Titanium (Ti) is always covered by thin passive films. Thus, valence band (VB) spectra, obtained using X‐ray photoelectron spectroscopy (XPS), are superpositions of the VB spectra of passive films and that of the metallic Ti substrate. In this study, to obtain the VB spectra only of passive films, angular resolution (for eliminating the substrate Ti contribution) and argon ion sputtering (for removing passive films) were used along with XPS. The passive film on Ti was determined to consist of a very thin TiO ₂ layer with small amounts of Ti ₂ O ₃ , TiO, hydroxyl groups, and water with a thickness of 5.9 nm. The VB spectra of Ti were deconvoluted into four peak components: a peak at ~1 eV, attributed to the Ti metal substrate; a broad peak in the 3–10 eV range, mainly attributed to O 2p (~6 eV) and O 2p‐Ti 3d hybridized states (~8 eV), owing to the π (non‐bonding) and σ (bonding) orbitals in the passive oxide film; and a peak at ~13 eV, attributed to the 3σ orbital of O 2p as OH ⁻ or H ₂ O. The VB region spectrum between approximately 3 and 14 eV from Ti is originating from the passive film on Ti. In particular, characterization of VB spectrum obtained with a takeoff angle of less than 24° is effective to obtain VB spectrum only from the passive film on Ti. The property as n ‐type semiconductor of the passive film on Ti is probably higher than that of rutile TiO ₂ ceramics.

Recently, silver (Ag) and copper (Cu) have been incorporated into a titanium (Ti) surface to realize their antibacterial property. This study investigated both the durability of the antibacterial effect and the surface change of the Ag- and Cu-incorporated porous titanium dioxide (TiO₂) layer. Ag- and Cu-incorporated TiO₂ layers were formed by micro-arc oxidation (MAO) treatment using the electrolyte with Ag and Cu ions. Ag- and Cu-incorporated specimens were incubated in saline during a period of 0–28 days. The changes in both the concentrations and chemical states of the Ag and Cu were characterized using X-ray photoelectron spectroscopy (XPS). The durability of the antibacterial effects against Escherichia coli (E. coli) were evaluated by the international organization for standardization (ISO) method. As a result, the Ag- and Cu-incorporated porous TiO₂ layers were formed on a Ti surface by MAO. The chemical state of Ag changed from Ag₂O to metallic Ag, whilst that of Cu did not change by incubation in saline for up to 28 days. Cu existed as a stable Cu₂O compound in the TiO₂ layer during the 28 days of incubation in saline. The concentrations of Ag and Cu were dramatically decreased by incubation for up to 7 days, and remained a slight amount until 28 days. The antibacterial effect of Ag-incorporated specimens diminished, and that of Cu was maintained even after incubation in saline. Our study suggests the importance of the time-transient effects of Ag and Cu on develop their antibacterial effects.

The band structures and band gap energies, E_g, of passive films formed on titanium (Ti) in simulated bioliquids, Hanks’ solution (Hanks) and saline, were evaluated. Ti was polarized at 0, −0.1, and −0.2 V_Ag/AgCl, E_f, for 1 h. After polarization, the surfaces were characterized using X-ray photoelectron spectroscopy, and the photoelectrochemical responses were evaluated. The current change during photoirradiation was recorded as a photocurrent transient at each measuring potential, E_m, and by changing the wavelength of the incident light. Passive films consisted of a very thin TiO₂ layer containing small amounts of Ti₂O₃ and TiO, hydroxyl groups, and water. During polarization in Hanks, calcium and phosphate ions were incorporated or formed calcium phosphate but not in saline. Calcium phosphate and hydroxyl groups influenced the band structure. E_g was graded in Hanks but constant in saline, independent of E_f and E_m. The passive film on Ti behaved as an n-type semiconductor containing two layers: an inner oxide layer with a large E_g and an outer hydroxide layer with a small E_g. In Hanks, E_g was 3.3–3.4 eV in the inner oxide layer and 2.9 eV in the outer hydroxide layer. In saline, E_g was 3.3 eV in the inner layer and 2.7 eV in the outer layer. Calcium phosphate and hydroxyl groups influenced the band structure of the passive film. The E_g of the outermost surface was smaller than that of TiO₂ ceramics, which is probably one of the principles of the excellent biocompatibility of Ti among metals. Graphical abstract

Recently, biofilm formation caused by bacterial adhesion and colonization has been recognized as the major cause of failure in orthopedic and dental implant surgeries. In this study, a customized micro-arc oxidation (MAO) treatment technique was developed to obtain desirable antibacterial properties on Ti surfaces. The two-step MAO treatment was applied in the fabrication of specimens with Ag and with/without Zn in their surface oxide layer. In order to simulate practical usage, surface analyses and immersion tests were performed to evaluate the incorporation of Ag and Zn into the resulting oxide layer and ion release behavior, respectively. Additionally, the antibacterial properties of the specimens after long-term immersion in physiological saline were evaluated using Gram-negative facultative anaerobic bacteria. The MAO-treated specimens containing Ag and Zn exhibited excellent antibacterial properties against Escherichia coli, which were sustained even after 6 months of immersion in physiological saline to simulate practical usage. Moreover, the Ag ions released from the surface oxide indicate the antibacterial properties of the specimen in the early stage, while the release of the corrosion products of Zn demonstrates its antibacterial properties in the later stage.

To clarify the mechanism of localized corrosion on zirconium in chloride environments, corrosion tests of zirconium and its alloys were performed using conventional and micron-scale measurement systems with surface areas of 0.35 cm² and less than 0.04 cm², respectively. The pitting potential significantly dropped by more than 1 V when zirconium was alloyed with over 10 mol% of tin. Zr₄Sn and Zr₅Sn₃ intermetallics hindered the formation of passive films on the substrate. Additionally, tin was found on the surface of a commercially pure zirconium. From the micron-scale measurement results, the inclusion with the highest concentration of tin (at least 0.44 mol%) in the tested area was selected as the preferential initiation site for pitting corrosion. Thus, tin played an important role in determining the corrosion resistance of zirconium in chloride environments.

The electronic structures, including the semiconductive properties, of the passive films formed on Cr and Ti in a phosphate buffer solution of pH 7 were evaluated using photoelectrochemical response, electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy (XPS). Based on the results, electronic band structure models of the passive films were proposed: the passive films on Cr consisted of an inner p-type oxide layer with a band gap energy, E _g, of 3.6 eV and an outer p-type hydroxide layer with E _g of 2.5 eV whereas those on Ti consisted of an inner n-type oxide layer with E _g of 3.2 eV and an outer n-type hydroxide layer with E _g of 2.5 eV. The type of semiconductor evaluated for the oxide and hydroxide layers was strongly supported by valence-band XPS, which can provide the energy difference between the Fermi energy of the underlying metal and the highest energy of the valence bands of the oxide and hydroxide layers in the passive films.