Tunable Nanometer Electrode Gaps by MeV Ion Irradiation

We report the use of MeV ion-irradiation-induced plastic deformation of amorphous materials to fabricate electrodes with nanometer-sized gaps. Plastic deformation of the amorphous metal $\text{Pd}_{80}\text{Si}_{20}$ is induced by $4.64 \text{MeV O}^{2+}$ ion irradiation, allowing the complete closing of a sub-micrometer gap. We measure the evolving gap size in situ by monitoring the field emission current-voltage (I-V) characteristics between electrodes. The I-V behavior is consistent with Fowler-Nordheim tunneling. We show that using feedback control on this signal permits gap size fabrication with atomic-scale precision. We expect this approach to nanogap fabrication will enable the practical realization of single molecule controlled devices and sensors.Engineering and Applied SciencesPhysic

Ablation and optical third-order nonlinearities in Ag nanoparticles

The optical damage associated with high intensity laser excitation of silver nanoparticles (NPs) was studied. In order to investigate the mechanisms of optical nonlinearity of a nanocomposite and their relation with its ablation threshold, a high-purity silica sample implanted with Ag ions was exposed to different nanosecond and picosecond laser irradiations. The magnitude and sign of picosecond refractive and absorptive nonlinearities were measured near and far from the surface plasmon resonance (SPR) of the Ag NPs with a self-diffraction technique. Saturable optical absorption and electronic polarization related to self-focusing were identified. Linear absorption is the main process involved in nanosecond laser ablation, but non-linearities are important for ultrashort picosecond pulses when the absorptive process become significantly dependent on the irradiance. We estimated that near the resonance, picosecond intraband transitions allow an expanded distribution of energy among the NPs, in comparison to the energy distribution resulting in a case of far from resonance, when the most important absorption takes place in silica. We measured important differences in the ablation threshold and we estimated that the high selectiveness of the SPR of Ag NPs as well as their corresponding optical nonlinearities can be strongly significant for laser-induced controlled explosions, with potential applications for biomedical photothermal processes

Moore´s law, nanotechnology and nanosciences: synthesis and modification of nanoparticles using ion implantation

ArtículosEn este artículo resaltamos la importancia y el efecto que la nanotecnología y en general las nanociencias tendrán en la vida diaria de todos nosotros debido a las potenciales aplicaciones tecnológicas por venir. Como ejemplo presentamos la llamada ley de Moore, que constituye actualmente la motivación principal de la industria microelectrónica y de semiconductores para encontrar mejores materiales y para desarrollar dispositivos electrónicos más compactos, más rápidos, más eficientes y sobretodo más baratos. Esta carrera tecnológica nos lleva a la búsqueda de otros materiales con características novedosas, como son las nanopartículas metálicas que presentan propiedades ópticas muy importantes.No one can deny the impact of the nanotechnology revolution in our everyday life, even if some forthcoming technological applications seem unimaginable today. Moore´s Law, for example, has been the driving force behind the creation of increasingly complex, small and faster systems in the microelectronics and semiconductors industry. This technological race leads us to the search of materials with new properties, such as metallic nanoparticles exhibiting very interesting optical properties. At the UNAM´s Instituto de Física, we prepare metallic nanoparticles by means of the ion implantation technique using a Pelletron accelerator. We study the dependence of the nanoparticle size on the experimental parameters related to the implantation (ion type, energy, implantation dose) and to the thermal treatments (temperature, atmosphere). The samples were characterized by optical absorption measurements and transmission electron microscopy

Coexistence of two-photon absorption and saturable absorption in ion-implanted platinum nanoparticles in silica plates

"Platinum nanoparticles were nucleated in a high-purity silica matrix by an ion-implantation method. The third-order nonlinear optical response of the samples was studied using femtosecond pulses at 800 nm with the z-scan technique; picosecond pulses at 532 nm using a self-diffraction approach; and nanosecond pulses at 532 nm employing a vectorial two-wave mixing experiment. Nanosecond and picosecond explorations indicated an important thermal process participating in the optical Kerr effect evaluated. However, femtosecond results allowed us to distinguish a purely electronic response, related exclusively to ultrafast refractive and absorptive nonlinearities. Femtosecond experiments pointed out the possibility to switch the dominant physical mechanism responsible for the nonlinear optical absorption in the sample. This opens the potential for controlling quantum mechanisms of optical nonlinearity by femtosecond interactions.