Jacques Doumani1,2,Oliver Dewey1,Minhan Lou2,Yohei Yomogida3,Matteo Pasquali1,Kazuhiro Yanagi3,Junichiro Kono1,Weilu Gao2
Rice University1,The University of Utah2,Tokyo Metropolitan University3
Jacques Doumani1,2,Oliver Dewey1,Minhan Lou2,Yohei Yomogida3,Matteo Pasquali1,Kazuhiro Yanagi3,Junichiro Kono1,Weilu Gao2
Rice University1,The University of Utah2,Tokyo Metropolitan University3
In this work, we investigate the unique chiroptical response of large-scale aligned films of racemic, chirality-mixture carbon nanotubes (CNTs) prepared using the controlled vacuum filtration technique. The prepared solid-state films display large circular dichroism (CD) signals (45 mdeg/nm) in the ultraviolet (UV) range, peaked at 264 nm and 317 nm. The strength and sign of CD signals depend on sample positions and vary from sample to sample. Detailed scanning electron microscopy studies revealed a rotation of alignment directors between layers in aligned CNT films. This spontaneously formed twisted stack of aligned CNT thin layers during vacuum filtration leads to a structure-induced optical chirality. Finally, we demonstrate that CD signals can be controlled - either enhanced or suppressed - by engineering the vacuum filtration processes, such as tweaking the shape of the filtration-funnel and adding mechanical vibrations.