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The characterization of diamondlike carbon (DLC) films is a challenging subject, considering the diversity of carbon-based nanostructures depending on the deposition process. We propose to combine multiwavelength (MW) Raman spectroscopy and electron energy-loss spectroscopy (EELS) to probe the structural disorder and the carbon hybridizations of DLC films deposited by pulsed laser ablation performed either with a nanosecond laser (film labeled ns-DLC), either with a femtosecond laser (film labeled fs-DLC). Such deposition methods allow to reach a rather high carbon sp3 hybridization but with some significant differences in terms of structural disorder and carbonaceous chain configurations. MW Raman investigations, both in the UV and visible range, is a popular and nondestructive way to probe the structural disorder and the carbon hybridizations. EELS allows the determination of the carbon plasmon energy in the low-loss energy region of the spectra, as well as the fine structure of the ionization threshold in the high-loss energy region. The paper shows that the combination of MW Raman and EELS is a powerful way to elucidate the nanostructure of DLC films. Complementary nanoindentation investigations allow to correlate the analytical results with the mechanical properties of the films. The ns-DLC film presents a stronger sp3-bonded C character (74%-85%) with a significant content of sp2 chains, whereas the fs-DLC contains less sp3 bonds (35%-50%) with a significant content of sp2-bonded C rings. The ns-DLC film exhibits a higher proportion of disordered sp2 C mainly in the form of chains. Comparatively, the fs-DLC exhibits a predominance of more ordered sp2 C structures in the form of graphitic aggregates whose size has been estimated near three aromatic rings. The film characteristics are in agreement with their mechanical properties. We also propose a correlation between the nanostructure and composition of the films with the deposition mechanisms. The difference in kinetic energy distribution in the plasma plume, together with an absence of interaction between the plasma plume and the femtosecond laser, are responsible for the observed differences in sp3 C content and sp2 C configuration ranging between a predominance of more ordered sp2 rings in the fs-DLC film and a predominance of sp2 chains in the ns-DLC film. These results are consistent with the mechanisms of subplantation occurring during DLC deposition [ABSTRACT FROM AUTHOR]

We report on electrical measurements and structural characterization performed on boron-doped diamond-like carbon thin films deposited by femtosecond pulsed laser deposition. The resistance has been measured between 77 and 300 K using four probe technique on platinum contacts for different boron doping. Different behaviours of the resistance versus temperature have been evidenced between pure DLC and boron-doped DLC. The a-C:B thin film resistances exhibit Mott variable range hopping signature with temperature. Potential applications of DLC thin films to highly sensitive resistive thermometry is going to be discussed. [ABSTRACT FROM AUTHOR]

High-density tetrahedral amorphous carbon (ta-C) films have been prepared by nanosecond (17 ns) and femtosecond (150 fs) pulsed laser deposition (PLD) using fluences and repetition rates compatible with fast and homogeneous growth over large areas. Their optical properties were measured by spectroscopic ellipsometry from 1.0 to 4.7 eV and analyzed using a multi-layer Tauc-Lorentz model. In spite of very different ablation mechanisms, both PLD techniques produce high density bulk layers as revealed by a refractive index (n at 2 eV) of 2.7±0.1 for both fs-PLD and ns-PLD. Films are covered by a few nm-thick sp2-rich top layer which is denser and thicker in femtosecond PLD as compared to nanosecond PLD. The respective roles of low and high energies in the kinetic energy distribution of the incident carbon species are discussed in terms of densification and sp3↦sp2 configurational relaxation predicted by the subplantation growth model. The significantly higher optical gap found in the ns-PLD films is attributed to the larger contribution of energetic species with kinetic energies Ec≥200 eV, as revealed by time-of-flight optical studies. [ABSTRACT FROM AUTHOR]

Abstract: Femtosecond pulsed laser deposition (PLD) has been performed using a mode-locked Ti:sapphire laser including an amplification stage (150fs, 800nm, 1kHz) to deposit tetrahedral-amorphous carbon films (ta-C) on AISI 316L stainless steel and ultra high molecular weight polyethylene, in perspective to extend the wear resistance of materials used in hip joints. Ta-C films have been elaborated in high vacuum conditions at room temperature. The diamond-like coated silicon substrates exhibit high wear resistance (in the 10−8–10−9 mm3 (Nm)−1 range) with moderate hardness (in the 20–30GPa range), which may be favorable for the accommodation motion between contacting surfaces in a hip joint. In situ sputter cleaning of the orthopaedic substrates in argon plasma prior to carbon deposition has been investigated, leading to the enhancement of the adhesion of the films onto the stainless steel substrates. The adhesion properties of films deposited in various conditions on metallic substrates have been studied by tensile tests. The tribological behavior of the coatings deposited on cleaned substrates have been widely investigated in a pin-on-flat configuration in ambient air and Ringer solution. Finally, a DLC thin film with an homogeneous thickness has been deposited on hemispherical surface of 22.2mm in diameter of a stainless steel femoral head of a hip prosthesis, whose wear behavior will be quantified using a hip joint simulator during one million of cycles (corresponding to the human activity during one year). [Copyright &y& Elsevier]

Abstract: Metal-containing diamond-like carbon films (Me-DLC), with metallic particles embedded in a DLC matrix, have become good candidates to improve many film properties (including mechanical properties and adhesion) and to enhance the tribological behavior in severe conditions. Previous studies on the properties of Me-DLC coatings have reported lower compressive stresses and higher wear resistance compared to undoped DLC. In many cases, the presence of metal inclusions enhances adhesion on metallic substrates. The present study investigates the composition and nanostructure of DLC coating alloyed with 50 at.% concentration of nickel. The film is deposited by femtosecond pulsed laser ablation (PLD) by ablating sequentially graphite and nickel targets. The chemical composition and the bonding characteristics of this film are determined by X-ray Photoelectron Spectroscopy (XPS), Near Edge X-ray Absorption Spectroscopy (NEXAFS) and Electron Energy Loss Spectroscopy (EELS) imaging. The chemical composition, the carbon hybridization and the morphology of the a-C:Ni film at the microscopic scale are discussed, in relation to the thermodynamic phase diagram of the Ni–C system. [Copyright &y& Elsevier]

Compared to conventional nanosecond laser ablation, femtosecond pulsed laser deposition (PLD) allows the production of higher energy ions (up to a few keV) in the plasma plume, which strongly affect the structure and properties of the deposited films. In this work, tetrahedral diamond-like carbon (ta-C) films have been deposited by femtosecond PLD on various substrates, including 316L stainless steel, in order to extend the wear resistance of materials used for hip joint replacement. The deposition process has been optimized to obtain smooth and wear-resistant carbon films by ablating a graphite target in ultra-high vacuum conditions at room temperature, with a laser fluence (energy density) ranging from 1 to 6 J cm−2. In situ sputter cleaning of the substrates in an argon atmosphere prior to carbon deposition has been widely investigated: tensile tests show that the adhesion of the films on stainless steel substrates is remarkably enhanced by removing the contamination and oxidized top-coats. The films exhibit high wear resistance (in the 10−8 to 10−9 mm3 N−1 m−1 range) with moderate hardness (in the 20–30 GPa range), which may be favorable for the accommodation motion between contacting surfaces in a hip joint. The ability of these films to satisfy the biomedical requirements is discussed and the possibility to deposit homogeneous ta-C films on a 22.2-mm diameter hemispherical surface is examined. Finally, homogeneous films have been deposited on a 316L stainless steel femoral head, whose wear behavior will be quantified using a walking simulator during several millions of cycles (corresponding to the human activity during several years). [Copyright &y& Elsevier]