Compositional information

Considering existing microscopical techniques, one can find that non-destmctive information from the internal stmcture of an object in natural conditions can be obtained by transmission X-ray microscopy. Combination of X-ray transmission technique with tomographical reconstmction allows getting three-dimensional information about the internal microstmcture [1-3]. In this case any internal area can be reconstmcted as a set of flat cross sections which can be used to analyze the two- and three-dimensional morphological parameters [4]. For X-ray methods the contrast in the images is a mixed combination of density and compositional information. In some cases the compositional information can be separated from the density information [5]. Recently there has been a... 

Other techniques in which incident photons excite the surface to produce detected electrons are also Hsted in Table 1. X-ray photoelectron Spectroscopy (xps), which is also known as electron spectroscopy for chemical analysis (esca), is based on the use of x-rays which stimulate atomic core level electron ejection for elemental composition information. Ultraviolet photoelectron spectroscopy (ups) is similar but uses ultraviolet photons instead of x-rays to probe atomic valence level electrons. Photons are used to stimulate desorption of ions in photon stimulated ion angular distribution (psd). Inverse photoemission (ip) occurs when electrons incident on a surface result in photon emission which is then detected. 

Analysis of Surface Molecular Composition. Information about the molecular composition of the surface or interface may also be of interest. A variety of methods for elucidating the nature of the molecules that exist on a surface or within an interface exist. Techniques based on vibrational spectroscopy of molecules are the most common and include the electron-based method of high resolution electron energy loss spectroscopy (hreels), and the optical methods of ftir and Raman spectroscopy. These tools are tremendously powerful methods of analysis because not only does a molecule possess vibrational modes which are signatures of that molecule, but the energies of molecular vibrations are extremely sensitive to the chemical environment in which a molecule is found. Thus, these methods direcdy provide information about the chemistry of the surface or interface through the vibrations of molecules contained on the surface or within the interface. 

Polyester composition can be determined by hydrolytic depolymerization followed by gas chromatography (28) to analyze for monomers, comonomers, oligomers, and other components including side-reaction products (ie, DEG, vinyl groups, aldehydes), plasticizers, and finishes. Mass spectroscopy and infrared spectroscopy can provide valuable composition information, including end group analysis (47,101,102). X-ray fluorescence is commonly used to determine metals content of polymers, from sources including catalysts, delusterants, or tracer materials added for fiber identification purposes (28,102,103). 

Physical Composition Information and data on the physical composition of solid wastes including (1) identification of the individual components that make up industrial and municipal sohd wastes, (2) density of solid wastes, and (3) moisture content are presented below. 

Chemical Composition Information on the chemical composition of sohd wastes is important in evaluating alternative processing and recoveiy options. If solid wastes are to be used as fuel, the four most important properties to be known are ... 

Figure 5 Images of a thin region of an epitaxial film of Ge on Si grown by oxidation of Ge-implanted Si (a) conventional TEM phase contrast image with no compositional information and b) high-angle dark-field STEM image showing atomically sharp interface between Si and Ge. (Courtesy of S.J. Pennycook)...

The electron probe X-ray microanalyzer provides extraordinary power for measuring the elemental composition of solid matter with pm lateral spatial resolution. The spatial resolution, limited by the spread of the beam within the specimen, permits pg samples to be measured selectively, with elemental coverage from boron to the actinides. By incorporating the imaging capability of the SEM, the electron probe X-ray microanalyzer combines morphological and compositional information. 

In addition to elemental compositional information, RBS also can be used to study the structure of single-crystal samples. When a sample is channeled, the rows of atoms in the lattice are aligned parallel to the incident He ion beam. The bombard-... 

Various ion-optical tricks have to be used to compensate for the spread of energies of the extracted ions, which limit mass resolution unless corrected for. In the latest version of the atom probe (Cerezo et at. 1988), spatial as well as compositional information is gathered. The hole in the imaging screen is dispensed with and it is replaced by a position-sensitive screen that measures at each point on the screen the time of flight, and thus a compositional map with extremely high (virtually atomic) resolution is attained. Extremely sophisticated computer control is needed to obtain valid results. 

If listed toxic chemicals are present equal to or above the de minimis cut-off level, your supplier must identify the specific components as they appear in Table II and provide their percentage composition by weight in the mixture or product, tf your supplier maintains that the identity ot a toxic chemical is a trade secret, a generic identity that is structurally descriptive must be supplied on the notice. A maximum concentration level must be provided if your supplier contends that chemical composition information is a trade secret. In either case, you do not need to make a trade secret claim on behalf of your supplier (unless you consider your use of the proprietary mixture a trade secret). On Form R, identify the toxic chemical you are reporting according to its generic name provided in the notification. (See the instructions for Part III, Section 2 on page 18 for more information.) tf the listed chemical is present below the de minimis level, no notification is required. 

Select the detector. To acquire molecular weight distribution data, use a general detector such as a refractive index detector. To acquire structural or compositional information, employ a more selective detector such as an ultraviolet (UV) or infrared (IR) detector. Viscometric and light-scattering detectors facilitate more accurate molecular weight measurement when appropriate standards are not available. 

Variations in the composition of a copolymer can cause substantial differences in the properties of the copolymer. Compositional information about copolymers may be acquired using selective detectors. Figure 3.9 shows the separation of an ethylene-vinyl acetate (EVA) copolymer by FfPSEC using IR detectors. One IR detector monitors the vinyl acetate carbonyl at 5.75 /u,m, and the other IR detector monitors the total alkyl absorbance at 3.4 /cm. 

Even though it appears that the technology has not been adopted yet, it is expected that TOE MS will be useful to validate the power of the GC X GC separation experiment by proving the separate identities of the vast number of resolved peaks and so show that the analyst who does not use GC X GC is missing valuable chemical compositional information on their samples. In addition, it is just as significant to TOEMS that GC X GC becomes a widespread separation tool, since this will then provide a demand for the powerful capabilities of TOEMS for identification. The GC community must wait for this to be demonstrated, and those who are working in GC X GC development are convinced that the wait will be worth it ... 

Computer Techniques McLafferty (Ref 63) has pointed out that the usefulness of elemental composition information increases exponentially with increasing mass, since the number of elemental combinations with the same integral mass becomes larger. There are compilations of exact masses and elemental compositions available (Refs 12a, 13 18a). Spectral interpretation will be simplified in important ways if elemental compositions of all but, the smallest peaks are determined. Deriving the elemental compositions of several peaks in a spectrum is extremely laborious and time-consuming. However, with the availability of digital computers such tasks are readily performed. A modern data acquisition and reduction system with a dedicated online computer can determine peak centroids and areas for all peaks, locate reference peaks, interpolate between them to determine the exact masses of the unknown peaks, and find within minutes elemental compositions of all ions in a spectrum (Refs 28b 28c)... 

In POLYM the output data of KINREL are used with compositional information to calculate the number and mass average molecular masses (Rn and Rm, respectively) and number and end-group average functionalities (fp and fg> respectively) in the pre-gel region in all stages. In addition, the network characteristics such as sol fraction, mj, and the number of elastically active network chains per monomer (5), Ng, are calculated in the post-gel regime of stage 3. 

Dynamic SIMS, used for obtaining compositional information as a function of depth below the surface. With higher etch rates, the surface is eroded much more quickly than in static SIMS, and depth profiling can be achieved since each successive layer of atoms can be analysed as it is peeled away . 

There are three types of electron microscopes commonly used for microanalysis. These are the scanning electron microscope (SEM) with X-ray detectors, the electron probe microanalyser (EPMA), which is essentially a purpose built analytical microscope of the SEM type, and transmission microscopes (TEM and STEM) fitted with X-ray detectors. In a TEM, compositional information may also be obtained by... 

Quantitative Analysis. In its basic form, AES provides compositional information on a relatively large area ( 1 mm2 ) of surface, using a broad-focussed electron beam probe. Sufficient signal may be obtained in this way with a low incident electron flux, thus avoiding potential electron-induced modifications of the surface. 

Modern spectrometers only require electron beam currents in the range 0.1 lOnA and hence probe sizes of 20-200 nm may be readily achieved with thermionic sources and 5-15 nm with a FEG. Spatially resolved compositional information on heterogeneous samples may be obtained by means of the Scanning Auger Microprobe (SAM), which provides compositional maps of a surface by forming an image from the Auger electrons emitted by a particular element. 

There are two types of electron energy loss spectroscopy currently in use. The first of these is found in scanning transmission electron microscopes. As indicated in Figure 5.1, compositional information may be obtained in the TEM by measuring the energy loss of the inelastically scattered electrons transmitted through a thin specimen. 

In SAM the electron beam can be focussed to provide a spatial resolution of < 12 nm, and areas as small as a few micrometers square can be scanned, providing compositional information on heterogeneous samples. For example, the energy resolution is sufficient to distinguish the spectrum of elemental silicon from that of silicon in the form of its oxide, so that a contaminated area on a semiconductor device could be identified by overlaying the Auger maps of the two forms of silicon obtained from such a specimen. 

The strength of analytical TEM is that compositional information, images, and diffraction data can be simultaneously acquired from the same area of the specimen with a spatial resolution of < 1-2 nm. 

Gas chromatography-mass spectroscopy is used to obtain extensive compositional information on rubbers. It can identify minor components of the sample such as the breakdown products of the cure system and the antidegradants. 

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