A time of flight-energy recoil telescope system for mass and energy dispersive recoil spectrometry has been applied to study the formation of Mg2Si layers and depth profiling of Ga1−xAlxAs quantum well structures. Measurements of the energy (depth) dependence of the mass resolution showed that the telescope could be used over the energy range from 5 to 18 MeV to distinguish between recoils of 1 amu mass difference up to mass 28 amu. The energy dependence of the detection efficiency was found to be independent of the recoil energy for 12C and 28Si recoils and no strong evidence for a recoil species dependence of the detection efficiency for recoils heavier than 16O was found.

Quantitative mass and energy dispersive elastic recoil spectrometry: Resolution and efficiency considerations

Mechanisms of inner-shell vacancy production in slow ion-atom collisions

Ion beam analysis (IBA) includes a group of techniques for the determination of elemental concentration depth profiles of thin film materials. Often the final results rely on simulations, fits and calculations, made by dedicated codes written for specific techniques. Here we evaluate numerical codes dedicated to the analysis of Rutherford backscattering spectrometry, non-Rutherford elastic backscattering spectrometry, elastic recoil detection analysis and non-resonant nuclear reaction analysis data. Several software packages have been presented and made available to the community. New codes regularly appear, and old codes continue to be used and occasionally updated and expanded. However, those codes have to date not been validated, or even compared to each other. Consequently, IBA practitioners use codes whose validity, correctness and accuracy have never been validated beyond the authors’ efforts. In this work, we present the results of an IBA software intercomparison exercise, where seven different packages participated. These were DEPTH, GISA, DataFurnace (NDF), RBX, RUMP, SIMNRA (all analytical codes) and MCERD (a Monte Carlo code). In a first step, a series of simulations were defined, testing different capabilities of the codes, for fixed conditions. In a second step, a set of real experimental data were analysed. The main conclusion is that the codes perform well within the limits of their design, and that the largest differences in the results obtained are due to differences in the fundamental databases used (stopping power and scattering cross section). In particular, spectra can be calculated including Rutherford cross sections with screening, energy resolution convolutions including energy straggling, and pileup effects, with agreement between the codes available at the 0.1% level. This same agreement is also available for the non-RBS techniques. This agreement is not limited to calculation of spectra from particular structures with predetermined parameters, but also extends to extracting information from real data. In particular, we have shown data from an Sb implanted sample where the Sb fluence was certified with an uncertainty of 0.6%. For this sample, and using SRIM03 stopping powers for 1.5 MeV 4He in Si, the codes were able to extract the Sb fluence with an average 0.18% deviation from the certified value and a 0.11% agreement between the codes. Thus IBA is a suitable technique for accurate analysis where traceability is critical. These results confirm that available IBA software packages are, within their design limitations, consistent and reliable. The protocol established may be readily applied to validate future IBA software as well.

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International Atomic Energy Agency intercomparison of ion beam analysis software

Measurements of heavy-ion slowing down in matter differ in many aspects from experiments with light particles like protons and α-particles. An overview of the special experimental requirements, methods, data analysis and interpretation is presented for heavy-ion stopping powers, energy- and angular-straggling and ranges in the energy domain from keV/u up to GeV/u. Characteristic experimental results are presented and compared with theory and semiempirical predictions. New applications are outlined, which represent a challenge to continuously improve the knowledge of heavy-ion slowing down.

Experimental studies of heavy-ion slowing down in matter

This work gives a review about the response of silicon detectors to electrons, protons, deuterons and alpha particles The detector nonlinearity (pulse height as a function of particle energy) and the shape of the response function (pulse height distribution for monoenergetic particles) are discussed in detail For electrons, the measured nonlinearity is found to be negligible within the experimental uncertainties The response function of a particle implanted and passivated silicon detector (PIPS) for electrons (200 to 1000 keV) is measured with thin radionuclide sources of conversion electrons From these measurements an accurate value of the Fano factor is derived For light ions (protons, deuterons and helium ions), measurements are compared to calculations using a detector model, which assumes a thin dead layer at the front contact, followed by a fully sensitive region This model takes into account electronic energy loss straggling in the dead layer, thickness variations of the dead layer, multiple scattering and nonelectronic losses in the sensitive region, electron-hole pair statistics, a particle dependence of the energy per electron-hole pair and electronic resolution For H and He ions, at low energies (40 to 700 keV) the nonlinearity is mainly due to the finite thickness of the dead layer, and in the MeV range the particle dependence of the energy per electron-hole pair contributes considerably, in accordance with the model of Lennard Measurements of the response function for monoenergetic He ions yield a detector resolution of 8 keV (FWHM) in the energy range 3 to 6 MeV The well known asymmetric shape of the response function is found for both, H and He ions, at all energies Using our detector model, calculated spectra agree quantitatively with the corresponding measurements both in the width and in the shape, without any adjustable parameter in the calculations Based on this detector model, the ultimate resolution which can be obtained with silicon detectors is discussed

Energy resolution of silicon detectors: approaching the physical limit

We report measurements of the relative mean pulse height produced by 1H, 4He, 7Li and 16O ions in Si surface barrier detectors. The data are anomalous in that the pulse height for different ions of the same energy (after window and nonionizing losses are subtracted) increases with atomic number, contrary to observations for fission fragments. A simple model invoking a stopping power dependence of the energy required to create an electron-hole pair is consistent with all experimental data, suggesting that the response of Si detectors is nonlinear with particle energy.

Nonlinear response of Si detectors for low-Z ions

Presents new evidence for a sharing of projectile 2p vacancies in heavy-ion-atom collisions, Z1 approximately=Z2 approximately 35 and E/M<or approximately=0.5 MeV/amu. The sharing is effected by 3d pi -2p pi radial coupling and can be described through a function WL=(1+exp(1.79XL))-1, analogous to 2p sigma -1s sigma K-vacancy sharing. XL is a simple function of the projectile velocity and the 2p binding energies of the projectile and target atoms. The data may be used to show that the region of internuclear distances where 3d pi -2p pi radial coupling occurs is spatially distinct from the region of 2p pi -2p sigma rotational coupling.

D. Phillips

Papers

Nonlinear response of Si detectors for low-Z ions

3dπ-2pπ radial coupling in symmetric and near-symmetric heavy-ion-atom collisions

Dependence of specific energy loss on foil thickness

Time-of-flight system for slow heavy ions

Problems of interpreting energy loss data for non-zero emergent angles