  Two dimensional (2D) gamma-boron ({\gamma}-B28) thin films have been firstly
reported by the experiments of the chemical vapor deposition in the latest
study [Tai et al., Angew. Chem. Int. Ed. 54, 1-6 (2015)]. However, their
mechanical properties are still not clear. Here we predict the superhigh moduli
(1460 GPa at 1 K and 744 GPa at 300 K) and the tension-induced phase transition
of monolayer {\gamma}-B28 along a zigzag direction for large deformations at
finite temperatures using molecular dynamics (MD) simulations. The new phase
can be kept stable after unloading process at these temperatures. The predicted
mechanical properties are reasonable with our results from density functional
theory. This study provides physical insights into the origins of the new phase
transition of monolayer {\gamma}-B28 at finite temperatures.
