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Remarks on channeling radiation
Classified abstracts 6 7 4 1 ~ 7 5 0
V. Analysis of materials and surfaces 50. RUTHERFORD BACKSCATTERING AND NUCLEAR REACTIONS 50 6741. Nuclear reaction analysis of shallow B and BF2 implants in Si Impurity diffusion induced by rapid thermal annealing has been investigated for low-energy nB and 49BF2 implants in Si. Samples were annealed with an oxide cap in an AG Associates Heatpulse system. Depth profiles were determined with nuclear reaction analysis. This technique is sensitive to impurities at or near the surface and can reveal impurity diffusion to near-surface regions not usually detectable with secondary ion mass spectrometry. Significant B diffusion to the SiO2/Si interface was observed for a 1050°C/20-s anneal of 10-keV lIB implanted in crystalline and preamorphized Si. B interfacial concentrations were comparable to peak concentrations in unannealed samples. Diffusion of B and F to the SiO2/Si interface and impurity gettering by ion straggling damage was observed for a 1050°C/20-s anneal of45-keV 49BF2implanted in crystalline Si. Impurity segregation at the SiO 2/Si interface was minimal for a 1050°C/20-s anneal of 45-keV 49BF2 implanted in preamorphized Si, although a loss of F was apparent. M C Ridgway et al, Jappl Phys, 62, 1987, 3682-3687. 50 6742. Basic mechanisms for the lattice-site occupation of metallic elements implanted into aluminium In situ ion implantatiori combined with channeling spectroscopy was used to show that the most important parameter which determines the lattice site occupation of implanted atoms in AI is the size mismatch energy, AHsiz~.The lattice site occupation is governed by two basic processes: spontaneous recombination of the impurities with vacancies in the relaxation phase of the collision cascade and displacement from the substitutional site by trapping point defects in the cooling phase with a probability proportional to AHs~. R Gerber et al, Nucl Instrum Meth Phys Res, B31, 1988, 402-406. 50 6743. The effects of surface topography in nuclear microprobe Rutherford backscattering analysis The influence of two geometric surface topographies on Rutherford backscattering spectra in nuclear microprobe analysis has been investigated through computer simulation. Periodic triangular surfaces are shown to give structureless spectra of reduced yield in perpendicular incidence, but oscillatory features develop as the target is tilted. Steps on the surface give less structured spectra, though the total backscattering yield can vary dramatically, depending on geometry. The quantitative effects of topographical amplitude, finite beam width, target tilt and target atomic number, in the two detector geometries available at Harwell, 0 = 170° and 135°, on the distortion of flat target spectra, for two basic types of surface topography, are presented. The influence of energy straggling is shown to be small and multiple scattering is considered. The consequences of surface topography in practical nuclear microprobe analysis are discussed. C P Hobbs et al, Nucl Instrum Meth Phys Res, B30, 1988, 342-348. 50 6744. Lattice sites of Yb in Si-A planar channeling study The lattice positions of Yb in Si have been reinvestigated by the planar channeling method. Our results show that the "Yb-sites" proposed by Andersen et al. are only occupied with 50%, the other half being located at the tetrahedral interstitial sites. K Jousten and S Kaibitzer, Radiat Effects, 104, 1987, 57-65. 50 6745. A theory of interaction between fast ions and solids The velocity-dependent interaction potential theory between fast ions and the solid atoms is developed. The theory incorporates effects of the dynamical screening, electron stripping and quantum corrections to the interaction energy due to the projectile motion. Some experiments concerning a passage of fast ions through amorphous and crystalline targets are compared with the theoretical predictions. G V Dedkov, Radiat Effects, 103, 1987, 157-185.
50 6746. Remarks on channeling radiation For satisfactory determination of the radiation power emitted when an electron/positron beam interacts with the electrostatic lattice potential within a crystal film, the number of bound states and their population have to be known. A relative simple procedure to calculate these two, based on matrix method, is presented. Results are in full accordance with literature. While some physical insights are investigated, a full equivalence to the propagation of an electromagnetic wave in a dielectric slab is demonstrated. L Sehiichter, J appl Phys, 63, 1988, 712 716. 50 6747. Evaluation of crystalline quality of zirconium dioxide films on silicon by means of ion-beam channeling Zirconium dioxide (ZrO2) films have been grown on Si(100) and Si(111) substrates at 800°C by vacuum evaporation. A channeling spectrum of the Rutherford backscattering on the ZrO2 films shows that ZrO2 films [tetragonal (200)] are epitaxially grown on Si(100) substrate at 800°C, which is consistent with x-ray diffraction and reflection high-energy electron diffraction observations. The spread of crystallite orientation in the epitaxial film is estimated to be 0.32 °, by analyzing the angular dependence of the total backscattering yield. Yukio Osaka et al, Jappl Phys, 63, 1988, 581 582. 50 6748. Interatomic potential in solids and its applications to range calculations Using the Gordon-Kim statistical model, the hctero-nuclear potentials have been numerically evaluated from the first principle for various Z~Si combinations, where the charge distribution of the solid-state atom is constructed from the charge density of the Dirac-Hartree Fock-Slater gas-state atom. The corresponding projected ranges in silicon are calculated using the Monte Carlo simulation code ACAT. For e = 0.09 the calculated ranges show a little weaker Z~ oscillation than the experimental data, but they reproduce reasonably the experimental projected ranges. The convenient combination rule for constructing the hetero-nuclear potential from the corresponding homo-nuclear potentials is proposed. This combination rule is shown not only to reproduce well the heteronuclear potential which is calculated from the first principle, but also to yield the reasonable projected range. The analytic universal function is also proposed averaging the various homo-nuclear potentials, and it is found that the projected ranges calculated from the present universal screening function show a good agreement with the Kr C range at low energies. S T Nakagawa and Y Yamamura, Radiat Effects, 105, 1988, 239 256. 50 6749. Dechanneling at an interface of finite width Si crystals were implanted with 2.5 x 1016/cm2 boron ions. A surface layer of about 250 nm was melted several times with a pulsed laser causing an almost homogeneous distribution of the B atoms in the molten layer. The B depth distribution and lattice site were determined by nuclear reaction analysis. The B containing layer was found to be epitaxial with the pure silicon substrate and contracted in the direction perpendicular to the surface. This contraction causes a change in direction of all inclined planes and strings at the interface of the B containing layer and the substrate. In this work we study dechanneling of e particles at the interface. The dechanneling effect at the interface turned out to be very sensitive to the e-particle energy. This energy dependence was reproduced by Monte Carlo simulations. The amount of dechanneling at the interface is both determined by the magnitude of the contraction and the width over which the boron concentration drops from its constant value to zero. In principle it should be possible to determine both the width of the interracial region and the magnitude of the contraction from dechanneling measurements alone. However it turned out not to be straightforward to simulate all axial planar dechanneling data correctly with only one set of parameters. M Vos and D O Boerma, Nucl Instrum Meth Phys Res, B30, 1988, 173181. 50 6750. Measurement of channeling radiation using a 45 MeV betatron An experimental setup for the measurement of channeling radiation from relativistic electrons in single crystals is described. A betatron with a maximum beam energy of 45 MeV is used as electron source. The beam 523
V. Analysis of materials and surfaces 50. RUTHERFORD BACKSCATTERING AND NUCLEAR REACTIONS 50 6741. Nuclear reaction analysis of shallow B and BF2 implants in Si Impurity diffusion induced by rapid thermal annealing has been investigated for low-energy nB and 49BF2 implants in Si. Samples were annealed with an oxide cap in an AG Associates Heatpulse system. Depth profiles were determined with nuclear reaction analysis. This technique is sensitive to impurities at or near the surface and can reveal impurity diffusion to near-surface regions not usually detectable with secondary ion mass spectrometry. Significant B diffusion to the SiO2/Si interface was observed for a 1050°C/20-s anneal of 10-keV lIB implanted in crystalline and preamorphized Si. B interfacial concentrations were comparable to peak concentrations in unannealed samples. Diffusion of B and F to the SiO2/Si interface and impurity gettering by ion straggling damage was observed for a 1050°C/20-s anneal of45-keV 49BF2implanted in crystalline Si. Impurity segregation at the SiO 2/Si interface was minimal for a 1050°C/20-s anneal of 45-keV 49BF2 implanted in preamorphized Si, although a loss of F was apparent. M C Ridgway et al, Jappl Phys, 62, 1987, 3682-3687. 50 6742. Basic mechanisms for the lattice-site occupation of metallic elements implanted into aluminium In situ ion implantatiori combined with channeling spectroscopy was used to show that the most important parameter which determines the lattice site occupation of implanted atoms in AI is the size mismatch energy, AHsiz~.The lattice site occupation is governed by two basic processes: spontaneous recombination of the impurities with vacancies in the relaxation phase of the collision cascade and displacement from the substitutional site by trapping point defects in the cooling phase with a probability proportional to AHs~. R Gerber et al, Nucl Instrum Meth Phys Res, B31, 1988, 402-406. 50 6743. The effects of surface topography in nuclear microprobe Rutherford backscattering analysis The influence of two geometric surface topographies on Rutherford backscattering spectra in nuclear microprobe analysis has been investigated through computer simulation. Periodic triangular surfaces are shown to give structureless spectra of reduced yield in perpendicular incidence, but oscillatory features develop as the target is tilted. Steps on the surface give less structured spectra, though the total backscattering yield can vary dramatically, depending on geometry. The quantitative effects of topographical amplitude, finite beam width, target tilt and target atomic number, in the two detector geometries available at Harwell, 0 = 170° and 135°, on the distortion of flat target spectra, for two basic types of surface topography, are presented. The influence of energy straggling is shown to be small and multiple scattering is considered. The consequences of surface topography in practical nuclear microprobe analysis are discussed. C P Hobbs et al, Nucl Instrum Meth Phys Res, B30, 1988, 342-348. 50 6744. Lattice sites of Yb in Si-A planar channeling study The lattice positions of Yb in Si have been reinvestigated by the planar channeling method. Our results show that the "Yb-sites" proposed by Andersen et al. are only occupied with 50%, the other half being located at the tetrahedral interstitial sites. K Jousten and S Kaibitzer, Radiat Effects, 104, 1987, 57-65. 50 6745. A theory of interaction between fast ions and solids The velocity-dependent interaction potential theory between fast ions and the solid atoms is developed. The theory incorporates effects of the dynamical screening, electron stripping and quantum corrections to the interaction energy due to the projectile motion. Some experiments concerning a passage of fast ions through amorphous and crystalline targets are compared with the theoretical predictions. G V Dedkov, Radiat Effects, 103, 1987, 157-185.
50 6746. Remarks on channeling radiation For satisfactory determination of the radiation power emitted when an electron/positron beam interacts with the electrostatic lattice potential within a crystal film, the number of bound states and their population have to be known. A relative simple procedure to calculate these two, based on matrix method, is presented. Results are in full accordance with literature. While some physical insights are investigated, a full equivalence to the propagation of an electromagnetic wave in a dielectric slab is demonstrated. L Sehiichter, J appl Phys, 63, 1988, 712 716. 50 6747. Evaluation of crystalline quality of zirconium dioxide films on silicon by means of ion-beam channeling Zirconium dioxide (ZrO2) films have been grown on Si(100) and Si(111) substrates at 800°C by vacuum evaporation. A channeling spectrum of the Rutherford backscattering on the ZrO2 films shows that ZrO2 films [tetragonal (200)] are epitaxially grown on Si(100) substrate at 800°C, which is consistent with x-ray diffraction and reflection high-energy electron diffraction observations. The spread of crystallite orientation in the epitaxial film is estimated to be 0.32 °, by analyzing the angular dependence of the total backscattering yield. Yukio Osaka et al, Jappl Phys, 63, 1988, 581 582. 50 6748. Interatomic potential in solids and its applications to range calculations Using the Gordon-Kim statistical model, the hctero-nuclear potentials have been numerically evaluated from the first principle for various Z~Si combinations, where the charge distribution of the solid-state atom is constructed from the charge density of the Dirac-Hartree Fock-Slater gas-state atom. The corresponding projected ranges in silicon are calculated using the Monte Carlo simulation code ACAT. For e = 0.09 the calculated ranges show a little weaker Z~ oscillation than the experimental data, but they reproduce reasonably the experimental projected ranges. The convenient combination rule for constructing the hetero-nuclear potential from the corresponding homo-nuclear potentials is proposed. This combination rule is shown not only to reproduce well the heteronuclear potential which is calculated from the first principle, but also to yield the reasonable projected range. The analytic universal function is also proposed averaging the various homo-nuclear potentials, and it is found that the projected ranges calculated from the present universal screening function show a good agreement with the Kr C range at low energies. S T Nakagawa and Y Yamamura, Radiat Effects, 105, 1988, 239 256. 50 6749. Dechanneling at an interface of finite width Si crystals were implanted with 2.5 x 1016/cm2 boron ions. A surface layer of about 250 nm was melted several times with a pulsed laser causing an almost homogeneous distribution of the B atoms in the molten layer. The B depth distribution and lattice site were determined by nuclear reaction analysis. The B containing layer was found to be epitaxial with the pure silicon substrate and contracted in the direction perpendicular to the surface. This contraction causes a change in direction of all inclined planes and strings at the interface of the B containing layer and the substrate. In this work we study dechanneling of e particles at the interface. The dechanneling effect at the interface turned out to be very sensitive to the e-particle energy. This energy dependence was reproduced by Monte Carlo simulations. The amount of dechanneling at the interface is both determined by the magnitude of the contraction and the width over which the boron concentration drops from its constant value to zero. In principle it should be possible to determine both the width of the interracial region and the magnitude of the contraction from dechanneling measurements alone. However it turned out not to be straightforward to simulate all axial planar dechanneling data correctly with only one set of parameters. M Vos and D O Boerma, Nucl Instrum Meth Phys Res, B30, 1988, 173181. 50 6750. Measurement of channeling radiation using a 45 MeV betatron An experimental setup for the measurement of channeling radiation from relativistic electrons in single crystals is described. A betatron with a maximum beam energy of 45 MeV is used as electron source. The beam 523