ABSTRACT
The advancement of liquid phase electron/ion beam induced deposition has enabled an effective direct-write approach for functional nanostructure synthesis with the possibility of three-dimensional control of morphology. For formation of a metallic solid phase, the process employs ambient temperature, beam-guided, electrochemical reduction of precursor cations, resulting in rapid formation of structures, but with challenges for retention of resolution achievable via slower electron beam approaches. The possibility of spatial control of redox pathways via the use of water-ammonia solvents has opened avenues for improved nanostructure resolution without sacrificing the growth rate. In particular, ammonia enables "electrochemical lensing" in which a tightly confined and highly reducing environment is created locally to enable high resolution, rapid beam-directed nanostructure growth. We demonstrate this unique approach to high resolution synthesis through a combination of analysis and experiment.
ABSTRACT
Irradiation of a liquid solution generates solvated electrons and radiolysis products, which can lead to material deposition or etching. The chemical environment dictates the dominant reactions. Radiolysis-induced reactions in salt solutions have substantially different results in pure water versus water-ammonia, which extends the lifetime of solvated electrons. We investigate the interplay between transport and solution chemistry via the example of solid silver formation from e-beam irradiation of silver nitrate solutions in water and water-ammonia. The addition of ammonia results in the formation of a secondary ring-shaped deposit tens of micrometers in diameter (formed over tens of seconds) around the primary point of deposition (formed over milliseconds). Simulations uncover the relative importance of oxidizing and reducing reactions and transport effects. Our explanation of this behavior involves mechanisms beyond ammonia's role in extending solvated electron lifetimes.
