Microwave Plasma Chemical Vapor Deposition Research Articles

Boron atoms migration during epitaxial growth of boron-doped single-crystal diamond

Boron-doped diamond (BDD) films are essential for the fabrication of electronic devices with P+ or P− layers. However, the boron atoms in the intrinsic diamond substrates due to the concentration gradient may affect the height of the Schottky barrier based on these BDD films. BDD films with different concentrations of boron atoms were deposited on chemical vapor deposition (CVD) diamond seeds by microwave plasma chemical vapor deposition. Laser confocal Raman spectroscopy was utilized to investigate the migration of boron atoms during the CVD deposition process. The results indicate that the diffusion depth is below 20 μm with a boron atom concentration of 1020 cm−3 at a deposition time of 10 h. The boron atom diffusion depth is below 8 μm at a fixed CH4/H2 ratio of 2% after 5 h deposition. The characteristic peak of boron atoms is not detected by Raman spectroscopy after 3 h deposition, while the infrared spectrum indicates that the boron atom concentration is more than 1018 cm−3. Consequently, the boron atom concentration and the diffusion depth in CVD seeds can be regulated by controlling the CH4/H2 ratio and the deposition time. Planar diamond-based Schottky diodes based on the prepared P+ or P− layer exhibit distinct rectification characteristics.

High-concentration diamond nitrogen vacancy color center fabricated by microwave plasma chemical vapor deposition and its properties

Diamond nitrogen vacancy (NV) color centers have good stability at room temperature and long electron spin coherence time, and can be manipulated by lasers and microwaves, thereby becoming the most promising structure in the field of quantum detection. Within a certain range, the higher the concentration of NV color centers, the higher the sensitivity of detecting physical quantities is. Therefore, it is necessary to dope sufficient nitrogen atoms into diamond single crystals to form high-concentration NV color centers. In this study, diamond single crystals with different nitrogen content are prepared by microwave plasma chemical vapor deposition (MPCVD) to construct high-concentration NV color centers. By doping different amounts of nitrogen atoms into the precursor gas, many problems encountered during long-time growth of diamond single crystals under high nitrogen conditions are solved. Diamond single crystals with nitrogen content of about 0.205, 5, 8, 11, 15, 36, and 54 ppm (1ppm –10<sup>–6</sup>) are prepared. As the nitrogen content increases, the width of the step flow on the surface of the diamond single crystal gradually widens, eventually the step flow gradually disappears and the surface becomes smooth. Under the experimental conditions in this study, it is preliminarily determined that the average ratio of the nitrogen content in the precursor gas to the nitrogen atom content introduced into the diamond single crystal lattice is about 11. Fourier transform infrared spectroscopy shows that as the nitrogen content inside the CVD diamond single crystal increases, the density of vacancy defects also increases. Therefore, the color of CVD high nitrogen diamond single crystals ranges from light brown to brownish black. Compared with HPHT diamond single crystal, the CVD high nitrogen diamond single crystal has a weak intensity of absorption peak at 1130 cm<sup>–1</sup> and no absorption peak at 1280 cm<sup>–1</sup>. Three obvious nitrogen-related absorption peaks at 1371, 1353, and 1332 cm<sup>–1</sup> of the CVD diamond single crystal are displayed. Nitrogen atoms mainly exist in the form of aggregated nitrogen and single substitutional N<sup>+</sup> in diamond single crystals, rather than in the form of C-defect. The PL spectrum results show that defects such as vacancies inside the diamond single crystal with nitrogen content of 54 ppm are significantly increased after electron irradiation, leading to a remarkable increase in the concentration of NV color centers. The magnetic detection performance of the NV color center material after irradiation is verified, and the fluorescence intensity is uniformly distributed in the sample surface. The diamond single crystal with nitrogen content of 54 ppm has good microwave spin manipulation, and its longitudinal relaxation time is about 3.37 ms.

Diamond-coated quartz crystal microbalance sensors: Challenges in high yield production and enhanced detection of ethanol and sars-cov-2 proteins

This study presents the technological progress in the deposition of diamond thin films on quartz crystal microbalance (QCM) sensors. The linear antenna microwave plasma chemical vapour deposition (CVD) technique effectively grows thin diamond films on QCM substrates (Dia-QCM) differently oriented on the substrate holder in the deposition chamber, resulting in single-sided and double-sided coated QCMs. Each of these coated QCMs offers a distinctive advantage for sensing applications. The double-sided coated QCM sensors exhibited the most effective performance in ethanol detection, demonstrating approx. a 3-fold and 12-fold higher response than single-sided diamond-coated and bare gold QCM sensors, respectively. Furthermore, the single-sided Dia-QCM aptasensors demonstrated superior performance compared to bare gold QCM sensors, with a 2-fold higher response and a lower detection limit for S-RBD protein (LODDia-QCM = 0.09pg/mL vs. LODAu-QCM = 0.10pg/mL). In experiments conducted in human plasma, the Dia-QCM aptasensor demonstrated the ability to detect S-RBD protein at concentrations as low as 50pg/mL, with high percentage recoveries. These results highlight the potential of linear antenna microwave plasma CVD for the mass production of advanced diamond-coated QCM sensors with different diamond film morphologies (porous, micro- or nanocrystalline) for various applications.

Efficient Carboxylic Acid Synthesis through Electrolytic Reduction of CO2 using BDD Electrodes

Recent chemical advancements have brought a variety of products but also increased emissions of harmful substances, prompting the search for cleaner synthesis methods like organic electrolytic synthesis methods, using electrical energy for reactions. Meanwhile, with the urgent need to reduce CO2 emissions and achieve carbon neutrality, recycling and reducing technologies for CO2 have gained significant attention 1). This study focuses on electrolytic carboxylation, utilizing CO2 as a raw material, which presents a promising avenue for organic electrolytic synthesis, allowing the synthesis of high-value compounds from cost-effective materials using electrical energy as a reducing agent. Notably, it offers the advantage of producing less waste, positioning it as a robust option for industrial adoption centered on green chemistry. However, since electrocarboxylation reactions occur on electrode surfaces, conventional approaches utilize organic solvents and precious metals like platinum (Pt), prized for their corrosion resistance and durability. To address this challenge, we have directed our focus towards synthesizing boron-doped diamond (BDD) electrodes, incorporating boron into the diamond structure. BDD electrodes boast a wide potential window, high durability, and corrosion resistance, making them capable of inhibiting undesirable reactions and facilitating sustained synthesis. Herein, it aims to address challenges in electrolytic carboxylation reactions, enhance energy efficiency, analyze reactions using diamond electrodes, ultimately establish a new synthesis method contributing to carbon neutrality.A comparative analysis of BDD and platinum electrodes was conducted to confirm the superior performance of BDD. BDD electrodes were prepared using the microwave plasma chemical vapor deposition method, employing acetone and methanol as carbon sources and boron trioxide as the boron source. Plasma irradiation of a mixture of raw materials and hydrogen gas was used to deposit BDD on a silicon substrate. Prior to the experiment, the BDD surface underwent ultraviolet ozone treatment with oxygen to enhance stability and establish consistent initial conditions. Under N2 or CO2 atmospheric conditions, cyclic voltammetry (CV) was performed with a scanning rate of 10 mV/s in Bu4NBF4/acetonitrile (0.1 M) and acetophenone (0.01 M) to investigate the electrochemical behavior of BDD and Pt electrodes. CV studies were utilized to investigate the reduction potential. Finally, acetophenone was synthesized via constant current electrolysis under a CO2 atmosphere.Figure 1 displays the CV curves of a) BDD and b) Pt electrodes in acetonitrile solvent and acetophenone electrolyte, respectively. In the electrocarboxylation reaction, the electrochemical reduction of acetonitrile and CO2 occurs as a side reaction. Our findings indicate that the reduction of acetonitrile and CO2 does not occur at the reduction potential of acetophenone when using a BDD electrode. Conversely, when a Pt electrode is employed, acetonitrile is slightly reduced by the reduction potential of acetophenone, and CO2 reduction occurs as a side reaction. Figure 2(a) depicts the yield of atrolactic acid obtained using both BDD and Pt electrodes. In case of Pt electrode 13 % yield of atrolactic acid while in case of BDD electrode 25 % yield of atrolactic acid observed. These results demonstrate that the electrocarboxylation reaction efficiency of BDD electrodes is higher than that of platinum electrodes. Figure 2 (b) shows a schematic diagram of the electrocarboxylation reaction. Initially, acetophenone undergoes one electron reduction. The resulting substance reacts directly with CO2 and undergoes further reduction by one electron 2). This study showcases the potential of BDD electrodes for organic synthesis, particularly in the electrolytic carboxylation of acetophenone. References 1) S. Wang, T. Feng, Y. Wang, Y. Qiu, Chem. Asian. J. 17, e202200543 (2022).2) M. A. Stalcup, et al., ACS Sustainable Chem. Eng. 9, 10431-10436 (2021). Figure 1

Diamond Crystal Growth on Orientation-Controlled Carbon-Based Materials

Diamond is an excellent semiconductor material due to its wide band gap (5.45 eV), high mobility and high thermal conductivity. Diamond semiconductors are expected to be used in the construction of ultraviolet light-emitting devices, high-temperature devices and high-speed devices. Diamond have the potential to contribute to energy saving and miniaturization of various electrical products when diamond is widely used in practical applications. However, there are various problems in using diamond as a semiconductor. One of the problems is that size-limited and the high cost of the substrates in homoepitaxial growth used to fabricate high-quality diamond substrates. It is therefore preferable to establish a process for the fabricate of high-quality diamond substrate by heteroepitaxial growth.We used orientation-controlled graphite, an allotrope of diamond, as a substrate for diamond crystal growth. We present the results of our investigation into methods for diamond heteroepitaxial growth on graphite. Although there have been reported that of diamond crystal growth on graphite substrates after a pre-treatment. This is considered that this required pre-treatment because the crystal growth was on the plane of a honeycomb structure with hexagons lined up by carbon, and there were no bonding points. In the present study, crystals were grown without any pre-treatment process on the X-Y plane, where the configured by honeycomb structure, and on the Z plane, which intersects it at right angles and exposes the chemically active points as the dangling bonds. The effect of the orientation of the crystal growth substrate on diamond crystal growth was analyzed and the possibility of graphite substrates as diamond crystal growth substrates was examined.Here, it is considered that the dangling bonds on the Z-plane before crystal growth are terminated with hydrogen.In this study, polycrystalline diamond were fabricated on highly oriented pyrolytic graphite (HOPG) substrates using a microwave plasma chemical vapor deposition (MPCVD). The dependence of crystal size on raw gas ratio, deposition temperature, and substrate orientation was investigated. The raw gas ratio was fixed at CH4:H2 = 0.5:199.5 and the deposition temperatures were set at 600°C, 700°C, 800°C, 900°C and 980°C. The deposition pressure was kept constant at 10 kPa.The diamond crystal size deposited in the XY plane exceeded that deposited in the Z plane. The largest difference in crystal size was observed at a temperature of 980°C and a methane flow rate of 0.5, the crystal size in the XY and Z planes was 1.3311μm2 and 0.4232μm2, respectively, and the crystals in the XY plane were about three times larger than those in the Z plane. We attributed this change in crystal size due to the difference in substrate orientation to the distortion of part of the tetrahedral structure of diamond to match the hexagonal structure of graphite in the XY plane and the secondary bonding of the tetrahedral structure. In other words, although many active sites are exposed on the Z plane, the bonding distance of carbon atoms is not convenient for the generation of diamond crystals, and the hexagonal reticular structure of the XY plane is more convenient for the generation of crystals, so the diamond crystals on the XY plane are considered to have grown larger in these condition ranges. Figure 1

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

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.

Facile synthesis of novel nitrogen-doped diamond with excellent microwave absorption and thermal conductive performance

Herein, nitrogen doped polycrystalline diamond was prepared using the microwave plasma chemical vapor deposition (MPCVD) method with H2–CH4–N2 gas sources to achieve excellent electromagnetic (EM) wave absorption and thermal management properties. The effect of the nitrogen content (0 to 50 ppm) on its performance was studied. The 25-ppm nitrogen doped diamond demonstrated excellent EM wave absorption performance, achieving a minimum reflection loss (RLmin) of −44.8 dB at 6.7 GHz and a maximum effective absorption band (EAB) of 5.4 GHz (3.7–9.1 GHz). The superior absorption performance could be attributed to synergistic attenuation mechanisms including dipole and interface polarization, conduction loss, eddy current loss, and magnetic polarization, intensified by nitrogen vacancy centers. This multifunctional material, combining high thermal conductivity with effective low-frequency EM wave absorption, showed promise for applications in 5G communications and electronic devices.

Growth of homoepitaxial single crystal diamond by microwave plasma CVD in H2-CH4-O2 gas mixtures at high microwave power densities

Single crystal diamond growth by microwave plasma assisted CVD in oxygen-containing gas mixtures is attractive in view of possibility to realize a prolonged non-stoped synthesis process and to minimize defects and impurities in the produced material. We studied the homoepitaxial diamond growth on (100) oriented substrates in H2-CH4-O2 environment at high pressures (300 Torr) and high microwave power density (≈400 W/cm3) at variable O2 content (up to 3.5 %) in the plasma. A low-coherence optical interferometry and optical emission (OE) spectroscopy was used to measure in situ the growth rate and probe the plasma chemistry, respectively. Depending on CH4 content the growth rate dependence on the concentration [O2] either shows a maximum at certain [O2], or a monotonic decline, up to complete stop of the growth at some critical O2 percentage (specific for each methane content) in the mixture. We found CH, Hβ, C2 and C3 lines in OE spectra from the plasma to monotonically quenched with O2 adding, particularly, disappearance of the C2 line coincidences with growth rate going to zero. High-quality homoepitaxial diamond layers were produced at moderate growth rate at optimal gas composition and characterized with Raman spectroscopy. Moreover, a significant reduction in the stress on (111) oriented substrates owing to O2 addition was observed.

Observation of thickness-independent ultrafast relaxation times in MPCVD few-layer graphene

Graphene presents unique optoelectronic properties, making it attractive for the development of a wide range of new and advanced technological applications such as high-speed photodetectors and all-optical modulators. The study and control of the generated carriers in graphene, namely their ultrafast relaxation dynamics, are of great importance for these applications. Here, we report the ultrafast relaxation times of photogenerated carriers in few-layer graphene grown by microwave plasma chemical vapour deposition. Graphene samples with 3, 5 and 6 layers were studied by degenerate femtosecond optical pump-probe spectroscopy. We observed a fast relaxation constant on the order of 120−180fs and a slow relaxation constant below 1 ps, associated with carrier-carrier scattering and carrier-phonon scattering processes, respectively. These results suggest that small variations in the number of graphene layers do not affect the dynamics.

Nitrogen‐Induced Microcrystalline‐to‐Nanocrystalline Structure Transition in Diamond Films Grown by Microwave Plasma Chemical Vapor Deposition: Comparison of N2 and NH3 Precursors

The structure and properties of polycrystalline chemical vapor deposition (CVD) diamond coatings grown by microwave plasma CVD in H2–CH4 mixtures can be effectively controlled by nitrogen admixture in the process gas. Here, a comparative study of adding nitrogen from different precursors, N2 and ammonia NH3, in concentrations up to 0.4%vol on grain size, texture, surface roughness, and sp2/sp3 ratio of the produced films on Si substrates is performed. A transition from microcrystalline to smooth nanocrystalline diamond structure is found to occur at a certain concentration of the precursor, for NH3 this threshold concentration being much lower, 0.02–0.1%, than for N2. The higher activity of ammonia is associated with easier formation of cyano radicals in the plasma as detected with optical emission spectroscopy, in accord with the lower bond‐dissociation energy for NH3 compared to N2. On the contrary, a smaller addition (0.004%) of either N2 or NH3 promotes almost doubling of the growth rate, while preserving the microcrystalline structure of the film. The results establish ammonia as a convenient alternative precursor to commonly used N2 added in the plasma for the diamond film structure modifications.

Microcrystalline and nanocrystalline structure of diamond films grown by MPCVD with nitrogen additions: Study of transitional synthesis conditions

This research explores the complex influence of nitrogen concentration and substrate temperature on the resultant properties of polycrystalline diamond (PCD) films grown by microwave plasma chemical vapor deposition (CVD). In particular, we investigated the growth parameters to find the exact conditions for changing the morphology of the resulting film from microcrystalline (MCD) to nanocrystalline (NCD). A series of 2 µm-thick polycrystalline diamond films was grown on Si substrates in methane-hydrogen–nitrogen gas mixtures with varied: (i) nitrogen concentration (0–2 %) and (ii) substrate temperature (700–1050 °C). Comprehensive characterization techniques, including scanning electron microscopy (SEM), micro-Raman spectroscopy, and X-ray diffraction, were employed to assess the morphological, structural, and spectroscopic properties of the films. The study reveals that even minor additions of nitrogen significantly modulate secondary nucleation, impacting both film morphology and phase composition. Furthermore, substrate temperature emerges as another critical parameter, influencing the growth kinetics and crystallite size. The comparison of the characteristics of grown PCD films allowed us to find conditions for the formation of NCD films with minimal surface roughness and maximal growth rate: nitrogen concentration [N2] ≈ 0.2–0.5 % and temperature T ≈ 850–900 °C. These findings can be used to optimize the CVD synthesis parameters of PCD films for applications as protective or friction-reducing layers, as well as for superhard cutting tools and optical devices.

Dielectric behavior and defects of nitrogen-containing single crystal diamond films

Single crystal diamond (SCD) film, as a new substrate material, has attracted growing attention because of its low dielectric loss. The nitrogen was usually introduced into microwave plasma chemical vapor deposition (MPCVD) process in order to enhance the growth rate of SCD films. So SCD films with nitrogen were prepared by MPCVD compared with the undoped film. The impurities and defects of diamond films were characterized by Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) and photoluminescence spectroscopy (PL). The dielectric behavior of SCD films was measured using the LCR measurement in the frequency range of 1 kHz to 110 MHz. The results indicate that the primary dielectric loss in SCD films is conductivity loss and space charge polarization below 1 MHz, while the main dielectric loss is dipole orientation polarization and electronic relaxation polarization in the frequency range of 1 MHz to 110 MHz. Point defects like substitutional N+, NV− and SiV− exert a significant influence on polarization loss. This is essential to improve the growth of SCD with excellent dielectric properties.

Review of Materials Science and Technological Applications of a Unique Transformational Multifunctional Ultrananocrystalline Diamond (UNCD) Coating

Microcrystalline Diamond (MCD) (grains ≥ 1 µm) and Nanocrystalline Diamond (NCD) (grains 20-900 nm) coatings have been grown using Microwave Plasma Chemical Vapor Deposition (MPCVD), exciting H2/CH4 gas, via microwave power, in evacuated chambers, producing C atoms, bonding on surfaces with sp3 C atoms diamond bonds. Alternatively, MCD/NCD films have been grown via Hot Filament Chemical Vapor Deposition (HFCVD), using ~2200°C hot filaments, cracking CH4 into C atoms. Auciello-Gruen-Krauss developed (1990s) a transformational MPCVD process, growing unique multifunctional Ultrananocrystalline Diamond (UNCDTM) coating (3-5 nm grains), using patented Ar/CH4 gas mixture. Subsequently, Auciello’s group developed HFCVD process with Ar/CH4/H2 and H2/CH4. Gases flowing though filaments heated to ~2300°C. UNCD coatings exhibit unique multifunctionalities, enabling new industrial/high-tech/medical products, namely: 1) UNCD-coated pump seals/bearings/AFM tips (marketed worldwide since 2009); 2) unique electrically conductive Nitrogen atoms-grain boundary incorporated N-UNCD-coating on commercial graphite / copper anodes anodes, enabling superior stable capacity energy/safer Li-ion batteries; 3) Unique water corrosion resistant/electrically conductive Boron-doped B-UNCD-coated metal electrodes, purifying water, via viruses/pathogens’ killing by Ozone (O3) molecules generation.; 4) Best biocompatible UNCD coating (made of C atoms in human DNA/cells life’s elements) enable new medical products (e.g., UNCD-coated Si-microchip implanted on retina, to restore partial vision to blind people; UNCD-coated Dental Implants (DI), eliminating oral fluids corrosion of metal-DIs (clinical trials in progress),; 5) UNCD-coated magnet, outside eye, attracts injected biocompatible superparamagnetic nanoparticles, reattaching retina on eye’s wall; 6) superhydrophobic UNCD coated polymer-valves, drain inner eyes’ fluid of people with glaucoma, inhibiting blindness.

Uniform carbon pillars array grown on boron doped diamond for high-performance supercapacitors and hydrogen evolution reactions

Carbon materials have marvelous ability in energy storage and microelectronics as a result of the high specific surface area and electrical conductivity. However, the low stability and the low power density caused by low potential window make it particularly difficult for their application in aqueous electrolysis. In this study, boron doped diamond (BDD) with wide potential window is used as substrate and Ni as catalyst to grow uniform carbon pillars (CP) by microwave plasma chemical vapor deposition method. The composite structure (CP/BDD) yields significant specific capacity (91.64 mF cm−2 at 0.1 mA cm−2) and cycling stability (92.3 % retention rate after 20,000 cycles) when used as the electrode of supercapacitors, superior to most of BDD-based electrodes. The prepared symmetrical supercapacitor devices maintain their excellent electrochemical performance characteristics (power density of 4.4 mW cm−2 and energy density of 13.4 μW h cm−2), as well as high cycling stability. In addition, the electrode has considerable application potential in electrochemical hydrogen production with low hydrogen evolution potential and small Tafel slope value. These results illustrate the potential of BDD based composites for using as energy storage electrodes for electronic products and energy conversion equipment.

Study on the Simulation and Experimental Impact of Substrate Holder Design on 3-Inch High-Quality Polycrystalline Diamond Thin Film Growth in a 2.45 GHz Resonant Cavity MPCVD

In this study, three different substrate holder shapes—trapezoidal, circular frustum, and adjustable cyclic—were designed and optimized to enhance the quality of polycrystalline diamond films grown using microwave plasma chemical vapor deposition (MPCVD). Simulation results indicate that altering the shape of the substrate holder leads to a uniform distribution of the electric field on the surface, significantly suppressing the formation of secondary plasma. This design ensures a more even distribution of the temperature field and plasma environment on the substrate holder, resulting in a heart-shaped distribution. Polycrystalline diamond films were synthesized under these three different substrate holder conditions, and their morphology and crystal quality were characterized using optical microscopy, Raman spectroscopy, and high-resolution X-ray diffraction. Under conditions of 5 kW power and 90 Torr pressure, the adjustable cyclic substrate holder produced high-quality 3-inch diamond films with low stress and narrow Raman full width at half maximum (FWHM). The results confirm the reliability of the simulations and the effectiveness of the adjustable cyclic substrate holder. This approach provides a viable method for scaling up the size and improving the quality of polycrystalline diamond films for future applications.

Edge effect during microwave plasma chemical vapor deposition diamond-film: Multiphysics simulation and experimental verification

Edge effect during microwave plasma chemical vapor deposition diamond-film: Multiphysics simulation and experimental verification

(Invited) Preparation of N-Type and P-Type Doped Single Crystal Diamonds with Laser-Induced Doping and Microwave Plasma Chemical Vapor Deposition

In this study, n-type doped single crystal diamonds were successfully prepared under normal temperature and pressure conditions using laser-induced doping. 248nm pulsed laser beams with nanosecond duration were irradiated on the single crystal diamond substrate immersing in an 85% phosphoric acid solution and it introduced phosphorus doping to form an n-type doped thin layer. The resistivity of the doped region significantly decreased compared to that of the single crystal diamond. After depositing a titanium electrode, the resistivity of the doped film obtained by Van der Pauw Technique was determined to be 1.3×10-6 Ω·m. Raman spectroscopy confirmed the absence of carbon or graphite phases in the laser-induced doped diamond, indicating that the enhanced conductivity was due to phosphorus incorporation.Furthermore, p-type doped single crystal diamonds were successfully prepared by introducing boron during the growth process using Microwave Plasma Chemical Vapor Deposition（MPCVD）. It was demonstrated that the proposed technique can introduce impurities into single crystal diamonds to form doped conductive thin layers, which has potential applications in the field of microdevices and integrated circuits.

Nanocrystalline Diamond Lateral Overgrowth for High Thermal Conductivity Contact to Unseeded Diamond Surface

We demonstrate diamond lateral overgrowth as a way of increasing the thermal conductivity of thin layers of diamond. The technique can be used as a way of growing diamond on top of semiconductors, creating a thin layer of high thermal conductivity diamond in direct contact with semiconductors and allowing for the encasement of GaN in high thermal conductivity diamond.As we move to higher and higher power densities, the requirements for heat removal become extreme. The best passive way to remove heat from a semiconductor is to have a high thermal conductivity heat spreader near the heat source. Having diamond under the substrate is good. Having diamond under the epi is better and having diamond on top and bottom of the epi is better still.As-grown thin layers of diamond on non-diamond substrates have nano-diamond seeds as the starting material. The diamond thermal conductivity is a function of the grain size (Especially for small grain material) [1]. If we can increase the grain of the diamond near the junction, we can increase the thermal conductivity near the junction and more efficiently spread the heat away from the source before rejecting it into the surrounding material.In the experiment, we start with a bare silicon wafer seeded with nano-diamond seeds then grow about one micron of diamond. We coat it with a few nanometers of SiN. Then pattern the SiN layer with 2μm wide features to facilitate the coalescence of LOG-NCD over the SiN. Then we grow a 2μm thick microwave-plasma CVD NCD film (800W, 15Torr, 750°C, 0.3% CH4/H2) over the patterned SiN film initiating directly from the exposed areas of the host NCD. The diamond growth does not initiate on the patterned silicon nitride without seeds. The exposed diamond acts as a nucleating center initiating the diamond regrowth. The regrown diamond spreads from the diamond crystals exposed from the first growth. The edge crystals closest to the SiN patterned area expand over the silicon nitride forming diamond conformal to the SiN surface. This creates large crystals over the unseeded area. Figure 1 is a transmission electron microscope (TEM) image of the sample. The TEM, the image can be split into two regions. The left has no patterning, the called-out grain is 100nm wide. The right is patterned, and the diamond grains are between 1,000 to 2,000nm wide.We measured the thermal conductivity of the diamond on this samples using the TDTR method. This method uses a laser many times larger in diameter than the thickness of the film. As such, we probe the out-of-plane thermal conductivity. The initial diamond growth near the silicon had an average thermal conductivity of 100W/mK. We measured the second micron of growth without patterns to have Tc of 130W/mK. The diamond directly above the patterns had Tc of 260W/mK with grains 10X larger than the un-patterned diamond.Since the diamond grains are columnar, the difference in thermal conductivity between the patterned and un-patterned diamonds was 2X. Lateral measurements would likely show even larger changes in thermal conductivity. With grain sizes of 100 nm to 250 nm (as is the case with seeded diamond), the in-plane thermal conductivity will be dominated by the quality of the grain/grain interfaces and the lateral grain size dimensions rather than for the quality of the lattice. [1] We used lateral overgrowth to increase the grains to microns rather than 100s of nm. This means that we move into a regime where thermal conductivity is dominated by the quality of the diamond in the grains rather than the grain boundaries. As such the thermal conductivity is increased and can be further improved by improving the crystal quality - a parameter which is controlled by the diamond growth conditions. Typically, samples grown with more than 1% methane / hydrogen ratio show lower thermal conductivity [2]. However higher concentrations are important to establish the initial diamond film without damage to the underlying semiconductor. Here, the lateral overgrowth and methane concentration can be balanced to achieve both high thermal conductivity and low damage to the underlying substrate.

Spectroscopic analysis of pulsed-mode plasma with argon addition for diamond growth

The advancement of high-speed growth technology for large-scale single-crystal diamonds is desired. In the widely used microwave plasma chemical vapor deposition method, the gas temperature in the plasma atmosphere significantly contributes to the generation of reactive radicals and enhancement of crystal growth. However, the impact of electron-dominated reactions in the plasma on the crystal growth remains unclear. In this study, we actively controlled the plasma environment by adding argon gas and adopting microwave pulse modulation to generate the plasma. We estimated the gas temperature and electron density of the plasma using optical emission spectroscopy. Our results implied that an increase in gas temperature alone hardly explained the enhancement of the growth rate by the argon addition or pulse modulation. In addition to the increase in the electron density due to the argon addition and pulse modulation, gas-phase chemical reaction calculations showed that the radical production enhancement became remarkable under an electron density higher than a threshold (1017 m−3). Therefore, the enhancement of the growth rate mentioned above may be attributed to electron-dominated reactions in the discharge region. These findings suggest that increasing the electron density can further improve the growth rate and potentially enable diamond synthesis at lower temperatures than traditional methods.