Biomimetic route to hybrid nano-Composite scaffold for tissue engineering

Hydroxyapatite-poly(vinyl) alcohol-protein composites have been prepared by a biomimetic route at ambient conditions, aged for a fortnight at 30±2°C and given a shape in the form of blocks by thermal cycling. The structural characterizations reveal a good control over the morphology mainly the size and shape of the particles. Initial mechanical studies are very encouraging. Three biocompatibility tests, i.e., hemocompatibility, cell adhesion, and toxicity have been done from Shree Chitra Tirunal, Trivandrum and the results qualify their standards. Samples are being sent for more biocompatibility tests. Optimization of the blocks in terms of hydroxyapatite and polymer composition w.r.t the applications and its affect on the mechanical strength have been initiated. Rapid prototyping and a β-tricalcium – hydroxyapatite combination in composites are in the offing

Ultralong Copper Phthalocyanine Nanowires with New Crystal Structure and Broad Optical Absorption

The development of molecular nanostructures plays a major role in emerging organic electronic applications, as it leads to improved performance and is compatible with our increasing need for miniaturisation. In particular, nanowires have been obtained from solution or vapour phase and have displayed high conductivity, or large interfacial areas in solar cells. In all cases however, the crystal structure remains as in films or bulk, and the exploitation of wires requires extensive post-growth manipulation as their orientations are random. Here we report copper phthalocyanine (CuPc) nanowires with diameters of 10-100 nm, high directionality and unprecedented aspect ratios. We demonstrate that they adopt a new crystal phase, designated eta-CuPc, where the molecules stack along the long axis. The resulting high electronic overlap along the centimetre length stacks achieved in our wires mediates antiferromagnetic couplings and broadens the optical absorption spectrum. The ability to fabricate ultralong, flexible metal phthalocyanine nanowires opens new possibilities for applications of these simple molecules

Interaction between structural and electronic phase changes of metal oxide semiconductor nanocrystals

Semiconducting metal oxides have emerged as a core class of materials in functional electronic devices because of their versatile compositions and tunable electronic and optical properties. Applying a charge to metal oxides can modulate carrier properties and induce structural changes from charge-compensating defects. However, charge-mediated transformations are contingent upon efficient transport of carriers, compensating species, or field biases into the bulk. Nanostructured materials, including colloidal metal oxide nanocrystals, can accommodate efficient charge transport across the semiconductor interface, and exhibit sensitive optical and electronic properties that arise from their nanoscale geometry. This dissertation studies the relationship between charge-mediated electronic and structural phase changes in metal oxide nanocrystals, and correlates these transformations with their nanoscale geometry and interfacial environment. The first investigation studies anatase TiO₂ nanocrystals during electrochemical charging. TiO₂ nanocrystal films can undergo two independent charging processes within a Li-ion electrolyte: surface capacitance, which raises the Fermi level upon reduction and induces Drude-like infrared localized surface plasmon resonance without affecting structure, and intercalative charging caused by the insertion of Li⁺ into the nanocrystal lattice. These two charging processes create independent dual-spectrum visible (Li-ion intercalation) and infrared (plasmon resonance) optical responses to applied bias, with applications for versatile electrochromic smart windows. The optical and electrochemical properties of both charging mechanisms are isolated and studied independently to examine the role of structure and interfacial environments on these transformations. The second part of this dissertation explores charge-mediated transformations in nanocrystalline VO₂, which has a highly non-ideal, charge-correlated electronic structure. A charge-mediated electrochemical insulator to metal transformation in VO₂ is found to be highly sensitive to nanoscale grain size, leading to a secondary metal-insulator transformation for sufficiently confined particles. The results of these studies establish general principles to control the interplay between defect-mediated structural transformations, ideal semiconductor gating behavior and interfacial environments in metal oxide nanocrystals.Chemical Engineerin

Modelling and Simulation of Charging and Discharging Processes in Nanocrystal Flash Memories During Program and Erase Operations

This work is focused on the understanding of charging and discharging processes in silicon nanocrystal flash memories during program and erase operations through time-dependent numerical simulations. Time dependent simulations of the program and erase operations are based on a description of the nanocrystal memory dynamics in terms of a master equation. The related transition rates are computed with a one dimensional Poisson-Schroedinger solver which allows the computation of the tunnelling currents and of generation and recombination rates between the outer reservoir and localized states in the dielectric layer. Comparison between simulations and experiments available in the literature provides useful insights of the storing mechanisms. In particular, simulations allow us to rule out that electrons are stored in confined states in the conduction band of silicon nanocrystals, whereas they suggest that electrons are actually trapped in localized states in the silicon gap at an energy close to the silicon valence band edge, and located at the interface between the nanocrystals and the surrounding silicon oxide.Comment: 10 pages, this is an extended version of a paper presented at the first International Conference on Memory Technology and Design, to be published on Solid State Electronic

Symmetry breaking and spin-orbit coupling for individual vacancy-induced in-gap states in MoS2 monolayers

Spins confined to point defects in atomically-thin semiconductors constitute well-defined atomic-scale quantum systems that are being explored as single photon emitters and spin qubits. Here, we investigate the in-gap electronic structure of individual sulphur vacancies in molybdenum disulphide (MoS2) monolayers using resonant tunneling scanning probe spectroscopy in the Coulomb blockade regime. Spectroscopic mapping of defect wavefunctions reveals an interplay of local symmetry breaking by a charge-state dependent Jahn-Teller lattice distortion that, when combined with strong (~100 meV) spin-orbit coupling, leads to a locking of an unpaired spin-1/2 magnetic moment to the lattice at low temperature, susceptible to lattice strain. Our results provide new insights into spin and electronic structure of vacancy induced in-gap states towards their application as electrically and optically addressable quantum systems

Single crystal diamond nanobeam waveguide optomechanics

Optomechanical devices sensitively transduce and actuate motion of nanomechanical structures using light. Single--crystal diamond promises to improve the performance of optomechanical devices, while also providing opportunities to interface nanomechanics with diamond color center spins and related quantum technologies. Here we demonstrate dissipative waveguide--optomechanical coupling exceeding 35 GHz/nm to diamond nanobeams supporting both optical waveguide modes and mechanical resonances, and use this optomechanical coupling to measure nanobeam displacement with a sensitivity of $9.5$ fm/$\sqrt{\text{Hz}}$ and optical bandwidth $>150$nm. The nanobeams are fabricated from bulk optical grade single--crystal diamond using a scalable undercut etching process, and support mechanical resonances with quality factor $2.5 \times 10^5$ at room temperature, and $7.2 \times 10^5$ in cryogenic conditions (5K). Mechanical self--oscillations, resulting from interplay between photothermal and optomechanical effects, are observed with amplitude exceeding 200 nm for sub-$\mu$W absorbed optical power, demonstrating the potential for optomechanical excitation and manipulation of diamond nanomechanical structures.Comment: Minor changes. Corrected error in units of applied stress in Fig. 1

Institute of Ion Beam Physics and Materials Research: Annual Report 2002

Summary of the scientific activities of the institute in 2002 including selected highlight reports, short research contributions and an extended statistics overview