Air-stable $n$ -type carbon nanotube field-effect transistors (CNTFETs) were fabricated, with ${\mathrm{Si}}_3{\mathrm{N}}_4$ passivation films formed by catalytic chemical vapor deposition (Cat-CVD). Electrical measurements reveal that the $p$ -type characteristics of CNTFETs are converted to $n$ -type after fabricating ${\mathrm{Si}}_3{\mathrm{N}}_4$ passivation films at $270°\mathrm{C}$ . This indicates that adsorbed oxygen on the CNT sidewalls was removed during the formation process of the ${\mathrm{Si}}_3{\mathrm{N}}_4$ passivation films. In addition, the source-drain current of the $n$ -type CNTFETs does not change over time under vacuum, or in air. Consequently, the $n$ -type CNTFETs are completely protected by the ${\mathrm{Si}}_3{\mathrm{N}}_4$ passivation film from further effects of ambient gases. Therefore, Cat-CVD is one of the best candidates to fabricate ${\mathrm{Si}}_3{\mathrm{N}}_4$ passivation films on CNTFETs.

We propose a laser resonance chirality selection method to select single-walled carbon nanotubes (SWNTs) with specific chirality from mass of SWNTs by intense laser irradiation. This technique exploits the multiple Van Hove singularities in the density of states of SWNTs expected for one-dimensional confinement. Absorption of the exciting laser beam can be strongly enhanced for SWNTs with specific chirality when the energy of the incident photon matches the energy of the allowed electronic transitions. As a result of the resonance effect, when the excitation power density of the laser beam increases in an atmosphere of air, at a certain threshold excitation power density, only these SWNTs are oxidized and are removed selectively. With Raman scattering measurements, we have demonstrated that SWNTs with specific chirality are selectively removed after intense laser irradiation.