Quantum confinement effects on electronic photomobilities at nanostructured semiconductor surfaces: Si(111) without and with adsorbed Ag clusters

NASA Astrophysics Data System (ADS)

Hembree, Robert H.; Vazhappilly, Tijo; Micha, David A.

2017-12-01

The conductivity of holes and electrons photoexcited in Si slabs is affected by the slab thickness and by adsorbates. The mobilities of those charged carriers depend on how many layers compose the slab, and this has important scientific and technical consequences for the understanding of photovoltaic materials. A previously developed general computational procedure combining density matrix and electronic band structure treatments has been applied to extensive calculations of mobilities of photoexcited electrons and holes at Si(111) nanostructured surfaces with varying slab thickness and for varying photon energies, to investigate the expected change in mobility magnitudes as the slab thickness is increased. Results have been obtained with and without adsorbed silver clusters for comparison of their optical and photovoltaic properties. Band states were generated using a modified ab initio density functional treatment with the PBE exchange and correlation density functionals and with periodic boundary conditions for large atomic supercells. An energy gap correction was applied to the unoccupied orbital energies of each band structure by running more accurate HSE hybrid functional calculations for a Si(111) slab. Photoexcited state populations for slabs with 6, 8, 10, and 12 layers were generated using a steady state reduced density matrix including dissipative effects due to energy exchange with excitons and phonons in the medium. Mobilities have been calculated from the derivatives of voltage-driven electronic energies with respect to electronic momentum, for each energy band and for the average over bands. Results show two clear trends: (a) adding Ag increases the hole photomobilities and (b) decreasing the slab thickness increases hole photomobilities. The increased hole populations in 6- and 8-layer systems and the large increase in hole mobility for these thinner slabs can be interpreted as a quantum confinement effect of hole orbitals. As the slab thickness increases to ten and twelve layers, the effect of silver adsorbates decreases leading to smaller relative enhancements to the conduction electron and hole mobilities, but the addition of the silver nanoclusters still increases the absorbance of light and the mobility of holes compared to their mobilities in the pure Si slabs.

Charge density dependent mobility of organic hole-transporters and mesoporous TiO₂ determined by transient mobility spectroscopy: implications to dye-sensitized and organic solar cells.

PubMed

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

2013-06-18

Transient mobility spectroscopy (TMS) is presented as a new tool to probe the charge carrier mobility of commonly employed organic and inorganic semiconductors over the relevant range of charge densities. The charge density dependence of the mobility of semiconductors used in hybrid and organic photovoltaics gives new insights into charge transport phenomena in solid state dye sensitized solar cells. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Carrier mobility in double-helix DNA and RNA: A quantum chemistry study with Marcus-Hush theory.

PubMed

Wu, Tao; Sun, Lei; Shi, Qi; Deng, Kaiming; Deng, Weiqiao; Lu, Ruifeng

2016-12-21

Charge mobilities of six DNAs and RNAs have been computed using quantum chemistry calculation combined with the Marcus-Hush theory. Based on this simulation model, we obtained quite reasonable results when compared with the experiment, and the obtained charge mobility strongly depends on the molecular reorganization and electronic coupling. Besides, we find that hole mobilities are larger than electron mobilities no matter in DNAs or in RNAs, and the hole mobility of 2L8I can reach 1.09 × 10 -1 cm 2 V -1 s -1 which can be applied in the molecular wire. The findings also show that our theoretical model can be regarded as a promising candidate for screening DNA- and RNA-based molecular electronic devices.

Carrier mobility in double-helix DNA and RNA: A quantum chemistry study with Marcus-Hush theory

NASA Astrophysics Data System (ADS)

Wu, Tao; Sun, Lei; Shi, Qi; Deng, Kaiming; Deng, Weiqiao; Lu, Ruifeng

2016-12-01

Charge mobilities of six DNAs and RNAs have been computed using quantum chemistry calculation combined with the Marcus-Hush theory. Based on this simulation model, we obtained quite reasonable results when compared with the experiment, and the obtained charge mobility strongly depends on the molecular reorganization and electronic coupling. Besides, we find that hole mobilities are larger than electron mobilities no matter in DNAs or in RNAs, and the hole mobility of 2L8I can reach 1.09 × 10-1 cm2 V-1 s-1 which can be applied in the molecular wire. The findings also show that our theoretical model can be regarded as a promising candidate for screening DNA- and RNA-based molecular electronic devices.

Charge-transport anisotropy in black phosphorus: critical dependence on the number of layers.

PubMed

Banerjee, Swastika; Pati, Swapan K

2016-06-28

Phosphorene is a promising candidate for modern electronics because of the anisotropy associated with high electron-hole mobility. Additionally, superior mechanical flexibility allows the strain-engineering of various properties including the transport of charge carriers in phosphorene. In this work, we have shown the criticality of the number of layers to dictate the transport properties of black phosphorus. Trilayer black phosphorus (TBP) has been proposed as an excellent anisotropic material, based on the transport parameters using Boltzmann transport formalisms coupled with density functional theory. The mobilities of both the electron and the hole are found to be higher along the zigzag direction (∼10(4) cm(2) V(-1) s(-1) at 300 K) compared to the armchair direction (∼10(2) cm(2) V(-1) s(-1)), resulting in the intrinsic directional anisotropy. Application of strain leads to additional electron-hole anisotropy with 10(3) fold higher mobility for the electron compared to the hole. Critical strain for maximum anisotropic response has also been determined. Whether the transport anisotropy is due to the spatial or charge-carrier has been determined through analyses of the scattering process of electrons and holes, and their recombination as well as relaxation dynamics. In this context, we have derived two descriptors (S and F(k)), which are general enough for any 2D or quasi-2D systems. Information on the scattering involving purely the carrier states also helps to understand the layer-dependent photoluminescence and electron (hole) relaxation in black phosphorus. Finally, we justify trilayer black phosphorus (TBP) as the material of interest with excellent transport properties.

About mobility thickness dependence in molecularly doped polymers

NASA Astrophysics Data System (ADS)

Tyutnev, A. P.; Weiss, D. S.; Saenko, V. S.; Pozhidaev, E. D.

2017-09-01

We have investigated the dependence of hole mobility on thickness in free-standing films of bisphenol-A-polycarbonate (PC) doped with 30 wt% p-diethylaminobenzaldehyde diphenylhydrazone (DEH). Carrier generation in a time-of-flight (TOF) experiment was achieved through direct ionization of dopant molecules by electron impact using an electron gun supplying pulses of monoenergetic electrons in the range of 2-50 keV. The position of dopant ionization depends upon the electron energy and three TOF variants have been recently developed and used in this study. We have found that the hole mobility generally decreased with increasing film thickness with concomitant acceleration of the post-flight current decay indicating that the transport process approaches the steady-state regime, this process happening slightly faster than our model predicts. Numerical calculations have been compared with experimental data. The results are discussed in detail. The way to reconcile ostensibly contradictory interpretations of our results and those commonly reported in literature relying on photo injection technique has been proposed.

Charge Density Dependent Hole Mobility and Density of States Throughout the Entire Finite Potential Window of Conductivity in Ionic Liquid Gated Poly(3-hexylthiophene)

NASA Astrophysics Data System (ADS)

Paulsen, Bryan D.; Frisbie, C. Daniel

2012-02-01

Ionic liquids, used in place of traditional gate dielectric materials, allow for the accumulation of very high 2D and 3D charge densities (>10^14 #/cm^2 and >10^21 #/cm^3 respectively) at low voltage (<5 V). Here we study the electrochemical gating of the benchmark semiconducting polymer poly(3-hexylthiophene) (P3HT) with the ionic liquid 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([EMI][FAP]). The electrochemical stability of [EMI][FAP] allowed the reproducible accumulation of 2 x 10^21 hole/cm^3, or one hole (and stabilizing anion dopant) per every two thiophene rings. A finite potential/charge density window of high electrical conductivity was observed with hole mobility reaching a maximum of 0.86 cm^2/V s at 0.12 holes per thiophene ring. Displacement current measurements, collected versus a calibrated reference electrode, allowed the mapping of the highly structured and extremely broad density of states of the P3HT/[EMI][FAP] doped composite. Variable temperature and charge density hole transport measurements revealed hole transport to be thermally activated and non-monotonic, displaying a activation energy minimum of ˜20 meV in the region of maximum conductivity and hole mobility. To show the generality of this result, the study was extended to an additional four ionic liquids and three semiconducting polymers.

Kinetics of sub-spinodal dewetting of thin films of thickness dependent viscosity.

PubMed

Kotni, Tirumala Rao; Khanna, Rajesh; Sarkar, Jayati

2017-05-04

An alternative explanation of the time varying and very low growth exponents in dewetting of polymer films like polystyrene films is presented based on non-linear simulations. The kinetics of these films is explored within the framework of experimentally observed thickness dependent viscosity. These films exhibit sub-spinodal dewetting via formation of satellite holes in between primary dewetted holes under favorable conditions of excess intermolecular forces and film thicknesses. We find that conditions responsible for sub-spinodal dewetting concurrently lead to remarkable changes in the kinetics of dewetting of even primary holes. For example, the radius of the hole grows in time with a power-law growth exponent sequence of [Formula: see text], in contrast to the usual  ∼4/5. This is due to the cumulative effect of reduced rim mobility due to thickness dependent viscosity and hindrance created by satellite holes.

Origin of the different transport properties of electron and hole polarons in an ambipolar polyselenophene-based conjugated polymer

NASA Astrophysics Data System (ADS)

Chen, Zhuoying; Bird, Matthew; Lemaur, Vincent; Radtke, Guillaume; Cornil, Jérôme; Heeney, Martin; McCulloch, Iain; Sirringhaus, Henning

2011-09-01

Understanding the mechanisms limiting ambipolar transport in conjugated polymer field-effect transistors (FETs) is of both fundamental and practical interest. Here, we present a systematic study comparing hole and electron charge transport in an ambipolar conjugated polymer, semicrystalline poly(3,3''-di-n-decylterselenophene) (PSSS). Starting from a detailed analysis of the device characteristics and temperature/charge-density dependence of the mobility, we interpret the difference between hole and electron transport through both the Vissenberg-Matters and the mobility-edge model. To obtain microscopic insight into the quantum mechanical wave function of the charges at a molecular level, we combine charge modulation spectroscopy (CMS) measuring the charge-induced absorption signatures from positive and negative polarons in these ambipolar FETs with corresponding density functional theory (DFT) calculations. We observe a significantly higher switch-on voltage for electrons than for holes due to deep electron trap states, but also a higher activation energy of the mobility for mobile electrons. The CMS spectra reveal that the electrons that remain mobile and contribute to the FET current have a wave function that is more localized onto a single polymer chain than that of holes, which is extended over several polymer chains. We interpret this as evidence that the transport properties of the mobile electrons in PSSS are still affected by the presence of deep electron traps. The more localized electron state could be due to the mobile electrons interacting with shallow trap states in the vicinity of a chemical, potentially water-related, impurity that might precede the capture of the electron into a deeply trapped state.

Spontaneous breaking of Lorentz invariance, black holes and perpetuum mobile of the 2nd kind

NASA Astrophysics Data System (ADS)

Dubovsky, S. L.; Sibiryakov, S. M.

2006-07-01

We study the effect of spontaneous breaking of Lorentz invariance on black hole thermodynamics. We consider a scenario where Lorentz symmetry breaking manifests itself by the difference of maximal velocities attainable by particles of different species in a preferred reference frame. The Lorentz breaking sector is represented by the ghost condensate. We find that the notions of black hole entropy and temperature loose their universal meaning. In particular, the standard derivation of the Hawking radiation yields that a black hole does emit thermal radiation in any given particle species, but with temperature depending on the maximal attainable velocity of this species. We demonstrate that this property implies violation of the second law of thermodynamics, and hence, allows construction of a perpetuum mobile of the 2nd kind. We discuss possible interpretation of these results.

Informed peg-in-hole insertion using optical sensors

NASA Astrophysics Data System (ADS)

Paulos, Eric; Canny, John F.

1993-08-01

Peg-in-hole insertion is not only a longstanding problem in robotics but the most common automated mechanical assembly task. In this paper we present a high precision, self-calibrating peg-in-hole insertion strategy using several very simple, inexpensive, and accurate optical sensors. The self-calibrating feature allows us to achieve successful dead-reckoning insertions with tolerances of 25 microns without any accurate initial position information for the robot, pegs, or holes. The program we implemented works for any cylindrical peg, and the sensing steps do not depend on the peg diameter, which the program does not know. The key to the strategy is the use of a fixed sensor to localize both a mobile sensor and the peg, while the mobile sensor localizes the hole. Our strategy is extremely fast, localizing pegs as they are in route to their insertion location without pausing. The result is that insertion times are dominated by the transport time between pick and place operations.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stolterfoht, Martin; Armin, Ardalan; Pandey, Ajay K.

Photovoltaic performance in relation to charge transport is studied in efficient (7.6%) organic solar cells (PTB7:PC{sub 71}BM). Both electron and hole mobilities are experimentally measured in efficient solar cells using the resistance dependent photovoltage technique, while the inapplicability of classical techniques, such as space charge limited current and photogenerated charge extraction by linearly increasing voltage is discussed. Limits in the short-circuit current originate from optical losses, while charge transport is shown not to be a limiting process. Efficient charge extraction without recombination can be achieved with a mobility of charge carriers much lower than previously expected. The presence of dispersivemore » transport with strongly distributed mobilities in high efficiency solar cells is demonstrated. Reduced non-Langevin recombination is shown to be beneficial for solar cells with imbalanced, low, and dispersive electron and hole mobilities.« less

Theoretical Characterization of Charge Transport in Chromia (α-Cr2O3)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Iordanova, Nellie I.; Dupuis, Michel; Rosso, Kevin M.

2005-08-15

Transport of conduction electrons and holes through the lattice of ?-Cr2O3 (chromia) is modeled as a valence alternation of chromium cations using ab initio electronic structure calculations and electron transfer theory. In the context of the small polaron model, a cluster approach was used to compute quantities controlling the mobility of localized electrons and holes, i.e. the reorganization energy and the electronic coupling matrix element that enter Marcus? theory. The calculation of the electronic coupling followed the Generalized Mulliken-Hush approach and the quasi-diabatic method using the complete active space self-consistent field (CASSCF) method. Our findings indicate that hole mobility ismore » more than three orders of magnitude larger than electron mobility in both (001) and [001] lattice directions. The difference arises mainly from the larger internal reorganization energy calculated for electron transport relative to hole transport processes while electronic couplings have similar magnitudes. The much larger hole mobility vs electron mobility in ?-Cr2O3 is in contrast to similar hole and electron mobility in hematite ?-Fe2O3 previously calculated. Our calculations also indicate that the electronic coupling for all charge transfer processes of interest is smaller than for the corresponding processes in hematite. This variation is attributed to weaker interaction between the metal 3d states and the O(2p) states in chromia than in hematite, leading to smaller overlap between the charge transfer donor and acceptor wavefunctions and smaller super-exchange coupling in chromia. Nevertheless, the weaker coupling in chromia is still sufficiently large to suggest that charge transport processes in chromia are adiabatic in nature. The electronic coupling is found to depend on both the superexchange interaction through the bridging oxygen atoms and the d-shell electron spin coupling within the Cr-Cr donor-acceptor pair, while the reorganization energy is essentially independent of the electron spin coupling.« less

Theoretical characterization of charge transport in chromia (α-Cr2O3)

NASA Astrophysics Data System (ADS)

Iordanova, N.; Dupuis, M.; Rosso, K. M.

2005-08-01

Transport of conduction electrons and holes through the lattice of α-Cr2O3 (chromia) is modeled as a valence alternation of chromium cations using ab initio electronic structure calculations and electron-transfer theory. In the context of the small polaron model, a cluster approach was used to compute quantities controlling the mobility of localized electrons and holes, i.e., the reorganization energy and the electronic coupling matrix element that enter Marcus' theory. The calculation of the electronic coupling followed the generalized Mulliken-Hush approach using the complete active space self-consistent-field (CASSCF) method and the quasidiabatic method. Our findings indicate that hole mobility is more than three orders of magnitude larger than electron mobility in both (001) and [001] lattice directions. The difference arises mainly from the larger internal reorganization energy calculated for electron-transport relative to hole-transport processes while electronic couplings have similar magnitudes. The much larger hole mobility versus electron mobility in α-Cr2O3 is in contrast to similar hole and electron mobilities in hematite α-Fe2O3 previously calculated. Our calculations also indicate that the electronic coupling for all charge-transfer processes of interest is smaller than for the corresponding processes in hematite. This variation is attributed to the weaker interaction between the metal 3d states and the O(2p ) states in chromia than in hematite, leading to a smaller overlap between the charge-transfer donor and acceptor wave functions and smaller superexchange coupling in chromia. Nevertheless, the weaker coupling in chromia is still sufficiently large to suggest that charge-transport processes in chromia are adiabatic in nature. The electronic coupling is found to depend on both the superexchange interaction through the bridging oxygen atoms and the d-shell electron-spin coupling within the Cr-Cr donor-acceptor pair, while the reorganization energy is essentially independent of the electron-spin coupling.

Hall effect within the colossal magnetoresistive semimetallic state of MoTe2

NASA Astrophysics Data System (ADS)

Zhou, Qiong; Rhodes, D.; Zhang, Q. R.; Tang, S.; Schönemann, R.; Balicas, L.

2016-09-01

Here, we report a systematic study on the Hall effect of the semimetallic state of bulk MoTe2, which was recently claimed to be a candidate for a novel type of Weyl semimetallic state. The temperature (T ) dependence of the carrier densities and of their mobilities, as estimated from a numerical analysis based on the isotropic two-carrier model, indicates that its exceedingly large and nonsaturating magnetoresistance may be attributed to a near perfect compensation between the densities of electrons and holes at low temperatures. A sudden increase in hole density, with a concomitant rapid increase in the electron mobility below T ˜40 K, leads to comparable densities of electrons and holes at low temperatures suggesting a possible electronic phase transition around this temperature.

Charge-carrier mobilities in Cd(0.8)Zn(0.2)Te single crystals used as nuclear radiation detectors

NASA Technical Reports Server (NTRS)

Burshtein, Z.; Jayatirtha, H. N.; Burger, A.; Butler, J. F.; Apotovsky, B.; Doty, F. P.

1993-01-01

Charge-carrier mobilities were measured for the first time in Cd(0.8)Zn(0.2)Te single crystals using time-of-flight measurements of charge carriers produced by short (10 ns) light pulses from a frequency-doubled Nd:YAG laser (532 nm). The electron mobility displayed a T exp -1.1 dependence on the absolute temperature T in the range 200-320 K, with a room-temperature mobility of 1350 sq cm/V s. The hole mobility displayed a T exp -2.0 dependence in the same temperature range, with a room-temperature mobility of 120 sq cm/V s. Cd(0.8)Zn(0.2)Te appears to be a very favorable material for a room-temperature electronic nuclear radiation detector.

Charge transport in metal oxides: A theoretical study of hematite α-Fe2O3

NASA Astrophysics Data System (ADS)

Iordanova, N.; Dupuis, M.; Rosso, K. M.

2005-04-01

Transport of conduction electrons and holes through the lattice of α-Fe2O3 (hematite) is modeled as a valence alternation of iron cations using ab initio electronic structure calculations and electron transfer theory. Experimental studies have shown that the conductivity along the (001) basal plane is four orders of magnitude larger than the conductivity along the [001] direction. In the context of the small polaron model, a cluster approach was used to compute quantities controlling the mobility of localized electrons and holes, i.e., the reorganization energy and the electronic coupling matrix element that enter Marcus' theory. The calculation of the electronic coupling followed the generalized Mulliken-Hush approach using the complete active space self-consistent field method. Our findings demonstrate an approximately three orders of magnitude anisotropy in both electron and hole mobility between directions perpendicular and parallel to the c axis, in good accord with experimental data. The anisotropy arises from the slowness of both electron and hole mobilities across basal oxygen planes relative to that within iron bilayers between basal oxygen planes. Interestingly, for elementary reaction steps along either of the directions considered, there is only less than one order of magnitude difference in mobility between electrons and holes, in contrast to accepted classical arguments. Our findings indicate that the most important quantity underlying mobility differences is the electronic coupling, albeit the reorganization energy contributes as well. The large values computed for the electronic coupling suggest that charge transport reactions in hematite are adiabatic in nature. The electronic coupling is found to depend on both the superexchange interaction through the bridging oxygen atoms and the d-shell electron spin coupling within the Fe-Fe donor-acceptor pair, while the reorganization energy is essentially independent of the electron spin coupling.

Two-band analysis of hole mobility and Hall factor for heavily carbon-doped p-type GaAs

NASA Astrophysics Data System (ADS)

Kim, B. W.; Majerfeld, A.

1996-02-01

We solve a pair of Boltzmann transport equations based on an interacting two-isotropic-band model in a general way first to get transport parameters corresponding to the relaxation time. We present a simple method to calculate effective relaxation times, separately for each band, which compensate for the inherent deficiencies in using the relaxation time concept for polar optical-phonon scattering. Formulas for calculating momentum relaxation times in the two-band model are presented for all the major scattering mechanisms of p-type GaAs for simple, practical mobility calculations. In the newly proposed theoretical framework, first-principles calculations for the Hall mobility and Hall factor of p-type GaAs at room temperature are carried out with no adjustable parameters in order to obtain direct comparisons between the theory and recently available experimental results. In the calculations, the light-hole-band nonparabolicity is taken into account on the average by the use of energy-dependent effective mass obtained from the kṡp method and valence-band anisotropy is taken partly into account by the use the Wiley's overlap function.. The calculated Hall mobilities show a good agreement with our experimental data for carbon-doped p-GaAs samples in the range of degenerate hole densities. The calculated Hall factors show rH=1.25-1.75 over hole densities of 2×1017-1×1020 cm-3.

Indium antimonide quantum well structures for electronic device applications

NASA Astrophysics Data System (ADS)

Edirisooriya, Madhavie

The electron effective mass is smaller in InSb than in any other III-V semiconductor. Since the electron mobility depends inversely on the effective mass, InSb-based devices are attractive for field effect transistors, magnetic field sensors, ballistic transport devices, and other applications where the performance depends on a high mobility or a long mean free path. In addition, electrons in InSb have a large g-factor and strong spin orbit coupling, which makes them well suited for certain spin transport devices. The first n-channel InSb high electron mobility transistor (HEMT) was produced in 2005 with a power-delay product superior to HEMTs with a channel made from any other III-V semiconductor. The high electron mobility in the InSb quantum-well channel increases the switching speed and lowers the required supply voltage. This dissertation focuses on several materials challenges that can further increase the appeal of InSb quantum wells for transistors and other electronic device applications. First, the electron mobility in InSb quantum wells, which is the highest for any semiconductor quantum well, can be further increased by reducing scattering by crystal defects. InSb-based heteroepitaxy is usually performed on semi-insulating GaAs (001) substrates due to the lack of a lattice matched semi-insulating substrate. The 14.6% mismatch between the lattice parameters of GaAs and InSb results in the formation of structural defects such as threading dislocations and microtwins which degrade the electrical and optical properties of InSb-based devices. Chapter 1 reviews the methods and procedures for growing InSb-based heterostructures by molecular beam epitaxy. Chapters 2 and 3 introduce techniques for minimizing the crystalline defects in InSb-based structures grown on GaAs substrates. Chapter 2 discusses a method of reducing threading dislocations by incorporating AlyIn1-ySb interlayers in an AlxIn1-xSb buffer layer and the reduction of microtwin defects by growth on GaAs substrates that are oriented 2° away from the [011] direction. Chapter 3 discusses designing InSb QW layer structures that are strain balanced. By applying these defect-reducing techniques, the electron mobility in InSb quantum wells at room temperature was significantly increased. For complementary logic technology, p-channel transistors with high mobility are equally as important as n-channel transistors. However, achieving a high hole mobility in III-V semiconductors is challenging. A controlled introduction of strain in the quantum-well material is an effective technique for enhancing the hole mobility beyond its value in bulk material. The strain reduces the hole effective mass by splitting the heavy hole and light hole valence bands. Chapter 4 discusses a successful attempt to realize p-type InSb quantum well structures. The biaxial strain applied via a relaxed metamorphic buffer resulted in a significantly higher room-temperature hole mobility and a record high low-temperature hole mobility. To demonstrate the usefulness of high mobility in a device structure, magnetoresistive devices were fabricated from remotely doped InSb QWs. Such devices have numerous practical applications such as position and speed sensors and as read heads in magnetic storage systems. In a magnetoresistive device composed of a series of shorted Hall bars, the magnetoresistance is proportional to the electron mobility squared for small magnetic fields. Hence, the high electron mobility in InSb QWs makes them highly preferable for geometrical magnetoresistors. Chapter 5 reports the fabrication and characterization of InSb quantum-well magnetoresistors. The excellent transport properties of the InSb QWs resulted in high room-temperature sensitivity to applied magnetic fields. Finally, Chapter 6 provides the conclusions obtained during this research effort, and makes suggestions for future work.

Lorentz violation and perpetual motion

NASA Astrophysics Data System (ADS)

Eling, Christopher; Foster, Brendan Z.; Jacobson, Ted; Wall, Aron C.

2007-05-01

We show that any Lorentz-violating theory with two or more propagation speeds is in conflict with the generalized second law of black hole thermodynamics. We do this by identifying a classical energy-extraction method, analogous to the Penrose process, which would decrease the black hole entropy. Although the usual definitions of black hole entropy are ambiguous in this context, we require only very mild assumptions about its dependence on the mass. This extends the result found by Dubovsky and Sibiryakov, which uses the Hawking effect and applies only if the fields with different propagation speeds interact just through gravity. We also point out instabilities that could interfere with their black hole perpetuum mobile, but argue that these can be neglected if the black hole mass is sufficiently large.

P-type hole mobility measurement in Na-doped BaSnO3

NASA Astrophysics Data System (ADS)

Hong, Sungyun; Jang, Yeaju; Park, Jisung; Char, Kookrin

P-type doping in oxide materials has been a difficult task because of the oxygen vacancies. Taking advantage of the excellent oxygen stability in BaSnO3 (BSO), we replaced Ba with Na in BSO to achieve p-type doping. Ba1-xNaxSnO3 (BNSO) films with varying dopant ratios were epitaxially grown by the pulsed laser deposition technique. We confirmed that the BNSO films were properly grown and determined their lattice constants with respect to the dopant ratio by x-ray diffraction. Due to the high resistance of the films at room temperature, we measured the transport properties of the BNSO films at temperatures ranging from 200 C to 400 C. Hall resistance measurements in a +/- 5 kG magnetic field were performed to confirm that the films are indeed p-type. As the temperature increased, the hole carrier concentration of the films increased while the film resistance decreased. The hole mobility values, in the tens of cm2/Vsec range, were found to decrease with the temperature. We will present the complete doping rate and temperature dependence of the hole mobility and compare their behavior with those of n-type La-doped BSO. Samsung science and technology foundation.

Transverse magnetic focussing of heavy holes in a (100) GaAs quantum well

NASA Astrophysics Data System (ADS)

Rendell, M.; Klochan, O.; Srinivasan, A.; Farrer, I.; Ritchie, D. A.; Hamilton, A. R.

2015-10-01

We perform magnetic focussing of high mobility holes confined in a shallow GaAs/Al0.33Ga0.67As quantum well grown on a (100) GaAs substrate. We observe ballistic focussing of holes over a path length of up to 4.9 μm with a large number of focussing peaks. We show that additional structure on the focussing peaks can be caused by a combination of the finite width of the injector quantum point contact and Shubnikov-de Haas oscillations. These results pave the way to studies of spin-dependent magnetic focussing and spin relaxation lengths in two-dimentional hole systems without complications of crystal anisotropies and anisotropic g-tensors.

Magneto-transport analysis of an ultra-low-density two-dimensional hole gas in an undoped strained Ge/SiGe heterostructure

DOE PAGES

Laroche, D.; Huang, S. -H.; Chuang, Y.; ...

2016-06-06

We report the magneto-transport, scattering mechanisms, and e ective mass analysis of an ultralow density two-dimensional hole gas capacitively induced in an undoped strained Ge/Si0:2Ge0:8 heterostructure. This fabrication technique allows hole densities as low as p 1:1 1010 cm² to be achieved, more than one order of magnitude lower than previously reported in doped Ge/SiGe heterostructures. The power-law exponent of the electron mobility versus density curve, / n , is found to be 0:29 over most of the density range, implying that background impurity scattering is the dominant scattering mechanism at intermediate densities in such devices. A charge migration modelmore » is used to explain the mobility decrease at the highest achievable densities. The hole e ective mass is deduced from the temperature dependence of Shubnikov-de Haas oscillations. At p 1:0 1011cm², the e ective mass m is 0:105 m0, which is signi cantly larger than masses obtained from modulation-doped Ge/SiGe two-dimensional hole gases.« less

Influence of deep level intrinsic defects on the carrier transport in p-type Hg1- xCdxTe

NASA Astrophysics Data System (ADS)

Hoerstel, W.; Klimakow, A.; Kramer, R.

1990-04-01

The magnetic field dependence of the Hall effect in p-type Hg1- xCdxTe is analysed for determining the carrier densities and their mobilities in the mixed conduction range T = 70-250 K. A consistent description of the temperature dependence of the concentrations and mobilities of electrons and holes succeeds by taking into account energy-dependent momentum scattering times in the transport coefficients. Using this formalism, an energy level near 0.7 Eg above the valence band edge caused by intrinsic defects which were influenced by thermal treament is determined and discussed.

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

PubMed

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

2014-01-01

This article reviews the basic physical processes of charge transport and recombination in organic semiconductors. As a workhorse, LEDs based on a single layer of poly(p-phenylene vinylene) (PPV) derivatives are used. The hole transport in these PPV derivatives is governed by trap-free space-charge-limited conduction, with the mobility depending on the electric field and charge-carrier density. These dependencies are generally described in the framework of hopping transport in a Gaussian density of states distribution. The electron transport on the other hand is orders of magnitude lower than the hole transport. The reason is that electron transport is hindered by the presence of a universal electron trap, located at 3.6 eV below vacuum with a typical density of ca. 3 × 10¹⁷ cm⁻³. The trapped electrons recombine with free holes via a non-radiative trap-assisted recombination process, which is a competing loss process with respect to the emissive bimolecular Langevin recombination. The trap-assisted recombination in disordered organic semiconductors is governed by the diffusion of the free carrier (hole) towards the trapped carrier (electron), similar to the Langevin recombination of free carriers where both carriers are mobile. As a result, with the charge-carrier mobilities and amount of trapping centers known from charge-transport measurements, the radiative recombination as well as loss processes in disordered organic semiconductors can be fully predicted. Evidently, future work should focus on the identification and removing of electron traps. This will not only eliminate the non-radiative trap-assisted recombination, but, in addition, will shift the recombination zone towards the center of the device, leading to an efficiency improvement of more than a factor of two in single-layer polymer LEDs. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Charge Transport in Metal Oxides: A Theoretical Study of Hematite α-Fe2O3

DOE Office of Scientific and Technical Information (OSTI.GOV)

Iordanova, Nellie I.; Dupuis, Michel; Rosso, Kevin M.

2005-04-08

Transport of conduction electrons and holes through the lattice of ??Fe2O3 (hematite) is modeled as a valence alternation of iron cations using ab initio electronic structure calculations and electron transfer theory. Experimental studies have shown that the conductivity along the (001) basal plane is four orders of magnitude larger than the conductivity along the [001] direction. In the context of the small polaron model, a cluster approach was used to compute quantities controlling the mobility of localized electrons and holes, i.e. the reorganization energy and the electronic coupling matrix element that enter Marcus? theory. The calculation of the electronic couplingmore » followed the Generalized Mulliken-Hush approach using the complete active space self-consistent field (CASSCF) method. Our findings demonstrate an approximately three orders of magnitude anisotropy in both electron and hole mobility between directions perpendicular and parallel to the c-axis, in good accord with experimental data. The anisotropy arises from the slowness of both electron and hole mobility across basal oxygen planes relative to that within iron bi-layers between basal oxygen planes. Interestingly, for elementary reaction steps along either of the directions considered, there is only approximately one order of magnitude difference in mobility between electrons and holes, in contrast to accepted classical arguments. Our findings indicate that the most important quantity underlying mobility differences is the electronic coupling, albeit the reorganization energy contributes as well. The large values computed for the electronic coupling suggest that charge transport reactions in hematite are adiabatic in nature. The electronic coupling is found to depend on both the superexchange interaction through the bridging oxygen atoms and the d-shell electron spin coupling within the Fe?Fe donor-acceptor pair, while the reorganization energy is essentially independent of the electron spin coupling.« less

Band Transport and Trapping in Didodecyl[1]benzothieno[3,2-b][1]benzothiophene Probed by Terahertz Spectroscopy.

PubMed

Arend, Thomas R; Wimmer, Andreas; Schweicher, Guillaume; Chattopadhyay, Basab; Geerts, Yves H; Kersting, Roland

2017-11-02

Terahertz electromodulation spectroscopy provides insight into the material-inherent transport properties of charge carriers in organic semiconductors. Experiments on didodecyl[1]benzothieno[3,2-b][1]benzothiophene (C 12 -BTBT-C 12 ) devices yield for holes an intraband mobility of 9 cm 2 V -1 s -1 . The short duration of the THz pulses advances the understanding of the hole transport on the molecular scale. The efficient screening of Coulomb potentials leads to a collective response of the hole gas to external fields, which can be well described by the Drude model. Bias stress of the devices generates deep traps that capture mobile holes. Although the resulting polarization across the device hinders the injection of mobile holes, the hole mobilities are not affected.

Quantitative analysis of the guest-concentration dependence of the mobility in a disordered fluorene-arylamine host-guest system in the guest-to-guest regime

NASA Astrophysics Data System (ADS)

Nicolai, H. T.; Hof, A. J.; Lu, M.; Blom, P. W. M.; de Vries, R. J.; Coehoorn, R.

2011-11-01

The charge transport in a polyspirobifluorene derivative with copolymerized N,N,N',N'-tetraaryldiamino biphenyl (TAD) hole transport units is investigated as a function of the TAD content. For TAD concentrations larger than 5%, guest-to-guest transport is observed. It is demonstrated that in this regime the charge carrier density dependent mobility can be described consistently with the extended Gaussian disorder model, with a density of hopping sites which is proportional to the TAD concentration and comparable to the molecular density.

Time-of-Flight Measurements on TlBr Detectors

NASA Astrophysics Data System (ADS)

Suzuki, K.; Shorohov, M.; Sawada, T.; Seto, S.

2015-04-01

Carrier transport properties of TlBr crystals grown using the Bridgman method were investigated by the time-of-flight technique. The electron and hole mobilities were measured as 20 - 27 cm2 /Vs and 1.0 - 2.0 cm2/Vs respectively at room temperature. The temperature dependence of the electron mobility increases with decreasing temperature as approximated by a well-known empirical formula reflecting the reciprocal of the LO-phonon density.

Radiation effects on hole drift mobility in polysilanes

NASA Astrophysics Data System (ADS)

Seki, Shu; Shibata, Hiromi; Yoshida, Yoichi; Ishigure, Kenkichi; Tagawa, Seiichi

1997-03-01

The radiation effects on hole drift mobility in polysilane derivatives were studied in the present paper. The values of hole drift mobility (about 10 -4 cm 2/V·s) obtained by the DC Time-of-Flight (TOF) measurement were improved by ion beam irradiation for poly(methylphenylsilane) (PMPS) and poly(di-n-hexylsilane) (PDHS). The irradiated PMPS showed five times higher values of hole drift mobility than the non irradiated one. Their low photo-induced carrier yield, one of the highest barrier to use polysilanes as photoconductors, was also improved by the irradiation. The mechanism of the mobility improvement will be discussed in relation to the model of changes in the silicon skeleton structure induced by the radiation.

A simple model of electron beam initiated dielectric breakdown

NASA Technical Reports Server (NTRS)

Beers, B. L.; Daniell, R. E.; Delmer, T. N.

1985-01-01

A steady state model that describes the internal charge distribution of a planar dielectric sample exposed to a uniform electron beam was developed. The model includes the effects of charge deposition and ionization of the beam, separate trap-modulated mobilities for electrons and holes, electron-hole recombination, and pair production by drifting thermal electrons. If the incident beam current is greater than a certain critical value (which depends on sample thickness as well as other sample properties), the steady state solution is non-physical.

Ionization equilibrium at the transition from valence-band to acceptor-band migration of holes in boron-doped diamond

NASA Astrophysics Data System (ADS)

Poklonski, N. A.; Vyrko, S. A.; Poklonskaya, O. N.; Kovalev, A. I.; Zabrodskii, A. G.

2016-06-01

A quasi-classical model of ionization equilibrium in the p-type diamond between hydrogen-like acceptors (boron atoms which substitute carbon atoms in the crystal lattice) and holes in the valence band (v-band) is proposed. The model is applicable on the insulator side of the insulator-metal concentration phase transition (Mott transition) in p-Dia:B crystals. The densities of the spatial distributions of impurity atoms (acceptors and donors) and of holes in the crystal are considered to be Poissonian, and the fluctuations of their electrostatic potential energy are considered to be Gaussian. The model accounts for the decrease in thermal ionization energy of boron atoms with increasing concentration, as well as for electrostatic fluctuations due to the Coulomb interaction limited to two nearest point charges (impurity ions and holes). The mobility edge of holes in the v-band is assumed to be equal to the sum of the threshold energy for diffusion percolation and the exchange energy of the holes. On the basis of the virial theorem, the temperature Tj is determined, in the vicinity of which the dc band-like conductivity of holes in the v-band is approximately equal to the hopping conductivity of holes via the boron atoms. For compensation ratio (hydrogen-like donor to acceptor concentration ratio) K ≈ 0.15 and temperature Tj, the concentration of "free" holes in the v-band and their jumping (turbulent) drift mobility are calculated. Dependence of the differential energy of thermal ionization of boron atoms (at the temperature 3Tj/2) as a function of their concentration N is calculated. The estimates of the extrapolated into the temperature region close to Tj hopping drift mobility of holes hopping from the boron atoms in the charge states (0) to the boron atoms in the charge states (-1) are given. Calculations based on the model show good agreement with electrical conductivity and Hall effect measurements for p-type diamond with boron atom concentrations in the range from 3 × 1017 to 3 × 1020 cm-3, i.e., up to the Mott transition. The model uses no fitting parameters.

Phenomenological view at the two-component physics of cuprates

NASA Astrophysics Data System (ADS)

Teitel'baum, G. B.

2017-08-01

In the search for mechanisms of high- T c superconductivity it is critical to know the electronic spectrum in the pseudogap phase from which superconductivity evolves. The lack of ARPES data for every cuprate family precludes an agreement as to its structure, doping and temperature dependence and the role of charge ordering. No approach has been developed yet to address the issue theoretically, and we limit ourselves by the phenomenological analysis of the experimental data. We argue that, in the Fermi-liquid-like regime ubiquitous in underdoped cuprates, the spectrum consists of holes on the Fermi arcs and an electronic pocket in contrast to the idea of the Fermi surface reconstruction via charge ordering. At high temperatures, the electrons are dragged by holes while at lower temperatures they get decoupled. The longstanding issue of the origin of the negative Hall coefficient in YBCO and Hg1201 at low temperature is resolved: the electronic contribution prevails, as its mobility becomes temperature independent, while the mobility of holes, scattered by the shortwavelength charge density waves, decreases.

Magneto-transport analysis of an ultra-low-density two-dimensional hole gas in an undoped strained Ge/SiGe heterostructure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Laroche, D.; Lu, T. M., E-mail: tlu@sandia.gov; Huang, S.-H.

2016-06-06

We report the magneto-transport, scattering mechanisms, and effective mass analysis of an ultra-low density two-dimensional hole gas capacitively induced in an undoped strained Ge/Si{sub 0.2}Ge{sub 0.8} heterostructure. This fabrication technique allows hole densities as low as p ∼ 1.1 × 10{sup 10 }cm{sup −2} to be achieved, more than one order of magnitude lower than previously reported in doped Ge/SiGe heterostructures. The power-law exponent of the electron mobility versus density curve, μ ∝ n{sup α}, is found to be α ∼ 0.29 over most of the density range, implying that background impurity scattering is the dominant scattering mechanism at intermediate densities in such devices. A charge migrationmore » model is used to explain the mobility decrease at the highest achievable densities. The hole effective mass is deduced from the temperature dependence of Shubnikov-de Haas oscillations. At p ∼ 1.0 × 10{sup 11 }cm{sup −2}, the effective mass m* is ∼0.105 m{sub 0}, which is significantly larger than masses obtained from modulation-doped Ge/SiGe two-dimensional hole gases.« less

Monte-Carlo modelling of nano-material photocatalysis: bridging photocatalytic activity and microscopic charge kinetics.

PubMed

Liu, Baoshun

2016-04-28

In photocatalysis, it is known that light intensity, organic concentration, and temperature affect the photocatalytic activity by changing the microscopic kinetics of holes and electrons. However, how the microscopic kinetics of holes and electrons relates to the photocatalytic activity was not well known. In the present research, we developed a Monte-Carlo random walking model that involved all of the charge kinetics, including the photo-generation, the recombination, the transport, and the interfacial transfer of holes and electrons, to simulate the overall photocatalytic reaction, which we called a "computer experiment" of photocatalysis. By using this model, we simulated the effect of light intensity, temperature, and organic surface coverage on the photocatalytic activity and the density of the free electrons that accumulate in the simulated system. It was seen that the increase of light intensity increases the electron density and its mobility, which increases the probability for a hole/electron to find an electron/hole for recombination, and consequently led to an apparent kinetics that the quantum yield (QY) decreases with the increase of light intensity. It was also seen that the increase of organic surface coverage could increase the rate of hole interfacial transfer and result in the decrease of the probability for an electron to recombine with a hole. Moreover, the increase of organic coverage on the nano-material surface can also increase the accumulation of electrons, which enhances the mobility for electrons to undergo interfacial transfer, and finally leads to the increase of photocatalytic activity. The simulation showed that the temperature had a more complicated effect, as it can simultaneously change the activation of electrons, the interfacial transfer of holes, and the interfacial transfer of electrons. It was shown that the interfacial transfer of holes might play a main role at low temperature, with the temperature-dependence of QY conforming to the Arrhenius model. The activation of electrons from the traps to the conduction band might become important at high temperature, which accelerates the electron movement for recombination and leads to a temperature dependence of QY that deviates from the Arrhenius model.

Influence of acceptor on charge mobility in stacked π-conjugated polymers

NASA Astrophysics Data System (ADS)

Sun, Shih-Jye; Menšík, Miroslav; Toman, Petr; Gagliardi, Alessio; Král, Karel

2018-02-01

We present a quantum molecular model to calculate mobility of π-stacked P3HT polymer layers with electron acceptor dopants coupled next to side groups in random position with respect to the linear chain. The hole density, the acceptor LUMO energy and the hybridization transfer integral between the acceptor and polymer were found to be very critical factors to the final hole mobility. For a dopant LUMO energy close and high above the top of the polymer valence band we have found a significant mobility increase with the hole concentration and with the dopant LUMO energy approaching the top of the polymer valence band. Higher mobility was achieved for small values of hybridization transfer integral between polymer and the acceptor, corresponding to the case of weakly bound acceptor. Strong couplings between the polymer and the acceptor with Coulomb repulsion interactions induced from the electron localizations was found to suppress the hole mobility.

Microstructural control of charge transport in organic blend thin-film transistors

DOE PAGES

Hunter, Simon; Chen, Jihua; Anthopoulos, Thomas D.

2014-07-17

In this paper, the charge-transport processes in organic p-channel transistors based on the small-molecule 2,8-difluoro-5,11-bis(triethylsilylethynyl)anthradithiophene (diF-TES ADT), the polymer poly(triarylamine)(PTAA) and blends thereof are investigated. In the case of blend films, lateral conductive atomic force microscopy in combination with energy filtered transmission electron microscopy are used to study the evolution of charge transport as a function of blends composition, allowing direct correlation of the film's elemental composition and morphology with hole transport. Low-temperature transport measurements reveal that optimized blend devices exhibit lower temperature dependence of hole mobility than pristine PTAA devices while also providing a narrower bandgap trap distribution thanmore » pristine diF-TES ADT devices. These combined effects increase the mean hole mobility in optimized blends to 2.4 cm 2/Vs; double the value measured for best diF-TES ADT-only devices. The bandgap trap distribution in transistors based on different diF-TES ADT:PTAA blend ratios are compared and the act of blending these semiconductors is seen to reduce the trap distribution width yet increase the average trap energy compared to pristine diF-TES ADT-based devices. In conclusion, our measurements suggest that an average trap energy of <75 meV and a trap distribution of <100 meV is needed to achieve optimum hole mobility in transistors based on diF-TES ADT:PTAA blends.« less

Molecular origin of differences in hole and electron mobility in amorphous Alq3--a multiscale simulation study.

PubMed

Fuchs, Andreas; Steinbrecher, Thomas; Mommer, Mario S; Nagata, Yuki; Elstner, Marcus; Lennartz, Christian

2012-03-28

In order to determine the molecular origin of the difference in electron and hole mobilities of amorphous thin films of Alq(3) (meridional Alq(3) (tris(8-hydroxyquinoline) aluminium)) we performed multiscale simulations covering quantum mechanics, molecular mechanics and lattice models. The study includes realistic disordered morphologies, polarized site energies to describe diagonal disorder, quantum chemically calculated transfer integrals for the off-diagonal disorder, inner sphere reorganization energies and an approximative scheme for outer sphere reorganization energies. Intermolecular transfer rates were calculated via Marcus-theory and mobilities were simulated via kinetic Monte Carlo simulations and by a Master Equation approach. The difference in electron and hole mobility originates from the different localization of charge density in the radical anion (more delocalized) compared to the radical cation (more confined). This results in higher diagonal disorder for holes and less favourable overlap properties for the hole transfer integrals leading to an overall higher electron mobility.

Ionization equilibrium at the transition from valence-band to acceptor-band migration of holes in boron-doped diamond

DOE Office of Scientific and Technical Information (OSTI.GOV)

Poklonski, N. A., E-mail: poklonski@bsu.by; Vyrko, S. A.; Poklonskaya, O. N.

A quasi-classical model of ionization equilibrium in the p-type diamond between hydrogen-like acceptors (boron atoms which substitute carbon atoms in the crystal lattice) and holes in the valence band (v-band) is proposed. The model is applicable on the insulator side of the insulator–metal concentration phase transition (Mott transition) in p-Dia:B crystals. The densities of the spatial distributions of impurity atoms (acceptors and donors) and of holes in the crystal are considered to be Poissonian, and the fluctuations of their electrostatic potential energy are considered to be Gaussian. The model accounts for the decrease in thermal ionization energy of boron atomsmore » with increasing concentration, as well as for electrostatic fluctuations due to the Coulomb interaction limited to two nearest point charges (impurity ions and holes). The mobility edge of holes in the v-band is assumed to be equal to the sum of the threshold energy for diffusion percolation and the exchange energy of the holes. On the basis of the virial theorem, the temperature T{sub j} is determined, in the vicinity of which the dc band-like conductivity of holes in the v-band is approximately equal to the hopping conductivity of holes via the boron atoms. For compensation ratio (hydrogen-like donor to acceptor concentration ratio) K ≈ 0.15 and temperature T{sub j}, the concentration of “free” holes in the v-band and their jumping (turbulent) drift mobility are calculated. Dependence of the differential energy of thermal ionization of boron atoms (at the temperature 3T{sub j}/2) as a function of their concentration N is calculated. The estimates of the extrapolated into the temperature region close to T{sub j} hopping drift mobility of holes hopping from the boron atoms in the charge states (0) to the boron atoms in the charge states (−1) are given. Calculations based on the model show good agreement with electrical conductivity and Hall effect measurements for p-type diamond with boron atom concentrations in the range from 3 × 10{sup 17} to 3 × 10{sup 20 }cm{sup −3}, i.e., up to the Mott transition. The model uses no fitting parameters.« less

Enhancement of hole mobility in InSe monolayer via an InSe and black phosphorus heterostructure.

PubMed

Ding, Yi-Min; Shi, Jun-Jie; Xia, Congxin; Zhang, Min; Du, Juan; Huang, Pu; Wu, Meng; Wang, Hui; Cen, Yu-Lang; Pan, Shu-Hang

2017-10-05

To enhance the low hole mobility (∼40 cm 2 V -1 s -1 ) of InSe monolayer, a novel two-dimensional (2D) van der Waals heterostructure made of InSe and black phosphorus (BP) monolayers with high hole mobility (∼10 3 cm 2 V -1 s -1 ) has been constructed and its structural and electronic properties are investigated using first-principles calculations. We find that the InSe/BP heterostructure exhibits a direct band gap of 1.39 eV and type-II band alignment with electrons (holes) located in the InSe (BP) layer. The band offsets of InSe and BP are 0.78 eV for the conduction band minimum and 0.86 eV for the valence band maximum, respectively. Surprisingly, the hole mobility in the InSe/BP heterostructure exceeds 10 4 cm 2 V -1 s -1 , which is one order of magnitude larger than the hole mobility of BP and three orders larger than that of the InSe monolayer. The electron mobility is also increased to 3 × 10 3 cm 2 V -1 s -1 . The physical reason has been analyzed deeply, and a universal method is proposed to improve the carrier mobility of 2D materials by forming heterostructures with them and other 2D materials with complementary properties. The InSe/BP heterostructure can thus be widely used in nanoscale InSe-based field-effect transistors, photodetectors and photovoltaic devices due to its type-II band alignment and high carrier mobility.

SLS complementary logic devices with increase carrier mobility

DOEpatents

Chaffin, R.J.; Osbourn, G.C.; Zipperian, T.E.

1991-07-09

In an electronic device comprising a semiconductor material and having at least one performance characteristic which is limited by the mobility of holes in the semiconductor material, said mobility being limited because of a valence band degeneracy among high-mobility and low-mobility energy levels accessible to said holes at the energy-momentum space maximum, an improvement is provided wherein the semiconductor material is a strained layer superlattice (SLS) whose layer compositions and layer thicknesses are selected so that the strain on the layers predominantly containing said at least one carrier type splits said degeneracy and modifies said energy levels around said energy-momentum space maximum in a manner whereby said limitation on the mobility of said holes is alleviated. 5 figures.

SLS complementary logic devices with increase carrier mobility

DOEpatents

Chaffin, Roger J.; Osbourn, Gordon C.; Zipperian, Thomas E.

1991-01-01

In an electronic device comprising a semiconductor material and having at least one performance characteristic which is limited by the mobility of holes in the semiconductor material, said mobility being limited because of a valence band degeneracy among high-mobility and low-mobility energy levels accessible to said holes at the energy-momentum space maximum, an improvement is provided wherein the semiconductor material is a strained layer superlattice (SLS) whose layer compositions and layer thicknesses are selected so that the strain on the layers predominantly containing said at least one carrier type splits said degeneracy and modifies said energy levels around said energy-momentum space maximum in a manner whereby said limitation on the mobility of said holes is alleviated.

Density and mobility effects of the majority carriers in organic semiconductors under light excitation

NASA Astrophysics Data System (ADS)

Vagenas, N.; Giannopoulou, A.; Kounavis, P.

2015-01-01

This study demonstrates that the effect of light excitation on the density and the mobility of the majority carriers can be explored in organic semiconductors by modulated photocurrent spectroscopy. The spectra of phase and amplitude of the modulated photocurrent of pentacene films indicate a significant increase in the density of the photogenerated mobile holes (majority carriers). This increase is accompanied by a comparatively much smaller increase of the steady state photocurrent response which can be reconciled with a decrease in the mobility (μ) of holes. The decrease of μ is supported from an unusual increase of the Y/μ ratio of the out-of-phase modulated photocurrent (Y) signal to the mobility under light excitation. It is proposed that the mobile holes, which are generated from the dissociation of the light-created excitons more likely near the pentacene-substrate interface by electron trapping, populate grain boundaries charging them and producing a downward band bending. As a result, potential energy barriers are build up which limit the transport of holes interacting through trapping-detrapping with deep partially occupied traps in the charged grain boundaries. On the other hand, the transport of holes interacting through trapping-detrapping with empty traps is found unaffected.

Intrinsic phonon-limited charge carrier mobilities in thermoelectric SnSe

NASA Astrophysics Data System (ADS)

Ma, Jinlong; Chen, Yani; Li, Wu

2018-05-01

Within the past few years, tin selenide (SnSe) has attracted intense interest due to its remarkable thermoelectric potential for both n - and p -type crystals. In this work, the intrinsic phonon-limited electron/hole mobilities of SnSe are investigated using a Boltzmann transport equation based on first-principles calculated electron-phonon interactions. We find that the electrons have much larger mobilities than the holes. At room temperature, the mobilities of electrons along the a , b , and c axes are 325, 801, and 623 cm2/V s, respectively, whereas those of holes are 100, 299, and 291 cm2/V s, respectively. The anisotropy of mobilities is consistent with the reciprocal effective mass at band edges. The mode-specific analysis shows that the highest longitudinal optical phonons, rather than previously assumed acoustic phonons, dominate the scattering processes and consequently the mobilities in SnSe. The room-temperature largest mean free paths of electrons and holes in SnSe are about 21 and 13 nm, respectively.

Nondispersive hole transport in a spin-coated dendrimer film measured by the charge-generation-layer time-of-flight method

NASA Astrophysics Data System (ADS)

Markham, Jonathan P. J.; Anthopoulos, Thomas D.; Samuel, Ifor D. W.; Richards, Gary J.; Burn, Paul L.; Im, Chan; Bassler, Heinz

2002-10-01

Measurements of the mobility of a first-generation (G1) bis-fluorene cored dendrimer have been performed on spin-coated samples of 500 nm thickness using the charge-generation-layer time-of-flight (TOF) technique. A 10 nm perylene charge generation layer was excited by the 532 nm line of a Q-switched Nd:YAG laser and the generated carriers swept through the dendrimer film under an applied field. We observe nondispersive hole transport in the dendrimer layer with a room-temperature mobility mu=2.0 x10-4 cm2/V s at a field of 0.55 MV/cm. There is a weak field dependence of the mobility and it increases from mu=1.6 x10-4 cm2/V s at 0.2 MV/cm to mu=3.0 x10-4 cm2/V s at 1.4 MV/cm. These results suggest that the measurement of mobility by TOF in spin-coated samples on thickness scales relevant to organic light-emitting diodes can yield valuable information, and that dendrimers are promising materials for device applications.

Magnetotransport of High Mobility Holes in Monolayer and Bilayer WSe2

NASA Astrophysics Data System (ADS)

Tutuc, Emanuel

Transition metal dichalcogenides have attracted significant interest because of their two-dimensional crystal structure, large band-gap, and strong spin-orbit interaction which leads to spin-valley locking. Recent advances in sample fabrication have allowed the experimental study of low temperature magneto-transport of high mobility holes in WSe2. We review here the main results of these studies which reveal clear quantum Hall states in mono- and bilayer WSe2. The data allows the extraction of an effective hole mass of m* = 0.45me (me is the bare electron mass) in both mono and bilayer WSe2. A systematic study of the carrier distribution in bilayer WSe2 determined from a Fourier analysis of the Shubnikov-de Haas oscillations indicates that the two layers are weakly coupled. The individual layer density dependence on gate bias shows negative compressibility, a signature of strong electron-electron interaction in these materials associated with the large effective mass. We discuss the interplay between cyclotron and Zeeman splitting using the dependence of the quantum Hall state sequence on carrier density, and the angle between the magnetic field and the WSe2 plane. Work done in collaboration with B. Fallahazad, H. C. P. Movva, K. Kim, S. K. Banerjee, T. Taniguchi, and K. Watanabe. This work supported by the Nanoelectronics Research Initiative SWAN center, Intel Corp., and National Science Foundation.

Separation of electron and hole dynamics in the semimetal LaSb

DOE Office of Scientific and Technical Information (OSTI.GOV)

Han, F.; Xu, J.; Botana, A. S.

We report investigations on the magnetotransport in LaSb, which exhibits extremely large magnetoresistance (XMR). Foremost, we demonstrate that the resistivity plateau can be explained without invoking topological protection. We then determine the Fermi surface from Shubnikov–de Haas (SdH) quantum oscillation measurements and find good agreement with the bulk Fermi pockets derived from first-principles calculations. Using a semiclassical theory and the experimentally determined Fermi pocket anisotropies, we quantitatively describe the orbital magnetoresistance, including its angle dependence.We show that the origin of XMR in LaSb lies in its high mobility with diminishing Hall effect, where the high mobility leads to a strongmore » magnetic-field dependence of the longitudinal magnetoconductance. Unlike a one-band material, when a system has two or more bands (Fermi pockets) with electron and hole carriers, the added conductance arising from the Hall effect is reduced, hence revealing the latent XMR enabled by the longitudinal magnetoconductance. With diminishing Hall effect, the magnetoresistivity is simply the inverse of the longitudinal magnetoconductivity, enabling the differentiation of the electron and hole contributions to the XMR, which varies with the strength and orientation of the magnetic field. This work demonstrates a convenient way to separate the dynamics of the charge carriers and to uncover the origin of XMR in multiband materials with anisotropic Fermi surfaces. Our approach can be readily applied to other XMR materials.« less

Significance of the gate voltage-dependent mobility in the electrical characterization of organic field effect transistors

NASA Astrophysics Data System (ADS)

Kim, Jong Beom; Lee, Dong Ryeol

2018-04-01

We studied the effect of the addition of free hole- and electron-rich organic molecules to organic semiconductors (OSCs) in organic field effect transistors (OFETs) on the gate voltage-dependent mobility. The drain current versus gate voltage characteristics were quantitatively analyzed using an OFET mobility model of power law behavior based on hopping transport in an OSC. This analysis distinguished the threshold voltage shifts, depending on the materials and structures of the OFET device, and properly estimated the hopping transport of the charge carriers induced by the gate bias within the OSC from the power law exponent parameter. The addition of pentacene or C60 molecules to a one-monolayer pentacene-based OFET shifted the threshold voltages negatively or positively, respectively, due to the structural changes that occurred in the OFET device. On the other hand, the power law parameters revealed that the addition of charge carriers of the same or opposite polarity enhanced or hindered hopping transport, respectively. This study revealed the need for a quantitative analysis of the gate voltage-dependent mobility while distinguishing this effect from the threshold voltage effect in order to understand OSC hopping transport in OFETs.

Thermoelectric properties, Shubnikov-de Haas effect and mobility of charge carriers in bismuth antimony tellurides and selenides and nanocomposite based on these materials

NASA Astrophysics Data System (ADS)

Kulbachinskii, V. A.; Kytin, V. G.; Kudryashov, A. A.; Lunin, R. A.; Banerjee, A.

2017-04-01

We describe here the study of the Shubnikov-de Haas effect and thermoelectric properties of p-(Bi0.5Sb0.5)2Te3 single crystals doped with Ga, n-Bi2-xTlxSe3 and p-Sb2-xTlxTe3. Using Fourier spectra of the oscillations we calculated the mobility of charge carriers and its variation upon doping. We found that Ga has a donor effect in p-(Bi0.5Sb0.5)2Te3, Tl is an acceptor in n-Bi2-xTlxSe3 and increases the mobility of electrons, while in p-Sb2-xTlxTe3, Tl is a donor and decreases the mobility of holes. We consider the evolution of the defectiveness of crystals that leads to the observed effects. We also synthesized and investigated nanocomposites of solid solutions Sb2Te3-xSex (0 < x < 1). When Se concentration increases in Sb2Te3-xSex, the concentration of holes decreases. At the same time the Seebeck coefficient decreases. This is not typical for semiconductors but correlates with the earlier data. A theoretical model was developed to calculate simultaneously the dependences of the Seebeck coefficient, Hall coefficient and conductivity on the selenium concentration x. Calculations showed that for a simultaneous quantitative description of the thermoelectric and galvanomagnetic data it is necessary to take into consideration both the evolution of the band structure of Sb2Te3-xSex and partial localization of holes.

CsSnI[subscript 3]: Semiconductor or Metal? High Electrical Conductivity and Strong Near-Infrared Photoluminescence from a Single Material. High Hole Mobility and Phase-Transitions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chung, In; Song, Jung-Hwan; Im, Jino

CsSnI{sub 3} is an unusual perovskite that undergoes complex displacive and reconstructive phase transitions and exhibits near-infrared emission at room temperature. Experimental and theoretical studies of CsSnI{sub 3} have been limited by the lack of detailed crystal structure characterization and chemical instability. Here we describe the synthesis of pure polymorphic crystals, the preparation of large crack-/bubble-free ingots, the refined single-crystal structures, and temperature-dependent charge transport and optical properties of CsSnI{sub 3}, coupled with ab initio first-principles density functional theory (DFT) calculations. In situ temperature-dependent single-crystal and synchrotron powder X-ray diffraction studies reveal the origin of polymorphous phase transitions of CsSnI{submore » 3}. The black orthorhombic form of CsSnI{sub 3} demonstrates one of the largest volumetric thermal expansion coefficients for inorganic solids. Electrical conductivity, Hall effect, and thermopower measurements on it show p-type metallic behavior with low carrier density, despite the optical band gap of 1.3 eV. Hall effect measurements of the black orthorhombic perovskite phase of CsSnI{sub 3} indicate that it is a p-type direct band gap semiconductor with carrier concentration at room temperature of {approx} 10{sup 17} cm{sup -3} and a hole mobility of {approx} 585 cm{sup 2} V{sup -1} s{sup -1}. The hole mobility is one of the highest observed among p-type semiconductors with comparable band gaps. Its powders exhibit a strong room-temperature near-IR emission spectrum at 950 nm. Remarkably, the values of the electrical conductivity and photoluminescence intensity increase with heat treatment. The DFT calculations show that the screened-exchange local density approximation-derived band gap agrees well with the experimentally measured band gap. Calculations of the formation energy of defects strongly suggest that the electrical and light emission properties possibly result from Sn defects in the crystal structure, which arise intrinsically. Thus, although stoichiometric CsSnI{sub 3} is a semiconductor, the material is prone to intrinsic defects associated with Sn vacancies. This creates highly mobile holes which cause the materials to appear metallic.« less

A hole accelerator for InGaN/GaN light-emitting diodes

NASA Astrophysics Data System (ADS)

Zhang, Zi-Hui; Liu, Wei; Tan, Swee Tiam; Ji, Yun; Wang, Liancheng; Zhu, Binbin; Zhang, Yiping; Lu, Shunpeng; Zhang, Xueliang; Hasanov, Namig; Sun, Xiao Wei; Demir, Hilmi Volkan

2014-10-01

The quantum efficiency of InGaN/GaN light-emitting diodes (LEDs) has been significantly limited by the insufficient hole injection, and this is caused by the inefficient p-type doping and the low hole mobility. The low hole mobility makes the holes less energetic, which hinders the hole injection into the multiple quantum wells (MQWs) especially when a p-type AlGaN electron blocking layer (EBL) is adopted. In this work, we report a hole accelerator to accelerate the holes so that the holes can obtain adequate kinetic energy, travel across the p-type EBL, and then enter the MQWs more efficiently and smoothly. In addition to the numerical study, the effectiveness of the hole accelerator is experimentally shown through achieving improved optical output power and reduced efficiency droop for the proposed InGaN/GaN LED.

The Effect of Strain on the Base Resistance and Transit Time of Ungraded and Compositional-Graded SiGe HBTs

NASA Technical Reports Server (NTRS)

Rosenfeld, D.; Alterovitz, S. A.

1994-01-01

A theoretical study of the effects of the strain on the base properties of ungraded and compositional-graded n-p-n SiGe Heterojunction Bipolar Transistors (HBT) is presented. The dependencies of the transverse hole mobility and longitudinal electron mobility upon strain, composition and doping, are formulated using published Monte-Carlo data and, consequently, the base resistance and transit time are modeled and calculated. The results are compared to results obtained using common formulas that ignore these dependencies. The differences between the two sets of results are shown. The paper's conclusion is that for the design, analysis and optimization of high frequency SiGe HBTs the strain effects on the base properties cannot be ignored.

Silicon-compatible high-hole-mobility transistor with an undoped germanium channel for low-power application

NASA Astrophysics Data System (ADS)

Cho, Seongjae; Man Kang, In; Rok Kim, Kyung; Park, Byung-Gook; Harris, James S.

2013-11-01

In this work, Ge-based high-hole-mobility transistor with Si compatibility is designed, and its performance is evaluated. A 2-dimensional hole gas is effectively constructed by a AlGaAs/Ge/Si heterojunction with a sufficiently large valence band offset. Moreover, an intrinsic Ge channel is exploited so that high hole mobility is preserved without dopant scattering. Effects of design parameters such as gate length, Ge channel thickness, and aluminum fraction in the barrier material on device characteristics are thoroughly investigated through device simulations. A high on-current above 30 μA/μm along with a low subthreshold swing was obtained from an optimized planar device for low-power applications.

1,2,3,4-bis(p-methylbenzylidene sorbitol) accelerates crystallization and improves hole mobility of poly(3-hexylthiophene)

NASA Astrophysics Data System (ADS)

Yuan, Nana; Huo, Hong

2016-02-01

The addition of 1,2,3,4-bis(p-methylbenzylidene sorbitol) (MDBS) does not change the nucleation mechanism or the crystal form of poly(3-hexylthiophene) (P3HT), but its presence increases the crystallization temperature (T c) of P3HT, decreases the crystallization half-time (t 1/2) and accelerates P3HT crystallization, which indicates that MDBS is an effective nucleating agent for P3HT. An acceleration of P3HT crystallization by the addition of MDBS decreases the crystalline size and crystallinity of P3HT, and enhances the connectivity between ordered regions of P3HT, leading to the hole mobility rising from 1.99 × 10-6 to 7.57 × 10-5 cm2 V-1s-1 in P3HT:PCBM blend based hole-only devices with sandwich configurations. Our results suggest that accelerating P3HT crystallization by adding a nucleating agent might be an important factor to improve the hole mobility and balance the electron and hole mobility in a photovoltaic blend.

Shubnikov-de Haas oscillations of high mobility holes in monolayer and bilayer WSe2: spin-valley locking, effective mass, and inter-layer coupling

NASA Astrophysics Data System (ADS)

Fallahazad, Babak; Movva, Hema Chandra Prakash; Kim, Kyounghwan; Larentis, Stefano; Taniguchi, Takashi; Watanabe, Kenji; Banerjee, Sanjay K.; Tutuc, Emanuel

We study the magnetotransport properties of high mobility holes in monolayer and bilayer WSe2, measured in dual-gated samples with top and bottom hexagonal boron-nitride dielectrics, and using platinum bottom contacts. Thanks to the Pt high work-function combined with the a high hole density induced electrostatically by an applied top gate bias, the contacts remain ohmic down to low (1.5 K) temperatures. The samples display well defined Shubnikov-de Haas (SdH) oscillations, and quantum Hall states (QHS) in high magnetic fields. In both mono and bilayer WSe2, the SdH oscillations and the QHSs occur predominantly at even filling factors, evincing a two-fold Landau level degeneracy consistent with spin-valley locking. The Fourier transform analysis of the SdH oscillations in dual-gated bilayer WSe2 reveal the presence of two subbands, each localized in the top or the bottom layer, as well as negative compressibility. From the temperature dependence of the SdH oscillation amplitude we determine a hole effective mass of 0.45me for both mono and bilayer WSe2. The top and bottom layer densities can be independently tuned using the top and bottom gates, respectively, evincing a weak interlayer coupling. This work has been supported by NRI-SWAN and Intel corporation.

Charge Generation and Propagation in Igneous Rocks

NASA Technical Reports Server (NTRS)

Freund, Friedemann

2000-01-01

Resistivity changes, ground potentials, electromagnetic (EM) and luminous signals prior to or during earthquakes have been reported, in addition to ground uplift and tilt, and to changes in the seismic wave propagation parameters. However, no physical model exists that ties these diverse phenomena together. Through time-resolved impacts experiments it has been observed that, when igneous rocks (gabbro, diorite, granite) are impacted at low velocities (approx. 100 m/sec), highly mobile electronic charge carriers are generated, spreading from a small volume near the impact point, causing electric potentials, EM and light emission. The rock becomes momentarily conductive. When impacted at higher velocities (approx. 1.5 km/sec), the propagation of the P and S waves is registered through the transient piezoelectric response of quartz. At the same time, the rock volume is filled with mobile charge carriers, and a positive surface potential is registered. During the next 1-2 msec the surface potential oscillates, due to electron injection from ground. These observations are consistent with positive holes, e.g. defect electrons in the O(2-) sublattice, that can travel via the O 2p-dominated valence band of the silicate minerals at the speed of a phonon-mediated charge transfer. Before activation, the positive hole charge carriers lay dormant in form of positive hole pairs, PHP, electrically inactive, chemically equivalent to peroxy links in the structures of constituent minerals. PHPs are introduced by way of hydroxyl (O3Si-OH) incorporated into nominally anhydrous minerals when they crystallize in water-laden environments. Given that sound waves of even relatively low intensity appear to cause PHPs dissociation, thus generating mobile positive holes, it is proposed that microfracturing during rock deformation cause PHP dissociation. Depending on where and how much the rock volume is stressed, the positive holes are expected to form fluctuating charge clouds in the earthquake source region that may account for earthquake-related electrical phenomena and the reported low frequency EM signals.

Tunable Transport Gap in Phosphorene

DOE Office of Scientific and Technical Information (OSTI.GOV)

Das, Saptarshi; Zhang, Wei; Demarteau, Marcel

2014-08-11

In this paper, we experimentally demonstrate that the transport gap of phosphorene can be tuned monotonically from ~0.3 to ~1.0 eV when the flake thickness is scaled down from bulk to a single layer. As a consequence, the ON current, the OFF current, and the current ON/OFF ratios of phosphorene field effect transistors (FETs) were found to be significantly impacted by the layer thickness. The transport gap was determined from the transfer characteristics of phosphorene FETs using a robust technique that has not been reported before. The detailed mathematical model is also provided. By scaling the thickness of the gatemore » oxide, we were also able to demonstrate enhanced ambipolar conduction in monolayer and few layer phosphorene FETs. The asymmetry of the electron and the hole current was found to be dependent on the layer thickness that can be explained by dynamic changes of the metal Fermi level with the energy band of phosphorene depending on the layer number. We also extracted the Schottky barrier heights for both the electron and the hole injection as a function of the layer thickness. In conclusion, we discuss the dependence of field effect hole mobility of phosphorene on temperature and carrier concentration.« less

Post-operative day two versus day seven mobilization after burr-hole drainage of subacute and chronic subdural haematoma in Nigerians.

PubMed

Adeolu, Augustine Abiodun; Rabiu, Taopheeq Bamidele; Adeleye, Amos Olufemi

2012-10-01

The traditional care of patients with subacute/chronic subdural haematoma (S/CSDH) often involves delayed mobilization after burr-hole drainage. It is thought that delayed mobilization aids brain re-expansion thereby reducing the risk of recurrence. However, there is paucity of information regarding its efficacy and safety over early mobilization. We evaluated the efficacy and complications of each type of mobilization following burr-hole drainage of S/CSDH. This was a prospective study from October 2004 and September 2010. A total of 50 patients who had burr-hole drainage of S/CSDH were sequentially allocated to either early (day 2) or late (day 7) mobilization (EM or LM) groups (25 patients in each group). Wound related complications, recurrence of haematoma, complications of prolonged bed rest and Glasgow Outcome Score (GOS) at discharge were studied in the two groups. Patients who could not obey commands to mobilize in the early post-operative period were excluded. There were 43 (86%) males and 7 (14%) females. The mean age was 57 years (range: 27-90 years). Fourteen (28%) of the patients were elderly (age > 65 years). Two complications, wound infection in a 76-year old man in the LM group and tension pneumocephalus requiring re-opening burr-hole drainage in a 55-year old man in the EM group were recorded. There was no recurrence or problem associated with prolonged bed rest in the two groups. Five (10%) patients had moderate disability (GOS 4) at discharge (1 EM, 4 LM) while the others (90%) had good recovery (GOS 5) (24 EM, 21 LM). These differences were not statistically significant (p-value: 0.349). It appears that both EM and LM are equally beneficial in the post-operative care of patients following burr-hole drainage of S/CSDH. There is no significant complication referable to the specific type of mobilization. The authors, therefore, advocate EM of patients to reduce the length of hospital stay.

The importance of holes in aluminium tris-8-hydroxyquinoline (Alq{sub 3}) devices with Fe and NiFe contacts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Hongtao; Desai, P.; Kreouzis, T.

To study the dominant charge carrier polarity in aluminium tris-8-hydroxyquinoline (Alq{sub 3}) based spin valves, single Alq{sub 3} layer devices with NiFe, ITO, Fe, and aluminium electrodes were fabricated and characterised by Time of Flight (ToF) and Dark Injection (DI) techniques, yielding a lower hole mobility compared to electron mobility. We compare the mobility measured by DI for the dominant carrier injected from NiFe and Fe electrodes into Alq{sub 3}, to that of holes measured by ToF. This comparison leads us to conclude that the dominant charge carriers in Alq{sub 3} based spin valves with NiFe or Fe electrodes aremore » holes.« less

New non-linear photovoltaic effect in uniform bipolar semiconductor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Volovichev, I.

2014-11-21

A linear theory of the new non-linear photovoltaic effect in the closed circuit consisting of a non-uniformly illuminated uniform bipolar semiconductor with neutral impurities is developed. The non-uniform photo-excitation of impurities results in the position-dependant current carrier mobility that breaks the semiconductor homogeneity and induces the photo-electromotive force (emf). As both the electron (or hole) mobility gradient and the current carrier generation rate depend on the light intensity, the photo-emf and the short-circuit current prove to be non-linear functions of the incident light intensity at an arbitrarily low illumination. The influence of the sample size on the photovoltaic effect magnitudemore » is studied. Physical relations and distinctions between the considered effect and the Dember and bulk photovoltaic effects are also discussed.« less

Highly oriented diamond films on Si: growth, characterization, and devices

NASA Astrophysics Data System (ADS)

Stoner, Brian R.; Malta, D. M.; Tessmer, A. J.; Holmes, J.; Dreifus, David L.; Glass, R. C.; Sowers, A.; Nemanich, Robert J.

1994-04-01

Highly oriented, (100) textured diamond films have been grown on single-crystal Si substrates via microwave plasma enhanced chemical vapor deposition. A multistep deposition process including bias-enhanced nucleation and textured growth was used to obtain smooth films consisting of epitaxial grains with only low-angle grain boundaries. Boron-doped layers were selectively deposited onto the surface of these oriented films and temperature-dependent Hall effect measurements indicated a 3 to 5 times improvement in hole mobility over polycrystalline films grown under similar conditions. Room temperature hole mobilities between 135 and 278 cm2/V-s were measured for the highly oriented samples as compared to 2 to 50 cm2/V-s for typical polycrystalline films. Grain size effects and a comparison between the transport properties of polycrystalline, highly oriented and homoepitaxial films will be discussed. Metal-oxide- semiconductor field-effect transistors were then fabricated on the highly oriented films and exhibited saturation and pinch-off of the channel current.

Brownian escape and force-driven transport through entropic barriers: Particle size effect.

PubMed

Cheng, Kuang-Ling; Sheng, Yu-Jane; Tsao, Heng-Kwong

2008-11-14

Brownian escape from a spherical cavity through small holes and force-driven transport through periodic spherical cavities for finite-size particles have been investigated by Brownian dynamic simulations and scaling analysis. The mean first passage time and force-driven mobility are obtained as a function of particle diameter a, hole radius R(H), cavity radius R(C), and external field strength. In the absence of external field, the escape rate is proportional to the exit effect, (R(H)R(C))(1-a2R(H))(32). In weak fields, Brownian diffusion is still dominant and the migration is controlled by the exit effect. Therefore, smaller particles migrate faster than larger ones. In this limit the relation between Brownian escape and force-driven transport can be established by the generalized Einstein-Smoluchowski relation. As the field strength is strong enough, the mobility becomes field dependent and grows with increasing field strength. As a result, the size selectivity diminishes.

Conjugated foldamers with unusually high space-charge-limited current hole mobilities.

PubMed

Li, Yong; Dutta, Tanmoy; Gerasimchuk, Nikolay; Wu, Shijie; Shetye, Kuldeep; Jin, Lu; Wang, Ruixin; Zhu, Da-Ming; Peng, Zhonghua

2015-05-13

Charge carrier mobility and its optimization play a critical role in the development of cutting-edge organic electronic and optoelectronic devices. Even though space-charge-limited current (SCLC) hole mobilities as high as 1.4 cm(2) V(-1) s(-1) have been reported for microscopically sized highly ordered liquid-crystalline conjugated small molecules, the SCLC hole mobility of device-sized thin films of conjugated polymers is still much lower, ranging from 10(-6) to 10(-3) cm(2) V(-1) s(-1). Herein, we report the synthesis, characterizations, and thin-film SCLC mobility of three discotic conjugated polymers, INDT-TT, INDT-BT, and INDT-NDT. Optical studies indicate that polymer INDT-NDT adopts a folded conformation in solutions of good or poor solvents, whereas polymer INDT-TT stays as random monomeric chains in good solvents and interchain aggregates in poor solvents. INDT-BT polymer chains, however, stay as foldamers in dilute solutions of good solvents but interchain aggregates in concentrated solutions or poor solvents. Circular dichroism spectroscopy provides clear evidence for the helical folding of INDT-NDT in solutions. Thin films spin-coated from 1,2-dichlorobenzene solutions of the polymers show SCLC hole mobility of 2.20 × 10(-6), 8.79 × 10(-5), and 2.77 × 10(-2) cm(2) V(-1) s(-1) for INDT-TT, INDT-BT, and INDT-NDT, respectively. HRTEM and powder XRD measurements show that INDT-NDT pristine thin films contain nanocrystalline domains, whereas the INDT-TT and INDT-BT films are amorphous. Thin films of INDT-NDT:PC71BM blends show increased crystallinity and further improved SCLC hole mobility up to 1.29 × 10(-1) cm(2) V(-1) s(-1), one of the highest SCLC mobility values ever recorded on solution-processed organic semiconducting thin films. The persistent folding conformation of INDT-NDT is believed to be responsible for the high crystallinity of its thin films and its high SCLC mobilities.

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

PubMed

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

2015-06-01

This article reviews the charge transport and photogeneration in bulk-heterojunction solar cells made from blend films of regioregular poly(3-hexylthiophene) (RR-P3HT) and methano-fullerene (PCBM). The charge transport, specifically the hole mobility in the RR-P3HT phase of the polymer:fullerene photovoltaic blend, is dramatically affected by thermal annealing. The hole mobility increases more than three orders of magnitude and reaches a value of up to 2 × 10(-4) cm(2) V(-1) s(-1) after the thermal annealing process as a result of an improved semi-crystallinity of the film. This significant increase of the hole mobility balances the electron and hole mobilities in a photovoltaic blend in turn reducing space-charge formation, and this is the most important factor for the strong enhancement of the photovoltaic efficiency compared to an as cast, that is, non-annealed device. In fact, the balanced charge carrier mobility in RR-P3HT:PCBM blends in combination with a field- and temperature-independent charge carrier generation and greatly reduced non-geminate recombination explains the large quantum efficiencies mea-sured in P3HT:PCBM photovoltaic devices. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Molecular weight dependence of carrier mobility and recombination rate in neat P3HT films

DOE PAGES

Dixon, Alex G.; Visvanathan, Rayshan; Clark, Noel A.; ...

2017-11-02

The microstructure dependence of carrier mobility and recombination rates of neat films of poly 3-hexylthyophene (P3HT) were determined for a range of materials of weight-average molecular weights, Mw, ranging from 14 to 331 kDa. This variation has previously been shown to modify the polymer microstructure, with low molecular weights forming a one-phase, paraffinic-like structure comprised of chain-extended crystallites, and higher molecular weights forming a semicrystalline structure with crystalline domains being embedded in an amorphous matrix. Using Charge Extraction by Linearly Increasing Voltage (CELIV), we show here that the carrier mobility in P3HT devices peaks for materials of Mw = 48more » kDa, and that the recombination rate decreases monotonically with increasing molecular weight. This trend is likely due to the development of a semicrystalline, two-phase structure with increasing Mw, which allows for the spatial separation of holes and electrons into the amorphous and crystalline regions, respectively. This separation leads to decreased recombination.« less

Molecular weight dependence of carrier mobility and recombination rate in neat P3HT films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dixon, Alex G.; Visvanathan, Rayshan; Clark, Noel A.

The microstructure dependence of carrier mobility and recombination rates of neat films of poly 3-hexylthyophene (P3HT) were determined for a range of materials of weight-average molecular weights, Mw, ranging from 14 to 331 kDa. This variation has previously been shown to modify the polymer microstructure, with low molecular weights forming a one-phase, paraffinic-like structure comprised of chain-extended crystallites, and higher molecular weights forming a semicrystalline structure with crystalline domains being embedded in an amorphous matrix. Using Charge Extraction by Linearly Increasing Voltage (CELIV), we show here that the carrier mobility in P3HT devices peaks for materials of Mw = 48more » kDa, and that the recombination rate decreases monotonically with increasing molecular weight. This trend is likely due to the development of a semicrystalline, two-phase structure with increasing Mw, which allows for the spatial separation of holes and electrons into the amorphous and crystalline regions, respectively. This separation leads to decreased recombination.« less

Charge transport mechanism in lead oxide revealed by CELIV technique

PubMed Central

Semeniuk, O.; Juska, G.; Oelerich, J.-O.; Wiemer, M.; Baranovskii, S. D.; Reznik, A.

2016-01-01

Although polycrystalline lead oxide (PbO) belongs to the most promising photoconductors for optoelectronic and large area detectors applications, the charge transport mechanism in this material still remains unclear. Combining the conventional time-of-flight and the photo-generated charge extraction by linear increasing voltage (photo-CELIV) techniques, we investigate the transport of holes which are shown to be the faster carriers in poly-PbO. Experimentally measured temperature and electric field dependences of the hole mobility suggest a highly dispersive transport. In order to analyze the transport features quantitatively, the theory of the photo-CELIV is extended to account for the dispersive nature of charge transport. While in other materials with dispersive transport the amount of dispersion usually depends on temperature, this is not the case in poly-PbO, which evidences that dispersive transport is caused by the spatial inhomogeneity of the material and not by the energy disorder. PMID:27628537

Experimental and numerical investigation of contact-area-limited doping for top-contact pentacene thin-film transistors with Schottky contact.

PubMed

Noda, Kei; Wada, Yasuo; Toyabe, Toru

2015-10-28

Effects of contact-area-limited doping for pentacene thin-film transistors with a bottom-gate, top-contact configuration were investigated. The increase in the drain current and the effective field-effect mobility was achieved by preparing hole-doped layers underneath the gold contact electrodes by coevaporation of pentacene and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), confirmed by using a thin-film organic transistor advanced simulator (TOTAS) incorporating Schottky contact with a thermionic field emission (TFE) model. Although the simulated electrical characteristics fit the experimental results well only in the linear regime of the transistor operation, the barrier height for hole injection and the gate-voltage-dependent hole mobility in the pentacene transistors were evaluated with the aid of the device simulation. This experimental data analysis with the simulation indicates that the highly-doped semiconducting layers prepared in the contact regions can enhance the charge carrier injection into the active semiconductor layer and concurrent trap filling in the transistor channel, caused by the mitigation of a Schottky energy barrier. This study suggests that both the contact-area-limited doping and the device simulation dealing with Schottky contact are indispensable in designing and developing high-performance organic thin-film transistors.

Hole transport in pure and doped hematite

NASA Astrophysics Data System (ADS)

Liao, Peilin; Carter, Emily A.

2012-07-01

Hematite (α-Fe2O3) is a promising candidate for use in photovoltaic (PV) and photoelectrochemical devices. Its poor conductivity is one major drawback. Doping hematite either p-type or n-type greatly enhances its measured conductivity and is required for potential p-n junctions in PVs. Here, we study hole transport in pure and doped hematite using an electrostatically embedded cluster model with ab initio quantum mechanics (unrestricted Hartree-Fock theory). Consistent with previous work, the model suggests that hole hopping is via oxygen anions for pure hematite. The activation energy for hole mobility is predicted to be at least 0.1 eV higher than the activation energy for electron mobility, consistent with the trend observed in experiments. We examine four dopants—magnesium(II), nickel(II), copper(II), and manganese(II/III) in direct cation substitution sites—to gain insight into the mechanism by which conductivity is improved. The activation energies are used to assess qualitative effects of different dopants. The hole carriers are predicted to be attracted to O anions near the dopants. The magnitude of the trapping effect is similar among the four dopants in their +2 oxidation states. The multivalent character of Mn doping facilitates local hole transport around Mn centers via a low-barrier O-Mn-O pathway, which suggests that higher hole mobility can be achieved with increasing Mn doping concentration, especially when a network of these low-barrier pathways is produced. Our results suggest that the experimentally observed conductivity increase in Mg-, Ni-, and Cu-doped p-type hematite is mostly due to an increase in hole carriers rather than improved mobility, and that Mg-, Ni-, and Cu-doping perform similarly, while the conductivity of Mn-doped hematite might be significantly improved in the high doping concentration limit.

Thin-film transistors based on poly(3,3‴-dialkyl-quarterthiophene) and zinc oxide nanowires with improved ambient stability

NASA Astrophysics Data System (ADS)

Vieira, Sara M. C.; Hsieh, Gen-Wen; Unalan, Husnu E.; Dag, Sefa; Amaratunga, Gehan A. J.; Milne, William I.

2011-03-01

The ambient stability of thin-film transistors (TFTs) based on zinc oxide (ZnO) nanowires embedded in poly(3,3‴-dialkyl-quarterthiophene) was monitored through time dependence of electrical characteristics over a period of 16 months. The hybrid-based TFT showed an initial hole mobility in the linear regime of 4.2×10-4 cm2/V s. After 16 months storage in ambient conditions (exposed to air, moisture, and light) the mobility decreased to 2.3×10-5 cm2/V s. Comparatively the organic-based TFT lost total carrier mobility after one month storage making the hybrid-based TFTs more suitable for transistor applications when improved stability combined with structural flexibility are required.

Optimal Ge/SiGe nanofin geometries for hole mobility enhancement: Technology limit from atomic simulations

NASA Astrophysics Data System (ADS)

Vedula, Ravi Pramod; Mehrotra, Saumitra; Kubis, Tillmann; Povolotskyi, Michael; Klimeck, Gerhard; Strachan, Alejandro

2015-05-01

We use first principles simulations to engineer Ge nanofins for maximum hole mobility by controlling strain tri-axially through nano-patterning. Large-scale molecular dynamics predict fully relaxed, atomic structures for experimentally achievable nanofins, and orthogonal tight binding is used to obtain the corresponding electronic structure. Hole transport properties are then obtained via a linearized Boltzmann formalism. This approach explicitly accounts for free surfaces and associated strain relaxation as well as strain gradients which are critical for quantitative predictions in nanoscale structures. We show that the transverse strain relaxation resulting from the reduction in the aspect ratio of the fins leads to a significant enhancement in phonon limited hole mobility (7× over unstrained, bulk Ge, and 3.5× over biaxially strained Ge). Maximum enhancement is achieved by reducing the width to be approximately 1.5 times the height and further reduction in width does not result in additional gains. These results indicate significant room for improvement over current-generation Ge nanofins, provide geometrical guidelines to design optimized geometries and insight into the physics behind the significant mobility enhancement.

Carrier mobility degradation due to high dose implantation in ultrathin unstrained and strained silicon-on-insulator films

NASA Astrophysics Data System (ADS)

Dupré, C.; Ernst, T.; Hartmann, J.-M.; Andrieu, F.; Barnes, J.-P.; Rivallin, P.; Faynot, O.; Deleonibus, S.; Fazzini, P. F.; Claverie, A.; Cristoloveanu, S.; Ghibaudo, G.; Cristiano, F.

2007-11-01

Based on electrical measurements and transmission electron microscopy (TEM) imaging, we propose an explanation for the electron and hole mobility degradation with gate length reduction in metal-oxide-semiconductor field effect transistors (MOSFETs). We demonstrate that ion implantation, normally used for source/drain doping, is responsible for transport degradation for short-channel devices. Implantation impact on electrons and holes mobility was investigated both on silicon-on-insulator (SOI) and tensile strained silicon-on-insulator (sSOI) substrates. Wafers with ultrathin Si films (from 8 to 35 nm) were Ge implanted at 3 keV and various concentrations (from 5×1014 to 2×1015 atoms cm-2), then annealed at 600 °C for 1 h. Secondary ion mass spectrometry enabled us to quantify the Ge-implanted atoms concentrations. The end-of-range defects impact on mobility was investigated with the pseudo-MOSFET technique. Measurements showed a mobility decrease as the implantation dose increased. We demonstrated that sSOI mobility is more sensitive to implantation than SOI mobility, without any implantation-induced strain relaxation in sSOI (checked using the ultraviolet Raman technique). A 36% (25%) holes (electrons) mobility degradation was measured for sSOI, while SOI presented a 21% mobility degradation for holes and 5% for electrons. Finally, the electrical results were compared with morphological studies. Plan-view TEM showed the presence of interstitial defects formed during ion implantation and annealing. The defect density was estimated to be two times higher in sSOI than in SOI, which is in full agreement with electrical results mentioned before. The results are relevant for the optimization of the source and drain regions of advanced nanoscale SOI and sSOI transistors.

Quantitative evaluation of spatial scale of carrier trapping at grain boundary by GHz-microwave dielectric loss spectroscopy

NASA Astrophysics Data System (ADS)

Choi, W.; Tsutsui, Y.; Miyakai, T.; Sakurai, T.; Seki, S.

2017-11-01

Charge carrier mobility is an important primary parameter for the electronic conductive materials, and the intrinsic limit of the mobility has been hardly access by conventional direct-current evaluation methods. In the present study, intra-grain hole mobility of pentacene thin films was estimated quantitatively using microwave-based dielectric loss spectroscopy (time-resolved microwave conductivity measurement) in alternating current mode of charge carrier local motion. Metal-insulator-semiconductor devices were prepared with different insulating polymers or substrate temperature upon vacuum deposition of the pentacene layer, which afforded totally four different grain-size conditions of pentacene layers. Under the condition where the local motion was determined by interfacial traps at the pentacene grain boundaries (grain-grain interfaces), the observed hole mobilities were plotted against the grain sizes, giving an excellent correlation fit successfully by a parabolic function representative of the boarder length. Consequently, the intra-grain mobility and trap-release time of holes were estimated as 15 cm2 V-1 s-1 and 9.4 ps.

Influence of Electron–Holes on DNA Sequence-Specific Mutation Rates

PubMed Central

Suárez-Villagrán, Martha Y; Azevedo, Ricardo B R; Miller, John H

2018-01-01

Abstract Biases in mutation rate can influence molecular evolution, yielding rates of evolution that vary widely in different parts of the genome and even among neighboring nucleotides. Here, we explore one possible mechanism of influence on sequence-specific mutation rates, the electron–hole, which can localize and potentially trigger a replication mismatch. A hole is a mobile site of positive charge created during one-electron oxidation by, for example, radiation, contact with a mutagenic agent, or oxidative stress. Its quantum wavelike properties cause it to localize at various sites with probabilities that vary widely, by orders of magnitude, and depend strongly on the local sequence. We find significant correlations between hole probabilities and mutation rates within base triplets, observed in published mutation accumulation experiments on four species of bacteria. We have also computed hole probability spectra for hypervariable segment I of the human mtDNA control region, which contains several mutational hotspots, and for heptanucleotides in noncoding regions of the human genome, whose polymorphism levels have recently been reported. We observe significant correlations between hole probabilities, and context-specific mutation and substitution rates. The correlation with hole probability cannot be explained entirely by CpG methylation in the heptanucleotide data. Peaks in hole probability tend to coincide with mutational hotspots, even in mtDNA where CpG methylation is rare. Our results suggest that hole-enhanced mutational mechanisms, such as oxidation-stabilized tautomerization and base deamination, contribute to molecular evolution. PMID:29617801

Diverse carrier mobility of monolayer BNC_x: A combined density functional theory and Boltzmann transport theory study.

PubMed

Wu, Tao; Deng, Kaiming; Deng, Wei-Qiao; Lu, Ruifeng

2017-09-19

BNCX monolayer as a kind of two-dimensional material has numerous chemical atomic ratios and arrangements with different electronic structures. Via calculations on the basis of density functional theory and Boltzmann transport theory under deformation potential approximation, the band structures and carrier mobilities of BNCX (x=1,2,3,4) nanosheets are systematically investigated. The calculated results show that BNC2-1 is a material with very small band gap (0.02 eV) among all the structures while other BNCX monolayers are semiconductors with band gap ranging from 0.51 to 1.32 eV. The carrier mobility of BNCX varies considerably from tens to millions of cm2 V-1 s-1. For BNC2-1, the hole mobility and electron mobility along both x and y directions can reach 105 orders of magnitude, which is similar to the carrier mobility of graphene. Besides, all studied BNCX monolayers obviously have anisotropic hole mobility and electron mobility. In particular, for semiconductor BNC4, its hole mobility along y direction and electron mobility along x direction unexpectedly reach 106 orders of magnitude, even higher than that of graphene. Our findings suggest that BNCX layered materials with proper ratio and arrangement of carbon atoms will possess desirable charge transport properties, exhibiting potential applications in nanoelectronic devices. © 2017 IOP Publishing Ltd.

Carrier mobility in mesoscale heterogeneous organic materials: Effects of crystallinity and anisotropy on efficient charge transport

NASA Astrophysics Data System (ADS)

Kobayashi, Hajime; Shirasawa, Raku; Nakamoto, Mitsunori; Hattori, Shinnosuke; Tomiya, Shigetaka

2017-07-01

Charge transport in the mesoscale bulk heterojunctions (BHJs) of organic photovoltaic devices (OPVs) is studied using multiscale simulations in combination with molecular dynamics, the density functional theory, the molecular-level kinetic Monte Carlo (kMC) method, and the coarse-grained kMC method, which was developed to estimate mesoscale carrier mobility. The effects of the degree of crystallinity and the anisotropy of the conductivity of donors on hole mobility are studied for BHJ structures that consist of crystalline and amorphous pentacene grains that act as donors and amorphous C60 grains that act as acceptors. We find that the hole mobility varies dramatically with the degree of crystallinity of pentacene because it is largely restricted by a low-mobility amorphous region that occurs in the hole transport network. It was also found that the percolation threshold of crystalline pentacene is relatively high at approximately 0.6. This high percolation threshold is attributed to the 2D-like conductivity of crystalline pentacene, and the threshold is greatly improved to a value of approximately 0.3 using 3D-like conductive donors. We propose essential guidelines to show that it is critical to increase the degree of crystallinity and develop 3D conductive donors for efficient hole transport through percolative networks in the BHJs of OPVs.

High-Efficiency Nonfullerene Polymer Solar Cell Enabling by Integration of Film-Morphology Optimization, Donor Selection, and Interfacial Engineering.

PubMed

Zhang, Xin; Li, Weiping; Yao, Jiannian; Zhan, Chuanlang

2016-06-22

Carrier mobility is a vital factor determining the electrical performance of organic solar cells. In this paper we report that a high-efficiency nonfullerene organic solar cell (NF-OSC) with a power conversion efficiency of 6.94 ± 0.27% was obtained by optimizing the hole and electron transportations via following judicious selection of polymer donor and engineering of film-morphology and cathode interlayers: (1) a combination of solvent annealing and solvent vapor annealing optimizes the film morphology and hence both hole and electron mobilities, leading to a trade-off of fill factor and short-circuit current density (Jsc); (2) the judicious selection of polymer donor affords a higher hole and electron mobility, giving a higher Jsc; and (3) engineering the cathode interlayer affords a higher electron mobility, which leads to a significant increase in electrical current generation and ultimately the power conversion efficiency (PCE).

Achieving Ultrahigh Carrier Mobility in Two-Dimensional Hole Gas of Black Phosphorus.

PubMed

Long, Gen; Maryenko, Denis; Shen, Junying; Xu, Shuigang; Hou, Jianqiang; Wu, Zefei; Wong, Wing Ki; Han, Tianyi; Lin, Jiangxiazi; Cai, Yuan; Lortz, Rolf; Wang, Ning

2016-12-14

We demonstrate that a field-effect transistor (FET) made of few-layer black phosphorus (BP) encapsulated in hexagonal boron nitride (h-BN) in vacuum exhibits a room-temperature hole mobility of 5200 cm 2 /(Vs), being limited just by the phonon scattering. At cryogenic temperatures, the FET mobility increases up to 45 000 cm 2 /(Vs), which is five times higher compared to the mobility obtained in earlier reports. The unprecedentedly clean h-BN-BP-h-BN heterostructure exhibits Shubnikov-de Haas oscillations and a quantum Hall effect with Landau level (LL) filling factors down to v = 2 in conventional laboratory magnetic fields. Moreover, carrier density independent effective mass of m * = 0.26 m 0 is measured, and a Landé g-factor of g = 2.47 is reported. Furthermore, an indication for a distinct hole transport behavior with up- and down-spin orientations is found.

Synthesis, structural characterization and mobility measurement of electron accepting pyrazine derivatives

NASA Astrophysics Data System (ADS)

Lai, William W.

Several pyrazine based cyano aza derivatives have been synthesized and electronic devices made from them. Hole and electron mobilities were measured using a time of flight (TOF) method with silicon wafers as both the substrate and charge carrier generation layer. The high density of charge carriers generated from silicon allowed for film layers as thin as 100nm and up to 250nm. Two compounds, 2,3,6,7-tetracyano-1,4,5,8-tetraazanapthalene (TCNN) and 2,3,6,7-tetracyano-9,10-dioctyl-1,4,5,6,9,10-hexaazaanthracene (DOA) were shown to be good electron acceptors. The potentials at which TCNN and DOA are reduced was -0.03 and -1.5 volts respectively. Electron mobilities of both compounds were found to be 2x10-5 cm2V˙s . The previously unreported oxidation potential of 2,3,6,7-tetracyano-9,10-dioctyl 1,4,5,6,9,10-hexaazaanthracene was measured and the hole mobility was determined to be 2x10-5 cm2V˙s . In the case of DOA, the charge carrier density of the electron carriers was comparable to that of the charge carrier density of the hole carriers. In contrast, the electron TOF signal of TCNN, which does not exhibit an oxidation, is greater than the hole TOF signal by roughly 200 fold. The inability for TCNN to act as a hole carrier was remedied by combining it with tetrathiafulvalene (TTF) as an electron donor. Crystals of the 1:1 complex were grown and the solved structure revealed segregated stacking. Conductivity measurements, by both two and four point methods determined the range of conductivity ranging from 10-5 to 10-6 Scm . The electron and hole mobility of the material was determined to be 2x10-5 and 2x10-6 cm2V˙s respectively. With the complementary TTF:TCNN system, the electron V-s and hole TOF signals were comparable, indicating a material that can equally conduct electrons or holes.

Enhancing Hole Mobility in III-V Semiconductors

DTIC Science & Technology

2012-05-21

acteristics of the digital superlattice (n¼1,0, andþ 1) that was used in the metamorphic buffer. The GaSb channel peak gets buried in the n¼ 0...materials have been used for a variety of analog and high frequency applications driven by the high electron mobilities in III-V materials. On the other...hand, the hole mobility in III-V materials has always lagged compared to group-IV semiconductors such as germanium. In this paper, we explore the use

Carbon Allotrope Dependence on Temperature and Pressure During Thermal Decomposition of Silicon Carbide

DTIC Science & Technology

2014-03-27

temperature, to its electrical conductivity, while considering its dopant concentration ( or ) [2]. (1-2) As previously stated, temperature effects...electrons [2]. Equations (1-3) and (1-4) are used to calculate electron (or hole) mobility in Si based on total dopant concentration (N) at a given...nickel, or cobalt . The metal catalyst breaks down the carbon feedstock to produce CNTs. As shown in Figure 53 below, 83 gaseous carbon feedstock

Terahertz study of hole transport in pentacene thin films

NASA Astrophysics Data System (ADS)

Engelbrecht, Stefan G.; Prinz, Markus; Arend, Thomas R.; Kersting, Roland

2014-10-01

Terahertz electromodulation spectroscopy is a novel tool for studying charge carrier transport in polycrys­talline thin films. The technique selectively probes the high-frequency response of mobile carriers and is insensitive to scattering at grain boundaries as well as to trapping processes. In thin films of pentacene we find a hole mobility of 21 cm2 /Vs, which exceeds the largest previously reported values obtained in poly­ crystalline pentacene. Additionally, the data provide an upper limit of the hole conductivity effective mass of mh ≍ 0.8 me.

Development of III-V p-MOSFETs with high-kappa gate stack for future CMOS applications

NASA Astrophysics Data System (ADS)

Nagaiah, Padmaja

As the semiconductor industry approaches the limits of traditional silicon CMOS scaling, non-silicon materials and new device architectures are gradually being introduced to improve Si integrated circuit performance and continue transistor scaling. Recently, the replacement of SiO2 with a high-k material (HfO2) as gate dielectric has essentially removed one of the biggest advantages of Si as channel material. As a result, alternate high mobility materials are being considered to replace Si in the channel to achieve higher drive currents and switching speeds. III-V materials in particular have become of great interest as channel materials, owing to their superior electron transport properties. However, there are several critical challenges that need to be addressed before III-V based CMOS can replace Si CMOS technology. Some of these challenges include development of a high quality, thermally stable gate dielectric/III-V interface, and improvement in III-V p-channel hole mobility to complement the n-channel mobility, low source/drain resistance and integration onto Si substrate. In this thesis, we would be addressing the first two issues i.e. the development high performance III-V p-channels and obtaining high quality III-V/high-k interface. We start with using the device architecture of the already established InGaAs n-channels as a baseline to understand the effect of remote scattering from the high-k oxide and oxide/semiconductor interface on channel transport properties such as electron mobility and channel electron concentration. Temperature dependent Hall electron mobility measurements were performed to separate various scattering induced mobility limiting factors. Dependence of channel mobility on proximity of the channel to the oxide interface, oxide thickness, annealing conditions are discussed. The results from this work will be used in the design of the p-channel MOSFETs. Following this, InxGa1-xAs (x>0.53) is chosen as channel material for developing p-channel MOSFETs. Band engineering, strain induced valence band splitting and quantum confinement is used to improve channel hole mobility. Experimental results on the Hall hole mobility is presented for InxGa1-xAs channels with varying In content, thickness of the quantum well and temperature. Then, high mobility InxGa 1-xAs heterostructure thus obtained are integrated with in-situ deposited high-k gate oxide required for high performance p-MOSFET and discuss the challenges associated with the gated structure and draw conclusions on this material system. Antimonide based channel materials such as GaSb and InxGa 1-xSb are explored for III-V based p-MOSFETs in last two chapters. Options for Sb based strained QW channels to obtain maximum hole mobility by varying the strain, channel and barrier material, thickness of the layers etc. is discussed followed by the growth of these Sb channels on GaAs and InP substrates using molecular beam epitaxy. The physical properties of the structures such as the heterostructure quality, alloy content and surface roughness are examined via TEM, XRD and AFM. Following this, electrical measurement results on Hall hole mobility is presented. The effect of strain, alloy content, temperature and thickness on channel mobility and concentration is reported. Development of GaSb n- and p-MOS capacitor structures with in-situ deposited HfO2 gate oxide dielectric using in-situ deposited amorphous Si (a-Si) interface passivation layer (IPL) to improve the interface quality of high-k oxide and (In)GaSb surface is presented. In-situ deposited gate oxides such as Al2O3 and combination oxide of Al 2O3 and HfO2 with and without the a-Si IPL are also explored as alternate gate dielectrics. Subsequently, MOS capacitor structures using buried InGaSb QWs are demonstrated. Development of an inversion type bulk GaSb with implanted source-drain contacts and in-situ deposited gate oxide HfO2 gate oxide is discussed. The merits of biaxial compressive strain is demonstrated on strained surface and buried channel In0.36 Ga0.64Sb QW MOSFETs with thin top barrier and in-situ deposited a-Si IPL and high-k HfO2 as well as combination Al 2O3+HfO2 gate stacks and ex-situ atomic layer deposited (ALD) combination gate oxide and with thin 2 nm InAs surface passivation layer is presented. Finally, summary of the salient results from the different chapters is provided with recommendations for future research.

Contact-metal dependent current injection in pentacene thin-film transistors

NASA Astrophysics Data System (ADS)

Wang, S. D.; Minari, T.; Miyadera, T.; Tsukagoshi, K.; Aoyagi, Y.

2007-11-01

Contact-metal dependent current injection in top-contact pentacene thin-film transistors is analyzed, and the local mobility in the contact region was found to follow the Meyer-Neldel rule. An exponential trap distribution, rather than the metal/organic hole injection barrier, is proposed to be the dominant factor of the contact resistance in pentacene thin-film transistors. The variable temperature measurements revealed a much narrower trap distribution in the copper contact compared with the corresponding gold contact, and this is the origin of the smaller contact resistance for copper despite a lower work function.

Electro-optical modeling of bulk heterojunction solar cells

NASA Astrophysics Data System (ADS)

Kirchartz, Thomas; Pieters, Bart E.; Taretto, Kurt; Rau, Uwe

2008-11-01

We introduce a model for charge separation in bulk heterojunction solar cells that combines exciton transport to the interface between donor and acceptor phases with the dissociation of the bound electron/hole pair. We implement this model into a standard semiconductor device simulator, thereby creating a convenient method to simulate the optical and electrical characteristics of a bulk heterojunction solar cell with a commercially available program. By taking into account different collection probabilities for the excitons in the polymer and the fullerene, we are able to reproduce absorptance, internal and external quantum efficiency, as well as current/voltage curves of bulk heterojunction solar cells. We further investigate the influence of mobilities of the free excitons as well as the mobilities of the free charge carriers on the performance of bulk heterojunction solar cells. We find that, in general, the highest efficiencies are achieved with the highest mobilities. However, an optimum finite mobility of free charge carriers can result from a large recombination velocity at the contacts. In contrast, Langevin-type of recombination cannot lead to finite optimum mobilities even though this mechanism has a strong dependence on the free carrier mobilities.

Hole Transport in the Upper Hubbard Band in Ge:Cu under Uniaxial Pressure

NASA Astrophysics Data System (ADS)

Walukiewicz, W.; Dubon, O. D.; Silvestri, H. H.; Haller, E. E.

1998-03-01

We have reported recently on a uniaxial stress induced transformation of the ground state of Cu triple acceptors in Ge from highly localized 1s^3 to the much more extended 1s^22s^1 configuration (O.D. Dubon et. al., Phys Rev Lett. 78, 3519, (1997)). We find that the transformation leads to a gigantic enhancement of the low temperature conductivity. The conductivity is due to hole transport in the upper Hubbard band formed by overcharged 1s^22s^2 states. We have calculated hole mobilities in this band assuming that the states in the upper Hubbard band can be treated in the optical approximation as normal extended states with a well-defined effective mass. We find that for Cu concentrations below 10^15 cm-3 the experimentally observed mobilities approach 10^6 cm^2/Vs. These very high mobilities can be explained by hole scattering from ionized and neutral impurity centers. At higher Cu concentrations we observe an onset of Anderson localization that manifests itself in a thermally activated low temperature mobility. This work was supported by US DOE under Contract No. DE-AC03-76SF00098.

Diverse carrier mobility of monolayer BNC x : a combined density functional theory and Boltzmann transport theory study.

PubMed

Wu, Tao; Deng, Kaiming; Deng, Weiqiao; Lu, Ruifeng

2017-10-19

BNC x monolayer as a kind of two-dimensional material has numerous chemical atomic ratios and arrangements with different electronic structures. Via calculations on the basis of density functional theory and Boltzmann transport theory under deformation potential approximation, the band structures and carrier mobilities of BNC x (x  =  1,2,3,4) nanosheets are systematically investigated. The calculated results show that BNC 2 -1 is a material with very small band gap (0.02 eV) among all the structures while other BNC x monolayers are semiconductors with band gap ranging from 0.51 eV to 1.32 eV. The carrier mobility of BNC x varies considerably from tens to millions of cm 2 V -1 s -1 . For BNC 2 -1, the hole mobility and electron mobility along both x and y directions can reach 10 5 orders of magnitude, which is similar to the carrier mobility of graphene. Besides, all studied BNC x monolayers obviously have anisotropic hole mobility and electron mobility. In particular, for semiconductor BNC 4 , its hole mobility along the y direction and electron mobility along the x direction unexpectedly reach 10 6 orders of magnitude, even higher than that of graphene. Our findings suggest that BNC x layered materials with the proper ratio and arrangement of carbon atoms will possess desirable charge transport properties, exhibiting potential applications in nanoelectronic devices.

Diverse carrier mobility of monolayer BNC x : a combined density functional theory and Boltzmann transport theory study

NASA Astrophysics Data System (ADS)

Wu, Tao; Deng, Kaiming; Deng, Weiqiao; Lu, Ruifeng

2017-11-01

BNC x monolayer as a kind of two-dimensional material has numerous chemical atomic ratios and arrangements with different electronic structures. Via calculations on the basis of density functional theory and Boltzmann transport theory under deformation potential approximation, the band structures and carrier mobilities of BNC x (x  =  1,2,3,4) nanosheets are systematically investigated. The calculated results show that BNC2-1 is a material with very small band gap (0.02 eV) among all the structures while other BNC x monolayers are semiconductors with band gap ranging from 0.51 eV to 1.32 eV. The carrier mobility of BNC x varies considerably from tens to millions of cm2 V-1 s-1. For BNC2-1, the hole mobility and electron mobility along both x and y directions can reach 105 orders of magnitude, which is similar to the carrier mobility of graphene. Besides, all studied BNC x monolayers obviously have anisotropic hole mobility and electron mobility. In particular, for semiconductor BNC4, its hole mobility along the y direction and electron mobility along the x direction unexpectedly reach 106 orders of magnitude, even higher than that of graphene. Our findings suggest that BNC x layered materials with the proper ratio and arrangement of carbon atoms will possess desirable charge transport properties, exhibiting potential applications in nanoelectronic devices.

Molecular Packing of High-Mobility Diketo Pyrrolo-Pyrrole Polymer Semiconductors with Branched Alkyl Side Chains

DOE Office of Scientific and Technical Information (OSTI.GOV)

X Zhang; L Richter; D DeLongchamp

We describe a series of highly soluble diketo pyrrolo-pyrrole (DPP)-bithiophene copolymers exhibiting field effect hole mobilities up to 0.74 cm{sup 2} V{sup -1} s{sup -1}, with a common synthetic motif of bulky 2-octyldodecyl side groups on the conjugated backbone. Spectroscopy, diffraction, and microscopy measurements reveal a transition in molecular packing behavior from a preferentially edge-on orientation of the conjugated plane to a preferentially face-on orientation as the attachment density of the side chains increases. Thermal annealing generally reduces both the face-on population and the misoriented edge-on domains. The highest hole mobilities of this series were obtained from edge-on molecular packingmore » and in-plane liquid-crystalline texture, but films with a bimodal orientation distribution and no discernible in-plane texture exhibited surprisingly comparable mobilities. The high hole mobility may therefore arise from the molecular packing feature common to the entire polymer series: backbones that are strictly oriented parallel to the substrate plane and coplanar with other backbones in the same layer.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Putilov, L.P., E-mail: lev.putilov@gmail.com; Tsidilkovski, V.I.

The impact of deep acceptor centers on defect thermodynamics and oxidation of wide-band-gap acceptor-doped perovskites without mixed-valence cations is studied. These deep centers are formed by the acceptor-bound small hole polarons whose stabilization energy can be high enough (significantly higher than the hole-acceptor Coulomb interaction energy). It is shown that the oxidation enthalpy ΔH{sub ox} of oxide is determined by the energy ε{sub A} of acceptor-bound states along with the formation energy E{sub V} of oxygen vacancies. The oxidation reaction is demonstrated to be either endothermic or exothermic, and the regions of ε{sub A} and E{sub V} values corresponding tomore » the positive or negative ΔH{sub ox} are determined. The contribution of acceptor-bound holes to the defect thermodynamics strongly depends on the acceptor states depth ε{sub A}: it becomes negligible at ε{sub A} less than a certain value (at which the acceptor levels are still deep). With increasing ε{sub A}, the concentration of acceptor-bound small hole polarons can reach the values comparable to the dopant content. The results are illustrated with the acceptor-doped BaZrO{sub 3} as an example. It is shown that the experimental data on the bulk hole conductivity of barium zirconate can be described both in the band transport model and in the model of hopping small polarons localized on oxygen ions away from the acceptor centers. Depending on the ε{sub A} magnitude, the oxidation reaction can be either endothermic or exothermic for both mobility mechanisms.« less

TFB:TPDSi2 interfacial layer usable in organic photovoltaic cells

DOEpatents

Marks, Iobin J [Evanston, IL; Hains, Alexander W [Evanston, IL

2011-02-15

The present invention, in one aspect, relates to a solar cell. In one embodiment, the solar cell includes an anode; an active organic layer comprising an electron-donating organic material and an electron-accepting organic material; and an interfacial layer formed between the anode and active organic layer, where the interfacial layer comprises a hole-transporting polymer characterized with a hole-mobility higher than that of the electron-donating organic material in the active organic layer, and a small molecule that has a high hole-mobility and is capable of crosslinking on contact with air.

Solution-processed small molecule-polymer blend organic thin-film transistors with hole mobility greater than 5 cm2/Vs.

PubMed

Smith, Jeremy; Zhang, Weimin; Sougrat, Rachid; Zhao, Kui; Li, Ruipeng; Cha, Dongkyu; Amassian, Aram; Heeney, Martin; McCulloch, Iain; Anthopoulos, Thomas D

2012-05-08

Using phase-separated organic semiconducting blends containing a small molecule, as the hole transporting material, and a conjugated amorphous polymer, as the binder material, we demonstrate solution-processed organic thin-film transistors with superior performance characteristics that include; hole mobility >5 cm(2) /Vs, current on/off ratio ≥10(6) and narrow transistor parameter spread. These exceptional characteristics are attributed to the electronic properties of the binder polymer and the advantageous nanomorphology of the blend film. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Charge transport study in bis{2-(2-hydroxyphenyl) benzoxazolate} zinc [Zn(hpb)2

NASA Astrophysics Data System (ADS)

Rai, Virendra Kumar; Srivastava, Ritu; Chauhan, Gayatri; Kumar, Arunandan; Kamalasanan, M. N.

2008-10-01

The nature of the electrical transport mechanism for carrier transport in pure bis {2-(2-hydroxyphenyl) benzoxazolate} zinc [Zn(hpb)2] has been studied by current voltage measurements of samples at different thicknesses and at different temperatures. Hole-only devices show ohmic conduction at low voltages and space charge conduction at high voltages. The space charge conduction is clearly identifiable with a square law dependence of current on voltage as well as the scaling of current inversely with the cube of thickness. With a further increase in voltage, the current increases with a Vm dependence with m varying with temperature typical of trap limited conduction with an exponential distribution of trap states. From the square law region the effective charge carrier mobility of holes has been evaluated as 2.5 × 10-11 m2 V-1 s-1. Electron-only devices however show electrode limited conduction, which was found to obey the Scott Malliaras model of charge injection.

Correlation between microstructure and charge transport in poly(2,5-dimethoxy- p -phenylenevinylene) thin films

NASA Astrophysics Data System (ADS)

Sims, M.; Tuladhar, S. M.; Nelson, J.; Maher, R. C.; Campoy-Quiles, M.; Choulis, S. A.; Mairy, M.; Bradley, D. D. C.; Etchegoin, P. G.; Tregidgo, C.; Suhling, K.; Richards, D. R.; Massiot, P.; Nielsen, C. B.; Steinke, J. H. G.

2007-11-01

We report a study of thin films of poly(2,5-dimethoxy- p -phenylenevinylene) (PDMeOPV) prepared by a precursor route. Conversion at two different temperatures, namely, 120 and 185°C , produces partially and fully converted films. We study the structural, optical, and charge transport characteristics of these samples in order to relate transport properties to microstructure. Micro-Raman mapping and photoluminescence (PL) imaging reveal the existence of coarse, depth-averaged domains of around 50μm in lateral extent, with more pronounced contrast for conversion at the higher temperature. The contrast in both micro-Raman and PL maps can be attributed to fluctuations in film density. Spectroscopic ellipsometry studies of the films indicate that the average film density is approximately 15% higher for conversion at the higher temperature. Time-of-flight photocurrent transients, recorded here in PDMeOPV films, are typically dispersive but yield hole mobilities in excess of 10-4cm2/Vs at modest applied fields (˜1.2×105V/cm) in the fully converted films. To our knowledge, these are amongst the highest reported mobility values for a poly( p -phenylenevinylene) derivative. Fully converted films, while yielding higher hole mobilities, exhibit a stronger dependence on electric field than partially converted ones. The higher mobility can be attributed to the almost complete conversion of the flexible saturated subunits within precursor chains to conjugated vinylene moieties at elevated temperature. This results in a correspondingly higher packing density, an improvement in intrachain transport, and a reduction in the smallest interchain hopping distance. We suggest that the stronger electric field dependence is due to the increasing influence of intermolecular electrostatic interactions with decreasing interchain separation. We propose that a greater proportion of chains in the fully converted films packs in a three-dimensional, interdigitated arrangement similar to that described previously for crystalline samples of PDMeOPV [J. H. F. Martens , Synth. Met. 55, 449 (1993)].

Vertical Hole Transport and Carrier Localization in InAs /InAs1 -xSbx Type-II Superlattice Heterojunction Bipolar Transistors

NASA Astrophysics Data System (ADS)

Olson, B. V.; Klem, J. F.; Kadlec, E. A.; Kim, J. K.; Goldflam, M. D.; Hawkins, S. D.; Tauke-Pedretti, A.; Coon, W. T.; Fortune, T. R.; Shaner, E. A.; Flatté, M. E.

2017-02-01

Heterojunction bipolar transistors are used to measure vertical hole transport in narrow-band-gap InAs /InAs1 -xSbx type-II superlattices (T2SLs). Vertical hole mobilities (μh) are reported and found to decrease rapidly from 360 cm2/V s at 120 K to approximately 2 cm2/V s at 30 K, providing evidence that holes are confined to localized states near the T2SL valence-miniband edge at low temperatures. Four distinct transport regimes are identified: (1) pure miniband transport, (2) miniband transport degraded by temporary capture of holes in localized states, (3) hopping transport between localized states in a mobility edge, and (4) hopping transport through defect states near the T2SL valence-miniband edge. Region (2) is found to have a thermal activation energy of ɛ2=36 meV corresponding to the energy range of a mobility edge. Region (3) is found to have a thermal activation energy of ɛ3=16 meV corresponding to the hopping transport activation energy. This description of vertical hole transport is analogous to electronic transport observed in disordered amorphous semiconductors displaying Anderson localization. For the T2SL, we postulate that localized states are created by disorder in the group-V alloy of the InAs1 -xSbx hole well causing fluctuations in the T2SL valence-band energy.

Optical spin orientation of minority holes in a modulation-doped GaAs/(Ga,Al)As quantum well

NASA Astrophysics Data System (ADS)

Koudinov, A. V.; Dzhioev, R. I.; Korenev, V. L.; Sapega, V. F.; Kusrayev, Yu. G.

2016-04-01

The optical spin orientation effect in a GaAs/(Ga,Al)As quantum well containing a high-mobility two-dimensional electron gas was found to be due to spin-polarized minority carriers, the holes. The observed oscillations of both the intensity and polarization of the photoluminescence in a magnetic field are well described in a model whose main elements are resonant absorption of the exciting light by the Landau levels and mixing of the heavy- and light-hole subbands. After subtraction of these effects, the observed influence of magnetic fields on the spin polarization can be well interpreted by a standard approach of the optical orientation method. The spin relaxation of holes is controlled by the Dyakonov-Perel' mechanism. Deceleration of the spin relaxation by the magnetic field occurs through the Ivchenko mechanism—due to the cyclotron motion of holes. Mobility of holes was found to be two orders of magnitude smaller than that of electrons, being determined by the scattering of holes by the electron gas.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Merkulov, O.V., E-mail: merkulov@ihim.uran.ru; Samigullin, R.R.; Markov, A.A.

The electrical conductivity of SrFe{sub 1–x}Sn{sub x}O{sub 3–δ} (x=0.05, 0.10, 017) was measured by a four-probe dc technique in the partial oxygen pressure range of 10{sup –18}–0.5 atm at temperatures between 800 °Ð ÐŽ and 950 °Ð ÐŽ. The oxygen content in these oxides was measured under the same ambient conditions by means of coulometric titration. The thermodynamic analysis of oxygen nonstoichiometry data was carried out to determine the equilibrium constants for defect-formation reactions and to calculate the concentrations of ion and electron charge carriers. The partial contributions of oxygen ions, electrons and holes to charge transport were assessed, and the mobilitymore » of respective carriers was evaluated by an integral examination of the electrical conductivity and oxygen nonstoichiometry data. It has been found that the mobility of holes in SrFe{sub 1−x}Sn{sub x}O{sub 3−δ} varies in the range of ~0.005–0.04 cm{sup 2} V{sup −1} s{sup −1}, linearly increasing with the oxygen content and decreasing with increased tin concentration. The mobility of electron carriers was shown to be independent of the oxygen content. The average migration energy of an electron was estimated to be ~0.45 eV, with that of a hole being ~0.3 eV. - Highlights: • The conductivity and oxygen nonstoichiometry in SrFe{sub 1−x}Sn{sub x}O{sub 3−δ} were measured. • Tin substitution was found to affect insignificantly defect formation reactions. • The hole mobility was found to increase linearly with the oxygen content. • The hole mobility was found to be much higher than the electron mobility.« less

The use of charge extraction by linearly increasing voltage in polar organic light-emitting diodes

NASA Astrophysics Data System (ADS)

Züfle, Simon; Altazin, Stéphane; Hofmann, Alexander; Jäger, Lars; Neukom, Martin T.; Schmidt, Tobias D.; Brütting, Wolfgang; Ruhstaller, Beat

2017-05-01

We demonstrate the application of the CELIV (charge carrier extraction by linearly increasing voltage) technique to bilayer organic light-emitting devices (OLEDs) in order to selectively determine the hole mobility in N,N0-bis(1-naphthyl)-N,N0-diphenyl-1,10-biphenyl-4,40-diamine (α-NPD). In the CELIV technique, mobile charges in the active layer are extracted by applying a negative voltage ramp, leading to a peak superimposed to the measured displacement current whose temporal position is related to the charge carrier mobility. In fully operating devices, however, bipolar carrier transport and recombination complicate the analysis of CELIV transients as well as the assignment of the extracted mobility value to one charge carrier species. This has motivated a new approach of fabricating dedicated metal-insulator-semiconductor (MIS) devices, where the extraction current contains signatures of only one charge carrier type. In this work, we show that the MIS-CELIV concept can be employed in bilayer polar OLEDs as well, which are easy to fabricate using most common electron transport layers (ETLs), like Tris-(8-hydroxyquinoline)aluminum (Alq3). Due to the macroscopic polarization of the ETL, holes are already injected into the hole transport layer below the built-in voltage and accumulate at the internal interface with the ETL. This way, by a standard CELIV experiment only holes will be extracted, allowing us to determine their mobility. The approach can be established as a powerful way of selectively measuring charge mobilities in new materials in a standard device configuration.

Charge carrier mobility and electronic properties of Al(Op)3: impact of excimer formation

PubMed Central

Friederich, Pascal; Schäfer, Bernhard; Fattori, Valeria; Sun, Xiangnan; Strunk, Timo; Meded, Velimir; Hueso, Luis E; Wenzel, Wolfgang; Ruben, Mario

2015-01-01

Summary We have studied the electronic properties and the charge carrier mobility of the organic semiconductor tris(1-oxo-1H-phenalen-9-olate)aluminium(III) (Al(Op)3) both experimentally and theoretically. We experimentally estimated the HOMO and LUMO energy levels to be −5.93 and −3.26 eV, respectively, which were close to the corresponding calculated values. Al(Op)3 was successfully evaporated onto quartz substrates and was clearly identified in the absorption spectra of both the solution and the thin film. A structured steady state fluorescence emission was detected in solution, whereas a broad, red-shifted emission was observed in the thin film. This indicates the formation of excimers in the solid state, which is crucial for the transport properties. The incorporation of Al(Op)3 into organic thin film transistors (TFTs) was performed in order to measure the charge carrier mobility. The experimental setup detected no electron mobility, while a hole mobility between 0.6 × 10−6 and 2.1 × 10−6 cm2·V−1·s−1 was measured. Theoretical simulations, on the other hand, predicted an electron mobility of 9.5 × 10−6 cm2·V−1·s−1 and a hole mobility of 1.4 × 10−4 cm2·V−1·s−1. The theoretical simulation for the hole mobility predicted an approximately one order of magnitude higher hole mobility than was observed in the experiment, which is considered to be in good agreement. The result for the electron mobility was, on the other hand, unexpected, as both the calculated electron mobility and chemical common sense (based on the capability of extended aromatic structures to efficiently accept and delocalize additional electrons) suggest more robust electron charge transport properties. This discrepancy is explained by the excimer formation, whose inclusion in the multiscale simulation workflow is expected to bring the theoretical simulation and experiment into agreement. PMID:26171287

Trap densities and transport properties of pentacene metal-oxide-semiconductor transistors. I. Analytical modeling of time-dependent characteristics

NASA Astrophysics Data System (ADS)

Basile, A. F.; Cramer, T.; Kyndiah, A.; Biscarini, F.; Fraboni, B.

2014-06-01

Metal-oxide-semiconductor (MOS) transistors fabricated with pentacene thin films were characterized by temperature-dependent current-voltage (I-V) characteristics, time-dependent current measurements, and admittance spectroscopy. The channel mobility shows almost linear variation with temperature, suggesting that only shallow traps are present in the semiconductor and at the oxide/semiconductor interface. The admittance spectra feature a broad peak, which can be modeled as the sum of a continuous distribution of relaxation times. The activation energy of this peak is comparable to the polaron binding energy in pentacene. The absence of trap signals in the admittance spectra confirmed that both the semiconductor and the oxide/semiconductor interface have negligible density of deep traps, likely owing to the passivation of SiO2 before pentacene growth. Nevertheless, current instabilities were observed in time-dependent current measurements following the application of gate-voltage pulses. The corresponding activation energy matches the energy of a hole trap in SiO2. We show that hole trapping in the oxide can explain both the temperature and the time dependences of the current instabilities observed in pentacene MOS transistors. The combination of these experimental techniques allows us to derive a comprehensive model for charge transport in hybrid architectures where trapping processes occur at various time and length scales.

Device physics of hydrogenated amorphous silicon solar cells

NASA Astrophysics Data System (ADS)

Liang, Jianjun

This dissertation reports measurements on and modeling of hydrogenated amorphous silicon (a-Si:H) nip solar cells. Cells with thicknesses from 200-900 nm were prepared at United Solar Ovonic LLC. The current density-voltage (J-V) relations were measured under laser illumination (685 nm wavelength, up to 200 mW/cm2) over the temperature range 240 K--350 K. The changes in the cells' open-circuit voltage during extended laser illumination (light-soaking) were measured, as were the cell properties in several light-soaked states. The J-V properties of cells in their as-deposited and light-soaked states converge at low-temperatures. Electromodulation spectra for the cells were also measured over the range 240 K--350 K to determine the temperature-dependent bandgap. These experimental results were compared to computer calculations of J-V relations using the AMPS ((c)Pennsylvania State University) computer code. Bandtail parameters (for electron and hole mobility and recombination) were consistent with published drift-mobility and transient photocurrent measurements on a-Si:H. The open-circuit voltage and power density measurements on as-deposited cells, as a function of temperature and thickness, were predicted well. The calculations support a general "hole mobility limited" approach to analyzing a-Si:H solar cells, and indicate that the doped electrode layers, the as-deposited density of dangling bonds, and the electron mobility are of secondary importance to as-deposited cells. For light-soaked a-Si:H solar cells, incorporation of a density of dangling bonds in the computer calculations accounted satisfactorily for the power and open-circuit voltage measurements, including the low-temperature convergence effect. The calculations indicate that, in the light-soaked state at room-temperature, electron recombination is split nearly evenly between holes trapped in the valence bandtail and holes trapped on dangling bonds. The result supports Stutzmann, Jackson, and Tsai's 1985 conjecture that dangling bond creation results only from bandtail recombination events. We compared the predictions of the hydrogen-collision model proposed by Branz with the kinetics of the open-circuit voltage as light-soaking progressed. We obtained satisfactory agreement for the initial phases of light-soaking with the conjecture that only bandtail recombination leads to dangling bond creation, and the computer calculations for this recombination channel's diminishment in the cell as the dangling bond density grows.

Compound Semiconductors for Low-Power p-Channel Field-Effect Transistors

DTIC Science & Technology

2009-07-01

making III–V FETs has been different than for silicon FETs. Growth techniques such as molecular beam epitaxy (MBE) are used to create heterostructures in...lities for III–V compounds. This article reviews the recent work to enhance hole mobilities in antimonide-based quantum wells. Epitaxial heterostructures...article reviews the recent work to enhance hole mobilities in antimonide-based quantum wells. Epitaxial heterostructures have been grown with the channel

Black Phosphorus Based Field Effect Transistors with Simultaneously Achieved Near Ideal Subthreshold Swing and High Hole Mobility at Room Temperature.

PubMed

Liu, Xinke; Ang, Kah-Wee; Yu, Wenjie; He, Jiazhu; Feng, Xuewei; Liu, Qiang; Jiang, He; Dan Tang; Wen, Jiao; Lu, Youming; Liu, Wenjun; Cao, Peijiang; Han, Shun; Wu, Jing; Liu, Wenjun; Wang, Xi; Zhu, Deliang; He, Zhubing

2016-04-22

Black phosphorus (BP) has emerged as a promising two-dimensional (2D) material for next generation transistor applications due to its superior carrier transport properties. Among other issues, achieving reduced subthreshold swing and enhanced hole mobility simultaneously remains a challenge which requires careful optimization of the BP/gate oxide interface. Here, we report the realization of high performance BP transistors integrated with HfO2 high-k gate dielectric using a low temperature CMOS process. The fabricated devices were shown to demonstrate a near ideal subthreshold swing (SS) of ~69 mV/dec and a room temperature hole mobility of exceeding >400 cm(2)/Vs. These figure-of-merits are benchmarked to be the best-of-its-kind, which outperform previously reported BP transistors realized on traditional SiO2 gate dielectric. X-ray photoelectron spectroscopy (XPS) analysis further reveals the evidence of a more chemically stable BP when formed on HfO2 high-k as opposed to SiO2, which gives rise to a better interface quality that accounts for the SS and hole mobility improvement. These results unveil the potential of black phosphorus as an emerging channel material for future nanoelectronic device applications.

Carrier mobility and scattering lifetime in electric double-layer gated few-layer graphene

NASA Astrophysics Data System (ADS)

Piatti, E.; Galasso, S.; Tortello, M.; Nair, J. R.; Gerbaldi, C.; Bruna, M.; Borini, S.; Daghero, D.; Gonnelli, R. S.

2017-02-01

We fabricate electric double-layer field-effect transistor (EDL-FET) devices on mechanically exfoliated few-layer graphene. We exploit the large capacitance of a polymeric electrolyte to study the transport properties of three, four and five-layer samples under a large induced surface charge density both above and below the glass transition temperature of the polymer. We find that the carrier mobility shows a strong asymmetry between the hole and electron doping regime. We then employ ab initio density functional theory (DFT) calculations to determine the average scattering lifetime from the experimental data. We explain its peculiar dependence on the carrier density in terms of the specific properties of the electrolyte we used in our experiments.

Estimation of carrier mobility and charge behaviors of organic semiconductor films in metal-insulator-semiconductor diodes consisting of high-k oxide/organic semiconductor double layers

NASA Astrophysics Data System (ADS)

Chosei, Naoya; Itoh, Eiji

2018-02-01

We have comparatively studied the charge behaviors of organic semiconductor films based on charge extraction by linearly increasing voltage in a metal-insulator-semiconductor (MIS) diode structure (MIS-CELIV) and by classical capacitance-voltage measurement. The MIS-CELIV technique allows the selective measurement of electron and hole mobilities of n- and p-type organic films with thicknesses representative of those of actual devices. We used an anodic oxidized sputtered Ta or Hf electrode as a high-k layer, and it effectively blocked holes at the insulator/semiconductor interface. We estimated the hole mobilities of the polythiophene derivatives regioregular poly(3-hexylthiophene) (P3HT) and poly(3,3‧‧‧-didodecylquarterthiophene) (PQT-12) before and after heat treatment in the ITO/high-k/(thin polymer insulator)/semiconductor/MoO3/Ag device structure. The hole mobility of PQT-12 was improved from 1.1 × 10-5 to 2.1 × 10-5 cm2 V-1 s-1 by the heat treatment of the device at 100 °C for 30 min. An almost two orders of magnitude higher mobility was obtained in MIS diodes with P3HT as the p-type layer. We also determined the capacitance from the displacement current in MIS diodes at a relatively low-voltage sweep, and it corresponded well to the classical capacitance-voltage and frequency measurement results.

Simulation of hole-mobility in doped relaxed and strained Ge layers

NASA Astrophysics Data System (ADS)

Watling, Jeremy R.; Riddet, Craig; Chan, Morgan Kah H.; Asenov, Asen

2010-11-01

As silicon based metal-oxide-semiconductor field-effect transistors (MOSFETs) are reaching the limits of their performance with scaling, alternative channel materials are being considered to maintain performance in future complementary metal-oxide semiconductor technology generations. Thus there is renewed interest in employing Ge as a channel material in p-MOSFETs, due to the significant improvement in hole mobility as compared to Si. Here we employ full-band Monte Carlo to study hole transport properties in Ge. We present mobility and velocity-field characteristics for different transport directions in p-doped relaxed and strained Ge layers. The simulations are based on a method for over-coming the potentially large dynamic range of scattering rates, which results from the long-range nature of the unscreened Coulombic interaction. Our model for ionized impurity scattering includes the affects of dynamic Lindhard screening, coupled with phase-shift, and multi-ion corrections along with plasmon scattering. We show that all these effects play a role in determining the hole carrier transport in doped Ge layers and cannot be neglected.

Charge transport mechanism in p-type copper ion containing triazine thiolate metallopolymer thin film devices

NASA Astrophysics Data System (ADS)

K, Deepak; Roy, Amit; Anjaneyulu, P.; Kandaiah, Sakthivel; Pinjare, Sampatrao L.

2017-10-01

The charge transport mechanism in copper ions containing 1,3,5-Triazine-2,4,6-trithiolate (CuTCA) based polymer device in sandwich (Ag/CuTCA/Cu) geometry is studied. The current-voltage (I-V) characteristics of the metallopolymer CuTCA device have shown a transition in the charge transport mechanism from Ohmic to Space-charge limited conduction when temperature and voltage are varied. The carriers in CuTCA devices exhibit hopping transport, in which carriers hop from one site to the other. The hole mobility in this polymer device is found to be dependent on electric field E ( μpα√{E } ) and temperature, which suggests that the polymer has inherent disorder. The electric-field coefficient γ and zero-field mobility μ0 are temperature dependent. The values of mobility and activation energies are estimated from temperature (90-140 K) dependent charge transport studies and found to be in the range of 1 × 10-11-8 × 10-12 m2/(V s) and 16.5 meV, respectively. Temperature dependent electric-field coefficient γ is in the order of 17.8 × 10-4 (m/V)1/2, and the value of zero-field mobility μ0 is in the order of 1.2 × 10-11 m2/(V s) at 140 K. A constant phase element (Q) is used to model the device parameters, which are extracted using the Impedance spectroscopy technique. The bandgap of the polymer is estimated to be 2.6 eV from UV-Vis reflectance spectra.

Ambipolar-transporting coaxial nanotubes with a tailored molecular graphene–fullerene heterojunction

PubMed Central

Yamamoto, Yohei; Zhang, Guanxin; Jin, Wusong; Fukushima, Takanori; Ishii, Noriyuki; Saeki, Akinori; Seki, Shu; Tagawa, Seiichi; Minari, Takeo; Tsukagoshi, Kazuhito; Aida, Takuzo

2009-01-01

Despite a large steric bulk of C60, a molecular graphene with a covalently linked C60 pendant [hexabenzocoronene (HBC)–C60; 1] self-assembles into a coaxial nanotube whose wall consists of a graphite-like π-stacked HBC array, whereas the nanotube surface is fully covered by a molecular layer of clustering C60. Because of this explicit coaxial configuration, the nanotube exhibits an ambipolar character in the field-effect transistor output [hole mobility (μh) = 9.7 × 10−7 cm2 V−1 s−1; electron mobility (μe) = 1.1 × 10−5 cm2 V−1 s−1] and displays a photovoltaic response upon light illumination. Successful coassembly of 1 and an HBC derivative without C60 (2) allows for tailoring the p/n heterojunction in the nanotube, so that its ambipolar carrier transport property can be optimized for enhancing the open-circuit voltage in the photovoltaic output. As evaluated by an electrodeless method called flash-photolysis time-resolved microwave conductivity technique, the intratubular hole mobility (2.0 cm2 V−1 s−1) of a coassembled nanotube containing 10 mol % of HBC–C60 (1) is as large as the intersheet mobility in graphite. The homotropic nanotube of 2 blended with a soluble C60 derivative [(6,6)-phenyl C61 butyric acid methyl ester] displayed a photovoltaic response with a much different composition dependency, where the largest open-circuit voltage attained was obviously lower than that realized by the coassembly of 1 and 2. PMID:19940243

Comparative studies of Ge and Si p-channel metal-oxide-semiconductor field-effect-transistors with HfSiON dielectric and TaN metal gate

NASA Astrophysics Data System (ADS)

Hu, Ai-Bin; Xu, Qiu-Xia

2010-05-01

Ge and Si p-channel metal-oxide-semiconductor field-effect-transistors (p-MOSFETs) with hafnium silicon oxynitride (HfSiON) gate dielectric and tantalum nitride (TaN) metal gate are fabricated. Self-isolated ring-type transistor structures with two masks are employed. W/TaN metal stacks are used as gate electrode and shadow masks of source/drain implantation separately. Capacitance-voltage curve hysteresis of Ge metal-oxide-semiconductor (MOS) capacitors may be caused by charge trapping centres in GeO2 (1 < x < 2). Effective hole mobilities of Ge and Si transistors are extracted by using a channel conductance method. The peak hole mobilities of Si and Ge transistors are 33.4 cm2/(V · s) and 81.0 cm2/(V · s), respectively. Ge transistor has a hole mobility 2.4 times higher than that of Si control sample.

Remarkable Enhancement of the Hole Mobility in Several Organic Small-Molecules, Polymers, and Small-Molecule:Polymer Blend Transistors by Simple Admixing of the Lewis Acid p-Dopant B(C6F5)3.

PubMed

Panidi, Julianna; Paterson, Alexandra F; Khim, Dongyoon; Fei, Zhuping; Han, Yang; Tsetseris, Leonidas; Vourlias, George; Patsalas, Panos A; Heeney, Martin; Anthopoulos, Thomas D

2018-01-01

Improving the charge carrier mobility of solution-processable organic semiconductors is critical for the development of advanced organic thin-film transistors and their application in the emerging sector of printed electronics. Here, a simple method is reported for enhancing the hole mobility in a wide range of organic semiconductors, including small-molecules, polymers, and small-molecule:polymer blends, with the latter systems exhibiting the highest mobility. The method is simple and relies on admixing of the molecular Lewis acid B(C 6 F 5 ) 3 in the semiconductor formulation prior to solution deposition. Two prototypical semiconductors where B(C 6 F 5 ) 3 is shown to have a remarkable impact are the blends of 2,8-difluoro-5,11-bis(triethylsilylethynyl)anthradithiophene:poly(triarylamine) (diF-TESADT:PTAA) and 2,7-dioctyl[1]-benzothieno[3,2-b][1]benzothiophene:poly(indacenodithiophene-co-benzothiadiazole) (C8-BTBT:C16-IDTBT), for which hole mobilities of 8 and 11 cm 2 V -1 s -1 , respectively, are obtained. Doping of the 6,13-bis(triisopropylsilylethynyl)pentacene:PTAA blend with B(C 6 F 5 ) 3 is also shown to increase the maximum hole mobility to 3.7 cm 2 V -1 s -1 . Analysis of the single and multicomponent materials reveals that B(C 6 F 5 ) 3 plays a dual role, first acting as an efficient p-dopant, and secondly as a microstructure modifier. Semiconductors that undergo simultaneous p-doping and dopant-induced long-range crystallization are found to consistently outperform transistors based on the pristine materials. Our work underscores Lewis acid doping as a generic strategy towards high performance printed organic microelectronics.

Analysis of defect structure in silicon. Effect of grain boundary density on carrier mobility in UCP material

NASA Technical Reports Server (NTRS)

Dunn, J.; Stringfellow, G. B.; Natesh, R.

1982-01-01

The relationships between hole mobility and grain boundary density were studied. Mobility was measured using the van der Pauw technique, and grain boundary density was measured using a quantitative microscopy technique. Mobility was found to decrease with increasing grain boundary density.

Direct observation of hole transfer from semiconducting polymer to carbon nanotubes.

PubMed

Lan, Fei; Li, Guangyong

2013-05-08

Carbon nanotubes have been proven to play significant roles in polymer-based solar cells. However, there is intensive debate on whether carbon nanotube behaves as a donor or acceptor in the semiconducting polymer:carbon nanotube composite. In this paper, we report a direct observation via Kelvin probe force microscopy (KPFM) that single walled carbon nanotubes (SWNTs) behave as hole transporting channels in poly(3-hexylthiophene-2,5-diyl) (P3HT)/SWNT heterojunctions. By comparing the surface potential (SP) change of SWNT in dark and under illumination, we observed that electrons are blocked from SWNT while holes are transferred to SWNT. This observation can be well-explained by our proposed band alignment model of P3HT/SWNT heterojunction. The finding is further verified by hole mobility measurement using the space charge limited current (SCLC) method. SCLC results indicate that the existence of small amount of SWNT (wt 0.5%) promotes device hole mobility to around 15-fold, indicating SWNT act as hole transfer channel. Our finding of hole transporting behavior of SWNT in P3HT/SWNT blend will provide a useful guidance for enhancing the performance of polymer solar cells by carbon nanotubes.

Carrier mobility enhancement of nano-crystalline semiconductor films: Incorporation of redox -relay species into the grain boundary interface

NASA Astrophysics Data System (ADS)

Desilva, L. A.; Bandara, T. M. W. J.; Hettiarachchi, B. H.; Kumara, G. R. A.; Perera, A. G. U.; Rajapaksa, R. M. G.; Tennakone, K.

Dye-sensitized and perovskite solar cells and other nanostructured heterojunction electronic devices require securing intimate electronic contact between nanostructured surfaces. Generally, the strategy is solution phase coating of a hole -collector over a nano-crystalline high-band gap n-type oxide semiconductor film painted with a thin layer of the light harvesting material. The nano-crystallites of the hole - collector fills the pores of the painted oxide surface. Most ills of these devices are associated with imperfect contact and high resistance of the hole conducting layer constituted of nano-crystallites. Denaturing of the delicate light harvesting material forbid sintering at elevated temperatures to reduce the grain boundary resistance. It is found that the interfacial and grain boundary resistance can be significantly reduced via incorporation of redox species into the interfaces to form ultra-thin layers. Suitable redox moieties, preferably bonded to the surface, act as electron transfer relays greatly reducing the film resistance offerring a promising method of enhancing the effective hole mobility of nano-crystalline hole-collectors and developing hole conductor paints for application in nanostructured devices.

Analysis of energy states where electrons and holes coexist in pseudomorphically strained InAs high-electron-mobility transistors

NASA Astrophysics Data System (ADS)

Nishio, Yui; Sato, Takato; Hirayama, Naomi; Iida, Tsutomu; Takanashi, Yoshifumi

2016-04-01

In strained high-electron-mobility transistors (HEMTs) with InAs as the channel, excess electrons and holes are generated in the drain region by impact ionization. In the source region, electrons are injected to recombine with accumulated holes by the Auger process. This causes the shift of the gate potential, V GS,shift, for HEMTs. For a system where electrons and holes coexist, we established a theory taking into account the nonparabolicity of the conduction band in the InAs channel. This theory enables us to rigorously determine not only the energy states and the concentration profiles for both carriers but also the V GS,shift due to an accumulation of holes. We have derived the Auger recombination theory which takes into account the Fermi-Dirac statistics and is applicable to an arbitrary shape of potential energy. The Auger recombination lifetime τA for InAs-PHEMTs was estimated as a function of the sheet hole concentration, p s, and τA was on the order of psec for p s exceeding 1012 cm-2.

Efficient Vacuum-Deposited Ternary Organic Solar Cells with Broad Absorption, Energy Transfer, and Enhanced Hole Mobility.

PubMed

Shim, Hyun-Sub; Moon, Chang-Ki; Kim, Jihun; Wang, Chun-Kai; Sim, Bomi; Lin, Francis; Wong, Ken-Tsung; Seo, Yongsok; Kim, Jang-Joo

2016-01-20

The use of multiple donors in an active layer is an effective way to boost the efficiency of organic solar cells by broadening their absorption window. Here, we report an efficient vacuum-deposited ternary organic photovoltaic (OPV) using two donors, 2-((2-(5-(4-(diphenylamino)phenyl)thieno[3,2-b]thiophen-2-yl)thiazol-5-yl)methylene)malononitrile (DTTz) for visible absorption and 2-((7-(5-(dip-tolylamino)thiophen-2-yl)benzo[c]-[1,2,5]thiadiazol-4-yl)methylene)malononitrile (DTDCTB) for near-infrared absorption, codeposited with C70 in the ternary layer. The ternary device achieved a power conversion efficiency of 8.02%, which is 23% higher than that of binary OPVs. This enhancement is the result of incorporating two donors with complementary absorption covering wavelengths of 350 to 900 nm with higher hole mobility in the ternary layer than that of binary layers consisting of one donor and C70, combined with energy transfer from the donor with lower hole mobility (DTTz) to that with higher mobility (DTDCTB). This structure fulfills all the requirements for efficient ternary OPVs.

Density Functional Theory Calculations of the Role of Defects in Amorphous Silicon Solar Cells

NASA Astrophysics Data System (ADS)

Johlin, Eric; Wagner, Lucas; Buonassisi, Tonio; Grossman, Jeffrey C.

2010-03-01

Amorphous silicon holds promise as a cheap and efficient material for thin-film photovoltaic devices. However, current device efficiencies are severely limited by the low mobility of holes in the bulk amorphous silicon material, the cause of which is not yet fully understood. This work employs a statistical analysis of density functional theory calculations to uncover the implications of a range of defects (including internal strain and substitution impurities) on the trapping and mobility of holes, and thereby also on the total conversion efficiency. We investigate the root causes of this low mobility and attempt to provide suggestions for simple methods of improving this property.

Evaluation of the field-effect carrier mobility in single-grain (and polycrystalline) organic semconductors

NASA Astrophysics Data System (ADS)

Kwok, H. L.

2005-08-01

Mobility in single-grain and polycrystalline organic field-effect transistors (OFETs) is of interest because it affects the performance of these devices. While reasonable values of the hole mobility has been measured in pentacene OFETs, relatively speaking, our understanding of the detailed transport mechanisms is somewhat weak and there is a lack of precise knowledge on the effects of the materials parameters such as the site spacing, the localization length, the rms width of the density of states (DOS), the escape frequency, etc. This work attempts to analyze the materials parameters of pentacene OFETs extracted from data reported in the literature. In this work, we developed a model for the mobility parameter from first principle and extracted the relevant materials parameters. According to our analyses, the transport mechanisms in the OFETs are fairly complex and the electrical properties are dominated by the properties of the trap states. As observed, the single-grain OFETs having smaller values of the rms widths of the DOS (in comparison with the polycrystalline OFETs) also had higher hole mobilities. Our results showed that increasing the gate bias could have a similar but smaller effect. Potentially, increasing the escape frequency is a more effective way to raise the hole mobility and this parameter appears to be affected by changes in the molecular structure and in the degree of "disorder".

Charge-transfer mobility and electrical conductivity of PANI as conjugated organic semiconductors

NASA Astrophysics Data System (ADS)

Zhang, Yahong; Duan, Yuping; Song, Lulu; Zheng, Daoyuan; Zhang, Mingxing; Zhao, Guangjiu

2017-09-01

The intramolecular charge transfer properties of a phenyl-end-capped aniline tetramer (ANIH) and a chloro-substituted derivative (ANICl) as organic semiconductors were theoretically studied through the first-principles calculation based on the Marcus-Hush theory. The reorganization energies, intermolecular electronic couplings, angular resolution anisotropic mobilities, and density of states of the two crystals were evaluated. The calculated results demonstrate that both ANIH and ANICl crystals show the higher electron transfer mobilities than the hole-transfer mobilities, which means that the two crystals should prefer to function as n-type organic semiconductors. Furthermore, the angle dependence mobilities of the two crystals show remarkable anisotropic character. The maximum mobility μmax of ANIH and ANICl crystals is 1.3893 and 0.0272 cm2 V-1 s-1, which appear at the orientation angles near 176°/356° and 119°/299° of a conducting channel on the a-b reference plane. It is synthetically evaluated that the ANIH crystal possesses relatively lower reorganization energy, higher electronic coupling, and electron transfer mobility, which means that the ANIH crystal may be the more ideal candidate as a high performance n-type organic semiconductor material. The systematic theoretical studies on organic crystals should be conducive to evaluating the charge-transport properties and designing higher performance organic semiconductor materials.

Charge-transfer mobility and electrical conductivity of PANI as conjugated organic semiconductors.

PubMed

Zhang, Yahong; Duan, Yuping; Song, Lulu; Zheng, Daoyuan; Zhang, Mingxing; Zhao, Guangjiu

2017-09-21

The intramolecular charge transfer properties of a phenyl-end-capped aniline tetramer (ANIH) and a chloro-substituted derivative (ANICl) as organic semiconductors were theoretically studied through the first-principles calculation based on the Marcus-Hush theory. The reorganization energies, intermolecular electronic couplings, angular resolution anisotropic mobilities, and density of states of the two crystals were evaluated. The calculated results demonstrate that both ANIH and ANICl crystals show the higher electron transfer mobilities than the hole-transfer mobilities, which means that the two crystals should prefer to function as n-type organic semiconductors. Furthermore, the angle dependence mobilities of the two crystals show remarkable anisotropic character. The maximum mobility μ max of ANIH and ANICl crystals is 1.3893 and 0.0272 cm 2 V -1 s -1 , which appear at the orientation angles near 176°/356° and 119°/299° of a conducting channel on the a-b reference plane. It is synthetically evaluated that the ANIH crystal possesses relatively lower reorganization energy, higher electronic coupling, and electron transfer mobility, which means that the ANIH crystal may be the more ideal candidate as a high performance n-type organic semiconductor material. The systematic theoretical studies on organic crystals should be conducive to evaluating the charge-transport properties and designing higher performance organic semiconductor materials.

Hole polaron-polaron interaction in transition metal oxides and its limit to p-type doping

NASA Astrophysics Data System (ADS)

Chen, Shiyou; Wang, Lin-Wang

2014-03-01

Traditionally the origin of the poor p-type conductivity in some transition metal oxides (TMOs) was attributed to the limited hole concentration: the charge-compensating donor defects, such as oxygen vacancies and cation interstitials, can form spontaneously as the Fermi energy shifts down to near the valence band maximum. Besides the thermodynamic limit to the hole concentration, the limit to the hole mobility can be another possible reason, e.g., the hole carrier can form self-trapped polarons with very low carrier mobility. Although isolated hole polarons had been found in some TMOs, the polaron-polaron interaction is not well-studied. Here we show that in TMOs such as TiO2 and V2O5, the hole polarons prefer to bind with each other to form bipolarons, which are more stable than free hole carriers or separated polarons. This pushes the hole states upward into the conduction band and traps the holes. The rise of the Fermi energy suppresses the spontaneous formation of the charge-compensating donor defects, so the conventional mechanism becomes ineffective. Since it can happen in the impurity-free TMO lattices, independent of any extrinsic dopant, it acts as an intrinsic and general limit to the p-type conductivity in these TMOs. This material is based upon work performed by the JCAP, a US DOE Energy Innovation Hub, the NSFC (No. 61106087 and 91233121) and special funds for major state basic research (No. 2012CB921401).

Depletion region effect of highly efficient hole conductor free CH3NH3PbI3 perovskite solar cells.

PubMed

Aharon, Sigalit; Gamliel, Shany; El Cohen, Bat; Etgar, Lioz

2014-06-14

The inorganic-organic perovskite is currently attracting a lot of attention due to its use as a light harvester in solar cells. The large absorption coefficients, high carrier mobility and good stability of organo-lead halide perovskites present good potential for their use as light harvesters in mesoscopic heterojunction solar cells. This work concentrated on a unique property of the lead halide perovskite, its function simultaneously as a light harvester and a hole conductor in the solar cell. A two-step deposition technique was used to optimize the perovskite deposition and to enhance the solar cell efficiency. It was revealed that the photovoltaic performance of the hole conductor free perovskite solar cell is strongly dependent on the depletion layer width which was created at the TiO2-CH3NH3PbI3 junction. X-ray diffraction measurements indicate that there were no changes in the crystallographic structure of the CH3NH3PbI3 perovskite over time, which supports the high stability of these hole conductor free perovskite solar cells. Furthermore, the power conversion efficiency of the best cells reached 10.85% with a fill factor of 68%, a Voc of 0.84 V, and a Jsc of 19 mA cm(-2), the highest efficiency to date of a hole conductor free perovskite solar cell.

Progressive phase trends in plates with embedded acoustic black holes.

PubMed

Conlon, Stephen C; Feurtado, Philip A

2018-02-01

Acoustic black holes (ABHs) have been explored and demonstrated to be effective passive treatments for broadband noise and vibration control. Performance metrics for assessing damping concepts are often focused on maximizing structural damping loss factors. Optimally performing damping treatments can reduce the resonant response of a driven system well below the direct field response. This results in a finite structure whose vibration input-output response follows that of an infinite structure. The vibration mobility transfer functions between locations on a structure can be used to assess the structure's vibration response phase, and compare its phase response characteristics to those of idealized systems. This work experimentally explores the phase accumulation in finite plates, with and without embedded grids of ABHs. The measured results are compared and contrasted with theoretical results for finite and infinite uniform plates. Accumulated phase characteristics, their spatial dependence and limits, are examined for the plates and compared to theoretical estimates. The phase accumulation results show that the embedded acoustic black hole treatments can significantly enhance the damping of the plates to the point that their phase accumulation follows that of an infinite plate.

Anisotropic carrier mobility in single- and bi-layer C3N sheets

NASA Astrophysics Data System (ADS)

Wang, Xueyan; Li, Qingfang; Wang, Haifeng; Gao, Yan; Hou, Juan; Shao, Jianxin

2018-05-01

Based on the density functional theory combined with the Boltzmann transport equation with relaxation time approximation, we investigate the electronic structure and predict the carrier mobility of single- and bi-layer newly fabricated 2D carbon nitrides C3N. Although C3N sheets possess graphene-like planar hexagonal structure, the calculated carrier mobility is remarkably anisotropic, which is found mainly induced by the anisotropic effective masses and deformation potential constants. Importantly, we find that both the electron and hole mobilities are considerable high, for example, the hole mobility along the armchair direction of single-layer C3N sheets can arrive as high as 1.08 ×104 cm2 V-1 s-1, greatly larger than that of C2N-h2D and many other typical 2D materials. Owing to the high and anisotropic carrier mobility and appropriate band gap, single- and bi-layer semiconducting C3N sheets may have great potential applications in high performance electronic and optoelectronic devices.

High carrier mobility in ultrapure diamond measured by time-resolved cyclotron resonance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Akimoto, Ikuko, E-mail: akimoto@sys.wakayama-u.ac.jp; Handa, Yushi; Fukai, Katsuyuki

2014-07-21

We have performed time-resolved cyclotron resonance measurements in ultrapure diamond crystals for the temperature range of T=7.3–40 K and obtained the temperature-dependent momentum relaxation times based on the cyclotron resonance widths for optically generated electrons and holes. The relaxation time follows a T{sup −3/2} law down to 12 K, which is expected for acoustic-phonon scattering without impurity effect because of the high purity of our samples. The deviation from the law at lower temperatures is explained by the impurity scattering and the breakdown of the high-temperature approximation for the phonon scattering. We extract the carrier drift mobility by using the directly measuredmore » effective masses and the relaxation times. The mobility at 10 K for 600 ns delay time after optical injection is found to be μ{sub e}=1.5×10{sup 6} cm{sup 2}/V s for the electrons, and μ{sub lh}=2.3×10{sup 6} cm{sup 2}/V s and  μ{sub hh}=2.4×10{sup 5} cm{sup 2}/V s for the light and heavy holes, respectively. These high values are achieved by our high-sensitivity detection for low-density carriers (at <10{sup 11} cm{sup −3}) free from the carrier-carrier scattering as well as by the suppression of the impurity scattering in the high-purity samples.« less

Morphology and electronic transport of polycrystalline pentacene thin-film transistors

NASA Astrophysics Data System (ADS)

Knipp, D.; Street, R. A.; Völkel, A. R.

2003-06-01

Temperature-dependent measurements of thin-film transistors were performed to gain insight in the electronic transport of polycrystalline pentacene. Devices were fabricated with plasma-enhanced chemical vapor deposited silicon nitride gate dielectrics. The influence of the dielectric roughness and the deposition temperature of the thermally evaporated pentacene films were studied. Although films on rougher gate dielectrics and films prepared at low deposition temperatures exhibit similar grain size, the electronic properties are different. Increasing the dielectric roughness reduces the free carrier mobility, while low substrate temperature leads to more and deeper hole traps.

Simultaneous determination of built-in voltage and charge carrier mobility in organic diodes from light intensity dependent current-voltage characteristics

NASA Astrophysics Data System (ADS)

Huang, Fobao; Peng, Yingquan; Xu, Kun; Lv, Wenli; Xu, Sunan; Wang, Ying; Tang, Ying; Wei, Yi; Yang, Yuhuan; Liu, Guohan

2017-05-01

Built-in voltage (V bi) and charge carrier mobility are essential parameters of organic diodes, such as organic photodiodes, organic light-emitting diodes and organic solar cells. The existing methods for charge carrier mobility measurement require either expensive equipment, or stringent sample preparation. We demonstrate a method that simultaneously determines the V bi and charge carrier mobility in organic photodiodes and solar cells from incident light intensity dependent current-voltage characteristics. The V bi is determined from the saturation open-circuit voltage, while the charge carrier mobility from the space-charge limited photocurrent. The V bi for organic diodes, ‘ITO/copper phthalocyanine (CuPc)/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP)/Al’, ‘ITO/ lead phthalocyanine (PbPc)/BCP/Al’, ‘ITO/CuPc/C60/BCP/Al’, and ‘ITO/PbPc/C60/BCP/Al’, were measured to be 0.583  ±  0.019, 0.458  ±  0.002, 0.605  ±  0.009 and 0.538  ±  0.004 V, respectively; the hole mobility of CuPc and PbPc thin films were measured to be (1.383  ±  0.367)  ×  10-6 cm2 V-1 s-1 and (3.675  ±  0.887)  ×  10-6 cm2 V-1 s-1, respectively. The measured values for V bi and carrier mobility coincide with related experimental results reported in other literature.

Emergence of high-mobility minority holes in the electrical transport of the Ba (Fe1 -xMnxAs )2 iron pnictides

NASA Astrophysics Data System (ADS)

Urata, T.; Tanabe, Y.; Huynh, K. K.; Heguri, S.; Oguro, H.; Watanabe, K.; Tanigaki, K.

2015-05-01

In Fe pnictide (Pn) superconducting materials, neither Mn nor Cr doping to the Fe site induces superconductivity, even though hole carriers are generated. This is in strong contrast with the superconductivity appearing when holes are introduced by alkali-metal substitution on the insulating blocking layers. We investigate in detail the effects of Mn doping on magnetotransport properties in Ba (Fe1 -xMnxAs )2 for elucidating the intrinsic reason. The negative Hall coefficient for x =0 estimated in the low magnetic field (B ) regime gradually increases as x increases, and its sign changes to a positive one at x =0.020 . Hall resistivities as well as simultaneous interpretation using the magnetoconductivity tensor including both longitudinal and transverse transport components clarify that minority holes with high mobility are generated by the Mn doping via spin-density wave transition at low temperatures, while original majority electrons and holes residing in the paraboliclike Fermi surfaces of the semimetallic Ba (FeAs )2 are negligibly affected. Present results indicate that the mechanism of hole doping in Ba (Fe1 -xMnxAs )2 is greatly different from that of the other superconducting FePn family.

Experimental and Theoretical Demonstration on the Transport Properties of Fused Ring Host Materials for Organic Light-Emitting Diodes

NASA Astrophysics Data System (ADS)

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

2006-01-01

The charge transport properties of three tertiary-butyl (t-Bu) substituted anthracene derivatives (ADN), critical blue host materials for organic light-emitting diodes (OLEDs), have been investigated experimentally and computationally. From time-of-flight (TOF) measurements, all ADN compounds exhibit ambipolar characters. The hole and electron mobilities are in the range (1--5)× 10-7 cm2 V-1 s-1 under an external applied field of about 1 MV cm-1. Un-substituted ADN has the highest carrier mobilities while heavily t-Bu substituted ADN has the least. The electron and hole conducting properties of are consistent with ab initio calculation, which indicates that the frontier orbitals are localized mainly on the anthracene moiety. t-Bu substitutions in ADN increase the hopping path lengths among the molecules and hence reduce the electron and hole mobilities. The results demonstrate that t-Bu substitution is an effective means of engineering the conductivity of organic charge transporter for OLED applications.

Solution-processable ambipolar diketopyrrolopyrrole-selenophene polymer with unprecedentedly high hole and electron mobilities.

PubMed

Lee, Junghoon; Han, A-Reum; Kim, Jonggi; Kim, Yiho; Oh, Joon Hak; Yang, Changduk

2012-12-26

There is a fast-growing demand for polymer-based ambipolar thin-film transistors (TFTs), in which both n-type and p-type transistor operations are realized in a single layer, while maintaining simplicity in processing. Research progress toward this end is essentially fueled by molecular engineering of the conjugated backbones of the polymers and the development of process architectures for device fabrication, which has recently led to hole and electron mobilities of more than 1.0 cm(2) V(-1) s(-1). However, ambipolar polymers with even higher performance are still required. By taking into account both the conjugated backbone and side chains of the polymer component, we have developed a dithienyl-diketopyrrolopyrrole (TDPP) and selenophene containing polymer with hybrid siloxane-solubilizing groups (PTDPPSe-Si). A synergistic combination of rational polymer backbone design, side-chain dynamics, and solution processing affords an enormous boost in ambipolar TFT performance, resulting in unprecedentedly high hole and electron mobilities of 3.97 and 2.20 cm(2) V(-1) s(-1), respectively.

Nanohole Structuring for Improved Performance of Hydrogenated Amorphous Silicon Photovoltaics.

PubMed

Johlin, Eric; Al-Obeidi, Ahmed; Nogay, Gizem; Stuckelberger, Michael; Buonassisi, Tonio; Grossman, Jeffrey C

2016-06-22

While low hole mobilities limit the current collection and efficiency of hydrogenated amorphous silicon (a-Si:H) photovoltaic devices, attempts to improve mobility of the material directly have stagnated. Herein, we explore a method of utilizing nanostructuring of a-Si:H devices to allow for improved hole collection in thick absorber layers. This is achieved by etching an array of 150 nm diameter holes into intrinsic a-Si:H and then coating the structured material with p-type a-Si:H and a conformal zinc oxide transparent conducting layer. The inclusion of these nanoholes yields relative power conversion efficiency (PCE) increases of ∼45%, from 7.2 to 10.4% PCE for small area devices. Comparisons of optical properties, time-of-flight mobility measurements, and internal quantum efficiency spectra indicate this efficiency is indeed likely occurring from an improved collection pathway provided by the nanostructuring of the devices. Finally, we estimate that through modest optimizations of the design and fabrication, PCEs of beyond 13% should be obtainable for similar devices.

Terahertz magneto-optical spectroscopy of a two-dimensional hole gas

DOE PAGES

Kamaraju, N.; Pan, W.; Ekenberg, U.; ...

2015-01-21

Two-dimensional hole gases (2DHGs) have attracted recent attention for their unique quantum physics and potential applications in areas including spintronics and quantum computing. However, their properties remain relatively unexplored, motivating the use of different techniques to study them. We used terahertz magneto-optical spectroscopy to investigate the cyclotron resonance frequency in a high mobility 2DHG, revealing a nonlinear dependence on the applied magnetic field. This is also shown to be due to the complex non-parabolic valence band structure of the 2DHG, as verified by multiband Landau level calculations. We also find that impurity scattering dominates cyclotron resonance decay in the 2DHG,more » in contrast with the dominance of superradiant damping in two-dimensional electron gases. Furthermore, these results shed light on the properties of 2DHGs, motivating further studies of these unique 2D nanosystems.« less

Electronic transport properties of Ti-impurity band in Si

NASA Astrophysics Data System (ADS)

Olea, J.; González-Díaz, G.; Pastor, D.; Mártil, I.

2009-04-01

In this paper we show that pulsed laser melted high dose implantation of Ti in Si, above the Mott transition, produces an impurity band (IB) in this semiconductor. Using the van der Pauw method and Hall effect measurements we find strong laminated conductivity at the implanted layer and a temperature dependent decoupling between the Ti implanted layer (TIL) and the substrate. The conduction mechanism from the TIL to the substrate shows blocking characteristics that could be well explained through IB theory. Using the ATLAS code we can estimate the energetic position of the IB at 0.36 eV from the conduction band, the density of holes in this band which is closely related to the Ti atomic density and the hole mobility in this band. Band diagrams of the structure at low and high temperatures are also simulated in the ATLAS framework. The simulation obtained is fully coherent with experimental results.

Anomalous low-temperature Coulomb drag in graphene-GaAs heterostructures.

PubMed

Gamucci, A; Spirito, D; Carrega, M; Karmakar, B; Lombardo, A; Bruna, M; Pfeiffer, L N; West, K W; Ferrari, A C; Polini, M; Pellegrini, V

2014-12-19

Vertical heterostructures combining different layered materials offer novel opportunities for applications and fundamental studies. Here we report a new class of heterostructures comprising a single-layer (or bilayer) graphene in close proximity to a quantum well created in GaAs and supporting a high-mobility two-dimensional electron gas. In our devices, graphene is naturally hole-doped, thereby allowing for the investigation of electron-hole interactions. We focus on the Coulomb drag transport measurements, which are sensitive to many-body effects, and find that the Coulomb drag resistivity significantly increases for temperatures <5-10 K. The low-temperature data follow a logarithmic law, therefore displaying a notable departure from the ordinary quadratic temperature dependence expected in a weakly correlated Fermi-liquid. This anomalous behaviour is consistent with the onset of strong interlayer correlations. Our heterostructures represent a new platform for the creation of coherent circuits and topologically protected quantum bits.

Terahertz magneto-optical spectroscopy of a two-dimensional hole gas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kamaraju, N., E-mail: nkamaraju@lanl.gov; Taylor, A. J.; Prasankumar, R. P., E-mail: rpprasan@lanl.gov

2015-01-19

Two-dimensional hole gases (2DHGs) have attracted recent attention for their unique quantum physics and potential applications in areas including spintronics and quantum computing. However, their properties remain relatively unexplored, motivating the use of different techniques to study them. We used terahertz magneto-optical spectroscopy to investigate the cyclotron resonance frequency in a high mobility 2DHG, revealing a nonlinear dependence on the applied magnetic field. This is shown to be due to the complex non-parabolic valence band structure of the 2DHG, as verified by multiband Landau level calculations. We also find that impurity scattering dominates cyclotron resonance decay in the 2DHG, inmore » contrast with the dominance of superradiant damping in two-dimensional electron gases. Our results shed light on the properties of 2DHGs, motivating further studies of these unique 2D nanosystems.« less

Remarkable Enhancement of the Hole Mobility in Several Organic Small‐Molecules, Polymers, and Small‐Molecule:Polymer Blend Transistors by Simple Admixing of the Lewis Acid p‐Dopant B(C6F5)3

PubMed Central

Panidi, Julianna; Paterson, Alexandra F.; Khim, Dongyoon; Fei, Zhuping; Han, Yang; Tsetseris, Leonidas; Vourlias, George; Patsalas, Panos A.; Heeney, Martin

2017-01-01

Abstract Improving the charge carrier mobility of solution‐processable organic semiconductors is critical for the development of advanced organic thin‐film transistors and their application in the emerging sector of printed electronics. Here, a simple method is reported for enhancing the hole mobility in a wide range of organic semiconductors, including small‐molecules, polymers, and small‐molecule:polymer blends, with the latter systems exhibiting the highest mobility. The method is simple and relies on admixing of the molecular Lewis acid B(C6F5)3 in the semiconductor formulation prior to solution deposition. Two prototypical semiconductors where B(C6F5)3 is shown to have a remarkable impact are the blends of 2,8‐difluoro‐5,11‐bis(triethylsilylethynyl)anthradithiophene:poly(triarylamine) (diF‐TESADT:PTAA) and 2,7‐dioctyl[1]‐benzothieno[3,2‐b][1]benzothiophene:poly(indacenodithiophene‐co‐benzothiadiazole) (C8‐BTBT:C16‐IDTBT), for which hole mobilities of 8 and 11 cm2 V−1 s−1, respectively, are obtained. Doping of the 6,13‐bis(triisopropylsilylethynyl)pentacene:PTAA blend with B(C6F5)3 is also shown to increase the maximum hole mobility to 3.7 cm2 V−1 s−1. Analysis of the single and multicomponent materials reveals that B(C6F5)3 plays a dual role, first acting as an efficient p‐dopant, and secondly as a microstructure modifier. Semiconductors that undergo simultaneous p‐doping and dopant‐induced long‐range crystallization are found to consistently outperform transistors based on the pristine materials. Our work underscores Lewis acid doping as a generic strategy towards high performance printed organic microelectronics. PMID:29375962

Exploring the electrochemical properties of hole transport materials with spiro-cores for efficient perovskite solar cells from first-principles.

PubMed

Chi, Wei-Jie; Li, Quan-Song; Li, Ze-Sheng

2016-03-21

Perovskite solar cells (PSCs) with organic small molecules as hole transport materials (HTMs) have attracted considerable attention due to their power conversion efficiencies as high as 20%. In the present work, three new spiro-type hole transport materials with spiro-cores, i.e. Spiro-F1, Spiro-F2 and Spiro-F3, are investigated by using density functional theory combined with the Marcus theory and Einstein relation. Based on the calculated and experimental highest occupied molecular orbital (HOMO) levels of 30 reference molecules, an empirical equation, which can predict the HOMO levels of hole transport materials accurately, is proposed. Moreover, a simplified method, in which the hole transport pathways are simplified to be one-dimensional, is presented and adopted to qualitatively compare the molecular hole mobilities. The calculated results show that the perovskite solar cells with the new hole transport materials can have higher open-circuit voltages due to the lower HOMO levels of Spiro-F1 (-5.31 eV), Spiro-F2 (-5.42 eV) and Spiro-F3 (-5.10 eV) compared with that of Spiro-OMeTAD (-5.09 eV). Furthermore, the hole mobilities of Spiro-F1 (1.75 × 10(-2) cm(2) V(-1) s(-1)) and Spiro-F3 (7.59 × 10(-3) cm(2) V(-1) s(-1)) are 3.1 and 1.4 times that of Spiro-OMeTAD (5.65 × 10(-3) cm(2) V(-1) s(-1)) respectively, due to small reorganization energies and large transfer integrals. Interestingly, the stability properties of Spiro-F1 and Spiro-F2 are shown to be comparable to that of Spiro-OMeTAD, and the dimers of Spiro-F2 and Spiro-F3 possess better stability than that of Spiro-OMeTAD. Taking into consideration the appropriate HOMO level, improved hole mobility and enhanced stability, Spiro-F1 and Spiro-F3 may become the most promising alternatives to Spiro-OMeTAD. The present work offers a new design strategy and reliable calculation methods towards the development of excellent organic small molecules as HTMs for highly efficient and stable PSCs.

Influence of high Mg doping on the microstructural and opto-electrical properties of AlGaN alloys

NASA Astrophysics Data System (ADS)

Xu, Qingjun; Zhang, Shiying; Liu, Bin; Tao, Tao; Xie, Zili; Xiu, Xiangqian; Chen, Dunjun; Chen, Peng; Han, Ping; Zheng, Youdou; Zhang, Rong

2018-07-01

Mg-doped AlxGa1-xN (x = 0.23 and 0.35) alloys have been grown on GaN templates with high temperature AlN (HT-AlN) interlayer by metalorganic chemical vapor deposition (MOCVD). A combination of secondary ion mass spectrometry (SIMS) and transmission electron microscopy (TEM) indicates the formation of more inversion domains in the high Al mole fraction Mg-doped AlGaN alloys at Mg concentration ∼1020 cm-3. For Mg-doped Al0.23Ga0.77N epilayer, the analysis of cathodoluminescence (CL) spectra supports the existence of self-compensation effects due to the presence of intrinsic defects and Mg-related centers. The energy level of Mg is estimated to be around 193 meV from the temperature dependence of the resistivity measured by Hall effect experiments. And hole concentration and mobility are measured to be 1.2 × 1018 cm-3 and 0.56 cm2/V at room temperature, respectively. The reduction of acceptor activation energy and low hole mobility are attributed to inversion domains and self-compensation. Moreover, impurity band conduction is dominant in carrier transport up to a relatively higher temperature in high Al content Mg-doped AlGaN alloys.

Fermi-edge exciton-polaritons in doped semiconductor microcavities with finite hole mass

NASA Astrophysics Data System (ADS)

Pimenov, Dimitri; von Delft, Jan; Glazman, Leonid; Goldstein, Moshe

2017-10-01

The coupling between a 2D semiconductor quantum well and an optical cavity gives rise to combined light-matter excitations, the exciton-polaritons. These were usually measured when the conduction band is empty, making the single polariton physics a simple single-body problem. The situation is dramatically different in the presence of a finite conduction-band population, where the creation or annihilation of a single exciton involves a many-body shakeup of the Fermi sea. Recent experiments in this regime revealed a strong modification of the exciton-polariton spectrum. Previous theoretical studies concerned with nonzero Fermi energy mostly relied on the approximation of an immobile valence-band hole with infinite mass, which is appropriate for low-mobility samples only; for high-mobility samples, one needs to consider a mobile hole with large but finite mass. To bridge this gap, we present an analytical diagrammatic approach and tackle a model with short-ranged (screened) electron-hole interaction, studying it in two complementary regimes. We find that the finite hole mass has opposite effects on the exciton-polariton spectra in the two regimes: in the first, where the Fermi energy is much smaller than the exciton binding energy, excitonic features are enhanced by the finite mass. In the second regime, where the Fermi energy is much larger than the exciton binding energy, finite mass effects cut off the excitonic features in the polariton spectra, in qualitative agreement with recent experiments.

Charge transport and electron-hole asymmetry in low-mobility graphene/hexagonal boron nitride heterostructures

NASA Astrophysics Data System (ADS)

Li, Jiayu; Lin, Li; Huang, Guang-Yao; Kang, N.; Zhang, Jincan; Peng, Hailin; Liu, Zhongfan; Xu, H. Q.

2018-02-01

Graphene/hexagonal boron nitride (G/h-BN) heterostructures offer an excellent platform for developing nanoelectronic devices and for exploring correlated states in graphene under modulation by a periodic superlattice potential. Here, we report on transport measurements of nearly 0 ° -twisted G/h-BN heterostructures. The heterostructures investigated are prepared by dry transfer and thermally annealing processes and are in the low mobility regime (approximately 3000 cm2 V-1 s-1 at 1.9 K). The replica Dirac spectra and Hofstadter butterfly spectra are observed on the hole transport side, but not on the electron transport side, of the heterostructures. We associate the observed electron-hole asymmetry with the presence of a large difference between the opened gaps in the conduction and valence bands and a strong enhancement in the interband contribution to the conductivity on the electron transport side in the low-mobility G/h-BN heterostructures. We also show that the gaps opened at the central Dirac point and the hole-branch secondary Dirac point are large, suggesting the presence of strong graphene-substrate interaction and electron-electron interaction in our G/h-BN heterostructures. Our results provide additional helpful insight into the transport mechanism in G/h-BN heterostructures.

Fast Holes, Slow Electrons, and Medium Control of Polaron Size and Mobility in the DA Polymer F8BT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bird, Matthew J.; Bakalis, Jin; Asaoka, Sadayuki

For this research, the nature of electron and hole polarons on poly(9,9-di-n-hexylfluorenyl-2,7-diyl) (pF) and a copolymer poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4,8-diyl)] (F8BT) has been studied by chemical doping, pulse radiolysis, charge modulation spectroscopy, quantum chemical calculations, and microwave conductivity. While pF exhibits very similar behavior in all respects for the electron and the hole, this paper explores the hypothesis that the donor acceptor (push–pull) nature of F8BT will tend to localize charges. Optical spectra and quantum chemical calculations point to an electron localized on the thiadiazole unit in polar liquids but becoming more delocalized as the solvent polarity decreases. Indeed, in the nonpolar solventmore » benzene, the electron mobility is only 2.7 times lower than that of the hole, which conversely is shown to be delocalized in all environments and has a similar mobility to polarons on the homopolymer polyfluorene. Lastly, advantageous modifications to the optoelectronic properties of conjugated polymers that come about by using alternating donor acceptor repeat units have thus been shown to not significantly hinder charge transport despite the corrugated energy landscape along the backbone.« less

Fast Holes, Slow Electrons, and Medium Control of Polaron Size and Mobility in the DA Polymer F8BT

DOE PAGES

Bird, Matthew J.; Bakalis, Jin; Asaoka, Sadayuki; ...

2017-06-28

For this research, the nature of electron and hole polarons on poly(9,9-di-n-hexylfluorenyl-2,7-diyl) (pF) and a copolymer poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4,8-diyl)] (F8BT) has been studied by chemical doping, pulse radiolysis, charge modulation spectroscopy, quantum chemical calculations, and microwave conductivity. While pF exhibits very similar behavior in all respects for the electron and the hole, this paper explores the hypothesis that the donor acceptor (push–pull) nature of F8BT will tend to localize charges. Optical spectra and quantum chemical calculations point to an electron localized on the thiadiazole unit in polar liquids but becoming more delocalized as the solvent polarity decreases. Indeed, in the nonpolar solventmore » benzene, the electron mobility is only 2.7 times lower than that of the hole, which conversely is shown to be delocalized in all environments and has a similar mobility to polarons on the homopolymer polyfluorene. Lastly, advantageous modifications to the optoelectronic properties of conjugated polymers that come about by using alternating donor acceptor repeat units have thus been shown to not significantly hinder charge transport despite the corrugated energy landscape along the backbone.« less

Black holes as antimatter factories

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bambi, Cosimo; Petrov, Alexey A.; Dolgov, Alexander D., E-mail: cosimo.bambi@ipmu.jp, E-mail: dolgov@fe.infn.it, E-mail: apetrov@physics.wayne.edu

2009-09-01

We consider accretion of matter onto a low mass black hole surrounded by ionized medium. We show that, because of the higher mobility of protons than electrons, the black hole would acquire positive electric charge. If the black hole's mass is about or below 10{sup 20} g, the electric field at the horizon can reach the critical value which leads to vacuum instability and electron-positron pair production by the Schwinger mechanism. Since the positrons are ejected by the emergent electric field, while electrons are back-captured, the black hole operates as an antimatter factory which effectively converts protons into positrons.

From computational discovery to experimental characterization of a high hole mobility organic crystal

PubMed Central

Sokolov, Anatoliy N.; Atahan-Evrenk, Sule; Mondal, Rajib; Akkerman, Hylke B.; Sánchez-Carrera, Roel S.; Granados-Focil, Sergio; Schrier, Joshua; Mannsfeld, Stefan C.B.; Zoombelt, Arjan P.; Bao, Zhenan; Aspuru-Guzik, Alán

2011-01-01

For organic semiconductors to find ubiquitous electronics applications, the development of new materials with high mobility and air stability is critical. Despite the versatility of carbon, exploratory chemical synthesis in the vast chemical space can be hindered by synthetic and characterization difficulties. Here we show that in silico screening of novel derivatives of the dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene semiconductor with high hole mobility and air stability can lead to the discovery of a new high-performance semiconductor. On the basis of estimates from the Marcus theory of charge transfer rates, we identified a novel compound expected to demonstrate a theoretic twofold improvement in mobility over the parent molecule. Synthetic and electrical characterization of the compound is reported with single-crystal field-effect transistors, showing a remarkable saturation and linear mobility of 12.3 and 16 cm2 V−1 s−1, respectively. This is one of the very few organic semiconductors with mobility greater than 10 cm2 V−1 s−1 reported to date. PMID:21847111

Magnetic correlations in La(2-x)Sr(x)CuO4 from NQR relaxation and specific heat

NASA Technical Reports Server (NTRS)

Borsa, F.; Rigamonti, A.

1990-01-01

La-139 and Cu-63 Nuclear Quadrupole Resonance (NQR) relaxation measurements in La(2-x)Sr(x)CuO4 for O = to or less than 0.3 and in the temperature range 1.6 + 450 K are analyzed in terms of Cu(++) magnetic correlations and dynamics. It is described how the magnetic correlations that would result from Cu-Cu exchange are reduced by mobile charge defects related to x-doping. A comprehensive picture is given which explains satisfactorily the x and T dependence of the correlation time, of the correlation length and of the Neel temperature T(sub n)(x) as well as being consistent with known electrical resistivity and magnetic susceptibility measurements. It is discussed how, in the superconducting samples, the mobile defects also cause the decrease, for T yields T(sub c)(+) of the hyperfine Cu electron-nucleus effective interaction, leading to the coexistence of quasi-localized, reduced magnetic moments from 3d Cu electrons and mobile oxygen p-hole carriers. The temperature dependence of the effective hyperfine field around the superconducting transition yields an activation energy which could be related to the pairing energy. New specific heat measurements are also presented and discussed in terms of the above picture.

Organic photosensitive devices

DOEpatents

Peumans, Peter; Forrest, Stephen R.

2013-01-22

A photoactive device is provided. The device includes a first electrode, a second electrode, and a photoactive region disposed between and electrically connected to the first and second electrodes. The photoactive region further includes an organic donor layer and an organic acceptor layer that form a donor-acceptor heterojunction. The mobility of holes in the organic donor region and the mobility of electrons in the organic acceptor region are different by a factor of at least 100, and more preferably a factor of at least 1000. At least one of the mobility of holes in the organic donor region and the mobility of electrons in the organic acceptor region is greater than 0.001 cm.sup.2/V-sec, and more preferably greater than 1 cm.sup.2/V-sec. The heterojunction may be of various types, including a planar heterojunction, a bulk heterojunction, a mixed heterojunction, and a hybrid planar-mixed heterojunction.

Spiro-OMeTAD single crystals: Remarkably enhanced charge-carrier transport via mesoscale ordering

PubMed Central

Shi, Dong; Qin, Xiang; Li, Yuan; He, Yao; Zhong, Cheng; Pan, Jun; Dong, Huanli; Xu, Wei; Li, Tao; Hu, Wenping; Brédas, Jean-Luc; Bakr, Osman M.

2016-01-01

We report the crystal structure and hole-transport mechanism in spiro-OMeTAD [2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenyl-amine)9,9′-spirobifluorene], the dominant hole-transporting material in perovskite and solid-state dye-sensitized solar cells. Despite spiro-OMeTAD’s paramount role in such devices, its crystal structure was unknown because of highly disordered solution-processed films; the hole-transport pathways remained ill-defined and the charge carrier mobilities were low, posing a major bottleneck for advancing cell efficiencies. We devised an antisolvent crystallization strategy to grow single crystals of spiro-OMeTAD, which allowed us to experimentally elucidate its molecular packing and transport properties. Electronic structure calculations enabled us to map spiro-OMeTAD’s intermolecular charge-hopping pathways. Promisingly, single-crystal mobilities were found to exceed their thin-film counterparts by three orders of magnitude. Our findings underscore mesoscale ordering as a key strategy to achieving breakthroughs in hole-transport material engineering of solar cells. PMID:27152342

Interrelation of transport properties, defect structure and spin state of Ni3+ in La1.2Sr0.8Ni0.9Fe0.1O4+δ

NASA Astrophysics Data System (ADS)

Gilev, A. R.; Kiselev, E. A.; Zakharov, D. M.; Cherepanov, V. A.

2017-10-01

The total conductivity, Seebeck coefficient and oxygen non-stoichiometry for La1.2Sr0.8Ni0.9Fe0.1O4+δ have been measured vs temperature and oxygen partial pressure P(O2). The measurements were carried out at 800, 850, 900 and 950 °C within the P(O2) range of 10-5-0.21 atm. La1.2Sr0.8Ni0.9Fe0.1O4+δ was shown to be oxygen deficient in all temperature and P(O2) ranges studied. The calculated values of the partial molar enthalpy of oxygen depend very slightly on oxygen content (δ), indicating that La1.2Sr0.8Ni0.9Fe0.1O4+δ with the oxygen deficiency can be considered an ideal solution. The model of point defect equilibria in La1.2Sr0.8Ni0.9Fe0.1O4+δ has been proposed and fitted to experimental dependencies. Subsequent joint analysis of the defect structure and transport properties revealed that electron holes can coexist in both localized and quasi-delocalized states in the oxide: the former corresponded to high-spin state Ni3+ and the latter - to low-spin state Ni3+. The mobilities of localized electron holes were shown to be significantly lower in comparison to quasi-delocalized ones. The behavior of localized electron holes was explained in terms of a small polaron conduction mechanism; in contrast, quasi-delocalized electron holes were described in terms of a band conduction approach. The small polaron conduction mechanism was shown to be predominant in the Sr- and Fe-co-doped lanthanum nickelate.

High-resolution charge carrier mobility mapping of heterogeneous organic semiconductors

NASA Astrophysics Data System (ADS)

Button, Steven W.; Mativetsky, Jeffrey M.

2017-08-01

Organic electronic device performance is contingent on charge transport across a heterogeneous landscape of structural features. Methods are therefore needed to unravel the effects of local structure on overall electrical performance. Using conductive atomic force microscopy, we construct high-resolution out-of-plane hole mobility maps from arrays of 5000 to 16 000 current-voltage curves. To demonstrate the efficacy of this non-invasive approach for quantifying and mapping local differences in electrical performance due to structural heterogeneities, we investigate two thin film test systems, one bearing a heterogeneous crystal structure [solvent vapor annealed 5,11-Bis(triethylsilylethynyl)anthradithiophene (TES-ADT)—a small molecule organic semiconductor] and one bearing a heterogeneous chemical composition [p-DTS(FBTTh2)2:PC71BM—a high-performance organic photovoltaic active layer]. TES-ADT shows nearly an order of magnitude difference in hole mobility between semicrystalline and crystalline areas, along with a distinct boundary between the two regions, while p-DTS(FBTTh2)2:PC71BM exhibits subtle local variations in hole mobility and a nanoscale domain structure with features below 10 nm in size. We also demonstrate mapping of the built-in potential, which plays a significant role in organic light emitting diode and organic solar cell operation.

Complex quantum transport in a modulation doped strained Ge quantum well heterostructure with a high mobility 2D hole gas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morrison, C., E-mail: c.morrison.2@warwick.ac.uk; Casteleiro, C.; Leadley, D. R.

The complex quantum transport of a strained Ge quantum well (QW) modulation doped heterostructure with two types of mobile carriers has been observed. The two dimensional hole gas (2DHG) in the Ge QW exhibits an exceptionally high mobility of 780 000 cm{sup 2}/Vs at temperatures below 10 K. Through analysis of Shubnikov de-Haas oscillations in the magnetoresistance of this 2DHG below 2 K, the hole effective mass is found to be 0.065 m{sub 0}. Anomalous conductance peaks are observed at higher fields which deviate from standard Shubnikov de-Haas and quantum Hall effect behaviour due to conduction via multiple carrier types. Despite this complex behaviour,more » analysis using a transport model with two conductive channels explains this behaviour and allows key physical parameters such as the carrier effective mass, transport, and quantum lifetimes and conductivity of the electrically active layers to be extracted. This finding is important for electronic device applications, since inclusion of highly doped interlayers which are electrically active, for enhancement of, for example, room temperature carrier mobility, does not prevent analysis of quantum transport in a QW.« less

γ-Herringbone Polymorph of 6,13-Bis(trimethylsilylethynyl)pentacene: A Potential Material for Enhanced Hole Mobility.

PubMed

Bhat, Vinayak; Gopan, Gopika; Nair, Nanditha G; Hariharan, Mahesh

2018-04-06

The introduction of the trialkylsilylethynyl group to the acene core is known to predominantly transform the herringbone structure of pentacene to a slip-stacked packing. However, herein, the occurrence of an unforeseen polymorph of 6,13-bis(trimethylsilylethynyl)pentacene (TMS-pentacene), with an atypical γ-herringbone packing arrangement, is reported. Intermolecular noncovalent interactions in the γ-herringbone polymorph are determined from Hirshfeld surface and quantum theory of atoms-in-molecules (QTAIM) analyses. Furthermore, a comparative truncated symmetry-adapted perturbation theory (SAPT(0)) energy decomposition analysis discloses the role of exchange repulsions that govern molecular packing in the γ-herringbone polymorph. Moreover, the computationally predicted electronic coupling and anisotropic mobility reveal the possibility of enhanced hole transport (μ h =3.7 cm 2  V -1  s -1 ) in the γ-herringbone polymorph, in contrast to the reported polymorph with a hole mobility of μ h =0.1 cm 2  V -1  s -1 . © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Dissociation and recombination of positive holes in minerals

NASA Technical Reports Server (NTRS)

Freund, Friedemann; Batllo, Francois; Freund, Minoru M.

1990-01-01

The formation mechanisms are described of positive holes - electronic defects in the O2 sublattice - with attention given to detecting the positive surface charge of minerals with these holes. Charge distribution analysis (CDA) is presented which measures dielectric polarization in an inhomogeneous field. CDA can be applied to the detection of the peroxide/superoxide functionality caused by positive holes on the surface. It is demonstrated with obsidian that the measurements provide data on O(-) mobility as a function of surface-charge carrier density and on O(-) generation as a function of temperature.

Photovoltage detection of edge magnetoplasmon oscillations and giant magnetoplasmon resonances in a two-dimensional hole system

NASA Astrophysics Data System (ADS)

Mi, Jian; Wang, Jianli; Pfeiffer, Loren N.; West, Ken W.; Baldwin, Kirk W.; Zhang, Chi

In our high mobility p-type AlGaAs/GaAs two-dimensional hole samples, we originally observe the B - periodic oscillation induced by microwave (MW) in photovoltage (PV) measurements. In the frequency range of our measurements (5 - 40 GHz), the period is inversely proportional to the microwave frequency (f). The distinct oscillations come from the edge magnetoplasmon (EMP) in the high quality heavy hole system. Simultaneously, we observe the giant plasmon resonance signals in our measurements on the shallow two-dimensional hole system (2DHS).

Effect of tunneling layers on the performances of floating-gate based organic thin-film transistor nonvolatile memories

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Wei, E-mail: wwei99@jlu.edu.cn; Han, Jinhua; Ying, Jun

2014-09-22

Two types of floating-gate based organic thin-film transistor nonvolatile memories (FG-OTFT-NVMs) were demonstrated, with poly(methyl methacrylate co glycidyl methacrylate) (P(MMA-GMA)) and tetratetracontane (TTC) as the tunneling layer, respectively. Their device performances were measured and compared. In the memory with a P(MMA-GMA) tunneling layer, typical unipolar hole transport was obtained with a relatively small mobility of 0.16 cm{sup 2}/V s. The unidirectional shift of turn-on voltage (V{sub on}) due to only holes trapped/detrapped in/from the floating gate resulted in a small memory window of 12.5 V at programming/erasing voltages (V{sub P}/V{sub E}) of ±100 V and a nonzero reading voltage. Benefited from the well-ordered moleculemore » orientation and the trap-free surface of TTC layer, a considerably high hole mobility of 1.7 cm{sup 2}/V s and a visible feature of electrons accumulated in channel and trapped in floating-gate were achieved in the memory with a TTC tunneling layer. High hole mobility resulted in a high on current and a large memory on/off ratio of 600 at the V{sub P}/V{sub E} of ±100 V. Both holes and electrons were injected into floating-gate and overwritten each other, which resulted in a bidirectional V{sub on} shift. As a result, an enlarged memory window of 28.6 V at the V{sub P}/V{sub E} of ±100 V and a zero reading voltage were achieved. Based on our results, a strategy is proposed to optimize FG-OTFT-NVMs by choosing a right tunneling layer to improve the majority carrier mobility and realize ambipolar carriers injecting and trapping in the floating-gate.« less

Identification of microscopic hole-trapping mechanisms in nitride semiconductors

DOE PAGES

John L. Lyons; Krishnaswamy, Karthik; Luke Gordon; ...

2015-12-17

Hole trapping has been observed in nitride heterostructure devices, where the Fermi level is in the vicinity of the valence-band maximum. Using hybrid density functional calculations, we examine microscopic mechanisms for hole trapping in GaN and AlN. In a defect-free material, hole trapping does not spontaneously occur, but trapping can occur in the vicinity of impurities, such as C-a common unintentional impurity in nitrides. As a result, using Schrodinger-Poisson simulations, we assess the effects of C-derived hole traps on N-face high-electron mobility transistors, which we find to be more detrimental than the previously proposed interface traps.

A Methoxydiphenylamine-Substituted Carbazole Twin Derivative: An Efficient Hole-Transporting Material for Perovskite Solar Cells.

PubMed

Gratia, Paul; Magomedov, Artiom; Malinauskas, Tadas; Daskeviciene, Maryte; Abate, Antonio; Ahmad, Shahzada; Grätzel, Michael; Getautis, Vytautas; Nazeeruddin, Mohammad Khaja

2015-09-21

The small-molecule-based hole-transporting material methoxydiphenylamine-substituted carbazole was synthesized and incorporated into a CH3NH3PbI3 perovskite solar cell, which displayed a power conversion efficiency of 16.91%, the second highest conversion efficiency after that of Spiro-OMeTAD. The investigated hole-transporting material was synthesized in two steps from commercially available and relatively inexpensive starting reagents. Various electro-optical measurements (UV/Vis, IV, thin-film conductivity, hole mobility, DSC, TGA, ionization potential) have been carried out to characterize the new hole-transporting material. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

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

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.

Electrostatic modulation of the electronic properties of Dirac semimetal Na3Bi thin films

NASA Astrophysics Data System (ADS)

Hellerstedt, Jack; Yudhistira, Indra; Edmonds, Mark T.; Liu, Chang; Collins, James; Adam, Shaffique; Fuhrer, Michael S.

2017-10-01

Large-area thin films of topological Dirac semimetal Na3Bi are grown on amorphous SiO2:Si substrates to realize a field-effect transistor with the doped Si acting as a back gate. As-grown films show charge carrier mobilities exceeding 7 000 cm2/V s and carrier densities below 3 ×1018cm-3 , comparable to the best thin-film Na3Bi . An ambipolar field effect and minimum conductivity are observed, characteristic of Dirac electronic systems. The results are quantitatively understood within a model of disorder-induced charge inhomogeneity in topological Dirac semimetals. The hole mobility is significantly larger than the electron mobility in Na3Bi which we ascribe to the inverted band structure. When present, these holes dominate the transport properties.

Mg doping of GaN by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Lieten, R. R.; Motsnyi, V.; Zhang, L.; Cheng, K.; Leys, M.; Degroote, S.; Buchowicz, G.; Dubon, O.; Borghs, G.

2011-04-01

We present a systematic study on the influence of growth conditions on the incorporation and activation of Mg in GaN layers grown by plasma-assisted molecular beam epitaxy. We show that high quality p-type GaN layers can be obtained on GaN-on-silicon templates. The Mg incorporation and the electrical properties have been investigated as a function of growth temperature, Ga : N flux ratio and Mg : Ga flux ratio. It was found that the incorporation of Mg and the electrical properties are highly sensitive to the Ga : N flux ratio. The highest hole mobility and lowest resistivity were achieved for slightly Ga-rich conditions. In addition to an optimal Ga : N ratio, an optimum Mg : Ga flux ratio was also observed at around 1%. We observed a clear Mg flux window for p-type doping of GaN : 0.31% < Mg : Ga < 5.0%. A lowest resistivity of 0.98 Ω cm was obtained for optimized growth conditions. The p-type GaN layer then showed a hole concentration of 4.3 × 1017 cm-3 and a mobility of 15 cm2 V-1 s-1. Temperature-dependent Hall effect measurements indicate an acceptor depth in these samples of 100 meV for a hole concentration of 5.5 × 1017 cm-3. The corresponding Mg concentration is 5 × 1019 cm-3, indicating approximately 1% activation at room temperature. In addition to continuous growth of Mg-doped GaN layers we also investigated different modulated growth procedures. We show that a modulated growth procedure has only limited influence on Mg doping at a growth temperature of 800 °C or higher. This result is thus in contrast to previously reported GaN : Mg doping at much lower growth temperatures of 500 °C.

Electrical characterisation of deep level defects in Be-doped AlGaAs grown on (100) and (311)A GaAs substrates by MBE

PubMed Central

2011-01-01

The growth of high mobility two-dimensional hole gases (2DHGs) using GaAs-GaAlAs heterostructures has been the subject of many investigations. However, despite many efforts hole mobilities in Be-doped structures grown on (100) GaAs substrate remained considerably lower than those obtained by growing on (311)A oriented surface using silicon as p-type dopant. In this study we will report on the properties of hole traps in a set of p-type Be-doped Al0.29Ga0.71As samples grown by molecular beam epitaxy on (100) and (311)A GaAs substrates using deep level transient spectroscopy (DLTS) technique. In addition, the effect of the level of Be-doping concentration on the hole deep traps is investigated. It was observed that with increasing the Be-doping concentration from 1 × 1016 to 1 × 1017 cm-3 the number of detected electrically active defects decreases for samples grown on (311)A substrate, whereas, it increases for (100) orientated samples. The DLTS measurements also reveal that the activation energies of traps detected in (311)A are lower than those in (100). From these findings it is expected that mobilities of 2DHGs in Be-doped GaAs-GaAlAs devices grown on (311)A should be higher than those on (100). PMID:21711687

Dependence of electrical and time stress in organic field effect transistor with low temperature forming gas treated Al2O3 gate dielectrics.

PubMed

Lee, Sunwoo; Chung, Keum Jee; Park, In-Sung; Ahn, Jinho

2009-12-01

We report the characteristics of the organic field effect transistor (OFET) after electrical and time stress. Aluminum oxide (Al2O3) was used as a gate dielectric layer. The surface of the gate oxide layer was treated with hydrogen (H2) and nitrogen (N2) mixed gas to minimize the dangling bond at the interface layer of gate oxide. According to the two stress parameters of electrical and time stress, threshold voltage shift was observed. In particular, the mobility and subthreshold swing of OFET were significantly decreased due to hole carrier localization and degradation of the channel layer between gate oxide and pentacene by electrical stress. Electrical stress is a more critical factor in the degradation of mobility than time stress caused by H2O and O2 in the air.

Black holes thermodynamics in a new kind of noncommutative geometry

NASA Astrophysics Data System (ADS)

Faizal, Mir; Amorim, R. G. G.; Ulhoa, S. C.

Motivated by the energy-dependent metric in gravity’s rainbow, we will propose a new kind of energy-dependent noncommutative geometry. It will be demonstrated that like gravity’s rainbow, this new noncommutative geometry is described by an energy-dependent metric. We will analyze the effect of this noncommutative deformation on the Schwarzschild black holes and Kerr black holes. We will perform our analysis by relating the commutative and this new energy-dependent noncommutative metrics using an energy-dependent Moyal star product. We will also analyze the thermodynamics of these new noncommutative black hole solutions. We will explicitly derive expression for the corrected entropy and temperature for these black hole solutions. It will be demonstrated that, for these deformed solutions, black remnants cannot form. This is because these corrections increase rather than reduce the temperature of the black holes.

Effect of thallium doping on the mobility of electrons in Bi{sub 2}Se{sub 3} and holes in Sb{sub 2}Te{sub 3}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kudryashov, A. A.; Kytin, V. G.; Lunin, R. A.

2016-07-15

The Shubnikov–de Haas effect and the Hall effect in n-Bi{sub 2–x}Tl{sub x}Se{sub 3} (x = 0, 0.01, 0.02, 0.04) and p-Sb{sub 2–x}Tl{sub x}Te{sub 3} (x = 0, 0.005, 0.015, 0.05) single crystals are studied. The carrier mobilities and their changes upon Tl doping are calculated by the Fourier spectra of oscillations. It is found shown that Tl doping decreases the electron concentration in n-Bi{sub 2–x}Tl{sub x}Se{sub 3} and increases the electron mobility. In p-Sb{sub 2–x}Tl{sub x}Te{sub 3}, both the hole concentration and mobility decrease upon Tl doping. The change in the crystal defect concentration, which leads to these effects, ismore » discussed.« less

Performance Evaluation of AODV with Blackhole Attack

NASA Astrophysics Data System (ADS)

Dara, Karuna

2010-11-01

A Mobile Ad Hoc Network (MANET) is a temporary network set up by a wireless mobile computers moving arbitrary in the places that have no network infrastructure. These nodes maintain connectivity in a decentralized manner. Since the nodes communicate with each other, they cooperate by forwarding data packets to other nodes in the network. Thus the nodes find a path to the destination node using routing protocols. However, due to security vulnerabilities of the routing protocols, mobile ad-hoc networks are unprotected to attacks of the malicious nodes. One of these attacks is the Black Hole Attack against network integrity absorbing all data packets in the network. Since the data packets do not reach the destination node on account of this attack, data loss will occur. In this paper, we simulated the black hole attack in various mobile ad-hoc network scenarios using AODV routing protocol of MANET and have tried to find a effect if number of nodes are increased with increase in malicious nodes.

AC transport in p-Ge/GeSi quantum well in high magnetic fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Drichko, I. L.; Malysh, V. A.; Smirnov, I. Yu.

2014-08-20

The contactless surface acoustic wave technique is implemented to probe the high-frequency conductivity of a high-mobility p-Ge/GeSi quantum well structure in the regime of integer quantum Hall effect (IQHE) at temperatures 0.3–5.8 K and magnetic fields up to 18 T. It is shown that, in the IQHE regime at the minima of conductivity, holes are localized and ac conductivity is of hopping nature and can be described within the “two-site” model. The analysis of the temperature and magnetic-field-orientation dependence of the ac conductivity at odd filing factors enables us to determine the effective hole g-factor, |g{sub zz}|≈4.5. It is shownmore » that the in-plane component of the magnetic field leads to a decrease in the g-factor as well as increase in the cyclotron mass, which is explained by orbital effects in the complex valence band of germanium.« less

Determination of Charge-Carrier Mobility in Disordered Thin-Film Solar Cells as a Function of Current Density

NASA Astrophysics Data System (ADS)

Mäckel, Helmut; MacKenzie, Roderick C. I.

2018-03-01

Charge-carrier mobility is a fundamental material parameter, which plays an important role in determining solar-cell efficiency. The higher the mobility, the less time a charge carrier will spend in a device and the less likely it is that it will be lost to recombination. Despite the importance of this physical property, it is notoriously difficult to measure accurately in disordered thin-film solar cells under operating conditions. We, therefore, investigate a method previously proposed in the literature for the determination of mobility as a function of current density. The method is based on a simple analytical model that relates the mobility to carrier density and transport resistance. By revising the theoretical background of the method, we clearly demonstrate what type of mobility can be extracted (constant mobility or effective mobility of electrons and holes). We generalize the method to any combination of measurements that is able to determine the mean electron and hole carrier density, and the transport resistance at a given current density. We explore the robustness of the method by simulating typical organic solar-cell structures with a variety of physical properties, including unbalanced mobilities, unbalanced carrier densities, and for high or low carrier trapping rates. The simulations reveal that near VOC and JSC , the method fails due to the limitation of determining the transport resistance. However, away from these regions (and, importantly, around the maximum power point), the method can accurately determine charge-carrier mobility. In the presence of strong carrier trapping, the method overestimates the effective mobility due to an underestimation of the carrier density.

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

PubMed

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

2015-02-17

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

Effect of mechanical strain on mobility of polycrystalline silicon thin-film transistors fabricated on stainless steel foil

NASA Astrophysics Data System (ADS)

Kuo, Po-Chin; Jamshidi-Roudbari, Abbas; Hatalis, Miltiadis

2007-12-01

The effect of uniaxial tensile strain parallel to the channel on mobility of polycrystalline silicon thin-film transistors (TFTs) on stainless steel foil has been investigated. The electron mobility increases by 20% while the hole mobility decreases by 6% as the strain increases to 0.5%, and both followed by saturation as the strain increases further. The off current decreases for both types of TFTs under strain. All TFTs remained functional at the applied strain of 1.13%.

Radioactive hot cell access hole decontamination machine

DOEpatents

Simpson, William E.

1982-01-01

Radioactive hot cell access hole decontamination machine. A mobile housing has an opening large enough to encircle the access hole and has a shielding door, with a door opening and closing mechanism, for uncovering and covering the opening. The housing contains a shaft which has an apparatus for rotating the shaft and a device for independently translating the shaft from the housing through the opening and access hole into the hot cell chamber. A properly sized cylindrical pig containing wire brushes and cloth or other disks, with an arrangement for releasably attaching it to the end of the shaft, circumferentially cleans the access hole wall of radioactive contamination and thereafter detaches from the shaft to fall into the hot cell chamber.

Amplified Emission and Field-Effect Transistor Characteristics of One-Dimensionally Structured 2,5-Bis(4-biphenylyl)thiophene Crystals.

PubMed

Hashimoto, Kazumasa; Sasaki, Fumio; Hotta, Shu; Yanagi, Hisao

2016-04-01

One-dimensional (1D) structures of 2,5-bis(4-biphenylyl)thiophene (BP1T) crystals are fabricated for light amplification and field-effect transistor (FET) measurements. A strip-shaped 1D structure (10 µm width) made by photolitography of a vapor-deposited polycrystalline film shows amplified spontaneous emission and lasing oscillations under optical pumping. An FET fabricated with this 1D structure exhibits hole-conduction with a mobility of µh = 8.0 x 10(-3) cm2/Vs. Another 1 D-structured FET is fabricated with epitaxially grown needle-like crystals of BP1T. This needle-crystal FET exhibits higher mobility of µh = 0.34 cm2/Vs. This improved hole mobility is attributed to the single-crystal channel of epitaxial needles while the grain boudaries in the polycrystalline 1 D-structure decrease the carrier transport.

Vacuum-processed polyethylene as a dielectric for low operating voltage organic field effect transistors

PubMed Central

Kanbur, Yasin; Irimia-Vladu, Mihai; Głowacki, Eric D.; Voss, Gundula; Baumgartner, Melanie; Schwabegger, Günther; Leonat, Lucia; Ullah, Mujeeb; Sarica, Hizir; Erten-Ela, Sule; Schwödiauer, Reinhard; Sitter, Helmut; Küçükyavuz, Zuhal; Bauer, Siegfried; Sariciftci, Niyazi Serdar

2012-01-01

We report on the fabrication and performance of vacuum-processed organic field effect transistors utilizing evaporated low-density polyethylene (LD-PE) as a dielectric layer. With C60 as the organic semiconductor, we demonstrate low operating voltage transistors with field effect mobilities in excess of 4 cm2/Vs. Devices with pentacene showed a mobility of 0.16 cm2/Vs. Devices using tyrian Purple as semiconductor show low-voltage ambipolar operation with equal electron and hole mobilities of ∼0.3 cm2/Vs. These devices demonstrate low hysteresis and operational stability over at least several months. Grazing-angle infrared spectroscopy of evaporated thin films shows that the structure of the polyethylene is similar to solution-cast films. We report also on the morphological and dielectric properties of these films. Our experiments demonstrate that polyethylene is a stable dielectric supporting both hole and electron channels. PMID:23483783

Improving the Charge Carrier Transport and Suppressing Recombination of Soluble Squaraine-Based Solar Cells via Parallel-Like Structure

PubMed Central

Zhu, Youqin; Liu, Jingli; Zhao, Jiao; Li, Yang; Qiao, Bo; Song, Dandan; Huang, Yan; Xu, Zheng; Zhao, Suling; Xu, Xurong

2018-01-01

Small molecule organic solar cells (SMOSCs) have attracted extensive attention in recent years. Squaraine (SQ) is a kind of small molecule material for potential use in high-efficiency devices, because of its high extinction coefficient and low-cost synthesis. However, the charge carrier mobility of SQ-based film is much lower than other effective materials, which leads to the pretty low fill factor (FF). In this study, we improve the performance of SQ derivative-based solar cells by incorporating PCDTBT into LQ-51/PC71BM host binary blend film. The incorporation of PCDTBT can not only increase the photon harvesting, but also provide an additional hole transport pathway. Through the charge carrier mobility and transient photovoltage measurement, we find that the hole mobility and charge carrier lifetime increase in the ternary system. Also, we carefully demonstrate that the charge carrier transport follows a parallel-like behavior. PMID:29747394

Anomalous effective magnetoconductivity in disordered bipolar semiconductors: Theory and experimental simulation

NASA Astrophysics Data System (ADS)

Chaikovsky, Isaak; Alperovich, Leonid; Gurvich, Yuri; Melnikov, Andrey; Biryukov, Sergey

2002-05-01

We present the results of measuring transverse conductivity α⊥c of bipolar heterogeneous semiconductors in classical strong magnetic fields. A stochastic distribution of current carriers (electrons and holes) was created by interband illumination through special masks. The main parameters of crystalline p-Si:B placed in liquid He were the concentrations of the main and compensating impurities, 7×1015 and 4×1012 cm-3, respectively; and the mobilities of electrons and holes, 1×106 and 5×104 cm2/V s, respectively. An anomaly in α⊥c was observed: the ratio of α⊥c for heterogeneous and homogeneous samples depended on magnetic field in a nonmonotonic way, i.e., alternation of increasing and decreasing regions of relative α⊥c for H=0-10 kGs and monotonic growth for H=10-40 kGs. To explain this effect, a theory is presented which is a development of the α⊥c theory for heterogeneous semiconductors with one kind of carrier. It is shown that the effect is due to the redistribution of roles of electrons and holes in magnetoconductivity of homogeneous semiconductors. This effect has high sensitivity to degree of disorder and can be used for detection of small irregularities and as a diagnostic of semiconductor purity.

Role of Adsorbed Water on Charge Carrier Dynamics in Photoexcited TiO2

PubMed Central

2017-01-01

Overall photocatalytic water splitting is one of the most sought after processes for sustainable solar-to-chemical energy conversion. The efficiency of this process strongly depends on charge carrier recombination and interaction with surface adsorbates at different time scales. Here, we investigated how hydration of TiO2 P25 affects dynamics of photogenerated electrons at the millisecond to minute time scale characteristic for chemical reactions. We used rapid scan diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS). The decay of photogenerated electron absorption was substantially slower in the presence of associated water. For hydrated samples, the charge carrier recombination rates followed an Arrhenius-type behavior in the temperature range of 273–423 K; these became temperature-independent when the material was dehydrated at temperatures above 423 K or cooled below 273 K. A DFT+U analysis revealed that hydrogen bonding with adsorbed water stabilizes surface-trapped holes at anatase TiO2(101) facet and lowers the barriers for hole migration. Hence, hole mobility should be higher in the hydrated material than in the dehydrated system. This demonstrates that adsorbed associated water can efficiently stabilize photogenerated charge carriers in nanocrystalline TiO2 and suppress their recombination at the time scale up to minutes. PMID:28413570

Fourier-domain Mobility Spectrum Analysis (FMSA) for Characterizing Semiconductors with Multi-Electron/Hole Species

NASA Astrophysics Data System (ADS)

Cui, Boya; Kielb, Edward; Luo, Jiajun; Tang, Yang; Grayson, Matthew

Superlattices and narrow gap semiconductors often host multiple conducting species, such as electrons and holes, requiring a mobility spectral analysis (MSA) method to separate contributions to the conductivity. Here, a least-squares MSA method is introduced: the QR-algorithm Fourier-domain MSA (FMSA). Like other MSA methods, the FMSA sorts the conductivity contributions of different carrier species from magnetotransport measurements, arriving at a best fit to the experimentally measured longitudinal and Hall conductivities σxx and σxy, respectively. This method distinguishes itself from other methods by using the so-called QR-algorithm of linear algebra to achieve rapid convergence of the mobility spectrum as the solution to an eigenvalue problem, and by alternately solving this problem in both the mobility domain and its Fourier reciprocal-space. The result accurately fits a mobility range spanning nearly four orders of magnitude (μ = 300 to 1,000,000 cm2/V .s). This method resolves the mobility spectra as well as, or better than, competing MSA methods while also achieving high computational efficiency, requiring less than 30 second on average to converge to a solution on a standard desktop computer. Acknowledgement: Funded by AFOSR FA9550-15-1-0377 and AFOSR FA9550-15-1-0247.

Diffusion length of non-equilibrium minority charge carriers in β-Ga2O3 measured by electron beam induced current

NASA Astrophysics Data System (ADS)

Yakimov, E. B.; Polyakov, A. Y.; Smirnov, N. B.; Shchemerov, I. V.; Yang, Jiancheng; Ren, F.; Yang, Gwangseok; Kim, Jihyun; Pearton, S. J.

2018-05-01

The spatial distribution of electron-hole pair generation in β-Ga2O3 as a function of scanning electron microscope (SEM) beam energy has been calculated by a Monte Carlo method. This spatial distribution is then used to obtain the diffusion length of charge carriers in high-quality epitaxial Ga2O3 films from the dependence of the electron beam induced current (EBIC) collection efficiency on the accelerating voltage of a SEM. The experimental results show, contrary to earlier theory, that holes are mobile in β-Ga2O3 and to a large extent determine the diffusion length of charge carriers. Diffusion lengths in the range 350-400 nm are determined for the as-grown Ga2O3, while processes like exposing the samples to proton irradiation essentially halve this value, showing the role of point defects in controlling minority carrier transport. The pitfalls related to using other popular EBIC-based methods assuming a point-like excitation function are demonstrated. Since the point defect type and the concentration in currently available Ga2O3 are dependent on the growth method and the doping concentration, accurate methods of diffusion length determination are critical to obtain quantitative comparisons of material quality.

Holes influence the mutation spectrum of human mitochondrial DNA

NASA Astrophysics Data System (ADS)

Villagran, Martha; Miller, John

Mutations drive evolution and disease, showing highly non-random patterns of variant frequency vs. nucleotide position. We use computational DNA hole spectroscopy [M.Y. Suarez-Villagran & J.H. Miller, Sci. Rep. 5, 13571 (2015)] to reveal sites of enhanced hole probability in selected regions of human mitochondrial DNA. A hole is a mobile site of positive charge created when an electron is removed, for example by radiation or contact with a mutagenic agent. The hole spectra are quantum mechanically computed using a two-stranded tight binding model of DNA. We observe significant correlation between spectra of hole probabilities and of genetic variation frequencies from the MITOMAP database. These results suggest that hole-enhanced mutation mechanisms exert a substantial, perhaps dominant, influence on mutation patterns in DNA. One example is where a trapped hole induces a hydrogen bond shift, known as tautomerization, which then triggers a base-pair mismatch during replication. Our results deepen overall understanding of sequence specific mutation rates, encompassing both hotspots and cold spots, which drive molecular evolution.

Characterization of few-layered graphene grown by carbon implantation

NASA Astrophysics Data System (ADS)

Lee, Kin Kiong; McCallum, Jeffrey C.; Jamieson, David N.

2014-02-01

Graphene is considered to be a very promising material for applications in nanotechnology. The properties of graphene are strongly dependent on defects that occur during growth and processing. These defects can be either detrimental or beneficial to device performance depending on defect type, location and device application. Here we present experimental results on formation of few-layered graphene by carbon ion implantation into nickel films and characteristics of graphene devices formed by graphene transfer and lithographic patterning. Micro-Raman spectroscopy was used to determine the number of graphene layers formed and identify defects arising from the device processing. The graphene films were cleaned by annealing in vacuum. Transport properties of cleaned graphene films were investigated by fabrication of back-gated field-effect transistors, which exhibited high hole and electron mobility of 1935 and 1905 cm2/Vs, respectively.

Intrachain versus interchain electron transport in poly(fluorene-alt-benzothiadiazole): a quantum-chemical insight.

PubMed

Van Vooren, Antoine; Kim, Ji-Seon; Cornil, Jérôme

2008-05-16

Poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) [F8BT], displays very different charge-transport properties for holes versus electrons when comparing annealed and pristine thin films and transport parallel (intrachain) and perpendicular (interchain) to the polymer axes. The present theoretical contribution focuses on the electron-transport properties of F8BT chains and compares the efficiency of intrachain versus interchain transport in the hopping regime. The theoretical results rationalize significantly lowered electron mobility in annealed F8BT thin films and the smaller mobility anisotropy (mu( parallel)/mu( perpendicular)) measured for electrons in aligned films (i.e. 5-7 compared to 10-15 for holes).

NMR Hole-Burning Experiments on Superionic Conductor Glasses

NASA Astrophysics Data System (ADS)

Kawamura, J.; Kuwata, N.; Hattori, T.

2004-04-01

Inhomogeneity is an inherent nature of glass, which is the density and concentration fluctuation frozen at glass transition temperature. The inhomogeneity of the glass plays significant role in so called superionic conductor glasses (SIG), since the mobile ions seek to move through energetically favorable paths. The localization of mobile ions in SIG near the 2nd glass transition is a remaining issue, where the trapping, percolation and many-body interactions are playing the roles. In order to investigate the trapping process in SIG, the authors have applied 109Ag NMR Hole-Burning technique to AgI containing SIG glasses. By using this technique, the slowing down process of the site-exchange rates between different sites were evaluated.

Study of certain features of the electronic structure of the ternary alloys Ni2(Mn, Fe) and Ni3(Mn, Co)

NASA Technical Reports Server (NTRS)

Zhukova, V. M.; Fadin, V. P.

1981-01-01

The changes in electronic structure related to transport processes occurring during the alloying of he alloy Ni3Mn with iron and cobalt, and the ordering of the ternary alloys thus formed are presented. The Hall effect, the absolute thermal emf, the internal saturation induction, the Nernst-Ettingshausen constant, and the electrical resistivity were measured. Results show a decrease in the contribution of hole sections of the Fermi surface to the transport process occurs together with a considerable increase in the contribution of electron sections. In this case, the mobility of 3 dimensional holes decreases and the mobility of 4s electrons increases considerably.

Experimental and numerical investigation of dual phase steels formability during laser-assisted hole-flanging

NASA Astrophysics Data System (ADS)

Motaman, S. A. H.; Komerla, K.; Storms, T.; Prahl, U.; Brecher, C.; Bleck, W.

2018-05-01

Today, in the automotive industry dual phase (DP) steels are extensively used in the production of various structural parts due to their superior mechanical properties. Hole-flanging of such steels due to simultaneous bending and stretching of sheet metal, is complex and associated with some issues such as strain and strain rate localization, development of micro-cracks, inhomogeneous sheet thinning, etc. In this study an attempt is made to improve the formability of DP sheets, by localized Laser heating. The Laser beam was oscillated in circular pattern rapidly around the pre-hole, blanked prior to the flanging process. In order to investigate formability of DP steel (DP1000), several uniaxial tensile tests were conducted from quasi to intermediate strain rates at different temperatures in warm regime. Additionally, experimentally acquired temperature and strain rate-dependent flow curves were fed into thermomechanical finite element (FE) simulation of the hole-flanging process using the commercial FE software ABAQUS/Explicit. Several FE simulations were performed in order to evaluate the effect of blank's initial temperature and punch speed on deformation localization, stress evolution and temperature distribution in DP1000 sheets during warm hole-flanging process. The experimental and numerical analyses revealed that prescribing a distribution of initial temperature between 300 to 400 °C to the blank and setting a punch speed that accommodates strain rate range of 1 to 5 s-1 in the blank, provides the highest strain hardening capacity in the considered rate and temperature regimes for DP1000. This is in fact largely due to the dynamic strain aging (DSA) effect which occurs due to pinning of mobile dislocations by interstitial solute atoms, particularly at elevated temperatures.

Face-on stacking and enhanced out-of-plane hole mobility in graphene-templated copper phthalocyanine.

PubMed

Mativetsky, Jeffrey M; Wang, He; Lee, Stephanie S; Whittaker-Brooks, Luisa; Loo, Yueh-Lin

2014-05-25

Efficient out-of-plane charge transport is required in vertical device architectures, such as organic solar cells and organic light emitting diodes. Here, we show that graphene, transferred onto different technologically-relevant substrates, can be used to induce face-on molecular stacking and improve out-of-plane hole transport in copper phthalocyanine thin films.

Solution-Processed Cu(In, Ga)(S, Se)2 Nanocrystal as Inorganic Hole-Transporting Material for Efficient and Stable Perovskite Solar Cells.

PubMed

Xu, Lu; Deng, Lin-Long; Cao, Jing; Wang, Xin; Chen, Wei-Yi; Jiang, Zhiyuan

2017-12-01

Perovskite solar cells are emerging as one of the most promising candidates for solar energy harvesting. To date, most of the high-performance perovskite solar cells have exclusively employed organic hole-transporting materials (HTMs) such as 2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-OMeTAD) or polytriarylamine (PTAA) which are often expensive and have low hole mobility. Almost all these HTMs reported needed lithium salt, e.g., lithium bis(trifluoromethylsulfonyl)imide (Li-TFSI) doping, to improve hole mobility and performance. However, the use of Li-TFSI should be avoided because the hygroscopic nature of Li-TFSI could cause decomposition of perovskite and reduce device stability. Herein, we employed solution-processed CuIn 0.1 Ga 0.9 (S 0.9 Se 0.1 ) 2 (CIGSSe) nanocrystals as a novel inorganic HTM in perovskite solar cells. A power conversion efficiency of 9.15% was obtained for CIGSSe-based devices with improved stability, compared to devices using spiro-OMeTAD as HTM. This work offers a promising candidate of Cu-based inorganic HTM for efficient and stable perovskite solar cells.

Defect chemistry and characterization of (Hg, Cd)Te

NASA Technical Reports Server (NTRS)

Vydyanath, H. R.

1981-01-01

Single crystal samples of phosphorus doped Hg sub 0.8 Cd sub 0.2 Te were anneald at temperatures varying from 450 C to 600 C in various Hg atmospheres. The samples were quenched to room temperature from the annealing temperatures. Hall effect and mobility measurements were performed at 77 K on all these samples. The results indicate the crystals to be p type for a total phosphorus concentration of 10 to the 19th power/cu cm in all the samples. The hole concentration at 77 K increases with increasing Hg pressures at 450 C and 500 C contrary to the observation in undoped crystals. Also, at low Hg pressures the concentration of holes in the phosphorus doped crystals is lower than in the undoped crystals. The hole concentration in all the samples is lower than the intrinsic carrier concentration at the annealing temperatures. The hole mobility in the doped crystals is similar to that in the undoped crystals. A defect model according to which phosphorus behaves as a single acceptor interstitially, occupying Te lattice sites while it acts as a single donor occupying Hg lattice sites was established. Equilibrum constants established for the incorporation of all the phosphorus species explain the experimental results

Influence of Nonfused Cores on the Photovoltaic Performance of Linear Triphenylamine-Based Hole-Transporting Materials for Perovskite Solar Cells.

PubMed

Wu, Yungen; Wang, Zhihui; Liang, Mao; Cheng, Hua; Li, Mengyuan; Liu, Liyuan; Wang, Baiyue; Wu, Jinhua; Prasad Ghimire, Raju; Wang, Xuda; Sun, Zhe; Xue, Song; Qiao, Qiquan

2018-05-30

The core plays a crucial role in achieving high performance of linear hole transport materials (HTMs) toward the perovskite solar cells (PSCs). Most studies focused on the development of fused heterocycles as cores for HTMs. Nevertheless, nonfused heterocycles deserve to be studied since they can be easily synthesized. In this work, we reported a series of low-cost triphenylamine HTMs (M101-M106) with different nonfused cores. Results concluded that the introduced core has a significant influence on conductivity, hole mobility, energy level, and solubility of linear HTMs. M103 and M104 with nonfused oligothiophene cores are superior to other HTMs in terms of conductivity, hole mobility, and surface morphology. PSCs based on M104 exhibited the highest power conversion efficiency of 16.50% under AM 1.5 sun, which is comparable to that of spiro-OMeTAD (16.67%) under the same conditions. Importantly, the employment of M104 is highly economical in terms of the cost of synthesis as compared to that of spiro-OMeTAD. This work demonstrated that nonfused heterocycles, such as oligothiophene, are promising cores for high performance of linear HTMs toward PSCs.

Extremely large magnetoresistance induced by Zeeman effect-driven electron-hole compensation and topological protection in MoSi2

NASA Astrophysics Data System (ADS)

Matin, M.; Mondal, Rajib; Barman, N.; Thamizhavel, A.; Dhar, S. K.

2018-05-01

Here, we report an extremely large positive magnetoresistance (XMR) in a single-crystal sample of MoSi2, approaching almost 107% at 2 K in a 14-T magnetic field without appreciable saturation. Hall resistivity data reveal an uncompensated nature of MoSi2 with an electron-hole compensation level sufficient enough to expect strong saturation of magnetoresistance in the high-field regime. Magnetotransport and the complementary de Haas-van Alphen (dHvA) oscillations results, however, suggest that strong Zeeman effect causes a magnetic field-induced modulation of the Fermi pockets and drives the system towards perfect electron-hole compensation condition in the high-field regime. Thus, the nonsaturating XMR of this semimetal arises under the unconventional situation of Zeeman effect-driven electron-hole compensation, whereas its huge magnitude is decided solely by the ultralarge value of the carrier mobility. Intrinsic ultralarge carrier mobility, strong suppression of backward scattering of the charge carriers, and nontrivial Berry phase in dHvA oscillations attest to the topological character of MoSi2. Therefore, this semimetal represents another material hosting combination of topological and conventional electronic phases.

Radiation characteristics of multiple and single sound hole vihuelas and a classical guitar.

PubMed

Bader, Rolf

2012-01-01

Two recently built vihuelas, quasi-replicas of the Spanish Renaissance guitar, one with a small body and one sound hole and one with a large body with five sound holes, together with a classical guitar are investigated. Frequency dependent radiation strengths are measured using a 128 microphone array, back-propagating the frequency dependent sound field upon the body surface. All three instruments have a strong sound hole radiation within the low frequency range. Here the five tone holes vihuela has a much wider frequency region of strong sound hole radiation up to about 500 Hz, whereas the single hole instruments only have strong sound hole radiations up to about 300 Hz due to the enlarged radiation area of the sound holes. The strong broadband radiation of the five sound hole vihuela up to about 500 Hz is also caused by the sound hole phases, showing very consistent in-phase relations up to this frequency range. Also the radiation strength of the sound holes placed nearer to the center of the sound box are much stronger than those near the ribs, pointing to a strong position dependency of sound hole to radiation strength. The Helmholtz resonance frequency of the five sound hole vihuela is influenced by this difference in radiation strength but not by the rosettas, which only have a slight effect on the Helmholtz frequency. © 2012 Acoustical Society of America.

Engineering of electronic properties of single layer graphene by swift heavy ion irradiation

NASA Astrophysics Data System (ADS)

Kumar, Sunil; Kumar, Ashish; Tripathi, Ambuj; Tyagi, Chetna; Avasthi, D. K.

2018-04-01

In this work, swift heavy ion irradiation induced effects on the electrical properties of single layer graphene are reported. The modulation in minimum conductivity point in graphene with in-situ electrical measurement during ion irradiation was studied. It is found that the resistance of graphene layer decreases at lower fluences up to 3 × 1011 ions/cm2, which is accompanied by the five-fold increase in electron and hole mobilities. The ion irradiation induced increase in electron and hole mobilities at lower fluence up to 1 × 1011 ions/cm2 is verified by separate Hall measurements on another irradiated graphene sample at the selected fluence. In contrast to the adverse effects of irradiation on the electrical properties of materials, we have found improvement in electrical mobility after irradiation. The increment in mobility is explained by considering the defect annealing in graphene after irradiation at a lower fluence regime. The modification in carrier density after irradiation is also observed. Based on findings of the present work, we suggest ion beam irradiation as a useful tool for tuning of the electrical properties of graphene.

Electron-acoustic phonon coupling in single crystal CH3NH3PbI3 perovskites revealed by coherent acoustic phonons

NASA Astrophysics Data System (ADS)

Mante, Pierre-Adrien; Stoumpos, Constantinos C.; Kanatzidis, Mercouri G.; Yartsev, Arkady

2017-02-01

Despite the great amount of attention CH3NH3PbI3 has received for its solar cell application, intrinsic properties of this material are still largely unknown. Mobility of charges is a quintessential property in this aspect; however, there is still no clear understanding of electron transport, as reported values span over three orders of magnitude. Here we develop a method to measure the electron and hole deformation potentials using coherent acoustic phonons generated by femtosecond laser pulses. We apply this method to characterize a CH3NH3PbI3 single crystal. We measure the acoustic phonon properties and characterize electron-acoustic phonon scattering. Then, using the deformation potential theory, we calculate the carrier intrinsic mobility and compare it to the reported experimental and theoretical values. Our results reveal high electron and hole mobilities of 2,800 and 9,400 cm2 V-1 s-1, respectively. Comparison with literature values of mobility demonstrates the potential role played by polarons in charge transport in CH3NH3PbI3.

Intrinsic Charge Carrier Mobility in Single-Layer Black Phosphorus.

PubMed

Rudenko, A N; Brener, S; Katsnelson, M I

2016-06-17

We present a theory for single- and two-phonon charge carrier scattering in anisotropic two-dimensional semiconductors applied to single-layer black phosphorus (BP). We show that in contrast to graphene, where two-phonon processes due to the scattering by flexural phonons dominate at any practically relevant temperatures and are independent of the carrier concentration n, two-phonon scattering in BP is less important and can be considered negligible at n≳10^{13}  cm^{-2}. At smaller n, however, phonons enter in the essentially anharmonic regime. Compared to the hole mobility, which does not exhibit strong anisotropy between the principal directions of BP (μ_{xx}/μ_{yy}∼1.4 at n=10^{13} cm^{-2} and T=300  K), the electron mobility is found to be significantly more anisotropic (μ_{xx}/μ_{yy}∼6.2). Absolute values of μ_{xx} do not exceed 250 (700)  cm^{2} V^{-1} s^{-1} for holes (electrons), which can be considered as an upper limit for the mobility in BP at room temperature.

Hawking radiation power equations for black holes

NASA Astrophysics Data System (ADS)

Mistry, Ravi; Upadhyay, Sudhaker; Ali, Ahmed Farag; Faizal, Mir

2017-10-01

We derive the Hawking radiation power equations for black holes in asymptotically flat, asymptotically Anti-de Sitter (AdS) and asymptotically de Sitter (dS) black holes. This is done by using the greybody factor for these black holes. We observe that the radiation power equation for asymptotically flat black holes, corresponding to greybody factor at low frequency, depends on both the Hawking temperature and the horizon radius. However, for the greybody factors at asymptotic frequency, it only depends on the Hawking temperature. We also obtain the power equation for asymptotically AdS black holes both below and above the critical frequency. The radiation power equation for at asymptotic frequency is same for both Schwarzschild AdS and Reissner-Nordström AdS solutions and only depends on the Hawking temperature. We also discuss the power equation for asymptotically dS black holes at low frequency, for both even or odd dimensions.

Growth of strained Si/relaxed SiGe heterostructures on Si(110) substrates using solid-source molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Arimoto, Keisuke; Nakazawa, Hiroki; Mitsui, Shohei; Utsuyama, Naoto; Yamanaka, Junji; Hara, Kosuke O.; Usami, Noritaka; Nakagawa, Kiyokazu

2017-11-01

A strained Si/relaxed SiGe heterostructure grown on Si(110) substrate is attractive as a platform for high-hole-mobility Si-based electronic devices. To improve the electrical property, a smoother surface is desirable. In this study, we investigated surface morphology and microstructural aspects of strained Si/relaxed SiGe/Si(110) heterostructures grown by solid-source (SS) molecular beam epitaxy (MBE). It was revealed that SSMBE provides a way to grow strained Si/relaxed SiGe heterostructures with smooth surfaces. In addition, it was found that the strain in the SiGe layer of the SSMBE-grown sample is highly anisotropic whereas that of the GSMBE-grown sample is almost biaxially relaxed. Along with the surface morphology, the symmetry in degree of strain relaxation has implications for the electrical property. Results of a calculation shows that anisotropic strain is preferable for device application since it confines holes solely in the strained Si layer where hole mobility is enhanced.

Effect of strain on the Curie temperature and band structure of low-dimensional SbSI

NASA Astrophysics Data System (ADS)

Wang, Yiping; Hu, Yang; Chen, Zhizhong; Guo, Yuwei; Wang, Dong; Wertz, Esther A.; Shi, Jian

2018-04-01

Photoferroelectric materials show great promise for developing alternative photovoltaics and photovoltaic-type non-volatile memories. However, the localized nature of the d orbital and large bandgap of most natural photoferroelectric materials lead to low electron/hole mobility and limit the realization of technologically practical devices. Antimony sulpho-iodide (SbSI) is a photoferroelectric material which is expected to have high electron/hole mobility in the ferroelectric state due to its non-local band dispersion and narrow bandgap. However, SbSI exhibits the paraelectric state close to room temperature. In this report, as a proof of concept, we explore the possibility to stabilize the SbSI ferroelectric phase above room temperature via mechanical strain engineering. We synthesized thin low-dimensional crystals of SbSI by chemical vapor deposition, confirmed its crystal structure with electron diffraction, studied its optical properties via photoluminescence spectroscopy and time-resolved photoluminescence spectroscopy, and probed its phase transition using temperature-dependent steady-state photoluminescence spectroscopy. We found that introducing external mechanical strain to these low-dimensional crystals may lead to an increase in their Curie temperature (by ˜60 K), derived by the strain-modified optical phase transition in SbSI and quantified by Kern formulation and Landau theory. The study suggests that strain engineering could be an effective way to stabilize the ferroelectric phase of SbSI at above room temperature, providing a solution enabling its application for technologically useful photoferroelectric devices.

CuI as Hole-Transport Channel for Enhancing Photoelectrocatalytic Activity by Constructing CuI/BiOI Heterojunction.

PubMed

Sun, Mingjuan; Hu, Jiayue; Zhai, Chunyang; Zhu, Mingshan; Pan, Jianguo

2017-04-19

In this paper, CuI, as a typical hole-transport channel, was used to construct a high-performance visible-light-driven CuI/BiOI heterostructure for photoelectrocatalytic applications. The heterostructure combines the broad visible absorption of BiOI and high hole mobility of CuI. Compared to pure BiOI, the CuI/BiOI heterostructure exhibited distinctly enhanced photoelectrocatalytic performance for the oxidation of methanol and organic pollutants under visible-light irradiation. The photogenerated electron-hole pairs of the excited BiOI can be separated efficiently through CuI, in which the CuI acts as a superior hole-transport channel to improve photoelectrocatalytic oxidization of methanol and organic pollutants. The outstanding photoelectrocatalytic activity shows that the p-type CuI works as a promising hole-transport channel to improve the photocatalytic performance of traditional semiconductors.

Extremely large nonsaturating magnetoresistance and ultrahigh mobility due to topological surface states in the metallic Bi2Te3 topological insulator

NASA Astrophysics Data System (ADS)

Shrestha, K.; Chou, M.; Graf, D.; Yang, H. D.; Lorenz, B.; Chu, C. W.

2017-05-01

Weak antilocalization (WAL) effects in Bi2Te3 single crystals have been investigated at high and low bulk charge-carrier concentrations. At low charge-carrier density the WAL curves scale with the normal component of the magnetic field, demonstrating the dominance of topological surface states in magnetoconductivity. At high charge-carrier density the WAL curves scale with neither the applied field nor its normal component, implying a mixture of bulk and surface conduction. WAL due to topological surface states shows no dependence on the nature (electrons or holes) of the bulk charge carriers. The observations of an extremely large nonsaturating magnetoresistance and ultrahigh mobility in the samples with lower carrier density further support the presence of surface states. The physical parameters characterizing the WAL effects are calculated using the Hikami-Larkin-Nagaoka formula. At high charge-carrier concentrations, there is a greater number of conduction channels and a decrease in the phase coherence length compared to low charge-carrier concentrations. The extremely large magnetoresistance and high mobility of topological insulators have great technological value and can be exploited in magnetoelectric sensors and memory devices.

Black phosphorus-monolayer MoS2 van der Waals heterojunction p-n diode.

PubMed

Deng, Yexin; Luo, Zhe; Conrad, Nathan J; Liu, Han; Gong, Yongji; Najmaei, Sina; Ajayan, Pulickel M; Lou, Jun; Xu, Xianfan; Ye, Peide D

2014-08-26

Phosphorene, a elemental 2D material, which is the monolayer of black phosphorus, has been mechanically exfoliated recently. In its bulk form, black phosphorus shows high carrier mobility (∼10,000 cm(2)/V·s) and a ∼0.3 eV direct band gap. Well-behaved p-type field-effect transistors with mobilities of up to 1000 cm(2)/V·s, as well as phototransistors, have been demonstrated on few-layer black phosphorus, showing its promise for electronics and optoelectronics applications due to its high hole mobility and thickness-dependent direct band gap. However, p–n junctions, the basic building blocks of modern electronic and optoelectronic devices, have not yet been realized based on black phosphorus. In this paper, we demonstrate a gate-tunable p–n diode based on a p-type black phosphorus/n-type monolayer MoS2 van der Waals p–n heterojunction. Upon illumination, these ultrathin p–n diodes show a maximum photodetection responsivity of 418 mA/W at the wavelength of 633 nm and photovoltaic energy conversion with an external quantum efficiency of 0.3%. These p–n diodes show promise for broad-band photodetection and solar energy harvesting.

Transport properties of ultrathin black phosphorus on hexagonal boron nitride

DOE Office of Scientific and Technical Information (OSTI.GOV)

Doganov, Rostislav A.; Özyilmaz, Barbaros; Department of Physics, National University of Singapore, 2 Science Drive 3, 117542 Singapore

2015-02-23

Ultrathin black phosphorus, or phosphorene, is a two-dimensional material that allows both high carrier mobility and large on/off ratios. Similar to other atomic crystals, like graphene or layered transition metal dichalcogenides, the transport behavior of few-layer black phosphorus is expected to be affected by the underlying substrate. The properties of black phosphorus have so far been studied on the widely utilized SiO{sub 2} substrate. Here, we characterize few-layer black phosphorus field effect transistors on hexagonal boron nitride—an atomically smooth and charge trap-free substrate. We measure the temperature dependence of the field effect mobility for both holes and electrons and explainmore » the observed behavior in terms of charged impurity limited transport. We find that in-situ vacuum annealing at 400 K removes the p-doping of few-layer black phosphorus on both boron nitride and SiO{sub 2} substrates and reduces the hysteresis at room temperature.« less

Black Phosphorus Quantum Dots for Hole Extraction of Typical Planar Hybrid Perovskite Solar Cells.

PubMed

Chen, Wei; Li, Kaiwen; Wang, Yao; Feng, Xiyuan; Liao, Zhenwu; Su, Qicong; Lin, Xinnan; He, Zhubing

2017-02-02

Black phosphorus, famous as two-dimensional (2D) materials, shows such excellent properties for optoelectronic devices such as tunable direct band gap, extremely high hole mobility (300-1000 cm 2 /(V s)), and so forth. In this Letter, facile processed black phosphorus quantum dots (BPQDs) were successfully applied to enhance hole extraction at the anode side of the typical p-i-n planar hybrid perovskite solar cells, which remarkably improved the performance of devices with photon conversion efficiency ramping up from 14.10 to 16.69%. Moreover, more detailed investigations by c-AFM, SKPM, SEM, hole-only devices, and photon physics measurements discover further the hole extraction effect and work mechanism of the BPQDs, such as nucleation assistance for the growth of large grain size perovskite crystals, fast hole extraction, more efficient hole transfer, and suppression of energy-loss recombination at the anode interface. This work definitely paves the way for discovering more and more 2D materials with high electronic properties to be used in photovoltaics and optoelectronics.

Hall effect measurements of high-quality M n3CuN thin films and the electronic structure

NASA Astrophysics Data System (ADS)

Matsumoto, Toshiki; Hatano, Takafumi; Urata, Takahiro; Iida, Kazumasa; Takenaka, Koshi; Ikuta, Hiroshi

2017-11-01

The physical properties of M n3CuN were studied using thin films. We found that an annealing process was very effective to improve the film quality, the key of which was the use of Ti that prevented the formation of oxide impurities. Using these high-quality thin films, we found strong strain dependence for the ferromagnetic transition temperature (TC) and a sign change of the Hall coefficient at TC. The analysis of Hall coefficient data revealed a sizable decrease of hole concentration and a large increase of electron mobility below TC, which is discussed in relation to the electronic structure of this material.

Electron holes appear to trigger cancer-implicated mutations

NASA Astrophysics Data System (ADS)

Miller, John; Villagran, Martha

Malignant tumors are caused by mutations, which also affect their subsequent growth and evolution. We use a novel approach, computational DNA hole spectroscopy [M.Y. Suarez-Villagran & J.H. Miller, Sci. Rep. 5, 13571 (2015)], to compute spectra of enhanced hole probability based on actual sequence data. A hole is a mobile site of positive charge created when an electron is removed, for example by radiation or contact with a mutagenic agent. Peaks in the hole spectrum depict sites where holes tend to localize and potentially trigger a base pair mismatch during replication. Our studies of reveal a correlation between hole spectrum peaks and spikes in human mutation frequencies. Importantly, we also find that hole peak positions that do not coincide with large variant frequencies often coincide with cancer-implicated mutations and/or (for coding DNA) encoded conserved amino acids. This enables combining hole spectra with variant data to identify critical base pairs and potential cancer `driver' mutations. Such integration of DNA hole and variance spectra could also prove invaluable for pinpointing critical regions, and sites of driver mutations, in the vast non-protein-coding genome. Supported by the State of Texas through the Texas Ctr. for Superconductivity.

Effect of traps on the charge transport in semiconducting polymer PCDTBT

NASA Astrophysics Data System (ADS)

Khan, Mohd Taukeer; Agrawal, Vikash; Almohammedi, Abdullah; Gupta, Vinay

2018-07-01

Organic semiconductors (OSCs) are nowadays called upon as promising candidates for next generation electronics devices. Due to disorder structure of these materials, a high density of traps are present in their energy band gap which affect the performance of these devices. In the present manuscript, we have investigated the role of traps on charge transport in PCDTBT thin film by measuring the temperature dependent J(V) characteristics in hole only device configuration. The obtained results were analyzed by space charge limited (SCL) conduction model. It has been found that the room temperature J(V) characteristics follow Mott-Gurney square law for trap-free SCL conduction. But below 278 K, the current increases according to trap-filling SCL law with traps distributed exponentially in the band gap of semiconductor. Furthermore, after reaching a crossover voltage of VC ∽ 12 V, all the traps filled by injected carriers and the trap-filling SCL current switch to trap-free SCL current. The hole mobility of trap-free SCL current is about one order higher as compared trap-filling SCL current and remains constant with temperature.

High-performance multilayer WSe 2 field-effect transistors with carrier type control

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pudasaini, Pushpa Raj; Oyedele, Akinola; Zhang, Cheng

In this paper, high-performance multilayer WSe 2 field-effect transistor (FET) devices with carrier type control are demonstrated via thickness modulation and a remote oxygen plasma surface treatment. Carrier type control in multilayer WSe 2 FET devices with Cr/Au contacts is initially demonstrated by modulating the WSe 2 thickness. The carrier type evolves with increasing WSe 2 channel thickness, being p-type, ambipolar, and n-type at thicknesses <3, ~4, and >5 nm, respectively. The thickness-dependent carrier type is attributed to changes in the bandgap of WSe 2 as a function of the thickness and the carrier band offsets relative to the metalmore » contacts. Furthermore, we present a strong hole carrier doping effect via remote oxygen plasma treatment. It non-degenerately converts n-type characteristics into p-type and enhances field-effect hole mobility by three orders of magnitude. Finally, this work demonstrates progress towards the realization of high-performance multilayer WSe 2 FETs with carrier type control, potentially extendable to other transition metal dichalcogenides, for future electronic and optoelectronic applications.« less

High-performance multilayer WSe 2 field-effect transistors with carrier type control

DOE PAGES

Pudasaini, Pushpa Raj; Oyedele, Akinola; Zhang, Cheng; ...

2017-07-06

In this paper, high-performance multilayer WSe 2 field-effect transistor (FET) devices with carrier type control are demonstrated via thickness modulation and a remote oxygen plasma surface treatment. Carrier type control in multilayer WSe 2 FET devices with Cr/Au contacts is initially demonstrated by modulating the WSe 2 thickness. The carrier type evolves with increasing WSe 2 channel thickness, being p-type, ambipolar, and n-type at thicknesses <3, ~4, and >5 nm, respectively. The thickness-dependent carrier type is attributed to changes in the bandgap of WSe 2 as a function of the thickness and the carrier band offsets relative to the metalmore » contacts. Furthermore, we present a strong hole carrier doping effect via remote oxygen plasma treatment. It non-degenerately converts n-type characteristics into p-type and enhances field-effect hole mobility by three orders of magnitude. Finally, this work demonstrates progress towards the realization of high-performance multilayer WSe 2 FETs with carrier type control, potentially extendable to other transition metal dichalcogenides, for future electronic and optoelectronic applications.« less

Prediction of charge mobility in organic semiconductors with consideration of the grain-size effect

NASA Astrophysics Data System (ADS)

Park, Jin Woo; Lee, Kyu Il; Choi, Youn-Suk; Kim, Jung-Hwa; Jeong, Daun; Kwon, Young-Nam; Park, Jong-Bong; Ahn, Ho Young; Park, Jeong-Il; Lee, Hyo Sug; Shin, Jaikwang

2016-09-01

A new computational model to predict the hole mobility of poly-crystalline organic semiconductors in thin film was developed (refer to Phys. Chem. Chem. Phys., 2016, DOI: 10.1039/C6CP02993K). Site energy differences and transfer integrals in crystalline morphologies of organic molecules were obtained from quantum chemical calculation, in which the periodic boundary condition was efficiently applied to capture the interactions with the surrounding molecules in the crystalline organic layer. Then the parameters were employed in kinetic Monte Carlo (kMC) simulations to estimate the carrier mobility. Carrier transport in multiple directions has been considered in the kMC simulation to mimic polycrystalline characteristic in thin-film condition. Furthermore, the calculated mobility was corrected with a calibration equation based on the microscopic images of thin films to take the effect of grain boundary into account. As a result, good agreement was observed between the predicted and measured hole mobility values for 21 molecular species: the coefficient of determination (R2) was estimated to be 0.83 and the mean absolute error was 1.32 cm2 V-1 s-1. This numerical approach can be applied to any molecules for which crystal structures are available and will provide a rapid and precise way of predicting the device performance.

Compensation of native donor doping in ScN: Carrier concentration control and p-type ScN

NASA Astrophysics Data System (ADS)

Saha, Bivas; Garbrecht, Magnus; Perez-Taborda, Jaime A.; Fawey, Mohammed H.; Koh, Yee Rui; Shakouri, Ali; Martin-Gonzalez, Marisol; Hultman, Lars; Sands, Timothy D.

2017-06-01

Scandium nitride (ScN) is an emerging indirect bandgap rocksalt semiconductor that has attracted significant attention in recent years for its potential applications in thermoelectric energy conversion devices, as a semiconducting component in epitaxial metal/semiconductor superlattices and as a substrate material for high quality GaN growth. Due to the presence of oxygen impurities and native defects such as nitrogen vacancies, sputter-deposited ScN thin-films are highly degenerate n-type semiconductors with carrier concentrations in the (1-6) × 1020 cm-3 range. In this letter, we show that magnesium nitride (MgxNy) acts as an efficient hole dopant in ScN and reduces the n-type carrier concentration, turning ScN into a p-type semiconductor at high doping levels. Employing a combination of high-resolution X-ray diffraction, transmission electron microscopy, and room temperature optical and temperature dependent electrical measurements, we demonstrate that p-type Sc1-xMgxN thin-film alloys (a) are substitutional solid solutions without MgxNy precipitation, phase segregation, or secondary phase formation within the studied compositional region, (b) exhibit a maximum hole-concentration of 2.2 × 1020 cm-3 and a hole mobility of 21 cm2/Vs, (c) do not show any defect states inside the direct gap of ScN, thus retaining their basic electronic structure, and (d) exhibit alloy scattering dominating hole conduction at high temperatures. These results demonstrate MgxNy doped p-type ScN and compare well with our previous reports on p-type ScN with manganese nitride (MnxNy) doping.

Role of electron-phonon coupling and thermal expansion on band gaps, carrier mobility, and interfacial offsets in kesterite thin-film solar cells

NASA Astrophysics Data System (ADS)

Monserrat, Bartomeu; Park, Ji-Sang; Kim, Sunghyun; Walsh, Aron

2018-05-01

The efficiencies of solar cells based on kesterite Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4 (CZTSe) are limited by a low open-circuit voltage due to high rates of non-radiative electron-hole recombination. To probe the origin of this bottleneck, we calculate the band offset of CZTS(Se) with CdS, confirming a weak spike of 0.1 eV for CZTS/wurtzite-CdS and a strong spike of 0.4 eV for CZTSe/wurtzite-CdS. We also consider the effects of temperature on the band alignment, finding that increasing temperature significantly enhances the spike-type offset. We further resolve an outstanding discrepancy between the measured and calculated phonon frequencies for the kesterites, and use these to estimate the upper limit of electron and hole mobilities based on optic phonon Fröhlich scattering, which uncovers an intrinsic asymmetry with faster (minority carrier) electron mobility.

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

PubMed Central

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

2013-01-01

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

Light intensity dependence of open-circuit voltage and short-circuit current of polymer/fullerene solar cells

NASA Astrophysics Data System (ADS)

Koster, L. Jan A.; Mihailetchi, Valentin D.; Ramaker, Robert; Xie, Hangxing; Blom, Paul W. M.

2006-04-01

The open-circuit voltage (Voc) of polymer/fullerene bulk heterojunction solar cells is investigated as a function of light intensity for different temperatures. The observed photogenerated current and V oc are at variance with classical p-n junctionbased models. The influence of light intensity and recombination strength on V oc is consistently explained by a model based on the notion that the quasi-Fermi levels are constant throughout the device, including both drift and diffusion of charge carriers. The light intensity dependence of the short-circuit current density (J sc) is also addressed. A typical feature of polymer/fullerene based solar cells is that Jsc does not scale exactly linearly with light intensity (I). Instead, a power law relationship is found given by Jsc~ Iα, where α ranges from 0.9 to 1. In a number of reports this deviation from unity is attributed to the occurrence of bimolecular recombination. We demonstrate that the dependence of the photocurrent in bulk heterojunction solar cells is governed by the build-up of space charge in the device. The occurrence of space-charge stems from the difference in charge carrier mobility of electrons and holes. In blends of poly(3-hexylthiophene) and 6,6- phenyl C61-butyric acid methyl ester this mobility difference can be tuned in between one and three orders of magnitude, depending on the annealing conditions. This allows us to experimentally verify the relation between space charge build-up and intensity dependence of Jsc. Model calculations confirm that bimolecular recombination leads only to a typical loss of 1% of all free charge carriers at Jsc for these devices. Therefore, bimolecular recombination plays only a minor role as compared to the effect of space charge in the intensity dependence of J sc.

Bipolar molecular composites: a new class of high-electron-mobility organic solids

NASA Astrophysics Data System (ADS)

Lin, Liang-Bih; Jenekhe, Samson A.; Borsenberger, Paul M.

1997-10-01

We describe high electron mobility in organic solids in the form of bipolar molecular composites of N,N'-bis(1,2-dimethylpropyl)-1,4,5,8-naphthalenetetracarboxylic diimide (NTDI) and tri-p-tolylaniine (TTA). The electron mobility in the NTDI/TTA composites is ~2 x 10 cm2/Vs, which is a factor of 4 to 6 higher than in pure NTDI and isone of the highest values reported for disordered organic solids. The field and temperature dependencies of the charge mobility can be described using the disorder formalism due to Bassler and co-workers, which provides an estimation of the energy width σ of the hopping site manifold. Analysis of the data gave σ=0.081 and 0.060 eV for the electron and hole mobilities in a NTDI/TTA composite of 0.5510.45 molar ratio. The energetic disorder for electron transport in the bipolar composites is substantially lower than for pure NTDI, which is 0.093 eV. The results suggest that the observed enhancement arises from a substantial reduction of energetic disorder in the electron transport manifold of the bipolar composites. The reduction of energetic disorder may be due to intermolecular charge transfer between NTDI and TTA. Such a charge transfer could stabilize the electron transport manifold by better charge delocalization, and consequently, less energetic disorder. Another possible reason for the observed enhanced electron mobility is the reduction of NTDI dimers that can act as carrier traps by the presence of TTA molecules in the bipolar composites. These results also suggest that bipolar composites represent a promising new class of high electron mobility organic solids.

Radical Beam Gettering Epitaxy of Zno and Gan

NASA Astrophysics Data System (ADS)

Georgobiani, A. N.; Demin, V. I.; Vorobiev, M. O.; Gruzintsev, A. N.; Hodos, I. I.; Kotljarevsky, M. B.; Kidalov, V. V.; Rogozin, I. V.

2002-11-01

P-type ZnO layers with a hole mobility about 23 cm2/(V s), and a hole concentration about 1015 cm-3 were grown by means of radical-beam gettering epitaxy (the annealing of n-ZnO single crystals in atomic oxygen flux). The effect of native defects on the photoluminescence spectra of the layers was studied. The dominant bands in the spectra peaked at 370.2 and 400 nm. These bands were attributed to the annihilation of exciton localised on neutral Vzn and to electron transitions from the conduction band to singly positively charged Vzn correspondingly. The effect of annealing in atomic nitrogen flux of p-CaN:Mg films on their photoluminescence spectra and on the value of their conductivity were studied. Such annealing leads to appearance of a number of emission bands that peaked at 404.9, 390.8 and 378.9 nm and increases hole concentration from 5 × 1015 to 5 × 1016 cm-3, and the hole mobility from 120 to 150 cm2/(V s). The n-ZnO - p-GaN:Mg electroluminescence heterostructures were obtained. Their spectrum contains bands in the excitonic region of GaN at the wavelength 360.2 nm and in the edge region at wavelengths 378.9 and 390.8 nm.

Soft hair of dynamical black hole and Hawking radiation

NASA Astrophysics Data System (ADS)

Chu, Chong-Sun; Koyama, Yoji

2018-04-01

Soft hair of black hole has been proposed recently to play an important role in the resolution of the black hole information paradox. Recent work has emphasized that the soft modes cannot affect the black hole S-matrix due to Weinberg soft theorems. However as soft hair is generated by supertranslation of geometry which involves an angular dependent shift of time, it must have non-trivial quantum effects. We consider supertranslation of the Vaidya black hole and construct a non-spherical symmetric dynamical spacetime with soft hair. We show that this spacetime admits a trapping horizon and is a dynamical black hole. We find that Hawking radiation is emitted from the trapping horizon of the dynamical black hole. The Hawking radiation has a spectrum which depends on the soft hair of the black hole and this is consistent with the factorization property of the black hole S-matrix.

Comparative investigation of surface transfer doping of hydrogen terminated diamond by high electron affinity insulators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Verona, C.; Marinelli, Marco; Verona-Rinati, G.

We report on a comparative study of transfer doping of hydrogenated single crystal diamond surface by insulators featured by high electron affinity, such as Nb{sub 2}O{sub 5}, WO{sub 3}, V{sub 2}O{sub 5}, and MoO{sub 3}. The low electron affinity Al{sub 2}O{sub 3} was also investigated for comparison. Hole transport properties were evaluated in the passivated hydrogenated diamond films by Hall effect measurements, and were compared to un-passivated diamond films (air-induced doping). A drastic improvement was observed in passivated samples in terms of conductivity, stability with time, and resistance to high temperatures. The efficiency of the investigated insulators, as electron acceptingmore » materials in hydrogenated diamond surface, is consistent with their electronic structure. These surface acceptor materials generate a higher hole sheet concentration, up to 6.5 × 10{sup 13} cm{sup −2}, and a lower sheet resistance, down to 2.6 kΩ/sq, in comparison to the atmosphere-induced values of about 1 × 10{sup 13} cm{sup −2} and 10 kΩ/sq, respectively. On the other hand, hole mobilities were reduced by using high electron affinity insulator dopants. Hole mobility as a function of hole concentration in a hydrogenated diamond layer was also investigated, showing a well-defined monotonically decreasing trend.« less

Adaptive threshold determination for efficient channel sensing in cognitive radio network using mobile sensors

NASA Astrophysics Data System (ADS)

Morshed, M. N.; Khatun, S.; Kamarudin, L. M.; Aljunid, S. A.; Ahmad, R. B.; Zakaria, A.; Fakir, M. M.

2017-03-01

Spectrum saturation problem is a major issue in wireless communication systems all over the world. Huge number of users is joining each day to the existing fixed band frequency but the bandwidth is not increasing. These requirements demand for efficient and intelligent use of spectrum. To solve this issue, the Cognitive Radio (CR) is the best choice. Spectrum sensing of a wireless heterogeneous network is a fundamental issue to detect the presence of primary users' signals in CR networks. In order to protect primary users (PUs) from harmful interference, the spectrum sensing scheme is required to perform well even in low signal-to-noise ratio (SNR) environments. Meanwhile, the sensing period is usually required to be short enough so that secondary (unlicensed) users (SUs) can fully utilize the available spectrum. CR networks can be designed to manage the radio spectrum more efficiently by utilizing the spectrum holes in primary user's licensed frequency bands. In this paper, we have proposed an adaptive threshold detection method to detect presence of PU signal using free space path loss (FSPL) model in 2.4 GHz WLAN network. The model is designed for mobile sensors embedded in smartphones. The mobile sensors acts as SU while the existing WLAN network (channels) works as PU. The theoretical results show that the desired threshold range detection of mobile sensors mainly depends on the noise floor level of the location in consideration.

Use of interfacial layers to prolong hole lifetimes in hematite probed by ultrafast transient absorption spectroscopy

NASA Astrophysics Data System (ADS)

Paradzah, Alexander T.; Diale, Mmantsae; Maabong, Kelebogile; Krüger, Tjaart P. J.

2018-04-01

Hematite is a widely investigated material for applications in solar water oxidation due primarily to its small bandgap. However, full realization of the material continues to be hampered by fast electron-hole recombination rates among other weaknesses such as low hole mobility, short hole diffusion length and low conductivity. To address the problem of fast electron-hole recombination, researchers have resorted to growth of nano-structured hematite, doping and use of under-layers. Under-layer materials enhance the photo-current by minimising electron-hole recombination through suppressing of back electron flow from the substrate, such as fluorine-doped tin oxide (FTO), to hematite. We have carried out ultrafast transient absorption spectroscopy on hematite in which Nb2O5 and SnO2 materials were used as interfacial layers to enhance hole lifetimes. The transient absorption data was fit with four different lifetimes ranging from a few hundred femtoseconds to a few nanoseconds. We show that the electron-hole recombination is slower in samples where interfacial layers are used than in pristine hematite. We also develop a model through target analysis to illustrate the effect of under-layers on electron-hole recombination rates in hematite thin films.

Characterization of n-Type and p-Type Long-Wave InAs/InAsSb Superlattices

NASA Astrophysics Data System (ADS)

Brown, A. E.; Baril, N.; Zuo, D.; Almeida, L. A.; Arias, J.; Bandara, S.

2017-09-01

The influence of dopant concentration on both in-plane mobility and minority carrier lifetime in long-wave infrared InAs/InAsSb superlattices (SLs) was investigated. Unintentially doped ( n-type) and various concentrations of Be-doped ( p-type) SLs were characterized using variable-field Hall and photoconductive decay techniques. Minority carrier lifetimes in p-type InAs/InAsSb SLs are observed to decrease with increasing carrier concentration, with the longest lifetime at 77 K determined to be 437 ns, corresponding to a measured carrier concentration of p 0 = 4.1 × 1015 cm-3. Variable-field Hall technique enabled the extraction of in-plane hole, electron, and surface electron transport properties as a function of temperature. In-plane hole mobility is not observed to change with doping level and increases with reducing temperature, reaching a maximum at the lowest temperature measured of 30 K. An activation energy of the Be-dopant is determined to be 3.5 meV from Arrhenius analysis of hole concentration. Minority carrier electrons populations are suppressed at the highest Be-doping levels, but mobility and concentration values are resolved in lower-doped samples. An average surface electron conductivity of 3.54 × 10-4 S at 30 K is determined from the analysis of p-type samples. Effects of passivation treatments on surface conductivity will be presented.

High performance unipolar MoTe2 field effect transistors enabled by doping and Al2O3 capping

NASA Astrophysics Data System (ADS)

Qu, Deshun; Liu, Xiaochi; Ahmed, Faisal; Yoo, Won Jong

We carry out the first systematic experiment on carrier type modulation of MoTe2 FET in this work. unipolar p- and n-type MoTe2 FETs with 105 and 106 on-off ratios are achieved through rapid thermal annealing (RTA) and Benzyl Viologen (BV) doping respectively. By varying the vacuum level in RTA chamber before annealing and BV dopant concentration, annealing condition, both hole and electron doping concentration can be modulated in a wide range from slight doping to degenerate like doping. Furthermore, Al2O3 is deposited onto the device surfaces for the mobility engineering. Hole and electron mobilities are improved to 62 cm2/Vs and 82 cm2/Vs respectively after Al2O3 capping; they are among the highest carrier mobilities of MoTe2 transistors ever obtained. A lateral homogeneous MoTe2 p-n diode is fabricated combining the electron and hole doping techniques, the device displays excellent diode properties with a high rectification ratio of 104 at 0 gate bias and an ideality factor of 1.2. This work was supported by the Global Research Laboratory and Global Frontier R&D Programs at the Center for Hybrid Interface Materials, both funded by the Ministry of Science, ICT & Future Planning via the National Research Foundation of Korea (NRF).

Electron–acoustic phonon coupling in single crystal CH 3NH 3PbI 3 perovskites revealed by coherent acoustic phonons

DOE PAGES

Mante, Pierre-Adrien; Stoumpos, Constantinos C.; Kanatzidis, Mercouri G.; ...

2017-02-08

The intrinsic properties of CH 3NH 3PbI 3 are still largely unknown in spite of the great amount of attention it has received for its solar cell application. Mobility of charges is a quintessential property in this aspect; however, there is still no clear understanding of electron transport, as reported values span over three orders of magnitude. Here we develop a method to measure the electron and hole deformation potentials using coherent acoustic phonons generated by femtosecond laser pulses. Furthermore, we apply this method to characterize a CH 3NH 3PbI 3 single crystal.We measure the acoustic phonon properties and characterizemore » electron-acoustic phonon scattering. Then, using the deformation potential theory, we calculate the carrier intrinsic mobility and compare it to the reported experimental and theoretical values. These results reveal high electron and hole mobilities of 2,800 and 9,400 cm 2V -1 s -1 , respectively. Comparison with literature values of mobility demonstrates the potential role played by polarons in charge transport in CH 3NH 3PbI 3.« less

Electron–acoustic phonon coupling in single crystal CH 3NH 3PbI 3 perovskites revealed by coherent acoustic phonons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mante, Pierre-Adrien; Stoumpos, Constantinos C.; Kanatzidis, Mercouri G.

The intrinsic properties of CH 3NH 3PbI 3 are still largely unknown in spite of the great amount of attention it has received for its solar cell application. Mobility of charges is a quintessential property in this aspect; however, there is still no clear understanding of electron transport, as reported values span over three orders of magnitude. Here we develop a method to measure the electron and hole deformation potentials using coherent acoustic phonons generated by femtosecond laser pulses. Furthermore, we apply this method to characterize a CH 3NH 3PbI 3 single crystal.We measure the acoustic phonon properties and characterizemore » electron-acoustic phonon scattering. Then, using the deformation potential theory, we calculate the carrier intrinsic mobility and compare it to the reported experimental and theoretical values. These results reveal high electron and hole mobilities of 2,800 and 9,400 cm 2V -1 s -1 , respectively. Comparison with literature values of mobility demonstrates the potential role played by polarons in charge transport in CH 3NH 3PbI 3.« less

Stability and carrier transport properties of phosphorene-based polymorphic nanoribbons

NASA Astrophysics Data System (ADS)

Kaur, Sumandeep; Kumar, Ashok; Srivastava, Sunita; Pandey, Ravindra; Tankeshwar, K.

2018-04-01

Few-layer black phosphorene has recently attracted significant interest in the scientific community. In this paper, we consider several polymorphs of phosphorene nanoribbons (PNRs) and employ deformation potential theory within the effective mass approximation, together with density functional theory, to investigate their structural, mechanical and electronic properties. The results show that the stability of a PNR strongly depends on the direction along which it can be cut from its 2D counterpart. PNRs also exhibit a wide range of line stiffnesses ranging from 6 × 1010 eV m-1 to 18 × 1011 eV m-1, which has little dependence on the edge passivation. Likewise, the calculated electronic properties of PNRs show them to be either a narrow-gap semiconductor (E g < 1 eV) or a wide-gap semiconductor (E g > 1 eV). The carrier mobility of PNRs is found to be comparable to that of black phosphorene. Some of the PNRs show an n-type (p-type) semiconducting character owing to their higher electron (hole) mobility. Passivation of the edges leads to n-type ↔ p-type transition in many of the PNRs considered. The predicted novel characteristics of PNRs, with a wide range of mechanical and electronic properties, make them potentially suitable for use in nanoscale devices.

Electric transport coefficients in highly epitaxial LaBaCo{sub 2}O{sub 5 + δ} films with “p-to-n” transition induced by oxygen deficiency

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shaibo, J.; Zhang, Q. Y., E-mail: qyzhang@dlut.edu.cn; Hu, H. C.

2016-08-14

Electric transport coefficients such as carrier type, density, and mobility are the important physical parameters in designing functional devices. In this work, we report the study on the electric transport coefficients of the highly epitaxial LaBaCo{sub 2}O{sub 5 + δ} (LBCO) films, which were discussed as a function of electric conductivity for the first time and compared with the results calculated by the theory for mixed conduction. The mobility in the LBCO films was determined to be ∼0.85 and ∼40 cm{sup 2}/V s for holes and electrons, respectively, and the density of p-type carriers strongly depends on the oxygen deficiency. Solid evidence ismore » presented to demonstrate that the oxygen deficiency cannot make LBCO materials changed from p- to n-type. The n-type conduction observed in experiment is a counterfeit phenomenon caused by the deficiency in Hall measurement, rather than a realistic transition induced by oxygen deficiency. In addition, the temperature-dependent conductivity was discussed using the differential coefficients, which might be useful in the study of the samples with magnetic transition.« less

Valence Band Structure of Highly Efficient p-type Thermoelectric PbTe-PbS Alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jaworski, C. M.; Nielsen, Mechele; Wang, Hsin

New experimental evidence is given relevant to the temperature-dependence of valence band structure of PbTe and PbTe1-xSx alloys (0.04 x 0.12), and its effect on the thermoelectric figure of merit zT. The x = 0.08 sample has zT ~ 1.55 at 773K. The magnetic field dependence of the high-temperature Hall resistivity of heavily p-type (> 1019 cm-3) Na-doped PbTe1-xSx reveals the presence of high-mobility electrons. This put in question prior analyses of the Hall coefficient and the conclusion that PbTe would be an indirect gap semiconductor at temperatures where its zT is optimal. Possible origins for these electrons are discussed:more » they can be induced by photoconductivity, or by the topology of the Fermi surface when the L and -bands merge. Negative values for the low-temperature thermopower are also observed. Our data show that PbTe continues to be a direct gap semiconductor at temperatures where the zT and S2 of p-type PbTe are optimal e.g. 700-900K. The previously suggested temperature induced rapid rise in energy of the heavy hole LVB relative to the light hole UVB is not supported by the experimental data.« less

Resonant photoluminescence studies of carrier localisation in c-plane InGaN/GaN quantum well structures

NASA Astrophysics Data System (ADS)

Blenkhorn, W. E.; Schulz, S.; Tanner, D. S. P.; Oliver, R. A.; Kappers, M. J.; Humphreys, C. J.; Dawson, P.

2018-05-01

In this paper we report on changes in the form of the low temperature (12 K) photoluminescence spectra of an InGaN/GaN quantum well structure as a function of excitation photon energy. As the photon energy is progressively reduced we observe at a critical energy a change in the form of the spectra from one which is determined by the occupation of the complete distribution of hole localisation centres to one which is determined by the resonant excitation of specific localisation sites. This change is governed by an effective mobility edge whereby the photo-excited holes remain localised at their initial energy and are prevented from scattering to other localisation sites. This assignment is confirmed by the results of atomistic tight binding calculations which show that the wave function overlap of the lowest lying localised holes with other hole states is low compared with the overlap of higher lying hole states with other higher lying hole states.

Structural control of mixed ionic and electronic transport in conducting polymers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rivnay, Jonathan; Inal, Sahika; Collins, Brian A.

Poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate), PEDOT:PSS, has been utilized for over two decades as a stable, solution-processable hole conductor. While its hole transport properties have been the subject of intense investigation, recent work has turned to PEDOT:PSS as a mixed ionic/electronic conductor in applications including bioelectronics, energy storage and management, and soft robotics. Conducting polymers can efficiently transport both holes and ions when sufficiently hydrated, however, little is known about the role of morphology on mixed conduction. Here, we show that bulk ionic and electronic mobilities are simultaneously affected by processing-induced changes in nano- and meso-scale structure in PEDOT:PSS films. Wemore » quantify domain composition, and find that domain purification on addition of dispersion co-solvents limits ion mobility, even while electronic conductivity improves. We show that an optimal morphology allows for the balanced ionic and electronic transport that is critical for prototypical mixed conductor devices. As a result, these findings may pave the way for the rational design of polymeric materials and processing routes to enhance devices reliant on mixed conduction.« less

Structural control of mixed ionic and electronic transport in conducting polymers

DOE PAGES

Rivnay, Jonathan; Inal, Sahika; Collins, Brian A.; ...

2016-04-19

Poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate), PEDOT:PSS, has been utilized for over two decades as a stable, solution-processable hole conductor. While its hole transport properties have been the subject of intense investigation, recent work has turned to PEDOT:PSS as a mixed ionic/electronic conductor in applications including bioelectronics, energy storage and management, and soft robotics. Conducting polymers can efficiently transport both holes and ions when sufficiently hydrated, however, little is known about the role of morphology on mixed conduction. Here, we show that bulk ionic and electronic mobilities are simultaneously affected by processing-induced changes in nano- and meso-scale structure in PEDOT:PSS films. Wemore » quantify domain composition, and find that domain purification on addition of dispersion co-solvents limits ion mobility, even while electronic conductivity improves. We show that an optimal morphology allows for the balanced ionic and electronic transport that is critical for prototypical mixed conductor devices. As a result, these findings may pave the way for the rational design of polymeric materials and processing routes to enhance devices reliant on mixed conduction.« less

Balance the Carrier Mobility To Achieve High Performance Exciplex OLED Using a Triazine-Based Acceptor.

PubMed

Hung, Wen-Yi; Chiang, Pin-Yi; Lin, Shih-Wei; Tang, Wei-Chieh; Chen, Yi-Ting; Liu, Shih-Hung; Chou, Pi-Tai; Hung, Yi-Tzu; Wong, Ken-Tsung

2016-02-01

A star-shaped 1,3,5-triazine/cyano hybrid molecule CN-T2T was designed and synthesized as a new electron acceptor for efficient exciplex-based OLED emitter by mixing with a suitable electron donor (Tris-PCz). The CN-T2T/Tris-PCz exciplex emission shows a high ΦPL of 0.53 and a small ΔET-S = -0.59 kcal/mol, affording intrinsically efficient fluorescence and highly efficient exciton up-conversion. The large energy level offsets between Tris-PCz and CN-T2T and the balanced hole and electron mobility of Tris-PCz and CN-T2T, respectively, ensuring sufficient carrier density accumulated in the interface for efficient generation of exciplex excitons. Employing a facile device structure composed as ITO/4% ReO3:Tris-PCz (60 nm)/Tris-PCz (15 nm)/Tris-PCz:CN-T2T(1:1) (25 nm)/CN-T2T (50 nm)/Liq (0.5 nm)/Al (100 nm), in which the electron-hole capture is efficient without additional carrier injection barrier from donor (or acceptor) molecule and carriers mobilities are balanced in the emitting layer, leads to a highly efficient green exciplex OLED with external quantum efficiency (EQE) of 11.9%. The obtained EQE is 18% higher than that of a comparison device using an exciplex exhibiting a comparable ΦPL (0.50), in which TCTA shows similar energy levels but higher hole mobility as compared with Tris-PCz. Our results clearly indicate the significance of mobility balance in governing the efficiency of exciplex-based OLED. Exploiting the Tris-PCz:CN-T2T exciplex as the host, we further demonstrated highly efficient yellow and red fluorescent OLEDs by doping 1 wt % Rubrene and DCJTB as emitter, achieving high EQE of 6.9 and 9.7%, respectively.

Copper Vacancies and Heavy Holes in the Two-Dimensional Semiconductor KCu 3–xSe 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rettie, Alexander J. E.; Sturza, Mihai; Malliakas, Christos D.

The two-dimensional material KCu 3–xSe 2 was synthesized using both a K 2Se 3 flux and directly from the elements. It crystallizes in the CsAg 3S 2 structure (monoclinic space group C2/m with a = 15.417(3) Å, b = 4.0742(8) Å, c = 8.3190(17) Å, and β = 112.94(3)°), and single-crystal refinement revealed infinite copper-deficient [Cu 3–xSe 2]– layers separated by K + ions. Thermal analysis indicated that KCu 3–xSe 2 melts congruently at ~755 °C. UV–vis spectroscopy showed an optical band gap of ~1.35 eV that is direct in nature, as confirmed by electronic structure calculations. Electronic transport measurementsmore » on single crystals yielded an in-plane resistivity of ~6 × 10 –1 Ω cm at 300 K that has a complex temperature dependence. The results of Seebeck coefficient measurements were consistent with a doped p-type semiconductor (S = +214 μV K –1 at 300 K), with doping being attributed to copper vacancies. Transport is dominated by low-mobility (on the order of 1 cm 2 V –1 s –1) holes caused by relatively flat valence bands with substantial Cu 3d character and a significant concentration of Cu ion vacancy defects (p ~ 10 19 cm –3) in this material. In conclusion, electronic band structure calculations showed that electrons should be significantly more mobile in this structure type.« less

Copper Vacancies and Heavy Holes in the Two-Dimensional Semiconductor KCu 3–xSe 2

DOE PAGES

Rettie, Alexander J. E.; Sturza, Mihai; Malliakas, Christos D.; ...

2017-06-21

The two-dimensional material KCu 3–xSe 2 was synthesized using both a K 2Se 3 flux and directly from the elements. It crystallizes in the CsAg 3S 2 structure (monoclinic space group C2/m with a = 15.417(3) Å, b = 4.0742(8) Å, c = 8.3190(17) Å, and β = 112.94(3)°), and single-crystal refinement revealed infinite copper-deficient [Cu 3–xSe 2]– layers separated by K + ions. Thermal analysis indicated that KCu 3–xSe 2 melts congruently at ~755 °C. UV–vis spectroscopy showed an optical band gap of ~1.35 eV that is direct in nature, as confirmed by electronic structure calculations. Electronic transport measurementsmore » on single crystals yielded an in-plane resistivity of ~6 × 10 –1 Ω cm at 300 K that has a complex temperature dependence. The results of Seebeck coefficient measurements were consistent with a doped p-type semiconductor (S = +214 μV K –1 at 300 K), with doping being attributed to copper vacancies. Transport is dominated by low-mobility (on the order of 1 cm 2 V –1 s –1) holes caused by relatively flat valence bands with substantial Cu 3d character and a significant concentration of Cu ion vacancy defects (p ~ 10 19 cm –3) in this material. In conclusion, electronic band structure calculations showed that electrons should be significantly more mobile in this structure type.« less

Magnetotransport of indium antimonide doped with manganese

NASA Astrophysics Data System (ADS)

Kuzmina, K.; Aronzon, B. A.; Kochura, A. V.; Lashkul, A. V.; Lisunov, K. G.; Lähderanta, E.; Shakhov, M. A.

2014-07-01

Magnetotransport, including the magnetoresistance (MR) and the Hall effect, isinvestigated in polycrystalline In1-xMnxSb samples with x = 0.02 - 0.06, containing nanosize MnSb precipitates. The relative MR, Δρ/ρ, is positive within the whole range of B= 0 - 10 T and T ~ 20 - 300 K. The Hall resistivity, ρH, exhibits a nonlinear dependence on B up to the room temperature.MR is interpreted with the two-band model, suggesting two types of holes with different concentration and mobility. In addition, analysis of ρH (B, T) is performed by taking into account both the normal and the anomalous contributions. The latter is attributable to the effect of MnSb nanoprecipitates, having the ferromagnetic Curie temperature well above 300 K.

Mechanism of photocatalytic water oxidation on small TiO 2 nanoparticles

DOE PAGES

Muuronen, Mikko; Parker, Shane M.; Berardo, Enrico; ...

2016-12-07

Here, we present the first unconstrained nonadiabatic molecular dynamics (NAMD) simulations of photocatalytic water oxidation by small hydrated TiO 2 nanoparticles using Tully surface hopping and time-dependent density functional theory. The results indicate that ultrafast electron–proton transfer from physisorbed water to the photohole initiates the photo-oxidation on the S 1 potential energy surface. The new mechanism readily explains the observation of mobile hydroxyl radicals in recent experiments. Two key driving forces for the photo-oxidation reaction are identified: localization of the electron–hole pair and stabilization of the photohole by hydrogen bonding interaction. Our findings illustrate the scope of recent advances inmore » NAMD methods and emphasize the importance of explicit simulation of electronic excitations.« less

Coulomb drag in electron-hole bilayer: Mass-asymmetry and exchange correlation effects

NASA Astrophysics Data System (ADS)

Arora, Priya; Singh, Gurvinder; Moudgil, R. K.

2018-04-01

Motivated by a recent experiment by Zheng et al. [App. Phys. Lett. 108, 062102 (2016)] on coulomb drag in electron-hole and hole-hole bilayers based on GaAs/AlGaAs semiconductor heterostructure, we investigate theoretically the influence of mass-asymmetry and temperature-dependence of correlations on the drag rate. The correlation effects are dealt with using the Vignale-Singwi effective inter-layer interaction model which includes correlations through local-field corrections to the bare coulomb interactions. However, in this work, we have incorporated only the intra-layer correlations using the temperature-dependent Hubbard approximation. Our results display a reasonably good agreement with the experimental data. However, it is crucial to include both the electron-hole mass-asymmetry and temperature-dependence of correlations. Mass-asymmetry and correlations are found to result in a substantial enhancement of drag resistivity.

Evidence for spin injection and transport in solution-processed TIPS-pentacene at room temperature

NASA Astrophysics Data System (ADS)

Mooser, S.; Cooper, J. F. K.; Banger, K. K.; Wunderlich, J.; Sirringhaus, H.

2012-10-01

Recently, there has been growing interest in the field of organic spintronics, where the research on organic semiconductors (OSCs) has extended from the complex aspects of charge carrier transport to the study of the spin transport properties of those anisotropic and partly localized systems.1 Furthermore, solution-processed OSCs are not only interesting due to their technological applications, but it has recently been shown in 6,13-bis(triisopropylsilylethynyl)-pentacene (TIPS-pentacene) thin film transistors that they can exhibit a negative temperature coefficient of the mobility due to localized transport limited by thermal lattice fluctuations.2 Here, spin injection and transport in solution-processed TIPS-pentacene are investigated exploiting vertical CoPt/TIPSpentacene/AlOx/Co spin valve architectures.3 The antiparallel magnetization state of the relative orientation of CoPt and Co is achieved due to their different coercive fields. A spin valve effect is detected from T = 175 K up to room temperature, where the resistance of the device is lower for the antiparallel magnetization state. The first observation of the scaling of the magnetoresistance (MR) with the bulk mobility of the OSC as a function of temperature, together with the dependence of the MR on the interlayer thickness, clearly indicates spin injection and transport in TIPS-pentacene. From OSC-spacer thickness-dependent MR measurements, a spin relaxation length of TIPS-pentacene of (24+/-6) nm and a spin relaxation time of approximately 3.5 μs at room temperature are estimated, taking the measured bulk mobility of holes into account.

Donor-acceptor cocrystal based on hexakis(alkoxy)triphenylene and perylenediimide derivatives with an ambipolar transporting property

NASA Astrophysics Data System (ADS)

Su, Yajun; Li, Yan; Liu, Jiangang; Xing, Rubo; Han, Yanchun

2015-01-01

An organic donor-acceptor cocrystal with an ambipolar transporting property was constructed based on N,N'-bis(1-ethylpropyl)-perylene-3,4,9,10-tetracarboxylic diimide (EP-PDI) and 2,3,6,7,10,11-hexakis-(hexyloxy)-triphenylene (H6TP). The cocrystal with an alternating stacking of H6TP and EP-PDI molecules was formed through both drop-casting and spin-coating processes, especially at the optimized ratios of H6TP/EP-PDI (2/1, 1/1). The formation of the cocrystal was driven by the strong π-π interaction and the weaker steric hindrance, resulting from the smaller side groups, between the donor and acceptor molecules. Field effect transistors (FETs) based on the H6TP/EP-PDI cocrystal exhibited relatively balanced hole/electron transport, with a hole mobility of 1.14 × 10-3 cm2 V-1 s-1 and an electron mobility of 1.40 × 10-3 cm2 V-1 s-1.An organic donor-acceptor cocrystal with an ambipolar transporting property was constructed based on N,N'-bis(1-ethylpropyl)-perylene-3,4,9,10-tetracarboxylic diimide (EP-PDI) and 2,3,6,7,10,11-hexakis-(hexyloxy)-triphenylene (H6TP). The cocrystal with an alternating stacking of H6TP and EP-PDI molecules was formed through both drop-casting and spin-coating processes, especially at the optimized ratios of H6TP/EP-PDI (2/1, 1/1). The formation of the cocrystal was driven by the strong π-π interaction and the weaker steric hindrance, resulting from the smaller side groups, between the donor and acceptor molecules. Field effect transistors (FETs) based on the H6TP/EP-PDI cocrystal exhibited relatively balanced hole/electron transport, with a hole mobility of 1.14 × 10-3 cm2 V-1 s-1 and an electron mobility of 1.40 × 10-3 cm2 V-1 s-1. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr05915h

Interface engineering in high-performance low-voltage organic thin-film transistors based on 2,7-dialkyl-[1]benzothieno[3,2-b][1]benzothiophenes.

PubMed

Amin, Atefeh Y; Reuter, Knud; Meyer-Friedrichsen, Timo; Halik, Marcus

2011-12-20

We investigated two different (2,7-dialkyl-[1]benzothieno[3,2-b][1]benzothiophenes; C(n)-BTBT-C(n), where n = 12 or 13) semiconductors in low-voltage operating thin-film transistors. By choosing functional molecules in nanoscaled hybrid dielectric layers, we were able to tune the surface energy and improve device characteristics, such as leakage current and hysteresis. The dipolar nature of the self-assembled molecules led to a shift in the threshold voltage. All devices exhibited high charge carrier mobilities of 0.6-7.0 cm(2) V(-1) s(-1). The thin-film morphology of BTBT was studied by means of atomic force microscopy (AFM), presented a dependency upon the surface energy of the self-assembled monolayer (SAM) hybrid dielectrics but not upon the device performance. The use of C(13)-BTBT-C(13) on hybrid dielectrics of AlO(x) and a F(15)C(18)-phosphonic acid monolayer led to devices with a hole mobility of 1.9 cm(2) V(-1) s(-1) at 3 V, on/off ratio of 10(5), small device-device variation of mobility, and a threshold voltage of only -0.9 V, thus providing excellent characteristics for further integration. © 2011 American Chemical Society

Oriented Liquid Crystalline Polymer Semiconductor Films with Large Ordered Domains.

PubMed

Xue, Xiao; Chandler, George; Zhang, Xinran; Kline, R Joseph; Fei, Zhuping; Heeney, Martin; Diemer, Peter J; Jurchescu, Oana D; O'Connor, Brendan T

2015-12-09

Large strains are applied to liquid crystalline poly(2,5-bis(3-tetradecylthiophen-2yl)thieno(3,2-b)thiophene) (pBTTT) films when held at elevated temperatures resulting in in-plane polymer alignment. We find that the polymer backbone aligns significantly in the direction of strain, and that the films maintain large quasi-domains similar to that found in spun-cast films on hydrophobic surfaces, highlighted by dark-field transmission electron microscopy imaging. The highly strained films also have nanoscale holes consistent with dewetting. Charge transport in the films is then characterized in a transistor configuration, where the field effect mobility is shown to increase in the direction of polymer backbone alignment, and decrease in the transverse direction. The highest saturated field-effect mobility was found to be 1.67 cm(2) V(-1) s(-1), representing one of the highest reported mobilities for this material system. The morphology of the oriented films demonstrated here contrast significantly with previous demonstrations of oriented pBTTT films that form a ribbon-like morphology, opening up opportunities to explore how differences in molecular packing features of oriented films impact charge transport. Results highlight the role of grain boundaries, differences in charge transport along the polymer backbone and π-stacking direction, and structural features that impact the field dependence of charge transport.

Coexistence of two electronic phases in LaTiO3+δ (0.01⩽δ⩽0.12) and their evolution with δ

NASA Astrophysics Data System (ADS)

Zhou, H. D.; Goodenough, J. B.

2005-04-01

Although LaTiO3+δ(0.01⩽δ⩽0.12) is single-phase to powder x-ray diffraction, its properties reveal that a hole-poor strongly correlated electronic phase coexists with a hole-rich itinerant-electron phase. With δ⩽0.03 , the hole-rich phase exists as a minority phase of isolated, mobile itinerant-electron clusters embedded in the hole-poor phase. With δ⩾0.08 , isolated hole-poor clusters are embedded in an itinerant-electron matrix. As δ>0.08 increases, the hole-poor clusters become smaller and more isolated until they are reduced to superparamagnetic strong-correlation fluctuations by δ=0.12 . This behavior is consistent with prediction from the virial theorem of a first-order phase change at the crossover from localized (or strongly correlated) to itinerant electronic behavior, a smaller equilibrium (Ti-O) bond length being in the itinerant-electron phase. Accordingly, the variation of volume with oxidation state does not obey Végard’s law; the itinerant-electron minority phase exerts a compressive force on the hole-poor matrix, and the hole-poor minority phase exerts a tensile stress on the hole-rich matrix.

Modeling hole transport in wet and dry DNA.

PubMed

Pavanello, Michele; Adamowicz, Ludwik; Volobuyev, Maksym; Mennucci, Benedetta

2010-04-08

We present a DFT/classical molecular dynamics model of DNA charge conductivity. The model involves a temperature-driven, hole-hopping charge transfer and includes the time-dependent nonequilibrium interaction of DNA with its molecular environment. We validate our method against a variety of hole transport experiments. The method predicts a significant hole-transfer slowdown of approximately 35% from dry to wet DNA with and without electric field bias. In addition, in agreement with experiments, it also predicts an insulating behavior of (GC)(N) oligomers for 40 < N < 1000, depending on the experimental setup.

Growth of low disorder GaAs/AlGaAs heterostructures by molecular beam epitaxy for the study of correlated electron phases in two dimensions

NASA Astrophysics Data System (ADS)

Watson, John D.

The unparalleled quality of GaAs/AlGaAs heterostructures grown by molecular beam epitaxy has enabled a wide range of experiments probing interaction effects in two-dimensional electron and hole gases. This dissertation presents work aimed at further understanding the key material-related issues currently limiting the quality of these 2D systems, particularly in relation to the fractional quantum Hall effect in the 2nd Landau level and spin-based implementations of quantum computation. The manuscript begins with a theoretical introduction to the quantum Hall effect which outlines the experimental conditions necessary to study the physics of interest and motivates the use of the semiconductor growth and cryogenic measurement techniques outlined in chapters 2 and 3, respectively. In addition to a generic introduction to the molecular beam epitaxy growth technique, chapter 2 summarizes some of what was learned about the material purity issues currently limiting the low temperature electron mobility. Finally, a series of appendices are included which detail the experimental methods used over the course of the research. Chapter 4 presents an experiment examining transport in a low density two-dimensional hole system in which the hole density could be varied by means of an evaporated back gate. At low temperature, the mobility reached a maximum of 2.6 x 106 cm2/Vs at a density of 6.2 x 1010 cm-2 which is the highest reported mobility in a two-dimensional hole system to date. In addition, it was found that the mobility as a function of density did not follow a power law with a single exponent. Instead, it was found that the power law varied with density, indicating a cross-over between dominant scattering mechanisms at low density and high density. At low density the mobility was found to be limited by remote ionized impurity scattering, while at high density the dominant scattering mechanism was found to be background impurity scattering. Chapter 5 details an experiment examining transport in a series of two-dimensional hole gases in which the dopant setback distance and the Al mole fraction in the barriers of the quantum well were varied. The hole density was tuned in this way from 0.18 -- 1.9 x 1011 cm-2. Surprisingly, the mobility at T = 0.3 K was found to peak at 2.3 x 10 6 cm-2 at an intermediate density of 6.5 x 10 10 cm-2. Self-consistent Schrodinger/Poisson calculations were performed for each wafer to examine the scattering rates due to a variety of potentials at low temperature. The drop in mobility at high density could be accounted for with the inclusion of interface roughness scattering, but using the same interface roughness scattering parameters for similar two-dimensional electron gases produced inconsistent results. This leaves open the possibility of contributions from other scattering mechanisms in the hole samples at high density. Chapter 6 presents an in-depth study of in-situ backgated two-dimensional gases used for studying the fragile fractional quantum Hall states in the 2nd Landau level. It was found that leakage currents as small as 4 pA could cause noticeable heating of the electron gas if the lattice was not properly thermally anchored to the cryostat. However, it was also found that when the heterostructure design and device fabrication recipe were properly optimized, gate voltages as large as 4 V could be applied before the leakage turned on, allowing the density to be tuned from full depletion to over 4 x 1011 cm-2. As a result, heating effects at dilution refrigerator temperatures were negligible and the gap at nu = 5/2 could be tuned continuously with density to a maximum value of 625 mK, the largest reported to date. An unusual evolution of the reentrant integer quantum Hall states as a function of density is also reported. Such devices should prove useful for the study of electron correlations in nanostructures in the 2nd Landau level.

Effect of the phenoxy groups on PDIB and its derivatives

NASA Astrophysics Data System (ADS)

Song, Peng; Guan, Baijie; Zhou, Qiao; Zhao, Meiyu; Huang, Jindou; Ma, Fengcai

2016-10-01

The anisotropic hole and electron mobilities in N,N‧-3,4,9,10-perylenediimide-1,7-phenoxy (PDIB-2OPh) and N,Nʹ-3,4,9,10-perylenediimide (PDIB) were theoretically predicted using the Marcus-Hush theory. The substituent effect of phenoxy on their mobility rates, absorption spectra, electron affinities, and ionization potentials was explored. By comparing the simulated hole mobility in PDIB and PDIB-2OPh, it is found that the phenoxy rings act as spacers between adjacent stacking columns in the phenoxy-substituted derivatives. The increasement of the number of benzene oxygen groups leads to the absorption spectra red-shift of these molecular systems. This coincides with their change tendency of the adiabatic ionization potentials, vertical ionization potentials. However, the calculated adiabatic electron affinities and vertical electron affinities of N,N‧-butyl-3,4,9,10-perylenediimide-1,6,7,12-phenoxy (PDIB-4OPh) are larger than those of PDIB;OPh. The steric effect in PDIB-4OPh is expected to cause space reversal and thus to changes in the properties of the molecule.

Effect of the phenoxy groups on PDIB and its derivatives

PubMed Central

Song, Peng; Guan, Baijie; Zhou, Qiao; Zhao, Meiyu; Huang, Jindou; Ma, Fengcai

2016-01-01

The anisotropic hole and electron mobilities in N,N′-3,4,9,10-perylenediimide-1,7-phenoxy (PDIB-2OPh) and N,Nʹ-3,4,9,10-perylenediimide (PDIB) were theoretically predicted using the Marcus–Hush theory. The substituent effect of phenoxy on their mobility rates, absorption spectra, electron affinities, and ionization potentials was explored. By comparing the simulated hole mobility in PDIB and PDIB-2OPh, it is found that the phenoxy rings act as spacers between adjacent stacking columns in the phenoxy-substituted derivatives. The increasement of the number of benzene oxygen groups leads to the absorption spectra red-shift of these molecular systems. This coincides with their change tendency of the adiabatic ionization potentials, vertical ionization potentials. However, the calculated adiabatic electron affinities and vertical electron affinities of N,N′-butyl-3,4,9,10-perylenediimide-1,6,7,12-phenoxy (PDIB-4OPh) are larger than those of PDIB;OPh. The steric effect in PDIB-4OPh is expected to cause space reversal and thus to changes in the properties of the molecule. PMID:27759050

Effect of molecular properties on the performance of polymer light-emitting diodes

NASA Astrophysics Data System (ADS)

Ramos, Marta M. D.; Almeida, A. M.; Correia, Helena M. G.; Ribeiro, R. Mendes; Stoneham, A. M.

2004-11-01

The performance of a single layer polymer light-emitting diode depends on several interdependent factors, although recombination between electrons and holes within the polymer layer is believed to play an important role. Our aim is to carry out computer experiments in which bipolar charge carriers are injected in polymer networks made of poly(p-phenylene vinylene) chains randomly oriented. In these simulations, we follow the charge evolution in time from some initial state to the steady state. The intra-molecular properties of the polymer molecules obtained from self-consistent quantum molecular dynamics calculations are used in the mesoscopic model. The purpose of the present work is to clarify the effects of intra-molecular charge mobility and energy disorder on recombination efficiency. In particular, we find that charge mobility along the polymer chains has a serious influence on recombination within the polymer layer. Our results also show that energy disorder due to differences in ionization potential and electron affinity of neighbouring molecules affects mainly recombinations that occur near the electrodes at polymer chains parallel to them.

An origin of good electrical conduction in La{sub 4}BaCu{sub 5}O{sub 13+δ}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mori, Daiki; Asai, Shinichiro; Terasaki, Ichiro, E-mail: terra@cc.nagoya-u.ac.jp

2015-07-21

We have prepared a set of polycrystalline samples of the metallic copper oxide La{sub 4}BaCu{sub 5−x}Co{sub x}O{sub 13+δ} (0 ≤ x ≤ 0.35) and have measured the resistivity from 4 to 800 K. All the resistivities show metallic temperature dependence with a small magnitude less than 2 mΩ cm at 800 K, indicating that the metallic conduction is robust against impurities. The robust metallic conduction further suggests that this class of oxide is a promising candidate for electrical leads at high temperature, which might replace platinum. A detailed measurement and analysis on the Hall resistivity have revealed that at least two components are responsible for the electricalmore » conduction, in which a large number of electrons of moderate mobility coexist with a much smaller number of holes of extremely high mobility. This large electron density well screens the impurity potential and retains the metallic conduction against 7% impurity doping.« less

Exciton diffusion in disordered small molecules for organic photovoltaics: insights from first-principles simulations.

PubMed

Li, Z; Zhang, X; Lu, G

2014-05-07

Exciton diffusion in small molecules 3,6-bis(5-(benzofuran-2-yl)thiophen-2-yl)-2,5-bis(2-ethylhexyl)pyrrolo[3,4-c]pyrrole-1,4-dione [DPP(TBFu)2] is studied using first-principles simulations. We have examined dependence of exciton diffusion on structure disorder, temperature and exciton energy. We find that exciton diffusion length and diffusivity increase with structural order, temperature and the initial exciton energy. Compared to conjugated polymer poly(3-hexylthiophene) (P3HT), DPP(TBFu)2 small molecules exhibit a much higher exciton diffusivity, but a shorter lifetime. The exciton diffusion length in DPP(TBFu)2 is 50% longer than that in P3HT, yielding a higher exciton harvesting efficiency; the physical origin behind these differences is discussed. The time evolutions of exciton energy, electron-hole distance, and exciton localization are explored, and the widely speculated exciton diffusion mechanism is confirmed theoretically. The connection between exciton diffusion and carrier mobilities is also studied. Finally we point out the possibility to estimate exciton diffusivity by measuring carrier mobilities under AC electric fields.

Effects of a Knee Brace With a Patellar Hole Versus Without a Patellar Hole in Patients With Knee Osteoarthritis: A Double-Blind, Randomized Controlled Trial.

PubMed

Added, Marco Aurélio Nemitalla; Added, Caroline; Kasawara, Karina Tamy; Rotta, Viviane Perez; de Freitas, Diego Galace

2017-01-01

The objective of this study was to observe the immediate effect of a knee brace with a patellar hole versus without a patellar hole on pain perception in patients with knee osteoarthritis. To accomplish this, a double-blind, randomized controlled trial enrolled 108 patients divided into two groups (knee brace with a patellar hole or without a patellar hole). Patients were evaluated by the Visual Analogue Scale (VAS) in order to measure their pain sensation, the Timed Up and Go (TUG) test was used to evaluate their ability to walk, and the 8-m walking test (8MWT) was used to estimate their walking speed. Both groups presented significant reduction in pain perception, higher function of the lower extremities, and greater mobility while wearing a knee brace. However, the patients who wore a knee brace without a patellar hole presented more favorable results than those who wore a knee brace with a patellar hole: a 1.6-point reduction was found versus 1.1 points in the VAS, the patients presented 0.7 s less time versus 0.4 s in the TUG, and the speed was reduced by 1.4 s versus 0.8 s in the 8MWT. Therefore, the knee brace without a patellar hole presented more favorable results when compared with the knee brace with a patellar hole.

High-Frequency, 6.2 Angstrom pN Heterojunction Diodes

DTIC Science & Technology

2012-01-01

this paper were grown by solid- source molecular beam epitaxy (MBE). Here, the use of a lower- case letter (p) for the narrow bandgap layer and upper...electron and hole mobilities. High electron mobil- ity transistors ( HEMTs ) fabricated from these materials have shown good operating characteristics [1,2...Furthermore, the first monolithic microwave integrated circuits (MMICs) fabricated using 6.1 Å based HEMTs have been demonstrated [3]. New mate- rials

Multipole moments of bumpy black holes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vigeland, Sarah J.

General relativity predicts the existence of black holes, compact objects whose spacetimes depend only on their mass, spin, and charge in vacuum (the 'no-hair' theorem). As various observations probe deeper into the strong fields of black hole candidates, it is becoming possible to test this prediction. Previous work suggested that such tests can be performed by measuring whether the multipolar structure of black hole candidates has the form that general relativity demands, and introduced a family of 'bumpy black hole' spacetimes to be used for making these measurements. These spacetimes have generalized multipoles, where the deviation from the Kerr metricmore » depends on the spacetime's 'bumpiness'. In this paper, we show how to compute the Geroch-Hansen moments of a bumpy black hole, demonstrating that there is a clean mapping between the deviations used in the bumpy black hole formalism and the Geroch-Hansen moments. We also extend our previous results to define bumpy black holes whose current moments, analogous to magnetic moments of electrodynamics, deviate from the canonical Kerr value.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wagner, B.

A specially designed wire line retrievable continuous coring system cored its initial project wells to total depth in hard rock formations in less than half the time that would have been required by conventional coring rigs. The hybrid wire line coring systems have since been used on other wells in similar lithologies, with a total of 38,000 m (124,640 ft) of hole cored and with penetration rates averaging 2.27 m/hr (7.45 ft/hr). This paper reports that Parker Drilling Co. designed the hybrid rigs and has recently been contracted to wire line core several holes for oil and gas exploration inmore » the Congo. The first core hole has been completed to 1,490 m, and total depth was reached in 21 days. The rig is now being mobilized to a second hole in the Congo.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Michael E. McIlwain; Nick Thompson; Da Gao

Considerable interest is given to the excellent scintillation properties of cerium doped lanthanum chloride (LaCl3) and lanthanum bromide (LaBr3). The scintillation efficiencies are much greater than other materials, even those containing cerium. This high efficiency is attributed to the high mobility of electrons and holes, unique placement of the cerium 5d states within the band gap, and energy of the band gap. To better understand the scintillation process and better define the nature of the Self Trapped Exciton (STE) within these unique scintillation materials, density functional theory (DFT), and Ab-inito (HF-MP2) calculations are reported. DFT calculations have yielded a qualitativemore » description of the orbital composition and energy distribution of the band structure in the crystalline material. MP2 and single configuration interaction calculations have provided quantitative values for the band gap and provided energies for the possible range of excited states created following hole and electron creation. Based on this theoretical treatment, one possible description of the STE is the combination of Vk center (Br2-1) and LaBr+1 species that recombine to form a distorted geometry LaBr3* (triplet state). Depending on the distance between the LaBr and Br2, the STE emission band can be reproduced.« less

Crystal growth and transport properties of CuAlO2 single crystal

NASA Astrophysics Data System (ADS)

Brahimi, R.; Rekhila, G.; Trari, M.; Bessekhouad, Y.

2014-12-01

The transport properties of the delafossite CuAlO2 single crystal, grown by the flux method, are confined in ∞[AlO2] layers extending in the (001) plans. The dielectric properties are measured up to 490 K in the frequency range (102-105 Hz). The small variation of the dielectric loss tan(δ) is attributed to the wide space charge region. The linear plot log (conductivity) vs. 1000/ T follows an Arrhenius type law and the results are discussed in terms of electron hopping among localized states. The activation energy (0.18 eV) gives an effective mass of 16 m 0 indicating that the levels in the vicinity of the Fermi level are strongly localized. Hence, the increase of the conductivity (σ) results from a thermal activation of the mobility (μ300 K = 1.2 × 10-5 cm-2 V-1 s-1). The sign of hole like small polarons is that of p type carriers originating from oxygen intercalation. The thermopower is little temperature dependent and characteristic of non degenerate conductivity with a low holes concentration and a large concentration of surface states within the gap region.

High-efficiency red electroluminescent device based on multishelled InP quantum dots.

PubMed

Jo, Jung-Ho; Kim, Jong-Hoon; Lee, Ki-Heon; Han, Chang-Yeol; Jang, Eun-Pyo; Do, Young Rag; Yang, Heesun

2016-09-01

We report on the synthesis of highly fluorescent red-emitting InP quantum dots (QDs) and their application to the fabrication of a high-efficiency QD-light-emitting diode (QLED). The core/shell heterostructure of the QDs is elaborately tailored toward a multishelled structure with a composition-gradient ZnSeS intermediate shell and an outer ZnS shell. Using the resulting InP/ZnSeS/ZnS QDs as an emitting layer, all-solution-processible red InP QLEDs are fabricated with a hybrid multilayered device structure having an organic hole transport layer (HTL) and an inorganic ZnO nanoparticle electron transport layer. Two HTLs of poly(9-vinlycarbazole) or poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4^'-(N-(4-sec-butylphenyl))diphenyl-amine), whose hole mobilities are different by at least three orders of magnitude, are individually applied for QLED fabrication and such HTL-dependent device performances are compared. Our best red device displays exceptional figures of merit such as a maximum luminance of 2849  cd/m², a current efficiency of 4.2  cd/A, and an external quantum efficiency of 2.5%.

Electrical and galvanomagnetic properties of nanoporous carbon samples impregnated with bromine

NASA Astrophysics Data System (ADS)

Danishevskii, A. M.; Popov, V. V.; Kyutt, R. N.; Gordeev, S. K.

2013-07-01

Nanoporous carbon samples with a large specific surface area can be filled with heavier elements or their compounds, which makes it possible to investigate the interaction of their electronic subsystems with carbon. One of the elements convenient for filling pores of carbon materials is bromine. Impregnation of nanoporous carbon samples with bromine causes the occurrence of the processes of micropore filling, monolayer adsorption, and intercalation. It has been found that samples impregnated with bromine substantially change their electrical and galvanomagnetic properties, and these changes depend on the structure of the samples. It has been shown that, if in the skeleton of a porous carbon sample there is a fraction of graphite clusters, the impregnation of the sample with bromine increases the concentration of charged carriers (holes). But when the sample has a quasi-amorphous structure, the injection of bromine into the sample leads to the appearance of a certain concentration of electrons in addition to charged mobile holes of the initial sample; i.e., the electrical conductivity becomes bipolar. In the former case, bromine molecules intercalate graphite clusters and, since bromine is an acceptor during intercalation of graphite, the hole concentration in the carbon skeleton network increases. In the latter case, bromine molecules can only be adsorbed on pore walls. As a result, the adsorption interaction between the electron shells of bromine molecules and the carbon surface leads to the formation of a donor layer near the surface and to the generation of electrons in the carbon skeleton network.

Hole localization, migration, and the formation of peroxide anion in perovskite SrTiO3

NASA Astrophysics Data System (ADS)

Chen, Hungru; Umezawa, Naoto

2014-07-01

Hybrid density functional calculations are carried out to investigate the behavior of holes in SrTiO3. As in many other oxides, it is shown that a hole tend to localize on one oxygen forming an O- anion with a concomitant lattice distortion; therefore a hole polaron. The calculated emission energy from the recombination of the localized hole and a conduction-band electron is about 2.5 eV, in good agreement with experiments. Therefore the localization of the hole or self-trapping is likely to be responsible for the green photoluminescence at low temperature, which was previously attributed to an unknown defect state. Compared to an electron, the calculated hole polaron mobility is three orders of magnitude lower at room temperature. In addition, two O- anions can bind strongly to form an O22- peroxide anion. No electronic states associated with the O22- peroxide anion are located inside the band gap or close to the band edges, indicating that it is electronically inactive. We suggest that in addition to the oxygen vacancy, the formation of the O22- peroxide anion can be an alternative to compensate acceptor doping in SrTiO3.

Dopant-Free Zinc Chlorophyll Aggregates as an Efficient Biocompatible Hole Transporter for Perovskite Solar Cells.

PubMed

Li, Mengzhen; Li, Yue; Sasaki, Shin-Ichi; Song, Jiaxing; Wang, Chen; Tamiaki, Hitoshi; Tian, Wenjing; Chen, Gang; Miyasaka, Tsutomu; Wang, Xiao-Feng

2016-10-06

Chlorophylls (Chls) are abundant, naturally occurring pigments that play key roles in light-harvesting and electron/energy transfer in natural photosynthetic apparatus. To demonstrate the idea that Chls are suitable hole transporters, we employed two Chl derivatives, Chl-1 and Chl-2, which self-assembled readily into π-stacking aggregates through a simple spincasting process, in perovskite solar cells (PSCs). The Chl aggregate films exhibit an ultra-smooth film surface, high hole mobility, appropriate energy levels, and efficient hole injection efficiencies that are all key characteristics for efficient hole transporters in PSCs. CH 3 NH 3 PbI 3-x Cl x -based PSCs with these Chls as hole transporters were fabricated and compared with P3HT as a standard hole transporter. PSCs based on Chl-1 and Chl-2 without the use of typical additives, such as 4-tert-butylpyridine and lithium bis(trifluoromethanesulfinyl)imide, gave power conversion efficiencies of 11.44 and 8.06 %, respectively. This research provides a unique way to incorporate low-cost and environmentally friendly natural photosynthetic materials in the development of highly efficient photovoltaic devices. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Influence of the geometric configuration of accretion flow on the black hole spin dependence of relativistic acoustic geometry

NASA Astrophysics Data System (ADS)

Tarafdar, Pratik; Das, Tapas K.

Linear perturbation of general relativistic accretion of low angular momentum hydrodynamic fluid onto a Kerr black hole leads to the formation of curved acoustic geometry embedded within the background flow. Characteristic features of such sonic geometry depend on the black hole spin. Such dependence can be probed by studying the correlation of the acoustic surface gravity κ with the Kerr parameter a. The κ-a relationship further gets influenced by the geometric configuration of the accretion flow structure. In this work, such influence has been studied for multitransonic shocked accretion where linear perturbation of general relativistic flow profile leads to the formation of two analogue black hole-type horizons formed at the sonic points and one analogue white hole-type horizon which is formed at the shock location producing divergent acoustic surface gravity. Dependence of the κ-a relationship on the geometric configuration has also been studied for monotransonic accretion, over the entire span of the Kerr parameter including retrograde flow. For accreting astrophysical black holes, the present work thus investigates how the salient features of the embedded relativistic sonic geometry may be determined not only by the background spacetime, but also by the flow configuration of the embedding matter.

Chlorophyll-Based Organic-Inorganic Heterojunction Solar Cells.

PubMed

Li, Yue; Zhao, Wenjie; Li, Mengzhen; Chen, Gang; Wang, Xiao-Feng; Fu, Xueqi; Kitao, Osamu; Tamiaki, Hitoshi; Sakai, Kotowa; Ikeuchi, Toshitaka; Sasaki, Shin-Ichi

2017-08-10

Solid-state chlorophyll solar cells (CSCs) employing a carboxylated chlorophyll derivative, methyl trans-3 2 -carboxypyropheophorbide a, as a light-harvesting dye sensitizer chlorophyll (DSC) deposited on mesoporous TiO 2 , on which four zinc hydroxylated chlorophyll derivatives were spin-coated for hole transporter chlorophylls (HTCs), are described. Key parameters, including the effective carrier mobility of the HTC films, as determined by the space charge-limited current method, and the frontier molecular orbitals of these DSCs and HTCs, as estimated from cyclic voltammetry and electronic absorption spectra, suggest that both charge separation and carrier transport are favorable. The power conversion efficiencies (PCEs) of the present CSCs with fluorine-doped tin oxide (FTO)/TiO 2 /DSC/HTCs/Ag were determined to follow the order of HTC-1>HTC-2>HTC-3>HTC-4, which coincided perfectly with the order of their hole mobilities. The maximum PCE achieved was 0.86 % with HTC-1. The photovoltaic devices studied herein with two types of chlorophyll derivatives as dye sensitizers and hole transporters provide a unique solution for the utilization of solar energy with a view to truly realizing "green energy". © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mg incorporation in GaN grown by plasma-assisted molecular beam epitaxy at high temperatures

NASA Astrophysics Data System (ADS)

Yang, W. C.; Lee, P. Y.; Tseng, H. Y.; Lin, C. W.; Tseng, Y. T.; Cheng, K. Y.

2016-04-01

The influence of growth conditions on the incorporation and activation of Mg in GaN grown by plasma-assisted molecular beam epitaxy at high growth temperature (>700 °C) is presented. It is found that the highest Mg incorporation with optimized electrical properties is highly sensitive both to the Mg/Ga flux ratio and III/V flux ratio. A maximum Mg activation of ~5% can be achieved at a growth temperature of 750 °C. The lowest resistivity achieved is 0.56 Ω-cm which is associated with a high hole mobility of 6.42 cm2/V-s and a moderately high hole concentration of 1.7×1018 cm-3. Although the highest hole concentration achieved in a sample grown under a low III/V flux ratio and a high Mg/Ga flux ratio reaches 7.5×1018 cm-3, the mobility is suffered due to the formation of defects by the excess Mg. In addition, we show that modulated beam growth methods do not enhance Mg incorporation at high growth temperature in contrast to those grown at a low temperature of 500 °C (Appl. Phys. Lett. 93, 172112, Namkoong et al., 2008 [19]).

Mobility spectrum analytical approach for the type-II Weyl semimetal Td-MoTe2

NASA Astrophysics Data System (ADS)

Pei, Q. L.; Luo, X.; Chen, F. C.; Lv, H. Y.; Sun, Y.; Lu, W. J.; Tong, P.; Sheng, Z. G.; Han, Y. Y.; Song, W. H.; Zhu, X. B.; Sun, Y. P.

2018-02-01

The extreme magnetoresistance (XMR) in orthorhombic W/MoTe2 arises from the combination of the perfect electron-hole (e-h) compensation effect and the unique orbital texture topology, which have comprised an intriguing research field in materials physics. Herein, we apply a special analytical approach as a function of mobility (μ-spectrum) without any hypothesis. Based on the interpretations of longitudinal and transverse electric transport of Td-MoTe2, the types and the numbers of carriers can be obtained. There are three observations: the large residual resistivity ratio can be observed in the MoTe2 single crystal sample, which indicates that the studied crystal is of high quality; we observed three electron-pockets and three hole-ones from the μ-spectrum and that the ratio of h/e is much less than 1, which shows that MoTe2 is more e-like; different from the separated peaks obtained from the hole-like μ-spectrum, those of the electron-like one are continuous, which may indicate the topological feature of electron-pockets in Td-MoTe2. The present results may provide an important clue to understanding the mechanism of the XMR effect in Td-MoTe2.

Room-temperature processed tin oxide thin film as effective hole blocking layer for planar perovskite solar cells

NASA Astrophysics Data System (ADS)

Tao, Hong; Ma, Zhibin; Yang, Guang; Wang, Haoning; Long, Hao; Zhao, Hongyang; Qin, Pingli; Fang, Guojia

2018-03-01

Tin oxide (SnO2) film with high mobility and good transmittance has been reported as a promising semiconductor material for high performance perovskite solar cells (PSCs). In this study, ultrathin SnO2 film synthesized by radio frequency magnetron sputtering (RFMS) method at room temperature was employed as hole blocking layer for planar PSCs. The room-temperature sputtered SnO2 film not only shows favourable energy band structure but also improves the surface topography of fluorine doped SnO2 (FTO) substrate and perovskite (CH3NH3PbI3) layer. Thus, this SnO2 hole blocking layer can efficiently promote electron transport and suppress carrier recombination. Furthermore, the best efficiency of 13.68% was obtained for planar PSC with SnO2 hole blocking layer prepared at room temperature. This research highlights the room-temperature preparation process of hole blocking layer in PSC and has a certain reference significance for the usage of flexible and low-cost substrates.

CuSCN-Based Inverted Planar Perovskite Solar Cell with an Average PCE of 15.6%.

PubMed

Ye, Senyun; Sun, Weihai; Li, Yunlong; Yan, Weibo; Peng, Haitao; Bian, Zuqiang; Liu, Zhiwei; Huang, Chunhui

2015-06-10

Although inorganic hole-transport materials usually possess high chemical stability, hole mobility, and low cost, the efficiency of most of inorganic hole conductor-based perovskite solar cells is still much lower than that of the traditional organic hole conductor-based cells. Here, we have successfully fabricated high quality CH3NH3PbI3 films on top of a CuSCN layer by utilizing a one-step fast deposition-crystallization method, which have lower surface roughness and smaller interface contact resistance between the perovskite layer and the selective contacts in comparison with the films prepared by a conventional two-step sequential deposition process. The average efficiency of the CuSCN-based inverted planar CH3NH3PbI3 solar cells has been improved to 15.6% with a highest PCE of 16.6%, which is comparable to that of the traditional organic hole conductor-based cells, and may promote wider application of the inexpensive inorganic materials in perovskite solar cells.

Hole effective masses and subband splitting in type-II superlattice infrared detectors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ting, David Z., E-mail: David.Z.Ting@jpl.nasa.gov; Soibel, Alexander; Gunapala, Sarath D.

We explore band structure effects to help determine the suitability of n-type type-II superlattice (T2SL) absorbers for infrared detectors. It is often assumed that the exceedingly large growth-direction band-edge curvature hole effective mass in n-type long wavelength infrared (LWIR) T2SL would lead to low hole mobility and therefore low detector collection quantum efficiency. We computed the thermally averaged conductivity effective mass and show that the LWIR T2SL hole conductivity effective mass along the growth direction can be orders of magnitude smaller than the corresponding band-edge effective mass. LWIR InAs/GaSb T2SL can have significantly smaller growth-direction hole conductivity effective mass thanmore » its InAs/InAsSb counterpart. For the InAs/InAsSb T2SL, higher Sb fraction is more favorable for hole transport. Achieving long hole diffusion length becomes progressively more difficult for the InAs/InAsSb T2SL as the cutoff wavelength increases, since its growth-direction hole conductivity effective mass increases significantly with decreasing band gap. However, this is mitigated by the fact that the splitting between the top valence subbands also increases with the cutoff wavelength, leading to reduced inter-subband scattering and increased relaxation time.« less

Electrically tunable hole g factor of an optically active quantum dot for fast spin rotations

NASA Astrophysics Data System (ADS)

Prechtel, Jonathan H.; Maier, Franziska; Houel, Julien; Kuhlmann, Andreas V.; Ludwig, Arne; Wieck, Andreas D.; Loss, Daniel; Warburton, Richard J.

2015-04-01

We report a large g factor tunability of a single hole spin in an InGaAs quantum dot via an electric field. The magnetic field lies in the in-plane direction x , the direction required for a coherent hole spin. The electrical field lies along the growth direction z and is changed over a large range, 100 kV/cm. Both electron and hole g factors are determined by high resolution laser spectroscopy with resonance fluorescence detection. This, along with the low electrical-noise environment, gives very high quality experimental results. The hole g factor ghx depends linearly on the electric field Fz,d ghx/d Fz=(8.3 ±1.2 ) ×10-4 cm/kV, whereas the electron g factor gex is independent of electric field d gex/d Fz=(0.1 ±0.3 ) ×10-4 cm/kV (results averaged over a number of quantum dots). The dependence of ghx on Fz is well reproduced by a 4 ×4 k .p model demonstrating that the electric field sensitivity arises from a combination of soft hole confining potential, an In concentration gradient, and a strong dependence of material parameters on In concentration. The electric field sensitivity of the hole spin can be exploited for electrically driven hole spin rotations via the g tensor modulation technique and based on these results, a hole spin coupling as large as ˜1 GHz can be envisaged.

Current-voltage characteristics of manganite-titanite perovskite junctions.

PubMed

Ifland, Benedikt; Peretzki, Patrick; Kressdorf, Birte; Saring, Philipp; Kelling, Andreas; Seibt, Michael; Jooss, Christian

2015-01-01

After a general introduction into the Shockley theory of current voltage (J-V) characteristics of inorganic and organic semiconductor junctions of different bandwidth, we apply the Shockley theory-based, one diode model to a new type of perovskite junctions with polaronic charge carriers. In particular, we studied manganite-titanate p-n heterojunctions made of n-doped SrTi1- y Nb y O3, y = 0.002 and p-doped Pr1- x Ca x MnO3, x = 0.34 having a strongly correlated electron system. The diffusion length of the polaron carriers was analyzed by electron beam-induced current (EBIC) in a thin cross plane lamella of the junction. In the J-V characteristics, the polaronic nature of the charge carriers is exhibited mainly by the temperature dependence of the microscopic parameters, such as the hopping mobility of the series resistance and a colossal electro-resistance (CER) effect in the parallel resistance. We conclude that a modification of the Shockley equation incorporating voltage-dependent microscopic polaron parameters is required. Specifically, the voltage dependence of the reverse saturation current density is analyzed and interpreted as a voltage-dependent electron-polaron hole-polaron pair generation and separation at the interface.

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

PubMed

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

2013-12-06

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.

Growth and Characterization of the p-type Semiconductors Tin Sulfide and Bismuth Copper Oxy Selenide

NASA Astrophysics Data System (ADS)

Francis, Jason

BiCuOSe and SnS are layered, moderate band gap (epsilon G ≈ 1 eV) semiconductors that exhibit intrinsic p type conductivity. Doping of BiCuOSe with Ca results in a slight expansion of the lattice and an increase of the hole concentration from 10 18 cm--3 to greater than 1020 cm --3. The large carrier density in undoped films is the result of copper vacancies. Mobility is unaffected by doping, remaining constant at 1.5 cm2V--1s--1 in both undoped and doped films, because the Bi-O layers serve as the source of carriers, while transport occurs within the Cu-Se layers. Bi possesses a 6s2 lone pair that was expected to hybridize with the oxygen p states at the top of the valence band, resulting in high hole mobility as compared to similar materials such as LaCuOSe, which lack this lone pair. However, both LaCuOSe and BiCuOSe have similar hole mobility. X-ray absorption and emission spectroscopy, combined with density functional theory calculations, reveal that the Bi 6 s states contribute deep within the valence band, forming bonding and anti-bonding states with O 2p at 11 eV and 3 eV below the valence band maximum, respectively. Hence, the Bi lone pair does not contribute at the top of the valence band and does not enhance the hole mobility. The Bi 6p states contribute at the bottom of the conduction band, resulting in a smaller band gap for BiCuOSe than LaCuOSe (1 eV vs. 3 eV). SnS is a potential photovoltaic absorber composed of weakly coupled layers stacked along the long axis. This weak coupling results in the formation of strongly oriented films on amorphous substrates. The optical band gap is 1.2 eV, in agreement with GW calculations. Absorption reaches 105 cm--1 within 0.5 eV of the band gap. The p type conduction arises from energetically favorable tin vacancies. Variation of growth conditions yields carrier densities of 1014 -- 1016 cm--3 and hole mobility of 7 -- 15 cm2V--1s--1. SnS was alloyed with rocksalt CaS, which was predicted to form a rocksalt structure when the calcium content is increased past 18%. Films of Sn1--x CaxS with x from 0.4 to 0.9 adopt the rocksalt structure with a band gap of 1.1-1.3 eV, with absorption greater than 105 cm--1 within about 0.7 eV of the band gap. The lattice contracts as the calcium content of the films is increased, reaching 5.7 A when x = 0.93. Films are highly insulating, but Seebeck measurements do indicate p type conduction.

Direct measurement of the thickness-dependent electronic band structure of MoS2 using angle-resolved photoemission spectroscopy.

PubMed

Jin, Wencan; Yeh, Po-Chun; Zaki, Nader; Zhang, Datong; Sadowski, Jerzy T; Al-Mahboob, Abdullah; van der Zande, Arend M; Chenet, Daniel A; Dadap, Jerry I; Herman, Irving P; Sutter, Peter; Hone, James; Osgood, Richard M

2013-09-06

We report on the evolution of the thickness-dependent electronic band structure of the two-dimensional layered-dichalcogenide molybdenum disulfide (MoS2). Micrometer-scale angle-resolved photoemission spectroscopy of mechanically exfoliated and chemical-vapor-deposition-grown crystals provides direct evidence for the shifting of the valence band maximum from Γ to K, for the case of MoS2 having more than one layer, to the case of single-layer MoS2, as predicted by density functional theory. This evolution of the electronic structure from bulk to few-layer to monolayer MoS2 had earlier been predicted to arise from quantum confinement. Furthermore, one of the consequences of this progression in the electronic structure is the dramatic increase in the hole effective mass, in going from bulk to monolayer MoS2 at its Brillouin zone center, which is known as the cause for the decreased carrier mobility of the monolayer form compared to that of bulk MoS2.

Understanding the Effects of a High Surface Area Nanostructured Indium Tin Oxide Electrode on Organic Solar Cell Performance.

PubMed

Cao, Bing; He, Xiaoming; Sorge, Jason B; Lalany, Abeed; Ahadi, Kaveh; Afshar, Amir; Olsen, Brian C; Hauger, Tate C; Mobarok, Md Hosnay; Li, Peng; Cadien, Kenneth C; Brett, Michael J; Luber, Erik J; Buriak, Jillian M

2017-11-08

Organic solar cells (OSCs) are a complex assembly of disparate materials, each with a precise function within the device. Typically, the electrodes are flat, and the device is fabricated through a layering approach of the interfacial layers and photoactive materials. This work explores the integration of high surface area transparent electrodes to investigate the possible role(s) a three-dimensional electrode could take within an OSC, with a BHJ composed of a donor-acceptor combination with a high degree of electron and hole mobility mismatch. Nanotree indium tin oxide (ITO) electrodes were prepared via glancing angle deposition, structures that were previously demonstrated to be single-crystalline. A thin layer of zinc oxide was deposited on the ITO nanotrees via atomic layer deposition, followed by a self-assembled monolayer of C 60 -based molecules that was bound to the zinc oxide surface through a carboxylic acid group. Infiltration of these functionalized ITO nanotrees with the photoactive layer, the bulk heterojunction comprising PC 71 BM and a high hole mobility low band gap polymer (PDPPTT-T-TT), led to families of devices that were analyzed for the effect of nanotree height. When the height was varied from 0 to 50, 75, 100, and 120 nm, statistically significant differences in device performance were noted with the maximum device efficiencies observed with a nanotree height of 75 nm. From analysis of these results, it was found that the intrinsic mobility mismatch between the donor and acceptor phases could be compensated for when the electron collection length was reduced relative to the hole collection length, resulting in more balanced charge extraction and reduced recombination, leading to improved efficiencies. However, as the ITO nanotrees increased in height and branching, the decrease in electron collection length was offset by an increase in hole collection length and potential deleterious electric field redistribution effects, resulting in decreased efficiency.

Coulomb scattering rates of excited states in monolayer electron-doped germanene

NASA Astrophysics Data System (ADS)

Shih, Po-Hsin; Chiu, Chih-Wei; Wu, Jhao-Ying; Do, Thi-Nga; Lin, Ming-Fa

2018-05-01

Excited conduction electrons, conduction holes, and valence holes in monolayer electron-doped germanene exhibit unusual Coulomb decay rates. The deexcitation processes are studied using the screened exchange energy. They might utilize the intraband single-particle excitations (SPEs), the interband SPEs, and the plasmon modes, depending on the quasiparticle states and the Fermi energies. The low-lying valence holes can decay through the undamped acoustic plasmon, so that they present very fast Coulomb deexcitations, nonmonotonous energy dependence, and anisotropic behavior. However, the low-energy conduction electrons and holes are similar to those in a two-dimensional electron gas. The higher-energy conduction states and the deeper-energy valence ones behave similarly in the available deexcitation channels and have a similar dependence of decay rate on the wave vector k .

Thickness dependences of solar cell performance

NASA Technical Reports Server (NTRS)

Sah, C. T.

1982-01-01

The significance of including factors such as the base resistivity loss for solar cells thicker than 100 microns and emitter and BSF layer recombination for thin cells in predicting the fill factor and efficiency of solar cells is demonstrated analytically. A model for a solar cell is devised with the inclusion of the dopant impurity concentration profile, variation of the electron and hole mobility with dopant concentration, the concentration and thermal capture and emission rates of the recombination center, device temperature, the AM1 spectra and the Si absorption coefficient. Device equations were solved by means of the transmission line technique. The analytical results were compared with those of low-level theory for cell performance. Significant differences in predictions of the fill factor resulted, and inaccuracies in the low-level approximations are discussed.

Vibrational relaxation of hot carriers in C60 molecule

NASA Astrophysics Data System (ADS)

Madjet, Mohamed; Chakraborty, Himadri

2017-04-01

Electron-phonon coupling in molecular systems is at the heart of several important physical phenomena, including the mobility of carriers in organic electronic devices. Following the optical absorption, the vibrational relaxation of excited (hot) electrons and holes to the fullerene band-edges driven by electron-phonon coupling, known as the hot carrier thermalization process, is of particular fundamental interest. Using the non-adiabatic molecular dynamical methodology (PYXAID + Quantum Espresso) based on density functional approach, we have performed a simulation of vibrionic relaxations of hot carriers in C60. Time-dependent population decays and transfers in the femtosecond scale from various excited states to the states at the band-edge are calculated to study the details of this relaxation process. This work was supported by the U.S. National Science Foundation.

Reducing the contact resistance in bottom-contact-type organic field-effect transitors using an AgO x interface layer

NASA Astrophysics Data System (ADS)

Minagawa, Masahiro; Kim, Yeongin; Claus, Martin; Bao, Zhenan

2017-09-01

Bottom-contact organic field-effect transistors (OFETs) are prepared by inserting an AgO x layer between a pentacene layer and the source-drain electrodes. The contact resistance in the device is ˜8.1 kΩ·cm with an AgO x layer oxidized for 60 s but reaches 116.9 kΩ·cm with a non-oxidized Ag electrode. The drain current and mobility in the OFETs with the AgO x layer increase with the oxidization time and then gradually plateau, and this trend strongly depends on the work function of the Ag surface. Further, the hole injection is enhanced by the presence of Ag2O but inhibited by the presence of AgO.

Experimental study of uniaxial stress effects on Coulomb-limited mobility in p-type metal-oxide-semiconductor field-effect transistors

NASA Astrophysics Data System (ADS)

Kobayashi, Shigeki; Saitoh, Masumi; Nakabayashi, Yukio; Uchida, Ken

2007-11-01

Uniaxial stress effects on Coulomb-limited mobility (μCoulomb) in Si metal-oxide-semiconductor field-effect transistors (MOSFETs) are investigated experimentally. By using the four-point bending method, uniaxial stress corresponding to 0.1% strain is applied to MOSFETs along the channel direction. It is found that μCoulomb in p-type MOSFETs is enhanced greatly by uniaxial stress; μCoulomb is as sensitive as phonon-limited mobility. The high sensitivity of μCoulomb in p-type MOSFETs to stress arises from the stress-induced change of hole effective mass.

Enhanced photovoltaic performance in nanoimprinted pentacene-PbS nanocrystal hybrid device

NASA Astrophysics Data System (ADS)

Dissanayake, D. M. N. M.; Adikaari, A. A. D. T.; Silva, S. R. P.

2008-03-01

Pentacene and PbS nanocrystal bilayer photovoltaic devices are fabricated after the pentacene layer is subjected to nanoimprinting using a laser textured silicon stamp. Increased short circuit current densities are observed for the imprinted devices, which are attributed to increased charge mobility in the pentacene film caused by the decrease in the intermolecular distances during nanoimprinting. This work is consistent with previous reports where hydrostatic pressure induced mobility increases have been observed in polyacenes under gigapascal pressure regimes. It is believed that the pentacene film undergoes localized high pressures during nanoimprinting, giving rise to the increased hole mobilities.

Sulphide mineral evolution and metal mobility during alteration of the oceanic crust: Insights from ODP Hole 1256D

NASA Astrophysics Data System (ADS)

Patten, C. G. C.; Pitcairn, I. K.; Teagle, D. A. H.; Harris, M.

2016-11-01

Fluxes of metals during the hydrothermal alteration of the oceanic crust have far reaching effects including buffering of the compositions of the ocean and lithosphere, supporting microbial life and the formation of sulphide ore deposits. The mechanisms responsible for metal mobilisation during the evolution of the oceanic crust are complex and are neither fully constrained nor quantified. Investigations into the mineral reactions that release metals, such as sulphide leaching, would generate better understanding of the controls on metal mobility in the oceanic crust. We investigate the sulphide and oxide mineral paragenesis and the extent to which these minerals control the metal budget in samples from Ocean Drilling Program (ODP) Hole 1256D. The ODP Hole 1256D drill core provides a unique sample suite representative of a complete section of a fast-spreading oceanic crust from the volcanic section down to the plutonic complex. The sulphide population at Hole 1256D is divided into five groups based on mineralogical assemblage, lithological location and texture: the magmatic, metasomatised, high temperature hydrothermal, low temperature and patchy sulphides. The initiation of hydrothermal alteration by downward flow of moderate temperature (250-350 °C) hydrothermal fluids under oxidising conditions leads to metasomatism of the magmatic sulphides in the sheeted dyke and plutonic complexes. Subsequent increase in the degree of hydrothermal alteration at temperatures >350 °C under reducing conditions then leads to the leaching of the metasomatised sulphides by rising hydrothermal fluids. Mass balance calculations show that the mobility of Cu, Se and Au occurs through sulphide leaching during high temperature hydrothermal alteration and that the mobility of Zn, As, Sb and Pb is controlled by silicate rather than sulphide alteration. Sulphide leaching is not complete at Hole 1256D and more advanced alteration would mobilise greater masses of metals. Alteration of oxide minerals does not release significant quantities of metal into the hydrothermal fluid at Hole 1256D. Mixing of rising high temperature fluids with low temperature fluids, either in the upper sheeted dyke section or in the transitional zone, triggers local high temperature hydrothermal sulphide precipitation and trapping of Co, Ni, Cu, Zn, As, Ag, Sb, Se, Te, Au, Hg and Pb. In the volcanic section, low temperature fluid circulation (<150 °C) leads to low temperature sulphide precipitation in the form of pyrite fronts that have high As concentrations due to uptake from the circulating fluids. Deep late low temperature circulation in the sheeted dyke and the plutonic complexes results in local precipitation of patchy sulphides and local metal remobilisation. Control of sulphides over Au, Se and Cu throughout fast-spreading mid-oceanic crust history implies that the generation of hydrothermal fluids enriched in these metals, which can eventually form VMS deposits, is strongly controlled by sulphide leaching.

Drill-back studies examine fractured, heated rock

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wollenberg, H.A.; Flexser, S.; Myer, L.R.

1990-01-01

To investigate the effects of heating on the mineralogical, geochemical, and mechanical properties of rock by high-level radioactive waste, cores are being examined from holes penetrating locations where electric heaters simulated the presence of a waste canister, and from holes penetration natural hydrothermal systems. Results to date indicate the localized mobility and deposition of uranium in an open fracture in heated granitic rock, the mobility of U in a breccia zone in an active hydrothermal system in tuff, and the presence of U in relatively high concentration in fracture-lining material in tuff. Mechanical -- property studies indicate that differences inmore » compressional- and shear-wave parameters between heated and less heated rock can be attributed to differences in the density of microcracks. Emphasis has shifted from initial studies of granitic rock at Stripa, Sweden to current investigations of welded tuff at the Nevada Test Site. 7 refs., 8 figs.« less

An efficient collaborative approach for black hole attack discovery and mitigating its impact in manet

NASA Astrophysics Data System (ADS)

Devipriya, K.; Ivy, B. Persis Urbana; Prabha, D.

2018-04-01

A mobile ad hoc network (MANET) is an assemblage of nodes composed of mobile devices coupled in various ways wirelessly which do not have any central administration. Each node in MANET cooperates in forwarding packets in the network. This type of collaboration incurs high cost but there exits nodes that declines to cooperate leading to selfish conduct of nodes which effects overall network performance. To discover the attacks caused by such nodes, a renowned mechanism using watchdog can be deployed. In infrastructure less network attack detection and reaction and high false positives, false negatives initiating black hole attack becomes major issue in watchdog. This paper put forward a collaborative approach for identifying such attacks in MANET. Through abstract analysis and extensive simulation of this approach, the detection time of misbehaved nodes is reduced and substantial enhancement in overhead and throughput is witnessed.

Ambipolar insulator-to-metal transition in black phosphorus by ionic-liquid gating.

PubMed

Saito, Yu; Iwasa, Yoshihiro

2015-03-24

We report ambipolar transport properties in black phosphorus using an electric-double-layer transistor configuration. The transfer curve clearly exhibits ambipolar transistor behavior with an ON-OFF ratio of ∼5 × 10(3). The band gap was determined as ≅0.35 eV from the transfer curve, and Hall-effect measurements revealed that the hole mobility was ∼190 cm(2)/(V s) at 170 K, which is 1 order of magnitude larger than the electron mobility. By inducing an ultrahigh carrier density of ∼10(14) cm(-2), an electric-field-induced transition from the insulating state to the metallic state was realized, due to both electron and hole doping. Our results suggest that black phosphorus will be a good candidate for the fabrication of functional devices, such as lateral p-n junctions and tunnel diodes, due to the intrinsic narrow band gap.

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

NASA Astrophysics Data System (ADS)

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

2013-09-01

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

Characterisation of Redlen high-flux CdZnTe

NASA Astrophysics Data System (ADS)

Thomas, B.; Veale, M. C.; Wilson, M. D.; Seller, P.; Schneider, A.; Iniewski, K.

2017-12-01

CdZnTe is a promising material for the current generation of free electron laser light sources and future laser-driven γ-ray sources which require detectors capable of high flux imaging at X-ray and γ-ray energies (> 10 keV) . However, at high fluxes CdZnTe has been shown to polarise due to hole trapping, leading to poor performance. Novel Redlen CdZnTe material with improved hole transport properties has been designed for high flux applications. Small pixel CdZnTe detectors were fabricated by Redlen Technologies and flip-chip bonded to PIXIE ASICs. An XIA Digital Gamma Finder PIXIE-16 system was used to digitise each of the nine analogue signals with a timing resolution of 10 ns. Pulse shape analysis was used to extract the rise times and amplitude of signals. These were measured as a function of applied bias voltage and used to calculate the mobility (μ) and mobility-lifetime (μτ) of electrons and holes in the material for three identical detectors. The measured values of the transport properties of electrons in the high-flux-capable material was lower than previously reported for Redlen CdZnTe material (μeτe ~ 1 × 10-3 cm2V-1 and μe ~ 1000 cm2V-1s-1) while the hole transport properties were found to have improved (μhτh ~ 3 × 10-4 cm2V-1 and μh ~ 100 cm2V-1s-1).

Transient carrier dynamics in a Mott insulator with antiferromagnetic order

NASA Astrophysics Data System (ADS)

Iyoda, Eiki; Ishihara, Sumio

2014-03-01

We study transient dynamics of hole carriers injected into a Mott insulator with antiferromagnetic long-range order. This "dynamical hole doping" contrasts with chemical hole doping. The theoretical framework for the transient carrier dynamics is presented based on the two-dimensional t-J model. The time dependencies of the optical conductivity spectra, as well as the one-particle excitation spectra, are calculated based on the Keldysh Green's function formalism at zero temperature combined with the self-consistent Born approximation. In the early stage after dynamical hole doping, the Drude component appears, and then incoherent components originating from hole-magnon scattering start to grow. Fast oscillatory behavior owing to coherent magnon and slow relaxation dynamics are confirmed in the spectra. The time profiles are interpreted as doped bare holes being dressed by magnon clouds and relaxed into spin polaron quasiparticle states. The characteristic relaxation times for Drude and incoherent peaks strongly depend on the momentum of the dynamically doped hole and the exchange constant. Implications for recent pump-probe experiments are discussed.

Theoretical insights into the effect of a conjugated core on the hole transport properties of hole-transporting materials for perovskite solar cells.

PubMed

Zhang, Zemin; Hu, Weixia; Cui, Jianyu; He, Rongxing; Shen, Wei; Li, Ming

2017-09-20

Conjugated bifluorenylidene and naphthalene central cores are introduced into hole-transporting materials DT1 and DT2 to replace the spiro-core of the reported, highly efficient FDT. The effects of the conjugated core on the geometrics, electronic properties and hole transport properties are investigated by using density functional theory coupled with Marcus theory and the Einstein relation. The calculated results show that DT1 (-5.21 eV) and DT2 (-5.23 eV) have lower HOMO levels than FDT (-5.15 eV), which indicates that the perovskite solar cells with conjugated hole-transporting materials can have higher open-circuit voltages. The introduction of the conjugated core is beneficial to the more efficient face-to-face packing pattern of the dimer, resulting in a larger intermolecular electronic coupling. Importantly, it is found that DT1 (1.6 × 10 -3 cm 2 V -1 s -1 ) and DT2 (2.7 × 10 -2 cm 2 V -1 s -1 ) exhibit relatively higher hole mobilities than FDT (1.3 × 10 -4 cm 2 V -1 s -1 ) owing to the larger electronic coupling. Therefore, enhanced hole transport ability can be achieved by switching from the spiro-core to the conjugated core. The present work provides a new strategy to improve the hole transport properties of hole-transporting materials, which will contribute to the development of conjugated small molecules as hole-transporting materials in efficient perovskite solar cells.

Effect of organic small-molecule hole injection materials on the performance of inverted organic solar cells

NASA Astrophysics Data System (ADS)

Li, Jie; Zheng, Yifan; Zheng, Ding; Yu, Junsheng

2016-07-01

In this study, the influence of small-molecule organic hole injection materials on the performance of organic solar cells (OSCs) as the hole transport layer (HTL) with an architecture of ITO/ZnO/P3HT:PC71BM/HTL/Ag has been investigated. A significant enhancement on the performance of OSCs from 1.06% to 2.63% is obtained by using N, N‧-bis(1-naphthalenyl)-N, N‧-bis-phenyl-(1, 1‧-biphenyl)-4, 4‧-diamine (NPB) HTL. Through the resistance simulation and space-charge limited current analysis, we found that NPB HTL cannot merely improve the hole mobility of the device but also form the Ohmic contact between the active layer and anode. Besides, when we apply mix HTL by depositing the NPB on the surface of molybdenum oxide, the power conversion efficiency of OSC are able to be further improved to 2.96%.

Charged BTZ black holes in the context of massive gravity's rainbow

NASA Astrophysics Data System (ADS)

Hendi, S. H.; Panahiyan, S.; Upadhyay, S.; Eslam Panah, B.

2017-04-01

Banados, Teitelboim, and Zanelli (BTZ) black holes are excellent laboratories for studying black hole thermodynamics, which is a bridge between classical general relativity and the quantum nature of gravitation. In addition, three-dimensional gravity could have equipped us for exploring some of the ideas behind the two-dimensional conformal field theory based on the AdS3/CFT2 . Considering the significant interest in these regards, we examine charged BTZ black holes. We consider the system contains massive gravity with energy dependent spacetime to enrich the results. In order to make high curvature (energy) BTZ black holes more realistic, we modify the theory by energy dependent constants. We investigate thermodynamic properties of the solutions by calculating heat capacity and free energy. We also analyze thermal stability and study the possibility of the Hawking-Page phase transition. At last, we study the geometrical thermodynamics of these black holes and compare the results of various approaches.

Mobile Phone Dependence, Social Support and Impulsivity in Chinese University Students.

PubMed

Mei, Songli; Chai, Jingxin; Wang, Shi-Bin; Ng, Chee H; Ungvari, Gabor S; Xiang, Yu-Tao

2018-03-13

This study examined the frequency of mobile phone dependence in Chinese university students and explored its association with social support and impulsivity. Altogether, 909 university students were consecutively recruited from a large university in China. Mobile phone use, mobile phone dependence, impulsivity, and social support were measured with standardized instruments. The frequency of possible mobile phone use and mobile phone dependence was 78.3% and 7.4%, respectively. Multinomial logistic regression analyses revealed that compared with no mobile phone dependence, possible mobile phone dependence was significantly associated with being male ( p = 0.04, OR = 0.7, 95% CI: 0.4-0.98), excessive mobile phone use ( p < 0.001, OR = 1.2, 95% CI: 1.09-1.2), and impulsivity ( p < 0.001, OR = 1.05, 95% CI: 1.03-1.06), while mobile phone dependence was associated with length of weekly phone use ( p = 0.01, OR = 2.5, 95% CI: 1.2-5.0), excessive mobile phone use ( p < 0.001, OR = 1.3, 95% CI: 1.2-1.4), and impulsivity ( p < 0.001, OR = 1.08, 95% CI: 1.05-1.1). The frequency of possible mobile phone dependence and mobile phone dependence was high in this sample of Chinese university students. A significant positive association with impulsivity was found, but not with social support.

Hole diffusivity in GaAsBi alloys measured by a picosecond transient grating technique

NASA Astrophysics Data System (ADS)

Nargelas, S.; Jarašiunas, K.; Bertulis, K.; Pačebutas, V.

2011-02-01

We applied a time-resolved transient grating technique for investigation of nonequilibrium carrier dynamics in GaAs1-xBix alloys with x =0.025-0.063. The observed decrease in carrier bipolar diffusivity with lowering temperature and its saturation below 80 K revealed a strong localization of nonequilibrium holes. Thermal activation energy ΔEa=46 meV of diffusivity and low hole mobility value μh=10-20 cm2/V s at room temperature confirmed the hybridization model of the localized Bi states with the valence band of GaAs. Nonlinear increase in carrier recombination rate with the Bi content, 1/τR∝Bi(x )3.2 indicated an increasing structural disorder in the alloy.

An Overview of Radiation-Induced Interface Traps in MOS (Metal-Oxide Semiconductor) Structures

DTIC Science & Technology

1989-11-01

to be Controlled by hole transport to the Si/S1 02 interface and by neutral hydrogen diffusion, respectively. ’We also discuss several models which...trivalent Si which is undergo a dispersive hopping transport which not mobile and a mobile nonbridging oxygen. controls the rate of interface state... control the buildup of ping event itself seems to be a phonon-assisted radiation-induced interface states are subjects tunneling transition between

Remarks on the necessity and implications of state-dependence in the black hole interior

NASA Astrophysics Data System (ADS)

Papadodimas, Kyriakos; Raju, Suvrat

2016-04-01

We revisit the "state-dependence" of the map that we proposed recently between bulk operators in the interior of a large anti-de Sitter black hole and operators in the boundary CFT. By refining recent versions of the information paradox, we show that this feature is necessary for the CFT to successfully describe local physics behind the horizon—not only for single-sided black holes but even in the eternal black hole. We show that state-dependence is invisible to an infalling observer who cannot differentiate these operators from those of ordinary quantum effective field theory. Therefore the infalling observer does not observe any violations of quantum mechanics. We successfully resolve a large class of potential ambiguities in our construction. We analyze states where the CFT is entangled with another system and show that the ER =EPR conjecture emerges from our construction in a natural and precise form. We comment on the possible semiclassical origins of state-dependence.

A charge carrier transport model for donor-acceptor blend layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fischer, Janine, E-mail: janine.fischer@iapp.de; Widmer, Johannes; Koerner, Christian

2015-01-28

Highly efficient organic solar cells typically comprise donor-acceptor blend layers facilitating effective splitting of excitons. However, the charge carrier mobility in the blends can be substantially smaller than in neat materials, hampering the device performance. Currently, available mobility models do not describe the transport in blend layers entirely. Here, we investigate hole transport in a model blend system consisting of the small molecule donor zinc phthalocyanine (ZnPc) and the acceptor fullerene C{sub 60} in different mixing ratios. The blend layer is sandwiched between p-doped organic injection layers, which prevent minority charge carrier injection and enable exploiting diffusion currents for themore » characterization of exponential tail states from a thickness variation of the blend layer using numerical drift-diffusion simulations. Trap-assisted recombination must be considered to correctly model the conductivity behavior of the devices, which are influenced by local electron currents in the active layer, even though the active layer is sandwiched in between p-doped contacts. We find that the density of deep tail states is largest in the devices with 1:1 mixing ratio (E{sub t} = 0.14 eV, N{sub t} = 1.2 × 10{sup 18 }cm{sup −3}) directing towards lattice disorder as the transport limiting process. A combined field and charge carrier density dependent mobility model are developed for this blend layer.« less

Charge-Trapping-Induced Non-Ideal Behaviors in Organic Field-Effect Transistors.

PubMed

Un, Hio-Ieng; Cheng, Peng; Lei, Ting; Yang, Chi-Yuan; Wang, Jie-Yu; Pei, Jian

2018-05-01

Organic field-effect transistors (OFETs) with impressively high hole mobilities over 10 cm 2 V -1 s -1 and electron mobilities over 1 cm 2 V -1 s -1 have been reported in the past few years. However, significant non-ideal electrical characteristics, e.g., voltage-dependent mobilities, have been widely observed in both small-molecule and polymer systems. This issue makes the accurate evaluation of the electrical performance impossible and also limits the practical applications of OFETs. Here, a semiconductor-unrelated, charge-trapping-induced non-ideality in OFETs is reported, and a revised model for the non-ideal transfer characteristics is provided. The trapping process can be directly observed using scanning Kelvin probe microscopy. It is found that such trapping-induced non-ideality exists in OFETs with different types of charge carriers (p-type or n-type), different types of dielectric materials (inorganic and organic) that contain different functional groups (OH, NH 2 , COOH, etc.). As fas as it is known, this is the first report for the non-ideal transport behaviors in OFETs caused by semiconductor-independent charge trapping. This work reveals the significant role of dielectric charge trapping in the non-ideal transistor characteristics and also provides guidelines for device engineering toward ideal OFETs. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mobility spectrum analytical approach for intrinsic band picture of Ba(FeAs)2

NASA Astrophysics Data System (ADS)

Huynh, K. K.; Tanabe, Y.; Urata, T.; Heguri, S.; Tanigaki, K.; Kida, T.; Hagiwara, M.

2014-09-01

Unconventional high temperature superconductivity as well as three-dimensional bulk Dirac cone quantum states arising from the unique d-orbital topology have comprised an intriguing research area in physics. Here we apply a special analytical approach using a mobility spectrum, in which the carrier number is conveniently described as a function of mobility without any hypothesis, both on the types and the numbers of carriers, for the interpretations of longitudinal and transverse electric transport of high quality single crystal Ba(FeAs)2 in a wide range of magnetic fields. We show that the majority carriers are accommodated in large parabolic hole and electron pockets with very different topology as well as remarkably different mobility spectra, whereas the minority carriers reside in Dirac quantum states with the largest mobility as high as 70,000 cm2(Vs)-1. The deduced mobility spectra are discussed and compared to the reported sophisticated first principle band calculations.

Quinoline-Flanked Diketopyrrolopyrrole Copolymers Breaking through Electron Mobility over 6 cm2 V-1 s-1 in Flexible Thin Film Devices.

PubMed

Ni, Zhenjie; Dong, Huanli; Wang, Hanlin; Ding, Shang; Zou, Ye; Zhao, Qiang; Zhen, Yonggang; Liu, Feng; Jiang, Lang; Hu, Wenping

2018-03-01

Herein, the design and synthesis of novel π-extended quinoline-flanked diketopyrrolopyrrole (DPP) [abbreviated as QDPP] motifs and corresponding copolymers named PQDPP-T and PQDPP-2FT for high performing n-type organic field-effect transistors (OFETs) in flexible organic thin film devices are reported. Serving as DPP-flankers in backbones, quinoline is found to effectively tune copolymer optoelectric properties. Compared with TDPP and pyridine-flanked DPP (PyDPP) analogs, widened bandgaps and strengthened electron deficiency are achieved. Moreover, both hole and electron mobility are improved two orders of magnitude compared to those of PyDPP analogs (PPyDPP-T and PPyDPP-2FT). Notably, featuring an all-acceptor-incorporated backbone, PQDPP-2FT exhibits electron mobility of 6.04 cm 2 V -1 s -1 , among the highest value in OFETs fabricated on flexible substrates to date. Moreover, due to the widened bandgap and strengthened electron deficiency of PQDPP, n-channel on/off ratio over 10 5 with suppressed hole transport is first realized in the ambipolar DPP-based copolymers. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mine roof driller-bolter apparatus and method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hibbard, G.A.; Lumbra, R.C.; Morrison, W.D.

1983-12-13

An apparatus for bolting the roof of an underground mine is disclosed comprising a mobile frame, a boom extending from the frame and a housing provided at the end of the frame. The housing supports an upwardly extending stinger, a drilling mechanism including a drill centralizer having a central bore therethrough and a passageway in communication with the central bore, a device for delivering a container of roof bolting anchoring media through the passageway and through the drill centralizer and into a drilled hole, a device for indexing a roof bolt into alignment with the drilled hole and a spinnermore » for driving the roof bolt into the drilled hole. The present invention also provides a method for bolting the roof of an underground mine comprising the steps of stinging a housing against the roof of the mine, moving a drill centralizer into communication with the roof and drilling a hole in the roof. Without retracting the drill centralizer from communication with the roof, a container of roof bolt anchoring media is delivered through the centralizer and into the drilled hole. The drill centralizer is thereafter retracted and the housing is moved to align a roof bolt with a drilled hole. Then the roof bolt is driven into the drilled hole and the bolt anchoring media sets around the bolt.« less

Rogue waves lead to the instability in GaN semiconductors

PubMed Central

Yahia, M. E.; Tolba, R. E.; El-Bedwehy, N. A.; El-Labany, S. K.; Moslem, W. M.

2015-01-01

A new approach to understand the electron/hole interfaced plasma in GaN high electron mobility transistors (HEMTs). A quantum hydrodynamic model is constructed to include electrons/holes degenerate pressure, Bohm potential, and the exchange/correlation effect and then reduced to the nonlinear Schrödinger equation (NLSE). Numerical analysis of the latter predicts the rough (in)stability domains, which allow for the rogue waves to occur. Our results might give physical solution rather than the engineering one to the intrinsic problems in these high frequency/power transistors. PMID:26206731

The x-ray time of flight method for investigation of ghosting in amorphous selenium-based flat panel medical x-ray imagers.

PubMed

Rau, A W; Bakueva, L; Rowlands, J A

2005-10-01

Amorphous selenium (a-Se) based real-time flat-panel imagers (FPIs) are finding their way into the digital radiology department because they offer the practical advantages of digital x-ray imaging combined with an image quality that equals or outperforms that of conventional systems. The temporal imaging characteristics of FPIs can be affected by ghosting (i.e., radiation-induced changes of sensitivity) when the dose to the detector is high (e.g., portal imaging and mammography) or the images are acquired at a high frame rate (e.g., fluoroscopy). In this paper, the x-ray time-of-flight (TOF) method is introduced as a tool for the investigation of ghosting in a-Se photoconductor layers. The method consists of irradiating layers of a-Se with short x-ray pulses. From the current generated in the a-Se layer, ghosting is quantified and the ghosting parameters (charge carrier generation rate and carrier lifetimes and mobilities) are assessed. The x-ray TOF method is novel in that (1) x-ray sensitivity (S) and ghosting parameters can be measured simultaneously, (2) the transport of both holes and electrons can be isolated, and (3) the method is applicable to the practical a-Se layer structure with blocking contacts used in FPIs. The x-ray TOF method was applied to an analysis of ghosting in a-Se photoconductor layers under portal imaging conditions, i.e., 1 mm thick a-Se layers, biased at 5 V/ microm, were irradiated using a 6 MV LINAC x-ray beam to a total dose (ghosting dose) of 30 Gy. The initial sensitivity (S0) of the a-Se layers was 63 +/- 2 nC cm(-2) cGy(-1). It was found that S decreases to 30% of S0 after a ghosting dose of 5 Gy and to 21% after 30 Gy at which point no further change in S occurs. At an x-ray intensity of 22 Gy/s (instantaneous dose rate during a LINAC x-ray pulse), the charge carrier generation rate was 1.25 +/- 0.1 x 10(22) ehp m(-3) s(-1) and, to a first approximation, independent of the ghosting dose. However, both hole and electron transport showed a strong dependence on the ghosting dose: hole transport decreased by 61%, electron transport by up to approximately 80%. Therefore, degradation of both hole and electron transport due to the recombination of mobile charge carriers with trapped carriers (of opposite polarity) were identified as the main cause of ghosting in this study.

Towards predictive many-body calculations of phonon-limited carrier mobilities in semiconductors

NASA Astrophysics Data System (ADS)

Poncé, Samuel; Margine, Elena R.; Giustino, Feliciano

2018-03-01

We probe the accuracy limit of ab initio calculations of carrier mobilities in semiconductors, within the framework of the Boltzmann transport equation. By focusing on the paradigmatic case of silicon, we show that fully predictive calculations of electron and hole mobilities require many-body quasiparticle corrections to band structures and electron-phonon matrix elements, the inclusion of spin-orbit coupling, and an extremely fine sampling of inelastic scattering processes in momentum space. By considering all these factors we obtain excellent agreement with experiment, and we identify the band effective masses as the most critical parameters to achieve predictive accuracy. Our findings set a blueprint for future calculations of carrier mobilities, and pave the way to engineering transport properties in semiconductors by design.

Failure mechanisms of uni-ply composite plates with a circular hole under static compressive loading

NASA Technical Reports Server (NTRS)

Khamseh, A. R.; Waas, A. M.

1992-01-01

The objective of the study was to identify and study the failure mechanisms associated with compressive-loaded uniply graphite/epoxy square plates with a central circular hole. It is found that the type of compressive failure depends on the hole size. For large holes with the diameter/width ratio exceeding 0.062, fiber buckling/kinking initiated at the hole is found to be the dominant failure mechanism. In plates with smaller hole sizes, failure initiates away from the hole edge or complete global failure occurs. Critical buckle wavelengths at failure are presented as a function of the normalized hole diameter.

Mobile Phone Dependence, Social Support and Impulsivity in Chinese University Students

PubMed Central

Mei, Songli; Chai, Jingxin; Wang, Shi-Bin; Ng, Chee H.; Ungvari, Gabor S.; Xiang, Yu-Tao

2018-01-01

This study examined the frequency of mobile phone dependence in Chinese university students and explored its association with social support and impulsivity. Altogether, 909 university students were consecutively recruited from a large university in China. Mobile phone use, mobile phone dependence, impulsivity, and social support were measured with standardized instruments. The frequency of possible mobile phone use and mobile phone dependence was 78.3% and 7.4%, respectively. Multinomial logistic regression analyses revealed that compared with no mobile phone dependence, possible mobile phone dependence was significantly associated with being male (p = 0.04, OR = 0.7, 95% CI: 0.4–0.98), excessive mobile phone use (p < 0.001, OR = 1.2, 95% CI: 1.09–1.2), and impulsivity (p < 0.001, OR = 1.05, 95% CI: 1.03–1.06), while mobile phone dependence was associated with length of weekly phone use (p = 0.01, OR = 2.5, 95% CI: 1.2–5.0), excessive mobile phone use (p < 0.001, OR = 1.3, 95% CI: 1.2–1.4), and impulsivity (p < 0.001, OR = 1.08, 95% CI: 1.05–1.1). The frequency of possible mobile phone dependence and mobile phone dependence was high in this sample of Chinese university students. A significant positive association with impulsivity was found, but not with social support. PMID:29533986

Ambipolar nature of dimethyl benzo difuran (DMBDF) molecule: A charge transport study

NASA Astrophysics Data System (ADS)

Sahoo, Smruti Ranjan; Sahu, Sridhar

2017-05-01

We describe a theoretical study of the charge transport properties of the organic dimethyl benzo difuran (DMBDF) molecule based on density functional theory (DFT). Reorganization energy, ionization potential (IP), electron affinity (EA), energy gaps, transfer integral (t) and charge mobility (μ) has been studied to depict the transport properties in the conjugated organic molecules. We computed, large homo transfer integral and IP value leading to high hole mobility (4.46 cm2/V sec). However, the electron reorganization energy (0.34 eV) and the electron mobility of 1.62 cm2/V sec, infers that the DMBDF organic molecule bears an ambipolar character.

VITRECTOMY FOR MACULAR DISORDERS ASSOCIATED WITH LAMELLAR MACULAR HOLE EPIRETINAL PROLIFERATION.

PubMed

Choi, Won Seok; Merlau, Daniel J; Chang, Stanley

2018-04-01

To compare the surgical outcome of a lamellar macular hole (LMH) depending on lamellar hole-associated epiretinal proliferation (LHEP) and full-thickness macular hole. This is a retrospective chart review. Thirty-three patients were enrolled for this study. The patients were divided into three groups depending on the type of macular hole and presence of LHEP. Group 1 had epiretinal membranes with LMH without LHEP, Group 2 had LMH with LHEP, and Group 3 had full-thickness macular hole with LHEP. The best-corrected visual acuity was recorded and optical coherence tomography scans were obtained. Preoperative best-corrected visual acuity showed no significant difference between groups (P = 0.968). Final visual acuity of Group 1 was better than that of Group 2 (P = 0.009). Group 1 showed less postoperative ellipsoid zone disruption compared with Group 2 (P = 0.010), and the duration of LHEP to surgery had no significant correlation with postoperative visual acuity (P = 0.629). Lamellar macular hole with LHEP showed poorer visual outcomes compared with those with highly reflective epiretinal membranes. Lamellar macular hole with LHEP showed a greater chance of ellipsoid zone disruption. These findings may explain the wide variability of visual outcomes previously reported after vitrectomy for LMH.

Many-body Effects in a Laterally Inhomogeneous Semiconductor Quantum Well

NASA Technical Reports Server (NTRS)

Ning, Cun-Zheng; Li, Jian-Zhong; Biegel, Bryan A. (Technical Monitor)

2002-01-01

Many body effects on conduction and diffusion of electrons and holes in a semiconductor quantum well are studied using a microscopic theory. The roles played by the screened Hartree-Fock (SHE) terms and the scattering terms are examined. It is found that the electron and hole conductivities depend only on the scattering terms, while the two-component electron-hole diffusion coefficients depend on both the SHE part and the scattering part. We show that, in the limit of the ambipolax diffusion approximation, however, the diffusion coefficients for carrier density and temperature are independent of electron-hole scattering. In particular, we found that the SHE terms lead to a reduction of density-diffusion coefficients and an increase in temperature-diffusion coefficients. Such a reduction or increase is explained in terms of a density-and temperature dependent energy landscape created by the bandgap renormalization.

Interdye Hole Transport Accelerates Recombination in Dye Sensitized Mesoporous Films.

PubMed

Moia, Davide; Szumska, Anna; Vaissier, Valérie; Planells, Miquel; Robertson, Neil; O'Regan, Brian C; Nelson, Jenny; Barnes, Piers R F

2016-10-12

Charge recombination between oxidized dyes attached to mesoporous TiO 2 and electrons in the TiO 2 was studied in inert electrolytes using transient absorption spectroscopy. Simultaneously, hole transport within the dye monolayers was monitored by transient absorption anisotropy. The rate of recombination decreased when hole transport was inhibited selectively, either by decreasing the dye surface coverage or by changing the electrolyte environment. From Monte Carlo simulations of electron and hole diffusion in a particle, modeled as a cubic structure, we identify the conditions under which hole lifetime depends on the hole diffusion coefficient for the case of normal (disorder free) diffusion. From simulations of transient absorption and transient absorption anisotropy, we find that the rate and the dispersive character of hole transport in the dye monolayer observed spectroscopically can be explained by incomplete coverage and disorder in the monolayer. We show that dispersive transport in the dye monolayer combined with inhomogeneity in the TiO 2 surface reactivity can contribute to the observed stretched electron-hole recombination dynamics and electron density dependence of hole lifetimes. Our experimental and computational analysis of lateral processes at interfaces can be applied to investigate and optimize charge transport and recombination in solar energy conversion devices using electrodes functionalized with molecular light absorbers and catalysts.

Anomalous Buckling Characteristics of Laminated Metal-Matrix Composite Plates with Central Square Holes

NASA Technical Reports Server (NTRS)

Ko, William L.

1998-01-01

Compressive buckling analysis was performed on metal-matrix composite (MMC) plates with central square holes. The MMC plates have varying aspect ratios and hole sizes and are supported under different boundary conditions. The finite-element structural analysis method was used to study the effects of plate boundary conditions, plate aspect ratio, hole size, and the composite stacking sequence on the compressive buckling strengths of the perforated MMC plates. Studies show that by increasing the hole sizes, compressive buckling strengths of the perforated MMC plates could be considerably increased under certain boundary conditions and aspect ratios ("anomalous" buckling behavior); and that the plate buckling mode could be symmetrical or antisymmetrical, depending on the plate boundary conditions, aspect ratio, and the hole size. For same-sized plates with same-sized holes, the compressive buckling strengths of the perforated MMC plates with [90/0/0/90]2 lamination could be as much as 10 percent higher or lower than those of the [45/- 45/- 45/45]2 laminations, depending on the plate boundary conditions, plate aspect ratios, and the hole size. Clamping the plate edges induces far stronger "anomalous" buckling behavior (enhancing compressive buckling strengths at increasing hole sizes) of the perforated MMC plates than simply supporting the plate edges.

Hole Transport in A-form DNA/RNA Hybrid Duplexes

NASA Astrophysics Data System (ADS)

Wong, Jiun Ru; Shao, Fangwei

2017-01-01

DNA/RNA hybrid duplexes are prevalent in many cellular functions and are an attractive target form for electrochemical biosensing and electric nanodevice. However the electronic conductivities of DNA/RNA hybrid duplex remain relatively unexplored and limited further technological applications. Here cyclopropyl-modified deoxyribose- and ribose-adenosines were developed to explore hole transport (HT) in both DNA duplex and DNA/RNA hybrids by probing the transient hole occupancies on adenine tracts. HT yields through both B-form and A-form double helixes displayed similar shallow distance dependence, although the HT yields of DNA/RNA hybrid duplexes were lower than those of DNA duplexes. The lack of oscillatory periods and direction dependence in HT through both helixes implied efficient hole propagation can be achieved via the hole delocalization and coherent HT over adenine tracts, regardless of the structural variations.

Hole Transport in A-form DNA/RNA Hybrid Duplexes

PubMed Central

Wong, Jiun Ru; Shao, Fangwei

2017-01-01

DNA/RNA hybrid duplexes are prevalent in many cellular functions and are an attractive target form for electrochemical biosensing and electric nanodevice. However the electronic conductivities of DNA/RNA hybrid duplex remain relatively unexplored and limited further technological applications. Here cyclopropyl-modified deoxyribose- and ribose-adenosines were developed to explore hole transport (HT) in both DNA duplex and DNA/RNA hybrids by probing the transient hole occupancies on adenine tracts. HT yields through both B-form and A-form double helixes displayed similar shallow distance dependence, although the HT yields of DNA/RNA hybrid duplexes were lower than those of DNA duplexes. The lack of oscillatory periods and direction dependence in HT through both helixes implied efficient hole propagation can be achieved via the hole delocalization and coherent HT over adenine tracts, regardless of the structural variations. PMID:28084308

Time-dependent, optically thick accretion onto a black hole

NASA Technical Reports Server (NTRS)

Gilden, D. L.; Wheeler, J. C.

1980-01-01

A fully relativistic hydrodynamics code which incorporates diffusive radiation transport is used to study time-dependent, spherically symmetric, optically thick accretion onto a black hole. It is found that matter free-falls into the hole regardless of whether the diffusion time scale is longer or shorter than the dynamical time. Nonadiabatic heating due to magnetic field reconnection is included. The internal energy thus generated affects the flow in a purely relativistic way, again ensuring free-fall collapse of the inflowing matter. Any matter enveloping a black hole will thus be swallowed on a dynamical time scale with relatively small net release of energy. The inclusion of angular momentum will not necessarily affect this conclusion.

Relative permittivity and Hubbard U of pentacene extracted from scanning tunneling microscopy studies of p-doped films

NASA Astrophysics Data System (ADS)

Ha, Sieu D.; Qi, Yabing; Kahn, Antoine

2010-08-01

Temperature-dependent I- V measurements determine that pentacene is effectively p-doped by tetrafluoro-tetracyanoquinodimethane (F 4-TCNQ). It has been shown by scanning tunneling microscopy (STM) that the donated hole is localized by the ionized dopant counter potential, and that the hole can be visualized [4]. Here, it is argued that the effect of the localized hole on STM images should depend on distance as 1/ ɛr, as per the Coulomb potential. By fitting line profiles of localized hole features to the Coulomb potential, it is shown that approximate values for the relative permittivity and Hubbard U of pentacene can be extracted.

Doping dependence of critical temperature for superconductivity induced by hole-phonon interaction

NASA Astrophysics Data System (ADS)

Durajski, A. P.; Szczȩśniak, R.

2017-10-01

To understand the nature of the high-temperature superconductors (cuprates) we have taken into consideration the interaction terms, which possess the structure of the hole-phonon (HP) and hole-hole-phonon (HHP) type. It was shown that for the high value of the HHP potential in comparison to HP, the superconducting critical temperature (TC) reaches the maximum value for the low concentration of holes, which fairly corresponds with the observed maximum of TC for hole-doped cuprates. The analysis was performed within the framework of the Eliashberg approach.

Trap controlled minority-carrier mobility in heavily doped silicon

NASA Technical Reports Server (NTRS)

Neugroschel, A.; Lindholm, F. A.; Sah, C. T.

1985-01-01

The activation behavior of the minority-carrier mobility and diffusivity in heavily doped (about 10 to the 20th per cu cm) Si(Si:As) was investigated in the temperature range, 20 - 350 K. Experimental results indicate that hole transitions between the valence band and localized shallow states give rise to the observed behavior. The activation energy is about 10 meV, which suggests that the localized states originate from band tails but does not rule out trapping at boron atoms in the compensated n(+) region.

Chemical Defects, Electronic Structure, and Transport in N-type and P-type Organic Semiconductors: First Principles Theory

DTIC Science & Technology

2012-11-29

of localized states extending into the gap. We also introduced a simple model allowing estimates of the upper limit of the intra-grain mobility in...well as to pentacene , and DATT. This research will be described below. In addition to our work on the electronic structure and charge mobility, we have...stacking distance gives rise to a tail of localized states which act as traps for electrons and holes. We introduced a simple effective Hamiltonian model

The relationship between the Tg depression and the speeding up of physical aging in polystyrene/gold nanocomposites

NASA Astrophysics Data System (ADS)

Boucher, Virginie M.; Cangialosi, Daniele; Alegria, Angel; Colmenero, Juan

2011-03-01

The effect of gold nanoparticles on the segmental dynamics, glass transition (Tg) and physical aging of polystyrene (PS) was studied in PS/Gold nanocomposites samples containing 5 and 15 wt.% of 60 nm spherical gold nanoparticles, surface-treated with thiolated-PS. While the segmental dynamics of PS, as assessed by broadband dielectric spectroscopy (BDS), was found to be unchanged in presence of gold nanoparticles, the calorimetric Tg of PS was shown to decrease with increasing the amount of nanoparticles in the samples. Furthermore, the physical aging of PS, monitored by measuring the enthalpy relaxation below Tg by means of DSC, was shown to speed up with increasing the nanoparticles weight fraction, i.e. the amount of PS/Gold interface in the hybrid material. Thus, the main conclusion of our work is that PS molecular mobility and out-of-equilibrium dynamics are decoupled in these nanocomposites. The significant effect of the amount of PS/Gold interface on both the physical aging rate of PS and the calorimetric Tg depression are quantitatively accounted for by a model based on the diffusion of free volume holes towards polymer interfaces, with a diffusion coefficient depending only on the molecular mobility.

Energy-dependent topological anti-de Sitter black holes in Gauss-Bonnet Born-Infeld gravity

NASA Astrophysics Data System (ADS)

Hendi, S. H.; Behnamifard, H.; Bahrami-Asl, B.

2018-03-01

Employing higher-curvature corrections to Einstein-Maxwell gravity has garnered a great deal of attention motivated by the high-energy regime in the quantum nature of black hole physics. In addition, one may employ gravity's rainbow to encode quantum gravity effects into black hole solutions. In this paper, we regard an energy-dependent static spacetime with various topologies and study its black hole solutions in the context of Gauss-Bonnet Born-Infeld (GB-BI) gravity. We study the thermodynamic properties and examine the first law of thermodynamics. Using a suitable local transformation, we endow the Ricci-flat black hole solutions with a global rotation and study the effects of rotation on thermodynamic quantities. We also investigate thermal stability in a canonical ensemble by calculating the heat capacity. We obtain the effects of various parameters on the horizon radius of stable black holes. Finally, we discuss a second-order phase transition in the extended phase space thermodynamics and investigate the critical behavior.

Tips pentacene crystal alignment for improving performance of solution processed organic thin film transistors

NASA Astrophysics Data System (ADS)

He, Zhengran

A newly-developed p-type organic semiconductor 6,13-bis (triisopropylsilylethynyl) pentacene (TIPS pentacene) demonstrates various advantages such as high mobility, air stability and solution processibility, but at the same time its application is restricted by major issues, such as crystal misorientation and performance variation of organic thin-film transistors (OTFTs). This dissertation demonstrates several different approaches to address these issues. As a result, both crystal orientation and areal coverage can be effectively improved, leading to an enhancement of average mobility and performance consistency of OTFTs. Chapter 1 presents an introduction and background of this dissertation. Chapter 2 explores the usage of inorganic silica nanoparticles to manipulate the morphology of TIPS pentacene thin films and the performance of solution-processed organic OTFTs. The resultant drop-cast films yield improved morphological uniformity at ~10% SiO2 loading, which also leads to a 3-fold increase in average mobility and nearly 4-times reduction in the ratio of standard deviation of mobility (μStdev) to average mobility (μAvg). The experimental results suggest that the SiO2 nanoparticles mostly aggregate at TIPS pentacene grain boundaries, and that 10% nanoparticle concentration effectively reduces the undesirable crystal misorientation without considerably compromising TIPS pentacene crystallinity. Chapter 3 discusses the utilization of air flow to effectively reduce the TIPS pentacene crystal anisotropy and enhance performance consistency in OTFTs. Under air-flow navigation (AFN), TIPS pentacene forms thin films with improved crystal orientation and increased areal coverage, which subsequently lead to a four-fold increase of average hole mobility and one order of magnitude enhancement in performance consistency. Chapter 4 investigates the critical roles of lateral and vertical phase separation in the performance of the next-generation organic and hybrid electronic devices. A novel method is demonstrated here to switch between lateral and vertical phase separation in semiconducting TIPS pentacene/ polymer blend films by simply varying the alkyl length of the polyacrylate polymer component. The phase separation modes depend on intermolecular interactions between small molecule TIPS pentacene and polymer additives. The blend film with a dominant vertical phase separation exhibits a significant enhancement in average mobility and performance consistency of organic OTFTs. Chapter 5 demonstrates an effective approach to improve both charge transport and performance consistency in solution-processed OTFTs by blending TIPS pentacene with a series of small-molecule additives: 4-butylbenzoic acid (BBA), 4-hexylbenzoic acid (HBA), and 4-octylbenzoic acid (OBA). These three small molecules share a benzoic acid moiety, but have different length of hydrophobic tails. The self-assembled interfacial layer of small molecules on the gate oxide surface leads to uniform deposition of TIPS pentacene crystal seeds and facilitates TIPS pentacene to grow along the tilted orientation of substrate, which results in a film of enhanced crystal orientation and areal coverage. OTFTs based on TIPS pentacene/small molecule blends demonstrate greatly improved average hole mobility and performance consistency, which correlates with the length of hydrophobic tail of the small-molecule additives. Chapter 6 summarizes the conclusions of this dissertation and the related future work.

A study of effects of electrode contacts on performance of organic-based light-emitting field-effect transistors

NASA Astrophysics Data System (ADS)

Kim, Dae-Kyu; Choi, Jong-Ho

2018-02-01

Herein is presented a comparative performance analysis of heterojunction organic-based light-emitting field-effect transistors (OLEFETs) with symmetric (Au only) and asymmetric (Au and LiF/Al) electrode contacts. The devices had a top source-drain contact with long-channel geometry and were produced by sequentially depositing p-type pentacene and n-type N,N‧-ditridecylperylene-3,4,9,10-tetracarboxylic diimide (P13) using a neutral cluster beam deposition apparatus. The spectroscopic, structural and morphological properties of the organic thin films were examined using photoluminescence (PL) spectroscopy, X-ray diffraction (XRD) method, laser scanning confocal and atomic force microscopy (LSCM, AFM). Based upon the growth of high-quality, well-packed crystalline thin films, the devices demonstrated ambipolar field-effect characteristics, stress-free operational stability, and light emission under ambient conditions. Various device parameters were derived from the fits of the observed characteristics. The hole mobilities were nearly equal irrespective of the electrode contacts, whereas the electron mobilities of the transistors with LiF/Al drain electrodes were higher due to the low injection barrier. For the OLEFETs with symmetric electrodes, electroluminescence (EL) occurred only in the vicinity of the hole-injecting electrode, whereas for the OLEFETs with asymmetric electrodes, the emission occurred in the vicinity of both hole- and electron-injecting electrodes. By tuning the carrier injection and transport through high- and low-work function metals, the hole-electron recombination sites could be controlled. The operating conduction and light emission mechanism are discussed with the aid of EL images obtained using a charge-coupled device (CCD) camera.

Evolution in the charge injection efficiency of evaporated Au contacts on a molecularly doped polymer

NASA Astrophysics Data System (ADS)

Ioannidis, Andronique; Facci, John S.; Abkowitz, Martin A.

1998-08-01

Injection efficiency from evaporated Au contacts on a molecularly doped polymer (MDP) system has been previously observed to evolve from blocking to ohmic over time. In the present article this contact forming phenomenon is analyzed in detail. The initially blocking nature of the Au contact is in contrast with that expected from the relative workfunctions of Au and of the polymer which suggest Au should inject holes efficiently. It is also in apparent contrast to a differently prepared interface of the same materials. The phenomenon is not unique to this interface, having been confirmed also for evaporated Ag and mechanically made liquid Hg contacts on the same MDP. The MDP is a disordered solid state solution of electroactive triarylamine hole transporting TPD molecules in a polycarbonate matrix. The trap-free hole-transport MDP provides a model system for the study of metal/polymer interfaces by enabling the use of a recently developed technique that gives a quantitative measure of contact injection efficiency. The technique combines field-dependent steady state injection current measurements at a contact under test with time-of-flight (TOF) mobility measurements made on the same sample. In the present case, MDP films were prepared with two top vapor-deposited contacts, one of Au (test contact) and one of Al (for TOF), and a bottom carbon-loaded polymer electrode which is known to be ohmic for hole injection. The samples were aged at various temperatures below the glass transition of the MDP (85 °C) and the evolution of current versus field and capacitance versus frequency behaviors are followed in detail over time and analyzed. Control measurements ensure that the evolution of the electrical properties is due to the Au/polymer interface behavior and not the bulk. All evaporated Au contacts eventually achieved ohmic injection. The evaporated Au/MDP interface was also investigated by transmission electron microscopy as a function of time and showed no evidence of Au interdiffusion in the MDP layer, remaining abrupt to within ˜10 Å over the course of the evolution in injection efficiency. Mechanisms related to Au penetration into the MDP are therefore unlikely. Rapid sequence data acquisition enabled the detection of two main processes in the injection evolution. The evolving injection efficiency is very well fit by two exponentials, enabling the characterization of time and temperature dependence of the evolution processes.

Quantum ballistic transport in strained epitaxial germanium

NASA Astrophysics Data System (ADS)

Gul, Y.; Holmes, S. N.; Newton, P. J.; Ellis, D. J. P.; Morrison, C.; Pepper, M.; Barnes, C. H. W.; Myronov, M.

2017-12-01

Large scale fabrication using Complementary Metal Oxide Semiconductor compatible technology of semiconductor nanostructures that operate on the principles of quantum transport is an exciting possibility now due to the recent development of ultra-high mobility hole gases in epitaxial germanium grown on standard silicon substrates. We present here a ballistic transport study of patterned surface gates on strained Ge quantum wells with SiGe barriers, which confirms the quantum characteristics of the Ge heavy hole valence band structure in 1-dimension. Quantised conductance at multiples of 2e2/h is a universal feature of hole transport in Ge up to 10 × (2e2/h). The behaviour of ballistic plateaus with finite source-drain bias and applied magnetic field is elucidated. In addition, a reordering of the ground state is observed.

Electron and hole transport in the organic small molecule α-NPD

NASA Astrophysics Data System (ADS)

Rohloff, R.; Kotadiya, N. B.; Crǎciun, N. I.; Blom, P. W. M.; Wetzelaer, G. A. H.

2017-02-01

Electron and hole transport properties of the organic small molecule N,N'-Di(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine are investigated by space-charge-limited current measurements. The hole transport shows trap-free behavior with a mobility of 2.3 × 10-8 m2/Vs at vanishing carrier density and electric field. The electron transport, on the other hand, shows heavily trap-limited behavior, which leads to highly unbalanced transport. A trap concentration of 1.3 × 1024 m-3 was found by modeling the electron currents, similar to the universal trap concentration found in conjugated polymers. This indicates that electron trapping is a generic property of organic semiconductors, ranging from vacuum-deposited small-molecules to solution-processed conjugated polymers.

Effective mass in bilayer graphene at low carrier densities: The role of potential disorder and electron-electron interaction

NASA Astrophysics Data System (ADS)

Li, J.; Tan, L. Z.; Zou, K.; Stabile, A. A.; Seiwell, D. J.; Watanabe, K.; Taniguchi, T.; Louie, Steven G.; Zhu, J.

2016-10-01

In a two-dimensional electron gas, the electron-electron interaction generally becomes stronger at lower carrier densities and renormalizes the Fermi-liquid parameters, such as the effective mass of carriers. We combine experiment and theory to study the effective masses of electrons and holes me* and mh* in bilayer graphene in the low carrier density regime on the order of 1 ×1011c m-2 . Measurements use temperature-dependent low-field Shubnikov-de Haas oscillations observed in high-mobility hexagonal boron nitride supported samples. We find that while me* follows a tight-binding description in the whole density range, mh* starts to drop rapidly below the tight-binding description at a carrier density of n =6 ×1011c m-2 and exhibits a strong suppression of 30% when n reaches 2 ×1011c m-2 . Contributions from the electron-electron interaction alone, evaluated using several different approximations, cannot explain the experimental trend. Instead, the effect of the potential fluctuation and the resulting electron-hole puddles play a crucial role. Calculations including both the electron-electron interaction and disorder effects explain the experimental data qualitatively and quantitatively. This Rapid Communication reveals an unusual disorder effect unique to two-dimensional semimetallic systems.

Adaptive timing of detachment in a tick parasitizing hole-nesting birds.

PubMed

White, J; Heylen, D J A; Matthysen, E

2012-02-01

In non-permanent parasites with low intrinsic mobility such as ticks, dispersal is highly dependent on host movements as well as the timing of separation from the hosts. Optimal detachment behaviour is all the more crucial in nidicolous ticks as the risk of detaching in non-suitable habitat is high. In this study, we experimentally investigated the detachment behaviour of Ixodes arboricola, a nidicolous tick that primarily infests birds roosting in tree-holes. We infested great tits with I. arboricola larvae or nymphs, and submitted the birds to 2 experimental treatments, a control treatment in which birds had normal access to nest boxes and an experimental treatment, in which the birds were prevented access to their nest boxes for varying lengths of time. In the control group, most ticks detached within 5 days, whereas in the experimental group, ticks remained on the bird for as long as the bird was prevented access (up to 14 days). This prolonged attachment caused a decrease in survival and engorgement weight in nymphs, but not in larvae. The capacity of I. arboricola larvae to extend the duration of attachment in non-suitable environments with no apparent costs, may be an adaptation to unpredictable use of cavities by roosting hosts during winter, and at the same time may facilitate dispersal of the larval instars.

Spectroscopic evidence for temperature-dependent convergence of light- and heavy-hole valence bands of PbQ (Q = Te, Se, S)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, J.; Malliakas, C. D.; Wijayaratne, K.

2017-01-01

We have conducted a temperature- dependent angle-resolved photoemission spectroscopy (ARPES) study of the electronic structures of PbTe, PbSe and PbS. Our ARPES data provide direct evidence for the light-hole upper valence bands (UVBs) and hitherto undetected heavy-hole lower valence bands (LVBs) in these materials. An unusual temperature-dependent relative movement between these bands leads to a monotonic decrease in the energy separation between their maxima with increasing temperature, which is known as band convergence and has long been believed to be the driving factor behind extraordinary thermoelectric performances of these compounds at elevated temperatures.

Spectroscopic evidence for temperature-dependent convergence of light- and heavy-hole valence bands of PbQ (Q = Te, Se, S)

NASA Astrophysics Data System (ADS)

Zhao, J.; Malliakas, C. D.; Wijayaratne, K.; Karlapati, V.; Appathurai, N.; Chung, D. Y.; Rosenkranz, S.; Kanatzidis, M. G.; Chatterjee, U.

2017-01-01

We have conducted a temperature-dependent angle-resolved photoemission spectroscopy (ARPES) study of the electronic structures of PbTe, PbSe and PbS. Our ARPES data provide direct evidence for the light-hole upper valence bands (UVBs) and hitherto undetected heavy-hole lower valence bands (LVBs) in these materials. An unusual temperature-dependent relative movement between these bands leads to a monotonic decrease in the energy separation between their maxima with increasing temperature, which is known as band convergence and has long been believed to be the driving factor behind extraordinary thermoelectric performances of these compounds at elevated temperatures.

Improved open-circuit voltage in polymer/oxide-nanoarray hybrid solar cells by formation of homogeneous metal oxide core/shell structures.

PubMed

Wu, Fan; Cui, Qi; Qiu, Zeliang; Liu, Changwen; Zhang, Hui; Shen, Wei; Wang, Mingtai

2013-04-24

Incorporation of vertically aligned nanorod/nanowire arrays of metal oxide (oxide-NAs) with a polymer can produce efficient hybrid solar cells with an ideal bulk-heterojunction architecture. However, polymer/oxide-NAs solar cells still suffer from a rather low (normally, < 0.4 V) open-circuit voltage (Voc). Here we demonstrate, for the first time, a novel strategy to improve the Voc in polymer/oxide-NAs solar cells by formation of homogeneous core/shell structures and reveal the intrinsic principles involved therein. A feasible hydrothermal-solvothermal combined method is developed for preparing homogeneous core/shell nanoarrays of metal oxides with a single-crystalline nanorod as core and the aggregation layer of corresponding metal oxide quantum dots (QDs) as shell, and the shell thickness (L) is easily controlled by the solvothermal reaction time for growing QDs on the nanorod. The core/shell formation dramatically improves the device Voc up to ca. 0.7-0.8 V depending on L. Based on steady-state and dynamic measurements, as well as modeling by space-charge-limited current method, it is found that the improved Voc originates from the up-shifted conduction band edge in the core by the interfacial dipole field resulting from the decreased mobility difference between photogenerated electrons and holes after the shell growth, which increases the energy difference between the quasi-Fermi levels of photogenerated electrons in the core and holes in the polymer for a higher Voc. Our results indicate that increasing Voc by the core/shell strategy seems not to be dependent on the kinds of metal oxides.

Sn-based Ge/Ge{sub 0.975}Sn{sub 0.025}/Ge p-i-n photodetector operated with back-side illumination

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chang, C.; Li, H.; Huang, S. H.

2016-04-11

We report an investigation of a GeSn-based p-i-n photodetector grown on a Ge wafer that collects light signal from the back of the wafer. Temperature dependent absorption measurements performed over a wide temperature range (300 K down to 25 K) show that (a) absorption starts at the indirect bandgap of the active GeSn layer and continues up to the direct bandgap of the Ge wafer, and (b) the peak responsivity increases rapidly at first with decreasing temperature, then increases more slowly, followed by a decrease at the lower temperatures. The maximum responsivity happens at 125 K, which can easily be achieved with themore » use of liquid nitrogen. The temperature dependence of the photocurrent is analyzed by taking into consideration of the temperature dependence of the electron and hole mobility in the active layer, and the analysis result is in reasonable agreement with the data in the temperature regime where the rapid increase occurs. This investigation demonstrates the feasibility of a GeSn-based photodiode that can be operated with back-side illumination for applications in image sensing systems.« less

Dressed Hard States and Black Hole Soft Hair.

PubMed

Mirbabayi, Mehrdad; Porrati, Massimo

2016-11-18

A recent, intriguing Letter by Hawking, Perry, and Strominger suggests that soft photons and gravitons can be regarded as black hole hair and may be relevant to the black hole information paradox. In this Letter we make use of factorization theorems for infrared divergences of the S matrix to argue that by appropriately dressing in and out hard states, the soft-quanta-dependent part of the S matrix becomes essentially trivial. The information paradox can be fully formulated in terms of dressed hard states, which do not depend on soft quanta.

Absolute measurements of the triplet-triplet annihilation rate and the charge-carrier recombination layer thickness in working polymer light-emitting diodes based on polyspirobifluorene

NASA Astrophysics Data System (ADS)

Rothe, C.; Al Attar, H. A.; Monkman, A. P.

2005-10-01

The triplet exciton densities in electroluminescent devices prepared from two polyspirobifluorene derivatives have been investigated by means of time-resolved transient triplet absorption as a function of optical and electrical excitation power at 20 K. Because of the low mobility of the triplet excitons at this temperature, the triplet generation profile within the active polymer layer is preserved throughout the triplet lifetime and as a consequence the absolute triplet-triplet annihilation efficiency is not homogeneously distributed but depends on position within the active layer. This then gives a method to measure the charge-carrier recombination layer after electrical excitation relative to the light penetration depth, which is identical to the triplet generation layer after optical excitation. With the latter being obtained from ellipsometry, an absolute value of 5 nm is found for the exciton formation layer in polyspirobifluorene devices. This layer increases to 11 nm if the balance between the electron and the hole mobility is improved by chemically modifying the polymer backbone. Also, and consistent with previous work, triplet diffusion is dispersive at low temperature. As a consequence of this, the triplet-triplet annihilation rate is not a constant in the classical sense but depends on the triplet excitation dose. At 20 K and for typical excitation doses, absolute values of the latter rate are of the order of 10-14cm3s-1 .

Black hole superradiance and polarization-dependent bending of light

NASA Astrophysics Data System (ADS)

Plascencia, Alexis D.; Urbano, Alfredo

2018-04-01

An inhomogeneous pseudo-scalar field configuration behaves like an optically active medium. Consequently, if a light ray passes through an axion cloud surrounding a Kerr black hole, it may experience a polarization-dependent bending. We explore the size and relevance of such effect considering both the QCD axion and a generic axion-like particle.

Carrier-density-dependent recombination dynamics of excitons and electron-hole plasma in m -plane InGaN/GaN quantum wells

NASA Astrophysics Data System (ADS)

Liu, W.; Butté, R.; Dussaigne, A.; Grandjean, N.; Deveaud, B.; Jacopin, G.

2016-11-01

We study the carrier-density-dependent recombination dynamics in m -plane InGaN/GaN multiple quantum wells in the presence of n -type background doping by time-resolved photoluminescence. Based on Fermi's golden rule and Saha's equation, we decompose the radiative recombination channel into an excitonic and an electron-hole pair contribution, and extract the injected carrier-density-dependent bimolecular recombination coefficients. Contrary to the standard electron-hole picture, our results confirm the strong influence of excitons even at room temperature. Indeed, at 300 K, excitons represent up to 63 ± 6% of the photoexcited carriers. In addition, following the Shockley-Read-Hall model, we extract the electron and hole capture rates by deep levels and demonstrate that the increase in the effective lifetime with injected carrier density is due to asymmetric capture rates in presence of an n -type background doping. Thanks to the proper determination of the density-dependent recombination coefficients up to high injection densities, our method provides a way to evaluate the importance of Auger recombination.

Feast and Famine: regulation of black hole growth in low-redshift galaxies

NASA Astrophysics Data System (ADS)

Kauffmann, Guinevere; Heckman, Timothy M.

2009-07-01

We analyse the observed distribution of Eddington ratios (L/LEdd) as a function of supermassive black hole mass for a large sample of nearby galaxies drawn from the Sloan Digital Sky Survey. We demonstrate that there are two distinct regimes of black hole growth in nearby galaxies. The first is associated with galaxies with significant star formation [M*/starformationrate (SFR) ~ a Hubble time] in their central kiloparsec regions, and is characterized by a broad lognormal distribution of accretion rates peaked at a few per cent of the Eddington limit. In this regime, the Eddington ratio distribution is independent of the mass of the black hole and shows little dependence on the central stellar population of the galaxy. The second regime is associated with galaxies with old central stellar populations (M*/SFR >> a Hubble time), and is characterized by a power-law distribution function of Eddington ratios. In this regime, the time-averaged mass accretion rate on to black holes is proportional to the mass of stars in the galaxy bulge, with a constant of proportionality that depends on the mean stellar age of the stars. This result is once again independent of black hole mass. We show that both the slope of the power law and the decrease in the accretion rate on to black holes in old galaxies are consistent with population synthesis model predictions of the decline in stellar mass loss rates as a function of mean stellar age. Our results lead to a very simple picture of black hole growth in the local Universe. If the supply of cold gas in a galaxy bulge is plentiful, the black hole regulates its own growth at a rate that does not further depend on the properties of the interstellar medium. Once the gas runs out, black hole growth is regulated by the rate at which evolved stars lose their mass.

The Dependence of the Peak Velocity of High-Speed Solar Wind Streams as Measured in the Ecliptic by ACE and the STEREO satellites on the Area and Co-latitude of Their Solar Source Coronal Holes.

PubMed

Hofmeister, Stefan J; Veronig, Astrid; Temmer, Manuela; Vennerstrom, Susanne; Heber, Bernd; Vršnak, Bojan

2018-03-01

We study the properties of 115 coronal holes in the time range from August 2010 to March 2017, the peak velocities of the corresponding high-speed streams as measured in the ecliptic at 1 AU, and the corresponding changes of the Kp index as marker of their geoeffectiveness. We find that the peak velocities of high-speed streams depend strongly on both the areas and the co-latitudes of their solar source coronal holes with regard to the heliospheric latitude of the satellites. Therefore, the co-latitude of their source coronal hole is an important parameter for the prediction of the high-speed stream properties near the Earth. We derive the largest solar wind peak velocities normalized to the coronal hole areas for coronal holes located near the solar equator and that they linearly decrease with increasing latitudes of the coronal holes. For coronal holes located at latitudes ≳ 60°, they turn statistically to zero, indicating that the associated high-speed streams have a high chance to miss the Earth. Similarly, the Kp index per coronal hole area is highest for the coronal holes located near the solar equator and strongly decreases with increasing latitudes of the coronal holes. We interpret these results as an effect of the three-dimensional propagation of high-speed streams in the heliosphere; that is, high-speed streams arising from coronal holes near the solar equator propagate in direction toward and directly hit the Earth, whereas solar wind streams arising from coronal holes at higher solar latitudes only graze or even miss the Earth.

Orbital-dependent Electron-Hole Interaction in Graphene and Associated Multi-Layer Structures

PubMed Central

Deng, Tianqi; Su, Haibin

2015-01-01

We develop an orbital-dependent potential to describe electron-hole interaction in materials with structural 2D character, i.e. quasi-2D materials. The modulated orbital-dependent potentials are also constructed with non-local screening, multi-layer screening, and finite gap due to the coupling with substrates. We apply the excitonic Hamiltonian in coordinate-space with developed effective electron-hole interacting potentials to compute excitons’ binding strength at M (π band) and Γ (σ band) points in graphene and its associated multi-layer forms. The orbital-dependent potential provides a range-separated property for regulating both long- and short-range interactions. This accounts for the existence of the resonant π exciton in single- and bi-layer graphenes. The remarkable strong electron-hole interaction in σ orbitals plays a decisive role in the existence of σ exciton in graphene stack at room temperature. The interplay between gap-opening and screening from substrates shed a light on the weak dependence of σ exciton binding energy on the thickness of graphene stacks. Moreover, the analysis of non-hydrogenic exciton spectrum in quasi-2D systems clearly demonstrates the remarkable comparable contribution of orbital dependent potential with respect to non-local screening process. The understanding of orbital-dependent potential developed in this work is potentially applicable for a wide range of materials with low dimension. PMID:26610715

Thermal fluctuations of dilaton black holes in gravity's rainbow

NASA Astrophysics Data System (ADS)

Dehghani, M.

2018-06-01

In this work, thermodynamics and phase transition of some new dilaton black hole solutions have been explored in the presence of the rainbow functions. By introducing an energy dependent space time, the dilaton potential has been obtained as the linear combination of two Liouville-type potentials and three new classes of black hole solutions have been constructed. The conserved and thermodynamic quantities of the new dilaton black holes have been calculated in the energy dependent space times. It has been shown that, even if some of the thermodynamic quantities are affected by the rainbow functions, the thermodynamical first law still remains valid. Also, the impacts of rainbow functions on the stability or phase transition of the new black hole solutions have been investigated. Finally, the quantum gravitational effects on the thermodynamics and phase transition of the solutions have been studied through consideration of the thermal fluctuations.

A cyano-terminated dithienyldiketopyrrolopyrrole dimer as a solution processable ambipolar semiconductor under ambient conditions.

PubMed

Wang, Li; Zhang, Xiaojie; Tian, Hongkun; Lu, Yunfeng; Geng, Yanhou; Wang, Fosong

2013-12-14

A cyano-terminated dimer of dithienyldiketopyrrolopyrrole (TDPP), DPP2-CN, is a solution processable ambipolar semiconductor with field-effect hole and electron mobilities of 0.066 and 0.033 cm(2) V(-1) s(-1), respectively, under ambient conditions.

High Efficiency Inverted Planar Perovskite Solar Cells with Solution-Processed NiOx Hole Contact.

PubMed

Yin, Xuewen; Yao, Zhibo; Luo, Qiang; Dai, Xuezeng; Zhou, Yu; Zhang, Ye; Zhou, Yangying; Luo, Songping; Li, Jianbao; Wang, Ning; Lin, Hong

2017-01-25

NiO x is a promising hole-transporting material for perovskite solar cells due to its high hole mobility, good stability, and easy processability. In this work, we employed a simple solution-processed NiO x film as the hole-transporting layer in perovskite solar cells. When the thickness of the perovskite layer increased from 270 to 380 nm, the light absorption and photogenerated carrier density were enhanced and the transporting distance of electron and hole would also increase at the same time, resulting in a large charge transfer resistance and a long hole-extracted process in the device, characterized by the UV-vis, photoluminescence, and electrochemical impedance spectroscopy spectra. Combining both of these factors, an optimal thickness of 334.2 nm was prepared with the perovskite precursor concentration of 1.35 M. Moreover, the optimal device fabrication conditions were further achieved by optimizing the thickness of NiO x hole-transporting layer and PCBM electron selective layer. As a result, the best power conversion efficiency of 15.71% was obtained with a J sc of 20.51 mA·cm -2 , a V oc of 988 mV, and a FF of 77.51% with almost no hysteresis. A stable efficiency of 15.10% was caught at the maximum power point. This work provides a promising route to achieve higher efficiency perovskite solar cells based on NiO or other inorganic hole-transporting materials.

Donor-acceptor cocrystal based on hexakis(alkoxy)triphenylene and perylenediimide derivatives with an ambipolar transporting property.

PubMed

Su, Yajun; Li, Yan; Liu, Jiangang; Xing, Rubo; Han, Yanchun

2015-02-07

An organic donor-acceptor cocrystal with an ambipolar transporting property was constructed based on N,N'-bis(1-ethylpropyl)-perylene-3,4,9,10-tetracarboxylic diimide (EP-PDI) and 2,3,6,7,10,11-hexakis-(hexyloxy)-triphenylene (H6TP). The cocrystal with an alternating stacking of H6TP and EP-PDI molecules was formed through both drop-casting and spin-coating processes, especially at the optimized ratios of H6TP/EP-PDI (2/1, 1/1). The formation of the cocrystal was driven by the strong π-π interaction and the weaker steric hindrance, resulting from the smaller side groups, between the donor and acceptor molecules. Field effect transistors (FETs) based on the H6TP/EP-PDI cocrystal exhibited relatively balanced hole/electron transport, with a hole mobility of 1.14 × 10(-3) cm(2) V(-1) s(-1) and an electron mobility of 1.40 × 10(-3) cm(2) V(-1) s(-1).

Enhanced doping effect on tuning structural phases of monolayer antimony

NASA Astrophysics Data System (ADS)

Wang, Jizhang; Yang, Teng; Zhang, Zhidong; Yang, Li

2018-05-01

Doping is capable to control the atomistic structure, electronic structure, and even to dynamically realize a semiconductor-metal transition in two-dimensional (2D) transition metal dichalcogenides (TMDs). However, the high critical doping density (˜1014 electron/cm2), compound nature, and relatively low carrier mobility of TMDs limits broader applications. Using first-principles calculations, we predict that, via a small transition potential, a substantially lower hole doping density (˜6 × 1012 hole/cm2) can switch the ground-state structure of monolayer antimony from the hexagonal β-phase, a 2D semiconductor with excellent transport performance and air stability but an indirect bandgap, to the orthorhombic α phase with a direct bandgap and potentially better carrier mobility. We further show that this structural engineering can be achieved by the established electrostatic doping, surface functional adsorption, or directly using graphene substrate. This gives hope to dynamically tuning and large-scale production of 2D single-element semiconductors that simultaneously exhibit remarkable transport and optical performance.

Organic electrical double layer transistors gated with ionic liquids

NASA Astrophysics Data System (ADS)

Xie, Wei; Frisbie, C. Daniel

2011-03-01

Transport in organic semiconductors gated with several types of ionic liquids has been systematically studied at charge densities larger than 1013 cm-2 . We observe a pronounced maximum in channel conductance for both p-type and n-type organic single crystals which is attributed to carrier localization at the semiconductor-electrolyte interface. Carrier mobility, as well as charge density and dielectric capacitance are determined through displacement current measurement and capacitance-voltage measurement. By using a larger-sized and spherical anion, tris(pentafluoroethyl)trifluorophosphate (FAP), effective carrier mobility in rubrene can be enhanced substantially up to 3.2 cm2 V-1 s -1 . Efforts have been made to maximize the charge density in rubrene single crystals, and at low temperature when higher gate bias can be applied, charge density can more than double the amount of that at room temperature, reaching 8*1013 cm-2 holes (0.4 holes per rubrene molecule). NSF MRSEC program at the University of Minnesota.

Thallous chalcogenide (Tl 6I 4Se) for radiation detection at X-ray and γ-ray energies

NASA Astrophysics Data System (ADS)

Liu, Zhifu; Peters, John A.; Wessels, Bruce W.; Johnsen, Simon; Kanatzidis, Mercouri G.

2011-12-01

The optical and charge transport properties of the thallous chalcogenide compound Tl6I4Se were characterized. The semiconductor crystals are grown by the modified Bridgman method. We have measured the refractive index, and absorption coefficient of the compound ranging from 300 to 1500 nm by analysis of the UV-vis-near IR transmission and reflection spectra. The band gap is 1.8 eV. For the evaluation of detector performance, the mobility-lifetime products for both the electron and hole carriers were measured. Tl6I4Se has mobility-lifetime products of 7.1×10-3 and 5.9×10-4 cm2/V for electron and hole carriers, respectively, which are comparable to those of Cd0.9Zn0.1Te. The γ-ray spectrum for a Tl6I4Se detector was measured. Its response to the 122 keV of 57Co source is comparable to that of Cd0.9Zn0.1Te.

Two Hop Adaptive Vector Based Quality Forwarding for Void Hole Avoidance in Underwater WSNs

PubMed Central

Javaid, Nadeem; Ahmed, Farwa; Wadud, Zahid; Alrajeh, Nabil; Alabed, Mohamad Souheil; Ilahi, Manzoor

2017-01-01

Underwater wireless sensor networks (UWSNs) facilitate a wide range of aquatic applications in various domains. However, the harsh underwater environment poses challenges like low bandwidth, long propagation delay, high bit error rate, high deployment cost, irregular topological structure, etc. Node mobility and the uneven distribution of sensor nodes create void holes in UWSNs. Void hole creation has become a critical issue in UWSNs, as it severely affects the network performance. Avoiding void hole creation benefits better coverage over an area, less energy consumption in the network and high throughput. For this purpose, minimization of void hole probability particularly in local sparse regions is focused on in this paper. The two-hop adaptive hop by hop vector-based forwarding (2hop-AHH-VBF) protocol aims to avoid the void hole with the help of two-hop neighbor node information. The other protocol, quality forwarding adaptive hop by hop vector-based forwarding (QF-AHH-VBF), selects an optimal forwarder based on the composite priority function. QF-AHH-VBF improves network good-put because of optimal forwarder selection. QF-AHH-VBF aims to reduce void hole probability by optimally selecting next hop forwarders. To attain better network performance, mathematical problem formulation based on linear programming is performed. Simulation results show that by opting these mechanisms, significant reduction in end-to-end delay and better throughput are achieved in the network. PMID:28763014

Two Hop Adaptive Vector Based Quality Forwarding for Void Hole Avoidance in Underwater WSNs.

PubMed

Javaid, Nadeem; Ahmed, Farwa; Wadud, Zahid; Alrajeh, Nabil; Alabed, Mohamad Souheil; Ilahi, Manzoor

2017-08-01

Underwater wireless sensor networks (UWSNs) facilitate a wide range of aquatic applications in various domains. However, the harsh underwater environment poses challenges like low bandwidth, long propagation delay, high bit error rate, high deployment cost, irregular topological structure, etc. Node mobility and the uneven distribution of sensor nodes create void holes in UWSNs. Void hole creation has become a critical issue in UWSNs, as it severely affects the network performance. Avoiding void hole creation benefits better coverage over an area, less energy consumption in the network and high throughput. For this purpose, minimization of void hole probability particularly in local sparse regions is focused on in this paper. The two-hop adaptive hop by hop vector-based forwarding (2hop-AHH-VBF) protocol aims to avoid the void hole with the help of two-hop neighbor node information. The other protocol, quality forwarding adaptive hop by hop vector-based forwarding (QF-AHH-VBF), selects an optimal forwarder based on the composite priority function. QF-AHH-VBF improves network good-put because of optimal forwarder selection. QF-AHH-VBF aims to reduce void hole probability by optimally selecting next hop forwarders. To attain better network performance, mathematical problem formulation based on linear programming is performed. Simulation results show that by opting these mechanisms, significant reduction in end-to-end delay and better throughput are achieved in the network.

A new electrode design for ambipolar injection in organic semiconductors.

PubMed

Kanagasekaran, Thangavel; Shimotani, Hidekazu; Shimizu, Ryota; Hitosugi, Taro; Tanigaki, Katsumi

2017-10-17

Organic semiconductors have attracted much attention for low-cost, flexible and human-friendly optoelectronics. However, achieving high electron-injection efficiency is difficult from air-stable electrodes and cannot be equivalent to that of holes. Here, we present a novel concept of electrode composed of a bilayer of tetratetracontane (TTC) and polycrystalline organic semiconductors (pc-OSC) covered by a metal layer. Field-effect transistors of single-crystal organic semiconductors with the new electrodes of M/pc-OSC/TTC (M: Ca or Au) show both highly efficient electron and hole injection. Contact resistance for electron injection from Au/pc-OSC/TTC and hole injection from Ca/pc-OSC/TTC are comparable to those for electron injection from Ca and hole injection from Au, respectively. Furthermore, the highest field-effect mobilities of holes (22 cm 2  V -1  s -1 ) and electrons (5.0 cm 2  V -1  s -1 ) are observed in rubrene among field-effect transistors with electrodes so far proposed by employing Ca/pc-OSC/TTC and Au/pc-OSC/TTC electrodes for electron and hole injection, respectively.One of technological challenges building organic electronics is efficient injection of electrons at metal-semiconductor interfaces compared to that of holes. The authors show an air-stable electrode design with induced gap states, which support Fermi level pinning and thus ambipolar carrier injection.

Watching excitons move: the time-dependent transition density matrix

NASA Astrophysics Data System (ADS)

Ullrich, Carsten

2012-02-01

Time-dependent density-functional theory allows one to calculate excitation energies and the associated transition densities in principle exactly. The transition density matrix (TDM) provides additional information on electron-hole localization and coherence of specific excitations of the many-body system. We have extended the TDM concept into the real-time domain in order to visualize the excited-state dynamics in conjugated molecules. The time-dependent TDM is defined as an implicit density functional, and can be approximately obtained from the time-dependent Kohn-Sham orbitals. The quality of this approximation is assessed in simple model systems. A computational scheme for real molecular systems is presented: the time-dependent Kohn-Sham equations are solved with the OCTOPUS code and the time-dependent Kohn-Sham TDM is calculated using a spatial partitioning scheme. The method is applied to show in real time how locally created electron-hole pairs spread out over neighboring conjugated molecular chains. The coupling mechanism, electron-hole coherence, and the possibility of charge separation are discussed.

Supersonic gas streams enhance the formation of massive black holes in the early universe

NASA Astrophysics Data System (ADS)

Hirano, Shingo; Hosokawa, Takashi; Yoshida, Naoki; Kuiper, Rolf

2017-09-01

Supermassive black holes existed less than a billion years after the Big Bang. Because black holes can grow at a maximum rate that depends on their current mass, it has been difficult to understand how such massive black holes could have formed so quickly. Hirano et al. developed simulations to show that streaming motions—velocity offsets between the gas and dark matter components—could have produced black holes with tens of thousands of solar masses in the early universe. That's big enough to grow into the supermassive black holes that we observe today.

Hole dephasing caused by hole-hole interaction in a multilayered black phosphorus.

PubMed

Li, Lijun; Khan, Muhammad Atif; Lee, Yoontae; Lee, Inyeal; Yun, Sun Jin; Youn, Doo-Hyeb; Kim, Gil-Ho

2017-11-01

We study the magnetotransport of holes in a multilayered black phosphorus in a temperature range of 1.9 to 21.5 K. We observed a negative magnetoresistance at magnetic fields up to 1.5 T. This negative magetoresistance was analyzed by weak localization theory in diffusive regime. At the lowest temperature and the highest carrier density we found a phase coherence length of 48 nm. The linear temperature dependence of the dephasing rate shows that the hole-hole scattering processes with small energy transfer are the dominant contribution in breaking the carrier phase coherence.

High p-type doping, mobility, and photocarrier lifetime in arsenic-doped CdTe single crystals

NASA Astrophysics Data System (ADS)

Nagaoka, Akira; Kuciauskas, Darius; McCoy, Jedidiah; Scarpulla, Michael A.

2018-05-01

Group-V element doping is promising for simultaneously maximizing the hole concentration and minority carrier lifetime in CdTe for thin film solar cells, but there are roadblocks concerning point defects including the possibility of self-compensation by AX metastability. Herein, we report on doping, lifetime, and mobility of CdTe single crystals doped with As between 1016 and 1020 cm-3 grown from the Cd solvent by the travelling heater method. Evidence consistent with AX instability as a major contributor to compensation in samples doped below 1017 cm-3 is presented, while for higher-doped samples, precipitation of a second phase on planar structural defects is also observed and may explain spatial variation in properties such as lifetime. Rapid cooling after crystal growth increases doping efficiency and mobility for times up to 20-30 days at room temperature with the highest efficiencies observed close to 45% and a hole mobility of 70 cm2/Vs at room temperature. A doping limit in the low 1017/cm3 range is observed for samples quenched at 200-300 °C/h. Bulk minority carrier lifetimes exceeding 20 ns are observed for samples doped near 1016 cm-3 relaxed in the dark and for unintentionally doped samples, while a lifetime of nearly 5 ns is observed for 1018 cm-3 As doping. These results help us to establish limits on properties expected for group-V doped CdTe polycrystalline thin films for use in photovoltaics.

A Dancing Black Hole

NASA Astrophysics Data System (ADS)

Shoemaker, Deirdre; Smith, Kenneth; Schnetter, Erik; Fiske, David; Laguna, Pablo; Pullin, Jorge

2002-04-01

Recently, stationary black holes have been successfully simulated for up to times of approximately 600-1000M, where M is the mass of the black hole. Considering that the expected burst of gravitational radiation from a binary black hole merger would last approximately 200-500M, black hole codes are approaching the point where simulations of mergers may be feasible. We will present two types of simulations of single black holes obtained with a code based on the Baumgarte-Shapiro-Shibata-Nakamura formulation of the Einstein evolution equations. One type of simulations addresses the stability properties of stationary black hole evolutions. The second type of simulations demonstrates the ability of our code to move a black hole through the computational domain. This is accomplished by shifting the stationary black hole solution to a coordinate system in which the location of the black hole is time dependent.

SHORT-PULSE ELECTROMAGNETIC TRANSPONDER FOR HOLE-TO-HOLE USE.

USGS Publications Warehouse

Wright, David L.; Watts, Raymond D.; Bramsoe, Erik

1983-01-01

Hole-to-hole observations were made through nearly 20 m of granite using an electromagnetic transponder (an active reflector) in one borehole and a single-hole short-pulse radar in another. The transponder is inexpensive, operationally simple, and effective in extending the capability of a short-pulse borehole radar system to allow hole-to-hole operation without requiring timing cables. A detector in the transponder senses the arrival of each pulse from the radar. Each pulse detection triggers a kilovolt-amplitude pulse for retransmission. The transponder 'echo' may be stronger than that of a passive reflector by a factor of as much as 120 db. The result is an increase in range capability by a factor which depends on attenuation in the medium and hole-to-hole wavepath geometry.

Fabrication of eco-friendly PNP transistor using RF magnetron sputtering

NASA Astrophysics Data System (ADS)

Kumar, B. Santhosh; Harinee, N.; Purvaja, K.; Shanker, N. Praveen; Manikandan, M.; Aparnadevi, N.; Mukilraj, T.; Venkateswaran, C.

2018-05-01

An effort has been made to fabricate a thin film transistor using eco-friendly oxide semiconductor materials. Oxide semiconductor materials are cost - effective, thermally and chemically stable with high electron/hole mobility. Copper (II) oxide is a p-type semiconductor and zinc oxide is an n-type semiconductor. A pnp thin film transistor was fabricated using RF magnetron sputtering. The films deposited have been subjected to structural characterization using AFM. I-V characterization of the fabricated device, Ag/CuO/ZnO/CuO/Ag, confirms transistor behaviour. The mechanism of electron/hole transport of the device is discussed below.

Eliminating dependence of hole depth on aspect ratio by forming ammonium bromide during plasma etching of deep holes in silicon nitride and silicon dioxide

NASA Astrophysics Data System (ADS)

Iwase, Taku; Yokogawa, Kenetsu; Mori, Masahito

2018-06-01

The reaction mechanism during etching to fabricate deep holes in SiN/SiO2 stacks by using a HBr/N2/fluorocarbon-based gas plasma was investigated. To etch SiN and SiO2 films simultaneously, HBr/fluorocarbon gas mixture ratio was controlled to achieve etching selectivity closest to one. Deep holes were formed in the SiN/SiO2 stacks by one-step etching at several temperatures. The surface composition of the cross section of the holes was analyzed by time-of-flight secondary-ion mass spectrometry. It was found that bromine ions (considered to be derived from NH4Br) were detected throughout the holes in the case of low-temperature etching. It was also found that the dependence of hole depth on aspect ratio decreases as temperature decreases, and it becomes significantly weaker at a substrate temperature of 20 °C. It is therefore concluded that the formation of NH4Br supplies the SiN/SiO2 etchant to the bottom of the holes. Such a finding will make it possible to alleviate the decrease in etching rate due to a high aspect ratio.

Black holes and the multiverse

NASA Astrophysics Data System (ADS)

Garriga, Jaume; Vilenkin, Alexander; Zhang, Jun

2016-02-01

Vacuum bubbles may nucleate and expand during the inflationary epoch in the early universe. After inflation ends, the bubbles quickly dissipate their kinetic energy; they come to rest with respect to the Hubble flow and eventually form black holes. The fate of the bubble itself depends on the resulting black hole mass. If the mass is smaller than a certain critical value, the bubble collapses to a singularity. Otherwise, the bubble interior inflates, forming a baby universe, which is connected to the exterior FRW region by a wormhole. A similar black hole formation mechanism operates for spherical domain walls nucleating during inflation. As an illustrative example, we studied the black hole mass spectrum in the domain wall scenario, assuming that domain walls interact with matter only gravitationally. Our results indicate that, depending on the model parameters, black holes produced in this scenario can have significant astrophysical effects and can even serve as dark matter or as seeds for supermassive black holes. The mechanism of black hole formation described in this paper is very generic and has important implications for the global structure of the universe. Baby universes inside super-critical black holes inflate eternally and nucleate bubbles of all vacua allowed by the underlying particle physics. The resulting multiverse has a very non-trivial spacetime structure, with a multitude of eternally inflating regions connected by wormholes. If a black hole population with the predicted mass spectrum is discovered, it could be regarded as evidence for inflation and for the existence of a multiverse.

Black holes and the multiverse

DOE Office of Scientific and Technical Information (OSTI.GOV)

Garriga, Jaume; Vilenkin, Alexander; Zhang, Jun, E-mail: jaume.garriga@ub.edu, E-mail: vilenkin@cosmos.phy.tufts.edu, E-mail: jun.zhang@tufts.edu

Vacuum bubbles may nucleate and expand during the inflationary epoch in the early universe. After inflation ends, the bubbles quickly dissipate their kinetic energy; they come to rest with respect to the Hubble flow and eventually form black holes. The fate of the bubble itself depends on the resulting black hole mass. If the mass is smaller than a certain critical value, the bubble collapses to a singularity. Otherwise, the bubble interior inflates, forming a baby universe, which is connected to the exterior FRW region by a wormhole. A similar black hole formation mechanism operates for spherical domain walls nucleatingmore » during inflation. As an illustrative example, we studied the black hole mass spectrum in the domain wall scenario, assuming that domain walls interact with matter only gravitationally. Our results indicate that, depending on the model parameters, black holes produced in this scenario can have significant astrophysical effects and can even serve as dark matter or as seeds for supermassive black holes. The mechanism of black hole formation described in this paper is very generic and has important implications for the global structure of the universe. Baby universes inside super-critical black holes inflate eternally and nucleate bubbles of all vacua allowed by the underlying particle physics. The resulting multiverse has a very non-trivial spacetime structure, with a multitude of eternally inflating regions connected by wormholes. If a black hole population with the predicted mass spectrum is discovered, it could be regarded as evidence for inflation and for the existence of a multiverse.« less

Oxasmaragdyrins as New and Efficient Hole-Transporting Materials for High-Performance Perovskite Solar Cells.

PubMed

Mane, Sandeep B; Sutanto, Albertus Adrian; Cheng, Chih-Fu; Xie, Meng-Yu; Chen, Chieh-I; Leonardus, Mario; Yeh, Shih-Chieh; Beyene, Belete Bedemo; Diau, Eric Wei-Guang; Chen, Chin-Ti; Hung, Chen-Hsiung

2017-09-20

The high performance of the perovskite solar cells (PSCs) cannot be achieved without a layer of efficient hole-transporting materials (HTMs) to retard the charge recombination and transport the photogenerated hole to the counterelectrode. Herein, we report the use of boryl oxasmaragdyrins (SM01, SM09, and SM13), a family of aromatic core-modified expanded porphyrins, as efficient hole-transporting materials (HTMs) for perovskite solar cells (PSCs). These oxasmaragdyrins demonstrated complementary absorption spectra in the low-energy region, good redox reversibility, good thermal stability, suitable energy levels with CH 3 NH 3 PbI 3 perovskite, and high hole mobility. A remarkable power conversion efficiency of 16.5% (V oc = 1.09 V, J sc = 20.9 mA cm -2 , fill factor (FF) = 72%) is achieved using SM09 on the optimized PSCs device employing a planar structure, which is close to that of the state-of-the-art hole-transporting materials (HTMs), spiro-OMeTAD of 18.2% (V oc = 1.07 V, J sc = 22.9 mA cm -2 , FF = 74%). In contrast, a poor photovoltaic performance of PSCs using SM01 is observed due to the interactions of terminal carboxylic acid functional group with CH 3 NH 3 PbI 3 .

Breaking Through the Multi-Mesa-Channel Width Limited of Normally Off GaN HEMTs Through Modulation of the Via-Hole-Length.

PubMed

Chien, Cheng-Yen; Wu, Wen-Hsin; You, Yao-Hong; Lin, Jun-Huei; Lee, Chia-Yu; Hsu, Wen-Ching; Kuan, Chieh-Hsiung; Lin, Ray-Ming

2017-12-01

We present new normally off GaN high-electron-mobility transistors (HEMTs) that overcome the typical limitations in multi-mesa-channel (MMC) width through modulation of the via-hole-length to regulate the charge neutrality screen effect. We have prepared enhancement-mode (E-mode) GaN HEMTs having widths of up to 300 nm, based on an enhanced surface pinning effect. E-mode GaN HEMTs having MMC structures and widths as well as via-hole-lengths of 100 nm/2 μm and 300 nm/6 μm, respectively, exhibited positive threshold voltages (V th ) of 0.79 and 0.46 V, respectively. The on-resistances of the MMC and via-hole-length structures were lower than those of typical tri-gate nanoribbon GaN HEMTs. In addition, the devices not only achieved the E-mode but also improved the power performance of the GaN HEMTs and effectively mitigated the device thermal effect. We controlled the via-hole-length sidewall surface pinning effect to obtain the E-mode GaN HEMTs. Our findings suggest that via-hole-length normally off GaN HEMTs have great potential for use in next-generation power electronics.

Research on High-Bandgap Materials and Amorphous Silicon-Based Solar Cells, Final Technical Report, 15 May 1994-15 January 1998

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schiff, E. A.; Gu, Q.; Jiang, L.

1998-12-28

This report describes work performed by Syracuse University under this subcontract. Researchers developed a technique based on electroabsorption measurements for obtaining quantitative estimates of the built-in potential Vbi in a-Si:H-based heterostructure solar cells incorporating microcrystalline or a-SiC:H p layers. Using this new electroabsorption technique, researchers confirmed previous estimates of Vbi {yields} 1.0 V in a-Si:H solar cells with ''conventional'' intrinsic layers and either microcrystalline or a-SiC:H p layers. Researchers also explored the recent claim that light-soaking of a-Si:H substantially changes the polarized electroabsorption associated with interband optical transitions (and hence, not defect transitions). Researchers confirmed measurements of improved (5') holemore » drift mobilities in some specially prepared a-Si:H samples. Disturbingly, solar cells made with such materials did not show improved efficiencies. Researchers significantly clarified the relationship of ambipolar diffusion-length measurements to hole drift mobilities in a-Si:H, and have shown that the photocapacitance measurements can be interpreted in terms of hole drift mobilities in amorphous silicon. They also completed a survey of thin BP:H and BPC:H films prepared by plasma deposition using phosphine, diborane, trimethylboron, and hydrogen as precursor gases.« less

High-Performance, Solution-Processed Quantum Dot Light-Emitting Field-Effect Transistors with a Scandium-Incorporated Indium Oxide Semiconductor.

PubMed

He, Penghui; Jiang, Congbiao; Lan, Linfeng; Sun, Sheng; Li, Yizhi; Gao, Peixiong; Zhang, Peng; Dai, Xingqiang; Wang, Jian; Peng, Junbiao; Cao, Yong

2018-05-22

Light-emitting field-effect transistors (LEFETs) have attained great attention due to their special characteristics of both the switching capacity and the electroluminescence capacity. However, high-performance LEFETs with high mobility, high brightness, and high efficiency have not been realized due to the difficulty in developing high electron and hole mobility materials with suitable band structures. In this paper, quantum dot hybrid LEFETs (QD-HLEFETs) combining high-luminous-efficiency quantum dots (QDs) and a solution-processed scandium-incorporated indium oxide (Sc:In 2 O 3 ) semiconductor were demonstrated. The red QD-HLEFET showed high electrical and optical performance with an electron mobility of 0.8 cm 2 V -1 s -1 , a maximum brightness of 13 400 cd/m 2 , and a maximum external quantum efficiency of 8.7%. The high performance of the QD-HLEFET is attributed to the good energy band matching between Sc:In 2 O 3 and QDs and the balanced hole and electron injection (less exciton nonradiative recombination). In addition, incorporation of Sc into In 2 O 3 can suppress the oxygen vacancy and free carrier generation and brings about excellent current and optical modulation (the on/off current ratio is 10 5 and the on/off brightness ratio is 10 6 ).

Dihedral angle control to improve the charge transport properties of conjugated polymers in organic field effect transistors

NASA Astrophysics Data System (ADS)

Dharmapurikar, Satej S.; Chithiravel, Sundaresan; Mane, Manoj V.; Deshmukh, Gunvant; Krishnamoorthy, Kothandam

2018-03-01

Diketopyrrolopyrrole (DPP) and i-Indigo (i-Ind) are two monomers that are widely explored as active materials in organic field effect transistor and solar cells. These two molecules showed impressive charge carrier mobility due to better packing that are facilitated by quadrupoles. We hypothesized that the copolymers of these monomers would also exhibit high charge carrier mobility. However, we envisioned that the dihedral angle at the connecting point between the monomers will play a crucial role in packing as well as charge transport. To understand the impact of dihedral angle on charge transport, we synthesized three copolymers, wherein the DPP was sandwiched between benzenes, thiophenes and furans. The copolymer of i-Indigo and furan comprising DPP showed a band gap of 1.4 eV with a very high dihedral angle of 179°. The polymer was found to pack better and the coherence length was found to be 112 Å. The hole carrier mobility of these polymer was found to be highest among the synthesized polymer i.e. 0.01 cm2/vs. The copolymer comprising benzene did not transport hole and electrons. The dihedral angle at the connecting point between i and Indigo and benzene DPP was 143 Å, which the packing and consequently charge transport properties.

Gate dielectric surface treatments for performance improvement of poly(3-hexylthiophene-2,5-diyl) based organic field-effect transistors

NASA Astrophysics Data System (ADS)

Nawaz, Ali; de, Cristiane, , Col; Cruz-Cruz, Isidro; Kumar, Anshu; Kumar, Anil; Hümmelgen, Ivo A.

2015-08-01

We report on enhanced performance in poly(3-hexylthiophene-2,5-diyl) (P3HT) based organic field effect transistors (OFETs) achieved by improvement in hole transport along the channel near the insulator/semiconductor (I/S) interface. The improvement in hole transport is demonstrated to occur very close to the I/S interface, after treatment of the insulator layer with sodium dodecyl sulfate (SDS). SDS is an anionic surfactant, with negatively charged heads, known for formation of micelles above critical micelle concentration (CMC), which contribute to the passivation of positively charged traps. Investigation of field-effect mobility (μFET) as a function of channel bottleneck thickness in OFETs reveals the favorable gate voltage regime where mobility is the highest. In addition, it shows that the gate dielectric surface treatment not only leads to an increase in mobility in that regime, but also displaces charge transport closer to the interface, hence pointing toward passivation of the charge traps at I/S interface. OFETs with SDS treatment were compared with untreated and vitamin C or hexadecyltrimethylammonium bromide (CTAB) treated OFETs. All the treatments resulted in significant improvements in specific dielectric capacitance, μFET, on/off current ratio and transconductance.

Mobile Genetic Elements: In Silico, In Vitro, In Vivo

PubMed Central

Arkhipova, Irina R.; Rice, Phoebe A.

2016-01-01

Mobile genetic elements (MGEs), also called transposable elements (TEs), represent universal components of most genomes and are intimately involved in nearly all aspects of genome organization, function, and evolution. However, there is currently a gap between fast-paced TE discovery in silico, stimulated by exponential growth of comparative genomic studies, and a limited number of experimental models amenable to more traditional in vitro and in vivo studies of structural, mechanistic, and regulatory properties of diverse MGEs. Experimental and computational scientists came together to bridge this gap at a recent conference, “Mobile Genetic Elements: in silico, in vitro, in vivo,” held at the Marine Biological Laboratory (MBL) in Woods Hole, MA, USA. PMID:26822117

Simulating the X-ray luminosity of Be X-ray binaries: the case for black holes versus neutron stars

NASA Astrophysics Data System (ADS)

Brown, R. O.; Ho, W. C. G.; Coe, M. J.; Okazaki, A. T.

2018-04-01

There are over 100 Be stars that are known to have neutron star companions but only one such system with a black hole. Previous theoretical work suggests this is not due to their formation but due to differences in X-ray luminosity. It has also been proposed that the truncation of the Be star's circumstellar disc is dependent on the mass of the compact object. Hence, Be star discs in black hole binaries are smaller. Since accretion onto the compact object from the Be star's disc is what powers the X-ray luminosity, a smaller disc in black hole systems leads to a lower luminosity. In this paper, simulations are performed with a range of eccentricities and compact object mass. The disc's size and density are shown to be dependent on both quantities. Mass capture and, in turn, X-ray luminosity are heavily dependent on the size and density of the disc. Be/black hole binaries are expected to be up to ˜10 times fainter than Be/neutron star binaries when both systems have the same eccentricity and can be 100 times fainter when comparing systems with different eccentricity.

Spectroscopic evidence for temperature dependent relative movement of light and heavy hole valence bands of PbQ (Q=Te,Se,S)

NASA Astrophysics Data System (ADS)

Chatterjee, Utpal; Zhao, Junjing; Kanatzidis, Mercouri; Malliakas, Christos

We have conducted temperature dependent Angle Resolved Photoemission Spectroscopy (ARPES) studies of the electronic structures of PbTe, PbSe and PbS. Our ARPES measurements provide direct evidences for the light hole upper valence bands (UVBs) and the so-called heavy hole lower valence bands (LVBs), and an unusual temperature dependent relative movement between their band maxima leading to a monotonic decrease in the energy separation between LVBs and UVBs with increase in temperature. This enables convergence of these valence bands and consequently an effective increase in the valley degeneracy in PbQ at higher temperatures, which has long been believed to be the driving factor behind their extraordinary thermoelectric performance.

Transport properties of massless Dirac fermions in an organic conductor α-(BEDT-TTF)2I3 under pressure

NASA Astrophysics Data System (ADS)

Tajima, N.; Sugawara, S.; Tamura, M.; Kato, R.; Nishio, Y.; Kajita, K.

2007-11-01

A zero-gap state with the Dirac cone-type energy dispersion was found in an organic conductor α-(BEDT-TTF)2I3 under high hydrostatic pressures. This is the first two-dimensional zero-gap state discovered in bulk crystals with layered structures. In contrast to the case of graphene, the Dirac cone in this system is highly anisotropic. The present system, therefore, provides a new type of massless Dirac fermions with anisotropic Fermi velocity. From the galvano-magnetic measurements, the density and mobilities of electrons and holes were determined in the temperature region between 77 K and 2 K. In this region, the carrier density (n) depends on temperature (T) as n~T2 and decreases by about four orders of magnitude. On the other hand, the sheet resistance per BEDT-TTF layer (RS) stays almost constant in the region. The value is written as RS=gh/e2 in terms of the quantum resistance h/e2=25.8 kΩ, where g is a parameter that depends weakly on temperature.

Micro-spectroscopy on silicon wafers and solar cells

PubMed Central

2011-01-01

Micro-Raman (μRS) and micro-photoluminescence spectroscopy (μPLS) are demonstrated as valuable characterization techniques for fundamental research on silicon as well as for technological issues in the photovoltaic production. We measure the quantitative carrier recombination lifetime and the doping density with submicron resolution by μPLS and μRS. μPLS utilizes the carrier diffusion from a point excitation source and μRS the hole density-dependent Fano resonances of the first order Raman peak. This is demonstrated on micro defects in multicrystalline silicon. In comparison with the stress measurement by μRS, these measurements reveal the influence of stress on the recombination activity of metal precipitates. This can be attributed to the strong stress dependence of the carrier mobility (piezoresistance) of silicon. With the aim of evaluating technological process steps, Fano resonances in μRS measurements are analyzed for the determination of the doping density and the carrier lifetime in selective emitters, laser fired doping structures, and back surface fields, while μPLS can show the micron-sized damage induced by the respective processes. PMID:21711723

Ambipolar nonvolatile memory based on a quantum-dot transistor with a nanoscale floating gate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Che, Yongli; Zhang, Yating, E-mail: yating@tju.edu.cn; Song, Xiaoxian

2016-07-04

Using only solution processing methods, we developed ambipolar quantum-dot (QD) transistor floating-gate memory (FGM) that uses Au nanoparticles as a floating gate. Because of the bipolarity of the active channel of PbSe QDs, the memory could easily trap holes or electrons in the floating gate by programming/erasing (P/E) operations, which could shift the threshold voltage both up and down. As a result, the memory exhibited good programmable memory characteristics: a large memory window (ΔV{sub th} ∼ 15 V) and a long retention time (>10{sup 5 }s). The magnitude of ΔV{sub th} depended on both P/E voltages and the bias voltage (V{sub DS}): ΔV{sub th}more » was a cubic function to V{sub P/E} and linearly depended on V{sub DS}. Therefore, this FGM based on a QD transistor is a promising alternative to its inorganic counterparts owing to its advantages of bipolarity, high mobility, low cost, and large-area production.« less

Regional Sediment Management (RSM) Strategy for Mobile Bay, Alabama

DTIC Science & Technology

2015-04-01

shrimp , eastern oyster, and blue crab. In terms of the entire fishery assemblages, white shrimp was the numerically dominant species captured in Brookley...Brookley Hole, threadfin shad was the third most dominant species. Commercially important shellfish taken at both sites include both brown and white

Dynamics of stellar black holes in young star clusters with different metallicities - II. Black hole-black hole binaries

NASA Astrophysics Data System (ADS)

Ziosi, Brunetto Marco; Mapelli, Michela; Branchesi, Marica; Tormen, Giuseppe

2014-07-01

In this paper, we study the formation and dynamical evolution of black hole-black hole (BH-BH) binaries in young star clusters (YSCs), by means of N-body simulations. The simulations include metallicity-dependent recipes for stellar evolution and stellar winds, and have been run for three different metallicities (Z = 0.01, 0.1 and 1 Z⊙). Following recent theoretical models of wind mass-loss and core-collapse supernovae, we assume that the mass of the stellar remnants depends on the metallicity of the progenitor stars. We find that BH-BH binaries form efficiently because of dynamical exchanges: in our simulations, we find about 10 times more BH-BH binaries than double neutron star binaries. The simulated BH-BH binaries form earlier in metal-poor YSCs, which host more massive black holes (BHs) than in metal-rich YSCs. The simulated BH-BH binaries have very large chirp masses (up to 80 M⊙), because the BH mass is assumed to depend on metallicity, and because BHs can grow in mass due to the merger with stars. The simulated BH-BH binaries span a wide range of orbital periods (10-3-107 yr), and only a small fraction of them (0.3 per cent) is expected to merge within a Hubble time. We discuss the estimated merger rate from our simulations and the implications for Advanced VIRGO and LIGO.

Thickness-dependent magneto-optical effects in hole-doped GaS and GaSe multilayers: a first-principles study

NASA Astrophysics Data System (ADS)

Li, Fei; Zhou, Xiaodong; Feng, Wanxiang; Fu, Botao; Yao, Yugui

2018-04-01

Recently, two-dimensional (2D) GaS and GaSe nanosheets were successfully fabricated and the measured electronic, mechanical, and optoelectronic properties are excellent. Here, using the first-principles density functional theory, we investigate the magnetic, optical, and magneto-optical (MO) Kerr and Faraday effects in hole-doped GaS and GaSe multilayers. GaS and GaSe monolayers (MLs) manifest ferromagnetic ground states by introducing even a small amount of hole doping, whereas the magnetism in GaS and GaSe multilayers are significantly different under hole doping. Our results show that ferromagnetic states can be easily established in GaS bilayers and trilayers under proper hole doping, however, most of GaSe multilayers are more favorable to nonmagnetic states. The magnetic moments in GaS multilayers are weakened remarkably with the increasing of thin film thickness and are negligible more than three MLs. This leads to the thickness dependence of MO Kerr and Faraday effects. Furthermore, the MO effects strongly depend on the doping concentration and therefore are electrically controllable by adjusting the number of holes via gate voltage. The substrate effects on the MO properties are also discussed. Combining the unique MO and other interesting physical properties make GaS and GaSe a superior 2D material platform for semiconductor MO and spintronic nanodevices.

Remote p-type Doping in GaSb/InAs Core-shell Nanowires

PubMed Central

Ning, Feng; Tang, Li-Ming; Zhang, Yong; Chen, Ke-Qiu

2015-01-01

By performing first-principles calculation, we investigated the electronic properties of remotely p-type doping GaSb nanowire by a Zn-doped InAs shell. The results show that for bare zinc-blende (ZB) [111] GaSb/InAs core-shell nanowire the Zn p-type doped InAs shell donates free holes to the non-doped GaSb core nanowire without activation energy, significantly increasing the hole density and mobility of nanowire. For Zn doping in bare ZB [110] GaSb/InAs core-shell nanowire the hole states are compensated by surface states. We also studied the behaviors of remote p-type doing in two-dimensional (2D) GaSb/InAs heterogeneous slabs, and confirmed that the orientation of nanowire side facet is a key factor for achieving high efficient remote p-type doping. PMID:26028535

Black hole evaporation in conformal gravity

NASA Astrophysics Data System (ADS)

Bambi, Cosimo; Modesto, Leonardo; Porey, Shiladitya; Rachwał, Lesław

2017-09-01

We study the formation and the evaporation of a spherically symmetric black hole in conformal gravity. From the collapse of a spherically symmetric thin shell of radiation, we find a singularity-free non-rotating black hole. This black hole has the same Hawking temperature as a Schwarzschild black hole with the same mass, and it completely evaporates either in a finite or in an infinite time, depending on the ensemble. We consider the analysis both in the canonical and in the micro-canonical statistical ensembles. Last, we discuss the corresponding Penrose diagram of this physical process.

Studies of the Effects of Control Bandwidth and Dark-Hole Size on the HCIT Contrast Performance

NASA Technical Reports Server (NTRS)

Sidick, Erkin; Shaklan, Stuart; Balasubramanian, Kunjithapatha; Cady, Eric

2015-01-01

We have carried out both theoretical and experimental studies of the sensitivity of dark hole contrast to the control bandwidth and dark-hole dimensions in high-contrast broadband stellar coronagraphy. We have evaluated the performance of DM actuator solutions in the presence of occulting mask defects using one to five 2% -wide bands spanning a 10% bandpass. We have also investigated the dependence of the HCIT contrast performance on the size of dark -hole area including large dark holes formed at the Nyquist limit of the DM.

Studies of the effects of control bandwidth and dark-hole size on the HCIT contrast performance

NASA Astrophysics Data System (ADS)

Sidick, Erkin; Shaklan, Stuart; Balasubramanian, Kunjithapatham; Cady, Eric

2015-09-01

We have carried out both theoretical and experimental studies of the sensitivity of dark hole contrast to the control bandwidth and dark-hole dimensions in high-contrast broadband stellar coronagraphy. We have evaluated the performance of DM actuator solutions in the presence of occulting mask defects using one to five 2%-wide bands spanning a 10% bandpass. We have also investigated the dependence of the HCIT contrast performance on the size of dark-hole area including large dark holes formed at the Nyquist limit of the DM.

Black hole evaporation in conformal gravity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bambi, Cosimo; Rachwał, Lesław; Modesto, Leonardo

We study the formation and the evaporation of a spherically symmetric black hole in conformal gravity. From the collapse of a spherically symmetric thin shell of radiation, we find a singularity-free non-rotating black hole. This black hole has the same Hawking temperature as a Schwarzschild black hole with the same mass, and it completely evaporates either in a finite or in an infinite time, depending on the ensemble. We consider the analysis both in the canonical and in the micro-canonical statistical ensembles. Last, we discuss the corresponding Penrose diagram of this physical process.

Modulated Hawking radiation and a nonviolent channel for information release

NASA Astrophysics Data System (ADS)

Giddings, Steven B.

2014-11-01

Unitarization of black hole evaporation requires that quantum information escapes a black hole; an important question is to identify the mechanism or channel by which it does so. Accurate counting of black hole states via the Bekenstein-Hawking entropy would indicate this information should be encoded in radiation with average energy flux matching Hawking's. Information can be encoded with no change in net flux via fine-grained modulation of the Hawking radiation. In an approximate effective field theory description, couplings to the stress tensor of the black hole atmosphere that depend on the internal state of the black hole are a promising alternative for inducing such modulation. These can be picturesquely thought of as due to state-dependent metric fluctuations in the vicinity of the horizon. Such couplings offer the prospect of emitting information without extra energy flux, and can be shown to do so at linear order in the couplings, with motivation given for possible extension of this result to higher orders. The potential advantages of such couplings to the stress tensor thus extend beyond their universality, which is helpful in addressing constraints from black hole mining.

Characterization and Effects of Fiber Pull-Outs in Hole Quality of Carbon Fiber Reinforced Plastics Composite.

PubMed

Alizadeh Ashrafi, Sina; Miller, Peter W; Wandro, Kevin M; Kim, Dave

2016-10-13

Hole quality plays a crucial role in the production of close-tolerance holes utilized in aircraft assembly. Through drilling experiments of carbon fiber-reinforced plastic composites (CFRP), this study investigates the impact of varying drilling feed and speed conditions on fiber pull-out geometries and resulting hole quality parameters. For this study, hole quality parameters include hole size variance, hole roundness, and surface roughness. Fiber pull-out geometries are quantified by using scanning electron microscope (SEM) images of the mechanically-sectioned CFRP-machined holes, to measure pull-out length and depth. Fiber pull-out geometries and the hole quality parameter results are dependent on the drilling feed and spindle speed condition, which determines the forces and undeformed chip thickness during the process. Fiber pull-out geometries influence surface roughness parameters from a surface profilometer, while their effect on other hole quality parameters obtained from a coordinate measuring machine is minimal.

Time-resolved electric force microscopy of charge trapping in polycrystalline pentacene.

PubMed

Jaquith, Michael; Muller, Erik M; Marohn, John A

2007-07-12

Here we introduce time-resolved electric force microscopy measurements to directly and locally probe the kinetics of charge trap formation in a polycrystalline pentacene thin-film transistor. We find that the trapping rate depends strongly on the initial concentration of free holes and that trapped charge is highly localized. The observed dependence of trapping rate on the hole chemical potential suggests that the trapping process should not be viewed as a filling of midgap energy levels, but instead as a process in which the very creation of trapped states requires the presence of free holes.

Replacement of Biphenyl by Bipyridine Enabling Powerful Hole Transport Materials for Efficient Perovskite Solar Cells.

PubMed

Wu, Fei; Shan, Yahan; Qiao, Jianhui; Zhong, Cheng; Wang, Rui; Song, Qunliang; Zhu, Linna

2017-10-09

Here, 2,2'- and 3,3'-bipyridine are introduced for the first time as the core structure to get two new hole transport materials (HTMs), namely F22 and F33. The electron-withdrawing nature of bipyridine lowers the HOMO level of the new compounds and enhances the open-circuit voltage of perovskite solar cells. Especially for F33, the better planarity leads to better conjugation in the whole molecule and the molecular interaction is enhanced. Hole-mobility tests, steady-state photoluminescence (PL) spectra as well as time-resolved PL decay results demonstrate that the new HTMs exhibit good hole extraction and hole-transporting property. Impressive power conversion efficiencies of 17.71 and 18.48 % are achieved in conventional planar perovskite (CH 3 NH 3 PbI 3-x Cl x ) solar cells containing F22 and F33 as HTMs, respectively. As far as we know, this is the first report on bypiridine-based HTMs with leading efficiencies, and the design motif in this work opens a new way for devising HTMs in the future. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Addressing the efficiency roll-off in a fluorescent OLED by facile electron transport layer doping and carrier confinement

NASA Astrophysics Data System (ADS)

Soman, Anjaly; M, Manuraj; Unni, K. N. Narayanan

2018-05-01

Organic light emitting diodes (OLEDs) often face the issue of decreasing power efficiency with increasing brightness. Loss of charge carrier balance is one of the factors contributing to the efficiency roll-off. We demonstrate that by using a combination of doped electron transport layer (ETL) and a specially chosen electron blocking layer (EBL) having high hole mobility, this efficiency roll-off can be effectively suppressed. A tris-(8-hydroxyquinoline) aluminium (Alq3) based OLED has been fabricated with 2,3,6,7-Tetrahydro-1,1,7,7,-tetramethyl-1H, 5H,11H-10-(2-benzothiazolyl) quinolizino-[9,9a, 1n gh]coumarin (C545T) as the emissive dopant. Bulk doping of the ETL with lithium fluoride (LiF) was optimized to increase the luminous intensity as well as the current efficiency. An EBL with high hole mobility introduced between the EML and the hole transport layer (HTL) improved the performance drastically, and the device brightness at 9 V got improved by a factor of 2.5 compared to that of the control device. While increasing the brightness from 100 cd/m2 to 1000 cd/m2, the power efficiency drop was 47% for the control device whereas only a drop of 15% was observed for the modified device. The possible mechanisms for the enhanced performance are discussed.

Highly mobile oxygen holes in magnesium oxide

NASA Technical Reports Server (NTRS)

Freund, Minoru M.; Freund, Friedemann; Batllo, Francois

1989-01-01

High-purity MgO exhibits an unexpected giant anomaly of the apparent static dielectric constant and a positive surface charge of the order of 5 x 10 to the 21st/cu cm in the top 15 nm. It is postulated that the MgO matrix contains traces of peroxy defects, O2(2-), associated with Mg(2+) vacancies. Above approximately 400 C the O2(2-) dissociates to vacancy bound O(-) and highly mobile O(-) states, which diffuse to the surface, giving rise to a high surface conductivity.

Electrical characterization of fluorinated benzothiadiazole based conjugated copolymer - a promising material for high-performance solar cells

NASA Astrophysics Data System (ADS)

Toušek, J.; Toušková, J.; Remeš, Z.; Chomutová, R.; Čermák, J.; Helgesen, M.; Carlé, J. E.; Krebs, F. C.

2015-12-01

Measurements of electrical conductivity, electron work function, carrier mobility of holes and the diffusion length of excitons were performed on samples of conjugated polymers relevant to polymer solar cells. A state of the art fluorinated benzothiadiazole based conjugated copolymer (PBDTTHD - DTBTff) was studied and benchmarked against the reference polymer poly-3-hexylthiophene (P3HT). We employed, respectively, four electrode conductivity measurements, Kelvin probe work function measurements, carrier mobility using charge extraction by linearly increasing voltage (CELIV) measurements and diffusion length determinaton using surface photovoltage measurements.

Major and Trace Element Variations in Impact Crater Clay from Chicxulub, Lonar, and Mistastin, Implications for the Martian Soil

NASA Technical Reports Server (NTRS)

Newsom, H. E.; Nelson, M. J.; Shearer, C. K.; Rietmeijer, F. J. M.; Gakin, R.; Lee, K.

2004-01-01

The catastrophic Chicxulub event should have generated a large hydrothermal system with volatile element mobilization, producing interesting alteration materials and clays. The Yaxcopoil-1 (YAX) drill hole is located in the annular trough, about 70 km southwest of the crater center, in an area where the impactite layers are relatively thin (approx. 100 m thick). We have analyzed samples from the YAX drill core and from other impact craters including Mistastin and Lonar to determine the nature of alteration and trace element mobilization.

Enhanced Circular Dichroism of Gold Bilayered Slit Arrays Embedded with Rectangular Holes.

PubMed

Zhang, Hao; Wang, Yongkai; Luo, Lina; Wang, Haiqing; Zhang, Zhongyue

2017-01-01

Gold bilayered slit arrays with rectangular holes embedded into the metal surface are designed to enhance the circular dichroism (CD) effect of gold bilayered slit arrays. The rectangular holes in these arrays block electric currents and generate localized surface plasmons around these holes, thereby strengthening the CD effect. The CD enhancement factor depends strongly on the rotational angle and the structural parameters of the rectangular holes; this factor can be enhanced further by drilling two additional rectangular holes into the metal surfaces of the arrays. These results help facilitate the design of chiral structures to produce a strong CD effect and large electric fields.

The region interior to the event horizon of the regular Hayward black hole

NASA Astrophysics Data System (ADS)

Perez-Roman, Ivan; Bretón, Nora

2018-06-01

The Painlevé-Gullstrand coordinates allow us to explore the interior of the regular Hayward black hole. The behavior of an infalling particle in traversing the Hayward black hole is compared with the one inside the Schwarzschild and Reissner-Nordstrom singular black holes. When approaching the origin the test particle trajectories present differences depending if the center is regular or singular. The velocities of the infalling test particle into the modified Hayward black hole are analyzed as well. As compared with the normal Hayward, in the modified Hayward black hole the particle moves faster and the surface gravity is smaller.

Growth and characterization of In1-xGaxAs/InAs0.65Sb0.35 strained layer superlattice infrared detectors

NASA Astrophysics Data System (ADS)

Ariyawansa, G.; Duran, J. M.; Reyner, C. J.; Steenbergen, E. H.; Yoon, N.; Wasserman, D.; Scheihing, J. E.

2017-02-01

Type-II strained layer superlattices (SLS) are an active research topic in the infrared detector community and applications for SLS detectors continue to grow. SLS detector technology has already reached the commercial market due to improvements in material quality, device design, and device fabrication. Despite this progress, the optimal superlattice design has not been established, and at various times has been believed to be InAs/GaSb, InAs/InGaSb, or InAs/InAsSb. Building on these, we investigate the properties of a new mid-wave infrared SLS material: InGaAs/InAsSb SLS. The ternary InGaAs/InAsSb SLS has three main advantages over other SLS designs: greater support for strain compensation, enhanced absorption due to increased electron-hole wavefunction overlap, and improved vertical hole mobility due to reduced hole effective mass. Here, we compare three ternary SLSs, with approximately the same bandgap (0.240 eV at 150 K), comprised of Ga fractions of 5%, 10%, and 20% to a reference sample with 0% Ga. Enhanced absorption is both theoretically predicted and experimentally realized. Furthermore, the characteristics of ternary SLS infrared detectors based on an nBn architecture are reported and exhibit nearly state-of-the-art dark current performance with minimal growth optimization. We report standard material and device characterization information, including dark current and external quantum efficiency, and provide further analysis that indicates improved quantum efficiency and vertical hole mobility. Finally, a 320×256 focal plane array built based on the In0.8Ga0.2As/InAs0.65Sb0.35 SLS design is demonstrated with promising performance.

P-type surface effects for thickness variation of 2um and 4um of n-type layer in GaN LED

NASA Astrophysics Data System (ADS)

Halim, N. S. A. Abdul; Wahid, M. H. A.; Hambali, N. A. M. Ahmad; Rashid, S.; Ramli, M. M.; Shahimin, M. M.

2017-09-01

The internal quantum efficiency of III-Nitrides group, GaN light-emitting diode (LED) has been considerably limited due to the insufficient hole injection and this is caused by the lack of performance p-type doping and low hole mobility. The low hole mobility makes the hole less energetic, thus reduced the performance operation of GaN LED itself. The internal quantum efficiency of GaN-based LED with surface roughness (texture) can be changed by texture size, density, and thickness of GaN film or by the combined effects of surface shape and thickness of GaN film. Besides, due to lack of p-type GaN, attempts to look forward the potential of GaN LED relied on the thickness of n-type layer and surface shape of p-type GaN layer. This work investigates the characteristics of GaN LED with undoped n-GaN layer of different thickness and the surface shape of p-type layer. The LEDs performance is significantly altered by modifying the thickness and shape. Enhancement of n-GaN layer has led to the annihilation of electrical conductivity of the chip. Different surface geometry governs the emission rate extensively. Internal quantum efficiency is also predominantly affected by the geometry of n-GaN layer which subjected to the current spreading. It is recorded that the IQE droop can be minimized by varying the thickness of the active layer without amplifying the forward voltage. Optimum forward voltage (I-V), total emission rate relationship with the injected current and internal quantum efficiency (IQE) for 2,4 µm on four different surfaces of p-type layer are also reported in this paper.

Colonisation of fish and crabs of wave energy foundations and the effects of manufactured holes - a field experiment.

PubMed

Langhamer, Olivia; Wilhelmsson, Dan

2009-10-01

Several Western European countries are planning for a significant development of offshore renewable energy along the European Atlantic Ocean coast, including many thousands of wave energy devices and wind turbines. There is an increasing interest in articulating the added values of the creation of artificial hard bottom habitats through the construction of offshore renewable energy devices, for the benefit of fisheries management and conservation. The Lysekil Project is a test park for wave power located about 100 km north of Gothenburg at the Swedish west coast. A wave energy device consists of a linear wave power generator attached to a foundation on the seabed, and connected by a wire to a buoy at the surface. Our field experiment examined the function of wave energy foundations as artificial reefs. In addition, potentials for enhancing the abundance of associated fish and crustaceans through manufactured holes of the foundations were also investigated. Assemblages of mobile organisms were examined by visual censuses in July and August 2007, 3 months after deployment of the foundations. Results generally show low densities of mobile organisms, but a significantly higher abundance of fish and crabs on the foundations compared to surrounding soft bottoms. Further, while fish numbers were not influenced by increased habitat complexity (holes), it had a significantly positive effect on quantities of edible crab (Cancer pagurus), on average leading to an almost five-fold increase in densities of this species. Densities of spiny starfish (Marthasterias glacialis) were negatively affected by the presence of holes, potentially due to increased predator abundance (e.g. C. pagurus). These results suggest a species-specific response to enhanced habitat complexity.

Modeling charge transport in organic photovoltaic materials.

PubMed

Nelson, Jenny; Kwiatkowski, Joe J; Kirkpatrick, James; Frost, Jarvist M

2009-11-17

The performance of an organic photovoltaic cell depends critically on the mobility of charge carriers within the constituent molecular semiconductor materials. However, a complex combination of phenomena that span a range of length and time scales control charge transport in disordered organic semiconductors. As a result, it is difficult to rationalize charge transport properties in terms of material parameters. Until now, efforts to improve charge mobilities in molecular semiconductors have proceeded largely by trial and error rather than through systematic design. However, recent developments have enabled the first predictive simulation studies of charge transport in disordered organic semiconductors. This Account describes a set of computational methods, specifically molecular modeling methods, to simulate molecular packing, quantum chemical calculations of charge transfer rates, and Monte Carlo simulations of charge transport. Using case studies, we show how this combination of methods can reproduce experimental mobilities with few or no fitting parameters. Although currently applied to material systems of high symmetry or well-defined structure, further developments of this approach could address more complex systems such anisotropic or multicomponent solids and conjugated polymers. Even with an approximate treatment of packing disorder, these computational methods simulate experimental mobilities within an order of magnitude at high electric fields. We can both reproduce the relative values of electron and hole mobility in a conjugated small molecule and rationalize those values based on the symmetry of frontier orbitals. Using fully atomistic molecular dynamics simulations of molecular packing, we can quantitatively replicate vertical charge transport along stacks of discotic liquid crystals which vary only in the structure of their side chains. We can reproduce the trends in mobility with molecular weight for self-organizing polymers using a cheap, coarse-grained structural simulation method. Finally, we quantitatively reproduce the field-effect mobility in disordered C60 films. On the basis of these results, we conclude that all of the necessary building blocks are in place for the predictive simulation of charge transport in macromolecular electronic materials and that such methods can be used as a tool toward the future rational design of functional organic electronic materials.

Probing the magnetic field dependence of the light hole transition in GaAs/AlGaAs quantum wells using optically pumped NMR

NASA Astrophysics Data System (ADS)

Willmering, Matthew M.; Sesti, Erika L.; Hayes, Sophia E.; Wood, Ryan M.; Bowers, Clifford R.; Thapa, Sunil K.; Stanton, Christopher J.; Reyes, Arneil P.; Kuhns, Philip; McGill, Stephen

2018-02-01

Optically pumped NMR (OPNMR) of the NMR-active Ga/7169 species has been shown to be a unique method to probe electronic energy bands in GaAs, with sensitivity to the light hole-to-conduction band transition. This transition is often obscured in other optical measurements such as magnetoabsorption. Using OPNMR, we exploit the hyperfine interaction between conduction band electrons (and their spin states) and nuclear spins, which are detected through phase-sensitive radio-frequency (NMR) spectroscopy. Measurements were made over a range of external magnetic fields (B0) in two different labs with separate experimental setups to obtain the magnetic field dependence of the light hole-to-conduction band transition energy. In addition, k .p theory was used to interpret the experimental results, mapping out this specific transition's magnetic field dependence in an AlGaAs/GaAs quantum well. The combination of theory and experiment point to a mixing of valence bands at a field of approximately B0=4.7 T, swapping the dominant character of the absorption transition and, thus, explaining the magnetic field dependence. Lastly, the experimental dependence of the light hole-to-conduction band transition energy on B0 is found to be less steep compared to the calculated trend, indicating that inclusion of additional effects may be necessary to accurately model the spin-split band structure. The additional insight gained by Ga/7169 OPNMR about the light hole states will facilitate future testing of more complex band structure models.

Enhancement of field effect mobility of poly(3-hexylthiophene) thin film transistors by soft-lithographical nanopatterning on the gate-dielectric surface

NASA Astrophysics Data System (ADS)

Park, Jeong-Ho; Kang, Seok-Ju; Park, Jeong-Woo; Lim, Bogyu; Kim, Dong-Yu

2007-11-01

The submicroscaled octadecyltrichlorosilane (OTS) line patterns on gate-dielectric surfaces were introduced into the fabrication of organic field effect transistors (OFETs). These spin-cast regioregular poly(3-hexylthiophene) films on soft-lithographically patterned SiO2 surfaces yielded a higher hole mobility (˜0.072cm2/Vs ) than those of unpatterned (˜0.015cm2/Vs) and untreated (˜5×10-3cm2/Vs) OFETs. The effect of mobility enhancement as a function of the patterned line pitch was investigated in structural and geometric characteristics. The resulting improved mobility is likely attributed to the formation of efficient π-π stacking as a result of guide-assisted, local self-organization-involved molecular interactions between the poly(3-hexylthiophene) polymer and the geometrical OTS patterns.

Hopping and band mobilities of pentacene, rubrene, and 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) from first principle calculations.

PubMed

Kobayashi, Hajime; Kobayashi, Norihito; Hosoi, Shizuka; Koshitani, Naoki; Murakami, Daisuke; Shirasawa, Raku; Kudo, Yoshihiro; Hobara, Daisuke; Tokita, Yuichi; Itabashi, Masao

2013-07-07

Hopping and band mobilities of holes in organic semiconductors at room temperature were estimated from first principle calculations. Relaxation times of charge carriers were evaluated using the acoustic deformation potential model. It is found that van der Waals interactions play an important role in determining accurate relaxation times. The hopping mobilities of pentacene, rubrene, and 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) in bulk single crystalline structures were found to be smaller than 4 cm(2)∕Vs, whereas the band mobilities were estimated between 36 and 58 cm(2)∕Vs, which are close to the maximum reported experimental values. This strongly suggests that band conductivity is dominant in these materials even at room temperature.

Efficient Molecular Organic Light-Emitting Diodes Based on Silole Derivatives

DTIC Science & Technology

2003-01-01

TPD) and tris-(8-hydroxyquinoline) aluminum ( Alq3 ), commonly used in MOLEDs, have hole and electron mobilities that differ by a factor of ~1000 (~10...and subsequent device degradation. In addition to the widely used electron transporter Alq3 , [8] derivatives of nathrolines, [7] oxadiazoles, [9

Electrical transport properties of thermally evaporated phthalocyanine (H 2Pc) thin films

NASA Astrophysics Data System (ADS)

El-Nahass, M. M.; Farid, A. M.; Attia, A. A.; Ali, H. A. M.

2006-08-01

Thin films of H 2Pc of various thicknesses have been deposited onto glass substrates using thermal evaporation technique at room temperature. The dark electrical resistivity measurements were carried out at different temperatures in the range 298-473 K. An estimation of mean free path ( lo) of charge carriers in H 2Pc thin films was attempted. Measurements of thermoelectric power confirm that H 2Pc thin films behave as a p-type semiconductor. The current density-voltage characteristics of Au/H 2Pc/Au at room temperature showed ohmic conduction mechanism at low voltages. At higher voltages the space-charge-limited conduction (SCLC) accompanied by an exponential trap distribution was dominant. The temperature dependence of current density allows the determination of some essential parameters such as the hole mobility ( μh), the total trap concentration ( Nt), the characteristic temperature ( Tt) and the trap density P( E).

Impact of amorphization on the electronic properties of Zn-Ir-O systems.

PubMed

Muñoz Ramo, David; Bristowe, Paul D

2016-09-01

We analyze the geometry and electronic structure of a series of amorphous Zn-Ir-O systems using classical molecular dynamics followed by density functional theory taking into account two different charge states of Ir (+3 and  +4). The structures obtained consist of a matrix of interconnected metal-oxygen polyhedra, with Zn adopting preferentially a coordination of 4 and Ir a mixture of coordinations between 4 and 6 that depend on the charge state of Ir and its concentration. The amorphous phases display reduced band gaps compared to crystalline ZnIr2O4 and exhibit localized states near the band edges, which harm their transparency and hole mobility. Increasing amounts of Ir in the Ir(4+) phases decrease the band gap further while not altering it significantly in the Ir(3+) phases. The results are consistent with recent transmittance and resistivity measurements.

Droplet manipulation by an external electric field for crystalline film growth.

PubMed

Komino, Takeshi; Kuwabara, Hirokazu; Ikeda, Masaaki; Yahiro, Masayuki; Takimiya, Kazuo; Adachi, Chihaya

2013-07-30

Combining droplet manipulation by the application of an electric field with inkjet printing is proposed as a unique technique to control the surface wettability of substrates for solution-processed organic field-effect transistors (FETs). With the use of this technique, uniform thin films of 2,7-dioctyl[1]benzothieno[2,3,-b][1]benzothiopene (C8-BTBT) could be fabricated on the channels of FET substrates without self-assembled monolayer treatment. High-speed camera observation revealed that the crystals formed at the solid/liquid interface. The coverage of the crystals on the channels depended on the ac frequency of the external electric field applied during film formation, leading to a wide variation in the carrier transport of the films. The highest hole mobility of 0.03 cm(2) V(-1) s(-1) was obtained when the coverage was maximized with an ac frequency of 1 kHz.

Stable doping of carbon nanotubes via molecular self assembly

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, B.; Chen, Y.; Podzorov, V., E-mail: podzorov@physics.rutgers.edu

2014-10-14

We report a novel method for stable doping of carbon nanotubes (CNT) based on methods of molecular self assembly. A conformal growth of a self-assembled monolayer of fluoroalkyl trichloro-silane (FTS) at CNT surfaces results in a strong increase of the sheet conductivity of CNT electrodes by 60–300%, depending on the CNT chirality and composition. The charge carrier mobility of undoped partially aligned CNT films was independently estimated in a field-effect transistor geometry (~100 cm²V⁻¹s⁻¹). The hole density induced by the FTS monolayer in CNT sheets is estimated to be ~1.8 ×10¹⁴cm⁻². We also show that FTS doping of CNT anodesmore » greatly improves the performance of organic solar cells. This large and stable doping effect, easily achieved in large-area samples, makes this approach very attractive for applications of CNTs in transparent and flexible electronics.« less

TESTING THE NO-HAIR THEOREM WITH OBSERVATIONS IN THE ELECTROMAGNETIC SPECTRUM. II. BLACK HOLE IMAGES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johannsen, Tim; Psaltis, Dimitrios, E-mail: timj@physics.arizona.ed, E-mail: dpsaltis@email.arizona.ed

2010-07-20

According to the no-hair theorem, all astrophysical black holes are fully described by their masses and spins. This theorem can be tested observationally by measuring (at least) three different multipole moments of the spacetimes of black holes. In this paper, we analyze images of black holes within a framework that allows us to calculate observables in the electromagnetic spectrum as a function of the mass, spin, and, independently, the quadrupole moment of a black hole. We show that a deviation of the quadrupole moment from the expected Kerr value leads to images of black holes that are either prolate ormore » oblate depending on the sign and magnitude of the deviation. In addition, there is a ring-like structure around the black hole shadow with a diameter of {approx}10 black hole masses that is substantially brighter than the image of the underlying accretion flow and that is independent of the astrophysical details of accretion flow models. We show that the shape of this ring depends directly on the mass, spin, and quadrupole moment of the black hole and can be used for an independent measurement of all three parameters. In particular, we demonstrate that this ring is highly circular for a Kerr black hole with a spin a {approx}< 0.9 M, independent of the observer's inclination, but becomes elliptical and asymmetric if the no-hair theorem is violated. Near-future very long baseline interferometric observations of Sgr A* will image this ring and may allow for an observational test of the no-hair theorem.« less

The x-ray time of flight method for investigation of ghosting in amorphous selenium-based flat panel medical x-ray imagers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rau, A.W.; Bakueva, L.; Rowlands, J.A.

2005-10-15

Amorphous selenium (a-Se) based real-time flat-panel imagers (FPIs) are finding their way into the digital radiology department because they offer the practical advantages of digital x-ray imaging combined with an image quality that equals or outperforms that of conventional systems. The temporal imaging characteristics of FPIs can be affected by ghosting (i.e., radiation-induced changes of sensitivity) when the dose to the detector is high (e.g., portal imaging and mammography) or the images are acquired at a high frame rate (e.g., fluoroscopy). In this paper, the x-ray time-of-flight (TOF) method is introduced as a tool for the investigation of ghosting inmore » a-Se photoconductor layers. The method consists of irradiating layers of a-Se with short x-ray pulses. From the current generated in the a-Se layer, ghosting is quantified and the ghosting parameters (charge carrier generation rate and carrier lifetimes and mobilities) are assessed. The x-ray TOF method is novel in that (1) x-ray sensitivity (S) and ghosting parameters can be measured simultaneously (2) the transport of both holes and electrons can be isolated, and (3) the method is applicable to the practical a-Se layer structure with blocking contacts used in FPIs. The x-ray TOF method was applied to an analysis of ghosting in a-Se photoconductor layers under portal imaging conditions, i.e., 1 mm thick a-Se layers, biased at 5 V/{mu}m, were irradiated using a 6 MV LINAC x-ray beam to a total dose (ghosting dose) of 30 Gy. The initial sensitivity (S{sub 0}) of the a-Se layers was 63{+-}2 nC cm{sup -2} cGy{sup -1}. It was found that S decreases to 30% of S{sub 0} after a ghosting dose of 5 Gy and to 21% after 30 Gy at which point no further change in S occurs. At an x-ray intensity of 22 Gy/s (instantaneous dose rate during a LINAC x-ray pulse), the charge carrier generation rate was 1.25{+-}0.1x10{sup 22} ehp m{sup -3} s{sup -1} and, to a first approximation, independent of the ghosting dose. However, both hole and electron transport showed a strong dependence on the ghosting dose: hole transport decreased by 61%, electron transport by up to {approx}80%. Therefore, degradation of both hole and electron transport due to the recombination of mobile charge carriers with trapped carriers (of opposite polarity) were identified as the main cause of ghosting in this study.« less

Self-reported dependence on mobile phones in young adults: A European cross-cultural empirical survey

PubMed Central

Lopez-Fernandez, Olatz; Kuss, Daria J.; Romo, Lucia; Morvan, Yannick; Kern, Laurence; Graziani, Pierluigi; Rousseau, Amélie; Rumpf, Hans-Jürgen; Bischof, Anja; Gässler, Ann-Kathrin; Schimmenti, Adriano; Passanisi, Alessia; Männikkö, Niko; Kääriänen, Maria; Demetrovics, Zsolt; Király, Orsolya; Chóliz, Mariano; Zacarés, Juan José; Serra, Emilia; Griffiths, Mark D.; Pontes, Halley M.; Lelonek-Kuleta, Bernadeta; Chwaszcz, Joanna; Zullino, Daniele; Rochat, Lucien; Achab, Sophia; Billieux, Joël

2017-01-01

Background and aims Despite many positive benefits, mobile phone use can be associated with harmful and detrimental behaviors. The aim of this study was twofold: to examine (a) cross-cultural patterns of perceived dependence on mobile phones in ten European countries, first, grouped in four different regions (North: Finland and UK; South: Spain and Italy; East: Hungary and Poland; West: France, Belgium, Germany, and Switzerland), and second by country, and (b) how socio-demographics, geographic differences, mobile phone usage patterns, and associated activities predicted this perceived dependence. Methods A sample of 2,775 young adults (aged 18–29 years) were recruited in different European Universities who participated in an online survey. Measures included socio-demographic variables, patterns of mobile phone use, and the dependence subscale of a short version of the Problematic Mobile Phone Use Questionnaire (PMPUQ; Billieux, Van der Linden, & Rochat, 2008). Results The young adults from the Northern and Southern regions reported the heaviest use of mobile phones, whereas perceived dependence was less prevalent in the Eastern region. However, the proportion of highly dependent mobile phone users was more elevated in Belgium, UK, and France. Regression analysis identified several risk factors for increased scores on the PMPUQ dependence subscale, namely using mobile phones daily, being female, engaging in social networking, playing video games, shopping and viewing TV shows through the Internet, chatting and messaging, and using mobile phones for downloading-related activities. Discussion and conclusions Self-reported dependence on mobile phone use is influenced by frequency and specific application usage. PMID:28425777

Self-reported dependence on mobile phones in young adults: A European cross-cultural empirical survey.

PubMed

Lopez-Fernandez, Olatz; Kuss, Daria J; Romo, Lucia; Morvan, Yannick; Kern, Laurence; Graziani, Pierluigi; Rousseau, Amélie; Rumpf, Hans-Jürgen; Bischof, Anja; Gässler, Ann-Kathrin; Schimmenti, Adriano; Passanisi, Alessia; Männikkö, Niko; Kääriänen, Maria; Demetrovics, Zsolt; Király, Orsolya; Chóliz, Mariano; Zacarés, Juan José; Serra, Emilia; Griffiths, Mark D; Pontes, Halley M; Lelonek-Kuleta, Bernadeta; Chwaszcz, Joanna; Zullino, Daniele; Rochat, Lucien; Achab, Sophia; Billieux, Joël

2017-06-01

Background and aims Despite many positive benefits, mobile phone use can be associated with harmful and detrimental behaviors. The aim of this study was twofold: to examine (a) cross-cultural patterns of perceived dependence on mobile phones in ten European countries, first, grouped in four different regions (North: Finland and UK; South: Spain and Italy; East: Hungary and Poland; West: France, Belgium, Germany, and Switzerland), and second by country, and (b) how socio-demographics, geographic differences, mobile phone usage patterns, and associated activities predicted this perceived dependence. Methods A sample of 2,775 young adults (aged 18-29 years) were recruited in different European Universities who participated in an online survey. Measures included socio-demographic variables, patterns of mobile phone use, and the dependence subscale of a short version of the Problematic Mobile Phone Use Questionnaire (PMPUQ; Billieux, Van der Linden, & Rochat, 2008). Results The young adults from the Northern and Southern regions reported the heaviest use of mobile phones, whereas perceived dependence was less prevalent in the Eastern region. However, the proportion of highly dependent mobile phone users was more elevated in Belgium, UK, and France. Regression analysis identified several risk factors for increased scores on the PMPUQ dependence subscale, namely using mobile phones daily, being female, engaging in social networking, playing video games, shopping and viewing TV shows through the Internet, chatting and messaging, and using mobile phones for downloading-related activities. Discussion and conclusions Self-reported dependence on mobile phone use is influenced by frequency and specific application usage.

High p-type doping, mobility, and photocarrier lifetime in arsenic-doped CdTe single crystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nagaoka, Akira; Kuciauskas, Darius; McCoy, Jedidiah

Here, Group-V element doping is promising for simultaneously maximizing the hole concentration and minority carrier lifetime in CdTe for thin film solar cells, but there are roadblocks concerning point defects including the possibility of self-compensation by AX metastability. Herein, we report on doping, lifetime, and mobility of CdTe single crystals doped with As between 10 16 and 10 20 cm –3 grown from the Cd solvent by the travelling heater method. Evidence consistent with AX instability as a major contributor to compensation in samples doped below 10 17 cm –3 is presented, while for higher-doped samples, precipitation of a secondmore » phase on planar structural defects is also observed and may explain spatial variation in properties such as lifetime. Rapid cooling after crystal growth increases doping efficiency and mobility for times up to 20–30 days at room temperature with the highest efficiencies observed close to 45% and a hole mobility of 70 cm 2/Vs at room temperature. A doping limit in the low 10 17/cm 3 range is observed for samples quenched at 200–300 °C/h. Bulk minority carrier lifetimes exceeding 20 ns are observed for samples doped near 10 16 cm –3 relaxed in the dark and for unintentionally doped samples, while a lifetime of nearly 5 ns is observed for 10 18 cm –3 As doping. These results help us to establish limits on properties expected for group-V doped CdTe polycrystalline thin films for use in photovoltaics.« less

Charge Mobility Enhancement for Conjugated DPP-Selenophene Polymer by Simply Replacing One Bulky Branching Alkyl Chain with Linear One at Each DPP Unit

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Zhijie; Liu, Zitong; Ning, Lu

Here, we demonstrate a simple, but efficient, approach for improving the semiconducting performances of DPP-based conjugated D-A polymers. This approach involves the replacement of one bulky branching alkyl chain with the linear one at each DPP unit in regular polymer PDPPSe-10 and PDPPSe-12. The UV–vis absorption, Raman spectra, PDS data, and theoretical calculations support that the replacement of bulky branching chains with linear ones can weaken the steric hindrance, and accordingly conjugated backbones become more planar and rigid. GIWAXS data show that the incorporation of linear alkyl chains as in PDPPSe-10 and PDPPSe-12 is beneficial for side-chain interdigitation and interchainmore » dense packing, leading to improvement of interchain packing order and thin film crystallinity by comparing with PDPPSe, which contains branching alkyl chains. On the basis of field-effect transistor (FET) studies, charge mobilities of PDPPSe-10 and PDPPSe-12 are remarkably enhanced. Hole mobilities of PDPPSe-10 and PDPPSe-12 in air are boosted to 8.1 and 9.4 cm 2 V –1 s –1, which are about 6 and 7 times, respectively, than that of PDPPSe (1.35 cm 2 V –1 s –1). Furthermore, both PDPPSe-10 and PDPPSe-12 behave as ambipolar semiconductors under a nitrogen atmosphere with increased hole/electron mobilities up to 6.5/0.48 cm 2 V –1 s –1 and 7.9/0.79 cm 2 V –1 s –1, respectively.« less

Charge Mobility Enhancement for Conjugated DPP-Selenophene Polymer by Simply Replacing One Bulky Branching Alkyl Chain with Linear One at Each DPP Unit

DOE PAGES

Wang, Zhijie; Liu, Zitong; Ning, Lu; ...

2018-04-17

Here, we demonstrate a simple, but efficient, approach for improving the semiconducting performances of DPP-based conjugated D-A polymers. This approach involves the replacement of one bulky branching alkyl chain with the linear one at each DPP unit in regular polymer PDPPSe-10 and PDPPSe-12. The UV–vis absorption, Raman spectra, PDS data, and theoretical calculations support that the replacement of bulky branching chains with linear ones can weaken the steric hindrance, and accordingly conjugated backbones become more planar and rigid. GIWAXS data show that the incorporation of linear alkyl chains as in PDPPSe-10 and PDPPSe-12 is beneficial for side-chain interdigitation and interchainmore » dense packing, leading to improvement of interchain packing order and thin film crystallinity by comparing with PDPPSe, which contains branching alkyl chains. On the basis of field-effect transistor (FET) studies, charge mobilities of PDPPSe-10 and PDPPSe-12 are remarkably enhanced. Hole mobilities of PDPPSe-10 and PDPPSe-12 in air are boosted to 8.1 and 9.4 cm 2 V –1 s –1, which are about 6 and 7 times, respectively, than that of PDPPSe (1.35 cm 2 V –1 s –1). Furthermore, both PDPPSe-10 and PDPPSe-12 behave as ambipolar semiconductors under a nitrogen atmosphere with increased hole/electron mobilities up to 6.5/0.48 cm 2 V –1 s –1 and 7.9/0.79 cm 2 V –1 s –1, respectively.« less

High p-type doping, mobility, and photocarrier lifetime in arsenic-doped CdTe single crystals

DOE PAGES

Nagaoka, Akira; Kuciauskas, Darius; McCoy, Jedidiah; ...

2018-05-07

Here, Group-V element doping is promising for simultaneously maximizing the hole concentration and minority carrier lifetime in CdTe for thin film solar cells, but there are roadblocks concerning point defects including the possibility of self-compensation by AX metastability. Herein, we report on doping, lifetime, and mobility of CdTe single crystals doped with As between 10 16 and 10 20 cm –3 grown from the Cd solvent by the travelling heater method. Evidence consistent with AX instability as a major contributor to compensation in samples doped below 10 17 cm –3 is presented, while for higher-doped samples, precipitation of a secondmore » phase on planar structural defects is also observed and may explain spatial variation in properties such as lifetime. Rapid cooling after crystal growth increases doping efficiency and mobility for times up to 20–30 days at room temperature with the highest efficiencies observed close to 45% and a hole mobility of 70 cm 2/Vs at room temperature. A doping limit in the low 10 17/cm 3 range is observed for samples quenched at 200–300 °C/h. Bulk minority carrier lifetimes exceeding 20 ns are observed for samples doped near 10 16 cm –3 relaxed in the dark and for unintentionally doped samples, while a lifetime of nearly 5 ns is observed for 10 18 cm –3 As doping. These results help us to establish limits on properties expected for group-V doped CdTe polycrystalline thin films for use in photovoltaics.« less

Transport properties of triarylamine based dendrimers studied by space charge limited current transients

NASA Astrophysics Data System (ADS)

Szymanski, Marek Z.; Kulszewicz-Bajer, Irena; Faure-Vincent, Jérôme; Djurado, David

2012-08-01

We have studied hole transport in triarylamine based dendrimer using space-charge-limited current transient technique. A mobility of 8 × 10-6 cm2/(V s) and a characteristic detrapping time of about 100 ms have been obtained. We found that quasi-ohmic contact is formed with gold. The obtained mobility differs from the apparent one given by the analysis of stationary current-voltage characteristics because of a limited contact efficiency. The comparison between transients obtained from fresh and aged samples reveals no change in mobility with aging. The deterioration of electrical properties is exclusively caused by trap formation and accumulation of ionic conducting impurities. Finally, repeated transient measurements have been applied to analyze the dynamics of charge trapping process.

Cumulative effects of electrode and dielectric surface modifications on pentacene-based transistors

NASA Astrophysics Data System (ADS)

Devynck, Mélanie; Tardy, Pascal; Wantz, Guillaume; Nicolas, Yohann; Vellutini, Luc; Labrugère, Christine; Hirsch, Lionel

2012-01-01

Surface modifications of the dielectric and the metal of pentacene-based field effect transistors using self-assembled monolayer (SAM) were studied. First, a low interfacial trap density and pentacene 2D-growth were favored by the nonpolar and low surface energy of octadecyltrichlorosilane-based SAM. This treatment leaded to increased mobility up to 0.4 cm2 V-1 s-1 and no observable hysteresis on transfer curves. Second, reduced hole injection barrier and contact resistance were achieved by fluorinated thiols deposited on gold contacts resulting in an increased mobility up to 0.6 cm2 V-1 s-1. Finally, a high mobility of 2.6 cm2 V-1 s-1 was achieved by cumulative effects of both treatments.

Experimental Demonstration on Air Cavity Mode of Violin Using Holed Sheets of Paper

ERIC Educational Resources Information Center

Matsutani, Akihiro

2018-01-01

The fundamental air cavity mode (A0) of a violin was investigated from the viewpoint of its dependence on the opening area and shape by using holed sheets of paper. The dependences of the frequency response of the A0 cavity mode on the shape, opening area, and orientation of the openings were observed. It was also demonstrated that the change of…

Switching Oxide Traps

NASA Technical Reports Server (NTRS)

Oldham, Timothy R.

2003-01-01

We consider radiation-induced charge trapping in SiO2 dielectric layers, primarily from the point of view of CMOS devices. However, SiO2 insulators are used in many other ways, and the same defects occur in other contexts. The key studies, which determined the nature of the oxide charge traps, were done primarily on gate oxides in CMOS devices, because that was the main radiation problem in CMOS at one time. There are two major reviews of radiation-induced oxide charge trapping already in the literature, which discuss the subject in far greater detail than is possible here. The first of these was by McLean et al. in 1989, and the second, ten years later, was intended as an update, because of additional, new work that had been reported. Basically, the picture that has emerged is that ionizing radiation creates electron-hole pairs in the oxide, and the electrons have much higher mobility than the holes. Therefore, the electrons are swept out of the oxide very rapidly by any field that is present, leaving behind any holes that escape the initial recombination process. These holes then undergo a polaron hopping transport toward the Si/SiO2 interface (under positive bias). Near the interface, some fraction of them fall into deep, relatively stable, long-lived hole traps. The nature and annealing behavior of these hole traps is the main focus of this paper.

Time-of-flight Measurement Of Hole-tunneling Properties And Emission Color Control In Organic Light-emitting Diodes

NASA Astrophysics Data System (ADS)

Kurata, K.; Kashiwabara, K.; Nakajima, K.; Mizoguchi, Y.; Ohtani, N.

2011-12-01

Hole transport properties of organic light-emitting diodes (OLEDs) with a thin hole-blocking layer (HBL) were evaluated by time-of-flight measurement. Electroluminescence (EL) spectra of OLEDs with various HBL thicknesses were also evaluated. The results clearly show that the time-resolved photocurrent response and the emission color strongly depend on HBL thickness. This can be attributed to hole-tunneling through the thin HBL. We successfully fabricated a white OLED by controlling the thickness of HBL.

Old/Past/Ancient/Historic Frontiers in Black Hole Astrophysics

NASA Astrophysics Data System (ADS)

Trimble, Virginia

Basic questions about black holes, some of which are fairly old, include (1) What is a black hole? (2) Do black holes exist? And the answer to this depends a good deal on the answer to (1), (3) Where, when, why, and how have they formed? and (4) What are they good for? Here I attempt some elaboration of the questions and partial answers, noting that general relativity is required to described some of the phenomena, while dear old Isaac Newton is OK for others.

A study of inter-crystallite spaces in some polycrystalline inorganic systems using positron annihilation lifetime spectroscopy

NASA Astrophysics Data System (ADS)

Shantarovich, V. P.; Suzuki, T.; Ito, Y.; Kondo, K.; Gustov, V. W.; Melikhov, I. V.; Berdonosov, S. S.; Ivanov, L. N.; Yu, R. S.

2007-02-01

Positron annihilation lifetime spectroscopy (PALS) was used for calculation of number density and effective sizes of free volume holes (inter-crystallite spaces) in polycrystal CaSO 4, CaCO 3 (vaterit) and Ca 10(PO 4) 6(OH) 2 (apatite). The effect of substitution of two-valence Ca(II) for three-valence Eu(III) on annihilation characteristics of apatite, studied together with the data on thermo-stimulated luminescence (TSL) and low-temperature sorption of gas (N 2), helped to elucidate mechanism of positronium atom (Ps) localization in the free volume holes and perform corresponding calculations. It came out that PALS is more sensitive to inter-crystallite sites (10 16 cm -3) in polycrystallites than to the free volume holes in polymer glasses (10 19 cm -3). This is due to higher mobility of the precursor of localized Ps in crystallites.

Identification and design principles of low hole effective mass p-type transparent conducting oxides

PubMed Central

Hautier, Geoffroy; Miglio, Anna; Ceder, Gerbrand; Rignanese, Gian-Marco; Gonze, Xavier

2013-01-01

The development of high-performance transparent conducting oxides is critical to many technologies from transparent electronics to solar cells. Whereas n-type transparent conducting oxides are present in many devices, their p-type counterparts are not largely commercialized, as they exhibit much lower carrier mobilities due to the large hole effective masses of most oxides. Here we conduct a high-throughput computational search on thousands of binary and ternary oxides and identify several highly promising compounds displaying exceptionally low hole effective masses (up to an order of magnitude lower than state-of-the-art p-type transparent conducting oxides), as well as wide band gaps. In addition to the discovery of specific compounds, the chemical rationalization of our findings opens new directions, beyond current Cu-based chemistries, for the design and development of future p-type transparent conducting oxides. PMID:23939205

Novel Solid-State Solar Cell Based on Hole-Conducting MOF-Sensitizer Demonstrating Power Conversion Efficiency of 2.1.

PubMed

Ahn, Do Young; Lee, Deok Yeon; Shin, Chan Yong; Bui, Hoa Thi; Shrestha, Nabeen K; Giebeler, Lars; Noh, Yong-Young; Han, Sung-Hwan

2017-04-19

This work reports on designing of first successful MOF-sensitizer based solid-state photovoltaic device, perticularly with a meaningful output power conversion efficiency. In this study, an intrinsically conductive cobalt-based MOFs (Co-DAPV) formed by the coordination between Co (II) ions and a redox active di(3-diaminopropyl)-viologen (i.e., DAPV) ligand is investigated as sensitizer. Hall-effect measurement shows p-type conductivity of the Co-DAPV film with hole mobility of 0.017 cm 2 V -1 s -1 , suggesting its potential application as hole transporting sensitizer. Further, the energy levels of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of Co-DAPV are well-matched to be suitably employed for sensitizing TiO 2 . Thus, by layer-by-layer deposition of hole conducting MOF-sensitizer onto mesoporous TiO 2 film, a power conversion efficiency of as high as 2.1% is achieved, which exceeds the highest efficiency values of MOF-sensitized liquid-junction solar cells reported so far.

Proactive Alleviation Procedure to Handle Black Hole Attack and Its Version

PubMed Central

Babu, M. Rajesh; Dian, S. Moses; Chelladurai, Siva; Palaniappan, Mathiyalagan

2015-01-01

The world is moving towards a new realm of computing such as Internet of Things. The Internet of Things, however, envisions connecting almost all objects within the world to the Internet by recognizing them as smart objects. In doing so, the existing networks which include wired, wireless, and ad hoc networks should be utilized. Moreover, apart from other networks, the ad hoc network is full of security challenges. For instance, the MANET (mobile ad hoc network) is susceptible to various attacks in which the black hole attacks and its versions do serious damage to the entire MANET infrastructure. The severity of this attack increases, when the compromised MANET nodes work in cooperation with each other to make a cooperative black hole attack. Therefore this paper proposes an alleviation procedure which consists of timely mandate procedure, hole detection algorithm, and sensitive guard procedure to detect the maliciously behaving nodes. It has been observed that the proposed procedure is cost-effective and ensures QoS guarantee by assuring resource availability thus making the MANET appropriate for Internet of Things. PMID:26495430

Proactive Alleviation Procedure to Handle Black Hole Attack and Its Version.

PubMed

Babu, M Rajesh; Dian, S Moses; Chelladurai, Siva; Palaniappan, Mathiyalagan

2015-01-01

The world is moving towards a new realm of computing such as Internet of Things. The Internet of Things, however, envisions connecting almost all objects within the world to the Internet by recognizing them as smart objects. In doing so, the existing networks which include wired, wireless, and ad hoc networks should be utilized. Moreover, apart from other networks, the ad hoc network is full of security challenges. For instance, the MANET (mobile ad hoc network) is susceptible to various attacks in which the black hole attacks and its versions do serious damage to the entire MANET infrastructure. The severity of this attack increases, when the compromised MANET nodes work in cooperation with each other to make a cooperative black hole attack. Therefore this paper proposes an alleviation procedure which consists of timely mandate procedure, hole detection algorithm, and sensitive guard procedure to detect the maliciously behaving nodes. It has been observed that the proposed procedure is cost-effective and ensures QoS guarantee by assuring resource availability thus making the MANET appropriate for Internet of Things.

Characterization and Effects of Fiber Pull-Outs in Hole Quality of Carbon Fiber Reinforced Plastics Composite

PubMed Central

Alizadeh Ashrafi, Sina; Miller, Peter W.; Wandro, Kevin M.; Kim, Dave

2016-01-01

Hole quality plays a crucial role in the production of close-tolerance holes utilized in aircraft assembly. Through drilling experiments of carbon fiber-reinforced plastic composites (CFRP), this study investigates the impact of varying drilling feed and speed conditions on fiber pull-out geometries and resulting hole quality parameters. For this study, hole quality parameters include hole size variance, hole roundness, and surface roughness. Fiber pull-out geometries are quantified by using scanning electron microscope (SEM) images of the mechanically-sectioned CFRP-machined holes, to measure pull-out length and depth. Fiber pull-out geometries and the hole quality parameter results are dependent on the drilling feed and spindle speed condition, which determines the forces and undeformed chip thickness during the process. Fiber pull-out geometries influence surface roughness parameters from a surface profilometer, while their effect on other hole quality parameters obtained from a coordinate measuring machine is minimal. PMID:28773950

Bifurcation from stable holes to replicating holes in vibrated dense suspensions.

PubMed

Ebata, H; Sano, M

2013-11-01

In vertically vibrated starch suspensions, we observe bifurcations from stable holes to replicating holes. Above a certain acceleration, finite-amplitude deformations of the vibrated surface continue to grow until void penetrates fluid layers, and a hole forms. We studied experimentally and theoretically the parameter dependence of the holes and their stabilities. In suspensions of small dispersed particles, the circular shapes of the holes are stable. However, we find that larger particles or lower surface tension of water destabilize the circular shapes; this indicates the importance of capillary forces acting on the dispersed particles. Around the critical acceleration for bifurcation, holes show intermittent large deformations as a precursor to hole replication. We applied a phenomenological model for deformable domains, which is used in reaction-diffusion systems. The model can explain the basic dynamics of the holes, such as intermittent behavior, probability distribution functions of deformation, and time intervals of replication. Results from the phenomenological model match the linear growth rate below criticality that was estimated from experimental data.

Evidence of Electron-Hole Imbalance in WTe2 from High-Resolution Angle-Resolved Photoemission Spectroscopy

NASA Astrophysics Data System (ADS)

Wang, Chen-Lu; Zhang, Yan; Huang, Jian-Wei; Liu, Guo-Dong; Liang, Ai-Ji; Zhang, Yu-Xiao; Shen, Bing; Liu, Jing; Hu, Cheng; Ding, Ying; Liu, De-Fa; Hu, Yong; He, Shao-Long; Zhao, Lin; Yu, Li; Hu, Jin; Wei, Jiang; Mao, Zhi-Qiang; Shi, You-Guo; Jia, Xiao-Wen; Zhang, Feng-Feng; Zhang, Shen-Jin; Yang, Feng; Wang, Zhi-Min; Peng, Qin-Jun; Xu, Zu-Yan; Chen, Chuang-Tian; Zhou, Xing-Jiang

2017-08-01

WTe2 has attracted a great deal of attention because it exhibits extremely large and nonsaturating magnetoresistance. The underlying origin of such a giant magnetoresistance is still under debate. Utilizing laser-based angle-resolved photoemission spectroscopy with high energy and momentum resolutions, we reveal the complete electronic structure of WTe2. This makes it possible to determine accurately the electron and hole concentrations and their temperature dependence. We find that, with increasing the temperature, the overall electron concentration increases while the total hole concentration decreases. It indicates that the electron-hole compensation, if it exists, can only occur in a narrow temperature range, and in most of the temperature range there is an electron-hole imbalance. Our results are not consistent with the perfect electron-hole compensation picture that is commonly considered to be the cause of the unusual magnetoresistance in WTe2. We identified a flat band near the Brillouin zone center that is close to the Fermi level and exhibits a pronounced temperature dependence. Such a flat band can play an important role in dictating the transport properties of WTe2. Our results provide new insight on understanding the origin of the unusual magnetoresistance in WTe2.

Modulated Hawking radiation and a nonviolent channel for information release

DOE PAGES

Giddings, Steven B.

2014-09-16

The unitarization of black hole evaporation requires that quantum information escapes a black hole; an important question is to identify the mechanism or channel by which it does so. Accurate counting of black hole states via the Bekenstein–Hawking entropy would indicate this information should be encoded in radiation with average energy flux matching Hawking’s. Information can be encoded with no change in net flux via fine-grained modulation of the Hawking radiation. In an approximate effective field theory description, couplings to the stress tensor of the black hole atmosphere that depend on the internal state of the black hole are amore » promising alternative for inducing such modulation. These can be picturesquely thought of as due to state-dependent metric fluctuations in the vicinity of the horizon. Such couplings offer the prospect of emitting information without extra energy flux, and can be shown to do so at linear order in the couplings, with motivation given for possible extension of this result to higher orders. The potential advantages of such couplings to the stress tensor thus extend beyond their universality, which is helpful in addressing constraints from black hole mining.« less

Stabilization of primary mobile radiation defects in MgF2 crystals

NASA Astrophysics Data System (ADS)

Lisitsyn, V. M.; Lisitsyna, L. A.; Popov, A. I.; Kotomin, E. A.; Abuova, F. U.; Akilbekov, A.; Maier, J.

2016-05-01

Non-radiative decay of the electronic excitations (excitons) into point defects (F-H pairs of Frenkel defects) is main radiation damage mechanism in many ionic (halide) solids. Typical time scale of the relaxation of the electronic excitation into a primary, short-lived defect pair is about 1-50 ps with the quantum yield up to 0.2-0.8. However, only a small fraction of these primary defects are spatially separated and survive after transformation into stable, long-lived defects. The survival probability (or stable defect accumulation efficiency) can differ by orders of magnitude, dependent on the material type; e.g. ∼10% in alkali halides with f.c.c. or b.c.c. structure, 0.1% in rutile MgF2 and <0.001% in fluorides MeF2 (Me: Ca, Sr, Ba). The key factor determining accumulation of stable radiation defects is stabilization of primary defects, first of all, highly mobile hole H centers, through their transformation into more complex immobile defects. In this talk, we present the results of theoretical calculations of the migration energies of the F and H centers in poorely studied MgF2 crystals with a focus on the H center stabilization in the form of the interstitial F2 molecules which is supported by presented experimental data.

Impact of carrier doping on electrical properties of laser-induced liquid-phase-crystallized silicon thin films for solar cell application

NASA Astrophysics Data System (ADS)

Umishio, Hiroshi; Matsui, Takuya; Sai, Hitoshi; Sakurai, Takeaki; Matsubara, Koji

2018-02-01

Large-grain-size (>1 mm) liquid-phase-crystallized silicon (LPC-Si) films with a wide range of carrier doping levels (1016-1018 cm-3 either of the n- or p-type) were prepared by irradiating amorphous silicon with a line-shaped 804 nm laser, and characterized for solar cell applications. The LPC-Si films show high electron and hole mobilities with maximum values of ˜800 and ˜200 cm2 V-1 s-1, respectively, at a doping level of ˜(2-4) × 1016 cm-3, while their carrier lifetime monotonically increases with decreasing carrier doping level. A grain-boundary charge-trapping model provides good fits to the measured mobility-carrier density relations, indicating that the potential barrier at the grain boundaries limits the carrier transport in the lowly doped films. The open-circuit voltage and short-circuit current density of test LPC-Si solar cells depend strongly on the doping level, peaking at (2-5) × 1016 cm-3. These results indicate that the solar cell performance is governed by the minority carrier diffusion length for the highly doped films, while it is limited by majority carrier transport as well as by device design for the lowly doped films.

Field dependence of interface-trap buildup in polysilicon and metal gate MOS devices

NASA Astrophysics Data System (ADS)

Shaneyfelt, M. R.; Schwank, J. R.; Fleetwood, D. M.; Winokur, P. S.; Hughes, K. L.

1990-12-01

The electric field dependence of radiation-induced oxide- and interface-trap charge (Delta Vot and Delta Vit) generation for polysilicon- and metal-gate MOS transistors is investigated at electric fields (Eox) from -4.2 MV/cm to +4.7 MV/cm. If electron-hole recombination effects are taken into account, the absolute value of Delta Vot and the saturated value of Delta Vit for both polysilicon- and metal-gate transistors are shown to follow an approximate E exp -1/2 field dependence for Eox = 0.4 MV/cm or greater. An E exp -1/2 dependence for the saturated value of Delta Vit was also observed for negative-bias irradiation followed by a constant positive-bias anneal. The E exp -1/2 field dependence observed suggests that the total number of interface traps created in these devices may be determined by hole trapping near the Si/SiO2 interface for positive-bias irradiation or near the gate/SiO2 interface for negative bias irradiation, though H+ drift remains the likely rate-limiting step in the process. Based on these results, a hole-trapping/hydrogen transport model-involving hole trapping and subsequent near-interfacial H+ release, transport, and reaction at the interface-is proposed as a possible explanation of Delta Vit buildup in these polysilicon- and metal-gate transistors.

``Stable'' Quasi-periodic Oscillations and Black Hole Properties from Diskoseismology

NASA Astrophysics Data System (ADS)

Wagoner, Robert V.; Silbergleit, Alexander S.; Ortega-Rodríguez, Manuel

2001-09-01

We compare our calculations of the frequencies of the fundamental g-, c-, and p-modes of relativistic thin accretion disks with recent observations of high-frequency quasi-periodic oscillations (QPOs) in X-ray binaries with black hole candidates. These classes of modes encompass all adiabatic perturbations of such disks. The frequencies of these modes depend mainly on the mass and angular momentum of the black hole; their weak dependence on disk luminosity is also explicitly indicated. Identifying the recently discovered, relatively stable QPO pairs with the fundamental g- and c-modes provides a determination of the mass and angular momentum of the black hole. For GRO J1655-40, M=5.9+/-1.0 Msolar and J=(0.917+/-0.024)GM2/c, in agreement with spectroscopic mass determinations. For GRS 1915+105, M=42.4+/-7.0 Msolar and J=(0.926+/-0.020)GM2/c or (less favored) M=18.2+/-3.1 Msolar and J=(0.701+/-0.043)GM2/c. We briefly address the issues of the amplitude, frequency width, and energy dependence of these QPOs.

Substitutional Electron and Hole Doping of WSe2 : Synthesis, Electrical Characterization, and Observation of Band-to-Band Tunneling

NASA Astrophysics Data System (ADS)

Mukherjee, R.; Chuang, H. J.; Koehler, M. R.; Combs, N.; Patchen, A.; Zhou, Z. X.; Mandrus, D.

2017-03-01

Transition-metal dichalcogenides (TMDs) such as MoS2 , MoSe2 , and WSe2 have emerged as promising two-dimensional semiconductors. Many anticipated applications of these materials require both p -type and n -type TMDs with long-term doping stability. Here, we report on the synthesis of substitutionally doped WSe2 crystals using Nb and Re as p - and n -type dopants, respectively. Hall coefficient and gate-dependent transport measurements reveal drastically different doping properties between nominally 0.5% Nb- and 0.5% Re-doped WSe2 . While 0.5% Nb-doped WSe2 (WSe2∶Nb ) is degenerately hole doped with a nearly temperature-independent carrier density of approximately 1019 cm-3 , electrons in 0.5% Re-doped WSe2 (WSe2 ∶Re ) are largely trapped in localized states below the mobility edge and exhibit thermally activated behavior. Charge transport in both WSe2∶Nb and WSe2 ∶Re is found to be limited by Coulomb scattering from ionized impurities. Furthermore, we fabricate vertical van der Waals-junction diodes consisting of multilayers of WSe2∶Nb and WSe2 ∶Re . Finally, we demonstrate reverse rectifying behavior as a direct proof of band-to-band tunneling in our WSe2∶Nb /WSe2∶Re diodes.

GOOD HEALTH AND THE BRIDGING OF STRUCTURAL HOLES

PubMed Central

Cornwell, Benjamin

2009-01-01

Bridges that span structural holes are often explained in terms of the entrepreneurial personalities or rational motivations of brokers, or structural processes that lead to the intersection of social foci. I argue that the existence and use of bridges in interpersonal networks also depends on individuals’ health. Poor health may make it more difficult to withstand the pressures and to execute some of the common tasks associated with bridging (e.g., brokerage). I examine this possibility using egocentric network data on over 2,500 older adults drawn from the recent National Social Life, Health, and Aging Project (NSHAP). Multivariate regression analyses show that both cognitive and functional health are significantly positively associated with bridging, net of sociodemographic and life-course controls. The relationship between functional (kinesthetic) health and bridging appears to be partially mediated by network composition, as older adults who have poorer functional health also tend to have networks that are richer in strong ties. Several potential mediation mechanisms are discussed. Cognitive function remains significantly associated with bridging net of network composition, suggesting that the inherent challenges of maintaining bridging positions may be more difficult to cope with for those who have cognitive impairments than for those who have functional impairments such as limited mobility. An alternative explanation is that cognitively impaired individuals have more difficulty recognizing (and thus strategically using) bridges in their networks. Theoretical implications and possibilities for future research are discussed. PMID:20046998

Enhanced Charge Carrier Transport and Device Performance Through Dual-Cesium Doping in Mixed-Cation Perovskite Solar Cells with Near Unity Free Carrier Ratios.

PubMed

Ye, Tao; Petrović, Miloš; Peng, Shengjie; Yoong, Jeremy Lee Kong; Vijila, Chellappan; Ramakrishna, Seeram

2017-01-25

PbI 2 -enriched mixed perovskite film [FA 0.81 MA 0.15 Pb(I 0.836 Br 0.15 ) 3 ] has been widely studied due to its great potential in perovskite solar cell (PSC) applications. Herein, a FA 0.81 MA 0.15 Pb(I 0.836 Br 0.15 ) 3 film has been fabricated with the temperature-dependent optical absorption spectra utilized to determine its exciton binding energy. A ∼13 meV exciton binding energy is estimated, and a near-unity fraction of free carriers out of the total photoexcitons has been obtained in the solar cell operating regime at equilibrium state. PSCs are fabricated with this mixed perovskite film, but a significant electron transport barrier at the TiO 2 -perovskite interface limited their performance. Cs 2 CO 3 and CsI are then utilized as functional enhancers with which to substantially balance the electron and hole transport and increase the carriers (both electrons and holes) mobilities in PSCs, resulting in much-improved solar-cell performance. The modified PSCs exhibit reproducible power conversion efficiency (PCE) values with little hysteresis effect in the J-V curves, achieving PCEs up to 19.5% for the Cs 2 CO 3 -modified PSC and 20.6% when subsequently further doped with CsI.

pn-Heterojunction effects of perylene tetracarboxylic diimide derivatives on pentacene field-effect transistor.

PubMed

Yu, Seong Hun; Kang, Boseok; An, Gukil; Kim, BongSoo; Lee, Moo Hyung; Kang, Moon Sung; Kim, Hyunjung; Lee, Jung Heon; Lee, Shichoon; Cho, Kilwon; Lee, Jun Young; Cho, Jeong Ho

2015-01-28

We investigated the heterojunction effects of perylene tetracarboxylic diimide (PTCDI) derivatives on the pentacene-based field-effect transistors (FETs). Three PTCDI derivatives with different substituents were deposited onto pentacene layers and served as charge transfer dopants. The deposited PTCDI layer, which had a nominal thickness of a few layers, formed discontinuous patches on the pentacene layers and dramatically enhanced the hole mobility in the pentacene FET. Among the three PTCDI molecules tested, the octyl-substituted PTCDI, PTCDI-C8, provided the most efficient hole-doping characteristics (p-type) relative to the fluorophenyl-substituted PTCDIs, 4-FPEPTC and 2,4-FPEPTC. The organic heterojunction and doping characteristics were systematically investigated using atomic force microscopy, 2D grazing incidence X-ray diffraction studies, and ultraviolet photoelectron spectroscopy. PTCDI-C8, bearing octyl substituents, grew laterally on the pentacene layer (2D growth), whereas 2,4-FPEPTC, with fluorophenyl substituents, underwent 3D growth. The different growth modes resulted in different contact areas and relative orientations between the pentacene and PTCDI molecules, which significantly affected the doping efficiency of the deposited adlayer. The differences between the growth modes and the thin-film microstructures in the different PTCDI patches were attributed to a mismatch between the surface energies of the patches and the underlying pentacene layer. The film-morphology-dependent doping effects observed here offer practical guidelines for achieving more effective charge transfer doping in thin-film transistors.

Anisotropic carrier mobility in buckled two-dimensional GaN.

PubMed

Tong, Lijia; He, Junjie; Yang, Min; Chen, Zheng; Zhang, Jing; Lu, Yanli; Zhao, Ziyuan

2017-08-30

Developing nanoelectronic engineering requires two-dimensional (2d) materials with both usable carrier mobility and proper large band-gap. In this study, we present a detailed theoretical investigation of the intrinsic carrier mobilities of buckled 2d GaN. This buckled 2d GaN is accessed by hydrofluorination (FGaNH) and hydrogenation (HGaNH). We predict that the anisotropic carrier mobilities of buckled 2d GaN can exceed those of 2d MoS 2 and can be altered by an alterable surface chemical bond (convert from a Ga-F-Ga bond of FGaNH to a Ga-H bond of HGaNH). Moreover, converting FGaNH to HGaNH can significantly suppress hole mobility (even close to zero) and result in a transition from a p-type-like semiconductor (FGaNH) to an n-type-like semiconductor (HGaNH). These features make buckled 2d GaN a promising candidate for application in future conductivity-adjustable electronics.

Theoretical predictions on the electronic structure and charge carrier mobility in 2D Phosphorus sheets

PubMed Central

Xiao, Jin; Long, Mengqiu; Zhang, Xiaojiao; Ouyang, Jun; Xu, Hui; Gao, Yongli

2015-01-01

We have investigated the electronic structure and carrier mobility of four types of phosphorous monolayer sheet (α-P, β-P,γ-P and δ-P) using density functional theory combined with Boltzmann transport method and relaxation time approximation. It is shown that α-P, β-P and γ-P are indirect gap semiconductors, while δ-P is a direct one. All four sheets have ultrahigh carrier mobility and show anisotropy in-plane. The highest mobility value is ~3 × 105 cm2V−1s−1, which is comparable to that of graphene. Because of the huge difference between the hole and electron mobilities, α-P, γ-P and δ-P sheets can be considered as n-type semiconductors, and β-P sheet can be considered as a p-type semiconductor. Our results suggest that phosphorous monolayer sheets can be considered as a new type of two dimensional materials for applications in optoelectronics and nanoelectronic devices. PMID:26035176

Linear perturbations of black holes: stability, quasi-normal modes and tails

NASA Astrophysics Data System (ADS)

Zhidenko, Alexander

2009-03-01

Black holes have their proper oscillations, which are called the quasi-normal modes. The proper oscillations of astrophysical black holes can be observed in the nearest future with the help of gravitational wave detectors. Quasi-normal modes are also very important in the context of testing of the stability of black objects, the anti-de Sitter/Conformal Field Theory (AdS/CFT) correspondence and in higher dimensional theories, such as the brane-world scenarios and string theory. This dissertation reviews a number of works, which provide a thorough study of the quasi-normal spectrum of a wide class of black holes in four and higher dimensions for fields of various spin and gravitational perturbations. We have studied numerically the dependance of the quasi-normal modes on a number of factors, such as the presence of the cosmological constant, the Gauss-Bonnet parameter or the aether in the space-time, the dependance of the spectrum on parameters of the black hole and fields under consideration. By the analysis of the quasi-normal spectrum, we have studied the stability of higher dimensional Reissner-Nordstrom-de Sitter black holes, Kaluza-Klein black holes with squashed horizons, Gauss-Bonnet black holes and black strings. Special attention is paid to the evolution of massive fields in the background of various black holes. We have considered their quasi-normal ringing and the late-time tails. In addition, we present two new numerical techniques: a generalisation of the Nollert improvement of the Frobenius method for higher dimensional problems and a qualitatively new method, which allows to calculate quasi-normal frequencies for black holes, which metrics are not known analytically.

Dithiopheneindenofluorene (TIF) Semiconducting Polymers with Very High Mobility in Field-Effect Transistors.

PubMed

Chen, Hu; Hurhangee, Michael; Nikolka, Mark; Zhang, Weimin; Kirkus, Mindaugas; Neophytou, Marios; Cryer, Samuel J; Harkin, David; Hayoz, Pascal; Abdi-Jalebi, Mojtaba; McNeill, Christopher R; Sirringhaus, Henning; McCulloch, Iain

2017-09-01

The charge-carrier mobility of organic semiconducting polymers is known to be enhanced when the energetic disorder of the polymer is minimized. Fused, planar aromatic ring structures contribute to reducing the polymer conformational disorder, as demonstrated by polymers containing the indacenodithiophene (IDT) repeat unit, which have both a low Urbach energy and a high mobility in thin-film-transistor (TFT) devices. Expanding on this design motif, copolymers containing the dithiopheneindenofluorene repeat unit are synthesized, which extends the fused aromatic structure with two additional phenyl rings, further rigidifying the polymer backbone. A range of copolymers are prepared and their electrical properties and thin-film morphology evaluated, with the co-benzothiadiazole polymer having a twofold increase in hole mobility when compared to the IDT analog, reaching values of almost 3 cm 2 V -1 s -1 in bottom-gate top-contact organic field-effect transistors. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Evaluation of Anisotropic Biaxial Stress Induced Around Trench Gate of Si Power Transistor Using Water-Immersion Raman Spectroscopy

NASA Astrophysics Data System (ADS)

Suzuki, Takahiro; Yokogawa, Ryo; Oasa, Kohei; Nishiwaki, Tatsuya; Hamamoto, Takeshi; Ogura, Atsushi

2018-05-01

The trench gate structure is one of the promising techniques to reduce on-state resistance (R on) for silicon power devices, such as insulated gate bipolar transistors and power metal-oxide-semiconductor field-effect transistors. In addition, it has been reported that stress is induced around the trench gate area, modifying the carrier mobilities. We evaluated the one-dimensional distribution and anisotropic biaxial stress by quasi-line excitation and water-immersion Raman spectroscopy, respectively. The results clearly confirmed anisotropic biaxial stress in state-of-the-art silicon power devices. It is theoretically possible to estimate carrier mobility using piezoresistance coefficients and anisotropic biaxial stress. The electron mobility was increased while the hole mobility was decreased or remained almost unchanged in the silicon (Si) power device. The stress significantly modifies the R on of silicon power transistors. Therefore, their performance can be improved using the stress around the trench gate.

Defect chemistry and characterization of Hg(1-x)Cd(x)Te

NASA Technical Reports Server (NTRS)

Vydyanath, H. R.

1981-01-01

Undoped mercury cadmium telluride crystals were subjected to high temperature equilibration at temperatures ranging from 400 C to 655 C in various Hg atmospheres. Hall effect and mobility measurements were carried out on the crystals quenched to room temperature subsequent to the high temperature equilibration. The variation of the hole concentration in the cooled crystals at 77 K as a function of the partial pressure of Hg at the equlibration temperatures, together with a comparison of the hole mobility in the undoped samples with that in the copper and phosphorous doped samples yielded a defect model for the undoped crystals, according to which, the undoped crystals are essentially intrinsic at the equilibration temperatures and the native acceptor defects are doubly ionized. Native donor defects appear to be negligible in concentration, implying that the p to n conversion in these alloys is mainly due to residual foreign donor impurities. The thermodynamic constants for the intrinsic excitation process as well as for the incorporation of the doubly ionized native acceptor defects in the undoped crystals were obtained.

Hall-effect measurements of metalorganic vapor-phase epitaxy-grown p-type homoepitaxial GaN layers with various Mg concentrations

NASA Astrophysics Data System (ADS)

Horita, Masahiro; Takashima, Shinya; Tanaka, Ryo; Matsuyama, Hideaki; Ueno, Katsunori; Edo, Masaharu; Suda, Jun

2016-05-01

Mg-doped p-type gallium nitride (GaN) layers with doping concentrations in the range from 6.5 × 1016 cm-3 (lightly doped) to 3.8 × 1019 cm-3 (heavily doped) were investigated by Hall-effect measurement for the analysis of hole concentration and mobility. p-GaN was homoepitaxially grown on a GaN free-standing substrate by metalorganic vapor-phase epitaxy. The threading dislocation density of the p-GaN was 4 × 106 cm-2 measured by cathodoluminescence mapping. Hall-effect measurements of p-GaN were carried out at a temperature in the range from 160 to 450 K. A low compensation ratio of less than 1% was revealed. We also obtained the depth of the Mg acceptor level of 235 meV considering the lowering effect by the Coulomb potential of ionized acceptors. The hole mobilities of 33 cm2 V-1 s-1 at 300 K and 72 cm2 V-1 s-1 at 200 K were observed in lightly doped p-GaN.

High hole mobility p-type GaN with low residual hydrogen concentration prepared by pulsed sputtering

NASA Astrophysics Data System (ADS)

Arakawa, Yasuaki; Ueno, Kohei; Kobayashi, Atsushi; Ohta, Jitsuo; Fujioka, Hiroshi

2016-08-01

We have grown Mg-doped GaN films with low residual hydrogen concentration using a low-temperature pulsed sputtering deposition (PSD) process. The growth system is inherently hydrogen-free, allowing us to obtain high-purity Mg-doped GaN films with residual hydrogen concentrations below 5 × 1016 cm-3, which is the detection limit of secondary ion mass spectroscopy. In the Mg profile, no memory effect or serious dopant diffusion was detected. The as-deposited Mg-doped GaN films showed clear p-type conductivity at room temperature (RT) without thermal activation. The GaN film doped with a low concentration of Mg (7.9 × 1017 cm-3) deposited by PSD showed hole mobilities of 34 and 62 cm2 V-1 s-1 at RT and 175 K, respectively, which are as high as those of films grown by a state-of-the-art metal-organic chemical vapor deposition apparatus. These results indicate that PSD is a powerful tool for the fabrication of GaN-based vertical power devices.

Vacuum-and-solvent-free fabrication of organic semiconductor layers for field-effect transistors

PubMed Central

Matsushima, Toshinori; Sandanayaka, Atula S. D.; Esaki, Yu; Adachi, Chihaya

2015-01-01

We demonstrate that cold and hot isostatic pressing (CIP and HIP) is a novel, alternative method for organic semiconductor layer fabrication, where organic powder is compressed into a layer shape directly on a substrate with 200 MPa pressure. Spatial gaps between powder particles and the other particles, substrates, or electrodes are crushed after CIP and HIP, making it possible to operate organic field-effect transistors (OFETs) containing the compressed powder as the semiconductor. The CIP-compressed powder of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) had a hole mobility of (1.6 ± 0.4) × 10–2 cm2/Vs. HIP of C8-BTBT powder increased the hole mobility to an amorphous silicon-like value (0.22 ± 0.07 cm2/Vs) because of the growth of the C8-BTBT crystallites and the improved continuity between the powder particles. The vacuum and solution processes are not involved in our CIP and HIP techniques, offering a possibility of manufacturing OFETs at low cost. PMID:26416434

Achievement of normally-off AlGaN/GaN high-electron mobility transistor with p-NiOx capping layer by sputtering and post-annealing

NASA Astrophysics Data System (ADS)

Huang, Shyh-Jer; Chou, Cheng-Wei; Su, Yan-Kuin; Lin, Jyun-Hao; Yu, Hsin-Chieh; Chen, De-Long; Ruan, Jian-Long

2017-04-01

In this paper, we present a technique to fabricate normally off GaN-based high-electron mobility transistor (HEMT) by sputtering and post-annealing p-NiOx capping layer. The p-NiOx layer is produced by sputtering at room temperature and post-annealing at 500 °C for 30 min in pure O2 environment to achieve high hole concentration. The Vth shifts from -3 V in the conventional transistor to 0.33 V, and on/off current ratio became 107. The forward and reverse gate breakdown increase from 3.5 V and -78 V to 10 V and -198 V, respectively. The reverse gate leakage current is 10-9 A/mm, and the off-state drain-leakage current is 10-8 A/mm. The Vth hysteresis is extremely small at about 33 mV. We also investigate the mechanism that increases hole concentration of p-NiOx after annealing in oxygen environment resulted from the change of Ni2+ to Ni3+ and the surge of (111)-orientation.

Vacuum-and-solvent-free fabrication of organic semiconductor layers for field-effect transistors.

PubMed

Matsushima, Toshinori; Sandanayaka, Atula S D; Esaki, Yu; Adachi, Chihaya

2015-09-29

We demonstrate that cold and hot isostatic pressing (CIP and HIP) is a novel, alternative method for organic semiconductor layer fabrication, where organic powder is compressed into a layer shape directly on a substrate with 200 MPa pressure. Spatial gaps between powder particles and the other particles, substrates, or electrodes are crushed after CIP and HIP, making it possible to operate organic field-effect transistors (OFETs) containing the compressed powder as the semiconductor. The CIP-compressed powder of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) had a hole mobility of (1.6 ± 0.4) × 10(-2) cm(2)/Vs. HIP of C8-BTBT powder increased the hole mobility to an amorphous silicon-like value (0.22 ± 0.07 cm(2)/Vs) because of the growth of the C8-BTBT crystallites and the improved continuity between the powder particles. The vacuum and solution processes are not involved in our CIP and HIP techniques, offering a possibility of manufacturing OFETs at low cost.

Vacuum-and-solvent-free fabrication of organic semiconductor layers for field-effect transistors

NASA Astrophysics Data System (ADS)

Matsushima, Toshinori; Sandanayaka, Atula S. D.; Esaki, Yu; Adachi, Chihaya

2015-09-01

We demonstrate that cold and hot isostatic pressing (CIP and HIP) is a novel, alternative method for organic semiconductor layer fabrication, where organic powder is compressed into a layer shape directly on a substrate with 200 MPa pressure. Spatial gaps between powder particles and the other particles, substrates, or electrodes are crushed after CIP and HIP, making it possible to operate organic field-effect transistors (OFETs) containing the compressed powder as the semiconductor. The CIP-compressed powder of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) had a hole mobility of (1.6 ± 0.4) × 10-2 cm2/Vs. HIP of C8-BTBT powder increased the hole mobility to an amorphous silicon-like value (0.22 ± 0.07 cm2/Vs) because of the growth of the C8-BTBT crystallites and the improved continuity between the powder particles. The vacuum and solution processes are not involved in our CIP and HIP techniques, offering a possibility of manufacturing OFETs at low cost.

Balanced Ambipolar Organic Field-Effect Transistors by Polymer Preaggregation.

PubMed

Janasz, Lukasz; Luczak, Adam; Marszalek, Tomasz; Dupont, Bertrand G R; Jung, Jaroslaw; Ulanski, Jacek; Pisula, Wojciech

2017-06-21

Ambipolar organic field-effect transistors (OFETs) based on heterojunction active films still suffer from an imbalance in the transport of electrons and holes. This problem is related to an uncontrolled phase separation between the donor and acceptor organic semiconductors in the thin films. In this work, we have developed a concept to improve the phase separation in heterojunction transistors to enhance their ambipolar performance. This concept is based on preaggregation of the donor polymer, in this case poly(3-hexylthiophene) (P3HT), before solution mixing with the small-molecular-weight acceptor, phenyl-C61-butyric acid methyl ester (PCBM). The resulting heterojunction transistor morphology consists of self-assembled P3HT fibers embedded in a PCBM matrix, ensuring balanced mobilities reaching 0.01 cm 2 /V s for both holes and electrons. These are the highest mobility values reported so far for ambipolar OFETs based on P3HT/PCBM blends. Preaggregation of the conjugated polymer before fabricating binary blends can be regarded as a general concept for a wider range of semiconducting systems applicable in organic electronic devices.

Predictors of Mobile Phone and Social Networking Site Dependency in Adulthood.

PubMed

Burnell, Kaitlyn; Kuther, Tara L

2016-10-01

The present study explored social and psychological predictors of social networking site (SNS) and mobile phone dependency in a sample of emerging adults (ages 18-25, n = 159, M = 21.87, SD = 2.08) and young adults (ages 26-40, n = 97, M = 31.21, SD = 4.11). Path analysis revealed that SNS dependency mediated the relationship of social comparison, SNS support, and impulsivity on mobile phone dependency. Impulsivity also showed direct links to mobile phone dependency. The present findings suggest that individuals with a strong orientation toward social comparison, who perceive a strong sense of support through SNS networks, or who show difficulty with self-regulation may be at risk for SNS and mobile phone dependency.

Thermodynamics and phase transition of charged AdS black holes with a global monopole

NASA Astrophysics Data System (ADS)

Deng, Gao-Ming; Fan, Jinbo; Li, Xinfei; Huang, Yong-Chang

2018-01-01

Thermodynamical properties of charged AdS black holes with a global monopole still remain obscure. In this paper, we investigate the thermodynamics and phase transition of the black holes in the extended phase space. It is shown that thermodynamical quantities of the black holes exhibit an interesting dependence on the internal global monopole, and they perfectly satisfy both the first law of thermodynamics and Smarr relation. Furthermore, analysis of the local and the global thermodynamical stability manifests that the charged AdS black hole undergoes an elegant phase transition at critical point. Of special interest, critical behaviors of the black holes resemble a Van der Waals liquid-gas system. Our results not only reveal the effect of a global monopole on thermodynamics of AdS black holes, but also further support that Van der Waals-like behavior of the black holes is a universal phenomenon.

Experimental Study on Environment Friendly Tap Hole Clay for Blast Furnace

NASA Astrophysics Data System (ADS)

Siva kumar, R.; Mohammed, Raffi; Srinivasa Rao, K.

2018-03-01

Blast furnace (BF) is the best possible route of iron production available. Blast furnace is a high pressure vessel where iron ore is melted and liquid iron is produced. The liquid iron is tapped through the hole in Blast Furnace called tap hole. The tapped liquid metal flowing through the tap hole is plugged using a clay called tap hole clay. Tap hole clay (THC) is a unshaped refractory used to plug the tap hole. The tap hole clay extruded through the tap hole using a gun. The tap hole clay is designed to expand and plug the tap hole. The tap hole filled with clay is drilled using drill bit and the hole made through the tap hole to tap the liquid metal accumulated inside the furnace. The number of plugging and drilling varies depending on the volume of the furnace. The tap hole clay need to have certain properties to avoid problems during plugging and drilling. In the present paper tap hole clay properties in industrial use was tested and studied. The problems were identified related to tap hole clay manufacturing. Experiments were conducted in lab scale to solve the identified problems. The present composition was modified with experimental results. The properties of the modified tap hole clay were found suitable and useful for blast furnace operation with lab scale experimental results.

Remarkable enhancement of charge carrier mobility of conjugated polymer field-effect transistors upon incorporating an ionic additive

PubMed Central

Luo, Hewei; Yu, Chenmin; Liu, Zitong; Zhang, Guanxin; Geng, Hua; Yi, Yuanping; Broch, Katharina; Hu, Yuanyuan; Sadhanala, Aditya; Jiang, Lang; Qi, Penglin; Cai, Zhengxu; Sirringhaus, Henning; Zhang, Deqing

2016-01-01

Organic semiconductors with high charge carrier mobilities are crucial for flexible electronic applications. Apart from designing new conjugated frameworks, different strategies have been explored to increase charge carrier mobilities. We report a new and simple approach to enhancing the charge carrier mobility of DPP-thieno[3,2-b]thiophene–conjugated polymer by incorporating an ionic additive, tetramethylammonium iodide, without extra treatments into the polymer. The resulting thin films exhibit a very high hole mobility, which is higher by a factor of 24 than that of thin films without the ionic additive under the same conditions. On the basis of spectroscopic grazing incidence wide-angle x-ray scattering and atomic force microscopy studies as well as theoretical calculations, the remarkable enhancement of charge mobility upon addition of tetramethylammonium iodide is attributed primarily to an inhibition of the torsion of the alkyl side chains by the presence of the ionic species, facilitating a more ordered lamellar packing of the alkyl side chains and interchain π-π interactions. PMID:27386541

A Comprehensive Study of Data Collection Schemes Using Mobile Sinks in Wireless Sensor Networks

PubMed Central

Khan, Abdul Waheed; Abdullah, Abdul Hanan; Anisi, Mohammad Hossein; Bangash, Javed Iqbal

2014-01-01

Recently sink mobility has been exploited in numerous schemes to prolong the lifetime of wireless sensor networks (WSNs). Contrary to traditional WSNs where sensory data from sensor field is ultimately sent to a static sink, mobile sink-based approaches alleviate energy-holes issues thereby facilitating balanced energy consumption among nodes. In mobility scenarios, nodes need to keep track of the latest location of mobile sinks for data delivery. However, frequent propagation of sink topological updates undermines the energy conservation goal and therefore should be controlled. Furthermore, controlled propagation of sinks' topological updates affects the performance of routing strategies thereby increasing data delivery latency and reducing packet delivery ratios. This paper presents a taxonomy of various data collection/dissemination schemes that exploit sink mobility. Based on how sink mobility is exploited in the sensor field, we classify existing schemes into three classes, namely path constrained, path unconstrained, and controlled sink mobility-based schemes. We also organize existing schemes based on their primary goals and provide a comparative study to aid readers in selecting the appropriate scheme in accordance with their particular intended applications and network dynamics. Finally, we conclude our discussion with the identification of some unresolved issues in pursuit of data delivery to a mobile sink. PMID:24504107

Undoped GaAs bilayers for exciton condensation experiments

NASA Astrophysics Data System (ADS)

Lilly, M. P.

2005-03-01

Experimental progress in transport studies of exciton condensation of in electron and hole bilayers at high magnetic fields [1,2] has shown this novel physics can be observed. Fabrication of the bipolar electron-hole bilayers for zero field studies of exciton condensation still remains elusive. We describe a series of experiments on undoped GaAs/AlGaAs heterostructures with the motivation of making electron-hole bilayers. In these undoped devices, external electric fields induce carriers rather than the traditional doping techniques. Single layer electron (or hole) devices demonstrate a high mobility over a wide range of density. More recently, fully undoped bilayers have been made where the density in each layer is independently controlled with gates on the top and bottom of the bilayer. In this talk we present high field transport of undoped electron-electron bilayers, and describe recent progress towards extending the fabrication techniques to creating electron-hole bilayers for exciton condensation studies at zero magnetic field. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC04-94AL85000. 1. M. Kellogg, J. P. Eisenstein, L. N. Pfeiffer, and K. W. West, Phys. Rev. Lett. 93 036801 (2004). 2. E. Tutoc, M. Shayegan, and D. A. Huse, Phys. Rev. Lett. 93, 036802 (2004).

Statistical mechanics of gravitons in a box and the black hole entropy

NASA Astrophysics Data System (ADS)

Viaggiu, Stefano

2017-05-01

This paper is devoted to the study of the statistical mechanics of trapped gravitons obtained by 'trapping' a spherical gravitational wave in a box. As a consequence, a discrete spectrum dependent on the Legendre index ℓ similar to the harmonic oscillator one is obtained and a statistical study is performed. The mean energy 〈 E 〉 results as a sum of two discrete Planck distributions with different dependent frequencies. As an important application, we derive the semiclassical Bekenstein-Hawking entropy formula for a static Schwarzschild black hole by only requiring that the black hole internal energy U is provided by its ADM rest energy, without invoking particular quantum gravity theories. This seriously suggests that the interior of a black hole can be composed of trapped gravitons at a thermodynamical temperature proportional by a factor ≃ 2 to the horizon temperature Th.

Model for thickness dependence of radiation charging in MOS structures

NASA Technical Reports Server (NTRS)

Viswanathan, C. R.; Maserjian, J.

1976-01-01

The model considers charge buildup in MOS structures due to hole trapping in the oxide and the creation of sheet charge at the silicon interface. The contribution of hole trapping causes the flatband voltage to increase with thickness in a manner in which square and cube dependences are limiting cases. Experimental measurements on samples covering a 200 - 1000 A range of oxide thickness are consistent with the model, using independently obtained values of hole-trapping parameters. An important finding of our experimental results is that a negative interface charge contribution due to surface states created during irradiation compensates most of the positive charge in the oxide at flatband. The tendency of the surface states to 'track' the positive charge buildup in the oxide, for all thicknesses, applies both in creation during irradiation and in annihilation during annealing. An explanation is proposed based on the common defect origin of hole traps and potential surface states.

The remnants in Reissner-Nordström-de Sitter quintessence black hole

NASA Astrophysics Data System (ADS)

Feng, Zhongwen; Zhang, Li; Zu, Xiaotao

2014-08-01

According to the effects of quantum gravity, we investigated the fermion tunneling from the Reissner-Nordström-de Sitter quintessence (RN-dSQ) black hole. The corrected temperature is not only determined by the mass and charge of the black hole, but also depended on the quantum number of the emitted fermion and β, which is a small value representing the effects of quantum gravity. The effects of quantum gravity slowed down the increase of the temperature and led to the remnants of the black hole. We think it is a method to avoid the information loss paradox of black holes.

Modified Bloch equations and spectral hole burning in solids

NASA Astrophysics Data System (ADS)

Asadullina, N. Ya; Asadullin, T. Ya; Asadullin, Ya Ya

2001-06-01

On the grounds of Bloch equations modified by taking into account the power dependence of the dispersion and damping parameters, we give general expressions for hole shapes burnt in the absorption and polarization spectra of the two-level systems. The general expressions are used for detailed numerical calculations of the hole shapes and hole widths in a concrete paramagnetic system (quartz with [AlO4]0 centres). This system earlier was studied experimentally and theoretically through the transient nutation and free induction decay methods. The results on the hole width in our modified-Bloch-equations model are in good qualitative agreement with the FID data.

Efficient charge injection in p-type polymer field-effect transistors with low-cost molybdenum electrodes through V2O5 interlayer.

PubMed

Baeg, Kang-Jun; Bae, Gwang-Tae; Noh, Yong-Young

2013-06-26

Here we report high-performance polymer OFETs with a low-cost Mo source/drain electrode by efficient charge injection through the formation of a thermally deposited V2O5 thin film interlayer. A thermally deposited V2O5 interlayer is formed between a regioregular poly(3-hexylthiophene) (rr-P3HT) or a p-type polymer semiconductor containing dodecyl-substituted thienylenevinylene (TV) and dodecylthiophene (PC12TV12T) and the Mo source/drain electrode. The P3HT or PC12TV12T OFETs with the bare Mo electrode exhibited lower charge carrier mobility than those with Au owing to a large barrier height for hole injection (0.5-1.0 eV). By forming the V2O5 layer, the P3HT or PC12TV12T OFETs with V2O5 on the Mo electrode exhibited charge carrier mobility comparable to that of a pristine Au electrode. Best P3HT or PC12TV12T OFETs with 5 nm thick V2O5 on Mo electrode show the charge carrier mobility of 0.12 and 0.38 cm(2)/(V s), respectively. Ultraviolet photoelectron spectroscopy results exhibited the work-function of the Mo electrode progressively changed from 4.3 to 4.9 eV with an increase in V2O5 thickness from 0 to 5 nm, respectively. Interestingly, the V2O5-deposited Mo exhibits comparable Rc to Au, which mainly results from the decreased barrier height for hole carrier injection from the low-cost metal electrode to the frontier molecular orbital of the p-type polymer semiconductor after the incorporation of the transition metal oxide hole injection layer, such as V2O5. This enables the development of large-area, low-cost electronics with the Mo electrodes and V2O5 interlayer.

Electronic and transport properties of Li-doped NiO epitaxial thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, J. Y.; Li, W. W.; Hoye, R. L. Z.

NiO is a p-type wide bandgap semiconductor of use in various electronic devices ranging from solar cells to transparent transistors. Understanding and improving its optical and transport properties have been of considerable interest. In this work, we have investigated the effect of Li doping on the electronic, optical and transport properties of NiO epitaxial thin films grown by pulsed laser deposition. We show that Li doping significantly increases the p-type conductivity of NiO, but all the films have relatively low room-temperature mobilities (<0.05 cm2 V -1s -1). The conduction mechanism is better described by small-polaron hoping model in the temperaturemore » range of 200 K < T <330 K, and variable range hopping at T <200 K. A combination of x-ray photoemission and O K-edge x-ray absorption spectroscopic investigations reveal that the Fermi level gradually shifts toward the valence band maximum (VBM) and a new hole state develops with Li doping. Both the VBM and hole states are composed of primarily Zhang-Rice bound states, which accounts for the small polaron character (low mobility) of hole conduction. Our work provides guidelines for the search for p-type oxide materials and device optimization.NiO is a p-type wide bandgap semiconductor of use in various electronic devices ranging from solar cells to transparent transistors. This work reports the controlling of conductivity and increase of work functions by Li doping.« less

Thermodynamic phase transition in the rainbow Schwarzschild black hole

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gim, Yongwan; Kim, Wontae, E-mail: yongwan89@sogang.ac.kr, E-mail: wtkim@sogang.ac.kr

2014-10-01

We study the thermodynamic phase transition in the rainbow Schwarzschild black hole where the metric depends on the energy of the test particle. Identifying the black hole temperature with the energy from the modified dispersion relation, we obtain the modified entropy and thermodynamic energy along with the modified local temperature in the cavity to provide well defined black hole states. It is found that apart from the conventional critical temperature related to Hawking-Page phase transition there appears an additional critical temperature which is of relevance to the existence of a locally stable tiny black hole; however, the off-shell free energymore » tells us that this black hole should eventually tunnel into the stable large black hole. Finally, we discuss the reason why the temperature near the horizon is finite in the rainbow black hole by employing the running gravitational coupling constant, whereas it is divergent near the horizon in the ordinary Schwarzschild black hole.« less

Hawking temperature of constant curvature black holes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cai Ronggen; Myung, Yun Soo; Institute of Basic Science and School of Computer Aided Science, Inje University, Gimhae 621-749

2011-05-15

The constant curvature (CC) black holes are higher dimensional generalizations of Banados-Teitelboim-Zanelli black holes. It is known that these black holes have the unusual topology of M{sub D-1}xS{sup 1}, where D is the spacetime dimension and M{sub D-1} stands for a conformal Minkowski spacetime in D-1 dimensions. The unusual topology and time-dependence for the exterior of these black holes cause some difficulties to derive their thermodynamic quantities. In this work, by using a globally embedding approach, we obtain the Hawking temperature of the CC black holes. We find that the Hawking temperature takes the same form when using both themore » static and global coordinates. Also, it is identical to the Gibbons-Hawking temperature of the boundary de Sitter spaces of these CC black holes.« less

Main Properties of Forbush Effects Related to High-Speed Streams from Coronal Holes

NASA Astrophysics Data System (ADS)

Melkumyan, A. A.; Belov, A. V.; Abunina, M. A.; Abunin, A. A.; Eroshenko, E. A.; Oleneva, V. A.; Yanke, V. G.

2018-03-01

The IZMIRAN database of Forbush effects and interplanetary disturbances was used to study features of the action of high-speed solar wind streams from coronal holes on cosmic rays. Three hundred and fifty Forbush effects created by coronal holes without other actions were distinguished. The mean values and distributions have been found for different characteristics of events from this group and compared with all Forbush effects and Forbush effects caused by coronal ejections. Despite the great differences in high-speed streams from coronal holes, this group turned out to be more compact and uniform as compared to events related to coronal ejections. Regression dependences and correlation relations between different parameters of events for the studied groups have been obtained. It has been shown that Forbush effects caused by coronal ejections depend considerably more strongly on the characteristics of interplanetary disturbances as compared to Forbush effects related to coronal holes. This suggests a significant difference between the modulation mechanisms of Forbush effects of different types and corroborates earlier conclusions based on indirect data.

Universal instability of hairy black holes in Lovelock-Galileon theories in D dimensions

NASA Astrophysics Data System (ADS)

Takahashi, Kazufumi; Suyama, Teruaki; Kobayashi, Tsutomu

2016-03-01

We analyze spherically symmetric black hole solutions with time-dependent scalar hair in a class of Lovelock-Galileon theories, which are the scalar-tensor theories with second-order field equations in arbitrary dimensions. We first show that known black hole solutions in five dimensions are always plagued by the ghost/gradient instability in the vicinity of the horizon. We then generalize such black hole solutions to higher dimensions and show that the same instability found in five dimensions appears universally in any number of dimensions.

Scattering and absorption of massless scalar waves by Born-Infeld black holes

NASA Astrophysics Data System (ADS)

Sanchez, Pablo Alejandro; Bretón, Nora; Bergliaffa, Santiago Esteban Perez

2018-06-01

We present the results of a study of the scattering of massless planar scalar waves by a Born-Infeld black hole. The scattering and absorption cross sections are calculated using partial-wave methods. The numerical results are checked by reproducing those of the Reissner-Nordstrom black hole, and also using several approximations, with which our results are in very good agreement. The dependence of these phenomena on the effective potential, the charge of the black hole, and the value of the Born-Infeld parameter is discussed.

Black holes from large N singlet models

NASA Astrophysics Data System (ADS)

Amado, Irene; Sundborg, Bo; Thorlacius, Larus; Wintergerst, Nico

2018-03-01

The emergent nature of spacetime geometry and black holes can be directly probed in simple holographic duals of higher spin gravity and tensionless string theory. To this end, we study time dependent thermal correlation functions of gauge invariant observables in suitably chosen free large N gauge theories. At low temperature and on short time scales the correlation functions encode propagation through an approximate AdS spacetime while interesting departures emerge at high temperature and on longer time scales. This includes the existence of evanescent modes and the exponential decay of time dependent boundary correlations, both of which are well known indicators of bulk black holes in AdS/CFT. In addition, a new time scale emerges after which the correlation functions return to a bulk thermal AdS form up to an overall temperature dependent normalization. A corresponding length scale was seen in equal time correlation functions in the same models in our earlier work.

Electroluminescence property of organic light emitting diode (OLED)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Özdemir, Orhan; Kavak, Pelin; Saatci, A. Evrim

2013-12-16

Transport properties of electrons and holes were investigated not only in a anthracene-containing poly(p-phenylene-ethynylene)- alt - poly(p-phenylene-vinylene) (PPE-PPV) polymer (AnE-PVstat) light emitting diodes (OLED) but also in an ITO/Ag/polymer/Ag electron and ITO/PEDOT:PSS/polymer/Au hole only devices. Mobility of injected carriers followed the Poole-Frenkel type conduction mechanism and distinguished in the frequency range due to the difference of transit times in admittance measurement. Beginning of light output took place at the turn-on voltage (or flat band voltage), 1.8 V, which was the difference of energy band gap of polymer and two barrier offsets between metals and polymer.

Electrospun Polyaniline/Polyethylene Oxide Nanofiber Field Effect Transistor

NASA Technical Reports Server (NTRS)

Pinto, N. J.; Johnson, A. T.; MacDiarmid, A. G.; Mueller, C. H.; Theofylaktos, N.; Robinson, D. C.; Miranda, F. A.

2003-01-01

We report on the observation of field effect transistor (FET) behavior in electrospun camphorsulfonic acid doped polyaniline(PANi)/polyethylene oxide(PE0) nanofibers. Saturation channel currents are observed at surprisingly low source/drain voltages. The hole mobility in the depletion regime is 1.4 x 10(exp -4) sq cm/V s while the 1-D charge density (at zero gate bias) is calculated to be approximately 1 hole per 50 two-ring repeat units of polyaniline, consistent with the rather high channel conductivity (approx. 10(exp -3) S/cm). Reducing or eliminating the PEO content in the fiber is expected to enhance device parameters. Electrospinning is thus proposed as a simple method of fabricating 1-D polymer FET's.

Characterization of dynamics in complex lyophilized formulations: II. Analysis of density variations in terms of glass dynamics and comparisons with global mobility, fast dynamics, and Positron Annihilation Lifetime Spectroscopy (PALS)

PubMed Central

Chieng, Norman; Cicerone, Marcus T.; Zhong, Qin; Liu, Ming; Pikal, Michael J.

2013-01-01

Amorphous HES/disaccharide (trehalose or sucrose) formulations, with and without added polyols (glycerol and sorbitol) and disaccharide formulations of human growth hormone (hGH), were prepared by freeze drying and characterized with particular interest in methodology for using high precision density measurements to evaluate free volume changes and a focus on comparisons between “free volume” changes obtained from analysis of density data, fast dynamics (local mobility), and PALS characterization of “free volume” hole size. Density measurements were performed using a helium gas pycnometer, and fast dynamics was characterized using incoherent neutron scattering spectrometer. Addition of sucrose and trehalose to hGH decreases free volume in the system with sucrose marginally more effective than trehalose, consistent with superior pharmaceutical stability of sucrose hGH formulations well below Tg relative to trehalose. We find that density data may be analyzed in terms of free volume changes by evaluation of volume changes on mixing and calculation of apparent specific volumes from the densities. Addition of sucrose to HES decreases free volume, but the effect of trehalose is not detectable above experimental error. Addition of sorbitol or glycerol to HES/trehalose base formulations appears to significantly decrease free volume, consistent with the positive impact of such additions on pharmaceutical stability (i.e., degradation) in the glassy state. Free volume changes, evaluated from density data, fast dynamics amplitude of local motion, and PALS hole size data generally are in qualitative agreement for the HES/disaccharide systems studied. All predict decreasing molecular mobility as disaccharides are added to HES. Global mobility as measured by enthalpy relaxation times, increases as disaccharides, particularly sucrose, are added to HES. PMID:23623797

First-principle simulations of electronic structure in semicrystalline polyethylene

NASA Astrophysics Data System (ADS)

Moyassari, A.; Unge, M.; Hedenqvist, M. S.; Gedde, U. W.; Nilsson, F.

2017-05-01

In order to increase our fundamental knowledge about high-voltage cable insulation materials, realistic polyethylene (PE) structures, generated with a novel molecular modeling strategy, have been analyzed using first principle electronic structure simulations. The PE structures were constructed by first generating atomistic PE configurations with an off-lattice Monte Carlo method and then equilibrating the structures at the desired temperature and pressure using molecular dynamics simulations. Semicrystalline, fully crystalline and fully amorphous PE, in some cases including crosslinks and short-chain branches, were analyzed. The modeled PE had a structure in agreement with established experimental data. Linear-scaling density functional theory (LS-DFT) was used to examine the electronic structure (e.g., spatial distribution of molecular orbitals, bandgaps and mobility edges) on all the materials, whereas conventional DFT was used to validate the LS-DFT results on small systems. When hybrid functionals were used, the simulated bandgaps were close to the experimental values. The localization of valence and conduction band states was demonstrated. The localized states in the conduction band were primarily found in the free volume (result of gauche conformations) present in the amorphous regions. For branched and crosslinked structures, the localized electronic states closest to the valence band edge were positioned at branches and crosslinks, respectively. At 0 K, the activation energy for transport was lower for holes than for electrons. However, at room temperature, the effective activation energy was very low (˜0.1 eV) for both holes and electrons, which indicates that the mobility will be relatively high even below the mobility edges and suggests that charge carriers can be hot carriers above the mobility edges in the presence of a high electrical field.

The interaction of Dirac particles with a Hawking charged radiating black hole

NASA Astrophysics Data System (ADS)

Kubik, Erik

2007-08-01

The interaction of spin 1/2 fields with a charged, evaporating black hole (EBH) is investigated. Using the Vaidya metric to model the Hawking evaporating black hole, the wave equation for a massless spinor field is obtained. The resulting field equation is solved utilizing techniques developed by Brill and Wheeler. Unlike previous efforts, a charged, evaporating black hole has never been used as a background to investigate spin 1/2 quantum field propagation, e.g., Brill and Wheeler considered massless spin 1/2 interactions in a static, Schwarzschild background. Using the WKB approximation, the wave equation is solved for the case of an EBH with constant luminosity. Analysis of the effective potential at different stages of evaporation is made including the dependence on the parameters of the system such as the total angular momentum, energy of the incident field, and luminosity of the evaporating black hole. Utilizing techniques of Mukhopad-hey, the transmission and reflection coefficients for the massless spinors are computed and compared to Schwarzschild result for both the high energy and hard scattering cases. The effect of the time dependence of the space-time metric has an important effect on the behavior of quantum fields over the lifetime of the evaporating black hole and may provide a signature for the detection of such objects.

Tidal disruption of stars in a supermassive black hole binary system: the influence of orbital properties on fallback and accretion rates

NASA Astrophysics Data System (ADS)

Vigneron, Quentin; Lodato, Giuseppe; Guidarelli, Alessio

2018-06-01

The disruption of a star by a supermassive black hole generates a sudden bright flare. Previous studies have focused on the disruption by single black holes, for which the fallback rate decays as ∝ t-5/3. In this paper, we generalize the study to the case of a supermassive black hole binary (SMBHB), using both analytical estimates and hydrodynamical simulations, looking for specific observable signatures. The range of binary separation for which it is possible to distinguish between the disruption created by a single or a binary black hole concerns typically separations of the order of a few milliparsecs for a primary of mass ˜106 M⊙. When the fallback rate is affected by the secondary, it undergoes two types interruptions, depending on the initial inclination θ of the orbit of the star relative to the plane of the SMBHB. For θ ≲ 70°, periodic sharp interruptions occur and the time of first interruption depends on the distance of the secondary black hole with the debris. If θ ≳ 70°, a first smooth interruption occurs, but not always followed by a further recovery of the fallback rate. This implies that most of the TDEs around a SMBHB will undergo periodic sharp interruptions of their light curve.

Point Defect Structure of Cr203

DTIC Science & Technology

1987-10-01

Calculation of Electron Hole Mobility ........................ 104 6.2.3 Construction of the Defect Concentration vs. Oxygen Pressure Diagram...1000’ to 16000C ............ 123 7.7 Calculated diffusion coefficient vs. oxygen partial pressure diagram for pure Cr203 at 1100 0 C...127 7.10 Calculated parabolic rate constant vs. oxygen partial pressure diagram for pure Cr203 at

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ghosh, Tushar; Basak, Durga

A rapid dark thermal annealing process at 800 deg. C of radio frequency sputtered P doped ZnO thin films have resulted in improved electrical transport properties with hole concentration of 1 x 1018 cm-3, mobility 4.37 cm2/Vs and resistivity 1.4 {Omega}-cm. X-ray photoelectron spectroscopy shows the presence of inactivated P in as-grown ZnO films.

Reciprocal capacitance transients?

NASA Astrophysics Data System (ADS)

Gfroerer, Tim; Simov, Peter; Wanlass, Mark

2007-03-01

When the reverse bias across a semiconductor diode is changed, charge carriers move to accommodate the appropriate depletion thickness, producing a simultaneous change in the device capacitance. Transient capacitance measurements can reveal inhibited carrier motion due to trapping, where the depth of the trap can be evaluated using the temperature-dependent escape rate. However, when we employ this technique on a GaAs0.72P0.28 n+/p diode (which is a candidate for incorporation in multi-junction solar cells), we observe a highly non-exponential response under a broad range of experimental conditions. Double exponential functions give good fits, but lead to non-physical results. The deduced rates depend on the observation time window and fast and slow rates, which presumably correspond to deep and shallow levels, have identical activation energies. Meanwhile, we have discovered a universal linear relationship between the inverse of the capacitance and time. An Arrhenius plot of the slope of the reciprocal of the transient yields an activation energy of approximately 0.4 eV, independent of the observation window and other experimental conditions. The reciprocal behavior leads us to hypothesize that hopping, rather than escape into high-mobility bands, may govern the transport of trapped holes in this system.

Hawking radiation in a d-dimensional static spherically symmetric black hole surrounded by quintessence

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen Songbai; Wang Bin; Su Rukeng

2008-06-15

We present a solution of Einstein equations with quintessential matter surrounding a d-dimensional black hole, whose asymptotic structures are determined by the state of the quintessential matter. We examine the thermodynamics of this black hole and find that the mass of the black hole depends on the equation of state of the quintessence, while the first law is universal. Investigating the Hawking radiation in this black hole background, we observe that the Hawking radiation dominates on the brane in the low-energy regime. For different asymptotic structures caused by the equation of state of the quintessential matter surrounding the black hole,more » we learn that the influences by the state parameter of the quintessence on Hawking radiation are different.« less

Decoherence in attosecond photoionization.

PubMed

Pabst, Stefan; Greenman, Loren; Ho, Phay J; Mazziotti, David A; Santra, Robin

2011-02-04

The creation of superpositions of hole states via single-photon ionization using attosecond extreme-ultraviolet pulses is studied with the time-dependent configuration-interaction singles (TDCIS) method. Specifically, the degree of coherence between hole states in atomic xenon is investigated. We find that interchannel coupling not only affects the hole populations, but it also enhances the entanglement between the photoelectron and the remaining ion, thereby reducing the coherence within the ion. As a consequence, even if the spectral bandwidth of the ionizing pulse exceeds the energy splittings among the hole states involved, perfectly coherent hole wave packets cannot be formed. For sufficiently large spectral bandwidth, the coherence can only be increased by increasing the mean photon energy.

Aspects of noncommutative (1+1)-dimensional black holes

NASA Astrophysics Data System (ADS)

Mureika, Jonas R.; Nicolini, Piero

2011-08-01

We present a comprehensive analysis of the spacetime structure and thermodynamics of (1+1)-dimensional black holes in a noncommutative framework. It is shown that a wider variety of solutions are possible than the commutative case considered previously in the literature. As expected, the introduction of a minimal length θ cures singularity pathologies that plague the standard two-dimensional general relativistic case, where the latter solution is recovered at large length scales. Depending on the choice of input parameters (black hole mass M, cosmological constant Λ, etc.), black hole solutions with zero, up to six, horizons are possible. The associated thermodynamics allows for the either complete evaporation, or the production of black hole remnants.

Thermal stability of black holes with arbitrary hairs

NASA Astrophysics Data System (ADS)

Sinha, Aloke Kumar

2018-02-01

We have derived the criteria for thermal stability of charged rotating black holes, for horizon areas that are large relative to the Planck area (in these dimensions). In this paper, we generalized it for black holes with arbitrary hairs. The derivation uses results of loop quantum gravity and equilibrium statistical mechanics of the grand canonical ensemble and there is no explicit use of classical spacetime geometry at all in this analysis. The assumption is that the mass of the black hole is a function of its horizon area and all the hairs. Our stability criteria are then tested in detail against some specific black holes, whose metrics provide us with explicit relations for the dependence of the mass on the area and other hairs of the black holes. This enables us to predict which of these black holes are expected to be thermally unstable under Hawking radiation.

Post-Newtonian Dynamics in Dense Star Clusters: Highly Eccentric, Highly Spinning, and Repeated Binary Black Hole Mergers

NASA Astrophysics Data System (ADS)

Rodriguez, Carl L.; Amaro-Seoane, Pau; Chatterjee, Sourav; Rasio, Frederic A.

2018-04-01

We present models of realistic globular clusters with post-Newtonian dynamics for black holes. By modeling the relativistic accelerations and gravitational-wave emission in isolated binaries and during three- and four-body encounters, we find that nearly half of all binary black hole mergers occur inside the cluster, with about 10% of those mergers entering the LIGO/Virgo band with eccentricities greater than 0.1. In-cluster mergers lead to the birth of a second generation of black holes with larger masses and high spins, which, depending on the black hole natal spins, can sometimes be retained in the cluster and merge again. As a result, globular clusters can produce merging binaries with detectable spins regardless of the birth spins of black holes formed from massive stars. These second-generation black holes would also populate any upper mass gap created by pair-instability supernovae.

Characterization of nitride hole lateral transport in a charge trap flash memory by using a random telegraph signal method

NASA Astrophysics Data System (ADS)

Liu, Yu-Heng; Jiang, Cheng-Min; Lin, Hsiao-Yi; Wang, Tahui; Tsai, Wen-Jer; Lu, Tao-Cheng; Chen, Kuang-Chao; Lu, Chih-Yuan

2017-07-01

We use a random telegraph signal method to investigate nitride trapped hole lateral transport in a charge trap flash memory. The concept of this method is to utilize an interface oxide trap and its associated random telegraph signal as an internal probe to detect a local channel potential change resulting from nitride charge lateral movement. We apply different voltages to the drain of a memory cell and vary a bake temperature in retention to study the electric field and temperature dependence of hole lateral movement in a nitride. Thermal energy absorption by trapped holes in lateral transport is characterized. Mechanisms of hole lateral transport in retention are investigated. From the measured and modeled results, we find that thermally assisted trap-to-band tunneling is a major trapped hole emission mechanism in nitride hole lateral transport.

Post-Newtonian Dynamics in Dense Star Clusters: Highly Eccentric, Highly Spinning, and Repeated Binary Black Hole Mergers.

PubMed

Rodriguez, Carl L; Amaro-Seoane, Pau; Chatterjee, Sourav; Rasio, Frederic A

2018-04-13

We present models of realistic globular clusters with post-Newtonian dynamics for black holes. By modeling the relativistic accelerations and gravitational-wave emission in isolated binaries and during three- and four-body encounters, we find that nearly half of all binary black hole mergers occur inside the cluster, with about 10% of those mergers entering the LIGO/Virgo band with eccentricities greater than 0.1. In-cluster mergers lead to the birth of a second generation of black holes with larger masses and high spins, which, depending on the black hole natal spins, can sometimes be retained in the cluster and merge again. As a result, globular clusters can produce merging binaries with detectable spins regardless of the birth spins of black holes formed from massive stars. These second-generation black holes would also populate any upper mass gap created by pair-instability supernovae.

Miniature Ion-Mobility Spectrometer

NASA Technical Reports Server (NTRS)

Hartley, Frank T.

2006-01-01

The figure depicts a proposed miniature ion-mobility spectrometer that would be fabricated by micromachining. Unlike prior ion-mobility spectrometers, the proposed instrument would not be based on a time-of-flight principle and, consequently, would not have some of the disadvantageous characteristics of prior time-of-flight ion-mobility spectrometers. For example, one of these characteristics is the need for a bulky carrier-gas-feeding subsystem that includes a shutter gate to provide short pulses of gas in order to generate short pulses of ions. For another example, there is need for a complex device to generate pulses of ions from the pulses of gas and the device is capable of ionizing only a fraction of the incoming gas molecules; these characteristics preclude miniaturization. In contrast, the proposed instrument would not require a carrier-gas-feeding subsystem and would include a simple, highly compact device that would ionize all the molecules passing through it. The ionization device in the proposed instrument would be a 0.1-micron-thick dielectric membrane with metal electrodes on both sides. Small conical holes would be micromachined through the membrane and electrodes. An electric potential of the order of a volt applied between the membrane electrodes would give rise to an electric field of the order of several megavolts per meter in the submicron gap between the electrodes. An electric field of this magnitude would be sufficient to ionize all the molecules that enter the holes. Ionization (but not avalanche arcing) would occur because the distance between the ionizing electrodes would be less than the mean free path of gas molecules at the operating pressure of instrument. An accelerating grid would be located inside the instrument, downstream from the ionizing membrane. The electric potential applied to this grid would be negative relative to the potential on the inside electrode of the ionizing membrane and would be of a magnitude sufficient to generate a moderate electric field. Positive ions leaving the membrane holes would be accelerated in this electric field. The resulting flux of ions away from the ionization membrane would create a partial vacuum that would draw more of the gas medium through the membrane. The figure depicts a filter electrode and detector electrodes located along the sides of a drift tube downstream from the accelerator electrode. These electrodes would apply a transverse AC electric field superimposed on a ramped DC electric field. The AC field would effect differential transverse dispersal of ions. At a given instant of time, the trajectories of most of the ions would be bent toward the electrodes, causing most of the ions to collide with the electrodes and thereby become neutralized. The DC field would partly counteract the dispersive effect of the AC field, straightening the trajectories of a selected species of ions; the selection would vary with the magnitude of the applied DC field. The straightening of the trajectories of the selected ions would enable them to pass into the region between the detector electrodes. Depending on the polarity of the voltage applied to the detector electrodes, the electric field between the detector electrodes would draw the selected ions to one of these electrodes. Hence, the current collected by one of the detector electrodes would be a measure of the abundance of ions of the selected species. The ramping of the filter- electrode DC voltage would sweep the selection of ions through the spectrum of ionic species.

Coarse-grained model of conformation-dependent electrophoretic mobility and its influence on DNA dynamics

NASA Astrophysics Data System (ADS)

Pandey, Harsh; Underhill, Patrick T.

2015-11-01

The electrophoretic mobility of molecules such as λ -DNA depends on the conformation of the molecule. It has been shown that electrohydrodynamic interactions between parts of the molecule lead to a mobility that depends on conformation and can explain some experimental observations. We have developed a new coarse-grained model that incorporates these changes of mobility into a bead-spring chain model. Brownian dynamics simulations have been performed using this model. The model reproduces the cross-stream migration that occurs in capillary electrophoresis when pressure-driven flow is applied parallel or antiparallel to the electric field. The model also reproduces the change of mobility when the molecule is stretched significantly in an extensional field. We find that the conformation-dependent mobility can lead to a new type of unraveling of the molecule in strong fields. This occurs when different parts of the molecule have different mobilities and the electric field is large.

Prevalence of Mobile Phone Dependence in Secondary School Adolescents.

PubMed

Nikhita, Chimatapu Sri; Jadhav, Pradeep R; Ajinkya, Shaunak A

2015-11-01

Mobile phones have become an essential part of modern human life. They have many attributes which makes them very attractive to both young and old. There has been an increasing trend of use of mobile phones among students. Data has now started emerging with respect to the negative physical and psychological consequences of excessive use of mobile phones. New research has shown excessive use of mobile phones leading to development of symptoms suggestive of dependence syndrome. To study the prevalence of Mobile Phone Dependence (MPD) in secondary school adolescents. Cross-sectional, observational study conducted in secondary section of English-medium schools at Navi Mumbai (India). Four hundred and fifteen students studying in 8(th), 9(th) and 10(th) standards of schools at Navi Mumbai (India) having personal mobile phone were randomly included in the study. Participant information like age, gender, family type, phone type, duration of use per day and years of mobile phone usage was recorded. They were administered an MPD questionnaire based upon the dependence syndrome criteria as per ICD-10. According to their responses, participants who fulfilled three or more of the diagnostic criteria were rated as having MPD. Mobile Phone Dependence was found in 31.33% of sample students. It was significantly associated with gender (p=0.003, OR=1.91, CI: 1.23-2.99), family type (p=0.0012), type of mobile phone used (p<0.001, OR=2.6, CI: 1.63-4.35), average time per day spent using mobile phone (p<0.001) and years of mobile phone usage (p =0.004, OR=2.4, CI: 1.31-4.55). Mobile Phone Dependence has been found to be an emerging public health problem. There is need to recognize and identify early the growing trends and negative consequences of inappropriate mobile phone use in young users so as to generate awareness, and plan educational and treatment interventions, if need be, so as to prevent a major public health concern.

Perceptual organization reconsidered in the light of the watercolor illusion: The problem of perception of holes and the object-hole effect.

PubMed

Pinna, Baingio; Tanca, Maria

2008-05-23

The watercolor illusion is a long-range color assimilation (coloration effect) imparting a figure-ground segregation (figural effect) across large enclosed areas (B. Pinna, 1987; B. Pinna, G. Brelstaff, & L. Spillmann, 2001; B. Pinna, L. Spillmann, & J. S. Werner, 2003; B. Pinna, J. S. Werner, & L. Spillmann, 2003). The watercolored figure has a very poorly reversible or univocal figure-ground segregation and strongly enhances the unilateral belongingness of the boundaries (E. Rubin, 1915), a principle stating that the boundaries belong only to the figure and not to the background. The figural effect determines grouping and figure-ground segregation more strongly than the well-known Gestalt principles. Under watercolor conditions both the figure and the background assume new properties becoming respectively bulging object and hole both with a 3-D volumetric appearance (object-hole effect). Our purposes were: (i) to demonstrate that the hole induced by the watercolor illusion has unique figural properties comparable to those of the object and not present in the background induced by the known figure-ground principles; (ii) to demonstrate a dissociation of the object-hole effect from the coloration one; (iii) to demonstrate that the object-hole effect depends on a new principle. This was psychophysically tested by weakening (ungrouping) the whole figural organization of the watercolor illusion, i.e. by imparting motion to only some components of a stimulus, while other components remain stationary. The results showed that (i) subjects perceived moving holes more strongly than moving figures or objects enlarging and shrinking. (ii) Paradoxically, moving holes appear more as figures than the bulging surfaces. (iii) When motion was imparted to components that while stationary were perceived as objects, their figurality is further enhanced (summation effect). (iv) When object-hole and coloration effects were dissociated no significant difference compared to illusory colored conditions was reported. Coloration can be considered independent from the object-hole effect of the watercolor illusion. The object-hole effect may depend on the "asymmetric luminance contrast principle" (B. Pinna, 2005).

Collection of holes in thick TlBr detectors at low temperature

NASA Astrophysics Data System (ADS)

Dönmez, Burçin; He, Zhong; Kim, Hadong; Cirignano, Leonard J.; Shah, Kanai S.

2012-10-01

A 3.5×3.5×4.6 mm3 thick TlBr detector with pixellated Au/Cr anodes made by Radiation Monitoring Devices Inc. was studied. The detector has a planar cathode and nine anode pixels surrounded by a guard ring. The pixel pitch is 1.0 mm. Digital pulse waveforms of preamplifier outputs were recorded using a multi-channel GaGe PCI digitizer board. Several experiments were carried out at -20 °C, with the detector under bias for over a month. An energy resolution of 1.7% FWHM at 662 keV was measured without any correction at -2400 V bias. Holes generated at all depths can be collected by the cathode at -2400 V bias which made depth correction using the cathode-to-anode ratio technique difficult since both charge carriers contribute to the signal. An energy resolution of 5.1% FWHM at 662 keV was obtained from the best pixel electrode without depth correction at +1000 V bias. In this positive bias case, the pixel electrode was actually collecting holes. A hole mobility-lifetime of 0.95×10-4 cm2/V has been estimated from measurement data.

Filters for Submillimeter Electromagnetic Waves

NASA Technical Reports Server (NTRS)

Berdahl, C. M.

1986-01-01

New manufacturing process produces filters strong, yet have small, precise dimensions and smooth surface finish essential for dichroic filtering at submillimeter wavelengths. Many filters, each one essentially wafer containing fine metal grid made at same time. Stacked square wires plated, fused, and etched to form arrays of holes. Grid of nickel and tin held in brass ring. Wall thickness, thickness of filter (hole depth) and lateral hole dimensions all depend upon operating frequency and filter characteristics.

Renyi Entropies of a Black Hole

NASA Astrophysics Data System (ADS)

Bialas, A.; Czyz, W.

2008-08-01

The Renyi entropies, Hl, of Hawking radiation contained in a thin shell surrounding the black hole are evaluated. When the width of the shell is adjusted to the energy content corresponding to the mass defect, the Bekenstein-Hawking formula for the Shannon (S=H1) entropy of a black hole is reproduced. This result does not depend on the distance of the shell from the horizon. The Renyi entropies of higher order, however, are sensitive to it.

Cosmic black-hole hair growth and quasar OJ287

DOE Office of Scientific and Technical Information (OSTI.GOV)

Horbatsch, M.W.; Burgess, C.P., E-mail: horbatm@mcmaster.ca, E-mail: cburgess@perimeterinstitute.ca

An old result (astro-ph/9905303) by Jacobson implies that a black hole with Schwarzschild radius r{sub s} acquires scalar hair, Q∝r{sub s}{sup 2}μ, when the (canonically normalized) scalar field in question is slowly time-dependent far from the black hole, ∂{sub t}φ ≅ μM{sub p} with μr{sub s} << 1 time-independent. Such a time dependence could arise in scalar-tensor theories either from cosmological evolution, or due to the slow motion of the black hole within an asymptotic spatial gradient in the scalar field. Most remarkably, the amount of scalar hair so induced is independent of the strength with which the scalar couplesmore » to matter. We argue that Jacobson's Miracle Hair-Growth Formula{sup ©} implies, in particular, that an orbiting pair of black holes can radiate dipole radiation, provided only that the two black holes have different masses. Quasar OJ287, situated at redshift z ≅ 0.306, has been argued to be a double black-hole binary system of this type, whose orbital decay recently has been indirectly measured and found to agree with the predictions of General Relativity to within 6%. We argue that the absence of observable scalar dipole radiation in this system yields the remarkable bound |μ| < (16 days){sup −1} on the instantaneous time derivative at this redshift (as opposed to constraining an average field difference, Δφ, over cosmological times), provided only that the scalar is light enough to be radiated — i.e. m∼<10{sup −23} eV — independent of how the scalar couples to matter. This can also be interpreted as constraining (in a more model-dependent way) the binary's motion relative to any spatial variation of the scalar field within its immediate vicinity within its host galaxy.« less

On the motion of hairy black holes in Einstein-Maxwell-dilaton theories

NASA Astrophysics Data System (ADS)

Julié, Félix-Louis

2018-01-01

Starting from the static, spherically symmetric black hole solutions in massless Einstein-Maxwell-dilaton (EMD) theories, we build a "skeleton" action, that is, we phenomenologically replace black holes by an appropriate effective point particle action, which is well suited to the formal treatment of the many-body problem in EMD theories. We find that, depending crucially on the value of their scalar cosmological environment, black holes can undergo steep "scalarization" transitions, inducing large deviations to the general relativistic two-body dynamics, as shown, for example, when computing the first post-Keplerian Lagrangian of EMD theories.

Non-renormalization for non-supersymmetric black holes

DOE PAGES

Charles, Anthony M.; Larsen, Finn; Mayerson, Daniel R.

2017-08-11

We analyze large logarithmic corrections to 4D black hole entropy and relate them to the Weyl anomaly. We use duality to show that counter-terms in EinsteinMaxwell theory can be expressed in terms of geometry alone, with no dependence on matter terms. We analyze the two known N = 2 supersymmetric invariants for various non-supersymmetric black holes and find that both reduce to the Euler invariant. The c-anomaly therefore vanishes in these theories and the coefficient of the large logarithms becomes topological. It is therefore independent of continuous black hole parameters, such as the mass, even far from extremality.

Non-renormalization for non-supersymmetric black holes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Charles, Anthony M.; Larsen, Finn; Mayerson, Daniel R.

We analyze large logarithmic corrections to 4D black hole entropy and relate them to the Weyl anomaly. We use duality to show that counter-terms in EinsteinMaxwell theory can be expressed in terms of geometry alone, with no dependence on matter terms. We analyze the two known N = 2 supersymmetric invariants for various non-supersymmetric black holes and find that both reduce to the Euler invariant. The c-anomaly therefore vanishes in these theories and the coefficient of the large logarithms becomes topological. It is therefore independent of continuous black hole parameters, such as the mass, even far from extremality.

Development of a thermally-assisted piercing (TAP) process for introducing holes into thermoplastic composites

NASA Astrophysics Data System (ADS)

Brown, Nicholas W. A.

Composite parts can be manufactured to near-net shape with minimum wastage of material; however, there is almost always a need for further machining. The most common post-manufacture machining operations for composite materials are to create holes for assembly. This thesis presents and discusses a thermally-assisted piercing process that can be used as a technique for introducing holes into thermoplastic composites. The thermally-assisted piercing process heats up, and locally melts, thermoplastic composites to allow material to be displaced around a hole, rather than cutting them out from the structure. This investigation was concerned with how the variation of piercing process parameters (such as the size of the heated area, the temperature of the laminate prior to piercing and the geometry of the piercing spike) changed the material microstructure within carbon fibre/Polyetheretherketone (PEEK) laminates. The variation of process parameters was found to significantly affect the formation of resin rich regions, voids and the fibre volume fraction in the material surrounding the hole. Mechanical testing (using open-hole tension, open-hole compression, plain-pin bearing and bolted bearing tests) showed that the microstructural features created during piercing were having significant influence over the resulting mechanical performance of specimens. By optimising the process parameters strength improvements of up to 11% and 21% were found for pierced specimens when compared with drilled specimens for open-hole tension and compression loading, respectively. For plain-pin and bolted bearing tests, maximum strengths of 77% and 85%, respectively, were achieved when compared with drilled holes. Improvements in first failure force (by 10%) and the stress at 4% hole elongation (by 18%), however, were measured for the bolted bearing tests when compared to drilled specimens. The overall performance of pierced specimens in an industrially relevant application ultimately depends on the properties required for that specific scenario. The results within this thesis show that the piercing technique could be used as a direct replacement to drilling depending on this application.

Entropy bound of horizons for accelerating, rotating and charged Plebanski–Demianski black hole

DOE Office of Scientific and Technical Information (OSTI.GOV)

Debnath, Ujjal, E-mail: ujjaldebnath@yahoo.com

We first review the accelerating, rotating and charged Plebanski–Demianski (PD) black hole, which includes the Kerr–Newman rotating black hole and the Taub-NUT spacetime. The main feature of this black hole is that it has 4 horizons like event horizon, Cauchy horizon and two accelerating horizons. In the non-extremal case, the surface area, entropy, surface gravity, temperature, angular velocity, Komar energy and irreducible mass on the event horizon and Cauchy horizon are presented for PD black hole. The entropy product, temperature product, Komar energy product and irreducible mass product have been found for event horizon and Cauchy horizon. Also their sumsmore » are found for both horizons. All these relations are dependent on the mass of the PD black hole and other parameters. So all the products are not universal for PD black hole. The entropy and area bounds for two horizons have been investigated. Also we found the Christodoulou–Ruffini mass for extremal PD black hole. Finally, using first law of thermodynamics, we also found the Smarr relation for PD black hole.« less