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Model catalyst for confined catalysis studies consisting of an ordered Cu2-xO film grown between Cu(111) and a h‑BN overlayer.

Published Manuscript: Kretz, P., K. Waltar, Y. Geng, C. Metzger, M. Graus, A. Schöll, F. Reinert, S.-X. Liu, S. Decurtins, M. Hengsberger, J. Osterwalder, and L. Castiglioni (2021). "Adsorption geometry and electronic structure of a charge-transfer-complex: TTF-PYZ2 on Ag(110)." New J. Phys. 23, 013002. DOI: https://doi.org/10.1088/1367-2630/abcace *** Data format *** Photoemission data: He-Ia line (photon energy 21.22 eV, Omicron HIS-13 source, not monochromated, unpolarised), Specs Phoibos WAL spectrometer and a manipulator with home-built goniometer. Samples were mono- and bilayers of TTF-PYZ_2 adsorbed on Ag(110). Full 4D data sets were taken as constant energy images as function of two detector dimensions (energy and detector angle dimension over 60 degrees), as function of polar angle for typically 9 settings of the azimuthal angle: Raw Data saved in binary HDF5 format. Raw Data: HDF5 binary files with full header information. .h5 Imported and cropped data, full stack, saved as .TXT files: 600 blocks (polar, azimuth settings) * 348 lines (energies) * 256 columns (pixels in non-dispersive dir.) Scaling given below for each data set. Measurement parameters for momentum maps: 7-16 exposures, dwelltime 0.5 s, pass energy 10 eV Fermi energy at Ekin=16.8 eV The data correspond to broad slices, which were average where the images overlapped, finally binned onto a angular grid with constant solid angle density in parallel projection (thus linear in momentum) and integrated in energy over the width the corresponding state. This yields the final photoelectron momentum maps PMM: Processed data in TXT format: Columns: Intensity Polar angle (deg) Azimuthal angle (deg) Software used: home-made Labview data acquisition, Wavemetrics Igor Pro (version 7) for data processing. The valence band spectra are obtained by scanning the kinetic energy and binned in 120 channels of the non-dispersive dimension of the 2D detector (=emission angle along azimuthal direction): Software used: SpecsLab Prodigy, saved in text format as .XY files with full header. Low-energy-electron diffraction (LEED) images were taken with a commercial CMOS camera and saved as PNG. LEED patterns recorded from a OCI Microengineering MCP detector. Typical sample currents < 1 µA. Note that the screen is not spherical as in standard LEED but flat, the projection of the raw data therefore scaling with the tangent of the scattering angle. The scaling was numerically corrected for afterwards to scale with the sine (parallel projection), thus linear in momentum. ********************************** Fig. 3 LEED images ******************************************* Monolayer E=45 eV LEED_20180309_ML_45eV_cropped.png >> original image cropped to detector size LEED_20180309_ML_45eV_corrected.png >> scaling corrected to sin(angle) Partial bilayer E=46 eV LEED_20180405_MLBL_46eV_cropped.png LEED_20180405_MLBL_46eV_corrected.png Bilayer E=47 eV LEED_20180427_BL_47eV_cropped.png LEED_20180427_BL_47eV_corrected.png ************************ Figs. 4/5/6 Valence band spectra and PPMs of the HOMOs ****************** Valence band spectra: polar angle 50 deg, corresponds to emission at momentum 1.5/Å along [1,-1,0] of Ag(110) (azimuthal angle 0) The data shown correspond to the center angular channels, i.e. around curves 59 and 60 in each file. UPS20180206_MLshort_50deg.xy >> Monolayer UPS20180427_BLshort.xy >> Bilayer UPS20171120_Ag110_theta50.xy >> pristine Ag(110) substrate ************ PM Maps taken around binding energy 2.2 eV: (HOMO) ************ ** Monolayer ** WAL_20180309_UZH_KW_HOLO_042.h5 >> raw data WAL_20180309_HOLO_042.txt Type: Single Float 32 bit >> imported, cropped and scaled raw data Rows: 348 Start: 14.0237 Delta: 0.00333264 Units: eV Columns: 256 Start: -28.6062 Delta: 0.219668 Units: deg Layers: 600 Start: 0 Delta: 1 Units: ** Bilayer ** WAL_20180427_UZH_KW_HOLO_007.h5 >> raw data WAL_20180427_HOLO_007.txt >> imported, cropped and scaled raw data Type: Single Float 32 bit Rows: 348 Start: 14.0237 Delta: 0.00333264 Units: eV Columns: 256 Start: -28.6062 Delta: 0.219668 Units: deg Layers: 600 Start: 0 Delta: 1 Units: PMM007_BL_HOMO_Fig4.txt >> processed PMM of pristine Ag at EB=2.2 eV PMM007_BL_HOMO_Fig5.txt >> processed PMM of pristine Ag at EB=2.0 eV ** Ag(110)** WAL_20180205_UZH_KW_HOLO_014.h5 >> raw data WAL_20180205_HOLO_014.txt >> imported, cropped and scaled raw data Type: Single Float 32 bit Rows: 348 Start: 14.4237 Delta: 0.00333264 Units: eV Columns: 256 Start: -29.0849 Delta: 0.223423 Units: deg Layers: 400 Start: 0 Delta: 1 Units: PMM014_Ag110_2eV >> processed PMM of pristine Ag at HOMO energy ******** PM Maps taken around binding energy 3-3.6 eV: (HOMO-1, -2, -3) ******** ** Monolayer ** WAL_20180206_UZH_KW_HOLO_019.h5 >> raw data WAL_20180206_HOLO_019.txt >> imported, cropped and scaled raw data Type: Single Float 32 bit Rows: 348 Start: 14.4237 Delta: 0.00333264 Units: eV Columns: 256 Start: -29.0849 Delta: 0.223423 Units: deg Layers: 400 Start: 0 Delta: 1 Units: HOMO-1/-2 of 1 ML TTF-PYZ2: integration range around 13.8 eV (kinetic energy) HOMO-3 of 1 ML TTF-PYZ2: integration range around 13.2 eV ** Bilayer ** WAL_20180427_UZH_KW_HOLO_009.h5 >> raw data WAL_20180427_HOLO_009.txt >> imported, cropped and scaled raw data Type: Single Float 32 bit Rows: 348 Start: 12.8237 Delta: 0.00333264 Units: eV Columns: 256 Start: -28.1274 Delta: 0.216852 Units: deg Layers: 600 Start: 0 Delta: 1 Units: HOMO-1/-2 of 2 ML TTF-PYZ2: integration range around 13.8 eV (kinetic energy) HOMO-3 of 2 ML TTF-PYZ2: integration range around 13.2 eV ****************************** Fig. 7 PMM for bilayer at EF *************************************** WAL_20180427_UZH_KW_HOLO_011.h5 >> raw data WAL_20180427_HOLO_011.txt >> imported, cropped and scaled raw data Type: Single Float 32 bit Rows: 348 Start: 16.0237 Delta: 0.00333264 Units: eV Columns: 256 Start: -31 Delta: 0.237505 Units: deg Layers: 600 Start: 0 Delta: 1 Units: PMM011_BL_EF >> processed PMM of the bilayer at Fermi energy 16.6-16.8 eV, Additional funding through Deutsche Forschungsgemeinschaft (Projects SCHO1260/4-2 and RE1469/12-2)

Full data set for publication: Published Manuscript: Lisa Grad, Fabian O. von Rohr, Matthias Hengsberger, Jürg Osterwalder Charge carrier dynamics and self-trapping on Sb2S3(100) Physical Review Materials 5, 075401 (2021) DOI: 10.1103/PhysRevMaterials.5.075401 *** Data format *** Photoemission data: Time-resolved photoemission Data were acquired using home-built Labview-based software package as function of emission angle and time delay. The detector images were saved in the Specs GmbH proprietary SpecsLab data format which was loaded, scaled and saved as text file using the software Wavemetrics Igor Pro (version 7) and Igor Pro macro packages provided by Specs GmbH. No further processing like intensity scaling, binning or similar was applied to the data. Static photoemission data were acquired using the SpecsLab Prodigy software provided by Specs GmbH, Berlin, Germany. The data were processed for image distortions by the measurement software and saved as text files (extension .xy) including full header information: two columns Energy, Intensity *** Experimental parameters and reference data *** Specs Phoibos 100 spectrometer and a manipulator with home-built goniometer. The energy settings includes the work function of the electron detector, i.e. the photoelectrons from the Fermi energy appear at a kinetic energy value which equals the photon energy minus the (optional) sample bias voltage. In present measurements (raw data): WF of analyzer: Reference data set from polycrystalline metal using 21.22 eV photons and bias -5 V "Measurement_EF.txt" (text file with header information) Fitting: EF at 26.24 eV Pre-defined analyser WF 4.408 eV Light Sources - He-Ia line (photon energy 21.22 eV, Omicron HIS-13 source, not monochromated, unpolarised) - High-harmonic (HH5) of the second harmonic at 414 nm, wavelength 82 nm, photon energy 15.3 eV - Pump-probe (time-resolved) data taken using the second harmonic (414 nm) of the femtosecond laser as pump and the fourth harmonic (207 nm) as probe pulse. Samples were crystals of Sb2S3, cleaved in ultra-high vacuum Sample temperature was room temperature (290 K) *********************** Fig. 2 Valence Band in normal emission ********************* Static data taken using the HHG light source, i.e. photon energy 15.3 eV 140 deg refers to the manipulator angle setting for normal emission Sample bias -5 V - Fermi energy at 20.3 eV "Spec_Gamma_140deg.txt" full data set, energy from 8.0 eV in steps of 0.05 eV "VBM_Gamma_140deg.txt" zoom on valence band maximum, energy from 13.0 eV in steps of +0.05 eV Raw data as measured with SpecsLab Prodigy: "VB_1.xy" ****** Fig. 3 Time-resolved photoemission spectra including "vertical cuts" above the Fermi energy, i.e. energy distribution curves ********** Photoemission data taken at +0.3 - 3 eV with respect to the Fermi energy of the sample Raw Data set #1855, detector settings: kinetic energy 12.5 eV (center energy) pass energy 15.0 eV sample bias -5 V with respect to ground delays at non equidistant steps between -2 ps and +40 ps with respect to delay zero (coincidence of pump and probe pulses) Raw Data as .ZIP file: "1855 Sb2S3.zip" List of delays: Delays_DataSet1855.txt Raw data: "1855 Sb2S3" Series of detector images for one delay after 80 scans as text files ".tsv" Name is position of delay stage in mm; the temporal coincidence between pump and probe is -7.33 mm ("delay zero") "Info.tsv" contains measured time delays Raw data, preprocessed by cropping and scaling: 3D data cube intensity as function of detector angle (x), energy (y), time delay (z) Data: "Data_1855N80.txt" The different energy, angle, delay settings are given in the following text files: x (196 rows): detector angle (degrees, center=normal emission) "AngleScale_deg_Rows.txt" y (301 columns): energy (eV) "EnergyScale_eV_Cols.txt" z (231 layers): time delays (fs) "TimeDelays_fs_Layers.txt", Additional funding from University of Zurich through the Research Priority Programme LightChEC.

To achieve high power conversion efficiencies in photovoltaic or photoelectrochemical cells, an understanding of the dynamical processes in the electrode materials upon photoexcitation is crucial. Antimony sulfide is a promising candidate material. The authors present time-resolved two-photon photoemission measurements from a Sb${}_{2}$S${}_{3}$(100) single crystal surface. A first laser pulse generates a population of free charge carriers that are probed by a second pulse. Ultrafast relaxation towards the conduction band minimum is followed by a fast decay within 1.3 ps into two longer-lived trap states, self-trapped electrons and self-trapped excitons states, with lifetimes of 27 and 63 ps, respectively. The results support a polaronic self-trapping mechanism by optical phonons.

Antimony selenide (${\mathrm{Sb}}_{2}{\mathrm{Se}}_{3}$) consists of one-dimensional ribbons that are van der Waals bonded to each other. Due to its favorable optoelectronic properties, it is a promising material for solar energy conversion. Owing to its narrow direct band gap and its high absorption coefficient it is an efficient absorber for solar light. Besides, it is cheap, stable in harsh environments, and abundant with low toxicity. For its use in solar devices, efficient transport of photoexcited charge carriers towards the active interface and long lifetimes at sufficiently high energies are mandatory. Here time-resolved two-photon photoemission experiments on the (100) surface of ${\mathrm{Sb}}_{2}{\mathrm{Se}}_{3}$ are presented. Data were taken along and perpendicular to the direction of the one-dimensional ribbons in order to unravel the anisotropic lifetimes and relaxation dynamics of photoexcited charge carriers. In both cases, various conduction bands could be populated and within the first picosecond ultrafast scattering towards the lowest conduction band was observed. Moreover, long lifetimes of up to 35 ps in the conduction band bottom at the surface were obtained and no sign of trapping in defect states was found. These measurements shed light on the relaxation and scattering of free carriers in ${\mathrm{Sb}}_{2}{\mathrm{Se}}_{3}$, which is the key for the design of ${\mathrm{Sb}}_{2}{\mathrm{Se}}_{3}$-based electrodes.

Cuprous oxide (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\hbox {Cu}}_2 {\hbox {O}}$$\end{document}Cu2O) is a promising material for photoelectrochemical energy conversion due to its small direct band gap, high absorbance, and its Earth-abundant constituents. High conversion efficiencies require transport of photoexcited charges to the interface without energy loss. We studied the electron dynamics in \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\hbox {Cu}}_2 {\hbox {O}}$$\end{document}Cu2O(111) by time-resolved two-photon photoemission for different surface defect densities in order to elucidate the influence on charge carrier transport. On the pristine bulk terminated surface, the principal conduction bands could be resolved, and ultrafast, elastic transport of electrons to the surface was observed. On a reconstructed surface the carrier transport is strongly suppressed and defect states dominate the spectra. Evidence for surface oxygen vacancies acting as efficient carrier traps is provided, what is important for further engineering of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\hbox {Cu}}_2 {\hbox {O}}$$\end{document}Cu2O based photoelectrodes.

Optica 6(11), 1431 - 1436 (2019). doi:10.1364/OPTICA.6.001431, Intense THz fields can be used to excite specific low-frequency modes in condensed matter or drive confined currents in nano-structured arrays, paving the way for a new class of optoelectronic devices. The long wavelength enables spatially confined field enhancement due to interaction with metallic structures and interference effects at dielectric interfaces. We use THz photoelectron streaking for the polarization-sensitive reconstruction of all electric field components at dielectric and metallic interfaces. This is realized in a THz/x-ray pump–probe experiment where x-ray emitted photoelectrons probe the effective THz field in close surface proximity. We observe distinct differences in the THz response of a nano-structured Pt thin film and a Pt(111) bulk crystal, in particular for the parallel field component. Simulations of the nanoscale spatial field modulation at metallic islands on the thin film provide design parameters for different sensitivity regimes with respect to local fields., Published by OSA, Washington, DC

Orbital tomography has recently been established as a technique to reconstruct molecular orbitals directly from photoemission data using iterative phase retrieval algorithms. In this work, we present a detailed description of steps for processing of the photoemission data followed by an improved iterative phase retrieval procedure and the interpretation of reconstructed two-dimensional orbital distributions. We address the issue of background subtraction by suggesting a signal restoration routine based on the maximization of mutual information algorithm and solve the problem of finding the geometrical center in the reconstruction by using a tight-centered object support in a two-step phase retrieval procedure. The proposed image processing and improved phase retrieval procedures are used to reconstruct the highest occupied molecular orbital of pentacene on Ag(110), using photoemission data only. The results of the reconstruction agree well with the density functional theory simulation, modified to comply with the experimental conditions. By comparison with photoelectron holography, we show that the reconstructed two-dimensional orbital distribution can be interpreted as a superposition of the in-focus orbital distribution evaluated at the $z=0$ plane and out-of-focus distributions evaluated at other $z=\mathrm{const}$ planes. Three-dimensional molecular orbital distributions could thus be reconstructed directly from two-dimensional photoemission data, provided the axial resolution of the imaging system is high enough.

We present a time-resolved angle-resolved photoelectron spectroscopy study of IrTe$_2$, which undergoes two first-order structural and charge-ordered phase transitions on cooling below 270 K and below 180 K. The possibility of inducing a phase transition by photoexcitation with near-infrared femtosecond pulses is investigated in the charge-ordered phases. We observe changes of the spectral function occuring within a few hundreds of femtoseconds and persisting up to several picoseconds, which we interpret as a partial photoinduced phase transition (PIPT). The necessary time for photoinducing these spectral changes increases with increasing photoexcitation density and reaches timescales longer than the rise time of the transient electronic temperature. We conclude that the PIPT is driven by a transient increase of the lattice temperature following the energy transfer from the electrons. However, the photoinduced changes of the spectral function are small, which indicates that the low temperature phase is particularly robust against photoexcitation. We suggest that the system might be trapped in an out-of-equilibrium state, for which only a partial structural transition is achieved., 8 pages, 5 figures, accepted for publication in Phys. Rev. B

The precise knowledge of the electric field in close proximity to metallic and dielectric surfaces is a prerequisite for pump-probe experiments aiming at the control of dynamic surface processes. We describe a model to reconstruct this electric field in immediate surface proximity from data taken in photoelectron THz-streaking experiments with an angle-resolved electron analyzer. Using Monte-Carlo simulations we are able to simulate streaking experiments on arbitrary surfaces with a variety of initial electron momentum distributions and to reconstruct the effective electric field at the surface. Our results validate the approach and suggest energy regimes for optimal pulse reconstruction.

An efficient and fast way to measure photoelectron diffraction data over the full 2π angular range with high data point density is presented, taking advantage of the massive parallel detection capabilities of modern two-dimensional electron detectors. We introduce generic routines for data binning and for the mapping of the detector signal onto emission angles. X-ray photoelectron diffraction patterns taken from Bi(1 1 1) with the new detection scheme are compared to data sets taken with a conventional hemispherical analyzer equipped with a channeltron detector. As a result, the data acquisition time can be reduced by roughly a factor of ten while obtaining comparable if not superior data quality. The sampling technique is extended to UV-excited angle-resolved photoelectron spectroscopy as illustrated by a mapping of the Fermi surface of Cu(1 1 1).