20334
Our friction measurements revealed that graphene , once exfoliated from the bulk crystal , tends to maintain its corrugation level even after it is folded onto an atomically flat substrate and that ultra - flatness in both graphene and the substrate is required to achieve the intimate contact necessary for strong adhesion .
 Chemical: graphene; Chemical: graphene
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
 Entities: graphene, graphene 
Answer:
 Chemical: graphene; Chemical: graphene