The Experts below are selected from a list of 231 Experts worldwide ranked by ideXlab platform

Michael J. Ford - One of the best experts on this subject based on the ideXlab platform.

  • van der Waals Forces Control the Internal Chemical Structure of Monolayers within the Lamellar Materials CuInP2S6 and CuBiP2Se6
    The Journal of Physical Chemistry C, 2018
    Co-Authors: Sherif Abdulkader Tawfik, Jeffrey R. Reimers, Catherine Stampfl, Michael J. Ford
    Abstract:

    Following the recent demonstration that van der Waals Forces control the ferroelectric ordering of layers within nanoflakes and bulk samples of CuBiP2Se6 and CuInP2S6, it is demonstrated that they also control the internal geometrical structure of isolated monolayers of these materials. This internal structure involves large displacements of copper atoms, either normal to the layer plane or else within the plane, that change its ligation environment. In both cases, the van der Waals Dispersion Force out-competes traditional bonding effects to control the structure. However, we find that the aspects of the Dispersion Force giving rise to each effect are uncorrelated: long-range effects control the interlayer ferroelectric ordering, whereas short-range effects control the internal layer structure. These conclusions are drawn considering the predicted properties of monolayers, bilayers, and bulk materials obtained using 14 density-functional theory-based methods. Although the different methods used often pre...

M. Philip Schwarz - One of the best experts on this subject based on the ideXlab platform.

  • Quantifying sub-grid scale (SGS) turbulent Dispersion Force and its effect using one-equation SGS large eddy simulation (LES) model in a gas–liquid and a liquid–liquid system
    Chemical Engineering Science, 2011
    Co-Authors: Mandar Tabib, M. Philip Schwarz
    Abstract:

    Abstract The one-equation SGS LES model has shown promise in revealing flow details as compared to the Dynamic model, with the additional benefit of providing information on the modelled SGS-turbulent kinetic energy ( Niceno et al., 2008 ). This information on SGS-turbulent kinetic energy (SGS-TKE) offers the possibility to more accurately model the physical phenomena at the sub-grid level, especially the modelling of the SGS-turbulent Dispersion Force (SGS-TDF). The use of SGS-TDF Force has the potential to account for the Dispersion of particles by sub-grid scale eddies in an LES framework, and through its use, one expects to overcome the conceptual drawback faced by Eulerian–Eulerian LES models. But, no work has ever been carried out to study this aspect. Niceno et al. (2008) could not study the impact of SGS-TDF effect as their grid size was comparable to the dispersed bubble diameter. A proper extension of research ahead would be to quantify the effect of sub-grid scale turbulent Dispersion Force for different particle systems, where the particle sizes would be smaller than filter-size. This work attempts to apply the concept developed by Lopez de Bertodano (1991) to approximate the turbulent diffusion of the particles by the sub-grid scale liquid eddies. This numerical experimentation has been done for a gas–liquid bubble column system ( Tabib et al., 2008 ) and a liquid–liquid solvent extraction pump-mixer system ( Tabib et al., 2010 , Tabib and Schwarz, 2010 ). In liquid–liquid extraction system, the organic droplet size is around 0.5 mm, and in bubble columns, the bubble size is around 3–5 mm. The simulations were run with mesh size coarser than droplet size in pump-mixer, and for bubble column, two simulations were run with mesh size finer and coarser than bubble diameter. The magnitude of SGS-TDF values in all the cases were compared with magnitude of other interfacial Forces (like drag Force, lift Force, resolved turbulent Dispersion Force, Force due to momentum advection and pressure). The results show that the relative magnitude of SGS-TDF as compared to other Forces were higher for the pump-mixer than for the coarser and finer mesh bubble column simulations. This was because in the pump-mixer, the ratio of “dispersed phase particle diameter to the grid-size” was smaller than that for the bubble column runs. Also, the inclusion of SGS-TDF affected the radial hold-up, even though the magnitudes of these SGS-TDF Forces appeared to be small. These results confirms that (a) the inclusion of SGS-TDF will have more pronounced effect for those Eulerian–Eulerian LES simulation where grid-size happens to be more than the particle size, and (b) that the SGS-TDF in combination with one-equation-SGS-TKE LES model serves as a tool to overcome a conceptual drawback of Eulerian–Eulerian LES model.

Haiping Lan - One of the best experts on this subject based on the ideXlab platform.

  • Role of the Dispersion Force in modeling the interfacial properties of molecule-metal interfaces: adsorption of thiophene on copper surfaces
    Scientific reports, 2014
    Co-Authors: Haiping Lan
    Abstract:

    Role of the Dispersion Force in modeling the interfacial properties of molecule-metal interfaces: adsorption of thiophene on copper surfaces

  • Adsorption of thiophene on copper surfaces: role of the Dispersion Force and electron-corehole interaction
    arXiv: Materials Science, 2012
    Co-Authors: Haiping Lan
    Abstract:

    We present density functional theory calculations of the geometry, adsorption energy, electronic density of states and bonding picture of thiophene adsorbed on Cu(111), Cu(110) and Cu(100). Standard PBE functional, DFT-D corrections and self-consistent vdW-DF functionals for including the Dispersion Force, and the ionic final-state (IFS) approximation that considers electron-corehole interactions were employed to model these interfaces. According to the theory-experiment comparison, RPBE-G06, the RPBE functional together with Grimme's Dispersion correction proposed in 2006, was suggested the "best" method for predicting structural and energetic properties of thiophene/Cu interfaces so far, while vdW-DF is also very recommendable if a proper exchange functional is used together with the vdW correlation. The consideration of IFS approximation could solve some discrepancies between x-ray standing waves measurements and density functional theory calculations. Nevertheless, it remains an open question that the theory-experiment discrepancy of the adsorption site of thiophene/Cu(100), which calls for further experiments and higher level theories to clarify. The standard PBE functional reveals covalent bonding picture for all the interfaces, while the inclusion of dispersive contributions does not change the covalent bonding picture to the vdW one.

Guilherme J Delben - One of the best experts on this subject based on the ideXlab platform.

  • Dispersion Force for materials relevant for micro- and nanodevices fabrication
    Journal of Physics D: Applied Physics, 2008
    Co-Authors: André Gusso, Guilherme J Delben
    Abstract:

    The Dispersion (van der Waals and Casimir) Force between two semi-spaces is calculated using Lifshitz theory for different materials relevant for micro- and nanodevices fabrication, namely, gold, silicon, gallium arsenide, diamond and two types of diamond-like carbon, silicon carbide, silicon nitride and silicon dioxide. The calculations were performed using recent experimental optical data available in the literature, usually ranging from the far infrared up to the extreme ultraviolet bands of the electromagnetic spectrum. The results are presented in the form of a correction factor to the Casimir Force predicted between perfect conductors, for the separation between the semi-spaces varying from 1 nm up to 1 µm. The relative importance of the contributions to the Dispersion Force of the optical properties in different spectral ranges is analysed. The role of temperature in semiconductors and insulators is also addressed. The results are meant to be useful for the estimation of the impact of the Casimir and van der Waals Forces on the operational parameters of micro- and nanodevices.

  • Dispersion Force for materials relevant for micro and nanodevices fabrication
    arXiv: Other Condensed Matter, 2008
    Co-Authors: André Gusso, Guilherme J Delben
    Abstract:

    The Dispersion (van der Waals and Casimir) Force between two semi-spaces are calculated using the Lifshitz theory for different materials relevant for micro and nanodevices fabrication, namely, gold, silicon, gallium arsenide, diamond and two types of diamond-like carbon (DLC), silicon carbide, silicon nitride and silicon dioxide. The calculations were performed using recent experimental optical data available in the literature, usually ranging from the far infrared up to the extreme ultraviolet bands of the electromagnetic spectrum. The results are presented in the form of a correction factor to the Casimir Force predicted between perfect conductors, for the separation between the semi-spaces varying from 1 nanometre up to 1 micrometre. The relative importance of the contributions to the Dispersion Force of the optical properties in different spectral ranges is analyzed. The role of the temperature for semiconductors and insulators is also addressed. The results are meant to be useful for the estimation of the impact of the Casimir and van der Waals Forces on the operational parameters of micro and nanodevices.

Klaus Husemann - One of the best experts on this subject based on the ideXlab platform.

  • Modeling of the Dispersion Force and Experimental Study of Influence of Dispersion Stress
    Chemical Engineering & Technology, 2000
    Co-Authors: Sabine Niedballa, Klaus Husemann
    Abstract:

    The dry Dispersion is the deglomeration of fine aggregate particles in an air stream. It is necessary for deglomeration that the existing van der Waals adhesive Forces are smaller than the Dispersion Force. The angle-dependent Dispersion Force on a model aggregate particle was theoretically analyzed for the acceleration in an air stream. The stress by the angle-dependent Dispersion Force and the centrifugal Force is compared with the mean adhesive Force of the agglomerate. The derived Dispersion model is able to give a decision whether the model agglomerate can be dispersed due to the stress in the flow. The theoretical results were checked and proved by experiments with three materials. A high stress and a real rough particle surface is the prerequisite for Dispersion of fine particles.