Axial and radial development of the hot electron distribution in a helicon plasma source, measured by a retarding field energy analyzer (RFEA)

The information about the electron population of a helicon source plasma that expands along a magnetic nozzle is important for understanding the plasma acceleration across the potential drop that forms in the nozzle. The electrons need an energy higher than the potential drop to escape from the source. At these energies the signal of a Langmuir probe is less accurate. An inverted RFEA measures the high-energy tail of the electrons. To reach the probe, they must have energies above the plasma potential VP, which can vary over the region of the measurement. By constructing a full distribution by applying the electron temperature Te obtained from the electron IV-curve and the VP obtained from the ion collecting RFEA or an emissive probe, a density measure of the hot electron distribution independent of VP can be obtained. The variation of the high-energy tail of the EEDF in both radial and axial directions, in the two different cases of 1) a purely expanding magnetic field nozzle, and 2) a more constricted one by applying current in a third, downstream coil was investigated. The electron densities and temperatures from the source are then compared to two analytic models of the downstream development of the electron density. The first model considers the development for a pure Boltzmann distribution while the second model takes an additional magnetic field expansion into account. A good match between the measured densities and the second model was found for both configurations. The RFEA probe also allows for directional measurement of the electron current to the probe. This property is used to compare the densities from the downstream and upstream directions, showing a much lower contribution of downstream electrons into the source for a purely expanding magnetic field in comparison to the confined magnetic field configuration.

Mechanistic insight into deep holes from interband transitions in Palladium nanoparticle photocatalysts

Photocatalysis of metallic nanoparticles, especially utilizing hot electrons generated from localized surface plasmon resonance, is of widespread interest. However, the role of hot holes, especially generated from interband transitions, has not been emphasized in exploring the photocatalytic mechanism yet. In this study, a photocatalyzed Suzuki-Miyaura reaction using mesoporous Pd nanoparticle photocatalyst served as a model reaction to study the role of hot holes by accurately measuring the quantum yields of the photocatalyst. The quantum yields increase under shorter wavelength excitations and correlate to the “deeper” energy of the holes from the Fermi level. Our mechanistic study suggests that deeper holes in the d-band can catalyze the oxidative addition of aryl halide R-X onto Pd0 at the surface of nanoparticles to form the R-PdII-X complex, the rate-determining step of the established catalytic cycle. We pointed out that this deep hole mechanism should deserve as much attention as the well-known hot electron transfer mechanism in previous studies.

Simulation study on parametric dependence of whistler-mode hiss generation in the plasmasphere

We conduct electromagnetic particle simulations to examine the applicability of nonlinear wave growth theory to the generation process of plasmaspheric hiss. We firstly vary the gradient of the background magnetic field from a realistic model to a rather steep gradient model. Under such variation, the threshold amplitude in the nonlinear theory increases quickly and the overlap between threshold and optimum amplitude disappears correspondingly, the nonlinear process is suppressed. In the simulations, as we enlarge the gradient coefficient of the background magnetic field, waves generated near the equator do not grow through propagation. By examining the range of suitable values of inhomogeneity factor S (i.e., $$|S|<2$$ | S | < 2 ), we find the generation of wave packets is limited to the equatorial region when the background field is steep, showing a good agreement with what is indicated by critical distance in the theory. We then check the dependence of generation of hiss emissions on different hot electron densities. Since the overlap between threshold and optimum amplitude vanishes, the nonlinear process is weakened when hot electron density becomes smaller. In the simulation results, we find similar wave structures in all density cases, yet with different magnitudes. The existence of suitable S values implies that the nonlinear process occurs even at a low level of hot electron density. However, by examining $$J_E$$ J E that closely relates to the wave growth, we find energy conveyed from particles to waves is much limited in small density cases. Therefore, the nonlinear process is suppressed when hot electron density is small, which agrees with the theoretical analysis. Graphical Abstract

Consideration of contribution of hot-electron injection to the resistive switching of sputter-deposited silicon oxide film

<p>This paper considers the contribution of hot electrons to the resistive switching of sputter-deposited silicon oxide films based on experiments together with semi-2D Monte Carlo simulations. Using various device stack structures, this paper examines the impact of hot-electron injection on resistive switching, where conduction-band offset and fermi-level difference are utilized. Support is found for the predictions that hot-electron injection reduces the switching voltage and this should reduce the dissipation energy of switching. It is predicted that two-layer metal stacks can significantly reduce the number of oxygen vacancies in the sputter-deposited silicon oxide film after the reset process. It is also demonstrated that, in unipolar switching, the number of E’ or E” centers of the sputter-deposited silicon oxide film is relatively large.</p>