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As an improvement over organic or inorganic layered crystals, the synthetic monolayer ZnO(M) inherits semiconductivity and hostability from its bulk, yet it acts as a promising host for dilute magnetic semiconductors. Here, we report the electronic and magnetic properties of ZnO(M) doped with one 3d transition metal ion and simultaneously adsorbed with another 3d transition metal ion. Two sequences are studied, one where the dopant is fixed to Mn and the adsorbate is varied from Sc to Zn and another where the dopant and adsorbate are reversed. First-principles results show that the stable adsorbed−doped systems possess a lower bandgap energy than that of the host. System magnetic moments can be tuned to |5 − x|μB, where x refers to the magnetic moment of the individual 3d atom. An interplay between superexchange and direct exchange yields a ferromagnetic system dually adsorbed−doped with Mn. In addition to a novel material design route, the magnetic interaction mechanism is found beyond two dimensions, having been identified for its three-dimensional bulk and zero-dimensional cluster counterparts.

Free bare gold clusters in the size range from few tens to few hundred atoms (<= 1 nm dimensions) have been produced in a beam, and the size-dependent development of their full valence band including the 5d and 6s parts has been mapped 'on the fly' by synchrotron-based photoelectron spectroscopy. The Au 4f core level has been also probed, and the cluster-specific Au 4f ionization energies have been used to estimate the cluster size. The recorded in the present work valence spectra of the small clusters are compared with the spectra of the large clusters (N similar to 10(3)) created by us using a magnetron-based gas aggregation source. The comparison shows a substantially narrower 5d valence band and the decrease in its splitting for gold clusters in the size range of few hundred atoms and below. Our DFT calculations involving the pseudopotential method show that the 5d band width of the ground state increases with the cluster size and by the size N = 20 becomes comparable with the experimental width of the valence photoelectron spectrum. Similar to the earlier observations on supported clusters we interpret our experimental and theoretical results as due to the undercoordination of a large fraction of atoms in the clusters with N similar to 10(2) and below. The consequences of such electronic structure of small gold clusters are discussed in connection with their specific physical and chemical properties related to nanoplasmonics and nanocatalysis.

Xe 1s photoelectron spectra were measured at SPring-8, Japan. The core-hole lifetime broadening was found to be 9.6 eV, yielding a lifetime of similar to 68 as. The amount of radiative versus nonradiative decay was assessed by recording Auger LMM spectra below and above the K edge. Below the K edge, L vacancies are produced only by direct photoionization, while above the K edge some of these vacancies are mainly produced by KL emission following 1s photoionization. Due to the dipole selection rule for x-ray emission, the dominant role of the KL relaxation process is rather directly observed.

Formation and growth of CsBr clusters embedded in unsupported Ar clusters was studied using synchrotron radiation photoelectron spectroscopy. The development of the core-level electronic structure for cluster sizes between a few and a few hundred atoms contained information about the local coordination of the constituent particles. The experimental results indicate that a gradual structural phase transition from NaCl structure to CsCl structure for CsBr clusters takes place at around 160 atoms per cluster.

Concentration dependent solvation of RbBr in freestanding sub-2 nm water clusters was studied using core level photoelectron spectroscopy with synchrotron radiation. Spectral features recorded from dilute to saturated clusters indicate that either solvent shared or contact ion pairs are present in increasing amount when the concentration exceeds 2 mol kg−1. For comparison, spectra from anhydrous RbBr clusters are also presented.

We present calculations on the quantum electrodynamics (QED) effects in 1s and 2s single and double ionization potentials of noble gases from Ne to Rn as perturbations on relativistic four-component Dirac-Fock wavefunctions. The most dominant effect originates from the self-energy of the core-electron that yields corrections of similar order as the transverse interaction. For 1s ionization potentials, a match within few eV against the known experimental values is obtained, and our work reveals considerable QED effects in the photoelectron binding energies across the periodic table — most strikingly even for Ne. We perform power-law fits for the corrections as a function of Z and interpolate the QED correction of ∼−0.55 eV for S1s. Due to this, the K-edge electron spectra of the third row and below need QED for a match in the absolute energy when using state-of-the-art instrumentation.

Gifted with unique optical and hydrophobic properties, the plant leaves have been recently considered as micro/nanostructure prototypes for functional surface engineering. Imprinting bio-inspired structures onto surfaces can yield in similar functional properties than in the nature. In this article, we report on a simple and effective method to copy leaf surface structures onto poly-(methyl methacrylate) sheets. The replicated surface structures reduce optical reflectance and enhance optical haze. Besides, the artificial polymer sheets exhibit good hydrophobic properties. Correlation between optical haze and hydrophobicity was studied.

In this work, evolution of structural properties of anhydrous and hydrated alkali halide clusters are studied using synchrotron radiation based photoelectron spectroscopy. Alkali metal core level spectra of small anhydrous RbCl, RbBr, CsCl and CsBr clusters indicate a NaCl structure. For larger CsBr clusters a structural phase transition to CsCl structure is likely the case. Alkali halide core level spectra of mixed RbBr-water clusters indicate that at dilute concentration the salt is dissolved by the water cluster but ion pairing increases with concentration. Modeling of gas phase cluster formation and electronic structure calculations of core level chemical shifts are used to interpret the experimental spectra.

In this work, we present laser coloration on 304 stainless steel using nanosecond laser. Surface modifications are tuned by adjusting laser parameters of scanning speed, repetition rate, and pulse width. A comprehensive study of the physical mechanism leading to the appearance is presented. Microscopic patterns are measured and employed as input to simulate light-matter interferences, while chemical states and crystal structures of composites to figure out intrinsic colors. Quantitative analysis clarifies the final colors and RGB values are the combinations of structural colors and intrinsic colors from the oxidized pigments, with the latter dominating. Therefore, the engineering and scientific insights of nanosecond laser coloration highlight large-scale utilization of the present route for colorful and resistant steels.

Xe 1s photoelectron spectra were measured at SPring-8, Japan. The core-hole lifetime broadening was found to be 9.6 eV, yielding a lifetime of ~68 as. The amount of radiative versus nonradiative decay was assessed by recording Auger LMM spectra below and above the K edge. Below the K edge, L vacancies are produced only by direct photoionization, while above the K edge some of these vacancies are mainly produced by KL emission following 1s photoionization. Due to the dipole selection rule for x-ray emission, the dominant role of the KL relaxation process is rather directly observed.

Photoinduced reformation of chemical bonds is investigated in the CH3Cl molecule experimentally and computationally. The observation of stable HCl+ fragment formation after resonant Cl 2p photoexcitation is confirmed by an electron-ion coincidence experiment, and its possible creation mechanism is reported. We attribute the formation of HCl+ to specific final states populated by the resonant Auger decay. Quantum chemical computations support this attribution and suggest that in at least one of those states the system is placed on a potential energy surface which favors creation of HCl+ by moving one hydrogen atom to a closer proximity of the chlorine atom. This work demonstrates the effect of targeted core-shell excitation on the chemical bond breaking and reformation process, often called photoinduced chemistry., QC 20161019

The main cause of temperature and composition fluctuations in the electric arc furnace (EAF) process is the scrap used as a raw material. Process conditions in EAF can vary significantly from heat to heat because there is no accurate information of scrap composition. Due to harsh process conditions, there are currently few sensors available for direct on-line measurement of the EAF process. In this work new information about stainless steelmaking EAF process conditions is sought with optical emission spectrum measurement. The measurement system relies on transportation of the light emitted from the measured furnace to a remotely situated spectrometer. Analysing the slag composition from the arc emission spectrum was tested in the laboratory and on a pilot scale. The laboratory measurements indicate that changes in the amount of CrOx and MnO in the slag have the highest impact on optical emission spectra. The pilot scale measurements show that the Cr2O3 content of the slag can be measured from the arc emission spectrum using suitable reference lines with an average absolute error of 0.62 %-points and a standard deviation of 0.49 %-points. The results from measurements at Outokumpu Stainless Oy, Tornio Works, indicate that measurement of the optical emission spectrum from industrial EAF is feasible in a practical sense, and can be used in analysing of EAF atmosphere, scrap melting and slag surface. Furthermore, the results of industrial measurements indicate that the atoms in the arc plasma mainly originate from the slag. The measurement of scrap melting could be potentially used in EAF control in optimization of arc voltages and second scrap bucket charging. The potential use of slag CrOx measurements is in optimization of reductant additions as well as defining the further processing of EAF slag., Tiivistelmä Valokaariuunien ohjaus on perinteisesti ollut uunioperaattorin käsissä. Valokaaariuuniprosessin on-line mittaukseen on olevassa vähän menetelmiä johtuen uunin hyvin haastavaista olosuhteista. Tässä työssä on tutkittu optiseen emissiospektroskopiaan perustuvaa menetelmää uuden jatkuva-aikaisen tiedon tuottamisessa valokaariuuniprosessista. Mittausjärjestelmä perustuu valon keräämiseen mitattavasta uunista valokuidun avulla, joka johtaa valon analysoitavaksi etäälle prosessista sijoitettuun spektrometriin. Mittauksia suoritettiin laboratorio-, pilot- ja tehdas-mittakaavassa. Valokaariuunin kuonan koostumuksen analysointia testattiin laboratorio- ja pilot-mittakaavan uuneilla. Laboratoriomittaukset osoittivat että kuonan komponenteista CrOx ja MnO ja vaikuttavat eniten mitattuun emissiospektriin. Pilot-mittakaavan kokeissa havaittiin, että kuonan Cr2O3-pitoisuutta voidaan mitata valokaaren emissiospektristä 0,62 %-yksikön keskimääräisellä absoluuttisella virheellä ja 0,49 %-yksikkön hajonnalla. Teollisella valokaariuunilla suoritetuista mittauksista havaittiin että optisen emissiospektrin mittaus voidaan suorittaa ilman ylitsepääsemättömiä teknisiä esteitä. Mittauksen tuloksia voidaan puolestaan käyttää kaasufaasin reaktioiden, romun sulamisen ja kuonapinnan ominaisuuksien arvioinnissa. Valokaaren emissiospektrin analyysi osoitti, että valokaaren plasman komponentit ovat pääosin peräisin kuonasta, joka mahdollistaa kuonan koostumuksen arvioinnin valokaaren emissiospektrin perusteella. Romun sulamisen mittausta voidaan prosessinohjauksessa käyttää jänniteportaiden ja toisen korin panostuksen optimointiin. Kuonan kromipitoisuuden mittaamista voidaan puolestaan käyttää pelkistinaineiden lisäyksen optimointiin ja kuonan jatkokäsittelyn valintaan.

Among the other applications, vanadium oxide thin films are considered to be excellent candidates for gas sensing. To understand the origins of the sensing capability, we carried out X-ray photoelectron and X-ray absorption spectroscopy measurements to determinate the surface valence states of thin films with mixed V7O16 and V2O5 compounds. Thin films were fabricated by pulsed laser deposition, and the crystal structure and symmetry of the deposited films was studied using grazing incidence X-ray diffraction and Raman spectroscopy. These results together with X-ray photoelectron and absorption spectra showed that the thin-film crystal structures varied between orthorhombic V2O5 phase and another phase of triclinic V7O16. X-ray photoelectron spectroscopy was used to quantitatively confirm the high amount of V4+ ions on surfaces of the films, especially of films with V7O16 phase present. This result was confirmed in the quantitative analysis of the V2p near -edge X-ray absorption spectra. Through the observed electronic structures, it was found that in addition to unique crystal structure and morphology, the enhanced gas sensitivity of these layers is attributed to the increase in the amount of surface oxygen vacancies. (C) 2016 Elsevier B.V. All rights reserved., Funding Agencies|Finnish Funding Agency for Innovations-TEKES project CHEMPACK [1427/31/2010]; European Communitys Seventh Framework Programme CALIPSO [312284]; Tauno Tonning foundation; Henry Ford foundation; Ulla Tuominen foundation; Riitta and Jorma J. Takanen foundation

We report on vacuum ultraviolet (VUV) excited photoluminescence (PL) spectra emitted from a chemical vapor deposited MoS₂ few-layered film. The excitation spectrum was recorded by monitoring intensities of PL spectra at ~1.9 eV. A strong wide excitation band peaking at 7 eV was found in the excitation. The PL excitation band is most intensive at liquid helium temperature and completely quenched at 100 K. Through first-principles calculations of photoabsorption in MoS₂, the excitation was explicated and attributed to transitions of electrons from p- and d- type states in the valence band to the d- and p-type states in the conduction band. The obtained photon-in/photon-out results clarify the excitation and emission behavior of the low dimensional MoS₂ when interacting with the VUV light sources.

Neutral Pb clusters in the size range from a few tens of atoms up to similar to 100 atoms are studied using synchrotron-based photoelectron spectroscopy. The electronic structure is seen to differ increasingly from that of the solid when the cluster size decreases. The valence band narrows gradually - down to about one fifth of the solid-state band width at the smallest size of few tens of atoms. Simultaneously the Fermi-edge energy shifts further away from the solid value by more than 2 eV. The Pb 5d core level binding energy also increases and the spectral features broaden and change in shape. The changes observed for the valence and for the 5d response energies and shapes are discussed in the context of the metal-to-insulator transition observed earlier in Pb clusters below the critical size of 20-30 atoms/cluster. (C) 2014 Elsevier B.V. All rights reserved.

The evolution of electronic properties in free antimony (Sb) nanoclusters as a function of the cluster size has been studied experimentally using synchrotron radiation. Antimony 4d core-level and valence-band regions have been probed, and the 4d binding energies and valence ionization potentials of clusters of various mean sizes have been determined. The binding-energy shifts with respect to polycrystalline solid have been used for deriving the electronic properties of the clusters. The observed results suggest that even large Sb clusters are not metallic.

In this work an experimental study of size varied, neutral, and free metal clusters using synchrotron radiation excited photoelectron spectroscopy was performed. The combined core-level and valence photoelectron spectroscopic investigation indicates metallic properties for nanoscale Rb, K, Sn, and Bi clusters. In the case of Sn the experimental results suggest a metal-to-insulator transition occurring at the studied size range. In addition to the experimental results the technical implementation of the cluster production set-up is presented and jellium-model-based simulations are compared with the experimental results of the Rb and K clusters.

Evolution of metallic properties of free and initially neutral nanoscale Bi clusters has been studied using synchrotron radiation excited photoelectron spectroscopy. The 4f and 5d core as well as the valence levels have been probed. The cross-level analysis indicates metallic properties in Bi clusters in the observed size range from 0.5 nm to 1.4 nm. The behavior of the core-level and valence binding energies as a function of cluster size has been observed to be smooth and relatively consistent. Valence responses for the largest clusters have their shape and width similar to those of the polycrystalline solid Bi.

This presentation is intended to illustrate various types of collisional processes relevant for free clusters probed by x-ray photoelectron spectroscopy using our own examples ranging from free-electron-metal clusters, through half-metal and semiconductor clusters to dielectrics, the latter from van-der-Waals to ionic clusters.

Silver clusters in the size range of ∼102 constituent atoms have been studied using photoelectron spec-troscopy. The 5s and 4d valence bands have been probed with 40 and 60.5 eV photon energies. Differences in the valence band spectral features have been observed and are discussed in view of earlier results on copper clusters and in terms of differences in mean free path for electrons of different energies.

The electronic structure and fragmentation of the hydrofluorocarbon compound 1,1,1,2-tetrafluoroethane (CF3-CH2F) were studied using spectroscopical methods and quantum chemical calculations. Valence photoelectron spectra and the ionic fragmentation products were recorded with synchrotron radiation in the vacuum ultraviolet (VUV) region. The geometric and electronic structures of the CF3-CH2F molecule were calculated using the complete active space perturbation theory of second order. The calculated vertical ionization energies were used to interpret the experimental photoelectron spectrum. VUV photodissociation of the sample molecule was studied with photoelectron-photoion coincidence spectroscopy. Coincident ion yields are shown for several cations as a function of electron binding energy. The experimental data are discussed in comparison with theory and previous work.

Electronic structure of free and neutral Rb and K clusters containing from few tens to few hundred atoms has been studied using synchrotron radiation. Core-level photoelectron spectroscopy has been used to probe the metallic nature of Rb and K clusters. We show that the metallicity exists down to the dimensions of few nanometers. Simultaneously the emergence and evolution of the valence band structure has been monitored by the valence-level photoelectron spectroscopy.

We show that the valence band response to photon impact in metallic nanoparticles is highly energy dependent. This is seen as drastic variations of cross sections in valence photoionization of free and initially charge-neutral nanosized metal clusters. The effect is demonstrated in a combined experimental and theoretical study of Rb clusters. The experimental findings are interpreted theoretically using a jellium model and superatom description. The variations are attributed to the changing overlap with the photon energy between the wave functions of diffuse delocalized valence electrons and continuum electrons producing a series of minima in the cross section.

Free nanoscale tin clusters in the average size range of a few tens up to similar to 500 atoms are studied by means of valence and core-level photoelectron spectroscopy. A self-consistent picture arises from comparison of the work functions derived from the 4d core-level spectra, the experimental ionization energies extracted from the 5p valence spectra, and the expectations from the metallic sphere model for the clusters. The present studies demonstrate that the 4d core-level energy changes are a sensitive probe of the metal-to-semiconductor transition in the size range under investigation.

The valence photoelectron spectrum of Sb-4 clusters and the following fragmentation patterns have been studied using synchrotron radiation and electron-ion coincidence technique. An experimental photoelectron spectrum of the 5t(2) ionization of Sb-4 is presented. Theoretical molecular calculations, together with the existing data on the noble gas xenon, were used to describe the experimental results. The bonding properties of the molecular orbitals involved are used to qualitatively describe the dissociation process., QC 20110427

Photoelectron studies of laser-excited atomic states can reveal more information about the final ionic states than ground-state photoemission. The possibility to tune the laser to distinct fine-structure sub-states of the excited states allows to select specific angular-momentum couplings of the valence electron that are conserved during photoemission. In the 4s photoemission of laser-excited rubidium we use this method to determine the final-state energies and widths of doubly excited ionic states and characterize the angular-momentum couplings.

Fine-structure resolved 5p photoemission spectra of Cs in the ground state and after laser excitation into the [Xe]6p P-2(1/2) and 6p(2)P(3/2) states have been studied. The 5p(5)6p final states have been reached by the 5p(6)6s -> 5p(5)6p conjugate shakeup process from ground-state atoms as well as by direct photoemission from laser-excited atoms. The laser-excited spectra can be well described with calculations based on the jK-coupling model. Calculations based on a multiconfiguration Dirac-Fock approach have been performed to investigate the deviations created by intermediate coupling from the pure jK-coupling scheme.

The 3d(-1) photoionization and subsequent M4,5N2,3N2,3 Auger electron spectra of free initially laser-excited rubidium atoms have been investigated. The rubidium atoms were excited from the ground state [Kr]5s(1/2) to the [Kr]5p(1/2) and [Kr]5p(3/2) states. Emphasis was put on the changes in coupling and electron correlation between the three different initial states. The ground state 3d photoelecton spectrum of free Rb atoms was interpreted in detail. The binding energies for 3d(3/2,5/2) orbitals of initially ground-state and laser-excited Rb atoms were obtained. Extensive multiconfiguration Dirac-Fock calculations performed in the relativistic jj coupled basis were compared to the experimental photoelectron and Auger electron spectra.