2. IONIZATION SPECTROSCOPY EQUIPMENT

• 2.1. Electron spectrometer
• 2.2. Electron gun

The primary beam parameters (effective diameter, beam current ip and electron energy Ep) are substantially influencing the possibilities of the whole spectrometer. In particular, the minimal lateral dimensions of investigated areas of the sample are limited by the effective beam diameter. The majority of spectrometers operate with beam no larger than several micrometers.

The beam current ip limits the minimal beam diameter and determines the time t, required to record the IL with the given signal-to-noise ratio: . The electron guns of commercial AES spectrometers deliver ip = 0.1...1.0 microampers with accelerating voltage of Vp = 0.2...10.0 kV. This current is enough for recording of intensive ILs within the time of . It is desirable to increase the ip for decreasing of recording time and detection of less intensive ILs.

The primary electron energy Ep is of special importance in IS (paragraph 6.2). Usually in IS the Ep =200...1200 eV, which is substantially lower than standard values of Ep in commercial spectrometers. Lowering of Ep in commercial spectrometers decreases the beam current ip and increases its diameter above nominal value.

Look further: 3. IL DETECTION