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Polyethylene glycol (PEG) is widely used as a phase change material (PCM) in thermal energy storage systems due to its high latent heat and chemical stability. However, practical application has been hindered by its low thermal conductivity and leakage issues. Therefore, developing shape-stable high thermal conductivity PCM is of great importance. In this study, new shape-stable composite PCM with high thermal conductivity and leak-prevention capabilities were designed. The porous carbon skeleton of diamond foam (DF) and dual-3D carbon nanotube-diamond foam (CDF) were prepared using the microwave plasma chemical vapor deposition method. The composite materials (DF/PEG and CDF/PEG) were produced by vacuum impregnation with PEG and skeletons. The results showed that CDF/PEG had the highest thermal conductivity, measuring 2.30 W·m−1·K−1, which is 707% higher than that of pure PEG. The employing of 3D networks of CNTs, which can improve the phonon mean free path in DF/PEG (1.79 W·m−1·K−1) while reducing phonon dispersion.The phonon vibration of dual-3D CDF plays an important role in heat transfer. PEG was physically absorbed and well-distributed in CDF, alleviating leakage of liquid PEG. The weight loss of CDF/PEG was only 25% at 70 °C for 120 s. Using CDF is an attractive and efficient strategy to increase the heat transfer of PEG and improve heat storage efficiency, alleviate the problem of poor shape-stability. [ABSTRACT FROM AUTHOR]

With its excellent properties such as high thermal conductivity, strong radiation resistance and high electron mobility, diamond has become one of the most suitable materials for radiation detectors. Detector-grade diamond requires low impurity content, low dislocation density and other defects. However, it is very difficult to keep low impurities and low dislocations simultaneously in the actual crystal growth process. In this study, microwave plasma chemical vapor deposition (MPCVD) method was used to grow diamond layer on two high-quality HPHT diamond substrates with the previously optimized process conditions. The nitrogen impurity content and structure of the HPHT substrate and growth layer were characterized and analyzed. The results show that, the content of nitrogen impurity on two HPHT substrates are 7. 1 x 10-6% and 4. 04 x 10-8%, respectively, whereas in their epitaxial diamond layers, the nitrogen impurity content are 2. 1 x 10-7% and 5 x 10-8%, respectively. The full width at half-maximum of the rocking curve shows that the dislocation density of the MPCVD growth layer is comparable to the HPHT substrate, though some dislocations were introduced into the MPCVD growth layer, which increases the stress. Overall, the dislocations in the HPHT substrate and epitaxial layer of single crystal diamond are in the same order of magnitude. The high-purity single crystal diamond prepared in this work may be used in nuclear radiation detection and semiconductor fields. [ABSTRACT FROM AUTHOR]

In this paper, we present a novel method for growing carbon nanotubes (CNTs) via microwave plasma chemical vapor deposition (MPCVD) on diamond and silicon substrates. Scanning electron microscopy (SEM) and Raman spectroscopy analyses revealed dense, multi-walled carbon nanotubes growing on the diamond substrate. Optical Emission Spectroscopy (OES) showed that in the process of growing carbon nanotubes with the MPCVD method, the CH4 introduced into the system is excited by microwaves and dissociated to form active radicals such as C2 and CH, which are considered the C source of the synthesized carbon nanotube. Observation with high-resolution transmission electron microscopy (HRTEM) showed that most Ni catalyst nanoparticles that catalyze the growth of carbon nanotubes are located close to the diamond surface. In contrast, on the Si substrate, Ni catalyst nanoparticles were randomly distributed. A unique transition layer was observed between the diamond and carbon nanotubes, with the Ni particles being immersed into this transition layer and acting as anchors to fix the carbon nanotubes, resulting in a robust connection between the diamond and the CNT coating. [ABSTRACT FROM AUTHOR]

The demand of small-angle x-ray scattering (SAXS) windows for in-situ characterization of materials nano-structures in a heated vacuum environment has been increased dramatically. High-quality diamond prepared by chemical vapor deposition (CVD) has become the preferred window material due to its excellent optical and mechanical properties. However, impurities and defects in diamonds may lead to the strong X-ray scattering especially in the heating process, affecting the testing accuracy of the object. In this work, single-crystal diamond (SCD) and polycrystalline diamond (PCD) films with different quality were prepared, and their SAXS properties were investigated at room temperature and heating under vacuum. The results show that the scattering intensity of the undoped high-quality SCD is small and uniform, while that of the SCD window doped with a small amount of nitrogen increases, mainly due to the nitrogen atoms and vacancy clusters scattering. While for the PCDs, the grain boundaries and the dark features lead to strong scattering background. As the temperature rises from room temperature to 280 °C, although the phonon vibration of diamonds exhibits the obvious temperature dependence, the coherent scattering of diamonds with X-ray hardly changes, indicating no new scatterers with the changed gyration radius were generated in the heating process. SCD and PCD windows were successfully applied in an in-situ heating SAXS cell. [ABSTRACT FROM AUTHOR]

In the present study, two types of diamond films with a diameter of 123 mm were deposited by DC arc plasma jet chemical vapor deposition (CVD) operating in the gas recycling mode. These two diamond films were found to possess peculiar grain family morphologies. The fracture strengths of the samples were 182.65 and 995.58 MPa, respectively. To investigate the possible reason for the large difference in the fracture strength between the samples, the surface and fracture morphologies of the two types of diamond films as well as their grain size were characterized. The results revealed that the sample with low fracture strength suffered from a typical intergranular fracture. Weak grain boundary, impurities distributed in the boundary, and low strength of diamond grains led to a decrease in the fracture strength. However, the sample with high fracture strength mainly suffered from transgranular fracture and the columnar grain exhibited numerous voids. Owing to the impact of twinning, the voids could be occupied, thus increasing the contact area between the adjacent grains. Moreover, large grain family on the growth side contained numerous small grains and twins. These small grains, twins on growth side along with the difference of stress on surfaces inhibit fracture strength from decreasing rapidly. All these features benefitted fracture strength. Moreover, when the sample was loaded, the tips located in the voids probably resulted in increase of risk of stress concentration, which might have led to initiation of crack origin and eventual fracture. [ABSTRACT FROM AUTHOR]

Y 2 O 3 anti-reflection films were deposited on freestanding chemical vapor deposited (CVD) diamond substrates by radio frequency magnetron sputtering. The effects of oxygen–argon ratio on microstructure, composition, optical property and mechanical property were analyzed by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, spectroscopic ellipsometry, Fourier transformed infrared spectroscopy, and nanoindentation. The results showed that the crystal structure of Y 2 O 3 films transformed from cubic to monoclinic with the increase of oxygen–argon ratio. Meanwhile, the degree of non-stoichiometry of the film with the monoclinic phase was higher than the film with the cubic phase. Both monoclinic and cubic Y 2 O 3 film had an anti-reflection effect on diamond in the 8–12 μm long-wavelength infrared (LWIR) range. However, the maximum transmittance of the Y 2 O 3 film-coated diamond was shifted to lower wavelengths, which were mainly attributed to the reflective indexes of the Y 2 O 3 film that decreased with the increase of the oxygen–argon ratio. The Y 2 O 3 film with a cubic phase had high resistance to abrasion and plastic deformation. Therefore, the Y 2 O 3 film with a cubic phase was much more suitable for long-wave infrared application. [ABSTRACT FROM AUTHOR]

To improve the transmittance of chemical vapor deposition (CVD) diamond, erbium(III) oxide (Er 2 O 3) antireflective films were deposited on CVD diamond substrates by radio frequency (RF) magnetron sputtering. Effects of deposition temperature on structure, chemical composition and properties of the samples were investigated. A strong correlation was observed between the deposition temperature and crystalline structure evolution of the Er 2 O 3 antireflective films. With rising deposition temperature, the deposition rate, grain size and surface roughness of the Er 2 O 3 antireflective films increased. Changes of composition and chemical bonding of the films were analyzed. Results showed that the amount of bonding between Er and O atoms surface as the temperature increased. The films were structured by amorphous, monoclinic and cubic phase, with preferential orientations of C-Er 2 O 3 {222} at deposition temperature increased to 400 °C. A thickness of 10 nm transition layer was observed between the Er 2 O 3 antireflective films and the CVD diamond substrates by transmission electron microscopy (TEM). Moreover, the transition layer feature primarily consisted of Er, O and C. The hardness and modulus of Er 2 O 3 antireflective films were increased for higher deposition temperature, which positively affects the IR transmittance and adhesion strength of the Er 2 O 3 antireflective films on CVD diamond substrates. • The maximum transmittance of Er 2 O 3 /diamond sample was 80% in 7–11 μm range. • Texturization of Er 2 O 3 film interface was studied by HRTEM. • The higher deposition temperature favors crystallization of Er 2 O 3 film. • This study meets the requirements of windows for infrared (IR) imaging systems coating in the LWIR range. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) and diamonds are allotropes of carbon, exhibiting excellent thermal, mechanical, optical, and electrical properties. Integrating CNTs with diamonds could advance the thermal management of high-heat-flux devices, light absorption, and novel semiconductor devices. This study reports the synthesis of vertical CNTs on a diamond substrate using microwave plasma chemical vapor deposition (MPCVD). Enhanced interfacial adhesion between the CNTs and diamond was confirmed by subjecting the CNT/diamond composite to ultrasonic vibrations and analyzing the morphology via scanning electron microscopy. The growth mechanism of CNTs on the diamond and the CNT/diamond interface bonding behavior were investigated using scanning transmission electron microscopy, electron energy loss spectroscopy, energy-dispersive X-ray spectroscopy, and optical emission spectroscopy. The results indicate that the carbon supplied from two different sources drove the growth of CNTs primarily through the root-growth mechanism and, to a lesser extent, through the tip-growth mechanism. The tip-growth mechanism may involve the formation of a covalent connection at the CNT/diamond interface. For the root-growth mechanism, two interfaces emerged in the CNT/diamond composite, namely Fe/diamond and CNT/Fe. Additionally, mixed cementite phases connected the CNTs to the diamond substrate. Elucidating the bonding mechanism between the CNTs and diamond can provide insights into the dynamics of the carbon atoms in the catalyst and offer a deeper understanding of the growth mechanism of CNTs on the diamond substrate. [Display omitted] • Vertical carbon nanotubes were prepared on a diamond substrate using MPCVD. • Carbon nanotubes exhibited excellent adhesion responses on the diamond substrate. • The growth of vertical carbon nanotubes was driven by a dual-carbon source supply. • The robust connection of the carbon nanotubes and diamond substrate strongly relied on a cementite mixture. [ABSTRACT FROM AUTHOR]

Optical diamond materials are essential for infrared optical windows, microwave windows, and laser windows due to their exceptional properties. However, dark features inside the diamond are significant factors limiting optical properties, particularly at high deposition rates. This work focuses on adjusting crystallographic parameters to prepare (110) oriented optical-grade polycrystalline diamond films, aiming to mitigate dark features. Diamond films deposited via microwave plasma chemical vapor deposition (MPCVD) exhibit discernible quality stratification. Characterization analysis of diamond film samples with varying levels of black defects reveals a correlation: films with higher dark feature content tend to exhibit a preference for the (111) orientation, accompanied by a significant presence of penetration twins and interstitial voids. Conversely, transparent diamond films demonstrate a prominent (110) orientation, featuring numerous contact twins that alleviate competition from penetration twins and original grains during growth. Electron backscatter diffraction (EBSD) and scanning electron microscope (SEM) results reveal that transparent diamond films cultivated with a pronounced preference for the (110) orientation manifest consistent and seamless contact twins, leading to fewer dark features and improved optical transmittance. In contrast, (111) oriented diamond film exhibits numerous penetration twins, and holes form between them. Based on the analysis, 5-inch optical polycrystalline diamond films with (110) orientation were achieved successfully by suppressing dark features. [ABSTRACT FROM AUTHOR]

Graphite-based metal transition-layer substrates hold great potential for preparing large-area diamond films and achieving crack-free release. In this study, a five-inch crack-free free-standing diamond film was prepared on a graphite substrate with a sacrificial Mo/Ti double-layer transition layer using direct-current arc plasma jet chemical vapor deposition (DC jet CVD). The interfacial bonding and diffusion behavior between the diamond and the transition layers were investigated. The effect of abundant metal particles and elemental diffusion between layers on film adhesion and stress release are discussed and analyzed. The surface of Ti layer prepared by the multi-arc ion-plating contains numerous metal particles that provide a template for the fine-crystalline Mo layer. Metal particles are encapsulated and embedded in the diamond and act as anchors that ensure the stability of the substrate–diamond bond during high-temperature deposition. After deposition, those metal particles act as weak points and play crucial stress-release roles. Mutual elemental diffusion occurs between the Ti, Mo, and diamond layers. Ti penetrates the Mo layer to form a continuous 140-nm-thick thin layer during the initial deposition period, facilitating diamond nucleation. Carbon from the plasma and diamond diffuses into the metal transition layer. Thermal stress generated between the diamond and the graphite substrate is released by destroying the metal transition layer with high thermal expansion coefficient and low elastic modulus during cooling from the deposition temperature. Cracks rapidly propagate along the interface between destroyable transition layers and graphite substrate, which results in the liftoff of a fully crack-free diamond film. [Display omitted] [ABSTRACT FROM AUTHOR]

In the present investigation, a nitrogen-doped multilayer homoepitaxial single crystal diamond is synthesized on a high-pressure high temperature (HPHT) Ib-type diamond substrate using the microwave plasma chemical vapor deposition (MPCVD) method. When 0.15 sccm of nitrogen was added in the gas phase, the growth rate of the doped layer was about 1.7 times that of the buffer layer, and large conical and pyramidal features are formed on the surface of the sample. Raman mapping and photoluminescence imaging of the polished cross sectional slice shows a broadband emission, with a characteristic zero phonon line (ZPL) at 575 nm in the doped layers, and large compressive stress was formed in the nitrogen-doped layers. X-ray topography shows that the defects at the interface can induce dislocation. The pyramid feature is formed at the defect, and more nitrogen-related defects are formed in the pyramid region. Thin nitrogen-doped multilayers were successfully prepared, and the thickness of the nitrogen-doped and buffer layers was about 650 nm each. The indentation measurements reveal that the thin nitrogen-doped multilayers are ultra-tough (at least ~22 MPa m1/2), compared to the Ib-type HPHT seed substrate (~8 MPa m1/2) and the unintentionally doped chemical vapor deposition (CVD) single crystal diamond (~14 MPa m1/2). [ABSTRACT FROM AUTHOR]

Reducing the self-heating of SiC- and GaN/SiC-based high-powered devices by integrating diamond films offers promising performance enhancement of these devices. However, such a reduction strategy faces serious problems, such as diamond nucleation on SiC and stress accumulation greater than 10 GPa. In this work, a SiN x dielectric layer (∼50 nm) was coated onto the C polar face of a 4H–SiC wafer using microwave plasma chemical vapor deposition (MPCVD) to improve direct dense diamond nucleation and growth, significantly reduce the stress, and build Si–C(SiC)⋯Si⋯C(diamond) bond bridges. This SiN x thin layer, prepared by activating Si ions under Ar/N plasma during magnetron sputtering, gave rise to local Si 3 N 4 crystal features and a low effective work function (EWF) for promoting surface dipoles with electronegative carbon-containing groups. In the H plasma environment during diamond growth, the local Si 3 N 4 crystal was amorphized, and the N atoms escaped as a result of atomic H and the high temperature. At the same time, C atoms diffused into the SiN x and formed C–Si bonds (49.7% of the total C bonds) by replacing N–Si and Si–Si, thus increasing the direct nucleation density of the diamond grains. The diamond thin film grew rapidly and uniformly, with a grain size of approximately 2 μm in mixed orientation, and the stress of the 2-inch SiC-on-diamond wafer was extremely low (to ∼0.1–0.2 GPa). In comparison, partially connected diamond grains (>10 μm) on the bare SiC in the preferential (110) orientation resulted in a film with twin-grain features and significant stress, which was associated with the hexagonal lattice interface of 4H–SiC. These results are considered the material and surface/interface bases for actively controlling wafer fabrication and enhancing the heat dissipation of SiC and GaN/SiC electronics. [ABSTRACT FROM AUTHOR]

In this study, standard diamond bars were prepared using an ultra-thick diamond plate, and the bars had sizes consistent with the International Organization for Standardization (ISO) 14704:2016(E) three-point bending method for measuring the fracture strength. Ultra-thick diamond plate with dimensions of 125 mm (diameter) × 6.5 mm (thickness) were deposited using direct current arc plasma jet chemical vapour deposition. After cutting, grinding, and polishing, 12 diamond bars meeting the requirements of the ISO standard were prepared (36 mm × 4 mm × 3 mm) and tested for fracture strength using the cited ISO standard and elastic modulus using deflection measurements. The fracture strength of the ultra-thick diamond plate was found to be 580 ± 66 MPa. In addition, for comparison, the fracture strengths of standard ZnS, sapphire, and alumina were also analysed. Crucially, this is the first report of the fracture strength of standard-sized diamond plate. The effects of the defects and grain size on the crack formation and failure of the diamond film were analysed. The diamond's fracture strength was affected by the sample thickness, which caused the gradual accumulation of defects as this dimension increased, but not by its length and width. The elastic moduli of sapphire and alumina were compared. Overall, the measurement of the fracture strengths of ultra-thick diamond plate via the ISO standard is important for industrial applications. [ABSTRACT FROM AUTHOR]

Deposition of a consistent diamond coating on intricate surfaces has historically posed a difficulty. This article presents the advancement in research on depositing a uniform diamond coating on three-dimensional (3D) silicon spheres, utilizing a faraday cage within a microwave plasma chemical vapor deposition (MPCVD) reactor. A self-consistent three-dimensional multi-physics field model has been established for simulating the microwave electric field and plasma inside a reactor with or without a faraday cage. Results indicate the cage effectively reduces the discharge at the top of the silicon sphere and improves uniformity of the distribution of the microwave electric field and plasma electron density on the sphere's surface. MPCVD trials have demonstrated that a powerful discharge takes place at the apex of the silicon sphere resulting in an excessive thermal gradient if the cage is not added. The apex of the silicon sphere is covered with a blend of diamond and graphite phases. Due to the excessive internal stress of the coating, approximately 50 % of the samples experience coating detachment. After the addition of the cage, the strong discharge is transferred to the top of the cage, effectively suppressing the microwave electric field and plasma inside the cage. Improved quality, reduced internal stress, and enhanced uniformity of the polycrystalline diamond coating are achievable on the silicon spheres within the cage. Moreover, this technique offers a novel approach to coat diamond on complex 3D geometries. [Display omitted] • Three-dimensional multi-physics modeling verifies that faraday cage suppresses microwave electric field and plasma. • The Faraday cage improves the uniformity of the distribution of microwave electric fields and plasma in the internal space. • Uniform, high crystal quality, low stress diamond coating. [ABSTRACT FROM AUTHOR]

Slightly graphitization might be incurred on CVD diamond films when suffering instantaneous high temperature thermal shock. In this paper, phase transitions of CVD free-standing diamond films have been studied experimentally at the temperature range of 1500–1800 °C through a plasma rapid heating process. Raman spectra and X-ray photoelectron spectra (XPS) are compared and discussed for the purpose of measuring the percentage of graphitic carbon component in CVD diamond films after heat treatment at different temperatures. An obvious optical degradation took place in both visible and infrared bands with the increased treating temperature. The result indicates that graphitization is dominated along grain boundaries rather than in internal grains. In addition, the nitrogen related absorption peaks were not covered by the enhanced optical absorption background, which was caused by the opaque graphitic carbon formed at high temperature. Nitrogen concentrations have also been evaluated for these graphitized diamond films and there is no evidence to show the movement or aggregation of nitrogen atoms. [ABSTRACT FROM AUTHOR]

Abstract: Single‐crystal diamonds are successfully synthesized using microwave plasma chemical vapor deposition. A smooth and flat single‐crystal surface is obtained by optimizing the size relationship between the seed substrate and the square hole of the shielding ring. When the sample grows higher than the polycrystalline diamond on the molybdenum holder, the surface becomes uneven. The polarization characteristics of two kinds of chemical vapor deposition (CVD) layers are compared between flat and uneven surfaces. Abnormal high‐order birefringence occurs in both morphologies, which is related to the dislocation density in the CVD layers. The higher the dislocation density of the sample, the more obvious the high‐order anomalous birefringence. High‐pressure high‐temperature seed substrates have obvious defects, such as dislocations, stacking faults, and boundaries of the growth sector, and these defects are mostly distributed at the edge of seed substrates. When the diamond surface demonstrates an edge‐to‐center morphology, the dislocations in the seed substrate, interface‐induced dislocations, and dislocations formed in the growth layer begin to converge toward the central region of the CVD layer, which results in a smaller area of low stress in the center of the CVD layer. High dislocation density causes the crystal to have a mosaic structure and orientation deviation. [ABSTRACT FROM AUTHOR]

Microwave plasma chemical vapor deposition (MPCVD) was used to grow single-crystal diamonds on two types of single-crystal diamond seed substrates prepared by high-pressure, high-temperature (HPHT) and chemical vapor deposition (CVD) methods. The quality of diamonds grown on the different seed substrates was compared. Fluorescence characteristics showed that the sectors of the HPHT seed substrates were obviously partitioned. Raman and absorption spectra showed that the CVD seed substrate produced higher-quality crystals with fewer nitrogen impurities. X-ray topography showed that the HPHT seed substrate had obvious growth sector boundaries, inclusions, dislocations, and stacking faults. The polarization characteristics of HPHT seed substrate were obvious, and the stress distribution was not uniform. When etching HPHT and CVD seed substrates using the same parameters, the etching morphology and extent of different growth sectors of the two substrates differed. Although extended defects were inevitably formed at the interface and propagated in the CVD layer, the dislocation density of a 1 mm-thick CVD layer grown on a CVD seed substrate was only half that of a 1 mm-thick CVD layer grown on an HPHT seed substrate. Therefore, the use of CVD seed substrate enabled the growth of a relatively higher-quality CVD single-crystal diamond. [ABSTRACT FROM AUTHOR]

The CVD diamond films at different growth stages were prepared on the same substrate by DC arc plasma jet CVD. The surface morphologies and residual stress of diamond films were characterized by scanning electron microscope and Raman spectroscopy. The intrinsic stress of diamond films were obtained by subtracting thermal stress from residual stress. The results showed that the intrinsic compress stress was 0.42 GPa for the precoalescence stage due to the sp 2 carbon inclusions in diamond islands. With the diamond islands growing up and even snapping together to form grain boundary at the coalescence stage the intrinsic compress stress was 0.06 GPa. Eventually, the diamond islands coalesced into a continuous polycrystalline film, the intrinsic compress stress vanished and converted to tensile stress, the intrinsic tensile stress reached 1.41 GPa due to the number of grain boundaries increasing. The evolution of intrinsic stress during diamond film initial growth was mainly attributed to the surface free energy of diamond islands changed to the free energy of grain boundaries which was consistent with the Nix-Clemens model. [ABSTRACT FROM AUTHOR]

Polycrystalline CVD free-standing diamond films have been heat treated through a rapid heating process using a direct current (DC) arc plasma jet system within the temperature range of 1500–2000 °C. The optical transmission of the diamond film decreases when the treatment temperature exceeds 1500 °C. When the diamond film was annealed to 1800 °C for just 1 min, the infrared (IR) transmittance at λ = 10.6 μm of the film was significantly decreased from 60.5% to 4.0%, due to the transformation from diamond to graphite. Further increase of the temperature to 2000 °C leads to complete loss of optical transmittance in only 30 s, due to the detrimental occurrence of graphitization. XRD patterns indicate that graphite ultimately grows preferentially along the (0002) plane by forming disordered or turbostratic graphite as intermediate product. Raman spectra and SEM images verify that at 1500–1850 °C graphitic carbon transforms from the diamond surface in the form of protruding submicron crystallites, which were still containing a number of sp 3 C C bonds. In addition to graphitization on the external surface, the diamond-graphite phase transition also occurs along the grain boundaries and the calculated activation energy of the grain boundary graphitization process is 276 kJ·mol − 1 for the CVD diamond. [ABSTRACT FROM AUTHOR]

[Display omitted] • The La-doped Er 2 O 3 anti-reflection films was prepared by the power of magnetron sputtering. • The compound of La 2 O 3 formed along the grain boundary of the columnar crystal structure of the polycrystalline film. • The highest hardness and yield strength of the La-doped Er 2 O 3 film was two times higher than that of pure Er 2 O 3 film. • The transmittance of the La-doped Er 2 O 3 anti-reflection films only decreased 1% after erosion. The composition and microstructure consisting of anti-reflection films was obtained by the power of magnetron sputtering. X-ray photoelectron spectroscopy (XPS) and High-resolution transmission electron microscopy (HRTEM) provided evidence to support that the doping La element exists as oxide in the grain boundaries of the matrix Er 2 O 3 films. The undoped and La-doped Er 2 O 3 films show a columnar crystal structure of the main cubic (2 2 2) plane. Twinning and a large number of dislocations show up in the undoped Er 2 O 3 films due to the competitive growth of the columnar crystal. In addition, the La-doped Er 2 O 3 films show a lower roughness (RMS) value in comparison with undoped Er 2 O 3 films. The grain size of columnar crystals decreases significantly with increasing La concentration in the La-doped Er 2 O 3 films. The fine grains resulted in the La-doped Er 2 O 3 films developing high mechanical and impact resistance properties, with an increase in hardness from 12.6 ± 2.1 GPa to 26.1 ± 3.4 GPa and the eroding area rate decreasing from 38.9 % to 1.9 %. Moreover, the La-doped Er 2 O 3 anti-reflection films on the chemical vapor deposition (CVD) diamond substrate maintained 74 % transmittance in the long-wavelength infrared range of 8–12 μm after sand eroding. [ABSTRACT FROM AUTHOR]

Y 2 O 3 anti-reflection films were deposited on freestanding CVD diamond substrates by radio frequency magnetron sputtering. The thermal shock resistance and oxidation resistance of Y 2 O 3 /diamond/Y 2 O 3 samples at 727 °C and 800 °C in atmospheric air were investigated. No delamination of the Y 2 O 3 films occurred after thermal shock, thereby demonstrating extreme adhesion to freestanding diamond substrates. After thermal shock, Y atoms in the films were almost fully oxidized. Moreover, the majority of monoclinic phase in the Y 2 O 3 films transformed into cubic phase, crystallinity was enhanced, and the average grain size significantly increased. The maximum transmittance in the 8–12 μm long-wave IR range of the Y 2 O 3 /diamond/Y 2 O 3 samples increased from 81.3% ± 0.3% to 84.7% ± 0.2% and 83.6% ± 0.4%. These findings indicated that the Y 2 O 3 anti-reflection films displayed good resistance to thermal shock and provided sufficient protection for diamond substrates against elevated temperature oxidation. [ABSTRACT FROM AUTHOR]

In this study, the effect of defects on fracture toughness in different directions was investigated. Two diamond films with a diameter of 122 mm and as-deposited thicknesses of 2.2 and 1.5 mm, respectively, were deposited by DC arc plasma jet chemical vapor deposition. To accurately obtain the fracture toughness, the films were ground and polished to 1.6 and 0.8 mm, respectively. The results indicate that many defects, including pores, are introduced into the films during the growth process, particularly on the side close to the growth surface in thicker film. The size of pores reaches micrometres, which affects the fracture toughness under loading in different directions. Due to the minimum grain size, both films exhibit a maximum toughness of 8.2 and 10.0 MPa·m1/2, respectively, with growth-surface cracks. For the thinner sample, the maximum value is followed by that of the edge-surface cracks. As the grain size of the edge surface falls between that of the growth surface and that of the nucleation surface, the results indicate that fracture toughness is affected by grain size. However, the number of pores near the growth side increases when the thickness exceeds 0.8 mm. Pores reduce the toughness, resulting in the minimum fracture toughness (6 MPa·m1/2) of the thicker diamond film with edge-surface laser cracks. The sample with an edge-surface sharp pre-crack has a similar fracture toughness of 5.6 MPa·m1/2. This study provides guidance for selecting the applied load direction. • Two thick diamond films with thicknesses 2.18 and 1.48 mm were deposited. • Fracture toughnesses of the diamond films in three directions were investigated. • Numerous pores were formed in the diamond films during orientation growth. • Due to the effect of pores, the toughness values among three directions differ. [ABSTRACT FROM AUTHOR]

In order to realize the practical use of diamond as a semiconductor material, large-area single-crystal diamond wafers with uniform quality are required. Mosaic growth is an effective method to produce inch-grade single-crystal diamonds. However, the quality of the wafer is limited by the junction interface seriously, because cracking occurs easily due to the high internal stress. In this paper, the repetition growth method was adopted to grow mosaic splicing single-crystal diamond without polycrystalline diamond interface. The high-quality single crystal diamond slices were reduplicated by microwave plasma chemical vapor deposition (MPCVD). The substrates were obtained by cutting a piece of CVD diamond along a plane perpendicular to 〈001〉 (with a (100)-oriented surface). The evolution of the growth characteristics around the junction of the substrates at different stages was studied. The results show that the surface of the epitaxial layers gradually evolves from blurry terraces to a regular well-ordered step flow. When the substrates have the same deviation direction and the off-direction angles are within 3°, the junction of the substrates can connect smoothly. Raman mapping shows that there is a mixture of tensile stress and compressive stress near the junction. As the thickness of the epitaxial layer increases from 280 μm to 560 μm, the range of tensile stress near the joint area expands from 85 μm to 150 μm, the maximum tensile stress increases from 0.08 GPa to 0.16 GPa. In addition, the value of FWHM in the X-ray rocking curve is less than 2.80 cm−1 around the junction, which indicates good crystal quality. [Display omitted] • The evolution of growth characteristics around the junction in the mosaic diamond was studied. • The mosaic boundary evolved from blurry terraces to a well-ordered step flow and finally connected. • The lowest value of tensile stress near the joint area was reported as the film thickness increased. • The larger FWHM of Raman peak around the junction is caused by the increased tensile stress. • The "inherit" effect of NV content of the epitaxial layer was observed for the corresponding substrate. [ABSTRACT FROM AUTHOR]