Leif Persson

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.

Improvements in quantitative source preparation

Quantitative source preparation is indispensable for radionuclide standardisation. To improve the source quality, a device has been developed to accelerate the evaporation of solvents from a drop deposited on a substrate. Short drying times were reached by stirring the rotating drop with multiple jets of dry nitrogen at elevated temperature. Uniform deposits with a large number of small crystals were obtained. The source-quality was checked by micrographs and scans of autoradiographs and by the shape parameters of alpha-particle spectra.

RBS, SY-XRF, INAA and ICP-IDMS of Antimony Implanted in Silicon. A Multi-Method Approach to Characterize and Certify a Reference Material.

A layer of Sb atoms, implanted with an energy of 400 keV and a nominal dose of 5×1016 atoms/cm2 into a high purity silicon wafer, was certified for its areal density (atoms/cm2) using Rutherford backscattering spectrometry (RBS), instrumental neutron activation analysis (INAA) and inductively coupled plasma isotope dilution mass spectrometry (ICP-IDMS) and for its isotope ratio using INAA and ICP-IDMS. Excellent agreement between the results of the different independent methods was found. In the present work, the measurements of the homogeneity of the areal density of Sb, previously determined with RBS in spots having 1 mm diameter, are improved with synchrotron X-ray fluorescence analysis: Higher precision in even smaller sample spots allows to estimate a reduced inhomogeneity of the whole batch of samples of the order of only 0.4%. Thus the uncertainty of the certified value can further be reduced. Down to fractions of a chip with 0.3×0.4 mm2 area, the areal density is now certified as (4.81±0.06)×1016 Sb atoms/cm2, where the expanded uncertainty 0.06 (coverage factor k=2) corresponds to only 1.2%. The relative merits of the different analytical methods are discussed.

Antimony implanted in silicon – A thin layer reference material for surface analysis

Abstract A reference material has been produced which can be used for the calibration of surface and near-surface analytical methods like secondary ion mass spectrometry (SIMS), Auger electron spectrometry (AES), X-ray fluorescence analysis (XRF), particle induced X-ray emission (PIXE) and Rutherford backscattering spectrometry (RBS). 400 keV Sb ions with a nominal dose of 5×10 16 cm −2 were implanted into a high-purity silicon wafer. The areal density of the implanted Sb-layer was determined with instrumental neutron activation analysis (INAA) and with RBS. The isotopic ratio of Sb-121 and Sb-123 was determined with INAA. The depth profile of the implanted Sb was measured with RBS and a thorough check of the homogeneity of the implanted layer was also performed with RBS.

Standardisation of 204Tl at IRMM

IRMM participated in a recent international comparison for the standardisation of a 204Tl solution organised by BIPM. The activity concentration of the 204Tl solution was measured at IRMM using 3 independent methods; Liquid Scintillation Counting using the CIEMAT/NIST method, 4pi-CsI counting and 4pibeta counting using a large pressurised proportional counter. This article describes the measurements in detail and discusses potential problems in the standardisation of 204Tl.

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.

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.