Nanotechnological applications of carbon nanotubes have been significantly developed in a recent couple of years. In this article, starting from a general introduction, we overview the recent progress of the quantum transport properties of carbon nanotubes.
Electron emission from various types of nanotubes, e.g., multiwall nanotubes (MWNTs) with capped and open ends, and single-wall nanotubes (SWNTs), was investigated by field emission microscopy (FEM). Field emission patterns originating from the pentagons placed on a cap of a nanotube were observed for the capped MWNTs with clean surfaces. Emission current versus voltage characteristics revealed that open MWNTs possess the most excellent properties as field emitters among the nanotubes investigated. As an application of nanotube field emitters, field emission displays (FED) equipped with nanotube cathodes are now attracting considerable attention. Fabrication and performance of nanotube-based FED elements are also reviewed briefly. When a positive electric potential, being an opposite potential to the case of electron emission, was applied to nanotubes, carbon clusters were directly emitted from nanotubes through field evaporation. We found that C20+ were selectively emitted from both MWNTs and SWNTs under an extremely high field over 10 V/nm.
A family of fulleren including C60 and in addition carbon nanotubes have been discovered as new allotropes of carbon at the final stage of 20th century. These materials are characterized not only in terms of small sized shapes but also of unique electronic, electrical and mechanical properties, which are not possessed by well known carbon materials, graphite and diamond. Especially, nanotubes have several advantages to be used as the probes for scanning probe microscopy. Recently, we have developed a well controlled process to bring about carbon-nanotube probes for practical devices. The process consists of electrophoresis of the nanotubes we developed previously and handling nanotubes in a scanning electron microscope equipped with two individual manipulatable stages. In this article, we review how nanotubes have been applied to scanning-probe-microscope probes and what have been observed by the new devices, and also view a future scope in this field.
It is predicted that carbon nanotubes have high stiffness and axial strength, such as Young's modulus as high as ∼1 TPa, due to their seamless cylindrical graphitic structure. However, direct measurements of their mechanical properties are difficulties, because of their very small dimensions. In this article, we review experimental techniques and data of mechanical properties of individual multiwalled carbon nanotubes reported so far. We also mention of the nanomechanics of carbon nanotubes, that we have examined by scanning electron microscopy using manipulation technique. Young's modulus of the nanotubes, estimated from the buckling under the force acting on the axial direction, agrees well with the value estimated from the bending under the force acting on the side face. These findings indicate that the nanotube can be treated as an isotropic material in conventional mechanics.
A single walled nanotube (SWNT) has been placed a lot of attention, simply because this new form carbon material has been shown to be a potential material for many types of applications. In this paper, we will describe some new aspects of SWNTs, placing special emphasis on the characteristic feature of gas storage property.
This article illustrates several examples of self-assembled multi-phase nanostructures found in the nanotubes and nanoparticles in the BCN ternary system. Spatially resolved EELS is proved to be an efficient technique to diagnose such composite nano-structures. Examples cover wide range of specimens: carbon nanotube with boron or nitrogen, BN/C composite nanotube and BN/C nanobox. These composite nanotubes and nanoparticles can be prospects for the future nanodevices.
Two examples of spectroellipsometric (SE) analysis for surfaces and thin films are given. The first example is ZnO epitaxial layers deposited on C- and A-surfaces of sapphire substrates. The surface roughness layer in terms of Bruggeman effective medium approximation was inevitable to explain the measured ψ and Δ spectra. Thickness of the surface layer deposited on C-surface is larger than that on A-surface. SEM and AFM observations are made to check the data by optical measurements. The second example is a simultaneous evaluation of the surface adsorption layer thickness and the Si substrate temperature. Influence of statistical deviation of the initial values in the multiparameter analysis is demonstrated. XPS observation is made to check the optical measurements and the advantage of SE comparing with XPS is described.
One of the striking capability of atomic force microscopy (AFM) is the direct observation of surface atoms and adsorbed molecules on nonconductive materials such as zeolites. The observation can be made under various environments including vacuum, ambient and underwater. We have been successful in observing in situ atomic images of heulandite and stilbite (010) surfaces under aqueous environments, and also molecular images of liquid-phase-adsorbed organics on these surfaces. The unprecedented resolution of the AFM imaging enabled us to determine, for the first time, the positions of framework oxygen and extra-framework cations, and furthermore the array and orientation structures of adsorbed molecules such as pyridine bases. The present paper reviews our recent findings on the structure and energetics of those adsorption systems.
The behavior of Na in SiO2 film during SIMS depth profiling was characterized by varying the sample temperature from 154 K to 303 K under the condition of self-compensation of charges. The depth distributions of the defects in the films were analyzed also using ESR and FT-IR, and the influence of the defects on Na behavior during SIMS analysis is discussed. At lower temperatures, the SIMS profiles almost fit that of a simulated Na distribution and it is considered that Na distributions are hardly affected by the defects in the film. However, with increasing temperature, the migration of Na toward the defects occurs and the resultant Na distributions are affected by the defects in the film. Thus, it was clarified that Na migration is induced by the defects in the film during SIMS analysis, even in the absence of the electric field caused by charging.
The growth process of a self-assembled monolayer (SAM) of thiophene on Au(111) was studied by Fourier-transform infrared reflection absorption spectroscopy (FT-IR-RAS). FT-IR-RAS measurements of the SAM revealed two stages of growth process and the polymorphism. In the primary stage, thiophene in the SAM orients parallel to the gold substrate. In the second stage, thiophene reorients to the perpendicular position against the gold substrate. The phase transition of the molecular orientation in the growth process is mainly controlled by the balance between the intermolecular and the thiophene-gold interactions.