Accelerated Exciton Dissociation and Electron Extraction across Metallic Sulfide-Carbon Nitride Ohmic Interface for Efficient Photocatalytic Hydrogen Production

Herein, MOF derived transition metal sulfide (Co3S4) with metallic characteristic is introduced to create an ohmic contacted Co3S4-CN heterojunction interface. By the virtue of electron injection from lower work function...

Influence of Vacancy Defect on Surface Feature and Adsorption of Cs on GaN(0001) Surface

The effects of Ga and N vacancy defect on the change in surface feature, work function, and characteristic of Cs adsorption on a2×2GaN(0001) surface have been investigated using density functional theory with a plane-wave ultrasoft pseudopotential method based on first-principles calculations. The covalent bonds gain strength for Ga vacancy defect, whereas they grow weak for N vacancy defect. The lower work function is achieved for Ga and N vacancy defect surfaces than intact surface. The most stable position of Cs adatom on Ga vacancy defect surface is at T1site, whereas it is atBGasite on N vacancy defect surface. TheEadsof Cs on GaN(0001) vacancy defect surface increases compared with that of intact surface; this illustrates that the adsorption of Cs on intact surface is more stable.

SPECTRA OF RADIATION EMITTED FROM OPEN-ENDED AND CLOSED CARBON NANOTUBES EXPOSED TO MICROWAVE FIELDS

We performed experiments in which both open-ended and closed carbon nanotubes were exposed to 2.46 GHz microwaves over the course of several irradiation and cooling cycles at a pressure of ~ 10-6 torr. The spectra of the radiation emitted from the nanotubes indicate that the intensity of the emitted radiation with wavelengths of 650–1000 nm increased during the irradiation cycles. However, the intensity of the radiation emitted from untreated nanotubes increased substantially more than the intensity of the radiation emitted from nanotubes that had been chemically treated in order to open nanotube ends. As open-ended nanotubes have a lower work function than closed nanotubes, and as nanotube ends are known to open as they are heated, our results suggest that the mechanism responsible for the emission of infrared, visible and ultraviolet radiation from carbon nanotubes exposed to microwaves is field emission-induced luminescence.

Real Time Study of Cu Diffusion through a Ru Thin Film by Photoemission Electron Microscopy (PEEM)

We demonstrate the efficacy of Photoemission Electron Microscopy (PEEM) as a tool to detect metal diffusion processes at nanoscale spatial resolution in real time. For a sample comprising a nominally 1 nm physical vapor-deposited (PVD) Ru thin film covering a thick Cu substrate, we have observed the appearance of bright features on a dark background as the temperature is monotonically increased and irradiated with photons from a Hg arc lamp. These bright features are the result of a lower work function due to Cu diffusion through the Ru film.

Kontaktpotential und heterogene Katalyse / Contact Potential and Heterogenous Catalysis

It is shown that in the case of metals connected by a first order conductor the decomposition of formic acid is less at the element of lower work function while it is more at the element of higher work function. The metals used were Ni, Cd, Zn. The results correspond to the investigations of other authors 1 who showed that the activation energy on alloys depends on how far the concentration of electrons is from full saturation of the lattice type. This effect is explicable in terms of the development of a contact potential, the conditions in the case of metals being similar to those in the case of alloys.

Photoelectric measurements on nickel and nickel oxide film

In order to gain a clearer understanding of how molecular oxygen and hydrogen react with the surfaces of metals and metallic oxides, the electronic work function has been measured during the oxidation of evaporated nickel films and the reduction of nickel oxide with hydrogen. The measurements included changes in the spectral sensitivity of surfaces prepared under varied conditions, and in the photoelectric yield (at constant photon energy) during the admission of gas. Admission of oxygen to nickel films at 20°C resulted in several distinct effects. Lightly oxidized films (< 1 monolayer equivalent total uptake) gave composite spectral sensitivity curves. By using the Fowler equation in the form of a plot of frequency against (photo-electric yield) ½ , these were analyzed in terms of two work functions, which remained unaltered until the films were saturated with respect to the rapid chemisorption of oxygen. As further quantities of oxygen were absorbed, both work functions rose. When the films were stood in vacuo , the lower work function decreased, finally reaching a lower value than that measured for clean nickel; at the same time the films recovered the capacity to adsorb oxygen. The process is regarded as identical with the known ‘thermal regeneration’, namely, the ability of oxidized films to take up oxygen rapidly after they have been heated in vacuo at 200 to 400°C. Although the lower work function fell markedly as thermal regeneration occurred, the larger work function did not fall below about 5∙7 eV. It is considered that the observations point to two kinds of surface structure in the lightly oxidized films. The work function of 5∙7 eV is assigned to areas thinly covered with the nickel oxide crystal lattice, while the lower work function is assigned to areas on which the oxide, as such, does not form. It is suggested that the initial interaction of oxygen with the surface is largely non-polar, and that nickel oxide only forms on certain areas as a result of migration, charge transfer and rearrangement. Those parts of the surface not covered with the nickel oxide crystal lattice undergo modification, as a result of penetration of oxygen into the surface layers of the metallic lattice. Photoemission from nickel oxide films (> 1000Å thick) has been examined, and the interaction of hydrogen with these films was studied in detail. Changes in photoelectric yield show that there is some small degree of chemisorption at 20°C, and it is postulated that this represents formation of H + 2 which either penetrates the nickel oxide lattice or occupies vacant cation sites in or near the surface. At higher temperatures the surface potential becomes increasingly negative as dissociative chemisorption takes place extensively by the mechanism already recognized. With the desorption of water and the continuation of reaction, nuclei of nickel form. The findings are in agreement with, but amplify, the accepted generalized model for oxidation and reduction processes.