Low-temperature field ion microscopy of carbon nanotubes

Abstract

The methods of high-resolution field ion microscopy with sample cooling to liquid helium temperature are used in a study of the products of gas-phase catalytic pyrolysis of hydrocarbons in the form of graphitized fibers containing carbon nanotubes. Full atomic resolution of the end cap of closed carbon nanotubes is achieved for the first time. It is found that the atomic structure of the tops of the caps of subnanometer carbon tubes consists predominantly of hexagonal rings. A possible reason for the improvement of the resolution of field ion images of nanotubes upon deep cooling is discussed.

Field-Ion Microscopy of Quantum Oscillations of Linear Carbon Atomic Chains

“…With that end in view, one can try to use high-resolution field-ion microscopy (FIM) of one-dimensional objects. Taking into account the general trend toward enhancement of the FIM resolution with the miniaturization of pointed nanospecimens – the method of low-temperature FIM can be considered a promising candidate for realizing and visualization of the quantum ground state of a mechanical oscillator based on carbon atomic chains. The purpose of this work is revealing and exploring quantum oscillations of free-standing carbon atomic chains using a high-resolution method of field ion microscopy.…”

“…Free-standing carbon nanotubes were revealed during field evaporation of needle-shaped specimens prepared from the pyrolytic carbon fibers 1−5 μm in diameter and of the order of a millimeter in length. These fibers were obtained by the gas-phase catalytic pyrolysis of hydrocarbons . They had a graphitized carcass containing a large number of multiwall carbon nanotubes which were oriented along the axis of the fiber.…”

“…In conventional FIM of specimens corresponding to an atomically smooth paraboloid, β is about 1.5, and the geometrical field factor χ has an approximate value of 5. However, for one-dimensional nanoprotrusions on the tips these values are drastically understated …”

“…These fibers were obtained by the gas-phase catalytic pyrolysis of hydrocarbons. 10 They had a graphitized carcass containing a large number of multiwall carbon nanotubes which were oriented along the axis of the fiber.…”

“…However, for one-dimensional nanoprotrusions on the tips these values are drastically understated. 10 To calculate the trajectories, magnification, and resolution of FIM images of the single carbon atomic chain on the needle-shaped (paraboloidal) electrode, we used the analytical model of the potential distribution, in which the chain stands normally on the parabolic electrode with the radius of curvature r 0 , having a cylindrical shape of height l and closed with a hemispherical cap with radius F ) 0.12 nm. 14,15 Our calculations are limited to points near the tip symmetry axis, which corresponds to the z-direction, with z ) 0 being the top of cylindrical part of the model (the inset in Figure 1).…”