Yutaka Majima

Generation of Maxwell displacement current from spread monolayers containing azobenzene

The Maxwell displacement current generated from single fatty acid monolayers containing azobenzene by photoisomerization was investigated in the context of the phase diagram of monolayers on a water surface. Transient displacement‐current pulses were found to be produced when successive isomerizations were induced in monolayers by irradiation with ultraviolet and visible light. In contrast, the displacement current was never generated in the so‐called solid phase by the application of surface pressure or photoirradiation, probably because of the lack of free volume for the isomerizing chromophore in single monolayers and as well as the aggregation of molecules in the monolayer. The displacement current generated during monolayer compression was also investigated in connection with phase transitions.

Investigations of the dynamic behavior of fatty acid monolayers at the air–water interface using a displacement current‐measuring technique coupled with the Langmuir‐film technique

The dynamic behavior of fatty acid monolayers at the air–water interface was investigated using a displacement current‐measuring technique coupled with the so‐called Langmuir‐film technique and also the dipole moment of the acids was determined. The displacement current flowing though a short circuit was generated only when induced charges on an electrode suspended in air was changed by monolayer compression. The displacement current measurement was found to be a very sensitive method used for a better understanding of the relationship between the structure and function of the monolayers placed on the water surface and it was also found to be a very useful method for detecting the dynamic motion of molecules in the entire range from the so‐called gaseous state to the solid state at the same time. Finally, the generalized displacement current was theoretically analyzed.

Simultaneous fabrication of nanogap gold electrodes by electroless gold plating using a common medical liquid

We report a simple and high yield method for fabricating multiple nanogaps simultaneously by an electroless gold plating technique using electroless gold plating solution which consists of common medical liquid of iodine tincture and L(+)-ascorbic acid (vitamin C). The distance between the gold electrodes (33nm in average) on the SiO2∕Si substrate was decreased by selective deposition of gold onto the surface of the gold electrodes. By electroless gold plating, we fabricated nanogaps below 5nm in width with a 41% process yield. We also demonstrated the Coulomb blockade effect in octanethiol(C8)-protected Au nanoparticles by using such a fabricated nanogap.

Logic operations of chemically assembled single-electron transistor.

Double-gate single-electron transistors (SETs) were fabricated by chemical assembling using electroless gold-plated nanogap electrodes and chemisorbed chemically synthesized gold nanoparticles. The fabricated SET showed periodic and stable Coulomb oscillations under application of voltages of both gates. The sole SET also exhibited all two-input logic operations-XOR, XNOR, NAND, OR, NOR, and AND-with an on/off ratio of 10(2). This demonstrates the potential of chemical assembling to give highly stable SETs exhibiting all logic operations.

Determination of the Dipole Moment of a Monolayer at the Air/Water Interface Using a Current-Measuring Technique

A new technique for determining the dipole moment of the constituent molecules of a monolayer at the air/water interface has been developed. In this technique, two electrodes parallel to the water surface are used. One electrode (Electrode 2) is placed in the water and the other electrode (Electrode 1) is suspended in the air. Both electrodes are grounded. The displacement current due to the induced change on Electrode 1 is measured with the surface pressure-aria isotherm. Since the induced change is caused by the dipoles of the constituent molecules, the dipole moments of the molecules are determined. In this study, fatty acids are used as examples. A theoretical analysis for determining dipole moments by the present technique is also described.

A new displacement current measuring system coupled with the Langmuir‐film technique

The new displacement current measuring system used for detecting the dynamic behavior of monolayers at the air‐water interface is described. It basically consists of a film balance, a light source and a pair of electrodes connected to each other through a sensitive ammeter. Here, one electrode is suspended in air and the other electrode is placed in the water. Using the system, displacement current generated from a single monolayer by either the application of surface pressures or the photoirradiation can be detected. Since the displacement current flows due to the dynamic behavior of polar molecules at the air‐water interface, the physicochemical properties of monolayers, e.g., dipole moment of the constituent molecules and the molecular structural change due to the photoisomerization, can be investigated without destroying the monolayers themselves.

Uniform charging energy of single-electron transistors by using size-controlled Au nanoparticles

Single-electron transistors have the potential to become next-generation nanodevices and sensors owing to their small size, low power consumption, and high charge sensitivity, where the charging energy of the devices is the most important parameter determining the operational temperature. Here, we have demonstrated that the charging energy of single-electron transistors can be controlled (48 ± 4 meV) by adopting electroless gold plating to make separation-defined nanogap electrodes and employing size-controlled chemically synthesized Au nanoparticles (5.2 ± 0.5 nm) as a Coulomb island. At this charging energy, the devices can be operated up to 160 K with on/off current ratio of 60%.

Single-Electron Transistor Fabricated by Two Bottom-Up Processes of Electroless Au Plating and Chemisorption of Au Nanoparticle

Coulomb diamonds were clearly observed on single-electron transistors (SETs) fabricated by bottom-up processes of electroless plating of Au nanogap electrodes and chemisorption of a Au nanoparticle at 80 K. In the drain current–drain voltage characteristics, Coulomb staircases were modulated by the side gate voltage. Tunneling resistances and source/drain/gate capacitances of the SET were evaluated by fitting the theoretical Coulomb staircase determined on the basis of the full orthodox theory in a double-barrier tunneling junction to the experimental results of Coulomb blockade under the application of side gate voltages. The theoretical results for the Coulomb diamond are in good agreement with the experimental results.

Bias Stress Induced Threshold Voltage Shift in Pentacene Thin-Film Transistors

Threshold voltage instabilities in SiO2/polyimide dual-gate dielectric pentacene thin-film transistors are investigated as a function of bias stress time for 1000 s at temperatures between 260 and 340 K in nitrogen atmosphere. Field-effect mobility maintains constant values at every measurement temperature during the application of constant bias stress voltage. The threshold voltage shift at all measurement temperatures is described by the stretched exponential stress time dependence of ΔVth(t) = ΔVth0{1-exp [-(t/τ)β]}. These experimental results suggest that our threshold voltage shift can be interpreted as carrier injection from the pentacene channel into traps located at the channel/gate dielectric interface.

Room-Temperature Coulomb Blockade from Chemically Synthesized Au Nanoparticles Stabilized by Acid–Base Interaction

Sub-2-nm-size basic ligand Au nanoparticles were chemically synthesized and chemisorbed on an acidic self-assembled monolayer/Au(111) substrate by acid–base interaction. Coulomb blockade behaviors with clear Coulomb gaps were observed in current–voltage (I–V) and log I–V curves of the chemisorbed Au nanoparticles by scanning tunneling spectroscopy at room temperature. By fitting the measured I(V) and log I(V) to a Coulomb blockade model, we estimated the charging energy of one electron on the Au nanoparticles to be 10 times greater than the thermal energy k T; the tunneling resistance of the Au core–Au(111) surface was evaluated to be 3.5 GΩ ±15%.