High anisotropy of the field-effect transistor mobility in magnetically aligned discotic liquid-crystalline semiconductors.
A magnetic field has been utilized for producing highly oriented films of a substituted hexabenzocoronene (HBC). Optical microscopy studies revealed large area HBC monodomains that covered the entire film, while wide-angle X-ray measurements showed that the HBC molecules are aligned with their planes along the applied field. On the basis of this method, solution-processed field-effect transistors (FET) have been constructed with charge carrier mobilities of up to 10(-3) cm2/V.s, which are significantly enhanced with respect to the unaligned material. Exceptionally high mobility anisotropies of 25-75 for current flow parallel and perpendicular to the alignment direction have been measured as a function of the channel length. Atomic force microscopy performed on the FET structures reveals fibril superstructures that are oriented perpendicularly to the magnetic field direction, consisting of molecular columns with a slippage angle of 40 degrees between the molecules. For channel lengths larger than 2.5 mum, the fibrils are smaller than the electrode spacing, which adversely affects the device performance.
Shklyarevskiy
Igor O
IO
High Field Magnet Laboratory, Institute for Molecules and Materials, Radboud University Nijmegen, Toernooiveld 7, 6525 ED Nijmegen, The Netherlands.
Jonkheijm
Pascal
P
Stutzmann
Natalie
N
Wasserberg
Dorothee
D
Wondergem
Harry J
HJ
Christianen
Peter C M
PC
Schenning
Albertus P H J
AP
de Leeuw
Dago M
DM
Tomović
Zeljko
Z
Wu
Jishan
J
Müllen
Klaus
K
Maan
Jan C
JC