Mohamed El Bouanani

Multivariate analysis method for energy calibration and improved mass assignment in recoil spectrometry

Abstract Heavy ion recoil spectrometry is rapidly becoming a well established analysis method, but the associated data analysis processing is still not well developed. The pronounced nonlinear response of silicon detectors for heavy ions leads to serious limitation and complication in mass gating, which is the principal factor in obtaining energy spectra with minimal cross talk between elements. To overcome the above limitation, a simple empirical formula with an associated multiple regression method is proposed for the absolute energy calibration of the time of flight-energy dispersive detector telescope used in recoil spectrometry. A radical improvement in mass assignment was realized, which allows a more accurate and improved depth profiling with the important feature of making the data processing much easier.

Recoil spectrometry : ion accelerator based elemental characterisation of surface layers

Recoil Spectrometry covers a group of techniques that are very similar to the well known Rutherford backscattering Spectrometry technique, but with the important difference that one measures the recoiling target atom rather than the projectile ion. This makes it possible to determine both the identity of the recoil and its depth of origin from its energy and velocity, using a suitable detector system. The incident ion is typically high-energy (30–100MeV)35C1,81Br or127I. Low concentrations of light elements such as C, O and N can be profiled in a heavy matrix such as Fe or GaAs. Here we present an overview of mass and energy dispersive recoil Spectrometry and illustrate its successful use in some typical applications.

INTERFACIAL REACTION STUDIES OF CR, NI, TI, AND PT METALLIZATION ON INP

Interfacial reactions between (100) InP and thin films of the transition metals Cr, Ni, Pt, and Ti have been studied. A thin layer of metal was deposited onto the InP substrates using e‐beam evaporation and parts of the samples were then subjected to heat treatment in vacuum for 30 min at several temperatures up to 500 °C. Separate characterizations of the metal, In, and P depth distributions were carried out using mass and energy dispersive recoil spectrometry. The different crystalline phases observed were determined using x‐ray diffraction. The near‐noble metals (Ni, Pt) formed ternary phases, while Ti and Cr formed phosphides. The phases formed were generally stable up to 500 °C with the major exception being Pt where the ternary phase decomposed to form PtIn2, PtP2, and Pt3In7.

Effects of energy deposition by nuclear scattering in silicon p-i-n diode detectors

Abstract The changes in thick (∼300 μm) and thin (15 μm) Si p-i-n diode detectors that take place as a result of alpha particle and 63Cu5+ ion irradiation have been studied by Deep Level Transient Spectroscopy (DLTS) and by monitoring the reverse-bias leakage currents. A linear increase in reverse-bias current with α-particle dose was observed that could be attributed to the formation of vacancy-associated defects (divacancy, A- and E-centres). Damage within the active layer of the device, characterised by the increase in leakage current per unit active volume, together with literature pion, proton and heavy ion data, exhibited a linear dependence on the energy deposited in nuclear processes over many orders of magnitude. Annealing at temperatures of 150°C for 4 h (vacuum bakeout) resulted in a reduction in leakage current and the size of the DLTS peaks became smaller. This temperature is much lower than expected for removal of divacancies, suggesting that recovery of the reverse bias current is mediated by other defect centres.

Empirical characterisation of mass distribution broadening in ToF-E recoil spectrometry

Abstract The mass broadening function in mass and energy dispersive recoil spectrometry using a detector telescope for time-of-flight and energy determination, has been characterised for a number of isotopes in the range A = 12 to 197. The broadening was well described by a Gaussian function where the standard deviation is given by the empirical equation: θ A ( E, A ) = C 1 + C 2 A 3/2 E − 1 + C 3 A 2 E − 2/3 + C 4 AE 1/2

Recoil spectrometry of thin film reactions in the Pd/InP system

Interfacial reactions between (100) InP and Pd were investigated as part of a systematic study aimed at investigating the stability of planar nonalloyed metallizations to InP. A 50‐nm‐thick Pd film was deposited on an InP substrate, and parts of it were subsequently thermally treated for 30 min at temperatures varying from 100 to 500 °C in steps of 50 °C. Separate characterizations of the Pd, In, and P depth distributions were obtained using mass and energy dispersive recoil spectrometry. The different phases were determined using x‐ray diffraction, and scanning electron microscopy was used to study the surface topography. It is assumed that the interaction starts in the as‐deposited sample, and definite formation of a ternary phase with the suggested composition Pd5In2P2 starts at an annealing temperature of 100 °C. At 250 °C all Pd is chemically reacted. Preferential outdiffusion of P leads to a loss of P from the surface at 500 °C, and the only phase observed in the x‐ray diffraction spectrum from the ...

Formation of thin films of CoSi2 on GaAs

CoSi2 exhibits the features of low resistivity and stability at elevated temperatures which make it interesting to employ for metallization on GaAs. The interfacial reactions in GaAs samples with thin film overlayers of Si and Co [Si(220 nm)/Co(50 nm)/(〈100〉‐GaAs)] were studied using x‐ray diffraction, scanning electron microscopy, x‐ray photoelectron spectroscopy, and mass and energy dispersive recoil spectrometry. Samples were vacuum furnace annealed for time periods between 1 and 8 h at temperatures ranging from 300 to 700 °C. It was found that a CoSi2 layer formed without observable reaction with the substrate at 500 °C and above. The excess Si (Si/Co atomic ratio of 2.41) remained near the surface as elemental Si and as SiO2 for the 500 and 600 °C annealings. For the 700 °C annealing the excess near‐surface Si was not observed.

Separation of mass-overlapped time of flight-energy elastic recoil detection analysis data using Ryan and Jamieson's dynamic analysis method

Time of flight-energy (ToF-E) elastic recoil detection analysis (ERDA) data often contains mass signals with considerable overlap from adjacent isotopes in the mass-energy plane. An evaluation has been carried out of the suitability of the dynamic analysis method proposed by Ryan and Jamieson to decompose elemental signals with overlapping mass. This method is shown to work very well on generated test data and the result when it was applied to experimental data appears quite promising. Very accurate mass calibration and lineshape determination was found to be a prerequisite for the application of the method.

Metal/InP thin film reactions: Studies using mass and energy dispersive recoil spectrometry

Abstract Preliminary results are presented from a study of transition metal/lnP reactions using mass and energy dispersive recoil spectrometry. 50 nm films of Ni, Pd and Pt were evaporated on InP substrates, heat treated in vacuum and subsequently analysed with X-ray diffraction and mass and energy dispersive recoil spectrometry using 77 MeV 127 I 10+ ions as projectiles. The unique information on the elemental distributions in the surface layers which can be obtained using the latter technique has allowed us to follow the progress of the solid state reactions. These reactions are quite different for the three metals studied, with significant P loss in the Pd/InP case.

Mass and energy dispersive elastic recoil detection studies of low temperature Si/Pd/GaAs and Si/Pd/AlxGa(1 − x)As interfacial reactions

Abstract Interface reactions between bi-layer films of Si (75 nm), Pd (50 nm) and GaAs or substrates of AlxGa(1 − x)As have been studied using mass and energy dispersive elastic recoil detection (ERD) to identify the formation and thermal stability of Pd-silicides on GaAs-based systems. Samples were prepared by sequential vacuum evaporation and subsequently annealed in a vacuum furnace at temperatures up to 700°C. Pd and Si signals indicate that silicidation has started at 250°C and developed further as the temperature increased for both systems. The results indicate PdSi was formed in the surface layer, and PdSi2 in a region deeper than 2.5 × 1017at. cm−2 without significant reaction with the underlying substrate at temperatures up to 500°C. In the GaAs system at 700°C, all the Pd was bound into the substrate together with excess Si, whilst volatile As was lost from the surface. The results indicate that the same reactions occurred during the heat treatments of both GaAs and AlxGa(1 − x)As systems.