Synchronous chemical vapor deposition of large-area hybrid graphene–carbon nanotube architectures Maziar Ghazinejad a) Department of Mechanical Engineering, University of California, Riverside, California 92521; and Department of Electrical Engineering, University of California, Riverside, California 92521 Shirui Guo a) Department of Chemistry, University of California, Riverside, California 92521 Wei Wang Department of Materials Science and Engineering Program, University of California, Riverside, California 92521 Mihrimah Ozkan Department of Electrical Engineering, University of California, Riverside, California 92521 Cengiz S. Ozkan b) Department of Mechanical Engineering, University of California, Riverside, California 92521; and Department of Materials Science and Engineering Program, University of California, Riverside, California 92521 (Received 18 July 2012; accepted 6 November 2012) We report on the successful synthesis of a graphene–carbon nanotube (CNT) hybrid architecture by a parallel chemical vapor deposition (CVD) of the two carbon allotropes. The carbon hybrid is a three-dimensional (3D) nanostructure with tuneable architecture comprising vertically grown CNTs as pillars and a large-area graphene plane as the floor. The formation of CNTs and graphene occurs simultaneously in a single CVD growth that we describe as a synchronous synthesis method. Unique nature of the fabrication approach contributes significantly to the quality and composure of final nanohybrid. Detailed characterization elucidates the cohesive structure and robust contact between the graphene floor and the CNTs in the hybrid structure. The functionality of the synthesized graphene hybrid structure has been demonstrated by its incorporation into a super- capacitor cell. Our fabrication approach provides an attractive pathway for the fabrication of novel 3D hybrid nanostructures and efficient device integration. I. INTRODUCTION Graphene has recently produced a major scientific sen- sation due to its promising properties such as high charge carrier mobility, unique band structure, mechanical robust- ness, high thermal transport, and chemical stability. 1–7 Consequently, there has been a considerable amount of the- oretical and experimental research toward potential appli- cations of graphene nanostructures in field effect transistors, actuators, solar cells, batteries, and sensors. 8–12 Carbon nanotubes (CNTs), another carbon allotrope, have also been the subject of intensive research over the last two decades because of their exceptional electronic, optical, mechanical, and chemical properties. 13–15 Several outstanding features, such as peculiar electronic transport, the ability to carry large current densities, high aspect ratio, and fast electron-transfer kinetics, make CNTs appealing for applications in electrochemical sensing, energy storage, field emission devices, and photovoltaics. 15–18 For realistic utilization of graphene and CNTs, how- ever, there is a need for these carbon allotropes to have engineered architectures with sp 2 hybridized carbon atoms as building blocks. Resulting hybrid structures will combine attractive material properties of both CNTs and graphene with the capability to develop a variety of geometries. 19–26 Therefore, devising a fabrication methodology for spatial distribution of graphene layers and CNTs in hybrid carbon architectures is crucial and rewarding. The method by which graphene is prepared is critical in functionality of the synthesized carbon hybrid. For example, in hybrids that are constructed from reduction of graphene oxides, there are concerns regarding the uniformity and quality of resultant graphene layers. 27 Alternatively, when graphene layers are prepared by me- chanical exfoliation of graphite or graphite oxide, there are certain limitations in terms of scalability and reproduc- ibility. 2 Synthesis of large-area uniform graphene layers is essential for incorporation of graphene-based structures into nano- and optoelectronic devices. 28,29 While the quality of mechanically cleaved graphene in some micrometer-sized flakes is superior, mechanical exfoliation is size limited and incapable of high-throughput production of large-scale graphene. a) These authors contributed equally to this work. b) Address all correspondence to this author. e-mail: cengiz.ozkan@ucr.edu DOI: 10.1557/jmr.2012.413 J. Mater. Res., Vol. 28, No. 7, Apr 14, 2013 Ó Materials Research Society 2013 958