Beam-based analysis

MICROSTRUCTURE AND PRESUMPTIONS FROM BEAM-BASED ANALYSIS... 

Ion beam spectrochemical analysis (IBSCA) is a sputtering-based surface analytical technique similar to SIMS/SNMS. In IBSCA the radiation emitted by excited sputtered secondary neutrals or ions is detected. IBSCA was developed parallel to SIMS in the nineteen-sixties and early nineteen-seventies [4.246, 4.247]. It is also known... 

With respect to the practical considerations of gas flow and vacuum requirements, the PHPMS experiment might, upon cursory consideration, appear to be easily extended into the VHP region. That is, several MS-based analysis techniques routinely use ion source pressures of 1 atm. However, when an attempt to increase the pressure within a PHPMS ion source is made, the factors that do become problematic are those related to the subtle principles on which the method is based. Most importantly, the PHPMS method requires that the fundamental mode of diffusion be quickly established within the ion source after each e-beam pulse, so that all ions are transported to the walls in accordance with a simple first-order rate law while the IM reactions of interest are occurring. This ensures that a constant relationship exists between the ion density in the cell and the detected ion signal. The rates of the IM reactions can then be quantitatively determined from the observed time dependencies of the reactant ion signal because the contribution of diffusion to the time dependencies are well known and easily accounted for. 

A closed loop optimization experiment was presented in order to investigate the ability to control the ionization of NaK clusters in a molecular beam. The analysis of the optimized pulse shows that the maximum intensity of the ion signal was obtained with a pulse structure containing intensity maxima separated by a multiple of half vibrational periods. The proposed simple model in order to explain the pulse structure is based on previously performed pump-probe experiments [6]. 

Bimodal or not bimodal—critical comments Is the bimodal distribution as observed by beam based positron lifetime analysis (BPALS) real or a systematic effect of the data analysis To date the answer cannot be given with certainty. Arguments could be made why such a distribution is not observed by SAXS and is observed by BPALS in data shown here [62], and in work by Gidley et al.[46] Positrons are implanted at specific depths and only after measuring at different mean depth can one... 

The application of laser Doppler velocimetry (LDV) to measure the electrophoretic mobility n of charged colloidal particles is known as laser Doppler electrophoresis (LDE). In a typical LDE experiment, an applied electric field drives the collective motion of charged colloidal particles. The particles pass through an interference pattern created by a dual-beam experimental setup (Section III.A.2). The collective electrophoretic velocity of the particles is then determined via intensity- or spectrum-based analysis of the scattered light, and the electrophoretic mobility n is calculated by dividing the velocity by the applied electric field strength. 

In addition to laser beam- or ion beam-based methods, other matrix-free-based methods using a gas/liquid jetstream can also be used for desorption and ionization of compounds from the sample surface. This is the case of the DESI method under ambient conditions. DESI has very recently started to be explored for the analysis of small compounds imaging on intact surfaces (88). In contrast to MALDI and SIMS in which the sample must be confined (in most cases) in a high-vacuum region of the instrument, in DESI-IMS the... 

Microwave measurements of uracil in a heated cell suggested the diketo form as the most abundant [54]. Brown et al. reported the first microwave measurements in a seeded molecular beam and also concluded that the diketo form was predominant [55]. Viant et al. reported the first rotationaUy resolved gas phase IR spectra of uracil [28]. This work employed a slit nozzle, an IR diode laser, and a multipass arrangement to obtain high resolution IR absorption spectra of the out-of-phase V(, C2—0, 4=0) stretching vibration. The rotational analysis unambiguously assigned the species to the diketo tautomer. Brown et al. also observed the diketo form of thymine in a seeded molecular beam, based on the hyperfine structure in the 14440-133,11 transition [56]. 

Mass spectra are similarly meant to complement existing data bases. Mass spectra are very suitable to identify additives in solvent extracts of food contact polymers. For substances that can be analysed by GC the mass spectra were measured on two GC-MS systems to generate classical electron-impact spectra. However many additives cannot be analysed by GC for reasons of e.g. low volatility or thermal instability. For these substances the rapidly developing technique of LC-MS is suitable. A limitation of current LC-MS instrumentation is that most ionisation interfaces do not give consistent and library-searchable spectra. One exception to this is the particle-beam interface which gives classical electron-impact spectra. So for additives that could not be analysed by GC, then direct source injection or flow-injection particle beam MS analysis was applied. These spectra were recorded twice in the same laboratory (separated by several weeks) to check for consistency. 

SAM is a technique that can sample extremely small volumes of material (probably the smallest of any technique without the need for extensive sample preparation) and for this reason the choice of sample and the manner in which the analysis is carried out is extremely important. As with any electron microscopy-based analysis method, the need to acquire data from a representative sample of the specimen must be uppermost in the mind of the analyst. As SAM is an electron beam technique it is really only applicable to conductors or semiconductors, a useful guide being that if the specimen can be imaged in an SEM without sample charging SAM will be possible. For these reasons the role of AES/SAM in adhesion studies is restricted to the analysis of metallic substrates and pretreatment layers. There are ways in which it is possible to apply the technique to insulators (Baer et al. 2010) but analysis of polymers by AES is not practicable the usual approach being to use XPS or ToF-SIMS. 

In the BS and ISO methods, additionally an experimental compliance and a corrected beam theory analysis are specified for the determination of Qc- The experimental compliance method is based on Berry s method (Berry 1960) and is given by ... 

The subscript v is attached to both of these intensities as a reminder that the foregoing analysis is based on the assumption of vertical polarization for the incident light beam. The ratio of these intensities gives the fraction of light scattered per molecule by vertically polarized light ... 

Edx is based on the emission of x-rays with energies characteristic of the atom from which they originate in Heu of secondary electron emission. Thus, this technique can be used to provide elemental information about the sample. In the sem, this process is stimulated by the incident primary beam of electrons. As will be discussed below, this process is also the basis of essentially the same technique but performed in an electron spectrometer. When carried out this way, the technique is known as electron microprobe analysis (ema). 

Electron Microprobe A.na.Iysis, Electron microprobe analysis (ema) is a technique based on x-ray fluorescence from atoms in the near-surface region of a material stimulated by a focused beam of high energy electrons (7—9,30). Essentially, this method is based on electron-induced x-ray emission as opposed to x-ray-induced x-ray emission, which forms the basis of conventional x-ray fluorescence (xrf) spectroscopy (31). The microprobe form of this x-ray fluorescence spectroscopy was first developed by Castaing in 1951 (32), and today is a mature technique. Primary beam electrons with energies of 10—30 keV are used and sample the material to a depth on the order of 1 pm. X-rays from all elements with the exception of H, He, and Li can be detected. 

Transmission electron microscopy (tern) is used to analyze the stmcture of crystals, such as distinguishing between amorphous siUcon dioxide and crystalline quartz. The technique is based on the phenomenon that crystalline materials are ordered arrays that scatter waves coherently. A crystalline material diffracts a beam in such a way that discrete spots can be detected on a photographic plate, whereas an amorphous substrate produces diffuse rings. Tern is also used in an imaging mode to produce images of substrate grain stmctures. Tern requires samples that are very thin (10—50 nm) sections, and is a destmctive as well as time-consuming method of analysis. 

All the early calculations were based on simple beam analysis. The method was improved when the summation of moments was introduced by Myklestead [5] and Prohl [6],... 

Cathodoluminescence (CL), i.e., the emission of light as the result of electron-beam bombardment, was first reported in the middle of the nineteenth century in experiments in evacuated glass tubes. The tubes were found to emit light when an electron beam (cathode ray) struck the glass, and subsequendy this phenomenon led to the discovery of the electron. Currendy, cathodoluminescence is widely used in cathode-ray tube-based (CRT) instruments (e.g., oscilloscopes, television and computer terminals) and in electron microscope fluorescent screens. With the developments of electron microscopy techniques (see the articles on SEM, STEM and TEM) in the last several decades, CL microscopy and spectroscopy have emerged as powerfirl tools for the microcharacterization of the electronic propenies of luminescent materials, attaining spatial resolutions on the order of 1 pm and less. Major applications of CL analysis techniques include ... 

Electron Probe X-Ray Microanalysis (EPMA) is a spatially resolved, quantitative elemental analysis technique based on the generation of characteristic X rays by a focused beam of energetic electrons. EPMA is used to measure the concentrations of elements (beryllium to the actinides) at levels as low as 100 parts per million (ppm) and to determine lateral distributions by mapping. The modern EPMA instrument consists of several key components ... 

The classical approach for determining the structures of crystalline materials is through diflfiaction methods, i.e.. X-ray, neutron-beam, and electron-beam techniques. Difiiaction data can be analyzed to yield the spatial arrangement of all the atoms in the crystal lattice. EXAFS provides a different approach to the analysis of atomic structure, based not on the diffraction of X rays by an array of atoms but rather upon the absorption of X rays by individual atoms in such an array. Herein lie the capabilities and limitations of EXAFS. 

Within the last 5—10 years PIXE, using protons and helium ions, has matured into a well-developed analysis technique with a variety of modes of operation. PIXE can provide quantitative, nondestructive, and fast analysis of essentially all elements. It is an ideal complement to other techniques (e.g., Rutherford backscattering) that are based on the spectroscopy of particles emitted during the interaction of MeV ion beams with the surface regions of materials, because... 

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