The influence of Mn addition on the Positive Temperature Coefficient (PTC) effect of BaTiO3 ceramic semiconductors is investigated in this report. Mn free and Mn doped specimens were sintered at 1350°C for 1h in air. Mn addition significantly promoted the magnitude of the PTC effect. The activation energy was evaluated from Arrhenius plots of electrical conductivity. The trap densities of the grain boundaries above and below the Curie temperature, Tc, were estimated from the activation energy, permittivity, and mean radius of the grains. Addition of Mn increased the difference between the trap densities above and below Tc. SEM observation of the fractured surface of the specimens revealed the points to be analyzed which correspond to the grain boundaries, and AES spectra were obtained on these analysis points. As a result, no Mn was found at the grain boundaries. It appears that the Mn elements which dissolves in the grains increases the change of the trap density of the grain boundaries at Tc, and this could be one of the causes which promotes the magnitude of the PTC.
Surface electric resistance and chemical state have been investigated for TiO2 bombarded with 8keV ions (B+, C+, N+, O+, F+ and Ne+ ions). The tendencies of the resistivity change by the ion irradiation are divided into three groups; 1) no chemical change but significant decrease of electric resistance is observed (B+ and C+ ions), 2) neither chemical change nor decrease of electric resistance is observed (N+, O+ and F+ ions), and 3) both chemical change and decrease of electric resistance are observed (Ne+ ions). For the Ne+ ion irradiation, a Ti3d-derived new band appears near the Fermi level. It suggests that a part of electrons in its level becomes carrier of the conductivity. On the other hand, the Fermi edge in the UPS spectra remains unchanged for the B+ and C+ ion irradiations, which implies that carrier of the conductivity is positive holes created by the implanted ions.
Factor analysis and Auger electron spectroscopy (AES) were applied to the high resolution depth profiling of a GaAs/AlAs Superlattice grown by metal-organic chemical vapor deposition. Factor analysis was found to be utilized very successfully to extract clearly the depth profile of GaAs/AlAs interfaces from low energy Auger spectra (22∼70eV) containing overlapped peaks of Ga (MMM) and Al (LMM). Since the depth resolution Δz was found to be almost constant for every interface, the sputtering induced roughness was considered to be very small. From the experiments with various Ar+ ion energies EiO (0.5∼3.0 keV), the depth resolution Δz was found to increase linearly with increasing EiO following the relation (Δz=z0O+kEiO). From the comparison of depth profiles obtained from low and high kinetic energy regions, it was suggested that the interface profiles analyses from several different energy regions could give some useful informations about the energy dependency of inelastic mean free path.
The frictional properties of the lubricants on a magnetic thin film medium (evaporated metal tape) are presented. The perfluoro carboxylic acid stearyl amine salt has better frictional characteristics compared with the corresponding amide. The microscopic coverage of the lubricant film on the magnetic medium also is investigated by means of FTIR. The Coverage does not change during friction test for the carboxylic acid amine salt which tightly anchors to the magnetic surface ; the frictional coefficient is low and steady. However for the amide, rubbing contact Causes breaks in the lubricant film, and consequently the dry contact, results in a great increase in friction coefficient ; the amide has a weak interaction with the surfaces.
Chemical activities of fresh surfaces of Cu, Zn, Al, Sn and Pb and copper-base alloys were investigated at room temperature. The fresh surfaces were formed by scratching under high vacuum conditions. Fresh copper surfaces exhibited the highest chemical activity among 1B∼4B metals used. On the other hand, no organic compound chemisorbed on fresh lead surfaces. Judging from the chemisorption activities of organic compounds, the activities of fresh metal surfaces decreased in the following order; Pb < Sn< Al< Zn< Cu. The order of the adsorption activity of organic compounds on the fresh copper surfaces was : ether < sulfide <oleffin and benzene < iodide. The order can be explained in terms of softness of functional groups. XPS measurements revealed that lead was concentrated on scratched surface of Cu-Pb alloys. Chemical activity of Cu-Pb alloy was similar to that of Pb. This can be explained by the concentrated Pb on the fresh surface. The chemical activity of copper-alloys for propyl iodide decreased by the addition of zinc or tin to copper. It was concluded that the chemical activity of fresh surfaces was controlled by chemical properties of metals and the functional groups to be adsorbed.
A new method for the observation of surface morphology of insulating ceramic powders by means of atomic force microscopy (AFM) has been proposed. Several parameters for the measurements, such as the fixation methods of powders on a steel holder, the removing effect of static electricity and the influence of scan rates in AFM operation were examined. The quality of AFM images depended on how the powders were supported. In particular, a clear image was obtained when the powder was rigidly fixed on the holder by use of commercially available epoxy-type adhesives having Shore hardness values of 85 or above. Removal of static electricity by the combined use of an ion-blower and a conductive tip and also by slow-moving scanning of a probe led to a better clarity of the image. A detailed surface morphology (30nm × 3Onm) of silica fine powder could be obtained with a high resolution under the optimized operative conditions for AFM observation.
We studied solid state reactions of magnesium oxide/titanium oxide ceramics superlattice thin films in the air in the temperature range from 525 to 600°C by using X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). Two different kinds of solid state reactions took place at the interface and on the surface. The periodicity of the superlattice, of about 6nm, increased monotonously depending on the annealing time. The change was caused by the homogeneous interfacial reaction between magnesium oxide layer and titanium oxide layer resulting in the growth of inverse spinel crystals (Mg2TiO4). Simultaneously with this process, spinel crystals (Mg2TiO4 or MgTi2O4) were formed as distinctly shown by XRD. It was clarified by HRTEM that these spinels were formed on the surface of the films. The growth rate of the spinel crystals obeyed a parabolic equation. We confirmed that the surface reaction rate was murh hitcher than the interfacial reaction rate.
A SrSe : Ce thin film is expected to be an effective blue-emitting electroluminescent material with a good chromaticity. SrSe and SrSe : Ce thin films have been prepared by utilizing a multisource deposition technique ; their structural and luminescent properties have been investigated. The quality of the films is influenced by the ratio of Sr to Se atoms arriving at the substrates. When the ratio is kept at 1 : 3, stoichiometric SrSe films are formed. The structural property depends on the substrate temperature. The SrSe films prepared at temperatures lower than 400°C indicate to be -oriented and the orientation deteriorates gradually at higher temperatures than 400°C. The crystallinity, on the other hand, becomes better with increasing the substrate temperature. Both photoluminescent and electroluminescent spectra of SrSe : Ce and its EL device demon strate a blue emission with an intensity peak at about 470 nm ; these spectra shift toward longer wavelengths with increasing Ce concentration.
Time-of-flight secondary ion mass spectrometry (TOF-SIMS) has become a powerful tool to analyze surface chemical structures of organic materials. In this study, TOF-SIMS imaging and quantitative analysis were done with two immiscible polymer alloys : polystyrene (PS)/ethylene/ vinyl acetate (EVA) and nylon-6/poly phenylene ether (PPE). It was confirmed that TOF-SIMS imaging technique could be used to identify the micro chemical structure of polymer alloys. In the surface quantitative analysis of these polymer alloys, however, the surface compositions calculated from the characteristic fragment ion intensities varied to a large extent. The maximum scattering of data occurred at near the composition of 1 : 1. The scattering might be caused by differential charging on the polymer surfaces.
Amphiphilic organic single crystals of stearic acid of B- and C-types, sodium dodecylsulfate (SDS) and dodecyltrimethylammonium bromide (DTAB) were observed by AFM. The exposed methyl groups for stearic acid and SDS, and trimethylammonium group for DTAB were imaged as circular formed peaks, but more detailed structure of these groups were not defined. Since the image of the cleavaged surface of stearic acid was easily and reproducibly observed, this will be useful for standard sample of AFM for alkyl organic compounds.
Ultrathin films of LiBr were epitaxially grown on a clean Si (100)-(2×1) substrate by molecular beam epitaxy. The surface and interface phonon (Fuchs-Kliewer mode phonon) in the grown films were measured by high resolution electron energy loss spectroscopy. The intensity and frequency of the F-K phonon depends on the film thickness. The dielectric theory is found to be applicable to 3∼12 nm thick films, but it fails for thinner films.