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Macroporous (mp-) In2O3-based microspheres as a NO2 sensing material were prepared by the pyrolysis of atomized In(NO3)3 aqueous solutions containing polymethylmethacrylate (PMMA) microspheres (150 nm in diameter) as a template. Well-developed spherical macropores (less than 100 nm in diameter) reflecting the morphology of the PMMA microsphere templates could be formed in the In2O3-based microspheres. The introduction of macropores into In2O3-based microspheres was very effective in improving the NO2 response of their thick films fabricated on an alumina substrate equipped with interdigitated Pt electrodes (gap size: ca. 200 μm) by screen-printing. In addition, the addition of a little amount of SnO2 to the mp-In2O3 microspheres not only lowered the resistance in air but also improved the NO2 response. NO2 sensing properties of non-stacked microspheres of the mp-In2O3 mixed with SnO2 were also investigated by utilizing nano-gap Au electrodes (gap size: ca. 200 nm). The non-stacked microspheres showed fast response and recovery speeds to NO2, because of better diffusion capability of NO2., Sensors and Actuators B: Chemical, 151(1), pp.265-273; 2010

The CNTs with 20–50 nm in diameter were directly grown on Au microgap electrode by means of thermal CVD at700∘C for 60 minutes under EtOH-Ar-H2atmosphere (6 kPa). The CNTs with entangled shape formed the network structure with contacting each other. In the CNTs-WO3composite,WO3grains with disk shape (50–200 nm) were independently trapped. The CNTs-WO3composite sensor showed the fairly good sensor response (Ra/Rg = 3.8 at200∘C). The sensor response was greatly improved with CNTs-WO3composite, comparing with that of CNT sensor (Ra/Rg = 1.05). This phenomenon can be explained by formation of p-n junction, between CNT(p) andWO3(n), and thus improvement ofNO2adsorption. The sensor response was decreased with increasing theWO3amount in CNTs-WO3composite, suggesting the electronic conduction due toWO3connection.

This paper deals with a pyrolyzed polymer as a kind of carbon materials obtained by pyrolysis of polymers. Through a combination of micromachining of polymers and following pyrolysis process, we can obtain pyrolyzed polymer MEMS structures for various applications. This work focuses on the effect of NO2 gas adsorption on electrical properties of pyrolyzed polymers. The resistance of the sensor is dramatically decreased when the sensor is exposed to the NO2 gas. It is found that low pyrolysis temperature and high operating temperature contribute to higher sensitivity against gas mixture of NO2.

The WO3 thin film nanosensors have been fabricated by dropping and calcination of H2WO4 suspension onto Au nano-gap electrode (100 nm of gap-size and 10 µm in width), which was fabricated by means of MEMS (Micro Electro-Mechanical Systems) techniques, photolithography and FIB. The amount of WO3-electrode interface was controlled by changing amount of WO3 grains packed in the nano-gap electrode. The sensitivity to dilute NO2 was increased with increasing amount of interface, suggesting the importance of oxide-electrode interface in NO2 sensing. Further, the response behavior was affected by the amount of WO3 grains packed in nano-gap electrode.

Nickel pyrophosphates containing metal cations were prepared from aqueous solutions. The obtained phosphates were characterized with inductively coupled plasma (ICP), differential thermal analyses (DTA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), specific surface area, acid strength, amount of acidic sites, and adsorbed carbon measurements. The phosphates were used as a catalyst for decomposition of trifluoromethane. The kinds and ratios of metal cation added were discussed. The nickel pyrophosphate catalysts containing magnesium had higher selectivity to CO 2 and longer lifetimes than aluminum orthophosphate for decomposition of trifluoromethane.

A semiconductor gas sensor using SnO 2 was loaded with acidic or basic oxides (5 wt.%) to investigate ethanol-gas sensing properties and related catalytic properties. The sensitivity to ethanol gas at 300°C increased tremendously with an addition of a basic oxide (e.g., La 2 O 3 ), while it hardly changed with that of an acidic oxide (WO 3 ). It turned out that the addition of the basic metal oxide to SnO 2 brought about enhancement of catalytic activity not only for the dehydrogenation of ethanol gas to CH 3 CHO but also for the consecutive oxidation of CH 3 CHO to CO 2 . On the other hand, the acidic metal oxide enhanced only the dehydration reaction, showing even an adverse effect on the consecutive oxidation. Based on these results, it was concluded that the enhancement of the catalytic oxidation activity to an appropriate level could be a reason for the high sensitivity to ethanol gas for the sensors loaded with basic oxides, particularly one loaded with La 2 O 3 .

Aiming at developing a semiconductor CO sensor applicable to the safety control of gas appliances, we carried out an extensive material search for promoters to In2O3-based elements. Among the elements added (0.5 wt%) with each of 12 transition metal oxides, the Co3O4-added one was outstanding in sensitivity and selectivity to CO at 200°C. Remarkably the sensing properties of this element could be improved further by the addition of Au (0.04 wt%). The doubly promoted element, Au (0.04 wt%)-Co(0.5 wt%)-In2O3, gave excellent characteristics in sensitivity to CO, selectivity to CO over H2 and other selected gases, and response rates at 250°C. The promoting effects of the additives were shown to originate from the proper enhancement of catalytic activity for CO oxidation.

Metal oxide-based semiconductor gas sensors have been exploited for detecting various odorous components generated in the process of aging and/or putrefaction of beef, such as ethyl acetate, isoamyl alcohol, acetoin, and so on. Among various sensor elements tested, WO3(5wt%)-ZnO showed the highest sensitivity to ethyl acetate (20ppm in wet air) at 500°C. On the other hand, acetoin could be detected with excellent sensitivity and selectivity by WO3(0.5wt%)-ZnO element at 300°C. The effect of WO3 additive was evalutated in the catalytic oxidation of acetoin over ZnO-based materials. As a result, the increase in acetoin sensitivity was found to be correlated with the catalytic activity in oxidative dehydrogenation of acetoin to diacetyl. These two elements obtained appeared to be applicable to evaluate beef freshness. Actually, it was confirmed that the sensitivities of these sensors to the headspace volatiles of the beef kept at 5°C increased gradually during the preservation term of 5 days.

Tin dioxide thin films of various thicknesses up to 150 nm were prepared on quartz glass substrates from a sol solution of SnO2 (particle size 3 nm) by a spin-coating method and subjected to calcination at different temperatures up to 800°C for 30 min. The grain size of SnO2 was found to be far smaller than those obtained from the SnO2 sol-derived powder under the same calcination conditions. The suppression of grain growth of SnO2 was more conspicuous as the film thickness decreased so that in the thinnest film (20 nm thick) the SnO2 grain size remained as small as 6 nm after calcination at 800°C. It is suggested that the SnO2 grains in the ultrathin film deposited on the substrate are restrained from moving and coalescing with each other, resulting in the suppression of grain growth.

The sensitivity of a semiconductor sensor using SnO2 to H2S in air could be enormously promoted by loading SnO2 with a small amount of CuO. However, response kinetics began to deteriorate rather sharply as the H2S concentration decreased below a certain limit, which depended on CuO loadings. XPS measurements on a series of CuO-SnO2 samples calcined in air revealed that the binding energies (BEs) for O1s and Sn3d5/2 levels shifted downward from those of pure SnO2, while Cu2p3/2 level showed an upward shift from that of pure CuO. With increasing CuO loading, the shifts in BE increased or decreased linearly for O1s and Sn3d5/2 levels or Cu2p3/2 level, respectively, indicating continuous shifts in Fermi levels of SnO2 and CuO. For a fixed CuO loading, the magnitudes of the BE shifts were dependent on the methods of CuO loading, reflecting differences in the dispersion of CuO particles on SnO2 grains. These phenomena were well consistent with the formation of p-n contacts between the finely dispersed CuO (p) and the underlying SnO2 (n) grains. The sensitivity to H2S was shown to be well correlated with the magnitudes of the BE shifts, indicating that the formation of the p-n contacts in air and the rupture of them upon exposure to H2S are the origin of the high H2S sensitivity.

A sensor array system was composed by using four gas sensor elements based on semiconducting oxides, i.e., Rh(0.4wt%)-WO3, MoO3(5wt%)-ZnO, Er2O3(5wt%)-ZnO and Pr6O11(5wt%)-Fe2O3. These elements were sensitive and selective to the important flavor components of beef consomme soup of methylpyrazine, acetone, capronaldehyde and dimethyldisulfide, respectively. Upon exposure to the vapor of consomme soup, the sensor array was found to give a sensitivity pattern which changed sensitively depending on the quality of consomme soup. This suggests the possibility of applying such a multi-sensor array system for the soup-quality control.

Iron oxide-based semiconductor gas sensors were exploited for detecting dimethyldisulfide (DMDS) gas, an important flavor component of consomme soup. Among the various metals and metal oxides tested, Pr6O11 was the most effective additive to Fe2O3 for promoting the sensitivity to DMDS vapor (20 ppm) in air at 300°C, giving the highest sensitivity at a Pr6o11 content of 5wt%. The sensor using 5wt%Pr6O11-added Fe2O3 was also fairly good in selectivity to DMDS among various flavor components of consomme soup. As characterized by XRD, 5wt%Pr6O11-added Fe2O3 system contained no crystalline phases other than Fe2O3, while PrFeO3 was observed at Pr6O11 contents of 1Owt% and above. The Pr4+/Pr3+ ratio as revealed from XPS analysis remained far higher for Pr6O11-added systems than that for pure Pr6O11, though it tended to decrease with increasing Pr6O11 content. These results suggest that, at low Pr6O11 contents, a major part of Pr components added exist as finely dispersed Pr4+ species on the surface of Fe2O3 particles and that such surface Pr4+ species are responsible for the observed enhancement of gas sensitivity to DMDS.

The titania nanotube arrays (TNAs) with smooth surface was synthesized by anodization of titanium foil with 3 cm2in square area using the electrolyte composed of 0.2 wt% NH4F and 0.5 vol% H2SO4in ethylene glycol in order to evaluate the methylene blue photodegradation under ultra-violet irradiation. The tube length and inner diameter as a size parameter were controlled by the anodization time from 5 to 10 h and applied voltage from 10 to 50 V. The titania nanotube arrays (TNAs) annealed at 300 to 500°C were assigned to anatase phase, and TNAs at 600°C had both phase of anatase and rutile. The crystallite size and the apparent rate constant were increased with the increase in the annealing temperature of TNAs from 300 to 500°C. The bigger crystallite size of TNAs is suggested to be related to the increase in the amount of hole at the valence band, leading to the decrease in the apparent rate constant of MB degradation. Interestingly, the four kinds of linear relationship with the apparent rate constant were seen in both the inner diameter of TNAs and the length. Consequently, the apparent rate constant strongly depended on inner diameter of TNAs.

In order to improve the sensitivity to NO in air, WO3 based sensor elements were loaded with a small amount (0.004 wt%) of noble metals. Among the various noble metals added, Au and Ru were found to be effective promoters. The addition of Au enhanced the sensitivity to 200 ppm NO in air by about one order of magnitude, making the Au-loaded element attached with Pt electrodes the most sensitive to NO in the temperature range (200∼500°C). Ru-WO3 element also exhibited high NO sensitivity at 250 and 300°C, but the promoting effect of Ru quickly decreased as temperature increased. Such promoting effects were hardly consistent with the catalytic activity of the noble metals for the oxidation of NO to NO2, which were in the order Pt>Ru>Au=0. TPD experiments provided evidence supporting that the enhancement of the oxidative adsorption of NO as NO2 would be a major reason for the promoting effects of Au and Ru.

In order to stabilize ultrafine particles of SnO2 which is essential to obtain high gas sensitivity, a systematic investigation was undertaken regarding the stabilizing effects of 5 at% impregnated foreign additives, consisting of oxides or polyoxy compounds of 31 metals and 3 non-metals. The data of specific surface area, SA, as well as SnO2 crystallite size, D, evaluated from X-ray diffraction showed that the additives could be classified into several groups according to the effectiveness. The most effective group, consisting of P-Ba, Sm, Ba, P, Mo, W, Ca, Sr, Cr and In, could keepD less than 10 nm even after calcination at 900°C, whereas pure SnO2 underwent grain growth to haveD of 13 and 27 nm at 600 and 900°C, respectively. Electron microscopy revealed that neck sizes, X, between crystallites were fairly proportional toD(X/D = 0.80). A simple analysis of SA and D data based on a monosized sphere model suggested that each crystallite was coordinated with 3–4.5 neighbours through the necks. The existing state and stabilizing mechanism of additives are discussed in conjunction with the electrical resistance of porously sintered elements.

In an effort to develop a semiconductor type NH3 sensor, the NH3 sensing properties of WO3 semiconductors loaded with colloidal noble metals were investigated. Among the various noble metals tested, Au was proven to be the most excellent promoter for the WO3-based NH3 sensor, whereas Pt gave a very high NH3 sensitivity at 200°C, but the response was too slow. Thus Au-WO3 element could respond to NH3 in air over a wide NH3 concentration range of 5 ppb-50 ppm at 450°C, showing excellent characteristics in both NH3 sensitivity and response rate. An optimum Au loading amount was shown to be 0.8 wt % with respect to the NH3 sensitivity. The electrical resistance of Au-WO3 element in air increased with an increase in Au loading. From the measure-ments of Seebeck coefficients it was revealed that the Au particles loaded interact with WO3 and take the conduction electrons away when exposed to air, while those electrons are given back to WO3 on exposure to NH3-containing atmospheres. It is concluded that such an electronic interac-tion between Au and WO3, susceptible to a change in atmosphere, is responsible for the prominent promoter action of Au.

Pd-SnO2ガスセンサーにおけるPdの増感効果を基礎的に理解するため,SnO2上に担持されたPd粒子の存在状態(粒子径,分散度,形態)をTEMにより明らかにするとともに,Pd-SnO2問の電子的相互作用をXPSにより調べた。900℃ で焼成して粒子をある程度大きく成長させたSnO2粉末を用いることにより,明瞭なTEM像が得られた。粒子の形状は,還元状態(Pd)では球形に近いが,酸化状態(PdO)では半球形に変化し,PdOの方がSnO2と強く接合することが示唆された。また,いずれの状態でもSnO2とのエピタキシーが認められた。Pd平均粒子径は,担持量3wt%以下では5nmと比較的小さいが,5wt%となると10nmと急激に増大した。これを反映して,試料1g当たりのPd表面積,および単位SnO,面積当たりのPd粒子数(粒子密度)は,どちらも3wt%で極大値を示した。Sn3dおよびO1sのXPSシグナルの束縛エネルギー(BE)は,酸化状態では純粋なSnO2にくらべて低BE側にシフトし,シフト幅は担持量に依存して3wt%で極大となった。一方,還元状態ではシフトが完全に消失した。このようなシフトはPdO-SnO2接合部での強い電子的相互作用によるものであり,その大きさはSnO2表面における接合点の密度によって支配されると推定される。

Nd-doped BaTiO3 nanopowders with ca. 200 nm in average diameter were prepared by hydrothermal synthesis at 200 and 240 °C for 24 h. Neodymium (III) nitrate hexahydrate (Nd(NO3)3·6H2O) as a donor dopant was added to the powder mixtures of barium hydroxide (Ba(OH)2) and titanium dioxide (TiO2) ranging from 0.25 to 0.45 mol%. A green compact of the powder mixtures obtained was heated at 1340 °C for 2 h with/without three steps of ramp heating processes. Sintered without these steps, 0.35 mol% Nd-doped BaTiO3 with the resistivity of 124 ohm·cm at R. T. indicated insufficient PTCR effect; resistance change of 3 × 102 in the vicinity of Curie temperature. On the other hand, a pellet of 0.35 mol% Nd-doped BaTiO3 sintered via the step-heating process exhibited the large resistance change of 7.5 × 103.

Four types of WO3 particles, spherical, disk, cuboid, and hexagonal, were prepared and WO3 film sensors were deposited on Au comb-type microelectrodes by dropping suspension using the various WO3 powders obtained. The sensing properties to dilute NO2 revealed that the cuboid WO3 film sensor had the best response-recovery characteristics with the 90% response and 90% recovery times of 1.3 and 0.9 min to 0.05 ppm NO2 at 200°C, respectively. On the other hand, the hexagonal WO3 film sensor showed extremely high sensor response of 41.1 even to 0.01 ppm NO2 at 200°C, but the sensor response fluctuates widely with the operating temperature ranging from 80 to 300 °C. The adsorption-desorption behaviours of NO2 on various surfaces of WO3 particles with different morphologies were investigated using temperature programmed desorption (TPD) technique, which suggesting that NO2 molecules were adsorbed easily on the WO3 surface. The desorbed amount of NO decreased in the order of hexagonal, cuboid, disk and spherical, which agreed with the respective sensor response of the four WO3 film sensors.

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The structure of the Ru film prepared by the RF sputtering method changed with film growth. This influenced the activity and the selectivity in the hydrogenation of 1,3-butadiene. It has been found that the partial hydrogenation of 1,3-butadiene proceeds preferably over (002) face of Ru.

PIV組成比(原子比)がo.75～1.70の触媒を調製して,XPSによる表面分析を行い,触媒表面の酸化状態や表面組成を調べ,ブタン酸化触媒能に与える影響について検討した。触媒の表面状態は,触媒調製法や焼成条件(温度,時間,雰囲気)またP/V(パルク)比により大きく異なり,N2気流中で焼成した場合,触媒表面のバナジウムの酸化数はほぼ四価であったが空気中で焼成すると五緬が主となった。ブタン酸化反応後の触媒表面状態には,PIV(バルク)比の影響が顕著に現われ,N2気流中焼成した触媒は,P/V＜1.0において表面バナジウムの一部が五価に酸化された。これに対し空気中焼成した触媒は,表面に多く存在するV5+がP/V＞1.0においてブタン酸化反応糊気中,V4+に還元された。このようにリンが過剰に存在すると,触媒反応時にV4+按定化させる効果が顕著であった。一方,触媒表面のリンの酸化数は,焼成雰囲気によらず五価と考えられるが,PIV比が1.0～1.1付近においてBE値にシフトが見られ,リンの結合状態がP/V比により異なるものと示唆される。V-P系触媒の仕込(バルク)組成と裏面組成との関係を調べたところ,パルク組成が0.85を越えるとリンが多くなり,さらに表面組成がプラトー(PIV=1.6～1.9)になる領域が見られた。このような触媒を用いてブタン酸化反応を行ったところ,無水マレイン酸(MA)選択性は表面組成に大きく依存し,表面組成がプラトーとなる領域において最大となった。したがって,選択的なMA生成活性はバルク中に(VO)2P207相を含み,その表面にリンが豊富なプラトー表面層(P/V=1.6～1・9)が形成したものが有効と示唆され,この表面層がMA生成に選択的な表面を提供するものと考えられる。

Palladium-(boron, phosphorus) thin films have been prepared by an RF sputtering method. The palladium f c c structure was destroyed by adding boron or phosphorus and the palladium films finally became amorphous in structure. Boron, whose interaction with palladium was very weak, donated electrons to palladium, whereas phosphorus accepted electrons from palladium. The palladium-(boron, phosphorus) films showed high selectivity (above 97%) for the partial hydrogenation of diolefins (cyclopentadiene and 1,3-butadiene) and acetylene. The activity and the selectivity changed with the boron or phosphorus concentration. The changes in the selectivity were explained in terms of the ensemble and the ligand effect in the palladium films. It was found that the palladium-boron films with PdB like structure and the amorphous palladium-phosphorus films were excellent for partial hydrogenation.

Pd–(B, P) thin film alloys have been prepared by an RF sputtering method. Before heat treatment, the selectivity for the partial hydrogenation of olefins increased with the increase in the B or P concentration in the Pd–(B, P) films. After the heat treatment, on the other hand, the selectivity for the partial hydrogenation was reduced over the Pd films with a low B or P concentration. However, in the case of the Pd films with a high B or P concentration, the selectivity was enhanced by the heat treatment. The high selectivity after the heat treatment was explainable in terms of the small ensemble size, the low electron density of Pd, and the appearance of a Pd3B, Pd4.8P, or Pd5P2 phase in the Pd films with a high B or P concentration. A sputtered film is known to have a columnar structure. This columnar structure was deduced to be controlled both by the alloying of Pd with B or P and by the heat treatment, so as to exhibit the high selectivity for the partial hydrogenation of olefins.

アモルファス薄膜Ni-B合金を,グロー放電を用いたRFスパッタリング法により薄膜状に調製した。ターゲットには高純度ニッケルヒ板を,放電ガスにはアルゴン,ジボラン(B2H6),ならびに水素の混合ガスを用い,放電ガス圧を6～33Paとしてグロー放電を行ない,パイレックスガラス板上に合金薄膜を付着させた。合金の表面組成と表面状態を,X線光電子分光法(XPS)により測定した結果,放電ガス組成を変化させることにより種々の組成のアモルファスNi-B薄膜合金を調製できることがわかった。またXPSのNi2p3/2レベルのスペクトルにおいて,ホウ素濃度増加とともにサテライトピーク強度が弱くなり,その位置が主ピークから離れ,また主ピークの対称性がよくなった。これは,ホウ素濃度増加とともにニッケルの電子密度が高くなることを示し,ホウ素からニッケルへ電子が移動していることがわかった。このようにニッケルの電子密度の異なる種々の組成のNi-B合金を用いて,1,3-ブタジエンの水素化反応を行なったところ,その生成物分布に変化が見られた。これについてニッケルの電子密度と関連づけて説明することができ,ニッケルの電子密度増大とともにニッケルの水素化能が増大することがわかった。

Pd films prepared by the UHV RF sputtering system had the tapered columnar structure as observed using SEM. The microstructure of the films changed with the film thickness. This affected the hydrogenation of acetylene. The Pd films which showed the strong (220) intensity in XRD exhibited the high ethylene selectivity.