Unity‐Order Nonlinear Optical Index Change in Epsilon‐Near‐Zero Composite Materials of Gain Media and Metal Nanoparticles

This work reports giant optical nonlinearity of active gain composites containing metal nanoparticles. In the epsilon‐near‐zero regime, the effective index of the composite strongly depends on the magnitude of host material's saturable gain and one can obtain unity‐order nonlinear optical index change for the pump with gain saturation intensity. For pump intensity of about 100 kW/cm², the nonlinear refractive index (the refractive index change per unit pump intensity) reaches 10^?5 cm²/W, which is 6–8 orders‐of‐magnitude larger than the records recently obtained in epsilon‐near‐zero bulk materials. If the gain value of the host medium is slightly larger than a critical value, such large optical nonlinearity can be obtained without loss or even accompanying with amplification. The proposed materials also have the advantage of wide tunability of operating wavelength range from visible to infrared by changing the gain value of the host and the shape parameters and filling factors of metal nanoparticles.     

Composite‐Assisted Phase‐Matching: Efficient Wavelength Conversion in Nonlinear Optical Composite Materials Containing Metal Nanoparticles

A novel phase‐matching scheme which is based on the dispersion compensation in the nonlinear optical composite materials containing metal nanoparticles is proposed. Anomalous dispersion originating from the plasmon resonance in metal nanoparticles compensates the dispersion of the host nonlinear material, leading to the perfect phase‐matching and high efficiency of nonlinear optical wavelength conversion. The effectiveness of this approach is theoretically demonstrated, taking third‐order nonlinear processes such as the direct third‐harmonic generation and four‐wave mixing in ZnO composites containing silica‐core–silver‐shell nanoparticles as examples. The results show that with the proposed phase‐matching scheme, unprecedentedly high conversion efficiency can be obtained compared with preceding results in third‐order nonlinear optical solid‐state materials.     

Efficiency Improvement in Polymer Light‐Emitting Diodes by “Far‐Field” Effect of Gold Nanoparticles

The “far‐field” effect of metal nanoparticles (NPs), when chromophores localized nearby metal NPs (typically the distance >λ/10), is an important optical effect to enhance emission in photoluminescence. The far‐field effect originates mainly from the interaction between origin emission and mirror‐reflected emission, resulting in the increased irradiative rate of chromophores on the mirror‐type substrate. Here, the far‐field effect is used to improve emission efficiency of polymer light‐emitting diodes (PLEDs). A universal performance improvement is achieved for the full visible light (red, green, blue) PLEDs, utilizing gold (Au) NPs to modify the indium tin oxide (ITO) substrates; this is shown by experimental and theoretical simulation to mainly come from the far‐field effect. The optimized distance, between the NPs and chromophores with visible light emission ranging from 400 to 700 nm, is 80–120 nm. Thus the scope of the far‐field may overlap the light‐emitting profile very well to enhance the efficiency of optoelectronic devices. The 30–40% enhancement is obtained for different color‐emitting materials through distance optimization. The far‐field effect is demonstrated to enhance device performance for materials in the full‐visible spectral range, which extends the optoelectric applications of Au NPs.     

New concept of organic homo‐rank compounds and its application in estimating enthalpy of formation of mono‐substituted alkanes

Based on the topological characteristics of distance matrices and adjacency matrices of molecular graphs, a new concept of organic homo‐rank compounds was proposed. Based on this concept, compounds can be classified into new groups other than the traditional homologues. Furthermore, novel structure–property relationship approach named as homo‐rank compounds method can be developed. The feasibility of homo‐rank compounds method was explored by estimating the enthalpy of formation of organic compounds. The group contribution index (GCI_X) and group polarizability potential index (GPI_X) of substituents X were defined and determined for mono‐substituted alkanes RX (X includes 20 substituents). The research results show that the enthalpies of formation of organic homo‐rank compounds and their isomers can be correlated very well with the parameters GCI_X and GPI_X. Combining the method of homologues with that of homo‐rank compounds, a general and simple quantitative correlation equation (8) was established to estimate the enthalpy of formation for RX, and the calculation precision is within the chemical accuracy ‘1 kcal/mol’. For 242 samples of RX, the average absolute deviation between the experimental and the calculated values is 2.42 kJ/mol. In addition, the enthalpies of formation of more than 2800 samples of RX were estimated. The approaches of organic homo‐rank compounds and organic homologues are independent of but complementary to each other. The combination of these two methods can help us to understand the organic molecular structure–property relationships more deeply, and to investigate these relationships more conveniently and accurately. Copyright © 2015 John Wiley & Sons, Ltd.     

Acceleration and mitigation of carrier‐induced degradation in p‐type multi‐crystalline silicon

Recently, a new carrier‐induced defect has been reported in multi‐crystalline silicon (mc‐Si), and has been shown to be particularly detrimental to the performance of passivated emitter and rear contact (PERC) cells. Under normal conditions, this defect can take years to fully form. This Letter reports on the accelerated formation and subsequent passivation of this carrier‐induced defect through the use of high illumination intensity and elevated temperatures resulting in passivation within minutes. The process was tested on industrial mc‐Si PERC solar cells, where degradation after a 100 hour stability test was suppressed to only 0.1% absolute compared to 2.1% for non‐treated cells. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

High‐Capacity Anode Materials for Lithium‐Ion Batteries: Choice of Elements and Structures for Active Particles

Growing market demand for portable energy storage has triggered significant research on high‐capacity lithium‐ion (Li‐ion) battery anodes. Various elements have been utilized in innovative structures to enable these anodes, which can potentially increase the energy density and decrease the cost of Li‐ion batteries. In this review, electrode and material parameters are considered in anode fabrication. The periodic table is then used to explore how the choice of anode material affects rate performance, cycle stability, Li‐ion insertion/extraction potentials, voltage hysteresis, volumetric and specific capacities, and other critical parameters. Silicon (Si), germanium (Ge), and tin (Sn) anodes receive more attention in literature and in this review, but other elements, such as antimony (Sb), lead (Pb), magnesium (Mg), aluminum (Al), gallium (Ga), phosphorus (P), arsenic (As), bismuth (Bi), and zinc (Zn) are also discussed. Among conversion anodes focus is placed on oxides, nitrides, phosphides, and hydrides. Nanostructured carbon (C) receives separate consideration. Issues in high‐ capacity research, such as volume change, insufficient coulombic efficiency, and solid electrolyte interphase (SEI) layer stability are elucidated. Finally, advanced carbon composites utilizing carbon nanotubes (CNT), graphene, and size preserving external shells are discussed, including high mass loading (thick) electrodes and electrodes capable of providing load‐bearing properties.     

Nanoparticle Distribution in Three‐Layer Polymer–Nanoparticle Composite Films: Comparison of Experiment and Theory

The distribution of hydrophobic nanoparticles deposited on a hydrophilic polymer film is investigated by scanning electron microscopy, transmission electron microscopy, and atomic force microscopy before and after spin‐coating a polymer solution on the particle film and drying it at room temperature. Various polymers and solvents are used. To reach equilibrium, all investigated systems are annealed additionally above the glass transition temperature (T_g) of the polymers. The compatibility of the interacting components is estimated by calculating their surface energy, solubility, and mutual interaction parameters. The experimental results show a redistribution of the particles on both interfaces of the polymer film. This corresponds to the calculated immiscibility of particles and polymers. The distribution of the nanoparticles at the interfaces is related mainly to the vapor pressure of the solvent, that is, kinetic effects during spin‐coating. Only minor contributions result from surface energy, solubility, and interaction parameters.     

Comparing the Contribution of Visible‐Light Irradiation,Gold Nanoparticles,and Titania Supports in Photocatalytic Nitroaromatic Coupling and Aromatic Alcohol Oxidation

Under visible‐light irradiation, gold nanoparticles (Au NPs) supported by titania (TiO₂) nanofibers show excellent activity and high selectivity for both reductive coupling of nitroaromatics to corresponding azobenzene or azoxylbenzene and selective oxidation of aromatic alcohols to corresponding aldehydes. The Au NPs act as active centers mainly due to their localized surface plasmon resonance (LSPR) effect. They can effectively couple the photonic energy and thermal energy to enhance reaction efficiency. Visible‐light irradiation has more influence on the reduction than on the oxidation, lowering the activation energy by 24.7 kJ mol^?1 and increasing the conversion rate by 88% for the reductive coupling, compared to merely 8.7 kJ mol^?1 and 46% for the oxidation. Furthermore, it is found that the conversion of nitroaromatics significantly depends on the particle size and specific surface area of supported Au NPs; and the catalyst on TiO₂(B) support outperforms that on anatase phase with preferable ability to activate oxygen. In contrast, for the selective oxidation, the effect of surface area is less prominent and Au NPs on anatase exhibit higher photo‐catalytic activity than other TiO₂ phases. The catalysts can be recovered efficiently because the Au NPs stably attach to TiO₂ supports by forming a well‐matched coherent interface observed via high‐resolution TEM.     

Metal‐nanoparticle‐coating‐induced enhancement and weakening of resonant Raman scattering in ZnO: effect of surface electric field

Effects of Ag and Ti nanoparticle coatings on resonant Raman scattering in various ZnO thin films are presented. The longitudinal optical (LO) phonons, irrespective of the ZnO quality, exhibit an enhancement and a weakening by the Ag and Ti nanoparticle coatings, respectively. The enhancement (weakening) is always accompanied by a reduced (an increased) intensity ratio of the second to first‐order LO phonons, which can be associated with changes in the electron‐phonon coupling strength in the probed area of ZnO. Angle‐resolved X‐ray photoelectron spectroscopy provides evidence for the bending of the surface energy bands and their changes induced by the metal coatings. The effect of metal nanoparticle coatings on the Raman scattering of ZnO is thus attributed to the changes in the surface electric field. Copyright © 2011 John Wiley & Sons, Ltd.     

Influence of light waves on the thermoelectric power under large magnetic field in III‐V,ternary and quaternary materials

We study theoretically the influence of light waves on the thermoelectric power under large magnetic field (TPM) for III‐V, ternary and quaternary materials, whose unperturbed energy‐band structures, are defined by the three‐band model of Kane. The solution of the Boltzmann transport equation on the basis of this newly formulated electron dispersion law will introduce new physical ideas and experimental findings in the presence of external photoexcitation. It has been found by taking n‐InAs, n‐InSb, n‐Hg_1‐xCd_xTe and n‐In_1‐xGa_xAs_yP_1‐y lattice matched to InP as examples that the TPM decreases with increase in electron concentration, and increases with increase in intensity and wavelength, respectively in various manners. The strong dependence of the TPM on both light intensity and wavelength reflects the direct signature of light waves that is in direct contrast as compared with the corresponding bulk specimens of the said materials in the absence of external photoexcitation. The rate of change is totally band‐structure dependent and is significantly influenced by the presence of the different energy‐band constants. The well‐known result for the TPM for nondegenerate wide‐gap materials in the absence of light waves has been obtained as a special case of the present analysis under certain limiting conditions and this compatibility is the indirect test of our generalized formalism. Besides, we have also suggested the experimental methods of determining the Einstein relation for the diffusivity:mobility ratio, the Debye screening length and the electronic contribution to the elastic constants for materials having arbitrary dispersion laws.     

Evaluation of the scientific impact,productivity and biological age based upon the h‐index in three Latin American countries: the materials science case

We discuss the scientific impact of Latin American scientists in the field of materials science. The analysis is based on the h‐index as the scientometric index used to quantify the scientific productivity of an individual. In particular, we focus our analysis in México, Chile and Colombia. We compare the level of productivity between all these countries. We also analyzed the h‐index as function of the biological age, by using the first year of publication of a given scientists as a reference and discussed the general distribution of its quantification. We do not find a clear relationship between these two quantities. Based in our results we propose some political measures that these countries could implement to improve productivity as well as scientific development in this field.