Abstract: Organic-inorganic photovoltaic systems which attempt to integrate benefits of both material types in terms of ease of fabrication, stability and efficiency are reviewed. Three broad categories; inorganic-small molecule systems, carbon naotube incorporated organic photovoltaics and nanostructured organic surfaces-based photovoltaics have been discussed with reference to recent literature. Nanocrystal-organic systems are designed to improve broadband photon collection possibilty, nanostructred organic surfaces-based systems attempt to enhance exciton dissociation at the increased area interface. Incorporation of carbon nanotubes in donor-acceptor type photovoltaic systems have been shown as a technique to mitigate drawbacks from short carrier diffusion lengths of organic materials. The concepts present new opportunities for complex photovoltaic systems, which need to be cheap, large area and efficient in order to arrive at an economically viable level for mass uptake.
Abstract: For any future cost-effective applications of inorganic nanostructures in particular hybrid photovoltaic cell, solution processable and selective printable of inorganic nanomaterials is essential. The patterning and growth of highly ordered arrays of crystalline ZnO inorganic nanostructures use simple soft lithography technique and mild reaction conditions; both low in temperature and free from harmful organic additives. Variable yet controllable anisotropic growth of ZnO nanowires has been demonstrated on the transferred patterns of ZnO nanocystals.
Abstract: Nano films of polytetrafluoroethylene (PTFE; commercially coded as Teflon) shows advantage over inorganic spacer materials like Al2O3 and MgO in fabricating tunneling magneto resistive devices due to its relative dielectric constant and chemical inertness to provide a homogenous metal-organic interface. Pulsed electron deposition proves useful in fabricating such thin PTFE films (3-6 nm) for trilayer device such as Fe (100 nm)/ PTFE (3-6 nm) /Fe (100 nm) on Si (100). Characteristic magnetic hysteresis loops demonstrating the magnetic tunnel junctions were realized for a PTFE organic layer thickness >3 nm. The tunneling magnetoresistance measurement at room temperature shows a typical magneto resistive feature, increasing with increasing PTFE thickness.
Abstract: Amorphous ribbons of composition Fe68.5Cu1Nb3Si18.5B9 were produced by melt spun unit. Positron annihilation technique along with DSC and XRD studies has been employed to characterize the nanocrystallization process. XRD results confirmed presence of Fe3Si and Fe2B phases. Two life time components could be fitted to life time spectra of amorphous and heat treated samples. Life time of positron in amorphous matrix was found to be 163.3 ps. Small life time components in nanocrystallized samples could be ascribed to positron annihilation within amorphous and nanocrystalline particles. Larger life time component could be attributed to positron annihilation in interfaces associated with primary and secondary phase particles.
Abstract: Effect of copper addition in a Metallic glass 2714A on the nanocrystallization characteristics have been examined in this study. Amorphous ribbon of the alloy composition Co64.5 Fe3.5 Si16.5 B13.5 Ni1Cu1 were prepared by melt spinning technique. Nanocrystallization kinetics was studied using differential scanning calorimeter technique. The kinetic parameters such as activation energy and Avrami exponent were determined using two different non-isothermal analysis methods. The kinetic behavior of individual crystallization event has been rationalized on the basis of these results. The role of addition of copper on the crystallization behavior has been understood by comparing with Metallic glass 2714A. The isothermally annealed nanocrystallized microstructures were characterized by X-ray diffraction.
Abstract: A dislocation near a free surface feels a force towards the boundary, which is called the image force. In this investigation, a simple edge dislocation is simulated using Finite Element Method (FEM) by feeding-in the appropriate stress-free strain in idealized domains, corresponding to the introduction of an extra half-plane of atoms. The strains are imposed as thermal strains in the numerical model using standard commercially available software. The results of the simulation (stress fields and energy) are compared with the standard theoretical equations to validate the model. The energy of the system as a function of the position of the simulated dislocation is plotted and the gradient of the curve is calculated at various points along the curve. This slope corresponds to the image force experienced by the dislocation. The image force can be resolved into a glide component and a climb component, which are determined from the simulation by appropriately positioning the dislocation at various points in the domain. The term image force is used in literature (for the force experienced by a dislocation in the vicinity of a free-surface), because a hypothetical negative dislocation is assumed to exist on the other side of the boundary for the calculation of the force. In the current model no such assumption is required for the determination of the image force. In nanocrystals the dislocation will be proximal to more than one surface and hence the resultant image force experienced by the dislocation is superimposition of these forces. The utilization of the numerical model for the calculation of image forces in nanocrystals requires no further modifications to the simulation methodology as the image force is determined from 'first principles' as a gradient of the energy field.
Abstract: Single phase M-type barium hexaferrite nano radar absorbing material (NRAM) i.e., BaFe12O19 were synthesized by modified flux method that combines the controlled chemical co-precipitation process for nucleation and complete uniform growth during annealing with NaCl flux under microwave annealing (MWA) and vacuum annealing (VA). Uniform morphological transformation of nano crystals from spherical (~ 10 nm) to prism faces (~ 35 nm) were observed under TEM during annealing. The effect of such systematic nano morphological transformation of NRAM was observed on magnetic and reflection loss (RL) properties. Maximum reflection loss (RL) was improved to 37.15 dB at 16.00 GHz for MWA at 760 watt and 27.56 dB at 15.75 GHz for VA at 1200 oC with continuous increasing absorption range under −10 dB for 2 mm thick coating layer in the Ku Band (12.4-18.0 GHz).. Excellent microwave absorption properties are a consequence of accurate EM match in the nano morphological planes, a strong natural resonance, as well as multipolarization. This process of crystal growth, morphology evolution and RL enhancement with respect to the heat treatments were also explained in terms of Ostwald ripening and quantum size effect.
Abstract: High energy ball milling (HEBM) had been carried out to produce submicron size titanium aluminide intermetallics (TiAl) using elemental powders of Ti and Al alongwith Ni-P coated graphite. 1% graphite powders was added to stoichiometric composition of Ti48Al and ball milling was conducted for different milling time at varying rpm. The effect of milling time and rpm on particle size has been studied. The prepared samples have been characterized using X-ray diffraction, differential scanning calorimetry (DSC) and scaning elecron microscopy (SEM). Grain size as low as 500 nm could be achieved. Formation of Ti3Al, TiAl and carbon containing intermetallic compounds had been confirmed through X-ray diffraction. Milling time and rpm of mill is found to be important factors which control the final particle size.
Abstract: Severe plastic deformation processes (SPD) are gaining importance as advanced materials processing techniques and hold immense potential in obtaining ultra fine-grained high strength materials. Among the SPD techniques, Equal channel angular pressing (ECAP) has its own merits to produce materials with ultra fine grains in bulk with better mechanical properties. The material deforms with high level of plastic strain inside the channel resulting in grain refinement of the output material with improvement in mechanical properties.
A very viable die configuration was conceptualized and die was made with 1200 channel angle. Processing of 25 mm dia. of Al alloy AA2219 at room temperature was successfully carried out and grain refinement was observed. The mechanism of grain refinement has been studied using optical and transmission electron microscopy (TEM). It was observed that low energy dislocation structure (LEDS) forms concurrently with sub-grain structure due to dislocation rearrangements, which provide stability to the evolving sub-grain structure. Dislocation mobility is hindered by the presence of precipitates and / or intermetallic dispersoids present in the matrix and results in presence of dislocations in grain interiors. The pile up of dislocations at intermetallic dispersoids was confirmed from the dark field TEM micrographs.
Present paper describes the experimental procedure and followed to attain severe plastic deformation through ECAP. Increase in hardness as well as refinement in the grain size after 5-passes have been discussed in light of extensive optical and TEM. The mechanisms of grain refinement to achieve nano-grained structure and strengthening accrued from the grain refinement through ECAP has been discussed.