Diamond Peak Research Articles

Growth of boron-doped diamond-like carbon films from a low-pressure high-density plasma in inductively coupled chemical vapour deposition

The main objective of this work was the preparation and optimization of boron-doped diamond-like carbon (DLC) films having a good crystalline structure, and electronic and optical properties, at an extremely low deposition pressure and relatively low growth temperature, by varying the flow rates of precursor gases (CH4, B2H6, and Ar) in the plasma controlled at 800 W of RF power. Planar inductively coupled plasma-enhanced chemical vapour deposition technique was used to enable deposition at ∼5.33 Pa and 450 °C, at a constant negative substrate bias of -40 V. The flow rate of the dopant gas (B2H6) was changed to obtain a set of samples, while the precursor gas (CH4) flow rate was kept fixed. The doped sample, prepared with B2H6/CH4 ratio (r) = 1 %, was found to possess a maximum ID/IG (intensity ratio of the D peak with the G peak) of ∼0.819 and a minimum IDia/IG ratio (relative intensity of the Diamond peak to the G peak) of ∼1.149. A high sp3 content of ∼50 % was revealed from the X-ray photoelectron spectroscopy analysis and the transmission electron microscopy images also indicated the presence of prominent 〈111〉, 〈220〉, and 〈311〉 crystallographic planes. The B-doped DLC film possessed enhanced electrical conductivity (σRT) of ∼3.02 ×10−5 S cm−1 relative to the intrinsic DLC films, a corresponding minimum of activation energy (ΔEH) (as calculated in the above room-temperature regime) of ∼170 meV, an optical band gap (Eg) of ∼3.35 eV, and the root mean square roughness of ∼48.12 nm.

Weak oxidant fraction in the microwave plasma influencing the evolution of nanocrystalline-diamond–imbedded diamond–like carbon network at low temperatures and its orbital hybridization dependent wide optical band gaps

The diamond-like carbon (DLC) thin films having intrinsic nanocrystalline diamond (NCD) components were synthesized on bare glass substrates at 300 °C, employing a (C2H2/CO2/H2/) gas mixture in MW-PECVD. Relevant influence of the weak oxidant fraction [F = CO2/(CO2 + C2H2)] in the plasma on the specific hybridized constituents (sp3 and sp2) in the C-network, optical transmission characteristics of the film, and its accomplished degree of nanocrystallinity were investigated. A substantial segment of the NCD was achieved in the DLC matrix. An optimized diamond-phase component corresponding to the minimized bond angle disorder in the matrix was accounted from the manifestation of the maxima of IDia/IG and IDia/ID simultaneous to the minimum of ID/IG ratio in Raman response, along with an allied diamond peak appearing near 1332 cm−1. The optimal DLC film at F = 0.23 revealed a wide optical band gap (Eg) of ∼3.60 eV, ∼59% sp3-hybridized C component of the diamond phase, and a significant sp3/sp2 ratio of ∼2.1. The film microstructure seemed homogeneous with uniformly distributed NCDs of average diameter ∼7.5 nm and dominant 〈111〉 crystallographic orientation. The sp3/sp2 fraction in the film matrix has been correlated directly to the IDia/IG and IDia/ID, and inversely to ID/IG ratios of the Raman data. Atomic-O, including atomic-H, remains instrumental in chemical reactions, facilitating the etching of graphitic and a-C phases while preserving the superior sp3-hybridized NCD component growing uninterruptedly in the DLC network that subsists shielded from the high-energy ion impact within secondary plasma under the shadow mask.

Turning the optical properties of microcrystalline diamond films by boron ion implantation and annealing

We investigated the correlation between microstructures and optical properties of boron ion implanted microcrystalline diamond (B-MCD) thin films annealed at different temperatures. Ellipsometry characterization of B-MCD films was performed in the wavelength range of 380–1000 nm and the disperse parameters of the films such as single oscillator energy and dispersive energy were uniquely determined by using a Gaussian model. The results show that the refractive index increases from 2.18 to 2.21 to 2.28–2.29 with annealing temperature increasing from 700 to 800 °C and then it slightly decreases to 2.25–2.28 with annealing temperature further increasing to 900 °C, implying that the annealing temperature has a significant impact on the optical properties of B-MCD films. Raman spectra reveal that the full width at half maximum of diamond peak significantly decreases after 800 °C annealing, indicating a better quality of diamond crystalline. X-ray photoelectron spectroscopy results show that this sample contains higher sp3 carbon content, lower sp2 and C–O contents on the film surface after 800 °C annealing, implying that fewer defects exist. The results are of great significance for the preparation of excellent boron ion implanted microcrystalline diamond for waveguide based Mach-Zehnder Interferometer liquid sensing.

The luminescence study of GeV centers and damage in diamond induced by 300keV Ge ion implantation

In this paper, the germanium-vacancy (GeV) in diamond produced by 300 keV Ge ion implantation and subsequent annealing, were investigated by Raman spectroscopy and photoluminescence (PL) spectroscopy, and meanwhile the different ion injection models were given by the Stopping and the Rang of Ions in Matter (SRIM) simulation. Results showed that the Raman peak of diamond shifted to the lower wavenumber after Ge ion implantation, indicating the ion implantation caused amorphous graphitization in the crystal that generated the local tensile stress. Most of the amorphous graphitization was eliminated at an annealing temperature of 300–700 °C by evidence of the variation of ID/IG value. When the annealing temperature was higher than 700 °C, the vacancy migrate a longer distance to find Ge ions, then convert Ge ions into GeV centers, and thus an interesting zero phonon line (ZPL) at 602.8 nm appeared which was associated with GeV center.

Investigation on the preparation of large area diamond films with 150–200 mm in diameter using 915 MHz MPCVD system

In this work, the diamond films with 150 mm in diameter were prepared in our home-made 915 MHz microwave plasma chemical vapor deposition (MPCVD) system. The appropriate height of the pocketed substrate holder was researched in order to reduce the edge effect as much as possible. And the diamond thin films which were deposited in the designed substrate holder present relative high uniformity which demonstrated the feasibility of the structure of the substrate holder. Furthermore, the φ 150 mm diamond thick film was deposited using relative higher gas mixture flow rate and microwave power. The thickness variation of the diamond thick film is about 13.4% and the full width at half maximum (FWHM) of the diamond peak increases from 5.78 cm−1 to 7.23 cm−1 with the distance to the center of the diamond film increasing from 0 mm to 70 mm. The I(C2)/I(Hα) across the plasma shows a relative uniform distribution which was kept in the range of 2.9–3.4 in our experiments. Besides that, the φ 200 mm diamond film was attempt to synthesis which illustrates the feasibility of depositing the diamond films with the diameter more than 150 mm, although some improvements on the plasma environment should be considered.

Effect of frequency on low temperature synthesis of diamond by pulsed discharge MPCVD

Low-temperature synthesis of diamond has broader application prospects compared to traditional diamond synthesis, but it faces issues such as low deposition rate and poor diamond quality. In this study, CH4–CO–H2 were used as reaction gases, and a pulsed discharge MPCVD apparatus was used to deposit diamond films at a substrate temperature of 400 °C and different frequencies were investigated. The results showed that the deposition rate of the pulse discharge was faster than that of continuous microwave discharge. The fastest deposition rate was observed at 500Hz, and crystal size became finer with increasing frequency, while the crystal orientation changed from (100) to (111). A diamond peak at 1333 cm−1 was observed in the Raman spectrum, and the diamond grain size was found to be biggest at 750Hz based on the measured half-width of the peak. Plasma OES analysis revealed that the brightness of CO increased gradually with increasing frequency, while the brightness of H showed an initial increase followed by a decrease. Comparison of emission spectra during low-temperature deposition with a single carbon source showed that CO participated in the reaction for low-temperature diamond synthesis.

Study on the growth characteristics of type Ⅰb silicon-doped diamond in FeNi catalyst under high temperature and pressure

Silicon-related impurities are widely present in natural diamonds. Exploring the properties of silicon-doped diamonds provides vital guidelines for elucidating the composition of the mantle and the growth mechanism of natural diamonds. In this study, a high-capacity cubic high-pressure device was used to simulate the high-temperature and high-pressure environment for diamond growth. The regulation of transition-metal solvent catalyst (silicon) in the crystallization process, morphology, and impurity concentration of diamond crystals is reported. In a series of experiments, silicon powder was added to regulate its concentration in the diamond growth system. An Fe/Ni alloy was used as the catalyst, with a pressure of 5.8 GPa, a temperature range of 1600–1700 K, and a growth time of 12 h. As the silicon concentration increased, the diamond crystal displayed a slower growth rate, its color changed from yellow to light yellow, and the number of diamond inclusions gradually increased. The nitrogen concentration in the diamond crystals gradually decreased from 279 to 68 ppm, and nitrogen mainly existed in the form of single atoms (C-centers). Raman data showed that the Si-doped diamond crystal displayed a high-quality sp3 structure. The first-order Raman peak of the Si-doped diamond shifted from 1331.75 to 1331.18 cm−1, and its half-peak width increased from 4.18 to 5.41 cm−1. Silicon doping can increase the internal stress of the diamond crystal and decrease its crystalline quality. The X-ray photoelectron spectroscopy results of the diamond crystal indicated that silicon in the Fe–Ni–C–Si system entered into the diamond lattice. The photoluminescence spectroscopy results revealed that after silicon atoms entered the diamond lattice, crystal defects and more vacancies were formed. The vacancies combined with displaced nitrogen atoms to form nitrogen-vacancy centers. Moreover, this study provides guidelines for exploring the formation environment and morphology of natural diamonds.

Strain-Relaxed Nanocrystalline Diamond Thin Films with Silicon Vacancy Centers Using Femtosecond Laser Irradiation for Photonic Applications

Nanocrystalline diamond thin (thickness of 100–500 nm) films with ensembles of negatively charged light-emitting silicon vacancy (SiV) centers might find an application in the field of photonics or biosensing due to their scalable and low-price fabrication process in comparison with monocrystalline diamond. The potential application of diamond thin films is, however, limited due to the presence of radiative and nonradiative defects. The former type is a source of an unwanted background in the photoluminescence spectra, the latter lowers the quantum efficiency of light emission, and both types of defects cause the reabsorption of SiV emission during its propagation within the layer. Here we show that femtosecond (fs) laser pulses focused via a microscope objective on a nanocrystalline diamond thin film can be employed to reduce background photoluminescence intensity by a factor of 5 with respect to the luminescence of SiV centers. Raman spectra show that this decrease is mainly caused by laser ablation of the sp2-related carbon phase present in-between the grains. The reduction of the sp2 carbon phase also leads to a local decrease in the optical absorption followed by an almost twofold increase in the SiV emission peak intensity. Moreover, the fs-irradiation also entails the release of strain inside such a layer as manifested by the observed shift of the Raman diamond peak toward the value measured in the monocrystalline diamond and by a blue-shift of the zero-phonon-line peak position of the SiV centers. Such a finding might enable the improvement of the optical quality of the nanocrystalline diamond-based photonic nanostructures or even might be employed over a larger area by defocusing the irradiation laser in order to create large-scale strain-relaxed nanocrystalline diamond thin films.

Electrochemical properties and morphology of boron-doped diamond thin films

A boron-doped diamond (BDD) thin film was synthesized using the hot filament chemical vapor deposition (HFCVD) method. The surface shape, growth rate, bonding structure, and electrochemical properties of the BDD thin films were estimated through scanning electron microscopy (SEM), Raman spectroscopy, and cyclic voltammetry. As the boron doping concentration increased, the growth rate and crystal size of the diamond thin film decreased. Through Raman analysis, it was confirmed that the 1332 cm[Formula: see text] peak of diamond gradually became less intense, and peaks were generated at 480 cm[Formula: see text] and 1220 cm[Formula: see text] due to the bonding of boron to carbon. Cyclic voltammetry analysis of the BDD thin film showed a large potential window with a width of approximately 2.8 V. The highest applied voltage (2 V) versus response current (0.02 A) was obtained at a B/C ratio of 2000 ppm.

The effect of CO2 addition to the (C2H2 + H2) gas system on the low-temperature growth of diamond-like carbon (DLC) with prominent nano-diamond phase

Diamond-like carbon (DLC) films were grown on untreated glass substrates by MW-PECVD system utilizing a (C2H2/H2/CO2) gas combination at low temperature (∼300 °C). Regulating the flow of CO2, we investigate the relevant influence on the sp3 and sp2 hybridized carbon components, optical transmittance, and surface morphology of the DLC films, using Raman spectroscopy, UV–Vis absorption spectroscopy, and field emission scanning electron microscopy, respectively. The results demonstrated a superior quality of the nano-diamond phase in the DLC film, having the most significant magnitude of IDia/IG ratio ∼ 1.13, the corresponding minimum magnitude of ID/IG ratio ∼ 0.90, and the narrowest width of the diamond peak at ∼ 1332 cm−1 when an optimized flow of CO2 gas at 3 sccm was added to the (C2H2 + H2) gas mixture. The optimum DLC film demonstrated the maximum optical transmittance of ∼ 89%, and the corresponding FE-SEM image revealed a uniform surface microstructure. It has been established that in addition to atomic-H, atomic-O played a key role in chemically reacting with the a-C and other non-diamond graphitic phases and etching out those components to facilitate the growth of DLC films, preserving the sp3 hybridized superior nano-diamond component within the network.

The NV0 defects in diamond: A quantum mechanical characterization through its vibrational and Electron Paramagnetic Resonance spectroscopies

The NV0 defect in diamond has been investigated quantum-mechanically, by analyzing its structural, electronic, vibrational and magnetic properties. The possible spin states for NV0 are a quartet NVq0 (4A2 symmetry) and a doublet (2E symmetry). In the latter state a single electron occupies a double degenerate level producing a Jahn Teller distortion that removes the degeneracy and lowers the total energy. The symmetry reduces from C3v to CS and two local minima are indeed identified, to be indicated as NVd10 (2A′ symmetry) and NVd20 (2A″ symmetry). NVd10 is the ground state, and is more stable than NVq0 by ~ 0.5 eV, and than NVd20 by ~ 0.2 eV, irrespective of the functional or basis set adopted.The EPR hyperfine coupling tensor has been computed for NVq0 and has been found to be in excellent agreement with available experimental data. The IR spectra of the NV defects (the three neutral cases and also the negatively charged one, for comparison) show specific peaks and shape that characterize each system and differentiate the spectra according to the spin and charge state. The Raman spectra of the NV0 defects shows a single peak, redshifted with respect to the single peak of pristine diamond by 2 cm−1 only, but in turn well separated from the negatively charged form of the defect.

Overgrowth of Single Crystal Diamond Using Defect-Selective Etching and Epitaxy Technique in Chemical Vapor Deposition

In this study, we demonstrated the defect-selective etching and epitaxy technique for defect reduction of a heteroepitaxial chemical vapor deposition (CVD) diamond substrate. First, an 8 nm layer of nickel was deposited on the diamond surface using an e-beam evaporator. Then, defect-selective etching was conducted through an in situ single process using microwave plasma chemical vapor deposition (MPCVD). After defect-selective etching, the diamond layer was overgrown by MPCVD. The defect density measured from the atomic force microscope image decreased from 3.27×108 to 2.02×108 cm-2. The first-order Raman peak of diamond shifted from 1340 to 1336 cm-1, and the full width at half maximum (FWHM) decreased from 9.66 to 7.66 cm-1. Through the defect-selective etching and epitaxy technique, it was confirmed that the compressive stress was reduced and the crystal quality improved.

Raman micro-spectroscopy of nanodiamonds from the Kapoeta meteorite

Nanodiamonds, found in a carbonaceous-chondrite material from the gas-rich meteorite Kapoeta, have been studied by micro-Raman spectroscopy. The Raman spectra of these nanodiamonds show the first-order Raman peak of diamond at 1333 cm-1, along with the “D” and “G” peaks of graphitic/amorphous carbon phases. The spectra also show additional Raman peaks and features that are attributable to trans-polyacetylene at grain boundaries of the nanocrystalline diamonds, tetrahedral amorphous carbon, and presence of nitrogen and hydrogen. The spectra and the associated parameters are very similar to those of chemical-vapor-deposition (CVD) nanocrystalline diamonds and may suggest a similar formation process for the Kapoeta nanodiamonds, possibly in the solar nebula. The Kapoeta nanodiamonds and the associated amorphous carbon phases are probably the main carriers of the abundant noble gases found in the Kapoeta meteorite.

Development of High-Performance Polycrystalline CVD Diamond-Coated Cutting Tools Using Femtosecond Lasers

Pulse laser grinding (PLG), an edge-shaping process, was developed previously to implement high-performance cutting tools. In this study, two femtosecond (fs) lasers with wavelengths of 1045 nm and 257 nm were used to conduct PLG on chemical vapor deposited (CVD) diamond-coated tool edges, as the fs laser is reported to have less thermal impact and the potential to improve the material crystallinity. We investigated the effects of the laser parameters on the tool edge formation and microstructural changes. The results show that although the infrared fs laser could – compared to the conventional nanosecond (ns)-laser PLG – naturally suppress surface thermal damage, the roughness of the processed surface remained relatively high with an Rz of 0.21 μm. However, under the optimal laser parameters proposed in this paper, an ultraviolet fs-laser PLG was used to obtain a much smoother edge, reducing Rz to approximately 0.08 μm. Moreover, scanning electron microscopy images indicated that the longitudinal machining marks on the ns-laser-processed surface were significantly reduced, with virtually no attached debris on the surface. Furthermore, from the Raman spectra, a significant increase in the diamond peak intensity was observed, indicating that the crystallinity of the CVD diamond (CVDD) was improved following ultraviolet-fs-laser PLG. These results demonstrate that edge shaping and structural modification of polycrystalline CVDDs can be integrated into ultraviolet-fs-laser PLG.

Tribological Properties of Chemical Vapor Deposited Diamond Film on YT14 Cemented Carbide under Water Lubrication Condition

Abstract A diamond film was deposited on YT14 cemented carbide using chemical vapor deposition technique. The surface and cross-section morphologies and chemical compositions of obtained diamond film were analyzed using a scanning electron microscope, energy dispersive spectroscopy, Raman spectroscope, and X–ray diffractometer, respectively. The friction and wear tests of diamond film under the water lubrication condition were conducted using a wear tester with the minimum quantity lubrication system, and the effects of wear loads on tribological properties of diamond film were also discussed. The results show that the chemical vapor deposited diamond film is primarily composed of diamond (111) peak, and its hardness, elastic modulus, bonding strength, and roughness are 16.27 GPa, 166.18 GPa, 26.2 N, and 79.2 nm, respectively. Under the water lubrication condition, the average coefficients of friction (COF) of diamond film under the wear loads of 4, 6, and 8 N are 0.117, 0.139, and 0.163, respectively, and the corresponding wear rates of diamond film under the wear loads of 4, 6, and 8 N are 3.87 × 10−7, 4.26 × 10−7, and 4.67 × 10−7 mm3/N • m. This shows that the average COFs and wear rates increase with an increase of wear loads and that the wear mechanism is abrasive wear.

Effect of Co Leaching on the Vertical Turning Lathe Wear Properties of Polycrystalline Diamond Compact Manufactured by High Temperature and High Pressure Sintering Process

Polycrystalline diamond compact (PDC) has excellent wear resistance, high impact resistance, superior fatigue properties, and has been used in the oil and gas drilling industries. This study investigated the effect of Co leaching on the microstructure, vertical turning lathe (VTL) wear properties of PDCs manufactured by high-temperature and high-pressure (HTHP) sintering. The VTL wear test has the advantage of simulating the actual oil drilling environment by using granite as the workpiece. PDC sintered material that did not receive Co leaching was named HTHP sintered PDC-A, and the material subjected to Co leaching was called Co-leached PDC-B in this study. As a result of XRD analysis of both PDCs, diamond and WC peaks were detected, and only the HTHP sintered PDC-A exhibited some Co peaks. In the HTHP sintered PDC-A, the binder WC and Co were evenly distributed at the diamond interface. However, in the Co-leached PDC-B, some empty spaces were observed at the diamond interface. The HTHP sintered PDCA exhibited a similar or slightly higher VTL wear resistance than the Co-leached PDC-B, but only in the short sliding distance. In the long sliding distance after 9 km, Co-leached PDC-B showed significantly superior wear resistance compared to the HTHP sintered PDC-A. The HTHP sintered PDC-A exhibited both abrasive and adhesive wear behaviors, while the Co-leached PDC-B showed only abrasive wear. Based on the above results, the VTL wear mechanism of PDCs, and ways of improving wear resistance were also discussed.

Physical and electrochemical properties of boron - doped diamond (BDD) electrode

The physical and electrochemical behaviors of BDD electrode are clarified in this work. The surface morphology of BDD is investigated by scanning electron microscopy (SEM) before and after electrolysis in different conditions. There is not any corrosion found on the surface based on the studies of SEM and electrochemical corrosion process. The contact angle of BDD surface with pure water is changed from hydrophobic to hydrophilic (characterized by 97º and 28º) after several runs. In order to thoroughly investigate chemical composition of BDD, Raman spectroscopy is used. The featured peak of diamond is found at 1332 cm-1 Raman shift. The comparison between H-terminated and O-terminated peaks (O 1s and C 1s) as a result of electrochemical processes is made using X-ray photoelectron spectroscopy (XPS). The cyclic voltammogram (CV) of BDD is studied in acid and alkaline media in the range of hydrogen and oxygen evolution.

Crystallization and characteristics of {100}-oriented diamond with CH4N2S additive under high pressure and high temperature**Project supported by the National Natural Science Foundation of China (Grant No. 11604246), Natural Science Foundation of Guizhou Province Education Department of China (Grant Nos. KY2017053 and KY2018343), Natural Science Foundation of Guizhou Procince Science and Technology Agency of China (Grant Nos. 20181163 and LH 20177311),

Diamond crystallization was carried out with CH4N2S additive in the FeNiCo-C system at pressure 6.0 GPa and temperature ranging from 1290 °C to 1300 °C. The crystallization qualities of the synthetic crystals were characterized by Raman spectra and the Raman peaks located at 1331 cm−1. Fourier transform infrared (FTIR) results showed that the hydrogen-related absorption peak of the as-grown diamond was at 2920 cm−1, respectively. Interestingly, A-center nitrogen was observed in the obtained diamond and the characteristic absorption peaks located at 1095 cm−1 and 1282 cm−1. Especially, the absorption peak at 1426 cm−1 attributing to the aggregation B-center nitrogen defect was distinctly found when the CH4N2S content reached 0.3 mg in the synthesis system, which was extremely rare in synthetic diamond. Furthermore, optical color centers in the synthesized crystals were investigated by photoluminescence (PL).

Effects of air annealing on microstructure and optical properties of HFCVD grown microcrystalline diamond thin films

In this report, we investigate the annealing effects on microcrystalline diamond thin films of 1 μm thickness grown on silicon substrate by hot filament chemical vapor deposition technique. Annealing is important from the perspective of etching away the non-diamond/graphitic phase situated mainly at the grain boundaries to yield a high-quality continuous diamond film with higher sp3 %. From the Raman spectroscopy and also from the morphology of the films, we could see that with annealing in air, the degradation of the sp2 component sets in at around 500 °C leaving behind the sp3 component in the films, however the films are completely oxidised with annealing at 700 °C. Our results show that annealing at 500 °C has been able to etch away the sp2 phase efficiently as evident from the Raman spectroscopic analysis making the characteristic diamond peak more intense compared to graphitic peaks and also led to the decrease in FWHM of the diamond peak. The photoluminescence properties reveal the presence of silicon-vacancy centers in the film whose zero-phonon line (ZPL) shows a drastic decrease in the FWHM as we anneal at higher temperatures of more than 700 °C.

Improvement of crystallization in CVD diamond coating induced by femtosecond laser irradiation

Herein, structural modification of a chemical vapor deposit (CVD) diamond film by a low fluence femtosecond laser irradiation has been studied with Raman spectroscopy, X-ray adsorption fine structure (XAFS) spectroscopy, and X-ray diffraction (XRD). Polycrystalline CVD diamond films of approximately 20 μm thickness were irradiated with femtosecond laser of varied defocus distances corresponding to the laser fluence range of 0.1–127.3 J/cm2. At fluences below 1.27 J/cm2, although there was no observable change in the appearance of the film surface, however, the FWHM of the diamond peak in the Raman spectra was observed to reduce considerably from 17 to 7 cm−1. Furthermore, the higher fraction of diamond phase with the increase in laser fluence strongly suggests that the microstructure of the diamond film has been modified by the femtosecond laser. By employing XAFS measurement, it can be found that after irradiation, the weak π* fine structure in the pre-edge almost vanished in response to the significant increase in σ* adsorption; further, a distinct diamond crystal characteristic peak was observed, which further confirms the femtosecond laser-induced modification, and its occurrence inside the bulk film. XRD results also pointed out that the improved diamond crystallinity with the integral intensities increased by approximately 20% after the femtosecond irradiation. Based on the above-mentioned results, an improvement in the crystallinity of CVD diamond under the low-fluence femtosecond laser irradiation has been confirmed in this study; this is attributed to a photo-induced phase transition from amorphous carbon to diamond.