Abstract: Our aim is to develop and optimize a model for a dielectric barrier discharge used as a chemical reactor for gas treatment. In order to determine the optimum operating conditions, we have studied the influence of the gas flow rate, reactor geometry and applied voltage parameters on the discharge characteristics. For this purpose, a two-dimensional time-dependent fluid model has been applied to an atmospheric pressure DBD in helium with nitrogen impurities, in a cylindrical geometry. The numerical model is based on the continuity and flux equations for each type of particles treated, the electron energy equation and the Poisson equation. The gas flow is incorporated in the flux equations as a source term. The set of coupled partial differential equations is solved by the so-called modified strongly implicit method. The background gas flow is numerically treated separately, assuming in the model that there is no influence of the plasma on the flow. Indeed, the gas convection velocity is calculated using the commercial code Fluent and it is used as input into the 2D fluid model. The plasma characteristics have been studied in terms of gas flow rate, applied voltage amplitude and frequency, and geometrical effects. The electric currents as a function of time for a given applied potential have been obtained, as well as the number densities and fluxes of plasma species.

Abstract: The peculiar potential transition metal dichalcogenides in regard to sensor and device applications have been exhibited by both experimental and theoretical studies. The use of these materials, thermodynamically stable even at elevated temperatures, particularly in nano- and optoelectronic technology, is about to come true. On the other hand, the distinct electronic and thermal transport properties possessing unique coherency, which may result in higher thermoelectric efficiency, have also been reported. However, exploiting this potential in terms of power generation and cooling applications requires a deeper understanding of these materials in this regard. This perspective study, concentrated with this intention, summarizes thermoelectric research based on transition metal dichalcogenides from a broad perspective and also provides a general evaluation of future theoretical investigations inevitable to shed more light on the physics of electronic and thermal transport in these materials and to lead future experimental research.

Abstract: In the present paper, a statistical model-based method to count the number of atoms of monotype crystalline nanostructures from high resolution high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) images is discussed in detail together with a thorough study on the possibilities and inherent limitations. In order to count the number of atoms, it is assumed that the total scattered intensity scales with the number of atoms per atom column. These intensities are quantitatively determined using model-based statistical parameter estimation theory. The distribution describing the probability that intensity values are generated by atomic columns containing a specific number of atoms is inferred on the basis of the experimental scattered intensities. Finally, the number of atoms per atom column is quantified using this estimated probability distribution. The number of atom columns available in the observed STEM image, the number of components in the estimated probability distribution, the width of the components of the probability distribution, and the typical shape of a criterion to assess the number of components in the probability distribution directly affect the accuracy and precision with which the number of atoms in a particular atom column can be estimated. It is shown that single atom sensitivity is feasible taking the latter aspects into consideration.

Abstract: Statistical parameter estimation theory is proposed as a quantitative method to measure unknown structure parameters from electron microscopy images. Images are then purely considered as data planes from which structure parameters have to be determined as accurately and precisely as possible using a parametric statistical model of the observations. For this purpose, an efficient algorithm is proposed for the estimation of atomic column positions and intensities from high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) images. Furthermore, the so-called CramérRao lower bound (CRLB) is reviewed to determine the limits to the precision with which continuous parameters such as atomic column positions and intensities can be estimated. Since this lower bound can only be derived for continuous parameters, alternative measures using the principles of detection theory are introduced for problems concerning the estimation of discrete parameters such as atomic numbers. An experimental case study is presented to show the practical use of these measures for the optimization of the experiment design if the purpose is to decide between the presence of specific atom types using STEM images.

Abstract: Carbon nanotubes (CNTs) are nowadays routinely grown in a thermal CVD setup. State-of-the-art plasma-enhanced CVD (PECVD) growth, however, offers advantages over thermal CVD. A lower growth temperature and the growth of aligned freestanding single-walled CNTs (SWNTs) makes the technique very attractive. The atomic scale growth mechanisms of PECVD CNT growth, however, remain currently entirely unexplored. In this contribution, we employed molecular dynamics simulations to focus on the effect of applying an electric field on the SWNT growth process, as one of the effects coming into play in PECVD. Using sufficiently strong fields results in (a) alignment of the growing SWNTs, (b) a better ordering of the carbon network, and (c) a higher growth rate relative to thermal growth rate. We suggest that these effects are due to the small charge transfer occurring in the Ni/C system. These simulations constitute the first study of PECVD growth of SWNTs on the atomic level.

Abstract: Pb cations in PbS quantum rods made from CdS quantum rods by successive complete cationic exchange reactions are partially re-exchanged for Cd cations. Using STEM-HAADF, we show that this leads to the formation of unique multiple dot-in-rod PbS/CdS heteronanostructures, with a photoluminescence quantum yield of 4555%. We argue that the formation of multiple dot-in-rods is related to the initial polycrystallinity of the PbS quantum rods, where each PbS crystallite transforms in a separate PbS/CdS dot-in-dot. Effective mass modeling indicates that electronic coupling between the different PbS conduction band states is feasible for the multiple dot-in-rod geometries obtained, while the hole states remain largely uncoupled.

Abstract: We report the direct formation of multiwalled carbon nanotubes (MWNT) by ultrasonication of graphite in dimethylformamide (DMF) upon addition of ferrocene aldehyde (Fc-CHO). The tubular structures appear exclusively at the edges of graphene layers and contain Fe clusters. Pc in conjunction with benzyl aldehyde, or other Fc derivatives, does not induce formation of NT. Higher amounts of Fc-CHO added to the dispersion do not increase significantly MWNT formation. Increasing the temperature reduces the amount of formation of MWNTs and shows the key role of ultrasound-induced cavitation energy. It is concluded that Fc-CHO first reduces the concentration of radical reactive species that slice graphene into small moieties, localizes itself at the edges of graphene, templates the rolling up of a sheet to form a nanoscroll, where it remains trapped, and finally accepts and donates unpaired electron to the graphene edges and converts the less stable scroll into a MWNT. This new methodology matches the long held notion that CNTs are rolled up graphene layers. The proposed mechanism is general and will lead to control the production of carbon nanostructures by simple ultrasonication treatments.

Abstract: In spite of global actions, biodiversity is declining at an alarming rate. Despite the need for objectively comparable monetary standards to include biodiversity arguments in policymaking, research on the relationship between species diversity and its valuation from a societal perspective is still scarce. In this paper, a methodological framework for the valuation of natural predators based on their ecological role in the agroecosystem is introduced. The framework integrates a dynamic ecological model simulating interactions between species with an economic model, thereby quantifying the effect of reduced numbers of natural predators on the net farm income. The model attributes an objective monetary value to increased species diversity through the changes in the provisioning of a marketable good. Results indicate that the loss of three predators could decrease net farm income with 88.86 ha− 1 to 2186.5 ha− 1. For the pear production sector in Flanders in 2011, this constitutes to an indirect use value of 0,68 million for one predator and 16.63 million for the presence of three predators. The aim is to provide a justification for the argument for biodiversity conservation, based on the ecological function of species, through the delivery of comparable monetary standards.

Abstract: We present a decision-support system that guides heritage guardians in selecting mitigation actions to improve the indoor air quality and thus the preservation conditions of indoor collections in heritage buildings. This contribution shows that it is feasible to build a decision support system dedicated to preventive conservation when the following barriers are overcome: 1) simultaneous measurement of a wide range of environmental parameters in order to detect a larger number of undesired situations; 2) development of an algorithm to perform reproducible indoor air quality assessments; and 3) transformation of the air quality assessment into a graph that can be read intuitively without causing a wide variation of interpretations among stakeholders. An important aspect of the decision support system is that it reduces several sources of uncertainty that hamper reliable indoor air quality assessments. The possibilities of such a system are illustrated with a measurement campaign in a church where a heating system has been installed and used for the first time.

Abstract: In this paper, we examined the effects of proximity-induced interactions such as Rashba spin-orbit coupling and effective Zeeman fields (EZFs) on the optical spectrum of n-type and p-type monolayer (ML)-MoS2. The optical conductivity is evaluated using the standard Kubo formula under random-phase approximation by including the effective electron-electron interaction. It has been found that there exist two absorption peaks in n-type ML-MoS2 and two knife shaped absorptions in p-type ML-MoS2, which are contributed by the inter-subband spin-flip electronic transitions within conduction and valence bands at valleys K and K ' with a lifted valley degeneracy. The optical absorptions in n-type and p-type ML-MoS 2 occur in THz and infrared radiation regimes and the position, height, and shape of them can be effectively tuned by Rashba parameter, EZF parameters, and carrier density. The interesting theoretical predictions in this study would be helpful for the experimental observation of the optical absorption in infrared to THz bandwidths contributed by inter-subband spin-flip electronic transitions in a lifted valley degeneracy monolayer transition metal dichalcogenides system. The obtained results indicate that ML-MoS2 with the platform of proximity interactions make it a promising infrared and THz material for optics and optoelectronics.

Abstract: The early stages of nanocrystal nucleation and growth are still an active field of research and remain unrevealed. In this work, by the combination of aberration-corrected transmission electron microscopy (TEM) and electrochemical characterization of the electrodeposition of different metals, we provide a complete reformulation of the VolmerWeber 3D island growth mechanism, which has always been accepted to explain the early stages of metal electrodeposition and thin-film growth on low-energy substrates. We have developed a Generalized Electrochemical Aggregative Growth Mechanism which mimics the atomistic processes during the early stages of thin-film growth, by incorporating nanoclusters as building blocks. We discuss the influence of new processes such as nanocluster self-limiting growth, surface diffusion, aggregation, and coalescence on the growth mechanism and morphology of the resulting nanostructures. Self-limiting growth mechanisms hinder nanocluster growth and favor coalescence driven growth. The size of the primary nanoclusters is independent of the applied potential and deposition time. The balance between nucleation, nanocluster surface diffusion, and coalescence depends on the material and the overpotential, and influences strongly the morphology of the deposits. A small extent of coalescence leads to ultraporous dendritic structures, large surface coverage, and small particle size. Contrarily, full recrystallization leads to larger hemispherical monocrystalline islands and smaller particle density. The mechanism we propose represents a scientific breakthrough from the fundamental point of view and indicates that achieving the right balance between nucleation, self-limiting growth, cluster surface diffusion, and coalescence is essential and opens new, exciting possibilities to build up enhanced supported nanostructures using nanoclusters as building blocks.

Abstract: The intensity levels in a three-dimensional (3D) reconstruction, obtained by electron tomography, can be influenced by several experimental imperfections. Such artifacts will hamper a quantitative interpretation of the results. In this paper, we will correct for artificial intensity variations by determining the 3D point spread function (PSF) of a tomographic reconstruction based on high angle annular dark field scanning transmission electron microscopy. The large tails of the PSF cause an underestimation of the intensity of smaller particles, which in turn hampers an accurate radius estimate. Here, the error introduced by the PSF is quantified and corrected a posteriori.

Abstract: We demonstrate the production of an ordered array of electron vortices making use of an electron optical setup consisting of two electrostatic biprisms. The biprism filaments are oriented nearly orthogonal with respect to each other in a transmission electron microscope. Matching the position of the filaments, we can choose to form different topological features in the electron wave. We outline the working principle of the setup and demonstrate fist experimental results. This setup partially bridges the gap between angular momentum carried by electron spin, which is intrinsic and therefore present in any position of the wave, and angular momentum carried by the vortex character of the wave, which can be extrinsic depending on the axis around which it is measured. (C) 2013 Elsevier B.V. All rights reserved.