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.

High-flux ultrafast extreme-ultraviolet photoemission spectroscopy at 18.4 MHz pulse repetition rate.

Abstract: Laser-dressed photoelectron spectroscopy, employing extreme-ultraviolet attosecond pulses obtained by femtosecond-laser-driven high-order harmonic generation, grants access to atomic-scale electron dynamics. Limited by space charge effects determining the admissible number of photoelectrons ejected during each laser pulse, multidimensional (i.e. spatially or angle-resolved) attosecond photoelectron spectroscopy of solids and nanostructures requires high-photon-energy, broadband high harmonic sources operating at high repetition rates. Here, we present a high-conversion-efficiency, 18.4-MHz-repetition-rate cavity-enhanced high harmonic source emitting 5 × 105 photons per pulse in the 25-to-60-eV range, releasing 1 × 1010 photoelectrons per second from a 10-µm-diameter spot on tungsten, at space charge distortions of only a few tens of meV. Broadband, time-of-flight photoelectron detection with nearly 100% temporal duty cycle evidences a count rate improvement between two and three orders of magnitude over state-of-the-art attosecond photoelectron spectroscopy experiments under identical space charge conditions. The measurement time reduction and the photon energy scalability render this technology viable for next-generation, high-repetition-rate, multidimensional attosecond metrology. Space charge effects can distort the results of photoelectron spectroscopic measurements, and usually limit the allowable photon flux in an experiment. Here, the authors present an 18.4 MHz repetition rate high harmonic source in the 25–60 eV range, with a large count rate improvement over state-of-the-art attosecond setups under identical space charge conditions.

Angular momentum-induced delays in solid-state photoemission enhanced by intra-atomic interactions

Abstract: Attosecond time-resolved photoemission spectroscopy reveals that photoemission from solids is not yet fully understood. The relative emission delays between four photoemission channels measured for the van der Waals crystal tungsten diselenide (WSe2) can only be explained by accounting for both propagation and intra-atomic delays. The intra-atomic delay depends on the angular momentum of the initial localized state and is determined by intra-atomic interactions. For the studied case of WSe2, the photoemission events are time ordered with rising initial-state angular momentum. Including intra-atomic electron-electron interaction and angular momentum of the initial localized state yields excellent agreement between theory and experiment. This has required a revision of existing models for solid-state photoemission, and thus, attosecond time-resolved photoemission from solids provides important benchmarks for improved future photoemission models.

Determination of frontier orbital alignment and band bending at an organic semiconductor heterointerface by combined x-ray and ultraviolet photoemission measurements

Abstract: The alignment of the highest occupied molecular orbitals (HOMO) at the tris (8-hydroxy quinoline) aluminum (Alq3)/N,N′-di-(3-methylphenyl)-N,N′diphenyl-4,4′-diaminobiphenyl (TPD) heterojunction, used in organic light-emitting diodes (OLED), was determined by growing a TPD layer in several steps on a thick Alq3 substrate layer After each growth step the sample was characterized in situ by x-ray and ultraviolet photoemission spectroscopy The offset of the HOMO maxima at the interface was determined to be −013 eV from Alq3 to TPD By including the known HOMO–lowest occupied molecular orbital (LUMO) gaps for both molecules into the evaluation, the offset of the LUMO minima was determined to be −033 eV from Alq3 to TPD These values are consistent with previous assumptions that this interface represents a higher barrier for electron injection from Alq3 to TPD than for hole injection from TPD to Alq3