Masahito Kushida

Study on the Electrical Conduction Mechanism in Al2O3/Polyimide Langmuir-Blodgett Film Systems

We fabricated Al/Al2O3/polyimide Langmuir-Blodgett films (PI LB)/Al (MIM) and Al/Al2O3/PI LB/Al/Al2O3/PI LB/Al (MIMIM) junctions by means of the LB technique, and then examined the electrical transport properties of the junctions from the tan δ values of these junctions. For MIM junctions, the tunneling conduction mechanism dominated in PI LB films when the number of deposited PI LB films was less than 4. In contrast, the bulk conduction mechanism dominated when the number of deposited PI LB films was greater than 5. For MIMIM junctions, the tan δ value of the junctions was about 10% of that of MIM-external wire-MIM junctions. It was concluded that middle Al/Al2O3 layers sandwiched between top Al and base Al electrodes control the number of electrons passing through MIMIM junctions.

Energy Quenching Effects on Dry-Etching Durability of Copolymers and Polymer Blends of Vinylnaphthalene or α-Methyl Styrene with Methyl Methacrylate

Durabilities for O2 reactive ion etching (O2RIE) were studied as a function of number-average molecular weight (Mn) of poly(methyl methacrylate) [PMMA], poly(α-methyl styrene) [PMSt] and poly(2-vinylnaphthalene) [PVN]. Etching rates were independent of the Mn and in the descending order of PMMA, PMSt and PVN. Dry-etching durability which was defined as the reciprocal of etching rate relative to PMMA, of PVN was higher than that of PMSt. 2-Vinylnaphthalene (VN) moiety was found to be more effective for enhancing dry-etching durability than α-methyl styrene (MSt). Dry etching durabilities of copolymers (PMMA-co-MSt, PMMA-co-VN) were equal to those of polymer blends (PMMA/PMSt, PMMA/PVN) of the same composition and larger than the values calculated from the constituent homopolymers assuming the wt% or vol% additivity as the estimated bombardment probability by ion and neutral active species.

Organic Bistable Memory Switching Phenomena in Squarylium-Dye Langmuir-Blodgett Films

We have investigated the relationship between the switching phenomena and H-like aggregates in squarylium-dye Langmuir-Blodgett (SQ LB) films. The current-voltage characteristics of SQ LB films sandwiched between the top gold electrode and the bottom aluminum electrode indicated conductance switching phenomena below the temperature of 100°C but not at 140°C. Current densities suddenly increased at switching voltages between 2 and 4 V. The switching voltage increased as the temperature increased between room temperature and 100°C. Current densities were 50–100 µA/cm2 in a low-impedance state (ON state). A high-impedance state (OFF state) can be recovered by applying a reverse bias, and therefore, these bistable devices are ideal for memory applications. The dependence of conductance switching phenomena and ultraviolet-visible absorption spectra on annealing temperatures was studied. The results revealed that conductance switching phenomena were caused by the presence of H-like aggregates in the SQ LB films.

Large Electric Conductance in the Interface Direction of Polar/Nonpolar Double-Layered Hetero-Langmuir-Blodgett Films

Aluminum, arachidic acid (C20) multilayered and/or 2-dodecyl-7,7,8,8-tetracyanoquinodimethane (C12TCNQ) multilayered Langmuir-Blodgett (LB) films, and aluminum were deposited successively on a substrate. The electric conductance in the interface direction of the upper-Al/C12TCNQ/C20/under-Al structure, upper-Al/C20/C12TCNQ structure, and other control structures was measured using the four-point probe method. The electric conductance in the interface direction of only the upper-Al/C12TCNQ/C20/under-Al structure with the number of deposited LB layers between 3 and 5 was 10 or 100 times larger than that of the control structures, including aluminum thin films.

Dry-Etching Durability of Copolymers and Polymer Blends of Vinylnaphthalene or α-Methylstyrene with Methyl Methacrylate

Dry-etching durabilities of poly(2-vinylnaphthalene-co-methyl methacrylate), the blend of poly(2-vinylnaphthalene) and poly(methyl methacrylate) [PMMA], and poly(α-methylstyrene-co-methyl methacrylate) films were studied as a function of vinylnaphthalene or α-methylstyrene content against four types of dry etching: 1) O2 plasma etching ( O2 PE), 2) O2 reactive ion etching ( O2 RIE), 3) Ar+ sputter etching (Ar SE), and 4) Ar ion beam etching (Ar IBE). Since the etching depth increased linearly with etching time the two-component polymer films were regarded to be etched uniformly without selected removal of aliphatic monomer units. Substantial enhacement of the durability was observed by incorporating or blending small amounts of aromatic moiety into PMMA for physical etching (Ar SE, Ar IBE) and physical/chemical etching ( O2 RIE) as well as chemical etching ( O2 PE). O2 RIE is a synergetic process involving both physical bombardment and chemical reaction.

Study on the dielectric loss tan σ of metal-insulator-metal and metal-insulator-metal-insulator-metal junctions with polyimide Langmuir-Blodgett films

Abstract We fabricated metal-insulator-metal-insulator-metal (MIMIM) junctions and MIM-external wire-MIM junctions by means of the conventional Langmuir-Blodgett technique in order to clarify the dielectric and electrical transport properties of MIM condensers. The tan σ value of MIMIM junctions was one-third or one-fourth as large as that of MIM-external wire-MIM junctions. In contrast, the capacitance of MIMIM junctions was nearly equal to that of MIM-external wire-MIM junctions. These experimentals results were explained by assuming that middle Al Al 2 O 3 layers in MIMIM junctions control the number of electrons passing through the MIMIM junctions.

Conductance switching phenomena and H-like aggregates in squarylium-dye Langmuir-Blodgett films

The current–voltage characteristics of sandwich devices with the structure of top gold electrode/squarylium-dye Langmuir-Blodgett (SQ LB) films/bottom aluminum electrode indicated four kinds of conductivity depending on the evaporation conditions of the top gold electrode. The current densities of two, which showed conductance switching, of the four samples were 30–40 µA/cm2 and 20–30 mA/cm2 in the ON state. In the former case, the dependence of conductance switching voltage on the number of SQ LB films and ultraviolet-visible absorption spectra were studied. The results revealed that conductance switching phenomena were induced at the interface between the top gold electrode and SQ LB films, and caused by the presence of H-like aggregates in SQ LB films.

Ultralow Resistivity in Langmuir-Blodgett Heterofilms of Much Less than the Metal Resistivity and Ultrahigh Current Density

Ultralow resistivity in Langmuir-Blodgett (LB) heterofilms of much less than the metal resistivity was briefly reported in the previous paper, and such remarkable characteristics seem to be due to the two-dimensional potential well with electron gas generated in the LB heterofilms. In the present paper, detailed data of the ultralow resistivity are described with data related to temperature (room temperature ~75°C) and ambient air pressure. The minimum resistivity of 4.0×10-12Ωcm was measured; furthermore, an ultrahigh current density of 2.0×106 A/cm2 was observed.

Preparation and characterization of oriented poly(vinyl alcohol)/carbon nanotube composite nanofibers

Oriented nanofiber mats blended with carbon nanotubes (CNTs) are expected to be applied as cell seeding scaffolds. Biomaterials that are often used for cell seeding scaffolds generally have low mechanical strength and low electrical conductivity; thus, it has been difficult to apply them to tissues such as heart and nerve. In this study, we prepared oriented poly(vinyl alcohol) (PVA) nanofiber mats blended with various CNT concentrations (up to 10 wt %) by electrospinning using the parallel plate electrodes as collectors with applied voltage. The morphology, mechanical properties, and electrical properties of the prepared oriented nanofiber mats were measured by using various techniques such as scanning electron microscopy (SEM). The tensile strength of the oriented nanofiber mats in the applied voltage direction increased from 2.5 to 9.7 MPa with CNT concentration. Furthermore, the electrical conductivity of the oriented nanofiber mats in the applied voltage direction increased from 0.67 × 10−7 to 4.3 × 10−7 Sm−1. Also, the mechanical strength and electrical conductivity of the oriented nanofiber mats in the applied voltage direction were 3–4 and 2–3 times higher than those in the perpendicular direction, respectively.

Film fabrication of Fe or Fe3O4 nanoparticles mixed with palmitic acid for vertically aligned carbon nanotube growth using Langmuir–Blodgett technique

Vertically aligned carbon nanotubes (VA-CNTs) were studied as a new catalyst support for polymer electrolyte fuel cells (PEFCs). Controlling the number density and the diameter of VA-CNTs may be necessary to optimize PEFC performance. As the catalyst for CNT growth, we fabricated Fe or Fe3O4 nanoparticle (NP) films by the Langmuir–Blodgett (LB) technique. The catalyst Fe or Fe3O4 NPs were widely separated by mixing with filler molecules [palmitic acid (C16)]. The number density of VA-CNTs was controlled by varying the ratio of catalyst NPs to C16 filler molecules. The VA-CNTs were synthesized from the catalyst NP–C16 LB films by thermal chemical vapor deposition (CVD) using acetylene gas as the carbon source. The developing solvents used in the LB technique and the hydrogen reduction conditions of CVD were optimized to improve the VA-CNT growth rate. We demonstrate that the proposed method can independently control both the density and the diameter of VA-CNTs.