Ruslan Ovsyannikov

In this study, we use time- and angle-resolved photoelectron spectroscopy to investigate electron relaxation dynamics in an epitaxially grown graphene monolayer on SiC. Our findings reveal significantly faster relaxation of photoexcited electrons in non-hydrogen-intercalated epitaxial graphene compared to that for previously reported hydrogen-intercalated graphene structures. The differences in relaxation time are modeled by a combination of density function theory in conjunction with nonadiabatic molecular dynamics, providing a comprehensive explanation of electron relaxation pathways. This study highlights the critical influence of substrate interactions on the relaxation mechanisms in graphene, offering different perspectives for tailoring graphene electronic properties through controlled intercalation techniques.

Since 2003, the Macromolecular Crystallography (MX) group at Helmholtz-Zentrum Berlin (HZB) has been operating three MX beamlines at the BESSY II storage ring in Berlin. These beamlines were established to support the emerging structural genomics initiatives founded in Germany, Europe, and overseas around the turn of the century. Over the past two decades, these beamlines have been continuously developed to enable state-of-the-art diffraction experiments and to provide supporting facilities such as a sample preparation laboratory, a spectroscopy laboratory, a Biosafety Level 1 laboratory and all necessary computing resources for the MX and chemical crystallography user community. Currently, more than 100 independent research groups from the greater Berlin area, Germany, and Europe utilize these beamlines. Over time, more than 4500 Protein Data Bank depositions have been accrued based on data collected at the beamlines. This paper presents historical aspects of the beamlines, their current status including their research output, and future directions.

In this work, we study the interface obtained by depositing a monolayer of a Blatter radical derivative on polycrystalline cobalt. By examining the occupied and unoccupied states at the interface, using soft X‐ray techniques, combined with electronic structure calculations, we could simultaneously determine the electronic structure of both the molecular and ferromagnetic sides of the interface, thus obtaining a full understanding of the interfacial magnetic properties. We found that the molecule is strongly hybridized with the surface. Changes in the core level spectra reflect the modification of the molecule and the cobalt electronic structures inducing a decrease in the magnetic moment of the cobalt atoms bonded to the molecules which, in turn, lose their radical character. Our method allowed us to screen, beforehand, organic/ferromagnetic interfaces given their potential applications in spintronics.

In this work, we study the interface obtained by depositing a monolayer of a Blatter radical derivative on polycrystalline cobalt. By examining the occupied and unoccupied states at the interface, using soft X‐ray techniques, combined with electronic structure calculations, we could simultaneously determine the electronic structure of both the molecular and ferromagnetic sides of the interface, thus obtaining a full understanding of the interfacial magnetic properties. We found that the molecule is strongly hybridized with the surface. Changes in the core level spectra reflect the modification of the molecule and the cobalt electronic structures inducing a decrease in the magnetic moment of the cobalt atoms bonded to the molecules which, in turn, lose their radical character. Our method allowed us to screen, beforehand, organic/ferromagnetic interfaces given their potential applications in spintronics.

We investigate the interfacial electronic structure of n-type bulk MoS2 upon the adsorption of CoPc and CoPcF16 mono- and few-layers using advanced spectroscopic techniques. These include X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), angle-resolved photoelectron spectroscopy (ARPES), and ultraviolet photoelectron spectroscopy (UPS). Our findings indicate that the adsorption of CoPc enhances the degree of n-doping at the interface with MoS2. In contrast, CoPcF16 results in a nearly intrinsic position of the Fermi level. Furthermore, we note the formation of an induced gap state near the valence band maximum for monolayer CoPcF16 on MoS2. These observations underscore the potential to fine-tune the interfacial electronic properties of transition metal dichalcogenides through molecular functionalization for tailored electronic applications.

Lithium metal and anode-free batteries has the potential to increase the energy density and specific energy of the batteries drastically. However, when regular electrolyte materials are tried for these concepts they are plagued with problems due to degradation of the electrolyte at the interface and processes like dendrite formation which leads to poor capacity retention.[1] A strategy to mitigate these problems is to use Solid Polymer Electrolytes (SPEs), as these have better stability towards lithium metal. In order to find appropriate chemistries to use in SPE-based cells it is important to investigate and understand their anode interface, as this is where the Solid Electrolyte Interphase (SEI) is created from the degradation products during cycling. This work investigates three polyethylene oxide (PEO)-based SPEs, using lithium tetrafluoroborate (LiBF₄), lithium bis(oxalate)borate (LiBOB), and lithium difluoro(oxalate)borate (LiDFOB) as the lithium conducting salts. The interfaces of these SPEs (PEO:LiBF₄, PEO:LiBOB, and PEO:LiDFOB) was studied using Photo-Electron Spectroscopy (PES) with in situ lithium deposition, where lithium atoms are evaporated on top of the SPE film. The analysis of the core-level spectra before and after lithium deposition is compared to Ab Initio Molecular Dynamics (AIMD) simulations of the interface, where lithium atoms are gradually added during the simulation. These experimental and theoretical methods are meant to mimic the electrochemical plating of lithium at the lithium|SPE interface during charging of a lithium metal or anode-less cell. The interfaces of PEO:LiBOB and PEO:LiBF₄ show, among other compounds, polyethylene as a breakdown product at the interface. PEO:LiDFOB shows a much lesser degree of degradation compared to the other two systems. The degradation layer is however still effective at protecting the SPE from further breakdown, as PEO:LiDFOB has a relatively high capacity retention compared to PEO:LiBF₄ and PEO:LiBOB. Suggested is that the LiF provides a better electrochemical stability, while the boron and oxalate breakdown products provides a higher mechanical stability at the interface. [1] Huang WZ, Zhao CZ, Wu P, Yuan H, Feng WE, Liu ZY, Lu Y, Sun S, Fu ZH, Hu JK, Yang SJ. Anode‐Free Solid‐State Lithium Batteries: A Review. Advanced Energy Materials. 2022 Jul;12(26):2201044. Figure 1

Heterostructures consisting of transition metal dichalcogenides (TMDCs) and organic molecules are currently of enormous interest for a variety of applications. Comparably weakly interacting molecules like phthalocyanines exhibit a high potential for the tuning of electronic properties of TMDCs. Knowledge of the molecular orientation is a prerequisite for the understanding of the nature and strength of the interfacial interaction. We study the molecular orientation of cobalt phthalocyanine (CoPc) and perfluorinated (CoPcF16) on both large molybdenum disulfide (MoS2) single crystals and small MoS2 flakes using synchrotron-based techniques: X-ray absorption spectroscopy (XAS) at the Co L3 edge and spectromicroscopy in a photoemission electron microscope (PEEM). We show that the orientation can be radically different on both substrates. Whereas on large crystals an almost flat-lying orientation is observed, significant tilt angles were found on smaller flakes. The orientation depends crucially on the number of MoS2 layers and/or the size of flat terraces.

Electron spectroscopy with the unprecedented transmission of angle-resolved time-of-flight detection, in combination with pulsed X-ray sources, brings new impetus to functional materials science. We showcase recent developments towards chemical sensitivity from electron spectroscopy for chemical analysis and structural information from photoelectron diffraction using the phase transition properties of 1T-TaS₂. Our development platform is the SurfaceDynamics instrument located at the Femtoslicing facility at BESSY II, where femtosecond and picosecond X-ray pulses can be generated and extracted. The scientific potential is put into perspective to the current rapidly developing pulsed X-ray source capabilities from Lasers and Free-Electron Lasers.

The growth as well as vacuum ultraviolet (VUV) radiation-induced degradation of sodium chloride (NaCl) on Ag(111) is investigated by ultraviolet and x-ray photoelectron spectroscopy. In line with previous scanning tunneling microscopy studies, our results confirm that NaCl grows initially as a bilayer before island growth starts. Simple spectroscopic methods for calibrating the closure of the NaCl bilayer are further presented. In addition, the energy level alignment is studied as a function of NaCl film thickness and VUV-light intensity. When measuring with ultra-low photon flux, a sharp interface dipole lowers the sample work function by 0.65 eV upon adsorption of the first bilayer, which is followed by vacuum level alignment for subsequently deposited layers. In contrast, measurements performed with standard photon fluxes, such as those provided by commercial He discharge lamps, shows ‘downward band-bending’-like characteristics in the NaCl films. Upon extended exposure time to the standard VUV intensity, photoemission measurements further reveal that strong modifications of the electronic properties of the NaCl surface occur. These are likely correlated with halogen emission, eventually resulting in the formation of Na clusters promoting low work function of parts of the sample surface. This study provides general guidelines for obtaining reliable spectroscopic measurements on alkali halide thin films on metals.