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Function is dynamic and originates at atomic interfaces. Combining the degrees of freedom of molecules with the peculiar properties of 2D quantum materials can create novel functionality. Here, we report the manipulation and ultrafast imaging of a unidirectional gearing motion in molecules on a 2D quantum material. To visualize and disentangle the intertwined structural and electronic dynamics of such a hybrid interface, we record a 'full molecular movie' by imaging the atomic positions, the evolution of the molecular orbital wavefunctions and the modification of electronic states of the substrate. In a multimodal investigation in a single setup, we disentangle dynamics in valence and core electrons of both the molecule and the surface with femtosecond and sub-{\aa}ngstr\"om precision. The ultrafast rotational motion is fueled by the transfer of hot holes into the molecules that results in 'supercharging' of the film. As hot carriers move through the interface, we track a transient modification of the frontier molecular orbitals and observe a chiral symmetry breaking associated with local structural rearrangements. Our calculations show that the 'supercharging' changes the interfacial potential energy landscape and triggers the gearing motion. The experiment offers all-in-one imaging of the electronic, molecular orbital, chemical and structural dynamics during the flow of charge and energy across the hybrid interface. Our approach provides detailed dynamical information on the mechanism underlying surface-adsorbed molecular gears and enables tailoring novel functionalities in hybrid active matter., Comment: 19 pages, 6 figures

A nanometer sized solid solution of NiO and Al2O3 was synthesized by calcination of Ni–Al layered double hydroxides (LDHs). The crystal structure of the obtained compound was determined by XRD and XAFS analyses: Ni2+ and Al3+ ions are located at the metal ion site of the rock salt structure and a certain amount of cation vacancies are also introduced for charge compensation. The electrochemical properties of the Ni–Al binary metal oxide as an anode material for lithium ion batteries were examined by the constant current charge–discharge test. Ni–Al oxide showed higher charging capacity in comparison with pristine NiO. In particular, the capacity in the lower voltage region (below 1.5 V), the limited capacity in this region is the weak point of the conversion anode, was improved to 540 mA h g−1 that is about twice that of pristine NiO. This improvement in the capacity in the lower voltage region is concluded to be due to the redox activity of Al3+ ions during the charge–discharge on the basis of the results of electrochemical measurements and ex situ XAFS measurements at the Ni and Al edge. The reaction mechanism of this compound is investigated using ex situ XRD and XAFS methods. For the charge (reduction) in the higher voltage region (OCV–1.0 V), lithium ion intercalation into the cation vacancy sites and/or lithium ion adsorption on the surface of particles are proceeding. For the charge in the lower voltage region (1.0–0.03 V), conversion reaction occurs by the reduction of Ni2+ and Al3+ ions to metal particles with surface electrolyte interface (SEI) layer formation. For the discharge in the lower voltage region (0.03–1.5 V), only Al metal particles are oxidized to Al3+ ions and some intermediate complexes are formed. For the discharge in the higher voltage region (1.5–3.0 V), the lattice of the Ni–Al binary oxide solid solution is reconstructed with the oxidation of Ni to Ni2+.

Photoconversion of CO2 into fuels completes the carbon neutral cycle in a sustainable society. To exclude the contribution of adventitious carbon, monitoring the time course of 13CO2 conversion into 13C-fuel is essential, but has been rarely reported. In the present work, a composite of Au nanoparticles with ZrO2 was found to be effective in converting 13CO2 into 13CO at a rate of 0.17 μmol h−1 gcat−1 in the presence of H2 and UV–vis light. The detected 12CO as a minor byproduct (11.9 %) was identified as due to adsorbed 12CO2 from the air. The 12C ratio in the total amount of CO2 was evaluated based on a 13CO2 photoexchange reaction (8.7 %). The discrepancy between these values suggested a slower exchange reaction step between the chemisorption site for CO2 reduction and the physisorption site for CO2 compared to the reduction step to CO. Furthermore, based on in-profile kinetic studies using sharp-cut filters and control reactions in the dark, the contribution ratio for CO2 conversion was determined to be via charge separation at the band-gap of ZrO2 (λ 1 2 k T ): 31 %. Localized surface plasmon resonance (LSPR) absorption of Au and infrared absorption in the range of λ > 320 nm did not promote catalysis. The LSPR absorption was further investigated by Au L3-edge extended X-ray absorption fine structure analysis. Ambient heat on the Au nanoparticles should have promoted H2 activation enough, supplying protons to the CO2 reduction sites over ZrO2; however, a temperature increase of 26 K on the Au surface was marginal for further H2 activation. CO2 photoconversion with added moisture was also attempted; the CO formation rate using ZrO2 under these conditions was 0.15 μmol h−1 gcat−1. However, 47 % was characterized as 12CO originating from chemisorbed 12CO2, and H2 was also formed at a comparable rate of 0.14 μmol h−1 gcat−1 from a competing reaction. The addition of Au to ZrO2 was found to suppress CO formation and promote H2 formation, and Mg2+ addition to Au–ZrO2 effectively suppressed H2 formation directing to the CO formation.

International audience; We measured an Al K-edge x-ray absorption near edge structure (XANES) spectrum of Al doped NiO for anode materials of lithium ion batteries. We found that the spectrum of the Al doped NiO is similar to that of γ-Al2O3. Calculated site-specific XANES spectra strongly correspond to the coordination nature around the absorbing Al ion, indicating aggregation of cation vacancies surrounded by Al ions in the Al doped NiO. These finding could be useful to understand how Li ions migrate in the anode.

International audience; We present an effect of the spin-orbit interaction (SOI) at surrounding atoms on K-edge magnetic extended x-ray absorption fine structure (MEXAFS). A contribution of the SOI to a K-edge MEXAFS spectrum is described by a perturbative way within a multiple scattering (MS) theory. A numerical calculation shows that a photoelectron single scattering by the SOI at surrounding atomic sites has a negligibly small contribution to MEXAFS. Although a negligible contribution of the SOI at surrounding atoms has been attributed to a cancellation of various MS contributions, this small contribution can be understood by the small number of its effective partial wave components, at least within the single scattering approximation. For further detailed analyses of MS with a path expansion method, only the small number of the partial wave components for the SOI is necessary. This leads to faster computations for MEXAFS including the photoelectron scattering by the SOI.

A many-body photoemission theory based on Keldysh nonequilibrium Green's functions is developed and applied to photoemission from extended states of organic molecules and their crystals, in particular excited by ultraviolet and soft X-ray radiation. In this energy region, electron-phonon interaction and radiation filed screening play some important roles. To incorporate the latter effects, we should use quantum electrodynamics (QED) approach. To discuss the electron-phonon interaction, we apply the Hedin equation including the screened Coulomb interaction mediated by the electron-phonon interaction. This theoretical framework gives us a unified picture of the UPS spectra from organic solids. Furthermore some illustrative numerical calculations are shown to discuss the relative importance of the multiple scatterings, Debye-Waller factors, the peak width of the quasi-particles, and the angular dependence of the phonon satellites. We demonstrate some specific features of ultraviolet photoemission spectroscopy (UPS) spectra from particularly anisotropic organic solids.

To understand the relationship between the shape of X-ray magnetic circular dichroism (XMCD) and magnetic moments, we calculate V L2, 3-edge XMCD spectra for Mn2VAl while varying the magnetic moment of an absorbing atom V. We find that XMCD spectra change depending on the magnetic moment of the absorbing atom. We explain these changes based on the magnetic moment dependence of atomic terms, which are components of XMCD. When the overlaps between radial functions and photoelectron wave functions are considered, an atomic term has a value at its energy. The peak positions of the radial integral for up and down spin are different, which leads to multiple peaks of the atomic terms and determines the positive and negative direction of the peak.

Keldysh Green's function approach is extensively used in order to derive practical formulas to analyze pump–probe ultrafast photoemission and X-ray absorption spectra. Here the pump pulse is strong enough whereas the probe X-ray pulse can be treated by use of a perturbation theory. We expand full Green's function in terms of renormalized Green's function without the interaction between electrons and probe pulse. The present theoretical formulas allow us to handle the intrinsic and extrinsic losses, and furthermore resonant effects in X-ray Absorption Fine Structures (XAFS). To understand the radiation field screening in XPS spectra, we have to use more sophisticated theoretical approach. In the ultrafast XPS and XAFS analyses the intrinsic and extrinsic loss effects can interfere as well. In the XAFS studies careful analyses are necessary to handle extrinsic losses in terms of damped photoelectron propagation. The nonequilibrium dynamics after the pump pulse irradiation is well described by use of the time-dependent Dyson orbitals. Well above the edge threshold, ultrafast photoelectron diffraction and extended X-ray absorption fine structure (EXAFS) provide us with transient structural change after the laser pump excitations. In addition to these slow processes, the rapid oscillation in time plays an important role related to pump electronic excitations. Near threshold detailed information could be obtained for the combined electronic and structural dynamics. In particular high-energy photoemission and EXAFS are not so influenced by the details of excited states by pump pulse. Random-Phase Approximation (RPA)-boson approach is introduced to derive some practical formulas for time-dependent intrinsic amplitudes.

At first we discuss one-electron X-ray magnetic circular dichroism (XMCD) theory on the basis of Gesztesy expansion of Dirac Green’s function in terms of nonrelativistic ones with potential. Applyi...

A short review is presented on theoretical approach to plasmon losses in core-level photoemission from simple metals. Full multiple elastic scatterings of photoelectrons are taken into account before and after the plasmon losses within the quantum cumulant (Landau) formula that can describe both intrinsic and extrinsic losses, and overall features of core level photoemission. Far from normal emission and in low energy excitation, we cannot apply these simple exponential formulas.

Keldysh Green’s function approach is used in order to derive a practical formula to study pump-probe ultrafast photoemission spectra. The pump pulse is strong whereas the probe pulse can be treated by use of a perturbation theory: We expand the full Green’s function in terms of electron-probe pulse interaction and renormalized Green’s function including pump pulse excitation. Random Phase Approximation (RPA)-boson approach is introduced to estimate some important factors. Well above the edge, ultrafast photoelectron diffraction provides us with information on the transient structural change after the pump pulse excitation. In addition to these slow processes, the rapid oscillation plays an important role related to electronic excitation by pump pulse.

In this short review we discuss recent progress in photoemission theory for organic molecules and their crystals. We discuss some important features in Keldysh Green's function theory for the photoemission. We briefly discuss many-body aspects in photoemission from core and extended levels. In particular phonon effects are investigated in more detail since organic solids are typically soft where electron–phonon interaction is important. Debye–Waller factor suppresses the interference effects of photoelectron waves which makes ARPES analyses useless, particularly in high energy region.

International audience; Angle resolved photoemission spectroscopy (ARPES) gives detailed information about the surface electronic structures and oriented molecules. In the so-called orbital tomography method, the ARPES intensity is obtained by a simple Fourier transform of the initial state molecular orbital. While this method has given good results for a number of π-orbital systems, it is known to have strong limitations because the final state is approximated as a plane wave and thus photoelectron scattering is completely neglected. Here we propose an ARPES theory where the initial states are taken from a quantum chemistry method and the final states are calculated in multiple scattering theory. The initial molecular orbitals are reexpanded in a multi-site spherical wave basis and the multiple scattering potential is constructed from the ab initio charge density. These computations are performed algebraically using newly developed algorithms. The method is applied to pentance and the results are compared with the plane wave approximation. © 2017

We have successfully determined the internuclear distance of I2 molecules in an alignment laser field by applying our molecular structure determination methodology to an I 2p X-ray photoelectron diffraction profile observed with femtosecond X-ray free electron laser pulses. Using this methodology, we have found that the internuclear distance of the sample I2 molecules in an alignment Nd:YAG laser field of 6 × 1011 W/cm2 is elongated by from 0.18 to 0.30 Å “in average” relatively to the equilibrium internuclear distance of 2.666 Å. Thus, the present experiment constitutes a critical step towards the goal of femtosecond imaging of chemical reactions and opens a new direction for the study of ultrafast chemical reaction in the gas phase.

Frictional force was measured on directional calcite (1 0 -1 4) surface, where triangular carbonate ions are all tilted to [4 2 -1] direction. With the normal load -[4 2 -1], was the same as that measured in nm-scale. In the higher normal load range, a new component was added to the friction in -[4 2 -1] direction, and the asymmetry was reversed. Only in the direction of stronger friction, characteristic triangular deformation patterns were formed. Microscopic observation after indentation experiments revealed that the patterns were formed by slip on c (0 0 0 1) faces on one side of the stylus, followed by cleavage on r{1 0 -1 4} faces. A mechanical model was proposed to explain why the deformation occurs only in one quadrant of the surface. The result of scratch perpendicularly in [0 1 0] direction, also supports the mechanism of deformation. The results show when and how the contribution of plastic deformation is added to intrinsic surface friction and affects the frictional asymmetry. The frictional force in the -[4 2 -1] scratch increased linearly with the total lengths of the traces of c-slip.

Micro-facet formation processes were observed, with atomic force microscopy (AFM), at various crystal faces of two aragonite-type minerals, cerussite (PbCO 3 ) and strontianite (SrCO 3 ), in dilute aqueous acetic acid. Among the prismatic faces, parallel to the c -axis, electrically neutral (1 0 0) and (1 3 0) faces were stabilized in the acidic environment, as in the case of aragonite (CaCO 3 ). On the other hand, polar (1 1 0) and (0 1 0) faces of PbCO 3 remained to be stable, in contrast with the case of aragonite. Even atom-resolved AFM images were observed with the (1 1 0) face, corresponding to the arrangement of carbonate ions, most probably protonated. Since Pb 2+ is a more polarizable soft acid, Pb–O bonds bear covalent nature in addition to Coulombic nature. Due to diminished polarity with the bonds, the (1 1 0) face remained stable even in the acidic condition. Among the crystal faces intersecting with the c -axis, stabilization, in the acidic condition, of (1 1 1) faces of SrCO 3 and (0 2 1) faces of PbCO 3 was observed in contrast to the stabilization of (1 1 2) faces of aragonite, suggesting flexible nature of the mineral faces having larger cations. Relationship between natural crystal forms and growth environment was discussed.

Typical core-level X-ray photoemission spectra have plasmon loss bands in addition to a main sharp band. The loss of energy from the photoelectron may simultaneously occur in the excitation process (intrinsic loss) or when the photoelectron travels in the solid on its way out through the surface (extrinsic loss). They can interfere each other so these two loss mechanisms are not possible to separate. The quantum Landau formula which originally derived by Hedin et al., can explain overall plasmon loss features accompanied by core level photoemission where elastic scattering before and after the losses are completely neglected. We calculate plasmon loss features associated with Li 1s photoemission using the quantum Landau formula that includes elastic scattering before and after the losses. Li is light and a weak scatter, however we observe a prominent effect due to elastic scatterings from surrounding atoms. We also have found that the elastic scatterings can considerably change the relative intensities of bulk and surface plasmon peaks.

Some important phonon effects observed in X-ray absorption and X-ray photoemission spectra are discussed on the basis of nonequilibrium Green's function theory. This theoretical framework allows us to incorporate phonon effects, such as Debye–Waller (DW) factors, Franck–Condon (FC) factors and electron–phonon interactions in a natural way. In the case of core level excitations, we can take into account the core–hole effects in lesser Green's function g and photoelectron propagation in greater Green's function g > . For the core–hole propagation we derive some formulas to describe the thermally displaced core functions: we have p components even for deep core s orbital due to the thermal motion. We should notice that the thermal fluctuation is quite small but it is already in the order of the spread of the core functions. Applying Mermin's theorem, we can calculate the thermal average of the hole propagator g : here an important ingredient is the Debye–Waller factor used in X-ray and neutron diffraction. For the pre-edge structures, the intensity associated with forbidden electric dipole transition is sensitive to the temperature compared with allowed electric quadrupole transition. We also discuss the FC and their interference, which have negligible contribution to pre-edge intensity and energy shift. The quasi-particle energy is also influenced by the core displacement which can be responsible for the peak shift of the pre-edges. We also discuss the changes of the photoelectron angular distributions caused by the thermal atomic vibration.

We study the angular and energy dependence of surface and bulk plasmon losses accompanying deep core excitations in simple metals. Here full multiple scatterings of photoelectrons are taken into account before and after the plasmon losses within the quantum Landau formula, which can describe overall features of the photoemission bands. For example, multiple plasmon loss features can be calculated by use of the formula. Two simple metals, Al and Na, are studied here. The depth profiles of the plasmon losses are strongly influenced by the elastic scatterings. The model assuming single elastic scatterings overestimates the losses from deep emitters due to the forward focusing effects, whereas the model accounting for full multiple scatterings gives a much rapidly decaying function of the depth due to the defocusing effects and rich structures due to the photoelectron diffraction. The single elastic scattering approximation gives a poor result both for the depth profiles and for the loss spectra. The present multiple scattering calculations successfully explain the azimuthal dependence of the loss spectra, which reflect the local geometry around the emitters.

The effects of the spin-orbit interaction on surrounding atoms for XMCD spectra are studied by a real-space multiple-scattering theory. The present numerical calculation for Fe K-edge XMCD spectra from BCC iron demonstrates the importance of the spin-orbit interaction on scattering atoms, which has been disregarded in previous works. These effects will be inevitable for K-edge XMCD analyses of light elements surrounded by heavy magnetic atoms.