▎ 摘　　要

We study spin-dependent electron transport properties of two dimensional graphene double and triple barrier junctions via first-principles calculations. The double barrier junction consists of two graphene leads, a quantum well of zigzag graphene nanoribbon (ZGNR) in the center, and two vacuum barriers separating the ZGNR from the two leads. Resonant electron tunneling occurs when the energy bands of graphene and ZGNR are well aligned in energy and wavevector. Highly spin-polarized electron transmission arises in such junctions when the two edges of the center ZGNR are in the ferromagnetic configuration. The spin polarization of the electron transmission at the Fermi energy can be tuned by gate voltage. We further investigate the dependence of the electron transmission on the width of the ZGNR, effects on barrier height when replacing vacuum by h-BN, and the consequence of replacing a double barrier by a triple barrier. (C) 2018 Published by Elsevier Ltd.