Nanoparticles of CdCl2 with closed cage structures

Nanoparticles of various layered compounds having a closed cage or nanotubular structure, designated also inorganic fullerene-like (IF) materials, have been reported in the past. In this work IF-CdCl₂ nanoparticles were synthesized by two methods. In one technique, a high temperature evaporation and subsequent condensation of dried cadmium chloride powder was used. In the other method, electron beam irradiation of the source powder led to its recrystallization into closed nanoparticles with a nonhollow core. The two methods are shown to produce nanoparticles of different topologies. While mostly spherical nested structures are obtained from the high temperature process, polyhedra with hexagonal or elongated rectangular characters are obtained by the electron beam induced process. The analysis also shows that, while the source (dried) powder is orthorhombic cadmium chloride monohydrate, the crystallized IF cage consists of the anhydrous 3R polytype which is not stable as bulk material in ambient atmosphere. Consistent with previous observations, this study shows that the seamless structure of the IF materials can stabilize phases, which are otherwise unstable in ambient conditions.     

Fullerene-like Re-Doped MoS2 Nanoparticles as an Intercalation Host with Fast Kinetics for Sodium Ion Batteries

Sodium ion batteries (SIBs) are considered as a promising alternative to threaten the reign of lithium ion batteries (LIBs) among various next-generation rechargeable energy storage systems, including magnesium ion, metal air, and metal sulfur batteries. Since both sodium and lithium are located in Group 1 of the periodic table, they share similar (electro)chemical properties with regard to ionization pattern, electronegativity, and electronic configuration; thus the vast number of compounds developed from LIBs can provide guidance to design electrode materials for SIBs. However, the larger ionic radius of the sodium cation and unique (de)sodiation processes may also lead to uncertainties in terms of thermodynamic or kinetic properties. Herein, we present the first construction of SIBs based on inorganic fullerene-like (IF) MoS₂ nanoparticles. Closed-shell-type structures, represented by C₆₀ fullerene, have largely been neglected for studies of alkali-metal hosting materials due to their inaccessibility for intercalating ions into the inner spaces. However, IF-MoS₂, with faceted surfaces, can diffuse sodium ions through the defective channels, thereby allowing reversible sodium ion intercalation/deintercalation. Interestingly, Re-doped MoS₂ showed good electrochemical performances with fast kinetics (ca. 74 mA h g⁻¹ at 20 C). N-type doping caused by Re substitution of Mo in IF-MoS₂ revealed enhanced electrical conductivity and an increased number of diffusion defect sites. Thus, chemical modification of fullerene-like structures through doping is proven to be a promising synthetic strategy to prepare improved electrodes.     

Application of cathodoluminescence imaging for the investigation of CdTe: The effect of photoetching

Cathodoluminescence together with secondary electron imaging techniques are employed to correlate morphological and electronic properties of the (11$\text{2}$1) face of n-CdTe before and after photoetching. It is shown first that the quantum efficiency of the Cathodoluminescence increases considerably after photoetching. This increase is attributed to the selective removal of defects from the CdTe surface after photoetching. Furthermore no spatial correlation is found between the uniformly distributed etch pits (≈10⁹ cm^?2) and material defects, e.g. dislocations, inclusions. Consequently the unique morphology of photoetched CdTe surfaces must be attributed to yet another property of the semiconductor surface, e.g. the variations in dopant distribution close (10–100 Å) to the semiconductor surface.     

Inorganic nanotubes

Following the discovery of carbon fullerenes and carbon nanotubes, it was hypothesized that nanoparticles of inorganic compounds with layered (two-dimensional) structure, such as MoS(2), will not be stable against folding and form nanotubes and fullerene-like structures: IF. The synthesis of numerous other inorganic nanotubes has been reported in recent years. Various techniques for the synthesis of inorganic nanotubes, including high-temperature reactions and strategies based on 'chemie douce' (soft chemistry, i.e. low-temperature) processes, are described. First-principle, density functional theory based calculations are able to provide substantial information on the structure and properties of such nanotubes. Various properties of inorganic nanotubes, including mechanical, electronic and optical properties, are described in brief. Some potential applications of the nanotubes in tribology, protection against impact, (photo)catalysis, batteries, etc., are discussed.     

An algorithm for computationally expensive engineering optimization problems

Abstract

Modern engineering design often relies on computer simulations to evaluate candidate designs, a scenario which results in an optimization of a computationally expensive black-box function. In these settings, there will often exist candidate designs which cause the simulation to fail, and can therefore degrade the search effectiveness. To address this issue, this paper proposes a new metamodel-assisted computational intelligence optimization algorithm which incorporates classifiers into the optimization search. The classifiers predict which candidate designs are expected to cause the simulation to fail, and this prediction is used to bias the search towards designs predicted to be valid. To enhance the search effectiveness, the proposed algorithm uses an ensemble approach which concurrently employs several metamodels and classifiers. A rigorous performance analysis based on a set of simulation-driven design optimization problems shows the effectiveness of the proposed algorithm.     

Synthesis and characterization of inorganic fullerene-like WSe2 material

Lately M0S₂ and WS₂ fullerene-like nanoparticles, generically termed inorganic fullerene-like (IF) materials, were reproducibly obtained by gas phase^4,6 and solid state⁶ reactions and the growth mechanism of such structures was elucidated⁶. the present work deals with the synthesis of IF-WSe₂ from tungsten oxide and selenium vapors. Thermodynamic calculations of the sulfidization and selenization processes are provided, and indicate salient differences between the two processes. Notwithstanding, the growth model of IF-WSe₂ is similar to that of sulfide fullerene-like material. the IF-WSe₂ was characterized by X-ray powder diffraction, transmission electron microscopy and high resolution transmission electron microscopy.     

Enhanced Field Emission of WS2 Nanotubes

Results on electron field emission from free standing tungsten disulfide (WS₂) nanotubes (NTs) are presented. Experiments show that the NTs protruding on top of microstructures are efficient cold emitters with turn‐on fields as low as 1 V/μm and field enhancement of few thousands. Furthermore, the emission current shows remarkable stability over more than eighteen hours of continuous operation. Such performance and long‐term stability of the WS₂ cathodes is comparable to that reported for optimized carbon nanotube (CNTs) based emitters. Besides this, it is found that the WS₂ cathodes prepared are less sensitive than CNTs in chemical reactive ambients. The high field enhancement and superior reliability achieved indicates a potential for vacuum nanoelectronics and flat panel display applications.