Superparamagnetic relaxation of Fe deposited on MgO(001)

Superparamagnetic behavior is investigated for Fe grown at 700 K onto MgO(001) to a thickness equivalent to that of a ten monolayer film. Two such Fe deposits separated by a 200-Å deposit of MgO exhibit a ferromagnetic response with no hysteresis at either 300 or 150 K, but with identical reduced magnetization curves M(H/T) which confirms the existence of superparamagnetism. M(H) data at 300 K were fitted to a Langevin function to yield an average particle size of 100 Å diameter. M(T) for field-cooled and zero-field-cooled samples shows behavior characteristic of superparamagnetic particles with a distribution in particle size. Time-dependent remanent magnetization data measured over a 20 h period at various temperatures show nonexponential decay attributed to the distribution in particle size and interactions among the particles

Observation of photon-pair generation in the normal group-velocity-dispersion regime with slight detuning from the pump wavelength

A fiber-based photon-pair source in the telecom C-band is suitable for quantum information science including quantum communications. Spontaneous four-wave mixing effects are known to create photon pairs that are slightly detuned from the pump wavelength only in the anomalous group-velocity-dispersion (GVD) regime. Here, we achieve high-quality photon-pair generation slightly detuned from the pump wavelength in the normal GVD regime through a dispersion shifted fiber, for the first time. The photon pairs in C-band exhibit strong temporal correlation with each other and excellent heralded anti-bunching property. This photon-pair generation scheme can be exploited as telecom-band quantum light sources for quantum information applications.11Ysciescopu

Magnetic response of ultrathin Fe on MgO: A polarized neutron reflectometry study

The magnetization of ultrathin bcc Fe films (two and three monolayers) on MgO was measured and compared with the behavior predicted for a two-dimensional ferromagnet. The experiment indicated that no hysteresis was present in the magnetization. Instead, the magnetization at low temperature was affected by a marked field cooling effect. These observations lead to the conclusion that films of Fe on MgO of such thickness exhibit superparamagnetibc behavior as if they were not entirely continuous. In contrast, films thicker than five monolayerse exhibit a magnetic response close to that of bulk iron

Correlation Properties of Photon Pairs Generated near the Pump in the Normal Group-Velocity-Dispersion Regime

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Temporally coherent real-time video dehazing

A real-time video dehazing algorithm, which reduces flickering artifacts and yields high quality output videos, is proposed in this work. Assuming that a scene point yields highly correlated transmission values between adjacent image frames, we develop the temporal coherence cost. Then, we add the temporal coherence cost to the contrast cost and the truncation loss cost to define the overall cost function. By minimizing the overall cost function, we obtain the optimal transmission. Moreover, to reduce the computational complexity and facilitate real-time applications, we approximate the conventional edge preserving filter by the overlapped block filter. Experimental results demonstrate that the proposed algorithm is sufficiently fast for real-time applications and effectively removes haze and flickering artifacts

Overcoming the “retention vs. voltage” trade-off in nonvolatile organic memory: Ag nanoparticles covered with dipolar self-assembled monolayers as robust charge storage nodes

Organic non-volatile memory devices with significantly enhanced retention are explored with C-60 thin-film transistors containing silver nanoparticles (Ag-NPs) within gate dielectrics as charge storage nodes. Dipolar self-assembled monolayers covering Ag-NPs effectively prevent stored charges from being lost by providing an additional energy threshold for back-tunneling process. This enables long retention even with ultrathin tunneling dielectric layers, providing a simple means to realize long retention without causing an excessive increase in operation voltage. (C) 2013 Elsevier B.V. All rights reserved.1881sciescopu

Improving the Performance of Solution−Processed Quantum Dot Light−Emitting Diodes via a HfO_x Interfacial Layer

One of the major obstacles in the way of high−performance quantum dot light−emitting diodes (QLEDs) is the charge imbalance arising from more efficient electron injection into the emission layer than the hole injection. In previous studies, a balanced charge injection was often achieved by lowering the electron injection efficiency; however, high performance next−generation QLEDs require the hole injection efficiency to be enhanced to the level of electron injection efficiency. Here, we introduce a solution−processed HfOx layer for the enhanced hole injection efficiency. A large amount of oxygen vacancies in the HfOx films creates gap states that lower the hole injection barrier between the anode and the emission layer, resulting in enhanced light−emitting characteristics. The insertion of the HfOx layer increased the luminance of the device to 166,600 cd/m2, and the current efficiency and external quantum efficiency to 16.6 cd/A and 3.68%, respectively, compared with the values of 63,673 cd/m2, 7.37 cd/A, and 1.64% for the device without HfOx layer. The enhanced light−emitting characteristics of the device were elucidated by X−ray photoelectron, ultra−violet photoelectron, and UV−visible spectroscopy. Our results suggest that the insertion of the HfOx layer is a useful method for improving the light−emitting properties of QLEDs

Direct electron injection into an oxide insulator using a cathode buffer layer

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Decoupling the effects of self-assembled monolayers on gold, silver, and copper organic transistor contacts

International audienceIn bottom-contact organic field-effect transistors (OFETs), the functionalization of source/drain electrodes leads to a tailored surface chemistry for film growth and controlled interface energetics for charge injection. This report describes a comprehensive investigation into separating and correlating the energetic and morphological effects of a self-assembled monolayers (SAMs) treatment on Au, Ag, and Cu electrodes. Fluorinated 5,11-bis(triethylsilylethynyl) anthradithiophene (diF-TES-ADT) and pentafluorobenzenethiol (PFBT) are employed as a soluble small-molecule semiconductor and a SAM material, respectively. Upon SAM modification, the Cu electrode devices benefit from a particularly dramatic performance improvement, closely approaching the performance of OFETs with PFBT-Au and PFBT-Ag. Ultraviolet photoemission spectroscopy, polarized optical microscopy, grazing-incidence wide-angle X-ray scattering elucidate the metal work function change and templated crystal growth with high crystallinity resulting from SAMs. The transmission-line method separates the channel and contact properties from the measured OFET current–voltage data, which conclusively describes the impact of the SAMs on charge injection and transport behavior