Synthesis of 2D Materials by Chemical Vapor Deposition for Smart Applications

Abstract

Two-dimensional (2D) materials, which exist in layered structure, have been explosively researched over the last few years since graphene was firstly mechanically exfoliated. Although mechanical exfoliation provides high quality 2D materials, their micro-scale crystals limit their practical applications. Chemical vapor deposition (CVD) provides an answer for the scalable and reliable production. Currently the growth and development of the CVD based synthesis methods are the basis for industrial application of 2D materials. Among these practical applications, 2D materials show promising prospect in fields of electromagnetic interference (EMI) shielding and electrochemical catalysts because of their ultra-thin thickness and large surface area. Many world-wide groups have published reports on the synthesis of CVD based 2D materials for EMI shielding and electrochemical applications. We also summarize our experimental results related to these new materials and future applications.

First, we demonstrate heat generation originated from the unique electromagnetic (EM) wave absorption synthesized by low pressure chemical vapor deposition (LPCVD). The EM wave induces an oscillating magnetic moment generated by the orbital motion of moving electrons, which efficiently absorbs the EM energy and dissipate it as a thermal energy. In this case, the mobility of electron is more important than the conductivity, because the EM-induced diamagnetic moment is directly proportional to the speed of electron in an orbital motion. We expect that the efficient and fast heating of graphene films by EM waves can be utilized for smart heating windows and defogging windshields.

In addition, we report the graphene based highly conducting contact lens platform that reduces the exposure to EM waves and dehydration. The EM wave shielding function of the graphene-coated contact lens was tested on egg whites exposed to strong EM waves inside a microwave oven. We also demonstrated the enhanced dehydration protection effects of the graphene-coated lens by monitoring the change in water evaporation rate from the vial capped with the contact lens. Thus, we believe that the graphene-coated contact lens would provide a healthcare and bionic platform for wearable technologies in the future.

Second, we focus on the electrochemical application of beyond graphene materials. We devise a simple strategy to use conventional laser printer toner materials as precursors for graphitic carbon electrodes. The toner was laser-printed on metal foils, followed by thermal annealing in hydrogen environment, finally resulting in the patterned thin graphene-graphitic carbon electrodes for supercapacitors. The electrochemical cells made of the graphene-graphitic carbon electrodes show remarkable higher energy and power performance compared to conventional supercapacitors.

Finally, we demonstrate that metal organic chemical vapor deposition (MOCVD) and UV-ozone treatment on bilayer MoS2 could introduce more active sites and increased conductivity via the small grain size and oxygen doping, leading to a high density of exposed edges and a significant improvement of the hydrogen evolution activity. The mechanisms of increased electrochemical hydrogen evolutions are explained by enhanced photoluminescence (PL) and extended exciton life times. Our approach can be used directly to increase the hydrogen production activity in electrochemical reaction of 2D materials, and help to understand the catalytic effects and mechanisms of 2D materials.