Journal Article

Hexagonal boron nitride nanomechanical resonators with spatially visualized motion

Feng, Philip X.-L., Zheng, Xu-Qian, Lee, Jaesung

2017

Overview

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. Resonators: Atomic layer crystals for next-generation nanomechanical devices Next-generation ultrathin sensors and ultralow-power signal processors could be a step closer thanks to single-atom layers of hexagonal boron nitride (h-BN) (aka ‘white’ graphene). Two-dimensional (2D) crystals of h-BN exhibit ultrawide bandgap, remarkable mechanical and optical properties and are chemically and thermally more stable than graphene — making them attractive building blocks for cutting-edge nanoelectromechanical systems (NEMS). By measuring the elasticity and optical properties of extremely thin flakes of h-BN, Philip Feng and his colleagues from Case Western Reserve University in Ohio, United States, were able to fabricate h-BN-based devices that function as highly sensitive nanomechanical resonators, with spatially visualized mutlimode motions. The team ’s work holds promise for the development of 2D devices for emerging applications such as nanoscale sensors and multiphysical transducers. It could also enable future investigations of piezoelectric effects in 2D electromechanical and optoelectromechanical devices made from atomic layers of h-BN and their heterostructures with other 2D materials.

• Publisher: Nature Publishing Group UK,Springer Nature B.V,Nature Publishing Group
• Subject: 639/301/357/537 / 639/925/357/537 / 639/925/927/356 / 639/925/927/359 / Boron / Boron nitride / Construction materials / Crystal structure / Diaphragms / Elastic properties / ENGINEERING / Hexagonal boron nitride (h-BN) / High frequencies / MATERIALS SCIENCE / Mechanical properties / Modulus of elasticity / multimode resonances / Nanoelectromechanical systems / nanoelectromechanical systems (NEMS) / Resonators / spatial mapping / Transducers / Very high frequencies / Young’s modulus