Nanoparticulate metals and semiconductors that have atomic arrangements at the interface of molecular clusters and "infinite" solid-state arrays of atoms have distinctive properties determined by the extent of confinement of highly delocalized valence electrons. At this interface, the total number of atoms and the geometrical disposition of each atom can be used to significantly modify the electronic and photonic response of the medium. In addition to teh novel inherent physical properties of the quantum-confined moieties, their "packaging" into nanocomposite bulk materials can be used to define the confinement surface states and environment, intercluster interactions, the quantum-confinement geometry, and the effective charge-carrier density of the bulk. Current approaches for generating nanostructures of conducting materials are briefly reviewed, especially the use of three-dimensional crystalline superlattices as hosts for quantum-confined semiconductor atom arrays (such as quantum wires and dots) with controlled inter-quantum-structure tunneling.

https://science.sciencemag.org/content/sci/247/4943/669.full.pdf

Quantum confinement and host/guest chemistry: probing a new dimension.

The structure of selenium clusters — Se3 TO Se8

A molecular-dynamics simulation has been carried out for liquid and amorphous selenium in the temperature range 350\char21{}720 K. The simulation used 64 atoms in a constant-volume simple cubic cell, and the energy surfaces and forces were calculated using the density-functional formalism, with a local-density approximation for the exchange-correlation energy. The main focus is on the microscopic atomic structure, with the associated short- and intermediate-range ordering phenomena. Ring statistics, pair correlation functions g(r), structure factors S(Q), bond angle and dihedral angle distribution functions, phonon densities of states, and diffusion constants D were computed and compared with experimental and theoretical data where available. Several structural models proposed previously for Se are evaluated and their predictions compared with the results of the present simulation. Special emphasis is given to the concentration, structure, and stability of the dominant defects, and a new structure and defect model is presented.

First-principles molecular-dynamics simulation of liquid and amorphous selenium.

Sulfur and selenium iodine compounds: from non-existence to significance

Inhibition of Candida albicans biofilm by pure selenium nanoparticles synthesized by pulsed laser ablation in liquids.

A new allotrope of selenium has been found. X-ray analysis has revealed that the new form consists of hexameric molecules, Se6, with symmetry D3d. It has been ascertained by rotational and Weissenberg methods that the crystal has a rhombohedral unit cell with lattice parameters in hexagonal axes, a=11.362±0.001 A, c=4.429±0.008 A, and belongs to space group R. Refinement of atomic parameters using the full matrix least squares method gives the following structural quantities: x=0.16021±0.00048, y=0.20227±0.00047, z=0.12045±0.00120, bond length 2.356±0.009 A, bond angle 101.1±0.3°, and dihedral angle 76.2±0.4°. Studies on the transformation by DSC and X-ray measurements revealed that the rhombohedral phase is irreversibly converted to the polycrystalline trigonal phase at temperatures above 105°C.

https://iopscience.iop.org/article/10.1143/JJAP.19.1813/pdf

Yasuhiko Miyamoto

Papers

Structure and Phase Transformation of Rhombohedral Selenium Composed of Se 6 Molecules