Francis Leonard Deepak

Boron nitride nanotubes and nanowires

Simple methods of preparing boron nitride nanotubes and nanowires have been investigated. The methods involve heating boric acid with activated carbon, multi-walled carbon nanotubes, catalytic iron particles or a mixture of activated carbon and iron particles, in the presence of NH 3 . While with activated carbon, boron nitride nanowires constitute the primary product, high yields of clean boron nitride nanotubes are obtained with multi-walled carbon nanotubes. Aligned boron nitride nanotubes are produced when aligned multi-walled carbon nanotubes are employed as the starting material suggesting the templating role of the nanotubes. Boron nitride nanotubes with different structures have been obtained by reacting boric acid with NH 3 in the presence of a mixture of activated carbon and Fe particles.

Synthetic strategies for Y-junction carbon nanotubes

Y-junction carbon nanotubes can be produced in relatively large quantities by the vapor phase pyrolysis of a mixture of cobaltocene or ferrocene with thiophene in a hydrogen atmosphere. Pyrolysis of Ni- and Fe-phthalocyanines or Fe(CO) 5 with thiophene also yields Y-junction nanotubes. Good yields of Y-junction nanotubes were obtained by pyrolyzing thiophene over an Ni(Fe)/SiO 2 catalyst as well. Many of the nanotubes show multiple Y-junctions. Of the various methods employed by us, the pyrolysis of thiophene with metallocenes or over a Ni(Fe)/SiO 2 catalyst yields the best results and the latter is a less expensive route. The availability of large quantities of Y-junctions by the procedures employed here should render them useful for exploitation in nanoelectronics.

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.

Experimental evidence of icosahedral and decahedral packing in one-dimensional nanostructures.

The packing of spheres is a subject that has drawn the attention of mathematicians and philosophers for centuries and that currently attracts the interest of the scientific community in several fields. At the nanoscale, the packing of atoms affects the chemical and structural properties of the material and, hence, its potential applications. This report describes the experimental formation of 5-fold nanostructures by the packing of interpenetrated icosahedral and decahedral units. These nanowires, formed by the reaction of a mixture of metal salts (Au and Ag) in the presence of oleylamine, are obtained when the chemical composition is specifically Ag/Au = 3:1. The experimental images of the icosahedral nanowires have a high likelihood with simulated electron micrographs of structures formed by two or three Boerdijk-Coxeter-Bernal helices roped on a single structure, whereas for the decahedral wires, simulations using a model of adjacent decahedra match the experimental structures. To our knowledge, this is the first report of the synthesis of nanowires formed by the packing of structures with 5-fold symmetry. These icosahedral nanowire structures are similar to those of quasicrystals, which can only be formed if at least two atomic species are present and in which icosahedral and decahedral packing has been found for bulk crystals.

Photoluminescence spectra and ferromagnetic properties of GaMnN nanowires

Abstract Mn-doped GaN nanowires have been prepared by reacting a mixture of acetylacetonates with NH 3 at 950 °C in the presence of multi-walled (MWNTs) and single-walled (SWNTs) carbon nanotubes, the nanowires prepared with SWNTs being considerably smaller in diameter. GaMnN nanowires with 1%, 3% and 5% Mn so obtained have been characterized by X-ray diffraction, EDAX analysis and photoluminescence (PL) spectra. The GaMnN nanowires are all ferromagnetic even at 300 K, exhibiting magnetic hysteresis. The PL spectra of the GaMnN nanowires prepared with SWNTs show a large blue-shift of the Mn 2+ emission.

Fullerene‐like Mo(W)1−xRexS2 Nanoparticles

Inorganic fullerene-like (IF) Mo(1-x)Re(x)S(2) and W(1-x)Re(x)S(2) nanoparticles have been synthesized by a gas-phase reaction involving the respective metal halides with H(2)S. The IF-Mo(W)(1-x)Re(x)S(2) nanoparticles, containing up to 5 % Re, were characterized by a variety of experimental techniques. Analyses of the X-ray powder diffraction and different electron microscopy techniques show that the Re is doped in the MoS(2) host lattice. Interestingly, Re-doped MoS(2) nanotubes are present as well, although in small quantities ( approximately 5 %). XPS results confirm the nanoparticles to be more n-type arising from the effect of Re doping. Additionally, density-functional tight-binding (DFTB) calculations support the observed n-type behavior.

Fullerene-like WS2 nanoparticles and nanotubes by the vapor-phase synthesis of WCln and H2S

Inorganic fullerene-like (IF) nanoparticles and nanotubes of WS(2) were synthesized by a gas phase reaction starting from WCl(n) (n = 4, 5, 6) and H(2)S. The effect of the various metal chloride precursors on the formation of the products was investigated during the course of the study. Various parameters have been studied to understand the growth and formation of the IF-WS(2) nanoparticles and nanotubes. The parameters that have been studied include flow rates of the various carrier gases, heating of the precursor metal chlorides and the temperature at which the reactions were carried out. The best set of conditions wherein maximum yields of the high quality pure-phase IF-WS(2) nanoparticles and nanotubes are obtained have been identified. A detailed growth mechanism has been outlined to understand the course of formation of the various products of WS(2).

Nanorotors using asymmetric inorganic nanorods in an optical trap

We demonstrate how light force, irrespective of the polarization of the light, can be used to run a simple nanorotor. While the gradient force of a single beam optical trap is used to hold an asymmetric nanorod, we utilize the scattering force to generate a torque on the nanorod, making it rotate about the optic axis. The inherent textural irregularities or morphological asymmetries of the nanorods give rise to the torque under the radiation pressure. Even a small surface irregularity with non-zero chirality is sufficient to produce enough torque for moderate rotational speed. Different sized rotors can be used to set the speed of rotation over a wide range with fine tuning possible through the variation of the laser power. We present a simple dimensional analysis to qualitatively explain the observed trend of the rotational motion of the nanorods.

Advanced Transmission Electron Microscopy

This book highlights the current understanding of materials in the context of new and continuously emerging techniques in the field of electron microscopy. The authors present applications of electron microscopic techniques in characterizing various well-known & new nanomaterials. The applications described include both inorganic nanomaterials as well as organic nanomaterials

Synthesis and characterization of reduced graphene oxide/spiky nickel nanocomposite for nanoelectronic applications

The surface modification of graphene oxide (GO) sheets with Ni nanoparticles has been a subject of intense research in order to develop new preeminent materials with increased performance for different application areas. In this work, we develop a new hydrothermal one-step method for the simple and controllable synthesis of reduced GO/nickel (GO/Ni) nanocomposites. Different reaction parameters have been investigated in order to control the synthetic process: reaction temperature, concentration of the nickel precursor and reducing agent. It was observed that the critical parameter for effective control of nickel particle size, morphology, crystalline structure and distribution at the GO surface during the reaction process was the concentration of hydrazine. The results obtained showed that control of hydrazine concentration allows obtaining crystalline metallic Ni nanoparticles, from spherical to spiky morphologies. For nanocomposites with spiky Ni nanoparticle, the reaction time allows controlling the growth of the nanothorn. The electrical properties of reduced graphene nickel nanocomposites containing spiky nickel particles showed a large resistive switching, which is essentially due to the switchable diode effect that can be used as a built-in part of graphene-based embedded electronics.