Pierre-Yves Tessier

Plasma etching : principles, mechanisms, application to micro- and nano-technologies

Abstract Nowadays, plasma-etching processes are asked to produce patterns from the nanometer to the micrometer range with the same efficiency. The very severe requirements in terms of etch rate, selectivity, profile control and surface damage plasma-etching processes lead to, have been at the origin of the development of mechanistic studies by means of plasma diagnostics and surface analysis, as well as the development of new etching devices. We review here the basic concepts of plasma etching, and using examples, we describe more in details important features. We recall, in particular, the important role of the surface layer, the ion bombardment and the substrate temperature.

Highly Ordered Hollow Oxide Nanostructures: The Kirkendall Effect at the Nanoscale

Highly ordered ultra-long oxide nanotubes are fabricated by a simple two-step strategy involving the growth of copper nanowires on nanopatterned template substrates by magnetron sputtering, followed by thermal annealing in air. The formation of such tubular nanostructures is explained according to the nanoscale Kirkendall effect. The concept of this new fabrication route is also extendable to create periodic zero-dimensional hollow nanostructures.

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.

Carbon nanowalls as material for electrochemical transducers

The electrochemical reactivity of a carbon nanowalls electrode was highlighted. The carbon nanowalls were synthesized at 520 °C in an acetylene/ammonia electron cyclotronic resonance plasma without any metal catalyst. The electrode surface was characterized by scanning and transmission electron microscopy. Its electrochemical reactivity was studied by both cyclic voltammetry and electrochemical impedance spectroscopy. After the carbon nanowalls deposition, the electronic transfer rate constant and the electroactive surface area were found to be increased by a factor of 7 and 3, respectively.

Unusual dealloying effect in gold/copper alloy thin films: the role of defects and column boundaries in the formation of nanoporous gold.

Understanding the dealloying mechanisms of gold-based alloy thin films resulting in the formation of nanoporous gold with a sponge-like structure is essential for the future design and integration of this novel class of material in practical devices. Here we report on the synthesis of nanoporous gold thin films using a free-corrosion approach in nitric acid applied to cosputtered Au-Cu thin films. A relationship is established between the as-grown Au-Cu film characteristics (i.e., composition, morphology, and structure) and the porosity of the sponge-like gold thin films. We further demonstrate that the dealloying approach can be applied to nonhomogenous Au-Cu alloy thin films consisting of periodic and alternate Au-rich/Au-poor nanolayers. In such a case, however, the dealloying process is found to be altered and unusual etching stages arise. Thanks to defects and column boundaries playing the role of channels, the nitric acid is found to quickly penetrate within the films and then laterally (i.e., parallel to the film surface) attacks the nanolayers rather than perpendicularly. As a consequence to this anisotropic etching, the Au-poor layers are etched preferentially and transform into Au pillars holding the Au-rich layers and preventing them against collapsing. A further exposure to nitric acid results in the collapsing of the Au-rich layers accompanied by a transition from a multilayered to a sponge-like structure. A scenario, supported by experimental observations, is further proposed to provide a detailed explanation of the fundamental mechanisms occurring during the dealloying process of films with a multilayered structure.

Impact of magnetron configuration on plasma and film properties of sputtered aluminum nitride thin films

We have investigated the growth of the c-axis oriented aluminum nitride (AlN) thin films on (100) silicon by reactive dc magnetron sputtering at low temperature, considering the effect of the magnet configuration on plasma and film properties. It appears that a magnet modification can significantly modify both the plasma characteristics and the film properties. Electrical and optical characterizations of the plasma phase highlight that depending on the magnet configuration, two very different types of deposition process can be involved in the same deposition chamber. On the one hand, with a balanced magnetron (type 1), the deposition process enhances the production of AlN dimers in the plasma phase and enables to synthesize AlN films with different preferential orientations (100, 002, and even 101). On the other hand, a strongly unbalanced magnetron (type 2) provides a limited production of AlN species in the plasma phase and a strong increase in the ratio of ions to metal atom flux on the growing films. ...

Electron Beam Nanosculpting of Kirkendall Oxide Nanochannels

The nanomanipulation of metal nanoparticles inside oxide nanotubes, synthesized by means of the Kirkendall effect, is demonstrated. In this strategy, a focused electron beam, extracted from a transmission electron microscope source, is used to site-selectively heat the oxide material in order to generate and steer a metal ion diffusion flux inside the nanochannels. The metal ion flux generated inside the tube is a consequence of the reduction of the oxide phase occurring upon exposure to the e-beam. We further show that the directional migration of the metal ions inside the nanotubes can be achieved by locally tuning the chemistry and the morphology of the channel at the nanoscale. This allows sculpting organized metal nanoparticles inside the nanotubes with various sizes, shapes, and periodicities. This nanomanipulation technique is very promising since it enables creating unique nanostructures that, at present, cannot be produced by an alternative classical synthesis route.

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.

Planar Arrays of Nanoporous Gold Nanowires: When Electrochemical Dealloying Meets Nanopatterning

Nanoporous materials are of great interest for various technological applications including sensors based on surface-enhanced Raman scattering, catalysis, and biotechnology. Currently, tremendous efforts are dedicated to the development of porous one-dimensional materials to improve the properties of such class of materials. The main drawback of the synthesis approaches reported so far includes (i) the short length of the porous nanowires, which cannot reach the macroscopic scale, and (ii) the poor organization of the nanostructures obtained by the end of the synthesis process. In this work, we report for the first time on a two-step approach allowing creating highly ordered porous gold nanowire arrays with a length up to a few centimeters. This two-step approach consists of the growth of gold/copper alloy nanowires by magnetron cosputtering on a nanograted silicon substrate, serving as a physical template, followed by a selective dissolution of copper by an electrochemical anodic process in diluted sulfuric acid. We demonstrate that the pore size of the nanowires can be tailored between 6 and 21 nm by tuning the dealloying voltage between 0.2 and 0.4 V and the dealloying time within the range of 150-600 s. We further show that the initial gold content (11 to 26 atom %) and the diameter of the gold/copper alloy nanowires (135 to 250 nm) are two important parameters that must carefully be selected to precisely control the porosity of the material.

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.