Science publications

List of publications from the diamond growth research group on the works performed at the ARDIS reactor

Growth of polycrystalline and single-crystal CVD diamonds with bright photoluminescence of Ge-V color centers using germane GeH4 as the dopant source.

«Germanium-Vacancy (Ge-V) color center in diamond possesses a narrow band photoluminescence (PL) emission in the orange spectral range interesting as a single-photon source for quantum optical technologies and thermometry, therefore, development of methods for the controllable doping of diamond with Ge is of high importance for such applications. Here, we report on the synthesis of polycrystalline and epitaxial single crystal Ge-doped films using microwave plasma chemical vapor deposition (CVD) technique by addition of the germane GeH4 gas into the H2-CH4 plasma. It is demonstrated, that GeH4 addition affects the CVD growth of microcrystalline diamond, reducing the film growth rate and increasing the average diamond grain size. The films show bright photoluminescence of Ge-V centers at ≈602 nm under the optimized GeH4 concentration, with a zero-phonon line width of 1.6 nm (FWHM) for Ge-V ensemble at low temperatures (5 K). The developed in-situ doping from the germane gas opens a way for a better control of the Ge-V color center formation in diamond for photonic applications.»

Vertical-substrate epitaxial growth of single-crystal diamond by microwave plasma-assisted chemical vapor deposition.

«Epitaxial diamond growth by microwave plasma CVD in a CH4/H2 mixture was performed on vertically standing single crystal diamond substrates with high aspect (height-to-width) ratio. This “vertical growth” mode allows simultaneous diamond deposition on two large (1 0 0) faces of the substrate, in contrast to only one working face upon conventional horizontal arrangement of the substrate plate. A high plasma density gradient in vertical direction, the characteristic feature of the geometry used (the substrate acts as an antenna), coupled to high substrate temperature gradient (ΔT ≈ 150 °C in the particular experiment), are shown to have a strong impact on the epilayer structure, that was characterized with laser scanning microscopy, Raman and photoluminescence confocal spectroscopy mapping across ≈3 mm high specimen. The single crystal film transformation to polycrystalline, and further, to nanocrystalline layer, going from top to bottom of the substrate, is described. The vertical distributions of the growth rate, intensity of photoluminescence of NV and SiV color centers imbedded in the diamond film, are measured with high spatial resolution on growth surface and in cross-section, which are also related to the film structure variation. These findings are of importance for search of optimal growth regimes of 3D diamond mosaics and large single crystals by MPCVD.»

Luminescent diamond window of the sandwich type for X-ray visualization.

«A two-layered diamond plate is proposed as a transparent X-ray window visualizer. The plate consists of a thick substrate of a synthetic single-crystal high-pressure high-temperature (HPHT) diamond on which a thin ∼10μm optically active layer of chemical vapor deposition (CVD) diamond doped with silicon and nitrogen, and is epitaxially grown. The photoluminescent properties of the diamond sandwich plate were studied under the influence of X-ray radiation before and after treatment of the plate with high-energy electrons and its thermal annealing. It was established that broadband luminescence with a maximum near 500 nm, associated with defects of the HPHT diamond substrate, dominates before electron treatment. The electron irradiation and subsequent annealing of the plate completely suppressed the broadband luminescence and significantly (by more than two orders of magnitude) increased emission intensity of nitrogen-vacancy centers (NV) in the CVD diamond layer. As a result, the luminescence of neutrally charged NV centers with a zero-phonon line at 575 nm became dominant. No luminescence of the silicon-vacancy (SiV) centers in the CVD diamond film was detected. The first results demonstrating the two-layered diamond plate as an X-ray visualizer are presented.»

Frictional coefficients between aluminum–silicon alloy and cutting inserts with MPCVD diamond coatings.

«The frictional coefficients at the front and rear surfaces of a VK6 hard-alloy cutter with experimental nano- and microcrystalline CVD diamond coatings applied in microwave plasma are determined by extrapolation to zero cut-layer thickness. It is found that, for diamond coatings with a single microcrystalline layer and those with both a microcrystalline layer and a nanocrystalline layer, the frictional coefficients are less than for an uncoated hard-alloy cutter and also for a cutter with a Sandvik diamond coating.»

Diamond-EuF3 nanocomposites with bright orange photoluminescence.

«We report the manufacturing of a novel diamond – rare-earth (RE) composite material with EuF3 nanoparticles (NP) embedded in the synthesized microcrystalline diamond films that show strong photoluminescence in the orange part of the visible spectrum. Synthesis of the aforementioned composite includes placement of EuF3 NP on the diamond substrate and subsequent coating of them with an additional polycrystalline diamond layer grown by microwave plasma chemical vapor deposition (CVD). The produced composite films exhibit high intensity localized photoluminescence (PL) at 612 nm with the decay time of 0.34 ms, which is generated by the EuF3 particles buried within a very stable transparent diamond matrix. The proposed synthetic approach is quite versatile, as it allows preparation of the luminescent diamond - RE particles nanocomposites of different sizes and natures which perform well over a broad range of the visible spectrum.»

2D inverse periodic opal structures in single crystal diamond with incorporated silicon-vacancy color centers.

«Well-ordered opal-diamond composite and inverted opal structure in single crystal (SC) diamond have been prepared by microwave plasma CVD. The process is based on epitaxial diamond growth through a monolayer of densely packed SiO2 spheres placed on a (100) HPHT diamond substrate. Finally, the opal monolayer with ≈ 600 nm sphere diameter was completely embedded in SC CVD diamond forming a new type of ordered diamond composite. In addition, the inverse opal structures (air cavities in diamond) were produced by SiO2 etching. The XRD analysis confirmed the single crystal nature of the deposit. The photoluminescence spectrum exhibits a strong peak at 738 nm wavelength of silicon-vacancy defects in diamond, indicating Si doping during the CVD process. The optical properties of the diamond structures were evaluated also with Raman spectroscopy and optical reflection spectrometry. The developed epitaxy-through-mask approach is considered as a potential strategy to fabricate multilayered (3D) SC diamond photonic crystals.»

Plateholder design for deposition of uniform diamond coatings on WC-Co substrates by microwave plasma CVD for efficient turning application.

«Polycrystalline diamond coatings have been grown on cemented carbide WC-6% Co substrates with different aspect ratios by microwave plasma CVD in CH4/H2 gas mixtures. Special plateholder with holes for group growth has been used to protect the edges of the substrates from non-uniform heating due to the plasma edge effect. The difference in heights Δh of the substrates and plateholder, and its influence on the diamond film mean grain size, growth rate, phase composition and stress was investigated. Diamond growth rate of 0.3–1 μm/h and compressive stress of 2.2–2.5 GPa, respectively were determined in the optimal Δh region. The substrate temperature range of 740–760 °C, within which uniform diamond films are produced with good adhesion, is determined. The diamond-coated samples produced at optimized process conditions exhibited a reduction of cutting force and wear resistance by a factor of two, and increase of cutting path length up to 8150 m or by 4.3 times upon turning А390 Al-Si alloy as compared to performance of uncoated tools.»

Etching kinetics of (100) single crystal diamond surfaces in a hydrogen microwave plasma, studied with in situ low-coherence interferometry.

«A low‐coherence interferometry (LCI) was used to measure in situ the etch rate (ER) of synthetic single crystal (SC) diamonds in H2 microwave plasma, at substrate temperatures in the broad range of 800–1370 °C. The method allows the collection of the kinetic data on a single sample without switching off the plasma. (100)‐orientated SC plates of CVD and IIa type HPHT diamond were systematically etched in pure hydrogen at pressure p = 130 Torr and microwave power density of ≈300 W cm−3. The activation energies Ea of 42 ± 5 and 32 ± 4 kCal mol−1 have been determined for the CVD and HPHT substrates. An enhanced etching rate of a subsurface defected layer with thickness of ∼1 μm or less, formed upon polishing of the samples, is revealed. Surface morphology, roughness, and the shape of etch pits produced by a selective etching of defects, were characterized with optical profilometry. CH and dimer C2 radicals were detected in the H2 plasma with optical emission spectroscopy, as a result of the diamond etching, and the emission intensity of these species was linked to the substrate etch rate.»

SiV color centers in Si-doped isotopically enriched 12C and 13C CVD diamonds.

«The effect of isotopic modification of diamond lattice on photoluminescence (PL) and optical absorption spectra of ensembles of SiV− centers was studied. Thin epitaxial diamond layers were grown by a microwave plasma CH4/H2 mixtures using methane enriched to 99.96% for either 12C or 13C isotopes, while the Si doping was performed by adding a small percentage of silane SiH4 into the plasma. Temperature dependent SiV− ZPL spectra in absorption were measured at 3–80 K to monitor the evolution of the ZPL fine structure. It is found that the SiV− ZPL at 736.9 nm observed in PL for 12C diamond at T = 5 K, exhibits a blue shift of 1.78 meV, to 736.1 nm in 13C diamond matrix. Narrow ZPL with the width (FWHM) of 0.09 meV (21 GHz) was measured in absorption spectra at T = 3–30 K in the Si‐doped 13C diamond. Besides the charged SiV− center, the absorption of the neutral SiV0 defect at 946 nm wavelength has also been detected. From changes observed in SiV− phonon band structure in PL with isotopic modification, the band at 64 meV was confirmed to be a local vibration mode (LVM) involving a Si atom.»

Polycarbynes: A new synthetic approach and application to the nucleation of CVD diamond.

«New methods have been developed for obtaining three preceramic polycarbyne-family polymers. Poly(hydridocarbyne) (PHC) and poly(phenylcarbyne) (PPC) have been synthesized via a mechanically activated reaction between magnesium metal and CRX3 (R = H, Ph; X = Br, Cl). Poly(naphthalene-co-hydridocarbyne) (PNHC) have been obtained by reacting CHBr3 with sodium naphthalide. The efficiencies of PHC, PPC, and PNHC as sources of diamond nuclei in the microwave plasma chemical vapor deposition of diamond films on silicon substrates have been compared. The highest efficiency has been demonstrated by PHC with a high molecular weight, for which the nucleation density has been estimated at ≥ 109 nuclei per square centimeter of the substrate surface.»

Morphology of diamond layers grown on different facets of single crystal diamond substrates by a microwave plasma CVD.

«Epitaxial growth of diamond films on different facets of synthetic IIa-type single crystal (SC) high-pressure high temperature (HPHT) diamond substrate by a microwave plasma CVD in CH4-H2-N2 gas mixture with the high concentration (4%) of nitrogen is studied. A beveled SC diamond embraced with low-index {100}, {110}, {111}, {211}, and {311} faces was used as the substrate. Only the {100} face is found to sustain homoepitaxial growth at the present experimental parameters, while nanocrystalline diamond (NCD) films are produced on other planes. This observation is important for the choice of appropriate growth parameters, in particular, for the production of bi-layer or multilayer NCD-on-microcrystalline diamond (MCD) superhard coatings on tools when the deposition of continuous conformal NCD film on all facet is required. The development of the film morphology with growth time is examined with SEM. The structure of hillocks, with or without polycrystalline aggregates, that appear on {100} face is analyzed, and the stress field (up to 0.4 GPa) within the hillocks is evaluated based on high-resolution mapping of photoluminescence spectra of nitrogen-vacancy NV optical centers in the film.»

Effect of crystal structure on the tribological properties of diamond coatings on hard-alloy cutting tools.

«Micro- and nanocrystalline uniform diamond coatings with barrier tungsten layers for improved adhesion were deposited in a microwave plasma from methane-hydrogen mixtures on cemented carbide WC–6% Co substrates with high aspect ratios. Dynamic study of cutting forces and sliding friction has shown a significant improvement in the tribological properties of diamond-coated tools in cutting highly abrasive materials, such as A390 silumin and carbon-carbon composites. Confocal Raman spectrometry has been used to examine the features of wear mechanism in nano- and microcrystalline diamond coatings deposited in a microwave plasma.»

Growth of CVD diamond nanopillars with embedded silicon-vacancy color centers.

«Silicon-doped diamond nanopillars have been produced by a microwave plasma chemical vapor deposition (CVD) on a single crystal diamond substrate through holes in a Si mask perforated with a focused ion beam. Arrays of 400 nm diameter pillars with aspect ratio up to 2.8 are grown epitaxially being confined by channels in the mask, the latter serving also as the Si doping source. Strong photoluminescent (PL) emission of the SiV centers at 738.7 nm wavelength, localized within the pillars, has been detected and imaged with a fluorescence microscope. The SiV PL decay time of 1.1 ns has been deduced from PL kinetics measurements. An increase of specific PL intensity (intensity per unit volume of the pillar) with the aspect ratio is noted.»

Express in situ measurement of epitaxial CVD diamond film growth kinetics.

«We used a low-coherence interferometry for precise continuous in situ measurements of thickness and growth rate of epitaxial single crystal diamond layers in microwave plasma CVD in H2-CH4 gas mixtures in a broad range of substrate temperatures Ts (750–1150 °C) and CH4 concentrations (1–13%). Rich growth kinetics is collected in a single experiment by depositing about 60 layers on one (100) Ib HPHT diamond substrate in different regimes (the substrate temperature was controlled by the microwave power) at fixed pressure P = 130 Torr, without the plasma switch-off. The growth rate is found to follow Arrhenius dependence with activation energy Ea = 11.1 ± 1.0 kcal/mol. By appropriate choice of the substrate temperature the growth rate can be significantly enhanced. The growth rate as high as 82 μm/h is achieved by optimizing the temperature and gas composition. At low CH4 content (1%) growth competes with etching by atomic hydrogen, the etching dominating at high Ts (> 1000 °C in the present conditions). The etching rate in pure H2 plasma was measured and activation energy Ea = 9.8 ± 0.8 kcal/mol was deduced. Gas temperature Tg in the plasma core evaluated from optical emission spectra for dimer C2 (Swan band), was found to be either constant or slightly and monotonically increasing with absorbed power, whereas the absorbed microwave power density shows a decreasing, although slight, trend. This suggests the temperature depended surface reactions to play a major role in the diamond growth kinetics under variable microwave power. Raman mapping of cross-section of the produced multilayered sample confirmed high quality of diamond structure over all the deposition regimes explored.»

High-rate growth of single crystal diamond inmicrowave plasma in CH4/H2 and CH4/H2/Ar gas mixtures in presence of intensive soot formation.

«The growth of single crystal diamond plates in a microwave plasma using H2-CH4 and H2-CH4-Ar gas mixtures in a broad range of methane concentration (2–15%) is studied. The growth rates up to 60 μm/h in H2-CH4 mixtures and up to 105 μm/h in Ar-H2-CH4 mixtures are achieved at high CH4 content, without adding nitrogen, still obtaining transparent crystals. The thermal conductivity k of the SCs in the temperature range of 220–420 K is measured by a laser flash technique. High thermal conductivity k ≈ 2300 W/m ⋅ K at room temperature is found for the sample grown at low growth rate in H2-CH4, this value reducing to k ≈ 2000 W/mK for the material produced in high rate regime at 15% CH4. The spatial profiles of Hα and C2 line intensities in the plasma were determined with optical emission spectroscopy (OES). Soot formation at high CH4 contents is observed at the plasma border both for Ar-free and Ar-containing mixtures, the soot yield being roughly proportional to diamond growth rate. The soot temperature Ts, as measured with OES, is almost constant (3800 ± 300 K) in H2-CH4 mixtures over the all methane concentration range explored, while for Ar-containing plasma the Ts is even higher (4100–4200 K) at [CH4] < 10%, reducing, however, below 3800 K in CH4-reach mixtures. Raman spectra of collected soot correspond to crystalline graphite with high density of defects. The estimated carbon conversion efficiency from CH4 precursor to the soot can exceed 10% and should be taken into account in overall carbon balance in the CVD process.»

Precise control of photoluminescence of silicon-vacancy color centers in homoepitaxial single-crystal diamond: Evaluation of efficiency of Si doping from gas phase.

«Ability to precisely control the Si-related color center abundance in diamond is important for the use of silicon-vacancy (SiV) defects with bright photoluminescence (PL) in quantum information technologies and optical biomarkers. Here, we evaluated the efficiency of Si incorporation in (100) plane of homoepitaxial diamond layers upon in situ doping by adding silane SiH4 in the course of diamond chemical vapor deposition in microwave plasma using CH4–H2 mixtures. Both the Si concentration in the doped samples, as determined by secondary ion mass spectrometry, and PL intensity of SiV centers at 738 nm wavelength, measured at excitation wavelength of 473 nm, demonstrate a linear increase with silane content in feed gas in the range. The incorporation efficiency f, defined as the ratio of Si concentration in diamond to that in gas, f = [Si/C]dia/[Si/C]gas is found to be (1.1 ± 0.5) × 10−3 for the silane concentrations explored, [SiH4/CH4] < 0.7 %; thus, the Si atoms are accommodated in (100) diamond face easier than nitrogen and phosphorus, but more difficult than boron. This finding allows a tailoring of the Si content and photoluminescence intensity of SiV centers in in situ doped CVD diamond.»

Color centers in silicon-doped diamond films.

«Silicon-doped microcrystalline diamond films of 1 μm thickness were grown by chemical vapor deposition in microwave plasma from mixtures of methane–hydrogen–silane on substrates of aluminum nitride, tungsten, and silicon. The diamond films were found to contain optically active silicon vacancy (SiV) centers giving rise to the 737-nm band in the photoluminescence spectra. The spectral features of a newly discovered narrow band of comparable intensity at 720–722 nm were studied. It is shown that the band at 720–722 nm occurs in the photoluminescence spectra only in the presence of silica in the diamond, regardless of the substrate material. The temperature dynamics of the photoluminescence spectra in the range of 5–294 K were investigated. The possible nature and mechanisms of formation of the color centers responsible for the 720–722 nm band are discussed.»

High-order stokes and anti-stokes Raman generation in monoisotopic CVD 12C-diamond.

«We determined, for the first time, the room temperature phonon energy related to the F2g vibration mode (ωSRS(12C) ∼ 1333.2 cm–1) in a mono‐crystalline single‐isotope CVD 12C‐diamond crystal by means of stimulated Raman scattering (SRS) spectroscopy. Picosecond one‐micron excitation using a Nd3+:Y3Al5O12‐laser generates a nearly two‐octave spanning SRS frequency comb (∼12000 cm–1) consisting of higher‐order Stokes and anti‐Stokes components. The spacing of the spectral lines was found to differ by ΔωSRS ∼ 0.9 cm–1 from the comb spacing (ωSRS(natC) ∼ 1332.3 cm–1) when pumping a conventional CVD diamond crystal with a natural composition of the two stable carbon isotopes 12C (98.93%) and 13C (1.07%). (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim).»

Synthesis of single crystal diamond by microwave plasma assisted chemical vapor deposition with in situ low-coherence interferometric control of growth rate.

«We performed synthesis of single crystal (SC) diamond by microwave plasma chemical vapor deposition in methane-enriched H2–CH4 gas mixtures, and achieved growth rates more than 30 μm/h, without adding nitrogen in reaction mixture. A low-coherence interferometry (LCI) was employed for precise measurements of the thickness and growth rate of the epitaxial diamond layers in the course of the process. The performance of this in situ technique is demonstrated by continuously monitoring the SC diamond thickness in a single growth run upon variation of CH4 percentage in steps, up to 17%, without switching off the plasma, to produce a “multilayer” diamond film. In addition, etching rate of diamond in pure hydrogen plasma has been evaluated with the same method. The LCI technique allows quick collection of growth kinetics data upon systematic variation of a selected process parameter for the growth optimization.»

Photoluminescence of SiV centers in single crystal CVD diamond in situ doped with Si from silane.

«Homoepitaxial single crystal diamond layers with bright photoluminescence (PL) of silicon‐vacancy (SiV) color centers at 738 nm wavelength have been grown on (100) diamond substrates by a microwave plasma CVD using a controlled Si doping via adding silane to CH4-H2 reaction gas mixture in the course of the deposition process. In the range of the silane concentrations SiH4/CH4 explored, from 0 to 2.4%, the SiV PL intensity shows a nonmonotonic behavior with silane addition, with a maximum at 0.6%SiH4/CH4, and a rapid PL quenching at higher Si doping. The maximum SiV concentration of ≈450 ppb in the samples has been determined from optical absorption spectra. It is found that the SiV PL intensity can strongly, an order of magnitude, increase within non‐epitaxial inclusions in single crystal diamond film.»

Stimulated Raman scatting in CVD diamond 12C.

«In this report, we describe the gas-phase synthesis of an isotopically modified single crystal diamond with the content of 12C isotope up to 99.96% and increased heat conductivity (31.7 W cm–1 K–1 at room temperature) and the first results of studying its steady-state picosecond generation of stimulated Raman scattering.»

Fabrication of diamond microstub photoemitters with strong photoluminescence of SiV color centers: bottom-up approach.

«Arrays of diamond photoemitters with silicon-vacancy (SiV) photoluminescent (PL) centers have been produced by epitaxy of CVD diamond inside laser-ablated channels in a-Si mask on single crystal or polycrystalline diamond substrates, the mask also serving as Si-doping source. Strong PL emission from the SiV centers with zero-phonon line at 738.6 nm wavelength (6 nm width, 0.8 ns decay time), localized within the photoemitters, has been measured.»

Si-doped nano- and microcrystalline diamond films with controlled bright photoluminescence of silicon-vacancy color centers.

«Nanocrystalline diamond (NCD) and microcrystalline diamond (MCD) films with bright photoluminescence (PL) of silicon-vacancy (SiV) color centers at 738 nm have been grown using a microwave plasma CVD technique. The films were doped with Si via adding silane to CH4–H2 reaction gas mixture in the course of the deposition process. The dependence of SiV PL intensity on silane concentration in gas shows a maximum at SiH4/CH4 ratios of 0.2% and 0.6% for NCD and MCD films, respectively, the maximum intensity for MCD being an order of magnitude stronger compared with that for NCD. The PL quenching at higher CH4 addition occurs, however, no significant degradation of the film structure, such as Si-induced amorphous carbon formation, was observed within the SiH4 concentration range studied (0%–0.9%). The higher PL efficiency of the MCD films is related to their less defective structure, as deduced from Raman spectroscopy analysis.»

CVD-diamond 13C: A new SRS-active crystal.

«Stimulated Raman scattering has been discovered in a monoisotopic 13C diamond single crystal grown by chemical vapor deposition. The first results of the experimental study of impulsive χ(3)-nonlinear lasing under femtosecond IR pumping are presented.»

Growth dynamics of nanocrystalline diamond films produced by microwave plasma enhanced chemical vapor deposition in methane/hydrogen/air mixture: Scaling analysis of surface morphology.

«Nanocrystalline diamond (NCD) films were produced by microwave plasma enhanced chemical vapor deposition (MPCVD) in methane/hydrogen/air plasma. The thickness of the films was varied from 0.15 to 22 μm. X-ray diffraction (XRD), Raman spectroscopy and atomic force microscopy (AFM) were used to investigate the structure and surface morphology of the films. During a short initial period of the deposition, i.e. from 2.5 min to 60 min, the growth dynamics involve relatively strong non-local effects, followed by a growth stage, which is characterized by a contribution of non-local and non-linear effects to the growth dynamics. The later regime of growth with roughness exponent α ~ 0.35–0.4 and growth exponent β ~ 0.25 can be related with the Kardar–Parisi–Zhang (KPZ) scaling regime of growth. The morphological peculiarities observed on the NCD film surface after already 2.5 min of deposition influence the morphology of the films for prolonged deposition time. Therefore, control over the size and distribution of these peculiarities by systematic variation of the deposition parameters allows to optimize the surface morphology for specific applications. The mountain-like patterns observed on the NCD films surface can be related to conformal KPZ growth regime, in contrast to the cusp-like patterns caused by non-local effects and noise.»

Size-dependent luminescence of color centers in composite nanodiamonds.

«Luminescence properties of nitrogen‐vacancy (NV) and silicon‐vacancy (SiV) centers were investigated for the series of O‐terminated composite nanodiamonds consisting of a high‐pressure–high‐temperature (HPHT) diamond core and a chemical‐vapor‐deposition (CVD) diamond outer layer of different thickness. It was found that emission of NV and SiV centers cease to “feel” the diamond surface at a distance of 12 and 4 nm, respectively, from it. This finding determines minimum sizes of O‐terminated nanodiamonds in which stable single photon emitters could be formed based on NV and SiV centers. Suggested composite diamond nanostructure are optimal for design of two‐color luminescent markers. The studied diamond nanoparticles present composite structure of “core‐outer layer” type. The core is 20 nm HPHT diamond containing NV centers, whereas outer diamond layer containing SiV centers is formed by CVD synthesis.»

Multi-octave frequency comb generation by χ(3)-nonlinear optical processes in CVD diamond at low temperatures.

«We study stimulated Raman scattering (SRS) and Raman four-wave mixing (RFWM) processes in chemical vapour deposition (CVD) diamond crystals. The strong interaction of picosecond laser pulses at 1.064 and 0.532 µm wavelength with the dominant Raman-active F2g mode results in a more than two-octave-spanning frequency comb, ranging from the UV to the NIR spectral region. In addition to spectroscopic analysis of the χ(3)-nonlinear emission at room temperature, comparative measurements have been carried out at cryogenic temperature of 10 K. The Raman shift and the Raman gain are found to change only weakly. Moreover, the potential of SRS frequency comb generation in CVD diamond for ultra-short pulse synthesis is discussed.»