Conversion Electron Mossbauer

Conversion electron Mossbauer studies of compounds containing iron. F. J. Berry, Transition Met. Chem. (Weinheim, Ger.), 1979,4, 209-218 (60). 

Typical Mossbauer spectra for the fresh, reduced, carblded and used Fe/ZSM-5 system are shown in a composite Fig. 5. Similar spectra were obtained for the Fe-Co/ZSM-5 system. The product distribution for the F-T reaction, using the Fe and Fe-Co systems, are shown in Table 1. The gasoline range hydrocarbon yield increased from 75 to 94%, when the Fe-Co clusters were used in place of Fe only. In a typical CEMS (Conversion Electron Mossbauer Spectroscopy) of the Fe-Co system, no spectrum for 57pg vas observed even after one week from this. It was concluded that in the Fe-Co clusters Co was predominantly in the "mantle" and Fe species were In their "core," in the parlance of metallurgy/geophysics. This model Is sometimes referred to as the cherry model. 

Fig. 7.67 Conversion electron Mossbauer spectra of the 73 keV y-rays in Ir recored at 4.2 K using a metal source, (a, b) metallic iridium, 5 mg cm, (c, d) iridium dioxide, 5 and 1 mg cm , respectively. Measuring time about 10 h for spectra a-c and 20 h for spectrum d (from [308])...

Conversion electron Mossbauer spectroscopy (CEMS) measurements with back scattering geometry have the merit that spectra can be obtained from a sample with much less isotope content compared with transmission measurements. Another merit is that a sample, deposited on a thick substrate, could be measured, and that because of the limited escape depth of the conversion electrons, depth-selective surface studies are possible. The CEMS technique was found to be best applicable to specimens of 10-100 pg Au cm, i.e., about two orders of magnitudes thinner than required for measurements in transmission mode [443]. This way (1) very thin films of gold alloys, as well as laser- and in beam-modified surfaces in the submicrometers range of depth [443], and (2) metallic gold precipitates in implanted MgO crystals [444] were investigated. 

Fig. 6. Basic equipment for measuring a conversion electron Mossbauer spectrum.

It is noteworthy that a low-temperature apparatus has been described recently that allows y-ray and conversion electron Mossbauer spectroscopy measurements at the same time, in the temperature range from 10 K to room temperature (28). 

CEMS = conversion electron Mossbauer spectroscopy DFT = density functional theory EFG = electric field gradient EPR = electron paramagnetic resonance ESEEM = electron spin echo envelope modulation spectroscopy GTO = Gaussian-type orbitals hTH = human tyrosine hydroxylase MIMOS = miniaturized mossbauer spectrometer NFS = nuclear forward scattering NMR = nuclear magnetic resonance RFQ = rapid freeze quench SAM = S -adenosyl-L-methionine SCC = self-consistent charge STOs = slater-type orbitals TMP = tetramesitylporphyrin XAS = X-ray absorption spectroscopy. 

The Mossbauer-effect experiment can also be applied to the study of surfaces in the variation known as conversion electron Mossbauer spectroscopy (CEMS). Here, what is monitored as a function of incident y-ray energy is not absorption, but the emission of electrons through a process of internal conversion (i.e., as a byproduct of the absorption of Mossbauer y rays). Since the conversion electrons can only escape from the surface layers of the solid, data are selectively acquired for the surface region, arising from the Mossbauer effect in the (most commonly iron) atoms of the surface layers. The monitoring of emitted electrons results in a mirror image of the usual absorption spectrum. Transmission and CEM spectra of vivianite [Ee3(P04)2-8H20] are illustrated in Fig. 2.49 (after Tricker et al., 1979]. 

Jones, W., J. M. Thomas, R. K. Thorpe, and M. J. Tricker (1978). Conversion electron Mossbauer spectroscopy and the study of surfaee properties and reactions. Appl. Surf. Sci. 1, 388 07. 

Nolle G, Ullrich H, Muller JB, Hesse J (1983) A microprocessor controlled spectrometer for thermal scan Mossbauer spectroscopy. Nucl Instr Meth Phys Res 207 459-463 Nomura K, UjiMra Y, Vertes A (1996) Apphcations of conversion electron Mossbauer spectrometry (GEMS). J Radioanal Nucl Chem 202 103-199... 

We have also studied the photolysis of europium(III) oxalate by means of the conversion electron MOssbauer and ESR technique... 

Application of Depth-resolved Conversion Electron MOssbauer Spectroscopy to Photochemistry in the Solid Surface... 

The ordinary (or integral) conversion electron MOssbauer technique thus measures electrons scattered from the surface layer several thousand A deep irrespective of their energies. If we resolve the energy of the scattered electrons by coupling the conversion electron MOssbauer spectrometer with an electron spectrometer, the solid surface can be characterized into a thinner... 

Figure 3 demonstrates the electron spectrometer part of a depth-resolved conversion electron MOssbauer spectrometer specially designed for such measurements in our laboratory (10, 11). The electron spectrometer is of the cylindrical mirror type back-scattered K conversion electrons from resonantly excited Fe nuclei are resolved by the electrostatic field between the inner and outer cylinders (cylindrical mirror analyzer) and then detected by a ceramic semiconductor detector (ceratron). The electron energy spectra taken with this spectrometer indicate that peaks of 7.3-keV K conversion electrons, 6.3-keV KLM Auger electrons, 5.6-keV KLL Auger electrons, etc., can be resolved well, with energy resolution better than 4%. 

Fig, 3. The electron spectrometer part of the depth-resolved conversion electron MOssbauer spectrometer (10,11). 

Angle-resolved X-ray photoemission spectroscopy (3, 38, 39, 49, 50) Conversion electron Mossbauer spectroscopy (4, 52-55)... 

M.J. Tricker, J.M. Thomas, and A.P. Winterbottom. Conversion Electron Mossbauer Spectroscopy for the Study of Solid Surfaces. Surf. Sci. 45 601 (1974). 

Figure 10, Conversion-electron Mossbauer spectrum (293 K) of a Chinese bronze coin, Hsiang-fu Yuan-pao (65)...

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