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Semiconductor Thin Film Growth Dynamics During Molecular Beam Epitaxy
Published in Arthur T. Hubbard, The Handbook of Surface Imaging and Visualization, 2022
The two normal modes of the dihydride-terminated steps show vibrational-energy relaxation times of roughly 80 ps, while the lifetime of the terrace monohydride mode is significantly longer, roughly 420 ps. On a Si(111) surface cut to produce monohydride-terminated steps, the relaxation time of the step Si-H mode is observed to be 10 times longer than that of the dihydride-terminated steps. The results are explained by energy transfer between the terrace and the step Si-H modes. The different dynamics on the monohydride- and dihydride-stepped surfaces arise because the short-lifetime dihydride steps act as energy drains, while the long-lifetime monohyride steps do not. Dipole-dipole coupling between the Si-H modes can account for the transfer rates observed. The solid lines in Figure 55.7 are fits to a kinetic model described in Morin et al.34 These results, and others like them, provide new information on the coupling of adsorbate vibrational modes to electronic and nuclear modes of the surface, and to other adsorbates. This information, in turn, will help refine theories of surface interactions.
Photo-induced primary processes of trans-[Co(acac)2(N3)(py)] in liquid solution studied by femtosecond vibrational and electronic spectroscopies
Published in Molecular Physics, 2021
Tobias Unruh, Luis I. Domenianni, Peter Vöhringer
To observe exclusively the dynamic evolution of the IA-bands unperturbed by the overlapping GSB-contributions, the inverted and properly scaled FTIR spectrum of the sample can be added to the raw data. The resultant, so-called purely absorptive product spectra are reproduced in Figure 3(c,d). These data reveal that the combined set of three induced absorptions seen at early delay smoothly transform into a spectrum, whose shape is identical to that of the FTIR spectrum, and that this dynamic transformation comprises only a continuous frequency upshift combined with a gradual spectral narrowing and a steady rise of the band integrals. Such a spectro-temporal evolution is highly indicative of the photo-excited complex ultra-rapidly recovering its electronic ground state in a highly vibrationally excited fashion and subsequently undergoing vibrational energy relaxation (VER) on a time scale of a few picoseconds [31, 46, 54]. It is therefore tempting to assign the three IA-bands, in the order of increasing wavenumber, to the acac-CH-wagging, the acac-C=O-stretching, and the azide-antisymmetric stretching mode, respectively, of the vibrationally excited electronic ground state. If this assignment were correct, we would have to conclude here that even for delays as short as 1 ps, no unambiguous spectroscopic fingerprint of the electronically excited state of the complex is observed. We will later see that this is a premature conclusion.
Statistical quasi-particle theory for open quantum systems
Published in Molecular Physics, 2018
Hou-Dao Zhang, Rui-Xue Xu, Xiao Zheng, YiJing Yan
Figure 3 demonstrates the simulated 2D spectroscopy at 77 K under three circumstances, i.e. the pure Drude dissipation without vibronic coupling, the one with Franck–Condon coupling and the one with Herzberg–Teller coupling. In the presence of the vibronic coupling, vibrational peaks on both diagonal and off-diagonal are observed, while the exciton–exciton off-diagonal peak is concealed. In particular, an electronic-vibrational cross peak (CP) appears right to the excitonic diagonal peak (DP) with the frequency difference around ωBO, as observed in the middle- and bottom-left panels of Figure 3. It suggests that this CP measures the cross correlation between the first and the zeroth vibrational levels within the excited electronic state. With the non-Condon vibronic coupling, the above vibrational signals are more prominent. The right panels show the t2 time-evolution of the signals along the dashed horizontal line, covering both the excitonic DP and the electronic-vibrational CP. With the vibronic coupling, the duration of the quantum beats is elongated obviously. As shown in the middle- and bottom-right panels, the vibronic CPs oscillate for at least 1 ps with both Condon and non-Condon vibronic couplings. For DPs, however, the oscillation with non-Condon coupling is more persistent than that with Condon coupling. Moreover, the non-Condon coupling results in larger oscillation amplitude. Evidently, the vibronic coupling facilitates the quantum coherence in the EET dynamics. In particular, the non-Condon transition greatly enhances the excitation of higher vibrational levels in the excited state. The subsequent vibrational energy relaxation preserves the long-lived coherence and amplifies the oscillation amplitudes in 2D spectroscopy.