Iiro Riihimäki - Academia.edu (original) (raw)
Papers by Iiro Riihimäki
Physical Review B, 2003
ABSTRACT The intrinsic As diffusion properties have been determined in relaxed Si1-xGex epilayers... more ABSTRACT The intrinsic As diffusion properties have been determined in relaxed Si1-xGex epilayers. The properties were studied as a function of composition x for the full range of materials with x=0, 0.20, 0.35, 0.50, 0.65, 0.8, and 1. The activation enthalpy Ea was found to drop systematically from 3.8 eV (x=0) to 2.4 eV (x=1). Comparisons with other impurity atom- and self-diffusion results in Si, Ge, and SiGe show that both interstitials and vacancies contribute as diffusion vehicles in the composition range 0<~x<~0.35 and that vacancy mechanism dominates diffusion in the composition range 0.35<x<~1.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2006
In recent years there has been increasing interest in radio-epidemiological techniques to retrosp... more In recent years there has been increasing interest in radio-epidemiological techniques to retrospectively measure the radon dose exposure by determining the activity of 210 Pb, the longest-lived 222 Rn progeny, in glass surface layers. In this study the diffusion of 39 keV 209 Pb + ions implanted into glass using the IGISOL facility has been studied under conditions that mimic the recoil implantation of 210 Pb from 222 Rn. The resulting depth distributions of 209 Pb were then measured after heat treatment in vacuum at different temperatures by a sputter erosion technique. The diffusion coefficient could be described by an Arrhenius equation D = D 0 exp(ÀH/kT) where D 0 ¼ 0:30 þ1:14 À0:24 m 2 s À1 and H = 2.81 ± 0.11 eV. No statistically significant loss of 209 Pb from the sample was observed for annealing between 470 and 600°C.
Radiation Protection Dosimetry, 2008
In retrospective radon measurements, the 22-y half life of (210)Pb is used as an advantage. (210)... more In retrospective radon measurements, the 22-y half life of (210)Pb is used as an advantage. (210)Pb is often considered to be relatively immobile in glass after alpha recoil implanted by (222)Rn progenies. The diffusion of (210)Pb could, however, lead to uncertain wrong retrospective radon exposure estimations if (210)Pb is mobile and can escape from glass, or lost as a result of cleaning-induced surface modification. This diffusion was studied by a radiotracer technique, where (209)Pb was used as a tracer in a glass matrix for which the elemental composition is known. Using the ion guide isotope separator on-line technique, the (209)Pb atoms were implanted into the glass with an energy of 39 keV. The diffusion profiles and the diffusion coefficients were determined after annealing at 470-620 degrees C and serial sectioning by ion sputtering. In addition, the effect of surface cleaning on diffusion was tested. From the Arrhenius fit, the activation enthalpy (H) was determined, which is equal to 3.2 +/- 0.2 eV, and also the pre-exponential factor D(0), in the order of 20 m(2)s(-1). This result confirms the assumption that over a time period of 50 y (209)Pb (and (210)Pb) is effectively immobile in the glass. The boundary condition obtained from the measurements had the characteristic of a sink, implying loss of (209)Pb in the topmost surface at high temperatures.
Physical Review Letters, 2002
ABSTRACT Self-diffusion of implanted 31Si and 71Ge in relaxed Si0.20Ge0.80 layers has been studie... more ABSTRACT Self-diffusion of implanted 31Si and 71Ge in relaxed Si0.20Ge0.80 layers has been studied in the temperature range 730-950 °C by means of a modified radiotracer technique. The temperature dependences of the diffusion coefficients were found to be Arrhenius-type with activation enthalpies of 3.6eV and 3.5eV and preexponential factors of 7.5×10-3 m2 s-1 and 8.1×10-3 m2 s-1 for 31Si and 71Ge, respectively. These results suggest that, as in Ge, in Si0.20Ge0.80 both 31Si and 71Ge diffuse via a vacancy mechanism. Since in Si0.20Ge0.80 71Ge diffuses only slightly faster than 31Si, in self-diffusion studies on Si-Ge 71Ge radioisotopes may be used as substitutes for the ``uncomfortably'' short-lived 31Si radiotracer atoms.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2004
ABSTRACT In the modified radiotracer technique ion beams within a broad energy range are employed... more ABSTRACT In the modified radiotracer technique ion beams within a broad energy range are employed. They include energetic light particles ensuring radioactive isotope production via nuclear reactions, keV-ion implantation of radiotracers and sputtering by low energy heavy ions for depth profiling. If the involved ion–solid interactions are properly taken into account, the technique provides an effective means for solid-state diffusion studies under demanding conditions. The various aspects related to the modified radiotracer technique are surveyed and discussed. The reliability of the procedure is demonstrated by comparisons with corresponding profiles obtained by secondary ion mass spectrometry. Also previously unpublished diffusion data for 71Ge self-diffusion in relaxed Si0.87Ge0.13 are provided for comparison purposes.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2004
A novel device for versatile sputtering applications is described. The apparatus design is realis... more A novel device for versatile sputtering applications is described. The apparatus design is realised for fulfilling the demands of both nuclear physics experiment target production and serial sectioning in solid-state diffusion studies with radiotracers. Results of several tests are reported, characterising the devise performance in these two differing applications.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2006
We have irradiated Czochralski silicon (Cz-Si) and Float Zone silicon (Fz-Si) detectors with 24Ge... more We have irradiated Czochralski silicon (Cz-Si) and Float Zone silicon (Fz-Si) detectors with 24GeV/c and 10MeV protons. Samples were characterized with Capacitance-Voltage measurements (CV), Transient Current Technique (TCT) and secondary electron backscattering recorded by Scanning Electron Microscope (SEM). We present the evolution of the effective doping concentration as a function of irradiation fluence as well as the introduction rate of
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2003
ABSTRACT Introducing oxygen into the silicon material is believed to improve the radiation hardne... more ABSTRACT Introducing oxygen into the silicon material is believed to improve the radiation hardness of silicon detectors. In this study, oxygenated and non-oxygenated silicon samples were processed and irradiated with 15MeV protons. In order to speed up the defect reactions after the exposure to particle radiation, the samples were heat treated at elevated temperatures. In this way, the long-term stability of silicon detectors in hostile radiation environment could be estimated. Current–voltage measurements and Surface Photovoltage (SPV) method were used to characterize the samples.
IEEE Transactions on Nuclear Science, 2002
ABSTRACT The effect of oxygenation on the radiation hardness of silicon detectors was studied. Ox... more ABSTRACT The effect of oxygenation on the radiation hardness of silicon detectors was studied. Oxygen-enriched and standard float-zone silicon pin-diodes and oxidized samples were processed and irradiated with 15-MeV protons. After the irradiations, the surface photovoltage (SPV) method was applied to extract minority carrier diffusion lengths of the silicon samples. Adding oxygen to silicon was found to improve the radiation hardness of silicon. The effect was visible in minority carrier diffusion lengths as well as in reverse bias leakage currents. The suitability of SPV method for characterizing irradiated silicon samples was proved.
Philosophical Magazine, 2004
The self-diffusion of silicon in single crystal MoSi 2 was studied by means of a radiotracer tech... more The self-diffusion of silicon in single crystal MoSi 2 was studied by means of a radiotracer technique using the short-lived radioisotope 31 Si (half-life t 1=2 ¼ 2:6 h), which was produced and implanted into the samples at the ion-guide isotope separator on-line device at the University of Jyva¨skyla¨in Finland. Diffusion annealing and subsequent serial sectioning of the specimens were performed immediately after the radiotracer implantation. In the entire temperature region investigated (835-1124 K), the 31 Si diffusivities in both principal directions of the tetragonal MoSi 2 crystals obey Arrhenius laws, where the diffusion perpendicular to the tetragonal axis is faster than parallel to it. In previous studies the same features were observed for the 71 Ge diffusivities in MoSi 2 , except that these are somewhat higher than those of 31 Si. Furthermore, it is noteworthy that in MoSi 2 the diffusivities of 31 Si and 71 Ge are orders of magnitude faster than the diffusivity of 99 Mo. This large difference suggests that silicon diffusion and molybdenum diffusion are completely decoupled and that silicon diffusion takes place exclusively on the silicon sublattice. Literature data on the phase growth of MoSi 2 are in accordance with the present results on the 31 Si diffusivities; Monte Carlo simulations of the correlation effects of vacancy-mediated diffusion on the silicon sublattice of MoSi 2 lead to their rationalization. . Schematic illustration of the growth of the phases Mo 5 Si 3 (a) and MoSi 2 (g) in an interdiffusion couple initially consisting of pure molybdenum and silicon.
Physical Review B, 2003
ABSTRACT The intrinsic As diffusion properties have been determined in relaxed Si1-xGex epilayers... more ABSTRACT The intrinsic As diffusion properties have been determined in relaxed Si1-xGex epilayers. The properties were studied as a function of composition x for the full range of materials with x=0, 0.20, 0.35, 0.50, 0.65, 0.8, and 1. The activation enthalpy Ea was found to drop systematically from 3.8 eV (x=0) to 2.4 eV (x=1). Comparisons with other impurity atom- and self-diffusion results in Si, Ge, and SiGe show that both interstitials and vacancies contribute as diffusion vehicles in the composition range 0<~x<~0.35 and that vacancy mechanism dominates diffusion in the composition range 0.35<x<~1.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2006
In recent years there has been increasing interest in radio-epidemiological techniques to retrosp... more In recent years there has been increasing interest in radio-epidemiological techniques to retrospectively measure the radon dose exposure by determining the activity of 210 Pb, the longest-lived 222 Rn progeny, in glass surface layers. In this study the diffusion of 39 keV 209 Pb + ions implanted into glass using the IGISOL facility has been studied under conditions that mimic the recoil implantation of 210 Pb from 222 Rn. The resulting depth distributions of 209 Pb were then measured after heat treatment in vacuum at different temperatures by a sputter erosion technique. The diffusion coefficient could be described by an Arrhenius equation D = D 0 exp(ÀH/kT) where D 0 ¼ 0:30 þ1:14 À0:24 m 2 s À1 and H = 2.81 ± 0.11 eV. No statistically significant loss of 209 Pb from the sample was observed for annealing between 470 and 600°C.
Radiation Protection Dosimetry, 2008
In retrospective radon measurements, the 22-y half life of (210)Pb is used as an advantage. (210)... more In retrospective radon measurements, the 22-y half life of (210)Pb is used as an advantage. (210)Pb is often considered to be relatively immobile in glass after alpha recoil implanted by (222)Rn progenies. The diffusion of (210)Pb could, however, lead to uncertain wrong retrospective radon exposure estimations if (210)Pb is mobile and can escape from glass, or lost as a result of cleaning-induced surface modification. This diffusion was studied by a radiotracer technique, where (209)Pb was used as a tracer in a glass matrix for which the elemental composition is known. Using the ion guide isotope separator on-line technique, the (209)Pb atoms were implanted into the glass with an energy of 39 keV. The diffusion profiles and the diffusion coefficients were determined after annealing at 470-620 degrees C and serial sectioning by ion sputtering. In addition, the effect of surface cleaning on diffusion was tested. From the Arrhenius fit, the activation enthalpy (H) was determined, which is equal to 3.2 +/- 0.2 eV, and also the pre-exponential factor D(0), in the order of 20 m(2)s(-1). This result confirms the assumption that over a time period of 50 y (209)Pb (and (210)Pb) is effectively immobile in the glass. The boundary condition obtained from the measurements had the characteristic of a sink, implying loss of (209)Pb in the topmost surface at high temperatures.
Physical Review Letters, 2002
ABSTRACT Self-diffusion of implanted 31Si and 71Ge in relaxed Si0.20Ge0.80 layers has been studie... more ABSTRACT Self-diffusion of implanted 31Si and 71Ge in relaxed Si0.20Ge0.80 layers has been studied in the temperature range 730-950 °C by means of a modified radiotracer technique. The temperature dependences of the diffusion coefficients were found to be Arrhenius-type with activation enthalpies of 3.6eV and 3.5eV and preexponential factors of 7.5×10-3 m2 s-1 and 8.1×10-3 m2 s-1 for 31Si and 71Ge, respectively. These results suggest that, as in Ge, in Si0.20Ge0.80 both 31Si and 71Ge diffuse via a vacancy mechanism. Since in Si0.20Ge0.80 71Ge diffuses only slightly faster than 31Si, in self-diffusion studies on Si-Ge 71Ge radioisotopes may be used as substitutes for the ``uncomfortably'' short-lived 31Si radiotracer atoms.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2004
ABSTRACT In the modified radiotracer technique ion beams within a broad energy range are employed... more ABSTRACT In the modified radiotracer technique ion beams within a broad energy range are employed. They include energetic light particles ensuring radioactive isotope production via nuclear reactions, keV-ion implantation of radiotracers and sputtering by low energy heavy ions for depth profiling. If the involved ion–solid interactions are properly taken into account, the technique provides an effective means for solid-state diffusion studies under demanding conditions. The various aspects related to the modified radiotracer technique are surveyed and discussed. The reliability of the procedure is demonstrated by comparisons with corresponding profiles obtained by secondary ion mass spectrometry. Also previously unpublished diffusion data for 71Ge self-diffusion in relaxed Si0.87Ge0.13 are provided for comparison purposes.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2004
A novel device for versatile sputtering applications is described. The apparatus design is realis... more A novel device for versatile sputtering applications is described. The apparatus design is realised for fulfilling the demands of both nuclear physics experiment target production and serial sectioning in solid-state diffusion studies with radiotracers. Results of several tests are reported, characterising the devise performance in these two differing applications.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2006
We have irradiated Czochralski silicon (Cz-Si) and Float Zone silicon (Fz-Si) detectors with 24Ge... more We have irradiated Czochralski silicon (Cz-Si) and Float Zone silicon (Fz-Si) detectors with 24GeV/c and 10MeV protons. Samples were characterized with Capacitance-Voltage measurements (CV), Transient Current Technique (TCT) and secondary electron backscattering recorded by Scanning Electron Microscope (SEM). We present the evolution of the effective doping concentration as a function of irradiation fluence as well as the introduction rate of
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2003
ABSTRACT Introducing oxygen into the silicon material is believed to improve the radiation hardne... more ABSTRACT Introducing oxygen into the silicon material is believed to improve the radiation hardness of silicon detectors. In this study, oxygenated and non-oxygenated silicon samples were processed and irradiated with 15MeV protons. In order to speed up the defect reactions after the exposure to particle radiation, the samples were heat treated at elevated temperatures. In this way, the long-term stability of silicon detectors in hostile radiation environment could be estimated. Current–voltage measurements and Surface Photovoltage (SPV) method were used to characterize the samples.
IEEE Transactions on Nuclear Science, 2002
ABSTRACT The effect of oxygenation on the radiation hardness of silicon detectors was studied. Ox... more ABSTRACT The effect of oxygenation on the radiation hardness of silicon detectors was studied. Oxygen-enriched and standard float-zone silicon pin-diodes and oxidized samples were processed and irradiated with 15-MeV protons. After the irradiations, the surface photovoltage (SPV) method was applied to extract minority carrier diffusion lengths of the silicon samples. Adding oxygen to silicon was found to improve the radiation hardness of silicon. The effect was visible in minority carrier diffusion lengths as well as in reverse bias leakage currents. The suitability of SPV method for characterizing irradiated silicon samples was proved.
Philosophical Magazine, 2004
The self-diffusion of silicon in single crystal MoSi 2 was studied by means of a radiotracer tech... more The self-diffusion of silicon in single crystal MoSi 2 was studied by means of a radiotracer technique using the short-lived radioisotope 31 Si (half-life t 1=2 ¼ 2:6 h), which was produced and implanted into the samples at the ion-guide isotope separator on-line device at the University of Jyva¨skyla¨in Finland. Diffusion annealing and subsequent serial sectioning of the specimens were performed immediately after the radiotracer implantation. In the entire temperature region investigated (835-1124 K), the 31 Si diffusivities in both principal directions of the tetragonal MoSi 2 crystals obey Arrhenius laws, where the diffusion perpendicular to the tetragonal axis is faster than parallel to it. In previous studies the same features were observed for the 71 Ge diffusivities in MoSi 2 , except that these are somewhat higher than those of 31 Si. Furthermore, it is noteworthy that in MoSi 2 the diffusivities of 31 Si and 71 Ge are orders of magnitude faster than the diffusivity of 99 Mo. This large difference suggests that silicon diffusion and molybdenum diffusion are completely decoupled and that silicon diffusion takes place exclusively on the silicon sublattice. Literature data on the phase growth of MoSi 2 are in accordance with the present results on the 31 Si diffusivities; Monte Carlo simulations of the correlation effects of vacancy-mediated diffusion on the silicon sublattice of MoSi 2 lead to their rationalization. . Schematic illustration of the growth of the phases Mo 5 Si 3 (a) and MoSi 2 (g) in an interdiffusion couple initially consisting of pure molybdenum and silicon.