Conductive Boron-doped Diamond Research Articles

A closed bipolar electrochemical cell for the interrogation of BDD single particles: Electrochemical advanced oxidation

A closed bipolar electrochemical cell containing two conductive boron-doped diamond (BDD) particles of size ∼ 250 – 350 μm, produced by high-pressure high-temperature (HPHT) synthesis, has been used to demonstrate the applicability of single BDD particles for electrochemical oxidative degradation of the dye, methylene blue (MB). The cell is fabricated using stereolithography 3D printing and the BDD particles are located at either end of a solution excluded central channel. Platinum wire electrodes placed in each of the two outer solution compartments are used to drive electrochemical reactions at the two BDD particles, which, under bipolar conditions do not require direct electrical connection to a potential source. Experiments using ultra high-performance liquid chromatography coupled with mass spectrometry (UHPLC-MS) show that the anodic pole BDD particle is able to electrochemically remove > 99 % of the dye (originally present at 1 × 10−4 M) to undetectable UHPLC-MS products in 600 s. Monitoring of the time dependant change in MB peak area, from the UHPLC chromatograms, enables a pseudo first order rate constant of 0.54 min−1 to be determined for MB removal. Given the large scale at which such particles can be produced (tonnes), such data bodes well for scale up opportunities using HPHT-grown BDD particles, where the particles can be assembled into high surface area electrode formats.

Exploring the effect of surface chemistry and particle size of boron-doped diamond powder as catalyst and catalyst support for the oxygen reduction reaction

The interest for the electrodes based on conductive boron-doped diamond powder (BDDP) is increasing in recent years due to their excellent physical and chemical stability, the wide potential window in both aqueous and organic electrolytes, the relatively large specific surface area, and their versatility in comparison to boron-doped diamond thin film electrodes. These materials have been proposed as alternative cathode catalyst support due to their high corrosion resistance when subjected to the highly positive potentials originated during the start-stop operations in fuel cells, especially in automobiles. In this work, we present three BDDP supports with different particle sizes and different surface oxygen contents as supports of different iron species for oxygen reduction reaction in alkaline solution. BDDP supports were modified with carbon nitride (C3N4) or phthalocyanines (Pc) as anchoring points for iron. The different electrocatalytic performance observed confirmed the strong influence of the surface chemistry of the BDDP supports on the activity of the metallic sites for FePc samples while, for Fe-C3N4 samples, the determining effect was the particle size of the BDDP support. Additionally, DFT calculations were used to obtain some insights about the interaction of the FePc with the diamond surface.

Conductive Boron-doped Diamond Powder/Nanoparticles for Electrochemical Applications

Abstract Boron-doped diamond powder (BDDP) and boron-doped nanodiamond (BDND) were developed with the aim of expanding the area of application of conductive diamond electrodes. BDDP and BDND are conductive diamond powders obtained by depositing a boron-doped diamond (BDD) layer on the surface of diamond powder (DP) and nanodiamond (ND) substrates, respectively, by using the chemical vapor deposition method. As the particle size of BDDP depends on that of the DP substrate, it can be arbitrarily selected in the range of at least submicrometer to several micrometers. BDDP can be used for an electrode material of screen-printed diamond electrode, which is a disposable and sensitive electrode for electrochemical detection even from biological fluids. BDDP can also be applied to a durable cathode catalyst support of a polymer electrolyte fuel cell. BDND is a conductive diamond particle with a large specific surface area of 650 m2/g or more, and is expected to be used as an electrode material for aqueous electric double-layer capacitors with a large cell voltage leading to high energy and high-power densities. BDDP and BDND are highly versatile functional electrode materials that can be made into inks and pastes, and can be combined easily with other compounds. Therefore, they should be useful for greatly expanding the application fields of diamond electrodes.

Boron-doped diamond electrochemical aptasensors for trace aflatoxin B1 detection

An electrochemical aptasensor for detecting trace aflatoxin B1 (AFB1) is designed and fabricated consisting of aptamers and gold nanoparticles on conductive boron-doped diamond (BDD) electrode. By examining the relative impedance shift from electrochemical impedance spectroscopy as a function of AFB1 concentration, the low detection limit (wide linear relationship range) of the aptasensor is realized to be 5.5 × 10−14 mol L−1 (1.0 × 10−13‒1.0 × 10−8 mol L−1). The variation in impedance property of the aptasensor is determined by the specific adsorption of AFB1 molecules to the aptamer at a certain concentration covering the electrode. By means of multiple characteristic processes, it is demonstrated that the constructed aptasensor is favorable for testing the trace AFB1 with high specificity, sensitivity, stability, repeatability, and reusability, which lead to a possibility to achieve high performance biosensor for practical application to quantitatively detract trace AFB1 in environments.

Study of high-frequency microspark-erosion of boron-doped polycrystalline diamond

The native property of weakly conductive Boron-doped polycrystalline diamond (B-doped PCD) as a high-melting point, resistant, super-hard material makes it particularly difficult to machine. This paper focuses on the relative merits of eroding B-doped PCD by spark-erosion based on different power sources: commercial transistorized, Resistance-Capacitance (R-C), and designed high-frequency microspark-erosion power. Experimental results show B-doped PCD endures spark-erosion longer under commercial transistorized power although its Material-Erosion-Rate (MER) is higher. This greatly facilitates surrounding air scurries into the PCD matrix during melting and cooling. A poorer material-erosion-rate presents under R-C power due to its lower duty cycle. In contrast, dense eroded microcraters realizing a solid and regular distribution on the PCD matrix occur under high-frequency microspark-erosion power. The erosion-energy beam is supplied by a current train of high-frequency, high-peak and short-pulse-time, resulting relatively more diamond being vaporized than melted. The amount of eroded diamond is so little that debris is exceedingly slight and swiftly cleared away between each pulse-on-time. The extensive solid erosion craters resulting from the process are very useful as chip-pockets on the PCD wheel-tool for disposal of ground chips during microgrinding. Additionally, aspects relating to the merits of B-doped PCD are evaluated in detail: spark-erosion-ability (SEA) of B-doped PCD, surface roughness on B-doped PCD, depositional amounts of cobalt, and graphitization of diamond.

Flexible Boron-Doped Diamond Films for Bio-Potential Sensing in Plants

Introduction Recently, it has become obvious that the bioelectric potential of plants is influenced by environmental factors such as atmospheric temperature, humidity, and light intensity. In general, two different methods, being used to measure electric potentials in plants, are namely extracellular and intracellular measurement. On the other hand, conductive boron-doped diamond (BDD) has been investigated for the superior electrochemical properties including a low background current and a wide potential window. Then, as an extracellular potential measurement, we reported a highly sensitive measurement system involving BDD electrodes for plant monitoring1. Although the BDD electrodes seemed to be promising materials to measure the bioelectric potential for plant monitoring, further research is needed for the development of inexpensive and flexible film as an electrode of sensor elements to fit on the various plants. Therefore, in the current study, low cost and flexible BDD electrodes, using BDD powder 2 (BDDP) and resins (Nafion (R) or Vylon-KE1830 3), were prepared for plant monitoring. Experimental BDDP was prepared by depositing BDD onto the surface of natural diamond powder through microwave plasma-assisted chemical vapor deposition. When preparing the BDD/Nafion electrodes, adding 2-propanol to an ion-exchange polymer dispersion (20 wt % Nafion (R), Sigma-Aldrich Japan Co., Ltd.), a dispersion with a 2-propanol/20 wt % Nafion (R) ratio of 1:1 was achieved and used to prepare the BDD/Nafion ink. Pt foils (10 mm × 10 mm, Nilaco Co., Ltd.) were painted with the ink and heated in an oven at 60 °C for 1 h and then at 120 °C for 10 min to form flexible BDD electrodes (BDD/Nafion film). Next, for the preparation of the BDD/Vylon electrodes, BDDP, Vylon (amorphous co-polyester, TOYOBO Co., Ltd.), KE-1830 (Silicon resin, Shin-Etsu Chemical Co., Ltd.), and toluene were taken in the weight ratio of 5:4:1:100. The prepared BDD/Vylon ink was then painted and heated under the same conditions as those used in the preparation of the BDD/Nafion film electrodes. Polycrystalline BDD plates (10 mm × 10 mm, Electrochemistry Polycrystalline, Element Six Ltd.) were also used as sensor electrodes. Each BDD plate and film-type electrode was attached with conductive carbon tape onto 3M™ Red Dot™ electrocardiogram (ECG) monitoring electrodes (Figure (a)). Each pair of electrodes was attached to the leaves of a potted Aloe. Bioelectric potential changes in the plant were detected as changes in the potential gaps between the pairs of sensor electrodes and the signal was amplified using a handmade amplifier. An AC/DC converter (ADC-24, Pico Technology Ltd.) was set up to record the amplified potential gap data. The BDD electrodes were assessed for their response reproducibility against a bare finger touch stimulus at least three times on every recording time. To maintain constant conditions for the potted Aloe, it was watered and moved into a room in which the temperature was maintained between 19 and 23 °C for at least 30 min before any finger touch stimulus was given. Result and discussion Statistical analyses of the results were performed as follows. The coefficient of variability (CoV) for the signal measured by each electrode was calculated using the mean and standard deviation (SD) of the bioelectric potential change (Figure (b)). The calculated means (absolute value) and SD/Means of potential changes between each pair of electrodes on the Aloe for a finger touch stimulus are plotted on Figure (c) and (d), respectively. The potential gap between a pair of electrodes attached to the plants changes as the plants are stimulated artificially with a finger touch, suggesting that the bioelectric potentials in the plant also changed, manifesting as changes in the potential gap between the electrodes. The BDD electrodes were assessed for their response reproducibility to a finger stimulus for 140 days. Conclusions The results of the study allow us to conclude that BDD electrodes can be used to detect biopotential changes on a potted Aloe as changes in the potential gap between a pair of electrodes. In addition, the flexible and inexpensive BDD electrodes consisting of BDD powder and resins, successfully proved the stability for long term use. Acknowledgements The authors are grateful to Seitaro Suzuki for his help to preparing handmade amplifiers. This work was supported by JSPS KAKENHI Grant Number JP17K05958. Reference 1 T. Ochiai, S. Tago, M. Hayashi, A. Fujishima, ECS Transactions 2016, 75, 233. 2 T. Kondo, H. Sakamoto, T. Kato, M. Horitani, I. Shitanda, M. Itagaki, M. Yuasa, Electrochemistry Communications 2011, 13, 1546. 3 S. Tago, T. Ochiai, S. Suzuki, M. Hayashi, T. Kondo, A. Fujishima, Sensors 2017, 17, 1638. Figure 1

All-Diamond Microfiber Electrodes for Neurochemical Analysis

Neurochemical sensing with implantable microelectrodes has created multiple research opportunities in the field of neuroscience. The ability to record extracellular biopotentials and detect neurotransmitters with high sensitivity has enabled deeper understanding of brain and nervous system function. Diamond has many advantages over other electrode materials such as good biocompatibility, wide potential window, low double-layer capacitance, long-term stability, resistance to corrosion/fouling, and fabrication flexibility. In this work, we present a micromachined, implantable, all-diamond microfiber capable of reliable, precise neurochemical sensing. The all-diamond fiber consists of a conductive boron-doped polycrystalline diamond (BDD) core encapsulated in layers of insulating polycrystalline diamond (PCD) cladding. The PCD serves as a biocompatible and hermetic package while also acting as a dielectric barrier to prevent signal cross-talking. The all-diamond microelectrodes were thoroughly characterized using topographical and electrochemical methods. The capability for neurotransmitter sensing was completed using dopamine (DA) as the model analyte. Fast-scan cyclic voltammetry (FSCV) of DA was also completed to demonstrate the practicality for in vivo sensing at rapid rates. The fabrication is described in great detail and the capability for batch-scale process is demonstrated. These novel all-diamond microelectrodes have commercial-scale potential, generating a powerful tool for neurochemical analysis.

Surface Redox Chemistry of Immobilized Nanodiamond: Effects of Particle Size and Electrochemical Environment

The size of the diamond particle is tailored to nanoscale (nanodiamond, ND), and the ND surface is engineered targeting specific (electrochemical and biological) applications. In this work, we investigated the complex surface redox chemistry of immobilized ND layer on conductive boron-doped diamond electrode with a broad experimental parameter space such as particle size (nano versus micron), scan rate, pH (cationic/acidic versus anionic/basic), electrolyte KCl concentration (four orders of magnitude), and redox agents (neutral and ionic). We reported on the significant enhancement of ionic currents while recording reversible oxidation of neutral ferrocene methanol (FcMeOH) by almost one order of magnitude than traditional potassium ferricyanide (K3Fe(CN)6) redox agent. The current enhancement is inversely related to ND particle diameter in the following order: 1 μm << 1000 nm < 100 nm < 10 nm ≤ 5 nm < 2 nm. We attribute the current enhancement to concurrent electrocatalytic processes, i.e. the electron transfer between redox probes and electroactive surface functional (e.g. hydroxyl, carboxyl, epoxy) moieties and the electron transfer mediated by adsorbed FcMeOH+ (or Fe(CN)63+) ions onto ND surface. The first process is pH dependent since it depends upon ND surface functionalities for which the electron transfer is coupled to proton transfer. The adsorption mediated process is observed most apparently at slower scan rates owing to self-exchange between adsorbed FcMeOH+ ions and FcMeOH redox agent molecules in diffusion-limited bulk electrolyte solution. Alternatively, it is hypothesized that the surface functionality and defect sites (sp2-bonded C shell and unsaturated bonds) give rise to surface electronic states with energies within the band gap (midgap states) in undoped ND. These surface states serve as electron donors (and acceptors) depending upon their bonding (and antibonding) character and, therefore, they can support electrocatalytic redox processes in the presence of specific redox-active molecules via feedback mechanism. Apparently, FcMeOH+ tended to have electrostatic affinity for negatively charged ND surface functionalities, corroborated by present experiments. We also attempted to study biocatalytic process using model metalloprotein (cytochrome c; Cyt c) immobilized on ND particles for investigating interfacial electron transfer kinetics and compared with those of functionalized graphene (graphene oxide; GO and reduced GO). The findings are discussed in terms of interplay of sp3-bonded C (ND core) and sp2-bonded C (ND shell and graphene-based systems).

Surface Treatment of Boron Doped Diamond Using Atmospheric-Pressure Nitrogen Plasma Jet

Conductive boron-doped diamond (BDD) exhibits high physical and chemical stability, a wide potential window, a low background current. Owing to the typical characters, BDD is expected for use as an electrode material in the electrochemical applications such as electrolysis, waste water treatment, pH sensing, and electroanalysis. In order to further functionalize BDD, the surface treatment technique, e.g., enlargement the surface (reaction) area, control the morphology, chemical functionalization, is required and several kinds of the treatment method have been attempted including catalytic etching, oxygen treatment and so-on. We attempted to use atmospheric-pressure nitrogen plasma jet (APN2PJ) for the surface treatment of BDD for the first time. APN2PJ is a unique technique and can generate NH and nitrogen radicals at high density even under atmospheric pressure. In this presentation, the effects of APN2PJ on the chemical as well as electrochemical properties of BDD, especially the electrochemical double layer capacitance and the behavior at high potential region up to 2.5 V vs. RHE, are reported. In addition, the effect of following ultrasonic treatment is also reported. BDD electrode (De Nora Permelec Ltd., Nb substrate, thickness of BDD layer = 2.5 mm, boron content = 9.000 ppm) was used as purchased. APN2PJ treatment was carried out original apparatus. The treatment time was restricted at 3, 5 and 7 minutes. Mixture gas of nitrogen and hydrogen was used as the atmospheric gas. The applied voltage and pulse current of APN2PJ was set at 5 kV and 1 A, respectively. Hereafter, BDD without APN2PJ treatment is denoted as BDD-0 and BDD after plasma treatment as BDD-(APN2PJ treatment time). After APN2PJ treatment, the morphology of BDD was observed by FE-SEM and the chemical analysis was carried out by XPS. Cyclic voltammetry was carried out in a three-electrode electrochemical cell under nitrogen atmosphere. A gold mesh and Ag|AgCl electrode was used as the counter electrode and the reference electrode. 0.5 mol dm-3 H2SO4 aqueous solution was used as the electrolyte. The electrochemical double layer capacitance of each BDD electrodes was estimated in the potential region between 0.5 V and 0.6 V vs. RHE. Figure 1 a) and b) shows FE-SEM images of BDD-0 and BDD-7. The surface of BDD-0 was consisted by tiny single crystals of BDD of several micrometer sizes. On the other hand, many boundary (grooves), pits and the granular precipitates were clearly observed on the surface of BDD-7, which shows APN2PJ treatment gives morphology change of the surface of BDD. From XPS analysis, the peaks were observed in the spectra of C1s, O1s and N1s for each BDD electrodes after APN2PJ treatment, although only C1s peak was observed for BDD-0. In particular, in N1s XP spectra of BDD electrodes after APN2PJ treatment, four peak components assigned to Nitride, N-C sp3 bond, N-C sp2 bond and N-O bond were observed, showing that nitrogen was introduced into BDD surface and simultaneously, the morphology change as shown in Fig 1 b) was taken place. We also investigated the effects of following ultrasonic treatment. This was carried out in pure water. Figure 1 c) shows FE-SEM image of BDD-7 following ultrasonic treatment. Here, thus BDD was named as U-BDD-(APN2PJ treatment time). The granular precipitates, which are observed on the surface of BDD-7 (Fig. 1 b)), were disappeared and the grooves and holes became to be clearly observed. The electrochemical double layer capacitance was increased with an increase in APN2PJ treatment time and was further increased by following ultrasonic treatment. If we assumed that the capacitance relates to the geometric surface area of the electrode, the surface area of BDD would be increased with appearance of the grooves and the pits by APN2PJ. Furthermore, it was reasonably considered that the ultrasonic treatment gives disappearance of the precipitates as well as cleaning of the surface, which would lead to increase in the capacitance (surface area). The behavior at high potential region will be also presented. Figure 1

Diamond - towards a "one material" multi electrode array for neuronal recording

Event Abstract Back to Event Diamond - towards a "one material" multi electrode array for neuronal recording Paul A. Nistor1, 2, Paul W. May2 and Maeve A. Caldwell1 1 University of Bristol, Regenerative Medicine Laboratory, United Kingdom 2 University of Bristol, School of Chemistry, United Kingdom Introduction: Neuronal network activity can be investigated by in vitro neuronal recording, using Multi Electrode Arrays (MEAs). The advent of MEAs opened the possibility of simultaneous recording from multiple interconnecting neurons. The efficiency of the method is however dependent on the duration for which the cells can be maintained viable and functional; usually this ranges from hours to a few days. One critical aspect concerns the incompatibility between metallic electrodes and the cells which generate an electrical signal. To address this, frequently, the electrodes are coated in “bio-friendly” materials. Thus, a separation is introduced between the cellular and electrical interface, with consequences on the resolution of signal, particularly important for low, synaptic, currents. Diamond is a material investigated as a possible interface material for neurons: it is biologically inert, it does not induce an immune response when implanted[1],[2] and it has been shown to be supportive for neuronal growth and differentiation[3],[4]. Furthermore, diamond, which is insulating when pure, can be made semiconductive by doping with electron acceptors or donors, one example being boron. We propose here a MEA which is fully biocompatible and for which the insulating and conductive parts are made from the same material: diamond. Material and Methods: Diamond films can be produced relatively inexpensively by the method of chemical vapour deposition. In this work, a thin (5 µm) film of conductive boron-doped diamond was deposited onto a synthetic pure diamond substrate. Conductive diamond electrodes were then revealed by selective laser etching of the boron-doped diamond layer. Human pluripotent stem cells were then differentiated onto diamond substrates, using a specifically developed protocol[5]. After 2-4 months, when these cells had formed mature neurons, the interaction with the diamond substrate was assessed. Results and Discussion: Neurons differentiated in vitro, from human pluripotent cells, can be maintained on our diamond substrates for many weeks without the loss of viability or function. No difference was observed in the supportive properties of boron-doped diamond versus diamond. Scanning Electron Microscopy revealed that the neurons interacted intimately with the substrate, both at the cell body and neurite level. This study represents a step towards the production of a fully biocompatible single material MEA for the in vitro study of neuronal network activity. Furthermore, we provide a platform for the investigation of artificial human neuronal networks, with the aim of challenging the “animal model” supremacy, which has dominated the neuronal electrophysiology studies for decades. Conclusion: We present here a novel diamond MEA for optimal neuronal electrical recording. We significantly increased the time cells can be maintained in culture, a fundamental prerequisite for the study of long-term neuronal plasticity. Furthermore, the neurons used are derived form human pluripotent cells, which can be sourced from patients and thus, amenable to targeted drug screening studies. Dr. James Smith (School of Chemistry) for outstanding technical support; Dr. Tilo Kunath (University of Edinburgh) for the kind gift of NAS2 hIPS cell line and advice; This research was supported by EPSRC grant numberP: EP/K002503/1

SPM probe-assisted surface nanostructuring of boron-doped diamond

Surface modification of conductive boron-doped diamond has been conducted using the electrical field of the probe of a scanning probe microscope (SPM) at varying relative humidity (RH) of the ambient environment. It has been found that, under the action of positive polarity pulses applied to the sample via a grounded SPM probe, the sample material undergoes modification. The modification pattern depends on atmospheric RH: low (up to 32%) and high humidity values (above 35%) lead to the formation of cavities and protrusions, respectively. It has been found that the resulting protrusions exhibit temporary instability; that is, a protrusion is partially transformed into an array of nanoobjects. The mechanism of modification of boron-doped diamond–local anodic oxidation–has been discussed.

Electrochemical oxidation of amoxicillin in its pharmaceutical formulation at boron doped diamond (BDD) electrode

In this work, voltammetric andelectrolysis experiments have been carried out on a conductive boron dopeddiamond (BDD) electrode in solution containing amoxicillin in itspharmaceutical formulation. The physical characterization of the BDD surface byscanning electron microscopy (SEM) reveals a polycrystalline structure withgrain sizes ranging between 0.3 and 0.6 µm. With Raman spectroscopy, BDDsurface is composed of diamons (Csp3) type carbon (Csp3)and graphitic type carbon (Csp2). The electrochemical characterization of the BDD electrode in sulfuric acid electrolyte showed a wide potential window worthing 2.74 V. The oxidation of Amoxicillin showed an irreversible anodic wave on the voltammogram in the domain of water stability indicating a direct oxidation of amoxicillin at BDD surface. The treatment of Amoxicillin in the synthetic wastewaters under various constant current densities 20, 50, 100, 135 mA cm-2 on BDD showed that Amoxicillin is highly reducedunder 100 mA cm-2 reaching 92% of the Chemical Oxygen Demand (COD)removal after 5 h of electrolysis. Investigation performed in perchloric acidas supporting electrolyte led to 87% of COD removal after 5 h of electrolysis.Mineralization of amoxicillin occurs on BDD and the chemical oxygen demandremoval was higher in sulfuric acid than in perchloric acid owing to theinvolvement of the in-situ formed persulfate and perchlorate to the degradation process mainly in the bulkof the solution. The instantaneous current efficiency (ICE) presents anexponential decay indicating that the process was limited by diffusion. Thespecific energy consumed after 5h of the amoxicillin electrolysis was 0.096 kWh COD-1and 0.035 kWh COD-1 in sulfuric acid and in perchloric acidrespectively.

Thermally stable, electrically conductive diamond material prepared by high-pressure, high-temperature processing of a graphite + boron carbide mixture

An electrically conductive boron-doped diamond material with high thermal stability and good mechanical properties has been synthesized at high pressures from powder mixtures of graphite and boron carbide. Specific microstructure and high elastic moduli of samples obtained indicate the formation of polycrystalline diamond matrix in the material. The unique combination of physicochemical properties offered by heavily boron-doped diamond can extend its application area as an electrostructural material capable of operating in aggressive media.

Formation of Highly Conductive Boron-Doped Diamond on TiO2 Nanotubes Composite for Supercapacitor or Energy Storage Devices

In the present paper, we report the phenomena of the formation of the novel composite nanostructures based on TiO2 nanotubes (NTs) over-grown by thin boron-doped diamond (BDD) film produced in Microwave Plasma Enhanced Chemical Vapor Deposition (PE MWCVD). The TiO2 nanotube array overgrown by boron-doped diamond immersed in 0.1 M NaNO3 can deliver high specific capacitance of 7.46 mF cm−2. The composite electrodes were characterized by scanning electron microscopy (SEM), Raman spectroscopy, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques. The depth-resolved investigations reveal that the primary anatase structure of TiO2 NTs was partially transformed into Ti2O3 and non-stoichiometric TiC fractions. The explanation for this effect is the decomposing of TiO2 NTs in the presence of activated hydrogen and carbon in the plasma leading to enhanced dehydration of NTs and carbon bonding originating from dissociated methane. This phenomena description fits also to processes demonstrated at hydrogenated TiO2 (H-TiO2) nanotube arrays used as electrode material for supercapacitors. Nevertheless, the increase of electrochemical performance can be attributed to several reasons: (1) the unique morphology of titania nanotubes and columnar BDD with intergrain defects and valley increasing specific area of electrode and (2) presence of TiC and Ti2O3 fractions introducing additional capacitance.

Boron-doped ultrananocrystalline diamond synthesized with an H-rich/Ar-lean gas system

This paper reports the recent development and applications of conductive boron-doped ultrananocrystalline diamond (BD-UNCD). The authors have determined that BD-UNCD can be synthesized with an H-rich gaseous chemistry and a high CH4/H2 ratio, which is opposite to previously reported methods with Ar-rich or H-rich gas compositions but utilizing very low CH4/H2 ratios. The BD-UNCD reported here has a resistivity as low as 0.01ohmcm, with low roughness (<10nm) and a wide deposition temperature range (450–850°C). The properties of this BD-UNCD were studied systematically using resistivity characterization, scanning and transmission electron microscopy, Raman spectroscopy, and roughness measurements. Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy confirms that up to 97% of the UNCD is deposited as sp3 carbon. These various measurements also reveal additional special properties for this material, such as an “M” shape Raman signature, line-granular nano-cluster texture and high CH bond surface content. A hypothesis is provided to explain why this new deposition strategy, with H-rich/Ar-lean gas chemistry and a high CH4/H2 ratio, is able to produce high sp3-content and/or heavily doped UNCD. In addition, a few emerging applications of BD-UNCD in the field of atomic force microscopy, electrochemistry and biosensing are reviewed here.

Characterization of Optical and Electrical Properties of Transparent Conductive Boron-Doped Diamond thin Films Grown on Fused Silica

Abstract A conductive boron-doped diamond (BDD) grown on a fused silica/quartz has been investigated. Diamond thin films were deposited by the microwave plasma enhanced chemical vapor deposition (MW PECVD). The main parameters of the BDD synthesis, i.e. the methane admixture and the substrate temperature were investigated in detail. Preliminary studies of optical properties were performed to qualify an optimal CVD synthesis and film parameters for optical sensing applications. The SEM micro-images showed the homogenous, continuous and polycrystalline surface morphology; the mean grain size was within the range of 100-250 nm. The fabricated conductive boron-doped diamond thin films displayed the resistivity below 500 mOhm cm-1 and the transmittance over 50% in the VIS-NIR wavelength range. The studies of optical constants were performed using the spectroscopic ellipsometry for the wavelength range between 260 and 820 nm. A detailed error analysis of the ellipsometric system and optical modelling estimation has been provided. The refractive index values at the 550 nm wavelength were high and varied between 2.24 and 2.35 depending on the percentage content of methane and the temperature of deposition.

Microstructure and tribological properties of cubic boron nitride films on Si3N4 inserts via boron-doped diamond buffer layers

Cubic boron nitride (cBN) coatings were deposited on silicon nitride (Si3N4) cutting inserts through conductive boron-doped diamond (BDD) buffer layers in an electron cyclotron resonance microwave plasma chemical vapor deposition (ECR MPCVD) system. The adhesion and crystallinity of cBN coatings were systematically characterized, and the influence of doping level of BDD on the phase composition and microstructure of the cBN coatings were studied. The nano-indentation tests showed that the hardness and elastic modulus of the obtained cBN coatings were 78GPa and 732GPa, respectively. The tribological properties of the cBN coatings were evaluated by using a ball-on-disc tribometer with Si3N4 as the counterpart. The coefficient of the friction and the wear rate of the cBN coatings were estimated to be about 0.17 and 4.1×10−7mm3/Nm, respectively, which are remarkably lower than those of titanium aluminum nitride (TiAlN) coatings widely used in machining ferrous metal. The results suggest that cBN/BDD coated Si3N4 inserts may have great potentials for advanced materials machining.

Porous boron-doped diamond electrodes fabricated via two-step thermal treatment

A two-step thermal treatment method was developed for the fabrication of porous conductive boron-doped diamond (BDD) electrodes. The first step involved graphitization of the BDD thin film surface to form a fine microstructure by heating in an argon atmosphere at 1000°C. The second step was removal of the graphitic components by oxidation in air at 425°C. The heat treatment resulted in the formation of dense pores with several tens to several hundred nanometer sizes or smaller on the BDD surface. The pore formation mechanism was discussed by microscopic observation of the (111) and (100) crystal facets on the treated BDD surface. The porous BDD electrode exhibited a double-layer capacitance (Cdl) of ca. 140μFcm−2, which was estimated from cyclic voltammetry (CV) and galvanostatic measurements in an aqueous electrolyte. This Cdl value was approximately 40 times larger than that for the as-deposited BDD electrode, while the potential window remained wide at ca. 3V.

Ultra-thin nanocrystalline diamond membranes as pressure sensors for harsh environments

Glass and diamond are suitable materials for harsh environments. Here, a procedure for fabricating ultra-thin nanocrystalline diamond membranes on glass, acting as an electrically insulating substrate, is presented. In order to investigate the pressure sensing properties of such membranes, a circular, highly conductive boron-doped nanocrystalline diamond membrane with a resistivity of 38 mΩ cm, a thickness of 150 nm, and a diameter of 555 μm is fabricated in the middle of a Hall bar structure. During the application of a positive differential pressure under the membrane (0–0.7 bar), four point piezoresistive effect measurements are performed. From these measurements, it can be concluded that the resistance response of the membrane, as a function of differential pressure, is highly linear and sensitive.

Development of Conductive Boron-Doped Diamond Electrode: A microscopic, Spectroscopic, and Voltammetric Study.

Building on diamond characteristics such as hardness, chemical inertness and low electron emission threshold voltage, the current microscopic, spectroscopic and voltammetric investigations are directed towards improving the properties of electrode coating materials for their future use in clinical studies of deep brain stimulation via fast-scan cyclic voltammetry (FSCV). In this study we combine the capabilities of confocal Raman mapping in providing detailed and accurate analysis of local distributions of material constituents in a series of boron-doped polycrystalline diamond films grown by chemical vapor deposition, with information from the more conventional techniques of scanning electron microscopy (SEM) and infrared absorption spectroscopy. Although SEM images show a uniform distribution of film crystallites, they have the limitation of being unable to differentiate the distribution of boron in the diamond. Values of 1018–1021 atoms/cm3 of boron content have been estimated from the absorption coefficient of the 1290 cm−1 infrared absorption band and from the 500 cm−1 Raman vibration. The observed accumulation of boron atoms and carbon sp2 impurities at the grain boundaries suggests that very high doping levels do not necessarily contribute to improvement of the material’s conductivity, corroborating with voltammetric data. FSCV results also indicate an enhanced stability of analyte detection.