STATIONARY AND ULTRASONIC NANOPARTICLE ASSEMBLY ON NOTABLE SURFACES

Abstract

Frequently used wettable (SiO[Formula: see text] and nonwettable highly oriented pyrolytic graphite (HOPG) surfaces have been investigated for the deposition and shape separation of gold nanorods and rod–sphere mixture using the droplet evaporation method. In this paper, we explore and compare the resulting assembly using immovable and ultrasonic systems. On HOPG, stable evaporation produces monolayer arrays of gold nanorods on the terraces whereas aligned arrays of nanorods at the step-edges of HOPG. However, isolated large islands of nanorods on the terraces of HOPG and aligned nanorods at the step-edges become chaotic under the ultrasonic deposition. Also besides gold nanorods, excess cetyltrimethylammonium bromide (CTAB) molecules in suspension are deposited on the terraces in the form of mono- and multilayers revealed by an atomic force microscope (AFM). Both stable as well as ultrasonic vibration techniques were employed on the rod–sphere mixture over the SiO2 substrate. Stable drying of a droplet showed order arrays of gold nanorods separated from nanospheres everywhere in the coffee-stain ring. The fascinating assembly has been observed for such suspension deposits obtained under ultrasonic vibrations. Aligned arrays of nanorods covered with CTAB surfactants have been sterically as well as osmotically depleted first nearly all CTAB-coated nanospheres and then self-assembled them with the similar geometries within the coffee-stain ring on the SiO2 surface. The same separation effect has been observed within the initial pinning as well as everywhere over the terraces of the HOPG.