Carbon Nanotube Bridges Research Articles

Bonding Process for Nanoscale Wiring Using Carbon Nanotube by STM Tip

A nano-scale bonding process using a multi-wall carbon nanotube (CNT) has been successfully applied in a scanning electron microscope (SEM)/scanning tunneling microscope (STM) combined system. Under the SEM observation, a Ti-coated STM tip was approached onto a CNT bridging Ti pads, which is patterned with a 4 µm gap on a SiO2 surface, to investigate the conduction property of the CNT. A voltage pulse of 12 V peak and 50 µs duration was applied in order to deposit Ti clusters onto the CNT, which is well known as a field evaporation process in the STM regime. The two-terminal current-voltage characteristics of the CNT have been improved from a nonlinear behavior at 2.5 V of 208 kΩ to a linear one of 1.8 kΩ.

Toward Large Arrays of Multiplex Functionalized Carbon Nanotube Sensors for Highly Sensitive and Selective Molecular Detection.

Arrays of electrical devices with each comprising multiple single-walled carbon nanotubes (SWNT) bridging metal electrodes are obtained by chemical vapor deposition (CVD) of nanotubes across prefabricated electrode arrays. The ensemble of nanotubes in such a device collectively exhibits large electrical conductance changes under electrostatic gating, owing to the high percentage of semiconducting nanotubes. This leads to the fabrication of large arrays of low-noise electrical nanotube sensors with 100% yield for detecting gas molecules. Polymer functionalization is used to impart high sensitivity and selectivity to the sensors. Polyethyleneimine coating affords n-type nanotube devices capable of detecting NO2 at less than 1 ppb (parts-per-billion) concentrations while being insensitive to NH3. Coating Nafion (a polymeric perfluorinated sulfonic acid ionomer) on nanotubes blocks NO2 and allows for selective sensing of NH3. Multiplex functionalization of a nanotube sensor array is carried out by microspotting. Detection of molecules in a gas mixture is demonstrated with the multiplexed nanotube sensors.

Fabrication of multiwalled carbon nanotube bridges by poly-methylmethacrylate suspended dispersion

We report on the fabrication of multiwalled carbon nanotube (MWCNT) bridges using poly-methylmethacrylate (PMMA) suspended dispersion. This method makes it possible to suspend nanotubes between metal electrodes, without any chemical etching of the substrate, and to remove unwanted nanotubes from the substrate. Using a spacer layer of PMMA with a known thickness, it is also possible to control the suspended height of the MWCNT bridges. The electrical measurement results on suspended MWCNT bridges reveals that the room temperature resistance ranges from under a kΩ to a few MΩ, with the majority around 2–4 kΩ. It was shown that a plasma-enhanced chemical vapor deposition grown MWCNT with a diameter ∼55 nm can sustain current densities of ∼108 A/cm2, which will make them suitable for applications as integrated field emission cathodes.

熱化学気相成長法によるカーボンナノチューブ 金属微粒子間架橋構造の形成

We synthesized carbon nanotube (CNT) bridges between Fe nanoparticles by low pressure thermal chemical vapor deposition using etylene gas. At low temperatures, randomly oriented CNTs were dominantly grown with increasing gas pressure. By optimizing the growth conditions, horizontally oriented straight CNTs bridged between Fe particles were obtained under a low pressure of 100 Pa.

Synthesis of carbon nanotube bridges on patterned silicon wafers by selective lateral growth

Floated carbon nanotube bridges were synthesized on a patterned silicon wafer by thermal chemical vapor deposition of acetylene. A conventional photolithography was used to define the catalytic nickel line patterns. The carbon nanotubes grow laterally from the side face to side face of the nickel catalyst by a SiO2 vertical growth barrier deposited on the nickel layer. The typical diameter of carbon nanotube bridges is 10–30 nm and it depends on the thickness of the catalytic nickel layer. Our laterally grown carbon nanotubes have a bamboo structure in which the spacing of compartment layers increases with an increase in temperature. We can control the length, linearity, and density of the carbon nanotube bridges by adjusting various synthetic process parameters and find they may possibly be applied to nanoelectronic devices.

Direct Nanowiring of Carbon Nanotubes for Highly Integrated Electronic and Spintronic Devices

A feasible fabrication technique for nanomachines that are based on carbon nanotubes (CNTs) is demonstrated. Direct nanowiring of CNTs between micrometer islands is reported to have been achieved by a growth barrier technique, which prevents vertical growth of the CNTs, i.e., towards the substrate. The result is “straight” or “Y-shaped” CNT bridges between predefined electrodes (see Figure).