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The fabrication of GaN-on-diamond structure by the process of diamond growth on GaN technology is becoming more and more attractive for high-power GaN devices. However, due to the high-temperature steps employed during the GaN epitaxial layer transfer process, significant stress accumulates in the GaN-on-diamond structure and induces the formation of cracks or deformations in the GaN layer. To improve the stress characteristics of the GaN layer, in this work, dual-sided diamond film deposition was carried out to accomplish the GaN-on-diamond structure. The surface morphology, interface microstructure and crystal quality of diamond on GaN were analyzed by using scanning electron microscopy, atomic force microscopy, transmission electron microscopy and X-ray diffraction. The results showed that the stress accumulation originating from the GaN epitaxial layer transfer process was effectively alleviated as compared with other reporteds in the literature and that the crystal quality of the GaN was only slightly altered. The stress relaxation was attributed to the low-quality diamond used as the temporary carrier during the GaN transfer process. In addition, a thin SiC transition layer in the interface is also beneficial in alleviating the mismatch between the coefficients of thermal expansion for the GaN and the diamond.

To study the interface characteristics between substrates and homoepitaxially grown single crystalline diamond layers, the high-pressure/high-temperature Ib diamond seeds with homoepitaxial diamond layers were annealed by low-pressure/high-temperature treatment in a hydrogen environment. The stress evolution and related impurity transformation near the interface were characterized by Raman spectroscopy, photoluminescence, and micro-infrared spectroscopy before and after annealing. It is found that the stress is the smallest in a 100 µm wide zone near the interface, accompanying with the similar change in substitutional nitrogen (Ns) concentration. After annealing at 1050 °C, 1250 °C, and 1450 °C, the local compressive stress is released gradually with temperature change. It is decreased by 1.03 GPa in maximum after annealing at 1450 °C. The concentration of nitrogen–vacancy (NV) complexes in the chemical vapor deposition (CVD) layer is dramatically reduced at 1450 °C. The value of ${{{I_{{\rm{N}}{{\rm{V}}^-}}}}/{{I_{{\rm{diamond}}}}}}$ decreases much more than ${{{I_{{\rm{N}}{{\rm{V}}^0}}}}/{{I_{{\rm{diamond}}}}}}$ in the CVD layer, which is due to the lower stability of NV− compared with NV0 at high temperature.

As we know that more effective synthesis of diamond combined with physical and chemical properties of hy- drogen termination in aqueous environment as well as device structure design can greatly facilitate the chemical and electrochemical applications of higher cost-performance diamond. For this purpose, the direct-current (DC) characteristics, surface reaction and reparation of a hydrogen-terminated DC arc jet plasma CVD polycrystalline diamond, which has a high cost-performance, were characterized byI-Vexperiments based on a FET-like structure device in multiple aqueous solutions. The variation trends of theI-Vproperties of device based on pH were similar in different aqueous solutions but could be affected by disparate ions (such as K+ions) or organic molecules (such as citric acid radicals or a benzene ring). Especially, owing to the founded replacement of hydrogen termination with hydroxyl (eOH), carboxyl radical (eCOOH) or carbon-oxygen bond (eCeOeCe) in mixed solution, i.e., KHP + H2SO4(and +NaOH) solutions, the resistance of the device was remarkably in- creased from 13.57 kΩto 95.78 kΩ. However, the raised resistance of surface reacted diamond (SRD) can be reduced prominently by repairing hydrogen termination through negative potential sweeps (NPS) at a low ne- gative potential (−1 to−3 V) if the SRD was introduced as an electrode in a strong inorganic acid. What's more, the NPS repaired device, which subsequently stored for four weeks, was more sensitive than the original hy- drogen plasma-treated diamond in aqueous solution environments. This repaired result was coming out of NPS re-formed CeH bonds with higher intensity. Thesefindings will be the references of failure and reparation of diamond hydrogen termination in aqueous environment.

A multilayer Re/Ir coating was deposited on WC substrate by RF magnetron sputtering deposition system. SEM, AFM, XRD, HRTEM, Nano Indenter and contact angle were used to characterize the morphology, micro-structure and anti-sticking property. The results demonstrated that the multilayer Re/Ir coating presented higher anti-sticking property and mechanic performance comparing with the monolayer coatings. The formation of TaC at elevated temperature and coherent boundary between Ta and Ir crystalline were both assumed to impede the further diffusion of C or Co atoms. Moreover, the ordered nanostructure enhanced the bonding between Re and Ir at interface, which made it difficult for Ca, Ba of glass network modifiers elements to penetrate in protective films, and alleviate adhesion of glass at elevated temperature. The motion of edge dislocations and stacking faults were also significantly impeded due to the increase of interfaces and grain boundaries. This restriction probably contributes to improving the mechanical property, which is benefit to the lifetime of mold and the quality of the optical glass product. The wetting angle at high temperature was adopted to evaluate the anti-sticking property of multilayer coating, and shown the coherent results as mentioned before.

To unfold the promise of diamond as an advanced technical material, single-crystal diamonds (SCDs) and polycrystalline diamonds (PCDs) were smoothed by high-precision three-dimensional movement dynamic friction polishing (3DM-DFP) to achieve the ultra-smooth surface with roughness

The surface conductivity on the H-terminated diamond is still an interesting topic in the field of diamond electronics. Until now, the carrier mobility in the conductive channel has been limited to below 200cm2/Vs due to the various surface scattering mechanisms. In this paper, a high mobility conductive channel on the H-terminated diamond surface was reported. Firstly, the high quality diamond films were deposited on the commercial CVD diamond substrates. After polishing, the H-termination was obtained by hydrogen plasma treatment. The surface morphology of the H-terminated diamond was observed by atomic force microscope (AFM) and scanning electron microscope (SEM). The crystal quality on the diamond surface was characterized by Raman spectroscopy. The impurities in the crystals were tested by photoluminescence spectroscopy. The surface conductivity of H-terminated diamond was monitored comprehensively by Hall test. It can be found that the sheet resistance decreases much and the carrier mobility increases dramatically after the hydrogen plasma treatment and mechanical cleaning. The maximum mobility value is up to 365cm2/Vs with carrier density of 2.9 × 1012 cm−2, which is the highest value reported. Raman spectra of diamond surface show that a peak appears at 1121.4 cm−2 after the hydrogen plasma treatment, which corresponds to the nanocrystal diamond or carbon clusters of sp3 bonded material. The corresponding mobility enhancement mechanism on the H-terminated diamond surface was proposed.

The strength of diamond films prepared by chemical vapor deposition (CVD) is usually much lower than that of natural-type IIa single-crystal diamonds. In this work, the fracture strength of free-standing diamond films deposited by direct current arc plasma jet CVD has been examined by conducting three-point bending experiments. The results obtained for both the polished and as-grown samples were in good agreement with a well-known Hall–Petch equation describing the relationship between the fracture strength and grain size, indicating that grain refinement represented an effective way of improving the mechanical properties of CVD diamond films. Furthermore, the diversification of the crystalline texture of the films achieved by polishing apparently increased their fracture strength, which was inversely proportional to the film thickness. A theoretical method for estimating the fracture strength of free-standing CVD diamond films by approximating their intrinsic strength was proposed, whereas their fracture toughness was determined by conducting simplified four-point bending tests at room temperature, 25 °C, using a single-edge pre-cracked beam method.

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.

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.

This paper is focused on the in-plane crushing of two-dimensional (2D) porous structures with a special attention on the effect of functionally graded (FG) porosities. The dynamic response and energy absorption of closed-cell metal foams with different porosity distributions are investigated by using finite element (FE) analysis. Two symmetric, two asymmetric and one uniform distributions of internal pores along the impact direction are constructed with Voronoi tessellation. The proposed porous structure is crushed under the impact of a rigid panel with a constant velocity. The deformation of cell walls is simulated using a plastic kinematic material model. The erosion criteria and hourglass control are applied to ensure the accuracy of numerical results, which are validated against the experimental data from open literature. The effects of varying parameters on the energy absorption, deformation pattern, and stress-strain curve of the FG porous structure are discussed. The dynamic response is found to be influenced by different random cell geometries, porosity gradients, cell wall thicknesses, internal pore numbers, and impact velocities. The effective way to improve the energy absorption capability of the porous structure under a constant-velocity impact is proposed, shedding new insights into the deformation mechanism of the FG porous structure for engineering design.

A plasma arc generator was used to heat treat the free-standing CVD diamond films at 1450–1900 °C. An Arrhenius curve was fit according to trends in the measured Raman peak intensity ratio of diamond to graphite as a function of heat treatment temperature, and the curve was extrapolated linearly. It was found that the extrapolation lines intersected at the Debye temperature, ΘD = 2021 K. By comparing the activation energies of diamond graphitization in literature and from different measurement modes in our study, it was found that the graphitization mechanisms were different on both sides of Debye temperature due to differences in the excited lattice vibration modes. When the heat treatment temperature was just below the Debye temperature, the graphitization process was promoted by generating vacancies or the breaking of single C C bonds, and the apparent activation energy was 366 ± 60 kJ·mol−1. When the heat treatment temperature was above the Debye temperature, the graphitization process was promoted by the simultaneous breaking of multiple C C bonds, and the apparent activation energy was 887 ± 141 kJ·mol−1. In combination with the morphology changes on the surface of the CVD diamond film after high temperature heat treatment, the mechanism of the micro-cyclic phase transition on the surface of the diamond film at temperatures lower than Debye temperature was summarized as follows. First, C C bonds on the diamond surface were activated and broken at high temperatures, and some diamond carbon atoms dissociated from solid phase sites to the gas phase by forming hydrocarbon free radicals. Then, the carbon atoms from these hydrocarbons entered the graphite lattice step by step to complete the spontaneous deposition of sp2 clusters.

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.

To improve the transmittance of chemical vapor deposition (CVD) diamond, erbium(III) oxide (Er2O3) 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 Er2O3 antireflective films. With rising deposition temperature, the deposition rate, grain size and surface roughness of the Er2O3 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-Er2O3 {222} at deposition temperature increased to 400 °C. A thickness of 10 nm transition layer was observed between the Er2O3 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 Er2O3 antireflective films were increased for higher deposition temperature, which positively affects the IR transmittance and adhesion strength of the Er2O3 antireflective films on CVD diamond substrates.

In-situ micro-area analysis of precisely polished polycrystalline diamond (PCD) film by high-speed three-dimensional dynamic friction polishing (3DM-DFP) is carried out in this work, continuing from the previous works focusing on the subsurface cleavage and polishing mechanism. Multi-orientational grains with variable hardness anisotropy are generally considered the reason for the surface irregularity of PCD after smoothing. The unreached surface ultra-smoothness in local region after polishing is mainly resulted from the height difference at grain boundary (GB) area (e.g., a selected GB micro-region is of around Ra roughness of 5.7 nm and altitude intercept of 6.6 nm). However, different individual grains nearby showing (100), (110), (111) orientations are all of roughness

Polycrystalline CVD diamond films were subjected to transient heat treatment at the temperature range of 1500–1900 °C in the Ar/H2 plasma arc environment. The structural changes of the diamond grain boundaries (GB) were indirectly investigated by employing IR optical absorption, Raman spectroscopy, X-ray diffraction (XRD), and fractographic scanning electron microscopy (SEM). The graphitization difference between near-nucleation side and near-growth side is mainly due to the difference in the GBs' content. It is proposed that the bonded‑hydrogen atoms, of which a large amount remained in the diamond GBs, play an active role in the process of graphitization. We recognized the intensity evolution of a peak in Raman spectra located at 1470 cm−1, which was attributed to the trans-polyacetylene at diamond GBs. This result suggests the likelihood that the long-chain hydrocarbon precursor is involved in a mechanism for the sp3-to-sp2 transformation. As the propagation of the graphitization from diamond GB to grain interior, sp2 carbon with compressed state forms in its place due to the limited space for expansion. The graphite along GBs affects the fracture mode of the diamond films, which causes partial GBs to tear, while transgranular fracture occurs instead of directly intergranular fracture.

The H-terminated diamond films, which exhibit high surface conductivity, have been used in high-frequency and high-power electronic devices. In this paper, the surface conductive channel on specimens from the same diamond film was obtained by hydrogen plasma treatment and by heating under a hydrogen atmosphere, respectively, and the surface carrier transport characteristics of both samples were compared and evaluated. The results show that the carrier mobility and carrier density of the sample treated by hydrogen plasma are 15 cm2·V−1·s−1 and greater than 5 × 1012 cm−2, respectively, and that the carrier mobilities measured at five different areas are similar. Compared to the hydrogen-plasma-treated specimen, the thermally hydrogenated specimen exhibits a lower surface conductivity, a carrier density one order of magnitude lower, and a carrier mobility that varies from 2 to 33 cm2·V−1·s−1. The activated hydrogen atoms restructure the diamond surface, remove the scratches, and passivate the surface states via the etching effect during the hydrogen plasma treatment process, which maintains a higher carrier density and a more stable carrier mobility.

The growth process of carbon film on the surface of hydrocooling copper substrate in high-density direct current (DC) arc plasma was studied. Scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, nuclear magnetic resonance spectroscopy, and UV confocal Raman spectroscopy were used to analyze the structural constituents of the intermediate products generated at different growth periods. Results show that despite the remarkable heating effect of DC arc plasma to the copper substrate, one layer of cauliflower saturated carbon and double carbon bond as main component loose matter are first formed because of water-cooled copper substrate. With the increase in thickness of carbon film, the surface temperature gradually increases, the etching ability of the atomic hydrogen is enhanced and high concentration reactive units are maintained on the surface of carbon film. The cauliflower structure may effectively reduce the diamond nucleation barrier and promote the generation of nano-diamond. The diamond grains gradually grow up to the micron scale by the continuing influence of carbon-based active group and plasma. The growth pattern of carbon film on the hydrocooling copper substrate in high-density DC arc plasma may provide a new way to prepare large crack-free diamond films.

Y 2 O 3 films with different microstructures were deposited through radio frequency magnetron sputtering. The optical properties and the antireflection effects of the cubic and the monoclinic Y 2 O 3 films on diamond substrates were investigated. Results showed that the cubic Y 2 O 3 film had denser and more uniform grains with larger grain size. The band gap energies of the cubic and the monoclinic Y 2 O 3 films were 5.79 and 5.88 eV, respectively. This finding was mainly attributed to the decrease in grain size from 30.1 nm to 20.6 nm. Meanwhile, the reflective indices of the cubic and the monoclinic films were 1.887 and 1.817, respectively. Furthermore, the monoclinic and the cubic Y 2 O 3 films that have the same thickness generated antireflection effects on diamond at the 8–12 μm long-wave infrared (LWIR) range. However, due to the lower reflective index of the monoclinic Y 2 O 3 film compared with that of the cubic Y 2 O 3 film, the maximum antireflection effects of the Y 2 O 3 films on diamond shifted to lower wavelengths.

The addition of titanium (Ti) interlayer was verified to reduce the residual stress of diamond films. The evolution of interfacial stress during the cooling process is critical for the fabrication of large-area crack-free diamond films, so it is very worthy of further study. Variable-temperature X-ray diffraction (XRD) tests and finite element simulation were performed to evaluate the stress evolution of a diamond film. The film (with diameter of 150 mm) was prepared on a graphite substrate with Ti interlayer using DC arc plasma jet. Residual compressive stress in the diamond film is gradually increased during the cooling process. Moreover, the value and growth rate of the residual stress from the XRD tests are significantly lower than the finite element simulation results. All XRD peaks of diamond, graphite, and titanium carbide (TiC) generated on both sides of the Ti interlayer shift to a larger angle. By contrast, several XRD peaks of Ti deviate to a low angle. Elastic deformation of the Ti layer may offset the lattice contraction caused by the cooling effect. Elasticity modulus of TiC is significantly greater than that of Ti, which is more inclined to release the stress of the diamond film by self-fracturing. After the variable-temperature tests, residual compressive stress of the diamond film at room temperature is 1.1 GPa, whereas that before the tests is 1.4 GPa. These values are significantly lower than the finite element simulation results (3.05 GPa).

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 sp3 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.

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.

Y2O3 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 Y2O3 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 Y2O3 film had an anti-reflection effect on diamond in the 8–12 μm long-wavelength infrared (LWIR) range. However, the maximum transmittance of the Y2O3 film-coated diamond was shifted to lower wavelengths, which were mainly attributed to the reflective indexes of the Y2O3 film that decreased with the increase of the oxygen–argon ratio. The Y2O3 film with a cubic phase had high resistance to abrasion and plastic deformation. Therefore, the Y2O3 film with a cubic phase was much more suitable for long-wave infrared application.

The Y2O3 film deposited on chemical oxidation diamond substrate exhibited high adhesion strength and survived thermal shock at 800 °C. Oxygenated functionalization of the diamond surface had been successfully achieved via wet chemical oxidation with the increase in O/C atomic ratio from 0.04 to 0.13. The surface energy of the diamond substrate was significantly improved from 35.7 mJ/m2 to 61.4 mJ/m2. After depositing Y2O3 film on the diamond substrate, the COY bonds were observed at the interface. In addition, the quantity of COY bonds significantly increased with the chemisorbed oxygen concentration increasing. The critical scratch load of Y2O3 film deposited on chemical oxidation diamond substrate increased from 22.5 N to 34.1 N. Furthermore, the Y2O3 film deposited on chemical oxidation diamond substrate can withstand harsh thermal change and protect the diamond substrate from elevated temperature oxidation in atmospheric air without showing degradation of infrared optical performance. Keywords: CVD freestanding diamond, Chemical oxidation, Y2O3 antireflection film, Adhesion strength

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.