Self-sputtering of thin films (Application of the invariant immersion method)

The analytic solution to the problem of self-sputtering of thin homogeneous films is considered. Invariant immersion principles were used for deriving integral equations describing the flow of sputtered atoms. Approximate solutions of the integral equation are found for the functions describing the spectra of atoms emitted from the film surface in the case of self-sputtering.     

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.     

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     

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.     

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.     

Sputtering-yield studies on silicon and silver targets

The sputtering yield of vacuum-deposited silicon and silver targets has been measured with 15 different 45-keV ions throughout the periodic system. The dependence of the yield on the projectile atomic number follows rather closely Sigmund's prediction, especially for silicon. The self-sputtering yield of silver was measured in the 30–500 keV energy range. Similar to what is known to be the case for other heavy particles on silver, the maximum of the yield was found to be much more pronounced than predicted by Sigmund's theory. This effect, together with small systematic deviations in the Z₁ dependence, is explained as being caused by non-linear effects in very dense collision cascades. This point of View is strongly supported by a comparison of the sputtering yield per atom for irradiation with atomic and molecular ions.     

Classical molecular dynamic simulation of (111) Si and Al surface sputtering under bombardment by polyatomic clusters

The self-sputtering processes of (111) Si and Al surfaces under bombardment by Si _N and Al _N ions and clusters (N = 1−60) with the same energy per particle-projectile atom (1 keV/atom) are studied in this paper. The nonlinear effects produced in the target during the development stage of an atomic-collision cascade and during the postcascade stage are analyzed, and a correlation between these effects and secondary emission characteristics is found. The study has been carried out in the framework of classical molecular dynamics. As a result, a number of features of (111) Si and Al surface sputtering and erosion have been revealed. Thus, it has been established that the sputtering yield increases nonadditively as the size N of the implanted cluster increases at N > 10, which is related to the appearance of nonlinear cascades and the postcascade heat spike, and is accompanied by microcrater formation. It is shown that the implantation of clusters into the Si target leads to the formation of amorphous regions.     

高压耦合高功率脉冲磁控溅射的增强放电效应

等离子体源离子注入与沉积技术作为一种可生产高结合力、高致密度涂层的真空镀膜技术,具有广阔的应用前景,尤其适用于高载荷工况下服役的功能涂层制备.该技术中金属等离子体源是关键,而现有的脉冲阴极弧源结构复杂,且由于伴随"金属液滴"而需要增加过滤装置.本文研究了另一种简单结构的金属等离子体源备选一高功率脉冲磁控溅射源(HPPMS)的放电特性,采用等离子体发射光谱仪探索了不同的耦合高压对HPPMS放电靶电流特性和等离子体特性的作用.发现耦合高压对HPPMS放电有明显的促进作用,相同靶电压下的放电强度大幅增加,相对于金属放电,耦合高压对气体放电的促进作用更加明显,但在自溅射为主的高压放电阶段对金属放电的促进作用明显增强.讨论了耦合高压对HPPMS放电的增强机制,发现耦合高压自辉光放电、耦合高压和HPPMS电压构成双向负压形成的空心阴极效应,以及耦合高压鞘层改善的双极扩散效应都对HPPMS放电的增强有明显作用.     

Simultaneous magneto-optical trapping of a boson-fermion mixture of metastable helium atoms

We simultaneously confine fermionic metastable 3He atoms and bosonic metastable 4He atoms in a magneto-optical trap. The trapped clouds, containing up to 1.5 x 10(8) atoms of each isotope, are characterized by measuring ions and metastable helium atoms escaping from the trap. Optical pumping of 3He atoms to a nontrapped hyperfine state is investigated and it is shown that large atom numbers can be confined without additional repumping lasers. Unique possibilities for quantum degeneracy experiments with mixtures of spin-polarized metastable 3He and 4He atoms are indicated.     

(Ga,Mn)As 体系中Mn自补偿效应的第一性原理研究

基于密度泛函理论的赝势平面波方法计算了处于填隙位置磁性原子(MnI)对(Ga,Mn) As体系电子结构和磁性的影响. 计算结果表明MnI在GaAs中是施主；代替Ga位的MnGa 与MnI的自旋按反铁磁序排列；静电相互作用使MnGa，MnI倾向于形成MnGa_MnI对. MnI的存在一方面补偿了(Ga,Mn)As中的空穴，降低了空穴浓度；同时还使邻近的MnG a失活. MnI的存在对获得高居里温度的(Ga,Mn)As是极为不利的. 关键词： (Ga Mn)As 稀磁半导体 密度泛函理论     

Simulation of surfactant effects on the growth of metal homoexpitaxial Sb-Ag/Ag(111)

A kinetic Monte Carlo simulation is performed in order to study the effect of Sb atoms as a surfactant on the growth of Ag on Ag(111).In our model the repulsive mechanism in which the surfactant Sb atoms repel diffusing Ag adatoms,and the exchange mechanism between Ag and Sb atoms,are considered.Our simulations show that the effects of Sb atoms for Ag/Ag(111) growth system are mainly to increase the chances for Ag atoms to overcome the Ehrlich-Schwoebel barrier both in the interlayer growth and along the edge diffusion.The influence of the coverage of Sb atoms and substrate temperature on the growth of Ag/Sb/Ag(111) is discussed.     

Effects of dipole-dipole interaction on entanglement transfer

A system consisting of two different atoms interacting with a two-mode vacuum, where each atom is resonant only with one cavity mode, is considered. The effects of dipole-dipole （dd） interaction between two atoms on the atom-atom entanglement and mode--mode entanglement are investigated. For a weak dd interaction, when the atoms are initially separable, the entanglement between them can be induced by the dd interaction, and the entanglement transfer between the atoms and the modes occurs efficiently; when the atoms are initially entangled, the entanglement transfer is almost not influenced by the dd interaction. However, for a strong dd interaction, it is difficult to transfer the entanglement from the atoms to the modes, but the atom-atom entanglement can be maintained when the atoms are initially entangled.     

Regularities and mechanisms of hydrogen trapping in graphitized carbon composite upon irradiation by atoms with thermal velocities

Experiments are performed to study particle trapping in a graphitized carbon composite upon its exposure to a flux of deuterium atoms. It is shown that irradiation by deuterium atoms with thermal velocities ensures trapping according to a potential mechanism: atoms of the irradiating flux and hydrogen atoms from a layer of water molecules sorbed on the surface are both trapped. Mechanisms of trapping are discussed. Based on the experimental results, the contribution to deuterium-atom trapping in CFC irradiated in deuterium plasma is determined for each component-ions, electrons, and atoms.     

Probabilistic teleportation of an arbitrary pure state of two atoms

In the context of microwave cavity QED, this paper proposes a new scheme for teleportation of an arbitrary pure state of two atoms. The scheme is very different from the previous ones which achieve the integrated state measurement, it deals in a probabilistic but simplified way. In the scheme, no additional atoms are involved and thus only two atoms are required to be detected. The scheme can also be used for the teleportation of arbitrary pure states of many atoms or two-mode cavities.     

Computation of vector coupling coefficients for atoms with one and two open shells in the Hartree–Fock approximation

A new way to introduce and calculate vector coupling coefficients (VCCs) is proposed for computations in a Hartree–Fock approximation of atoms with one and two open shells. In the case of atoms with one open shell (Roothaan method), the obtained formulas for VCCs are applicable to the calculation of all terms of such atoms without exception. The VCCs are also calculated for a number of configurations of atoms with two open shells (Huzinaga method). The correctness of the obtained VCCs is confirmed by numerous calculations of energies and dipole polarizabilities for atoms with one and two open shells.     

A new handshaking of Tight-Binding and Molecular Dynamics in multi-scale simulation

A new handshake scheme is presented for tight-binding (TB) and molecular dynamics (MD) for multi-scale simulation of covalent crystals. In the present scheme, when calculating the forces on MD atoms in the handshake region, the TB atoms in close proximity to the MD atoms are treated as MD atoms. The scheme is thus seamless for calculation of MD atoms. When determining the electronic states of the TB subsystem, instead of the four basic atomic orbitals, hybrid orbitals are employed as bases in TB method and also as representing the action of MD atoms on TB atoms. The present handshaking methodology has several advantages. Firstly, it avoids determining the physical parameters required by introducing a new orbital model. Secondly, the “seam” almost decreases by one order of magnitude compared to that of Silogen model. Thirdly, the whole scheme is stable for dynamic simulation.     

速度调控的双原子纠缠

当光学腔中光场处于相干态,而原子处于运动中时,双原子的纠缠演化与光学腔场模结构相关联. 假如初始时刻原子的位置固定在腔中某一位置,双原子的纠缠演化将是无序的.然而,假如一开始双原子在光学腔相干态光场中处于运动状态,则双原子的纠缠随时间的变化将变得规则有序.如此,通过适当的选择双原子的速度和初始光场,就能对双原子的周期性纠缠进行控制,让纠缠在指定时刻出现.     

Ab initio study of the fcc-WC(1 0 0) surface and its interaction with cobalt monolayers

The WC(1 0 0) surface has been studied by using ab initio methods of the density functional theory and pseudopotentials. Calculations have shown that surface and undersurface atoms move from their bulk positions. Namely, carbon atoms moved outward, while tungsten atoms moved inward. Five geometric cases for Co/WC(1 0 0) system were compared: (A) Co atoms are above C atoms; (B) Co atoms are above W atoms; (C) Co atoms are in the four-fold sites above WC pairs; (D and E) Co atoms are above the W-W-C and C-C-W three-fold sites, respectively - and the (A) case has been found to be energetically preferable. In all cases, Co layers have been found to be ferromagnetic. The densities of states for the bulk fcc-WC, the WC(1 0 0) surface, and the WC/Co system were compared.