Fabrication of Freestanding Graphene Nanoribbon Network by Utilizing Laser Technology
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Fabrication of Freestanding Graphene Nanoribbon Network by Utilizing Laser Technology
Hai H. Van, Kaelyn Badura, and Mei Zhang Department of Industrial and Manufacturing Engineering, FAMU-FSU College of Engineering; High-Performance Materials Institute, Florida State University, 2525 Pottsdamer Street, Tallahassee, FL 32310, U.S.A.
ABSTRACT Laser is used to produce graphene nanoribbons (GNRs) by unzipping carbon nanotubes (CNTs). It is found that laser can not only unzip CNTs, but also join GNRs through covalent reconnections. Because the CNTs are aligned in a freestanding CNT sheet, the laser irradiation process results in a freestanding GNR network. Experimental results show that the expected results can be achieved by controlling the delivery of laser beam energy to the sheet. Moreover, this process is a solid-state process and a scalable manufacturing process. INTRODUCTION Graphene has been attracting a lot of attentions due to its superior physical properties. One of the unique properties of graphene is the tunable electronic property, which means that it could behave as a metal or a semiconductor. The tunability depends on the edge shape, the length, the width, the number of layers, and the chemical structure along its edge. Especially, the graphene with the width less than 10 nm exhibits the semiconducting behaviors. Such long thin graphene strip is called graphene nanoribbon (GNR). There have been many researches relating to the manufacture methodologies of the GNRs with the controllable geometries. CNTs are promising candidate for producing GNRs. The CNT structures is considered as rolled up from the GNRs. Therefore, if a CNT is cut along the cylindrical axis, its tubular structure will be opened, i.e. unzipped, producing a GNR. There are several methods to unzip CNTs, which can be categorized as the chemical scissor methods and the non-chemical based methods. In the chemical scissor methods, the chemical compounds were used to create the chemical reactions to cut the graphitic walls [1, 2]. The GNRs produced by these methods were contaminated by the utilized chemicals. Additionally, the edges of GNRs were functionalized with oxygen-contained groups, thus reducing the electronic properties of the GNRs. The non-chemical based methods utilized various forms of energy, such as kinetic energy of ions (plasma) [3–5], photon energy (laser) [6], or thermal energy (electric current) [7] to unzip CNTs. In addition, the thermal stress was also utilized to break or exfoliate the graphitic shells [8, 9]. Although chemicals were not the main factor to unzip the CNTs, the produced GNRs could be contaminated. For example, in the plasma methods, polymer was used to protect CNTs from the over-bombardment of the ions. Thus the further chemical process was required to remove these protective layers. For the methods that employed the thermal stress to unzip the tubes, the breaking directions of the graphitic shells were dependent on the defect levels, the defect location, and the chirality degrees of the tubes. Because these
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