Nanometer size effects in nucleation, growth and characterization of templated CdS nanocrystal assemblies

Abstract

We report on the oriented nucleation of CdS nanocrystals on well-defined polydiacetylene Langmuir film templates. Nucleation on the red phase of polydiacetylene resulted in ordered linear arrays of CdS nanocrystals that are aligned with respect to the template. High resolution transmission electron microscopy showed crystalline particles of ~5 to 8 nm size. Selected area electron diffraction micrographs showed spot patterns which are attributed to the well-defined orientations of both polymorphs: the cubic zinc blende and the hexagonal wurtzite polymorphs of CdS. We present a unique growth mechanism where oriented nucleation of CdS on the polydiacetylene template initially takes place in the zinc blende phase. Beyond a certain size threshold, growth proceeds in the more stable wurtzite phase. This transformation keeps the stacking direction of the close packed planes, while altering only their stacking sequence. Notably, size-confinement effects were observed in electron diffraction patterns from the wurtzite phase. These effects originated from off-axis planes that do not fulfill the Bragg conditions, yet their elongated Bragg rods intersect with the Ewald sphere, giving rise to unexpected reflections.

Effects of crystalline phase and morphology on the visible light photocatalytic H2-production activity of CdS nanocrystals

“…This implies that en can make the one-dimensional growth of CdS nanocrystals. 35 With further increasing the ratio of en (15-50%), more en molecules are adsorbed and gradually accumulated on the surfaces of CdS nanocrystals because of the strong coordination interaction between en and Cd 2+ , and the CdS nanocrystals adopt a cubic ZB structure at the initial stage of nucleation, and then transform to the bulk stable WZ structure during the growth process, resulting in the appearance of multi-armed nanostructures. 32 This growth mechanism of the multi-armed nanorods corresponds with the typical model in the literature.…”

Controlled preparation of CdS nanoparticle arrays in amphiphilic perylene tetracarboxylic diimides: organization, electron-transfer and semiconducting properties

“…11 Very recently, nucleation of CdS nanocrystals on the red phase of PDA was found to have a size dependent cubic-to-hexagonal transformation. 12 Perylene tetracarboxylic diimide (PDI) derivatives have been extensively and intensively investigated as advanced molecular materials. 13,14 In particular, because of their great potential application as organic semiconductors in different molecular electronic devices, the fabrication of ordered nanostructures of these functional molecular materials has become an attractive research area in the past decade.…”

Mapping Charge Distribution in Single PbS Core – CdS Arm Nano-Multipod Heterostructures by Off-Axis Electron Holography

“…Here, we report on mapping charge distribution in a single PbS–CdS heterostructure, which is a system with potential applications in photovoltaic cells. It has been shown that CdS increases power conversion efficiency and photostability of PbS based solar cells. , Chemical synthesis procedures for the preparation of PbS − and CdS , nanocrystals have been established. Previous reports of PbS–CdS heterostructures are core–shell and thin film structures, but the synthesis of heterostructures with rock salt–wurtzite phases resulting in differing geometries than core–shell (rock salt–zinc blende) has not been reported.…”

“…Our motivation to map charge distribution in single PbS–CdS NMHs was their ensemble optical measurements compared to their separate constituents; CdS particles show an absorption edge at 470 nm (Figure a), which is blue-shifted with respect to bulk CdS (515 nm), indicating quantum confinement in nanoparticles. PbS nanoparticles (Figure a) show a blue-shifted sharp onset absorption at 2250 nm, relative to the bulk PbS (3100 nm) .…”

“…At the interface, DFT calculations show a slight increase in S−S distances and significant decrease in distances between adjacent layers of metal atoms. Thus, we attribute the decrease in three interplanar layers at the interface observed in the phase of the reconstructed exit wave (0.31 nm, SI Figure S3) to the adjustment of the S atoms to the two different chemical Our motivation to map charge distribution in single PbS− CdS NMHs was their ensemble optical measurements compared to their separate constituents; CdS particles show an absorption edge at 470 nm (Figure 4a), which is blue-shifted with respect to bulk CdS (515 nm), 34 indicating quantum confinement in nanoparticles. PbS nanoparticles (Figure 4a) show a blue-shifted sharp onset absorption at 2250 nm, relative to the bulk PbS (3100 nm).…”