Hexagonal boron nitride nanomechanical resonators with spatially visualized motion

Abstract

Atomic layers of hexagonal boron nitride (h-BN) crystal are excellent candidates for structural materials as enabling ultrathin, two-dimensional (2D) nanoelectromechanical systems (NEMS) due to the outstanding mechanical properties and very wide bandgap (5.9 eV) of h-BN. In this work, we report the experimental demonstration of h-BN 2D nanomechanical resonators vibrating at high and very high frequencies (from~5 to~70 MHz), and investigations of the elastic properties of h-BN by measuring the multimode resonant behavior of these devices. First, we demonstrate a dry-transferred doubly clamped h-BN membrane with 6.7 nm thickness, the thinnest h-BN resonator known to date. In addition, we fabricate circular drumhead h-BN resonators with thicknesses ranging from~9 to 292 nm, from which we measure up to eight resonance modes in the range of~18 to 35 MHz. Combining measurements and modeling of the rich multimode resonances, we resolve h-BN's elastic behavior, including the transition from membrane to disk regime, with built-in tension ranging from 0.02 to 2 N m − 1 . The Young's modulus of h-BN is determined to be E Y ≈392 GPa from the measured resonances. The ultrasensitive measurements further reveal subtle structural characteristics and mechanical properties of the suspended h-BN diaphragms, including anisotropic built-in tension and bulging, thus suggesting guidelines on how these effects can be exploited for engineering multimode resonant functions in 2D NEMS transducers.

Hexagonal Boron Nitride Phononic Crystal Waveguides

“…Following a similar strategy for displacement estimation, we employ a well-investigated h-BN drumhead resonator as reference and calibrate the transduction gain or conversion loss of the system. 7 The h-BN drumhead resonator shares similar diameter as the unit cell of the phononic waveguide and is measured under similar excitation and detection conditions in the same laser interferometry system. Therefore, we assume the system transmission can be canceled out by comparing the total transmission of these two devices and compensating the differences in the optical interferometry responsivity ( dis-opt  ) (as discussed in Subsection III.5).…”

“…The considerable research efforts on exploring the unconventional properties of van der Waals (vdW) layered materials have already led to exciting breakthroughs across a variety of disciplines from fundamental science to device engineering [1,2,3,4,5,6]. Among families of vdW crystals, hexagonal boron nitride (h-BN), having prevailed as gate dielectric and passivation layers in twodimensional (2D) electronics and optoelectronics [7], is emerging as an attractive material platform for nanophotonics and quantum optics [8,9,10]. The ultrawide bandgap (5.9 eV) of h-BN is beneficial not only for providing excellent electrical insulation, but also for hosting robust single photon emitters (SPEs) even at room temperature [10].…”

“…In this work, we take an initiative to experimentally demonstrate one type of building blocks essential for future on-chip phononic integration, namely phononic crystal waveguides, in h-BN crystals. Distinct from individual nanomechanical resonators reported previously [31,34], phononic crystal waveguides comprise periodic arrays of coupled mechanical structures with Y. Wang, J. Lee, X.-Q. Zheng, Y. Xie, P. X.-L. Feng, ACS Photonics 6, 3225-3232 (2019) [Proof Corrected Version] DOI: 10.1021/acsphotonics.9b01094.…”

<inline-formula> <tex-math notation="LaTeX">$\beta$ </tex-math> </inline-formula>-Ga2O3 NEMS Oscillator for Real-Time Middle Ultraviolet (MUV) Light Detection

“…We use a 633nm laser to interferometrically resolve the device motion, which is detected by a sensitive PD. For detecting the undriven thermomechanical motion, only the 633nm laser is employed, with the signal PD output being fed to a spectrum analyzer [9,15,16]. In the driven response measurement (path ① in Fig.…”

“…In the driven response measurement (path ① in Fig. 2), a network analyzer is used to modulate the intensity of an amplitude-modulated 405nm laser in order to photothermally drive the nanoflake, and then detect the device motion using the 633nm laser through the PD [16].…”