New Forms of CdSe: Molecular Wires, Gels, and Ordered Mesoporous Assemblies

Abstract

This work investigates the structure and properties of soluble chalcogenidocadmates, a molecular form of cadmium chalcogenides with unprecedented one-dimensional bonding motifs. The single crystal X-ray structure reveals that sodium selenocadmate consists of infinite one-dimensional wires of (CdSe) charge balanced by Na and stabilized by coordinating solvent molecules. Exchanging the sodium cation with tetraethylammonium or didodecyldimethylammonium expands the versatility of selenocadmate by improving its solubility in a variety of polar and nonpolar solvents without changing the anion structure and properties. The introduction of a micelle-forming cationic surfactant allows for the templating of selenocadmate, or the analogous telluride species, to create ordered organic-inorganic hybrid CdSe or CdTe mesostructures. Finally, the interaction of selenocadmate "wires" with Cd ions creates an unprecedented gel-like form of stoichiometric CdSe. We also demonstrate that these low-dimensional CdSe species show characteristic semiconductor behavior, and can be used in photodetectors and field-effect transistors.

Surface Modification of CdSe Quantum-Dot Floating Gates for Advancing Light-Erasable Organic Field-Effect Transistor Memories

“…The films included a crystalline morphology whose structure corresponded to the typical wurtzite structure of CdSe, identified using X-ray diffraction (XRD) analysis (Figure S1b). , After surface modifications of QDs with a perfluorinated thiol and brush-type polystyrene, we performed X-ray photoemission spectroscopy (XPS) measurements to investigate the atomic compositions at the surface of the QDs. From the XPS spectra (Figure S2) over a wide range of energies (20 to 1250 eV), the atomic compositions of ODPA-QDs, F-QDs, and PS brush-QDs were calculated, and the results are summarized in Figure e.…”

Ligand-Mediated Band Engineering in Bottom-Up Assembled SnTe Nanocomposites for Thermoelectric Energy Conversion

“…We hypothesize that the ligand could be a variety of chalcogenidocadmates such as (Cd 2 Se 3 ) n 2 n – or CdSe 2 2– as previously reported for hydrazinum based CdSe solutions. 46,47 In order to replace the organic ligands on the NC surface by the CdSe-based ligand, a phase transfer reaction was used: a solution of SnTe NCs in hexane was layered on top of a solution of the CdSe ink in N -methylformamide. The change of colloidal stabilization from steric to electrostatic was evidenced by the color change of the solutions, reaching a colorless hexane phase and colored polar phase.…”

Unraveling the Growth Mechanism of Magic-Sized Semiconductor Nanocrystals

“…While the images suggest that the particles are faceted (discussed further below), the crystallites do not exhibit strong shape anisotropy, eliminating nanoplatelets or CdSe polymers as possible species. 8,35,36 Furthermore, the particle size is well below the exciton Bohr radius of CdSe (5.6 nm), indicating that the discrete jumps observed in the optical spectra indeed come from changes in the carrier confinement as the particle size increases. By analyzing images from the 434, 455, 476, and 494 samples in more detail we extracted average effective diameters of 2.1±0.3, 2.4±0.4, 2.6±0.3, and 2.7±0.4 nm, respectively, where we have listed standard deviations for thousands of particle measurements (Figure S6).…”

“…While this extension to longer wavelengths suggests formation of larger MSNCs, discrete evolution of absorption features during nanocrystal growth has also been assigned to other structures, such as nanoplatelets 7,8 and polymeric forms of CdSe. 35,36 Therefore, our products must first be isolated and characterized to determine if MSNCs are indeed present. Fortunately, our protocol allows isolation of specific species for analysis.…”