The European Physical Journal - Applied Physics
Volume 43 Issue 3: topical issue itfpc (innovations on thin films p...
Topical Issue ITFPC (Innovations on Thin Films Processing and Characterisation)
T. Czerwiec, M. Belmahi, S. Andrieu
Crystal growth and elasticity
P. Müller
Published online by Cambridge University Press: 30 April 2008, pp. 271-276
The purpose of this paper is to review some elasticity effects in epitaxial growth. We start by a description of the main ingredients needed to describe elasticity effects (elastic interactions, surface stress, bulk and surface elasticity, thermodynamics of stressed solids). Then we describe how bulk and surface elasticity affect growth mode and surface morphology by means of stress-driven instabilities. At last stress-strain evolution during crystal growth is reported.
Application of plasma processes in NanoBiotechnology
F. Rossi, F. Bretagnol, A. Valsesia, P. Colpo
Published online by Cambridge University Press: 06 May 2008, pp. 277-281
We present an overview of the possibilities offered by the combination of plasma polymers deposition and nanopatterning by colloidal and electron beam lithography. It is shown that chemical and topographical patterns can be obtained on different substrates, with dimensions of the order of a few 100 nm. Two examples of applications of these nanostructures for protein adsorption studies are presented.
Thin Films Processing and Surface Engineering
Surface alloying of metallic substrates with pre-deposited films through a pulsed electron-beam mixing
A. V. Batrakov, A. B. Markov, G. E. Ozur, D. I. Proskurovsky, V. P. Rotshtein
Microstructure and properties of the surface alloys resulted from a pulsed liquid-phase mixing of metallic substrates with pre-deposited films were studied. As a tool for the liquid-phase mixing, a low-energy (~30 keV), high-current (~30 kA) pulsed (0.8–3 µs) electron beam of energy density ranging from 1 to 15 J cm−2 has been employed. Three immiscible systems (Ta/Fe; Al/Si/Al/Si/Al/Si/Al; Al/C/Al/C/Al) and two systems with different solid solubility of components (Cu/316 stainless steel; Zr/Ti/Ti-6Al-4V) were chosen for the surface alloying investigation.
Surface treatment of a polypropylene film with a nitrogen DBD at medium pressure
R. Morent, N. De Geyter, L. Gengembre, C. Leys, E. Payen, S. Van Vlierberghe, E. Schacht
Surface treatment of polymer films is usually necessary to improve surface wetting and adhesion characteristics. Traditional liquid chemical processes have several disadvantages in contrast to dry finishing processes, like plasma technology. Dielectric barrier discharges at atmospheric pressure are extensively studied for surface treatment, however, almost no research has been done on surface treatment with a dielectric barrier discharge at medium pressure. Therefore, in this paper, a polypropylene (PP) film is plasma-treated with a dielectric barrier discharge (DBD) in nitrogen at medium pressure (5.0 kPa). The surface properties of the plasma-treated samples are examined using contact angle measurements, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Results show that the surface wettability is significantly enhanced after plasma treatment. The incorporation of nitrogen on the surface is significant (10 at%), demonstrating the ability of the used DBD set-up to generate nitrogen-containing functional groups on the PP surface. Nevertheless, a considerable amount of oxygen (10 at%) is incorporated onto the PP surface underlining the extreme reactivity of oxygen active species and the difficulty in overcoming the air contamination problem. Moreover, AFM analysis reveals that the nitrogen plasma creates large changes in the surface morphology of the PP film due to the selective etching of the amorphous regions of the polymer film.
Structural and morphological studies of GaN thin films grown on different oriented LiNbO3 substrates by MOVPE
T. Moudakir, G. Orsal, N. Maloufi, A. A. Sirenko, S. Gautier, M. Bouchaour, S. Ould Saad, J. P. Salvestrini, A. Ougazzaden
Published online by Cambridge University Press: 25 July 2008, pp. 295-299
GaN epilayers were grown by metal-organic vapor phase epitaxy (MOVPE) on z- and x-cut lithium niobate substrates. Ex-situ characterizations of the epilayers by means of scanning electron microscope, atomic force microscope, X-ray diffraction and micro-Raman scattering measurements have revealed same growth features on both substrates. The observation of the morphology shows homogeneous and relatively smooth surface. The shape and density of GaN islands as well as the observed columnar growth mode are not dependent of the orientation of the LN substrates. The X-ray diffraction analysis of 450 nm thick GaN layers grown at 730 °C on z- and x-cuts showed that both GaN layers reveal the same crystallographic orientation, i.e. c-axis orientation normal to the substrate plane and in-plane orientation that coincides with the primary axis of LN substrates. The Raman scattering measurements confirm the growth of an oriented epitaxial GaN layer on LN substrate. Moreover, the deposited layer exhibit a quite good homogeneity, since the Raman spectra recorded for different positions in the layer do not reveal any significant variations in their relative intensities and frequency shifts.
Comparison of CO2 laser and atmospheric plasma treatments on thermal stability and structural modifications of microporous poly(vinyl chloride)/Silica composites
C. Becker, S. Etienne, J. Bour, D. Ruch, F. Aubriet
Several ways using surface modification are commonly used to enhance thermal stability of polymer matrices. In this study, Continuous-Wave carbon dioxide (CW CO2) laser irradiation and atmospheric pressure non-thermal He plasma treatment on microporous poly(vinyl chlo-ride)/Silica composite have been investigated and compared. On one hand the alternative was based on the efficiency of the thermal energy afforded by CW CO2 laser irradiation and induced photodegradation processes to release HCl and form polyene sequences under well-controlled condition. On the other hand atmospheric plasma treatment involved surface modification by formation of unstable radicals, inducing crosslinking and dehydrochlorination. In both cases a global thermal stabilization of the composite was noticed by partial dehydrochlorination of PVC, even for short exposure time. The main effects observed after laser irradiation were related to the formation of a very dense structure on surface with very low chlorine content and an important chlorine atoms in-depth gradient on the cross section up to 150 μm in thickness; whereas atmospheric He plasma treatment led to a homogeneous decrease of the chlorine in-depth content due to the plasma interpenetration in the porous microstructure. Structural and chemical modifications both on extreme surface and in the thickness have been investigated respectively by Environmental Scanning Electron Microscope (ESEM) coupled with an Energy Dispersive X-ray analysis (EDX) and X-ray Photoelectron Spectroscopy (XPS). Composites thermal stability and investigation on chlorine release have been evaluated by Thermo Gravimetric Analysis (TGA) coupled with Mass Spectrometry (MS).
Thickness and substrate effects on AlN thin film growth at room temperature
B. Abdallah, C. Duquenne, M. P. Besland, E. Gautron, P. Y. Jouan, P. Y. Tessier, J. Brault, Y. Cordier, M. A. Djouadi
Hexagonal AlN thin films have been deposited by DC reactive magnetron sputtering at room temperature. For a first set of samples, sputtered AlN films were deposited on silicon Si (100) substrates. For a second set, AlN films were deposited on 200 nm (002) oriented AlN epitaxial layer obtained by Molecular Beam Epitaxy (MBE) on Si (111). X-ray Diffraction (XRD) and High Resolution Transmission Electron Microscopy (HRTEM) analysis of the synthesized films on Si (100) substrate have shown an amorphous phase close to the interface followed by a nano-crystalline layer exhibiting (100) and (002) orientations of the hexagonal AlN crystalline phase. Finally a relatively well crystallised layer with a single (002) orientation has been observed for the thickest films. This improvement of crystalline quality with film thickness has been consistent with a drastic decrease of the films stress from –1.2 GPa at 300 nm to no stress around 800 nm and even 0.3 GPa tensile stress for 1.5 μm thick film. This behaviour was different when epitaxial AlN was used as substrate. In fact, we have observed thanks to HRTEM images and Selected Area Electron Diffraction (SAED) patterns, that the AlN film deposited on such a substrate exhibits the same crystalline quality and have the same orientation as the AlN epitaxial layer during the first 500 nm of thickness. A further increase of film thickness has caused a decrease on the crystalline quality. The films became polycrystalline while preserving a (002) preferential orientation.
Simulation and Thin Films Characterization
Modeling the stress enhancement of plasma enhanced chemical vapor deposited silicon nitride films by UV post treatment – impact of the film density
P. Morin, D. Benoit, J. Metz
Plasma Enhanced Chemical Vapour Deposited (PECVD) tensile nitride liners have been introduced in the 90 nm CMOS technology node to generate mechanical strain within the transistor silicon channel. With strain, because of the silicon piezoresistance effect, the electron mobility is enhanced within the silicon channel, so the nMOS transistor performance. Since that time, significant work has been carried out to develop silicon nitride films with enhanced tensile stress values to increase the gain provided by these process induced stressors along the introduction of the new technologies. For the 45 nm node, an additional UV post treatment has been introduced to achieve highly tensile residual stress. This study determines the relevant as deposited PECVD nitride film properties that modulate the final stress achievable after UV cure. Thanks to a simple stress model, it is demonstrated that as deposited nitride films must present a nitrogen rich composition and an intrinsic low density to become highly tensile after post UV treatment. With these design rules, nitride films with final stress of 1.6 GPa have been synthesized.
A simple model for the deposition of W-O coatings by reactive gas pulsing process
N. M. G. Parreira, T. Polcar, N. J. M. Carvalho, A. Cavaleiro
In this study we will present a simple semi-empirical method to predict the chemical composition and the deposition rate of tungsten oxide coatings deposited by magnetron sputtering with reactive gas pulsing process (RGPP) as a function of two easily measured deposition parameters: target potential and total pressure. The coatings were deposited by DC magnetron sputtering from a pure tungsten target in reactive atmosphere (Ar + O2) using the conventional process (CP) with constant oxygen flow and the RGPP. The oxygen flow was varied from 0 (pure tungsten deposition) to 20 sccm corresponding to tungsten trioxide during the conventional process. When RGPP was used, a 20 sccm oxygen flow was pulsed using a square regulation signal, defined by a pulsing period (T) and an oxygen injection time (t ON ). The conventional and RGPP process parameters (target potential, total pressure and deposition rate) and the corresponding chemical composition were used to build a simple model predicting the deposition rate and the average chemical composition of the coatings deposited by RGPP as a function of the pulsing parameters. It was shown that the measured total pressure could be used to calculate the deposition rate and the chemical composition of the RGPP coatings with reasonable precision.
Protective Applications of Thin Films
Mechanism of surface modifications on a NiTi alloy treated with low energy high current pulsed electron beam
J. X. Zou, T. Grosdidier, K. M. Zhang, C. Dong, S. Weber
A NiTi shape memory alloy was subjected to low energy high current pulsed electron beam (LEHCPEB) irradiation. The samples were treated with the same electron beam parameters and increasing number of pulses. The treatment induces superfast melting, evaporation and rapid solidification at the top surface. As a result of selective evaporation of Ni, the Ti content was increased in the melted layer of the 5 pulse treated sample. However, for the 10 pulsed sample, a part of the vapor condensed on the surface. It is shown also that in the sub-surface, below the melted layer, the martensitic transformation was triggered due to the effects of the thermal stresses and shock waves propagating in the material.
Microstructural and chemical characterisation techniques for nanostructured and amorphous coatings
V. Godinho, C. Fernández-Ramos, D. Martínez-Martínez, J. García-López, J. C. Sánchez-López, A. Fernández
A full characterization of amorphous or nanostructured coatings at the microstructural level has some intrinsic difficulties associated with the lack of long range order and reference compounds, which often make difficult their study. Only by the combination of different characterization techniques is possible in many cases to achieve valuable chemical and structural information. In this paper, three different systems were used to illustrate how the combination of characterization techniques, as TEM associated to ED or EELS, EFTEM, SEM, XPS, RBS and XRD was determinant to correlate microstructure with deposition parameters and properties in such complex systems. The coatings were deposited on silicon and AISI M2 steel substrates by magnetron sputtering under different Ar/N2 gas mixtures from Ti and C targets (system 1 and 2) or a Si target (system 3). In each case, the performed characterization allowed to get a deeper understanding of the whole system and explain their mechanical response. The studied systems are: (i) Ti-TiN-CN x multilayered coatings: the chemical and structural analysis shows that a gradual enrichment in nitrogen and nitride phases from the metallic substrate to the CN x top layer is responsible for the improvement of the adhesion properties. (ii) Ti-C-N: the existence of a nanocrystalline TiC phase embedded in an amorphous carbon matrix is demonstrated by the microstructural and chemical analysis for samples prepared under pure Ar. When N2 is introduced in the gas phase, the nanocrystalline structure is not seen and the chemical composition is enriched in amorphous non-stoichiometric CN x . (iii) SiO x N y : although the coatings present similar composition, small differences in microstructure are observed, which can be responsible for different mechanical properties.
Rapid surface alloying by Ti of AISI 316L stainless steel using. Low energy high current pulsed electron beam
K. M. Zhang, J. X. Zou, T. Grosdidier, C. Dong, S. Weber
This paper reports the first results of an ongoing research work on rapid surface alloying of an AISI 316L stainless steel by low energy, high current pulsed electron beam (LEHCPEB) with the aim of enhancing the corrosion resistance of this material against aggressive halide ions. A Ti powder layer was deposited on the substrate and in-corporate at the top surface by using LEHCPEB. Due to the rapid surface melting, liquid state mixing occurred and a Ti-rich layer formed. The alloyed layer contained a mixture of the $\alpha $ and γ phases because the addition of Ti favors the formation of α. The corrosion resistance of the AISI 316L stainless steel in the simulated body fluid was effectively improved after surface alloying by Ti.
Surface evolution during low temperature plasma assisted nitriding of austenitic stainless steel
M. Drouet, J. C. Stinville, P. Villechaise, J. P. Rivière, C. Templier
Plasma-assisted nitriding is an attractive surface treatment for metallurgical surface modification to improve wear, hardness and fatigue resistance of austenitic stainless steels. However, this technique requires low temperature processing in order to avoid chromium nitride precipitation and hence the degradation of corrosion properties. This paper presents a low temperature high rate plasma nitriding process and will emphasis on the consequences of nitrogen incorporation on the metallographic and crystallographic properties of the sample surface.
Micro and Nanosystems
Synthesis of carbon nanbotubes by plasma-enhanced CVD process: gas phase study of synthesis conditions
M. Guláš, C. S. Cojocaru, C. T. Fleaca, S. Farhat, P. Veis, F. Le Normand
To support experimental investigations, a model based on ChemkinTM software was used to simulate gas phase and surface chemistry during plasma-enhanced catalytic CVD of carbon nanotubes. According to these calculations, gas phase composition, etching process and growth rates are calculated. The role of several carbon species, hydrocarbon molecules and ions in the growth mechanism of carbon nanotubes is presented in this study. Study of different conditions of gas phase activation sources and pressure is performed.
Influence of interfacial oxygen on single-crystal magnetic tunnel junctions
F. Bonell, A. M. Bataille, S. Andrieu, C. Tiusan, B. Kierren, G. Lengaigne, D. Lacour
The influence of adsorbed oxygen at the first interface of single-crystal Fe(001)/MgO(001)/Fe(001) magnetic tunnel junctions is investigated. Firstly, the adsorption kinetics of O2 on the Fe(001) surface is studied in the monolayer regime by X-ray photoelectrons spectroscopy and scanning tunnelling microscopy experiments. We show that different species exist at the oxidized surface. The tunnel magneto-resistance of oxygen-doped magnetic tunnel junctions is found to decrease but remains large even for oxygen coverages exceeding one monolayer.
New Materials and Health Applications of Thin Films
Investigation of structural and optical properties of sputtered Zirconia thin films
F. Rebib, N. Laidani, G. Gottardi, V. Micheli, R. Bartali, Y. Jestin, E. Tomasella, M. Ferrari, L. Thomas
Zirconium oxide thin films were deposited by sputtering a ZrO2 target under an argon-oxygen gas mixture and different total gas pressures. Their composition, structure and optical constants were characterised by mean of Auger profiles, XRD, XPS, m-line and UV-visible spectroscopies. All the deposits were found to be sub-stoechiometric with O/Zr ratio decreasing from 1.6 to 1.45 when the deposition pressure increased from 0.01 to 0.05 Torr. A SRIM simulation was used to explain this behaviour. The XRD showed a monoclinic phase for all sample with different grain size and residual stress. Finally, the optical constants were determined. The refractive index decreased slightly when the deposition pressure increased whereas the optical gap and the Urbach energy were found to be quite constant whatever the sputtering pressure.