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In contrast , the friction of graphene folded onto bulk - like graphene was indistinguishable from that of mono - layer graphene on SiO2 despite the ultra - smoothness of bulk - like graphene .
 Chemical: graphene; Chemical: graphene; Chemical: graphene; Chemical: SiO2; Chemical: graphene
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: graphene; Chemical: graphene; Chemical: graphene; Chemical: SiO2; Chemical: graphene