Photoemission spectroscopy

About: Photoemission spectroscopy is a research topic. Over the lifetime, 10821 publications have been published within this topic receiving 250888 citations. The topic is also known as: photoelectron spectroscopy & PES.

Strongly bound excitons in anatase TiO2 single crystals and nanoparticles

Abstract: Anatase TiO$_2$ is among the most studied materials for light-energy conversion applications, but the nature of its fundamental charge excitations is still unknown. Yet it is crucial to establish whether light absorption creates uncorrelated electron-hole pairs or bound excitons and, in the latter case, to determine their character. Here, by combining steady-state angle-resolved photoemission spectroscopy and spectroscopic ellipsometry with state-of-the-art ab initio calculations, we demonstrate that the direct optical gap of single crystals is dominated by a strongly bound exciton rising over the continuum of indirect interband transitions. This exciton possesses an intermediate character between the Wannier-Mott and Frenkel regimes and displays a peculiar two-dimensional wavefunction in the three-dimensional lattice. The nature of the higher-energy excitations is also identified. The universal validity of our results is confirmed up to room temperature by observing the same elementary excitations in defect-rich samples (doped single crystals and nanoparticles) via ultrafast two-dimensional deep-ultraviolet spectroscopy.

Electronic structure of strontium titanate

Abstract: We have employed the techniques of photoelectron spectroscopy (with tunable synchrotron radiation $30\ensuremath{\le}h\ensuremath{ u}\ensuremath{\le}100$ eV) and inverse photoemission spectroscopy at $h\ensuremath{ u}=9.7$ eV to study respectively the occupied and unoccupied electronic states of $n$-type ${\mathrm{SrTiO}}_{3}$ doped with 1 at.% Nb. Doped samples have the advantage that charging effects are avoided and hence a rather accurate determination of peak positions is possible. The total (occupied and empty) experimental density of states agrees with the calculated density of states of Pertosa and Michel-Calendini when their band-gap energy is readjusted. We have no evidence for intrinsic surface states either in the band gap or in the conduction band, as was calculated by Wolfram et al. The admixture of Ti $3d$ states in the O $2p$ valence states is small, as can be concluded from the Ti $3p\ensuremath{\rightarrow}3d$ resonance behavior.

Ultrafast photodoping and effective Fermi-Dirac distribution of the Dirac particles in Bi2Se3

Abstract: We exploit time- and angle-resolved photoemission spectroscopy to determine the evolution of the out-of-equilibrium electronic structure of the topological insulator Bi2Se3. The response of the Fermi-Dirac distribution to ultrashort IR laser pulses has been studied by modeling the dynamics of hot electrons after optical excitation. We disentangle a large increase in the effective temperature (T*) from a shift of the chemical potential (mu*), which is consequence of the ultrafast photodoping of the conduction band. The relaxation dynamics of T* and mu* are k independent and these two quantities uniquely define the evolution of the excited charge population. We observe that the energy dependence of the nonequilibrium charge population is solely determined by the analytical form of the effective Fermi-Dirac distribution.

The Ã2E/B̃2B2 Photoelectron Bands of Allene beyond the Linear Coupling Scheme: An ab Initio Dynamical Study Including All Fifteen Vibrational Modes†

Abstract: In an earlier publication [J. Chem. Phys. 1999, 111, 10452] we theoretically investigated the photoelectron spectrum of allene (C3H4+) pertinent to the A2E/B2B2 interacting electronic manifold of its radical cation (C3H4+). Employing a linear vibronic coupling scheme it was demonstrated that in addition to the E⊗B Jahn−Teller activity within the 2e electronic manifold, there is a strong (E⊗B) + E pseudo-Jahn−Teller interaction with the B2B2 electronic state, which causes the diffuse structures observed at high energies. Here, the same photoelectron spectrum is reinvestigated including all fifteen vibrational degrees of freedom of the system and a higher order coupling scheme. The coupling parameters of the Hamiltonian are calculated by ab initio methods. The photoelectron band is calculated by the wave packet propagation method within the multiconfiguration time-dependent Hartree (MCTDH) scheme and compared with the experimental results of Baltzer et al. [Chem. Phys. 1995, 196, 551]. The progressions at...