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.

Resonant-photoemission study of SnO 2 : Cationic origin of the defect band-gap states

Abstract: The electronic properties of tin dioxide single-crystalline (110) surfaces have been studied in correlation with their structure by low-energy electron diffraction, angle-integrated and resonant photoemission using synchrotron radiation [ultraviolet photoemission spectroscopy (UPS)]. Energy distribution curves were measured from the Sn 4d core levels and from the valence band. The experimental valence band is compared with the theoretical density of states (DOS) from perfect and defective surfaces. UPS difference curves, normalized to the Sn 4d intensity, reflect mainly the increase in the oxygen partial DOS when the sample is annealed at increasing temperatures up to 1000 K after sputtering. Their comparison with simulated theoretical difference curves favors a bridging oxygen termination for annealing temperatures above 900 K. After argon-ion bombardment, band-gap defect states that are not predicted by the calculations are found at a maximum density 1.4 eV above the valence-band maximum (VBM). Various degrees of resonant enhancement occur throughout the valence band when the photon energy crosses the Sn 4d\ensuremath{\rightarrow}5p photoabsorption threshold, and these are used to establish the tin-derived character of the gap states, for which a tin 5s origin is proposed. Partial-yield spectra allow the localization of unoccupied Sn 5p states in the conduction band starting from 8 eV above the VBM with a maximum at 10 eV. The Sn 4d\ensuremath{\rightarrow}5p absorption threshold also shows possible core exciton formation for sputtered surfaces only.

Femtosecond electron and spin dynamics in Ni/W(110) films

Abstract: The collapse of the magnetic exchange splitting in 7 monolayer thick epitaxial Ni/W(110) films following a femtosecond laser pulse was measured using time-resolved photoemission spectroscopy Ultrafast demagnetization during the laser induced hot electron cascade proceeds via spin-flip excitations with a relaxation time constant of 300+/-70 fs At longer times the electronic system cools down and the magnetization is finally reestablished with a time constant of 32+/-02 ps

Photoemission spectroscopy—from early days to recent applications

Abstract: In this review we describe the development of photoemission spectroscopy (PES) from the first historic observations of the photoelectric effect by Hertz and Hallwachs to state-of-the-art experiments. We present several examples for the application of PES for chemical analysis of solids (ESCA), the determination of the valence band structure by angle-resolved photoemission (ARUPS), and the investigation of many-body effects, in particular by high-resolution PES on the meV-scale. Furthermore, we give a brief overview about the wide spectrum of experimental methods based on PES.

Energy level alignment and two-dimensional structure of pentacene on Au(111) surfaces

Abstract: X-ray photoemission, ultraviolet photoemission spectroscopy (UPS), and scanning tunneling microscopy (STM) have been used to determine the energy level alignment and the molecular ordering of monolayer and submonolayer pentacene films on Au(111) in ultrahigh vacuum. Pentacene evaporated onto the van der Waals surface of SnS2 was used as a noninteracting substrate for comparison. A large interface dipole was measured for pentacene on Au(111) (0.95 eV) whereas pentacene on SnS2 showed a relatively small interface dipole (0.26 eV). The different interface dipoles are related to the different orientations of the pentacene molecules due to different pentacene substrate interaction energies. Differences in the UPS spectra also support changing molecular orientations of the two substrates. STM images of pentacene on Au(111) revealed that the molecules lay flat on the substrate and are oriented parallel to each other, forming striped structures that are commensurate with the Au(111) lattice. The pentacene coverag...

XPS and UPS characterization of the TiO2/ZnPcGly heterointerface: Aligmment of energy levels

Abstract: The electronic structure and the highest occupied molecular orbitals (HOMO)/the lowest unoccupied molecular orbitals (LUMO) alignment at the molecular semiconductor heterointerface of nanostructured TiO2/ZnPcGly dye sensitizer were characterized by X-ray and ultraviolet photoemission spectroscopy (XPS and UPS). The HOMO level of the dye ZnPcGly was determined to be located at 1.62 eV below the Fermi edge, and the corresponding LUMO level was estimated to be 0.10 eV above the conduction band of TiO2 based on the HOMO/LUMO gap (1.82 eV) of ZnPcGly determined by optical absorption measurements. This energy level matching between the orbitals of the dye and the bands of TiO2 can enable efficient electron transfer from photoexcited ZnPcGly to TiO2, which is very important in photoinduced charge-transfer reactions and for applications in dye-sensitized solar cells.