B. Angleraud

Bonding structure of carbon nitride films deposited by reactive plasma beam sputtering

This work is devoted to the study of the reactive plasma beam sputtering deposition of carbon nitride thin films. To investigate the variations of the bonding structure, induced by modifying the main deposition parameters, a systematic characterization of the films by X-ray photoelectron spectroscopy (XPS) is performed. With increasing the nitrogen partial pressure, the deposition rate and the nitrogen atomic fraction in the films increase, and the valence band spectrum shape is modified. The curve fitting of the C1s and N1s peak spectra shows that C and N atoms exhibit several chemical states, representative of different type of chemical bonds.

Effect of nitrogen incorporation in CNx thin films deposited by RF magnetron sputtering

Abstract Carbon nitride thin films were deposited by RF magnetron sputtering of a graphite target in a pure N 2 or mixed Ar/N 2 plasma. The effect of nitrogen incorporation on the growth kinetics, composition, structure and type of bonding of CN x films in a large range of N 2 pressure (0.5–40 Pa) and N 2 fraction in the discharge gas mixture was studied. Observations by scanning electron microscopy (SEM) of the film cross-sections revealed different morphologies depending on the N 2 pressure. Transmission electron microscopy (TEM) measurements revealed that the CN x films were amorphous. By changing the deposition conditions, the N/C ratio, deduced from XPS analysis, varied from 0 to a maximum value of 0.7. Various chemical bonds for C and N atoms were found by curve fitting of N 1s and C 1s XPS peaks and by study of FTIR spectra. The optical properties of these materials were also investigated using UV-Vis-NIR absorption.

Effect of a r.f. antenna on carbon nitride films deposited by ionized r.f. magnetron sputtering

This work deals with the study of an original physical vapor deposition process, called ionized magnetron sputtering applied to carbon nitride films. The magnetron discharge is coupled to an inductively induced radio-frequency one generated by a coil (antenna) placed between the target and the substrate. The high density plasma generated by the antenna, allows an increase of the ion bombardment of the film growing surface which can greatly modify the properties of the deposited films. In order to investigate the variation of the film composition, induced by the antenna, a systematic characterization by X-ray photoelectron spectroscopy is performed vs. the substrate bias, the antenna to target r.f. power ratio and the discharge gas pressure. Optical emission spectroscopy has been used to characterize the plasma.

Shape control of nickel nanostructures incorporated in amorphous carbon films: From globular nanoparticles toward aligned nanowires

The growth of nickel/carbon nanocomposite thin films by a hybrid plasma process, which combines magnetron sputtering and plasma enhanced chemical vapor deposition, has been investigated. This study has shown that the films consist of nickel-rich nanostructures embedded in an amorphous carbon matrix. The size, the distribution, the density, and the shape of these nanostructures are directly dependent to the total carbon content within the films. At low carbon content (∼28 at. %), dense nanowire array perpendicularly oriented to the surface of the substrate can be fabricated. For an intermediate carbon concentration (∼35 at. %), the nickel phase was organized into elongated nanoparticles. These nanoparticles became spherical when reaching a higher carbon content (∼54 at. %). The extensive structural study allowed the representation of a structure zone diagram, as well as, the development of a scenario describing the growth mechanisms that take place during the deposition of such nanocomposite material.

Titanium carbide/carbon composite nanofibers prepared by a plasma process

The incorporation of metal or metal carbide nanoparticles into carbon nanofibers modifies their properties and enlarges their field of application. The purpose of this work is to report a new non-catalytic and easy method to prepare organized metal carbide-carbon composite nanofibers on nanopatterned silicon substrates prepared by laser interference lithography coupled with deep reactive ion etching. Titanium carbide-carbon composite nanofibers were grown on the top of the silicon lines parallel to the substrate by a hybrid plasma process combining physical vapor deposition and plasma enhanced chemical vapor deposition. The prepared nanofibers were analyzed by scanning electron microscopy, x-ray photoelectron spectroscopy, Raman spectroscopy and transmission electron microscopy. We demonstrate that the shape, microstructure and the chemical composition of the as-grown nanofibers can be tuned by changing the plasma conditions.

Hierarchical carbon nanostructure design: ultra-long carbon nanofibers decorated with carbon nanotubes

Hierarchical carbon nanostructures based on ultra-long carbon nanofibers (CNF) decorated with carbon nanotubes (CNT) have been prepared using plasma processes. The nickel/carbon composite nanofibers, used as a support for the growth of CNT, were deposited on nanopatterned silicon substrate by a hybrid plasma process, combining magnetron sputtering and plasma-enhanced chemical vapor deposition (PECVD). Transmission electron microscopy revealed the presence of spherical nanoparticles randomly dispersed within the carbon nanofibers. The nickel nanoparticles have been used as a catalyst to initiate the growth of CNT by PECVD at 600°C. After the growth of CNT onto the ultra-long CNF, SEM imaging revealed the formation of hierarchical carbon nanostructures which consist of CNF sheathed with CNTs. Furthermore, we demonstrate that reducing the growth temperature of CNT to less than 500°C leads to the formation of carbon nanowalls on the CNF instead of CNT. This simple fabrication method allows an easy preparation of hierarchical carbon nanostructures over a large surface area, as well as a simple manipulation of such material in order to integrate it into nanodevices.

Highly ordered ultralong magnetic nanowires wrapped in stacked graphene layers.

Summary We report on the synthesis and magnetic characterization of ultralong (1 cm) arrays of highly ordered coaxial nanowires with nickel cores and graphene stacking shells (also known as metal-filled carbon nanotubes). Carbon-containing nickel nanowires are first grown on a nanograted surface by magnetron sputtering. Then, a post-annealing treatment favors the metal-catalyzed crystallization of carbon into stacked graphene layers rolled around the nickel cores. The observed uniaxial magnetic anisotropy field oriented along the nanowire axis is an indication that the shape anisotropy dominates the dipolar coupling between the wires. We further show that the thermal treatment induces a decrease in the coercivity of the nanowire arrays. This reflects an enhancement of the quality of the nickel nanowires after annealing attributed to a decrease of the roughness of the nickel surface and to a reduction of the defect density. This new type of graphene–ferromagnetic-metal nanowire appears to be an interesting building block for spintronic applications.

Model for power coupled to RF planar magnetrons. Experimental validation and application to CNx thin film deposition

We focus here on the particular case of radio frequency (RF-13.56 MHz) planar magnetrons from fundamental point of view, which is supported by experiments. The description of the power coupled to the discharge through the plasma bulk electrons can be expressed as a sum of two terms. One can be related to the drift heating and the other one to the ohmic heating. The relative importance of these two terms gives a pressure interval for the normal operation of RF magnetrons, lying between 0.2 Pa and approximately 13 Pa. Radio frequency compensated Langmuir probe results are in good agreement with model predictions showing two distinct regimes. The normal one is the low pressure-high efficiency magnetron regime while the diffusion one is the high-pressure regime. Contrasting carbon nitride film properties are evidenced, when the discharge operates at normal or at high-pressure regimes. Proposed model can partially explain film features.

Carbon nanochannels elaborated by buckle delamination control on patterned substrates

Carbon nanochannels were achieved using lithographically patterned lines on a silicon substrate as a template to control the buckle delamination of highly equibiaxial compressively stressed thin films. Carbon films were synthesized by ionized physical vapor deposition through inductively coupled plasma magnetron sputtering. The obtained structures exhibit dimensions as small as 500nm wide and 80nm high, and may be used in nanofluidic applications. Results regarding the characterization of their growth mechanism and structural analyses by Raman microspectroscopy are presented.