Two-dimensional
(2D) materials with strong in-plane anisotropy
are of interest for enabling orientation-dependent, frequency-tunable,
optomechanical devices. However, black phosphorus (bP), the 2D material
with the largest anisotropy to date, is unstable as it degrades in
air. In this work we show that As2S3 is an interesting
alternative, with a similar anisotropy to bP, while at the same time
having a much higher chemical stability. We probe the mechanical and
optical anisotropy in As2S3 by three distinct
angular-resolved experimental methods: Raman spectroscopy, atomic
force microscopy (AFM), and resonance frequency analysis. Using a
dedicated angle-resolved AFM force-deflection method, an in-plane
anisotropy factor of is found in the Young’s
modulus
of As2S3 with Ea-axis = 79.1 ± 10.1 GPa and Ec-axis = 47.2 ± 7.9 GPa.
The high mechanical anisotropy is also shown to cause up to 65% difference
in the resonance frequency, depending on crystal orientation and aspect
ratio of membranes.