Another useful method that only requires one line is Directory.GetFiles :
string[] matchingFiles = Directory.GetFiles("F:\\", "student_*.xml", SearchOption.AllDirectories);
var RootDir = new System.IO.DirectoryInfo("F:\\")
Just be aware that you need to specify a doube backslash in order to be interpreted a s a single one.
I recommend using @-style string literal for the search path in this case, as it results in code that in my opinion is a little clearer and easier to read:
string[] matchingFiles = Directory.GetFiles(@"F:\", "student_*.xml", SearchOption.AllDirectories);