Michiko Yoshitake

Self-lubrication mechanism of chlorine implanted TiN coatings

Different from the conventional physical modifications, significant reduction of wear and friction in severe dry conditions can be accommodated to titanium nitride (TiN) coating via the chlorine ion implantation. High friction coefficient with μ=0.8–1.2 for the as-deposited TiN is reduced to be less than 0.2 at room temperature. Titanium mono-oxide (TiO) and oxides with oxygen deficiency or Magneli phase with TinO2n−1, were formed inside the wear track of Cl-implanted TiN coating. Due to the shear deformability of titanium mono-oxide and crystallographic shearing planes in this Magneli phase, vicinity of the Cl-implanted TiN surface can be elasto-plastically deformed, resulting in reduction of shear stress, wear and friction. Micro-X-ray photoelectron spectroscopy (XPS) measurement as well as high-resolution transparent electron microscopy (HRTEM), were an effective tool to describe local surface reaction taking place inside and outside of the wear track. Oxidation process of TiN during wear is drastically changed at the presence of Cl-atoms on the surface. Cl-atoms diffuse from the inside of TiN to the surface to accelerate the formation of titanium oxides, and to escape out of the system together with oxide debris. Both wear volume and friction coefficient, are preserved to be as low as or lower than diamond like carbon (DLC) coatings. This preferable tribological property comes from self-lubrication mechanism of the Cl-implanted TiN due to significant change of surface reaction by the effect of Cl-atoms.

General rule for predicting surface segregation of substrate metal on film surface

We studied surface segregation of substrate metal on the top of a deposited film in a vacuum. A metallic polycrystalline film of submicron or micrometer thickness was deposited on a substrate and heated in an Auger electron spectroscopy (AES) or x-ray photoelectron spectroscopy (XPS) apparatus. The surface composition was monitored during heating. The specimen was heated until the substrate metal was observed on the surface of the deposited film and the surface concentration of the substrate metal became saturated. The depth profile of the heated specimen was obtained by measuring AES/XPS with Ar ion etching. Al, Ti, Cr, Ni, Cu, Nb, and Fe were used as substrate materials and Al, Ti, Cr, Cu, Zr, Nb, and Fe were used as film materials. More than 25 combinations of film–substrate materials have been investigated. For some film–substrate combinations, substrate metal was observed on the surface by heating at rather low temperature and substrate metal was only observed at the surface (i.e., surface segregatio...

Oxygen adsorption on Cu–9 at. %Al(111) studied by low energy electron diffraction and Auger electron spectroscopy

Cu-based alloys have been used for electric cables for long time. In the field of microelectronics, Al had been used for electrical wiring. However, it became clear that electromigration occurs in Al that causes breaking of wires in minute wirings. Due to this problem, Cu wiring is used in most advanced microprocessors. Cu metal is more corrosive than Al and Cu-based alloys with a small amount of Al is expected to solve problems both on electromigration and corrosion. The initial stage of corrosion is oxygen adsorption. We studied surface segregation of Al on Cu–9% Al(111) and oxygen adsorption on the surface with/without Al segregation in ultrahigh vacuum by low energy electron diffraction (LEED) and Auger electron spectroscopy. It was found that Al segregates on the surface to form (∛×∛)R30° structure and the structure vanishes above 595 K to give (1×1) structure while Al still segregates. The specimen was exposed to oxygen at different temperatures. The amount of oxygen uptake was not structure depende...

Temperature effect on growth of well-ordered thin Al2O3 film on NiAl(110)

We have investigated the effect of temperature on the growth of thin Al2O3 film on NiAl(110) surface. 1200 L oxygen was adsorbed at temperatures 570, 620, 670, 700, and 720 K while the pressure was kept constant at 6.6×10−5 Pa. After oxygen absorption the specimen was subsequently annealed at 1070 K for epitaxial growth of crystalline oxide. Low energy electron diffraction (LEED) and Auger electron spectroscopy were used to characterize oxide formation and surface composition. LEED patterns showed that the crystallinity depended on temperature and the brightest crystalline oxide spots were obtained at temperature between 620 and 670 K. Temperature has little effect on film thickness. The average film thickness estimated was around 4 A. Stoichiometry of O–Al bonds during oxygen absorption and realignment during annealing is important in epitaxial growth of well-ordered crystalline oxide.

Interface termination and band alignment of epitaxially grown alumina films on Cu-Al alloy

Epitaxial ultrathin alumina films were grown on a Cu−9 at. % Al(111) substrate by selective oxidation of Al in the alloy in ultrahigh vacuum. The photoelectron spectra of Al 2p and valence band were measured in situ during oxidation. By analyzing multiple peaks of Al 2p, the interface atomic structure was discussed. The energy difference between the Fermi level of the substrate and the valence band maximum of alumina (band offset) was obtained. The relation between the interface atomic structure and the band offset was compared with the reported first-principles calculations. A novel method for controlling the band offset was proposed.

Evaluation of Various Metallic Coatings on Steel to Mitigate Biofilm Formation

In marine environments and water systems, it is easy for many structures to form biofilms on their surfaces and to be deteriorated due to the corrosion caused by biofilm formation by bacteria. The authors have investigated the antibacterial effects of metallic elements in practical steels so far to solve food-related problems, using Escherichia coli and Staphylococcus aureus. However, from the viewpoint of material deterioration caused by bacteria and their antifouling measures, we should consider the biofilm behavior as aggregate rather than individual bacterium. Therefore, we picked up Pseudomonas aeruginosa and Pseudoalteromonas carageenovara in this study, since they easily form biofilms in estuarine and marine environments. We investigated what kind of metallic elements could inhibit the biofilm formation at first and then discussed how the thin films of those inhibitory elements on steels could affect biofilm formation. The information would lead to the establishment of effective antifouling measures against corrosion in estuarine and marine environments.

Feasibility study of self-lubrication by chlorine implantation

Implantation of chlorine into titanium nitride (TiN) coating on the high-speed steel substrate has succeeded in significant reduction of wear rate and friction coefficient for original TiN under dry wear condition. Through precise investigation on the surface reaction in the wear track, in situ formation of oxygen-deficient titanium oxides was found to play a role as a lubricious oxide. In the present paper, this self-lubrication mechanism is further investigated for various wearing conditions. For wide range of sliding speed and normal load in the wear map, the wear volume of a counter material is actually reduced with comparison to the un-implanted TiN. Effect of the ion implantation dose on this self-lubrication mechanism is also studied for practical use. Some comments are made on further application of this self-lubrication to manufacturing.

Interface reaction between sputter-deposited Al2O3 and stainless steels

Abstract Alumina films were deposited onto two types of stainless steels, type 304 and type 321, by the ion beam sputtering method. When the steels are heated in a vacuum, titanium carbide precipitates on the surface of type 321 steel whereas sulphur segregates to the surface of type 304. In this work, we studied the mechanism of adhesion of an alumina film to type 321 steel (adhered well) and to type 304 steel (adhered poorly) from the viewpoint of an interfacial reaction between Al2O3 and the stainless steels. X-ray photoelectron spectroscopy (XPS) measurements were made on type 304 and type 321 steels before and after deposition of Al2O3. Moreover changes in the XPS and Auger electron spectra were measured before and after heating the Al2O3-coated stainless steel. The results of Auger and XPS measurements suggest that the precipitated TiC forms Ti—O bonds at the Al2O3-type 321 interface and suppresses the segregation of sulphur which leads to Fe—O bond rupture and causes exfoliation of Al2O3 from stainless steels.

Influences of annealing in reducing and oxidizing ambients on flatband voltage properties of HfO2 gate stack structures

We have applied a combinatorial technique to fabricate work function (WF) tuned Pt-W alloy films and used the films as metal electrodes for HfO2∕SiO2∕Si capacitors. As the ratio, RPt, of Pt to W changes from 0 to 1, the WF value varies continuously from 4.7 to 5.5 eV. This tunability enables us to systematically investigate the effect of WF variation on electrical properties. After a forming gas annealing process, the values of flatband voltage (Vfb) from capacitance-voltage properties are almost constant, regardless of the WF variation, because of oxygen vacancy formation that results in Fermi level pinning. On additional oxidizing gas annealing (OGA), the effect of WF value on Vfb becomes dominant. However, the difference in Vfb between W and Pt is 0.34 V, which is much smaller than the observed WF difference of 0.8 eV. We attribute this phenomenon to the lowering of the effective WF due to an electric dipole, induced by oxygen vacancy formation at the metal/HfO2 interface. Moreover, a decrease in Vfb i...

Morphology and Thickness of Ultra-Thin Epitaxial Al2O3 Film on Cu-9%Al(111)

We investigated the surface morphology, film thickness and natures of the chemical bonds of oxide films on Cu-9%Al(111) single crystal using Auger electron spectroscopy (AES) and a scanning electron microscope (SEM). In the oxide film obtained by introducing 1300 L oxygen at 725°C, only Al was oxidized and the epitaxial Al2O3 film grew on the clean Cu-9%Al(111) surface. The Al2O3 film surface had two morphologies that consisted of a rough surface and a flat one. The rough surface was markedly observed in the sputtered region to obtain a clean surface. The rough surface had a thickness of about 3.0–3.5 nm. On the other hand, the uniform film whose thickness was about 3.5 nm grew on the flat surface. It was considered that the surface roughness of more than 0.5 nm for the Al2O3 film was related to the roughness of the clean surface. Therefore, to grow a flat uniform film over a large area, it is essential to prepare a flat surface prior to oxidation.