12000
We have investigated by photoemission spectroscopy and scanning tunnelling microscopy what are the chemical and structural changes induced by nitrogen ion implantation ( 500 eV ) on highly oriented pyrolytic graphite and how the defects induced by this process modify the growth and thermal stability of palladium nanoparticles , deposited in situ by physical vapour deposition .
 Chemical: nitrogen; Chemical: graphite; Chemical: palladium
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: nitrogen; Chemical: graphite; Chemical: palladium