20329
The friction of graphene on SiO2 decreased with increasing thickness and converged around the penta - layers due to incomplete contact between the two surfaces .
 Chemical: graphene; Chemical: SiO2
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: SiO2