Electron spatially-resolved measurement

In this section, we describe time-resolved, local in-situ measurements of chemical potentials /, ( , f) with solid galvanic cells. It seems as if the possibilities of this method have not yet been fully exploited. We note that the spatial resolution of the determination of composition is by far better than that of the chemical potential. The high spatial resolution is achieved by electron microbeam analysis, analytical transmission electron microscopy, and tunneling electron microscopy. Little progress, however, has been made in improving the spatial resolution of the determination of chemical potentials. The conventional application of solid galvanic cells in kinetics is completely analogous to the time-dependent (partial) pressure determination as explained in Section 16.2.2. Spatially resolved measurements are not possible in this way. 

Fundamentals. Movement of charged particles (e.g. an electronic current) causes a magnetic field. Very small fields can be detected with a SQUID." The small size of the sensitive elements in a SQUID allows spatially resolved measurements of magnetic fields down to a resolution of about 1 mm. 

Accordingly, an overpopulation of the argon metastable levels would explain both the overionization as well as the high electron number density in the ICP. Indeed, it may be that argon metastables act as ionizers, but at the same time are easily ionized [236]. This could explain the rather low interference caused by easily ionized elements, and the fact that ionic lines are excited very efficiently, despite the fact that their standard temperatures are much higher than the plasma temperatures. However, discrepancies are not encountered to such a great extent when the temperatures from the Saha equation are used in the calculations [237]. Nevertheless, a number of processes may be considered to predominate in well-defined zones of the plasma, as indicated by spatially resolved measurements of various plasma parameters [238]. 

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 technique of photoemission electron spectroscopy (PEEM) is a particularly attractive and important one for spatially resolved work function measurements, as both the Kelvin probe technique and UPS are integral methods with very poor ( mm) spatial resolution. The PEEM technique, pioneered in the area of catalysis by Ertl,72-74 Block75 76 and Imbihl,28 has been used successfully to study catalytic oscillatory phenomena on noble metal surfaces.74,75... 

Niu H, Houk RS (1994) Langmuir probe measurements of the ion extraction process in inductively coupled plasma mass spectrometry-I. Spatially resolved determination of electron density and electron temperature. Spectrochim Acta 498 1283-1303... 

Laser-induced fluorescence is a sensitive, spatially resolved technique for the detection and measurement of a variety of flame radicals. In order to obtain accurate number densities from such measurements, the observed excited state population must be related to total species population therefore the population distribution produced by the exciting laser radiation must be accurately predicted. At high laser intensities, the fluorescence signal saturates (1, 2, 3 ) and the population distribution in molecules becomes independent of laser intensity and much less dependent on the quenching atmosphere (4). Even at saturation, however, the steady state distribution is dependent on the ratio of the electronic quenching to rotational relaxation rates (4, 5, 6, 7). When steady state is not established, the distribution is a complicated function of state-to-state transfer rates. 

Bings N. H., Olschewski M. and Broekaert J. A. C. (1997) Two-dimensional spatially resolved excitation and rotational temperatures as well as electron number density measurements in capadtively coupled microwave plasmas using argon, nitrogen and air as working gases by spectroscopic methods, Spectrochim Acta, Part B 52 1965-1981. 

Pan, J., Han, J., Borchers, C.H., Konermann, L. (2008) Electron captrrre dissociation of electrosprayed protein ions for spatially resolved hydrogen exchange measurements. JAm Chem Soc, 130 (35), 11574-11575. 

Most of the spatially resolved analytical techniques involve probing the sample by exposing it to a flux of particles (photons, electrons, ions, neutrals) and simultaneously measuring the energy distribution of a specific class of emitted or scattered particles. 

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