Ag nanoparticles with a diameter of 10 ( 5 nm were generated in the gas phase by using a sputtering/ aggregation source and deposited onto NaCl prisms. Internal reflection spectroscopy was utilized to acquire UV-vis spectra of the nanoparticles in situ as they were being deposited. As the deposition proceeded, the interparticle spacing decreased steadily to effectively zero (contact). When the interparticle spacing was in the ca. sub-10 nm range, near-field coupling between the particles caused an increase in the intensity of the quadrupolar absorption, relative to the dipolar one. The deposition of gas-phase nanoparticles onto NaCl allows the average interparticle spacing to be varied, even in the 0-10 nm region, which is beyond the resolution of lithography techniques. This is the region where near-field interparticle coupling effects are important. To our knowledge, these are the first absorption spectra of quadrupolar resonances in particles less than ∼40 nm in diameter.

Minimal quenching of fluorescence emission was observed when the fluorescent dye AlexaFluor 514 (AF514) was covalently bound to gold monolayer protected clusters (AuMPCs) that have negligible plasmon bands (diameters <2 nm). The fluorescence emission of the conjugated dye was measured as a function of dye-AuMPC mixing ratio with a combination of steady-state and time-resolved ensemble spectroscopic measurements in conjunction with single-molecule fluorescence microscopy. Fluorescence emission of the conjugated samples decreased slightly as a function of dye mixing ratio, which, in combination with a negligible change in fluorescence lifetime, was attributed to static quenching of the dye by the AuMPCs. From the single-molecule fluorescence measurements, it was observed that luminescent conjugates could still be detected, and, at all loading ratios, almost all of the dye-particle conjugates photobleached in either a single-or doublestep process, with a small subpopulation exhibiting more than two photobleaching events. Beyond simple, irreversible photobleaching, no additional blinking dynamics were detected at the single-molecule level within the time resolution of the experiment. Emission intensities of coupled fluorophores were comparable with those measured of dye molecules that had not been attached to the AuMPCs, suggesting that the statically quenched fluorophores are entirely nonemissive, whereas the remaining dyes are essentially unquenched. These results are discussed in the context of other dye-AuMPC coupled systems described in the literature.

The sensitivity of various polymers to radiation damage by soft X-rays has been measured previously with scanning transmission X-ray microscopes. However, the critical dose values reported by different groups for the same material differ by more than 100%. Possible sources of this variability are investigated here for poly(methyl methacrylate) (PMMA) using controlled exposure to monochromatic soft X-rays at 300 eV. Radiation sensitivity, judged by several different criteria, was evaluated as a function of dose rate, pre-exposure thermal treatments and X-ray polarization. Both the measured critical dose and the dose required to initiate negative mode (cross-linking) were observed to depend only on dose, not the other factors explored. A method of determining detector efficiency from the dose required to initiate negative mode in PMMA is outlined. This method was applied to many of the soft X-ray STXMs presently operating to derive the efficiencies of their transmitted X-ray detectors in the C 1s absorption-edge region.

We present a new method to fabricate wedged multilayer Laue lenses, in which the angle of diffracting layers smoothly varies in the lens to achieve optimum diffracting efficiency across the entire pupil of the lens. This was achieved by depositing a multilayer onto a flat substrate placed in the penumbra of a straight-edge mask. The distance between the mask and the substrate was calibrated and the multilayer Laue lens was cut in a position where the varying layer thickness and the varying layer tilt simultaneously satisfy the Fresnel zone plate condition and Bragg's law for all layers in the stack. This method can be used to extend the achievable numerical aperture of multilayer Laue lenses to reach considerably smaller focal spot sizes than achievable with lenses composed of parallel layers.