Structure and spatial distribution of Ge nanocrystals subjected to fast neutron irradiation

The influence of fast neutron irradiation on the structure and spatial distribution of Ge nanocrystals (NC) embedded in an amorphous SiO2 matrix has been studied. The investigation was conducted by means of laser Raman Scattering (RS), High Resolution Transmission Electron Microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS). The irradiation of NC-Ge samples by a high dose of fast neutrons lead to a partial destruction of the nanocrystals. Full reconstruction of crystallinity was achieved after annealing the radiation damage at 800 deg. C, which resulted in full restoration of the RS spectrum. HR-TEM images show, however, that the spatial distributions of NC-Ge changed as a result of irradiation and annealing. A sharp decrease in NC distribution towards the SiO2 surface has been observed. This was accompanied by XPS detection of Ge oxides and elemental Ge within both the surface and subsurface region

Regret Minimization for Branching Experts

We study regret minimization bounds in which the dependence on the number of experts is replaced by measures of the realized complexity of the expert class. The measures we consider are defined in retrospect given the realized losses. We concentrate on two interesting cases. In the first, our measure of complexity is the number of different "leading experts", namely, experts that were best at some point in time. We derive regret bounds that depend only on this measure, independent of the total number of experts. We also consider a case where all experts remain grouped in just a few clusters in terms of their realized cumulative losses. Here too, our regret bounds depend only on the number of clusters determined in retrospect, which serves as a measure of complexity. Our results are obtained as special cases of a more general analysis for a setting of branching experts, where the set of experts may grow over time according to a tree-like structure, determined by an adversary. For this setting of branching experts, we give algorithms and analysis that cover both the full information and the bandit scenarios

Regret minimization for branching experts

We study regret minimization bounds in which the dependence on the number of experts is replaced by measures of the realized complexity of the expert class. The measures we consider are defined in retrospect given the realized losses. We concentrate on two interesting cases. In the first, our measure of complexity is the number of different "leading experts", namely, experts that were best at some point in time. We derive regret bounds that depend only on this measure, independent of the total number of experts. We also consider a case where all experts remain grouped in just a few clusters in terms of their realized cumulative losses. Here too, our regret bounds depend only on the number of clusters determined in retrospect, which serves as a measure of complexity. Our results are obtained as special cases of a more general analysis for a setting of branching experts, where the set of experts may grow over time according to a tree-like structure, determined by an adversary. For this setting of branching experts, we give algorithms and analysis that cover both the full information and the bandit scenarios

In situ spectroscopic applications to the study of rechargeable lithium batteries. Final report

A new experimental approach has been developed and implemented for the study of various aspects of lithium electrochemistry under utmost conditions of cleanliness. This novel strategy takes advantage of the low vapor pressure of ultrapure lithium salt/polyethylene oxide electrolytes for conducting conventional electrochemical experiments in ultrahigh vacuum environments with a wide variety of electrodes prepared and characterized by surface analytical techniques. Two processes were investigated using a LiClO{sub 4}/PEO electrolyte at temperatures in the range of 55-70 {degrees}C: (1) electrochemical insertion of lithium into the basal plane of highly ordered pyrolytic graphite, HOPG(bp), (2) underpotential deposition (UPD) of Li onto polycrystalline Au. The results provided conclusive evidence (except for impurity effects) that the electrochemical behavior observed in UHV is indeed characteristic of the systems selected for these studies, and therefore, is not affected in any discernible way by the ultralow pressures. In the case of Li UPD on polycrystalline Au, the voltammetric curves were similar to those observed in liquid non- aqueous solvent electrolytes, displaying deposition and stripping peaks with a charge equivalent to the adsorption and desorption of a single Li{sup +} per surface site

Unusually stable and highly electrochemically reversible n-doping of regioregular alternate copolymer of dialkylthiophene and fluorenone

We describe detailed studies on the electrochemical activity of thin films of a new conjugated copolymer, namely, poly[(2,7-fluoren-9-one)-alt-(5,5′-(3,3′-di-n-octyl-2,2′-bithiophene))] (abbreviated PFDOBT-HH (HH = head-to-head)), which has been synthesized electrochemically by a mild oxidation process at low current density. The dynamics of both p- and n-dopings of PFDOBT-HH in sulfolane/TEABF4 solution was fully characterized by a combination of cyclic voltammetry (CV) and electrochemical impedance spectroscopic (EIS) investigations. The development of a stable and highly electrochemically reversible n-doping capacity of the polymer film is presented as a function of the vertex potential in the CV curves of the n-doped PFDOBT-HH. Using EIS, clear evidence is furnished for the presence of trapped, negatively charged species in the polymer bulk as a consequence of prolonged, consecutive n-doping. Qualitative differentiation between the responses originating from mobile and trapped charge carriers has been established. In contrast to the cases of pristine polythiophene, polyfluorothiophene and nanoscale aryleneethynylene oligomers, n-doping of PFDOBT-HH, although leading to a partial trapping of the negatively charged carriers, does not result in any irreversible change in the electrochemical behavior of this polymer. Keywords: CV, PITT, n-doping, Charge trapping, Poly(fluorenone-bithiophene) copolyme