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

Abstract

The family of group IV-VI monochalcogenides has an atomically puckered layered structure, and their atomic bond configuration suggests the possibility for the realization of various polymorphs. Here, we report the synthesis of the first hexagonal polymorph from the family of group IV-VI monochalcogenides, which is conventionally orthorhombic. Recently predicted four-atomic-thick hexagonal GeSe, so-called γ-GeSe, is synthesized and clearly identified by complementary structural characterizations, including elemental analysis, electron diffraction, high-resolution transmission electron microscopy imaging, and polarized Raman spectroscopy.The electrical and optical measurements indicate that synthesized γ-GeSe exhibits high electrical conductivity of 3×10 5 S/m, which is comparable to those of other two-dimensional layered semimetallic crystals. Moreover, γ-GeSe can be directly grown on h-BN substrates, demonstrating a bottom-up approach for constructing vertical van der Waals heterostructures incorporating γ-GeSe. The newly identified crystal symmetry of γ-GeSe warrants further studies on various physical properties of γ-GeSe. ASSOCIATED CONTENT Supporting Information. The Supporting Information is available free of charge on the ACS Publications website. Extra data on the synthesized products, extra EDX mapping data, extra SAED/STEM analysis data along various zone axes, polarized Raman spectra, and extra electronic bandstructure calculations, synthesis and characterizations of vertical γ-GeSe/hBN heterostructures, Raman shift calculations, and γ-GeSe crystallographic information file.

Tunable bulk photovoltaic effect in strained $γ$-GeSe

“…The crystal structure of pristine γ-GeSe is fully relaxed with the 13 × 13 × 3 Monkhorst-Pack k-grid until the total force is fully converged below 10 −6 Ry/Bohr. The fully relaxed lattice constants were calculated as a 1.86 Å and c 15.15 Å, which are in good agreement with the experiment [41]. Under a strain, we fixed the lattice constant only along the strained axis and relaxed the internal atomic coordinates and the other cell parameters.…”

“…Experimentally, γ-GeSe is suggested as a low-gap semiconductor in Ref. [41]. However, their optical conductivity clearly shows the Drude peak in the direct current limit, which inarguably necessitates further explorations to pin down the electronic state.…”

“…Despite these outstanding explorations, topological aspects of shift current are remained largely unexplored to date, which is partly due to the lack of suiable topological platforms. Encouragingly, a recent experiment reports the synthesis of a new polar monochalcogenide system GeSe [41], providing an opportunity to explore the shift current phenomena.…”

Br-Induced Orientation Control of PbI2 van der Waals Nanowires and Their Optoelectronics

“…The vapor–liquid–solid (VLS) method using catalytic seeds has been widely used to grow nanostructures of covalent crystalline group IV or III–V semiconductors with a high degree of structure engineering (e.g., phase, composition, and orientation) − and correspondingly tunable properties such as photon, electron, and phonon transport. ,, Recently, the VLS method has been expanded to other material systems, specifically with 2D-layered geometries, including GeS, GeSe, GaS, and GaSe. − Taking advantage of a kinetically driven growth process, these anisotropic 2D-layered materials can be prepared in twisted nanowires or ribbon-like morphologies with unique properties. The GeS vdW layers grown with Au catalysts display helical nanowire growth with continuous interlayer twists, suggesting tunable optical/thermal conductivity .…”

Fast Intercalation of Lithium in Semi‐Metallic γ‐GeSe Nanosheet: A New Group‐IV Monochalcogenide for Lithium‐Ion Battery Application

“…However, a recent work [42] reported that a new layered structure (γ-phase) of group-IV monochalcogenides can exist in stabilized state and is energetically favorable compared to αand βphases. Interestingly, the γ-phase of germanium selenide (GeSe) has been recently successfully synthesized on the hexagonal boron nitride (h-BN) substrate [43] through chemical vapor deposition (CVD). The γ-GeSe was reported to be semimetal in bulk phase and has a high electrical conductivity of 3 × 10 5 S m À 1 , which is even higher than graphite.…”