Mechanisms for Regioselective Synthesis of Anisotropic Nano-Heterostructures

D. Fischli, Konstanz/DE, S. Sutter, Konstanz/DE, F. Enders, Konstanz/DE, K. Boldt, Konstanz/DE

University of Konstanz, Department of Chemistry, Konstanz, Germany

E-mail: danja.fischli@uni-konstanz.de

Anisotropic semiconductor nano-heterostructures are available e.g. in the form of seeded¹ or tipped rods.² While literature is able to provide several synthetic routes towards such structures, mechanistic studies on the emergence of anisotropy scarce. The leading hypothesis assumes fast growth at high monomer concentration under reaction control and the influence of selectively passivating ligands.³ However, recently the role of reaction intermediates such as magic size clusters (MSCs) and coordination polymers (CPs) has come into focus.⁴

We show that two classes of reaction intermediates occur under different reaction conditions and play an important role in reaction control. Polymeric reaction intermediates act as monomer reservoirs that result in a highly localized rather than homogeneous concentration of monomer in the reaction solution. They decompose preferentially at the reactive facets of a seed particle, which leads to 1D growth at the respective crystal facet, and consequently an increase in anisotropy. The reaction is thus kinetically controlled through the monomer feed.⁵ Nanorods with a single particle grown selectively on one tip can be formed under conditions in which the availability of monomer is limited by slow precursor addition and high anion excess. Here the formation of magic size clusters indicates conditions with a high energy barrier for homogeneous nucleation. Tip formation can occur for the respective material if clusters can form under high enough temperatures that allow heterogeneous crystal growth.⁶

A good understanding of reaction paths that lead to anisotropy is mandatory to achieve an additional level of control over particle morphology. Furthermore, it opens up a new range of precursors that can be manipulated by chemical means and thus allows for the synthesis of more complex structures, e.g. branched or locally doped heterostructures.

References

[1] L. Carbone et al., Nano Lett. 2007, 7, 2942-2950.

[2] F. Enders et al., Nanoscale 2018, 10, 22362-22373.

[3] D. Kim et al., ACS Nano 2017, 11, 12461-12472.

[4] D. Wurmbrand et al., Chem. Commun. 2018, 54, 7358-7361.

[5] D. Fischli et al., J. Phys. Chem. C, 2020, 124, 12774-12783.

[6] F. Enders et al., Chem. Mater. 2020, under review.