures, systems and components (SSCs) performed by the MGR Safety Assurance Department. This analysis also provides the basis for revision of YMP/90-55Q, Q-List (YMP 1998). The Q-List identifies those MGR SSCs subject to the requirements of DOE/RW-0333P, ''Quality Assurance Requirements and Description'' (QARD) (DOE 1998).

S.E. Salzman

1999-08-30

127

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

Code of Federal Regulations, 2011 CFR

...involving animals during air transport. 234.13 Section...involving animals during air transport. (a) Any air carrier that provides scheduled passenger air transportation...of an animal during air transport provided by the air...

2011-01-01

128

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

Code of Federal Regulations, 2010 CFR

...involving animals during air transport. 234.13 Section...involving animals during air transport. (a) Any air carrier that provides scheduled passenger air transportation...of an animal during air transport provided by the air...

2010-01-01

129

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

Code of Federal Regulations, 2013 CFR

...involving animals during air transport. 234.13 Section...involving animals during air transport. (a) Any air carrier that provides scheduled passenger air transportation...of an animal during air transport provided by the air...

2013-01-01

130

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

Code of Federal Regulations, 2014 CFR

...involving animals during air transport. 234.13 Section...involving animals during air transport. (a) Any air carrier that provides scheduled passenger air transportation...of an animal during air transport provided by the air...

2014-01-01

131

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

Code of Federal Regulations, 2012 CFR

...involving animals during air transport. 234.13 Section...involving animals during air transport. (a) Any air carrier that provides scheduled passenger air transportation...of an animal during air transport provided by the air...

2012-01-01

132

Time-resolved measurements of charge carrier dynamics and optical nonlinearities in narrow-bandgap semiconductors  

NASA Astrophysics Data System (ADS)

All-optical time-resolved measurement techniques provide a powerful tool for investigating critical parameters that determine the performance of infrared photodetector and emitter semiconductor materials. Narrow-bandgap InAs/GaSb type-II superlattices (T2SLs) have shown great promise as a next generation source of these materials, due to superior intrinsic properties and versatility. Unfortunately, InAs/GaSb T2SLs are plagued by parasitic Shockley-Read-Hall recombination centers that shorten the carrier lifetime and limit device performance. Ultrafast pump-probe techniques and time-resolved differential transmission measurements are used here to demonstrate that Ga-free InAs/InAsSb T2SLs and InAsSb alloys do not have this same limitation and thus have significantly longer carrier lifetimes. Measurements at 77 K provided minority carrier lifetimes of 9 mus and 3 mus for an unintentionally doped mid-wave infrared (MWIR) InAs/InAsSb T2SL and InAsSb alloy, respectively; a two order of magnitude increase compared to the 90 ns minority carrier lifetime measured in a comparable MWIR InAs/GaSb T2SL. Through temperature-dependent lifetime measurements, the various carrier recombination processes are differentiated and the dominant mechanisms identified for each material. These results demonstrate that these Ga-free materials are viable options over InAs/GaSb T2SLs for potentially improved infrared photodetectors. In addition to carrier lifetimes, the drift and diffusion of excited charge carriers through the superlattice growth layers (i.e. vertical transport) directly affects the performance of photodetectors and emitters. Unfortunately, there is a lack of information pertaining to vertical transport, primarily due to difficulties in making measurements on thin growth layers and the need for non-standard measurement techniques. However, all-optical ultrafast techniques are successfully used here to directly measure vertical diffusion in MWIR InAs/GaSb T2SLs. By optically generating excess carriers near one end of a MWIR T2SL and measuring the transit time to a thin, 2 lower-bandgap superlattice placed at the other end, the time-of-flight of vertically diffusing carriers is determined. Through investigation of both unintentionally doped and p-type superlattices at 77 K, the vertical hole and electron diffusion coefficients are determined to be 0.04+/-0.03 cm2/s and 4.7+/-0.5 cm2/s, corresponding to vertical mobilities of 6+/-5 cm 2/Vs and 700+/-80 cm2/Vs, respectively. These measurements are, to my knowledge, the first direct measurements of vertical transport properties in narrow-bandgap superlattices. Lastly, the widely tunable two-color ultrafast laser system used in this research allowed for the investigation of nonlinear optical properties in narrow-bandgap semiconductors. Time-resolved measurements taken at 77 K of the nondegenerate two-photon absorption spectrum of bulk n-type GaSb have provided new information about the nonresonant change in absorption and two-photon absorption coefficients in this material. Furthermore, as the nondegenerate spectrum was measured over a wide range of optical frequencies, a Kramers-Kronig transformation allowed the dispersion of the nondegenerate nonlinear refractive index to be calculated.

Olson, Benjamin Varberg

133

Order of decay of mobile charge carriers in P3HT:PCBM solar cells  

NASA Astrophysics Data System (ADS)

The charge carrier dynamics of organic solar cells are strongly influenced by trapping and allow to draw conclusions on the loss mechanisms limiting the photovoltaic performance. In this study, we derive the recombination order ? of mobile charge carriers. For annealed P3HT:PCBM solar cells, it allows us to pinpoint the dominant recombination of mobile with trapped charge carriers in tail states. While the characteristic tail state energy of about 40 meV rises to about 100 meV for 30 h oxygen exposure under illumination, ? decreases only weakly from 1.70 to 1.62. This corresponds to a slight shift towards trap-assisted recombination.

Deibel, Carsten; Rauh, Daniel; Foertig, Alexander

2013-07-01

134

Magnetoresistance and charge transport in graphene governed by nitrogen dopants.  

PubMed

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

Rein, Markus; Richter, Nils; Parvez, Khaled; Feng, Xinliang; Sachdev, Hermann; Kläui, Mathias; Müllen, Klaus

2015-02-24

135

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

PubMed

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

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

2015-03-11

136

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

PubMed Central

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

2015-01-01

137

Carrier screening, transport, and relaxation in three-dimensional Dirac semimetals  

NASA Astrophysics Data System (ADS)

A theory is developed for the density and temperature-dependent carrier conductivity in doped three-dimensional (3D) Dirac materials focusing on resistive scattering from screened Coulomb disorder due to random charged impurities (e.g., dopant ions and unintentional background impurities). The theory applies both in the undoped intrinsic ("high-temperature," T ?TF ) and the doped extrinsic ("low-temperature," T ?TF ) limit with analytical scaling properties for the carrier conductivity obtained in both regimes, where TF is the Fermi temperature corresponding to the doped free carrier density (electrons or holes). The scaling properties describing how the conductivity depends on the density and temperature can be used to establish the Dirac nature of 3D systems through transport measurements. We also consider the temperature-dependent conductivity limited by the acoustic phonon scattering in 3D Dirac materials. In addition, we theoretically calculate and compare the single-particle relaxation time ?s, defining the quantum level broadening, and the transport scattering time ?t, defining the conductivity, in the presence of screened charged impurity scattering. A critical quantitative analysis of the ?t/?s results for 3D Dirac materials in the presence of long-range screened Coulomb disorder is provided.

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

2015-01-01

138

On-top ?-stacking of quasiplanar molecules in hole-transporting materials: inducing anisotropic carrier mobility in amorphous films.  

PubMed

Dimers of partially oxygen-bridged triarylamines were designed and synthesized as hole-transporting materials. X-ray structural analyses revealed that these compounds form on-top ?-stacking aggregates in the crystalline state. TRMC measurements showed that high levels of anisotropic charge transport were induced in the direction of the ?-stacking. Surprisingly, even in vacuum-deposited amorphous films, these compounds retained some of the face-on ?-stacking, thus facilitating an out-of-plane carrier mobility. PMID:24764307

Wakamiya, Atsushi; Nishimura, Hidetaka; Fukushima, Tatsuya; Suzuki, Furitsu; Saeki, Akinori; Seki, Shu; Osaka, Itaru; Sasamori, Takahiro; Murata, Michihisa; Murata, Yasujiro; Kaji, Hironori

2014-06-01

139

The origin of dispersion of transiting charge carriers in molecular l y doped polymers  

Microsoft Academic Search

The dispersion of transiting charge carriers in organic solids is analysed by examining the normalized time-of-flight current signals obtained over a wide range of electric fields, sample thicknesses and temperatures. Carriers injected into polycarbonate molecularly doped with N, N?-diphenyl-N, N-bis(3-methylphenyl)-[1, 1?-biphenyl]-4, 4?-diamine reach dynamic equilibrium with the environment in a small fraction of the overall transit time. The carrier dispersion

H.-J. Yuh; M. Stolka

1988-01-01

140

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

NASA Astrophysics Data System (ADS)

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.

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

2011-12-01

141

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

E-print Network

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 ...

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

2006-01-01

142

Hot-carrier trap-limited transport in switching chalcogenides  

NASA Astrophysics Data System (ADS)

Chalcogenide materials have received great attention in the last decade owing to their application in new memory systems. Recently, phase-change memories have, in fact, reached the early stages of production. In spite of the industrial exploitation of such materials, the physical processes governing the switching mechanism are still debated. In this paper, we work out a complete and consistent model for transport in amorphous chalcogenide materials based on trap-limited conduction accompanied by carrier heating. A previous model is here extended to include position-dependent carrier concentration and field, consistently linked by the Poisson equation. The results of the new model reproduce the experimental electrical characteristics and their dependences on the device length and temperature. Furthermore, the model provides a sound physical interpretation of the switching phenomenon and is able to give an estimate of the threshold condition in terms of the material parameters, a piece of information of great technological interest.

Piccinini, Enrico; Cappelli, Andrea; Buscemi, Fabrizio; Brunetti, Rossella; Ielmini, Daniele; Rudan, Massimo; Jacoboni, Carlo

2012-10-01

143

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

PubMed

This article reviews the basic physical processes of charge transport and recombination in organic semiconductors. As a workhorse, LEDs based on a single layer of poly(p-phenylene vinylene) (PPV) derivatives are used. The hole transport in these PPV derivatives is governed by trap-free space-charge-limited conduction, with the mobility depending on the electric field and charge-carrier density. These dependencies are generally described in the framework of hopping transport in a Gaussian density of states distribution. The electron transport on the other hand is orders of magnitude lower than the hole transport. The reason is that electron transport is hindered by the presence of a universal electron trap, located at 3.6 eV below vacuum with a typical density of ca. 3 × 10¹? cm?³. The trapped electrons recombine with free holes via a non-radiative trap-assisted recombination process, which is a competing loss process with respect to the emissive bimolecular Langevin recombination. The trap-assisted recombination in disordered organic semiconductors is governed by the diffusion of the free carrier (hole) towards the trapped carrier (electron), similar to the Langevin recombination of free carriers where both carriers are mobile. As a result, with the charge-carrier mobilities and amount of trapping centers known from charge-transport measurements, the radiative recombination as well as loss processes in disordered organic semiconductors can be fully predicted. Evidently, future work should focus on the identification and removing of electron traps. This will not only eliminate the non-radiative trap-assisted recombination, but, in addition, will shift the recombination zone towards the center of the device, leading to an efficiency improvement of more than a factor of two in single-layer polymer LEDs. PMID:24458577

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

2014-01-01

144

34 nm Charge Transport through DNA  

NASA Astrophysics Data System (ADS)

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.

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

2011-03-01

145

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

SciTech Connect

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

Antoniadis, H.; Miller, J.N.; Roitman, D.B. [Hewlett-Packard Labs., Palo Alto, CA (United States)] [Hewlett-Packard Labs., Palo Alto, CA (United States); Campbell, I.H. [Los Alamos National Lab., NM (United States)] [Los Alamos National Lab., NM (United States)

1997-08-01

146

Novel macrocyclic carriers for proton-coupled liquid membrane transport  

SciTech Connect

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

Lamb, J.D.

1991-06-10

147

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

USGS Publications Warehouse

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.

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

2006-01-01

148

Environmental effects on temperature-dependent carrier transports in poly(3-hexylthiophene) films  

NASA Astrophysics Data System (ADS)

Applications of poly(3-hexylthiophene) (P3HT) to solar cells have been reported. The reliability of organic solar cells is a key factor of full-scale applications in commercial optoelectronics. In this study, the environmental effect on the carrier transport in P3HT is researched. Charge-trapping phenomena are studied through time-domain measurement for P3HT thin-film transistors. The time-domain data confirm the hole-trapping model, indicating that water vapor influences the response by producing additional hole traps that serve to increase the current time constant. To understand the P3HT degradation mechanisms, an analysis through the temperature-dependent transfer characteristics is presented. It is shown that the hopping conduction behavior can be affected by exposure to ambient humidity and ambient atmosphere, inducing fluctuations in the hopping distance and the barrier height for hopping that serve to influence the carrier mobility.

Lin, Yow-Jon; Chin, Yi-Min; Chang, Hsing-Cheng

2015-04-01

149

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

Code of Federal Regulations, 2011 CFR

...placarding, and motor carriers transporting passengers in a CMV, are prohibited from operating a CMV...that holds an “unsatisfactory” rating to transport passengers in a CMV or to transport hazardous materials in quantities...

2011-10-01

150

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

Code of Federal Regulations, 2014 CFR

...placarding, and motor carriers transporting passengers in a CMV, are prohibited from operating a CMV...that holds an “unsatisfactory” rating to transport passengers in a CMV or to transport hazardous materials in quantities...

2014-10-01

151

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

Code of Federal Regulations, 2013 CFR

...placarding, and motor carriers transporting passengers in a CMV, are prohibited from operating a CMV...that holds an “unsatisfactory” rating to transport passengers in a CMV or to transport hazardous materials in quantities...

2013-10-01

152

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

Code of Federal Regulations, 2010 CFR

...placarding, and motor carriers transporting passengers in a CMV, are prohibited from operating a CMV...that holds an “unsatisfactory” rating to transport passengers in a CMV or to transport hazardous materials in quantities...

2010-10-01

153

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

Code of Federal Regulations, 2012 CFR

...placarding, and motor carriers transporting passengers in a CMV, are prohibited from operating a CMV...that holds an “unsatisfactory” rating to transport passengers in a CMV or to transport hazardous materials in quantities...

2012-10-01

154

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

Code of Federal Regulations, 2012 CFR

...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,...

2012-07-01

155

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

Code of Federal Regulations, 2014 CFR

...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,...

2014-07-01

156

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

Code of Federal Regulations, 2011 CFR

...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,...

2011-07-01

157

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

Code of Federal Regulations, 2010 CFR

...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,...

2010-07-01

158

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

Code of Federal Regulations, 2013 CFR

...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,...

2013-07-01

159

Study of junction charge transport properties of boron subphthalocyanine chloride thin film  

NASA Astrophysics Data System (ADS)

The charge carrier transport properties and conduction mechanism of boron subphthalocyanine chloride (Cl-BsubPc) thin film based junction was analyzed by using current-voltage ( I-V) characteristics and dielectric spectroscopy technique. I-V characteristic of ITO/Cl-BsubPc/Al junction confirmes the domination of space charge limited conduction (SCLC) in the high voltage region (7-9 V). The AC conductivity study indicates the presence of frequency induced hopping conduction mechanism in Cl-BsubPc thin film with hopping relaxation time of 16.6-4.1 ms. The temperature dependence of AC conductivity suggests that conduction in the films dominated by hopping of carriers between the localized states at low temperature and movements of thermally excited carriers from energy levels within the band gap at higher temperature. The activation energy of the charge carriers responsible for conduction was found to lie between 0.35-0.40 eV.

Singh, Mandeep; Mahajan, Aman; Gupta, Neeru; Bedi, R. K.

2015-01-01

160

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)

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.

Mendels, Dan; Tessler, Nir

2015-03-01

161

Increase in the mobility of photogenerated positive charge carriers in polythiophene.  

PubMed

We report the increase in the mobility of charge carriers in regioregular poly 3-hexyl thiophene (RR-P3HT) films by mixing them with tetracyanoethylene (TCNE), which is examined by in situ time-resolved microwave conductivity (TRMC) and transient optical spectroscopy (TOS). TCNE acts not only as an electron acceptor which increases the number of charge carriers on photoexposure but also as a functional additive which enhances the mobility of the charge carriers. This conclusion was deduced from the results of fluorescence quenching, transient optical absorption and photobleaching, and comparison of the TRMC signal with the TOS signal. The combination of the TRMC and TOS techniques represents a comprehensive and fully experimental approach to the determination of the intrinsic carrier mobility in conjugated polymers. PMID:16852211

Saeki, Akinori; Seki, Shu; Koizumi, Yoshiko; Sunagawa, Takeyoshi; Ushida, Kiminori; Tagawa, Seiichi

2005-05-26

162

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

SciTech Connect

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.

Sun, Yong, E-mail: sun@ele.kyutech.ac.jp; Maeda, Yuki; Sezaimaru, Hiroki; Sakaino, Masamichi [Department of Applied Science for Integrated System Engineering, Kyushu Institute of Technology, Senshuimachi, Tobata, Kitakyushu, Fukuoka 804-8550 (Japan); Kirimoto, Kenta [Department of Electrical and Electronic Engineering, Kitakyushu National College of Technology, 5-20-1 shii, Kokuraminami, Kitakyushu, Fukuoka 802-0985 (Japan)

2014-07-21

163

Negative correlation between charge carrier density and mobility fluctuations in graphene  

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

164

Superconductivity: coherent "tunnelling" by a dielectric array of charge-carriers  

E-print Network

Superconduction manifests when a steady-state current flows through a material without an electric field being present. It is argued here that the absence of scattering of the charge-carriers, although absolutely necessary, is not sufficient to explain why an electric field is zero when a current flows between two contacts to a superconducting material. It is concluded that an electric field, and thus a resistance, must manifest unless (i) the charge-carriers form part of an array of dielectric charge centres, and (ii) the charge-carriers can increase their velocities without increasing their kinetic energies. A model is propoased which allows these requirements to manifest. The model is fitted to selected experimental results which have been published for low temperature metals, YBCO, and highly-doped p-type diamond. In each case a satisfactory description of the experimental results is demonstrated.

Johan F. Prins

2006-07-25

165

Macroscopic acoustoelectric charge transport in graphene  

NASA Astrophysics Data System (ADS)

We demonstrate macroscopic acoustoelectric transport in graphene, transferred onto piezoelectric lithium niobate substrates, between electrodes up to 500 ?m apart. Using double finger interdigital transducers we have characterised the acoustoelectric current as a function of both surface acoustic wave intensity and frequency. The results are consistent with a relatively simple classical relaxation model, in which the acoustoelectric current is proportional to both the surface acoustic wave intensity and the attenuation of the wave caused by the charge transport.

Bandhu, L.; Lawton, L. M.; Nash, G. R.

2013-09-01

166

Characterisation of charge carrier traps in polymeric insulators  

Microsoft Academic Search

The presence of space charge is thought to play a significant role in determining the electric field distribution of an insulating material such as polyethylene. The present paper focuses on the relation between atomic defects and space charge formation. The ability of defects to trap electrons in a model material is investigated using density functional theory calculations. A set of

M. Meunier; N. Quirket; A. Aslanides

2000-01-01

167

The effects of charge transport traps on organic light-emitting diode performance  

Microsoft Academic Search

The role of charge carrier trapping on the efficiency of single-layer organic light-emitting diodes (OLEDs) is investigated both theoretically, by incorporating trapping effects into the OLED device model of Davids et al., and experimentally, via the fabrication and characterization of polymeric and oligomeric OLEDs. Carrier trapping directly modifies charge carrier injection and charge carrier mobility and therefore indirectly modifies carrier

Steven James Konezny

2005-01-01

168

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

169

Molecular Level Manipulation of Interfacial Charge Transport  

NASA Astrophysics Data System (ADS)

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.

Song, Charles Kiseok

170

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

PubMed Central

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

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

2013-01-01

171

Determining the Drift Time of Charge Carriers in P-Type Point-Contact HPGe Detectors  

E-print Network

An algorithm to measure the drift time of charge carriers in p-type point contact (PPC) high-purity germanium (HPGe) detectors from the signals processed with a charge-sensitive preamplifier is introduced. It is demonstrated that the drift times can be used to estimate the distance of charge depositions from the point contact and to characterize losses due to charge trapping. A correction for charge trapping effects over a wide range of energies is implemented using the measured drift times and is shown to improve the energy resolution by up to 30%.

R. D. Martin; M. Amman; Y. D. Chan; J. A. Detwiler; J. C. Loach; Q. Looker; P. N. Luke; A. W. P. Poon; J. Qian; K. Vetter; H. Yaver

2011-10-01

172

Charge transport and injection in amorphous organic electronic materials  

NASA Astrophysics Data System (ADS)

This thesis presents how we use various measuring techniques to study the charge transport and injection in organic electronic materials. Understanding charge transport and injection properties in organic solids is of vital importance for improving performance characteristics of organic electronic devices, including organic-light-emitting diodes (OLEDs), photovoltaic cells (OPVs), and field effect transistors (OFETs). The charge transport properties of amorphous organic materials, commonly used in organic electronic devices, are investigated by the means of carrier mobility measurements. Transient electroluminescence (EL) technique was used to evaluate the electron mobility of an electron transporting material--- tris(8-hydroxyquinoline) aluminum (Alq3). The results are in excellent agreement with independent time-of-flight (TOF) measurements. Then, the effect of dopants on electron transport was also examined. TOF technique was also used to examine the effects of tertiary-butyl (t-Bu) substitutions on anthracene derivatives (ADN). All ADN compounds were found to be ambipolar. As the degree of t-Bu substitution increases, the carrier mobilities decrease progressively. The reduction of carrier mobilities with increasing t-butylation can be attributed to a decrease in the charge-transfer integral or the wavefunction overlap. In addition, from TOF measurements, two naphthylamine-based hole transporters, namely, N,N'-diphenyl-N,N'-bis(1-naphthyl)(1,1'-biphenyl)-4,4'diamine (NPB) and 4,4',4"-tris(n-(2-naphthyl)-n-phenyl-amino)-triphenylamine (2TNATA) were found to possess electron-transporting (ET) abilities. An organic light-emitting diode that employed NPB as the ET material was demonstrated. The electron conducting mechanism of NPB and 2TNATA in relation to the hopping model will be discussed. Furthermore, the ET property of NPB applied in OLEDs will also be examined. Besides transient EL and TOF techniques, we also use dark-injection space-charge-limited current (DISCLC) to study the charge injection properties of three phenylamine-based (PA) compounds, MTDATA (4,4',4''-Tris(N-3-methylphenyl-N-phenyl-amino)triphenylamine), NPB, and TPD (N,N'-diphenyl-N,N'-bis(3-methyl phenyl) (1,1'-biphenyl)-4,4'diamine).Poly(3,4-ethylenedioxythiophene) doped with polystyrenesulphonic acid (PEDOT:PSS) was used as a hole-injecting anode in current-voltage (JV) and DISCLC. Clear DISCLC transient peaks were observed over a wide range of electric fields in all cases. For MTDATA and NPB, hole mobilities evaluated by DI experiments are in excellent agreement with mobilties deduced from TOF technique. It can be concluded that, for the purpose of JV and DI experiments, PEDOT:PSS forms an Ohmic contact with MTDATA and a quasi-Ohmic contact with NPB despite the relatively low-lying highest occupied molecular orbital of the later. In the case of TPD, hole injection from PEDOT:PSS deviates substantially from Ohmic injection, leading to a lower than expected DI-extracted hole mobility. Finally, a composite anode will be demonstrated to improve the hole injection efficiency.

Tse, Shing Chi

173

The steady-state theory of the carrier transport of ions  

Microsoft Academic Search

Summary The theory for the carrier transport of ions across lipid membranes is extended to consider the potential dependence of the association-dissociation reactions between the carrier and the ions and to consider the effects of aqueous unstirred layers on the exchange of the carrier molecules between the membrane and the aqueous phases. Theoretical expressions are presented under the assumptions that

S. B. Hladky

1972-01-01

174

Dependence of the carrier mobility and trapped charge limited conduction on silver nanoparticles embedment in doped polypyrrole nanostructures  

NASA Astrophysics Data System (ADS)

The present article demonstrates an intensive study upon the temperature dependent current density (J)-voltage (V) characteristics of moderately doped polypyrrole nanostructure and its silver nanoparticles incorporated nanocomposites. Analysis of the measured J-V characteristics of different synthesized nano-structured samples within a wide temperature range revealed that the electrical conduction behavior followed a trapped charge-limited conduction and a transition of charge transport mechanism from deep exponential trap limited conduction to shallow traps limited conduction had been occurred due to the incorporation of silver nanoparticles within the polypyrrole matrix. A direct evaluation of carrier mobility as a function of electric field and temperature from the measured J-V characteristics illustrates that the incorporation of silver nanoparticles within the polypyrrole matrix enhances the carrier mobility at a large extent by reducing the concentration of traps within the polypyrrole matrix. The calculated mobility is consistent with the Poole-Frenkel form for the electrical field up to a certain temperature range. The nonlinear low temperature dependency of mobility of all the nanostructured samples was explained by Mott variable range hopping conduction mechanisms. Quantitative information regarding the charge transport parameters obtained from the above study would help to extend optimization strategies for the fabrication of new organic semiconducting nano-structured devices.

Biswas, Swarup; Dutta, Bula; Bhattacharya, Subhratanu

2013-10-01

175

Unusual Charge Transport Transitions in Ion-Implanted Polymers.  

NASA Astrophysics Data System (ADS)

A systematic charge transport study was conducted on three ion implanted strong and stable polymers, PBO, PBT, and BBL. An implantation-induced insulator-metal transition with increased ion dosage was observed and interpreted in terms of an Anderson transition due to the increase in the density of charged carriers in the implanted layer upon ion implantation. In higher dosage samples ( phi >= 4 times 10^{16} cm^{-2}), all the experimental results suggest the existence of a semi -metallic phase in which the charge transport is dominated by the weak localization and electron-electron (e-e) interaction effects above 30 K. At 30 K, a dramatic change was observed consistently in all the transport properties, indicating a transition to a non-metallic phase with the enhanced e-e interactions dominating the transport below 30 K. It is proposed that this transition is due to the opening of a Coulomb gap in the density of states at the Fermi level as a result of the enhanced long range Coulomb interactions. This observed 'metallic' state differs dramatically from that of earlier implanted polymers. It is proposed that, upon implantation, the chemical structure of these implanted materials is reformed into an inter-connected graphite-like carbon network, responsible for the semi -metallic behavior. Another finite temperature transport transition was observed in an implanted PBO sample at a low ion dosage (phi = 7 times 10^{15} cm^ {-2}). This transition is discussed in light of available theoretical models. However, further theoretical investigation is needed to understand this unusual phenomenon.

Du, Gang

176

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

PubMed Central

The electrophoretic export of ATP against the import of ADP in mitochondria bridges the intra- versus extramitochondrial ATP potential gap. Here we report that the electrical nature of the ADP/ATP exchange by the mitochondrial ADP/ATP carrier (AAC) can be directly studied by measuring the electrical currents via capacitive coupling of AAC-containing vesicles on a planar lipid membrane. The currents were induced by the rapid liberation of ATP or ADP with UV flash photolysis from caged nucleotides. Six different transport modes of the AAC were studied: heteroexchange with either ADP or ATP inside the vesicles, initiated by photolysis of caged ATP or ADP; homoexchange with ADPex/ADPin or ATPex/ATPin; and caged ADP or ATP with unloaded vesicles. The heteroexchange produced the largest currents with the longest duration in line with the electrical charge difference ATP4- versus ADP3-. Surprisingly, also in the homoexchange and with unloaded vesicles, small currents were measured with shorter duration. In all three modes with caged ATP, a negative charge moved into the vesicles and with caged ADP it moved out of the vesicles. All currents were completely inhibited by a mixture of the inhibitors of the AAC, carboxyatractyloside and hongkrekate, which proves that the currents are exclusively due to AAC function. The observed charge movements in the heteroexchange system agree with the prediction from transport studies in mitochondria and reconstituted vesicles. The unexpected charge movements in the homoexchange or unloaded systems are interpreted to reveal transmembrane rearrangements of charged sites in the AAC when occupied with ADP or ATP. The results also indicate that not only ATP4- but also ADP3- contribute, albeit in opposite direction, to the electrical nature of the ADP/ATP exchange, which is at variance with former conclusions from biochemical transport studies. These measurements open up new avenues of studying the electrical interactions of ADP and ATP with the AAC. Images Fig. 5 PMID:8570612

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

1996-01-01

177

Two-dimensional charge transport in self-organized, high-mobility conjugated polymers  

Microsoft Academic Search

Self-organization in many solution-processed, semiconducting conjugated polymers results in complex microstructures, in which ordered microcrystalline domains are embedded in an amorphous matrix. This has important consequences for electrical properties of these materials: charge transport is usually limited by the most difficult hopping processes and is therefore dominated by the disordered matrix, resulting in low charge-carrier mobilities (<=10-5cm2V-1s-1). Here we use

H. Sirringhaus; P. J. Brown; R. H. Friend; M. M. Nielsen; K. Bechgaard; B. M. W. Langeveld-Voss; A. J. H. Spiering; R. A. J. Janssen; E. W. Meijer; PT Herwig; D. M. de Leeuw

1999-01-01

178

Diverse transport modes by the solute carrier 26 family of anion transporters  

PubMed Central

The solute carrier 26 (SLC26) transporters are anion transporters with diverse substrate specificity. Several members are ubiquitous while others show limited tissue distribution. They are expressed in many epithelia and to the extent known, play a central role in anion secretion and absorption. Members of the family are primarily Cl? transporters, although some members transport mainly SO42?, Cl?, HCO3? or I?. A defining feature of the family is their functional diversity. Slc26a1 and Slc26a2 function as specific SO42? transporters while Slc26a4 functions as an electroneutral Cl?/I?/HCO3? exchanger. Slc26a3 and Slc26a6 function as coupled electrogenic Cl?/HCO3? exchangers or as bona fide anion channels. SLC26A7 and SLC26A9 function exclusively as Cl? channels. This short review discusses the functional diversity of the SLC26 transporters. PMID:19015189

Ohana, Ehud; Yang, Dongki; Shcheynikov, Nikolay; Muallem, Shmuel

2009-01-01

179

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

NASA Astrophysics Data System (ADS)

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.

Chen, Wei; Wang, Fei; Qin, Shiqiao; Fang, Jingyue; Wang, Chaocheng; Wang, Guang; Wang, Li; Zhang, Xue-Ao

2015-01-01

180

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

PubMed Central

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

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

2015-01-01

181

Electron transport model of dielectric charging  

NASA Technical Reports Server (NTRS)

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

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

1979-01-01

182

Carrier-mediated transport of riboflavin in Ashbya gossypii.  

PubMed

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

Förster, C; Revuelta, J L; Krämer, R

2001-01-01

183

Charge Transport and Glassy Dynamics in Ionic Liquids  

SciTech Connect

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

Sangoro, Joshua R [ORNL; Kremer, Friedrich [University of Leipzig

2012-01-01

184

Energytransport models for charge carriers involving impact ionization in semiconductors  

E-print Network

Choquet \\Lambda Pierre Degond y Christian Schmeiser z April 20, 2000 Abstract Energy­transport models. In High Electron Mobility Transistors and Metal Semiconductor Field Effect Transistors for instance [4], it causes a gate current. In Metal­ Oxide Semiconductor Field Effect Transistors it creates a substrate

Schmeiser, Christian

185

Variational multiscale models for charge transport.  

PubMed

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

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

2012-01-01

186

Variational multiscale models for charge transport  

PubMed Central

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

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

2012-01-01

187

Improving carrier injection in organic diodes by incorporating charge trapping molecules  

Microsoft Academic Search

We demonstrate improved charge injection in organic diodes by incorporating charge trapping molecules near the injecting electrode that dynamically alter the effective Schottky energy barrier to carrier injection between a metal electrode and the organic electronic material. Hole injection from Al and Cu anodes into the electroluminescent polymer poly[2-methoxy,5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] was improved by incorporating C60 molecules into the polymer near

I. H. Campbell; B. K. Crone

2006-01-01

188

Improving carrier injection in organic diodes by incorporating charge trapping molecules  

Microsoft Academic Search

We demonstrate improved charge injection in organic diodes by incorporating charge trapping molecules near the injecting electrode that dynamically alter the effective Schottky energy barrier to carrier injection between a metal electrode and the organic electronic material. Hole injection from Al and Cu anodes into the electroluminescent polymer poly[2-methoxy,5-(2’-ethyl-hexyloxy)-1,4-phenylene vinylene] was improved by incorporating C60 molecules into the polymer near

I. H. Campbell; B. K. Crone

2006-01-01

189

Nonlinear cyclotron acceleration of massless Dirac charge carriers in graphene and topological insulators  

NASA Astrophysics Data System (ADS)

Two-dimensional motion of quasiparticles with the Dirac dispersion relation in an external magnetic field in the presence of electromagnetic radiation has been investigated. It has been shown that the mechanisms of acceleration in the phase-locked (autoresonance) regime known for classical charged particles can also take place for massless charge carriers. In this case, the energy distribution function of electrons exhibits a gap, the magnitude of which is governed by the magnetic field.

Tokman, M. D.; Erukhimova, M. A.; Belyanin, A.

2014-11-01

190

Charge Transport in Melanin, a Disordered Bio-Organic Conductor  

E-print Network

Charge Transport in Melanin, a Disordered Bio-Organic Conductor Clare Giacomantonio A thesis-cream deliveries to the honours room. v #12;vi #12;Abstract Melanins are biological macromolecules with many roles presents a systematic investigation into charge transport physics in melanin. Charge transport

Powell, Ben

191

Charged Particle Transport in Turbulent Media  

NASA Astrophysics Data System (ADS)

The interstellar medium as well as the heliosphere is permeated by non-thermal particles with energies ranging from a few keV to 1020 eV. The transport of these particles is dominated by wave-particle interactions with the turbulent magnetic fields of the background plasma. Since these are complicated nonlinear processes, a detailed study is possible only with numerical simulations. The general problem in performing numerical simulations of high-energy charged particle transport is the large scale separation of the thermal background and the non-thermal component. We have targeted this problem from two sides: Using a hybrid-MHD model incorporating charged test particles and a fluid background we have investigated the physics of wave-particle interaction. These results have then been compared with particle-in-cell simulation results. In this presentation we will show the possibilities and limitations of both numerical approaches. The second major topic is the actual connection between the numerical experiment and the physics behind this: Charged particle transport in space plasmas is studied by means of pitch angle diffusion coefficients as long as field-line wandering is not dominant (cf. Laitinen et al. 2013). The derivation of these coefficients from simulations is prone to errors. We present two new methods to analyze data.

Spanier, F.; Ivascenko, A.; Lange, S.; Schreiner, C.

2014-09-01

192

Fundamentals of Charge Transport through DNA  

NASA Astrophysics Data System (ADS)

Achieving charge transport (CT) through DNA comlements its inherent biological recognition capabilities and its unmatched capacity to be patterned into precise, nanoscale shapes. We have probed the length and temperature dependence of DNA charge transport with DNA-mediated electrochemistry. Cyclic voltammetry of 100-mer and 17-mer DNA monolayers on gold revealed sizable peaks from distally-bound Nile Blue redox probes for well matched duplexes, but highly attenuated redox peaks from monolayers containing a single base pair mismatch, demonstrating that the charge transfer is DNA-mediated. The similarity in electron transfer rates through 100-mer and 17-mer monolayers is consistent with fast transport through the DNA and rate-limiting tunneling injection. Temperature dependence studies of 17-mer and 34-mer duplexes showed CT is thermally activated and highly sensitive to the integrity of the DNA base pair pi stack. Activation energies are increased by the presence and identity of single base pair mismatches. Furthermore, the yield of DNA CT with temperature argues that this CT is conformationally gated. These results elucidate the mechanism of DNA CT and direct the use of DNA as molecular wires in electronic applications.

Slinker, Jason; Muren, Natalie; Renfrew, Sara; Barton, Jackie; Wohlgamuth, Chris; McWilliams, Marc

2011-10-01

193

Particle transport through hydrogels is charge asymmetric.  

PubMed

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

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

2015-02-01

194

Structures of yeast mitochondrial ADP/ATP carriers support a domain-based alternating-access transport mechanism  

PubMed Central

The mitochondrial ADP/ATP carrier imports ADP from the cytosol and exports ATP from the mitochondrial matrix. The carrier cycles by an unresolved mechanism between the cytoplasmic state, in which the carrier accepts ADP from the cytoplasm, and the matrix state, in which it accepts ATP from the mitochondrial matrix. Here we present the structures of the yeast ADP/ATP carriers Aac2p and Aac3p in the cytoplasmic state. The carriers have three domains and are closed at the matrix side by three interdomain salt-bridge interactions, one of which is braced by a glutamine residue. Glutamine braces are conserved in mitochondrial carriers and contribute to an energy barrier, preventing the conversion to the matrix state unless substrate binding occurs. At the cytoplasmic side a second salt-bridge network forms during the transport cycle, as demonstrated by functional analysis of mutants with charge-reversed networks. Analyses of the domain structures and properties of the interdomain interfaces indicate that interconversion between states involves movement of the even-numbered ?-helices across the surfaces of the odd-numbered ?-helices by rotation of the domains. The odd-numbered ?-helices have an L-shape, with proline or serine residues at the kinks, which functions as a lever-arm, coupling the substrate-induced disruption of the matrix network to the formation of the cytoplasmic network. The simultaneous movement of three domains around a central translocation pathway constitutes a unique mechanism among transport proteins. These findings provide a structural description of transport by mitochondrial carrier proteins, consistent with an alternating-access mechanism. PMID:24474793

Ruprecht, Jonathan J.; Hellawell, Alex M.; Harding, Marilyn; Crichton, Paul G.; McCoy, Airlie J.; Kunji, Edmund R. S.

2014-01-01

195

Optimization of white organic light emitting diodes based on emitting layer charge carrier conduction properties  

NASA Astrophysics Data System (ADS)

We have fabricated white organic light emitting diodes (OLEDs) with multi-emitting layer (EML) structures in which 4,4'-N,N'-dicarbazole-biphenyl (CBP) layers doped with the phosphorescent dopants fac-tris(2-phenylpyridine) iridium (Ir(ppy)3) and bis(2-(2'-benzo[4,5-a]thienyl)pyridinato-N,C3')iridium(acetylacetonate) (btp2Ir(acac)) and the fluorescent dopant 4,4'-bis[2-{4-(N,N-diphenylamino) phenyl}vinyl]biphenyl (DPAVBi) were used as green (G), red (R) and blue (B) EMLs, respectively. A higher efficiency was expected with the R/G/B EML sequence from the hole transport layer interface than with the G/R/B sequence because of the differences in the charge carrier conduction properties of the EMLs doped with phosphorescent dopants and the luminance balance between the phosphorescent and fluorescent emissions. A high efficiency of 18.3 cd A-1 (an external quantum efficiency of 8.5%) at 100 cd m-2 and good colour stability were achieved with the R/G/B EML sequence as expected, with an additional non-doped CBP interlayer used between the G and B EMLs. In addition, the OLED with this sequence was found to have the longest lifetime of the white devices we tested.

Baek, H. I.; Lee, C. H.

2008-05-01

196

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

NASA Astrophysics Data System (ADS)

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.

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

2014-07-01

197

1\\/f noise in hot-carrier damaged MOSFET's: effects of oxide charge and interface traps  

Microsoft Academic Search

The 1\\/f noise in the drain current of hot-carrier damaged MOSFETs biased in weak inversion has been studied. By the use of a biased annealing treatment to simultaneously decrease the density of oxide trapped charge (Not) and increase the density of interface traps (Dit), the authors have separated the contributions of these two kinds of defects. The results clearly indicate

Ming-Horn Tsai; Tso-Ping Ma

1993-01-01

198

The charge carrier trap energy levels of two different polyimide films characterized by three methods  

Microsoft Academic Search

The charge carrier trap energy level is an important parameter that will affect the electrical and optical properties of insulating and semiconducting materials. Depending on the characterizing methods, it has a remarkable difference. The trap energy levels of two kinds of polyimide films, original (100 HN) and corona-resistant (100 CR) ones produced by Dupont, are estimated by depolarization current, space

Peihong Zhang; Xuan Wang; Chun Yang; Qingquan Lei

2009-01-01

199

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

E-print Network

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

Powell, Ben

200

47 CFR 69.4 - Charges to be filed.  

Code of Federal Regulations, 2012 CFR

...a) The end user charges for access service filed with this...carrier's carrier charges for access service filed with this Commission...Tandem-switched transport; (6) Direct-trunked transport; (7) Special access; and (8) Line...

2012-10-01

201

47 CFR 69.4 - Charges to be filed.  

Code of Federal Regulations, 2014 CFR

...a) The end user charges for access service filed with this...carrier's carrier charges for access service filed with this Commission...Tandem-switched transport; (6) Direct-trunked transport; (7) Special access; and (8) Line...

2014-10-01

202

47 CFR 69.4 - Charges to be filed.  

Code of Federal Regulations, 2011 CFR

...a) The end user charges for access service filed with this...carrier's carrier charges for access service filed with this Commission...Tandem-switched transport; (6) Direct-trunked transport; (7) Special access; and (8) Line...

2011-10-01

203

47 CFR 69.4 - Charges to be filed.  

Code of Federal Regulations, 2013 CFR

...a) The end user charges for access service filed with this...carrier's carrier charges for access service filed with this Commission...Tandem-switched transport; (6) Direct-trunked transport; (7) Special access; and (8) Line...

2013-10-01

204

Dust Charging and Transport on Surfaces  

NASA Astrophysics Data System (ADS)

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.

Wang, X.; Robertson, S.; Horányi, M.

2011-11-01

205

Dust Charging and Transport on Surfaces  

SciTech Connect

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.

Wang, X. [Colorado Center for Lunar Dust And Atmospheric Studies, University of Colorado, Boulder, CO 80309 (United States); Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 80309 (United States); Robertson, S. [Colorado Center for Lunar Dust And Atmospheric Studies, University of Colorado, Boulder, CO 80309 (United States); Department of Physics, University of Colorado, Boulder, CO 80309 (United States); Horanyi, M. [Colorado Center for Lunar Dust And Atmospheric Studies, University of Colorado, Boulder, CO 80309 (United States); Department of Physics, University of Colorado, Boulder, CO 80309 (United States); Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 80309 (United States)

2011-11-29

206

Charge-carrier trapping in polyfluorene-type conjugated polymers  

Microsoft Academic Search

The trap spectrum of a fluorene-based conjugated polymer poly[9,9-bis(2-ethylhexyl)fluorene-2,7-diyl] (PF2\\/6) and poly[9,9-bis(2-ethylhexyl)fluorene-2,7-diyl] end capped with hole-transporting moieties N, N-bis(4-methylphenyl)-N-phenylamine (PF2\\/6am10) is investigated by means of thermally stimulated current (TSC) and thermally stimulated luminescence (TSL) techniques. A high-temperature TSC peak observed at 240 K in PF2\\/6 is strongly affected by photooxidation and could be identified as electron trap with a depth

A. Kadashchuk; R. Schmechel; H. von Seggern; U. Scherf; A. Vakhnin

2005-01-01

207

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

Code of Federal Regulations, 2011 CFR

... false What must my travel accounting system do in relation to common...COMMON CARRIER TRANSPORTATION Accounting for Common Carrier Transportation...301-72.100 What must my travel accounting system do in relation to...

2011-07-01

208

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

Code of Federal Regulations, 2010 CFR

... false What must my travel accounting system do in relation to common...COMMON CARRIER TRANSPORTATION Accounting for Common Carrier Transportation...301-72.100 What must my travel accounting system do in relation to...

2010-07-01

209

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

Code of Federal Regulations, 2013 CFR

...2012-07-01 true What must my travel accounting system do in relation to common...COMMON CARRIER TRANSPORTATION Accounting for Common Carrier Transportation...301-72.100 What must my travel accounting system do in relation to...

2013-07-01

210

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

Code of Federal Regulations, 2012 CFR

... false What must my travel accounting system do in relation to common...COMMON CARRIER TRANSPORTATION Accounting for Common Carrier Transportation...301-72.100 What must my travel accounting system do in relation to...

2012-07-01

211

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

Code of Federal Regulations, 2014 CFR

... false What must my travel accounting system do in relation to common...COMMON CARRIER TRANSPORTATION Accounting for Common Carrier Transportation...301-72.100 What must my travel accounting system do in relation to...

2014-07-01

212

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

NASA Astrophysics Data System (ADS)

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.

Scully, Shawn Ryan

213

Energy Models for One-Carrier Transport in Semiconductor Devices  

NASA Technical Reports Server (NTRS)

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.

Jerome, Joseph W.; Shu, Chi-Wang

1991-01-01

214

Light-Induced Charge Transport within a Single Asymmetric Nanowire  

SciTech Connect

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.

Liu, Chong [Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States); Hwang, Yun Yeong [Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States); Jeong, Hoon Eui [Univ. of California, Berkeley, CA (United States); Yang, Peidong [Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)

2011-01-21

215

Charge and Spin Transport in Dilute Magnetic Semiconductors  

SciTech Connect

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.

Ullrich, Carsten A.

2009-07-23

216

A general relationship between disorder, aggregation and charge transport in conjugated polymers.  

PubMed

Conjugated polymer chains have many degrees of conformational freedom and interact weakly with each other, resulting in complex microstructures in the solid state. Understanding charge transport in such systems, which have amorphous and ordered phases exhibiting varying degrees of order, has proved difficult owing to the contribution of electronic processes at various length scales. The growing technological appeal of these semiconductors makes such fundamental knowledge extremely important for materials and process design. We propose a unified model of how charge carriers travel in conjugated polymer films. We show that in high-molecular-weight semiconducting polymers the limiting charge transport step is trapping caused by lattice disorder, and that short-range intermolecular aggregation is sufficient for efficient long-range charge transport. This generalization explains the seemingly contradicting high performance of recently reported, poorly ordered polymers and suggests molecular design strategies to further improve the performance of future generations of organic electronic materials. PMID:23913173

Noriega, Rodrigo; Rivnay, Jonathan; Vandewal, Koen; Koch, Felix P V; Stingelin, Natalie; Smith, Paul; Toney, Michael F; Salleo, Alberto

2013-11-01

217

A general relationship between disorder, aggregation and charge transport in conjugated polymers  

NASA Astrophysics Data System (ADS)

Conjugated polymer chains have many degrees of conformational freedom and interact weakly with each other, resulting in complex microstructures in the solid state. Understanding charge transport in such systems, which have amorphous and ordered phases exhibiting varying degrees of order, has proved difficult owing to the contribution of electronic processes at various length scales. The growing technological appeal of these semiconductors makes such fundamental knowledge extremely important for materials and process design. We propose a unified model of how charge carriers travel in conjugated polymer films. We show that in high-molecular-weight semiconducting polymers the limiting charge transport step is trapping caused by lattice disorder, and that short-range intermolecular aggregation is sufficient for efficient long-range charge transport. This generalization explains the seemingly contradicting high performance of recently reported, poorly ordered polymers and suggests molecular design strategies to further improve the performance of future generations of organic electronic materials.

Noriega, Rodrigo; Rivnay, Jonathan; Vandewal, Koen; Koch, Felix P. V.; Stingelin, Natalie; Smith, Paul; Toney, Michael F.; Salleo, Alberto

2013-11-01

218

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

NASA Astrophysics Data System (ADS)

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

Zhu, Di

2011-12-01

219

Current-voltage analysis of PCBM:PCDTBT blend to find out charge transport path  

NASA Astrophysics Data System (ADS)

Transport path(s) of charge carrier were identified through I-V measurement within the structure of ITO/PEDOT:PSS/PCDTBT:PCBM/TiOx/Ca/Ag in which ohmic regime was enrolled in low bias side while space charge limited conduction mechanism governed at high bias side. Moreover, influence of each constitituent parts of the present device on the dc transport properties was investigated by preparing ITO/PEDOT:PSS/PCDTBT/Ca/Ag and ITO/PEDOT:PSS/ PCBM/Ca/Ag structures and repeating the mentioned experimental techniques.

Saatci, A. Evrim; Kavak, Pelin; Parlak, Elif Altürk; Gökdemira, F. P?nar; Menda, U. Deneb; Özdemir, Orhan; Kutlu, Kubilay

2013-12-01

220

Enhanced hole carrier transport due to increased intermolecular contacts in small molecule based field effect transistors.  

PubMed

Small molecules and oligomers can be synthesized with very high purity and precise molecular weights, but they often do not form uniform thin films while processed from solution. Decreased intermolecular contacts between the small molecules are another disadvantage. To increase the intermolecular contacts in small molecules, we have chosen i-indigo, as one of the conjugated molecular units. The electron poor i-indigo has been connected with electron rich triphenylamine to synthesize a donor-acceptor-donor type small molecule. The propeller shaped triphenylamine helps to increase the solubility of the small molecule as well as isotropic charge transport. The intermolecular spacing between the molecules has been found to be low and did not vary as a function of thermal annealing. This implies that the intermolecular contacts between the small molecules are enhanced, and they do not vary as a function of thermal annealing. Organic field effect transistors (OFET) fabricated using a small molecule exhibited a hole carrier mobility (?) of 0.3 cm(2)/(V s) before thermal annealing. A marginal increase in ? was observed upon thermal annealing at 150 °C, which has been attributed to changes in thin film morphology. The morphology of the thin films plays an important role in charge transport in addition to the intermolecular spacing that can be modulated with a judicious choice of the conjugated molecular unit. PMID:23808768

Dharmapurikar, Satej S; Arulkashmir, Arulraj; Das, Chayanika; Muddellu, Pooja; Krishnamoorthy, Kothandam

2013-08-14

221

49 CFR 377.209 - Additional charges.  

Code of Federal Regulations, 2010 CFR

... 2010-10-01 false Additional charges. 377.209 Section 377.209 Transportation...REGULATIONS PAYMENT OF TRANSPORTATION CHARGES Extension of Credit to Shippers by...Forwarders § 377.209 Additional charges. When a carrier— (a) Has...

2010-10-01

222

Trap Limited Charge Transport In GexSe80-xPb20 Films  

NASA Astrophysics Data System (ADS)

Charge transport and trap density distribution of glassy GexSe80-xPb20 films have been investigated as a function of temperature and voltage. From room temperature to 220 K, space charge limited current, with an exponential distribution of trapping states, dominates the conduction mechanism. Below 220 K, mobility of charge carriers becomes field dependent. The characteristic energy of trap distribution and its density minimizes at x = 20 which reveals the high structural stability of Ge20Se60Pb20 glass.

Kumar, Kamal; Purohit, L. P.; Kumar, R.; Mehra, R. M.

2011-07-01

223

A novel method of identifying the carrier transport path in metal oxide resistive random access memory  

NASA Astrophysics Data System (ADS)

Characterization of defect energy levels is of crucial importance to understand the carrier transport and conduction mechanism of a conducting filament. Currently, it is difficult to probe the defect energy level of a conducting filament in random access memory (RRAM) by experiment. Based on the activation energy of carrier transport from the first-principles calculations, we present a physical model correlating macroscopic I–V characteristics with material microstructure to analyze the defect energy level of a conducting filament in metal oxide RRAM. The carrier transport path in the conducting filament can be specially extracted using the defect energy level.

Lu, Nianduan; Li, Ling; Sun, Pengxiao; Wang, Ming; Liu, Qi; Lv, Hangbing; Long, Shibing; Liu, Ming

2015-02-01

224

Ultrafast vibrational spectroscopy of charge-carrier dynamics in organic photovoltaic materials.  

PubMed

Ultrafast vibrational spectroscopy is used to examine the dynamics of interfacial electron transfer, free-carrier formation, and bimolecular charge recombination and trapping in an organic photovoltaic material. The carbonyl (C[double bond, length as m-dash]O) stretch of the functionalized fullerene, PCBM, is probed as a local vibrational reporter of the dynamics in a blend with a conjugated polymer, CN-MEH-PPV. Ultrafast interfacial electron transfer from CN-MEH-PPV to PCBM occurs on time scales ranging from less than 100 fs to 1 ps. PCBM molecules at interfaces with the polymer have carbonyl vibrations that are higher in frequency compared to the ensemble. The frequency variation results in part from a vibrational Stark shift arising from an interfacial dipole formed by spontaneous charge transfer from the polymer to PCBM. The Stark shift provides a means to observe directly the formation of free carriers through the spectral evolution of the carbonyl stretch. Free carrier formation occurs surprisingly quickly on the 1-10 ps time scale, suggesting that the charges experience a smaller effective Coulombic binding energy than expected. The interfacial dipole decreases the Coulombic binding energy because the negative pole of the dipole repels electrons at the PCBM domain interface. Following free-carrier formation, electrons diffuse within the material and become trapped on the microsecond time scale resulting in the formation of a distinct peak in the vibrational spectra. The time scale of charge trapping corresponds to the carrier lifetime of similar PPV-based polymer blends that have been reported in the literature on the basis of transient photocurrent measurements. PMID:19421513

Pensack, Ryan D; Banyas, Kyle M; Barbour, Larry W; Hegadorn, Maureen; Asbury, John B

2009-04-21

225

Scattering of the charge carriers by ordered arrays of defect pairs in ternary chalcopyrite semiconductors  

NASA Astrophysics Data System (ADS)

The electrical properties of CuIn3Se5, CuGa3Te5, and CuIn3Te5 that contain arrays of donor-acceptor defect pairs (DADPs) in the lattice structure are studied. An expression for the scattering of the charge carriers with the DADPs, calculated from simple first principles, is proposed. This, when combined with other well-established mechanisms, explains the temperature dependence of the relatively low carrier mobility in these compounds in the activation regime very well.

Rincón, C.; Wasim, S. M.; Marín, G.

2002-02-01

226

Direct lateral profiling of hot-carrier-induced oxide charge and interface traps in thin gate MOSFET's  

Microsoft Academic Search

A simple charge pumping method has been developed to measure the localized hot-carrier damage in scaled thin-gate MOSFET's. Lateral distributions of both interface traps and oxide charge can be derived directly from experimental charge pumping results without numerical simulation. By the use of this method, we have studied the erase-induced hot-carrier damage in flash EPROM devices, including the lateral distributions

Chun Chen; Tso-Ping Ma

1998-01-01

227

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

PubMed Central

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

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

2012-01-01

228

75 FR 7616 - Mitigation of Carrier Fines for Transporting Aliens Without Proper Documents; Modification of...  

Federal Register 2010, 2011, 2012, 2013, 2014

...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...

2010-02-22

229

Wage Differentials of Intermodal Transportation Carriers and Ports: Deregulation Versus Regulation  

Microsoft Academic Search

This paper investigates the wage differentials of intermodal transportation carriers and ports under carrier economic regulation and deregulation. The estimation results suggest that the union wages of truck drivers, rail engineers and port dockworkers were comparable in the regulation period; in the deregulation period the union wages of truck drivers and rail engineers declined relative to those of dockworkers. The

Wayne K. Talley

2004-01-01

230

The intestinal peptide carrier: A potential transport system for small peptide derived drugs  

Microsoft Academic Search

Several laboratories have recently shown that many peptides and peptide-type drugs are absorbed in the small intestine via the peptide transporter for nutrient di-and tripeptides. The peptide carrier has a broad substrate specificity and can provide an efficient route for the absorption of peptide drugs that may not readily penetrate the lipophilic intestinal membrane. The peptide carrier is an active

Elke Walter; Thomas Kissel; Gordon L. Amidon

1996-01-01

231

Electronic and charge-transport properties of 1,1,2,3,4,5-hexaphenysilole (HPS) crystal from theoretical calculations  

NASA Astrophysics Data System (ADS)

The structural, electronic, and charge transport properties of 1,1,2,3,4,5-hexaphenysilole (HPS) crystal are investigated using density functional theory (DFT). The influences of the temperature and pressure variations on the mechanical as well as the charge transport properties of HPS crystal are studied by molecular dynamics simulations combining with DFT calculations. By the analysis of the carrier mobilities and the band structures, we find that the hole may move slightly easier than the electron for the HPS crystal. MD simulation results show that moderately higher pressure and temperature are in favor of better charge transport properties for HPS crystals.

Liu, Yu-Hua; Xie, Yu; Lu, Zhong-Yuan

2010-02-01

232

Charge Carrier Dynamics of Quantum Confined Semiconductor Nanoparticles Analyzed via Transient Absorption Spectroscopy  

NASA Astrophysics Data System (ADS)

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

Thibert, Arthur Joseph, III

233

Preface: Charge transport in nanoscale junctions  

NASA Astrophysics Data System (ADS)

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

Albrecht, Tim; Kornyshev, Alexei; Bjørnholm, Thomas

2008-09-01

234

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

SciTech Connect

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.

Vukmirovic, Nenad; Wang, Lin-Wang

2009-11-10

235

Phenol photodegradation on platinized-TiO2 photocatalysts related to charge-carrier dynamics.  

PubMed

Three commercial TiO2 compounds (Degussa P25, Sachtleben UV100, and Millenium PC50) and their platinized forms have been studied by the time-resolved microwave conductivity (TRMC) method to follow their charge-carrier dynamics and to relate it to the photocatalytic activity for phenol degradation in TiO2 aqueous suspensions. The degradation reaction has been studied in detail, following the time evolution of the concentration of phenol and its intermediates by liquid chromatography. The results show that platinization has a distinct influence on the commercial compounds, decreasing globally the activity of P25 and increasing the activity of PC50 and UV100. An influence of charge-carrier lifetimes on the photoactivity of pure and platinized TiO2 samples has been evidenced. PMID:16584233

Emilio, Carina A; Litter, Marta I; Kunst, Marinus; Bouchard, Michel; Colbeau-Justin, Christophe

2006-04-11

236

Features of current transients of photogenerated charge carriers, extracted by linearly increased voltage  

NASA Astrophysics Data System (ADS)

Dependencies of photogenerated charge carrier's extraction current by linearly increased voltage (photo-CELIV) on the light intensity, absorption coefficient and recombination rate were calculated numerically. The simple method for the determination of reduction factor of the Langevin recombination is presented. According to calculations, the time necessary to reach maximum of the CELIV current transient varies more than 10 times depending on parameters mentioned above. Thus, the latter can cause large errors in the estimation of charge carrier's mobility, which can be corrected using results of the numerical calculations. Numerically calculated photo-CELIV transients were compared with the experimentally obtained current transient in the blends of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) with regioregular poly(3-hexylthiophene) (RR-P3HT), and PCBM with poly(2-methoxy-5-(3,7-dimethyloctyloxy)-para-phenylenevinylene) (MDMO-PPV).

Nekrašas, N.; Genevi?ius, K.; Vili?nas, M.; Juška, G.

2012-08-01

237

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

PubMed

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

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

2013-04-01

238

Temperature dependent investigation of carrier transport, injection, and densities in 808 nm AlGaAs multi-quantum-well active layers for VCSELs  

NASA Astrophysics Data System (ADS)

The electro-optical efficiency of semiconductor vertical-cavity surface-emitting lasers (VCSELs) strongly depends on the efficient carrier injection into the quantum wells (QWs) in the laser active region. However, carrier injection degrades with increasing temperature which limits the VCSEL performance particularly in high power applications where self heating imposes high temperatures in operation. By simulation we investigate the transport of charge carriers in 808 nm AlGaAs multi-quantum-well active layers with special attention to the temperature dependence of carrier injection into the QWs. Experimental reference data was extracted from oxide-confined, top-emitting VCSELs. The transport simulations follow a drift-diffusion-model complemented by a customized, energy-resolved, semi-classical carrier capture theory. QW gain was calculated in the screened Hartree-Fock approximation with band structures from 8x8 k.p-theory. Using the gain data and by setting losses and the optical confinement factor according to experimental reference results, the appropriate threshold condition and threshold carrier densities in the QWs for a VCSEL are established in simulation for all transport considerations. With the combination of gain and transport model, we can explain experimental reference data for the injection efficiency and threshold current density. Our simulations show that the decreasing injection efficiency with temperature is not solely due to increased thermionic escape of carriers from the QWs. Carrier injection is also hampered by state filling in the QWs initiated from higher threshold carrier densities with temperature. Consequently, VCSEL properties not directly related to the active layer design like optical out-coupling or internal losses link the temperature dependent carrier injection to VCSEL mirror design.

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

2014-05-01

239

Liquid-crystalline semiconducting polymers with high charge-carrier mobility  

Microsoft Academic Search

Organic semiconductors that can be fabricated by simple processing techniques and possess excellent electrical performance, are key requirements in the progress of organic electronics. Both high semiconductor charge-carrier mobility, optimized through understanding and control of the semiconductor microstructure, and stability of the semiconductor to ambient electrochemical oxidative processes are required. We report on new semiconducting liquid-crystalline thieno[3,2-b ]thiophene polymers, the

Iain McCulloch; Martin Heeney; Clare Bailey; Kristijonas Genevicius; Iain MacDonald; Maxim Shkunov; David Sparrowe; Steve Tierney; Robert Wagner; Weimin Zhang; Michael L. Chabinyc; R. Joseph Kline; Michael D. McGehee; Michael F. Toney

2006-01-01

240

Kinetics of optically excited charge carriers at the GaN surface  

NASA Astrophysics Data System (ADS)

In this work, we combine conductance and contact potential difference measurements in a consistent and systematic way, in steady-state and transient modes, both in the dark and under illumination. With this we obtain valuable information about the kinetics of charges at and close to the surface of GaN. We compare the processes involved in the accumulation and the decay of charge carriers generated via excitation with above and below band-gap light with varying light intensity. In particular, we probed the role played by localized defect states in the kinetics of photogenerated charges. These states are responsible for the trapping of photogenerated electrons in the space-charge region close to the surface, which explains the slow response of the photocurrent to illumination. These states are also involved in the transfer of electrons back to the surface after illumination, which results in the slow recovery of the photocurrent and the contact potential difference in the dark.

Winnerl, A.; Pereira, R. N.; Stutzmann, M.

2015-02-01

241

Detection of Negative Charge Carriers in Superfluid Helium Droplets: The Metastable Anions He*– and He2*–  

PubMed Central

Helium droplets provide the possibility to study phenomena at the very low temperatures at which quantum mechanical effects are more pronounced and fewer quantum states have significant occupation probabilities. Understanding the migration of either positive or negative charges in liquid helium is essential to comprehend charge-induced processes in molecular systems embedded in helium droplets. Here, we report the resonant formation of excited metastable atomic and molecular helium anions in superfluid helium droplets upon electron impact. Although the molecular anion is heliophobic and migrates toward the surface of the helium droplet, the excited metastable atomic helium anion is bound within the helium droplet and exhibits high mobility. The atomic anion is shown to be responsible for the formation of molecular dopant anions upon charge transfer and thus, we clarify the nature of the previously unidentified fast exotic negative charge carrier found in bulk liquid helium. PMID:25068008

2014-01-01

242

Three-Dimensional Model for Analyzing Charge Carrier Motion Around a Charged Spherical Object in the Presence of Flow and Electric Field  

Microsoft Academic Search

Generalized models in three dimensions are systematically developed reduced from the fundamental two-dimensional model for analyzing charge carrier motion around a charged spherical object with flow and electric field. As an example of its application in three dimensions, the collection efficiency in charged droplet scrubber is calculated. The purpose of this paper is to show a firm basis for work

Satoru Sumiyoshitani

1996-01-01

243

Charge Transport in Trehalose-Derived Sugar Glasses  

NASA Astrophysics Data System (ADS)

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.

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

2013-03-01

244

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

E-print Network

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

Kazuhiko Seki

2014-08-03

245

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

PubMed

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

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

2014-08-01

246

Hot carrier diffusion in graphene  

E-print Network

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. Spatiotemporal...

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

2010-11-01

247

Charge-carrier transport in amorphous organic semiconductors  

E-print Network

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 ...

Limketkai, Benjie, 1982-

2008-01-01

248

Charge and Spin Carrier Transport in Graphene and its Derivatives  

NASA Astrophysics Data System (ADS)

The electron-phonon interaction in carbon nanotubes (CNT) and graphene (mono- and bilayer) is studied using various theoretical techniques. In particular, a new mechanism of spin-lattice relaxation via flexural modes is proposed and theoretically studied for localized and delocalized electronic states in semiconducting carbon nanotubes in the presence of a magnetic field. The recent experimental and theoretical studies of CNT-based quantum dots confirmed that flexural modes play an exceptionally important role in spin relaxation in CNTs. We then employ ab initio methods (DFT and GW) to estimate the strength of electron-phonon coupling (EPC) in monolayer (MLG) and bilayer (BLG) graphene. We estimate the effective deformation potential constants associated with all acoustic phonons to be ˜ 4.5 -- 5 eV and 15 eV in MLG and BLG, respectively. We point out at distinct differences between these two systems: while the acoustic phonon scattering is clearly the dominant mechanism in BLG, the in-plane optical phonons play a considerable role in MLG and cannot be disregarded. The results of Monte Carlo simulations are presented, together with the estimated intrinsic mobilities and saturation velocities. These numbers provide an ultimate limit of graphene-based electronic device performance. Finally, we explore the impact of EPC on Klein tunneling in MLG at room temperature. Within the framework of the time-dependent perturbation theory, we demonstrate that this impact is negligible in a broad range of parameters (electron energy, gate voltage, device size). We show that even by the most conservative estimate, the device size can be up to 10 ¦Im.

Borysenko, Kostyantyn

249

Control of Charge Transport in the Perovskite CH3 NH3 PbI3 Thin Film.  

PubMed

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

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

2015-03-16

250

J. CHEM. SOC. FARADAY TRANS., 1992, 88(17), 2529-2535 2529 Picosecond Generation of Transient Charge Carriers in  

E-print Network

-transfer complexes can easily be obtained. An example is given by Ni phthalocyanine crystals doped with iodine, which, at room temperature.' The charge carriers, which are responsible for conductivity properties, can also

Paris-Sud XI, Université de

251

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

E-print Network

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 ...

Difley, Seth

2010-01-01

252

Consequence of silver nanoparticles embedment on the carrier mobility and space charge limited conduction in doped polyaniline  

NASA Astrophysics Data System (ADS)

The present study depicts a one-pot strategy to fabricate silver-polyaniline hybrid nanocomposites with superior and tunable electrical properties, supported by structural characterizations and detail analysis of their temperature dependent current density (J)-voltage (V) characteristics. TEM micrographs clearly reveal that the nanocomposites synthesized by this one-pot strategy contain higher dispersion of sliver nanoparticle within the polyaniline matrix with respect to that obtained from the embedment of externally pre-synthesized silver nanoparticles. The results obtained from the analysis of J-V characteristics indicate the prevalence of trapped charge-limited conduction mechanism in doped polyaniline and its nanocomposites. For the nanocomposites obtained from one-pot strategy, a transition of charge transport mechanism from deep exponential trap limited to shallow traps limited conduction has been occurred due to higher dispersion of silver nanoparticles within the polyaniline matrix. Such distinct variation of charge conduction is absent in the nanocomposites obtained from the embedment of externally pre-synthesized silver nanoparticles. A direct evaluation of carrier mobility as a function of electric field and temperature illustrates that the incorporation of only ?13 to 18 wt% of silver nanoparticles within the polyaniline matrix enhances the carrier mobility in a large extent by reducing the concentration of traps within the polymer matrix. The calculated mobility is consistent with the Poole-Frenkel form for the electrical field up to a certain temperature range. The nonlinear low temperature dependency of mobility of all the nanostructured samples has been explained by Mott variable range hopping conduction mechanisms. Qualitative estimation of various disorder parameters such as optimal hopping distance, localization lengths etc., would help us to outspread the strategies for the fabrication of new organic semiconducting nano-structured devices.

Biswas, Swarup; Dutta, Bula; Bhattacharya, Subhratanu

2014-02-01

253

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

Federal Register 2010, 2011, 2012, 2013, 2014

...by Air Carriers on Incidents Involving Animals During Air Transport AGENCY: Office of...regarding the reporting of incidents involving animals during air transport, 14 CFR 234.13...seats, to expand the definition of ``animal'' to include all cats and dogs...

2012-06-29

254

On the Mechanism of Proton Transport by the Neuronal Excitatory Amino Acid Carrier 1  

Microsoft Academic Search

Uptake of glutamate from the synaptic cleft is mediated by high affinity transporters and is driven by Na 1 , K 1 , and H 1 concentration gradients across the membrane. Here, we characterize the molecular mechanism of the intracellular pH change associated with glutamate transport by combining current recordings from excita- tory amino acid carrier 1 (EAAC1)-expressing HEK293 cells

Natalie Watzke; Thomas Rauen; Ernst Bamberg; Christof Grewer

2000-01-01

255

Influence of charge carrier mobility and morphology on solar cell parameters in devices of mono- and bis-fullerene adducts  

NASA Astrophysics Data System (ADS)

Herein, we analyze charge carrier mobility and morphology of the active blend layer in thin film organic solar cells and correlate them with device parameters. A low band gap donor-acceptor copolymer in combination with phenyl-C61-butyric acid methyl ester (PCBM) or two bis-adduct fullerenes, bis-PCBM and bis-o-quino-dimethane C60 (bis-oQDMC), is investigated. We study the charge transport of polymer:fullerene blends in hole- and electron-only devices using the space-charge limited current method. Lower electron mobilities are observed in both bis-adduct fullerene blends. Hole mobility, however, is decreased only in the blend containing bis-oQDMC. Both bis-adduct fullerene blends show very high open circuit voltage in solar cell devices, but poor photocurrent compared to the standard PCBM blend for an active layer thickness of 200 nm. Therefore, a higher short circuit current is feasible for the polymer:bis-PCBM blend by reducing the active layer thickness in order to compensate for the low electron mobility, which results in a PCE of 4.3%. For the polymer:bis-oQDMC blend, no such improvement is achieved due to an unfavorable morphology in this particular blend system. The results are supported by external quantum efficiency measurements, atomic force microscopy, transmission electron microscopy and UV/vis spectroscopy. Based on these results, the investigations presented herein give a more scientific basis for the optimization of solar cells.

Muth, Mathis-Andreas; Mitchell, William; Tierney, Steven; Lada, Thomas A.; Xue, Xiang; Richter, Henning; Carrasco-Orozco, Miguel; Thelakkat, Mukundan

2013-12-01

256

The role of charge-transfer integral in determining and engineering the carrier mobilities of 9,10-di(2-naphthyl)anthracene compounds  

NASA Astrophysics Data System (ADS)

The charge transporting properties of t-butylated 9,10-di(2-naphthyl)anthracene (ADN) compounds have been investigated experimentally and computationally in relation to their molecular structures. The ADN compounds are found to be ambipolar with both electron and hole mobilities in the range of 1-4 × 10 -7 cm 2 V -1 s -1 (electric field 0.5-0.8 MV/cm). As the degree of t-butylation increases, the carrier mobility decreases progressively. The mobility reduction was examined by Marcus theory of reorganization energies. All ADN compounds possess similar reorganization energies of ˜0.3 eV. The reduction of carrier mobilities with increasing t-butylation can be attributed to a decrease in the charge-transfer integral or the wavefunction overlap.

Tse, S. C.; So, S. K.; Yeung, M. Y.; Lo, C. F.; Wen, S. W.; Chen, C. H.

2006-05-01

257

Brownian dynamics determine universality of charge transport in ionic liquids  

SciTech Connect

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

Sangoro, Joshua R [ORNL; Iacob, Ciprian [University of Leipzig; Mierzwa, Michal [University of Silesia, Uniwersytecka, Katowice, Poland; Paluch, Marian [University of Silesia, Uniwersytecka, Katowice, Poland; Kremer, Friedrich [University of Leipzig

2012-01-01

258

Charge Transport through Organized Organic Assemblies in Confined Geometries  

E-print Network

................................................................................. 1 1.2 Background ............................................................................. 3 1.3 Measurement of Charge Transport in Molecular Assemblies . 17 1.4 Porphyrinoids on Surfaces... for charge transport measurements of molecular configurations on metal and semiconductor surfaces using Scanning Tunneling Microscopy (STM) or Conducting Probe Atomic Force Microscopy (CP-AFM) as well as in junctions such as nanogap electrodes, break...

Schuckman, Amanda Eileen

2012-07-16

259

Dual character of excited charge carriers in graphene on Ni(111)  

NASA Astrophysics Data System (ADS)

The dynamics of excited charge carriers at the graphene/Ni(111) interface has been investigated by means of time-resolved two-photon photoemission spectroscopy, employing femtosecond-XUV pulses with an energy of 39.2 eV produced by high-order-harmonic generation. Due to the interplay of substrate and adsorbate band structures, the dependence of the lifetimes on the energy (E-EF) of the excited carriers was found to be similar to that of Ni 3d electrons measured for clean Ni in the energy range (E-EF)<1 eV, while it resembled that of graphite from 1 eV above EF onwards. This result is suggested to be the effect of the peculiar electronic structure of the interface, which still possesses features belonging to the pristine graphene layer, such as a residual saddle point.

Bignardi, L.; Haarlammert, T.; Winter, C.; Montagnese, M.; van Loosdrecht, P. H. M.; Voloshina, E.; Rudolf, P.; Zacharias, H.

2014-02-01

260

Scaling theory for percolative charge transport in molecular semiconductors: Correlated versus uncorrelated energetic disorder  

NASA Astrophysics Data System (ADS)

We recently introduced a scaling theory for charge transport in molecular semiconductors with uncorrelated Gaussian energetic disorder, considering Miller-Abrahams as well as Marcus hopping and different lattice structures [Cottaar , Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.107.136601 107, 136601 (2011)]. A compact expression was derived for the dependence of the charge-carrier mobility on temperature and carrier concentration. We show here that for Miller-Abrahams hopping the theory can also be applied to non-Gaussian energetic disorder, without parameter changes. Moreover, we show how it can be applied to correlated energetic disorder as obtained from randomly oriented molecular dipoles, which experiments suggest to be often more suitable. The same compact expression still describes the charge-carrier mobility, with new parameter values as determined from numerically exact results. The critical scaling exponent for correlated disorder is about twice as large as for uncorrelated disorder, which is caused by a different topology of the percolating network. The temperature dependence of the mobility for correlated disorder is significantly weaker than for uncorrelated disorder, while the carrier-concentration dependence is slightly weaker, due to small deviations of the density of states from a Gaussian. We indicate how comparison with experiments could distinguish between the different models.

Cottaar, J.; Coehoorn, R.; Bobbert, P. A.

2012-06-01

261

Ambipolar charge transport in non-peripherally substituted octahexyl zinc phthalocyanine  

NASA Astrophysics Data System (ADS)

Time-of-flight measurements on 2\\ \\mu\\text{m} thick drop-cast films of 1,4,8,11,15,18,22,25-octakis(hexyl)phthalocyaninato zinc complex in a sandwich configuration between transparent indium tin oxide and aluminum metal electrodes have been performed. The results show that intrinsic ambipolar transport characteristics are exhibited by this very stable compound having values in the order of 10^{-4}\\ \\text{cm}^{2}\\,\\text{V}^{-1}\\,\\text{s}^{-1} for both types of charge carrier. Both electron and hole transport are dispersive due to a high degree of positional disorder of the molecules.

Chaure, Nandu B.; Barard, Seema; Ray, Asim K.; Cammidge, Andrew N.; Cook, Michael J.

2013-12-01

262

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

PubMed

The utilization of electron-hole pairs (EHPs) generated from multiple excitons in quantum dots (QDs) is of great interest toward efficient photovoltaic devices and other optoelectronic devices; however, extraction of charge carriers remains difficult. Herein, we extract photocharges from Ag2S QDs and investigate the dependence of the electric field on the extraction of charges from multiple exciton generation (MEG). Low toxic Ag2S QDs are directly grown on TiO2 mesoporous substrates by employing the successive ionic layer adsorption and reaction (SILAR) method. The contact between QDs is important for the initial charge separation after MEG and for the carrier transport, and the space between neighbor QDs decreases with more SILAR cycles, resulting in better charge extraction. At the optimal electric field for extraction of photocharges, the results suggest that the threshold energy (h?th) for MEG is 2.41Eg. The results reveal that Ag2S QD is a promising material for efficient extraction of charges from MEG and that QDs prepared by SILAR have an advantageous electrical contact facilitating charge separation and extraction. PMID:25504257

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

2015-01-28

263

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

SciTech Connect

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.

Bale, Derek S.; Szeles, Csaba [eV Microelectronics, a division of Endicott Interconnect Technologies Inc., Saxonburg, Pennsylvania 16056 (United States)

2010-06-15

264

Carrier?Mediated Transport of Amino Acids Through Bulk Liquid Membranes  

Microsoft Academic Search

A novel carrier, the N?methyl, N?dodecyl?ephedrinium ion, was studied for the selective transport of some aromatic amino acids [phenylalanine (Phe), histidine (His) and tryptophan (Trp)] through bulk liquid membranes. Investigations of the main parameters limiting the aided transport of the amino acids were carried out. Transport rates that resulted were affected by the amino acid lipophilicity, the pH variations of

R. Bucci; S. Canepari; E. Cardarelli; A. M. Girelli; A. Pietrodangelo; M. Valiente

2004-01-01

265

Ultrafast Charge Carrier Recombination and Trapping in Hematite Photoanodes under Applied Bias  

PubMed Central

Transient absorption spectroscopy on subpicosecond to second time scales is used to investigate photogenerated charge carrier recombination in Si-doped nanostructured hematite (?-Fe2O3) photoanodes as a function of applied bias. For unbiased hematite, this recombination exhibits a 50% decay time of ?6 ps, ?103 times faster than that of TiO2 under comparable conditions. Anodic bias significantly retards hematite recombination dynamics, and causes the appearance of electron trapping on ps??s time scales. These ultrafast recombination dynamics, their retardation by applied bias, and the associated electron trapping are discussed in terms of their implications for efficient water oxidation. PMID:24950057

2014-01-01

266

Long-lived charge carrier dynamics in polymer/quantum dot blends and organometal halide perovskites  

NASA Astrophysics Data System (ADS)

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.

Nagaoka, Hirokazu

267

Photosensitive Properties and a Mechanism for Photogeneration of Charge Carriers in Polymeric Layers Containing Organometallic Complexes  

SciTech Connect

New polyamide acids (prepolymers of polybenzoxazinimides) containing 2,2-biquinolyl units in their main chain are synthesized. It is shown that these polymers form stable complexes with acids derived from the transition and rare-earth metals. The results of photophysical studies support the assumption that the process of generation of free charge carriers via a state of a pair bound by a Coulomb interaction includes two stages and that metal-polymer complexes are involved in this process. The quantum yield of photogeneration amounts to 0.007-0.05.

Aleksandrova, E.L. [Ioffe Physicotechnical Institute, Russian Academy of Sciences, Politekhnicheskaya ul. 26, St. Petersburg, 194021 (Russian Federation); Goikhman, M.Ya.; Podeshvo, I.V.; Kudryavtsev, V.V. [Institute of Macromolecular Compounds, Russian Academy of Sciences, Bol'shoi proezd 31, St. Petersburg, 199004 (Russian Federation)

2005-07-15

268

Influence of defects on excess charge carrier kinetics studied by transient PC and transient PA  

SciTech Connect

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.

Feist, H.; Kunst, M.; Swiatkowski, C.

1997-07-01

269

RoF transport systems with OSNR enhanced multi-band optical carrier generator.  

PubMed

A combination of an economic multi-band optical carrier generator and a novel optical signal to noise ratio (OSNR) enhancement circuit is proposed and demonstrated for radio over fiber (RoF) transport systems. Different from normal RoF transport systems which a central station (CS) needs multiple dedicate wavelength laser diodes (LDs) to support various base stations (BSs), the proposed scheme can employ a single LD to provide multiple optical carriers for various BSs. To verify this scheme, 8 coherent optical carriers are firstly generated using a single LD and a local oscillator (LO). Subsequently, their OSNR values are optimized by the developed OSNR enhancement circuit. An up to 15 dB OSNR enlargement in those optical carriers is experimentally achieved. To demonstrate the practice of the proposal, a pair of those optical carriers is employed to experimentally achieve frequency up-conversion process in a RoF transport system. Clear eye diagram and error free transmission reveal that with a proper carrier selector the proposed scheme can be employed to support multiple RoF transmissions. Furthermore, this proposal also presents a high possibility to achieve 60 GHz RoF transmission using a 10 GHz LO, a LD and a low frequency external modulator. PMID:21935221

Su, Heng-Sheng; Li, Chung-Yi; Lu, Hai-Han; Chang, Ching-Hung; Peng, Peng-Chun; Wu, Po-Yi; Chen, Hwan-Wen

2011-09-12

270

Measurement of carrier transport and recombination parameter in heavily doped silicon  

NASA Technical Reports Server (NTRS)

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.

Swanson, Richard M.

1986-01-01

271

Transmembrane auxin carrier systems – dynamic regulators of polar auxin transport  

Microsoft Academic Search

Recent investigations of the biochemistry, physiology and molecular genetics of polar auxin transport have greatly advanced our understanding of the process and of the part it plays in the regulation of development and in the responses of cells, tissues and organs to internal and external stimuli. The molecular and physiological characterization of mutants which exhibit lesions in polar auxin transport

David A. Morris

2000-01-01

272

DNA charge transport over 34 nm  

NASA Astrophysics Data System (ADS)

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.

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

2011-03-01

273

DNA charge transport over 34 nm.  

PubMed

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. PMID:21336329

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

2011-03-01

274

Charge carrier relaxation and effective masses in silicon probed by terahertz spectroscopy  

NASA Astrophysics Data System (ADS)

Charge transport in silicon is investigated on a metal-oxide-semiconductor structure, which is driven into depletion, accumulation, or inversion. Terahertz electromodulation spectroscopy provides momentum relaxation times as well as conductivity effective masses of electrons and holes. At room temperature the conductivity effective masses of electrons and holes are close to those values reported for cryogenic temperatures.

Engelbrecht, S. G.; Reichel, A. J.; Kersting, R.

2012-12-01

275

Charge-carrier-trapping kinetics in a chain with chaotically distributed traps and broken bonds: Biased-random-walk model  

Microsoft Academic Search

An exact expression for the Laplace transform of the configurationally averaged survival probability of a charged particle executing biased (asymmetric) random walks in a chain with traps and broken bonds (barriers) is derived. By inverting this expression, it has been shown that in high fields the charge-carrier density decays exponentially at the initial stage of the trapping process. For long

Alexander I. Onipko

1991-01-01

276

Reversible Formation of Charge Carrier Traps in Poly(Phenylenevinylene) Derivative due to the Phototransformation of a Photochromic Additive  

Microsoft Academic Search

Kinetics of photochromic reaction of spiropyran dissolved in a poly(phenylenevinylene) derivative MEH-PPV was studied by optical and impedance spectroscopy. Spiropyran forms metastable, highly polar merocyanine under illumination with light of an appropriate wavelength. Due to charge-dipole interactions, charge carrier traps are formed and affect electrical properties of the polymer matrix, namely capacitance and photoconductivity.

Martin Weiter; Martin Vala; Ota Salyk; Old?ich Zmeškal; Stanislav Nešp?rek; Juliusz Sworakowski

2005-01-01

277

Ultrafast Carrier Relaxation in InN Nanowires Grown by Reactive Vapor Transport  

NASA Astrophysics Data System (ADS)

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.

Othonos, Andreas; Zervos, Matthew; Pervolaraki, Maria

2009-02-01

278

Ultrafast Carrier Relaxation in InN Nanowires Grown by Reactive Vapor Transport  

PubMed Central

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.

2009-01-01

279

The Role of Surface Ligands in Electronic Charge Transport in Semiconductor Nanocrystal Arrays  

NASA Astrophysics Data System (ADS)

The long, insulating ligands commonly used in the synthesis of colloidal semiconductor nanocrystals (NCs) inhibit strong interparticle coupling and charge transport once NCs are assembled in the solid state into NC arrays. We introduce ammonium thiocyanate (NH4SCN) and its derivatives, ammonium selenocyanate and selenourea to exchange the long, insulating ligands commonly used in the synthesis of colloidal semiconductor NCs. NCs may be exchanged with the new ligand in solution to form dispersions from which NC arrays are deposited or NC arrays with the long, insulating ligands may be exchanged in the solid state with the new ligands. The new compact ligands enhance interparticle coupling and charge transport in thin film, NC arrays as seen by red-shifts in the optical absorption and concomitant increases in carrier mobilities. Thiocyanate-capped CdSe thin film, NC arrays form sensitive photodetectors and n-type field-effect transistors with electron mobilities of ˜10 cm^2/Vs and current modulation of >10^6, while preserving NC quantum confinement. Temperature-dependent transport measurements reveal band-like transport in NC arrays, overcoming carrier hopping that has typified transport in NC arrays until recently. The non-caustic, chemically benign nature of the ammonium thiocyanate treatment enables the fabrication of NC thin film devices and circuits on flexible plastics.

Kagan, Cherie

2012-02-01

280

Carrier transport simulation in a model liquid crystalline system with the biaxial Gay-Berne potential  

NASA Astrophysics Data System (ADS)

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.

Goto, Masanao; Takezoe, Hideo; Ishikawa, Ken

2010-02-01

281

Carrier Transport Properties of p-Type Silicon-Metal Silicide Nanocrystal Composite Films  

NASA Astrophysics Data System (ADS)

In this study, we synthesized p-type nanocomposite films consisting of Si-nickel silicide and Si-molybdenum silicide nanocrystals and measured the temperature dependence of their electrical properties. To evaluate grain boundary potential barrier height, we developed a theoretical model taking into account the effect of ionized impurities, acoustic phonons, and grain boundaries. The potential barrier height was sufficiently low not to substantially affect carrier transport in the Si-nickel silicide composite film. Carrier transport in the Si-molybdenum silicide composite film was found to be affected by a scattering mechanism not included in this model. Thus, the transition metal significantly affects carrier transport and the thermoelectric properties of Si-metal silicide nanocomposite films.

Ohishi, Yuji; Miyazaki, Yoshinobu; Muta, Hiroaki; Kurosaki, Ken; Yamanaka, Shinsuke; Uchida, Noriyuki; Tada, Tetsuya

2015-02-01

282

Snapshots of the retarded interaction of charge carriers with ultrafast fluctuations in cuprates  

E-print Network

One of the pivotal questions in the physics of high-temperature superconductors is whether the low-energy dynamics of the charge carriers is mediated by bosons with a characteristic timescale. This issue has remained elusive since electronic correlations are expected to dramatically speed up the electron-boson scattering processes, confining them to the very femtosecond timescale that is hard to access even with state-of-the-art ultrafast techniques. Here we simultaneously push the time resolution and the frequency range of transient reflectivity measurements up to an unprecedented level that enables us to directly observe the 16 fs build-up of the effective electron-boson interaction in hole-doped copper oxides. This extremely fast timescale is in agreement with numerical calculations based on the t-J model and the repulsive Hubbard model, in which the relaxation of the photo-excited charges is achieved via inelastic scattering with short-range antiferromagnetic excitations.

Conte, S Dal; Golež, D; Mierzejewski, M; Soavi, G; Peli, S; Banfi, F; Ferrini, G; Comin, R; Ludbrook, B M; Chauviere, L; Zhigadlo, N D; Eisaki, H; Greven, M; Lupi, S; Damascelli, A; Brida, D; Capone, M; Bon?a, J; Cerullo, G; Giannetti, C

2015-01-01

283

Model ab initio study of charge carrier solvation and large polaron formation on conjugated carbon chains.  

PubMed

Using long C(N)H(2) conjugated carbon chains with the polyynic structure as prototypical examples of one-dimensional (1D) semiconductors, we discuss self-localization of excess charge carriers into 1D large polarons in the presence of the interaction with a surrounding polar solvent. The solvation mechanism of self-trapping is different from the polaron formation due to coupling with bond-length modulations of the underlying atomic lattice well known in conjugated polymers. Model ab initio computations employing the hybrid B3LYP density functional, in conjunction with the polarizable continuum model, are carried out demonstrating the formation of both electron and hole polarons. Polarons can emerge entirely due to solvation but even larger degrees of charge localization occur when accompanied by atomic displacements. PMID:19355762

Mayo, M L; Gartstein, Yu N

2009-04-01

284

Charge carrier mobility and concentration as a function of composition in AgPO3-AgI glasses  

NASA Astrophysics Data System (ADS)

Conductivity data of the xAgI(1 - x)AgPO3 system (0 ? x ? 0.5) were collected in the liquid and glassy states. The difference in the dependence of ionic conductivity on temperature below and above their glass transition temperatures (Tg) is interpreted by a discontinuity in the charge carrier's mobility mechanisms. Charge carrier displacement occurs through an activated mechanism below Tg and through a Vogel-Fulcher-Tammann-Hesse mechanism above this temperature. Fitting conductivity data with the proposed model allows one to determine separately the enthalpies of charge carrier formation and migration. For the five investigated compositions, the enthalpy of charge carrier formation is found to decrease, with x, from 0.86 to 0.2 eV, while the migration enthalpy remains constant at ?0.14 eV. Based on these values, the charge carrier mobility and concentration in the glassy state can then be calculated. Mobility values at room temperature (?10-4 cm2 V-1 s-1) do not vary significantly with the AgI content and are in good agreement with those previously measured by the Hall-effect technique. The observed increase in ionic conductivity with x would thus only be due to an increase in the effective charge carrier concentration. Considering AgI as a weak electrolyte, the change in the effective charge carrier concentration is justified and is correlated to the partial free energy of silver iodide forming a regular solution with AgPO3.

Rodrigues, Ana Candida Martins; Nascimento, Marcio Luis Ferreira; Bragatto, Caio Barca; Souquet, Jean-Louis

2011-12-01

285

User charges in international air transportation  

E-print Network

The charges dealt with here are those paid by international airline operators for the use of airports and airways. At airports, there are charges for landings and takeoffs and various fees or rentals for other facilities ...

Seagrave, Norman P.

1979-01-01

286

The role of surface states in modification of carrier transport in silicon nanowires  

NASA Astrophysics Data System (ADS)

We investigate transport properties of polyacrylic acid (PAA) capped n and p-type silicon nanowire (SiNW) arrays. PAA diluted with deionized water at different concentrations was spun directly on vertically grown SiNW arrays prepared by metal assisted electroless chemical etching. PAA provides mechanical support to electrical contacts and acts as a source of interface doping by creating acceptor like states (holes) on SiNWs surface. PAA capping results in increase in current in p-type SiNWs and decrease in current in n-type SiNWs. Schottky emission model fits current voltage (IV) characteristics of p-type SiNWs/PAA device. Ohmic like conduction at lower voltages followed by space charge limited current (SCLC) with and without traps is observed in p-type SiNWs, n-type SiNWs, and n-type SiNWs/PAA devices. Using SCLC model with exponential distribution of traps, the extracted trap density was 7.20 × 1011/cm3 and 6.0 × 1011/cm3 for p-type SiNWs and n-type SiNWs devices, respectively. Our findings also demonstrate that the carrier concentration in SiNWs depends not only on doping concentration but also depends significantly on density of surface states.

Rasool, Kamran; Rafiq, M. A.; Ahmad, Mushtaq; Imran, Zahid; Hasan, M. M.

2013-05-01

287

Charge carrier trapping and enhanced electroluminescent efficiency of blue light emitting polymer with gold nanoparticles.  

PubMed

We investigated the current injection, transport, and luminous efficiency behavior of organic light emitting diode (OLED) containing the 5-10 nm-sized gold particles mixed in the polyfluorene-type copolymer. This nanoparticle-conjugated polymer mixture layer was used as hole injection, transport, and light emitting layer for various structures of OLED based on the phosphorescent and fluorescent emitters. Due to the hole trapping at the nanopaticle, carrier injection is significantly reduced while the hole transport behavior is found to be barely affected. Hole trapping of nanoparticle in light emitting layer (at 4.7 approximately 9.4 x 10(-5) w/w fraction) resulted in an enhancement of efficiency (from 5.23 cd/A to 6.50 cd/A). The existence of the outcoupling effect also supports the carrier trapping behavior, which is amended mechanism of the improved efficiency compared to previously reported mechanism of enhanced photoluminescent stability by a hindrance of photo-oxidation. PMID:19908807

Park, Jong Hyeok; Choi, Yu-Ri; Chin, Byung Doo

2009-12-01

288

Energy Carrier Transport In Surface-Modified Carbon Nanotubes  

E-print Network

Carbon nanotubes are made into films or bulks, their surface or junction morphology in the networks can be modified to obtain desired electrical transport properties by various surface modification methods. The methods include incorporation...

Ryu, Yeontack

2012-11-30

289

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

PubMed Central

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

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

2014-01-01

290

A new charge pumping method for determining the spatial distribution of hot-carrier-induced fixed charge in p-MOSFETs  

Microsoft Academic Search

A charge pumping method is proposed for the direct measurement of the hot-carrier-induced fixed charge near the drain junction of p-MOSFETs. By holding the rising and falling slopes of the gate pulse constant and then varying the highest and lowest levels, the local threshold and local flatband voltages are readily obtained. The spatial distribution of fixed charges is directly calculated

Masakatsu Tsuchiaki; Hisashi Hara; Toyota Morimoto; Hiroshi Iwai

1993-01-01

291

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

NASA Astrophysics Data System (ADS)

Solar conversion to electricity or to fuels based on electron-hole pair production in semiconductors is a highly evolved scientific and commercial enterprise. Recently, it has been posited that charge carriers either directly transferred from the plasmonic structure to a neighbouring semiconductor (such as TiO2) or to a photocatalyst, or induced by energy transfer in a neighbouring medium, could augment photoconversion processes, potentially leading to an entire new paradigm in harvesting photons for practical use. The strong dependence of the wavelength at which the local surface plasmon can be excited on the nanostructure makes it possible, in principle, to design plasmonic devices that can harvest photons over the entire solar spectrum and beyond. So far, however, most such systems show rather small photocatalytic activity in the visible as compared with the ultraviolet. Here, we report an efficient, autonomous solar water-splitting device based on a gold nanorod array in which essentially all charge carriers involved in the oxidation and reduction steps arise from the hot electrons resulting from the excitation of surface plasmons in the nanostructured gold. Each nanorod functions without external wiring, producing 5 × 1013 H2 molecules per cm2 per s under 1 sun illumination (AM 1.5 and 100 mW cm-2), with unprecedented long-term operational stability.

Mubeen, Syed; Lee, Joun; Singh, Nirala; Krämer, Stephan; Stucky, Galen D.; Moskovits, Martin

2013-04-01

292

Electrical Conductivity of Rocks and Dominant Charge Carriers. Part 1; Thermally Activated Positive Holes  

NASA Technical Reports Server (NTRS)

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.

Freund, Friedemann T.; Freund, Minoru M.

2012-01-01

293

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

NASA Astrophysics Data System (ADS)

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 .

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

2015-01-01

294

Proton intercalated two-dimensional WO3 nano-flakes with enhanced charge-carrier mobility at room temperature  

NASA Astrophysics Data System (ADS)

Quasi two-dimensional (Q2D) semiconducting metal oxides with enhanced charge carrier mobility hold tremendous promise for nano-electronics, photonics, catalysis, nano-sensors and electrochromic applications. In addition to graphene and metal dichalcogenides MX2 (M = Mo, W; X = S, Se, Te), 2D sub-stoichiometric WO3-x is gaining importance as a promising semiconductor material for field-effect-transistor (FET) based devices. A combination of high permittivity, suppression of the Coulomb effects, and their stratified structure enhances the carrier mobility in such a material. Additionally, the sub-stoichiometry of this semiconductor oxide allows the reduction of the bandgap and increase of the free charge carriers at the same time. Here, we report for the first time H+ intercalated WO3 FETs, made of Q2D nano-flakes, with enhanced charge-carrier mobility exceeding 319 cm2 V-1 s-1 comparable with the charge-carrier mobility of Q2D dichalcogenides MoS2 and WSe2. Analyses indicate that the enhanced electrical properties of the sub-stoichiometric WO3-x depend on the oxygen vacancies in the intercalated nano-flakes. These findings confirmed that Q2D sub-stoichiometric WO3-x is a promising material for various functional FET devices.Quasi two-dimensional (Q2D) semiconducting metal oxides with enhanced charge carrier mobility hold tremendous promise for nano-electronics, photonics, catalysis, nano-sensors and electrochromic applications. In addition to graphene and metal dichalcogenides MX2 (M = Mo, W; X = S, Se, Te), 2D sub-stoichiometric WO3-x is gaining importance as a promising semiconductor material for field-effect-transistor (FET) based devices. A combination of high permittivity, suppression of the Coulomb effects, and their stratified structure enhances the carrier mobility in such a material. Additionally, the sub-stoichiometry of this semiconductor oxide allows the reduction of the bandgap and increase of the free charge carriers at the same time. Here, we report for the first time H+ intercalated WO3 FETs, made of Q2D nano-flakes, with enhanced charge-carrier mobility exceeding 319 cm2 V-1 s-1 comparable with the charge-carrier mobility of Q2D dichalcogenides MoS2 and WSe2. Analyses indicate that the enhanced electrical properties of the sub-stoichiometric WO3-x depend on the oxygen vacancies in the intercalated nano-flakes. These findings confirmed that Q2D sub-stoichiometric WO3-x is a promising material for various functional FET devices. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr05008h

Zhuiykov, Serge; Kats, Eugene; Carey, Benjamin; Balendhran, Sivacarendran

2014-11-01

295

Essential physics of carrier transport in nanoscale MOSFETs  

Microsoft Academic Search

The device physics of nanoscale MOSFETs is explored by numerical simulations of a model transistor. The physics of charge control, source velocity saturation due to thermal injection, and scattering in ultrasmall devices are examined. The results show that the essential physics of nanoscale MOSFETs can be understood in terms of a conceptually simple scattering model

Mark Lundstrom; Zhibin Ren

2002-01-01

296

Transportation of carriers in silicon implanted SiO 2 films during ionizing radiation  

NASA Astrophysics Data System (ADS)

Silicon ion implantation has been proved to be an effective method for total-dose hardening of SiO 2 in MOS devices such as buried oxides in SOI devices, while the mechanisms are still in discussion. In this work, behavior of 10 keV X-ray induced carriers in silicon implanted thermal SiO 2 was investigated by comparing with Ar implanted SiO 2. Photoluminescence (PL) spectroscopy and TRIM calculation were used to characterize the defects of the ion implanted SiO 2 films. Metal-Oxide-Semiconductor (MOS) structures were fabricated for electrical characterization of the oxides. Positive or negative gate bias was applied during the irradiation to control the separation and transportation of radiation induced electrons and holes. Flatband voltage shifts and are extracted from high frequency capacitance-voltage (C-V) measurement results which are taken prior to and after certain total dose irradiation. The experiment result shows that both Ar and Si implantation and followed anneal could eliminate the net positive charge in SiO 2 irradiated by X-ray. But different with Ar implanted oxide, in Si implanted oxide, the reduction of positive charge is highly dependent on the implanted Si ion fluence, and is well consistent with silicon nanoclusters evolvement tendency. From these results we conclude that along with increased electron trapping at the nanostructures which is suggested by previous studies, enhanced hole trapping and recombination caused by implantation induced vacancy defects are critical mechanism of reduced total ionizing dose effects on Si implanted oxides.

Chen, Ming; Zhang, Zhengxuan; Wei, Xing; Bi, Dawei; Zou, Shichang; Wang, Xi

2012-02-01

297

Dependence of nonproportionality in scintillators on diffusion of excitons and charge carriers  

NASA Astrophysics Data System (ADS)

The dipole-dipole and free-carrier Auger quenching processes that are generally regarded to be at the root of nonproportionality depend respectively on the 4th or 6th power of the electron track radius if modeled as cylindrical. In an initial time interval ? when nonlinear quenching and diffusion compete to reduce the density of excited states, the track radius expands as (Deff?)1/2 where Deff is the effective diffusion coefficient for the mixture of excitons and charge carriers. The range of Deff across semiconductor and scintillator radiation detectors is large, illustrated by 8 decades between mobilities of self-trapped holes in CsI:Tl and holes in high purity Ge. We present the functional form of nonlinear quenching predicted by diffusive track dilution and show that the simple model provides a surprisingly good fit of empirical nonproportionality across a wide range of semiconductor and oxide radiation detectors. We also show how diffusion drives nonlinear branching between excitons and free carriers in the track when electron and hole mobilities are unequal, and that this nonlinear branching coupled with linear trapping on defects can produce the "halide hump" seen in electron yield data for activated halide scintillators. Picosecond time-resolved spectroscopy in alkali halides, as well as quantitative comparison of recently measured 2nd order quenching rate constants K2 and results of K-dip spectroscopy, provide experimental benchmarks for consideration of carrier thermalization and the initial track or cluster radius r0 from which (nearly thermalized) diffusion is assumed to commence. The ratio of initial rate of 2nd order quenching to that of dilution by diffusion in a cylindrical track is proportional to K2/Deff and does not depend on r0 in lowest order; however, the absolute rates of both processes decrease with increasing r0.

Williams, R. T.; Li, Qi; Grim, Joel Q.; Ucer, K. B.

2011-09-01

298

Charge transport in columnar mesophases of carbazole macrocycles.  

PubMed

Charge transport properties of a columnar mesophase of carbazole macrocycles are analyzed. Realistic morphologies are sampled using all-atom molecular dynamics simulations while charge transport is simulated using the kinetic Monte Carlo method with transfer rates obtained from the high temperature nonadiabatic limit of Marcus theory. It is shown that the molecular design with side chains pointing inside the macrocycle allows close approach between molecules of neighboring columns, thus enabling three-dimensional transport and helping to circumvent charge trapping on structural defects. PMID:20942556

Vehoff, Thorsten; Baumeier, Björn; Andrienko, Denis

2010-10-01

299

DNA charge transport within the cell.  

PubMed

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

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

2015-02-01

300

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

...actual weight of HHG, PBP&E and temporary storage is less than the minimum weight charged...RELOCATION ALLOWANCES TRANSPORTATION AND STORAGE OF PROPERTY 7-TRANSPORTATION AND TEMPORARY STORAGE OF HOUSEHOLD GOODS AND PROFESSIONAL...

2010-07-01

301

Effects of Stress Activated Positive-Hole Charge Carriers on Radar Reflectance of Gabbro-Diorite  

NASA Astrophysics Data System (ADS)

When load is applied to igneous or high-grade metamorphic rocks, trapped electron vacancy defects are activated and become mobile positive-hole charge carriers. These mobile charge carriers repel each other through Coulomb interactions and move outward from the stressed region. As large numbers of positive-holes reach the surface of the rock, this surface charge may cause an observable change in radar reflectance. In this experiment, a series of holes is drilled into a large gabbro-diorite boulder from the A.R. Wilson Quarry in Aromas, CA. Bustar, an expansive, non-explosive demolition agent, is poured into the holes while a 1.2 GHz radar system measures the amplitude of radar waves reflected from the rock's surface. Over the course of the experiment, the radar antenna is swept repeatedly across one face of the rock, pausing in one of twelve positions to collect data before moving to the next position. At the end of each sweep, the radar is calibrated against both a corner reflector and a flat-plate reflector. This sampling method is employed to detect and assign a cause to transient effects observed at any one location. An initial analysis of the radar data shows a high level of agreement between readings from the flat-plate and corner reflectors, supporting the use of flat-plate reflectors as a calibration source for this omnidirectional radar system. Fitting a trend to the amplitude of the wave reflected from the rock's surface is complicated by the presence of unexpected outliers and noise artifacts from the radar system itself. It appears that such a trend, if present, would likely indicate a change in amplitude of the reflected signal of less than 5 percent over the course of the experiment.

Williams, C.; Vanderbilt, V. C.; Dahlgren, R.; Cherukupally, A.; Freund, F. T.

2011-12-01

302

Mobility and decay kinetics of charge carriers in photoexcited PCBM/PPV blends  

NASA Astrophysics Data System (ADS)

The transient photoconductivity of blends of a highly soluble C60 derivative (PCBM) and a dialkoxy-phenylene-vinylene polymer (MDMO-PPV) has been studied using the electrodeless flash-photolysis time-resolved microwave conductivity technique (FP-TRMC). Films approximately 100 nm thick on a quartz substrate were prepared by spin-coating PCBM/PPV solutions with PCBM weight fractions (WPCBM) from 0.2 to 0.95. For all blends, the wavelength dependence of the photoconductivity in the range 420 700 nm closely resembled the photon attenuation spectrum, indicating that photoexcitation of both components contributes to mobile charge carrier formation. The product of the quantum yield for charge separation ? and the sum of the charge carrier mobilities ?? was determined from the maximum (end-of-pulse) value of the transient photoconductivity. On excitation at 500 nm, ??? remained almost constant in going from WPCBM=0.2 to 0.6 with an average value of 0.6×10-3 cm2/V s. Above WPCBM=0.6, ??? increased dramatically, reaching a maximum value of 83×10-3 cm2/V s for WPCBM=0.85. This effect is attributed to the occurrence of phase separation above WPCBM=0.6 and to the resulting formation of highly mobile electrons within PCBM-rich aggregates. The much lower value of ??? observed below WPCBM=0.6 is assigned mainly to mobile holes within the polymer component of the blend. Possible explanations for the decrease in ??? with increasing light intensity, found for all blend compositions, are discussed.

Savenije, Tom J.; Kroeze, Jessica E.; Wienk, Martijn M.; Kroon, Johannes M.; Warman, John M.

2004-04-01

303

Charge transport studies of polymeric photovoltaic thin films with an electron blocking and trapping layer  

NASA Astrophysics Data System (ADS)

The transport properties of two photovoltaic polymers, poly(3-hexylthiophene) (P3HT) and poly(2,7-carbazole) derivative (PCDTBT), and their polymer:fullerene bulk heterojunction (BHJ) are studied by space-charge-limited current (SCLC), dark-injection space-charge-limited current (DI-SCLC), and admittance spectroscopy(AS). For a nominally hole-only device, electrons leakage occurs. This results in a current larger than the theoretical SCLC and ill-defined DI-SCLC and AS signals. In order to prevent electron leakage, a hole-transporting but electron blocking/trapping thin layer is added between active layer and Au. The layer composed of copper phthalocyanine (CuPc) doped into an amine-based small molecule. Using this interlayer, well-defined carrier transit time can be obtained for mobility extraction. With a suitable interlayer to suppress undesirable carrier injection and transport, these techniques should find broad applications in the transport characterization of narrow gap photovoltaic polymers and BHJ blends.

Lee, Harrison K. H.; Chan, Kevin K. H.; So, S. K.

2012-06-01

304

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

Code of Federal Regulations, 2014 CFR

...SECURITY THREAT ASSESSMENTS Transportation of Hazardous Materials From Canada or Mexico To and Within the United States by Land Modes § 1572.203 Transportation of explosives from Canada to the United States via railroad carrier. (a)...

2014-10-01

305

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

Code of Federal Regulations, 2010 CFR

...SECURITY THREAT ASSESSMENTS Transportation of Hazardous Materials From Canada or Mexico To and Within the United States by Land Modes § 1572.203 Transportation of explosives from Canada to the United States via railroad carrier. (a)...

2010-10-01

306

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

Code of Federal Regulations, 2013 CFR

...SECURITY THREAT ASSESSMENTS Transportation of Hazardous Materials From Canada or Mexico To and Within the United States by Land Modes § 1572.203 Transportation of explosives from Canada to the United States via railroad carrier. (a)...

2013-10-01

307

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

Code of Federal Regulations, 2011 CFR

...SECURITY THREAT ASSESSMENTS Transportation of Hazardous Materials From Canada or Mexico To and Within the United States by Land Modes § 1572.203 Transportation of explosives from Canada to the United States via railroad carrier. (a)...

2011-10-01

308

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

Code of Federal Regulations, 2012 CFR

...SECURITY THREAT ASSESSMENTS Transportation of Hazardous Materials From Canada or Mexico To and Within the United States by Land Modes § 1572.203 Transportation of explosives from Canada to the United States via railroad carrier. (a)...

2012-10-01

309

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

NASA Astrophysics Data System (ADS)

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

Kim, Kwangsik; Won, Taeyoung

2013-10-01

310

CHARACTERIZING COUPLED CHARGE TRANSPORT WITH MULTISCALE MOLECULAR DYNAMICS  

SciTech Connect

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.

Swanson, Jessica

2011-08-31

311

Liquid-phase microextraction based on carrier mediated transport combined with liquid chromatography–mass spectrometry  

Microsoft Academic Search

Recently, we demonstrated for the first time liquid-phase microextraction (LPME) of polar drugs based on carrier mediated transport. In this new extraction technique, selected analytes were extracted as ion-pairs from small volumes of biological samples, through a thin layer of a water immiscible organic solvent immobilised in the pores of a porous hollow fibre (liquid membrane), and into a ?l

Tung Si Ho; Jan Leon Egge Reubsaet; Hanne Sofie Anthonsen; Stig Pedersen-Bjergaard; Knut Einar Rasmussen

2005-01-01

312

Polar transport of auxin: carrier-mediated flux across the plasma membrane or neurotransmitter-like  

E-print Network

Polar transport of auxin: carrier-mediated flux across the plasma membrane or neurotransmitter of Bonn, Institute of Botany, Kirschallee 1, Bonn, D-53115, Germany. Auxin (indole-3-acetic acid) has its and development. Auxin is a small molecule derived from the amino acid tryptophan and has both hormone

Bonn, Universität

313

Carrier transport properties in single-walled carbon nanotubes studied by photoluminescence spectroscopy  

E-print Network

Carrier transport properties in single-walled carbon nanotubes studied by photoluminescence. We have investigated the photoluminescence (PL) of in individual single-walled carbon nanotubes-field dependence of PL intensity. Time-resolved photoluminescence of SWNTs dispersed in surfactant solution has

Maruyama, Shigeo

314

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

E-print Network

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

Miller, David A. B.

315

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

NASA Astrophysics Data System (ADS)

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.

Shaw, Bikash Kumar; Saha, Shyamal K.

2014-09-01

316

14 CFR 382.21 - May carriers limit access to transportation on the basis that a passenger has a communicable...  

Code of Federal Regulations, 2013 CFR

...carriers limit access to transportation on the basis that a passenger has a communicable disease...REGULATIONS NONDISCRIMINATION ON THE BASIS OF DISABILITY IN AIR TRAVEL Nondiscrimination...carriers limit access to transportation on the basis that a passenger has a communicable...

2013-01-01

317

14 CFR 382.21 - May carriers limit access to transportation on the basis that a passenger has a communicable...  

Code of Federal Regulations, 2014 CFR

...carriers limit access to transportation on the basis that a passenger has a communicable disease...REGULATIONS NONDISCRIMINATION ON THE BASIS OF DISABILITY IN AIR TRAVEL Nondiscrimination...carriers limit access to transportation on the basis that a passenger has a communicable...

2014-01-01

318

14 CFR 382.21 - May carriers limit access to transportation on the basis that a passenger has a communicable...  

Code of Federal Regulations, 2011 CFR

...carriers limit access to transportation on the basis that a passenger has a communicable disease...REGULATIONS NONDISCRIMINATION ON THE BASIS OF DISABILITY IN AIR TRAVEL Nondiscrimination...carriers limit access to transportation on the basis that a passenger has a communicable...

2011-01-01

319

14 CFR 382.21 - May carriers limit access to transportation on the basis that a passenger has a communicable...  

Code of Federal Regulations, 2012 CFR

...carriers limit access to transportation on the basis that a passenger has a communicable disease...REGULATIONS NONDISCRIMINATION ON THE BASIS OF DISABILITY IN AIR TRAVEL Nondiscrimination...carriers limit access to transportation on the basis that a passenger has a communicable...

2012-01-01

320

Design and Development of SPC90 Slag Pot Carrier of Large Steel Slag Transportation Special Device for Steel Mills  

Microsoft Academic Search

In order to ease the contradiction between steel slag transportation and the development of steel mills equipment technology of domestic, the SPC90 slag pot carrier has been designed and developed. The maximum rated load of SPC90 Slag pot Carrier is 90 ton, which can cooperate with many kinds of bridge machine for the railway passenger transport special line to complete

Guo Rui; Li Na; Zhao Jingyi

2010-01-01

321

Towards high charge-carrier mobilities by rational design of the shape and periphery of discotics  

Microsoft Academic Search

Discotic liquid crystals are a promising class of materials for molecular electronics thanks to their self-organization and charge transporting properties. The best discotics so far are built around the coronene unit and possess six-fold symmetry. In the discotic phase six-fold-symmetric molecules stack with an average twist of 30o, whereas the angle that would lead to the greatest electronic coupling is

Xinliang Feng; Valentina Marcon; Wojciech Pisula; Michael Ryan Hansen; James Kirkpatrick; Ferdinand Grozema; Denis Andrienko; Kurt Kremer; Klaus Müllen

2009-01-01

322

An acoustic charge transport imager for high definition television applications  

NASA Technical Reports Server (NTRS)

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.

Hunt, William D.; Brennan, Kevin F.; Summers, Chris J.

1992-01-01

323

Selection of Metal Oxide Charge Transport Layers for Colloidal Quantum  

E-print Network

02139 L ight emitting devices (LEDs) that uti- lize colloidal quantum dots (QDs) as luminescent centersSelection of Metal Oxide Charge Transport Layers for Colloidal Quantum Dot LEDs V. Wood,* M. J. To date, QD-LED demonstrations used semi- conducting polymers, molecular organics, and ceramics as charge

324

Triboelectric charging of polymer powders in fluidization and transport processes  

Microsoft Academic Search

In this paper, we investigated the role of tribocharging in fluidization, flowability, and q\\/m distribution as functions of particle size distribution (PSD), fluidization time, and transport tubes of different materials. A charge separator was used to determine mass fractions of powder that had positive, zero, and negative charges. For the two acrylic powders tested, one (Sample A) had volume median

Malay K. Mazumder; Robert A. Sims; David L. Wankum; Tony Chasser

2001-01-01

325

Charge transport properties of CdMnTe radiation detectors  

Microsoft Academic Search

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

Kim K; R. Rafiel; M. Boardman; I. Reinhard; A. Sarbutt; G. Watt; C. Watt; S. Uxa; D. A. Prokopovich; E. Belas; A. E. Bolotnikov; R. B. James

2012-01-01

326

Proton intercalated two-dimensional WO3 nano-flakes with enhanced charge-carrier mobility at room temperature.  

PubMed

Quasi two-dimensional (Q2D) semiconducting metal oxides with enhanced charge carrier mobility hold tremendous promise for nano-electronics, photonics, catalysis, nano-sensors and electrochromic applications. In addition to graphene and metal dichalcogenides MX2 (M = Mo, W; X = S, Se, Te), 2D sub-stoichiometric WO(3-x) is gaining importance as a promising semiconductor material for field-effect-transistor (FET) based devices. A combination of high permittivity, suppression of the Coulomb effects, and their stratified structure enhances the carrier mobility in such a material. Additionally, the sub-stoichiometry of this semiconductor oxide allows the reduction of the bandgap and increase of the free charge carriers at the same time. Here, we report for the first time H(+) intercalated WO(3) FETs, made of Q2D nano-flakes, with enhanced charge-carrier mobility exceeding 319 cm(2) V(-1) s(-1) comparable with the charge-carrier mobility of Q2D dichalcogenides MoS(2) and WSe(2). Analyses indicate that the enhanced electrical properties of the sub-stoichiometric WO(3-x) depend on the oxygen vacancies in the intercalated nano-flakes. These findings confirmed that Q2D sub-stoichiometric WO(3-x) is a promising material for various functional FET devices. PMID:25367432

Zhuiykov, Serge; Kats, Eugene; Carey, Benjamin; Balendhran, Sivacarendran

2014-12-21

327

Disorder-induced transition from Gaussian to dispersive carrier transport in molecularly doped polymers  

Microsoft Academic Search

Dynamics of hopping charge transport in a polymer matrix doped with two different charge-transport molecules was studied by means of time-of-flight (TOF) photoconductivity measurements. In polymers doped with two molecules of little different ionization potential, the Gaussian (near-rectangular) TOF signal was observed over all compositions and the tail of the Gaussian TOF signal is broadened by a wide distribution of

Yoshihiko Kanemitsu; Hiroshi Funada; Yasuaki Masumoto

1991-01-01

328

Effect of uniaxial compression on traps of excitons and charge carriers in poly(9-vinylcarbazole) films  

NASA Astrophysics Data System (ADS)

The effect of uniaxial pressure (1 × 108 Pa) on the photoluminescence spectra and thermally stimulated luminescence curves of poly(9-vinylcarbazole) has been investigated in the temperature range of 5-295 K. The thermally stimulated luminescence curve of crystalline carbazole has been measured for comparison. The high-temperature wings of the thermally stimulated luminescence curves are approximated by a Gaussian function, the half-width of which characterizes the disorder of energy states of deep structural traps. It is concluded that the pressure inhibits conformational changes of polymer chains of poly(9-vinylcarbazole), which leads to the formation of sandwich-like excimers as well as to an ordering of the spatial arrangement of the side carbazolyl groups. As a result, the concentration of "excimer-forming" centers increases, whereas the degree of disorder of energy states of deep structural traps of charge carriers is reduced by almost half and remains unchanged after the depressurization.

Skryshevski, Yu. A.

2014-03-01

329

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

PubMed

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

Maragliano, C; Lilliu, S; Dahlem, M S; Chiesa, M; Souier, T; Stefancich, M

2014-01-01

330

Charge-carrier dynamics in single-wall carbon nanotube bundles: a time-domain study  

NASA Astrophysics Data System (ADS)

We present a real-time investigation of ultra-fast carrier dynamics in single-wall carbon nanotube bundles using femtosecond time-resolved photoelectron spectroscopy. The experiments allow us to study the processes governing the sub-picosecond and the picosecond dynamics of non-equilibrium charge carriers. On the sub-picosecond time scale the dynamics are dominated by ultra-fast electron-electron scattering processes, which lead to internal thermalization of the laser-excited electron gas. We find that quasiparticle lifetimes decrease strongly as a function of their energy up to 2.38 eV above the Fermi level - the highest energy studied experimentally. The subsequent cooling of the laser-heated electron gas to the lattice temperature by electron-phonon interaction occurs on the picosecond time scale and allows us to determine the electron-phonon mass-enhancement parameter ?. The latter is found to be over an order of magnitude smaller if compared, for example, with that of a good conductor such as copper.

Hertel, T.; Fasel, R.; Moos, G.

331

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

PubMed Central

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

Maragliano, C.; Lilliu, S.; Dahlem, M. S.; Chiesa, M.; Souier, T.; Stefancich, M.

2014-01-01

332

Electrodeless measurement of charge carrier mobility in pentacene by microwave and optical spectroscopy techniques  

NASA Astrophysics Data System (ADS)

Photoinduced transient conductivity of pentacene thin films prepared by thermal vapor deposition is investigated using time-resolved microwave conductivity (TRMC) measurements, giving intrinsic charge carrier mobility in highly ordered structures without any electrode attached. The real and imaginary conductivity values are analyzed and compared with those predicted by molecular orbital calculations. The effects of substrate surface treatment by hexamethyldisilazane are discussed on the basis of kinetic traces of conductivity and morphology. A mobility of >0.7cm2/Vs was obtained from the TRMC measurements and analysis of transient absorption spectra. The measurement of field-effect-transistor mobility in single-crystal domains requires not only complicated fabrication techniques but also many assumptions on the carrier channels, density, injection, etc. The combination of TRMC and transient optical spectroscopy provides an approach for addressing this issue. The present technique is applicable to a wide variety of organic semiconducting materials. Moreover, it is the only technique revealing the intrinsic potentials of mobility in materials that is supported by complete experimental and quantitative procedures not based on any assumptions.

Saeki, Akinori; Seki, Shu; Tagawa, Seiichi

2006-07-01

333

Ultrahigh-frequency surface acoustic wave generation for acoustic charge transport in silicon  

NASA Astrophysics Data System (ADS)

We demonstrate piezo-electrical generation of ultrahigh-frequency surface acoustic waves on silicon substrates, using high-resolution UV-based nanoimprint lithography, hydrogen silsequioxane planarization, and metal lift-off. Interdigital transducers were fabricated on a ZnO layer sandwiched between two SiO2 layers on top of a Si substrate. Excited modes up to 23.5 GHz were observed. Depth profile calculations of the piezoelectric field show this multilayer structure to be suitable for acoustic charge transport in silicon at extremely high frequencies with moderate carrier mobility requirements.

Büyükköse, S.; Vratzov, B.; van der Veen, J.; Santos, P. V.; van der Wiel, W. G.

2013-01-01

334

Carriers transport properties in GaInP solar cells grown by molecular beam epitaxy  

NASA Astrophysics Data System (ADS)

The transport properties of carriers in GaInP solar cells grown by molecular beam epitaxy are investigated by temperature-dependent current-voltage (I-V) measurements. In contrast to GaInP/AlGaInP heterostructure, a long PL decay time is observed in GaInP/AlInP, which is ascribed to a lower interface recombination due to an improved carriers' confinement in the case of the high-energy barrier. However, the series resistance induced by the high potential barrier at GaInP/AlInP interface due to a big valence band offset prevents the improvement of solar cell's performance. An S-shape like I-V characteristic observed at low temperatures indicates that the transport of major carriers is limited by the barrier. A calculation based on the combination of a normal photovoltaic device with a barrier-affected thermal carriers transport explicitly explains this abnormal I-V characteristic. Our study demonstrates the critical role of the barrier-induced series resistance in the determination of solar cell's performance.

Dai, P.; Lu, S. L.; Arimochi, M.; Uchida, S.; Watanabe, T.; Luo, X. D.; Yang, H.

2014-12-01

335

Simulation of charge transport in pixelated CdTe  

NASA Astrophysics Data System (ADS)

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.

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

2014-12-01

336

Simulation of charge transport in pixelated CdTe  

PubMed Central

The Voxel Imaging PET (VIP) Pathfinder project intends to show the advantages of using pixelated semiconductor technology for nuclear medicine applications to achieve an improved image reconstruction without efficiency loss. It proposes designs for Positron Emission Tomography (PET), Positron Emission Mammography (PEM) and Compton gamma camera detectors with a large number of signal channels (of the order of 106). The design is based on the use of a pixelated CdTe Schottky detector to have optimal energy and spatial resolution. An individual read-out channel is dedicated for each detector voxel of size 1 × 1 × 2 mm3 using an application-specific integrated circuit (ASIC) which the VIP project has designed, developed and is currently evaluating experimentally. The behaviour of the signal charge carriers in CdTe should be well understood because it has an impact on the performance of the readout channels. For this purpose the Finite Element Method (FEM) Multiphysics COMSOL software package has been used to simulate the behaviour of signal charge carriers in CdTe and extract values for the expected charge sharing depending on the impact point and bias voltage. The results on charge sharing obtained with COMSOL are combined with GAMOS, a Geant based particle tracking Monte Carlo software package, to get a full evaluation of the amount of charge sharing in pixelated CdTe for different gamma impact points. PMID:25729404

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

2014-01-01

337

Glucose transport carrier of human erythrocytes. Radiation target size measurement based on flux inactivation  

SciTech Connect

Intact human erythrocytes frozen in the presence of cryoprotective reagents and irradiated with an electron beam retained their diffusion barrier to L-glucose. The carrier-mediated flux of D-glucose, on the other hand, was inactivated as a simple exponential function of the radiation dose. Classical target size analysis of this data yielded a molecular size of 185,000 daltons for the carrier. This represents the first measurement of the functional size of a transport protein based directly on flux inactivation.

Cuppoletti, J.; Jung, C.Y.; Green, F.A.

1981-02-10

338

Tuning charge transport in pentacene thin-film transistors using the strain-induced electron-phonon coupling modification  

NASA Astrophysics Data System (ADS)

Tuning charge transport in the bottom-contact pentacene-based organic thin-film transistors (OTFTs) using a MoO x capping layer that serves to the electron-phonon coupling modification is reported. For OTFTs with a MoO x front gate, the enhanced field-effect carrier mobility is investigated. The time domain data confirm the electron-trapping model. To understand the origin of a mobility enhancement, an analysis of the temperature-dependent Hall-effect characteristics is presented. Similarly, the Hall-effect carrier mobility was dramatically increased by capping a MoO x layer on the pentacene front surface. However, the carrier concentration is not affected. The Hall-effect carrier mobility exhibits strong temperature dependence, indicating the dominance of tunneling (hopping) at low (high) temperatures. A mobility enhancement is considered to come from the electron-phonon coupling modification that results from the contribution of long-lifetime electron trapping.

Lin, Yow-Jon; Chang, Hsing-Cheng; Liu, Day-Shan

2015-03-01

339

[Evidence for mobile transport structures (carriers) involved in ion transport in plants and kinetics of anion transport in elodea in light and dark].  

PubMed

Influx and efflux of anions in leaves of Elodea canadensis were investigated. A major component of phosphate efflux was found to be a function of the external phosphate concentration in accord with saturation kinetics, i.e. it was found to be proportional to phosphate influx. This suggests that the transport structures which mediate ion transport in plant membranes are mobile and can work in both directions (Fig. 7C). The higher the external concentration the more bound ions (A b (-) , Fig. 7C) are exchanged for external ions (A a (-) ) instead of being transported back to the inside of the membrane. Thus it was demonstrated that ion transport in plants is mediated by carriers or transportases. The action of the carriers is supported by ATP or another "energy-rich" compound which is regenerated by ATP; ATP may be supplied by the mitochondria or/and chloroplasts. In line with these findings some transport phenomena exhibited features of coenzyme kinetics.Magnitude and molecular nature of the carrier motion are unknown. There is no evidence for rotating or shuttling monovalent carriers. The carriers may be polyvalent and may be part of bigger structural units within the membrane. Nevertheless, these experimental observations are rather consistent with the idea that plant membranes contain tertiary or quarternary formed proteins or lipoproteins than with the conventional lipid bilayer models of cell membranes. PMID:24549340

Weigl, J

1967-12-01

340

Verification of three dimensional charge transport simulations using ion microbeams  

SciTech Connect

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

Horn, K.M.; Dodd, P.E. [Sandia National Labs., Albuquerque, NM (United States); Breese, M.B.H. [Oxford Univ. (United Kingdom). Dept. of Physics; Doyle, B.L. [Sandia National Labs., Albuquerque, NM (United States)

1996-12-31

341

Scaling theory for percolative charge transport in disordered molecular semiconductors.  

PubMed

We present a scaling theory for charge transport in disordered molecular semiconductors that extends percolation theory by including bonds with conductances close to the percolating one in the random-resistor network representing charge hopping. A general and compact expression is given for the charge mobility for Miller-Abrahams and Marcus hopping on different lattices with Gaussian energy disorder, with parameters determined from numerically exact results. The charge-concentration dependence is universal. The model-specific temperature dependence can be used to distinguish between the hopping models. PMID:22026880

Cottaar, J; Koster, L J A; Coehoorn, R; Bobbert, P A

2011-09-23

342

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

SciTech Connect

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.

Said, H.M.; Redha, R.

1987-01-01

343

41 CFR 301-10.309 - What will I be reimbursed if I am authorized to use common carrier transportation and I use a POV...  

Code of Federal Regulations, 2010 CFR

...not to exceed the total constructive cost of the authorized method of common carrier transportation plus per diem. Your agency must determine the constructive cost of transportation and per diem by common carrier...

2010-07-01

344

Effect of reduction of trap charge carrier density in organic field effect transistors by surface treatment of dielectric layer  

SciTech Connect

In this work, we have studied the effect of surface treatment of SiO{sub 2} dielectric layer on the reduction of the trap charge carrier density at dielectric/semiconducting interface by fabricating a metal–insulator–semiconductor (MIS) device using ?, ?-dihexylcarbonylquaterthiophene as semiconducting layer. SiO{sub 2} dielectric layer has been treated with 1,1,1,3,3,3-hexamethyldisilazane (HMDS) to modify the chemical group acting as charge traps. Capacitance-voltage measurements have been performed on MIS devices fabricated on SiO{sub 2} and HMDS treated SiO{sub 2}. These data have been used for the calculation of trap charge carrier density and Debye length at the dielectric-semiconductor interface. The calculated trap charge carrier density has been found to reduce from (2.925?±?0.049) × 10{sup 16}?cm{sup ?3} to (2.025?±?0.061) × 10{sup 16}?cm{sup ?3} for the MIS device with HMDS treated SiO{sub 2} dielectric in comparison to that of untreated SiO{sub 2}. Next, the effect of reduction in trap charge carrier density has been studied on the performance of organic field effect transistors. The improvement in the device parameters like mobility, on/off ratio, and gate leakage current has been obtained with the effect of the surface treatment. The charge carrier mobility has been improved by a factor of 2 through this treatment. Further, the influence of the treatment was observed by atomic force microscope and Fourier transform infrared spectroscopy techniques.

Dagar, Janardan; Yadav, Vandana; Kumar Singh, Rajiv; Suman, C. K.; Srivastava, Ritu, E-mail: ritu@mail.nplindia.org [Physics of Energy Harvesting Division, CSIR-National Physical Laboratory, CSIR-Network of Institute for Solar Energy (NISE), Dr. K.S.Krishnan Road, New Delhi 110012 (India); Tyagi, Priyanka [Physics of Energy Harvesting Division, CSIR-National Physical Laboratory, CSIR-Network of Institute for Solar Energy (NISE), Dr. K.S.Krishnan Road, New Delhi 110012 (India); Center for Applied Research in Electronics, Indian Institute of Technology Delhi, New Delhi 110016 (India)

2013-12-14

345

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

NASA Technical Reports Server (NTRS)

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.

Von Roos, O.

1983-01-01

346

Transparent Conducting Oxides: Texture and Microstructure Effects on Charge Carrier Mobility in MOCVD-Derived CdO  

E-print Network

Transparent Conducting Oxides: Texture and Microstructure Effects on Charge Carrier Mobility of highly conductive and transparent CdO thin films. One member of the series, bis(1,1,1,5,5,5-hexafluoro-2 such as transparent conducting oxides1-3 (TCOs) and photovoltaic (PV) active layers.4 The widespread use of TCOs

Poeppelmeier, Kenneth R.

347

Surface charge transport and decay in dielectric barrier discharges  

NASA Astrophysics Data System (ADS)

In this work, we investigate the decay of electric charge that remains after the extinction of a barrier discharge on top of a dielectric surface. The amount of surface charge is determined spatially and temporally resolved via the Pockels effect of a BSO crystal. It is shown that the decay of charge is performed by two different processes. One channel of decay can be identified as the photoconductivity of the BSO crystal. The other decay channel is found to depend on the polarity of charge and the working gas parameters. For an inhomogeneous surface charge distribution, charge transport on the crystal surface has been observed. It takes place on a time scale of several seconds.

Wild, R.; Benduhn, J.; Stollenwerk, L.

2014-10-01

348

Charge transport analysis of poly(3-hexylthiophene) by electroreflectance spectroscopy  

NASA Astrophysics Data System (ADS)

The charge transport in organic semiconductors is still not completely understood. We use electroreflectance spectroscopy to investigate charge transport in organic field effect devices in order to obtain optical information on the charges within the charge accumulation layer at the organic semiconductor-insulator interface. Here, the reflectance geometry allows an analysis of devices prepared on opaque substrates. The recorded spectra were analyzed based on optical layer stack simulations to extract quantitatively the change of the dielectric function due to the charge injection of the accumulation layer in poly(3-hexylthiophene) (P3HT). For the simulation the anisotropic optical response of spin-coated P3HT layers is experimentally determined by spectroscopic ellipsometry. Using the developed theoretical approach the characteristic change of three different preparations of the organic semiconductor-insulator interface is analyzed. Laterally resolved measurements close to an injecting contact have revealed characteristic spectral changes in dependence of the preparation conditions, and significant spectral changes within the first 90?m from the contact were found, which were attributed to an energetic relaxation of charges during the charge transport process.

Pittner, Steve; Lehmann, Daniel; Zahn, Dietrich R. T.; Wagner, Veit

2013-03-01

349

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

PubMed Central

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

Wilson, Mike R.; Hou, Zhanjun

2014-01-01

350

The major facilitative folate transporters solute carrier 19A1 and solute carrier 46A1: biology and role in antifolate chemotherapy of cancer.  

PubMed

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

Matherly, Larry H; Wilson, Mike R; Hou, Zhanjun

2014-04-01

351

77 FR 15187 - Released Rates of Motor Common Carriers of Household Goods  

Federal Register 2010, 2011, 2012, 2013, 2014

...DEPARTMENT OF TRANSPORTATION Surface Transportation Board [Docket No. RR...Common Carriers of Household Goods AGENCY: Surface Transportation Board. ACTION: Notice...addition, the Board affirmed that the charges for full-value protection when the...

2012-03-14

352

Homodimeric Intrinsic Membrane Proteins. Identification and Modulation of Interactions between Mitochondrial Transporter (Carrier) Subunits  

PubMed Central

Transporter (carrier) proteins of the inner mitochondrial membrane link metabolic pathways within the matrix and the cytosol with transport/exchange of metabolites and inorganic ions. Their strict control of these fluxes is required for oxidative phosphorylation. Understanding the ternary complex transport mechanism with which most of these transporters function requires an accounting of the number and interactions of their subunits. The phosphate transporter (PTP, Mir1p) subunit readily forms homodimers with intersubunit affinities changeable by mutations. Cys28, likely at the subunit interface, is a site for mutations yielding transport inhibition or a channel-like transport mode. Such mutations yield a small increase or decrease in affinity between the subunits. The PTP inhibitor N-ethylmaleimide decreases subunit affinity by a small amount. PTP mutations that yield the highest (40%) and the lowest (2%) liposome incorporation efficiencies (LIE) are clustered near Cys28. Such mutant subunits show the lowest and highest subunit affinities respectively. The oxaloacetate transporter (Oac1p) subunit has an almost 2-fold lower affinity than the PTP subunit. The Oac1p, dicarboxylate (Dic1p) and PTP transporter subunits form heterodimers with even lower affinities. These results form a firm basis for detailed studies to establish the effect of subunit affinities on transport mode and activity and for the identification of the mechanism that prevents formation of heterodimers that surely will negatively impact oxidative phosphorylation and ATP levels with serious consequences for the cell. PMID:20171189

Wohlrab, Hartmut

2010-01-01

353

Magnetic and charge carriers properties of metamagnetic Fe3Ga4  

NASA Astrophysics Data System (ADS)

Single crystals of Fe3Ga4 were grown via an iodine vapor transport method. Previous investigations of arc-melted polycrystalline samples identify metallic conduction with a magnetic phase transition at 400 K and interesting temperature-dependent metamagnetic behavior. The single crystal samples allow a much fuller exploration of the magnetic properties and have yielded some interesting differences with the previous data. This includes a sharp reduction of the magnetization within the magnetically ordered phase associated with a sharp onset of the metamagnetic behavior in the field dependence near room temperature. A previously identified second phase transition occurs below 50 K where the metamagnetic behavior is replaced by a ferromagnetic magnetization with little hysteresis. We find substantial anisotropy in the magnetization which is particularly apparent between 50 and 300 K. Charge transport experiments are underway to explore the magnetoresistance and Hall effect of this magnet.

Mendez, Joshua; Wu, Yan; Fulfer, Bradford; Chan, Julia; Ditusa, John

2012-02-01

354

High-field charge transport on the surface of Bi2Se3  

NASA Astrophysics Data System (ADS)

We present a theoretical study on the high-field charge transport on the surface of Bi2Se3 and reproduce all the main features of the recent experimental results, i.e., the incomplete current saturation and the finite residual conductance in the high applied field regime [Costache et al., Phys. Rev. Lett. 112, 086601 (2014), 10.1103/PhysRevLett.112.086601]. Due to the hot-electron effect, the conductance decreases and the current shows a tendency of saturation with the increase of the applied electric field. Moreover, the electric field can excite carriers within the surface bands through interband precession and leads to a higher conductance. As a joint effect of the hot-electron transport and the carrier excitation, the conductance approaches a finite residual value in the high-field regime and the current saturation becomes incomplete. We thus demonstrate that, contrary to the conjecture in the literature, the observed transport phenomena can be understood qualitatively in the framework of surface transport alone. Furthermore, if a constant bulk conductance which is insensitive to the field is introduced, one can obtain a good quantitative agreement between the theoretical results and the experimental data.

Weng, M. Q.; Wu, M. W.

2014-09-01

355

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)

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.

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

2015-01-01

356

Comparison of two dynamic transportation models: The case of Stockholm congestion charging  

E-print Network

, Congestion pricing, Road pricing, Transportation models, Dynamic assignment, Mesoscopic models, Departure1 Comparison of two dynamic transportation models: The case of Stockholm congestion charging Leonid) Abstract This paper reviews the transportation models used for predicting impacts of congestion charging

Paris-Sud XI, Université de

357

Effect of Molecular Chain Orientation on Carrier Transport and Trapping in Polymer Blends  

Microsoft Academic Search

Carrier transport and trapping effects, as they are influenced by molecular chain orientation, were investigated by Thermally Stimulated Currents (TSC) and Current-Voltage (IV) characteristics in the samples of poly(9-vinylcarbazole) (PVK) doped with 30% wt 4-dibutylamino-4?-nitrostilbene (DBANS). The orientation of DBANS, diode-like molecules, was performed by electric field above the glass transition temperature. We demonstrate that the orientation of polar molecules

V. Kažukauskas; V. ?yras; L. Sicot; C. Sentein

2006-01-01

358

pH Regulation of Divalent/Monovalent Ca/K Cation Transport Selectivity by a Macrocyclic Carrier Molecule  

NASA Astrophysics Data System (ADS)

The lipophilic dicarboxylic acid-dicarboxamide macrocycle 1 is an efficient carrier for calcium and potassium transport through a liquid membrane. The process involves competitive Ca2+/K+ symport coupled to proton antiport in a pH gradient. It presents a very pronounced phenomenon of pH regulation of transport selectivity from preferential K+ transport to preferential Ca2+ transport as the pH increases from 2 to 9 in the starting aqueous phase containing the metal ions. The results demonstrate how carrier design allows control of the rate and selectivity of divalent/monovalent M2+/M+ cation transport.

Hriciga, Ann; Lehn, Jean-Marie

1983-10-01

359

Charge and spin transport in PEDOT:PSS nanoscale lateral devices  

NASA Astrophysics Data System (ADS)

The electrical transport of the highly conductive poly-(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) is investigated with Ohmic and spin-polarized tunnel contacts at nanoscale lateral dimensions. Temperature-dependent charge transport measurements reveal that electrical conductivity scales non-linearly as a function of electrode spacing, which is attributed to the localization of carriers induced by the disorder introduced by the PSS polyelectrolyte. In addition, we demonstrate the integration of this conducting polymer in nanoscale lateral spin-valve devices by increasing the pH of the PEDOT:PSS solution. We present charge and magnetotransport measurement results of NiFe/AlOx/PEDOT:PSS/AlOx/NiFe lateral structures for various thicknesses of the alumina tunnel barriers. We discuss the absence of magnetoresistance of our spin valves within the framework of Valet-Fert theory, and estimate an upper limit for the spin lifetime of carriers in PEDOT:PSS to ?sf ? 50 ns.

de Oliveira, Thales V. A. G.; Gobbi, Marco; Porro, José M.; Hueso, Luis E.; Bittner, Alexander M.

2013-11-01

360

Carrier Transport in High Mobility InAs Nanowire Junctionless Transistors.  

PubMed

The ability to understand and model the performance limits of nanowire transistors is the key to the design of next generation devices. Here, we report studies on high-mobility junctionless gate-all-around nanowire field effect transistor with carrier mobility reaching 2000 cm(2)/V·s at room temperature. Temperature-dependent transport measurements reveal activated transport at low temperatures due to surface donors, while at room temperature the transport shows a diffusive behavior. From the conductivity data, the extracted value of sound velocity in InAs nanowires is found to be an order less than the bulk. This low sound velocity is attributed to the extended crystal defects that ubiquitously appear in these nanowires. Analyzing the temperature-dependent mobility data, we identify the key scattering mechanisms limiting the carrier transport in these nanowires. Finally, using these scattering models, we perform drift-diffusion based transport simulations of a nanowire field-effect transistor and compare the device performances with experimental measurements. Our device modeling provides insight into performance limits of InAs nanowire transistors and can be used as a predictive methodology for nanowire-based integrated circuits. PMID:25658044

Konar, Aniruddha; Mathew, John; Nayak, Kaushik; Bajaj, Mohit; Pandey, Rajan K; Dhara, Sajal; Murali, K V R M; Deshmukh, Mandar M

2015-03-11

361

Carrier injection and transport in blue phosphorescent organic light-emitting device with oxadiazole host.  

PubMed

In this paper, we investigate the carrier injection and transport characteristics in iridium(III)bis[4,6-(di-fluorophenyl)-pyridinato-N,C2']picolinate (FIrpic) doped phosphorescent organic light-emitting devices (OLEDs) with oxadiazole (OXD) as the bipolar host material of the emitting layer (EML). When doping Firpic inside the OXD, the driving voltage of OLEDs greatly decreases because FIrpic dopants facilitate electron injection and electron transport from the electron-transporting layer (ETL) into the EML. With increasing dopant concentration, the recombination zone shifts toward the anode side, analyzed with electroluminescence (EL) spectra. Besides, EL redshifts were also observed with increasing driving voltage, which means the electron mobility is more sensitive to the electric field than the hole mobility. To further investigate carrier injection and transport characteristics, FIrpic was intentionally undoped at different positions inside the EML. When FIrpic was undoped close to the ETL, driving voltage increased significantly which proves the dopant-assisted-electron-injection characteristic in this OLED. When the undoped layer is near the electron blocking layer, the driving voltage is only slightly increased, but the current efficiency is greatly reduced because the main recombination zone was undoped. However, non-negligible FIrpic emission is still observed which means the recombination zone penetrates inside the EML due to certain hole-transporting characteristics of the OXD. PMID:22837713

Chiu, Tien-Lung; Lee, Pei-Yu

2012-01-01

362

Carrier Injection and Transport in Blue Phosphorescent Organic Light-Emitting Device with Oxadiazole Host  

PubMed Central

In this paper, we investigate the carrier injection and transport characteristics in iridium(III)bis[4,6-(di-fluorophenyl)-pyridinato-N,C2?]picolinate (FIrpic) doped phosphorescent organic light-emitting devices (OLEDs) with oxadiazole (OXD) as the bipolar host material of the emitting layer (EML). When doping Firpic inside the OXD, the driving voltage of OLEDs greatly decreases because FIrpic dopants facilitate electron injection and electron transport from the electron-transporting layer (ETL) into the EML. With increasing dopant concentration, the recombination zone shifts toward the anode side, analyzed with electroluminescence (EL) spectra. Besides, EL redshifts were also observed with increasing driving voltage, which means the electron mobility is more sensitive to the electric field than the hole mobility. To further investigate carrier injection and transport characteristics, FIrpic was intentionally undoped at different positions inside the EML. When FIrpic was undoped close to the ETL, driving voltage increased significantly which proves the dopant-assisted-electron-injection characteristic in this OLED. When the undoped layer is near the electron blocking layer, the driving voltage is only slightly increased, but the current efficiency is greatly reduced because the main recombination zone was undoped. However, non-negligible FIrpic emission is still observed which means the recombination zone penetrates inside the EML due to certain hole-transporting characteristics of the OXD. PMID:22837713

Chiu, Tien-Lung; Lee, Pei-Yu

2012-01-01

363

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

NASA Astrophysics Data System (ADS)

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.

Wampler, William R.; Myers, Samuel M.

2015-01-01

364

Coherent quantum transport of charge density waves  

NASA Astrophysics Data System (ADS)

Recent experiments show oscillations of dominant period h/2e in conductance vs magnetic flux of charge density wave (CDW) rings above 77 K, revealing macroscopically observable quantum behavior. The time-correlated soliton tunneling model discussed here is based on coherent, Josephson-like tunneling of microscopic quantum solitons of charge 2e. The model interprets the CDW threshold electric field as a Coulomb blockade threshold for soliton pair creation, often much smaller than the classical depinning field but with the same impurity dependence (e.g., ˜ni2 for weak pinning). This picture draws upon the theory of time-correlated single-electron tunneling to interpret CDW dynamics above threshold. Similar to Feynman's derivation of the Josephson current-phase relation for a superconducting tunnel junction, the picture treats the Schrödinger equation as an emergent classical equation to describe the time-evolution of Josephson-coupled order parameters related to soliton dislocation droplets. Vector or time-varying scalar potentials can affect the order parameter phases to enable magnetic quantum interference in CDW rings or lead to interesting behavior in response to oscillatory electric fields. The ability to vary both magnitudes and phases is an aspect important to future applications in quantum computing.

Miller, J. H., Jr.; Wijesinghe, A. I.; Tang, Z.; Guloy, A. M.

2013-03-01

365

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

E-print Network

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.

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

366

Charge transport and recombination in P3HT:PbS solar cells  

NASA Astrophysics Data System (ADS)

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.

Firdaus, Yuliar; Vandenplas, Erwin; Khetubol, Adis; Cheyns, David; Gehlhaar, Robert; Van der Auweraer, Mark

2015-03-01

367

Simulation of bipolar charge transport in nanocomposite polymer films  

NASA Astrophysics Data System (ADS)

This paper describes 3D particle-in-cell simulation of bipolar charge injection and transport through nanocomposite film comprised of ferroelectric ceramic nanofillers in an amorphous polymer matrix. The classical electrical double layer (EDL) model for a monopolar core is extended (eEDL) to represent the nanofiller by replacing it with a dipolar core. Charge injection at the electrodes assumes metal-polymer Schottky emission at low to moderate fields and Fowler-Nordheim tunneling at high fields. Injected particles migrate via field-dependent Poole-Frenkel mobility and recombine with Monte Carlo selection. The simulation algorithm uses a boundary integral equation method for solution of the Poisson equation coupled with a second-order predictor-corrector scheme for robust time integration of the equations of motion. The stability criterion of the explicit algorithm conforms to the Courant-Friedrichs-Levy limit assuring robust and rapid convergence. The model is capable of simulating a wide dynamic range spanning leakage current to pre-breakdown. Simulation results for BaTiO3 nanofiller in amorphous polymer matrix indicate that charge transport behavior depend on nanoparticle polarization with anti-parallel orientation showing the highest leakage conduction and therefore lowest level of charge trapping in the interaction zone. Charge recombination is also highest, at the cost of reduced leakage conduction charge. The eEDL model predicts the meandering pathways of charge particle trajectories.

Lean, Meng H.; Chu, Wei-Ping L.

2015-03-01

368

Charge carrier dynamics of photoexcited Co3O4 in methanol: extending high harmonic transient absorption spectroscopy to liquid environments.  

PubMed

Charge carrier dynamics in Co3O4 thin films are observed using high harmonic generation transient absorption spectroscopy at the Co M2,3 edge. Results reveal that photoexcited Co3O4 decays to the ground state in 600 ± 40 ps in liquid methanol compared to 1.9 ± 0.3 ns in vacuum. Kinetic analysis suggests that surface-mediated relaxation of photoexcited Co3O4 may be the result of hole transfer from Co3O4 followed by carrier recombination at the Co3O4-methanol interface. PMID:25222441

Baker, L Robert; Jiang, Chang-Ming; Kelly, Stephen T; Lucas, J Matthew; Vura-Weis, Josh; Gilles, Mary K; Alivisatos, A Paul; Leone, Stephen R

2014-10-01

369

Nanotubes in polar solvents: Solvation and physical properties of excess charge carriers  

NASA Astrophysics Data System (ADS)

An excess charge carrier added to a one-dimensional (1D) semiconductor immersed in a polar solvent can undergo self- localization into a large-radius adiabatic polaron whose physical properties differ significantly from band states. Using a simplified theoretical model for small-diameter tubular structures immersed in a 3D polarizable solvent, we explore some testable signatures of these solvation-induced polarons. We discuss optical (infrared) absorption due to transitions between localized electronic states formed in the self-consistent polarization potential well, local dielectric relaxation modes around the polaron, and its mobility. Numerical estimates indicate that the dissipative drag of the polar environment can reduce the mobility by orders of magnitude in comparison with intrinsic values. Thermal fluctuations of the medium also cause a substantial broadening of the local optical absorption from the polaron. For more detail, see Yu. N. Gartstein and G. L. Ussery, Phys. Lett. A, 372, 5909 (2008) and G. L. Ussery and Yu. N. Gartstein, J. Chem. Phys., 130, 014701 (2009).

Ussery, Geoffrey; Gartstein, Yuri

2009-04-01

370

Computational Confirmation of the Carrier for the "XCN" Interstellar Ice Bank: OCN(-) Charge Transfer Complexes  

NASA Technical Reports Server (NTRS)

Recent experimental studies provide evidence that carrier for the so-called XCN feature at 2165 cm(exp -1) (4.62 micron) in young stellar objects is an OCN(-)/NH4(+) charge transfer (CT) complex that forms in energetically processed interstellar icy grain mantles. Although other RCN nitriles and RCN iosonitriles have been considered, Greenberg's conjecture that OCN(-) is associated with the XCN feature has persisted for over 15 years. In this work we report a computational investigation that thoroughly confirms the hypothesis that the XCN feature observed in laboratory studies can result from OCN(-)/NH4(+) CT complexes arising from HNCO and NH3, in a water ice environment. Density functional theory calculations with theory calculations with HNCO, NH3, and up to 12 waters reproduce seven spectroscopic measurements associated with XCN: the band origin of the asymmetric stretching mode of OCN(-), shifts due to isotopic substitutions of C, N, O, and H, and two weak features. However, very similar values are also found for the OCN(-)/NH4(+) CT complex arising from HOCN and NH3. In both cases, the complex forms by barrierless proton transfer from HNCO or HOCN to NH3 during the optimization of the solvated system. Scaled B3LYP/6-31+G** harmonic frequencies for HNCO and HOCN cases are 2181 and 2202 cm(exp -1), respectively.

Park, J.-Y.; Woon, D. E.

2004-01-01

371

Synthesis of p -and n-type Gels Doped with Ionic Charge Carriers  

NASA Astrophysics Data System (ADS)

In this study, we synthesized the new kinds of semiconducting polymeric gels having negative ( n-type) and positive ( p-type) counter ions as charge carriers. The polyacrylamide gel was doped with pyranine (8-hydroxypyrene-1,3,6-trisulfonic acid, trisodium salt), having {text{SO}}3^{ - } ions as side groups and Na+ as counter ions, so-called p-type semiconducting gel. The doping process was performed during the polymerization where the pyranine binds to the polymer strands over OH group chemically via radical addition. In a similar way, N-isopropylacrylamide (NIPA) gel was doped with methacrylamidopropyltrimethyl ammonium chloride (MAPTAC), having Cl- as counter ions, so-called n-type semiconducting gel. Here MAPTAC was embedded by copolymerization within the polymer network (NIPA). These semiconducting gels can show different electrical properties by changing the concentration of the doping agents, swelling ratio etc. We have shown that the pn junction, formed by combining p-type and n-type gels together in close contact, rectifies the current similar to the conventional Si and Ge diodes.

Alveroglu, E.; Yilmaz, Y.

2010-03-01

372

Specific features of intervalley scattering of charge carriers in n-Si at high temperatures  

SciTech Connect

In n-Si, intervalley scattering of electrons can be of two types, f scattering and g scattering. With the purpose of establishing the contributions of f- and g-type transitions to intervalley scattering, the piezoresistance of n-Si crystals is studied in the temperature range T = 295-363 K. The initial concentration of charge carriers in the n-Si samples is 1.1 x 10{sup 14} cm{sup -3}, and the resistivity at 300 K is {rho} = 30 {Omega} cm. As the temperature is increased, the region of leveling-off of the piezoresistance shifts to lower voltages. The characteristic feature of the dependence {rho} = {rho}(T) plotted in the double logarithmic coordinates (log{rho} = f(logT)) is the transition from the slope 1.68 to the slope 1.83 at T > 330 K. This is attributed to the substantial contribution of g transitions to intervalley scattering in the high-temperature region. For verification of the interpretation of the dependence {rho} = {rho}(T), the dependence is calculated on the basis of the theory of anisotropic scattering with consideration for intervalley transitions.

Fedosov, A. V.; Luniov, S. V., E-mail: luniovser@mail.ru [Lutsk National Technical University (Ukraine); Fedosov, S. A., E-mail: ftt@univer.lutsk.ua [Lesya Ukrainka Volyn National University (Ukraine)

2010-10-15

373

Ruthenium cation substitutional doping for efficient charge carrier transfer in organic/inorganic hybrid solar cells  

NASA Astrophysics Data System (ADS)

Solution-processed organic/inorganic hybrid solar cells have emerged as a new platform for low-cost optoelectronics. At the heart of photovoltaic devices lies the matching of a junction, which requires the suitable energy level alignment of n-type and p-type semiconductors. Incorporating foreign ions into bulk semiconductors has been largely employed for many decades, yet electronically active doping in energy level control of the hybrid bulk heterojunctions has been rarely involved and the demonstration of robust functional optoelectronic devices had thus far been elusive. Herein, we introduce Ru ions into TiO2 to decorate the energy level of the acceptor to gain better energy level alignment between the donor and acceptor. By reducing the 'excess' energy offset between the n-type and p-type semiconductors, the electron transfer becomes faster, thus leading to a notable enhancement in power conversion efficiency, i.e., from 2.20% to 2.89%. The results demonstrate that the energy level can be controlled effectively by the versatile Ru dopants. This work opens an effective route for accelerating the charge carrier transfer at the interface and achieving high-performance organic/inorganic hybrid optoelectronic devices.

Kong, Degui; Jin, Xiao; Sun, Weifu; Du, Jiaxing; Tong, Jifeng; Chen, Changyong; Yang, Xuwei; Cheng, Yuanyuan; Li, Qinghua

2015-01-01

374

Unified Theory of Charge Transport in Wide-Band and Narrow-Band Semiconductors  

NASA Astrophysics Data System (ADS)

The charge carrier mobility is often calculated within one of the two limiting cases: wide bands or narrow bands. In the case of wide-band systems, usually pure band transport is assumed along with a calculated relaxation time. In contrast, for narrow-band materials, hopping is usually considered prevalent and the interaction with lattice vibrations is described within the polaron concept. In this talk, we will present a unified approach to the description of charge transport based upon the Kubo formalism applied to a Holstein Hamiltonian. As a result, we obtain an analytical formula for the temperature dependence and anisotropy of the mobility describing a seamless transition from band transport at low temperatures to hopping transport at high temperatures. The results are illustrated for naphthalene crystals and a comparison to previous approaches [1,2] is made. [3pt] [1] V.M. Kenkre, Phys. Lett. A 305, 443 (2002)[0pt] [2] K. Hannewald and P.A. Bobbert, Phys. Rev. B 69, 075212 (2004)

Ortmann, Frank; Bechstedt, Friedhelm; Hannewald, Karsten

2009-03-01

375

Carrier transport in InxGa1-xN thin films grown by modified activated reactive evaporation  

Microsoft Academic Search

In the present work, we report the temperature dependent carrier transport properties of InxGa1-xN thin films in the entire composition range grown by modified activated reactive evaporation. The carrier transport in these degenerate semiconductors is controlled by impurity band conduction. A transition from metallic to semiconducting type resistivity was observed for indium rich films. The semiconducting behavior originates from electron-electron

S. R. Meher; R. V. Muniswami Naidu; Kuyyadi P. Biju; A. Subrahmanyam; Mahaveer K. Jain

2011-01-01

376

A microscopic model for non-fermi-liquid behavior and charge carrier pairing in a purely repulsive two-dimensional electron system  

NASA Astrophysics Data System (ADS)

This thesis examines the properties of a new microscopic model for non-Fermi-liquid behavior and d-wave pairing in a strongly correlated quasi-two-dimensional (2D) electron gas with purely repulsive interactions. The microscopic Hamiltonian for this system involves a nearest neighbor electron hopping matrix element t, an on-site Coulomb repulsion U, and a nearest neighbor Coulomb repulsion V. We suggest that nearest neighbor Coulomb repulsion on the energy scale of t stabilizes a state in which electrons undergo a "somersault" in their internal spin-space (spin-flux). Spin-flux is a new form of spontaneous symmetry breaking in a strongly correlated electron system in which the Hamiltonian acquires a term with the symmetry of spin-orbit coupling at the mean-field level. Spin-flux modifies the single quasi-particle dispersion relations from that of a conventional antiferromagnet (AFM). When this spin-1/2 AFM insulator is doped, the charge carriers are mobile, charged, bosonic meron-vortex solitons accompanied by unoccupied states deep inside the Mott-Hubbard charge-transfer gap. This model provides a unified microscopic basis for (i) non-Fermi-liquid transport properties for low and intermediate doping, (ii) mid-infrared optical absorption, (iii) destruction of AFM long range order with doping, (iv) angled resolved spectroscopy (ARPES), (v) d-wave preformed charge carrier pairs, and (vi) a transition from the non-Fermi liquid state to a conventional Fermi-liquid metal for large doping. The approximations used to study the 2D spin-flux Hubbard model are the unrestricted Hartree-Fock Approximation and the Configuration Interaction (CI) Method. In 1D, the CI approximation leads to excellent agreement with the exact Bethe Ansatz solution of the Hubbard model, as well as a clear demonstration of the spin-charge separation: the charge of the doping hole is carried by charged bosonic domain-walls, while the spin of the doping hole is carried by neutral fermionic domain-walls. In 2D, the CI method suggests a precursor to the spin-charge separation: addition of a single hole leads to the appearance of a charge-carrying vortex (the meron-vortex) bound to a spin-carrying antivortex.

Berciu, Mona Inesa

2000-10-01

377

Charge transport properties of spin crossover systems.  

PubMed

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

Ruiz, Eliseo

2014-01-01

378

On the Structure of the Fixed Charge Transportation Problem  

ERIC Educational Resources Information Center

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,…

Kowalski, K.

2005-01-01

379

Parametrization of extended Gaussian disorder models from microscopic charge transport  

E-print Network

to compound synthesis. 1 Introduction The optimization of organic photovoltaic cells,1,2 light emitting diodesParametrization of extended Gaussian disorder models from microscopic charge transport simulations atomic-scale (microscopic) simulations. To do this, a stochastic network model, parametrized on atomistic

Schmidt, Volker

380

Two-Dimensional Mineral [Pb2BiS3][AuTe2]: High-Mobility Charge Carriers in Single-Atom-Thick Layers.  

PubMed

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 Bi2Sr2CaCu2O6+?. 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

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

381

Charge transport in conjugated polymers: a multiscale picture  

NASA Astrophysics Data System (ADS)

A framework to study charge transport in conjugated polymers using realistic morphologies is developed. First, the atomistic force field is refined using first-principles calculations. Systematic coarse graining is then performed to extend simulation times and system sizes accessible to molecular dynamics simulations. Material morphologies are generated using the coarse grained and atomistic models. Finally, the charge mobility is obtained using temperature activated hopping picture for charge transport [1]. The framework is tested on neutral and oxidized polypyrrole with different structural ordering [2]. [4pt] [1] J. Kirkpatrick, V. Marcon, J. Nelson, K. Kremer, D. Andrienko, Phys. Rev. Lett. 98, 227402 (2007)[0pt] [2] V. Ruehle, J. Kirkpatrick, K. Kremer, D. Andrienko, Phys. Stat. Solidi B, 245, 844 (2008)

Ruehle, Victor; Kirkpatrick, James; Kremer, Kurt; Andrienko, Denis

2009-03-01

382

Physical constraints on charge transport through bacterial nanowires  

PubMed Central

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

Polizzi, Nicholas F.; Skourtis, Spiros S.

2012-01-01

383

Physical constraints on charge transport through bacterial nanowires  

SciTech Connect

Extracellular appendages of the dissimilatory metal-reducing bacterium Shewanella oneidensis MR-1 were recently shown to sustain currents of 10{sup 10} 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 10{sup 10} 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.

Polizzi, Nicholas F.; Skourtis, Spiros S.; Beratan, David N.

2012-01-01

384

PAH charge state distribution and DIB carriers: Implications from the line of sight toward HD 147889  

NASA Astrophysics Data System (ADS)

We have computed physical parameters such as density, degree of ionization and temperature, constrained by a large observational data set on atomic and molecular species, for the line of sight toward the single cloud HD 147889. Diffuse interstellar bands (DIBs) produced along this line of sight are well documented and can be used to test the PAH hypothesis. To this effect, the charge state fractions of different polycyclic aromatic hydrocarbons (PAHs) are calculated in HD 147889 as a function of depth for the derived density, electron abundance and temperature profile. As input for the construction of these charge state distributions, the microscopic properties of the PAHs, e.g., ionization potential and electron affinity, are determined for a series of symmetry groups. The combination of a physical model for the chemical and thermal balance of the gas toward HD 147889 with a detailed treatment of the PAH charge state distribution, and laboratory and theoretical data on specific PAHs, allow us to compute electronic spectra of gas phase PAH molecules and to draw conclusions about the required properties of PAHs as DIB carriers. We find the following. 1) The variation of the total charge state distribution of each specific class (series) of PAH in the translucent cloud toward HD 147889 (and also of course for any other diffuse/translucent cloud) depends strongly on the molecular symmetry and size (number of ? electrons). This is due to the strong effects of these parameters on the ionization potential of a PAH. 2) Different wavelength regions in the DIB spectrum are populated preferentially by different PAH charge states depending on the underlying PAH size distribution. 3) The PAH size distribution for HD 147889 is constrained by the observed DIB spectrum to be Gaussian with a mean of 50 carbon atoms. 4) For the given PAH size distribution it is possible to constrain the total small catacondensed PAH column density along the line of sight to HD 147889 to 2.4×1014 cm-2 by comparing the total observed UV extinction to the strong UV absorptions of neutral PAHs in the 2000-3000 Å region. 5) Catacondensed PAHs with sizes above some 40 C-atoms are expected to show strong DIBS longward of 10 000 Å. Large condensed PAHs in the series, pyrene, coronene, ovalene, .... , on the other hand, mainly absorb between 4000 and 10 000 Å but extrapolation to even larger pericondensed PAHs in this series also shows strong absorptions longward of 10 000 Å. 6) Only the weak DIBs in HD 147889 could be reproduced by a mix of small catacondensed PAHs (<50 C atoms) while for large pericondensed PAHs (50 < C atoms < 100) the intermediate DIBs are well reproduced. Small catacondensed PAHs cannot contribute more than 50% of the total observed equivalent width toward HD 147889. Strong DIBs can only be reproduced by addition of very specific PAH molecules or homologue series to the sample set (i.e., a small number of PAHs with high oscillator strength or a large number of PAHs with a low oscillator strength). An outline is provided for a more general application of this method to other lines of sight, which can be used as a pipeline to compute the spectroscopic response of a PAH or group of PAHs in a physical environment constrained by independent (non-DIB) observations. Based on observations made at the European Southern Observatory, Paranal, Chile (ESO programs 67.C-0281 and 64.H-0224). Appendices A-C are only available in electronic form at http://www.edpsciences.org

Ruiterkamp, R.; Cox, N. L. J.; Spaans, M.; Kaper, L.; Foing, B. H.; Salama, F.; Ehrenfreund, P.

2005-03-01

385

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

386

Exosomes as Hedgehog carriers in cytoneme-mediated transport and secretion.  

PubMed

The Hedgehog signalling pathway is crucial for development, adult stem cell maintenance, cell migration and axon guidance in a wide range of organisms. During development, the Hh morphogen directs tissue patterning according to a concentration gradient. Lipid modifications on Hh are needed to achieve graded distribution, leading to debate about how Hh is transported to target cells despite being membrane-tethered. Cytonemes in the region of Hh signalling have been shown to be essential for gradient formation, but the carrier of the morphogen is yet to be defined. Here we show that Hh and its co-receptor Ihog are in exovesicles transported via cytonemes. These exovesicles present protein markers and other features of exosomes. Moreover, the cell machinery for exosome formation is necessary for normal Hh secretion and graded signalling. We propose Hh transport via exosomes along cytonemes as a significant mechanism for the restricted distribution of a lipid-modified morphogen. PMID:25472772

Gradilla, Ana-Citlali; González, Esperanza; Seijo, Irene; Andrés, German; Bischoff, Marcus; González-Mendez, Laura; Sánchez, Vanessa; Callejo, Ainhoa; Ibáñez, Carmen; Guerra, Milagros; Ortigão-Farias, João Ramalho; Sutherland, James D; González, Monika; Barrio, Rosa; Falcón-Pérez, Juan M; Guerrero, Isabel

2014-01-01

387

Mathematical properties of a kinetic transport model for carriers and phonons in semiconductors  

NASA Astrophysics Data System (ADS)

We present studies on the mathematical properties of a multigroup formulation of the Bloch Boltzmann Peierls equations. The considered model equations are based on a general carrier dispersion law and contain the full quantum statistics of both the carriers and the phonons. Moreover, the transport model allows the investigation of particle distributions with arbitrary anisotropy with respect to the main direction. We prove the boundedness of the solution according to the Pauli principle and study the conservational properties of the multigroup equations. In addition, the existence of a Lyapounov functional to the proposed model equations is proved and expressions for the equilibrium solution are given. Numerical results are presented for the stationary state distributions of a coupled system of electrons and longitudinal optical phonons in GaAs.

Galler, M.; Schürrer, F.

2007-11-01

388

Carrier transport in green AlInGaN based structures on c-plane substrates  

NASA Astrophysics Data System (ADS)

In this paper, the carrier transport in (Al)InGaN based test structures with In-rich quantum wells on c-plane substrates is investigated under high current operation. To get access to the injection efficiency, the devices are processed as ridge waveguide lasers and examined above threshold. The slope efficiency reveals a slight decrease as a function of current even under pulsed operation that can be related to a reduction of the injection efficiency based on carrier leakage. As the test structure contains an InGaN detection layer on the n-side, it is possible to verify hole overflow across the active region. Moreover, by analysing the current dependence of the radiative recombination in the detection layer, the reduction of slope efficiency can be correlated to increasing hole leakage.

Hager, T.; Binder, M.; Brüderl, G.; Eichler, C.; Avramescu, A.; Wurm, T.; Gomez-Iglesias, A.; Stojetz, B.; Tautz, S.; Galler, B.; Gerhard, S.; Zeisel, R.; Strauss, U.

2013-06-01

389

The Effects of Polydispersity and Energetic Disorder on Carrier Injection and Transport  

NASA Astrophysics Data System (ADS)

Large reductions in the quantum efficiency of conjugated polymer based LEDs are observed when there is large polydispersity in molecular weight of the polymer. (A. Menon et al., Chem. Mater. 14 (2002) 3668) We report studies designed to elucidate the degree to which these polydispersity effects are intrinsic and derive from effects of energetic disorder. The studies follow those of Crone et al. on MEH-PPV (B. K. Crone et al., J. Appl. Phys. 86 (1999) 5767) but in the present work we deliberately introduce a distribution of energy levels by using blends of phenylenevinylene oligomers to construct both LEDs and single carrier devices. We have adapted the theory of reference 2 to simulate polydispersity and to understand the effects of energetic disorder on carrier injection and transport.

Konezny, S. J.; Vaidyanathan, S.; Kas, O. Y.; Galvin, M. E.; Smith, D. L.; Rothberg, L. J.

2004-03-01

390

Carrier of Wingless (Cow), a secreted heparan sulfate proteoglycan, promotes extracellular transport of Wingless.  

PubMed

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

Chang, Yung-Heng; Sun, Yi Henry

2014-01-01

391

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

PubMed Central

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

Chang, Yung-Heng; Sun, Yi Henry

2014-01-01

392

Molecular Gas Adsorption Induced Carrier Transport Studies of Epitaxial Graphene using IR Reflection Spectroscopy  

E-print Network

We investigate molecular adsorption doping by electron withdrawing NO2 and electron donating NH3 on epitaxial graphene grown on C-face SiC substrates. Amperometric measurements show conductance changes upon introduction of molecular adsorbents on epitaxial graphene. Conductance changes are a trade-off between carrier concentration and scattering, and manifest at direct current and optical frequencies. We therefore investigate changes in the infrared (IR) reflection spectra to correlate these two frequency domains, as reflectance changes are due to a change of epitaxial graphene (EG) surface conductance. We match theory with experimental IR data and extract changes in carrier concentration and scattering due to gas adsorption. Finally, we separate the intraband and interband scattering contributions to the electronic transport under gas adsorption. The results indicate that, under gas adsorption, the influence of interband scattering cannot be neglected, even at DC.

B. K. Daas; W. K. Nomani; K. M. Daniels; T. S. Sudarshan; Goutam Koley; M. V. S. Chandrashekhar

2012-01-23

393

Thickness dependence of plasmonic charge carrier generation in ultrathin a-Si:H layers for solar cells.  

PubMed

Nanocomposite layers of Ag nanoparticles and a-Si:H film constitute attractive candidates for the realization of ultrathin "two-dimensional" plasmonic solar cells, with an ideal 18% efficiency predicted for an average layer thickness of only 20 nm. By combining optical spectroscopy with photoconductivity measurements, we here characterize different contributions to the light absorption and charge carrier generation in such nanocomposites. We focus in particular on the important role of the absorber layer thickness for these processes, by studying a range of a-Si:H thicknesses from 9 to 67 nm. Through detailed comparison with numerical calculations by the finite element method, observed experimental features are connected to specific resonance modes and charge carrier generation mechanisms. The influence of dipolar and quadrupolar near-field distributions are evaluated with respect to different figures of merit for plasmonic solar cells. We briefly discuss how the present findings may be implemented in practical solar cell configurations. PMID:21732654

Gusak, Viktoria; Kasemo, Bengt; Hägglund, Carl

2011-08-23

394

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

SciTech Connect

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.

Abdinov, A. Sh., E-mail: abdinov-axmed@yandex.ru [Baku State University (Azerbaijan); Babayeva, R. F., E-mail: Babaeva-Rena@yandex.ru [Azerbaijan State Economic University (Azerbaijan); Amirova, S. I.; Rzayev, R. M. [Baku State University (Azerbaijan)] [Baku State University (Azerbaijan)

2013-08-15

395

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

SciTech Connect

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.

Price, Michelle J.; Foley, Justin M. [Applied Physics Program, University of Michigan, 450 Church Street, Ann Arbor, Michigan 48109-1040 (United States); May, Robert A. [Department of Chemistry and Biochemistry, University of Texas at Austin, 1 University Station A5300, Austin, Texas 78712-0165 (United States); Maldonado, Stephen [Applied Physics Program, University of Michigan, 450 Church Street, Ann Arbor, Michigan 48109-1040 (United States); Department of Chemistry, University of Michigan, 930 N University, Ann Arbor, Michigan 48109-1055 (United States)

2010-08-23

396

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

PubMed

We report on our investigations on charge transport and recombination in TiO2-based mesoporous solar cells using PbI2 and various perovskite compositions, including CH3NH3PbI3, CH3NH3PbI2Br, CH3NH3PbIBr2, and CH3NH3PbBr3. The mesoporous TiO2 film is about 650 nm thick. Electron microscopy measurements show that no perovskite capping layer is formed on the top surface of the TiO2 film. Intensity-modulated photocurrent/photovoltage spectroscopies show that the electron diffusion coefficient and recombination lifetime are governed by the underlying mesoporous TiO2 film and thus do not depend on the perovskite composition. However, replacing the perovskite absorber with PbI2 leads to a diffusion coefficient that is about a factor of 5 slower than that in perovskite-based devices. We also find that TiCl4 treatment of the mesoporous TiO2 film prior to device fabrication substantially reduces the charge recombination kinetics in mesoporous perovskite solar cells. PMID:25407110

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

2015-01-01

397

Correlated small polaron hopping transport in 1D disordered systems at high temperatures: a possible charge transport mechanism in DNA.  

PubMed

Based on the generalized molecular crystal model (GMCM) and theoretical percolation arguments we investigate small polaron hopping transport in 1D disordered systems at high temperatures. Correlation (cr) effects are taken into account. An analytical expression for the temperature dependence of the electrical conductivity, ln?(h,cr)?T(-1/2), is obtained. This result reproduces satisfactorily the experimental data reported for ?-DNA and for poly(dA)-poly(dT) DNA, considering DNA as a one-dimensional disordered molecular wire in which small polarons are the charge carriers. ln?(h,cr) versus T(-1/2) plots permit the evaluation of the maximum hopping distance. The results indicate that correlation effects are probably responsible for large hopping distances in DNA samples. PMID:21817272

Triberis, G P; Dimakogianni, M

2009-01-21

398

An Efficient Scheduling Scheme on Charging Stations for Smart Transportation  

NASA Astrophysics Data System (ADS)

This paper proposes a reservation-based scheduling scheme for the charging station to decide the service order of multiple requests, aiming at improving the satisfiability of electric vehicles. The proposed scheme makes it possible for a customer to reduce the charge cost and waiting time, while a station can extend the number of clients it can serve. A linear rank function is defined based on estimated arrival time, waiting time bound, and the amount of needed power, reducing the scheduling complexity. Receiving the requests from the clients, the power station decides the charge order by the rank function and then replies to the requesters with the waiting time and cost it can guarantee. Each requester can decide whether to charge at that station or try another station. This scheduler can evolve to integrate a new pricing policy and services, enriching the electric vehicle transport system.

Kim, Hye-Jin; Lee, Junghoon; Park, Gyung-Leen; Kang, Min-Jae; Kang, Mikyung

399

Charge transport properties of CdMnTe radiation detectors  

NASA Astrophysics Data System (ADS)

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 charge collection is reduced with increasing values of bias voltage. The electron drift velocity was calculated from the rise time distribution of the preamplifier output pulses at each measured bias. 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.

Rafiei, R.; Boardman, D.; Reinhard, M. I.; Sarbutt, A.; Kim, K.; Watt, G. C.; Uxa, S.; Prokopovich, D. A.; Belas, E.; Bolotnikov, A. E.; James, R. B.

2012-10-01

400

Theories of the Charge Transport Mechanism in Ordered Organic Semiconductors  

NASA Astrophysics Data System (ADS)

The traditional theories of charge transport in ordered organic semiconductors are reviewed and their limitations discussed. The recent contributions of computational chemistry to the understanding of the parameters that determine the charge mobility in bulk semiconductors are analyzed in detail. The effect of thermal motions on the electronic wavefunction and the effect of strong off-diagonal electron-phonon coupling are identified as essential ingredients for the proper description of the charge dynamics. The development of suitable methods to compute the charge mobility taking into account these new computational results is reviewed, with special emphasis on the models that allow the prediction of the structure-property relationship. The available experimental evidence is compared with the predictions made by the most recent models.

Troisi, Alessandro

401

Anisotropy of excitation and relaxation of photogenerated charge carriers in graphene.  

PubMed

We present a pump-probe experiment on graphene, which reveals a pronounced dependence of the pump-induced transmission on the angle between pump and probe polarization. It reflects a strong anisotropy of the pump-induced occupation of photogenerated carriers in momentum space. Within 150 fs after excitation, an isotropic carrier distribution is established. The experiments are well described by microscopic modeling, which identifies carrier-phonon scattering to be the main relaxation mechanism giving rise to an isotropic carrier distribution. PMID:24559191

Mittendorff, Martin; Winzer, Torben; Malic, Ermin; Knorr, Andreas; Berger, Claire; de Heer, Walter A; Schneider, Harald; Helm, Manfred; Winnerl, Stephan

2014-03-12

402

Computational investigation of charge injection and transport properties of a series of thiophene-pyrrole based oligo-azomethines.  

PubMed

The present study explores the structural, charge carrier injection and transport properties of a series of thiophene-pyrrole based oligo-azomethines using density functional theory (DFT) methods. Our findings show that the presence of a bulky substituent adversely affects these properties. However, the electronic effect of substituents may be utilized to tune these properties by substitutions at suitable positions. Values of frontier orbitals, ionization energies, and electron affinities are calculated for each compound to predict the ease of charge injection from metal electrodes to these azomethines and the stabilities of their ionic forms. In addition to having large injection barriers, lack of stability of the anions may hinder the electron injection. However, most of the compounds have excellent hole injection capability. Computation of reorganization energies and electronic couplings followed by charge transfer rates and mobilities show large carrier mobilities for some of the studied compounds. Considering both the injection capability and carrier mobilities, it is found that a thiophene-pyrrole azomethine without any substituent and substituted azomethines with a methyl, methoxy or amine group at the 3 position of the pyrrole ring may act as efficient materials for the hole transport layer. PMID:24671604

Sahu, Harikrishna; Panda, Aditya N

2014-05-14

403

Discrete charge carrier transfer sites on proteins? A D.C. conductivity study on ultrathin protein films.  

PubMed

D.C. electrical conduction in thin protein films (200 mg/cm2; approximately 2 mu in thickness) of bovine serum albumin and its dinitrophenylated derivatives with different stoichiometric composition was investigated at 17, 20 and 23% relative humidities and at room temperature. Statistically significant decrease in conductivity due to derivatization was observed even at protein-2,4-dinitrophenol stoichiometry as low as 1:2. A charge injection mechanism based upon discrete charge carrier transfer sites could account for the observations. Analogous events may operate in cellular signaling and coding. PMID:4084305

Karvaly, B; Jankun, J; Trivedi, S; Mallik, B; Kemeny, G

1985-12-31

404

Photogeneration of charge carrier correlated with amplified spontaneous emission in single crystals of a thiophene/phenylene co-oligomer  

NASA Astrophysics Data System (ADS)

Thiophene/phenylene co-oligomers have substantial promise for the use of not only organic electronics but also organic optical devices. However, considerably less is known about the correlation between their optical and optoelectronic properties. We have investigated the charge carrier generation in 1,4-bis(5-phenylthiophen-2-yl)benzene (AC5) single crystals by flash-photolysis time-resolved microwave conductivity (TRMC) and transient absorption spectroscopy (TAS). It was found that the dependence of photocarrier generation efficiency on excitation photon density differed from that of emission efficiency once amplified spontaneous emission (ASE) and resultant spectrally narrowed emission occur upon exposure to 355 nm. In contrast, the dependences of emission and photocarrier generation efficiencies were identical when ASE was not involved at a different excitation wavelength (193 nm). An approximated analytical solution of rate equation considering ASE or singlet-singlet annihilation was applied to the experiments, exhibiting good agreement. On the basis of TRMC, TAS, and extinction coefficient of radical cation assessed by pulse radiolysis, the minimum charge carrier mobility was estimated, without electrodes, to be 0.12 cm2 V-1 s-1. The dynamics of charge carrier and triplet excited state is discussed, accompanying with examination by time-dependent density functional theory. The present work would open the way to a deeper understanding of the fate of excited state in optically robust organic semiconducting crystals.

Saeki, Akinori; Seki, Shu; Shimizu, Yasuhiro; Yamao, Takeshi; Hotta, Shu

2010-04-01

405

Photogeneration of charge carrier correlated with amplified spontaneous emission in single crystals of a thiophene/phenylene co-oligomer.  

PubMed

Thiophene/phenylene co-oligomers have substantial promise for the use of not only organic electronics but also organic optical devices. However, considerably less is known about the correlation between their optical and optoelectronic properties. We have investigated the charge carrier generation in 1,4-bis(5-phenylthiophen-2-yl)benzene (AC5) single crystals by flash-photolysis time-resolved microwave conductivity (TRMC) and transient absorption spectroscopy (TAS). It was found that the dependence of photocarrier generation efficiency on excitation photon density differed from that of emission efficiency once amplified spontaneous emission (ASE) and resultant spectrally narrowed emission occur upon exposure to 355 nm. In contrast, the dependences of emission and photocarrier generation efficiencies were identical when ASE was not involved at a different excitation wavelength (193 nm). An approximated analytical solution of rate equation considering ASE or singlet-singlet annihilation was applied to the experiments, exhibiting good agreement. On the basis of TRMC, TAS, and extinction coefficient of radical cation assessed by pulse radiolysis, the minimum charge carrier mobility was estimated, without electrodes, to be 0.12 cm(2) V(-1) s(-1). The dynamics of charge carrier and triplet excited state is discussed, accompanying with examination by time-dependent density functional theory. The present work would open the way to a deeper understanding of the fate of excited state in optically robust organic semiconducting crystals. PMID:20387943

Saeki, Akinori; Seki, Shu; Shimizu, Yasuhiro; Yamao, Takeshi; Hotta, Shu

2010-04-01

406

Experimental study of the minority-carrier transport at the polysilicon-monosilicon interface  

NASA Astrophysics Data System (ADS)

This paper presents the results of an experimental study designed to explore both qualitatively and quantitatively the mechanism of the improved current gain in bipolar transistors with polysilicon emitter contacts. Polysilicon contacts were deposited and heat treated at different conditions. The electrical properties were measured using p-n junction test structures that are much more sensitive to the contact properties than are bipolar transistors. A simple phenomenological model was used to correlate the structural properties with electrical measurements. Possible transport mechanisms are examined and estimates are made about upper bounds on transport parameters in the principal regions of the devices. The main conclusion of this study is that the minority-carrier transport in the polycrystalline silicon is dominated by a highly disordered layer at the polysilicon-monosilicon interface characterized by very low minority-carrier mobility. The effective recombination velocity at the n(+) polysilicon-n(+) monosilicon interface was found to be a strong function of fabrication conditions. The results indicate that the recombination velocity can be much smaller than 10,000 cm/s.

Neugroschel, A.; Arienzo, M.; Isaac, R. D.; Komem, Y.

1985-04-01

407

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

SciTech Connect

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

Gupta, S. K.; Singh, Ajay; Samanta, Soumen; Kumar, Arvind; Debnath, A. K.; Aswal, D. K. [Technical Physics Division, Bhabha Atomic Research Center, Mumbai 400 085 (India)

2010-12-01

408

Pore network model of electrokinetic transport through charged porous media.  

PubMed

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

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

2014-04-01

409

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

PubMed

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. PMID:25079791

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

2014-09-21

410

Intermediate tunnelling–hopping regime in DNA charge transport  

NASA Astrophysics Data System (ADS)

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.

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

2015-03-01

411

Intermediate tunnelling-hopping regime in DNA charge transport.  

PubMed

Charge transport in molecular systems, including DNA, is involved in many basic chemical and biological processes, and its understanding is critical if they are to be used in electronic devices. This important phenomenon is often described as either coherent tunnelling over a short distance or incoherent hopping over a long distance. Here, we show evidence of an intermediate regime where coherent and incoherent processes coexist in double-stranded DNA. We measure charge transport in single DNA molecules bridged to two electrodes as a function of DNA sequence and length. In general, the resistance of DNA increases linearly with length, as expected for incoherent hopping. However, for DNA sequences with stacked guanine-cytosine (GC) base pairs, a periodic oscillation is superimposed on the linear length dependence, indicating partial coherent transport. This result is supported by the finding of strong delocalization of the highest occupied molecular orbitals of GC by theoretical simulation and by modelling based on the Büttiker theory of partial coherent charge transport. PMID:25698331

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

2015-02-20

412

Electric fields and dominant carrier transport mechanisms in CdTe Schottky detectors  

NASA Astrophysics Data System (ADS)

CdTe Schottky diodes for X- and ?-ray detection exhibit excellent spectroscopic performance, even though these are not stable under operative voltages. Improvements require the comprehension of the main carrier transport mechanisms, presently unclear. We address this issue by correlating the internal electric field and the flowing current. Depending on the temperature and applied voltage, different mechanisms become dominant where the deep levels always play a central role. Indeed, the partial ionization of deep levels directly controls the electric field distribution. Transient measurements show how, under high voltages, the field at the contacts controls the current flowing through the detector.

Cola, Adriano; Farella, Isabella

2013-03-01

413

Fano and Breit-Wigner resonances in carrier transport through Datta and Das spin modulators  

NASA Astrophysics Data System (ADS)

In this work we investigate the carrier transport through Datta and Das spin-modulator devices. We calculate the transmission coefficient of spin-polarized electrons taking into account their reflection from both ferromagnetic contacts. We show that the interfaces make the device behave as a Fabry-Perot cavity, so that Breit-Wigner resonances appear in the transmission coefficient. Moreover, interference of quantum-confined electron states with free electron states leads to appearance of asymmetric Fano-type resonances. These resonances can be seen in the conductivity dependence on the chemical potential in the channel at very low temperatures (<1K) .

Shelykh, I. A.; Galkin, N. G.

2004-11-01

414

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

NASA Astrophysics Data System (ADS)

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.

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

2015-02-01

415

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

PubMed

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

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

416

Railway transport of low temperature heat from large power stations by means of alternative heat carriers and water  

NASA Astrophysics Data System (ADS)

The feasibility of railway transport of liquid and solid heat carriers in tank cars so as to replace pipeline transport of small to medium large heat loads was investigated. The typical characteristics of railway transport were analyzed and all essential technical and economical variables were integrated in a transport model. Over 1000 complex chemical compounds were evaluated for their suitability as heat carriers. Of these, three ammonia compounds are considered as promising. Considering, however, that complicated and expensive facilities are needed for heat transfer to and from ammonia, water is identified as the better choice. Results, based on 1975 transport prices, show that railway heat transport becomes competitive for heat loads above 50 to 100 MW and transport distances over 20 km.

Luchtman, G.; Bracke, T.

1981-11-01

417

31 CFR 306.3 - Transportation charges and risks in the shipment of securities.  

Code of Federal Regulations, 2010 CFR

...Transportation charges and risks in the shipment of securities. 306.3 Section...REGULATIONS GOVERNING U.S. SECURITIES General Information § 306.3 Transportation charges and risks in the shipment of securities. The...

2010-07-01

418

31 CFR 306.3 - Transportation charges and risks in the shipment of securities.  

Code of Federal Regulations, 2011 CFR

...Transportation charges and risks in the shipment of securities. 306.3 Section...REGULATIONS GOVERNING U.S. SECURITIES General Information § 306.3 Transportation charges and risks in the shipment of securities. The...

2011-07-01

419

The human gene SLC25A29, of solute carrier family 25, encodes a mitochondrial transporter of basic amino acids.  

PubMed

The human genome encodes 53 members of the solute carrier family 25 (SLC25), also called the mitochondrial carrier family, many of which have been shown to transport carboxylates, amino acids, nucleotides, and cofactors across the inner mitochondrial membrane, thereby connecting cytosolic and matrix functions. In this work, a member of this family, SLC25A29, previously reported to be a mitochondrial carnitine/acylcarnitine- or ornithine-like carrier, has been thoroughly characterized biochemically. The SLC25A29 gene was overexpressed in Escherichia coli, and the gene product was purified and reconstituted in phospholipid vesicles. Its transport properties and kinetic parameters demonstrate that SLC25A29 transports arginine, lysine, homoarginine, methylarginine and, to a much lesser extent, ornithine and histidine. Carnitine and acylcarnitines were not transported by SLC25A29. This carrier catalyzed substantial uniport besides a counter-exchange transport, exhibited a high transport affinity for arginine and lysine, and was saturable and inhibited by mercurial compounds and other inhibitors of mitochondrial carriers to various degrees. The main physiological role of SLC25A29 is to import basic amino acids into mitochondria for mitochondrial protein synthesis and amino acid degradation. PMID:24652292

Porcelli, Vito; Fiermonte, Giuseppe; Longo, Antonella; Palmieri, Ferdinando

2014-05-01

420

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

SciTech Connect

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.

Fitting, H.-J. [Institute of Physics, University of Rostock, Universitaetsplatz 3, D-18051 Rostock (Germany); Touzin, M. [Unite Materiaux et Transformations, UMR CNRS 8207, Universite de Lille 1, F-59655 Villeneuve d'Ascq (France)

2011-08-15

421

Controlling protein transport in ultrafiltration using small charged ligands.  

PubMed

Previous studies have demonstrated that protein transport during ultrafiltration can be strongly influenced by solution pH and ionic strength. The objective of this study was to examine the possibility of controlling protein transmission using a small, highly charged ligand that selectively binds to the protein of interest. Experiments were performed using bovine serum albumin and the dye Cibacron Blue. Protein sieving data were obtained with essentially neutral and negatively charged versions of a composite regenerated cellulose membrane to examine the effects of electrostatic interactions. The addition of only 1 g/L of Cibacron Blue to an 8 g/L BSA solution reduced the BSA sieving coefficient through the negatively-charged membrane by more than two orders of magnitude, with this effect being largely eliminated at high salt and with the neutral membrane. Protein sieving data were in good agreement with model calculations based on the partitioning of a charged sphere in a charged pore accounting for the change in net protein charge due to ligand binding and the increase in solution ionic strength due to the free ligand in solution. PMID:15895379

Rao, Suma; Zydney, Andrew L

2005-09-20

422

Charge transport properties of CdMnTe radiation detectors  

SciTech Connect

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.

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

423

Novel macrocyclic carriers for proton-coupled liquid membrane transport. Final report  

SciTech Connect

The objective of this research program is to elucidate the chemical principles which are responsible for the cation selectivity and permeability of liquid membranes containing macrocyclic carriers. Several new macrocyclic carriers were synthesized during the last three year period. In addition, new, more convenient synthetic routes were achieved for several nitrogen-containing bicyclic and tricyclic macrocycles. The cation binding properties of these macrocycles were investigated by potentiometric titration, calorimetric titration, solvent extraction and NMR techniques. In addition, hydrophobic macrocycles were incorporated into dual hollow fiber and other membrane systems to investigate their membrane performance, especially in the proton-coupled transport mode. A study of the effect of methoxyalkyl macrocycle substituents on metal ion transport was completed. A new calorimeter was constructed which made it possible to study the thermodynamics of macrocycle-cation binding to very high temperatures. Measurements of thermodynamic data for the interaction of crown ethers with alkali and alkaline earth cations were achieved to 473 K. Molecular modeling work was begun for the first time on this project and fundamental principles were identified and developed for the establishment of working models in the future.

Lamb, J.D.; Izatt, R.M.; Bradshaw, J.S.; Shirts, R.B.

1996-08-24

424

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

PubMed

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

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

425

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

PubMed

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

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

2014-10-01

426

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

Code of Federal Regulations, 2013 CFR

... (e) Step 4. Beginning July 1, 2015, notwithstanding any other provision of...Each Price Cap Carrier shall calculate its 2015 Target Composite Terminating End Office Access Rate. The 2015 Target Composite Terminating End...

2013-10-01

427

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

Code of Federal Regulations, 2014 CFR

... (e) Step 4. Beginning July 1, 2015, notwithstanding any other provision of...Rate-of-Return Carrier shall calculate its 2015 Target Composite Terminating End Office Access Rate. The 2015 Target Composite Terminating End...

2014-10-01

428

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

Code of Federal Regulations, 2013 CFR

... (e) Step 4. Beginning July 1, 2015, notwithstanding any other provision...Rate-of-Return Carrier shall calculate its 2015 interstate Target Composite Terminating End Office Access Rate. The 2015 interstate Target Composite...

2013-10-01

429

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

Code of Federal Regulations, 2014 CFR

... (e) Step 4. Beginning July 1, 2015, notwithstanding any other provision of...Each Price Cap Carrier shall calculate its 2015 Target Composite Terminating End Office Access Rate. The 2015 Target Composite Terminating End...

2014-10-01

430

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

Code of Federal Regulations, 2012 CFR

... (e) Step 4. Beginning July 1, 2015, notwithstanding any other provision of...Each Price Cap Carrier shall calculate its 2015 Target Composite Terminating End Office Access Rate. The 2015 Target Composite Terminating End...