Five-Wave-Mixing Spectroscopy of Ultrafast Electron Dynamics at a Si(001) Surface

Voelkmann, C.; Reichelt, Matthias; Meier, Torsten; Koch, S. W.; Höfer, U.

doi:10.1103/physrevlett.92.127405

Cited by 37 publications

(38 citation statements)

References 20 publications

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“…Assuming that at time t = 0 the system is in its equilibrium state and that its value in the equilibrium state is ∆ρ eq = 1, the solution to Eq. (2.77) in the case of constant I is [18] ∆ρ(t, ω) = 1 400 µJ/cm 2 suggest the possibility of a dynamic dephasing time of approximately 20 fs [15,105]. This is in qualitative agreement with our results at a pump fluence of 400 µJ/cm 2 ,…”

Section: Dynamic Electronic Dephasing Times At the Si(111)7×7 Surfacesupporting

confidence: 82%

“…The main features of the data (except at the largest positive detuning, the data for which are displayed in This latter observation was also made by Voelkmann et al [15,105]. This observation is not surprising given that the Si(111)7×7 surface electronic band structure is not highly dispersive and given the timescales of mechanisms for relaxation of excited carriers back to the ground state such as radiative recombination, which is expected to occur on nanosecond timescales.…”

Section: Pump-probe Second-harmonic Generationsupporting

confidence: 57%

“…in fact, both a completely homogeneous model and a primarily inhomogeneous model can account for their data [15,105]. Secondly, there may be differences between the two sets of experimental results due to differences in the repetition rates of the lasers.…”

Section: Dynamic Electronic Dephasing Times At the Si(111)7×7 Surfacementioning

confidence: 99%

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Femtosecond nonlinear spectroscopy at surfaces: Second-harmonic probing of hole burning at the Si(111)7x7 surface and fourier-transform sum-frequency vibrational spectroscopy

McGuire¹

2004

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The high temporal resolution and broad bandwidth of a femtosecond laser system are exploited in a pair of nonlinear optical studies of surfaces.The dephasing dynamics of resonances associated with the adatom dangling bonds of the Si(111)7×7 surface are explored by transient second-harmonic hole burning, a process that can be described as a fourth-order nonlinear optical process. Spectral holes produced by a 100 fs pump pulse at about 800 nm are probed by the second harmonic signal of a 100 fs pulse tunable around 800 nm. The measured spectral holes yield homogeneous dephasing times of a few tens of femtoseconds. Fits with a Lorentzian spectral hole centered at zero probe detuning show a linear dependence of the hole width on pump fluence, which suggests that charge carrier-carrier scattering dominates the dephasing dynamics at the measured excitation densities. Extrapolation of the deduced homogeneous dephasing times to zero excitation density yields an intrinsic dephasing time of ∼ 70 fs. The presence of a secondary spectral hole indicates that scattering of the surface electrons with surface optical phonons at 570 cm −1 occurs within the first 200 fs after excitation.The broad bandwidth of femtosecond IR pulses is used to perform IR-visible sumfrequency vibrational spectroscopy. By implementing a Fourier-transform technique, we demonstrate the ability to obtain sub-laser-bandwidth spectral resolution. FT-SFG yields a greater signal when implemented with a stretched visible pulse than with a femtosecond visible pulse. However, when compared with multichannel spectroscopy using a femtosecond IR pulse but a narrowband visible pulse, Fourier-transform SFG is found to have an inferior signal-to-noise ratio. A mathematical analysis of the signal-to-noise ratio illustrates the constraints on the Fourier-transform approach.

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Section: Dynamic Electronic Dephasing Times At the Si(111)7×7 Surfacesupporting

confidence: 82%

Section: Pump-probe Second-harmonic Generationsupporting

confidence: 57%

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Femtosecond nonlinear spectroscopy at surfaces: Second-harmonic probing of hole burning at the Si(111)7x7 surface and fourier-transform sum-frequency vibrational spectroscopy

McGuire¹

2004

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“…36 The relaxation time on the Si͑100͒ surface is reported to be larger. [40][41][42] Subsequent energy relaxation at the Si surface proceeds via formation of surface excitons in the Si band gap on a time scale of 5 ps. 40,41 Thus the specific binding energies of luQWS at different thicknesses with respect to the Si CB can be considered to explain the two-time scales observed for B .…”

Section: Resultsmentioning

confidence: 99%

Ultrafast electron dynamics in Pb/Si(111) investigated by two-photon photoemission

Kirchmann

Bovensiepen

2008

Phys. Rev. B

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Ultrafast electron dynamics in Pb/Si͑111͒ quantum well structures have been investigated by femtosecond time-resolved two-photon photoemission spectroscopy. Three unoccupied quantum well states ͑or subbands͒ as well as an image potential state are identified and analyzed as a function of Pb thickness. Using 1.9 eV photon energy for optical excitation electron-hole pairs are formed in the Pb film and in the Si substrate. The hot electron population in the quantum well states exhibits a biexponential decay and both decay times increase when the energy difference to the Fermi level is reduced. The slower decay component with decay times of 130 and 900 fs is attributed to delayed filling of the states in the adlayer due to electronic relaxation in the Si͑111͒ substrate. The faster decay ͑30-140 fs͒ is caused by electron-electron scattering in the Pb film. At a first glance, the extracted decay times increase toward the Fermi level as predicted by the Fermi-liquid theory. However, by investigation of the quantized electronic structure more detailed insight into scattering among defined subbands has been gained. The rise of the excited electron population in the lowest unoccupied quantum well state is delayed by 70 fs which occurs concomitantly with a decay in the second lowest state. We describe this simultaneous decay and rise in the two adjacent subbands by coupled rate equations and attribute it to intersubband scattering. Thereby, we demonstrate the importance of intersubband decay in low-dimensional metallic systems in addition to intraband scattering processes considered in Fermi-liquid theory and derived descriptions.

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“…A particularly interesting case to study as semiconductor device dimensions shrink would be carrier dynamics and scattering occurring at material boundaries. Recent progress in experimental techniques suggests that five-wave mixing setups will provide access to such processes, (Voelkmann, 2004, Meier 2005. Another important recent development is the introduction of combined ultrafast laser and terahertz THz methods, such as Terahertz time-domain spectroscopy (THz-TDS).…”

Section: Main Spectroscopic Techniquesmentioning

confidence: 99%

Time-Resolved Laser Spectroscopy of Semiconductors - Physical Processes and Methods of Analysis

Brudevoll¹,

Storebø²,

Skaaring³

et al. 2011

Femtosecond-Scale Optics

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Five-Wave-Mixing Spectroscopy of Ultrafast Electron Dynamics at a Si(001) Surface

Cited by 37 publications

References 20 publications

Femtosecond nonlinear spectroscopy at surfaces: Second-harmonic probing of hole burning at the Si(111)7x7 surface and fourier-transform sum-frequency vibrational spectroscopy

Femtosecond nonlinear spectroscopy at surfaces: Second-harmonic probing of hole burning at the Si(111)7x7 surface and fourier-transform sum-frequency vibrational spectroscopy

Ultrafast electron dynamics in Pb/Si(111) investigated by two-photon photoemission

Time-Resolved Laser Spectroscopy of Semiconductors - Physical Processes and Methods of Analysis

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