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1

Charge carrier transport properties in layer structured hexagonal boron nitride  

SciTech Connect

Due to its large in-plane thermal conductivity, high temperature and chemical stability, large energy band gap (~ 6.4 eV), hexagonal boron nitride (hBN) has emerged as an important material for applications in deep ultraviolet photonic devices. Among the members of the III-nitride material system, hBN is the least studied and understood. The study of the electrical transport properties of hBN is of utmost importance with a view to realizing practical device applications. Wafer-scale hBN epilayers have been successfully synthesized by metal organic chemical deposition and their electrical transport properties have been probed by variable temperature Hall effect measurements. The results demonstrate that undoped hBN is a semiconductor exhibiting weak p-type at high temperatures (> 700?°K). The measured acceptor energy level is about 0.68 eV above the valence band. In contrast to the electrical transport properties of traditional III-nitride wide bandgap semiconductors, the temperature dependence of the hole mobility in hBN can be described by the form of ? ? (T/T{sub 0}){sup ??} with ? = 3.02, satisfying the two-dimensional (2D) carrier transport limit dominated by the polar optical phonon scattering. This behavior is a direct consequence of the fact that hBN is a layer structured material. The optical phonon energy deduced from the temperature dependence of the hole mobility is ?? = 192 meV (or 1546 cm{sup -1}), which is consistent with values previously obtained using other techniques. The present results extend our understanding of the charge carrier transport properties beyond the traditional III-nitride semiconductors.

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

2014-10-15

2

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

PubMed

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

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

2009-05-13

3

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

4

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

5

Charge carrier transport in molecularly doped polycarbonate as a test case for the dipolar glass model  

NASA Astrophysics Data System (ADS)

We present the results of Monte Carlo simulations of the charge carrier transport in a disordered molecular system containing spatial and energetic disorders using the dipolar glass model. Model parameters of the material were chosen to fit a typical polar organic photoconductor polycarbonate doped with 30% of aromatic hydrazone, whose transport properties are well documented in literature. Simulated carrier mobility demonstrates a usual Poole-Frenkel field dependence and its slope is very close to the experimental value without using any adjustable parameter. At room temperature transients are universal with respect to the electric field and transport layer thickness. At the same time, carrier mobility does not depend on the layer thickness and transients develop a well-defined plateau where the current does not depend on time, thus demonstrating a non-dispersive transport regime. Tails of the transients decay as power law with the exponent close to -2. This particular feature indicates that transients are close to the boundary between dispersive and non-dispersive transport regimes. Shapes of the simulated transients are in very good agreement with the experimental ones. In summary, we provide a first verification of a self-consistency of the dipolar glass transport model, where major transport parameters, extracted from the experimental transport data, are then used in the transport simulation, and the resulting mobility field dependence and transients are in very good agreement with the initial experimental data.

Novikov, S. V.; Tyutnev, A. P.

2013-03-01

6

Charge carrier transport in molecularly doped polycarbonate as a test case for the dipolar glass model.  

PubMed

We present the results of Monte Carlo simulations of the charge carrier transport in a disordered molecular system containing spatial and energetic disorders using the dipolar glass model. Model parameters of the material were chosen to fit a typical polar organic photoconductor polycarbonate doped with 30% of aromatic hydrazone, whose transport properties are well documented in literature. Simulated carrier mobility demonstrates a usual Poole-Frenkel field dependence and its slope is very close to the experimental value without using any adjustable parameter. At room temperature transients are universal with respect to the electric field and transport layer thickness. At the same time, carrier mobility does not depend on the layer thickness and transients develop a well-defined plateau where the current does not depend on time, thus demonstrating a non-dispersive transport regime. Tails of the transients decay as power law with the exponent close to -2. This particular feature indicates that transients are close to the boundary between dispersive and non-dispersive transport regimes. Shapes of the simulated transients are in very good agreement with the experimental ones. In summary, we provide a first verification of a self-consistency of the dipolar glass transport model, where major transport parameters, extracted from the experimental transport data, are then used in the transport simulation, and the resulting mobility field dependence and transients are in very good agreement with the initial experimental data. PMID:23514478

Novikov, S V; Tyutnev, A P

2013-03-14

7

A charge carrier transport model for donor-acceptor blend layers  

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

8

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

9

Carrier mobility in organic charge transport materials: Methods of measurement, analysis, and modulation  

NASA Astrophysics Data System (ADS)

The measurement and control of charge carrier mobility in organic semiconductors are two prevalent issues in the growing field of organic electronics. The mobility is a measure of the speed of net charge movement per unit of applied field. This quantity determines how fast circuits and elements can respond and how much current they can support at a given voltage. While there are many methods to measure the hole and electron mobilities of organic materials, each has its own limitations and requirements. There is room for new methods to allow the measurement of additional materials and in different circumstances. In addition, exploring the capability of molecular systems to modulate these mobilities provides opportunities for improvements in the performance of organic electronic devices. This thesis has focused on developing new methods of measuring the charge carrier mobility in organic semiconductors and on evaluating the capability of a series of hybrid compounds to modulate the emitting layer's mobilities for application in organic light-emitting diodes. Key results are summarized as follows: (1) The charge-retraction time-of-flight technique for carrier mobility measurements was explained, explored, and validated with two well know hole transport materials producing retraction transients nearly identical to those of photocurrent time-of-flight, while amenable to thinner samples and utilizing a simple, all-electrical experimental setup. In addition, a method to determine the transition voltage more accurately in these devices was developed. (2) The electron mobilities of a known electron transport material and an unknown polycrystalline electron transport material were measured by both charge-retraction time-of-flight and photocurrent time-of-flight. The results for the known compound were found to match within error for both techniques, and various measures of how dispersive the transport was also matched very closely, validating the charge-retraction time-of-flight technique for dispersive and electron transport. (3) The integrating-mode photocurrent time-of-flight technique was described in detail, and an analysis method extending Scher and Montroll's procedures to integrating-mode transients was derived and explored. The mobility values determined by this analysis, as well as three other methods (two of them from the literature) were compared and contrasted for nondispersive hole transport and dispersive electron transport, and the analysis developed here was found to be the only one to agree with traditional, current-mode time-of-flight for both cases. (4) Three compounds were synthesized to complete a series of hybrid materials designed to modulate the carrier mobilities in the emitter layer of organic light-emitting diodes. The hole and electron mobilities of these compounds were measured by photocurrent time-of-flight, in both current- and integrating-modes, as functions of field and temperature. It was found that the mobilities in these compounds spanned over four orders of magnitude, with the ratios of the hole to the electron mobility in neat layers ranging from 59:1 to 1:180. The trends in these mobilities were discussed using the disorder formalism for charge transport.

Wallace, Jason U.

10

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

PubMed

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

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

2014-12-10

11

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

12

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

PubMed

In a real bulk heterojunction polymer solar cell, after exciton separation in the heterojunction, the resulting negatively-charged carrier, a polaron, moves along the polymer chain of the acceptor, which is believed to be of significance for the charged carrier transport properties in a polymer solar cell. During the negative polaron transport, due to the external light field, the polaron, which is re-excited and induces deep localization, also forms a new local distortion of the alternating bonds. It is revealed that the excited polaron moves more slowly than the ground-state polaron. Furthermore, the velocity of the polaron moving along the polymer chain is crucially dependent on the photoexcitation. With an increase in the intensity of the optical field, the localization of the excited polaron will be deepened, with a decrease of the polaron's velocity. It is discovered that, for a charged carrier, photoexcitation is a significant factor in reducing the efficiency during the charged carrier transport in polymer solar cells. Mostly, the deep trapping effect of charged carrier in composite conjugated polymer solar cell presents an opportunity for the future application in nanoscale memory and imaging devices. PMID:25407625

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

2015-01-14

13

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

14

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

SciTech Connect

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

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

2009-03-01

15

Influence of high-pressure treatment on charge carrier transport in PbS colloidal quantum dot solids.  

PubMed

We investigated the effects of high-pressure treatment on charge carrier transport in PbS colloidal quantum dot (CQD) solids. We applied high pressure to PbS CQD solids using nitrogen gas to reduce the inter-dot distance. Using this simple process, we obtained conductive PbS CQD solids. Terahertz time-domain spectroscopy was used to study charge carrier transport as a function of pressure. We found that the minimum pressure needed to increase the dielectric constant, conductivity, and carrier mobility was 4 MPa. All properties dramatically improved at 5 MPa; for example, the mobility increased from 0.13 cm(2) V(-1) s(-1) at 0.1 MPa to 0.91 cm(2) V(-1) s(-1) at 5 MPa. We propose this simple process as a nondestructive approach for making conductive PbS CQD solids that are free of chemical and physical defects. PMID:24281416

Heo, Seung Jin; Yoon, Seokhyun; Oh, Sang Hoon; Yoon, Doo Hyun; Kim, Hyun Jae

2014-01-21

16

Electrical, magneto-transport and localization of charge carriers in nanocomposites based on carbon nanotubes  

Microsoft Academic Search

Here we investigate the electrical transport and magneto-transport properties of a network of singlewalled carbon nanotubes (SWNT) embedded into an insulating polymer matrix in order to build a nanocomposite. We show that the SWNT metallic character is lost in the nanocomposite. Intrinsic localization of the carriers at the bundle size is evidenced from conductivity results. It is confirmed by magnetoresistance

O. Chauvet; J. M. Benoit; B. Corraze

2004-01-01

17

Influence of high-pressure treatment on charge carrier transport in PbS colloidal quantum dot solids  

NASA Astrophysics Data System (ADS)

We investigated the effects of high-pressure treatment on charge carrier transport in PbS colloidal quantum dot (CQD) solids. We applied high pressure to PbS CQD solids using nitrogen gas to reduce the inter-dot distance. Using this simple process, we obtained conductive PbS CQD solids. Terahertz time-domain spectroscopy was used to study charge carrier transport as a function of pressure. We found that the minimum pressure needed to increase the dielectric constant, conductivity, and carrier mobility was 4 MPa. All properties dramatically improved at 5 MPa; for example, the mobility increased from 0.13 cm2 V-1 s-1 at 0.1 MPa to 0.91 cm2 V-1 s-1 at 5 MPa. We propose this simple process as a nondestructive approach for making conductive PbS CQD solids that are free of chemical and physical defects.We investigated the effects of high-pressure treatment on charge carrier transport in PbS colloidal quantum dot (CQD) solids. We applied high pressure to PbS CQD solids using nitrogen gas to reduce the inter-dot distance. Using this simple process, we obtained conductive PbS CQD solids. Terahertz time-domain spectroscopy was used to study charge carrier transport as a function of pressure. We found that the minimum pressure needed to increase the dielectric constant, conductivity, and carrier mobility was 4 MPa. All properties dramatically improved at 5 MPa; for example, the mobility increased from 0.13 cm2 V-1 s-1 at 0.1 MPa to 0.91 cm2 V-1 s-1 at 5 MPa. We propose this simple process as a nondestructive approach for making conductive PbS CQD solids that are free of chemical and physical defects. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr03641c

Heo, Seung Jin; Yoon, Seokhyun; Oh, Sang Hoon; Yoon, Doo Hyun; Kim, Hyun Jae

2013-12-01

18

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

PubMed

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

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

2015-01-01

19

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

PubMed Central

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

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

2015-01-01

20

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

SciTech Connect

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

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

2014-09-15

21

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

22

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

SciTech Connect

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

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

2014-10-21

23

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

24

Electric field dependence of charge-carrier hopping transport at large carrier concentrations in disordered organic solids: Meyer-Neldel and Gill energies  

NASA Astrophysics Data System (ADS)

Effective medium approach has been extended to describe the temperature dependent hopping charge-carrier mobility at arbitrary electric fields in the large carrier density transport regime. We take into account the spatial energy correlations in organic materials with Gaussian disorder. The theory is applied to describe recent experimental measurements of the electron transport properties in a C60-based OFET for different lateral electric fields FDS. Since this model is not limited to zero-field mobility, it allows a more accurate evaluation of important material parameters from experimental data measured at a given electric field. The shift of the Meyer-Neldel energy EMN upon applied lateral electric field FDS and the Gill energy EG upon the gate voltage VG in an OFET is shown to be a consequence of the spatial energy correlation effects in the organic semiconductor film. We showed that both the Meyer-Neldel and Gill energies can be used for estimating the width of the Gaussian density-of-states distribution.

Fishchuk, I. I.; Kadashchuk, A.; Ullah, Mujeeb; Sitter, H.; Sariciftci, N. S.; Bässler, H.

2012-07-01

25

Charge carrier transport mechanisms in perovskite CdTiO3 fibers  

NASA Astrophysics Data System (ADS)

Electrical transport properties of electrospun cadmium titanate (CdTiO3) fibers have been investigated using ac and dc measurements. Air annealing of as spun fibers at 1000 °C yielded the single phase perovskite fibers having diameter ˜600 nm - 800 nm. Both the ac and dc electrical measurements were carried out at temperatures from 200 K - 420 K. The complex impedance plane plots revealed a single semicircular arc which indicates the interfacial effect due to grain boundaries of fibers. The dielectric properties obey the Maxwell-Wagner theory of interfacial polarization. In dc transport study at low voltages, data show Ohmic like behavior followed by space charge limited current (SCLC) with traps at higher voltages at all temperatures (200 K - 420 K). Trap density in our fibers system is Nt = 6.27 × 1017 /cm3. Conduction mechanism in the sample is governed by 3-D variable range hopping (VRH) from 200 K - 300 K. The localized density of states were found to be N(EF) = 5.51 × 1021 eV-1 cm-3 at 2 V. Other VRH parameters such as hopping distance (Rhop) and hopping energy (Whop) were also calculated. In the high temperature range of 320 K - 420 K, conductivity follows the Arrhenius law. The activation energy found at 2 V is 0.10 eV. Temperature dependent and higher values of dielectric constant make the perovskite CdTiO3 fibers efficient material for capacitive energy storage devices.

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

2014-06-01

26

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

SciTech Connect

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

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

2014-06-15

27

Perforating gun charge carrier improvements  

SciTech Connect

This patent describes a perforating gun for perforating a casing located downhole in a cased borehole, the gun having a housing, shaped charges in the housing spaced from one another and connected to a detonation means, each shaped charge having a flange means on one end of a body portion, the other end of the body portion being the detonator end, the combination with the housing, charges, and detonation means of a charge carrier assembly. The charge carrier assembly comprises charge holders connected together along the longitudinal axis of the gun; each charge holder describes a polyhedron, each polyhedron being described by relatively thin wall surfaces joined together by lateral edges which extend parallel to the axial centerline of the gun and provide opposed fasteners for the shaped charge. Each charge holder has lateral faces, one of the faces is apertured to telescopingly receive a shaped charge therewithin, adjacent charge holders have means for orienting the shaped charges of alternate charge holders in different radial directions; and means for capturing a shaped charge within an aperture of a charge holder. The body portion of the shaped charge is received within the aperture of the charge holder with the flange means of the shaped charge abutting a lateral of the charge holder, and having the opposed fasteners extending towards an opposed fastener located on an alternate charge holder to capture the flange between two opposed fasteners and the lateral face of the charge holder so that the inner detonator end of the charge is positioned near the geometrical center of the charge holder.

Vann, R.R.; Colle, E.A. Jr.

1986-07-08

28

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

E-print Network

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

Sanjeev K. Gupta; Prafulla K. Jha

2009-04-15

29

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

SciTech Connect

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

Han, S.S.

1993-09-01

30

Energytransport models for charge carriers involving impact ionization in semiconductors  

E-print Network

Energy­transport models for charge carriers involving impact ionization in semiconductors Isabelle of conduction electrons and holes in a semiconductor. The charge carriers are assumed to obey a degenerate gas in semiconductors under relatively high electric fields. For example: The order of magnitude is above around 1.5 e

Schmeiser, Christian

31

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

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

32

Charge carrier injection and transport associated with thermally generated cracks in a 6,13-bis(triisopropylsilylethynyl) pentacene thin-film transistor  

NASA Astrophysics Data System (ADS)

We describe how the charge carrier injection and transport are influenced by thermal cracks in a 6,13-bis(triisopropylsilylethynyl) (TIPS) pentacene film in terms of the contact resistance and the channel resistance in a TIPS pentacene thin-film transistor (TFT). Through a post-thermal annealing (PTA) process at a certain temperature T a, the high structural order of TIPS-pentacene molecules is produced without thermal cracks, the carrier mobility of the TIPS pentacene TFT is maximized, and both the contact resistance and the channel resistance are minimized. Our quantitative description of the relationship between the PTA treatment and the interfacial resistance behavior would provide a useful basis for understanding the thermal stability and the electrical performance of a solution-processed organic TFT.

Bae, Jin-Hyuk; Kim, Hyeok; Horowitz, Gilles; Lee, Sin-Doo

2011-09-01

33

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

34

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

PubMed

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

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

2013-08-27

35

Dynamics of spin charge carriers in polyaniline  

NASA Astrophysics Data System (ADS)

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

Krinichnyi, V. I.

2014-06-01

36

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

Code of Federal Regulations, 2011 CFR

...2011-10-01 false Presubscribed interexchange carrier charge (PICC). 69.153 Section 69.153 Telecommunication... COMMON CARRIER SERVICES (CONTINUED) ACCESS CHARGES Computation of Charges for Price Cap Local Exchange Carriers §...

2011-10-01

37

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

...2014-10-01 false Presubscribed interexchange carrier charge (PICC). 69.153 Section 69.153 Telecommunication... COMMON CARRIER SERVICES (CONTINUED) ACCESS CHARGES Computation of Charges for Price Cap Local Exchange Carriers §...

2014-10-01

38

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

Code of Federal Regulations, 2013 CFR

...2013-10-01 false Presubscribed interexchange carrier charge (PICC). 69.153 Section 69.153 Telecommunication... COMMON CARRIER SERVICES (CONTINUED) ACCESS CHARGES Computation of Charges for Price Cap Local Exchange Carriers §...

2013-10-01

39

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

Code of Federal Regulations, 2012 CFR

...2012-10-01 false Presubscribed interexchange carrier charge (PICC). 69.153 Section 69.153 Telecommunication... COMMON CARRIER SERVICES (CONTINUED) ACCESS CHARGES Computation of Charges for Price Cap Local Exchange Carriers §...

2012-10-01

40

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

Code of Federal Regulations, 2010 CFR

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

2010-10-01

41

Charge carrier relaxation model in disordered organic semiconductors  

SciTech Connect

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

Lu, Nianduan; Li, Ling, E-mail: lingli@ime.ac.cn; Sun, Pengxiao; Liu, Ming, E-mail: liuming@ime.ac.cn [Institute of Microelectronics, Chinese Academy of Sciences, Beijing 100029 (China)] [Institute of Microelectronics, Chinese Academy of Sciences, Beijing 100029 (China)

2013-11-15

42

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

PubMed Central

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

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

2013-01-01

43

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

PubMed

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

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

2013-01-01

44

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

45

On the nature of photo charge carriers in ice  

NASA Astrophysics Data System (ADS)

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

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

1994-06-01

46

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

NASA Astrophysics Data System (ADS)

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

Zhang, Teng; Birgersson, Erik; Luther, Joachim

2015-01-01

47

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

PubMed

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

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

2015-01-01

48

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

49

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

PubMed Central

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

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

2014-01-01

50

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

PubMed

We have studied the effect of the spatial distribution of B, N and C domains in 2-dimensional borocarbonitrides and its influence on carrier mobility, based on density functional theory coupled with the Boltzmann transport equation. Two extreme features of C-domains in BN-rich B2.5CN2.5, namely, BCN-I (random) and BCN-II (localized), have been found to exhibit an electron (hole) mobility of ?10(6) cm(2) V(-1) s(-1) (?10(4) cm(2) V(-1) s(-1)) and ?10(3) cm(2) V(-1) s(-1) (?10(6) cm(2) V(-1) s(-1)), respectively. We have ascertained the underlying microscopic mechanisms behind such an extraordinarily large carrier mobility and the reversal of conduction polarity. Finally, we have derived the principle underlying the maximization of mobility and for obtaining a particular (electron/hole) conduction polarity of this nanohybrid in any stoichiometric proportion. PMID:25283315

Banerjee, Swastika; Pati, Swapan K

2014-11-21

51

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

NASA Astrophysics Data System (ADS)

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

Banerjee, Swastika; Pati, Swapan K.

2014-10-01

52

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

DOEpatents

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

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

1987-01-01

53

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

SciTech Connect

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

Zhu, Xiaoyang

2014-12-10

54

Injection of current densities over kA/cm2 in organic thin films and investigation of charge-carrier transport mechanisms in current density region between nA/cm2 and kA/cm2  

NASA Astrophysics Data System (ADS)

We investigate current density-voltage (J-V) characteristics of copper phthalocyanine thin-film devices, with active areas ranging from S = 1,000,000 to 7.9 ?m2, and analyze their charge-carrier transport mechanisms under current densities between nA/cm2 and kA/cm2. We demonstrate injection of 128 kA/cm2 in the smallest device having S = 7.9 ?m2. Furthermore, we find that J-V characteristics are divided into three regions between nA/cm2 and kA/cm2: ohm current, shallow-trap space-charge-limited current (SCLC), and trap-free SCLC. In a shallow-trap SCLC region, we observe a large shift in J-V characteristics depending upon the active areas. From analyses of carrier traps with a thermally stimulated current (TSC) measurement, we see that TSC signal intensities of these films decrease as the active area is reduced. Hence, we conclude that a large shift in J-V characteristics is attributable to the change of carrier trap concentrations in these films.

Matsushima, Toshinori; Adachi, Chihaya

2006-08-01

55

Charge Carrier Transport in LEDs Based on Multiple (Al x Ga1- x )0.5In0.5P/(Al0.54Ga0.46)0.5In0.5P Quantum Wells  

NASA Astrophysics Data System (ADS)

The results of experimental studies of forward current-voltage characteristics of LEDs with an active region consisting of the multiple (Al x Ga1- x )0.5In0.5P/(Al0.54Ga0.46)0.5In0.5P quantum wells are presented. The experiment showed that increasing the number of quantum wells and decreasing the Al content in the Al x Ga1- x solid solution lead to an increase in the forward current at a fixed voltage. An analysis showed that the results obtained can be interpreted using the theory of diffusion charge transport in a double heterostructure with a narrow-bandgap layer, the thickness of which is many times larger than the thickness of a single quantum well. The proposed approach takes into account the carrier transport by tunneling through the barriers in an active region with multiple quantum wells.

Prudaev, I. A.; Oleinik, V. L.; Romanov, I. S.; Brudnyi, V. N.; Ryaboshtan, Yu. L.; Gorlachuk, P. V.; Marmalyuk, A. A.

2014-11-01

56

Low-field carrier transport properties in biased bilayer graphene  

NASA Astrophysics Data System (ADS)

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

Hu, Bo

2014-07-01

57

Extended Hydrodynamical Model of Carrier Transport in Semiconductors  

E-print Network

Extended Hydrodynamical Model of Carrier Transport in Semiconductors Angelo Marcello Anile \\Lambda title: Extended Hydrodynamical Model in Semiconductors Abstract A hydrodynamical model based on the theory of Extended Thermo­ dynamics is presented for carrier transport in semiconductors. Closure

Russo, Giovanni

58

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

Code of Federal Regulations, 2011 CFR

...2011-10-01 false Per-minute carrier common line charge. 69.154 Section 69.154 Telecommunication... COMMON CARRIER SERVICES (CONTINUED) ACCESS CHARGES Computation of Charges for Price Cap Local Exchange Carriers §...

2011-10-01

59

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

...2014-10-01 false Per-minute carrier common line charge. 69.154 Section 69.154 Telecommunication... COMMON CARRIER SERVICES (CONTINUED) ACCESS CHARGES Computation of Charges for Price Cap Local Exchange Carriers §...

2014-10-01

60

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

Code of Federal Regulations, 2012 CFR

...2012-10-01 false Per-minute carrier common line charge. 69.154 Section 69.154 Telecommunication... COMMON CARRIER SERVICES (CONTINUED) ACCESS CHARGES Computation of Charges for Price Cap Local Exchange Carriers §...

2012-10-01

61

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

Code of Federal Regulations, 2013 CFR

...2013-10-01 false Per-minute carrier common line charge. 69.154 Section 69.154 Telecommunication... COMMON CARRIER SERVICES (CONTINUED) ACCESS CHARGES Computation of Charges for Price Cap Local Exchange Carriers §...

2013-10-01

62

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

63

Anisotropic charged impurity-limited carrier mobility in monolayer phosphorene  

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

64

Carrier and spin dynamics in charged quantum dots  

Microsoft Academic Search

Carrier and spin dynamics are measured in meutral, positively and negatively charged quantum dots using polarization-sensitive time-resolved photoluminescence. Carrier capture rates are observed to be strongly enhanced in charged quantum dots, suggesting that electron-hole scattering dominates this process. For positive quantum dots, the enhanced spin-polarized electron capture rate eliminates loss of electron spin information in the GaAs barriers prior to

Kimberley C. Hall; Kenan Gundogdu; Thomas F. Boggess; Oleg B. Shchekin; Dennis G. Deppe

2004-01-01

65

Modeling Carrier Behavior in Sequential Auction Transportation Markets  

E-print Network

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

Bertini, Robert L.

66

Resolving the ultrafast dynamics of charge carriers in nanocomposites  

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

67

Conformation sensitive charge transport in conjugated polymers  

SciTech Connect

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

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

2013-11-18

68

Nanoscale Charge Transport in Excitonic Solar Cells  

SciTech Connect

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

Venkat Bommisetty, South Dakota State University

2011-06-23

69

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

70

Self-trapped states of charge carriers in magnetic semiconductors  

Microsoft Academic Search

A review is given of theoretical results on self-trapped states of charge carriers in magnetic semiconductors and their experimental confirmation. The main emphasis is laid on ferrons (magnetic polarons) in antiferromagnetic semiconductors, though other magnetic materials are considered, too (ferromagnets, singlet magnets, solid helium, spin glasses and so on). Both single- and many-electron ferron states are discussed. In the latter

E. L. Nagaev

1992-01-01

71

Hydrodynamic model for charge carriers involving strong ionization in semiconductors  

E-print Network

Hydrodynamic model for charge carriers involving strong ionization in semiconductors Isabelle modeling strong ionization in semiconductors is formally derived from a kinetic framework. To that purpose equations for strong ionization di#11;ers from the usual hydrodynamic system for semiconductors, which

Schmeiser, Christian

72

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

PubMed Central

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

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

2013-01-01

73

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

E-print Network

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

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

2005-01-01

74

Band filling with free charge carriers in organometal halide perovskites  

NASA Astrophysics Data System (ADS)

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

Manser, Joseph S.; Kamat, Prashant V.

2014-09-01

75

Giant Reduction of Charge Carrier Mobility in Strained Graphene  

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

76

Energy Carrier Transport In Surface-Modified Carbon Nanotubes  

E-print Network

of organic molecules or inorganic nanoparticles, debundling of nanotubes by dispersing agents, and microwave irradiation. Because carbon nanotubes have unique carrier transport characteristics along a sheet of graphite in a cylindrical shape, the properties...

Ryu, Yeontack

2012-11-30

77

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

78

Imaging ultrafast carrier transport in nanoscale devices using femtosecond photocurrent microscopy  

E-print Network

One-dimensional nanoscale devices, such as semiconductor nanowires (NWs) and single- walled carbon nanotubes (SWNTs), have been intensively investigated because of their potential application of future high-speed electronic, optoelectronic, and sensing devices. To overcome current limitations on the speed of contemporary devices, investigation of charge carrier dynamics with an ultrashort time scale is one of the primary steps necessary for developing high-speed devices. In the present study, we visualize ultrafast carrier dynamics in nanoscale devices using a combination of scanning photocurrent microscopy and time- resolved pump-probe techniques. We investigate transit times of carriers that are generated near one metallic electrode and subsequently transported toward the opposite electrode based on drift and diffusion motions. Carrier dynamics have been measured for various working conditions. In particular, the carrier velocities extracted from transit times increase for a larger negative gate bias, becau...

Son, B H; Hong, J T; Park, Ji-Yong; Lee, Soonil; Ahn, Y H

2014-01-01

79

Transport and Structure of Charge Density Waves  

NASA Astrophysics Data System (ADS)

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

Dicarlo, David Anthony

80

Bipolar carrier transport in a conjugated polymer by complex admittance spectroscopy  

NASA Astrophysics Data System (ADS)

We report the bipolar transport properties of the LUMATION™ (Sumitomo Chemical) 1300 Series green-emitting polymer investigated by means of admittance spectroscopy. Analysis of the inductive response in single-carrier polymer diodes yields electron and hole mobilities which are in excellent agreement with the results of independent measurements. Admittance measurements in dual injection diodes, in combination with the analysis of current-voltage characteristics, provide evidence that the dual injection diodes operate in space-charge-limited regime, indicative of strong recombination within the material. Our results provide strong evidence that the space-charge-related admittance response of dual-carrier diodes is dominated by combined electron-hole response, which corresponds to the sum of electron and hole mobilities. This implies that electron and hole mobilities cannot be obtained separately from admittance measurements in space-charge-limited dual-carrier devices.

Poplavskyy, Dmitry; So, Franky

2006-02-01

81

Exceptional charge transport properties of graphene on germanium.  

PubMed

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

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

2014-10-28

82

Mechanisms of Carrier Transport Induced by a Microswimmer Bath.  

PubMed

Recently, it was found that a wedgelike microparticle (referred to as "carrier") which is only allowed to translate but not to rotate exhibits a directed translational motion along the wedge cusp if it is exposed to a bath of microswimmers. Here we model this effect in detail by resolving the microswimmers explicitly using interaction models with different degrees of mutual alignment. Using computer simulations we study the impact of these interactions on the transport efficiency of a V-shaped carrier. We show that the transport mechanisms itself strongly depends on the degree of alignment embodied in the modelling of the individual swimmer dynamics. For weak alignment, optimal carrier transport occurs in the turbulent microswimmer state and is induced by swirl depletion inside the carrier. For strong aligning interactions, optimal transport occurs already in the dilute regime and is mediated by a polar cloud of swimmers in the carrier wake pushing the wedge-particle forward. We also demonstrate that the optimal shape of the carrier leading to maximal transport speed depends on the kind of interaction model used. PMID:25347885

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

2014-10-20

83

Mechanisms of carrier transport induced by a microswimmer bath  

E-print Network

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

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

2014-08-08

84

Minority and majority carrier transport characterization in compound semiconductors  

SciTech Connect

A review of minority and majority carrier transport characterization techniques is presented. Minority transport is discussed in the context of base transport in HBTs where the base transit time can be an important component of the total transit time through the transistor. Characterization techniques to measure minority carrier mobilities in heavily-doped compound semiconductors and theoretical results are reviewed. Majority carrier transport in high-performance PHEMT structures is discussed. Parallel conduction of the heavily-doped contact layer and the 2-D electron gas makes measurements of the 2-D electron concentration difficult. Techniques to measure the 2-D concentration are reviewed. Recent application of these techniques have yielded new data for GaAs that has important implications for device design and shows the need for measurements of other CS-materials and devices to realize accurate device design and optimization.

Lovejoy, M.L.

1995-05-01

85

Charge transport in nanoscale junctions.  

PubMed

Understanding the fundamentals of nanoscale charge transfer is pivotal for designing future nano-electronic devices. Such devices could be based on individual or groups of molecular bridges, nanotubes, nanoparticles, biomolecules and other 'active' components, mimicking wire, diode and transistor functions. These have operated in various environments including vacuum, air and condensed matter, in two- or three-electrode configurations, at ultra-low and room temperatures. Interest in charge transport in ultra-small device components has a long history and can be dated back to Aviram and Ratner's letter in 1974 (Chem. Phys. Lett. 29 277-83). So why is there a necessity for a special issue on this subject? The area has reached some degree of maturity, and even subtle geometric effects in the nanojunction and noise features can now be resolved and rationalized based on existing theoretical concepts. One purpose of this special issue is thus to showcase various aspects of nanoscale and single-molecule charge transport from experimental and theoretical perspectives. The main principles have 'crystallized' in our minds, but there is still a long way to go before true single-molecule electronics can be implemented. Major obstacles include the stability of electronic nanojunctions, reliable operation at room temperature, speed of operation and, last but not least, integration into large networks. A gradual transition from traditional silicon-based electronics to devices involving a single (or a few) molecule(s) therefore appears to be more viable from technologic and economic perspectives than a 'quantum leap'. As research in this area progresses, new applications emerge, e.g. with a view to characterizing interfacial charge transfer at the single-molecule level in general. For example, electrochemical experiments with individual enzyme molecules demonstrate that catalytic processes can be studied with nanometre resolution, offering a route towards optimizing biosensors at the molecular level. Nanoscale charge transport experiments in ionic liquids extend the field to high temperatures and to systems with intriguing interfacial potential distributions. Other directions may include dye-sensitized solar cells, new sensor applications and diagnostic tools for the study of surface-bound single molecules. Another motivation for this special issue is thus to highlight activities across different research communities with nanoscale charge transport as a common denominator. This special issue gathers 27 articles by scientists from the United States, Germany, the UK, Denmark, Russia, France, Israel, Canada, Australia, Sweden, Switzerland, the Netherlands, Belgium and Singapore; it gives us a flavour of the current state-of-the-art of this diverse research area. While based on contributions from many renowned groups and institutions, it obviously cannot claim to represent all groups active in this very broad area. Moreover, a number of world-leading groups were unable to take part in this project within the allocated time limit. Nevertheless, we regard the current selection of papers to be representative enough for the reader to draw their own conclusions about the current status of the field. Each paper is original and has its own merit, as all papers in Journal of Physics: Condensed Matter special issues are subjected to the same scrutiny as regular contributions. The Guest Editors have deliberately not defined the specific subjects covered in this issue. These came out logically from the development of this area, for example: 'Traditional' solid state nanojunctions based on adsorbed layers, oxide films or nanowires sandwiched between two electrodes: effects of molecular structure (aromaticity, anchoring groups), symmetry, orientation, dynamics (noise patterns) and current-induced heating. Various 'physical effects': inelastic tunnelling and Coulomb blockade, polaron effects, switching modes, and negative differential resistance; the role of many particle excitations, new surface states in semiconductor electrodes, various mechanisms for

Albrecht, Tim; Kornyshev, Alexei; Bjørnholm, Thomas

2008-09-01

86

Magnetic pairing of charge carriers in doped Mott insulators  

SciTech Connect

The recent discovery of superconductivity in certain CuO{sub 2}-based layered perovskites with transition temperatures (T{sub c} {approximately} 30-125 K) spanning the boiling point of liquid nitrogen (77 K) has been one of the greatest surprises of the physics and chemistry of the transition metal oxides. There are now compelling reasons to believe that the possibly unconventional (non-BCS) superconductivity, the high transition temperatures, and almost certainly the highly anomalous normal-state properties of these layered oxides derive essentially from the strong electron-electron repulsion (correlation) and the low dimensionality found in these systems. In fact, these systems are best viewed as doped Mott insulators in the proximity of the (antiferromagnetic) insulator to (paramagnetic) metal transition. Presented here is a very specific (magnetic) mechanism for singlet pairing of charge carriers doped into the Mott insulators. The mechanism involves an intrinsically strong interaction of the charge carriers with the spin configurations of the antiferromagnetically (AF) correlated background.

Kumar, N. (Indian Institute of Science, and Jawaharalal Nehru Centre for Advanced Scientific Research, Bangalore (India))

1990-09-01

87

Charge transport in lightly reduced graphene oxide: A transport energy perspective  

NASA Astrophysics Data System (ADS)

Significant variation in the charge transport behaviour in graphene oxide (GO) ranging from Schottky to Poole-Frenkel and to space charge limited transport exists. These have been extensively reported in the literature. However, the validity of such conventional charge transport models meant for delocalized carriers, to study charge transport through localised states in GO, a disordered semiconductor is open to question. In this work, we use the concept of transport energy (TE) to model charge transport in lightly reduced GO (RGO) and demonstrate that the TE calculations match well with temperature dependent experimental I-V data on RGO. We report on a temperature dependent TE ranging from a few 10 meV to 0.1 eV in slightly reduced GO. Last, we point out that, despite the success of several delocalised charge transport models in estimating barrier heights that resemble the TE level, they remain largely accidental and lack the insight in which the TE concept provides in understanding charge transport in RGO.

Kajen, R. S.; Chandrasekhar, N.; Pey, K. L.; Vijila, C.; Jaiswal, M.; Saravanan, S.; Ng, Andrew M. H.; Wong, C. P.; Loh, K. P.

2013-02-01

88

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

89

Imaging ultrafast carrier transport in nanoscale field-effect transistors.  

PubMed

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

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

2014-11-25

90

Mapping Charge-Carrier Density Across the p-n Junction in Ambipolar Carbon-Nanotube Networks by Raman Microscopy.  

PubMed

In situ confocal Raman microscopy is used to map the recombination zone (induced p-n junction) in an ambipolar carbon-nanotube-network transistor with high spatial resolution. The shift of the 2D mode (G' mode) depending on hole and electron accumulation serves as a measure for the local charge-carrier density and provides complementary information about charge transport and recombination in ambipolar transistors. PMID:25338783

Grimm, Stefan B; Jakubka, Florian; Schießl, Stefan P; Gannott, Florentina; Zaumseil, Jana

2014-12-01

91

Transport of elliptic intense charged -particle beams  

E-print Network

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

Zhou, J. (Jing), 1978-

2006-01-01

92

Microscopic Simulations of Charge Transport in Disordered Organic Semiconductors  

PubMed Central

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

2011-01-01

93

Ultrafast and spatially resolved studies of charge carriers in atomically thin molybdenum disulfide  

NASA Astrophysics Data System (ADS)

Atomically thin molybdenum disulfide is emerging as a new nanomaterial with potential applications in the fields of electronic and photonics. Charge carrier dynamics plays an essential role in determining its electronic and optical properties. We report spatially and temporally resolved pump-probe studies of charge carriers in atomically thin molybdenum disulfide samples fabricated by mechanical exfoliation. Carriers are injected by interband absorption of a 390-nm pump pulse and detected by measuring differential reflection of a time-delayed and spatially scanned probe pulse that is tuned to an exciton transition. Several parameters on charge carrier dynamics are deduced, including carrier lifetime, diffusion coefficient, diffusion length, and mobility.

Wang, Rui; Ruzicka, Brian A.; Kumar, Nardeep; Bellus, Matthew Z.; Chiu, Hsin-Ying; Zhao, Hui

2012-07-01

94

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

95

14 CFR 382.19 - May carriers refuse to provide transportation on the basis of disability?  

...false May carriers refuse to provide transportation on the basis of disability? 382...OFFICE OF THE SECRETARY, DEPARTMENT OF TRANSPORTATION (AVIATION PROCEEDINGS) SPECIAL...19 May carriers refuse to provide transportation on the basis of disability?...

2014-01-01

96

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

NASA Astrophysics Data System (ADS)

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

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

2011-07-01

97

Layered distribution of charge carriers in organic thin film transistors.  

PubMed

Drain-source current in organic thin-film transistors has been monitored in situ and in real time during the deposition of pentacene. The current starts to flow when percolation of the first monolayer (ML) occurs and, depending on the deposition rate, saturates at a coverage in the range 2-7 MLs. The number of active layers contributing to the current and the spatial distribution of charge carriers are modulated by the growth mode. The thickness of the accumulation layer, represented by an effective Debye length, scales as the morphological correlation length. These results show that the effective Debye length is not just a material parameter, but depends on the multiscale morphology. Earlier controversial results can be unified within this framework. PMID:20867320

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

2010-06-18

98

Pulse radiolysis studies on charge carriers in conjugated polymers  

NASA Astrophysics Data System (ADS)

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 assigned to the positive one-electron charge state (positive polaron) of MEH-PPV. The slow absorption decay is unaffected by oxygen. Negative charge states (negative polarons), with absorptions around 1.4 eV, are produced upon pulse radiolysis of MEH-PPV in argon-saturated solutions in tetrahydrofuran (THF) or benzonitrile. A small solvatochromic shift is observed. In contrast to the behavior of the positive polaron, the MEH-PPV negative charge carriers decay fairly rapidly, and are readily quenched by molecular oxygen. Previous results on chemically produced positive and negative charge states of conjugated polymers and oligomers are discussed on the basis of these assignments, and comparison is made with theoretical calculations. Using benzophenone as a charge scavenger, pulse radiolysis of formic acid is shown to generate one-electron reducing species. Various derivatives of PPY, including a regioregular polymer (rPPY) and a hexyl substituted compound (HPPY) have been studied by pulse radiolysis in formic acid solution. With rPPY, new absorptions are observed at 2.59 and 1.40 eV, and are assigned to the one-electron reduced species. These are strongly quenched by molecular oxygen. With HPPY, the lower energy transition is broadened to give a maximum below 1.21 eV and a shoulder at 1.65 eV. The differences between rPPY and HPPY are interpreted on the basis of differences in the rigidity of the polymer. The relevance of these assignments to the identification of charged species in photoinduced absorption measurements is indicated.

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

2000-02-01

99

Field dependent and disorder-induced nonlinear charge transport in electrochemically doped polypyrrole devices  

NASA Astrophysics Data System (ADS)

Electric field activated charge transport is studied in the metal/polymer/metal device structure of electropolymerized polypyrrole down to 10?K with varying carrier density and disorder. Disorder induced nonlinear behaviour is observed in polypyrrole devices grown at room temperature which is correlated to delocalization of states. The slope parameter of current–voltage characteristics (in log–log scale) increases as the temperature decreases, which indicates the onset of stronger field dependence. The field dependence of mobility becomes dominant as the carrier density decreases. The sharp dip in differential conductance indicates the localization of carriers at low temperatures which reduces the effective number of carriers involved in the transport.

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

2014-12-01

100

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

101

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

PubMed Central

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

Steiner, Gerhard; Reischl, Georg P.

2012-01-01

102

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

SciTech Connect

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

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

2013-09-28

103

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

Federal Register 2010, 2011, 2012, 2013

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

2010-04-09

104

Bridging carrier transport and amorphous dynamics in phase change materials  

Microsoft Academic Search

Physics of amorphous chalcogenides sets the scaling potentials of PCM elements and their perspectives in multi-bit storage. Carrier transport, threshold switching, structural relaxation and crystallization processes have key importance from the application standpoint. They also represent peculiar effects which have always attracted interest and speculations by decades. The paper reviews experimental and modeling analysis of threshold voltage and resistance transients

Andrea L. Lacaita; Daniele Ielmini

105

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

ERIC Educational Resources Information Center

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

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

106

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

Code of Federal Regulations, 2010 CFR

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

2010-07-01

107

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

Code of Federal Regulations, 2011 CFR

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

2011-07-01

108

Carrier transport, polarization matching, and efficiency droop in GaN-based visible LEDs  

NASA Astrophysics Data System (ADS)

Transport of electrons and holes in GaInN/GaN LEDs is known to be largely asymmetric, due to differences in carrier mobility and the ionization energy for donors and acceptors. Sheet charges at heterointerfaces of devices grown in the c-direction, which arise due to mismatch in spontaneous and piezoelectric polarization, further hinder transport by increasing barriers for carrier injection into quantum wells. The effect of these sheet charges upon capture of carriers by quantum wells is analyzed with a quantum-mechanical calculation of the dwell time of electrons and holes over quantum wells. Wavefunctions and dwell times are calculated using the k.p quantum transmitting boundary method with the wurtzite 8-band Hamiltonian with Burt-Foreman operator ordering. The effect of quantum well width upon dwell time is also considered. It is shown that both reduction of sheet charges by polarization matching and the increase of well width result in substantially longer dwell times, and therefore higher probability of capture. Experimental results of LEDs with polarization-matched active regions are presented. Such LEDs are shown to have improved efficiency throughout the entire range of forward currents. This indicates that a reduction in carrier density is not solely responsible for the improved efficiency, since reduced carrier density would also lead to a higher Shockley-Reed-Hall rate at low currents. The implications of this result are discussed in detail. Further, experimental results of LEDs with varying doping in the active region are presented. It is shown that a reduction in doping -- which has the effect of slowing electron transport -- results in an increase in efficiency at large forward currents. This result is explained in detail using modeling results.

Schubert, Martin

2010-03-01

109

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

110

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

Code of Federal Regulations, 2013 CFR

... 2013-07-01 2013-07-01 false Delivery âto carriers for transportation to market...ACT General Scope of Agriculture Specified Delivery Operations § 780.155 Delivery “to carriers for transportation to...

2013-07-01

111

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

... 2014-07-01 2014-07-01 false Delivery âto carriers for transportation to market...ACT General Scope of Agriculture Specified Delivery Operations § 780.155 Delivery “to carriers for transportation to...

2014-07-01

112

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

Code of Federal Regulations, 2012 CFR

... 2012-07-01 2012-07-01 false Delivery âto carriers for transportation to market...ACT General Scope of Agriculture Specified Delivery Operations § 780.155 Delivery “to carriers for transportation to...

2012-07-01

113

Role of Molecular Charge in Nucleocytoplasmic Transport  

PubMed Central

Transport of genetic materials and proteins between the nucleus and cytoplasm of eukaryotic cells is mediated by nuclear pore complexes (NPCs). A selective barrier formed by phenylalanine-glycine (FG) nucleoporins (Nups) with net positive charges in the NPC allows for passive diffusion of signal-independent small molecules and transport-receptor facilitated translocation of signal-dependent cargo molecules. Recently, negative surface charge was postulated to be another essential criterion for selective passage through the NPC. However, the charge-driven mechanism in determining the transport kinetics and spatial transport route for either passive diffusion or facilitated translocation remains obscure. Here we employed high-speed single-molecule fluorescence microscopy with an unprecedented spatiotemporal resolution of 9 nm and 400 µs to uncover these mechanistic fundamentals for nuclear transport of charged substrates through native NPCs. We found that electrostatic interaction between negative surface charges on transiting molecules and the positively charged FG Nups, although enhancing their probability of binding to the NPC, never plays a dominant role in determining their nuclear transport mode or spatial transport route. A 3D reconstruction of transport routes revealed that small signal-dependent endogenous cargo protein constructs with high positive surface charges that are destined to the nucleus, rather than repelled from the NPC as suggested in previous models, passively diffused through an axial central channel of the NPC in the absence of transport receptors. Finally, we postulated a comprehensive map of interactions between transiting molecules and FG Nups during nucleocytoplasmic transport by combining the effects of molecular size, signal and surface charge. PMID:24558427

Goryaynov, Alexander; Yang, Weidong

2014-01-01

114

Electric Properties of Obsidian: Evidence for Positive Hole Charge Carriers  

NASA Astrophysics Data System (ADS)

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

Nordvik, R.; Freund, F. T.

2012-12-01

115

Life Time of Charge Carriers in Double Walled Carbon Nanotubes.  

NASA Astrophysics Data System (ADS)

We investigate the nature of low-energy excitations in double walled carbon nanotubes, DWNT, by pumping the states using fs IR pulses. The temporal evolution of the population is examined by ionizing the resulting population with delayed fs UV pulses. The electron time of flight of the ionized electrons is recorded for a range of energies above EF to investigate the relaxation dynamics of the charge carriers. The initial, fast relaxation is attributed to the internal thermalization of the electronic system, and is primarily driven by electron-electron (e-e) scattering processes. After the system returns to a Fermi-Dirac distribution it continues to decay with a slower rate associated with electron gas cooling electron-phonon (e-ph) interactions. We specifically want to see if the (e-e) scattering in DWNT follow a Fermi-liquid behavior, as observed in our previous study of MWNT^1. 1. Zamkov, M.; Woody, N.; Shan, B.; Chang, Z.; Richard, P. Phys. Rev. Lett. 2005, 94, 056803.

Chatzakis, Ioannis; Habib, Arifa; Zamkov, Mikhail; Lithvinuk, Igor; Richard, Patrick

2006-05-01

116

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

117

A Framework for the study of Carrier Strategies in an Auction Based Transportation Marketplace  

E-print Network

A Framework for the study of Carrier Strategies in an Auction Based Transportation Marketplace of Carrier Strategies in an Auction Based Transportation Marketplace Miguel A. Figliozzi, Hani S. Mahmassani for the study of carriers' strategies in a transportation auction marketplace is provided. The unique

118

The SLC10 carrier family: transport functions and molecular structure.  

PubMed

The SLC10 family represents seven genes containing 1-12 exons that encode proteins in humans with sequence lengths of 348-477 amino acids. Although termed solute carriers (SLCs), only three out of seven (i.e. SLC10A1, SLC10A2, and SLC10A6) show sodium-dependent uptake of organic substrates across the cell membrane. These include the uptake of bile salts, sulfated steroids, sulfated thyroidal hormones, and certain statin drugs by SLC10A1 (Na(+)-taurocholate cotransporting polypeptide (NTCP)), the uptake of bile salts by SLC10A2 (apical sodium-dependent bile acid transporter (ASBT)), and uptake of sulfated steroids and sulfated taurolithocholate by SLC10A6 (sodium-dependent organic anion transporter (SOAT)). The other members of the family are orphan carriers not all localized in the cell membrane. The name "bile acid transporter family" arose because the first two SLC10 members (NTCP and ASBT) are carriers for bile salts that establish their enterohepatic circulation. In recent years, information has been obtained on their 2D and 3D membrane topology, structure-transport relationships, and on the ligand and sodium-binding sites. For SLC10A2, the putative 3D morphology was deduced from the crystal structure of a bacterial SLC10A2 analog, ASBT(NM). This information was used in this chapter to calculate the putative 3D structure of NTCP. This review provides first an introduction to recent knowledge about bile acid synthesis and newly found bile acid hormonal functions, and then describes step-by-step each individual member of the family in terms of expression, localization, substrate pattern, as well as protein topology with emphasis on the three functional SLC10 carrier members. PMID:23177985

Döring, Barbara; Lütteke, Thomas; Geyer, Joachim; Petzinger, Ernst

2012-01-01

119

Molecular modeling and ligand docking for Solute Carrier (SLC) transporters  

PubMed Central

Solute Carrier (SLC) transporters are membrane proteins that transport solutes, such as ions, metabolites, peptides, and drugs, across biological membranes, using diverse energy coupling mechanisms. In human, there are 386 SLC transporters, many of which contribute to the absorption, distribution, metabolism, and excretion of drugs and/or can be targeted directly by therapeutics. Recent atomic structures of SLC transporters determined by X-ray crystallography and NMR spectroscopy have significantly expanded the applicability of structure-based prediction of SLC transporter ligands, by enabling both comparative modeling of additional SLC transporters and virtual screening of small molecules libraries against experimental structures as well as comparative models. In this review, we begin by describing computational tools, including sequence analysis, comparative modeling, and virtual screening, that are used to predict the structures and functions of membrane proteins such as SLC transporters. We then illustrate the applications of these tools to predicting ligand specificities of select SLC transporters, followed by experimental validation using uptake kinetic measurements and other assays. We conclude by discussing future directions in the discovery of the SLC transporter ligands. PMID:23578028

Schlessinger, Avner; Khuri, Natalia; Giacomini, Kathleen M.; Sali, Andrej

2014-01-01

120

Selective inhibition of human solute carrier transporters by multikinase inhibitors.  

PubMed

Solute carrier (SLC) transporters regulate the cellular influx and disposition of endogenous and xenobiotic compounds, including anticancer agents such as the multikinase inhibitors (MKIs). Recent evidence suggests that MKIs may also inhibit SLC-dependent transport of coadministered drugs, although present information on the relative susceptibilities of multiple SLC transporters is limited. This study evaluated 18 MKI drugs and metabolites as inhibitors of prototypic substrate uptake by 13 SLC transporters that were overexpressed in human embryonic kidney cells. Organic anion transporting polypeptides (OATPs) 1A2, 1B3, and 2B1, organic anion transporter 3 (OAT3), and organic cation transporter 1 (OCT1) were inhibited by most MKIs, whereas substrate uptake by OATP1B1, OAT1, 2, and 4, OCT2 and 3, and organic zwitterion/cation transporter 1 (OCTN1) was less susceptible to inhibition; OCTN2 was also inhibited by cediranib. In further studies, IC50 values were determined for the most effective MKIs, and erlotinib and cediranib were found to be potent competitive inhibitors of OATP2B1 (Ki = 41 nM) and OATP1A2 (Ki = 33 nM), respectively. From predictive approaches, several MKI-SLC interactions were found to be of potential in vivo significance. PMID:25165131

Johnston, Rosie A; Rawling, Tristan; Chan, Ting; Zhou, Fanfan; Murray, Michael

2014-11-01

121

34 nm Charge Transport through DNA  

NASA Astrophysics Data System (ADS)

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

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

2011-03-01

122

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

123

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

124

Spin relaxation in materials lacking coherent charge transport  

NASA Astrophysics Data System (ADS)

We describe a broadly applicable theory of spin relaxation in materials with incoherent charge transport; examples include amorphous inorganic semiconductors, organic semiconductors, quantum dot arrays, and systems displaying trap-controlled transport or transport within an impurity band. The theory can incorporate many different relaxation mechanisms, so long as electron-electron correlations can be neglected. We focus primarily on spin relaxation caused by spin-orbit effects, which manifest through inhomogeneities in the g factor and non-spin-conserving carrier hops, scattering, trapping, or detrapping. Analytic and numerical results from the theory are compared in various regimes with Monte Carlo simulations. Our results should assist in evaluating the suitability of various disordered materials for spintronic devices.

Harmon, N. J.; Flatté, M. E.

2014-09-01

125

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

126

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

127

Impedance spectroscopy of organic hetero-layer OLEDs as a probe for charge carrier injection and device degradation  

NASA Astrophysics Data System (ADS)

Impedance spectroscopy (IS) is a powerful method for characterizing the electrical properties of materials and their interfaces. In this study we use IS to investigate the charge carrier injection properties of different anodes and anode treatments in bottom-emitting organic light-emitting diodes (OLEDs). These are ITO-based (indium tin oxide) hetero-layer devices with TPD (N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4-diamine) as hole transporting layer (HTL) and Alq3 (tris-(8-hydroxyquinoline) aluminum) as emission and electron transporting layer (EML and ETL, respectively). A detailed analysis of the capacitance as function of frequency and DC bias yields information about trapped and interfacial charges as well as the dynamics of injected charges. Furthermore, we use IS to study degradation processes in OLEDs.

Nowy, Stefan; Ren, Wei; Wagner, Julia; Weber, Josef A.; Brütting, Wolfgang

2009-08-01

128

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

NASA Astrophysics Data System (ADS)

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

Brédas, Jean-Luc

2007-03-01

129

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

SciTech Connect

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

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

1997-08-01

130

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

Code of Federal Regulations, 2012 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...

2012-01-01

131

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

132

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

Code of Federal Regulations, 2011 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...

2011-01-01

133

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

...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...

2014-01-01

134

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

135

Non-ohmic behavior of carrier transport in highly disordered graphene  

NASA Astrophysics Data System (ADS)

We report measurements of disordered graphene probed by both a high electric field and a high magnetic field. By applying a high source-drain voltage, Vsd, we are able to study the current-voltage relation I-Vsd of our device. With increasing Vsd, a crossover from the linear I-Vsd regime to the non-linear one, and eventually to activationless-hopping transport occurs. In the activationless-hopping regime, the importance of Coulomb interactions between charged carriers is demonstrated. Moreover, we show that delocalization of carriers which are strongly localized at low T and at small Vsd occurs in the presence of high electric field and perpendicular magnetic field.

Lo, Shun-Tsung; Chuang, Chiashain; Puddy, R. K.; Chen, T.-M.; Smith, C. G.; Liang, C.-T.

2013-04-01

136

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

137

Charge transport characteristics of a high-mobility diketopyrrolopyrrole-based polymer.  

PubMed

In this study, we attempt to unveil the charge-transport abnormality of the widely studied diketopyrrolopyrrole (DPP)-based polymers with exceptionally high charge carrier mobility [>5 cm(2) V(-1) s(-1)]. Based on the electric field and temperature dependence of the charge-transport characteristics of the field effect transistor (FET) geometry of one of the highly conductive DPP derivatives, namely, (poly[2,5-bis(7-decylnonadecyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-(E)-(1,2-bis(5-(thiophen-2-yl)selenophen-2-yl)ethene) (PDPPDTSE), we show that the high gate-source bias drew the carriers closer to the interface of the semiconductor/dielectric layers where the density of state (DOS) of the charge carrier is significantly broader than the bulk. We argue that the intrinsically narrow DOS in the PDPPDTSE bulk resulted in significantly different charge-transport behavior between the semiconductor bulk and the semiconductor/dielectric interface, which was not visible in the other low-mobility organic semiconductors that contain intrinsically high density of trap states in their bulk. To avoid these charge transport abnormalities, we try to operate the FETs under low gate bias without compromising the accumulated charge carrier density. By carefully employing a thin metal oxide covered with a self-assembled monolayer (SAM) as a dielectric layer, we can demonstrate low-voltage PDPPDTSE FETs with near-ideal performance both in terms of hysteresis-free operation and operating reliability while maintaining a high charge carrier mobility of ~2.8 cm(2) V(-1) s(-1). PMID:23907664

Chung, Dae Sung; Kang, Il; Kim, Yun-Hi; Kwon, Soon-Ki

2013-09-21

138

Kinetics of manganese transport and gene expressions of manganese transport carriers in Caco-2 cell monolayers.  

PubMed

Two experiments were conducted to investigate the kinetics of manganese (Mn) transport in Caco-2 cell monolayers and the gene expressions of Mn transport carriers in apical (AP) and basolateral (BL) membranes. In experiment 1, the cells were treated with the medium containing 146 ?mol/L of Mn (MnSO4·H2O). Both the uptake and transport of Mn from AP-BL or from BL-AP at different time-points were assessed to determine the optimal time for kinetics of Mn transport. The transport of Mn increased linearly with higher efficiency values in AP-BL than in BL-AP direction, however, the uptake of Mn revealed an asymptotic pattern within 120 min. In experiment 2, the kinetics of Mn transport in AP-BL was determined with media containing Mn concentrations from 0 to 2,500 ?mol/L at 40 and 120 min, respectively, and mRNA levels of divalent metal transporter 1 (DMT1) and ferroportin (FPN1) were determined in Caco-2 cells treated with the medium containing 0 or 800 ?mol/L of Mn for 120 min. The kinetics of Mn transport showed a carrier-mediated process when Mn concentrations were lower than 1,000 ?mol/L and a linear increment when Mn concentrations exceeded 1,000 ?mol/L at either 40 or 120 min. Mn treatment decreased (P < 0.01) DMT1 mRNA level and increased (P < 0.01) FPN1 mRNA level. The results from the present study suggested that Mn transport in AP-BL fit both carrier-mediated saturable and non-saturable diffusion processes, and Mn transport carriers DMT1 and FPN1 mediate the apical uptake and basolateral exit of Mn in Caco-2 cells. PMID:23996061

Li, Xiaoli; Xie, Jingjing; Lu, Lin; Zhang, Liyang; Zhang, Lingyan; Zou, Yaxue; Wang, Qiuyue; Luo, Xugang; Li, Sufen

2013-12-01

139

Carrier transport properties of nanocrystalline Er3N@C80  

NASA Astrophysics Data System (ADS)

Electrical transport properties of the nanocrystalline Er3N@C80 with fcc crystal structure were characterized by measuring both temperature-dependent d.c. conductance and a.c. impedance. The results showed that the Er3N@C80 sample has characteristics of n-type semiconductor and an electron affinity larger than work function of gold metal. The Er3N@C80/Au interface has an ohmic contact behavior and the contact resistance was very small as compared with bulk resistance of the Er3N@C80 sample. The charge carriers in the sample were thermally excited from various trapped levels and both acoustic phonon and ionic scatterings become a dominant process in different temperature regions, respectively. At temperatures below 250 K, the activation energy of the trapped carrier was estimated to be 35.5 meV, and the ionic scattering was a dominant mechanism. On the other hand, at temperatures above 350 K, the activation energy was reduced to 15.9 meV, and the acoustic phonon scattering was a dominant mechanism. In addition, a polarization effect from the charge carrier was observed at low frequencies below 2.0 MHz, and the relative intrinsic permittivity of the Er3N@C80 nanocrystalline lattice was estimated to be 4.6 at frequency of 5.0 MHz.

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

2014-07-01

140

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

E-print Network

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

Johan F. Prins

2006-07-25

141

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

142

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

PubMed Central

Thermoelectric transport in semiconductors is usually considered under small thermal gradients and when it is dominated by the role of the majority carriers. Not much is known about effects that arise under the large thermal gradients that can be established in high-temperature, small-scale electronic devices. Here, we report a surprisingly large asymmetry in self-heating of symmetric highly doped silicon microwires with the hottest region shifted along the direction of minority carrier flow. We show that at sufficiently high temperatures and strong thermal gradients (~1?K/nm), energy transport by generation, transport and recombination of minority carriers along these structures becomes very significant and overcomes convective energy transport by majority carriers in the opposite direction. These results are important for high-temperature nanoelectronics such as emerging phase-change memory devices which also employ highly doped semiconducting materials and in which local temperatures reach ~1000?K and thermal gradients reach ~10–100?K/nm. PMID:24056703

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

2013-01-01

143

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

2013-01-01

144

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

145

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

146

Barrier-confinement-controlled carrier transport into quantum wires  

NASA Astrophysics Data System (ADS)

By using subpicosecond laser light pulses with a polarization perpendicular to deep etched In0.53Ga0.47As/InP quantum wires, initial spatial electron-hole distributions have been prepared that are predominantly located in the unpatterned InP buffer layer. Under these excitation conditions the photoluminescence rise time increases significantly with decreasing wire width from about 25 ps for a two-dimensional unetched reference structure to about 150 ps for 34-nm-wide wires. Temperature-dependent studies of the rise times indicate the existence of an effective barrier in the InP regions of the quantum wires. From detailed calculations of the electronic states, which extend from the unpatterned InP buffer into the quantum wires, we show that confinement effects in the InP barriers control the carrier transport from the buffer into the In0.53Ga0.47As wire.

Kieseling, F.; Braun, W.; Wang, K. H.; Forchel, A.; Knipp, P. A.; Reinecke, T. L.; Pagnod-Rossiaux, Ph.; Goldstein, L.

1995-10-01

147

Stochastic modeling of molecular charge transport networks  

NASA Astrophysics Data System (ADS)

We develop a stochastic network model for charge transport simulations in amorphous organic semiconductors, which generalizes the correlated Gaussian disorder model to realistic morphologies, charge transfer rates, and site energies. The network model includes an iterative dominance-competition model for positioning vertices (hopping sites) in space, distance-dependent distributions for the vertex connectivity and electronic coupling elements, and a moving-average procedure for assigning spatially correlated site energies. The field dependence of the hole mobility of the amorphous organic semiconductor, tris-(8-hydroxyquinoline)aluminum, which was calculated using the stochastic network model, showed good quantitative agreement with the prediction based on a microscopic approach.

Baumeier, Björn; Stenzel, Ole; Poelking, Carl; Andrienko, Denis; Schmidt, Volker

2012-11-01

148

Electron transport model of dielectric charging  

NASA Technical Reports Server (NTRS)

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

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

1979-01-01

149

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

150

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

NASA Astrophysics Data System (ADS)

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

Luo, Yan-Xiang; Shih, Chun-Hsing

2014-11-01

151

Variational multiscale models for charge transport  

PubMed Central

This work presents a few variational multiscale models for charge transport in complex physical, chemical and biological systems and engineering devices, such as fuel cells, solar cells, battery cells, nanofluidics, transistors and ion channels. An essential ingredient of the present models, introduced in an earlier paper (Bulletin of Mathematical Biology, 72, 1562-1622, 2010), is the use of differential geometry theory of surfaces as a natural means to geometrically separate the macroscopic domain from the microscopic domain, meanwhile, dynamically couple discrete and continuum descriptions. Our main strategy is to construct the total energy functional of a charge transport system to encompass the polar and nonpolar free energies of solvation, and chemical potential related energy. By using the Euler-Lagrange variation, coupled Laplace-Beltrami and Poisson-Nernst-Planck (LB-PNP) equations are derived. The solution of the LB-PNP equations leads to the minimization of the total free energy, and explicit profiles of electrostatic potential and densities of charge species. To further reduce the computational complexity, the Boltzmann distribution obtained from the Poisson-Boltzmann (PB) equation is utilized to represent the densities of certain charge species so as to avoid the computationally expensive solution of some Nernst-Planck (NP) equations. Consequently, the coupled Laplace-Beltrami and Poisson-Boltzmann-Nernst-Planck (LB-PBNP) equations are proposed for charge transport in heterogeneous systems. A major emphasis of the present formulation is the consistency between equilibrium LB-PB theory and non-equilibrium LB-PNP theory at equilibrium. Another major emphasis is the capability of the reduced LB-PBNP model to fully recover the prediction of the LB-PNP model at non-equilibrium settings. To account for the fluid impact on the charge transport, we derive coupled Laplace-Beltrami, Poisson-Nernst-Planck and Navier-Stokes equations from the variational principle for chemo-electro-fluid systems. A number of computational algorithms is developed to implement the proposed new variational multiscale models in an efficient manner. A set of ten protein molecules and a realistic ion channel, Gramicidin A, are employed to confirm the consistency and verify the capability. Extensive numerical experiment is designed to validate the proposed variational multiscale models. A good quantitative agreement between our model prediction and the experimental measurement of current-voltage curves is observed for the Gramicidin A channel transport. This paper also provides a brief review of the field. PMID:23172978

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

2012-01-01

152

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

NASA Astrophysics Data System (ADS)

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 induced by the Poisson effect, and be suppressed by compressive axial strain. Similar carrier separations are found in IIB-sulfides. This intrinsic charge separation and tensile strain induced enhancement are expected to shed light on solar cell designs.

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

2010-08-01

153

Hydrodynamical Model for Charge Transport in Graphene  

NASA Astrophysics Data System (ADS)

A hydrodynamical model for simulating charge transport in graphene is formulated by using of the maximum entropy principle. Both electrons in the conduction band and holes in the valence band are considered and it is assumed a linear dispersion relation for the energy bands around the equivalent Dirac points. The closure relations do not contain any fitting parameters except the ones already present in the kinetic description.

Camiola, V. D.; Romano, V.

2014-12-01

154

Particle Transport through Hydrogels Is Charge Asymmetric.  

PubMed

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

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

2015-02-01

155

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

E-print Network

Carrier Transport and Related Effects in Detectors of the Cryogenic Dark Matter Search by Kyle Effects in Detectors of the Cryogenic Dark Matter Search Copyright 2012 by Kyle Michael Sundqvist #12;1 Abstract Carrier Transport and Related Effects in Detectors of the Cryogenic Dark Matter Search by Kyle

California at Berkeley, University of

156

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

Microsoft Academic Search

Members of the mitochondrial carrier family have been reported in eukaryotes only, where they transport metabolites and cofactors across the mitochondrial inner membrane to link the metabolic pathways of the cytosol and the matrix. The genome of the giant virus Mimiviridae mimivirus encodes a member of the mitochondrial carrier family of transport proteins. This viral protein has been expressed in

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

2007-01-01

157

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

158

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 Dapp = 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

2012-04-24

159

Measuring Charge Transport in a Thin Solid Film Using Charge Sensing  

E-print Network

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 ...

MacLean, Kenneth

160

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

161

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

162

Polyamine transport is mediated by both endocytic and solute carrier transport mechanisms in the gastrointestinal tract.  

PubMed

The polyamines spermidine and spermine, and their precursor putrescine, are required for cell growth and cellular functions. The high levels of tissue polyamines are implicated in carcinogenesis. The major sources of exogenous polyamines are diet and intestinal luminal bacteria in gastrointestinal (GI) tissues. Both endocytic and solute carrier-dependent mechanisms have been described for polyamine uptake. Knocking down of caveolin-1 protein increased polyamine uptake in colon cancer-derived HCT116 cells. Dietary supplied putrescine was accumulated in GI tissues and liver in caveolin-1 knockout mice more than wild-type mice. Knocking out of nitric oxide synthase (NOS2), which has been implicated in the release of exogenous polyamines from internalized vesicles, abolished the accumulation of dietary putrescine in GI tissues. Under conditions of reduced endogenous tissue putrescine contents, caused by treatment with the polyamine synthesis inhibitor difluoromethylornithine (DFMO), small intestinal and colonic mucosal polyamine contents increased with dietary putrescine levels, even in mice lacking NOS2. Knocking down the solute carrier transporter SLC3A2 in HCT116-derived Hkh2 cells reduced the accumulation of exogenous putrescine and total polyamine contents in DFMO treated cells, relative to non-DFMO-treated cells. These data demonstrate that exogenous putrescine is transported into GI tissues by caveolin-1- and NOS2-dependent mechanisms, but that the solute carrier transporter SLC3A2 can function bidirectionally to import putrescine under conditions of low tissue polyamines. PMID:20522643

Uemura, Takeshi; Stringer, David E; Blohm-Mangone, Karen A; Gerner, Eugene W

2010-08-01

163

Analysis of facilitated transport in polymeric membrane with fixed site carrier 2. Series RC circuit model  

Microsoft Academic Search

A new mathematical model for facilitated mass transport in a polymeric membrane with a fixed-site carrier was developed by extending the single RC circuit model, which was derived by assuming concentration fluctuation and analogy between electron transport in a parallel resistor-capacitor (RC) circuit and mass transport in a facilitated transport membrane. Here, a series of parallel RC circuits was employed

Jae-Min Hong; Yong Soo Kang; Jyongsik Jang; Un Young Kim

1996-01-01

164

Effective masses of charge carriers in selected symmorphic and nonsymmorphic carbon nanotubes  

Microsoft Academic Search

We performed ab initio, self-consistent calculations for the electronic structure of selected semiconducting carbon nanotubes in the symmorphic and nonsymmorphic groups. We employed a real space approach in the linear combination of atomic orbital formalism. We utilized a nonlocal density-functional potential in the generalized gradient approximation. We present the electronic structure and effective masses of charge carriers in symmorphic nanotubes

G. L. Zhao; D. Bagayoko; L. Yang

2004-01-01

165

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

Code of Federal Regulations, 2010 CFR

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

2010-07-01

166

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

Code of Federal Regulations, 2011 CFR

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

2011-07-01

167

Single charge carrier type sensing with a parallel strip pseudo-Frisch-grid CdZnTe semiconductor radiation detector  

E-print Network

Single charge carrier type sensing with a parallel strip pseudo-Frisch-grid CdZnTe semiconductor CdZnTe semiconductor detector that incorporates a parallel strip pseudo-Frisch-grid detector design produced by the moving free charge carriers can be measured by an external circuit. Shockley1 and Ramo2

He, Zhong

168

Hydration water, charge transport and protein dynamics.  

PubMed

The hydration water of proteins is essential to biological activity but its properties are not yet fully understood. A recent study of dielectric relaxation of hydrated proteins [A. Levstik et al., Phys. Rev E.60 7604 (1999)] has found a behavior typical of a proton glass, with a glass transition of about 268 K. In order to analyze these results, we investigate the statistical mechanics and dynamics of a model of `two-dimensional water' which describes the hydrogen bonding scheme of bounded water molecules. We discuss the connection between the dynamics of bound water and charge transport on the protein surface as observed in the dielectric measurements. PMID:23345745

Peyrard, M

2001-06-01

169

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

NASA Astrophysics Data System (ADS)

The recent tremendous boost in the number and diversity of applications for light-emitting diodes (LEDs) indicates the emergence of the next-generation lighting and illumination technology. The rapidly improving LED technology is becoming increasingly viable especially for high-power applications. However, the greatest roadblock before finally breaching the main defensive position of conventional fluorescent and incandescent lamps still remains: GaN-based LEDs encounter a significant decrease in efficiency as the drive current increases, and this phenomenon is known as the efficiency droop. This dissertation focuses on uncovering the physical cause of efficiency droop in GaN-based LEDs and looks for solutions to it. GaN-based multiple-quantum-well (MQW) LEDs usually have abnormally high diode-ideality factors. Investigating the origin of the high diode-ideality factors could help to better understand the carrier transport in the LED MQW active region. We investigate the ideality factors of GaInN LEDs with different numbers of doped quantum barriers (QBs). Consistent with the theory, a decrease of the ideality factor as well as a reduction in forward voltage is found with increasing number of doped QBs. Experimental and simulation results indicate that the band profiles of QBs in the active region have a significant impact on the carrier transport mechanism, and the unipolar heterojunctions inside the active region play an important role in determining the diode-ideality factor. This dissertation will discuss several mechanisms leading to electron leakage which could be responsible for the efficiency droop. We show that the inefficient electron capture, the electron-attracting properties of polarized EBL, the inherent asymmetry in electron and hole transport and the inefficient EBL p-doping at high Al contents severely limit the ability to confine electrons to the MQWs. We demonstrate GaInN LEDs employing tailored Si doping in the QBs with strongly enhanced high-current efficiency and reduced efficiency droop. Compared with 4-QB-doped LEDs, 1-QB-doped LEDs show a 37.5% increase in light-output power at high currents. Consistent with the measurements, simulation shows a shift of radiative recombination among the MQWs and a reduced electron leakage current into the p-type GaN when fewer QBs are doped. The results can be attributed to a more symmetric carrier transport and uniform carrier distribution which help to reduce electron leakage and thus reduce the efficiency droop. In this dissertation, artificial evolution is introduced to the LED optimization process which combines a genetic algorithm (GA) and device-simulation software. We show that this approach is capable of generating novel concepts in designing and optimizing LED devices. Application of the GA to the QB-doping in the MQWs yields optimized structures which is consistent with the tailored QB doping experiments. Application of the GA to the EBL region suggests a novel structure with an inverted sheet charge at the spacer-EBL interface. The resulting repulsion of electrons can significantly reduce electron leakage and enhance the efficiency. Finally, dual-wavelength LEDs, which have two types of quantum wells (QWs) emitting at two different wavelengths, are experimentally characterized and compared with numerical simulations. These dual-wavelength LEDs allow us to determine which QW emits most of the light. An experimental observation and a quantitative analysis of the radiative recombination shift within the MQW active region are obtained. In addition, an injection-current dependence of the radiative recombination shift is predicted by numerical simulations and indeed observed in dual-wavelength LEDs. This injection-current dependence of the radiative recombination distribution can be explained very well by incorporating quantum-mechanical tunneling of carriers into and through the QBs into to the classical drift-diffusion model. In summary, using the LEDs with tailored QB doping and dual-wavelength LEDs, we investigate the origin of the high diode-ideality fa

Zhu, Di

2011-12-01

170

49 CFR 377.209 - Additional charges.  

Code of Federal Regulations, 2011 CFR

... 2011-10-01 false Additional charges. 377.209 Section 377.209 Transportation...REGULATIONS PAYMENT OF TRANSPORTATION CHARGES Extension of Credit to Shippers by...Forwarders § 377.209 Additional charges. When a carrier— (a) Has...

2011-10-01

171

49 CFR 377.209 - Additional charges.  

Code of Federal Regulations, 2012 CFR

... 2012-10-01 false Additional charges. 377.209 Section 377.209 Transportation...REGULATIONS PAYMENT OF TRANSPORTATION CHARGES Extension of Credit to Shippers by...Forwarders § 377.209 Additional charges. When a carrier— (a) Has...

2012-10-01

172

49 CFR 377.209 - Additional charges.  

Code of Federal Regulations, 2013 CFR

... 2013-10-01 false Additional charges. 377.209 Section 377.209 Transportation...REGULATIONS PAYMENT OF TRANSPORTATION CHARGES Extension of Credit to Shippers by...Forwarders § 377.209 Additional charges. When a carrier— (a) Has...

2013-10-01

173

49 CFR 377.209 - Additional charges.  

Code of Federal Regulations, 2010 CFR

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

2010-10-01

174

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

NASA Astrophysics Data System (ADS)

The utilization of electron-hole pairs (EHPs) generated from multiple excitons in quantum dots (QDs) is of great interest toward efficient photovoltaic devices and other optoelectronic devices; however, extraction of charge carriers remains difficult. Herein, we extract photocharges from Ag2S QDs and investigate the dependence of the electric field on the extraction of charges from multiple exciton generation (MEG). Low toxic Ag2S QDs are directly grown on TiO2 mesoporous substrates by employing the successive ionic layer adsorption and reaction (SILAR) method. The contact between QDs is important for the initial charge separation after MEG and for the carrier transport, and the space between neighbor QDs decreases with more SILAR cycles, resulting in better charge extraction. At the optimal electric field for extraction of photocharges, the results suggest that the threshold energy (h?th) for MEG is 2.41Eg. The results reveal that Ag2S QD is a promising material for efficient extraction of charges from MEG and that QDs prepared by SILAR have an advantageous electrical contact facilitating charge separation and extraction.The utilization of electron-hole pairs (EHPs) generated from multiple excitons in quantum dots (QDs) is of great interest toward efficient photovoltaic devices and other optoelectronic devices; however, extraction of charge carriers remains difficult. Herein, we extract photocharges from Ag2S QDs and investigate the dependence of the electric field on the extraction of charges from multiple exciton generation (MEG). Low toxic Ag2S QDs are directly grown on TiO2 mesoporous substrates by employing the successive ionic layer adsorption and reaction (SILAR) method. The contact between QDs is important for the initial charge separation after MEG and for the carrier transport, and the space between neighbor QDs decreases with more SILAR cycles, resulting in better charge extraction. At the optimal electric field for extraction of photocharges, the results suggest that the threshold energy (h?th) for MEG is 2.41Eg. The results reveal that Ag2S QD is a promising material for efficient extraction of charges from MEG and that QDs prepared by SILAR have an advantageous electrical contact facilitating charge separation and extraction. Electronic supplementary information (ESI) available: Experimental details, XRD analysis, EDX analysis, PIA spectra, J-V curves, differential resistance and static resistance, photon energy dependent carrier extraction measurement. See DOI: 10.1039/c4nr04463k

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

2015-01-01

175

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

NASA Astrophysics Data System (ADS)

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

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

2015-02-01

176

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

177

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

Microsoft Academic Search

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

Chun Chen; Tso-Ping Ma

1998-01-01

178

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

2009-12-01

179

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

E-print Network

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

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

2007-09-25

180

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

NASA Astrophysics Data System (ADS)

Semiconductor nanoparticles are tiny crystalline structures (typically range from 1 - 100 nm) whose shape in many cases can be dictated through tailored chemical synthesis with atomic scale precision. The small size of these nanoparticles often results in quantum confinement (spatial confinement of wave functions), which imparts the ability to manipulate band-gap energies thus allowing them to be optimally engineered for different applications (i.e., photovoltaics, photocatalysis, imaging). However, charge carriers excited within these nanoparticles are often involved in many different processes: trapping, trap migration, Auger recombination, non-radiative relaxation, radiative relaxation, oxidation / reduction, or multiple exciton generation. Broadband ultrafast transient absorption laser spectroscopy is used to spectrally resolve the fate of excited charge carriers in both wavelength and time, providing insight as to what synthetic developments or operating conditions will be necessary to optimize their efficiency for certain applications. This thesis outlines the effort of resolving the dynamics of excited charge carriers for several Cd and Si based nanoparticle systems using this experimental technique. The thesis is organized into five chapters and two appendices as indicated below. Chapter 1 provides a brief introduction to the photophysics of semiconductor nanoparticles. It begins by defining what nanoparticles, semiconductors, charge carriers, and quantum confinement are. From there it details how the study of charge carrier dynamics within nanoparticles can lead to increased efficiency in applications such as photocatalysis. Finally, the experimental methodology associated with ultrafast transient absorption spectroscopy is introduced and its power in mapping charge carrier dynamics is established. Chapter 2 (JPCC, 19647, 2011) introduces the first of the studied samples: water-solubilized 2D CdSe nanoribbons (NRs), which were synthesized in the Osterloh laboratory (UCD). The measured signals were decomposed into the constituent dynamics of three transient populations: hot tightly bound excitons, relaxed tightly bound excitons, and separated trapped carriers (holes and electrons). The influenes of three external factors affecting the observed dynamics were explored: (1) excitation wavelength, (2) excitation fluence, and (3) presence of the hole scavenger HS -. Both higher-energy excitation photons and higher-intensity excitation induce slower relaxation of charge carriers to the band edge due to the need to dissipate excess excitation energy. Nonlinear decay kinetics of the relaxed exciton population is observed and demonstrated to arise from bimolecular trapping of excitons with low-density trap sites located at CdSe NR surface sites instead of the commonly resolved multiparticle Auger recombination mechanism. This is supported by the observed linear excitation-fluence dependence of the trapped-carrier population that is n umerically simulated and found to deviate from the excitation fluence dependence expected of Auger recombination kinetics. Introducing hole scavenging HS- has a negligible effect on the exciton kinetics, including migration and dissociation, and instead passivates surface trap states to induce the rapid elimination of holes after exciton dissociation. This increases the lifetime of the reactive electron population and increases measured photocatalytic H2 generation activity. A broad (200 nm) and persistent (20 ps) stimulated emission observed in the tightly bound excitons suggests their potential use as broadband microlasers. In chapter 3 (JPCL, 2688, 2011), the photocatalytic H2O splitting activities of CdSe and CdSe/CdS core/shell quantum dots, which were also synthesized in the Osterloh laboratory (UCD) are contrasted. CdSe/CdS core/shell quantum dots constructed from 4.0 nm CdSe quantum dots are shown to be strongly active for visible-light-driven photocatalytic H2 evolution in 0.1M Na 2S/Na2SO3 solution with a turnover number of 9.94 after 5 h at 103.9 ?mol/h. CdSe quantum dots themselv

Thibert, Arthur Joseph, III

181

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

PubMed

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

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

2014-08-01

182

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

2013-10-21

183

Model ab initio study of excess charge carrier solvation on conjugated carbon chains  

NASA Astrophysics Data System (ADS)

When an excess charge carrier (electron or hole) is added to a semiconducting polymer chain, it is well known that the carrier may self-trap into a polaronic state accompanied by a bond length adjustment pattern. A different mechanism of self-localization is the solvation of charge carriers expected to take place when the polymer chain is immersed in polar media such as common solvents. We use density-functional computations in conjunction with the Polarizable Continuum Model to unequivocally demonstrate solvation-induced self-consistent charge localization into large-radius one-dimensional (1D) polarons on long CNH2 carbon chains with the polyynic structure. Within the computational framework used, the solvation results in a much more pronounced charge localization. When the lattice is allowed to relax, even larger degrees of charge localization are expected to occur. Our systematic study at various levels of ab initio theory investigates this conjecture. In all cases, solvation indeed increases charge localization however, within the framework of Hartree-Fock method we observe charge localization in the vacuum environment in the absence of lattice relaxation. In some of the cases, counterintuitively, lattice relaxation leads to slightly smaller degrees of localization in both HF and BHandHLYP methods. The ground state of odd-N polyynic oligomers C NH2 features kink-solitons in carbon-carbon bond-length alternation (BLA) patterns. We perform a systematic first-principles computational study of neutral and singly-charged kinks in long oligomers addressing relationships between BLA patterns, electron energy gaps, and accompanying distributions of spin and charge densities, both in vacuum and in the screening solvent environment. A quantitative comparison is made of the results derived with four different ab initio methods: from pure DFT to pure Hartree-Fock (HF) and including two popular hybrid density functionals, B3LYP and BHandHLYP. A clear correlation is demonstrated between the derived spatial extent of kinks and the amount of HF exchange used in the functionals. For charged kinks, we find a substantial difference in the behavior of charge and spin densities. We believe this work to be of relevance for various 1D semiconductors in polar environments.

Mayo, Michael Lynn

184

Printing technique dependent charge carrier velocity distribution in organic thin film transistors  

NASA Astrophysics Data System (ADS)

In this study we investigated the influence of the deposition technique on the surface topology and the resulting device performance in organic thin film transistors (OTFT). We varied the parameters of flexographic and gravure printing for the organic semiconductor (OSC) and did multilayer gravure printing for the dielectric, respectively. Therefore, we manufactured transistors in bottom contact top gate architecture and compared them to spin coated samples. As investigation tool for OTFTs, the charge carrier velocity distribution is correlated with the optical characteristics of the printed layers. We found a dependency of the printing technique on the surface topology of the semiconductor and, due to the resulting increase of the channel length, a broadening of the charge carrier velocity distribution. For the dielectric we found a dependency on the layer thickness which seems to be independent from the deposition technique.

Ganz, Simone; Pankalla, Sebastian; Sauer, Hans Martin; Glesner, Manfred; Doersam, Edgar

2013-09-01

185

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

186

Charge carrier mobility in organic molecular materials probed by electromagnetic waves.  

PubMed

Charge carrier mobility is an essential parameter providing control over the performance of semiconductor devices fabricated using a variety of organic molecular materials. Recent design strategies toward molecular materials have been directed at the substitution of amorphous silicon-based semiconductors; accordingly, numerous measurement techniques have been designed and developed to probe the electronic conducting nature of organic materials bearing extremely wide structural variations in comparison with inorganic and/or metal-oxide semiconductor materials. The present perspective highlights the evaluation methodologies of charge carrier mobility in organic materials, as well as the merits and demerits of techniques examining the feasibility of organic molecules, crystals, and supramolecular assemblies in semiconductor applications. Beyond the simple substitution of amorphous silicon, we have attempted to address in this perspective the systematic use of measurement techniques for future development of organic molecular semiconductors. PMID:24776977

Seki, Shu; Saeki, Akinori; Sakurai, Tsuneaki; Sakamaki, Daisuke

2014-06-21

187

Auger Recombination and Charge-Carrier Thermalization in Hg-n-Cluster Photoelectron Studies  

Microsoft Academic Search

Photoelectron spectra (PES) of Hg-n show strong dependence of spectral features on photon energy, i.e., peak tailing and band gap filling. This dependence suggests the existence of complex photoinduced processes in parallel with the direct photodetachment process. The ``corrupted'' PES, taken with intermediate photon energy, carry the signature of interband absorption followed by charge-carrier thermalization and Auger electron ejection in

R. Busani; R. Giniger; T. Hippler; O. Cheshnovsky

2003-01-01

188

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

SciTech Connect

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

Belyakov, V. A., E-mail: dragon_bel@mail.ru; Konakov, A. A.; Burdov, V. A. [Nizhni Novgorod State University (Russian Federation)

2010-11-15

189

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

PubMed

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

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

2013-01-01

190

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. PMID:23409243

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

2013-01-01

191

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

PubMed Central

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

2014-01-01

192

Statics and dynamics of electroactuation with single-charge-carrier ionomers.  

PubMed

A simple theory of electromechanical transduction for single-charge-carrier double-layer electroactuators is developed, in which the ion distribution and curvature are mutually coupled. The obtained expressions for the dependence of the curvature and charge accumulation on the applied voltage, as well as the electroactuation dynamics, are compared with literature data. The mechanical or sensor performance of such electroactuators appears to be determined by just three cumulative parameters, with all of their constituents measurable, permitting a scaling approach to their design. PMID:23364047

Lee, Alpha A; Colby, Ralph H; Kornyshev, Alexei A

2013-02-27

193

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

Code of Federal Regulations, 2010 CFR

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

2010-07-01

194

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

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

2011-07-01

195

Charge-carrier transport in amorphous organic semiconductors  

E-print Network

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

Limketkai, Benjie, 1982-

2008-01-01

196

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

E-print Network

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

Difley, Seth

2010-01-01

197

Hot carrier diffusion in graphene  

E-print Network

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

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

2010-11-01

198

Comparison between charge and spin transport in few-layer graphene  

NASA Astrophysics Data System (ADS)

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

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

2011-03-01

199

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

NASA Astrophysics Data System (ADS)

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

Freund, F.

2013-12-01

200

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

NASA Astrophysics Data System (ADS)

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

Biswas, Swarup; Dutta, Bula; Bhattacharya, Subhratanu

2014-02-01

201

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

202

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

Federal Register 2010, 2011, 2012, 2013

...of ``animal'' to include all cats and dogs transported by the carrier, regardless of whether the cat or dog is transported as a pet by its owner or...the loss, injury, or death of cats and dogs that occur while they are traveling in...

2012-06-29

203

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

PubMed

Herein, we analyze charge carrier mobility and morphology of the active blend layer in thin film organic solar cells and correlate them with device parameters. A low band gap donor-acceptor copolymer in combination with phenyl-C61-butyric acid methyl ester (PCBM) or two bis-adduct fullerenes, bis-PCBM and bis-o-quino-dimethane C60 (bis-oQDMC), is investigated. We study the charge transport of polymer:fullerene blends in hole- and electron-only devices using the space-charge limited current method. Lower electron mobilities are observed in both bis-adduct fullerene blends. Hole mobility, however, is decreased only in the blend containing bis-oQDMC. Both bis-adduct fullerene blends show very high open circuit voltage in solar cell devices, but poor photocurrent compared to the standard PCBM blend for an active layer thickness of 200 nm. Therefore, a higher short circuit current is feasible for the polymer:bis-PCBM blend by reducing the active layer thickness in order to compensate for the low electron mobility, which results in a PCE of 4.3%. For the polymer:bis-oQDMC blend, no such improvement is achieved due to an unfavorable morphology in this particular blend system. The results are supported by external quantum efficiency measurements, atomic force microscopy, transmission electron microscopy and UV/vis spectroscopy. Based on these results, the investigations presented herein give a more scientific basis for the optimization of solar cells. PMID:24196215

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

2013-12-01

204

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

SciTech Connect

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

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

2010-06-15

205

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

206

DNA charge transport over 34 nm.  

PubMed

Molecular wires show promise in nanoscale electronics, but the synthesis of uniform, long conductive molecules is a significant challenge. Deoxyribonucleic acid (DNA) of precise length, by contrast, is synthesized easily, but its conductivity over the distances required for nanoscale devices has not been explored. Here we demonstrate DNA charge transport (CT) over 34 nm in 100-mer monolayers on gold. Multiplexed gold electrodes modified with 100-mer DNA yield sizable electrochemical signals from a distal, covalent Nile Blue redox probe. Significant signal attenuation upon incorporation of a single base-pair mismatch demonstrates that CT is DNA-mediated. Efficient cleavage of these 100-mers by a restriction enzyme indicates that the DNA adopts a native conformation accessible to protein binding. Similar electron-transfer rates measured through 100-mer and 17-mer monolayers are consistent with rate-limiting electron tunnelling through the saturated carbon linker. This DNA-mediated CT distance of 34 nm surpasses that of most reports of molecular wires. PMID:21336329

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

2011-03-01

207

DNA charge transport over 34 nm  

NASA Astrophysics Data System (ADS)

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

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

2011-03-01

208

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

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

209

Generating free charges by carrier multiplication in quantum dots for highly efficient photovoltaics.  

PubMed

Conspectus In a conventional photovoltaic device (solar cell or photodiode) photons are absorbed in a bulk semiconductor layer, leading to excitation of an electron from a valence band to a conduction band. Directly after photoexcitation, the hole in the valence band and the electron in the conduction band have excess energy given by the difference between the photon energy and the semiconductor band gap. In a bulk semiconductor, the initially hot charges rapidly lose their excess energy as heat. This heat loss is the main reason that the theoretical efficiency of a conventional solar cell is limited to the Shockley-Queisser limit of ?33%. The efficiency of a photovoltaic device can be increased if the excess energy is utilized to excite additional electrons across the band gap. A sufficiently hot charge can produce an electron-hole pair by Coulomb scattering on a valence electron. This process of carrier multiplication (CM) leads to formation of two or more electron-hole pairs for the absorption of one photon. In bulk semiconductors such as silicon, the energetic threshold for CM is too high to be of practical use. However, CM in nanometer sized semiconductor quantum dots (QDs) offers prospects for exploitation in photovoltaics. CM leads to formation of two or more electron-hole pairs that are initially in close proximity. For photovoltaic applications, these charges must escape from recombination. This Account outlines our recent progress in the generation of free mobile charges that result from CM in QDs. Studies of charge carrier photogeneration and mobility were carried out using (ultrafast) time-resolved laser techniques with optical or ac conductivity detection. We found that charges can be extracted from photoexcited PbS QDs by bringing them into contact with organic electron and hole accepting materials. However, charge localization on the QD produces a strong Coulomb attraction to its counter charge in the organic material. This limits the production of free charges that can contribute to the photocurrent in a device. We show that free mobile charges can be efficiently produced via CM in solids of strongly coupled PbSe QDs. Strong electronic coupling between the QDs resulted in a charge carrier mobility of the order of 1 cm(2) V(-1) s(-1). This mobility is sufficiently high so that virtually all electron-hole pairs escape from recombination. The impact of temperature on the CM efficiency in PbSe QD solids was also studied. We inferred that temperature has no observable effect on the rate of cooling of hot charges nor on the CM rate. We conclude that exploitation of CM requires that charges have sufficiently high mobility to escape from recombination. The contribution of CM to the efficiency of photovoltaic devices can be further enhanced by an increase of the CM efficiency above the energetic threshold of twice the band gap. For large-scale applications in photovoltaic devices, it is important to develop abundant and nontoxic materials that exhibit efficient CM. PMID:25607377

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

2015-02-17

210

Photoconductive transients and one-dimensional charge carrier dynamics in discotic liquid crystals  

NASA Astrophysics Data System (ADS)

Carrier transits and photoconductivity in hexaalkoxytriphenylene- (HAT) based liquid crystals and their binary 1:1 mixtures with hexaalkylphenyltriphenylene (PTP) are analyzed using time-dependent diffusion theory. The HAT6 derivatives, which show the best transits, can be modeled with a homogeneously distributed single-trap model. The transit data for the compound formed by the 1:1 binary mixture of HAT11-PTP9, which exhibits better columnar stability and higher carrier mobility, cannot, however, be explained using homogeneous multiple trapping models alone. The evidence presented in this paper also suggests that the trap-limited carrier relaxation does indeed obey the law of one-dimensional transport, which says that with an electric field, i.e., in the drift-limited regime, carriers take less time to reach the equilibrium values of the diffusivity. This is a particularly exciting result, which directly confirms rigorous theoretical predictions and is consistent with the previously discussed data taken in the crystalline phase of HAT6.

Pecchia, A.; Lozman, O. R.; Movaghar, B.; Boden, N.; Bushby, R. J.; Donovan, K. J.; Kreouzis, T.

2002-03-01

211

Investigating charge transport mechanisms of Schottky barriers with a conducting polymer | inorganic semiconductor interface  

NASA Astrophysics Data System (ADS)

The interface between a poly(pyrrole) | phosphomolybdate hybrid material and the inorganic semiconductor indium phosphide forms a Schottky diode in which the electrical properties can be reversibly tuned by electrochemistry. While the transmission probability for energetic charge carriers at the interface is orders of magnitude smaller than the analogous metal | inorganic semiconductor Schottky diode, the electrical transport across the polymer | semiconductor interface closely follows classic thermionic emission theory. Using these properties as a tool in charge-transport studies at Schottky barriers, experiments were performed to determine how well-defined structural perturbations of the interface influences electrical transport, and how these changes relate to theories of lateral barrier heterogeneities and barrier pinning.

Jones, Frank; Lonergan, Mark

2002-03-01

212

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

PubMed

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

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

2015-01-01

213

Stress Activation and Propagation of Electronic Charge Carriers in Igneous Rocks  

NASA Astrophysics Data System (ADS)

Igneous and high-grade metamorphic rocks in the Earth's crust generate electric currents when subjected to deviatoric stresses. The reason is that these rocks contain dormant electronic charge carriers in the form of peroxy links. Peroxy links are sites in the crystal structures of the constituent minerals where oxygen anions have converted from their common 2- valence state to the 1- valence state, O3X-OO-XO3 with X=Si4+, Al3+ etc. As rocks are stressed and dislocations sweep through the mineral grains, the peroxy links break up, activating electrons and pholes ("phole" is an abbreviation for "positive hole", a defect electron on the oxygen sublattice, chemically O- in a matrix of O2-). The pholes are mobile electronic charge carriers that can spread out of the stressed rock into the surrounding unstressed rock. They travel via energy levels at the upper edge of the valence bands, cross grain boundaries and achieve a phase velocity on the order of 200±50 m/sec, consistent with phonon-assisted electron hopping. Due to mutual repulsion inside the rock volume the pholes spread to the surface, where they build up a positive surface charge. The surface charge can be measured with a non-contact capacitive sensor. If a Cu contact is applied to the surface of the rock, electrons are injected from ground into the rock in response to the evolving positive charge on the rock surface. We modeled surface potentials and burst-like electron injections following low and medium velocity impact experiments, 100 m/sec and 1.5 km/sec respectively.

Ling, J.; Freund, F. T.

2007-12-01

214

User charges in international air transportation  

E-print Network

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

Seagrave, Norman P.

1979-01-01

215

An overview of the bipartition model for charged particle transport  

Microsoft Academic Search

This paper systematically summarizes the progress to date and developments of the bipartition model, including its basic ideas and concepts, main mathematical formulae and numerical methods, and its relevant applications. The model has been extended from a transport theory for electrons in the medium energy range to a unified and accurate transport theory of charged particles, covering ion transport, atomic

Zhengming Luo

1998-01-01

216

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

Code of Federal Regulations, 2013 CFR

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

2013-07-01

217

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

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

2014-07-01

218

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

Code of Federal Regulations, 2012 CFR

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

2012-07-01

219

Transport of Sugars and Amino Acids in the Intestine: Evidence for a Common Carrier  

Microsoft Academic Search

D-Galactose, L-arginine, and their respective actively transported analogs are partially competitive inhibitors of the active transport of neutral amino acids in the small intestine of hamsters. Since the aforesaid classes of compounds are all transported by similar, sodium-ion-dependent mechanisms and elicit countertransport of each other, all may share a common, polyfunctional carrier in which a series of separate binding sites,

Francisco Alvarado

1966-01-01

220

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

PubMed Central

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 2 hours 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

2012-01-01

221

Influence of exciton lifetime on charge carrier dynamics in an organic heterostructure  

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

222

Optical absorption and scattering at one-particle states of charge carriers in semiconductor quantum dots  

SciTech Connect

A theory is developed for the interaction of an electromagnetic field with one-particle quantum-confined states of charge carriers in semiconductor quantum dots. It is shown that the oscillator strengths and dipole moments for the transitions involving one-particle states in quantum dots are rather large, exceeding the corresponding typical parameters of bulk semiconductor materials. In the context of dipole approximation it is established that the large optical absorption cross sections and attenuation coefficients in the quasi-zero-dimensional systems make it possible to use the systems as new efficient absorbing materials.

Pokutnii, S. I. [Mechnikov National University, Center of Science and Education (Ilyichevsk Branch) (Ukraine)], E-mail: univer@ivt.ilyichevsk.odessa.ua

2006-02-15

223

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

PubMed Central

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

2014-01-01

224

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

SciTech Connect

By comparison of transient photoconductivity (TPC) and transient photoinduced absorption (PA) the influence of the density of states in the bandgap on excess charge carrier kinetics is studied for a-Si:H films deposited at different temperatures and for state of the art a-Si:H films in two different states of light soaking. In both series the rising deep defect density leads to an enhancement of electron trapping rather than recombination via deep defects. The samples deposited at temperatures lower than 250 C additionally show a lower effective electron mobility, i.e., a broader conduction band tail.

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

1997-07-01

225

Verification of the dispersive charge transport in a hydrazone:polycarbonate molecularly doped polymer  

NASA Astrophysics Data System (ADS)

We report results of specially planned experiments intended to verify the dispersive character of the charge carrier transport in polycarbonate molecularly doped with hydrazone at 30 wt% loading, using for this purpose samples specifically featuring a well-defined plateau on a linear-linear plot. For this purpose we propose a new variant of the time-of-flight technique which allows easy changing of the generation zone width from about 0.5 µm (surface excitation) through intermediate values to full sample thickness (bulk excitation). To achieve this, we use electron pulses of 3-50 keV energy rather than traditional light pulses provided by lasers. Experimental results corroborated by numerical calculations uniquely prove that carrier transport in this molecularly doped polymer is dispersive, with the dispersion parameter equal to 0.75. Nevertheless, the mobility field dependence follows the famous Poole-Frenkel law.

Tyutnev, Andrey P.; Saenko, Vladimir S.; Pozhidaev, Evgenii D.; Kolesnikov, Vladislav A.

2009-03-01

226

Verification of the dispersive charge transport in a hydrazone:polycarbonate molecularly doped polymer.  

PubMed

We report results of specially planned experiments intended to verify the dispersive character of the charge carrier transport in polycarbonate molecularly doped with hydrazone at 30 wt% loading, using for this purpose samples specifically featuring a well-defined plateau on a linear-linear plot. For this purpose we propose a new variant of the time-of-flight technique which allows easy changing of the generation zone width from about 0.5 µm (surface excitation) through intermediate values to full sample thickness (bulk excitation). To achieve this, we use electron pulses of 3-50 keV energy rather than traditional light pulses provided by lasers. Experimental results corroborated by numerical calculations uniquely prove that carrier transport in this molecularly doped polymer is dispersive, with the dispersion parameter equal to 0.75. Nevertheless, the mobility field dependence follows the famous Poole-Frenkel law. PMID:21693912

Tyutnev, Andrey P; Saenko, Vladimir S; Pozhidaev, Evgenii D; Kolesnikov, Vladislav A

2009-03-18

227

Measurement of carrier transport and recombination parameter in heavily doped silicon  

NASA Technical Reports Server (NTRS)

The minority carrier transport and recombination parameters in heavily doped bulk silicon were measured. Both Si:P and Si:B with bulk dopings from 10 to the 17th and 10 to the 20th power/cu cm were studied. It is shown that three parameters characterize transport in bulk heavily doped Si: the minority carrier lifetime tau, the minority carrier mobility mu, and the equilibrium minority carrier density of n sub 0 and p sub 0 (in p-type and n-type Si respectively.) However, dc current-voltage measurements can never measure all three of these parameters, and some ac or time-transient experiment is required to obtain the values of these parameters as a function of dopant density. Using both dc electrical measurements on bipolar transitors with heavily doped base regions and transients optical measurements on heavily doped bulk and epitaxially grown samples, lifetime, mobility, and bandgap narrowing were measured as a function of both p and n type dopant densities. Best fits of minority carrier mobility, bandgap narrowing and lifetime as a function of doping density (in the heavily doped range) were constructed to allow accurate modeling of minority carrier transport in heavily doped Si.

Swanson, Richard M.

1986-01-01

228

Profiling solute carrier transporters in the human blood-brain barrier.  

PubMed

The neuroprotective function of the blood-brain barrier (BBB) presents a major challenge for drug delivery to the central nervous system (CNS). Critical to this function, BBB membrane transporters include the ATP-binding cassette (ABC) transporters, which limit drug penetration across the BBB, and the less-well-studied solute carrier (SLC) transporters. In this work, expression profiling of 359 SLC transporters, comparative expression analysis with kidney and liver, and immunoassays in brain microvessels (BMVs) identified previously unknown transporters at the human BBB. PMID:24013810

Geier, E G; Chen, E C; Webb, A; Papp, A C; Yee, S W; Sadee, W; Giacomini, K M

2013-12-01

229

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

PubMed

Charge transport in MoS2 in the low carrier density regime is dominated by trap states and band edge disorder. The intrinsic transport properties of MoS2 emerge in the high density regime where conduction occurs via extended states. Here, we investigate the transport properties of mechanically exfoliated mono-, bi-, and trilayer MoS2 sheets over a wide range of carrier densities realized by a combination of ion gel top gate and SiO2 back gate, which allows us to achieve high charge carrier (>10(13)?cm(-2)) densities. We discuss the gating properties of the devices as a function of layer thickness and demonstrate resistivities as low as 1?k? for monolayer and 420 ? for bilayer devices at 10?K. We show that from the capacitive coupling of the two gates, quantum capacitance can be roughly estimated to be on the order of 1??F/cm(2) for all devices studied. The temperature dependence of the carrier mobility in the high density regime indicates that short-range scatterers limit charge transport at low temperatures. PMID:25465059

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

2014-01-01

230

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

PubMed Central

Charge transport in MoS2 in the low carrier density regime is dominated by trap states and band edge disorder. The intrinsic transport properties of MoS2 emerge in the high density regime where conduction occurs via extended states. Here, we investigate the transport properties of mechanically exfoliated mono-, bi-, and trilayer MoS2 sheets over a wide range of carrier densities realized by a combination of ion gel top gate and SiO2 back gate, which allows us to achieve high charge carrier (>1013?cm?2) densities. We discuss the gating properties of the devices as a function of layer thickness and demonstrate resistivities as low as 1?k? for monolayer and 420 ? for bilayer devices at 10?K. We show that from the capacitive coupling of the two gates, quantum capacitance can be roughly estimated to be on the order of 1??F/cm2 for all devices studied. The temperature dependence of the carrier mobility in the high density regime indicates that short-range scatterers limit charge transport at low temperatures. PMID:25465059

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

2014-01-01

231

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

NASA Astrophysics Data System (ADS)

Charge transport in MoS2 in the low carrier density regime is dominated by trap states and band edge disorder. The intrinsic transport properties of MoS2 emerge in the high density regime where conduction occurs via extended states. Here, we investigate the transport properties of mechanically exfoliated mono-, bi-, and trilayer MoS2 sheets over a wide range of carrier densities realized by a combination of ion gel top gate and SiO2 back gate, which allows us to achieve high charge carrier (>1013 cm-2) densities. We discuss the gating properties of the devices as a function of layer thickness and demonstrate resistivities as low as 1 k? for monolayer and 420 ? for bilayer devices at 10 K. We show that from the capacitive coupling of the two gates, quantum capacitance can be roughly estimated to be on the order of 1 ?F/cm2 for all devices studied. The temperature dependence of the carrier mobility in the high density regime indicates that short-range scatterers limit charge transport at low temperatures.

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

2014-12-01

232

Carrier-carrier entanglement and transport resonances in semiconductor quantum dots  

E-print Network

We study theoretically the entanglement created in a scattering between an electron, incoming from a source lead, and another electron bound in the ground state of a quantum dot, connected to two leads. We analyze the role played by the different kinds of resonances in the transmission spectra and by the number of scattering channels, into the amount of quantum correlations between the two identical carriers. It is shown that the entanglement between their energy states is not sensitive to the presence of Breit-Wigner resonances, while it presents a peculiar behavior in correspondence of Fano peaks: two close maxima separated by a minimum, for a two-channel scattering, a single maximum for a multi-channel scattering. Such a behavior is ascribed to the different mechanisms characterizing the two types of resonances. Our results suggest that the production and detection of entanglement in quantum dot structures may be controlled by the manipulation of Fano resonances through external fields.

Buscemi, Fabrizio; Bertoni, Andrea

2007-01-01

233

Carrier-carrier entanglement and transport resonances in semiconductor quantum dots  

E-print Network

We study theoretically the entanglement created in a scattering between an electron, incoming from a source lead, and another electron bound in the ground state of a quantum dot, connected to two leads. We analyze the role played by the different kinds of resonances in the transmission spectra and by the number of scattering channels, into the amount of quantum correlations between the two identical carriers. It is shown that the entanglement between their energy states is not sensitive to the presence of Breit-Wigner resonances, while it presents a peculiar behavior in correspondence of Fano peaks: two close maxima separated by a minimum, for a two-channel scattering, a single maximum for a multi-channel scattering. Such a behavior is ascribed to the different mechanisms characterizing the two types of resonances. Our results suggest that the production and detection of entanglement in quantum dot structures may be controlled by the manipulation of Fano resonances through external fields.

Fabrizio Buscemi; Paolo Bordone; Andrea Bertoni

2007-06-15

234

DNA Charge Transport within the Cell.  

PubMed

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

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

2015-02-01

235

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

NASA Astrophysics Data System (ADS)

In this paper, we performed carrier transport simulation to understand the unusual temperature dependence of the carrier mobility observed in nematic liquid crystals. For this purpose, we made a model liquid crystalline system consisting of biaxial Gay-Berne particles, and then we simulated hopping transport between these particles. The hopping rate was formulated suitably for the biaxial Gay-Berne particles based on the investigation of the electronic overlaps between actual aromatic molecules. The carrier transport simulation was performed by master equation method on the model system prepared by N-P-T ensemble Monte Carlo simulation. We reproduced gradual mobility increase in the nematic phase as a result of the change in the short range molecular order.

Goto, Masanao; Takezoe, Hideo; Ishikawa, Ken

2010-02-01

236

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

237

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

Code of Federal Regulations, 2010 CFR

...Internal transport and freight charges for export shipments. 351...DUTIES Identification and Measurement of Countervailable Subsidies...Internal transport and freight charges for export shipments. ...internal transport and freight charges on export shipments, a...

2010-04-01

238

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

PubMed Central

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

2014-01-01

239

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

NASA Astrophysics Data System (ADS)

In this work, we have studied the effect of surface treatment of SiO2 dielectric layer on the reduction of the trap charge carrier density at dielectric/semiconducting interface by fabricating a metal-insulator-semiconductor (MIS) device using ?, ?-dihexylcarbonylquaterthiophene as semiconducting layer. SiO2 dielectric layer has been treated with 1,1,1,3,3,3-hexamethyldisilazane (HMDS) to modify the chemical group acting as charge traps. Capacitance-voltage measurements have been performed on MIS devices fabricated on SiO2 and HMDS treated SiO2. These data have been used for the calculation of trap charge carrier density and Debye length at the dielectric-semiconductor interface. The calculated trap charge carrier density has been found to reduce from (2.925 ± 0.049) × 1016 cm-3 to (2.025 ± 0.061) × 1016 cm-3 for the MIS device with HMDS treated SiO2 dielectric in comparison to that of untreated SiO2. Next, the effect of reduction in trap charge carrier density has been studied on the performance of organic field effect transistors. The improvement in the device parameters like mobility, on/off ratio, and gate leakage current has been obtained with the effect of the surface treatment. The charge carrier mobility has been improved by a factor of 2 through this treatment. Further, the influence of the treatment was observed by atomic force microscope and Fourier transform infrared spectroscopy techniques.

Dagar, Janardan; Yadav, Vandana; Tyagi, Priyanka; Kumar Singh, Rajiv; Suman, C. K.; Srivastava, Ritu

2013-12-01

240

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

E-print Network

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

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

2015-01-01

241

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

242

The stress-affected carrier injection and transport in organic semiconductor devices  

NASA Astrophysics Data System (ADS)

The current-voltage (I-V) characteristics of the thin films of methoxy-5-(2'-ethylhexyloxy)-1,4-phyenylenevinylene] (MEH-PPV) and tris-(8-hydroxyquinoline) aluminum (Alq) under different stresses have been measured, together with their Young's modulus, hardness, and loading curve. We propose a model on stress-affected carrier injection and transport to explain the experimental results. The model is based on the well-built space-charge-limited current (SCLC) and injection-limited current (ILC) model, together with the electrical and mechanic properties of organic semiconductor. By Monte Carlo simulation, we investigated the relationship between the conductance and strain. We found two trends in the current variation with the stress. One is fast at low current density, and the other is relatively slower at high current density, which may due to the SCLC in the bulk and the ILC at the interface, respectively. The working voltage of the present device with the highest sensitivity is about 1 V.

Dai, Weifeng; Zhang, Bin; Kang, Yonglong; Chen, Huamin; Zhong, Gaoyu; Li, Yuesheng

2013-09-01

243

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

E-print Network

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

Mátyás, Alpár; Jirauschek, Christian; 10.1063/1.3608116

2011-01-01

244

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

Microsoft Academic Search

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

Masakatsu Tsuchiaki; Hisashi Hara; Toyota Morimoto; Hiroshi Iwai

1993-01-01

245

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

246

Charge Transport Asymmetry in Cryogenic High Purity Germanium  

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

247

CHARACTERIZING COUPLED CHARGE TRANSPORT WITH MULTISCALE MOLECULAR DYNAMICS  

SciTech Connect

This is the final progress report for Award DE-SC0004920, entitled 'Characterizing coupled charge transport with multi scale molecular dynamics'. The technical abstract will be provided in the uploaded report.

Swanson, Jessica

2011-08-31

248

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

NASA Astrophysics Data System (ADS)

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

Kim, Kwangsik; Won, Taeyoung

2013-10-01

249

The mechanism of carrier-mediated transport of folates in BeWo cells: the involvement of heme carrier protein 1 in placental folate transport.  

PubMed

The aim of this study was to elucidate the mechanism of folate transport in the placenta. A study of folate was carried out to determine which carriers transport folates in the human choriocarcinoma cell line BeWo, a model cell line for the placenta. We investigated the effects of buffer pH and various compounds on folate uptake. In the first part of the study, the expression levels of the mRNA of the folate receptor alpha (FRalpha), the reduced folate carrier (RFC), and heme carrier protein 1 (HCP1) were determined in BeWo cells by RT-PCR analysis. Folate uptake into BeWo cells was greater under an acidic buffer condition than under a neutral one. Structure analogs of folates inhibited folate uptake under all buffer pH conditions, but anion drugs (e.g., pravastatin) inhibited folate uptake only under an acidic buffer condition. Although thiamine pyrophosphate (TPP), a substrate of RFC, had no effect on folate uptake, hemin (a weak inhibitor of folate uptake via HCP1) decreased folate uptake to about 80% of the control level under an acidic buffer condition. Furthermore, kinetic analysis showed that hemin inhibited the low-affinity phase of folate uptake under an acidic buffer condition. We conclude that pH-dependent folate uptake in BeWo cells is mediated by at least two carriers. RFC is not involved in folate uptake, but FRalpha (high affinity phase) and HCP1 (low affinity phase) transport folate in BeWo cells. PMID:18256483

Yasuda, Satoru; Hasui, Satoko; Kobayashi, Masaki; Itagaki, Shirou; Hirano, Takeshi; Iseki, Ken

2008-02-01

250

An acoustic charge transport imager for high definition television applications  

NASA Technical Reports Server (NTRS)

In this report we present the progress during the second six month period of the project. This includes both experimental and theoretical work on the acoustic charge transport (ACT) portion of the chip, the theoretical program modelling of both the avalanche photodiode (APD) and the charge transfer and overflow transistor and the materials growth and fabrication part of the program.

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

1992-01-01

251

Charged Transport in Porous Media Modeling, Analysis and Numerics  

E-print Network

field -µv + p = ze(c+ - c- ) in T · v = 0 in T v = 0 on D Poisson equation for the electrostatic potential - = ze 0r (c+ - c- ) in T · = 0 on N = D on D with viscosity µ, fluid velocity v, pressure p, permittivity 0r , electrostatic potential (D) and total charge ze. Nadja Ray Charged Transport in Porous Media

Gugat, Martin

252

Femtosecond Charge Transport in Polar Semiconductors  

Microsoft Academic Search

The transient current response of bulk GaAs and InP is investigated at ultrahigh electric fields. On ultrashort time scales, the electronic system is far from equilibrium and overshoot velocities as high as 8×107 cm\\/s are observed. Our studies also lead to a detailed understanding of the ionic response of polar semiconductors. For the first time, carrier motion is determined with

A. Leitenstorfer; S. Hunsche; J. Shah; M. C. Nuss; W. H. Knox

1999-01-01

253

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

E-print Network

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

Miller, David A. B.

254

Selective Transport of Cesium and Strontium Ions Through Polymer Inclusion Membranes Containing Calixarenes as Carriers  

Microsoft Academic Search

Cs and Sr are selectively removed over Na from acidic aqueous solutions with high Na concentrations by using membranes designed to selectively transport one of the two cations. To this end, calix[4]arene derivatives were used as carriers in polymer inclusion membranes (PIMs). The synthesis and characterization of new calix[4]arene derivatives (a bisamide (2) and three bisesters (3, 5 and 6))

G. Arena; A. Contino; A. Magri; D. Sciotto; J. D. Lamb

1998-01-01

255

Field-Modulated Carrier Transport in Carbon Nanotube Transistors  

Microsoft Academic Search

We have investigated the electrical transport properties of carbon nanotube field-effect transistors as a function of channel length, gate dielectric film thickness, and dielectric material. Our experiments show that the bulk properties of the semiconducting carbon nanotubes do not limit the current flow through the metal\\/nanotube\\/metal system. Instead, our results can be understood in the framework of gate and source-drain

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

2002-01-01

256

Charge-carrier generation in organic solar cells using crystalline donor polymers.  

PubMed

Charge generation and recombination dynamics in a blend film of a crystalline low-bandgap polymer, poly[(4,4-bis(2-ethylhexyl)dithieno[3,2-b:2',3'-d]silole)-2,6-diyl-alt-(4,7-bis(2-thienyl)-2,1,3-benzothiadiazole)-4,7-diyl] (PSBTBT), and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) were studied by transient absorption spectroscopy. Upon photoexcitation of the PSBTBT absorption band at 800 nm, singlet excitons were promptly generated, and then rapidly converted into polarons in a few picoseconds. We found that there are two different polarons in PSBTBT: one is ascribed to polarons generated in the disorder phase and the other is ascribed to polarons in the crystalline phase. On a time scale of nanoseconds, ?50% of polarons in the disorder phase recombined geminately to the ground state. On the other hand, such geminate recombination was negligible for polarons in the crystalline phase. As a result, the overall charge dissociation efficiency is as high as ?75% for PSBTBT/PCBM blend films. On the basis of these analyses, we discuss the role of polymer crystallinity in the charge-carrier generation in organic solar cells. PMID:24980903

Tamai, Yasunari; Tsuda, Kazuki; Ohkita, Hideo; Benten, Hiroaki; Ito, Shinzaburo

2014-10-14

257

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

258

Tuning transport properties of nanofluidic devices with local charge inversion  

PubMed Central

Nanotubes can selectively conduct ions across membranes to make ionic devices with transport characteristics similar to biological ion channels and semiconductor electron devices. Depending on the surface charge profile of the nanopore, ohmic resistors, rectifiers, and diodes can be made. Here we show that a uniformly charged conical nanopore can have all these transport properties by changing the ion species and their concentrations on each side of the membrane. Moreover, the cation vs. anion selectivity of the pores can be changed. We find that polyvalent cations like Ca2+ and the trivalent cobalt sepulchrate produce localized charge inversion to change the effective pore surface charge profile from negative to positive. These effects are reversible so that the transport and selectivity characteristics of ionic devices can be tuned, much as the gate voltage tunes the properties of a semiconductor. PMID:19317490

He, Yan; Gillespie, Dirk; Boda, Dezs?; Vlassiouk, Ivan; Eisenberg, Robert S.; Siwy, Zuzanna S.

2009-01-01

259

Simulation of charge transport in pixelated CdTe  

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

260

Collective charge transport in semiconductor-metal hybrid nanocomposite  

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

261

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

262

Efficient blue organic light-emitting devices with charge carrier confining nanostructure formed by wide band gap molecule doping  

NASA Astrophysics Data System (ADS)

We report on efficient blue organic light-emitting devices with an emission layer featuring a quasi-molecular quantum dot nanostructure as a charge carrier confining barrier, which was formed by doping a wide band gap molecule, 2-(2-hydroxyphenylbenzoxazole) lithium, into a newly synthesized blue host molecule, 9,10-bis-[4-(2,2-diphenylvinyl)-phenyl]-anthracene. The charge carrier confinement was greatly improved by doping with 10% wide band gap molecules, that led to a theoretical molecular quantum dot distance of 33 Å. The device showed enhanced efficiency ({\\sim }5\

Kim, Youngkyoo; Oh, Eonseok; Choi, Dongkwon; Lim, Hyuntaek; Ha, Chang-Sik

2004-01-01

263

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

264

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

PubMed

In the last years there has been a renewed interest for zinc oxide semiconductor, mainly triggered by its prospects in optoelectronic applications. In particular, zinc oxide thin films are being widely used for photovoltaic applications, in which the determination of the electrical conductivity is of great importance. Being an intrinsically doped material, the quantification of its doping concentration has always been challenging. Here we show how to probe the charge carrier density of zinc oxide thin films by Scanning Kelvin Probe Microscopy, a technique that allows measuring the contact potential difference between the tip and the sample surface with high spatial resolution. A simple electronic energy model is used for correlating the contact potential difference with the doping concentration in the material. Limitations of this technique are discussed in details and some experimental solutions are proposed. Two-dimensional doping concentration images acquired on radio frequency-sputtered intrinsic zinc oxide thin films with different thickness and deposited under different conditions are reported. We show that results inferred with this technique are in accordance with carrier concentration expected for zinc oxide thin films deposited under different conditions and obtained from resistivity and mobility measurements. PMID:24569599

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

2014-01-01

265

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

PubMed Central

In the last years there has been a renewed interest for zinc oxide semiconductor, mainly triggered by its prospects in optoelectronic applications. In particular, zinc oxide thin films are being widely used for photovoltaic applications, in which the determination of the electrical conductivity is of great importance. Being an intrinsically doped material, the quantification of its doping concentration has always been challenging. Here we show how to probe the charge carrier density of zinc oxide thin films by Scanning Kelvin Probe Microscopy, a technique that allows measuring the contact potential difference between the tip and the sample surface with high spatial resolution. A simple electronic energy model is used for correlating the contact potential difference with the doping concentration in the material. Limitations of this technique are discussed in details and some experimental solutions are proposed. Two-dimensional doping concentration images acquired on radio frequency-sputtered intrinsic zinc oxide thin films with different thickness and deposited under different conditions are reported. We show that results inferred with this technique are in accordance with carrier concentration expected for zinc oxide thin films deposited under different conditions and obtained from resistivity and mobility measurements. PMID:24569599

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

2014-01-01

266

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

NASA Astrophysics Data System (ADS)

In the last years there has been a renewed interest for zinc oxide semiconductor, mainly triggered by its prospects in optoelectronic applications. In particular, zinc oxide thin films are being widely used for photovoltaic applications, in which the determination of the electrical conductivity is of great importance. Being an intrinsically doped material, the quantification of its doping concentration has always been challenging. Here we show how to probe the charge carrier density of zinc oxide thin films by Scanning Kelvin Probe Microscopy, a technique that allows measuring the contact potential difference between the tip and the sample surface with high spatial resolution. A simple electronic energy model is used for correlating the contact potential difference with the doping concentration in the material. Limitations of this technique are discussed in details and some experimental solutions are proposed. Two-dimensional doping concentration images acquired on radio frequency-sputtered intrinsic zinc oxide thin films with different thickness and deposited under different conditions are reported. We show that results inferred with this technique are in accordance with carrier concentration expected for zinc oxide thin films deposited under different conditions and obtained from resistivity and mobility measurements.

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

2014-02-01

267

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

NASA Astrophysics Data System (ADS)

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

Tice, Daniel Boitnott

268

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

269

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.

2011-12-01

270

Charge-Retraction Time-of-Flight Measurement for Organic Charge Transport Materials  

SciTech Connect

This describes an all-electrical technique, charge-retraction time-of-flight (CR-TOF), to measure charge carrier mobility through an organic layer. Carriers are injected and accumulated at a blocking interface, then retracted. The retraction current transient is nearly indistinguishable from a traditional time-of-flight photocurrent. The CR-TOF technique is validated by measurement of the hole mobility of two well-known compounds, 4,4',4"-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine and 4,4'-bis[N-1-napthyl)-N-phenylamino]biphenyl, utilizing 1,3,5-tris(N-phenylbenzimidazol-2-yl)-benzene as a hole-blocking layer.

Wallace, J.U.; Young, R.H.; Tang, C.W.; Chen, S.H.

2007-10-22

271

Adenine nucleotide transport via Sal1 carrier compensates for the essential function of the mitochondrial ADP/ATP carrier.  

PubMed

The mitochondrial ADP/ATP carrier (Aac2p) of Saccharomyces cerevisiae links two biochemical pathways, glycolysis in the cytosol and oxidative phosphorylation in the mitochondria, by exchanging their common substrates and products across the inner mitochondrial membrane. Recently, the product of the SAL1 gene, which is essential in cells lacking Aac2p, has been implicated in a similar communication. However, the mechanism by which Sal1p rescues the growth of Deltaaac2 mutants is not clear and it was proposed that both Sal1p and Aac2p share a common vital function other than ADP/ATP exchange. Here, the impact of SAL1 deletion on mitochondrial reactions involving either synthesis or hydrolysis of ATP was investigated. We show that adenine nucleotide transport activity related to Sal1p can be demonstrated in isolated mitochondria as well as in intact cells under conditions when Aac2-mediated exchange is not functional. Our results indicate that the vital role of both Sal1p and Aac2p is to maintain the essential intramitochondrial ATP pool owing to their ability to transport adenine nucleotides. PMID:20141534

Laco, Juraj; Zeman, Igor; Pevala, Vladimír; Polcic, Peter; Kolarov, Jordan

2010-05-01

272

Charge Transport in DNA-based Devices  

Microsoft Academic Search

DNA is probably the molecule that carries the highest possible density of information. Information comes along with structuring\\u000a and recognition that offer the possibility of using DNA to build self-assembled molecular circuits for nanoelectronics applications.\\u000a This, however, must be complemented by suitable conductivity, which was tested in a series of experiments on charge migration\\u000a along DNA molecules. These issues together

Danny Porath; Noa Lapidot; Julio Gomez-Herrero

2005-01-01

273

Charge transport in polymer light-emitting diodes at high current density  

SciTech Connect

We present measured and calculated current{endash}voltage (I{endash}V) characteristics of diodes fabricated using a soluble poly({ital p}-phenylene vinylene) derivative. Steady-state and pulsed electrical excitation were used to acquire the I{endash}V characteristics for current densities from 1{times}10{sup {minus}3} to 1.3{times}10{sup 3}&hthinsp;A/cm{sup 2}. Hole current is predominant in the diode. The I{endash}V characteristics were fit using a device model that assumes an electric field-dependent hole mobility of the Poole{endash}Frenkel form that is independent of the charge carrier density. The measured and calculated I{endash}V characteristics are in good agreement over the full range of current density. The maximum electric field and carrier density is about 4{times}10{sup 6}&hthinsp;V/cm and 1{times}10{sup 18}&hthinsp;cm{sup {minus}3}, respectively. These results demonstrate that an electric field-dependent mobility, without carrier density dependence, provides an accurate description of hole transport in this polymer over this range of field and carrier density. {copyright} {ital 1999 American Institute of Physics.}

Campbell, I.H.; Smith, D.L. [Los Alamos National Laboratory, Los Alamos, New Mexico, 87545 (United States)] [Los Alamos National Laboratory, Los Alamos, New Mexico, 87545 (United States); Neef, C.J.; Ferraris, J.P. [The University of Texas at Dallas, Richardson, Texas, 75083 (United States)] [The University of Texas at Dallas, Richardson, Texas, 75083 (United States)

1999-08-01

274

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

SciTech Connect

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

Bizarri, G.; Dorenbos, P. [Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, 2629JB Delft (Netherlands)

2007-05-01

275

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

NASA Technical Reports Server (NTRS)

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

Von Roos, O.

1983-01-01

276

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

277

Molecular engineering to improve the balance of charge carrier in single-layer silole-based OLEDs.  

E-print Network

Molecular engineering to improve the balance of charge carrier in single-layer silole-based OLEDs = 0.8 cd/A at 7 V. Introduction15 Organic light-emitting diodes (OLEDs) using small molecules OLEDs structures11 . Nevertheless, this approach suffers of some drawbacks due to a large number

Paris-Sud XI, Université de

278

Changes in mRNA expression levels of solute carrier transporters in inflammatory bowel disease patients.  

PubMed

Inflammatory bowel disease (IBD) is an inflammatory condition that affects the gastrointestinal tract. The solute carrier (SLC) superfamily of transporters comprise proteins involved in the uptake of drugs, hormones, and other biologically active compounds. The purpose of this study was to determine the mRNA expression levels of 15 solute carrier transporters in two regions of the intestine in IBD patients. Endoscopic biopsy specimens were taken from two locations (terminal ileum and colon) for histological examination and RNA extraction. We quantitatively measured the mRNA expression of 15 SLC transporters in 107 IBD patients (53 with Crohn's disease and 54 with ulcerative colitis) and 23 control subjects. mRNA expression was evaluated using the quantitative reverse transcription-polymerase chain reaction technique. We observed that in the ileum of IBD patients, mRNA levels for serotonin transporter, equilibrative nucleoside transporter (ENT) 1, ENT2, and organic anion-transporting polypeptide (OATP) 2B1 were significantly elevated, whereas levels for apical sodium-dependent bile acid transporter (ASBT) and organic zwitterion/cation transporter (OCTN) 2 were significantly lower. In colon, mRNA levels for ENT1, ENT2, concentrative nucleoside transporter (CNT) 2, OATP2B1, and OATP4A1 were significantly higher, whereas mRNA levels for OCTN2 were significantly decreased. In inflamed colon of IBD patients the mRNA expression levels of ENT1, ENT2, CNT2, OATP2B1, OATP4A1, and peptide transporter 1 were significantly higher. We conclude that intestinal SLC mRNA levels are dysregulated in IBD patients, which may be linked to the inflammation of the tissue and provides an indication about the role of inflammatory signaling in regulation of SLC expression. PMID:19487253

Wojtal, Kacper A; Eloranta, Jyrki J; Hruz, Petr; Gutmann, Heike; Drewe, Jürgen; Staumann, Alex; Beglinger, Christoph; Fried, Michael; Kullak-Ublick, Gerd A; Vavricka, Stephan R

2009-09-01

279

Temperature-dependent coherent carrier transport in quantum cascade lasers This article has been downloaded from IOPscience. Please scroll down to see the full text article.  

E-print Network

Temperature-dependent coherent carrier transport in quantum cascade lasers This article has been of Physics Temperature-dependent coherent carrier transport in quantum cascade lasers Muhammad Anisuzzaman carrier transport in quantum cascade lasers (QCLs) is studied in this paper. It was found that coherent

Maryland, Baltimore County, University of

280

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

PubMed

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

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

2014-04-01

281

Ab Initio Time-Domain Study of Phonon-Assisted Relaxation of Charge Carriers in a PbSe Quantum Dot  

E-print Network

of inorganic semiconductors, known as artificial atoms or quantum dots (QD), exhibit a variety of uniqueAb Initio Time-Domain Study of Phonon-Assisted Relaxation of Charge Carriers in a PbSe Quantum Dot The phonon-induced relaxation dynamics of charge carriers in a PbSe quantum dot is studied for the first time

282

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

283

Subsurface Imaging of Coupled Carrier Transport in GaAs/AlGaAs Core-Shell Nanowires.  

PubMed

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

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

2015-01-14

284

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

PubMed

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

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

2011-11-01

285

Design rules for charge-transport efficient host materials for phosphorescent organic light-emitting diodes.  

PubMed

The use of blue phosphorescent emitters in organic light-emitting diodes (OLEDs) imposes demanding requirements on a host material. Among these are large triplet energies, the alignment of levels with respect to the emitter, the ability to form and sustain amorphous order, material processability, and an adequate charge carrier mobility. A possible design strategy is to choose a ?-conjugated core with a high triplet level and to fulfill the other requirements by using suitable substituents. Bulky substituents, however, induce large spatial separations between conjugated cores, can substantially reduce intermolecular electronic couplings, and decrease the charge mobility of the host. In this work we analyze charge transport in amorphous 2,8-bis(triphenylsilyl)dibenzofuran, an electron-transporting material synthesized to serve as a host in deep-blue OLEDs. We show that mesomeric effects delocalize the frontier orbitals over the substituents recovering strong electronic couplings and lowering reorganization energies, especially for electrons, while keeping energetic disorder small. Admittance spectroscopy measurements reveal that the material has indeed a high electron mobility and a small Poole-Frenkel slope, supporting our conclusions. By linking electronic structure, molecular packing, and mobility, we provide a pathway to the rational design of hosts with high charge mobilities. PMID:22845011

May, Falk; Al-Helwi, Mustapha; Baumeier, Björn; Kowalsky, Wolfgang; Fuchs, Evelyn; Lennartz, Christian; Andrienko, Denis

2012-08-22

286

GHB (gamma-hydroxybutyrate) carrier-mediated transport across the blood-brain barrier.  

PubMed

gamma-Hydroxybutyrate (sodium oxybate, GHB) is an approved therapeutic agent for cataplexy with narcolepsy. GHB is widely abused as an anabolic agent, euphoriant, and date rape drug. Recreational abuse or overdose of GHB (or its precursors gamma-butyrolactone or 1,4-butanediol) results in dose-dependent central nervous system (CNS) effects (respiratory depression, unconsciousness, coma, and death) as well as tolerance and withdrawal. An understanding of the CNS transport mechanisms of GHB may provide insight into overdose treatment approaches. The hypothesis that GHB undergoes carrier-mediated transport across the BBB was tested using a rat in situ brain perfusion technique. Various pharmacological agents were used to probe the pharmacological characteristics of the transporter. GHB exhibited carrier-mediated transport across the BBB consistent with a high-capacity, low-affinity transporter; averaged brain region parameters were V(max) = 709 +/- 214 nmol/min/g, K(m) = 11.0 +/- 3.56 mM, and CL(ns) = 0.019 +/- 0.003 cm(3)/min/g. Short-chain monocarboxylic acids (pyruvic, lactic, and beta-hydroxybutyric), medium-chain fatty acids (hexanoic and valproic), and organic anions (probenecid, benzoic, salicylic, and alpha-cyano-4-hydroxycinnamic acid) significantly inhibited GHB influx by 35 to 90%. Dicarboxylic acids (succinic and glutaric) and gamma-aminobutyric acid did not inhibit GHB BBB transport. Mutual inhibition was observed between GHB and benzoic acid, a well known substrate of the monocarboxylate transporter MCT1. These results are suggestive of GHB crossing the BBB via an MCT isoform. These novel findings of GHB BBB transport suggest potential therapeutic approaches in the treatment of GHB overdoses. We are currently conducting "proof-of-concept" studies involving the use of GHB brain transport inhibitors during GHB toxicity. PMID:15173314

Bhattacharya, Indranil; Boje, Kathleen M K

2004-10-01

287

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

PubMed

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

Chiu, Tien-Lung; Lee, Pei-Yu

2012-01-01

288

Charge Transport and Rectification in Arrays of SAM-Based Tunneling Junctions  

E-print Network

Charge Transport and Rectification in Arrays of SAM-Based Tunneling Junctions Christian A. Nijhuis of rectification with Fc-terminated SAMs seems to be charge transport processes that change with the polarity Nanoelectronics, molecular electronics, charge transport, self-assembled monolayers, rectification, charge

Church, George M.

289

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

NASA Astrophysics Data System (ADS)

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

Wampler, William R.; Myers, Samuel M.

2015-01-01

290

Charge transport through a molecular ?-stack: double helical DNA  

Microsoft Academic Search

Double helical DNA, containing a ?-stacked array of base pairs within its interior, can be considered as a molecular analogue of solid state ?-stacked arrays. Like the solid state materials, the DNA base pair stack provides a medium to facilitate charge transport. However, owing to the dynamical motions of the base pairs within the molecular stack, as well as sequence-dependent

Christopher R. Treadway; Michael G. Hill; Jacqueline K. Barton

2002-01-01

291

Heme oxygenase-1 enhances renal mitochondrial transport carriers and cytochrome C oxidase activity in experimental diabetes.  

PubMed

Up-regulation of heme oxygenase (HO-1) by either cobalt protoporphyrin (CoPP) or human gene transfer improves vascular and renal function by several mechanisms, including increases in antioxidant levels and decreases in reactive oxygen species (ROS) in vascular and renal tissue. The purpose of the present study was to determine the effect of HO-1 overexpression on mitochondrial transporters, cytochrome c oxidase, and anti-apoptotic proteins in diabetic rats (streptozotocin, (STZ)-induced type 1 diabetes). Renal mitochondrial carnitine, deoxynucleotide, and ADP/ATP carriers were significantly reduced in diabetic compared with nondiabetic rats (p < 0.05). The citrate carrier was not significantly decreased in diabetic tissue. CoPP administration produced a robust increase in carnitine, citrate, deoxynucleotide, dicarboxylate, and ADP/ATP carriers and no significant change in oxoglutarate and aspartate/glutamate carriers. The increase in mitochondrial carriers (MCs) was associated with a significant increase in cytochrome c oxidase activity. The administration of tin mesoporphyrin (SnMP), an inhibitor of HO-1 activity, prevented the restoration of MCs in diabetic rats. Human HO-1 cDNA transfer into diabetic rats increased both HO-1 protein and activity, and restored mitochondrial ADP/ATP and deoxynucleotide carriers. The increase in HO-1 by CoPP administration was associated with a significant increase in the phosphorylation of AKT and levels of BcL-XL proteins. These observations in experimental diabetes suggest that the cytoprotective mechanism of HO-1 against oxidative stress involves an increase in the levels of MCs and anti-apoptotic proteins as well as in cytochrome c oxidase activity. PMID:16595661

Di Noia, Maria Antonietta; Van Driesche, Sarah; Palmieri, Ferdinando; Yang, Li-Ming; Quan, Shuo; Goodman, Alvin I; Abraham, Nader G

2006-06-01

292

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

293

Modulation of phase behaviors and charge carrier mobilities by linkage length in discotic liquid crystal dimers.  

PubMed

A clear structure-property relationship was revealed in a series of triphenylene-based dimers, which contained two triphenylene nuclei each bearing five ?-OC4H9 substituents and are linked through a flexible O(CH2)nO polymethylene chain (n = 6-12). Dimers with the linkage close to twice the length of the free side chains (n = 8, 9) exhibited a single Colhp phase, while others with the linkage shorter (n = 6, 7) or longer (n = 10, 11, 12) showed multiphase behaviors with a transition from the Colhp phase to Colh phase; hole mobilities of Colhp phases reached 1.4 × 10(-2) cm(2) V(-1) s(-1) in the dimer for which the linkage is exactly twice the length of the free side chains (n = 8), and decreased regularly both with linkage length becoming shorter or longer. This modulation of phase behaviors and charge carrier mobilities was demonstrated to be generated by various steric perturbations introduced by linkages with different lengths, which result in different degrees of lateral fluctuations of discotic moieties in the columns. PMID:25467212

Wang, Yi-Fei; Zhang, Chun-Xiu; Wu, Hao; Zhang, Ao; Wang, Jian-Chuang; Zhang, Shuai-Feng; Pu, Jia-Ling

2015-01-28

294

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

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

295

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

296

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

PubMed

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 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. PMID:20672071

Alveroglu, E; Yilmaz, Y

2010-03-01

297

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

298

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.

2013-03-01

299

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

300

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

NASA Astrophysics Data System (ADS)

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

Berciu, Mona Inesa

2000-10-01

301

An Efficient Scheduling Scheme on Charging Stations for Smart Transportation  

NASA Astrophysics Data System (ADS)

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

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

302

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

PubMed

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

Sahu, Harikrishna; Panda, Aditya N

2014-05-14

303

Pore network model of electrokinetic transport through charged porous media  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

304

Pore network model of electrokinetic transport through charged porous media.  

PubMed

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

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

2014-04-01

305

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

PubMed

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

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

2014-01-01

306

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

PubMed Central

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

Chang, Yung-Heng; Sun, Yi Henry

2014-01-01

307

Correlated conformation and charge transport in multiwall carbon nanotube-conducting polymer nanocomposites.  

PubMed

The strikingly different charge transport behaviours in nanocomposites of multiwall carbon nanotubes (MWNTs) and conducting polymer polyethylenedioxythiophene-polystyrene-sulfonic-acid (PEDOT-PSS) at low temperatures are explained by probing their conformational properties using small-angle x-ray scattering (SAXS). The SAXS studies indicate the assembly of elongated PEDOT-PSS globules on the walls of nanotubes, coating them partially, thereby limiting the interaction between the nanotubes in the polymer matrix. This results in a charge transport governed mainly by small polarons in the conducting polymer despite the presence of metallic MWNTs. At T > 4 K, hopping of the charge carriers following one-dimensional variable range hopping is evident which also gives rise to a positive magnetoresistance (MR) with an enhanced localization length (?5 nm) due to the presence of MWNTs. However, at T < 4 K, the observation of an unconventional positive temperature coefficient of resistivity is attributed to small polaron tunnelling. The exceptionally large negative MR observed in this temperature regime is conjectured to be due to the presence of quasi-1D MWNTs that can aid in lowering the tunnelling barrier across the nanotube-polymer boundary resulting in large delocalization. PMID:21673397

Choudhury, Paramita Kar; Ramaprabhu, S; Ramesh, K P; Menon, Reghu

2011-07-01

308

950809 Charged particle transport updated multi-group diffusion  

SciTech Connect

In 1974, a charged particle transport scheme was introduced which utilized a multi-group diffusion method for the spatial transport and slowing down of energetic ions in a hot plasma. In this treatment a diffusion coefficient was used which was flux-limited to provide, hopefully, some degree of accuracy when the slowing down of an energetic charged particle is dominated by Coulomb collisions with thermal ions and electrons in a plasma medium. An advantage of this method was a very fast, memory-contained program for calculating the behavior of energetic charged particles which resulted in smoothly varying particle number densities and energy depositions. The main limitation of the original multi-group charged particle diffusion scheme is its constraint to a basic ten group structure; the same ten group structure for each of the five energetic ions tracked. This is regarded as a severe limitation, inasmuch as more groups would be desired to simulate more accurately the corresponding Monte Carlo results of energies deposited over spatial zones from a charged particle source. More generally, it seems preferable to have a different group structure for each particle type since they are created at inherently different energies. In this paper, the basic theory and multi-group description will be given. This is followed by the specific techniques that were used to solve the resultant equations. Finally, the modifications that were made to the cross section data as well as the methods used for energy and momentum deposition are described.

Corman, E.G.; Perkins, S.T.; Dairiki, N.T.

1995-09-01

309

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

PubMed

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

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

2014-11-19

310

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

E-print Network

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 to circumvent these difficulties is suggested. For purpose of comparison it is shown that the frequency-dependent dielectric permittivity of insulators satisfies all rigorous mathematical criteria. This permits us to conclude that in the presence of free charge carriers the concept of dielectric permittivity is not as well defined as for insulators and we make a link to widely discussed puzzles in the theory of thermal Casimir force which might be caused by the use of such kind permittivities.

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

2009-11-17

311

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

SciTech Connect

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

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

2010-08-23

312

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

PubMed

In this work, conductive atomic force microscopy (C-AFM) is used to study the local electrical properties in thin films of self-organized fibrillate poly(3-hexylthiophene) (P3HT), as a reference polymer semiconductor. Depending on the geometrical confinement in the transport channel, the C-AFM current is shown to be governed either by the charge transport in the film or by the carrier injection at the tip-sample contact, leading to either bulk or local electrical characterization of the semiconducting polymer, respectively. Local I-V profiles allow discrimination of the different dominating electrical mechanisms, i.e., resistive in the transport regime and space charge limited current (SCLC) in the local regime. A modified Mott-Gurney law is analytically derived for the contact regime, taking into account the point-probe geometry of the contact and the radial injection of carriers. Within the SCLC regime, the probed depth is shown to remain below 12 nm with a lateral electrical resolution below 5 nm. This confirms that high resolution is reached in those C-AFM measurements, which therefore allows for the analysis of single organic semiconducting nanostructures. The carrier density and mobility in the volume probed under the tip under steady-state conditions are also determined in the SCLC regime. PMID:25079791

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

2014-09-21

313

Role of MgO barriers for spin and charge transport in Co/MgO/graphene nonlocal spin-valve devices  

NASA Astrophysics Data System (ADS)

We investigate spin and charge transport in both single and bilayer graphene nonlocal spin-valve devices. An inverse dependence of the spin lifetime ?s on the carrier mobility ? is observed in devices with large contact-resistance-area products (RcA>1k??m2). Furthermore, we observe an increase of ?s with increasing RcA values, demonstrating that spin transport is limited by spin dephasing underneath the electrodes. In charge transport, we measure a second contact-induced Dirac peak at negative gate voltages in devices with larger RcA values, demonstrating different transport properties in contact-covered and bare graphene parts. We argue that the existence of the second Dirac peak complicates the analysis of the carrier mobilities and the spin scattering mechanisms.

Volmer, F.; Drögeler, M.; Maynicke, E.; von den Driesch, N.; Boschen, M. L.; Güntherodt, G.; Beschoten, B.

2013-10-01

314

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

315

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

NASA Astrophysics Data System (ADS)

We present a comprehensive study of free-charge carrier and structural properties of two sets of InN films grown by molecular beam epitaxy and systematically doped with Mg from 1.0 × 1018 cm-3 to 3.9 × 1021 cm-3. The free electron and hole concentration, mobility, and plasmon broadening parameters are determined by infrared spectroscopic ellipsometry. The lattice parameters, microstructure, and surface morphology are determined by high-resolution X-ray diffraction and atomic force microscopy. Consistent results on the free-charge carrier type are found in the two sets of InN films and it is inferred that p-type conductivity could be achieved for 1.0 × 1018 cm-3 ? [Mg] ? 9.0 × 1019 cm-3. The systematic change of free-charge carrier properties with Mg concentration is discussed in relation to the evolution of extended defect density and growth mode. A comparison between the structural characteristics and free electron concentrations in the films provides insights in the role of extended and point defects for the n-type conductivity in InN. It further allows to suggest pathways for achieving compensated InN material with relatively high electron mobility and low defect densities. The critical values of Mg concentration for which polarity inversion and formation of zinc-blende InN occurred are determined. Finally, the effect of Mg doping on the lattice parameters is established and different contributions to the strain in the films are discussed.

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

2014-04-01

316

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

317

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

318

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

319

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

PubMed Central

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

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

2012-01-01

320

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

2013-01-01

321

Charge transport in highly efficient iridium cored electrophosphorescent dendrimers  

NASA Astrophysics Data System (ADS)

Electrophosphorescent dendrimers are promising materials for highly efficient light-emitting diodes. They consist of a phosphorescent core onto which dendritic groups are attached. Here, we present an investigation into the optical and electronic properties of highly efficient phosphorescent dendrimers. The effect of dendrimer structure on charge transport and optical properties is studied using temperature-dependent charge-generation-layer time-of-flight measurements and current voltage (I-V) analysis. A model is used to explain trends seen in the I-V characteristics. We demonstrate that fine tuning the mobility by chemical structure is possible in these dendrimers and show that this can lead to highly efficient bilayer dendrimer light-emitting diodes with neat emissive layers. Power efficiencies of 20 lm/W were measured for devices containing a second-generation (G2) Ir(ppy)3 dendrimer with a 1,3,5-tris(2-N-phenylbenzimidazolyl)benzene electron transport layer.

Markham, Jonathan P. J.; Samuel, Ifor D. W.; Lo, Shih-Chun; Burn, Paul L.; Weiter, Martin; Bässler, Heinz

2004-01-01

322

Electric fields and dominant carrier transport mechanisms in CdTe Schottky detectors  

NASA Astrophysics Data System (ADS)

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

Cola, Adriano; Farella, Isabella

2013-03-01

323

Nature of Charge Transport in Quantum-Cascade Lasers  

Microsoft Academic Search

The first global quantum simulation of semiconductor-based quantum-cascade lasers is presented. Our three-dimensional approach allows us to study in a purely microscopic way the current-voltage characteristics of state-of-the-art unipolar nanostructures, and therefore to answer the long-standing controversial question: Is charge transport in quantum-cascade lasers mainly coherent or incoherent? Our analysis shows that (i) quantum corrections to the semiclassical scenario are

Rita Claudia Iotti; Fausto Rossi

2001-01-01

324

Semiconductor drift chamber --- An application of a novel charge transport scheme  

Microsoft Academic Search

B The purpose of this paper is to describe a novel charge transport scheme in semiconductors, in which the field responsible for the charge transport is independent of the depletion field. The application of the novel charge transport scheme leads to the following new semiconductor detectors: 1) Semiconductor drift chamber; 2) Ultralow capacitance - large area semiconductor X-ray spectrometers and

Emilio Gatti; Pavel Rehak

1984-01-01

325

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

PubMed

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

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

2014-05-01

326

Nonlinear charge transport in the helicoidal DNA molecule.  

PubMed

Charge transport in the twist-opening model of DNA is explored via the modulational instability of a plane wave. The dynamics of charge is shown to be governed, in the adiabatic approximation, by a modified discrete nonlinear Schro?dinger equation with next-nearest neighbor interactions. The linear stability analysis is performed on the latter and manifestations of the modulational instability are discussed according to the value of the parameter ?, which measures hopping interaction correction. In so doing, increasing ? leads to a reduction of the instability domain and, therefore, increases our chances of choosing appropriate values of parameters that could give rise to pattern formation in the twist-opening model. Our analytical predictions are verified numerically, where the generic equations for the radial and torsional dynamics are directly integrated. The impact of charge migration on the above degrees of freedom is discussed for different values of ?. Soliton-like and localized structures are observed and thus confirm our analytical predictions. We also find that polaronic structures, as known in DNA charge transport, are generated through modulational instability, and hence reinforces the robustness of polaron in the model we study. PMID:23278045

Dang Koko, A; Tabi, C B; Ekobena Fouda, H P; Mohamadou, A; Kofané, T C

2012-12-01

327

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

328

An acoustic charge transport imager for high definition television applications  

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

329

A novel mode of current switching dependent on activated charge transport  

NASA Astrophysics Data System (ADS)

We demonstrate a fully printed transistor with a planar triode geometry, using nanoparticulate silicon as the semiconductor material, which has a unique mode of operation as an electrically controlled two-way (double throw) switch. A signal applied to the base changes the direction of the current from between the collector and base to between the base and emitter. We further show that the switching characteristic results from the activated charge transport in the semiconductor material, and that it is independent of the dominant carrier type in the semiconductor and the nature of the junction between the semiconductor and the three contacts. The same equivalent circuit, and hence similar device characteristics, can be produced using any other material combination with non-linear current-voltage characteristics, such as a suitable combination of semiconducting and conducting materials, such that a Schottky junction is present at all three contacts.

Britton, David T.; Walton, Stanley D.; Zambou, Serges; Magunje, Batsirai; Jonah, Emmanuel O.; Härting, Margit

2013-08-01

330

The binding and translocation steps in transport as related to substrate structure. A study of the choline carrier of erythrocytes.  

PubMed

The relationships between structure, affinity and transport activity in the choline transport system of erythrocytes have been investigated in order to (i) explore the nature of the carrier site and its surroundings, and (ii) determine the dependence of the carrier reorientation process on binding energies and steric restraints due to the substrate molecule. Affinity constants and maximum transport rates for a series of trialkyl derivatives of ethanolamine were obtained by a method that involves measuring the trans effect of unlabeled analogs upon the movement of radioactive choline. The main conclusions are as follows: (1) An analysis of transport kinetics shows that the affinity constants determined experimentally differ from the actual dissociation constants in a predictable way. The better the substrate, the higher the apparent affinity relative to the true value, whereas the affinity of non-transported inhibitiors is underestimated by a constant factor. (2) The carrier-choline complex undergoes far more rapid reorientation (translocation) than the free carrier. (3) The carrier imposes a strict upper limit upon the size of a substrate molecule that can participate in the carrier reorientation process; this limit corresponds to the choline structure. A smaller substrate such as tetramethylammonium, despite relatively weak binding forces , is unhindered in its translocation, suggesting that a carrier conformational change, dependent upon substrate binding energy, is not required for transport. (4) Small increases in the size of the quaternary ammonium head, as in triethylcholine, sharply lower affinity, consistent with a high degree of specificity for the trimethylammonium group. (5) Lengthening the alkyl substituent in derivatives of dimethyl- and diethylaminoethanol causes a regular increase in affinity, suggestive of unspecific hydrophobic bonding in a region very near the substrate site. PMID:497194

Devés, R; Krupka, R M

1979-11-01

331

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

SciTech Connect

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

Halwachs, Sandra, E-mail: halwachs@vetmed.uni-leipzig.d [Institute of Pharmacology, Pharmacy and Toxicology, Faculty of Veterinary Medicine, University of Leipzig, Leipzig (Germany); Lakoma, Cathleen [Institute of Pharmacology, Pharmacy and Toxicology, Faculty of Veterinary Medicine, University of Leipzig, Leipzig (Germany); Gebhardt, Rolf [Institute of Biochemistry, Faculty of Medicine, University of Leipzig, Leipzig (Germany); Schaefer, Ingo; Seibel, Peter [Molecular Cell Therapy, Center for Biotechnology and Biomedicine, Faculty of Medicine, University of Leipzig, Leipzig (Germany); Honscha, Walther [Institute of Pharmacology, Pharmacy and Toxicology, Faculty of Veterinary Medicine, University of Leipzig, Leipzig (Germany)

2010-07-15

332

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

Code of Federal Regulations, 2012 CFR

... (e) Step 4. Beginning July 1, 2015, notwithstanding any other provision of...Each Price Cap Carrier shall calculate its 2015 Target Composite Terminating End Office Access Rate. The 2015 Target Composite Terminating End...

2012-10-01

333

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

... (e) Step 4. Beginning July 1, 2015, notwithstanding any other provision of...Each Price Cap Carrier shall calculate its 2015 Target Composite Terminating End Office Access Rate. The 2015 Target Composite Terminating End...

2014-10-01

334

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

Code of Federal Regulations, 2013 CFR

... (e) Step 4. Beginning July 1, 2015, notwithstanding any other provision of...Each Price Cap Carrier shall calculate its 2015 Target Composite Terminating End Office Access Rate. The 2015 Target Composite Terminating End...

2013-10-01

335

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

... (e) Step 4. Beginning July 1, 2015, notwithstanding any other provision of...Rate-of-Return Carrier shall calculate its 2015 Target Composite Terminating End Office Access Rate. The 2015 Target Composite Terminating End...

2014-10-01

336

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

Code of Federal Regulations, 2013 CFR

... (e) Step 4. Beginning July 1, 2015, notwithstanding any other provision...Rate-of-Return Carrier shall calculate its 2015 interstate Target Composite Terminating End Office Access Rate. The 2015 interstate Target Composite...

2013-10-01

337

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

Code of Federal Regulations, 2012 CFR

... (e) Step 4. Beginning July 1, 2015, notwithstanding any other provision...Rate-of-Return Carrier shall calculate its 2015 interstate Target Composite Terminating End Office Access Rate. The 2015 interstate Target Composite...

2012-10-01

338

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

PubMed

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

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

2014-10-01

339

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

NASA Astrophysics Data System (ADS)

By using the methods of transient gratings (TGs) and induced absorption, we have studied the kinetics of plasma of free charge carriers (FCCs) created by the action of a picosecond laser pulse in two high-purity diamond single crystals synthesised from the gas phase. The gratings with different spatial periods have been excited at the wavelengths of 266 or 213 nm (above and below the fundamental absorption edge in diamond) and probed with continuous-wave radiation in the visible region. At the moderate FCC concentrations (~7 × 1017 cm-3), the coefficient of ambipolar diffusion and the carrier recombination time of two crystals are 20.3 and 18.9 cm2 s-1 and 30 and 190 ns, respectively. The increase in the carrier concentration up to 5 × 1019 cm-3 reduces the TG lifetime. We have determined the conditions under which the relaxation of the grating of carriers leads to the formation of a thermal grating, with the amplitude sufficient for its experimental observation.

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

2014-11-01

340

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

SciTech Connect

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

Elmasry, F. [Graduate School of Science, Kobe University, 1-1 Rokkodai-cho, Nada, Kobe 657-8501 (Japan); Okubo, S. [Molecular Photoscience Research Center, Kobe University, 1-1 Rokkodai-cho, Nada, Kobe 657-8501 (Japan); Ohta, H., E-mail: hoht@kobe-u.ac.jp [Graduate School of Science, Kobe University, 1-1 Rokkodai-cho, Nada, Kobe 657-8501 (Japan); Molecular Photoscience Research Center, Kobe University, 1-1 Rokkodai-cho, Nada, Kobe 657-8501 (Japan); Fujiwara, Y. [Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871 (Japan)

2014-05-21

341

Transport of pyruvate nad lactate into human erythrocytes. Evidence for the involvement of the chloride carrier and a chloride-independent carrier.  

PubMed Central

The kinetics and activation energy of entry of pyruvate and lactate into the erythrocyte were studied at concentrations below 4 and 15mM respectively. The Km and Vmax. values for both substrates are reported, and it is shown that pyruvate inhibits competitively with respect to lactate and vice versa. In both cases the Km for the carboxylate as a substrate was the same as its Ki as an inhibitor. Alpha-Cyano-4-hydroxycinnamate and its analogues inhibited the uptake of both lactate and pyruvate competitively. Inhibition was also produced by treatment of cells with fluorodinitrobenzene but not with the thiol reagents or Pronase. At high concentrations of pyruvate or lactate (20mM), uptake of the carboxylate was accompanied by an efflux of Cl-ions. This efflux of Cl- was inhibited by alpha-cyano-4-hydroxycinnamate and picrate and could be totally abolished by very low (less than 10 muM) concentrations of the inhibitor of Cl- transport, 4,4'-di-isothiocyanostilbene-2,2'-disulphonic acid. This inhibitor titrated out the chlordie efflux induced by pyruvate, bicarbonate, formate and fluoride, in each case total inhibition becoming apparent when approximately 1.2x10(6) molecules of inhibitor were present per erythrocyte, that is, about one inhibitor molecule per molecule of the Cl- carrier. Evan when Cl- efflux was totally blocked pyruvate and lactate uptake occurred. Kinetic evidence is presented which suggests that the Cl- carrier can transport pyruvate and lactate with a high Km and high Vmax., but that an additional carrier with a low Km and a low Vmax. also exists. This carrier catalyses the exchange of small carboxylate anions with intracellular lactate, is competitively inhibited by alpha-cyano-4-hydroxycinnamate and non-competitively inhibited by picrate. The Cl- carrier shows a reverse pattern of inhibition. It is concluded that net efflux of lactic acid from the cell must occur on the Cl- carrier and involve exchange with HCO3 - followed by loss of CO2. The low Km carrier might be used in pyruvate/lactate or acetoacetate/beta-hydroxybutyrate exchanges involved in transferring reducing power across the cell membrane. The possibility that the Cl- carrier exists in cells other than the erythrocyte is discussed. It is concluded that its presence in other cell membranes together with a low intracellular Cl- concentration would explain why the pH in the cytoplasm is lower than that of the blood, and why permeable carboxylate anions do not accumulate within the cell when added from outside. PMID:942406

Halestrap, A P

1976-01-01

342

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

Code of Federal Regulations, 2013 CFR

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

2013-07-01

343

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

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

2014-07-01

344

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

Code of Federal Regulations, 2012 CFR

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

2012-07-01

345

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

346

Electrical Transport of Spin-Polarized Carriers in Disordered Ultrathin Films  

Microsoft Academic Search

Slow, nonexponential relaxation of electrical transport accompanied by memory effects has been induced in quench-condensed ultrathin amorphous Bi films by the application of a parallel magnetic field. This behavior, which is very similar to space-charge limited current flow, is found in extremely thin films well on the insulating side of the thickness-tuned superconductor-insulator transition. It may be the signature of

L. M. Hernandez; A. Bhattacharya; Kevin A. Parendo; A. M. Goldman

2003-01-01

347

Self-consistent coupled carrier transport full-wave EM analysis of semiconductor traveling-wave devices  

Microsoft Academic Search

We propose a rigorous finite-element-method (FEM) model for traveling-wave structures on doped semiconductor substrates based on a full-wave electromagnetic model coupled to a drift-diffusion description of carrier transport. The coupled model allows to describe field-carrier interactions in distributed structures, where strong low-frequency dispersion due to metal and semiconductor losses and multimodal behavior are observed. Slow-wave propagation, which is significant for

Francesco Bertazzi; Federica Cappelluti; Simona Donati Guerrieri; Fabrizio Bonani; Giovanni Ghione

2006-01-01

348

Interaction of the bioactive flavonol, icariin, with the essential human solute carrier transporters.  

PubMed

Solute carrier transporters (SLCs), in particular the organic anion transporting polypeptides (OATPs) and organic anion/cation transporters (OATs/OCTs), are responsible for the cellular entry of many clinically important drugs in body. They largely influence drug safety and efficacy. Icariin is a flavonol widely present in many herbal preparations, which is used to improve sexual function and prevent osteogenesis. However, precautions are necessary in therapies containing icariin due to its involvement in drug-drug/herb interactions, possibly mediated through competing drug uptake via membrane-transporter proteins. This study is the first to comprehensively evaluate the interactions between icariin and a range of essential SLCs. Our data demonstrated that icariin can significantly inhibit OATP1B3- and OATP2B1-mediated cellular uptake of specific substrates (IC?? of 3.0 ± 1.3 and 6.4 ± 1.9 ?M, respectively). Our study revealed that icariin can potentially compete with coadministrated drugs for particular SLCs, which may impact the therapeutic outcome of regimens. PMID:24265111

Li, Zhen; Cheung, Florence Shin Gee; Zheng, Jian; Chan, Ting; Zhu, Ling; Zhou, Fanfan

2014-02-01

349

Charging effects on the carrier mobility in silicon-on-insulator wafers covered with a high-k layer  

NASA Astrophysics Data System (ADS)

The carrier mobility ? in low-doped silicon-on-insulator wafers is found to be strongly modified by the deposition of a thin ZrO2 or SrZrO3 top layer grown by molecular-beam epitaxy. Pseudo-metal-oxide-semiconductor field-effect-transistor measurements performed on several samples clearly show a correlation between ? and the density of interface traps (Dit) at the Si/buried-oxide interface. The reduction of Dit by a forming gas anneal leads to a corresponding increase in mobility. Moreover, the high-k/Si interface can contribute to the total drain current via the creation of an inversion channel induced by trapped charges in the high-k layer. Using Hall-effect measurements, we took advantage of this additional current to evaluate the carrier mobility at the high-k/Si interface, without the need of a top gate electrode.

Halley, D.; Norga, G.; Guiller, A.; Fompeyrine, J.; Locquet, J. P.; Drechsler, U.; Siegwart, H.; Rossel, C.

2003-11-01

350

Charge transport mechanisms and memory effects in amorphous TaNx thin films  

PubMed Central

Amorphous semiconducting materials have unique electrical properties that may be beneficial in nanoelectronics, such as low leakage current, charge memory effects, and hysteresis functionality. However, electrical characteristics between different or neighboring regions in the same amorphous nanostructure may differ greatly. In this work, the bulk and surface local charge carrier transport properties of a-TaNx amorphous thin films deposited in two different substrates are investigated by conductive atomic force microscopy. The nitride films are grown either on Au (100) or Si [100] substrates by pulsed laser deposition at 157 nm in nitrogen environment. For the a-TaNx films deposited on Au, it is found that they display a negligible leakage current until a high bias voltage is reached. On the contrary, a much lower threshold voltage for the leakage current and a lower total resistance is observed for the a-TaNx film deposited on the Si substrate. Furthermore, I-V characteristics of the a-TaNx film deposited on Au show significant hysteresis effects for both polarities of bias voltage, while for the film deposited on Si hysteresis, effects appear only for positive bias voltage, suggesting that with the usage of the appropriate substrate, the a-TaNx nanodomains may have potential use as charge memory devices. PMID:24134740

2013-01-01

351

Charge transport mechanisms and memory effects in amorphous TaNx thin films.  

PubMed

Amorphous semiconducting materials have unique electrical properties that may be beneficial in nanoelectronics, such as low leakage current, charge memory effects, and hysteresis functionality. However, electrical characteristics between different or neighboring regions in the same amorphous nanostructure may differ greatly. In this work, the bulk and surface local charge carrier transport properties of a-TaNx amorphous thin films deposited in two different substrates are investigated by conductive atomic force microscopy. The nitride films are grown either on Au (100) or Si [100] substrates by pulsed laser deposition at 157 nm in nitrogen environment. For the a-TaNx films deposited on Au, it is found that they display a negligible leakage current until a high bias voltage is reached. On the contrary, a much lower threshold voltage for the leakage current and a lower total resistance is observed for the a-TaNx film deposited on the Si substrate. Furthermore, I-V characteristics of the a-TaNx film deposited on Au show significant hysteresis effects for both polarities of bias voltage, while for the film deposited on Si hysteresis, effects appear only for positive bias voltage, suggesting that with the usage of the appropriate substrate, the a-TaNx nanodomains may have potential use as charge memory devices. PMID:24134740

Spyropoulos-Antonakakis, Nikolaos; Sarantopoulou, Evangelia; Drazic, Goran; Kollia, Zoe; Christofilos, Dimitrios; Kourouklis, Gerasimos; Palles, Dimitrios; Cefalas, Alkiviadis Constantinos

2013-01-01

352

Role of proton hopping in surface charge transport on tin dioxide as revealed by the thermal dependence of conductance.  

PubMed

The presence of water on an oxide surface can dramatically alter its electrical properties with important consequences for electrical measurements by scanning probe microscopy, and for the use of semiconducting oxides in sensing applications. Here, the thermal dependence of the conductance of tin dioxide is interpreted by combining semiconductor equilibrium carrier statistics with a proton hopping mechanism. First, the functional form of this charge transport model is fit to experimental conductance data for tin dioxide. Next, the important energy parameters in the model are computed with density functional theory. Comparing the values of the energy parameters obtained by fitting, to the values for the same parameters obtained from electronic structure calculations, yields new insight into the surface charge transport in tin dioxide. In particular, it is found that mobile protons, freed from the dissociative adsorption of water on the [110] surface, are an essential component of the observed thermal dependence of conductance in tin dioxide. PMID:25275726

Wexler, Robert B; Sohlberg, Karl

2014-12-26

353

Charge transport in poly(3-hexylthiophene):CdSe nanocrystals hybrid thin films investigated with time-of-flight measurements  

NASA Astrophysics Data System (ADS)

Charge carrier mobilities and transport dispersivity are studied in hybrid films composed of poly(3-hexylthiophene) and CdSe nanocrystals by the time-of-flight method, using a field range of 105-106 V/cm. It is found that charge transport parameters pass through an optimum for 75 wt. % (36 vol. %) of nanocrystals in the polymer matrix, yielding balanced hole and electron mobilities around 10-3 cm2/V s. Changing the nanocrystal shape from spherical to branched increases the intersite coupling disorder in the hybrid whereas changing the surface ligands from stearate/oleylamine to pyridine decreases it. Both these modifications have an impact on the electric field dependence of the measured mobilities.

Couderc, Elsa; Bruyant, Nicolas; Fiore, Angela; Chandezon, Frédéric; Djurado, David; Reiss, Peter; Faure-Vincent, Jérôme

2012-09-01

354

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

355

The Charge Transport in Organic Field-Effect Transistor as an Interface Charge Propagation: The Maxwell-Wagner Effect Model and Transmission Line Approximation  

NASA Astrophysics Data System (ADS)

By analyzing electric field migration in the pentacene organic field-effect transistor channel (OFET), visualized using the time-resolved microscopic optical second harmonic generation (TRM-SHG) is analyzed the propagation of injected carriers. We find that the accumulated charge propagation on the pentacene-gate insulator interface of the three-electrode system is clearly different from the drift in electric field of the two-electrode system. The propagation of injected carriers is evaluated on the basis of the Maxwell-Wagner effect model and the transmission line approximation. We show that the interface charge accumulation has a significant contribution to the charge transport in OFET. Proposed model for the transient state is beyond the limits of common used impedance spectroscopy models and represents extension of the small-signal analysis. Found relation between mobility and transit time helps in analysis of OFET transit time sensitive experiments such as the time-of-flight technique (TOF) or TRM-SHG.

Martin Weis,; Jack Lin,; Dai Taguchi,; Takaaki Manaka,; Mitsumasa Iwamoto,

2010-07-01

356

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

SciTech Connect

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

Xie, M.-Y.; Ben Sedrine, N.; Hung, L.; Monemar, B.; Darakchieva, V., E-mail: vanya@ifm.liu.se [Department of Physics, Chemistry, and Biology, IFM, Linköping University, SE-581 83 Linköping (Sweden); Schöche, S.; Hofmann, T.; Schubert, M. [Center for Nanohybrid Functional Materials, Department of Electrical Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588-0511 (United States); Wang, X. [State Key Laboratory of Artificial Microstructure and Mesoscopic Physics, Peking University, Beijing (China); Yoshikawa, A. [Center for SMART Green Innovation Research, Chiba University, Chiba (Japan); Department of Information and Communication Engineering, Kogakuin University, Tokyo (Japan); Wang, K.; Araki, T. [Department of Photonics, Ritsumeikan University, 1-1-1 Noji Higashi, Kusatsu, Shiga 525-8577 (Japan); Nanishi, Y. [Department of Photonics, Ritsumeikan University, 1-1-1 Noji Higashi, Kusatsu, Shiga 525-8577 (Japan); WCU Hybrid Materials Program, Department of Materials Science and Engineering, Seoul National University, Seoul 151-744 (Korea, Republic of)

2014-04-28

357

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

NASA Astrophysics Data System (ADS)

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 CBP film, the electron mobility is similar for Ir(ppy)3-doped CBP but it is more than two orders of magnitude lower for btp2Ir(acac)-doped CBP. Because of such difference in the electrical conduction properties between the Ir(ppy)3- and btp2Ir(acac)-doped CBP, the main recombination zone position and the electron-hole balance changes. Based on these findings, we optimized white organic light emitting diodes (OLEDs) with multi-emitting layer (EML) structures in which CBP layers doped with Ir(ppy)3 and btp2Ir(acac) and fluorescent dopant of 4,4'-bis[2-{4-(N,N-diphenylamino)phenyl}vinyl]biphenyl (DPAVBi) were used as green (G), red (R), and blue (B) EMLs, respectively. The white OLEDs with the R/G/B EML sequence show improved electron and hole balance, resulting higher efficiency, better color stability and longer lifetime compared to the G/R/B EML sequence. A high luminous current efficiency of 13.5 cd/A at 100 cd/m2 was achieved with the R/G/B EML sequence.

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

2008-08-01

358

Nonequilibrium Spin Magnetization Quantum Transport Equations: Spin and Charge Coupling  

E-print Network

The classical Bloch equations of spin magnetization transport is extended to fully time-dependent and highly-nonlinear nonequilibrium spin magnetization quantum distribution function transport (SMQDFT) equations. The relevant variables are the spinor correlation functions which separate into charge and spin magnetization distributions that becomes highly coupled in SMQDFT equa- tions. The leading terms consist of the Boltzmann kinetic equation with spin-orbit coupling in a magnetic eld together with spin-dependent scattering terms which contribute to the torque. These do not have analogue within the classical relaxation-dephasing picture, but are inherently quantum many-body effects. These should incorporate the spatiotemporal-dependent phase-space dynam- ics of Elliot-Yafet and Dyakonov-Perel scatterings. The resulting SMQDFT equations should serve as a theoretical foundation for computational spintronic and nanomagnetic device applications, in ultrafast-switching-speed/low-power performance and reliability analyses.

F. A. Buot; R. A. Loberternos; R. E. S. Otadoy; D. L. Villarin

2011-12-19

359

Charge transport and electroluminescence of silicon nanocrystals/SiO2 superlattices  

NASA Astrophysics Data System (ADS)

Charge transport and electroluminescence mechanisms in Si-rich Si oxynitride/silicon oxide (SRON/SiO2) superlattices deposited on p-type Si substrate are reported. The superlattice structures were deposited by plasma-enhanced chemical-vapor deposition and subsequently annealed at 1150 °C to precipitate and crystallize the Si excess into Si nanocrystals. The dependence of the electrical conduction on the applied voltage and temperature was found to be well described by a Poole-Frenkel transport mechanism over a wide voltage range. On the other hand, the observed dependence of the electroluminescence on the SRON layer thickness is a clear proof of quantum confinement and was attributed to an excitonic radiative recombination taking place in the confined states within the Si quantum dots. A model is proposed based on thermal hopping of electrons between the quantum dots acting as trap states (Poole-Frenkel). A correlation between carrier transport and electroluminescence has been established considering impact ionization of high-kinetic energy electrons on the Si quantum dots.

López-Vidrier, J.; Berencén, Y.; Hernández, S.; Blázquez, O.; Gutsch, S.; Laube, J.; Hiller, D.; Löper, P.; Schnabel, M.; Janz, S.; Zacharias, M.; Garrido, B.

2013-10-01

360

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

SciTech Connect

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

Germanenko, A. V., E-mail: Alexander.Germanenko@usu.ru [Ural Federal University, Institute of Natural Sciences (Russian Federation); Minkov, G. M. [Russian Academy of Sciences, Institute of Metal Physics, Ural Branch (Russian Federation); Rut, O. E. [Ural Federal University, Institute of Natural Sciences (Russian Federation); Sherstobitov, A. A. [Russian Academy of Sciences, Institute of Metal Physics, Ural Branch (Russian Federation); Dvoretsky, S. A.; Mikhailov, N. N. [Russian Academy of Sciences, Institute of Semiconductor Physics, Siberian Branch (Russian Federation)

2013-12-15

361

The exocyst complex contributes to PIN auxin efflux carrier recycling and polar auxin transport in Arabidopsis.  

PubMed

In land plants polar auxin transport is one of the substantial processes guiding whole plant polarity and morphogenesis. Directional auxin fluxes are mediated by PIN auxin efflux carriers, polarly localized at the plasma membrane. The polarization of exocytosis in yeast and animals is assisted by the exocyst: an octameric vesicle-tethering complex and an effector of Rab and Rho GTPases. Here we show that rootward polar auxin transport is compromised in roots of Arabidopsis thaliana loss-of-function mutants in the EXO70A1 exocyst subunit. The recycling of PIN1 and PIN2 proteins from brefeldin-A compartments is delayed after the brefeldin-A washout in exo70A1 and sec8 exocyst mutants. Relocalization of PIN1 and PIN2 proteins after prolonged brefeldin-A treatment is largely impaired in these mutants. At the same time, however, plasma membrane localization of GFP:EXO70A1, and the other exocyst subunits studied (GFP:SEC8 and YFP:SEC10), is resistant to brefeldin-A treatment. In root cells of the exo70A1 mutant, a portion of PIN2 is internalized and retained in specific, abnormally enlarged, endomembrane compartments that are distinct from VHA-a1-labelled early endosomes or the trans-Golgi network, but are RAB-A5d positive. We conclude that the exocyst is involved in PIN1 and PIN2 recycling, and thus in polar auxin transport regulation. PMID:23163883

Drdová, Edita Janková; Synek, Lukáš; Pe?enková, Tamara; Hála, Michal; Kulich, Ivan; Fowler, John E; Murphy, Angus S; Zárský, Viktor

2013-03-01

362

Arabidopsis TT19 functions as a carrier to transport anthocyanin from the cytosol to tonoplasts.  

PubMed

Anthocyanins are synthesized in the cytosolic surface of the endoplasmic reticulum (ER) but dominantly accumulate in the vacuole. Little is known about how anthocyanins are transported from the ER to the vacuole. Here, we provide evidence supporting that Transparent Testa 19 (TT19), a glutathione S-transferase (GST), functions as a carrier to transport cyanidin and/or anthocyanins to the tonoplast. We identified a novel tt19 mutant (tt19-7), which barely accumulates anthocyanins but produces a 36% higher level of flavonol than the wild-type (WT), from ethyl methanesulfonate mutagenized seeds. Expressing TT19-fused green fluorescence protein (GFP) in tt19-7 rescues the mutant phenotype in defective anthocyanin biosynthesis, indicating that TT19-GFP is functional. We further showed that TT19-GFP is localized not only in the cytoplasm and nuclei, but also on the tonoplast. The membrane localization of TT19-GFP was further ascertained by immunoblot analysis. In vitro assay showed that the purified recombinant TT19 increases water solubility of cyanidin (Cya) and cyanidin-3-O-glycoside (C3G). Compared with C3G, Cya can dramatically quench the intrinsic tryptophan fluorescence of TT19 to much lower levels, indicating a higher affinity of TT19 to Cya than to C3G. Isothermal titration calorimetry analysis also confirmed physical interaction between TT19 and C3G. Taken together, our data reveal molecular mechanism underlying TT19-mediated anthocyanin transportation. PMID:22201047

Sun, Yi; Li, Hong; Huang, Ji-Rong

2012-03-01

363

Three-dimensional Poole-Frenkel analytical model for carrier transport in amorphous chalcogenides  

NASA Astrophysics Data System (ADS)

In this work, we propose a three-dimensional Poole-Frenkel (3DPF) analytical model for carrier transport in amorphous chalcogenides. 3DPF is based on the original Poole-Frenkel (PF) theory of non-interacting Coulombic traps responsible for carrier conduction in the bulk of the material. However, while in the original PF equation the device current-voltage characteristics is calculated by considering the barrier-lowering on the applied electric field direction only, in 3DPF we overcome this approximation by calculating the electronic current due to the integral effect of the Coulombic barrier shaping in three dimensions upon application of an electric field. As a consequence, 3DPF is capable to describe both the relatively-low and relatively-high electric fields regimes, while the PF equation implicitly assumes the device to be operated at high electric fields only. Thus, 3DPF features a better agreement with experimental data compared to original PF, predicting both (i) Poole-like behavior at low-fields, i.e., I ?sinh(V), and (ii) PF-like dependence in the higher fields regime, i.e., I ?exp(?V ), within a single coherent physical picture. The model is validated through I-V characterization on phase-change memory devices integrating amorphous Ge2Sb2Te5 as active material. Moreover, to address the model consistency, temperature dependence and correlations between model parameters are validated in comparison with experimental data.

Betti Beneventi, Giovanni; Guarino, Lucrezia; Ferro, Massimo; Fantini, Paolo

2013-01-01

364

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

NASA Astrophysics Data System (ADS)

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 thick polyurethane foam (PUF) to maintain the LNG below the cryogenic temperature, -162°C. Due to the repeated shock on the PUF, a crack could be developed on the tank wall causing a tremendous disaster for LNG carriers. To prevent the accidental crack on the tank, a continuous monitoring of the strain imposed on the PUF is recommended. In this work, a fiber-optic Bragg grating was imbedded inside the PUF for monitoring the strain parallel to the impact direction. The optical fiber sensor with a small diameter of 125 ?m was suitable to be inserted in the PUF through a small hole drilled after the PUF was cured. In-situ monitoring of the strain producing the change of Bragg reflection wavelength, a high speed wavelength interrogation method was employed by using an arrayed waveguide grating. By dropping a heavy mass on the PUF, we measured the strain imposed on the insulation panel.

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

2008-08-01

365

TRAPPING-RELATED RECOMBINATION OF CHARGE CARRIERS IN SILICON , N.-P. Harder  

E-print Network

. Brendel 1,3 1 Institute of Solar Energy Research Hamelen (ISFH), Emmerthal, Lower Saxony, Germany 2 conductance-based lifetime determination, such as in QSSPC-measurements. In our work here we show-SiNx prior to measurements of the effective carrier lifetime. When applied to single-crystalline float-zone

366

Structural factors impacting carrier transport and electroluminescence from Si nanocluster-sensitized Er ions.  

PubMed

We present an analysis of factors influencing carrier transport and electroluminescence (EL) at 1.5 µm from erbium-doped silicon-rich silica (SiOx) layers. The effects of both the active layer thickness and the Si-excess content on the electrical excitation of erbium are studied. We demonstrate that when the thickness is decreased from a few hundred to tens of nanometers the conductivity is greatly enhanced. Carrier transport is well described in all cases by a Poole-Frenkel mechanism, while the thickness-dependent current density suggests an evolution of both density and distribution of trapping states induced by Si nanoinclusions. We ascribe this observation to stress-induced effects prevailing in thin films, which inhibit the agglomeration of Si atoms, resulting in a high density of sub-nm Si inclusions that induce traps much shallower than those generated by Si nanoclusters (Si-ncs) formed in thicker films. There is no direct correlation between high conductivity and optimized EL intensity at 1.5 µm. Our results suggest that the main excitation mechanism governing the EL signal is impact excitation, which gradually becomes more efficient as film thickness increases, thanks to the increased segregation of Si-ncs, which in turn allows more efficient injection of hot electrons into the oxide matrix. Optimization of the EL signal is thus found to be a compromise between conductivity and both number and degree of segregation of Si-ncs, all of which are governed by a combination of excess Si content and sample thickness. This material study has strong implications for many electrically-driven devices using Si-ncs or Si-excess mediated EL. PMID:23037398

Cueff, Sébastien; Labbé, Christophe; Jambois, Olivier; Berencén, Yonder; Kenyon, Anthony J; Garrido, Blas; Rizk, Richard

2012-09-24

367

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

368

Controlling polymer translocation and ion transport via charge correlations.  

PubMed

We develop a correlation-corrected transport theory in order to predict ionic and polymer transport properties of membrane nanopores under physical conditions where mean-field electrostatics breaks down. The experimentally observed low KCl conductivity of open ?-hemolysin pores is quantitatively explained by the presence of surface polarization effects. Upon the penetration of a DNA molecule into the pore, these polarization forces combined with the electroneutrality of DNA sets a lower boundary for the ionic current, explaining the weak salt dependence of blocked pore conductivities at dilute ion concentrations. The addition of multivalent counterions to the solution results in the reversal of the polymer charge and the direction of the electroosmotic flow. With trivalent spermidine or quadrivalent spermine molecules, the charge inversion is strong enough to stop the translocation of the polymer and to reverse its motion. This mechanism can be used efficiently in translocation experiments in order to improve the accuracy of DNA sequencing by minimizing the translocation velocity of the polymer. PMID:25310861

Buyukdagli, Sahin; Ala-Nissila, T

2014-11-01

369

Controlling polymer translocation and ion transport via charge correlations  

E-print Network

We develop a correlation-corrected transport theory in order to predict ionic and polymer transport properties of membrane nanopores in physical conditions where mean-field electrostatics breaks down. The experimentally observed low KCl conductivity of open alpha-Hemolysin pores is quantitatively explained by the presence of surface polarization effects. Upon the penetration of a DNA molecule into the pore, these polarization forces combined with the electroneutrality of DNA sets a lower boundary for the ionic current, explaining the weak salt dependence of blocked pore conductivities at dilute ion concentrations. The addition of multivalent counterions into the solution results in the reversal of the polymer charge and the direction of the electroosmotic flow. With trivalent spermidine or quadrivalent spermine molecules, the charge inversion is strong enough to stop the translocation of the polymer and to reverse its motion. This mechanism can be used efficiently in translocation experiments in order to improve the accuracy of DNA sequencing by minimizing the translocation velocity of the polymer.

Sahin Buyukdagli; Tapio Ala-Nissila

2014-10-10

370

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

PubMed Central

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

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

2015-01-01

371

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

PubMed

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

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

2015-01-01

372

Determination of thermal and electronic carrier transport properties of SnS thinfilms using photothermal beam deflection technique  

SciTech Connect

Graphical abstract: Display Omitted Highlights: ? Determination of carrier transport properties of SnS thin films non-destructively. ? SnS thin films were deposited by chemical spray pyrolysis technique. ? Photothermal beam deflection technique is used for film analysis. ? Optimization of film deposition parameters. ? Photothermal imaging of SnS films. -- Abstract: Photothermal beam deflection technique is an efficient tool for non-destructive evaluation of thin films. Thin films of tin mono sulphide, which find application as absorber layer in photovoltaic cells, were deposited by chemical spray pyrolysis technique and their carrier transport properties were determined using photothermal beam deflection technique. Thermal diffusivity, minority carrier lifetime, mobility and surface recombination velocity of these films fabricated under different spray conditions like varying spray rate, Sn/S ratio and substrate temperature were determined. Photothermal beam deflection technique was also employed for constructing the thermal images of these films to evaluate the film uniformity.

Warrier, Anita R., E-mail: anitawarrier2@gmail.com [Cochin University of Science and Technology, Cochin 682 022 (India); Sajeesh, T.H.; Kartha, C. Sudha; Vijayakumar, K.P. [Cochin University of Science and Technology, Cochin 682 022 (India)] [Cochin University of Science and Technology, Cochin 682 022 (India)

2012-11-15

373

IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 17, NO. 9, SEPTEMBER 2005 1779 The Role of Carrier Transport on the Current Injection  

E-print Network

of the offset QW structures. The active region is closer to (a) p-cladding for Laser P and (b) n-cladding Transport on the Current Injection Efficiency of InGaAsN Quantum-Well Lasers Jeng-Ya Yeh, Luke J. Mawst efficiency of InGaAsN quantum-well (QW) lasers can be significantly affected by carrier transport

Gilchrist, James F.

374

Foundations of Molecular Electronics — Charge Transport in Molecular Conduction Junctions  

NASA Astrophysics Data System (ADS)

The most fundamental structure involved in molecular electronics is a molecular transport junction, consisting of one (ideally) or more molecules extending between two electrodes. These junctions combine the fundamental process of intramolecular electron transfer with the mixing of molecular and continuum levels at the electrodes and the nonequilibrium process of voltage-driven currents. Much of this book is devoted to the complicated but significant behaviors that arise from this conjunction. This introductory chapter attempts to sketch some of the principles and also some of the unresolved issues that characterize molecular transport junctions. Sections 1.2 1.4 deal with fundamental ideas. These include an appropriate theoretical formulation of the conductance calculation in terms of non-equilibrium Green’s functions, the relationship between junction conductance and nonadiabatic electron transfer rates in the same molecular entities, and the role and magnitude of interactions between the dynamics of the transferring electronic charges and the nuclear degrees of freedom. Section 1.5 addresses some of the outstanding and difficult issues in understanding junction transport, including geometry and its change with voltage, the electrostatic profile under applied voltage, electronic structure models and their limitations, and fluctuations and switching phenomena in junctions.

Jortner, Joshua; Nitzan, Abraham; Ratner, Mark A.

375

Controlling charge transport in single molecules using electrochemical gate.  

PubMed

We have studied charge transport through single molecules covalently bound to two gold electrodes in electrolytes by applying a voltage between the two electrodes and a reference electrode (gate). This electrochemical gating can effectively control the current through the molecules, depending on the electronic properties of the molecules. For electrochemically inactive molecules, such as 4,4'-bipyridine and 1,4'-benzenedithiol, the gate voltage influences the transport current only slightly (less than 30%). This lack of significant gate effect is attributed to the large LUMO-HOMO gaps of the molecules and the screening of the gate field by the two electrodes. For nitro-oligo(phenylene ethynylene) (OPE-NO2), which undergoes multiple irreversible reductions at negative gate voltages, the current through the molecules can be modulated several folds by the gate. This gate effect is irreversible and associated with the reduction of the NO2 group to different products that have different electron withdrawing capabilities from the conjugate backbone of the molecule. The most interesting molecules are perylene tetracarboxylic diimide compounds (PTCDI), which exhibit fully reversible redox reactions. The current through PTCDI can be reversibly varied and controlled over three orders of magnitude with the gate. Such a large gate effect is related to a redox state-mediated electron transport process. PMID:16512367

Li, Xiulan; Xu, Bingqian; Xiao, Xiaoyin; Yang, Xiaomei; Zang, Ling; Tao, Nongjian

2006-01-01

376

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

377

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

E-print Network

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

Yang, Zheng

378

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

E-print Network

for ferromagnetic exchange in ZnO:Co diluted magnetic semiconductor materials. © 2008 American Institute of PhysicsElectron carrier concentration dependent magnetization and transport properties in ZnO:Co diluted October 2008; published online 4 December 2008 Diluted magnetic semiconducting ZnO:Co thin films

Yang, Zheng

379

Photogenerated charge carrier recombination processes in CdS/P3OT solar cells: effect of structural and optoelectronic properties of CdS films  

NASA Astrophysics Data System (ADS)

Research and development activities in organic solar cells have been intensified in the last two decades, and the reported energy conversion efficiency in small cell samples is rapidly increased. However, the relation between cell performance and material preparation conditions is not fully understood. In this work charge carrier recombination processes in hybrid poly-3-octylthiophene (P3OT)/cadmium sulfide (CdS) photovoltaic cells were analyzed as a function of structural and optoelectronic properties of chemical bath deposited CdS thin films. The temperature of the bath solution varied between 60 and 80 °C, and the deposition time from 1 to 3 h. Charge carrier recombination times in CdS films were measured with photoconductance decay technique, whereas the same time in P3OT films was estimated by Time-of-Flight method. Charge carrier recombination rates at CdS/P3OT interface were determined by transient photovoltage technique. It is found that CdS films grown at lower solution temperature (60 °C) give a higher charge carrier recombination rate at CdS/P3OT interface and larger short-circuit current density and energy conversion efficiency values in the corresponding solar cells, in comparison with the 80 °C deposited ones. This improvement could come from the reduction of charge carrier trap density inside grains as well as at grain boundaries in lower temperature deposited CdS films.

Cortina, H.; Pineda, E.; Campos, J.; Nicho, M. E.; Hu, H.

2011-09-01

380

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

381

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

Code of Federal Regulations, 2010 CFR

...collected on originating access minutes and calculated using the weighting method set forth in paragraph (c) of this section. The...per-minute charge on terminating access calculated using the weighting method set forth in paragraph (c) of this section....

2010-10-01

382

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

383

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

Federal Register 2010, 2011, 2012, 2013

...FMCSA--001 Motor Carrier Management Information System. SYSTEM...FMCSA)--001 Motor Carrier Management Information System. SECURITY...safety performance. Safety Fitness Electronic Records (SAFER...enforcement officers. Enforcement Management Information System...

2013-09-25

384

Charge separation and charge transport in nanostructured TiO2 film electrodes  

NASA Astrophysics Data System (ADS)

Photoelectrochemical measurements have been performed on film electrodes consisting of linked nano-sized TiO2 colloids. The film thickness ranged from 1 - 40 micrometers. The film network was attached to a thin transparent conducting layer of SnO2 allowing for photogenerated electrons to be collected in an outer electrical circuit. By illuminating electrodes of different thicknesses with monochromatic light from either side, it was possible to induce charge separation in different regions of the film network. In this way, it was proved that electrons have different probabilities of reaching the back contact depending on the location in the film where they are created. The results also illustrate the importance of the redox species in the cavities of these porous electrodes. By adding acceptors to the electrolyte it was possible to alter the conditions for charge transfer in the nanocrystalline film. It was shown that electron acceptors such as oxygen or iodine in the solution strongly affects the rate of charge transfer at the particle-electrolyte interface and the transport of electrons throughout the TiO2 film-network. Modification of the semiconductor-electrolyte interface with surface adsorbed pyridine induced major changes in the charge transfer events at the interface. The photocurrent yields were greatly improved by this surface treatment. The effect of pH in solution was also investigated. The rate of charge transfer at the particle-electrolyte interface was changed at high surface density of OH--ions. This was explained due to the change of the surface energy causing different driving forces for redox reactions, but also due to the more negatively electrostatic surface potential of the particles preventing the encounter of negatively charged redox species with the colloid surface. Phototransient measurements indicated a depletion of redox species in the pores of the film. Thereby it was pointed out that the dynamics of the redox species in the confined cavities of the film are a limiting factor for the charge separation efficiency in nanocrystalline film. The photovoltage in anaerobic solutions sustained for very long periods, indicating that the linked particles may work as reservoirs for photoexcited electrons if the access to electron acceptors in the solution is choked. It was concluded that surface processes are favored at the small semiconductor particles used in this study.

Lindstrom, Henrik; Hagfeldt, Anders; Rensmo, Hakan; Solbrand, Anita; Sodergren, Sven; Lindquist, Sten-Eric

1995-08-01

385

Charge transport in cancer-related genes and early carcinogenesis  

NASA Astrophysics Data System (ADS)

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

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

2011-01-01

386

Charge transport in hybrid nanorod-polymer composite photovoltaiccells  

SciTech Connect

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

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

2002-06-21

387

Electron-phonon interaction and charge carrier mass enhancement in SrTiO3.  

PubMed

We report a comprehensive THz, infrared and optical study of Nb-doped SrTiO3 as well as dc conductivity and Hall effect measurements. Our THz spectra at 7 K show the presence of an unusually narrow (<2 meV) Drude peak. For all carrier concentrations the Drude spectral weight shows a factor of three mass enhancement relative to the effective mass in the local density approximation, whereas the spectral weight contained in the incoherent midinfrared response indicates that the mass enhancement is at least a factor two. We find no evidence of a particularly large electron-phonon coupling that would result in small polaron formation. PMID:18643435

van Mechelen, J L M; van der Marel, D; Grimaldi, C; Kuzmenko, A B; Armitage, N P; Reyren, N; Hagemann, H; Mazin, I I

2008-06-01

388

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. PMID:21643528

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

2010-01-01

389

Charge Transport Mechanism in Thin Cuticles Holding Nandi Flame Seeds  

PubMed Central

Metal-sample-metal sandwich configuration has been used to investigate DC conductivity in 4??m thick Nandi flame [Spathodea campanulata P. Beauv.] seed cuticles. J-V characteristics showed ohmic conduction at low fields and space charge limited current at high fields. Charge mobility in ohmic region was 4.06 × 10?5??(m2V?1s?1). Temperature-dependent conductivity measurements have been carried out in the temperature range 320?K < T > 450?K. Activation energy within a temperature of 320?K–440?K was about 0.86?eV. Variable range hopping (VRH) is the main current transport mechanism at the range of 330–440?K. The VRH mechanism was analyzed based on Mott theory and the Mott parameters: density of localized states near the Fermi-level N(EF) ? 9.04 × 1019??(eV?1cm?3) and hopping distance R ? 1.44 × 10?7?cm, while the hopping energy (W) was in the range of 0.72?eV–0.98?eV. PMID:20130799

Kipnusu, Wycliffe K.; Katana, Gabriel; Migwi, Charles M.; Rathore, I. V. S.; Sangoro, Joshua R.

2009-01-01

390

Transport of charge and energy in metal-molecule-metal junctions  

NASA Astrophysics Data System (ADS)

This dissertation presents the experimental study of the electrical conductance (G) and Seebeck coefficient (S) of metal-molecule-metal junctions. The dependence of the electrical conductance of metal-molecule-metal junctions on the molecule's structure is elucidated. The existence of a measurable Seebeck coefficient in metal-molecule-metal junctions is shown for the first time and the sign of the measured Seebeck coefficient is used to determine whether the charge transport in metal-molecule-metal junctions is dominated by positive (p-type) or negative (n-type) charge carriers. The electrical conductance of a series of thiol (-SH), amine (-NH 2) terminated aliphatic and aromatic molecules was measured using a modified scanning tunneling microscope break junction technique. A new method called the last-step analysis (LSA) was introduced to analyze data obtained in these measurements. This analysis in contrast to previous work does not require any data pre-selection, making the results less subjective and more reproducible. We first studied the electrical conductance of aliphatic molecular junctions. It was found that Au-hexanedithiol-Au, Au-octanedithiol-Au and Au-decanedithiol-Au junctions have an electrical conductance of 3.6 X 10 -4 Go, 4.4 X 10-5 Go and 5.7 X 10-6 Go, respectively, where Go is the fundamental quantum of electrical conductance. The electrical conductance decreases exponentially with the length of the alkane chains suggesting that the mechanism for electrical transport through these molecular junctions is quantum mechanical tunneling. On varying the end groups of aliphatic molecules 0rom thiols to amines we found that the electrical conductance was almost identical, suggesting that the end group had no significant effect on the electrical conductance in this case. We also measured the electrical conductance of aromatic molecular junctions: Au-1,4-benzenediamine-Au, Au-4,4'-dibenzenediamine-Au and Au-4.4''-tribenzenediamine-Au and they were found to have an electrical conductance of 1.05 X 10 -2 Go, 1.41 X 10-3 Go and 2.05 X 10-4 Go, respectively. Although, the electrical conductance decreases exponentially with the lengths of the molecules even in the case of aromatic molecules, the length dependence of the electrical conductance was much weaker than that of aliphatic molecular junctions. From the data it can be seen that for a given length aromatic molecular junctions have a larger conductance than aliphatic molecular junctions. The Seebeck coefficient (S) of molecular junctions was measured using a modified break junction technique by trapping molecules between two gold electrodes with a temperature difference across them. The junction Seebeck coefficient of Au-1,4-benzenedithiol-Au, Au-4,4'-dibenzenedithiol-Au and Au-4,4"-tribenzenedithiol-Au was measured at room temperature to be (+8.7 +/- 2.1) microvolts per Kelvin (muV/K), (+12.9 +/- 2.2) muV/K, and (+14.2 +/- 3.2) muV/K, respectively. The positive sign unambiguously indicates p-type (hole) conduction through these heterojunctions, and the Au Fermi level position for AuBDT-Au junctions was identified at 1.2 eV above the highest occupied molecular orbital (HOMO) level of BDT. Our study provides the first experimental answer to the question of whether charge transport through molecular junctions is dominated by p-type or n-type charge carriers. In perspective, the ability to study thermoelectricity in molecular junctions as demonstrated here allows us to address some of the fundamental transport problems in molecular electronics.

Sangi Reddy, Pramod Reddy

391

pH-responsive zwitterionic copolypeptides as charge conversional shielding system for gene carriers.  

PubMed

A novel rapid pH-responssive polymer polyethylenimine-poly(l-lysine)-poly(l-glutamic acid) (PELG) was designed as the shielding system. The zwitterionic copolypeptide PELG with negatively charged at physical pH can act as the shielding system to shield positively charged polyplexes. PELG was used to shield PEI25k/DNA to form ternary polyplex, the polyplex surface zeta potential can change from a negative to positive nearly pH value of 6.9. Because the pH value of tumor extracellular environment is about 6.5, the positive charges on the polyplexes could be restored in tumors, which is beneficial to the electrostatic interactions between positive polyplexes and negative tumor cells, leading to high cell uptake efficiency and high transfection efficiency. PMID:24240012

Tian, Huayu; Guo, Zhaopei; Lin, Lin; Jiao, Zixue; Chen, Jie; Gao, Shiqian; Zhu, Xiaojuan; Chen, Xuesi

2014-01-28

392

Acceptor-Compensated Charge Transport and Surface Chemical Reactions in Au-Implanted SnO2 Nanowires  

PubMed Central

A new deep acceptor state is identified by density functional theory calculations, and physically activated by an Au ion implantation technique to overcome the high energy barriers. And an acceptor-compensated charge transport mechanism that controls the chemical sensing performance of Au-implanted SnO2 nanowires is established. Subsequently, an equation of electrical resistance is set up as a function of the thermal vibrations, structural defects (Au implantation), surface chemistry (1?ppm NO2), and solute concentration. We show that the electrical resistivity is affected predominantly not by the thermal vibrations, structural defects, or solid solution, but the surface chemistry, which is the source of the improved chemical sensing. The response and recovery time of chemical sensing is respectively interpreted from the transport behaviors of major and minor semiconductor carriers. This acceptor-compensated charge transport mechanism provides novel insights not only for sensor development but also for research in charge and chemical dynamics of nano-semiconductors. PMID:24713609

Katoch, Akash; Sun, Gun-Joo; Choi, Sun-Woo; Hishita, Shunichi; Kulish, Vadym V.; Wu, Ping; Kim, Sang Sub

2014-01-01

393

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

NASA Astrophysics Data System (ADS)

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

Bondarenko, Anton; Vyvenko, Oleg

2014-02-01

394

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

SciTech Connect

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

Bondarenko, Anton [Interdisciplinary Resource Center for Nanotechnology, St. Petersburg State University, 198504 (Russian Federation); Vyvenko, Oleg [V.A. Fok Institute of Physics, St. Petersburg State University, Ulyanovskaya 1, Peterhof, St. Petersburg, 198504 (Russian Federation)

2014-02-21

395

Mass Transport Investigated with the Electrochemical and Electrogravimetric Impedance Techniques. 3. Complex Charge Transport in PPy/PSS Films  

E-print Network

Mass Transport Investigated with the Electrochemical and Electrogravimetric Impedance Techniques. 3/step electrochemical quartz crystal microbalance (EQCM) technique and the electrochemical/electrogravimetric impedance has been obtained, and also the ion transport behavior in the slow charge transport process has been

Kwak, Juhyoun

396

Magnetic Alignment and Charge Transport Improvement in Functional Soft Materials  

NASA Astrophysics Data System (ADS)

The realization of nanostructured functional materials by self-assembly in polymers and polymer nanocomposites is adversely affected by persisting structural defects which greatly diminish the performance of the material. The use of magnetic fields to impose long-range order is investigated in three distinct systems - ion-conducting block copolymers, semiconducting nanowire-polymer composites and lyotropic surfactant mesophases. The alignment process is quantitatively studied with X-ray scattering and microscopic methods. Time and temperature resolved data collected in situ during the magnetic experiments provide an insight into the thermodynamic and kinetic aspects of the process. These data together with simultaneous electrical conductivity measurements allow relating fundamental structural properties (e.g., morphology and long-range order) to transport properties (i.e., conductivity). In particular, it is demonstrated that magnetic fields offer a viable route for improvement of electric conductivity in these systems. More than an order of magnitude increase in conductivity is recorded in magnetically-annealed materials. The resulting aligned nanostructured systems are attractive for ordered solid polymer electrolyte membranes, heterojunction photovoltaic devices and generally help to understand charge transport mechanisms in anisotropic heterogeneous systems.

Majewski, Pawel W.

397

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

398

Electronic properties of meso-superstructured and planar organometal halide perovskite films: charge trapping, photodoping, and carrier mobility.  

PubMed

Solution-processed organometal trihalide perovskite solar cells are attracting increasing interest, leading to high performances over 15% in thin film architectures. Here, we probe the presence of sub gap states in both solid and mesosuperstructured perovskite films and determine that they strongly influence the photoconductivity response and splitting of the quasi-Fermi levels in films and solar cells. We find that while the planar perovskite films are superior to the mesosuperstructured films in terms of charge carrier mobility (in excess of 20 cm(2) V(-1) s(-1)) and emissivity, the planar heterojunction solar cells are limited in photovoltage by the presence of sub gap states and low intrinsic doping densities. PMID:24949826

Leijtens, Tomas; Stranks, Samuel D; Eperon, Giles E; Lindblad, Rebecka; Johansson, Erik M J; McPherson, Ian J; Rensmo, Håkan; Ball, James M; Lee, Michael M; Snaith, Henry J

2014-07-22

399

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

PubMed

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

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

2014-01-01

400

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

SciTech Connect

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

Danilov, L. V., E-mail: danleon84@mail.ru; Zegrya, G. G. [Russian Academy of Sciences, Ioffe Physical-Technical Institute (Russian Federation)] [Russian Academy of Sciences, Ioffe Physical-Technical Institute (Russian Federation)

2013-10-15

401

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

402

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

SciTech Connect

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

Antipov, S. A.; Belousov, Yu. M.; Solov'ev, V. R., E-mail: vic_sol@mail.ru [Moscow Institute of Physics and Technology (State University) (Russian Federation)

2012-11-15

403

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

SciTech Connect

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

Aleksandrova, E. L. [Russian Academy of Sciences, Ioffe Physicotechnical Institute (Russian Federation); Ivanov, A. G., E-mail: alexey.ivanov@bk.ru; Geller, N. M., E-mail: nin-hell@yandex.ru; Shamanin, V. V. [Russian Academy of Sciences, Institute of Macromolecular Compounds (Russian Federation)

2010-05-15

404

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

SciTech Connect

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

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

2012-04-05

405

Stereoselective transport of human His27- and Arg27-reduced folate carrier.  

PubMed

The stereoselective transport of methotrexate (L-amethopterin, L-MTX) and its antipode (D-amethopterin, D-MTX) by human reduced folate carrier (hRFC) has been examined in HEK293 cells expressing H27-hRFC and R27-hRFC. The uptake of both L-MTX and D-MTX increased as the extracellular pH increased from 6.0 to 7.4. The initial uptake rate of L-MTX into the H27- and R27-hRFCs of the HEK293 cells followed Michaelis-Menten kinetics with Km values of approximately 0.24 and 0.47?µM, respectively. Dixon plots revealed that the [(3)H]-L-MTX uptake mediated by the H27- and R27-hRFCs was inhibited competitively by unlabeled L-MTX with Ki values of approximately 0.1 and 0.5?µM, respectively. D-MTX also competitively inhibited the H27- and R27-hRFC mediated uptake of [(3)H]-L-MTX with Ki values of approximately 3.4 and 3.2?µM, respectively. The RFC-mediated uptake clearance of L-MTX was approximately 15-fold greater than that of D-MTX in the H27-hRFC-HEK293 cells, and was more than 30-fold greater than that of D-MTX in the R27-hRFC-HEK293 cells. The results of the current study have revealed that the enantiomers of MTX enantiomers can be transported in a stereoselective manner by the H27- and R27-hRFCs because of significant differences in the affinities of the enantiomers to the hRFC. PMID:24583862

Narawa, Tomoya; Yanagisawa, Hideaki; Itoh, Tomoo

2014-01-01

406

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

PubMed

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

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

2013-05-15

407

Carrier transport mechanism of Ohmic contact to p-type diamond  

NASA Astrophysics Data System (ADS)

The carrier transport mechanism through the p-diamond/metal interface was studied by measuring specific contact resistances (?c) using a transmission line method for Ti, Mo, and Cr (carbide forming metals) and Pd and Co (carbon soluble metals) metals contacting to the boron-doped polycrystalline diamond films. Schottky barrier heights (?B) of around 0.5 eV were measured for the annealed contacts. The present result indicates that formation of thermally stable graphite layers at the diamond/metal interfaces upon annealing would pin the Fermi level of the p-diamond. This model led to the preparation of in situ Ohmic contacts by depositing a thin diamondlike carbon on the p-diamond surface prior to metal deposition, and also to excellent Schottky contacts with breakdown voltages higher than 900 V. The present experiment concluded that the existence of a graphite layer at the diamond/metal interface controlled the electrical properties through the p-diamond/metal interface.

Yokoba, M.; Koide, Yasuo; Otsuki, A.; Ako, F.; Oku, T.; Murakami, Masanori

1997-05-01

408

A multilayered approach of Si/SiO to promote carrier transport in electroluminescence of Si nanocrystals  

PubMed Central

The electroluminescence (EL) and photoluminescence of Si nanocrystals (Si-nc) from multilayered samples of Si/SiO are investigated. Si-nc are formed within Si and SiO layers after furnace annealing. It is found that the presence of Si interlayers creates extra carrier paths for EL emission. A comparative study is further performed on a multilayered Si/SiO sample and a single-layered one with Si and SiO homogeneously mixed. Both samples have the same ratio of Si to O and the same contents of Si and O. The multilayered sample is found to have higher EL intensity, less turn-on voltage, lower resistance, and higher current efficiency than the single-layered one. The results indicate that Si interlayers in Si/SiO may act as carrier channels, which promote carrier transport and enhance the EL emission of Si-nc. PMID:22448989

2012-01-01

409

Substitution Behavior and Stable Charge Carrier Species in Long-Bond Length Layered Cuprates  

E-print Network

.; Rodriguez, J. C.; Owen, F. F.; Hitterman, R. L.; Jorgensen, J. D. Crystal Structures of the High, the transport properties, and the defect structures of the layered, quadruple perovskite La2Ba2Cu2Sn2O11 have for tin. However, oxygen defects are demonstrated to be important compensation species

Poeppelmeier, Kenneth R.

410

Involvement of carrier-mediated transport in the retinal uptake of clonidine at the inner blood-retinal barrier.  

PubMed

In the present study, the blood-to-retina transport across the inner BRB was investigated for clonidine, a compound which is expected to exhibit a neuroprotective effect for the treatment of severe retinal diseases. In the in vivo study, the integration plot analysis for [(3)H]clonidine exhibited an apparent influx permeability clearance of 457 ?L/(min·g retina) in the retina. The in vivo inhibition study suggests that the blood-to-retina transport of clonidine at the BRB is organic cation-sensitive since clonidine, pyrilamine, and propranolol, at a concentration of 40 mM, significantly reduced the retinal uptake index (RUI) of [(3)H]clonidine, and an inhibitory effect on the RUI was also exhibited by verapamil, at a concentration of 3 mM. The in vitro study with TR-iBRB2 cells, an in vitro model cell line of the inner BRB, suggests that carrier-mediated transport is involved in the blood-to-retina transport of clonidine at the inner BRB since the results obtained demonstrated time-, temperature-, pH-, and concentration-dependent [(3)H]clonidine uptake, with a Km of 286 ?M. In the in vitro inhibition study, the [(3)H]clonidine uptake was significantly reduced by several organic cations, such as clonidine, verapamil, pyrilamine, and propranolol, and was competitively inhibited by 200 ?M verapamil, in spite of slight or no significant alteration being produced with organic anions. Furthermore, the typical substrates and inhibitors of well-known organic cation transporters had no significant effect on the uptake of [(3)H]clonidine to suggest the involvement of novel transporter molecules in the transport of clonidine across the inner BRB. These results suggest that the blood-to-retina transport of clonidine across the inner BRB involves a carrier-mediated transport manner, suggesting the contribution of a novel organic cation transporter expressed by the retinal capillary endothelial cells. PMID:25222277

Kubo, Yoshiyuki; Tsuchiyama, Ai; Shimizu, Yoshimi; Akanuma, Shin-Ichi; Hosoya, Ken-Ichi

2014-10-01

411

Pore network model of electrokinetic transport through charged porous media Amael Obliger,1, 2, 3  

E-print Network

for the numerical determination of the steady-state response of complex charged porous media to pressure, saltPore network model of electrokinetic transport through charged porous media Ama¨el Obliger,1, 2, 3 concentration and electric potential gradients. The macro- scopic fluxes of solvent, salt and charge

Paris-Sud XI, Université de

412

Charge carrier accumulation and relaxation effects in the active region of polymer and composite (polymer-gold nanoparticles) field-effect transistor structures  

NASA Astrophysics Data System (ADS)

The charge carrier accumulation and relaxation effects in the active region of polymer field-effect transistor structures based on the semiconducting polymer poly(9-epoxypropylcarbazole) have been studied by means of Kelvin probe microscopy. It has been shown that the introduction of gold nanoparticles into the polymer noticeably accelerates the processes considered. The characteristic times of charge accumulation and dissipation upon the application and removal of the potential at the transistor gate in this case are of a few minutes.

Dement'ev, P. A.; Dunaevskii, M. S.; Aleshin, A. N.; Titkov, A. N.; Makarenko, I. V.

2014-05-01

413

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

414

Charge and spin transport in nanoscale junction from first principles  

NASA Astrophysics Data System (ADS)

Recently nanoscale junctions consisting of 0-D nanostructures (single molecule) or 1-D nanostructures (semiconducting nanowire) sandwiched between two metal electrodes are successfully fabricated and characterized. What lacks in the recent developments is the understanding of the mechanism behind the observed phenomena at the level of atoms and electrons. For example, the origin of observed switching effect in a semiconducting nanowire due to the influence of an external gate bias is not yet understood at the electronic structure level. On the same context, different experimental groups have reported different signs in tunneling magneto-resistance for the same organic spin valve structure, which has baffled researchers working in this field. In this thesis, we present the answers to some of these subtle questions by investigating the charge and spin transport in different nanoscale junctions. A parameter-free, single particle Green's function approach in conjunction with a posteriori density functional theory (DFT) involving a hybrid orbital dependent functional is used to calculate the tunneling current in the coherent transport limit. The effect of spin polarization is explicitly incorporated to investigate spin transport in a nanoscale junction. Through the electron transport studies in PbS nanowire junction, a new orbital controlled mechanism behind the switching of the current is proposed. It can explain the switching behavior, not only in PbS nanowire, but in other lead-chalcogenide nanowires as well. Beside this, the electronic structure properties of this nanowire are studied using periodic DFT. The quantum confinement effect was investigated by calculating the bandgap of PbS nanowires with different diameters. Subsequently, we explain an observed semiconducting to metallic phase transition of this nanowire by calculating the bandgap of the nanowire under uniform radial strain. The compressive radial strain on the nanowire was found to be responsible for the metallic to semiconducting phase transition. Apart from studying one dimensional nanostructure, we also present transport properties in zero dimensional single molecular junctions. We proposed a new codoping approach in a single molecular carborane junction, where a cation and an anion are simultaneously doped to find the role of a single atom in the device. The main purpose was to build a molecular junction where a single atom can dictate the flow of electrons in a circuit. Recent observations of both positive and negative sign in tunneling magnetoresistance (TMR) the using same organic spin-valve structure has mystified researchers. From our spin dependent transport studies in a prototypical