Surface element composition

Analysis of Surface Elemental Composition. A very important class of surface analysis methods derives from the desire to understand what elements reside at the surface or in the near-surface region of a material. The most common techniques used for deterrnination of elemental composition are the electron spectroscopies in which electrons or x-rays are used to stimulate either electron or x-ray emission from the atoms in the surface (or near-surface region) of the sample. These electrons or x-rays are emitted with energies characteristic of the energy levels of the atoms from which they came, and therefore, contain elemental information about the surface. Only the most important electron spectroscopies will be discussed here, although an array of techniques based on either the excitation of surfaces with or the collection of electrons from the surface have been developed for the elucidation of specific information about surfaces and interfaces. 

Nittler, L. R. and 15 coauthors (2001) X-ray fluorescence measurements of the surface elemental composition of asteroid 433 Eros. Meteoritics and Planetary Science, 36, 1673-1695. 

XPS will aid in understanding specifically the surface of the black deposit covering pictographs in Little Lost River Cave in Idaho. This work will complement other bulk analyses carried out with pyrolysis-GC-MS and thermally assisted hydrolysis /methylation (THM)-GC-MS (75). The objectives of this project were to use XPS to qualitatively determine the surface elemental composition of the black residue semiquantitatively characterize the surface, for comparison with other surface-related materials and examine the relationship between the chemistry and depth by using Ar+ sputtering. This, then, will aid in validating the radiocarbon date obtained through plasma-chemical oxidation and accelerator mass spectrometry by Steelman et al. (5). 

In this paper the hydroxide concentration dependence of the rate of hydrogen production in SrTi03 systems (12) is discussed in light of surface analytical results. The surface elemental composition before and after illumination in various aqueous electrolytes has been monitored with Auger electron spectroscopy... 

The determination of the surface structure of solid is possible using a variety of experimental methods, the methods chosen being dependent on the specific information required. Information on surface elemental composition is also desirable. 

UPS, XPS (ESCA) 3 nm 0.1% Species, surface elemental composition, valency, chemical bond Li-U... 

If the incident ion has a mass of Mi and kinetic energy of Eq, and the ion backscattered at an angle 0 (relative to the direction of the incident ion) has an energy of Ei, the two-collision model allows the determination of the surface elemental composition based on the following equation ... 

Surface Elemental Composition and Surface Phase Diagrams... 

The recorded differences in adsorption capability indicate a different mechanism of interaction between the carbon surface and the ionic metal species pre.sent in the aqueous solution (aqua and hydroxy complexes, hydroxide ions, and electronegative complexes). To discover the state of the adsorbed. species, some independent measurements of the surface layer of adsorbent were carried out. The selected carbon samples were studied by the XPS method in powdered form following copper uptake (Figs. 42 and 43). Several peaks attributable to carbon, oxygen, nitrogen, and copper were present. The XPS survey spectra of the initial modified carbons (before adsorption) were discussed in the previous section. The surface elemental composition estimated from XPS data for modified D43/1 car-... 

The irreversible adsorption layer of aromatic species was investigated by means of a specially constructed UHV and electrochemistry system where surface structure is observed by low-energy electron diffraction (LEED), surface elemental composition and cleanliness are monitored by Auger spectroscopy (AES). The vibrational bonds of the adsorbed species is observed by high resolution electron energy loss spectroscopy (EELS). 

XPS (also known as electron spectroscopy for chemical analysis) and XAES provide not only the surface elemental composition but also reveal the oxida-... 

The surface elemental compositions of both the sulfur dioxide and allyl phenyl sulfone plasma treated samples were analyzed by a Perkin-Elmer PHI 5400 ESCA System with its packaged XPS software. The x-ray source was generated with an Mg anode energized at 15 kV and 300 W. The distance between the sample surface and the tip of the x-ray source anode was maintained constant at about 1.5 in. The aperture of the spherical capacitor electron energy analyzer was set at a diameter of 4 mm so that the area of the sample surface to be analyzed was about 1.3 mm in diameter. Both XPS survey and multiplex spectra of the plasma treated LDPE were collected at takeoff angles (0) of 10°, 30°, 45° and 75° with respect to the spherical capacitor electron energy analyzer, Angle-... 

Upon introduction in vivo, the interface between the delivery system and the biological tissue and/or fluid is critically important to the in vivo performance [5]. Accordingly, surface properties including surface chemical composition and surface area must be well characterized. X-ray photoelectron spectroscopy (XPS) is a widely used technique to obtain surface elemental composition, and Branauer, Emmett, and Teller (BET) measurement is used to provide information on surface area. Surface morphology is typically assessed via light, electron, and atomic force microscopy (AFM). The amorphous and crystalline nature of materials can be determined from X-ray diffraction (XRD) and density measurements. 

Various characterization methods both in vitro and in vivo can provide information to understand, predict, and improve the performance of drug delivery systems. Selection of methods depends on the material properties and their applications. Viscoelastic properties can be measured using both DMA and oscillatory shear rheometry. DSC is a most useful method of measuring thermal transitions. Various microscopic methods are available to obtain the microstrac-ture and shape of the materials. Amorphous and crystaUine materials have different packing patterns of molecules, and these properties can be determined from XRD or density measurements. Surface properties such as surface elemental composition and material porosity can be obtained from various spectroscopic methods as well as from BET measurements. The biocompatibility of the material can be determined from both in vitro and in vivo assays. In vitro dissolution testing can be utilized to correlate with the in vivo performance of polymeric drug delivery systems. All these characterization methods can provide valuable information... 

Corning borosilicate cover glass (2940, No. 1 1/2, 24 x 50mm, 0.16-0.19mm thickness) was used as substrate. As determined by ESCA, surface elemental compositions of this borosilicate glass were B — 2.3, Si = 28, O = 63, C = 4.4 atomic percentages, respectively. Minor components below 1 % were Na, Al. Zn, K, N, and Ti. 

A number of copolymers of MDE and PDE based DETOSU poly (ortho esters) were examined w ith XPS by De Matteis et al. (1993) and the surface elemental compositions were found to be in accord with the bulk compositions of the copolymers. 

Table 1. Surface elemental composition of ASS and selected treated samples determined by ED AX.

Li to Zn has been reported [56], In XPS, the sensitivity factors cover a relatively small scale (within one order of magnitude of one another). Either special reference materials can be used which allow accurate measurement of sensitivity factors or an offline compensation method is used [20]. Having a set of previously determined sensitivity factors allows one to determine the surface elemental composition of the surface layer. Measuring the relative peak intensities, and dividing them by appropriate sensitivity factors lead to the concentration of different elements on a surface. With good instrumental design and standards, one can obtain a percentage analysis of surface composition (better than 10%). 

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