B-doped Diamond Research Articles

Novel BDD-loaded bimetallic phosphide electrodes enable interesting bifunctional seawater electrolysis

The direct electrolysis of seawater for the production of green hydrogen energy is an economically attractive approach. However, this technique confronts technical problems because to the oxygen evolution reaction (OER) weak stability and inadequate selectivity due to competition with the chlorine evolution process. This work focuses on improving the stability of the electrode and electrolysis efficiency. The phosphating NiCoP active layer with 3D porous morphology was created by electrodeposition on the B-doped diamond (BDD) as an electrode inspired by the bifunctional catalysis strategy. The successfully constructed unique cube-on-nanosheets structure in the NiCoP active layer enables the electrode to exhibit excellent electrocatalytic performance. The porous NiCoP/BDD (Por-NiCoP/BDD) electrodes showed good catalytic activity in alkaline-simulated seawater with the OER and hydrogen evolution reaction (HER) overpotentials of 400 and 261 mV, respectively, at a current density of 100 mA cm−2. More importantly, the electrode exhibits interesting stability of the catalytic performance and structural in alkaline-simulated seawater electrolysis, with the current density decaying by only 1.52 % and 4.06 % after OER and HER processes for 50 h, respectively. This work expands the valuable application scenarios of BDD electrode and provides novel ideas for the development of seawater electrolysis.

Controlled boron content in lightly B-doped single crystal diamond films by variation of methane concentration

Obtaining desirable electrical properties from B-doped single crystal diamond (SCD) films hinges on precise control of boron incorporation into the crystal lattice structure. In this study, the impact of methane concentration during plasma deposition on boron incorporation of lightly B-doped SCD films is investigated. SCD layers are grown successively by microwave plasma enhanced chemical vapor deposition (CVD) at different methane-to-hydrogen concentrations (1%, 2%, and 3%), with residual boron atoms present in the CVD reactor. An increase in methane concentration leads to surface defects such as unepitaxial crystallites and pyramidal hillocks. The charge carrier mobility, electrical conductivity, and boron content of samples are evaluated and discussed. The temperature-dependent mobility is analyzed through theoretical modeling, revealing dominant scattering mechanisms at different temperatures. At 300 K, the maximum hole mobility reached 1200 cm2/V·s for the 1% methane concentration sample, transitioning to hopping conduction at lower temperatures. An increase in boron-doping level with rising methane concentration is detected by Fourier transform infrared spectroscopy, cathodoluminescence spectroscopy, Hall effect, and X-ray photoelectron spectroscopy measurements. These findings highlight the potential of methane concentration in plasma feedgas to control boron concentration in CVD diamond and open avenues for crafting efficient high-power electronic applications using p-type SCD films.

CO2 reduction by visible-light-induced photoemission from heavily N-doped diamond nano-layer

While realizing carbon neutrality is an urgent priority, diamond materials with negative electron affinity (NEA) are considered productive sources of solvated electrons, which can help efficiently reduce CO2 in potential green chemistry applications. Recently, CO2 was photocatalytically reduced into CO by solvated electrons using commonly used H-terminated diamond with NEA under deep ultraviolet light irradiation. However, CO2 has never been reduced under visible-light irradiation, would be more practicable in the living environment, because of the wide band gap afforded by diamonds. In this study, electrons excited by visible light in heavily N-doped surface nano-layer of diamond platelets are emitted through the H-terminated surface with NEA toward a CO2-saturated aqueous solution, successfully reducing CO2 into CO. To this end, the B-doped p-type diamond films are grown by chemical vapor deposition on initial seed layers of detonation-synthesized nanodiamonds (DNDs). This approach allows incorporating the abundantly available N atoms in the DNDs into the surface nano-layer on the diamond platelets, resulting in the formation of an electron-excitation nano-layer having ≥1021 N atoms/cm3 and associated defects absorbing visible light. These results pave the way toward a new, energy-efficient technology for CO2 reduction with strong implications for achieving a carbon-negative society.

Synthetic pathway of shallow n-type donor: Theoretical study of Li and B co-doped diamonds

To find potential n-type diamonds with shallow donor energy levels and low formation energies, the thermodynamic and electronic properties of Lithium-Boron (LiB) co-doped diamonds have been investigated using density functional theory (DFT) and hybrid density functional theory (HSE06). The structure, formation energy, electronic property and the potential synthesis pathway are analyzed. The results of the single Li defect is not a suitable candidate for a shallow n-type donor, as it distorts the diamond lattice and forms clusters, in agreement with previous work. The calculated ionization energy of Lii2-B defect (0.29 eV) and the impurities formation energy (0.196 eV) is much lower than that of Lii defect. It suggests that the introduction of B helps improve the solubility of Li in diamond. Further structural analysis has shown that the incorporation of B atoms inhibits the diffusion of Li atoms and simultaneously reduces the internal strain in the diamond, resulting in a significant reduction in the distance between the two lithium atoms from 2.061 Å to 1.629 Å. At last, a non-molecular synthesis pathway of Lii2-B co-doped diamond is proposed via prior generation of B-doped diamond at which Li atom is mobile which indicates there is a potential window-of-opportunity to prepare Lii2-B co-doped diamond to achieve n-type diamond.

Optical and acoustic phonons in turbostratic and cubic boron nitride thin films on diamond substrates

We report an investigation of the bulk optical, bulk acoustic, and surface acoustic phonons in thin films of turbostratic boron nitride (t-BN) and cubic boron nitride (c-BN) grown on B-doped polycrystalline and single-crystalline diamond (001) and (111) substrates. The characteristics of different types of phonons were studied using Raman and Brillouin-Mandelstam light scattering spectroscopies. The atomic structure of the films was determined using high-resolution transmission electron microscopy (HRTEM) and correlated with the Raman and Brillouin-Mandelstam spectroscopy data. The HRTEM analysis revealed that the cubic boron nitride thin films consisted of a mixture of c-BN and t-BN phases, with c-BN being the dominant phase. It was found that while visible Raman spectroscopy provided information for characterizing the t-BN phase, it faced challenges in differentiating the c-BN phase either due to the presence of high-density defects or the overlapping of the Raman features with those from the B-doped diamond substrates. In contrast, Brillouin-Mandelstam spectroscopy clearly distinguishes the bulk longitudinal and surface acoustic phonons of the c-BN thin films grown on diamond substrates. Additionally, the angle-dependent surface Brillouin-Mandelstam scattering data show the peaks associated with the Rayleigh surface acoustic waves, which have higher phase velocities in c-BN films on diamond (111) substrates. These findings provide valuable insights into the phonon characteristics of the c-BN and diamond interfaces and have important implications for the thermal management of electronic devices based on ultra-wide-band-gap materials.

Thermoelectric properties of B-doped nanostructured bulk diamond with lowered thermal conductivity

Diamond exhibits high wear resistance and high chemical resistance. If diamond exhibits high thermoelectric performance, the thermoelectric application will be expanded for various situations such as the use of friction heat on turbines. However, bulk diamond exhibits low electrical conductivity and high thermal conductivity, leading to the low thermoelectric performance. In this study, to solve the above problem, we propose a strategy of heavy impurity doping in nanostructured bulk diamond which brings two things: (1) higher thermoelectric power factor, and (2) phonon scattering enhancement at impurities and nanostructure interfaces reducing the thermal conductivity drastically. We investigate the thermoelectric properties of heavily B-doped nanostructured bulk diamonds prepared by direct conversion sintering under ultra-high pressure and temperature using B-doped graphite as a starting material. This nanostructured bulk diamond exhibited high electrical conductivity due to heavy B doping, resulting in high power factor of 4 μWcm−1 K−2 at 1050 K. Furthermore, we found that this nanostructured bulk diamond exhibited drastic thermal conductivity reduction, resulting in quite low thermal conductivity among bulk diamond ever reported. This comes from phonon scattering both at nanostructure interfaces and by substitutional B atoms. From these results, the present study would be informative for expanding thermoelectric application to various situations such as the use of friction heat.

Research and Application Progress of Boron-doped Diamond Films

Thanks to its unique structure, diamond has many excellent properties, such as high hardness, low birefringence, high thermal conductivity, good chemical stability, etc., but pure diamond has extremely high resistivity (up to 1012 Ω∙m ), which is an insulator, so it is usually doped to expand the application of diamond in the electrochemical field. B atoms have a very small radius, which is an ideal material for doping diamond, and B-doped diamond has good electrical conductivity. In this paper, on the basis of introducing the phase composition and structure of boron-doped diamond (BDD) film, the common methods for preparing BDD film are analyzed, and the application status and prospect of its application in electrochemistry and other fields are summarized.

Insight into B S ratio model and surface atom interactions of co-doping diamond: First-principles studies

The complex co-doping structure of boron and sulfur is investigated using the density functional theory approach. Different ratio models show significant differences in electronic properties. More importantly, the interactions of boron, sulfur, and carbon atoms are studied on intrinsic/B-doped (001), (111), and (110) diamond surfaces. The most stable adsorption site, adsorption structure, and charge transfer are discussed. B atom induces a larger adsorption energy (intrinsic: −4.57 eV, −4.56 eV, and −4.00 eV; B-doped: −4.70 eV, −4.72 eV, and −4.86 eV). And a larger charge transfer between diamond and S radicals is also found. Therefore, the phenomenon that the sulfur contents in diamond increases after the introduction of boron in the experiment can be explained. Considering different crystal surfaces, larger adsorption strength is obtained from (111) and (110) surface. And different levels of strain are introduced into three different surfaces. The migration barrier of S atom is also considered. The lowest migration barrier is 0.06 eV on (111) surface, whereas the highest value is found on (001) surface (1.96 eV). B atom also benefits for the HxS radical adsorption. It can be concluded that B doping can help with S and HxS adsorption. This study can provide an explanation for the increased solubility of S on B-doped diamond.

A Review on Optoelectronical Properties of Non-Metal Oxide/Diamond-Based p-n Heterojunction.

Diamond holds promise for optoelectronic devices working in high-frequency, high-power and high-temperature environments, for example in some aspect of nuclear energetics industry processing and aerospace due to its wide bandgap (5.5 eV), ultimate thermal conductivity, high-pressure resistance, high radio frequency and high chemical stability. In the last several years, p-type B-doped diamond (BDD) has been fabricated to heterojunctions with all kinds of non-metal oxide (AlN, GaN, Si and carbon-based semiconductors) to form heterojunctions, which may be widely utilized in various optoelectronic device technology. This article discusses the application of diamond-based heterostructures and mainly writes about optoelectronic device fabrication, optoelectronic performance research, LEDs, photodetectors, and high-electron mobility transistor (HEMT) device applications based on diamond non-metal oxide (AlN, GaN, Si and carbon-based semiconductor) heterojunction. The discussion in this paper will provide a new scheme for the improvement of high-temperature diamond-based optoelectronics.

Electrochemical activation of persulfate by Al-doped blue TiO2 nanotubes for the multipath degradation of atrazine

The combination of electrolysis and persulfate activation (E/PDS) is a cost-effective method for the treatment of refractory organics. However, persulfate is difficult to be activated into radicals at the anode, resulting in insufficient electro-activation efficiency. Herein, Al doped blue TiO2 nanotube electrodes (Al-bTNT) were first employed as cost-effective anode materials to fully activate PDS to radicals. In E/PDS, the kinetic constant of atrazine removal by Al-bTNT (0.048 min−1) substantially outperformed the other anodes, including the blue TiO2 nanotube electrodes (bTNT) (0.024 min−1), Ti4O7 (0.02 min−1), and B doped diamond (BDD) anodes (0.023 min−1). The Al-bTNT-E/PDS exhibited a low energy consumption (EEO = 0.72 kWh m−3) and a high mineralization rate. Based on the results of electron paramagnetic resonance, quenching experiments, and probe experiments, we propose that atrazine degrades in the Al-bTNT-E/PDS system mainly via a novel radical pathway that involves both·OH and SO4·- and the generated SO4·- is responsible for the enhanced removal rate. The oxygen vacancies (VO) generated from interstitial Al may serve as the active sites to adsorb and dissociate the persulfate molecules based on extensive characterizations. The attempt at soil-washing wastewater disposal indicated the synergistic system possessed good potential for future practical application.

Inhomogeneity distribution of impurities in high temperature high pressure synthesized boron-doped diamond

The impurity distribution of different growth sectors in high temperature high pressure (HTHP) synthesized boron (B)-doped diamond has been investigated, after electron irradiation, at higher spatial resolution than in previous work that relied on absorption spectroscopy. Although high quantitative accuracy is claimed for absorption spectroscopy measurements, it should be borne in mind that this claim is only valid if the region studied is homogeneous, a situation that is not easily established. In this paper, micro–photoluminescence (PL) was employed to investigate the distribution of impurities in HTHP B-doped diamond, and the inhomogeneity within {100}, {111}, and {311} sectors but particularly in {311} sectors where alternations between B-rich and N-rich regions was observed together with decoration of growth horizons. It follows that it may not be reliable, as in the past, to describe a particular growth sector as enriched with a particular dopant.

Wohlleben Effect and Emergent π junctions in superconducting Boron doped Diamond thin films

Diamond is an excellent wide-bandgap electrical insulator. However, boron (B) doping is known to induce superconductivity in diamonds. We have performed electrical transport and magnetic measurements under pressure with doping concentrations of (1.4 and 2.6) × 1021 cm−3, in a temperature range 2 - 10 K and present two interesting effects in superconducting B doped diamond (BDD) thin films: (i) Wohlleben effect (paramagnetic Meissner effect, PME) and (ii) pressure-induced spin glass-like susceptibility anomaly. PME, a low field anomaly in inhomogeneous superconductors, could arise from flux trapping, flux compression, or for non-trivial reason such as emergent Josephson π junctions. The joint occurrence of PME and spin glass type anomalies points to the possible emergence of π junctions. BDD is a disordered s-wave superconductor; and π junctions could be produced by spin-flip scattering of spin ½ moments when present at weak superconducting regions. A frustrated network of 0 and π junctions will result in a distribution of spontaneous equilibrium supercurrents, a spin glass (phase glass) state. Anderson localized spin ½ spinons embedded in a metallic fluid (two-fluid model) could create π junction by spin-flip scattering. Our findings are consistent with the presence of π junctions, invoked to explain the observation of certain resistance anomaly in BDD.

Cleaning diamond surfaces via oxygen plasma inhibits the formation of a TiC interface

TiC at the diamond‑titanium interface is known to be a stable and beneficial layer for diamond based electronic devices. However, certain cleaning steps can alter the chemical composition of this interface. One such process is oxygen plasma etching, which terminates the surface of the diamond with oxygen. Oxygen is highly reactive with titanium, forming titanium oxides. Theoretically the titanium-diamond interface can be improved through sufficient annealing after device fabrication. To test this, we investigated the interface of oxygen-terminated polycrystalline B-doped diamond and titanium via XPS in an effort to determine if oxygen would rearrange away from the diamond surface and TiC would be formed through post-deposition annealing. After annealing at temperatures up to 900 °C, it was found that TiC was not detected at any point in this experiment. Oxygen-termination, despite its de-scumming capabilities, likely inhibits the formation of TiC at the diamond surface.

Characterization of deep interface states in SiO2/B-doped diamond using the transient photocapacitance method

We fabricated a diamond metal oxide semiconductor structure with a silicon dioxide (SiO2) film as the gate dielectric on B-doped diamond grown by a high-power-density microwave-plasma chemical vapor deposition method. The SiO2/B-doped diamond interface was characterized using a transient photocapacitance technique. The concentration of B in the B-doped diamond film was estimated to be 4.0 × 1017 cm−3, based on the intensity ratio of the exciton emissions observed in the cathodoluminescence measurements at approximately 80 K. Acceptor-type defects could be observed at approximately 1.28 and 1.82 eV above the valence-band edge. The observed defect at approximately 1.82 eV above the valence-band edge is expected to be an interface state of the SiO2/B-doped diamond.

Electrochemical reduction of carbon dioxide in an aqueous solution using phosphorus-doped polycrystalline diamond electrodes

Phosphorus-doped (P-doped) polycrystalline diamond thin films were deposited on a conductive Si substrate by microwave plasma-enhanced chemical vapor deposition (MWCVD), using a liquid source containing phosphorus atoms. The thin films were then used as electrodes for the electrochemical reduction of carbon dioxide (CO2) dissolved in aqueous solution. The P-doped diamond electrode exhibited approximately 1 V higher overpotential for the hydrogen evolution reaction than conventional boron-doped (B-doped) diamond electrodes in an aqueous electrolyte. A cathodic current attributed to the CO2 reduction reaction was observed at the P-doped diamond electrode in 0.2 M Na2SO4 bubbled with CO2. An analysis of the soluble products showed that the main reduction product was formic acid. We have experimentally demonstrated that P-doped diamond thin film is ideal as an electrode material for the electrochemical reduction of CO2 in aqueous solution, as it does not suffer from the interference of hydrogen evolution by water electrolysis.

Carbon Nanostructures, Nanolayers, and Their Composites.

The versatility of the arrangement of C atoms with the formation of different allotropes and phases has led to the discovery of several new structures with unique properties. Carbon nanomaterials are currently very attractive nanomaterials due to their unique physical, chemical, and biological properties. One of these is the development of superconductivity, for example, in graphite intercalated superconductors, single-walled carbon nanotubes, B-doped diamond, etc. Not only various forms of carbon materials but also carbon-related materials have aroused extraordinary theoretical and experimental interest. Hybrid carbon materials are good candidates for high current densities at low applied electric fields due to their negative electron affinity. The right combination of two different nanostructures, CNF or carbon nanotubes and nanoparticles, has led to some very interesting sensors with applications in electrochemical biosensors, biomolecules, and pharmaceutical compounds. Carbon materials have a number of unique properties. In order to increase their potential application and applicability in different industries and under different conditions, they are often combined with other types of material (most often polymers or metals). The resulting composite materials have significantly improved properties.

Long gap spark discharge ignition using a boron-doped diamond electrode

A long gap discharge offers an efficient method for achieving stable ignition in lean fuel/air mixtures, because it can reduce the heat loss to the electrodes, achieve efficient electrical energy transfer from the ignition coil to the discharge plasma, and reduce the initial flame curvature by converting the geometry of the ignition from a point to a line. However, the formation of such discharge requires increased discharge voltage to compensate for the reduction in the electric field between the electrodes, and this is not easily achieved in practice. Since the Townsend discharge criteria depend not only on the electron multiplication coefficient (α coefficient) but on the secondary electron emission (γ-process), we focused on the latter to reduce the discharge threshold voltage. In the present study, for the first time, B-doped diamond (BDD), which has a larger secondary electron emission coefficient than the metals used in conventional spark discharge ignition, was utilized as the cathode material, and its discharge and ignition characteristics were investigated. Under the same conditions, use of a BDD cathode resulted in a lower discharge threshold, greater discharge energy, less discharge energy variation, and more rapid flame development, than in the case of a metal cathode. The influence of the cathode material on discharge threshold suggests that the breakdown mechanism of ignition-coil spark discharge is based on Townsend discharge. To elucidate the effect of gap length, the temporal development of flame growth, using the same discharge energy in methane and propane mixtures, was compared between ignition with a short gap discharge with a metal cathode and long gap discharge with a BDD cathode. With a long gap discharge, only the flame growth of lean propane-air mixtures was accelerated, while no difference was observed in the case of lean methane or relatively rich propane mixtures, suggesting the effectiveness of long gap discharge ignition for mixtures with a large Lewis number, due to the small curvature of the initial flame kernel.

Photoluminescence study of N-rich B-doped diamonds grown in NiMnCo solvent before and after annealing

Incorporation of boron substantially decreases the luminescence of centers (NV−, Ni–N, and Co–N) in nitrogen-rich boron-doped diamonds before and after HPHT annealing.

Secondary electron emission properties of double-layer B-doped diamond films

B-doped double-layer diamond films were prepared by microwave plasma chemical vapor deposition. The effects of different B-doping concentrations on the crystal quality, surface morphology, surface composition and the conductivity, secondary electron emission performance of the films were investigated. It is found that the increased conductivity with increased B-doping is beneficial for secondary electron emission. However, the degraded crystal quality of diamond, increased surface sp2 carbon and the segregation of B element at surface due to increased B-doping could degrade the secondary electron emission performance of the film. So it can be considered as a competition between improved vertical conductance that tends to increase secondary electron escape depth and finally degrading surface properties as a function of B-doping. The double-layer film with a light B-doping concentration has good crystal quality and enough conductivity, which helps to obtain the best secondary electron emission performance.

Boron-dopant enhanced stability of diamane with tunable band gap

The structural, electronic, and superconducting properties of B-doped cubic and hexagonal diamane (single layer diamond) were investigated based on the first-principles methods. B atom tends to stay in the substitutional site, and the most stable configuration is the structure with vertical B–B dimer. The formation energy of B-doped diamane is lower than the counterpart of pristine diamane indicating that B dopant can facilitate the synthesis of diamane. The configurations with vertical B–B dimers are semiconductors with tunable band gaps, which decrease with the B concentration increasing due to the interaction between B–B dimers. For example, the band gap of 3.125 mol% and 6.25 mol% B-doped cubic diamane is 1.82 eV and 1.44 eV, respectively. Moreover, configurations with meta-stable B distributions are metals, which have comparable superconducting transition temperatures with B-doped diamond (~4 K).