Towards high performance near-infrared photo detectors based on SnS nanowires

Compared with bulk structures, semiconductor nanowires exhibit a higher surface-to-volume ratio, as well as unique electrical and optical properties. Due to its narrow band gap, tin (ii) sulfide (SnS) nano wire is a promising candidate for constructing near-infrared (NIR) photodetectors. Uniformly distributed and well aligned SnS nanowires were grown on mica substrate by chemical vapor deposition, and NIR photodetectors with Au (Au-device) and Al (Al-device) as the electrode were fabricated and characterized. Compared to Au-device, Al-device achieved higher photodetectivity due to reduced dark current. More importantly by incorporating photosensitive lead phthalocyanine (PbPc) film into Al-device, both responsivity and detectivity could be apparently improved, especially at weak light intensities. Under a weak light intensity of 0.79 mW/cm2 the photoresponsivity and specific detectivity were improved from ~0.56 A/W and 5.1×1010 Jones to 0.96 A/W and 8.4×1010 Jones, respectively.

Parametric studies on laser additive manufacturing of copper on stainless steel

Laser additive manufacturing using directed energy deposition (LAM-DED) technique is one of the recent techniques for fabricating engineering components directly from 3D CAD model data using high power lasers. In this respect, LAM-DED of copper (Cu) and stainless steel (SS) is an enduring research area. However, LAM-DED of Cu is challenging due to higher thermal conductivity, lower absorption to infrared radiation and oxide formation tendency. The present work reports an experimental investigation to evaluate the effect of process parameters on the track geometry, contact angle, inter-diffusion and micro-hardness of Cu tracks deposited on SS 304L substrate using LAM-DED. Analysis of variance is used to estimate the contribution percentage of process parameters on the track geometry. Further, Cu bulk structures are deposited at an identified combination of process parameters and they are subjected to optical microscopy for microstructural characterisation. Further, finite-element-based numerical simulation is performed to understand the temperature distribution during the processing of Cu bulk structures on SS304L and the temperature results are co-related with the microstructural transformation during the processing. This investigation paves a way to understand the effect of processing parameters for building Cu bulk structures on SS Substrate using LAM-DED.

Selective Laser Melting of Stainless Steel 316L for Mechanical Property-Gradation

With an end goal of creating single-alloy functionally-graded additively manufactured (FGAM) parts, this paper investigates the manufacture and properties of stainless steel 316L samples via a pulsed selective laser melting (SLM) process. The focus is on elucidating the underlying causes of property variations (within a functionally-acceptable range) through material characterization and testing. Five samples (made via different volumetric energy density-based process parameter sets) were down-selected from preliminary experimental results and analyzed for their microstructure, mechanical and physical properties (hardness, density/porosity, Young’s modulus). It was observed that property variations resulted from combinations of porosity types/amounts, martensitic phase fractions, and grain sizes. Based on these, various functionally-graded specimens of different sizes were built as per ASTM standards, each having intended property changes along its gauge volumes. The presented findings establish that a methodical control of microstructure and mechanical properties could be obtained in a repeatable and reproducible manner by changing the process parameters. This work lays the foundation for understanding and tuning the global mechanical performance of FGAM bulk structures as well as the role of interfacial zones.

Optimal control model for the formation of strength indicators of bulk structures

В данной статье рассматривается метод построения модели прочностных свойств композиционного материала. Особое внимание уделено установлению функциональных зависимостей рассматриваемых в статье параметров, оказывающих существенное влияние на получение композита с требуемыми эксплуатационными характеристиками. Показано как влияют различные характеристики композиционного материала на процесс получения изделия с требуемыми прочностными свойствами. This article discusses a method for constructing a model of the strength properties of a composite material. Particular attention is paid to the establishment of functional dependencies of the parameters considered in the article, which have a significant impact on obtaining a composite with the required performance characteristics. It is shown how different characteristics of a composite material influence the process of obtaining a product with the required strength properties.

Formation of Interstellar Silicate Dust via Nanocluster Aggregation: Insights From Quantum Chemistry Simulations

The issue of formation of dust grains in the interstellar medium is still a matter of debate. One of the most developed proposals suggests that atomic and heteromolecular seeds bind together to initiate a nucleation process leading to the formation of nanostructures resembling very small grain components. In the case of silicates, nucleated systems can result in molecular nanoclusters with diameters ≤ 2 nm. A reasonable path to further increase the size of these proto-silicate nanoclusters is by mutual aggregation. The present work deals with modeling this proto-silicate nanocluster aggregation process by means of quantum chemical density functional theory calculations. We simulate nanocluster aggregation by progressively reducing the size of a periodic array of initially well-separated nanoclusters. The resulting aggregation leads to a set of silicate bulk structures with gradually increasing density which we analyze with respect to structure, energetics and spectroscopic properties. Our results indicate that aggregation is a highly energetically favorable process, in which the infrared spectra of the finally formed amorphous silicates match well with astronomical observations.

A Computational Study of the Properties of Pd, Cu and Zn Surfaces

<p>We report a detailed Density Functional Theory (DFT) based investigation of the structure and stability of bulk and surface structures for the Group 10-12 elements Pd, Cu and Zn, considering the effect of the choice of exchange-correlation density functionals and computation parameters. For the initial bulk structures, the lattice parameter and cohesive energy are calculated, which are then augmented by calculation of surface energies and work functions for the lower-index surfaces. Of the 22 density functionals considered, we highlight the mBEEF density functional as providing the best overall agreement with experimental data. The optimal density functional choice is applied to the study of higher index surfaces for the three metals, and Wulff constructions performed for nanoparticles with a radius of 11nm, commensurate with nanoparticle sizes commonly employed in catalytic chemistry. For Pd and Cu, the low-index (111) facet is dominant in the constructed nanoparticles, covering ~50% of the surface, with (100) facets covering a further 10 to 25%; however, non-negligible coverage from higher index (332), (332) and (210) facets are also observed for Pd, and (322), (221) and (210) surfaces are observed for Cu. In contrast, only the (0001) and (10-10) facets are observed for Zn. Overall, our results highlight the need for carefully validation of computational settings before performing extensive density functional theory investigations of surface properties and nanoparticle structures of metals.</p>

A Computational Study of the Properties of Pd, Cu and Zn Surfaces

<p>We report a detailed Density Functional Theory (DFT) based investigation of the structure and stability of bulk and surface structures for the Group 10-12 elements Pd, Cu and Zn, considering the effect of the choice of exchange-correlation density functionals and computation parameters. For the initial bulk structures, the lattice parameter and cohesive energy are calculated, which are then augmented by calculation of surface energies and work functions for the lower-index surfaces. Of the 22 density functionals considered, we highlight the mBEEF density functional as providing the best overall agreement with experimental data. The optimal density functional choice is applied to the study of higher index surfaces for the three metals, and Wulff constructions performed for nanoparticles with a radius of 11nm, commensurate with nanoparticle sizes commonly employed in catalytic chemistry. For Pd and Cu, the low-index (111) facet is dominant in the constructed nanoparticles, covering ~50% of the surface, with (100) facets covering a further 10 to 25%; however, non-negligible coverage from higher index (332), (332) and (210) facets are also observed for Pd, and (322), (221) and (210) surfaces are observed for Cu. In contrast, only the (0001) and (10-10) facets are observed for Zn. Overall, our results highlight the need for carefully validation of computational settings before performing extensive density functional theory investigations of surface properties and nanoparticle structures of metals.</p>

A Computational Study of the Properties of Pd, Cu and Zn Surface

<p>We report a detailed Density Functional Theory (DFT) based investigation of the structure and stability of bulk and surface structures for the Group 10-12 elements Pd, Cu and Zn, considering the effect of the choice of exchange-correlation density functionals and computation parameters. For the initial bulk structures, the lattice parameter and cohesive energy are calculated, which are then augmented by calculation of surface energies and work functions for the lower-index surfaces. Of the 22 density functionals considered, we highlight the mBEEF density functional as providing the best overall agreement with experimental data. The optimal density functional choice is applied to the study of higher index surfaces for the three metals, and Wulff constructions performed for nanoparticles with a radius of 11nm, commensurate with nanoparticle sizes commonly employed in catalytic chemistry. For Pd and Cu, the low-index (111) facet is dominant in the constructed nanoparticles, covering ~50% of the surface, with (100) facets covering a further 10 to 25%; however, non-negligible coverage from higher index (332), (332) and (210) facets are also observed for Pd, and (322), (221) and (210) surfaces are observed for Cu. In contrast, only the (0001) and (10-10) facets are observed for Zn. Overall, our results highlight the need for carefully validation of computational settings before performing extensive density functional theory investigations of surface properties and nanoparticle structures of metals.</p>

Determination of Quantum Capacitance of Niobium Nitrides Nb2N and Nb4N3 for Supercapacitor Applications

The density of states and quantum capacitance of pure and doped Nb2N and Nb4N3 single-layer and multi-layer bulk structures are investigated using density functional theory calculations. The calculated value of quantum capacitance is quite high for pristine Nb2N and decent for Nb4N3 structures. However for cobalt-doped unpolarized structures, significant increase in quantum capacitance at Fermi level is observed in the case of Nb4N3 as compared to minor increase in case of Nb2N. These results show that pristine and doped Nb2N and Nb4N3 can be preferred over graphene as the electrode material for supercapacitors. The spin and temperature dependences of quantum capacitance for these structures are also investigated.

Two-dimensional oxides

The novel physical and chemical properties and functionalities of two-dimensional (2-D) oxide materials are assessed. The synthesis of one unit-cell thick 2-D oxides poses particular challenges, since in contrast to other 2-D materials, which can be fabricated by exfoliation of layered bulk compounds, the majority of oxides do not occur in layered bulk structures. Most 2-D oxides are therefore prepared by thin-film deposition methods on substrates. However the fabrication of free-standing quasi-2-D oxide nanosheets, with less restrictive several monolayer thickness, has been successfully achieved by wet chemical procedures. New geometry concepts and electronic properties are observed in 2-D oxides, due to quantum confinement and interface proximity effects. Atomic geometries, electronic structure, ferroic properties and catalytic behaviour of 2-D oxides are discussed, together with promising prototypical proof-of-concept experiments for prospective applications. The edge states in oxide nanoribbons, 2-D objects of limited width, and their polarity aspects are discussed.