Toshifumi Terui

Molecular stacking in epitaxial crystals of oxometal phthalocyanines

Molecular stacking structures in epitaxial crystals of oxotitanium and oxovanadium phthalocyanines (TiOPc and VOPc) prepared by physical vapor deposition (PVD) and molecular beam epitaxy (MBE), respectively, onto the (001) face of a KBr substrate were investigated by means of x-ray and electron diffraction studies. In thin epitaxial film of VOPc deposited by MBE at a substrate temperature of 20 °C, the flat-lying molecules oriented in the (3×3) commensurate square lattice (a=1.40 nm) were alternately stacked with body-centered head-to-head and a/4-slipped face-to-face dimeric bilayers. The crystal structure determined was the triclinic space group P1 with a=b=1.40, c=1.06 nm, α=109.2, β=133.9, γ=90.0°, Z=2. When TiOPc was thickly deposited by PVD at a substrate temperature of 200 °C, islandlike crystals epitaxially grew in a truncated pyramidal morphology and assumed the same orientation. In the pyramidal crystals the thick molecular layer stacking separate from the KBr surface was relaxed and had a squa...

Light Emission from Porphyrin Molecules Induced by a Scanning Tunneling Microscope

Positioning of a scanning tunneling microscope (STM) tip above Cu-tetra-(3,5-di-tertiary-butyl-phenyl)-porphyrin (Cu-TBPP) molecules on Cu(100) is found to induce plasmon-mediated emission and molecular luminescence when bias voltages are above ~ 2.3 V. Optical spectra acquired at a low current of 0.2 nA suggest not only the enhancement effect of the molecules on light emission but also new features associated with the molecules. The quantum efficiency of such light emission excited by inelastic tunneling is on the order of 10-6 photons per electron.

A photoresponsive single electron transistor prepared from oligothiophene molecules and gold nanoparticles in a nanogap electrode

Gold nanoparticle-oligothiophene pentamer networks were prepared in a nanogap electrode and their photoresponsive and conductive properties were measured. Coulomb diamond appeared in the differential conductance map of the device at cryogenic temperatures, indicating that the device worked as a single electron transistor. Upon irradiation with UV light, the current showed discontinuous changes. The I-VSD curve and differential conductance mapping before and after irradiation showed that the abrupt changes in current can be explained by a shift in the potential of the Coulomb island.

Photoresponses in Gold Nanoparticle Single-Electron Transistors with Molecular Floating Gates

We have proposed a simple method of activating advanced functions in single-electron transistors (SETs) based on the specific properties of individual molecules. As a prototype, we fabricated a copper phthalocyanine (CuPc)-doped SET. The device consists of a gold-nanoparticle (GNP)-based SET doped with CuPc as a photoresponsive floating gate. In this paper, we report the details of the photoresponses of the CuPc-doped SET, such as conductance switching, sensitivity to the wavelength of the incident light, and multiple induced states.

Charge transport in various dimensions of small networks composed of gold nanoparticles and terthiophene wire-molecules

We report the charge transport properties of networks composed of several to tens of gold nanoparticles (GNPs) linked by dithiolated terthiophene (3T) molecules. A large activation energy was observed for the conductance of networks with lesser dimensions. This bahavior is explained in terms of the charging energy of the GNPs in the current path. The Efros-Shklovskii variable range hopping model [A. L. Efros and B. I. Shklovskii, J. Phys. C 8, L49 (1975)] qualitatively describes the transport properties, where the dimensionality of the network and the small tunneling resistance of 3T serve as important factors.

Superperiodic conductance in a molecularly wired double-dot system self-assembled in a nanogap electrode

We examined charge transport properties of two gold nanoparticles (GNPs) in a nanogap transistor with a gap width of ∼10 nm. The GNPs connected to each other and to outer electrodes through a small number of dithiolated terthiophene wire molecules as a tunneling barrier. The transport property measured at 11 K was analyzed based on the theory of double-dot single-electron transistors and inelastic cotunneling. The results clearly show mutual Coulomb interactions between the two GNPs. Moreover, we found the appearance of superperiodic conductance, because of differences in the charging energy of the two GNPs.

Photoinduced conductance switching in a dye-doped gold nanoparticle transistor

Photoinduced conductance switching was demonstrated in a copper phthalocyanine (CuPc)-doped gold nanoparticle (GNP) transistor formed in a nanogap electrode with a back gate structure. Two specific states were reversibly induced in conductance of the CuPc-doped devices by light irradiation and applied voltages. The probability of occurrence of conductance switching decreased with a reduction in the number of incident photons. In addition, conductance switching was not observed in the devices before CuPc doping. Conductance switching originates from change in the local potential of GNPs, possibly induced by a charge-state bistability of an individual CuPc molecule worked as a floating gate.

Bacteriorhodopsin-based bipolar photosensor for biomimetic sensing

Bacteriorhodopsin (bR) is a promising biomaterial for several applications. Optical excitation of bR at an electrode-electrolyte interface generates differential photocurrents while an incident light is turned on and off. This unique functional response is similar to that seen in retinal neurons. The bR-based bipolar photosensor consists of the bR dip-coated thin films patterned on two ITO plates and the electrolyte solution. This bipolar photocell will function as a biomimetic photoreceptor cell. The bipolar structure, due to the photocurrent being generated in alignment with the cathodic direction, makes the excitatory and inhibitory regions possible. This scheme shows our bipolar cell can act as a basic unit of edge detection and forms the artificial visual receptive field.

Preparation of Ultrahigh-Density Magnetic Nanowire Arrays beyond 1 Terabit/Inch2 on Si Substrate Using Anodic Aluminum Oxide Template

Ultrahigh-density Co nanowire arrays were fabricated by the combined use of the anodic aluminum oxide (AAO) template formed on a Si substrate and pulse DC electrodeposition. The AAO templates were prepared with the anodic voltages from 3 to 40 V, whose diameters were from 15 to 40 nm. Using the AAO template with an anodic voltage less than 3 V, the wire density exceeded 2.88 Tbit/in.2. The magnetic property of the nanowire arrays indicated a strong perpendicular magnetic anisotropy, and we observed the tendency of increase in coercivity with decreasing nanowire diameter.

Filling of FePt in AAO Nanohole Array by DC Pulsed Electrodeposition

The ferromagnetic nanowires embedded in anodized aluminum oxide (AAO) are important candidates for the perpendicular magnetic recording media. In the current study, we filled FePt in the AAO nanohole arrays using a pulse DC electrodeposition. By changing the ratio between the on-time and the off-time of the pulse, we found it possible to uniformly fill FePt in AAO at the pulse off-time longer than the pulse on-time. Moreover, we found that the filling of FePt became more difficult with the shrinkage of holes diameter from 70 nm to 20 nm.