Control of the average spacing between aligned gold nanoparticles by varying the FIB dose

Abstract

This work presents a new method to align gold nanoparticles (Au NPs), based on three well-known techniques: self-assembled monolayer (SAM) formation, focused ion beam (FIB) lithography, and organo-metallic chemical vapour deposition (OMCVD). Silicon substrates are coated with CH₃-terminated silane SAMs as resists. A fine beam of Ga⁺ ions, applying different doses, damages/removes these SAMs to correspondingly form a pattern containing sets of lines. Atomic force microscopy (AFM) and time-of-flight secondary ion mass spectroscopy (ToF-SIMS) are used to study the SAM removal process. The FIB nano-lithographically patterned SAMs are re-filled with an SH-terminated silane SAM. An OMCVD process is carried out to grow Au NPs onto the SH-groups in the lines. The average spacing between the Au NPs is demonstrated to be controlled by varying the FIB dose. Scanning electron microscopy (SEM) image analysis indicates that the average spacing decreases exponentially with increasing the dose, up to a predefined threshold. In addition, the formation of OMCVD Au NPs spacing and its dose-dependence in the absence of the SH-terminated SAMs is studied.