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On the Past, Present and Future: 66 Essays by Isaac Asimov

By Isaac Asimov

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Fig. 10. XPS spectra of the two samples prepared in mixing atmosphere of NH3 and He with the different ratio of NH3/He (V/V): (a) NH3: He =1:1; (b) NH3: He=1:0. (Li et al. 2010a. Reproduced by permission of Elsevier Limited) Synthesis of Graphenes with Arc-Discharge Method 31 Fig. 11. High-resolution XPS spectra of N1s. (Li et al. 2010a. ( 2010) synthesized graphene in the atmosphere of air. The yield of their products was found to be strongly dependent on the initial air pressure. Fig. 12 shows the TEM images of the products corresponding to differing initial air pressure.

26 (Fig. 23 (Fig. 57. This indicates that the N-doped multilayered graphene produced by arc-discharge method bear well crystalline structure and the number of graphene’s layers is not influenced significantly by the content of NH3. Fig. 7. Raman spectra of the two samples prepared in mixing atmosphere of NH3 and He with the different ratio of NH3/He (V/V): (a) NH3: He =1:0; (b) NH3: He=1:1. (Li et al. 2010a. Reproduced by permission of Elsevier Limited) Fig. 8 shows the TGA curve of the N-doped multi-layered graphene.

Therefore, the graphene growth on Ni is confirmed to be non-uniform in thickness over a large area, but monolayer graphene can be found in small areas. One might notice that the backgrounds in Raman spectra are different when graphene is on Ni and on SiO2 . , 2008). Fig. 6. , 2006). Like CVD growth of CNTs, the achievement of graphene on nickel was not based on the solid understanding of the mechanism. g. 900 ◦ C). At the cooling step, the bulk Ni is subject to temperature decrease, leading to the solubility reduction since the solubility of carbon in Ni is temperature-dependent, and hence the excessive dissolved carbon atoms have no way out but to precipitate back onto the top surface, where they form graphene sheet (Figure 9).

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