Search

Silver nanoparticles were sputter deposited through self organized hexagonally ordered porous anodic alumina templates that were fabricated using a two-step anodization process. The average pore diameter of the template was 90 nm and the interpore spacing was 120 nm. Atomic force microscope studies of the sputter-deposited silver nanoparticle array on a Si substrate indicate an approximate replication of the porous anodic alumina mask. The nature of the deposition depends strongly on the process parameters such as sputtering voltage, ambient pressure and substrate temperature. We report a detailed study of the sputtering conditions that lead to an optimal deposition through the template.

We present results on hot electron and energetic ion (keV–MeV) generation from polished and nanostructured metallic surfaces excited by p-polarized, femtosecond laser pulses in the intensity range of 1×1015–1.5×1017 W cm-2. A clear enhancement in the hard X-ray spectrum from nanoparticle-coated surfaces is observed, indicating ‘hotter’ electron production in nanoparticle-produced plasma until the intensity of 2×1016 W cm-2 is reached. Contrary to the existing perception, we find that the hotter electrons do not lead to hotter ion emission. The total ion flux and the ion energy integrated over the 4–1400 keV energy range are found to be enhanced by 50% and 16%, respectively, for nanostructured targets in comparison to those from polished targets. 55% enhancement in yield is observed for ions at the lower end of the energy range, while hotter ions are actually found to be suppressed by ∼40%. The surface modulations present on the nanoparticle-coated targets are observed to reduce the maximum energy of the ions and showed an intensity-dependent increase in the divergence of the ion beam. [ABSTRACT FROM AUTHOR]

Physical vapor deposition techniques such as sputtering and laser ablation – which are very commonly used in thin film technology – appear to hold much promise for the synthesis of nanocrystalline thin films as well as loosely aggregated nanoparticles. We present a systematic study of the process parameters that facilitate the growth of nanocrystalline metals and oxides. The systems studied include TiO[sub 2] , ZnO, γ-Al[sub 2] O[sub 3] , Cu[sub 2] O, Ag and Cu. The mean particle size and crystallographic orientation are influenced mainly by the sputtering power, the substrate temperature and the nature, pressure and flow rate of the sputtering gas. In general, nanocrystalline thin films were formed at or close to 300 K, while loosely adhering nanoparticles were deposited at lower temperatures. [ABSTRACT FROM AUTHOR]

High-intensity ultrashort laser pulses focused on metal targets readily generate hot dense plasmas which accelerate ions efficiently and can pave way to compact table-top accelerators. Laser-driven ion acceleration studies predominantly focus on protons, which experience the maximum acceleration owing to their highest charge-to-mass ratio. The possibility of tailoring such schemes for the preferential acceleration of a particular ion species is very much desired but has hardly been explored. Here, we present an experimental demonstration of how the nanostructuring of a copper target can be optimized for enhanced carbon ion acceleration over protons or Cu-ions. Specifically, a thin (≈0.25 μm) layer of 25-30 nm diameter Cu nanoparticles, sputter-deposited on a polished Cu-substrate, enhances the carbon ion energy by about 10-fold at a laser intensity of 1.2×1018 W/cm2. However, particles smaller than 20 nm have an adverse effect on the ion acceleration. Particle-in-cell simulations provide definite pointers regarding the size of nanoparticles necessary for maximizing the ion acceleration. The inherent contrast of the laser pulse is found to play an important role in the species selective ion acceleration. [ABSTRACT FROM AUTHOR]

Applying γ-ray perturbed angular distribution method, we have investigated local magnetism of isolated Fe atoms implanted in nanocrystalline Ag host. The measured Curie–Weiss type local susceptibility of 54Fe indicate the existance of large magnetic moment for Fe in Ag nanoparticle, comparable to that in bulk metal. As an important feature we find that Kondo temperature TK∼23 K of Fe in nanocrystalline Ag is much higher than the value in bulk silver. [Copyright &y& Elsevier]