We construct a kink solution on a non-BPS D-brane using Berkovits' formulation of superstring field theory in the level truncation scheme. The tension of the kink reproduces 95% of the expected BPS D-brane tension. We also find a lump-like solution which is interpreted as a kink-antikink pair, and investigate some of its properties. These results may be considered as successful tests of Berkovits' superstring field theory combined with the modified level truncation scheme.
For obtaining molecular devices using metal-molecule-metal junctions, it is necessary to fabricate a steady conductive bridge-structure; that is stable chemical bonds need to be established from a single conductive molecule to two facing electrodes. In the present paper, we show that the steadiness of a conductive bridge-structure depends on the molecular structure of the bridge molecule for nanogap junctions using three types of modified oligo(phenylene vinylene)s (OPVs): alpha,omega-bis(thioacetate) oligo(phenylene vinylene) (OPV1), alpha,omega-bis(methylthioacetate) oligo(phenylene vinylene) (OPV2), and OPV2 consisting of ethoxy side chains (OPV3). We examined the change in resistance between the molecule-bridged junction and a bare junction in each of the experimental Au-OPV-Au junctions to confirm whether molecules formed steady bridges. Herein, the outcomes of whether molecules formed steady bridges were defined in terms of three types of result; successful, possible and failure. We define the ratio of the number of successful junctions to the total number of experimental junctions as successful rate. A 60% successful rate for OPV3 was higher than for the other two molecules whose successful rates were estimated to be approximately 10%. We propose that conjugated molecules consisting of methylthioacetate termini and short alkoxy side chains are well suited for fabricating a steady conductive bridge-structure between two facing electrodes.
Porous carbon materials were prepared by direct reduction of poly(tetrafluoroethylene) (PTFE) powder with potassium vapor. After the reaction, the black powder product under vacuum showed a Raman peak at around 1950 cm -1 , which was assigned to the CtC bond in a polyyne-type structure. After the byproduct, potassium fluoride, was removed, by using hydrogen fluoride, the powder was heat-treated up to 2800 °C in an argon atmosphere. The structural changes of the powder with heat treatment were analyzed by Raman spectroscopy. The changes in the pore structure were examined by N 2 adsorption. It was found that the product contains a high amount of mesopores as well as micropores. For example, the mesoand micropore volumes for the carbon heat-treated at 1000 °C were 669-844 and 200-233 mm 3 /g, respectively. The same experiments were performed by using γ-irradiated PTFE powder. The product gave a more porous structure, i.e., a higher total surface area of 1385-1516 m 2 /g and mesopore area of 877-1126 m 2 /g, while the carbon derived from the nonirradiated polymer showed 1041 and 620 m 2 /g, respectively. The formation mechanism of the porous carbons is discussed on the basis of the polymer aggregation, and the effects of defluorination and γ-irradiation on the polymer.
We describe a procedure for fabricating sub-5 nm gap junctions with sub-100 nm
electrode-width using conventional photolithography. The fabrication procedure involves
two photolithographic processes followed by shadow evaporation and electromigration.
After lift-off following the second metal shadow evaporation, a nanoscale wire with a
diameter less than 100 nm is fabricated along a sidewall of the second patterned
photo-resist. The nanowire is cut by a milliamp current flow, then a sub-5 nm gap metal
junction with a sub-100 nm electrode-width is fabricated. The temperature dependence of
the conductance of the molecular wires that were bridging the junctions over the ultrasmall
gap indicated a hopping conduction behaviour. The results demonstrate that these
junctions can be used in the study of conductance measurements through molecular
wires.
We describe a technique for acquiring current-voltage (I–V) characteristics of a metal-molecule-metal junction using a conducting probe atomic force microscopy (CP-AFM) technique. To conduct a repetitive experiment efficiently, we have utilized the current imaging tunneling spectroscopy (CITS) mode of the CP-AFM system. We have prepared a self-assembled monolayer of 1-decanethiol on Au(111) substrate where 4,4'-bis(mercaptomethyl)-trans-stilbene (BMMS) molecules have been incorporated. We demonstrate that we have constructed a conductivity map derived from a set of CITS data. Conductance peaks presumably involved by BMMS molecules have been found in the conductivity map and the corresponding I–V curves have exhibited fluctuations in current. The causes of the current fluctuations are also discussed.
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