Boron-doped Diamond Layers Research Articles

MnO2-Conductive Nanodiamond Composite Electrode for High Energy Density Aqueous Capacitor

Electric double-layer capacitors (EDLC) have the advantage of faster charge-discharge rates and superior cycle life compared to rechargeable batteries, but have the disadvantage of low energy density. In order to increase energy density of EDLCs, it is necessary to increase cell voltage and specific surface area. Another possible strategy to enhance the energy density is combination with redox-active compounds to form pseudocapacitor. We have developed boron-doped nanodiamond (BDND) as a novel electrode material for EDLC, which has a wide potential window in aqueous electrolytes, high voltage application capability, and large specific surface area. The aim of this study is to fabricate a pseudocapacitor by compositing BDND with MnO2 in order to further improve the energy density.BDND was prepared by depositing a boron-doped diamond (BDD) layer on the surface of nanodiamond particles by microwave plasma CVD followed by heat treatment in air to minimize the sp2 carbon impurities. BDND ink was prepared by mixing BDND and ethanol. The BDND ink was then applied on a glassy carbon current collector, and MnO2-BDND electrodes were prepared by electrodeposition of MnO2 on the BDND using constant potential electrolysis in 0.6 M MnSO4/0.8 M H2SO4 at +1.25 V vs. Ag/AgCl. Cyclic voltammetry (CV) in 1 M Na2SO4 was used to evaluate the electrochemical properties of the MnO2-BDND electrode.MnO2-BDND electrodes were prepared with various MnO2 deposition times of 1, 3, 5, and 15 min. It was found from the CV current density that the MnO2-BDND prepared at a deposition time of 3 min exhibited the largest capacitance of 43.5 F/g, while the capacitance of unmodified BDND electrode was 14.5 F/g. Therefore, MnO2 deposition time of 3 min was determined to be the optimum condition; the reason for the decrease in the CV current of MnO2-BDND with a deposition time of 5 and 15 min is considered to be due to excess amount of MnO2 with poor conductivity on the electrode surface. Energy density of the MnO2-BDND/1 M Na2SO4 system was calculated with a cell voltage of 1.5 V to be 21.2 Wh/kg, which was greater than that of the BDND/1 M Na2SO4 system (9.1 Wh/kg). Therefore, BDND-based high energy density aqueous capacitor is expected to be fabricated by the combination with MnO2.

(Invited) Electrolytic Application of Boron-Doped Diamond Powders

Boron-doped diamond (BDD) electrodes or diamond electrodes are known to be useful for a durable electrode for electrolysis with a high efficiency base on their wide potential window and physical and chemical stabilities. As a result of electrolysis of concentrated sulfuric acid at diamond electrode, reactive oxidizing species, such as peroxodisulfate, peroxomonosulfate, and hydrogen peroxide, can be generated at a high current efficiency. Such electrolyzed sulfuric acid exhibits strong oxidizing power, and is used for mineralization of organic compounds. Carbon fiber reinforced plastics (CFRP) are widely used because it is light in weight and corrosion resistant with high strength and stiffness. Technology for recycling carbon fibers from waste CFRP is desired because it can reduce the amount of carbon fibers disposed of in landfills as waste. When CFRP is treated with electrolyzed sulfuric acid, only the resin is completely decomposed, and nearly intact carbon fibers can be recovered. Therefore, the electrolyzed sulfuric acid method should be a promising candidate for carbon fiber recycling technology. Usually, diamond electrodes are used for the production of electrolyzed sulfuric acid. The diamond electrode consists of a polycrystalline BDD thin film deposited on a conductive substrate by chemical vapor deposition (CVD) method. Therefore, the size of diamond electrode is limited depending on the size and power of the CVD equipment. In this study, we developed a new method to fabricate a large-sized diamond electrode that can be used for electrolyzed sulfuric acid production using BDD powder (BDDP).BDDP was prepared by deposition of a BDD layer on the surface of diamond powder with a particle size of 3-6 μm via microwave plasma-assisted CVD. The BDDP was added to tetraethyl orthosilicate/ethanol solution, followed by addition of ultrapure water and nitric acid and stirring to prepare a BDDP/silica sol solution. The BDDP/silica sol solution was spray-coated on a hydrophilic titanium substrate, and after baking at 150 °C for 1 h, a spray-coated diamond electrode consisted of a BDDP/silica layer formed on the substrate was obtained. Constant-current electrolysis of 50% sulfuric acid was performed in a two-compartment electrochemical cell with the spray-coated diamond electrode as an anode. Concentrations of peroxodisulfate, peroxomonosulfate, and hydrogen peroxide in the sulfuric acid after electrolysis were estimated by titration method, and the current efficiency of the reactive oxidizing species formation was calculated.Scanning electron microscopy observation revealed that the BDDPs were packed densely on the surface of the spray-coated diamond electrode. 10 mL of 50% sulfuric acid was electrolyzed at a constant current density of 20 mA/cm2 for 90 min at a spray-coated diamond electrode (electrode area: 0.5 cm2). During the electrolysis, the electrode potential was stable around +3 V vs. Ag/AgCl, indicating that no deterioration of the electrode occurred even at highly positive potentials in concentrated sulfuric acid. Current efficiency of reactive oxidizing species formation was calculated from the concentration estimated by titration to be 41%. These results confirm that the spray-coated diamond electrode can be used for electrolyzed sulfuric acid production. A large-sized spray-coated diamond electrode was also prepared in the same way using a 20×20 cm2-sized titanium substrate. Electrolysis of 50% sulfuric acid was performed at selected points on the electrode surface (electrode area for electrolysis: 1 cm2), and a constant current density of up to 32 mA/cm2 could be applied for 90 min, with a current efficiency of 67% for reactive oxidizing species formation. Therefore, the spray coating method is expected to be useful for scaling up of a diamond electrode for sulfuric acid electrolysis.

Water Treatment Using Boron-Doped Diamond Powder-Packed Electrolysis Flow Cell

Water treatment by electrolysis can decompose persistent organic compounds, such as low-molecular-weight organic compounds in urine, which cannot be decomposed by microbial water treatments, into H2O and CO2. Anodic oxidation is being considered for use as one of the processes in the water reclamation system required for manned space exploration. Boron-doped diamond (BDD) electrodes can generate efficiently OH radical, which is a strong active oxidizing species, when high potential is applied in aqueous solution. In addition, BDD electrodes are known to be useful as electrode materials for electrolytic water treatment because of their physical and chemical stability. However, BDD electrodes are usually thin films, so their shape, size, and the configuration of electrolytic cells are restricted. Boron-doped diamond powder (BDDP)-packed electrolysis flow cell has been reported to be useful for water treatment with high efficiency because of the large electrode surface area. In this study, the BDDP-packed electrolytic flow cell with a closed system was developed for improvement of the decomposition efficiency.BDDP was prepared by using commercially available diamond powder with a particle size of 40-60 μm as a substrate material and depositing a BDD layer on its surface by microwave plasma CVD. The BDDP-packed electrolytic flow cell is as shown in Figure 1a. A plastic cylinder with an inner diameter of 1 cm was bonded to a glass filter (particle holding capacity: 20-25 μm, diameter: 10 mm), and a Pt wire was placed as a current collector above the filter. 0.8 g of BDDP was packed into the filter without a binder so that it was in full contact with the current collector. Electrolysis of 50 mL of 0.1 M Na2SO4 solution containing 50 μM methylene blue (MB) was performed for 60 min at a constant voltage of 5 V. The MB concentration after electrolysis was estimated by UV-vis absorption spectroscopy. In addition, the chemical oxygen demand (COD) of the electrolyte was measured before and after electrolysis.The result of MB constant voltage electrolysis with the BDDP-packed electrolysis flow cell is shown in Fig. 1b. MB was not sufficiently decomposed at a flow rate of 2.0 mL/min. The reason for this is thought to be that the bubbles generated on the BDDP surface caused insufficient contact between the BDDP. When the flow rate was increased to 20.0 mL/min to flush out all bubbles, about 90% MB degradation was achieved in 15 min and about 99% in 30 min. The higher the flow rate, the faster the MB concentration decreased. These results suggest that the closed BDDP-packed electrolysis flow cell allows bubbles generated on the electrode surface to be quickly flushed out with the treated water. The COD of the electrolyte before and after the electrolysis was measured and it ranged from 42.2 to 21.9. The decrease in COD suggests that part of MB was completely converted to CO2. In the future, we intend to quantitatively clarify the urine treatment capacity of the cell and apply it to a water recovery system in space. Figure 1

(Invited) Boron-Doped Diamond Powder/Nanoparticle Materials for Electrochemical Applications

Heavily boron-doped diamond (BDD) electrode exhibits several excellent electrochemical properties such as wide potential window, low background current, as well as extreme physical and chemical stabilities. Based on these properties, the BDD electrodes are expected to be used for highly sensitive electrochemical sensors and highly efficient electrolytic electrodes. The BDD electrodes are usually prepared by depositing a polycrystalline BDD thin film on a conductive substrate such as silicon wafer, and thus are used as hard planar electrodes. Furthermore, the size of the BDD electrode also has a limit depending on the CVD apparatus. These situations limit the range of applications of BDD electrodes, despite their excellent electrochemical properties. With the aim of expanding the range of applications of BDD in the electrochemical field, we have developed BDD powder (BDDP). BDDP is a conductive diamond material, which is prepared by the deposition of a BDD layer on the surface of commercially available diamond powder. BDDP has advantages over BDD thin films, such as a larger specific surface area and the ability to create electrodes by applying ink on a substrate, and can be used for applications that have not been possible with BDD thin-film electrodes.1. BDDP-packed electrolysis flow cellBDDP-packed electrolysis flow cell was developed for application to an efficient electrolytic water treatment system. A cylinder equipped with a filter was filled with BDDP (particle size of 40-60 μm) and the packed bed served as an anode. Since the BDDPs are in contact with each other in the BDDP-packed bed, the entire BDDP-packed bed is considered to be electrically connected without a binder. On the other hand, the interparticle voids in the BDDP-packed bed form a network-like narrow channel, and the electrolyte passing through the channel can be treated efficiently. 0.1 M Na2SO4 containing 50 μM methylene blue as a model for polluted water was treated with the BDDP-packed electrolysis flow cell at a voltage of 5 V applied to the two-electrode system of BDDP-packed bed anode and Pt cathode. As a result, it was found that as the amount of BDDP loaded increased, the decomposition rate of MB increased. This suggested that the entire BDDP-packed bed functioned as an anode. Moreover, no deterioration in the decomposition rate was observed even when repeated electrolysis experiments were performed using the BDDP-packed electrolysis flow cell. Therefore, the BDDP-packed electrolysis flow cell is expected to be useful for efficient and durable electrolytic water treatment systems.2. Pt/BDDP and Pt/BDND for a durable PEFC cathode catalystsA major cause of deterioration of polymer electrolyte fuel cell (PEFC) cathode catalysts is corrosion of the catalyst support due to application of high potential during start-stop operations. Therefore, there is a need for the development of a catalyst support with excellent high potential resistance. In this study, we prepared Pt-supported BDDP (Pt/BDDP) as a durable cathode catalyst, and investigated its electrochemical properties and durability to high potentials. In the CV of Pt/BDDP with a BDDP size of 200 and 300 nm, redox peaks characteristics for Pt was observed, confirming that the BDDP functions as a conductive catalyst support. Durability tests using high potential cycling (+1.0–+1.5 V vs. NHE) showed that the electrochemically active surface area (ECA) retention rate during the test was greater for Pt/BDDP than for conventional Pt/C. Therefore, the BDDP is expected to be used for a catalyst support durable to high potential application. In addition, Pt-supported boron-doped nanodiamond (Pt/BDND) showed also superior high potential durability compared to Pt/C.

Spectral and microstructural analysis of the effect of the Ga+ implantation on diamond: a CL-EELS study

Due to its capacity to achieve nanometre-scale machining and lithography, a focused ion beam (FIB) is an extended tool for semiconductor device fabrication and development, in particular, for diamond-based devices. However, some technological steps are still not fully optimized for its use. Indeed, ion implantation seems to affect the crystalline structure and electrical properties of diamond. For this study, a boron-doped ([B] ∼ 1017 atoms·cm−3) diamond layer grown by chemical vapour deposition was irradiated using Ga+ by FIB, with 1 nA current and 5, 20, and 30 keV of acceleration voltage. The Ga+ implanted diamond layer has been analysed through cathodoluminescence (CL) and scanning transmission electron microscopy (STEM)-related techniques. The beam penetration depth has been simulated by Monte Carlo calculations of both Ga+ (FIB) and e− (CL) beams at different energies. The comparative CL analysis of the layer as-grown and after implantation revealed peaks related to defects, such as A band, H3 centre, and defects present in the green band region. The STEM studies for the 30 keV implanted sample showed that the diamond lattice is affected by the damage, evidencing amorphisation in the layer with a sp2/sp3 ratio of 1.37, estimated by electron energy loss spectroscopy. Therefore, this study highlights the effects of the Ga+ implantation on the optical and structural characteristics of diamond, using different methods.

Thick crack-free {113} epitaxial boron-doped diamond layers for power electronics—Deposition with nitrogen addition and high microwave power

In this work, first, we investigate the effect of nitrogen addition in microwave plasma enhanced chemical vapor deposition on the growth of thick {113} epitaxial diamond layers. We identify a narrow range of nitrogen concentrations for the growth of crack-free thick epitaxial layers with a smooth surface morphology. Without nitrogen, cracks start to appear after a layer thickness of 7–10 μm due to elastic energy stored in the epitaxial layer, but the addition of nitrogen stabilizes layer growth. We also investigate the use of low microwave power density growth conditions to produce thick boron-doped epitaxial layers. We observe a very high boron incorporation efficiency using these growth conditions. Finally, we demonstrate the fabrication of a thick (>200 μm) {113} p+ monocrystal plate. The concentration of boron in heavily doped diamond with metallic conductivity has been investigated by the Hall effect measurement technique, Raman spectroscopy, and secondary ion mass spectroscopy. The growth of high quality thick {113} oriented epitaxial layer with high boron concentration (>1020 cm−3) and low resistivity and the fabrication for the freestanding p+ substrates are necessary steps for the fabrication of vertical electronic devices such as high power Schottky diodes.

Core-shells particles grown in a tubular reactor: Influence of the seeds nature and MPCVD conditions on boron-doped diamond crystalline quality

A trend in the synthesis of Boron Doped Diamond (BDD) materials resides in increasing surface areas to exalt reactivity at the BDD/electrolyte interface. This can be achieved either by surface structuration of BDD films or conformal growth on 3D substrates. Another strategy considers isolated BDD particles, mainly obtained by milling of BDD layers that can be further deposited on surfaces or embedded in a conductive matrix. Here, we propose an alternative method to obtain boron-doped diamond particles using a core-shell approach, which consists in growing diamond coatings on spherical silica templates seeded with nanodiamonds. We investigated the effects of the nature and the density of diamond seeds as well as growth parameters on the crystalline quality of the coatings. The microstructure and the boron incorporation in the diamond shell was investigated by combining Scanning Electron Microscopy (SEM), UV Raman and X-ray Photoemission Spectroscopy (XPS) investigations. Such characterizations were compared to Scanning TEM (STEM) imaging, Energy Dispersive Spectroscopy (EDS) and Electron energy loss spectroscopy (EELS) performed on thin cross-sections of core-shells prepared by focused ion beam (FIB) milling.

Construction of porous diamond film with enhanced electric double-layer capacitance via regrowth of diamond nanoplatelets

The engineering of porous boron-doped diamond (BDD) film has sparked significant interest in improving electric double-layer (EDL) capacitance. However, the presence of disordered and tortuous pores in the BDD film hinders the accessibility of the bottom pore surface area, leading to a decrease in specific EDL capacitance. Herein, a novel porous BDD film with vertically open pore channels is constructed through the overcoating of diamond nanoplatelet template with a BDD layer using chemical vapor deposition. Electrochemical investigations manifest that the specific areal EDL capacitance of the porous BDD is ∼428 times greater than that of the planar BDD film. More impressively, the porous BDD film demonstrates a higher specific volumetric EDL capacitance (39.30 F/cm3) and superior long-term stability (100% capacitance retention after 12,000 cycles), surpassing the performance of most developed porous BDD electrodes. The exceptional performance of the porous BDD film was attributed to the abundant vertically open pore channels, good hydrophilic property, maximized electrochemical available area, and good chemical/mechanical stability. This work benefits the development of the BDD film as an EDL micro-capacitor electrode, and the methodology proposed here shows great potentials to fabricate an ordered porous BDD nanostructure with large specific area for more electrochemical applications.

Pseudo‐Vertical Schottky Diode with Ruthenium Contacts on (113) Boron‐Doped Homoepitaxial Diamond Layers

Electrical properties of pseudo‐vertical Schottky barrier diodes (pVSBDs) prepared on (113)–oriented boron‐doped diamond (BDD) layers using ruthenium (Ru) for both the ohmic and Schottky contacts are investigated. First, Ru ohmic contacts are evaporated on homoepitaxial BDD layers with different resistivity, and their specific contact resistance is measured using circular transfer length method structures after annealing at various temperatures up to 750 °C. Then, pVSBD structures are fabricated on the boron‐doped bilayer consisting of a lower, heavily boron‐doped layer ensuring an ohmic contact and an upper, lightly doped layer providing a rectifying Schottky contact. After necessary mesa etching, both contacts are formed by the Ru evaporation. The results show that Ru forms a stable ohmic contact with very low contact resistance (10−5–10−6 Ω cm2) when deposited on BDD layers with metallic conductivity. It also provides an acceptable Schottky contact on low‐doped (113) homoepitaxial BDD. Both contacts, which are made simultaneously, realize pVSBDs with low on‐state resistance and low forward voltage drop. However, the lower barrier of the ruthenium contacts results in higher leakage. Ru pVSBDs thus show a lower rectification ratio, higher leakage, and a worse ideality factor compared to analogical pVSBDs using molybdenum contacts.

Diamond as Insulation for Conductive Diamond—A Spotted Pattern Design for Miniaturized Disinfection Devices

Boron-doped diamond (BDD) electrodes are well known for the in situ production of strong oxidants. These antimicrobial agents are produced directly from water without the need of storage or stabilization. An in situ production of reactive oxygen species (ROS) used as antimicrobial agents has also been used in recently developed medical applications. Although BDD electrodes also produce ROS during water electrolysis, only a few medical applications have appeared in the literature to date. This is probably due to the difficulties in the miniaturization of BDD electrodes, while maintaining a stable and efficient electrolytic process in order to obtain a clinical applicability. In this attempt, a cannula-based electrode design was achieved by insulating the anodic diamond layer from a cathodic cannula, using a second layer of non-conducting diamond. The undoped diamond (UDD) layer was successfully grown in a spotted pattern, resulting in a perfectly insulated yet still functional BDD layer, which can operate as a miniaturized flow reactor for medical applications. The spotted pattern was achieved by introducing a partial copper layer on top of the BDD layer, which was subsequently removed after growing the undoped diamond layer via etching. The initial analytical observations showed promising results for further chemical and microbial investigations.

Surface morphology-assisted electrochemical conversion of carbon dioxide to formic acid via nanocrystalline boron-doped diamond electrodes

Due to its unmatched corrosion stability and overall versatility, boron-doped diamond (BDD) has superb potential as an electrode material for the production of valuable chemicals via electrochemical reduction of carbon dioxide (CO2). To advance its practical application, it is necessary to explore ways to achieve cost-effective fabrication of BDD electrodes, which can enable significant selectivity for product formation during CO2 electroreduction. Here, BDD electrodes of nanocrystalline form were fabricated employing two distinct chemical vapor deposition (CVD) techniques, which allow for substantial upscaling of electrode dimensions to match industrial/wafer-size standards. Thin (<400 nm) nanocrystalline BDD layers were fabricated at various synthesis temperatures to investigate its effect on the electrical, structural, and electrochemical characteristics. Furthermore, modification of the BDD layer crystallinity and morphology has been performed to significantly alter the overall electrode structure and sp3/sp2-carbon phase-composition. Finally, when employed as cathodes in electrochemical CO2 reduction, nanocrystalline BDD electrodes of modified structure demonstrated enhanced values of faradaic efficiency (FE) towards production of formic acid (HCOOH), surpassing FEHCOOH values observed for microcrystalline form of BDD cathodes. Reported findings present a basis for further development of BDD cathodes, including their design, structure, and composition, which leverages the advantages of scalable and cost-effective synthesis of BDD electrodes.

Inkjet Printing-Manufactured Boron-Doped Diamond Chip Electrodes for Electrochemical Sensing Purposes.

Fabrication of patterned boron-doped diamond (BDD) in an inexpensive and straightforward way is required for a variety of practical applications, including the development of BDD-based electrochemical sensors. This work describes a simplified and novel bottom-up fabrication approach for BDD-based three-electrode sensor chips utilizing direct inkjet printing of diamond nanoparticles on silicon-based substrates. The whole seeding process, accomplished by a commercial research inkjet printer with piezo-driven drop-on-demand printheads, was systematically examined. Optimized and continuous inkjet-printed features were obtained with glycerol-based diamond ink (0.4% vol/wt), silicon substrates pretreated by exposure to oxygen plasma and subsequently to air, and applying a dot density of 750 drops (volume 9 pL) per inch. Next, the dried micropatterned substrate was subjected to a chemical vapor deposition step to grow uniform thin-film BDD, which satisfied the function of both working and counter electrodes. Silver was inkjet-printed to complete the sensor chip with a reference electrode. Scanning electron micrographs showed a closed BDD layer with a typical polycrystalline structure and sharp and well-defined edges. Very good homogeneity in diamond layer composition and a high boron content (∼2 × 1021 atoms cm-3) was confirmed by Raman spectroscopy. Important electrochemical characteristics, including the width of the potential window (2.5 V) and double-layer capacitance (27 μF cm-2), were evaluated by cyclic voltammetry. Fast electron transfer kinetics was recognized for the [Ru(NH3)6]3+/2+ redox marker due to the high doping level, while somewhat hindered kinetics was observed for the surface-sensitive [Fe(CN)6]3-/4- probe. Furthermore, the ability to electrochemically detect organic compounds of different structural motifs, such as glucose, ascorbic acid, uric acid, tyrosine, and dopamine, was successfully verified and compared with commercially available screen-printed BDD electrodes. The newly developed chip-based manufacture method enables the rapid prototyping of different small-scale electrode designs and BDD microstructures, which can lead to enhanced sensor performance with capability of repeated use.

BiVO4/boron-doped diamond heterojunction photoanode with boron doping engineering and enhanced photoelectrocatalytic activity

Photoelectrocatalysis is one of the most promising strategies to address ever-growing wastewater problems. A novel heterojunction photoanode formed by depositing a photocatalyst on a boron-doped diamond (BDD) layer has been considered an ideal material for the practical application of photoelectrocatalytic (PEC) degradation due to its advantages of light responsiveness, excellent charge transport, and robustness. In this study, various BiVO4/BDD heterojunction photoanodes with different diamond crystalline qualities and electrical conductivities were successfully fabricated by tuning the boron (B) doping concentration of the BDD layer. It was proposed that the charge transport efficiency of the photoanodes is promoted by optimizing the crystalline qualities and electrical conductivities of BDD films, thereby enhancing the PEC activity of the BiVO4/BDD heterojunction photoanode. Our results suggested that the electrical conductivity of BDD increased and the crystalline quality of BDD deteriorated with increasing B doping concentration. As a result, the PEC activity of the BiVO4/BDD heterojunction photoanode first increased and then decreased. The optimal PEC activity of the BiVO4/BDD heterojunction photoanode was achieved corresponding to the [B]/[C] gas ratio at 500 ppm, producing a current density of 3.3 mA/cm2 at 1.6 VRHE (the potential versus a reversible hydrogen electrode) in 0.1 M Na2SO4 under AM 1.5 irradiation, which was 1.7 times (1.9 mA/cm2) that of the photoanode with a [B]/[C] gas ratio of 3000 ppm. Meanwhile, the optimized tetracycline hydrochloride (TCH) degradation efficiency was 63.5 % within 9 min (500 ppm gas phase), which was 2.5 times (25.1 %) that of the highly doped photoanode with a [B]/[C] gas ratio of 3000 ppm. This study revealed that the excellent PEC performance benefited from the high crystalline quality and high electrical conductivity of BDD, which depended on the optimized B doping concentration. The idea of enhancing the PEC activity of the photoanode by optimizing the properties of the conductive electrode material proposed in this study provides a conceptual reference for fabricating potential high-performance photoanodes in the future.

Pseudovertical Schottky Diodes on Heteroepitaxially Grown Diamond

Substrates comprising heteroepitaxially grown single-crystalline diamond epilayers were used to fabricate pseudovertical Schottky diodes. These consisted of Ti/Pt/Au contacts on p− Boron-doped diamond (BDD) layers (1015–1016 cm−3) with varying thicknesses countered by ohmic contacts on underlying p+ layers (1019–1020 cm−3) on the quasi-intrinsic diamond starting substrate. Whereas the forward current exhibited a low-voltage shunt conductance and, for higher voltages, thermionic emission behavior with systematic dependence on the p− film thickness, the reverse leakage current appeared to be space-charge-limited depending on the existence of local channels and thus local defects, and depending less on the thickness. For the Schottky barriers ϕSB, a systematic correlation to the ideality factors n was observed, with an “ideal” n = 1 Schottky barrier of ϕSB = 1.43 eV. For the best diodes, the breakdown field reached 1.5 MV/cm.

Effect of substrate crystalline orientation on boron-doped homoepitaxial diamond growth

Boron-doped diamond layers have been grown by MW PECVD on substrates with a misorientation over the range of 0 to 90° relative to the (100) crystalline plane while keeping all other growth conditions constant. Deposited layers were characterized by scanning electron microscopy, atomic force microscopy, and Raman spectroscopy. The deposition rate, surface roughness, and boron incorporation vary according to the substrate misorientation. These results show the essential need for rigorous control of the substrate crystalline orientation in the synthesis of doped diamond for electronic applications. Thick, smooth, and free of surface defects boron-doped epitaxial diamond layers were obtained over a broad range of crystalline orientations at high growth rates and high boron incorporation efficiency. Novelty statementThis work reports on the effect of the substrate crystalline orientation on the morphology, growth rate, and boron incorporation in epitaxial diamond layers deposited by plasma-enhanced chemical vapor deposition.

High breakdown voltage of boron-doped diamond metal semiconductor field effect transistor grown on freestanding heteroepitaxial diamond substrate

We report the results of a device performance of a boron-doped diamond metal semiconductor field effect transistor (MESFET) grown on a heteroepitaxial diamond substrate using microwave plasma chemical vapor deposition. The 120 nm-thick lightly boron-doped p-type diamond layer indicates sheet resistance of 6 GΩ/sq. at room temperature (RT). A two-terminal buffer leakage test with pad distance of 10 μm shows that a heteroepitaxial grown diamond substrate withstands more than 3 kV. The fabricated device with gate–drain distance (Lgd) of 10 μm exhibits a drain current density (Id) of 66 nA/mm (gate voltage (Vsg) 0.5 V, drain voltage (Vds) 30 V, and at RT), and at 463 K, the Id increases to 9.4 μA/mm. The device with Lgd of 30 μm shows a high breakdown voltage of −2360 V at RT, and at 463 K, breakdown voltage reduces to −515 V owing to an increase in leakage current. A benchmark on breakdown voltage vs. on-resistance reveals that our breakdown result at RT is the highest value ever reported for a bulk p-doped diamond FETs.

Properties of boron-doped (113) oriented homoepitaxial diamond layers

Although significant efforts have been dedicated to optimize the quality of epitaxial diamond layers, reported properties of diamond based electronic devices do not yet approach expected theoretical values. Recent works indicate that boron-doped and phosphorous-doped diamond can be grown on atomically stepped (113) surfaces (A. Tallaire et al., 2016; M.-A. Pinault-Thaury et al., 2019), however the electrical properties of these layers have not been studied in detail. In this work, we report on structural and electrical properties of boron-doped epitaxial diamond layers grown on (113) substrates. Properties of the diamond layers have been investigated by means of scanning electron microscopy, atomic force microscopy, Hall effect, secondary ion mass spectrometry and Raman spectroscopy. Our results show that boron-doped diamond layers can be grown on (113) substrates at high deposition rates with atomically flat surfaces, excellent electrical properties and high boron incorporation efficiency.

Study of Early Stages in the Growth of Boron‐Doped Diamond on Carbon Fibers

With the aim to improve the properties of aeronautical carbon fiber (CF)‐reinforced polymer materials, boron‐doped diamond (BDD) has been grown on commercial CFs by microwave plasma‐enhanced chemical vapor deposition. The growth of a BDD layer on CF is expected to increase the mechanical, electrical, and thermal conductivities of the composite. The present contribution reports the different growth stages and their associated nanostructures of the BDD/CF resulting system using transmission electron microscopy, scanning electron microscopy, and Raman spectroscopy. The revealed carbon nanostructure shows four steps of growth with the following characteristics: 1) transitional interlayer, 2) graphite nanowall, 3) cauliflower‐like nanocrystalline diamond, and 4) microcrystalline diamond.

Deposition of Boron-Doped Thin CVD Diamond Films from Methane-Triethyl Borate-Hydrogen Gas Mixture

Boron-doped diamond is a promising semiconductor material that can be used as a sensor and in power electronics. Currently, researchers have obtained thin boron-doped diamond layers due to low film growth rates (2–10 μm/h), with polycrystalline diamond growth on the front and edge planes of thicker crystals, inhomogeneous properties in the growing crystal’s volume, and the presence of different structural defects. One way to reduce structural imperfection is the specification of optimal synthesis conditions, as well as surface etching, to remove diamond polycrystals. Etching can be carried out using various gas compositions, but this operation is conducted with the interruption of the diamond deposition process; therefore, inhomogeneity in the diamond structure appears. The solution to this problem is etching in the process of diamond deposition. To realize this in the present work, we used triethyl borate as a boron-containing substance in the process of boron-doped diamond chemical vapor deposition. Due to the oxygen atoms in the triethyl borate molecule, it became possible to carry out an experiment on simultaneous boron-doped diamond deposition and growing surface etching without the requirement of process interruption for other operations. As a result of the experiments, we obtain highly boron-doped monocrystalline diamond layers with a thickness of about 8 μm and a boron content of 2.9%. Defects in the form of diamond polycrystals were not detected on the surface and around the periphery of the plate.

Low temperature synthesis of transparent conductive boron doped diamond films for optoelectronic applications: Role of hydrogen on the electrical properties

Transparent conductive electrodes are principal components in various optoelectronic devices and technologies. As such, diamond coatings in the form of electrically conductive thin films are envisioned to provide advantageous chemical and mechanical characteristics/stability in a variety of modern technologies including optoelectronics, biosensing, electrochemical and micromechanical systems. However, deposition of electrically conductive polycrystalline diamond coatings for such applications is currently a challenging task, since temperatures above 600 °C are usually required to ensure good diamond layer quality, which in turn limits the selection of substrates, to materials capable of withstanding exposure to high temperatures. In the present work, we investigate routes toward enhancement of electrical characteristics of nanocrystalline boron-doped diamond (BDD) films fabricated at low temperatures via chemical vapour deposition. We found that post-growth processing of BDD layers enhances their electrical properties, which otherwise are dependent on the employed deposition temperature regime. Finally, we show that integration of an electrically conductive Ti grid opens a route for fabrication of highly transparent and conductive composite nanocrystalline BDD electrodes over large areas at temperatures as low as 250 °C.