Size-dependent properties of dithallium selenide

TL;DR

This study investigates how the electronic and magnetic properties of dithallium selenide (Tl2Se) change with size, revealing a transition from semimetal to semiconductor in nanorods due to quantum confinement effects.

Contribution

It provides the first comparative NMR analysis of bulk and nanorod Tl2Se, demonstrating size-dependent electronic structure transformations.

Findings

Nanorods are semiconductors with activation behavior in relaxation rates.

Bulk Tl2Se shows Korringa-like relaxation at low temperatures.

Size reduction induces a semimetal-to-semiconductor transition.

Abstract

We report on size-dependent properties of dithallium selenide, Tl2Se. We have carried out a comparative nuclear magnetic resonance (NMR) study of Tl2Se nanorods and bulk samples, measuring NMR spectra and spin-lattice relaxation rate of 203Tl and 205Tl isotopes. Though bulk Tl2Se was reported to be a metal, the Korringa-like spin-lattice relaxation behavior is observed only at low temperatures and is transformed to an activation regime above ~200 K. This finding is interpreted assuming a two-band model in the semimetallic compound. Our measurements show significant difference in the Knight shift and indirect nuclear exchange coupling for the bulk and nanorod Tl2Se samples, reflecting noticeable distinction in their electronic structure. At that, Tl2Se nanorods are semiconductors and exhibit a characteristic activation behavior in the spin-lattice relaxation rate due to the thermal excitation of carriers to the conduction band. The obtained size dependence of the Tl2Se properties is interpreted in terms of the semimetal-semiconductor transformation due to the quantum confinement.