separate characters and put in a csv file

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C#

I have the following code and I am passing a string example "1011010010" I want to store this string so that each 1 and 0 is in a separate column but I am getting in a separate row instead. What is wrong please?

private void csvExport(string s)
 {
     StreamWriter sw = new StreamWriter("C:\\testdata.csv", true);
     sw.WriteLine(s);
    
     sw.Close();
 }