Hitoshi Uchida

Oxidation behavior of (Ti1 − xAlx)N films perpared by r.f. reactive sputtering

Abstract (Ti, Al)N films have drawn much attention as alternatives for TiN coatings, which are oxidized easily in air above 500 °C. We have investigated the effect of Al content on the oxidation resistance of (Ti 1 − x Al x )N films prepared by r.f. reactive sputtering. (Ti 1 − x Al x N films (O ≤ x ≤ 0.55) were deposited onto fused quartz substrates by r.f. reactive sputtering. Composite targets with five kinds of Al-to-Ti area ratio were used. The sputtering gas was Ar (purity, 5 N) and N 2 (5 N). The flow rate of Ar and N 2 gas was kept constant at 0.8 and 1.2 sccm, respectively, resulting in a sputtering pressure of 0.4 Pa. The r.f. power was 300 W for all experiments. Substrates were not intentionally heated during deposition. The deposited films (thickness, 300 nm) were annealed in air at 600 ∼ 900 °C and then subjected to X-ray diffractometer and Auger depth profiling. The as-deposited (Ti 1 − x Al x )N films had the same crystal structure as TiN (NaCl type). Al atoms seemed to substitute for Ti in lattice sites. The preferential orientation of the films changed with the Al content of the film, x . Oxide layers of the films grew during annealing and became thicker as the annealing temperature increased. The thickness of the oxide layer grown on the film surface decreased with increasing Al content in the film. For high Al content films an Al-rich oxide layer was grown on the surface, which seemed to prevent further oxidation. All of the films, however, were oxidized by 900 °C annealing, even if the Al content was increased up to 0.55.

Electrochemical evaluation of pinhole defects in TiN films prepared by r.f. reactive sputtering

Abstract TiN films were deposited onto stainless steels by r.f. reactive sputtering and they contained more or less pinhole defects. The area ratio of pinhole defects was evaluated potentiodynamically with the ratio of critical passivation current density of TiN-coated and non-coated specimen in a deaerated 0.5 kmol/m3H2SO4 + 0.05 kmol/m3KSCN solution. The result coincided well with the true defect area ratio based on the optical micrographs before and after polarized anodically. Such electrochemical method was concluded to be a reliable evaluation technique for the pinhole defects of corrosion-resistible coating.

Effects of ion flux on the properties of dc magnetron-sputtered stainless steel films

Abstract We have studied the effect of ion flux on the properties of sputtered stainless steel films. To investigate the effect of ion flux, films have been deposited onto glass substrates using dc planar magnetron-sputtering apparatus, which is equipped with an external magnetic coil. As the external coil current changes, the magnetic field of the magnetron cathode changes from balanced to unbalanced mode smoothly. Targets used were commercial SUS304 and SUS310S steel disks. The applied dc power and Ar pressure were kept constant at 140xa0W and 0.5xa0Pa, respectively. The difference of the composition between as-deposited films and the target material appeared to be small. Films deposited using SUS304 target showed a bcc structure with (1xa01xa00) preferred orientation though the target material was metastable, austenitic stainless steel. When SUS310S steel with stable austenite was used as target material, as-deposited films consisted of a mixture of fcc and bcc phase. The ion flux showed very small effect on the structure and the composition of deposited SUS304 films. In the SUS310S films, however, the ion flux affected the volume ratio of fcc to bcc phase. Both films were superior in the corrosion resistance and the hardness as compared with bulk material.

Structure and composition of (Ti, Al)N films prepared by r.f. planar magnetron sputtering using a composite target

(Ti, Al) alloy nitride films have drawn much attention because of their excellent oxidation resistance. The purpose of this paper is to investigate the structure, morphology and composition of the (TixAl1 − x)Ny films prepared by r.f. reactive sputtering using a composite target where the area ratio of Ti to Al is unity. Nitrogen flow to total nitrogen and argon flow ratio (Fn2Ftotal) is used as a parameter. The partial pressures of these gases that resulted were monitored by their optical emission in the glow discharge. n nThe crystallographic structure of deposited films were divided into three groups by the Fn2Ftotal that was used in their preparation. The first group (Fn2Ftotal = 0) is a Ti and Al metal mixed structure. The second group (0.1 ≤FN2Ftotal<0.4) has an amorphous structure. The last group (FN2Ftotal≥ 0.4) has the wurtzite structure. Under all conditions, the composition of the films was richer in Al than the target area ratio of Ti to Al, as would be expected from their sputtering yields. This ratio changes with admission of nitrogen because of selective poisoning (the formation of nitrides on the sputtering target). The plot of composition ratio CTiCAl vs. FN2Ftotal showed the local minimum at about FN2Ftotal = 0.3. The ratio of Ti to Al emission intensity, IT1IAl, from optical measurements shows excellent agreement with CTiCAl. It is concluded that the optical emission signal is very useful for the composition control during deposition, both of the materials being sputtered and of the residual atmosphere.

Cell and tissue-autonomous development of the circadian clock in mouse embryos

The emergence of the circadian rhythm is a dramatic and physiologically essential event for mammals to adapt to daily environmental cycles. It has been demonstrated that circadian rhythms develop during the embryonic stage even when the maternal central pacemaker suprachiasmatic nucleus has been disrupted. However, the mechanisms controlling development of the circadian clock are not yet fully understood. Here, we show that the circadian molecular oscillation in primary dispersed embryonic cells and explanted salivary glands obtained from mPER2Luc mice embryos developed cell‐ or tissue‐autonomously even in tissue culture conditions. Moreover, the circadian clock in the primary mPER2Lu c fibroblasts could be reprogrammed by the expression of the reprogramming factors. These findings suggest that mammalian circadian clock development may interact with cellular differentiation mechanisms.

Regulation of the Epithelial Adhesion Molecule CEACAM1 Is Important for Palate Formation

Cleft palate results from a mixture of genetic and environmental factors and occurs when the bilateral palatal shelves fail to fuse. The objective of this study was to search for new genes involved in mouse palate formation. Gene expression of murine embryonic palatal tissue was analyzed at various developmental stages before, during, and after palate fusion using GeneChip® microarrays. Ceacam1 was one of the highly up-regulated genes during palate formation, and this was confirmed by quantitative real-time PCR. Immunohistochemical staining showed that CEACAM1 was present in prefusion palatal epithelium and was degraded during fusion. To investigate the developmental role of CEACAM1, function-blocking antibody was added to embryonic mouse palate in organ culture. Palatal fusion was inhibited by this function-blocking antibody. To investigate the subsequent developmental role of CEACAM1, we characterized Ceacam1-deficient (Ceacam1 −/−) mice. Epithelial cells persisted abnormally at the midline of the embryonic palate even on day E16.0, and palatal fusion was delayed in Ceacam1 −/− mice. TGFβ3 expression, apoptosis, and cell proliferation in palatal epithelium were not affected in the palate of Ceacam1−/−mice. However, CEACAM1 expression was retained in the remaining MEE of TGFβ-deficient mice. These results suggest that CEACAM1 has roles in the initiation of palatal fusion via epithelial cell adhesion.

Cryptochrome-dependent circadian periods in the arcuate nucleus

The circadian pacemaker in the suprachiasmatic nucleus (SCN) of the hypothalamus is responsible for controlling behavioral activity rhythms, such as a free running rhythm in constant darkness. Rodents have several circadian oscillators in other brain regions including the arcuate nucleus (ARC). In specific conditions such as food anticipatory activity rhythms in the context of timed restricted feeding, an alternative circadian pace-making system has been assumed by means of circadian oscillators like the SCN. Despite extensive lesion studies, the anatomic locations of extra-SCN circadian pacemakers responsible for regulating behavioral rhythms have not been found. In the present study, we investigated circadian rhythms in the SCN and extra-SCN region of the arcuate nucleus (ARC) by analyzing PER2::LUCIFERASE expression in specific regions from wild-type C57BL/6, Cry1(-/-), and Cry2(-/-) mice. Compared to wild-type animals, we observed period shortening in both the SCN and ARC of Cry1(-/-) mice and period lengthening in Cry2(-/-) mice. Interestingly, the periods in the ARC of both genotypes were identical to those in the SCN. Moreover, the amplitudes of PER2::LUC rhythms in the ARC of all animals were decreased compared to those in the SCN. These data suggest that the ARC is a candidate circadian pacemaker outside the SCN.

Melatonin Inhibits Embryonic Salivary Gland Branching Morphogenesis by Regulating Both Epithelial Cell Adhesion and Morphology

Many organs, including salivary glands, lung, and kidney, are formed by epithelial branching during embryonic development. Branching morphogenesis occurs via either local outgrowths or the formation of clefts that subdivide epithelia into buds. This process is promoted by various factors, but the mechanism of branching morphogenesis is not fully understood. Here we have defined melatonin as a potential negative regulator or “brake” of branching morphogenesis, shown that the levels of it and its receptors decline when branching morphogenesis begins, and identified the process that it regulates. Melatonin has various physiological functions, including circadian rhythm regulation, free-radical scavenging, and gonadal development. Furthermore, melatonin is present in saliva and may have an important physiological role in the oral cavity. In this study, we found that the melatonin receptor is highly expressed on the acinar epithelium of the embryonic submandibular gland. We also found that exogenous melatonin reduces salivary gland size and inhibits branching morphogenesis. We suggest that this inhibition does not depend on changes in either proliferation or apoptosis, but rather relates to changes in epithelial cell adhesion and morphology. In summary, we have demonstrated a novel function of melatonin in organ formation during embryonic development.

The central clock controls the daily rhythm of Aqp5 expression in salivary glands

Salivary secretion displays day–night variations that are controlled by the circadian clock. The central clock in the suprachiasmatic nucleus (SCN) regulates daily physiological rhythms by prompting peripheral oscillators to adjust to changing environments. Aquaporin 5 (Aqp5) is known to play a key role in salivary secretion, but the association between Aqp5 and the circadian rhythm is poorly understood. The aim of our study was to evaluate whether Aqp5 expression in submandibular glands (SMGs) is driven by the central clock in the SCN or by autonomous oscillations. We observed circadian oscillations in the activity of period circadian protein homolog 2 and luciferase fusion protein (PER2::LUC) in cultured SMGs with periodicity depending on core clock genes. A daily rhythm was detected in the expression profiles of Aqp5 in SMGs in vivo. In cultured SMGs ex vivo, clock genes showed distinct circadian rhythms, whereas Aqp5 expression did not. These data indicate that daily Aqp5 expression in the mouse SMG is driven by the central clock in the SCN.

Application of Synchrotron Radiation Photoemission Spectroscopy to Structure Analysis of Thin Corrosion Products Film on Hot-Dip Zn-Al Coatings

Introduction Structures of the thin corrosion products film, in the early stages which formed on hot-dip Zn-0.2%Al, Zn5%Al and Zn-55%Al coatings in humid atmosphere under the presence of NaCl particles, have been investigated by means of photoemission spectroscopy using synchrotron radiation (160 eV) and Al-K radiation (1487 eV). Moreover, the initial corrosion resistance mechanism of Zn-Al alloy coatings is discussed being related to the structure of corrosion products film.