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A key benefit of angle-resolved photoelectron spectroscopy (ARPES) in the X-ray range is the significant increase of the information depth, thanks to the large inelastic mean-free-path of the escaping photoelectrons. In practice hard X-ray ARPES (HARPES) faces severe challenges by low cross sections, large photon momentum transfer, and in particular strong phonon scattering and photoelectron diffraction effects. Here, we show that these challenges can be overcome by extending ultra-efficient time-of-flight momentum microscopy into the hard X-ray regime. Phonon scattering destroys the initial momentum distribution but subsequent diffraction at the lattice imprints a pronounced Kikuchi-type pattern on the background signal. Moreover, the pattern of the valence electrons is modulated by diffraction as well. For the examples of the medium-weight element materials Mo and layered TiTe2, we demonstrate how comprehensive valence-band and core-level photoemission data taken under identical conditions can be used to effectively remove photoelectron diffraction effects in HARPES band maps. The study of electronic structure of new materials has benefited from more widely available angle-resolved photoelectron spectroscopy (ARPES) at synchrotron sources, but hard X-ray ARPES, capable of mapping at a depth of some tens nanometres is still of limited access. The authors report on a method to obtain bulk electronic structure using hard X-rays ARPES combined with an effective data processing background removal strategy capable of revealing the valence band electronic dispersion of metal and semiconductor surfaces. [ABSTRACT FROM AUTHOR]

We investigated interfaces of halfmetallic Co2MnSi(1 0 0) Heusler thin films with Ag(1 0 0), Cr(1 0 0), Cu and Al layers relevant for spin valves by high energy x-ray photoemission spectroscopy (HAXPES). Experiments on Co2MnSi samples with an Ag(1 0 0) interface showed a characteristic spectral shoulder feature close to the Fermi edge, which is strongly diminished or suppressed at Co2MnSi (1 0 0) interfaces with the other metallic layers. This feature is found to be directly related to the Co2MnSi(1 0 0) layer, as reflected by control experiments with reference non-magnetic films, i.e. without the Heusler layer. By comparison with HAXPES calculations, the shoulder feature is identified as originating from an interface state related to a highly spin polarized surface resonance of Co2MnSi (1 0 0). [ABSTRACT FROM AUTHOR]

How and why the reliability of ferroelectric HfO2‐ and HZO (Hf0.5Zr0.5O2)‐based memory devices strongly depends on the choice of electrode materials is currently under intense discussion. Interface conditions such as band alignment, defect formation, and doping are recognized as decisive and interrelated parameters, but a unified picture of the physical mechanisms is still missing. Here, two opposite scenarios of band alignment are found in TiN/HZO/TiN and IrO2/HZO/IrO2 using hard X‐ray photoelectron spectroscopy, revealing on the one hand the conditions for a stable device performance, and the origin of their degradation on the other. As a key difference, TiN electrodes scavenge oxygen from the HZO, while IrO2 electrodes supply it. Considering the electronic doping limit of HfO2, a key condition for the stability of ferroelectric devices can be identified: The alignment of the charge neutrality levelwith respect to the metallic Fermi level, which is pinned by the doping limit. Stable device performance can only be achieved for oxygen‐deficient HfO2‐based interfaces, where the Fermi level of the metal electrode is close to the conduction band of the ferroelectric insulator. This empirical model explains the fatigue behavior of HfO2‐based capacitors using either oxygen‐scavenging TiN or oxygen‐supplying IrO2 electrodes. [ABSTRACT FROM AUTHOR]

We study the electronic structure of a nonsymmorphic Kondo lattice system, CeCuX2 (X = As/Sb), a promising class of correlated topological materials important for advanced technology. While both the materials show Kondo behavior in their transport properties, CeCuSb2 is antiferromagnetic and no magnetic order is observed in CeCuAs2. We studied high-quality single-crystalline samples employing hard x-ray photoemission spectroscopy. The sample cleaving exposes the square-net structured pnictogen layers. The CeCuSb2 valence band indicates a highly metallic phase. The spectral intensity at the Fermi level in CeCuAs2 is weak, revealing close to semi-metallic behavior of the system. The Ce 3d spectra exhibit multiple features; the intensity of the features changes with the change in surface sensitivity of the technique, suggesting significant differences in the surface and bulk electronic structure. The bulk spectra of the Kondo system do not exhibit the typical f0-feature often observed in such materials. Instead, a distinct feature is observed at the lower binding energy side of the well-screened peak; the signature of this feature is manifested in the spectra from high-quality single-crystalline samples. This is outstanding and calls for physics beyond existing theories of correlated systems. [ABSTRACT FROM AUTHOR]

Several CoTiSb based compounds were synthesized and investigated on their thermoelectric properties. The aim was to improve the thermoelectric properties of CoTiSb by the systematic substitution of atoms or the introduction of additional Co into the vacant sublattice. The solid solutions Co1+xTiSb, Co1[?]yCuyTiSb and CoTiSb1[?]zBiz were synthesized. X-ray diffraction was used to investigate the crystal structure. The resistivity, the Seebeck coefficient and the thermal conductivity were determined for all compounds in the temperature range from 2 to 400 K. The highest figure of merit for each solid solution is presented. We were able to improve the figure of merit by a factor of approximately seven. [ABSTRACT FROM AUTHOR]

We report structural, electronic, magnetic, and magnetocaloric studies of polycrystalline DyMnO 3 and its A-site Gd substituents, Dy 1−x Gd x MnO 3 , where 0 ≤ x ≤ 1. Detailed comparison of various magnetocaloric parameters shows that Dy 0.5 Gd 0.5 MnO 3 has the best values with a large isothermal magnetic entropy change, − ∆ S m max ~ 15.35 J/kg K, adiabatic temperature change, ∆ T ad max ~ 6.15 K and relative cooling power, RCP ~ 307 J/kg, suggesting that rare earth mixing plays a vital role in enhancing the magnetocaloric properties. In addition, absence of magnetic and thermal hysteresis also makes it one of the best candidates for magnetic refrigeration among all known potential candidates for cryogenic temperature applications. [Display omitted] • In search of finding materials with superior magnetocaloric properties suitable for magnetic cooling applications at cryogenic temperatures, Dy 1−x Gd x MnO 3 , where 0 ≤ x ≤ 1, series has been studied. • Structural evaluation shows the formation of single phase systems in orthorhombic P bnm symmetry. With increase in Gd, there is a systematic increase in lattice parameters and volume. • In Raman spectra, all the modes exhibit nearly linear decrease with Gd - substitutions. • Gd substitutions do not significantly alter the electronic structures. However, distinct splitting of the Mn 3 s spectra is observed arising from the exchange coupling between 3 s hole and 3 d electrons. • Assessment of isothermal magnetic entropy, adiabatic temperature change and relative cooling power were carried out. DyMnO 3 exhibits moderate magnetocaloric effect having − ∆ S m max ~ 7.48 J/kg K, ∆ T ad max ~ 4.68 K and RCP ~ 174 J/kg for a magnetic field change of 9 T which could be enhanced by Gd substitution resulting in a giant magnetocaloric effect for Dy 0.5 Gd 0.5 MnO 3 having − ∆ S m max ~ 15.35 J/kg K ∆ T ad max ~ 6.15 K and RCP ~ 307 J/kg. • Owing to simple synthesis, high chemical stability, good magnetocaloric parameters and absence of magnetic and thermal hysteresis make Dy 0.5 Gd 0.5 MnO 3 a potential magnetic refrigerant for cryogenic temperature applications. [ABSTRACT FROM AUTHOR]

Effect of tempering temperature on the composition of the passive film of a martensitic tool alloy was studied by synchrotron-based hard/soft X-ray photoelectron spectroscopy and electrochemical analyses. The contents of Cr and Mo in the passive film are affected by precipitation of tempering carbides. Increase of tempering temperature from 200 to 525°C leads to enhanced formation of Cr/Mo-rich tempering carbides and Cr depletion. Tempering at 525°C results in a Cr content < 11 at% in the underlying metallic layer and formation of a Cr-deficient defective passive film, and thus loss of passivity for the tool alloy in corrosive conditions. • A combination of Synchrotron-based hard and soft XPS allows for analysis of passive film with varying probing depth. • Increasing tempering temperature from 200 to 525°C leads to Cr- and Mo-deficient defective passive film. • Tempering at 525°C results in a significant Cr depletion in the underlying alloy layer more than 19 nm in depth. • Formation of Cr- and Mo-rich tempering carbides at 525 °C results in the loss of passivity. [ABSTRACT FROM AUTHOR]

In the present work, we report a correlation between crystal structure, magnetic, and electrical properties in an exotic magnetic compound, NdBaMn 2 O 6 having ∼92% ordering between Nd and Ba, investigated using temperature-dependent synchrotron x-ray diffraction (XRD), dc magnetization and transport measurements. Temperature-dependent XRD data reveals that the compound undergoes various complex crystallographic phase transitions from high-temperature (T > 320 K) P 4/ mmm phase to intermediate (320 K – 280 K) Cmmm phase to a mixed (Cmmm and P 2 1 am) phase (280 K – 220 K) and to low-temperature P 2 1 am phase (T < 220 K). It is found that these crystallographic phase compositions play a crucial role in controlling its magnetic and transport properties. Temperature-dependent dc magnetization data show a sharp drop at the onset of mixed phase (Cmmm + P 2 1 am) at 280 K followed by a broad hump at ∼ 220 K where mixed phase to P 2 1 am transition occurs, thus indicating a correlation between the structural and magnetic properties. The dc magnetization in the mixed phase region is calculated by considering a superposition of the magnetic moments of Cmmm and P 2 1 am phases weighted by the fraction of each phase, which exactly follows the experimental magnetization data. Temperature variation of resistivity data shows a jump at ∼260 K, a temperature corresponding to 50–50% phase composition of Cmmm and P 2 1 am phases. The compound shows insulating behavior over a whole temperature range as confirmed from the resistivity data. Further, application of magnetic field causes a shift of magnetic and transport transition temperatures which may be due to the magnetic field induced structural transition in the system. • Ordered NdBaMn 2 O 6 undergoes multiple crystallographic phase transitions with temperature. • Physical properties of system are controlled by crystallographic phase transition/compositions. • Phenomenological model is suggested for the observed magnetic behavior. • Proposed system has possibility of magnetic field induced structural phase transition. [ABSTRACT FROM AUTHOR]

[Display omitted] • Epitaxial GaP(As)(1 0 0) films were grown on Si(1 0 0) substrates by MOVPE. • Atomic composition and electronic properties were investigated by photoemission spectroscopies (AR-XPS, HAXPES, GCIB-XPS). • Arsenic is mostly localized at interface but also interdiffused into GaP overlayer. • Similar valence band offsets (VBO) of ∼0.6 eV were measured for all type of GaP(As)/Si heterostructures. • Flat-band alignment was obtained for n-- GaP(As)/n-Si(1 0 0) heterostructure. The epitaxial growth of the polar GaP(1 0 0) on the nonpolar Si(1 0 0) substrate suffers from inevitable defects at the antiphase domain boundaries (APDs), resulting from mono-atomic steps on the Si(1 0 0) surface. Stabilization of Si(1 0 0) substrate surfaces with As is a promising technological step enabling the preparation of Si substrates with double atomic steps and reduced density of the APDs. In this paper, 4–50-nm-thick GaP epitaxial films were grown on As-terminated Si(1 0 0) substrates with different types of doping, miscuts, and As-surface termination by metalorganic vapor phase epitaxy (MOVPE). The GaP(As)/Si(1 0 0) heterostructures were investigated by X-ray photoelectron spectroscopy (XPS) combined with gas cluster ion beam (GCIB) sputtering and by hard X-ray photoelectron spectroscopy (HAXPES). We found residuals of As atoms in the GaP lattice (∼0.2–0.3 at.%) and a localization of As atoms at the GaP(As)/Si(1 0 0) interface (∼1 at.%). Deconvolution of core level peaks revealed interface core level shifts. In As core levels, chemical shifts between 0.5 and 0.8 eV were measured and identified by angle-resolved XPS measurements. Similar valence band offset (VBO) values of 0.6 eV were obtained, regardless of the doping type of Si substrate, Si substrate miscut or type of As-terminated Si substrate surface. The band alignment diagram of the GaP(As)/Si(1 0 0) heterostructure was deduced. [ABSTRACT FROM AUTHOR]

The magnitude of the spin polarization at the Fermi level of ferromagnetic materials at room temperature is a key property for spintronics. Investigating the Heusler compound Co2MnSi, a value of 93% for the spin polarization has been observed at room temperature, where the high spin polarization is related to a stable surface resonance in the majority band extending deep into the bulk. In particular, we identified in our spectroscopical analysis that this surface resonance is embedded in the bulk continuum with a strong coupling to the majority bulk states. The resonance behaves very bulklike, as it extends over the first six atomic layers of the corresponding (001) surface. Our study includes experimental investigations, where the bulk electronic structure as well as surface-related features have been investigated using spin-resolved photoelectron spectroscopy (SR-UPS) and for a larger probing depth spin-integrated high energy x-ray photoemission spectroscopy (HAXPES). The results are interpreted in comparison with first-principles band structure and photoemission calculations which consider all relativistic, surface, and high-energy effects properly. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hard X-ray photoelectron spectroscopy study of interfaces in Ta/Co 2 FeAl/MgO heterostructure. • Element specific and depth-selective information is obtained using HAXPES under X-ray standing wave excitation. • Fe exhibits stronger interdiffusion at both the interfaces as compared to Co. • Oxidation state of both Fe and Co decreases as one moves away from the MgO interface. • Oxidation of Fe increases while that of Co decreases with thermal annealing. • As a result, the concentration profile of Fe gets shifted towards MgO layer relative to that of Co. Interfaces of the magnetic layer in the heterostructure Ta/Co 2 FeAl/MgO have been studied using hard X-ray photoelectron spectroscopy (HAXPES). Depth-selective information with sub-nanometer resolution is obtained using X-ray standing waves. It is found that the two magnetic species namely, Co and Fe behave very differently at the interfaces; 54% of Fe in the magnetic layer gets either oxidised or alloyed with Ta at the interfaces, as against 48% of Co. Oxidation state of both Co and Fe decreases, as one moves away from the MgO interface. On the average about 0.36 nm of Co 2 FeAl gets oxidised at MgO interface and 0.66 nm gets alloyed with Ta at the bottom interface. Thermal annealing at 200℃ results in further oxidation of Fe, accompanied by a partial reduction of Co. It is suggested that this opposite behaviour of Fe and Co at the MgO interface may be the cause of the thermal annealing induced shift of the centroid of Fe distribution towards MgO layer, as observed in some STEM studies in such heterostructures. [ABSTRACT FROM AUTHOR]

We present a detailed study of the electronic structure and band alignment in LaA1O3/SrTiO3 oxide heterostructures by hard x-ray photoelectron spectroscopy. Our spectroscopic measurements find no evidence for the strong potential gradient within the polar LaA1O3 film predicted by band theory. Due to the high interface sensitivity of the method, we are further able to determine the valence band offset between the LaA1O3 film and the SrTiO3 substrate, which is found to be independent of the number of LAO overlayers. Finally, we discuss several explanations for the apparent absence of the built-in field in ex situ prepared LaA1O3/SrTiO3 heterostructures. [ABSTRACT FROM AUTHOR]

Stoichiometric FeRh undergoes a temperature-induced antiferromagnetic (AFM) to ferromagnetic (FM) transition at --350 K. In this Letter, changes in the electronic structure accompanying this transition are investigated in epitaxial FeRh thin films via bulk-sensitive valence-band and core-level hard x-ray photoelectron spectroscopy with a photon energy of 5.95 keV. Clear differences between the AFM and FM states are observed across the entire valence-band spectrum and these are well reproduced using density-functional theory. Changes in the 2p core levels of Fe are also observed and interpreted using Anderson impurity model calculations. These results indicate that significant electronic structure changes over the entire valence-band region are involved in this AFM-FM transition. [ABSTRACT FROM AUTHOR]

• Microscopic chemical analysis of anative passive film on 25Cr-7Ni super duplex stainless steel was analyzed by synchrotron HAXPEEM. • Results reveal lateral variations in thickness and Cr content of the passive film between individual grains of ferrite and austenite phases. • The Cr content is higher on ferrite than austenite, whereas the thickness is rather uniform. • Grain orientation has a small but detectable influence, ferrite (111) grains have a lower Cr content than other ferrite grains. A native passive film on 25Cr-7Ni super duplex stainless steel was analyzed using synchrotron hard X-ray photoemission electron microscopy, focusing on variations between individual grains of ferrite and austenite phases. The film consists of an oxide inner layer and an oxyhydroxide outer layer, in total 2.3 nm thick. The Cr content is higher in the outer than the inner layer, ca. 80 % on average. The Cr content is higher on ferrite than austenite, whereas the thickness is rather uniform. The grain orientation has a small but detectable influence, ferrite (111) grains have a lower Cr content than other ferrite grains. [ABSTRACT FROM AUTHOR]

We present a detailed study of the Ti 3 d carriers at the interface of LaAlO 3 / SrTiO 3 heterostructures by high-resolution resonant inelastic soft x-ray scattering (RIXS), with special focus on the roles of overlayer thickness and oxygen vacancies. Our measurements show the existence of interfacial Ti 3 d electrons already below the critical thickness for conductivity. The (total) interface charge carrier density increases up to a LaAlO 3 overlayer thickness of 6 unit cells before it levels out. Furthermore, we observe strong Ti 3 d charge carrier doping by oxygen vacancies. The RIXS data combined with photoelectron spectroscopy and transport measurements indicate the simultaneous presence of localized and itinerant charge carriers. At variance with previous interpretations, we show that in our excitation energy dependent RIXS measurements the amounts of localized and itinerant Ti 3 d electrons in the ground state do not scale with the intensities of the Raman and fluorescence peaks, respectively. Rather, we attribute the observation of either Raman components or fluorescence signal to the specific nature of the intermediate state reached in the RIXS excitation process. [ABSTRACT FROM AUTHOR]

In perovskite oxide heterostructures, bulk functional properties coexist with emergent physical phenomena at epitaxial interfaces. Notably, charge transfer at the interface between two insulating oxide layers can lead to the formation of a 2D electron gas (2DEG) with possible applications in, e.g., high-electron-mobility transistors and ferroelectric field-effect transistors. So far, the realization of oxide 2DEGs is, however, largely limited to the interface between the single-crystal substrate and epitaxial film, preventing their deliberate placement inside a larger device architecture. Additionally, the substrate-limited quality of perovskite oxide interfaces hampers room-temperature (RT) 2DEG performance due to notoriously low electron mobility. In this work, the controlled creation of an interfacial 2DEG at the epitaxial interface between perovskite oxides BaSnO 3 and LaInO 3 is demonstrated with enhanced RT electron mobility values up to 119 cm 2 Vs -1 -the highest RT value reported so far for a perovskite oxide 2DEG. Using a combination of state-of-the-art deposition modes during oxide molecular beam epitaxy, this approach opens up another degree of freedom in optimization and in situ control of the interface between two epitaxial oxide layers away from the substrate interface. Thus this approach is expected to apply to the general class of perovskite oxide 2DEG systems and to enable their improved compatibility with novel device concepts and integration across materials platforms., (© 2024 The Author(s). Advanced Materials published by Wiley‐VCH GmbH.)

Proximity effects allow for the adjustment of magnetic properties in a physically elegant way. If two thin ferromagnetic (FM) films are brought into contact, electronic coupling alters their magnetic exchange interaction at their interface. For a low- T C  rare-earth FM coupled to a 3d transition metal FM, even room temperature magnetism is within reach. In addition, magnetic proximity coupling is particularly promising for increasing the magnetic order of metastable materials such as europium monoxide (EuO) beyond their bulk T C , since neither the stoichiometry nor the insulating properties are modified. We investigate the magnetic proximity effect at Fe/EuO and Co/EuO interfaces using hard X-ray photoelectron spectroscopy. By exciting the FM layers with circularly polarized light, magnetic dichroism is observed in angular dependence on the photoemission geometry. In this way, the depth-dependence of the magnetic signal is determined element-specifically for the EuO and 3d FM parts of the bilayers. In connection with atomistic spin dynamics simulations, the thickness of the EuO layer is found to be crucial, indicating that the observed antiferromagnetic proximity coupling is a short-ranged and genuine interface phenomenon. This fact turns the bilayer into a strong synthetic ferrimagnet. The increase in magnetic order in EuO occurs in a finite spatial range and is therefore particularly strong in the 2D limit-a counterintuitive but very useful phenomenon for spin-based device applications., (© 2024. The Author(s).)

One of the central challenges in condensed matter physics is to comprehend systems that have strong disorder and strong interactions. In the strongly localized regime, their subtle competition leads to glassy electron dynamics which ceases to exist well before the insulator-to-metal transition is approached as a function of doping. Here, we report on the discovery of glassy electron dynamics deep inside the good metal regime of an electron-doped quantum paraelectric system: KTaO 3 . We reveal that upon excitation of electrons from defect states to the conduction band, the excess injected carriers in the conduction band relax in a stretched exponential manner with a large relaxation time, and the system evinces simple aging phenomena-a telltale sign of glassy dynamics. Most significantly, we observe a critical slowing down of carrier dynamics below 35 K, concomitant with the onset of quantum paraelectricity in the undoped KTaO 3 . Our combined investigation using second harmonic generation technique, density functional theory and phenomenological modeling demonstrates quantum fluctuation-stabilized soft polar modes as the impetus for the glassy behavior. This study addresses one of the most fundamental questions regarding the potential promotion of glassiness by quantum fluctuations and opens a route for exploring glassy dynamics of electrons in a well-delocalized regime., (© 2024. The Author(s).)

Operando probing by x-ray photoelectron spectroscopy (XPS) of certain hydrogenation reactions are often limited by the scattering of photoelectrons in the gas phase. This work describes a method designed to partially circumvent this so called pressure gap. By performing a rapid switch from a high pressure (where acquisition is impossible) to a lower pressure we can for a short while probe a "remnant" of the high pressure surface as well as the time dynamics during the re-equilibration to the new pressure. This methodology is demonstrated using the CO 2 and the CO hydrogenation reaction over Rh(211). In the CO 2 hydrogenation reaction, the remnant surface of a 2 bar pressure shows an adsorbate distribution which favors chemisorbed CH x adsorbates over chemisorbed CO. This contrasts against previous static operando spectra acquired at lower pressures. Furthermore, the pressure jumping method yields a faster acquisition and more detailed spectra than static operando measurements above 1 bar. In the CO hydrogenation reaction, we observe that CH x accumulated faster during the 275 mbar low pressure regime, and different hypotheses are presented regarding this observation., (© 2023 The Authors. ChemPhysChem published by Wiley-VCH GmbH.)

Correlated electron materials (CEMs) host a rich variety of condensed matter phases. Vanadium dioxide (VO 2 ) is a prototypical CEM with a temperature-dependent metal-to-insulator (MIT) transition with a concomitant crystal symmetry change. External control of MIT in VO 2 -especially without inducing structural changes-has been a long-standing challenge. In this work, we design and synthesize modulation-doped VO 2 -based thin film heterostructures that closely emulate a textbook example of filling control in a correlated electron insulator. Using a combination of charge transport, hard X-ray photoelectron spectroscopy, and structural characterization, we show that the insulating state can be doped to achieve carrier densities greater than 5 × 10 21  cm -3 without inducing any measurable structural changes. We find that the MIT temperature (T MIT ) continuously decreases with increasing carrier concentration. Remarkably, the insulating state is robust even at doping concentrations as high as ~0.2 e - /vanadium. Finally, our work reveals modulation-doping as a viable method for electronic control of phase transitions in correlated electron oxides with the potential for use in future devices based on electric-field controlled phase transitions., (© 2023. Springer Nature Limited.)

We investigate the electronic structure of an antiferromagnetic Kondo lattice system CeAgAs 2 employing hard x -ray photoemission spectroscopy. CeAgAs 2 , an orthorhombic variant of HfCuSi 2 structure, exhibits antiferromagnetic ground state, Kondo like resistivity upturn and compensation of magnetic moments at low temperatures. The photoemission spectra obtained at different photon energies suggest termination of the cleaved surface at cis-trans-As layers. The depth-resolved data show significant surface-bulk differences in the As and Ce core level spectra. The As 2 p bulk spectrum shows distinct two peaks corresponding to two different As layers. The peak at higher binding energy correspond to cis-trans-As layers and is weakly hybridized with the adjacent Ce layers. The As layers between Ce and Ag-layers possess close to trivalent configuration due to strong hybridization with the neighboring atoms and the corresponding feature appear at lower binding energy. Ce 3 d core level spectra show multiple features reflecting strong Ce-As hybridization and strong correlation. Intense f peak is observed in the surface spectrum while it is insignificant in the bulk. In addition, we observe a features at binding energy lower than the well-screened feature indicating the presence of additional interactions. This feature becomes more intense in the bulk spectra suggesting it to be a bulk property. Increase in temperature leads to a spectral weight transfer to higher binding energies in the core level spectra and a depletion of spectral intensity at the Fermi level as expected in a Kondo material. These results reveal interesting surface-bulk differences, complex interplay of intra- and inter-layer covalency, and electron correlation in the electronic structure of this novel Kondo lattice system.0 peak is observed in the surface spectrum while it is insignificant in the bulk. In addition, we observe a features at binding energy lower than the well-screened feature indicating the presence of additional interactions. This feature becomes more intense in the bulk spectra suggesting it to be a bulk property. Increase in temperature leads to a spectral weight transfer to higher binding energies in the core level spectra and a depletion of spectral intensity at the Fermi level as expected in a Kondo material. These results reveal interesting surface-bulk differences, complex interplay of intra- and inter-layer covalency, and electron correlation in the electronic structure of this novel Kondo lattice system., (© 2023 IOP Publishing Ltd.)

We investigated the adsorption of severe acute respiratory syndrome corona virus 2 (SARS-CoV-2), the virus responsible for the current pandemic, on the surface of the model catalyst TiO 2 (101) using atomic force microscopy, transmission electron microscopy, fluorescence microscopy, and X-ray photoelectron spectroscopy, accompanied by density functional theory calculations. Three different methods were employed to inactivate the virus after it was loaded on the surface of TiO 2 (101): (i) ethanol, (ii) thermal, and (iii) UV treatments. Microscopic studies demonstrate that the denatured spike proteins and other proteins in the virus structure readsorb on the surface of TiO 2 under thermal and UV treatments. The interaction of the virus with the surface of TiO 2 was different for the thermally and UV treated samples compared to the sample inactivated via ethanol treatment. AFM and TEM results on the UV-treated sample suggested that the adsorbed viral particles undergo damage and photocatalytic oxidation at the surface of TiO 2 (101) which can affect the structural proteins of SARS-CoV-2 and denature the spike proteins in 30 min. The role of Pd nanoparticles (NPs) was investigated in the interaction between SARS-CoV-2 and TiO 2 (101). The presence of Pd NPs enhanced the adsorption of the virus due to the possible interaction of the spike protein with the NPs. This study is the first investigation of the interaction of SARS-CoV-2 with the surface of single crystalline TiO 2 (101) as a potential candidate for virus deactivation applications. Clarification of the interaction of the virus with the surface of semiconductor oxides will aid in obtaining a deeper understanding of the chemical processes involved in photoinactivation of microorganisms, which is important for the design of effective photocatalysts for air purification and self-cleaning materials.

The pyrochlore iridates (Eu1-xBi x ) 2 Ir 2 O 7 (0⩽ x ⩽1) undergo an anomalous negative lattice expansion for small Bi-doping (x⩽0.035) (region I) and a normal lattice expansion forx⩾0.1(region II); this is accompanied by a transition from an insulating (and magnetically ordered) to a metallic (and with no magnetic ordering) ground state. Here, we investigate (Eu1-xBi x ) 2 Ir 2 O 7 (0⩽ x ⩽1) using hard x-ray photoemission spectroscopy and x-ray absorption fine structure (XAFS) spectroscopy. By analyzing the Eu- L 3 , Ir- L 3 and Bi- L 2 & L 3 edges x-ray absorption near edge structure spectra and Eu-3 d core-level XPS spectra, we show that the metal cations retain their nominal valence, namely, Ir 4+ , Bi 3+ and Eu 3+ , respectively, throughout the series. The Ir-4 f and Bi-4 f core-level XPS spectra consist of screened and unscreened doublets. The unscreened component is dominant In the insulating range (x⩽0.035), and in the metallic region (x⩾0.1), the screened component dominates the spectra. The Eu-3 d core-level spectra remain invariant under Bi doping. The extended XAFS data show that the coordination around the Ir remains well preserved throughout the series. The evolution of the valence band spectra near the Fermi energy with increasing Bi doping indicates the presence of strong Ir(5d)-Bi(6p) hybridization which drives the metal-to-insulator transition., (© 2022 IOP Publishing Ltd.)

Band structure engineering has a strong beneficial impact on thermoelectric performance, where theoretical methods dominate the investigation of electronic structures. Here, we use angle-resolved photoemission spectroscopy (ARPES) to analyze the electronic structure and report on the thermoelectric transport properties of half-Heusler TiCoSb high-quality single crystals. High degeneracy of the valence bands at the L and Γ band maximum points was observed, which provides a band-convergence scenario for the thermoelectric performance of TiCoSb. Previous efforts have shown how crystallographic defects play an important role in TiCoSb transport properties, while the intrinsic properties remain elusive. Using hard X-ray photoelectron spectroscopy (HAXPES), we discard the presence of interstitial defects that could induce in-gap states near the valence band in our crystals. Contrary to polycrystalline reports, intrinsic TiCoSb exhibits p-type transport, albeit defects still affect the carrier concentration. In two initially identical p-type TiCoSb crystal batches, distinct metallic and semiconductive behaviors were found owing to defects not noticeable by elemental analysis. A varying Seebeck effective mass is consistent with the change at the Fermi level within this band convergence picture. This report tackles the direct investigation of the electronic structure of TiCoSb and reveals new insights and the strong impact of point defects on the optimization of thermoelectric properties.

The heavy-fermion behavior in intermetallic compounds manifests itself in a quenching of local magnetic moments by developing Kondo spin-singlet many-body states combined with a drastic increase of the effective mass of conduction electrons, which occurs below the lattice Kondo temperature T K electrons and itinerant electrons. A controversially discussed question in this context is how the localized electronic states contribute to the Fermi surface upon changing the temperature. One expects that hybridization between the local moments and the itinerant electrons leads to a transition from a small Fermi surface in a non-coherent regime at high temperatures to a large Fermi surface once the coherent Kondo lattice regime is realized below f electrons and itinerant electrons. A controversially discussed question in this context is how the localized electronic states contribute to the Fermi surface upon changing the temperature. One expects that hybridization between the local moments and the itinerant electrons leads to a transition from a small Fermi surface in a non-coherent regime at high temperatures to a large Fermi surface once the coherent Kondo lattice regime is realized below T K . We demonstrate, using hard x-ray angle-resolved photoemission spectroscopy that the electronic structure of the prototypical heavy fermion compound YbRh 2 = 25 K, of this system. Our results suggest a transition from a small to a large Fermi surface with decreasing temperature. This result is inconsistent with the prediction of the dynamical mean-field periodic Anderson model and supports the idea of an independent energy scale governing the change of band dispersion.2 changes with temperature between 100 and 200 K, i.e. far above the Kondo temperature, T K = 25 K, of this system. Our results suggest a transition from a small to a large Fermi surface with decreasing temperature. This result is inconsistent with the prediction of the dynamical mean-field periodic Anderson model and supports the idea of an independent energy scale governing the change of band dispersion., (© 2021 IOP Publishing Ltd.)

We demonstrate the emergence and control of magnetic phases between magnetite (Fe 3 O 4 ), a ferrimagnetic halfmetal, and SrTiO 3 , a transparent nonmagnetic insulator considered the bedrock of oxide-based electronics. The Verwey transition ( T V ) was detected to persist from bulk-like down to ultrathin Fe 3 O 4 films, decreasing from 117 ± 4 K (38 nm) to 25 ± 4 K (2 nm), respectively. Element-selective electronic and magnetic properties of the ultrathin films and buried interfaces are studied by angle-dependent hard X-ray photoelectron spectroscopy and X-ray magnetic circular dichroism techniques. We observe a reduction of Fe 2+ ions with decreasing film thickness, accompanied by an increase of Fe 3+ ions in both tetrahedral and octahedral sites and conclude on the formation of a magnetically active ferrimagnetic 2 u.c. γ-Fe 2 O 3 intralayer. To manipulate the interfacial magnetic phase, a postannealing process causes the controlled reduction of the γ-Fe 2 O 3 that finally leads to stoichiometric and ferrimagnetic Fe 3 O 4 /SrTiO 3 (001) heterointerfaces.

Because of their compatibility with modern Si-based technology, HfO 2 -based ferroelectric films have recently attracted attention as strong candidates for applications in memory devices, in particular, ferroelectric field-effect transistors or ferroelectric tunnel junctions. A key property defining the functionality of these devices is the polarization dependent change of the electronic band alignment at the metal/ferroelectric interface. Here, we report on the effect of polarization reversal in functional ferroelectric TiN/Hf 0.5 Zr 0.5 O 2 /TiN capacitors on the potential distribution across the stack and the electronic band line-up at the interfaces studied in operando by hard X-ray photoemission spectroscopy. By tracking changes in the position of Hf 0.5 Zr 0.5 O 2 core-level lines with respect to those of the TiN electrode in both short- and open-circuit configurations following in situ polarization reversal, we derive the conduction band offset to be 0.7 (1.0) eV at the top and 1.7 (1.0) eV at the bottom interfaces for polarization, pointing up (down), respectively. Energy dispersive X-ray spectroscopy profiling of the sample cross-section in combination with the laboratory X-ray photoelectron spectroscopy reveal the presence of a TiO x /TiON layer at  both interfaces. The observed asymmetry in the band line-up changes in the TiN/Hf 0.5 Zr 0.5 O 2 /TiN memory stack is explained by different origin of these oxidized layers and effective pinning of polarization at the top interface. The described methodology and first experimental results are useful for the optimization of HfO 2 -based ferroelectric memory devices under development.