Density functional study of ethylene oxidation on an Ag(111) surface

The mechanism of ethylene epoxidation on Ag surfaces has been investigated using the density functional method and Ag _n clusters (n = 3 to 10) modeling the Ag(111) surface. The adsorption energy of O₂ to the Ag clusters was strongly dependent on the HOMO level of the cluster, and the clusters with higher HOMO levels afforded larger O₂ adsorption energies. The energetics was investigated for both the molecular and atomic oxygen epoxidation mechanisms. For the atomic oxygen mechanism, epoxidation was found to proceed without an activation energy, whereas a small amount of activation energy (about 5 kcal/mol) was calculated for the molecular oxygen mechanism. Received: 2 July 1998 / Accepted: 9 September 1998 / Published online: 8 February 1999     

An EPR Study on Intramolecular Spin Exchange,Rotational Mobility of Nitroxides Linked by a Long-chain

The effects of pressure, solvent on the intramolecular spin exchange of biradicals having two nitroxide fragments linked by a long flexible chain were studied by means of highpressure EPR technique. It was found that the intramolecular exchange interaction between nitroxides of biradical took place through the direct contact between them. By analyzing the observed EPR spectra, we have estimated the ratio(Τ_in/Τ_out) value of the average lifetime of the radical fragments inside a cage(Τ_in) to that outside the cage(Τ_out). The Τ_in/Τ_out values decreased with decreasing temperature, increasing pressure. The results suggest that the nearly cyclic conformation in a cage is favorable in solution. Fur ther, the rotational correlation time of individual nitroxide was estimated from the anisotropic EPR signal,, the information on the segmental motion of the nitroxide group in biradical was obtained.     

Weyl transformation in Fermi systems

In the path integral representation, the Hamiltonian in a quantum system is associated with the Hamiltonian in a classical system through the Weyl transformation. From this, it is possible to describe the time evolution in a quantum system by the Hamiltonian in a classical system. In a Bose system, the Weyl transformation is defined by the eigenstates of the canonical operators, since the Hamiltonian is given by a function of the canonical operators. On the other hand, in a Fermi system, the Hamiltonian is usually described by a function of the creation and annihilation operators, and hence the Weyl transformation is defined by the coherent states which are the eigenstate of an annihilation operator. Here, we formulate the Weyl transformation in Fermi systems in terms of the eigenstates of the canonical operators so as to clarify the correspondence between both systems. Using this, we can derive the path integral representation in Fermi systems.     

Phenanthrene adsorption from solution on single wall carbon nanotubes

Phenanthrene was adsorbed from ethanol solution to the surface of single wall carbon nanotubes, which were previously physically and chemically characterized. Different anionic surfactants were added in the solutions to enhance the phenanthrene solubility and apparently have also improved the dispersion of two respective nanotube samples used. Adsorbed amount was determined through the concentration difference measured by UV-visible spectrophotometry. Results suggest that adsorption of phenanthrene is extremely improved in the case of nanotube purified with higher quality. These findings were confirmed by X-ray photoelectron spectroscopy. The influence of the surfactant on the adsorption kinetics of phenanthrene is suggested to be significant as well.     

Effect of Ampoule Rotation on Growth of InGaAs Ternary Bulk Crystals from Solution

In_xGa_1-xAs (x = 0.045) ternary bulk crystals were grown on GaAs seeds from an In–Ga–As solution by the temperature-difference method modified to rotate a growth ampoule. The effect of ampoule rotation on the profiles of the composition and the growth rate were investigated. The In compositional profiles were uniform irrespective of the ampoule rotation. On the other hand, the growth rate at the center of the crystal increased from 40 μm/h at 0 rpm to 55 μm/h at 100 rpm. The profile of growth rate changed from concave to convex toward the seed due to the ampoule rotation. Flow patterns and compositional profiles in the solution were simulated by solving four equations: Navier-Stokes, continuity, energy, and solute diffusion. The ampoule rotation enhanced the transportation of As component from the GaAs feed toward the seed at the central region in the solution. This led to the increase of the growth rate.     

General Design Concepts for CAPodes as Ionologic Devices

Capacitive analogues of semiconductor diodes (CAPodes) present a new avenue for energy-efficient and nature-inspired next-generation computing devices. Here, we disclose the generalized concept for bias-direction-adjustable n- and p-CAPodes based on selective ion sieving. Controllable-unidirectional ion flux is realized by blocking electrolyte ions from entering sub-nanometer pores. The resulting CAPodes exhibit charge-storage characteristics with a high rectification ratio (96.29 %). The enhancement of capacitance is attributed to the high surface area and porosity of an omnisorbing carbon as counter electrode. Furthermore, we demonstrate the use of an integrated device in a logic gate circuit architecture to implement logic operations (‘OR’, ‘AND’). This work demonstrates CAPodes as a generalized concept to achieve p-n and n-p analogue junctions based on selective ion electrosorption, provides a comprehensive understanding and highlights applications of ion-based diodes in ionologic architectures.