6556
We find that the edges of hydrogen - plasma - etched GNRs are generally flat , free of structural reconstructions , and terminated by hydrogen atoms with no rehybridization of the outermost carbon edge atoms .
 Chemical: hydrogen; Chemical: hydrogen; Chemical: carbon
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: hydrogen; Chemical: hydrogen; Chemical: carbon