Diffuse Surface Scattering in the Plasmonic Resonances of Ultra-Low Electron Density Nanospheres

Localized surface plasmon resonances (LSPRs) have recently been identified in extremely diluted electron systems obtained by doping semiconductor quantum dots. Here we investigate the role that different surface effects, namely electronic spill-out and diffuse surface scattering, play in the optical properties of these ultra-low electron density nanosystems. Diffuse scattering originates from imperfections or roughness at a microscopic scale on the surface. Using an electromagnetic theory that describes this mechanism in conjunction with a dielectric function including the quantum size effect, we find that the LSPRs show an oscillatory behavior both in position and width for large particles and a strong blueshift in energy and an increased width for smaller radii, consistent with recent experimental results for photodoped ZnO nanocrystals. We thus show that the commonly ignored process of diffuse surface scattering is a more important mechanism affecting the plasmonic properties of ultra-low electron density nanoparticles than the spill-out effect.Comment: 19 pages, 5 figures. Accepted for publication in The Journal of Physical Chemistry Letter

Surface scattering contribution to the plasmon width in embedded Ag nanospheres

Nanometer-sized metal particles exhibit broadening of the localized surface plasmon resonance (LSPR) in comparison to its value predicted by the classical Mie theory. Using our model for the LSPR dependence on non-local surface screening and size quantization, we quantitatively relate the observed plasmon width to the nanoparticle radius $R$ and the permittivity of the surrounding medium $\epsilon_m$. For Ag nanospheres larger than 8 nm only the non-local dynamical effects occurring at the surface are important and, up to a diameter of 25 nm, dominate over the bulk scattering mechanism. Qualitatively, the LSPR width is inversely proportional to the particle size and has a nonmonotonic dependence on the permittivity of the host medium, exhibiting for Ag a maximum at $\epsilon_m\approx2.5$. Our calculated LSPR width is compared with recent experimental data.Comment: 11 pages, 4 figures. Accepted for publication in Optics Expres

Properties of the SR Ca-ATPase in an Open Microsomal Membrane Preparation

SR vesicles isolated from rabbit muscle were treated by a SDS incubation and subsequent dialysis to obtain open membrane fragments that allow a direct access to the luminal membrane surface and especially to the ion-binding sites in the P-E2 conformation of the Ca-ATPase. The open membrane fragments showed about 80% of the enzyme activity in the untreated membranes. Pump function was investigated by using electrochromic styryl dyes. The kinetic properties of cytoplasmic ion binding showed no significant differences between the Ca-ATPases in SR vesicles and in membrane fragments. From pH-dependent Ca2+ binding it could be deduced that due to the SDS treatment the density of negatively charged lipid was increased by one elementary charge per 12 lipid molecules. Major differences between Ca-ATPase from SR vesicles and membrane fragments were the respective fluorescence amplitudes. This effect is, however, produced by dye-lipid interaction and not by pump function. It was demonstrated that time-resolved kinetics may be study by the use of caged compounds such as caged ATP or caged calcium also in the case of the membrane fragments

Inactivation of the Na,K-ATPase by radiation-induced free radicals Evidence for a radical-chain mechanism

AbstractFree radicals produced by water radiolysis were used to study the inactivation of the enzymatic activity of the Na,K-ATPase. A decrease of the activity to virtually zero with a mono-exponential dependence on the radiation dose was observed. The inactivation process is initiated by hydroxyl radicals. This was shown by the effect of appropriate radical scavengers such as t-butanol, formate and vitamin C. In all cases a significant increase in the characteristic D37 dose of inactivation was observed. Inactivation was found to show a so-called inverse dose-rate effect, i.e, the sensitivity of the enzyme to radical attack is increased if the dose rate is reduced. The data were found to agree with the relationship 1/D371̃/D1/2, which is known to be a strong indicator of a radical chain mechanism. This means that the inactivation, after initiation by single radicals, is amplified by a subsequent chain mechanism

Theory of a magnetic microscope with nanometer resolution

We propose a theory for a type of apertureless scanning near field microscopy that is intended to allow the measurement of magnetism on a nanometer length scale. A scanning probe, for example a scanning tunneling microscope (STM) tip, is used to scan a magnetic substrate while a laser is focused on it. The electric field between the tip and substrate is enhanced in such a way that the circular polarization due to the Kerr effect, which is normally of order 0.1% is increased by up to two orders of magnitude for the case of a Ag or W tip and an Fe sample. Apart from this there is a large background of circular polarization which is non-magnetic in origin. This circular polarization is produced by light scattered from the STM tip and substrate. A detailed retarded calculation for this light-in-light-out experiment is presented.Comment: 17 pages, 8 figure

Quantitative calculation of the role of the Na+,K+-ATPase in thermogenesis

AbstractThe Na+,K+-ATPase is accepted as an important source of heat generation (thermogenesis) in animals. Based on information gained on the kinetics of the enzyme's partial reactions we consider via computer simulation whether modifications to the function of the combined Na+,K+-ATPase/plasma membrane complex system could lead to an increased body temperature, either through the course of evolution or during an individual's lifespan. The enzyme's kinetics must be considered because it is the rate of heat generation which determines body temperature, not simply the amount of heat per enzymatic cycle. The results obtained indicate that a decrease in thermodynamic efficiency of the Na+,K+-ATPase, which could come about by Na+ substituting for K+ on the enzyme's extracellular face, could not account for increased thermogenesis. The only feasible mechanisms are an increase in the enzyme's expression level or an increase in its ion pumping activity. The major source of Na+,K+-ATPase-related thermogenesis (72% of heat production) is found to derive from passive Na+ diffusion into the cell, which counterbalances outward Na+ pumping to maintain a constant Na+ concentration gradient across the membrane. A simultaneous increase in both Na+,K+-ATPase activity and the membrane's passive Na+ permeability could promote a higher body temperature