6555
Using a combination of high - resolution scanning tunneling microscopy and first - principles calculations , we have determined the exact atomic structure of plasma - etched GNR edges and established the chemical nature of terminating functional groups for zigzag , armchair , and chiral edge orientations .
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Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
 Entities:  
Answer:
 None