Akinori Ohshita

Bulk plasmons in solid C60

Electron energy-loss spectra in a low loss region have been obtained from solid C60 by a 200 keV transmission electron microscope equipped with an electron energy analyzer. Bulk plasmons are observed at two characteristic energies, 6.5 and 26 eV, being attributed to collective oscillation of π-electrons, and to that of all the valence electrons (both the π- and σ-electrons), respectively.

Interference fringes observed in electron emission patterns of a multiwalled carbon nanotube

Field electron emission patterns from a MWNT with clean surface exhibit fine structures originating from pentagons located at the tip end. The field emission microscopy (FEM) has resolved six pentagons each of which has a small dark spot in its center. Moreover, the bright streaks have been observed at the boundary regions between adjacent pentagons. By calculations based on the formula of Youngs interference of two beams, Oshima et al. (2002) reported that the observed streaks are interference fringes. In this paper, we show experimental results to prove that the streaks are Youngs interference fringes.

Electron Energy Loss Spectrum Near Carbon K-Edge in Solid C60

The carbon K-edge excitation spectra of solid C60 have been obtained using electron energy-loss spectroscopy. In the near-edge region, in addition to the π* and σ* resonance bands well known for graphite and amorphous carbon, a shoulder is found at 289 eV, suggesting the presence of a peak in the density of unoccupied π* states. Another feature discernible to the solid C60 is the width of the σ* resonance band; it is about 15 eV, which is an intermediate value between those for graphite and amorphous carbon.

Oriented Tungsten Field Emitter Coated with Liquid Lithium Thin Film

Field electron emission patterns from a -oriented tungsten tip coated with liquid lithium film were observed. For the film thickness between 5 and 30 nm, emission patterns showed the formation of liquid lithium cones on the facets of the tungsten surface. The Fowler-Nordheim plots showed the presence of the space charge effect. The increase of the number of liquid cones with tip voltage was qualitatively explained in terms of the space charge effect. For the film thickness more than 30 nm, only pulsed explosive emission was observed.

A FEM study of liquid lithium on a 〈011〉-oriented tungsten tip

Abstract Field electron emission patterns from a 〈011〉-oriented tungsten tip coated with a liquid lithium film were observed. For the deposition thickness between 20 and 120 nm, emission patterns suggested the formation of liquid cones on the facets of the tungsten surface. Changes in emission current and patterns with the tip voltage were qualitatively explained in terms of the space charge effect. Though the emission current decreased linearly with time in the rate of 1.5 μA/min, its fluctuation was lower than 1%. For a film thicker than 120 nm, only pulsed explosive emission was observed. When the polarity of the tip voltage was reversed, this beam source operated as a liquid metal ion source.

Interference fringes observed in electron emission patterns of a multi-wall carbon nanotube

Field electron emission patterns from a MWNT with clean surface exhibit fine structures originating from pentagons located at the tip end. The field emission microscopy (FEM) has resolved six pentagons each of which has a small dark spot in its center. Moreover, the bright streaks have been observed at the boundary regions between adjacent pentagons. By calculations based on the formula of Youngs interference of two beams, Oshima et al. (2002) reported that the observed streaks are interference fringes. In this paper, we show experimental results to prove that the streaks are Youngs interference fringes.

Control of formation sites for liquid-Li cones on a W〈100〉 tip by means of the remolding method

Abstract For a liquid-Li coated W〈100〉 field emitter tip, control of the formation sites of field-stabilized Li cones was tried by applying the remolding method to the substrate W tip. Observation of the field emission patterns showed that the field-stabilized cones are reproductively formed on the remolded facets, namely (310), (411) and (111). This means that remolding is a useful method for control of the formation sites of the liquid-Li cones and the cones are formed on the facets on which strong electric fields exist.

The development of a new field emission source applying electrohydrodynamics of liquid metal

Abstract For liquid-Li coated W〈310〉 and W〈100〉 field emitters, the variations of electron emission patterns and electron emission currents with tip voltage were investigated by field emission microscopy, and they were compared with the result for a W〈110〉 tip, already reported. It was found that stable liquid-Li cones are formed on the {111} and {310} facets of the W tip. The characteristics of the total emission current against the tip voltage were similar to that for a W〈110〉 tip, and large total emission currents were obtained.

Control of emission current from a Li/W〈111〉 field emitter by sequential deposition of Li

Abstract For a W〈111〉 field electron emitter deposited with liquid Li, a field-stabilized cone of liquid Li is formed on the emitter tip and an electron beam with several hundreds of microamperes is emitted from the cone apex. However, the emission current decreases gradually with time because of the evaporation of deposited Li and the lifetime is about an hour. In order to prolong the lifetime, in this paper, we tried sequential deposition of Li whose amount corresponded to consumption by thermal evaporation. As a result, electron emission with a fluctuation of about 10% continued for more than 10 h. The critical pressure for stable electron emission was also investigated. An abrupt decrease of emission current was observed at the exposure of about 1 l of dry air. The decrease is probably caused by the solidification of the liquid Li at the emitter surface.

Stabilization Mechanism of Liquid-Lithium Cones during Field Electron Emission

For a liquid-lithium coated W field emitter tip, the mechanism of stabilization of the liquid cone during electron emission was investigated by the use of a probe-hole type field emission microscope. A single liquid-lithium cone was formed on the optical axis using a (111)-remolded tip and the emission current from the single cone was measured. An oscilloscope trace of the emission current passing through a small probe hole indicated a stable direct current with a fluctuation of less than 0.1%. The probe current obeyed the Child-Langmuir law approximately, and therefore it is reasonable to consider that the liquid-lithium cone is stabilized by the space charge. The angular intensity reached about 30 mA/sr at a total emission current of 300 µA.