Eiji Rokuta

A hetero-epitaxial-double-atomic-layer system of monolayer graphene/monolayer h-BN on Ni(111)

A double-atomic-layer system of monolayer graphene/monolayer h-BN has been prepared in an epitaxial manner on Ni(111) surface. The graphene overlayer formation changes drastically the pristine interface between the h-BN layer and Ni(111). As a result, a peculiar property of the pristine monolayer h-BN on Ni(111) changes to a bulk-like one. The π–d orbital hybridization at the interface disappears. Accordingly, a metallic character of monolayer h-BN disappears and softening TO phonons return to the normal one. The reduced lattice constant of h-BN presumably returns to the bulk one. The same phenomenon occurs by surface contaminations instead of monolayer graphene formation.

Vibrational spectra of the monolayer films of hexagonal boron nitride and graphite on faceted Ni(755)

Hexagonal boron nitride (h-BN) and graphite films on faceted Ni(755) have been investigated by means of vibrational spectroscopy, accompanied by low energy electron diffraction and Auger electron spectroscopy. A faceted surface consisting of the (111) face and high-Miller index face has been grown by the adsorption of monolayer films. Vibrational spectra of the monolayer h-BN have exhibited two peaks at 90 and 97 meV, which originate from the optical phonons with out-of-plane displacement (TO⊥) of the films adsorbed on the faceted (111) and the other high-index faces, respectively. These peaks indicate that the bond strength between h-BN films and a Ni face depends on the Ni face orientation. On the contrary, only one peak of TO⊥ mode has appeared in the monolayer graphite on the same faceted surface. The single peak means a similar strength of the interfacial bond on various surfaces.

Oxygen adsorption sites on the PrB6(100) and LaB6(100) surfaces

The adsorption of oxygen on the LaB6(100) and PrB6(100) surfaces has been studied with low energy electron diffraction (LEED) and high resolution electron energy loss spectroscopy (HREELS). Room temperature adsorption of oxygen gives a diffuse c(2×2) LEED pattern and several vibrational loss features with the most intense peak at 35 meV. Upon annealing to 600°C both the c(2×2) LEED pattern and the HREELS loss features become much sharper. Annealing to 700°C produces a sharp (2×1) LEED pattern and strong changes in the HREEL spectrum including a large decrease in intensity of the 35 meV peak. The work function of the 2×1 structure is 0.9 eV lower than that of the c(2×2) structure while Auger measurements show that the oxygen coverage is the same. The results are discussed in terms of possible oxygen adsorption sites.

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.

Macroscopic, freestanding, and tubular graphene architectures fabricated via thermal annealing.

Manipulation of individual graphene sheets/films into specific architectures at macroscopic scales is crucially important for practical uses of graphene. We present herein a versatile and robust method based on annealing of solid carbon precursors on nickel templates and thermo-assisted removal of poly(methyl methacrylate) under low vacuum of ∼0.6 Pa for fabrication of macroscopic, freestanding, and tubular graphene (TG) architectures. Specifically, the TG architectures can be obtained as individual and woven tubes with a diameter of ∼50 μm, a wall thickness in the range of 2.1-2.9 nm, a density of ∼1.53 mg·cm(-3), a thermal stability up to 600 °C in air, an electrical conductivity of ∼1.48 × 10(6) S·m(-1), and field emission current densities on the order of 10(4) A·cm(-2) at low applied electrical fields of 0.6-0.7 V·μm(-1). These properties show great promise for applications in flexible and lightweight electronics, electron guns, or X-ray tube sources.

Oxygen adsorption on LaB6 (100) and (111) surfaces

Abstract The adsorption of oxygen on LaB 6 (100) and (111) surfaces has been studied with high resolution electron energy loss spectroscopy (HREELS). In the HREELS spectra of the clean (100) surface, only one peak at 14 meV is observed, while two intense peaks appear at 16 and 27 meV in the spectra of the clean (111) surface. Oxygen adsorption on the (111) surface is quite different from the (100) surface: oxygen attacks the surface framework of boron on the (111) surface even at room temperature, resulting in the formation of a complex structure including BO bonds, while the superstructure with only LaO bonds is formed on the (100) surface at room temperature. Only after heating to above 700°C, a BO bond is formed on the (100) surface.

Vibrational spectra of oxygen on LaB6(100), (110), and (111) surfaces: A comparative study using high resolution electron energy loss spectroscopy

The vibrational properties of the (100), (110), and (111) surfaces of LaB6 with adsorbed oxygen are compared using high resolution electron energy loss spectroscopy (HREELS). Each surface offers a distinctly different set of possible adsorption sites and at room temperature the adsorption of oxygen yields a distinctly different HREELS spectrum. However, annealing the oxygen covered surfaces to 700 °C produces strikingly similar results, indicating a common oxygen induced structure for the three surfaces.

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.

Surface phonon dispersion curves of the LaB6(111) surface

Abstract Energy dispersion curves of the surface phonons of the LaB 6 (111) surface have been measured by using high resolution electron energy loss spectroscopy. We found two large loss peaks and three small loss peaks in the specular spectra and several branches in the off-specular spectra. On the basis of lattice dynamical calculations using bulk parameters, we have obtained the theoretical phonon dispersion curves of the unrelaxed surface. One vibrational mode appeared above the bulk phonon bands, which indicates stiffening of the BB bonds of the surface octahedra.

Multiaxis and multibeam technology for high throughput maskless E-beam lithography

The authors have devised a new maskless E-beam lithography method which can achieve a throughput of 10 wph which the authors are calling a “multiaxis programmable shaped beam” (multiaxis PSB). It is a kind of massive parallel electron beam lithography wherein more than 250 000 beams write a wafer and the total beam current reaches a hundred microamperes. It may be difficult to write a pattern finer than 10 nm with more than 1 μA beam current at 50 kV with a single column because of blurring from Coulomb interaction, so the multiaxis PSB system divides all the beams into 87 groups where each group has 2500–10 000 beams formed by a small column arrayed in a 26 × 33 mm2 lattice. The small column is called a column element (CE) and each CE has an emitter, apertures, deflectors, and small lenses. The key technologies of the multiaxis system are a lens, emitter, and blankers for individual beamlets. The authors have proposed new ideas for these issues and made fundamental experiments.