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To better understand how positive bias and deposition pressure affect the plasma flow properties in the deposition chamber during the bias-enhanced MPCVD process, a two-dimensional axisymmetric model based on the discharge mechanism of pure H2 was constructed. The coupling process between different physical field models of the electromagnetic field, plasma, and temperature field in the MPCVD reactor is realized. We studied the influence of positive bias voltage and deposition pressure variation on microwave plasma flow characteristics in the deposition chamber. There was a bias voltage threshold phenomenon in the case of positive bias, and the suitable value range was narrow. Additionally, with the increase in the deposition pressure, the electron temperature in the deposition chamber tends to increase locally and reaches its maximum value when the pressure is approximately 30 torr. It provides new ideas and guidance for optimizing the process parameter setting of the bias-enhanced MPCVD process. [ABSTRACT FROM AUTHOR]

To understand the process window of bias‐enhanced nucleation of diamond, it is important to study surface modifications of Ir substrates that occur under different conditions. Herein, various microstructures formed on Ir substrates are reported. The first microstructure contains rectangular particles with a size of several hundred nanometers obtained at a relatively high pressure of 12.5 kPa and a high temperature of 880 °C; these particles consist of epitaxially grown Ir3Si species. The second microstructure includes particles oriented along the [110] direction; these particles, however, consist of etched Ir pillars with a height of 400 nm when the substrate temperature increases to 1110 °C. Both microstructures form because of Ir sputtering due to the bombardment of energetic charged ions and the transport of Ir surface atoms. This study demonstrates two types of surface modifications under different bias‐enhanced nucleation conditions and provides a method for preparing an epitaxial Ir–Si compound that can be applied in various silicon‐based electronic devices. [ABSTRACT FROM AUTHOR]

Diamond nucleation on iridium (001) substrates was investigated under different bias conditions. High-density epitaxial nucleation can be obtained in a narrow bias window. This paper reports both the typical nucleation and growth behaviors of Ir substrates. The bias current change laws with the bias duration time were directly recorded; further, the surface modification of Ir substrates and nucleation behaviors at the interface were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In high-density epitaxial nucleation, the bias current decreases as the duration time increases when the iridium surface is dramatically modified with the furrows and arrows preferentially aligned along the [110] direction; however, no diamond grains can be observed from the TEM, except for the carbon layer at the interface. In bias-enhanced growth, the bias current initially decreased, then increased. The grains can be detected by SEM after the biasing stage. A competition mechanism between diamond nucleation and growth under a bias voltage is proposed for this phenomenon, in which the surface nucleation and bulk nucleation coexist and compete. [ABSTRACT FROM AUTHOR]

Diamond films on Si substrates were synthesized in a chemical vapor deposition (CVD) reactor with graphite plates as the carbon source, which were etched using hydrogen plasma. The effect of the hydrogen flow rate (13 to 200 sccm) on the diamond growth rate, morphology, and quality was investigated. While only nanocrystalline diamond was produced at the lowest flow rate of 13 sccm, microcrystalline diamond films were grown at a higher H2 flow rate, whose growth rate increased from 1.7 μm h−1 to ∼5 μm h−1 with the hydrogen flow rate decreasing from 200 sccm to 25 sccm, but at the expense of quality. The structure degradation of the films was quantified with Raman spectroscopy and XPS analysis. These results are ascribed to an increase of abundance of the produced hydrocarbon radicals, such as C2 and CH with reduced hydrogen flow rates, as deduced from the optical emission spectra of the plasma in the course of graphite-etching/diamond-deposition. [ABSTRACT FROM AUTHOR]

Infrared transparent windows on aircraft and missiles can be subjected to extreme aerothermodynamics, which can cause thermal shock failure. Finite element analysis and oxygen–propane flame jet impingement tests were performed to investigate the thermal shock failure of an yttrium oxide-coated chemical vapor deposition (CVD) ZnS infrared window. Good agreement was achieved between the simulation and experimental results, which indicated that thermal shock failure occurs under high temperature differences and thermal stresses. The temperature and stress in the samples increased rapidly in a few seconds and then trended to be stable. The center area of the window surface failed most easily because the maximum temperature and stress both occurred in this area. No delamination of the Y 2 O 3 films occurred during the thermal shock, which indicated good adhesion between the Y 2 O 3 films and CVD ZnS substrate. In the experiment, the center area of the specimen surface was damaged in the form of pits and line cracks. [ABSTRACT FROM AUTHOR]

A UV detector based on a planar quadrant electrode structure with a 100-μm isolating cross-gap deposited on chemical vapor deposition diamond was fabricated. An asymmetrical behavior was observed for the amplitude of photocurrent when in forward and reverse bias. A linear relationship between the sum of the photocurrents at biases U and −U, and the light spot position was also observed. The aim of this study is to clarify the mechanism underlying this asymmetrical behavior and exhibit its potential application based on this behavior. A mechanism involving lowering of the contact barrier height between gold and i-diamond by carrier generation upon UV illumination was adopted to account for the photocurrent behavior and confirmed when an opposite asymmetrical photocurrent behavior was observed in other samples. In addition, position-sensitive detection performance, based on this asymmetrical photocurrent behavior, was preliminarily studied. The results exhibited the potential for application as a position-sensitive detector. [ABSTRACT FROM AUTHOR]

Diamond micro powders have been synthesized by chemical vapor deposition via etching a graphite substrate in hydrogen microwave plasma, without a hydrocarbon (methane) gas addition. The graphite temperature, varying from 700 to 1000 °C, was found to significantly affect the diamond nucleation and growth, the growth rate of the diamond particles increasing from 2.4 to ≈ 4 μm/h with the temperature. The diamond powders had a better crystalline quality at the substrate temperature of 900 °C. Because of low adhesion of the deposited grit to the substrate the particles can be collected easily and mechanically disaggregated. The average size of ≈ 12 μm of the dispersed particles grown for 5 h, was determined with a laser particle size analyzer, while the maximum grain size estimated with electron microscopy, varied between 12 and ≈ 20 μm. The particle's surface exhibited many micro-pyramids with sharp tips, that could be beneficial for abrasive applications. X-ray diffraction and Raman spectroscopy revealed high purity and quality of the diamond powders. [ABSTRACT FROM AUTHOR]

Vacancy-related color centers in diamonds, such as nitrogen-vacancy (NV) and silicon-vacancy (SiV) centers, have good application prospects in solid-state quantum technologies. In various applications, shot noise-limited sensitivity is determined by coherence time and photoluminescence (PL) intensity, which depends on the color center density. However, the conversion efficiencies of impurity atoms to color centers are low and usually increased by electron irradiation, which destroy the lattice structure and create defects leading to decoherence. In this study, we epitaxially grew diamond layers containing color centers on surfaces coated with metal stripes. The PL intensities of NV0, NV−, and SiV− centers located directly above the metal surface were 3.27, 3.47, and 11.15 times higher than those of the diamond epitaxial region. The [N]–[NV] and [Si]–[SiV] conversion efficiencies were 63.26% and 35.68%, respectively, which were comparable to or even better than those achieved by electron irradiation. Moreover, the region above the metal exhibited a high lattice quality, longer transverse relaxation time, higher magnetic field sensitivity, and larger NV−/NV0 ratio. The findings of this study can help advance the existing research on NV-based magnetometers, biofluorescent labeling, and interfacial spin quantum memory and be potentially applied to other vacancy-related color centers, such as germanium-vacancy. [Display omitted] • Diamond layers with color centers are grown on surfaces with periodic metal stripes. • The color centers above the metal surface exhibit high photoluminescence intensity. • The enhanced conversion efficiencies of impurity atom to color centers exceed those enhanced by ion implantation. • The spin coherence time, magnetic field sensitivity, and ratio of NV−/NV0 are also improved. [ABSTRACT FROM AUTHOR]

Microwave plasma assisted chemical vapor deposition (MPCVD) is a technique for preparing high-quality diamonds. However, the low yield and easy bonding between particles are drawbacks in the preparation of nanodiamond (ND). These issues are mainly caused by the adverse phenomena such as substrate nucleation and the continuous growth of particles. To inhibit these phenomena, diamond vapor phase nucleation (VPN) is realized by adjusting the spatial distribution of the carbon and hydrogen groups in plasma. In this environment, NDs nucleate, grow and fall on the disk. As such, dispersed nanodiamonds are obtained and the yield limit of MPCVD prepared NDs is broken. Further, we analyze and improve the VPN growth mechanism. This study presents a new mode of using MPCVD, which can be used to grow dispersed NDs. The development and improvement of this method is expected to provide higher quality NDs for drug transportation, biological imaging, and quantum light sources. [Display omitted] • A method for preparing nanodiamonds by vapor phase nucleation in plasma developed. • Plasma group distribution adjusted to separate nucleation and collection regions. • Continuous growth of nanodiamonds inhibited. • Dispersed nanodiamonds obtained in high yields. [ABSTRACT FROM AUTHOR]

• An interdigital-electrode structured UV detector with back-contact is designed and fabricated on single crystal diamond. • Higher responsivity and higher detectivity were observed when the back electrode contact was activated. • The mechanism for the improved performance has been revealed by UV-vis transmittance test and electric field simulation. An interdigital electrode of 200-nm thickness, 160-μm spacing, and 160-μm width was fabricated on one side of a diamond fabricated by chemical vapor deposition. A gold contact of 200-nm thickness was deposited on the back side of the diamond. The back contact and one half of the interdigital electrode were connected by a switch. Higher responsivity and higher detectivity were observed when the back electrode contact was activated. The results of electrical field simulation showed that a stronger electrical field formed over the diamond region in the device with the back electrode than in that without the back electrode. This indicated that the detector performance improvement could be attributed to the higher carrier collection efficiency achieved with the back electrode, particularly under ultraviolet (UV) light at certain wavelengths, which have longer attenuation lengths in diamond. This structure could also be applied to UV detectors based on other wide-band-gap semiconductors. [ABSTRACT FROM AUTHOR]

Abstract We report on high-quality microcrystalline diamond films deposited on Si substrates in microwave hydrogen plasma (without methane feed gas) using graphite powders with different sizes from 2 μm to 150 μm as the carbon source. Hydrocarbon radicals, necessary for diamond growth, are produced in course of the graphite etching by atomic hydrogen, and supplied into the plasma for further participation in diamond formation on the substrate. Owing to the large open surface area of the powder the approach allows a continuous long-term stable flux of hydrocarbons (as determined via in situ optical emission spectroscopy of the plasma) during the 10 h graphite etching process. The produced diamond films with grain size of ~1 μm were characterized with scanning electron microscopy and Raman spectroscopy, and exhibited similar morphology and crystallinity independent on the graphite powder dimensions. Highlights • Diamond films are grown by etching graphite powder in hydrogen microwave plasma. • Continuous, stable flux of hydrocarbons is provided in graphite/hydrogen system. • Spontaneous diamond nucleation on graphite is impeded at high temperature. [ABSTRACT FROM AUTHOR]

Herein, we describe the fabrication of CuO-Cu 2 O@graphene nanosheet composites by one-step in situ anodic oxidation, showing that graphene nanosheets vertically oriented on the Cu foam skeleton can be easily grown by microwave plasma-enhanced chemical vapor deposition. Microstructural characterization revealed that the formation of CuO-Cu 2 O nanoparticles in the bottom gaps of graphene nanosheet arrays (i.e., at locations featuring active sites and having access to the Cu source) results in the generation of accurate hybrid nanostructures. Additionally, the spread of the electrolyte could be effectively adjusted to control the transition of the charge storage mechanism from electrical double-layer capacitor to pseudo-capacitor-type. Thus, at high scan rates, the composite electrode acted as an electrical double-layer capacitor, acting as a pseudo-capacitor at low scan rates. A specific capacitance of 243 mF cm −2 was determined at a scan rate of 10 mV s −1 in 6 M aqueous KOH, increasing by almost 20% after 5000 charge-discharge cycles. The fabricated electrode exhibited a maximum energy density of 5.06 mWh cm −3 at a power density of 0.18 W cm −3 and a maximum power density of 5.64 W cm −3 at an energy density of 2.27 mWh cm −3 , thus showing superior performance in terms of electrochemical property tunability and cyclability. [ABSTRACT FROM AUTHOR]

• A multiphysics coupling model of plasma generated by pure hydrogen excitation has been established. • As the input microwave power rises, the volume of the plasma increases, yet as the pressure rises, the plasma ball's volume decreases. • At the same input power, the average and peak electron density have opposite trends with the increase of deposition pressure. • Under the same deposition pressure, the greater the input power, the more the plasma parameters are affected by power changes. The state of the plasma plays a crucial role in the progress of the reaction in the deposition chamber and the deposition quality of the carbon material. And the information on plasma electric field distribution, electron number density, electron temperature, and gas temperature is essential to optimize the operation of the MPCVD system. Thus, this paper studied the characteristics of hydrogen plasma in microwave plasma chemical vapor deposition chambers at different conditions. The Multiphysics coupling model of plasma generated by pure hydrogen excitation has been established to calculate the effects of deposition pressure and microwave input power on the main characteristics of hydrogen plasma. As a result of this research, different characteristic quantities have differing sensitivities to process parameters. The electric field strength and electron density are greatly affected by microwave power, while the gas temperature and electron temperature are greatly affected by the deposition pressure. Also, the volume of the plasma ball increases with increasing microwave power and shrinks with increasing deposition pressure; therefore, to increase the power density without changing the plasma ball size, the two parameters must be balanced in tandem. And the temperature results are compared to the experiment, showing a very good correspondence that validates the simplifying assumptions made in the model. [ABSTRACT FROM AUTHOR]

A diamond Schottky alpha-voltaic nuclear battery (DSAB) is fabricated, and the alpha-particle degradation test is performed. The device is formed on oxygen-terminated intrinsic CVD diamond epitaxially grown on B-doped HPHT diamond. An open-circuit voltage of 1.13 V and a short-circuit current of 53.4 pA are measured under a low-activity alpha source with 8.85 μCi/cm 2 irradiation, and a total conversion efficiency of 0.83% is obtained. The DSAB simultaneously has better open-circuit voltage and short-circuit current stability than Si and SiC diodes, which means that DSAB has the highest potential for achieving high and stable conversion efficiency. [ABSTRACT FROM AUTHOR]

A highly selective anisotropic etching method for single-crystal diamond was investigated. After a thin film of Fe was deposited on the diamond surface, it was processed in H plasma activated by microwave plasma-assisted-chemical vapor deposition (MPCVD). Spurred by the high catalytic activity of Fe, the diamond was easily etched, with masked areas (i.e., with no Fe deposition) remaining smooth or barely damaged. The etch rate was 180 nm min −1 . This method provides a simple and alternative way for diamond processing and patterning. [ABSTRACT FROM AUTHOR]

Forests of vertically aligned carbonaceous microcones are fabricated directly on a nickel mesh by microwave-plasma-assisted chemical vapor deposition. The microstructure is formed through a simple one-step process involving self-assembly. The fabricated composite exhibits superhydrophobicity and superoleophilicity as well as low density, owing to which it floats on water and can be used for the in-situ separation of oil from water at the oil/water interface. Furthermore, the composite exhibits pH responsivity, and its water permeability can be varied simply by altering the pH of the aqueous solution. In addition, the composite is suitable for use as an electrode material for supercapacitors owing to its large geometric surface area, porous structure, and superior electrical properties, which allow for fast ion and electron transportation. Thus, this composite consisting of forests of vertically aligned carbonaceous microcones on a nickel mesh is expected to find use in a wide range of fields and applications, including in environmental cleanup, flow switches, and energy storage devices. [ABSTRACT FROM AUTHOR]

Aiming at the hot spots heat dissipation in power integrated circuits and challenging growth problems of large size single crystal diamond, a novel heat sink strategy is proposed, based on a diamond single crystal-polycrystalline hybrid microchannel for directional heat dissipation of hot spots. The numerical simulation results show that the distribution of radiator materials in different heat flux regions can greatly improve the overall temperature uniformity. Compared with the other two types of heat sinks, the heat dissipation performance of the diamond single crystal-polycrystalline hybrid microchannel radiator is improved by 61.8 % and 16.9 % respectively. And this advantage is more obvious in the case of high heat flux and large hot spot size. When the hot spot heat flux is 1600 W/m·K and the hot spot size is 5 mm × 5 mm, the maximum surface temperature of hybrid heat sink is only 336.5 K and 328.7 K, respectively, which is far lower than the device failure temperature. By microwave plasma chemical vapor deposition (MPCVD), 390 μm thick high quality bonding layer was obtained, and a diamond single crystal-polycrystalline hybrid microchannel heat sink was prepared. The heat dissipation scheme proposed in this study is a promising route, which is expected to improve the performance and stability of power devices through efficient directional heat dissipation, and will further promote the application of diamond materials in the field of heat dissipation. [Display omitted] • A novel heat dissipation strategy for power devices is proposed based on single and polycrystalline diamond-based design. • Directional heat dissipation is achieved using SCD for the central part of the heat sink and PCD for the background area. • The novel strategy proposed here shows superior performances compared to Si and PCD based heat sinks. • Growth experiments show that the proposed preparation scheme is easy to realize. [ABSTRACT FROM AUTHOR]

An ultraviolet (UV) detector on single crystal chemical vapor deposition (CVD) diamond with three-dimensional (3D) metal electrodes, is designed, and fabricated with the aim to improve collection efficiency of photo-induced carriers. Interdigitated Ti/Au electrodes were formed within 10 μm deep groove etched in diamond to ensure a more uniform field pattern in the diamond bulk. In the preliminary tests the groove-shaped 3D device performance was compared to a detector with a conventional planar structure on the same material at applied electric field of 1 V/μm. It is found that the responsivity of the 3D electrode structure in the spectral range of 220–280 nm is up to 50% higher than that for the planar structure. [ABSTRACT FROM AUTHOR]

Well-ordered opal-diamond composite and inverted opal structure in single crystal (SC) diamond have been prepared by microwave plasma CVD. The process is based on epitaxial diamond growth through a monolayer of densely packed SiO 2 spheres placed on a (100) HPHT diamond substrate. Finally, the opal monolayer with ≈ 600 nm sphere diameter was completely embedded in SC CVD diamond forming a new type of ordered diamond composite. In addition, the inverse opal structures (air cavities in diamond) were produced by SiO 2 etching. The XRD analysis confirmed the single crystal nature of the deposit. The photoluminescence spectrum exhibits a strong peak at 738 nm wavelength of silicon-vacancy defects in diamond, indicating Si doping during the CVD process. The optical properties of the diamond structures were evaluated also with Raman spectroscopy and optical reflection spectrometry. The developed epitaxy-through-mask approach is considered as a potential strategy to fabricate multilayered (3D) SC diamond photonic crystals. [ABSTRACT FROM AUTHOR]

Single-crystal diamond was synthesized in a microwave plasma assisted chemical vapor deposition system with periodical injection of methane/hydrogen mixture in a closed reaction chamber. The gas was refreshed during a short time based on monitoring of carbonaceous species in the plasma with optical emission spectroscopy. The utilization of the precursors was increased with this strategy by about 12 times compared with the common process of the diamond growth using continuous gas flow. The structure of homoepitaxial diamond films produced in common and the periodical injection regimes was analyzed with scanning electron microscopy, atomic force microscopy, photoluminescence and Raman spectroscopy. The samples grown in the gas economy mode demonstrated a faster growth rate and smoother surface. • Single crystal diamond is grown by microwave plasma CVD with periodic gas injection. • Enhanced utilization of CH 4 precursor is achieved in a closed reaction chamber. • In situ control of carbon content in plasma with optical emission spectroscopy. • Smooth diamond surface is observed in gas economy growth mode. [ABSTRACT FROM AUTHOR]

Transparency in the infrared (IR) light region and high conductivity for electromagnetic (EM) shielding performance are contradicting properties for conventional window materials. It is challenging to explore a new class of materials with both IR transmittance and high electrical conductivity. Herein, middle-IR transmittance and EM-shielding performance are realized by graphene network fabrics (GNFs). GNFs are fabricated by chemical vapor deposition using copper mesh with different geometric constructions as the sacrificial substrate. The structure of GNFs endows the as-fabricated material high IR transmittance, good electrical conductivity, and EM-shielding efficiency. The grid parameter τ with regard to the square aperture and wire width exerts a profound effect on the EM-shielding performance. The highest EM-shielding efficiency is 12.86 dB at 10 GHz with a transmittance of 70.85% at 4500 nm. Meanwhile, the highest IR light transmittance is 87.85% with an EM-shielding efficiency of 4 dB. Based on the experimental and theoretical analyses, the EM-shielding efficiency is prominently dependent on microwave absorption. [ABSTRACT FROM AUTHOR]

Highlights: [•] Transient temperature and thermal stress fields of CVD ZnS are simulated with FEM. [•] Thermal shock damage behavior is investigated by oxygen propane flame experiments. [•] Surface temperature increases sharply in short time results in a high thermal stress. [•] Cracks initiate from the shock region and then propagate towards the outside. [•] Give some suggests for future engineering application of CVD ZnS on infrared window at supersonic velocity. [Copyright &y& Elsevier]

Amorphous boron powders were applied to grow boron-doped diamond (BDD) films with chemical vapor deposition method. The material is nontoxic and noncorrosive compared to conventional boron sources such as boroethane. The mechanism for using solid boron source as the dopant in low temperature and low pressure has been explained with a non-equilibrium thermodynamic coupling model and optical emission spectroscopic analysis. The BDD film was utilized in a non-enzymatic glucose sensor. A porous Au/Ni layer was then placed on the BDD surface for enhanced sensitivity. The electrode was characterized by scanning electron microscopy, Raman spectra, X-ray diffraction, cyclic voltammograms and amperometric responses. Typically operated at a voltage of 500 mV, it demonstrated fast response to glucose thanks to its large surface, rapid electron transfer, and synergetic effects between Au and Ni. Two specific linear ranges are found, one between 0.02 and 2 mM, and a second one between 2 and 9 mM. The detection limit and the best sensitivity are 2.6 μM and 157.5 μAmM−1 cm−2. Unlabelled Image • The dopant made from boron and graphite powders was applied to deposit BDD films. • BH radical was detected by OES, meaning that solid boron was an effective dopant. • The thermodynamic mechanism of BDD growth in CVD process was revealed. • Porous bimetallic Au/Ni layer observably improved electrochemical property of BDD. • The Au/Ni/BDD electrode can detect glucose with high sensitivity and stability. [ABSTRACT FROM AUTHOR]

The Wenzel-Cassie coexistent underwater wetting state is the key to enabling highly effective underwater oxygen-consuming reactions. • The superhydrophobic and conductive carbon nano-onions were prepared by a simple one-step microwave plasma enhanced chemical vapor deposition. • The fabricated carbon nano-onions were used to modify the surfaces of various materials and structures toward their application to self-cleaning, oil-water separation, and enabling highly effective underwater oxygen-consuming reactions. • The Wenzel-Cassie coexistent underwater wetting state is the key to enabling highly effective underwater oxygen-consuming reactions. Electrode surfaces with superhydrophobic and conductive properties exhibit a unique energy-mass transfer behavior in electrolytes. Therefore, the rational design of electrode surface structures, conductivity, and infiltration performance is expected to yield more efficient electrochemical reactions and solve the gas-deficit problem that hinders many underwater gas-consuming reaction systems. In this paper, hydrogenated carbon nano-onions displaying superhydrophobicity and conductivity were prepared by microwave plasma-enhanced chemical vapor deposition, which exhibited remarkable transferability and designability. The fabricated carbon nano-onions were used to modify the surfaces of various materials and structures toward their application to self-cleaning, oil-water separation, and enabling highly effective underwater oxygen-consuming reactions. Systematic analyses of the different wetting states of the superhydrophobic electrodes coated with the fabricated carbon nano-onions indicated that the different wetting states have important effects on their behaviors for underwater nucleation reactions, thus changing the efficiency of underwater oxygen-consuming reaction systems. The results reveal that designing a superhydrophobic electrode with a Wenzel-Cassie coexistent underwater wetting state, rather than a Cassie state or Wenzel state, is the key to enabling highly effective underwater oxygen-consuming reactions. [ABSTRACT FROM AUTHOR]