No abstract available

[en] Silicon (1 0 0) wafers have been implanted with 1x10¹⁵ He⁺ or Ar⁺ ions/cm² and the vacancy (V)-He or -Ar complexes induced have been investigated with positron lifetime and coincidence Doppler broadening measurements using a positron beam. He⁺ ion implantation into Si gives rise to formation of V₂He complexes, which are transformed into V_xHe_y (x-y=1) complexes by annealing at 300 deg. C. The amorphous phase induced by Ar irradiation of Si is transformed into a crystalline phase around 700 deg. C. The crystallization accompanies formation of V-Ar complexes with six vacant sites, and these complexes are found to be stable above 800 deg. C. These results have proved that positrons are very useful probes to study the chemical state of vacancy-inert gas atoms complexes

[en] In the manufacture of SIMOX a Si wafer is implanted with 1.7x10¹⁸, 180 keV oxygen ions. After implantation the wafer is annealed at 1350 deg. C. This process creates a top layer of silicon, which almost has the quality of bulk silicon, and an insulating layer of buried oxide (BOX), that separates the top layer from the Si wafer. Positron annihilation techniques are very sensitive for the open-volume defects produced during the implantation. The Doppler broadening of the annihilation radiation technique was applied to investigate the effect of dose variations and anneal temperature. The positron annihilation results show that the top silicon layer in SIMOX still contains small vacancy-oxygen clusters which cannot be observed with TEM

No abstract available

[en] A low velocity positron transporting equipment was designed and fabricated on the basis of an electrostatic method. The injection of positron beams with 2 keV energy into ethanethiol/Au and pentanethiol/Au produced C₂H₅S⁺ and CH₃(CH₂)₄S⁺ molecular ions, which were examined from the experiments by mass spectrometry. Alkanethiol molecules adsorpted on Au surface were desorpted by positron annihilation excitation. The selective excitation only for the molecules was inferred from no observation of other fragmental ions. The production of the molecular ions was certainly caused by ionization due to positron annihilation excitation, but not by coulomb excitation caused by the impact by positron beam bombardments, which was confirmed from no observation of the molecular ions by electron beam bombardment with the same energy. (Y.K.)

[en] Coincidence Doppler broadening (CDB) technique has been applied to the study on vacancy-oxygen (V-O) complexes and vacancy-hydrogen (V-H) complexes in Si. In order to avoid the difference in the relative core-electron annihilation rate and the directional anisotropy in electron momentum distribution, the Si ion implanted Si is useful as the standard sample for the defect study. V-O complexes give the broad peak from 10 x 10^-3 m₀c² to 20 x 10^-3 m₀c² in the CDB ratio spectrum, while V-H complexes the peak with 8 x 10^-3 m₀c². Combined with the positron lifetime data, the structures of the defects induced by O and H implantations to Si are discussed. (orig.)

[en] Amorphous layers produced at the surface of iron by B⁺ and C⁺ implantation (50 kV, 1x10¹⁸ ions cm^-2) were analyzed by CEMS. The CEM spectrum of B⁺ implanted layer was composed of broad doublet and sextet. Spread hyperfine field distribution, P(H), indicates the formation of extremely disordered FeB layer. Annealing at 400⁰C brought about precipitation of FeB, which was converted to Fe₂B by annealing at 500⁰C. The P(H) for C⁺ implanted iron was resolved to 3 subpeaks with H values of 11.0, 18.0 and 22.5 T. The amorphous FeC phase was strongly correlated to crystalline Fe₅C₂ and Fe₂C, which precipitated at 300⁰C and were transformed into Fe₃C at 500⁰C. The amorphous layer disappeared by annealing at 600⁰C. (orig.)

[en] Two-detector coincidence measurements of the Doppler broadened annihilation spectra with a variable energy positron beam are carried out for the study of the annealing behavior of Si implanted with As, P, Cu and H ions. In P-implanted Si, growth of the defect complexes are observed in coincidence Doppler broadening spectra up to 400degC. In Cu-implanted Si, the formation of defect-Cu complexes is indicated. In H-implanted Si, the passivation effect of hydrogen on positron traps are observed in the low temperature region up to 400degC. (author)

[en] Defects in Si induced by B and BF₂ ion implantation have been investigated by means of coincidence Doppler broadening measurements with a variable energy positron beam. In case of B implantation, the annihilation profiles are almost same for CZ-Si and FZ-Si before annealing. Annealing at 900 C makes the line shape back to that of unimplanted Si for both Si. But, annealing behavior is different between CZ-Si and FZ-Si. This difference may be attributed to presence of oxygen in CZ-Si. For Si implanted with BF₂ ions, annihilation profile is different from that of B:Si. The defects are not fully recovered even by 900 C annealing. (orig.)

[en] Ion desorption induced by positrons is observed for the first time from molecules adsorbed on a metal surface with identification of ion species. Positrons with an energy of 2 keV cause ion desorption from ethanethiol/Au and pentanethiol/Au. Absence of ion desorption by electrons with the same energy suggests that ion desorption is due to annihilation of bonding electrons with positrons. Only molecular ions are observed without fragmentation. (orig.)