A New Family of Two-Dimensional Crystals: Open-Framework T₃X (T = C, Si, Ge, Sn; X = O, S, Se, Te) Compounds with Tetrahedral Bonding

Abstract

To accelerate development of innovative materials, their modelings and predictions with useful functionalities are of vital importance. Here, based on a recently developed crystal structure prediction method, we find a new family of stable two-dimensional crystals with an open-channel tetrahedral bonding network, rendering a potential for electronic and energy applications. The proposed structural prototype with a space group of Cmme hosts at least thirteen different freestanding T3X compounds with group IV (T=C, Si, Ge, Sn) and VI (X=O, S, Se, Te) elements. Moreover, the proposed materials display diverse electronic properties ranging from direct band gap semiconductor to topological insulator at their pristine forms, which are further tunable by mechanical strain. arXiv:1811.06894v2 [cond-mat.mtrl-sci]

Promising photovoltaic efficiency of a layered silicon oxide crystal Si3O

“…It is shown that the both have direct gaps, differing from other semiconducting 2D materials [24]. Considering other merits of Si 3 O such as earth-abundant, non-toxic and simple elements, light weight, a superb stability [22] and a very light effective mass [23], we expect that the proposed layered silicon oxide will play an important role in siliconbased energy applications once it be synthesized. We briefly discuss synthesis and stability of the Si 3 O in the Electronic Supplementary Information (ESI).…”

“…Recently, a family of novel 2D materials composed of group IV and VI elements, namely T 3 X (T=C, Si, Ge, Sn; X=O, S, Se, Te), have been predicted, demonstrating various electronic properties ranging from band insulator to quantum spin Hall insulator [22]. Those novel 2D crystals have been found by using a new crystal structure prediction method: SANDWICH (Search by Ab initio Novel Design via Wyckoff positions Iteration in Conformational Hypersurface) [22,23]. This method has a particular merit over the others in finding stable but unconventional 2D atomic structures with a low atomic density, e.g., hollow structures [22,23].…”

“…Those novel 2D crystals have been found by using a new crystal structure prediction method: SANDWICH (Search by Ab initio Novel Design via Wyckoff positions Iteration in Conformational Hypersurface) [22,23]. This method has a particular merit over the others in finding stable but unconventional 2D atomic structures with a low atomic density, e.g., hollow structures [22,23]. Among the T 3 X compounds, 2D Si 3 O crystal shown in Fig.…”

“…Among the T 3 X compounds, 2D Si 3 O crystal shown in Fig. 1 has the convex-hull stability and a direct band gap, making it a good candidate for optoelectronic devices [22,23].…”

“…We use atomic structures of a monolayer and layered bulk of Si 3 O obtained from our SANDWICH code, as shown in Figs. 1(b) and 1(c), respectively [22,23]. We perform the mean-field [26] density functional theory (DFT-PBE) calculations using QUANTUM ESPRESSO [27,28].…”