Low energy electron-induced reactions of model compounds for nano-scale fabrication and for application in chemoradiotherapy

Abstract

The interaction of low-energy electrons (LEEs) with neutral molecules plays an important role in various applications. In focused electron beam induced deposition (FEBID), a direct-write 3D nanofabrication technique, a high-energy focused electron beam is used to induce nanostructured deposition from precursor molecules (usually organometallic complexes) adsorbed onto a surface. At the current stage, this technique faces some challenges in regard to deposit purity and resolution. These limitations are mainly attributed to the low-energy secondary electrons generated by the impact of the primary electron beam on the surface. They are emitted with a large spatial distribution and can initiate electron-induced reactions that lead to incomplete fragmentation of the precursor molecules. Low-energy electron interactions are expected to play an important role also in chemoradiotherapy, i.e., concomitant chemotherapy and radiotherapy. In this cancer treatment, radiosensitizing agents are used to sensitize cancer cells to radiation. It has been shown that LEEs, generated by the interaction of ionizing radiation with biological tissues, can interact with a radiosensitizer producing radicals that can induce DNA damage. In order to improve the performance of FEBID precursors and radiosensitizers, it is important to study the energy dependence of the electron-induced processes. Low-energy electrons (LEEs) can induce fragmentation through four distinct processes: dissociative electron attachment (DEA), dissociative ionization (DI), dipolar dissociation (DD) and neutral dissociation (ND). Low-energy electron interactions are commonly investigated in gas phase experiments, under single electron-molecule collision conditions, with crossed molecular/electron beam instruments. In this Ph.D. project, the LEE-induced decomposition of FEBID precursors and some model compounds for application in chemoradiotherapy was investigated in the gasphase, specifically focusing on DEA and DI processes. The FEBID precursors that have been selected for this work are (η 3 -C3H5)Ru(CO)3Br and cis-Pt(CO)2Br2. For (η 3 -C3H5)Ru(CO)3Br , an extensive DI study was conducted as a follow-up of previous studies of this compound. For cis-Pt(CO)2Br2, both DEA and DI were investigated, with more emphasis on DEA, and the results were compared with previous gas-phase DEA studies on cis-Pt(CO)2Cl2 and cis-Pt(NH3)2Cl2, with surface studies on cis-Pt(CO)2Cl2 and with FEBID experiments on cis-Pt(CO)2Br2 and cis-Pt(CO)2Cl2. With the aim of enhancing the susceptibility of radiosensitizers towards LEEs, extensive DEA studies on the model compounds pentafluorothiophenol, 2-fluorothiophenol and pentafluorobenzoic acid, were conducted, where we explored the perfluorination and neutral HF formation as potential means to promote DEA reactions. The results were compared with previous work on DEA to pentafluorophenol and benzoic acid.