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The chiral light field has attracted great attention owing to its interaction with chiral matter. The generation of chiral light fields with rich structures has become crucial as it can expand application scenarios. Herein, we introduce a chiral optical vortex lattice. As a whole, the optical vortex lattice has a chiral intensity distribution, with each spiral arm having sub-vortices (chiral phase). By using an expansion factor to adjust the involute of a circular lattice, this helical optical vortex lattice can be continuously varied from a circular lattice. The chirality of intensity and phase can be controlled independently. Furthermore, the optical tweezers using the lattice demonstrate the capability of sub-vortices to manipulate particle movement, with the chiral intensity determining the trajectory of particle motion. As the lattice possesses both intensity and phase chirality, it may also find potential applications in tasks such as chiral structure microfabrication. [ABSTRACT FROM AUTHOR]

We report the voltage regulation of electrodeposited elliptical magnetostrictive Ni nanodot arrays from single-domain to nonvolatile vortex state at room temperature. On the piezoelectric substrate, isolated elliptical Ni nanodots are fabricated between a pair of square electrodes, with the long axis parallel to the joint line of the electrodes. By applying a voltage to the surface electrodes pair, local stress is generated to induce the magnetization of the nanodots from single-domain to vortex state. The magnetization state of the nanodots is characterized by a magnetic force microscope. Even after the voltage is removed or applying another voltage, the nanodots maintain a stable vortex magnetization state, which shows that the vortex state after regulation is nonvolatile. These results are of great significance for the study of the low-energy-consumption regulation of the nano-dimensional magnetic material and vortex state-based nonvolatile memory. [ABSTRACT FROM AUTHOR]

Composited p-type electrodes with high reflectivity have been investigated in AlGaN-based ultraviolet light emitting diodes (UV-LEDs) to improve the light extraction efficiency, which are composed of a patterned ITO layer and an Al reflector. It is verified that the patterned ITO with a thickness of 30 nm can not only well form Ohmic contact with p-GaN capping layer, but also be nearly 90% transparent to ultraviolet light, and thus presenting a reflectivity of 73% at 280 nm when combined with an Al reflector. Further experimental efforts confirm that the performance of the UV-LEDs is dramatically improved with such p-type electrodes. The maximum light output power and wall plug efficiency in the current range of 0–100 mA are severally increased by 49.8% and 54.2% compared to the device with traditional Ni/Au electrodes. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate a prototype of magnetic tunable bandstop filter by using magnetic multilayers of [FeGaB 25 nm/Al2O3 5 nm]4 prepared by magnetron sputtering. The multilayer structure exhibits a relatively low coercive field and RF loss compared to the single layer film with the same thickness. By placing a single transmission line on the top of magnetic multilayers, a prototype of tunable bandstop filter was fabricated and operates from 4.5 GHz to 7.08 GHz under very low magnetic bias fields from 100 Oe to 400 Oe. These low loss multilayer films are good candidates for RF/microwave applications. [ABSTRACT FROM AUTHOR]

Propagation of intense circularly polarized laser pulses in strongly magnetized inhomogeneous plasmas is investigated. It is shown that a left-hand circularly polarized laser pulse propagating up the density gradient of the plasma along the magnetic field is reflected at the left-cutoff density. However, a right-hand circularly polarized laser can penetrate up the density gradient deep into the plasma without cutoff or resonance and turbulently heat the electrons trapped in its wake. Results from particle-incell simulations are in good agreement with that from the theory. [ABSTRACT FROM AUTHOR]

The possibility to enrich paramagnetic dysprosium(III) ions in a magnetic field gradient is proved by means of interferometry, which may open the route for a magnetic separation of rare earth ions from aqueous solutions. The separation dynamics are studied for three different concentrations of DyCl3 and compared with those found recently in a sulphate solution of the 3d ion Mn(II). In view of the similar-sized hydration spheres for Dy(III) and Mn(II), the slower separation dynamics in DyCl3 is attributed to both a higher densification coefficient and the strong impact of Brownian motion due to the absence of ion-pair clusters. [ABSTRACT FROM AUTHOR]

AlGaN-based deep-ultraviolet light emitting diodes (DUV-LEDs) with thin p-GaN capping layer have been one of the most promising configurations, thanks to their excellent light extraction potential, which are, however, generally accompanied by insufficient hole supply. In this work, multi-graded p-AlGaN layers are adopted as an integrated p-type region, in which the electron blocking layer (EBL) is taken off to promote the carrier transport. The experimental results show that both the operation voltage and light output power of the DUV-LEDs are improved compared to the traditional ones, leading to a remarkable increase (by 114%) in their wall-plug efficiency. Further analysis confirms that the integrated p-type region serving as the hole supply layer helps holes to avoid the barrier between the p-GaN and integrated p-type region during their transport, and the absence of the EBL further eliminates part of the obstacles for hole drifting, giving rise to an enhanced hole concentration in quantum wells. Meanwhile, thanks to the modulation of the negative polarization induced bulk charges for conduction band, which is introduced within the integrated p-type region, the electron leakage is effectively suppressed even without the EBL, thus improving the device performance dramatically. [ABSTRACT FROM AUTHOR]

Magnetotransport measurements were performed on a cross-junction made from polycrystalline graphene grown at a low temperature. The Shubnikov-de Haas oscillation is observed, from which the cyclotron mass mc can be derived varying from 0.043 to 0.055 times that of free electron. The changing rate of electron temperature is found much lower than that in pristine graphene via the universal electron heating study. Investigations on the characteristic lengths of weak localization reveal that the atomically sharp defects dominate the elastic scattering process, while studies on the coherent rate report that the Nyquist effect governs the inelastic scattering process with a little modulation from the direct Coulomb interaction. The scattering lengths in the polycrystalline graphene are comparable to that of exfoliated graphene on SiO2. These findings indicate that some key scattering parameters which characterize the excellent properties of intrinsic graphene are preserved in the polycrystalline graphene, which may find potential applications in interconnects of integrated circuit. [ABSTRACT FROM AUTHOR]

We propose a pure-spin-current generator based on a single level quantum dot (QD) device subjected to time-dependent magnetic fields. Under low temperature and high magnetic fields, the spin-dependent Seebeck coefficient in the transition regime is rapidly enhanced by several orders of magnitude larger than that in the steady regime. This fact is attributed to a delay effect of the electron transmission probability with respect to the split of the QD energy level. When a temperature gradient is applied across the device, the pure spin current emerges. The findings here suggest a feasible way of enhancing thermospin effects and generating the pure spin current by time-dependent external fields. [ABSTRACT FROM AUTHOR]

Strain-induced graphene phonon softening and phonon band splitting are indeed fascinating, which were attributed to the phonon double resonant scattering without intrinsic involvement of C-C bond relaxation. Here, we show that the lengthening and weakening of the C-C bond softens the phonon and that the mismatching between the uniaxial strain and the C3v bond geometry splits the band. In addition to the force constant of 11.8 N/m for a C-C bond in graphene, consistency between theory and measurements derives that if the strain is along a bond, maximal band splitting happens; if the strain is perpendicular, no band splitting occurs. [ABSTRACT FROM AUTHOR]

From the perspective of bond order-length-strength correlation and the local bond averaging approach, we have formulated the number-of-layer resolved Raman shifts of graphene, with quantification of the referential origins from which the Raman shifts proceed and clarification of their origins. It is found that the primary D mode and the secondary 2D mode are dominated by the interaction between a specific atom and its nearest neighbors while the G mode by the dimer interaction, and therefore red shift happens to the D/2D phonons and blue shift to the G mode upon the number-of-layer is reduced. [ABSTRACT FROM AUTHOR]

The thermally softened and the mechanically stiffened graphene phonons have been formulated from the perspective of bond order-length-strength correlation with confirmation of the C-C bond length in the single-layer graphene contracting from 0.154 to 0.125 nm and the binding energy increasing from 0.65 to 1.04 eV. Matching theory to the measured temperature- and pressure-dependent Raman shift has derived that the Debye temperature drops from 2230 to 540 K, the atomic cohesive energy drops from 7.37 to 3.11 eV/atom, and the binding energy density increases from 250 to 320 eV/nm3 compared with the respective quantities of bulk diamond. [ABSTRACT FROM AUTHOR]

The B dopant stability and doping level tunability of <112> silicon nanowires (SiNWs) with alkene adsorption are revealed based on first-principles calculations. It is found that the alkenyl chains favor the middle location of (111) facet, and the B dopants prefer to locate at (110) facet of the <112> SiNW. Interestingly, the B doping levels are activated upon an alkene adsorption which introduces an intermediate energy level. This finding sheds light on how SiNWs can achieve effective doping. [ABSTRACT FROM AUTHOR]

The scattering processes of electrons in semiconductors with metal nanoinclusions were theoretically investigated in the framework of relaxation time approximation, in which perturbation theory was used to calculate scattering probabilities analytically. Our results reveal that it is not the single scattering at interface potential barriers caused by the nanoinclusions but the synergetic scattering of electrons at ionized impurities and the interface potential barriers or wells that can produce giant scattering parameter λ (=3.3-4.7). Due to giant λ and enhanced thermopower, the estimated figure of merit ZT=3.4 at 800 K for PbTe with Pb nanoinclusions. [ABSTRACT FROM AUTHOR]

We demonstrate temporal group delays in coherently coupled high-Q multicavity photonic crystals, in an all-optical analog to electromagnetically induced transparency. We report deterministic control of the group delay up to 4× the single cavity lifetime in our room-temperature chip. Supported by three-dimensional numerical simulations and theoretical analyses, our multipump beam approach enables control of the multicavity resonances and intercavity phase, in both single and double transparency peaks. The standing-wave wavelength-scale photon localization allows direct scalability for chip-scale optical pulse trapping and coupled-cavity quantum electrodynamics. [ABSTRACT FROM AUTHOR]

We present a linear relationship between the cohesive energies and the H/Si ratio for hydrogen-terminated Si semiconductor nanostructures based on our model analysis and first-principles calculations. The H/Si ratio is shown to be a universal predictor of the nanostructure’s energetic stability and allows easily searching of magic numbers in Si quantum dots. Our findings substantially improve the understanding of nanostructure stability and make practical the prediction of structural properties. [ABSTRACT FROM AUTHOR]

A single-shot, nondestructive, electro-optical, electron bunch length monitor is experimentally verified by encoding the Coulomb field of the bunch profile on the spatial intensity distribution of an unchirped femtosecond laser pulse in an orthogonal geometry, hence a temporal-to-spatial transformation. This electron bunch measurement scheme can simultaneously measure large timing jitter (approximately in picoseconds) with a wide measurement time span covering picosecond to subpicosecond ranges. [ABSTRACT FROM AUTHOR]

We report a prediction of enhanced surface passivation doping effect in silicon nanowires (SiNWs) by phosphorus adsorption based on first-principles calculations. Recent theoretical and experimental studies all showed that hydrogen-passivated SiNWs present typical p-type characteristic due to charge transfer between the surface passivant and the SiNW core. Here, we show that a phosphorus-passivated SiNW with a moderate diameter facilitates improved hole generation in the core and efficient separation of electron and hole, which may provide a practical avenue for fabricating low cost solar cells with high efficiency. [ABSTRACT FROM AUTHOR]

The vacancy-type defects in (Ga,Mn)N films grown by metal organic chemical vapor deposition were studied by positron annihilation technique. Doppler broadening spectra were measured for the films. Compared to the undoped GaN film, the positron trapping defects in the (Ga,Mn)N films have been changed to a new type defects and its concentration increases with the increasing Mn concentration. By analyzing the S-W correlation plots and our previous results, we identify this type defects in the (Ga,Mn)N as VN-MnGa complex. This type of defects should be considered when understand the magnetic properties in a real (Ga,Mn)N system. [ABSTRACT FROM AUTHOR]

First-principles calculations on the electronic properties of silicon nanofilms and nanowires that were adsorbed with nitrogen atoms on (110) facets revealed the formation of N–Si–N–Si chains, which causes the conduction and valence bands to intersect and metallizes the system. The interaction between the nitrogen and silicon atoms on the surface was found to induce energy bands near the Fermi level. The metallic electronic states induced by surface adsorption could be expected to significantly improve the conducting properties of the Si nanostructures due to their large surface-to-volume ratio and thus has great implications for SiNWs in nanoelectronic applications. [ABSTRACT FROM AUTHOR]

The lifetimes of a series of N-related photoluminescence lines (A2–A6) in GaAs1-xNx (x=0.1%) were studied under hydrostatic pressures at ∼30 K. The lifetimes of A5 and A6 were found to increase rapidly with increasing pressure: from 2.1 ns at 0 GPa to more than 20 ns at 0.92 GPa for A5 and from 3.2 ns at 0.63 GPa to 10.8 ns at 0.92 GPa for A6. The lifetime is found to be closely correlated with the binding energy of the N impurity states, which is shown either in the pressure dependence for a given emission line or in the lifetime variation from A2 to A6. [ABSTRACT FROM AUTHOR]

We report that the performances of blue polymer electrophosphorescent devices are crucially depending on the choice of the electron transporting material incorporated into the emissive layer. Devices with 1,3-bis[(4-tert-butylphenyl)-1,3,4-oxidiazolyl]phenylene (OXD-7) doped at ∼40 wt% into a poly(vinylcarbazole) matrix exhibited significantly higher efficiencies than those with 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD), yielding maximum luminous and power efficiency values of 18.2 Cd/A and 8.8 lm/W, respectively. Time resolved photoluminescence measurements revealed a long lifetime phosphorescence component in layers with PBD, which we assign to significant triplet harvesting by this electron-transporting component. [ABSTRACT FROM AUTHOR]

We report the design, growth, fabrication, and characterization of a GaAs-based resonant-cavity-enhanced (RCE) GaInNAs photodetector operating at 1.55 μm. The structure of the device was designed using a transfer-matrix method (TMM). By optimizing the molecular-beam epitaxy growth conditions, six GaInNAs quantum wells were used as the absorption layers. Twenty-five (25)- and 9-pair GaAs/AlAs-distributed Bragg reflectors were grown as the bottom and top mirrors. At 1.55 μm, a quantum efficiency of 33% with a full width at half maximum of 10 nm was obtained. The dark current density was 3×10-7 A/cm2 at a bias of 0 V and 4.3×10-5 A/cm2 at a reverse bias of 5 V. The primary time response measurement shows that the device has a rise time of less than 800 ps. [ABSTRACT FROM AUTHOR]

In this study, high current densities (i.e., 0.9 A/cm2) have been obtained in a hydrogen/air polymer electrolyte fuel cell using nanoscale tungsten carbide as the anode catalyst and carbon supported platinum as the cathode catalyst under normal operating conditions of 80 °C and 3 atm. These results show a possibility of replacing precious metal anode catalysts with transition metal compounds for hydrogen oxidation, thereby creating a fundamental technology to reduce the cost of future fuel cell engines. The tungsten carbide-based catalysts were synthesized by means of chemically reduced mechanical alloying. The high electrocatalytic activity toward hydrogen oxidation reaction is attributed to the inherent W–C valence and the unique nanostructure of synthesized carbides. These properties were confirmed by x-ray diffraction and transmission electron microscopy. [ABSTRACT FROM AUTHOR]

The nature of the ∼370-nm (3.35-eV) photoluminescence (PL) in Si oxide and nanostructures, which has a PL excitation band at ∼260 nm, is studied experimentally and theoretically. It is revealed that the PL occurs at the interface between Si structure and its oxide and is closely associated with a characteristic infrared absorption band at ∼1250 cm-1. Spectral analyses suggest that the ∼370-nm PL originates in the –SiO3 group, which bonds to Si structural surface. The density functional theory calculations are consistent with our experiments. This work clarifies some controversies regarding the ∼370-nm PL mechanisms in a number of Si oxide and nanostructures. [ABSTRACT FROM AUTHOR]

We report on the fabrication and operation of integrated field emission cathodes containing single tungsten (W) nanofibers selectively grown by nanoscale electron beam induced deposition (EBID). A nonorganometallic precursor, WF6, was used to deposit metallic W fibers. Vacuum electrical testing reveals electrons were successfully extracted from the W nanofiber tip and were collected by a phosphor anode. Direct current versus voltage (I–V) curves exhibited Fowler–Nordheim behavior, indicating the occurrence of cold field emission. Electrical testing of these devices indicated that EBID direct-write is a promising technique for direct production or repair of field emission cathodes. [ABSTRACT FROM AUTHOR]

Exciton localization in Te-rich ZnSTe epilayers has been studied by photoluminescence (PL) and time-resolved PL. The sulfur-related exciton emission is found to dominate the radiative recombination at low temperature and is shifted to the low energy with the increase of S concentration. By measuring the PL dependence on temperature and by analyzing the PL decay process, we have clarified the localization nature of the sulfur-related exciton emission. Furthermore, the difference of the localization effect in Te- and S-rich ZnSTe is also compared and discussed. [ABSTRACT FROM AUTHOR]

Multiwalled-carbon nanotubes (MWCNTs) are grown on top of vertically aligned carbon nanofibers (VACNFs) via microwave plasma-enhanced chemical vapor deposition (MPECVD). The VACNFs are first grown in a direct-current plasma-enhanced chemical vapor deposition reactor using nickel catalyst. A layer of carbon–silicon materials is then deposited on the VACNFs and the nickel catalyst particle is broken down into smaller nanoparticles during an intermediate reactive-ion-plasma deposition step. These nickel nanoparticles nucleate and grow MWCNTs in the following MPECVD process. Movable-probe measurements show that the MWCNTs have greatly improved field-emission properties relative to the VACNFs. [ABSTRACT FROM AUTHOR]

The recombination kinetics of Te isoelectronic centers in ZnS1-xTex (0.0065≤x≤0.85) alloys is studied by time-resolved photoluminescence (TRPL) at low temperature. The measured radiative recombination lifetimes of different Te bound exciton states are quite different, varying from a few nanoseconds to tens of nanosecond. As the bound exciton state evolves from a single Te impurity (Te1) to larger Te clusters (Ten,n=2,3,4), the recombination lifetime increases. It reaches maximum (∼40 ns) for the Te4 bound states at x=0.155. The increase of the exciton lifetime is attributed to the increasing exciton localization effect caused by larger localization potential. In the large Te composition range (x>0.155), the exciton recombination lifetime decreases monotonically with Te composition. It is mainly due to the hybridization between the Te localized states and the host valence band states. The composition dependences of the exciton binding energy and the photoluminescence (PL) line width show the similar tendency that further support the localization picture obtained from the TRPL measurement. [ABSTRACT FROM AUTHOR]

We demonstrate efficient single-layer polymer phosphorescent light-emitting devices based on a green-emitting iridium complex and a polymer host co-doped with electron-transporting and hole-transporting molecules. These devices can be operated at relatively low voltages, resulting in a power conversion efficiency of up to 24 lm/W at luminous efficiencies exceeding 30 cd/A. The overall performances of these devices suggest that efficient electrophosphorescent devices with acceptable operating voltages can be achieved in very simple device structures fabricated by spin coating. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have investigated the formation mechanism of the interfacial electric field in LiNbO3(or LiTaO3)/α-sapphire crystal structures, which is important in understanding the photoluminescence properties of this kind of ferroelectric film-coated crystal material. It is revealed that the interfacial electric field arises from the interfacial polarization charge generated during poling of LiNbO3(or LiTaO3) film near Curie temperature, which induces forced polarization of the α-sapphire crystal. As a result, lattice distortions of the α-sapphire crystal change the crystal field of Cr3+ ion in the sapphire crystal and therefore lead to intensity enhancement of R-line luminescence from Cr3+ centers. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The as-quenched structure of Zr[SUB80]Pt[SUB20] melt-spun ribbons containing measured oxygen contents) ranging from 184 to 4737 ppm mass was studied. Ribbons containing less than 500 ppm mass oxygen are fully crystallized and consist predominantly of a metastable ordered β-Zr phase with significant solution of Pt. Increasing oxygen content to 1053 and 1547 ppm mass produces a transition to fully amorphous and to mixed amorphous and quasicrystalline structures, respectively. Samples containing 4737 ppm mass consist of quasicrystalline and crystalline phases in an amorphous matrix. The results from this study suggest a critical level of oxygen is required to promote glass formation in Zr[SUB80]Pt[SUB20] melt-spun ribbons produced at a specific quench rate. [ABSTRACT FROM AUTHOR]

SiO[SUB2]/LiNbO[SUB3](LN)/SiO[SUB2] sandwich structures were fabricated for exploring efficient light emission. After annealing at 1000 °C in O[SUB2] for 30 min, this kind of sandwich structure shows a strong ultraviolet photoluminescence (PL) with an asymmetric spectral shape. This PL spectrum may be Gaussian divided into two bands peaked at 310 (α-band) and 346 nm (β-band). If the layer of LN film is replaced by an Fe-doped LN (LN:Fe) one, the β-band vanishes and the α-band redshifts. The α-band is greatly enhanced and simultaneously becomes asymmetrical after this kind of SiO[SUB2]/LN:Fe/SiO[SUB2] structure is annealed for 60 min. Spectral analysis suggests that the α-band arises from an optical transition in positively charged E8 centers at the interfaces between the LN(:Fe) film and the two SiO[SUB2] layers, while the β-band arises from intrinsic defects in the LN(:Fe) films. The mechanism for the PL enhancement is discussed in terms of a photorefractive effect in the LN(:Fe) films. [ABSTRACT FROM AUTHOR]

We have demonstrated that gas pressure (p[sub G]) is a key parameter for fabricating stoichiometric LiNbO[sub 3] thin films during laser ablation. To theoretically describe the influence of p[sub G], a cylindroid rigid-wall model was presented. It was shown that there exist two critical pressures related to Li and Nb: p[sub Li] and p[sub Nb](P[sub Li]

We demonstrate that an ultrathin photoaddressable polymer (PAP) layer with a thickness as small as 5 nm can be utilized for the monodomain alignment of thermotropic liquid crystalline polyfluorene. The optical anisotropies in absorption and emission are found to be independent of the PAP layer thickness within a range of 5 to 30 nm. On the other hand, decreasing the PAP layer thickness greatly improves the performance of polarized blue light-emitting diodes: With a PAP layer thickness of only 10 nm, the device turns on at 5 V and reaches a brightness of 100 cd/m² at 8 V with an efficiency of 0.66 cd/A. [ABSTRACT FROM AUTHOR]

The production of self-organized, spatially dense nanodots on a MgO(100) surface by Ar[sup +] bombardment at elevated sample temperatures (700 and 1000 °C) and ion energies in the range 0.5-5 keV is reported. The results show that at elevated temperatures, the size of the nanodots can be modified by varying the ion energy in a well-defined manner. The nanodot diameter is found to increase with increasing temperature and decrease with increasing ion flux and increasing ion energy. The dot diameter is several tens of nanometers and the height is several nanometers. These results can be interpreted in terms of a recently developed theoretical model. [ABSTRACT FROM AUTHOR]

InGaAsNSb/GaAs quantum wells (QWs) were grown by solid-source molecular-beam epitaxy using a N[sub 2] radio frequency plasma source. The effect of adding Sb during growth of InGaAsN/GaAs QWs was studied. X-ray diffraction, reflection high-energy electron diffraction and transmission electron microscopy studies indicate that Sb suppresses the three-dimensional growth and improves the interface of the QWs. X-ray diffraction and secondary ion mass spectroscopy analysis show that Sb gets incorporated into the quantum well, which becomes a quinternary compound that was previously unexplored. The introduction of Sb during growth of InGaAsN/GaAs QWs significantly enhances the optical properties of the QWs. 1.53 μm room-temperature photoluminescence was obtained from InGaAsNSb/GaAs QWs, which demonstrates the potential of fabricating 1.55 μm InGaAsNSb/GaAs QW lasers for long-haul applications. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A monohydrated Cu[sup II] dimer [Cu[sub 2](Sala)[sub 2](H[sub 2]O)][sub n] [H[sub 2]Sala=N-(2-hydroxybenzyl)-L-alanine] exists as a coordination-helical polymer in the solid state. Thermal dehydration at 340-373 K converts this helical polymer to three-dimensional chiral network polymer, [Cu[sub 2](Sala)[sub 2]][sub n]. Both the hydrated and the anhydrous samples exhibit canted antiferromagnetism at room temperature. A compensation temperature was observed at around 20 K. The hydrated sample has a magnetic ordering temperature of 300 K, while the anhydrous structure possessed a magnetic ordering temperature as high as 435 K. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Reports on the growth and characterization of a GaInNAs resonant cavity enhanced (RCE) photodetector. Optimization of device design; Fabrication of RCE photodetector in a single growth step using gallium alloy distributed Bragg reflectors for the top and bottom mirrors; Quantum efficiency.

Describes molecular beam epitaxial growth of InGaAsN:Sb/GaAs quantum wells for long-wavelength semiconductor lasers. Enhancement in the optical properties of the quantum wells revealed by photoluminescence; X-ray diffraction and reflection high-energy electron diffraction analyses.

The surface enhanced Raman scattering effect was used in conjunction with a micro-Raman system to produce an image of a pattern, on an evaporated silver surface, formed by microcontact printing of p-nitrothiophenol (PNTP). This surface is characterized by roughness on the scale of 50–100 nm. It was confirmed that this type of printing technique forms a self-assembled monolayer with PNTP. Even without roughening of the silver surface, the surface enhancement provided a high contrast image. The resolution of the resulting image was approximately 1 μm. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Investigates the surfactant-assisted silicon (Si), germanium (Ge) epitaxial growth. Use of high resolution photoemission; Reduction of surface energy; Change in the position of antimony (Sb), Si, and Ge atoms; Segregation of the Sb atoms top the growth front.

Power-dependent time-resolved optical spin orientation measurements were performed on In0.1Ga0.9As quantum well (QW) and In0.5Ga0.5As quantum dot (QD) tunnel-coupled structures with an 8-nm-thick GaAs barrier. A fast transient increase of electron spin polarization was observed at the QW ground state after circular-polarized pulse excitation. The temporal maximum of polarization increased with increasing pumping fluence owing to enhanced spin blocking in the QDs, yielding a highest amplification of 174% with respect to the initial spin polarization. Further elevation of the laser power gradually quenched the polarization dynamics, which was induced by saturated spin filling of both the QDs and the QW phase spaces. [ABSTRACT FROM AUTHOR]

Improving the contact characteristics of Ti/Al/Ni/Au on plasma etched n-AlGaN has been attempted by an active pretreatment, which can provide Si and N atoms to occupy the possible metal and N vacancies. It is found that the contacts on both the as-grown and plasma-etched + pretreatment n-Al0.5Ga0.5N present truly Ohmic in nature, whereas the contacts on plasma-etched samples without pretreatment still remain rectifying. Surface atomic concentration analysis indicates that the plasma etching induced N or metal vacancies mostly act as acceptor-like states, leading to a severe compensation. Fortunately, these states can be effectively removed by the presently proposed pretreatment, and thus the Fermi level is raised up toward the conduction band edge, ensuring the formation of Ohmic contacts. [ABSTRACT FROM AUTHOR]

High-efficiency heat engine requires a large output power at the cost of less input heat energy as possible. Here we propose a heat engine composed of serially connected two quantum dots sandwiched between two metallic electrodes. The efficiency of the heat engine can approach the maximum allowable Carnot efficiency ηC. We also find that the strong intradot Coulomb interaction can induce additional work regions for the heat engine, whereas the interdot Coulomb interaction always suppresses the efficiency. Our results presented here indicate a way to fabricate high-efficiency quantum-dot thermoelectric devices. [ABSTRACT FROM AUTHOR]

We have investigated the third-order optical nonlinearities of high-quality colloidal InP/ZnS core-shell quantum dots (QDs) using Z-scan technique with femtosecond pulses. The two-photon absorption cross-sections as high as 6.2 × 103 GM are observed at 800 nm (non-resonant regime) in InP/ZnS QDs with diameter of 2.8 nm, which is even larger than those of CdSe, CdS, and CdTe QDs at similar sizes. Furthermore, both of the 2.2 nm and 2.8 nm-sized InP/ZnS QDs exhibit strong saturable absorption in near resonant regime, which is attributed to large exciton Bohr radius in this material. These results strongly suggest the promising potential of InP/ZnS QDs for widespread applications, especially in two-photon excited bio-imaging and saturable absorbing. [ABSTRACT FROM AUTHOR]

We demonstrate the growth of full-composition-graded InxGa1−xN (0 ≤ x ≤ 1) on a GaN/sapphire template using plasma-assisted molecular beam epitaxy. Composition of indium in InxGa1−xN films is controlled by growth temperature and gallium flux. It was found that In composition increases gradually from x = 0 (GaN) to x = 1 (InN) along the growth direction accompanied by a gradual strain relaxation. At the initial stage of growth, multiple quantum wells like structures with low and high In composition InxGa1−xN layers are spontaneously formed, effectively relaxing the in-plane strain. Finally, the graded InxGa1−xN film exhibits a broadband absorption covering the full solar spectrum, which provides a promising path for the design and production of graded InxGa1−xN based photovoltaic devices. [ABSTRACT FROM AUTHOR]

1.3 μm InGaAsN:Sb/GaAs multiple-quantum-well laser diodes have been grown by solid-source molecular-beam epitaxy using Sb as a surfactant. A low threshold of 1.1 kA/cm2 was achieved for broad-area laser diodes under pulsed operation at room temperature. High-temperature device characterization revealed characteristic temperatures (T[sub 0]) of 92 and 54 K for operating temperatures below and above 75 °C, respectively, as well as a lasing-wavelength temperature dependence of 0.36 nm/ °C. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Developing efficient active region structures with low sensitivity to threading dislocation density (TDD) is of great technical significance for AlGaN-based deep ultraviolet (DUV) light-emitting devices. Here, we propose an active region strategy by introducing bunching effect to form self-assembled sidewall quantum wells (SQWs) with much stronger carrier confinement, resulting in a significant enhancement of internal quantum efficiency (from 46% to 59%) compared to the commonly adopted multiple quantum wells (MQWs) due to the lower sensitivity to TDD. As a demo, an AlGaN-based DUV light-emitting diode (LED) with the proposed active region involving both SQWs and MQWs presents dual-band emission and a consequent 68% enhancement in light output power compared to the DUV-LED with only MQWs as the active region, suggesting that the proposed architecture is fully suitable for the development of high performance DUV light-emitting devices even based on poor or medium quality materials. [ABSTRACT FROM AUTHOR]

The effect of high temperature annealing (HTA) on crystalline quality improvement of h-BN films grown on sapphire substrates has been investigated. It is found that BN grown using conventional molecular beam epitaxy is disordered due to the growth temperature below 1000 °C. By annealing at a temperature of 1700 °C, thermodynamically stable crystalline h-BN could be obtained at wafer scale, where diffusion of atoms in the as-grown BN film is enhanced and the structural defect density decreases. The crystalline h-BN has been confirmed by x-ray diffraction, Raman scattering, and atomic force microscopy measurements. This work demonstrates that HTA is a simple and effective way to achieve wafer-scale crystalline h-BN films, which have numerous potential applications in next-generation two-dimensional devices and flexible III-nitride optoelectronic devices. [ABSTRACT FROM AUTHOR]