Microstructure of direct current and pulse magnetron sputtered Cr-B coatings

Chromium diboride thin films possess desirable combinations of properties (such as high hardness, wear resistance, chemical inertness, high thermal and electrical conductivity), which are attractive for a wide range of potential industrial applications. However, these properties depend strongly on the deposition process and parameters. Investigation of the resultant coating structures could explain certain differences between them, giving important information about the characteristics of the deposition process (which in this particular case is a recently developed method involving magnetron sputtering of loosely packed blended powder targets) and pointing out directions for improvement.In this paper, Cr-B coatings deposited by direct current (DC) and DC-pulse magnetron sputtering of loosely packed blended powder targets are characterised by transmission electron microscopy (TEM) techniques (electron diffraction and bright-field/dark-field imaging). The structures of the coatings deposited with different parameters are investigated and compared, and the effect of oxygen contamination on the structure is discussed.Coatings with an extremely fine, nanocolumnar structure were observed. DC sputter deposited (and generally non-stoichiometric) Cr-B coatings exhibit a short range ordered ‘zone T’ microstructure, while DC-pulse deposited stoichiometric CrB₂ coatings are dense and defect-free, crystalline and show strong preferred orientation.A small amount of contamination by oxygen of the interfacial sub-layers (due to the target material being a powder) of the DC-pulse magnetron sputter deposited stoichiometric CrB₂ (and near-stoichiometric CrB) coatings was found to affect the structure by suppressing nanocolumnar growth and promoting equiaxed, nanometer-sized grains, close to the coating/substrate interface. The majority of the coating however remained nanocolumnar.     

Synthesis of MCM-41 frameworks incorporating oxygen-sulphur derivates of molybdenum and tungsten

The first examples of mesostructured materials containing Mo- and W-oxo-sulphur species incorporated into a poorly ordered MCM-41 framework have been prepared under hydrothermal condition and alkaline medium. The incorporation of oxygen-sulphur derivates of molybdenum and tungsten not only increases significantly the pore diameter, but also improves the thermal stability of the MCM-41-related mesoporous material.     

二维三氧化钨纳米结构的合成及其在光电探测器中的应用

三氧化钨（WO₃）是制造晶体管和光电探测器的理想材料,虽然在WO₃纳米结构的生长方面已经完成了一些工作,但是制造足够长的理想型纳米线仍然是一个挑战。在众多的合成方法中,作者选择了化学气相沉积（CVD）方法合成WO₃纳米线,并对其在光电传感器中的应用进行了研究。影响WO₃纳米线成品率的主要因素是前体材料温度、基片位置、载气流速和生长持续时间。在合适的生长条件下生长的纳米线长度最长约为100 μm。这些WO₃纳米线可用来制造高性能的光电探测器,WO₃光电探测器具有灵敏度高、响应速度快、模块微型化等优良的器件性能,表明二维WO₃纳米线在光电探测器的制造中具有很大的优势。      

Effects of alkaline and acid pretreatment on the physical properties and nanostructures of the gelatin from channel catfish skins

The objective of this study was to illustrate the correlation between the physical properties and nanostructure of gelatins made of channel catfish (Ictalurus punctatus) skins. The gelatin samples were first pretreated with sodium hydroxide, acetic acid, or water, and then extracted with hot water before the measurement. Physical properties including the yield of protein, viscosity and textural properties were determined on gelatins obtained with different pretreatment conditions. The acid pretreatment group showed the highest gel strength and protein yield, and a reasonable viscosity. The water pretreatment group showed the lowest values for all of the physical properties. Four samples including water, 0.1 M acid and 0.25 and 1.0 M alkaline-pretreated groups’ nanostructures were then studied using atomic force microscopy (AFM). The AFM images showed that the acid-pretreated gelatin was composed of sponge-like aggregates, while the others showed separated individual aggregates. Annular pores were only found in the alkaline pretreatment group. There was no significant correlation between the diameters of the spherical aggregates and the physical properties; however, the different AFM patterns may relate to the gelatin's physical properties.     

CuxNi1-xO nanostructures and their nanocomposites with reduced graphene oxide: Synthesis,characterization, and photocatalytic applications

NiO nanostructure was synthesized using a simple co-precipitation method and was embedded on reduced graphene oxide surface via ultrasonication. Structural investigations were made through X-ray diffraction (XRD) and functional groups were confirmed by Fourier transform infrared spectroscopy (FTIR). XRD analysis revealed the grain size reduction with doping. Fourier transform infrared spectroscopy confirmed the presence of metal-oxygen bond in pristine and doped NiO nanostructure as well as the presence of carbon containing groups. Scanning electron microscopy (SEM) indicated that the particle size decreased when NiO nanostructure was doped with copper. BET surface area was found to increase almost up to 43 m²/g for Cu doped NiO nanostructure/rGO composite. Current-voltage measurements were performed using two probe method. UV–Visible spectroscopic profiles showed the blue and red shift for Cu doped NiO nanostructure and Cu doped NiO Nanostructure/rGO composite respectively. Rate constant for Cu doped NiO nanostructure/rGO composite found to increase 4.4 times than pristine NiO nanostructure.     

A novel germanium/carbon nanotubes nanocomposite for lithium storage material

A new nanocomposite of Ge/carbon nanotubes (n-Ge/CNTs) was reported by a facile precursor method through a pyrolysis technique. Among it, germanium nanoparticles are encapsulated with a thin layer of amorphous carbon, which benefits to keep a good electronic contact with carbon nanotubes. Germanium nanoparticles are mainly supported inside the carbon nanotubes, which can effectively buffer the volume changes of Germanium. The composite was an effectively mixed (Li⁺ and e⁻) conducting network, which is vital to a quick Li insertion. The composite was shown to exhibit a reversible capacity of about 750 mAh g⁻¹ (74.4 mA g⁻¹) and an improved rate performance, compared with that of CNTs processed as the same condition. Our results demonstrated the composite to be a good active Li-storage material for Li batteries.     

Photoluminescence enhancement of quantum dots on Ag nanoneedles

ABSTRACT: Noble-metal nanostructure allows us to tune optical and electrical properties, which has high utility for real-world application. We studied surface plasmon induced emission of semiconductor quantum dots (QDs) on engineered metallic nanostructures. Highly passive organic ZnS capped CdSe QDs were spin coated on poly-(methyl methacrylate) (PMMA) covered Ag films which brought QDs near to metallic surface. We obtained the enhanced electromagnetic field and reduced fluorescence lifetimes from CdSe/ZnS quantum dots (QDs) due to the strong coupling of emitters wave function with the Ag plasmon resonance. Observed changes include a six-fold increase in the fluorescence intensity and striking reduction in fluorescence lifetimes of CdSe/ZnS QDs on rough Ag nanoneedle compared to the case of smooth surfaces. The advantages of using those nanocomposites are expected for high efficiency light-emitting diodes, platform fabrication of biological and environmental monitoring, and high contrast imaging.     

DNA-directed immobilization of horseradish peroxidase onto porous SiO2optical transducers

ABSTRACT: Multifunctional porous Si nanostructure is designed to optically monitor enzymatic activity of Horseradish Peroxidase. First, an oxidized PSi optical nanostructure, a Fabry-Perot thin film, is synthesized and is used as the optical transducer element. Immobilization of the enzyme onto the nanostructure is performed through DNA-Directed Immobilization. Preliminary studies demonstrate high enzymatic activity levels of the immobilized Horseradish Peroxidase, while maintaining its specificity. The catalytic activity of the enzymes immobilized within the porous nanostructure is monitored in real time by reflective interferometric Fourier transform spectroscopy. We show that we can easily regenerate the surface for consecutive biosensing analysis by mild de-hybridization conditions.     

Nanoausferritic matrix of ductile iron

Abstract

Austempered ductile iron is known for its excellent mechanical properties resulting from special phase composition and austempering heat treatment. Typical microstructure consists of ferrite plates of micrometre size submerged in untransformed austenite matrix. It has been recently shown that by use of appropriate chemical composition of cast iron and well targeted heat treatment parameters, it is possible to reduce ferrite plates width to submicron or even nanometric size. This creates the potential to achieve even higher mechanical properties of austempered ductile iron. The paper describes the influence of applied heat treatment parameters on microstructure of selected austempered ductile iron grades. Conditions necessary to reduce size of phases to a nanometric scale by heat treatment in austempered ductile iron are discussed.