Metal Additive Distribution in TiO2 and SnO2 Semiconductor Gas Sensor Nanostructured Materials

Recently, there has been an increasing interest in the electronics world for those aspects related to semiconducting gas sensor (SGS) materials. In view of the increasingly strict legal limits for pollutant gas emissions, there is a great interest in developing high performance gas sensors for applications such as controlling air pollution and exhaust gases. In this way, semiconductor gas sensors offer good advantages with respect to other gas sensor devices (such as spectroscopic and optic systems), due to their simple implementation, low cost and good reliability for real-time control systems. In the present work, we have been especially interested in the study of the different ways of metal additive distribution in the most common SGS materials used nowadays and furthermore in the physical and chemical sensing properties they can achieve

Engineering surface states of hematite based photoanodes for boosting photoelectrochemical water splitting

Hematite-based photoanodes are promising candidates for photoelectrochemical water splitting. However, the performance of pristine hematite semiconductors is unsatisfactory due to charge recombination occurring at different interfaces: Back contact, bulk and semiconductor/electrolyte interfaces. Increasing efforts have been focused on enhancing the performance of hematite based photoanodes via nanostructure control, doping, heterojunction construction, and surface modification with a secondary semiconductor or an oxygen evolution electrocatalyst. Most of the previous studies attributed the enhanced PEC water splitting performance to the changes in the donor density via doping, the formation of type II heterojunction via a secondary semiconductor coating and the improved water oxidation kinetics via coating oxygen evolution electrocatalysts. However, the role of surface states presented at the semiconductor/electrolyte interfaces of hematite-based photoanodes has been overlooked in previous investigations, which virtually play a critical role in determining the photoelectrochemical water oxidation process. In this review, we summarize the recent progress of various techniques employed for the detection of surface states of hematite photoanodes and highlight the important role of modifying surface states in the development of high performance hematite based photoanodes for photoelectrochemical water splitting application. The challenges and future prospects in the study of hematite based photoanodes are also discussed

Metal-organic framework-derived single atom catalysts for electrocatalytic reduction of carbon dioxide to C1 products

Electrochemical carbon dioxide reduction reaction (eCO RR) is an efficient strategy to relieve global environmental and energy issues by converting excess CO from the atmosphere to value-added products. Single-atom catalysts (SACs) derived from metal-organic frameworks (MOF), which feature unique active sites and adjustable structures, are emerging as extraordinary materials for eCO RR. By modulating the MOF precursors and their fabrication strategy, MOF-derived SACs with specific-site coordination configuration have been recently designed for the conversion of CO to targeted products. In the first part of this review, MOF synthesis routes to afford well-dispersed SACs along with the respective synthesis strategy have been systematically reviewed, and typical examples for each strategy have been discussed. Compared with traditional M-N active sites, SACs with regulated coordination structures have been rapidly developed for eCO RR. Secondly, the relationship between regulation of the coordination environment of the central metal atoms, including asymmetrical M-N sites, heteroatom doped M-N sites, and dual-metal active sites (M-M sites), and their respective catalytic performance has been systematically discussed. Finally, the challenges and future research directions for the application of SACs derived from MOFs for eCO RR have been proposed

Phonon confinement and plasmon-phonon interaction in nanowire based quantum wells

Resonant Raman spectroscopy is realized on closely spaced nanowire based quantum wells. Phonon quantization consistent with 2.4 nm thick quantum wells is observed, in agreement with cross-section transmission electron microscopy measurements and photoluminescence experiments. The creation of a high density plasma within the quantized structures is demonstrated by the observation of coupled plasmon-phonon modes. The density of the plasma and thereby the plasmon-phonon interaction is controlled with the excitation power. This work represents a base for further studies on confined high density charge systems in nanowires

Hollow metal nanostructures for enhanced plasmonics: synthesis, local plasmonic properties and applications

Hollow nanostructures; Surface plasmon resonances (SPRs); Plasmon hybridizationNanoestructures buides; Ressonància de superfície de plasmó; Hibridació de plasmóNanoestructures vacías; Resonancia de superficie de plasmón; Hibridación de plasmónMetallic nanostructures have received great attention due to their ability to generate surface plasmon resonances, which are collective oscillations of conduction electrons of a material excited by an electromagnetic wave. Plasmonic metal nanostructures are able to localize and manipulate the light at the nanoscale and, therefore, are attractive building blocks for various emerging applications. In particular, hollow nanostructures are promising plasmonic materials as cavities are known to have better plasmonic properties than their solid counterparts thanks to the plasmon hybridization mechanism. The hybridization of the plasmons results in the enhancement of the plasmon fields along with more homogeneous distribution as well as the reduction of localized surface plasmon resonance (LSPR) quenching due to absorption. In this review, we summarize the efforts on the synthesis of hollow metal nanostructures with an emphasis on the galvanic replacement reaction. In the second part of this review, we discuss the advancements on the characterization of plasmonic properties of hollow nanostructures, covering the single nanoparticle experiments, nanoscale characterization via electron energy-loss spectroscopy and modeling and simulation studies. Examples of the applications, i.e. sensing, surface enhanced Raman spectroscopy, photothermal ablation therapy of cancer, drug delivery or catalysis among others, where hollow nanostructures perform better than their solid counterparts, are also evaluated

Electric field assisted dissolution of metal clusters in metal island films for photonic heterostructures

The dissolution of metal clusters in metal island films by the simultaneous application of electric field and temperature is reported. The consequent fading of surface plasmon resonance greatly modifies the optical properties of the samples. The dissolution process is verified in island films of different metals, obtained under different conditions and covered by different dielectric materials, as well as on multilayer dielectric stacks showing interferential properties. The tailoring possibilities of the optical behavior of metal island films combined with the inexpensive technical requirements of this approach open up the possibility to produce low-cost photonic heterostructures

The Normative Implication of the B Corp Movement in the Business and Human Rights Context (abstract)

Over the past decades, issues of corporate accountability and social responsibility have risen to the forefront of international debate. The U.N. Guiding Principles on Business and Human Rights (Guiding Principles), endorsed by the U.N. HRC in June 2011, lays out authoritatively the state duty to protect and the corporate responsibility to respect human rights. In an effort to operationalize the Guiding Principles, the U.N. Working Group on Business and Human Rights has called on all states to develop a National Action Plan (NAP) regarding domestic implementation of the Guiding Principles. A key first-step in the creation of a NAP is the completion of a national baseline assessment, a taking of stock of the current conditions affecting the protection and promotion of human rights by the state and businesses alike. With over twenty-five countries now committed to the creation of a NAP, it is increasingly important to evaluate the existing corporate landscape, specifically structures that claim to be socially and ethically motivated. The B Corp movement began in 2006, through the work of California based non-profit B-Lab. A B Corp is a business certified by B-Lab as committed to creating and supporting social and environmental rights. The B Corp movement has grown in size and stature, spreading into over thirty countries and garnering a reputation for excellence. Boosts to the movement have recently come from the certification of large multinational companies, and the interest of others that followed. As the B Corp movement continues to proliferate, it’s normative value on the business and human rights field merits analysis. What are the normative implications of the B Corp movement?—Is it a tool that should be embraced by business and human rights activists or one that undermines the movement by enabling corporations to claim an inability to take into account ethical considerations without adoption of a special corporate form

UV Photosensing Characteristics of Nanowire-Based GaN/AlN Superlattices

We have characterized the photodetection capabilities of single GaN nanowires incorporating 20 periods of AlN/GaN:Ge axial heterostructures enveloped in an AlN shell. Transmission electron microscopy confirms the absence of an additional GaN shell around the heterostructures. In the absence of a surface conduction channel, the incorporation of the heterostructure leads to a decrease of the dark current and an increase of the photosensitivity. A significant dispersion in the magnitude of dark currents for different single nanowires is attributed to the coalescence of nanowires with displaced nanodisks, reducing the effective length of the heterostructure. A larger number of active nanodisks and AlN barriers in the current path results in lower dark current and higher photosensitivity, and improves the sensitivity of the nanowire to variations in the illumination intensity (improved linearity). Additionally, we observe a persistence of the photocurrent, which is attributed to a change of the resistance of the overall structure, particularly the GaN stem and cap sections. In consequence, the time response is rather independent of the dark current.Comment: This document is the unedited Author's version of a Submitted Work that was subsequently accepted for publication in Nano Letters (2016), copyright (C) American Chemical Society after peer review. To access the final edited and published work see http://dx.doi.org/10.1021/acs.nanolett.6b0080

Disentangling epitaxial growth mechanisms of solution derived functional oxide thin films

This study investigates the mechanisms of epitaxial development and functional properties of oxide thin films (Ce0.9Zr0.1O2−y, LaNiO3, and Ba0.8Sr0.2TiO3) grown on single crystal substrates (Y2O3:ZrO2, LaAlO3, and SrTiO3) by the chemical solution deposition approach. Rapid thermal annealing furnaces are very powerful tools in this study providing valuable information of the early stages of nucleation, the kinetics of epitaxial film growth, and the coarsening of nanocrystalline phases. Advanced transmission electron microscopies, X-ray diffraction, and atomic force microscopy are employed to investigate the film microstructure and morphology, microstrain relaxation, and epitaxial crystallization. This study demonstrates that the isothermal evolution toward epitaxial film growth follows a self-limited process driven by atomic diffusion, and surface and interface energy minimization. All investigated oxides experience a transformation from the polycrystalline to the epitaxial phase. This study unequivocally evidences that the film thickness highly influences the epitaxial crystallization rate due to the competition between heterogeneous and homogeneous nucleation barriers and the fast coarsening of polycrystalline grains as compared to epitaxial growth. The investigated films possess good functional properties, and this study successfully confirms an improvement at long annealing times that can be correlated with grain boundary healing processes. Thick epitaxial films can be crystallized by growing sequential individual epitaxial layers.We acknowledge financial support from Spanish Ministry of Economy and Competitiveness through the “Severo Ochoa” Programme for Centres of Excellence in R&D (SEV-2015-0496), CONSOLIDER Excellence Network (MAT2015-68994-REDC), COACHSUPENERGY project (MAT2014-56063-C2-1-R, co-financed by the European Regional Development Fund), and the projects MAT2011-28874-C02-01, ENE2014-56109-C3-3-R and Consolider Nanoselect (CSD2007-00041), and from the Catalan Government (2014-SGR-753 and Xarmae). AQ and MdlM are also grateful for JAE-Predoc fellowship from CSIC (E-08-2012-1321248 and E-08-2013-1028356, co-financed by the European Social Fund).Peer Reviewe