Structural and optical characterization of mechanochemically synthesized copper doped CdS nanopowders

Incorporation of copper into CdS crystals has been successfully prepared by mechanical alloying using a planetary ball mill. The powders are prepared with different milling times at 300 rpm with various Cu/Cd ratios from 0.1 to 25 at%. X-ray diffraction (XRD) analysis of milled powders showed peaks corresponding to hexagonal structure with a detection of phase transition to a cubic structure with increasing milling time. Grain sizes varied from 21 to 30 nm corresponding to different Cu/Cd ratios. Field emission scanning electron microscopy (FESEM) images reveal agglomerated materials with particle size of approximately 28 nm (5 Cu at%) and layered structures caused due to the milling process. Powder composition by energy dispersive analysis of X-rays (EDAX) reveals the incorporation of copper into the CdS. Micro Raman spectroscopy showed peaks approximately at 301 and 585 cm⁻¹ corresponding to first and second order scatterings of longitudinal optical phonon mode. The LO mode at 301 cm⁻¹ shifted towards lower wave number due to decrease of grain size by increase in milling time. From high resolution transmission electron microscope (HRTEM), the dominant phase of individual CdS nanocrystals was found to be hexagonal structure along with cubic structure.     

Inelastic neutron scattering in cuprate superconductors: Evidence for inhomogeneous materials properties

There is increasing experimental evidence for the coexistence of different types of local regions in doped high-T _c superconductors of 123 and 214 type. They may be classified into local regions of undoped, intermediately doped, and highly doped character. The doping mechanism makes the system inhomogeneous, and the superconducting state is reached by a percolation process. Very detailed information about the volume fractions and the spatial extent of the local regions can be obtained by neutron spectroscopic investigations of the crystal-field interaction at the rare-earth site which is an ideal local probe of the charge distribution in the superconducting copper oxide planes. The inhomogeneous materials properties have to be taken into account in any interpretation of the physical properties of doped high-T _c superconductors. This is exemplified for the static and dynamic copper spin correlations of YBa₂Cu₃O _x (6x7). We show that the spin fluctuations observed in the superconducting state can be associated with the undoped and intermediately doped regions of the system, whereas no magnetic scattering occurs for the highly doped regions.     

A more informative approach for characterization of polymer monolithic phases: small angle neutron scattering/ultrasmall angle neutron scattering

Neutron scattering techniques have been used frequently to characterize geological specimens and to determine the structures of glasses and of polymers as solutions, suspensions, or melts. Little work has been reported on their application in determining polymers' structural properties relevant to separations. Here, we present a comparison of characterization results from nitrogen porosimetry and from combined small angle neutron scattering (SANS) and ultrasmall angle neutron scattering (USANS) experiments. We show that SANS is extremely sensitive to the pore characteristics. Both approaches can provide information about porosity and pore characteristics, but the neutron scattering techniques provide additional information in the form of the surface characteristics of the pores and their length scales. Fits of the scattering data show that cylindrical pores are present with diameters down to 0.6 μm and that, for length scales down to approxmately 20 ?, the material shows self-similar (fractal) slopes of -3.4 to -3.6. Comparison of these characteristics with other examples from the scattering literature indicate that further investigation of their meaning for chromatographic media is required.     

Advanced techniques for characterization of ion beam modified materials

Understanding the mechanisms of damage formation in materials irradiated with energetic ions is essential for the field of ion-beam materials modification and engineering. Utilizing incident ions, electrons, photons, and positrons, various analysis techniques, including Rutherford backscattering spectrometry (RBS), electron RBS, Raman spectroscopy, high-resolution X-ray diffraction, small-angle X-ray scattering, and positron annihilation spectroscopy, are routinely used or gaining increasing attention in characterizing ion beam modified materials. The distinctive information, recent developments, and some perspectives in these techniques are reviewed. Applications of these techniques are discussed to demonstrate their unique ability for studying ion-solid interactions and the corresponding radiation effects in modified depths ranging from a few nm to a few tens of μm, and to provide information on electronic and atomic structure of the materials, defect configuration and concentration, as well as phase stability, amorphization and recrystallization processes. Such knowledge contributes to our fundamental understanding over a wide range of extreme conditions essential for enhancing material performance and also for design and synthesis of new materials to address a broad variety of future energy applications.     

Lamb wave scattering analysis for reflector characterization

The potential use of guided waves for defect characterization is studied. The influence of defect shape and size on transmitted and reflected fields is considered. Using the hybrid boundary element technique, the reflection and transmission coefficients for selected guided wave modes are numerically calculated and compared to experimental data. Selecting the aspect ratio as a shape parameter for various defects, the transmission and reflection coefficients are measured for certain guided wave modes input to the defect. The influence of defect size is then studied by monitoring the transmission and reflection coefficients for defects of various shapes and depths. The studies presented indicate that defect characterization is possible if a proper mode selection criteria can be established. The suitable features related to transmission and reflection coefficient data can also be used for algorithm development and implementation purposes of defect characterization.     

Advanced x-ray detectors for the analysis of materials

A crucial need exists to analyze the composition of materials nondestructively. Energy-dispersive spectrometers are widely used to perform this function, but their performance is limited by the energy resolution of the detector, typically 150 eV for Si(Li) at 6 keV. Calorimeters and tunnel junctions offer more than an order of magnitude improvement in energy resolution, with the prospect of vast improvements in performance for quantitative analysis. We present an analysis of the critical issues pertaining to the use of calorimeters for quantitative materials analysis, and show that significant performance advantages may be realized with the energy resolutions already achieved. We also describe other x-ray analysis methods for determining the chemical state of the material to be studied, which also may benefit from calorimeter technology.     

Cryogen-free cryostat for neutron scattering sample environment

Today all advanced neutron facilities maintain a fleet of Orange cryostats, or similar systems, to provide low temperature sample environment in neutron scattering experiments. However recent liquid helium cost increases, caused by global helium supply problems, have raised significant concern about the affordability of such cryostats. The ISIS facility is carrying out a development programme intended to substitute conventional cryostats with cryogen-free systems preferably based on pulse tube refrigerators. The main aim of the development is to create a cryogen-free system as a potential replacement for the conventional Orange cryostat. This paper describes the design and test results of a cryogen-free cryostat, based on a pulse tube refrigerator, with 50 mm diameter top-loading sample facilities for neutron scattering experiments. The sample temperature range is 1.45–300 K in the continuous flow regime. The cryostat may also be used with ultra-low temperature dilution refrigerator inserts.     

Small-angle neutron scattering investigations on sintering behavior of combustion synthesized La0.8Sr0.2CrO3

Pore morphology of La0.8Sr0.2CrO3 (LSC) powder compacts, sintered between 1200 degrees C and 1450 degrees C for a fixed time, has been characterized by small-angle neutron scattering (SANS) in the scattering wave vector 'q' range, 0.003-0.17 nm(-1) of a double crystal based instrument. Scattering profile of green compact exhibits fractal scaling at two regions of 'q' with magnitudes of fractal dimensionality 1.8 and 2.36. Scattering profiles of sintered pellets have been modeled assuming a random distribution of near spherical pores in the solid matrix. Estimated pore size distributions of sintered pellets indicate decrease in pore volume has taken place by progressive elimination of smallest pores and growth of relatively larger pores with increasing sintering temperature. SANS results are supplemented by light scattering measurement and TEM image of powder and SEM image of the fracture surface of sintered pellet.     

Ultra-small angle neutron scattering and X-ray tomography studies of caseinate–hydroxyapatite microporous materials

Microporous hydroxyapatite–protein composite materials of bimodal pore size distribution, intended for utilization as bone regeneration scaffolds, have been prepared by means of milk caseinate emulsion droplet templating. Ultra-small angle neutron scattering (USANS) has been utilized in order to obtain information on the size distribution of the smaller pores (less than tens of micrometers), as compared to the emulsions that have been initially used as templates. The samples were subsequently visualized in 3 dimensions using synchrotron radiation X-ray tomography, where information concerning the larger pores has been obtained. The examination of the samples confirmed a strong correlation between the size of the templating droplets and the produced pores. In addition, 1 μm-sized pores appear to adhere to the surface of 20–70 μm pores, providing an irregular surface on the large pore walls, a desirable feature in bone-mimicking materials.     

Non-resonant RF and microwave response: A novel technique for the characterization of superconducting materials

When examined using continuous wave electron paramagnetic resonance and nuclear magnetic resonance spectrometers, the highT _c superconductors give rise to intense, low field, ‘non-resonant’ absorption signals in the superconducting state. This phenomenon can be used as a highly sensitive, contactless technique for the detection and characterization of superconductivity even in samples containing only minute amounts of the superconducting phase. Further, it can also be applied to the determination of material parameters of interest such asJ _c andH _c2 in addition to being a powerful way of distinguishing between weak-link superconductivity and bulk superconductivity. The details of these aspects are discussed.     

Vibrational spectroscopic analysis of silicones: a Fourier transform-Raman and inelastic neutron scattering investigation

An inelastic neutron scattering spectrum of a poly(dimethylsiloxane) (PDMS) is reported, and a spectrum simulated using a monomer molecular unit as a model for comparison. FT-Raman spectra of a series of PDMS derivatives are reported and structure spectra correlations are shown to exist for the estimation of (a) PDMS average chain length, (b) ratio of the number of monofunctional units to quadrifunctional units in silicone resins, and (c) the percentage weight of PDMS in silicone emulsions.     

Advanced passive detectors for neutron dosimetry and spectrometry

Different neutron detectors have been developed in the past which exploit electrical and electrochemical processes in plastic foils and thin-film capacitors (namely metal-oxide-silicon devices) to trigger avalanche processes, which greatly facilitate the detection of neutron-induced charged particles. These detectors are: (i) spark-replica counter of neutron-induced fission-fragment holes in plastic films, thin-film breakdown counter of neutron-induced fission fragments, and electrochemically etched detectors of neutron-induced recoils in plastic foils. The major shortcomings of damage-track detectors for the measurement of low neutron fluencies, such as those of cosmic ray neutrons at civil aviation altitudes, are their large and unpredictable background and their small signal-to-noise ratio. These shortcomings have been overcome respectively by using long exposure times and large detector areas and counting coincidence-track events on matched pairs of detectors even for a few-micron-long tracks such as those of neutron recoils. The responses of all these detectors have been analysed both with neutrons with energy up to approximately 200 MeV and protons up to tens of gigaelectron volts. Applications of these detectors for the cosmic ray neutron dosimetry and/or spectrometry will be mentioned.     

Development of a technique using MCNPX code for determination of nitrogen content of explosive materials using prompt gamma neutron activation analysis method

Nuclear-based explosive detection methods can detect explosives by identifying their elemental components, especially nitrogen. Thermal neutron capture reactions have been used for detecting prompt gamma 10.8 MeV following radioactive neutron capture by ¹⁴N nuclei. We aimed to study the feasibility of using field-portable prompt gamma neutron activation analysis (PGNAA) along with improved nuclear equipment to detect and identify explosives, illicit substances or landmines. A ²⁵²Cf radio-isotopic source was embedded in a cylinder made of high-density polyethylene (HDPE) and the cylinder was then placed in another cylindrical container filled with water. Measurements were performed on high nitrogen content compounds such as melamine (C₃H₆N₆). Melamine powder in a HDPE bottle was placed underneath the vessel containing water and the neutron source. Gamma rays were detected using two NaI(Tl) crystals. The results were simulated with MCNP4c code calculations. The theoretical calculations and experimental measurements were in good agreement indicating that this method can be used for detection of explosives and illicit drugs.     

Advanced materials for neural surface electrodes

Designing electrodes for neural interfacing applications requires deep consideration of a multitude of materials factors. These factors include, but are not limited to, the stiffness, biocompatibility, biostability, dielectric, and conductivity properties of the materials involved. The combination of materials properties chosen not only determines the ability of the device to perform its intended function, but also the extent to which the body reacts to the presence of the device after implantation. Advances in the field of materials science continue to yield new and improved materials with properties well-suited for neural applications. Although many of these materials have been well-established for non-biological applications, their use in medical devices is still relatively novel. The intention of this review is to outline new material advances for neural electrode arrays, in particular those that interface with the surface of the nervous tissue, as well as to propose future directions for neural surface electrode development.     

Advanced ceramic tool materials for machining

Cutting tools made of advanced ceramics have the potential for high-speed finish machining as well as for high-removal-rate machining of difficult-to-machine materials. The raw materials used in these ceramics are abundant, inexpensive, and free from strategic materials. In spite of this, solid or monolithic ceramic tools are currently used only to a limited extent partly due to certain limitations of these materials and partly due to the inadequacy of the machine tools used. The advances in ceramic materials and processing technology, the need to use materials that are increasingly more difficult to machine, increasing competition, and the rapidly rising manufacturing costs, have opened new vistas for ceramics in machining applications. The development of ceramic tool materials can be broadly categorized into three types: monolithic forms, thin coatings, and whisker-reinforced composites. Such a classification provides a totally new perspective on ceramic tool materials and broadens their scope considerably, and is justified on the basis that it is the ceramic addition that makes the tool material more effective. A brief overview of these materials is presented in this paper.     

A 10 tesla cryomagnetic system for neutron scattering experiments

A cryomagnetic system is described in which the first main component is a cryostat providing variable temperatures and the second a superconducting coil. The cryostat enables the coil to operate at either 4.2 K or 2.16 K, and allows a sample of diameter 10 mm, height 10 mm, to be brought to temperatures varying from 1.5 K to 300 K.The magnet is an asymmetrical split coil with a vertical magnetic axis. Aluminium windows provide access vertically over 15°, horizontally over 340° to a bore of useful diameter 32 mm. The superconducting magnet is wound from multifilamentary NbTi and Nb₃Sn wires and provides a central field of 8.7 T at 4.2 K and 10 T at 2.16 K.     

Elastic neutron scattering studies at 96 MeV for transmutation

Elastic neutron scattering from (12)C, (14)N, (16)O, (28)Si, (40)Ca, (56)Fe, (89)Y and (208)Pb has been studied at 96 MeV in the10-70 degrees interval, using the SCANDAL (SCAttered Nucleon Detection AssembLy) facility. The results for (12)C and (208)Pb have recently been published, while the data on the other nuclei are under analysis. The achieved energy resolution, 3.7 MeV, is about an order of magnitude better than for any previous experiment above 65 MeV incident energy. A novel method for normalisation of the absolute scale of the cross section has been used. The estimated normalisation uncertainty, 3%, is unprecedented for a neutron-induced differential cross section measurement on a nuclear target. Elastic neutron scattering is of utmost importance for a vast number of applications. Besides its fundamental importance as a laboratory for tests of isospin dependence in the nucleon-nucleon, and nucleon-nucleus, interaction, knowledge of the optical potentials derived from elastic scattering come into play in virtually every application where a detailed understanding of nuclear processes is important. Applications for these measurements are dose effects due to fast neutrons, including fast neutron therapy, as well as nuclear waste incineration and single event upsets in electronics. The results at light nuclei of medical relevance ((12)C, (14)N and (16)O) are presented separately. In the present contribution, results on the heavier nuclei are presented, among which several are of relevance to shielding of fast neutrons.