Atomic switches: atomic-movement-controlled nanodevices for new types of computing

Atomic switches are nanoionic devices that control the diffusion of metal cations and their reduction/oxidation processes in the switching operation to form/annihilate a metal atomic bridge, which is a conductive path between two electrodes in the on-state. In contrast to conventional semiconductor devices, atomic switches can provide a highly conductive channel even if their size is of nanometer order. In addition to their small size and low on-resistance, their nonvolatility has enabled the development of new types of programmable devices, which may achieve all the required functions on a single chip. Three-terminal atomic switches have also been developed, in which the formation and annihilation of a metal atomic bridge between a source electrode and a drain electrode are controlled by a third (gate) electrode. Three-terminal atomic switches are expected to enhance the development of new types of logic circuits, such as nonvolatile logic. The recent development of atomic switches that use a metal oxide as the ionic conductive material has enabled the integration of atomic switches with complementary metal-oxide-semiconductor (CMOS) devices, which will facilitate the commercialization of atomic switches. The novel characteristics of atomic switches, such as their learning and photosensing abilities, are also introduced in the latter part of this review.     

Gas dwell time control for rapid and long lifetime growth of single-walled carbon nanotube forests

The heat history (i.e., "dwell time") of the carbon source gas was demonstrated as a vital parameter for very rapid single-walled carbon nanotube (SWNT) forest growth with long lifetime. When the dwell time was raised to 7 s from the 4 s used for standard growth, the growth rate increased to 620 μm/min: a benchmark for SWNT forest growth on substrates. Importantly, the increase in growth rate was achieved without decreasing either the growth lifetime or the quality of the SWNTs. We interpret that the conversion rate of the carbon feedstock into CNTs was selectively increased (versus catalyst deactivation) by delivering a thermally decomposed carbon source with the optimum thermal history to the catalyst site.     

Enhanced tensile ductility in bulk nanocrystalline nickel electrodeposited by sulfamate bath

Electrodeposition is one of the fabrication techniques to produce nanocrystalline materials. In this paper, bulk nanocrystalline Ni (nc-Ni) was electrodeposited by using a sulfamate bath which generated low residual stress. In order to enhance tensile property of bulk nc-Ni, we investigated influences of glossing agents and bath condition on tensile properties, as these are reported to have an influence on surface condition, grain size and microhardness. It was found that saccharin contents and current density have significant effects on tensile properties of bulk nc-Ni. Moreover, we successfully obtained bulk nc-Ni displaying tensile ductility of over 10%. In particular, bulk nc-Ni from sulfamate bath with 5.0 g/l saccharin exhibited superior plastic deformation and good tensile strength (UTS = 1.2 GPa, ε_f = 15%). We were able to develop the relationship between tensile strength and ductility to a higher level on nc-Ni.     

Enzyme biosensor based on plasma-polymerized film-covered carbon nanotube layer grown directly on a flat substrate

We report a novel approach to fabrication of an amperometric biosensor with an enzyme, a plasma-polymerized film (PPF), and carbon nanotubes (CNTs). The CNTs were grown directly on an island-patterned Co/Ti/Cr layer on a glass substrate by microwave plasma enhanced chemical vapor deposition. The as-grown CNTs were subsequently treated by nitrogen plasma, which changed the surface from hydrophobic to hydrophilic in order to obtain an electrochemical contact between the CNTs and enzymes. A glucose oxidase (GOx) enzyme was then adsorbed onto the CNT surface and directly treated with acetonitrile plasma to overcoat the GOx layer with a PPF. This fabrication process provides a robust design of CNT-based enzyme biosensor, because of all processes are dry except the procedure for enzyme immobilization. The main novelty of the present methodology lies in the PPF and/or plasma processes. The optimized glucose biosensor revealed a high sensitivity of 38 μA mM(-1) cm(-2), a broad linear dynamic range of 0.25-19 mM (correlation coefficient of 0.994), selectivity toward an interferent (ascorbic acid), and a fast response time of 7 s. The background current was much smaller in magnitude than the current due to 10 mM glucose response. The low limit of detection was 34 μM (S/N = 3). All results strongly suggest that a plasma-polymerized process can provide a new platform for CNT-based biosensor design.     

High electrical performance of carbon nanotubes/rubber composites with low percolation threshold prepared with a rotation-revolution mixing technique

The present study demonstrates a novel mixing approach for achieving a good dispersion of carbon nanotubes (CNTs) in a styrene-butadiene rubber (SBR), which leads to a significant improvement in electrical properties. Our mixing technique consists of (1) pretreatment by ultrasonication to disentangle the bundles of CNTs in organic solvent and (2) “rotation-revolution” mixing of the CNTs with SBR without mechanical shear, which prevents CNTs from collapsing during the mixing process. The present mixing method does not require the addition of any dispersing agents (amphiphilic molecules) or chemical modification of the CNTs to obtain a good dispersion. Compared with a conventional Banbury mixing technique, our method leads to a significant decrease in the percolation threshold (less than 1 phr), where the electrical conductivity suddenly increases due to the formation of percolation networks of CNTs in SBR. This is because the aspect ratio of the CNTs was maintained even after the mixing process, whereas CNTs were broken during the conventional Banbury mixing. The effect of using different types of CNTs on electrical conductivity was also investigated. The results show that the percolation threshold is largely related to the structural quality (graphitization) of the CNTs as well as their aspect ratio.     

Biomolecule-recognition gating membrane using biomolecular cross-linking and polymer phase transition

We present for the first time a biomolecule-recognition gating system that responds to small signals of biomolecules by the cooperation of biorecognition cross-linking and polymer phase transition in nanosized pores. The biomolecule-recognition gating membrane immobilizes the stimuli-responsive polymer, including the biomolecule-recognition receptor, onto the pore surface of a porous membrane. The pore state (open/closed) of this gating membrane depends on the formation of specific biorecognition cross-linking in the pores: a specific biomolecule having multibinding sites can be recognized by several receptors and acts as the cross-linker of the grafted polymer, whereas a nonspecific molecule cannot. The pore state can be distinguished by a volume phase transition of the grafted polymer. In the present study, the principle of the proposed system is demonstrated using poly(N-isopropylacrylamide) as the stimuli-responsive polymer and avidin-biotin as a multibindable biomolecule-specific receptor. As a result of the selective response to the specific biomolecule, a clear permeability change of an order of magnitude was achieved. The principle is versatile and can be applied to many combinations of multibindable analyte-specific receptors, including antibody-antigen and lectin-sugar analogues. The new gating system can find wide application in the bioanalytical field and aid the design of novel biodevices.     

Effect of pyrophosphates as supporting matrices on proton conductivity for NH4PO3 composites at intermediate temperatures

Composite electrolytes of NH₄PO₃/pyrophosphate (NH₄PO₃/ZrP₂O₇, NH₄PO₃/Sr₂P₂O₇, and NH₄PO₃/TiP₂O₇) with various molar ratios were fabricated, and their thermal and electrochemical properties were compared at intermediate temperatures. The XRD pattern of NH₄PO₃/Sr₂P₂O₇ composite was consistent with a mixed phase of crystalline NH₄PO₃ and Sr₂P₂O₇ regardless of the composition ratio, whereas those of the other composites were identical to pyrophosphates. A significant difference in conductivity was observed depending on the supporting matrices of pyrophosphates although each composite contained almost the same molar concentration of NH₄PO₃. Among the composites, NH₄PO₃/ZrP₂O₇ (molar ratio; 1:1) exhibited the highest proton conductivity, which was more than twice that of NH₄PO₃/TiP₂O₇ (1:1). The conductivity of NH₄PO₃/Sr₂P₂O₇ (2:1) composite was 2–3 orders of magnitude lower than that of NH₄PO₃/ZrP₂O₇ (1:1). These results suggest that the surface property of pyrophosphates strongly affects the electrochemical properties of composites. Furthermore, a fuel cell that used NH₄PO₃/ZrP₂O₇ composite as an electrolyte was successfully demonstrated at 300 °C.     

Cytotoxicity evaluation of reactive metabolites using rat liver homogenate microsome-encapsulated alginate gel microbeads

We present an improved cytotoxicity test for reactive metabolites, in which the S9 microsomal fraction of rat liver homogenate is encapsulated in alginate gel microbeads to avoid cytotoxic effects of S9-self-generated toxicants, microsomal lipid peroxides. The S9-encapsulated gel microbeads were prepared by a coaxial two-fluid nozzle and surfaces of the microbeads were coated with poly-L-lysine (PLL). Although the initial metabolic rate of the S9-encapsulated gel microbeads was about 20% slower than that of bare S9, the microbeads prevented the leakage of microsomal lipid peroxides thanks to the dense alginate and PLL polymer networks. In fact, the half maximal effective concentration of the indirect mutagen cyclophosphamide on NIH3T3 cells in the presence of the S9-encapsulated gel microbeads was about 5 times higher than that in the presence of bare S9. Use of the S9-encapsulated gel microbeads enabled the more accurate evaluation of the cytotoxicity of the reactive metabolites without the S9-based cytotoxicity.     

Formation of dioxins from incineration of foods found in domestic garbage

There has been great concern about the large amounts of garbage produced by domestic households in the modern world. One of the major sources of dioxins (PCDDs, PCDFs, and coplanar PCBs) in the environment is the combustion of domestic waste materials. Exhaust gases from an incinerator, in which mixtures of 67 food items--including fruits, vegetables, pasta, seafoods, meats, and processed foods and seasoned foods--were analyzed for dioxins. Gases collected at the chimney port (9.15 ng/g) contained less total dioxins than those collected at the chamber port (29.1 ng/g). The levels of Cl1-Cl6-PCDDs and Cl1-Cl5-PCDFs were much lower in the gas collected at the chimney port than in the gas collected at the chamber port. The levels of Cl7-Cl8-PCDDs and Cl6-Cl8-PCDFs were higher in the gas collected at the chimney port than in the gas collected at the chamber port. A total of Cl4-Cl8-PCDDs (1.84-3.04 ng/g) comprised over 80% of the total PCDDs formed (2.24-4.00 ng/g). Total PCDFs (16.2-22.6 ng/g) comprised 78-86% of the total dioxins formed (18.9-29.1 ng/g). The PCDFs formed in the greatest amounts were M1CDFs (9.68-10.7 ng/g). Mixtures of commonly consumed food items produced ppb levels of total dioxins in exhaust gases upon combustion, suggesting that incineration of domestic food wastes is one of the sources of dioxins in the environment. A mixture containing some seasoned foods, such as mayonnaise spread on bread, produced more dioxins (29.1 ng/g) than a mixture without seasoned foods did (18.9 ng/g).     

Analysis of estrogen-like compounds in the environment by high performance liquid chromatography bioassay

To identify chemicals with endocrine-disrupting activity easily, we developed a new bioassay system, consisting of bioassay using genetically modified yeast expressing human estrogen receptor and high performance liquid chromatography (HPLC), in which advantages of instrumental analysis and bioassay are combined. The peaks in the mixture of these estrogen-like compounds analyzed using an HPLC bioassay were similar to those obtained by analysis using an HPLC-UV detector. Underground water and sea sediment were analyzed by an HPLC bioassay, and detected a few estrogen-like compounds, respectively. Estrogen-like compounds and yeast-growth inhibitors can be separated by HPLC-bioassay.