Surface chemical composition

As an example, we present the surface structure of the sample perovskite LaCoOa catalyst [5] to identify the presence of chemical species, in particular, the oxidation state and the relative concentration of the elements at the surface, measuring the kinetic energy of the electrons emitted by the sample when excited by photoelectron X-ray. 

The XPS spectra (Fig. 11.4) are referred to the internal levels of La3d, Co2p, and 01s. The LaCoOa displays one peak for Co 2ps/2 centered at 781.39 eV, which is assigned to Co . Lanthanum for 4ds/2 is centered at 104.59 eV, which according to Hueso et al. [6] belongs to the lattice of the perovskite structure. 

Data relative to the O Is indicate one peak at 531.19 eV, which is assigned to the oxygen of hydroxide or carbonate species [5]. These carbonate ion structures are present at the surface due to the carbonation of the La cations [6]. 

Schmal et al. [5] analyzed results of perovskite under different treatments and showed that the binding energy of the different oxygen species on the surface is associated species such as oxygen in the perovskite lattice, segregated oxides, and carbonates and oxygen below state coordination. 

The quantification of surface species, taking into account the area of each peak of the components and sensitivity factors of each chemical species, is presented in 

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The physicochemical properties of carbon are highly dependent on its surface structure and chemical composition [66—68], The type and content of surface species, particle shape and size, pore-size distribution, BET surface area and pore-opening are of critical importance in the use of carbons as anode material. These properties have a major influence on (9IR, reversible capacity <2R, and the rate capability and safety of the battery. The surface chemical composition depends on the raw materials (carbon precursors), the production process, and the history of the carbon. Surface groups containing H, O, S, N, P, halogens, and other elements have been identified on carbon blacks [66, 67]. There is also ash on the surface of carbon and this typically contains Ca, Si, Fe, Al, and V. Ash and acidic oxides enhance the adsorption of the more polar compounds and electrolytes [66]. 

An obvious limitation to the use of bulk analysis studies is the direct result of sample heterogeneity. Not only do aerosol samples show wide variability in the physico-chemical characteristics of different particles, but even a single airborne particle may be highly heterogeneous. With regard to the latter, the surface chemical composition of a particle may bear little resemblance to that of its interior (11-14). 

Overall the surface chemical composition of the reinforcing fibers or the adherends is chemically quite different from the bulk composition of these materials. Specific interactions between epoxies and these surfaces without cognizance of the different surface chemistries can lead to erroneous conclusions about the epoxy-surface bonding or interphase structure. 

Over the past 10 years a multitude of new techniques has been developed to permit characterization of catalyst surfaces on the atomic scale. Low-energy electron diffraction (LEED) can determine the atomic surface structure of the topmost layer of the clean catalyst or of the adsorbed intermediate (7). Auger electron spectroscopy (2) (AES) and other electron spectroscopy techniques (X-ray photoelectron, ultraviolet photoelectron, electron loss spectroscopies, etc.) can be used to determine the chemical composition of the surface with the sensitivity of 1% of a monolayer (approximately 1013 atoms/cm2). In addition to qualitative and quantitative chemical analysis of the surface layer, electron spectroscopy can also be utilized to determine the valency of surface atoms and the nature of the surface chemical bond. These are static techniques, but by using a suitable apparatus, which will be described later, one can monitor the atomic structure and composition during catalytic reactions at low pressures (< 10-4 Torr). As a result, we can determine reaction rates and product distributions in catalytic surface reactions as a function of surface structure and surface chemical composition. These relations permit the exploration of the mechanistic details of catalysis on the molecular level to optimize catalyst preparation and to build new catalyst systems by employing the knowledge gained. 

Studies to correlate the reactivity and the surface structure and composition of platinum surfaces indicate that the active platinum crystal surface must be heterogeneous. The heterogeneity involves the presence of various atomic sites that are distinguishable by their number of nearest neighbors (atoms in terraces, steps, and kinks), and also variation in surface chemical composition. A model that depicts the active platinum surface is shown schematically in Fig. 28. Part of the surface is covered with a partially de-... 

The surface characteristics of reworked substrates and several rework processes are described later in several tables and the discussion. The substrate condition following the rework process is characterized by the results of three tests ESCA or XPS [19] surface chemical composition spectra, actual lithographic resist pattern lift testing [2, 6], and water droplet contact angle measurement, 0HjO [3]. 

The surface chemical composition of InP as a function of thermal cleaning temperature was studied by Cheng, et al. (19), also using AES. They used an arsenic molecular beam and temperature of about 500 C to clean a freshly oxide passivated InP. The surface oxides are replaced by arsenic oxides which then vaporize at these temperatures. An atomically flat and carbon contamination free surface was obtained, as monitored in situ with AES and RHEED OJ). 

Core - excitations are created, usually by 1 to 10-keV incident electrons Auger electrons of characteristic energies are emitted through a two - electron process as excited atoms decay to their ground state. AES gives information on the near - surface chemical composition. 

Ions and ionized clusters ejected from a surface during ion bombardment are detected with a mass spectrometer. Surface chemical composition and some information on bonding can be extracted from SIMS ion fragment distributions. 

The surface chemical composition plays an important role in STM imaging of metal surfaces. It is a well-known fact in STM experiments that... 

XPS data of surface chemical compositions and elemental dispersion factors... 

Surface chemical composition is controlled by Time-of-Flight Secondary Ion Mass Analysis (ToF-SIMS) and X-ray Photoelectron Spectroscopy (XPS).1 The analysis under ultra-high vacuum (UHV) conditions allows characterization... 

Fig. 8. The XPS survey scan spectra of the changes in the surface chemical compositions through the micropatterning process.

In this study, we have attempted to obtain a detailed, quantitative estimate of the surface chemical composition of two commercially available polyurethanes, i.e., Biomer and Avcothane, which have demonstrated a reasonable degree of blood compatibility. For example, Avcothane has been used as an intraaortic balloon pump for post-operative patients (5). Biomer also has been successfully used for artificial heart components in calves (14). 

Figure 7. Surface chemical composition—depth profile of Avothane. (O) Based on 1710 cm 1 based on 1600 cm 1, (a) The calibrated soft-segment content in air surface/substrate surface, (b) the calibrated silicone polymer content in air surface/substrate surface.

Table 6 Dispersion of Pd/C Catalysts Prepared by Supporting Pd(NH3)4(N03)2 on Carbons with Different Surface Chemical Composition Followed by Reduction in H2 at 150°C... 

In vivo, living cells constantly communicate with their surroundings. The interaction between the cells and the extracellular microenvironment regulates cell behavior. With nano and microfabrication techniques, researchers are now able to control cell functions and responses through precise manipulation over the physical and chemical environment around a cell, such as the surface chemical composition and topology of the substrate, the medium composition, and the cellular microenvironment [69],... 

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