Small Incident Energies Research Articles

The influence of corrugations on spin polarization in magnetic field

Noninteracting electrons confined to a corrugated surface are considered in the presence of magnetic field, and the effective Pauli equation is given in the thin-layer quantization formalism. We find that the Zeeman splitting gaps are considerably affected by the corrugations. Furthermore, the spin transport on the corrugated surface is numerically calculated for GaAs material by transfer matrix method. And we find that the spin polarization is substantially influenced by the corrugations when the incident energy takes small values. As a potential application, the corrugations can be used to design a spin transistor with small incident energy.

Rational design of Si/TiO2 heterojunction photocatalysts: Transfer matrix method

The charge transfer in semiconductor heterojunction photocatalyst is one of the key factors determining its catalytic efficiency and durability in an aqueous environment. The widely used interface model with the simplified rectangular potential barrier fails to precisely predict the carrier transfer process since the band bending and its variation caused by solar energy are both not considered. Here, utilizing transfer matrix method, we take the Si/TiO2 heterojunction as a prototype to shed light on the rational design of the semiconductor heterojunction photocatalyst in terms of its intrinsic characteristics, such as TiO2 thickness and the dopant concentration. We find that the minimum incident energy (MIE) for electrons (holes) tunneling through the Si/TiO2 heterojunction decreases (increases) as the thickness of TiO2 layer increases. Within a moderate condition (TiO2 thickness of 3nm and dopant concentration of 1×1018cm−3 (5×1019cm−3) in Si (TiO2)), both electrons and holes can transfer through the heterojunction barrier with relatively small incident energy. Furthermore, the photovoltage under illumination is beneficial for reducing MIE for electrons while increasing that for holes. Therefore, our transfer matrix scheme provides insights into rational design of the high efficient photocatalyst.

Invisibility of quantum systems to tunneling of matter waves

We show that an appropriate choice of the potential parameters in one-dimensional quantum systems allows for unity transmission of the tunneling particle at all incident tunneling energies, except at controllable exceedingly small incident energies. The corresponding dwell time and the transmission amplitude are indistinguishable from those of a free particle in the unity-transmission regime. This implies the possibility of designing quantum systems that are invisible to tunneling by a passing wave packet.

Energy loss of electrons passing through a laser flash in a storage ring

The problem of the electron beam energy spread damping using the linear back Compton scattering process is considered in the paper. The adjoint kinetic equation for the electron energy distribution is used to get the equations for the mean energy and for the energy distribution variance. The equations for the distribution moments are obtained and solved by an iteration method. It is shown that the variance of the energy distribution has a maximum at some value of light target thickness for the electron beams with small incident energy spread. The problem of radiation cooling in the laser-electron storage ring is discussed. The data of approximate analytical calculations agree with the results of the Monte Carlo simulation.

A New Numerical Model for Electron-Probe Analysis at High Depth Resolution

Characterizing dimensionally and chemically nanometric structures such as surface segregation or interface phases can be performed efficiently using electron probe (EP) techniques at very low excitation conditions, i.e. using small incident energies (0.5<E0<5 keV) and low incident overvoltages (1<U0<1.7). In such extreme conditions, classical analytical EP models are generally pushed to their validity limits in terms of accuracy and physical consistency, and Monte-Carlo simulations are not convenient solutions as routine tools, because of their cost in computing time. In this context, we have developed an intermediate procedure, called IntriX, in which the ionization depth distributions Φ(ρz) are numerically reconstructed by integration of basic macroscopic physical parameters describing the electron beam/matter interaction, all of them being available under pre-established analytical forms. IntriX’s procedure consists in dividing the ionization depth distribution into three separate contributions:

Dynamics of Coulomb dissociation in relativistic mean field theory

Time-dependent relativistic mean field theory is used to describe the dynamics of Coulomb excitations of nuclei. As an example we consider the nucleus 16O. At small incident energies of the projectile we observe isovector dipole oscillations that correspond to the giant dipole resonance. With increasing excitation energy, the motion becomes increasingly anharmonic, and finally a full dissociation of 16O into proton and neutron clusters is observed.

Coulomb excitations of a nuclear slab in relativistic mean-field theory

Time-dependent relativistic mean-field theory is used to describe the dynamic behaviour of a nuclear slab excited at time zero by a rapid Coulomb push. At small incident energies of the projectile, we observe oscillations of small amplitude with isovector character. With increasing excitation energy, the motion becomes increasingly anharmonic, and parts of the nuclear material are ejected. At the highest energies, we find a rapid dissociation between the proton and neutron part of the slab. It turns out that the character of the oscillations is strongly influenced by the strength of the ρ-meson coupling. For vanishing coupling, we observe two modes corresponding in nature to the Goldhaber-Teller mode and the Steinwedel-Jensen mode of the giant dipole resonance in realistic nuclei. At larger ρ-meson coupling, the Goldhaber-Teller mode is more and more suppressed, and one is left with one strongly damped mode of the Steinwedel-Jensen type.

Influence of the substrate on the low-temperature limit of the sticking probability of hydrogen atoms on He films.

We show that the sticking probability s of hydrogen atoms on the surface of He films in the limit of small incident energy may be determined by the dielectric properties of the substrate, and that considerably higher values of s may be found than in the case of bulk He.

Thin Cu/Ag(111) and Ag/Cu(111) structures studied with monoenergetic positrons.

The early stages of crystal growth have been studied with variable-energy positrons in conjunction with low-energy electron diffraction and Auger-electron spectroscopy. We report measurements of positron branching ratios for (0.1--10)-monolayer (ML) Cu overlayers grown on Ag(111) and for (0.1--100)-ML Ag overlayers grown on Cu(111). The results are discussed in terms of the structural and electronic properties of the surfaces as well as positron-interaction mechanisms at the surfaces. Our method is not sensitive to open-volume defects created during the early stages of crystal growth. Information on positron implantation at small incident energies, positron surface processes, and positron thermalization properties is extracted from experimental data.

Modified WKB Approximation Applied to the Solution of the Repulsive Singular Potential

The conventional WKB method for phase shift calculations is known to fail for singular repulsive potentials at small incident energies. We show in this paper that the modified WKB method due to Miller and Good can be used instead and that it gives better agreement with the exact results of the scattering phase shifts at small incident energies and in the small coupling constant limit, as more terms in ℏ2 are included.