Hiroshi Nanjo

Atomic images of 304SS surface after electrochemical treatments

Abstract Sputter-deposited 304 stainless steel was electrochemically treated in 0.1 M H 2 SO 4 aqueous solution, and was observed in air at atomic resolution with a scanning tunneling microscope. After passivation for 15 min at 400 mV (SCE), there was initially little order present, but the diameter of oxide particles (grains or partly ordered domains) increased from about 30 to 200 nm during 3 h after the treatment. Surface atoms of oxygen or hydroxyl gradually become ordered in air and the structure of the substrate surface becomes apparent on the surface of the passive film. This suggests that the surface is covered with a single oxide phase, which is initially rather disordered but crystallizes with time.

Chiral molecular patterns of self-assembled ion pairs composed of (R,S), (S)-16-methyloctadecanoic acid and 4,4′-bipyridine

Self-assembled monolayers of stearic acid, (R,S) and n(S)-16-methyloctadecanoic acid ion-paired with n4,4′-bipyridine have been observed on a solution–graphite ninterface by a scanning tunneling microscope (STM) and the observed nmacro-scale molecular patterns have been interpreted in terms of absolute nchirality of the constituent molecule.

Oriented thin film fabrication of organic non-linear optical crystals

Abstract Ordered thin films of organic non-linear optical crystals, 4-(4-dimethylaminostyryl)-1-methylpyridinium tosylate (DAST), 2-adamantylamino-5-nitroprydine (AANP) and 3-methyl-4-methoxy-4′-nitrostilbene (MMONS), have been fabricated by a novel simple technique where their microcrystals were dragged on the glass plate. Thickness of the ordered thin film was approximately 100 nm. In ordered DAST thin film, ab-plane appeared as their surface layer. They showed dichroism in polarized ultraviolet and visible absorption spectra measurements.

Atomic-force microscope observation and molecular-scale flattening of the single-crystal surface of 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST)

The surface of an organic electro-optic crystal tends to be covered with a degenerate rough layer, which may cause light scattering or unfavorable transmission of light. We demonstrate a novel method of removing this layer and flattening the (001) surface of a 4-dimethylamino- N -methyl-4-stilbazolium tosylate (DAST) crystal on a molecular scale by applying suitable force on the tip of an atomic-force microscope (AFM). When the loading force on the AFM tip is kept near 10 nN, the DAST molecules can be removed layer by layer. This method produced a large, flat terrace of 250,000 nm(2) , and the molecular-scale flatness of this area was confirmed by AFM observation.

Direct observation of the polymer and monomer Langmuir-Blodgett films with the atomic force microscope

Abstract Molecular arrangement of two kinds of Langmuir–Blodgett monolayers composed of poly(N-dodecylacrylamide) and N-octadecylacrylamide were characterized with the atomic force microscope (AFM). The dodecyl side chains in the polymer Langmuir–Blodgett monolayer were observed as random molecular arrangement. In contrast, alkyl chains in N-octadecylacrylamide monomer Langmuir–Blodgett film were highly ordered to form two dimensional crystals. The X-ray diffraction patterns of the monomer and polymer Langmuir–Blodgett films were consistent with the AFM observation. The polymer Langmuir–Blodgett monolayer was not destroyed by AFM tip scanned in the contact mode, indicating that the monolayer is mechanically appreciably stable.

Erosion-corrosion damage of aluminum alloy in a high-speed, high-temperature, two-phase flow

Abstract A study of aluminum alloy damage by erosion-corrosion in a two-phase jet flow is presented. The jet flow was characterized by a temperature of 392 K and a speed of 177 m s−1 at the specimen location. Slip occurred between droplets and steam in the two-phase jet flow dispersed from a nozzle, and the relative velocities of steam to droplets were found to depend on the length of the straight portion of the nozzle outlet, even though the mean velocities of the liquid and steam were held constant. We found that a nozzle with a long straight portion caused large droplet formation with large velocities at every volume flow rate ratio investigated. As a result, the mass loss was found to increase with increases in the length of the straight portion. A small number of pits were caused by just corrosion, and there was little mass loss of the aluminum alloy in the static hot condensate of the two-phase fluid. Although a large number of pits were induced by the flow, the mass loss corresponding to pit volumes calculated from their shapes was not so large. We believe that the alloy damage was mainly due to erosion, and subsequent corrosion follows owing to small cracks generated in the protective film of the alloy by droplet impingement.

The relation between corrosion and surface potential measured with the scanning Maxwell stress microscope

The topographies and the surface potentials on various corroded metal surfaces have been simultaneously measured with the scanning Maxwell stress microscope to investigate the microscopic relation between the topography of corroded surface and the surface potential in atmosphere. In the early stage of corrosion the potential was low at the corroded region. In the next stage, however, the region where the potential was low at the non-corroded area appeared since anodic region transferred from corroded area to non-corroded area. The microscope is very useful to study the time dependence of the relation between a corroding region and the surface potential.