Tatsuro Hanajiri

Single Electron Device with Asymmetric Tunnel Barriers

A single electron device with asymmetric tunnel barriers (ATBs) is proposed, and its operation simulated by computer. Current in the ATB structure is dominated by Fowler-Nordheim tunneling while that in a conventional symmetric tunnel barrier (STB) structure is determined by direct tunneling. Consequently, the ATB has two remarkable advantages over STB. First, the tunnel resistance of ATB depends on the energy of tunneling electron and is determined independently of the barrier capacitance. Second, the tunneling of electrons becomes almost unilateral in ATB and bilateral in STB. These advantages of ATB make it easier to fabricate single electron circuits with high speed, high temperature and low power consumption.

Suppression of short channel effects by full inversion in deep sub-micron gate SOI MOSFETs

Abstract Classical modeling of fully inverted SOI MOSFET (FI MOSFET) has been performed. In FI MOSFETs, the top Si layer is thinner than the thickness of the inversion layer at the conducting state and so the depleted region in the top Si layer is completely eliminated. It was found that the gate electric field induces carriers in the channel more effectively in FI MOSFET than in the fully depleted SOI MOSFETs (FD MOSFET), so that the short channel effects can be suppressed significantly.

Suppression of Drain-Induced Barrier Lowering in Silicon-on-Insulator MOSFETs Through Source/Drain Engineering for Low-Operating-Power System-on-Chip Applications

In this paper, the authors propose novel metal-oxide-semiconductor field-effect transistor (MOSFET) types featuring additional L-shaped counterdoped areas in the source and/or drain regions of silicon-on-insulator (SOI) MOSFETs to reduce drain-induced barrier lowering (DIBL) through the buried oxide (BOX) layer. The L-shaped region in the drain area shields the BOX layer from penetration by the drain electric field, thereby reducing DIBL in the body region. Simulation of the electrical characteristics of these novel MOSFETs demonstrated more remarkable DIBL suppression and subthreshold slope performance in short-channel regions than in conventional SOI MOSFETs. In addition to this suppression, these novel MOSFETs suppress breakdown voltage more effectively than conventional SOI MOSFETs. The authors concluded that the proposed devices are capable of contributing to the scaling of SOI MOSFETs in ultralarge-scale integration circuits.

Intracellular trafficking of superparamagnetic iron oxide nanoparticles conjugated with TAT peptide: 3-dimensional electron tomography analysis

Internalisation of nanoparticles conjugated with cell penetrating peptides is a promising approach to various drug delivery applications. Cell penetrating peptides such as transactivating transcriptional activator (TAT) peptides derived from HIV-1 proteins are effective intracellular delivery vectors for a wide range of nanoparticles and pharmaceutical agents thanks to their amicable ability to enter cells and minimum cytotoxicity. Although different mechanisms of intracellular uptake and localisation have been proposed for TAT conjugated nanoparticles, it is necessary to visualise the particles on a 3-D plane in order to investigate the actual intracellular uptake and localisation. Here, we study the intracellular localisation and trafficking of TAT peptide conjugated superparamagnetic ion oxide nanoparticles (TAT-SPIONs) using 3-D electron tomography. 3-D tomograms clearly show the location of TAT-SPIONs in a cell and their slow release from the endocytic vesicles into the cytoplasm. The present methodology may well be utilised for further investigations of the behaviours of nanoparticles in cells and eventually for the development of nano drug delivery systems.

Synthesis of an Ultradense Forest of Vertically Aligned Triple-Walled Carbon Nanotubes of Uniform Diameter and Length Using Hollow Catalytic Nanoparticles

It still remains a crucial challenge to actively control carbon nanotube (CNT) structure such as the alignment, area density, diameter, length, chirality, and number of walls. Here, we synthesize an ultradense forest of CNTs of a uniform internal diameter by the plasma-enhanced chemical vapor deposition (PECVD) method using hollow nanoparticles (HNPs) modified with ligand as a catalyst. The diameters of the HNPs and internal cavities in the HNPs are uniform. A monolayer of densely packed HNPs is self-assembled on a silicon substrate by spin coating. HNPs shrink via the collapse of the internal cavities and phase transition from iron oxide to metallic iron in hydrogen plasma during the PECVD process. Agglomeration of catalytic NPs is avoided on account of the shrinkage of the NPs and ligand attached to the NPs. Diffusion of NPs into the substrate, which would inactivate the growth of CNTs, is also avoided on account of the ligand. As a result, an ultradense forest of triple-walled CNTs of a uniform internal diameter is successfully synthesized. The area density of the grown CNTs is as high as 0.6 × 10(12) cm(-2). Finally, the activity of the catalytic NPs and the NP/carbon interactions during the growth process of CNTs are investigated and discussed. We believe that the present approach may make a great contribution to the development of an innovative synthetic method for CNTs with selective properties.

Synthesis of nanoparticles composed of silver and silver chloride for a plasmonic photocatalyst using an extract from a weed Solidago altissima (goldenrod)

Phytosynthesis of nanomaterials is advantageous since it is economical, ecofriendly, and simple, and, what is more, in the synthetic protocols, nontoxic chemicals and biocompatible materials are used. Here, a green synthetic methodology of nanoparticles (NPs) composed of silver (Ag) and silver chloride (AgCl) NPs is developed using a leaf extract of Solidago altissima as a reducing agent for the first time. Utilization of a terrestrial weed for the synthesis of Ag and AgCl NPs is a novel environmentally friendly approach considering that no toxic chemicals, external halide source, or elaborate experimental procedures are included in the process. The optical properties and elemental compositions of as-synthesized Ag and AgCl NPs are well characterized, and the degradation of an organic dye, i.e., rhodamine B (RhB), is investigated using the Ag and AgCl NPs. We find that degradation of RhB is effectively achieved thanks to both surface plasmon resonance and semiconductor properties of Ag and AgCl NPs. The surface-enhanced Raman scattering and antibacterial activities are also examined. The present approach to the synthesis of NPs using a weed may encourage the utilization of hazardous plants for the creation of novel nanomaterials.

Quantitative Extraction of Electric Flux in the Buried-Oxide Layer and Investigation of Its Effects on MOSFET Characteristics

Silicon-on-insulator (SOI) MOSFETs have advantages over conventional bulk MOSFETs in terms of their electrical characteristics, but also have inherent disadvantages due to the presence of their buried-oxide (BOX) layers. In this paper, focus was placed on drain electric flux passing via the BOX layer to the body region as an influence that induces disadvantages such as drain-induced barrier lowering in SOI MOSFETs. The electric flux in the BOX layer was visualized using stream functions, and was quantitatively evaluated for the first time ever. The results showed the dependence of electric flux on relative permittivity and the BOX layer thickness. These outcomes confirmed that the subthreshold slope (SS) in short-channel SOI MOSFETs is affected strongly by electric flux detouring via the BOX layer, and the compact model of the enhancement of SSs due to the flux is proposed.

Investigating the chemical mist deposition technique for poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) on textured crystalline-silicon for organic/crystalline-silicon heterojunction solar cells

Chemical mist deposition (CMD) of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) was investigated in terms of cavitation frequency f, solvent, flow rate of nitrogen, substrate temperature Ts, and substrate dc bias Vs as variables for efficient PEDOT:PSS/crystalline silicon (c-Si) heterojunction solar cells. The high-speed-camera and differential mobility analysis characterizations revealed that the average size and flux of PEDOT:PSS mist depend on f, type of solvent, and Vs. Film deposition occurred when positive Vs was applied to the c-Si substrate at Ts of 30–40 °C, whereas no deposition of films occurred with negative Vs, implying that the film is deposited mainly from negatively charged mist. The uniform deposition of PEDOT:PSS films occurred on textured c-Si(100) substrates by adjusting Ts and Vs. The adhesion of CMD PEDOT:PSS film to c-Si was greatly enhanced by applying substrate dc bias Vs compared with that of spin-coated film. The CMD PEDOT:PSS/c-Si heterojunction solar cell devices on textured c-Si(100) in 2 × 2 cm2 exhibited a power conversion efficiency η of 11.0% with better uniformity of the solar cell parameters. Furthermore, η was increased to 12.5% by adding an AR coating layer of molybdenum oxide MoOx formed by CMD. These findings suggest that CMD with negatively charged mist has great potential for the uniform deposition of organic and inorganic materials on textured c-Si substrates by suitably adjusting Ts and Vs.

In-depth profiling of electron trap states in silicon-on-insulator layers and local mechanical stress near the silicon-on-insulator/buried oxide interface in separation-by-implanted-oxygen wafers

In-depth profiling of electron trap states in silicon-on-insulator (SOI) layers of separation-by-implanted-oxygen (SIMOX) wafers was carried out using the drain current-gate voltage characteristics of metal-oxide-semiconductor field-effect transistors (MOSFETs) with different SOI thicknesses, and the density of electron trap states in a gate oxide (GOX) layer thermally grown on them was measured using the gate tunneling current-gate voltage characteristics of MOSFETs. It was found that in-depth profiles of electron trap states in SOI layers have a broad peak at around 25 nm from the SOI/buried oxide (BOX) interface, and that the density of electron trap states in a GOX layer grown on the 25-nm-thick SOI layer reaches a maximum there. A morphology study using Auger electron spectroscopy and Raman spectroscopic study revealed a correlation among the density of trap states in an SOI layer, roughness, and local mechanical stress near the SOI/BOX interface. This correlation is understood to imply that local me...

Capture of nonmagnetic particles and living cells using a microelectromagnetic system

We develop a microelectromagnetic system to trap nonmagnetic materials such as micropolystyrene particles and yeast cells in particular areas. We fabricate gold films, the width of the central narrow part is 22 μm, and flow an electric current through the films. We then apply an external uniform dc magnetic field to weaken the local magnetic field at the narrow part so that a nonuniform magnetic field is produced. We demonstrate that the particles, which are dispersed in magnetic fluid, are successfully trapped at the narrow part of the film. We evaluate the driving force acting on a microparticle in the nonuniform magnetic field and carry out a Stokesian dynamics simulation of the motion of the particles. We show that yeast cells are also trapped at the narrow part of the film. Finally, we fabricate multichannel microelectromagnets so that yeast cells are trapped at multiple points in the microelectromagnetic system. The present system may be applied to cell transfection on a cell microarray and, therefo...