Raman spectroscopy of pristine and PEI-doped graphene - Ballesteros, Laureen Ida Monzon; Pangasinan, Jamela; De Luna, Charlene; Madula, Rogie; Racho, Mary Baby Aizeil; Somintac, Armando; Salvador, Arnel (Proceedings of the Samahang Pisika ng Pilipinas, 2018)