G. Stergioudis

Room temperature oxidation behavior of TiN thin films

Abstract The room temperature oxidation process of thin TiNx films, grown by DC reactive magnetron sputtering, was studied by in-situ and real time spectroscopic ellipsometry, X-ray reflectivity, Auger electron spectroscopy, X-ray photoelectron spectroscopy and stress measurements. The films were deposited at various negative bias voltages (Vb) in order to vary the TiNx stoichiometry and then exposed to several gases and to air at room temperature. The oxidation rate was found to depend strongly on Vb and thus on film stoichiometry. Fast oxidation was observed in films deposited at low | V b | , that contain nitrogen which is weakly bonded to Ti and can be easily replaced by oxygen. At high |V b | values (above −80 V) stoichiometric TiN films were developed, that were stable and not prone to oxidation. The results showed that oxidation takes place in the bulk of the film and can proceed up to about 10% transformation of titanium nitride into titanium oxide. The fastest step in the film oxidation mechanism is diffusion of oxygen along the columnar grain boundary structure, followed by the reaction of oxygen with the weakly bonded TiN. The results suggest that the oxidation process proceeds with different stages involving formation of TiON, followed by a slow stage of TiO2 formation. These microstructural changes are consistent with the evolution of compressive stresses in the films and the increase in film density and thickness and the decrease in surface roughness as determined by X-ray reflectivity.

Studies of density and surface roughness of ultrathin amorphous carbon films with regards to thickness with x-ray reflectometry and spectroscopic ellipsometry

Specular x-ray reflectivity (XRR) measurements were used to study the density and surface roughness of ultrathin hydrogen-free amorphous carbon films deposited by sputtering, of thickness varying from 25 to 325 A. The film thickness and surface roughness obtained from XRR measurements are in good agreement with that found by spectroscopic ellipsometry (SE) and atomic force microscopy. The results for the film composition obtained from SE and XRR are supported by stress measurements. Films (especially those with thickness below 100 A) deposited with positive substrate bias voltage were found to exhibit a reduction in density, sp3 C–C bonding, and internal compressive stresses and an increase in surface roughness by increasing film thickness.

A comparative study of boride coatings obtained by pack cementation method and by fluidized bed technology

Abstract Pack cementation is a surface treatment method which has been used, during the last 50 years, for the deposition of a wide range of coatings, among them borides, onto steel substrates. Recently, a new method for the deposition of hard and/or corrosion-resistant coatings, the fluidized bed technology, has been developed. In this paper, a comparative study of the boride coatings on low-carbon steel, which were obtained both by fluidized bed and pack cementation methods, was carried out. In both cases, the produced coatings are characterized by very good adherence and it was found that only one phase belonging to Fe2B was formed during the treatments. The pack cementation procedure resulted in coatings with residual stresses and preferred orientation, while the fluidized bed borides are characterized by strain-free grains with random distribution.

Boron-aluminide coatings applied by pack cementation method on low-alloy steels

Abstract A simultaneous one-step boroaluminizing process has been performed on a 2.25Cr–Mo steel by means of pack cementation method using a B/Al boriding powder. Three distinct regions were found in the coatings consisting of an outer Al-rich layer, a transition region containing Al and Fe and an inner layer containing mostly B and Fe. The layers were characterized by means of optical and scanning electron microscopy (SEM) in terms of coatings morphology and thickness. X-ray diffraction (XRD) was used in order to detect the phases formed and the presence of iron aluminide and boride phases in the coating due to the boroaluminizing process.

Boride coatings on non-ferrous materials in a fluidized bed reactor and their properties

Abstract Fluidized bed technology has been successfully used in the formation of different types of coatings, e.g. aluminizing [Surf. Coat. Technol. 120 (1999) 151; Steel Res. 66 (1995) 318; J. Mater. Sci. 35 (2000) 5493], chromizing [Surf. Coat. Technol. 120 (1999) 151; Steel Res. 66 (1995) 318; J. Mater. Sci. 35 (2000) 5493], nitriding [Heat treatment in fluidized bed furnaces, 1993], carburizing [Heat treatment in fluidized bed furnaces, 1993], carbonitriding [Heat treatment in fluidized bed furnaces, 1993]. Recently, this technology has been used for the deposition of hard boride layers onto ferrous substrates [Mater. Lett. 51 (2001) 156; Fifth International Conference on Heat Treatment Materials, Budapest, Hungary, vol. 3, 1986]. In the present paper, we used fluidized bed technology to deposit boride coatings onto non-ferrous metals and alloys. The coatings were examined by means of optical microscopy, Vickers microhardness and X-ray diffraction, to determine thickness and morphology, phase formation and properties. The properties of dry wear and thermal cycling oxidation of the coatings were evaluated. The as-produced coatings were characterized by adequate thickness and improved wear and oxidation resistance.

Polycrystalline diamond formation by post-growth ion bombardment of sputter-deposited amorphous carbon films

Abstract Post-growth Ar + ion beam bombardment (IBB) of amorphous carbon (a-C) films on Si, with energies above 1 keV, induces several structural modifications in the films, including the formation of diamond, graphite and SiC grains. X-ray diffraction (in both conventional and grazing incidence geometry) and high resolution electron microscopy were used to study the structure of the as grown films and the phases – with emphasis to diamond – that resulted after IBB. The a-C films morphology and density were also studied by X-ray reflectivity and show an increase in film density upon IBB.

Boro-nitriding of steel US 37-1

In this paper, we present a novel duplex surface treatment carried out on steel US 37-1. The as-produced multi-layer coating was characterised by optical microscopy, SEM, EDX and X-ray diffraction (XRD) and exhibited excellent adherence and morphology. The resulting layers were mainly borides, nitrides and boronitrides.

Oxidation and structural changes in fcc TiNx thin films studied with X-ray reflectivity

Abstract The evolution of oxidation process at room temperature of thin fcc titanium nitride (TiNx) films grown by DC reactive magnetron sputtering was studied by X-ray reflectivity (XRR) measurements and supported with in situ spectroscopic ellipsometry (SE) measurements. Precise thin-film thickness and density as well as surface roughness were determined from X-ray specular reflectivity data analysis. The XRR measurements were conducted with a conventional diffractometer equipped with a Gobel mirror and a special reflectivity sample stage. The XRR results obtained from the TiNx films during exposure to air show an exponential increase in density and thickness and a decrease in the value of RMS surface roughness. Analysis of the SE results shows that oxidation takes place in the bulk of the TiNx film transforming it to titanium oxide. The percentage of transformation and the type of the oxide depends on the TiNx film stoichiometry. The above structural and compositional changes are consistent with the evolution of stress (compressive) measured in the TiNx films during exposure to air by cantilever technique.

On Magnetic Properties and Thermal Stability of Fe(M)‐Si‐B (M = V, Ni, Cu, Nb, Mo, Pd, Ag) Amorphous Alloys

Experimental results are presented regarding the variation of the atomic magnetic moment, the Curie temperature and the crystallization temperature of Fe 78-c M c Si 9 B 13 (M= V, Nb, Mo) and Fe 75-c M c Si 9 B 16 (M= Ni, Cu, Pd, Ag) amorphous alloys. Efforts were made to explain qualitatively the phenomena, based on the behavior of the amorphous alloys when various admixtures substitute Fe atoms.

Fabrication and examination of oxidation resistance of zinc coated copper and brass components by chemical deposition

Abstract In this work, the structure and the oxidation resistance of Zn deposited Cu and brass metallic components are examined. The deposition was accomplished with pack cementation chemical deposition. The examination of the samples was performed with electron microscopy and X-ray diffraction analysis. It was found that coatings on Cu substrate consist of two layers with different Zn concentrations, while coatings on brass were single layered with almost constant Zn concentration. The presence of distinct Zn–Cu phases was revealed in both cases. The subjection of the as coated samples together with the uncoated substrates in air at 400°C showed that both Zn coated samples have enhanced resistivity in such atmospheres, as most of the coating remained mostly unoxidised, and the substrates were fully protected. On the contrary, the bare substrates appear to have undergone severe damage as brittle oxides were formed on their surface.