Synthesis of structures ranging from nano- to microscale is of great practical importance in the field of nanosciences and engineering. In Liquid Phase Focused Electron Beam Induced Deposition (LP-FEBID), the state of the liquid phase—both its shape and composition—is the key to achieving nanomaterial synthesis with high growth rate and high resolution. The goal is complete control of deposit shape (including complex 3D and high aspect ratio structures).
Pure water-precursor based solutions lead to challenges in deposition of nanostructure. These include presence of higher concentrations of oxidizing species suppressing the growth rates of deposits and intrinsically thick (tens of micrometers) and spatially non-uniform (in lateral extent) films. Water-ammonia solvent based ultra-thin (sub-micron) films are the key to high resolution and spatially controlled nanostructure synthesis in LP-FEBID. Parasitic (off-target) deposition is mitigated in this approach by the unique redox chemistry of ammonia radiolysis, which produces a chemical “lens” effect for improved resolution and shape fidelity.
The addition of ammonia reduces the surface tension of the solution and increases substrate wetting. When a high energy, tightly focused e-beam penetrates through a very thin liquid layer with minimal scattering, the synthesis paradigm is altered, and the deposit growth is initiated at the substrate-solution interface via heterogeneous electrochemistry. This tight 1D confinement of the liquid phase enables precise position control and intrinsically strong attachment to the substrate. Additionally, the non-uniform distribution of charge due to e-beam electron transport causes the deposit to act as a non-equilibrium “virtual” electrode. Growth of such a structure does not follow conventional electrodeposition growth regime.