Вероятность ионизации атомов, распыленных при бомбардировке поверхности металлов одно- и многозарядными ионами

The processes of ionization of atoms sputtered under bombardment of clean metal surface by singly and multiply charged ions with kinetic energy of several keV were studied. Within the framework of simple phenomenological model of ion formation, the relaxation of local electron excitation in metal was taking into account. Analytical expressions for estimation of ionization probability of sputtered atoms was obtain. It was shown, that in comparison with singly charged ions, bombardment of metals with multiply charged ions results to significant increase of ionization probability of sputtered atoms due to more efficient excitation of electrons and increase of relaxation time of this excitation.

Anomalous dependence of ionization probability and electron angular distributions on orientation of molecular axis in photoionization of H+ 2: effect of two-center interference

A theoretical and computational study of photoionization of the one-electron molecular ion H+ 2 initially in the 1σu state is performed. The laser pulse is linearly polarized with the carrier wavelength in the extreme ultraviolet region. The electron wave function is obtained by solving the time-dependent Schrödinger equation with the help of the generalized pseudospectral method. The dependence of the total ionization probability and photoelectron spectra on the orientation of the molecular axis is analyzed. At the wavelength of 12.5 nm, anomalous behavior of the ionization probability is found, where the ionization probability increases with an increase of the angle between the polarization vector of the external field and the molecular axis and reaches a maximum at the perpendicular orientation of the molecule. The phenomenon is explained as resulting from the two-center interference in the wave function of the emitted electron. When the wavelength or internuclear distance change, the effect disappears, and the ionization probability exhibits its usual behavior with the maximum at the parallel orientation of the molecular axis.

Tunneling Calculation in the Field Ion Microscope

In this work we describe calculations of tunneling rate constants for the Field Ion Microscope (FIM) using one-dimensional model potential that simulates the ionization process in a FIM. We obtain expressions for the ionization rate constant (ionization probability per unit of time) of inert gas atoms as a function of their position above the surface. In order to calculate the probability of barrier penetration we have used the semiclassical (JWKB) approximation. We have also calculated ionization zone widths as the distance between points where ionization rate is a maximum and half of this value. An application to helium as the imaging gas is presented to highlight the power of the method.

Effects of inhomogeneous laser field in time and space on the generation of broad spectral continuum and ultrashort attosecond pulse

The inhomogeneous effects of laser field in time and space on the generations of high-order harmonic spectra and attosecond pulses from He atom have been investigated with the assistance of the frequency-chirping technique and the metallic nanostructure. We find that in different combinations of chirps and spatial inhomogeneous effects, not only can the harmonic cutoff be extended, but the single harmonic emission peak (HEP) can also be selected to contribute to the spectral continuum. In detail, with the combinations of (i) symmetric chirp in frequency and positive inhomogeneous effect in space or (ii) asymmetric down chirp in frequency and negative inhomogeneous effect in space, two broad spectral continua with bandwidths of 496 eV and 480 eV can be obtained. Further, by properly adding IR or UV controlling pulse, the harmonic emission efficiency can be enhanced by several orders of magnitude. The enhancement of harmonic yield from adding UV pulse is higher than that from adding IR pulse. Moreover, the difference of harmonic enhancement between UV combined field and IR combined field is much more obvious at lower controlling laser intensity. Through analyzing the ionization probability, we find that the higher enhancement of harmonic yield from UV combined field is because of UV-resonance-enhancement-ionization between the ground state and the excited state of He atom. Finally, by properly superposing some harmonics, a number of attosecond pulses with pulse durations of 45 as can be obtained.

The matrix effect in TOF-SIMS analysis of two-element inorganic thin films

Investigation of the matrix effect in Zr-based two-element alloys under continuous bombardment of a Ga+ primary ion beam in a study of ionization probability towards exploring the potential and limitations of gas-assisted TOF-SIMS.

The Effect of Magnetic Field Strength and Geometry on the Deposition Rate and Ionized Flux Fraction in the HiPIMS Discharge

We explored the effect of magnetic field strength | B | and geometry (degree of balancing) on the deposition rate and ionized flux fraction F flux in dc magnetron sputtering (dcMS) and high power impulse magnetron sputtering (HiPIMS) when depositing titanium. The HiPIMS discharge was run in two different operating modes. The first one we refer to as “fixed voltage mode” where the cathode voltage was kept fixed at 625 V while the pulse repetition frequency was varied to achieve the desired time average power (300 W). The second mode we refer to as “fixed peak current mode” and was carried out by adjusting the cathode voltage to maintain a fixed peak discharge current and by varying the frequency to achieve the same average power. Our results show that the dcMS deposition rate was weakly sensitive to variations in the magnetic field while the deposition rate during HiPIMS operated in fixed voltage mode changed from 30% to 90% of the dcMS deposition rate as | B | decreased. In contrast, when operating the HiPIMS discharge in fixed peak current mode, the deposition rate increased only slightly with decreasing | B | . In fixed voltage mode, for weaker | B | , the higher was the deposition rate, the lower was the F flux . In the fixed peak current mode, both deposition rate and F flux increased with decreasing | B | . Deposition rate uniformity measurements illustrated that the dcMS deposition uniformity was rather insensitive to changes in | B | while both HiPIMS operating modes were highly sensitive. The HiPIMS deposition rate uniformity could be 10% lower or up to 10% higher than the dcMS deposition rate uniformity depending on | B | and in particular the magnetic field topology. We related the measured quantities, the deposition rate and ionized flux fraction, to the ionization probability α t and the back attraction probability of the sputtered species β t . We showed that the fraction of the ions of the sputtered material that escape back attraction increased by 30% when | B | was reduced during operation in fixed peak current mode while the ionization probability of the sputtered species increased with increasing | B | , due to increased discharge current, when operating in fixed voltage mode.

Deformation of an inner valence molecular orbital in ethanol by an intense laser field

Valence molecular orbitals play a crucial role in chemical reactions. Here, we reveal that an intense laser field deforms an inner valence orbital (10a′) in the ethanol molecule. We measure the recoil-frame photoelectron angular distribution (RFPAD), which corresponds to the orientation dependence of the ionization probability of the orbital, using photoelectron-photoion coincidence momentum imaging with a circularly polarized laser pulse. Ab initio simulations show that the orbital deformation depends strongly on the laser field direction and that the measured RFPAD cannot be reproduced without taking the orbital deformation into account. Our findings suggest that the laser-induced orbital deformation occurs before electron emission on a suboptical cycle time scale.