Santosh Shaw

Thermal Processing of Silicones for Green, Scalable, and Healable Superhydrophobic Coatings.

The thermal degradation of silicones is exploited and engineered to make super-hydrophobic coatings that are scalable, healable, and ecofriendly for various outdoor applications. The coatings can be generated and regenerated at the rate of 1 m(2) min(-1) using premixed flames, adhere to a variety of substrates, and tolerate foot traffic (>1000 steps) after moderate wear and healing.

Building Materials from Colloidal Nanocrystal Arrays: Preventing Crack Formation during Ligand Removal by Controlling Structure and Solvation

Crack-free, ligand-free, phase-pure nanostructured solids, using colloidal nanocrystals as precursors, are fabricated by a scalable and facile approach. Films produced by this approach have conductivities comparable to those of bulk crystals over more than 1 cm (1.370 S cm-1 for PbS films).

Building Materials from Colloidal Nanocrystal Arrays: Evolution of Structure, Composition, and Mechanical Properties upon the Removal of Ligands by O2 Plasma

The mechanical properties of colloidal nanocrystal superlattices can be tailored through exposure to low-pressure plasma. The elastic modulus and hardness of the ligand-free 3.7 nm ZrO2 superlattice are found to be similar to bulk yttria-stabilized tetragonal polycrystals of the same relative density but without any doping.

Towards bulk syntheses of nanomaterials: a homeostatically supersaturated synthesis of polymer-like Bi2S3 nanowires with nearly 100% yield and no injection

This paper reports the implementation of a one-pot strategy for the synthesis of polymer-like Bi2S3 nanowires from supersaturated precursors. These conditions result in (i) a homeostatically regulated supersaturation of the growing phase during most of the reaction, (ii) a nearly 100% conversion of the limiting reagent, and (iii) an improved colloidal stability and polydispersity of the product (when compared to the hot-injection product) that allows the identification of three new exciton transitions in the absorption spectrum (one of them, importantly, being a weakly absorbing ground state at 1.64 eV). Three different commercial sources of ligands do not yield significantly different conversion rates. Scalability is further improved by lack of stirring after the initial stage of reaction and a lower reaction temperature (90 °C).

Optics-free, plasma-based lithography in inorganic resists made up of nanoparticles

Abstract. We describe a lithographic approach—nanocrystal plasma polymerization-based lithography—in which colloidal nanocrystal assemblies (CNAs) are used as the inorganic resist and, potentially, the active material. The patterning process is based on a change in the dispersibility of the CNAs in solvents as a result of the exposure to plasmas. Plasmas can etch the capping ligands from the exposed area. During the development step, the unexposed area of CNAs is redispersed, leaving behind the patterned area, similar to what is expected from negative photoresist.

Large Scale Synthesis of Colloidal Si Nanocrystals and their Helium Plasma Processing into Spin-On, Carbon-Free Nanocrystalline Si Films

This paper describes a simple approach to the large-scale synthesis of colloidal Si nanocrystals and their processing into spin-on carbon-free nanocrystalline Si films. The synthesized silicon nanoparticles are capped with decene, dispersed in hexane, and deposited on silicon substrates. The deposited films are exposed to nonoxidizing room-temperature He plasma to remove the organic ligands without adversely affecting the silicon nanoparticles to form crack-free thin films. We further show that the reactive ion etching rate in these films is 1.87 times faster than that for single-crystalline Si, consistent with a simple geometric argument that accounts for the nanoscale roughness caused by the nanoparticle shape.

Calcination does not remove all carbon from colloidal nanocrystal assemblies

Removing organics from hybrid nanostructures is a crucial step in many bottom-up materials fabrication approaches. It is usually assumed that calcination is an effective solution to this problem, especially for thin films. This assumption has led to its application in thousands of papers. We here show that this general assumption is incorrect by using a relevant and highly controlled model system consisting of thin films of ligand-capped ZrO2 nanocrystals. After calcination at 800 °C for 12 h, while Raman spectroscopy fails to detect the ligands after calcination, elastic backscattering spectrometry characterization demonstrates that ~18% of the original carbon atoms are still present in the film. By comparison plasma processing successfully removes the ligands. Our growth kinetic analysis shows that the calcined materials have significantly different interfacial properties than the plasma-processed counterparts. Calcination is not a reliable strategy for the production of single-phase all-inorganic materials from colloidal nanoparticles.Synthesis of all-inorganic nanomaterials often relies on organic templates, which are assumed to then be fully removed by calcination. Here, the authors use elastic backscattering spectroscopy to challenge this assumption, finding that calcination leaves behind considerable carbon content that can severely affect material function.

Optics-free lithography on colloidal nanocrystal assemblies

We describe a lithographic approach – Nanocrystal Plasma Polymerization (NPP)-based lithography (Figure 1) – where colloidal nanocrystal assemblies (CNAs) are used as the resist and, potentially, the active material. The patterning process is based on a change in the dispersibility of the CNAs in solvents as a result of the exposure to plasmas. Plasmas can etch the capping ligands from the exposed area. During the development step, the unexposed area of CNAs are redispersed leaving behind the patterned area.