Coherent Vibrations of Adsorbates Induced by Femtosecond Laser Excitation

Matsumoto, Yoshiyasu; Watanabe, Keiji

doi:10.1021/cr050165w

Cited by 60 publications

(43 citation statements)

References 213 publications

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“…This applies also to studies of structural dynamics, and therefore any pump-probe scheme using this technique requires the excitation of coherent molecular motion. Optical mechanisms for inducing vibrational coherence are well established and have permitted the study of vibrational relaxation on the femtosecond time scale by optical means, exploiting the transient changes of a macroscopic polarization 14 . Recently, the use of THz pulses, exerting a time-dependent torque on molecular dipoles, has been proposed as a trigger for coherent motion inducing a chemical reaction 15 …”

Section: Introductionmentioning

confidence: 99%

Following the molecular motion of near-resonant excited CO on Pt(111): A simulated x-ray photoelectron diffraction study based on molecular dynamics calculations

Greif

Nagy

Soloviov

et al. 2015

Structural Dynamics

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A THz-pump and x-ray-probe experiment is simulated where x-ray photoelectron diffraction (XPD) patterns record the coherent vibrational motion of carbon monoxide molecules adsorbed on a Pt(111) surface. Using molecular dynamics simulations, the excitation of frustrated wagging-type motion of the CO molecules by a few-cycle pulse of 2 THz radiation is calculated. From the atomic coordinates, the time-resolved XPD patterns of the C 1s core level photoelectrons are generated. Due to the direct structural information in these data provided by the forward scattering maximum along the carbon-oxygen direction, the sequence of these patterns represents the equivalent of a molecular movie.

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Section: Introductionmentioning

confidence: 99%

Following the molecular motion of near-resonant excited CO on Pt(111): A simulated x-ray photoelectron diffraction study based on molecular dynamics calculations

Greif

Nagy

Soloviov

et al. 2015

Structural Dynamics

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“…The spin-independent contribution to CP damping originates from interaction with defects, electrons, and thermal (incoherent) phonons [32]. Since the dynamics is driven by light, optically excited electrons and incoherent phonons excited by electron-phonon scattering contribute in particular to metallic systems where lowenergy excitations are allowed around E F [33,34].…”

Section: Damping Of the Coherent Phononsmentioning

confidence: 99%

Coherent Excitations at Ferromagnetic Gd(0001) and Tb(0001) Surfaces

Melnikov

Bovensiepen

2010

Dynamics at Solid State Surfaces and Interfaces

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It is shown that ferromagnetic lanthanide surfaces like Gd(0001) and Tb(0001) present good model systems to investigate excitation, interaction, and relaxation of electronic, phononic, and magnetic subsystems in the time domain. In particular, analysis of an optically excited coherent phonon (CP)-magnon mode by pump-probe experiments gives detailed insight into the intriguing interaction between lattice and magnetization dynamics on femtosecond timescales.The lanthanide series of elements (Ce-Lu) is well known for its consecutive filling of the 4f shell, which is localized at the ion core. Due to the poorly screened 4f orbitals, an effective increase of nuclear charge occurs with increasing electron count, which leads to the reduction in the ionic radius with increasing electron count. The orbital and the spin magnetic moments per ion are also related to the number of the 4f electrons by Hunds rules. Accordingly, the spin magnetic moment is largest for the half-filled configuration 4f 7 of gadolinium (Gd), S ¼ 7/2. The orbital magnetic moment vanishes (L ¼ 0) for this configuration. In terbium (Tb) with 4f 8 , the spin and orbital magnetic moments are given by S ¼ 3 and L ¼ 3, respectively. 1) Both elements crystallize in the hexagonal close-packed structure with the lattice constant a Gd ¼ 3:63 A and a Tb ¼ 3:60 A . Their structural and vibrational properties are accordingly similar [1]. The lanthanide elements exhibit rich and interesting magnetic ordering phenomena [2], which are closely related to the indirect (or RKKY) exchange interaction. This type of exchange couples the magnetic moments that are localized at the ion cores and, hence, have no direct wave function overlap. This indirect exchange acts through polarization of the delocalized conduction band electrons. As depicted in Figure 12.1b, for the simplified situation of a spin impurity embedded in free electron gas, the spin polarization (SP) surrounding the localized spin exhibits a damped oscillation as a function of distance r from the ion core. Since 1) The ionic configuration in Tb is actually 4f 9 6s 2 while it is 4f 7 5d 1 6s 2 for Gd. In a solid, which is of interest here, the number of 4f electrons increases as an integer count along the lanthanide series [1].

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“…SH intensity is modulated by coherent nuclear motions at the surface because the surface electronic structure, and hence the second-order nonlinear susceptibility responsible for SH generation, is affected by the nuclear motions [2]. Consequently, time-resolved second harmonic generation (TRSHG) spectroscopy is very versatile to monitor the coherent nuclear motions at surfaces [3,4].…”

Section: Introductionmentioning

confidence: 99%

Photoinduced Coherent Nuclear Motion at Surfaces: Alkali Overlayers on Metals

Matsumoto

Watanabe

2010

Dynamics at Solid State Surfaces and Interfaces

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Electron-phonon coupling is ubiquitous and is at the heart of many phenomena in physics and chemistry of condensed matter. Adsorbates on metal surfaces are no exception. Electron-phonon coupling plays a central role in various nuclear dynamics at metal surfaces: vibrational relaxation, diffusion, chemical reaction, and so on. Because of the coupling, transient changes in the distribution of electron density at metal surfaces induce adsorbate nuclear motions. Coupling also plays an important role in the reverse process: adsorbate nuclear motions are damped via electron-hole pair excitations in addition to phonon emissions into the bulk.One of the simplest processes in the study of the electron-phonon coupling at surfaces is adsorbate vibrational relaxation. Information of vibrational relaxation has been deduced from the analysis of a vibrational spectral line observed with frequency domain methods: high-resolution electron energy loss spectroscopy (HREELS), infrared reflection absorption spectroscopy (IRAS), and helium atom scattering (HAS).Thanks to the advent of ultrafast laser technology, time domain spectroscopy is now also a powerful means to investigate vibrational dynamics at metal surfaces. When electrons near a metal surface is excited by a femtosecond laser pump pulse with a duration extremely shorter than that of a vibrational mode of adsorbates, this ultrafast electronic excitation leads to in-phase collective vibrational motions of adsorbates, coherent surface phonons, through the electron-phonon coupling. Then, the evolution of coherent vibrations is monitored by a probe pulse as a function of pump-probe delay. Because transient electron temperatures achieved by the pump pulse excitation can be extremely higher than thermal desorption temperatures of adsorbates, the time domain pump-probe spectroscopy allows to explore the electron-phonon coupling under high electronic excitation conditions. Thus, the photoinduced coherent nuclear motions provide an interesting opportunity for studying the electron-phonon coupling and its effects on vibrational dynamics of

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Coherent Vibrations of Adsorbates Induced by Femtosecond Laser Excitation

Cited by 60 publications

References 213 publications

Following the molecular motion of near-resonant excited CO on Pt(111): A simulated x-ray photoelectron diffraction study based on molecular dynamics calculations

Following the molecular motion of near-resonant excited CO on Pt(111): A simulated x-ray photoelectron diffraction study based on molecular dynamics calculations

Coherent Excitations at Ferromagnetic Gd(0001) and Tb(0001) Surfaces

Photoinduced Coherent Nuclear Motion at Surfaces: Alkali Overlayers on Metals

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