Experimental evidence for the influence of the atomic shell structure on the energy loss of high energy heavy ions in matter

Secondary electron yield measurements for ²⁵²Cf fission products in carbon foils reveal significant deviations for the electronic stopping cross section from semiempirical predictions. This effect may correspond to the Z₁ oscillations observed previously at much lower ion velocities.     

Asymptotics of the cross section of the electron loss by fast ions in light media

The dependence of the single electron loss cross section on the nuclear charge Z of a projectile and on the nuclear charge Zt of a target atom for fast collisions is studied theoretically using the plane-wave Born approximation and the sum rule. The results of calculations for fast singly and triply charged ions show that the single electron loss cross section increases monotonically as Z and Zt increase. This can be used to interpolate cross sections of processes if there are no experimental data. The results of calculations compare with the experimental and theoretical data of other authors.     

Influence of electronic straggling on ion range distributions

The range straggling of ions above the stopping power maximum is shown in a large class of ion-target combinations to include a strong contribution from electronic collisions. Existing calculations based purely on the statistics of nuclear collisions may therefore have underestimated the true range straggling.     

Stopping cross sections of 50- to 230-keV nitrogen ions in silicon measured by ion backscattering spectroscopy

The energy dependence of the total stopping cross section of 50- to 230-keV nitrogen ions in silicon (σ _S (E)) is measured in order to develop the diagnostics of heavy impurities in films of a nanometer thickness by heavy ion backscattering (HIBS) spectroscopy. At ion energies lower than 150 keV, this σ _S (E) dependence occupies an intermediate position between the dependences given in the SRIM and MSTAR data-bases; at higher energies, our dependence is closer to the former dependence. The estimation of the effect of inelastic processes on the stopping cross section demonstrates that the effect of these processes for nitrogen ions can be neglected when heavy impurities in such films are studied by HIBS.     

The dependence of sputtering efficiency on ion energy and angle of incidence

Abstract

Earlier measurements of sputtering efficiency of polycrystalline targets (fraction of impinging ion energy leaving the target through sputtering and backscattering) have been extended to higher energies. Lead and copper targets were bombarded with several different projectiles with energies between 80 and 1200 keV. The sputtering efficiency decreases with increasing energy. This decrease is ascribed to the combined influence of changes in the scattering cross section with energy, and to electronic stopping. The results may be described as a function of the mass ratio M ₂/M ₁ and the reduced energy ? only.

The sputtering efficiency was measured as a function of angle of incidence of the bombarding ions. To ensure complete collection of sputtered and backscattered particles, it was possible to cover only the region of incidence angle from 0° to 45°. Targets of copper, silver, and lead were investigated with 17 different ion-target combinations. The sputtering efficiency increased with angle of incidence. This increase is described well by a simple interpolation formula by Sigmund.     

Non-Gaussian range profiles in amorphous solids

Range profiles of boron in amorphous silicon exhibit pronounced deviations from Gaussian at energies above about 40 keV due to increasing electronic stopping. A detailed comparison with computed profiles allows a semiempirical determination of the electronic stopping cross section (S_e ≈ E^0.4).     

Ranges and standard deviations of implanted ions

This paper presents a theoretical analysis and simple expressions for the calculation of ranges and standard deviations of implanted ions in amorphous targets. Nuclear energy loss models are discussed to introduce an approximation formula for the nuclear stopping cross section appropriate for Thomas-Fermi, Lenz-Jensen and intermediate type potentials. The Firsov electronic stopping model has been used to show its successful application. Algebraical expressions for the total range of ions in monoatomic and biatomic targets as a function of ion energy result from the considerations presented. A quasi-elastic multiscattering model is suggested, which permits an easy estimate of projected ion ranges. The standard range deviation is obtained by determining the total average-square energy loss fluctuations. Finally a comparison of calculated and experimental results is made to show that calculations based on the Firsov electronic stopping model and the nuclear stopping cross section proposed here provide a better agreement with the experimental results than the wellknown Johnson-Gibbons LSS-calculations.     

Stopping of slow ions

The 50th anniversary of the appearance of a series of seminal papers by O.B. Firsov is taken as an occasion to have a look at some central aspects of the stopping of slow ions in matter. A brief characterization of Firsov’s model of electronic energy loss is given in comparison with alternative views. The main part of the paper is devoted to central problems such as scaling behavior, Z ₁ and Z ₂ structure, deviations from velocity proportionality, threshold behavior, metal-insulator and gas-solid differences, and correlation between nuclear and electronic stopping.     

Stopping power of polymers for heavy ions: a comparative study

A comparative study of various stopping power tables and codes for heavy ions in polymers has been made by comparing the computed stopping power values with the corresponding experimental values. The energy loss of different heavy ions (3≤Z ₁≤29) in the energy domain of ～0.19–3.14 MeV/n has been studied in six different polymers mostly used as particle track detectors viz: Mylar (Polyethylene Terephthalate), PEN (Polyethylene Napthalate), Polycarbonate, CR-39 (Polyallyl Diglycol Carbonate), Kapton (Polypyromellitimide) and LR-115 (Cellulose Nitrate). The merits and demerits of the adopted formulations are highlighted. It has been observed that the calculations based on SRIM2003.26 and tables of ICRU-73 provide best agreement with the experimental data for projectiles (3≤Z ₁≤29) and (3≤Z ₁≤18), respectively. The MSTAR3.12 code shows good results for projectiles (3≤Z ₁≤18), except in case of CR-39 for O, Na, and Al projectiles. The statistical analysis on the basis of combined error reveals that the SRIM2003 and ICRU-73 tables are more reliable as compared to the other programs taken in the present study, whereas CasP3.1 is least reliable program in lower energy domain.     

电子阻止本领Se(E)的z振荡及其计算

本文应用Hartree-Fock-Slater势能代替Thomas-Fermi势能,得出电子阻止本领S_e(E)的归一化关系式;同时,结合有效原子序数概念,得出能量对S_e(E)影响的关系式,利用前一关系式,定量计算了S_e(E)随离子和靶原子的原子序数z变化的振荡关系,计算结果与实验值相当符合,利用后一关系式,定量计算了多种离子-靶体系的S_e(E),与文献[1]的关系式比较,本文结果更好地符合实验值,而且有更广的能量适用范 关键词：     

The channeled stopping powers of Boron ions and range calculations in Si

An analytical fitting expression is obtained for the channeled stopping power of B ions in crystalline silicon. Ions incident in the Si 〈100〉 direction at energies from 50 keV/amu to 900 keV/amu are considered. The mean projected ranges of ions have been determined within the framework of the transport theory formalism where the fitting relation obtained for the stopping power was used. For this purpose, a first order ordinary differential equation including second order stopping coefficients is solved numerically by usingFehlberg fourth-fifth order Runge-Kutta method. By using the results for the channeled ion ranges, a transformation relation is proposed for the conversion of channeled/random ion ranges for the ion target system under consideration. The obtained results are compared with widely used standard programs such as Crystal-TRIM, SRIM and PRAL and our program applied to crystalline targets is in good agreement with Crystal-TRIM.     

化合物和合金中离子投影射程分布矩的计算(Ⅱ)——轻离子(Z1≤10)的射程分布矩

本文根据离子在固体材料中电子阻止截面的实验资料,给出了低能Li⁺,Be⁺,B⁺,C⁺,N⁺,O⁺,F⁺,Ne⁺等离子在固体中电子阻止截面S_e的经验公式。这些经验公式既能够很好地反映电子阻止本领的Z₁和Z₂振荡、又能正确地给出S_e随离子能量E的变化关系。用这种以实验为基础的S_e经验公式和符合于WHB势的核散射函数,计数了从H⁺到Ne⁺十种轻离子在非晶Al₂O₃,SiO₂,20/25/Nb不锈钢,LiNbO₃和UO₂等材料中的投影射程分布的一次至三次矩。将计算值与近几年的实验测量及其他人的计算结果进行了比较,在低能端,我们计算的平均投影射程R_p与实验符合得更好。 关键词：     

Range of Er ions in amorphous Si

We have measured the range and range straggling for energetic 100-900 keV Er ions in amorphous Si by means of Rutherford backscattering followed by spectrum analysis. The results are compared with other experimental data and Monte Carlo (SRIM-2003) calculations. Our experimental results show that, although the measured values for both range and range straggling exceed the SRIM predictions, they are nevertheless consistent with trends that have been previously observed. We see no anomalous trends in range and range straggling parameters for the rare earth ions for implant energies E ≥ 100 keV. We present a detailed consideration of ⁴He stopping powers in Si due to its crucial impact on RBS range measurements.     

ESR of residual defects in silicon from recoil implantation of oxygen in Si/SiO2 systems

In ionic crystals or other insulators with partial ionic binding, the ion-target interaction differs from that of neutral atoms due to different electronic distributions and overall electrical charges Consequently, the nuclear stopping power and defect production by recoiling atoms will deviate from standard values, obtained from e g Moliere-potentials In the present paper, realistic potentials between projectile ion and target ion are determined by the free electron gas model of overlapping Hartree-Fock-Slater or Lenz-Jensen ions (and neutral atoms for comparison) With the new potentials, the transferred energies T and the range of interaction is determined for either damage production (T>E_d) and for nuclear stopping (T>hω> for bound ions) In addition the excitation of optical phonons is taken into account which are excited by the transient electrical field of the charged projectile     

Apparent velocity threshold in the electronic stopping of slow hydrogen ions in LiF

The electronic energy loss of hydrogen ions (protons and deuterons) in thin supported films of LiF has been studied in backscattering geometry for specific energies from 700 eV/u to 700 keV/u, using Rutherford backscattering spectroscopy and time-of-flight low-energy ion scattering spectroscopy. For specific energies below 8 keV/u, our data confirm velocity proportionality for the stopping cross section epsilon (like in a metal) down to 3.8 keV/u, as observed previously for protons and antiprotons despite the large band gap (14 eV) of LiF. Below 3.8 keV/u, the present results indicate an apparent velocity threshold at about 0.1 a.u. for the onset of electronic stopping.     

Velocity dependence in low-velocity electronic stopping power of heavy ions

The velocity dependence in the low-velocity electronic stopping power of heavy ions has been studied for Al and Si ions in Ta in the velocity region 0.4v₀−4v₀ (v₀ is the Bohr velocity). The first experimental information is obtained from the range distribution and Doppler-shift-attenuation data.     

Ionic Debye Screening in Dense Liquid Plasmas Observed for Li+p,d Reactions with Liquid Li Target

Thick target yields of a particles emitted in the ~6Li(d,a)~4 He and ~7Li(p,a)~4 He reactions were measured for Li target in the solid and liquid phase.Observed reaction rates for the liquid Li are always larger than those for the solid.This suggests that the stopping power of hydrogen ion in the liquid Li metal might be smaller than in the solid.Using the empirically obtained stopping power for the liquid Li,we have deduced the screening potentials of the Li+p and Li+d reactions in both phases.The deduced screening potential for the liquid Li is about 500 eV larger than for the solid.This difference is attributed to the effect of liquefied Li~+ ions.It is concluded that the ionic screening is much stronger than the electronic screening in a low-temperature dense plasmas.     

Intensity and detuning dependence of fine structure changing collisions in a 85 Rb magneto-optical trap

In an experimental study, the multi-ionisation of metallic clusters (Na_n) has been analysed in collisions with light ions in low charge states (H⁺, He⁺, He²⁺, O³⁺) at collision velocities below 1 a.u. Cluster ions are produced in charge states up to 5+. The average charge of the nano-particles is found to increase linearly with the variation of projectile velocity and the square of the effective projectile charge, well in agreement with the electronic stopping power of the bulk material. A fraction of 50% to 30% of the total projectile energy loss (decreasing with velocity) is transferred into vibrational modes in good agreement with recent theoretical predictions. Received 8 November 2000 and Received in final form 26 January 2001     

Electronic stopping power calculation method for molecular dynamics simulations using local Firsov and free electron-gas models

Molecular dynamics simulations have proven to be accurate in predicting depth distributions of low-energy ions implanted in materials. Free parameters adjusted for every ion-target combination are conventionally used to obtain depth profiles in accordance with the experimental ones. We have previously developed a model for predicting depth profiles in crystalline Si without free parameters. The electronic stopping power was calculated using local total electron density. The model underestimated the stopping in the ?1 1 0? channeling direction. We have now taken a new approach to calculate the electronic stopping power. We use the local valence (3p²) electron density to account for the electronic energy loss between collisions and the Firsov model to account for the electronic energy loss during collision. The lowest electron densities are adjusted with a parametrization that is same for all ions in all implanting directions to correct the problems in the ?1 1 0? channeling direction.     

Reliability of stopping power tables and codes for heavy ions (8 ≤ Z ≤ 92) in gases

A comparative study of various stopping power tables and codes for heavy ions in gases has been made through comparison of computed values and the corresponding experimental data. Ten gaseous media: five monatomic rare gases (He to Xe), two diatomic gases (H₂, N₂) and three polyatomic gaseous compounds (CH₄, CF₄ and CO₂) have been chosen to study the stopping power investigations of heavy ions (8 ≤ Z ≤ 92) having energy ranges of ∼0.10–10.00 MeV/n and ∼20.00–57.00 MeV/n. We compare the experimental data of stopping power to values calculated using various tables and computer codes by ICRU-73, Ziegler et al (SRIM2003.26), Grande and Schiwietz (CasP3.1), Paul and Schinner (MSTAR3.12), and Bazin and Tarasov (LISE ++:2-ATIMA1.2). On the basis of statistical analysis, we estimate the reliability of these tables and codes. It has been observed that the MSTAR3.12 code shows the best agreement with the experimental data for projectile ions (8 ≤ Z ≤ 18) in the entire energy range. The SRIM2003.26 code provides good results except for some heavy projectiles (Xe, Pb and U). The values tabulated by CasP3.1 code underestimate especially at low energy region. No significant trend is observed in case of LISE++:2-ATIMA1.2 code and ICRU-73 report.