Phonons of Atomically Thin ZnSe Nanoplatelets Grown by the Colloidal Method

Abstract

In this work, the phonon spectra of atomically thin ZnSe nanoplatelets (NPLs) were studied using Raman and infrared spectroscopies. Atomically thin ZnSe NPLs were grown on the Si substrate covered with a 100 nm thick gold layer by the colloidal method in the temperature range of 100−170 °C. The triangular and rectangular NPLs with 2.5-and 4-monolayer thicknesses, respectively, were synthesized, as determined by atomic force microscopy (AFM) measurements. Longitudinal optical (LO) and transverse optical (TO) phonon modes in ZnSe NPLs were found at 198 and 252 cm −1 , respectively, and the surface optical phonon mode was observed at about 216 cm −1 . The LO and TO phonon modes revealed the opposite frequency shifts with increasing growth temperature. The effect was induced by the phonon confinement, and it confirmed the formation of NPLs of different thicknesses. Comparing the frequency positions of longitudinal and TO phonon modes confined in ZnSe NPLs with the data on the dispersion of optical phonons in bulk ZnSe, the thickness of the NPLs formed at a low temperature was derived as 0.567 nm, correlating well with the AFM results.

Organoborane Se and Te Precursors for Controlled Modulation of Reactivity in Nanomaterial Synthesis

“…TEM analysis showed that this absorption profile corresponds to ZnSe NPLs (Figure S16). We determined that this population is 3 ML wurtzite ZnSe NPLs, as the observed transition energy of 3.92 eV (316 nm) and 4.06 eV (305 nm) match the calculated band energy for the heavy and light hole of 3 ML w-ZnSe, respectively. , The thickness measured from TEM images aligns with the expected thickness (Figure S17). However, due to the low image contrast, our conclusion is mainly driven by their optical properties.…”

Direct Synthesis of Zinc-Blende ZnSe Nanoplatelets

“…At this point, zinc chalcogenide-based semiconductors have been considered as a promising alternative with their suitable energy band gaps. , Particularly, ZnSe having a direct band gap of 2.7 eV is very attractive for blue light-emitting applications. So far, efforts have predominantly focused on spherical-shaped ZnSe-based NCs, with less exploration into other morphologies such as nanowires (NWs), nanorods (NRs), and NPLs. − In addition to the bare ZnSe NCs of varying sizes, studies have also investigated alloying high band gap ZnSe with low band gap ZnTe to further engineer emission colors within the blue/green spectral range (420–500 nm) . Recently, Kim et al demonstrated that the PLQY of ZnSe-based NCs could be increased to nearly unity by surface treatment with hydrofluoric acid to eliminate trap sites and with zinc chloride to effectively passivate the surfaces .…”