PRIMARY CONSIDERATIONS FOR IMAGE-ENHANCEMENT IN HIGH-PRESSURE SCANNING ELECTRON-MICROSCOPY .1. ELECTRON-BEAM SCATTERING AND CONTRAST

The mechanisms of electron beam scattering are examined to evaluate its effect on contrast and resolution in high‐pressure scanning electron microscopy (SEM) techniques reported in the literature, such as moist‐environment ambient‐temperature SEM (MEATSEM) or environmental SEM (ESEM). The elastic and inelastic scattering cross‐sections for nitrogen are calculated in the energy range 5–25 keV. The results for nitrogen are verified by measuring the ionization efficiency, and measurements are also made for water vapour. The effect of the scattered beam on the image contrast was assessed and checked experimentally for a step contrast function at 20 kV beam voltage. A considerable degree of beam scattering can be tolerated in high‐pressure SEM operation without a significant degradation in resolution. The image formation and detection techniques in high‐pressure SEM are considered in detail in the accompanying paper. 1990 Blackwell Science Ltd