Superclean Growth of Graphene Using a Cold‐Wall Chemical Vapor Deposition Approach

Chemical vapor deposition (CVD) has become a promising approach for the industrial production of graphene films with appealing controllability and uniformity. However, in the conventional hot‐wall CVD system, CVD‐derived graphene films suffer from surface contamination originating from the gas‐phase reaction during the high‐temperature growth. Shown here is that the cold‐wall CVD system is capable of suppressing the gas‐phase reaction, and achieves the superclean growth of graphene films in a controllable manner. The as‐received superclean graphene film, exhibiting improved optical and electrical properties, was proven to be an ideal candidate material used as transparent electrodes and substrate for epitaxial growth. This study provides a new promising choice for industrial production of high‐quality graphene films, and the finding about the engineering of the gas‐phase reaction, which is usually overlooked, will be instructive for future research on CVD growth of graphene.     

金属衬底在石墨烯化学气相沉积生长中的作用

以过渡金属为催化衬底的化学气相沉积法(Chemical Vapor Deposition,CVD)已经可以制备与机械剥离样品相媲美的石墨烯,是实现石墨烯工业应用的关键技术之一。原子尺度理论研究能够帮助我们深刻理解石墨烯生长机理,为实验现象提供合理的解释,并有可能成为将来实验设计的理论指导。本文从理论计算的角度,总结了各种金属衬底在石墨烯CVD生长过程中的各种作用与相应的机理,包括在催化碳源裂解、降低石墨烯成核密度等,催化加快石墨烯快速生长,修复石墨烯生长过程中产生的缺陷,控制外延生长石墨烯的晶格取向,以及在降温过程中石墨烯褶皱与金属表面台阶束的形成过程等。在本文最后,我们对当前石墨烯生长领域中亟需解决的理论问题进行了深入探讨与展望。     

Ultrafast Electron Transfer Kinetics of Graphene Grown by Chemical Vapor Deposition

High electrochemical reactivity is required for various energy and sensing applications of graphene grown by chemical vapor deposition (CVD). Herein, we report that heterogeneous electron transfer can be remarkably fast at CVD‐grown graphene electrodes that are fabricated without using the conventional poly(methyl methacrylate) (PMMA) for graphene transfer from a growth substrate. We use nanogap voltammetry based on scanning electrochemical microscopy to obtain very high standard rate constants k⁰≥25 cm s^?1 for ferrocenemethanol oxidation at polystyrene‐supported graphene. The rate constants are at least 2–3 orders of magnitude higher than those at PMMA‐transferred graphene, which demonstrates an anomalously weak dependence of electron‐transfer rates on the potential. Slow kinetics at PMMA‐transferred graphene is attributed to the presence of residual PMMA. This unprecedentedly high reactivity of PMMA‐free CVD‐grown graphene electrodes is fundamentally and practically important.     

Sustained and Controlled Release of Volatile Precursors for Chemical Vapor Deposition of Graphene at Atmospheric Pressure

Precursors and catalysts play vital roles in chemical reactions. Considerable efforts have been devoted to the investigation of catalysts for graphene growth by chemical vapor deposition in recent years. However, there has been little research on precursors because of a lack of innovation in term of creating a controllable feeding method. Herein, we present a novel sustained and controlled release approach, and develop a convenient, safe, and potentially scalable feeding system with the assistance of matrix materials and a simple portable feeder. As a result, a highly volatile liquid precursor can be fed accurately to grow large-area, uniform graphene films with optimal properties. This feeding approach will further benefit the synthesis of other two-dimensional materials from various precursors.     

The Structure and Stability of Magic Carbon Clusters Observed in Graphene Chemical Vapor Deposition Growth on Ru(0001) and Rh(111) Surfaces

To improve the atomically controlled growth of graphene by chemical vapor deposition (CVD), understanding the evolution from various carbon species to a graphene nucleus on various catalyst surfaces is essential. Experimentally, an ultrastable carbon cluster on Ru(0001) and Rh(111) surfaces was observed, while its structure and formation process were still under debate. Using ab initio calculations and kinetic analyses, we disclose a specific type of carbon cluster, composed of a C₂₁ core and a few dangling C atoms, which is exceptional stable in a size range from 21 to 27 C atoms. The most stable one of them, an isomer of C₂₄ characterized by three dangling C atoms attached to the C₂₁ core (denoted as C₂₁‐3C), is the most promising candidate of the experimental observation. The ultrastability of C₂₁‐3C originates from both the stable core and the appropriate passivation of the dangling carbon atoms by the catalyst surface.     

3D Graphene Foam by Chemical Vapor Deposition: Synthesis,Properties, and Energy-Related Applications

In this review, we highlight recent advancements in 3D graphene foam synthesis by template-assisted chemical vapor deposition, as well as their potential energy storage and conversion applications. This method offers good control of the number of graphene layers and porosity, as well as continuous connection of the graphene sheets. The review covers all the substrate types, catalysts, and precursors used to synthesize 3D graphene by the CVD method, as well as their most viable energy-related applications.     

超洁净石墨烯薄膜的制备方法

化学气相沉积(Chemical vapor deposition,CVD)法制备的石墨烯薄膜具有质量高、可控性好、可放大等优点,近年来受到了学术界和工业界的广泛关注。然而,近期研究结果表明,在高温CVD生长石墨烯的过程中,伴随着许多副反应,这些副反应会导致石墨烯薄膜表面沉积大量的无定形碳污染物,造成石墨烯薄膜的“本征污染”现象。同时,这些污染物的存在会导致转移后的石墨烯薄膜表面更脏,对石墨烯材料和器件的性能带来严重影响。这也是CVD石墨烯薄膜的性能一直无法媲美机械剥离石墨烯的重要原因之一。事实上,超洁净生长方法制备得到的超洁净石墨烯薄膜在诸多指标上都给出了目前文献报道的最好结果,代表着石墨烯薄膜材料制备技术的发展前沿。本文首先对CVD法制备石墨烯过程中表面污染物的形成机理进行分析,然后综述了超洁净石墨烯薄膜的制备方法,并列举了超洁净石墨烯薄膜的优异性质。最后,总结并展望了超洁净石墨烯未来可能的发展方向和规模化制备面临的机遇与挑战。     

From Amorphous Carbon to Carbon Nanobelts and Vertically Oriented Graphene Nanosheets Synthesized by Plasma-enhanced Chemical Vapor Deposition

Carbon materials with various structures were produced via plasma-enhanced chemical vapor deposition by controlling substrate temperature and mixed gases in the atmosphere. Scanning electron microscopy(SEM), transmission electron microscopy(TEM), high resolution transmission electron microscopy(HRTEM) and Raman spectroscopy were employed to investigate the morphology and structure of the materials. The results show that at a low substrate temperature(100 ℃) in CH₄:Ar(flow rate ratio was 100 cm³/min:10 cm³/min), amorphous carbon formed on Si(100) that could act as a support for the growth of carbon nanobelt and layer graphene at 800 ℃. Vertically oriented multi-layer graphene nanosheets(GNs) were catalyst-free synthesized on Si and Ni foam at 800 ℃ in a mixture of CH₄:Ar(20 cm³/min:60, 80 and 100 cm³/min). The capacitor character investigated by cyclic voltammetry and galvanostatic charge/discharge indicates that for the as-synthesized GNs, the electrochemical capacitance is very small(16 F/g at current density of 16 A/g). However, having been treated in acidic solution, the GNs exhibited good capacitive behavior, with a capacitance of 166 F/g, and after 800 charge/discharge cycles at 32 A/g, the capacitance could retain about 88.4%. The enhancement of specific capacitance is attributed to the increase of specific surface area after etching treatment of them.     

石墨烯纤维材料的化学气相沉积生长方法

石墨烯纤维材料是以石墨烯为主要结构基元沿某一特定方向组装而成或由石墨烯包覆纤维状基元形成的宏观一维材料。根据组成基元的不同可将石墨烯纤维材料分为石墨烯纤维和石墨烯包覆复合纤维。石墨烯纤维材料在一维方向上充分发挥了石墨烯高强度、高导电、高导热等特点,在智能纤维与织物、柔性储能器件、便携式电子器件等领域具有广阔的应用前景。随着化学气相沉积(Chemical Vapor Deposition,CVD)制备石墨烯薄膜技术的发展,CVD技术也逐渐应用于石墨烯纤维材料的制备。利用CVD法制备石墨烯纤维可避免传统纺丝工艺中繁琐的氧化石墨烯(Graphene Oxide,GO)还原过程。同时,通过CVD法直接将石墨烯沉积至纤维表面可以保证石墨烯与纤维基底之间强的粘附作用,提高复合纤维的稳定性,同时可实现对石墨烯质量的有效调控。本文综述了石墨烯纤维材料的CVD制备方法,石墨烯纤维材料优异的力学、电学、光学性质及其在智能传感、光电器件、柔性电极等领域的应用,并展望了CVD法制备石墨烯纤维材料未来的发展方向。     

化学气相沉积法制备氮化钛

本文以氮化钛的CVD制备为例,说明了源物质的选择对CVD过程的影响.在此基础上,综述了化学气相沉积技术在材料制备领域的最新进展.     

蓝宝石衬底上化学气相沉积法生长石墨烯

化学气相沉积(CVD)法是制备大面积、高质量石墨烯材料的主要方法之一,但存在衬底转移和碳固溶等问题,本文选用蓝宝石衬底弥补了传统CVD法的不足。利用CVD法在蓝宝石衬底上生长石墨烯材料,研究生长温度对石墨烯表面形貌和晶体质量的影响。原子力显微镜(AFM)、光学显微镜(OM)、拉曼光谱和霍尔测试表明,低温生长有利于保持材料表面的平整度,高温生长有利于提高材料的晶体质量。研究氢气和碳源对蓝宝石衬底表面刻蚀作用机理,发现氢气对蓝宝石衬底有刻蚀作用,而单纯的碳源不能对衬底产生刻蚀效果。在1200 ℃下,直径为50 mm的晶圆级衬底上获得平整度和质量相对较好的石墨烯材料,室温下载流子迁移超过1000 cm²·V^-1·s^-1。     

Growth Mechanism of Graphene on Graphene Films Grown by Chemical Vapor Deposition

We report an approach for the synthesis of mono‐ or bilayer graphene films by atmospheric‐pressure chemical vapor deposition that can achieve a low defect density through control over the growth time. Different heating ramp rates were found to lead to variation in the smoothness and grain size of the Cu foil substrate, which directly influenced the density of the graphene domains. The rough Cu surface induced by rapid heating creates a high density of graphene domains in the initial stage, ultimately resulting in a graphene film with a high defect density due to an increased overlap between domains. Conversely, a slow heating rate resulted in a smooth and flat Cu surface, thereby lowering the density of the initial graphene domains and ensuring a uniform monolayer film. From this, we demonstrate that the growth mechanism of graphene on existing graphene films is dependent on the density of the initial graphene domains, which is affected by the heating ramp rate.     

Microencapsulation of a Crop Protection Compound by Initiated Chemical Vapor Deposition

In this work, initiated chemical vapor deposition (iCVD) has been employed as a one‐step liquid‐free process combining polymerization and coating for the encapsulation of 3D non‐planar substrates. Coatings have been applied using iCVD specifically to encapsulate microparticles of a highly water‐soluble crop protection compound (CPC) for controlled release. Release behavior has been compared among different coatings synthesized using different iCVD processing conditions, including varying degrees of polymer hydrophobicity, continuous and pulsed deposition, and crosslinking. iCVD has been found to provide tunable synthesis of hydrophobic, crosslinked polymers with control over mass diffusivity, and coating thickness for enhancing barrier properties.     

化学气相沉积法合成二维过渡金属硫族化合物研究进展

二维晶体材料所独有的二维平面结构赋予了这类材料诸多独特的性质. 近年来围绕二维过渡金属硫族化合物的相关研究发展迅速. 本文以二维MoS₂、WS₂为代表概述了利用化学气相沉积法合成过渡金属硫族化合物二维晶体的研究进展, 阐述了基本合成策略, 讨论了主要影响因素, 归纳了以MoS₂、WS₂为结构基元的二维合金及异质结构的合成方法, 最后阐明了利用化学气相沉积法合成二维晶体存在的主要问题并展望了这一领域的发展前景.     

Low-Pressure Chemical Vapor Deposition of Silicon Carbide Thin Films from Organopolysilanes

(Me₃Si)₂SiMe₂, (Me₃Si)₃SiMe and (Me₃Si)₄Si were used as precursors for the deposition of polycrystalline β-SiC thin films on silicon substrates at 1000–1200°C in a low-pressure hot-wall chemical vapor deposition reactor. The thin films were analyzed by X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy.     

Molecular Beam Mass Spectrometry System for Characterization of Thermal Plasma Chemical Vapor Deposition

A molecular beam mass spectrometry system for in situ measurement of the concentration of gas phase species including radicals impinging on a substrate during thermal plasma chemical vapor deposition (TPCVD) has been designed and constructed. Dynamically controlled substrate temperature was achieved using a variable thermal contact resistance method via a backside flow of an argon/helium mixture. A high quality molecular beam with beamtobackground signal greater than 20 was obtained under film growth conditions by sampling through a small nozzle (75 m) in the center of the substrate. Mass discrimination effects were accounted for in order to quantify the species measurements. We demonstrate that this system has a minimum detection limit of under 100 ppb. Quantitative measurements of hydrocarbon species (H, H₂, C, CH₃, CH₄, C₂H₂, C₂H₄) using Ar/H₂/CH₄ mixtures and silicon species (Si, SiH, SiH₂, SiCl, SiCl₂, Cl, HCl) using Ar/H₂/SiCl₄ mixtures were obtained under thermal plasma chemical vapor deposition conditions.     

聚酰亚胺上催化剂增强化学气相沉积钯-铂双层膜

 以N2和O2为载气,采用催化剂增强化学气相沉积法于聚酰亚胺上获得了Pt和Pd-Pt双层金属薄膜. 当使用Pd(hfac)2和PtMe2(COD)为前驱体,在同一反应器内共沉积时,只有Pt被沉积. 金属Pd和Pt顺序沉积可形成Pd-Pt双层膜.     

聚砜上催化剂增强化学气相沉积钯-铂双层纳米膜

以N2和O2作载气,采用催化剂增强化学气相沉积法在聚砜上获得了Pt和Pd-Pt双层金属纳米薄膜.当使用Pd(hfac)2和Pt(COD)Me2为前驱体在同一反应器内共沉积时,只有Pt被沉积,铂和钯顺序沉积可以得到双层膜.聚砜上金属钯和铂微粒尺度为15~30 nm,双层膜厚度为120~180 nm.     

催化增强化学蒸气沉积法在聚酰亚胺上沉积钯-铂合金薄层

以N₂，O₂作载气，通过催化增强化学蒸气沉积(CECVD)分别制得在聚酰亚胺上的金属铂、钯及其合金薄层。铂、钯配合物的共同沉积可生成Pt-Pd合金薄膜。在Pd-Pt合金的沉积过程中，Pd/Pt的原子数比率随共同沉积的条件改变而变化。O₂为载气、300 ℃条件下,用Pd(η³-allyl)(hfac)和Pt(COD)Me₂作前驱体共沉积制备Pd-Pt合金，得到含Pd 37.2%，Pt 62.8%且不