Energy
released from an accelerated high-energy single/cluster
particle triggers solid-state polymerization and cross-linking reactions
of porphyrin-based π-conjugated monomers within a nanometer-scaled
one-dimensional spatial area along the ion trajectory, resulting in
the formation of an insoluble nanowire with a precise diameter and
length. The nanowires are isolated by the development processimmersion
of the irradiated film in organic solventsand their shape
and geometry are clearly characterized by atomic force microscopy.
The obtained nanowire bundles, reflecting precisely the number of
incident particles, show characteristic absorption spectra originating
from porphyrin chromophores without significant degradation of the
molecular cores. These porphyrin-based nanowires can be further functionalized
into metallocomplexes by immersing the nanowires into solutions containing
metal ion sources. The remarkable finding on the monomer structural
parameters is that terminal alkyne groups are preferentially reacted
and thus highly effective as a monomer structure for the present single
particle-triggered linear polymerization method. The porphyrin-based
nanowires show much higher photoconductivity than the precursor porphyrin
films and enhanced fluorescence on silver nanoparticle layers via
surface plasmon resonance. The porphyrin nanowires serve as photosensitizers
mediating the generation of singlet oxygens, which is attractive for
the use as a controlled nanosystem toward photocatalysis and photodynamic
therapy.
The critical dimension of semiconductor devices is approaching the single-nm regime, and a variety of practical devices of this scale are targeted for production. Planar structures of nano-devices are still the center of fabrication techniques, which limit further integration of devices into a chip. Extension into 3D space is a promising strategy for future; however, the surface interaction in 3D nanospace make it hard to integrate nanostructures with ultrahigh aspect ratios. Here we report a unique technique using high-energy charged particles to produce free-standing 1D organic nanostructures with high aspect ratios over 100 and controlled number density. Along the straight trajectory of particles penetrating the films of various sublimable organic molecules, 1D nanowires were formed with approximately 10~15 nm thickness and controlled length. An all-dry process was developed to isolate the nanowires, and planar or coaxial heterojunction structures were built into the nanowires. Electrical and structural functions of the developed standing nanowire arrays were investigated, demonstrating the potential of the present ultrathin organic nanowire systems.
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