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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.

All-trans oligo(para-phenylenevinylene) (OPV) methyl thiols of a two-ring phenylene-vinylene dimer and a three-ring trimer have been synthesized to prepare self-assembled monolayers (SMS) onto an Au(1 1 1) surface. The molecular level morphologies of the monolayers prepared on Au surfaces were probed by scanning tunneling microscopy (STM) or atomic force microscopy (AFM). The soluble dimer formed a highly ordered structure lying down on the Au surfaces. The molecules of trimer stand slantwise on the Au surfaces, but the structure of monolayers is less ordered. Another longer OPV methyl thioacetate, a slightly soluble four-ring tetramer, has also been synthesized. Although it was difficult for aggregative molecules of the longer OPV to self-assemble on Au, we could successfully insert the tetramer into tetradecane-1-thiol monolayers on Au surfaces by an exchange reaction. The mixture monolayer showed that the isolated tetramer was adsorbed almost vertically on the Au surfaces.

The electrical conduction of self-assembled monolayers (SAMs) made from conjugated molecules was measured using conductive probe atomic force microscopy (CP-AFM), with a focus on the molecular structural effect on conduction. First, the electrical conduction of SAMs made from phenylene oligomer SAMs was measured. The resistances through the monolayers increased exponentially with an increase in molecular length and the decay constants of transconductance beta were about 0.45 to 0.61 A(-1) measured at lower bias region. We further investigated the influence of applied load on the resistances. The resistances through terphenyl SAMs increased with an increase in the applied load up to 14 nN. Second, using an insertion technique into insulating alkanethiol SAMs, the electrical conduction of single conjugated terphenyl methanethiol and oligo(para-phenylenevinylene) (OPV) molecules embedded into insulating alkanethiol SAMs were measured. Electrical currents through these single molecules of OPVs were estimated to be larger than those through single terphenyl molecules, suggesting that the OPV structure can increase the electrical conduction of single molecules. Third, apparent negative differential resistance (NDR) was observed at higher bias measurements of SAMs. The appearance of NDR might be related to roughness of SAM surface, because apparent NDR was often observed on rough surfaces. In any case, the tip-molecule contact condition strongly affected carrier transport through metal tip/SAM/metal junction.

Oligo(para-phenylene-vinylene)-methanethiol of trimer and dimer have been synthesized to prepare monolayers onto Au(111). The trimer diluted in dichloromethane glows with a brilliant blue fluorescence when excited with UV light (365 nm). The absorption and emission spectra of the dimer diluted in CH 2 Cl 2 show a blue shift. The molecular level morphologies of the monolayers prepared on gold surfaces were probed by scanning tunneling microscopy or atomic force microscopy (AFM). The dimer is entire trans isomer, which formed highly ordered self-assembled monolayers (SAMs) on Au. The trimer is a mixture of cis–trans isomers, and did not form ordered monolayers on Au. However, the trimer molecules could be embedded in dodecanethiol SAM, and showed higher conductance than oligo(para-phenylene) molecules characterized using a conductive AFM.

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 C⋮C 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 N2 adsorption. It was found that the product contains a high amount of mesopores as well as micropores. For example, the meso- and micropore volumes for the carbon heat-treated at 1000 °C were 669−844 and 200−233 mm3/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 m2/g and mesopore area of 877−1126 m2/g, while ...

Polytetrafluoroethylene (PTFE) was defluorinated (carbonized) with lithium-naphthalene complex (radical anion) dissolved in dimethoxyethane. The defluorinated-PTFE exposed in air was found to be composed of fine LiF p articles and amorphous carbon matrix after heating at 70°C-700°C. Porous carbons with high BET specific surface area (1000-1800m2/g-1) were obtained by removal of LiF from these defluorinated PTFE using dilute HCI solution. The results of X-ray diffraction and N2 adsorption measurement suggested that the formation of mesopores in the porous carbons obtained was owing to the presence of LiF fine particle in the matrix carbon.

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.

We demonstrate a procedure for fabricating back-gate-type sub 5 nm gap junctions without using electron beam lithography. The fabricating procedure contains two photolithographic processes followed by shadow evaporation and oxygen plasma ashing. Oligo(para-phenylenevinylene) trimers (OPV3) attached to methylthiol at both ends were bridged between these junctions. The temperature dependence of OPV3 conductance indicated the characteristic behavior of hopping conduction. The results indicate 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.

Porous carbons (Brunauer-Emmett-Teller surface area 999 m 2 /g) prepared by defluorination of polytetrafluoroethylene (PTFE) powder with potassium metal showed a very high capacitance of the electrical double layer (229 F/g). Such a high value is considered to be due not only to the contribution of microporosity, but also to the development of mesoporosity. When the original PTFE was subjected to γ-ray irradiation to reduce the polymerization degree, the carbon obtained in the same procedure showed only a slightly higher value (237 F/g). The relationship between the capacitance and pore size was discussed by taking into consideration the results for conventional activated carbon fibers.