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We demonstrate the gate voltage (VGS) frequency dependences of displacement current (Idis) and channel current (IDS), which were simultaneously measured under the application of a triangular wave of VGS and a constant drain voltage in top-contact pentacene organic thin-film transistors (OTFTs). Carrier injection and carrier transport properties, such as field-effect mobility, threshold voltage, and carrier injection voltages at the source and drain electrodes, were evaluated; they showed no frequency dependences at frequencies between 1 and 50 kHz. From the source current -VGS and drain current -VGS characteristics, a charge sheet at the interface of the pentacene thin-film and gate dielectric was found to form below the source and drain electrodes in this frequency range. For the practical use of OTFTs, a simultaneous measurement system for Idis and IDS is a simple and powerful technique for evaluating both carrier injection and carrier transport properties under OTFT operations.

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.

The stochastic single-molecule conductance switchings of nitro-substituted oligo(phenylene–ethynylene) (OPE) molecules in three kinds of host matrices of octanethiol (C8), decanethiol (C10), and dodecanethiol (C12) self-assembled monolayers (SAMs) have been studied by scanning tunneling microscopy (STM). The stochastic single-molecule conductance switching of OPE molecules has been observed repeatedly in both the low-density striped phase of the C8 SAM and the high-density standing-up phases of the C10 and C12 SAMs by successive STM. The mean apparent height differences between the inserted OPE and the host matrices of the C8, C10, and C12 SAMs are approximately 11.9, 4.8, and 4.2 A, respectively.

Nontrivial multipass interference fringes are found in the photoluminescence spectra taken from a single-quantum-well structure in the backscattering geometry. Fringe spacing indicates light interference within the 3.3-µm-thick capping layer, whereas the transmission spectra apparently lack the corresponding fringes. This indicates that an otherwise unlikely detour of photons towards the rough backside of the 350-µm substrate is relevant, which gives rise to a 3.3-µm-thick ghost cavity. The visibility of such ghost-cavity fringes is the largest for a single emission layer and is even enhanced by forward-scattering, which can facilitate light-emitter design rather than compromising the peak assignment of spectra.

We fabricated light-emitting diodes (LEDs) having an n+-Ge/p+-Si structure with ferromagnetic metal/insulator tunnel contact. Clear electroluminescence (EL) with peak wavelength around 1600 nm from the direct band gap of the Ge layer was successfully observed at room temperature, which indicates that tunnel contacts allow efficient direct-gap EL from the LED. Our result is an important step toward developing Ge-based spin-polarized LEDs.

We studied the Bi wire-δ-doping process to achieve a high concentration of Bi donors in Si. Our process has two steps: (i) burial of Bi nanowires in Si by molecular beam epitaxy, and (ii) activation of Bi atoms in the δ-doped layer by laser annealing. The peak concentration of Bi atoms in the δ-doped layer is controlled by two parameters: the coverage of surfactant layer, and the growth temperature during the Si cap-layer growth, whose maximum concentration is larger than 1020 cm-3. Photoluminescence and electrical carrier transport measurements reveal that dense Bi atoms are activated upon heating the area at close to the melting point of Si. As a result, our doping process results in Bi donors in the wire-δ-doped layer with concentration of >1018 cm-3. This will be useful for establishing next-generation, quantum information processing platform.

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.

Alkanethiol-protected Au nanoparticles have been chemically immobilized on Au(111) substrates by alkanedithiol and alkanethiol mixed self-assembled monolayers (SAMs). Octanethiol SAMs on Au(111) have been used as host matrices for molecular insertion by 1,8-octanedithiol (C8S2) and 1,10-decanedithiol (C10S2). The dithiol molecules in the mixed SAMs and the Au nanoparticles on the mixed SAMs were observed by scanning probe microscopy. The densities of C8S2 and C10S2 mixed SAMs were controlled by varying the dithiol concentration from 0.5 to 50 mM. The densities of Au nanoparticles were almost equal to those of the dithiol molecules, indicating that the Au nanoparticle chemisorbed through the protruding sulfur of the dithiol molecules displaced the protecting group of the Au core. The chemisorbed Au nanoparticles were stable for scanning tunneling spectroscopy (STS) measurements. The resistance of the chemisorbed nanoparticles between the Au core and the Au(111) substrate is discussed.