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Tham khảo tài liệu 'science technology carbon nanotubes part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 170 in Fig. 7. The observed step-wise increase of the current can be explained in terms of single electron tunnelling through a CNT. Diameter nm Fig. 5. Relationship between observed band gap and the diameter of individual SWCNTs. Closed and open circles indicate the data from refs. 25 and 26 respectively. The data are fitted with the equation E lỵaQ.QỈd where the nearest-neighbour transfer integral Y is 2.7 eV and 2.5 eV for linear and broken lines respectively. Fig. 6. The image of the nanodevice using an individual SWCNT modified from ret 30 . The schematic model is depicted in Fig. 8. As the bias voltage increases the number of the molecular orbitals available for conduction also increases Fig. 8 and it results in the step-wise increase in the current. It was also found that the conductance peak plotted vs. the bias voltage decreases and broadens with increasing temperature to ca. 1 K. This fact supports the idea that transport of carriers from one electrode to another can take place through one molecular orbital delocalising over whole length of the CNT or at least the distance between two electrodes 140 nm . In other words individual CNTs work as coherent quantum wires. 171 Fig. 7. -Vbias curves of an individual SWCNT device with the gate voltage of A 88 2 meV B 104.1 meV and C 120 meV 31 Fig- 8- Schematic illustration of the tunnelling in a CNT-based device a under no bias voltage there are no orbitals available for conduction b with small bias voltage only one molecular orbital of a CNT contributes to the caưier transport and c when the next molecular orbital enters the bias window current increases stepwise. Gate voltage can shift all the orbitals upward or downward. AE indicates the energy separation of molecular orbitals. These results are surprising and such a high stability of molecular orbitals was considered to be a consequence of the stiff and almost defect-free structure of metallic CNTs 31 From the gate voltage dependence of the current the energy
