Try to follow the preferred usage as much as possible. A paragraph of acknowledgments, if needed, should be placed after the text and before the references. Treat the word Acknowledgments as a first-level heading without a number. If the section contains only one acknowledgment, use the singular word in the heading. Type the heading as an unnumbered first-level heading.
References are a very important feature of the paper.
All references quoted must be accessible. The reference list should not contain citations of correspondence or interoffice memoranda that are not accessible for loan. The reference list is numbered in order of appearance in the text. Phys., Vol 19, No. 7, pp.882-885, July 1948. Schafer, H.F., Electronic Structure of Atoms and Molecules, Addison-Wesley Publishing Co., Reading, MA, 1972.