Revisiting the Polyol Synthesis and Plasmonic Properties of Silver Nanocubes
Authors: Wang Hongyue , Guo Yangyang , Zhang Miao , Li Huixin , Wei Yang , Qian Yiming , Zhang Yunhan , Tang Bo , Sun Zhenhua , Wang Hongqiang 
Published: December 2020

Background:
Noble-metal nanocrystals have been extensively studied over the past decades
because of their unique optical properties. The polyol process is considered an effective method
for silver (Ag) nanocrystals’ synthesis in solution even though the reproducibility of its shape
controlling is still a challenge. Here, Ag nanowires and nanocubes were synthesized by the polyol
process, in which the Ag+ ions are directly reduced by ethylene glycol with a certain amount of Cl−
ions added. We present the relationship between the final morphology of the Ag nanostructures with
the parameters of reaction, including temperature, growth time, injection rate, and the amount of
sodium chloride. The as-synthesized nanowires and nanocubes were characterized by scanning electron
microscopy, transmission electron microscopy and X-ray diffraction. The uniformly distributed
nanocubes with a mean edge length of 140 nm were obtained. The localized surface plasmon resonance
of Ag nanocubes was characterized by laser scanning fluorescence confocal microscopy. The
photoluminescence enhancement was observed on the perovskite film coupled with Ag nanocubes.

Objective:
We aimed to synthesize uniform and controllable silver nanocubes and nanowires
through the polyol process and explore the interaction between CsPbBr3 perovskite film and Ag
nanocubes antennas.

Methods:
We synthesized silver nanocubes and nanowires through the polyol process where the
silver nitrate (AgNO3) was reduced by Ethylene Glycol (EG) in the presence of a blocking agent
polyvinylpyrrolidone (PVP).

Results:
We successfully synthesized Ag nanocubes with an average edge length of 140 nm and Ag
nanowires with a uniform distribution in terms of both shape and size through a polyol process with
sodium chloride (NaCl) as the additive. In addition, the local photoluminescence (PL) enhancement
was observed in a perovskite film by combining Ag nanocubes, which is attributed to the antennas
plasmonic effect of the Ag nanocubes.

Conclusion:
In summary we studied the parameters in the polyol process such as reaction temperature,
growth time, injection rate, kind of halide ion and NaCl amount for the synthesis of Ag
nanowires and nanocubes. Our results suggest that the concentration of Cl- and the growth time have
the main influence on Ag nanowires and nanocubes formation. The optimum growth time was found
to be 60 min and 120 min for the formation of Ag nanowires and nanocubes, respectively. In addition,
we revealed that the opportune reaction temperature of Ag nanowires was 140 °C. The injection
rate of precursors was also found to play an important role in the final morphology of Ag nanowires
and nanocubes. In addition, for the generation of Ag nanocubes, the presence of Cl− ion in
the reaction is critical, which can eliminate most of the byproducts. We obtained the Ag nanowires
with a uniform distribution in terms of both shape and size, and nanocubes with average lengths of
140 nm by the polyol process with the optimal parameters. Plasmon-coupled emission induced by
noble-metal nanocrystals has attracted more attention in recent years. In this work, the PL of a perovskite
film was enhanced by the coupling of Ag nanocubes due to the surface plasmonic effect.