Channeling And Wake Effect In The Interaction Of Energetic Charged Particles With Nanostructure Materials

The nanostructure materials are expected to have an impact on electronics, computing, communications, biology, medicine, energy and others, due to they have very unique electronic, structural, mechanical and optical properties. The nanotechnology is regarded as the key technology of the modern materical science and physics. Especially, the effects of the charged particles on nanostructure substance have been attracted considerable attention in the aspect of ion beam surface modification, ion beam injection technology, the deposition and preparation of nanoscale devices. Such as, due to the remarkable physical characters and electric properties, much work has been devoted to the feasibility of transport and channeling of charged particles through carbon nanotubes, in the technology of nanoscale ion beam, ion implantation and field emission. Besides, new challenges in the design and applications of metallic nanofabrication techniques require better understanding and manipulation of the collective phenomena that arise from the interactions of photons or charged particles with metallic nanostructures. Finally, based on the research of wake effect in the rough surface by charged particles, much useful information can also be obtained by quantitative measurement and analysis in the point of energy distribution.As a fast charged particle moves near or traverses metals, the quasi-free electrons will be excited, giving rise to the wake effect, and then the induced density, the space induced potential, the transverse stopping power and the longitudinal image force. Thus, the wake effect of electrons is closely related to the energy loss and channeling trajectory of moving charge. In this dissertation, we study the channeling process by the interactions of charged particles (keV-MeV) with carbon nanotubes, and the wake effect of point charges with nano-metallic slab and nano-roughness metal surface. The contents of this dissertation are presented as follows:Firstly, in Chapter 2, a theoretical model, is established to describe the interaction of energetic ions and carbon nanotubes, dependent on different electron band structure and geometric properties:based on a combination of the semi-classical kinetic model and dielectric response theory, the dynamic polarization effect of electrons on channeling of ions in single-walled carbon nanotubes (SWCNTs) is investigated; when the projectile ion moves near the carbon atoms of CNTs, collisions between them are described by using molecular dynamic (MD) model. By adopting the REBO potential in MD simulation, the interactive effect from the carbon atoms show attractive and then repulsive along the radial direction. The simulation results show that, under the effect of dynamic polarization potential and REBO potential, the ions can keep channeling in the nanotubes with consecutive reflections off the wall:along helical trajectories if the incident radial position is around the minimum point of the total potential, or large-amplitude oscillating channeling when it is far away from the minimum point, or even escape the nanotube with very large impact angle. The channeling trajectories are dependent on the initial conditions. In addition, we also made a rough estimate that the total channeling distance of the proton with 56.25keV can reach as far as 10μm by the calculation of its energy loss. The above simulation models and conclusion are put forward and may obtain helpful theoretical evidences to nanotube and ion beam application. Finally, we investigate the wake effects in the transport of charged particles through SWCNT and double-walled carbon nanotubes (2WCNTs), and notice that the wake effect on the outer wall of 2WCNTs is more obviously than that in SWCNT without the inner wall.In Chapter 3, based on the quantum hydrodynamic (QHD) model, we study the wake effect due to plasmon excitation in a nano-scale metal slab by a point charge moving inside the slab. In the QHD model, the contributions to the quantum effect arise in the form of the Thomas-Fermi pressure and a gradient correction from the appearance of the Bohm quantum potential. Since the equation of motion for the perturbed electron gas density is more complex in the QHD model, we search for two additional BCs-the Bohm potential or the normal component of the Bohm force should vanish at the boundary, to get the induced density and potential. Except for the wake potential inside the metal slab at very large distances behind the charged particle, all our results show that practically no differences arise due to using two different sets of BCs in the QHD model. On the other hand, we compare the QHD model with the standard hydrodynamic (SHD) model, and find that important and systematic differences also seen in the wake potential, particularly close to the charged particle and a large distance from the charged particle, which come from the gradient correction in the QHD model. Besides, those differences are particularly large when the slab is thinner or the charged particle speed is closer to the kinematic threshold velocity for the excitation of bulk plasmons in the electron gas. Finally, we find that the quantum effects can reduce the amplitudes in both the induced potential and the stopping power in QHD model and SHD model, compared with the local hydrodynamic (LHD) model. Our results, particularly for the different BCs, may shed some light in studying the nonlocal effects in plasmon propagation in metal slabs of interest in nanoplasmonics.Using the Green’s function formulation with the perturbative theory of dielectric response formalism, we study the wake effect of a rough metal surface by a single charged particle and by a pair of charged particles that move parallel to the surface in Chapter 4. The profile of a rough metal surface is described by a random function. When single point charge moves above the metal, the wake effect will be enhanced by the roughness of surface, followed by the increased wake potential, the image potential and the stopping power. On the other hand, while the effect of roughness is barely visible in the inter-particle interaction potential between two co-moving charged particles, the stopping ratio exhibits strong effects of surface roughness. Then, the distance dependence of the stopping ratio for two particles moving parallel to a rough surface exhibits wake-related oscillations.