Unicode text file

This one is bugging me for a week:

How do I force a text file to be a unicode text file
when I save a text file in my HD?

here are some more details:
I have a string variable. I want to write the text in the string variable into a unicode text file. I am able to convert the string to unicode, but when I save the file - the file itself is not saved as unicode.

What I want to know is how to save the text file as unicode


any help will be appreciated