Nobuyoshi Kawaguchi

Surface Morphology of Gold Thin Films Deposited on Poly(ethylene naphthalate) Organic Films for Quantum Cross Devices

The surface morphology of gold thin films deposited on poly(ethylene naphtalate) (PEN) organic films has been investigated for quantum cross devices. The surface roughness of gold thin films on the PEN films is 1.5–1.9 nm and the appearance of mound structures is observed. The mound grain sizes are 28.0±4.6 nm for 5-nm-thick gold films and 45.8±5.8 nm for 10-nm-thick gold films. From the result of the scaling investigation of the surface roughness, the surface roughness of 5-nm-thick gold films is 0.22 nm, corresponding to one atomic size, in the scanning scale of 5 nm. These experimental results indicate that gold thin films on PEN films are suitable for use in quantum cross devices, and may open up a novel research field on the electric characteristics of quantum cross devices using a few atoms or molecules leading to high-density memories.

Study of very low airborne particle count in clean-unit system platform

Cleanliness of a clean-unit system platform consisting of multiply connectable clean boxes with feedback loop is studied and the time dependence of particle count is clarified experimentally and theoretically in order to achieve highly clean environment. Based on this analysis, we have demonstrated airborne particle counts as low as 5particles∕ft3 for the diameter of 0.1μm, 0.6 particles for 0.2μm, and 0.01 particles for 0.5μm by a reduction of particle density coming out from the in-wall in the system. The clean-unit system with feedback loop can serve as a platform for cross-disciplinary experiments and production for fields such as nanotechnologies and biotechnologies.

Ultra-High Cleanliness of ISO Class Minus 1 Measured in Triply Connected Clean-Unit System Platform

A clean environment ISO class minus 1 free of particulate contamination is realized in clean-unit system platform (CUSP), made of airtight multiply-connected clean-box unit with an air feedback loop, by stepwise reducing particles coming out from the high efficiency particulate air (HEPA) filter and a number of particles coming out through the filter of the particle counter due to the imperfect air filtration. The particles coming out from the HEPA filter to the CUSP environment are minimized by connecting the ultra low penetration air (ULPA) filter just after the HEPA filter. By decoupling the particle counter from the advanced CUSP unit, the contribution of the particle counter for deteriorating the cleanliness is significantly reduced. Experimental results from a double use of HEPA and ULPA filters and the separation of particle counter from the advanced CUSP unit, demonstrate the ultra-high cleanliness of ISO class minus 1, which would be the key factor for increasing the product yield and reliability in the burgeoning cross-disciplinary research.

Ultrasmooth Ni thin films evaporated on polyethylene naphthalate films for spin quantum cross devices

Surface morphology of Ni thin films vacuum-deposited on polyethylene naphtalate (PEN) organic films has been investigated as a function of Ni film thickness for spin quantum cross devices. The surface roughness of the Ni films decreases from 1.3nm, being the roughness of PEN films, down to 0.69nm as the thickness of Ni films increases up to 41nm. As a result of the scaling investigation of the surface roughness, the surface roughness for Ni films of sub-10-nm thickness, in the scanning scale of the film thickness, is less than 0.23nm, corresponding to one atomic layer thickness. These experimental results indicate that Ni thin films on PEN films are suitable as a candidate of metal/insulator hybrid materials used for spin quantum cross devices and may open up a novel research field on the electric characteristics of a few atoms or molecules, which leads to high-density memories.

Physical analysis of connected clean units in clean-unit system platform

The time dependence of airborne particle count in connected clean units with a feedback loop in a clean-unit system platform (CUSP) is studied. We have estimated the mutual conductance of air flow in connected CUSP units, and the conductance is confirmed to be irrespective of the sizes of airborne particles. The connected CUSP units can maintain a cleanliness as good as ISO class 1–2 even when they are set in a typical office room. The emission rate of physically adsorbed particles from the inner walls of our CUSP unit is found to be 0.012 m-2 s-1 for particles with diameters of 0.3 µm. The airborne particle count in a deactivated CUSP unit, under the condition that the neighboring CUSP unit is activated, remains only ~5 times larger than that in the activated CUSP units even for particles with diameters of 0.1 µm. The CUSP can serve as a platform for cross-disciplinary fields such as nanostructure physics as well as nanobiotechnologies.

The fabrication of Ni quantum cross devices with a 17 nm junction and their current-voltage characteristics

Quantum cross (QC) devices which consist of two Ni thin films deposited on polyethylene naphthalate substrates with their edges crossing have been fabricated and their current-voltage characteristics have been investigated. The cross-sectional area between the two Ni electrodes, which was obtained without the use of electron-beam or optical lithography, can be as small as 17 nm x 17 nm. We have successfully obtained ohmic current-voltage characteristics, which show good agreement with calculation results within the framework of the modified Anderson model. The calculated results also predict a high switching ratio in excess of 100,000:1 for QC devices having the molecule sandwiched between the Ni electrodes. This indicates that QC devices having the molecule can be expected to have potential application in novel switching devices.

Fabrication of Nickel/Organic-Molecule/Nickel Nanoscale Junctions Utilizing Thin-Film Edges and Their Structural and Electrical Properties

Metal/organic-molecule/metal nanoscale junctions, which consist of poly(3-hexylthiophene):6,6-phenyl C61-butyric acid methyl ester (P3HT:PCBM) organic molecules sandwiched between two Ni thin films whose edges are crossed, which are called quantum cross (QC) devices, have been fabricated and their structural and electrical properties have been investigated. The area of the crossed section, which was obtained without using electron-beam or optical lithography, can be as small as 16×16 nm2. We have obtained ohmic current–voltage characteristics, which show quantitative agreement with the theoretical calculation results performed within the framework of the Anderson model under the strong coupling limit. Calculation results also predict that a high on–off ratio beyond 100000:1 can be obtained in Ni/P3HT:PCBM/Ni QC devices under the weak coupling condition. These results indicate that our method utilizing thin-film edges is useful for creating nanoscale junctions and Ni/P3HT:PCBM/Ni QC devices can be expected to have potential application in next-generation switching devices with high on–off ratios.

Fabrication and Current-Voltage Characteristics of Ni Spin Quantum Cross Devices with P3HT:PCBM Organic Materials

We have proposed spin quantum cross (SQC) devices, in which organic materials are sandwiched between two edges of magnetic thin films whose edges are crossed, towards the realization of novel beyond-CMOS switching devices. In SQC devices, nanometer-size junctions can be produced since the junction area is determined by the film thickness. In this study, we have fabricated Ni SQC devices with poly-3-hexylthiophene (P3HT): 6, 6-phenyl C61-butyric acid methyl ester (PCBM) organic materials and investigated the current-voltage (I-V) characteristics experimentally and theoretically. As a result of I-V measurements, ohmic I-V characteristics have been obtained at room temperature for Ni SQC devices with P3HT:PCBM organic materials, where the junction area is as small as 16 nm x 16 nm. This experimental result shows quantitative agreement with the theoretical calculation results performed within the framework of the Anderson model under the strong coupling limit. Our calculation also shows that a high on/off ratio beyond 10000:1 can be obtained in Ni SQC devices with P3HT:PCBM organic materials under the weak coupling condition.