Circular electromechanical resonators based on hexagonal-boron nitride-graphene heterostructures

Abstract

2D materials such as graphene and hexagonal-boron nitride (h-BN), to name a few, when layered on top of each other offer a class of metamaterials with interesting properties. For example, the twisting degree of freedom between two layers has started the field of twistronics. The exceptional attributes of 2D materials like ultra-low mass, robustness, and high tunability make them very suitable for nanoelectromechanical systems (NEMS). Yet the mechanical properties of these heterostructures in the form of NEMS have not been studied extensively. Such 2D NEMS hold promise for various technological applications, namely, ultrafast sensors, actuators, etc. We report fabrication and characterization of h-BN graphene heterostructure-based circular nanoelectromechanical resonators on sapphire substrates. The devices are measured at cryogenic temperatures and exhibit multiple mode frequencies, which are highly tunable with gate voltage. A continuum mechanics model is employed to analyze the transmission (S21) data of the fundamental mode. Parameters like built-in tension obtained from the fit are used to identify the indices (m, n) of higher mechanical modes observed for the device, providing further device characterization. Such 2D NEMS could offer a way to study diverse electronic phenomena such as superconductivity in twisted bilayer graphene (tBLG) heterostructures.

Ultrawide Frequency Tuning of Atomic Layer van der Waals Heterostructure Electromechanical Resonators

“…Three devices exhibit continuous frequency tuning behavior with increasing V G , that is, a moderate frequency tuning in the low-voltage regime (around | V G | < 10 V for 1LMoS 2 –1LGr and 1LMoS 2 –3LGr devices and | V G | < 15 V for the 1LMoS 2 –FLGr device) and increasingly wider tuning ranges as | V G | increases. It should be noted that we have not observed any measurable “kinks” described in previous reports , and attributed to interfacial slippage or other nonideal effects therein, suggesting clean and tightly bonded MoS 2 –graphene interfaces in our vdW devices. To attain quantitative analysis and understanding, we employ two analytical models (see the Supporting Information for detailed equation derivations of these analytical models) and an FEM model by employing COMSOL Multiphysics simulations.…”

“…We find that all the devices exhibit continuous, ultrabroad frequency tuning with Δf/f 0 > 200%, with the largest tuning range up to Δf/f 0 ≈ 370%, which is much wider than the reported data hitherto in electrostatically tuned resonators made of single 2D materials. 17−21 Unlike in previous reports, 14,15 we observe no "kink" in the frequency tuning curves for any devices, even over a much wider applied voltage range, suggesting clean interfaces and strong vdW bonding. In parallel to the frequency tuning measurement, we employ two different analytical models and FEM simulations to reveal the governing mechanisms in tuning vdW heterostructure resonators.…”

“…Third, a clear comparison of tuning capabilities between NEMS made of single 2D materials and those of vdW heterostructures is needed but is still lacking. Importantly, according to recent reports [14,15], interlayer slip between MoS2 and graphene layers could occur presumably, even under a moderate applied gate voltage (VG) (~2.3V to 8.3V), which might limit the applications of vdW heterostructure resonators. All these unknowns may inevitably result in an underestimation of the potential of vdW heterostructure NEMS.…”

“…For example, suspended MoS 2 –graphene heterostructures exhibit robust resonances in the high and very high frequency (HF and VHF) bands . Whereas initial efforts have been made to study the basic resonance characteristics − and moderate tunability , in such early devices, a clear understanding of the frequency tuning in vdW heterostructures is still lacking. Specifically, there are several obvious open questions on this topic.…”

Nanomechanical Resonators: Toward Atomic Scale

“…142 In another example, an h-BN/graphene heterostructure resonator shows a frequency tuning range of about 100%. 158 By coupling graphene/niobium diselenide (NbSe2)/graphene resonators to a superconducting cavity, very high Q up to 245,000 at 8.5mK in mechanical resonance at > 50 MHz has been reported. 154 These findings suggest that by designing different vdW HSs, it is possible to create resonant devices with tailored and enhanced mechanical, electrical, and optical properties.…”