Xenon incorporated thin films with potential use in cancer treatment, developed by plasma technique free vacuum pumping during deposition

Author(s)

Gustavo Alexandre Viana

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Física Gleb Wataghin
• Defense date: 2010-05-08

Examining board members

Francisco das Chagas Marques; Abner de Siervo; Lorena Pozzo; Márcia de Abreu Fantini; Monica de Mesquita Lacerda

• Advisor: Francisco das Chagas Marques

Abstract

In this PhD thesis a Sputtering and PECVD (Plasma Enhanced Chemical Vapor Deposition) deposition system, appropriated for deposition free of gas pumping along the procedure, was projected and built. Hydrogenated amorphous (a-C:H) with Diamond-Like carbon (DLC) and Polymer-Like carbon (PLC) structures were deposited by PECVD under different methane (CH4) flow rate. The properties of the films changes significantly as the CH4 flow rate decreases from high flow (~80 sccm) to zero flow (pumping free deposition). An increase in the deposition rate of the DLC (PLC) films by 83% (54%), accompanied by a fall of 44% (56%) of the CH4 volume consumed to deposited the films, was observed at CH4 flow rate of 3.9 sccm, compared to films deposited at high flow rate. For smaller CH4 flow rate, the deposition rate decreases due to H2 saturation of the deposition atmosphere. The optical gap (determined by uv-visible transmission spectroscopy) and hydrogen concentration (determined by FTIR) varies in a similar fashion for both series of films (DLC and PLC) as a function of CH4 flow rate. Electrical conductivity measurements revealed that the PLC films are always more insulating than the DLC films. The concentration of hydrogen (determined by FTIR) is much higher in PLC films. The behavior of the index of refraction and the stress as a function of CH4 flow rate, for both series of films, are quite different from each other. PLC films has very small stress and the index of refraction decreases as the CH4 decrease, while the opposite is observed for DLC films, which are very compressive stressed and the index of refraction increases in the same range. Visible Raman scattering, performed on the DLC films, shows an increase of the G peak position and ID/IG rate, as the CH4 decreases, indicating an increase in the sp2/sp3 ratio. Nanohardness measurements also show that the harder films (~20 GPa) are obtained at relatively low flow rate. Non-hydrogenated amorphous carbon films (a-C) were deposited by Sputtering a graphite target in argon (Ar) or xenon (Xe) atmosphere. Differently from the result observed in films deposited by PECVD, the highest deposition rate obtained by sputtering was under pumping free deposition (zero argon flow rate). In this case an increase of 70% in the deposition rate was obtained, accompanied by six order of magnitude drop of the gas consumption. All the depositions performed in Xe atmosphere were carried out in pumping free regime to reduce Xe consumption and also to determine the best deposition setup in order to acquire the higher incorporation on Xe into the a-C matrix. High concentration of xenon (3.6%) was obtained with an extremely low consumption of xenon gas. Optoelectronic and mechanical characterization were carried out in the films deposited by sputtering and revealed that their stress, index of refraction and optical gap are consistent with graphite-like carbon films (GLC). Thermal desorption spectroscopy, performed in Xe incorporated samples, allowed, for the first times, to the best of our knowledge, to determine the diffusion coefficient and the free diffusion energy (~19eV) of Xe atoms trapped into amorphous GLC matrix. Activation procedure followed by gamma counting spectroscopy, carried out in a-C:Xe films, confirm the isotopic transmutation ability of the stable 124Xe(0.1% of natural abundance), by thermal neutrons bombardment and electrons capture, to the radionuclide 125I, which is an element largely employed in anticancer treatment, like the prostate one, for example. Thus, based on the activation and gamma counting results, on the 125I therapeutic ability and the a-C hemo/biocompatibility, in this PhD thesis it is proposed a model for commercial clinical seeds, used in local anticancer treatment named Brachytherapy, based on the isotope 124Xe incorporated amorphous carbon film (i.e., a-C:124Xe), with appropriate dose and activity to this purpose (AU)