Deng Li-Ying,Zhang Qing,Li Wang-Yang,Ye Xiao-Yuan,Zhao Yi-Fan,Chen Shen-Zhong,Wang Yu-Lan,Wang Xing-Hui,Chen Hui-Peng,Yu Zhi-Yang,Yan Qun,Cheng Shu-Ying,Guo Tai-Liang,Hu Wen-Ping,Ding Feng,Sun Jie
Two-dimensional (2D) metal oxides (2DMOs), such as MoO 2 , have made impressive strides in recent years, and their applicability in a number of fields such as electronic devices, optoelectronic devices and lasers has been demonstrated. However, 2DMOs present challenges in their synthesis using conventional methods due to their non-van der Waals nature. We report that KCl acts as a flux to prepare large-area 2DMOs with sub-millimeter scale. We systematically investigate the effects of temperature, homogeneous time and cooling rate on the products in the flux method, demonstrating that in this reaction a saturated homogenous solution is obtained upon the melting of the salt and precursor. Afterward, the cooling rate was adjusted to regulate the thickness of the target crystals, leading to the precipitation of 2D non-layered material from the supersaturated solution; by applying this method, the highly crystalline non-layered 2D MoO 2 flakes with so far the largest lateral size of up to sub-millimeter scale (~ 464 μm) were yielded. Electrical studies have revealed that the 2D MoO 2 features metallic properties, with an excellent sheet resistance as low as 99 Ω·square −1 at room temperature, and exhibits a property of charge density wave in the measurement of resistivity as a function of temperature. Graphical abstract TOC (Table of Content)
Layered metallic transition metal dichalcogenides (TMDs) with bonding-free surfaces and weak Fermi-level pinning properties have exhibited potential application as electrode materials in two-dimensional (2D) semiconductor devices. However, various TMDs metallic materials are still limited in certain areas, especially due to the lack of a low-work function (<4.5 eV) counterpart. Herein, we report a polytelluride flux growth method for TiTe2 single crystals and determine the work function of this IVB group metallic TMD for the first time. The obtained crystal adopts a typical 1T-type structure (Pm1 space group, no. 164) with the lattice parameters a = 3.7668(4) Å and c = 6.4918(10) Å. The TiTe2 crystal showed metallic behavior with decreased resistivity upon cooling and a relatively low resistivity value (4.39 × 10−4 Ω cm) at room temperature. By ultraviolet photoelectron spectroscopy, the work function of TiTe2 was determined as 4.31 eV, which is much smaller than the reported data of other metallic TMDs. Our study demonstrates the interesting work function data of 1T-TiTe2, which can be utilized to make excellent metal–semiconductor contacts in 2D semiconductor devices.
Ruru Ma,Dongdong Xu,Yun Yang,Xin Su,Binghua Lei,Zhihua Yang,Shilie Pan
Two new isostructural rare-earth oxyborates ScMO(BO3) (M = Ca and Cd) with a three-dimensional (3D) cationic framework and parallel arranged [BO3] triangles have been synthesized by the flux method. In the 3D cationic framework, an interesting sandwich-like basic building unit (BBU) is constructed by two ∞1[Ca(1)O4]6− chains and two ∞1[Sc(1)O4]5− chains. ScMO(BO3) melt incongruently, which shows that title compounds can be grown by the flux method. The UV cut-off edges for ScCaO(BO3) and ScCdO(BO3) are 230 and 249 nm, respectively. In addition, the first-principles calculations are performed to gain further insights into the relationship between the microscopic electronic structures and associated optical properties.
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