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Plasma hydrogenation of graphene has been proposed as a tool to modify the properties of graphene. However, hydrogen plasma is a complex system and controlled hydrogenation of graphene suffers from a lack of understanding of the plasma chemistry. Here, we correlate the modifications induced on monolayer graphene studied by Raman spectroscopy with the hydrogen ions energy distributions obtained by mass spectrometry. We measure the energy distribution of H+, H2+, and H3+ ions for different plasma conditions showing that their energy strongly depends on the sample position, pressure, and plasma power and can reach values as high as 45 eV. Based on these measurements, we speculate that under specific plasma parameters, protons should possess enough energy to penetrate the graphene sheet. Therefore, a graphene membrane could become, under certain conditions, transparent to both protons and electrons. [ABSTRACT FROM AUTHOR]

Abstract: We study the 514 and 244 nm Raman spectra of a wide variety of hydrogenated amorphous carbons (a-C:H). The hydrogen content can be estimated from the slope of the photoluminescence background (PL) of the spectra measured at 514.5 nm. Generally, the evolution of the sp2 and sp3 phases is not independent for as-deposited a-C:H samples. This, in principle, allows us to derive their structural and optical properties just by studying the visible Raman spectra. For highly hydrogenated samples, the PL background overshadows the visible Raman spectra, and UV excitation is the only way to measure a Raman spectrum. [Copyright &y& Elsevier]

Storage density is presently doubling every year. This requires the read head to approach closer to the magnetic layer, and ever-thinner layers of carbon. Film thickness below 2 nm and roughness well below 1 nm are needed for the storage of ∼1 Tb/in2. Here we present an analytical and functional characterisation of ultra-thin carbon nitride and pure carbon films produced by magnetron sputtering and filtered high current vacuum arc. The main focus is the effect of nitrogen composition and decreasing film thickness on the relevant mechanical and tribological properties. The carbon bonding has been monitored by using a combination of Raman spectra, taken at two wavelengths (514 and 244 nm). We show that the density, nitrogen content, scratching resistance and Young''s modulus of ultra-thin films can all be monitored by the G peak dispersion. Also, the G peak full width at half maximum is a useful parameter in order to investigate the structural evolution of thin films. [Copyright &y& Elsevier]

Diamond-like carbon (DLC) films have been synthesised by KrF-excimer pulsed laser deposition (PLD) at a wavelength of 248 nm, with laser fluences between 1 and 37 J cm−2, in vacuum and in a nitrogen atmosphere. The substrates were (100) Si wafers coated with a polycarbonate (PC, LEXAN type) layer a few μm thick. Structural analysis was performed by combined visible and UV Raman spectroscopy. In visible Raman spectra, D and G bands are found; in UV Raman spectra, the blue-shifted G band and the T peak are observed. A further band at approximately 1400 cm−1 is found in spectra from vacuum-deposited films at low fluences. The evolution of Raman fitting parameters with increasing laser fluence shows that in the films deposited in vacuum, a structural transition from mainly disordered graphitic to predominantly amorphous, tetrahedrally bonded carbon (ta-C) has occurred at 10 J cm−2. In the presence of an N2 atmosphere during deposition, important modifications of the Raman spectra, associated with changes in the expansion dynamics of the carbon plasma plume are observed. Fourier-transform infrared (FTIR) spectroscopy on such films gave evidence of bands due to vibrations of the C&z.sbnd;N, C&z.sbnd;H and N&z.sbnd;H groups. Mechanical properties of the films were measured by nanoindentation; the hardness H of vacuum-deposited films with the highest sp3 content was 8 GPa. The hardness of DLC films prepared in a nitrogen atmosphere at the highest fluence was 5 GPa. [Copyright &y& Elsevier]

Abstract: UV Raman spectroscopy is a powerful technique for the investigation of diamond-like carbon (DLC) films because it can provide information on the density, mechanical and optical properties. Here we show a detailed analysis of the G and D peak Raman intensity of hydrogenated DLC (a-C:H) with hydrogen (H) content ranging from 25 to 50 at.%. We show that the G peak Raman intensity strongly increases with the H content. This has been attributed to a strong enhancement of the UV Raman cross-section with the H incorporation. [Copyright &y& Elsevier]

Homogenous wear resistant carbon coatings with an optical gap of 3 eV but low stress are needed to increase the storage density in optical storage disks in order to reach 100 GB in 12-cm diameter disks. Here, hydrogenated amorphous carbon (a-C:H) films are deposited at room temperature using a large area electron cyclotron wave resonance plasma beam source of 14.2-inch diameter. Methane is used as the precursor. The ion flux and energy, plasma pressure, distance between the extraction grid and the substrate were varied. The films are characterized in terms of hydrogen content, stress, optical gap, refractive index, wear resistance, surface roughness and homogeneity by a variety of characterization techniques. Resonant Raman spectroscopy is used in order to non-destructively monitor the disk quality. We show how it is possible to produce homogenous, wear resistant a-C:H coatings with an optical gap of 3 eV and low stress (<500 MPa), without damaging the plastic disks. [Copyright &y& Elsevier]