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Applied Electric Field (applied + electric_field)
Selected AbstractsNumerical studies of electrokinetic control of DNA concentration in a closed-end microchannelELECTROPHORESIS, Issue 5 2010Yasaman Daghighi Abstract A major challenge in lab-on-a-chip devices is how to concentrate sample molecules from a dilute solution, which is critical to the effectiveness and the detection limit of on-chip bio-chemical reactions. A numerical study of sample concentration control by electrokinetic microfluidic means in a closed-end microchannel is presented in this paper. The present method provides a simple and efficient way of concentration control by using electrokinetic trapping of a charged species of interest, controlling liquid flow and separating different sample molecules in the microchannel. The electrokinetic-concentration process and the controlled transport of the sample molecules are numerically studied. In this system, in addition to the electroosmotic flow and the electrophoresis, the closed-end of the chamber causes velocity variation at both ends of the channel and induces a pressure gradient and the associated fluid movement in the channel. The combined effects determine the final concentration field of the sample molecules. The influences of a number of parameters such as the channel dimensions, electrode size and the applied electric field are investigated. [source] Electrophoresis of a charge-regulated toroid normal to a large diskELECTROPHORESIS, Issue 2 2008Jyh-Ping Hsu Abstract The electrophoresis of a charge-regulated toroid (doughnut-shaped entity) normal to a large disk is investigated under the conditions of low surface potential and weak applied electric field. The system considered is capable of modeling the electrophoretic behavior of various types of biocolloids such as bacterial DNA, plasmid DNA, and anabaenopsis near a perfectly conducting planar wall. The influences of the size of the toroid, the separation distance between the toroid and the disk, the charged conditions on the surfaces of the toroid and the disk, and the thickness of electric double layer on the electrophoretic mobility of the toroid are discussed. The results of numerical simulation reveal that under typical conditions the electrophoretic behavior of the toroid can be different from that of an integrated entity. For instance, if the surface of the toroid carries both acidic and basic functional groups, its mobility may have a local maximum as the thickness of double layer varies. We show that the electrophoretic behavior of the toroid is different, both qualitatively and quantitatively, from that of the corresponding integrated particle (particle without hole). [source] Temperature gradient focusing in a PDMS/glass hybrid microfluidic chipELECTROPHORESIS, Issue 24 2007Takuya Matsui Abstract This paper reports the application of temperature gradient focusing (TGF) in a PDMS/glass hybrid microfluidic chip. With TGF, by the combination of a temperature gradient along a microchannel, an applied electric field, and a buffer with a temperature-dependent ionic strength, analytes are focused by balancing their electrophoretic velocities against the bulk velocity of the buffer containing the analytes. In this work, Oregon Green 488 carboxylic acid was concentrated approximately 30 times as high as the initial concentration in 45,s at moderate electric strength of 70,V/cm and a temperature gradient of 55°C across the PDMS/glass hybrid microfluidic chip with a 1,cm long capillary. [source] A novel microfluidic mixer utilizing electrokinetic driving forces under low switching frequencyELECTROPHORESIS, Issue 9 2005Lung-Ming Fu Abstract This paper presents a novel technique in which low-frequency periodic electrokinetic driving forces are utilized to mix electrolytic fluid samples rapidly and efficiently in a double-T-form microfluidic mixer. Without using any additional equipment to induce flow perturbations, only a single high-voltage power source is required for simultaneously driving and mixing the sample fluids which results in a simple and low-cost system for the mixing purpose. The effectiveness of the mixer as a function of the applied electric field and the periodic switching frequency is characterized by the intensity distribution calculated downstream from the mixing zone. The present numerical and experimental results confirm that the proposed double-T-form micromixer has excellent mixing capabilities. The mixing efficiency can be as high as 95% within a mixing length of 1000 ,m downstream from the secondary T-junction when a 100 V/cm driving electric field strength and a 2 Hz periodic switching frequency are applied. The results reveal that the optimal switching frequency depends upon the magnitude of the main applied electrical field. The rapid double-T-form microfluidic mixer using the periodic driving voltage switching model proposed in this study has considerable potential for use in lab-on-a-chip systems. [source] High-efficiency peptide analysis on monolithic multimode capillary columns: Pressure-assisted capillary electrochromatography/capillary electrophoresis coupled to UV and electrospray ionization-mass spectrometryELECTROPHORESIS, Issue 21 2003Alexander R. Ivanov Abstract High-efficiency peptide analysis using multimode pressure-assisted capillary electrochromatography/capillary electrophoresis (pCEC/pCE) monolithic polymeric columns and the separation of model peptide mixtures and protein digests by isocratic and gradient elution under an applied electric field with UV and electrospray ionization-mass spectrometry (ESI-MS) detection is demonstrated. Capillary multipurpose columns were prepared in silanized fused-silica capillaries of 50, 75, and 100 ,m inner diameters by thermally induced in situ copolymerization of methacrylic monomers in the presence of n -propanol and formamide as porogens and azobisisobutyronitrile as initiator. N -Ethylbutylamine was used to modify the chromatographic surface of the monolith from neutral to cationic. Monolithic columns were termed as multipurpose or multimode columns because they showed mixed modes of separation mechanisms under different conditions. Anion-exchange separation ability in the liquid chromatography (LC) mode can be determined by the cationic chromatographic surface of the monolith. At acidic pH and high voltage across the column, the monolithic stationary phase provided conditions for predominantly capillary electrophoretic migration of peptides. At basic pH and electric field across the column, enhanced chromatographic retention of peptides on monolithic capillary column made CEC mechanisms of migration responsible for separation. The role of pressure, ionic strength, pH, and organic content of the mobile phase on chromatographic performance was investigated. High efficiencies (exceeding 300,000 plates/m) of the monolithic columns for peptide separations are shown using volatile and nonvolatile, acidic and basic buffers. Good reproducibility and robustness of isocratic and gradient elution pressure-assisted CEC/CE separations were achieved for both UV and ESI-MS detection. Manipulation of the electric field and gradient conditions allowed high-throughput analysis of complex peptide mixtures. A simple design of sheathless electrospray emitter provided effective and robust low dead volume interfacing of monolithic multimode columns with ESI-MS. Gradient elution pressure-assisted mixed-mode separation CE/CEC-ESI-MS mass fingerprinting and data-dependent pCE/pCEC-ESI-MS/MS analysis of a bovine serum albumin (BSA) tryptic digest in less than 5 min yielding high sequence coverage (73%) demonstrated the potential of the method. [source] The Effect of Nanoparticle Shape on the Photocarrier Dynamics and Photovoltaic Device Performance of Poly(3-hexylthiophene):CdSe Nanoparticle Bulk Heterojunction Solar CellsADVANCED FUNCTIONAL MATERIALS, Issue 16 2010Smita Dayal Abstract The charge separation and transport dynamics in CdSe nanoparticle:poly(3-hexylthiophene) (P3HT) blends are reported as a function of the shape of the CdSe-nanoparticle electron acceptor (dot, rod, and tetrapod). For optimization of organic photovoltaic device performance it is crucial to understand the role of various nanostructures in the generation and transport of charge carriers. The sample processing conditions are carefully controlled to eliminate any processing-related effects on the carrier generation and on device performance with the aim of keeping the conjugated polymer phase constant and only varying the shape of the inorganic nanoparticle acceptor phase. The electrodeless, flash photolysis time-resolved microwave conductivity (FP-TRMC) technique is used and the results are compared to the efficiency of photovoltaic devices that incorporate the same active layer. It is observed that in nanorods and tetrapods blended with P3HT, the high aspect ratios provide a pathway for the electrons to move away from the dissociation site even in the absence of an applied electric field, resulting in enhanced carrier lifetimes that correlate to increased efficiencies in devices. The processing conditions that yield optimum performance in high aspect ratio CdSe nanoparticles blended with P3HT result in poorly performing quantum dot CdSe:P3HT devices, indicating that the latter devices are inherently limited by the absence of the dimensionality that allows for efficient, prolonged charge separation at the polymer:CdSe interface. [source] Hysteresis in Conjugated Polymer Thin Film Transistors Generated by Chain RelaxationADVANCED FUNCTIONAL MATERIALS, Issue 6 2010Neng-Jye Yang Abstract The hysteresis phenomenon in a polymer thin film transistor (PTFT) with either poly(3-hexylthiophene), poly(3-dodecylthiophene), or poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene vinylene] is investigated over a wide range of temperatures, and found to be generated by the delay in main chain ring distortion with an applied electric field. In the temperature range for side chain relaxation, main chain motion induced by side chain motion already starts such that polarization of the main chain by the applied electric field is permitted but in a limited extent and is not in phase with the variation in electric field. In the main chain relaxation temperature range, the extent of segmental motion increases, which leads to the main chain being more realignable by the applied electric field and thus a reduced hysteresis. After main chain relaxation is complete, the ring can distort more freely and chain segments are able to realign in phase with the applied electric field, which leads to a leveling off of the hysteresis. This investigation shows for first time that the chain relaxation in conjugated polymers is the origin of the hysteresis in PTFT devices. [source] Magnetoelectric Effects in Complex Oxides with Competing Ground StatesADVANCED MATERIALS, Issue 34 2009Hajo J. A. Molegraaf Direct, charge-mediated magnetoelectric coupling is demonstrated in a heterogeneous multiferroic that takes advantage of the sensitivity of a strongly correlated magnetic system to competing electronic ground states. Using magneto-optic Kerr effect magnetometry, we observe large magnetoelectric coupling in ferroelectric/lanthanum manganite heterostructures, resulting in control of the magnetic state by means of an applied electric field, as illustrated in the figure. [source] The Inlaid Al2O3 Tunnel Switch for Ultrathin Ferroelectric FilmsADVANCED MATERIALS, Issue 28 2009An Quan Jiang Ferroelectric switching in ultrathin Al2O3/PZT bilayers is studied and used to modulate the applied electric field, allowing the development of novel applications of the combined dielectric tunnel switch/ferroelectric functional layer that can assist in the development of completely new types of electronic, electromechanical, and electrochemical devices. [source] Electric-Field-Driven Assembly of Oriented Molecular-Sieve Films,ADVANCED MATERIALS, Issue 21 2004J.-C. Lin Thin films of rod-shaped molecular-sieve crystals have been deposited by sedimentation with preferred orientation under an applied electric field. When the pores of the crystal were filled with dye, the film exhibited polarization-angle-dependent light absorption due to the preferred pore direction. [source] Charge transport in stacking metal and metal-free phthalocyanine iodides.JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 13 2009Effects of packing, central metals, core modification, dopants, external electric field, substitutions Abstract The charge-transport properties of the one-dimensional stacking metal phthalocyanine iodides (M(Pc)I, M = Fe, Co, Ni, Cu) and metal-free phthalocyanine iodide (H2(Pc)I) have been theoretically investigated. On the basis of the tight-binding approximation and two-state theory, both the site-energy corrected energy splitting in dimer and Fock-matrix-based methods are used to calculate the transfer integral. The intermolecular motions, including interplanar translation, rotation, slip, and tilt, exert remarkable impacts on the transfer integral. The order/disorder of the dopant stack and the long-range electrostatic interactions are also demonstrated to be crucial factors for modulation of charge-transport properties. The transfer integral undergoes slight changes under an applied electric field along the stacking direction in the range of 106 , 107 V cm,1. The change of central metals in MPc has little effect on the transfer integrals, but significantly affects the reorganization energies. The extension of the ,-conjugation in macrocyclic ligand brings about considerable influence on the transfer integrals. Peripheral substitutions by animo, hydroxyl, and methyl lead to deviations from planarity of macromolecular rings, and hence affect the valence bands significantly. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009 [source] Evaluation of electroosmotic drag coefficient of water in hydrated sodium perfluorosulfonate electrolyte polymerJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 9 2009Liuming Yan Abstract The electroosmotic drag coefficient of water molecules in hydrated sodium perfluorosulfonate electrolyte polymer is evaluated on the basis of the velocity distribution functions of the sodium cations and water molecules with an electric field applied using molecular dynamics simulations. The simulation results indicate that both velocity distribution functions of water molecules and of sodium cations agree well with the classic Maxwellian velocity distribution functions when there is no electric field applied. If an electric field is applied, the distribution functions of velocity component in directions perpendicular to the applied electric field still agree with the Maxwellian velocity distribution functions but with different temperature parameters. In the direction of the applied electric field, the electric drag causes the velocity distribution function to deviate from the Maxwellian velocity distribution function; however, to obey the peak shifted Maxwellian distribution function. The peak shifting velocities coincide with the average transport velocities induced by the electric field, and could be applied to the evaluation of the electroosmotic drag coefficient of water. By evaluation of the transport velocities of water molecules in the first coordination shells of sodium cations, sulfonate anion groups, and in the bulk, it is clearly shown that the water molecules in the first coordination shell of sodium cations are the major contribution to the electroosmotic drag and momentum transfer from water molecules within the first coordination shell to the other water molecules also contributes to the electroosmotic drag. © 2008 Wiley Periodicals, Inc. J Comput Chem 2009 [source] In Situ Transmission Electron Microscopy of Electric Field-Triggered Reversible Domain Formation in Bi-Based Lead-Free PiezoceramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2010Jens Kling A lead-free piezoelectric 0.91(Bi1/2Na1/2)TiO3,0.06BaTiO3,0.03(K0.5Na0.5)NbO3 ceramic with high strain was examined in situ under an applied electric field using the transmission electron microscope. No domain structure is observed without an electric field, but an alternating electric field leads to the reversible formation of a lamellar domain structure. Correlations to polarization and strain hysteresis loop measurements indicate an electric field-induced phase transition from a nonpolar to a ferroelectric state and vice versa. [source] Strength Properties of Poled Lead Zirconate Titanate Subjected to Biaxial Flexural Loading in High Electric FieldJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2010Hong Wang The mechanical strength of poled lead zirconate titanate (PZT) has been studied using ball-on-ring (BoR) biaxial flexure tests with a high electric field applied concurrently. Both the as-received and the aged PZT specimens were tested. The Weibull plot and a 95% confidence ratio ring were used to characterize the responses of mechanical strength under various electric loading conditions. A fractographical study has been conducted at the same time, and the fracture origins or strength-limiting flaws of tested PZT specimens have been identified and characterized accordingly. The fracture toughness was further estimated to correlate with the obtained fracture stresses and flaws. It has been observed that electric field affects the mechanical strength of poled PZT, and the degree of the effect depends on the sign and magnitude of the applied electric field. Within the examined electric field range of ,3 to +3 times the coercive field, an increasing electric field resulted in a rapid strength decrease and a sharp increase with the turning point around the negative coercive field. Surface-located volume-distributed flaws were identified to be strength limiting for this PZT material. Variations of the mechanical strength with the electric field were believed to be related to the domain switching and amount of switchable domains. An aging effect on the mechanical strength of poled PZT could be significant, especially in the OC condition. These results and observations have the potential to serve probabilistic reliability analysis and design optimization of multilayer PZT piezo actuators. [source] Subcoercive Cyclic Electrical Loading of Lead Zirconate Titanate Ceramics II: Time-Resolved X-Ray DiffractionJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2009Abhijit Pramanick Structural changes such as non-180° domain wall motion and lattice strains in Pb(Zr,Ti)O3 ceramics are measured during the application of subcoercive cyclic electric fields using time-resolved high-energy X-ray diffraction with a stroboscopic data collection technique. The contributions to the electric-field-induced strains from non-180° domain wall motion and lattice distortions are determined as a function of material composition and type of dopant. For the different compositions studied, the largest strains due to non-180° domain wall motion are measured for La-doped tetragonal ceramics with a composition close to the morphotropic phase boundary. It is further observed that strain contributions from both non-180° domain wall motion and lattice distortions can be nonlinear with respect to the applied electric field. The correlation between the electric-field-induced structural changes and the macroscopic piezoelectric properties is discussed. [source] High Tunability of Highly (100)-Oriented Lead Zirconate Titanium Thin FilmsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2008Jiagang Wu Highly (100)-oriented Pb(Zr0.20Ti0.80)O3 (PZT) thin films for electrically tunable applications were prepared on Pt(111)/Ti/SiO2/Si(100) substrates by RF magnetron sputtering with a PbOx buffer layer. The dielectric properties of PZT films were investigated. These results indicated that the applied electric field and measured frequency strongly affected the films' tunability. The PZT films exhibited good dielectric tunability (69.3%) as measured at 1 kHz and 18 V. The related physics mechanism for enhanced tunability was also discussed. The enhanced tunability is attributed to the (100) orientation of PZT films and is a result of the biaxial tensile stress making the polar axis oriented in plane. [source] Polarization effects and phase equilibria in high-energy-density polyvinylidene-fluoride-based polymersACTA CRYSTALLOGRAPHICA SECTION A, Issue 5 2010V. Ranjan Using first-principles calculations, the phase diagrams of polyvinylidene fluoride (PVDF) and its copolymers under an applied electric field are studied and phase transitions between their nonpolar , and polar , phases are discussed. The results show that the degree of copolymerization is a crucial parameter controlling the structural phase transition. In particular, for tetrafluoroethylene (TeFE) concentration above 12%, PVDF,TeFE is stabilized in the , phase, whereas the , phase is stable for lower concentrations. As larger electric fields are applied, domains with smaller concentrations ( 12%) undergo a transition from the , to the , phase until a breakdown field of ~600,MV,m,1 is reached. These structural phase transitions can be exploited for efficient storage of electrical energy. [source] Binding energy of relativistic hydrogenic impurities in cylindrical quantum well wires under an applied electric fieldPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 15 2004A. I. Me Abstract The ground state binding energy of a hydrogenic impurity in infinite cylindrical GaAs quantum well wires subjected to an external electric field applied perpendicular to the symmetry axis of the wire is studied within the relativistic approach. A rapid decrease of the binding energy for different intensities of the electric field with increasing wire radius is predicted. Furthermore, the relativistic effects are emphasised by comparing them with the non-relativistic results. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Laplace DLTS of molecular beam epitaxy GaAs grown on (100) and (211)B substratesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2009R. H. Mari Abstract Deep Level Transient Spectroscopy (DLTS) and Laplace DLTS (LDLTS) techniques have been employed to study defects in n-type GaAs grown by MBE on (100) and (211)B GaAs planes. The DLTS spectra were different for the two GaAs substrate orientations. Five and four defect states are found in samples grown on (100) and (211)B GaAs planes, respectively with activation energies ranging from 0.054 eV to 0.570 eV. For all of the traps observed in our samples we obtained small activation energies as compared to the previous data published in literature on n-GaAs samples grown by MBE. This can be explained by the fact that the emission of the carriers depends on the applied electric field and temperature dependence of the carrier concentration. These two phenomena seem to explain the small trap energies seen in our samples. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Excited states and spontaneous transition lifetimes of donor impurities in quantum dotsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2007G. Murillo Abstract We calculate the 2p,1s-like transition energy and the spontaneous lifetime of an on-center shallow donor impurity in a spherical parabolic GaAs-(Ga,Al)As quantum dot (PQD) as a function of the radius of the structure and the strength of an applied electric field. In our calculations we use a variational method, within the effective mass and dipolar approximations. We find that the spontaneous lifetimes increase with the radius of the PQD and the applied electric field. In this direction our results revel that the electric field can be used to suppress the electron-phonon interaction driving to the increasing of the 2p-1s spontaneous life-time, showing the feasibility of using impurity states to be used in quantum computing developments. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] High-field electron transport in AlGaN/GaN heterostructuresPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005J. M. Barker Abstract Experimental studies have been performed on the velocity-field characteristics of AlGaN/GaN heterostructures. A pulsed voltage input in combination with a four-point measurement was used in a 50 , environment to determine the drift velocity of electrons in the two-dimensional electron gas as a function of the applied electric field. These measurements show an apparent saturation velocity near 3.1 × 107 cm/s, at a field of 140 kV/cm. A comparison of these studies shows that the experimental velocities are close to previously published simulations based upon Monte Carlo techniques. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Investigations of the bond-selective response in a piezoelectric Li2SO4·H2O crystal to an applied external electric fieldACTA CRYSTALLOGRAPHICA SECTION A, Issue 4 2009O. Schmidt Piezoelectric lithium sulfate monohydrate, Li2SO4·H2O, was analyzed with respect to the relationship between the static structural properties of the crystal and its response to an external electric field. The static electron density was determined via standard low-temperature X-ray data collection at 90,(5) K using an Enraf,Nonius CAD-4 diffractometer, Mo K, radiation and multipole model refinement. Then a synchrotron-radiation experiment using the D3 beamline at HASYLAB was conducted in order to investigate the structural deformations in Li2SO4·H2O caused by an applied external electric field. In particular, the shifts of Bragg-peak positions induced by the electric field were measured and the piezoelectric constants d211, d222, d233 and d213 of Li2SO4·H2O were obtained from the shifts. With the same experimental setup the variations of more than 100 Bragg intensities were measured under an applied electric field. The data were used to refine the corresponding displacements of individual atoms within the unit cell. The distortions of the cation,anion bond lengths in the LiO4, LiO3(H2O) and SO4 tetrahedra were evaluated and then analyzed in terms of the electron-density-related properties of the Li,O and S,O bonds. The two lithium structural units were found to be strongly deformed by the applied electric field, while the SO4 tetrahedron changed less. This is in agreement with the low bond strength of the Li,O bonds. [source] Simulation of polycrystalline ferroelectrics based on discrete orientation distribution functionsPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2005Ingo Kurzhöfer Ferroelectric materials exhibit a spontaneous polarization, which can be reversed by an applied electric field of sufficient magnitude. The resulting nonlinearities are expressed by characteristic dielectric and butterfly hysteresis loops. These effects are correlated to the structure of the crystal and especially to the axis of spontaneous polarization in case of single crystals. We start with a representative meso scale, where the domains consist of unit cells with equal spontaneous polarization. Each domain is modeled within a coordinate invariant formulation for an assumed transversely isotropic material as presented in [10], in this context see also [8]. In this investigation we obtain the macroscopic polycrystalline quantities via a simple homogenization procedure, where discrete orientation distribution functions are used to approximate the different domains. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A review of charge transport and recombination in polymer/fullerene organic solar cellsPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 8 2007A. Pivrikas Abstract The charge carrier transport and recombination in two types of thermally treated bulk-heterojunction solar cells is reviewed: in regioregular poly(3-hexylthiophene) (RRP3HT) mixed with 1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]-methanofullerene (PCBM) and in the blend of poly[2-methoxy-5-(3,7-dimethyloctyloxy)-phenylene vinylene] (MDMO-PPV) mixed with PCBM. The charge carrier mobility and bimolecular recombination coefficient have been comparatively studied by using various techniques including Time-of-Flight (ToF), Charge Extraction by Linearly Increasing Voltage (CELIV), Double Injection (DI) transients, Current,Voltage (I,V) technique. It was found that the carrier mobility is at least an order of magnitude higher in RRP3HT/PCBM blends compared to MDMO-PPV/PCBM. Moreover, all used techniques demonstrate a heavily reduced charge carrier recombination in RRP3HT/PCBM films compared to Langevin-type carrier bimolecular recombination in MDMO-PPV/PCBM blends. As a result of long carrier lifetimes the formation of high carrier concentration plasma in RRP3HT/PCBM blends is demonstrated and plasma extraction methods were used to directly estimate the charge carrier mobility and bimolecular recombination coefficients simultaneously. A weak dependence of bimolecular recombination coefficient on the applied electric field and temperature demonstrates that carrier recombination is not dominated by charge carrier mobility (Langevin-type recombination) in RRP3HT/PCBM blends. Furthermore, we found from CELIV techniques that electron mobility in RRP3HT/PCBM blends is independent on relaxation time in the experimental time window (approx. hundreds of microseconds to tens of milliseconds). This reduced carrier bimolecular recombination in RRP3HT/PCBM blends implies that the much longer carrier lifetimes can be reached at the same concentrations which finally results in higher photocurrent and larger power conversion efficiency of RRP3HT/PCBM solar cells. Copyright © 2007 John Wiley & Sons, Ltd. [source] Studies of electric field induced structural and electron-density modifications by X-ray diffractionACTA CRYSTALLOGRAPHICA SECTION A, Issue 5 2004Niels K. Hansen During the last two decades, a number of X-ray diffraction studies on the response of a crystal to an applied electric field have been carried out. In a few cases, the electron-density polarizations could be determined. The analysis of the induced variations of the structural properties on an atomic scale are of prime importance in order to acquire a better understanding of physical properties like the piezoelectric and dielectric properties of crystals. This article reviews the experimental technique used and the modelling methods of the Bragg scattering variations induced by the field. Some noteworthy results are presented that illustrate the possibility of detecting subtle structural changes, for example as small as 0.1° in bond angles arising from applying a strong field, 10,40,kV,cm,1, as well as the pitfalls of such an approach for clarifying the relevance of the structural properties in physical mechanisms. [source] In situ investigation of the non-linear optical crystal rubidium titanyl arsenate, RbTiOAsO4, under applied electric field using X-ray imagingJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3 2007P. A. Thomas Recent work on the non-linear optical single-crystal rubidium titanyl arsenate (RbTiOAsO4, RTA) has shown that it exhibits behaviour consistent with a ferroelectric semiconductor under large applied electric fields, with the development of a non-uniform field in the near-surface region. To confirm aspects of the proposed model, the behaviour of 001 slices of initially single-domain RTA, patterned with periodic Ag electrodes of spacing 38,µm, as for periodic poling in non-linear optics, were investigated using synchrotron X-ray section topography with the electric field applied in situ while under X-ray illumination at the ID19 topography beamline of the ESRF, Grenoble. The results of white-beam section topography as both a function of crystal to film distance, and under DC voltage are reported, confirming that there is a bending of the planes in the near-surface region. The strain in the near-surface region was examined directly using high-resolution monochromatic X-ray section topography. This revealed an extensive strain of 3,(±1) × 10,4 at 1,kV, indicating that the electrostrictive coefficient, ,3333, in RTA is positive in sign. [source] | |||||||||||||||||||