Artifacts in the sputtering of inorganics by C60

In the present study, the basic issues in C₆₀ⁿ⁺ sputtering are studied using silicon, gold and platinum samples. Sputtering yields are measured for energies in the range of 5-30 keV, by sputtering micrometre sized craters on the surface of flat clean samples and measuring their volumes using atomic force microscopy (AFM). Net deposition of carbon occurs for all three materials at 5 keV, and is not specific to silicon which forms a carbide. The threshold energy for net sputtering is dependent on the sputtering yield and the stopping power of the substrate. Away from the threshold, the sputtering yields agree well with Sigmund and Claussen's thermal spike model after allowance for the sputtering of the deposited carbon atoms. AFM images show the formation of unusual surface topography around the transition region between sputtering and deposition. Analysis of the bottom of a crater using imaging SIMS shows a significant enhancement of carbon clusters as well as various silicon-carbon groups, indicating the importance of carbon deposition and implantation in a gradual mixed layer formed from sputtering. The thickness of this interface layer is shown to be approximately 5 nm.     

kinetic energy reflection from polycrystals bombarded with Ar+, Kr+, and Xe+ ions

When the surface of a solid is bombarded with ions a fraction of the primary energy is reemitted by ion reflection and sputtering. The contribution of ion reflection or sputtering to energy reflection is determined by the mass ratio of the bombarding ions to the target atoms.^1,2 In the case of light ions the contribution of reflected ions is dominant. Results for He⁺ and Ne⁺ bombardment were described in a previous paper.³ The present paper deals with results for Ar⁺, Kr⁺, and Xe⁺ bombardment of the same targets as investigated before.³ The energies of the mass selected bombarding ions range from 9 to 16 keV. The measurements were carried out by means of the thermic detector described in a separate paper.⁴ For the given mass ratios most of the reemitted energy is related to sputtering.     

Sputter yields in diamond bombarded by ultra low energy ions

Artificial diamond is an ideal material for high power, high voltage electronic devices, and for engineering use in extreme environments. Diamond process development requires parallel development in characterization techniques such as ultra low energy SIMS (uleSIMS), especially in the ability to depth profile for impurities and dopants at high depth resolution.As a contribution to the background knowledge required, we have measured the sputter yields of single crystal high pressure high temperature (HPHT) diamond using O₂⁺, Cs⁺ and Ar⁺ primary ions in the energy range 300 eV to 2 keV. We compare these with yields for silicon and GaAs. We show that the erosion rates with oxygen are ∼10 times what would be expected from ballistic processes and essentially energy independent in the measured range. This result agrees with the anomalously high sputter yield observed in the ion etching context. Conversely, positive ion yields for elements such as boron are very low in comparison with silicon. This points to a reactive ion etching process liberating CO or CO₂ rather than sputtering as the principal erosion process.This is both problematic and beneficial for SIMS analysis. Oxygen can be used to reach buried structures in diamond efficiently, and the effects of the near-normal incidence beam are planarizing as they are in silicon. Conversely, since positive ion yields are low, alternative probes or strategies must be found for high sensitivity profiling of electropositive elements.     

Yields of H+ and He+ at the energy for elastic scattering from H2+3He+ incident on Ag and Pd

Yields, Y, of H⁺ and He⁺ emerging specularly with the energy for single binary elastic collisions have been measured from polycrystalline Ag and Pd surfaces bombarded with mixed monoenergetic (300 < E₀ < 2600 eV) beams of H₂⁺³He⁺ impinging at an angle of 45° from the surface normal. The surfaces were exposed to H₂⁺ at a dynamic pressure of 8 × 10^?3 Pa (6 × 10^?5 Torr) during the measurements. The He⁺ yields from Pd are slightly larger than from Ag, and the H⁺ yields from Pd are 10 to 40 times as large as those from Ag. These results suggest that differences between Pd and Ag in the amount of hydrogen adsorbed and in the character of the hydrogen-metal bond may be responsible for the yield differences through shadowing by, and possibly the sputtering of, adsorbed hydrogen. The Y versus E₀ curves for all four systems have qualitatively the same singly peaked shape which implies that reactive and noble gas ions undergo similar neutralization processes during elastic surface collisions. The ratios of the yields from Ag and Pd do not exhibit the theoretically expected exponential dependence on collision time over the entire range studied, but at the lowest energies the ratios lead to estimates of the difference of neutralization constants which do agree with theory. The potential utility of the large difference in proton yields from Ag and Pd for studying the Ag-Pd alloy system is noted.     

Ion sputtering of minerals and glasses: a first step to the simulation of solar wind erosion

Selected rockforming minerals (plagioclase, augite, olivine, ilmenite, silicate and metal phases of the meteorite “Brenham”) as well as silicate and phosphate glasses were irradiated with heavy ions (⁴He⁺, ¹⁴N+, ²⁰Ne⁺, ⁴⁰Ar+, ⁵⁶Fe+, Xe⁺ _nat) in the energy range of 50-130 keV in order to study ion-induced sputtering. Sputtering yields were measured independently by means of multiple beam interferometry and particle track autoradiography.

The theory of sputtering by Sigmund, modified by Smith, was used to convert experimental heavy ion sputtering yields to H⁺- and He⁺-sputtering yields of the same target. Taking into account solar wind irradiation conditions at the lunar surface, an estimate of lunar erosion rates due to solar wind sputtering is given for the targets studied.     

Measurement of lifetimes for high spin states in 152Sm, 154Gd and 156Gd by the Doppler broadened lineshape method

Lifetimes of the ground band levels up to spin 10⁺ in ¹⁵²Sm, ¹⁵⁴Gd and ¹⁵⁶Gd have been measured by the Doppler broadened lineshape (DBLS) analysis of peaks observed following Coulomb excitation of enriched metallic targsts by 132–143 MeV ³⁵Cl beams. The γ-ray lineshapes were measured in time coincidence with backscattered ions and were analyzed with a computer program incorporating tabulated electronic stopping powers. The nuclear stopping power of Lindhard et al and multiple scattering treatment by Blaugrund were assumed. Renormalization of the electronic stopping powers given by Northclifie and Schilling was found necessary to reproduce the accurately known lifetime of the 6⁺ state in ¹⁵²Sm. Stopping powers for Sm in Sm inferred from the tabulated ⁴He stopping power of Ziegler and Chu support this renormalization. The stretching parameter a derived from the lifetimes of the ground band are (2.0 ± 0.6) × 10^?3, (1.85 ± 0.40) × 10^?3 and (0.0 ± 0.45) × 10^?3, in ¹⁵²Sm, ¹⁵⁴Gd and ¹⁵⁶Gd, respectively.     

Experiments on the sputtering of neutral Cu2 dimers from Cu by Ar+ ions (60–300 eV)

A planar polycrystalline copper target was bombarded normally by Ar⁺ ions with energies ranging from 60 to 300 eV. in the source of a mass spectrometer. The neutral particles sputtered normally from the target were post-ionized and analyzed in the mass spectrometer. A thermionically sustained, magnetically confined low pressure arc plasma was used to supply the bombarding ions, and for post-ionization of the neutral sputtered species. It was found that the relative yields of the sputtered neutral post-ionized Cu₂ dimers are linearly proportional to S², where S is the total sputtering yield for Ar⁺ -Cu. The results support the recombination model for the formation of neutral dimers in sputtering.     

Aluminum-assisted crystallization and <Emphasis Type="Italic">p</Emphasis>-type doping of polycrystalline Si

Aluminum-doped p-type polycrystalline silicon thin films have been synthesized on glass substrates using an aluminum target in a reactive SiH₄+Ar+H₂ gas mixture at a low substrate temperature of 300 °C through inductively coupled plasma-assisted RF magnetron sputtering. In this process, it is possible to simultaneously co-deposit Si–Al in one layer for crystallization of amorphous silicon, in contrast to the conventional techniques where alternating metal and amorphous Si layers are deposited. The effect of aluminum target power on the structural and electrical properties of polycrystalline Si films is analyzed by X-ray diffraction, Raman spectroscopy, scanning electron microscopy and Hall-effect analysis. It is shown that at an aluminum target power of 100 W, the polycrystalline Si film features a high crystalline fraction of 91%, a vertically aligned columnar structure, a sheet resistance of 20.2 kΩ/□ and a hole concentration of 6.3×10¹⁸ cm⁻³. The underlying mechanism for achieving the semiconductor-quality polycrystalline silicon thin films at a low substrate temperature of 300 °C is proposed.     

A new technique for the measurement of sputtering yields

We have measured the yields of 90 keV ⁴⁰Ar⁺ and V⁴He⁺ sputtering of Mo and V samples by the use of a new radio-tracer technique. This technique involves activating the samples by high-energy charged-particle irradiation before sputtering, and using conventional γ-ray counting methods to analyze the material subsequently sputtered onto collector foils. We have also measured angular distributions of the sputtered material, and compared these results and our total sputtering yields with the predictions of Sigmund's sputtering theory. Further comparisons between our radiotracer results and those obtained for ⁴⁰Ar⁺ sputtering of unactivated Mo and V samples, determined from elastic backscattering measurements using 12 MeV ¹⁶O ions, show that the techniques give consistent results.     

Cluster ion emission from LiF induced by MeV N<Superscript>q+</Superscript> projectiles and <Superscript>252</Superscript>Cf fission fragments

Ion cluster desorption yields from LiF were measured at PUC-Rio with ≈0.1 MeV/u N ^q+ (q = 2,4,5,6) ion beams by means of a time-of-fight (TOF) mass spectrometer. A ²⁵²Cf source mounted in the irradiation chamber allows immediate comparison of cluster emissions induced by ≈65 MeV fission fragments (FF). Emission of (LiF) _n Li⁺ clusters are observed for both the N beams and the ²⁵²Cf fission fragments. The observed cluster size n varies from 1 to 6 for N ^q+ projectiles and from 1 to ≈40 for the ²⁵²Cf-FF. The size dependence of the Y(n) distributions suggests two cluster formation regimes: (i) recombination process in the outgoing gas phase after impact and (ii) emission of pre-formed clusters from the periphery of the impact site. The corresponding distribution of ejected negative cluster ions (LiF) _n F⁻ closely resembles that of the positive secondary (LiF) _n Li⁺ ions. The desorption yields of positive ions scale as Y(n) ∼ q ⁵. A calculation with the CASP code shows that this corresponds to a cubic scaling ∼S _e ³ with the electronic stopping power S _e , as predicted by collective shock wave models for sputtering and models involving multiple excitons (Frenkel pair sputtering). We discuss possible interpretations of the functional dependence of the evolution of the cluster emission yield Y(n) with cluster size n, fitted by a number of statistical distributions.     

Emission of charged clusters during metal sputtering by ions

A method for simulating processes of metal sputtering by ion bombardment in the form of large neutral and charged clusters with a number of atoms N≥5 based on simple physical assumptions and in fair agreement with experiment is suggested. As an example, the ionization degrees and ionization coefficients, as well as the relative cluster yields, are calculated as a function of the number of atoms in clusters of different metals (Ag, Nb, and Ta) bombarded by singly charged Ar⁺¹ and Au⁻¹ ions. A fluctuation mechanism of charge state formation for large clusters, which describes the dependence of the charge state distributions on cluster size and target temperature, is developed.     

Vacancy-type defect distributions near argon sputtered Al(100) surface studied by variable-energy positrons and molecular dynamics simulations

A beam of variable-energy positrons, whose back-diffusion probability is measured as a function of positron implantation energy, is applied to studies of depth distribution of sputtering damage in aluminum. The defects are produced by argon ion bombardment of an Al(110) surface in ultra-high vacuum. We have varied the Ar⁺ energy, incident angle and dose, as well as sputtering and annealing temperatures. The extracted defect profiles have typically a narrow peak at the surface with a width of 10–20 A and a broader tail extending down to 50–100 Å. The shape of the defect profile varies only slightly with the sputtering energy and angle. Defect production at less than 1 keV Ar⁺ energies is typically 1–5 vacancies per incident ion. The defect profiles become fluence-independent at about 2 × 10¹⁶ Ar⁺ cm⁻². The defect density at the outer atomic layers saturates at high argon fluences to a few at%, depending on sputtering conditions. The sputtering temperature (below or above the vacancy migration stage at 250 K) has little effect on vacancy profiles. Defects anneal out gradually between 100 °C and 400 °C. Sputtering damage was also evaluated with the molecular dynamics technique. The shape and depth scale of the simulated collision cascades are in agreement with the experimentally extracted quantities.     

The interaction of oxygen with polycrystalldve niobium studied using aes and low-energy sims

The interaction of oxygen with polycrystalline niobium has been studied using both Auger electron spectroscopy and low-energy secondary ion mass spectrometry in the temperature range from 300–1250 K. At higher temperatures there is oxygen dissolution into the bulk but a preferential surface segregation on recooling. Between 300 and 1250 K, there is a rapid initial adsorption into a very stable state which is associated with increases in the Nb⁺ and NbO⁺ yields that are linear with coverage. At 1250 K, further changes are very slow. At 900 K, the initial stage is followed by the adsorption with a lower sticking coefficient (<0.1) as coverage increases from θ = 0.5 to 0.7. This produces an additional larger increase in the yield of Nb⁺ but a much smaller change in NbO⁺. At 300 K, the sticking probability falls more slowly with coverage above θ = 0.5 and the amount of oxygen continues to increase slowly with exposure. The SIMS spectrum shows dramatic increases in Nb⁺, NbO⁺ and NbO⁺₂ yields and the successive appearance of small yields of ions such as Nb₂O⁺₂ and Nb₂O⁺₃ as oxide formation begins. The Nb⁺ yield slowly decreases as further oxidation occurs. Each stage of oxidation has a characteristic secondary ion mass spectrum.     

Absolute measurement of sputtered ion fractions using matrix isolation spectroscopy

Sputtering yields for neutrals and ions have been measured by collecting the sputtered species in a noble gas matrix and determining their amounts from optical absorption spectroscopy. The atomic ion fractions for Ti and Zr bombarded by O₂⁺ at 2 keV are 0.8 and 0.4, respectively, whereas TiO and ZrO are sputtered largely as neutrals. Neutral sputtering yields from Ar⁺ bombardment arc consistent with previous measurements. The experimental results are compared with various theoretical models for the sputtering process.     

Mössbauer study of ferromagnetic metallic glasses irradiated by swift heavy ions at temperatures 100 and 300 K

The effect of swift heavy ion irradiation on ferromagnetic metallic glasses Fe₄₀Ni₃₈Mo₄B₁₈ and Fe₇₈Si₉B₁₃ has been studied. The ion beams used are 100 MeV ¹²⁷I and 180 MeV ¹⁹⁷Au. The specimens were irradiated at fluences ranging from 3 × 10¹² to 1.5 × 10¹⁴ ions/cm². The irradiations have been carried out at temperatures 100 and 300 K. The magnetic moments are sensitive towards the irradiation conditions such as irradiation temperature and stopping power of incident ion beam. The irradiation-induced effects have been monitored, by using Mössbauer spectroscopy. The modifications in magnetic anisotropy and hyperfine magnetic field distributions, as an effect of different irradiation temperature as well as different stopping power have been discussed. After irradiation, all the samples remain amorphous and magnetic anisotropy considerably changes from its original in-plane direction. The results show enhancement in magnetic anisotropy in the specimen irradiated at 100 K, as compared to that of irradiated at 300 K. It is expected that at low temperature, the stresses produced in the material would remain un-annealed, compared to the samples irradiated at room temperature and therefore, the modification in magnetic anisotropy would be enhanced. A distribution of hyperfine magnetic field, of the samples irradiated at low temperature, show a small but distinct peak at ～?11 Tesla, indicating Fe-B pairing.     

4He+在Al和Si单晶晶面沟道中的半波长及阻止本领

采用高分辨探测系统,在不同的入射角θ_in和出射角θ_out的条件下,测量了1—2MeV⁴He⁺入射在Al(100)面和Si(110),(100)面中的背散射能谱。得到了背散射能谱振荡峰的间距ΔE与cosθ_in/cosθ_out的直线关系,从而获得了1—2MeV⁴He⁺在这三个晶面中的振荡半波长及阻止本领。实验得到的半波长与理论计算值在误差范围内一致,晶面沟道方向的阻止本领略大于随机方向的阻止本领。 关键词：     

Synthesis and Spectral Study of Several Solid M3[Eu(2,6-Pyridinedicarboxylate)3] Salts (M=Li+, Na+, K+, Rb+, Cs+, NH4 +, and Pyridinium+)

Abstract

Salts of the [Eu(2,6-pyridinedicarboxylate)₃]^3- complex anion and various monovalent inorganic and organic counterions (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, NH₄ ⁺, and pyridinium⁺) have been synthesized and studied by emission spectroscopy. The Eu³⁺ ion emission spectra exhibited by these salts have been observed with high resolution (less than 1.0 cm^?1) and at low temperature (77 K). The emission spectra of these compounds indicate that changing the attached counterion does not affect the site symmetry observed by the europium ion beyond slight distortions indicated by small shifts in the energies of the Eu³⁺ electronic levels.     

Sputtering yields for light ions as a function of angle of incidence

The sputtering yield of Ni, Mo, and Au have been measured at oblique angles of incidence for H⁺-, D⁺-, and⁴He⁺-ion irradiation in the energy region from 1 to 8 keV. The yields were determined from the weight loss of the targets. For Ni and Mo the dependence of the sputtering yield on the angle of incidence was found to be much stronger for H⁺- and D⁺-ion than for⁴He⁺-ion irradiation. In all cases the maximum in the yield was found at angles of incidence ϑ≧80°, where ϑ is the angle measured from the surface normal. Furthermore the ratio of the maximum yield to the yeild at normal incidence increases with increasing surface binding energy of the target material as well as with increasing ion energy in the energy region inveestigated. The results are discussed qualitatively in view of a model for the sputtering mechanism for light ions.     

FA(Ga+,In+,Tl+) tunable laser activity and interaction of halogen atoms (F,Cl,Br,I,At) at the (001) surface of KCl crystal: ab initio calculations

An attempt has been made to examine F_A(Ga⁺,In⁺,Tl⁺) tunable laser activity and adsorptivity of halogen atoms (F,Cl,Br,I,At) at the (0 0 1) surface of KCl crystal using an embedded cluster model, CIS and density functional theory calculations with effective core potentials. The ion clusters were embedded in a simulated Coulomb field that closely approximates the Madelung field at the host surface. The nearest neighbor ions to the defect site were then allowed to relax to equilibrium. Based on the calculated strength of electron–phonon coupling and Stokes-shifted optical transition bands, The F_A(Tl⁺) center was found to be the most laser active in agreement with the experimental observation that the optical emissions of F_A(In⁺) and F_A(Ga⁺) centers were strongly quenched. The disappearance of the anisotropy and np splitting observed in the absorption of F_A(Ga⁺,In⁺,Tl⁺) centers were monotonically increasing functions of the size of the impurity cation. The F_A(Ga⁺,In⁺,Tl⁺) defect formation energies followed the order F_A(Ga⁺)>F_A(In⁺)>F_A(Tl⁺). The Glasner–Tompkins empirical relationship between the principal optical absorption of F centers in solids and the fundamental absorption of the host crystal was generalized to include the positive ion species. As far as the adsorptivity of the halogen atoms is concerned, the F and F_A(In⁺,Tl⁺) centers were found to change the nature of adsorption from physical adsorption to chemical adsorption. The adsorption energies were monotonically increasing functions of the electronegativity of the halogen and the amount of charge transferred from the defect-free surface. The calculated adsorption energies were explainable in terms of the electron affinity, the effective nuclear charge and the electrostatic potentials at the surface. The spin pairing mechanism played the dominant role in the course of adsorbate–substrate interactions and the KCl defect-free surface can be made semiconducting by F or F_A(In⁺,Tl⁺) surface imperfections.     

Sputtering and secondary ion emission of a two-phase system composed of small oxide precipitates dispersed in a copper matrix

This paper deals with the ion emission of a two-phase system composed of a copper single crystal matrix in which small precipitates of Al₂O₃ or BeO oxide of a few hundreds Å in diameter (from 60 to 470 Å) are included. It is observed that ions originate from three regions of the sample: region I. copper matrix: Cu⁺, Cu⁺₂, Cu⁺₃,…; region II. precipitates: Al⁺, Al⁺₂, AlO⁺ Al₂O⁺, …; respectively Be⁺, Be⁺₂, BeO⁺ Be₂O⁺,…; region III, matrix-precipitate interface: Cu⁺, CuAl⁺ or CuBe⁺,…. The presence of CuAl⁺ or CuBe⁺ ions and the enhancement of Cu⁺ emission at the periphery of precipitates in region III, makes the principle of the linear superposition of mass spectra of the two phases invalid. The interpretation of the results is based upon a simple model of sputtering which involves a coupling between the sputtering of precipitates and matrix. This model shows that, under steady state conditions, the surface density of precipitates is roughly proportional to the ratio S/S_p of the sputtering yields of the matrix and precipitates. We have taken advantage of the dependence of S on the crystal orientation of the sample with respect to the bombarding direction, to change the surface density of precipitates. Any change in S is followed by a time evolution of ion intensities originating from regions H and III. The average time of evolution allows one to characterize the size of precipitates. The sputtering process of a two-phase system (formation of cones) is discussed together with the ionization process.