Justification for the use of Markovian Langevin statistics in the modelling of activated surface diffusion.

Low temperature surface diffusion is driven by the thermally activated hopping of adatoms between adsorption sites. Helium spin-echo techniques, capable of measuring the sub-picosecond motion of individual adatoms, have enabled the bench-marking of many important adsorbate-substrate properties. The well-known Markovian Langevin equation has emerged as the standard tool for the interpretation of such experimental data, replacing adatom-substrate interactions with stochastic white noise and linear friction. However, the consequences of ignoring the colored noise spectrum and non-linearities inherent to surface systems are not known. Through the computational study of three alternative models of adatom motion, we show that the hopping rate and jump distributions of an adatom are fixed to within a few percent by the potential energy surface and a new generalized energy exchange rate parameter alone, independent of the model used. This result justifies the use of the Markovian Langevin equation, regardless of the true statistical nature of adatom forces, provided results are quoted in terms of the new energy exchange rate parameter. Moreover, numerous mechanisms for the effect of noise correlations and non-linear friction on the energy exchange rate are proposed which likely contribute to activated surface diffusion and activated processes more generally.

H2O and H2S adsorption by assistance of a heterogeneous carbon-boron-nitrogen nanocage: Computational study

A model of heterogeneous carbon-boron-nitrogen (C-B-N) nanocage was investigated in this work for adsorbing H2O and H2S substances. To achieve this goal, quantum chemical calculations were performed to obtain optimized configurations of substances towards the surface of nanocage. The calculations yielded three possible configurations for relaxing each of substances towards the surface. Formation of acid-base interactions between vacant orbitals of boron atom and full orbitals of each of oxygen and sulfur atoms yielded the strongest complexes of substance-nanocage in comparison with orientation of substances through their hydrogen atoms towards the surface of nanocage. As a consequence, formations of interacting H2O@C-B-N and H2S@C-B-N complexes were achievable, in which mechanism of action showed different strengths for the obtained complexes. Variations of molecular orbital features and corresponding energy gap and Fermi energy for the models before/after adsorption could help for detection of adsorbed substance through a sensor function. And finally, such C-B-N nanocage showed benefit of providing activated surface for efficient adsorption of each of H2O and H2S substance with possibility of differential adsorption regarding the strength of complex formations.

Electrical Promotion-Assisted Automotive Exhaust Catalyst: Highly Active and Selective NO Reduction to N2 at Low-Temperatures

Pd catalyst (Pd/Ce_0.7Zr_0.3O₂) in an electric field exhibits extremely high three-way catalytic activity (TWC: NO-C₃H₆-CO-O₂-H₂O). By applying an electric field to the semiconductor catalyst, low-temperature operation of TWC can be achieved even at 473 K by virtue of the activated surface-lattice oxygen.

Electrical Promotion-Assisted Automotive Exhaust Catalyst: Highly Active and Selective NO Reduction to N2 at Low-Temperatures

Pd catalyst (Pd/Ce_0.7Zr_0.3O₂) in an electric field exhibits extremely high three-way catalytic activity (TWC: NO-C₃H₆-CO-O₂-H₂O). By applying an electric field to the semiconductor catalyst, low-temperature operation of TWC can be achieved even at 473 K by virtue of the activated surface-lattice oxygen.

Plasma surface modification technique–induced gelatin grafting on bio-originated polyurethane porous matrix: Physicochemical and in vitro study

In this study, polyurethane (TPU) scaffolds were fabricated using freeze-drying technique and gelatin macromolecules immobilized on the activated surface by oxygen plasma treatment. Scanning electron microscopy (SEM) micrographs indicated an interconnected porous microstructure with randomly oriented pores. According to the results, the diameter of pores increased after plasma treatment and gelatin grafting. Fourier transform infrared spectroscopy illustrated that there is no inappropriate interaction between materials during processing; furthermore, attenuated total reflection Fourier transform infrared spectroscopy confirmed the immobilization of gelatin molecules on the surface of the plasma-treated polymeric scaffolds. Waterdrop contact angle analysis presented that wettability and hydrophilicity of constructs increased after grafting gelatin on the activated surface. Phosphate-buffered saline absorption and hydrolytic biodegradation enhanced after surface modification of the polymeric samples. Cellular behavior demonstrated better adhesion and spreading after grafting gelatin of oxygen plasma-treated constructs. No evidence of toxicity was observed for 7 days. DNA content determined that the number of viable cells increased in TPU-gelatin matrixes after 1 day in contrast with TPU scaffolds. Based on results, oxygen plasma treatment can create an activated surface to graft gelatin macromolecules and achieve optimum physicochemical, mechanical, and biological features for the neo-tissue formation.