Energy-dispersive spectroscopy

The electron-hole pairs, as the electric charge, are swept from the detector diode. A preamplifier collects the charge to produce an output of electrical pulse whose voltage amplitude is proportional to the X-ray photon energy. The energy resolution of the detector (R) in eV can be estimated. 

E is the energy of characteristic X-ray line and Fisa constant called the Fano factor, which has a value of 0.12 for Si(Li). rnoise, the electronic noise factor, plays an important role in the resolution. Reduction of the electronic noise will improve the resolution of the EDS detector. Thus, the Si(Li) diode and the preamplifier are mounted in a cylindrical column (the cryostat) so that they can operate at the temperature of liquid nitrogen (-196°C) in order to reduce the electrical noise and increase the signal-to-noise ratio. 

X-ray photons must pass through a window to reach the Si(Li) diode. This window is typically made of a light element, beryllium. Beryllium, like any material, will absorb X-ray photons, even though its absorption is weak. Thus, the sensitivity of the detector will be affected by the beryllium window. In order to reduce the photon absorption, the beryllium has to be as thin as possible, especially for detecting light elements of which the characteristic energies are on the order of 100 eV. The typical thickness of the beryllium window is about 10 ptm. 

All the early EDS systems were operated in a primary mode in which X-rays emitted from the X-ray tube irradiate the specimen direcdy. This had drawbacks because the X-rays could excite more photons than could be counted by the detector, because there is a maximum counting rate of photons for an energy detector. If the number of characteristic photons excited in the specimen is too great, a portion of photons may not be counted. Thus, the measured intensities may be lower than the actual emitted intensity of X-ray photons. The period during which the detector cannot respond to the number of photons correctly is called the dead time of the detector. The dead time is in the order of 0.5 x 10-7 seconds. 

a secondary mode of EDS was developed to overcome this intrinsic limitation of the detector when handling a large influx of photons. In the secondary mode, a selected pure element standard with absorption filters is placed in the optical path between the primary X-ray source and the specimen. The element standard only allows the X-ray photons in a selected range of energy (secondary photons) to strike the sample. Thus, in secondary photon radiation, the amount of photons emitted from the sample is controlled by preventing unwanted X-ray excitation of the specimen. 

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A scanning electron microscope can also be equipped with additional instmmentation for electron-excited x-ray analysis (9). In many systems, this is performed in the mode known as energy dispersive x-ray analysis (edx). Other common acronyms for this method are eds for energy dispersive spectroscopy or edax for energy dispersive analysis of x-rays. 

Internal surfaces were covered with a tan deposit layer up to 0.033 in. (0.084 cm) thick. The deposits were analyzed by energy-dispersive spectroscopy and were found to contain 24% calcium, 17% silicon, 16% zinc, 11% phosphorus, 7% magnesium, 2% each sodium, iron, and sulfur, 1% manganese, and 18% carbonate by weight. The porous corrosion product shown in Fig. 13.11B contained 93% copper, 3% zinc, 3% tin, and 1% iron. Traces of sulfur and aluminum were also found. Near external surfaces, up to 27% of the corrosion product was sulfur. 

Removal of deposits and corrosion products from internal surfaces revealed irregular metal loss. Additionally, surfaces in wasted areas showed patches of elemental copper (later confirmed by energy-dispersive spectroscopy) (Fig. 13.12). These denickelified areas were confined to regions showing metal loss. Microscopic analysis confirmed that dealloying, not just redeposition of copper onto the cupronickel from the acid bath used during deposit removal, had occurred. 

The incoming electron beam interacts with the sample to produce a number of signals that are subsequently detectable and useful for analysis. They are X-ray emission, which can be detected either by Energy Dispersive Spectroscopy, EDS, or by Wavelength Dispersive Spectroscopy, WDS visible or UV emission, which is known as Cathodoluminescence, CL and Auger Electron Emission, which is the basis of Auger Electron Spectroscopy discussed in Chapter 5. Finally, the incoming... 

Catalysts were characterized using SEM (Hitachi S-4800, operated at 15 keV for secondary electron imaging and energy dispersive spectroscopy (EDS)), XRD (Bruker D4 Endeavor with Cu K radiation operated at 40 kV and 40 mA), TEM (Tecnai S-20, operated at 200 keV) and temperature-programmed reduction (TPR). Table 1 lists BET surface area for the selected catalysts. 

In order to confirm the formation of nanodots, the fabricated nanodot arrays on a substrate were examined using energy dispersive spectroscopy (EDS). The EDS analysis of niobium oxide arrays on Si film before etching (Fig. 2(a)) was shown in Fig. 3(a). The Si peak as well as Nb and O peaks was observed because niobium oxide on Si film was so thin. 

Secondly, the characteristic X-rays, emitted as the electrons displaced from the inner shells of the atoms are replaced, can be detected by use of an energy-sensitive detector placed close to the specimen. An account of the application of both the energy dispersive spectroscopy (EDS) of the emitted X-rays and EELS to the... 

EPMA is a technique for chemically analysing small selected areas of solid samples, in which X-rays are excited by a focused electron beam. Spatial distribution of specific elements can be recorded as two-dimensional X-ray maps using either energy dispersive spectroscopy (EDS) or... 

FIGURE 11.64 Energy-dispersive spectroscopy light-element spectra acquired from (a) one of the small microcrystallites attached to NaCl after exposure to gaseous HNO, (see Fig. 11.630 and (b) an adjacent area of the NaCl crystal (adapted from Allen et al., 1996). 

Although a number of secondary minerals have been predicted to form in weathered CCB materials, few have been positively identified by physical characterization methods. Secondary phases in CCB materials may be difficult or impossible to characterize due to their low abundance and small particle size. Conventional mineral identification methods such as X-ray diffraction (XRD) analysis fail to identify secondary phases that are less than 1-5% by weight of the CCB or are X-ray amorphous. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM), coupled with energy dispersive spectroscopy (EDS), can often identify phases not seen by XRD. Additional analytical methods used to characterize trace secondary phases include infrared (IR) spectroscopy, electron microprobe (EMP) analysis, differential thermal analysis (DTA), and various synchrotron radiation techniques (e.g., micro-XRD, X-ray absorption near-eidge spectroscopy [XANES], X-ray absorption fine-structure [XAFSJ). 

Kamiya et al. [83] evaluated particulate contamination in 199 samples of admixed and un-admixed parenteral nutrition solution bags from 10 hospitals in Japan. Seven samples were used as controls since they had not been mixed with ampoules or vials (un-admixed samples). Size and number of particles were measured using a particle counter, and the identification of elements was carried out by scanning electron microscopy coupled to energy dispersion spectroscopy. The authors collected the residual volume of the samples (10-60 mL) after their usage. The results are presented in Table 40. 

FIGURE 19 Identification of two types of particles by scanning electron microscopy coupled to energy dispersion spectroscopy (a) suggests glass particles (b) suggests rubber particles [83]. 

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