Introduction

STM is able to acquire data regarding the electronic structure of a single nanotube[1,2]. There are some differences in STM imaging of a three dimensional object ''floating'' over the surface of the support as compared with STM applied on flat surfaces.

1.

Convolution effects arise from the geometry at the very end of STM tip. As we reported earlier[5] this will produce an apparent broadening of the nanotube.

2.

Existence of two tunneling gaps: one between the tip and the nanotube and the second, between the nanotube and the surface over which it is floating.

3.

Differences in the electronic structure of the nanotube and that of the support may have significant effect on tunneling current. This may be particularly important when other materials then HOPG are used as support material for nanotubes.

We have used computer simulation to investigate these effects and to compare experimental data with the simulation. Two cases will be analysed: i) the nanotube is placed on a support with identical physical properties, i.e., on a ''raft''[5], and ii) the case of a nanotube on HOPG.