Resolving and Tuning Mechanical Anisotropy in Black Phosphorus via Nanomechanical Multimode Resonance Spectromicroscopy

TL;DR

This paper introduces a nanomechanical resonance spectromicroscopy technique to precisely determine and tune the mechanical anisotropy and crystal orientation of black phosphorus, providing a new in situ characterization method.

Contribution

It presents a novel multimode nanomechanical resonant approach for in situ resolution of black P's crystal orientation and anisotropy, and demonstrates electrostatic tuning of these properties.

Findings

Young's moduli of black P are 116.1 GPa (zigzag) and 46.5 GPa (armchair)

Mechanical anisotropy can be continuously tuned via electrostatic gating

Spatially resolved multimode resonances accurately determine crystal orientation

Abstract

Black phosphorus (P) has emerged as a layered semiconductor with a unique crystal structure featuring corrugated atomic layers and strong in-plane anisotropy in its physical properties. Here, we demonstrate that the crystal orientation and mechanical anisotropy in free-standing black P thin layers can be precisely determined by spatially resolved multimode nanomechanical resonances. This offers a new means for resolving important crystal orientation and anisotropy in black P device platforms in situ beyond conventional optical and electrical calibration techniques. Furthermore, we show that electrostatic-gating-induced straining can continuously tune the mechanical anisotropic effects on multimode resonances in black P electromechanical devices. Combined with finite element modeling (FEM), we also determine the Young's moduli of multilayer black P to be 116.1 and 46.5 GPa in the zigzag and armchair directions, respectively.