Dynamically-enhanced strain in atomically thin resonators

Abstract

Graphene and related two-dimensional (2D) materials associate remarkable mechanical, electronic, optical and phononic properties. As such, 2D materials are promising for hybrid systems that couple their elementary excitations (excitons, phonons) to their macroscopic mechanical modes. These built-in systems may yield enhanced strain-mediated coupling compared to bulkier architectures, e.g., comprising a single quantum emitter coupled to a nano-mechanical resonator. Here, using micro-Raman spectroscopy on pristine monolayer graphene drums, we demonstrate that the macroscopic flexural vibrations of graphene induce dynamical optical phonon softening. This softening is an unambiguous fingerprint of dynamically-induced tensile strain that reaches values up to ≈4 × 10−4 under strong non-linear driving. Such non-linearly enhanced strain exceeds the values predicted for harmonic vibrations with the same root mean square (RMS) amplitude by more than one order of magnitude. Our work holds promise for dynamical strain engineering and dynamical strain-mediated control of light-matter interactions in 2D materials and related heterostructures.

Dynamics of 2D material membranes

“…These methods convert the position or velocity of the membrane into an electrical signal that is subsequently analyzed by measurement equipment such as network, lock-in and/or spectrum analyzers. Mostly, the out-of-plane motion of the membrane w(x, y, t) is measured, since the in-plane dynamic motion is usually much smaller and more difficult to detect, although techniques like Raman [61] and piezoresistive [62] readout are able to probe it. Figure 2 lists the three main readout methods for studying the dynamics of 2D material membranes that will be discussed in the following subsections: optical, transconductive and capacitive readout.…”

“…A third method is characterization of the membrane's pretension by AFM or Raman methods and analytical or finite element method (FEM) calculation of the modal dynamic stiffness. Many studies have focused on AFM and Raman spectroscopy for studying the tension and stiffness of suspended 2D materials and their uniformity [51,52,61,[113][114][115].…”

Dynamics of 2D Material Membranes

“…Laser Doppler Vibrometry (LDV) has also been used for characterization of graphene membrane dynamics using optical interferometry [65][66][67] . Another interesting development is the use of Raman spectroscopy to determine the dynamically induced strain in the membrane, allowing one to obtain information on the in-plane strain, in addition to the out-of-plane motion 61 .…”

Nanomechanical probing and strain tuning of the Curie temperature in suspended Cr$_2$Ge$_2$Te$_6$ heterostructures

“…Emerging nanomechanical methods allow for high-precision strain manipulation and control when 2D materials are suspended forming ultrathin membrane resonators [14,15]. Due to the combination of low mass with high strength, these membranes find potential use in high-performance devices [14,16] and wide range of sensor applications [17].…”

“…Due to the combination of low mass with high strength, these membranes find potential use in high-performance devices [14,16] and wide range of sensor applications [17]. The resonance frequency of these membranes can be tuned over a large range by strain [14], which can be controlled both statically [18] and dynamically [14,15]. Moreover, the thermal expansion of suspended 2D layers provides an additional parameter for strain tuning [19,20].…”