115 / 2020-01-29 21:58:00

Gold nanoparticles self-agglomeration on glass and Si wafer surfaces

The gold nanoparticles (AuNPs) attract much attention owing to the unique optical, electronic, and catalytic properties based on localized surface plasmon resonance (LSPR). Further progress in designing AuNPs-based devices depends on the ability to fabricate complex hybrid organometallic assemblies processing required optoelectronic properties.
In this work, we created an assembly of AuNPs interconnected with dithiol molecules. The main goal was to monitor the level of an optical signal from AuNPs dimers in the presence of the halo from the intrinsically agglomerated AuNPs. The AuNPs aqueous colloidal solution with AuNPs diameter of 17±2 nm was synthesized following the Turkevich protocol. At the first stage, the pre-coated with (3-aminopropyl)-triethoxysilane (APTES) glass slides and Si wafers were immersed in the solution of AuNPs. In the solution, WdV interaction of negatively charged core of AuNPs and positively charged –NH3+ terminal groups of APTES allows forming AuNPs monolayer on the surface. This monolayer remains stable after drying. During the second stage, the AuNPs on the wafers were modified with nona-1.9-dithiol and hexane-1,6-dithiol. The SEM and AFM revealed that already after the first stage, the monolayer contained not only single AuNPs but already some dimers, trimers, etc, appeared due to self-aggregation. After the secont stage, in addition to dimers formation, progressive enlargement of aggregates was detected. We have used different methods to characterize the monolayers. In brief, X-ray reflectivity and reciprocal space maps around the (000) reciprocal lattice point analysis allowed determining the features of morphology, such as thickness and roughness of the AuNPs assembly's deposited on different substrates. The correlation between the morphology of SAMs and the absorbance and reflectance spectral signals from single AuNPs and dimers in the presence of intrinsically formed agglomerates using FTIR, Vis-NIR and modulation - polarization spectroscopy methods was established. Excitation of different modes of LSPR: on single nanoparticles (520 nm), dimers (620 nm) and hybridized modes from agglomerates of nanoparticles with different shapes, nanoparticle amount, and nonlocal effects influence were monitored. Using of modulation of polarization states of light for LSPR excitation made it possible to register features of linear and phase anisotropy effects based on in-plane and out-plane resonances.