Displaying numbers with leading zeros

I construct a time as follows:
string sTime = OrderTime.TimeOfDay.Hours.ToString(). + ":" + OrderTime.TimeOfDay.Minutes.ToString() + ":" + OrderTime.TimeOfDay.Seconds.ToString();
How can I ensure that each component of the time (Hours, minutes or seconds) is prefixed with zero of the value is less than 10?
Many thanks.



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