Thermoelectric Power of a Single van der Waals Interface between Carbon Nanotubes.

Control of van der Waals interfaces is crucial for fabrication of nanomaterial-based high-performance thermoelectric devices because such interfaces significantly affect the overall thermoelectric performances of the device due to their relatively high thermal resistance. Such interfaces could induce different thermoelectric power from the bulk, i.e., interfacial thermoelectric power. However, from a macroscopic point of view, a correct evaluation of the interfacial thermoelectric power is difficult owing to various interface configurations. Therefore, the study of the thermoelectric properties at a single interface is crucial to address this problem. Herein, we used in situ transmission electron microscopy and nanomanipulation to investigate the thermoelectric properties of carbon nanotubes and their interfaces. The thermoelectric power of the bridged carbon nanotubes was individually measured. The existence of the interfacial thermoelectric power was determined by systematically changing the contact size between the two parallel nanotubes. The effect of interfacial thermoelectric power was qualitatively supported by Green's function calculations. When the contact length between two parallel nanotubes was less than approximately 100 nm, the experimental results and theoretical calculations indicated that the interface significantly contributed to the total thermoelectric power. However, when the contact length was longer than approximately 200 nm, the total thermoelectric power converged to the value of a single nanotube. The findings herein provide a basis for investigating thermoelectric devices with controlled van der Waals interfaces and contribute to thermal management in nanoscale devices and electronics.

Electrical conductivity of a single parallel contact between carbon nanotubes.

Interfacial resistance plays a critical role in the transport properties of nanomaterial-based assemblies. However, understanding of them remains limited due to the difficulty of experimental approaches. Here we report in situ measurements of the electrical resistance of a single parallel contact between carbon nanotubes. By varying the contact length systematically, we derive the electrical conductivities of carbon nanotubes and interfaces. The interface between nanotubes exhibits conductivity intermediate between those of pyrolytic and single-crystal graphite. The threshold contact length between interface- and bulk-dominant electrical transport is quantitatively estimated.

Visualization of Thermal Transport within and between Carbon Nanotubes.

Despite the excellent thermal properties of individual carbon nanotubes (CNTs), the thermal characteristics of macroscopic CNT assemblies are poor. This is probably due to the presence of numerous nontrivial intertube boundaries. Currently, clarity on the inherent difference between intra- and inter-CNT thermal conductivities is not well-established. Herein, we report an in situ nanoscale observation on the anisotropic thermal transport of a single bundle of CNTs by monitoring evaporated gold nanoparticles as "thermomarkers". The experimental results indicate that even a small bundle shows colossal thermal anisotropy due to the intertube boundaries. The results are validated by finite element analysis that estimates an anisotropic thermal conductivity ratio greater than 100. The estimated value is much greater than most of the reported values measured on macroscopic specimens and matches with that of highly ordered pyrolytic graphite. Our study reveals the intrinsic thermal anisotropy of bundled CNTs and aids in visualizing nanoscale thermal transport.

Development of a sample holder for synchrotron radiation-based computed tomography and diffraction analysis of extraterrestrial materials.

A sample holder for a suite of synchrotron radiation measurements on extraterrestrial materials, which are fragile and irregularly shaped, was developed using carbon nanotubes and polyimide. The holder enables investigation of such samples with multiple analytical instruments, which means that we can reduce the number of sample transfers between holders. The holder developed in our study also enables investigation of such samples without exposure to the terrestrial atmosphere, which contains abundant contaminants, such as water vapor and organic substances. The stability of the samples in the holder during the measurements and disturbance of the analysis result by the holder were evaluated, which showed that sample drift motion and image disturbance due to x-ray attenuation and scattering of the holder materials are insignificant.

Experimental determination of the diameter-dependent wettability of carbon nanotubes as studied using atomic force microscopy.

The wettability of individual carbon nanotubes (CNTs) with <20 nm diameter was experimentally evaluated on the basis of the Wilhelmy method via atomic force microscopy to visualize the effect of the nanometer-scale curvature of a solid surface on the solid-liquid and solid-vapor interface tensions. The experimental results showed the deviation of force owing to wetting for diameters <10 nm. In particular, for nanotubes with <4.5 nm diameter, the wettability tended to differ from its previously predicted behavior. The diameter-dependent wettability seen below 10 nm can be attributed to the interaction between the curved solid surface and the curved liquid adsorption layer formed on the CNT surface. In the scale where the radius of curvature is less than 5 nm, the thermodynamics perspective may not be valid, and thus, an atomistic perspective must be considered.

In Situ Observation of Wetting Ionic Liquid on a Carbon Nanotube.

The wetting behavior of an ionic liquid (IL) on individual carbon nanotubes (CNTs) was experimentally investigated using in situ electron microscopy. The tip of a single CNT was brought into contact with the surface of the IL using a nanomanipulator. The formation of a meniscus was observed immediately at the contact point. A thin layer of IL also formed simultaneously across the entire CNT surface. The force because of wetting was measured using the Wilhelmy method. After correcting the macroscale classical equations by considering an "apparent" diameter that corresponds well with the thickness of the IL layer on individual CNTs, the experimental data indicated that the wettability of single CNTs with diameters of over 10 nm was subjected to classical laws at the macroscale.

Refilling of carbon nanotube cartridges for 3D nanomanufacturing.

Metal-filled carbon nanotubes (CNTs) are known to be used as pen-tip injectors for 3D manufacturing on the nanoscale. However, the CNT interior cannot accumulate enough material to fabricate complex metallic nanostructures. Therefore a method for refilling the CNT cartridge needs to be developed. The strategy for refilling of CNT cartridges is suggested in this study. Controlled growth of gold nanowires in the interior of isolated CNTs using a real-time manipulator installed in a transmission electron microscope is reported herein. The encapsulation process of discrete gold nanoparticles in the hollow spaces of open-ended multi-wall CNTs was evaluated in detail. The experimental results reveal that the serial loading of isolated gold nanoparticles allows the control of the length of the loaded nanowires with nanometer accuracy. Thermophoresis and the coalescence of gold nanoparticles are assumed to be the primary mechanisms responsible for gold loading into a CNT cartridge.

Thermal/electron irradiation assisted coalescence of Sc3N@C80 fullerene in carbon nanotube and evidence of charge transfer between pristine/coalesced fullerenes and nanotubes.

Sc3N@C80 fullerenes are inserted inside carbon nanotubes (CNTs). The results show that the thermal stability of Sc3N@C80 fullerenes is around 1200 °C for the fullerenes resting on the wall of CNTs. Internal fullerenes show stability up to 1300 °C, which portrays them as one of most stable types of fullerenes. Electron irradiation of the peapods at 90 kV leads to the formation of capsules inside the CNTs at 5 × 10(9) e nm(-2) electron dosage. This value is an order of magnitude higher than the threshold of electron-induced damage in C60 molecules. Electron energy loss spectroscopy confirms the presence of Sc atoms in capsules. Encapsulation of fullerenes and capsule formation changes the oxidation state of Sc atoms from +2.5 towards +3. This is an evidence of charge transfer between the fullerene/capsule cage and CNT walls.

A molecular linear motor consisting of carbon nanotubes.

We experimentally investigated a "molecular-linear-motor" system consisting of a capsule-like carbon nanotube (CNT) in the interior space of a host CNT. Transmission electron microscopy revealed the capsule traveled back and forth between both ends of the hollow space along the axial direction and rotated simultaneously. The mechanism was well explained with molecular dynamics simulation by considering the driving force supplied from thermal energy. The present system operates around room temperature and this opens up the possibility of designing novel nanodevices such as oscillators and switching memory devices.

Single-step synthesis of gold-silver alloy nanoparticles in ionic liquids by a sputter deposition technique.

The simultaneous sputter deposition of gold and silver onto ionic liquids formed bimetallic alloy nanoparticles, which exhibited composition-sensitive surface plasmon resonance, the peak wavelength being red-shifted with an increase in the surface area of the gold foil targets sputtered.

Direct observation of six-membered rings in the upper and lower walls of a single-wall carbon nanotube by spherical aberration-corrected HRTEM.

Atomic arrangements of the continuous network of six-membered rings in a single graphene sheet constituting a single-wall carbon nanotube was imaged successfully by employing a spherical aberration-corrected HRTEM operated at 120 kV acceleration voltage. Utilizing two advantages of the aberration-corrected HRTEM, the images separately resolved the rings in the upper and lower walls. Such images can be considered to be the first "tomographic" atomic images taken by HRTEM. This is a striking result that changes the conventional concept of HRTEM as a projection image.