P. Mazur

Determination of structural, mechanical and corrosion properties of Nb2O5 and (NbyCu1 − y)Ox thin films deposited on Ti6Al4V alloy substrates for dental implant applications

In this paper comparative studies on the structural, mechanical and corrosion properties of Nb2O5/Ti and (NbyCu1-y)Ox/Ti alloy systems have been investigated. Pure layers of niobia and niobia with a copper addition were deposited on a Ti6Al4V titanium alloy surface using the magnetron sputtering method. The physicochemical properties of the prepared thin films were examined with the aid of XRD, XPS SEM and AFM measurements. The mechanical properties (i.e., nanohardness, Youngs modulus and abrasion resistance) were performed using nanoindentation and a steel wool test. The corrosion properties of the coatings were determined by analysis of the voltammetric curves. The deposited coatings were crack free, exhibited good adherence to the substrate, no discontinuity of the thin film was observed and the surface morphology was homogeneous. The hardness of pure niobium pentoxide was ca. 8.64GPa. The obtained results showed that the addition of copper into pure niobia resulted in the preparation of a layer with a lower hardness of ca. 7.79 GPa (for niobia with 17 at.% Cu) and 7.75 GPa (for niobia with 25 at.% Cu). The corrosion properties of the tested thin films deposited on the surface of titanium alloy depended on the composition of the thin layer. The addition of copper (i.e. a noble metal) to Nb2O5 film increased the corrosion resistance followed by a significant decrease in the value of corrosion currents and, in case of the highest Cu content, the shift of corrosion potential towards the noble direction. The best corrosion properties were obtained from a sample of Ti6Al4V coated with (Nb0.75Cu0.25)Ox thin film. It seems that the tested materials could be used in the future as protection coatings for Ti alloys in biomedical applications such as implants.

Influence of the surface properties on bactericidal and fungicidal activity of magnetron sputtered Ti-Ag and Nb-Ag thin films.

In this study the comparative investigations of structural, surface and bactericidal properties of Ti-Ag and Nb-Ag thin films have been carried out. Ti-Ag and Nb-Ag coatings were deposited on silicon and fused silica substrates by magnetron co-sputtering method using innovative multi-target apparatus. The physicochemical properties of prepared thin films were examined with the aid of X-ray diffraction, grazing incidence X-ray diffraction, scanning electron microscopy, atomic force microscopy and X-ray photoelectron spectroscopy methods. Moreover, the wettability of the surface was determined. It was found that both, Ti-Ag and Nb-Ag thin films were nanocrystalline. In the case of Ag-Ti film presence of AgTi3 and Ag phases was identified, while in the structure of Nb-Ag only silver occurred in a crystal form. In both cases the average size of crystallites was ca. 11 nm. Moreover, according to scanning electron microscopy and atomic force microscopy investigations the surface of Nb-Ag thin films was covered with Ag-agglomerates, while Ti-Ag surface was smooth and devoid of silver particles. Studies of biological activity of deposited coatings in contact with Bacillus subtilis, Pseudomonas aeruginosa, Enterococcus hirae, Klebisiella pneumoniae, Escherichia coli, Staphylococcus aureus and Candida albicans were performed. It was found that prepared coatings were bactericidal and fungicidal even in a short term-contact, i.e. after 2 h.

Pd/GaN(0001) interface properties

This report concerns the properties of an interface formed between Pd films deposited onto the surface of (0001)-oriented n-type GaN at room temperature (RT) under ultrahigh vacuum. The surface of clean substrate and the stages of Pd-film growth were characterized in situ by X-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), ultraviolet photoelectron spectroscopy (UPS), and low energy electron diffraction (LEED).As-deposited Pd films are grainy, cover the substrate surface uniformly and reproduce its topography. Electron affinity of the clean n-GaN surface amounts to 3.1 eV. The work function of the Pd-film is equal to 5.3 eV. No chemical interaction has been found at the Pd/GaN interface formed at RT. The Schottky barrier height of the Pd/GaN contact is equal to 1.60 eV.

Double electric layer at the LiBrNaCl interface

Abstract The effect of formation of the potential barrier at the interfaces of LiBr NaCl and NaCl LiBr was investigated using the method of ultraviolet photoelectron spectroscopy (UPS). This barrier is created by the displacement of positive and negative ions from their equilibrium positions in the boundary region. The measured barrier height is 0.4 eV and when NaCl is evaporated on LiBr it has positive sign (electrons are accelerated in this barrier). For the system LiBr/NaCl/LiBr effective barrier height is equal to zero, as the barrier at the NaCl LiBr has an opposite sign. The results could be important for technology of protecting of semiconductor devices using insulating layers.

Photoemission study of alkali halide/Si and alkali halide/LiBr interfaces

Abstract Photoemission spectra obtained during the NaCl and KF deposition on a clean Si(100) surface and a LiBr Si system are reported. The electronic structure of the interfaces between two different alkali halides as well as between alkali halide and silicon is deduced from the experiments. Large negative electron affinity values have been found for the KF and NaCl films deposited on a Si(100) surface.

Photoemission investigations of the BaF2-CaF2 interface

Abstract Photoemission spectra obtained during BaF2 and CaF2 deposition on a Si(100) surface are reported. The electronic structure of the interfaces is deduced from the experiments. The measured valence band offset for the BaF 2 CaF 2 interface is equal to 0.5 eV.

Potential barrier at the CaF2-BaF2 interface

Abstract The potential barrier at the interface between CaF 2 and BaF 2 layers deposited onto a Si(111) substrate is studied using UPS. It is stated that the evaporation of the BaF 2 layer onto a composite CaF 2 /Si substrate decreases the photoelectron threshold by about 0.5 eV. For the multilayer systems the reversible changes of the photoelectron work function are observed after subsequent film evaporation.

Photoemission investigations of the interface between a thermally oxidized Si(111) surface and a NaCl layer

Abstract The potential barrier at the interface of a thermally oxidized silicon and a NaCl layer has been studied using the UPS method. For all investigated oxidation procedures of the Si sample, deposition of the NaCl layer leads to a decrease of the photoemission threshold of the system examined. The value of the potential barrier decreases (down to 0.5 eV) with increasing oxygen exposures independent of the sample temperature during the oxidation process.

UPS study of KOH layers on Si (100) surface

Abstract The adsorption of potassium hydroxide on a silicon (100) surface was investigated using the photoelectron spectroscopy method. Two OH induced valence orbitals were found at 5.2 and 9.5 eV below the silicon Fermi level. It was stated that adsorbed KOH does not dissociate at the surface. To explain the work function changes during adsorption of KOH molecules we assumed the model of an oriented dipole layer on the surface. The effective dipole moment (equal to about 1 D) of KOH molecule on the Si(100) surface was estimated.