Macroscopic Thin Film Of Carbon Nanomaterials: Fabrications, Physical Properties And Applications

Macroscopic structures of nanomaterials have been the focus of scientific and applied research of nanotechnology, due to their superior physical properties inherited from nanomaterials and the excellent operability by their macroscopic sizes. In this thesis, based on the super-aligned carbon nanotube thin film(SACNT film) and graphene, we have studied the fabrications, physical properties together with applications of macroscopic thin film of carbon nanomaterials.Due to strong van der Waals interactions between SACNT network and graphene, large-area graphene grown by chemical vapor deposition(CVD) method was cleanly exfoliated from the copper foil. As a result, centimeter-sized, ultrathin, optical transparent and conductive CNT-graphene hybrid film with high mechanical performance have been achieved. The porous feature of the CNT network enables the existence of large-area quasi-continuous suspended graphene in the hybrid film. Thanks to its unique structure with one side of single layer graphene and the other side of porous CNT network, the hybrid film possesses an electron transparency close to 90%. Based on these features, CNT-graphene hybrid films have been applied as high-performance gate electrodes in vacuum electronic devices and sample support films for transmission electron microscopy characterizations. Such a “van der Waals” type method was found to also work for CVD MoS2, resulting in successful exfoliation of MoS2 from the substrate and fabrication of CNT-MoS2 hybrid film.Based on its continuous and aligned features, SACNT film has been used as the template for continuous fabrication of aligned carbon fiber and graphitic fiber thin film, by deposition of pyrolytic carbon on the CNT film followed by high temperature treatment. The as-fabricated graphitic fiber with high degree of graphitization shows some structural changes in the stacking of graphitic layers and the shape of its cross-section, which have been theoretically analyzed considering the strain energy change of the fiber. Application of the thin film as the electrode of lithium-ion batteries has been demonstrated utilizing the merits of improved electrical conductivity and mechanical strength. Such a “pyrolytic carbon deposition & graphitization” method has been further applied on CNT yarns, resulting in yarns with improved tensile strength and Young’s modulus.As SACNT film features appreciable thermoacoustic effect, we realized the fabrication of a CNT thin yarn thermoacoustic chip by integrating SACNT thin yarn films into silicon substrates with patterned grooves. Such a thermoacoustic chip was adopted to study the fundamental mechanism of thermoacoustic effect. Theoretical derivation predicts a spatial-localized temperature fluctuation in the air apart from the thermoacoustic loudspeaker. The typical length of such a temperature fluctuation can be defined by the temperature wavelength. By changing the depth of the groove in the chip, the distance between the CNT thin yarn film and the substrate can be accurately modulated. Influence of such a distance on the thermoacoustic performance has been evaluated, which verified the temperature wave concept and realized the quantitative measurement of the temperature wavelength. In addition, CNT thin yarn thermoacoustic earphones have been successfully fabricated, after further optimizations according to these results.