Legionella inactivation with diamond electrodes

The DiaCell® technology has been successfully tested against Legionella infection in several water types and under various working conditions. Depending on the water composition, Legionella can be completely inactivated with current densities as small as 50 mA/cm² with low contact times (<5 min). The higher the oxidant concentration in the electrolyzed water, the more rapid is the Legionella inactivation after injection. Bicarbonates in contaminated water were identified as very good supports for electrochemical disinfectants production for Legionella inactivation without high chlorine concentration. At the same time, sulfates in water do not provide any disinfection capacity by DiaCell® electrolysis.     

O-terminated nano-diamond ISFET for applications in harsh environment

The concept of an ion-sensitive FET (ISFET) on diamond with boron delta-doped channel and oxygen-terminated surface for pH sensing has been successfully transferred to large-area nano-crystalline diamond on silicon substrates. The nano-crystalline diamond layers, including the boron delta-doped channels of the FETs, were grown by hot-filament CVD. The fabricated layers were characterised by their peak concentration of boron of 3 × 10²⁰ 1/cm³ and FWHM of about 1 nm. This allowed approx. 50% modulation of the channel current within the gate potential range corresponding to the potential window of water electrolysis on the diamond surface. The O-termination by combination of oxygen-plasma and wet chemical treatments resulted in a pH sensitivity of the ISFETs close to the Nernst's limit in the range between pH1 and pH13. The ISFET characteristics were stable even after anodic treatment in KOH. This allows using nano-crystalline diamond ISFETs with O-termination also as electrodes and even at anodic overpotentials.     

Transparent diamond electrodes for tunable micro-optical devices

Boron-doped nanocrystalline diamond (NCD:B) elastic layers combined with aluminum nitride (AlN) piezo-actuators are well suitable for ultrathin, highly transparent and mechanically stable micro-optical devices operating at high frequencies. In such unimorph structures NCD:B layers serve as advanced transparent electrodes instead of commonly used indium tin oxide. The carrier transport properties of heavily p-doped NCD thin films are characterized by temperature-dependent voltage-current and Hall measurements. In addition, the piezo-driven aspheric deformation of NCD:B/AlN micro lenses is demonstrated by means of integrated multi-sector actuators.     

Electrolysis of progesterone with conductive‐diamond electrodes

BACKGROUND: Progesterone is considered an endocrine disruptor chemical. It can be found in industrial discharges, municipal wastewaters, and, in some instances, even in treated effluents at the level of ng dm^?3. RESULTS: Conductive diamond electrolysis can be used to remove progesterone from aqueous solutions. Increases in current density lead to less efficient processes, indicating mass transfer control of the process rate. Occurrence of chlorides in the electrolytic media favors the depletion of progesterone compared with sulphates, although it does not affect the mineralization rate. Independently of the solubilizing agent used, the process behaves similarly during a first stage of the electrolysis (at the four ranges of pollutant concentration studied). However, in a second stage, the rate changes abruptly due to reduced action of hydroxyl radicals in methanol media. CONCLUSIONS: Progesterone can be removed efficiently by conductive diamond electrolysis from aqueous solutions within the range of initial concentrations 10^?2 to 10² mg dm^?3. The process efficiency increases with the current density. Removal rate does not depend on the nature of the electrolyte, but this parameter affects the intermediates formed during the experiment. When pure methanol is used as solubilizing agent, only direct electro‐oxidation takes place. Copyright © 2012 Society of Chemical Industry     

A novel detector with graphitic electrodes in CVD diamond

A synthetic single crystal diamond sample has been prepared with graphitic in bulk electrodes by laser induced graphitisation of diamond. A geometry with an array of electrodes has been fabricated to demonstrate the functionality of a “3D diamond detector” for ionising radiation. The detection capability has been studied with synchrotron radiation.     

Electrochemical behaviour of electrodes assembled with Ti-containing diamond films

High quality polycrystalline diamond films containing Ti dispersions have been produced by means of a hybrid CVD/powder flowing technique and used to assemble electrochemical probes. The electrochemical response was evaluated by performing cyclic voltammetry and fixed potential amperometry of both inorganic [Fe(CN)₆⁴⁻], and organic (ascorbic acid, epinephrine) compounds. The electro-analytical responses of these diamond-based electrodes have been compared with those of conventional glassy carbon and pyrolytic graphite electrodes. In view of their rather good performances, the Ti-containing diamond-based electrodes appear to be suitable for analytical purposes, and especially promising for applications in systems requiring absolute biocompatibility.     

Ordered array of diamond ultramicroband electrodes for electrochemical analysis

Boron-doped diamond ultramicroband arrays with different array densities and interelement spacings were fabricated using silicon technology and selective diamond deposition (SAD) technique to yield microvoltammetric electrodes. The electroactive ultramicroband elements were designed with one microscopic critical dimension to impart microelectrode behavior while the other dimension was made larger to yield an increase in signal current. Cyclic voltammetry studies in this work showed that with sufficient interelement separation, the ultramicroband arrays display sigmoidal pseudo-steady-state cyclic voltammograms characteristic of microband electrodes. The ultramicroband arrays yielded higher faradaic current per unit area, than either square ultramicroelectrode array or conventional planar diamond electrode from earlier reported work. This is due to enhanced mass transport to the ultramicroband elements at slow scan rates. Larger current density and higher signal-to-noise (S/N) ratio leads to better limits of detection, making it possible to fabricate a more sensitive electrode for applications such as electroanalysis, electrocatalysis, trace element analysis, mechanistic and fast transfer kinetics studies, electrochemistry in highly resistive media, as well as sensors in flow and biological system.     

Rhenium alloys as ductile substrates for diamond thin-film electrodes

Molybdenum–rhenium (Mo/Re) and tungsten–rhenium (W/Re) alloys were investigated as substrates for thin-film, polycrystalline boron-doped diamond electrodes. Traditional, carbide-forming metal substrates adhere strongly to diamond but lose their ductility during exposure to the high-temperature (1000 °C) diamond, chemical vapor deposition environment. Boron-doped semi-metallic diamond was selectively deposited for up to 20 h on one end of Mo/Re (47.5/52.5 wt.%) and W/Re (75/25 wt.%) alloy wires. Conformal diamond films on the alloys displayed grain sizes and Raman signatures similar to films grown on tungsten; in all cases, the morphology and Raman spectra were consistent with well-faceted, microcrystalline diamond with minimal sp² carbon content. Cyclic voltammograms of dopamine in phosphate-buffered saline (PBS) showed the wide window and low baseline current of high-quality diamond electrodes. In addition, the films showed consistently well-defined, dopamine electrochemical redox activity. The Mo/Re substrate regions that were uncoated but still exposed to the diamond-growth environment remained substantially more flexible than tungsten in a bend-to-fracture rotation test, bending to the test maximum of 90° and not fracturing. The W/Re substrates fractured after a 27° bend, and the tungsten fractured after a 21° bend. Brittle, transgranular cleavage fracture surfaces were observed for tungsten and W/Re. A tension-induced fracture of the Mo/Re after the prior bend test showed a dimple fracture with a visible ductile core. Overall, the Mo/Re and W/Re alloys were suitable substrates for diamond growth. The Mo/Re alloy remained significantly more ductile than traditional tungsten substrates after diamond growth, and thus may be an attractive metal substrate for more ductile, thin-film diamond electrodes.     

Nano-crystalline diamond electrodes with cap layer decorated by gold particles

We describe the electrochemical characteristics of a nano-crystalline diamond (NCD) electrode with a thin (～ 60 nm) low-doped cap layer on a highly boron-doped diamond contact layer, where the grain boundary areas of the surface are decorated by gold particles by electroplating. The presence of the surface cap layer leads to a reduced background current compared to the highly doped NCD electrodes. At the same time, the electrical resistance to the gold particles via grain boundary defects of the cap layer does not limit the activity of the particles in 0.1 M H₂SO₄ electrolyte. The equivalent circuit of the decorated cap-layer electrodes is discussed using the results of electrochemical impedance spectroscopy and data on gold–diamond Schottky diodes fabricated on identical NCD layers. This equivalent circuit can be reduced to a low number of key elements, which could be useful for optimizing such electrodes for high sensitivity/low noise applications.     

Comparison of GaN and AlN nucleation layers for the oriented growth of GaN on diamond substrates

In this study, {0001} oriented GaN crystals have been grown on freestanding, polycrystalline diamond substrates using AlN and GaN nucleation layers (NLs). XRD measurements and SEM analysis showed that the application of a thin AlN NL gives the best structural results, because AlN has a thermal expansion coefficient in between GaN and diamond and thus delocalizes the stress to two interfaces. The optical quality of the layers, investigated with Raman microscopy and photoluminescence spectroscopy, is similar. Although no lateral epitaxy is obtained, new insight is gained on the nucleation of GaN on diamond substrates facilitating the growth of GaN epilayers on polycrystalline diamond substrates.     

Plasma etching treatment for surface modification of boron-doped diamond electrodes

Boron-doped diamond (BDD) thin film surfaces were modified by brief plasma treatment using various source gases such as Cl₂, CF₄, Ar and CH₄, and the electrochemical properties of the surfaces were subsequently investigated. From X-ray photoelectron spectroscopy analysis, Cl and F atoms were detected on the BDD surfaces after 3 min of Cl₂ and CF₄ plasma treatments, respectively. From the results of cyclic voltammetry and electrochemical AC impedance measurements, the electron-transfer rate for Fe(CN)₆^3−/4− and Fe^2+/3+ at the BDD electrodes was found to decrease after Cl₂ and CF₄ plasma treatments. However, the electron-transfer rate for Ru(NH₃)₆^2+/3+ showed almost no change after these treatments. This may have been related to the specific interactions of surface halogen (C-Cl and C-F) moieties with the redox species because no electrical passivation was observed after the treatments. In addition, Raman spectroscopy showed that CH₄ plasma treatment of diamond surfaces formed an insulating diamond-like carbon thin layer on the surfaces. Thus, by an appropriate choice of plasma source, short-duration plasma treatments can be an effective way to functionalize diamond surfaces in various ways while maintaining a wide potential window and a low background current.     

Electrochemical behaviour of graphite- and molybdenum electrodes modified with thin-film diamond

Films of undoped polycrystalline diamond were deposited on molybdenum or graphite substrates by hot filament chemical vapour deposition (HFCVD), using a precursor gas mixture of methane in excess hydrogen. The morphology and quality of the as-deposited films were monitored by scanning electron microscopy, Raman spectroscopy, and X-ray diffraction, and the electrochemical activity monitored with cyclic voltammetry. The results suggest a direct correlation between electrochemical activity, film thickness, and quality. Analysis of the ferrocyanide–ferricyanide couple at a diamond-modified molybdenum or graphite electrode suggest some extent of electrochemical reversibility, but the rates of charge transfer across the diamond–substrate interface varied with the methane concentration and substrate type. The ratio of the anodic and cathodic peak currents was always close to unity. Ex situ studies with energy dispersive spectroscopy show that some Prussian Blue was deposited on the graphite-modified electrode, grown using 0.5% CH₄ in H₂.     

Covalent modification of boron-doped diamond electrodes with an imidazolium-based ionic liquid

An ionic liquid (IL, 1-(methylcarboxylic acid)-3-octylimidazolium-bis (trifluoromethylsulfonyl)imide) was covalently coupled onto a boron-doped diamond (BDD) surface through an esterification reaction. The resulting surface was characterized by X-ray photoelectron spectroscopy, water contact angle and electrochemical measurements. Selective electron transfer towards positively and negatively charged redox species was recorded. While the presence of Fe(CN)₆⁴⁻ could be detected on the IL-modified BDD interface, no surface-immobilized Ru(NH₃)₆³⁺ was recorded. The IL-modified BDD electrode showed in addition changes in surface wettability when immersed into aqueous solution containing different anions.     

Surface modification of single-crystal boron-doped diamond electrodes for low background current

An all-diamond sub-microelectrode array structure with an insulating cap layer was fabricated on 100-oriented single crystal diamond substrate by epitaxial growth. The cap layer represented a nitrogen-doped layer on top of a highly boron doped film, thus forming a surface p–n junction. The presence of the cap layer reduced the background current down to the pA/mm² range and shifted the hydrogen—and the oxygen evolution to higher potentials, leading to a potential window of approx. 6 V. Individual electrodes of 600 nm in diameter were introduced using e-beam lithography and plasma etching through the cap layer down to the p⁺ diamond, leading to a sub-microelectrode array structure. The activity of the sub-microelectrodes could be observed within this 6 V-window at lower potentials. At the same time, the interface capacitance and the background current remained unchanged compared to the initial p–n junction electrode without etched holes.     

Deposition of clusters and nanoparticles onto boron-doped diamond electrodes for electrocatalysis

Metal and metal oxide particles and nanoparticles, differing from each other by their nature and synthesis technique, were deposited onto boron-doped diamond (BDD) thin film electrodes. The applicability in electrocatalysis of thermally decomposed IrO₂ and Au nanoparticles, electrodeposited Pt particles, dendrimer-encapsulated Pt nanoparticles (Pt DENs) and microemulsion-synthesized Pt/Ru nanoparticles was studied, once deposited on BDD substrate. In all cases, the electrochemical response of the composite electrodes could be solely attributed to the supported particles. All the particles, with the exception of Pt DENs, exhibited electrocatalytic activity. Pt DENs inactivity has been attributed to insufficient removal of the dendrimer polymer matrix. It was concluded that the BDD electrode is a suitable substrate for the electrochemical investigation of supported catalytic nanoparticles.     

An electrolyte-free system for ozone generation using heavily boron-doped diamond electrodes

An electrolyte-free system for electrochemical ozone generation was developed using boron-doped diamond (BDD) electrodes as the anode and cathodes in combination with Nafion® N117/H⁺ as the separating membrane. Trials using BDD with various B/C ratios suggested that heavily boron-doped BDD with sp² impurities yielded high concentration of ozone. Further experiments by replacement of the feedstock solutions with 0.85 M Na₂SO₄ or 0.85 M NaCl resulted in no significant difference, suggesting that the use of pure water as the feedstock is the most appropriate method for ozone production. A high efficiency could be achieved by applying water as a feedstock for the anode and the cathode chambers. In addition, comparison with Pt electrodes confirmed that the excellent structural stability of BDD was the main factor contributing to this success.     

Oxidation of carboxylic acids at boron-doped diamond electrodes for wastewater treatment

Thin boron-doped diamond films have been prepared by HF CVD (hot filament chemical vapour deposition technique) on conductive p-Si substrate (Si/Diamond). The morphology of these Si/diamond electrodes has been investigated by SEM and Raman spectroscopy. The electrochemical behaviour of the Si/diamond electrodes in 1 M H₂SO₄ and in 1 M H₂SO₄ + carboxylic acids has been investigated by cyclic voltammetry. Finally, the electrochemical oxidation of some simple carboxylic acids (acetic, formic, oxalic) has been investigated by bulk electrolysis. These acids can be oxidized at Si/diamond anodes to CO₂, in the potential region of water and/or the supporting electrolyte decomposition, with high current efficiency.     

掺硼金刚石电极电化学再生粉末活性炭

使用200目粉末活性炭吸附苯酚模拟废水至饱和,用BDD电极作为阳极再生饱和炭,以再生效率为评价指标,研究不同因素对活性炭再生效果的影响。在电解质为0.05 mol/L的Na_2SO_4溶液,pH为7,电流密度为50 mA/cm~2,再生时间为2 h条件下,活性炭再生率达74.8%。同时不同电解质对再生效果也有不同影响,硫酸钠优于氯化钠,再生效率随着pH的增加而增加。采用正交实验方法对影响再生效果的各因素进行评价,其影响的主次顺序是:电解质浓度、pH、电解时间。     

掺硼金刚石电极电化学再生粉末活性炭

使用200目粉末活性炭吸附苯酚模拟废水至饱和,用BDD电极作为阳极再生饱和炭,以再生效率为评价指标,研究不同因素对活性炭再生效果的影响。在电解质为0.05 mol/L的Na_2SO_4溶液,pH为7,电流密度为50 mA/cm²,再生时间为2 h条件下,活性炭再生率达74.8%。同时不同电解质对再生效果也有不同影响,硫酸钠优于氯化钠,再生效率随着pH的增加而增加。采用正交实验方法对影响再生效果的各因素进行评价,其影响的主次顺序是:电解质浓度、pH、电解时间。     

Electrical and Raman-imaging characterization of laser-made electrodes for 3D diamond detectors

Pulsed laser writing of graphitic electrodes in diamond is a promising technique for innovative particle detectors. Although of great relevance in 3D fabrication, the processes involved in sub-bandgap bulk irradiation are still not well understood. In this work, Raman imaging is exploited to correlate resistivity and graphitic content in 5–10 μm-thick electrodes, obtained both in the domains of femtoseconds and of nanoseconds of pulse duration. A wide interval of resistivities (60–900 mΩcm), according to the irradiation technique employed, are correlated with an sp² content of the modified material ranging over a factor 2.5. The stress distribution (maximum of about 10 GPa) and the presence of nanostructured sp³ material around the graphitic columns have also been studied by Raman spectroscopy, and a rationale for the conductive behavior of the material is presented in terms of the thermodynamics of the process.