Ultra-small crystals with modulated shell thickness

When Professor Noelio Oliveira Dantas, at the Brazilian Federal University of Uberlândia (UFU), had the idea of a new chemical method for the synthesis of quantum dots (semiconductor crystals with only a few nanometers of size), he was studying ways to synthesize the tiny crystals aiming to biotechnological applications.
However, the results exceeded the initial expectations. In addition to produce ultra-small quantum dots, composed from a cadmium selenide (CdSe) core and a cadmium sulfide (CdS) shell, the new method (which is cheap and highly reproducible) was a surprise because of its capacity to modulate the quantum dots’ shell thickness, an innovation compared to other known routes.  

The study was developed during the PhD research that Anielle Christine Almeida Silva develops at the Physics Institute at UFU, under Professor Dantas' supervision.

“The main scientific contribution of this article is the proposal of a new synthesis route, via an aqueous solution, which allowed the modulation of the CdS shells’ thickness in CdSe ultra-small quantum dots, depending on the concentration of 1-thioglycerol”, summarized Anielle. More precisely, the researchers discovered that although smaller concentrations of 1-thioglycerol limit the growth of the cores of the quantum dots, larger amounts of the compound promote the modulated growth of their shells.

“The main scientific contribution of this article is the proposal of a new synthesis route, via an aqueous solution..."Anielle Christine Almeida Silva, Physics Institute at the Brazilian Federal University of Uberlândia (UFU).

The produced ultra-small crystals had less than 2 nm in the core, and from 0.50 to 1.25 nm in the shell. In order to calculate these dimensions from Raman spectra, the authors of the article used a model of phonon confinement with modifications proposed by themselves and another author.

Regarding the biotechnological application initially expected, the authors explain that such quantum dots obtained with the new route are promising due their capacity to be easily dispersed in aqueous environments. According to the scientists, the structure of the produced ultra-small crystals (which is similar to a sandwich with two slices of bread and a fine filling) may contribute to a higher quantum efficiency and stability in biological environments.

This story is reprinted from material from Sociedade Brasileira de Pesquisa em Materiais (SBPMat), with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.