Unveiling surface charge on chalcogen atoms toward the high aspect-ratio colloidal growth of two-dimensional transition metal chalcogenides.

Controlling surface energies of each facet is essential for the anisotropic growth of two-dimensional transition metal chalcogenides (TMCs). However, it is a challenge due to stronger binding energies of ligand head groups to the edge facets compared to the planar facets. Herein, we demonstrate that the adsorption of ligands on metal positions can induce partial electron localization on the chalcogen sites, and then accelerate metal-chalcogen bond formation for enhanced anisotropic growth of nanosheets. And only in the case of trioctylphosphine oxide (TOPO)-adsorbed nanosheets, surface polarization can be unveiled on the surface of the colloidal nanosheets due to restricted development of nonpolar ligand shells by the steric effects of the ligands. Moreover, density functional theory (DFT) calculation results reveal that the decrease of surface energy on the (100) edge facets as well as the increase on the (001) basal facets by the adsorption of triorganylphosphine oxide also contribute to the preferentially lateral growth. As a result, various 2D TMCs, including MoSe2, WSe2, and SnSe2 synthesized with TOPO, show enhanced anisotropic growth.

FeIn2S4 Nanocrystals: A Ternary Metal Chalcogenide Material for Ambipolar Field-Effect Transistors.

An ambipolar channel layer material is required to realize the potential benefits of ambipolar complementary metal-oxide-semiconductor field-effect transistors, namely their compact and efficient nature, reduced reverse power dissipation, and possible applicability to highly integrated circuits. Here, a ternary metal chalcogenide nanocrystal material, FeIn2S4, is introduced as a solution-processable ambipolar channel material for field-effect transistors (FETs). The highest occupied molecular orbital and the lowest unoccupied molecular orbital of the FeIn2S4 nanocrystals are determined to be -5.2 and -3.75 eV, respectively, based upon cyclic voltammetry, X-ray photoelectron spectroscopy, and diffraction reflectance spectroscopy analyses. An ambipolar FeIn2S4 FET is successfully fabricated with Au electrodes (EF = -5.1 eV), showing both electron mobility (14.96 cm2 V-1 s-1) and hole mobility (9.15 cm2 V-1 s-1) in a single channel layer, with an on/off current ratio of 105. This suggests that FeIn2S4 nanocrystals may be a promising alternative semiconducting material for next-generation integrated circuit development.