Modulating Ferroelectric Response in Colloidal Semiconductor Nanocrystals through Cation Exchange

Abstract

We report the appearance of ferroelectric behavior in CdSSe nanocrystals arising from a room-temperature cation exchange of semiconductor nanoparticles. Cation exchange reactions were performed on colloidal CdSSe nanocrystals using antimony, tin, and gold salts. The degree of exchange was determined using scanning transmission electron microscopy–energy-dispersive spectroscopy and the ferroelectric response was measured using a Sawyer-Tower circuit. As the percent exchange of tin­(IV) was varied, the ferroelectric properties were optimized at ∼30 and 70% as a result of intracrystal atomic displacements. The amount of disorder can be minimized by selecting the exchange cation that exhibits the largest change in saturation polarization with the least amount of exchange. The ability to tune the structure and ferroelectric response of nanostructures could offer new routes toward the development of ferroelectric random-access memory devices as well as lower the cost of energy-harvesting applications.

Fluorescent Colloidal Ferroelectric Nanocrystals

“…29 Ferroelectric properties were then optimized through changes in exchange cation identity and percent exchange. 30 However, this synthesis consistently resulted in aggregation as well as loss of fluorescence. This is likely due to the presence of defects as a result of that cation exchange which leads to charge carrier trapping.…”

“…We have synthesized ferroelectric nanocrystals through cation exchange that exhibit higher remnant and saturation polarization than current nanoferroelectrics, such as bulk barium titanate; a classic ferroelectric material that has been prepared by glycothermal and hydrothermal syntheses and has been utilized in capacitors and data-storage devices. ,, Additionally, ferroelectric properties in nanoscale BaTiO 3 synthesized by this method have shown a dependence of ferroelectric response on size. Specifically, as the diameter for BaTiO 3 was reduced to 10–30 nm, the crystal structure was observed to shift from tetragonal (noncentrosymmetric) to a cubic (centrosymmetric) phase, resulting in a lower ferroelectric response. − This highlights the importance of maintaining the crystal framework at the nanoscale in order to retain ferroelectric behavior.…”

“…In 2015, Wrenn et al discovered the emergence of ferroelectric properties through room temperature cation exchange using colloidal cadmium selenide QDs and antimony­(III) chloride dissolved in toluene . Ferroelectric properties were then optimized through changes in exchange cation identity and percent exchange . However, this synthesis consistently resulted in aggregation as well as loss of fluorescence.…”

Generation of out-of-plane ferroelectric behavior in a one-atom-thick monolayer

“…Additionally, in some bulk material systems, substitutional impurities have been shown to stabilize or induce FE behavior, e.g. in HfO 2 [28,29] and CdSe [30], and bulk wurtzite III-nitrides [31].…”