Low‐Temperature and Rapid Growth of Large Single‐Crystalline Graphene with Ethane

Future applications of graphene rely highly on the production of large‐area high‐quality graphene, especially large single‐crystalline graphene, due to the reduction of defects caused by grain boundaries. However, current large single‐crystalline graphene growing methodologies are suffering from low growth rate and as a result, industrial graphene production is always confronted by high energy consumption, which is primarily caused by high growth temperature and long growth time. Herein, a new growth condition achieved via ethane being the carbon feedstock to achieve low‐temperature yet rapid growth of large single‐crystalline graphene is reported. Ethane condition gives a growth rate about four times faster than methane, achieving about 420 µm min^?1 for the growth of sub‐centimeter graphene single crystals at temperature about 1000 °C. In addition, the temperature threshold to obtain graphene using ethane can be reduced to 750 °C, lower than the general growth temperature threshold (about 1000 °C) with methane on copper foil. Meanwhile ethane always keeps higher graphene growth rate than methane under the same growth temperature. This study demonstrates that ethane is indeed a potential carbon source for efficient growth of large single‐crystalline graphene, thus paves the way for graphene in high‐end electronical and optoelectronical applications.     

High‐Quality Monolayer Graphene Synthesis on Pd Foils via the Suppression of Multilayer Growth at Grain Boundaries

The segregation of carbon from metals in which carbon is highly soluble, such as Ni (≈1.1 atom% at 1000 °C), is a typical method for graphene growth; this method differs from the surface‐catalyzed growth of graphene that occurs on other metals such as Cu (<0.04 atom%). It has not been established whether strictly monolayer graphene could be synthesized through the traditional chemical vapor deposition route on metals where carbon is highly soluble, such as Pd (≈3.5 atom%). In this work, this issue is investigated by suppressing the grain boundary segregation using a pretreatment comprising the annealing of the Pd foils; this method was motivated by the fact that the typical thick growths at the grain boundaries revealed that the grain boundary functions as the main segregation channel in polycrystalline metals. To evaluate the high crystallinity of the as‐grown graphene, detailed atomic‐scale characterization with scanning tunneling microscopy is performed.     

Germanium‐Assisted Direct Growth of Graphene on Arbitrary Dielectric Substrates for Heating Devices

Direct growth of graphene on dielectric substrates is a prerequisite to the development of graphene‐based electronic and optoelectronic devices. However, the current graphene synthesis methods on dielectric substrates always involve a metal contamination problem, and the direct production of graphene patterns still remains unattainable and challenging. Herein, a semiconducting, germanium (Ge)‐assisted, chemical vapor deposition approach is proposed to produce monolayer graphene directly on arbitrary dielectric substrates. By the prepatterning of a catalytic Ge layer, the graphene with desired pattern can be achieved conveniently and readily. Due to the catalysis of Ge, monolayer graphene is able to form on Ge‐covered dielectric substrates including SiO₂/Si, quartz glass, and sapphire substrates. Optimization of the process parameters leads to complete sublimation of the catalytic Ge layer during or immediately after formation of the monolayer graphene, enabling direct deposition of large‐area and continuous graphene on dielectric substrates. The large‐area, highly conductive graphene synthesized on a transparent dielectric substrate using the proposed approach has exhibited a wide range of applications, including in both defogger and thermochromic displays, as already successfully demonstrated here.     

Direct Synthesis of Few‐Layer Graphene on NaCl Crystals

Chemical vapor deposition is used to synthesize few‐layer graphene on micro crystalline sodium chloride (NaCl) powder. The water‐soluble nature of NaCl makes it convenient to produce free standing graphene layers via a facile and low‐cost approach. Unlike traditional metal‐catalyzed or oxygen‐aided growth, the micron‐size NaCl crystal planes play an important role in the nucleation and growth of few‐layer graphene. Moreover, the possibility of synthesizing cuboidal graphene is also demonstrated in the present approach for the first time. Raman spectroscopy, optical microscopy, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy are used to evaluate the quality and structure of the few‐layer graphene along with cuboidal graphene obtained in this process. The few‐layer graphene synthesized using the present method has an adsorption ability for anionic and cationic dye molecules in water. The present synthesis method may pave a facile way for manufacturing few‐layer graphene on a large scale.     

Switching Vertical to Horizontal Graphene Growth Using Faraday Cage‐Assisted PECVD Approach for High‐Performance Transparent Heating Device

Plasma‐enhanced chemical vapor deposition (PECVD) is an applicable route to achieve low‐temperature growth of graphene, typically shaped like vertical nanowalls. However, for transparent electronic applications, the rich exposed edges and high specific surface area of vertical graphene (VG) nanowalls can enhance the carrier scattering and light absorption, resulting in high sheet resistance and low transmittance. Thus, the synthesis of laid‐down graphene (LG) is imperative. Here, a Faraday cage is designed to switch graphene growth in PECVD from the vertical to the horizontal direction by weakening ion bombardment and shielding electric field. Consequently, laid‐down graphene is synthesized on low‐softening‐point soda‐lime glass (6 cm × 10 cm) at ≈580 °C. This is hardly realized through the conventional PECVD or the thermal chemical vapor deposition methods with the necessity of high growth temperature (1000 °C–1600 °C). Laid‐down graphene glass has higher transparency, lower sheet resistance, and much improved macroscopic uniformity when compare to its vertical graphene counterpart and it performs better in transparent heating devices. This will inspire the next‐generation applications in low‐cost transparent electronics.