Abstract. Mid-Proterozoic granulites in SW Sweden, having opaque minerals hematiteilmenite with minor magnetite, and occurring in an area with negative aeromagnetic anomalies, have strong and stable reversed natural remanent magnetization -9.2 A/m, with 100% remaining after demagnetization to 100 mT. Samples were characterized by optical microscopy, electron microprobe (EMP), transmission electron microscopy (TEM), and rockmagnetic measurements. Earliest oxide equilibrium was between grains of titanohematite and ferri-ilmenite at 650ø-600øC. Initial contacts were modified by many exsolution cycles.
Measurements of the electron range R, and the backscattering coefficient η and the secondary electron yield δ at normal and tilted incidence for different elements show characteristic differences for electron energies in the range of 0.5 to 5 keV, compared with energies larger than 5 keV. The backscattering coefficient does not increase monotonically with increasing atomic number; for example, the secondary electron yield shows a lesser increase with increasing tilt angle. This can be confirmed in back‐scattered electron (BSE) and secondary electron (SE) micrographs of test specimens.
The results are in rather good agreement with Monte Carlo simulations using elastic Mott cross‐sections and a continuous‐slowing‐down model with a Rao Sahib‐Wittry approach for the stopping power at low electron energies. Therefore, this method can be used to calculate quantities of BSE and SE emission, which need a larger experimental effort. Calculations of the angular distribution of BSEs show an increasing intensity with increasing atomic number at high takeoff angles than expected from a cosine law that describes the angular characteristics at high electron energies. When simulating the energy distribution of BSEs, the continuous‐slowing‐down model should be substituted by using an electron energy‐loss spectrum (EELS) that considers plasmon losses and inner‐shell ionizations individually (single‐scattering‐function model). The EELS can be approached via the theory for aluminium or from EELS spectra recorded in a transmission electron microscope for other elements.
Measurements of electron range Rα En of 1 to 10 keV electrons are obtained from transmission experiments with thin films of known mass thickness. In agreement with other authors the exponent n is lower than at higher electron energies.
The contrast thicknesses ( x k ) of thin carbon and platinum films have been measured in the transmission mode of a low-voltage scanning electron microscope for apertures of 40 and 100mrad and electron energies (E) between 1 and 30 keV. The measured values overlap with those previously measured for E ( 2 1 7 keV) in a transmission electron microscope. Differences in the decrease of x k with decreasing E between carbon and platinum agree with Wentzel-Kramer-Brillouin calculations of the elastic cross-sections. Knowing the value of x k allows the exponential decrease IX exp(-x/xk) in transmission with increasing massthickness (x = pt) of the specimen and the increasing gain of contrast for stained biological sections with decreasing electron energy to be calculated for brightfield and darkfield modes.
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