I. Bogdanović Radović

Helium elastic scattering from carbon for 30° to 150° in the energy region from 2 to 4.8 MeV

Abstract The differential cross-sections for elastic scattering of 4 He ions by carbon atoms were measured at scattering angles of 30°, 45°, 60°, 135° and 150° in the energy range from 2 to 4.8 MeV. Up to now mostly data for angles larger than 150° were published in the literature. A thick carbon target with a thin evaporated Cu layer on the surface was used for the measurement. The number of impinging projectiles was obtained from the He ions scattered by the Cu layer assuming Rutherford cross-sections. The carbon scattering cross-sections were then obtained from comparison of measured He energy spectra with the simulated ones. Above 2 MeV all evaluated cross-sections become non-Rutherford. Deviations from Rutherford cross-sections are about 50% for 30° scattering angle and amount up to a factor 30 for 150° scattering angle. The measured experimental cross-sections were compared with the calculated theoretical cross-sections and already published data. Satisfactory agreement was obtained for all measured scattering angles and energies.

Determination of H recoil cross-sections for He ions incident at 2.5–4.5 MeV and recoil angles from 30° to 60°

Proton diAerential recoil cross-sections were measured for impact of He ions in the energy range from 2.5 to 4.5 MeV and for recoil angles from 30∞ to 60∞. For the first time, H recoil cross-sections at angles from 45∞ to 60∞ are reported. All the measured cross-sections, except those for 60∞, deviate from the Rutherford cross-sections. Thin melamine foils (50 lg=cm 2 ) evaporated on50 lg=cm 2 thick Cu were prepared as targets. Two surface barrier detectors positioned at forward angles were used to detect the recoiled and scattered atoms. One detector was kept all the time at 40∞ and was used to measure the loss of H due to irradiation. The experimental results were compared with the other available experimental data for lower recoil angles and a good agreement is found. A comparison is also made with the theoretical calculations obtained by fitting the phase shifts of the kinematic inverse reaction using the principle of detailed balance. Again an agreement is found for low recoil angles, but for 55∞ and 60∞ the experimental cross-sections are significantly smaller than the theoretical values. ” 2001 Elsevier Science B.V. All rights reserved.

Stopping Power of Different Ions in Si Measured with a Bulk Sample Method and Bayesian Inference Data Analysis

The accuracy of ion beam analysis experiments depends critically on the stopping power values available. While for H and He ions accuracies normally better than 5% are achieved by usual interpolative schemes such as SRIM, for heavier ions the accuracy is worse. One of the main reasons is that the experimental data bases are very sparse, even for important materials such as Si. New measurements are therefore needed. Measurement of stopping power is often made with transmission in thin films, with the usual problems of film thickness homogeneity. We have previously developed an alternative method based on measuring bulk spectra, and fitting the yield by treating the stopping power as a fit parameter in a Bayesian inference Markov chain Monte Carlo procedure included in the standard IBA code NDF. We report on improvements of the method and on its application to the determination of the stopping power of 7Li in Si. To validate the method, we also apply it to the stopping of 4He in Si, which is known with 2% a...

Elastic recoil detection analysis for large recoil angles (LA-ERDA)

Abstract In this paper, elastic recoil detection (ERD) measurements at recoil angle of 60° using ion-induced electron emission (IEE) for particle identification are presented. In our IEE system for particle identification, recoiled target atoms and scattered projectiles penetrate a set of thin carbon foils before their energy is analyzed in a solid state detector. Particle identification is based on the fact that the total number of electrons emitted from the foils depends on the particle nuclear charge. This method is characterized by its low minimum detectable energy, which stimulated us to study ERDA at 60°. Due to collision kinematics and due to the angular dependence of the scattering cross-sections, it is expected that the sensitivity can be significantly improved. In this work, the detection efficiency of the IEE particle identification system for H recoils at energies below 1 MeV was determined. LA-ERDA measurements were performed with 4He and 12C projectiles using two different types of samples with a well-known amount and depth distribution of H atoms near the surface. Sample 1 consisted of a 50 μg/cm2 melamine layer evaporated on a flat Si substrate, sample 2 was a Si wafer with implanted H. Sensitivity and depth resolution were measured using LA-ERDA with a recoil angle of 60° and ERDA with recoil angles of 30° and 45°. The results for different recoil geometries and projectiles are discussed and compared with theoretical predictions.

IBICC characterisation of defect structures in polycrystalline silicon

Abstract The low-cost polycrystalline substrates used in solar cell production suffer from a high concentration of impurities and defects. The influence of the particular defect on the electrical properties of material is important information and can be obtained only by the application of complementary characterisation techniques. The ion beam induced charge collection (IBICC) technique provides information about the spatial distribution of imperfections in charge collection, while the origin of these imperfections is not known. Therefore, various samples of edge-defined film-fed grown (EFG) and Czochralski (Cz) silicon were also analysed by deep level transient spectroscopy (DLTS), identifying the most important deep levels in the band gap. The influence of twin boundaries in EFG samples and high oxygen content of Cz material on the IBICC results are discussed as well as the IBICC-induced defects in test samples.

Characterisation of amorphous silicon solar cells by IBA methods

Abstract Hydrogenated amorphous silicon solar cells were studied by the use of Rutherford backscattering and elastic recoil detection analysis. By the application of different ion types, energies and geometry, the layered structure of solar cells as well as their hydrogen content were determined. Results were correlated to optical and electrical properties of samples and the difference between the two types of solar cells, with “higher” and “lower efficiency”, is discussed.

Stopping Power Of He, C And O In InN

Group III nitrides such as InN, GaN, and their alloys are increasingly important in a host of optoelectronic and electronic devices. The presence of unintentional impurities is one of the factors that can strongly affect the electronic properties of these materials, and thus ion beam analysis techniques can play a fundamental role, in particular heavy ion elastic recoil detection analysis tracing and quantifying these contaminations. However, stopping powers in InN and GaN have not yet been measured, and data analysis relies on using the Bragg rule, which is often inaccurate. We have used a bulk method, previously developed by us and applied successfully to other systems, to determine experimentally the stopping power of several ions in InN. The results of our measurements and bulk method analysis are presented.