The Researchs On The Electromagnetic Waves In Nano-thin Films And The Plasmons In Atomic Clusters

Surface plasmon is a surface electromagnetic model, originating from the interaction of light and the electronic on metal surface. The appearance of s urface plasmon always accompanies with remarkable extinction 、 local field enhancement and breaking through diffraction limit ch aracteristics, which make surface plasmon play important roles in the modern science and technology, such as nanosensing, bio-imaging, optical cloaking, etc. At present, researchers mainly use density functional theory and hydrodynamical drude model to respectively study the plasmons in metallic clusters and nanostructures. In this paper, on the one hand, we study nonlocal effect in surface plasmon polariton of ultrathin metal films, using thenonlocal conductivity obtained by quantumresponse theoryinstead of the ones obtained by h ydrodynamical drude model to overcome the deficiencies that hydrodynamical drude model can’t effectively describe the transport features of nanostructures; on the other hand, we research the plasmon in clusters, using the eigen-equation obtained by density functional theory and self-consistent linear response approximationinstead of density functional theory to overcome the deficiencies that when ones find plasmon using density functional theory the results are always dependent on the external electric field. Specifically, we conducted theworks as follow:(1)Employing a nonlocal conductivity based on the quantumresponse theory, we have studied optical properties of s-polarization electromagnetic wave in metal film. In the studies of the frequencyand thin film thickness dependences of absorption coefficients, we find even when there are no plasmon excitations and anyscattering experienced by electrons in the system, nonlocalresponse theory still gives a considerable energy abs orptioncaused by electron-hole pair excitation; however, local-response theory only presents zero absorption in this case. In the study of distributions of electric field and current, we find even nonlocal andlocal electric fields are the same; their elect ric currentsstill display an obvious difference near the interface. In the studies of the distributions of the averaged energyflow density, we find, in the metal film, the energy flow ofnonlocal-response theory displays an anomalous oscillation;however, th e energy flow of local-response theory is nooscillation. Further studies show that the oscillation energy flowcan be ascribed to the negative work done by electric field insome regions of the film.(2)As well known,the s-polarized wave cannot excite the su rface plasmon polaritons(SPPs) of the systems, but p-polarizedwave can. Therefore, the p-polarized wave in the system has more plentifuland interesting optical properties and is very worthy to investigate. Therefore, we then study the optical properties ofp-polarized wave in quartz –metal–film–air structures. In absorption spectrum, the resonant peak of SPP is found,and the dependence of the resonant peak on film thickness shows that nonlocal effect in the SPP resonance is enhanced significantly with the decrease of film-thickness, especially in the less than 20 nmmetal film. In the studies of the distributions of the averaged energyflow density, we find,just like in the case of s-polarized, the energy flow ofnonlocal-response theory displays an anomalous oscillation due to the negative work done by electric field insome regions of the film;We calculate the surface charge density as a function of frequency, and find that the frequencies at the charge and absorption peaks are the same. This clearly confirms th at the absorption peakstems from SPP resonance excitation, and SPPs absorb the energy of the electromagnetic wave via chargeoscillations. In the case of SPP resonance, the charge and electric field on the down-surface of thin filmare always greater than th at on the up-surface; however, the situation is just opposite in the case of no SPP resonance. This implies that the SPP resonance occurs near the down-surface of the film.(3) Based on the time-dependent density-functional theory and linear response theory, we derive the eigen-equations for the square and round atomic clustersystems.Respectively using energy loss spectra and eigen-equation, we research the plasmon models that the systems canmaintain. Results show some plasmon models can’t be found due that they have not beenexcited by external field, however all plasmons models can be obtained by eigen-equation. The charge distributions of plasmon show the square and round atomic clustersystems can maintain the plasmons models of antisymmetric and symmetricchargeoscillations which respectivelydenotedipole plasmon and quadrupole plasmon.In the studies of energy loss spectra, we find, with the increase of system scale, the number of the plasmon increases and the frequency of the mainplasmons which represent the plasmon of strong loss abilitygenerates redshift.In addition, in the rectangular atomic clusters, we find, with the length increases of the systems, longitudinal plasmon modelsdecrease, but transverse plasmon models increase and finally tend to constant. The charge distributions show transverse plasmon models gradually turn into the end models and the central models.