Active polarimetric assessment of surface weathering

This study examines the application of laser ablation to the characterization and decontamination of painted and unpainted concrete and metal surfaces that are typical of many facilities within the US Department of Energy complex. The utility of this promising technology is reviewed and the essential requirements for efficient ablation extracted. Recent data obtained on the ablation of painted steel surfaces and concrete are presented. The affects of beam irradiance, ablation speed and efficiency, and characteristics of the aerosol effluent are discussed. Characterization of the ablated components of the surface offers the ability of concurrent determination of the level of contamination. This concept can be applied online where the ablation endpoint can be determined. A conceptual system for the characterization and decontamination of surfaces is proposed.

Nearly two-dimensional (2D) metallic systems formed in charge inversion layers and artificial layered materials permit the existence of low-energy collective excitations, called 2D plasmons, which are not found in a three-dimensional (3D) metal. These excitations have caused considerable interest because their low energy allows them to participate in many dynamical processes involving electrons and phonons, and because they might mediate the formation of Cooper pairs in high-transition-temperature superconductors. Metals often support electronic states that are confined to the surface, forming a nearly 2D electron-density layer. However, it was argued that these systems could not support low-energy collective excitations because they would be screened out by the underlying bulk electrons. Rather, metallic surfaces should support only conventional surface plasmons-higher-energy modes that depend only on the electron density. Surface plasmons have important applications in microscopy and sub-wavelength optics, but have no relevance to the low-energy dynamics. Here we show that, in contrast to expectations, a low-energy collective excitation mode can be found on bare metal surfaces. The mode has an acoustic (linear) dispersion, different to the dependence of a 2D plasmon, and was observed on Be(0001) using angle-resolved electron energy loss spectroscopy. First-principles calculations show that it is caused by the coexistence of a partially occupied quasi-2D surface-state band with the underlying 3D bulk electron continuum and also that the non-local character of the dielectric function prevents it from being screened out by the 3D states. The acoustic plasmon reported here has a very general character and should be present on many metal surfaces. Furthermore, its acoustic dispersion allows the confinement of light on small surface areas and in a broad frequency range, which is relevant for nano-optics and photonics applications.

An original 2D3V (two-dimensional in coordinate space and three-dimensional in velocity space) particle-in-cell code has been developed for simulation of multipactor discharge on a dielectric in a parallelplate metal waveguide with allowance for secondary electron emission (SEE) from the dielectric surface and waveguide walls, finite temperature of secondary electrons, electron space charge, and elastic and inelastic scattering of electrons from the dielectric and metal surfaces. The code allows one to simulate all stages of the multipactor discharge, from the onset of the electron avalanche to saturation. It is shown that the threshold for the excitation of a single-surface multipactor on a dielectric placed in a low-profile waveguide with absorbing walls increases as compared to that in the case of an unbounded dielectric surface due to escape of electrons onto the waveguide walls. It is found that, depending on the microwave field amplitude and the SEE characteristics of the waveguide walls, the multipactor may operate in two modes. In the first mode, which takes place at relatively low microwave amplitudes, a single-surface multipactor develops only on the dielectric, the surface of which acquires a positively potential with respect to the waveguide walls. In the second mode, which occurs at sufficiently high microwave intensities, a single-surface multipactor on the dielectric and a two-surface multipactor between the waveguide walls operate simultaneously. In this case, both the dielectric surface and the interwall space acquire a negative potential. It is shown that electron scattering from the dielectric surface and waveguide walls results in the appearance of high-energy tails in the electron distribution function.

Electron dynamics of image potential states in weakly bound adsorbate layers: A short review

Hybrid bonding achieves mechanical and electrical connection between device wafers or dies, by directly joining dielectric and metal surfaces to form an all-inorganic interface. This direct bond interconnect (DBI) technology enables very fine pitch interconnects for high bandwidth interfaces. DBI is currently used for mass production of image sensors and is actively investigated for NAND, DRAM and MEMS applications. Characterizing and controlling nanoscale topography are essential for this type of bonding. After chemical mechanical polishing (CMP), the dielectric surface (usually SiO2) should have high planarity and sub-nm roughness, and the metal surface (usually Cu) should be slightly recessed below the dielectric surface in general. Atomic force microscopy (AFM) is a critical technique required to monitor the CMP process module and ensure a robust manufacturing process. While AFM and related techniques have been known for decades, nanoscale or sub-nm scale characterization for DBI requires careful choice of the analysis configurations and parameters to avoid misinterpretation. Here we discuss key considerations for AFM analysis, extraordinary AFM artifacts in the relative heights of the Cu and SiO2 areas, and topographic characteristics of Cu/SiO_2 surface for successful hybrid bonding. The force between an AFM tip and a sample should be sufficiently low for consistent roughness measurement but sufficiently high for minimizing the effects of surface contamination or artifacts. Proper data processing such as flattening should be done to make realistic images. Occasionally we observed artifacts that produced an incorrect Cu height, which could render an actually recessed Cu area as protruding. This artifact tends to occur more if the tip is not fresh or the tapping force is low. If a data image is unusually blurry and the oxide roughness is much smaller than usual, it may be a sign of this artifact. Replacing the tip or scanning in contact mode can usually demonstrate if there was an artifact. AFM analysis revealed that a curved SiO2 surface (oxide rounding) tends to occur in the vicinity of Cu interconnect areas. Optimized CMP conditions can reduce the size of seams and eliminate them.

Accurate measurement of particle size distribution by a cascade impactor requires that particles remain on the collection surfaces after impaction. Recent studies show that, when a solid aerosol is sampled, significant rebound and re-entrainment of particles occur in cascade impactors. A mathematical model of a cascade impactor including collection efficiency functions for solid aerosols on various impaction surfaces was developed and used to operate upon a series of log-normal size distributions. The impactor modeled was a six stage Andersen operated at 28.3 L/min. When bare metal or glass impaction surfaces are used, the impactor indicates non-log-normal distributions and the estimated distribution parameters are in error by as much as a factor of 7. When glass fiber impaction surfaces are used, although less serious errors are indicated, the deviation from log-normality is significant for aerosols with MMD larger than 3 micrometers. When oil covered impaction stages are used the indicated distributions parameters are acceptably close to the input parameters. The accuracy of the model was verified experimentally.

We report the electrochemical potential dependence of photocatalysis produced by hot electrons in plasmon-resonant grating structures. Here, corrugated metal surfaces with a period of 520 nm are illuminated with 785 nm wavelength laser light swept as a function of incident angle. At incident angles corresponding to plasmon-resonant excitation, we observe sharp peaks in the electrochemical photocurrent and dips in the photoreflectance consistent with the conditions under which there is wavevector matching between the incident light and the spacing between the lines in the grating. In addition to the bare plasmonic metal surface (i.e., Au), which is catalytically inert, we have measured grating structures with a thin layer of Pt, Ru, and Ni catalyst coatings. For the bare Au grating, we observe that the plasmon-resonant photocurrent remains relatively featureless over the applied potential range from -0.8 to +1.2 V vs NHE. For the Pt-coated grating, we observe a sharp peak around -0.3 V vs NHE, three times larger than the bare Au grating, and near complete suppression of the oxidation half-reaction, reflecting the reducing nature of Pt as a good hydrogen evolution reaction catalyst. The photocurrent associated with the Pt-coated grating is less noisy and produces higher photocurrents than the bare Au grating due to the faster kinetics (i.e., charge transfer) associated with the Pt-coated surface. The plasmon-resonant grating structures enable us to compare plasmon-resonant excitation with that of bulk metal interband absorption simply by rotating the polarization of the light while leaving all other parameters of the experiment fixed (i.e., wavelength, potential, electrochemical solution, sample surface, etc.). A 64X plasmon-resonant enhancement (i.e., p-to-s polarized photocurrent ratio) is observed for the Pt-coated grating compared to 28X for the bare grating. The nickel-coated grating shows an increase in the hot-electron photocurrent enhancement in both oxidation and reduction half-reactions. Similarly, Ru-coated gratings show an increase in hot-electron photocurrents in the oxidation half-reaction compared to the bare Au grating. Plasmon-resonant enhancement factors of 36X and 15X are observed in the p-to-s polarized photocurrent ratio for the Ni and Ru gratings, respectively.

A key parameter that controls the formation of a local galvanic element during the deadhesion of paint from base metals is the potential gradient between a defect in the paint and the intact metal oxide/polymer interface. The suitable development of zinc coatings allows for control of the potential at the intact interface and thus improvement of the delamination behavior. However, no systematic in-depth study on the origin and meaning of electrode potentials at polymer/metal interfaces or even bare metal surfaces has been presented yet, although in many recent publications Volta potential differences between inclusions and matrix measured on the surfaces of alloys are often interpreted as providing information on the galvanic activity during corrosion. It is the focus of this paper to present a detailed analysis of the origin of the potentials measured on the different materials and to point out what conclusion can be drawn from their values. Special focus is given to the technologically important system .

The results of selected surface science studies of catalytic processes are described. Our conclusions, drawn from many such studies, are that reactions which occur over metal based catalysts can be divided into three classes: 1) those occurring on the bare metal surface, 2) those occurring on active overlayers bound to the metal, and 3) those occurring on coadsorbate modified metal surfaces. Case histories are given describing catalytic processes fitting each category. The surface properties of iron and its oxides are then described. We review the photochemical studies using iron oxides that are aimed at the photocatalytic dissociation of water.

An in situ cutting technique has been developed to expose bare lithium metal in various organic electrolyte environments. The corrosion potential-time transients have been measured. The electrolytes investigated were LiAsF/sub 6/, LiPF/sub 6/, LiBF/sub 4/, LiClO/sub 4/, and Li(CF/sub 3/SO/sub 2/)/sub 2/N in tetrahydrofuran (THF), 2-methyl tetrahydrofuran (2Me-THF), and propylene carbonate (PC). The transients permit the ranking of the reactivity of the electrolytes and show that the passivating reactions are completed in less than one second, even for very carefully purified electrolytes. Cyclic voltammetry and normal Raman spectroscopy (NRS) have also been used to characterize the lithium/organic electrolyte interface. For LiAsF/sub 4//THF and 2Me-THF, NRS has given evidence for reduction of As(V) to As(III) by the bare lithium metal at open-circuit potential. The measurements have shed light on the understanding of the stability of various salts and solvents in contact with lithium. >

Optical and spectroscopic techniques offer unique possibilities for non destructive or micro-destructive characterization of surfaces, with widespread applications, starting from in-line monitoring of industrial processes. A significant group of industrial applications concerns nuclear grade material characterization and plasma diagnostics relevant to the thermonuclear fusion process. However, technologies and methodologies originally developed for specific in-vessel utilization, can easily find additional in-situ and remote application to environmental and cultural heritage (CH) diagnostics addressed to preventive conservation and restoration of surfaces. At ENEA Frascati different prototypes have been developed and patented to collect reflectance and fluorescence images excited at different ultraviolet and visible laser wavelengths, Raman and LIBS signals. Portable integrated instruments suitable for operation at different distances from a 1.5 to 30 m, have been assembled and operated in laboratory on multilayered samples and in field campaigns for Security and on CH painted surfaces. Significant results relevant to the cross fertilization among different applications will be presented and discussed.

This paper presents an overview of the physical properties and sedimentologic results from six Ocean Drilling Program Leg 151 sites cored on the Iceland Plateau (Hole 907A), in the Fram Strait region (Sites 908 and 909), and on the Yermak Plateau (Sites 910-912).The primary objective of this paper is to determine to what extent wet bulk density measured using the gamma-ray attenuation porosity evaluator (GRAPE) can be used to interpret textural and compositional changes in sediment accumulation at the various sites around the Nordic Seas and Arctic Ocean.To accomplish this objective, we have first established quantitative relationships between discrete measurements of bulk density and GRAPE bulk density at nine holes and have evaluated the frequency distribution of GRAPE bulk density data at the same holes to detect significant differences between sites.We have also evaluated the frequency distribution of magnetic susceptibility data at these holes because this rock magnetic parameter is most often used in combination with GRAPE measurements for correlation purposes.These two parameters are also used for evaluating compositional and textural changes in sedimentary inputs.Composite depth profiles have been developed for three sites (Sites 908, 909, and 911) using both GRAPE bulk density and magnetic susceptibility measurements made on cores from multiple, adjacent holes at these sites.The composite depth profiles provide a more continuous record of property variations in the upper 100 meters below seafloor at a given site than is provided by the data collected at a single hole.The composites also provide the framework for more detailed paleoceanographic and paleoclimatic analyses of the records from these sites (i.e., spectral analysis of time series, astronomic tuning of records, etc.).These activities will be pursued in future contributions related to these data.Efforts have been made to identify the sources of variation in the GRAPE bulk density records, and to a lesser extent the magnetic susceptibility records, using the available "ground truth" provided by sedimentologic analyses of discrete samples from selected holes.Textural and mineralogic analyses are compared to GRAPE bulk density records to identify to what extent we are able to explain the density fluctuations in terms of (1) changes in the accumulation of coarse-grained material in various grain-size subfractions, which are primarily transported to the deep sea by sea ice and icebergs during glacial intervals and are influenced by oceanic currents to varying extents, and (2) by changes in the mineralogy and in the relative percentages of various sedimentary inputs, which may provide information about changing source regions for these materials between glacial and interglacial periods in the Nordic Seas and Arctic Ocean.

Interest in polarization properties of the rendered materials is growing, but so far discussions on polarization have been restricted only to surface reflection, and the reflection due to subsurface scattering is assumed to be unpolarized. Findings from other field (e.g. optics and atmospheric science) show that volumetric interaction of light can contribute to polarization. So we investigated the polarized nature of the radiance field due to subsurface scattering as a function of the thickness of the material layer for various types of materials. Though our computations shows negligible polarization for material layers of high thickness, thin layered materials show significant degree of polarization. That means polarization cannot be ignored for subsurface component of reflection from painted surfaces (particularly painted metal surfaces) or from coated materials. In this paper we employ the vector radiative transfer equation (VRTE), which is the polarized version of the radiative transfer equation inside the material. We use a discrete ordinate based method to solve the VRTE and compute the polarized radiance field at the surface of the material layer. We generate the polarimetric BRDF from the solutions of the VRTE for incident irradiance with different polarizations. We validate our VRTE solution against a benchmark and demonstrate our results through renderings using the computed BRDF.

14 - Metal Pigments as Antimicrobial Agent and Coating Additives

Electrochemistry of active chromium: Part II. Three hydrogen evolution reactions on chromium in sulfuric acid