This is basically what I use:

public void writetofile(string yourfilename, string yourstringtowritetofile)
{
FileStream fs = new FileStream(yourfilename, FileMode.Create);

for (int i = 0; i < yourstringtowritetofile.Length; i++)
fs.WriteByte((byte)yourstringtowritetofile[i]);

fs.Close();
}

The above is provided "as is" and is without warranty of any kind...