  Materials with electromagnetic interference (EMI) shielding in the terahertz
(THz) regime, while minimizing the quantity used, are highly demanded for
future information communication, healthcare and mineral resource exploration
applications. Currently, there is often a trade-off between the amount of
material used and the absolute EMI shielding effectiveness (EESt) for the EMI
shielding materials. Here, we address this trade-off by harnessing the unique
properties of two-dimensional (2D) beta12-borophene (beta12-Br) nanosheets.
Leveraging beta12-Br's light weight and exceptional electron mobility
characteristics, which represent among the highest reported values to date, we
simultaneously achieve a THz EMI shield effectiveness (SE) of 70 dB and an EESt
of 4.8E5 dB cm^2/g (@0.87 THz) using a beta12-Br polymer composite. This
surpasses the values of previously reported THz shielding materials with an
EESt less than 3E5 dB cm^2/g and a SE smaller than 60 dB, while only needs 0.1
wt.% of these materials to realize the same SE value. Furthermore, by
capitalizing on the composite's superior mechanical properties, with 158%
tensile strain at a Young's modulus of 33 MPa, we demonstrate the
high-efficiency shielding performances of conformably coated surfaces based on
beta12-Br nanosheets, suggesting their great potential in EMI shielding area.
