8644
Nanostructure of the films was studied using Doppler broadening of annihilation radiation ( DBAR ) , positron annihilation lifetime ( PAL ) , X - ray photoelectron spectroscopy ( XPS ) , an atomic force microscope ( AFM ) and contact angle measurements .
 None
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 None