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Creation of phonons

There exists an extensive literature on theoretical calculations of the vibrational damping of an excited molecule on a metal surface. The two fundamental excitations that can be made in the metal are creation of phonons and electron-hole pairs. The damping of a high frequency mode via the creation of phonons is a process with small probability, because from pure energy conservation, it requires about 6-8 phonons to be created almost simultaneously. [Pg.24]

In this subsection we analyze the way the theory in Section III.B.l.b allows us to interpret the structures of the excitation spectra and of the emission spectra. Since the intrasurface relaxation proceeds first by the creation of phonons and of vibrations, we consider one of the resulting modes, of energy hi20, without specifying it, and we call it vibration . [Pg.164]

An infrared absorption which lies between 1400and 2350 wave number (cm ). The IR absorption is related to the creation of phonons and the intrinsic muKiphonon d)sorption. Absorption is nil above 7/im (this includes all the major atmospheric windows in the 8 -14/um waveband)... [Pg.264]

Fig. 2.5 Evolution of the ionic temperature during the FEMD simulations at different electronic temperatures. For low electron excitations below about 2eV, no chemical bond dismption was observed and the net effect is only the creation of phonons (blue line). On the contrary, increasing excitations (laser frequency) induce chemical and topological modifications on the system and the... Fig. 2.5 Evolution of the ionic temperature during the FEMD simulations at different electronic temperatures. For low electron excitations below about 2eV, no chemical bond dismption was observed and the net effect is only the creation of phonons (blue line). On the contrary, increasing excitations (laser frequency) induce chemical and topological modifications on the system and the...
The first term in Eq. (14) describes a photo-transition without creation of phonons. Therefore, this optical line is called a zero-phonon line (ZPL). The n-th term in Eq. (15) describe a photo-transition which is accompanied by the creation of n phonons. The sum over n describes the so-called phonon de band (PSB). [Pg.133]

Although it falls somewhat out of the scope of this paper and has furthermore been reviewed comprehensively recently,16 it would be remiss to overlook the exciting new work on chemicurrents. As we have seen for vibrational energy transfer, it is also observed that dissipation of chemical energy released in exothermic reactions at metal surfaces may happen adiabati-cally by creation of excited phonons or nonadiabatically by excitation of... [Pg.403]

A different view of the OMT process is that the molecule, M, is fully reduced, M , or oxidized, M+, during the tunneling process [25, 26, 92-95]. In this picture a fully relaxed ion is formed in the junction. The absorption of a phonon (the creation of a vibrational excitation) then induces the ion to decay back to the neutral molecule with emission (or absorption) of an electron - which then completes tunneling through the barrier. For simplicity, the reduction case will be discussed in detail however, the oxidation arguments are similar. A transition of the type M + e —> M is conventionally described as formation of an electron affinity level. The most commonly used measure of condensed-phase electron affinity is the halfwave reduction potential measured in non-aqueous solvents, Ey2. Often these values are tabulated relative to the saturated calomel electrode (SCE). In order to correlate OMTS data with electrochemical potentials, we need them referenced to an electron in the vacuum state. That is, we need the potential for the half reaction ... [Pg.204]

This formula describes the exchange of a single phonon of wavevector Q, frequency co(0 ) and polarization e(Q,j). n is the Bose factor for annihilation (—) or creation (+) of a phonon, respectively, i.e. the phonon occupation number. [Pg.230]

Inelastic scattering of radiation in solids is typified by the Raman effect, which involves the creation or annihilation of phonons or magnons. If a single phonon is involved, the scattering event is referred to as the first-order Raman effect in second-order Raman effect two phonons are involved. The polarizability associated with a phonon mode can be represented as a power series of the phonon amplitude, u, as follows ... [Pg.312]

T. Kobayashi I would like to make the comment that an interesting application of wavepacket control [1] is phonon squeezing in molecular systems and the creation of the Schrodinger cat state. It was theoretically predicted that there are several mechanisms that lead to squeezing of phonon states. [Pg.382]

Solid-state theories ascribe electron relaxation to the coupling of electronic spin transitions with transitions between lattice vibrational levels, or more generally with phonons. Disappearance (depopulation of a vibrational level) or creation (population of a vibrational level) of phonons modulate the orbital component of the electron magnetic moment. [Pg.83]

Bai et al. (2005) observed a phonon sideband with a frequency shift of 40-50 cm-1 located on the low-energy side of the 5Do <- 7Fo zero-phonon line (ZPL) in the 77 K excitation spectrum of Eu3+ Y203 NTs and NWs. However, vibronic sidebands generally appears at the high-energy side of the ZPL in the low-temperature excitation spectra since the vibronic transition involving the creation of a phonon with the annihilation of a photon is much more favored than the annihilation of a phonon at low temperature. The origin of this anomaly sideband remains unknown. [Pg.163]

It is discussed how the primary processes of defect formation during irradiation occur via electronic excitation. This can take the form of either the creation of electron-hole pairs, followed by trapping into localized energy states, or of exciton creation leading to the formation of stable vacancy and interstitial defects. Heating the sample after the irradiation causes the release of this stored energy in the form of phonons or photons. Photon emission, ie. luminescence, results from either electron-hole recombination or from vacancy-interstitial recombination. Several examples of both types are discussed for crystalline CaF and SiC. ... [Pg.168]

The interaction between light and matter can be viewed as the creation of a coherent quantum superposition of initial and final electron states that has an associated polarization [3], as shown in Figure 1. The coherence between states with different wave vector requires an intermediate virtual state and the presence of a coherent phonon. A transition between the initial and final states may occur when the coherence of the system is broken either due to the finite width of an optical wave packet or by scattering from the environment. The transition results in the absorption of a photon and the creation of a hot electron-hole pair. Otherwise, the photon is re-radiated with a different phase and, perhaps, polarisation. [Pg.205]

In the second example BCS theory relates the appearance of a superconducting state to the breakdown of electromagnetic gauge symmetry by interaction with regular ionic lattice phonons and the creation of bosonic excitations. This theory cannot be extended to deal with high Tc ceramic superconductors and it correlates poorly with normal-state properties, such as the Hall effect, of known superconductors. It is therefore natural to look for alternative models that apply to all forms of superconductivity. [Pg.270]

Thus obtained results show that the polyamorphic transitions occur not only at compression (Si02, H20, etc.) but at extension as well (C) in the systems having stable or metastable crystal analogs with a different density and a different coordination number z. At the minimal z=2 (chain structures) the transitions may occurs only at compression, at the maximal z=12 (close-packed structures) - only at extension, at the intermediate z (2structure-sensitive properties change and new metastable phases can appear. Amorphization under radiation (crystal lattice extension) can be associated with a softening of phonon frequencies. The transitions in the molecular glasses consisted from the molecules with unsaturated bonds are accompanied by creation of atomic or polymeric amorphous systems. [Pg.743]

Figure 2.9. Detail of the 0-0, b-polarized reflectivity at 5 K (cf. Fig. 2.8). The arrow indicates the threshold of creation of 46-cm phonons. Part A is due to reflection from the front face alone, part B to the total reflectivity of incoherent contributions from front and back faces, and part C to the reflectivity resulting from coherent superposition of front and back faces (oscillations). Figure 2.9. Detail of the 0-0, b-polarized reflectivity at 5 K (cf. Fig. 2.8). The arrow indicates the threshold of creation of 46-cm phonons. Part A is due to reflection from the front face alone, part B to the total reflectivity of incoherent contributions from front and back faces, and part C to the reflectivity resulting from coherent superposition of front and back faces (oscillations).
Figure 2.20. Right part The polariton dispersion at a few tens of reciprocal centimeters below the bottom of the excitonic band, vs the wave vector, or the refractive index n = ck/w (notice the logarithmic scale). The arrows indicate transitions with creation of one acoustical phonon, with linear dispersion in k (with a sound velocity of 2000 m/s). For the transitions T, Tt, T3 the final momentum is negligible compared to the initial momentum, and the unidimensional picture suffices. For the transitions between T3 and the point A, the direction of the final wave vectors should be taken into account. Left part The density of states m( ) (2.141) of the polaritons in the same energy region. This diagram explains why the transitions T, will be much slower than the transitions around T3 and the point A. The very rapid increase of m( ) at a few reciprocal centimeters below E0 shows the effect of the thermal barrier. Figure 2.20. Right part The polariton dispersion at a few tens of reciprocal centimeters below the bottom of the excitonic band, vs the wave vector, or the refractive index n = ck/w (notice the logarithmic scale). The arrows indicate transitions with creation of one acoustical phonon, with linear dispersion in k (with a sound velocity of 2000 m/s). For the transitions T, Tt, T3 the final momentum is negligible compared to the initial momentum, and the unidimensional picture suffices. For the transitions between T3 and the point A, the direction of the final wave vectors should be taken into account. Left part The density of states m( ) (2.141) of the polaritons in the same energy region. This diagram explains why the transitions T, will be much slower than the transitions around T3 and the point A. The very rapid increase of m( ) at a few reciprocal centimeters below E0 shows the effect of the thermal barrier.
Figure 2.21. Scheme of the various distributions D, and D2 of the polaritons leading to the observed bulk fluorescence. The model of two main distributions accounts for the narrow lines, the satellite broad bands, and their relative intensities. The energy of the main fluorescence lines is given in reciprocal centimeters. The bold arrow represents the relaxation in the excitonic band to states above 0. The primary distribution of excitons ( >,) relaxes by the creation of acoustical phonons (wavy arrow) to the secondary distribution of polaritons (D2) below E0 as well as to other vibrations in the ground state as given by the spectral model85 or the dynamical model (second ref. 87). [Pg.117]

In the last subsection, we invoked phonons to explain the nonradiative broadening of the surface structures. However, at very low temperature, the surface state at the bottom of the excitonic band cannot undergo broadening either by phonon absorption or by phonon creation the phonon bath at 2 K does not suffice to account for the 3- to 4-cm 1 nonradiative width of the first surface resonance. Nevertheless, we assume the intrinsic nature of this broadening, since it is observed, constant, for all our best crystals.67120... [Pg.151]

To explain the observed width, it is necessary to look for strong surface-to-bulk interactions, i.e. large magnitudes of surface-exciton wave vectors. Such states, in our experimental conditions, may arise from virtual interactions with the surface polariton branch, which contains the whole branch of K vectors. We propose the following indirect mechanism for the surface-to-bulk transfer The surface exciton, K = 0, is scattered, with creation of a virtual surface phonon, to a surface polariton (K / 0). For K 0, the dipole sums for the interaction between surface and bulk layers may be very important (a few hundred reciprocal centimeters). Through this interaction the surface exciton penetrates deeply into the bulk, where the energy relaxes by the creation of bulk phonons. The probability of such a process is determined by the diagram... [Pg.152]

Figure 3.15. Diagram of a nonlocal surface-exciton transfer, corresponding to the optical creation of a surface exciton followed by its relaxation to the bulk. The essential virtual stage is the scattering of a surface phonon (K 0) and the creation of a surface polariton with a large wave vector (K 0), producing large interaction energies with the bulk. 21 Then relaxation in the bulk is ultrafast. Figure 3.15. Diagram of a nonlocal surface-exciton transfer, corresponding to the optical creation of a surface exciton followed by its relaxation to the bulk. The essential virtual stage is the scattering of a surface phonon (K 0) and the creation of a surface polariton with a large wave vector (K 0), producing large interaction energies with the bulk. 21 Then relaxation in the bulk is ultrafast.

See other pages where Creation of phonons is mentioned: [Pg.313]    [Pg.152]    [Pg.296]    [Pg.496]    [Pg.19]    [Pg.88]    [Pg.313]    [Pg.152]    [Pg.296]    [Pg.496]    [Pg.19]    [Pg.88]    [Pg.369]    [Pg.387]    [Pg.498]    [Pg.65]    [Pg.21]    [Pg.64]    [Pg.239]    [Pg.247]    [Pg.483]    [Pg.110]    [Pg.153]    [Pg.581]    [Pg.224]    [Pg.165]    [Pg.46]    [Pg.46]    [Pg.111]    [Pg.115]    [Pg.116]   
See also in sourсe #XX -- [ Pg.189 , Pg.190 ]




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