Silvina Segui

Collective excitations (plasmons) in solids and nanostructures

In this work, we summarize the studies on the interaction of moving charged particles with bulk and surface plasmons in systems ranging from macro to nanoscopic scale, analyzing the differences and similarities that arise when the size and shape of the system are modified. In particular, we discuss the strong interference effects in the excitation of plasmons that arise in the interaction of particles with systems of nanoscale dimensions.

Photoionization of image states around metallic nanotubes

In this work we study a theoretical approach to the ionization of electrons bound in an image state around a metallic nanotube by the impact of photons. In a close analogy to the already studied case of ionization by electron impact [1], we calculate and analyze photoionization cross sections of tubular image states [2] within a first Born approximation. We consider various situations, including different energies and polarizations of the incident photon, ejection directions of the outgoing electron, and angular momenta of the image state.

Plasmon decay in the context of the dielectric formalism

We address the problem of quantifying the decay of plasmons excited in the electron gas of a condensed medium. Within the dielectric formalism, we use various methods to define and assess the damping constant γ.

Coherent-states calculation of electronic density fluctuations associated to the excitation of plasmons

We study the fluctuations in the electronic density associated with the wake potential generated by an external charged particle, using a coherent-states description for the plasmon states excited in planar geometry. We consider different trajectories of the external particle and analyze the effect of parameters such as its velocity, and distance to the surface.

Plasmon excitation in single wall carbon nanotubes by penetrating charged particles

In this work we study the excitation of plasmons due to the incidence of a charged particle passing through a single wall carbon nanotube. We use a quantized hydrodynamic, in which the σ and π electrons characteristic of these carbonaceous structures are depicted as two interacting 2-dimensional fluids, to calculate the average number of plasmons excited. We analyze the contribution of the different plasmon modes in a variety of configurations, and study the energy lost by the incident particle.

Lα, Lβ, and Lγ x-ray production cross sections for heavy elements by electron impact

We have calculated Lα, Lβ, and Lγ x-ray production cross sections by the impact of electrons on Hf, W, Re, Os, Au, and Pb. We used the distorted-wave Born approximation to calculate ionization cross sections of the L subshells of these atoms. Atomic relaxation parameters were taken from the literature. The theoretical predictions are compared with published experimental information. Good agreement is generally found except for Re, where the measured cross sections are systematically lower than the theoretical estimates by around 20 %. The observed discrepancy may be due to the relatively large uncertainty in the determination of the sample thickness.

Quantization of plasmon excitation in carbon nanotubes: Two-dimensional two-fluids hydrodynamic model

In this work we present a quantization of the hydrodynamic model to describe the excitation of plasmons in a single-walled carbon nanotube due to the interaction with a fast point charge moving near its surface. In this approach we consider a two-dimensional system with two interacting fluids, to take into account the different nature of the σ and π electrons. The implemented quantization procedure allows us to study the average number of plasmons excited in each mode, as well as the stopping power and energy loss spectra.