# A Simple Single-Pot, Heat-Up Reaction for Uniform Hexagonal CuInS2 Nanoplatelets and the Role of Disubstituted Thiourea Chain Length in Their Growth

## TL;DR

A new heat-up method produces uniform hexagonal CuInS2 nanoplatelets, with the thiourea chain length affecting their growth and size.

## Contribution

A robust and tunable single-pot heat-up synthesis for hexagonal-phase CIS nanoplatelets using disubstituted thioureas.

## Key findings

- Using disubstituted thioureas allows altering nanoplatelet growth by changing thiourea substitutions.
- Two thiourea series (N-butyl and N-isopropyl) produced nanoplatelets with sizes between 15 and 29 nm.
- Monodisperse sizes at ~15 and 20 nm showed the highest reproducibility.

## Abstract

Copper indium sulfide (CIS) nanocrystals are actively
being investigated
for a variety of applications due to their favorable optical and electronic
properties. While the most popular syntheses of these materials are
simple heat-up reactions that form uniform crystals, they are not
very tunable, which can limit the use of the crystals in certain applications.
In this work, we present a robust heat-up synthetic method for hexagonal-phase
CIS nanoplatelets, which offers the potential for increased tunability
by decoupling the sulfur precursor from the solvent. By using disubstituted
thioureas for the sulfur precursor, the growth process of the reaction
may be altered by changing the substitutions on the thiourea. Two
series of thioureas were investigated: N-butylthiourea
and N-isopropylthiourea, with a butyl, octyl, or
dodecyl group on the opposite nitrogen. The reaction was monitored
by transmission electron microscopy (TEM), and it was found that following
the initial nucleation and growth, there was first a size-focusing
stage and then a second ripening stage. All particles were characterized
by TEM and were found to have sizes ranging from 15 to 29 nm depending
on the thiourea used and the duration of growth, with the greatest
reproducibility of monodisperse sizes at approximately 15 and 20 nm.