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As a prototype of organic–inorganic hybrid compounds, metal-organic frameworks (MOFs) have attracted enormous interest for their diverse physical and chemical properties. Recently, the magnetic and electric properties of MOFs have started to draw much attention. In particular, the coexistence of multiple orders (magnetic, electric, and elastic) in some MOFs makes them as emerging multiferroic materials. In terms of the strong and tunable ferroelectricity, the long-distance superexchange interaction, the order–disorder transition of hydrogen bonds in combination with the structural flexibility, and multiferroic MOFs represent a unique family beyond conventional inorganic multiferroics. This perspective provides a brief overview of recent progress in the field of multiferroic MOFs. First, the multiferroic MOFs reported so far are summarized and classified. Then, various cross coupling effects, i.e., the magnetic field control of electric polarization, electric field manipulation of magnetization, and pressure tuning of magnetic and electric properties, are described and discussed. In addition, a number of unusual phenomena such as the giant thermal expansion and quantum effects are introduced. Finally, some promising topics that have not yet been fully explored in multiferroic MOFs are proposed. [ABSTRACT FROM AUTHOR]

Ferrite samples of Li+ substituted MnFe2O4 nano particles were synthesized by sol-gel auto-combustion method. The samples were obtained by annealing at relatively low temperature at 600 °C and characterized by x-ray diffraction, transmission electron microscopy, vibrating sample magnetometry, and infrared (IR) spectroscopy. Lattice parameter, x-ray density, specific surface area, and porosity are found to increase, whereas bulk density and crystallite size showed the decreasing trend with the Li+ content. Splitting of major absorption bands related to Li+ substituted ferrites were observed in IR spectra. Substitution of Li+ ions for Fe3+ caused a decrease in the saturation magnetization from 75.69 to 58.57 emu/g and the coercivity increased from 157 to 308 Oe. DC resistivity decreases with increase in Li+ content. The temperature dependent results indicate that the values of dielectric constant ([variant_greek_epsilon]′) and loss tangent ([variant_greek_epsilon]″) increase with the increase in temperature. [ABSTRACT FROM AUTHOR]

Physical and physico-chemical properties of polymer filled with carbon black (CB) particles, namely, the microstructure dependence of these properties, are not only interesting on their own but are particularly important for electronic applications as they can impose limits on the sensitivity of a device. With this purpose, we report on an experimental study of the structural and electrical properties of semi-crystalline ethylene-co-butyl acrylate polymer filled with conductive CB nano-particles. We found that the value of the direct current conductivity exhibits a jump of 12 orders of magnitude over a small change in CB concentration and is due to a percolation-like behavior. To assess the temperature evolution of supercolative samples, we present measurements of the conductivity as function of temperature. Above the glass transition temperature of the polymer, the CB network restricts the motions of the polymer chains. This behavior was ascribed to the change in CB mesostructure in the polymer matrix as probed by scanning electron microscopy and atomic force microscopy as well as to the difference in the thermal expansion between the two phases. In addition to the observed conductivity increase, the effect of adding CB particles in the polymer matrix is to increase the thermal stability as is probed by thermogravimetric analysis tests. The room temperature alternating current conductivity, studied over the frequency range from 100 Hz to 15 MHz, is interpreted as arising mainly from inter-aggregate polarization effects. By considering carefully the CB content of the alternating current conductivity, we found that our experimental data agree well with the Sheng's model of fluctuation-induced tunnelling of charge carriers over nanometric gaps between adjacent CB aggregates. For studying the filler content dependence of the effective permittivity, several mixing laws and effective medium theories have been used. The observed discrepancies between our experimental data and these theoretical predictions may be occur partly because these analysis contain an inaccurate knowledge of the physicochemical properties of the carbonaceous phase, give a poor description of the interfaces in these complex heterostructures, or both. As part of the present investigation, present results are compared to transport properties of polystyrene-cobutyl acrylate latex and epoxy resin matrices filled with different loadings of multiwalled carbon nanotubes (MWCNT) and over wide temperature and frequency ranges. It is remarkable that the MWCNT's anisotropy (length-to-diameter ratio close to 100) manifests itself in percolation-like behavior with lower threshold volume fraction and different mesostructure than that evidenced for CB filled samples. [ABSTRACT FROM AUTHOR]

The inclusion of graphene into composite energetic materials to enhance their performance is a new area of interest. Studies have shown that the addition of graphene significantly enhances the thermal transport properties of an energetic composite, but how graphene influences the composite's ignition sensitivity has not been studied. The objective of this study is to examine the influence of carbon additives in composite energetic material composed of aluminum and polytetrafluoroethylene (Teflon™) on ignition sensitivity due to low velocity, drop weight impact. Specifically, three forms of carbon additives were investigated and selected based on different physical and structural properties: spherically shaped amorphous nano particles of carbon, cylindrically shaped multi walled carbon nanotubes, and sheet like graphene flakes. Results show an interesting trend: composites consisting of carbon nanotubes are significantly more sensitive to impact ignition and require the lowest ignition energy. In contrast, graphene is least sensitive to ignition exhibiting negligible reduction in ignition energy with low concentrations of graphene additive. While graphene does not significantly sensitize the energetic composite to ignition, graphene does, however, result in greater overall reactivity as observed through images of the reaction. The enhanced thermal transport properties of graphene containing composites may promote greater energy transport once ignited, but those properties do not also increase ignition sensitivity. These results and the understanding of the structural arrangement of particles within a composite as a key parameter affecting impact ignition sensitivity will have an impact on the safe handling and use of composite energetic materials. [ABSTRACT FROM AUTHOR]

Experiments have shown strong effects of some substrates on the localized plasmons of metallic nano particles but they are inconclusive on the affecting parameters. Here, we have used discrete dipole approximation in conjunction with Sommerfeld integral relations to explain the effect of the substrates as a function of the parameters of incident radiation. The radiative coupling can both quench and enhance the resonance and its dependence on the angle and polarization of incident radiation with respect to the surface is shown. Non-radiative interaction with the substrate enhances the plasmon resonance of the particles and can shift the resonances from their free-space energies significantly. The non-radiative interaction of the substrate is sensitive to the shape of particles and polarization of incident radiation with respect to substrate. Our results show that the plasmon resonances in coupled and single particles can be significantly altered from their free-space resonances and are quenched or enhanced by the choice of substrate and polarization of incident radiation. [ABSTRACT FROM AUTHOR]

The three-dimensional (3D) rotation of a single cell is a fundamental manipulation process at the cellular level for physiological and pathological characterization. However, the motion of the cells is affected by factors such as fluid forces and gravitation forces; hence, it is difficult to maintain a stable spatial position of a single cell. Therefore, ensuring stable spatial positions for single-cell rotation is an essential problem that needs to be addressed. In this paper, we present a single cell microfluidic chip based on dielectrophoresis, for single-cell self-adaptive spatial localization and 3D rotation. Numerical simulation was performed to analyze the electric field under different signal configurations, effect of cell self-adaption, and levitation of individual cells. Based on the results, self-adaptive spatial localization and 3D rotation of single cells were successfully realized. By altering the electric signal profile, a greater level of control on cell rotation modes can be obtained. Furthermore, utilizing the out-of-plane rotation, we realize 3D morphology reconstruction of the single cell. The developed single-cell 3D rotation chip is directly applicable to cellular research processes including tomographic imaging and the acquisition of biophysical parameters. [ABSTRACT FROM AUTHOR]

We investigated the effects of poling conditions on the piezoelectric performance of potassium sodium niobate [(K,Na)NbO3, KNN]/polymer composites, to obtain their unsteady energy harvesting potential. KNN nanoparticle/polymer composites were designed and fabricated and the poling condition test was performed. The composites were polarized using the corona poling method for various poling conditions and then the piezoelectric coefficient d33 was measured. It was found that piezoelectricity does not decrease over days. Scanning electron microscopic observations were conducted to study the distribution of the nanoparticles in the matrix. Meanwhile, the microstructure of the composites was studied by X-ray diffraction. Unsteady wind energy harvesting tests were accomplished to investigate the output voltage characteristics in the KNN nanoparticle/polymer composites in unsteady winds. The study represents an important step in developing flexible energy harvesters with stable performance. [ABSTRACT FROM AUTHOR]

This report demonstrates the fabrication of a transparent slippery surface and an investigation of its transparent property by systematically controlling the refractive index. The slippery surface, fabricated by a simple method, was shown to have a water-repellent property similar to those of captured insects sliding into the pitcher of Nepenthes. The as-fabricated opaque porous structures were covered by a siloxane lubricant and showed high optical transmittance in the visible light region. In particular, the difference in the refractive indices between the lubricant and porous structure served as a crucial variable for obtaining a transparent surface. Slippery surfaces were fabricated by using various kinds of nanoparticles (SiO2, Al2O3, ZrO2, and TiO2), and the mechanism behind the transparency of these surfaces was investigated by comparing their transmittances using a UV spectrophotometer. The results show that SiO2 nanoparticle, with a refractive index of 1.46, is the most suitable material for use with the siloxane lubricant. The average transmittance of the slippery surface composed of SiO2 nanoparticle is approximately 80% in the visible light region. Through this study, the transparency of slippery surfaces can be further understood. [ABSTRACT FROM AUTHOR]

The temperature dependence of a steady-state fluorescence spectrum of anthracene crystals ranging from 300 K to 500 K had been investigated, which was in the temperature range of most tabletop laser driven shock wave experiments. An interesting finding is that the fluorescence intensity of the 2-0 transition increases more rapidly than other transitions as the temperature increases. In particular, the logarithm of intensity ratios γn shows a linear correlation with inverse temperature, which can be used for fluorescence temperature sensing. The analysis of sensitivity η and random uncertainty ΔT has demonstrated that the intensity ratio γ1 is the best comprehensive performance physical quantity for temperature sensing. Theoretical analysis and experimental results demonstrated that the unusual increase in the intensity of 2-0 transition originated from a second excited triplet state T2, which was thermally coupled with the first excited singlet state S1. In a word, we established a new fluorescence temperature sensing method based on the intensity ratio and clarified that the mechanism of this method was the thermally activated singlet-triplet intersystem crossing. [ABSTRACT FROM AUTHOR]

We report an experimental investigation of the electronic structure and magnetic properties of bulk and nanosized MnCo 2 O 4 diluted with Zn. The cationic distribution for tetrahedral A-site dilution is ( Co 1 − y A 2 + Zn y A 2 +) A [ Mn 3 + Co 3 + ] B O 4 ± δ , whereas B-site dilution results in ( Co 2 +) A [ Mn 1 − x B 3 + Zn x B 2 + Co 3 + ] B O 4 − δ . The strength of exchange interaction J i j between the magnetic ions in a bulk spinel lattice decreases by ∼ 15 % for A-site dilution relative to the undiluted compound; however, B-site dilution results in an enhancement in J i j by 17%. The frequency and temperature dependence of dynamic-susceptibility [ χ ac (f , T) ] studies of nanostructured compounds reveals the existence of spin-glass like behavior below the freezing temperature T F ∼ 125.7 K (for x B = 0.2) and 154.3 K (y A = 0.1). Relaxation time τ follows the Power-Law variation with a dynamical critical exponent z ν = 6.17 and microscopic spin relaxation time τ o = 4.4 × 10 − 15 s for x B = 0.2 (for y A = 0.1 , z ν = 5.2 and τ o = 5.4 × 10 − 13 s). The amplitude and peak position in χ ac (T) decreases with an increase in the DC bias field, which indicates that the spin-glass phase can survive in the presence of low fields forming a critical line with an exponent 2/3. This behavior is similar to the de Almeida-Thouless (AT-line) analysis in the T-H phase diagram which supports the existence of spin-glass like behavior below T F in these Zn diluted spinels. [ABSTRACT FROM AUTHOR]

In this study, we produced self-assembly structures (desiccation patterns) in the drying sessile drops of SnO2-R6G colloidal suspension that have functional applications. Colloidal suspensions of SnO2 nanoparticles were synthesized using the sol-gel method and, subsequently, R6G molecules were added into the suspension. Centimeter-sized honeycomb- or tree-like self-assembled structures of the nanoparticle-dye composite are formed from the evaporating droplets on a flat glass surface. The usual "coffee ring" effect observed in the case of drying of a sessile drop of dye solution is inhibited this way, which is desirable in many applications. The structures were investigated using optical microscopy and spectroscopy. The resemblance between transmission and fluorescence images illustrates the feasibility of organizing dye molecules in a specific way using self-assembled nanoparticles as a template. However, dye fluorescence from the self-assembly is very weak, which might be due to photoinduced interfacial electron transfer from the excited dye molecules to the nanoparticles. [ABSTRACT FROM AUTHOR]

We present the enhancement of frequency doubled and tripled light in zinc oxide (ZnO) by utilizing arrays of Mie-resonant dielectric nanoantennas. The cylindrical antennas exhibit resonances at the fundamental excitation wavelength, enabling strong localization of light and redistribution of the electric field inside the structures. Linear transmission spectroscopy reveals the resonant behavior of the fabricated nanoantennas and confirms the performed theoretical simulations. Nonlinear spectroscopic measurements show direct dependency between the resonant behavior and the amplification of nonlinear signals. Comparing the unpatterned ZnO thin films with the dielectric nanostructures shows a maximum enhancement by factors of about 22 for SHG and 7 for THG from resonant excitations of the nanoantennas. [ABSTRACT FROM AUTHOR]

We report Raman and photoluminescence (PL) emission spectroscopy studies on monolayer MoS 2 /gold micro-disc hybrid structures. The observed frequency shift and broadening of phonon modes of the monolayer MoS 2 are mainly the manifestations of the mechanical strain rather than the plasmonic field induced electron doping. We also observe considerable enhancement of the phonon mode intensities as a consequence of the surface enhanced Raman scattering caused by the plasmonic fields. The interaction of localized surface plasmon resonances (LSPRs) excited near the edge of the micro-discs with excitons in the monolayer MoS 2 enhances A exciton emission, while suppressing that from B excitons and the trions. The changes in the PL emission near the edge are attributed to the modification of the emission rate via the Purcell effect, whereas the PL quenching on a relatively flat disc surface is due to lower density and the non-radiative nature of LSPRs. [ABSTRACT FROM AUTHOR]

The development of a material with high ampacity to allow current to flow through narrow channels is one of the most promising ways to address the progressive miniaturization and light weight of electronic devices. The efficient synergistic electron transmission by compounding 1D/2D carbon materials with a metal matrix via various methods in recent years has attracted great research interest due to their potential utilization in electronics. In this study, a copper (Cu) matrix with a 3D nitrogen (N) doped-multi-walled carbon nanotubes (MCNTs) interface with prominent physical features is reported and fabricated, involving the use of nano-self-assembly-heat-modification by adopting polyethyleneimine-nano-Cu and carboxyl MCNTs. Young's modulus was enhanced from 28.8 to 92.2 GPa due to a higher efficiency of stress transfer and interfacial adhesion, and the hardness fitted by Gauss distribution was increased by ∼69% (∼39.7 HRC). Toward the stability after a modification of vacuum reduction sintering, the initial oxidation temperature (Td) was increased largely from 232 °C to 286 °C, and thermal conductivity was enhanced eminently from 358 to 548 W/(m K) due to more efficient electron/phonon motion. Moreover, synergistic electron transmission endowed the final Cu-N-CNTs with a higher ampacity (7.23–16.98 × 104 A cm−2), which could be further observed by the time-evolution of electrical resistivity under a constant current density. The improved physical features state that the assembled 3D N-CNTs interface possesses prominent characteristics and potential for directing the deep applications of 1D or 2D carbon materials in electronic science. [ABSTRACT FROM AUTHOR]

We theoretically investigate the optical force exerted on an isotropic particle illuminated by a superposition of plane waves. We derive explicit analytical expressions for the exerted force up to quadrupolar polarizabilities. Based on these analytical expressions, we demonstrate that an illumination consisting of two tilted plane waves can provide a full control on the optical force. In particular, optical pulling, pushing, and lateral forces can be obtained by the proper tuning of illumination parameters. Our findings might unlock multiple applications based on a deterministic control of the spatial motion of small particles. [ABSTRACT FROM AUTHOR]

We investigate here the structural phase transformation and electrical resistive switching properties of TiO 2 thin films (80 nm) after their self-ion implantation with 50 keV Ti + ions at several fluences. UV-Raman, grazing incidence x-ray diffraction (GIXRD), transmission electron microscopy, x-ray photoelectron spectroscopy, and atomic force microscopy techniques have been utilized to investigate the modifications in thin films. Both, the as-grown and ion implanted, films display mixed phases of rutile (R) and anatase (A). Surprisingly, however, a phase transition from A to R is observed at a critical fluence, where some anatase content transforms into rutile. This A to R transformation increases with additional fluence. The critical fluence found by GIXRD is slightly smaller (1 × 10 13 ions/cm 2) than from UV-Raman (1 × 10 14 ions/cm 2), indicating the first initiation of phase transformation probably in bulk. All the films contain anatase in nanocrystalline form also and the phase transformation seems to take place via aggregation of anatase nanoparticles. Thin films also show the presence of oxygen vacancies (O V) Ti 3 + , whose number grows with fluence. These O V as well as thermal spikes created during Ti + ion implantation are also crucial for the A-R transition. After implantation at the highest fluence, TiO 2 thin films show bipolar resistive switching behavior. The development of conducting filaments, formed by the migration of many oxygen vacancies generated during ion implantation, can be responsible for this behavior. [ABSTRACT FROM AUTHOR]

The influence of size-dependent effects on mechanical behavior of a cylindrical silicon electrode particle within a lithium-ion battery is investigated, and it is shown that these effects sensitively determine critical buckling behavior. The mathematical framework used for this investigation incorporates the bond-order-length-strength (BOLS) theory correlation in a general finite deformation theory model that includes the two-way coupling between diffusion-induced stress and stress-influenced diffusion. Additionally, the possibility of plastic flow is accounted for in the model to allow probing situations with relatively high charging rates. Significant differences, arising due to the consideration of the size-dependent effects and captured through the BOLS theory, are highlighted. In particular, it is found that, in most cases studied, both stresses and plastic stretches are amplified in magnitude. Tensile to compressive stress reversal also takes place faster on considering the BOLS theory. The modeling framework is further applied to estimate critical lengths that are safe against buckling. Thus, it is expected that the presented framework will provide an improved aid for the design of nanowire-based lithium ion battery silicon electrodes. [ABSTRACT FROM AUTHOR]

A systematic study of near room temperature magnetoresistance (MR) behavior is carried out for magnetoelectric CoFe2O4-BiFeO3 core-shell nanoparticles. The analysis of MR data reveals that the MR is guided by the anisotropic magnetoresistance (AMR) and the giant magnetoresistance (GMR) effect. The GMR effect is predominant in the sample having a maximum shell thickness, whereas the AMR effect dominates the least shell thickness and bare CoFe2O4. Analysis of the MR data in conjunction with the resistivity suggests that the electrical conduction in these samples is due to (a) tunneling and (b) hopping of electrons across the domains. The impedance and modulus spectra analysis shows that the core-shell particles as a whole are participating in the relaxation process, thus indicating a strong coupling between the core and shell, which may be highly desirable while fetching their magnetoelectric based applications. [ABSTRACT FROM AUTHOR]

Nano-crystalline LaFe1−xZnxO3 (0 ≤ x ≤ 0.3) samples synthesized through the sol-gel auto-combustion technique have been studied. X-ray diffraction patterns reveal that all the samples have an orthorhombic crystal structure and exist in a single phase. Bond lengths and bond angles determined using Rietveld refinement change with the concentration, leading to the modification of the parent structure. The change in the structure is reflected in the thermal measurements too. The morphological studies reveal a wide-range of particle size distribution, consisting of nanometer-sized particles to macro-agglomerations. FTIR spectra show two strong active vibrational bands present at 564 cm−1 and 410 cm−1, which are related to the functional groups present in the material. The optical bandgap has been determined and is found to decrease with the increase in the concentration of Zn. Raman spectroscopy rules out the symmetry breaking or any other structural phase transition in the system. The Raman spectra reveal the strain present in the samples on increasing the concentration of Zn doping. The doping of Zn in place of Fe produces distortion mainly in the oxygen bending and stretching vibrations. Specific heat as a function of temperature has been studied and found to be sensitive to magnetic ordering. The Neel temperature decreases from 411 °C to 377 °C with the increase in the Zn concentration, which is concomitant with the Rietveld analysis. The density of our system decreases with Zn doping and leads to the increased value of specific heat. Hysteresis loops indicate that Zn doping increases the magnetic moment and decreases the coercivity. [ABSTRACT FROM AUTHOR]

Multiferroic La1-xNaxFeO3 (x = 0.0, 0.05, 0.10, and 0.15) nanoparticles have been synthesized by the citrate sol-gel auto-combustion method. It is uniquely known for the homogeneous distribution of particle size due to the low temperature synthesis condition. The Rietveld refinement of the X-ray diffraction pattern has exhibited the single phase orthorhombic perovskite structure. It is confirmed from micro-Raman analysis that hole doping (Na) produces a structural crossover from the Pnma to Pbnm space group. The red shift observed in UV-visible spectroscopy indicates the shrinkage of bandgap. Photoluminescence analysis supports independently the bandgap shrinkage by the existence of violet-blue emission due to charge disproportion by oxygen related defects. A changeover from semiconductor to metallic nature accompanied by the hopping of charge carriers from Fe3+ to Fe2+/Fe4+ exchange interaction has revealed a considerable increase in conductivity and dielectric constant. Finally, the doping helps to induce transition from an antiferromagnetic to a weak ferromagnetic state due to free carrier concentration. It is found that the hole driven Fe3+ to Fe2+/Fe4+ exchange interactions with change in the Bohr magneton values from 5.9 μB to 4.9/4 μB are responsible for variation in the magnetization values. [ABSTRACT FROM AUTHOR]

We report the femtosecond laser (100 fs, 800 nm) ablation properties of Er3+ ion doped zinc-sodium tellurite glass. Ablation thresholds in dependence of the beam radius (13.9 and 32.0 μm), pulse number, and Er3+ ion dopant concentration have been determined. The ablation rate and crater profile depended on the applied fluence. [ABSTRACT FROM AUTHOR]

Nano silicon is emerging as an active element for UV applications due to quantum confinement-induced widening of the Si bandgap, amenability to integration on Si, and less sensitivity to temperature. NanoSi-based UV applications include deep space exploration, high temperature propulsion, solar photovoltaics, and particle detection in high energy accelerators. However, the viability of the technology is limited by a complex nanoSi optical quenching instability. Here, we examined the time dynamics of UV-induced luminescence of sub 3-nm nanoSi. The results show that luminescence initially quenches, but it develops a stability at ∼50% level with a time characteristic of minutes. Upon isolation, partial luminescence recovery/reversibility occurs with a time characteristics of hours. To discern the origin of the instability, we perform first principles atomistic calculations of the molecular/electronic structure in 1-nm Si particles as a function of Si structural bond expansion, using time dependent density functional theory, with structural relaxation applied in both ground and excited states. For certain bond expansion/relaxation, the results show that the low-lying triplet state dips below the singlet ground state, providing a plausible long-lasting optical trap that may account for luminescence quenching as well as bond cleavage and irreversibility. Time dynamics of device-operation that accommodates the quenching/recovery time dynamics is suggested as a means to alleviate the instability and allow control of recovery, which promises to make it an effective alternative to UV-enhanced Si or metal-based wide-bandgap sensing technology. [ABSTRACT FROM AUTHOR]

La2NiMnO6 is prepared for two different sintering time durations: 4 hour (4H) and 24 hour (24H). The magnetization data suggest a double ferromagnetic (FM) transition for 24H, whereas a single FM transition for 4H sample. The 4H sample was found to possess several microscopic pores compared with the 24H sample, and thus, these pores are vacuum impregnated with polyvinylidene fluoride (PVDF). The PVDF in the impregnated sample is found to crystallize in beta phase. The first and second order magnetoelectric coefficients are extracted from the measured data and plotted as a function of temperature. The room temperature region is found to be dominated by the magnetoconductivity/magnetoloss and thus resulting low ME voltage. With lowering of temperature, the situation improves, and for T < 200 K, the loss component becomes negligible so that the true magnetoelectricity is observed. A comparative study on all the three samples (4H, 24H, and 4H + PVDF) shows a significant enhancement in the magnetoelectricity in the 4H + PVDF sample. The highlight of this report is the unique way to arrest the porosity by PVDF impregnation into the pores of La2NiMnO6 so that leakage is minimized. [ABSTRACT FROM AUTHOR]

Most studies on the mechanical properties of silica aerogels neglected the influence of structural randomness and dead-ends of nano-porous materials, whereas both of them have a considerable effect on the mechanical properties of silica aerogels. In this study, we propose a cubic frame model with random orientation as the representative volume element of a silica aerogel to investigate the dead-ends' effect on its mechanical properties. To characterize the structural randomness in open-cell porous materials, a new constitutive model is established by a statistical average of the mechanical response of the random structure. This constitutive model reveals the inherent isotropy of open-cell porous materials. It also indicates that the widely used Gibson-Ashby model may overestimate the Young's modulus and shear modulus for open-cell porous materials. Then the mass ratio of dead-ends and effective skeleton is derived using the available experimental results. It shows that the mass ratio of dead-ends increases with the decreasing density of silica aerogels because of the additional space resulting from the slimmer effective skeleton, which results in the abnormal exponent of the Young's modulus-density power-law relation. We suggest the mass ratio of the effective skeleton to be an intuitive and practical index to reflect the connectivity in silica aerogels. Besides, the dead-ends can significantly enhance the compressive strength of silica aerogels, especially for low-density silica aerogels. We hope this work can provide a new idea to consider the structural randomness in porous materials and give guidance on the mechanical reinforcement of aerogels. [ABSTRACT FROM AUTHOR]

Temperature-dependent radiative and non-radiative dynamics of photoexcited carriers were studied in In0.3Ga0.7N nanodisks (NDs) fabricated from quantum wells (QWs) by neutral-beam etching using bio-nano-templates. The NDs had a diameter of 5 nm, a thickness of 2 and 3 nm, and a sheet density of 2 × 1011 cm–2. The radiative decay time, reflecting the displacement between the electron and hole wavefunctions, is about 0.2 ns; this value is almost constant as a function of temperature in the NDs and not dependent on their thickness. We observed non-exponential decay curves of photoluminescence (PL) in the NDs, particularly at temperatures above 150 K. The thermal activation energies of PL quenching in the NDs are revealed to be about 110 meV, corresponding to the barrier heights of the valence bands in the disks. Therefore, hole escape is deemed responsible for the PL quenching, while thermal activation energies of 12 meV due to the trapping of carriers by defects were dominant in the mother QWs. The above-mentioned non-exponential PL decay curves can be attributed to variations in the rate of hole escape in the NDs because of fluctuations in the valence-band barrier height, which, in turn, is possibly due to compositional fluctuations in the QWs. We found that non-radiative trapping, characteristic of the original QW, also exists in about 1% of the NDs in a form that is not masked by other newly formable defects. Therefore, we suggest that additional defect formation is not significant during our ND fabrication process. [ABSTRACT FROM AUTHOR]

We report on the electronic structure of gallium oxide (Ga2O3) single crystals as studied by resonant photoelectron spectroscopy (resPES). We identify intrinsic electronic defects that are formed by mixed-atomic valence states. We differentiate three coexisting defect states that differ in their electronic correlation energy and their spatial localization lengths. Their relative abundance is described by a fractional ionicity with covalent and ionic bonding contributions. For Ga2O3, our analyses of the resPES data enable us to derive two main aspects: first, experimental access is given to determine the ionicity based on the original concepts of Pauling and Phillips. Second, we report on multi-atomic energy loss processes in the Ga2p core level and X-ray absorption data. The two experimental findings can be explained consistently in the same context of mixed-atomic valence states and intrinsic electronic defects. [ABSTRACT FROM AUTHOR]

A high-density plasma in a pin-to-pin configuration was sustained in liquid organosilicon precursors (hexamethyldisiloxane, tetraethyl orthosilicate, and tetramethylcyclotetrasiloxane) by the application of a high-voltage at a frequency of 1 kHz and a duty cycle of 30%. For all organosilicon precursors investigated, the current-voltage characteristics revealed a spark mode, with typical discharge duration of about 50 ns. Both the number of microdischarges and the total amount of charges per microdischarge increased with the amplitude of the applied voltage. The optical emission spectroscopy revealed strong emission from the C2 Swan system along with H I, Si I, and O I emission lines, indicating very high fragmentation levels of the organosilicon precursors upon discharge ignition. This was confirmed by Transmission Electron Microscopy and Energy-Dispersive X-ray spectroscopy indicating the formation of amorphous silicon oxycarbide nanoparticles. However, W I emission lines as well as W crystalline nanoparticles could also be seen; a feature ascribed to plasma-electrode interactions. [ABSTRACT FROM AUTHOR]

The reduction reactions and densification of nanochains assembled from c-Fe2 O3 nanoparticles were investigated using in situ transmission electron microscopy (TEM). Morphological changes and reduction of the metal oxide nanochains were observed during in situ TEM annealing through simultaneous imaging and quantitative analysis of the near-edge fine structures of Fe L2,3 absorption edges acquired by spatially resolved electron energy loss spectroscopy. A change in the oxidation states during annealing of the iron oxide nanochains was observed with phase transformations due to continuous reduction from F2 O3 over Fe3O4, FeO to metallic Fe. Phase transitions during the in situ heating experiments were accompanied with morphological changes in the nanochains, specifically rough-to-smooth surface transitions below 500°C, neck formation between adjacent particles around 500°C, and subsequent neck growth. At higher temperatures, coalescence of FeO particles was observed, representing densification. [ABSTRACT FROM AUTHOR]

CoFe2-xBixO4 nanoferrites with x=0, 0.05, 0.1, 0.5, and 1.0 have been synthesized by the glycine nitrate process. The present study investigates the effect of Bi3+ substitution on the microstructural, dielectric, ferroelectric, magnetic, and Mossbauer properties of CoFe2O4 nanoparticles. The X-ray diffraction technique was used to confirm the phase purity and estimate the crystallite size which revealed the formation of a secondary phase when Bi3+ concentration exceeds x=0.5. Transmission electron microscopy indicated the formation of grains by aggregation of small crystallites with a reduction in grain size to 20nm with an increase in Bi3+ content and also divulged the lattice parameter value to be 8.378Å , confirming the crystalline nature of the synthesised sample. Dielectric properties performed in the frequency range of 100Hz to 1MHz determined that the dielectric behavior is attributed to the Maxwell-Wagner polarization and the activation energy of the specimens is calculated from the dielectric measurements. The hysteresis curve indicated the ferrimagnetic nature of the samples. The samples also exhibited a well saturated P-E loop with gradual lowering in remenant polarization, coercive field, and saturation polarization with an increase in bismuth concentration. Mössbauer spectroscopy analysis confirmed the changes in magnetic moment of ions, their coupling with neighbouring ions, and cation exchange interactions. Owing to the high physical, thermal, and chemical stabilities, these magnetic ceramics, CoFe2-xBixO4, possesses tremendous potential in major understanding of magnetism and in magnetic recording applications for high density information storage. [ABSTRACT FROM AUTHOR]

The CoFe2O4-BaTiO3 core-shell (CFO@BTO) nanocomposites have been synthesized, and a particular volume fraction of 15% CoFe2O4–85% BaTiO3 has been studied for its magnetic, ferroelectric, and magnetoelectric properties. The optimization of synthesis conditions showed that a temperature of at least 800 °C is required to obtain pure phase BaTiO3, whereas for the tetragonality to be visible in the x-ray diffraction (XRD) pattern, BaTiO3 needed to be sintered to at least 1050 °C. Even though the CFO@BTO composite began to react at the interface at 1050 °C and a small amount of the secondary phase was observed in the XRD pattern, the ferroelectric and magnetic properties were found to be not affected. Upon treating the living epithelial cells with either CFO@BTO or BTO nanoparticles, no toxicity was observed for up to 7 days. Together, these results establish the potential for the use of CFO@BTO nanoparticles in biomedical applications. [ABSTRACT FROM AUTHOR]

We have modeled a multilayer quantum dot organic solar cell that explores the current-voltage characteristic of the solar cell whose characteristics can be tuned by varying the fabrication parameters of the quantum dots (QDs). The modeled device consists of a hole transport layer (HTL) which doubles up as photon absorbing layer, several quantum dot layers, and an electron transport layer (ETL). The conduction of charge carriers in HTL and ETL has been modeled by the drift-diffusion transport mechanism. The conduction and recombination in the quantum dot layers are described by a system of coupled rate equations incorporating tunneling and bimolecular recombination. Analysis of QD-solar cells shows improved device performance compared to the similar bilayer and trilayer device structures without QDs. Keeping other design parameters constant, solar cell characteristics can be controlled by the quantum dot layers. Bimolecular recombination coefficient of quantum dots is a prime factor which controls the open circuit voltage (VOC) without any significant reduction in short circuit current (JSC). [ABSTRACT FROM AUTHOR]

Composites of CoFe2O4 and ZnO (CFO@ZnO) nanomaterials were synthesized using double stage co-precipitation. The structural properties have been investigated by x-ray diffraction which shows the presence of hexagonal ZnO and spinel CoFe2O4. Variation in lattice parameters, after annealing at elevated temperature, indicates the diffusion of cations from the ZnO to CoFe2O4 and vice versa. Magnetic properties were measured by Mössbauer spectroscopy and superconducting quantum interference device magnetometer. The transition from ferrimagnet to paramagnet at 973K is due to the formation of ZnFe2O4. High quadrupole splitting values in Mössbauer spectra depict the presence of interstitial Co defects. The Co cations diffuse in the ZnO lattice in the course of annealing at 1273 K, forming CoxZn1-xO resulting in ferromagnetism. [ABSTRACT FROM AUTHOR]

P-doped 6H-SiC substrates were implanted with 57Fe ions at 380 °C or 550 °C to produce a diluted magnetic semiconductor with an Fe homogeneous concentration of about 100 nm thickness. The magnetic properties were studied with 57Fe Conversion Electron M€ossbauer Spectrometry at room temperature (RT). Results obtained by this technique on annealed samples prove that ferromagnetism in 57Fe-implanted SiC for Fe concentrations close to 2% and 4% is mostly due to Fe atoms diluted in the matrix. In contrast, for Fe concentrations close to 6%, it also comes from Fe in magnetic phase nano-clusters. This study allows quantifying the Fe amount in the interstitial and substitutional sites and the nanoparticles and shows that the majority of the diluted Fe atoms are substituted on Si sites inducing ferromagnetism up to RT. [ABSTRACT FROM AUTHOR]

The Dynamic ultraSound Scattering (DSS) technique, which is an acoustic analog of dynamic light scattering (DLS), has been developed to achieve particle sizing with a wide range of particle sizes from nanometers to micrometers. In the submicron regime, it was difficult to evaluate the particle size by DSS because of the competition between the Brownian and sedimentation motions as we addressed in the previous work [Igarashi et al., J. Appl. Phys. 115, 203506 (2014)]. We propose here a new function to evaluate the particle size in the submicron regime, and with 10% accuracy, the good agreement between DSS and Field-Emission Scanning Electron Microscopy results was confirmed. By improving the transducer, the recording system, as well as the analysis technique, the detectable particle size by the DSS technique now could be extended down to several tens of nanometers. [ABSTRACT FROM AUTHOR]

Atomic Force Microscopes (AFMs) have been widely used as nanomanipulators due to their versatility to work with a broad range of materials and their controllable interaction force, among other features. While AFMs can effectively grasp, move, and position nanoscale objects in 2D environments through basic pull/push operations, they often lack the high precision required in many 3D pick and place applications, especially in non-vacuum environments. In this study, a novel method to resolve the adhesion problem between nanoscale objects and the AFM tip has been developed and tested. The method is based on the application of a high electrostatic voltage to the tip to produce the repulsive force required for the release of the nanoobject. The method is proposed for conductive nanoparticles and tips used in many nanomanipulation applications, and can be easily implemented on typical AFMs with minimal alterations. The applicability of the proposed method is investigated through a series of combined Molecular Dynamics/Finite Element simulations. Published by AIP Publishing. [ABSTRACT FROM AUTHOR]

Particle feeding is used in the most important applications of radio frequency (r.f.) thermal plasmas like synthesis of nanoparticles and particle spheroidization. The study reports an in-situ investigation of radial distribution of temperature in such devices using yttrium ion emission lines under different rates of particle loading during synthesis of yttria nanoparticles. A number of interesting facts about the response of r.f. plasma to the rate of particle loading, hitherto unknown, are revealed. Observed phenomena are supported with experimental data from fast photographic experiments and actual synthesis results. The use of the Abel inversion technique together with simultaneous multi-track acquisition of emission spectra from different spatial locations using a CCD based spectrometer allowed us to extract accurate distribution of temperature inside the plasma in the presence of inherent instabilities. The temperature profiles of this type of plasma have been measured possibly for the first time while particles are being fed into the plasma. Observed changes in the temperature profiles as the particle feed rate increases are very significant. Reaction forces resulting from particle evaporation, and increased skin depth owing to the decrease in electrical conductivity in the edge region are proposed as the two different mechanisms to account for the observed changes in the temperature profile as the powder feed rate is increased. Quantitative analyses supporting the proposed mechanisms are presented. [ABSTRACT FROM AUTHOR]

Three-dye-stacked structures were grown on ZnO surfaces by the liquid-phase molecular layer deposition (LP-MLD) using electron-accepting p-type dyes of rose bengal (RB) and eosine (EO), and an electron-donating n-type dye of crystal violet (CV) as source molecules. It was found that the dye adsorption strength is strong for combinations of p-n, and weak for combinations of p-p and n-n, which satisfies requirements for the source molecules in LP-MLD when dyes are provided with a sequence of p-n-p-n- on n-type ZnO. Surface potential and photoluminescence measurements revealed that monomolecular-step growth is achieved in LP-MLD for growth of the three-dye- stacked structure of [ZnO/RB/CV/EO]. To evaluate the sensitization effects of multi-dye-stacked structures, photocurrent spectra induced in the dye-sensitized ZnO layers were measured in situ in each growth step of the dye molecule adsorption. In step 1, p-type RB was adsorbed onto an n-type ZnO surface to induce a photocurrent spectrum in a range of 400-580 nm. In step 2, n-type CV was provided to connect it to p-type RB. Then, photocurrents attributed to CV were superposed to the photocurrent spectrum attributed to RB, raising photocurrents in the longer wavelength region. In step 3, p-type EO was provided to grow the three-dye-stacked structure of [ZnO/RB/CV/EO]. This structure enhanced the photocurrents and, at the same time, widened the photocurrent spectrum extending from 390 nm to 610 nm, which is regarded as a superposition of RB, CV, and EO spectra, suggesting that the multi-dye-stacked structure acts as a light-harvesting antenna to enhance the sensitization effect on ZnO. [ABSTRACT FROM AUTHOR]

Finite-size (d=5.4-112 nm) and surface effects on the structural, optical, and magnetic properties of ferrimagnetic inverse-spinel MnCo2O4 are reported. For d ≥ 87 nm, partial tetragonal distortion of the inverse spinel-lattice was observed. The Curie temperature TC of MnCo2O4 nanostructures, as determined by dc-magnetic susceptibility (χ) measurements, follows a finite-size scaling relation TC(d)=TC(1)[1-(ζ0/d)λ] with a shift exponent λ=0.75±0.15 and microscopic correlation length ζ0=1.4±0.3 nm, which is consistent with the mean field theory. For T>TC, χ(T) fits Néel's expression for the two-sublattice model with antiferromagnetic molecular field (exchange) constants NBB~85.16 (JBB~2.94×10-22 J), NAB~110.96 (JAB~1.91×10-22 J), and NAA~43.8 (JAA~1.13×10-22 J) and asymptotic Curie temperature Ta~717.63 K. The optical energy bandgap Eg, evaluated from the Kubelka-Munk function ([F(R∞)hω]2 =C2(hω - Eg)) is blueshifted to 2.4 eV (d~5.4 nm) from 1.73 eV (d~112 nm) due to the quantum confinement and nonstoichiometry. The role of tetragonal distortion and grain-size-effects in the intensity of crystal field transitions and variation in the magnetic ordering are further discussed and compared with Co3O4 nanostructures. [ABSTRACT FROM AUTHOR]

Shrinkage and relaxation motions of flexible FePd nanohelices of FePd nanorobots are simulated by a molecular dynamics (MD) model where FePd is a paramagnetic shape memory alloy that can exhibit phase transformation accompanied by softening of the nanohelix under an applied magnetic field (H-field). Two designs of FePd nanorobots are used: (i) a FePd cylindrical head connected to a FePd nanohelix tail and (ii) a FePd nanohelix alone. The geometry and dimensions of the FePd robots are taken after the as-processed FePd nanorobots. In the MD simulation, the FePd head and nanohelix are divided into a number of segmented FePd spheres, each having its magnetic moment. The results of the MD model reveal that upon the applied constant magnetic field, the initial gaps (g=3 nm) between the adjacent turns of the FePd nanohelix are closed, resulting in the total shrinkage (Stot) of 47 nm of the FePd nanorobot. The effects of the applied H-field on Stot are examined by using the MD model and the M-H curve of FePd fitted with Langevin type, resulting in the smaller applied magnetic field leading to the smaller Stot. The results of the MD model provide us with an effective tool in the analysis and design of new nanorobots based on the paramagnetic shape memory alloy of FePd nanohelices that can exert dynamic vibrations on target cells under the oscillating magnetic field. [ABSTRACT FROM AUTHOR]

We report the room temperature synthesis of ZnS in the wurtzite phase by using ethylenediamine, which acts as a template as well as a capping agent. With the addition of ethylenediamine, structural transformation in ZnS from cubic to wurtzite phase is observed. This is accompanied by an increase in the real permittivity by an order of 2, and reduction in dielectric loss by a factor of 6 as compared to a sample without ethylenediamine. Thus, suggesting that ethylenediamine capped wurtzite ZnS is more suitable for miniaturied capactive devices. [ABSTRACT FROM AUTHOR]

There has been significant work investigating the use of self assembled monolayers (SAMs) made of ferrocenyl terminated alkanethiols for realizing molecular diodes, leading to remarkably large forward-to-reverse current rectification ratios. In this study, we use a multiband barrier tunneling model to examine the electrical properties of SAM-based molecular diodes made of HSC9Fc, HSC11Fc, and HSCiFcC13-i (0 ≤ I ≤ 13). Using our simple physical model, we reproduce the experimental data of charge transport across various ferrocenyl substituted alkanethiols performed by Nijhuis, Reus, and Whitesides [J. Am. Chem. Soc. 132, 18386184016 (2010)] and Yuan et al. [Nat. Commun. 6, 6324 (2015)]. Especially, the model allows predicting the rectification direction in HSCiFcC13-i (0 ≤I ≤13) based molecular diodes depending on the position of the ferrocenyl (Fc) moiety within the molecules. We show that the asymmetry of the barrier length at both sides of the Highest Occupied Molecular Orbital of the ferrocenyl moiety strongly contributes to the rectifying properties of ferrocenyl-alkanethiol based molecular junctions. Furthermore, our results reveal that bound and quasi-bound states play an important role in the charge transport. [ABSTRACT FROM AUTHOR]

We study the physics of adhesion and the contact mechanics at the nanoscale with a peeling experiment of a carbon nanotube on a flat substrate. Using an interferometric atomic force microscope and an extended force modulation protocol, we investigate the frequency response of the stiffness of the nano-contact from DC to 20 kHz. We show that this dynamic stiffness is only weakly frequency dependent, increasing by a factor 2 when the frequency grows by 3 orders of magnitude. Such behavior may be the signature of amorphous relaxations during the mechanical solicitation at the nano-scale. [ABSTRACT FROM AUTHOR]

Naturally occurring zinc sulfide (ZnS) contains a substantial amount of iron (Fe) in its crystal structure. This study explores the possible effects of such Fe impurity on the physical properties of its two phases: B3 and B1, crystallizing in a cubic system with zinc blend (ZB, space group: F-43m) and rock salt (RS, space group: Fm-3m) structures. We have performed ab-initio calculations within density functional theory (DFT) to determine the equilibrium volumes of B3- and B1-ZnS phases, doped with Fe in varying concentrations (0% to 25%), and their corresponding lattice structures. Using the enthalpy cross-over, we determine the pressure-dependent B3 to B1 transition as a function of Fe concentration. Our DFT calculations suggest an inverse relation of the transition pressure with Fe content. For pure ZnS, the transition occurs at 17 GPa, which drops to ~12 GPa for 25% Fe. This study also provides a first-hand analysis of the elastic constants (C11, C12, and C44) to show the effects of Fe impurity on the mechanical properties of ZnS phases. Their values generally drop due to Fe and the differences widen with increasing pressure. Fe causes large softening of C44, especially for the B1 phase. We have also performed phonon calculations to characterize the vibrational properties and explain the pressure dependent structural instability of the B3- ZnS. Finally, our calculations of the electronic structures show a transition of semi-conductor to conductor behavior of ZnS with incorporation of Fe impurity. [ABSTRACT FROM AUTHOR]

A new approach was employed in explaining the weak ferromagnetic behavior of conventionally synthesized Zr4+ modified Bi0.8La0.2FeO3. Rietveld refinement of XRD patterns revealed a polar-tonon-polar R3c → Pnma structural transition in Zr4+substituted samples. Magnetic properties were discovered to be remarkably enhanced, with extracted coercivity and remanence as high as 14 kOe and 0.2 emu/g, respectively. More importantly, an answer to the essential question of the magnetic domain state of the samples has been put forward. Our analysis established, nearly without doubt, the presence of grains consisting of a single magnetic domain. Separated ferromagnetic and anti-ferromagnetic components of the total M-H curves helped to reveal an immense effect of the structural transition on the shape of the hysteresis loops. The orthorhombic magnetocrystalline anisotropy of the Pnma phase has been primarily deemed responsible for the high coercivity and remanence of the Zr4+ modified samples. The effect of the grain size and Fe-O-Fe bond angle on the magnetic properties of the samples has also been discussed. Ferroelectricity was found to be absent in Zr-substituted samples because of their non-polar structure. However, the leakage current was reduced by up to two orders of magnitude compared to Bi0.8La0.2FeO3 upon addition of Zr4+. Dielectric measurements conformed to the ferroelectric and leakage current characteristics, and Zr4+ substitution was again found to be beneficial. [ABSTRACT FROM AUTHOR]

By means of molecular dynamics simulation, we investigate the interaction of picosecond-duration compression pulses excited by a flat impactor with flat and nano-structured rear surfaces of copper and aluminum samples. It is shown that protrusions on the rear surface can increase the threshold value of the impact velocity, leading to spallation. As the shock wave reaches the perturbed rear surface, an unloading on the lateral surfaces of the protrusions begins; it leads to an intensive plastic deformation in the surface layer of metal. A part of the compression pulse energy is spent on the plastic deformation that restricts the rarefaction wave amplitude and suppresses the spall fracture. An increase in threshold velocity can be observed for all investigated thicknesses of the targets. The increase is substantial with respect to comparability between the protrusion height and the compression pulse width (the impactor thickness). Another condition is the ratio of the protrusion cross-section to the total surface area, which should be neither small nor large-approximately 0.3-0.4 for the best case. At high protrusion heights (higher than the compression pulse width), as well as at large protrusion cross sections, instability develops on the rear surface of the target and is accompanied by mass ejection. The instability violates the rear surface integrity and restricts the threshold velocity, although the loss of integrity in this case goes through mass ejection, not spallation. [ABSTRACT FROM AUTHOR]

In this work, we generalize the cascading scattering matrix algorithm for calculating the optical response of concentric multilayered structures comprised of either plasmonic metal or dielectric, within the framework of hydrodynamic convection-diffusion model of electrodynamics. Two additional boundary conditions, namely, the continuity of first order pressure of free electron density and the continuity of normal components of free charge velocity, respectively, are adopted in order to handle the behaviour at interfaces involving metals. Scattering matrices at interfaces can be readily obtained and cascaded to obtain the modal coefficients in each layer by expanding electromagnetic waves in harmonic modes with cylindrical vector wave functions. We have validated the proposed method by analyzing the optical responses of several configurations of nanostructures, including a bi-metallic nanocylinder and a hyperlens. We found that nonlocal effects can be important for small structures, when the characteristic size is comparable to the Fermi wavelength. The proposed method shows its capability and flexibility to solve hybrid metal-dielectric multilayer structures even when the number of layers is large. Although we have discussed our method in the context of the retarded radiation regime, it can be applied in quasi-static scenarios without any difficulties. Furthermore, it may be extended to solve similar problems in other areas of physics, such as acoustics. [ABSTRACT FROM AUTHOR]

An Eu-doped ZnO (ZnO:Eu) is an extensively investigated optical material. While most studies reported photoluminescence (PL) from Eu3+ ions resulting from the electronic transitions between 4f levels (5D0→7FJ), the evidence of emissions from Eu2+ ions remains limited. Here, we report that a violet emission in the wavelength region between 450 and 500 nm emerged from the sputterdeposited ZnO:Eu films that were post-annealed at 900 °C in an O2 ambient. This emission peak was away from the band edge and the defect green emissions of ZnO, and it was identified as being from Eu2+ ions. Simultaneous emergence of the red emission bands at wavelengths longer than 600 nm indicated that Zn vacancies (VZn) were created during a high-temperature annealing and that producing VZn promoted substitution at Zn2+ sites with Eu2+ ions. In contrast, when annealing was done in a vacuum, the defect emissions were attenuated and the PL spectra showed only bandedge emissions. Here, it can be interpreted that this reduced state, where some oxygen atoms have been removed from the ZnO lattice, has a short lifetime of excitons. In contrast, loading hydrogen atoms into the a ZnO lattice by annealing in an H2 ambient at 350 °C generated a weak Eu3+ emission at 612 nm along with an orange emission band ranging from 550 to 650 nm, which was from the OH termination at the surfaces and interfaces of the ZnO crystals. In this system, a codoping of H+ with Eu3+ ions assists the substitution at Zn2+ sites through a charge compensation. The present results, thus, demonstrate that the emergence of Eu2+ and Eu3+ emissions can be simply controlled by selecting the annealing conditions. [ABSTRACT FROM AUTHOR]

The effective microwave permittivity of a composite comprising anisotropic particles suspended in a liquid (also known as an artificial Kerr material) is calculated using a numerical scheme. The results are compared to those calculated using analytic effective medium expressions. Several composite materials are predicted to have permittivity that can be tuned over a greater range than liquid crystals, which are currently used in many tunable microwave devices such as phase-shifters and modulators. Estimates for the static electric field required to tune such materials are provided and show that such materials are realistic. [ABSTRACT FROM AUTHOR]

Formation of metal-semiconductor (M-S) contacts at sub-20 nanometer range is a key requirement for down-scaling of semiconductor devices. However, electrical measurements of M-S contacts at this scale have exhibited dramatic change in the current-voltage (I-V) characteristics compared to that of conventional (or planar) Schottky contacts. This change is actually attributed to the limited metal contact region where the transferred charge from the semiconductor into the metal is confined to a small surface area, which in turn results in an enhanced electric field at the nano-M-S interface. We here present detailed theoretical models to analyze the nano-M-S junctions at 10 nm contact range and then implement this analysis on the experimental data we conducted under these conditions. Both theoretical and experimental results demonstrate a significant effect of the contact size on the electronic structure of the M-S junctions and thus on the I-V characteristics. This effect is rather prominent when the size of the metal contact is substantially smaller than the width of conventional depletion region of the relevant planar M-S contacts. [ABSTRACT FROM AUTHOR]

The majority of intuition on phonon transport has been derived from studies of homogenous crystalline solids, where the atomic composition and structure are periodic. For this specific class of materials, the solutions to the equations of motions for the atoms (in the harmonic limit) result in plane wave modulated velocity fields for the normal modes of vibration. However, it has been known for several decades that whenever a system lacks periodicity, either compositional or structural, the normal modes of vibration can still be determined (in the harmonic limit), but the solutions take on different characteristics and many modes may not be plane wave modulated. Previous work has classified the types of vibrations into three primary categories, namely, propagons, diffusions, and locons. One can use the participation ratio to distinguish locons, from propagons and diffusons, which measures the extent to which a mode is localized. However, distinguishing between propagons and diffusons has remained a challenge, since both are spatially delocalized. Here, we present a new method that quantifies the extent to which a mode's character corresponds to a propagating mode, e.g., exhibits plane wave modulation. This then allows for clear and quantitative distinctions between propagons and diffusons. By resolving this issue quantitatively, one can now automate the classification of modes for any arbitrary material or structure, subject to a single constraint that the atoms must vibrate stably around their respective equilibrium sites. Several example test cases are studied including crystalline silicon and germanium, crystalline silicon with different defect concentrations, as well as amorphous silicon, germanium, and silica. [ABSTRACT FROM AUTHOR]