26803
The enhancement is due to current - associated charge trapping at the graphene / SiO2 interface , which introduces a vertical electric field across the SiO2 / Si interface that produces electric field - induced SHG .
 Chemical: graphene; Chemical: SiO2; Chemical: SiO2; Chemical: Si
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; Chemical: SiO2; Chemical: Si