Study of outermost surface lavers of organic solids by penning ionization electron spectroscopy

Abstract

Assignment of photoelectro bands for naphthalene and anthracene by penning ionization electron spectroscopy

Study of outermost surface layers of organic solids by penning ionization electron spectroscopy

Pre- and initial stages of epitaxy in alkali halide systems: II. Interaction of molecular beams of CsCl with (100) surfaces of NaCl

Surface of matter normally contains sublayers with molecular or electronic structure different from the outmost surface and the bulk, which may play a critical role in surface energy and/or charge transfer processes. Therefore, the development of layer-resolved characterization methods is of great importance for surface science and techniques. Although optical spectroscopy methods are very sensitive to structure, their spatial resolution is often much larger than the inter-layer distance of the sublayers, resulting in the inability to achieve laminar resolution. In this work, we discuss the possibilities of utilizing two-dimensional (2D) electronic spectroscopy to distinguish spectral information and energy transfer between different layers, which cannot otherwise be obtained from linear spectroscopy methods owing to lineshape broadening. By theoretical 2D spectral simulations, we investigated two layered systems by numerical simulations, material surface:subsurface:bulk and molecule:surface:subsurface:bulk. The directional energy transfer rates from the bulk to the surface layer owing to the surface-bulk coupling was preset. Due to the fact that the energy transfer between the subsurface and the outermost surface layer is faster than that between the bulk and the outermost surface layer, there will be special time periods during which only the former takes place and gives rise to the distinguishable dynamics of off-diagonal peaks. Our simulation results showed that by analyzing the difference between the projections of the off-diagonal peak, the excitation energy of the surface, subsurface and bulk layers can be determined. Furthermore, for the four-layer system, the off-diagonal peaks can be kept away from the interference of diagonal peaks, providing a better chance for realizing laminar resolution compared with the three-layer system.

Defining the cooling and heating solar efficiency of a building component skin: application to a modular living wall

A team of Japanese chemists is developing a technique to study experimentally the electron densities of the very outermost molecular orbitals in molecules. These orbitals are the ones most important in chemical reactions, because it is-through them that molecules usually interact with each other. Koichi Ohno, Hideki Mutoh, and Yoshiya Harada of the chemistry department of the University of Tokyo find that a technique called Penning ionization electron spectroscopy can be used to study the spatial electron distributions of individual molecular orbitals [ J. Am. Chem. Soc. , 105 , 4555 (1983)]. Molecular orbitals, which are mathematical constructs of regions in space where electrons have particular probabilities of being located, arise out of quantum mechanics. Originally, they were purely theoretical creations, but in the past 15 years or so researchers have been able to relate these orbitals to a number of measurable physical properties of molecules such as ionization potentials. The Japanese chemists car...

We have demonstrated the unique surface sensitivity of ion neutralization spectroscopy (INS) using a series of Si(111) surfaces, which had been subjected to a common cleaning procedure but different subsequent heat treatments. The surfaces produced each showed a sharp 7×7 LEED pattern and the measured initial‐state transition densities by INS were closely similar. In contrast, the electron spectra by uv photoemission spectroscopy (UPS) for these surfaces showed remarkable differences with respect to each other.The INS evidence is taken to mean that for each such surface the outermost surface layer is cleaner than would be concluded from the UPS spectra. Since the UPS spectra include a large component from the selvedge or near‐surface bulk, we propose that the impurities which cause the differences in the spectra reside largely in the selvedge. Thus UPS is shown to be less sensitive than INS to the outermost surface layer which must be probed in the study of chemisorption.Longer heatings of a particular sa...

In the present study, the methods of optical, scanning electron, and transmission electron microscopy as well as X-ray diffraction analysis gained insights into the mechanisms of surface finish and microstructure formation of Ti–6Al–4V parts during an EBF3-process. It was found that the slip band propagation within the outermost surface layer provided dissipation of the stored strain energy associated with martensitic transformations. The latter caused the lath fragmentation as well as precipitation of nanosized β grains and an orthorhombic martensite α″ phase at the secondary α lath boundaries of as-built Ti–6Al–4V parts. The effect of continuous electron beam post-treatment on the surface finish, microstructure, and mechanical properties of EBF3-fabricated Ti–6Al–4V parts was revealed. The brittle outermost surface layer of the EBF3-fabricated samples was melted upon the treatment, resulting in the formation of equiaxial prior β grains of 20 to 30 μm in size with the fragmented acicular α′ phase. Electron-beam irradiation induced transformations within the 70 μm thick molten surface layer and 500 μm thick heat affected zone significantly increased the Vickers microhardness and tensile strength of the EBF3-fabricated Ti–6Al–4V samples.

We morphologically determined the effects of xylitol on the remineralization of artificially demineralized enamel. The samples were demineralized and then immersed in a remineralizing solution with or without 20% xylitol at 37 degrees C for 2 weeks. Samples were observed using contact microradiography, a multipurpose image processor (MIP) and a high-resolution electron microscope (HRTEM). Contact microradiography indicated that remineralization occurred in the surface and deep layers of samples immersed in a non-xylitol solution. Samples immersed in a xylitol solution demonstrated less mineralization in the outer 10 microm of the outermost surface layers, but more mineralization in the middle and deep layers, than was observed in the non-xylitol samples. The MIP evaluation indicated that remineralization was more prominent in layers at depths of 50-60 microm in the xylitol samples than in the non-xylitol samples. Observation of the xylitol samples by HRTEM revealed crystals of various sizes and irregular shapes with unclear crystal angles in the outermost surface layers. In the middle layers, they had thickened and angles of crystals are clear. These results indicate that xylitol can induce remineralization of deeper layers of demineralized enamel by facilitating Ca2+ movement and accessibility.

Investigation of the surface composition of powders often requires compaction. To study the effect of compaction on surface analysis, samples have been compacted at various pressures ranging from 0 Pa (i.e. no compaction) up to 2000 MPa (2 × 10 4 kg cm −2 ) Low‐energy ion scattering (LEIS) was used to determine the composition of the outermost atomic surface layer. Using scanning electron microscopy, changes in the morphology due to compaction have been detected in the SiO 2 test samples. The LEIS yield of a compacted silica powder is found to be independent of the applied pressure during compaction between 2 MPa and 2000 MPa (2 × 10 4 kg cm −2 ). Analysis of a submonolayer of Ta 2 O 5 on a silica support shows that the composition of the outermost atomic layer is not changed after compaction up to a pressure of at least 300 MPa. When compaction is applied, the absolute LEIS yield appears to be independent of the specific surface area of silica supports in the range 50–380 m 2 g −1 . A minor difference in LEIS signals is observed between compacted silica supports and flat quartz samples. In order to determine the surface roughness factor independently, and to study the material dependence of the surface roughness factor, angle‐dependent LEIS measurements have been carried out on oxidized silicon, gallium and gold surfaces. The results on the oxidized silicon confirm the small influence of surface roughness for silica particles, whereas measurements on the more closely packed metallic gallium and gold surfaces indicate a significant surface roughness effect. Copyright © 2004 John Wiley & Sons, Ltd.

Alkali hydroxides as promoters of Mn 3O 4 in the selective reduction of nitrobenzene; an X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy and ion scattering spectroscopy study

A detailed understanding of the stability of glasses toward liquid or atmospheric attack is of considerable importance for preserving numerous objects of our cultural heritage. Glasses produced in the ancient periods (Egyptian, Greek, or Roman glasses), as well as modern glass, can be classified as soda-lime-silica glasses. In contrast, potash was used as a flux in medieval Northern Europe for the production of window panes for churches and cathedrals. The particular chemical composition of these potash-lime-silica glasses (low in silica and rich in alkali and alkaline earth components), in combination with increased levels of acidifying gases (such as SO(2), CO(2), NO(x), or O(3)) and airborne particulate matter in today's urban or industrial atmospheres, has resulted in severe degradation of important cultural relics, particularly over the last century. Rapid developments in the fields of microelectronics and computer sciences, however, have contributed to the development of a variety of nondestructive, surface analytical techniques for the scientific investigation and material characterization of these unique and valuable objects. These methods include scanning electron microscopy in combination with energy- or wavelength-dispersive spectrometry (SEM/EDX or SEM/WDX), secondary ion mass spectrometry (SIMS), and atomic force microscopy (AFM). In this Account, we address glass analysis and weathering mechanisms, exploring the possibilities (and limitations) of modern analytical techniques. Corrosion by liquid substances is well investigated in the glass literature. In a tremendous number of case studies, the basic reaction between aqueous solutions and the glass surfaces was identified as an ion-exchange reaction between hydrogen-bearing species of the attacking liquid and the alkali and alkaline earth ions in the glass, causing a depletion of the latter in the outermost surface layers. Although mechanistic analogies to liquid corrosion are obvious, atmospheric attack on glass ("weathering") is much more complex due to the multiphase system (atmosphere, water film, glass surface, and bulk glass) and added complexities (such as relative humidity and atmospheric pollutant concentration). Weathered medieval stained glass objects, as well as artifacts under controlled museum conditions, typically have less transparent or translucent surfaces, often with a thick weathering crust on top, consisting of sulfates of the glass constituents K, Ca, Na, or Mg. In this Account, we try to answer questions about glass analysis and weathering in three main categories. (i) Which chemical reactions are involved in the weathering of glass surfaces? (ii) Which internal factors (such as the glass composition or surface properties) play a dominant role for the weathering process? Can certain environmental or climatic factors be identified as more harmful for glasses than others? Is it possible to set up a quantitative relationship or at least an approximation between the degree of weathering and the factors described above? (iii) What are the consequences for the restoration and conservation strategies of endangered glass objects? How can a severe threat to precious glass objects be avoided, or at least minimized, to preserve these artifacts of our cultural heritage for future generations?

Patterned organic light-emitting-diode substrates were treated by oxygen (O2) and tetrafluoromethane (CF4) radio-frequency (rf, 13.56 MHz) plasmas of low-power (close to 1 W) that were capacitively-coupled. An unexpected wettability contrast (water contact angle difference up to 90°) between the indium-tin-oxide anode and the bank resist regions was achieved, providing excellent conditioning prior to the ink-jet printing. This selectivity was found to be adjustable by varying the relative exposure time to the O2 and CF4 sequential plasmas. Static contact angle measurements and extensive x-ray photoelectron spectroscopy analyses showed that the wetting properties depend on the carbon and fluorine chemical functional groups formed at the outermost surface layers, whereas atomic force microscopy images did not show a morphological change. Plasma optical emission spectroscopy and ion mass spectroscopy suggested that surface functionalization was initiated by energy transfer from ionic species (O+, O2+, CF+, CF2+, and CF3+) and excited neutrals (O∗ and F∗). The absolute ion fluxes measured on the substrates were up to 1014 cm−2 s−1 and the ion energies up to 20 eV, despite the low powers applied during the process.

Platinized Ni and Co nanoparticles have been constructed on glassy carbon electrode (GCE) by a two steps process. First, Ni or Co nanoparticles were electrodeposited on GCE and subsequently converted of their outermost surface layer with Pt monoatomic layer. Oxygen reduction reaction (ORR) activity of these electrocatalysts was investigated by the rotating disk electrode and we demonstrated that the ORR activity of these electrocatalysts was better than that of the Pt polycrystalline electrode.