The22 Ne(p,γ) 23 Na reaction is included in the neon-sodium cycle of hydrogen burning. A number of narrow resonances in the Gamow window dominate the thermonuclear reaction rate. Several resonance strengths are only poorly known. As a result, the 22 Ne(p,γ) 23 Na thermonuclear reaction rate is the most uncertain rate of the cycle. Here, a new experimental study of the strengths of the resonances at 436, 479, 639, 661, and 1279 keV proton beam energy is reported. The data have been obtained using a tantalum target implanted with 22 Ne. The strengths ωγ of the resonances at 436, 639, and 661 keV have been determined with a relative approach, using the 479-and 1279-keV resonances for normalization. Subsequently, the ratio of resonance strengths of the 479-and 1279-keV resonances was determined, improving the precision of these two standards. The new data are consistent with, but more precise than, the literature with the exception of the resonance at 661 keV, which is found to be less intense by one order of magnitude. In addition, improved branching ratios have been determined for the gamma decay of the resonances at 436, 479, and 639 keV.

No abstract

Ultra-small molecule-like AuN nanoclusters made by a number of atoms N less than 30 were produced by ion implantation in silica substrates. Their room temperature photoluminescence properties in the visible and near-infrared range have been investigated and correlated with the Er sensitization effects observed in Er-Au co-implanted samples. The intense photoluminescence emission under 488 nm laser excitation occurs in three different spectral regions around 750 nm (band A), 980 nm (band B) and 1150 nm (band C) as a consequence of the formation of discrete energy levels in the electronic structure of the molecule-like AuN nanoclusters. Indeed, energy maxima of bands A and C scale with N(-1/3) as expected for quantum confined systems. Conversely, the energy maximum of band B appears to be almost independent of size, suggesting a contribution of electronic surface states. A clear correlation between the formation of band B in the samples and Er-related photoemission is demonstrated: the band at 980 nm related to AuN nanoclusters resonant with the corresponding Er(3+) absorption level, is suggested as an effective de-excitation channel through which the Au-related photon energy may be transferred from Au nanoclusters to Er ions (either directly or mediated by photon absorption), eventually producing the Er-related infrared emission at 1540 nm.

Au-polyimide nanocomposites have been synthesized by implanting different doses of Au+ ions in 100 nm thick films of pyromellitic dianhydride-4,4(') oxydianiline polyimide, prepared by glow discharge vapor deposition polymerization. Unambiguous evidence of Au nanoclusters growth is found only at the highest implantation doses (5x10(16) Au+/cm(2)). Structural, compositional, and optical characterizations show that the implantation induces the compactation of the initial film due to H and C loss. The resulting structure is a composite containing 2-3 nm gold nanoparticles arranged in a layer of about 40 nm and, just beneath the sample surface, a 15 nm thick carbon-rich layer. Optical simulations suggest the presence of a gold-carbon core-shell structure in the nanoparticles

Nowadays nanophotonics aims towards low-cost, chip-scale devices that can tailor electromagnetic properties, one of which is the control of the circular polarization at the nanoscale, important for novel optical devices. Here we show that nanosphere lithography, combined with tilted metal deposition, can provide novel metasurfaces with chiral properties.We apply the photo-acoustic technique to characterize the circular dichroism at 633 nm of polystyrene nanospheres covered by three different metals: Au-and Cr-covered samples show extrinsic chiral behavior, while the Ag-covered sample shows circular dichroism at normal incidence, characteristic for intrinsic chirality. As the experimental data are in good agreement with numerical predictions, we believe that such design can be optimized to get efficient circularly polarized detection at the nanoscale. THE MANUSCRIPTChirality, a lack of the mirror symmetry of an object 1 , is an important property of some of the building blocks of our world: many molecules, amino-acids, DNA, sugars, drugs are chiral. Two mirror images of the same object differently interact with circularly polarized light of the opposite handedness, while having other measurable properties equal. In particular, chirality can affect the absorption and/or phase velocity of circularly polarized light, therefore it is possible to measure a difference in absorption directly related to the molecules' chirality. This measurement is known as Circular Dichroism (CD). At the nanoscale, when the nanostructures are comparable or smaller than the light wavelength, and organized periodically, they form a metasurface; generally, if the symmetry of the metasurface is broken, a chiral behavior is expected 2 . Chiral metasurfaces can manipulate electromagnetic fields and enhance the interaction with chiral molecules, important for chiral sensing 3 . On the other hand, they can control the polarization state of the optical field, or emit circularly polarized light, thus leading to applications in optical and quantum communications 4 . Geometric features of intrinsically chiral metasurfaces (the nanostructure in the unit cell is usually helix or gammadion-like) can be complicated to fabricate and implement at the nanoscale. This problem can be solved by a proper experimental set-up following the rule that the impinging light wavevector, the average surface normal, and the sample direction must be nonplanar. Such chiral behavior is called extrinsic chirality as it is governed by both experimental set-up and the a) Electronic mail:

Silica films co-implanted with Er and Au ions show an enhancement of rare earth photoluminescence after gold introduction in the matrix. Er excitation originates in a broad spectral region, from the red to the near ultraviolet. We have investigated the influence of gold aggregation on the optical properties of co-doped samples by varying the temperature of post-Au implantation annealing in the 400-900 degrees C range. Optical measurements and extended x-ray absorption analysis support the hypothesis of an energy transfer process mediated by sub-nanometric Au aggregates with metallic character that are optically activated mostly through electron interband transitions between d and sp-conduction levels

The control of the spontaneous emission properties of quantum emitters with limited losses by near-field coupling with plasmons-supporting nanostructures is one of the keys for next-generation high-efficiency and high-coherence plasmonic devices. In the present work, gold nanohole arrays are demonstrated to be an effective plasmonic system for controlling radiative rate and quantum efficiency of the 1540 nm emission of Er3+ ions embedded in silica. Finite element method electrodynamic simulations were used to describe the interaction between dipolar Er3+ emitters and the nanohole arrays. The results are in agreement with those of photoluminescence measurements performed in different coupling configurations. Particularly, we demonstrated that owing to the combination of strong emission enhancement and low level of ohmic losses in the metal, nanohole arrays are able to enhance the far-field photon yield up to 74%. This in turn is related to an extremely high far-field quantum efficiency: more than 90% of the emitted photons reach the far-field for the most efficient configurations investigated in which the extraordinary optical transmission peak of the nanohole array is matched with the Er3+ emission.

Silver nanostructures are widely employed for Surface Enhanced Raman Scattering (SERS) characterizations owing to their excellent properties of field confinement in plasmonic resonances. However, the strong tendency to oxidation at room temperature of these substrates may represent a major limitation to their performances. In the present work, we investigated in detail the effects of oxidation on the SERS response of a peculiar kind of Ag nanostructured substrates, i.e., bi-dimensional ordered arrangements of Ag nanoprisms synthesized by nanosphere lithography. Particularly, wavelength-scanned SERS measurements were performed on Ag nanoprism arrays with a different level of oxidation to determine the SERS enhancement curves as a function of the excitation wavelength around the dipolar plasmonic resonance of the arrays. The experimental results were compared with those obtained by finite elements method simulations. With this approach, we were able to decouple the effects of spectral shift and decrease of the maximum value of the SERS enhancement observed for the different oxidation conditions. The results could be interpreted taking into account the inhomogeneities of the electromagnetic field distribution around the Ag nanostructures, as demonstrated by the simulations