SKM 2023 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 30: 2D Materials I: Electronic Structure

O 30.6: Vortrag

Dienstag, 28. März 2023, 11:45–12:00, GER 37

Observing Duffing oscillations in 2D materials by ultrafast electron imaging — •Alexander Schröder, Lina Hansen, and Sascha Schäfer — Institute of Physics, University of Oldenburg, Germany

Two-dimensional materials are an ideal test bed for probing non-linear mechanical resonances. With sample thicknesses down to the atomic scale, the nonlinear regime of mechanical resonances can be observed even for small actuation forces. Previously, the response of such nano- and micromechanical systems was probed by optical or electronic means, leaving details of the mechanical mode structures and their connection to atomic defects unresolved. Here, we present the nanoscale probing of nonlinear Duffing resonances in free-standing graphite membranes using large-angle convergent-beam diffraction in an ultrafast transmission electron microscope equipped with an event-based electron detector with nanosecond temporal resolution. The vibrational membrane modes are excited by a diode laser beam with a tunable modulation rate and a series of resonances are observed in the MHz frequency range with high quality factors (up to 10⁴). As expected for prototypical Duffing resonances, increasing the optical excitation strength yields a strong nonlinear hardening of the oscillator, with an increase in vibrational amplitude, an asymmetric broadening of the resonance line shape, bistable behavior, and a characteristic frequency-dependent phase shift. The novel detection scheme as proposed here is ideally suited for characterizing the behavior of ultra-small resonators difficult to address with other techniques.