Boron-doped Polycrystalline Diamond Research Articles

Boron acceptor concentration in diamond from excitonic recombination intensities

Excitonic recombinations are investigated by cathodoluminescence in a series of homoepitaxial diamond layers doped with boron in the range $(2\ifmmode\times\else\texttimes\fi{}{10}^{16})$--$(5\ifmmode\times\else\texttimes\fi{}{10}^{18}) \mathrm{at} {\mathrm{cm}}^{\ensuremath{-}3}.$ As opposed to earlier observations made on polycrystalline boron-doped diamond, we show that the ratio between the neutral-boron bound exciton and the free-exciton recombination intensities is proportional to the boron content up to $6\ifmmode\times\else\texttimes\fi{}{10}^{17}$cm${}^{\ensuremath{-}3}$ and starts to saturate above this value. The probability of an exciton in diamond being trapped by only one boron impurity is calculated and appears to be in good agreement with the observed saturation, suggesting the formation of excitons bound to near-neighbor boron pairs at high boron concentrations.

Dry etching of diamond nanowires using self-organized metal droplet masks

In a top–down approach diamond nanowires (DNW) were fabricated by anisotropic oxygen plasma etching of undoped or boron doped polycrystalline diamond layers. Dewetting an evaporated metal film, resulting in randomly distributed metal droplets of 5–50 nm in diameter, created the etching mask. This study focused on the investigation of the effect of the metal layer type, i.e., Al, Ti, Co, Ni, Cu, Pd, Pt and Au, and thickness on surface density, shape and size of the resulting droplets. Two dry etching techniques were studied: (1) Capacitively Coupled Plasma Reactive Ion Etching (CCP-RIE) and (2) Inductively Coupled Plasma Reactive Ion Etching (ICP-RIE). Using CCP-RIE diamond etch rates were between 10 nm/min and 50 nm/min; however, diamond/Ni selectivity was not high enough to fabricate nanowires > longer than 250 nm. ICP-RIE etching created tapered, high aspect diamond nanostructures at 1000 W plasma power, 10 W platen power for ion acceleration and long etching times (> 40 min) while preserving the mask. Anisotropy can be improved by the addition of Ar in the plasma and the reduction of the pressure. So far, vertically aligned diamond nanowires of 800 nm in length were obtained by ICP-RIE etching in appropriate conditions.

Electrodeposition of Nickel Hydroxide Nanoparticles on Boron-Doped Diamond Electrodes for Oxidative Electrocatalysis

We demonstrate, for the first time, the electrosynthesis of uniformly dispersed nickel hydroxide nanoparticles (NPs) on polycrystalline boron-doped diamond (pBDD). This has been achieved by electrogenerating OH− at the pBDD surface in the presence of Ni2+ to create local conditions near the electrode where highly supersaturated (relative saturation ratio > 105) nickel hydroxide solutions are generated for short periods of time (approximately seconds). This results in the deposition of nickel hydroxide NPs directly on the electrode surface, as confirmed by X-ray photoelectron spectroscopy. The NPs have a reasonably homogeneous size distribution and are deposited uniformly across the heterogeneous pBDD surface. We show that by simply increasing the electrogeneration time and, hence, increasing both the local concentration of OH− and extent of the precipitation reaction, it is possible to increase the size of the NPs. For example, after 1 s, NPs with dimensions of 12 ± 3 nm form, whereas after 15 s, NPs of s...

Electrochemical behaviour of (111) B-Doped Polycrystalline Diamond: Morphology/surface conductivity/activity assessed by EIS and CS-AFM

Electrochemical activity, morphology and surface electrical conductivity of Boron-Doped Polycrystalline Diamond films prepared by MPCVD have been investigated. Heterogeneous apparent rate constants of three different redox systems, [Fe(CN)6]3−/4−, [IrCl6]2−/3− and [Ru(NH3)6]3+/2+ have been measured by both Cyclic Voltammetry and Electrochemical Impedance Spectroscopy on<100>textured films with a predominance of (111) faces: first measurements have been done with [Fe(CN)6]3−/4− only on as grown samples, and secondly after a mild electrochemical pretreatment the three redox systems have been investigated. “As-grown” samples showed a moderate average activity which was related to the presence of a minority of electronically conducting areas among insulating zones. Electrochemical treatment in neutral conditions substantially increased the activity and heterogeneous apparent rate constants kapp for the three couples were measured in the range of 10−2cms−1 with a good stability in time. Current-sensing AFM images performed ex situ showed that the electrochemically pre-treated material presented a high superficial conductivity whereas the grown sample showed major area of low conductivity.

Adsorption of cytochrome c on diamond

AbstractThe adsorption and conformational state of the electron transfer protein cytochrome c (cyt c) on flat, boron doped polycrystalline diamond electrodes was investigated using electrochemical techniques and atomic force microscopy (AFM). An electrochemical reduction wave from the adsorbed protein was identified as oxygen reduction, which is catalysed by the deformed heme redox centre of cyt c. We show that this catalytic activity only occurs after partial denaturation of cyt c. Therefore the reduction peak was used for characterization of the conformational state of adsorbed cyt c. AFM characterizations with molecular resolution show different conformational states of cyt c on diamond surfaces ranging from native to denaturated. Both applied techniques indicate that hydrophobic hydrogenated diamond tends to denaturate cyt c upon adsorption, while wet chemically oxidized diamond surfaces can provide extensive but non‐denaturating cyt c adsorption. The conformation and orientation of cyt c on wet chemically oxidized diamond is beneficial for the electron transfer between the protein redox centre and the diamond electrode even in the presence of oxygen.

Spatially correlated microstructure and superconductivity in polycrystalline boron-doped diamond

Scanning tunneling spectroscopies are performed below 100 mK on polycrystalline boron-doped diamond films characterized by transmission electron microscopy and transport measurements. We demonstrate a strong correlation between the local superconductivity strength and the granular structure of the films. The study of the spectral shape, amplitude, and temperature dependence of the superconductivity gap enables us to differentiate intrinsically superconducting grains that follow the BCS model, from grains showing a different behavior involving the superconducting proximity effect.

Electroless oxidation of diamond surfaces in ceric and ferricyanide solutions: An easy way to produce “C–O” functional groups

Despite many works are devoted to oxidation of diamond surfaces, it is still a challenge, to successfully produce well defined “C–O” functions, particularly for functionalization purposes. In this paper we describe and compare, for the first time, the “electroless” oxidation of as-deposited polycrystalline boron-doped diamond (BDD) films in ceric and ferricyanide solutions at room temperature. Both reactions efficiently generate oxygen functionalities on BDD surface. While a higher amount of “C–O” moieties is produced with Ce 4+ as oxidizing agent, the use of ferricyanide specie seems the most interesting to specifically generate hydroxyl groups. Additionally, this easy to perform oxidative method appears not damaging for diamond surfaces and adapted to conductive or non-conductive materials. The resulting surfaces were characterized using X-ray photoelectron spectroscopy, contact angle and capacitance–voltage analysis.

Giant electric double-layer capacitance of heavily boron-doped diamond electrode

The physical and electrochemical properties of boron-doped polycrystalline diamond electrodes, prepared with various B/C ratio, i.e., 0.1%, 0.5% (BDD-A), 1% (BDD-B), and 5% (BDD-C), were investigated. Electrochemical measurements of the heavily boron-doped films (BDD-C) showed giant electric double-layer capacitance and activity which is significantly larger than BDD-A and BDD-B as well as glassy carbon electrodes. However, interestingly, actual boron concentration of BDD-C was observed to be almost the same as that of BDD-B by secondary ion mass spectroscopy (SIMS) and glow discharge optical emission spectroscopy (GDOES) analysis. It is suggested that the large capacitance is due to a few sp 2-bonded carbon impurities, which was observed only in BDD-C, although the amount of the sp 2-bonded nondiamond species are very small. In the present work, the reason for the interesting electrochemical properties of heavily boron-doped diamond electrodes is discussed. Furthermore, dimensional stability of the electrodes was also confirmed by conducting harsh anodic treatment.

Surface analysis of CVD diamond exposed to fusion plasma

Microcrystalline undoped and heavily boron-doped polycrystalline diamond layers have been deposited on various substrates by hot filament CVD and exposed to hydrogen plasma in a linear plasma reactor (Pilot-PSI, The Netherlands) that simulates the high flux and high density plasma conditions of tokamak divertors, as well as in the DIII-D tokamak (US). Pre- and post-exposure analysis by SEM and Raman spectroscopy characterised the surface appearance and the sp 3 and sp 2 components of the diamond films respectively. Surface roughness variation was measured by AFM. Hardness and Young's modulus were assessed by nanoindentation in order to characterise the effect of the plasma on the mechanical properties. HRTEM and EELS have been used to evaluate the nature of the modification induced at the diamond surface by the plasma exposure. The measurements have shown that, despite some surface amorphisation of the exposed layers, further long-term exposure studies are warranted as neither delamination, dramatic film failure nor entire erosion of the film were observed.

Comparison of the XPS spectra from homoepitaxial {111}, {100} and polycrystalline boron-doped diamond films

In this work, we have used X-ray photoelectron spectroscopy (XPS) to investigate the nature of surface adsorbed species and their sensitivity to the boron concentration [B] in two sets of as-grown diamond films: homoepitaxial {111} and polycrystalline. These sets cover each one at least three of the four doping ranges: low doping (5 × 10 16 < [B] < 1.5 × 10 19 cm − 3 ), high doping (1.5 × 10 19 < [B] < 3 × 10 20 cm − 3 ), heavy doping (3 × 10 20 < [B] < 2 × 10 21 cm − 3 ), and phase separation ([B] > 2 × 10 21 cm − 3 ). The results are compared to those we have previously obtained on {100} homoepitaxial films in the same doping ranges. A detailed description of both the nature and the relative concentrations of the main surface chemical species on every set of films is reported. Besides the usual CH x bonds on the diamond surface, the following oxygen-related groups: Ether (C–O–C), hydroxyl (C–OH, only on polycrystalline films), carbonyl (> C=O) and carboxyl (HO–C=O) have been found on the surface of grown diamond films, upon spontaneous oxidation under air (no oxidation treatment has been applied). The evolution of each surface chemical group according to the boron concentration in the films is.

Preparation of superhydrophobic and oleophobic diamond nanograss array

The paper reports on the fabrication of superhydrophobic boron-doped diamond nanograss surfaces. The boron-doped diamond nanograss array (BDD NG) was prepared simply by reactive ion etching (RIE) with oxygen plasma of highly boron-doped (the boron doping level is 8 × 1019 B cm−3) polycrystalline diamond electrodes. Depending on the RIE conditions, substrates with different nanograss densities can be prepared. Chemical functionalization of the NG array surface with octadecyltrichlorosilane (OTS) or 1H,1H,2H,2H-perfluorodecyltrichlorosilane (PFTS) led to the formation of superhydrophobic surfaces. Under optimized conditions, BDD NG surfaces with contact angles as high as 160° and quasi null hysteresis (< 2°) can be reached. A water droplet deposited on the surface tends to roll off when the NG surface was tilted by a few degrees. Furthermore, the BDD NG array chemically modified with PFTS displays oleophobic properties. A contact angle of 94° was measured for hexadecane. The resulting surfaces were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray (EDX) analysis, and contact angle (CA) measurements.

Trace voltammetric detection of serotonin at carbon electrodes: comparison of glassy carbon, boron doped diamond and carbon nanotube network electrodes

The characteristics of three different carbon electrodes, glassy carbon (GC), oxygen-terminated polycrystalline boron-doped diamond (pBDD) and "pristine" carbon nanotube networks (CNTN) as voltammetric sensors for detection of the neurotransmitter serotonin have been investigated. For each electrode, detection sensitivity was determined using cyclic voltammetry (CV), a technique often used to provide information on chemical identity in electrochemical assays. The CNTN electrodes were found to exhibit background current densities ca. two orders of magnitude smaller than the GC electrode and ca. twenty times smaller than pBDD, as a consequence of their "pristine" low capacitance and low surface coverage. This was a major factor in determining serotonin detection limits from CV, of 10 nM for the CNTN electrode, 500 nM for pBDD and 2 microM for GC. The two most sensitive electrodes (CNTN and pBDD) were further investigated in terms of resistance to electrode fouling. CV analysis showed that fouling was less on the pBDD electrode compared to the CNTN and, furthermore, for the case of pBDD could be significantly minimised by careful selection of the CV potential limits, in particular by scanning the electrode potential to suitably cathodic values after oxidation of the serotonin.

Correlation between Plasma OES and Properties of B-doped Diamond Films Grown by MW PE CVD

Boron doped polycrystalline diamond films were grown using MW PE CVD method. Optical emission spectra (OES) of MW-plasma in the region from 200 nm to 800 nm during boron doped polycrystalline diamond films growth were in situ investigated. Raman spectroscopy method was used for morphology investigation of grown polycrystalline diamond films. Also, absorption spectroscopy method was used for optical properties investigation of all grown films.

Chronic in vivo nerve electrical recordings of Aplysia californica using a boron-doped polycrystalline diamond electrode

Custom diamond electrodes for in vivo, passive electrical nerve recording were developed and implanted in an intact, freely behaving Aplysia californica. A diamond electrode may have advantages for electrical recording because of its chemical stability, higher signal-to-noise ratio, and reduced biological fouling relative to traditional nerve-recording electrode materials. For example, thin stainless steel electrodes used for chronic extracellular recording in Aplysia typically last on the order of seven days in vivo. We have developed a first-generation diamond electrode with a flexible lead to withstand the complicated movements of Aplysia and to enable direct comparison with implanted stainless steel electrodes. Boron-doped polycrystalline diamond was grown onto tungsten wire substrates by hot filament chemical vapor deposition. The wires were pre-shaped into a hook (for nerve recording) or a loop (for a ground wire) and masked for selective growth on only 2–3 mm of the wire. After diamond growth, the uncoated portion of the wire substrates was removed and the intact diamond-coated hook or loop attached to a stainless steel electrical lead with conductive epoxy. After epoxy curing, these electrodes were insulated and implanted in the animal. The diamond and stainless steel electrodes were attached extracellularly to buccal nerve 2, a primary nerve for the feeding behavior of A . californica. The two electrodes were implanted adjacent to each other so that the recordings would be nearly synchronous. In vivo recordings were successfully obtained on a diamond hook electrode during a feeding behavior for up to 9 days after the implantation. The electrode remained intact for a total of 28 days in the animal and upon retrieval.

Influence of growth pressure on the electrical properties of boron-doped polycrystalline diamond films

Heavily boron-doped diamond films are synthesized by the hot-filament chemical vapor deposition method under the gas mixtures of H2, CH4 and trimethyl borate. The measurement results of scanning electron microscopy, Raman spectroscopy, X-ray diffractometer and electrical properties showed the morphologies, microstructures, carrier concentration and superconducting transition temperature for as-grown diamond films were dependent on the change of growth pressure, and specially its carrier concentrations could be adjusted from 1019 to 1021 cm−3 by increasing growth pressures from 2.5 to 5 kPa. And further, the effects of growth pressure on the film microstructural property and the doping level dependence of the superconducting transition temperature were discussed.

Selective Nanomolar Detection of Dopamine Using a Boron-Doped Diamond Electrode Modified with an Electropolymerized Sulfobutylether-β-cyclodextrin-Doped Poly(N-acetyltyramine) and Polypyrrole Composite Film

N-acetyltyramine was synthesized and electropolymerized together with a negatively charged sulfobutylether-beta-cyclodextrin on a boron-doped diamond (BDD) electrode followed by the electropolymerization of pyrrole to form a stable and permselective film for selective dopamine detection. The selectivity and sensitivity of the formed layer-by-layer film was governed by the sequence of deposition and the applied potential. Raman results showed a decrease in the peak intensity at 1329 cm(-1) (sp(3)), the main feature of BDD, upon each electrodeposition step. Such a decrease was correlated well with the change of the charge-transfer resistance derived from impedance data, i.e., reflecting the formation of the layer-by-layer film. The polycrystalline BDD surface became more even with lower surface roughness as revealed by scanning electron and atomic force microscopy. The modified BDD electrode exhibited rapid response to dopamine within 1.5-2 s and a low detection limit of 4-5 nM with excellent reproducibility. Electroactive interferences caused by 4-dihydroxyphenylalanine, 3,4-dihydroxyphenylacetic acid, ascorbic acid, and uric acid were completely eliminated, whereas the signal response of epinephrine and norepinephrine was significantly suppressed by the permselective film.

Fabrication of electrochemically stable fluorinated nano-carbon film compared with other fluorinated carbon materials

We fabricated electrochemically stable fluorinated nano-carbon film that had an sp 2 and sp 3 hybrid nanocrystalline structure formed using the electron cyclotron resonance (ECR) sputtering method. This fluorinated ECR (F-ECR) nano-carbon film prepared with a short CF 4 plasma treatment has a high fluorine content (F/C:0.20) and a low oxygen content (O/C:0.02) on its surface and retains its original morphology. This F-ECR nano-carbon is capable of a lower capacitance current, and a wider potential window than untreated ECR nano-carbon. The electron transfer rates at an F-ECR electrode are as high as those of untreated carbons for Ru ( NH 3 ) 6 2 + / 3 + , whereas they are much slower than those of untreated ECR nano-carbon for Fe 2+/3+ and Fe ( CN ) 6 3 - / 4 - owing to its selective sp 2 fluorination. These slow electron transfer rates for Fe 2+/3+ and Fe ( CN ) 6 3 - / 4 - are maintained during potential cycles due to its robust nanocrystalline structure. In contrast, these slow electron transfer rates were easily recovered for fluorinated glassy carbon under same condition. Furthermore, a smaller fluorination effect was observed for polycrystalline boron-doped diamond owing to the low reactivity of its sp 3 bonds. Our ECR nano-carbon film is suitable for the effective fabrication of a fluorinated surface while maintaining a relatively active electrochemical interface and excellent stability.

Electrochemical characteristics of boron doped polycrystalline diamond electrode sintered by high pressure and high temperature

The bulk B-doped polycrystalline diamond (PCD) electrode in this study was prepared by high-pressure, high-temperature (HPHT) technology. The PCD was sintered under HPHT conditions, using B-doped diamond powders and a metal catalyst as raw materials, then the metal solvent phase was dissolved by aqua regia. The morphology and composition of the PCD were investigated with a scanning electron microscope (SEM), X-ray diffraction (XRD), and energy dispersion spectrum (EDS). The results show that the sintered body possesses a polycrystalline structure with direct diamond–diamond bond and irregularly shaped pores of 1–10 μm distributed on the grain boundaries after the metal solvent phase was removed. The cyclic voltammogram and electrochemical impedance spectroscopy of this B-doped electrode have been investigated. The B-doped PCD electrode exhibits stable electrochemistry in a KCl support solution over a wide potential range. The quasi-reversible reaction occurs on the electrode for the [Fe(CN)6]3−/4− couples. The electrode process combines the diffusion-controlled mass transport plus the kinetic process. The electrochemical impedance spectroscopy (EIS) analysis shows the porous structure characteristic of the PCD electrode.

Amperometric Oxygen Sensor Based on a Platinum Nanoparticle-Modified Polycrystalline Boron Doped Diamond Disk Electrode

Pt nanoparticle (NP)-modified polycrystalline boron-doped diamond (pBDD) disk electrodes have been fabricated and employed as amperometric sensors for the determination of dissolved oxygen concentration in aqueous solution. pBDD columns were cut using laser micromachining techniques and sealed in glass, in order to make disk electrodes which were then characterized electrochemically. Electrodeposition of Pt onto the diamond electrodes was optimized so as to give the maximum oxygen reduction peak current with the lowest background signal. Pt NPs, >0-10 nm diameter, were found to deposit randomly across the pBDD electrode, with no preference for grain boundaries. The more conductive grains were found to promote the formation of smaller nanoparticles at higher density. With the use of potential step chronoamperometry, in which the potential was stepped to a diffusion-limited value, a four electron oxygen reduction process was found to occur at the Pt NP-modified pBDD electrode. Furthermore the chronoamperometric response scaled linearly with dissolved oxygen concentration, varied by changing the oxygen/nitrogen ratio of gas flowed into solution. The sensor was used to detect dissolved oxygen concentrations with high precision over the pH range 4-10.

Electrooxidation of ethylenediaminetetraacetic acid at a polycrystalline boron-doped diamond anode

Electrooxidation of ethylenediaminetetraacetic acid at a thin-film boron-doped polycrystalline diamond anode is studied by cyclic voltammetry and amperometry. It is shown that diamond electrodes can be used in the analytical determination of ethylenediaminetetraacetic acid: they have low background current; the detection limit is also rather low.