TY - JOUR
T1 - Unexpected softness of bilayer graphene and softening of A-A stacked graphene layers
AU - Sun, Yiwei
AU - Holec, David
AU - Gehringer, Dominik
AU - Fenwick, O.
AU - Dunstan, David J.
AU - Humphreys, C.J.
N1 - Publisher Copyright: © 2020 American Physical Society.
PY - 2020/3/20
Y1 - 2020/3/20
N2 - Density functional theory has been used to investigate the behavior of the π electrons in bilayer graphene and graphite under compression along the c axis. We have studied both conventional Bernal (A-B) and A-A stackings of the graphene layers. In bilayer graphene, only about 0.5% of the π-electron density is squeezed through the sp2 network for a compression of 20%, regardless of the stacking order. However, this has a major effect, resulting in bilayer graphene being about six times softer than graphite along the c axis. Under compression along the c axis, the heavily deformed electron orbitals (mainly those of the π electrons) increase the interlayer interaction between the graphene layers as expected, but, surprisingly, to a similar extent for A-A and Bernal stackings. On the other hand, this compression shifts the in-plane phonon frequencies of A-A stacked graphene layers significantly and very differently from the Bernal stacked layers. We attribute these results to some sp2 electrons in A-A stacking escaping the graphene plane and filling lower charge-density regions when under compression, hence, resulting in a nonmonotonic change in the sp2-bond stiffness.
AB - Density functional theory has been used to investigate the behavior of the π electrons in bilayer graphene and graphite under compression along the c axis. We have studied both conventional Bernal (A-B) and A-A stackings of the graphene layers. In bilayer graphene, only about 0.5% of the π-electron density is squeezed through the sp2 network for a compression of 20%, regardless of the stacking order. However, this has a major effect, resulting in bilayer graphene being about six times softer than graphite along the c axis. Under compression along the c axis, the heavily deformed electron orbitals (mainly those of the π electrons) increase the interlayer interaction between the graphene layers as expected, but, surprisingly, to a similar extent for A-A and Bernal stackings. On the other hand, this compression shifts the in-plane phonon frequencies of A-A stacked graphene layers significantly and very differently from the Bernal stacked layers. We attribute these results to some sp2 electrons in A-A stacking escaping the graphene plane and filling lower charge-density regions when under compression, hence, resulting in a nonmonotonic change in the sp2-bond stiffness.
UR - http://www.scopus.com/inward/record.url?scp=85083384083&partnerID=8YFLogxK
U2 - 10.1103/PhysRevB.101.125421
DO - 10.1103/PhysRevB.101.125421
M3 - Article
SN - 0163-1829
VL - 101.2020
JO - Physical review : B, Condensed matter and materials physics
JF - Physical review : B, Condensed matter and materials physics
IS - 12
M1 - 125421
ER -