# Functional Inversion of Trisodium Citrate from a [0001] Growth Suppressor to a Promoter in ZnO Thin Film Fabrication

## TL;DR

Trisodium citrate changes from suppressing to promoting ZnO nanorod growth under fast fabrication conditions, enabling aligned nanostructures.

## Contribution

Demonstrates a functional inversion of trisodium citrate's role in ZnO growth under different synthesis kinetics.

## Key findings

- Trisodium citrate promotes [0001] growth under fast mist-based fabrication.
- The growth unit changes from Zn(OH)₂ to Zn(OH)₄²⁻ under fast conditions.
- Synthesis kinetics dictate the function of molecular additives in nanostructure fabrication.

## Abstract

Trisodium citrate is a well-established molecular modifier
for
ZnO thin films renowned for its role in suppressing [0001] growth
by selectively passivating the (0002) facet in conventional, slow-growth
fabrication methods. A paradoxical functional inversion is demonstrated
herein: under fast-growth conditions using a mist-based fabrication,
trisodium citrate acts as a powerful promoter, yielding well-aligned,
high-aspect-ratio nanorods with a strong [0001] orientation. This
functional switch is attributed to a fundamental change in the dominant
growth unit, from the neutral Zn­(OH)2 species prevalent
under slow-growth conditions to the anionic Zn­(OH)4
2– complex enabled by the fast-growth process. This
change in growth unit chemistry activates the transformation of citrate
from a static suppressor into a mobile promoter via surface diffusion
and lowering the crystallization energy barrier. These findings establish
a new framework where the synthesis kinetics dictate the dominant
growth unit chemistry, which, in turn, governs the ultimate function
of a molecular additive, offering a new strategy for the rational
fabrication of anisotropic nanostructures.