Susumu Kawase

Investigation of the SiO2/Si interface. II: Oxidation of an HF-cleaned Si(100) surface using photoemission spectroscopy with synchrotron radiation

The surface oxidation process of Si(100), and the distribution of intermediary oxidation states at the SiO2/Si interface have been extensively studied by high resolution (ΔE<0.3 eV) photoemission spectroscopy using synchrotron radiation. The results show that the ratio at the SiO2/Si interface for three intermediary states, Si3+, Si2+, and Si1+ (SiOx), is strongly dependent on SiO2 layer thickness. In particular, the proportion of Si3+ increases with the formation of the 0∼1 nm thick SiO2 layer. However, the three intermediary components at the interface are distributed with ratios of Si3+:Si2+:Si1+=7:2.5:1 in the oxidation stage where a SiO2 layer is formed over 1 nm.

Electron emission properties and surface atom behavior of an impregnated cathode coated with tungsten thin film containing Sc2O3

A new cathode has been developed which shows similar electron emission characteristics as a previously reported Sc2O3 mixed matrix impregnated cathode (Sc2O3 MM Cathode). Contrary to the Sc2O3 MM cathode, the new cathode is resistive to prolonged heating at high temperatures and to ion bombardment. This has been made possible by applying to a standard impregnated cathode a tungsten thin-film containing about 5 weight percent Sc2O3. The electron-emission property is found to be strongly linked to the surface atom composition as well as to the distribution of surface atoms.

Impregnated cathode coated with tungsten thin film containing Sc2O3

An impregnated cathode of a novel structure is proposed, fabricated, and evaluated. A thin tungsten film 100–400 nm in thickness containing various amounts of Sc2O3 is coated on a standard impregnated cathode composed of a porous tungsten body in which electron emissive materials are impregnated. The electron emission property measured with a diode configuration is found to be dependent on Sc2O3 content and surface atom distribution. Surface atom distribution is depicted by means of Auger electron spectroscopy. For high electron emission enhancement it is necessary for Sc2O3 content to be 2.5–6.5 wt. % and for a layer of the order of a monolayer in thickness composed of Ba, Sc, and O to develop on the cathode surface.

Some fundamental properties of Sc2O3 mixed matrix impregnated cathodes

Abstract Some fundamental properties of Sc 2 O 3 mixed matrix impregnated cathodes are studied by means of electron emission measurements and surface analysis is performed by Auger electron spectroscopy. The powders of W and Sc 2 O 3 are mixed and sintered in vacuum to form a porous body in which Ba-Ca aluminate (4BaO·CaO·Al 2 O 3 0 is impregnated. The saturation current density is 10 A/cm 2 at 850–900°C (brightness temperature) for 1–13 wt% Sc 2 O 3 mixed matrix cathodes. This high current density is due to low work function patches distributed over the cathode surface, which is composed of Ba, Sc and O in a certain ratio.

Study of metal film coating on Sc2O3 mixed matrix impregnated cathodes

Abstract Electron emission and surface properties of the Sc 2 O 3 mixed matrix impregnated cathode coated with Ir, Os, Pt and Mo are studied. The cathode is composed of porous body of a metal matrix (5 wt% Sc 2 O 3 in W) and an impregnant of 4BaO·CaO·Al 2 3 , on which metal films of about 500 nm are evaporated. Sc atoms do not appear on the film surface even after prolonged heating at 1150°C, and the coated cathodes do not show the emission anomaly usually seen for Sc 2 O 3 mixed matrix cathodes. The Mo film, however, alloys easily with W in a short heat treatment time and the Sc atoms are distributed nonuniformly over the surface. The Mo coated cathode does show the emission anomaly. A simple coating with Sc film on the ordinary W matrix cathode reveals neither the surface properties nor the emission properties of Sc 2 O 3 mixed matrix cathodes.

Electron emission properties and surface atom behavior of impregnated cathodes with rare earth oxide mixed matrix base metals

As an extension of the work on Sc2O3 mixed matrix impregnated cathodes, mixed matrix cathodes containing rare earth oxides of 12 kinds are fabricated, and their electron emission properties and surface atom behavior are examined. According to the level of the saturation current density, cathodes can be classified into three groups. The cathodes are also classified into two groups depending on the type of surface atom distribution. The saturation current density level relies more upon the composition of the surface layer of Ba and O as well as the binding energy of the surface layer on cathode surfaces, rather than upon the type of surface atom distribution. The low work function surface layer unique to Sc2O3 mixed matrix cathodes is not found in this work on the impregnated cathode with rare earth oxide mixed matrix base metals.

Influence of Ion Sputtering on Auger Electron Spectroscopy Depth-Profiling of GaAs/AlGaAs Superstructure

The resolution of depth profiling by Auger electron spectrscopy (AES) changes depending on ion sputtering conditions due to implanted ion effects such as knock-on and cascade mixing. To evaluate the influence of these effects on depth profiling, profile broadening due to ion sputtering was measured using different levels of energy and species of ions. In addition, the altered layers thickness was estimated.

Some fundamental properties of zirconiated W(100) field‐emission cathode

Fundamental properties of zirconiated tungsten field‐emission cathodes are examined in order to clarify their high current stability mechanism. High stability is found to be restricted to (100) faces, on which a Zr‐O complex is formed, preventing adsorption of gases such as H2, CO, and CO2 at moderate temperatures (1200–1500 °C). As the Zr‐O layer is immobile, current fluctuations induced by Zr‐O migration are minimum. In order to maintain high stability, especially long‐term stability, a well controlled oxygen supply is necessary.

Auger electron emission micrographic studies of the cleavage surface of graphite single crystal

A new primary beam scanning Auger electron energy analyzer was constructed. The diameter of the primary beam is about 3 μm at 9 keV. Using this apparatus, Auger electron emission microanalysis was carried out on the cleavage surface of a natural graphite single crystal by selecting analyzing points in the sample current image of the specimen surface. In addition, by synchronizing the scanning of the primary beam on the specimen surface with the flying spot of the cathode ray tube, Auger emission micrographs were obtained as the brightness modulation due to a particular Auger spectral line emitted from the specimen. By analyzing the microanalysis spectra, the micrographs, and the sample current images, the chemical composition and the texture of the specimen surface were determined with a spatial resolution of 3 μm.

Photoemission studies of Si(100) oxidation process (abstract)

Photoemission spectroscopy using synchrotron radiation is a powerful tool to investigate electronic states of solid surfaces. In the present study, the oxidation process of the Si(100) surface has been extensively examined. Experiments were carried out with soft x‐rays monochromatized by the grazing incidence monochromator,1 at beamline 8A at the Photon Factory. The energy resolution, including both the electron energy analyzer (a double‐pass type CMA) and the monochromator, was estimated from the Au Fermi edge. The Au foil was sputter cleaned by Ar ions. For the photon energy between 40 and 200 eV, the resolution is about 0.3 eV with electron pass energy of 10 eV and monochromator exit slit width of 10 μm. The oxidation process of a Si(100) surface has been examined in situ at the base pressure of 5×10−8 Pa. The Si(100) clean surface is obtained by repeating Ar ion sputtering and annealing. We have measured the Si 2p photoelectron spectra of the Si(100) surface exposed to oxygen. At the early stage of 20...