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Recently we discovered that for 1 - dimensional ( 1D ) nanocrystals ( Au nanorods ) , the catalytic activity is not constant along the same side facets of single nanorods but rather differs significantly and further shows a gradient along its length , which we attributed to an underlying gradient of surface defect density resulting from their linear decay in growth rate during synthesis ( Nat . Nanotechnol . 2012 , 7 , 237 - 241 ) .
 Chemical: Au
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: Au