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The vacuum ultraviolet (VUV) optical properties in the range 4 eV to 15 eV of GaSb have been determined by rotating analyzer ellipsometry (RAE) using synchrotron light. The localized surface plasmon resonances (LSPRs) and surface plasmon polaritons (SPPs) are studied as a means to understand the plasmonic behavior of GaSb. The large imaginary part of the dielectric function causes poor confinement of the SPP. Self-assembled GaSb nanopillars of 35 nm height are studied experimentally by RAE at different angles of incidence. The pillars are simulated numerically using an effective medium approach and the finite element method (FEM), where clear similarities between the simulations and experiment are observed. Additional dips in the reflectivity accompanied by increased nanopillar absorption and local field enhancement were observed near the surface of the pillars. These results demonstrate GaSb nanopillars to be promising candidates for photocathodes.

Pulsed laser deposition (PLD) is a powerful technique for prototyping thin film materials, both single component (single composition) films and films with a varying composition (e.g., lateral continuous compositional spread, CCS). In this work, we improve one of the simulation methods used to design the deposition of PLD films: We extend the mathematical model for the material spread on the substrate, [Formula: see text], for each laser pulse hitting the target, and we use a more accurate method to determine [Formula: see text] experimentally. The deposition of the material on the substrate is simulated by repetitively adding [Formula: see text], from one or more targets, at the selected location on the substrate. Using the new model, a high agreement between the simulated and grown films’ thickness and composition across the substrate was obtained. The basis for the high agreement is the use of variable angle spectroscopic ellipsometry to carefully determine [Formula: see text] by measuring at 794 locations on the 50.8 mm (2 in.) diameter substrates. Factors, such as variation in optical properties and porosity across the plume/calibration films, were considered in the determination of the thicknesses. As test cases, we simulated and deposited (single component) [Formula: see text] thin films and (CCS) [Formula: see text] films doped with Cr and N, deposited on 50.8 mm diameter Si wafers. The modeling and simulations are implemented in an open-source Python library, pyPLD.

Mueller matrix ellipsometry has been used to precisely characterize quartz waveplates for demanding applications in the semiconductor industry and high precision polarimetry. We have found this experimental technique to be beneficial to use because it enables us to obtain absolute and precise measurement of retardation in a wide spectral range, waveplate orientation, and compound waveplate adjustment. In this paper, the necessity of including the optical activity in the Mueller matrix model and data treatment is demonstrated. Particularly, the optical activity of the quartz influences the adjustment of misalignment between the perpendicularly oriented waveplates of the compound biplate. We demonstrate that omitting the optical activity from the model leads to inaccurate values of the misalignment. In addition, the depolarization effects caused by a finite monochromator bandwidth is included in the model. Incorporation of the optical activity to the Mueller matrix model has required a development of rigorous theory based on appropriate constitutive equations. The generalized Yeh's matrix algebra to bianisotropic media has been used for the calculation of the eigenmodes propagation in chiral materials with reduced symmetry. Based on the applied method, the authors have proposed approximated analytical form of the Mueller matrix representing optically active waveplate and biplate and provided discussion on the analytical and numerical limits of the method.

Spectroscopic polar angle resolved Mueller matrix ellipsometry at multiple azimuthal incidences, together with a full-field model, reveal new details in the interplay between localized gap surface plasmon resonances and propagating surface plasmon polaritons (SPPs) in a rectangular array of metal–insulator–metal patches. A plane-wave expansion of the field in the insulator shows that the fundamental localized resonances are composed of oppositely propagating modes. Sharp dispersive resonances observed in p-polarization, excited near the opening of diffracted orders, are shown to be grating coupled SPPs. The SPPs show strong coupling with localized modes of similar symmetry, while they appear suppressed by modes of dissimilar symmetry.

We report on surface topographical, chemical and optoelectronic properties of sub-stoichiometric MoO3 thin films, MoO3-x, made by pulsed laser deposition. MoO3-x is a promising candidate for a sustainable intermediate band material. The absorption coefficient for photon energies below the MoO3 bandgap increases for films made in oxygen poor environments, and is explained by the occurrence of states in the bandgap related to oxygen vacancies and to phase mixtures of MoO3-x compositions with 0

The authors report here on the optical response and extraction of the morphological properties of three sizes of self-assembled nearly hexagonal arrays of gold (Au) nanoparticles (NPs), deposited on the native oxide on c-Si. The arrays were prepared by templating gold NP growth with self-assembled cylindrically organized block copolymer thin films, with consecutive removal of the polymer matrix by plasma etching. The particle sizes were controlled by using block copolymers of different molecular weights when assembling the templates. The resulting gold nanostructures were characterized by scanning probe microscopy. Spectroscopic ellipsometry was used to record the optical response of the samples, and the modeling of the spectra and the extraction of morphological parameters were performed using a modification of the Bedeaux–Vlieger formalism implemented in GranFilm. The modeling issues upon the introduction of a thin intermediate (oxide) layer between the particle and the substrate are discussed in detail, and a solution to the model procedure is proposed. The particles were modeled as truncated oblate Au spheroids in a hexagonal lattice on the native oxide on c-Si. The model fit converged to a solution indicating that the particles present a low wetting of the native oxide substrate, with parameters describing the particles and lattice in good correspondence with AFM. The extended GranFilm model simulations are also supported by finite element modeling. The authors report here on the optical response and extraction of the morphological properties of three sizes of self-assembled nearly hexagonal arrays of gold (Au) nanoparticles (NPs), deposited on the native oxide on c-Si. The arrays were prepared by templating gold NP growth with self-assembled cylindrically organized block copolymer thin films, with consecutive removal of the polymer matrix by plasma etching. The particle sizes were controlled by using block copolymers of different molecular weights when assembling the templates. The resulting gold nanostructures were characterized by scanning probe microscopy. Spectroscopic ellipsometry was used to record the optical response of the samples, and the modeling of the spectra and the extraction of morphological parameters were performed using a modification of the Bedeaux–Vlieger formalism implemented in GranFilm. The modeling issues upon the introductio...

Spectroscopic Mueller matrix ellipsometry is used to study an array of rectangular Au patches on a S i O 2 film backed by optically thick Au. The array supports resonances related to gap surface plasmons and Rayleigh anomalies, and these are mapped out by full rotation of the azimuthal angle of incidence. The finite element method is used to model the system, and it is found that the Ti adhesion layers at S i O 2 / A u interfaces used in the manufacture process must be included in the model for accurate results. We show how oxidation of the Ti layer beneath the Au patch causes the optical response to drift in time, and we demonstrate an extreme sensitivity of the Mueller matrix to the dimensions of the patch.

Silicon nano-crystals have been studied intensively due to their photoluminescence properties and possible applications in new generation opto-electronic devices. Their importance in lightning and display technologies is increasing due to the abundance and non-toxicity of silicon. Here we report a single batch solution based synthesis route to silicon nano-crystal organic hybrid films exhibiting white light photoluminescence at room temperature upon excitation by ultraviolet light. Films prepared by ethylene glycol terminated Si nano-crystals showed maximum 240 nm red shift in photoluminescence response upon excitation at 350 nm. The shift was found to decrease in order for hybrid films fabricated using acrylic acid, 1-octanol acid and oleic acid terminated Si nano-crystals. The mean size of the Si nano-crystals (~ 2–10 nm) estimated by Raman spectroscopy were smallest for the ethylene glycol capped Si nano-crystal films. The calculated Tauc bandgaps of the hybrid films varied between 1.51 and 2.35 eV.

Molybdenum oxide films are required for a large range of optical, electronic and catalytic applications, and optimal film characteristics are similarly broad. Furthermore, the layered crystal structure of MoO3 is suited to nanostructuring, which can be adapted to enhance the film properties. Here, we present a simple, aqueous route to MoO3 thin films and attain nanostructured morphologies by control of solution parameters. Smooth and homogeneous thin films were achieved by control of the molecular species in solution by pH. The sensitivity of film quality to pH was demonstrated with the addition of PVA to the solution, which resulted in large spherical particulates on the surface. Film thickness was adjusted from 10 to 60 nm, whilst maintaining good film quality, by changing the solution concentration. Moreover, the grain size and nanocrystallite orientation varied with solution concentration. The importance of film morphology is revealed in the compositional changes of the films during hydrogen reduction, with differences in breakdown of film coverage and growth of reduced phases. Furthermore, spectroscopic ellipsometry was used to determine the optical properties of the films. This revealed changes in the dielectric function and band gap that were dependent on the level of reduction. The nanoscale morphologies presented demonstrate the potential to precisely control film morphology, dimensions, oxygen stoichiometry and phase composition by a low-cost wet chemical route. This is a submitted manuscript of an article published by Elsevier Ltd in Applied Surface Science, 30 July 2018.

Optical properties of highly chromium doped (2–4 at.%) zinc sulfide made by pulsed laser deposition have been studied by spectroscopic ellipsometry in the spectral range of 0.73–5.90 eV. The characteristic optical features of the ZnS are a direct bandgap with absorption onset at 3.6 eV, with E0, E1 and E2 critical points around 3.7, 5.7 and 7 eV. Excitonic effects were observed to be strong in this material – in line with the literature. The sub-bandgap absorption accredited to the chromium doping appears as a broad sub-bandgap feature increasing monotonously with increased doping concentration at a given growth temperature. In this report, we discuss three different approaches to extract and analyze the optical properties in terms of the complex dielectric function.

A computationally efficient algorithm based on the reduced Rayleigh equation, combined with an optimization scheme, is used to accurately retrieve the morphological parameters of a two-dimensional plasmonic photonic crystal from angle-resolved spectroscopic Mueller matrix ellipsometric measurements. The numerical method is successfully tested against experimental data and gives morphological parameters consistent with SEM and AFM measurements.

The design of complete broadband polarimeters with high performance is challenging due to the wavelength dependence of optical components. An efficient genetic algorithm computer code was recently developed in order to design and re-optimize complete broadband Stokes polarimeters and Mueller matrix ellipsometers. Our results are improvements of previous patented designs based on two and three ferroelectric liquid crystals (FLCs). FLC based polarimeters are suited for broadband hyperspectral imaging, or multichannel spectroscopy applications. We have realized and implemented one design using two FLCs and compare the spectral range and precision with previous designs.

A partial in and out of incidence plane Mueller matrix scattering ellipsometry (MMSE) experiment is presented, where the Stokes vectors of the scattered light are detected in slightly more than a quarter hemisphere. The MMSE system is briefly reviewed. The Mueller scattering matrix obtained in reflection from as-cut rough solar grade mc-Si surfaces is reported. For the as-cut surface with an estimated correlation length of 4 μm and root mean square roughness of 550 nm, using an illumination wavelength of 532 nm, the degree of polarization is observed to be larger than 0.86, even far away from the incidence plane.

Producing surfaces textured with a homogeneous pattern of nanoscale structures is increasingly important for fabrication of semiconductor devices. Although techniques exist for imaging surface nanostructures on a local scale, these techniques are often impractical for use over large areas for finding average structural information. The nanostructured surface in this study consists of densely packed cones produced by sputtering a mono-crystalline GaSb substrate with a low-energy unfocused ion beam, yielding self-organized cones that are slightly tilted away from the sample normal. Here, we devise an all-optical non-destructive characterization scheme using Grazing-Incidence Small-Angle X-ray Scattering (GISAXS) and Spectroscopic Mueller Matrix Ellipsometry (MME) for obtaining all main dimensions including average height, lateral spacing and packing motifs, and the cone top and bottom diameters. It is further shown that both MME and GISAXS are sensitive to small tilts of the nanocone axis from the surface normal.

Small-scale solidification simulations were carried out in order to study the effect of the grain orientation and cooling rate on the stresses in mono- and bi-crystals. First, a 2D-axisymetric heat-transfer model of the global furnace is established to provide input to the sub-model. The sub-model takes into account only the crucible and silicon ingot. The flux histories are transferred from the global model. A finite element crystal plasticity model solves the mechanical deformation in the ingot. Ingots were grown in the small-scale Bridgman furnace with different pulling rates ranging from 0.2 to 50 mm/min. The results show the asymmetric effect of the crystal orientation and the stress build-up at the grain boundary due to different orientations. The change in pulling rate affects strongly the solidification front shape and the residual stresses. The 3D mechanical model illustrates also the limitations of the 2D-axisymmetric approach when silicon crystal anisotropy is taken into account.

We report here on the optical response of elliptical gold particles arranged in a rectangular lattice on glass and probed at non-normal incidence in reflection using spectroscopic Mueller matrix ellipsometry in the energy range 0.73–5.9 eV. The surface plasmon resonances, reshaped near the Rayleigh anomalies, are mapped out by full azimuthal rotation of the sample. The experimental Mueller matrices are discussed, and interpretation is supported by finite element modeling of the Mueller–Jones matrix elements, which allows for identification of the dipolar and multipolar responses observed in the experimental spectra. The data show a strong polarization conversion around the surface plasmon resonances as a function of the azimuthal angle of incidence, also reshaped near the Rayleigh lines. An effective strong circular diattenuation is observed from the recorded Mueller matrix. We further argue the importance of Mueller matrix ellipsometry for metrology in the manufacture of metasurfaces, for understanding the effect of the lattice in metasurface design, and finally in validating computational methods.

A gold nanowired grid polarizer is studied in the mid-IR range by means of spectroscopic Mueller matrix ellipsometry. This material is also an example of a so-called 2-dimensional hyperbolic metamaterial/metasurface, and produced by low-cost large area scalable manufacturing techniques. We present the IR spectroscopic Mueller matrix optical response of such sample for a full azimuthal rotation. It is observed strong in-plane anisotropy due to the gold wire grid. The main objective is to show a characterization methodology to reveal the complete polarimetric response over a large spectral range, providing information about the effective optical properties of the sample. Three different optical models are proposed that catch the main features of experimental data. The first one is based on the Rigorous Coupled-Wave Analysis (RCWA) assuming the profile of the sample to be periodic, second, a Generalized Effective Medium Approximation (G-EMA) assuming oriented gold ellipsoids aligned along the lines of the wire grid, and third, a biaxial dispersion model. Experimental data is compared with simulated data obtained from the three optical models and a comparative analysis between them is presented. The different models allow to retrieve information on the characteristic dimensions of the nanowires, and also to obtain the two in-plane components of the effective dielectric tensor of the nanostructured layer. The tensor component parallel to the nanowires shows a metallic response whereas the component perpendicular to them behaves as a transparent dielectric. Moreover, we have also shown that the nanowired grid behaves as a hyperbolic material.

Square arrays of gold (Au) hemispheroids deposited on a UV-transparent glass substrate reveal a rich optical response when investigated by spectroscopic Mueller Matrix Ellipsometry. Two samples were studied; the first consisted of hemispheroids of parallel radius of 58 nm and height 30 nm with lattice constant 210 nm; the corresponding parameters for the second sample were 38 nm, 20 nm and 125 nm, respectively. By a full azimuthal rotation of the samples, we observe all the Rayleigh anomalies corresponding to grazing diffracted waves, with strong resonances for co-polarization scattered light near the high symmetry points and cross-polarization scattered light around the Localized Surface Plasmon Resonance. Polarization-conversion becomes particularly important at grazing incidence, and the cross-polarization follows the Rayleigh lines. The optical response (neglecting polarization conversion) is modelled in the quasi-static approximation using the so-called Bedeaux-Vlieger formalism, and the Finite Element Method using COMSOL. The direct inversion of the effective (substrate dependent) dielectric function is discussed.

International audience; Hyperbolic metamaterials use the concept of controlling the propagative modes through the engineering of the dispersion relation, and are considered highly promising to reach different meta-properties. Here we propose a novel bottom-up fabrication technique for uniaxial anisotropic metamaterials presenting a strongly anisotropic dispersion relation in the visible wavelength range, using self-assembled nanostructured block copolymers hybridized with gold nanoparticles. The materials consist in periodic lamellar stacks of period 28 nm, of alternating layers of pure polymer (dielectric) and layers of composite of polymer loaded with a high density of 7 nm gold nanoparticles. The spectral variation of their anisotropic effective dielectric permittivity is determined by variable-angle spectroscopic ellipsometry using appropriate effective medium models, as a function of the density of plasmonic nanoparticles. For large gold loading and close to the plasmon resonance of the nanoparticles, the lamellar stack presents ordinary and extraordinary components of the dielectric function of opposite signs. We therefore demonstrate for the first time the possibility of using a self-assembly methodology for the fabrication of bulk hyperbolic metamaterial.

We report on the design and performance of a near infra-red Mueller matrix imaging ellipsometer, and apply the instrument to retardance imaging of strain in near infra-red transparent solids. Particularly, we show that the instrument can be used to investigate complex strain domains in multi-crystalline silicon wafers.

The dynamic response of a near infrared Ferroelectric Liquid Crystal based Mueller matrix ellipsometer (NIR FLC-MME) is presented. A time dependent simulation model, using the measured time response of the individual FLCs, is used to describe the measured temporal response. Furthermore, the impulse response of the detector and the pre-amplifier is characterized and included in the simulation model. The measured time-dependent intensity response of the MME is reproduced in simulations, and it is concluded that the switching time of the FLCs is the limiting factor for the Mueller matrix measurement time of the FLC-based MME. Based on measurements and simulations our FLC based NIR-MME system is estimated to operate at the maximum speed of approximately 16 ms per Mueller matrix measurement. The FLC-MME may be operated several times faster, since the switching time of the crystals depends on the individual crystal being switched, and to what state it is switched. As a demonstration, the measured temporal response of the Mueller matrix and the retardance of a thick liquid crystal variable retarder upon changing state is demonstrated., to be published in Journal of Modern Optics 20 pages, 6 figures

Nanostructured GaSb surfaces are investigated and characterised by Spectroscopic Ellipsometry (SE). In particular, the parameters of a recently developed graded anisotropic effective medium model are tentatively fitted to the data recorded from surfaces of densely packed long cones (higher than 60 nm). Both single graded and double graded, anisotropic effective medium models are tested. In particular, we discuss the results from modelling the cones sputtered at normal incidence, with heights ranging from 80 to 230 nm as determined by e.g. AFM and SEM.

High resolution field emission experiments from nanopatterned GaSb surfaces consisting of densely packed nanocones prepared by low ion-beam-energy sputtering are presented. Both uncovered and metal-covered nanopatterned surfaces were studied. Surprisingly, the field emission takes place by regular steps in the field emitted current. Depending on the field, the steps are either regular, flat, plateaus, or saw-tooth shaped. To the author’s knowledge, this is the first time that such results have been reported. Each discrete jump in the field emission may be understood in terms of resonant tunneling through an extended surface space charge region in an n-type, high aspect ratio, single GaSb nanocone. The staircase shape may be understood from the spatial distribution of the aspect ratio of the cones.

Mueller matrix ellipsometers (MMEs) are known to be less affected by noise if the compensators have a 132° phase shift between the slow and fast axis. This paper reports on the design and characterization of two custom-made achromatic compensators with minimal deviation from 132° retardation as a function of wavelength. The compensators are based on the dual Fresnel rhomb geometry. One pair was made of CaF2 and the other of fused silica. These materials were selected due to their extended transparency range and optical quality. The CaF2 compensators were experimentally characterized in the 450–8000 nm range, whereas the less IR-transparent fused silica prisms were characterized between 450 and 1900 nm. Both kinds of retarders possessed the necessary properties needed for a broad-band achromatic Mueller matrix ellipsometer, since they were both shown to give well-conditioned system matrices within the measured wavelength regions. Specifically, the condition number for the dual prisms used as a Polarization...

Fast near-infra-red spectroscopic Mueller matrix ellipsometer based on ferroelec-tric liquid crystal retarders

Optical measurements of nanostructured GaSb prepared by sputtering is presented. The optical response is studied by Mueller Matrix Ellipsometry (MME) in the visible range (430--850nm), and by spectroscopic ellipsometry in the range 0.6--6.5eV. The nano-structured surfaces reported in this work, consist of densely packed GaSb cones approximately 50nm high, on bulk GaSb. The nanostructured surfaces are here shown to considerably modify the optical response of the surface, hence giving a strong sensitivity to the far field spectroscopic (Mueller matrix) ellipsometric measurements. The off-specular scattering and the depolarization is found to be low. The anisotropic response is particularly emphasized by studying nano-structured GaSb cones approximately 45 degrees tilted with respect to the surface normal. In the latter case, one observes upon rotating the sample around the surface normal, that the Mueller matrix elements $m_{13}$ and $m_{14}$ oscillate as a function of the rotation angle. Finally, Mueller matrix techniques have been applied to the measured data, in order to analyze the acquired Mueller matrix in terms of physical realizability and noise.

Product decomposition of measured Mueller matrices from the FLC based NIR Mueller Matrix Ellipsometer

Hyperbolic metamaterials use the concept of controlling the propagative modes through the engineering of the dispersion relation, and are considered highly promising to reach different meta-properties. Spectroscopic Mueller Matrix Ellipsometry with variable angle of incidence and full azimuthal rotation of the sample is a powerful optical technique to characterize both anisotropic and bi-anisotropic materials. We here discuss the experimentally extracted uniaxial and biaxial optical properties of two self-assembled plasmonic systems that appear to have the appropriate meta-dispersion relations. The metasurface was produced by oblique incidence angle ion beam sputtering of glass followed by shadow deposition of Au [1]. The second bulk metamaterial was a block-copolymer based self-assembled hyperbolic metamaterial of nanocomposites based on metal nanoparticles embedded in a self-assembled anisotropic polymer host, presenting a strong spectrally selective optical anisotropy [2]. The extracted effective dielectric functions and the resulting dispersion relations are presented.

International audience; We consider the possibility of monitoring silver solid-state dewetting with in situ ellipsometry. We first study the optical response of partially dewetted samples in correlation with their morphological structure measured by Atomic Force Microscopy (AFM). We find that the main features observed in microscopy are identifiable in ellipsometry spectra. Then, we analyse the dielectric function extracted from in situ measurements to predict the progression in the dewetting process. We also identify two different behaviours leading to different final states.

The deposition and annealing in ultra high vacuum (UHV) of 5-6 monolayers (ML) of cerium on clean reconstructed Si-face 4H-SiC (0001) is studied by x-ray photoemission spectroscopy (XPS). Band bending as a function of annealing was studied by shifts of the bulk peak contribution in the C1s and Si2p spectra relative to the clean reconstructed surface. Additional datapoints for Schottky barrier formation on 4H-SiC are thus obtained by the low work function rareearth metals, and presented in the framework of the metal-induced-gap states and electronegativity model. A Ce/CeSi2-x/4H-SiC interface alloy forms by annealing to 850-1050oC. Kinetic information from the oxidation of the Ce/CeSi2-x/4H-SiC interface alloy is also reported. In particular, a SiO2- x/Ce-Si mixed oxide/4H-SiC forms upon oxidation. The shift of the C1s SiC-bulk-peak towards higher binding energies upon oxidation indicates that the mixed Ce-Si oxide interface layer appears to passivate the near Fermi-level 4H-SiC interface states at least as well as SiO2, and are expected to modify the electrical interface characteristics.

Vapour deposition of Ce onto a Rh(1 1 0) single crystal at room temperature is studied by X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS) and low energy electron diffraction (LEED). The thicknesses of the deposited Ce layers are estimated to be between 2 and 9 A. To study the changes in the Ce–Rh surface layer, the samples are annealed at temperatures between 500 and 1000 °C after Ce deposition. After heating, a c(2 × 2) LEED pattern appears for the sample with the thinnest deposited Ce layer (2.4 A). For samples with thicker Ce-films, the LEED pattern co-exists of a c(2 × 2) structure and a more diffuse 6% contracted (2 × 1) structure. This appears at the same temperature as the Ce 3d and Rh 3d core levels exhibit sharp intensity changes and binding energy shifts. The intensity of the f0, f1 and f2 multiplets in the Ce 3d core level spectra change when the annealing temperature is increased. The relative intensity of the Ce 3d f0 and f2 features compared to the Ce 3d f1 features is largest after annealing to 500 °C. This is below the temperature at which the ordered surface alloy is formed. When the sample is heated above the formation temperature of the surface alloy, the relative intensity of the Ce 3d f0 and f2 features decrease.

We report a spectroscopic Mueller matrix experimental study of a plasmonic photonic crystal consisting of gold hemispheroidal particles (lateral radius 54 nm, height 25 nm) arranged on a square lattice (lattice constant 210 nm) and supported by a glass substrate. Strong polarization coupling is observed for ultraviolet wavelengths and around the surface plasmon resonance for which the off-block-diagonal Mueller matrix elements show pronounced anisotropies. Due to the Rayleigh anomalies, the block-diagonal Mueller matrix elements produce a direct image of the Brillouin Zone (BZ) boundaries of the lattice and resonances are observed at the M-point in the first and at the X-point in the second BZ. These elements show also the dispersion of the localized surface plasmon resonance.

The formation of a Sm/SiC alloy after deposition of 2-3 ML of Sm in UHV on clean reconstructed carbon(000-1)- and silicon(0001)-terminated SiC surfaces is studied by photoemission (XPS and UPS) and low energy electron diffraction (LEED). The valence of the Sm overlayer after deposition at RT is estimated to be approximately 2.75, while upon annealing the Sm/SiC surface alloys on the bulk crystal becomes predominately 3+ valent. After further oxidation of the 1-2 ML thick Sm/4H-SiC surface alloys, the initial growth appears to proceed in a nearly epitaxial manner, and a modified oxide-SiC interface is formed. Samarium does not appear to induce a catalytically enhanced oxidation growth rate. Growth proceeds on the Si-face by forming SiO 2 on top of a samarium silicide oxide, whereas at the interface primarily silicon oxide is found.

Oxidation of Sm/4H–SiC is studied by X-ray photoemission spectroscopy (XPS) and low energy electron diffraction (LEED). In particular, we report kinetic information from the oxidation of a SmSix (1 × 1) surface alloy formed on (0 0 0 1) 4H–SiC. During the initial oxidation of the SmSix alloy, a (2 × 2)-LEED pattern is observed. Furthermore, the Sm 2+ valency observed from the clean SmSix surface alloy, which is related to surface samarium atoms, disappear at 15 L oxygen exposure. The oxygen atom is consequently deduced to be located at bridge or hollow sites involving one Sm atom. The initial oxidation result in an oxygen deficit SmSiOx interface oxide, probably as a consequence of the high oxidation temperatures in this work (900–1050 °C). We report that in a prolonged oxidation (longer than 10 kL) a SiO2 layer forms on top of the samarium silicon oxide interface layer.

Thin deposited films of Sm on a polycrystalline Ag are investigated by X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS) and photoemission electron microscopy (PEEM). The Sm valence is mainly divalent for low Sm coverage, while the trivalent contribution to the XPS intensity increases considerably for higher coverage. For an Sm overlayer thicker than 4 A, the average valence is estimated to be 2.65. The mixed valence in this system is concluded to be heterogeneous (all Sm atoms have integer and site-dependent valence). Alloy formation between Sm and Ag is observed upon annealing to temperatures between 400 and 550 °C. For these temperatures the change in average Sm valence is dependent on the initial Sm coverage deposited onto the Ag-foil. Systems with low initial coverage exhibit an increase in the average valence, while a decrease is observed for systems with coverage above 6 A. For intermediate coverages around 3 A an initial decrease in average valence is followed by a rapid increase for temperatures above 400 °C due to morphological changes in the surface layer.

Formation of surface alloys by annealing of thin Tm layers which were deposited on Pt(1 1 1) are investigated by photoemission and low energy electron diffraction (LEED). In addition, adsorption of CO was studied by temperature programmed desorption (TPD). For deposition of more than a monolayer of Tm, a (2 · 2) LEED pattern forms upon heating the sample to 600 � C. The appearance of the (2 · 2) pattern is assigned to alloy formation (‘‘thick alloy’’). The Tm 5p and 4f core levels show shifts of 0.8 eV to lower binding energies upon alloying, while the major Tm 4d multiplet shows a 1.1 eV shift to lower binding energy. These Tm shifts are interpreted to be caused by different coordination in the alloys. The present experiments indicate that the surface of the alloy is Pt enriched. For Tm coverages of less than about one monolayer a modified (1 · 1) LEED pattern is observed (‘‘thin’’ alloy). The core level shifts as observed for the ‘‘thick’’ alloy is not seen for the ‘‘thin’’ alloy. Finally, the work function of a thick evaporated Tm film was measured to be 3.3 eV. � 2005 Elsevier B.V. All rights reserved.

An automated spark test system based on combining field emission and spark measurements, exploiting a discharging capacitor is investigated. In particular, the remaining charge on the capacitor is analytically solved assuming the field emitted current to follow the Fowler Nordheim expression. The latter allows for field emission measurements from pA to A currents, and spark detection by complete discharge of the capacitor. The measurement theory and experiments on Cu and W are discussed.

International audience; Silica-based hybrid materials doped with gold nanoparticles (AuNPs) of different shapes were prepared with an adapted sol–gel technology (using MTEOS) and polished to high optical quality. Both spherical (23 and 45 nm in diameter) and bipyramidal (36, 50 and 78 nm in length) AuNPs were prepared and used as dopants. The AuNPs were functionalized with a novel silicone polymer for compatibilization with the sol–gel medium. The glass materials showed well defined localized surface plasmon resonance (SPR) absorbance from the visible to NIR. No redshifts in the spectra, due to the increase in doping concentration, were observed in the glasses, proving that no or very small SPR coupling effects occur. Spectroscopic Muller Matrix Ellipsometry showed that the shorter bipyramidal AuNPs (36 and 50 nm in length) have a clear preferred orientation in the MTEOS matrix, i.e. a tendency to be oriented with their long axis in the plane parallel to the glass surfaces. Dispersions of AuNPs have proven to be good optical power limiters that depend on particle size and geometry. The solid-state glass materials showed good optical power limiting at 532 nm for nanosecond pulses, which did not depend on the size or geometry of the AuNPs. In contrast to the observation at 532 nm, at 600 nm no optical limiting effect was observed. In these solids, as for dispersions of AuNPs, the optical limiting response is caused by scattering.

The bandgap of iron-doped ZnS has been reported by others to change significantly under the addition of a few atomic percent of iron, which would have significant implications for solar energy. Here, thin films of FexZn1-xS with x = 0 to 0.24 were made by co-deposition of Fe and ZnS using thermal evaporation. In contrast to results on nanoparticles and electrodeposited materials, all co-deposited films had optical properties consistent with a direct bandgap of ~3-3.5 eV. The absorption peak at 2.7 µm from substitutional Fe2+ in the ZnS films was well isolated up to concentrations of over 2% (~1021cm−3), despite the small crystallite size, suggesting the films may have applications as mid-infrared saturable absorbers. Increasing dopant concentration resulted in band edge softening. Density functional calculations are presented and are consistent with our observations of the Fe:ZnS films, demonstrating spin-polarized midgap states and additional states at the band edge. © 2015 Optical Society of America. Users may use, reuse, and build upon the article, or use the article for text or data mining, so long as such uses are for non-commercial purposes and appropriate attribution is maintained. All other rights are reserved.

We have investigated the structural and optical properties of Cr-doped ZnS (ZnS:Cr) thin films (0–7.5 at.% Cr) for use in intermediate band solar cells. The films were grown on Si(100) in molecular beam epitaxy (MBE) and pulsed laser deposition (PLD) equipments. Introducing Cr into ZnS resulted in Cr related subbandgap absorption, but also reduced the grain size. The sub-bandgap absorption increased with increasing Cr content, and with increasing growth temperature, but did not depend on the growth method. In contrast, the crystallinity depended strongly on the growth method, and smoother and highly textured films were obtained by PLD. The data indicate that stacking faults are present in all films. This is the authors' submitted manuscript of an article published by Elsevier in Solar Energy Materials and Solar Cells.

The chemisorption of acetylene on the Co(0 0 0 1) single crystal surface has been studied using high resolution core level photoemission, X-ray absorption spectroscopy and low energy electron diffraction. At low temperatures ( 6 300 K) acetylene forms a strong chemisorption bond to the substrate, creating a state of hybridisation close to sp 3 . The molecules are confirmed to be oriented with the C–C axis parallel to the surface. The vibrational splitting in the photoemission spectra due to excitation of the C–H stretch vibration is determined to be (389 � 8) meV, which is � 6% lower then the reported C–H stretch vibration frequency for gaseous acetylene. The S-factor of the C–H-vibrational mode is determined to be (0:17 � 0:02), considerably higher than those reported for C2H2 adsorbed on other substrates. 2002 Published by Elsevier Science B.V.

The optical properties of the below band-gap uniaxial dielectric function are studied as a function of the degree of hexagonality. The polytypes investigated were lightly doped 4H, 6H, 15R, and 21R silicon carbide. The ordinary component of the dielectric function is extracted from phase modulated spectroscopic ellipsometric measurements including mathematical removal of the overlayer. Accurate spectroscopic birefringence measurements are performed using a θ–2θ ellipsometric setup. The resulting birefringence varies as a third order polynomial as a function of the degree of hexagonality, with a turning point at 50% hexagonality. Furthermore, birefringence resulting from the intraconduction band transitions is studied both directly from the variation in the measured birefringence, and through Kramers–Kronig analysis of the extinction coefficient measured by p and s polarized transmission spectroscopy at 70° incidence. The second derivative of the dielectric function of the strongest below band-gap transition in the extraordinary component fit a one-dimensional critical point, while its energy position appears to be a linear function of the degree of hexagonality of the polytypes under investigation.

The main topic of this thesis is the investigation of small molecules adsorbed on the transition metals cobalt and rhodium surfaces by means of predominantly high-resolution core level photoemission and near edge x-ray absorption fine structure (NEXAFS). The thesis can be divided into three parts where the following phenomena are examined:1) internal molecular vibrations in the core level photoemission spectra2) hybridisation and thermal decomposition of adsorbates3) growth and surface alloy formation of metal-on-metal systemsThe influence on the C 1s spectra of photoemission induced internal vibrations after chemisorption is presented for two molecules, acetylene (C2H2) and carbonmonoxide (CO). In the former case the fine structure of the C-H vibrational stretch mode of acetylene on Co(0001) single crystal surface is resolved. The measured vibrational energy splitting is (389 ± 8) meV, which is ~6 % lower than what has been reported for gaseous acetylene. The corresponding Sfactor of 0.17 ± 0.02 is considerably higher than those reported for other systems. For CO molecules adsorbed on metal surfaces the C-O stretch vibration has a vibrational energy which is about half that of the C-H stretch in hydrocarbons. The progression of this vibrational mode for the systems CO/Co(0001), CO/Rh(100) and CO/Rh(111) have been thoroughly investigated. CO adsorbs in on-top sites on Co(0001) resulting in a vibrational splitting of (210 ± 3) meV from the adiabatic C 1s peak. For CO on Rh(100) two adsorption sites, on-top and bridge, are populated. Similar analyses of the vibrational fine structure gives a vibrational splitting of (221 ± 4) meV for on-top site and (174 ± 11) meV for bridge site. Investigations of the C-O vibrational properties on Rh(111), where CO populates on-top and three-fold hollow sites, show the same trend as for CO on Rh(100), namely decreasing vibrational splitting with increasing co-ordination. A tendency of increasing S-factor with increasing co-ordination is also reported.Acetylene hybridisation and thermal decomposition on two crystal orientation of cobalt, Co(0001) and Co(1120) , have been investigated using a variety of experimental techniques: NEXAFS shows that acetylene chemisorb strongly to both cobalt surfaces. For the system C2H2/Co(0001) a state of hybridisation close to sp3 has been deduced, which is considerably stronger than what has been reported earlier. Photoemission spectroscopy measurements show that acetylene starts to decompose at a temperature ~100 K lower for Co(1120) compared to Co(0001). For the anisotropic Co(1120) surface the acetylene decomposition lead to formation of an ordered carbon overlayer. By combining these results with STM and LEED measurements a hard sphere model has been proposed for this overlayer.Rare earth metals induce solid state reactions when thin overlayers are deposited onto a variety of metals and followed by annealing. Using high-resolution photoemission spectroscopy, LEED and temperature programmed desorption (TPD) a true surface alloy is shown to form with new electronic states when La on Rh(100) is annealed to 1350 K. These states alter the hybridisation of CO significantly compared to clean Rh(100) and as-deposited La on Rh(100). TPD experiments show CO desorption peaks at significantly lower temperature than CO on the as-deposited La/Rh(100), but still higher than the desorption peaks found for CO on Rh(100).The homoepitaxial growth of cobalt on Co(1120) has been studied by STM. The diffusion of Co adatoms is found to be highly anisotropic with larger mobility of added Co atoms parallel than perpendicular to [0001], i.e. along the zigzag rows of the unreconstructed Co(1120) surface.

Adsorption of carbon monoxide on La–Rh(1 0 0) surface alloys has been studied by photoelectron spectroscopy,lowenergy electron diffraction (LEED) and temperature programmed desorption (TPD). The surface alloys were formed by depositing overlayers of La in the monolayer regime on a Rh(1 0 0) substrate,and by subsequent annealing to about 1350 K. Carbon monoxide (CO) was dosed to saturation at various temperatures. The LEED pattern of the dissociated CO overlayer shows a c(4 � 4) structure with respect to the Rh(1 0 0) substrate. The LEED structure for the submonolayer alloy takes on a ring structure superposed on a (1 � 1) structure. At higher temperatures an apparent (10 � 10) superstructure is superposed on the ring structure. The TPD results shows that four different peaks are present in the desorption traces. From the core level spectroscopic data it is argued that the two first peaks are a combination of direct CO desorption,CO dissociation and associative CO desorption. The remaining two peaks are assumed to be related to associative desorption from atomic carbon and oxygen in a combination of different bonding states and different adsorbate interactions. Rh 3d core level spectra shows that the two peaks related to the surface atoms are shifted towards the bulk peak for CO on the alloy. The La 5p core level spectra shows the splitting of the core level into two peaks for CO and dissociated CO on the alloy. The 4r and 5r=1p molecular levels of CO on the alloy are observed in the valence band spectra,with similar binding energies as for CO on a disordered La layer. In particular,a stronger rehybridisation of the CO 4 r state with the electronic states of the surface alloy as compared to CO on clean Rh(1 0 0),is argued to be responsible for dissociation of CO on the alloy at low temperatures. 2001 Published by Elsevier Science B.V.

Human atherosclerotic samples collected by carotid endarterectomy were investigated using electronic paramagnetic resonance imaging (EPRI) for visualization of reactive oxygen species, and nonlinear optical microscopy (NLOM) to study structural features. Regions of strong EPRI signal, indicating a higher concentration of reactive oxygen species and increased inflammation, were found to colocalize with regions dense in cholesterol crystals as revealed by NLOM.

Previous studies of CO on Ni(1 0 0) by Fohlisch et al. [Phys. Rev. Lett. 81 (1998) 1730] have shown that the intramolecular stretch vibration mode observed in the C 1s photoelectron lines depends strongly on the chemical state of the adsorbate. In the current investigation analogous analyses have been done for CO on Co(0 0 0 1) and Rh(1 0 0). CO adsorbs in on-top sites on Co(0 0 0 1) resulting in a vibrational splitting of (210±3) meV from the adiabatic C 1s peak. Including the measured intensities and comparing with similar data from electron energy loss spectroscopy experiments the change in the equilibrium distance between the initial state and the ionised state has been deduced to be (4.2±0.2) pm. For CO on Rh(1 0 0) two adsorption sites, on-top and bridge, are populated. Similar analysis of the vibrational fine structure gives a vibrational splitting of (221±4) meV for the on-top site and (174±11) meV for the bridge site. The respective changes in the equilibrium distances are (3.8±0.2) and (5.6±0.3) pm. These results are compared with available data in literature.

The main topic of this thesis is the investigation of small molecules adsorbed on the transition metals cobalt and rhodium surfaces by means of predominantly high-resolution core level photoemission and near edge x-ray absorption fine structure (NEXAFS). The thesis can be divided into three parts where the following phenomena are examined:1) internal molecular vibrations in the core level photoemission spectra2) hybridisation and thermal decomposition of adsorbates3) growth and surface alloy formation of metal-on-metal systemsThe influence on the C 1s spectra of photoemission induced internal vibrations after chemisorption is presented for two molecules, acetylene (C2H2) and carbonmonoxide (CO). In the former case the fine structure of the C-H vibrational stretch mode of acetylene on Co(0001) single crystal surface is resolved. The measured vibrational energy splitting is (389 ± 8) meV, which is ~6 % lower than what has been reported for gaseous acetylene. The corresponding Sfactor of 0.17 ± 0.02 is considerably higher than those reported for other systems. For CO molecules adsorbed on metal surfaces the C-O stretch vibration has a vibrational energy which is about half that of the C-H stretch in hydrocarbons. The progression of this vibrational mode for the systems CO/Co(0001), CO/Rh(100) and CO/Rh(111) have been thoroughly investigated. CO adsorbs in on-top sites on Co(0001) resulting in a vibrational splitting of (210 ± 3) meV from the adiabatic C 1s peak. For CO on Rh(100) two adsorption sites, on-top and bridge, are populated. Similar analyses of the vibrational fine structure gives a vibrational splitting of (221 ± 4) meV for on-top site and (174 ± 11) meV for bridge site. Investigations of the C-O vibrational properties on Rh(111), where CO populates on-top and three-fold hollow sites, show the same trend as for CO on Rh(100), namely decreasing vibrational splitting with increasing co-ordination. A tendency of increasing S-factor with increasing co-ordination is also reported.Acetylene hybridisation and thermal decomposition on two crystal orientation of cobalt, Co(0001) and Co(1120) , have been investigated using a variety of experimental techniques: NEXAFS shows that acetylene chemisorb strongly to both cobalt surfaces. For the system C2H2/Co(0001) a state of hybridisation close to sp3 has been deduced, which is considerably stronger than what has been reported earlier. Photoemission spectroscopy measurements show that acetylene starts to decompose at a temperature ~100 K lower for Co(1120) compared to Co(0001). For the anisotropic Co(1120) surface the acetylene decomposition lead to formation of an ordered carbon overlayer. By combining these results with STM and LEED measurements a hard sphere model has been proposed for this overlayer.Rare earth metals induce solid state reactions when thin overlayers are deposited onto a variety of metals and followed by annealing. Using high-resolution photoemission spectroscopy, LEED and temperature programmed desorption (TPD) a true surface alloy is shown to form with new electronic states when La on Rh(100) is annealed to 1350 K. These states alter the hybridisation of CO significantly compared to clean Rh(100) and as-deposited La on Rh(100). TPD experiments show CO desorption peaks at significantly lower temperature than CO on the as-deposited La/Rh(100), but still higher than the desorption peaks found for CO on Rh(100).The homoepitaxial growth of cobalt on Co(1120) has been studied by STM. The diffusion of Co adatoms is found to be highly anisotropic with larger mobility of added Co atoms parallel than perpendicular to [0001], i.e. along the zigzag rows of the unreconstructed Co(1120) surface.