Trace element quantification in high-resolution Rutherford backscattering spectrometry

The potential of high resolution Rutherford Backscattering (RBS) for identification and quantification of trace elements in thin films was investigated. A beam of 250 keV d⁺ ions from the AN700 van de Graaff accelerator in Linz was used to characterize the composition of an organic multi-element compound, i.e. a thin film of dried human blood on a carbon substrate. It was possible to identify more than 10 chemical elements with high accuracy, in the absence of any matrix effects. For instance, the Fe concentration was determined with a relative error <3% (400 ± 10 ppm), in perfect agreement with standard blood test values. The detection limit of heavy elements with atomic number higher than Fe was found to be below 50 ppm.     

Determination of the electronic energy loss of light ions in a silicon lattice by using the transmission ion channeling method

Charged particle activation analysis (CPAA) is able to analyze light elements such as carbon and oxygen at trace levels in semiconductor materials. This technique requires the knowledge of the stopping powers of these materials for channeled ions. The electronic energy loss for ions entering the crystal lattice in a random direction is well established. The electronic energy losses for protons, deuterons, ³He⁺ and ⁴He⁺ ions entering a 3.6 μm thick silicon single crystal along the 1 0 0 direction were measured by using the transmission of particles technique. Data obtained were compared with those obtained by other authors using theoretical and experimental methods.     

Study of iodine diffusion in silicon carbide

Diffusion of iodine in 6H-SiC and polycrystalline CVD-SiC was investigated using Rutherford backscattering spectroscopy and electron microscopy. A fluence of 1 × 10¹⁶ cm⁻² of ¹²⁷I⁺ was implanted with an energy of 360 keV at room temperature, producing an amorphous surface layer of approximately 220 nm thickness. The implantation profile reached an atomic density of approximately 1.3% at the projected range of about 95 nm. Broadening of the implantation profile and iodine loss through the front surface during isochronal and isothermal vacuum annealing was determined. At a temperature of 1100 °C no iodine loss was observed after 120 h and a diffusion coefficient of less than 10⁻²¹ m² s⁻¹ was extracted from the analysis of profile widths. Relatively strong broadening occurred after 60 h annealing at 1200 °C with the iodine profile extending beyond 300 nm into the bulk, accompanied by a surprisingly modest iodine loss through the surface. Electron microscopic studies reveal a drastic restructuring of the surface region at this temperature, indicating possible chemical reactions between iodine and silicon carbide.     

Ion–solid interactions and defects in silicon carbide

Experimental and computational approaches are used to study the defects, defect clusters and long-range structural disorder produced by interaction of energetic ions with silicon carbide (SiC). The accumulation and recovery of disorder on the Si and C sublattices are determined by ion-beam analysis methods in channeling geometry. Ab initio calculations have determined the most stable interstitial configurations, which are consistent with multi-axial channeling measurements. Molecular dynamics (MD) methods have been used to study both the energy dependence of defect production and the dynamic processes of cascade overlap. The experimental measurements of damage accumulation and the results of MD are consistent with each other. Thus, the integration of experimental and computational studies is providing atomic-level understanding of irradiation-induced defects and disordering processes in SiC.     

Density functional study on helium and hydrogen interstitials in silicon carbide

Silicon carbide with various defects such as carbon or silicon vacancies, anti-sites, and helium or hydrogen interstitials are studied in detail by ab initio calculations. The energy minimized structures of vacancies and helium or hydrogen interstitials are investigated. The calculated electronic spectra explain well some of the important features of silicon carbide observed in experiments. The phonon spectra of silicon carbide with hydrogen interstitials between silicon and carbon bond are calculated, and the frequency of the hydrogen-carbon stretching mode is consistent with experiments.     

The effects of intense gamma-irradiation on the alpha-particle response of silicon carbide semiconductor radiation detectors

Silicon Carbide (SiC) semiconductor radiation detectors are being developed for alpha-particle, X-ray and Gamma-ray, and fast-neutron energy spectrometry. SiC detectors have been operated at temperatures up to 306 °C and have also been found to be highly resistant to the radiation effects of fast-neutron and charged-particle bombardments. In the present work, the alpha-particle response of a SiC detector based on a Schottky diode design has been carefully monitored as a function of ¹³⁷Cs gamma-ray exposure. The changes in response have been found to be negligible for gamma exposures up to and including 5.4 MGy, and irradiations to higher doses are in progress.     

用低能X射线反散射法测定泥炭的灰分含量

泥炭的一个重要指标是灰分含量。目前化验室分析灰分含量采用烧灰方法,这种方法耗时费力,测一个样品需8小时左右。本文介绍用低能X射线反散射方法测定泥炭的灰分含量。这种方法简单、快速、测一个样品仅需1分钟。测量结果与化学常规分析比较,平均标准偏差约为3％。     

Determination of sulphur and copper depth distribution in patina layers using nuclear reaction techniques

A method for Cu and S profiling in patina layers was developed by applying a combination of nuclear reaction analysis (NRA) and Rutherford backscattering spectroscopy (RBS). The copper profiling was performed by using the 1327 keV γ-ray deexciting the third excited state to the ground state of ⁶³Cu produced by the reaction ⁶³Cu(p,p^′γ)⁶³Cu. For the determination of sulphur the 2230 keV γ-ray was used deexciting the first excited state to the ground state of ³²S formed through the reaction ³²S(p,p^′γ)³²S, which exhibits three sharp resonances at projectile energies 3.094, 3.195 and 3.379 MeV. The relevant cross-sections were measured in the energy range between 3.0 and 3.7 MeV in steps of 20 keV at 125° to the incident proton beam direction. The technique was tested using artificially produced and natural copper patina layers. Supporting information on the depth distribution of the constituent elements of the patina samples was obtained by p-RBS (E_p: 1.5 MeV, θ: 160°).     

高能离子弹性散射测定高温超导薄膜的元素配比

本文介绍了用8.8MeV氦离子弹性散射测定Y-Ba-Cu-O超导薄膜元素配比的一种新方法。由于在8.8MeV时~(16)O(α,α)~(16)O非卢瑟福共振散射截面比卢瑟福弹性散射截面大25倍,因而一次测量即能得到Y-Ba-Cu-O全部元素的配比。本方法也适用于Bi-Sr-Ca-Cu-O和Tl-Ba-Ca-Cu-O等其它超导体系元素配比的测定。     

Influence of nitrogen ion implantation energies on surface chemical bonding structure and mechanical properties of nitrogen-implanted silicon carbide ceramics

Nitrogen ions were implanted into silicon carbide ceramics (N⁺-implanted SiC) at different ions energies. The surface chemical bonding structure of N⁺-implanted SiC ceramics were investigated by using X-ray photoelectron spectroscopy (XPS). The hardness of N⁺-implanted SiC ceramics was measured using nano-indenter, and the friction and wear properties of the N⁺-implanted SiC/SiC tribopairs were studied using ball-on-disk type tribo-meter in water lubrication. The wear tracks were observed using non-contact surface profilometer and scanning electron microscope (SEM). The results showed that the surface roughness of N⁺-implanted SiC ceramic was higher than that of SiC ceramic, and some chemical bonds such as Si–N, C–C, CN and C–N bonds were formed in N⁺-implanted layer besides Si–C bonds. In comparison of SiC ceramic’s hardness, the hardness of N⁺-implanted SiC ceramics at 30 and 50 keV was higher while that at 65 keV was lower. Under water lubrication, the friction coefficient and the specific wear rates for the N⁺-implanted SiC/SiC tribopairs were all lower than those of the SiC/SiC tribopairs, and displayed the lowest values at 50 keV. According to XPS analysis, it was concluded that the high wear resistance and low friction coefficient for the N⁺-implanted SiC/SiC tribopairs were attributed to the formation of carbon rich composite on the surface of N⁺-implanted SiC ceramics.     

Study of annealing induced redistribution of implanted Au in Si: Fluence dependence

One hour 500 °C air annealing induced movement of implanted Au in Si have been studied for 32 keV Au implantation in Si, in the fluence range of . Samples were characterized using Rutherford backscattering spectrometry and cross-sectional transmission electron microscopy. The results indicate that, depending on the initial state of Au in the matrix, there is a clear difference in the diffusion behaviour of Au in Si. When Au is precipitated as gold-silicide nanoclusters inside the Si matrix, annealing is found to cause diffusion of Au into the bulk Si. Compared to this, for a random atomic distribution of Au in an amorphous Si matrix, annealing is found to result in out-diffusion of Au towards the surface.     

Enhancement of ferromagnetism in Ni-implanted HfO2 dielectric thin films

We report thermal annealing and 100 MeV Si⁸⁺ swift heavy ion irradiation effects on the structural and magnetic properties of Ni-implanted HfO₂ thin films. At low Ni doping concentration (∼1%), HfO₂ thin films show ferromagnetic behavior. We clearly demonstrate the cluster free nature of our film using cross-sectional high resolution transmission microscopy and magnetization vs. temperature data. Rutherford backscattering spectrometry is used to estimate the film thickness and to establish that Ni-ions are placed in the HfO₂ matrix. By comparing the results for the annealed and swift heavy ion irradiated samples, it is concluded that the enhancement in magnetic signal is closely related to the dispersion/diffusion of implanted Ni and defect creation such as oxygen vacancies. The results of magnetic force microscopy supported the observation of room temperature ferromagnetism in Ni-implanted HfO₂ films.     

Sputtering and crystalline structure modification of bismuth thin films deposited onto silicon substrates under the impact of 20-160 keV Ar ions

The sputtering of bismuth thin films induced by 20-160 keV Ar⁺ ions has been studied using Rutherford backscattering spectrometry, scanning electron microscopy and X-ray energy dispersive and diffraction spectroscopy. These techniques revealed increasing modifications of the Bi film surfaces with increasing both ion beam energy and fluence up to their complete deterioration under irradiation conditions E = 160 keV and φ = 1.5 × 10¹⁶ cm⁻², leaving isolated islands of preferred (0 1 2) orientation on the Si substrate. The observed surface morphology and crystalline structure evolutions are likely due to a complex interplay of interaction mechanisms involving both elastic nuclear collisions and inelastic electronic ones. The measured Bi sputtering yields versus Ar⁺ ion fluence for a fixed ion energy exhibit a significant depression at very low φ-values followed by a steady state regime above ∼2.0 × 10¹⁴ cm⁻². Measured sputtering yields versus Ar⁺ ion energy with fixing ion fluence to 1.2 × 10¹⁶ cm⁻² in the upper part of the yield saturation regime are also reported. Their comparison to theoretical model and SRIM 2008 Monte Carlo simulation predictions is discussed.     

Study on preventing segregation of erbium atoms to a silicon surface by annealing in oxygen atmosphere at high temperature

The damage produced by implantation of Er ions of 400 keV at a fluence of 5 × 10¹⁵ ions/cm² in silicon was investigated by Rutherford backscattering spectrometry with 2.1 MeV He²⁺ ions with multiple scattering models. It was found that the damage around the Si surface was almost removed after annealing in oxygen and nitrogen atmospheres successively at 1000 °C, and only a small portion of the Er atoms segregated to the silicon surface. Most of the Er atoms diffused to deeper depths because of the affinity of Er for oxygen.     

Determination of migration of ion-implanted helium in silica by proton backscattering spectrometry

Understanding the processes caused by ion implantation of light ions in dielectric materials such as silica is important for developing the diagnostic systems used in fusion and fission environments. Recently, it has been shown that ion-implanted helium is able to escape from SiO₂ films. To study this process in details, helium was implanted into the central part of a buried SiO₂ island up to a fluence of 4 × 10¹⁷ He/cm². The implanted helium could be detected in the SiO₂ island, if the oxide was insulated properly from the vacuum. The shape of the helium depth distributions was far from SRIM simulation because helium distributed in the whole 1 μm thick oxide layer. After the ion implantation, helium was observed only on the implanted spot. After nine months the implanted helium filled out the whole oxide island as it was expected from the high diffusivity.     

Partitioning to elastic and inelastic processes of the energy deposited by low energy ions in silicon detectors

The energy partitioning into elastic and ionization collisions for low energy ions (<200 keV) slowing down in silicon is important for the prediction of the detection efficiency of silicon detectors and the calculation of the damage induced by such ions in electronic devices. The partition factor calculated using Lindhard’s theory as well as the results extracted from TRIM calculations do not agree with recent experimental data of Funsten et al. for low energy ions. A new partition factor is calculated using Monte Carlo simulations based on a model which splits the inelastic losses into local and nonlocal modes. The calculated factor is in good agreement with existing experimental data and with molecular dynamic calculations. The calculated partition factor is expressed in a form convenient for different applications.     

Basic characterization of U: Determination of age and U content using sector field ICP-MS, gamma spectrometry and alpha spectrometry

The possibility to determine the age, i.e. the time since the last chemical separation, of ²³³U was studied using two fundamentally different measurement techniques: inductively coupled plasma mass spectrometry (ICP-MS) and gamma spectrometry. Moreover, the isotope ratio ²³²U/²³³U was measured using both alpha spectrometry and gamma spectrometry. For the two materials analysed, all measurement results were in agreement, i.e. consistent within the combined uncertainties. One of the materials was also measured using gamma spectrometry under field conditions. This measurement was also in agreement with the other results on this material.     

Measurement of (p,p) elastic differential cross-sections for carbon, nitrogen, oxygen, aluminium and silicon in the 500–2500 keV range at 140° and 178° laboratory scattering angles

We measured the (p,p) elastic scattering cross-sections of natural samples of carbon, nitrogen, oxygen, aluminium and silicon at energies ranging between 500 and 2500 keV and at laboratory scattering angles of 178° and 140°. Results are compared with previous literature data and simulations and are presented in graphical form. The measured cross-sections have been used to simulate spectra taken from know samples and have been found appropriate for quantitative calculations.     

The range of penetration and the backscattering coefficient by using both the analytic and the stochastic theoretical ways of electron slowing down in solid targets: Comparative study

The aim of this paper is to determine the best theoretical way (stochastic or analytic) to use in the study of the range of penetration and the backscattering coefficient of electron impinging in solid target, by adopting the same input in the form of collision cross-sections. For this purpose, differential elastic cross sections has been calculated by using our semi-empirical model [A. Bentabet, Z. Chaoui, A. Aydin, A. Azbouche, Vacuum 85 (2010) 156]; and that of inelastic cross sections has been calculated by using Gryzinski’s excitation function. Moreover, in stochastic case, the obtained quantities are calculated by using both Monte Carlo schemes based on continuous slowing down approximation (CSDA) and on individual electron scattering events methods.     

Reduction and compensation of lattice stress in high energy P+ and P+Sb implanted silicon

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