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An enhanced efficiency organic light-emitting device (OLED) with corrugated nanostructures on a small-molecule organic film has been demonstrated. By patterning the hole transport layer via soft nano-imprinting lithography and coating with Ag, a nanostructured cathode is introduced to enhance the light extraction of the OLED without affecting the flatness and conductivity of the indium-tin-oxide film. Both luminance and current efficiency are improved compared with those of conventional planar devices. The observable improvement in luminance and current efficiency can be ascribed to the surface plasmonic and scattering effects caused by the Ag nanostructures. Moreover, theoretical simulations also demonstrate that the power loss to surface plasmon-polariton modes has been recovered. [ABSTRACT FROM AUTHOR]

The increasing density of electronic devices underscores the need for efficient thermal management. Silver nanowires (AgNWs), as one-dimensional nanostructures, possess a high aspect ratio and intrinsic thermal conductivity. However, high electrical conductivity of AgNWs limits their application for electronic packaging. We synthesized boron nitride-coated silver nanowires (AgNWs@BN) using a flexible and fast method followed by incorporation into synthetic polyimide (PI) for enhanced thermal conductivity and dielectric properties of nanocomposites. The thinner boron nitride intermediate nanolayer on AgNWs not only alleviated the mismatch between AgNWs and PI but also enhanced their interfacial interaction. Hence, the maximum thermal conductivity of an AgNWs@BN/PI composite with a filler loading up to 20% volume was increased to 4.33W/m K, which is an enhancement by nearly 23.3 times compared with that of the PI matrix. The relative permittivity and dielectric loss were about 9.89 and 0.015 at 1MHz, respectively. Compared with AgNWs@SiO2/PI and Ag@BN/PI composites, boron nitride-coated core-shell structures effectively increased the thermal conductivity and reduced the permittivity of nanocomposites. The relative mechanism was studied and discussed. This study enables the identification of appropriate modifier fillers for polymer matrix nanocomposites. [ABSTRACT FROM AUTHOR]

We have demonstrated that the island nucleation in the initial stage of epitaxial thin film growth can be tuned by substrate surface charge doping. This charge effect was investigated using spin density functional theory calculation in Fe-deposition on graphene substrate as an example. It was found that hole-doping can noticeably increase both Fe-adatom diffusion barrier and Fe interadatom repulsion energy occurring at intermediate separation, whereas electron-doping can decrease Fe-adatom diffusion barrier but only slightly modify inter-adatom repulsion energy. Further kinetic Monte Carlo simulation showed that the nucleation island number density can be increased up to six times larger under hole-doping and can be decreased down to ten times smaller under electron doping than that without doping. Our findings indicate a route to tailor the growth morphology of magnetic metal nanostructure for spintronics and plasmonic applications via surface charge doping. [ABSTRACT FROM AUTHOR]

Organo-metal halide perovskite solar cells based on planar architecture have been reported to achieve remarkably high power conversion efficiency (PCE, >16%), rendering them highly competitive to the conventional silicon based solar cells. A thorough understanding of the role of each component in solar cells and their effects as a whole is still required for further improvement in PCE. In this work, the planar heterojunction-based perovskite solar cells were simulated with the program AMPS (analysis of microelectronic and photonic structures)-1D. Simulation results revealed a great dependence of PCE on the thickness and defect density of the perovskite layer. Meanwhile, parameters including the work function of the back contact as well as the hole mobility and acceptor density in hole transport materials were identified to significantly influence the performance of the device. Strikingly, an efficiency over 20% was obtained under the moderate simulation conditions. [ABSTRACT FROM AUTHOR]

In order to get an air stable solar cell with high open circuit voltage (Voc), we fabricated an inverted tandem solar cell based on hybrid wet chemistry and vacuum thermal deposition techniques. A thin metallic interfacial layer was applied to improve charge recombination and maximize both the fill factor and Voc of the tandem solar cell. A cationic dye doped electron transport layer was used to minimize space charge induced Voc loss. The tandem cell Voc reached 1.02 V, which equals the sum of the two subcells' Voc. Increase of the metal nanoparticles' layer thickness reduces the short circuit current density of the tandem owing to increasing light extinction. Our tandem cell design offers superior air stability due to additional encapsulation effect from top metal oxide layers. It retains about 80% of its original efficiency after storage in air for three months. [ABSTRACT FROM AUTHOR]

Based on the mean-field Hubbard model (J. Guo et al., Appl. Phys. Lett. 92, 163109 (2008)), ballistic spin transport in zigzag graphene nanoribbons is investigated theoretically. A giant magnetoresistance effect is found with 100% change in resistance as the two transverse electrodes switch from the parallel to antiparallel magnetic configuration. Such change is shown to arise from different coupling between the subbands near the Fermi level, which is dependent of the orbital symmetry. In addition, the operating energy window of giant magnetoresistance exists in a wide range of ribbon widths, easing the way for experimental validation of the proposed device. [ABSTRACT FROM AUTHOR]

Nine AuPd nanoparticle samples selectively capped with tetraoctylphosphonium bromide, primary amine and tertiary amine molecules were studied with the Au L3-edge x-ray absorption spectroscopy (XAS). The AuPd mixing patterns were analyzed by comparing the XAS results with the theoretical coordination numbers of 24 AuPd model clusters of varied size, Au concentration, and bimetal mixing pattern. It was found that the use of amines, particularly tertiary amine, produced a more homogeneous AuPd mixing pattern and the Au d-electron density was fine-tunable by tailoring the density of Au–Pd bonds. Mechanisms for the tailored structural and electronic properties of these nanoparticles were proposed. [ABSTRACT FROM AUTHOR]

Eu2+, Dy3+, and Er3+ ions codoped SrAl2O4 phosphors with near infrared (NIR) (at 1530 nm) long-persistent phosphorescence were synthesized by a combustion method. The NIR phosphorescence emission was realized through a persistent energy transfer process from Eu2+ ions to Er3+ ions. Optimal Er3+ concentration for the maximum energy transfer efficiency was determined and NIR phosphorescence persisting for more than 10 min was achieved. A model of charge trapping and energy transfer process among Eu, Dy, and Er ions in SrAl2O4 host was proposed. [ABSTRACT FROM AUTHOR]

A molecular device fabricated from metallic deoxyribonucleic acid (M-DNA) exhibits a negative differential resistance (NDR) behavior. When two gold electrodes were connected by Ni2+-chelated DNA, which was converted from λ-DNA, not only was the conductivity of DNA improved, but a NDR device was formed as a full cyclic voltage sweep was applied to measure its current versus voltage characteristics at room temperature and in an ambient environment. Such electronic characteristics of a M-DNA device may have been caused by the redox reactions of Ni ions. This finding provides a simple way to construct electrical nanodevices from biological molecules. [ABSTRACT FROM AUTHOR]

Electron density was measured by Stark broadening in an ablative pulsed plasma thruster. The asymmetrical deconvolution is used to obtain Stark broadening. The result shows that the electron density in the discharge channel is 2.534×1022 m-3 when the discharge energy is 5 J and the measured electron temperature is 18 000 K, and it is in excellent agreement with other experimental and theoretical data. The electron density in the discharge channel increases very minimally with increasing discharge energy. [ABSTRACT FROM AUTHOR]

Investigates a gain-switched Fabry-Perot semiconductor laser using a continuous injection seeded laser. Identification of pulse width dependence on seeding power and seeding wavelength; Effect of increased seeding power on side-mode suppression ratio; Implication of timing jitters on applied external seeding.

Examines the pulse broadening of the 2.2 picosecond pulse amplification using semiconductor laser traveling-wave amplifier. Analysis of input pulse energy below the saturation energy of amplifier; Effect of nonlinear gain compression on temporal broadening; Application of traveling-wave rate equation simulation.

Investigates the dynamic characteristics of indium gallium arsenic phosphide distributed feedback semiconductor laser. Observation of the laser period quadrupling; Importance of laser signal modulation for optical fiber communication; Exhibition of the laser resonance frequency shift.

Examines the generation of a train of two picosecond pulses by fiber compression of gain-switched pulse from a 1.3 micrometer distributed-feedback laser diodes. Analytic model for the pulse compression in fiber; Use of the analytical results in the design of the fiber compressor for semiconductor lasers.

We reveal the underlying physics of the anomalous Josephson effect in a magnetic Josephson junction between two noncentrosymmetric superconductors. The key point is that the two effective superconducting gaps provide two sets of Andreev bound states which carry two supercurrents with different amplitudes. When the magnetization direction of the ferromagnet is suitably chosen, the two supercurrents experience opposite phase shifts from the conventional sinusoidal currentphase relation. Then the total Josephson current results in a continuously tunable ground-state phase difference by adjusting the ferromagnet parameters and the triplet-singlet ratio of noncentrosymmetric superconductors. The emergence of anomalous Josephson current can definitely confirm the existence of triplet pairing and the ground-state phase difference serves as a tool to determine the triplet-singlet ratio of noncentrosymmetric superconductors. [ABSTRACT FROM AUTHOR]

We report highly efficient small molecule solar cells (SMSCs) by using dichloromethane solvent vapor annealing method. The resulted devices delivered a power conversion efficiency (PCE) of 8.3%, which is among the highest in SMSCs. Comparing to the control devices, the short circuit current (Jsc), fill factor, and PCE of solvent vapor annealed devices are significantly improved. Summarizing the results of optical absorption, film morphology, and charge carrier transporting properties, we see that the enhanced structure order and reduced size of phase separation are major reasons for the improved device performances, establishing a solid structure-property relationship. The solvent vapor annealing method can thus be a useful method in device fabrication to enhance performances of SMSCs. [ABSTRACT FROM AUTHOR]

Hole injection improvement in organic light-emitting devices with Fe3O4 as a buffer layer on indium tin oxide (ITO) has been demonstrated. The luminance and the current density are significantly enhanced by using the Fe3O4/ITO anode, as well as the turn-on voltage is reduced by 1.5 V compared to the devices without the buffer. Results of atom force microscopy, x ray, and UV photoelectron spectroscopy studies reveal that the enhanced hole injection is attributed to the modification of the ITO surface and the reduced hole-injection barrier by the insertion of the Fe3O4 thin film between the ITO and hole-transporting layer. [ABSTRACT FROM AUTHOR]

Lead halide perovskites are attracting a great deal of interest for optoelectronic applications such as solar cells, LEDs, and lasers because of their unique properties. In solar cells, heat dissipation by hot carriers results in a major energy loss channel responsible for the Shockley–Queisser efficiency limit. Hot carrier solar cells offer the possibility to overcome this limit and achieve energy conversion efficiency as high as 66% by extracting hot carriers. Therefore, fundamental studies on hot carrier relaxation dynamics in lead halide perovskites are important. Here, we elucidated the hot carrier cooling dynamics in all-inorganic cesium lead iodide (CsPbI3) perovskite using transient absorption spectroscopy. We observe that the hot carrier cooling rate in CsPbI3 decreases as the fluence of the pump light increases and the cooling is as slow as a few 10 ps when the photoexcited carrier density is 71018 cm-3, which is attributed to phonon bottleneck for high photoexcited carrier densities. Our findings suggest that CsPbI3 has a potential for hot carrier solar cell applications. [ABSTRACT FROM AUTHOR]

Spectral interference is experimentally demonstrated by two terahertz pulses emitting from filaments induced by two successive femtosecond laser pulses in air. Here, a leading pulse is set to be weaker than a trailing pulse and their temporal separation is larger than the pulse duration of the terahertz pulses. When the leading pulse is stronger than the trailing pulse, the frequency modulation within the whole terahertz envelope is greatly deteriorated due to nonlinear effects applying on the trailing pulse through the plasmas generated by the leading pulses. Such unique terahertz spectrum may find applications in terahertz spectroscopy. [ABSTRACT FROM AUTHOR]

Dual-frequency terahertz radiation from air-plasma filaments produced with two-color lasers in air has been demonstrated experimentally. When a focusing lens is tilted for a few degrees, it is shown that the laser filament evolves from a single one to two sub-filaments. Two independent terahertz sources emitted from the sub-filaments with different frequencies and polarizations are identified, where the frequency of terahertz waves from the trailing sub-filament is higher than that from the leading sub-filament. [ABSTRACT FROM AUTHOR]

Multilayer dielectric mirrors (niobium pentoxide/silica) were irradiated by single 800 nm-38fs laser pulses. A circular blister feature appeared in the chirped mirrors at a wide range of laser fluence, while only existed above a few percent of the damage threshold for the high-reflector. Absorptive source of laser energy can be determined by combining theoretical simulation with focused ion beam technology. Mechanical analysis with a linear-elastic buckling model reveals the blister evolution belonging to a stable-buckling process until the blister radius confined by limited laser spot size. [ABSTRACT FROM AUTHOR]

We report the coupling between surface plasmons and dipole-localized surface plasmons in a composite hole-patch structure at terahertz frequencies. The coupling is found to be changed by increasing the inner patch size, which causes prominent resonance frequency shift in the enhanced transmission. The experimental results show good agreement with numerical simulation. The study clarifies well the nature of coupling between surface plasmons and dipole-localized surface plasmons and is thus of help to identify the role of surface plasmons in the enhanced transmission observed in subwavelength metallic structures. [ABSTRACT FROM AUTHOR]

SiGe nanomembranes and nanowires provide one important class of stretchable electronic materials. We have investigated a very interesting wiggling phenomenon of SiGe nanoribbons bonded to Si substrate as experimentally observed in a Hall-bar structure. Based on continuum linear stability analysis, we establish a scaling rule between the wiggling period and surface bonding area, in relation to the ratio of strain energy over the interfacial bonding energy. [ABSTRACT FROM AUTHOR]

We report on tuning interfacial properties of epitaxially-grown graphenes with different kinds of metal substrates based on scanning tunneling microscopy experiments and density functional theory calculations. Three kinds of metal substrates, Ni(111), Pt(111), and Ru(0001), show different interactions with the epitaxially grown graphene at the interfaces. The different interfacial interaction making graphene n-type and p-type doped, leads to the polarity change of the thermoelectric property of the graphene/metal systems. These findings may give further insights to the interfacial interactions in the graphene/metal systems and promote the use of graphene-based heterostructures in devices. [ABSTRACT FROM AUTHOR]

Monodispersed crystalline platinum nanoclusters (NCs) have been grown on a template of graphene Moiré pattern formed on Ru(0001). The Pt NCs are directed to nucleate at a unique site in the Moiré unit cell, and grow in a layer-by-layer mode up to 4-atomic-layer height without coalescence at room temperature. The size of Pt NCs can be controlled by tuning the coverage. This system may find application in the study of Pt nanocatalyst, and the graphene Moiré pattern may be generally applied as template to direct self-assembled growth of metallic or nonmetallic NCs. [ABSTRACT FROM AUTHOR]

Terahertz radiation generated by focusing the fundamental laser pulse and its second harmonic into ambient air strongly saturates with increasing pump laser energy. We demonstrate a simple method to control the Gaussian pump laser beam to improve the output of terahertz radiation with an adjustable aperture. With the optimal aperture-limited pump laser beams, the terahertz wave amplitudes can be enhanced by more than eight times depending on the pump laser parameters than those of aperture-free cases. [ABSTRACT FROM AUTHOR]

Uniformly patterned Pt/PbTiO3/PbZr0.3Ti0.7O3/PbTiO3/Pt capacitor arrays were etched in noncrystalline phase. The ferroelectric layer was well crystallized and contains uniform grains. The capacitors exhibit well-saturated hysteresis loop and excellent fatigue properties in terms of larger saturation polarization Pmax of 53.2 μC/cm2 at an applied voltage of 12 V, higher remnant polarization Pr of 30.5 μC/cm2 for a coercive field of 58 kV/cm, remnant polarization of about 81.2% at 1010 switching cycles, and a low leakage current density of 10-8 A/cm2 at an applied voltage of 3 V. The etching effects on the properties of capacitor were reduced to minimal values, confirmed by scanning electron microscope, energy-dispersive x-ray microanalysis, and piezoresponse force microscopy results. The reliable electric properties and fine profile of the patterns indicate that the capacitors are suitable for ferroelectric random access memories and other integrated ferroelectric devices. [ABSTRACT FROM AUTHOR]

Both high contrast and high transmittance are preferred for optical polarizers. To achieve high transmittance for aluminum nanowire-grid polarizers, a narrow linewidth is required. In this letter, aluminum nanowire-grid polarizers with 30-nm-wide linewidth and 200 nm depth were fabricated by UV-nanoimprint lithography, which leads to ultrahigh transmittance. To achieve a high contrast, the authors fabricated the 30-nm-wide aluminum nanowire structures on both sides of the glass wafers. An extremely high contrast up to 10 000:1 was achieved, in the visible range, along with good transmittance of 83%–87% for the double-side aluminum nanowire-grid polarizers. [ABSTRACT FROM AUTHOR]

The authors report a method of precisely fabricating the large-scale nanocrystals with well-defined shape and size. The (111) oriented Pb islands deposited on Si(111)-7×7 substrate were investigated with a manipulation technique based on scanning tunneling microscopy. By applying a series of voltage pulses on the as-grown islands, artificial center-full-hollowed or half-hollowed nanowells are created, and the thickness and shape can be precisely regulated via tuning the manipulation parameters. Artificial nanoarray patterns in micron scale are also constructed using this method. [ABSTRACT FROM AUTHOR]

Oxidation of an ultrathin metal layer (less than 1 nm) to form a tunnel barrier oxide, without oxidizing adjacent layers, is of critical importance in making nanoscale devices such as magnetic tunnel junctions. It is extremely difficult, if not impossible, to achieve this objective using conventional methods that rely on kinetic control of the oxidation process. We present an alternative approach using a gas mixture with a fixed chemical potential of oxygen as the oxidizing medium. This mixture, chosen with thermodynamic calculations, tends to uniformly oxidize the tunnel barrier to the thermodynamically favored stoichiometry without oxidizing the adjacent layers. Experiments on a model system show that a thin-film layer such as Al can be oxidized without oxidizing common ferromagnetic alloys, such as Co–Fe, using a mixture of CO2/CO or H2/H2O. The chemical states of the Al and Co–Fe based example were characterized using x-ray photoelectron and synchrotron-source Fourier transform infrared spectroscopy. [ABSTRACT FROM AUTHOR]