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.
It has been reported that lubricants are degraded at the head/disk sliding interface of thin film magnetic media as a result of the decomposition of the molecules. The lubricant degradation is a serious problem for the magnetic recording apparatus since it leads to the wear of important magnetic recording layer. One of the possible reactions that result in the decomposition of the lubricant molecules is caused by the electrons emitted from the wearing overcoat surface of the thin film magnetic disk. However, the electron emission mechanism of the carbon films has not yet been investigated in detail so far. This paper discribes the electron emission characteristic of a frictional system of Al203 ball sliding on amorphous carbon(a-C) and hydrogenated carbon(a-C:H) films which are used as overcoat films for the thin film magnetic disk. The characteristic of the electron emission is discussed with the wear mechanism of the carbon films.
In order to develop ultra-thin magnetic films, we investigated the structure and magnetism of Langmuir-Blodgett (LB) multilayers of polydiacetylene by X-ray diffraction and electron paramagnetic resonance (EPR). Using X-ray diffraction, we determined the orders of interlayer and of in-plane directions of the LB films. Upon ultraviolet irradiation, the LB film was found to tilt and to increase the ordering. In EPR measurements, angular variation of linewidth of monomer PDA LB films indicated a spin chain interaction of one-dimension. On the other hand, the polymeric PDA LB films exhibited a drastic extinction of EPR signal due to the onset of antiferromagnetic coupling by the decrease of distance between Mn ions. We concluded that the PDA LB films may permit the novel order structure with the low-dimensional spin magnetism.
We propose a new method for experimentally measuring the electron attenuation length in solid from Auger electron spectroscopic analysis on the aslant-smoothed surface of a metallic multilayer system. The demonstration is performed for the electrons with kinetic energies corresponding to Auger transitions using a ring pattern sputtered surface of Fe and Si02 multilayers. The obtained attenuation lengths are qualitatively in good agreement with the Seah-Dench formalism as well as the TPP-2 formalism for a kinetic energy region of 50 to 1600eV. The experimental values are quantitatively larger than the theoretical ones for Si02, but smaller than those for Fe.
Atomic force microscope (AFM) was used to determine the atomic configuration and topography of the surfaces of KMn8O16 powders containing K ions. By affixing a powder to mica, we successfully determined the first surface structure of KMn8O16 powder. The low-resolution imaging showed that the powder has needle-like crystallites, and the high-resolution imaging revealed that the powder surface has a “faceted”; structure. Periodicities on the faceted plane that correspond to the configuration of surface OH groups and bridging O atoms of the (110) plane was found by the atomic-scale imaging. The close agreement between the images and the bulk structure suggests that the (110) surface of KMn8O16 is a termination of the bulk structure without reconstruction.
Sample bias dependence of plasma oxidation rate of silicon has been studied using real-time ellipsometry and probe measurements. The results reveal that the rate determining process in the ultra thin oxide regime (≤2nm) is different from that in the thick oxide regime (>2nm). In the ultra thin oxide regime the oxidation rate is enhanced not only by positive bias but also by negative bias. The enhancement of the oxidation rate is explained mainly in terms of the collision of electrons with the adsorbed oxygen species by positive bias and also of the collision of cations to surface by negative bias. In the thicker oxide regime (>2nm) the oxidation rate is enhanced only by positive bias and is constant at the negative bias. This reflects that anions and/or neutral species contribute to the oxidation of silicon in the thicker oxide process. The plasma oxidation rate as a function of sample bias exhibits a minimum at around +27V, which corresponds to the plasma potential for short oxidation time, and starts to rise at about +10V, which corresponds to the floating potential for long oxidation times.
Catalytic reactivities of Ni-Fe oxides (atomic ratio of Ni to Fe is 1) prepared by coprecipitation and by physical mixing have been investigated in order to use such oxides in the synthesis of phenol from benzoic acid. It was found that the phenol yield of the oxide prepared by coprecipitation was 3 to 5 times higher than that prepared by physical mixing. Microstructures of these oxides have been studied by analytical electron microscopy (AEM). We found that only for the oxide prepared by coprecipitation about a half of catalyst particles exists as complex particles in which the NiO and NiFe2O4 particles have a coherent relationship. This epitaxial structures might play an important role in the higher catalytic activity of the oxide for phenol synthesis.
Two different methods for CuO powder, mounting using adhesive tape and compressed powder pellets were compared as to how these methods influence the XPS measurements. In Ar+ sputtering, these methods showed differences in the extent of selective sputtering by oxygen and the reduction rate. In a long period of sputtering, the reduction rate was greater with the powders mounted on tapes than with those compressed into pellets. During data acquisition, the amount of carbon on the sample surface on the tape increased with time to a greater extent compared with the pellet sample surface. This is interpreted in terms of the contamination from the tape materials. In addition, the pellet samples gave nearly twice the signal intensity of the samples on tapes and a smaller FWHM value of Cu2p3/2 peak by approximately 0.05eV. These results indicate that the pellet method is better than the tape method in terms of low contamination, signal intensity and energy resolution.
The hydrophobic process of the Si(111) surface was investigated by FT-IR attenuated total reflection (ATR) method using a Si prism. By changing the immersion time in hydrofluoric solution, thermally grown silicon-dioxides and some chemically grown oxides on the Si(111) surface were removed. The variations in the ATR spectra of Si-H and O-H were compared with those in the contact angle (CA) of water on the surfaces. After the removal of the silicon-dioxide film, a hydrophobic surface is formed and Si-H and Si-OH structures appear. The surface structures having low CA (10∼40°) depend on the way to form the oxides. The degree of hydrophobia represented by CA does not directly relate to the quantity of Si-OH. At higher CA (more than 40°) surfaces, the main surface reaction is etching of Si. The growth of terraces and reduction of step-edge structures create a smooth surface and Si-OH structures are gradually removed at the same time. The re-oxidation and the etching process in hydrofluoric solution seem to occur on these surfaces.
A new procedure to obtain accurate SIMS depth profiles of Na in SiO2 has been studied. SiO2/Si samples implanted with Na were treated with HF solution to etch off a certain volume of the oxide. The surface was analysed with SIMS after being coated with Ag. The Na+ intensity at the Ag/SiO2 interface was plotted against the etched off depth and thus the depth profile of Na was obtained. This procedure is useful and easy to perform. It needs no special devices nor systems and has a possibility of wide application to various SiO2 samples.
The cluster model calculations using the discrete variational (DV)-Xα molecular orbital method have been employed to investigate the electronic structure of the silicon nitride surface. It is found that, even though the small silicon nitride cluster is used, the hydrogen termination of edge Si atoms can successfully eliminate the edge effect and give the reasonable electronic structure.