Precursors for direct-write nanofabrication with electrons

Focused electron beam-induced deposition (FEBID) is a maskless, direct-write nanolithography approach for the growth of nanostructures. In recent years, significant progress has been made demonstrating highly controlled writing processes with complex nanostructure geometries and intricate methods of preparing inorganic deposits of sufficient purity for applications in materials science and condensed matter physics. For instance, fields of research include sensors, electrical contacts, magnetics, photonics etc. The deposition process itself is simple and highly complex at the same time. Interdisciplinary efforts are required to understand individual reaction paths in the molecule-electron interactions and the impact of several parameters governing the overall process that determines the material's composition. Since the deposition hinges on volatile precursors, a description of chemical aspects and potential avenues for the development of tailored precursor synthesis are described herein. Literature data are used to describe the process and the influence of the precursor constitution on the deposits' nature. Results on molecule-electron interactions in the gas phase as well as condensed precursor layers are compared to FEBID deposit's composition illustrating the benefits and shortcomings of these supporting investigations in explaining the precursor decomposition characteristics in FEBID processes. This is also associated with the need of understanding the role of deposition conditions and reporting as many details as possible in experimental sections, which is of utmost importance in order to ensure reproducibility of reported data in the FEBID community. Moreover, we outline the potential impact of the vacuum level and associated water content in the deposition equipment on the deposited material's composition, which should be a major contributor to the compositional variations being described in the literature. A few additional experiments are suggested to unravel the impact of this parameter enabling secondary reaction paths in the FEBID process initiated by water-molecule-electron interactions. Finally, we summarize the classes of precursors used for FEBID to date and add our thoughts on approaches how to choose new precursors for this direct-write technique.