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Lu M.,Physical and Theoretical Chemistry Laboratory | Toghill K.E.,Physical and Theoretical Chemistry Laboratory | Phillips M.A.,Asylum Research UK Ltd. | Compton R.G.,Physical and Theoretical Chemistry Laboratory
International Journal of Environmental Analytical Chemistry | Year: 2013

Antimony is an element of significant environmental concern, yet has been neglected relative to other heavy metals in electroanalysis. As such very little research has been reported on the electroanalytical determination of antimony at unmodified carbon electrodes. In this paper we report the electrochemical determination of Sb(III) in HCl solutions using unmodified carbon substrates, with focus on non-classical carbon materials namely edge plane pyrolytic graphite (EPPG), boron doped diamond (BDD) and screen-printed electrodes (SPE). Using differential pulse anodic stripping voltammetry, EPPG was found to give a considerably greater response towards antimony than other unmodified carbon electrodes, allowing highly linear ranges in nanomolar concentrations and a detection limit of 3.9 nM in 0.25 M HCl. Furthermore, the sensitivity of the response from EPPG was 100 times greater than for glassy carbon (GC). Unmodified GC gave a comparable response to previous results using the bare substrate, and BDD gave an improved, yet still very high limit of detection of 320 nM compared to previous analysis using an iridium oxide modified BDD electrode. SPEs gave a very poor response to antimony, even at high concentrations, observing no linearity from standard additions, as well as a major interference from the ink intrinsic to the working electrode carbon material. Owing to its superior performance relative to other carbon electrodes, the EPPG electrode was subjected to further analytical testing with antimony. The response of the electrode for a 40 nM concentration of Sb(III) was reproducible with a mean peak current of 1.07 μA and variation of 8.4% (n = 8). The effect of metals copper, bismuth and arsenic were investigated at the electrode, as they are common interferences for stripping analysis of antimony. © 2013 Copyright Taylor and Francis Group, LLC. Source


Toghill K.E.,University of Oxford | Xiao L.,University of Oxford | Phillips M.A.,Asylum Research UK Ltd. | Compton R.G.,University of Oxford
Sensors and Actuators, B: Chemical | Year: 2010

A nickel modified boron-doped diamond (Ni-BDD) electrode or nickel foil electrode were used in the non-enzymatic determination of glucose in alkaline solutions. The Ni-BDD electrode was electrodeposited from a 1 mM Ni(NO3)2 solution (pH 5), followed by repeat cycling in KOH. Subsequent analysis utilised the Ni(OH)2/NiOOH redox couple to electrocatalyse the oxidation of glucose. Glucose was determined to limits of 2.7 μM with a sensitivity of 1.04 μA μM-1 cm-2 at the Ni-BDD electrode. The foil electrode was comparably sensitive achieving a limit of 1.8 μM but a relatively lower sensitivity of 0.67 μA μM-1 cm-2. SEM analysis of the electrodes found the Ni-BDD to be modified by a quasi-random microparticle assembly, with approximately 7.6 μg cm-2 of nickel present on the surface. © 2010 Elsevier B.V. All rights reserved. Source


Marsden A.J.,University of Warwick | Phillips M.,Asylum Research UK Ltd. | Wilson N.R.,University of Warwick
Nanotechnology | Year: 2013

At a single atom thick, it is challenging to distinguish graphene from its substrate using conventional techniques. In this paper we show that friction force microscopy (FFM) is a simple and quick technique for identifying graphene on a range of samples, from growth substrates to rough insulators. We show that FFM is particularly effective for characterizing graphene grown on copper where it can correlate the graphene growth to the three-dimensional surface topography. Atomic lattice stick-slip friction is readily resolved and enables the crystallographic orientation of the graphene to be mapped nondestructively, reproducibly and at high resolution. We expect FFM to be similarly effective for studying graphene growth on other metal/locally crystalline substrates, including SiC, and for studying growth of other two-dimensional materials such as molybdenum disulfide and hexagonal boron nitride. © 2013 IOP Publishing Ltd. Source


Seah M.P.,National Physical Laboratory United Kingdom | Mulcahy C.P.A.,Cascade Scientific Inc. | Mulcahy C.P.A.,Asylum Research UK Ltd. | Biswas S.,Cascade Scientific Inc.
Journal of Vacuum Science and Technology B:Nanotechnology and Microelectronics | Year: 2010

An analysis is made of the sputter depth profiling of ultrathin silicon dioxide layers on silicon to evaluate the variation in the sputtering rate in the first few nanometers. Such changes in sputtering rate are important for the development of the analysis of nanoparticles. Cs+ ions are chosen as an example of a metal ion popular in secondary ion mass spectrometry (SIMS) studies that provide excellent depth resolution. It is found that, if it is assumed that the signal is linear with oxygen content, the sputtering rate falls rapidly by a factor of 4.8, with an exponential decay near 1.2 nm when using 600 eV Cs+ ions at 60° incidence angle. The interface may be described by the integral of the response function of Dowsett developed for SIMS depth profiling of delta layers with λu =0.5 nm, λd =0.7 nm, and σ=0.4 nm, showing the excellent depth resolution. However, if published data for the nonlinearity of the signal with oxygen content are used, the rapid change is still seen but with an initial sputtering rate that is reduced from the above 4.8 to 3.5 times that at equilibrium. © 2010 American Vacuum Society. Source


Chiesa M.,Masdar Institute of Science and Technology | Gadelrab K.R.,Masdar Institute of Science and Technology | Verdaguer A.,Catalan Institute of Nanoscience and Nanotechnology | Segura J.J.,Catalan Institute of Nanoscience and Nanotechnology | And 5 more authors.
EPL | Year: 2012

Amplitude modulation atomic force microscopy allows quantifying energy dissipation in the nanoscale with great accuracy with the use of analytical expressions that account for the fundamental frequency and higher harmonics. Here, we focus on the effects of sub-harmonic excitation on energy dissipation and its quantification. While there might be several mechanisms inducing sub-harmonics, a general analytical expression to quantify energy dissipation whenever sub-harmonics are excited is provided. The expression is a generalization of previous findings. We validate the expression via numerical integration by considering capillary forces and provide experimental evidence of sub-harmonic excitation for a range of operational parameters. © Copyright EPLA, 2012. Source

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