A method of preparing large area patterned 2D arrays of uncapped gold (Au) nanoparticles has been developed. The pattern has been formed using self-assembly of uncapped Au nanoparticles. The Au nanoparticles were synthesized via toluene/water two phase systems using a reducing agent and colloidal solution of Au nanoparticles was produced. These nanoparticles have been prepared without using any kind of capping agent. Analysis by TEM showed discrete Au nanoparticles of 4 nm average diameter. AFM analysis also showed similar result. The TEM studies showed that these nanoparticles formed self-assembled coherent patterns with dimensions exceeding 500 nm. Spin coating on silicon substrate by suitably adjusting the speed can self-assemble these nanoparticles to lengths exceeding 1 𝜇m.

We report the synthesis and optical properties of compact and aligned ZnO nanorod arrays (dia, ∼ 50–200 nm) grown on a glass substrate with varying seed particle density. The suspension of ZnO nanoparticles (size, ∼ 15 nm) of various concentrations are used as seed layer for the growth of nanorod arrays via selfassembly of ZnO from solution. We studied the effect of various growth parameters (such as seeding density, microstructure of the seed layer) as well as the growth time on the growth and alignment of the nanorods. We find that the growth, areal density and alignment of the nanorods depend on the density of seed particles which can be controlled. It is observed that there is a critical density of the seed particles at which nanorod arrays show maximum preferred orientation along [002] direction. The minimum and maximum radius of the aligned nanorods synthesized by this method lie in the range 50–220 nm which depend on the seeding density and time of growth. These nanorods have a bandgap of 3.3 eV as in the case of bulk crystals and show emission in the UV region of the spectrum (∼ 400 nm) due to excitonic recombination and defect related emission in the visible region.