We developed a new method for mass synthesis
of BN nanotubes of high purity by using carbon free CVD technique
as shown in the next figure.
2.Hydrogen absorption of BN nanotubes
We found that BN nanotubes absorb hydrogen gas. The absorption increases until 4 wt% at 10 MPa of hydrogen pressure by surface modifying with platinum fine particles. The nanotubes are expected to serve as new hydrogen accumulators.
3.Fluorine doping of BN nanotubes
It was found that BN nanotubes change to semiconductor from insulator by fluorine doping. A following figure shows a measurement of electrical properties of a BN nanotube by four-probe technique.
4.Functionalization of BN nanotubes
and creation of polymer films
BN nanotubes can be dispersed in a chloroform solution uniformly by surface treatment with a PmPV polymer. Combination with polymers such as polystyrene results in an insulating film that is transparent and mechanically, and thermally stable. The films are expected to serve as a new light-weight material for IC boards having good thermal conductance, and mechanical, and thermal stability.
5.Creation of BN nanocables
We succeeded in creation of BN nanocables in which a single crystalline metal such as a Fe-Ni Invar nanowire is embedded. Since BN nanotubes are insulating, the cables are expected to find use in electronic devices.
6.Discovery of BN nanocones
We found that BN nanocones have a characteristic structure with a sharp apex angle of 39 degrees. Since they are chemically and mechanically stable, it is suggested that they may be utilized for AFM probes.
7.Creation of conical BN nanotubes
We found BN nanotubes that have walls made of a conically wrapped BN sheet. The length of the nanotube reaches 100 micrometers.
Discovery of nanothermometer
1.Discovery of carbon nanothermometer
We found that a carbon nanotube including liquid gallium can work as a thermometer. The expansion of liquid gallium in the carbon nanotube is proportional to temperature and fully reversible. Gallium is supercooled up to -80 oC and it remains liquid due to a confinement effect. The results were published in Nature (2002), and reviewed in The Dairy Yomiuri and New York Times, and had a wide resonance. Furthermore, the nanothermometer was recorded in the Guinness Book as the world smallest thermometer. Nanothermometers are expected to be used as a local temperature sensor on a micron scale, and to be useful for trouble-shooting of semiconducting devices and bio-sensors.
2.Nanothermometer using oxide nanotubes
Carbon nanotubes are easily oxidized above 500 oC in air. By using an oxide nanotube that is stable at high temperature, it is possible to measure higher temperature than that by carbon nanothermometer. We succeeded to create novel single crystalline nanotubes of In2O3 and MgO. A following figure shows a SEM image of a single crystalline MgO nanotube that has a rectangle shape with 50 nm dimensions and its core is empty. These tubes may be used as liquid metal containers for the use as nanothermometers. We also succeeded in creation of SiO2 and Ga2O3 nanothermometers.
Novel non-carbon inorganic nanotubes
We investigate novel nanotubes with various compositions different from carbon. Here some nanotubes created in our group are shown.
1.Si nanotubes and microtubes
We succeeded in fabrication of Si single crystalline nanotubes. The process was completed in 4 steps: creation of ZnS single crystalline nanowires of 50 nm in diameter, reaction with Si vapor, creation of core-shell type nanowire of ZnS/Si of 100 nm in diameter, and finally dissolution of ZnS nanowires with hydrochloric acid. Also Si amorphous microtubes with several micrometers in diameter can be fabricated by thermal decomposition of a SiO powder.
2.Novel nanotubes of ZnS, GaN, AlN and
InN
Numerous novel nanotubes are made by a CVD method and their structures are analyzed.
In-situ TEM electrical and
mechanical measurements on nanotubes
In-situ TEM setup using a piezo-driven
holder for the analysis of electron transport and deformation
of nanotubes (left) and a representative I-V curve measured
on an individual Boron Nitride nanotube inside TEM (right)
Structure and properties of
filled nanotubes
Types and applications of filled nanotubes
analyzed within the Group (left); low- and high-resolution
TEM images of a Fe-Co magnetic alloy filled Carbon nanotube;
the interface between the Fe-Co alloy nanowire and the shielding
nanotube clearly reveals atomic steps on the wire/tube boundary.
Making electrical nanoswitch
based on liquid Ga-filled C nanotube
Electrical nanoswitch made of a liquid
Ga-filled Carbon nanotube; (left) the nanotube is placed between
two metal electrodes and a gap in a Ga-filling is made with
the aid of an atomic force microscope tip (1); under heating
the two Ga columns approach each other due to thermal expansion
and finally merge (2-4); two-probe electrical resistance of
the filled tube is measured at various stages of the process
(top-right); when the columns merge the resistance drastically
drops producing a unique switching action. (Low-right) the
process of column approaching recorded in TEM.
Unusual behavior of Indium liquid
in silica nanotubes
We succeeded to synthesize silica nanotubes encapsulating indium metal. (Adv. Mater. 16, 37, 2004) Unusual dynamical behaivior can be revealed during 'in-situ' observations in an electron microscope.
Dynamical observation of bending and kinking of BN nanotubes
Real-time movies of individual multi-walled Boron Nitride nanotube bending (upper frame) and kinking (low frame) recorded inside a high-resolution 300 kV JEOL-3000F transmission electron microscope using a new fully integrated TEM-AFM piezo-driven holder under continuous tracking of force-displacement values. These results were reported by us in Nano Lett. Vol. 7, No. 7, 2146-2157, 2007: [Golberg D. et al. “Direct force measurements and kinking under elastic deformation of individual multiwalled Boron Nitride nanotubes”].
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