Synthetic Boron-doped Diamond Research Articles

Laser-Induced Luminescence of Boron-Doped Synthetic Diamond at Various Laser Pulse Durations

Laser-Induced Luminescence of Boron-Doped Synthetic Diamond at Various Laser Pulse Durations

Compacts of Boron-Doped Synthetic Diamond: Acceleration of Cathodic Reactions by Plasma-Assisted and Electrochemical Treatment of the Electrodes

Compacts of Boron-Doped Synthetic Diamond: Acceleration of Cathodic Reactions by Plasma-Assisted and Electrochemical Treatment of the Electrodes

Laser-induced luminescence of boron-doped synthetic diamond at various laser pulse durations

Excitation of type IIb synthetic diamond by ultrashort laser pulses in the visible range causes broadband luminescence in the UV visible range; the observed luminescence band can be attributed to the A band characteristic of diamonds. The photoluminescence spectra were obtained at different laser pulse durations (0.3-6.2 ps) depending on the pulse energy. A nonlinear dependence of the luminescence yield on the intensity of ultrashort pulses is established. Keywords: broadband luminescence, boron doped diamond, two-photon luminescence, A-band.

Effect of plasma-assisted electrochemical treatment of the boron-doped synthetic diamond compact electrodes on the oxygen electroreduction kinetics

The effect of plasma electrochemical activation of boron-doped diamond compact electrodes on the oxygen electroreduction reaction kinetics is studied. The conducting compact electrodes are prepared via graphite-to-diamond conversion in C–B growth system at high pressure and high temperature. The diamond compact electrode surface was modified in Na2SO4 aqueous solution by exposition to cathodic–anodic electrolytic plasma produced by the application of voltage pulses with amplitude up to 300 V. The cathodic–anodic plasma alone proved to produce but negligible catalytic effect with respect to the oxygen reduction reaction. However, on the cathodic reduction of thus treated electrode, it acquired significant electrocatalytical activity manifested itself in the predominant O2-to-H2O reduction by a four-electron pathway. At the same time, the cathodic treatment of the plasma-modified electrodes has no real impact on the rate constant of electron transfer in the “fast” [Ru(NH3)6]2+/3+ and [Fe(CN)6]4–/3– redox systems. The observed electrocatalytical effect with respect to the oxygen reduction reaction is assumed to be caused by the quinone groups formation at the boron-doped diamond electrode surface under the combined action of cathodic–anodic plasma and cathodic polarization, these groups being active centers for the four-electron oxygen reduction.

The compacts of boron-doped synthetic diamond: Methods for the increasing of their electrochemical activity

Conducting diamond-compact electrode materials are obtained by graphite transformation to diamond at high pressure and high temperature (8–9 GPa, ~ 2500 К) in two- and three-component B4C–C (graphite), Pt–C, and Pt–C–B growth systems; their physical and electrochemical properties are studied. Results of voltametric studies are in good agreement with the electrochemical impedance spectroscopy data obtained in f-sweep and E-sweep modes. The compacts’ electroactivity can be improved in two ways: either extremely heavy doping with boron or adding with catalytically active metal, platinum. The boron content reached in the diamond compacts is as high as ~ 4 at %. The obtained compacts showed the highest electroactivity of all diamond, diamond-based, and diamond-like materials we have studied (by example of the reaction of anodic chlorine evolution from KCl solution). In compliance with the earlier found general trend for all studied diamond, diamond-based, and diamond-like materials, the increase in the material’s electroactivity occurs with the increasing of the compact doping level. The diamond electrode added with Pt in the Pt–C growth system behaves in the chloride-ion anodic oxidation reaction like a purely platinum one, with due allowance for the platinum actual amount at the electrode surface. The combined platinum and boron adding to the diamond grown in the Pt–C–B system produced electrodes electroactive with respect to the chloride-ion anodic oxidation reaction; the electroactivity increased with the increasing of the platinum content at the electrode surface.

The Compacts of Boron-Doped Synthetic Diamond: Electrochemical Properties of Samples with Extremely High Doping Level

Compacts of boron-doped synthetic diamond with extremely high doping level are obtained at a pressure of 8–9 GPa and temperature about 2500 K from graphite-boron carbide (5 or 7%) mixtures. The boron content in the diamond estimated by the diamond lattice parameter (0.3573–0.3575 and 0.3576–0.3578 nm, respectively) is about 1–3% and 3–4%, respectively. Thus obtained compacts showed the highest electroactivity of all known diamond, diamond-based, and diamond-like materials (by example of anodic chlorine evolution reaction). In compliance with the earlier found general trend for all known diamond, diamond-based, and diamond-like materials, with the increasing of the compact doping level some increase in the material’s electroactivity also occurs. The heavily boron-doped diamond compacts can be used as indicator electrodes in the electroanalytical determination of ethylenediaminetetraacetic acid in aqueous solutions (by its electrooxidation current).

Low Temperature Thermal Conductivity of Heavily Boron-Doped Synthetic Diamond: Influence of Boron-Related Structure Defects

Thermal conductivity of single-crystal boron-doped diamonds (BDD) with ∼2 × 1019 cm−3 (∼120 ppm) and 5 × 1019 cm−3 (∼300 ppm) boron content was studied by a steady-state method in a temperature range of 20–400 K. The obtained data were analyzed within Callaway model framework. The values of dislocation density obtained from best fit of experimental data and from density of etch pits measuring were compared. Their discrepancy suggests presence of some other boron-related defects in crystal lattice.

Electrical Properties of High-Quality Synthetic Boron-Doped Diamond Single Crystals and Schottky Barrier Diodes on Their Basis

The temperature dependences of the specific resistance and Hall coefficient of high-quality synthetic boron-doped diamond single crystals grown via a high-pressure high-temperature method are studied. The concentration of acceptors in the (001) cut plates was varied in a range of 2 × 1015–3 × 1017 cm–3 by varying the concentration of boron in the growth mixture (0.0004–0.04 at %). Thin rectangular plates with the uniform concentration of boron and free from extended structural defects are cut out by a laser after the X-ray topography and mapping of UV luminescence. The concentrations of donors and acceptors in the samples are calculated from the data of the Hall effect and capacitance–voltage characteristics. The obtained results correlate with the concentration of boron in the growth mixture. The minimum compensation ratio of acceptors with donors (below 1%) is observed in the crystals grown with the concentration of boron in the growth mixture of 0.002 at %. The ratio increases when the amount of boron is increased or decreased. The samples grown at such a concentration of boron have the maximum mobility of charge carriers (2200 cm2/(V s) at T = 300 K and 7200 cm2/(V s) at T = 180 K). The phonon scattering of holes dominates throughout the range of temperatures (180–800 K), while the scattering by point defects (neutral and ionized atoms of the impurity) is insignificant. The diamond crystals which are grown from a mixture containing 0.0005–0.002 at % boron and have perfect quality and a lattice mechanism of scattering can be considered as a reference semiconductor.

Compacts of Boron-Doped Synthetic Diamond: Lowering of Synthesis Temperature and Its Effect on the Doping Level and Electrochemical Behavior

Substituting of metal (Co, Ni) borides for boron carbide in the boron carbide–graphite growth system for the process of diamond growth in the region of diamond thermodynamic stability allowed lowering the synthesis temperature for the electrodes of this new electrode material―boron-doped diamond compacts―significantly (by ~1000°C) without any deterioration of their electrochemical properties. On the other hand, using of amorphous boron with finer grain as compared with the boron carbide, mixed with graphite, results in a marked increase of the electrodes’ electrochemical efficiency, due to increase in their roughness after the chemical removing of boron-containing inclusions from their surfaces. Thus obtained compact electrodes have wide potential window and low background current in supporting electrolytes, they are well reproducible. Special features of their electrochemical impedance spectroscopy are similar to those of the recently studied compacts synthesized on the basis of boron carbide.

Bosonic Anomalies in Boron-Doped Polycrystalline Diamond

Allotropes of carbon are promising materials for the next generation of electronics. In particular, boron-doped synthetic diamond, which is typically highly disordered, provides a powerful stage for studying superconductivity in a three-dimensional granular system. The authors find that, even deep in the metallic regime, heavily doped granular diamond still shows pronounced quantum effects in its transport properties, which needs to be accounted for---and could be exploited---in diamond-based SQUIDs and nanodevices.

Electrochemical behavior of new electrode material: Compact of boron-doped synthetic diamond

Electrochemical properties of new electrode material—compact of boron-doped synthetic diamond—is studied for the first time. Cylindrical samples 3.5–4 mm in diameter and 2.5 mm in height were obtained by thermobaric processing of graphite–boron carbide mixtures in the diamond thermodynamic stability region (at the pressure of 8–9 GPa and temperature of ~2500 K). Their electrode behavior is studied using cyclic voltammetry and electrochemical impedance spectroscopy techniques. The cyclic voltammograms of the compact samples showed that their electrode characteristics are similar to those of traditional thin-film diamond electrodes obtained by the chemical vapor deposition (CVD) technique. In particular, they demonstrate rather wide potential window, low background current in indifferent electrolytes, and good reproducibility. It can be concluded that the diamond compacts practically are not inferior to the thin-film CVD-diamond electrodes and can serve as indicator electrodes, e.g., in electroanalysis. At the same time their compact form may be a convenience in the designing of electrolyzers and other electrochemical devices.

Evaluation of the efficiency of monopolar and bipolar BDD electrodes for electrochemical oxidation of anthraquinone textile synthetic effluent for reuse

The efficiency of the electrochemical degradation of synthetic wastewater containing an anthraquinone dye has been comparatively studied in two electrolytic cells with a synthetic boron-doped diamond (Si/BDD) as an anode. The first is an individual cell (Cell 1) with monopolar electrode BDD and the second (Cell 2) has two bipolar electrodes BDD self-polarized. The bulk electrolysis was performed at the same initial operating conditions in order to quantify the influence of the initial pH and current density on dye discoloration and global mineralization removal. The current efficiency and the consumption energy were also evaluated. When the same solutions have been comparatively treated with the two cells, a quite good mineralization is found in Cell 2. This result supposed more fraction of the applied current is used for the electrocombustion reaction on Cell 2 if compared to Cell 1 and small amount rest for the side reaction of oxygen evolution. The HPLC analyses confirmed this hypothesis and showed that the concentration trend of intermediates (sulfanilic acid, phthalate acid and salicylic acid) with electrolysis time was different on two cells. Phototoxicity tests show that the electrochemical oxidation with BDD electrodes could be useful as a pretreatment technique for reducing hazardous wastewater toxicity.

Complementary Mechanism Model for the Electrochemical Mineralization

Comninellis and his research group have elucidated a theoretical model that permits us to predict the chemical oxygen demand (COD) and instantaneous current efficiency (ICE), during the electrochemical oxidation of organic pollutants on a synthetic boron-doped diamond thin film electrodes (BDD) in a batch recirculation system under galvanostatic conditions. Several studies highlight the good correlation between theoretical predictions and empirical data, but it was noted that some data, from some experiments, were not in agreement with the theoretical model, since it achieved efficiencies above 100%. Recently, few studies have reported phenomena that occur in electrocatalytic systems which were not deducted in the first models. Thus, we emphasize that the mineralization of organic compounds on BDD electrodes involves not only hydroxyl radicals but also the molecular oxygen present in air, in saturated aqueous solutions or strong oxidants generated from simultaneous reactions. Therefore, this highlights summarizes the results reported by other electrochemists until nowadays to understand the electrochemical oxidation mechanisms. Keywords: Dissolved oxygen, Hydroxyl radicals, Complementary mechanism model, Strong oxidant species, electrochemical oxidation, galvanostatic, organic pollutants, anode, hydroxyl radicals, biodegradable

Kinetic experiments of electrochemical oxidation of iohexol on BDD electrodes for wastewater treatment

Electrolysis of iohexol, an iodinated X-ray contrast medium, on synthetic boron-doped diamond (BDD) thin film electrodes was investigated for the first time. Kinetic experiments of electrochemical oxidation resulted in complete elimination of iohexol. Data from the kinetic experiments were compared against estimates by the kinetic model proposed previously by Comninellis et al. Excellent agreement between the experimental results and the kinetic model was observed. The results suggest that electrolysis on BDD electrodes is a promising method for the elimination of iohexol from wastewater.

Electrochemical treatment of wastewater containing chlorophenols using boron-doped diamond film electrodes

The electrochemical treatment of wastewater containing chlorophenols (2-monochlorophenol, 4-monochlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol) was carried out experimentally with synthetic boron-doped diamond (BDD) thin film electrodes. Current vs time curves under different cell voltages were measured. Removal rate of COD, instant current efficiency (ICE) and energy consumption were investigated under different current densities. The influence of supporting media is reported, which plays an important role in determining the global oxidation rate. The oxidative chloride is stronger than peroxodisulphate. The electrochemical characteristics of boron-doped diamond electrodes were investigated in comparison with active coating Ti substrate anode (ACT). The experimental results show that BDD is markedly superior to ACT due to its different absorption properties.

Electrochemical Treatment of Wastewater Containing Chlorophenols Using Boron-Doped Diamond Film Electrodes

The electrochemical treatment of wastewater containing 2, 4, 6-trichlorophenol has been carried out experimentally with synthetic boron-doped diamond (BDD) thin film electrodes. Removal rate of COD, instant current efficiency (ICE) and energy consumption were investigated under different current density. The influence of supporting media is reported, which plays an important role in determining the global oxidation rate. The oxidative chloride is stronger than peroxodisulphate. The electrochemical characteristics of boron-doped diamond electrodes were investigated in comparison with active coating Ti substrate anode (ACT). The experimental results show that BDD is markedly superior to ACT due to its different absorption properties.

High-pressure, high-temperature processing of low-nitrogen boron-doped diamond

We have studied high-pressure, high-temperature processing (7.0 GPa, 2000–2100°C) of low-nitrogen boron-doped synthetic diamonds grown in the Fe-Ni-C system (5.5–6.0 GPa, 1350–1450°C) with boron and titanium additions. The results indicate that, during the growth of low-nitrogen boron-doped diamonds, there is a competition between different acceptors (boron and nickel). The system of point defects and their distribution over the crystal are not influenced by the processing; the uniformity of coloration in natural diamonds is governed by the prevalence of octahedron growth sectors.

Evidence for a hard gap and Wigner lattice in heavily boron-doped synthetic diamond

We have measured low frequency generation-recombination noise (g-r noise) spectra of a heavily boron-doped diamond crystal over the temperature range $20--300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The experimental results show that there are two peaks in the g-r noise spectrum at $120\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and $67\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, respectively. The $120\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ peak corresponds to experimental evidence for existence of a hard gap having width of $10.4\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$. We interpret the $67\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ peak as evidence for Wigner lattice formation whose gap width is $5.8\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$.

Optical centers introduced in boron-doped synthetic diamond by near-threshold electron irradiation

Near-threshold irradiation of B-doped synthetic diamonds has been performed using a transmission electron microscope operated at 200 kV. Both chemical vapor deposited and high-pressure high-temperature synthesized samples have been studied. The B levels were in the range 1017–1019 cm−3. After irradiation the samples were studied by low temperature (∼7 K) photoluminescence spectroscopy using various excitation wavelengths. A number of characteristic optical centers have been observed in the spectral range 500–800 nm and these centers are reviewed. Details of the properties of the optical centers have been investigated and the results are summarized. In particular, two zero-phonon lines (ZPLs) at 636 and 666 nm, formed in boron-doped diamond materials after near displacement-threshold electron radiation damage, were found to be related. The nature of this relationship is studied by laser power dependence (at different wavelengths) of their intensities over a wide temperature range. The results are interpreted in terms of a three-level model for a single optical center that involves a dipole-forbidden excited state of lower energy and a dipole-allowed state of 90 meV higher energy. Similar behavior of a further pair of ZPLs at 650 and 668 nm also formed in these materials is discussed. The spatial distribution of centers and their alteration by ultraviolet excitation was used to investigate the nature of the 636 and 666 nm centers.

Platinum particles deposited on synthetic boron-doped diamond surfaces. Application to methanol oxidation

Two methods have been used for the deposition of Pt particles on synthetic boron-doped diamond (BDD) surfaces: chemical deposition and electrodeposition under potentiostatic conditions. However, electrodeposition leads much higher platinum dispersion than chemical deposition. The mechanism of nucleation and growing of the electrodeposited platinum was investigated by means of chronoamperometric studies in acid medium. The electrodeposition on diamond surfaces shows a mechanism of progressive nucleation as deduced from the chronoamperometric studies in acid medium. The stability of the deposited platinum is very low and the platinum particle are dissolved/detached by cycling. The modified BDD electrodes by deposition of platinum have been tested for the oxidation of methanol, showing that multi-step deposition results in higher values of surface and mass activities for methanol oxidation than one-step deposition process.