Hot filament chemical vapour deposition of diamond ultramicroelectrodes

Abstract

The hot filament chemical vapour deposition of boron-doped diamond was optimised for the fabrication of diamond ultramicroelectrodes. Applications of ultramicroelectrodes require thin, conformal and non-porous diamond coatings, which display electrochemical properties similar to those associated with good quality doped diamond electrodes. The growth conditions to attain these goals are elucidated. The influence of the use of nanodiamond ultrasonic seeding prior to growth, in order to promote nucleation, and varying the negative electrical bias and methane concentration during growth, to control the growth chemistry, are explored. Although Raman spectroscopy shows a deterioration of diamond phase quality with increased negative bias voltage during growth, cyclic voltammetry indicates an improved electrochemical performance due to decreased porosity at reduced grain size under moderate bias voltage. At even higher bias voltage, the electrochemical properties deteriorate due to aggregation of sp(2) hybridised carbon at grain boundaries. By combining efficient nucleation methods and appropriate methane concentrations and electrical bias during growth, small grain polycrystalline diamond coatings can be obtained, which show optimal electrochemical properties most suitable for ultramicroelectrode applications.

Focused Ion Beam Fabrication of Boron-Doped Diamond Ultramicroelectrodes

“…Boron doping was introduced by bubbling the hydrogen through an ice-cooled bubbler containing trimethylborate (99%, Aldrich). A negative electrical bias of −60 V was applied throughout the growth to improve the diamond morphology, and full details of the optimal growth conditions for this application are discussed elsewhere …”

“…A negative electrical bias of -60 V was applied throughout the growth to improve the diamond morphology, and full details of the optimal growth conditions for this application are discussed elsewhere. 26 The diamond-coated tungsten needles were insulated with cathodic electrophoretic paint for insulation. The diamond electrode was used as cathode and a platinum coil was used as anode.…”

“…Although conformal, smooth, thin nanodiamond coatings might give a more favorable morphology for use with electrophoretic paints, we have shown elsewhere that such material does not display optimal electrochemical properties. 26 A better way, therefore, would appear to use thick insulating paint coatings but then exploit a controlled route to opening the insulation to allow electrolyte access to the diamond electrode.…”

Deposition and Patterning of Polycrystalline Diamond Films Using Traditional Photolithography and Reactive Ion Etching

“…A specialized CVD reactor, based on the known method of "hot filaments" [14,15], was used to deposit the films. In this method, the activation of the gas mixture (H 2 :CH 4 ) is carried out thermally, by means of incandescent tungsten filaments.…”

All-Diamond Microelectrodes as Solid State Probes for Localized Electrochemical Sensing

“…By introducing boron in the usual methane-hydrogen gas chemistry of CVD diamond, a first layer of this material is grown on top of a tungsten sharp wire. The choice for tungsten relies in its ability to form an electrically conductive carbide interlayer that precedes the nucleation of diamond crystals 14 . Moreover, being the metal with highest melting point it is perfectly suitable for the relatively high temperatures used for the CVD technique, usually in the range of 500-1000 ºC.…”