Abstract: Compositions for promoting growth and/or differentiation of a stem cell are disclosed. The composition comprises: a) a diamond film; b) a stem cell cultured on the diamond film; and c) a medium bathing the stem cell. The stem cell may be a mammalian neural stem cell and the diamond film may comprise a hydrogen-terminated or an oxygen-terminated surface. The hydrogen-terminated surface promotes proliferation and differentiation of a neural stem cell into neurons, and the oxygen-terminated surface promotes a neural stem cell to proliferate and differentiate into oligodendrocytes.