Conclusion

• As long as the electronic structure of the nanotube and support is similar the major distortion arises from geometric convolution of the shape of the tip with the tube geometry. This is found experimentally in the case of nanotubes placed on the top of rafts of similar nanotubes.
• When the electronic structure of the support is different from that of the nanotube, i. e., when HOPG, gold, or other support is used, further distortions arise from the modification of the width of tunneling gap over the nanotube if compared to the value found over the support.
• Existence of second tunneling gap, between nanotube and support may introduce complications in the interpretation of scanning tunneling spectroscopy data.

Helpful discussion with Prof. Ph. Lambin of FUNDP, Namur, are gratefully acknowledged. The work was partly supported by AKP grant No. 96/2-637.