Chapter 6
Group 13–15 Needle-Shaped Oligomers
and Nanorods: Structures and Electronic
Properties
Anna V. Pomogaeva and Alexey Y. Timoshkin
Abstract Synthetic approaches, structures, and reactivity of group 13–15 needleshaped oligomers have been reviewed. Computational studies reveal that needleshaped oligomers are more stable than fullerene-like isomers for all 13–15 pairs.
Formation of such oligomers in the gas phase is energetically favorable and feasible
from the thermodynamic point of view. However, many competitive reaction
pathways are kinetically possible which leads to cascade of reactions and different
reaction products. A systematic study of the various effects of structural variations
on the electronic properties of Ga-N-based nanorods has been performed. On the
basis of DFT computations, we demonstrate that terminal groups have a crucial
impact on the electronic properties of the rod-shaped [RGaNH] 3n (R=H, CH 3 )
oligomers. Oligomers capped with GaR and NH groups adopt almost periodic
structure in which terminal groups affect only the very edges of the oligomer.
The band gap energy of the [HGaNH] 3n+1 is defined by states localized at the
different ends of the oligomer. The value of the band gap is converging fast
with increase of n, and for n = 38 it is about 93% of the value of the band
gap of the [HGaNH] 3∞ polymer. In contrast, termination of the [HGaNH] 3n rodshaped oligomer by saturation of dangling bonds with H or CH 3 groups destroys
the periodic pattern and increases the number of states, localized at the ends of
the oligomer. This way of termination is characterized by systematic change in
structural parameters of the oligomer and near exponential decrease of the band gap
energy with the oligomer length. The band gap energy for the rod-shaped oligomer
of 10 nm of length (n = 38) amounts to only 27% of the value for the band gap of
the [HGaNH] 3∞ polymer. Substitution of Ga atoms by Al and In has also been
considered. Absorption spectra undergo a red shift if Ga atoms are replaced by
In atoms and a small blue shift if Ga atoms are replaced by Al atoms. The effect
of electron-donating and electron-withdrawing terminal groups (H, CH 3 , F, CF 3 )
on a dipole moment and energy gap values is found to be significant. The band
gap energy of long tube-shaped Ga-N-based oligomers can be tuned within 2 eV
A. V. Pomogaeva · A. Y. Timoshkin ()
Institute of Chemistry, St. Petersburg State University, St. Petersburg, Russia
e-mail: a.y.timoshkin@spbu.ru
© Springer Nature Singapore Pte Ltd. 2020
T. Onishi (ed.), Theoretical Chemistry for Advanced Nanomaterials,
https://doi.org/10.1007/978-981-15-0006-0_6
201
Group 13–15 Needle-Shaped Oligomers
and Nanorods: Structures and Electronic
Properties
Anna V. Pomogaeva and Alexey Y. Timoshkin
Abstract Synthetic approaches, structures, and reactivity of group 13–15 needleshaped oligomers have been reviewed. Computational studies reveal that needleshaped oligomers are more stable than fullerene-like isomers for all 13–15 pairs.
Formation of such oligomers in the gas phase is energetically favorable and feasible
from the thermodynamic point of view. However, many competitive reaction
pathways are kinetically possible which leads to cascade of reactions and different
reaction products. A systematic study of the various effects of structural variations
on the electronic properties of Ga-N-based nanorods has been performed. On the
basis of DFT computations, we demonstrate that terminal groups have a crucial
impact on the electronic properties of the rod-shaped [RGaNH] 3n (R=H, CH 3 )
oligomers. Oligomers capped with GaR and NH groups adopt almost periodic
structure in which terminal groups affect only the very edges of the oligomer.
The band gap energy of the [HGaNH] 3n+1 is defined by states localized at the
different ends of the oligomer. The value of the band gap is converging fast
with increase of n, and for n = 38 it is about 93% of the value of the band
gap of the [HGaNH] 3∞ polymer. In contrast, termination of the [HGaNH] 3n rodshaped oligomer by saturation of dangling bonds with H or CH 3 groups destroys
the periodic pattern and increases the number of states, localized at the ends of
the oligomer. This way of termination is characterized by systematic change in
structural parameters of the oligomer and near exponential decrease of the band gap
energy with the oligomer length. The band gap energy for the rod-shaped oligomer
of 10 nm of length (n = 38) amounts to only 27% of the value for the band gap of
the [HGaNH] 3∞ polymer. Substitution of Ga atoms by Al and In has also been
considered. Absorption spectra undergo a red shift if Ga atoms are replaced by
In atoms and a small blue shift if Ga atoms are replaced by Al atoms. The effect
of electron-donating and electron-withdrawing terminal groups (H, CH 3 , F, CF 3 )
on a dipole moment and energy gap values is found to be significant. The band
gap energy of long tube-shaped Ga-N-based oligomers can be tuned within 2 eV
A. V. Pomogaeva · A. Y. Timoshkin ()
Institute of Chemistry, St. Petersburg State University, St. Petersburg, Russia
e-mail: a.y.timoshkin@spbu.ru
© Springer Nature Singapore Pte Ltd. 2020
T. Onishi (ed.), Theoretical Chemistry for Advanced Nanomaterials,
https://doi.org/10.1007/978-981-15-0006-0_6
201