7969
PENs , which have segments that are either gold or " empty " ( solvent - filled ) surrounded by a silica shell , were produced from striped metal nanowires by first coating with silica and then removing sacrificial segments by acid etching .
 Chemical: silica; Chemical: silica
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: silica; Chemical: silica