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A. Basillais R. Benzerga H. Sanchez E. Le Menn C. Boulmer-Leborgne J. Perrière 《Applied Physics A: Materials Science & Processing》2005,80(4):851-859
The pulsed-laser-deposition (PLD) method is particularly well suited for the growth of oxide thin films, but in the case of other compounds, such as nitrides, PLD presents some limitations which are mainly due to the low reactivity of nitrogen in comparison with oxygen. A possible way to overcome this problem is to increase the reactivity of the constituent species, via plasma assisted-pulsed-laser deposition. A plasma is coupled to the ablation chamber, in order to increase the density of reactive atomic species, which can be further incorporated in the growing film. This approach is described in this paper as well as the nature, energy, and concentration of the atomic and molecular species in the plasma as determined by various plasma diagnostics. These results are correlated to the growth of thin films in the particular case of the aluminum nitride compound. The composition and structure of the films are studied as a function of the growth conditions, and the positive effects of the additional discharge are evidenced on the film purity and properties. The fundamental problem with the PLD technique, especially with metallic targets, is the production of unwanted droplets that significantly worsen the properties of the films. To eliminate these droplets, a thin film has been grown with an experimental setup using two targets and crossed laser beams which gave positive results. PACS 81.15.Fg; 52.80.Pi; 77.84.Bw 相似文献
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C. Boulmer-Leborgne J. Hermann B. Dubreuil 《Applied Physics A: Materials Science & Processing》1992,55(4):340-346
In many laser applications such as drilling, welding and cutting, the role of the plasma in the transfer of energy between the laser beam and the metal surface appears to be rather important. It depends on several parameters such as laser wavelength, irradiation time and deposited energy but especially on the buffer gas nature. In this work the plasma is initiated by a TEA-CO2 laser beam perpendicularly focussed onto a Ti target (100 MW/cm2), in a cell containing He, Ar or a He-Ar mixture as buffer gas. The plasma is studied by time and space resolved spectroscopic diagnostics. The results show that helium allows target erosion whereas a highly absorbing breakdown plasma develops in argon shielding the target from the subsequent laser heating. With only 20% Ar in He, a strong quenching of the He plasma by Ar occurs, and the Ar plasma effect is dominant. 相似文献
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Materials used in electrical contact applications are usually constituted of multilayered compounds (e.g.: copper alloy electroplated with a nickel layer and finally by a gold layer). After the electro-deposition, micro-channels and pores within the gold layer allow undesirable corrosion of the underlying protection. In order to modify the gold-coating microstructure, a laser surface treatment was applied. The laser treatment suppressing porosity and smoothing the surface sealed the original open structure as a low roughness allows a good electrical contact. Corrosion tests were carried out in humid synthetic air containing three polluting gases. SEM characterization of cross-sections was performed to estimate the gold melting depth and to observe the modifications of gold structure obtained after laser treatment. The effects of the laser treatment were studied according to different surface parameters (roughness of the substrate and thickness of the gold layer) and different laser parameters (laser wavelength, laser fluence, pulse duration and number of pulses). A thermokinetic model was used to understand the heating and melting mechanism of the multilayered coating to optimize the process in terms of laser wavelength, energy and time of interaction. 相似文献
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A. L. Thomann A. Basillais M. Wegscheider C. Boulmer-Leborgne A. Pereira P. Delaporte M. Sentis T. Sauvage 《Applied Surface Science》2004,230(1-4):350-363
This study focuses on the chemical, morphological and structural characterization of iron surfaces treated by laser in ambient air. Incorporation of nitrogen over a 1–2 μm thickness (10–30 at.% at the profile maximum) and superficial oxidation on 200–400 nm depth have been evidenced by nuclear reaction analyses. X-ray diffraction at grazing incidence has shown the formation of FeO and Fe3O4 oxide phases as well as γ-Fe(N), and ε-FexN for a sufficiently high amount of nitrogen incorporated. Treatments performed with different laser beams indicate that the parameter playing the major role in surface modification processes is the wavelength. Nitrogen incorporation has been found to occur via the interaction of reactive N, present in the laser-induced plasma, and the iron molten bath. The nitriding process is promoted in the IR wavelength range. Oxidation takes place by chemical reaction during the cooling step, and is furthered in the case of UV treatment. 相似文献
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A. Basillais C. Boulmer-Leborgne J. Mathias N. Laidani A. Laurent J. Perrière 《Applied Physics A: Materials Science & Processing》2000,71(6):619-625
We have studied the growth of Al nitride films by laser ablation in order to check the potential of the method. The influence
of process parameters such as nature of the target, laser energy density, nitrogen partial pressure, etc. on the composition,
chemical nature and structure of the films has been investigated. Rutherford backscattering spectrometry, nuclear reaction
analysis, X-ray diffraction and X-ray photoelectron spectroscopy were used to characterize the films. Literature reports on
AlN film growth by laser ablation but oxygen contamination is poorly discussed whereas it is the main problem encountered.
The origin of this contamination and the mechanisms of incorporation were studied, and the crucial parameter was found to
be the residual pressure during ablation. Due to the difference in chemical reactivity between oxygen and nitrogen atomic
species, to obtain pure AlN films it is necessary to increase the concentration of atomic nitrogen. Thus, a RF discharge device
was added allowing a better nitrogen molecule dissociation. Finally, despite composition deviations, the AlN phase can be
formed in the laser-deposited films. Highly textured films presenting epitaxial relationships with crystalline Al2O3 substrates can be grown even with a 10% oxygen concentration.
Received: 7 October 1999 / Accepted: 17 April 2000 / Published online: 13 September 2000 相似文献
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E. Le BoulbarE. Millon J. MathiasC. Boulmer-Leborgne M. NistorF. Gherendi N. SbaïJ.B. Quoirin 《Applied Surface Science》2011,257(12):5380-5383
Pure and Nb-doped titanium oxide thin films were grown on sapphire substrates by pulsed-laser deposition in vacuum (10−7 mbar). The PLD growth leads to titanium oxide thin films displaying a high oxygen deficiency (TiO1.5) compared with the stoichiometric TiO2 compound. The structural and electrical properties (phase, crystalline orientation, nature and concentration of charge carriers, etc.) of these titanium oxide films were studied by XRD measurements and Hall effect experiments, respectively. The undoped TiO1.5 phase displayed a p-type semiconductivity. Doping this titanium oxide phase with Nb5+ leads to an n-type behaviour as is generally observed for titanium oxide films with oxygen deficiency (TiOx with 1.7 < x < 2). Multilayer homojunctions were obtained by the stacking of TiO1.5 (p-type) and Nb-TiO1.5 (n-type) thin films deposited onto sapphire substrates. Each layer is 75 nm thick and the resulting heterostructure shows a good transparency in the visible range. Finally, the I-V curves obtained for such systems exhibit a rectifying response and demonstrate that it is possible to fabricate p-n homojunctions based only on transparent conductive oxide thin films and on a single chemical compound (TiOx). 相似文献
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E. Sicard C. Boulmer-Leborgne C. Andreazza-Vignolle M. Frainais 《Applied Physics A: Materials Science & Processing》2001,73(1):55-60
The excimer laser nitriding process reported is developed to enhance the mechanical and chemical properties of aluminum alloys.
An excimer laser beam is focused onto the alloy surface in a cell containing 1-bar nitrogen gas. A vapor plasma expands from
the surface and a shock wave dissociates and ionizes nitrogen. It is assumed that nitrogen from plasma in contact with the
surface penetrates to some depth. Thus it is necessary to work with a sufficient laser fluence to create the plasma, but this
fluence must be limited to prevent laser-induced surface roughness. The nitrogen-concentration profiles are determined from
Rutherford backscattering spectroscopy and scanning electron microscopy coupled to energy-dispersive X-ray analysis. Crystalline
quality is evidenced by an X-ray diffraction technique. Transmission electron microscopy gives the in-depth microstructure.
Fretting coefficient measurements exhibit a lowering for some experimental conditions. The polycrystalline nitride layer obtained
is several micrometers thick and composed of a pure AlN (columnar microstructure) top layer (200–500 nm thick) standing on
an AlN (grains) in alloy diffusion layer. From the heat conduction equation calculation it is shown that a 308-nm laser wavelength
would be better to increase the nitride thickness, as it corresponds to a weaker reflectance R value for aluminum.
Received: 17 October 2000 / Accepted: 19 October 2000 / Published online: 23 May 2001 相似文献
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T. Gonthiez T. Gibert P. Brault C. Boulmer-Leborgne C. Olivero M.C. Castex 《Applied Physics A: Materials Science & Processing》1999,69(7):S171-S173
We report here first results about single-photon VUV laser photoionization of desorbed species from a silicon surface irradiated by a pulsed and tunable UV laser (290-300 nm). The combination of VUV photoionization at 10 eV with laser-induced surface desorption offers a largely non-destructive and sensitive method for quantitative analysis. Indeed it allows mass spectrometry measurements with uniform sensitivity and without breaking the chemical bonds in the probed species. The energy of the VUV photons (9.91 eV) is above the ionization limits of a number of molecules and fragments. Moreover, adjustment of the delay between the desorbing and the probe lasers allows the measurement of the time-of- flight distribution of the ejected species. Data extracted from these measurements are fundamental for a better understanding of laser-surface interaction phenomena. 相似文献