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In contrast to graphene , monolayer MoS ( 2 ) is a non - centrosymmetric material with a direct energy gap .
 Chemical: graphene; Chemical: MoS ( 2 )
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: MoS ( 2 )