STM AND AFM INVESTIGATION OF CARBON NANOTUBES
L. P. Biro1, 2, G. I. Márk1, J. Gyulai1, P. A. Thiry 2
1 MTA-Research Institute
for Technical Physics and Materials Science, H-1525
Budapest, P. O. Box 49, Hungary
2 Facultés Universitaires Notre Dame de La
Paix, LASMOS, B-5000, Namur, Rue de Bruxelles 61, Belgium
e-mail : biro@mfa.kfki.hu
Carbon nanotubes are a new allotrope of carbon discovered in 1991 by Iijima [1]. The single wall carbon nanotubes are constituted of an atomic plane with a graphite like arrangement of C atoms - called a graphene sheet - which is perfectly rolled into a cylinder, their typical diameter is in 1 nm range. The multi-wall carbon nanotubes are built from several concentric layers of graphene cylinders with an interlayer spacing of 3.4 A in-between the layers, their external diameters are in the range of several 10 of nm. The ends of a carbon nanotube may be capped by a fullerene-like (or a higher fullerene-like hemisphere), or the tube end may be open.
The carbon nanotubes have remarkable electronic and mechanic properties which made them to be in the focus of research in the last years. The carbon nanotubes may have metallic or semiconducting behavior depending on the way the graphene sheet is rolled to form the tube. The results of theoretic and experimental work have been summarized recently [2, 3].
Scanning tunneling microscopy (STM), and atomic force microscopy (AFM) are uniquely suited for the investigation of nano-objects with typical dimensions in the nm range. These techniques have been successfully used for the geometric characterization of carbon nanotubes, and to acquire data about the electronic, electric and mechanic properties of individual carbon nanotubes. An overview of the STM and AFM results will be given.
The application of STM to the investigation of carbon nanotubes grown by different procedures will be presented with emphasis on the image formation mechanism [4] and the tunneling particularities which arise from the fact that the carbon nanotube is not integral part of the support on which it is placed, but floats on the van der Waals potential [5]. Results of computer simulations by the numerical solving of the time dependent Schrödinger equation will be discussed.
AFM investigation of carbon nanotubes produced by very high energy heavy ion irradiation of graphite will be discussed. Carbon nanotubes are found to grow from the clouds of sputtered carbon atoms where dense nuclear cascades intersect the sample surface. Frequently the carbon nanotubes exhibit a regular vibration pattern when scanned by the AFM tip. Computer modeling of the vibration will be presented.