Seiji Usami

Transition metal oxide films prepared by pulsed laser deposition for atomic beam detection

Abstract Resistivity of sintered metal oxides is known to change as a result of irradiation of atomic hydrogen, deuterium, nitrogen, and oxygen, but not as a result of irradiation of symmetrical diatomic molecules of these atoms. Thin films of nickel oxide, cobalt oxide and manganese oxide were formed by pulsed-laser deposition so as to enhance the sensitivity to atomic beams. The 4th harmonic of the Nd:YAG laser (λ=266 nm 4.8 J cm −2 ) was focused on sintered pellets, and thin films were deposited on pyrex glass substrates. The partial pressure of the oxygen gas P o2 , and the substrate temperature, T g , are crucial parameters for the formation of transparent monoxide-like films. Optimum conditions were determined in the range of P o2 =1.3×10 −4 –1.3×10 Pa and T g =400–600°C. The films were characterized by X-ray photoelectron spectroscopy and X-ray diffraction. The monoxide-like films are found to be more sensitive to atomic beams than sintered oxides and even NiO single crystals.

Optical Emission Analysis of Triple-Fold Plume Formed at Pulsed IR Laser Ablation of Graphite

A sheet of sintered graphite was ablated by a pulsed Nd:YAG laser in He gas and air at 1 atm. Triple-fold plumes were produced in both gases. The time-resolved emission spectrograms of the plume were measured and the plume was analyzed as follows. The plume is generated near the target surface and expands while separating into three because of different expansion speeds of its components. The fastest component is gas plasma mainly composed of carbon ions in the He atmosphere, and nitrogen and oxygen ions in air. The second fastest component is very hot and compressed neutral molecules of the gas, that is, the shock wave. The slowest component is radical vapor of the graphite target.

Theoretical Study on the High-Energy Electron Energy Loss Spectroscopy Compared with X-Ray Absorption Spectroscopy. I. Deep Core Excitation from K and L2,3 Edge of Atoms

In this series of papers we are investigating the magnitude of the dipole and non-dipole processes observed in the high-energy electron energy loss spectroscopy (EELS) related to deep core orbitals. The present paper describes the atomic excitation from deep K and L2,3 edges. We discuss the amount of discrepancy which emerged in the intensity of electron scattering when only assuming a dipole interaction and its dependence on the scattering angle, excitation energy and type of excited core levels. From this discussion, one can justify the means to obtain the same electronic and geometric information by an analysis of electron energy loss fine structure and the near-edge structure observed in high-energy EELS for small-angle scattering.

Ferromagnetic Crystalline Anisotropy of Fe-Mn-Ferrite System

Ferromagnetic resonance absorption of microwave (9300 Mc/s) in synthetic single crystals of Mn x Fe 3- x O 4 (0.2≦ x ≦1.15) has been investigated to study their magnetic crystalline anisotropy, g -factor and line width. The pronounced valley in the curve, magnetic crystalline anisotropy (- K 1 / M ) v s . composition ( x ), was observed in the temperature region between 90°K and 300°K. - K 1 / M was a minimum in the region 0.6 0.6. It seems difficult to explain these experimental results on the view point of one-ion-model which proved successful in many other ferrites.

Optical observation of plumes formed at laser ablation of carbon materials

Abstract When a sintered carbon target is irradiated strongly in the atmosphere by a Nd: YAG laser at an irradiance of more than 1 GW/cm 2 , a flame-like plume jets out of the target during laser ablation. This characteristics plume was optically observed with a streak camera system combined with either a monochromator or a spectrograph. The observation reveals the chemical and dynamical structures of the plume as follows; (1) plasma of the atmosphere extends at the highest velocity in the plume, (2) very hot and dense neutral molecules of the atmosphere expand more slowly, (3) finally, vapor of the carbon target spreads further slowly.

Exelfs of vanadium carbide with primary electrons of a few keV

Grazing incidence electron energy loss spectroscopy with primary electrons of a few keV was applied to find the interatomic distance in the outer-most layer of a (111) single crystal surface of vanadium carbide V 6 C 5 . To compare with this, it was attempted to observe the energy loss spectrum of back-scattered electrons using a higher glancing angle for the same specimen. The atomic distance between vanadium and carbon was found to be 0.174 nm, which is considerably smaller than 0.207 nm, the bulk value. On the other hand, the spectrum of back-scattered electrons gave the distance 0.276 nm, which is much greater than the others. These results are discussed from the theoretical point of view.

Velocity analysis of ablated particles in pulsed laser deposition of NiO film

Abstract Optical emission of the ablated particles in pulsed laser deposition of NiO films was measured dynamically. The emission spectra showed species of the ablated particles. There are three types of light emitting particles, that is, the laser induced plasma near the target, two groups of the depositing ionized particles or the neutrals. The streak photography displayed their kinetic motions. Velocities of the ionized particles were almost proportional to the square root of the incident laser fluence ranging from 5 to 150 J cm−2. It is possible to control the kinetic energy of particles incident onto a substrate by adjusting the laser fluence.

Adsorption of Nitric Oxide on Tungsten

The characterization of the W(100) surface adsorbing nitric oxide at room temperature has been conducted with the conventional LEED and AES technique. Nitric oxide on the W(100) has shown ordered (2×2) and (4×1) patterns at the exposure of 0.8 L and 1.6 L respectively without any heat treatment. The sequential heating of the fully NO-covered surface has revealed (2×2), (4×1) and (2×1) structures. In the AES, as the exposure was increased the nitrogen and oxygen peaks did not grow up at the same rate, the latter kept nearly constant over the exposure of about 3 L. The surface potential of nitric oxide on W(100) was -1.52±0.03 V by the retarding field method.

Energy loss near‐edge structure for materials containing light elements by reflection electron energy loss spectroscopy

A reflection electron energy loss spectroscopy system has been developed to investigate local surface atomic structures around light elements such as C, N, and O. Electrons scattered inelastically on a surface with a small scattering angle are energy analyzed. This system was used to measure energy loss near‐edge structures (ELNESs) for materials such as BN, graphite, and NiO. The comparison between ELNES and x‐ray absorption near edge structure suggests that the ELNES is useful for the atomic structure analyses of surfaces.

Theoretical Study on the High-Energy Electron Energy Loss Spectroscopy Compared with X-Ray Absorption Spectroscopy. II. Effects of Single Elastic Scattering

In this paper we propose a new theoretical approach to high-energy electron energy loss spectroscopy (EELS) based on the short-range order theory which includes elastic scattering before and after deep core excitation. Within the single elastic scattering approximation for the fast electron, numerical calculations have been performed on the K-edge EELS from diamond (111) and Al (111), (001) surfaces for three different modes: the grazing incidence and low takeoff angle detection mode, the backward scattering reflection mode and the transmission mode. The calculated results show that the dipole excitation mainly contributes at small-angle scattering as expected, and the elastic scatterings recover the dipole excitation contribution substantially at large-angle scattering; however, the nondipole processes are dominant even under the large-angle scattering condition.