Sp3 Content Research Articles

Influence of particulate on surface energy and mechanical property of diamond-like carbon films synthesized by pulsed laser deposition

We report a detailed structural study of particulate laden diamond-like carbon (DLC) films synthesized by pulsed laser deposition (PLD) and its influence on surface energy and mechanical properties. A detailed analysis of various parameters such as: Dispersion (G), I(D)/I(G), T-peak position and FWHM(G) obtained from UV Raman spectroscopy for flat and particulate region of all DLC specimens indicate that the vibrational properties vary in both the regions depending on growth mechanism and modification of particulates in the plasma, respectively. The influence of these heterogeneous vibrational properties on surface energy and hardness is extensively studied by contact angle measurement and nano-indentation, respectively. DLC surface energy is observed to be influenced by sp2 cluster size, sp3 content, bond length and angle disorder of sp2 clusters found in the particulate regions, whereas indentation hardness (H) and modulus (E) of DLC films at 0.3 mN applied indentation load follows the evolution of sp3 content in the flat region.

Combined study of the ground and excited states in the transformation of nanodiamonds into carbon onions by electron energy-loss spectroscopy

The electron momentum density and sp2/sp3 ratio of carbon materials in the thermal transformation of detonation nanodiamonds (ND) into carbon nano-onions are systematically studied by electron energy-loss spectroscopy (EELS). Electron energy-loss near-edge structures of the carbon K-ionization in the electron energy-loss spectroscopy are measured to determine the sp2 content of the ND-derived samples. We use the method developed by Titantah and Lamoen, which is based on the ability to isolate the π* spectrum and has been shown to give reliable and accurate results. Compton profiles (CPs) of the ND-derived carbon materials are obtained by performing EELS on the electron Compton scattering region. The amplitude of the CPs at zero momentum increases with increasing annealing temperature above 500 °C. The dramatic changes occur in the temperature range of 900–1300 °C, which indicates that the graphitization process mainly occurs in this annealing temperature region. Our results complement the previous work on the thermal transformation of ND-derived carbon onions and provide deeper insight into the evolution of the electronic properties in the graphitization process.

Tribological performance of graphite-like carbon films with varied thickness

Graphite-like carbon (GLC) films with different thickness were deposited on 316 L stainless steel using closed field unbalanced magnetron sputtering system to investigate the influence of film thickness on the microstructure, mechanical and tribological properties. The results showed that the surface of the deposited films exhibited granular-like morphology, and the sp2 content, surface roughness increase with the increase of film thickness, leading to the lower of hardness and higher of the internal stress. Both of the friction curves obtained by nano-tribological tests and fretting wear experiments revealed a three-stage evolution tendency with the same wear mechanism for the first two stages. The intermediate thick GLC film had the lowest specific wear rate, whilst the fretting fatigue life increased with film thickness.

Copper (Cu) and Cadmium (Cd) toxicity on growth, chlorophyll-a and carotenoid content of phytoplankton Nitzschia sp

This research aimed to study the toxicity of copper (Cu) and cadmium (Cd) on growth, chlorophyll-a and carotenoid content of phytoplankton Nitzschia sp. and to study the IC50-96 h value on growth and chlorophyll-a content, LOEC, and NOEC. This research was done in Research Center of Oceanography, Indonesian Institute of Sciences through four steps: phytoplankton cultivation, definitive test, cell density counting, and chlorophyll-a and carotenoid test. Result showed that increasing heavy metals concentration lead to the decreasing of cell density and intracellular pigment content of Nitzschia sp. Based on the research, the IC50-96 h value of copper (Cu) and cadmium (Cd) on growth was 0,268 mgCu/L and 0,159 mgCd/L. The IC50-96 h value of copper (Cu) and cadmium (Cd) on chlorophyll-a content was 0,274 mgCu/L and 0,150 mgCd/L. LOEC to Nitzschia sp. was 0,18 mgCu/L and 0,18 mgCd/L, while NOEC to Nitzschia sp. was 0,1 mgCu/L and <0,18 mgCd/L. Copper and cadmium toxicity significantly affected the carotenoid content of toxicant concentration of 0,1 mgCu/L and 0,18 mgCd/L.

Effect of oxygen on degradation of defects on ta-C coatings deposited by filtered arc deposition

Among diamond-like carbon (DLC) coatings, tetrahedral amorphous carbon (ta-C) coatings show particularly high thermal stability and oxidation resistance due to their high sp3 content and hydrogen-free structure. On the other hand, it is well known that high-temperature annealing leads to degradation of the ta-C structure, resulting in a release of stress, decrease of hardness, increase in surface roughness, and transformation of the coating nature. Although optical observation is a powerful candidate for imaging the surface conditions of ta-C coatings, strong light emission due to high temperature prevents the acquisition of clear images. In this paper, we establish a novel in situ observation method using environment scanning electron microscopy (ESEM), which allows us to view ta-C surface defects and droplets at 650 °C. A heater embedded in the ESEM increased the temperature on ta-C coatings to 650 °C at gas pressure of 120 Pa. Using a variety of gas conditions including ambient air, dry nitrogen, or dry oxygen, we clarified the effect of the gases on the degradation of the defects. In a dry oxygen atmosphere, defects grew dramatically with annealing time, whereas nitrogen caused no significant transformation to ta-C surfaces. Raman spectroscopy analysis revealed significant structural change in one type of defect, while no noticeable Raman shift was detected in the other type. A focused ion beam created a cross-section of an annealed defect on the ta-C coating. Subsequently, energy dispersive X-ray spectroscopy (EDS) revealed the characteristics of defect growth; one type of defect was associated with a droplet on the interlayer, and the other with graphitization due to oxidization of ta-C on the droplets.

Effect of SiNx interlayer thickness on adhesion and friction properties of diamond-like carbon films

A suitable interlayer thickness is critical to reduce film mismatch and roughness. In this text, diamond-like carbon (DLC) films with different SiNx interlayer thicknesses were successfully synthesized on Si (100) substrates by radio frequency (RF) and direct current (DC) magnetron sputtering method. The effect of SiNx interlayer thickness on surface morphology, adhesion, tribological and mechanical properties of DLC films was investigated. The results show that, due to the use of SiNx interlayer in the DLC films, the adhesion is significantly enhanced, the surface roughness is increased, and the sp3 content and modulus are lowered. When the SiNx interlayer is introduced, the internal stress and the roughness decrease first decrease and then increase. The reason may be related to the accumulation of nitrogen vacancy centers (NVC). A sample of about 10 nm SiNx interlayer was found to have the best combination of tribology, mechanical properties, and surface roughness.

Tuning the tribological property of PLD deposited DLC-Au nanocomposite thin films

Nonhydrogenated Diamond-like Carbon-gold (DLC-Au) nanocomposite thin films with various Au contents and cluster size (<10 nm) have been engineered using Excimer Pulsed Laser Deposition (PLD) on silicon (100) substrates with an aim to achieve reduced coefficient of friction (CoF). Structure, microstructure, chemical bonding and chemical composition of these films were comprehensively investigated using X-ray diffraction (XRD), High resolution transmission electron microscopy (HRTEM), Raman and X-ray photoelectron spectroscopy (XPS), respectively. It is observed that the DLC matrix with lowest Au content sustained higher sp3 content due to enhanced interaction of carbon and smaller Au nano-cluster formed in these films. DLC-Au Nanocomposite formation takes place due to the low compatibility between carbon and gold which resulted in ultra-smaller Au crystallites in DLC matrix at lowest Au content. This enhanced the sp3 content in DLC films and induces tribofilm nucleation on the ball counter body with large amount of sp2 phase fraction which significantly reduced the CoF.

Benchmarking of graphene-based materials: real commercial products versus ideal graphene

There are tens of industrial producers claiming to sell graphene and related materials (GRM), mostly as solid powders. Recently the quality of commercial GRM has been questioned, and procedures for GRM quality control were suggested using Raman Spectroscopy or Atomic Force Microscopy. Such techniques require dissolving the sample in solvents, possibly introducing artefacts.A more pragmatic approach is needed, based on fast measurements and not requiring any assumption on GRM solubility. To this aim, we report here an overview of the properties of commercial GRM produced by selected companies in Europe, USA and Asia. We benchmark: (A) size, (B) exfoliation grade and (C) oxidation grade of each GRM versus the ones of ‘ideal’ graphene and, most importantly, versus what reported by the producer. In contrast to previous works, we report explicitly the names of the GRM producers and we do not re-dissolve the GRM in solvents, but only use techniques compatible with industrial powder metrology.A general common trend is observed: products having low defectivity (%sp2 bonds >95%) feature low surface area (<200 m2 g−1), while highly exfoliated GRM show a lower sp2 content, demonstrating that it is still challenging to exfoliate GRM at industrial level without adding defects.

Microstructure, adhesion and tribological behaviors of Si interlayer/Si doping diamond-like carbon film developed on nitrile butadiene rubber

Si doping diamond-like carbon (Si-DLC) films were prepared on NBR (nitrile-butadiene rubber) in order to improve its friction and wear resistance. Prior to the Si-DLC film deposition, a Si layer was firstly deposited on NBR as an interlayer, and the influence of the Si interlayer thickness on the microstructure, adhesion and tribological behavior of the films on the NBR and Si wafer substrates were systematically compared. The results showed that the surface morphology of the Si-DLC top layer on NBR exhibits a fractured morphology (crack-like network), and all Si-DLC films were characterized by a dense columnar-free microstructure. The deposition rate of films on NBR is faster than that of films on Si wafer. Furthermore, the highest ID/IG ratio and G peak position (sp2 content) could be obtained by the introduction of Si interlayer with a proper thickness of ~1.04 μm, which effectively relieves the compressive stress and thus significantly enhances the adhesion strength between film and NBR, and guarantees an excellent tribological performance. The lowest friction coefficient was achieved (~0.23 compared to 0.27 for the film without Si interlayer and 0.87 for the original NBR) under the relatively high load of 3 N. Meanwhile, the brittle fracture of Si-DLC films on NBR is one of the main factors leading to its lubricating failure under a high load, which suggests that it is necessary to deposit an interlayer to enhance the adhesion and the load-bearing capacity of the film (reducing its hysteresis), and to apply the different element doping and multi-layer composite structures to improve the toughness of the film.

Modifications of surface and bulk properties of magnetron-sputtered carbon films employing a post-treatment of atmospheric pressure plasma

Control of the bonding structure in carbon materials is achieved by a post-treatment of atmospheric pressure plasma (APP) for magnetron-sputtered carbon films. The APP post-treatment changes the films morphologically owing to the removal and modification of sp2 bonds on the basis of the near edge X-ray absorption fine structure analysis of sp2 contents. By APP post-treatment, the resulting changes in surface and bulk properties modify the optical and electrical properties of the carbon films. The control of the film properties can be utilized for various applications, such as gas sensors and solar cells.

Effect of component content variation on composition and structure of activated carbon in PVDF:K2CO3.

Percolative composites consisting of potassium carbonate dispersed in polyvinylidene fluoride (PVDF) polymeric matrix have shown high dielectric constant and electrical conductivity due to the formation of chemically activated carbon interfaces in the composite. In this paper, a series of PVDF/K2CO3 films with different component contents were prepared and investigated by Raman and X-ray photoelectron spectroscopies to clarify chemical composition, structure and formation mechanism of activated carbon. The results revealed the presence of a reaction loop to consume both constituent phases and the formation of sp2 carbon rings in the yielded activated carbon due to cross-linking dehydrofluorination of PVDF during thermal treatment. The sp2 content showed a non-linear dependence on K2CO3 content with the presence of an optimal value corresponding to the highest dielectric constant and electrical conductivity. This study thus can give a direction for future fabrication of PVDF/K2CO3 electrode materials for supercapacitors.

The sp2-sp3 carbon hybridization content of nanocrystalline graphite from pyrolyzed vegetable oil, comparison of electrochemistry and physical properties with other carbon forms and allotropes

Nanocrystalline (nc) graphite produced from pyrolyzed vegetable oil has properties that deviate from typical graphites, but is similar to the previously reported Graphite from the University of Idaho Thermolyzed Asphalt Reaction (GUITAR). These properties include (i) fast heterogeneous electron transfer (HET) at its basal plane and (ii) corrosion resistance beyond graphitic materials. To discover the structural basis for these properties, characterization of this nc-graphite was investigated with Raman and X-ray photoelectron spectroscopies, nano-indentation, density, X-ray diffraction (XRD), thermogravimetric and elemental analyses. The results indicate that this nc-graphite is in Stage-2 of Ferrari's amorphization trajectory between amorphous carbon (a-C) and graphite with a sp2/sp3 carbon ratio of 85/15. The nano-crystallites size of 1.5 nm from XRD is consistent with fast HET rates as this increases the density of electronic states at the Fermi-level. However, d-spacing from XRD is 0.350 nm vs. 0.335 for graphite. This wider distance does not explain its corrosion resistance. Literature trends suggest that increasing sp2 content in a-C's increase both HET and corrosion rates. While nc-graphite's HET rate follows this trend, it exhibits higher than predicted corrosion resistance. In general, this form of nc-graphite matches the best examples of boron-doped diamond in HET and corrosion rates.

DLC deposition inside of a long tube by using the pulsed-DC PECVD process

In this study, the pulsed-DC PECVD deposition system was used to produce Diamond-like carbon (DLC) film on the internal surface of a long metal tube (200 cm in length and 10 cm in diameter) employed as the deposition chamber itself. Firstly, the features of plasma discharges and the temperature distribution along the tube external surface were studied using argon, silane, and acetylene. The experimental results demonstrate that a stable discharge can be established inside the tube. It was found that when the precursor gas is employed, a temperature gradient on the tube surface is formed. Secondly, PECVD experiments regarding DLC film deposition inside the inner surface of the tube are described. For this purpose, polished stainless steel and silicon wafer samples were mounted on the inside tube surface for subsequent analysis of the coatings. It was found that the growth rate and the structure properties of the DLC film varied along the axial direction of the tube. However, surfaces of DLC film with high sp3 content provided better tribological characteristics. These results were mainly attributed to complex processes of local dissociation and activation happened by collision between the electrons and neutrals.

Decorative black coatings on titanium surfaces based on hard bi-layered carbon coatings synthesized by carbon implantation

New approaches to synthesize decorative black coatings on metallic surfaces are of significant research and commercial interest to manufacturing industries. In this work, decorative hard black coatings were deposited on a titanium surface by carbon ion implantation at ambient temperature. A 10 keV C+ beam was implanted on a Ti substrate to a fluence of 1–1.25 × 1018 C cm−2. Rutherford backscattering spectrometry and transmission electron microscopy results show that the implantation resulted in a bi-layered coating structure with a ~50 nm amorphous carbon layer at the surface followed by a ~50 nm amorphous titanium carbide intermixing layer deposited on top of a crystalline Ti surface. Raman spectroscopy confirms the formation of carbide intermixing layer and shows that the amorphous carbon layer has 15–20% sp3 content. Nanoindentation measurements show that the surface hardness of the implanted surface has increased by 72%, from 3.7 to 6.6 GPa, upon carbon implantation. Scratch tests further demonstrate a reduction in coefficient of friction in the implanted surface by 25%, signifying an improvement in wear-resistance of the coated materials. Colorimetry measurements reveal that carbon implantation reduces the luminosity of the Ti surface from 77 to 49 and chromaticity from 4.67 to 1.36, confirming incorporation of black color on Ti surface. The results demonstrate that C implantation onto a Ti surface at high fluence results in a black coating with high surface hardness and wear-resistance that can be employed in decorative surface applications for manufacturing industries.

Ion-beam irradiation of DLC-based nanocomposite: Creation of a highly biocompatible surface

Ion-beam irradiation of diamond-like carbon (DLC) by He ions was studied. Molecular dynamics simulation was performed to understand the effects of irradiation on the nano-topography and chemical state of the coatings and determine the optimal irradiation conditions. Then, the experiment was conducted to validate the results of the simulation and correlate surface modifications to biomedical properties. It was demonstrated that the irradiation led to the formation of a low-density and low-sp3 content surface layer. The structural and chemical properties of the final surface were nearly independent of the initial sp3 content and irradiation energy. The biocompatibility of DLC-based nanocomposite coatings was significantly improved by ion-beam irradiation. Nanocomposite coatings were irradiated by 1 keV He ions. Irradiation with a dose of 4.2 × 1015 ion/cm2 increased the adhesion of MG63 cells dramatically from 10 to ∼100%.

Strategies towards expansion of chemical space of natural product-based compounds to enable drug discovery

Natural products (NPs) are an excellent source of biologically active molecules that provide many biologically biased features that enable innovative designing of synthetic compounds. NPs are characterized by high content of sp3 -hybridized carbon atoms; oxygen; spiro, bridged, and linked systems; and stereogenic centers, with high structural diversity. To date, several approaches have been implemented for mapping and navigating into the chemical space of NPs to explore the different aspects of chemical space. The approaches providing novel opportunities to synthesize NP-inspired compound libraries involve NP-based fragments and ring distortion strategies. These methodologies allow access to areas of chemical space that are less explored, and consequently help to overcome the limitations in the use of NPs in drug discovery, such as lack of accessibility and synthetic intractability. In this review, we describe how NPs have recently been used as a platform for the development of diverse compounds with high structural and stereochemical complexity. In addition, we show developed strategies aiming to reengineer NPs toward the expansion of NP-based chemical space by fragment-based approaches and chemical degradation to yield novel compounds to enable drug discovery.

Effect of substrate bias and substrate/plasma generator distance on properties of a-C:H:SiOx films synthesized by PACVD

In this paper the a-C:H:SiOx films were synthesized on silicon (100) and glass substrates by plasma-assisted chemical vapor deposition combined with pulsed bipolar substrate bias from mixtures of argon and polyphenylmethylsiloxane vapor. The process of a-C:H:SiOx films formation was investigated by controlling processing conditions such as amplitude of negative pulse of substrate bias and the distance between the substrate and plasma generator. Physico-mechanical characteristics of a-C:H:SiOx films were studied by the nanoindentation technique, atomic force microscopy, Fourier transform infrared and Raman spectroscopy. The contact angle and surface free energy were determined by the sessile drop method using couple liquids (water and glycerin). It was found that the films' properties are interrelated with the density of the ion current on the substrate, which was measured using a guarded planar probe. The obtained results show that film prepared at the smaller substrate/plasma generator distance and optimal substrate biasing has a higher content of sp3 bonded carbon and, accordingly, has higher hardness, Young's modulus and resistance to plastic deformation. At the same time the a-C:H:SiOx films show large hydrophobicity with a contact angle for water of about 91° and small total surface free energy of about 17.9 mN/m.

Improvement of thermal stability, adhesion strength and corrosion performance of diamond-like carbon films with titanium doping

Ti-doped diamond-like carbon (Ti-doped DLC) films were deposited on 304 stainless steel through a pulsed filtered cathodic vacuum arc deposition with an individual cathodic arc source. Structural dependent thermal stability, mechanical properties, adhesion, and corrosion performance were thoroughly investigated as a function of the Ti content. Only 0.8 at.% Ti content in the DLC films offers the relatively high hardness (28.8 GPa), high corrosion resistance, enhanced adhesion strength as well as improved thermal stability compared to the undoped DLC films. The reduction in the internal stress and the sp3 content associated with a slight decrease in the mechanical properties is from Ti doping. Higher thermal stability is due to the TiC phase in the Ti-doped DLC structure. Enhancement of the adhesion strength is owing to the relief of the internal stress and the occurrence of the strong atomic intermixing bond at a Ti-doped DLC/Ti intermediate layer interface. Interestingly, the formation of the TiO2 film on the Ti-doped DLC surface due to a small amount of Ti doping significantly exhibited a better corrosion performance. Ti-doped DLC films, therefore, are a promising coating for tribological applications.

The influence of positive pulses on HiPIMS deposition of hard DLC coatings

Diamond-like Carbon (DLC) coatings were deposited by a novel HiPIMS method that incorporates positive voltage pulses at the end of the conventional HiPIMS discharge. Different positive voltage amplitudes (100, 200, 300, 400 and 500 V) were used to evaluate the effect of this operation mode on the discharge process and the mechanical properties of the deposited DLC coatings. The application of positive pulses was observed to enhance the ionization of both the sputtered carbon and argon species. Mass spectroscopy measurements showed that a larger amount of high-energy C+ ions are generated, with ion energies proportional to the amplitude of the overshoot voltage. The ion bombardment induced by the positive pulses led to higher compressive residual stresses and densification of deposited DLC coatings. Moreover, their Raman spectra exhibited lower D-band and G-band intensity ratios (ID/IG) as the pulses voltage was increased which is indicative of higher sp3 content. Mechanical properties were evaluated by nanoindentation testing and the hardness of the deposited DLC films was observed to increase from 9.6 GPa (for no voltage pulse applied) to 22.5 GPa (for an applied positive pulse voltage of 500 V).

The effect of thiamine on the growth and fatty acid content of Aurantiochytrium sp

Aurantiochytrium sp. is a heterotrophic microorganism that accumulates high amounts of fatty acids (FAs), including odd-chain FAs and an essential FA, docosahexaenoic acid (DHA). Since complex nutrient sources such as tryptone and yeast extract are conventionally utilized in the growth medium for Aurantiochytrium, it is difficult to investigate which individual vitamins affect growth and FA production. Thus, in the present study, we simplified the nitrogen source and defined the vitamins required for Aurantiochytrium sp. cultivation. Glutamate was found to be the most effective simple nitrogen source in cultivation media and thiamine (vitamin B1) was identified as a unique essential vitamin for this organism. Media supplemented with thiamine, as the only member of the vitamin B complex added, allowed for propagation of four strains of Aurantiochytrium. The ratio of odd-chain FAs significantly decreased in the medium containing glucose, glutamate, and thiamine when compared with the conventional medium containing glucose, tryptone, and yeast extract. This is likely caused by a decreased availability of branched-chain amino acids. Under thiamine starvation, FA content per dry cell weight gradually decreased throughout cultivation, and the specific activity of pyruvate dehydrogenase (PDH), a thiamine-dependent enzyme, was severely repressed. These results indicate that when thiamine is absent, the cells compensate some amount of acetyl-CoA through β-oxidation of FAs in vivo, instead of from the reaction by pyruvate, as occurs under normal growth conditions. Providing experimental evidence that the activity of vitamin-dependent enzymes affects biosynthesis of FAs is critical to a better understanding of the effect of vitamin supplementation in Aurantiochytrium sp. media. In the present study, we demonstrated the close relationship between PDH activity, FA content and the importance of thiamine supplementation in the culture medium in Aurantiochytrium sp.