Growth and characterization of gold nanoislands & quantum dots on marker-based SiO2/Si substrate for SEM resolution intercomparison studies

Abstract

A scanning electron microscope (SEM) is the powerhouse tool of nanoscience & nanotechnology and the high resolution is one of the important parameters that decide the instrument’s quality. The reference materials (RM) like gold nanoislands or tin spheres on carbon substrate separated by a nanogap are often used to get the practically attainable resolution of the SEM instrument. Such RM contains millions of gold nanoislands and nanogaps but all of these RMs are non-traceable. Hence the practically obtained high resolution of an SEM remains doubtful unless and until intercompared with traceable RM. The development of a new SEM resolution test specimen sample with localized markers for the identification of a traceable critical dimension of a nanogap on a user-friendly SiO2/Si or Si3N4/Si chip is reported here. First, thin films of gold with thickness < 5 nm (ultra-thin film) and of about 10 nm (thin film) were deposited on a pre-patterned marker SiO2/Si chip to form the gold nanoparticles (Au NPs) by thermal annealing technique. The high-resolution SEM images show the formation of gold quantum dots (Au QDs) (average particle diameter <D> ∼ (18 ± 1) nm and average gap between two particles <S> ∼ (6 ± 1) nm) and gold nano-islands (Au NIs) (<D> ∼ (101 ± 3) nm and <S> ∼ (104 ± 2) nm). FESEM images show densely packed nano-islands exhibiting spherical geometry which is explained using dewetting mechanism followed by Ostwald ripening and coalescence resulting formation of Au QDs and Au NPs. Further, these marker-based resolution test chips can be used in inter or intra-comparison studies due to pre-patterned markers. First-time development of QDs on marker chip gives access to a particular nanogap among the millions of nanogaps present on the substrate, this type of RM will be used for inter-laboratory comparison studies in the future.