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1

Transport of Photogenerated Charge Carriers in Polymer Semiconductors  

Microsoft Academic Search

The electrical transport of photogenerated charge carriers in disordered polymer semiconductors is reviewed. We emphasize that the mobility parameter in these disordered semiconducting systems is not a well-defined quantity. We highlight the utility of scanning probe photocurrent technique on variety of polymers in an asymmetric-electrode patterned configuration. The multiple length and time scales present in carrier transport processes are indicated

Dhritiman Gupta; N. S. Vidhyadhiraja; K. S. Narayan

2009-01-01

2

Communications: A nonperturbative quantum master equation approach to charge carrier transport in organic molecular crystals.  

PubMed

We present a nonperturbative quantum master equation to investigate charge carrier transport in organic molecular crystals based on the Liouville space hierarchical equations of motion method, which extends the previous stochastic Liouville equation and generalized master equation methods to a full quantum treatment of the electron-phonon coupling. Diffusive motion of charge carriers in a one-dimensional model in the presence of nonlocal electron-phonon coupling was studied, and two different charge carrier diffusion mechanisms are observed for large and small average intermolecular couplings. The new method can also find applications in calculating spectra and energy transfer in various types of quantum aggregates where the perturbative treatments fail. PMID:20192281

Wang, Dong; Chen, Liping; Zheng, Renhui; Wang, Linjun; Shi, Qiang

2010-02-28

3

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

4

Hydrodynamical Modeling of Charge Carrier Transport in Semiconductors  

Microsoft Academic Search

Enhanced functional integration in modern electron devices requires an accurate modeling of energy transport in semiconductors in order to describe high-field phenomena such as hot electron propagation, impact ionization and heat generation in the bulk material. The standard drift-diffusion models cannot cope with high- field phenomena because they do not comprise energy as a dynamical variable. Furthermore for many applications

ANGELO MARCELLO ANILE; VITTORIO ROMANO

2000-01-01

5

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

6

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

7

Role of carrier density and disorder on anisotropic charge transport in polypyrrole  

NASA Astrophysics Data System (ADS)

Polypyrrole (PPy) has been synthesized electrochemically on platinum substrate by varying synthesis temperature and dopant concentration. The charge transport in PPy has been investigated as a function of temperature for both in-plane and out-of-plane geometry in a wide temperature range of 5 K-300 K. The charge transport showed strong anisotropy and various mechanisms were used to explain the transport. The conductivity ratio, ?r = ?(300 K)/?(5 K) is calculated for each sample to quantify the relative disorder. At all the temperatures, the conductivity values for in-plane transport are found to be more for PPy synthesized at lower temperature, while the behavior is found to be different for out-of-plane transport. The carrier density is found to play a crucial role in case of in-plane transport. An effort has been made to correlate charge transport to morphology by analyzing temperature and frequency dependence of conductivity. Charge transport in lateral direction is found to be dominated by hopping whereas tunneling mechanisms are dominated in vertical direction. Parameters such as density of states at the Fermi level [N(EF)], average hopping distance (R), and average hopping energy (W) have been estimated for each samples in both geometry.

Varade, Vaibhav; Anjaneyulu, P.; Suchand Sangeeth, C. S.; Ramesh, K. P.; Menon, Reghu

2013-01-01

8

Rational design of benzotrithiophene-diketopyrrolopyrrole-containing donor-acceptor polymers for improved charge carrier transport.  

PubMed

Two new donor-acceptor polymers containing benzo[2,1-b:3,4-b':5,6-c'']trithiophene (BTT) as donor and diketopyrrolopyrrole (DPP) as acceptor are synthesized and applied in OFETs. By tuning the alkyl substituents of the polymers, a striking difference in packing order, thin-film arrangement, and charge carrier transport is observed. The polymer without substituents at the BTT exhibits a hole mobility two orders of magnitude higher than that with alkyl chains therein. PMID:23873786

Guo, Xin; Puniredd, Sreenivasa Reddy; Baumgarten, Martin; Pisula, Wojciech; Müllen, Klaus

2013-07-21

9

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

10

Charge transport, carrier balance, and blue electrophosphorescence in diphenyl[4-(triphenylsilyl)phenyl]phosphine oxide devices  

NASA Astrophysics Data System (ADS)

Diphenyl[4-(triphenylsilyl)phenyl]phosphine oxide (EMPA1) displays a wide highest occupied molecular orbital-lowest unoccupied molecular orbital gap (4.1 eV), singlet (4.3 eV) and triplet (3.4 eV), and an electron-dominated charge transport that follows a trap-free space charge limited model with an average electron mobility of 5.7×10-6 cm2 V-1 s-1 and a hole mobility of 1.1×10-6 cm2 V-1 s-1. At high driving voltages (>6 V), ambipolar charge transport is observed, resulting in a balanced charge density in the active layer. Highly efficient blue phosphorescent organic light-emitting diodes were realized, showing a high external quantum efficiency (21%) and a luminance efficiency of 45 cd/A using a bis[2-(4',6'-difluorophenyl)-pyridinato-N,C2']iridium(III) picolinate dopant.

Mamada, Masashi; Ergun, Selin; Pérez-Bolívar, César; Anzenbacher, Pavel

2011-02-01

11

Intramolecular transport of charge carriers in trimeric aniline upon a three-step acid doping process.  

PubMed

The "acid doping" of a methyl-capped aniline trimer, N-[4-(dimethylamino)phenyl]-N-(4-{[4-(dimethylamino)phenyl]imino}-2,5- cyclohexadien-1-ylidene)-amine (TANI), was performed stoichiometrically to study the nature of charge carriers induced by the acid protonation process. The redox centers in TANI were found to undergo a reversible three-step protonation with 1 equiv, 2 equiv and a large molar excess of dodecylbenzenesulfonic acid (DBSA) in chloroform, as evidenced by three different chromophores (doping levels I, II and III) observed using UV-vis-NIR. Acidity of the dopants and solvent polarity were controlling factors. As revealed by electron paramagnetic resonance spectroscopy (EPR), the doping levels I, II, and III achieved by doping 0.1 mM TANI/chloroform solutions with different amounts of DBSA exhibited relative spin densities of 1:1.2:2.2. Since the expected maximum spin population of TANI through acid doping is two spins per molecule, the reduced paramagnetism given by the doubly protonated TANI (doping level II) indicated partially coupled unpaired spins. The third protonation step (doping level III) produced almost double the unpaired spin concentration compared to the lower doping levels and a multiline EPR spectrum likely comprising two overlapping signals of similar overall line width. The hyperfine couplings contributing to the splittings in this signal were estimated by simulation incorporating 6-H and 1-N nuclei most likely from one highly localized unpaired spin on a terminal dimethylamino group, with an underlying apparent singlet arising from a delocalized unpaired spin; the diradical proposed as the species exhibiting the multiplet EPR signal is isolated by the bridging ammonium cation created by the third doping step. The phenomena suggested the stepwise evolution of partly formed diamagnetic bipolarons from polaron interactions at doping level II and the transformation to the more isolated unsymmetrical system we label "two polarons on a chain" in a triplet state at doping level III. The results provide the characterization of novel doping behaviors for a trimeric aniline molecule in organic solution. PMID:22784005

Zhang, Qi; Khajo, Abdelahad; Sai, Tsunehiro; de Albuquerque, Ian; Magliozzo, Richard S; Levon, Kalle

2012-07-11

12

Effects of doped dye on the charge carrier injection, transport, and electroluminescent performance in polymeric light-emitting diodes  

NASA Astrophysics Data System (ADS)

The effects of doped fluorescent dye 4-(dicyanomethylene)-2-i-propyl-6-(1, 1, 7, 7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTI) on the charge carrier injection, transport and electroluminescence (EL) performance in polyfluorene (PFO)-based polymer light-emitting diodes (PLEDs) were investigated by steady-state current-voltage (I-V) characteristics and transient EL measurements. A red EL from DCJTI was observed and the EL performance depended strongly on the DCJTI concentration. The analysis of the steady-state I-V characteristics at different DCJTI concentrations found that three regions was shown in the I-V characteristics, and each region was controlled by different processes depending on the applied electric field. The effect of the dopant concentration on the potential-barrier height of the interface is estimated using the Fowler-Nordheim model. The dopant concentration dependence of the current-voltage relationship indicated clearly the carrier trapping by the DCJTI molecules. The mobility in DCJTI: PFO changed significantly with the DCJTI concentration, and showed a nontrivial dependence on the doping level. The behavior may be understood in terms of the formation of an additional energy disorder due to potential fluctuation caused by the Coulomb interaction of the randomly distributed doping molecules.

Chen, Zhenyu; Ma, Dongge

2007-07-01

13

The role of transport processes of nonequilibrium charge carriers in radiative properties of arrays of InAs/GaAs quantum dots  

SciTech Connect

The results of time-resolved photoluminescence studies of heterostructures containing monolayer arrays of InAs/GaAs quantum dots are presented. A two-component time dependence of intensity of photoluminescence from the ground state of quantum dots, with characteristic times of the slow component up to hundreds of nanoseconds and those of rapid one several nanoseconds, is studied. It is shown that the slow component is determined by the transport of nonequilibrium charge carriers between the quantum dots. At low temperatures, the time of the slow component is determined by tunneling, and at high temperatures by thermal escape of nonequilibrium charge carriers. The ratio of the contributions of tunneling and thermal escape is determined by the degree of isolation of quantum dots. A theoretical model is constructed that describes the effect of the dynamics of carrier transport on the emergence and decay of the slow component of photoluminescence.

Shkolnik, A. S., E-mail: alix@mbepl.ioffe.ru [Russian Academy of Sciences, Ioffe Physicotechnical Institute (Russian Federation); Savelyev, A. V. [St. Petersburg State Polytechnical University (Russian Federation); Karachinsky, L. Ya.; Gordeev, N. Yu.; Seisyan, R. P.; Zegrya, G. G. [Russian Academy of Sciences, Ioffe Physicotechnical Institute (Russian Federation); Pellegrini, S.; Buller, G. S. [Heriot-Watt University, School of Engineering and Physical Science (United Kingdom); Evtikhiev, V. P. [Russian Academy of Sciences, Ioffe Physicotechnical Institute (Russian Federation)

2008-03-15

14

Surface and Bulk Charge Carrier Transport in InAs Epilayers.  

National Technical Information Service (NTIS)

The purpose of this study was to characterize the electrical properties of InAs single crystal epilayers over a temperature range from 4K to 300K and to determine the effect of the surface transport characteristics on the measured galvanomagnetic paramete...

J. R. Sites H. H. Wieder

1975-01-01

15

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

NASA Astrophysics Data System (ADS)

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

Shahini, Ali.; Abbasian, Karim.

2012-08-01

16

Charge Carrier Transport Properties in Single-Walled Carbon Nanotube Fibers  

Microsoft Academic Search

Transport properties via temperature dependences of sample resistance R(T) and influence of microwave field of 10 GHz on the conductivity of the single-walled carbon nanotubes fibers are investigated. The R(T) dependences studied within 4.2-300 K can be well approximated by the Mott law for 3D variable range hopping below T=80 K and by typical law for fluctuation-induced tunnelling model within

V. K. Ksenevich; D. Seliuta; Z. Martunas; I. Kasalynas; G. Valusis; J. Galibert; M. E. Kozlov; V. A. Samuilov

2008-01-01

17

Transport of the charge carriers in SiC-detector structures after extreme radiation fluences  

NASA Astrophysics Data System (ADS)

The charge collection efficiency (CCE) of SiC-detectors preliminarily irradiated with 8 MeV protons at a fluence of 1014 cm-2 was investigated. Nuclear spectrometric techniques were employed, with 5.4 MeV alpha particles used to test the detectors. A concentration of primarily created defects of 4×1016 cm-3 was estimated and deep compensation of SiC conductivity was observed. In order to obtain a more uniform electric field distribution across the detectors, it is suggested to connect the structure in the forward direction. The experimental data obtained are processed using a simple model of signal formation. The model makes it possible to separate the contributions of the electrons and holes to the CCE.

Strokan, N. B.; Ivanov, A. M.; Lebedev, A. A.

2006-12-01

18

The Study Of Charge Carrier Transport On The Calamitic Liquid Crystals `` 5, 5'-Di-(Alkyl-Pyridin-Yl) - 2' Bithiophenes''  

NASA Astrophysics Data System (ADS)

The hole and electron mobilities in both types of calamitic liquid crystals C9 [5,5'-Di-(5-n-nonyl-pyridin-2-yl)-2,2'-bithiophenes] and C10 [5,5'-Di-(5-n-decyl-pyridin-2-yl)-2,2'-bithiophenes] were studied. The charge carrier mobilities were strongly electric field dependent. The mobilities decreased continuously with increase in the electric field up to a certain value, after which it became constant. Both types of charge carrier mobilities are independent of the temperature over our temperature range. The qualitative feature of our results could be tentatively explained by the Monte--Carlo modeling proposed by H Bassler. However, the results require further study for better understanding.

Shakya, Naresh; Pokhrel, Chandra; Ellman, Brett; Getmanenko, Yulia; Twieg, Robert

2010-03-01

19

Photocurrent spectroscopy for the investigation of charge carrier generation and transport mechanisms in organic p\\/n-junction solar cells  

Microsoft Academic Search

The photovoltaic behavior in a perylene\\/phthalocyanine hetero-p\\/n-junction solar cell was investigated using intensity-dependent I\\/V-characteristics and short circuit photocurrent spectroscopy. It is concluded that the charge carrier generation occurs only in a very thin active region at the contact. By optimizing the light trapping, a maximum solar AM 1.5 efficiency of about 2% can be obtained. A further increase requires better

Jörn Rostalski; Dieter Meissner

2000-01-01

20

Photocurrent spectroscopy for the investigation of charge carrier generation and transport mechanisms in organic p\\/n-junction solar cells  

Microsoft Academic Search

The photovoltaic behavior in a perylene\\/phthalocyanine hetero-p\\/n-junction solar cell was investigated using intensity-dependent I\\/<-characteristics and short circuit photocurrent spec- troscopy. It is concluded that the charge carrier generation occurs only in a very thin active region at the contact. By optimizing the light trapping, a maximum solar AM 1.5 e$ciency of about 2% can be obtained. A further increase requires

Dieter Meissner

2000-01-01

21

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

22

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

NASA Astrophysics Data System (ADS)

Time-resolved differential transmission measurements were used to investigate vertical charge carrier transport in mid-wave infrared InAs/GaSb type-II superlattices (T2SLs). By optically generating excess carriers near one end of the mid-wave T2SL and measuring the transit time to a thin, lower-bandgap T2SL at the other end, the time-of-flight of vertically diffusing carriers was measured. Through investigation of both unintentionally doped and p-type T2SLs, the vertical hole and electron diffusion coefficients were measured to be 0.04 +/- 0.03 cm2/s and 4.7 +/- 0.5 cm2/s, corresponding to vertical mobilities of 6 +/- 5 cm2/Vs and 700 +/- 80 cm2/Vs, respectively, at a temperature of 77 K.

Olson, B. V.; Murray, L. M.; Prineas, J. P.; Flatté, M. E.; Olesberg, J. T.; Boggess, T. F.

2013-05-01

23

Charge carrier scattering by defects in semiconductors  

NASA Astrophysics Data System (ADS)

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

Lordi, Vincenzo; Erhart, Paul; Åberg, Daniel

2010-06-01

24

Dynamical aspects of carrier transport in quantum well intersubband photodetectors  

Microsoft Academic Search

We report on the dynamics of the transport processes which determine the photoresponse of quantum well intersubband IR detectors. Immediately after intersubband excitation, coherent transport is important. This process can be identified via interference effects between photoexcited carriers. The carriers are re-captured subsequently within a few picoseconds. These fast transport processes give rise to space charges, which induce an additional,

Harald Schneider; Stefan Ehret; G. Bihlmann; Gerhard Boehm

1997-01-01

25

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

26

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

2013-07-24

27

Light-Enhanced Charge Mobility in a Molecular Hole Transporter  

Microsoft Academic Search

We present an investigation into the charge transport through a molecular hole transporter. Under illumination, photoinduced charge transfer occurs from a sensitizer to the hole transporter. The increased hole density results in striking enhancements in film conductivity, up to 106, and charge carrier mobility, up to 103. Such enhancements in mobility at low charge densities have not previously been observed

Henry J. Snaith; Michael Grätzel

2007-01-01

28

Analysis of photoexcited charge carrier density profiles in Si wafers by using an infrared camera  

NASA Astrophysics Data System (ADS)

We demonstrate the mapping of lateral photoexcited charge carrier density profiles in a Si wafer that is illuminated in a spot by strongly absorbed light, using an infrared camera. The radial decay measured for the charge carrier density yields information on the effective carrier lifetime. The lifetime is extracted from the infrared camera image by modeling the transport. The carrier lifetime determined with the infrared camera technique is in accord with results obtained by conventional transient microwave reflectance measurements.

Brendel, Rolf; Bail, Michael; Bodmann, Benno; Kentsch, Jörg; Schulz, Max

2002-01-01

29

The transport of potassium through lipid bilayer membranes by the neutral carriers valinomycin and monactin  

Microsoft Academic Search

Summary Stationary conductance experiments on neutral and negatively charged bilayer membranes in the presence of valinomycin or monactin agree with a recently proposed carrier transport model, which is common to both carrier types. This model assumes an interface reaction between a cation from the aqueous solution and a carrier molecule from the membrane phase to establish charge transport across the

G. Stark; R. Benz

1971-01-01

30

Charge-Carrier Screening in Single-Layer Graphene  

NASA Astrophysics Data System (ADS)

The effect of charge-carrier screening on the transport properties of a neutral graphene sheet is studied by directly probing its electronic structure. We find that the Fermi velocity, Dirac point velocity, and overall distortion of the Dirac cone are renormalized due to the screening of the electron-electron interaction in an unusual way. We also observe an increase of the electron mean free path due to the screening of charged impurities. These observations help us to understand the basis for the transport properties of graphene, as well as the fundamental physics of these interesting electron-electron interactions at the Dirac point crossing.

Siegel, David A.; Regan, William; Fedorov, Alexei V.; Zettl, A.; Lanzara, Alessandra

2013-04-01

31

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

Code of Federal Regulations, 2012 CFR

...CONTINUED) ACCESS CHARGES Computation of Charges for Price Cap Local Exchange Carriers § 69.153 Presubscribed interexchange...interexchange carrier to recover revenues totaling Average Price Cap CMT Revenues per Line month times the number of base...

2012-10-01

32

Charge transport in the ?-helix proteins  

NASA Astrophysics Data System (ADS)

In this paper we investigate charge transport in the a- helix proteins. It is considered that charge carriers are partially dressed small polarons, that are formed by electron self-trapping in the weak coupling limit. Polaron properties are considered by applying mean-field theory based upon the modified Lang-Firsov transformation and the Bogolyubov theorem. The transport properties have been calculated on the basis of the Holstein MC model. The obtained results are compared with the results of previous models.

?evizovi?, D.; Galovi?, S.; Zekovi?, S.; Ivi?, Z.

2010-11-01

33

Carrier loss in dispersive transport in amorphous semiconductors  

SciTech Connect

The effects on dispersive transport of carrier loss due to deep trapping or monomolecular recombination are calculated via simple arguments. The Hecht analysis of charge collection is shown to be valid in the presence of dispersive transport. Approximate solutions are given for the case of an exponential tail.

Eggert, J.R.

1984-01-01

34

HOT CARRIER EFFECTS WITHIN MACROSCOPIC TRANSPORT MODELS  

Microsoft Academic Search

The distribution function of hot carriers in state-of-the-art devices is insu ciently de-scribed using just the electric eld or the average carrier energy as parameters. Still, the standard models to describe carrier transport in semiconductor devices, namely the drift-di usion model and the energy-transport model rely on these assumptions. In this article we summarize our work on six moments transport

TIBOR GRASSER; HANS KOSINA; SIEGFRIED SELBERHERR

35

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

36

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

Rehak, P.; Gatti, E.

1987-08-18

37

Charge carrier dynamics in metalated polymers investigated by optical-pump terahertz-probe spectroscopy.  

PubMed

We report charge carrier dynamics in solid films of a series of metalated polymers based on Pt- and 4,7-di-2'-thienyl-2,1,3,-benzothiadiazole or 4,7-di-2'-thienothienyl-2,1,3,-benzothiadiazole upon photoexcitation of the pi-pi* transition using optical-pump terahertz-probe spectroscopy. Subpicosecond generated charge carriers recombine within 100 ps, but bound excitons persist. Application of the Drude-Smith model allows for estimation of the intrinsic mobility and internal quantum yield of charge carrier generation in these films. Thermal annealing is found to have no effect on nanometer scale charge transport. PMID:19886608

Cunningham, Paul D; Hayden, L Michael; Yip, Hin-Lap; Jen, Alex K-Y

2009-11-26

38

Organic (opto)electronic materials: understanding charge carrier dynamics  

NASA Astrophysics Data System (ADS)

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

Ostroverkhova, Oksana

2008-05-01

39

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

Code of Federal Regulations, 2012 CFR

...COMMUNICATIONS COMMISSION (CONTINUED) COMMON CARRIER SERVICES (CONTINUED) ACCESS CHARGES Computation of Charges for Price Cap Local Exchange Carriers § 69.154 Per-minute carrier common line charge. (a) Local exchange carriers may...

2012-10-01

40

Charge transport in cobalt-doped iron pyrite  

Microsoft Academic Search

The Hall effect and resistivity of the carrier-doped magnetic semiconductor Fe1-xCoxS2 were measured for 0<=x<=0.16 , temperatures between 0.05 and 300 K, and fields of up to 9 T. Our Hall data indicate electron charge carriers with a density of only 10-30% of the Co density of our crystals. The charge-carrier transport is dominated by a Kondo-like anomaly below 20

S. Guo; D. P. Young; R. T. Macaluso; D. A. Browne; N. L. Henderson; J. Y. Chan; L. L. Henry; J. F. Ditusa

2010-01-01

41

Mobility of charge carriers in porous silicon layers  

Microsoft Academic Search

The (conduction) mobility of majority charge carriers in porous silicon layers of the n and p types is estimated by joint measurements of electrical conductivity and free charge carrier concentration, which is determined from IR absorption spectra. Adsorption of donor and acceptor molecules leading to a change in local electric fields in the structure is used to identify the processes

P. A. Forsh; M. N. Martyshov; A. P. Latysheva; A. S. Vorontsov; V. Yu. Timoshenko; P. K. Kashkarov

2008-01-01

42

Anomalous Charge Transport in Disordered Organic Semiconductors  

SciTech Connect

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

Muniandy, S. V.; Woon, K. L. [Department of Physics, University of Malaya, 50603 Kuala Lumpur (Malaysia); Choo, K. Y. [Faculty of Engineering, Multimedia University, 63100 Cyberjaya, Selangor (Malaysia)

2011-03-30

43

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

44

Generation and transport of photo-excited carriers in diamond  

NASA Astrophysics Data System (ADS)

Photo-excited carrier transport in diamond has generated substantial interest in the past few years. The combination of high thermal conductivity, large band-gap, and large dielectric breakdown make diamond attractive in optoelectronic, high-power and high-frequency applications. Here we present measurements of electrical conduction by sub-band gap photo-excited carriers between metallic gates lithographically patterned on the surface of single-crystal type Ib diamond. The time-dependent charging and discharging photo-currents follow a ``stretched exponential'' form, which results from a trap state conduction mechanism mitigated by a local space charge. We also perform photo-excited magneto-transport as well as energy-dependant photo-conduction measurements to investigate the detailed origins of this sub-gap photo-excited conduction.

Heremans, F. J.; Fuchs, G. D.; Wang, C. F.; Awschalom, D. D.; Hanson, Ronald

2009-03-01

45

Minority carrier transport in heavily doped silicon  

NASA Astrophysics Data System (ADS)

The physics of minority carrier transport in heavily doped regions of small bipolar transistors is investigated. Minority carrier transport in heavily doped quasi neutral regions can be modeled by two coupled differential equations of the first order including the effects of density of states distortion. The energy dependent mobility and lifetime are incorporated into the transport equations. The quantum mechanical tail model is simplified by an empirical exponential expression. Densities of states, for both conduction and valence bands, are derived from photoluminescence spectra. At room temperatures, the presence of band tails in both bands increases the equilibrium minority carrier concentration by a factor of two. For modeling of very small bipolar transistors, classical macroscopic models cannot be used. The fluctuation in the base current was studied by using the two dimensional ensemble Monte Carlo technique. The most important result is that the fluctuation in the minority carrier current is a limitation for scaling bipolar transistors. The minority hole transport parameters were measured in highly doped emitters. A numerical method to solve the inhomogeneous profile problem was developed. The transport parameters were measured on doped arsenic. No lifetime degradation in arsenic implanted layers was observed. This suggests a controlled annealing process and gettering, expected to remove most of the defects from the emitters.

Pan, Yang

46

Grating competition for charge carriers in photorefractive bismuth silicon oxide  

NASA Astrophysics Data System (ADS)

Charge carrier competition between the gratings produced in degenerate four-wave mixing in bismuth silicon oxide reduces steady-state diffraction efficiency, suppresses several processes of transient diffraction efficiency, and changes the concavity of reflection grating development.

Khoury, Jehad; Cronin-Golomb, Mark; Woods, Charles

1995-01-01

47

Temperature delocalization of charge carriers in semiconductor lasers  

SciTech Connect

The temperature dependences of emission characteristics are investigated for laser diodes based on asymmetric separate-confinement heterostructures with a broadened waveguide. It is established that an increase in the charge-carrier concentration in the waveguide layer is the basic mechanism of saturation in the light-current characteristic with increasing temperature in the CW mode. It is experimentally shown that the temperature delocalization of charge carriers leads to increasing internal optical losses and decreasing external differential quantum efficiency. It is shown that the degree of delocalization of charge carriers depends on the charge-carrier temperature distribution, the threshold concentration, and the quantum-well depth. The effect of thickness and energy depth of the quantum well on the temperature sensitivity of the threshold current and output optical power is considered.

Slipchenko, S. O., E-mail: serghpl@mail.ioffe.ru; Shashkin, I. S.; Vavilova, L. S.; Vinokurov, D. A.; Lyutetskiy, A. V.; Pikhtin, N. A.; Podoskin, A. A.; Stankevich, A. L.; Fetisova, N. V.; Tarasov, I. S. [Russian Academy of Sciences, Ioffe Physicotechnical Institute (Russian Federation)

2010-05-15

48

Quantum control of charge carrier dynamics in layered semiconductor heterostructures  

Microsoft Academic Search

This dissertation presents theoretical studies of charge carrier dynamics in layered semiconductor heterostructures. Carrier dynamics are investigated by solving the Schrodinger equation numerically on a grid. Control methods are used to discover laser pulses that actively manipulate and control dynamics in quantum well systems. Results indicate that a wide array of possible target objectives can be achieved successfully using simple,

Kevin Lee Shuford

2003-01-01

49

Mobility of charge carriers in porous silicon layers  

Microsoft Academic Search

The (conduction) mobility of majority charge carriers in porous silicon layers of the n and p types is estimated by joint measurements of electrical conductivity and free charge carrier concentration, which is determined\\u000a from IR absorption spectra. Adsorption of donor and acceptor molecules leading to a change in local electric fields in the\\u000a structure is used to identify the processes

P. A. Forsh; M. N. Martyshov; A. P. Latysheva; A. S. Vorontsov; V. Yu. Timoshenko; P. K. Kashkarov

2008-01-01

50

Spatially Correlated Charge Transport in Organic Thin Film Transistors  

Microsoft Academic Search

Hole mobility in organic ultrathin film field-effect transistors is studied as a function of the coverage. For layered sexithienyl films, the charge carrier mobility rapidly increases with increasing coverage and saturates at a coverage of about two monolayers. This shows that the first two molecular layers next to the dielectric interface dominate the charge transport. A quantitative analysis of spatial

Franco Dinelli; Mauro Murgia; Pablo Levy; Massimiliano Cavallini; Fabio Biscarini; Dago M. de Leeuw

2004-01-01

51

Models of charge transport in electron-beam irradiated insulators  

Microsoft Academic Search

Charge transport in electron-beam irradiated insulators can be studied with various theoretical models based on different assumptions concerning generation, drift, trapping, and recombination of the charge carriers. In the past, two models have been of particular interest. A first macroscopic approach is based on the concept of a radiation-induced conductivity (RIC) generated by the injected electrons. As opposed to this,

G. M. Sessler; M. T. Figueiredo; G. F. Leal Ferreira

2004-01-01

52

Anisotropic dynamics of charge carriers in graphene  

NASA Astrophysics Data System (ADS)

Computer simulation by numerically solving the time-dependent Schrödinger equation was used to investigate the spreading of electronic wave packets on the graphene surface injected from a local probe. The simulations show a highly anisotropic in-plane dynamics following a 60? angular periodicity even near the Fermi energy. The wave packet first tunnels onto the small graphene clusters below the tip and the electronic states of these clusters govern the further spreading of the electron on the graphene surface. It was found that in the vicinity of the injection point the molecular physical behavior dominates, but at larger distances the wave propagation is governed by solid-state physical rules. The calculations show complex charge-spreading phenomena at graphene grain boundaries. Our results reveal a new picture of charge propagation in graphene, which has important consequences for nanoelectronic applications.

Márk, Géza I.; Vancsó, Péter; Hwang, Chanyong; Lambin, Philippe; Biró, László P.

2012-03-01

53

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

2012-06-07

54

Models of charge transport in electron-beam irradiated insulators  

Microsoft Academic Search

Carrier generation in an insulator due to electron-beam irradiation causes a radiation-induced conductivity. This phenomenon can be considered in the equations for charge transport in two different ways: A first, macroscopic, approach takes into account only the radiation-induced conductivity while a second, microscopic, scheme is based on a detailed description of the carrier generation and recombination in the insulator including

G. M. Sessler; M. T. Figueiredo; G. F. L. Ferreira

2002-01-01

55

Charge transport in desolvated DNA  

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

56

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

57

Cyclodextrin carriers of positively charged porphyrin sensitizers.  

PubMed

The cationic sensitizer 5,10,15,20-tetrakis(N-methylpyridinium-4-yl)porphyrin (TMPyP) forms supramolecular complexes with native, per-methylated, sulfonated and dimethyl-sulfonated cyclodextrins (CDs). Binding interactions were proved by NMR, mass spectra, capillary zone electrophoresis, UV-Vis and fluorescence spectroscopy. The 2D-NMR experiments on native CDs indicate that the interaction of TMPyP with the external CD surface is the dominant binding mode. The high binding affinity of TMPyP towards sulfonated CDs is due to electrostatic interactions. Binding is accompanied by an increase of the TMPyP basicity. Whereas betaCD does not affect the lifetime of the TMPyP triplet states, binding with sulfonated CDs causes the protonation of the TMPyP triplet states even in neutral solution. The diprotonated anionic sensitizer 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPSH(2)(2+)) forms host-guest complexes with native betaCD and gammaCD, similarly as in its non-protonated state. The positive charge of pyrrole nitrogen atoms does not significantly influence the mode of the interaction. In contrast to TMPyP, the lifetimes of the triplet states of bound TPPSH(2)(2+) to native CDs increase. PMID:19707685

Mosinger, Jirí; Slavetínská, Lenka; Lang, Kamil; Coufal, Pavel; Kubát, Pavel

2009-07-20

58

Visualization of Charge Transport Through Landau Levels in Graphene  

SciTech Connect

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

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

2010-11-01

59

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

PubMed

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

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

2013-07-19

60

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

NASA Astrophysics Data System (ADS)

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.

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

2013-08-01

61

Protonic and Electronic Charge Carriers in Solvated Biomacromolecules.  

National Technical Information Service (NTIS)

Evidence for intrinsic protonic conduction in solvated biomacromolecules was sought during vectorial charge transport. The methodology involved the adsorption of water and other organic liquids on biomacromolecules and subsequent solid-state electrolysis....

M. R. Powell

1989-01-01

62

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

63

Trapping-related recombination of charge carriers in silicon  

NASA Astrophysics Data System (ADS)

We present experimental evidence and theoretical explanation for simultaneous occurrence of trapping related increased apparent carrier lifetime and decreased actual recombination lifetime in low injection. This correlation is not describable by the common Hornbeck and Haynes [Phys. Rev. 97, 311 (1955)] trapping model. McIntosh, Paudyal, and Macdonald [J. Appl. Phys. 104, 084503 (2008)] recently used Shockley-Read-Hall (SRH) recombination statistics [Phys. Rev. 87, 835 (1952)] for describing the temperature dependence of trapping. Our study shows that these SRH statistics for traps also explain a causal connection between trapping-related increased apparent charge carrier lifetime and reduced actual lifetime in low injection.

Harder, N. P.; Gogolin, R.; Brendel, R.

2010-09-01

64

Carrier transport in magnesium diboride: Role of nano-inclusions  

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

65

An experimental investigation of charge transport through rubber  

Microsoft Academic Search

The d.c. and a.c. electrical properties of rubber have been investigated as a function of temperature to determine the mechanism for charge transport through the bulk and the nature of the charge carriers involved. Hopping appears to be the predominant mechanism, although a transition from hopping-type to an effectively band-type conduction may occur. High bulk polarization is present and peaks

R E Carley Read; C D Stow

1969-01-01

66

Flexible cobalt-phthalocyanine thin films with high charge carrier mobility  

SciTech Connect

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

Singh, Ajay [Technical Physics Division, Bhabha Atomic Research Center, Mumbai 400 085 (India); Universite Paris Diderot, Sorbonne Paris Cite, ITODYS, UMR 7086, CNRS F-75013 Paris (France); Kumar, Arvind; Kumar, Ashwini; Samanta, Soumen; Debnath, Anil K.; Jha, Purushottam; Prasad, Rajeshwar; Aswal, Dinesh K.; Gupta, Shiv K. [Technical Physics Division, Bhabha Atomic Research Center, Mumbai 400 085 (India); Salmi, Zakaria; Nowak, Sophie; Chehimi, Mohamed M. [Universite Paris Diderot, Sorbonne Paris Cite, ITODYS, UMR 7086, CNRS F-75013 Paris (France)

2012-11-26

67

Charge carrier mobility in a two-phase disordered organic system in the low-carrier concentration regime  

NASA Astrophysics Data System (ADS)

In this paper we use a three-dimensional Pauli master equation to investigate the charge carrier mobility of a two-phase system which can mimic donor-acceptor and amorphous-crystalline bulk heterojunctions. By taking the energetic disorder of each phase, their energy offset, and domain morphology into consideration, we show that the carrier mobility can have a completely different behavior when compared to a one-phase system. When the energy offset is equal to zero, the mobility is controlled by the more disordered phase. When the energy offset is nonzero, we show that the mobility electric field dependence switches from negative to positive at a threshold field proportional to the energy offset. Additionally, the influence of morphology, through the domain size and volume ratio parameters, on the transport is investigated and an approximate analytical expression for the zero field mobility is provided.

Woellner, Cristiano F.; Li, Zi; Freire, José A.; Lu, Gang; Nguyen, Thuc-Quyen

2013-09-01

68

Carrier transport in amorphous SiC/crystalline silicon heterojunctions  

NASA Astrophysics Data System (ADS)

Charge carrier transport in chemical vapor-deposited amorphous SiC/p-type crystalline Si heterostructures has been studied over the temperature range 80-400 K, using current-voltage (I-V), current-temperature (I-T), capacitance-voltage (C-V), and capacitance relaxation (C-t) characteristics. These heterojunctions exhibit high breakdown voltages (230 V) and a diode rectification ratio of 103 at +/-0.5 V. At low temperatures (80-120 K) the a-SiC behaves like a dielectric, and the interface built-in voltage can be determined from the capacitance-voltage plot. The corresponding low forward bias current flow is limited by variable-range electron hopping conductivity at Fermi level in the a-SiC layer. At increasing temperature and forward bias voltage, an additional hole current component is found with the transport governed by a multistep tunneling hole emission process through the a-SiC/c-Si heterobarrier. At still higher forward bias voltages (>0.8 V), space-charge-limited hole conduction in the presence of traps in the a-SiC bulk limits transport.

Nazarov, A. N.; Vovk, Ya. N.; Lysenko, V. S.; Turchanikov, V. I.; Scryshevskii, V. A.; Ashok, S.

2001-04-01

69

Renal glutathione transport: Identification of carriers, physiological functions, and controversies.  

PubMed

Glutathione (GSH) is an endogenous tripeptide composed of the amino acids L-glutamate, L-cysteine, and glycine. It is found in virtually all aerobic cells and plays critical roles in maintenance of cellular redox homeostasis and drug metabolism. An important component of its regulation is transport across biological membranes. Because GSH is a charged, hydrophilic molecule, transport occurs via catalysis by specific carrier proteins rather than by simple diffusion. Although it has been clearly understood that efflux of GSH across membranes such as the canalicular and sinusoidal plasma membranes in hepatocytes and the brush-border plasma membrane in renal proximal tubules is a key step in GSH turnover and interorgan metabolism, the existence and physiological functions of uptake of GSH across various epithelial plasma membranes has been subject to some debate. Besides transport across plasma membranes, GSH transport across intracellular membranes, most notably the mitochondrial inner membrane, has received some attention in recent years because of the importance of mitochondrial redox status and the mitochondrial GSH pool in cellular physiology and pathology. This commentary will focus on renal transport processes for GSH and will discuss some of the controversies that have existed and still seem to exist in the literature, specifically regarding uptake of intact GSH by basolateral membranes of renal proximal tubular cells and uptake of intact GSH by the mitochondrial inner membrane. PMID:19904718

Lash, Lawrence H

70

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

71

Charge carrier dynamics in phonon-induced fluctuation systems from time-dependent wavepacket diffusion approach.  

PubMed

A time-dependent wavepacket diffusion method is proposed to deal with charge transport in organic crystals. The electron-phonon interactions in both site energies and electronic couplings are incorporated by the time-dependent fluctuations which are generated from the corresponding spectral density functions. The numerical demonstrations reveal that the present approach predicts the consistent charge carrier dynamics with the rigorous quantum approaches. In addition, the diffusion coefficients obtained from the Marcus formula are well reproduced at the weak electronic coupling and high temperature limits. It is also found that the charge mobility feature of the crossover from the band-like to the hopping-type cannot be predicted from the fluctuations induced by the linear electron-phonon interactions with an Ohmic spectral density; however, it indeed appears as the electronic coupling fluctuation exponentially depends on the nuclear coordinates. Finally, it should be noted that although the present approach neglects the imaginary fluctuation, it essentially incorporates the coherent motion of the charge carrier and quantum effect of the phonon motion with a broad regime of the fluctuations for symmetric systems. Besides, the approach can easily be applied to systems having thousands of sites, which allows one to investigate charge transport in nanoscale organic crystals. PMID:21992285

Zhong, Xinxin; Zhao, Yi

2011-10-01

72

Small signal admittance spectroscopy applied for extraction of charge carrier mobility in thin organic layers  

NASA Astrophysics Data System (ADS)

The work presents new way of extraction of charge carrier mobility from small signal spectra of admittance. It can be a useful method for thin organic layers in a sandwich arrangement. It is better than the version of small signal admittance currently applied for getting charge carrier mobility, since the final result is not charged with uncertainty of geometric capacitance and the upper limit of measurable charge carrier mobility is higher.

Jarosz, G.; Signerski, R.

2011-12-01

73

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

Code of Federal Regulations, 2011 CFR

...Computation of Charges for Price Cap Local Exchange Carriers § 69.154 Per-minute carrier common line charge. (a) Local exchange carriers may recover a per-minute...the lower of: (1) The per-minute rate using base period demand that would...

2011-10-01

74

Heterojunction effect on the charge injection and transport  

NASA Astrophysics Data System (ADS)

The charge injection and transport across an organic heteroinjection of is investigated. The heteroinjection is formed by a poly-p-phenylene vinylene derivative (MEH-PPV) hole injection layer with a poly(9,9-dioctylfluorene) (PFO) hole accepting layer on top. The electric field in the accepting layer is obtained after correcting the applied voltage for the voltage drop across the injecting layer due to the buildup of space charge. The distribution of electric field in the accepting layer has effect on the transport of charge. At high electric fields, the current across the heterojunction exhibits only a weak dependence on the field. The strong dependence at low fields can be explained by taking the increase of the Fermi level into account, which effectively modifies the barrier for charge carriers waiting for a jump across the heterojunction.

Quan, Shanyu; Yang, Linmei; Teng, Feng; Xu, Zheng; Wang, Yongsheng

2010-01-01

75

Charge carrier tuning of mid-infrared plasmonic devices  

NASA Astrophysics Data System (ADS)

There is currently a wide variety of passive plasmonic technologies, with applications in the fields of sensing, security, and optical interconnects and computing. Development of a rapidly and broadly tunable plasmonic device would be an enabling technology, giving active control over these traditionally passive devices. The free charge carrier concentration directly affects the dielectric permittivity of a semiconductor, which in turn determines the plasmonic resonance. Metal-oxide-semiconductor capacitors using n-type substrates permit the modulation of free charge carriers in a semiconductor by applying a bias. In this study, MOS-capacitors were fabricated with an extraordinary optical transmission gratings built into the top gate. Tuning of the optical resonance of an EOT spectrum is shown applying a reverse bias across the semiconductor. The oxide layer used was hafnium dioxide, grown by atomic layer deposition. The electrical properties of the hafnia were studied in order to maximize the capabilities of this design. The samples were processed using standard photolithography and wet etching techniques, and characterized by optical microscopy, probe testing, and transmission spectroscopy. Resonant tuning of 30 nm has been demonstrated. The maximum depletion width in the semiconductor limited the effect and prohibited broader tuning.

Anglin, Kevin

76

Charge transport in non-irradiated and irradiated silicon detectors  

NASA Astrophysics Data System (ADS)

A model describing the transport of the charge carriers generated in n-type silicon detectors by ionizing particles is presented. In order to reproduce the experimental current pulse responses induced by /? and /? particles in non-irradiated and irradiated detectors up to fluences /(?) much beyond the n to p-type inversion, an n-type region 15 /?m deep is introduced on the p+ side of the diode. This model also gives mobilities which decrease linearly up to fluences of around 5×1013 particles/cm2 and beyond, converging to saturation values of about 1000 and 450 cm2/Vs for electrons and holes, respectively. The charge carrier lifetime degradation with increased fluence, due to trapping, is responsible for a predicted charge collection deficit for /? particles and for /? particles which is found to agree with direct CCE measurements.

Leroy, C.; Roy, P.; Casse, G. L.; Glaser, M.; Grigoriev, E.; Lemeilleur, F.

1999-09-01

77

Self-consistent analytical solution of a problem of charge-carrier injection at a conductor/insulator interface  

NASA Astrophysics Data System (ADS)

We present a closed description of the charge-carrier injection process from a conductor into an insulator. Common injection models are based on single electron descriptions, being problematic especially once the amount of charge-carriers injected is large. Accordingly, we developed a model, which incorporates space-charge effects in the description of the injection process. The challenge of this task is the problem of self-consistency. The amount of charge carriers injected per unit time strongly depends on the energy barrier emerging at the contact, while at the same time the electrostatic potential generated by the injected charge carriers modifies the height of this injection barrier itself. In our model, self-consistency is obtained by assuming continuity of the electric displacement and the electrochemical potential all over the conductor/insulator system. The conductor and the insulator are properly taken into account by means of their respective density of state distributions. The electric-field distributions are obtained in a closed analytical form and the resulting current-voltage characteristics show that the theory embraces injection-limited as well as bulk-limited charge-carrier transports. Analytical approximations of these limits are given, revealing physical mechanisms responsible for the particular current-voltage behavior. In addition, the model exhibits the crossover between the two limiting cases and determines the validity of respective approximations. The consequences resulting from our exactly solvable model are discussed on the basis of a simplified indium tin oxide/organic semiconductor system.

Neumann, F.; Genenko, Y. A.; Melzer, C.; Yampolskii, S. V.; von Seggern, H.

2007-05-01

78

High speed quantum-well lasers and carrier transport effects  

Microsoft Academic Search

Carrier transport can significantly affect the high-speed properties of quantum-well lasers. The authors have developed a model and derived analytical expressions for the modulation response, resonance frequency, damping rate, and K factor to include these effects. They show theoretically and experimentally that carrier transport can lead to significant low-frequency parasitic-like rolloff that reduces the modulation response by as much as

Radhakrishnan Nagarajan; Masayuki Ishikawa; Toru Fukushima; Randall S. Geels; John E. Bowers

1992-01-01

79

Charge transport across multiple p-n junctions in graphene  

NASA Astrophysics Data System (ADS)

Transmission resonances due to Fabry-Perot interference can be realized with multiple p-n junctions in graphene. Edge state mixing and equilibration of the edge channels near the p-n junction in the presence of magnetic field give rise to fractionally quantized plateaus in the conductance which can be used as an interconnect-less quantum Hall resistance standard. Motivated by these, we study charge transport across multiple p-n junctions and have observed Fabry-Perot oscillation in the conductance. We have probed the effect of density of carriers and the height of potential barrier as a function of the magnetic field in these devices. We have observed quantum Hall plateaus in the two probe resistance measurement over a larger range of charge carrier densities. This holds for the situation where we have charge carriers of the same type (electrons or holes) with different densities. We will also discuss the possibility of studying charge transport parallel and perpendicular to the p-n junctions.

Dubey, Sudipta; Singh, Vibhor; Bhat, Ajay; S, Abhilash T.; Deshmukh, Mandar

2012-02-01

80

Interface recombination influence on carrier transport  

NASA Astrophysics Data System (ADS)

A theory of interface recombination in the semiconductor-semiconductor junction is developed. The interface recombination rate dependence on the nonequilibrium carrier densities is derived on the basis of a model in which the interface recombination occurs through the mechanism of trapping. The general relation between the interface recombination parameters at small carrier density deviation from the equilibrium ones is obtained. The validity of this relation is proved considering the generation of the Hall electric field in the extrinsic semiconductor sample. The anomalous Hall electromotive force in a weak magnetic field was investigated and interpreted by means of a new interface recombination model. The experimental data corroborate the developed theory.

Konin, A.

2013-02-01

81

Effect of charge carrier doping in YbRh2Si2  

NASA Astrophysics Data System (ADS)

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

Gegenwart, Philipp

2013-03-01

82

Fractal spectrum of charge carriers in quasiperiodic graphene structures  

NASA Astrophysics Data System (ADS)

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.

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

2010-11-01

83

Effects of intrinsic base-pair fluctuations on charge transport in DNA.  

PubMed

We investigate propagation of a charge carrier along intrinsically dynamically disordered double-stranded DNA. This is realized by the semiclassical coupling of the charge with a nonlinear lattice model that can accurately describe the statistical mechanics of the large amplitude fluctuations of the base pairs leading to the thermal denaturation transition of DNA. We find that the fluctuating intrinsic disorder can trap the charge and inhibit polaronic charge transport. The dependence of the mean distance covered by the charge carrier until its trapping, as a function of the energy of the fluctuations of the base pairs is also presented. PMID:12188757

Komineas, S; Kalosakas, G; Bishop, A R

2002-06-17

84

Why positive hole carriers and negatively charged planes are conducive to high temperature superconductivity  

NASA Astrophysics Data System (ADS)

The vast majority of superconducting materials have positive Hall coefficient in the normal state, indicating that hole carriers dominate the normal state transport. This was noticed even before BCS theory, and has been amply confirmed by materials found since then: the sign of the Hall coefficient is the strongest normal state predictor of superconductivity. In the superconducting state instead, superfluid carriers are always electron-like, i.e. negative, as indicated by the fact that the magnetic field generated by rotating superconductors is always parallel, never antiparallel, to the body's angular momentum ("London moment"). BCS theory ignores these facts. In contrast, the theory of hole superconductivity, developed over the past 20 years (papers listed in http://physics.ucsd.edu/˜jorge/hole.html) makes charge asymmetry the centerpiece of the action. The Coulomb repulsion between holes is shown to be smaller than that between electrons, thus favoring pairing of holes, and this fundamental electron-hole asymmetry is largest in materials where the conducting structures have excess negative charge, as is the case in the cuprates, arsenides and MgB2. Charge asymmetry implies that superconductivity is driven by lowering of kinetic energy, associated with expansion of the carrier wavefunction and with expulsion of negative charge from the interior to the surface of the material, where it carries the Meissner current. This results in a macroscopic electric field (pointing outward) in the interior of superconductors, and a macroscopic spin current flowing near the surface in the absence of external fields, a kind of macroscopic zero point motion of the superfluid (spin Meissner effect). London's electrodynamic equations are modified in a natural way to describe this physics. It is pointed out that a dynamical explanation of the Meissner effect requires radial outflow of charge in the transition to superconductivity, as predicted by this theory and not predicted by BCS. The theory provides clear guidelines regarding where new higher Tc superconductors will and will not be found.

Hirsch, J. E.

2011-03-01

85

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

PubMed

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 (241)Am 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

2012-12-01

86

Carrier-mediated transport to enhance drug delivery to brain  

Microsoft Academic Search

Drug delivery to brain can be improved through the design of novel therapeutic agents that are rapidly and selectively shuttled into the nervous system across the blood–brain barrier (BBB) by the facilitated influx transporters of brain capillaries. Messenger RNA analysis has demonstrated high expression of >20 influx transporters at the BBB, including carriers for glucose (GLUT1), monocarboxylic acids (MCT1), large

Quentin R. Smith

2005-01-01

87

Valley-polarized massive charge carriers in gapped graphene  

NASA Astrophysics Data System (ADS)

The lifting of the fourfold degeneracy of the zeroth Landau level in graphene under high magnetic fields has been the subject of numerous experimental studies, and attributed to various mechanisms such as pure spin splitting, spin splitting combined with subsequent valley splitting, or the formation of a quantum Hall insulator. Unexplored, however, is the influence of an energy gap on the quantum Hall effect (QHE) states in graphene. Here we demonstrate, using measurements of the magnetoresistance of graphene antidot lattices (GALs) in magnetic fields up to 30 T and temperatures between 2 and 100 K, that gap opening in these samples is accompanied by valley polarization and a change from linear to parabolic band structure at low carrier energies. The emergence of a massive character of the carriers profoundly alters the transport characteristics of the zeroth Landau level, which manifests itself in a linear increase of the activated gap with magnetic field. Furthermore, samples of the highest quality display spin splitting on top of the valley splitting, albeit of significantly smaller magnitude.

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

2013-05-01

88

Morphogenesis of post-Golgi transport carriers  

Microsoft Academic Search

The trans-Golgi network (TGN) is one of the main, if not the main, sorting stations in the process of intracellular protein trafficking.\\u000a It is therefore of central importance to understand how the key players in the TGN-based sorting and delivery process, the\\u000a post-Golgi carriers (PGCs), form and function. Over the last few years, modern morphological approaches have generated new\\u000a insights

Alberto Luini; Alexander A. Mironov; Elena V. Polishchuk; Roman S. Polishchuk

2008-01-01

89

Experimental determination of the rate law for charge carrier decay in a polythiophene: Fullerene solar cell  

Microsoft Academic Search

We use transient photovoltage and differential charging experiments, complemented by transient absorption data, to determine charge carrier lifetimes and densities in a poly(3-hexylthiophene): methanofullerene solar cell at Voc as a function of white light-bias intensity. For a typical device, the charge carrier decay dynamics are observed to exhibit an approximately third order dependence on charge density (dn\\/dt~n3).

C. G. Shuttle; B. O'Regan; A. M. Ballantyne; J. Nelson; D. D. C. Bradley; J. de Mello; J. R. Durrant

2008-01-01

90

Energy resolution and related charge carrier mobility in LaBr3:Ce scintillators  

NASA Astrophysics Data System (ADS)

The scintillation response of LaBr3: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% Ce3+ doped LaBr3, 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.

2013-09-01

91

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

92

Charge transport and mass transport in imidazolium-based ionic liquids.  

PubMed

The mechanism of charge transport in the imidazolium-based ionic liquid 1,3-dimethylimidazolium dimethylphosphate is analyzed by combining broadband dielectric spectroscopy (BDS) and pulsed field gradient nuclear magnetic resonance (PFG NMR). The dielectric spectra are dominated-on the low-frequency side-by electrode polarization effects while, for higher frequencies, charge transport in a disordered matrix is the underlying physical mechanism. Using the Einstein and Einstein-Smoluchowski equations enables one to determine-in excellent agreement with direct measurements by PFG NMR-the diffusion coefficient of the charge carriers. By that, it becomes possible to extract from the dielectric spectra separately the number density and the mobilities of the charge carriers and the type of their thermal activation. It is shown that the observed Vogel-Fulcher-Tammann (VFT) dependence of the dc conductivity can be traced back to a similar temperature dependence of the mobility while for the number density an Arrhenius-type thermal activation is found. Extrapolating the latter to room temperature indicates that nearly all charge carriers are participating in the conduction process. PMID:18643055

Sangoro, J R; Serghei, A; Naumov, S; Galvosas, P; Kärger, J; Wespe, C; Bordusa, F; Kremer, F

2008-05-02

93

Quantum control of charge carrier dynamics in layered semiconductor heterostructures  

NASA Astrophysics Data System (ADS)

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

Shuford, Kevin Lee

94

Electron and molecular dynamics: Penning ionization and molecular charge transport  

NASA Astrophysics Data System (ADS)

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

Madison, Tamika Arlene

95

Charge generation, charge transport, and residual charge in the electrospinning of polymers: A review of issues and complications  

NASA Astrophysics Data System (ADS)

Electrospinning has become a widely implemented technique for the generation of nonwoven mats that are useful in tissue engineering and filter applications. The overriding factor that has contributed to the popularity of this method is the ease with which fibers with submicron diameters can be produced. Fibers on that size scale are comparable to protein filaments that are observed in the extracellular matrix. The apparatus and procedures for conducting electrospinning experiments are ostensibly simple. While it is rarely reported in the literature on this topic, any experience with this method of fiber spinning reveals substantial ambiguities in how the process can be controlled to generate reproducible results. The simplicity of the procedure belies the complexity of the physical processes that determine the electrospinning process dynamics. In this article, three process domains and the physical domain of charge interaction are identified as important in electrospinning: (a) creation of charge carriers, (b) charge transport, (c) residual charge. The initial event that enables electrospinning is the generation of region of excess charge in the fluid that is to be electrospun. The electrostatic forces that develop on this region of charged fluid in the presence of a high potential result in the ejection of a fluid jet that solidifies into the resulting fiber. The transport of charge from the charge solution to the grounded collection device produces some of the current which is observed. That transport can occur by the fluid jet and through the atmosphere surrounding the electrospinning apparatus. Charges that are created in the fluid that are not dissipated remain in the solidified fiber as residual charges. The physics of each of these domains in the electrospinning process is summarized in terms of the current understanding, and possible sources of ambiguity in the implementation of this technique are indicated. Directions for future research to further articulate the behavior of the electrospinning process are suggested.

Collins, George; Federici, John; Imura, Yuki; Catalani, Luiz H.

2012-02-01

96

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

Code of Federal Regulations, 2012 CFR

...requirements for using common carrier transportation? 301-10.105 Section 301-10...ALLOWANCES ALLOWABLE TRAVEL EXPENSES 10-TRANSPORTATION EXPENSES Common Carrier Transportation § 301-10.105 What are the...

2012-07-01

97

Mean free paths of charge carriers in CZT crystal  

NASA Astrophysics Data System (ADS)

The asymmetrical distortion of the Cadmium Zinc Telluride ((CZT) energy spectrum is mainly caused by the hole trapping in the CZT crystal, and it can be characterized by the mean free path of hole. The mean free paths of the charge carriers in the CZT crystal can be extracted from fitting the peak shape of the measured energy spectrum. The energy spectra of ?-rays from 241Am, and that of ? particles from 238Pu were measured with a CZT with 5×5×5 mm3. The mean free path of the electron was determined from the bias dependence of ?-particle response. The energy spectra of ?-ray were simulated with EGSnrc code, in which Hecht equation was included, and the mean free path of the hole was determined by comparing the measured spectrum with the simulated one. The energy spectrum of 662 keV ?-ray was measured with the CZT detector, and it was compared with the simulated spectrum, in which newly determined mean free paths of the electron and the hole were used.

Park, Se-Hwan; Kim, Yong-Kyun; Jeon, Sung-Dae; Ha, Jang-Ho; Hong, Duk-Geun

2007-08-01

98

The influence of space charge regions on effective charge carrier lifetime in thin films and resulting opportunities for materials characterization  

NASA Astrophysics Data System (ADS)

The analysis of injection-dependent charge carrier lifetimes is a well-established method to determine material and interface quality in crystalline silicon wafer-based device structures such as solar cells. However, for thin films, this method has rarely been used. One reason is that the physical interpretation of experimental data must rely on advanced theoretical models. In this study, we show by numerical simulations and analytical approximations that the effective charge carrier lifetime in thin films is heavily affected by space charge regions (SCR) over a wide range of injection levels. By analysis of the characteristic features in the injection-dependent effective charge carrier lifetime curves, qualitative information about SCRs that occur at grain boundaries or interfaces can be obtained. In contrast, information about the defect density can only be extracted in a very limited range of injection levels and the relationship between effective charge carrier lifetime and the quasi-Fermi level splitting, which is limiting the open circuit voltage of wafer-based solar cells, is not valid in thin films. On the basis of this theoretical study, we analyze measurements of effective charge carrier lifetime in 1.5 ?m thin and 2 ?m fine-grained polycrystalline silicon films with lifetimes of up to 100 ?s and find experimental evidence for grain boundary potential barriers. Finally, we present guidelines for optimized photoconductance measurements and the evaluation of charge carrier lifetimes in thin films, in general.

Leendertz, C.; Teodoreanu, A.-M.; Korte, L.; Rech, B.

2013-01-01

99

Noise and charge transport in polymer thin film structures  

NASA Astrophysics Data System (ADS)

The low frequency noise (LFN) properties of the field-effect transistors (FETs) using polymers as the semiconducting material in thin-film transistor (TFT) structures are investigated and discussed in terms of the charge carrier transport. Results obtained from several research groups are summarized. Injection-drift limited model (IDLM) for charge transport in amorphous PFETs is discussed. IDLM has some advantages in comparison to the commonly used metal-oxide-semiconductor (MOS) transistor models. A general trend of proportionality between noise power density and the DC power applied to the polymer FET"s (PFET"s) channel is observed in the data from several research groups. This trend implies mobility fluctuation in PFET as the dominant noise source.

Marinov, Ognian; Deen, M. Jamal; Yu, J.; Vamvounis, G.; Holdcroft, Steven; Woods, W.

2003-05-01

100

An alternative approach to charge transport in semiconducting electrodes  

NASA Astrophysics Data System (ADS)

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

Thomchick, J.; Buoncristiani, A. M.

1980-12-01

101

MultiCharge Carrier Trapping in Organic Crystals: Quantized Internal Macrotrap Energy Levels  

Microsoft Academic Search

Multi-charge carrier capture by each member of a set of discrete spatially extended domains (macrotraps) is considered as a trapping mechanism responsible for the space charge evolution in the high-concentration regime of the charge introduced to organic crystals.Finite dimension and energy depth limit the number of carriers of the same sign to be captured by such a macrotrap. Due to

J. Kalinowski; J. Godlewski

1991-01-01

102

Theoretical characterization of charge transport in organic molecular crystals  

NASA Astrophysics Data System (ADS)

The rapid growth in the interest to explore new synthetic crystalline organic semiconductors and their subsequent device characterization has revived the debate on the development of theoretical models to better understand the intrinsic charge transport mechanisms in organic materials. At the moment, several charge-transport theories for organic molecular crystals have been proposed and have observed a comparable agreement with experimental results. However, these models are limited in scope and restricted to specific ranges of microscopic parameters and temperatures. A general description that is applicable in all parameter regimes is still unavailable. The first step towards a complete understanding of the problem associated with the charge transport in organic molecular crystals includes the development of a first-principles theoretical methodology to evaluate with high accuracy the main microscopic charge-transport parameters and their respective couplings with intra- and intermolecular vibrational degrees of freedom. In this thesis, we have developed a first-principles methodology to investigate the impact of electron-phonon interactions on the charge-carrier mobilities in organic molecular crystals. Well-known organic materials such as oligoacene and oligothienoacene derivatives were studied in detail. To predict the charge-transport phenomena in organic materials, we rely on the Marcus theory of electron-transfer reactions. Within this context, the nature of the intramolecular vibronic coupling in oligoacenes was studied using an approach that combines high-resolution gas-phase photo-electron spectroscopy measurements with first-principles quantum-mechanical calculations. This further led to investigation of the electron interactions with optical phonons in oligoacene single crystals. The lattice phonon modes were computed at both density functional theory (DFT) and empirical force field levels. The low-frequency optical modes are found to play a significant role in dictating the temperature dependence of the charge-transport properties in the oligoacene crystals. A combined classical molecular dynamics and quantum-chemical study on organic molecular crystals revealed that the lattice vibrations are a key component to be taken into account when designing organic materials with improved charge mobilities. Finally, we investigated the microscopic charge-transport parameters in the pentathienoacene, 1,4-diiodobenzene, and 2,6-diiododithieno[3,2- b:2',3'-d]thiophene crystals. In the first case, a combined DFT and gas-phase ultraviolet photoelectron spectroscopy approach revealed that the intrinsic charge transport properties in the pentathienoacene crystal might be higher than that in two benchmark high-mobility organic crystals, i.e., pentacene and sexithienyl. For 1,4-diiodobenzene crystal, a detailed quantum-mechanical study of the electronic and vibrational couplings indicated that its high mobility is primarily associated with the iodine atoms. In the 2,6-diiododithieno[3,2-b:3',2'- d]thiophene crystal, the main source of electronic interactions were found along the pi-stacking direction. For negatively charged carriers, these two halogen-functionalized molecular crystals show a very large polaron binding energy, which suggests significantly low charge-transport mobility for electrons.

Sanchez-Carrera, Roel S.

103

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

NASA Astrophysics Data System (ADS)

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

Sundqvist, Kyle Michael

104

Dependence of the conductivity on the concentration and the hopping frequency of charge carriers in fluoride glasses  

NASA Astrophysics Data System (ADS)

The conductivity spectra of fluoride glasses in the system ZrF4-BaF2-YF2-LiF with varying LiF content has been reported at different temperatures in the frequency range 10 Hz-2 MHz. The experimental data have been analyzed in the framework of the Almond-West formalism. The concentration and hopping frequency of the charge carriers, the dc conductivity, and the activation energy have been determined from the analysis of the data. The concentration of the charge carriers is observed to be almost independent of temperature and weakly dependent on composition. Both the hopping frequency and the dc conductivity exhibit a minimum at LiF content xLiF=0.20. It is observed that the charge transport in these glasses occurs by the hopping mechanism and the strong electrolyte model is applicable.

Sural, M.; Ghosh, A.

2000-04-01

105

Nanocone Tip-Film Solar Cells with Efficient Charge Transport  

SciTech Connect

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

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

2011-01-01

106

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

107

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.

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

2013-01-01

108

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

109

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

Code of Federal Regulations, 2011 CFR

...prevent the PICC from recovering all the residual common line/marketing and residual interconnection charge revenues, the PICC shall recover all residual common line/marketing revenues before it recovers residual interconnection charge...

2011-10-01

110

Free charge carrier repartition over the surface of photosensitive materials: Why and how to manage?  

Microsoft Academic Search

The free charge carrier repartition over the surface of the photosensitive solids can be efficiently managed by selective\\u000a elimination of the “parasite” free charge carriers (FCCs) from the exited body. This makes it possible to “correct” the natural\\u000a FCC repartition law represented by the well-known fifty-fifty ratio (1 generated electron in conduction band versus 1 hole\\u000a formed in valence band)

A. A. Evstratov; C. Chis; A. A. Malygin; J.-M. Taulemesse; P. Gaudon; T. Vincent

2008-01-01

111

Carrier transport characteristics of small-size field effect transistors  

NASA Astrophysics Data System (ADS)

The quantum wave transport of carriers driven by an external electric field (drain bias) is studied numerically in a typical GaAs/AlGaAs heterojunction field effect transistor as a function of the gate bias. We have shown that when the size of the transistor is reduced so that quantum effects become important, the operational characteristics of the transistor are dominated by the conductance quantization effect at infinitely small drain bias and zero temperature. The conductance quantization is diminished when the temperature is increased due to the thermal excitation effect. Normal I-V characteristics of the transistor performance are obtained for small-size field effect transistor where quantum wave transmission is the principal carrier transport mechanism.

Fu, Y.; Willander, M.

1999-04-01

112

Impact of Carrier Transport on Aquamarine--Green Laser Performance  

NASA Astrophysics Data System (ADS)

We studied the carrier transport phenomena of the multiple-quantum-well (MQW) active region and their impact on the performance of aquamarine and green laser diodes (LDs) grown on polar and semipolar planes. The ballistic carrier transport mechanism was found to be dominant in the MQW region. For the c-plane, because of the high hole capture probability and slow escape rate, mainly the quantum wells (QWs) positioned close to the p-side are electrically pumped. The optical loss induced by the underpumped QWs further away from the p-side leads to significantly higher laser threshold current density and a longer lasing wavelength with increased number of QWs. These effects are not significant for semipolar LD structures.

Sizov, Dmitry S.; Bhat, Rajaram; Zakharian, Aramais; Napierala, Jerome; Song, Kechang; Allen, Donald; Zah, Chung-en

2010-12-01

113

Transport of Polymeric Nanoparticle Gene Carriers in Gastric Mucus  

Microsoft Academic Search

Nanoparticle transport through mucosal barriers is often restricted owing to mucoad- hesion and the highly viscoelastic nature of mucus gels, which may limit efficient drug and gene delivery. We formulated sub-200 nm particulates from poly(D,L-lactic-co- glycolic) acid (PLGA) and the cationic surfactant dimethyldioctadecylammonium bromide (DDAB). Subsequently, anionic DNA was condensed to the surface to obtain gene carriers with transfection rates

Michelle Dawson; Eric Krauland; Denis Wirtz; Justin Hanes

2004-01-01

114

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

SciTech Connect

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

Devizis, A.; Serbenta, A.; Peckus, D. [Center for Physical Sciences and Technology, Savanoriu 231, LT-02300 Vilnius (Lithuania); Thiessen, A.; Alle, R.; Meerholz, K.; Hertel, D. [Department of Chemistry, Physical Chemistry, University of Cologne, Luxemburgerstr. 116, 50939 Cologne (Germany); Gulbinas, V. [Center for Physical Sciences and Technology, Savanoriu 231, LT-02300 Vilnius (Lithuania); Vilnius University, Sauletekio 9, LT-10220 Vilnius (Lithuania)

2010-10-28

115

The composite picture of the charge carriers in La2-xSrxCuO4 (0.063 <= x <= 0.11) superconductors  

NASA Astrophysics Data System (ADS)

Through far-infrared studies of La2-xSrxCuO4 single crystals for x = 0.063, 0.07, 0.09, and 0.11, we found that only {\\sim }0.2{%} of the total holes participated in the nearly dissipationless normal state charge transport and superconductivity. We have also observed characteristic collective modes at \\omega \\sim 18 and 22 cm-1 due to the bound carriers in an electronic lattice (EL) state, and the free carriers are massively screened by the EL. Our findings lead us to propose a composite picture of the charge system where the free carriers are coupled to and riding on the EL. This unique composite system of charge carriers may provide further insights into the understanding of the cuprate physics.

Kim, Y. H.; Hor, P. H.; Dong, X. L.; Zhou, F.; Zhao, Z. X.; Song, Y. S.; Ti, W. X.

2003-12-01

116

Temperature Dependent Kinetics DNA Charge Transport  

NASA Astrophysics Data System (ADS)

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

Wohlgamuth, Chris; McWilliams, Marc; Slinker, Jason

2012-10-01

117

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

118

Direct Observation of Charge-Carrier Heating at WZ-ZB InP Nanowire Heterojunctions.  

PubMed

We have investigated the dynamics of hot charge carriers in InP nanowire ensembles containing a range of densities of zinc-blende inclusions along the otherwise wurtzite nanowires. From time-dependent photoluminescence spectra, we extract the temperature of the charge carriers as a function of time after nonresonant excitation. We find that charge-carrier temperature initially decreases rapidly with time in accordance with efficient heat transfer to lattice vibrations. However, cooling rates are subsequently slowed and are significantly lower for nanowires containing a higher density of stacking faults. We conclude that the transfer of charges across the type II interface is followed by release of additional energy to the lattice, which raises the phonon bath temperature above equilibrium and impedes the carrier cooling occurring through interaction with such phonons. These results demonstrate that type II heterointerfaces in semiconductor nanowires can sustain a hot charge-carrier distribution over an extended time period. In photovoltaic applications, such heterointerfaces may hence both reduce recombination rates and limit energy losses by allowing hot-carrier harvesting. PMID:23919626

Yong, Chaw Keong; Wong-Leung, Jennifer; Joyce, Hannah J; Lloyd-Hughes, James; Gao, Qiang; Tan, H Hoe; Jagadish, Chennupati; Johnston, Michael B; Herz, Laura M

2013-08-12

119

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

120

Transport in charged colloids driven by thermoelectricity.  

PubMed

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

Würger, Alois

2008-09-05

121

Theoretical study of carrier transport and screening in topological insulator Bi2Se3  

NASA Astrophysics Data System (ADS)

This theoretical work is motivated by two recent experiments on Bi2Se3 examining the charge inhomogeneity [1-2] close to the topologically protected crossing point of surface bands in these bulk topological insulators. Reminiscent of graphene close to charge neutrality [3-4], the energy landscape becomes highly inhomogeneous, forming a sea of electron and hole puddles, which determine the properties at low carrier density. Here, we show that the induced carrier density fluctuations are of order 1 % of the impurity density, providing a small-parameter with which we can perform a controlled perturbation theory. Analytic results are obtained for the minimum conductivity and puddle auto-correlation length. We also find that the band asymmetry between electron and holes states is a necessary ingredient to understand the aforementioned experiments. References: [1] H. Beidenkopf et al, ``Spatial fluctuations of helical Dirac fermions on the surface of topological insulators,'' Nat. Phys. online publ., (2011) [2] D. Kim et al., ``Minimum conductivity and charge inhomogeneity in Bi2Se3,'' arXiv:1105.1410. [3] S. Adam et al., ``A self-consistent theory for graphene transport,'' PNAS 104, 18392 (2007). [4] S. Das Sarma et al., ``Electronic transport in 2D graphene,'' Rev. Mod. Phys. 83, 407 (2011).

Adam, Shaffique; Hwang, E. H.; Stiles, M. D.; Das Sarma, S.

2012-02-01

122

Hijacking Solute Carriers for Proton-Coupled Drug Transport  

NSDL National Science Digital Library

The physiological role of mammalian solute carrier (SLC) proteins is to mediate transmembrane movement of electrolytes, nutrients, micronutrients, vitamins, and endogenous metabolites from one cellular compartment to another. Many transporters in the small intestine, kidney, and solid tumors are H+-coupled, driven by local H+-electrochemical gradients, and transport numerous drugs. These transporters include PepT1 and PepT2 (SLC15A1/2), PCFT (SLC46A1), PAT1 (SLC36A1), OAT10 (SLC22A13), OATP2B1 (SLCO2B1), MCT1 (SLC16A1), and MATE1 and MATE2-K (SLC47A1/2).

Catriona Anderson (Newcastle University); David Thwaites (Newcastle University)

2010-12-01

123

Charge Transport in Functionalized Fluorinated Pentacenes  

NASA Astrophysics Data System (ADS)

We report on charge transport in fluorinated functionalized pentacenes and discuss the effect of trialkylsilyl and the number of fluorine atoms. We show that modifications in the chemical composition influence the molecular packing, crystal formation and electrical properties, allowing us to measure mobilities from 10-5 to 1.7 cm^2/Vs. The mobilities correlate with the packing, demonstrating that tuning the solid-state order to induce pi-stacking improves electrical properties. By combining Raman measurements with theoretical calculations predicting the vibrational spectrum, we explore the vibrational modes of the crystals, providing information about the intermolecular coupling and electron-phonon interactions governing charge transport. We calculate the intermolecular electronic couplings and band structures by using density functional theory, and study the effect of fluorination and trialkylsilyl substitution on crystal packing and the electronic properties.

Jurchescu, Oana; David, Daniel; McLellan, Claire; Purushothaman, Balaji; Liu, Shubin; Coropceanu, Veaceslav; Anthony, John; McNeil, Laurie

2011-03-01

124

Determining the drift time of charge carriers in p-type point-contact HPGe detectors  

NASA Astrophysics Data System (ADS)

An algorithm to determine 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%.

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

2012-06-01

125

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

126

Temperature Dependence of DNA Charge Transport  

NASA Astrophysics Data System (ADS)

Charge transport (CT) through DNA has been extensively studied, and yet the mechanism of this process is still not yet fully understood. DNA CT has been utilized in sensing proteins and DNA fragments, and it has been postulated that it may assist DNA damage prevention and repair. Besides the benefits of understanding charge transport through this fundamental molecule, further understanding of this process will elucidate the biological implications of DNA CT and advance sensing technology. Therefore, we have investigated the temperature dependence of DNA CT by measuring the electrochemistry of DNA monolayers modified with a redox-active probe. By using multiplexed electrodes on silicon chips, we compare the cyclic and square wave voltammetry of distinct DNA sequences under identical experimental conditions. Accordingly, we compare well matched DNA duplexes to those containing a single base pair mismatch, which has been shown to attenuate CT. The yield of CT is shown to follow Arrhenius behavior, with increased activation energies for mismatches that structurally distort the duplex. These observations suggest that charge transport is thermally activated and highly dependent upon DNA conformation.

Wohlgamuth, Chris; McWilliams, Marc; Slinker, Jason

2011-10-01

127

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

128

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

129

Charge transport and glassy dynamics in ionic liquids.  

PubMed

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

Sangoro, Joshua R; Kremer, Friedrich

2011-11-14

130

A transportation and logistic support model for aircraft aboard navy carriers  

Microsoft Academic Search

The U.S. Navy's 13 carrier battle groups play a critical role in support of U.S. defense strategy. However, the mission of the combat aircraft aboard these aircraft carriers cannot be sustained unless they have sufficient transportation and logistic support. This paper describes the development of an econometric model of the transportation and logistic support system that keeps the carrier's combat

Shu S. Liao; Thomas P. Moore; Andrew G. Mackel

1992-01-01

131

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

Federal Register 2010, 2011, 2012, 2013

...Docket No. EP 698] Establishment of the Toxic by Inhalation Hazard Common Carrier Transportation...ACTION: Notice of establishment of the Toxic by Inhalation Hazard Common Carrier Transportation...Administration, the Board will create the Toxic by Inhalation Hazard Common Carrier...

2010-08-10

132

Charge density dependent mobility of organic hole-transporters and mesoporous TiO? determined by transient mobility spectroscopy: implications to dye-sensitized and organic solar cells.  

PubMed

Transient mobility spectroscopy (TMS) is presented as a new tool to probe the charge carrier mobility of commonly employed organic and inorganic semiconductors over the relevant range of charge densities. The charge density dependence of the mobility of semiconductors used in hybrid and organic photovoltaics gives new insights into charge transport phenomena in solid state dye sensitized solar cells. PMID:23637046

Leijtens, Tomas; Lim, Jongchul; Teuscher, Joël; Park, Taiho; Snaith, Henry J

2013-05-02

133

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

134

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

135

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

Code of Federal Regulations, 2010 CFR

...incidents involving animals during air transport. 234.13 Section 234.13...incidents involving animals during air transport. (a) Any air carrier that...or death of an animal during air transport provided by the air...

2009-01-01

136

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

Code of Federal Regulations, 2010 CFR

...incidents involving animals during air transport. 234.13 Section 234.13...incidents involving animals during air transport. (a) Any air carrier that...or death of an animal during air transport provided by the air...

2010-01-01

137

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

Code of Federal Regulations, 2013 CFR

...incidents involving animals during air transport. 234.13 Section 234.13...incidents involving animals during air transport. (a) Any air carrier that...or death of an animal during air transport provided by the air...

2013-01-01

138

Effects of charge carrier trapping on polycrystalline PbO x-ray imaging detectors  

Microsoft Academic Search

The effects of charge carrier trapping on the x-ray sensitivity, resolution, and detective quantum efficiency (DQE) in polycrystalline lead oxide (PbO) x-ray imaging detectors are theoretically analyzed. The theoretical models for calculating carrier trapping-limited x-ray sensitivity and modulation transfer function (MTF), and DQE incorporating polyenergetic x-ray spectrum are described. A cascaded linear system model is developed for calculating the spatial

M. Z. Kabir

2008-01-01

139

29 CFR 780.155 - Delivery âto carriers for transportation to market.â  

Code of Federal Regulations, 2013 CFR

...transportation to marketâ 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

140

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

141

Influence of chemical treatments on the photoinduced charge carrier kinetics of nanocrystalline porous TiO 2 films  

Microsoft Academic Search

Effects of Ti(iso-C3H7O)4 and TiCl4 treatments on the photoinduced charge carrier kinetics of nanocrystalline porous TiO2 films were studied by time-resolved microwave conductivity measurements. Both treatments greatly influence the transient microwave photoconductivity decay behaviors by increasing the photogenerated charge carrier concentration and diminishing the charge carrier recombination via suppressing the hole-trapping defects. This leads to improve the I–V behaviors of

Yuan Lin; Xu Rui Xiao; Wei Yin Li; Wei Bo Wang; Xue Ping Li; Jing Yong Cheng

2003-01-01

142

Efficient photogeneration of charge carriers in silicon nanowires with a radial doping gradient  

NASA Astrophysics Data System (ADS)

by performing electrodeless time-resolved microwave conductivity measurements, the efficiency of charge carrier generation, their mobility, and the decay kinetics on photoexcitation were studied in arrays of Si nanowires grown by the vapor-liquid-solid mechanism. Large enhancements in the magnitude of the photoconductance and charge carrier lifetime are found depending on the incorporation of impurities during the growth. They are explained by the internal electric field that builds up, due to higher doped sidewalls, as revealed by detailed analysis of the nanowire morphology and chemical composition.

Murthy, D. H. K.; Xu, T.; Chen, W. H.; Houtepen, A. J.; Savenije, T. J.; Siebbeles, L. D. A.; Nys, J. P.; Krzeminski, C.; Grandidier, B.; Stiévenard, D.; Pareige, P.; Jomard, F.; Patriarche, G.; Lebedev, O. I.

2011-08-01

143

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

144

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

145

Ferrocene-Decorated Nanocrystalline Cellulose with Charge Carrier Mobility.  

PubMed

Ferrocene-decorated cellulose nanowhiskers were prepared by the grafting of ethynylferrocene onto azide functionalized cotton-derived cellulose nanowhiskers using azide-alkyne cycloaddition. Successful surface modification and retention of the crystalline morphology of the nanocrystals was confirmed by elemental analysis, inductively coupled plasma-atomic emission spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The coverage with ferrocenyl is high (approximately 1.14 × 10(-3) mol g(-1) or 4.6 × 10(13) mol cm(-2) corresponding to a specific area of 61 Å(2) per ferrocene). Cyclic voltammetry measurements of films formed by deposition of ferrocene-decorated nanowhiskers showed that this small spacing of redox centers along the nanowhisker surface allowed conduction hopping of electrons. The apparent diffusion coefficient for electron (or hole) hopping via Fe(III/II) surface sites is estimated as D(app) = 10(-19) m(2)s(-1) via impedance methods, a value significantly less than nonsolvated ferrocene polymers, which would be expected as the 1,2,3-triazole ring forms a rigid linker tethering the ferrocene to the nanowhisker surface. In part, this is believed to be also due to "bottleneck" diffusion of charges across contact points where individual cellulose nanowhiskers contact each other. However, the charge-communication across the nanocrystal surface opens up the potential for use of cellulose nanocrystals as a charge percolation template for the preparation of conducting films via covalent surface modification (with applications similar to those using adsorbed conducting polymers), for use in bioelectrochemical devices to gently transfer and remove electrons without the need for a solution-soluble redox mediator, or for the fabrication of three-dimensional self-assembled conducting networks. PMID:22486421

Eyley, Samuel; Shariki, Sara; Dale, Sara E C; Bending, Simon; Marken, Frank; Thielemans, Wim

2012-04-10

146

Pulse radiolysis studies on charge carriers in conjugated polymers  

Microsoft Academic Search

The charged states of the conjugated polymers poly(2-methoxy,5-(2'-ethylhexyloxy)-p- phenylenevinylene) (MEH-PPV) and poly(2,5-pyridinediyl) (PPY) have been studied by pulse radiolysis. Following pulse radiolysis of argon-saturated solutions of MEH-PPV in chloroform, a new absorption is seen to grow in over a few hundred microseconds. This has a principal absorption at 1.43 eV and a weaker, low energy band (<=0.80 eV), and is

H. D. Burrows; M. Da G. Miguel; A. P. Monkman; L. E. Horsburgh; I. Hamblett; S. Navaratnam

2000-01-01

147

Pulse radiolysis studies on charge carriers in conjugated polymers  

Microsoft Academic Search

The charged states of the conjugated polymers poly(2-methoxy,5-(2?-ethylhexyloxy)-p- phenylenevinylene) (MEH-PPV) and poly(2,5-pyridinediyl) (PPY) have been studied by pulse radiolysis. Following pulse radiolysis of argon-saturated solutions of MEH-PPV in chloroform, a new absorption is seen to grow in over a few hundred microseconds. This has a principal absorption at 1.43 eV and a weaker, low energy band (?0.80 eV), and is

H. D. Burrows; M. da G. Miguel; A. P. Monkman; L. E. Horsburgh; I. Hamblett; S. Navaratnam

2000-01-01

148

Charge transport in organic crystals: role of disorder and topological connectivity.  

PubMed

We analyze the relationship among the molecular structure, morphology, percolation network, and charge carrier mobility in four organic crystals: rubrene, indolo[2,3-b]carbazole with CH(3) side chains, and benzo[1,2-b:4,5-b']bis[b]benzothiophene derivatives with and without C(4)H(9) side chains. Morphologies are generated using an all-atom force field, while charge dynamics is simulated within the framework of high-temperature nonadiabatic Marcus theory or using semiclassical dynamics. We conclude that, on the length scales reachable by molecular dynamics simulations, the charge transport in bulk molecular crystals is mostly limited by the dynamic disorder, while in self-assembled monolayers the static disorder, which is due to the slow motion of the side chains, enhances charge localization and influences the transport dynamics. We find that the presence of disorder can either reduce or increase charge carrier mobility, depending on the dimensionality of the charge percolation network. The advantages of charge transporting materials with two- or three-dimensional networks are clearly shown. PMID:20666495

Vehoff, Thorsten; Baumeier, Björn; Troisi, Alessandro; Andrienko, Denis

2010-08-25

149

Measurement of charge carrier properties in mercuric iodide  

NASA Astrophysics Data System (ADS)

The transport properties of electrons and holes in mercuric iodide determine the performance of detectors. The relatively low levels of these properties limit the volume of detectors with high spectral resolution that can be fabricated and leads to long pulse collection times. These transport parameters can be increased by optimizing the material processing, the crystal growth, and the detector fabrication. This paper will present our own results obtained by analysis of individual pulse shapes. The values for the mobilities generally measured are between 60-90 cm2/Vsec for electrons and 2-4 cm2/Vsec for holes. These results will be compared with the values published by other investigators. Possible reasons for the differences in the reported values will be discussed and explanations will be suggested.

van den Berg, Lodewijk; Alexander, William B.; Pohl, Kenneth R.; Sandoval, John S.

2005-08-01

150

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

2013-08-04

151

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

PubMed

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

2013-09-23

152

Interface Charge Transport in Organic Transistors as Investigated by Field-Induced Electron Spin Resonance  

NASA Astrophysics Data System (ADS)

Most of high-performance organic thin-film transistors (OTFTs) as recently developed is attainable with non-doped, single-component ?-conjugated materials that exhibit high layer crystallinity both for small-molecules and polymers. The layer crystallinity is quite suitable to compose channel transport layers of the OTFTs, although the main origin to hinder the charge transport or the intrinsic carrier mobility is still controversial; intra- or intermolecular electron-phonon coupling, polarization effects by the gate-dielectrics, or thermal or extrinsic disorder effects. Here we discuss the interface charge transport in the OTFTs, as investigated by field-induced electron spin resonance (FESR) technique that probes 1/2 spin of carriers induced by gate voltage. It is shown that the FESR technique is extremely useful especially for OTFTs, because of the fairly small spin-orbit interactions in organic materials as well as of the high layer crystallinity and the anisotropy. The following important aspects of the interface charge transport are presented and discussed: (1) Carrier motion in OTFTs can be understood in terms of the multiple trap-and-release (MTR) transport. The analyses of the motional narrowing effects allow us to estimate the average trap residence time that reaches about 1 ns [1]. (2) Carriers are frozen at the respective trap sites at low temperature. The low-temperature spectral analyses allow us to obtain the distribution of trapped carriers over their degree of localization [2, 3]. (3) We also developed a unique technique to investigate the intra- and inter-domain transport in polycrystalline OTFTs by using anisotropic FESR measurements. The method allows us to evaluate the potential barrier height at the domain boundaries within the films [4].[4pt] [1] Phys. Rev. Lett. 100, 126601 (2008).[0pt] [2] Phys. Rev. Lett. 104, 056602 (2010).[0pt] [3] Phys. Rev. B 85.085211 (2012).[0pt] [4] Phys. Rev. B 85.035308 (2012).

Hasegawa, Tatsuo

2013-03-01

153

Supramolecular organization and charge transport properties of self-assembled ?-? stacks of perylene diimide dyes.  

PubMed

Molecular dynamics (MD) simulations have been coupled to valence bond/Hartree-Fock (VB/HF) quantum-chemical calculations to evaluate the impact of diagonal and off-diagonal disorder on charge carrier mobilities in self-assembled one-dimensional stacks of a perylene diimide (PDI) derivative. The relative distance and orientation of the PDI cores probed along the MD trajectories translate into fluctuations in site energies and transfer integrals that are calculated at the VB/HF level. The charge carrier mobilities, as obtained from time-of-flight numerical simulations, span several orders of magnitude depending on the relative time scales for charge versus molecular motion. Comparison to experiment suggests that charge transport in the crystal phase is limited by the presence of static defects. PMID:21361330

Idé, Julien; Méreau, Raphaël; Ducasse, Laurent; Castet, Frédéric; Olivier, Yoann; Martinelli, Nicolas; Cornil, Jérôme; Beljonne, David

2011-03-01

154

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

155

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

156

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

SciTech Connect

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

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

1986-01-01

157

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

SciTech Connect

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

Sizov, D. S., E-mail: Dsizov@mail.ioffe.ru; Zavarin, E. E.; Ledentsov, N. N.; Lundin, V. V.; Musikhin, Yu. G.; Sizov, V. S.; Suris, R. A.; Tsatsul'nikov, A. F. [Russian Academy of Sciences, Ioffe Physicotechnical Institute (Russian Federation)

2007-05-15

158

Intrinsic and extrinsic charge carrier photogeneration in phenyl-substituted polyphenylenevinylene-trinitrofluorenone blend systems  

NASA Astrophysics Data System (ADS)

Spectral, field, and temperature dependencies of steady-state photoconductivity were studied in thin films of pure phenyl substituted copolymeric polyphenylenevinylene (PhPPV) and PhPPV doped by trinitrofluorenone. The films were sandwiched between indium tin oxide (ITO) and aluminum as well as between two aluminum contacts. Typical surface extrinsic carrier photogeneration was observed in ITO/PhPPV/Al samples with positively biased ITO while the intrinsic photoconductivity dominated in Al/PhPPV/Al samples and ITO/PhPPV/Al sandwiches with negatively biased ITO. Charge carrier photogeneration in both doped and undoped PhPPV at higher photon excess energies was found to be in good agreement with predictions of the hot exciton dissociation model. At low excess photon energy of the inducing light, carrier photogeneration is ascribed to dissociation of optical excitations on charge transfer centers which are either dopant molecules in the doped samples or intrinsic defects in the pure material.

Im, C.; Emelianova, E. V.; Bassler, H.; Spreitzer, H.; Becker, H.

2002-08-01

159

Carrier transport in amorphous silicon utilizing picosecond photoconductivity  

NASA Astrophysics Data System (ADS)

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

Johnson, A. M.

1981-08-01

160

Effects of charge carrier trapping on polycrystalline PbO x-ray imaging detectors  

NASA Astrophysics Data System (ADS)

The effects of charge carrier trapping on the x-ray sensitivity, resolution, and detective quantum efficiency (DQE) in polycrystalline lead oxide (PbO) x-ray imaging detectors are theoretically analyzed. The theoretical models for calculating carrier trapping-limited x-ray sensitivity and modulation transfer function (MTF), and DQE incorporating polyenergetic x-ray spectrum are described. A cascaded linear system model is developed for calculating the spatial frequency f dependent DQE of PbO detectors by incorporating the effects of bulk charge carrier trapping on the MTF and the x-ray interaction depth dependent charge collection efficiency and noise. The theoretical calculations are compared with the published experimental data and show a very good agreement. From the fittings of the sensitivity and MTF curves, the electron and hole ranges in polycrystalline PbO are found to be 3.5×10-7 and ~10-8 cm2/V, respectively. The f dependent noise power spectrum NPS(f) and DQE(f) performances are analyzed as a function of applied electric field and carrier lifetimes. The calculation shows that the carrier trapping is responsible for a 21% reduction in the MTF at the applied field of 1.0 V/?m at the Nyquist frequency (fN) and the aliased NPS at fN is reduced to 63% of that at zero spatial frequency. The sensitivity, MTF, NPS(f), and DQE(f) strongly depend on the applied electric field and carrier ranges. It is found that the DQE(f) for fluoroscopic applications can be improved dramatically by simply enhancing the carrier lifetimes through improving material properties of the PbO sample.

Kabir, M. Z.

2008-10-01

161

Visualization of charge-carrier propagation in water.  

PubMed

The electrical properties of water in the region between parallel electrodes were investigated using pH indicator dyes. Different pH values corresponded to different colors, which could be registered by a video camera. Imposition of electrical current was able to produce zones of constant pH around, and well beyond each electrode: extremely low pH around the positive electrode and extremely high pH around the negative electrode. The border between alkaline and acid zones was jagged and separated by only a narrow layer of water with neutral pH. When the water was replaced by various salt solutions, similar zones were observed. Again, passage of current produced large zones of extreme pH values near and beyond each electrode. Alkaline zones appeared to propagate from the negative to the positive electrode in narrow channels through the neutral solution. When the power supply was disconnected from the electrodes and replaced by a resistive load, a potential difference was registered, and current flowed through the resistor for some period of time. Hence, the acid and alkaline zones appear to carry opposite charges throughout their volume. PMID:17939693

Klimov, Andrey; Pollack, Gerald H

2007-10-16

162

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

PubMed

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

2012-06-15

163

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.

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

2012-01-01

164

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

SciTech Connect

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

Sinyavskii, E. P., E-mail: sinyavskii@gmail.com [Academy of Sciences of Moldova, Institute of Applied Physics (Moldova, Republic of); Karapetyan, S. A., E-mail: karapetyan.sa@gmail.com [Shevchenko Pridnestrovskii State University (Moldova, Republic of)

2011-08-15

165

Non-Markovian stochastic Schrödinger equation at finite temperatures for charge carrier dynamics in organic crystals.  

PubMed

A new non-Markovian stochastic Schrödinger equation at finite temperatures is presented to correctly describe charge carrier dynamics in organic molecular crystals. The electron-phonon interactions in both site energies and electronic couplings are incorporated by the time-dependent complex-valued random fluctuations which are generated from corresponding spectral density functions. The approach is thus easily extended to investigate coherent-to-hopping charge transfer in systems with thousands of molecular sites. The capability of present approach is demonstrated by numerical simulations of carrier dynamics in the spin-boson model and a realistic Fenna-Matthews-Olson complex. The results manifest that the non-Markovian effect and complex-valued random forces are essential to guarantee the detailed balance. In an application to a long-chain donor-acceptor system, it is also interesting to find a property of coherent-to-hopping charge transfer from temperature dependence of diffusion coefficients. PMID:23298032

Zhong, Xinxin; Zhao, Yi

2013-01-01

166

Photogeneration of free charge carriers in ?-conjugated polymers with bulky side groups  

NASA Astrophysics Data System (ADS)

Photogeneration of free charge carriers in poly{1-[4-(trimethylsilyl)phenyl]-2-phenylacetylene} has been studied theoretically. In our work we have utilized our data obtained previously using photoinduced discharge experiment, which showed a steep slope of the dependence of the free charge carriers photogeneration yield on the applied electric field at the low electric field limit, but no saturation plateau. For the theoretical explanation we have utilized our recently developed model (Menšík et al., 2011) [20] that generalizes the model of Arkhipov et al. (2003) [19] by adding an assumption of a resonant reversible coupling of localized excitation to charge transfer states and, consequently, and dependence of internal parameters (permittivity, effective mass of the hole, rate constants) on electric field. Compared to our previous article this work provides a refined analysis of the experimental results on a large variety of intervals of the model parameters.

Menšík, M.; Jex, M.; Pfleger, J.; Jung, J.

2012-08-01

167

Cost Models for Coal Transportation by Common Carrier. Appendix 1: User's Manual. Final Report.  

National Technical Information Service (NTIS)

This manual provides the technical information needed to operate the computerized transportation cost models developed in EA--675, Cost Models for Coal Transportation by Common Carrier, prepared for the Electric Power Research Institute by Manalytics, Inc...

S. J. White J. P. Hynes

1980-01-01

168

Imaging Photoinduced Charge Transport in Single Molecules  

NASA Astrophysics Data System (ADS)

The ability to perform sub-Angstrom imaging of photoinduced charge transport in single molecules in ultrahigh vacuum with a low temperature scanning tunneling microscope (STM) indicates the defeat of diffraction limited resolution and the opportunity to understand in new directions nanostructures and their functions. The experiments are enabled by the enhanced field due to coupling of the light from cw and femtosecond lasers to the plasmons in the STM nano-junction and the enhanced field to the molecule that can be monitored by tunneling electrons. By imaging the tunneling electrons as a function of energy and time, it is then possible to record the spatial and temporal evolution of the topography, and the electronic, vibrational, and magnetic states of single molecules. The observation of photoinduced phenomena in nanostructures, including molecules, is relevant to a number of technologies, such as photocatalysis, solar energy harvesting, and optical communication.

Ho, Wilson

2010-03-01

169

DNA Charge Transport over 34 nm  

PubMed Central

Molecular wires show promise in nanoscale electronics but the synthesis of uniform, long conductive molecules is a significant challenge. DNA of precise length, by contrast, is easily synthesized, but its conductivity has not been explored over the distances required for nanoscale devices. 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 that is accessible to protein binding. Similar electron transfer rates are measured through 100-mer and 17-mer monolayers, consistent with rate-limiting electron tunneling through the saturated carbon linker. This DNA-mediated CT distance of 34 nm surpasses most reports of molecular wires.

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

2011-01-01

170

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

171

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

Code of Federal Regulations, 2013 CFR

...Cleaning and disinfection of transport carriers for export. 91...Cleaning and disinfection of transport carriers for export...of 1 pound to 3 gallons of water. (b) 4 percent sodium...percent purity to 6 gallons of water, or one 131/2...

2013-01-01

172

Ultrafast charge-carrier and phonon dynamics in GaP  

NASA Astrophysics Data System (ADS)

The ultrafast energy relaxation of GaP is analyzed through charge-carrier and phonon dynamics. Early timescales show hot electron intervalley scattering from the ? valley into the X sidevalley, with 700 and 4000 fs time constants for scattering to and from the X7 valley. Later timescales show carrier-phonon interactions in the X6 valley with hot phonon and screening effects. Fluence-dependent relaxation is observed over 30 to 52 ps for 2.3 to 72 ?J/cm2 fluences. The prolonged relaxation of GaP is due to impeded (hot) phonon decay and screening at low and high fluences, respectively.

Collier, C. M.; Born, B.; Jin, X.; Holzman, J. F.

2013-08-01

173

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

SciTech Connect

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

Jafarov, M. B., E-mail: cmentiq@box.az [Azerbaijan State Agrarian University (Azerbaijan)

2010-10-15

174

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

PubMed Central

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.

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

2013-01-01

175

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

2013-03-18

176

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

DOEpatents

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

Luke, P.

1996-06-25

177

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

DOEpatents

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

Luke, Paul (Castro Valley, CA)

1996-01-01

178

Nanoscale quantification of charge injection and transportation process in Si-nanocrystal based sandwiched structure  

NASA Astrophysics Data System (ADS)

Si nanocrystals are formed by using KrF pulsed laser crystallization of an amorphous SiC/ultrathin amorphous Si/amorphous SiC sandwiched structure. Electrons and holes are injected into Si nanocrystals via a biased conductive AFM tip and the carrier decay and transportation behaviours at the nanoscale are studied by joint characterization techniques of Kelvin probe force microscopy (KPFM) and conductive atomic force microscopy (CAFM). Quantification of the surface charge density is realized by solving the Poisson equation based on KPFM measurements. Besides, the asymmetric barrier height for electrons and holes is considered to play a dominant role in controlling the charge retention and transportation characteristics. The methodology developed in this work is promising for studying the charge injection and transportation process in other materials and structures at the nanoscale.

Xu, Jie; Xu, Jun; Zhang, Pengzhan; Li, Wei; Chen, Kunji

2013-09-01

179

Nanoscale quantification of charge injection and transportation process in Si-nanocrystal based sandwiched structure.  

PubMed

Si nanocrystals are formed by using KrF pulsed laser crystallization of an amorphous SiC/ultrathin amorphous Si/amorphous SiC sandwiched structure. Electrons and holes are injected into Si nanocrystals via a biased conductive AFM tip and the carrier decay and transportation behaviours at the nanoscale are studied by joint characterization techniques of Kelvin probe force microscopy (KPFM) and conductive atomic force microscopy (CAFM). Quantification of the surface charge density is realized by solving the Poisson equation based on KPFM measurements. Besides, the asymmetric barrier height for electrons and holes is considered to play a dominant role in controlling the charge retention and transportation characteristics. The methodology developed in this work is promising for studying the charge injection and transportation process in other materials and structures at the nanoscale. PMID:23989206

Xu, Jie; Xu, Jun; Zhang, Pengzhan; Li, Wei; Chen, Kunji

2013-09-26

180

Theoretical modelling of carrier transports in molecular semiconductors: molecular design of triphenylamine dimer systems  

NASA Astrophysics Data System (ADS)

Charge transport in molecular systems and biosystems can be different from that in inorganic, rigid semiconductors. The electron-nuclear motion couplings play an important role in the former case. We have developed a theoretical scheme to employ the Marcus electron transfer theory coupled with a direct diabatic dimer model and the Brownian diffusion assumption to predict the carrier mobility for molecular materials. For triphenylamine, a typical molecular transport material, the design strategies regarding the formation a cyclic or a linear dimer are evaluated from theoretical calculations for the carrier mobility. We made a comparison between the mobility and the electrical polarizability. It is found that in the case of triphenylamine dimer, these two quantities have different trends. The fact that the macrocycle possesses higher mobility but lower polarizability than the linear chain is due to the difference in the reorganization energy. The theoretical predicted temperature dependences are analysed within the hopping mechanism. The calculated room-temperature mobilities are in reasonable agreement with experimental values.

Yang, Xiaodi; Li, Qikai; Shuai, Zhigang

2007-10-01

181

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

NASA Astrophysics Data System (ADS)

Organic photovoltaics (OPV) represent an attractive route towards inexpensive, lightweight, and abundant renewable energy. The principal criticisms of OPV are low power conversion efficiency and unstable materials resulting in short device lifetimes. Hybrid OPV (h-OPV) devices with ZnO functioning either as the electron acceptor in the heterojunction, or as an electron transport layer in a polymer/fullerene based heterojunction, present useful device structures for investigating the functional mechanisms within OPV devices and a possible pathway towards air-stable high efficiency devices. Such use allows the vast knowledge surrounding oxide nanostructure morphology, band position, and carrier concentration control to be used in designing bulk-heterojunction OPV devices. The work presented in this thesis explores the effects of carrier concentration modulation in the polymer and/or oxide layers of these devices. Exposure to air is known to induce chemical defects in polymer semiconductors, which act as dopants in OPV devices. This increase in doping density can be used to improve OPV devices, however the low work-function metallic electrodes are often highly air sensitive. Using a silver back electrode and a ZnO interlayer at the transparent front contact in a polymer-based bulk heterojunction device allows for fabrication and testing in air. Relatively efficient devices are fabricated in this manner, but the devices show a characteristic aging time that indicates that air is a requirement to function as a quality diode. Air exposure may be effecting any of the layers in the device, but evidence is presented that shows the increased doping density in the polymer is largely responsible for the change in device quality over this time period. When oxides are used as the electron acceptor material in the device heterojunction, the carrier concentration in both the oxide and the polymer determine the strength of the electric field at the junction. Oxygen related doping of the polymer is a requisite for functional devices, but intentional doping of the oxide provides an additional degree of control over interfacial electric fields. By using planar hybrid heterojunctions, the utility of this effect is shown by increasing the driving force for charge separation. Interfacial barrier layers are required on highly doped ZnO to prevent recombination and preserve high fill factors. The measurable carrier concentration in the depletion region of polymer and polymer-fullerene blend films is shown to be significantly larger under illumination than in the dark. This effect is not related to breaking of the conjugated bonds in the polymer, as is the device aging phenomenon, but stems from low mobility of photo-generated electrons. The depletion width and maximum electric field in devices are influenced by the presence of an increased effective doping density under illumination.

White, Matthew Schuette

182

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

PubMed Central

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

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

2013-01-01

183

The role of non-equilibrium charge carriers in thermoelectric cooling  

NASA Astrophysics Data System (ADS)

This paper is devoted to the analysis of thermoelectric cooling phenomena in semiconductors containing potential barriers (p-n-junction). The formulation of an adequate self-consistent theoretical model describing the effect is presented. The role of the recombination rate in lineal approximation of the electric current leads to a new formulation of the set of equations describing the Peltier effect that is discussed in detail. The importance of re-distribution of non-equilibrium charge carriers, which has been ignored in most of the publications on this subject, is also shown. Moreover, it is proved that the conventional theory of thermoelectric cooling, which does not take into account the influence of non-equilibrium charge carriers, is not correct in general. In the present work, it is demonstrated that the Peltier effect strongly depends on the recombination rate. In particular, it is shown that the sign of the Peltier effect changes with the value of the recombination rate.

Gurevich, Yu. G.; Velázquez-Pérez, J. E.

2013-07-01

184

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

185

Precise Measurement of Effective Mass of Positive and Negative Charge Carriers in Liquid Helium II  

Microsoft Academic Search

The resonance of charge carriers trapped under the surface of He II is observed at 200 MHz. The effective masses are found to be m+*=(45+\\/-2)m4 and m-*=(76+\\/-2)m4, where m4 is a bare 4He mass. The ionic radii are deduced to be R+=6.0+\\/-0.1 Å and R-=11.4+\\/-0.1 Å.

J. Poitrenaud; F. I. B. Williams

1972-01-01

186

Charge carrier separation induced by intrinsic surface strain in pristine ZnO nanowires  

Microsoft Academic Search

We predict by first-principles calculations a spontaneous charge carrier separation mechanism in pristine [0001]-oriented ZnO nanowires. We find that the shrinking strain induced by surface reconstruction causes electrons and holes to separate and move toward the core and surface region, respectively. Such separation can be enhanced by axially applied tensile strain as a result of the enhancement of surface strain

Liangzhi Kou; Chun Li; Zi-Yue Zhang; Changfeng Chen; Wanlin Guo

2010-01-01

187

Charge carrier avalanche multiplication in high-voltage diodes triggered by ionizing radiation  

Microsoft Academic Search

Non-destructive strong carrier avalanche multiplication reaching levels up to four orders of magnitude as compared to the initially deposited charge was investigated in high-voltage diodes for a variety of initiating high-energy ions and for high-energy protons. Current levels of several amperes were detected with the current flowing only over time periods up to 50 ns. This indicates that no internal

Gerald Soelkner; Peter Voss; Winfried Kaindl; Gerhard Wachutka; K. H. Maier; H.-W. Becker

2000-01-01

188

Defect states and disorder in charge transport in semiconductor nanowires  

NASA Astrophysics Data System (ADS)

We present a comprehensive investigation into disorder-mediated charge transport in InP nanowires in the statistical doping regime. At zero gate voltage, transport is well described by the space charge limited current model and hopping transport, but positive gate voltage (electron accumulation) reveals a previously unexplored regime of nanowire charge transport that is not well described by existing theory. The ability to continuously tune between these regimes provides guidance for the extension of existing models and directly informs the design of next-generation nanoscale electronic devices.

Ko, Dongkyun; Zhao, X. W.; Reddy, Kongara M.; Restrepo, O. D.; Mishra, R.; Lemberger, T. R.; Beloborodov, I. S.; Trivedi, Nandini; Padture, Nitin P.; Windl, W.; Yang, F. Y.; Johnston-Halperin, E.

2013-07-01

189

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

2011-01-30

190

Single-step Charge Transport through DNA over Long Distances  

PubMed Central

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

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

2011-01-01

191

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

NASA Astrophysics Data System (ADS)

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 ?-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

2010-06-01

192

Measuring charge transport in a thin solid film using charge sensing.  

PubMed

We measure charge transport in a hydrogenated amorphous silicon (a-Si:H) thin film using a nanometer scale silicon MOSFET as a charge sensor. This charge detection technique makes possible the measurement of extremely large resistances even in the presence of blocking contacts. At high temperatures, where the resistance of the a-Si:H is not too large, the charge detection measurement agrees with a direct measurement of current. The device geometry allows us to probe both the field effect and dispersive transport in the a-Si:H using charge sensing and to extract the density of states near the Fermi energy. PMID:20178356

Maclean, Kenneth; Mentzel, Tamar S; Kastner, Marc A

2010-03-10

193

Charge extraction analysis of charge carrier densities in a polythiophene\\/fullerene solar cell: Analysis of the origin of the device dark current  

Microsoft Academic Search

We demonstrate the use of a simple charge extraction measurement to determine the charge carrier densities n in annealed poly(3-hexylthiophene):methanofullerene solar cells under operating conditions. By applying charge extraction to the device under forward bias in the dark (Jdark), we find Jdark~n2.6. This dependence on charge density is the same as that we find for bimolecular recombination losses observed in

C. G. Shuttle; A. Maurano; B. O'Regan; J. C. de Mello; J. R. Durrant

2008-01-01

194

Effect of electron-electron interactions on the charge carrier transitions in trans-polyacetylene.  

PubMed

By employing a newly developed nonadiabatic dynamical simulation method, which is a combination of classical molecular dynamics and the adaptive time-dependent density matrix renormalization group, we investigate the dynamics of charge carrier transitions in trans-polyacetylene (PA) with the inclusion of both electron-phonon and electron-electron interactions. The calculations are performed within a modified Su-Schrieffer-Heeger model in which electron-electron interactions are taken into account via the combination with extended Hubbard model (EHM). We find that removing an electron from a trans-PA chain bearing a positively charged polaron leads to the formation of a pair of charged solitons. Furthermore, we study the effect of electron-electron interactions on such charge carrier transitions in trans-PA. Our results show that increasing the on-site Coulomb interaction and the nearest-neighbor Coulomb repulsion will not change the qualitative behavior of the transition from a polaron to a soliton pair in the evolution process but will quantitatively reduce the moving velocities of the both formed solitons significantly and change the conditions for the soliton collisions. PMID:20387867

Ma, Haibo; Schollwöck, Ulrich

2010-05-01

195

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

NASA Astrophysics Data System (ADS)

The DUSEL facility will enable unique opportunities for field experiments that would otherwise not be possible at surface facilities (Lesko, K.T., TAUP, 2007) and support a host of undergraduate and graduate educational projects. In this presentation, some of the proposed geophysics experiments will be described as part of the subsurface Imaging and Sensing (SIS) project to study charge carrier movement in crustal rock as a function of various perturbations. The electric conductivity of the Earth’s crust is dominated by positive hole charge carriers, e.g. mobile electron vacancy defects (EVD) in the oxygen anion sublattice of minerals that make up the bulk of crustal rocks. We are interested in (i) coupling of fundamental processes linked to the activation of additional EVDs in rocks deep in the crust subjected to tectonic stresses and the outflow of these charge carriers into the surrounding rocks, (ii) their manifestation across the electromagnetic spectrum and other measuands, (iii) induced forces that arise when these charge carriers are subjected to the episodic or daily magnetic field variations coming from geomagnetic storms or from the ionospheric current vortex, and (iv) in the movement of positive holes in the shallow crust when a thunderstorm system drifts overhead, dragging along a charge cloud in the ground. We propose to conduct active rock stressing experiments in situ using expanding grout technique (performing electrical, electromagnetic, and VolksMeter tilt measurements) and to monitor the electric and magnetic field variations penetrating into the Earth’s crust. Additionally optical phenomena will be investigated (anomalous infrared signatures, visible light arising from atomic oxygen and corona discharge, and infrared imaging). If budget permits, measurement of changes of acoustic velocity, evolution of chemical species (H2, O*, Rn, etc) and radar reflectivity as a function of stresses will also be attempted. We propose to study the charge distribution on the inside walls of cavities or along drifts and how the local electric field is modified when a geomagnetic storm passes overhead or lightning strikes nearby. Detection of signals with this passive experiment at different depths will greatly improve understanding of propagation mechanisms and test predictive capabilities. We have demonstrated with 20 earthquake events that we can provide 1 - 3 day predictions of the earthquakes, using ground-based receivers, a combination of GPS and UHF/VHF satellite signals, and radio-tomography of the ionosphere as the analytical tool. Based on that methodology, we hope to correlate crustal plate boundary, precursory signatures with the sub-surface currents and fields evident at DUSEL.

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

2009-12-01

196

Exploring carrier transport phenomena in a CVD-assembled graphene FET on hexagonal boron nitride.  

PubMed

The supporting substrate plays a crucial role in preserving the superb electrical characteristicsof an atomically thin 2D carbon system. We explore carrier transport behavior in achemical-vapor-deposition- (CVD-) assembled graphene monolayer on hexagonal boron nitride (h-BN) substrate. Graphene-channel field-effect transistors (GFETs) were fabricated on ultra-thin h-BN multilayers to screen out carrier scattering from the underlying SiO2 substrate. To explore the transport phenomena, we use three different approaches to extract carrier mobility, namely, effective carrier mobility (?FE), intrinsic carrier mobility (?), and field-effect mobility (?FE). A comparative study has been conducted based on the electrical characterization results, uncovering the impacts of supporting substrate material and device geometry scaling on carrier mobility in GFETs with CVD-assembled graphene as the active channel. PMID:22414953

Kim, Edwin; Jai, Nikhil; Jacobs-Gedri, Robin; Xu, Yang; Yu, Bin

2012-03-30

197

Exploring carrier transport phenomena in a CVD-assembled graphene FET on hexagonal boron nitride  

NASA Astrophysics Data System (ADS)

The supporting substrate plays a crucial role in preserving the superb electrical characteristics of an atomically thin 2D carbon system. We explore carrier transport behavior in a chemical-vapor-deposition- (CVD-) assembled graphene monolayer on hexagonal boron nitride (h-BN) substrate. Graphene-channel field-effect transistors (GFETs) were fabricated on ultra-thin h-BN multilayers to screen out carrier scattering from the underlying SiO2 substrate. To explore the transport phenomena, we use three different approaches to extract carrier mobility, namely, effective carrier mobility (?eff), intrinsic carrier mobility (?), and field-effect mobility (?FE). A comparative study has been conducted based on the electrical characterization results, uncovering the impacts of supporting substrate material and device geometry scaling on carrier mobility in GFETs with CVD-assembled graphene as the active channel.

Kim, Edwin; Jain, Nikhil; Jacobs-Gedrim, Robin; Xu, Yang; Yu, Bin

2012-03-01

198

Persistence time of charge carriers in defect states of molecular semiconductors.  

PubMed

Charge carriers in organic crystals are often trapped in point defects. The persistence time of the charge in these defect states is evaluated by computing the escape rate from this state using non-adiabatic rate theory. Two cases are considered (i) the hopping between separate identical defect states and (ii) the hopping between a defect state and the bulk (delocalized) states. We show that only the second process is likely to happen with realistic defect concentrations and highlight that the inclusion of an effective quantum mode of vibration is essential for accurate computation of the rate. The computed persistence time as a function of the trap energy indicates that trap states shallower than ?0.3 eV cannot be effectively investigated with some slow spectroscopic techniques such as THz spectroscopy or EPR commonly used to study the nature of excess charge in semiconductors. PMID:21526236

McMahon, David P; Troisi, Alessandro

2011-04-27

199

Charge transport in chemically synthesized, DNA-doped polypyrrole  

NASA Astrophysics Data System (ADS)

The charge transport properties of chemically synthesized, DNA-doped polypyrrole (PPY) are described here. The polymer showed a significant change in microstructural morphology and optical absorption spectra with increase in DNA concentrations (0.36-14% w/v). Both the dark and photo-induced I-V characteristics of the polymers showed an increase in the degree of linearity with increase in DNA concentration. The temperature-dependent dc electrical conductivity (sgr) exhibited a significant dependence on the nature of carrier hopping dominant in this DNA-doped PPY: sgr showed a change from T-1/4 to T-1/2 dependence on temperature as the degree of doping increased from 0.36% to 3%, respectively. Further increase in DNA doping to 14% led to a T-1 dependence of the dc electrical conductivity. The results were interpreted in terms of the localized polaronic and bipolaronic states caused by the disorder in polymeric chains, variation in chain length, interchain interactions, etc.

Dutta, P.; Mandal, S. K.

2004-10-01

200

Simulation of carrier transport and nonlinearities in quantum-well laser diodes  

Microsoft Academic Search

The two-dimensional (2-D) quantum-well (QW) laser diode simulator Minilase-II is presented in detail. This simulator contains a complete treatment of carrier dynamics including bulk transport, quantum carrier capture, spectral hole burning, and quantum carrier heating. The models used in the simulator and their connectivity are first presented. Then the simulator is used to demonstrate the effects of various nonlinear processes

Matt Grupen; Karl Hess

1998-01-01

201

Charge carrier trapping and acoustic phonon modes in single CdTe nanowires.  

PubMed

Semiconductor nanostructures produced by wet chemical synthesis are extremely heterogeneous, which makes single particle techniques a useful way to interrogate their properties. In this paper the ultrafast dynamics of single CdTe nanowires are studied by transient absorption microscopy. The wires have lengths of several micrometers and lateral dimensions on the order of 30 nm. The transient absorption traces show very fast decays, which are assigned to charge carrier trapping into surface defects. The time constants vary for different wires due to differences in the energetics and/or density of surface trap sites. Measurements performed at the band edge compared to the near-IR give slightly different time constants, implying that the dynamics for electron and hole trapping are different. The rate of charge carrier trapping was observed to slow down at high carrier densities, which was attributed to trap-state filling. Modulations due to the fundamental and first overtone of the acoustic breathing mode were also observed in the transient absorption traces. The quality factors for these modes were similar to those measured for metal nanostructures, and indicate a complex interaction with the environment. PMID:22559050

Lo, Shun Shang; Major, Todd A; Petchsang, Nattasamon; Huang, Libai; Kuno, Masaru K; Hartland, Gregory V

2012-05-14

202

Neonatal carrier: An easy to make alternative device to costly transport chambers  

PubMed Central

The transport of sick neonates to the surgical centers or transportation within the center is an essential requirement of neonatal surgery. Neonatal transport incubators are costly, space occupying, and are not available at many places in the developing countries. We report here a cheap yet effective and easy to make, alternate neonatal carrier device.

Joshi, Milind; Singh, Sangram; Negi, Anupama; Vyas, Tanmay; Chourishi, Vigya; Jain, Anvesh

2010-01-01

203

Charge transport in columnar mesophases of carbazole macrocycles  

NASA Astrophysics Data System (ADS)

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.

Vehoff, Thorsten; Baumeier, Björn; Andrienko, Denis

2010-10-01

204

Carrier control via charge transfer at the topological-insulator/organic-molecule interface  

NASA Astrophysics Data System (ADS)

A topological insulator is a material that behaves as an insulator as a bulk state, while permitting metallicity on its Dirac cone surface state. One of the most serious issues of recent researches in this field, however, has been the fact that the Fermi levels in many TIs actually fall in either the conduction or valence band due to the naturally occurring defects and must be controlled by further doping. We report here that the major electron carriers on the SS of a Bi2-xSbxTe3-ySey(BSTS) single crystal can be converted to the hole carriers via interface control using 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane(F4-TCNQ), with strong electron affinity. The evidence can be elucidated using a detailed three-carrier model. The results apparently demonstrate that the charge transfer at the TI/organic-molecule interface is very efficient in order to control the carrier density of TIs, particularly on the SS. Our present results will be very important for studying the fundamental aspects of TIs as well as their future device applications.

Tanigaki, Katsumi; Tanabe, Yoichi; Kuynh, Khuong; Urata, Takahiro; Nouchi, Ryo; Heguri, Satoshi; Shimotani, Hidekazu

2013-03-01

205

Charge carrier lifetime modification in silicon by high energy H+ or He+ ion implantation  

NASA Astrophysics Data System (ADS)

H+ or He+ was implanted at energies of 1, 2.5 and 4 MeV into n-type <100> 4-7.5 ? cm CZ-Si with doses in the range from 3×1010/cm2 to 1×1012/cm2. A reduction in minority carrier lifetime was measured by the microwave photoconductive decay (?-PCD) method using a 904 nm laser pulse. It was shown that the modified lifetime can be directly measured by ?-PCD when the damaged region and the excess charge pocket generated by the laser pulse exactly overlap. This was the case for 4 MeV H+ implantation. For shallower defects, the measured lifetime value is influenced by the diffusion process of excess minority carriers. To extract the real lifetime in this case, a three layer model is presented.

Khánh, N. Q.; Jároli, E. N.; Bíró, L. P.; Gyulai, J.; Tütt, P.; Buiu, O.; Manuaba, A.

1997-05-01

206

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

207

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

NASA Astrophysics Data System (ADS)

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

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

2012-07-01

208

A multiscale description of charge transport in conjugated oligomers.  

PubMed

By relating inter- and intrachain ordering to charge dynamics a correlation between the morphology and charge mobility of neutral and doped states of a conjugated polymer, in this case polypyrrole, is established. Morphologies are generated using an all-atom force field, while charge dynamics is simulated within the framework of high temperature nonadiabatic Marcus theory. For short oligomers, charge carrier mobility is insensitive to the orientational molecular ordering and is determined by the threshold transfer integral which connects percolating clusters of molecules, forming interconnected networks. The value of this transfer integral can be estimated from the radial distribution function. We therefore find that charge mobility is mainly determined by the local molecular packing and is independent of global morphology, at least in such a noncrystalline state of a polymer. PMID:20387917

Rühle, Victor; Kirkpatrick, James; Andrienko, Denis

2010-04-01

209

A multiscale description of charge transport in conjugated oligomers  

NASA Astrophysics Data System (ADS)

By relating inter- and intrachain ordering to charge dynamics a correlation between the morphology and charge mobility of neutral and doped states of a conjugated polymer, in this case polypyrrole, is established. Morphologies are generated using an all-atom force field, while charge dynamics is simulated within the framework of high temperature nonadiabatic Marcus theory. For short oligomers, charge carrier mobility is insensitive to the orientational molecular ordering and is determined by the threshold transfer integral which connects percolating clusters of molecules, forming interconnected networks. The value of this transfer integral can be estimated from the radial distribution function. We therefore find that charge mobility is mainly determined by the local molecular packing and is independent of global morphology, at least in such a noncrystalline state of a polymer.

Rühle, Victor; Kirkpatrick, James; Andrienko, Denis

2010-04-01

210

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

NASA Astrophysics Data System (ADS)

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

Majumdar, Kausik; Kallatt, Sangeeth; Bhat, Navakanta

2012-09-01

211

Charge Transport in Self-Assembling Discotic Liquid Crystalline Materials.  

National Technical Information Service (NTIS)

Since the discovery of charge transport in doped polyacetylene increased attention has been paid to electronic conduction in organic systems. Successful applications of organic semiconductors as active components in electronic devices have been realized f...

A. M. van de Craats

2000-01-01

212

Efficient calculation of Coulomb matrix elements for bilayers of confined charge carriers with arbitrary spatial separation  

NASA Astrophysics Data System (ADS)

We describe a practical procedure to calculate the Coulomb matrix elements of 2D spatially separated and confined charge carriers, which are needed for detailed theoretical descriptions of important condensed matter finite systems. We derive an analytical expression, for arbitrary separations, in terms of a single infinite series and apply a u-type Levin transform in order to accelerate the resulting infinite series. This procedure has proven to be efficient and accurate. Direct consequences concerning the functional dependence of the matrix elements on the separation distance, transition amplitudes and the diagonalization of a single electron-hole pair in vertically stacked parabolic quantum dots are presented.

Mondragon-Shem, Ian; Rodríguez, Boris A.; López, Francisco E.

2010-09-01

213

Systematic improvement in charge carrier mobility of air stable triarylamine copolymers.  

PubMed

The electrical performance of organic semiconducting polymers in field-effect transistor devices is now sufficient for initial low complexity circuit applications. To achieve high performance, either operation in an inert atmosphere or a hydrophobic surface treatment and annealing step is typically required. In this communication we report a strategy to prepare fully air stable, amorphous semiconducting polymers which can achieve charge carrier mobilities in the range of 0.04 cm(2)/(V s), remaining over a period of over 3 months in ambient conditions. PMID:19603817

Zhang, Weimin; Smith, Jeremy; Hamilton, Rick; Heeney, Martin; Kirkpatrick, James; Song, Kigook; Watkins, Scott E; Anthopoulos, Thomas; McCulloch, Iain

2009-08-12

214

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

215

Charge and spin transport in graphene-based heterostructure  

Microsoft Academic Search

We investigate electron transport properties of a heterostructure based on zigzag graphene nanoribbon (ZGNR) by first-principles calculations. This heterostructure consists of hydrogen-terminated ZGNR (ZGNR-H) and oxygen-terminated ZGNR (ZGNR-O). We find that both charge and spin transport can be well controlled with the ZGNR-H\\/ZGNR-O heterostructure. A large charge transmission gap appears near the Fermi energy, and rectification behavior is observed. Moreover,

Minggang Zeng; Lei Shen; Ming Yang; Chun Zhang; Yuanping Feng

2011-01-01

216

Space Charge Limited Transient Transport Simulation by the Monte Carlo Technique  

NASA Astrophysics Data System (ADS)

Recently (Murayama & Mitsunori, 1992), a mechanism of transient dispersive transport has been proposed for the explanation of the temperature dependence of the dispersion parameters of a-Si:H. By contructing several percolation clusters in a cubic lattice, each one with a different factor of filled sites, they calculated the transient current of particles through the clusters. The occupied sites factor for the percolation clusters and the density of states of the system were related by means of the fraction of space allowed to particles with energy E, i.e. the number of occupied states at energy E divided by the total number of states. The percolaction path was related to the minimum energy barrier path. They showed that the simulated results fit quite well the experimental data of a-Si:H transient currents. Modifying the above model it is possible to simulate the effect of space charge in the transient transport. If we consider that the non-equilibrium charge carriers ganerated near to one electrode and they are space limited in the same region, the released charge carriers will have a time distribution and the transient current will be directly affected. In the present work a set of Monte Carlo experiments, for different applied electric fields and trapping probabilities, was performed in order to compare with the experimental results of the transient transport measured with the time of flight (TOF) technique.

Picos-Vega, Abraham; Ramirez-Bon, Rafael; Espinoza-Beltran, Francisco; Zelaya-Angel, Orlando

1998-03-01

217

ac conductivity in a DNA charge transport model  

Microsoft Academic Search

We present the ac response of a DNA charge transport model, where the charge in the pi -stack interacts with the base-pair opening dynamics of the double strand. The calculated ac conductivity exhibits prominent peaks at polaron normal modes with electronic character, while weaker response appears at lower frequencies in the vibrational part of the polaron normal mode spectrum. Examples

P. Maniadis; G. Kalosakas; K. Ø. Rasmussen; A. R. Bishop

2005-01-01

218

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

Code of Federal Regulations, 2010 CFR

...commercial carrier transports my mobile home overland or over water? 302-10...commercial carrier transports my mobile home overland or over water? Your agency...for permits to transport mobile homes...transporting over water cost must...

2009-07-01

219

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

Code of Federal Regulations, 2010 CFR

...commercial carrier transports my mobile home overland or over water? 302-10...commercial carrier transports my mobile home overland or over water? Your agency...for permits to transport mobile homes...transporting over water cost must...

2010-07-01

220

Sensitivity analysis of laterally resolved free carrier absorption determination of electronic transport properties of silicon wafers  

NASA Astrophysics Data System (ADS)

Simulations are performed to investigate the uniqueness of simultaneous determination of electronic transport properties (the carrier lifetime, the carrier diffusivity, and the front surface recombination velocity) of silicon wafers by laterally resolved modulated free carrier absorption (MFCA) and multiparameter fitting. The dependences of MFCA amplitude and phase on these transport properties at different pump-probe-beam separations and modulation frequencies are analyzed. The uncertainties of the fitted parameter values are analyzed by investigating the dependences of a mean square variance including both the amplitude error and phase error on corresponding electronic transport parameters. Simulation results show that the electronic transport parameters can be determined accurately through fitting experimental MFCA data carrying both frequency- and space-domain information of carrier diffusion to a rigorous MFCA model. Among the three transport parameters, the carrier diffusivity can be determined most precisely, with an uncertainty of less than +/-5%, due to the highest sensitivity of the laterally resolved MFCA signal to the diffusivity. The highly accurate determination of the diffusivity further improves the precision of the carrier lifetime and the front surface recombination velocity values simultaneously determined via multiparameter fitting. Experiments were performed with a silicon wafer and the results were in good agreement with the theoretical simulations.

Zhang, Xiren; Li, Bincheng; Gao, Chunming

2008-02-01

221

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

Code of Federal Regulations, 2011 CFR

...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...

2011-07-01

222

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

Code of Federal Regulations, 2012 CFR

...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...

2012-07-01

223

DNA Charge Transport for Sensing and Signaling  

PubMed Central

Conspectus The DNA duplex is an exquisite macromolecular array that stores genetic information to encode proteins and regulate pathways, but its unique structure imparts chemical function that allows it also to mediate charge transport (CT). We have utilized diverse platforms to probe DNA CT, using spectroscopic, electrochemical, and even genetic methods. These studies have established powerful features of DNA CT chemistry. DNA CT can occur over long molecular distances as long as the bases are well stacked; perturbations in base stacking as arise with single base mismatches, DNA lesions, and the binding of some proteins that kink the DNA, all serve to inhibit DNA CT. Significantly, single molecule studies of DNA CT show that ground state CT can occur over 34 nm as long as the duplex is well stacked; one single base mismatch inhibits CT. The DNA duplex is an effective sensor for the integrity of the base pair stack. Moreover the efficiency of DNA CT is what one would expect for a stack of graphite sheets, equivalent to the stack of DNA base pairs, and independent of the sugar-phosphate backbone. Since DNA CT offers a means to carry out redox chemistry from a distance, we have considered how this chemistry might be used for long range signaling in a biological context. We have taken advantage of our chemical probes and platforms to characterize DNA CT also in the context of the cell. CT can occur over long distances, perhaps funneling damage to particular sites and insulating others from oxidative stress. Significantly, transcription factors that activate the genome to respond to oxidative stress can also be activated from a distance through DNA CT. Numerous proteins work to maintain the integrity of the genome and increasingly they have been found to contain [4Fe-4S] clusters that do not appear to carry out either structural or enzymatic roles. Using electrochemical methods, we find that DNA binding shifts the redox potentials of the clusters, activating them towards oxidation at physiological potentials. We have proposed a model describing how repair proteins may utilize DNA CT to efficiently search the genome for lesions. Importantly, many of these proteins are in low copy number, and thus a processive mechanism is insufficient to explain how they find and repair lesions before the cell divides. Using atomic force microscopy and genetic assays, we find that repair proteins proficient at DNA CT are able to relocalize in the vicinity of DNA lesions and, within the cell, they cooperate in their repair of lesions. Conversely, proteins defective in DNA CT cannot relocalize in the vicinity of lesions and do not provide help to other proteins involved in repair within the cell; moreover these genetic defects are associated with disease in human protein analogues. As we continue to unravel this chemistry and discover more proteins with redox cofactors involved in genome maintenance, we are learning more regarding opportunities for long range signaling and sensing, and more examples of DNA CT chemistry that may play critical roles within the cell.

Sontz, Pamela A.; Muren, Natalie B.; Barton, Jacqueline K.

2012-01-01

224

DNA charge transport for sensing and signaling.  

PubMed

The DNA duplex is an exquisite macromolecular array that stores genetic information to encode proteins and regulate pathways. Its unique structure also imparts chemical function that allows it also to mediate charge transport (CT). We have utilized diverse platforms to probe DNA CT, using spectroscopic, electrochemical, and even genetic methods. These studies have established powerful features of DNA CT chemistry. DNA CT can occur over long molecular distances as long as the bases are well stacked. The perturbations in base stacking that arise with single base mismatches, DNA lesions, and the binding of some proteins that kink the DNA all inhibit DNA CT. Significantly, single molecule studies of DNA CT show that ground state CT can occur over 34 nm if the duplex is well stacked; one single base mismatch inhibits CT. The DNA duplex is an effective sensor for the integrity of the base pair stack. Moreover, the efficiency of DNA CT is what one would expect for a stack of graphite sheets: equivalent to the stack of DNA base pairs and independent of the sugar-phosphate backbone. Since DNA CT offers a means to carry out redox chemistry from a distance, we have considered how this chemistry might be used for long range biological signaling. We have taken advantage of our chemical probes and platforms to characterize DNA CT in the context of the cell. CT can occur over long distances, perhaps funneling damage to particular sites and insulating others from oxidative stress. Significantly, transcription factors that activate the genome to respond to oxidative stress can also be activated from a distance through DNA CT. Numerous proteins maintain the integrity of the genome and an increasing number of them contain [4Fe-4S] clusters that do not appear to carry out either structural or enzymatic roles. Using electrochemical methods, we find that DNA binding shifts the redox potentials of the clusters, activating them towards oxidation at physiological potentials. We have proposed a model that describes how repair proteins may utilize DNA CT to efficiently search the genome for lesions. Importantly, many of these proteins occur in low copy numbers within the cell, and thus a processive mechanism does not provide a sufficient explanation of how they find and repair lesions before the cell divides. Using atomic force microscopy and genetic assays, we show that repair proteins proficient at DNA CT can relocalize in the vicinity of DNA lesions and can cooperate in finding lesions within the cell. Conversely, proteins defective in DNA CT cannot relocalize in the vicinity of lesions and do not assist other proteins involved in repair within the cell. Moreover such genetic defects are associated with disease in human protein analogues. As we continue to unravel this chemistry and discover more proteins with redox cofactors involved in genome maintenance, we are learning more regarding opportunities for long range signaling and sensing, and more examples of DNA CT chemistry that may provide critical functions within the cell. PMID:22861008

Sontz, Pamela A; Muren, Natalie B; Barton, Jacqueline K

2012-08-03

225

A study on intelligent charge system of city public transport  

Microsoft Academic Search

In this paper, for analyzing the problem of the charge system of city public transport system, we put forward a new method to build the integrated circuit card autocharge system in city public transport system. We describe how to realize this system in detail.

Liu Peng; Liu Gang; Li Changsheng

2002-01-01

226

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

PubMed

Solar conversion to electricity or to fuels based on electron-hole pair production in semiconductors is a highly evolved scientific and commercial enterprise. Recently, it has been posited that charge carriers either directly transferred from the plasmonic structure to a neighbouring semiconductor (such as TiO?) or to a photocatalyst, or induced by energy transfer in a neighbouring medium, could augment photoconversion processes, potentially leading to an entire new paradigm in harvesting photons for practical use. The strong dependence of the wavelength at which the local surface plasmon can be excited on the nanostructure makes it possible, in principle, to design plasmonic devices that can harvest photons over the entire solar spectrum and beyond. So far, however, most such systems show rather small photocatalytic activity in the visible as compared with the ultraviolet. Here, we report an efficient, autonomous solar water-splitting device based on a gold nanorod array in which essentially all charge carriers involved in the oxidation and reduction steps arise from the hot electrons resulting from the excitation of surface plasmons in the nanostructured gold. Each nanorod functions without external wiring, producing 5 × 10(13) H? molecules per cm(2) per s under 1 sun illumination (AM 1.5 and 100 mW cm(-2)), with unprecedented long-term operational stability. PMID:23435280

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

2013-02-24

227

Gas transport in combined membrane system with moving liquid carrier  

Microsoft Academic Search

The study of selective membrane valve (SMV)—the membrane system which consists of two polymeric membranes and a layer of liquid between them (moving or non-moving) is presented in this paper. Permeability of pure gases such as oxygen, carbon dioxide and hydrogen are investigated. Distilled water and aqueous solutions of potassium carbonate were used as liquid carriers. Aqueous potassium carbonate was

M. G. Shalygin; E. V. Vorobieva; V. V. Teplyakov

2007-01-01

228

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

Code of Federal Regulations, 2010 CFR

...false Transportation of explosives from Canada to the United States via railroad carrier...Transportation of Hazardous Materials From Canada or Mexico To and Within the United States...203 Transportation of explosives from Canada to the United States via railroad...

2010-10-01

229

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

Code of Federal Regulations, 2010 CFR

...false Transportation of explosives from Canada to the United States via railroad carrier...Transportation of Hazardous Materials From Canada or Mexico To and Within the United States...203 Transportation of explosives from Canada to the United States via railroad...

2009-10-01

230

Charge Transport and Electroluminescence in Novel Heterocyclic Liquid Crystals  

NASA Astrophysics Data System (ADS)

Start your abstract by replacing this line with your text. We have investigated charge transport in a family of novel liquid crystals containing five member ring heterocycles (oxadiazoles, thiadiazoles, etc.). Efficient electron transport was observed in the smectic phase. The electric field and temperature dependence of the electron mobility was studied. Apart from being able to simultaneously function as liquid crystals and charge transport agents, these materials are highly fluorescent, allowing the fabrication of organic light emitting diodes. Their electroluminescent properties in devices with various electrode materials were studied.

Fan, Rong; Malliaras, George; Sukhomlinova, L.; Gu, S.; Twieg, R. J.

2000-03-01

231

Coexistence of passive and carrier-mediated processes in drug transport  

Microsoft Academic Search

The permeability of biological membranes is one of the most important determinants of the pharmacokinetic processes of a drug. Although it is often accepted that many drug substances are transported across biological membranes by passive transcellular diffusion, a recent hypothesis speculated that carrier-mediated mechanisms might account for the majority of membrane drug transport processes in biological systems. Based on evidence

Per Artursson; Alex Avdeef; Stefanie Bendels; Li Di; Gerhard F. Ecker; Bernard Faller; Holger Fischer; Grégori Gerebtzoff; Hans Lennernaes; Frank Senner; Kiyohiko Sugano; Manfred Kansy

2010-01-01

232

Scaling Theory for Percolative Charge Transport in Disordered Molecular Semiconductors  

NASA Astrophysics Data System (ADS)

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.

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

2011-09-01

233

Polarized recombination of acoustically transported carriers in GaAs nanowires  

PubMed Central

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

2012-01-01

234

Charge transport properties in electrically aged organic light-emitting diodes  

NASA Astrophysics Data System (ADS)

Organic light-emitting diodes (OLEDs) are a rapidly developing technology with high innovation potential for displays, lighting, and further applications. Critical issues for current research remain the extension of lifetimes and, related to this aim, a deeper understanding of degradation processes in OLEDs. In the present work, we used the charge-based deep level transient spectroscopy technique to investigate changes in the charge transport in OLEDs induced by electrical aging. Both trap states capturing electrons and holes, respectively, were detected. Temperature-dependent measurements enabled estimating the depth of the trap states for electrons. Comparison of spectra of electrically aged and undriven devices revealed that aging seemed to increase the density of traps but did not lead to the occurrence of new types of trap states. Furthermore, experiments with different voltage pulses to fill the charge carrier trap states allowed conclusions on age-induced changes of the injection barrier for holes.

Huber, R.; Witt, F.; Borchert, H.; von Hauff, E.; Heun, S.; Buchholz, H.; Parisi, J.

2013-01-01

235

Intrinsic dynamical disorder and charge transport in DNA  

Microsoft Academic Search

We present temperature effects on the characteristic time at which charge carriers remain spatially confined while interacting with fluctuational openings of DNA. Using semiclassical molecular dynamics simulations, we find that in the low temperature regime this characteristic time decreases in a power-law fashion with temperature and coincides with the polaronic life-time. However, above 50-70 K the confinement time is exponentially

Kim Rasmussen; George Kalosakas; Alan R. Bishop

2003-01-01

236

Dynamics and transport in charged porous media  

Microsoft Academic Search

Charged porous media are filled at least by counterions and often water and occasionally coions. The dynamics of those counterions, water molecules and coions depends strongly on the water content of the medium. For very compact media the water content is low and water and ions are slowed down. For less compact media the dynamics of inserted water and counterions

V. Marry; J. F. Dufreche; M. Jardat; G. Meriguet; P. Turq; F. Grun

2003-01-01

237

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

238

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

SciTech Connect

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

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

1988-03-01

239

Charge transport study of high mobility polymer thin-film transistors based on thiophene substituted diketopyrrolopyrrole copolymers.  

PubMed

In this paper, we report on the device physics and charge transport characteristics of high-mobility dual-gated polymer thin-film transistors with active semiconductor layers consisting of thiophene flanked DPP with thienylene-vinylene-thienylene (PDPP-TVT) alternating copolymers. Room temperature mobilities in these devices are high and can exceed 2 cm(2) V(-1) s(-1). Steady-state and non-quasi-static measurements have been performed to extract key transport parameters and velocity distributions of charge carriers in this copolymer. Charge transport in this polymer semiconductor can be explained using a Multiple-Trap-and-Release or Monroe-type model. We also compare the activation energy vs. field-effect mobility in a few important polymer semiconductors to gain a better understanding of transport of DPP systems and make appropriate comparisons. PMID:23673383

Ha, Tae-Jun; Sonar, Prashant; Dodabalapur, Ananth

2013-05-14

240

Charge transport and velocity distribution in ambipolar organic thin film Transistors based on a diketopyrrolopyrrole-benzothiadiazole copolymer  

NASA Astrophysics Data System (ADS)

There have been reports of charge transport mechanisms in organic thin film transistors (OTFTs) focusing on steady-state characteristics but these measurements provide limited information. Time-resolved measurements can provide additional information in understanding transport mechanisms but existing reports have focused on unipolar organic characteristics. No previous reports on ambipolar organic devices have involved entire velocity distribution and charge transport mechanisms. Recently, we have fabricated ambipolar OTFTs based on a diketopyrrolopyrrole-benzothiadiazole copolymer (PDPP-TBT) with a field-effect mobility of more than 0.2 cm^2 V-1 s-1. Velocity distributions are measured by performing specialized dynamic measurements while keeping the RC-time constant of the measurement circuit small. This yields a distribution in arrival times of charge carriers from source to drain which can be converted to velocity distributions. We will also describe dynamic transport measurements on high-k-dielectric PDPP-TBT OTFTs.

Ha, Tae-Jun; Sonar, Prashant; Pratap Singh, Samarendra; Dodabalapur, Ananth

2011-03-01

241

Jahn-Teller assisted polaronic hole hopping as a charge transport mechanism in CuO nanograins  

NASA Astrophysics Data System (ADS)

Impedance spectroscopy has been employed to investigate the dielectric and electric transport phenomena in sol-gel synthesized CuO nanograins. Semiconducting features of the grains and grain boundaries have been endorsed to the thermal activation of the localized charge carriers. On cooling below 303 K, a transition from Jahn-Teller polaron hopping mechanism to the Mott's variable range hopping mechanism has been observed owing to random potential fluctuations among localized sites. Activation energies for conduction and relaxation processes at grain boundaries provide strong signatures for the involvement of Jahn-Teller adiabatic small polarons as a charge transport mechanism in CuO nanograins.

Younas, M.; Nadeem, M.; Idrees, M.; Akhtar, M. J.

2012-04-01

242

Investigation of carrier transport through silicon wafers by photocurrent measurements  

NASA Astrophysics Data System (ADS)

A model for the minority-carrier diffusion processes which are basic to the operation of light addressable potentiometric sensor (LAPS) devices is demonstrated. Photocurrent measurements as a function of frequency provide an alternative method of measuring bulk minority-carrier lifetime, whose main advantage is to less sensitive to surface recombination. The dependence of the ac photocurrent/frequency curves for the same wafer at different wafer thicknesses was evaluated to verify the consistency of the theoretical model used. The obtained values from the semiconductor bulk and recombination velocity with the photocurrent measurement were compared with those obtained with a noncontact photoconductive decay (PCD) technique. The fundamental dependency of the ac photocurrent amplitude in LAPS devices was characterized on various parameters, namely modulation frequency, semiconductor substrate thickness, and the choice of the side of the device which is illuminated.

Bousse, Luc; Mostarshed, Shahriar; Hafeman, Dean; Sartore, Marco; Adami, Manuela; Nicolini, Claudio

1994-04-01

243

49 CFR 375.401 - Must I estimate charges?  

Code of Federal Regulations, 2011 CFR

...Continued) FEDERAL MOTOR CARRIER SAFETY ADMINISTRATION, DEPARTMENT...TRANSPORTATION FEDERAL MOTOR CARRIER SAFETY REGULATIONS TRANSPORTATION...You must conduct a physical survey of the household goods to...estimate, based on the physical survey, of the charges for the...

2011-10-01

244

Preface: Charge transport in nanoscale junctions  

Microsoft Academic Search

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

Tim Albrecht; Alexei Kornyshev; Thomas Bjørnholm

2008-01-01

245

Electronic transport characterization of silicon wafers by laterally resolved free-carrier absorption and multiparameter fitting  

NASA Astrophysics Data System (ADS)

Laterally resolved modulated free-carrier absorption (MFCA) is applied to the simultaneous determination of the electronic transport properties of semiconductor wafers. A rigorous three-dimensional carrier diffusion model is used to fit the observed dependences of the MFCA signal amplitude and phase on the separation between the pump and probe laser spots, measured at several modulation frequencies covering an appropriate range. This leads to a simultaneous and unambiguous determination of the values of three transport parameters, namely, the minority-carrier lifetime ?, the carrier diffusivity D, and the front surface recombination velocity s1. The extracted values for a n-type Si wafer with a resistivity of 7-10 ? cm are 53 ?s (?), 16.6 cm2/s (D), and <200 cm/s (s1), respectively.

Zhang, Xiren; Li, Bincheng; Gao, Chunming

2006-09-01

246

TRANSPORT STUDIES ON MACROMOLECULES USED AS DRUG CARRIERS  

Microsoft Academic Search

Modecular transport of drugs through carier polymeric materds has been an active area of research. A number of soluble polymers have been used to deliver the drugs selectively to specific parts of the body. The literature in this area of research is extensive and diverse. An effort has been made to review the transport of drug molecules through physiological systems

P. V. Kulkarni; S. B. Rajur; P. P. Antich; T. M. Aminabhavi; M. I. Aralaguppi

1990-01-01

247

Nanoscale Morphology and Charge Transport in Hybrid Solar Cells by Conducting Probe Atomic Force Microscopy  

NASA Astrophysics Data System (ADS)

Measurements of the dependence of photoactive response on nanoscale morphology provide essential insights to further improve processing and achieve morphologies with enhanced device performance. To study the correlation between local morphology and photoactive response, we have fabricated hybrid polymer/zinc oxide thin films and have characterized their electrical properties at nanoscale resolution with conducting probe atomic force microscopy (c-AFM). The charge carrier mobilities were extracted based on local IV characteristics. The surface morphology and current mapping were recorded simultaneously under various illumination and biasing conditions, enabling direct study of morphology dependent transport processes in these photoactive devices.

Sun, Jiebing; Wagner, Sean R.; Enderich, Daniel; Duxbury, Phillip; Zhang, Pengpeng

2011-03-01

248

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

Code of Federal Regulations, 2011 CFR

...carrier presumed to be the most advantageous method of transportation? 301-72.1 Section...carrier presumed to be the most advantageous method of transportation? Travel by common...is presumed to be the most advantageous method of transportation because it...

2011-07-01

249

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

SciTech Connect

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

Dadamirzayev, M. G., E-mail: Gulyamov1949@rambler.ru [Namangan Engineering Pedagogical Institute (Uzbekistan)

2011-03-15

250

All Electronic Charge Carrier Transit Time Mobility Measurements and Data Analysis in Pentacene Organic Field Effect Transistors  

Microsoft Academic Search

In organic field-effect transistors (OFETs), the most common method of estimating mobility is to extract it from the transfer characteristics (e.g., Id-Vds and Id-Vdg curves). Time-of-flight measurements via optical excitation of charge carriers in the organic material are also used, but this technique measures the mobility of carriers perpendicular to their motion in the OFET geometry. Additionally, in some polycrystalline

Lawrence Dunn; Debarshi Basu; Liang Wang; Ananth Dodabalapur

2006-01-01

251

Ultrafast carrier transport in GaAs measured by optical pump-terahertz probe spectroscopy  

Microsoft Academic Search

Femtosecond optical pump-terahertz probe studies of carrier dynamics and transport characteristics in semi-insulating GaAs have been investigated under different pump powers at room temperature. The transmission of the terahertz pulse is monitored as a function of delay time between pump and probe pulse, we found that because the more optical generated carriers under the higher power, the terahertz transmission decreased

Hai-Yan Yang; Yu-Lei Shi; Qing-Li Zhou; Dong-Mei Zhao; Lei Li; Cun-Lin Zhang

2009-01-01

252

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

Microsoft Academic Search

.  We present studies on the mathematical properties of a multigroup formulation of the Bloch–Boltzmann–Peierls equations. The\\u000a considered model equations are based on a general carrier dispersion law and contain the full quantum statistics of both the\\u000a carriers and the phonons. Moreover, the transport model allows the investigation of particle distributions with arbitrary\\u000a anisotropy with respect to the main direction. We

M. Galler; F. Schürrer

2007-01-01

253

Sustained release micellar carrier systems for iontophoretic transport of dexamethasone across human sclera.  

PubMed

A challenge in ocular drug delivery is to maintain the therapeutic concentration of a drug at the site of action in the eye. The objective of the present study was to investigate the feasibility of micellar carrier systems for sustained drug delivery in transscleral iontophoresis in vitro. Simple and mixed micelles prepared using sodium taurocholate (TA) alone or with egg lecithin (LE) were the carrier systems studied. Dexamethasone (DEX), a poorly water soluble corticosteroid, was the model drug. The micellar carrier systems were first characterized for their solubilization and encapsulation of the drug. Passive and 2-mA iontophoretic (both cathodal and anodal) transport experiments were conducted using these micellar carrier systems in side-by-side diffusion cells with excised human sclera in vitro. Drug release studies were performed after the transport experiments. Saturated DEX solution without the micellar carriers was used as a control. It was found that the solubilization capacity of the micellar carrier systems increased as the total lipid concentration of the systems increased. Drug release from the sclera was significantly prolonged with the micellar carrier systems as compared to the control after passive and iontophoretic delivery. Less than ~20% of DEX was released from the sclera in approximately 2h after cathodal iontophoretic delivery of the micellar carrier systems, whereas more than ~50% of DEX was released from the control in the same time period under the same condition. Micellar carrier systems can be a suitable transscleral drug delivery system for poorly water soluble drugs by enhancing their aqueous solubilities and providing sustained drug delivery. These micellar carrier systems can be efficiently delivered into and across the sclera by iontophoresis for drug delivery. PMID:22306336

Chopra, Poonam; Hao, Jinsong; Li, S Kevin

2012-01-27

254

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

NASA Astrophysics Data System (ADS)

We report an electron spin resonance study of Ge nanowires doped with chromium. The Ge0.99Cr0.01 nanowires contain both diluted Sr3+ and Sr2+ ions and a large amount of Cr-based nanoclusters revealing spin-glass properties at T<60 K. The observed antiferromagnetic resonance at low temperatures is attributed to Ge-Cr nanoclusters. Additionally, we detect an asymmetric, isotropic resonant line clearly distinguished in the whole temperature range, T=4-300 K, which corresponds to a paramagnetic resonance of the charge carriers in the Ge0.99Cr0.01 nanowires. On the base of our previous studies, we compare properties of the charge carriers in germanium nanowires doped with different transition metals. We demonstrate that the effective g-factor related to charge carriers is reduced with an increase in the spin-orbital interaction in the row: Mn2+, Cr2+, Fe3+, and Co2+.

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

2009-05-01

255

Direct Observation of Charge Carrier Diffusion and Localization in an InGaN Multi Quantum Well  

NASA Astrophysics Data System (ADS)

The temperature dependence of the diffusion constant of an InGaN/GaN multi quantum well (MQW) emitting at 465 nm is studied by time of flight measurements. Utilizing a confocal microscopy setup and scanning the pinhole across the image plane allows us to observe charge carrier diffusion in real space with submicron resolution and to determine the diffusion constant by fitting the time delays of the spatially dependent photoluminescence signal using a simple diffusion model. We see direct evidence for a strong decrease of charge carrier mobility below 110 K and for localization of charge carriers at 10 K. The diffusion constant increases continuously with temperature up to about 0.27 cm2 s-1 at 293 K.

Solowan, Hans-Michael; Danhof, Julia; Schwarz, Ulrich T.

2013-08-01

256

Mitochondrial ADP/ATP carrier: preventing conformational changes by point mutations inactivates nucleotide transport activity.  

PubMed

The mitochondrial ADP/ATP carrier (Ancp) is a paradigm of the mitochondrial carrier family (MCF); its members allow metabolic fluxes between mitochondria and the cytosol. The members of the MCF share numerous structural and functional characteristics. Ancp is very specifically inhibited by two classes of compounds, which stabilize the carrier in two different conformations involved in nucleotide transport. Resolution of the atomic structure of the bovine Ancp, in complex with one of its specific inhibitors, is that of the carrier open toward the intermembrane space. To gain insights into the interconversion from one conformation to the other, we introduced point mutations in the yeast carrier at positions Cys73 in the first matrix loop and Tyr97 and Gly298 in transmembrane helices 2 and 6. We demonstrate in this paper that they impair stabilization of the carrier in one conformation or the other, resulting in an almost complete inactivation of nucleotide transport in both cases. The results are discussed on the basis of the atomic structure of the conformation open to the cytosol. These mutant proteins could afford convenient tools for undertaking structural studies of both conformations of the yeast carrier. PMID:22928843

Babot, Marion; Blancard, Corinne; Zeman, Igor; Lauquin, Guy J-M; Trézéguet, Véronique

2012-09-04

257

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

NASA Astrophysics Data System (ADS)

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

Riha, Shannon C.

258

Production, transport and charge capture measurements of highly charged recoil ions  

SciTech Connect

An experiment is described to study highly charged recoil ions on-line to the heavy accelerator UNILAC at GSI. The highly charged recoil ions are produced by heavy-ion bombardment of a gas target. Subsequently the slow highly charged recoil ions are extracted from the ionization volume, and guided through a beam transport line to a Wien filter for charge state selection and to a collision region to study charge transfer processes. Several experiments were carried out to show the efficient charge state separation. Charge states up to q = 15 were observed. When using a retarding field analyzer cross sections for single electron capture were determined for different charge states of Xe{sup q+} for q = 4 to 11 and He gas. The experiments demonstrated increasing charge transfer cross sections with increasing charge state q and indicated the effect of near resonant charge capture for q = 6. The flexible data acquisition system used, is described and other future experiments, such as for instance in flight ion-trapping are indicated in the appendix.

Trebus, U.E.

1989-01-01

259

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

260

Transport in Charged Defect-Rich ..pi..-Conjugated Polymers  

SciTech Connect

Some models of charge transport in {pi}-conjugated polymers treat these materials as if they were electrical insulators. Although this may be appropriate for a few materials, many polymers are effectively doped p-type by a high density of charged defects. Herein, limits are estimated for the charged defect density above which the resulting electrostatic fluctuations may govern transport and for the corresponding free hole density above which space-charge-limited currents should not occur. These limits are lower than the experimentally observed values in many {pi}-conjugated polymers, suggesting that these materials are more accurately described by models of doped semiconductors. This analysis also provides an explanation for two otherwise puzzling experimental observations, the low-field Poole-Frenkel mobility and the correlated energetic disorder.

Gregg, B. A.

2009-01-01

261

Charged-particle calculations using Boltzmann transport methods  

SciTech Connect

Several aspects of radiation damage effects in fusion reactor neutron and ion irradiation environments are amenable to treatment by transport theory methods. In this paper, multigroup transport techniques are developed for the calculation of charged particle range distributions, reflection coefficients, and sputtering yields. The Boltzmann transport approach can be implemented, with minor changes, in standard neutral particle computer codes. With the multigroup discrete ordinates code, ANISN, determination of ion and target atom distributions as functions of position, energy, and direction can be obtained without the stochastic error associated with atomistic computer codes such as MARLOWE and TRIM. With the multigroup Monte Carlo code, MORSE, charged particle effects can be obtained for problems associated with very complex geometries. Results are presented for several charged particle problems. Good agreement is obtained between quantities calculated with the multigroup approach and those obtained experimentally or by atomistic computer codes.

Hoffman, T.J.; Dodds, H.L. Jr.; Robinson, M.T.; Holmes, D.K.

1981-01-01

262

Efficient charge transport in semisynthetic zinc chlorin dye assemblies.  

PubMed

We have studied the charge transport properties of self-assembled structures of semisynthetic zinc chlorins (ZnChls) in the solid state by pulsed radiolysis time-resolved microwave conductivity measurements. These materials can form either a two-dimensional (2D) brickwork-type slipped stack arrangement or a one-dimensional (1D) tubular assemblies, depending on the exact molecular structure of the ZnChls. We have observed efficient charge transport with mobilities as high as 0.07 cm(2) V(-1) s(-1) for tubular assemblies of 3(1)-hydroxy ZnChls and up to 0.28 cm(2) V(-1) s(-1) for 2D stacked assemblies of 3(1)-methoxy ZnChls at room temperature. The efficient charge transporting capabilities of these organized assemblies opens the way to supramolecular electronics based on biological systems. PMID:22985422

Patwardhan, Sameer; Sengupta, Sanchita; Siebbeles, Laurens D A; Würthner, Frank; Grozema, Ferdinand C

2012-09-21

263

Stripes and Charge Transport Properties of HIGH-TC Cuprates  

NASA Astrophysics Data System (ADS)

Unusual features in the in-plane charge transport in lightly hole-doped La2-xSrxCuO4 single crystals are described. Notably, both the in-plane resistivity and the Hall coefficient show a metallic behavior at moderate temperatures even in the long-range-ordered antiferromagnetic phase, which obviously violates the Mott-Ioffe-Regel criterion for the metallic transport and can hardly be understood without employing the role of charge stripes. Moreover, the mobility of holes in this "metallic" antiferromagnetic state is found to be virtually the same as that in optimally-doped crystals, which strongly suggests that the stripes govern the charge transport in a surprisingly wide doping range up to optimum doping.

Ando, Yoichi

2003-06-01

264

Formation and mobility of protonic charge carriers in methyl sulfonic acid–water mixtures: A model for sulfonic acid based ionomers at low degree of hydration  

Microsoft Academic Search

The formation of ionic charge carriers and their transport in methyl sulfonic acid (CH3SO3H)–water mixtures (MSA–H2O) have been investigated by 1H NMR and impedance spectroscopy. The dissociation constant is close to K=1.8 at high water contents, and the maximum molar concentration of ions (H3O+ and CH3SO3?) is found at a water hydration number of ?=[H2O]\\/[MSA]=1.5. For this concentration also minima

A. Telfah; G. Majer; K. D. Kreuer; M. Schuster; J. Maier

2010-01-01

265

Analysis of modulated free-carrier absorption measurement of electronic transport properties of silicon wafers  

NASA Astrophysics Data System (ADS)

Based on a three-dimensional modulated free carrier absorption (MFCA) model, theoretical analysis is performed to investigate the dependences of MFCA amplitude and phase on the electronic transport properties (the carrier lifetime, the carrier diffusivity, and the front surface recombination velocity) at different pump-to-probe separations and different modulation frequencies. The sensitivity of the multi-parameter estimate employing the dependences of the MFCA amplitude and phase on the modulation frequency at several pump-to-probe separations is theoretically compared with that employing the dependences on the pump-to-probe separation measured at several modulation frequencies. Simulation results show that the two approaches have comparable sensitivities to the electronic transport properties of silicon wafers. As for the MFCA experiments, the frequency scan data measured at different pump-to-probe separations have higher signal-to-noise ratios and therefore should be preferable to the simultaneous determination of the multiple transport properties.

Li, Wei; Li, Bincheng

2010-03-01

266

On the mechanisms of photogeneration of charge carriers in PEPC-C60 composites  

NASA Astrophysics Data System (ADS)

Photogeneration of electric charge carriers at high strengths of the external electric field and the temperature of transition to the viscous-flow state ( T visc) of thin PEPC-C60 composite films obtained by casting from a toluene solution have been studied. The rheology of the composite films has been investigated by the nondestructive optical method. The consistent correlated change in the values of T visc and the effective temperature in the expression for the photogeneration quantum yield ( T 0) in the Meltz representation with variations in the C60 concentration has been established. The difference between T visc and T 0 in thin composite films does not exceed 2-3% of T visc ( T 0).

Zabolotny, M. A.; Barabash, Yu. M.; Dmitrenko, O. P.; Kulish, N. P.; Davidenko, N. A.; Studzinskii, S. L.; Olasyuk, A. P.; Demchenko, A. V.

2013-08-01

267

Methylmercury transport across the placenta via neutral amino acid carrier  

Microsoft Academic Search

Methylmercury (MeHg) penetrates the placental barrier to affect developing fetuses in the uterus. However, the mechanism\\u000a of placental MeHg transport is not well defined. To clarify the MeHg transport system that functions in the placenta, pregnant\\u000a rats were intravenously administered MeHg on day 18 of gestation. The fetal blood was collected from the umbilical cord at\\u000a 30 and 60 min

Y. Kajiwara; A. Yasutake; T. Adachi; K. Hirayama

1996-01-01

268

ac conductivity in a DNA charge transport model.  

PubMed

We present the ac response of a DNA charge transport model, where the charge in the pi-stack interacts with the base-pair opening dynamics of the double strand. The calculated ac conductivity exhibits prominent peaks at polaron normal modes with electronic character, while weaker response appears at lower frequencies in the vibrational part of the polaron normal mode spectrum. Examples of the former, strong peaks, show redshifts as the amplitude of the ac field increases. PMID:16196609

Maniadis, P; Kalosakas, G; Rasmussen, K O; Bishop, A R

2005-08-29

269

Anisotropy of the resistivity and charge-carrier sign in nanolaminated Ti2AlC: Experiment and ab initio calculations  

NASA Astrophysics Data System (ADS)

The anisotropy of Ti2AlC transport properties is investigated focusing on the Hall effect and resistivity vs temperature measurements performed on a highly (000l)-oriented thin film and a bulk polycrystalline sample. Experimental data are interpreted on the basis of density functional theory calculations including transport coefficients obtained with the Boltzmann semiclassical transport equation in the isotropic relaxation time approximation. It is shown that the Hall constant is independent of the temperature and that the charge-carrier sign depends on the investigated crystallographic orientation. Charge carriers exhibit a holelike character along the basal plane of the Ti2AlC, whereas the bulk sample Hall constant is negative. The resistivity anisotropy is also evidenced: using an effective medium approach, the room temperature basal plane resistivity is shown to be more than one order of magnitude lower than that along the c axis. This very important anisotropy is shown to result from the anisotropy of the Fermi surface increased by electron-phonon interactions. These interactions are much more important along the c axis than within the basal plane, a situation opposite to that observed in literature for Ti2GeC where resistivity was reported to be isotropic.

Mauchamp, Vincent; Yu, Wenbo; Gence, Loïk; Piraux, Luc; Cabioc'h, Thierry; Gauthier, Véronique; Eklund, Per; Dubois, Sylvain

2013-06-01

270

Charge Transport in Semiconductor Nanocrystal Solids  

NASA Astrophysics Data System (ADS)

Self-assembly of chemically-synthesized nanocrystals can yield complex long-range ordered structures which can be used as model systems for studying transport phenomena in low-dimensional materials [1]. Treatment of close-packed PbSe nanocrystal arrays with hydrazine enhanced exchange coupling between the nanocrystals and improved conductance by more than ten orders of magnitude compared to native nanocrystal films [2]. The conductivity of PbSe nanocrystal solids can be switched between n- and p-type transports by controlling the saturation of electronic states at nanocrystal surfaces. Nanocrystal arrays form the n- and p-channels of field-effect transistors with electron and hole mobilities of 2.5 cm^2V-1s-1 and 0.3 cm^2V-1s-1, respectively, and current modulation Ion/Ioff˜10^3-10^4. The field-effect mobility in PbSe nanocrystal arrays is higher than the mobility of organic transistors while the easy switch between n- and p-transport allows realization of complimentary circuits and p-n junctions for nanocrystal-based solar cells and thermoelectric devices. [1] E. V. Shevchenko, D. V. Talapin, N. A. Kotov, S. O'Brien, C. B. Murray. Nature 439, 55 (2006). [2] D. V. Talapin, C. B. Murray. Science 310, 86 (2005).

Talapin, Dmitri; Shevchenko, Elena; Lee, Jong Soo; Urban, Jeffrey; Mitzi, David; Murray, Christopher

2007-03-01

271

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

272

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

273

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 >0.7 cm2/V s 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

274

Lorentz number and Hall factor in degenerate semiconductors during resonance scattering of charge carriers  

SciTech Connect

In highly degenerate semiconductors, the Lorentz number L and Hall factor A{sub R} differ significantly from universal constants {pi}{sup 2}/3 and 1, respectively, due to the pronounced energy dependence of the relaxation time during resonance scattering of carriers. The values of L and A{sub R} are calculated for various values of the resonant impurity bandwidth, band filling with current carriers, and the relative contribution of resonance scattering. The available published data on the bandwidth of thallium impurity states in lead telluride, where intense resonance scattering of holes was observed, are discussed. The previously obtained data on the energy of Tl in PbTe resonant states were corrected taking into account the calculated Hall factor. An analysis of the experimental data on the dependence of the PbTe:Tl thermal conductivity on the temperature and content of additional Na dopant both showed that phonon scattering by polarized regions around charged impurity atoms is negligible and confirmed the results of theoretical calculations of the Lorentz number at dominant resonance scattering of holes.

Prokof'eva, L. V., E-mail: l.prokofieva@mail.ioffe.ru; Shabaldin, A. A. [Russian Academy of Sciences, Ioffe Physicotechnical Institute (Russian Federation); Korchagin, V. A.; Nemov, S. A.; Ravich, Yu. I. [St. Petersburg State Polytechnical University (Russian Federation)

2008-10-15

275

Temperature dependence of charge carrier mobility in single-crystal chemical vapour deposition diamond  

NASA Astrophysics Data System (ADS)

Measurements of the temperature dependence of the charge carrier mobility in single-crystal chemical vapour deposition diamond using the transient current technique are presented in a temperature range from 2 K to room temperature. An ?-source is used to create free charge carriers in the diamond bulk. The evolution of the current signal induced by their drift under the influence of an externally applied field is studied as a function of the temperature and the electric field strength. The electric field strength is varied by a factor of 30. The measurements are used to extract the transit time, the drift velocity, the saturation velocity, and the low-field mobility in terms of which the results are interpreted. Three samples have been studied which show the same behaviour. For holes, the mobility increases with decreasing temperature due to the acoustic phonon scattering, but it saturates for ultra-cold temperatures. The low-field mobility for holes at room temperature is measured as ?0h(295K)=(2534+/-20) cm2/Vs saturating against ?0h(-->2K)=(11130+/-120) cm2/Vs. For electrons, only a lower limit on the low-field mobility can be given. It is measured as ?0e(295K)=(1802+/-14) cm2/Vs saturating against ?0e(-->2K)=(3058+/-27) cm2/Vs. The electron transit time at low fields shows a different behaviour than the hole transit time and is not following the expected behaviour. This is likely to be caused by a high temperature valley re-population effect.

Jansen, Hendrik; Dobos, Daniel; Eisel, Thomas; Pernegger, Heinz; Eremin, Vladimir; Wermes, Norbert

2013-05-01

276

Surface-Charge-Governed Ion Transport in Nanofluidic Channels  

NASA Astrophysics Data System (ADS)

A study of ion transport in aqueous-filled silica channels as thin as 70nm reveals a remarkable degree of conduction at low salt concentrations that departs strongly from bulk behavior: In the dilute limit, the electrical conductances of channels saturate at a value that is independent of both the salt concentration and the channel height. Our data are well described by an electrokinetic model parametrized only by the surface-charge density. Using chemical surface modifications, we further demonstrate that at low salt concentrations, ion transport in nanochannels is governed by the surface charge.

Stein, Derek; Kruithof, Maarten; Dekker, Cees

2004-07-01

277

Enhanced Carrier Transport of N-Doped TiO2 for Photoelectrochemical Cells  

NASA Astrophysics Data System (ADS)

The carrier transport kinetics of the TiO2 film doped with N (TiO2:N) were investigated by measuring the current and open circuit potential transients under light on/off illumination. These measurements were compared to an undoped film. The N in TiO2 not only shifted the light absorption into a longer wavelength region (known effect) but also enhanced the carrier transport. The combination of these two effects improved the photogeneration of the electron-hole pairs and suppressed their recombination, resulting in much better photoelectrochemical performance, compared to that of the undoped TiO2.

Kim, Jae-Hong; Yun, Tae Kwan; Bae, Jae-Yung; Ahn, Kwang-Soon

2009-12-01

278

Molecular reorganization in organic field-effect transistors and its effect on two-dimensional charge transport pathways.  

PubMed

Charge transport in organic thin film transistors takes place in the first few molecular layers in contact with the gate dielectric. Here we demonstrate that the charge transport pathways in these devices are extremely sensitive to the orientational defects of the first monolayers, which arise from specific growth conditions. Although these defects partially heal during the growth, they cause depletion of charge carriers in the first monolayer, and drive the current to flow in the monolayers above the first one. Moreover, the residual defects induce lower crystalline order and charge mobility. These results, which are not intuitively explained by electrostatics arguments, have been obtained by combining in situ real time structural and electrical characterization together with ex situ AFM measurements, on thin films of a relevant n-type organic semiconductor, N,N'-bis(n-octyl)-dicyanoperylene-3,4:9,10-bis dicarboximide grown by sublimation in a quasi-layer-by-layer mode at different substrate temperatures. PMID:23350706

Liscio, Fabiola; Albonetti, Cristiano; Broch, Katharina; Shehu, Arian; Quiroga, Santiago David; Ferlauto, Laura; Frank, Christian; Kowarik, Stefan; Nervo, Roberto; Gerlach, Alexander; Milita, Silvia; Schreiber, Frank; Biscarini, Fabio

2013-02-06

279

Simulation of non-linear recombination of charge carriers in sensitized nanocrystalline solar cells  

NASA Astrophysics Data System (ADS)

Electron transport and recombination in electrolyte-filled sensitized nanocrystalline solar cell was investigated using Monte-Carlo simulation. Multiple-trapping in an exponential tail of trap states was used as an electron transport model. For simulation of the recombination, a new approach based on Marcus theory of charge transfer was developed and utilized to simulate both linear and non-linear (trap-assisted) recombination of electrons with holes in the electrolyte. Monte-Carlo simulation results, based on this approach, reproduced the non-constant diffusion length, recently observed in several experimental works. All simulation results were compared with theoretical predictions of the Marcus theory of charge transfer. Based on this comparison, interestingly it was found that random walk electron lifetime is different from the one which is obtained experimentally by small-perturbation techniques. This result is similar to the well-known Darken equation that describes the difference between jump and chemical diffusion coefficient. An interpretation based on the transport-limited recombination picture was provided to describe this result. These simulations establish a clear picture that describes how the localized trap states contribute to the recombination, leading to the non-linear recombination kinetics in sensitized solar cells.

Ansari-Rad, M.; Abdi, Y.; Arzi, E.

2012-10-01

280

Collective charge transport processes in condensed matter and biological systems  

NASA Astrophysics Data System (ADS)

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

Cardenas, Gustavo

281

Dynamics of oppositely charged carriers in a metal\\/coupled poly( p-phenylene vinylene) chains\\/metal structure  

Microsoft Academic Search

By using the extended version of the Su-Schrieffer-Heeger (SSH) tight-binding model and a non-adiabatic dynamic evolution method, we present a study of the dynamic process of oppositely charged carriers in a metal\\/two coupled poly(p-phenylene vinylene) chains\\/metal structure. Electrons and holes can be injected into the polymer chains from metal electrodes by applying voltage biases. The behavior of the injected charged

Dong-Mei Li; Yuan Li; Hai-Hong Li; De-Sheng Liu

2011-01-01

282

Charge transport in a zigzag silicene nanoribbon  

NASA Astrophysics Data System (ADS)

Nanoscale transport properties of a zigzag silicene nanoribbon (zSiNR) are studied using first-principles calculations based on the non-equilibrium Green's function approach. Our theoretical analysis demonstrates how the scattering wavefunctions in the device region can shed light on the conductance behavior of a nanoelectronic device, made up of 3-zSiNR, spanning the width of three hexagons. The lowering of conductance at 100 mV bias is due mainly to the dominant character of the lowest unoccupied molecular orbital (LUMO) in the transmission profile. A zSiNR, having higher conductance than germanene, can thus be a potential candidate for silicon-based nanoelectronic devices due to its rich optoelectronic properties.

Mehrotra, Nakul; Kumar, Niraj; Sen, Arijit

2013-02-01

283

Photogeneration and charge transport mechanisms in thin films of organic electron acceptor 2,4,7-trinitro-9-fluorenone  

NASA Astrophysics Data System (ADS)

The photogeneration process in thin films of vacuum-evaporated amorphous 2,4,7-trinitro-9-fluorenone (a-TNF) is investigated by steady-state photoconductivity measurements and by the photoinduced discharge method. It was found that in the intrinsic spectral range of absorption (?<=400 nm) the charge carrier photogeneration mechanism includes several steps. The final step, thermal dissociation of light generated electron-hole pairs, is realized according to the Onsager mechanism. The effect of trapping centers on the conductivity of thin films of a-TNF is investigated by space charge limited current (SCLC), steady-state photoconductivity, and transient photoconductivity methods. It is suggested that the transport of charge carriers in a-TNF is controlled by traps.

Kachirski, I. M.

2008-11-01

284

Electronic charge transport in sapphire studied by optical-pump\\/THz-probe spectroscopy  

Microsoft Academic Search

THz time-domain spectroscopy (THz TDS) with ultrafast photo-excitation is applied to probe the complex conductivity of the charge carriers in sapphire over the temperature range of 40 - 350 K. A comparison of the measured complex conductivity to the Drude model yields the carrier scattering rate and density. The dependence of the carrier scattering rate on temperature and sample purity

Feng Wang; Jie Shan; Ernst Knoesel; Mischa Bonn; Tony F. Heinz

2004-01-01

285

Influences of space charge and electrode on the electrical transport through (Ba,Sr)TiO 3 thin film capacitors  

Microsoft Academic Search

The combined model of thermionic emission and carrier drift-diffusion is derived to simulate the electrical transport through BST thin film capacitors. In the model the field-dependent permittivity is obtained from the derivative of the polarization distinguished with the traditional characterization. The simulated currents show the hysteresis. The influences of space charges and electrode materials on the current density-applied voltage characteristics

J. Sun; X. J. Zheng; W. Yin; M. H. Tang; W. Li

2011-01-01

286

Optimization of white OLEDs based on charge carrier conduction properties of phosphorescent emitting layers  

Microsoft Academic Search

The charge conduction properties of the organic phosphorescent emission layer doped with iridium-based green and red phosphorescent emitters, fac-tris(2-phenylpyridine) iridium(III) (Ir(ppy)3) and bis(2-(2'-benzo [4,5-a]thienyl)pyridinato-N,C3')iridium(acetyl-acetonate) (btp2Ir(acac)), were studied and compared to those of the reference host of 4,'-N,N'-dicarbazole-biphenyl (CBP). In the CBP host layer, both dopants act as hole traps but they affect the electron transport differently. Compared with the pristine

Changhee Lee; Heume-Il Baek; Jeonghun Kwak; Joon Youp Kim; Byung Doo Chin

2008-01-01

287

Generalized charge transport model for organic\\/inorganic material systems  

Microsoft Academic Search

This paper introduces a generalized charge transport model for hybrid organic-inorganic semiconducting systems. The model is formed of five coupled nonlinear partial differential equations consisting of the Poisson's equation and four continuity equations for electrons, holes, excitons, and triplets. The model allows transformation of one particle (electron\\/hole, excitons, and triplets) to another through a transformation ratio. Variables are electric potential,

Seyyed Sadegh Mottaghian; Mahdi Farrokh Baroughi; Khadijeh Bayat; Matt Biesecker; Jung-Han Kimn

2010-01-01

288

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

Federal Register 2010, 2011, 2012, 2013

...sites and elsewhere by air carriers, their agents, and third party sellers of air transportation in view of recent amendments...Washington, DC 20590, (202) 366-9349. United States of America, Department of Transportation, Office of the...

2011-01-14

289

Apical membrane proteins are transported in distinct vesicular carriers  

Microsoft Academic Search

The function of polarized epithelial cells and neurons is achieved through intracellular sorting mechanisms that recognize classes of proteins in the trans-Golgi network (TGN) and deliver them into separate vesicles for transport to the correct surface domain. Some proteins are delivered to the apical membrane after their association with membrane detergent-insoluble glycophosphatidylinositol\\/cholesterol (DIG) membrane microdomains [1], while some do not

Ralf Jacob; Hassan Y. Naim

2001-01-01

290

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.

Polizzi, Nicholas F.; Skourtis, Spiros S.

2012-01-01

291

On the definition of dielectric permittivity for media with temporal dispersion in the presence of free charge carriers  

Microsoft Academic Search

We show that in the presence of free charge carriers the definition of the frequency-dependent dielectric permittivity requires additional regularization. As an example, the dielectric permittivity of the Drude model is considered and its time-dependent counterpart is derived and analyzed. The respective electric displacement cannot be represented in terms of the standard Fourier integral. The regularization procedure allowing the circumvention

M. Bordag; B. Geyer; G. L. Klimchitskaya; V. M. Mostepanenko

2010-01-01

292

Charge Density and Molecular Weight of Polyphosphoramidate Gene Carrier Are Key Parameters Influencing Its DNA Compaction Ability and Transfection Efficiency  

PubMed Central

A series of polyphosphoramidates (PPA) with different molecular weights (MWs) and charge densities were synthesized and examined for their DNA compaction ability and transfection efficiency. A strong correlation was observed between the transfection efficiency of PPA/DNA nanoparticles and the MW and net positive charge density of the PPA gene carriers in three different cell lines (HeLa, HEK293 and HepG2 cells). An increase in MW and/or net positive charge density of PPA carrier yielded higher DNA compaction capacity, smaller nanoparticles with higher surface charges and higher complex stability against challenges by salt and polyanions. These favorable physicochemical properties of nanoparticles led to enhanced transfection efficiency. PPA/DNA nanoparticles with the highest complex stability showed comparable transfection efficiency as PEI/DNA nanoparticles likely by compensating the low buffering capacity with higher cellular uptake and affording higher level of protection to DNA in endolysosomal compartment. The differences in transfection efficiency were not attributed by any difference in cytotoxicity among the carriers, as all nanoparticles showed minimal level of cytotoxicity under the transfection conditions. Using PPA as a model system, we demonstrated the structural dependence of transfection efficiency of polymer gene carrier. These results offer more insights into nanoparticle engineering for non-viral gene delivery.

Ren, Yong; Jiang, Xuan; Pan, Deng; Mao, Hai-Quan

2011-01-01

293

Mathematical simulation of the distribution of minority charge carriers generated in a multilayer semiconducting structure by a wide electron beam  

SciTech Connect

A method of calculation of the distributions of minority charge carriers generated in a two-layer semiconductor by a wide electron beam with energies 5-30 keV based on the use of the model of independent sources is described.

Burylova, I. V. [Tsiolkovskii Kaluga State Pedagogical University (Russian Federation); Petrov, V. I. [Moscow State University (Russian Federation); Snopova, M. G. [Bauman Moscow State Technical University, Kaluga Branch (Russian Federation); Stepovich, M. A. [Tsiolkovskii Kaluga State Pedagogical University (Russian Federation)

2007-04-15

294

tRNA Transport from the Nucleus in a Eukaryotic Cell: Carrier-Mediated Translocation Process  

Microsoft Academic Search

The mechanism by which a tRNA molecule is delivered from the nucleus of a cell to the cytoplasm has been studied in the Xenopus laevis oocyte utilizing nuclear microinjection and manual microdissection techniques. tRNA nuclear transport in this cell resembles a carrier-mediated translocation process rather than diffusion through a simple pore or channel. tRNA transport is saturable by tRNA, with

Michael Zasloff

1983-01-01

295

Cost models for coal transportation by common carrier. Appendix 1: User's Manual. Final report  

Microsoft Academic Search

This manual provides the technical information needed to operate the computerized transportation cost models developed in EA--675, Cost Models for Coal Transportation by Common Carrier, prepared for the Electric Power Research Institute by Manalytics, Inc., March 1979. Three models were developed: one for rail; one for inland river, Great Lakes, and coastal ocean waterways; and one for origin\\/destination loading\\/unloading and

S. J. White; J. P. Hynes

1980-01-01

296

Iontophoretic Transport of Charged Macromolecules across Human Sclera  

PubMed Central

The mechanisms of transscleral iontophoresis have been investigated previously with small molecules in rabbit sclera. The objective of the present study was to examine transscleral iontophoretic transport of charged macromolecules across excised human sclera. Passive and 2-mA iontophoretic transport experiments were conducted in side-by-side diffusion cells with human sclera. The effects of iontophoresis upon transscleral transport of model permeants bovine serum albumin (BSA) and polystyrene sulfonic acid (PSS) as well as a model drug bevacizumab (BEV) were determined. Passive and iontophoretic transport experiments of tetraethylammonium (TEA) and salicylic acid (SA) and passive transport experiments of the macromolecules served as the controls. The results of iontophoresis enhanced transport of TEA and SA across human sclera were consistent with those in a previous rabbit sclera study. For the iontophoretic transport of macromolecules BSA and BEV, higher iontophoretic fluxes were observed in anodal iontophoresis as compared to passive and cathodal iontophoresis. This suggests the importance of electroosmosis. For the polyelectrolyte PSS, higher iontophoretic flux was observed in cathodal iontophoresis compared to anodal iontophoresis. Both electroosmosis and electrophoresis affected iontophoretic fluxes of the macromolecules; the relative contributions of electroosmosis and electrophoresis were a function of molecular size and charge of the macromolecules.

Chopra, Poonam; Hao, Jinsong; Li, S. Kevin

2010-01-01

297

In-situ strain monitoring in liquid containers of LNG transporting carriers  

Microsoft Academic Search

Liquefied natural gas (LNG) transport carriers are exposed to a risk by the repeated bump in the LNG container during the vessel traveling over the wave in ocean. The liquid inside the container, especially when it was not fully contained, make a strong bump onto the insulation panel of the tank wall. The insulation panel consists of several layers of

Min-Cheol Oh; Jun-Kyu Seo; Kyung-Jo Kim; Sang-Min Lee; Myung-Hyun Kim

2008-01-01

298

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

Microsoft Academic Search

The appropriate prediction of the fate of the contaminant is an essential step when evaluating the risk of severe groundwater pollutions—in particular in the context of natural attenuation. We numerically study the reactive transport of phenanthrene at the field scale in a multilayer soil profile based on experimental data. The effect of carrier facilitation by dissolved organic carbon is emphasized

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

2002-01-01

299

Ion Transport Dynamics in Acid Variable Charge Subsoils  

SciTech Connect

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

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

2005-06-06

300

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

SciTech Connect

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

Panja, S.; Dakshinamoorthy, A.; Munshi, S.K.; Dey, P.K. [Fuel Reprocessing Division, B.A.R.C., Trombay, Mumbai-400085 (India); Mohapatra, P.K.; Manchanda, V.K. [Radiochemistry Division, B.A.R.C., Trombay, Mumbai-400085 (India)

2008-07-01

301

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

302

Novel macrocyclic carriers for proton-coupled liquid membrane transport  

SciTech Connect

A number of new macrocyclic ligands was prepared for transport studies. The cryptands were prpepared (18-40% yield) by a new metal carbonate-catalyzed one-step method from 1 mole oligoethyleneoxy diamine and 2 moles diahlide derivative of oligoethylene glycol. Bis-crown ethers were also isolated in 17-30% yields. Cage compounds were also prepared; they interact with various metal ions and protons. Back extraction and dual module hollow fiber membrane separation experiments were used to study the cation selectivity of new ligands, including crown thioethers. An isothermal flow calorimeter is being constructed for studies of macrocycle-cation reactions. 3 figs, 2 tabs.

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

1992-07-01

303

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

304

Characterization of the carrier dynamics and interface-state charge fluctuations in quaternary AlInGaN multiple quantum well heterostructures  

NASA Astrophysics Data System (ADS)

Nitride-based light-emitting diodes (LEDs) have recently attracted to understand the emission mechanisms in novel multiple quantum well (MQW) heterosturctures. To understand substantially the unique spectral response, it is necessary to examine the carrier transport behavior. In this work, we studied the unique correlations between the carrier dynamics and optical characteristics of the quaternary AlInGaN MQW heterostructures with different barrier widths. It has been found that the photoluminescence peak energy of quaternary AlInGaN MQW blueshifts when decreasing the barrier width. This is attributed to the redistribution among the well and barrier of the strong electrostatic fields induced by polarization effect. It resulted in not only the diminutions of the charge density induced by piezoelectric field, but also the increments of the interface-state charge distribution from the collective influence of alloy disorder and interface roughness. We resort the Arrhenius plots to demonstrate the localized effect originated from indium fluctuation. Our results show the exciton-localization effect can be enhanced monotonically by increasing the barrier widths. On the other hand, we corroborated the surface charge density increased while increasing barrier widths between the epitaxial layers in this investigation.

Ke, Chih-Chun; Hung, Cheng-Wei; Kuo, Da-Chuan; Chen, Wei-Jen; Shen, Hui-Tang; Wu, Ya-Fen; Wang, Jen-Cheng; Nee, Tzer-En

2007-02-01

305

?-Isopropylmalate, a Leucine Biosynthesis Intermediate in Yeast, Is Transported by the Mitochondrial Oxalacetate Carrier*  

PubMed Central

In Saccharomyces cerevisiae, ?-isopropylmalate (?-IPM), which is produced in mitochondria, must be exported to the cytosol where it is required for leucine biosynthesis. Recombinant and reconstituted mitochondrial oxalacetate carrier (Oac1p) efficiently transported ?-IPM in addition to its known substrates oxalacetate, sulfate, and malonate and in contrast to other di- and tricarboxylate transporters as well as the previously proposed ?-IPM transporter. Transport was saturable with a half-saturation constant of 75 ± 4 ?m for ?-IPM and 0.31 ± 0.04 mm for ?-IPM and was inhibited by the substrates of Oac1p. Though not transported, ?-ketoisocaproate, the immediate precursor of leucine in the biosynthetic pathway, inhibited Oac1p activity competitively. In contrast, leucine, ?-ketoisovalerate, valine, and isoleucine neither inhibited nor were transported by Oac1p. Consistent with the function of Oac1p as an ?-IPM transporter, cells lacking the gene for this carrier required leucine for optimal growth on fermentable carbon sources. Single deletions of other mitochondrial carrier genes or of LEU4, which is the only other enzyme that can provide the cytosol with ?-IPM (in addition to Oac1p) exhibited no growth defect, whereas the double mutant ?OAC1?LEU4 did not grow at all on fermentable substrates in the absence of leucine. The lack of growth of ?OAC1?LEU4 cells was partially restored by adding the leucine biosynthetic cytosolic intermediates ?-ketoisocaproate and ?-IPM to these cells as well as by complementing them with one of the two unknown human mitochondrial carriers SLC25A34 and SLC25A35. Oac1p is important for leucine biosynthesis on fermentable carbon sources catalyzing the export of ?-IPM, probably in exchange for oxalacetate.

Marobbio, Carlo M. T.; Giannuzzi, Giulia; Paradies, Eleonora; Pierri, Ciro L.; Palmieri, Ferdinando

2008-01-01

306

Charge transport measurements of vertically aligned carbon nanofibers  

NASA Astrophysics Data System (ADS)

Vertically aligned carbon nanofibers (VACNFs) have found a variety of electronic applications. To further realize these applications, a good understanding of the charge transport properties is essential. In this work, charge transport properties have been systematically measured for three types of VACNF forests with Ni as catalyst, namely VACNFs grown by direct current PECVD, and inductively coupled PECVD at both normal pressure and low pressure. The structure and composition of these nanofibers have also been investigated in detail prior to the charge transport measurements. Four-probe I-V measurements on individual nanofibers have been enabled by the fabrication of multiple metal ohmic contacts on individual fibers that exhibited resistance of only a few kO. An O2 plasma reactive ion etch method has been used to achieve ohmic contacts between the nanofibers and Ti/Au, Ag/Au, Cd/Au, and Cr/Au electrodes. Direct current VACNFs exhibit linear I-V behavior at room temperature, with a resistivity of approximately 4.2 x 10-3 O·cm. Our measurements are consistent with a dominant transport mechanism of electrons traveling through intergraphitic planes in the dc VACNFs. The resistivity of these fibers is almost independent of temperature, and the contact resistance decreases as temperature increases. Further studies reveal that the 10--15 nm thick graphitic outer layer dominates the charge transport properties of do VACNFs. This is demonstrated by comparison of charge transport properties of as-grown VACNFs and VACNFs with the outer layer partially removed by oxygen plasma reactive ion etch. The linear I-V behavior of the fibers does not vary as this outer layer becomes thinner, but displays a drastic shift to a rectifying behavior when this layer is completely stripped away from some regions of the nanofiber. This shift may be related with the compositional differences in the outer layer and the inner core of the nanofibers. Two-probe charge transport measurements on inductively coupled PECVD grown VACNFs indicate linear I-V behavior, and the resistivity of both types of inductively coupled PECVD grown VACNFs is on the order of 10-3 to 10-4 O·cm.

Zhang, Lan

307

The implications of spontaneous polarization effects for carrier transport measurements in GaN  

NASA Astrophysics Data System (ADS)

In wurtzite-phase GaN, AlN and InN, the dimensions of the crystallographic unit cell are distorted from the ideal c :a ratio of (8/3)1/2 . This produces a net dipole moment across the cell, with a resultant internal electric field in excess of 1 MV cm-1 , and corresponding polarization charges of +/-3-8 × 10-6 C cm-2 on the two surfaces of the epitaxial layer. The effect of this field on the carrier distribution within a film of doped GaN is considered, and shown to produce accumulation and inversion layers of free carriers at opposite surfaces. Theoretical expressions are derived for the effective carrier density and mobility of such films obtained from Hall measurements, and compared with characteristic experimental results. Qualitatively consistent behaviour is observed in some, but not all, samples, but quantitative agreement is generally lacking, and possible explanations for this are considered.

Harris, J. J.; Lee, K. J.; Webb, J. B.; Tang, H.; Harrison, I.; Flannery, L. B.; Cheng, T. S.; Foxon, C. T.

2000-04-01

308

Hopping conductivity and charge transport in low density polyethylene  

NASA Astrophysics Data System (ADS)

The properties and behaviors of charge transport mechanisms in highly insulating polymers are investigated by measuring conduction currents through thin film samples of low density polyethylene (LDPE). Measurements were obtained using a constant voltage method with copper electrodes inside a chamber adapted for measurements under vacuum and over a wide range of temperatures and applied fields. Field-dependent behaviors, including Poole-Frenkel conduction, space charge limited current (SCLC), and Schottky charge injection, were investigated at constant temperature. These field-dependent mechanisms were found to predict incorrect values of the dielectric constant and the field dependence of conductivity in LDPE was not found to be in agreement with SCLC predicted behavior. A model of thermally assisted hopping was a good fit at low applied fields and produced activation energies within the accepted range for LDPE. Low applied field measurements over the range of 213 K to 338 K were used to investigate two prominent hopping conduction mechanisms: thermally assisted hopping and variable range hopping. The observed temperature dependence of LDPE was found to be consistent with both thermally assisted hopping and variable range hopping. Activation energies determined for the range of temperatures were consistent with values reported in the literature for LDPE under similar conditions. A third aspect of charge transport behavior is a bulk response with time dependence. Conductivity behavior is examined in relation to transient current behavior, long time decay currents, and electrostatic discharge. Comparing charging and discharging cycles allowed qualitative separation of polarization and multiple trapping behaviors.

Brunson, Jerilyn

309

Analytical impurity transport model: Coupling between particle and charge state transports in tokamak plasmas  

Microsoft Academic Search

Interpretation and understanding of a set of coupled continuity equations commonly used in impurity tokamak transport studies are found to be syncretic and inadequate, since they do not distinguish between the cross-field fluxes of impurity particles and of their charge states (cs). An analytical approach to impurity transport studies previously developed is generalized to the case of diffusive-convective cs dynamics

V. A. Shurygin

2008-01-01

310

An acoustic charge transport imager for high definition television applications  

NASA Astrophysics Data System (ADS)

The progress during the third six month period of the project is presented. This includes both experimental and theoretical work on the acoustic charge transport (ACT) portion of the chip, the theoretical program modeling of the avalanche photodiode (APD) and the charge overflow transistor, and the materials growth and fabrication part of the program. Among other results from a comprehensive experimental study, it was found that the use of a ZnO thin film piezoelectric overlay can reduce the RF power consumption of a typical ACT device from 28 dBm to 8 dBm.

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

1993-05-01

311

Statistics of Charge Transport and Modified Time Ordering  

NASA Astrophysics Data System (ADS)

The statistics of charge transport across a tunnel junction with energy-dependent scattering is investigated. A model with quadratic dispersion relation is discussed in general and, independently, in the two limiting cases of a large detector and of a linear dispersion relation. The measurement of charge takes place according to various protocols. It is found that, as a rule, the statistics is expressed by means of time-ordered current correlators. However the ordering prescription differs from the usual ones (Dyson and Keldysh) by the Matthews modification. Nevertheless binomial statistics is confirmed in all cases.

Beaud, V.; Graf, G. M.; Lebedev, A. V.; Lesovik, G. B.

2013-08-01

312

Statistics of Charge Transport and Modified Time Ordering  

NASA Astrophysics Data System (ADS)

The statistics of charge transport across a tunnel junction with energy-dependent scattering is investigated. A model with quadratic dispersion relation is discussed in general and, independently, in the two limiting cases of a large detector and of a linear dispersion relation. The measurement of charge takes place according to various protocols. It is found that, as a rule, the statistics is expressed by means of time-ordered current correlators. However the ordering prescription differs from the usual ones (Dyson and Keldysh) by the Matthews modification. Nevertheless binomial statistics is confirmed in all cases.

Beaud, V.; Graf, G. M.; Lebedev, A. V.; Lesovik, G. B.

2013-10-01

313

Extraction of Transport Dynamics in AlGaN/GaN HFETs Through Free Carrier Absorption  

NASA Astrophysics Data System (ADS)

The importance of AlGaN/GaN heterostructure field-effect transistor (HFETs) in high-power high-frequency applications is now well established. However, detailed information on high-field mobilities, velocity field relations, carrier temperature, and momentum and energy relaxation times are not available. In this paper we carry out theoretical simulations based on Monte Carlo techniques to show that transport dynamics can be effectively extracted through free carrier absorption. Using short pulses of infrared radiation, it is possible to obtain the velocity field curve by fitting the absorption spectrum without heating the device. We show this by solving the classical transport equation and then verify the results through Monte Carlo simulations. With the model presented it would be possible to extract carrier dynamics from experimentally measured results. Our work suggests that free carrier absorption experiments on AlGaN/GaN HFETs would provide important transport information, which would be very useful in device design and modeling.

Wu, Yuh-Renn; Hinckley, John M.; Singh, Jasprit

2008-05-01

314

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

PubMed Central

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), havingions 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.

2010-01-01

315

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

316

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

317

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

NASA Astrophysics Data System (ADS)

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

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

2012-08-01

318

Carrier transport in photorefractive multiple-quantum-well spatial light modulators  

NASA Astrophysics Data System (ADS)

In this thesis, we present theoretical and experimental analysis of PR-MQW operation, specifically carrier transport in PR-MQW structures. We study the carrier transport by illuminating the devices with a sinusoidal grating pattern and measuring the diffraction efficiency as a function of time. We begin by introducing the basic concepts and device structures. We then present the picosecond time-resolved four-wave mixing (TR-FWM) data on the first device structure and describe the turn-on and turn-off mechanisms in a PR-MQW structure. We show that holes contribute to the turn-on time as a slower rise of the diffraction efficiency. Furthermore, the diffraction grating is dominated by either electrons or holes, depending on the applied polarity relative to the direction of illumination. The granting decays in 0.4--8.5 ns, depending on the grating spacing. We show that the decay is due to the lateral transport of carriers at the MQW/dielectric interfaces, where low-temperature-grown (LTG) layers can increase the diffraction efficiency and resolution. In the third chapter we investigate the carrier transport length as function of trap density. The trap density in a LTG-MQW structure was dynamically adjusted for optimum sensitivity and resolution by passivating some traps with photocarriers. We show that without pre-illumination, sensitivity and the transport length is 350 A, however with the pre-illumination, sensitivity and the transport length increases by a factor of 10. We also calculate the trap density and the longitudinal mobility of electrons in the device. In our theoretical studies, we present a self-consistent numerical model that combines both the standard photorefractive material calculations and the carrier transport in MQW devices to represent the transient response of PRMQW devices. In the model we show that turn-on time of the device is mainly determined by carrier drift and escape from the quantum wells. We also show that the polarity dependence of the turn-on time is due to large absorption of the device combined with the difference between electron and hole escape and drift times. Numerical simulation results also indicate that when highly trapped materials are used throughout MQW region, device sensitivity reduces.

Canoglu, Ergun

319

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

320

67 FR 48964 - Passenger Facility Charge Audit Guide for Air Carriers-Procedures for Examining Air Carrier...  

Federal Register 2010, 2011, 2012, 2013

...Internet at http://www.faa.gov/arp/ Reports/acaudit.pdf. Interested parties may access the Passenger Facility Charge...Internet at http://www.faa.gov/arp/ Reports/acaudit.pdf. Alternatively, the guide may be obtained by contacting...

2002-07-26

321

Two types of charge carrier localization centers in (DOEO)4[HgBr4] · TCE single crystals  

NASA Astrophysics Data System (ADS)

Using ESR spectroscopy, it has been found that the additional paramagnetic centers appear in the (DOEO)4[HgBr4] · TCE crystals at temperatures of 5-70 K. The symmetry of their crystal field differs from that observed for charge carriers in a temperature range of 70-300 K. The comparison of the temperature dependences of resistivity with parameters of the ESR spectra makes it possible to assume that the carriers localize at two types of sites differing by the crystalline surrounding at 70 K.

Chernenkaya, A. S.; Koplak, O. V.; Kotov, A. I.; Morgunov, R. B.; Yagubskii, E. B.

2012-12-01

322

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

NASA Astrophysics Data System (ADS)

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

Baker, David R.

323

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

NASA Astrophysics Data System (ADS)

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 (~0.1 cm2/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 LaAlO3) and amorphous (quartz) substrates using molecular beam epitaxy system. The films grown on LaAlO3 substrates exhibited a higher value of mobility (~4 cm2/V-s) while those grown on Al2O3 and quartz showed mobility value of ~1 cm2/V-s. High mobility for LaAlO3 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 SrTiO3 substrates. The results showed that current along bi-crystal grain boundary is three orders of magnitude higher than for films on SrTiO3 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.

2010-12-01

324

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

325

Lyapunov stability of charge transport in miniband semiconductor superlattices  

NASA Astrophysics Data System (ADS)

We discuss a numerical method for the calculation of the spectrum of Lyapunov exponents for spatially extended systems described by coupled Poisson and continuity equations. This approach was applied to the model of collective charge transport in semiconductor superlattices operating in the miniband transport regime. The method is in very good agreement with analytical results obtained for the steady state. As an illustrative example, we consider the collective electron dynamics in the superlattice subjected to an ac voltage and a tilted magnetic field, and conclusively show that, depending on the field parameters, the dynamics can exhibit periodic, quasiperiodic, or chaotic behavior.

Koronovskii, A. A.; Hramov, A. E.; Maximenko, V. A.; Moskalenko, O. I.; Alekseev, K. N.; Greenaway, M. T.; Fromhold, T. M.; Balanov, A. G.

2013-10-01

326

Ratchet transport for a chain of interacting charged particles  

NASA Astrophysics Data System (ADS)

We study analytically and numerically the overdamped, deterministic dynamics of a chain of charged, interacting particles driven by a longitudinal alternating electric field and additionally interacting with a smooth ratchet potential. We derive the equations of motion, analyze the general properties of their solutions and find the drift criterion for chain motion. For ratchet potentials of the form of a double-sine and a phase-modulated sine it is demonstrated that both, a so-called integer and fractional transport of the chain, can occur. Explicit results for the directed chain transport for these two classes of ratchet potentials are presented.

Denisov, S. I.; Denisova, E. S.; Hänggi, Peter

2005-01-01

327

Ratchet transport for a chain of interacting charged particles.  

PubMed

We study analytically and numerically the overdamped, deterministic dynamics of a chain of charged, interacting particles driven by a longitudinal alternating electric field and additionally interacting with a smooth ratchet potential. We derive the equations of motion, analyze the general properties of their solutions and find the drift criterion for chain motion. For ratchet potentials of the form of a double-sine and a phase-modulated sine it is demonstrated that both, a so-called integer and fractional transport of the chain, can occur. Explicit results for the directed chain transport for these two classes of ratchet potentials are presented. PMID:15697655

Denisov, S I; Denisova, E S; Hänggi, Peter

2005-01-04

328

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

2008-12-15

329

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

SciTech Connect

The electron-phonon coupling is critical in determining the intrinsic charge carrier and exciton transport properties in organic materials. In this study, we consider a Su-Schrieffer-Heeger (SSH) model for molecular crystals, and perform numerical benchmark studies for different strategies of simulating the mixed quantum-classical dynamics. These methods, which differ in the selection of initial conditions and the representation used to solve the time evolution of the quantum carriers, are shown to yield similar equilibrium diffusion properties. A hybrid approach combining molecular dynamics simulations of nuclear motion and quantum-chemical calculations of the electronic Hamiltonian at each geometric configuration appears as an attractive strategy to model charge dynamics in large size systems ''on the fly,'' yet it relies on the assumption that the quantum carriers do not impact the nuclear dynamics. We find that such an approximation systematically results in overestimated charge-carrier mobilities, with the associated error being negligible when the room-temperature mobility exceeds {approx}4.8 cm{sup 2}/Vs ({approx}0.14 cm{sup 2}/Vs) in one-dimensional (two-dimensional) crystals.

Wang Linjun; Beljonne, David [Laboratory for Chemistry of Novel Materials, University of Mons, Place du Parc 20, B-7000 Mons (Belgium); Chen Liping; Shi Qiang [State Key Laboratory for Structural Chemistry of Unstable and Stable Species, Beijing National Laboratory for Molecular Sciences (BNLMS), Institute of Chemistry, Chinese Academy of Sciences, Zhongguancun, 100190 Beijing (China)

2011-06-28

330

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

PubMed

The electron-phonon coupling is critical in determining the intrinsic charge carrier and exciton transport properties in organic materials. In this study, we consider a Su-Schrieffer-Heeger (SSH) model for molecular crystals, and perform numerical benchmark studies for different strategies of simulating the mixed quantum-classical dynamics. These methods, which differ in the selection of initial conditions and the representation used to solve the time evolution of the quantum carriers, are shown to yield similar equilibrium diffusion properties. A hybrid approach combining molecular dynamics simulations of nuclear motion and quantum-chemical calculations of the electronic Hamiltonian at each geometric configuration appears as an attractive strategy to model charge dynamics in large size systems "on the fly," yet it relies on the assumption that the quantum carriers do not impact the nuclear dynamics. We find that such an approximation systematically results in overestimated charge-carrier mobilities, with the associated error being negligible when the room-temperature mobility exceeds ?4.8 cm(2)?Vs (?0.14 cm(2)/Vs) in one-dimensional (two-dimensional) crystals. PMID:21721621

Wang, Linjun; Beljonne, David; Chen, Liping; Shi, Qiang

2011-06-28

331

Acoustic charge transport in GaN nanowires  

NASA Astrophysics Data System (ADS)

We present acoustic charge transport in GaN nanowires (GaN NWs). The GaN NWs were grown by molecular beam epitaxy (MBE) on silicon(111) substrates. The nanowires were removed from the silicon substrate, aligned using surface acoustic waves (SAWs) on the piezoelectric substrate LiNbO3 and finally contacted by electron beam lithography. Then, a SAW was used to create an acoustoelectric current in the GaN NWs which was detected as a function of radio-frequency (RF) wave frequency and its power. The presented method and our experimental findings open up a route towards new acoustic charge transport nanostructure devices in a wide bandgap material such as GaN.

Ebbecke, J.; Maisch, S.; Wixforth, A.; Calarco, R.; Meijers, R.; Marso, M.; Lüth, H.

2008-07-01

332

Reduction and transition in thermal activation for charge transport through electrolyte-gated polythiophene thin films with high hole densities  

NASA Astrophysics Data System (ADS)

We investigate the activation energy for electrical charge transport through a polythiophene thin film. The results are particularly obtained under high hole density (5.9 × 1020 holes/cm3) through electrolyte-gating and are compared with previous results attained from the same polymer film but with low induced carrier densities. Comparative analyses show that introducing high hole densities into the polymer results in (i) suppression of the transport activation energy and (ii) reduction of the temperature that yields transition in the activation energy. These results are explained based on the formation of bipolaron states, which are generated at such high hole densities.

Lee, Jiyoul; Cho, Boeun; Won Chung, Jong; Sung Kang, Moon

2013-10-01

333

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

334

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

Code of Federal Regulations, 2011 CFR

...utilize methods of transportation other than common carrier (e.g., POVs, chartered vehicles, etc.)? 301-72.2...utilize methods of transportation other than common carrier (e.g., POVs, chartered vehicles, etc.)? Yes, but...

2011-07-01

335

Transport Model for Converting Charged Species in Drift Tubes  

Microsoft Academic Search

The three-dimensional transport equations of converting charged species are solved, taking into consideration the effect of the following for both primary and secondary species: different electron and\\/or ion temperatures, different initial radial distributions, an absorbing drift-tube wall, and the distinction between radial and axial diffusion coefficients. The solution bears explicit dependence on all the relevant geometries of the drift-tube assembly,

Shien-Biau Woo; John H. Whealton

1969-01-01

336

Wave-optics applications in charged-particle-beam transport  

Microsoft Academic Search

An overview of electron wave-optics applications to charged-particle-beam transport is presented in the context of the thermal\\u000a wave model (TWM). The quantization of the electron optics is presented both in the configuration space and in the phase space.\\u000a The former provides a description in terms of the Schrödinger-like equation for a complex function whose squared modulus is\\u000a proportional to the

R. Fedele; M. A. Man'ko; V. I. Man'ko

2000-01-01

337

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

NASA Astrophysics Data System (ADS)

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

Huang, Qiuping; Li, Bincheng

2011-01-01

338

The solute carrier family SLC10: more than a family of bile acid transporters regarding function and phylogenetic relationships  

Microsoft Academic Search

The solute carrier family 10 (SLC10) comprises two sodium-dependent bile acid transporters, i.e. the Na+\\/taurocholate cotransporting polypeptide (NTCP; SLC10A1) and the apical sodium-dependent bile acid transporter (ASBT; SLC10A2). These carriers are essentially involved in the maintenance of the enterohepatic circulation of bile acids mediating the first step of active bile acid transport through the membrane barriers in the liver (NTCP)

J. Geyer; T. Wilke; E. Petzinger

2006-01-01

339

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

340

Charge transport in columnar arrays of self-organizing molecular dendrons  

NASA Astrophysics Data System (ADS)

We report a universal design strategy in which functional fluorinated tapered dendrons are programmed to self-assemble into supramolecular nanocylinders containing pi-electron stacks of high carrier mobility donors (D), acceptors (A) or D-A complexes in the core. The resulting helical columnar structure suggests that supramolecular order and electronic function can be independently manipulated for facile functional design. The cylinders form columnar liquid crystal phases that can be aligned into large domain structures both parallel and perpendicular to a conducting substrate. We report on measurements of time-of-flight charge carrier mobility, and discuss the temperature and electric field-independent high hole mobility of 1-3.5 X 10-3cm^2/Vs of fluorinated tapered first generation dendrons that contain pyrene and naphthalene groups in their core. The anomalous temperature behavior of the mobility is consistent with polaron transport mechanisms. Studies of time-of-flight transients, which reveal evidence for dynamic defects with lifetimes in the range of 10-6 s, are presented as aspects of charge generation and recombination kinetics. We also describe how these materials can be formed into mechanically robust phases such as fine polymer fibers and ribbons, as well as room-temperature glasses.

Singer, Kenneth; Shiyanovskaya, Irina; Percec, Virgil; Glodde, Martin

2003-03-01

341

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.

Wohlrab, Hartmut

2010-01-01

342

Space-Charge Transport Limits in Periodic Channels  

SciTech Connect

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

Lund, S M; Chawla, S R

2005-05-16

343

Influence of gas molecules on the charge carrier mobility in thin films of semiconducting perylene tetracarboxylic imides  

NASA Astrophysics Data System (ADS)

Thin films (30 nm) of crystalline N,N'-dimethylperylene-3,4,9,10-biscarboximide (MePTCDI) or amorphous 1,6,7,12-tetrachloro-N,N'-dimethylperylene-3,4,9,10-biscarboximide (Cl4MePTCDI) were prepared by physical vapor deposition and characterized by conductivity and field effect measurements at pristine films and under increasing partial pressure of oxygen, ethanol, acetone, or n-butane. Changes in the conductivity of the films were observed. Field effect measurements served to differentiate between changes in the charge carrier mobility ? and changes of the charge carrier concentration n. ? was found to decrease significantly, whereas rather small changes were found in n. Gas molecules that diffused into the films changed ? at least ten times more efficiently than those molecules just adsorbed on the surface.

Graaf, Harald; Schlettwein, Derck

2006-12-01

344

Classical two-dimensional numerical algorithm for ?-Induced charge carrier advection-diffusion in Medipix-3 silicon pixel detectors  

NASA Astrophysics Data System (ADS)

A classical hybrid alternating-direction implicit difference scheme is used to simulate two-dimensional charge carrier advection-diffusion induced by alpha particles incident upon silicon pixel detectors at room temperature in vacuum. A mapping between the results of the simulation and a projection of the cluster size for each incident alpha is constructed. The error between the simulation and the experimental data diminishes with the increase in the applied voltage for the pixels in the central region of the cluster. Simulated peripheral pixel TOT values do not match the data for any value of applied voltage, suggesting possible modifications to the current algorithm from first principles. Coulomb repulsion between charge carriers is built into the algorithm using the Barnes-Hut tree algorithm. The plasma effect arising from the initial presence of holes in the silicon is incorporated into the simulation. The error between the simulation and the data helps identify physics not accounted for in standard literature simulation techniques.

Biamonte, Mason; Idarraga, John

2013-04-01

345

Dependence of the conductivity on the concentration and the hopping frequency of charge carriers in fluoride glasses  

Microsoft Academic Search

The conductivity spectra of fluoride glasses in the system ZrF4-BaF2-YF2-LiF with varying LiF content has been reported at different temperatures in the frequency range 10 Hz-2 MHz. The experimental data have been analyzed in the framework of the Almond-West formalism. The concentration and hopping frequency of the charge carriers, the dc conductivity, and the activation energy have been determined from

M. Sural; A. Ghosh

2000-01-01

346

IR absorption by free charge carriers with the participation of optical phonons in structures with quantum wells  

Microsoft Academic Search

The absorption of light by free charge carriers with the participation of surface and bulk optical phonons is considered in\\u000a terms of the Boltzmann statistics and Pekar-Frhlich Hamiltonian for the electron-photon interaction in a polar semiconductor\\u000a layer within the framework of the model of a rectangular quantum well. It is found that the contributions of the surface and\\u000a bulk modes

S. I. Beril; S. M. Sokovnich; A. S. Starchuk

2005-01-01

347

Characterization of thermal, optical and carrier transport properties of porous silicon using the photoacoustic technique  

Microsoft Academic Search

In this work, the porous silicon layer was prepared by the electrochemical anodization etching process on n-type and p-type silicon wafers. The formation of the porous layer has been identified by photoluminescence and SEM measurements. The optical absorption, energy gap, carrier transport and thermal properties of n-type and p-type porous silicon layers were investigated by analyzing the experimental data from

Chan Kok Sheng; W. Mahmood Mat Yunus; Zainal Abidin Talib; Anuar Kassim

2008-01-01

348

Global seamless network demonstrator: carrier grade automatic switched transport network implementation in realistic telecom field environment  

Microsoft Academic Search

The Global Seamless Network (GSN) Demonstrator is presented, a joint effort of system vendors and Deutsche Telekom Group R&D to demonstrate network functions and management integration and enable, for the first time, experiences with a carrier grade Automatically Switched Transport Network (ASTN) implementation and the envisaged main ASTN clients, IP and Ethernet. For end-to-end monitoring capability, integrating the view on

Hans-Martin Foisel; Norbert Hanik; Ralf-Peter Braun; Georg Lehr; Andreas Gladisch

2004-01-01

349

Timber transported to Antarctica: a potential and undesirable carrier for alien fungi and insects  

Microsoft Academic Search

Antarctica’s severe climate and its geographical isolation are the factors that hinder the arrival of non-native species by\\u000a natural means. However, the movement of people and cargo associated with national scientific programs and tourism render Antarctica\\u000a much more accessible to exotic organisms. Both the transport routes and carriers are varied. The wide range of uses to which\\u000a timber is put

Piotr Osyczka; Piotr Mleczko; Dariusz Karasi?ski; Andrzej Chlebicki

350

Selective Disruption of Nuclear Import by a Functional Mutant Nuclear Transport Carrier  

Microsoft Academic Search

p10\\/NTF2 is a nuclear transport carrier that mediates the uptake of cytoplasmic RanGDP into the nucleus. We constructed a point mutant of p10, D23A, that exhibited unexpected behavior both in digitonin- permeabilized and microinjected mammalian cells. D23A p10 was markedly more efficient than wild-type (wt) p10 at supporting Ran import, but simultaneously acted as a dominant-negative inhibitor of classical nu-

Ian Cushman; Mary Shannon Moore

2000-01-01

351

Transcellular Transport of Benzole Acid Across Caco-2 Cells by a pH-Dependent and Carrier-Mediated Transport Mechanism  

Microsoft Academic Search

The pH-dependent transcellular transport of [14 C]benzoic acid across a Caco-2 cell monolayer is shown to be mediated by a monocarboxylic acid-specific carrier-mediated transport system, localized on the apical membrane. Evidence for the carrier-mediated transport of benzoic acid includes (a) the significant temperature and concentration dependence, (b) the metabolic energy dependence, (c) the inhibition by unlabeled benzoic acid and other

Akira Tsuji; Hitomi Takanaga; Ikumi Tamai; Tetsuya Terasaki

1994-01-01

352

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

353

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

354

Analysis of free carrier absorption measurement of electronic transport properties of silicon wafers  

NASA Astrophysics Data System (ADS)

Sensitivity analysis of electronic transport property measurement of silicon wafers with modulated free carrier absorption (MFCA) technique and multi-parameter fitting procedure is performed. The sensitivity of the multi-parameter estimate employing the dependences of the MFCA amplitude and phase on the pump-probe-beam separation measured at several modulation frequencies covering an appropriate range is theoretically compared with that employing only the dependences of the MFCA amplitude and phase on the modulation frequency. Simulation results show that the dependences of the MFCA amplitude and phase on the pump-probe beam separation are more sensitive to the electronic transport properties of silicon wafers than the frequency dependences. The electronic transport properties of the silicon wafers determined with the two-beam separation dependence are therefore more accurate than that determined with the frequency dependence. Comparative experiments with a silicon wafer are performed and the carrier lifetime, the carrier diffusivity, and the front surface recombination velocity are determined simultaneously and unambiguously with both techniques.

Zhang, X.; Li, B.; Gao, C.

2008-01-01

355

Photoluminescence dynamics due to exciton and free carrier transport in GaAs/AlAs superlattices  

NASA Astrophysics Data System (ADS)

Photogenerated carrier transfer is investigated in a set of three GaAs/AlAs short-period superlattices (SPSs) with different barrier thicknesses by steady-state and time-resolved photoluminescence (PL) spectroscopy at 15-20 K as a function of excitation power. The tunneling transport of carriers is evaluated by detecting excitonic PL signals from an embedded GaAs single quantum well (SQW) in the middle of the SPS layer. We find that, as the barrier thickness is decreased, the PL intensity ratio of SQW/SPS increases systematically due to enhanced tunneling efficiencies of both electrons and holes. However, the PL intensity ratio significantly increases with decreases in the excitation power by more than two orders of the magnitude. We attribute the enhanced PL intensity of SQW relative to the SPS to the faster transport of electrons that can recombine with residual holes to form excitons in SQW. The PL dynamics of SQW and SPS thus shows unique density-dependent PL intensity and time behaviors due to variations in relative amounts of excitons and free carriers to be transported into the SQW layer.

Kido, R.; Satake, A.; Fujiwara, K.

2010-09-01

356

Comparative study of hole transport in polyspirobifluorene polymers measured by the charge-generation layer time-of-flight technique  

NASA Astrophysics Data System (ADS)

Hole transport in a polyspirobifluorene homopolymer and a statistical polyspirobifluorene-triarylamine copolymer has been studied in detail employing the charge-generation layer time-of-flight (TOF) technique over a wide range of electric fields and temperatures. Both materials exhibit nondispersive TOF signals after injection of a sheet of charge carriers from a thin (10 nm) perylene-diimide charge-carrier generation layer into a relatively thick (d>1 ?m) polymer film. Results were analyzed within the framework of the Gaussian disorder model and the charge transport parameters were extracted for both polymers. The zero-field hole mobility of the spirohomopolymer was found to be on the order of 10-6 cm2/V s, whereas the copolymer showed a considerably lower hole mobility of 6×10-8 cm2/V s. The width of the density of states ? was determined to be 86 meV for the homopolymer and 107 meV for the copolymer. The latter polymer also showed an increased positional disorder due to the statistically incorporated triarylamine units.

Laquai, Frédéric; Wegner, Gerhard; Im, Chan; Bässler, Heinz; Heun, Susanne

2006-01-01

357

Carrier transport and bandgap shift in n-type degenerate ZnO thin films: The effect of band edge nonparabolicity  

NASA Astrophysics Data System (ADS)

Contribution of band edge nonparabolicity to the charge carrier transport in degenerate n-type zinc oxide thin films has been investigated theoretically in order to understand the fundamental aspects of electron scattering in such thin films regardless of precise details of the preparation procedure. To conduct this, the theoretical evaluated results have been compared to the experimental values taken from literatures. The results indicate that the nonparabolicity (introducing through effective mass of charge carriers) has a strong effect on the total mobility of carriers in zinc oxide films so that a satisfactory agreement with experimental data is fulfilled. The dependence of nonparabolicity on bandgap shift is also discussed. Studying the optoelectronic properties of numerous moderately and heavily doped samples revealed that their optical bandgap has lower blueshift than the theoretical value obtained from the well-known Burstein-Moss effect. So, the observed bandgap shift was dependent on the carrier concentration and the total shift of bandgap was evaluated by combining the Burstein-Moss and bandgap narrowing effects. Two different cases were also examined; parabolic and nonparabolic (modified) Burstein-Moss effects. The results show that the modified Burstein-Moss effect leads to great agreement with experimental data.

Abdolahzadeh Ziabari, A.; Rozati, S. M.

2012-12-01

358

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

PubMed

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

Naftalin, Richard J

2008-07-25

359

Charge Transport in Azobenzene-Based Single-Molecule Junctions  

NASA Astrophysics Data System (ADS)

The azobenzene class of molecules has become an archetype of molecular photoswitch research, due to their simple structure and the significant difference of the electronic system between their cis and trans isomers. However, a detailed understanding of the charge transport for the two isomers, when embedded in a junction with electrodes is still lacking. In order to clarify this issue, we investigate charge transport properties through single Azobenzene-ThioMethyl (AzoTM) molecules in a mechanically controlled break junction (MCBJ) system at 4.2 K. Single-molecule conductance, I-V characteristics, and IETS spectra of molecular junctions are measured and compared with first-principles transport calculations. Our studies elucidate the origin of a slightly higher conductance of junctions with cis isomer and demonstrate that IETS spectra of cis and trans forms show distinct vibrational fingerprints that can be used for identifying the isomer.[1] 1. Y. Kim, A. Garcia-Lekue, D. Sysoiev, T. Frederiksen, U. Groth, E. Scheer, Phys. Rev. Lett. (accepted).

Garcia-Lekue, Aran; Kim, Youngsang; Sysoiev, Dmytro; Frederiksen, Thomas; Groth, Ulrich; Scheer, Elke

2013-03-01

360

Transport of cadmium ions from zinc plant leach solutions through emulsion liquid membrane-containing Aliquat 336 as carrier  

Microsoft Academic Search

The zinc plant purification cake (CINKUR Co., Turkiye) was leached with sulphuric acid. The transport of cadmium from this leach solution-containing zinc, iron, copper, aluminum, cadmium, nickel and cobalt through emulsion liquid membrane (ELM) using amine extractant dissolved in kerosene as a mobile carrier was studied. The ELM consists of Aliquat 336 as a carrier, Span 80 as a surfactant,

Recep Ali Kumbasar

2008-01-01

361

Monte Carlo simulation of charged particle transport in biomatter.  

PubMed

Knowledge of the microscopic distribution of interactions in irradiated matter is of fundamental importance for a mechanistic understanding of subsequent effects. This may be obtained by Monte Carlo codes which simulate event-by-event the transport of charged particles in matter. The development of such codes necessitates accurate interaction cross-sections for all the important collision processes. A semi-theoretical formalism has been developed and implemented in a Monte Carlo code which fairly accurately predicts energy-loss spectra for charged particle impact on water molecules. The extension of the formalism for establishing the necessary cross-sections for liquid/solid water (i.e. more realistic biomatter) is discussed and preliminary results are presented. PMID:11770524

Emfietzoglou, D; Papamichael, G; Moscovitch, M

2001-01-01

362

Charge and energy transport in one-dimensional nanomaterials  

NASA Astrophysics Data System (ADS)

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

Blaustein, Gail S.

363

Selective contacts drive charge extraction in quantum dot solids via asymmetry in carrier transfer kinetics  

NASA Astrophysics Data System (ADS)

Colloidal quantum dot solar cells achieve spectrally selective optical absorption in a thin layer of solution-processed, size-effect tuned, nanoparticles. The best devices built to date have relied heavily on drift-based transport due to the action of an electric field in a depletion region that extends throughout the thickness of the quantum dot layer. Here we study for the first time the behaviour of the best-performing class of colloidal quantum dot films in the absence of an electric field, by screening using an electrolyte. We find that the action of selective contacts on photovoltage sign and amplitude can be retained, implying that the contacts operate by kinetic preferences of charge transfer for either electrons or holes. We develop a theoretical model to explain these experimental findings. The work is the first to present a switch in the photovoltage in colloidal quantum dot solar cells by purposefully formed selective contacts, opening the way to new strategies in the engineering of colloidal quantum dot solar cells.

Mora-Sero, Ivan; Bertoluzzi, Luca; Gonzalez-Pedro, Victoria; Gimenez, Sixto; Fabregat-Santiago, Francisco; Kemp, Kyle W.; Sargent, Edward H.; Bisquert, Juan

2013-08-01

364

Charge and spin transport through a ferromagnet/insulator/unconventional superconductor junction  

NASA Astrophysics Data System (ADS)

We analyze the charge and spin transport through a ballistic ferromagnet/insulator/superconductor junction by means of the Bogoliubov-de Gennes equations. For the ferromagnetic side we assume that ferromagnetism may be driven by an unequal mass renormalization of oppositely polarized carriers, i.e., a spin bandwidth asymmetry, and/or by a rigid splitting of up- and down-spin electron bands, as in a standard Stoner ferromagnet, whereas the superconducting side is assumed to exhibit a d-wave symmetry of the order parameter, which can be pure or accompanied by a minority component breaking time-reversal symmetry. Several remarkable features in the charge conductance arise in this kind of junction, providing useful information about the mechanism of ferromagnetism in the ferromagnetic electrode, as well as of the order-parameter symmetry in the superconducting one. In particular, we show that when a time-reversal symmetry-breaking superconductor is considered, the use of the two kinds of ferromagnet mentioned above represents a valuable tool to discriminate between the different superconducting mixed states. We also explain how this junction may mimic a switch able to turn on and off a spin current, leaving the charge conductance unchanged, and we show that for a wide range of insulating barrier strengths, a spin-bandwidth asymmetry ferromagnet may support a spin current larger than a standard Stoner one.

Annunziata, Gaetano; Cuoco, Mario; Gentile, Paola; Romano, Alfonso; Noce, Canio

2011-03-01

365

Charge transport in pn and npn junctions of silicene  

NASA Astrophysics Data System (ADS)

We investigate charge transport of pn and npn junctions made from silicene, a Si analogue of graphene. The conductance shows the distinct gate-voltage dependencies peculiar to the topological and nontopological phases, where the topological phase transition is caused by external electric field. Namely, the conductance is (not) suppressed in the np (nn) regime when both sides are topological, and in the nn (np) regime when one side is topological and the other side is nontopological. Furthermore, we find that the conductance is almost quantized to be 0, 1, and 2. Our findings will open a new way to nanoelectronics based on silicene.

Yamakage, Ai; Ezawa, Motohiko; Tanaka, Yukio; Nagaosa, Naoto

2013-08-01

366

Phase Coherent Charge Transport in Graphene Quantum Billiards  

NASA Astrophysics Data System (ADS)

As an emergent model system for condensed matter physics and a promising electronic material, graphene's electrical transport properties has become a subject of intense focus. Via low temperature transport spectroscopy on single and bi-layer graphene devices, we show that the minimum conductivity value is geometry dependent and approaches the theoretical value of 4e^2/?h only for wide and short graphene strips. Moreover, we observe periodic conductance oscillations with bias and gate voltages, arising from quantum interference of multiply-reflected waves of charges in graphene. When graphene is coupled to superconducting electrodes, we observe gate tunable supercurrent and sub-gap structures, which originate from multiple Andreev reflection at the graphene-superconductor interfaces. Our results demonstrate that graphene can act as a quantum billiard with a long phase coherence length. This work was supported in part by DOD/DMEA-H94003-06-2-0608.

Lau, Chun Ning

2008-03-01

367

Parameters of the Constant-Energy Surface and Features of Charge Carrier Scattering of Bi2Te3-Based Epitaxial Films  

NASA Astrophysics Data System (ADS)

Galvanomagnetic properties of epitaxial Bi0.5Sb1.5Te3 films grown by the hot-wall technique were investigated in magnetic fields of H = 5 T to 14 T through the temperature interval of 10 K to 300 K. The results were analyzed in terms of a many-valley model of the energy spectrum and anisotropic charge carrier scattering. The degeneracy parameter ? d, and ratios of components of the reciprocal effective-mass tensor {leftrightarrow}over ?} and relaxation time tensor {{leftrightarrow}over ? } (\\varepsilon ) were estimated. Substantial anisotropy of charge carrier scattering was observed in the investigated temperature interval. Anisotropy of charge carrier scattering along bisector axes is enhanced, as compared with that of corresponding bulk samples. High charge carrier mobility and higher angular factor of the temperature dependence of mobility promote enhancement of the figure of merit Z of the films as compared with that of corresponding bulk solid solutions.

Lukyanova, L. N.; Boikov, Yu. A.; Danilov, V. A.; Volkov, M. P.; Kutasov, V. A.

2013-07-01

368

Influence of humidity on the electrostatic charge and aerosol performance of dry powder inhaler carrier based systems.  

PubMed

To investigate the influence of storage relative humidity (RH) on the aerosolisation efficiency and tribo-electrification of carrier based dry powder inhaler (DPI) formulations using the next generation impactor (NGI) in vitro methodology and the electrostatic low pressure impactor (ELPI). Micronised salbutamol (d (0.5) 1.48 +/- 0.03 microm) was blended with 63-90 microm sieve fractioned alpha-lactose monohydrate carrier and stored at a range of humidities (0-84% RH). The aerosolisation efficiency after storage for 24 h periods was investigated using the NGI. The same experiment was conducted using the ELPI, with corona charger switched off, to measure the net charge vs. mass deposition profile. Significant variations in the aerosolisation efficiency of the formulation were observed with respect to storage RH. In general, the fine particle fraction aerosol performance measured by NGI and ELPI (fraction with mass median aerodynamic diameter <4.46 and 4.04 microm, respectively) followed a positive parabola with aerosol performance increasing over the range 0-60% RH before decreasing >60% RH. Analysis of the ELPI charge data suggested that the micronised salbutamol sulphate had an electronegative charge when aerosolised from lactose based carriers, which was most electronegative at low RH. Increased storage RH resulted in a reduction in net charge to mass ratio with the greatest reduction at RH >60%. The aerosol performance of this binary system is dependent on both electrostatic and capillary forces. The use of the ELPI allows a degree of insight into how these forces affect formulation performances after storage at different RH. PMID:17377746

Young, Paul M; Sung, Adrian; Traini, Daniela; Kwok, Philip; Chiou, Herbert; Chan, Hak-Kim

2007-03-22

369

Modulation waves of charge carriers in n- and p-type semiconductor layers  

SciTech Connect

The effect of the carrier mobility dependence on the electric field strength, {mu}(F), on the propagation of waves of injected carriers in n- and p-type layers in the quasi-neutral drift mode has been studied. It is shown that consideration of the dependence {mu}(F) differently affects the motion of minority carriers in n- and p-type layers. The motion of an electron wave in the p-type base of a p{sup +}-p-n{sup +} structure is slowed down, and that of a hole wave in the n-base of a p{sup +}-n-n{sup +} structure is speeded up. The results obtained supplement the previously suggested classical description of the propagation of a wave of minority carriers, which disregarded the effect of {mu}(F) dependences. The results of an analytical calculation are confirmed using a numerical experiment.

Mnatsakanov, T. T. [All-Russia Electrotechnical Institute (Russian Federation); Levinshtein, M. E., E-mail: Melev@nimis.ioffe.ru [Russian Academy of Sciences, Ioffe Physical Technical Institute (Russian Federation); Tandoev, A. G.; Yurkov, S. N. [All-Russia Electrotechnical Institute (Russian Federation)

2011-02-15

370

Measurement of the drift mobilities and the mobility-lifetime products of charge carriers in a CdZnTe crystal by using a transient pulse technique  

NASA Astrophysics Data System (ADS)

In this work we present results on the measurement of the drift mobility and the mobility-lifetime product of charge carriers in a 16-pixellated CdZnTe detector. For the determination of an interaction position based on the pulse rise-time method in a CZT detector, it is necessary to characterize the transport properties governed by drift mobility and lifetime for electrons and holes. In order to extract the transport properties of an electron and a hole, we bombarded 5.5-MeV alpha particles from a 241Am source and 81-keV gamma rays emitted from a 133Ba source on the negatively biased contact of the CZT detector. A time-of-flight (TOF) method was used to measure the electron drift mobility at room temperature whose value turned out to be 906.4 cm2/V? s. With the Hecht's equation, the electron mobility-lifetime product was also determined from the bias-dependent alpha response and was equal to (9.88 ± 2.33) × 10-3 cm2/V. On the other hand, the hole mobility-lifetime product was evaluated by a model based on the average charge collection efficiency which accounts for the absorption probability with a given photon energy. By using a single parameter fitting of the model, we obtained the hole mobility-lifetime product of (8.28 ± 0.17) × 10-4 cm2/V.

Cho, H. Y.; Lee, J. H.; Kwon, Y. K.; Moon, J. Y.; Lee, C. S.

2011-01-01

371

Point-contact Andreev-reflection spectroscopy of doped manganites: Charge carrier spin-polarization and proximity effects (Review Article)  

NASA Astrophysics Data System (ADS)

Materials with spin-polarized charge carriers are the most demanded in the spin-electronics. Particularly requested are the so-called half-metals which have the maximum attainable value of carrier spin polarization. Doped manganites are in the list of compounds with, potentially, half-metallic properties. The point-contact (PC) Andreev-reflection (AR) spectroscopy is a robust and direct method to measure the degree of current spin polarization. In this report, advances in PCAR spectroscopy of ferromagnetic manganites are reviewed. The experimental results obtained on ``classic'' s-wave superconductor--ferromagnetic manganites PCs, as well as related theoretical models applied to deduce the actual value of charge carrier spin-polarization, are discussed. Data obtained on ``proximity affected'' contacts is also outlined. Systematic and repeatable nature of a number of principal experimental facts detected in the AR spectrum of proximity affected contacts suggests that some new physical phenomena have been documented here. Different models of current flow through a superconductor-half-metal ferromagnet interface, as well as possibility of unconventional superconducting proximity effect, have been discussed.

Krivoruchko, V. N.; D'yachenko, A. I.; Tarenkov, V. Yu.

2013-03-01

372

Trapping of charge carriers in colloidal particles of self-assembled films from TiO(2) and poly(vinyl sulfonic acid).  

PubMed

Self-assembled electrodes consisting of TiO(2) nanoparticles and poly(vinyl sulfonic acid) (PVS) were prepared by the layer-by-layer (LbL) technique. The electrostatic interaction between the TiO(2) nanoparticles and PVS allowed the growth of visually uniform multilayers of the composite, with high control of the thickness and nanoarchitecture. The electrochemical and chromogenic properties of these TiO(2)/PVS films were examined in an electrolytic solution of 0.5 M LiClO(4)/propylene carbonate. The presence of two intercalation sites was noted during the positive potential scan, and they were attributed to different mobilities of charge carriers. Several charge/discharge cycles demonstrated the trapping of charge carriers in the TiO(2) sites. The absorbance change associated with the oxidation of the trapping sites was attributed to electronic transitions involving energy states in the gap band formed due to the strong distortion of the TiO(2) host. Using the quadratic logistic equation (QLE), it was possible to analyze the electronic intervalence transfer from Ti(3+) to Ti(4+). Using the parameters obtained from this fitting, the amount of trapping sites in the LbL film was also determined. Electrochemical impedance spectroscopy (EIS) data gave the time constant associated with diffusion and the trapping sites. The diffusion coefficient of lithium ions changed from ca. 4.5 x 10(-13) cm(2) s(-1) to 3.0 x 10(-14) cm(2) s(-1) for all the potential range applied, indicating that PVS did not hinder the ionic transport within the LbL film. Finally, on the basis of the spectroelectrochemical data and scanning electron micrographs, the trapping effects were attributed to the colloidal particles of Li(0.55)TiO(2). PMID:17134222

Galiote, Nelson A; Carvalho, Antonio J F; Huguenin, Fritz

2006-12-01

373

Quantum charge transport and conformational dynamics of macromolecules.  

PubMed

We study the dynamics of quantum excitations inside macromolecules which can undergo conformational transitions. In the first part of the paper, we use the path integral formalism to rigorously derive a set of coupled equations of motion which simultaneously describe the molecular and quantum transport dynamics, and obey the fluctuation/dissipation relationship. We also introduce an algorithm which yields the most probable molecular and quantum transport pathways in rare, thermally activated reactions. In the second part of the paper, we apply this formalism to simulate the propagation of a quantum charge during the collapse of a polymer from an initial stretched conformation to a final globular state. We find that the charge dynamics is quenched when the chain reaches a molten globule state. Using random matrix theory we show that this transition is due to an increase of quantum localization driven by dynamical disorder. We argue that collapsing conducting polymers may represent a physical realization of quantum small-world networks with dynamical rewiring probability. PMID:22697534

Boninsegna, L; Faccioli, P

2012-06-01

374

Effects of cytosine methylation on DNA charge transport  

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

375

Electron transport and electroluminescence in polymer layers  

Microsoft Academic Search

We shell discuss the transport of charge carriers (electron and holes) in disordered polymeric dielectric matrices and electroluminescence phenomena in transport layers of various structures, and also the injection of charges into transport layers through a boundary bearing a solid layer of a different type. The temperature, field, and concentration dependences of the mobility of the carriers will be considered,

Anatolii V. Vannikov; Antonina D. Grishina; S. V. Novikov

1994-01-01

376

Parity Effects and Charge Transport in the Single - Transistor  

NASA Astrophysics Data System (ADS)

We report the results of an experimental study of the single-electron transistor, a device in which a small metal island is weakly coupled to two bias leads through low-capacitance tunnel junctions, and capacitively coupled to a gate electrode. The capacitance of the island to the external circuit is so small that single-electron charging effects dominate the behavior of this device. We demonstrate that if the island is a superconductor, its behavior depends strongly on whether it contains an even or an odd number of electrons, even when this number is as large as 10^9. This rather remarkable behavior results from electron pairing in the superconductor, and we refer to it as a parity effect. We develop an equilibrium model to describe this parity effect and show that it correctly predicts the temperature at which the effect disappears as a function of the applied magnetic field. We have conducted a detailed study of charge transport in the normal-superconductor-normal (NSN) single-electron transistor system in which the superconducting island is coupled to normal-metal leads. We demonstrate that at low bias voltages in this system, single-electron tunneling is suppressed and charge is primarily transported by Andreev reflection (two-electron tunneling). The experimental data clearly show the Coulomb blockade of Andreev reflection as well as the effects of quasiparticle "trapping" on the superconducting island. The data also exhibit striking voltage thresholds that correspond to specific one- and two-electron tunneling processes. By analyzing the energetics of various tunneling events, we show that the positions of these thresholds agree quantitatively with theory. When the single-electron transistor with a superconducting island is exposed to small amounts of cryogenic blackbody radiation, charge transport is modified dramatically and new peaks appear in the current versus gate voltage characteristic. We demonstrate that these new experimental features are in excellent quantitative agreement with simulations that include photon-assisted tunneling. Under suitable bias conditions, this device behaves as a photon-activated switch. The absorption of a single microwave photon switches the device from a low- to a high-current state, and more than 100 electrons can tunnel through the system for every absorbed photon. This provides a possible new and very sensitive mechanism for microwave detection.

Hergenrother, John Michael

1995-01-01

377

Identification of a third secondary carrier (DcuC) for anaerobic C4-dicarboxylate transport in Escherichia coli: roles of the three Dcu carriers in uptake and exchange.  

PubMed Central

In Escherichia coli, two carriers (DcuA and DcuB) for the transport of C4 dicarboxylates in anaerobic growth were known. Here a novel gene dcuC was identified encoding a secondary carrier (DcuC) for C4 dicarboxylates which is functional in anaerobic growth. The dcuC gene is located at min 14.1 of the E. coli map in the counterclockwise orientation. The dcuC gene combines two open reading frames found in other strains of E. coli K-12. The gene product (DcuC) is responsible for the transport of C4 dicarboxylates in DcuA-DcuB-deficient cells. The triple mutant (dcuA dcuB dcuC) is completely devoid of C4-dicarboxylate transport (exchange and uptake) during anaerobic growth, and the bacteria are no longer capable of growth by fumarate respiration. DcuC, however, is not required for C4-dicarboxylate uptake in aerobic growth. The dcuC gene encodes a putative protein of 461 amino acid residues with properties typical for secondary procaryotic carriers. DcuC shows sequence similarity to the two major anaerobic C4-dicarboxylate carriers DcuA and DcuB. Mutants producing only DcuA, DcuB, or DcuC were prepared. In the mutants, DcuA, DcuB, and DcuC were each able to operate in the exchange and uptake mode.

Zientz, E; Six, S; Unden, G

1996-01-01

378

Electrodeless time-resolved microwave conductivity study of charge-carrier photogeneration in regioregular poly(3-hexylthiophene) thin films  

NASA Astrophysics Data System (ADS)

The electrodeless flash-photolysis time-resolved microwave conductivity technique ( FP-TRMC ) has been used to study the photogeneration of charge carriers in spin-coated films of regioregular poly(3-hexylthiophene) (P3HT) , over the photon energy range from 1.9 to 5.2eV for incident light intensities from 1013 to 1016 photons/cm2 per (3ns) pulse. The initial, single-photon quantum yield of photoionization, ? , has been estimated from the low-intensity limit to the photoconductivity based on a charge carrier mobility of 0.014cm2/Vs (determined in separate pulse-radiolysis TRMC experiments on bulk P3HT ). The value of ? is constant at (1.7±0.4)% within the range 1.9-3.0eV , which encompasses the first electronic absorption band of P3HT . Above 3.0eV , ? increases, up to a value of (7±2)% at 5.2eV . The activation energy of the photoconductivity was found to be approximately 50meV at all photon energies. The high-intensity, sublinear dependence of the photoconductivity can be described by the occurrence of either exciton-exciton annihilation or diffusional charge recombination with rate coefficients of 2.3×10-8cm3/s and 1.1×10-8cm3/s .

Dicker, Gerald; de Haas, Matthijs P.; Siebbeles, Laurens D. A.; Warman, John M.

2004-07-01

379

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

380

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

PubMed

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

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

381

Study of charge transport mechanisms in ZnO-ZnTe nanojunctions  

NASA Astrophysics Data System (ADS)

Improved carrier transport is crucial for enhancing the performance of semiconductor devices such as radiation detectors. Conventionally, semiconductor devices employ planar p-n junctions in which carrier loss occurs mostly in the p-type and n-type diffusion regions. In a nanoscale three-dimensional (3-D) junction, the carriers can be efficiently collected cross the nanostructure by electric field distribution without trapping in the p-n regions. In addition, a nanocone junction should further improve carrier transport properties because this structure can be tailored to be completely depleted. In this work, we studied carrier transport mechanisms in nanojunctions made of vertically aligned ZnO nanostructures and ZnTe matrix using theoretical and experimental methods.

Xu, Jun; Lee, Sang Hyun; Bell, Zane W.; Smith, Barton; Zhang, X.-G.; Ju, Tong; Chen, An-Jen; Pan, Zhengwei

2010-08-01

382

Study of Charge Transport Mechanisms in ZnO-ZnTe Nanojunctions  

SciTech Connect

Improved carrier transport is crucial for enhancing the performance of semiconductor devices such as radiation detectors. Conventionally, semiconductor devices employ planar p-n junctions in which carrier loss occurs mostly in the p-type and n-type diffusion regions. In a nanoscale three-dimensional (3-D) junction, the carriers can be efficiently collected cross the nanostructure by electric field distribution without trapping in the p-n regions. In addition, a nanocone junction should further improve carrier transport properties because this structure can be tailored to be completely depleted. In this work, we studied carrier transport mechanisms in nanojunctions made of vertically aligned ZnO nanostructures and ZnTe matrix using theoretical and experimental methods.

Xu, Jun [ORNL; Lee, Sang Hyun [ORNL; Bell, Zane W [ORNL; Smith, Barton [ORNL; Zhang, Xiaoguang [ORNL; Ju, Tong [ORNL; Pan, Zhengwei [University of Georgia, Athens, GA

2010-01-01

383

Study of charge transport mechanisms in ZnO-ZnTe nanojunctions  

Microsoft Academic Search

Improved carrier transport is crucial for enhancing the performance of semiconductor devices such as radiation detectors. Conventionally, semiconductor devices employ planar p-n junctions in which carrier loss occurs mostly in the p-type and n-type diffusion regions. In a nanoscale three-dimensional (3-D) junction, the carriers can be efficiently collected cross the nanostructure by electric field distribution without trapping in the p-n

Jun Xu; Sang Hyun Lee; Zane W. Bell; Barton Smith; Xiaoguang Zhang; Tong Ju; An-Jen Chen; Zhengwei Pan

2010-01-01

384

Faster lactate transport across red blood cell membrane in sickle cell trait carriers.  

PubMed

The physical and physiological behavior of sickle cell trait carriers (AS) is somewhat equivocal under strenuous conditions, although this genetic abnormality is generally considered to be a benign disorder. The occurrence of incidents and severe injuries in AS during exercise might be explained, in part, by the lactic acidosis due to a greater lactate influx into AS red blood cells (RBCs). In the present study, the RBC lactate transport activity via the different pathways was compared between AS and individuals with normal hemoglobin (AA). Sixteen Caribbean students, nine AS and seven AA, performed a progressive and maximal exercise test to determine maximal oxygen consumption. Blood samples were obtained at rest to assess haematological parameters and RBC lactate transport activity. Lactate influxes [total lactate influx and monocarboxylate transporter (MCT-1)-mediated lactate influx] into erythrocytes were measured at four external [14C]-labeled lactate concentrations (1.6, 8.1, 41, and 81.1 mM). The two groups had similar maximal oxygen consumption. Total lactate influx and lactate influx via the MCT-1 pathway were significantly higher in AS compared with AA at 1.6, 41, and 81.1 mM. The maximal lactate transport capacity for MCT-1 was higher in AS than in AA. Although AS and AA had the same maximal aerobic physical fitness, the RBCs from the sickle cell trait carriers took up more lactate at low and high concentrations than the RBCs from AA individuals. The higher MCT-1 maximal lactate transport capacity found in AS suggests greater content or greater activity of MCT-1 in AS RBC membranes. PMID:16239612

Sara, Fagnété; Fagnété, Sara; Connes, Philippe; Philippe, Connes; Hue, Olivier; Olivier, Hue; Montout-Hedreville, Mona; Mona, Montout-Hedreville; Etienne-Julan, Maryse; Maryse, Etienne-Julan; Hardy-Dessources, Marie-Dominique; Marie-Dominique, Hardy-Dessources

2005-10-20

385

Effects of intrinsic base-pair fluctuations on charge transport in DNA  

Microsoft Academic Search

We investigate propagation of a charge carrier along intrinsically dynamically disordered double-stranded DNA. This is realized by the semiclassical coupling of the charge with a nonlinear lattice model that can accurately describe the statistical mechanics of the large amplitude fluctuations of the base pairs leading to the thermal denaturation transition of DNA. We find that the fluctuating intrinsic disorder can

S. Komineas; G. Kalosakas; A. R. Bishop

2002-01-01

386

Solution phase epitaxial self-assembly and high charge-carrier mobility nanofibers of semiconducting molecular gelators.  

PubMed

Trithienylenevinylenes having amide end functional groups form supramolecular gels in nonpolar solvents, comprised of self-assembled nanowires. These gels exhibit the unique property of solution phase epitaxy leading to the alignment of fibers on mica surface. FP-TRMC studies revealed high charge carrier mobility for xerogels from decane-chloroform whereas films obtained from chloroform solutions showed less mobility, highlighting the role of self-assembly and gelation on the electronic properties of semiconducting molecular gelators. This study opens the window for a new class of conducting gelators which may find wide application in organic electronic devices. PMID:20536178

Prasanthkumar, Seelam; Saeki, Akinori; Seki, Shu; Ajayaghosh, Ayyappanpillai

2010-07-01

387

Is There an Intrinsic Limit to the Charge-Carrier-Induced Increase of the Curie Temperature of EuO?  

NASA Astrophysics Data System (ADS)

Rare earth doping is the key strategy to increase the Curie temperature (TC) of the ferromagnetic semiconductor EuO. The interplay between doping and charge carrier density (n), and the limit of the TC increase, however, are yet to be understood. We report measurements of n and TC of Gd-doped EuO over a wide range of doping levels. The results show a direct correlation between n and TC, with both exhibiting a maximum at high doping. On average, less than 35% of the dopants act as donors, raising the question about the limit to increasing TC.

Mairoser, T.; Schmehl, A.; Melville, A.; Heeg, T.; Canella, L.; Böni, P.; Zander, W.; Schubert, J.; Shai, D. E.; Monkman, E. J.; Shen, K. M.; Schlom, D. G.; Mannhart, J.

2010-12-01

388

Charge transport in graphene field effect transistors with ferroelectric gating  

NASA Astrophysics Data System (ADS)

Recent experiments on ferroelectrically gated graphene field effect transistors (GFeFETs) open new opportunities for exploring new graphene physics and functionalities. The non-linear, hysteretic dielectric response of ferroelectrics introduces non-volatility in GFeFETs, which can be utilized for memory and data storage applications. Here, we present a comprehensive way in understanding and controlling ferroelectric gating in GFeFETs. We quantitatively characterize the hysteretic ferroelectric gating using the reference of an independent background doping (nback) provided by normal dielectric gating. More importantly, we prove that nback can be used to control the ferroelectric gating by uni-directionally shifting the hysteretic ferroelectric doping in graphene. Utilizing this electrostatic effect, we demonstrate symmetrical bit writing in graphene-ferroelectric FETs with resistance change over 500% and reproducible no-volatile switching over 10^5 cycles. In the quantum hall regime (2K and 9T), by controlling the polarization magnitude in the ferroelectric dielectric layer, we observe additional integer quantization steps besides the well-known (N+1/2)e^2/h steps. We also explore the possibility to introduce ultra-high charge carrier doping in graphene by ferroelectric gating.

Özyilmaz, Barbaros

2010-03-01

389

Three-dimensional transport imaging for the spatially resolved determination of carrier diffusion length in bulk materials.  

PubMed

A contact-free optical technique is developed to enable a spatially resolved measurement of minority carrier diffusion length and the associated mobility-lifetime (??) product in bulk semiconductor materials. A scanning electron microscope is used in combination with an internal optical microscope and imaging charge-coupled device (CCD) to image the bulk luminescence from minority carrier recombination associated with one-dimensional excess carrier generation. Using a Green's function to model steady-state minority carrier diffusion in a three-dimensional half space, non-linear least squares analysis is then applied to extract values of carrier diffusion length and surface recombination velocity. The approach enables measurement of spatial variations in the ?? product with a high degree of spatial resolution. PMID:22559534

Blaine, K E; Phillips, D J; Frenzen, C L; Scandrett, C; Haegel, N M

2012-04-01

390

Charge transport in amorphous low bandgap conjugated polymer/fullerene films  

NASA Astrophysics Data System (ADS)

The structural and charge transport properties of a low bandgap copolymer poly(3-hexylthiophene-alt-6,7-dimethyl-4,9-bis-(4-hexylthien-2yl)-[1,2,5]thiadiazolo[3,4-g]quinoxaline) (P(3HT-MeTDQ)) and its blend with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) are investigated. Thermal analysis, X-ray scattering diffraction (XRD), atomic force microscopy and transmission electron microscopy (TEM) of P(3HT-MeTDQ) reveal that the polymer is amorphous in solid state. As the hole mobility of P(3HT-MeTDQ) was measured by the time-of-flight photoconductivity method, the mobility was 3.35 × 10-4 cm2/V s, which is very comparable to that of semicrystalline poly(3-hexyl thiophene). When the mobility of amorphous P(3HT-MeTDQ) was analyzed according to the Gaussian disorder model, the polymer has the energetic and positional disorders with the values of ? = 62 meV and ? = 1.7, respectively, indicating that the polymer has a relatively narrow Gaussian distribution of transport states. Interestingly, when P(3HT-MeTDQ) is blended with PCBM, the amorphous P(3HT-MeTDQ) becomes partially ordered, as evidenced by observation of two discernible XRD peaks at 2? = 5° (d = 17.7 A?) and 25.5° (d = 3.5 A?) corresponding to the interchain distance and ?-stacking distance, respectively. The bicontinuous network morphology was identified at the blend with 60 wt. % PCBM by TEM, at which the charge carrier transport changes from hole-only to ambipolar.

Kim, Jung Yong; Cho, Hyunduck; Noh, Seunguk; Lee, Yoonkyoo; Nam, Young Min; Lee, Changhee; Jo, Won Ho

2012-02-01

391

Some properties of a new electrogenic transport system: the ammonium (methylammonium) carrier from Clostridium pasteurianum.  

PubMed

Clostridium pasteurianum is able to build up about 100-fold gradients of methylammonium across the cell membrane. Methylammonium enters the cell by means of a carrier as shown by the energy requirement, saturation kinetics and a pH profile with a narrow maximum between pH 6.2 and 6.8. The methyl ammonium transport (apparent Km = 150 microM, V = 100 mumol/min per g dry weight) is competitively inhibited by ammonium (apparent Ki = 9 microM). The low Ki value and the observation that methylammonium cannot serve as a carbon or nitrogen source for Cl. pasteurianum strongly indicate that ammonium rather than methylammonium is the natural substrate. Uncouplers and inhibitors of energy metabolism or of the membrane-bound ATPase inhibit transport. Cl. pasteurianum maintains a membrane potential (interior negative) in the range 80-130 mV. This membrane potential was identified as the energy source: the same agents that block transport also decrease the membrane potential, and artificial generation of a membrane potential (by addition of valinomycin to K+-loaded cells) induces concentrative uptake of methylammonium. Thus NH4+ (or CH3NH3+) must be the transported species. Digestion of the cell wall by lysozyme does not abolish the transport activity. PMID:7213710

Kleiner, D; Fitzke, E

1981-02-20

392

Energy system analysis of utilizing hydrogen as an energy carrier for wind power in the transportation sector in Western Denmark  

Microsoft Academic Search

Hydrogen is an energy carrier that can potentially be used for introducing renewably generated electricity into the transportation sector. This paper presents a methodology for an overall energy system analysis of a hydrogen infrastructure, which meets a transportation hydrogen demand profile. The methodology starts by building a mathematical model for optimizing the economic operation of electrolyzers on the electricity market

Georges Salgi; Bjarne Donslund; Poul Alberg Østergaard

2008-01-01

393

Electronic transport of the manganite-based heterojunction with high carrier concentrations  

NASA Astrophysics Data System (ADS)

The transport property of the manganite heterojunction La0.9Ca0.1MnO3+?/SrTiO3 (doped by 1 wt %Nb) has been experimentally studied. The most important results of the present work are the discovery of the charge tunneling-dominated transport process, characterized by the appearance of the rectifying behaviors fairly described by the Newman equation I~exp(?T)exp(?V) in a considerable temperature range (? and ? are constants, and I and V are current and voltage, respectively). Significant modification of magnetic field to charge tunneling is also observed. It is believed that magnetic field depresses junction resistance by reducing depletion width of the junction.

Xie, Y. W.; Sun, J. R.; Wang, D. J.; Liang, S.; Lü, W. M.; Shen, B. G.

2007-05-01

394

Alternating Carrier Models of Asymmetric Glucose Transport Violate the Energy Conservation Laws  

PubMed Central

Alternating access transporters with high-affinity externally facing sites and low-affinity internal sites relate substrate transit directly to the unliganded asymmetric “carrier” (Ci) distribution. When both bathing solutions contain equimolar concentrations of ligand, zero net flow of the substrate-carrier complex requires a higher proportion of unliganded low-affinity inside sites (\\documentclass[10pt]{article} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{pmc} \\usepackage[Euler]{upgreek} \\pagestyle{empty} \\oddsidemargin -1.0in \\begin{document} \\begin{equation*}{\\propto}1/K_{{\\mathrm{D}}}^{{\\mathrm{in}}}\\end{equation*}\\end{document}) and slower unliganded “free” carrier transit from inside to outside than in the reverse direction. However, asymmetric rates of unliganded carrier movement, kij, imply that an energy source, ?Gcarrier = RT ln (koi/kio) = RT ln (Cin/Cout) = RT ln (\\documentclass[10pt]{article} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{pmc} \\usepackage[Euler]{upgreek} \\pagestyle{empty} \\oddsidemargin -1.0in \\begin{document} \\begin{equation*}K_{{\\mathrm{D}}}^{{\\mathrm{in}}}/K_{{\\mathrm{D}}}^{{\\mathrm{out}}}\\end{equation*}\\end{document}), where R is the universal gas constant (8.314 Joules/M/K°), and T is the temperature, assumed here to be 300 K°, sustains the asymmetry. Without this invalid assumption, the constraints of carrier path cyclicity, combined with asymmetric ligand affinities and equimolarity at equilibrium, are irreconcilable, and any passive asymmetric uniporter or cotransporter model system, e.g., Na-glucose cotransporters, espousing this fundamental error is untenable. With glucose transport via GLUT1, the higher maximal rate and Km of net ligand exit compared to net ligand entry is only properly simulated if ligand transit occurs by serial dissociation-association reactions between external high-affinity and internal low-affinity immobile sites. Faster intersite transit rates occur from lower-affinity sites than from higher-affinity sites and require no other energy source to maintain equilibrium. Similar constraints must apply to cotransport.

Naftalin, Richard J

2008-01-01

395

Charge transfer and carrier density in Bi2212 high-Tc superconductors  

Microsoft Academic Search

Muon spin relaxation and neutron diffraction measurements were performed in Y and Pb substituted Bi-2212 superconductors in order to study the correlation between Tc and hole density. We observe first an increase of both Tc and the superconducting carrier density via hole transfer, but subsequently (at higher ``doping'') more and more holes are prevented from forming superconducting pairs.

H. Maletta; M. Weber; A. Amato; J. Bock; V. N. Duginov; V. G. Grebinnik; F. N. Gygax; S. Kapusta; B. F. Kirillov; V. G. Olshevsky; A. V. Pirogov; Y. Yu. Pomjakushin; A. N. Ponomarev; E. Preisler; A. Schenck; V. G. Storchak; V. A. Zhukov

1992-01-01

396

Capture of charge carriers and output power of a quantum well laser  

SciTech Connect

The effect of noninstantaneous carrier capture by a nanoscale active region on the power characteristics of a semiconductor laser is studied. A laser structure based on a single quantum well is considered. It is shown that delayed carrier capture by the quantum well results in a decrease in the internal differential quantum efficiency and sublinearity of the light-current characteristic of the laser. The main parameter of the developed theoretical model is the velocity of carrier capture from the bulk (waveguide) region to the two-dimensional region (quantum well). The effect of the capture velocity on the dependence of the following laser characteristics on the pump current density is studied: the output optical power, internal quantum efficiency of stimulated emission, current of stimulated recombination in the quantum well, current of spontaneous recombination in the optical confinement layer, and carrier concentration in the optical confinement layer. A decrease in the carrier capture velocity results in a larger sublinearity of the light-current characteristic, which results from an increase in the injection current fraction expended to parasitic spontaneous recombination in the optical confinement layer and, hence, a decrease in the injection current fraction expended to stimulated recombination in the quantum well. A comparison of calculated and experimental light-current characteristics for a structure considered as an example shows that good agreement between them (up to a very high injection current density of 45 kA/cm{sup 2}) is attained at a capture velocity of 2 Multiplication-Sign 10{sup 6} cm/s. The results of this study can be used to optimize quantum well lasers for generating high optical powers.

Sokolova, Z. N., E-mail: Zina.Sokolova@mail.ioffe.ru; Tarasov, I. S. [Russian Academy of Sciences, Ioffe Physical Technical Institute (Russian Federation); Asryan, L. V. [Virginia Polytechnic Institute and State University (United States)

2011-11-15

397

Charge transport at the metal-organic interface.  

PubMed

This review focuses on the impacts of metal-organic interfacial bonding interactions on the charge-transport dynamics involved in molecular junctions as well as organically capped nanoparticles. Whereas mercapto derivatives have been used extensively as the ligands of choice to functionalize metal and nanoparticle surfaces with the formation of metal-thiolate interfacial bonds, recent studies show that metal-carbon covalent linkages may be fabricated by the deliberate design and selection of functional moieties. With enhanced electronic interactions between metals and organic ligands, the interfacial contact resistance diminishes drastically, leading to the emergence of unprecedented optical and electronic properties of the junctions and nanoparticles. These mechanistic insights are of fundamental significance in the development of molecule- and nanoparticle-based electronic devices, in particular, in light of the diverse metal-nonmetal bonding interactions that have been extensively observed in organometallic chemistry. PMID:23298247

Chen, Shaowei; Zhao, Zhenhuan; Liu, Hong

2013-01-04

398

Monte Carlo simulation of charge transport in amorphous chalcogenides  

NASA Astrophysics Data System (ADS)

The I(V) characteristics of amorphous GST devices show a peculiar S-shape behavior, that is a swift rise of the current along with a voltage snap-back. This type of characteristics led to a growing research interest in view of the future application of such materials to the manufacturing of phase-change memory devices. In this work we adopt a generalization of the variable-range hopping theory to simulate charge transport in a layer of amorphous Ge2Sb2Te5 sandwiched between two planar metallic electrodes. The numerical implementation of a current-driven Monte Carlo code allows one both to provide a complete microscopic particle picture of electrical conduction in the device and to better analyze the mechanisms governing the snap-back effect.

Piccinini, E.; Buscemi, F.; Rudan, M.; Brunetti, R.; Jacoboni, C.

2009-11-01

399

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

400

Transport of intense beams of highly charged ions  

NASA Astrophysics Data System (ADS)

The new generation of ion sources delivers beams with intensities of several mA. This requires a careful design of the analysing system and the low-energy beam transport (LEBT) from the source to the subsequent systems. At INFN-LNS, high intensity proton sources (TRIPS [L. Celona, G. Ciavola, S. Gammino et al ., Rev. Sci. Instrum. 75(5) 1423 (2004)], PM-TRIPS [G. Ciavola, L. Celona, S. Gammino et al ., Rev. Sci. Instrum. 75(5) 1453 (2004)]) as well as ECR ion sources for the production of highly charged high-intensity heavy ion beams are developed (SERSE [S. Gammino, G. Ciavola, L. Celona et al ., Rev. Sci. Instrum. 72(11) 4090 (2001), and references therein], GyroSERSE [S. Gammino et al ., Rev. Sci. Instrum. 75(5) 1637 (2004)], MS-ECRIS [G. Ciavola et al ., (2005), 11th Int. Conf. on Ion Sources, Caen, (in press)]). In this paper, we present ion-optical design studies of various LEBT systems for ion-sources devoted to the production of intense beams. Calculations were performed using the computer codes GIOS [H. Wollnik, J. Brezina and M. Berz, NIM A 258 (1987)], GICO [M. Berz, H.C. Hoffmann, and H. Wollnik, NIM A 258 (1987)], and TRANSPORT [K.L. Brown, F. Rothacker and D.C. Carey, SLAC-R-95-462, Fermilab-Pub-95/069, UC-414 (1995)]. Simulations take into account the expected phase space growth of the beam emittance due to space-charge effects and image aberrations introduced by the magnetic elements.

Winkler, M.; Gammino, S.; Ciavola, G.; Celona, L.; Spadtke, P.; Tinschert, K.

2005-10-01

401

Metal Complexes for DNA-Mediated Charge Transport  

PubMed Central

In all organisms, oxidation threatens the integrity of the genome. DNA-mediated charge transport (CT) may play an important role in the generation and repair of this oxidative damage. In studies involving long-range CT from intercalating Ru and Rh complexes to 5?-GG-3? sites, we have examined the efficiency of CT as a function of distance, temperature, and the electronic coupling of metal oxidants bound to the base stack. Most striking is the shallow distance dependence and the sensitivity of DNA CT to how the metal complexes are stacked in the helix. Experiments with cyclopropylamine-modified bases have revealed that charge occupation occurs at all sites along the bridge. Using Ir complexes, we have seen that the process of DNA-mediated reduction is very similar to that of DNA-mediated oxidation. Studies involving metalloproteins have, furthermore, shown that their redox activity is DNA-dependent and can be DNA-mediated. Long range DNA-mediated CT can facilitate the oxidation of DNA-bound base excision repair proteins to initiate a redox-active search for DNA lesions. DNA CT can also activate the transcription factor SoxR, triggering a cellular response to oxidative stress. Indeed, these studies show that within the cell, redox-active proteins may utilize the same chemistry as that of synthetic metal complexes in vitro, and these proteins may harness DNA-mediated CT to reduce damage to the genome and regulate cellular processes.

Barton, Jacqueline K.; Olmon, Eric D.; Sontz, Pamela A.

2010-01-01

402

Concentration and mobility of charge carriers in thin polymers at high temperature determined by electrode polarization modeling  

NASA Astrophysics Data System (ADS)

Charge carrier concentration (n0) and effective mobility (?eff) are reported in two polymer films (<10 ?m) and in a very high temperature range (from 200 to 400 °C). This was possible thanks to an electrode polarization modeling of broadband dielectric spectroscopy data. It is shown that the glass transition temperature (Tg) occurrence has a strong influence on the temperature dependence of n0 and ?eff. We carry out that n0 presents two distinct Arrhenius-like behaviors below and above Tg, while ?eff exhibits a Vogel-Fulcher-Tamman behavior only above Tg whatever the polymer under study. For polyimide films, n0 varies from 1 × 1014 to 4 × 1016 cm-3 and ?eff from 1 × 10-8 to 2 × 10-6 cm2 V-1 s-1 between 200 °C to 400 °C. Poly(amide-imide) films show n0 values between 6 × 1016 and 4 × 1018 cm-3 from 270 °C to 400 °C, while ?eff varies between 1 × 10-10 and 2 × 10-7 cm2 V-1 s-1. Considering the activation energies of these physical parameters in the temperature range of investigation, n0 and ?eff values appear as coherent with those reported in the literature at lower temperature (<80 °C). Surface charge carrier concentrations (nS) are reported and discussed for potential passivation (i.e., surface electrical insulation) applications. Polyimide films appear as good candidates due to nS values less than 1011 cm-2 up to 300 °C.

Diaham, Sombel; Locatelli, Marie-Laure

2012-07-01

403

Efficient organic electroluminescent devices using single-layer doped polymer thin films with bipolar carrier transport abilities  

Microsoft Academic Search

Detailed studies of electroluminescent devices made from single-layer doped polymer blend thin films having bipolar carrier transport abilities are presented. The active organic layer consists of the hole-transport polymer poly(N-vinylcarbazole) (PVK) containing dispersed electron-transport molecules, as well as different fluorescent small molecules or polymers as emitting centers to vary the emission color. Both the photoluminescence and electroluminescence (EL) properties are

Chung-Chih Wu; James C. Sturm; Richard A. Register; Jing Tian; Elena P. Dana; M. E. Tnompson

1997-01-01

404

Charged-particle transport in the condensed phase.  

PubMed

Traditionally, studies of the biological effects of ionizing radiation have rested on the triumvirate: (gas-phase) radiation physics, biophysical modeling, and radiation biology. Two technical developments, the advent of supercomputing as a routine tool in quantum solid-state material science and molecular dynamics on the one hand, and molecular biology on the other hand, have created--perhaps for the first time-the possibility of directly linking a more realistic description of the radiation field to observable events at biomolecular level. It also becomes increasingly clear that the identification of specific molecular targets imposes a challenge to the radiation physics community to be equally specific in treating the energy--deposition stage of radiation action. In this paper: a) I review--and exemplify with results from our own work--the current status in Monte Carlo simulation of gas-phase material (particle transport and stochastic chemistry); b) examine the link between these essentially geometric representations of the track and the concept of "spatial distribution of energy deposition," a staple in radiation modeling; c) advocate an effort towards developing conceptually and calculationally, the field of solid-state microdosimetry; and d) describe methods based on semi-empirical Hamiltonians or quasi-particle techniques for obtaining the frequency-dependent and wave-vector-dependent dielectric response function for biomolecular crystalline systems, which are the main ingredients for describing charged-particle transport. PMID:1811471

Zaider, M

1991-01-01

405

Identification of Inhibitor Concentrations to Efficiently Screen and Measure Inhibition Ki Values against Solute Carrier Transporters  

PubMed Central

The objective was to identify inhibitor concentrations to efficiently screen and measure inhibition Ki values of solute carrier (SLC) transporters. The intestinal bile acid transporter and its native substrate taurocholate were used as a model system. Inhibition experiments were conducted using 27 compounds. For each compound, the inhibition constant Ki was obtained from the comprehensive inhibition profile, and referred as the reference Ki. Ki values were also estimated from various partial profiles and were compared to the reference Ki. A screening Ki was estimated from one data point and also compared to the reference Ki. Results indicate that Ki can be accurately measured using an inhibitor concentration range of only 0-Ki via five different inhibitor concentrations. Additionally, a screening concentration of 10-fold the substrate affinity Kt for potent inhibitors (Ki < 20Kt) and 100-fold Kt for nonpotent inhibitors (Ki > 20Kt) provided an accurate Ki estimation. Results were validated through inhibition studies of two other SLC transporters. In conclusion, experimental conditions to screen and measure accurate transporter inhibition constant Ki are suggested where a low range of inhibitor concentrations can be used. This approach is advantageous in that minimal compound is needed to perform studies and accommodates compounds with low aqueous solubility.

Zheng, Xiaowan; Polli, James

2010-01-01

406

A superconducting copper oxide compound with electrons as the charge carriers  

Microsoft Academic Search

The discovery of a family of superconducting copper oxides in which the carriers are electrons is reported. The new superconductors are Ce(4+)-doped compounds with the formula Ln(2-x)Ce(x)CuO(4-y), where Ln stands for the lanthanides Pr, Nd, or Sm. The compounds have the Nd2CuO4 (T-prime phase) structure, which is composed of sheets of Cu-O squares. This structure has no apical oxygen atoms,

Y. Tokura; H. Takagi; S. Uchida

1989-01-01

407

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

408

Charge transport in hexagonal columnar liquid crystals self-organized from supramolecular cylinders based on acene-functionalized dendrons  

NASA Astrophysics Data System (ADS)

We report measurements of time-of-flight charge carrier mobility and thermal optical polarized microscopy on a new class of hexagonal columnar (?h) liquid crystals (LC) self-organized from supramolecular cylinders self-assembled from acene functionalized dendrons. We discuss the temperature and electric field-independent high hole mobility of 1 3.5×10-3 cm2/V s of fluorinated tapered first generation dendrons that contain pyrene and naphthalene groups in their core and self-assemble into supramolecular nanocylinders. The anomalous temperature behavior of the mobility is consistent with polaron transport mechanisms. Studies of time-of-flight transients, which reveal evidence for dynamic defects with lifetimes in the range of 10-6 s, are presented as aspects of charge generation and recombination kinetics.

Shiyanovskaya, I.; Singer, K. D.; Percec, V.; Bera, T. K.; Miura, Y.; Glodde, M.

2003-01-01

409

Preparation of ZnO nanoparticles for blend of P3HT:ZnO nanoparticles:PCBM thin film and its charge carrier dynamics characterization  

NASA Astrophysics Data System (ADS)

Recently, many researchers have paid attention to develop active material of solar cell which plays an important role in absorbing solar spectrum. This active material should have an ability to transfer charge carrier resulted from the absorption of solar spectrum. The hybrid organic-inorganic solar cell has been developed due to the combining advantages between organic material Poly(3-hexylthiophene) (P3HT) and fullerene PCBM with inorganic material ZnO nanoparticles. The investigation of charge carrier dynamics in blend P3HT:ZnO nanoparticles:PCBM film as an active material of solar cell devices is an important things to enhance the solar cell performance. The charge carrier dynamics properties is needed to control the morphology of active material to produce an efficient and effective charge dissociation. In this study we synthezed the ZnO nanoparticles by using sol-gel methods. The size of nanoparticles resulted from the reflux process of zinc acetate in methanol by the presence of catalist sodium hydroxide is around 10 nm. Photo-induced Infra-red (PI-IR) Absorption Spectroscopy was used to investigate the charge carrier dynamics of P3HT:ZnO nanoparticles:PCBM thin film. Measurement of PI-IR Absorption Spectroscopy has been carried out under variation of temperature conditions from 78 to 300 K, using a 532-nm laser as a light source. At low temperature, the charge carrier recombination was performed by positive polarons along the intrachain of P3HT while at high temperature the charge carrier recombination was attributed to positive polarons along the interchain of P3HT.

Safriani, Lusi; Aprilia, Annisa; Bahtiar, Ayi; Risdiana; Kartawidjaja, Mariah; Apriani, Trisa; Kanazawa, Kei; Furukawa, Yukio

2013-09-01

410

Charge transport and current in non-polar liquids  

Microsoft Academic Search

Surfactant molecules in a non-polar liquid form charged and uncharged inverse micelles. When a potential difference is applied over the mixture, the charged inverse micelles drift towards the electrode with the opposite polarity. The motion of charges is associated with a transient current, which can be measured in an external circuit. In this paper, transient currents and steady state charge

Kristiaan Neyts; Filip Beunis; Filip Strubbe; Matthias Marescaux; Bart Verboven; Masoumeh Karvar; Alwin Verschueren

2010-01-01

411

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

SciTech Connect

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

Baturin, A. S.; Gorelkin, V. N.; Soloviev, V. R.; Chernousov, I. V., E-mail: ichernousov@inbox.ru [Moscow Institute of Physics and Technology (Russian Federation)

2010-07-15

412

Potassium transport through lipid bilayer membranes facilitated by tentoxin dimers. A new mechanism of ion carrier transport?  

PubMed

The cyclic tetrapeptide tentoxin at concentrations greater than 5 X 10(-7) M selectively increases the ion conductivity for potassium of lipid bilayer membranes, while the naturally occurring derivative dihydrotentoxin has no influence on this property. Current-voltage curves, zero-current potential and charge-pulse measurements were used to characterize the action of tentoxin. The results suggest that a new mechanism of facilitated ion transport operates. The model of tentoxin dimerization and tentoxin-K+ association developed is in contradiction to the model of tentoxin pore formation described recently by Heitz et al. (Biophys. Chem. 23 (1986) 245). PMID:3663841

Klotz, M G; Müller, E; Liebermann, B

1987-08-01

413

Experimental studies of the relationship between DNA structure and chemical modification, and its charge transport properties  

Microsoft Academic Search

We experimentally investigate the influence of the physico-chemical properties of DNA molecules on its charge transport capabilities. By performing comparative rather than absolute charge transport measurements, we probe the effect of chemical modifications on the electronic properties of the molecule. Modifications include the introduction of phosphodiester bond breaks, and intercalation of metal cations, as probes to ascertain the relationship between

V. Soghomonian; D. E. Davis; A. A. Belak; J. F. Dowd; J. J. Heremans

2007-01-01

414

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

PubMed Central

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

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

2008-01-01

415

Inkjet printing of carrier transport layers for inverted organic solar cells  

NASA Astrophysics Data System (ADS)

Inverted organic solar cells, which utilize a transparent cathode and a high work function metal anode, have been the subject of extensive research. Their advantages over conventional organic solar cells include increased resistance to environmental degradation and compatibility with large area fabrication techniques. Carrier transport layers are essential for achieving high power conversion efficiencies in inverted organic solar cells and therefore need to be compatible with these large area fabrication techniques. Inkjet printing is one such technique that can be integrated into the low cost mass production of these cells via roll to roll fabrication. N-type metal oxides such as ZnO or zinc tin oxide (ZTO) have been previously used as electron transport layers for inverted cells, but only as spin coated films. We have developed inkjet printable ZTO solutions for use as electron transport layers in inverted organic solar cells, and achieve power conversion efficiencies of over 3% in inverted P3HT:PC71BM solar cells. We also discuss the effect of printing parameters on the electrical performance of these layers in inverted organic solar cells.

Danielson, Eric; Subbaraman, Harish; Dodabalapur, Ananth

2013-09-01

416

Simulation and modelling of charge transport in dye-sensitized solar cells based on carbon nano-tube electrodes  

NASA Astrophysics Data System (ADS)

For a better understanding of the mechanisms of dye-sensitized solar cells (DSSCs), based on carbon nano-tube (CNT) electrodes, a phenomenological model is proposed. For modelling purposes, the meso-scopic porous CNT electrode is considered as a homogeneous nano-crystalline structure with thickness L. The CNT electrode is covered with light-absorbing dye molecules, and interpenetrated by the tri-iodide (I-/I3-) redox couple. A simulation platform, designed to study coupled charge transport in such cells, is presented here. The work aims at formulating a mathematical model that describes charge transfer and charge transport within the porous CNT window electrode. The model is based on a pseudo-homogeneous active layer using drift-diffusion transport equations for free electron and ion transport. Based on solving the continuity equation for electrons, the model uses the numerical finite difference method. The numerical solution of the continuity equation produces current-voltage curves that fit the diode equation with an ideality factor of unity. The calculated current-voltage (J-V) characteristics of the illuminated idealized DSSCs (100 mW cm-2, AM1.5), and the different series resistances of the transparent conductor oxide (TCO) layer were introduced into the idealized simulated photo J-V characteristics. The results obtained are presented and discussed in this paper. Thus, for a series resistance of 4 ? of the TCO layer, the conversion efficiency (?) was 7.49% for the CNT-based cell, compared with 6.11% for the TiO2-based cell. Two recombination kinetic models are used, the electron transport kinetics within the nano-structured CNT film, or the electron transfer rate across the CNT-electrolyte interface. The simulations indicate that both electron and ion transport properties should be considered when modelling CNT-based DSSCs and other similar systems. Unlike conventional polycrystalline solar cells which exhibit carrier recombination, which limits their efficiency, the CNT matrix (in CNT-based cells) serves as the conductor for majority carriers and prevents recombination. This is because of special conductivity and visible-near-infrared transparency of the CNT. Charge transfer mechanisms within the porous CNT matrix and at the semiconductor-dye-electrolyte interfaces are described in this paper.

Gacemi, Yahia; Cheknane, Ali; Hilal, Hikmat S.

2013-03-01

417

Photogeneration and carrier transport in amorphous silicon/crystalline silicon devices  

SciTech Connect

Hydrogenated amorphous silicon (a-Si:H)/crystalline silicon (c-Si) type heterodiodes in solar cell structures have been studied by rf glow discharge, dc magnetron sputtering, and a remote plasma deposition of a-Si:H onto p type c-Si. Carrier transport and photogeneration in such structures have been investigated by current-voltage-temperature, thermally stimulated capacitance (TSCAP), and spectral response experiments. Dark carrier conduction is found to be a combination of tunneling and interface recombination, but is dominated by either one depending on the deposition/sputtering conditions. The conditions investigated include energy of the plasma species, type of plasma cleaning, and substrate preparation techniques. For each of the conditions, the trap type, energy and concentration have been identified by TSCAP. Solar cells fabricated by the optimized fabrication scheme routinely yield 10.5% efficient devices having a short circuit current density (J{sub sc}) of 30 mA/cm{sup 2}, a open circuit voltage of 0.55 volts and a fill factor (FF) of 0.64, without an AR coating, over 0.3 cm{sup 2} area.

Jagannathan, B.; Anderson, W.A.

1997-07-01

418

Charge carrier dynamics of vapor-deposited small-molecule/fullerene organic solar cells.  

PubMed

Although small-molecule organic solar cells (SMOSCs) have shown increasingly promising prospects as a source of solar power, there have been few studies concerning the photophysics of these systems. Here, we report the time scale and efficiency of charge separation and recombination in a vapor-deposited SMOSC material that produces 5.81% power conversion efficiency. Transient absorption and time-resolved photoluminescence (trPL) studies of thin film blends comprising DTDCTB, a narrow-band gap electron donor, and either C60 or C70 as an electron acceptor show that charge separation occurs in ~100 fs, while charge recombination takes place over sub-ns and ns time scales. trPL indicates a donor electron-hole pair lifetime of ~33 ps in the neat film and reveals that ~20% of donors fail to charge separate in donor-acceptor mixed films, likely owing to some spatially extended donor-rich regions that interact poorly with acceptors. Our results suggest that morphological manipulations of this material could further improve device efficiency. PMID:23718234

Chang, Angela Y; Chen, Yi-Hong; Lin, Hao-Wu; Lin, Li-Yen; Wong, Ken-Tsung; Schaller, Richard D

2013-06-11

419

Microscopic modeling of charge transport in sensing proteins.  

PubMed

: Sensing proteins (receptors) are nanostructures that exhibit very complex behaviors (ions pumping, conformational change, reaction catalysis, etc). They are constituted by a specific sequence of amino acids within a codified spatial organization. The functioning of these macromolecules is intrinsically connected with their spatial structure, which modifications are normally associated with their biological function. With the advance of nanotechnology, the investigation of the electrical properties of receptors has emerged as a demanding issue. Beside the fundamental interest, the possibility to exploit the electrical properties for the development of bioelectronic devices of new generations has attracted major interest. From the experimental side, we investigate three complementary kinds of measurements: (1) current-voltage (I-V) measurements in nanometric layers sandwiched between macroscopic contacts, (2) I-V measurements within an AFM environment in nanometric monolayers deposited on a conducting substrate, and (3) electrochemical impedance spectroscopy measurements on appropriate monolayers of self-assembled samples. From the theoretical side, a microscopic interpretation of these experiments is still a challenging issue. This paper reviews recent theoretical results carried out within the European project, Bioelectronic Olfactory Neuron Device, which provides a first quantitative interpretation of charge transport experiments exploiting static and dynamic electrical properties of several receptors. To this purpose, we have developed an impedance network protein analogue (INPA) which considers the interaction between neighboring amino acids within a given radius as responsible of charge transfer throughout the protein. The conformational change, due to the sensing action produced by the capture of the ligand (photon, odour), induces a modification of the spatial structure and, thus, of the electrical properties of the receptor. By a scaling procedure, the electrical change of the receptor when passing from the native to the active state is used to interpret the macroscopic measurement obtained within different methods. The developed INPA model is found to be very promising for a better understanding of the role of receptor topology in the mechanism responsible of charge transfer. Present results point favorably to the development of a new generation of nano-biosensors within the lab-on-chip strategy. PMID:22726939

Reggiani, Lino; Millithaler, Jean-Francois; Pennetta, Cecilia

2012-06-22

420

Microscopic modeling of charge transport in sensing proteins  

NASA Astrophysics Data System (ADS)

Sensing proteins (receptors) are nanostructures that exhibit very complex behaviors (ions pumping, conformational change, reaction catalysis, etc). They are constituted by a specific sequence of amino acids within a codified spatial organization. The functioning of these macromolecules is intrinsically connected with their spatial structure, which modifications are normally associated with their biological function. With the advance of nanotechnology, the investigation of the electrical properties of receptors has emerged as a demanding issue. Beside the fundamental interest, the possibility to exploit the electrical properties for the development of bioelectronic devices of new generations has attracted major interest. From the experimental side, we investigate three complem