Electron background

Figure 5-13. Low binding energy Purl of Ihe Me I UPS spectra ol DHPPV recorded during successive" deposition of calcium. The inset shows the fully doped (one Ca atom per monomer) DltPPV with a simple estimate of the inelastic electron background to emphasize the calcium-induced structures (lixnn Ret. lfifip.

Finally, the width of the total UPS spectrum may be used to obtain a reasonable estimate of the work function of the solid sample under consideration49. The energy of the intensity cut-off of the secondary electron background in the UPS spectrum is... 

Electron induced Auger Electron Spectroscopy (EAES) makes use of high-energy electrons to remove core electrons via impact-ionization. However, in many instances the utility of EAES is limited by problems associated with the large secondary electron background and the lack of surface specificity inherent in the EAES excitation process [2, 8]. 

This is the classical ion chromatography detector and measures the eluate conductivity, which is proportional to ionic sample concentration (provided that the cell is suitably constructed). Its sensitivity decreases as the specific conductivity of the mobile phase increases. The active cell volume of 2 gl is very small. Good conductivity detectors have automatic temperature compensation (conductivity is highly temperature-dependent) and electronic background conductivity suppression. The linear range is not large. 

Indicator-mediated optrodes frequently have an optical isolation at the fiber tip to prevent ambient light and sample from interfering in the optical system, and a fairly constant tip chemistry with its almost invariable refractive index (see Figure 18-11). However, as with plain fiber sensors, additional discriminations such as pulsed excitation plus electronic background subtraction or sequential excitation are useful techniques for improving selectivity. 

PAES (positron annihilation Auger electron spectroscopy) is another technique for producing true AES peak shapes that are free of the secondary electron background. PAES is identical to conventional Auger electron spectroscopy except that the sample excitation is done with a low energy beam of positrons rather than a higher energy beam of electrons. 

Very similar tendencies can be observed in the case of surface studies. Now, the basics are well-known, which provides the possibility to investigate complicated systems. Defects near the surface are studied in ion implanted MgO (van Huis et al. 2001), in BF2 implanted Si (Akahane et al. 2001), and in bioactive ceramic coatings (Harting et al. 2001). As regards beams, both their efficiency and their electronic background have been improved greatly in recent years. Due to this development, new methods become available for everyday practice. Although most of these methods were worked out and some kinds of equipment buQt more than 20 years ago, they are new in the sense that now they are not exotic possibilities but useful spectroscopic methods. 

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