I. Synthesis and Reactivity of Novel β-Diketiminato-cadmium Complexes, II. Synthesis of Lead Selenide Nanoparticles for Use in Solar Cells

<p>Rising levels of carbon dioxide (CO₂) in the atmosphere has led to metal amide and alkoxide complexes being explored as potential CO₂ activators. A wide variety of M–O and M–N bonds have been shown to activate CO₂, however to date there are no examples with cadmium. A range of novel cadmium amide and alkoxide complexes have been synthesised, using the β-diketiminato ligand (BDI) as an ancilliary ligand. Initial reactivity studies have suggested CO₂ activation may be possible, although no products were isolated. Homonuclear metallic bonding (M–M) has been explored since the 1950’s and complexes containing M–M bonds are known for almost all transition and main group metals. There are only two reported Cd–Cd bonds, both using sterically bulky monoanionic ligands, like the β-diketiminato ligand. A novel β-diketiminato-cadmium chloride complex was synthesised and treated with a range of different reducing agents to generate a Cd–Cd bond. Different reactivities were observed for the reducing agents, however evidence of a Cd–Cd bond was not obtained. Group 14-16 materials, such as lead selenide, are p-type semi-conductors and have the potential to replacing silicon as a photon acceptor in solar cells. Lead selenide nanoparticles display quantum confinement effects, which allows one to tailor the band gap energies to maximise their absorbance of solar energy. The synthesis of PbSe nanoparticles is described in this study from the reaction between selenium and the lead complex [(BDIph)₂Pb], as well as from the decomposition of [(BDIdipp)PbSeP{Se}Cy₂]. Differences in the size and shapes of the nanoparticles was observed, highlighting the need for controlled nucleation and growth conditions.</p>

I. Synthesis and Reactivity of Novel β-Diketiminato-cadmium Complexes, II. Synthesis of Lead Selenide Nanoparticles for Use in Solar Cells

<p>Rising levels of carbon dioxide (CO₂) in the atmosphere has led to metal amide and alkoxide complexes being explored as potential CO₂ activators. A wide variety of M–O and M–N bonds have been shown to activate CO₂, however to date there are no examples with cadmium. A range of novel cadmium amide and alkoxide complexes have been synthesised, using the β-diketiminato ligand (BDI) as an ancilliary ligand. Initial reactivity studies have suggested CO₂ activation may be possible, although no products were isolated. Homonuclear metallic bonding (M–M) has been explored since the 1950’s and complexes containing M–M bonds are known for almost all transition and main group metals. There are only two reported Cd–Cd bonds, both using sterically bulky monoanionic ligands, like the β-diketiminato ligand. A novel β-diketiminato-cadmium chloride complex was synthesised and treated with a range of different reducing agents to generate a Cd–Cd bond. Different reactivities were observed for the reducing agents, however evidence of a Cd–Cd bond was not obtained. Group 14-16 materials, such as lead selenide, are p-type semi-conductors and have the potential to replacing silicon as a photon acceptor in solar cells. Lead selenide nanoparticles display quantum confinement effects, which allows one to tailor the band gap energies to maximise their absorbance of solar energy. The synthesis of PbSe nanoparticles is described in this study from the reaction between selenium and the lead complex [(BDIph)₂Pb], as well as from the decomposition of [(BDIdipp)PbSeP{Se}Cy₂]. Differences in the size and shapes of the nanoparticles was observed, highlighting the need for controlled nucleation and growth conditions.</p>

Quantifying Fluctuations of Average Environments for Embedding Calculations

In the context of employing embedding methods to study spectroscopic properties, the viability and effectiveness of replacing an ensemble of calculations by a single calculation using an average description of the system of study are evaluated. This work aims to provide a baseline of the expected fluctuations in the average description of the system obtained in the two cases: from calculations of an ensemble of geometries, and from an average environment constructed with the same ensemble. To this end, the classical molecular dynamics simulation of a very simple system was used: a rigid molecule of acetone in a solution of rigid water. We perform a careful numerical analysis of the fluctuations of the electrostatic potential felt by the solute, as well as the fluctuations in the effect on its electronic density, measure through the dipole moment and the atomic charges derived from the corresponding potential. At the same time, we inspect the accuracy of the methods used to construct average environments. Finally, the proposed approach to generate the embedding potential from an average environment density is applied to estimate the solvatochromic shift of the first excitation of acetone. In order to account for quantum-confinement effects that may be important in certain cases, the fluctuations on the shift due to the interaction with the solvent are evaluated using Frozen-Density Embedding Theory. Our results demonstrate that, for normally-behaved environments, the constructed average environment is a reasonably good representation of a discrete solvent environment.

Quantum Confinement Effects of Thin Co3O4 Films

Thin Co films were deposited on quartz and Corning glass by radio frequency magnetron sputtering. The films were postannealed at 500 °C in a furnace in air atmosphere. The resulting samples were examined with X-ray diffraction experiments, which revealed that they consist of single-phase, polycrystalline Co3O4. The morphology of selected samples was recorded by atomic force microscopy. Ultraviolet-visible light absorption spectroscopy experiments probed the absorbance of the films in the wavelength range 200–1,100 nm. Two types of transitions (energy gaps) were clearly identified. Both of them were found to be “blue shifted” with decreasing film thickness; this is interpreted as evidence of quantum confinement effects. For the case of the first gap value, this was corroborated by calculations based on a combination of the Potential Morphing Method and the effective mass approximation.

Design and Self-Consistent Schrodinger-Poisson Model Simulation of Ultra-Thin Si-Channel Nanowire FET

Since at the regime of nanometer, the quantum confinement effects are observed and the wave nature of electrons is more dominant. Therefore, the classical approach of current formulation in mesoelectonics and nanoelectronics results in inaccuracy as it does not consider the quantum effect, which is only applicable for the bulk electronic device. For accurate modeling and simulation of nanoelectronics, device atomic-level quantum mechanical models are required. In this work, an ultra-thin (3 nm diameter) Silicon- channel Cylindrical Nanowire FET (CNWFET) is designed and simulated by invoking non-equilibrium green function (NEGF) formalism and self-consistent Schrodinger-Poisson’s equation model. Then impact variation of temperature, oxide thickness, and metal work function variation in the proposed NWFET is investigated to analyze the distinct performance parameters of the device e.g. threshold voltage (Vth) drain induced barrier lowering (DIBL), sub-threshold swing (SS), and ION/IOFF ratio. The designed device exhibits reliable results and shows a SS of 57.8 mV/decade and ION to IOFF ratio of order 109 at room temperature.

Precise Layer Separation of Two-Dimensional Nanomaterials for Scalable Optoelectronics

The biggest challenge in the field of low-dimensional nanomaterials, in terms of practical application, is scalable production with structural uniformity. As the size of materials is becoming smaller, the tendency of their structure-dependent properties, which directly affects the device reliability of largescale applications, is to become stronger due to quantum confinement effects. For example, one-dimensional (1D) carbon nanotubes have various electrical/optical properties based on their structures (e.g., diameter, chirality, etc.). Likewise, two-dimensional (2D) layered materials also exhibit different properties based on their thickness. To overcome such structural heterogeneity, isopycnic density gradient ultracentrifugation (i-DGU) will be introduced to achieve monodispersity of nanomaterials in structure based on their buoyant density differentiations. The i-DGU approach makes it possible to sort 1D carbon nanotubes and 2D layered materials such as graphene, transition metal dichalcogenides and hexagonal boron nitride with high structural purity, based on their structure. Various largescale optoelectronic applications, electrically driven light emitters and photodetectors demonstrated based on the monodisperse nanomaterials will be discussed.

High-performance quasi-2D perovskite light-emitting diodes: from materials to devices

Quasi-two-dimensional (quasi-2D) perovskites have attracted extraordinary attention due to their superior semiconducting properties and have emerged as one of the most promising materials for next-generation light-emitting diodes (LEDs). The outstanding optical properties originate from their structural characteristics. In particular, the inherent quantum-well structure endows them with a large exciton binding energy due to the strong dielectric- and quantum-confinement effects; the corresponding energy transfer among different n-value species thus results in high photoluminescence quantum yields (PLQYs), particularly at low excitation intensities. The review herein presents an overview of the inherent properties of quasi-2D perovskite materials, the corresponding energy transfer and spectral tunability methodologies for thin films, as well as their application in high-performance LEDs. We then summarize the challenges and potential research directions towards developing high-performance and stable quasi-2D PeLEDs. The review thus provides a systematic and timely summary for the community to deepen the understanding of quasi-2D perovskite materials and resulting LED devices.

Precursor state of chemi-ionization reactions and confinement of valence electrons by anisotropic intermolecular forces

Modifications in atomic alignment and in molecular alignment/orientation determine a different structure of the adduct, formed by collisions of reagents, which represents the precursor state of many elementary chemical–physical processes. The following evolution of the system is directly controlled by the confinement of interacting partners in such a precursor state. However, a deep characterization of these phenomena is still today not fully available, especially when weak intermolecular forces are operative, although the inquiry is of general relevance for the control of the stereodynamics of processes, occurring under a variety of conditions both in gas phase and at surface. In this paper recent advances in the knowledge of the selective role of atomic alignment and molecular orientation effects on the stereodynamics of chemi-ionization reactions will be presented and discussed. These advances represent a basic step along a path whose final target is the complete and internally consistent rationalization and revaluation of the experimental findings already obtained, and published, in our and in other laboratories on chemi-ionization reactions involving as reagent molecules which are of great relevance in several fields. The basic idea is to export important guidelines provided by a recent detailed study of chemi-ionization of noble gas atoms to more complex reactions involving molecules. The main focus of the present paper is on the quantum confinement effects of valence electrons within the reaction transition state. Graphic abstract

Synthesis and Characterization of Silica-Lead Sulfide Core Shell Nanospheres For Applications in Optoelectronic Devices

Nanoscale miniaturization of chalcogenides semiconductors, such as lead sulfide (galena), can generate interesting quantum confinement effects in the field of optoelectronic applications. At this work, a process in order to obtain SiO2 nanospheres coated with Galena, as the denominated core-shell system, is developed, this process it is based in Stöber’s method, where only the magnetic stirring was replaced by an ultrasonic bath, to achieve well rounded, and highly stable silica nanoparticles with diameters average of 70 nm. The PbS shell cover presents a thickness of 10 nm around. Nanostructures chemical composition, morphology and optical properties were determined by Transmission Electron Microscopy and UV-Vis spectroscopy, respectively. As a result, the nano shells correspond to cubic PbS, presenting some interplanar distances of 2.95 Å and 3.41 Å; this nano shell also shown a toward blue optical spectrum shift and a remarkable increase in its band gap, 3.75 eV, was obtained, compared with the PbS bulk value. The chemical composition it is studied by energy scattering spectroscopy, and X-ray photoelectron spectroscopy analyzes.