Femtosecond Transfer Dynamics of Photogenerated Electrons at a Surface Resonance of Reconstructed InP(100)

Abstract

Time-dependent two-photon photoemission spectra are used to resolve the femtosecond dynamics of hot electrons at the energetically lowest surface resonance of reconstructed InP(100). Two different cases are studied, where electrons either are lifted into the surface resonance via a direct optical transition or are captured from bulk states. These data are the first of this kind recorded with a time resolution below 70 fs. The microscopic analysis shows that electron-phonon scattering is a major mechanism for electron transfer between surface and bulk states.

Escape dynamics of photoexcited electrons at catechol:TiO2(110)

“…60 Both the time dependence and the continuous energy distribution in the spectra shown in Fig. 4 do not show any sign of a single dominant surface resonance for the catechol:rutile ͑110͒ interface prepared as described above.…”

“…Figure 4 shows an additional rather surprising result, i.e., the energy distribution is hardly changing with increasing delay time, a behavior that is strikingly different from, for example, the hot electron relaxation in the case of InP͑100͒ that has been measured also with 2PPE. 60,62 The surprising conclusion here is that the energy relaxation of the electrons injected into the unoccupied states at the catechol:rutile ͑110͒ interface is negligible on the time scale of the measured decay, i.e., 200 fs. The same observation has been made for electron injection into rutile ͑110͒ from the excited state of various perylene dyes.…”

“…51 In cooperation with a theory group we have investigated recently the influence of specific final and intermediate states on the shape of 2PPE spectra. 60,61 In the case of InP it was found that the experimental data are much less influenced by a mismatch in the effective mass of intermediate and final state than would be expected for the free electron as the final state. Since this is an unexplored area and since the shape of Fig.…”

“…[11][12][13] Work on semiconductor surfaces has mainly concentrated on silicon 14,15 and on hot electron dynamics at the surface of III-V semiconductors. 16,17 We report here on the time-dependent escape of photogenerated electrons from the surface into the bulk of rutile TiO 2 ͑110͒. The latter process was measured as time-dependent decay of 2PPE signals.…”

Microscopic theory of electron dynamics and time-resolved two-color two-photon photoemission at semiconductor surfaces

“…Although the second quantization formalism is not necessary for the examination of the optical interaction, thus leading to the same equations as a single particle approach, 26 it is of central importance in the treatment of the phonon-electron interaction, which is necessary to understand recent experiments. 27 Before being specified to a certain material system, the derived equations represent a general description of the electron dynamics at semiconductor surfaces. For the numerical evaluation, typically the restriction to a few-band system is necessary.…”