Science and technology: A radiochemist's view

A historical perspective is presented from a radiochemist's point of view.     

Directional dispersion of extraordinary phonons in layer compound InSe

The resonant Raman scattering of polar optical phonons has been measured in trigonal γ-InSe at the E'₁ exciton edge. The two-phonon scattering spectrum widely spreads over the frequency range of 50 cm^-1 with an extremely asymmetric lineshape. This spectrum has been interpreted in terms of the directional dispersion of extraordinary LO and TO phonons.     

Field-ion microscopy of GaAs and GaP

Clean surfaces of GaAs and GaP were studied by field-ion microscope (FIM). Field-ion images with ordered surfaces were first obtained in pure hydrogen, neon-50% hydrogen and pure neon gases at 78 K, by using channeltron electron multiplier arrays (CEMA). The field-ion images of GaAs were quite similar to those of GaP with respect to the surface structure and the image contrast. They showed the anisotropies of the ion emission and the surface structure between the [111] and $\text{[}\text{1}\text{1}\text{1}\text{]}$ orientations. Ring steps expected from a spherical surface were observed on the (111) and {100} planes, but not on the $\text{[}\text{1}\text{1}\text{1}\text{]}$ and {110} planes. The regional brightness of the FIM patterns was discussed in terms of the Knor and Müller model and the atomic and electronic structures of the surface. The image field of these crystals was much lower than that of metals usually used in FIM. For example, the image field strength for the hydrogen and GaAs system was about 1.1 V/Å. The reduction of the field necessary to image was also discussed in terms of the field penetration effect.     

Exafs study of FeCl3-doped polyacetylene

FeK absorption spectra of FeCl₃-doped polyacetylene [CH(FeCl₃)_y]_x having y values of 0.024, 0.087 and 0.13, were measured by use of synchrotron radiation. The analyses of observed EXAFS data showed that Fe atom is surrounded by about four Cl atoms with Fe-Cl distance of 2.18–2.20 Å. It is concluded that the dopant exists mainly in the form of FeCl₄^-, and the following reaction takes place in the FeCl₃ doping process. 2FeCl₃ + e^- → FeCl₄^- + FeCl₂     

Production of heavy resonances with electron and muon beams

The inelastic leptoproduction of heavy resonances J (J = J/ψ, Ψ,…) is investigated in a model where γ_vg → Jg is assumed to be the dominant mechanism. Analytic expressions for the differential cross section as well as for the helicity amplitudes are presented. A detailed numerical analysis of the angular distribution of the muon pair arising from the decay of the heavy resonance in its rest frame is presented.     

High-order harmonic generation from boron plasma in the extreme-ultraviolet range

We demonstrate the generation of up to the 63rd harmonic (lambda = 12.6 nm) of a Ti:sapphire laser pulse (150 fs, 10 mJ), using a prepulse- (210-ps,24-mJ) produced boron plasma as the nonlinear medium. The influence of various parameters on the harmonic conversion efficiency was analyzed. The steep decrease in intensity for low-order harmonics (up to 19th order) was followed by a plateau. Typical conversion efficiencies were evaluated to be 10(-4) (for a 3rd harmonic) to 10(-7) (within the plateau region). Harmonic generation appeared to be efficient for the plasma that comprised neutral atoms and singly ionized boron.     

Nonameric porphyrin assemblies--formation and intra-assembly energy transfer reactions

The nonameric porphyrin assemblies constructed with the series of free base tetraphenylporphyrins Pn having four pyrazine moieties linked with alkyl chains of different lengths, (CH2)n (n = 1, 5, 9, 17, 30), and dimeric [meso-tetrakis(2-carboxy-4-nonylphenyl)porphyrinato]zinc(II), ZnP2, show the effective light-collection effect and the typical Forster-type energy transfer from ZnP2 to Pn.     

Nonlinear optical characteristics of CdS and ZnS nanoparticles implanted into zirconium oxide thin films

The nonlinear refractive indices γ and nonlinear absorption coefficients of ZrO₂ films doped with CdS or ZnS nanoparticles, as well as with various metals, are measured. The effects of semiconductor and metal nanoparticles and annealing on the nonlinear optical properties of films are studied. The structural parameters of films, determined by electron microscopy and x-ray dispersion spectroscopy, are compared to the optical and nonlinear optical characteristics of these media. The high magnitude of γ of the films ((3±0.6)×10^?11 cm² W^{? 1}) is attributed to the surface enhancement effect in semiconductor nanoparticles. On the basis of Z-scan data obtained at different intensities of radiation, it is shown that the variations in γ of the ZrO₂:CdS(Cr) and ZrO₂:ZnS(Mn) films are related to the generation of free carriers.