Preferential Emission Research Articles

COMPUTER SIMULATION OF NANO-DIMENSIONAL EDUCATION STRUCTURES ON THE SURFACE OF A MONOCRYSTAL AT THE SLIDE ION BOMBING

This work deals with the computer simulation of low- and medium energy (E0=0.5÷10 keV) N+, Ne+, Ar+, Kr+, Be+ и Se+ions sliding collisions on the surface of a Cu(100), Ag(110), Si(001), SiC(001) and GaAs(001) solids, and of the accompanying effects, namely, scattering, sputtering and surface implantation. It has been shown that under these conditions the inelastic energy losses become predominant over the elastic ones. The anomalous energy losses observed experimentally at the grazing ion scattering by the single crystal surface were explained. It has been shown that from the correlation of the experimental and calculated energy distributions of the scattered particles, one may determine a spatial extension of the isolated atomic steps on the single crystal surface damaged by the ion bombardment. Results obtained can be also used to study short-range order in alloys undergoing ordering. Dissociative and non-dissociative desorption of adsorbed molecules were simulated. It was shown that at grazing ion bombardment the intensive nondissociative desorption of adsorbed molecules is possible. A preferential emission of Cu atoms in the case of Cu3Au (001) surface sputtering is observed. It was shown that in the case of grazing ion bombardment the layer-by-layer sputtering is possible and its optimum are observed within the small angle range of the glancing angles near the threshold sputtering angle. The obtained results allow to select the optimum conditions for obtaining implanted depth distributions with demanded shape in narrow near-surface region (5–10 atomic layers) of crystals. The highly sensitive layer-by-layer analysis method was proposed on the basis of layer-by-layer sputtering mechanism.

Asymmetric Light Absorption and Radiation of Ag–Cu Hybrid Nanoparticles

In this article, we study the plasmonic properties of phase-separated Ag–Cu nanoparticles. The particles are fabricated using simple thin film evaporation followed by particle formation by vacuum annealing. The formed particles feature a two-faced Janus structure. Characterization is carried out at the single particle level utilizing transmission electron microscopy in combination with electron energy loss spectroscopy and cathodoluminescence, and modeled by finite element method simulations. We find that these particle sustain two kinds of resonances: resonances localized to the Ag half of the particle and resonances involving the entire particle. This is due to the difference in onset energy for interband transitions for the two metals. As the resonances are excited in Ag, large enhancements of energy absorption can be achieved in the Cu half of the particle. We also find a slight asymmetry to the emission of the particles in cathodoluminescence, with a preferential emission toward the silver side of th...

Efficient up-conversion red emission from TiO2:Yb,Er nanocrystals.

Usually, up-conversion (UC) green emission is easily observed by using rare-earth doped fluoride nanocrystals. However, preferential red emission is desired for some actual applications especially in biological field. Here, we demonstrated that the dominant UC red emission can be realized by preparing TiO2:Yb,Er nanocrystals under 980 nm exciation. By controlling the crystal symmetry and size via the annealing temperature and Yb3+ ions concentration, the enhanced UC red emission is achieved. The multi-photon relaxation and cross-relaxation mechanisms may be responsible for the energy transform process and in turn the UC emission.

Both Directional Organic Light-Emitting Diodes Using Thin Film Electrodes

Recently, transparent organic light-emitting diodes (TOLEDs) have attracted much interest, because they can open new applications for bi-directional displays, transparent displays, wearable displays, smart glass, and window lighting. Typically, the device structure of TOLEDs needs to consist of an ITO bottom anode, emitting layer, and a thin metal cathode. To protect underlying organic layer from sputtering damage, a thin metal-based semi-transparent cathode was necessarily used by thermal evaporation. In this system, there were many problems in application of ITO electrodes to high efficient TOLEDs. First, these TOLEDs usually have a preferential one-sided emission due to differences in reflection between ITO and Ag electrodes. In particular, the ITO-side emission ratio has a strong intensity which is more than 70% of the total emission ratio because of the relatively low reflection of ITO compared with Ag film. Second, the majority of the light generated in the organic layers is confined in the ITO anode and glass substrates due to the large difference in the refractive index between their layers. This results in out-coupling efficiencies of around only 20% due to the total internal reflection at the ITO / glass and glass / air interfaces. These problems can be solved by employing a thin metal (Ag) electrode as an ITO alternative. However, it is very difficult to form smooth and very thin Ag layers for transparent anode. Ag layers exhibit three-dimensional island growth as a result of the poor wettability of Ag on the substrate. A discrete Ag film consisting of an island structure exhibits strong absorption and scattering of incident light, because of localized surface plasmon resonance. Thus, thin Ag film was not considered as a transparent electrode for TOLED. Here, we demonstrate an innovative method to make transparent and high performance OLEDs on substrates using only ultra-thin Ag electrodes as both the top and bottom transparent electrodes. We show that merely a minute-plasma treatment on the glass before the deposition of Ag layer leads to significantly improved growth homogeneity of the Ag layer. The ultra-thin Ag film is formed after oxygen plasma treatment, leading to improved visible range transmittance and sheet resistance. By designing the weak micro-cavity structure with the ultra-thin Ag electrodes, waveguide modes could be suppressed and optical transmittance of TOLEDs could be improved. According to FDTD simulation, waveguide modes in ITO and glass substrate can be remarkably extracted because of weak micro-cavity effect. Consequently, the luminance of TOLED could be improved by 47 %. In addition, the transmittance of TOLED with the ultra-thin Ag electrode showed a high transmittance (73.84 %), which was similar than that of ITO (73.19%). The optimized weak micro-cavity structured shows the high optical transmittance, identical emission rate and reduced wave-guided mode were achieved, enhancing the luminance of devices.

Near-horizon geometry and the entropy of a minimally coupled scalar field in the Kerr black hole

In this article we will discuss a Lorentzian sector calculation of the entropy of a minimally coupled scalar field in the Kerr black hole background. We will use the brick wall model of t' Hooft. In the Kerr black hole, complications arise due to the absence of a global timelike Killing field and the presence of the ergosphere. Nevertheless, it is possible to calculate the entropy of a thin shell of matter field in the near-horizon region using the brick wall model. The corresponding leading order entropy of the nonsuperradiant modes is found to be proportional to the area of the horizon and is logarithmically divergent. Thus, the entropy of a three dimensional system in the near-horizon region is proportional to the boundary surface. This is similar to that of the black hole entropy itself. The corresponding internal energy remains finite if the entropy is chosen to be of the order of the black hole entropy itself. For a fixed value of the brick wall cut-off, the leading order entropy in the Kerr black hole is found to be half of the corresponding term in the Schwarzschild black hole. This is consistent with the preferential emission of particles in the Kerr black hole with azimuthal angular momentum in the same direction as that of the black hole itself. However, we can obtain the Schwarzschild case expression by including a subleading term and taking the appropriate limit. The results obtained in this article may be relevant to entropy bound and holographic principle.

Rapid and Energy-Saving Microwave-Assisted Solid-State Synthesis of Pr(3+)-, Eu(3+)-, or Tb(3+)-Doped Lu2O3 Persistent Luminescence Materials.

Persistent luminescence materials Lu2O3:R(3+),M (Pr,Hf(IV); Eu; or Tb,Ca(2+)) were successfully and rapidly (22 min) prepared by microwave-assisted solid-state synthesis (MASS) using a carbon microwave susceptor and H3BO3 as flux. Reaction times are reduced by up to 93% over previous synthetic methods, without special gases application and using a domestic microwave oven. All materials prepared with H3BO3 flux exhibit LuBO3 impurities that were quantified by Rietveld refinement from synchrotron radiation X-ray powder diffraction patterns. The flux does not considerably affect the crystalline structure of the C-Lu2O3, however. Scanning electron micrographs suggest low surface area when H3BO3 flux is used in the materials' synthesis, decreasing the amount of surface hydroxyl groups in Lu2O3 and improving the luminescence intensity of the phosphors. The carbon used as the susceptor generates CO gas, leading to complete reduction of Tb(IV) to Tb(3+) and partial conversion of Pr(IV) to Pr(3+) present in the Tb4O7 and Pr6O11 precursors, as indicated by X-ray absorption near-edge structure data. Persistent luminescence spectra of the materials show the red/near-IR, reddish orange, and green emission colors assigned to the 4f(n) → 4f(n) transitions characteristics of Pr(3+), Eu(3+), and Tb(3+) ions, respectively. Differences between the UV-excited and persistent luminescence spectra can be explained by the preferential persistent luminescence emission of R(3+) ion in the S6 site rather than R(3+) in the C2 site. In addition, inclusion of Hf(IV) and Ca(2+) codopants in the Lu2O3 host increases the emission intensity and duration of persistent luminescence due to generation of traps caused by charge compensation in the lattice. Photonic materials prepared by MASS with H3BO3 flux show higher persistent luminescence performance than those prepared by the ceramic method or MASS without flux. Color tuning of persistent luminescence in Lu2O3:R(3+),M provides potential applications in bioimaging as well as in solar cell sensitizers.

Preferential emission into epsilon-near-zero metamaterial [Invited

We report the use of epsilon near zero (ENZ) metamaterial to control spontaneous emission from Zinc-Oxide (ZnO) excitons. The ENZ material consists of alternating layers of silver and alumina with subwavelength thicknesses, resulting in an effective medium where one of the components of the dielectric constant approach zero between 370nm-440nm wavelength range. Bulk ZnO with photoluminescence maximum in the ENZ regime was deposited via atomic layer deposition to obtain a smooth film with near field coupling to the ENZ metamaterial. Preferential emission from the ZnO layer into the metamaterial with suppression of forward emission by 90% in comparison to ZnO on silicon is observed. We attribute this observation to the presence of dispersionless plasmonic modes in the ENZ regime as shown by the results of theoretical modeling presented here. Integration of ENZ metamaterials with light emitters is an attractive platform for realizing a low threshold subwavelength laser.

Infrared to Visible Up-conversion in Biocellulose–yttrium Vanadate Nanoparticle Composite Membranes. Demonstration of Chloroaluminum Phthalocyanine Light Emission Under Up-converted Light Excitation

YVO4:(Yb3+–Er3+/Ho3+) nanoparticles were incorporated in biocellulose membranes obtained from Gluconacetobacter xylinus. Materials present the property of converting near-infrared (NIR) into higher-energy visible light. Nanoparticles were prepared by optimizing towards higher emission intensity at the absorption wavelength range of chloroaluminum phthalocyanine (ClAlPc) used as a photosensitizer in the photodynamic therapy. The NIR excitation wavelength is advantageous for biological applications, as it allows deeper penetration into tissues than the UV–visible radiation commonly used for luminescence excitation. Up-conversion emission spectra obtained under excitation at 980nm showed a preferential green emission for the Yb3+–Er3+ system and a red emission for the Yb3+–Ho3+ one. In the last case, by using mixtures of nanoparticles and ClAlPc the red emission (680nm) of the phtalocyanine was observed through excitation by the up-converted emission of the nanoparticles (650nm) which were excited in NIR (980nm).

Sociosexual and communication deficits after traumatic injury to the developing murine brain.

Despite the life-long implications of social and communication dysfunction after pediatric traumatic brain injury, there is a poor understanding of these deficits in terms of their developmental trajectory and underlying mechanisms. In a well-characterized murine model of pediatric brain injury, we recently demonstrated that pronounced deficits in social interactions emerge across maturation to adulthood after injury at postnatal day (p) 21, approximating a toddler-aged child. Extending these findings, we here hypothesized that these social deficits are dependent upon brain maturation at the time of injury, and coincide with abnormal sociosexual behaviors and communication. Age-dependent vulnerability of the developing brain to social deficits was addressed by comparing behavioral and neuroanatomical outcomes in mice injured at either a pediatric age (p21) or during adolescence (p35). Sociosexual behaviors including social investigation and mounting were evaluated in a resident-intruder paradigm at adulthood. These outcomes were complemented by assays of urine scent marking and ultrasonic vocalizations as indices of social communication. We provide evidence of sociosexual deficits after brain injury at p21, which manifest as reduced mounting behavior and scent marking towards an unfamiliar female at adulthood. In contrast, with the exception of the loss of social recognition in a three-chamber social approach task, mice that received TBI at adolescence were remarkably resilient to social deficits at adulthood. Increased emission of ultrasonic vocalizations (USVs) as well as preferential emission of high frequency USVs after injury was dependent upon both the stimulus and prior social experience. Contrary to the hypothesis that changes in white matter volume may underlie social dysfunction, injury at both p21 and p35 resulted in a similar degree of atrophy of the corpus callosum by adulthood. However, loss of hippocampal tissue was greater after p21 compared to p35 injury, suggesting that a longer period of lesion progression or differences in the kinetics of secondary pathogenesis after p21 injury may contribute to observed behavioral differences. Together, these findings indicate vulnerability of the developing brain to social dysfunction, and suggest that a younger age-at-insult results in poorer social and sociosexual outcomes.

Herschelobservations of gas and dust in comet C/2006 W3 (Christensen) at 5 AU from the Sun

We aimed to measure the H2O and dust production rates in C/2006 W3 (Christensen) with the Herschel Space Observatory at a heliocentric distance of ~ 5 AU. We have searched for emission in the H2O and NH3 ground-state rotational transitions at 557 GHz and 572 GHz, simultaneously, with HIFI onboard Herschel on UT 1.5 September 2010. Photometric observations of the dust coma in the 70 and 160 {\mu}m channels were acquired with the PACS instrument on UT 26.5 August 2010. A tentative 4-{\sigma} H2O line emission feature was found in the spectra obtained with the HIFI wide-band and high-resolution spectrometers, from which we derive a water production rate of $2.0(5) \times 10^{27}$ molec. s$^{-1}$. A 3-{\sigma} upper limit for the ammonia production rate of <$1.5 \times 10^{27}$ molec. s$^{-1}$ is obtained taking into account the contribution from all hyperfine components. The blueshift of the water line detected by HIFI suggests preferential emission from the subsolar point. However, it is also possible that water sublimation occurs in small ice-bearing grains that are emitted from an active region on the nucleus surface at a speed of ~ 0.2 km s$^{-1}$. The dust thermal emission was detected in the 70 and 160 {\mu}m filters, with a more extended emission in the blue channel. The dust production rates, obtained for a dust size distribution index that explains the fluxes at the photocenters of the PACS images, lie in the range 70-110 kg s$^{-1}$. Scaling the CO production rate measured post-perihelion at 3.20 and 3.32 AU, these values correspond to a dust-to-gas production rate ratio in the range 0.3-0.4. The dust production rates derived in August 2010 are roughly one order of magnitude lower than in September 2009, suggesting that the dust-to-gas production rate ratio remained approximately constant during the period when the activity became increasingly dominated by CO outgassing.

Conceptual Proposal for Compound Moderators with Preferential Emission Directions

Large spallation neutron facilities share with compact sources the constraint that the moderation of neutrons relies on a random scattering process. Recently, proposals have been made how to furnish cold moderators with some preferential direction for the scattering and the emission of cold neutrons. Propositions presented so far aim primarily at enhancing the emission of moderated neutrons out of the scattering volume. The use of silicon single crystals and nano-structured material has been proposed to boost or suppress scattering along selected directions, respectively. The recent implementation of a beryllium reflector-filter for a hydrogen moderator system at the Manuel Lujan neutron scattering center augmented moderated neutron flux by reflecting thermal neutrons back into a cold moderator. This installation has met with striking success and proved the technical feasibility of selectable preferential provision of cold and thermal neutrons. In this short contribution a tiny scoping study is presented together with a conceptual sketch of a novel moderator set-up. The approach strives to combine the existing results with some additional measures for increasing the primary neutron flux inside a cold moderator. Even base-lining some generic boundary conditions and not taking peculiarities of materials into account, moderator performance can be improved by mere geometrical internal modifications. Conceiving a “pre-moderator” primarily as “primary reflector” appears to offer additional possibilities for optimization. The expectation is that, depending on design and materials’ choices, mixed or cold spectra can be obtained, with the flux of demanded neutrons increased along selected directions of preferential emission. Anticipating more extensive confirmative numerical simulations, the obvious next step could be a first test of the proposed concept at a compact neutron source.

Seismic evidence of shallow gas from Lake Van, eastern Turkey

Analysis of multi-channel seismic reflection and chirp data from Lake Van (eastern Turkey) reveals various shallow gas indicators including seismic chimneys, enhanced reflections, bright spots, mud volcanoes, pockmarks, and acoustic blanking. The enhanced reflections, suggesting the presence of free gas, are most dominant and observed at more than 200 locations. They are characterized by very-high amplitude reflections and occur in both deep and shallow sedimentary sections. Some enhanced reflections are accompanied by very subtle seafloor expressions such as mounds, which may suggest active venting activity. Seismic chimneys or columnar zones of amplitude blanking have been observed in much of the surveyed area. Seismic chimneys in the study area cannot be associated with any known faults that would act as migration pathways for deep fluids. This suggests that the observed structures in Lake Van sediments allow the preferential emission of gases which might be for a large share of biogenic origin. The acoustic blanking, characterized by transparent or chaotic seismic facies, is seen in the eastern part of the lake. The lakeward edge of the acoustic blanking largely coincides with the 100 m water depth contour, indicating that (past) changes of the hydrostatic pressure may be responsible for the distribution of these anomalies. Mound-like features, interpreted as mud volcanoes, occur in a few locations. The presence of these features may suggest active gas emission. Very strong amplitude anomalies or bright spots with negative polarity, indicating gas-charged zones, are also seen in a number of locations. Pockmarks are observed only in the northeastern part of the study area. The scarce occurrence of pockmarks in the study area might be ascribed to a higher permeability of the lake sediments or to the absence of the substrate/reservoir providing the critical mass of gases necessary to produce such features. Turbidites, tephra layers, and deltaic deposits have the potential to provide ideal conditions to allow the sediments to act as a gas reservoir.

Fabrication and Characterization of Light-Emitting Diodes Comprising Highly Ordered Arrays of Emissive InGaN/GaN Nanorods

A simple approach to fabricating ordered InGaN/GaN nanorod arrays light-emitting diodes (LEDs) with strongly directional light emission is reported. The far field radiation pattern of the nanorod arrays LEDs shows preferential emission in a ±10° cone about the surface normal and contained other features arising from diffraction associated with the periodicity of the nanorod array. The output power per unit in-plane emissive area at 300-mA drive current is three times larger than that of an equivalent planar LED.

Optimal irreversible stimulated emission

We studied the dynamics of an initially inverted atom in a semi-infinite waveguide, in the presence of a single propagating photon. We show that atomic relaxation is enhanced by a factor of 2, leading to maximal bunching in the output field. This optimal irreversible stimulated emission is a novel phenomenon that can be observed with state-of-the-art solid-state atoms and waveguides. When the atom interacts with two one-dimensional electromagnetic environments, the preferential emission in the stimulated field can be exploited to efficiently amplify a classical or a quantum state.

Dynamic control of photoluminescence polarization properties in GaAs/AlAs quantum wells by surface acoustic waves

We have investigated the dynamic polarization properties of photoluminescence (PL) spectra in GaAs/AlAs quantum wells (QWs) modulated by surface acoustic waves (SAWs) in various configurations. One-dimensional standing SAWs, which are formed by the interference of two counterpropagating SAW beams, exhibit emission energy oscillations due to strain-induced band gap modulation. When the band gap energy reaches its minimum value, the PL spectra exhibit the strongest polarization anisotropy, with preferential emission along the direction perpendicular to SAW propagation. Two-dimensional SAWs formed by the interference between two orthogonally propagating SAW beams also cause the emission energy to oscillate, while no polarization anisotropy appears. In contrast, a \ensuremath{\pi}/2 relative phase difference, which is electrically introduced between the two SAWs, significantly alters both the PL spectra and the polarization anisotropy. The oscillation of the emission energies disappears and the polarized direction changes every quarter SAW period. These SAW phase-dependent changes in the polarization properties are explained by considering the exciton motion under the quadrupolelike SAW modulation, which is formed by the two orthogonal unbalanced standing SAWs with a phase difference of \ensuremath{\pi}/2.

Unilateral Climate Policy and Competitiveness: Economic Implications of Differential Emission Pricing

AbstractUnilateral climate policy raises concerns about international competitiveness and emission leakage that result in preferential regulatory treatment of domestic energy‐intensive and trade‐exposed (EITE) industries. Our applied analysis of unilateral EU abatement illustrates the potential pitfalls of climate policy design which narrowly focuses on competitiveness concerns about EITE industries. The sector‐specific gains of differential emission pricing in favour of these branches must be traded off with the additional burden imposed on other industries. From the perspective of the unilaterally abating region preferential EITE emission pricing can induce non‐negligible excess cost as policy concedes (too) low emission prices to EITE industries and thereby foregoes relatively cheap abatement options in these sectors. With respect to global cost‐effectiveness of unilateral climate policy, we find that differential emission pricing in favour of EITE industries can reduce emission leakage and thereby provide global cost savings compared with uniform pricing. However, the scope for cost savings is limited and may change into substantial cost increases if unilateral reduction targets are moderate and EITE industries get close to exemptions.

Fundamental temperature-dependent properties of the Si nanocrystal band gap

Ever since the first reports about low-temperature photoluminescence (PL) measurements of Si nanocrystals Si (NCs), a severe deviation from the equations commonly used to describe the temperature dependence of the band-gap energy for bulk materials was reported. Our analysis reveals that the formerly observed deviation is solely attributed to too high excitation power densities that cause a preferential emission enhancement of the smaller NCs within a size distribution, due to the temperature dependence of the radiative exciton lifetime. We report on the successful fit of the temperature-dependent band-gap energy of quantum-confined silicon. By means of four size-controlled Si NC samples (1.5 to 4.5 nm), we are able to prove the validity of these equations down to liquid He temperatures, if sufficiently low excitation power densities (500 $\ensuremath{\mu}$W/cm${}^{2}$) are used. Thereby, it is shown that the characteristics of the band-gap widening of quantum-confined nanocrystalline Si obeys to the same physical law as the bulk Si crystal. In addition, the previously observed decrease of the PL intensity for decreasing temperatures is demonstrated to have its origin in the same measurement artifact caused by excitation saturation.

The effect of grain orientation on secondary ion mass spectrometry (SIMS) analysis of rutile

In situ high precision U–Pb analysis of rutile by secondary ion mass spectrometry (SIMS) reveals that instrumental bias for isotope ratios and count rates vary due to crystal orientation. Electron backscatter diffraction (EBSD) techniques have been combined with SIMS data to show consistent and systematic crystal orientation effects, whilst confirming that all analyses are on single crystals and that there is random variation from grain to grain. The result of the orientation effect is to produce an extremely large calibration slope, more than an order of magnitude larger than for other minerals, which can result in highly inaccurate and spurious U–Pb ages from rutile if not taken into account. We present a large standard dataset to highlight this effect and show that by collecting good standard data, from grains in multiple orientations, these effects can be negated and accurate U–Pb SIMS data for rutile can be obtained using a standard calibration slope of ln(Pb+/U+) vs ln(UO2+/UO+)=1.12. Examples from the Anantangiri region, Eastern Ghats, India are used to show the magnitude of these effects on the calibration of unknowns. Evidence is presented to show that the cause of these orientation effects is most likely a combination of channelling of primary ions into the crystal and preferential emission of secondary ions along preferred lattice directions.

On chemiluminescent emission from an infiltrated chiral sculptured thin film

The theory describing the far-field emission from a dipole source embedded inside a chiral sculptured thin film (CSTF), based on a spectral Green function formalism, was further developed to allow for infiltration of the void regions of the CSTF by a fluid. In doing so, the extended Bruggeman homogenization formalism — which accommodates constituent particles that are small compared to wavelength but not vanishingly small — was used to estimate the relative permittivity parameters of the infiltrated CSTF. For a numerical example, we found that left circularly polarized (LCP) light was preferentially emitted through one face of the CSTF while right circularly polarized (RCP) light was preferentially emitted through the opposite face, at wavelengths within the Bragg regime. The centre wavelength for the preferential emission of LCP/RCP light was red shifted as the refractive index of the infiltrating fluid increased from unity, and this red shift was accentuated when the size of the constituent particles in our homogenization model was increased. Also, the bandwidth of the preferential LCP/RCP emission regime decreased as the refractive index of the infiltrating fluid increased from unity.

Directed flow in ultrarelativistic heavy-ion collisions

We study the generation of the directed flow in the hydrodynamic expansion of hot matter formed in ultrarelativistic heavy-ion collisions at $\sqrt{s}=200$ GeV. The experimentally observed negative-directed flow in a wide range of central pseudorapidities is reproduced, assuming that the fireball is tilted away from the collision axis. The tilt of the source is consistent with a preferential emission in the forward-backward hemisphere from forward-backward participating nucleons. The model reproduces the experimentally observed scaling of the directed flow when going from Au-Au to Cu-Cu systems.