A p- or n-conductive semiconductor material comprises a compound of the general formula Pb1-A1x1A2x2. The method is characterized in that the threshold value is pregiven in dependence upon the signal of the exhaust-gas probe rearward of the catalytic converter. Possible configurations are generally V-shaped, may involve parallel or perpendicular recording geometry, and are conceptually similar to magnetoresistive or giantmagnetoresistive thin film transducers. As a result, a loss in matching due to the difference between the low-band signal negative path and the low-band signal positive path can be enough reduced, and the characteristic of a low-band signal balance amplifier can be enhanced. Vibrations and displacement errors in the base are filtered through two sets of isolation mounts operatively between the base and reference frame and between the reference frame and a projection frame of the projection system and therefore disturbance of the projection system is reduced. The boron ion stream has both vertical tilt and horizontal rotation components relative to the sidewalls andor the silicon device, to provide a better line of sight onto the sidewalls.