Combined Computational and Experimental Study of CdSeS/ZnS Nanoplatelets: Structural, Vibrational, and Electronic Aspects of Core–Shell Interface Formation

Abstract

In the past few years, core−shell nanoparticles have opened new perspectives for the optoelectronic applications of semiconductor quantum dots. In particular, it has become possible to localize electrons in either part of these heterostructures. Understanding and controlling this phenomenon require a thorough characterization of the interfaces. In this study, we prepared quasi-2D CdSeS/ZnS core−shell nanoplatelets (NPLs) by colloidal atomic layer deposition. This technique allows fine control over the quantum confinement, the surfaces, and the interfaces. The layer-by-layer formation of a the ZnS shell around the CdSeS core was monitored using UV−vis absorption, XRD, and Raman spectroscopy. The measured band gaps and structural distortions were compared with results obtained from density functional theory (DFT) calculations. Modeling has also shown that 34% of the photoexcited electrons are delocalized into the ZnS shell. The herein presented combined modeling and experimental characterization strategy is of general interest since it can be applied to a large choice of layered semiconductor heterostructures in optoelectronics. The present approach paves the way for the synthesis of nanocrystals with precisely engineered properties for light-emitting diodes and solar cells.

Colloidal-ALD-Grown Core/Shell CdSe/CdS Nanoplatelets as Seen by DNP Enhanced PASS–PIETA NMR Spectroscopy

“…Core/shell CdSe/CdS NPLs ,,, and CdSe/ZnS NPLs − are thus by far the most commonly studied colloidal NPL heterostructures. The most recent additions to the class of colloidal NPLs are CdSe/CdS/CdSe, CdSe/CdS/ZnS, and CdSe/CdSe/CdZnS core/shell1/shell2 NPLs. , With the epitaxial extension of the crystallites, the band gap and other physical parameters are substantially altered. ,,,− ,,− For instance, the PL QY raises from about 30% for core-only CdSe NPLs (green-emissive, 4.5 monolayers thick) to 85–98% upon the addition of a wider-band gap shell (red-emissive) . With the goal of putting the exceptional PL properties to work, numerous applications of CdSe-based NPLs are being pursued, e.g., light-emitting devices, − solar cells, , photodetectors, , and lasers. ,,,,,− …”

Exciton-optical phonon coupling in II-VI semiconductor nanocrystals

“…As there is very little quantum confinement in the x and y dimensions, it may be possible for computational purposes to treat them as infinite in these dimensions and take advantage of the methods used for infinite crystals to make the computations tractable. [60][61][62][63] A number of quantum chemical calculations have been reported on nanoplatelets [61][62][63] including calculations of vibrational spectra, 63 but none, to my knowledge, have addressed exciton-phonon coupling. Such studies may also aid in understanding any role of EPC in determining the exciton size in nanoplatelets.…”

Raman and Infrared Studies of CdSe/CdS Core/Shell Nanoplatelets

“…[31], comparative analysis of vibrational spectra of CdSe/CdS nanostructures of the core/shell and core/crown types was carried out. Recently, it was proposed that the ZnS shell formation and its thickness in quasi-2D CdSeS/ZnS core/shell nanostructures can be monitored by Raman spectroscopy [32].…”

“…In this regard, along with traditional optical spectroscopy, vibrational spectroscopy of semiconductor nanostructures [24] can provide valuable information on their structure, composition [25], sizes [26], mechanical stresses [18], and on the geometry of the surface layer. Despite a large number of publications devoted to quasi-2D structures, systematic studies of the lattice dynamics of both singlephase nanoplatelets and heterostructures based on them has been limited by few works [27][28][29][30][31][32]. In Ref.…”