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Título: | Time-dependent excited state response in nanostructures |
Autor: | Batson, Philip E.; Konečná, Andrea CSIC ORCID; Lagos, M. J.; Aizpurua, Javier CSIC ORCID | Fecha de publicación: | 2017 | Citación: | EDGE 2017 | Resumen: | Recently, we calculated the lateral forces imposed by a keV electron on a metal nanoparticle, using the time- and spatially-dependent EM fields for the swift electron – nanoparticle system. We can also evaluate, in space and time, the parallel forces which drive electron energy loss. The result describes a dielectric response in time and space. In principle, this quantity is accessible by Fourier analysis of the complex frequency dependent specimen response to a driving force having a known amplitude and phase. For a Causal process, we should be able to obtain the complex experimental result from EELS spectra by a Kramers-Kronig (KK) transform, provided we can obtain complete, error-free spectra. Usually, we also restrict this treatment to uniform, thin materials, correcting for surface scattering to remove non-material dependent behavior. Nanoscale objects are very hard to treat using this approach. Surfaces and interfaces, as mentioned above, shift resonant frequencies, introduce damping mechanisms that do not exist in the bulk material, and create coupling between bulk and aloof behavior in nearby free space. Controlling this behavior would be valuable for the design of better photovoltaics, photocatalysis, and other devices that depend on light matter interaction. We are looking at theoretical details of the microscopic, time dependent behavior of materials, nanoparticles, surfaces and interfaces to better understand the nature of spatially resolved inelastic scattering. We hope to develop tools that allow a more direct spatial probe of behavior on a point by point level in nanostructures. And we think that understanding the time dependence of these processes may be important for better understanding of energy transfer among resonant modes of nanostructures, in the same way that understanding the detailed time dependence of the lateral forces revealed many unforeseen behaviors. We will review the work on the time dependence of lateral forces, showing how, for instance, expected attractive dielectric forces become repulsive diamagnetic forces during the very close approach of a relativistic electron to a 2nm diameter Au sphere. We will also describe the prediction of a “mini-wake” that occurs within 10-20 attoseconds of the close approach. This remarkable excitation describes a ~ 1nm wavelength fluctuation in charge density that likely packs hundreds of eV energy into the nm sized particle during the close approach of the electron. Later, this fluctuation decays into surface plasmons during femtosecond times. In MgO similar calculations show the decay processes continuing into picosecond times with phonon modes. We will also discuss progress on the project to create a time resolved picture of excited states of a nanoparticle, derived from experimental energy loss data. | Descripción: | Resumen del trabajo presentado al 8th International Workshop on Electron Energy Loss Spectroscopy and Related Techniques, celebrado en Okuma, Okinawa (Japan) del 14 al 19 de mayo de 2017. | URI: | http://hdl.handle.net/10261/178757 |
Aparece en las colecciones: | (CFM) Comunicaciones congresos |
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