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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]

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]

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, Θ D = 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. [Display omitted] • The morphological changes of diamond surface dependent on temperature and hydrogen plasma environment were observed. • Taking the Debye temperature as a critical point, the graphitization activation energy exhibits a significant difference. • The graphitization mechanism of CVD diamond surface was proposed based on the kinetics analysis. [ABSTRACT FROM AUTHOR]

Polycrystalline CVD diamond films were subjected to transient heat treatment at the temperature range of 1500–1900 °C in the Ar/H 2 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. [Display omitted] • A transient heat treatment method was employed to effectively keep the GB graphitization at an early stage. • The Graphitization model demonstrated the long-chain hydrocarbon precursor was involved in the sp3-to-sp2 transformation. • The fracture of annealed diamond was completed between transgranular and intergranular crack propagation. [ABSTRACT FROM AUTHOR]

Advanced synchrotron radiation sources are major facilities for analyzing the formation and evolution of material structure in multidisciplinary research, owing to their high luminosity, low emittance, wide energy bandwidth and other characteristics. In China, several advanced synchrotron radiation sources are under construction, including the HEPS (High Energy Photon Source) and SHINE (Shanghai high repetition rate X-ray Free Electron Laser and extreme light facility). These facilities are poised to become major multidisciplinary research platforms in China. To meet the requirements of pixel detectors in these facilities, dedicated pixel readout chips are being developed, including HEPS-BPIX and HYLITE. This paper presents a high-speed serializer circuit developed in a commercial 130-nm CMOS technology for the full-scale (128 × 128) pixel readout chip of HYLITE, which requires a data rate of 4 Gbps currently. The serializer consists of a 16-to-1 binary-tree multiplexer, a ring-oscillating-based phase-locked loop (RO-PLL) and a current-mode logic driving stage with a multi-stage pre-amplifier. Test results demonstrate its expected functionality within a wide operating range from 0.52 Gbps to 5.5 Gbps. At 5.12 Gbps, the measured jitter values are about 2 ps for random jitter, 20 ps for deterministic jitter, and 47 ps for total jitter with a 10−12 bit error rate. Additionally, the horizontal and vertical eye openings are 0.84 UI and 72%, respectively. These positive results indicate that the serializer meets the requirements of HYLITE. [ABSTRACT FROM AUTHOR]

Effectively regulating and promoting the charge separation and transfer of photoanodes is a key and challenging aspect of photoelectrochemical (PEC) water oxidation. Herein, a Ti-doped hematite photoanode with a CoFe-LDH cocatalyst loaded on the surface was prepared through a series of processes, including hydrothermal treatment, annealing and electrodeposition. The prepared CoFe-LDH/Ti:α-Fe2O3 photoanode exhibited an outstanding photocurrent density of 3.06 mA/cm2 at 1.23 VRHE, which is five times higher than that of α-Fe2O3 alone. CoFe-LDH modification and Ti doping on hematite can boost the surface charge transfer efficiency, which is mainly attributed to the interface interaction between CoFe-LDH and Ti:α-Fe2O3. Furthermore, we investigated the role of Ti doping in enhancing the PEC performance of CoFe-LDH/Ti:α-Fe2O3. A series of characterizations and theoretical calculations revealed that, in addition to improving the electronic conductivity of the bulk material, Ti doping also further enhances the interface coupling of CoFe-LDH/α-Fe2O3 and finely regulates the interfacial electronic structure. These changes promote the rapid extraction of holes from hematite and facilitate charge separation and transfer. The informative findings presented in this work provide valuable insights for the design and construction of hematite photoanodes, offering guidance for achieving excellent performance in photoelectrochemical (PEC) water oxidation. [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]

A pico-second timing (PIST) front-end electronic chip has been developed using 55 nm CMOS technology for future electron–positron collider experiments (namely Higgs factories). Extensive tests have been performed to evaluate the timing performance of a dedicated SiPM-readout system equipped with a PIST chip. The results show that the system timing resolution can achieve 30 ps for SiPM signals corresponding to minimum-ionizing particles (MIP) level (200 p.e.) and better than 10 ps for signals larger than 800 p.e. , while the PIST intrinsic timing resolution is 4. 76 ± 0. 09 ps. The time-over-threshold (ToT) response of the PIST ASIC has been attained, which can cover the SiPM response spanning from ∼ 560 p.e. to ∼ 25 , 000 p.e.. [ABSTRACT FROM AUTHOR]

70/30 copper-nickel alloy was manufactured by laser powder bed fusion (LPBF), followed by the comprehensive investigation on the relationship between its microstructures and mechanical properties as well as corrosion behavior. The results show that dislocation tangles at cellular boundaries can greatly contribute to its superior tensile properties than the commercial counterpart. In addition, the combination of dislocation tangles and nanoscale copper enrichment/nickel depletion directly leads to the heterogeneous film formation process during immersion in corrosive media. Moreover, experimental and computational results both suggest that exposed facets are another important role to determine the corrosion behavior of LPBF 70/30 copper-nickel alloy. • 70/30 copper-nickel alloy has been successfully manufactured via LPBF. • Fine grains and dislocation tangles contribute to its superior mechanical properties. • Elemental segregation and dislocation tangles lead to a nonuniform film formation. • More exposed (001) facets grains on X-Z plane promotes its faster oxidation rate. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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). [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]

The Y 2 O 3 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/m 2 to 61.4 mJ/m 2 . After depositing Y 2 O 3 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 Y 2 O 3 film deposited on chemical oxidation diamond substrate increased from 22.5 N to 34.1 N. Furthermore, the Y 2 O 3 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. [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]

The addition of titanium (Ti) interlayer was verified to reduce the residual stress of diamond films by self-fracturing and facilitate the harvest of a crack-free free-standing diamond film prepared by direct current (DC) arc plasma jet. In this study, the evolution of the Ti interlayer between large-area diamond film and substrate was studied and modeled in detail. The evolution of the interlayer was found to be relevant to the distribution of the DC arc plasma, which can be divided into three areas (arc center, arc main, and arc edge). The formation rate of titanium carbide (TiC) in the arc main was faster than in the other two areas and resulted in the preferred generation of crack in the diamond film in the arc main during cooling. Sandwich structures were formed along with the growth of TiC until the complete transformation of the Ti interlayer. The interlayer released stress via self-fracture. Avoiding uneven fragile regions that formed locally in the interlayer and achieving cooperatively released stress are crucial for the preparation of large crack-free diamond films. [ABSTRACT FROM AUTHOR]

Electrochemical etching method has been used to construct anode aluminum foils with large surface area for electrolytic capacitor application. The applied current concentrated on surface defects would cause excessive corrosion of aluminum substrate and accelerate the initiation of merged tunnels. Self-assembly treatment with sodium oleate presents considerable improvement on optimization of size and structure of etched tunnels. Experimentally, aluminum foils with high etched tunnel density nearly 1.5027 × 107 cm−2 could be prepared after 0.10 mmol L−1 sodium oleate treatment. Theoretically, molecular dynamic and quantum chemistry calculations reveal the self-assembly process of sodium oleate in forms of oleic acid on Al (100) facet. The results indicate that the oleic acid monolayer will form at molecular density nearly 0.855, 0.847 and 0.844 mol. nm−2 as electric field E equal 0, 0.10 V Å−1 and 1.00 V Å−1, respectively. Based on the calculations of surface coverage in electric field conditions, experimental adsorption isotherm has been corrected to determine the optimal concentration of self-assembly composition. • Self-assembly sodium oleate improved current distribution on aluminum surface. • Electric field facilitated formation of self-assembled oleic acid monolayer. • Electrostatic attraction promoted continuous adsorption of oleic acid molecule. • Computational surface coverage corrected adsorption isotherm in electric field. [ABSTRACT FROM AUTHOR]

Surface etching of single-crystal diamond (SCD) in hydrogen plasma plays a decisive role for high-quality homoepitaxy and surface conduction of diamond. The complexity of surface/subsurface condition such as defects would give rise to the distinct morphology features and even further result in the unpredictable properties. Correspondingly, the evolutionary relationship between the morphology and electrical properties of mechanically polished SCDs which have typical cleavage damage in microns depth after hydrogen plasma treatment still needs to be further completed. In this work, the chemical vapor deposited (CVD) SCDs with uniform polishing-caused subsurface cleavage were immersed in microwave hydrogen plasma for variable duration. Time-dependent morphological evolution, multi-mode etched pits (EPs) (resulting from local defects/cracks and dislocations) and associated etching mechanism were comprehensively studied. At the early stage of plasma treatment before 60 min, owing to the obvious surface roughing generated by preferential etching (with the rate of >400 nm/h) of severe mechanically damaged regions, the hole mobility was significantly deteriorated, also accompanying with the apparent drop of sheet concentration. Concurrently, the deposited surface sp 2 amorphous carbon (a -C) nanodots on diamond surface and non- sp 3 hydrogen bonds reconstruction, which arising from defect-etching produced local abundant carbon-containing radicals or possible exfoliation generated by hydrogen penetration of massive defective regions, also would play an adverse role for the conduction associated with (100) C–H surface. However, the surface roughness was reduced from the maximum 13.2 nm–4.2 nm by prolonging etching, resulting from the smoothing effect of small-angle crystal misorientation on waved height difference related to the uniform (111) cleavage and the removal of dense irregular EPs associated with polishing-induced local defects as well as the vanishing of surface a -C nanodots. In this case, the improvement of surface electrical properties together with the negative correlation of the mobility and sheet concentration were appeared by the gradual formation of (100) diamond surface and the building of uniform (100) C–H bonds. • CVD SCDs with typical subsurface damages(defects) were treated in pure hydrogen plasma. • Morphology evolution associated with polishing defects was time-dependently presented. • Surface sp2 nanodots deposition from defect-etching and CH reconstruction would affect electrical properties. [ABSTRACT FROM AUTHOR]

• Less Shockley partial dislocations (SPDs) are observed as the grain size decreases, which may be due to the transformation from intragranular to intergranular evolutionary mechanisms within a nanoscale range. • Stacking faults are markedly suppressed as the average grain size decreases. • The interaction of cluster defects with the SPDs produces a promoting effect on the nucleation of stacking faults. • Dislocation nucleation rate seems to be increased as a linear relationship following the increase in the grain sizes. Medium/high-entropy alloys (MEAs/HEAs) have become one of the primary research highlights in the material field due to their superior microstructure and mechanical properties. By means of molecular dynamic (MD) simulation, the tensile behavior of polycrystalline Fe 80-x Mn x Co 10 Cr 10 (x=20, 30, 40, 50) MEAs was investigated under uniaxial stretching. The effects of various strain rates (1 × 108 s−1, 1 × 109 s−1, 1 × 1010 s−1) and deformation temperatures (77 K, 300 K, 600 K, 800 K) on tensile properties and deformation mechanisms of Fe 80-x Mn x Co 10 Cr 10 (x=30, 40) MEAs were explored, and the interaction of dislocation defects with stacking fault including intrinsic and extrinsic stacking fault (ISF/ESF) as well as the evolution of dislocation and cluster defects were further discussed. Moreover, the relationship between grain size and flow stress of polycrystalline Fe 50 Mn 30 Co 10 Cr 10 MEAs was discussed. Results indicated that Fe 40 Mn 40 Co 10 Cr 10 and Fe 50 Mn 30 Co 10 Cr 10 alloys exhibited higher yield stresses and Young's moduli. The yield stresses, Young's moduli and average flow stresses of Fe 40 Mn 40 Co 10 Cr 10 and Fe 50 Mn 30 Co 10 Cr 10 MEAs increased with an increase in strain rates from 1 × 108 to 1 × 1010 s−1. Besides, the deformation temperature produced a considerable influence on its mechanical properties. The phase transformation, grain boundary glide, dislocation slip and twinning formation together accounted for the plastic deformation behavior of Fe 80-x Mn x Co 10 Cr 10 MEAs under uniaxial stretching on an atomic scale. [Display omitted] [ABSTRACT FROM AUTHOR]

• Transferred electrons facilitated stable inhibiting adsorption layers. • Negative free energy of complexation reaction accelerated aluminum dissolution. • High binding energy enhanced the interaction with aluminum surface atoms. • Inhibiting adsorption layer improved tunnel density on etched aluminum foils. • Computational descriptor processed design of inhibitors for aluminum etching. The tunnel density and capacitance of etched aluminum foils would be significantly decreased for excessive dissolution during electrochemical etching process. The addition of low-concentration corrosion inhibitor solutions effectively improved the tunnel distribution. Various organic molecules as 8HQ, BTA, MBT, Citric Acid and Oleic Acid were analyzed using DFT and MD simulations and etching solutions with corrosion inhibitors at concentration of 0.10 mmol L −1 were designed. Relationship of physicochemical parameter and experimental tunnel density was established. The results indicate that Oleic Acid presents excellent corrosion inhibiting performance on the improvement of tunnel density as ρ = 1.5925 × 10 7 cm −2 and predicted capacitance as C = 0.72 μF cm −2 at 520 V. [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]