P. Mérel

Direct evaluation of the sp3 content in diamond-like-carbon films by XPS

The analysis of the X-ray photoelectron spectra (XPS) of the C 1s core level of pulsed laser deposited diamond-like carbon thin films, obtained at different laser intensities is presented. These spectra are deconvoluted into two different contributions, at 284.4 eV and 285.2 eV, which are respectively attributed to sp2 and sp3 hybridized carbon atoms. From the deconvoluted spectra, the sp3 content in the films is evaluated. It is found to increase from 33% to about 60% as laser intensity is varied from 0.9×108 to 7.1×108 W/cm2. These measurements have been compared to those obtained by the analysis of the C KLL X-ray excited Auger electron spectra. The two methods provide the same qualitative variation of the sp3 content with laser intensity. However, the XPS of the C 1s core level yields systematically higher sp3 content values. These differences are attributed to the presence of an sp2 rich outer layer on the surface of the DLC films, as confirmed by angle-resolved XPS. The analysis of the C 1s peak is shown to be a very simple and direct method to evaluate the sp3 content in unhydrogenated DLC thin films.

X-RAY PHOTOELECTRON SPECTROSCOPY OF CARBON NITRIDE FILMS DEPOSITED BY GRAPHITE LASER ABLATION IN A NITROGEN POSTDISCHARGE

Carbon nitride thin films have been deposited on silicon substrates, using a newly developed surface wave discharge/pulsed laser deposition system. Nitrogen incorporation in the films is examined by x‐ray photoelectron spectroscopy (XPS). It shows that interaction between the laser ablated carbon species and nitrogen atoms from the surface‐wave N2 plasma enhances the incorporation of N in the carbon nitride layers, for example, up to 19% at a deposition pressure of 2 mTorr. Increasing the deposition temperature decreases nitrogen incorporation and changes the local chemical environment of nitrogen atoms.

Effect of laser intensity on the microstructural and mechanical properties of pulsed laser deposited diamond-like-carbon thin films

Diamond-like-carbon (DLC) thin films have been deposited at room temperature on Si substrates by ablation of a graphite target using a KrF excimer laser at intensities ranging from 0.9×108 W/cm2 to 6.0×109 W/cm2. The microstructure of the films was studied by x-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The macroscopic properties were evaluated by measurement of their optical constants using in-situ laser reflectometry and their hardness using the continuous stiffness measurement technique. Analysis of the XPS C 1s core level spectra of the DLC films shows that their sp3 hybridized carbon atom content increases with laser intensity up to a maximum value of about 60% obtained at 7.0×108 W/cm2. At higher laser intensities, the sp3 content appears to stabilize at about 53%. Such an evolution of the sp3 content can be understood in terms of the subsurface carbon ions implantation model which has been proposed for ion beam deposited films. On the other hand, Raman analysis indicates that an i...

Correlation between the sp2-phase nanostructure and the physical properties of unhydrogenated carbon nitride

This paper consists of an investigation of the structural arrangement of the sp2 phase in amorphous unhydrogenated carbon nitride (a‐CNx) films and its effect on their physical properties. The a‐CNx films (0.16 1020∕cm3) and the EPR linewidth (of a few gausses) along with a decrease in nitrogen content. Visible Raman measurements indicate that these effects are accompanied by an increase in the degree of disorder of the sp2 phase, as inferred from the broadening and downshift of the G Raman band, and a reduction of the CN triple bond signal. The a...

XPS and FTIR analysis of nitrogen incorporation in CNx thin films

Abstract CNX thin films have been deposited on Si(100) substrates using a new hybrid deposition system. This system combines excimer laser ablation of a graphite target and an atomic nitrogen source from a remote surface wave plasma. The films were characterized using X-ray photoelectron spectroscopy (XPS), elastic recoil detection (ERD) and Fourier transform infrared spectroscopy (FTIR). We found that the atomic nitrogen source enhances the incorporation of N in the CN x layers, for example, from N/C = 0.04 (plasma off) to 0.18 (plasma on). In addition, as nitrogen pressure in the deposition chamber is increased from 2mTorr to 1 Torr, the N/C ratio increases from 0.18 to 0.56. The XPS and FTIR spectra indicate that at deposition pressures above 100 mTorr, nitrogen incorporation is enhanced through the formation of hydrogenated carbon nitride groups, while at lower pressures, only simple and double CN bonds are detected.

The influence of atomic nitrogen flux on the composition of carbon nitride thin films

Carbon nitride (CNx) thin films have been deposited using a hybrid system combining pulsed laser deposition of graphite with the surface-wave discharge atomic nitrogen source (3% N2 in Ar). Using this system, an experiment is designed to study the influence of the atomic nitrogen flux on the composition of the CNx thin films at various laser intensities. The nitrogen percentage in the thin films is positively correlated with the N atom flux impinging on the substrate surface but it is counter-productive to use excessively high values of laser intensities on the graphite target. For a laser intensity of 6×108 W/cm2, the nitrogen percentage increases with the N atom flux and saturates at only about 16 at. %. On the other hand, a maximum nitrogen percentage of 30 at. % is obtained at the much lower laser intensity of 5×107 W/cm2.

Synthesis of diamond-like-carbon coatings by pulsed laser deposition: optimization of process parameters

Abstract In this work, we report on both the microstructural (sp 3 carbon atoms content) and the mechanical properties (hardness and elastic modulus) of pulsed laser deposited diamond-like-carbon (DLC) thin films. The sp 3 content of the films was determined by analysis of the XPS C 1s core-level signal, and the hardness and elastic modulus were measured by nanoindentation using the continuous stiffness measurement (CSM) technique. By investigating the effect of process parameters, such as deposition temperature and KrF excimer laser intensity on the diamond-like characteristics of the films, we were able to point out that: (1) deposition at 25°C, as opposed to deposition at 300°C, enhances the diamond-like properties of the coatings, (2) the sp 3 content increases with laser intensity up to a maximum value of about 60% obtained at 7.0×10 8 W/cm 2 and (3) the hardness and elastic modulus of the coatings both increase with laser intensity as they respectively reach 44 and 375 GPa at 7.0×10 8 W/cm 2 . It is finally shown that the observed variations in the hardness value and elastic modulus correlate well with the variations of the sp 3 content of the DLC coatings.

Phase segregation in pulsed laser deposited carbon nitride thin films

Abstract Carbon nitride thin films have been deposited at room temperature by plasma assisted pulsed laser deposition and the effect of varying the KrF excimer laser intensity was studied by examination of the bonding and hardness of the films. X-ray photoelectron spectroscopy shows that the nitrogen content in the films decreases from 24 to 16 at.% when laser intensity is increased from 2.5×10 7 to 9.4×10 8 W/cm 2 and that the nitrogen atoms are incorporated in the films under two different bonding configurations, as deduced by two distinct contributions to the N 1s signal at 398.4±0.2 and 400.1±0.2 eV. However, it was found that the stoichiometry of the CN bonded structures is independent of laser intensity as it remains constant at 33±3 at.% of N. This suggests that the microstructure of the films consists of a nearly stoichiometric C 2 N phase mixed with amorphous carbon regions. Such a picture is further supported by the observation that the binding energy of the two components of the N 1s XPS signal is not affected by laser intensity. By using continuous stiffness measurement nanoindentation, a hardness value of 24 GPa, was determined for the film synthesized at the highest laser intensity used in this work but it was found to deteriorate with increasing nitrogen content. These effects could be explained in terms of an intermixing between the C 2 N phase and pure carbon domains rather than a modification of nitrogen bonding configuration in the films.