Seiji Yamamoto

Scanning tunneling microscopy and atomic force microscopy study of graphite defects produced by bombarding with highly charged ions

The defects produced on a graphite surface by single ion impact using highly charged Ar ions (charge state q⩽8) is investigated by scanning tunneling microscopy (STM) and atomic force microscopy (AFM). The defect looks like a protrusion in the STM image, while it is flat in the AFM image. From these two contrasting images, the defects are considered to be due to the increase in the local charge density of state at the surface caused by carbon atom sputtering. The average value for the defect size increases remarkably with the charge state of incident Ar ions. This is explained by the enhancement of potential sputtering due to the Coulomb repulsion between surface holes which are generated by the neutralization of highly charged Ar ions.

Stability of carbon field emission current

The stability of field emission (FE) current is evaluated for glassy carbon FE tips. Experimental findings are as follows: (1) Instability is proportional to the product of FE current level and the pressure under operation. (2) Instability is large for CO ambient and small for H2 ambient. (3) Instability consists mainly of steps and spikes instead of 1ƒ type. (4) Instability is reduced by heating the lip during operation. As a result, it is concluded that instability is due to dislodgement of adsorbed molecules on the tip surface by impinging ions formed near the tip by FE electron beam bombardment.

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.

Field emission characteristics of carbon tips

Field emission (FE) of glassy carbon tips is investigated. Experimental FE characteristics are as follows: (1) The decrease in FE current after flashing is very small or not recognized. (2) The FE current (about 1 micro A) is more stable than that of a tungsten tip for the same conditions as time increases. Current instabilities appear as step-wise fluctuations. (3) Instability dependences of FE current on ambient gases are in decreasing order, CO, H2O,O2 and H2. Dependence on CO is particularly remarkable. (4) FE angle is confined to 14–15 of that of a conventional tungsten tip, and depends only on geometrical tip shape.

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.

Application of an impregnated cathode coated with W-Sc2O3 to a high current density electron gun

Abstract The electron emission properties of a previously proposed [1,2] W-Sc2O3-coated impregnated cathode are evaluated in a high current density electron gun. It is found that the cathode can be operated at a temperature 100–150°C lower than that of Os-coated impregnated cathodes usually operated at 1000°C for a beam average current density of ∼5 A/cm2. The superiority of this cathode increases when used in high resolution, high brightness electron guns where the electron extracting field is high at the cathode surface.

Desorption induced by electronic potential energy of multiply charged ions

Abstract Particle desorption is investigated in terms of bombardment of a GaAs surface by slow multiply charged Ar ions (charge state q ⩽ 9, kinetic energy E k ⩽ 3 keV). The desorption yield of Ga and As atoms as well as H + ions drastically increased with the charge state of the incident Ar ions, but was changed little by the kinetic energy of the Ar ions. These results demonstrate that desorption reactions at the surface are greatly enhanced by the potential energy of the incident ions. From an analysis of the potential energy dependence of the desorption yield based on the Coulomb explosion model, it is found that the lifetime of multiple holes created by the multiply charged Ar ions is longer than that of a single hole by 2 to 3 orders of magnitude.

Positive Charge Generation at a SiO2/Si Interface due to Bombardment with Metastable Atoms.

The influence of metastable atoms on a SiO2/Si structure is examined to determine the source of damage in ULSI devices during plasma enhanced processes. Holes were generated at the SiO2 surface by the impact of metastable atoms of rare gases. Holes trapped at the interface formed positive charges, and the density of these positive charges increased with the increasing energy of the metastable atoms. The yields of the positive charge generation were between 0.01 and 0.1, which are on the same order as those caused by vacuum ultraviolet photons, and these values are not negligible. Thus, the influence of metastable atoms must be taken into consideration to control the damage that occurs during plasma enhanced processes.

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 (1200–1500u2009°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.

Low‐temperature synchrotron‐radiation‐excited etching of silicon dioxide with sulfur hexafluoride adsorption

Ultralarge‐scale integration circuits now require innovative microfabrication processes in order to achieve gigabit‐scale integration. One approach is to use soft x rays, because they can give excellent spatial resolution by their short wavelength and high‐reaction selectivity by core‐electron excitation. Synchrotron‐radiation (SR) ‐excited etching of SiO2 and Si is studied from the viewpoints of pattern replicability and analysis of etching selectivity between two layers. Deep‐submicron patterns of SiO2 are formed by cooling the specimen with liquid N2 and adsorbing SF6 reaction gas during SR irradiation. Photon‐stimulated desorption ions from SF6‐adsorbed SiO2 and Si surfaces are first investigated. As a result, ion species such as SiF+n and SO+n, which are etching products from the surface, are obtained only from SiO2, and this selective etching of SiO2 is also investigated by x‐ray photoelectron spectroscopy. In this selective etching mechanism, constraint of Si‐etching by passivation of photofragment...