Seiji Seki

Observation of Hg diffusion in CdTe by means of 40‐MeV O5+ ion backscattering

The diffusion profile of Hg in CdTe crystals was observed by means of heavy ion (40 MeV O5+) backscattering. The near‐surface region of CdTe immersed in Hg was investigated up to 1.4 μm from the surface. The observed Hg profile indicated that the concentration of Hg atom at the surface reached 4×1020 cm−3 and the distribution was interpreted by a simple diffusion model. Temperature dependence of the diffusion coefficient was determined to be D=5×103 exp[(−2.0±0.3) eV/kT] (cm2/s). In the case of CdTe immersed in Hg which contained a small amount of Cd, it was found that Hg diffusion did not occur. These experimental facts suggest that the rate of Hg diffusion is controlled by the diffusion of a Cd vacancy which is introduced by the outdiffusion of Cd atoms from CdTe crystals.

Hg content and thermal stability of the anodic sulfide films on Hg1−xCdxTe investigated by 30–40‐MeV O5+ ion backscattering

The Hg content of anodic sulfide films on Hg1−xCdxTe (MCT) were investigated for as‐grown and heat‐treated films by using 30–40‐MeV O5+ ion backscattering. Heat treatments were performed in a vacuum for 60 min at various temperatures up to 300 °C for the samples with x=0.20 and up to 350 °C for the samples with x=0.30 and 0.35. A significant Hg content of about 15 at. % of Cd was found in the as‐grown anodic sulfide film on MCT samples with x=0.20, 0.30, and 0.35. After heat treatment above 260 °C for x=0.30 and 0.35 and above 210–240 °C for x=0.20, the Hg atoms were removed from the films, and Hg deficient layers were formed near the interface region of the MCT crystal. This suggests that the residual Hg in the anodic sulfide films introduced during the sulfidization process plays an important role toward the degradation of the passivation properties of the sulfide film on MCT.

Epitaxial Growth of α-Fe Film on Si(111) Substrate by Low-Energy Direct Ion Beam Deposition

Fe film growth on Si(111) substrate was carried out by low-energy direct ion beam deposition. Fe films of about 1000 A thick were grown at Fe+ ion energies of 10 eV, 20 eV, 50 eV and 100 eV without removing the native oxide layer on the Si substrate. Single-crystal α-Fe(111) films were obtained at 20 eV, 50 eV and 100 eV at room temperature, while (110)-preferred-oriented α-Fe film was obtained at 10 eV. Cross-sectional high-resolution transmission electron microscopy (TEM) studies show that the removal of the native oxide layers on the Si substrates by Fe+ ion irradiation results in the epitaxial ordering of the α-Fe films when the films are grown at 20 eV, 50 eV and 100 eV.

Test of phototube bases for high counting rates

Abstract We report on test measurements of the counting efficiency using a newly developed miniature photomultiplier R1635. Two methods of the voltage stabilization have been used: (1) the emitter follower type by NPN transistors and (2) the booster type in which the constant dynode voltage is supplied from a separate power supply. The test was performed by using a light emitting diode and 10 MeV protons from a tandem accelerator. Both methods of voltage stabilization have shown good results. A counting efficiency of about 100% could be obtained up to a flux of 2×10 6 particles/s (pps) and 85% at 10 7 pps.

Charge states of fast heavy ions in glancing collisions with aligned atoms in single crystals

Abstract Spectroscopy of ion-induced secondary electrons emitted from single crystals allows observation of high-energy shadowing which is the initial stage of ion channeling. The high-energy shadowing effect is sensitive to short-range (∼ 0.1 A) screening of the ions nuclear charge by inner-shell electrons and, accordingly, reflects the charge states of the ions moving in the crystal. This article reports recent progress in the study of charge states of MeV/u ions in glancing collisions with crystal atoms.

Atomic migration and surface evaporation of Hg in Hg1−x CdxTe crystals observed by 40‐MeV O5+ ion backscattering method

Dissociation and evaporation of Hg from the near‐surface region of Hg1−xCdxTe crystals was investigated, up to several microns, by means of 40‐MeV O5+ backscattering. Samples with x=0.18 and 0.32 were heat treated in a vacuum for 60 min at various temperatures up to 320 and 340 °C, respectively. The change of the backscattering spectra with the temperature of heat treatment indicated that the Hg atoms outdiffused partly from the near‐surface region of the crystals at higher temperatures than 280 and 320 °C for x=0.18 and 0.32, respectively. This behavior of outdiffusion is in contrast to the case of HgTe crystal.

Observation of surface evaporation of Hg from HgTe crystals by means of energetic oxygen ion backscattering

Dissociation of Hg from the near‐surface region of HgTe crystals was observed, up to 10 μm, by means of 42‐MeV O5+ backscattering. Samples were annealed in vacuum at various temperatures up to 280 °C. The change of the backscattering spectra with annealing time and temperature indicated that the Hg atoms evaporated almost completely from the near‐surface region to a depth d(t,T) and that only Te atoms remained there. The interface between the Te region and the HgTe crystal migrated at a velocity u(T) which was determined as u(T)=1.2×105 exp(−1.2 eV/kT) cm/sec. This is accounted for by a simple phenomenological model which suggests that the migration of the Hg atoms across the interface is the rate controlling process for the whole boundary migration process.

Hg content of anodic oxide films on Hg1−xCdxTe after heat treatment as measured by 40 MeV‐O5+ ion backscattering

The Hg concentration of anodic oxide films on Hg1−xCdxTe and its change after heat treatment were investigated by using 40 MeV‐O5+ backscattering. Heat treatment in a vacuum for 60 min was performed at various temperatures up to 350 and 400 °C, respectively, for the samples with x=0.19 and x=0.32. A significant Hg content in the as‐grown anodic oxide was found in accordance with the recent result of C. M. Stahle, D. J. Thomson, C. R. Helms, C. H. Becker, and A. Simmons [Appl. Phys. Lett. 47, 521 (1985)]. The Hg in the film gradually decreased with increasing heat treatment temperature up to about 290 °C and rapidly disappeared above 290 °C for both x=0.19 and x=0.32.

Atomic Migration of Metals in the Interfaces of Au-Si and Ni-Si for Crystalline and Amorphous Si Observed by 40 MeV-O5+ Ion Backscattering

Atomic migration of metallic atoms in the interfaces of Au-Si and Ni-Si is investigated with emphasis on the difference among c-Si, a-Si:H/c-Si and a-Si:F:H/c-Si. 40 MeV-O5+ ion backscattering spectra of the Au-Si system heat-treated at 350°C for 30 min indicate that Au atoms of more than 1020cm-3 were distributed in Si up to a depth of about 1 µm and 3 µm for a-Si:F:H/c-Si and a-Si:H/c-Si, respectively. Because the thickness of a-Si is about 5000 A, this means that a large amount of Au migrated not only in the a-Si film but also into the substrate of c-Si even below the eutectic point, while Au-migration was not observed in the case of direct contact interface between Au and c-Si.

Emittance measurement of mass-separated high-current ion beams

Abstract We have developed an emittance measurement system which can observe emittance both in the horizontal plane (dispersive plane of a mass separator) and in the vertical plane of mass-separated high-current ion beams. Using this system, we have measured the emittance of several ion species and charge states from ion sources at various operational conditions. A large displacement of the deduced image of the ion source from the actual position due to the space charge effect, which depends basically on the current density of the total extracted beam and slightly on the ion species or the charge state, was observed. Mass dependent angular fluctuations observed from an identical plasma indicate that the extracted ion suffers from a strong scattering effect.