Graphene, often known as a wonder material due to its remarkable properties, is the thinnest membrane available to us. In this project we have synthesised and characterised different types of graphene membranes and graphene-based membranes. Firstly, we have developed a simple fabrication technique to produce pressurised single-layer graphene membranes that can hold up to reversible strain of ~2%. The graphene balloons were investigated by Raman Spectroscopy: red shift of Raman peaks was observed with increasing strain, in good agreement with theoretical calculation. [2] Also, a characteristic broadening of the Raman peaks is observed beyond 1% strain, which has been attributed to nanoscale strain variations in the membranes. Another type of graphene-based membrane is prepared by assembling millions of tiny graphene flakes together into a laminate. Liquid-phase exfoliation is used to disperse graphene nanoflakes in a solution [3]; the dispersion is then deposited as a laminate by simple fabrication techniques such as drop casting. Because the properties of a graphene laminate strongly depend on the flake size and thickness distribution in the dispersion, it is important to be able to characterise LPE graphene. Here, we have developed a simple qualitative protocol based on Raman spectroscopy to characterise this materials. This protocol was first validated in two works, aimed at studying the enhancement of the yield of LPE graphene using two different stabilisers, n-octylbenzene and perchlorocoronene. We then applied our method to graphene/PIM-1 composite membrane. PIMs are a new class of polymers showing great potential in separation applications. An improvement in the performance of the membrane (e.g. permeability) is expected by adding graphene as a nanofiller. However, little is experimentally known about how the material disperses in PIM. Our results show that Raman spectroscopy is able to identify the presence of re-aggregated graphene-based materials in the composite. This is expected to produce strong changes in the mechanical properties and the physical ageing of the membrane. Lastly, we demonstrated fabrication of self-catalytic reactor membrane composed of graphitic carbon nitride (g-C3N4). Simple LPE and vacuum filtration techniques are employed, maximising the surface area and exposure of the active sites. The g-C3N4 membrane showed significantly enhanced catalytic performance compared to the bulk g-C3N4, achieving ~100% conversion efficiency for photo-degradation of several organic dyes. In conclusion, we investigated different types of graphene-based membranes, showing that LPE is simple technique with high versatility for different applications and Raman spectroscopy is a powerful technique for characterisation of graphene in all cases.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22895号 / 工博第4792号 / 新制||工||1749(附属図書館) / 京都大学大学院工学研究科分子工学専攻 / (主査)教授 SIVANIAH Easan, 教授 田中 庸裕, 教授 今堀 博 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

This diploma thesis is focused on the application of Kelvin probe microscopy on graphene fabricated by the chemical vapour deposition. The theoretical part of the thesis deals with basic principles of Kelvin force microscopy and focus ion beam. Further, basic properties of graphene and its possible fabrication methods are discussed. The experimental part is focused on the surface potential measurements on graphene membranes fabricated on the substrate modified by focus ion beam. Finally, atomic force microscope lithography was used for nanopatterning of graphene sheets.

This diploma thesis is focused on the applications and fabrication of graphene membrane from graphene prepared by the chemical vapor deposition. Theoretical part deals with transport properties of the graphene and multiple scattering processes limiting the charge carrier mobility in this material. Included is short review of graphene membrane applications. Experimental part provides fabrication process for achieving suspended graphene device by utilizing electron beam lithography, focused ion beam, chemical etching and patterning of graphene. Graphene membrane is characterized by transport properties measurement and compared to non-suspended graphene.