Surface-induced orientation control of CuPc molecules for the epitaxial growth of highly ordered organic crystals on graphene.
The epitaxial growth and preferred molecular orientation of copper phthalocyanine (CuPc) molecules on graphene has been systematically investigated and compared with growth on Si substrates, demonstrating the role of surface-mediated interactions in determining molecular orientation. X-ray scattering and diffraction, scanning tunneling microscopy, scanning electron microscopy, and first-principles theoretical calculations were used to show that the nucleation, orientation, and packing of CuPc molecules on films of graphene are fundamentally different compared to those grown on Si substrates. Interfacial dipole interactions induced by charge transfer between CuPc molecules and graphene are shown to epitaxially align the CuPc molecules in a face-on orientation in a series of ordered superstructures. At high temperatures, CuPc molecules lie flat with respect to the graphene substrate to form strip-like CuPc crystals with micrometer sizes containing monocrystalline grains. Such large epitaxial crystals may potentially enable improvement in the device performance of organic thin films, wherein charge transport, exciton diffusion, and dissociation are currently limited by grain size effects and molecular orientation.
Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States. xiaok@ornl.gov
Kai
K
Xiao
Wan
W
Deng
Jong K
JK
Keum
Mina
M
Yoon
Ivan V
IV
Vlassiouk
Kendal W
KW
Clark
An-Ping
AP
Li
Ivan I
II
Kravchenko
Gong
G
Gu
Edward A
EA
Payzant
Bobby G
BG
Sumpter
Sean C
SC
Smith
James F
JF
Browning
David B
DB
Geohegan
D003460:Crystallization; D006108:Graphite / Q000737:chemistry*; D007211:Indoles / Q000737:chemistry*; D008958:Models, Molecular; D009942:Organometallic Compounds / Q000737:chemistry*; D010316:Particle Size; D013499:Surface Properties
D007211:Indoles; D009942:Organometallic Compounds; C015445:copper phthalocyanine; D006108:Graphite