Perforated Carbon Nanotube Film Assisted Growth of Uniform Monolayer MoS2 (Small 23/2023)

Scaling up the chemical vapor deposition (CVD) of monolayer transition metal dichalcogenides (TMDCs) is in high demand for practical applications. However, for CVD-grown TMDCs on a large scale, there are many existing factors that result in their poor uniformity. In particular, gas flow, which usually leads to inhomogeneous distributions of precursor concentrations, has yet to be well controlled. In this work, the growth of uniform monolayer MoS₂ on a large scale by the delicate control of gas flows of precursors, which is realized by vertically aligning a well-designed perforated carbon nanotube (p-CNT) film face-to-face with the substrate in a horizontal tube furnace, is achieved. The p-CNT film releases gaseous Mo precursor from the solid part and allows S vapor to pass through the hollow part, resulting in uniform distributions of both gas flow rate and precursor concentrations near the substrate. Simulation results further verify that the well-designed p-CNT film guarantees a steady gas flow and a uniform spatial distribution of precursors. Consequently, the as-grown monolayer MoS₂ shows quite good uniformity in geometry, density, structure, and electrical properties. This work provides a universal pathway for the synthesis of large-scale uniform monolayer TMDCs, and will advance their applications in high-performance electronic devices.     

Synthesis of Co-Doped MoS2 Monolayers with Enhanced Valley Splitting

Internal magnetic moments induced by magnetic dopants in MoS₂ monolayers are shown to serve as a new means to engineer valley Zeeman splitting (VZS). Specifically, successful synthesis of monolayer MoS₂ doped with the magnetic element Co is reported, and the magnitude of the valley splitting is engineered by manipulating the dopant concentration. Valley splittings of 3.9, 5.2, and 6.15 meV at 7 T in Co-doped MoS₂ with Co concentrations of 0.8%, 1.7%, and 2.5%, respectively, are achieved as revealed by polarization-resolved photoluminescence (PL) spectroscopy. Atomic-resolution electron microscopy studies clearly identify the magnetic sites of Co substitution in the MoS₂ lattice, forming two distinct types of configurations, namely isolated single dopants and tridopant clusters. Density functional theory (DFT) and model calculations reveal that the observed enhanced VZS arises from an internal magnetic field induced by the tridopant clusters, which couples to the spin, atomic orbital, and valley magnetic moment of carriers from the conduction and valence bands. The present study demonstrates a new method to control the valley pseudospin via magnetic dopants in layered semiconducting materials, paving the way toward magneto-optical and spintronic devices.     

Grains in Selectively Grown MoS2 Thin Films

Transition metal dichalcogenides (TMDCs) have recently been studied using various synthesis methods, such as chemical vapor deposition for large‐scale production. Despite the realization of large‐scale production with high material quality, a range of approaches have been made to solve the patterning issue of TMDCs focusing on the application of integrated devices; however, patterning is still under study to accurately represent nanoscale‐sized patterns, as well as the desired positions and shapes. Here, an insulating substrate is treated selectively with O₂ plasma, and MoS₂ growth is induced in the superhydrophilic area. Selectively well‐grown MoS₂ patterns are confirmed by atomic force microscopy and Raman and photoluminescence spectroscopy. In addition, the grain size, according to the growth size, and grain boundary are analyzed by annual dark field transmission electron microscopy (TEM) and spherical aberration‐corrected scanning TEM to confirm the selective growth. An analysis of the device performance and the optical properties reveals an enhancement with increasing grain size. This method presents the path of the growth technique for patterning, as well as the direction that can be applied to devices and integrated circuits.     

Recent Advances in Growth of Large‐Sized 2D Single Crystals on Cu Substrates

Large‐scale and high‐quality 2D materials have been an emerging and promising choice for use in modern chemistry and physics owing to their fascinating property profile. The past few years have witnessed inspiringly progressing development in controlled fabrication of large‐sized and single‐crystal 2D materials. Among those production methods, chemical vapor deposition (CVD) has drawn the most attention because of its fine control over size and quality of 2D materials by modulating the growth conditions. Meanwhile, Cu has been widely accepted as the most popular catalyst due to its significant merit in growing monolayer 2D materials in the CVD process. Herein, very recent advances in preparing large‐sized 2D single crystals on Cu substrates by CVD are presented. First, the unique features of Cu will be given in terms of ultralow precursor solubility and feasible surface engineering. Then, scaled growth of graphene and hexagonal boron nitride (h‐BN) crystals on Cu substrates is demonstrated, wherein different kinds of Cu surfaces have been employed. Furthermore, the growth mechanism for the growth of 2D single crystals is exhibited, offering a guideline to elucidate the in‐depth growth dynamics and kinetics. Finally, relevant issues for industrial‐scale mass production of 2D single crystals are discussed and a promising future is expected.     

Chemical Vapor Deposition of High‐Quality and Atomically Layered ReS2

Recently, anisotropic 2D materials, such as black phosphorus and rhenium disulfides (ReS₂), have attracted a lot attention because of their unique applications on electronics and optoelectronics. In this work, the direct growth of high‐quality ReS₂ atomic layers and nanoribbons has been demonstrated by using chemical vapor deposition (CVD) method. A possible growth mechanism is proposed according to the controlled experiments. The CVD ReS₂‐based filed‐effect transistors (FETs) show n‐type semiconducting behavior with a current on/off ratio of ≈10⁶ and a charge carrier mobility of ≈9.3 cm² Vs⁻¹. These results suggested that the quality of CVD grown ReS₂ is comparable to mechanically exfoliated ReS₂, which is also further supported by atomic force microscopy imaging, high‐resolution transmission electron microscopy imaging and thickness‐dependent Raman spectra. The study here indicates that CVD grown ReS₂ may pave the way for the large‐scale fabrication of ReS₂‐based high‐performance optoelectronic devices, such as anisotropic FETs and polarization detection.     

石墨衬底上具有（220）/（400）择优取向多晶硅薄膜的制备及性质

在石墨衬底上分别制备了具有(220)和(400)择优取向的多晶硅薄膜.首先利用磁控溅射技术直接在石墨衬底上制备非晶硅薄膜层,以及先制备 ZnO 过渡层,再在 ZnO 过渡层上制备非晶硅薄膜层;然后采用快速退火法对非晶硅薄膜晶化,使其形成多晶硅薄膜籽晶层.XRD 测试表明,未引入 ZnO 过渡层的多晶硅薄膜籽晶层具有高度(220)择优取向,而引入 ZnO 过渡层的多晶硅薄膜籽晶层具有高度(400)择优取向;最后在多晶硅籽晶层上通过对流辅助化学气相沉积(CoCVD)制备多晶硅薄膜.根据 SEM、XRD、拉曼测试表明,多晶硅薄膜的性质延续了多晶硅籽晶层的性质,未引入 ZnO 过渡层的样品,具有高度(220)择优取向.引入 ZnO 过渡层后的样品,具有高度(400)择优取向,(400)择优取向的转变有利于后续多晶硅薄膜太阳电池的制作.同时对 Si(220)和 Si (400)择优取向的形成原因做了初步分析.     

化学气相沉积法在液态金属上制备2D MoP单晶

二维过渡金属磷化物(TMPs)有许多新奇的性质和应用.作为二维TMPs的一员,二维MoP有许多独特的物理化学性质.然而由于缺乏制备二维MoP的方法,目前还未成功制备二维MoP,因此限制了对二维MoP众多性质的探索.本文采用化学气相沉积法在液态金属镓(Ga)上制备了厚度为10 nm的二维MoP单晶.液态Ga具有原子级平整的表面,能作为制备二维材料的合适生长基底.在生长过程中, Mo源扩散到Ga表面与磷源反应,从而在Ga表面反应得到二维MoP单晶.此外,由于二维MoP具有本征的非中心对称结构,文中首次研究了二维MoP的二次谐波信号的产生.本文为其他二维TMPs的制备和性质探索提供了新思路.     

SnO_2纳米线的合成与结构表征

采用化学气相沉积法在经表面活性剂与硝酸镍的混合溶液处理过的硅衬底上成功制备出了直径均匀可控的二氧化锡(SnO2)纳米线。利用扫描电子显微镜、透射电子显微镜、选区电子衍射、X射线衍射等手段对样品的表面形貌、微结构及成分等进行了表征分析。并在此基础上讨论了纳米线所遵循的生长机理。     

Si(111)衬底上生长GaN晶绳的研究

利用热壁化学气相沉积在Si(111)衬底上获得GaN品绳，采用傅里叶红外吸收谱(FTIR)、扫描电子显微镜(SEM)、选区电子衍射(SAED)、X射线衍射(XRD)和光致发光谱(PL)对晶绳进行组成、结构、形貌和光学特性分析。初步结果证明：在Si(111)衬底上获得择优生长的六方纤锌矿结构的GaN晶绳。SEM显示在均匀的薄膜上出现φ6μm的晶绳，FTIR显示GaN薄膜的主要成分为GaN同时含有少量的C污染，由XRD和SAED的综合分析得出晶绳呈六方纤锌矿单晶结构，PL测试表明晶绳呈现不同于GaN薄膜的发光特性。