Communication: Effect of Oxidation on Excited State Dynamics of Neutral TinO2n-x (n<10, x<4) Clusters

Excited state lifetimes of neutral titanium oxide clusters (TinO2n-x, n < 10, x < 4) were measured using a sequence of 400 nm pump and 800 nm probe femtosecond laser pulses. Despite large differences in electronic properties between the closed shell stoichiometric TinO2n clusters and the suboxide TinO2n-x (x = 1-3) clusters, the transient responses for all clusters contain a fast response of 35 fs followed by a sub-picosecond excited state lifetime. In this non-scalable size regime, subtle changes in the sub-ps lifetimes are attributed to variations in the coordination of Ti atoms and localization of charge carriers following UV photoexcitation. In general, clusters exhibit longer lifetimes with increased size and also with addition of O atoms. This suggests that removal of O atoms develops stronger Ti-Ti interactions as the system transitions from a semiconducting character into a fast metallic electronic relaxation mechanism.

Tuning two-dimensional electron and hole gases at LaInO3/BaSnO3 interfaces by polar distortions, termination, and thickness

Two-dimensional electron gases (2DEG), arising due to quantum confinement at interfaces between transparent conducting oxides, have received tremendous attention in view of electronic applications. Here, we explore the potential of interfaces formed by two lattice-matched wide-gap oxides of emerging interest, i.e., the polar, orthorhombic perovskite LaInO3 and the nonpolar, cubic perovskite BaSnO3, employing first-principles approaches. We find that the polar discontinuity at the interface is mainly compensated by electronic relaxation through charge transfer from the LaInO3 to the BaSnO3 side. This leads to the formation of a 2DEG hosted by the highly dispersive Sn-s-derived conduction band and a 2D hole gas of O-p character, strongly localized inside LaInO3. We rationalize how polar distortions, termination, thickness, and dimensionality of the system (periodic or non-periodic) can be exploited in view of tailoring the 2DEG characteristics, and why this material is superior to the most studied prototype LaAlO3/SrTiO3.

X-ray transient absorption reveals the 1Au (nπ*) state of pyrazine in electronic relaxation

Electronic relaxation in organic chromophores often proceeds via states not directly accessible by photoexcitation. We report on the photoinduced dynamics of pyrazine that involves such states, excited by a 267 nm laser and probed with X-ray transient absorption spectroscopy in a table-top setup. In addition to the previously characterized 1B2u (ππ*) (S2) and 1B3u (nπ*) (S1) states, the participation of the optically dark 1Au (nπ*) state is assigned by a combination of experimental X-ray core-to-valence spectroscopy, electronic structure calculations, nonadiabatic dynamics simulations, and X-ray spectral computations. Despite 1Au (nπ*) and 1B3u (nπ*) states having similar energies at relaxed geometry, their X-ray absorption spectra differ largely in transition energy and oscillator strength. The 1Au (nπ*) state is populated in 200 ± 50 femtoseconds after electronic excitation and plays a key role in the relaxation of pyrazine to the ground state.

X-Ray Transient Absorption Reveals the 1Au (Nπ*) State of Pyrazine in Electronic Relaxation

Electronic relaxation in organic chromophores often proceeds via states not directly accessible by photoexcitation. We report on the photoinduced dynamics of pyrazine that involves such states, excited by a 267 nm laser and probed with X-ray transient absorption spectroscopy in a table-top setup. In addition to the previously characterized ¹B_2u (ππ*) (S₂) and ¹B_3u (nπ*) (S₁) states, the participation of the optically dark ¹A_u (nπ*) state is assigned by a combination of experimental X-ray core-to-valence spectroscopy, electronic structure calculations, nonadiabatic dynamics simulations, and X-ray spectral computation. Despite ¹A_u (nπ*) and ¹B_3u (nπ*) states having similar energies at relaxed geometry, their X-ray absorption spectra differ largely in transition energy and oscillator strength. The ¹A_u (nπ*) state is populated about 200 femtoseconds after electronic excitation and plays a key role in the relaxation of pyrazine to the ground state.

X-Ray Transient Absorption Reveals the 1Au (Nπ*) State of Pyrazine in Electronic Relaxation

Electronic relaxation in organic chromophores often proceeds via states not directly accessible by photoexcitation. We report on the photoinduced dynamics of pyrazine that involves such states, excited by a 267 nm laser and probed with X-ray transient absorption spectroscopy in a table-top setup. In addition to the previously characterized ¹B_2u (ππ*) (S₂) and ¹B_3u (nπ*) (S₁) states, the participation of the optically dark ¹A_u (nπ*) state is assigned by a combination of experimental X-ray core-to-valence spectroscopy, electronic structure calculations, nonadiabatic dynamics simulations, and X-ray spectral computation. Despite ¹A_u (nπ*) and ¹B_3u (nπ*) states having similar energies at relaxed geometry, their X-ray absorption spectra differ largely in transition energy and oscillator strength. The ¹A_u (nπ*) state is populated about 200 femtoseconds after electronic excitation and plays a key role in the relaxation of pyrazine to the ground state.