Diamond electrodes modified by argon ion bombardment

The electrochemical properties of boron-doped chemical vapour deposited diamond films following argon ion bombardment are investigated. The argon ion treatments used produce defects at the electrode surface, but are below the amorphisation threshold for this material, and indeed can be readily reversed by sample annealing. Photoemission studies indicate downwards band-bending of about 0.8 eV as a result of the argon ion treatment, and the photoemission spectra and associated energy loss spectra are used to examine the changes occurring. The higher argon ion exposures to the surface are found to very significantly degrade the electrochemical characteristics of diamond. However for smaller ion doses, the electrochemical properties of some redox couples are not influenced by the argon ion treatments used, whereas others are strongly inhibited. The work therefore demonstrates that argon ion bombardment can be used to selectively modify the properties of diamond electrodes. © 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim

Electrochemically controlled modification of CVD diamond surfaces

The surface chemical properties of CVD diamond play a crucial role in many of the potential device applications using diamond, encompassing areas such as, cold cathodes and photocathodes, surface conductive FET's, electrochemistry, and genomics and proteomics. There is therefore great interest in developing routes for surface modification, and in understanding the influences, which such surface modifications produce. In the present work, an electrochemical procedure was developed to produce chemically stable negative electron affinity (NEA) surfaces. CVD diamond electrodes were electrochemically oxidised at anodic potentials to produce oxygen functionalities, which were subsequently subjected to ion exchange with aqueous Cs+ ions. Characterisation with XPS reveals the presence of a surface monolayer phase with the expected presence of Cs and O. The surface modified with Caesium displays negative electron affinity (NEA) and high field emission yields, and is much more stable than caesiated diamond surfaces produced by vacuum techniques. This new process represents an example of how simple electrochemical procedures can be used to achieve surface modification results, which are not so easily realised using other approaches. © 2003 Elsevier B.V. All rights reserved

Palynology of miocene sediments in brunei darussalam: First SEM investigations of pollen and spores, and their taxonomy and palaeoenvironmental interpretation

Brunei Darussalam\u2019s geology is characterized by extensive Neogene fluvio-deltaic to shallow marine siliciclastic deposits, which have been studied here to highlight their palynological content. So far, there are only few reports that investigate fossil pollen and only one focuses on detailed taxonomical description using light microscopy (LM). The rest are studies on a wider regional scale in northwest Borneo sometimes including Brunei but without much emphasizes on taxonomy. To investigate pollen thoroughly, the use of scanning electron microscopy (SEM) is important, as this can provide valuable information on the sculptures of the pollen grains which with LM alone cannot be observed. Our study here provides LM images alongside the first SEM images of pollen and spores from Miocene sediments in Brunei Darussalam. The results point to a moderate-diverse flora comprising 37 families and 62 pollen and spore taxa. Most common ones are mangrove types which are Rhizophoraceae and Lythraceae taxa. The families of Combretaceae, Malvaceae, and other less common pollen groups are typical of tropical floral elements. The recovered families of Anacardiaceae, Arecaceae (five taxa), Calophyllaceae, Dilleniaceae, Dipterocarpaceae (two taxa), Elaeocarpaceae, Euphorbiaceae (four taxa), Phyllanthaceae (two taxa), Podocarpaceae, Proteaceae, Rubiaceae, Sapindaceae and Sapotaceae indicate mixed Dipterocarpaceae forests ranging from hinterland to peat swamp areas

Sonoelectrochemistry at tungsten-supported boron-doped CVD diamond electrodes

Highly boron-doped (atomic concentration 1020-1021 cm-3) conductive diamond films were deposited on tungsten substrates by hot-filament assisted chemical vapour deposition from a gaseous feed of methane and diborane in hydrogen. The boron-doped diamond film electrodes were characterised by Raman spectroscopy, scanning electron microscopy (SEM), and both conventional and sonoelectrochemical methods. The one-electron reduction of Ru(NH3)3+6 was investigated in aqueous solutions under normal and power ultrasound conditions. Well-defined voltammetric responses were observed from which the standard rate constant for electron transfer, k0=3×10-3 cm s-1, was estimated ignoring the effect of surface roughness. The electrode was used for electrochemical processes in the presence of 90 W cm-2 ultrasound without any significant deterioration of the properties. Although diamond is known to be exceptionally chemically inert, it was found that anodic polarisation of the boron-doped diamond electrode gave rise to changes in the surface properties. In order to rejuvenate the diamond electrode surface, a hydrogen plasma treatment was used. The two-electron reduction of dioxygen to give H2O2 was studied in an aqueous 0.1 M phosphate buffer solution (pH 2). This process was found to be strongly affected by the state of the electrode surface with an increase in the observed current after negative polarisation. Voltammograms obtained under ultrasound conditions suggest that a potential pretreatment can switch the process from being nearly mass-transport controlled to one where mass transport effects are virtually absent.&gt

Surface Modification of Chemical Vapor Deposited Diamond Induced by Power Ultrasound

Surface composition changes at the surface of chemical vapor deposited diamond samples are reported after immersion in an aqueous phosphate buffer solution and exposure to 24 kHz power ultrasound (30 W cm-2). Based on X-ray photoelectron spectroscopy data it is demonstrated that heterogeneous sonochemical processes give rise to surface functionalization of diamond surfaces and that the type of gas present during the treatment has a strong effect on the interfacial process

Electron induced modification of the surface electrochemical properties of diamond electrodes

A novel method has been developed to modify the surface properties of boron-doped CVD diamond electrodes by electron stimulated desorption (ESD) of hydrogen and oxygen from as grown diamond surfaces allowing the selective electrochemical silver deposition on the areas not irradiated with electrons

Electrochemically induced surface modifications of boron-doped diamond electrodes: an X-ray photoelectron spectroscopy study

The activity of diamond electrodes depends on the chemical state of the diamond surface, and the present work is focussed on understanding how chemical changes either produced in situ electrochemically, or by ex situ plasma treatments, influence the electrochemical properties. Conductive boron-doped diamond electrodes were produced by depositing adherent boron-doped diamond films on tungsten substrates using a hot filament reactor and were characterised by Raman spectroscopy, scanning electron microscopy (SEM), high-resolution X-ray photoelectron spectroscopy (XPS) and electrochemical methods. In order to produce electrochemically induced surface modifications, anodic and cathodic polarisation experiments were performed in an aqueous 0.2 M phosphate buffer solution (pH = 2). The surface composition of the electrode, as determined by ex situ high-resolution XPS measurements, could be linked to the electrochemical performance of diamond film electrodes. The extent to which changes in surface composition and electrode performance can be controlled and reversed by suitable plasma treatments is explored. (C) 2000 Elsevier Science S.A. All rights reserved

Nanodiamond thin film electrodes: Metal electro-deposition and stripping processes

The properties of a nanodiamond thin film deposit formed on titanium substrates in a microwave-plasma enhanced CVD process, are investigated for applications in electroanalysis. The nanodiamond deposit consists of intergrown nano-sized platelets of diamond with a high sp2 carbon content giving it high electrical conductivity and electrochemical reactivity. Nanodiamond thin film electrodes (of approximately 2 μm thickness) are characterized by electron microscopy and electrochemical methods. First, for a reversible one electron redox system, Ru(NH3)63+/2+, nanodiamond is shown to give well-defined diffusion controlled voltammetric responses. Next, metal deposition processes are shown to proceed on nanodiamond with high reversibility and high efficiency compared to processes reported on boron-doped diamond. The nucleation of gold is shown to be facile at edge sites, which are abundant on the nanodiamond surface. For the deposition and stripping of both gold and copper, a stripping efficiency (the ratio of electro-dissolution charge to electro-deposition charge) of close to unity is detected even at low concentrations of analyte. The effect of thermal annealing in air is shown to drastically modify the electrode characteristics probably due to interfacial oxidation, loss of active sp2 sites, and loss of conductivity

Sonoelectrochemistry at highly boron-doped diamond electrodes: silver oxide deposition and electrocatalysis in the presence of ultrasound

The use of boron-doped diamond has a considerable impact in electrochemistry owing to the wide potential range accessible, low background currents, extreme hardness, and the ease of chemical modification of diamond surfaces. It is shown here that, although the electrodeposition of silver metal is known to yield very poorly adhering films with a poor electrical contact, a silver oxysalt deposit formed on anodically pre-treated diamond surfaces adheres strongly with good electrical contact. The deposit is stable even in the presence of ultrasound. Voltammetric and XPS studies reveal that the silver oxide deposit, in contrast to the silver metal deposit, is efficiently stripped from the diamond surface by applying a sufficiently negative potential. The silver oxysalt Ag7O8NO3, deposited onto two types of borondoped diamond electrodes, a 50 μm thick polycrystalline thin film deposited on a tungsten substrate and a polished free standing diamond plate, is shown to act as an electrocatalyst for oxygen evolution and for the oxidation of toluene. This development opens up the possibility of boron-doped diamond being applied as an inert and conducting substrate material for a wide range of oxidic materials, which can then be utilised as active electrocatalysts at high applied potentials