Efficient orbital imaging based on ultrafast momentum microscopy and sparsity-driven phase retrieval

Jansen, G. S. Matthijs; Keunecke, Marius; Düvel, M.; Möller, Christina; Schmitt, David R.; Bennecke, Wiebke; Kappert, F. Jasmin; Steil, Daniel; Lüke, D.; Steil, Sabine; Mathias, Stefan

doi:10.1088/1367-2630/ab8aae

Cited by 34 publications

(25 citation statements)

References 38 publications

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“…While well-known surface investigating techniques such as scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED) primarily focus on determining structural aspects, (angle-resolved) ultraviolet photoemission spectroscopy (ARUPS) traditionally reveals the electronic (band) structure of the adsorbate layers. However, when utilizing the connection between ARUPS intensity maps and the Fourier transform of molecular orbitals, known as photoemission tomography (PT), ARUPS has been utilized to simultaneously reveal the electronic and geometric structure for a number of organic adsorbate systems. ,− …”

Section: Introductionmentioning

confidence: 99%

Demonstrating the Impact of the Adsorbate Orientation on the Charge Transfer at Organic–Metal Interfaces

et al. 2021

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Charge-transfer processes at molecule–metal interfaces play a key role in tuning the charge injection properties in organic-based devices and thus, ultimately, the device performance. Here, the metal’s work function and the adsorbate’s electron affinity are the key factors that govern the electron transfer at the organic/metal interface. In our combined experimental and theoretical work, we demonstrate that the adsorbate’s orientation may also be decisive for the charge transfer. By thermal cycloreversion of diheptacene isomers, we manage to produce highly oriented monolayers of the rodlike, electron-acceptor molecule heptacene on a Cu(110) surface with molecules oriented either along or perpendicular to the close-packed metal rows. This is confirmed by scanning tunneling microscopy (STM) images as well as by angle-resolved ultraviolet photoemission spectroscopy (ARUPS). By utilizing photoemission tomography momentum maps, we show that the lowest unoccupied molecular orbital (LUMO) is fully occupied and also, the LUMO + 1 gets significantly filled when heptacene is oriented along the Cu rows. Conversely, for perpendicularly aligned heptacene, the molecular energy levels are shifted significantly toward the Fermi energy, preventing charge transfer to the LUMO + 1. These findings are fully confirmed by our density functional calculations and demonstrate the possibility to tune the charge transfer and level alignment at organic–metal interfaces through the adjustable molecular alignment.

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Section: Introductionmentioning

confidence: 99%

Demonstrating the Impact of the Adsorbate Orientation on the Charge Transfer at Organic–Metal Interfaces

et al. 2021

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“…Future directions for developments in kMap.py include the reconstruction of real space orbital distributions from measured momentum map. The necessary numerical retrieval of the phase information has been demonstrated already in a number of publications [9,51,52,53,54] and should be straightforward to implement also into kMap.py. A more fundamental aspect of photoemission tomography concerns the underlying approximation of the final state as a plane wave which certainly has known limitations [5].…”

Section: Discussionmentioning

confidence: 99%

kMap.py: A Python program for simulation and data analysis in photoemission tomography

Brandstetter¹,

Yang²,

Lüftner³

et al. 2020

Preprint

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Ultra-violet photoemission spectroscopy is a widely-used experimental technique to investigate the valence electronic structure of surfaces and interfaces. When detecting the intensity of the emitted electrons not only as a function of their kinetic energy, but also depending on their emission angle, as is done in angle-resolved photoemission spectroscopy (ARPES), extremely rich information about the electronic structure of the investigated sample can be extracted. For organic molecules adsorbed as well-oriented ultra-thin films on metallic surfaces, ARPES has evolved into a technique called photoemission tomography (PT). By approximating the final state of the photoemitted electron as a free electron, PT uses the angular dependence of the photocurrent, a so-called momentum map or k-map, and interprets it as the Fourier transform of the initial state's molecular orbital, thereby gains insights into the geometric and electronic structure of organic/metal interfaces.In this contribution, we present kMap.py which is a Python program that enables the user, via a PyQt-based graphical user interface, to simulate photoemission momentum maps of molecular orbitals and to perform a one-toone comparison between simulation and experiment. Based on the plane wave approximation for the final state, simulated momentum maps are computed numerically from a fast Fourier transform (FFT) of real space molecular or- * Corresponding author.

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“…[129,136,288] Proof-of-principle experiments have been performed for a number of exciting emerging applications of time-resolved momentum microscopy, including ultrafast molecular orbital imaging and tracking transient changes of topological properties and orbital texture of out-of-equilibrium states of matter, where currently XUV excitation energies are used, but which could be translated into the hard X-ray regime in the future. [199,[390][391][392] A new powerful tool, that is already using hard X-rays, is emerging in the form of full-field photoelectron diffraction for structural analysis, which has been demonstrated in first static experiments using hard X-rays. [204,205] A serious obstacle for time resolved studies is the Coulomb interaction of electrons confined in a small spatio-temporal phase-space volume.…”

Section: Outlook and Futurementioning

confidence: 99%

Hard x-ray photoelectron spectroscopy: a snapshot of the state-of-the-art in 2020

Kalha

Fernando

Bhatt

et al. 2021

J. Phys.: Condens. Matter

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Hard X-ray photoelectron spectroscopy (HAXPES) is establishing itself as an essential technique for the characterisation of materials. The number of specialised photoelectron spectroscopy techniques making use of hard X-rays is steadily increasing and ever more complex experimental designs enable truly transformative insights into the chemical, electronic, magnetic, and structural nature of materials. This paper begins with a short historic perspective of HAXPES and spans from developments in the early days of photoelectron spectroscopy to provide an understanding of the origin and initial development of the technique to state-of-the-art instrumentation and experimental capabilities. The main motivation for and focus of this paper is to provide a picture of the technique in 2020, including a detailed overview of available experimental systems worldwide and insights into a range of specific measurement modi and approaches. We also aim to provide a glimpse into the future of the technique including possible developments and opportunities.

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Efficient orbital imaging based on ultrafast momentum microscopy and sparsity-driven phase retrieval

Cited by 34 publications

References 38 publications

Demonstrating the Impact of the Adsorbate Orientation on the Charge Transfer at Organic–Metal Interfaces

Demonstrating the Impact of the Adsorbate Orientation on the Charge Transfer at Organic–Metal Interfaces

kMap.py: A Python program for simulation and data analysis in photoemission tomography

Hard x-ray photoelectron spectroscopy: a snapshot of the state-of-the-art in 2020

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