5391
By using two - stage , metal - catalyst - free chemical vapor deposition ( CVD ) , it is demonstrated that high - quality polycrystalline graphene films can directly grow on silicon nitride substrates .
 Chemical: graphene; Chemical: silicon nitride
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: silicon nitride