  Two-dimensional (2D) bismuth oxyselenide (Bi2O2Se) with high electron
mobility is advantageous in future high-performance and flexible electronic and
optoelectronic devices. However, transfer of thin Bi2O2Se flakes is rather
challenging, restricting measurements of its mechanical properties and
application exploration in flexible devices. Here, we develop a reliable and
effective polydimethylsiloxane (PDMS)-mediated method that allows transferring
thin Bi2O2Se flakes from grown substrates onto target substrates like
micro-electro-mechanical system substrates. The high fidelity of the
transferred thin flakes stems from the high adhesive energy and flexibility of
PDMS film. For the first time, the mechanical properties of 2D Bi2O2Se are
experimentally acquired with nanoindentation method. We found that few-layer
Bi2O2Se exhibits a large intrinsic stiffness of 18-23 GPa among 2D
semiconductors, and a Young' s modulus of 88.7 +- 14.4 GPa which is consistent
with the theoretical values. Furthermore, few-layer Bi2O2Se can withstand a
high radial strain of more than 3%, demonstrating excellent flexibility. The
development of the reliable transfer method and documentation of mechanical
properties of 2D Bi2O2Se jointly fill the gap between theoretical prediction
and experimental verification of mechanical properties of this emerging
material, and will promote flexible electronics and optoelectronics based on 2D
Bi2O2Se.
