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Pool boiling has been considered as an effective method for heat transfer, which is extensively used in semiconductor microprocessors and aerospace. The prevention of critical heat flux (CHF) and improvement of heat transfer coefficient (HTC) are the keys to strengthen the pool boiling heat transfer. It has been reported that porous pillars can delay CHF by reducing vapor–liquid counter flow and nano-porous structure can significantly improve the liquid replenishment capacity and HTC. Herein, we modulate micro-nano porous structures by etching nanostructures on the surface of microporous pillars in order to utilize the advantages of above two structures. The boiling phenomenon inside the micro-nano composite pores is clearly demonstrated based on our visualization experiment. It is observed that the main vapor motion is regular periodic growth and recession. Through the quantitative analysis of the vapor–liquid interface area and vapor movement frequency, we find that they are both positively correlated with the heat transfer performance of porous structures. Hence, it is proved that the vapor–liquid phase distribution is the decisive factor affecting the heat transfer performance of micro-nano porous structures. Following the principle of maintaining larger vapor–liquid interface area and accelerating vapor movement frequency, the micro-nano porous structures with better performance can be obtained. Our approach establishes the relationship between the internal boiling phenomenon and the performance of micro-nano porous structures. In addition, it also provides a feasible direction for improving the performance of engineered boiling micro-nano structures. [ABSTRACT FROM AUTHOR]

We present a design for a quantum photodetector operating in the terahertz range, at 3.45 THz (15 meV, 87 μm). Our device relies on biased GaAs/AlGaAs heterostructure, designed to exploit LO phonon scattering as an extraction mechanism. In our design, the external potential due to the applied bias forms an extraction miniband and allows accommodating an LO phonon transition (36 meV) and use it as an extraction mechanism, even though its energy exceeds the detector's absorbing transition at 15 meV. Spectral-resolved measurements performed on arrays of patch antenna microcavities reveal a peak photocurrent at the designed photon energy with a responsivity of 80 mA/W at 20 K. The maximum operating temperature of the photodetector is found to be 40 K. Detector characterizations were performed both with a black-body source as well as with a terahertz quantum cascade laser emitting at 3.5 THz. [ABSTRACT FROM AUTHOR]

With the forthcoming laser intensities (I ≥ 1023 W/cm2), synchrotron radiation in a laser-plasma interaction has attracted particular interest because it can lead to an extremely bright source of γ-rays. Here, a scheme to generate a bright γ-ray pulse with high efficiency is proposed and numerically demonstrated. Using a circularly polarized (CP) laser pulse impinged on a thin foil, a relativistic flying plasma layer is formed. With another counterpropagating CP pulse colliding with the flying layer, it is found that the electrons are efficiently accelerated in the longitudinal direction by the space-charge field. The energetic electrons interact with the counterpropagating CP pulse, producing ultra-brilliant (∼1024 photons/s/mm2/mrad2/0.1%BW) highly dense (∼270nc) femtosecond (∼5 fs) γ-ray pulses. At a moderate laser intensity of 4 × 1022 W/cm2, the fraction of laser energy transferred into the γ-ray pulse is as high as 10%, which is comparable to that previously predicted for an order of magnitude higher in laser intensity. The enhanced γ-photon emission might pave the way for its potential applications in the near future. [ABSTRACT FROM AUTHOR]

The thermal and electrical properties including the permittivity spectra in radio frequency region were investigated for copper/yttrium iron garnet (Cu/YIG) composites. Interestingly, the percolation behaviors in electrical and thermal conductivity were obtained due to the formation of copper particles' networks. Beyond the electrical percolation threshold, negative permittivity was observed and plasmon frequency was reduced by several orders of magnitude. With the increase in copper content, the thermal conductivity was gradually increased; meanwhile, the phonon scattering effect and thermal resistance get enhanced, so the rate of increase in thermal conductivity gradually slows down. Hopefully, Cu/YIG composites with tunable electrical and thermal properties have great potentials for electromagnetic interference shielding and electromagnetic wave attenuation. [ABSTRACT FROM AUTHOR]

Deep level optical spectroscopy (DLOS) and deep level transient spectroscopy (DLTS) measurements performed on Ni/β-Ga2O3 Schottky diodes fabricated on unintentionally doped (010) substrates prepared by edge-defined film-fed growth revealed a rich spectrum of defect states throughout the 4.84eV bandgap of β-Ga2O3. Five distinct defect states were detected at EC-0.62eV, 0.82eV, 1.00eV, 2.16eV, and 4.40eV. The Ec-0.82eV and 4.40eV levels are dominant, with concentrations on the order of 1016cm-3. The three DLTS-detected traps at EC -- 0.62 eV, 0.82 eV, and 1.00 eV are similar to traps reported in Czochralski-grown β-Ga2O3, [K. Irmscher et al., J. Appl. Phys. 110, 063720 (2011)], suggesting possibly common sources. The DLOS-detected states at EC -- 2.16 eV and 4.40 eV exhibit significant lattice relaxation effects in their optical transitions associated with strongly bound defects. As a consequence of this study, the Ni/β-Ga2O3 (010) Schottky barrier height was determined to be 1.55 eV, with good consistency achieved between different characterization techniques. [ABSTRACT FROM AUTHOR]

We report dissipative soliton generation from an Yb-doped all-fiber nonlinearity- and dispersionmanaged nanotube mode-locked laser. A simple all-fiber ring cavity exploits a photonic crystal fiber for both nonlinearity enhancement and dispersion compensation. The laser generates stable dissipative solitons with large linear chirp in the net normal dispersion regime. Pulses that are 8.7 ps long are externally compressed to 118 fs, outperforming current nanotube-based Yb-doped fiber laser designs. [ABSTRACT FROM AUTHOR]

Excitation of surface plasmons enables super-Planckian thermal radiation far beyond the blackbody limit. By patterning a single layer of graphene sheet into ribbons, the closed circular dispersion of graphene plasmons is opened to become hyperbolic, leading to broadband singularities of density of states. Extremely high-k evanescent waves can now couple with hyperbolic graphene plasmons. Consequently, a giant enhancement of the near-field radiative heat flux, by more than one order of magnitude, is demonstrated in this study using rigorous numerical simulations. The findings may open promising pathways for highly efficient thermal management, energy harvesting, and subwavelength thermal imaging. [ABSTRACT FROM AUTHOR]

Influence of the barrier layer on the electrical properties of V/Al-based Ohmic contact is investigated by comparing the surface morphology and alloying results of V/Al/Ni/Au (with barrier Ni) and V/Al/Cr/Au (with barrier Cr) contacts on n-AlGaN (Al molar fraction>60%) after 850 °C annealing. Due to the clustering of Ni during annealing, a thin Al layer (AlOx) and a number of Al-Au alloy clusters are formed at the contact interface of n-AlGaN, which increases the contact resistance of the V/Al/Ni/Au Ohmic contacts. In contrast, the annealed V/Al/Cr/Au electrodes cover the surface uniformly, which not only contributes to the increased contact area, but also suppresses the formation of high resistance products. Thanks to the Cr barrier layer, the specific contact resistivity of V/Al-based Ohmic contact is reduced by 26%. [ABSTRACT FROM AUTHOR]

The impact of proton irradiation on the deep level states throughout the Mg-doped p-type GaN bandgap is investigated using deep level transient and optical spectroscopies. Exposure to 1.8 MeV protons of 1 × 1013cm-2 and 3×1013cm-2 fluences not only introduces a trap with an EV + 1.02 eV activation energy but also brings monotonic increases in concentration for as-grown deep states at EV + 0.48 eV, EV + 2.42 eV, EV + 3.00 eV, and EV + 3.28 eV. The non-uniform sensitivities for individual states suggest different physical sources and/or defect generation mechanisms. Comparing with prior theoretical calculations reveals that several traps are consistent with associations to nitrogen vacancy, nitrogen interstitial, and gallium vacancy origins, and thus are likely generated through displacing nitrogen and gallium atoms from the crystal lattice in proton irradiation environment. [ABSTRACT FROM AUTHOR]

Graphene has attracted great attention in nanoelectronics, optics, and energy harvesting. Here, the near-field radiative heat transfer between graphene-covered corrugated silica is investigated based on the exact scattering theory. It is found that graphene can improve the radiative heat flux between silica gratings by more than one order of magnitude and alleviate the performance sensitivity to lateral shift. The underlying mechanism is mainly attributed to the improved photon tunneling of modes away from phonon resonances. Besides, coating with graphene leads to nonlocal radiative transfer that breaks Derjaguin's proximity approximation and enables corrugated silica to outperform bulk silica in near-field radiation. [ABSTRACT FROM AUTHOR]

We report a universal softening phenomenon that the shear modulus decreases linearly with increasing the base metal content and verify the local fluctuations, both positive and negative, in metallic glasses. By quantitatively evaluating the fluctuation amplitude, we propose an intuitive physical picture that metallic glasses are atomic level hybrids composed of clusters and amorphous base metals. The local fluctuation characters were further correlated to the mechanical properties of metallic glasses. The study provides insights on the long-standing issues of the atomic level structures, the structure-property relationships, and the mechanisms of plastic deformation and glass transition in metallic glasses. [ABSTRACT FROM AUTHOR]

A complex target (CT) configuration tailored for generating high quality proton bunch by circularly polarized laser pulses at intensities of 1020-21 W/cm2 is proposed. Two-dimensional particle-in-cell simulations show that both the collimation and mono-energetic qualities of the accelerated proton bunch obtained using a front-shaped thin foil can be greatly enhanced by the backside inhomogeneous plasma layer. The main mechanisms for improving the accelerated protons are identified and discussed. These include stabilization of the photon cavity, providing hole-boring supplementary acceleration and suppressing the thermal-electron effects. A theory for tailoring the CT parameters is also presented. [ABSTRACT FROM AUTHOR]

Based on nonequilibrium Green's functions in combination with density-function theory, the transport properties of trigonal graphenes, with the vertex carbon atom substituted by one phosphorus or boron atom and bounded through a B-N pair, coupled to gold electrodes are investigated. The rectification behavior can be observed because a potential barrier similar to the p-n junction is formed in the B-N region of central molecule. When the size of a central molecule is enlarged, rectification ratio is improved greatly since the barrier height in it is enhanced as well. [ABSTRACT FROM AUTHOR]

Deep level defects in nonpolar m-plane GaN grown by ammonia-based molecular beam epitaxy were characterized using deep level transient spectroscopy (DLTS) and deep level optical spectroscopy (DLOS) and compared with polar c-plane GaN that was grown simultaneously in the same growth run. Significant differences in both the levels present and their concentrations were observed upon comparison of both growth orientations. DLTS revealed electron traps with activation energies of 0.14 eV, 0.20 eV, and 0.66 eV in the m-plane material, with concentrations that were ∼10-50 × higher than traps of similar activation energies in the c-plane material. Likewise, DLOS measurements showed ∼20 × higher concentrations of both a CN acceptor-like state at EC - 3.26 eV, which correlates with a high background carbon concentration observed by secondary ion mass spectroscopy for the m-plane material [A. Armstrong, A. R. Arehart, B. Moran, S. P. DenBaars, U. K. Mishra, J. S. Speck, and S. A. Ringel, Appl. Phys. Lett. 84, 374 (2004)], and the VGa-related state level at EC - 2.49 eV, which is consistent with an enhanced yellow luminescence observed by photoluminescence. The findings suggest a strong impact of growth dynamics on the incorporation of impurities and electrically active native point defects as a function of GaN growth plane polarity. [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]

The magnetization oscillation driven by spin transfer torque (STT) in a nano-pillar composed of a large in-plane anisotropy fixed layer and a soft free layer is studied. It is found that instead of frequency continuously changing with current as most nano-oscillators do, this kind of nano-oscillator can only oscillate in two stable states with specific frequencies. In each state, the frequency is almost invariant with current density. The oscillation state could be easily manipulated by the magnetization state of the free layer or an applied pulse magnetic field as the working current density is lower than a critical value (Jc). The critical current density and the frequency difference of the two states can be tuned by the saturation magnetization (Ms) of the two layers and the anisotropy constant K of fixed layer. Phase-locked oscillation is obtained in a two-nanopillar system, suggesting that it may be possible to amplify the oscillation signal by building an array of this kind of nanopillar system. This kind of STT-based nano-oscillator may have various applications in the field of spintronics. [ABSTRACT FROM AUTHOR]

We report a dual-color ultraviolet (UV) photodetector based on mixed-phase-MgZnO/i-MgO/p-Si double heterojunction. The device exhibits distinct dominant responses at solar blind (250 nm) and visible blind (around 330 nm) UV regions under different reverse biases. By using the energy band diagram of the structure, it is found that the bias-tunable two-color detection is originated from different valence band offset between cubic MgZnO/MgO and hexagonal MgZnO/MgO. Meanwhile, due to the large conduction band offset at the Si/MgO interface, the visible-light photoresponse from Si substrate is suppressed. [ABSTRACT FROM AUTHOR]

Both wavelength selectivity and directional insensitivity are highly desired in thermophotovoltaic applications. A concept of a magnetic-polariton-enhanced thermophotovoltaic emitter is presented. The predicted normal emittance from such a nanoengineered surface exceeds 0.8 in the wavelength region from 0.62 to 1.98 μm and is below 0.2 at wavelengths longer than 2.4 μm. Furthermore, thermal emission from the proposed structure is diffuse-like as the emittance changes little with the direction up to 75° from the normal. The strip width allows tuning of the emittance spectrum to match particular photovoltaic cells to potentially enhance power generation with improved conversion efficiency. [ABSTRACT FROM AUTHOR]

We used depth-resolved cathodoluminescence spectroscopy (DRCLS) to describe the strong dependence of Li acceptor formation on thermal treatment in Li-doped ZnO. Within a 500-600 °C annealing temperature range, subsequent quenching ZnO leaves Li as interstitial donors, resulting in low room temperature resistivity, while slow cooling in air allows these interstitials to fill Zn vacancies forming Li acceptors 3.0 eV below the conduction band edge. DRCLS reveals an inverse relationship between the optical emission densities of lithium on zinc sites versus zinc vacancy sites, demonstrating the time dependence of Li interstitials to combine with zinc vacancies in order to form substitutional Li acceptors. [ABSTRACT FROM AUTHOR]

The synthesis, morphology, and magneto-transport properties of nanostructure-engineered charge-ordered Pr0.5Ca0.5MnO3 grown on ZnO nanowires are reported. The stability of the charge-ordering can be tuned, but more interestingly, the sign of the magnetoresistance is inverted at low temperatures. Coexistence of ferromagnetic clusters on the surface and antiferromagnetic phase in the core of the grains were considered in order to understand these features. This work suggests that such a process of growing on nanowires (NW) network can be readily extended to other transition metal oxides and open doors towards tailoring their functionalities. [ABSTRACT FROM AUTHOR]

Polymorphic transformation mechanism of η and η′ in single crystalline Cu6Sn5 has been investigated in this study. η phase exists at room temperature in the quenched specimens and transforms to η′ phase under aging at 150 °C for 40 d. The nucleation and growth of η′ phase is observed by field emission scanning electron microscope and surface reconstruction of polymorphic transformation is confirmed by both x-ray diffractometer and differential scanning calorimetry analysis. The results show that the volumetric strain energy is the dominant reason for occurring polymorphic transformation rather than order-disorder transition of η and η′ phases. [ABSTRACT FROM AUTHOR]

Molecular devices are constructed based on a molecule connected into both electrodes with different metal materials, and their transport properties are investigated by the first-principles method. The result shows that such devices can generate two asymmetrical Schottky barriers at contacts; the current rectification thus is created. This rectification is also fully rationalized by the calculated transmission spectra and the spatial distribution of the lowest unoccupied molecular orbital and highest occupied molecular orbital states. Our study suggests that it might be a very important way for both electrodes using different materials to realize a molecular rectification. [ABSTRACT FROM AUTHOR]

Using the discrete dipole approximation method, two visible extinction peaks are found for Ag nanohelixes. Both of them redshift periodically in an approximate half pitch with the helix height and redshift linearly with the helix diameter and pitch height. At the two absorbance peaks, an integer number of E-field maxima occur along the helix. These field maxima could be treated as results of collective electron oscillations by periodic effective dipoles within a half pitch along the helix. The wavelengths of the absorbance peaks are found to scale with the effective dipole length, which is consistent with the periodic structure of the helix. [ABSTRACT FROM AUTHOR]

We design the A-R rectifier based on the D-σ-A molecules to examine the rectifying performances by the first-principles method. The calculated results show that the electronic structures for all of our systems perfectly match the A-R rectifier, as expected, but their rectifying direction is very strikingly opposite and working mechanism is completely different. This behavior can be rationalized through an asymmetrical shift of molecular levels under bias of different polarities, which is because of always-existing intrinsic asymmetrical coupling effects of molecular levels to electrodes. Detailed analysis demonstrates that the rectifying direction induced by this mechanism is always in opposition to that induced by the A-R mechanism. [ABSTRACT FROM AUTHOR]

Based on first-principles approach, the end-group effects on negative differential resistance (NDR) and rectifying performance of polyyne-based molecular wires are investigated. The NDR behaviors are observed when the polyyne is attached to asymmetric (-NO2 and -NH2) or symmetric (double -S) end groups, and rectifying performance emerges with the presence of asymmetric groups. The analysis on microscopic nature reveals the intrinsic origin of these phenomena. Our results show the possibility of a multifunctional molecular device design simultaneously with NDR and rectifying performances by using a technology of capping certain end groups to polyyne. [ABSTRACT FROM AUTHOR]

Using the first-principles method, we investigate rectifying performances of D-π-A molecules based on cyanovinyl aniline derivatives. The calculated results show that different functional groups can change the location of molecular orbitals and thus change the rectifying properties of molecules. Interestingly, we find that although the electronic structure for our studied systems is in agreement with that proposed originally by Aviram and Ratner [Chem. Phys. Lett. 29, 277 (1974)], the rectifying direction is opposite from it due to the asymmetric shift of molecular levels under biases of different polarities. Only for model (M4), it shows a forward rectifying performance under larger bias. [ABSTRACT FROM AUTHOR]

We report first-principles calculations of transport behaviors for a molecular device whose electrode surface is contaminated by various diatomic groups. It has been found that such a device demonstrates less transport variations for the contamination of the group PO or SO in the whole bias range but it shows more transport variations for contamination of the group CN, HS, or NO only under low bias, which suggests that contamination of all diatomic groups studied here always affects high-bias transport properties of a device in an extremely gentle manner. [ABSTRACT FROM AUTHOR]

We report on the structure and transport properties of nanocrystalline manganite La0.7Sr0.3MnO3 (LSMO) synthesized on nanowires-engineered MgO substrates by pulsed laser deposition, which is compared with reference samples deposited directly on flat MgO substrates. Such LSMO/MgO nanocomposites show enhanced low field magnetoresistance, especially at low temperature, due to the dominant spin-polarized intergrain tunneling. This work suggests that growing on nanoengineered substrates is a viable route to achieve nanostructured materials with desired crystalline structure and physical properties. [ABSTRACT FROM AUTHOR]

A heterostructure comprised of a 2.7 nm (7 unit cell) thick layer of the metallic ferromagnet La2/3Ca1/3MnO3 and two 50 nm thick layers of the high-temperature superconductor YBa2Cu3O7 epitaxially grown on (100) SrTiO3 by pulsed-laser deposition was characterized by magnetization measurements and spherical-aberration-corrected high-resolution transmission electron microscopy (HRTEM). The saturation magnetization is about half of that in bulk La2/3Ca1/3MnO3. A massive reduction in the magnetization previously inferred from sputter-deposited La2/3Ca1/3MnO3–YBa2Cu3O7 heterostructures can be ruled out. HRTEM image analysis, combined with image simulation and a focus series reconstruction, revealed atomically sharp epitaxial structures with stacking sequences –(La,Ca)O–CuO2– and –BaO–MnO– at the top and bottom interface. [ABSTRACT FROM AUTHOR]

An analytical solution is given for the self-heating conduction equation of a suspended one-dimensional (1D) object. The conductivity of the 1D object is given by combining Umklapp and second-order three-phonon processes. Using this analytical solution, several relations among some important parameters are discussed and are shown to be consistent with existing experimental results. A method to retrieve the coefficients for thermal conductivity is proposed for a general thermal conductor without knowing the detailed temperature profile along the 1D object. [ABSTRACT FROM AUTHOR]

Near-field thermal radiation can significantly exceed that predicted by the Stefan–Boltzmann law, especially when surface polaritons are excited such that the energy transfer is through photon tunneling. The penetration depth, or skin depth, of evanescent waves is usually a few tenths of a wavelength. This letter demonstrates that an extremely small skin depth (on the order of a nanometer) can exist for nanoscale thermal radiation between two plates separated by a vacuum gap, even though the dominant wavelengths are in the infrared. Furthermore, the skin depth is proportional to the separation distance. [ABSTRACT FROM AUTHOR]

Resonance transmission or absorption has been observed in metallic deep gratings and previously characterized as coupled surface plasmon polaritons or Fabry–Pérot-like resonances. This letter provides a quantitative explanation of this phenomenon by means of localized magnetic polaritons. Rigorous coupled-wave analysis is used to predict the spectral transmittance and absorptance of subwavelength gratings. The resonance condition is compared with that predicted by the LC circuit model. Some geometric effects that cannot be explained by previous models can be well understood in terms of magnetic polaritons. The insight gained from this study may facilitate future design and applications of subwavelength periodic structures. [ABSTRACT FROM AUTHOR]

The effects of anisotropic strain on wurtzite GaN valence subbands are investigated both theoretically and experimentally. k•p perturbation theory reveals that the in-plane asymmetric strain not only affects the transition energies, but also determines the polarization properties, which is analyzed to be the essential cause of the optical anisotropy. Considerable in-plane anisotropy of strained C-plane GaN in polarized photoluminescence is reported. The experimental result in good agreement with theoretical study directly proves the strain effects on the transitions polarization states. The fine accordance of observed and simulated photoluminescence dependences on strain asymmetry degree demonstrates a primary realization of strain controlled optical anisotropy, and such modulation indicates the great potential of utilizing GaN-based semiconductors in polarization-sensitive optoelectronics. [ABSTRACT FROM AUTHOR]

The “hot spots” mechanism is a common wisdom for surface enhanced Raman scattering (SERS). We argue that this is true when the hot spots are directly exposed to the detector. For complex SERS substrates with layered structures such as nanorod arrays, the structure and the layer absorbance both play important roles, which make the effect of hot spots less significant. Using a numerical calculation of the local electric field distribution of an Ag nanorod array substrate, we demonstrate that the layer absorbance must be considered in order to obtain polarization-dependent SERS intensity that is consistent with experimental data. [ABSTRACT FROM AUTHOR]

We have investigated the surface enhanced Raman scattering (SERS) from Au nanocombs and nanorods under different excitation conditions. The SERS intensity from nanocombs is always larger than that from nanorods, but the polarized SERS dependence is similar for the two nanostructures. These results agree quantitatively well with the local E-field calculations, and the nanospine in the nanocomb increases the local E-field over all surfaces of the nanocomb structure. The combination of experimental and numerical results predicts that the Raman enhancement at 633 nm excitation is estimated to be from seven to eight times that at 785 nm excitation. [ABSTRACT FROM AUTHOR]

We report that magnetic properties of an Fe-6.5 wt. % Si alloy can be improved through texture control by using directional recrystallization. Columnar grain structures with column sizes of ∼0.38×1.2 mm2 were developed during directional recrystallization. It was found that there are low energy boundaries between columns and main textures of the specimen were {110}<111> and {111}<110>. As a result, the coercivity of a directionally recrystallized specimen is reduced by a factor of 5 when measured along 60° away from the growth direction, as compared to a specimen consisting of ∼77 μm equiaxed grains. [ABSTRACT FROM AUTHOR]

Surface-enhanced Raman scattering intensity versus the separation of 100 nm diameter Au nanopost array on Si substrate was investigated. The relative Raman peak intensity per nanopost at different Raman modes rapidly decreases in a similar manner with the increase in the separation. This experimental result agrees well with the localized electric field enhancement calculation by three dimensional finite-difference time-domain method. The Raman peak intensity is mainly due to the edge enhancement of the nanopost through the coupling effect, and the nonenhancement contribution from the top of the nanopost also plays an important role. [ABSTRACT FROM AUTHOR]

We show here that the plasmonic array based on nanoapertures in ultrathin silver film radiates at optical frequency and behaves as an optical antenna array (OAA). The far-field radiation originates from the coherent superposition of plasmonic emissions on each bank of the aperture. The radiation of OAA presents a strong directivity, which depends on the in-plane rotation of aperture array, and on the polarization and incidence angle of the excitation light as well. We suggest that these features have potential applications in photovoltaics, light-emitting devices, and optical sensors. [ABSTRACT FROM AUTHOR]

A bandgap and intersublevel spacing tuned laser has been realized by using a modulation C-doped InGaAs/GaAs quantum dot structure, which utilizes a postgrowth annealing process. The intermixed laser exhibits comparable light-current characteristics, indicating little detrimental change to the quantum dot laser material, and show a ground state bandgap blueshift of ∼13 nm and intersublevel energy spacing reduction of ∼30 nm compared to the unannealed device. The differences in the samples during annealing are attributed to the suppression of Ga vacancy propagation for samples with modulation C doping. [ABSTRACT FROM AUTHOR]

Using valence electron energy loss spectroscopy and ab initio band structure calculations, we have studied the basic electronic structure of a potential optical crystal YBa3B9O18. Its optical band gap Eg is experimentally estimated as 6.3 eV and the origins of the individual interband transitions have been identified. In addition, the theoretical calculation reveals the strong anisotropic characteristic of the material band structure, accounting for its large birefringence. [ABSTRACT FROM AUTHOR]

High-performance top-gated n-type single-walled carbon nanotube (CNT) field-effect transistors (FETs) have been fabricated using scandium contacts and HfO2 gate oxide and are benchmarked against the state-of-the-art n-type Si metal-oxide semiconductor FETs. Two key device metrics, the intrinsic gate-delay (CV/I) and energy-delay product (CV/I·CV2) per unit width, of the n-type CNT FETs are found to show significant improvement over the Si devices. In particular, the gate-delay time is estimated to be 2.1 ps for an n-type CNT FET which is based on a CNT with a diameter of 1.1 nm and a channel length of 220 nm. [ABSTRACT FROM AUTHOR]

We have combined the reflection and transmission Z-scan (RZ- and TZ-scans) techniques under femtosecond laser at 800 nm to extract both the third- and fifth-order nonlinear refractive indices (n2 and n4) in InN thin films. The observation of the nonlinear refractive index saturation in the intensity-dependent RZ-scan measurement indicates the existence of the fifth-order effect. By the aid of the TZ-scan, the fifth-order nonlinear effect has been enhanced by enlarging the cascaded contribution from the increased laser interaction length, where large n2 of -2.5×10-11 cm2/W and n4 of 2.1×10-19 cm4/W2 have been determined. [ABSTRACT FROM AUTHOR]

Silicon oxide nanowires (SiONWs) smaller than 10 nm were synthesized by vaporization of SiO2 powders without catalytic assistance. The SiONWs resemble bamboos and the knots comprise Si nanocrystals of different orientations. A SiONW water suspension prepared ultrasonically was subjected to photoluminescence and photoluminescence excitation spectral examinations. Strong blue emission which arises from band-to-band recombination in the quantum confined Si nanocrystals in the knots is observed. Our results show that the emission characteristics can be tuned by adjusting the size of the knots. [ABSTRACT FROM AUTHOR]

It is shown that n-type doping of AlGaAs/GaAs distributed Bragg reflectors (DBRs) grown by metal-organic vapor-phase epitaxy has a profound negative impact on the performance of vertical-cavity surface-emitting lasers (VCSELs) based on such mirrors. Using an intracavity contact scheme, 1.3-μm-range InGaAs VCSELs with and without doping in the bottom DBR are directly compared. Doped mirrors lead to lower slope efficiency, lower output power, and higher threshold current. From x-ray diffraction, high-accuracy reflectance measurements, and atomic force microscopy studies, it is suggested that this performance degradation is due to the doping-enhanced Al–Ga interdiffusion, leading to interface roughening and increased scattering loss. [ABSTRACT FROM AUTHOR]

The authors report the creation of low reflectivity angled facets by focused-ion-beam postfabrication etching. A method to directly measure the effective facet reflectivity of such facets, utilizing gain saturation effects in the quantum dots is described. The reflectivities of the angled facets are shown to decrease by increasing the facet angle from 0° to 15°. With a reflectivity of <1×10-6 obtained for a facet with a 15° angle, allowing quantum dot superluminescent light-emitting diodes to be fabricated. The use of different angled facets to control the emission wavelength of both quantum dot lasers and superluminescent light-emitting diodes is outlined. [ABSTRACT FROM AUTHOR]

The extinction spectra and field distribution of Ag helical nanostructures have been calculated using the discrete dipole approximation method. The plasmon peak of the Ag helix can be tuned not only by the structural parameters but also by the polarizations of the incident light, especially the circular polarizations. In addition, the polarization direction of the incident light can change the spatial distribution of the maximum E field, which provides a simple way to spatially resolve analyte’s distribution on the nanostructures for sensing applications. [ABSTRACT FROM AUTHOR]

The authors find that metallic glass can be controlled to create regularly arrayed fine multiple shear bands under small punch test, indicating that metallic glass essentially has a good plastic deformation ability and thus high ductility under suitable loading condition. The current findings imply that the initiation and propagation of shear bands in metallic glass strongly depends on the stress state and the small punch test can also be regarded as an effective method to characterize the shear deformation ability and distinguish ductile-brittle transition of different metallic glasses. [ABSTRACT FROM AUTHOR]

Carbon nanotubes have a significant application in nanotechnology as nanopipes conveying fluids. In this letter, a pressure control model for transport of liquid mercury through carbon nanotubes using classical molecular dynamics simulations in conjunction with an atomistic model is presented. Wetting of single-walled carbon nanotubes by mercury occurs above a threshold pressure of liquid mercury. The liquid mercury can be transported through carbon nanotubes with the continuous increase of its internal pressure. Also, the authors show that single-walled carbon nanotubes can transport liquid mercury discontinuously when a periodical pressure is applied on the liquid. [ABSTRACT FROM AUTHOR]

Dynamic instability is one of the typical cleavage fracture features in brittle materials. The authors find that dynamic instability of metallic glass starts to occur in the mirror region on the fracture surface through a wavy cracking propagation with the formation of periodic nanoscale steps. This kind of dynamic instability is associated with the early crack curving due to the intrinsic isotropic structure of metallic glass. Furthermore, they classify dynamic instabilities of cleavage fracture as crack curving at low velocity and crack branching at high velocity, corresponding to the mirror and hackle regions of metallic glass, respectively. [ABSTRACT FROM AUTHOR]

The polarization directions of domains in BaTiO3 single crystal are determined by convergent-beam electron diffraction directly. The intensity distributions in the (001) and (001) diffraction disks are different, which is due to the noncentrosymmetric unit cell of ferroelectrics. The in situ transmission electron microscopy observations on the evolution of domains under external fields indicate that the disk with a little brighter center fringes is the (001) disk and the polarization vector is toward this disk. The method provides a straightforward criterion for polarization direction determination of ferroelectric domains. [ABSTRACT FROM AUTHOR]