An integrated and open-ended experiment: study of chemical waves in time and space

In this article we discuss an exciting experiment in non-linear dynamics. This provides an imaginative platform for bringing in chemical, physical, biological, mathematical and computational sciences together. There are implications for earth sciences as well

Optical Modulation, Assembly And Advanced Applications Of Ultra Narrow Nanomaterials And Heterojunctions

This thesis aims at achieving superior control over the material synthesis of different dimensional nanostructure and their heterostructures to achieve the modulation of the optical properties. The proposed route of synthesis of semiconductor nanocrystals are particularly significant for optical applications due to superior transport and optical properties, and find application in diode lasers, amplifiers, and biomedical applications.The research was conducted under the supervision of Prof. Somobrata Acharya of CAM under SMS [School of Materials Sciences]The research was carried out under DST gran

Shape-Dependent Confinement in Ultrasmall Zero-, One-, and Two-Dimensional PbS Nanostructures

Spatial dimensionality affects the degree of confinement when an electron-hole pair is squeezed from one or more dimensions approaching the bulk exciton Bohr radius (alpha(B)) limit. The etectron-hole interaction in zero-dimensional (0D) dots, one-dimensional (1D) rods/wires, and two-dimensional (2D) wells/sheets should be enhanced by the increase in confinement dimensions in the order 0D > 1D > 2D. We report the controlled synthesis of PbS nanomateriats with 0D, 1D, and 2D forms retaining at least one dimension in the strongly confined regime far below alpha(B) (similar to 10 nm for PbS) and provide evidence through varying the exciton-phonon coupling strength that the degree of confinement is systematically weakened by the loss of confinement dimension. Geometry variations show distinguishable far-field optical polarizations, which could find useful applications in polarization-sensitive devices

Long-Range Visible Fluorescence Tunability Using Component-Modulated Coupled Quantum Dots

A simple route for tailoring emissions in the visible wavelength region by chemically coupling quantum dots composed of ZnSe and CdS is reported. coupled quantum dots offer a novel route for tuning electronic transitions via band-offset engineering at the material interface. This novel class of asymmetric. coupled quantum structures may offer a basis for a diverse set of building blocks for optoelectronic devices, ultrahigh density memories, and quantum information processing

Chemical Tailoring of Band Offsets at the Interface of ZnSe–CdS Heterostructures for Delocalized Photoexcited Charge Carriers

Monocomponent quantum dots (QDs) possess limited electron–hole delocalization capacity upon photoexcitation that suppresses the efficiency of photoenergy harvesting devices. Type II heterostructures offer band offsets at conduction and valence bands depending upon the band gaps of the constituent QDs which largely depend on their sizes. Hence, by keeping the size of one constituent QD fixed while varying the size of the other QD selectively, the band offsets at the interface can be engineered selectively. We report on the tuning of band offsets by synthesizing component size modulated heterostructures composed of a fixed sized ZnSe QD and size tuned CdS QDs with variable band gaps. The resultant heterostructures show spontaneous charge carrier separation across the interface upon photoexcitation depending on the extent of band offsets. Formation mechanism, epitaxial relationship, and the intrinsic nature of interface of the heterostructures are investigated. Experimental results are corroborated with <i>ab initio</i> electronic structure calculations based on density functional theory. Spontaneous charge carrier delocalization across the interface depends on the magnitude of band offsets, which facilitates fabrication of QD sensitized solar cells (QDSSCs). Improved device performances of QDSSCs in comparison to the limited photon-to-current conversion efficiencies of monocomponent QDs demonstrates the significance of band offsets for natural charge carrier separation

Oriented Attachment: A Path to Columnar Morphology in Chemical Bath Deposited PbSe Thin Films

We have studied columnar PbSe thin films obtained using chemical bath deposition. The columnar microstructure resulted from an oriented attachment growth mechanism, in which nuclei precipitating from solution attached along preferred crystallographic facets to form highly oriented, size-quantized columnar grains. This is shown to be an intermediate growth mechanism between the ion-by-ion and cluster growth mechanisms. A structural zone model depicting the active growth mechanisms is presented for the first time for semiconductor thin films deposited from solution. The columnar films showed well-defined twinning relations between neighboring columns, which exhibited 2D quantum confinement, as established by photoluminescence spectroscopy. In addition, anisotropic nanoscale electrical properties were investigated using current sensing AFM, which indicated vertical conductivity, while maintaining quantum confinement

The basic structural motif and major biophysical properties of Amyloid-β are encoded in the fragment 18–35

Aggregation and misfolding of the amyloid beta (Aβ) peptide is thought to initiate Alzheimer’s disease (AD). Here we study the role played by its central segment (Aβ18–35) in determining these properties. Aβ18–35 has a solubility of 18 μM. The soluble fraction consists mainly of small oligomers, which have mixed β-sheet and random coil structures. The monomer is mostly a random coil with some residual compactness. Aggregated Aβ18–35 forms fibrils of width 3.0 ± 0.7 nm, which is consistent with a hairpin shape. Each of these properties has a close similarity to Aβ40. Remarkably, solid state NMR indicates that the fibrils also retain the secondary structure and tertiary contacts of Aβ40. This is the shortest fragment of Aβ reported so far which preserves its fibrillar architecture, including the hairpin turn, as well as its solution phase conformational properties. Residues 18–35 should therefore be a key target of AD therapeutics