Resonant plasma oscillation

Metal nanoparticles present localized surface plasmon resonances (LSPRs) that are collective excitations of the electrons at the interface between a conductor and a dielectric. The resonant plasma oscillation causes local field enhancement, and this is utilized in SERS [61,62], second-harmonic generation [63], and scanning near-field optical microscopy [64]. In particular, certain metals such as silver and gold have been much studied due to the feet that they present this LSPR in the visible spectral region. 

Due to the symmetry constraints in a 2D electron system with a periodically modulated electron density, one can anticipate that strong chromatic conversion of the EW polarization will occur due to resonant coupling between the EW and plasma oscillations even without dc magnetic field applied. The theory of EW polarization conversion in the 2D electron system with a rectangular electron density profile was developed within the first principles electromagnetic approach... 

We are interested here in resonant interaction between incident EW and plasma oscillations in the 2D electron system. As it is well-known [5], the plasmon wavelengths in 2D electron system are several orders of magnitude shorter than the wavelength of the EW of the same fi equency. To ensure a resonant coupling between the EW and plasma oscillations, the period of the structure has to be of the order o f the plasmon wavelength, which means that L 2n/ko. In this case, only transmitted and reflected EWs of the zero diffraction order survive at distances much longer than the EW wavelength away from 2D electron system. 

Langmuir Plasma Oscillations and Molecular Oscillations. Calculate the plasma density required to reach the resonance condition between plasma oscillations and the vibration of molecules. Is it possible to use such resonance for direct vibrational excitation of molecules in plasma without any electron impacts ... 

Optical properties of copper nanoparticles are quite remarkable because the energy of the dipolar mode of surface collective electron plasma oscillations (surface plasmon resonance or SPR) coincides with the onset of interband transition. Therefore, optical spectroscopy gives an opportunity to study the particle-size dependence of both valence and conduction electrons. The intrinsic size effect in metal nanoparticles, caused by size and interface damping of the SPR, is revealed experimentally by two prominent effects a red shift of the surface plasmon band and its broadening. 

For centuries, metal nanoparticles have never ceased to attract scientists and artists from many diverse cultures. In this section we briefly introduce a phenomenon of metal nanoparticles that still inspires scientists localized surface plasmon resonance (LSPR) (Hutter and Fendler, 2004). Metal nanoparticles show nonlinear electronic transport (single-electron transport of Coulomb blockade) and nonlinear/ultrafast optical response due to the SPR. Conduction electrons (—) and ionic cores (-F) in a metal form a plasma state. When external electric fields (i.e., electromagnetic waves, electron beams etc.) are applied to a metal, electrons move so as to screen perturbed charge distribution, move beyond the neutral states, return to the neutral states, and so on. This collective motion of electrons is called a plasma oscillation. SPR is a collective excitation mode of the plasma localized near the surface. Electrons confined in a nanoparticle conform the LSPR mode. The resonance frequency of the surface plasmon is different... 

If metal particles become very small, reaching the nanometer-size scale, a color may occur. This is a typical phenomenon of nanometric metals. Actually, optical absorption may result in the ultraviolet or visible part of the spectrum, and this arises from a surface plasmon resonance. This is due to a collective electron plasma oscillation (plasmon) that is coupled to an external transverse electromagnetic field through the particle surface. It is possible to quantitatively relate the absorption coefficient to the wavelength of the exciting radiation by the Mie theory for spherical inclnsions in a dielectric matrix (34). Far-IR Inminescence is another optical phenomenon frequently observed with nanosized metals (46). 

The energy loss function, Im[—l/ (w)] shown in Figure 153 exhibits a well-defined peak with maximum at 1.1 eV [1160]. The maximum in Im[—l/e(plasma edge [1191]. In simple metals, the maximum of the loss function occurs near collective plasma oscillations occur at energies where Im[-l/e( w)] is large and where and 2 are both small [1171]. The plasma resonance can be distinguished from an interband transition by the fact that both ei and S2 are small in the vicinity of the maximum in the loss function. 

One can imagine from these experimental results that PDA chains inside poly(DCHD)shell may contact with some points on the surface of Ag core [47,49]. These contact points at hetero nano-interface might be anchors to disturb and depress the plasma oscillation, and then diminish the mean-free-path of conduction free electrons in VB of Ag core. In other words, the LSP of Ag core would damp simply without changing the resonance frequency, owing to the reduction of electronic conductive domain induced by locally and strongly physicochemical interaction at the core/shell interface in the hybridized NCs [103,105]. 

We now want to study the consequences of such a model with respect to the optical properties of a composite medium. For such a purpose, we will consider the phenomenological Lorentz-Drude model, based on the classical dispersion theory, in order to describe qualitatively the various components [20]. Therefore, a Drude term defined by the plasma frequency and scattering rate, will describe the optical response of the bulk metal or will define the intrinsic metallic properties (i.e., Zm((a) in Eq.(6)) of the small particles, while a harmonic Lorentz oscillator, defined by the resonance frequency, the damping and the mode strength parameters, will describe the insulating host (i.e., /((0) in Eq.(6)). 

Fig. 7. Model calculations for the reflectivity (a) and the optical conductivity (b) for a simple (bulk) Drude metal and an effective medium of small metallic spherical particles in a dielectric host within the MG approach. The (bulk) Drude and the metallic particles are defined by the same parameters set the plasma frequency = 2 eV, the scattering rate hr = 0.2 eV. A filling factor/ = 0.5 and a dielectric host-medium represented by a Lorentz harmonic oscillator with mode strength fttOy, 1 = 10 eV, damping ftF] = I eV and resonance frequency h(H = 15 eV were considered for the calculations.

Figure 6.1-13 To illustrate the electromagnetic (EM) enhancement of SERS a simple model of a small metal sphere (radius is much less than the wavelength) experienced by an electromagnetic oscillating field is considered. If the sphere is illuminated at the plasma resonance frequency of the metal electrons a high electric field on the metal surface is generated, whose efectric field lines are shown (Creighton, 1988).

An optical transduction method that is often used with ultrathin hlms, such as LB hlms, is that of surface plasmon resonance [30, 31]. Surface plasma waves are collective oscillations of the free electrons at the boundary of a metal and a dielectric. These can be excited by means of evanescent electromagnetic waves. This excitation is associated with a minimum in the intensity of the radiation reflected from the thin him system, called surface plasmon resonance (SPR). The sensitivity of SPR is noteworthy, and changes in refractive index of 10 may be monitored thus the technique compares favorably with ellipsometry. The method has been used with LB hlms to provide both gas detectors [29] and sensors for metal ions in solution [32]. 

An atmospheric pressure helium MIP is generated using a 2.45 GHz microwave generator and an electromagnetic cavity resonator, called a Beenakker cavity. The hehum gas is passed through a discharge tube placed in the cavity, as seen in Fig. 7.48. The plasma is initiated by a spark from a Tesla coil. The electrons produced by the spark oscillate in the... 

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