METHOD FOR LOW ATOMIC NUMBER SUB-MICRONIC FILM PRODUCTION FOR keV ELECTRON SCATTERING MEASUREMENTS

Attenuating mediums and targets made of sub-micron layers with low average atomic number (Low Z) and minimal surface density that decreases elastic scattering and absorption of radiation are required for many applications with low energy experiments in physics, biology and chemistry and can be used for surface studies, electron interactions with matter researches, radiation attenuation, etc.

This work describes the development and characterization of sub-micron Lexan polymer foils with low Z for two new IMFP (Inelastic Mean Free Path) estimation methods and validation experiments. 120÷240 nm Lexan layers were developed and fabricated from 1.56, wt.% solution by using Spin Coating on glass substrates.

The sub-micron layers were characterized by AFM and Interferometry, for thickness, roughness and levelness. Roughness found to be, overall 10 ± 1 nm rms, local 1.0 ÷ 2.4 nm rms, total thickness change within ± 7.5%.

To test the foil and its suitability for IMFP "Total Current Measurement" experiment, 177 nm Lexan foil was coated with 7 nm gold layer and irradiated under 1÷15 keV SEM electron beam.

The integral electron current attenuation was measured and same behavior as previous measurements on carbon film was observed, meaning, energy shift from inelastic scattering and typical attenuation form to a measured thickness. As the foil was well characterized, threshold values needed for the experiments were set. Foil durability was tested by attempt to penetrate it with the electron beam without success. Observation with HR SEM revealed no findings.

A first step of "Wide Spectrum" experiment was performed at ESRF. The spectrum on Lexan showed the signal peak, as well as the multi inelastic scattering peak (MIC peak) similar to previous measurements on carbon films.