Phthalocyanine molecular nanowires that were prepared using porous alumina as a template: Development in the sample preparation procedure to evaluate electronic properties

We have proposed the synthesis of organic molecular nanowires using porous alumina as a template. We also proposed the use of a magnetic field to control the molecular packing structure in the nanowires. In this paper, we developed the method to evaluate the electronic properties of the nanowire of a phthalocyanine derivative that was synthesized using porous alumina as a template. The developed method facilitates the study in the organic molecular nanowires that were synthesized using templates and helps their use in future electronic devices.     

Structural analysis and transistor properties of hetero-molecular bilayers

We examined the film morphologies and transistor properties of hetero-molecular bilayer consisting of N, N’-dioctyl-3, 4, 9, 10-perylenedicarboximide (PTCDI-C₈) and quaterrylene. First, the structure and carrier conduction of PTCDI-C₈ films were studied, followed by an analysis of the carrier accumulation process in a PTCDI-C₈/quaterrylene hetero-bilayer transistor. Based on the displacement current measurement (DCM), we stress the potential of the hetero-bilayer for tuning carrier accumulation like carrier doping techniques in field-effect transistors.     

Perfect Bi4Ti3O12 Single‐Crystal Films via Flux‐Mediated Epitaxy

Excellent crystallinity of material films and atomic control of their surface/interface, sufficient for the realization of their optimal physical properties, are technological premises for modern functional‐device applications. Bi₄Ti₃O₁₂ and related compounds attract much interest as highly insulating, ferroelectric materials for use in ferroelectric random‐access memories. However, it has been difficult thus far for Bi₄Ti₃O₁₂ films to satisfy such requirements when formed using vapor‐phase epitaxy, owing to the high volatility of Bi in a vacuum. Here, we demonstrate that flux‐mediated epitaxy is one of the most promising and widely applicable concepts to overcome this inevitable problem. The key point of this process is the appropriate selection of a multi‐component flux system. A combinatorial approach has led to the successful discovery of the novel flux composition of Bi–Cu–O for Bi₄Ti₃O₁₂ single‐crystal film growth. The perfect single‐crystal nature of the stoichiometric Bi₄Ti₃O₁₂ film formed has been verified through its giant grain size and electric properties, equivalent to those of bulk single crystals. This demonstration has broad implications, opening up the possibility of preparing stoichiometric single‐crystal oxide films via vapor‐phase epitaxy, even if volatile constituents are required.     

Dynamic mechanical properties of crosslinked polyisoprene under deformation

Summary Molecular motions of elastomers under deformations were observed through dynamic mechanical measurements. Composite master curves of dynamic moduli E and E and loss tangent tan over a wide range of frequency and in a state of elongation were obtained by the time-temperature superposition procedure. It is found that both moduli increase with strain, . The slope of the dispersion curve of E become more gradual with the increase in , while that of E is almost unchanged. The increment of E is generally larger than that of E, which does not agree with the N. W. Tschoegl prediction, E ^* ()=f() E _o ^* (), where E ^* () and E _o ^* () are complex moduli at the strain of and O, respectively, and f() is the function of only . The difference in the strain dependence of E from E was found to correspond to the strain dependence of the equilibrium modulus.     

Anomalous Hall effect governed by electron doping in a room-temperature transparent ferromagnetic semiconductor

Ferromagnetic semiconductors are believed to be suitable for future spintronics, because both charge and spin degrees of freedom can be manipulated by external stimuli. One of the most important characteristics of ferromagnetic semiconductors is the anomalous Hall effect. This is because the ferromagnetically spin-polarized carrier can be probed and controlled electrically, leading to direct application for electronics. Control of the Curie temperature and magnetization direction by electronic field, and photo-induced ferromagnetism have been performed successfully using the anomalous Hall effect for group III-V ferromagnetic semiconductors. In these cases, the operation temperature was much below room temperature because of the limited Curie temperature of less than 160 K (ref. 6). Here, we report on the anomalous Hall effect governed by electron doping in a room-temperature transparent ferromagnetic semiconductor, rutile Ti(1-x)Co(x)O(2-delta) (of oxygen deficiency delta). This result manifests the intrinsic nature of ferromagnetism in this compound, and represents the possible realization of transparent semiconductor spintronics devices operable at room temperature.     

Single‐Electron Tunneling through Molecular Quantum Dots in a Metal‐Insulator‐Semiconductor Structure

A sigle‐electron tunneling (SET) in a metal‐insulator‐semiconductor (MIS) structure is demonstrated, in which C₆₀ and copper phthalocyanine (CuPc) molecules are embedded as quantum dots in the insulator layer. The SET is found to originate from resonant tunneling via the energy levels of the embedded molecules, (e.g., the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO)). These findings show that the threshold voltages for SET are tunable according to the energy levels of the molecules. Furthermore, SET is observable even near room temperature. The results suggest, together with the fact that these properties are demonstrated in a practical device configuration, that the integration of molecular dots into the Si‐MIS structure has considerable potential for achieving novel SET devices. Moreover, the attempt allows large‐scale integration of individual molecular functionalities.     

Growth and structural characterization of molecular superlattice of quaterrylene and N,N′-dioctyl-3,4,9,10-perylenedicarboximide

A molecular superlattice consisting of alternate layers of N,N′-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C₈) and quaterrylene was prepared by using an ultra-slow deposition technique. Film growth under equilibrium conditions with precise optimization of the substrate temperature enabled the layer-by-layer stacking of hetero-molecules at a single-layer level. The morphology of the films and the orientation of the molecules in each layer were analyzed by atomic force microscopy (AFM) and an X-ray reflection (XRR) technique.     

Variable temperature characterization of N,N′-Bis(n-pentyl)terrylene-3,4:11,12-tetracarboxylic diimide thin film transistor

Organic thin film transistors (OTFT) based on N,N′-Bis(n-pentyl)terrylene-3,4:11,12-tetracarboxylic diimide (TTCDI-5C) with Al or Au top-contact electrodes were deposited on SiO₂ (200 nm)/p-Si (0 0 1) substrates. Carrier mobility was examined as a function of temperature in the range from 50 to 310 K. Two distinct carrier transfer behaviours were observed: temperature independent behaviour below 150 K and thermally activated behaviour above 150 K. Activation energies presented values of 85–130 meV depending on the metal electrodes (Au, Al), which can be attributed to the carrier traps at the interface and the energy-level offset between the lowest unoccupied molecular orbital (LUMO) and the work functions of the respective metals.     

Stability of Si impurity in high-κ oxides

The interface structure of a high permittivity (high-κ) oxide with Si substrate affects the electrical properties of the high-κ based transistors. Our theoretical analysis suggests that the formation of a SiO₂ layer at the high-κ/Si interface originates from the instability of a Si impurity in the high-κ oxide. Our computational results revealed that the Si impurity is much more stable in La₂O₃ than in HfO₂, indicating La₂O₃ is a silicate former, while SiO₂ is likely to precipitate at the HfO₂/Si interface.