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We demonstrate the control of resonance characteristics of a drum-type graphene mechanical resonator in a nonlinear oscillation regime using the photothermal effect, which is induced by a standing wave of light between graphene and a substrate. Unlike the resonance characteristics of a conventional Duffing-type nonlinearity, those of the nonlinear oscillation regime are modulated by the standing wave of light with a contribution of the scattered light of an actuation laser, despite a slight variation of amplitude. Numerical calculations conducted with a combination of equations of heat and motion with the Duffing-type nonlinearity explain this modulation: the photothermal effect delays the modulation of graphene stress or tension.

Heterogeneously integrated nanomaterial devices show interesting characteristics for transistors and sensors due to their band diagram or steep material junctions. If these junctions and band alignments can be tuned by an electrical input bias, the device platform not only could be expanded but also could be used to explore fundamental characteristics. However, most reports on hetero-nanomaterial junctions use a global back-gate voltage, which makes it difficult to control band alignment at an interface. To explore device junctions, this study reports a laterally integrated heterojunction of graphene and a carbon nanotube (CNT) network film with individual gate electrodes to tune the band alignment corresponding to the Fermi level shift of graphene in contact with the semiconducting CNT network film. By developing the fabrication process, multiple gate structures are designed to apply a gate bias to CNTs and graphene separately. The threshold voltage shift of the CNT transistor depends on the gate voltage of graphene. Based on the thermionic emission theory, the barrier height between graphene and CNTs for both the conduction and valence band sides varies from 70 to 85 meV, with a linear change as a function of the applied gate voltage to graphene. Although the current Fermi level shift is small, this device platform may realize the exploration of fundamental properties and device concepts.

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