Angular distribution of copper atoms sputtered with energetic ions

Measurements of the angular distribution of copper atoms which are sputtered by noble gas ions within the energy range between 0.1 and 1 MeV have been carried out for different angles of ion incidence. The hemisphere over the target surface could be studied with a microphotometer inside the sputtering chamber and the distributions can be plotted in tri-dimensional diagrams. The results are in principle similar to those obtained at lower energies. The angle of maximum emission varies with ion energy and with the angle of incidence and can be related to the sputtering yield.     

An empirical relationship between atoms and ions sputtered from single crystal surfaces

The temperature dependence of long range order at a (100) surface of Cu₃Au has been determined by low energy electron diffraction. Auger electron spectroscopy revealed that the composition of the alloy near the surface is changed by ion bombardment, but the stoichiometric composition is reconstituted by annealing. The order parameter of the surface, which was obtained from the temperature dependence of a superlattice beam, appears to be a continuous function of temperature, unlike the bulk order parameter. The disordering process at the surface begins about 60°K below a critical temperature which is common to both the surface and the volume. Monte Carlo calculations of the order parameter as a function of temperature for a model incorporating nearest- and next-nearest-neighbor interactions reproduce the experimental results and also provide an evaluation of the change in order parameter as a function of layer number for boundary conditions corresponding to a copper or a copper-gold surface.     

Control of branching ratio in the photofragmentation of DCl+ ions: Effect of initial vibrational state

Photofragmentation of DCl⁺ ions alternatively leads to the formation of D⁺ + Cl or Cl⁺ + D in competing reaction channels. The branching ratio of the product yields D⁺/Cl⁺ has been investigated theoretically by numerically solving coupled time dependent Schrödinger equations and experimentally by femtosecond (fs) dissociative ionization of DCl. The theoretical analysis shows that this branching ratio increases step-like at intensities, which characteristically depend on the initial vibrational state for nonresonant multiphoton excitation. In general the threshold decreases with increasing initial vibrational quantum number. Experimental studies exhibit a similar step-like behavior of the D⁺/Cl⁺ branching ratio. Here the intensity at which the step occurs characteristically depends on the chirp of the fs-laser pulses, suggesting that different chirp may lead to intermediate DCl⁺ ions differing in the effective vibrational quantum number.     

Dependence of phase dynamics of light interacting with two-level atoms on the initial state of atoms

We have studied the phase properties of initially coherent light interacting with two identical two-level atoms using the Hermitian phase operator of Pegg and Barnett. The results show that, in a certain initial state of the atoms, the field would, to a certain extent, preserve its order in phase, even for a long interaction time with the two atoms.     

Thermalization of the flow of sputtered target atoms during ion-plasma deposition of films

The boundary of the zone in which sputtered atoms are thermalized in the substrate–target drift space during the ion-plasma magnetron deposition of films is determined theoretically and experimentally. A comparison of the thicknesses of films deposited on the front and back sides of substrates situated at different distances from the target makes it possible to divide the flow of atoms sputtered toward substrates into direct and diffusion flows and to determine the dimensions of the spatial zone in which sputtered atoms are thermalized. The experimental data are in quantitative agreement with the results of a statistical simulation of the thermalization process of atomic particles during the ion-plasma deposition. This simulation enables optimization of the technology of defect-free growth of films with uniform thickness on substrates with complex 3D configuration.     

Experimental investigation of the energy distribution of sputtered excited target atoms bombarded by medium-energy ions

In this paper we experimentally investigate the parameter dependence of a model energy distribution of excited potassium atoms, knocked out by bombarding a KCl monocrystal with normally incident Ar⁺ ions, on the ion energy and the partial oxygen pressure in the chamber. On the basis of the obtained results a model of the energy distribution is proposed that corresponds to the kinetic formation mechanism for the excited atoms during the sputtering of the target.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 9–12, March, 1985.     

Calculation of the flow of sputtered atoms returning to a target with a surface relief during sputtering in glow discharge

A model is constructed that describes the transport of a sputtered substance near a target with a relief surface that is sputtered in glow discharge. For a periodic relief with small amplitude, distribution of a return flow of sputtered atoms from a discharge gap is calculated by a perturbation method. It is shown that nonuniform repeated deposition of the substance sputtered from the target could be one of the causes of formation of a relief on its surface.     

Influence of the chemisorption state on the charge distribution of low energy Si scattered from I adatoms

The ion fractions of 5 keV Si⁺ ions singly scattered from iodine adatoms adsorbed on Al(1 0 0), Si(1 1 1) and pre-oxidized Si(1 1 1) were measured with time-of-flight spectroscopy. A considerable ion yield was observed, which did not change significantly with exit angle or I coverage. The mechanism of ion formation is assigned to valence electron resonant charge transfer (RCT) assisted by promotion of the Si ionization level. The yields are smaller than those of Si scattered from Cs adatoms, however, which suggests that electron tunneling from the occupied chemisorption states of the I adatom provides an additional neutralization channel.     

Creation of quantum correlations between two atoms in a dissipative environment from an initial vacuum state

We have investigated the effect of counter-rotating terms on the dynamics of entanglement and quantum discord between two identical atoms interacting with a lossy single mode cavity field for a system initially in a vacuum state. The counter-rotating terms are found to lead to steady states in the long-time limit which can have high quantum discord, but have no entanglement. The effect of cavity decay rate on this steady-state quantum discord has been also investigated, surprisingly, the increase in cavity decay rate is found to enhance the steady-state quantum discord.     

Effects of substrate bias and nitrogen flow ratio on the surface morphology and binding state of reactively sputtered ZrNx films before and after annealing

ZrN_x films were sputtered in an Ar + N₂ atmosphere, with different substrate biases (0 to −200 V) at various nitrogen flow ratios (%N₂ = 0.5-24%). The surface morphology, resistivity, crystllinity, and bonding configuration of ZrN_x films, before and after vacuum annealing, were investigated. As compared with ZrN_x films grown without substrate bias, before and after annealing, the resistivity of 1% and 2% N₂ films decreases with increasing substrate biases. Simultaneously, if the applied bias is too high, the crystallinity of ZrN_x film will decrease. The surfaces of 1% and 2% N₂ flow films deposited without bias have small nodules, whereas the surface morphology of films deposited at −100 V of substrate bias exhibits large nodules and rugged surface. Once a −200 V of substrate bias is applied to the substrate, the surface morphology of ZrN_x films, grown at 1% and 2% nitrogen flow ratios, is smooth. Furthermore, there are two deconvoluted peaks in XPS spectra (i.e., Zr-O and Zr-N) of ZrN_x films deposited at −200 V of substrate bias before and after annealing. On the other hand, the surface morphology changes dramatically from rugged surfaces for film deposited at lower nitrogen flow ratio (%N₂ < 1%) to smoother and denser surfaces for film grown at higher nitrogen flow ratio (%N₂ ≥ 1%). The Zr-N bonding in 2% N₂ films still exist after annealing at 700 °C, while the Zr-N bonding in 0.5% and 16% N₂ flow film vanish at the same temperature. The connection between the resistivity, crystallinity, surface morphology, and bonding configuration of ZrN_x films and how they are influenced by the substrate bias and nitrogen flow ratio are discussed in this paper.     

Directed flow from global symmetry and initial state Fluctuations

Collective flow is studied in a 3+1D fluid dynamical model with globally symmetric, peripheral initial conditions, taking into account the shear flow. At $\sqrt {s_{NN} } $ = 2.76 TeV in semi-peripheral Pb+Pb collisions this leads to rotation, while at more peripheral collisions with high resolution and low numerical viscosity, the initial development of a Kelvin-Helmholz instability is observed. This effect provides a precision tool for studying the viscosity of Quark-Gluon Plasma.     

Deposition of sputtered iridium oxide—Influence of oxygen flow in the reactor on the film properties

Thin films of iridium oxide have been deposited by reactive magnetron sputtering. The influence of oxygen partial pressure in the sputtering plasma on the composition, surface structure and morphology of the films has been studied by XRD, SEM and AFM analysis. An optimal combination of sputtering parameters yields stable microporous amorphous films with highly extended fractal surface. The electrochemical properties of these films have been investigated in view of their application as catalysts for water splitting, using the electrochemical techniques of cyclovoltammetry, electrochemical impedance spectroscopy, and steady state polarization. The SIROFs have shown an excellent electrochemical reversibility and a high catalytic activity toward the oxygen evolution reaction in 0.5 M H₂SO₄. A current density of 150 mA cm⁻² at potential of 1.7 V (versus Ag/AgCl) has been obtained at catalyst load of only 100 μg cm⁻². These results combined with the established long-term mechanical stability of the sputtered iridium oxide films (SIROFs) proved the advantages of the reactive magnetron sputtering as simple and reliable method for preparation of catalysts with precisely controlled composition, loading, and surface characteristics.     

Enhanced anomalous diffusion of sputtered atoms in nanosized pores

Plasma sputtering deposition of platinum catalysts in porous anodic aluminum oxide (AAO) templates is shown to generate an anomalous superdiffusion concentration profile. The growth of an overlayer between the hexagonal array of pores is shown to enhance the diffusion into the pores, leading to a diffusion coefficient having superlinear time dependence. The Pt clusters in the pores have a mean size of 10 nm and almost concentrate on the inner pore surface, and are present up to a depth of 6 μm.     

Influence of isolated adatoms on surface electronic states

The electron spectrum of a crystal with an adsorbed centre is considered, using the mathematical techniques of the quantum mechanical theory of scattering. A special pole approximation is developed which is substantiated by specific features of the problem. Formulas are derived for the adsorption-caused changes of the thermodynamical characteristics and compared with the experimental data. The behaviour of the density of states as an adatom recedes away from the crystal is elucidated. The dynamic effects of surface states are considered using field emission as an example. The formula obtained is compared with experiment.     

Lateral manipulation of adatoms and native substrate atoms with the low-temperature scanning tunneling microscope

Received: 27 March 1998     

A simple calculation of the angular distribution of sputtered atoms

Angular distributions of atoms sputtered with fast ions from smooth amorphous targets are estimated by a straightforward treatment of the collision cascade. When the geometrical situation at oblique ion impact is considered, the angle of maximum emission and the sputtering yield in dependence on the angle of ion incidence are described.