Ti-based Thin Films Research Articles

Influence of zirconium and copper sub-layer in cell integrations on femtosecond laser-processed Ti thin films

The creation of novel biocompatible Ti-based thin films with a Zr or Cu sub-layer modified by ultrafast laser processing is studied. To prepare bioactive surfaces, ultrafast laser processing is focused on the formation of laser-induced periodic surface structures (LIPSS) with the production of oxide phases at the surfaces. Two differently designed multilayer thin films Ti/Cu/Ti and Ti/Zr/Ti were deposited on the silicon using the ion sputtering method. The Ti thin film contains Cu or Zr sub-layer (thickness of 10 nm) at the 10 nm below the surface. The composition and surface morphology variations for these systems, deposited and laser-processed under the same experimental conditions, were caused only by different thermo-physical properties of the sub-layer (Cu or Zr). The surface morphology in the form of LIPSS, led to improved cell adhesion and stable cells/thin films interface compared to as-deposited samples. Field-emission scanning electron microscopy and MTT analysis revealed that laser processing of both systems increased cell adhesion, proliferation, and metabolical activity of L929 mouse fibroblast cells compared to non-modified flat surfaces. Overall, the biocompatibility of Zr-containing thin films is better than Ti/Cu/Ti system. Further, laser processing and formation of LIPSS makes Ti/Zr/Ti thin films excellent candidate for biomedical .

An in situ ToF-LEIS characterization of the surface of Ti-based thin films under oxygen exposure and at elevated temperatures

Ti-based coatings are utilized in a wide variety of applications, from biomedical implants to mechanical tools. Insight into initial stages of processes triggered by gas exposure and temperature change in the near-surface region of such coatings is essential for the understanding of their macroscopic behavior. We present an in situ time-of-flight low-energy ion scattering (ToF-LEIS) approach for the non-destructive and depth-resolved study of composition and morphology of the immediate surface region with sub-nm resolution. Ti-based coatings, with increasing compositional complexity, starting from in situ grown Ti, followed by ex situ grown Ti, TiN, and (Ti,Al)N, are studied concerning effects of exposure to oxygen and elevated temperatures. On the clean in situ deposited Ti surface, a 1.9 nm thick oxide layer is observed after exposure to 4000 Langmuir oxygen at room temperature. In contrast, for ex situ grown samples, an oxidic surface layer not removable by surface ion sputtering is found to limit effects of further oxygen exposure. TiN does not show significant changes when exposed to oxygen at 370 °C. For (Ti,Al)N, a nm-thick Al-rich surface layer is observed at annealing temperatures above 600 °C, both in ultra-high vacuum and in 1.0 × 10-3 Pa of oxygen.

Cell Response on Laser-Patterned Ti/Zr/Ti and Ti/Cu/Ti Multilayer Systems

Arranged patterns obtained via ultrafast laser processing on the surface of Ti/Cu/Ti/Si and Ti/Zr/Ti/Si thin-film systems are reported. Two differently designed multilayer thin films Ti/Cu/Ti/Si and Ti/Zr/Ti/Si were deposited on silicon using the ion sputtering method. The bioactive surfaces of these systems involve the formation of laser-induced periodic surface structures (LIPSS) in each of the laser-written lines of mesh patterns on 5 × 5 mm areas. The formation of nano- and micro-patterns with an ultra-thin oxide film on the surfaces was used to observe the effects of morphology and proliferation of the MRC-5 cell culture line. To determine whether Ti-based thin films have a toxic effect on living cells, an MTT assay was performed. The relative cytotoxic effect, as a percentage of surviving cells, showed that there was no difference in cell number between the Ti-based thin films and the control cells. There was also no difference in the viability of the MRC-5 cells, except for the Ti/Cu/Ti/Si system, where there was a slight 10% decrease in cell viability.

Adsorption of Titanium Halides on Nitride and Oxide Surfaces during Atomic Layer Deposition: A DFT Study

Various processes based on atomic layer deposition (ALD) have been reported for growing Ti-based thin films such as TiN and TiO2. To improve the uniformity and conformity of thin films grown via ALD, fundamental understanding of the precursor–substrate surface reactions is required. Herein, we present a density functional theory (DFT) study of the initial nucleation process of some titanium halide precursors (TiCl4, TiBr4, and TiI4) on Si surfaces having –OH or –NH2 functional groups. We consider the most favorable adsorption site in the reaction between the precursor and functional group of the surface, based on the thermodynamics and kinetics of the reaction. Sequential dissociation reaction mechanisms of halide ligands were systematically investigated. The exothermicity of the dissociative adsorption was found to be in the order of: TiI4 > TiBr4 > TiCl4. In addition, the precursors were observed to be more exothermic and show higher reaction rate constant when adsorbed on the –OH–terminated surface than on the –NH2–terminated surface. These observations reveal the selectivity of deposition by surface functional groups.

Analysis of the composition of Ti-based thin films deposited on silicon by means of self-ion assisted deposition

The composition of Ti-based thin films deposited on silicon using a self-ion assisted deposition (SIAD) method was investigated by utilising the Rutherford backscattering spectrometry technique and RUMP simulation code. The hydrogen affinity of the coatings produced by means of SIAD was investigated using the 1H(15N, αγ)12C nuclear resonance reaction. The titanium–based films on silicon were found to have a high content of oxygen, carbon, hydrogen and substantial concentration of the substrate. Near 10% H content enrichment was found at the surface of coatings but no hydrogen enrichment at the coating–substrate interfaces was observed.

Oxidation and wear behaviors of Ti-based thin films

The degradation of Ti-based coatings is known to be due to the formation of titanium oxide (TiO 2) at their surfaces. In this study, wear and thermal oxidation behaviors of various magnetron sputtered Ti-based thin films were studied after static oxidation and sliding wear. The oxidized surfaces after the static oxidation and the wear debris generated from pin-on-disc wear tests with alumina ball were characterized to identify the compounds, particularly titanium oxides, to gain a better understanding of the tribochemical reactions. The coatings that were examined include TiN, TiCN (N rich), TiCN (C rich), TiAlN, AlTiN, TiSiN, and TiCNO thin films. These coatings were characterized using Raman spectroscopy, scanning electron microscopy, and X-Ray diffractometer. The results show that TiSiN and AlTiN have the highest oxidation resistance, comparing with other coatings. As for the analyses of wear debris, all of the Ti-based coatings are worn by the mechanism of forming TiO 2, except AlTiN. AlTiN is worn by ploughing wear.

Vacuum pressure dependence of the tribological properties of Ti, TiO2, and TiN thin films

AbstractThe tribological properties of Ti‐based (Ti, TiO2, and TiN) thin films on a stainless steel (304SS) substrate were investigated at several pressures in air. Films 0.2 μm thick were prepared on a mirror‐polished substrate using the methods of ion‐beam‐assisted deposition, ion‐beam‐assisted reactive deposition, and dynamic ion beam mixing. Tribological testing was carried out with a tribometer of a pin‐on‐disk type in a high‐vacuum chamber. The wear surface was observed with a scanning laser microscope and a scanning electron microscope.The friction coefficient of stainless steel at a pressure of 1 × 105 Pa was lower than that at 1 × 10−5 Pa, because oxygen or moisture in the air acted as lubricants. Also the TiN thin film prepared at 1 × 105 Pa showed a low friction coefficient until wear of the TiN layer on the substrate occurred at a sliding distance of 10 m. However, the friction coefficients of the TiO2 and Ti thin films were hardly dependent on the gas pressure. At a sliding distance of 5 m, the friction coefficients of Ti‐based thin films converged to 0.3 at a pressure of 1 × 10−3 Pa. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 149(3): 1–7, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20020

Ti，TiO<sub>2</sub>およびTiN薄膜の摩擦·摩耗特性に対する雰囲気圧力依存性

Tribological properties of Ti-based (Ti, TiO2 and TiN) thin films on a stainless steel (304SS) substrate were investigated at several pressures in an atmosphere of the air. Films 0.2 µm thick were prepared on a mirror-polished substrate using each method of ion beam assisted deposition, ion beam assisted reactive deposition and dynamic ion beam mixing. The tribological test was carried out with a tribo meter of a pin-on-disk type in a high vacuum chamber. The wear surface was observed with a scanning laser microscope and a scanning electron microscope. The friction coefficient of stainless steel in a pressure of 1×105 Pa showed a lower value than that in 1×10-5 Pa, because oxygen or moisture contained in the air played a role of lubrication. Also the TiN thin film in 1×105 Pa showed a low friction coefficient until wearing the TiN layer on a substrate at a sliding distance of 10 m. However friction coefficients of the TiO2 and Ti thin film were hardly dependent on a gas pressure. In the case of 5 m in a sliding distance, friction coefficients of Ti-based thin films converged on 0.3 at a pressure of 1×10-3 Pa.

ステンレス基板上に作製したＴｉ系薄膜の高真空中における摩擦・摩耗特性

ステンレス基板上に作製したＴｉ系薄膜の高真空中における摩擦・摩耗特性

Ion beam assisted deposition of metallic and ceramic thin films

Experiments on ion beam assisted deposition (IBAD) of metallic (Mo, Ti, Al) and ceramic (Al 2O 3, ZrO 2) thin films were performed within the ion beam energy range of 100–600 eV. As our experimental facilities did not allow us to keep the ion-to-atom arrival ratio constant for all ion energies, the ion “energy” dependence of the thin film characteristics discussed in the paper also includes a dependence on this ratio. The ion beam bombardment of the growing thin films led to a decrease of thin film thicknesses with increasing energies, to an increase of the surface roughness of metallic films on silicon substrates and initiated amorphisation processes in the originally polycrystalline films. The RBS spectra of the metallic films did not show any dramatic changes with ion energy variations. Higher ion beam energies and doses led to higher values of the index of refraction of Al- and Ti-based thin films. Al 2O 3 and ZrO 2 thin films revealed good optical properties.