Principles of invariant embedding in the problem of self-sputtering of solids

Principles of invariant embedding are applied to investigation into the phenomenon of self-sputtering of solids. Integral equations describing the flux of the sputtered atoms with regard for the boundary conditions are obtained. Approximate solutions to the integral equation for a function that describes the energy and angular spectra of the atoms escaping from the material surface in the case of self-sputtering are found.     

Self-sustained self-sputtering: a possible mechanism for thesuperdense glow phase of a pseudospark

Self-sustained self-sputtering occurring during high current pseudospark operation (≈10⁴ A/cm², I>10³ A) is shown to be a possible mechanism for the superdense glow. The mean-free-path for ionization of cathode material sputtered in the low-current hollow-cathode phase can be shorter than the cathode-anode gap distance, and ionized atoms can return to the cathode surface, self-sputtering with a yield greater than one. The self-sputtered cathode atoms become ionized in the beam of electrons accelerated in the cathode sheath. A large fraction of the discharge current at the cathode surface can be carried uniformly over the surface by ions and a very high electron emission density is not required to maintain the high current     

Emission Theory of the Sputtering of Amorphous Materials: Self-Sputtering

The dependences of the coefficient of self-sputtering on the type of accelerated ions, their energy, and the angle of incidence on a target are calculated. Satisfactory coincidence between the calculated and experimental results is obtained for С–С and W–W systems. Two mechanisms of the entry of secondary particles into a flow of sputtered atoms are proposed.     

Calculation of self-sputtering spectra of thin films by the discrete flow method

Self-sputtering of plane-parallel layers is described theoretically on the basis of the invariant immersion method combined with the discrete flow technique. Differential equations are derived for forward and backward self-sputtering functions, and exact solutions to these equations are obtained. Energy distributions of self-sputtered ions are calculated; total self-sputtering coefficients are compared to the results of computer experiment. The dependences of the total self-sputtering coefficients on the film thickness and the initial energy of ions are analyzed.     

Influence of motion of radiating particles on the concentration distribution at the boundary of a flat,semi-infinite layer

The distribution of excited atoms near the surface limiting the half space has been determined. The transfer of the excited state by two mechanisms, absorption and reradiation of photons and space motion, has been taken into account. An analytical solution has been found for the integral equation describing joint diffusion of the photons and particles. The concentration of excited atoms at the half-space boundary, determined after accounting for their space motion, may differ by orders of magnitude from the values obtained by solving the Biberman-Holstein equation.     

Effects of including the counterrotating term and virtual photons on the eigenfunctions and eigenvalues of a scalar photon collective emission theory

We find eigenmodes of an integral equation describing N 2-level atoms interacting with a scalar field, one atom being initially excited. Neglect of virtual field quanta would replace the correct kernel by its real part. This has serious consequences both for small and large samples.     

Distribution function for random interaction fields in disordered magnets: Spin and macrospin glass

Systems with an arbitrary dependence of exchange integral on the distance between atoms which are randomly scattered in an amorphous substance are investigated by averaging over random fields of interaction in the framework of the Ising model. This method is also used for describing long-term magnetization relaxation in a system of single-domain particles scattered in a nonmagnetic matrix. Random field distribution functions are obtained for the dipole-dipole and the Ruderman-Kittel-Kasuya-Yoshida (RKKY) interactions. Long-term relaxation in macrospin glasses is investigated.     

Evidence for self-sputtering during pulsed laser deposition of Zn

Thin films of Zn have been prepared by pulsed laser deposition with a KrF excimer laser (248 nm). The laser energy density (E.D.) on the target has been varied in the 1 to 5 J/cm² range. The results show that as the E.D. increases the material distribution changes. For low E.D.( 1.6 J/cm²) the maximum of the distribution is at the substrate center, for intermediate E.D. it is displaced to the side, and a clear minimum appears at the center of the substrate for the higher E.D. (4.5 J/cm²). The growth velocity at the center of the substrate reaches a maximum value for E.D. of 2.8 J/cm², and decreases for higher E.D. as a result of the competition between deposition and self-sputtering. Virtually a zero growth velocity is obtained for E.D. above 4.5 J/cm². The self-sputtering process is most likely responsible for the increase of the film surface roughness as a function of the laser E.D. The low cohesive energy for metal Zn, compared to other metals (Fe, Ag, Cu) is correlated with the high efficiency of the self-sputtering for this material. PACS 81.15.Fg, 68.55.Ac, 68.37.-d     

Collective electronically excited states of a uniform chain of atoms

Electronically excited states of finite uniform chains of atoms were considered taking into account the influence of the continuous energy spectrum. Traditional quantum-chemical methods for calculating two-electron transitions between neighboring chain atoms were combined with the asymptotic theory of interactions between excited atoms and neutral particles and the mathematical apparatus of the theory of multiple scattering for taking into account intercenter transitions in an ensemble of interacting centers. Recurrence equations for describing energy zones containing symmetrical and antisymmetric excited state levels of chains with an arbitrary length were obtained. Depending on system parameters, different modes of the distribution of the electron density of collective excited states were possible. At a certain ratio between level shifts and exchange integral values, excited states with a uniform electron density distribution over all chain nodes could form for certain solutions. This was a fortuitous circumstance caused by the influence of the continuous spectrum. Such states appeared at small principal quantum number n values, they were similar to one-electron excitations of the type of Frenkel excitons, when an electron was localized near its Coulomb center. These conditions were rapidly disturbed as n increased, and one-electron excitations of a linear molecule were formed in the system (that is, limiting excitations of the type of Wannier-Mott excitons did not form).     

金属目标原子晶格结构对其量子雷达散射截面的影响

量子雷达散射截面是描述光量子态照射下目标可见性的重要参数. 本文对量子雷达散射截面的推导进行了扩展, 使其可以应用于非平面凸目标的QRCS计算. 针对面心立方、体心立方以及密排六方三种金属原子晶格所构成的目标的量子雷达散射截面进行了计算, 结果表明不同的原子排列方式下, 目标QRCS主瓣基本不变, 而量子旁瓣在原子排列稀疏的目标中更为明显.     

Dependence of the self-sputtering yield upon ion incidence angle

Solution of the problem of angular dependence of sputtering yield is divided into three parts: calculation of the number of cascade particles as a function of their path length, definition of the path length distribution of reflected particles, and convolution of the two results obtained. The theory is valid for the case of equal ion and target atom masses (self-sputtering) and contains two parameters: the ratio of the transport path length to the mean free path length and the parameter of inelastic energy losses.     

Electron-Stimulated Desorption of Sodium and Potassium Atoms from Oxidized Tungsten

Technical Physics - We have analyzed electron-stimulated desorption (ESD) of neutral sodium and potassium atoms on oxidized tungsten. We propose a model describing ESD of atoms from the oxidized...     

The scattering of slow atoms by light

A kinetic equation has been obtained describing the motion of atoms in a resonant field of standing light wave. This equation is used to describe the scattering of atoms for conditions close to experimental ones [1]. It is shown that the dependence of atomic scattering has a dip at the resonance frequency of the field.     

AES analysis of nitridation of Si(100) by 2–10 keV N+2 ion beams

Ion beam nitridation of Si(100) as a function of N⁺₂ ion energy in the range of 2–10 keV has been investigated by in-situ Auger electron spectroscopy (AES) analysis and Ar⁺ depth profiling. The AES measurements show that the nitride films formed by 4–10 keV N⁺₂ ion bombardment are relatively uniform and have a composition of near stoichiometric silicon nitride (Si₃N₄), but that formed by 2 keV N⁺₂ ion bombardment is N-rich on the film surface. Formation of the surface N-rich film by 2 keV N⁺₂ ion bombardment can be attributed to radiation-enhanced diffusion of interstitial N atoms and a lower self-sputtering yield. AES depth profile measurements indicate that the thicknesses of nitride films appear to increase with ion energy in the range from 2 to 10 keV and the rate of increase of film thickness is most rapid in the 4–10 keV range. The nitridation reaction process which differs from that of low-energy (< 1 keV) N⁺₂ ion bombardment is explained in terms of ion implantation, physical sputtering, chemical reaction and radiation-enhanced diffusion of interstitial N atoms.     

Spatial and temporal effects upon deposition of particles onto thin films of silicon dioxide produced using high-energy deposition processes

The interaction of deposited atoms with a silicon dioxide film is simulated for the case of using high-energy processes for the deposition of optical nanocoatings. The method of molecular dynamics with a classical force field is used for describing the interaction between the atoms. The characteristic time of fast relaxation of the kinetic energy of the deposited atom and the characteristic depth of its penetration into the film are estimated. It is shown that the angular distribution of the velocities of the deposited atoms is significant for the formation of a coating.     

The effect of surface channeling of neutral atoms

Special features of reflection of neutral atoms from crystal surfaces are considered in the case of grazing incidence. It is shown that polarization effects and the long-range part of the potential of interaction of ions with atomic chains and planes can play an important role in describing processes of reflection of atoms from the surface. The analysis in this paper shows that the polarization of accelerated neutral atoms in the case of grazing incidence on the surface can lead to the formation of bound surface states. The threshold condition for the angle of arrival of atoms at the plane at which the capture by such states is possible is obtained.     

Relations between Varshni and Morse potential energy parameters

A set of relationships between the Morse and Varshni potential functions for describing covalent bondstretching energy has been developed by imposing equal force constant and equal energy integral. In view of the extensive adoption of Morse function in molecular force fields, this paper suggests two sets of parameter conversions from Varshni to Morse. The parameter conversion based on equal force constant is applicable for small change in bond length, while the parameter conversion based on equal energy integral is more applicable for significant bond-stretching. Plotted results reveal that the Varshni potential function is more suitable for describing hard bonds rather than soft bonds.      

Superradiance from three-level systems in atomic coherent state representation

A Fokker-Planck equation describing the coherent spontaneous emission from a system of 3-level atoms is derived using the atomic coherent states representation. The variables in this equation correspond directly to the number of atoms in the two excited states. The corresponding Langevin equations are discussed and their solutions for some special cases are presented.     

A method of determining the maximum in a deexcitation function

A method of determining a primary maximum in a deexcitation function is established analytically. An equation for describing the effective cross sections for the excitation and ionization of atoms by electron impact is obtained.     

Drastic deceleration of light pulses in atom traps: A semiclassical theory

The solution to the Maxwell-Bloch equations describing interaction of two light pulses with a gas of magnetically trapped cold atoms is used to establish fair quantitative agreement between theory and experimental results reported in [5]. The spacetime dependence of the probe-and coupling-pulse fields and nonlinear dynamics of atoms are analyzed.