Focused electron beam induced deposition (FEBID) is a versatile direct-write approach to produce nanostructures from organometallic precursor molecules. Ideally, the material is deposited only when precursors interact with and are dissociated by the impinging electrons so that the process is spatially defined by the electron beam. In reality, however, thermal surface reactions as known from chemical vapor deposition can also contribute to the dissociation of the precursors. They often produce material with higher purity but can also impair the spatial selectivity of the electron-induced deposit growth. This work aims at an approach to suppress such thermal chemistry and to re-enable it within an area defined by the electron beam. We have, thus, used a surface science approach to study the inhibition of autocatalytic growth (AG) of Fe from Fe(CO)5 by NH3 and the reactivation of AG on the surface by electron irradiation. The experiments were performed under ultrahigh vacuum conditions using thermal desorption spectrometry to characterize adsorption and reactivity of Fe(CO)5 on Fe seed layers that were prepared by dosing Fe(CO)5 during electron irradiation of the entire sample surface (referred to as EBID herein). Auger electron spectroscopy was used to monitor deposit growth and to reveal the potential inhibition of AG by NH3 as well as the reactivation of the surface by electron irradiation. The results show that adsorption of NH3 slows down AG on deposits prepared by EBID but not on Fe layers produced by AG. Electron irradiation after adsorption of NH3 reactivates the surface and thus re-establishes AG. We propose that co-injection of NH3 during FEBID from Fe(CO)5 could be a viable strategy to suppress unwanted AG contributions and, therefore, enhance the spatial control of the deposition process.