16739
We show that the derived in - plane ( shear ) and out - of - plane ( breathing ) force constants from experiment remain the same from two - layer 2D crystals to the bulk materials , suggesting that the nanoscale interlayer frictional characteristics of these excellent lubricants should be independent of the number of layers .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
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