Help Regarding Resignation letter

Hi,
Can anyone help me with writing a resignation letter,

I'm professor at same university i graduated from, and i wanto resign as i got another employment oppurtunity (mentionaing before notice period, i consider paying the ammount against it.)

i wanto mention my thanks for being a guide when i was student
n i also wanto thank for being a support as i worked there..

unable to find words to express formally, i seek help from you people..