?-GeSe: A New Hexagonal Polymorph from Group IV–VI Monochalcogenides

The family of group IV-VI monochalcogenides has an atomically puckered layered structure, and their atomic bond configuration suggests the possibility for realization various polymorphs. Here, we report synthesis first hexagonal polymorph from monochalcogenides, which is conventionally orthorhombic. Recently predicted four-atomic-thick GeSe, so-called {\gamma}-GeSe, synthesized clearly identified by complementary structural characterizations, including elemental analysis, electron diffraction, high-resolution transmission microscopy imaging, polarized Raman spectroscopy. electrical optical measurements indicate that {\gamma}-GeSe exhibits high conductivity 3x10^5 S/m, comparable to those other two-dimensional semimetallic crystals. Moreover, can be directly grown on h-BN substrates, demonstrating a bottom-up approach constructing vertical van der Waals heterostructures incorporating {\gamma}-GeSe. newly crystal symmetry warrants further studies physical properties