L. Pichon

Zirconium nitrides deposited by dual ion beam sputtering : physical properties and growth modelling

Abstract Zirconium nitrides reveal interesting optical and electrical properties which highly depend on the nitrogen stoichiometry. Indeed, the material exhibits a transition from the stable metallic ZrN (optical index for bulk at 633 nm: N=0.5−i3.2) to the metastable semi-transparent insulating Zr3N4 (N=3.2−i0.4). This work deals with the elaboration of homogeneous ZrN-like and Zr3N4-like coatings. These have been prepared using reactive Dual Ion Beam Sputtering (DIBS) using a Zr target and N2 or N2+Ar reactive gas. The influence of different elaboration parameters (ion energy, gas composition of the reactive beam and substrate temperature) on the nitrides composition and on their optical and electrical properties was particularly studied. A model was proposed to explain the influence of energy and temperature on the nitrogen composition. The nitrogen stoichiometry was shown to be controlled by a competitive mechanism between implantation of excess nitrogen amount in the subsurface and their elimination by exodiffusion. The first phenomenon is mainly controlled by the ion energy whereas the second one is enhanced by a high temperature and a high irradiation defects density. Therefore, the Zr3N4-like nitrides were obtained with low temperature and high energy (200 eV) conditions whereas high temperature and low energy led to ZrN-like materials.

Nitrogen and oxygen transport and reactions during plasma nitridation of zirconium thin films

Zirconium nitride (ZrN) is a refractory material with good mechanical and thermal properties. It is therefore a good candidate for hard surface treatment at high temperature. In this work, we report the growth and characterization of ZrN by plasma assisted thermal nitridation of zirconium films in a NH3 atmosphere. The process was monitored by in situ monochromatic ellipsometry and the nitrides grown were profiled and analyzed by Auger electron spectroscopy. By using temperatures in the 700–800 °C range, the material obtained is quite close to ZrN, but, depending on experimental conditions, residual oxygen (impurities) can be easily incorporated by reaction with zirconium. The analysis of the ellipsometric data has shown that the nitridation did not occur by simple growth of nitride on zirconium. Auger profiles confirmed the presence of an oxidized zirconium layer localized between the nitrided surface and the remaining metal. This oxidation was observed to occur preferentially during temperature ramping,...

Production of stable and metastable phases of zirconium nitrides by NH3 plasma nitridation and by double ion beam sputtering of zirconium films

Abstract Nitrided surfaces and nitrogen composition gradients in thin films exhibit interesting mechanical, electrical and optical properties. Metal, semiconductor or oxide surfaces can be transformed into a nitrided compound via interactions of nitrogen species issued from a plasma or an ion beam. The thermal activation is a key factor in both cases to ensure chemical reactions and short/long-range diffusion necessary to allow the growth of stable or metastable structures. In this work, we focus our attention on zirconium nitrides prepared under controlled temperature through reaction and diffusion, in Zr films, of low energy NH x species produced in NH 3 plasma and through the implantation–diffusion of energetic N + 2 ions during Zr deposition by using double ion beam sputtering. Zirconium nitrides show optical and electrical properties that depend on the conditions and on kinetics of the nitrogen take-up; the material exhibits a transition from the stable metallic ZrN to a metastable phase Zr 3 N 4 that appears transparent and insulating. The influence of the energy of the nitriding species and of the temperature on nitride compositions and phases are addressed. A model using coupled implantation and thermal diffusion mechanisms is proposed to explain the phases produced. In relation with the described phenomena, a temperature-controlled plasma-immersion ion-implantation system is proposed for tailoring in-depth stable/metastable ceramic structures such as nitrides, oxides and carbides.

New method of plasma immersion ion implantation and also deposition of industrial components using tubular fixture and plasma generated inside the tube by high voltage pulses

A new method of Plasma Immersion Ion Implantation (PIII) and deposition (PIII and D) for treating industrial components in the batch mode has been developed. A metal tubular fixture is used to allocate the components inside, around, and along the tube, exposing only the parts of each component that are to be ion implanted to the plasma. Hollow cathode-like plasma is generated only inside the tube filled with the desired gas, by applying high negative voltage pulses to the hollow cylindrical fixture which is insulated from the vacuum chamber walls. This is a very convenient method of batch processing of industrial parts by ion implantation, in which a large number of small to medium sized components can be treated by PIII and PIII and D, very quickly, efficiently, and also at low cost.

Improved nitrogen transport in Fe–C alloys during NH3 plasma nitridation

Abstract In the thermochemical process of Fe–C alloy nitridation, improvements of mechanical properties are governed by the way the nitrogen diffusion profiles extend into the material. Up to now, thermal or ionic nitridation cannot be achieved at temperature lower than 550°C because of the strong lowering of nitrogen diffusivity. The present study shows that improved nitrogen transport can be obtained after nitridation in NH3 plasma without cathodic bias on the samples. Such cold conditions allow the iron matrix to be nitrided in a depth range of 100–400 μm at a temperature as low as 350°C. The top surface hardness was shown to be improved by a factor of 3. This surface strengthening, markedly superior to that obtained with the classical treatments, is a well-known consequence of the temperature lowering that avoids coarsening of nitride microprecipitates. In addition, using this particular process, no growth of compound layer was observed at the surface. This absence of diffusion barrier is clearly beneficial to the improvement of the nitrogen transport. The high nitridation efficiency obtained at low temperature may be explained by an enhanced grain boundary diffusion due to defects generated by hydrogenous radicals produced in the plasma.

Evidence of ω-phase in ion beam sputtered zirconium thin films

Abstract Zirconium thin films were sputtered at room temperature with Ar + ion beam (1200 eV, 80 mA) on different substrates (Si, oxidized Si, amorphous quartz,...). Although classical 2 atom hcp α -phase was expected at normal pressure conditions, present paper proves the occurrence of the high pressure phase of zirconium: three atom hexagonal ω -phase. TEM diffraction patterns and grazing incidence X-ray diffraction spectra clearly show the existence of a phase different from the α -one. The unexpected phase was identified as the ω -one by means of CEEXAFS experiments. Moreover, results show that significant fraction of ω -phase coexists with α -grains which present a considerable increase of the interplanar distances. Substrate curvature induced by the deposit reveals an important compressive stress in the film. This residual stress is explained by conditions of non equilibrium maintained during the growth by the continuous ion bombardment of the subsurface region. Annealings performed at 700°C show that the ω -phase relaxes in the α -phase.

Characterization of the AISI 304 Alloy Treated in a Large Vacuum Chamber PIII System with a New HV Pulser

Plasma immersion ion implantation (PIII) method is often used to cleaning and enhancing mechanical properties of the surface of materials. In this work, the AISI 304 was treated in a PIII system to improve tribological and wear resistance properties. The new HV pulser was prepared to reach high average power (10 kW) using solid-state technology and a pulse transformer rather than using a conventional one based on hard-tube tetrodes with HV storage capacitors. For preliminary tests, low-density nitrogen plasma and pulses of 10 kV, 30μs width, and 1 kHz were used. A larger vacuum chamber used (600 liters) is very important for treating large area components and for batch processing. This is necessary in industrial applications and in cases that require high quality processing as in spatial or medical components. Stainless steel support was used to hold the samples in our case. XRD, SEM, and pin-on-disk surface diagnostics were used for investigation and characterization of the treated surfaces.

Analysis of Component Depth Profiles at the Interface of Ti6242 Alloy and SiC, SiN Coatings after High Temperature Oxidation in Air

We have analyzed the interfacial elemental depth profile evolution after high temperature isothermal oxidation of SixCy and SixNy protective coatings deposited by dynamic ion mixing on a Ti6242 alloy (Ti-6Al-2Sn-4Zr-2Mo). Isothermal oxidation tests have been carried out at 600°C during 100 hours in air. We have observed a non-monotonic depth distribution of zirconium in GDOES and SIMS depth profiles after oxidation of SiC/Ti6242 and SiN/Ti6242 and we propose a kinetic model based on rate equations for analyzing the results. It is shown by modeling that a non-monotonic depth profile of zirconium occurs because zirconium from the Ti6242 alloy forms a zirconium oxide compound. As a result, the atomic concentration of zirconium decreases at the interface which induces a diffusion flux of zirconium from the bulk to the interface. This process leads to the increase of the total amount of zirconium at the film interface and thus formation of a non-monotonic depth profile.