Radiolytic effects in organic compounds induced and analyzed by a 15 N beam
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M. Behar Instituto de Fisica, Universidade Federal Rio Grande do Sul, 90510 Porto Alegre, Brazil (Received 30 August 1993; accepted 23 February 1994)
Cd-arachidat in the form of Langmuir-Blodgett films and thick photoresist layers of AZ5412H have been exposed to 15N-ion beams. The physico-chemical state of these targets as a function of the 15N fluence has been monitored by the 15N nuclear reaction with the respective H component. In this way, radiolytic changes in H distribution and bonding have been measured. In particular, diffusion and desorption processes have quantitatively been followed up to fluences of about 1 X 1016 N/cm 2 at temperatures as low as 40 K. The correlated changes in H bonding, obtained by analyzing the concomitant Doppler widths as a function of the 15N fluence, consist of both decomposition and restoration of C - H and H - H molecular groups.
I. INTRODUCTION Polymer thin films have become a subject of increased interest because of their high applied potential in many fields of advanced microtechnology, in micromechanics, microelectronics, etc. Therefore, the need for suitable analyzing techniques has become more and more pronounced. As regards the analysis of H, all presently established methods for materials analysis either fail completely, e.g., AES and XPS, or have difficulties with sensitive and quantitative determination of H distribution in solids, e.g., ERDA, RBS, and SIMS. It has been more recently that the nuclear resonant reaction of 15N with : H at 6.385 MeV has become accepted as an excellent tool for H analysis; high depth resolution and sensitivity are combined with the valuable property of probing the H bonding through the Doppler effect. A strong Gaussian broadening, of the order of 10 keV (FWHM), of the Lorentzian linewidth of 1.86 keV is caused by the vibrational motions of the H atoms in the solid; the magnitude of the Doppler broadening depends on the magnitude and direction of the velocity of the vibrating H atoms, which in turn depends on the bonding properties. 1 " 3 Therefore, the 15N analysis can be used to obtain three different characteristics of the H subsystem of the material simultaneously: atomic concentration, depth distribution, and bonding arrangement. This combination of features is especially useful when dealing with polymers that are known to be highly unstable under ionizing radiation.4 They desorb H 2 , CH n , and other molecular species as a consequence of the bond-breaking action of the ionizing irradiation.
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J. Mater. Res., Vol. 9, No. 6, Jun 1994 Downloaded: 30 Mar 2015
In addition, rebonding of unsaturated valences occurs in the remaining bulk. Variations in radiation hardness exist for different combinations of polymer type, ion species, and target temperature. With the aim of studying all these radiolytic effects by using the 15N reaction as a powerful monitor, we have selected two different organic systems of widely varying initial conditions: (i) a thin film
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