17503
First , a porous Si sample is prepared by electrochemical etch and then it is mildly oxidized , which places a thin layer of silicon oxide at the surface .
 Chemical: Si; Chemical: silicon oxide
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: Si; Chemical: silicon oxide