No abstract

Metal nanoparticles and H 2 induced etching of graphene are of significant interest to synthesis graphene nanoribbons and various other structures with crystallographically defined edges. Here, we demonstrate a controllable H 2 -induced etching process of graphene crystals to fabricate nanoribbons, and Y-junctions structures with pronounced edges. Individual graphene crystals and a continuous films were grown on Cu foil by solid source chemical vapor deposition (CVD) technique. The etching behavior of the synthesized graphene was investigated by annealing at 1000 0 C in a gas mixture of H 2 and Ar. A highly anisotropic etching creates hexagonal holes, nanoribbons and Y-junction graphene with clear edge structures. The distinct graphene edges of individual ribbon create 120° to form a Y-shape structure. The finding can be significant to fabricate well-defined graphene structures with controlled edges for electronic device applications as well as creating in-plane heterostructures with other two dimensional (2D) materials.obtain graphene with regular, zigzag or armchair edge structures. 26,28 In this prospect, exploring the anisotropic etching behavior of high quality CVD graphene is of great interest to fabricate nanoribbons with distinct edge structure. 29 Creating holes with defined edge structure also provide a platform to fabricate in-plane heterostructure with other 2D materials. Anisotropic etching of graphene basal plane has been explored with metal catalytic nanoparticles in presence of H 2 , selective oxidation, and water vapor at an elevated temperature. [30][31][32][33][34] Recently, anisotropic behavior of H 2 in the formation of graphene domains has been also observed, thereby obtaining pentagonal graphene domains with anisotropic growth and etching process. 35 Highly anisotropy etching of graphene can be achieved owing to significant differences in chemical reactivity of the zigzag and armchair edges. This has open new opportunities to control the structure of high quality exfoliated and CVD graphene in large-area for device integration. Again, fabrication of Y-shaped graphene nanoribbons with well-ordered edges can be significant, which is not yet addressed considerably. Theoretical analysis predicted specific properties of the Y-shaped zigzag graphene nanoribbons structure. [36][37][38][39][40] Formation of Y-shaped graphene nanoribbons by anisotropic etching process will enable to fabricate multi-terminal graphene-based nanoelectronic and spintronic devices. 41,42 However, synthesis of Y-shaped graphene nanoribbons with clear edges is significant area of graphene on Cu foil. Figure 5(b) shows formation of Y-shape graphene ribbons structure with edge etching from different directions. The perfect edges of individual ribbon create 120° to form an Y-shape structure. Previously, significant efforts have been made to synthesis Y-shape CNTs owing to its unique electrical properties. 45 The three-terminal Y-junction nanotubes exhibits the gating behavior, characteristic of transistors. Similarly, Y-junct...

H2 induced etching of graphene is of significant interest to understand graphene growth process as well as to fabricate nanoribbons and various other structures. Here, we demonstrate the structure dependent H2 induced etching behavior of graphene crystals. We synthesized graphene crystals on electro-polished Cu foil by an atmospheric pressure chemical vapor deposition process, where some of the crystals showed hexagonal shaped snowflake-dendritic morphology. Significant differences in H2 induced etching behavior were observed for the snowflake-dendritic and regular graphene crystals by annealing in a gas mixture of H2 and Ar. The regular graphene crystals were etched anisotropically creating hexagonal holes with pronounced edges, while etching of all the dendritic crystals occurred from the branches of lobs creating symmetrical fractal structures. The etching behavior provides important clue of graphene nucleation and growth as well as their selective etching to fabricate well-defined structures for nanoelectronics.

The synthesis of large-area monolayer tungsten disulphide (WS2) single crystal is critical for realistic application in electronic and optical devices. Here, we demonstrate an effective approach to synthesize monolayer WS2 crystals using tungsten hexachloride (WCl6) as a solid precursor in atmospheric chemical vapor deposition process. In this technique, 0.05M solution of WCl6 in ethanol was drop-casted on SiO2/Si substrate to create an even distribution of the precursor, which was reduced and sulfurized at 750 °C in Ar atmosphere. We observed growth of triangular, star-shaped, as well as dendritic WS2 crystals on the substrate. The crystal geometry evolves with the shape and size of the nuclei as observed from the dendritic structures. These results show that controlling the initial nucleation and growth process, large WS2 single crystalline monolayer can be grown using the WCl6 precursor. Our finding shows an easier and effective approach to grow WS2 monolayer using tungsten halide solution-casting, rather than evaporating the precursor for gas phase reaction.

No abstract