Fundamental Parameters Line Profile Fitting in Laboratory Diffractometers.

The fundamental parameters approach to line profile fitting uses physically based models to generate the line profile shapes. Fundamental parameters profile fitting (FPPF) has been used to synthesize and fit data from both parallel beam and divergent beam diffractometers. The refined parameters are determined by the diffractometer configuration. In a divergent beam diffractometer these include the angular aperture of the divergence slit, the width and axial length of the receiving slit, the angular apertures of the axial Soller slits, the length and projected width of the x-ray source, the absorption coefficient and axial length of the sample. In a parallel beam system the principal parameters are the angular aperture of the equatorial analyser/Soller slits and the angular apertures of the axial Soller slits. The presence of a monochromator in the beam path is normally accommodated by modifying the wavelength spectrum and/or by changing one or more of the axial divergence parameters. Flat analyzer crystals have been incorporated into FPPF as a Lorentzian shaped angular acceptance function. One of the intrinsic benefits of the fundamental parameters approach is its adaptability any laboratory diffractometer. Good fits can normally be obtained over the whole 20 range without refinement using the known properties of the diffractometer, such as the slit sizes and diffractometer radius, and emission profile

Mineral phosphorus drives glacier algal blooms on the Greenland Ice Sheet

Melting of the Greenland Ice Sheet is a leading cause of land-ice mass loss and cryosphere-attributed sea level rise. Blooms of pigmented glacier ice algae lower ice albedo and accelerate surface melting in the ice sheet’s southwest sector. Although glacier ice algae cause up to 13% of the surface melting in this region, the controls on bloom development remain poorly understood. Here we show a direct link between mineral phosphorus in surface ice and glacier ice algae biomass through the quantification of solid and fluid phase phosphorus reservoirs in surface habitats across the southwest ablation zone of the ice sheet. We demonstrate that nutrients from mineral dust likely drive glacier ice algal growth, and thereby identify mineral dust as a secondary control on ice sheet melting.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Fabrication and characterisation of ultra-thin tungsten-carbon (W/C) and platinum-carbon (Pt/C) multilayers for X-ray mirrors

Ultra-thin tungsten-carbon (W/C) and platinum-carbon (Pt/C) multilayers were fabricated using dc magnetron sputtering. The bilayer period and the total number of layers were varied for both systems to ascertain the X-ray reflectance response. As a preliminary investigation, in situ resistance measurements were made to determine the minimum continuous single layer thickness that could be produced for W and Pt. We used X-ray reflectivity to monitor the reflectance from the first order peaks and the number of layers in the multilayered structures. X-ray photoelectron spectroscopy showed that a distinct intermixing layer develops in both W/C and Pt/C. A repeating four-layer model was developed to characterise the X-ray reflectivity patterns with mixed interface layers. The model accounts for all the essential features in the observed reflectivity data with particular attention given to layer thickness and interfacial roughness. Assessment of the films by indentation indicated that they are mechanically reliable with no cracking events or delamination obvious from the load-displacement curves indicating excellent adhesion. An anomalous improvement in hardness and Young's modulus with increasing number of layers was observed. The present results indicate that high-quality ultra-thin W/C and Pt/C tailored multilayer films produced by dc magnetron sputtering show considerable promise as mirrors for high energy X-ray applications. © 2004 Elsevier B.V. All rights reserved

Investigation of the interfacial structure of ultra-thin platinum film deposited by cathodic-arc

Ultra-thin films are of interest in the production of X-ray mirrors that use a multilayer structure. The most commonly used deposition techniques are dc magnetron sputtering and electron beam evaporation; this paper presents results of cathodic-arc deposition. Ultra thin films of platinum with nominal thicknesses in the range 15-65 Å were deposited on silicon substrates and the film structure investigated using X-ray reflectivity and X-ray photoelectron spectroscopy. It has been found that the structure of the deposited films consists of three layers - the platinum film, a silicon oxide layer and a platinum silicide layer. In contrast to dc magnetron and electron beam deposited films, the silicide layer of cathodic-arc deposited films have a higher density and greater thickness, which is attributed to the higher energy process of this deposition technique. These attributes of the cathodic-arc deposited films suggest that the deposition technique is not suitable for production of mirrors of materials that react with each other, but for materials that do not the deposition technique is potentially more favourable than that of e-beam and magnetron sputtering. © 2003 Elsevier B.V. All rights reserved

The fabrication of stable platinum-silicon oxide multilayers for X-ray mirrors

An investigation has been carried out to determine the conditions required for the fabrication of stable SiO2-Pt multilayers using DC-magnetron sputtering for the Pt and RF-magnetron sputtering for the SiO2. As a preliminary investigation, single layers of Pt on SiO2 were analysed by X-ray reflectivity (XRR) and X-ray photoelectron spectroscopy (XPS) to develop a model of the Pt-SiO2 interface layer. The results indicated that a distinct interface layer develops as a Pt silicate approximately 6 Å thick. SiO2-Pt multilayers fabricated with a period d>65 Å using pure argon as the sputtering gas, display X-ray reflectivity patterns which can be accurately characterised by a repeating bilayer model. When d<65 Å the multilayer becomes unstable upon exposure to air. Additional peaks develop in the XRR pattern which increase in magnitude with time. These peaks arise from the expansion of the SiO2 layers in the multilayer starting from the top bilayer and gradually working through the multilayer. In the as-prepared specimens the SiO2 layers are incompletely oxidised and have a composition SiOx (x<2) and, on exposure to air, oxygen diffuses through the multilayer surface converting the SiOx to SiO2. By introducing a small partial pressure of oxygen into the sputtering gas during deposition, multilayers with d<65 Å remained stable on exposure to air. Under these conditions the density of the platinum layers determined from XRR measurements was reduced by approximately 25%. XPS showed that the platinum layer contained bonded oxygen in the form of platinum oxide PtOx (x<1). SiO2/PtOx multilayers have been fabricated with periods down to 13 Å, but the intensity of the first order peak drops off dramatically once the thickness of the PtOx layer is less that 10-12 Å. © 2002 Elsevier Science B.V. All rights reserved

X-ray reflectivity study of radio frequency sputtered silicon oxide on silicon

An X-ray reflectivity study carried out on 45-450 Å films of radio frequency sputtered silicon oxide on silicon, with particular attention given to the interface between film and substrate. In order to model reflectivity data it was necessary to include an interface layer for all films. This interface layer had a density approaching that of the substrate but due to differing compositions of the deposited film and substrate it was subject to a variation in scattering and absorption properties. © 2005 Elsevier B.V. All rights reserved