Pt(111)表面低能溅射现象的分子动力学模拟

利用嵌入原子方法的原子间相互作用势，通过分子动力学模拟，详细研究了贵金属原子在Pt (111)表面的低能溅射现象.模拟结果显示：对于垂直入射情况，入射原子的质量对Pt (11 1)表面的溅射阈值影响不大.当入射原子的能量小于溅射阈值时，入射原子基本以沉积为主 ；当入射原子的能量大于溅射阈值时，溅射产额随入射原子能量的增加而线性增大；当入射 原子能量达到200 eV时，各种入射原子的溅射产额都达到或接近1，此时入射原子主要起溅 射作用.溅射原子发射的角分布概率和溅射花样与高能溅射相类似.研究表明：与基于二体碰 撞近似的线性级联溅射理论不同，当入射原子能量大于溅射阈值时，低能入射原子的溅射产 额正比于入射原子的约化能量和入射原子与基体原子的质量比.通过对低能入射原子的钉扎 能力分析，提出了支配低能溅射的入射原子反射物理机理. 关键词： 分子动力学模拟、低能溅射     

Tuning the lifetime of the surface plasmon upon sputtering

The lifetime of the surface plasmon in sputtered Ag ultrathin films on Cu(111) was investigated by high‐resolution electron energy loss spectroscopy measurements. The linewidth of the surface plasmon was found to follow a square‐root dependence on the fluence. Such finding allows the tuning of the lifetime of the plasmonic excitation upon sputtering and has general implications in plasmon‐based spectroscopies and in plasmon‐mediated processes across the films and at their surfaces. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Interaction of low-energy Cu2 dimers with copper clusters on the graphite surface

The sputtering of clusters consisting of 13, 27, and 75 copper atoms from the (0001) graphite surface under bombardment by Cu₂ dimers with energies of 100, 200, and 400 eV has been simulated using the molecular dynamics method. A comparative analysis of the distributions of backscattered particles and their energies over polar angles and the energy distributions of sputtered atoms has been performed. The factors responsible for the large sputtering yield from surface clusters under their bombardment with dimers as compared to copper and xenon monomers have been discussed. It has been demonstrated that, in the case of bombardment with dimers, the substantial role in the sputtering of surface clusters is played by the overlap of collision cascades initiated by each atom of the incident dimer. The differences in the sputtering under cluster and atom bombardments are especially pronounced in the case of large surface clusters.     

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.     

Sputtering of Cu atoms by Ar ions

Sputtering of Cu single-crystal, polycrystal and amorphous targets by 5 keV Ar ions has been studied by the binary collision lattice simulation code Cosipo. The sputtering yields, angular distributions, energy distributions and the space distributions of the original positions of the sputtered Cu atoms have been calculated. The results are discussed within the framework of cascade generations and surface structure.     

Angular distributions of Au and Cu atoms sputtered from Au-Cu alloys by keV Ar+ ion bombardment

Angular distributions of Au and Cu atoms sputtered from Au-Cu alloys under 3 keV AR⁺ ion bombardment were measured to understand the preferential sputtering. The surface composition of sputter-deposited Au-Cu films on substrates mounted at different ejection angles was analyzed by Auger electron spectroscopy and electron probe microanalysis. Although the result indicated that the proportion of sputtered Cu atoms to the Au atoms in the Au-Cu alloy depends on the ejection angle, marked enhancement of the lighter component in the direction normal to the surface has not been observed in spite of the larger mass ratio of the constituent atoms of the Au-Cu alloy.     

Sputtered atom transport processes

It is noted that the transport of sputtered atoms can be described in terms of three pressure regimes: low pressure, where no collisions occur during the trajectory of the atom; intermediate pressure, where the atom undergoes perhaps several collisions but does not completely thermalize; and high pressure, where the sputtered atom effectively stops and begins a density-gradient-driven conventional gas-phase diffusion process. The intermediate region is the most complicated to model, given the dependence of the energy on the collision cross-section, the various distributions in energy and angle of the sputtered atoms, and the extended nature of most sputtering sources. Experimental studies reported here have measured the transport probability by observing the distribution of atoms around a chamber following sputtering. The transport is found to be quite dependent on the mass of both the sputtered atom and the background gas, as well as the particle density and geometry of the vacuum system. A strong effect of sputtered-atom-induced gas rarefaction has also been observed. This results in power-dependent transport of sputtered atoms, and as a result may also lead to power-dependent compositional variation in alloy depositions. The general result is that high discharge powers tend to correlate with lower power operation at a significantly lower operating pressure than had been assumed     

Analytical calculation of atom ejection from the Ni (111), Ni (001), and Au (001) surfaces in frames of a three-dimensional model

Atom ejection from lattice sites at the Ni (111) and Ni (001) surfaces in the azimuthal direction toward the center of a lens consisting of two nearest neighboring atoms in the surface plane is calculated using a developed analytical three-dimensional model. The types of scattering of ejected atoms are classified in frames of the constructed model. It is found that the first and second ejection cones are observed in the sputtering pattern in the case of atom ejection from the Ni (111) surface and that the contribution of strongly blocked atoms to sputtering is considerable. The focusing of sputtered atoms at some angle from the surface normal is observed. A maximum of the polar angular distribution of sputtered atoms is shifted nonmonotonically as the energy increases. It is shown that the energy spent by the ejected atom on the recoiling of the lens atoms can be larger than that spent by this atom to overcome the potential barrier. It is found that small changes in the potential hardness and the binding energy at the magnetic phase transition can lead to a qualitative change in the ejection pattern. The expressions for the final ejection angle and energy in the case of Ni in the f-state are found in the form of an expansion in terms of two small parameters. As one passes from the case of atom ejection from the Ni (001) face to the case of atom ejection from the Au (001) face, the interaction cross section increases significantly because of an increase in the atomic number and the effects of blocking and focusing turn out to be considerable.     

Sputtering—a review of some recent experimental and theoretical aspects

After a brief outline of the present sputtering theory for a random solid, recent results of the sputtering yieldS for polycrystalline targets are discussed, in particular in view of the influence of the projectile mass and the bombarding angle. The angle dependence ofS at low bombarding energies, and results on the angular distribution of sputtered particles for oblique ion incidence point out necessary modifications of present sputtering theories with respect to the anisotropy of the collision cascades in the solid and the influence of the target surface. The energy distribution of the neutral particles ejected along the target normals is related to the theoretically predictedE ^?2-distribution of low energy recoils in the Recent mass spectrometric studies of postionized sputtered neutrals are discussed in view of the formation of sputtered molecules and the application of sputtered neutral mass spectroscopy for surface analysis. Finally, the paper deals with ion-induced surface effects on non-elementary sputtering targets, and the protracted removal of foreign atoms from a matrix.     

A comparison of radiation from sputtered atoms with radiation from projectiles scattered on oxidized magnesium at varying angle of incidence

The intensity of light emitted from sputtered atoms and neutralized, scattered primary ions, excited during 4 keV Ne⁺ and Ar⁺ bombardment of oxidized magnesium has been measured as a function of the incidence angle. It was found that the photon yield of sputtered atoms increases with the angle of incidence much more rapidly than the theoretical sputtering yield and the photon yield of scattered projectiles. In order to explain the experimental results a numerical approach was made based on the following assumptions: (1) the sputtered atom can be excited when it crosses the surface after getting the momentum from the collision cascade; (2) at oblique incidence the sputtered excited atom can be directly emitted after a gentle collision between the incident ion and the surface atom; (3) the neutralized primary ion can only be excited in a violent collision with the surface atom.     

Progress in instrumentation,data reduction,and depth profiles in Auger electron spectroscopy

Progress in the use of Auger electron spectroscopy is discussed. Specifically limits to spatial resolution in the scanning Auger microprobe resulting from backscattered electrons is illustrated. Determination of chemical state by peak shapes and energies are discussed along with the use of correction factors in quantitating Auger electron data. Finally, the use of inverse Laplace transforms of angle-resolved electron spectroscopy data to generate composition depth profiles of sputtered GaAs is illustrated. It is concluded that Gibbsian surface segregation during sputtering caused depletion of As near the surface of GaAs.     

Al-50wt% Sn合金的离子溅射研究

用捕获膜技术和卢瑟福背散射(RBS)分析,测定Al-Sn多相合金在30keV Ar⁺离子轰击时Al和Sn的溅射原子角分布。溅射后的样品用扫描电子显微镜(SEM)进行观察,并用电子微探针分析仪(EPMA)对轰击样品(靶点)和未轰击样品作成分分析。结果表明,Al的溅射原子角分布近于cosine形状,而Sn却是over-cosine型角分布。本文给出一个按不同表面形貌特征划分的各元素富集区i进行叠加的产额表达式,Y(θ)=∑Y_i(θ),解释了实验结果。 关键词：     

Dynamical Analysis of Sputtering at Threshold Energy Range： Modelling of Ar＋Ni（100） Collision System

The sputtering process of Ar＋Ni（100） collision systems is investigated by means of constant energy molecular dynamics simulations. The Ni（100） slab is mimicked by an embedded-atom potential, and the interaction between the projectile and the surface is modelled by using the reparametrized ZBL potential. Ni atom emission from the lattice is analysed over the range of 20-50 eV collision energy. Sputtering yield, angular and energy distributions of the scattered Ar and of the sputtered Ni atoms are calculated, and compared to the available theoretical and experimental data.     

Point-defect properties of,and sputtering events in,the {001} surfaces of Ni3Al. II. Sputtering events at and near surfaces

Atomic recoil events at and near {001} surfaces of Ni₃Al due to elastic collisions between electrons and atoms have been simulated by molecular dynamics to obtain the sputtering threshold energy as a function of atomic species, recoil direction and atomic layer of the primary recoil atom. The minimum sputtering energy occurs for adatoms and is 3.5 and 4.5?eV for Al and Ni adatoms on the Ni–Al surface (denoted ‘M’), respectively, and 4.5?eV for both species on the pure Ni surface (denoted ‘N’). For atoms within the surface plane, the minimum sputtering energy is 6.0?eV for Al and Ni atoms in the M plane and for Ni atoms in the N surface. The sputtering threshold energy increases with increasing angle, θ, between the recoil direction and surface normal, and is almost independent of azimuthal angle, ?, if θ<60°; it varies strongly with ? when θ>60°, with a maximum at ??=?45° due to ?{110}? close-packed atomic chains in the surface. The sputtering threshold energy increases significantly for subsurface recoils, except for those that generate efficient energy transfer to a surface atom by a replacement collision sequence. The implications of the results for the prediction of the mass loss due to sputtering during microanalysis in a FEG STEM are discussed.     

Properties of indium phosphite and selected compounds under irradiation with swift heavy ions

Surface and bulk properties of indium phosphate single crystals with initial and previously irradiated by 25 MeV electrons structures were irradiated with ⁸⁶Kr (253 MeV) and ¹⁹⁷Au (200 MeV) up to various fluences. The modern methods of condensed matter studies were used for research of InP property changes before and after irradiation as scanning (SEM) and high resolution transmission electronic microscopy (HTEM), Rutherford backscattering spectroscopy (RBS/C) and atomic force microscopy (AFM). The comparison of obtained results with the results of other authors is carried out. The surface structure change of InP single crystal irradiated by high-energy 86Kr ions and electrons is studied. It is shown the changes of the InP surface have complicated character and caused by inelastic sputtering processes. It is observed the twice irradiated layer swells with the cracks creation on the surface. The swelling with cracks and strong sputtering of twice irradiated by electrons and ions with high energy layers of the InP and GaAs surfaces are explained using the model based on the influence of ionizing energy loss of swift ⁸⁶Kr ions. The small crystalline objects are detected on the InP surface irradiated with ⁸⁶Kr ions which may be nano- and micro-crystals of InP. All obtained effects are discussed in frame of models based on ionizing energy loss of swift heavy ions.     

离子轰击引起的表面形貌对Ag的溅射产额的影响

用捕获膜技术和卢瑟福背散射(RBS)谱仪测定Ag靶在27keV Ar⁺离子轰击下的溅射原子角分布,从而确定不同剂量下Ag的溅射产额,并对其靶点表面形貌进行扫描电子显微镜(SEM)观察。结果发现,所有的角分布都呈over-cosine形状,但其溅射产额却随着表面形貌不同而不同。根据溅射产额Y与轰击离子入射角φ变化关系,讨论不同轰击剂量下溅射产额的差别,肯定了表面形貌是影响溅射产额的一个重要因素,并由此提出“表观产额”的新概念。 关键词：     

Precise atomic scale studies of material sputtering by light-ion gases in the prethreshold energy region

The basis and prospects of a new original technique of determining the yields of the sputtering of conductive materials and subatomic films on their surface by light ion gases in the prethreshold energy region (from 10 to 500 eV) are discussed. This information is of great importance both for science and applications. The technique is based on special modes of field ion microscopy and includes the cleaning of specimens by field-induced desorption and evaporation, and subsequent operations with the atomically clean and atomically smooth surface in a wide temperature range from cryogenic temperatures. The technique enables one to identify single surface vacancies, that is, to directly count single sputtered atoms. The original results obtained with the developed technique are briefly reviewed. The energy thresholds of sputtering and the energy dependences of the sputtering yields in the prethreshold energy region are presented and analyzed for beryllium, tungsten, tungsten oxide, mixed tungsten-carbon layers, three carbon materials, and subatomic carbon films on the surface of certain metals bombarded by hydrogen, deuterium, and/or helium ions.     

Model for the emission of quasi-thermal atoms during sputtering of metals in the nonlinear collision cascade regime

The ion sputtering of metals and frozen inert gases in the nonlinear collision cascade regime, where the density of the energy released in the bulk of the thermal peak exceeds the critical medium temperature, initiates the emission of quasi-thermal atoms. The energy spectrum of such atoms is substantially shifted toward low energies and is not described by a Maxwellian distribution. A simple emission model is proposed on the assumption of collisional motion of sputtered atoms in their flight from a target, and this model is used to derive an analytical formula for the calculation of the energy spectra of quasi-thermal atoms. A comparison of the calculated energy spectra of indium, krypton, and xenon atoms and the spectra measured during ion sputtering of indium and frozen inert gases in the nonlinear collision cascade regime shows their agreement at reasonable values of fitting parameters.     

Molecular dynamics study of sputtering of Cu (111) under Ar ion bombardment

Abstract

We have used the molecular dynamics (MD) technique using many-body interaction potentials to analyse in detail the processes leading to sputter emission, in order to gain a microscopic understanding of low energy bombardment phenomena. Calculations were performed for a Cu (111) single crystal surface bombarded with Ar atoms in the energy range from 10–1000 eV. The results presented for low bombarding energies are mainly concerned with the near sputtering threshold behaviour, yields and depth of origin of sputtered atoms. Furthermore, it is found, that in addition to sputtered atoms, a large number of ad-atoms at the surface are generated during the evolution of the collision cascade. At higher energies the question of cluster emission and especially their energy distribution and angular distribution are addressed. It was found that the energy distributions for the dimers and monomer atoms exhibit a similar dependence on emission energy as has been observed recently also experimentally. For atoms good agreement with the theoretical Sigmund-Thompson energy distribution was observed. However, for dimers we found that the energy distributions exhibit an asymptotic behaviour at high energies with E^?3 rather than with E^?5, as predicted in previous modelling of cluster emission. Concerning the angular distributions six emission spots, three strong ones in the <110> and three weak ones in the <100> direction were found for atoms, but for dimers only emission spots in the <110> direction were observed, in agreement with experimental results.     

替位杂质对低能Pt原子与Pt(111)表面相互作用影响的分子动力学模拟

采用嵌入原子方法的原子间相互作用势，通过分子动力学方法模拟了低能Pt原子与Cu，Ag，Au，Ni，Pd替位掺杂Pt(111)表面的相互作用过程，系统研究了替位原子对表面吸附原子产额、溅射产额和空位缺陷产额的影响规律，分析了低能沉积过程中沉积原子与基体表面的相互作用机理以及替位原子的作用及其影响规律.研究结果显示：替位原子的存在不仅影响着沉积能量较低时的表面吸附原子的产额与空间分布，而且对沉积能量较高时的低能表面溅射过程和基体表面空位的形成产生重要影响.替位原子导致的表面吸附原子产额、表面原子溅射以及空位形 关键词： 分子动力学 低能粒子 替位掺杂 表面原子产额 溅射 空位