D. Milcius

On the mechanism of synthesis of PbTiO3 thin films by thermal annealing of Pb/Ti layers in air at atmospheric pressure

Abstract Single phase PbTiO3 thin films were synthesized by thermal treatment at temperatures 350–700 °C of Pb/Ti magnetron sputtered layered structures at atmospheric pressure in air. The film stoichiometry was accurately controlled by deposition of individual layers with the required thickness. Scanning electron microscopy views showed that initially smooth surfaces had porous and granular structure after thermal annealing. Surface morphology depends on the substrate material and the cooling rate. X-Ray diffraction patterns revealed the nanometric microstructure of synthesized films. The size of crystallites in oxidized films depends on the annealing temperature and does not depend on the annealing time. The atomic mixing and oxidation kinetics are discussed and applied to PbTiO3. The emphasis is made on the analysis of surface atom relocation and restructuring processes under reactive adsorption at elevated temperatures and their role in the formation of surface instabilities and initiation of transport of oxygen from the surface into the bulk directed to stabilize these instabilities. The experimental results support that the formation of PbTiO3 films homogeneous in structure and composition during the thermal oxidation is a result of intensive mixing of Pb/Ti layers with continuous supply of oxygen though the surface. Under non-equilibrium conditions on the surface, the oxygen atoms are driven into grain boundaries of crystallites, result in high compressive stress inducing fragmentation of grains and their oxidation by oxygen diffusion through boundaries into the nanograins. The oxidation kinetics and the size of crystallites is governed by the mass-transport processes.

Physical properties of zirconium oxynitride films deposited by reactive magnetron sputtering

The purpose of the present investigation is to analyze structural, optical, and electrical properties of transition zirconium oxynitride thin films deposited by direct current reactive magnetron sputtering. Films were prepared on Si(111) and glass substrates in an argon/nitrogen+oxygen atmosphere. The oxygen flow increased stepwise from 0 to 10 sccm, while at the same time the nitrogen flow decreased from 10 to 0 sccm. Working pressure was kept constant to reach 1.510-2 Pa pressure in the vacuum chamber by adjusting argon gas flow. Depending on the nitrogen-oxygen flow rates, cubic ZrN:O, cubic ZrO2:N, tetragonal ZrO2:N, and monoclinic ZrO2:N phases films were prepared. Optical and electrical properties depend on reactive gas (nitrogen+oxygen) flow. Refractive index vary from 2.13 to 2.38, band gap vary from 2.84 to 4.75. The electrical conductance of ZrNxOy films shows semiconductor-like behaviour.

Mass-transport driven by surface instabilities under high-flux, low-energy nitrogen ion irradiation at elevated temperatures

Flux effects in ion nitrided AISI 304 stainless steel have been investigated in an attempt to understand the mechanism of nitrogen transport. It is concluded that an interaction between a highly activated surface layer, the internal interfaces and the bulk is critical. Under conditions of non-equilibrium present on the surface, the nitrogen atoms are driven into the grain boundaries and highly compressive stress is formed. The stress relaxation processes initiate plastic flow of atoms in the grains and a corresponding flow of nitrogen atoms.

Formation and Characteristics of Thin Films of ZrO2-8 mol % Y2O3 Solid Electrolytes

Thin films of ZrO2-8mol%Y2O3 have been deposed by pulsed DC magnetron sputtering method. The substrates of Ni-cermet and alloy-600 for the films were used. The results of the investigation of the X-ray diffraction patterns and SEM showed that the films are nanocrystalline and belong to cubic symmetry. The relaxation process is related to the ion transport in thin films. The results of the investigation of the temperature dependencies of thin films ionic conductivity (σ) showed that the dependence σ(T) is caused by the temperature dependence of oxygen vacancy mobility, while the number of charge carriers remains constant with temperature.

Mass-transport driven by surface instabilities in metals under reactive plasma/ion beam treatment at moderate temperature

This paper presents a generalized approach to the mechanisms of oxidation, hydrogenation and nitriding of metals under ion irradiation with reactive particles at elevated temperatures. Experimental results on the plasma oxidation of bilayered Y/Zr films, the plasma hydrogenation of Mg films and the ion beam (1.2 keV N2+) nitriding of stainless steel are presented and discussed. We make special emphasis on the analysis of surface effects and their role in the initiation of mixing of bilayered films, the ingress of reactive species in the bulk and the restructuring of the surface layers. It is suggested that primary processes driving reactive atoms from the surface into the bulk are surface instabilities induced by thermal and ballistic surface atom relocations under reactive adsorption and ion irradiation, respectively. The diffusion of adatoms and vacancies, at temperature when they become mobile, provide the means to relax the surface energy. It is recognized that the stabilizing effect of surface adatom diffusion is significant at temperatures below 300–350°C. As the temperature increases, the role of surface adatom diffusion decreases and processes in the bulk become dominant. The atoms of subsurface monolayers occupy energetically favorable sites on the surface, and result in reduced surface energy.

Expanded Polystyrene Foam Formed from Polystyrene Beads Coated with a Nanocrystalline SiO2 Film and the Analysis of Its Moisture Adsorption and Resistance to Mechanical Stress

ABSTRACTConventional expanded polystyrene can absorb moisture, which significantly degrades its properties. In the present study, it was demonstrated that SiO2 can be deposited on polystyrene beads before pre-expansion and molding steps. Under the applied test conditions, expanded polystyrene with nanocrystalline SiO2 additives had approximately 10% lower moisture adsorption and an 8.4% better resistance to deformation. Expanded polystyrene analysis suggested that the observed improvements were caused by the hydrophobic nature of nanocrystalline SiO2 and, even more importantly, because SiO2 acted as an amalgamation catalyst and significantly increased adhesion between the expanded polystyrene beads during the expanded polystyrene molding process.

SiO2 films as heat resistant layers for protection of expandable polystyrene foam from flame torch–induced heat

Currently, polymeric insulation materials are widely used for energy saving in buildings. Despite of all benefits, these materials are generally sensitive to heat and highly flammable. This work discusses possibility to improve heat resistance of expanded polystyrene (EPS) foam using thin silicon dioxide (SiO2) films deposited by magnetron sputtering technique. In order to increase surface energy and adherence of SiO2 thin films to substrate EPS was plasma pretreated before films’ depositions using pulsed DC plasma generator for 40 s in argon gas. SiO2 formation was done in reactive argon and oxygen gas atmosphere. Laboratory made equipment was used for flame torch–induced heat resistance experiments. Results showed that silicon oxide films remains stable during heat resistance experiments up to 5 s and fully protects polystyrene (PS) substrate. Films are relatively stable for 30 s and 60 s and partially protect PS from melting and ignition. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy analysis confirmed that SiO2 layer, which is distributed uniformly on the EPS surface, could work as a good heat resistant material.

Role of Grain Boundaries in the Mechanism of Plasma Hydrogenation of Nanocrystalline MgAl Films

Nanocrystalline aluminum hydrides (alanates) are potential hydrogen storage materials for PEM fuel cell applications. One of candidates is magnesium alanate, Mg(AlH4)2, which contains 9.3 wt. % of hydrogen. In the present work, the effects of Ti catalyst in improving the kinetics of hydrogen uptake and release are investigated. The 2–5 μm thick MgAl films have been hydrogenated employing plasma immersion ion implantation technique as a function of Ti‐content. Nanocrystalline MgAl films were prepared by magnetron sputter deposition in vacuum. Titanium atoms were incorporated simultaneously into the growing film. Morphological and structural properties were studied by scanning electron and atomic force microcopies and X‐ray diffraction technique. It is shown that the microstructure of the hydrided/dehydrided MgAl film is highly defected and demonstrates dispersed/amorphous cluster‐like structure. Ti atoms in MgAl film kinetically enhance the dehydrogenation of magnesium alanate film. For Ti‐doped MgAl film ...

The Role of Processes on the Surface in Organization of Long Range Mass-Transport in the Bulk

Yttria-stabilized zirconia (YSZ) coatings were synthesized using dc magnetron sputter deposition of Y/Zr layers followed by thermal treatment in the range of temperatures 600-1000 °C at atmospheric pressure in air. The characterization of YSZ coating structure was carried out by X-ray diffraction. The secondary ion mass-spectrometry analysis was used for the recording of depth profiles of the most important elements in coatings and at interface. The conducted analysis showed that processes on the surface play a dominant role in the synthesis mechanism of YSZ coatings homogeneous in structure and composition during the thermal oxidation. The excess of surface thermodynamic potentials supports an intensive intermixing across Y/Zr layers with continuous supply of oxygen through the surface. Under highly non-equilibrium conditions on the surface, the adatoms are driven into grain boundaries of crystallites and result in high compressive stress in grains. The stress relaxation initiates the plastic flow of matrix material with incorporation of oxygen atoms. Thermally activated dislocation glide is considered as the dominant plasticdeformation mechanism in these materials.

Behavior of Hydrogen in Al, Mg and MgAl Plasma Saturated Films

The behaviors of hydrogen in Al, Mg and MgAl thin films on stainless steel substrate were investigated in this work. The hydrogen ions extracted from plasma were used to load hydrogen into the film material. Glow discharge optical emission spectroscopy (GDOES) was applied to obtain the hydrogen depth profiles in Al films versus hydriding parameters. The MgH2, AlH3 and Mg(AlH4)2 hydrides were identified in plasma hydrided films using X-ray diffraction (XRD). It is shown that efficient supply transport of hydrogen from the surface into the bulk for Mg films takes place at temperature above 100 °C and ion irradiation intensity above 1 mAcm-2.