Gautam Gundiah

Nanowires, nanobelts and related nanostructures of Ga2O3

Abstract By carrying out the reaction of Ga2O3 powder with carbon nanotubes around 1100 °C, nanowires, nanobelts and nanosheets of Ga2O3 have been obtained, the diameter and proportion of the nanowires depending on the flow rate of argon through the reaction zone. Reaction of Ga2O3 powder with activated carbon mainly gives rise to nanosheets and nanorods. The procedures employed in this study are attractive since they give high yields of nanowires and nanobelts. The nanowires are single crystalline with the growth direction perpendicular to the ( 1 0 2 ) planes. The Ga2O3 nanowires exhibit good photoluminescence characteristics.

Hydrogen storage in carbon nanotubes and related materials

Adsorption of hydrogen at 300 K has been investigated on well-characterized samples of carbon nanotubes, besides carbon fibres by taking care to avoid many of the pitfalls generally encountered in such measurements. The nanotube samples include single- and multi-walled nanotubes prepared by different methods, as well as aligned bundles of multi-walled nanotubes. The effect of acid treatment of the nanotubes has been examined. A maximum adsorption of ca. 3.7 wt% is found with aligned multi-walled nanotubes. Electrochemical hydrogen storage measurements have also been carried out on the nanotube samples and the results are similar to those found by gas adsorption measurements.

Synthesis and characterization of silicon carbide, silicon oxynitride and silicon nitride nanowires

Several methods have been employed to synthesize SiC nanowires. The methods include heating silica gel or fumed silica with activated carbon in a reducing atmosphere, the carbon particles being produced in situ in one of the methods. The simplest method to obtain β-SiC nanowires involves heating silica gel with activated carbon at 1360 °C in H2 or NH3. The same reaction, if carried out in the presence of catalytic iron particles, at 1200 °C gives α-Si3N4 nanowires and Si2N2O nanowires at 1100 °C. Another method to obtain Si3N4 nanowires is to heat multi-walled carbon nanotubes with silica gel at 1360 °C in an atmosphere of NH3. In the presence of catalytic Fe particles, this method yields α-Si3N4 nanowires in pure form.

Hydrogel route to nanotubes of metal oxides and sulfates

A tripodal cholamide-based hydrogel has been employed as a template to synthesize inorganic nanotubes. Besides nanotubes of oxides such as SiO2, TiO2, ZrO2, WO3 and ZnO, nanotubes of sulfates such as the water-soluble ZnSO4 as well as of BaSO4 have been obtained using this method. An advantage of the use of the hydrogel is that metal alkoxides are not required for the synthesis of the oxide nanotubes. The nanotubes have been characterized by X-ray diffraction and transmission electron microscopy.

Carbon-assisted synthesis of inorganic nanowires

Nanowires of a variety of inorganic materials such as metal oxides, sulfides, nitrides and carbides have been synthesized and characterized in the last three to four years. Among the several strategies developed for the synthesis of these materials, the carbothermal route is noteworthy since it provides a general method for preparing crystalline nanowires of many of these materials which include oxides such as ZnO, Al2O3 and Ga2O3, nitrides such as AlN and Si3N4, and carbides such as SiC. The method itself is quite simple and involves heating a mixture of an oxide with carbon in an appropriate atmosphere. The method has enabled the synthesis of crystalline nanowires of both silica and silicon. In the case of GaN, it has been possible to dope it with Mn, Mg and Si to bestow useful optical and magnetic properties. In this article, highlights of the recent results on the carbon-assisted synthesis of inorganic nanowires are presented.

Electrical properties of inorganic nanowire–polymer composites

Composites of nanowires of ZnO, RuO2 and Ag with polyaniline (PANI) as well as polypyrrole (PPy) have been prepared, for the first time, by an in-situ process, in order to investigate their electrical properties. Characterization by electron microscopy and IR spectroscopy indicates that there is considerable interaction between the oxide nanowires and the polymer. The room-temperature resistivity of the composites prepared in-situ varies in the 0.01–400 Ω cm range depending on the composition. While the resistivities of the PANI–ZnONW and PPy–ZnONW composites prepared by the in-situ process are generally higher than that of PANI/PPy, those of PANI–RuO2NW and PANI–AgNW are lower. Composites of ZnONW with polyaniline prepared by an ex-situ process exhibit a resistivity close to that of polyaniline.

Dip-pen nanolithography with magnetic Fe2O3 nanocrystals

Dip-pen nanolithography has been employed to obtain magnetic nanopatterns of γ-Fe2O3 nanocrystals on mica and silicon substrates. The chemical and magnetic nature of the patterns have been characterized employing low-energy electron microscopy, x-ray photoemission electron microscopy, and magnetic force microscopy measurements.

Macroporous oxide materials with three-dimensionally interconnected pores

Abstract Ordered mesoscale hollow spheres (1000 nm diameter) of binary oxides such as TiO 2 and ZrO 2 as well as of ternary oxides such as ferroelectric PbTiO 3 and Pb(ZrTi)O 3 have been prepared by templating against colloidal crystals of polystyrene, by adopting different procedures.

Macroporous carbons prepared by templating silica spheres

Abstract Macroporous carbons of different pore sizes, containing three-dimensionally connected voids, have been prepared by an elegant method. The method involves the coating of ordered silica spheres with sucrose, followed by carbonization using sulfuric acid, and the removal of silica with aqueous hydrofluoric acid. The carbon samples show the expected optical properties. The surface area of the macroporous carbon samples varies between 120 to 550 m 2 g −1 , depending on whether nonporous or mesoporous silica spheres were used as templates.

Crystalline silica nanowires

α-Cristobalite nanowires of 50-100 nm diameter with lengths of several microns have been synthesized for the first time by the solid-state reaction of fumed silica and activated charcoal. The nanowires have been characterized by X-ray diffraction, electron microscopy, photoluminescence, and Raman scattering. The nanowires are single crystalline as revealed by high-resolution electron microscope images. The crystalline nanowires are clad by an amorphous silica sheath when the carbon to fumed silica ratio in the starting mixture is small. Use of hydrogen along with Ar helps to eliminate the amorphous sheath.