Abstract
Nanocrystals sometimes adopt unusual crystal structure configurations in order to maintain structural stability with increasingly large surface-to-volume ratios. The understanding of these transformations is of great scientific interest and represents an opportunity to achieve beneficial materials properties resulting from different crystal arrangements. Here, the phase transformation from α to β phases of tin (Sn) nanocrystals is investigated in nanocrystals with diameters ranging from 6.1 to 1.6 nm. Ultra-small Sn nanocrystals are achieved through our highly non-equilibrium plasma process operated at atmospheric pressures. Larger nanocrystals adopt the β-Sn tetragonal structure, while smaller nanocrystals show stability with the α-Sn diamond cubic structure. Synthesis at other conditions produce nanocrystals with mean diameters within the range 2–3 nm, which exhibit mixed phases. This work represents an important contribution to understand structural stability at the nanoscale and the possibility of achieving phases of relevance for many applications.
Highlights
Nanocrystals sometimes adopt unusual crystal structure configurations in order to maintain structural stability with increasingly large surface-to-volume ratios
Size and structure selective NCs of Sn have been successfully synthesized using plasma synthesis operated at atmospheric pressure
NCs produced with flow rates at 0.25 sLm, 0.5 sLm, 0.75 sLm and 1.0 sLm resulted in NCs with mean diameters of 6.07, 2.32, 2.18 and 1.60 nm, respectively
Summary
Nanocrystals sometimes adopt unusual crystal structure configurations in order to maintain structural stability with increasingly large surface-to-volume ratios The understanding of these transformations is of great scientific interest and represents an opportunity to achieve beneficial materials properties resulting from different crystal arrangements. A major difference between the two phases of Sn is observed in the electronic structure as the metallic behavior of tetragonal tin becomes semi-metallic when it transforms to α-Sn (a zerobandgap semi-metal)[2] This results in drastically different optoelectronic properties. These characteristics are again largely affected at the nanoscale as properties depend on size and shape as much as they depend on the traditional parameters of structure and composition[4] This may complicate the analysis and amplify the experimental parameter space but it offers an opportunity for manipulating and tailoring phase transformations and corresponding properties. With a theoretical capacity three times higher than graphite[16], Sn has been used along with other technological important materials for enhancing their supercapacitive performance[13,19,20]
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