MAGNETIC-FIELD ASSISTED LAYER-BY-LAYER ELECTROSTATIC ASSEMBLY: FILM FORMATION AND CHARACTERIZATION

Layer-by-layer (LbL) electrostatic assembly has been a unique approach to grow ultrathin films of polyions. The method has later been extended to organic molecules and inorganic quantum dots. The LbL method relies on surface charge reversal during adsorption of anionic and cationic layers in sequence. Morphology of such films has been found to depend on pH of the ionic species in solutions and functional groups attached to the molecules/polymers. Since LbL layers are being used for a range of thin-film based applications, morphology of the films has become increasingly important. In many cases, it has a large impact on the efficiency or output of devices. Efforts have been made to control morphology of the films or LbL growth process. Since the materials used here are ionic in nature, electric field has been the natural choice to do so. LbL deposition process of polyions and suitably-capped quantum dots has been found to be greatly affected by an electric field. For ferromagnetic quantum dots, magnetic fields could orient their magnetic dipoles in a monolayer that in turn supplement electrostatic force of attraction for the subsequent layer and augment LbL deposition process. It can be intriguing to introduce an additional force that may supplement the electrostatic adsorption process. An external electric-field has been considered for LbL deposition of suitable organic molecules or nanoparticles. Magnetic-moments that are inherently present in magnetic materials can be another direction in this regard. Since the magnetic domains can be oriented with a suitable magnetic field, our target here is to enhance electrostatic adsorption process through magnetic force of attraction. We show how oriented magnetic-moments can accelerate adsorption process of subsequent monolayers in the LbL assembly process. Again, in the presence of external magnetic field, orientation of the paramagnetic organic molecules can be immobilized via the electrostatic adsorption of suitable polycations. The magnetic field-assisted LbL formation has been discussed in chapter three. The LbL films with oriented molecular morphology in each monolayer provide a unique system to study anisotropy of optical, dielectric, and electrical characteristics in these planer organic molecules. The alignment of magnetization-vectors in the monolayer of magnetic materials also offers an opportunity to understand the leading mechanism of conductance switching. The degree of electrical bistability (On/Off ratio), transport gap, and density of states of the materials has been found to depend on their alignment magnetization-vectors. Because of the large energy barrier, the carriers are strictly confined to the organic linker coated quantum dots. This quantum confinement effect could be relaxed for a selective type of carriers by reducing their corresponding energy barrier.The band-offset engineering in core/shell nanoparticles provides the type-selective localization of carriers.The research was conducted under the supervision of Prof. A J Pal of the Solid State Physics division under SPS [School of Physical Sciences]The research was carried out under CSIR fellowship and gran