Chuhei Oshima

Highly efficient electron gun with a single-atom electron source

The authors have demonstrated highly collimated electron-beam emission from a practical electron gun with a single-atom electron source; ∼80% of the total emission current entered the electron optics. This ratio was two or three orders of magnitude higher than those of the conventional electron sources such as a cold field emission gun and a Zr∕O∕W Schottky gun. At the pressure of less than 1×10−9Pa, the authors observed stable emission of 20nA, which generates the specimen current of 5pA required for scanning electron microscopes.

Direct Confirmation of the High Coherency of the Electron Beam from a Nanotip

The coherency of an electron beam from a nanotip was evaluated and compared to that from a tungsten (110) oriented tip by using nano-biprisms in a field-emission projection microscope (FPM). The FPM images were consistent with the corresponding field emission patterns of the employed tip. The nanotip generated much sharper biprism interference patterns than the W(110) tip, and comparison of the visibilities of interference patterns demonstrated directly that a highly coherent electron beam was emitted from the nanotip.

Phonon Density of States of Pseudomorphic fcc-Fe Film

The phonon density of states of a pseudomorphic fcc-Fe film with ∼3 monolayers has been investigated by nuclear resonant inelastic scattering. The fcc-Fe layers are intercalated into an interface between monolayer hexagonal boron nitride and a Ni(111) substrate with a commensurate relation. The in-plane nearest-neighbor distance of the fcc-Fe film is shorter than that of uncompressed fcc-Fe precipitates in Cu by -1.8%. The compression increases the mean force constant of the fcc-Fe film, which is higher than that of uncompressed fcc-Fe precipitates by 5.8%.

FEM study of Au-deposited nanopyramids grown on blunt W tips via assistive remolding treatment

Recently, atomic-scale, thermodynamically stable pyramids with a single atom end have been fabricated from W tips, and developed as a point source of field-emitted electrons. Not only did they exhibit superior characteristics like high brightness, narrow spread, and considerable stability of the e-beam [1], but they represented both self-repairing and demountable functions that were requisites for practical application [2]. As far as how to produce the nano-pyramids is concerned, various necessary conditions are involved in the recipe. One of the critical requisites is a use of so-called “ultra-sharp” W tips. To our best knowledge, even if the identical treatments are given to a “blunt” W tip, the nano-pyramid with a single-atom end does not grow, seemingly due to a heavy load of mass transport. Compared to the ultra-shape W tips, however, the blunt ones are considered more favorable because of high resistance against both thermal and mechanical damages. In this study, we have sharpened the W-tip end by means of remolding [3], which is a sort of thermal-field treatment, prior to the nano-pyramid production. Thus, we have tried and formed the nano-pyramid using originally blunt W tip as a starting substrate.

Extreme high vacuum field emission microscope for study on the inherent fluctuation of field emission

An extreme high vacuum field emission microscope (XHV FEM) was constructed for the study of inherent fluctuations of field emission (FE) current. The damping and fluctuation behaviors of FE current from clean W(111) tips at 90K were observed using the XHV FEM. Exposure to XHV of 7.5×10−10Pa continued to damp FE current for more than 2000min. The fluctuation (∼0.01%) of FE current (1nA) for the clean W(111) tips was comparable to the corresponding shot noise fluctuation (0.005%), demonstrating the suitability of the XHV FEM for the inherent fluctuation study of the FE process. After saturating the tip surface with hydrogen, the FE current showed fluctuations of <0.1%

Finite transverse coherent length of electron source evaluated by interference fringes with a natural bi-prism

In this paper, multi-walled carbon nanotubes (MWCNT) can play the role of biprism interferometer in projection microscopy (PM). The biprism interference patterns are analyzed in order to obtain information on the properties of the source, such as the effective source size, the transverse coherence width.

Coherent Electron Emission from Carbon Nanotubes and Nb Superconductors

In this article, two topics of coherent electron emission are discussed. Coherent electrons emitted at different sites of a carbon nanotube generate Youngs interference strips in a vacuum, which means that all the electrons emitted in different directions from one nanotube are coherent. The other topic is concerned with the electron emission from macroscopic coherent states in Nb superconductors; the energy width of these electrons is about 20 meV, which is an order of magnitude narrower than those of the conventional beams. By using this emitter, one can expect to improve the temporal coherence of the electron beams in a vacuum by factor 10.