Takashi Nakagiri

Switching and memory phenomena in Langmuir–Blodgett films

Reproducible memory switching has been observed in metal/ Langmuir–Blodgett (LB) film/metal sandwich structures: LB films consist of organic molecules such as dyes having a number of conjugated bonds. The device switches from a nonconducting off state to a conducting on state via an intermediate state, and it switches directly from the on to the off state within less than 10 ns upon the application of a voltage. Both off‐state and on‐state resistances of the device depend linearly on the number of monolayers, the conduction being predominantly through the LB films.

Nanometer scale conductance change in a Langmuir‐Blodgett film with the atomic force microscope

A nanometer scale metal/Langmuir‐Blodgett (LB) film/metal structure is realized with an atomic force microscope combined with scanning tunneling microscope (AFM/STM). Even in this nanometer scale configuration, increase in conductance can be induced at any point in the LB film by application of a voltage pulse. The AFM/STM observation shows little surface modification has occurred by the voltage application, which shows that the conductance of the LB film changes without pit formation in the LB film or metal cluster deposition from the tip of the probe.

Switching and memory phenomena in Langmuir–Blodgett films with scanning tunneling microscope

The current‐voltage characteristic has been measured for a probe/Langmuir–Blodgett (LB) film/metal structure with the scanning tunneling microscope (STM). The rapid increase of current and substantial increase in conductance have been found when a critical positive voltage was applied to the probe. A bright spot in the STM image has been observed at the position where the increase in the conductance occurred. The changes in the STM images are attributed to the change in the conductance of LB films themselves rather than the surface topography, and may be associated with the switching phenomena in LB films.

Glow discharge polycrystalline silicon thin‐film transistors

Thin‐film transistors were fabricated from polycrystalline silicon films which were produced by glow discharge decomposition of silane at 500 °C on thermal oxidized silicon substrates. The dependence of the crystalline and electrical properties was observed for thicknesses from about 500 to 4500 A. As the film grew thicker, the strongly (110) oriented polycrystalline structures became predominant. The conductivity changed from 4×10−9 to 10−6 (Ω cm)−1 and the activation energy from 0.57 to 0.5 eV. The field‐effect mobility of these thin‐film transistors also varied with the thickness of the film.

The dissolution of myristic acid monolayers in water

Abstract The measurement of surface pressure–area isotherms of short chain fatty acids on a Langmuir trough often shows irreproducible, large errors, in spite of high purity of materials, cleanliness of equipment and sophistication of routines. By controlling the timing during monolayer spreading, the spreading speed and the history and age of the subphase, these errors become systematic and reproducible. On the basis of myristic acid, where the effect is very large, and palmitic acid, for which the effect is far from negligible, it is shown that the governing effect is dissolution and saturation of the molecules in the subphase. This raises the question of metastability of such monolayers not only above the equilibrium spreading pressure but at any pressure. It also explains some, so far, ill-understood problems about Langmuir–Blodgett film fabrication and the measurement of equilibrium spreading pressures.

Electrical memory switching in Langmuir-Blodgett films

Abstract Electrical memory switching has been observed in the metal/Langmuir-Blodgett (LB) film/metal sandwich structure with a noble metal base electrode. Switching from a non-conducting OFF state to a conducting ON state (WRITE operation) and/or switching back to the OFF state (ERASE) are/is possible by applying adequate voltage; however, when the voltage is reduced, both OFF and ON states remain the same. A memory system utilizing an LB film and a scanning tunnelling microscope, has been proposed.

Construction and use of LB deposition machines for pilot production

Abstract We describe the construction of Langmuir-Blodgett (LB) deposition equipment that was designed for pilot production to prove (or disprove) whether it is feasible to bring the LB technology to a state that is compatible with the necessary reliability, throughput and quality for mass production. Encouraging first results indicate that this is feasible and suggest many useful ideas and procedures also for the laboratory environment.

X-ray standing wave method applied to the structural study of Langmuir-Blodgett films☆

Abstract An X-ray standing wave field excited during Bragg diffraction in 59 monolayers of lead stearate was used as a structural probe to determine the distance from the manganese atom plane to the nearest lead atom plane in a Langmuir-Blodgett film with a heterostructure (two monolayers of manganese stearate superimposed on top of the lead stearate layers). In this experiment, the intensities of Pb Lα and Mn Kα fluorescent X-rays excited by the standing wave field were measured as a function of the glancing angle of a monochromatized (13.4 keV) synchrotron X-ray beam. These two fluorescence intensity curves were compared with the calculated ones.

Conducting defects in Langmuir-Blodgett films

Abstract A copper decoration method was employed to visualize the conducting defects in Langmuir-Blodgett (LB) films under an optical microscope. The resulting copper decoration patterns strictly reflected the morphology of the LB films.

Barrier-height imaging of fatty acid Langmuir-Blodgett films

Abstract Behenic acid Langmuir-Blodgett films on graphite have been investigated by STM using the AC gap-modulation technique. Two significant differences were observed as compared to conventional topographic images. (1) The periodic contrast variation, which is superimposed on the structure of the behenic acid molecules in the lamellar arrangement, is greatly enhanced. This period corresponds to the width of 6 molecules. (2) The carboxyl groups appear featureless and cannot be distinguished, whereas in the topographic images they are the brightest signal and are clearly distinguished. The periodic variation of enhanced contrast corresponds to that of the positional relation between the adsorbed molecules and the underlying substrate. This means that the additional information of the interaction between the adsorbed molecules and the substrate can be obtained by the gap-modulation mode in STM.