Probing organic layers on the TiO2(110) surface

In this work, we use first principles simulations to provide features of the dynamic scanning force microscopy imaging of adsorbed organic layers on insulating surfaces. We consider monolayers of formic (HCOOH) and acetic (CH(3)COOH) acid and a mixed layer of acetic and trifluoroacetic acids (CF(3)COOH) on the TiO(2)(110) surface and study their interaction with a silicon dangling bond tip. The results demonstrate that the silicon tip interacts more strongly with the substrate and the COO(-) group than the adsorbed acid headgroups, and, therefore, molecules would appear dark in images. The pattern of contrast and apparent height of molecules is determined by the repulsion between the tip and the molecular headgroups and by significant deformation of the monolayer and individual molecules. The height of the molecule on the surface and the size of the headgroup play a large role in determining access of the tip to the substrate and, hence, the contrast in images. Direct imaging of the molecules themselves could be obtained by providing a functionalized tip with attraction to the molecular headgroups, for example, a positive potential tip.     

On the Rayleigh-Plateau instability

In this paper,we study the surface instability of a cylindrical pore in the absence of stress. This instability is called the Rayleigh-Plateau instabilty. We consider the model developed by Spencer et ...     

Synthesis,Antibacterial, and Antioxidant Evaluation of Novel Series of Condensed Thiazoloquinazoline with Pyrido,Pyrano, and Benzol Moieties as Five- and Six-Membered Heterocycle Derivatives

A novel synthesis of thiazolo[2,3-b]quinazolines 4(a–e), pyrido[2′,3′:4,5]thiazolo[2,3-b]quinazolines {5(a–e), 6(a–e), and 7(a–e)}, pyrano[2′,3′:4,5]thiazolo[2,3-b]quinazolines 8(a–e), and benzo[4,5]thiazolo[2,3-b]quinazoloine9(a–e) derivatives starting from 2-(Bis-methylsulfanyl-methylene)-5,5-dimethyl-cyclohexane-1,3-dione 2 as efficient α,α dioxoketen dithioacetal is reported and the synthetic approaches of these types of compounds will provide an innovative molecular framework to the designing of new active heterocyclic compounds. In our study, we also present optimization of the synthetic method along with a biological evaluation of these newly synthesized compounds as antioxidants and antibacterial agents against the bacterial strains, like S. aureus, E. coli, and P. aeruginosa. Among all the evaluated compounds, it was found that some showed significant antioxidant activity at 10 μg/mL while the others exhibited better antibacterial activity at 100 μg/mL. The results of this study showed that compound 6(c) possessed remarkable antibacterial activity, whereas compound 9(c) exhibited the highest efficacy as an antioxidant. The structures of the new synthetic compounds were elucidated by elemental analysis, IR, ¹H-NMR, and ¹³C-NMR.     

Theoretical prediction of intrinsic self-trapping of electrons and holes in monoclinic HfO2

We predict, by means of ab initio calculations, stable electron and hole polaron states in perfect monoclinic HfO2. Hole polarons are localized on oxygen atoms in the two oxygen sublattices. An electron polaron is localized on hafnium atoms. Small barriers for polaron hopping suggest relatively high mobility of trapped charges. The one-electron energy levels in the gap, optical transition energies and ESR g-tensor components are calculated.     

Electron localization and a confined electron gas in nanoporous inorganic electrides

The nanoporous main group oxide 12CaO.7Al(2)O3 (C12A7) can be transformed from a wide-gap insulator to an electride where electrons substitute anions in cages constituting a positive frame. Our ab initio calculations of the electronic structure of this novel material give a consistent explanation of its high conductivity and optical properties. They show that the electrons confined in the inert positive frame are localized in cages and undergo hopping between neighboring cages. The results are useful for the understanding of behavior of confined electron gas of different topology and electron-phonon coupling, and for designing new transparent conductors, electron emitters, and electrides.     

Paramagnetic defect centers at the MgO surface. An alternative model to oxygen vacancies

On the basis of embedded cluster calculations, we propose a new model for the structure of paramagnetic color centers at the MgO surface usually denoted as F(S)(H)(+) (an electron trapped near an adsorbed proton). These centers are produced by exposing the surface of polycrystalline MgO to H(2) followed by UV irradiation. We demonstrate that properties of H atom absorbed at surface sites such as step edges (MgO(step)) and reverse corner sites (MgO(RC)), formed at the intersection of two step edges, are compatible with a number of features observed for F(S)(H)(+). Our calculations suggest that (i) H(2) dissociates at the reverse corner site heterolytically and that there is no barrier for this exothermic reaction; (ii) the calculated vibrations of the resulting MgO(RC)(H(+))(H(-)) complex are fully consistent with the measured ones; (iii) desorption of a neutral H atom from the diamagnetic precursor requires UV light and leads to the formation of stable neutral paramagnetic centers at the surface, MgO(step)(H(+))(e(-))(trapped) and MgO(RC)(H(+))(e(-))(trapped). The computed isotropic hyperfine coupling constants and optical transitions of these centers are in broad agreement with the existing experimental data. We argue that these centers, which do not belong to the class of "oxygen vacancies", are two of the many possible forms of the F(S)(H)(+) defect center.