Microscopic properties of MPCVD diamond coatings studied by micro-Raman and micro-photoluminescence spectroscopy (original) (raw)
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Effect of the substrate material on diamond CVD coating properties
Materials Chemistry and Physics, 2003
Diamond coatings were deposited onto different substrates (Cu, Si, WC-Co, Mo) by hot-filament chemical vapor deposition (CVD). Characterization of the obtained coatings was performed using scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis, Raman spectroscopy and Fourier transform infrared reflection (FTIR) spectroscopy. The results and observed differences are discussed from the aspect of the chemical nature of the substrate and its reactivity with a gaseous medium.
Synthesis and characterisation of freestanding diamond coatings
Freestanding polycrystalline diamond (PCD) coatings are of immense technological importance. PCD has been grown over silicon substrates by microwave plasma assisted chemical vapor deposition (MWPACVD) process. The coatings are grown by suitable optimisation of the growth parameters of a 915 MHz microwave reactor. Thereafter, 1:1:1 solution of hydrofluoric acid (HF), nitric acid (HNO 3 ) and acetic acid (CH 3 COOH) is used to etch out the silicon wafer from the backside of the coating. Hereby, freshly generated nucleation surface, could be characterised by scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy and stylus profilometer and could be compared with the growth side. It is found that both the nucleation side and growth side are of very high quality (full width at half maxima, i.e., FWHM < 8 cm -1 ). The growth side is (111) textured, whereas, the nucleation side is very smooth with embedded detonation-nano-diamond (DND) agglomerates. These freestanding coatings are successfully laser cut into different geometrical shapes. They are found to be optically translucent having high refractive index. Cross-sectional microscopy of the laser cut edge reveals novel melting features of the CVD grown diamond columns.
Surface Roughness Effects on the Properties of Silicon-Doped Diamond-like Carbon Coatings
Coatings
This paper evaluates surface roughness effects on the properties of a-C:H:Si coatings obtained using plasma-assisted chemical vapor deposition (PACVD). Prior to coating deposition, the surfaces of the samples were subjected to grinding (Ra = 0.25) and then polishing (Ra = 0.05) or sandblasting (Ra = 1.41). Microscopic observations, measurements of thickness, wettability, surface topography, and tribological tests were used to characterize the substrate. The coating microstructure, thickness, and chemical content were investigated using scanning electron microscopy with energy dispersive spectroscopy (EDS). The geometric structure of the surface was examined using confocal microscopy before and after tribological tests. Tribological studies used a ball-on-disk sliding configuration in reciprocating motion under dry friction and cutting oil lubrication. The values of the contact angles were indicative of surface hydrophilic characteristics. Compared with the sandblasted surfaces, the ...
Property mapping of polycrystalline diamond coatings over large area
Journal of Advanced Ceramics, 2014
Large-area polycrystalline diamond (PCD) coatings are important for fields such as thermal management, optical windows, tribological moving mechanical assemblies, harsh chemical environments, biological sensors, etc. Microwave plasma chemical vapor deposition (MPCVD) is a standard technique to grow high-quality PCD films over large area due to the absence of contact between the reactive species and the filament or the chamber wall. However, the existence of temperature gradients during growth may compromise the desired uniformity of the final diamond coatings. In the present work, a thick PCD coating was deposited on a 100-mm silicon substrate inside a 915-MHz reactor; the temperature gradient resulted in a non-uniform diamond coating. An attempt was made to relate the local temperature variation during deposition and the different properties of the final coating. It was found that there was large instability inside the system, in terms of substrate temperature (as high as ΔT = 212 ℃), that resulted in a large dispersion of the diamond coating's final properties: residual stress (15.8 GPa to +6.2 GPa), surface morphology (octahedral pyramids with (111) planes to cubo-octahedrals with (100) flat top surfaces), thickness (190 µm to 245 µm), columnar growth of diamond (with appearance of variety of nanostructures), nucleation side hardness (17 GPa to 48 GPa), quality (Raman peak FWHM varying from 5.1 cm 1 to 12.4 cm 1 with occasional splitting). This random variation in properties over large-area PCD coating may hamper reproducible diamond growth for any meaningful technological application.
Superior hardness and Young’s modulus of low temperature nanocrystalline diamond coatings
We produce the hardest NCD coating at the lowest deposition temperature. We modify the deposition temperature to tailor the grain size and shape of the NCD coatings. We assess the mechanical properties (hardness and elastic modulus) of superhard NCD coating on a soft silicon substrate. a b s t r a c t Nanocrystalline diamond (NCD) coatings with thickness of about 3 mm were grown on silicon substrates at four deposition temperatures ranging from 653 to 884 C in CH 4 /H 2 /Ar microwave plasmas. The morphology, structure, chemical composition and mechanical and surface properties were studied by means of Atomic Force Microscopy (AFM), X-Ray Diffraction (XRD), Raman spectroscopy, nanoindentation and Water Contact Angle (WCA) techniques. The different deposition temperatures used enabled to modulate the chemical, structural and mechanical NCD properties, in particular the grain size and the shape. The characterization measurements revealed a relatively smooth surface morphology with a variable grain size, which affected the incorporated hydrogen amount and the sp 2 carbon content, and, as a consequence, the mechanical properties. Specifically, the hydrogen content decreased by increasing the grain size, whereas the sp 2 carbon content increased. The highest values of hardness (121 AE 25 GPa) and elastic modulus (1036 AE 163 GPa) were achieved in NCD film grown at the lowest value of deposition temperature, which favored the formation of elongated nanocrystallites characterized by improved hydrophobic surface properties.
Thickness of diamond-like carbon coatings quantified with Raman spectroscopy
Thin Solid Films
A model is developed for quantifying the thickness of thin coatings and wear scars using Raman spectroscopy. The model, which assumes that both incident and Raman light obey Beer's law, was applied to Raman spectra from a diamond-like carbon (DLC) coating containing Si and O, known as DLN (diamond-like nanocomposite). The coatings ranged in thickness from 10 nm to 2 mm, according to stylus profilometry. Systematic variations in the Raman carbon (G band) and Si (1st order) peak intensities vs. thickness were found. Fits to the model gave an optical mean free path of l;250 nm for DLN. This value is in good agreement with optical absorption coefficient values of other DLC films. Thickness profiles of wear tracks in the coatings determined by the model compared well with depths determined by profilometry.
Interfaces in nano-/microcrystalline multigrade CVD diamond coatings
ACS applied materials & interfaces, 2013
The interfaces of multilayered CVD diamond films grown by the hot-filament technique were characterized with high detail using HRTEM, STEM-EDX, and EELS. The results show that at the transition from micro-(MCD) to nanocrystalline diamond (NCD), a thin precursor graphitic film is formed, irrespectively of the NCD gas chemistry used (with or without argon). On the contrary, the transition of the NCD to MCD grade is free of carbon structures other than diamond, the result of a higher substrate temperature and more abundant atomic H in the gas chemistry. At those transitions WC nanoparticles could be found due to contamination from the filament, being also present at the first interface of the MCD layer with the silicon nitride substrate.
Diamond and Related Materials, 2020
Microcrystalline diamond (MCD) and nanocrystalline diamond (NCD) films were synthesized on Si substrates by a microwave plasma chemical vapor deposition in methane-hydrogen gas mixtures with a wide range of methane concentrations of 0.5-40%. The samples were investigated with scanning electron microscopy, atomic force microscopy, and Raman spectroscopy. We observed an unusual transition of the produced material structure from MCD to NCD and again to MCD with the increase in CH 4 content in the gas. The deposition rate, grain size, and the roughness of the films exhibited extrema in the middle of the methane concentration range ([CH 4 ] = 20%). Further increase of CH 4 percentage leads to improvement of the diamond film quality, as confirmed by Raman spectra and SEM images while keeping a high deposition rate. These results may be used for the growth of the wide range of PCD films to be used as multipurpose protective layers, hard coatings for the cutting tools, and the diamond base for composite MCD/NCD structures.
Effect of substrate surface roughness on mechanical properties of diamond-like carbon coatings
Tribology - Materials, Surfaces & Interfaces, 2007
A plasma enhanced chemical vapour deposition (PECVD) amorphous carbon coating was deposited onto 100Cr6 steel substrates having varying degrees of surface roughness. The samples were subsequently evaluated to determine the correlation between substrate roughness and coating performance. The steel substrates were prepared before coating deposition to attain five different levels of roughness: (a) ground; (b) superfinished (SF); (c) polished to 1000 grit; (d) polished to 220 grit and (e) polished to a 1 mm diamond finish. The aim of the investigation was to determine the degree of finish required for good tribological performance and coating adhesion. The mechanical and tribological properties of the samples were assessed by nanoindentation, ramped load scratch testing, and pin on disk wear testing. Nanoindentation testing was used to determine the hardness of the samples and the relative contributions to the system hardness from the substrate and coating were separated using the model of Korsunsky et al. 1 Nanoindentation testing showed that the coating hardness (when separated from the system hardness) was lower for the samples with the SF substrate than the others: the reasons for this are discussed in the light of Raman measurements on the fractions of diamond-like and graphite-like bonding in the coatings. Ramped load scratch testing was used to determine coating adhesion and the scratch test failure mode. With the exception of the samples with the ground substrate finish, studies of the friction coefficient plots during scratch testing showed little variation between the samples, and SEM imaging revealed a common failure mode of severe spallation at the scratch track border. The samples with the ground substrate showed differences in response between scratches parallel and perpendicular to the grinding direction, with scratches parallel to the grinding direction showing more severe spallation. The average critical load to failure, as determined by the point of first failure in the scanning electron microscope, was lower for the coatings on the SF substrate than the coatings on the 220 grit, 1000 grit and 1 micron finished substrates. The critical load to failure for the samples with ground substrates was lower than the other substrate surface finishes. Pin on disk wear testing of the samples against a steel ball revealed that the major effect of the varying substrate roughness was on the wear of the counterface, with rougher substrate finishes generally resulting in higher wear rates of the counterface, although the smoothest substrate finish, the micrometre finish, also resulted in higher wear. The sample whose substrate was superfinished gave least wear of the counterface and this was therefore the optimum finish for the samples when considering their performance in a tribological couple.
Properties of diamond like carbon coatings doped with silicon
AIP Conference Proceedings, 2018
The functionality and quality of many engineering materials depend on the mechanical loads imposed on them and on the specific requirements for their surface, e.g., abrasion resistance and low coefficient of friction. In this regard, covering friction pairs with diamond-like carbon DLC coatings is becoming a common option for lowering the friction coefficient. Several studies reported attempts to improve the behavior of DLC coatings by the addition of selected elements. The aim of this work was to assess the properties of silicon doped DLC coatings. The silicon doped a:C-H coatings were deposited on a 100Cr6 steel substrate by physical vapor deposition PVD. The surface topography of the DLC coatings was examined using atomic force microscopy AFM. The SEM/EDS analysis was used to determine the surface morphology, cross sections and chemical compositions of the coatings. The geometrical structure of the surface before and after tribological tests was measured using an optical profilometer. Coating thickness tests were also carried out. Tribological tests were carried out on a tribotester under technically dry friction.