Bidisperse silica nanoparticles close-packed monolayer on silicon substrate by three step spin method

We present the studies on the structural properties of monolayer Bidisperse silica (SiO2) nanoparticles (BDS) on Silicon (Si-100) substrate using spin coating technique. The Bidisperse silica nanoparticle was synthesised by the modified sol-gel process. Nanoparticles on the substrate are generally assembled in non-close/close-packed monolayer (CPM) form. The CPM form is obtained by depositing the colloidal suspension onto the silicon substrate using complex techniques. Here we report an effective method for forming a monolayer of bidisperse silica nanoparticle by three step spin coating technique. The samples were prepared by mixing the monodisperse solutions of different particles size 40 and 100 nm diameters. The bidisperse silica nanoparticles were self-assembled on the silicon substrate forming a close-packed monolayer film. The scanning electron microscope images of bidisperse films provided in-depth film structure of the film. The maximum surface coverage obtained was around 70-80%.by Sakshum Khanna, Priyanka Marathey, Utsav, Harsh Chaliawala, and Indrajit Mukhopadhya

Effective Photocurrent Enhancement in Nanostructured CuO by Organic Dye Sensitization: Studies on Charge Transfer Kinetics

Mercurochrome-sensitized nanostructured CuO grown directly on Cu has been used as efficient photocathode in photoelectrochemical cell. The photocurrent density of the sensitized electrode is found to enhance from −1 mA/cm² (unsensitized) to −2.2 mA/cm² (dye sensitized for 24 h) at 0 V vs RHE under AM1.5G artificial solar illumination in aqueous 0.5 M Na₂SO₄ solution. The photoluminescence spectra demonstrated a strong absorption at 465 nm by the mercurochrome. Subsequent transfer of the photoexcited electrons to CuO conduction band enhances the photocurrent density. An incident photon-to-current conversion efficiency (IPCE) of 8% has been observed in the visible region. This is so far the highest reported value in p-type CuO based organic dye-sensitized photocathode. The dye sensitized CuO has thus the potential of photoreduction with higher Faradaic efficiency for various redox species due to additional carrier injection

Fabrication of long-ranged close-packed monolayer of silica nanospheres by spin coating

In light of the importance of nanostructured surfaces for various technological applications, it becomes imperative to look for simple and reliable methods for assembling ordered nanostructures over a large area. Several methods have been employed for fabricating nanostructured surfaces but not many are compatible with large-scale fabrication. Here we demonstrate the fabrication of long-range ordered close-packed monolayer of silica nanospheres (SNs) (size approximately 200 nm) deposited on a silicon substrate by a three-step spin coating technique in atmospheric conditions, which could be realized on a very small time scale but has significant potential in numerous applications. The dispersity of the SNs and the influence of various deposition parameters like surface modification, SNs concentration, spin speed, spinning time and the volume of aliquot spread over the silicon substrate were studied to optimize uniform high surface coverage of the film. A relatively uniform monolayer film and high surface coverage of silica particles ranging from 85 to 90% were achieved by optimizing the above deposition parameters. These nanostructures templates can be used in the formation non-close-packed monolayer facilitating further development of ordered nanowires, which highlights the prospect of this approach as a simple preparation method for ordered arrays of nanospheres. We conclude that this method is highly suitable for industrial applications, because of faster and effective rate of production and scalability.by Sakshum Khannaa, Utsavb, Priyanka Maratheya, Harsh Chaliyawalaa, Narasimman Rajarama, Debmalya Royc, Rupak Banerjeeb and Indrajit Mukhopadhya