Modafinil is a very nice nootropic, but there is one fundamental thing you must understand with it. It will indeed increase your focus, and will move sleep aside. What I like about it, is that modafinil is rather safe in terms of side effects, and it is not addictive.
However, this is no magic pill that will do the job for you. If you are already struggling with studies because you spend too much time on facebook, modafinil won't help - you will only spend that time on facebook with more focus. That is, modafinil won't make you study - it will only improve the focus on what you do, but you still choose the things you do. Also, it may cause such a thing as tunnel vision, where you are way overfocused on something, and that does not let you see things from a different perspective. Therefore, for some creative activities it may in fact be counterproductive. These are just my two cents about it.