Silica encapsulating lanthanum complexes using the sol–gel technique

BACKGROUND: Because of its properties, silica gel is an excellent host for different compounds. Many types of chemical species (organics, organometallics, proteins, enzymes, etc.) can be encapsulated in xerogels, and the sol–gel technique has been shown to be very useful for this aim. RESULTS: Some host–guest systems based on silica and complexed lanthanum were prepared in order to develop fluorescence properties. Three pathways were used to prepare such systems: (1) obtaining the lanthanum complex with a dimethylsiloxane‐based ligand and its incorporation into a silica network; (2) preparation of a silica network having hydroxyazomethine groups and in situ lanthanum complexation; and (3) preparation of polydimethylsiloxane (PDMS)/silica composites that possess hydroxyazomethine groups on the silica and in situ lanthanum complexation. The sol–gel technique was used in all cases. CONCLUSION: The photophysical properties of the prepared compounds were evaluated using fluorescence spectroscopy. The investigations revealed that the systems belonging to the second series are the most fluorescent. In the third series, the presence of PDMS provokes a decrease of the fluorescence intensity, until its complete quenching when the PDMS content exceeds a certain threshold value. However, there is a range of silica/PDMS ratio for which fluorescent free‐standing films can be obtained. The presence of complexed lanthanum induces changes in the morphology of the silica/PDMS matrix, as evidenced by scanning electron microscopy studies. Copyright © 2008 Society of Chemical Industry     

Growth of carbon nanotubes at temperatures compatible with integrated circuit technologies

The potential applications of carbon nanotubes grown for semiconductor and sensor devices are immense. But, this growth must be CMOS compatible and over large-areas, in excess of 4 inches in diameter, for any industrial interest. Reports of low-temperature growth of carbon nanotubes have mostly resulted in false dawns in the context of CMOS production, with direct integration for mass manufacturing remaining a challenge, as lower synthesis temperatures matched to manufacturing result in nanotubes with high defect levels. We report a unique ‘top-down’ synthesis method that allows energy delivery directly to the catalyst, resulting in higher quality nanotube growth at compatible low substrate temperatures. This growth is demonstrated over a large-area, whilst maintaining the silicon substrate below 350 °C. Long-range ordering of carbon nanotubes is supported by well developed second-order Raman peaks and HREM. The methodology developed is suitable to produce many nano-material systems, including graphene and silicon nanowires.     

The abrasion endurance of hard weld deposits from chromium-manganese electrodes

The wear behaviour of hardfacing alloys obtained with five types of coated electrodes with various contents of chromium (1.6 to 12.5%) and manganese (0.8 to 1.8%), is presented. Relative abrasive endurance compared with carbon steel was determined by abrasive wear tests using a rotating disc machine. The highest relative endurance was obtained with a weld deposit with 1% manganese and 2.2% chromium, and a coarse grained austenite-martensite structure. Fully martensitic structures of higher hardness were inferior. The wear behaviour of hardfacing alloys depends upon both the structural components and the grain size shown by means of abrasive wear tests in laboratories or exploitation endurance tests. Abrasive wear testing can assess wear resistance and be a guide to service performance.     

Styrene–divinylbenzene copolymers: Influence of the diluent on network porosity

The formation of the permanent porosity in the classical matrix, styrene–divinylbenzene copolymers, using cyclohexane, cyclohexanol, or cyclohexanone as diluent was studied. The data concerning porous networks were corroborated with the solvent–polymer interaction factor and the cohesive energy density which are important in the prediction of copolymer porosity. Between diluents there are noticeable differences, though the diluent volume and the divinylbenzene percent strongly influence the porous structure of the network. Cyclohexanal was the most efficient diluent for building up the highest porosity even at low percents of divinylbenzene.     

Helium ion microscopy and its application to nanotechnology and nanometrology

Helium ion microscopy (HeIM) presents a new approach to nanotechnology and nanometrology, which has several potential advantages over the traditional scanning electron microscope (SEM) currently in use in research laboratories and manufacturing facilities across the world. Owing to the very high source brightness, and the shorter wavelength of the helium (He) ions, it is theoretically possible to focus the ion beam into a smaller probe size relative to that of the electron beam of an SEM. Hence, resolution 2 × – 4 × better than that of comparable SEMs is theoretically possible. In an SEM, an electron beam interacts with the sample and an array of signals are generated, collected and imaged. This interaction zone may be quite large depending upon the accelerating voltage and materials involved. Conversely, the helium ion beam interacts with the sample, but it does not have as large an excitation volume and, thus, the image collected is more surface sensitive and can potentially provide sharp images on a wide range of materials. Compared with an SEM, the secondary electron yield is quite high—allowing for imaging at extremely low beam currents and the relatively low mass of the helium ion, in contrast to other ion sources such as gallium, potentially results in minimal damage to the sample. This article reports on some of the preliminary work being done on the HeIM as a research and measurement tool for nanotechnology and nanometrology being done at NIST. SCANNING 30: 457–462, 2008. Published 2008 by Wiley Periodicals, Inc.     

Image sharpness measurement in scanning electron microscopy—part II

A method for qualitative and quantitative analysis of scanning electron microscope (SEM) images forthe determination of sharpness is presented in this paper. Described is a procedure for qualitative analysis based on a software program called SEM Monitor that can be applied to research or industrial SEMs for day-to-day performance monitoring. The idea is based on the fact that, as the electron beam scans the sample, the low-frequency changes in the video signal show information about the larger features and the high-frequency changes give data on finer details. The image contains information about the primary electron beam and about all the parts contributing to the signal formation in the SEM. If everything else is kept unchanged, with a suitable sample, the geometric parameters of the primary electron beam can be mathematically determined. An image of a sample, which has fine details at a given magnification, is sharper if there are more high frequency changes in it. In the SEM, a better focused electron beam yields a sharper image, and this sharpness can be measured. The method described is based on calculations in the frequency domain and can also be used to check and optimize two basic parameters of the primary electron beam, the focus, and the astigmatism.     

Development of Ti-6Al-4V and Ti-1Al-8V-5Fe Alloys Using Low-Cost TiH2 Powder Feedstock

Thermo-mechanical processing was performed on two titanium alloy billets, a beta-titanium alloy (Ti1Al8V5Fe) and an alpha-beta titanium alloy (Ti6Al4V), which had been produced using a novel low-cost powder metallurgy process that relies on the use of TiH₂ powder as a feedstock material. The thermomechanical processing was performed in the beta region of the respective alloys to form 16-mm diameter bars. The hot working followed by the heat treatment processes not only eliminated the porosity within the materials but also developed the preferred microstructures. Tensile testing and rotating beam fatigue tests were conducted on the as-rolled and heat-treated materials to evaluate their mechanical properties. The mechanical properties of these alloys matched well with those produced by the conventional ingot processing route.     

High current and low q95 scenario studies for FAST in the view of ITER and DEMO

The Fusion Advanced Study Torus (FAST) has been proposed as a possible European satellite, in view of ITER and DEMO, in order to: (a) explore plasma wall interaction in reactor relevant conditions, (b) test tools and scenarios for safe and reliable tokamak operation up to the border of stability, and (c) address fusion plasmas with a significant population of fast particles. A new FAST scenario has been designed focusing on low-q operation, at plasma current I_P = 10 MA, toroidal field B_T = 8.5 T, with a q₉₅ ≈ 2.3 that would correspond to I_P ≈ 20 MA in ITER. The flat-top of the discharge can last a couple of seconds (i.e. half the diffusive resistive time and twice the energy confinement time), and is limited by the heating of the toroidal field coils. A preliminary evaluation of the end-of-pulse temperatures and of the electromagnetic forces acting on the central solenoid pack and poloidal field coils has been performed. Moreover, a VDE plasma disruption has been simulated and the maximum total vertical force applied on the vacuum vessel has been estimated.     

A microfabricated low cost enzyme-free glucose fuel cell for powering low-power implantable devices

In the past decade the scientific community has showed considerable interest in the development of implantable medical devices such as muscle stimulators, neuroprosthetic devices, and biosensors. Those devices have low power requirements and can potentially be operated through fuel cells using reactants present in the body such as glucose and oxygen instead of non-rechargeable lithium batteries. In this paper, we present a thin, enzyme-free fuel cell with high current density and good stability at a current density of 10 μA cm⁻². A non-enzymatic approach is preferred because of higher long term stability. The fuel cell uses a stacked electrode design in order to achieve glucose and oxygen separation. An important characteristic of the fuel cell is that it has no membrane separating the electrodes, which results in low ohmic losses and small fuel cell volume. In addition, it uses a porous carbon paper support for the anodic catalyst layer which reduces the amount of platinum or other noble metal catalysts required for fabricating high surface area electrodes with good reactivity. The peak power output of the fuel cell is approximately 2 μW cm⁻² and has a sustainable power density of 1.5 μW cm⁻² at 10 μA cm⁻². An analysis on the effects of electrode thickness and inter electrode gap on the maximum power output of the fuel cell is also performed.