Luminescence and optical absorption associated with relaxed excitons in pure RbI have been studied by means of time-resolved spectroscopy. It is found that the emission band near 3.0 eV consists of an intrinsic component and an extrinsic component arising from Br - impurities. The intrinsic component, characterized by the same decay time as that of the π luminescence, exhibits an emission band peaking at 3.07 eV. The results indicate the presence of three intrinsic emission bands in RbI, the 3.07 eV, π and σ bands. The optical absorption originating from the initial states for the 3.07-eV and π luminescence is compared with the corresponding absorption in other alkali halides by means of the Mollwo-Ivey relation. It is shown that the absorption bands from the initial state of the π luminescence in alkali halides, except NaBr and NaI, can be categorized into two groups: one includes that for the 3.07-eV luminescence and the other that for the π luminescence.
Electronic excitation is a means to change materials properties. This book analyses the important features of the changes induced by electronic excitation, identifies what is critical, and provides a basis from which materials modification can be developed successfully. Electronic excitation by lasers or electron beams can change the properties of materials. In the last few years, there has been a mix of basic science, of new laser and electron beam tools, and of new needs from microelectronics, photonics and nanotechnology. This book extends and synthesises the science, addressing ideas like energy localisation and charge localisation, with detailed comparisons of experiment and theory. It also identifies the ways this understanding links to technological needs, like selective removal of material, controlled changes, altering the balance between process steps, and possibilities of quantum control. This book will be of particular interest to research workers in physics, chemistry, electronic engineering and materials science.
Abstract The effects of segregation on the preferred sputtering of alloy surfaces have been analyzed. The top layer of the surface is regarded as behaving differently from the layers beneath the second layer: segregation and dissolution rate constants between the top and second layers are included in the kinetic equations explicitly. It is shown that the fundamental kinetic equations are of a form similar to that developed by Ho, Webb, Carter and Collins, even though the coefficients of the equations are different. The time-dependent solution of the kinetic equations shows that the segregation rate constant plays an important role in the build-up of the steady state. Similarly to the previous result, the altered layer is shown to have a thickness of the diffusion constant divided by the velocity of the recession of the surface. The steady-state compositions at the top and second layers relative to the bulk composition were found to be a function of three parameters: the surface enrichment factor, the diffusion constant divided by the velocity, and the ratio of the yields of atomic removal from the top layer, a correction factor being needed in a particular boundary condition. The existing experimental data on Cu-Ni, Cu-Au and some other alloys are surveyed critically in terms of the results of the theoretical calculation.
Initial processes of self-trapping of holes and electron-hole pairs in KI and RbI crystals have been investigated by means of a femtosecond pump-probe spectroscopy. We have found that a new short-lived intermediate is formed as a precursor of the self-trapped hole in the form of the halogen molecular ion with a ${D}_{2h}$ symmetry. This state is identified to be a one-center type self-trapped hole on the basis of the quantum mechanical cluster calculations. A one-center self-trapped state is also created as a precursor for self-trapped excitons.
AbstractExperimental studies of optical absorption and electron paramagnetic resonance of naphthalene single crystal irradiated at liquid nitrogen, dry ice and room temperatures have been made. It is found that the epr spectrum associated with the l-hydronaphthyl radical is produced at all temperatures studied. Optical absorption bands at 337, 395 and 530 nm are assigned to be associated with the l-hydronaphthyl radical. Irradiation at liquid nitrogen temperature produces a broad doublet epr spectrum as well as that associated with the l-hydronaphthyl radical; the former is considered to be caused by the naphthyl radical. Irradiation at dry ice and room temperatures produces optical absorption bands which are associated neither with the hydronaphthyl nor the naphthyl radical. It is suggested that the radiation products at higher temperature are the hydronaphthyl radical and the naphthalene dimer which is formed as the result of reaction of the naphthyl radical with a neighboring molecule.
A Cu/Si layered-gate-structured MOSFET with Ta and TaN stacked barrier layers fabricated using a Cu damascene process has been developed for high-performance and reliable Si ULSI devices. A sheet resistance of 0.5 ohm/sq. was achieved with a 0.25 /spl mu/m gate length. The Ta and TaN layers guarantee reliable gate oxide (7.5 nm) after 500/spl deg/C thermal processing in nitrogen with forming gas annealing.
The immune-modulating effect following intradermal injection of various-sized amorphous silica particles was analyzed in terms of induction of ovalbumin-specific CD8+ T cells in vivo. IFN-gamma ELISPOT assays revealed that only nanosilica particles with a diameter of less than 100 nm significantly enhanced CD8+ T cell responses against ovalbumin. These results indicate that the size of nanomaterials is a critical determinant in terms of their safe use.
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