Surfactant-assisted room-temperature synthesis of CdSe nanoclusters

Abstract CdSe nanoclusters of about 22 nm average size have been synthesized by a surfactant-assisted chemical method at room temperature. The asgrown nanoclusters were near stoichiometric and 70% of them were of hexagonal wurtzite crystalline phase. With undefined shapes, the crystalline nanoclusters remained arbitrarily oriented in a compact powder form. The morphology and structural behavior of the nanoclusters were studied by scanning electron microscopy and transmission electron microscopy. Thermal stability of the nanoclusters was studied by thermogravimetric analysis. Presence of very small clusters (<5 nm) in the sample revealed a blue shifted excitonic absorption peak along with the excitonic peak of bigger clusters

Phase transitions in liquid crystals under negative pressures

We report the first measurements of orientational order parameters and phase transition temperatures in nematic and smectic A liquid crystals under negative pressures generated by an isochoric cooling of small droplets embedded in a glass former. Comparison of isobaric and isochoric measurements allows us to estimate the coefficients coupling the order parameter and density of an extended Landau-de Gennes model of the nematic phase

Surfactant-assisted room-temperature synthesis of CdSe nanoclusters

CdSe nanoclusters of about 22 nm average size have been synthesized by a surfactant-assisted chemical method at room temperature. The as-grown nanoclusters were near stoichiometric and 70% of them were of hexagonal wurtzite crystalline phase. With undefined shapes, the crystalline nanoclusters remained arbitrarily oriented in a compact powder form. The morphology and structural behavior of the nanoclusters were studied by scanning electron microscopy and transmission electron microscopy. Thermal stability of the nanoclusters was studied by thermogravimetric analysis. Presence of very small clusters (<5 nm) in the sample revealed a blue shifted excitonic absorption peak along with the excitonic peak of bigger clusters

Modulating surface plasmon resonance response by an external electromagnetic wave

We fabricated a highly sensitive layered structure of organic molecules and studied the influence of polarization of the external electromagnetic (EM) wave on the surface plasmon resonance response from the layered structure. The layered structure was formed by depositing a self-assembled monolayer (SAM) of mercaptoundecanoic acid (MUA) followed by a single layer of Langmuir-Schaefer (LS) film of traditional calamitic liquid crystal molecule, 4$^{\prime}$ -octyl-4-biphenylcarbonitrile (8CB). The SAM of MUA was found to be non-responsive towards the change in resonance angle (RA) of surface plasmon resonance (SPR) due to the change in polarization of the external EM wave. However, such layer provides a soft-surface platform for the single layer of 8CB molecules which gets perturbed locally due to the incidence of the external EM wave. We obtained an oscillatory modulation of the change in RA due to the change in polarization angle of the EM wave with respect to the plane of incidence. The magnitude of sensitivity was found to be ∼4 milli°/° angle of polarization of the external EM wave. This study strongly suggests that sensitivity of a SPR-based sensor can be controlled by altering the linear state of polarization of the incident external EM wave

Surfactant-assisted room-temperature synthesis of CdSe nanoclusters

CdSe nanoclusters of about 22 nm average size have been synthesized by a surfactant-assisted chemical method at room temperature. The as-grown nanoclusters were near stoichiometric and 70% of them were of hexagonal wurtzite crystalline phase. With undefined shapes, the crystalline nanoclusters remained arbitrarily oriented in a compact powder form. The morphology and structural behavior of the nanoclusters were studied by scanning electron microscopy and transmission electron microscopy. Thermal stability of the nanoclusters was studied by thermogravimetric analysis. Presence of very small clusters (<5 nm) in the sample revealed a blue shifted excitonic absorption peak along with the excitonic peak of bigger clusters

Langmuir–Blodgett films of stearic acid deposited on substrates at different orientations relative to compression direction: alignment layer for nematic liquid crystal

<p>The Langmuir monolayer at an air–water interface shows remarkably different surface pressure (<i>π</i>)–area (<i>A</i>) isotherm, when measured with the surface normal of a Wilhelmy plate parallel or perpendicular to the direction of compression of the monolayer. Such difference arises due to difference in stress exerted by the monolayer on the plate in different direction. In this article, we report the effect of changing the direction of substrate normal with respect to the compression of the monolayer during Langmuir–Blodgett (LB) film deposition on the morphology of the films. The morphology of the LB film of stearic acid is studied using an atomic force microscope. The morphology of the LB films is found to be different due to difference in the stress in different directions. The role of such surface morphology on the alignment of a nematic liquid crystal (LC) in LC cells is studied. The granular texture of LB films of stearic acid supports the homogeneous alignment of the LC whereas the uniform texture supports the homeotropic alignment of the LC.</p

Nanocrystalline CdSe thin films of different morphologies in thermal evaporation process

Cadmium selenide nanocrystalline thin films of quasi-spherical morphology are prepared by evaporating CdSe nanopowders on glass substrates. Slightly oval shaped CdSe particles of about 165 nm average size (in 2-D) could be assembled over glass substrates by controlling the film thickness. Morphologies like assembly of particles, interconnected particles with mosaic-like structures and thin films of smooth surfaces could be prepared simply by controlling film thickness. A mechanism for such morphological variations is proposed. Observed variation of band gap energy in the films is explained in terms of quantum confinement effect and substrate-film interface strain