Kiyoshi Takimoto

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.

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.

A new method to fabricate metal tips for scanning probe microscopy

A new method to fabricate sharp metal tips on cantilevers for a scanning probe microscope (SPM) is presented in this paper. The metal tip film, which is and patterned on a silicon mold with etch pits, is attached by metal-to-metal bonding to a metal pad on a cantilever. Then a tip is fabricated on the cantilever by peeling the metal tip film off the mold at room temperature. Because the back side of the metal tip film becomes the tip surface, the tip surface is very smooth without grain boundaries associated with deposited thin films. A platinum tip with a radius curvature of less than 15 nm was successfully fabricated. In addition, the mold can be reused because the silicon mold is not dissolved during the tip fabrication. By applying this method in which the tip fabrication process is independent of the cantilever process, we succeeded to form a tip on various cantilevers. Moreover, we used the cantilever with the tip in a piezoresistive atomic force microscope and an atomic force microscope combined with a scanning tunneling microscope (AFM/STM) apparatus and obtained simultaneously high resolution topography and surface conductance images of a sample surface.

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.

Information storage using a scanning probe

Publisher Summary Surface modification with a scanning probe microscope (SPM) is very attractive because the dimension of the modification ranges from sub-micron to sub-nanometer, which is much smaller than the limit of conventional photolithography. The surface modification according to a given pattern and its observation with a scanning probe can also be seen as a writing and reading procedure in an information storage device. Then the pattern produced by the surface modification is regarded as a set of data bits. The recording density estimated from the typical size of each modification becomes much higher than that of any present storage device. The concept of an information storage system is demonstrated based on the formation of ideal metal–insulator–metal (MIM) junctions using an atomic force microscope (AFM) with a conducting probe. In practice, polyimide Langmuir–Blodgett (LB) film is used as an insulating layer in an MIM junction, and a local conducting region in the polyimide LB film induced by applying a pulse voltage through the probe is considered to a recording bit. In this system, the surface topography of the medium is maintained even after writing data bits, which makes it possible to read and write data bits at fast rates without severe requirements for the mechanical resonance frequency of a cantilever. Then an extremely flat surface of the recording medium is required over a wide range. It is essential to fabricate a sufficiently flat and large medium. LB film is a suitable recording medium because the thickness of the film can be precisely controlled on a molecular scale.