Site-Selective Deposition of Silica Nanoframes and Nanocages onto Faceted Gold Nanostructures Using a Primer-free Tetraethyl Orthosilicate Synthesis.

Abstract

The Stöber method for forming spherical silica colloids is well-established as one of the pillars of colloidal synthesis. In a modified form, it has been extensively used to deposit both porous and protective shells over metal nanomaterials. Current best-practice techniques require that the vitreophobic surface of metal nanoparticles be primed with a surface ligand to promote silica deposition. Although such techniques have proved highly successful in forming core-shell configurations, the site-selective deposition of silica onto preselected areas of faceted metal nanostructures has proved far more challenging. Herein, a primer-free TEOS-based synthesis is demonstrated that is capable of forming architecturally complex nanoframes and nanocages on the pristine surfaces of faceted gold nanostructures. The devised synthesis overcomes vitreophobicity using elevated TEOS concentrations that trigger silica nucleation along the low-coordination sites where gold facets meet. Continued deposition sees the emergence of a well-connected frame followed by the lateral infilling of the openings formed over gold facets. With growth readily terminated at any point in this sequence, the synthesis distinguishes itself in being able to achieve patterned and tunable silica depositions expressing interfaces that are uncorrupted by primers. The so-formed structures are demonstrated as template materials capable of asserting high-level control over synthesis and assembly processes by using the deposited silica as a mask that deactivates selected areas against these processes while allowing them to proceed elsewhere. The work, hence, extends the capabilities and versatility of TEOS-based syntheses and provides pathways for forming multicomponent nanostructures and nanoassemblies with structurally engineered properties.