Akira Kinbara

Novel gas sensor using polymer-film-coated quartz resonator for environmental monitoring

Abstract The functional design of the smart electronic nose using polymer-film-coated quartz resonator gas sensors, based on the solubility parameter of sensing membrane and gases, is carried out in order to develop a sensor with excellent selectivity and high sensitivity for harmful gases such as toluene, acetaldehyde and ammonia gases. The polymer films such as propylene-butyl, polycarbonate and acrylic-resin of which the solubility parameter almost coincide with that of toluene, acetaldehyde and ammonia gases, respectively, are chosen as a sensing membrane material coated on the quartz resonator. It is found that propylene-butyl-film-coated quartz resonator gas sensor exhibits a high sensitivity and an excellent selectivity for toluene and p -xylene gas, as expected from a functional design based on solubility parameter. It is also found that polycarbonate-film-coated and acrylic-resin film-coated sensors exhibit high sensitivity and excellent selectivity for acetaldehyde and ammonia, respectively, also as expected. The results strongly suggest that solubility parameter is effective in the functional design of the sensing membrane of quartz resonator gas sensors. The successful identification of a specific gas is possible through the principal component pattern recognition analysis of the transient responses of each sensor for gases.

A smart gas sensor using polymer-film-coated quartz resonator microbalance

Abstract The copolymerized propylene–butyl, of which the “solubility parameter” almost coincides with that of harmful gases such as toluene, xylene, diethyether, chloroform and acetone, is chosen as a material of the sensing membrane coated on the quartz resonator. It is found that copolymerized propylene–butyl-film-coated quartz resonator microbalance gas sensor exhibits high sensitivity and excellent selectivity for these harmful gases, especially for toluene and xylene gas, suggesting that the “solubility parameter” is effective to the functional design of the sensing membrane of quartz resonator gas sensors.

Elastic and plastic energies in sputtered multilayered Ti-TiN films estimated by nanoindentation

Abstract Energetic parameters for describing mechanical properties, which makes it possible to discuss deformation behavior of a film elastically and plastically, are presented. Elastic energy and dissipated energy estimated from the area surrounded by a load–displacement curve obtained by nanoindentation measurement indicate the energy to deform a film elastically and plastically. The energy dissipated ratio defined as the ratio of dissipated energy to total applied energy to a film indicates the tendency for plastic deformation of a film. By considering the two energies and the energy dissipated ratio, deformation behavior of compositionally modulated Ti–TiN films with a multilayered structure was examined. At a modulation period of 10 nm, the reduction of the dissipated energy and the energy dissipated ratio were observed. Since the dissipated energy is consistent with energy for the propagation of the dislocations related to plastic deformation, it was assumed that the reduction was caused by a pinning effect for the propagation of the dislocations at interfaces of Ti and TiN.

Evaluation of adhesion strength of Ti films on Si(100) by the internal stress method

Abstract Titanium films were sputter deposited onto Si(100) surface. Adhesion strength of the Ti film was evaluated by the internal stress method. The Ti film was overcoated by a Ni coating in the state of a high internal stress, the value of which was about 0.5 GPa (tensile). The internal stress induces large normal and shear stress at the interface between the Ti film and the Si(100) surface. Those stresses increase with the increase of the Ni coating thickness. The stress distribution was evaluated by the finite element method. The evaluation shows that the normal stress on the interface is extremely large at the edge of the sample. This result suggests that a peeling of the Ti film is initiated at the edge and is consistent with observed spontaneous peeling phenomena. We could determine the adhesion strength of the Ti film by measuring the thickness of the Ni coating to peel off the Ti film. The value was found to range in 0.1–1 GPa region. The effect of the Ar ion bombardment of Si substrate on the adhesion enhancement was investigated in detail by this method.

Titanium carbide film deposition by DC magnetron reactive sputtering using a solid carbon source

Abstract Titanium carbide films with various C/Ti ratios have been deposited by DC magnetron sputtering using carbon sheets on the Ti target erosion area as a solid carbon source. By changing the number of carbon sheets (5 × 5 × 1 mm 3 ) from 0 to 24 pieces, the C/Ti compositional ratio of the films was changed. The composition, structure, and hardness of the deposited films were estimated as a function of the ratio of the source carbon area to the titanium target erosion area. The results of X-ray photoelectron spectroscopy showed that the C contents in the films increased to Ti: C = 60: 40 as the source C/Ti areal ratio increased. By X-ray diffraction, the films obtained for C/Ti areal ratios above 0.1 were found to possess the face-centered cubic structure and that the d -value of TiC (111) increased monotonically from 0.238 to 0.249 nm as the C/Ti areal ratio increased. The hardness of the films also increased monotonically as the C/Ti areal ratio increased, yielding a maximum of 11 GPa.

Adhesion and hardness of compositionally gradient TiO2/Ti/TiN, ZrO2/Zr/ZrN, and TiO2/Ti/Zr/ZrN coatings

Abstract A technique using compositionally gradient interlayers has been applied to TiO 2 /Ti/TiN, ZrO 2 /Zr/ZrN, and TiO 2 /Ti/Zr/ZrN multi-compositional coatings to enhance the adhesion of hard coatings to substrate. The coatings were prepared by dc reactive magnetron sputtering using a combination of a Zr or a Ti metal target and a pure Ar, an Ar-O 2 mixture, or an Ar-N 2 mixture discharge gas, onto a borosilicate glass substrate. Adhesion of coatings to the substrate was estimated by a scratch method. The hardness of coatings was measured by a nano-indentation method. Without an interface, ZrN coatings showed a very poor adhesion. By using glass/ZrO 2 /Zr or glass/TiO 2 /Ti compositionally gradient interface layers, the adhesion strength of ZrN coatings was enhanced to the adhesion strength almost equal to or higher than those of TiO 2 or ZrO 2 single layer coatings. From the results of internal stress evaluation, it was found that a high internal stress causes a poor adhesion of ZrN coatings. Hardness of coatings with a ZrN overlayer were 20 to 35 GPa and larger than those of coatings with a TiN overlayer. The increase in the hardness by inserting a compositionally gradient interface was observed in ZrO 2 /Zr/ZrN and TiO 2 /Ti/Zr/ZrN systems.

Time-dependent O2 mass balance change and target surface oxidation during mode transition in Ti–O2 reactive sputtering

Time-dependent O2 mass balance change among the amounts injected into the chamber, pumped out from the chamber, gettered by sputtered Ti metal, residing in the chamber, and consumed to oxidize the target surface has been investigated as a function of time elapsed after the discharge ignition in Ti–O2 reactive sputtering. From the mass balance results obtained, target surface coverage has been estimated. In the period of up to 10 s after discharge ignition, the gettering of O2 by sputtered Ti dominated the process change. In this period, the target surface oxidation rate was low. In the period of 20–50 s, the amount of O2 consumed to target surface oxidation surpassed the amount of O2 gettered by deposited Ti, resulting in a drastic increase in the target coverage. After the target surface oxidation was completed, the process became stable. In this period, the amount of O2 pumped out without causing any process changes increased and a very small amount of O2 was consumed to oxidize the target surface. The ...

Preparation of amorphous Si1−xCx (0≤x≤1) films by alternate deposition of Si and C thin layers using a dual magnetron sputtering source

Abstract Amorphous Si 1− x C x (0≤ x ≤1) films have been prepared by alternately depositing thin Si and C layers on aluminosilicate glass substrates by magnetron sputtering. The apparatus used in the experiment was a dual-cathode sputtering machine with a carrousel type substrate holder. When a substrate passes in front of the cathode by rotating the substrate holder at a rotation rate of 60 rev./min, a thin Si layer of 0.057 nm (d.c. current: 0.2 A) and a thin C layer of 0.028 nm (d.c. current: 0.4 A) were alternately deposited on the substrate, resulting in the preparation of SiC film. The C/Si compositional ratio of films deposited was controlled by changing the discharge power (the flux) of Si and C. The structural, optical and mechanical properties of the deposited films were examined as a function of C concentration ( x ). Results of X-ray photoelectron spectroscopy showed that the film composition changed from x =0 to x =1 with increasing C flux ratio. The peak positions of Si 2p and C 1s shifted also, showing the formation of SiC bond in the films. The X-ray diffraction measurements showed that films deposited were amorphous for all the composition. The maximum hardness of approximately 30 GPa was obtained for a film deposited at x ≈0.5 by a nanoindentation. This value was almost equal to that of a SiC film deposited by conventional r.f. sputtering of SiC. Internal stresses of films ranged from −0.5 to −1.0 GPa (compressive) and were 1/2–1/4 compared to that of the SiC film deposited from a by a conventional sputtering of SiC without rotating substrate.

Imidized organic thin films deposited on glass substrates

Imidized organic thin films were deposited onto glass substrates by rf magnetron sputtering of polyimide (Kapton) target. The mass spectra of sputtered species indicated that target materials were cracked into smaller molecules and the generated films on glass substrates were not identified to be polyimide but wear properties of the films were found to be rather superior to Kapton.

Investigation of the effects of pumping speed and Ar/O2 ratio on the transient time at mode transition in Ti-O2 reactive sputtering

Abstract The effects of the pumping speed and the Ar/O2 flow rate ratio on the transient time needed to reach a steady-state, after glow discharge ignition in Ti−O2 reactive sputtering, were investigated. It was shown that the O2 partial pressure, deposition rate, discharge voltage and the Ti emission intensity change continuously after glow discharge ignition until the process reaches a steady-state. The transient time increases as the pumping speed increases or as the Ar/O2 ratio increases. The results suggest that a low pumping speed or a low Ar/O2 ratio shortens the transient time for process operation parameter changes such as a reactive gas flow rate change.