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Abstract:
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Following the first report on electronic transport measurements of graphene , an atom -thick carbon material , many scientists have devoted effort to understand its fundamental properties . In this work , the mechanical properties of graphene -based materials , including monolayer graphene oxide and chemical vapor deposition (CVD ) grown graphene , were determined using membrane structures . Furthermore , a membrane structure was used to demonstrate thermoacoustic sound generation from monolayer graphene .
In order to realize the mechanical characterization , reproducible methods to fabricate graphene membranes were developed using dry and wet transfer techniques . A novel dry transfer technique produced graphene -sealed microchambers without trapping liquid inside . An improved wet transfer technique enabled the transfer of graphene onto perforated substrates .
Monolayer graphene oxide was mechanically tested using scanning atomic force microscopy (AFM ) combined with finite element analysis of the data . The mechanical deformation was measured by scanning AFM tips over the suspended graphene oxide membranes . The Young’s modulus of the membranes was obtained by analyzing the deformation using finite element analysis together with a mapping technique . In addition , membranes with 2 and 3 layers of graphene oxide were identified using transmission electron microscopy and mechanically characterized . Moreover , these same methods were used for measuring mechanical properties of ultra -thin amorphous carbon membranes .
Bulge tests , which apply uniform pressure on the suspended membrane , revealed the mechanical behavior of polycrystalline graphene grown on copper foils by chemical vapor deposition . In particular , the effect of grain boundaries on the elastic properties of polycrystalline graphene was studied by correlating its Young’s modulus with the density of grain boundaries within the membranes . It was observed that a large number of grain boundaries softened the graphene membranes .
Graphene , along with monolayer hexagonal boron nitride , is the ultimate limit of thin materials . Thus , it is an ideal candidate as a thermoacoustic sound source because of its low heat capacity per unit area . The work presented here provides the first demonstration of thermoacoustic sound generation from large -area monolayer graphene . A fundamental understanding of the influence of the underlying substrates was achieved by comparing the acoustic performance of graphene membranes on various patterned substrates with different porosities . |