Nitrogen ionization cross section by electron impact

A. P. L. BERTOL; P. PÉREZ; J. TRINCAVELLI; G. CASTELLANO; R. HINRICHS; M. A. Z. VASCONCELLOS

Gramado

Congreso; 13th International Conference on Particle Induced X-ray Emission; 2013

UFRGS, Brasil

The electron impact ionization cross sections (σ) of light elements were recently reviewed, however the developed models were based on data from the early nineteen-seventies that had used varied experimental setups, e.g. gaseous samples, or organic films of nucleic acid bases sublimated on thin carbon films mounted on TEM copper grids. More recently the σ of heavier elements have been determined with thin mono-elemental films deposited on substrates. It has been shown that the influence of chemical bonding on the s values is negligible, so the ionization cross section can also be experimentally determined measuring the characteristic X-ray spectrum emitted by a thin compound film containing the desired element (e.g. nitrides or oxides). In this work the nitrogen ionization cross section was determined using films of AlN, Si3N4, TiN, and FeN with 10 nm thickness, deposited by magnetron sputtering (AJA International model ATC, ORION 8 UHV, LCN, Instituto de Física of Univ. Federal do Rio Grande do Sul, Brasil) on carbon planchets. The mass thicknesses of the films were determined using Rutherford backscattering spectrometry (RBS) in a 3MeV ion accelerator (High Voltage Engineering, Tandetron 3MV in the Laboratório de Implantação Iônica, IF-UFRGS, Brasil). Nitrogen X-ray spectra were acquired in an electron microprobe (JEOL JXA 8230 in the Laboratorio de Microscopía Electrónica y Análisis por Rayos X of the Univ. Nacional de Córdoba, Argentina) equipped with a wavelength dispersive spectrometer (WDS) using a synthetic crystal (LDE1) with 2d≈60 Å. The spectra were measured at beam energies of 1.0, 1.2, 1.5, 2.0, 3.0, 4.0, and 5.0 keV. The spectrometer efficiency was determined comparing the WDS and EDS spectra of the bremsstrahlung generated on an aluminum substrate when irradiated with 15 keV electrons with simulations using the PENELOPE software. The obtained nitrogen ionization cross sections were compared with the old experimental data sets, and with recent semi-empirical and theoretical models.