Cetyltrimethylammonium bromide (CTAB)-stabilized low-aspect ratio gold nanorods have been synthesized using seed-mediated wet chemical approach. Freshly cleaved highly oriented pyrolytic graphite (HOPG) surface is used as asubstrate for the deposition of nanoparticles via the droplet drying technique. Owing to the presence of CTAB molecules in suspension, nanoparticles on the non-wetting HOPG surface get deposited in the form of a coffee-stain ring. Such deposits at various positions of the coffee-stain ring have been characterized by scanning helium ion microscopy (HIM) and atomic force microscopy (AFM). Besides the assembly of nanoparticles, AFM is specially employed to investigate the deposition of CTAB molecules. The deposition and distribution of nanoparticles are studied and quantified at various positions of thecoffee-stain ring. On flat HOPG terraces, HIM shows merely the deposits of the gold nanostructures whereas AFM reveals both nanoparticles and CTAB deposits over the surface. This research study primarily focused on the nanoparticle deposits within the coffee-stain ring formed over the non-wetting HOPG terraces.

Study of wetting and nonwetting surfaces is very significant in various fields of science. Stability of selfassembled wettable layers over any surface is vital in that respect. The generation and then detection of defect sites on such surfaces is also ominously important. In this study, self-assembled monolayers of PFDTS (1H,1H,2H,2H perfluorodecyltrichlorosilane) molecules on silicon-wafer have been created by vapour deposition method. Due to fluorinated tail of PFDTS molecule, the nature of surface will become hydrophobic. Such hydrophobic surface normally leaves no deposits, except at a single point over the surface. Defect sights on PFDTS region produces confined areas on the hydrophobic surface with different wettability. Such sights will facilitate narrowed deposition ofnanoparticles within the hydrophobic defects. These fluidic deposits will facilitate nanoscale interactions and drying capillaries to play their role within such regions. Hydrophobic regions without defects show clean surface with no deposition of nanoparticles, whereas close-packed gold nanorods have been observed within the confined defect regions on PFDTS.