Cation Exchange Combined with Kirkendall Effect in the Preparation of SnTe/CdTe and CdTe/SnTe Core/Shell Nanocrystals

Abstract

Controlling the synthesis of narrow band gap semiconductor nanocrystals (NCs) with a high-quality surface is of prime importance for scientific and technological interests. This Letter presents facile solution-phase syntheses of SnTe NCs and their corresponding core/shell heterostructures. Here, we synthesized monodisperse and highly crystalline SnTe NCs by employing an inexpensive, nontoxic precursor, SnCl2, the reactivity of which was enhanced by adding a reducing agent, 1,2-hexadecanediol. Moreover, we developed a synthesis procedure for the formation of SnTe-based core/shell NCs by combining the cation exchange and the Kirkendall effect. The cation exchange of Sn(2+) by Cd(2+) at the surface allowed primarily the formation of SnTe/CdTe core/shell NCs. Further continuation of the reaction promoted an intensive diffusion of the Cd(2+) ions, which via the Kirkendall effect led to the formation of the inverted CdTe/SnTe core/shell NCs.

Role of the Crystal Structure in Cation Exchange Reactions Involving Colloidal Cu2Se Nanocrystals

“… 10 − 12 The knowledge accumulated so far on CE reactions has enabled, this last year alone, the synthesis of new types of NHs, such as CdS nanowires covered by a monolayer of MoS 2 , 13 Cu 2 S-decorated CdS nanorods (NRs), 14 and new core@shell NC systems such as Mn 3 O 4 @CoMn 2 O 4 –Co x O y , 15 Ag–Zn–In-S@ZnS, 16 and SnTe@CdTe. 17 − 20 Moreover, the number of new NC materials that can be accessed by CE with control over the shape, 21 − 25 crystal structure, 26 and composition 27 − 34 has also increased significantly. In turn, these advanced nanostructures have found application in many different fields such as bioimaging, 16 , 20 , 28 , 30 , 35 chemical sensing, 30 supercapacitors, 21 electro- or photocatalysis, 14 , 15 and spintronic or optoelectronic devices.…”

Device Applications of Solution Processed MIR Semiconductor Nanocrystal Thin Films

“…For the samples that were subsequently used in devices the initial ATR results are shown in Figure 6.2. These spectra are similar to those previously reported in the literature for these materials [223,[226][227][228][229]. The largest SnTe QDs at 13.6 nm did not make reliable devices but are included to show the band edge progression with size.…”

“…It has been suggested that this feature is an LSPR [228], but if that were so it must change energy as the QD size and composition varies [231]. As well as noting the large variation in size and composition of the QDs shown here, these MIR absorption features have also been reported in various forms of SnTe QDs that are reported as being both Sn deficient [227] and Sn rich [228]. This strongly implies that the feature is a result of Sn-related surface chemistry rather than an LSPR or intraband state.…”

“…Yet the surface of MIR CQDs has always been treated as an area to passivate rather than utilise for detection. MIR absorption peaks have been shown in various reports of SnTe [226][227][228][229] and PbSnTe [223] QDs and have been variously ascribed to bandgap absorption [223,226], LSPR absorption [228] and ligand absorption [229]. Here we demonstrate that for films made from three sizes of SnTe QDs, as well as in PbSnTe QDs, there is an absorption peak that can be used to detect MIR photons due to changes in the resistance of the film.…”

“…Additionally, the band structure of SnTe QDs is similar to HgTe QDs which have tuneable bandgaps in the MIR and LWIR [96], and would therefore appear to be an ideal candidate for a mercury free device. However, even with the numerous published reports of mercury-free, MIR absorbing CQDs [223][224][225][226] there are no reports of successful MIR photodetectors using these materials [226][227][228][229]. Similarly, quantum confinement [75] and band edge tuning in Hg-based materials remains the only aspect of QD physics that has been effectively utilised in MIR photodetectors [230].…”