2,189 research outputs found
Argon plasma treatment techniques on steel and effects on diamond-like carbon structure and delamination
Copyright © 2011 Elsevier B.V. All rights reserved.We demonstrate alteration in diamond-like carbon (DLC) film structure, chemistry and adhesion on steel, related to variation in the argon plasma pretreatment stage of plasma enhanced chemical vapour deposition. We relate these changes to the alteration in substrate structure, crystallinity and chemistry due to application of an argon plasma process with negative self bias up to 600 V. Adhesion of the DLC film to the substrate was assessed by examination of the spallated fraction of the film following controlled deformation. Films with no pretreatment step immediately delaminated. At 300 V pretreatment, the spallated fraction is 8.2%, reducing to 1.2% at 450 V and 0.02% at 600V. For bias voltages below 450V the adhesion enhancement is explained by a reduction in carbon contamination on the substrate surface, from 59at.% with no treatment to 26at.% at 450V, concurrently with a decrease in the surface roughness, Rq, from 31.5nm to 18.9nm. With a pretreatment bias voltage of 600V a nanocrystalline, nanostructured surface is formed, related to removal of chromium and relaxation of stress; X-ray diffraction indicates this phase is incipient at 450V. In addition to improving film adhesion, the nanotexturing of the substrate prior to film deposition results in a DLC film that shows an increase in sp3/sp2 ratio from 1.2 to 1.5, a reduction in surface roughness from 31nm to 21nm, and DLC nodular asperities with reduced diameter and increased uniformity of size and arrangement. These findings are consistent with the substrate alterations due to the plasma pretreatment resulting in limitation of surface diffusion in the growth process. This suggests that in addition to deposition phase processes, the parameters of the pretreatment process need to be considered when designing diamond-like carbon coatings.This work is partially supported by the Technology Strategy Board, reference BD266E
The overlap operator as a continued fraction
We use a continued fraction expansion of the sign-function in order to obtain
a five dimensional formulation of the overlap lattice Dirac operator. Within
this formulation the inverse of the overlap operator can be calculated by a
single Krylov space method where nested conjugate gradient procedures are
avoided. We show that the five dimensional linear system can be made well
conditioned using equivalence transformations on the continued fractions. This
is of significant importance when dynamical overlap fermions are simulated.Comment: 3 pages, 1 figure, talk presented by U. Wenger at Lattice2001(chiral
Nanostructure and paramagnetic centres in diamond-like carbon: Effect of Ar dilution in PECVD process
Diamond-like carbon (DLC) films were deposited utilising plasma enhanced chemical vapour deposition (PECVD) with acetylene precursor, diluted with 0 – 45% argon. Electron paramagnetic resonance (EPR) measurements show the presence of one paramagnetic centre with no change in spin population over the range of film deposition conditions. However, the EPR linewidth decreases with increasing argon content of the precursor mix, suggesting an enhancement of motional narrowing due to an increase in electron delocalization, related to an increase in the sp2 cluster size. Atomic force microscopy (AFM) measurements indicate the surface of the DLC is formed of nanoscale asperities of material. With radii of tens of nanometres for films deposited with zero argon, the size of the features increases with the argon dilution of the acetylene. Energy dispersive x-ray analysis and electrical measurements further elucidate the changes in film structure
Energy Efficiency Improvements in Dry Drilling with Optimised Diamond-Like Carbon Coating
We demonstrate enhancements of performance and energy efficiency of cutting tools by deposition of diamond-like carbon (DLC) coatings on machine parts. DLC was deposited on steel drill bits, using plasma enhanced chemical vapour deposition (PECVD) with the acetylene precursor diluted with argon, to produce a surface with low friction and low wear rate. Drill bit performance in dry drilling of aluminium was quantified by analysis of power consumption and swarf flow. Optimised deposition conditions produced drill bits with greatly enhanced performance over uncoated drill bits, showing a 25% reduction in swarf clogging, a 36% reduction in power consumption and a greater than five-fold increase in lifetime. Surface analysis with scanning electron microscopy shows that DLC coated drills exhibit much lower aluminium build up on the trailing shank of the drill, enhancing the anti-adhering properties of the drill and reducing heat generation during operation, resulting in the observed improvements in efficiency. Variation of drilling efficiency with argon dilution of precursor is related to changes in the microstructure of the DLC coating
Gravitational Waves from Neutron Stars with Large Toroidal B-fields
We show that NS's with large toroidal B-fields tend naturally to evolve into
potent gravitational-wave (gw) emitters. The toroidal field B_t tends to
distort the NS into a prolate shape, and this magnetic distortion can easily
dominate over the oblateness ``frozen into'' the NS crust. An elastic NS with
frozen-in B-field of this magnitude is clearly secularly unstable: the wobble
angle between the NS's angular momentum J^i and the star's magnetic axis n_B^i
grow on a dissipation timescale until J^i and n_B^i are orthogonal. This final
orientation is clearly the optimal one for gravitational-wave (gw) emission.
The basic cause of the instability is quite general, so we conjecture that the
same final state is reached for a realistic NS. Assuming this, we show that for
LMXB's with B_t of order 10^{13}G, the spindown from gw's is sufficient to
balance the accretion torque--supporting a suggestion by Bildsten. The spindown
rates of most millisecond pulsars can also be attributed to gw emission sourced
by toroidal B-fields, and both these sources could be observed by LIGO II.
While the first-year spindown of a newborn NS is most likely dominated by em
processes, reasonable values of B_t and the (external) dipolar field B_d can
lead to detectable levels of gw emission, for a newborn NS in our own galaxy.Comment: 7 pages; submitted to PRD; only minor revision
Nano-scale composition of commercial white powders for development of latent fingerprints on adhesives
This is the post-print version of the article - Copyright @ 2010 Elsevier.Titanium dioxide based powders are regularly used in the development of latent fingerprints on dark surfaces. For analysis of prints on adhesive tapes, the titanium dioxide can be suspended in a surfactant and used in the form of a powder suspension. Commercially available products, whilst having nominally similar composition, show varying levels of effectiveness of print development, with some powders adhering to the background as well as the print. X-ray fluorescence (XRF), analytical transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and laser particle sizing of the fingerprint powders show TiO2 particles with a surrounding coating, tens of nanometres thick, consisting of Al and Si rich material, with traces of sodium and sulphur. Such aluminosilicates are commonly used as anti-caking agents and to aid adhesion or functionality of some fingerprint powders; however, the morphology, thickness, coverage and composition of the aluminosilicates are the primary differences between the white powder formulations and could be related to variation in the efficacy of print development.This work is part funded by the Home Office Scientific Development Branch, UK
Restricted three body problems at the nanoscale
In this paper, we investigate some of the classical restricted three body
problems at the nanoscale, such as the circular planar restricted problem for
three C60 fullerenes, and a carbon atom and two C60 fullerenes. We model the
van der Waals forces between the fullerenes by the Lennard-Jones potential. In
particular, the pairwise potential energies between the carbon atoms on the
fullerenes are approximated by the continuous approach, so that the total
molecular energy between two fullerenes can be determined analytically. Since
we assume that such interactions between the molecules occur at sufficiently
large distance, the classical three body problems analysis is legitimate to
determine the collective angular velocity of the two and three C60 fullerenes
at the nanoscale. We find that the maximum angular frequency of the two and
three fullerenes systems reach the terahertz range and we determine the
stationary points and the points which have maximum velocity for the carbon
atom for the carbon atom and the two fullerenes system
5,6-dihydroxyindole-2-carboxylic acid (DHICA): a First Principles Density-Functional Study
We report first principles density functional calculations for
5,6-dihydroxyindole-2-carboxylic acid (DHICA) and several reduced forms. DHICA
and 5,6-dihydroxyindole (DHI) are believed to be the basic building blocks of
the eumelanins. Our results show that carboxylation has a significant effect on
the physical properties of the molecules. In particular, the relative
stabilities and the HOMO-LUMO gaps (calculated with the SCF method) of
the various redox forms are strongly affected. We predict that, in contrast to
DHI, the density of unpaired electrons, and hence the ESR signal, in DHICA is
negligibly small.Comment: 5 pages, 2 figure
Environmental baseline monitoring - Vale of Pickering: Phase I - final report (2015/16)
This report presents the collated results from the BGS-led project Science-based environmental baseline monitoring associated with shale gas development in the Vale of Pickering (including supplementary air quality monitoring in Lancashire). The project has been funded by a grant awarded by DECC for the period August 2015 – 31st March 2016. It complements (and extends to air quality) an on-going project, funded by BGS and the other project partners, in which similar activities are being carried out in the Fylde area of Lancashire.
The project has initiated a wide-ranging environmental baseline monitoring programme that includes water quality (groundwater and surface water), seismicity, ground motion, atmospheric composition (greenhouse gases and air quality), soil gas and radon in air (indoors and outdoors). The motivation behind the project(s) was to establish independent monitoring in the area around the proposed shale gas hydraulic fracturing sites in the Vale of Pickering, North Yorkshire (Third Energy) and in Lancashire (Cuadrilla) before any shale gas operations take place.
As part of the project, instrumentation has been deployed to measure, in real-time or near real-time, a range of environmental variables (water quality, seismicity, atmospheric composition). These data are being displayed on the project’s web site (www.bgs.ac.uk/Valeofpickering). Additional survey, sampling and monitoring has also been carried out through a co-ordinated programme of fieldwork and laboratory analysis, which has included installation of new monitoring infrastructure, to allow compilation of one of the most comprehensive environmental datasets in the UK.
It is generally recognised that at least 12 months of baseline data are required. The duration of the grant award (7 months) has meant that this has not yet been possible. However there are already some very important findings emerging from the limited datasets which need be taken in to account when developing future monitoring strategy, policy and regulation. The information is not only relevant to the Vale of Pickering and Lancashire but will be more widely applicable in the UK and internationally. Although shale gas operations in other parts of the world are well-established there is a paucity of good baseline data and effective guidance on monitoring.
It is hoped that the monitoring project will continue to allow at least 12 months of data for each of the work packages to be compiled and analysed. It will also allow the experience gained and the scientifically-robust findings to be used to develop and establish effective environmental monitoring strategies for shale gas and similar industrial activities
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