Kunihiro Sakai

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.

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.

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.

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.

X-ray standing waves excited in multilayered structures

Abstract X-ray standing waves excited in inorganic and organic multilayered structures were respectively used as structural probes for (1) determination of interlayer distribution of entrapped argon atoms in a tungsten-silicon multilayer (48 layer pairs) prepared by sputter deposition techniques and for (2) the study of a heterostructure in a Langmuir-Blodgett film (two monolayers of barium arachidate and two monolayers of manganese stearate on top of 59 monolayers of lead stearate). In the first expeirment, the density of argon atoms in the silicon layers ( ≈ 18 A) was found to be 2–4 times higher than that in the tungsten layers ( ≈ 12 A). In the second experiment, the difference between barium-manganese and manganese-lead interlayer distances was successfully detected .

Negative resistance and electron emission in metal/Langmuir-Blodgett film/metal structures

Abstract Voltage-controlled negative resistance (VCNR) and electron emission have been observed in metal/Langmuir-Blodgett film/metal (M/LB/M) sandwich structures under vacuum. The electrons have been emitted from a complete junction area of the M/LB/M device through a top electrode with no physical damage on its surface. The emission current has been enhanced by the development of the VCNR. The results of the VCNR and the electron emission suggest that the electric conduction in the M/LB/M devices is dominated by the LB films themselves.

Temperature dependence of glow discharge polycrystalline silicon films and thin film transistor

Abstract We observed that the conductivity of glow discharge polycrystalline silicon films changed from 10 −5 to 10 −7 (Ω · cm) −1 at substrate temperature of about 350–400°C, which was associated with the change of activation energy. At substrate temperatures lower than about 350°C, the films showed broad ring patterns with randomly oriented microcrystallites, and at higher temperatures above 400°C the preferred (110) orientation appeared. The field effect mobility of polycrystalline silicon increased as substrate temperature increased.