Electron‐Beam‐Induced Deposition of Bimetallic Nanostructures from Bulk Liquids

Abstract

The fields of electron-beam-induced deposition (EBID) and pulse radiolysis have long been known to share a commonality where energetic particles, impinging on (or traversing though) condensed matter, cause chemical reactions in precursors. Further comparisons between these two techniques have been hampered as pulse radiolysis employs liquid-phase precursors, while EBID precursors are typically gases. Using a hybrid technique known as liquid-phase electron-beaminduced deposition (LP-EBID) we have investigated the application of well-known pulse radiolysis chemical kinetics to the LP-EBID process. We report that bimetallic deposits (AuAg and AuPt) produced with LP-EBID follow chemical kinetics found in pulse radiolysis studies, leading to predictable compositions. In addition, TEM results show the deposits are alloyed, consistent with high dose pulse radiolysis for similar materials.While previous results in LP-EBID have shown the successful deposition of metal nanostructures with high purity, [1][2][3] the chemical mechanism itself has received limited attention. It is likely that the mechanism shares similarities with both gas-phase EBID and pulse radiolysis. For instance, in pulse radiolysis, [4] aqueous solutions containing metal ion complexes are exposed to high-energy electrons, ions, or photons with megaelectron volt energy, resulting in suspended or otherwise randomly distributed nanoparticles over a large irradiated area. In EBID [5,6] the electron source is a relatively low-energy (keV) electron beam from a scanning electron microscope (SEM), allowing for site-specific patterning of nanoscale structures.While the methodologies for producing nanoscale structures differ, both techniques are thought to induce chemical reactions through the generation of secondary species, such as the solvated electron in pulse radiolysis and secondary electrons in EBID. Solvated electrons are well-known to act as reducing agents for the generation of metal clusters [7,8] and to cause damage in biological specimens such as DNA. [9] Similarly, secondary electrons with energies between 0-20 eV have been shown to bind to gas-phase EBID precursors, such as Pt(PF 3 ) 4[10] and Co(CO) 3 NO [11] leading to molecular dissociation.Since both pulse radiolysis and EBID have known mechanisms with secondary species, we hypothesize that similar mechanisms would be present in LP-EBID. As LP-EBID precursor solutions typically contain micro-to millimolar concentrations of ionic complexes, it is likely that primary electrons will react with H 2 O molecules to produce various radicals, including solvated electrons, rather than reacting directly with the ionic complexes. Indeed, here we demonstrate that established rate constants of reactions between solvated electrons and metal ions can be applied to the resulting LP-EBID nanostructures, resulting in an excellent fit to multiple precursor concentrations for both AuAg and AuPt. These results show that LP-EBID bears a strong similarity to pulse radiolysis, and furthermore that extant literature c...

Focused electron beam induced deposition meets materials science

“…This brief description shows an apparent conceptual similarity to 3D printing, in particular if one considers the 3D writing capabilities of FEBID. Even the use of "liquid ink" precursors has been pioneered by the Hastings group and holds great potential for metallic nanostructure fabrication with very decent writing speeds [26,27]. A closer look, however, reveals the intrinsic complexity of the FEBID process.…”

“…In this work, the influence of changes of the precursor pressure on the alloy composition was studied. Finally, we note that some work on bimetallic nanostructures, namely AuAg and AuPt, has been carried out by using liquid phase-electron beam induced deposition in the group of Todd Hastings [27].…”

In Situ Transmission Electron Microscopy Measurements of Ge Nanowire Synthesis with Liquid Metal Nanodroplets in Water

“…All materials irradiated by the electron beam (i.e., windows, solution, nanodroplets) release secondary electrons through scattering events with the primary beam. 44,52 These secondary electrons have an extremely short-range (∼5−10 nm) 53,54 but are capable of generating solvated electrons that can reduce species in solution. 41,43,55 The inferred faradaic current for GeO 2 reduction is roughly 2.5% of the incident primary electron beam density, a value roughly in agreement for the steady-state yield of secondary electron processes.…”

“…Although there are similarities to two separate types of phenomena, the data shown here are unlike anything ever reported in the in situ liquid TEM literature. Certainly the precedent for the electron beam in liquid TEM experiments to induce electrochemical reduction of species dissolved in solution is well established. ,− In fact, this premise was explicitly used here to generate liquid Ga and In nanodroplets directly in the liquid holder cell. However, this work makes clear that direct irradiation ( i .…”