bluuebunny/crossref_metadata_2025_split huggingface dataset:
Excitons in coupled quantum dots: hydrostatic pressure and electric field effects
Authors: López S. Y. , Porras‐Montenegro N. , Duque C. A. 
Published: December 2008

AbstractThe variational procedure, in the effective‐mass and parabolic‐band approximations, is used in order to investigate the effects of hydrostatic pressure and in‐growth direction applied electric field on the exciton states in vertically GaAs–Ga1–x Alx As coupled quantum dots. We have found that when the symmetrical lengths and radius of each QD are comparable with the Bohr radius of the GaAs material and for a finite value of the applied electric field, the binding energy always diminishes with the length of the central barrier because the two carriers in the exciton are localized in two well defined different regions of the system. However, for the zero electric field the binding energy decreases with the barrier width from the limit value corresponding to the exciton confined in one quantum dot of volume V up to reach a minimum and then increases to a value which corresponds to that of the exciton confined in an isolated quantum dot of volume V /2. Additionally, we have found that the applied electric field caninduce that the lowest structure in the photoluminescence‐peak energy transitions be associated to spatially indirect excitons, situation which in the zero limit of the electric field and independent of the dimensions of the two coupled dots, always corresponds to spatially direct excitons. The main hydrostatic pressure effect reveals an increasing in the exciton binding energy, without modifying the direct or indirect exciton regime, and a well defined rigid blue‐shift in the photoluminescence peak energy transitions in the presence of an applied electric field. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optical properties of di‐octyl substituted polyfluorene under hydrostatic pressure
Authors: Paudel K. , Arif M. , Chandrasekhar M. , Guha S. 
Published: December 2008

AbstractAlmost all polyfluorene (PF) derivatives utilize solubilizing side chain substituents for tailoring their optical and electronic properties. Side chain substitution, in addition to improving the solution processing and film forming characteristics, confers new functionality and dictates the backbone structure of polymers. The backbone conformation in di‐octyl substituted PF (PF8) is strongly dependent upon the conformation of the alkyl side chain. In this paper we present photoluminescence and Raman scattering studies of bulk PF8 as a function of hydrostatic pressure. These results are further contrasted with the optical studies of a branched side group substituted PF under hydrostatic pressure. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Luminescent detection of Cu(II) ions in aqueous solution using CdSe and CdSe‐ZnS quantum dots functionalised with mercaptosuccinic acid
Authors: Callan John F. , Mulrooney Ray C. 
Published: December 2008

AbstractCdSe (core) and CdSe‐ZnS (core‐shell) Quantum Dots (QD's) surface functionalised with mercaptosuccinic acid ligands were prepared. The conjugates were screened against a variety of common metal ions in aqueous solution and selectivity was established for Cu(II) ions based on an “On‐Off” change in fluorescence intensity. The presence of the ZnS shell was found to have a significant effect on both the sensitivity and the range of Cu2+ induced quenching. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Few‐electron semiconductor quantum dots in magnetic field
Authors: Ciftja Orion 
Published: December 2008

AbstractUsually, semiconductor quantum dots represent a twodimensional nanoscale system with few electrons confined in a semiconductor host crystal. Properties of fewelectron quantum dots in the weak magnetic regime are explained well through single‐electron theory concepts. However, as the strength of the external magnetic field increases the confined electrons in the quantum dot start to manifest collective quantum behavior as seen in the integer and fractional quantum Hall effect regime.In the limit of strong magnetic field, we see the confined electronic states in a semiconductor quantum dot transforming into Laughlin‐like states that describe strongly correlated electronic systems in the quantum Hall regime. While this is expected, our calculations further indicate that even a classical model of confined electrons provides quite an accurate presentation, suggesting that in this regime electrons stabilize in relatively rigid geometric structures. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Transport mechanism in the quantum well embedded with quantum dots
Authors: Kannan E. S. , Kim Gil‐Ho , Farrer I. , Ritchie D. A. 
Published: December 2008

AbstractElectron transport in single and double quantum well system embedded with InAs quantum dots is investigated by carrying out magnetoresistance measurements at 1.2 K. At low carrier densities, the electrons are strongly localized due to disorder and undergo magnetic field induced insulator to quantum Hall liquid transitions characterized by temperature independent crossing points. At higher carrier densities no such magnetic field induced transition are observed. The potential induced by the electrons in the quantum dots were found to enhance the scattering between the edge states resulting in the substantial reduction of the width of the Hall plateau in the single quantum well system. In the double quantum well system, instead of plateaus abrupt increase in the Hall resistance is observed at integer filling factors. On sweeping the gate bias at fixed magnetic field, hysteresis effect was observed in the double quantum well system due to the charge trapping in the defect levels. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Emission spectrum of a quantum dot embedded in a nanocavity
Authors: Tarel Guillaume , Savona Vincenzo 
Published: December 2008

AbstractWe model the emission spectrum of a quantum dot embedded in a (e.g. photonic crystal) nanocavity, using a semi‐classical approach to describe the matter‐field interaction. We start from the simple model of a quantum dot as a two‐level system, and recover the result expected from cavity quantum electrodynamics. Then, we study the influence of electron‐acoustic‐phonons interaction. We show that the surrounding semiconductor plays an essential role in the emission spectrum in strong coupling. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth behaviour of InGaN/GaN self‐assembled quantum dots with different growth conditions in horizontal MOCVD
Authors: Jung Woo‐Gwang , Jang Jae‐Min , Choi Seung‐Kyu , Kim Jin‐Yeol 
Published: December 2008

AbstractInGaN/GaN self‐assembled quantum dots (QDs) were grown on (0001) sapphire substrates by low pressure metalorganic chemical vapor deposition. The growth behavior of the InGaN/GaN QDs was examined under different experimental conditions. The InGaN/GaN QDs were formed in Stranski‐Krastanow growth mode by the continuous supply of metalorganic (MO) sources, whereas they were formed in the Volmer‐Weber growth mode by the periodic interruption of the MO sources. In addition, a quantum ring (QRs) structure was confirmed during the formation of InGaN QDs. The In content in the InGaN QDs appeared to increase with decreasing temperature. The photoluminescence spectrum (PL) showed peaks for the GaN buffer layer and the InGaN QDs layer at 362.2 nm (3.41 eV) and between 420–460 nm (2.96–2.70 eV), respectively. The composition of InGaN QDs was estimated from the PL peak position to be In0.12‐0.15Ga0.88‐0.85N. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
InP‐quantum dots in Al0.20Ga0.80InP with different barrier configurations
Authors: Schulz Wolfgang‐Michael , Roßbach Robert , Reischle Matthias , Beirne Gareth J. , Jetter Michael , Michler Peter 
Published: December 2008

AbstractSystematic ensemble photoluminescence studies have been performed on type‐I InP‐quantum dots in Al0.20Ga0.80InP barriers, emitting at approximately 1.85 eV at 5 K. The influence of different barrier configurations as well as the incorporation of additional tunnel barriers on the optical properties has been investigated. The confinement energy between the dot barrier and the surrounding barrier layers, which is the sum of the band discontinuities for the valence and the conduction bands, was chosen to be approximately 190 meV by using Al0.50Ga0.50InP. In combination with 2 nm thick AlInP tunnel barriers, the internal quantum efficiency of these barrier configurations can be increased by up to a factor of 20 at elevated temperatures with respect to quantum dots without such layers. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Coherent manipulation of excitons in a pair of quantum dots coupled by the dipole‐dipole interaction
Authors: Al‐Ahmadi Ameenah N. 
Published: December 2008

AbstractWe investigate coherent coupling effects that are generated between excitons (EXs) and biexcitons (BXs) in colloidal quantum dot system. We used the density matrix method to study the EX–BX system in a dimer consisting of two QDs coupled via dipole‐dipole interaction. The EX and BX levels in the donor dot are controlled by resonant picoseconds excitation, giving rise to Rabi oscillation. The resonant energy transfer processes keep memory of coherent donor interaction with the optical field and result in “Rabi oscillation memory”. Decoherence of Rabi oscillation of the donor dot is caused by biexciton, and population leakage to the acceptor dot via Förster coupling. The quality factor of the induced Rabi oscillation in the acceptor yields information on the energy transfer rate between the two dots. The effect of the BX levels is realized to be very week in such system. These results provide information about the properties of BX coherence that is important for quantum device application. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Atomic force microscopy based room temperature photocurrent‐spectroscopy of single subsurface InAs quantum dots
Authors: Brezna W. , Fasching G. , Unterrainer K. , Strasser G. , Smoliner J. 
Published: December 2008

AbstractIn this work, we present a scheme for room temperature detection of single subsurface InAs quantum dots buried in GaAs by Atomic Force Microscopy based local photocurrent spectroscopy. The measurements were performed at room temperature and ambient conditions. The AFM was used as a nanopositioning system and the AFM tip was used to create a nano‐scale Schottky contact in the vicinity of a QD. The photocurrent spectra clearly showed peaks from quantum dots located in the vicinity of the AFM tip. The spatial resolution of the method was determined to be in between 100 nm and 1000 nm. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Quantum dots to double concentric quantum ring structures transition
Authors: Bietti S. , Somaschini C. , Abbarchi M. , Koguchi N. , Sanguinetti S. , Poliani E. , Bonfanti M. , Gurioli M. , Vinattieri A. , Kuroda T. , Mano T. , Sakoda S. 
Published: December 2008

AbstractMaking use of the droplet–epitaxial technique, we realized a series of GaAs/AlGaAs nanostructured samples, starting from the same initial Ga droplet configuration, in which the nanostructure morphologies are progressively changed, via the As partial pressure provided during the growth, from islands, to single rings and, eventually, to concentric ring structures. We report a detailed characterization of the different structure morphologies, electronic structures and carrier dynamics via AFM and photoluminescence measurements as well as through theoretical simulations. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Evolution of InAs quantum dots grown on cross‐hatch substrates
Authors: Limwongse T. , Panyakeow S. , Kanjanachuchai S. 
Published: December 2008

AbstractInAs quantum dots (QDs) are grown on In0.2Ga0.8As/GaAs cross‐hatch layer by molecular beam epitaxy. The self‐assembled QDs form with the deposition of approximately 0.8 monolayer (ML) of InAs. The QDs distribute on the cross‐hatch surface unevenly: more are found along the [1‐10] crystallographic direction than the orthogonal [110] direction, while there exists even lower density of QDs on the flat areas. Height analyses indicate that QDs first form at the hatches' intersections, then they form along the [1‐10] direction, the [110] direction, and on the flat areas, respectively. This orderly evolution of QDs is attributed to the characteristic strain distribution of the cross‐hatch surface, giving rise to position‐ and orientation‐dependent critical thickness for QD formation. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Formation of nanoscale magnetic field by nuclear spin polarization in individual quantum dots
Authors: Sasakura H. , Adachi S. , Kaji R. , Muto S. 
Published: December 2008

AbstractWe demonstrated the creation of nanoscale magnetic field into the two isolated semiconductor quantum dots in spatially‐confined mesa structure of ∼150 nm diameter using an optical pumping of the nuclear spins. The amplitude of nuclear field between two isolated quantum dots under same pumping condition were clearly difference, suggesting that the nanoscale‐locality of the nuclear field was found to be around 100 nm. This method is based on the sensitivity of the critical magnitudes of the external magnetic field to the quantum dot properties in the bistable behavior of nuclear spin polarization. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Differential photoelectron holography of Cu(100) surface using laboratory‐level X‐ray sources
Authors: Hashimoto A. , Suzuki A. , Kisaka Y. , Miyasaka S. , Nojima M. , Owari M. , Nihei Y. 
Published: December 2008

AbstractX‐ray photoelectron diffraction (XPED) is a useful tool to analyze the surface structure. In order to reconstruct a three‐dimensional atomic structure, some methods based on photoelectron holography were studied. In our group, differential photoelectron holography (DPH) was proposed to reduce artifacts. DPH can be carried out by the subtraction of XPED patterns excited by different X‐ray energies. It was reported that DPH is a very effective technique with large‐scale synchrotron radiation. In this study, we developed a stripe‐type X‐ray target that can generate two different X‐rays alternately at the laboratory level. Subsequently, DPH was applied to obtain the atomic image of the Cu(100) surface by the stripe‐type target. Copyright © 2008 John Wiley & Sons, Ltd.
Wavefunctional analysis of electron transfers in 2D nanostructures under external fields
Authors: Tomiya Mitsuyoshi , Sakamoto Shoichi , Kusumoto Hanako , Nishikawa Masaki 
Published: December 2008

AbstractThe time‐evolution of the wave packet inside chaotic and integrable two‐dimensional nanostructures is numerically studied. Recently the time‐evolution of quantum states is seriously considered to treat the dynamical property of nanostructures. By computer simulation, we have found the enhancement around the classical periodic orbits, which has been theoretically predicted. It is similar to the scars in the standing wave of the chaotic billiards and is also beyond the naive prediction of the random nodal patterns from the chaotic nanostructure. The initial position and velocity and the shape of the wave packet are crucial for the enhancement, however, we can observe that the remnant of the initial wave packet travels along the unstable periodic orbit. Then the wave packet gradually diffuses around the structure. This behavior has close relation to the dynamical properties of electrons in the structure, e.g., the conductivity, the magneto‐resistance etc. Copyright © 2008 John Wiley & Sons, Ltd.
A Bayesian sensitivity model for intention‐to‐treat analysis on binary outcomes with dropouts
Authors: Kaciroti Niko A. , Schork M. Anthony , Raghunathan Trivellore , Julius Stevo 
Published: December 2008

AbstractIntention‐to‐treat (ITT) analysis is commonly used in randomized clinical trials. However, the use of ITT analysis presents a challenge: how to deal with subjects who drop out. Here we focus on randomized trials where the primary outcome is a binary endpoint. Several approaches are available for including the dropout subject in the ITT analysis, mainly chosen prior to unblinding the study. These approaches reduce the potential bias due to breaking the randomization code. However, the validity of the results will highly depend on untestable assumptions about the dropout mechanism. Thus, it is important to evaluate the sensitivity of the results across different missing‐data mechanisms. We propose here a Bayesian pattern‐mixture model for ITT analysis of binary outcomes with dropouts that applies over different types of missing‐data mechanisms. We introduce a new parameterization to identify the model, which is then used for sensitivity analysis. The parameterization is defined as the odds ratio of having an endpoint between the subjects who dropped out and those who completed the study. Such parameterization is intuitive and easy to use in sensitivity analysis; it also incorporates most of the available methods as special cases. The model is applied to TRial Of Preventing HYpertension. Copyright © 2008 John Wiley & Sons, Ltd.
Dynamic changes in salivary cortisol and secretory immunoglobulin A response to acute stress
Authors: Fan Yaxin , Tang Yiyuan , Lu Qilin , Feng Shigang , Yu Qingbao , Sui Danni , Zhao Qingbai , Ma Yinghua , Li Song 
Published: December 2008

AbstractPsychological stress leads to the secretion of cortisol. While this psychoneuroendocrine response helps to maintain physiological as well as psychological homeostasis under stress, exaggerated release of cortisol can suppress aspects of immune function and have negative effects on health. The present study set out to investigate the dynamic changes in salivary secretory immunoglobulin A (sIgA) and cortisol before and after acute stress, and to analyse the relationship between sIgA and cortisol trend. Thirty‐five healthy subjects took part in this study. All subjects underwent an acute stress test (mental arithmetic task). Salivary cortisol and sIgA responses were assessed repeatedly before the stress test, immediately after the stress test and 20 min after the stress test. The levels of salivary cortisol and sIgA both significantly increased after the acute mental arithmetic challenge. However, the increase of sIgA is transient; the sIgA fall was significantly correlated with the cortisol rise during the 20 min after stress (r = 0.569, p < 0.001). These results may help determine the timing of effective intervention in order to reduce the hypersecretion of cortisol and improve mucosal immune function. Copyright © 2008 John Wiley & Sons, Ltd.
Dealing with a ‘hidden stressor’: emotional disclosure as a coping strategy to overcome the negative effects of motive incongruence on health
Authors: Schüler Julia , Job Veronika , Fröhlich Stephanie M. , Brandstätter Veronika 
Published: December 2008

AbstractTaking the affiliation motive as an example, present research examines whether the negative effects of implicit–explicit motive incongruence on health is moderated by emotional disclosure. Starting from the point of view that motive incongruence works as a chronic stressor and therefore causes impairment of health, we predicted that participants who use the stress‐reducing coping strategy of emotional disclosure should be less affected by the negative effects of motive incongruence on health than participants who do not use this stress‐coping strategy. Two studies confirmed this hypothesis. Participants with affiliation motive incongruence who practiced emotional disclosure used less medication (Study 1, n = 85) and reported lower somatization symptoms (Study 2, n = 102) than motive incongruent individuals who did not disclose their emotions to others. Copyright © 2008 John Wiley & Sons, Ltd.
Bursting activation of prefrontal cortex drives sustained up states in nucleus accumbens spiny neurons in vivo
Authors: Gruber Aaron J. , O'Donnell Patricio 
Published: December 2008

AbstractHippocampal inputs to the nucleus accumbens (NA) have been proposed to implement a gating mechanism by driving NA medium spiny neurons (MSNs) to depolarized up states that facilitate action potential firing in response to brief activation of the prefrontal cortex (PFC). Brief PFC stimulation alone, on the other hand, could not drive NA up states. As these studies were conducted using single‐pulse PFC stimulation, it remains possible that PFC activation with naturalistic, bursty patterns can also drive up states in NA MSNs. Here, we assessed NA responses to PFC stimulation with a pattern similar to what is typically observed in awake animals during PFC‐relevant behaviors. In vivo intracellular recordings from NA MSNs revealed that brief 20–50 Hz PFC stimulus trains evoked depolarizations that were similar to spontaneous up states in NA MSNs and were sustained beyond stimulus offset. Similar train stimulation of corticoaccumbens afferents in a parasagittal slice preparation evoked large amplitude depolarizations in NA MSNs that were sustained during stimulation but decayed rapidly following stimulation offset, suggesting that activation of cortical afferents can drive MSN depolarizations but other mechanisms may contribute to sustaining up states. These data suggest that NA MSNs integrate temporal features of PFC activation and that the NA gating model can be reformulated to include a PFC‐driven gating mechanism during periods of high PFC firing, such as during cognitively demanding tasks. Synapse 63:173–180, 2009. © 2008 Wiley‐Liss, Inc.
In vivo microdialysis in awake, freely moving rats demonstrates HIV‐1 Tat‐induced alterations in dopamine transmission
Authors: Ferris Mark J. , Frederick‐Duus Danielle , Fadel Jim , Mactutus Charles F. , Booze Rosemarie M. 
Published: December 2008

AbstractIndividuals infected with human immunodeficiency virus (HIV) may develop neuropsychological impairment, and a modest percentage may progress to HIV‐associated dementia (HAD). Research using human and nonhuman, in vitro and in vivo models, demonstrates that subcortical dopamine (DA) systems may be particularly vulnerable to HIV‐induced neurodegeneration. The goal of the current investigation is to provide an understanding of the extent to which the HIV‐1 protein Tat induces alterations in striatal DA transmission using in vivo brain microdialysis in awake, freely moving rats. The current study was designed to investigate Tat‐induced neuronal dysfunction between 24‐h and 48‐h post‐Tat administration, and demonstrates a reduction in evoked DA for the Tat‐treated group relative to vehicle‐treated group at 24 and 48 h. The Tat‐induced reduction of DA overflow by 24 h suggests dysfunction of nerve terminals, and a compromised DA system in Tat‐treated animals. Furthermore, the current study provides direct support for HIV‐associated decline of DA function at a systemic level, helping to characterize the functional outcome of the relatively large amount of research on the molecular and behavioral levels of HIV‐induced neurotoxicity. This initial study may provide additional characteristics of Tat‐induced neuronal dysfunction to inform research on therapeutic intervention, and it provides a springboard for future in vivo research currently needed in the field. Synapse 63:181–185, 2009. © 2008 Wiley‐Liss, Inc.