Analysis of energy and force of Pt adatom on Pt (0 0 1) surface by MAEAM

The energy and perpendicular force of a Pt adatom on Pt (0 0 1) surface have been calculated by MAEAM. With increasing the distance of the adatom from the surface, the energy and force maps can be classified into four regions: repulsive region, transformed region, strongly attractive region and weakly attractive region. In repulsive region, the maximum (minimum) values of the energy and repulsive force appear on the top (hole) of the first layer atoms of Pt (0 0 1) surface due to stronger pair-potential interaction. In other regions, the energy and force maps are more complicated than those in repulsive region due to the effects of the many body interactions and nonspherical distribution of the electrons of the atoms in crystal. The most stable position is 0.1664 nm above the hole of the first layer atoms for a Pt adatom on Pt (0 0 1) surface.     

Atmospheric effects on the adhesion and friction between non-hydrogenated diamond-like carbon (DLC) coating and aluminum - A first principles investigation

Experimentally, non-hydrogenated DLC coatings were tested against 319 Al alloy in the nitrogen, hydrogen, dry air (0% RH), and ambient air (40% RH) environments using a vacuum pin-on-disc tribometer. The average coefficient of friction (COF) and the material transfer changed dramatically depending on the test environment. Density functional theory (DFT) calculations were performed to investigate the interaction of diamond surface, to represent non-hydrogenated DLC, with N₂, H₂, and H₂O molecules. These calculations suggested that hydrogen and water would dissociate and be chemically adsorbed at a diamond surface whereas the dissociation of nitrogen is very unlikely to happen. Therefore, the diamond/DLC surface is passivated by -H termination in hydrogen and by -OH termination in water vapor, but not passivated in nitrogen. The calculated work of separation for Al with non-passivated and reacted diamond surfaces indicated the same tendency of adhesive transfer as observed in the pin-on-disc tests. The calculated work of separation at the interfaces formed after material transfer has the same trend with the measured COF. Therefore, DFT calculations successfully explained the atmospheric dependency of the tribological behavior of non-hydrogenated DLC coatings.     

A semi-empirical study of polyacene molecules adsorbed on a Cu(1 1 0) surface

To describe the adsorption of large organic molecules on metal surfaces, to calculate the corresponding diffusion and rotation barriers, the semi-empirical mono-electronic Hamiltonian of the ASED molecular orbital method have been completed to take into account three body interaction terms. The full re-parametrization of this ASED+ version of ASED was determined on the specific case of benzene adsorbed on Cu(1 1 0) and a full transferability assumed for the member of the polyacene series also adsorbed on Cu(1 1 0). The adsorption energies, geometries, diffusion and rotation barriers are very well described by this new semi-empirical technique of calculation opening the way of optimizing larger conjugated molecule on surface for uni-molecular mechanics or electronics.     

Self-assembly of trimetallic nitride template fullerenes on surfaces studied by STM

Trimetallic nitride template fullerenes have been deposited onto a variety of substrates in order to elucidate the substrate-fullerene interactions. We have investigated self-assembled island formation and molecular detail of Er₃N@C₈₀ and Sc₃N@C₈₀ on Ag/Si(1 1 1), Au(1 1 1)/mica, Si(1 1 1), and Si(0 0 1) using variable temperature scanning tunnelling microscopy (STM). At room temperature, the fullerenes self-assemble into monolayer-high hexagonal close-packed islands on Ag-passivated Si(1 1 1) whereas annealing at elevated temperatures (250-300 °C) is necessary for the self-assembly of close-packed islands on Au(1 1 1). Intra-molecular resolution of the fullerenes has been achieved at liquid nitrogen temperature on Ag/Si(1 1 1) and already at room temperature on Si(0 0 1), when the rotation of the fullerenes is frozen. Whereas the bonding between the fullerenes and Si surfaces is mainly covalent, it appears to be mainly van-der-Waals on the other surfaces.     

Interaction of carbon monoxide and oxygen at the surface of inverse titania/Au model catalyst

Interaction of carbon monoxide and oxygen on the surface of titania/Au(1 1 1) inverse model catalyst held at 200 K has been studied by reflection absorption infrared spectroscopy. It was found that CO adsorbs on the oxide/Au perimeter interface, whereas no or very weak adsorption was observed on Au(1 1 1) or titania surface, respectively. Exposing of such species to oxygen results in their decay possibly due to carbon dioxide formation. Efficiency of this effect is higher at lower CO initial concentration which points at the importance of free surface sites for the reaction process.     

盐酸介质中TBP萃取树脂吸附金的研究

实验研究了TBP萃取树脂从盐酸介质中吸附金的行为，测定并讨论了溶液酸度、TBP含量和温度等因素对吸附的影响，确定了平衡方程式。对固定床吸附过程的破点时间进行了实验研究和分析，提出了估算的方法。     

Coverage dependence of neopentane trapping dynamics on Pt(111)

Adsorption probabilities for neopentane on Pt(111) were measured directly using supersonic molecular-beam techniques at coverages ranging from zero to monolayer saturation, incident translational energies between 18 and 110 kJ mol⁻¹ and incident angles between 0° and 60° at a surface temperature of 105 K. The adsorption probability was found to increase with coverage up to near monolayer saturation at all incident translational energies and incident angles. The coverage dependence of the adsorption probability predicted by a modified Kisliuk model with enhanced trapping into the second layer exhibits good quantitative agreement with the experimental values. The angular dependence of the adsorption probability decreases with increasing coverage, suggesting that the effective corrugation of the gas–surface interaction potential increases with the adsorbate coverage. The initial adsorption probability into the second layer onto the covered surface decreases from 0.95 to 0.75 with increasing energy over the energy range studied, and exhibits total energy scaling. A comparison with second-layer trapping data of simpler molecules onto covered Pt(111) indicates that the structural complexity of adsorbed neopentane molecules facilitates collisional energy transfer during adsorption.     

Separation of polypeptide antibiotics by reversed-phase high-performance liquid chromatography

Summary The influence of different reversed-phase packings and the addition of acidic modifiers to the mobile phase was observed on the separation of basic and neutral polypeptide antibiotics by gradient elution. A dependence of pore size, coverage, reaction type and endcapping of the packings was not observed. Nevertheless, not all reversed-phase packings were suitable for the separation of polypeptides, especially of basic molecules. The addition of phosphoric or perchloric acid to the mobile phase prevented adsorption of the basic polypeptide antibiotics on the stationary phase.     

Thermodynamics of vapour adsorption on heterogeneous microporous adsorbents

Fundamental thermodynamic functions have been derived for equations of adsorption isotherms including structural heterogeneity connected with micropore dimensions. Good agreement has been achieved between values of the differential molar enthalpy of adsorption and values of the isosteric adsorption heats obtained experimentally.