Energy dependence of gap survival probability and antishadowing

We discuss the energy dependence of the gap survival probability which follows from the rational form of the amplitude unitarization. In contrast to the eikonal form of unitarization which leads to a decreasing energy dependence of the gap survival probability, we predict a non-monotonous form for this dependence.Received: 8 April 2004, Revised: 31 October 2004, Published online: 25 January 2005     

Impact parameter dependence of the probability for K-shell ionization by nuclei

The probability W for the atomic ionization by nuclei as a function of the impact parameter x is expressed through the ionization matrix element M_if. Values of W(x) for K-shell ionization calculated with the first Born M_if are compared with the experimental data and other calculations.     

Caesium/xenon dual beam depth profiling: Velocity of the sputtered atom and ionization probability

In this work, a caesium/xenon co-sputtering gun was used to perform depth profiles of a RhSi layer with varying caesium beam concentration. The positive ion yields were monitored with respect to the varying work function of the solid and the intensities of the ions were plotted with respect to the caesium surface concentration. As expected by the tunneling model, all the M⁺ signals decrease exponentially with the increasing caesium beam concentration. Moreover, the heaviest ion yields decrease faster than the lighter ion ones. This phenomenon can be explained by the different velocities of the departing atoms, which has an important impact on the ionization processes. We then studied the variations of the MCs⁺ yields with respect to the caesium surface concentration and with respect to the nature of the departing atom. Finally, we applied models based on the tunneling model in order to fit our results.     

Light intensity dependence of the multiphoton ionization probability in the resonance case

The general intensity dependence of the five-photon ionization probability of triplet metastable helium was measured.     

Angular dependence of the in-plane magnetization of (100) Cu/Ni/Cu structures

(100) Cu/Ni/Cu sandwich structures have been deposited on (100) Si using the (100) Cu epitaxially grown as the seed layer. The in-plane epitaxial relation between the metal films and Si allows the study of angular dependence of the magnetization for the field parallel to the film plane. Keeping the Cu layers at 1000 Å each and varying the Ni layers between 50 and 1000 Å, the magnetization along the [110] edge is larger than that along the [100] one. This is observed for both structures with a Ni thickness of 1000 and 500 Å, respectively. For the thinner Ni layers, the angular dependence is interfered by the reversal in magnetic anisotropy reported earlier. For such structures, a squared hysteresis loop is observed for the field perpendicular to the film plane, whereas one with little loop is observed for the in-plane magnetization. The angular dependence observed for the 1000 and 500 Å Ni films is the same as that of single crystal Ni. The (100) Cu/Ni/Cu films thus grown can be used for other magnetic measurements in the exploration of two-dimensional magnetism with controlled orientations.     

Modeling the dissociation and ionization of a sputtered organic molecule

The evolution of an organic molecule after sputtering from a gold surface has been analyzed by classical molecular dynamics and ab initio calculations to gain insight into the ionization and fragmentation processes occurring in SIMS. The calculated ionization potential (6.2 eV) of the tetraphenylnaphthalene (TPN) molecule has been found to be close to the unimolecular dissociation energy (5.4 eV) of the most favorable reaction channel involving the loss of a phenyl ring. On the other hand, our calculations show that the internal energies of sputtered TPN molecules can be significantly larger than 5-6 eV. Therefore, it appears energetically possible to relax such excited molecules via both fragmentation and ionization.We propose to virtually decompose the TPN molecule into its basic fragments. The rationale is that, if the molecule is very excited, then separate parts (e.g. pendant phenyl rings) can interact with each other almost independently. The analysis of the molecular motion after emission shows that the oscillations along the phenyl-naphthalene bond direction, expected to induce the molecule fragmentation by the loss of a phenyl ring, are relatively small (they store only about 0.2 eV). On the other hand, the relative energy stored in the inter-phenyl interactions, modulated by their bending and responsible for ionization according to our hypothesis, oscillates over a range of 6-7 eV and favors ionization.     

Fe clusters on Ni and Cu: size and shape dependence of the spin moment

We present ab-initio calculations of the electronic structure of small Fe clusters (1–9 atoms) on Ni(001), Ni(111), Cu(001) and Cu(111) surfaces. Our focus is on the spin moments and their dependence on cluster size and shape. We derive a simple quantitative rule that relates the moment of each Fe atom linearly to its coordination number. Thus, for an arbitrary Fe cluster the spin moment of the cluster and of the individual Fe atoms can be readily found if the positions of the atoms are known. PACS 75.75.+a; 75.70.-i; 73.22.-f     

Model of ionization of atoms sputtered from solids

A new microscopical quantum-mechanical model of ionization of sputtered particles is described which takes into account electron excitations due to the atomic motions in the substrate. The substrate is represented by a simple atomic, metal-like, chain. Numerical calculations yield ionization probabilities R⁺ which have magnitudes close to the experimental values and have realistic velocity dependence. The function of R⁺ versus the sputtered atom ionization energy can be well approximated by the Maxwell-Boltzmann law with an effective temperature of about 3500 K.     

Determination of energy dependent ionization probabilities of sputtered particles

We present a novel method to determine the spectral ionization probability of sputtered species as a function of their emission velocity or energy. The technique is based on detection of neutral and ionic species in a reflectron time-of-flight mass spectrometer under otherwise identical experimental conditions. Using a pulsed ion extraction scheme in combination with sufficiently short primary ion pulses, the spectral ionization probability α⁺(v) can be determined without knowledge of possible energy discrimination effects in instrument transmission. Comparing the measured ionization probability with theoretical predictions, we find that none of the prevailing ionization models is capable of describing the experimental data over the whole velocity range studied.     

Ni3Al and Ni3Ge. Energy of plane surface defects and abnormal temperature dependence of flow stress

A significant temperature anomaly of the yield point is observed in Ni₃Al and Ni₃Ge alloys with the L1 ₂ superstructure. The temperature anomaly is caused by the thin structure of sliding superdislocations and plane defects in L1 ₂ entering the superdislocation structure. The temperature and concentration dependences of the parameters characterizing in the best way the temperature strengthening in Ni₃(Al_{1 ? x} , Ge _x ) alloys are investigated. It is shown that the alloying Ge element leads to more pronounced manifestation of the temperature strengthening effect in Ni₃(Al_{1 ? x} , Ge _x ).     

Temperature dependence of the optical properties of ion-beam sputtered ZrN films

The reflectivity of sputtered Zirconium nitride films on glass substrate has been investigated in the spectral energy range of 0.8–6.1 eV as a function of deposition temperature varying between 373 and 723 K. Optical constants of the prepared films have been determined using the Drude analysis. Experimental results showed strong dependency of optical properties of the films, such as optical resistivity on the substrate temperature. The temperature increase of the substrate has shown an increase in both the plasmon frequency and electron scattering time. The electrical behavior of the films showed a good agreement between their optical and electrical resistivity.     

Resonance enhanced multi-photon ionization of neutral atoms sputtered with Ga-FIB

Resonance enhanced multi-photon ionization (REMPI) of neutral aluminum atoms sputtered with gallium focused ion beam (Ga-FIB) was studied in terms of substrate temperature and chemical state of the surfaces. Aluminum has the lowest excitation state (3p ²P_3/2) at 112 cm⁻¹ above the ground state (3p ²P_1/2). The results showed that the total REMPI signal intensity of neutral aluminum atoms and the ratio of REMPI signal intensities attributed to ²P_1/2 to ²P_3/2 were increased at higher temperature. On the other hand, the REMPI signal and the ratio were decreased in the case of partially oxidized aluminum surfaces. Considering the result on Al₂O₃, it was confirmed that the REMPI signals of ground state ²P_1/2 and the first excited spate ²P_1/2 could be affected with surface oxidation state.     

Electron impact ionization. The probability of occupying states after ionization

The probability function of occupying states with a definite energy in the conduction band after collision in the process of electron impact ionization is calculated. The valence band is assumed of finite width. Several cases of the primary energy and the effective mass in the valence band are examined.

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This work was begun at the Institute of Technical Physics of the Czechoslovak Academy of Sciences in Prague. The author wishes to thank the Director of that Institute for the possibility of working there and especially Dr E. Antoník for suggesting the problem and for helpful discussions.     

Grain-size dependence of superconductivity in dc sputtered Nb films

The superconducting transition temperature and grain size of dc sputtered Nb films are systematically investigated. The results show that the superconductivity is closely related to the grain size, rather than to the scattering strength of electrons or the surface layer proximity effect of the films. Supported by the National Basic Research Program of China (Grant No. 2006CB-91304), and the Knowledge Innovation Project of Chinese Academy of Sciences Contributed by ZHANG DianLin     

Energy dependence of the Penning ionization electron spectrum of Ne* (3P2,0)+Kr

A crossed beam experiment is carried out to measure the energy of electrons emitted in Penning ionization processes by Ne^*(³P_2,0)–Kr collisions. The electron energy spectra have been measured at four different collision energies: 0.050, 0.140, 0.190, 0.460 eV. The analysis of the results allows the separation of spin orbit contributions both in the entrance and in the exit channels providing the related cross-section ratios. Some theoretical considerations have been made to clarify nature and role of interatomic potentials driving the collisions and some general features about the role of atomic fine structure in the Penning ionization processes.     

Ferromagnetic resonance study of sputtered Co|Ni multilayers

We report on room temperature ferromagnetic resonance (FMR) studies of [ t Co|2t Ni]  × N sputtered films, where 0.1 ≤ t ≤ 0.6 nm. Two series of films were investigated: films with the same number of Co|Ni bilayer repeats (N = 12), and samples in which the overall magnetic layer thickness is kept constant at 3.6 nm (N = 1.2/t). The FMR measurements were conducted with a high frequency broadband coplanar waveguide up to 50 GHz using a flip-chip method. The resonance field and the full width at half maximum were measured as a function of frequency for the field in-plane and field normal to the plane, and as a function of angle to the plane for several frequencies. For both sets of films, we find evidence for the presence of first and second order anisotropy constants, K₁ and K₂. The anisotropy constants are strongly dependent on the thickness t, and to a lesser extent on the total thickness of the magnetic multilayer. The Landé g-factor increases with decreasing t and is practically independent of the multilayer thickness. The magnetic damping parameter α, estimated from the linear dependence of the linewidth ΔH, on frequency, in the field in-plane geometry, increases with decreasing t. This behaviour is attributed to an enhancement of spin-orbit interactions with decreasing Co layer thickness and in thinner films, to a spin-pumping contribution to the damping.     

Stark width and shift dependence on the ionization potential

Analytic relations between the Stark widths and shifts and the ionization potential of the corresponding emitters have been found and are discussed.