Reduction of Peroxodisulfate at Porous and Crystalline Silicon Electrodes: An Anomaly\ud

Electroluminescence from n-type porous silicon can be generated in solution by reduction of peroxodisulfate. It has been assumed that the SO4•- radical ion, formed in the first reduction step, injects a hole into the valence band of the porous semiconductor. The hole should subsequently undergo radiative recombination with a conduction band electron. Using two techniques, viz., photocurrent quantum efficiency measurements with p-type porous and crystalline silicon electrodes and minority carrier injection studies with the “transistor technique”, we found that the reduction of peroxodisulfate is, however, not always accompanied by hole injection. The silicon results are compared with results obtained on GaAs electrodes. \u

Infrared induced visible emission from porous silicon: the mechanism of anodic oxidatio

The visible luminescence caused by anodic oxidation of p-type porous silicon has been studied. It is shown that similar luminescence can be observed in n-type material by illumination with near-infrared light. Addition of a suitable reducing agent to the electrolyte solution can both suppress the oxidation of the porous layer and quench its luminescence. These results confirm a previously suggested mechanism, in which the capture of a valence band hole in a surface bond of the porous semiconductor gives rise to a surface state intermediate capable of thermally injecting an electron into the conduction band.\ud \u

Photoselective Metal Deposition on Amorphous Silicon p-i-n Solar Cells\ud

A novel method is described for the patternwise metallization of amorphous silicon solar cells, based on photocathodic deposition. The electric field of the p-i-n structure is used for the separation of photogenerated charge carriers. The electrons are driven to the interface of the n+-layer with the solution where they reduce metal ions to metal. The large difference between the conductivity of dark and illuminated areas and the high sheet resistance of the n-type layer makes it possible to define a metal pattern by selective illumination. It is shown that both nickel and gold patterns can be deposited using this method. After annealing, an ohmic nickel contact is formed and the cell exhibits good photovoltaic characteristics

Focused ion beam milling of three dimensional nanostructures with high precision

The fabrication of an extended three-dimensional nanostructure with dimensions much larger than the feature size using a focused ion beam is described. By milling two identical patterns of pores with a designed diameter of 460 nm in orthogonal directions, a photonic crystal with an inverse woodpile structure was made in a gallium phosphide single crystal. The patterns are aligned with an unprecedented accuracy of 30 nm with respect to each other. The influence of GaP redeposition on the depth, shape, and size of the pores is described. The work is published in J. Vac. Sci. Technol. B [1]

Стандартизация в сфере менеджмента информационной безопасности

Описано сучасний стан стандартизації в сфері менеджменту інформаційної безпеки. Розглянуто вимоги до стандартів, що розробляються, типи стандартів, принципи, яких слід дотримуватись під час розроблення стандартів. Робота грунтується на матеріалах, прийнятих в підкомітеті ПК 27 «Методи захисту» об’єднаного технічного комітету ІСО/ МЕК ОТК 1 «Інформаційні технології».The article describes state of the art of the standardization in information security area. The requirements to the standards being developed, the types of standards, the principles to which it is required to follow are discussed. The contents of the article is based on the documents adopted within subcommittee 27 ”Security techniques” of the joint technical committee ISO/IEC JTC 1 “Information technology”

Channel Coupling in A(e⃗,e′N⃗)BA(\vec{e},e' \vec{N})B Reactions

The sensitivity of momentum distributions, recoil polarization observables, and response functions for nucleon knockout by polarized electrons to channel coupling in final-state interactions is investigated using a model in which both the distorting and the coupling potentials are constructed by folding density-dependent effective interactions with nuclear transition densities. Calculations for $^{16}$O are presented for 200 and 433 MeV ejectile energies, corresponding to proposed experiments at MAMI and TJNAF, and for $^{12}$C at 70 and 270 MeV, corresponding to experiments at NIKHEF and MIT-Bates. The relative importance of charge exchange decreases as the ejectile energy increases, but remains significant for 200 MeV. Both proton and neutron knockout cross sections for large recoil momenta, $p_m > 300$ MeV/c, are substantially affected by inelastic couplings even at 433 MeV. Significant effects on the cross section for neutron knockout are also predicted at smaller recoil momenta, especially for low energies. Polarization transfer for proton knockout is insensitive to channel coupling, even for fairly low ejectile energies, but polarization transfer for neutron knockout retains nonnegligible sensitivity to channel coupling for energies up to about 200 MeV. The present results suggest that possible medium modifications of neutron and proton electromagnetic form factors for $Q^2 \gtrsim 0.5 (GeV/c)^2$ can be studied using recoil polarization with relatively little sensitivity due to final state interactions.Comment: Substantially revised version accepted by Phys. Rev. C; shortened to 49 pages including 21 figure

Probabilities for dopant pair-state formation in a nanocrystal: simulations and theory

For certain dopants, luminescence measurements allow one to distin- guish between single-ion and pair-state dopant emission in a (semicon- ductor) host. In a bulk crystal the concentration of each of these dopant- states can be calculated from the dopant fraction present in the material, and is found to correlate with luminescence measurements. However, for a nanocrystalline host-lattice, these concentrations cannot be calculated due to the difference in coordination numbers for ions at the surface (a substantial fraction in nanocrystals) and in the bulk. Here simulations of dopant pair-state distributions are presented for a zincblende nanocrystal. The probability of finding at least one pair-state in the nanocrystal and the percentage of dopants forming part of a pair-state were calculated on the basis of a statistical average of 1 . 105 simulations for the same crystal size and dopant concentration. Furthermore, the distribution of nanocrystal lattice positions over the surface and the bulk of the crystal are computed from the simulations and found to agree well with a first- order theory. Finally, a closed-form approximation of the probabilities (valid in any crystal lattice) and a rigorous upper bound for the error in the approximation are discussed

Photoelectrochemical Characterization of Nanocrystalline ZnS :Mn^(2+) Layers

Measurements of the photoelectrochemical properties of nanocrystalline ZnS electrodes doped with Mn^(2+) are presented and discussed. The observation of both anodic and cathodic photocurrent is direct evidence for the nanocrystalline nature of the system. In-situ photoluminescence measurements showed stable Mn^(2+) related photoluminescence over a large potential range. Due to the unfavourable kinetics of electron and hole transfer across the interface between the nanocrystallites and solution, it is concluded that recombination accounts for most of the charge carriers generated by illumination. Breakdown of the ZnS into elementary Zn and S^(2-) in solution was also observed at negative potential. This breakdown introduces new non-radiative decay paths and is responsible for the slow luminescence decrease as a function of operating time