Solution-Processed Free-Standing Ultrathin Two-Dimensional PbS Nanocrystals with Efficient and Highly Stable Dielectric Properties

Abstract

Two-dimensional (2D) materials with downscaled thicknesses are the quest of the electronics industry because of their immense potential in modern microelectronics. Despite the discovery of several novel 2D materials, the flexible design of highperformance free-standing ultrathin 2D dielectric nanocrystals (NCs) with a large planar morphology remains the most challenging task. We develop a method for synthesizing high-quality free-standing ultrathin 2D NCs of PbS with a well-defined large rectangular morphology with a thickness of ∼2 nm. The lateral size can be tuned up to a few hundred nanometers by changing only the reaction annealing time. Microscopic and spectroscopic analyses at different stages of the reaction reveal formation of 2D NCs by a continuous growth mechanism. The 2D NCs exhibit a nearly temperature and frequency independent high dielectric constant (>13.4) with a small dielectric loss (0.0006 at 20 K and <0.06 at 350 K for 100 kHz) over broad temperature and frequency ranges. Low-frequency dispersion from 125 Hz to 1 MHz, frequency stability with a small dielectric loss (<0.03 at 100 kHz), and a stable temperature coefficient of the dielectric constant outline the merits of 2D NCs as a potential dielectric material. Complex impedance analyses demonstrate dominant intrinsic effects contributed by polarons in covalent NCs. Equal activation energies for the conduction and relaxation processes offer uniform energy barriers for the charges in NCs leading to high-performance dielectric behavior. This work opens up promising features of non-oxide binary semiconductors as dielectric alternatives for miniaturized electronics using flexible solution processing routes.

Impact of dimensionality and confinement on the electronic properties of mercury chalcogenide nanocrystals

“…To achieve absorption in the SWIR, narrow band gap materials 7,8 have to be used. PbS nanosheets 9,10 have been synthetized 11,12 and show tunable absorption 13 almost up to the bulk band gap value. 14 They also present a large lateral extension [15][16][17] (up to several µm) which is of great interest for the design of single-particle devices such as field effect transistors 18,19 (FETs) and photodetectors.…”

2D Materials Based on Main Group Element Compounds: Phases, Synthesis, Characterization, and Applications

“…[ 214 ] It is noteworthy that free‐standing ultrathin 2D PbS nanocrystals prepared using the same method were assigned to the rock‐salt phase in another work. [ 215 ] A comparison of the XRD results revealed that the crystal phase is more likely to be an orthorhombic phase. This material exhibits efficient and highly stable dielectric properties.…”

Nanocluster‐Mediated Synthesis of Diverse ZnTe Nanostructures: from Nanocrystals to 1D Nanobelts

“…[1][2][3][4][5][6] However,t he conditions suitable for nucleationg rain in uniform solutionm ight not be suitable for tuning the size and shape of nanocrystals. [1][2][3][4][5][6] However,t he conditions suitable for nucleationg rain in uniform solutionm ight not be suitable for tuning the size and shape of nanocrystals.…”

“…Colloidal semiconductor nanocrystals have attracted considerable attention due to their unique size‐ and shape‐dependent optical and electronic properties. During the past decades, researchers have made great effort to synthesize semiconductor nanocrystals with controllable size and shape, in order to explore their application in light emitting diodes, solar cells, and so on . However, the conditions suitable for nucleation grain in uniform solution might not be suitable for tuning the size and shape of nanocrystals .…”