•PF-TUNA has been used to simultaneously measure the topography and electron field emission from CVD diamond films.•The films analysed were as smooth as possible in order to eliminate topographical effects from the emission data.•PF-TUNA shows that emission arises preferentially from grain boundaries independent of the surrounding surface morphology.We present direct observation of the electron field emission sites over a large area of polycrystalline diamond using tunnelling atomic force microscopy. Any effects of surface topography have been reduced by measuring polycrystalline samples which have surface roughness values < 5 nm. Measurements show that emission arises preferentially from the grain boundaries independent of the surrounding surface morphology.Download high-res image (216KB)Download full-size image

•B + Li cooping of diamond is investigated by in situ CVD.•Electrical conductivity is dominated by the B, while the addition of Li decreases the film conductivity.•Li diffusion constants have been measured through diamond at temperatures ~ 1100 K.•Li diffuses rapidly via grain boundaries.•A Si substrate acts as a sink for Li, potentially absorbing all Li from a Li-doped diamond film.Lithium has been incorporated into heavily boron-doped single-crystal (SCD), microcrystalline (MCD) and nanocrystalline diamond (NCD) films at concentrations up to ~ 2 × 1020 cm−3 using Li3N as a solid-state Li source for in-diffusion and diborane as the B source. The quality, morphology, electrical resistance and concentration of B and Li dopants present in a range of B + Li co-doped SCD, MCD and NCD films have been studied. Analysis of the SIMS depth profiles for Li enabled the diffusion constants, D, to be measured (in units of cm2 s−1) as: 2.5 × 10−15, 1.3 × 10−14 and 7.0 × 10−14 for SCD, MCD and NCD, respectively, at 1100 K. The value for D for SCD agrees closely with that in the literature, while the much larger values for the polycrystalline films provide direct evidence that Li can diffuse rapidly along or through diamond grain boundaries at elevated temperatures. If prolonged diffusion allows the Li to reach the Si substrate, the Si acts as a sink for Li absorbing large quantities and reducing its concentration in the diamond film.Download high-res image (158KB)Download full-size image

A detailed investigation of electron emission from a set of chemical vapour deposited (CVD) diamond films is reported using high-resolution PeakForce-controlled tunnelling atomic force microscopy (PF-TUNA). Electron field emission originates preferentially from the grain boundaries in low-conductivity polycrystalline diamond samples, and not from the top of features or sharp edges. Samples with smaller grains and more grain boundaries, such as nanocrystalline diamond, produce a higher emission current over a more uniform area than diamond samples with larger grain size. Light doping with N, B or P increases the grain conductivity, with the result that the emitting grain-boundary sites become broader as the emission begins to creep up the grain sidewalls. For heavy B doping, where the grains are now more conducting than the grain boundaries, emission comes from both the grain boundaries and the grains almost equally. Lightly P-doped diamond samples show emission from step-edges on the (1 1 1) surfaces. Emission intensity was time dependent, with the measured current dropping to ∼10% of its initial value ∼30 h after removal from the CVD chamber. This decrease is ascribed to the build-up of adsorbates on the surface along with an increase in the surface conductivity due to surface transfer doping.

This report describes a method to fabricate high-surface-area boron-doped diamond (BDD) electrodes using so-called ‘black silicon’ (bSi) as a substrate. This is a synthetic nanostructured material that contains high-aspect-ratio nano-protrusions, such as spikes or needles, on the Si surface produced via plasma etching. We now show that coating a bSi surface composed of 15 μm-high needles conformably with BDD produces a robust electrochemical electrode with high sensitivity and high electroactive area. A clinically relevant demonstration of the efficacy of these electrodes is shown by measuring their sensitivity for detection of dopamine (DA) in the presence of an excess of uric acid (UA). Finally, the nanostructured surface of bSi has recently been found to generate a mechanical bactericidal effect, killing both Gram-negative and Gram-positive bacteria at high rates. We will show that BDD-coated bSi also acts as an effective antibacterial surface, with the added advantage that being diamond-coated it is far more robust and less likely to become damaged than Si.