R&D Projects

Carbon Nanotube Based Sensors Funded by: DST, Project no. 563

Carbon nanotubes are currently being studied in an effort to understand their novel structural, electronic, and mechanical properties and to explore their immense potential for many applications in nanoelectronics, and as sensors. This project has two parts; viz. (1) Device based on carbon nanotubes (CNTs) (2) Interaction of biomolecules with CNTs.

Part I: CNT based Sensors
(A) Recently it is seen that the flow of a liquid on single-walled carbon nanotube (SWNTs) bundles induces a voltage across the nanotube sample. The induced voltage depends logarithmically on the flow speed and is only along the flow direction. When the direction of flow is reversed, the polarity across the SWNTs sensor also changes its sign. We have used this flow-induced voltage in developing an application of the SWNTs as a vibration sensor in liquid environment as well as accelerometer. The frequency range that has been tested is from100 Hz to1 kHz. Therefore this device is highly sensitive to measure the low frequencies. The schematic diagram of the above sensor is shown in Figure.

(B) CNT based FET:
We have used A.C dielectrophoresis to align the nanotubes between two parallel electrodes of separation ~ 20 m. This aligned mat of nanotubes are using to make the FET devices which can be used as different sensors like gas sensor, bio sensor etc. The characteristics of different sensors can be attributed from the I-V curve of nanotube based FET. We are also making sensors based on nanotube polymer composites which can be also used as gas sensor by performing the field emission experiments of nanotube-polymer nanowires.

Part II: Interaction of biomolecules with CNTs:
Carbon nanotubes (CNTs) functionalized with biological molecules show great potential in nanotechnology and bioengineering. Recently, it has been reported that the wrapping of single wall carbon nanotubes (SWNT) by single-stranded DNA (ssDNA) enables not only the separation of metallic tubes from semi conducting tubes but also allow diameter-dependent separation. Here, we have undertaken ab-initio calculations to get the binding energy of different nucleobases (A, C, G, T) with a (5x5) single wall carbon nanotube (SWNT). It has been observed that there is a differential binding affinity of different nucleobases with SWNT. We have also performed the isothermal titration (micro) calorimetry (ITC) experiments to measure directly the binding energies of different nucleobases with single walled carbon nanotube (SWNT).

Raman spectroscopy of transition metal and rare earth oxides and carbon nanotubes Funded by: DST, Project no. 573

Raman spectroscopy is an excellent tool to probe the lattice vibrations and its couplings with the magnetic ions in the lattice. This project has two parts, viz. (1) Carbon nanotubes (2) Transition metal oxides like Manganites.

In the first category, our study focuses on the different aspects of carbon nanotubes and the tuning of its band-gap by electrochemical bias. In general carbon nanotubes have the radial breathing mode and the tangential modes, which are Raman active. The different transition energies (Eii) of carbon nanotube are related to the carbon-carbon overlapping integral (ã0). On application of bias voltage, ã0 changes thus changing the energy gap (Eii) which can be probed by Raman spectroscopy.

In the second part, our study focuses on the spin- phonon coupling in some of the manganites and magnetic materials among which LaFeO3, La(1- x)SrxFeO3, SrFeO3 and CaFeO3 have been extensively studied. Existence of metal-insulator transitions (MIT) and the magnetic phase transitions with temperature and pressure are the motivations behind this part of the project.

Novel Physical Properties of Single Crystals of PyrochloresFunded by: IFCPAR Project No. 3108-1

In comparison with the Rare earth cuprates and perovskite manganites that have been extensively investigated for their novel superconducting and magnetic properties, the pyrochlore oxides (A2B2O7) have just begun catching attention of solid state physicists and chemists.

The main interest in these systems lies in the behaviour of spins which, due to geometrical reason, are frustrated leading to the novel states like spin-ice, spin liquid etc.

The main objectives of this project:

  1. To obtain high quality cm-size single crystals of several pyrochlore compounds A2B2O7 (A = Y, Sm, Eu, Gd, Ho, Tb, Yb, Dy; B = Ti, Mo, Zr) by floating zone technique. (French part).
  2. To perform structural, magnetic, magnetotransport and Raman measurements as functions of pressure and temperature on these crystals.
  3. To understand the role of the magnetic ions as well as the cation and anion disorder on the spin ice, spin-glass, spin-liquid, ferromagnetic properties, metal-insulator transition and the magnetoresistance effect.

Development of Nanoscopic Raman instrumentation with Nanometer Spatial Resolution using near Field Enhancement.Funded by DRDO, Project no. 527

The main objective is to develop the near field Raman spectroscopy and imaging with nanometer spatial resolution in reflection scattering geometry.

This novel technique is based on the strong enhancement of Raman signal from the sample in the presence of a fine metal tip brought to within a few nanometer of the sample using atomic force microscope stage.

An atomic force microscope has been developed so that the metallic tip can be brought in close proximity of the sample in a controlled manner.

This requires designing of the mechanical stages for the movement of the tip and sample.

Figure. 1. Shows the mechanical assembly of the AFM.

Thermo-mechanical and Optical properties of polymer Nano-composite thin filmsFunding Agency : ISRO-IISc - STC (2005-2007)

Polymer nanocomposites (PNC) are a class of multifunctional materials, which promise to provide an attractive combination of mechanical, thermal, electrical, optical and several other physical or biophysical properties into one material.

These materials have the potential, if used judiciously, to harness maximum benefits from the advancement of nano science and technology that is taking place at an incredibly rapid pace and have been envisaged to have potential applications ranging from automotive technology to electronics. For instance if the tunability of electrical or optical properties of metallic or semiconducting nanoparticles can be combined with the flexibility or the ease of processibility of polymers without compromising on these properties of the individual components, materials with novel applications could be fabricated.

However, in spite of significant amount of work in this area, worldwide, a fundamental lack of understanding of the relation between the microstructure and the macroscopic properties that are of wide interest has so far impeded the growth and widespread commercialization of PNC as a substitute of the more widely used high performance composites.

Conformation and Phase Transformations of Charged and Uncharged Polymers Confined at InterfacesFunding Agency : DST (2006-2009)

The project aims at understanding the influence of confinement, at surfaces and interfaces, on conformation, phase behaviour and rheology of charged and uncharged polymers. We plan to investigate chain conformation and thermodynamics of 2D polymeric monolayers (uncharged) at air-liquid interface using the Langmuir-Blodgett technique (LB).

Systematic variation of thermodynamic variables like 2D pressure or surface area and temperature makes it possible to control the surface packing and conformation of polymers and hence to study their phase transformations, using ellipsometry and grazing incidence x-ray scattering (GIXS) measurements, and relate these to their structure.

In addition, surface rheological measurements to capture the dynamics of 2D polymeric layers, will be performed, to gain insight into the relaxation spectra of confined polymer chain segments.We also plan to study in detail the conformation of polyelectrolytes adsorbed on oppositely charged surfaces. Utilizing the LB method we will study the adsorption and conformation of polyelectrolytes on a charged monolayer of organic amphiphilic molecule using in-situ ellipsometry and GIXS measurements. Variation of parameters like surface charge density, salt concentration, temperature etc. would be made to identify the nature of the interactions governing the adsorption behaviour, especially with regards to the phenomenon of charge inversion.

Pattern Formation and Optical Properties Block Copolymer-Nanoparticle Composite Thin FilmsFunding Agency : DST (2005-2010)

Block copolymers (BCP) encompass the physics of liquid crystals in terms of the diversity of self-assembled structures and polymers in terms of their complex dynamics and rheology.

Under appropriate conditions, these can self-assemble into various periodic structures, ranging from 10-1000 nm, owing to micro-phase separation between dissimilar blocks and this bulk phase behaviour is relatively well understood. This is not the case in thin films – especially - the influence of substrate morphology and/or segment-substrate interaction on the resulting phase is still not clear.

The phase behaviour of BCP/nanoparticle (NP) mixtures, especially in thin films, is just beginning to be explored, both through experiments and numerical simulations. Recent, numerical simulations and experiments points to the possibility of a soft-lithographic route to formation of multiple length scale structures in thin films of BCP-NP mixtures. We would like to investigate the influence of NPs on the phase behaviour of BCP films. We also plan to study how, especially, the optical properties of the NPs gets modified under confinement. For this we would like to use a combination of SPM, NSOM and CRM to enable chemical-morphological mapping of the phase behaviour as well as study the nano-optical properties of the composites.

Centre for Condensed Matter Theory (CCMT) Theoretical Studies of Condensed MatterFunding Agency : DST (2003-2008)

This project supports the Centre for Condensed Matter Theory (CCMT), set up in 1998, consisting of condensed matter theorists drawn from several departments of the IISc. Under the above project, he DST has generously funded research activities by the members of CCMT on a wide spectrum of frontier areas in Theoretical Condensed Matter Physics. The centre has funds for supporting research assistants, research associates and visitors, for computational facilities, a contingency grant for day-to-day expenses and domestic travel, for books and software, and for holding conferences, workshops and schools.
The members of CCMT, their recent research activities and current research interests are listed below:

Faculty Members:

Physics H R Krishnamurthy (Convener), C Dasgupta, Prabal Maiti, Rahul Pandit, S Ramaswamy, Vijay Shenoy
CHEP D Sen
SSCU B Bagchi , S Ramasesha, D D Sarma, S Yashonath
MRC G Ananthakrishna
IPC B J Cherayil, K L Sebastian

Distinguished Visitor: T V Ramakrishnan BHU

Research Activities / Interests

Electronic structure, especially strongly Correlated Electron systems:
Dynamical effective medium theories; d-wave superconductivity in cuprates; Luttinger liquids and quantum wires; Molecular Magnetism and Photomagnetism; Electron-hole recombination, Triplet-triplet Annihilation and Excitation Transfer in Organic Light Emitting Diodes; Calculation of Auger spectra including matrix element effects; Calculation of X-ray magnetic circular dichroism spectra from compounds; Kinetically-driven magnetism in a class of magnetic compounds (double perovskites, dilute magnetic semiconductors); Spin-wave dispersions in double perovskites; Electronic structure of semiconducting nanomaterials by real space calculations; Study of a spintronic material, Mn-doped GaAs, in the nanometric size regime; Theories of doped manganites, including spin, charge and orbital ordering effects; Studies of low-dimensional interacting quantum systems using the density-matrix renormalization group and other numerical methods.

Equilibrium and Non-equilibrium Statistical Mechanics of soft condensed matter and other complex systems:
Systems of vortex lines in high-Tc superconductors in the presence of pinning; Frustrated magnetic systems; Study of Portevin-Le Chatelier effect through time series analysis and modeling; Study of martensitic transformations; Multiscaling in fluid and magnetohydrodynamic turbulence; Spatiotemporal chaos and spiral turbulence in excitable media, including models for ventricular fibrillation; Semiflexible polymers; Dynamic scaling in driven systems; Orientational and solvation dynamics in complex liquids; Phase diagrams and dynamics of charged micellar systems; Dynamics of ions in complex porous networks and biomembranes; Laser-induced freezing in colloidal systems; Numerical studies of the glass transition and slow dynamics in models of simple liquids; Equilibrium properties of classical fluids in a random potential; Complex networks in chemical, biological and social systems; Evolution of complexity in adaptive systems; Analytic and numerical studies of neural network models; Modeling ofgrowth of thin films under chemical vapour deposition and molecular beam epitaxy; The statistical mechanics of sedimentation; Dynamics and rheological chaos in surfactant solutions; Theory and experiments on ordered nonequilibrium steady states in agitated monolayers of granular rods; Statistical hydrodynamics of self-propelled organisms, from fish to bacteria to cell-membranes coupled to motors, filaments, and ATP; Rheology of the living cell.

The Mechanics of Living MatterFunding Agency : Indo-French Centre for the Promotion of Advanced Research (IFCPAR), project 3504-2

This project is a collaboration with the Institut Curie and the Ecole Sup\'{e}rieure de Physique et de Chimie Industrielles (ESPCI), Paris, the Raman Research Institute, Bangalore and the Institute of Mathematical Sciences, Chennai. Our interest is in the collective behaviour of active systems --- motile cells or bacteria, motors, filaments and ATP, biomembranes containing force centres and analogue systems in granular or colloidal matter. We will use analytical and numerical approaches to exploit coarse-grained hydrodynamic models that we have developed for such systems, to understand and predict shape-change, division and motion in individual cells, and patterns in the collective movement of microorganisms, and possibly to use these ideas to create biomimetic model systems.

Development of a miniaturized fluorescence based system for in-situ real time detection of PCRFunding Agency : CSIR-NMITLI (2006-2008)

This project is being carried out with an industrial partner to develop a microchip-based portable PCR analysis system for DNA analysis. The work to be carried out at Indian Institute of Science will primarily focus on the design, development and testing of a prototype miniaturized fluorescence based system for in situ real time detection of PCR amplification in microchips. The system will consist of a blue 470nm light source (GaN based LED or laser) for excitation of Sybr Green dye, appropriate lenses, beamsplitters, fiber optics and filters, followed by a sensitive silicon photodiode and its associated electronics. The source power, collection efficiency and detector electronics will be optimized to obtain the maximum signal intensity for the very small (few microliters) volume of reaction mixture used in the PCR microchips.

This project is an extension of the real-time inductively heated microchip PCR system developed by our group at Indian Institute of Science over the last four years. We have successfully demonstrated PCR on silicon surfaces using simple induction heating. We have also fabricated an indigenously designed bench-top fluorescence unit for simultaneous excitation and detection of Sybr Green dye. This system is successfully being used to monitor the PCR amplification process in real time. The results agree well with gel electrophoresis experiments.

Magneto-transport studies of Magnetic Tunnel JunctionsFunding Agency : DAE-BRNS (2005-2008)

In this project we will investigate the tunnel magneto-resistance (TMR) effect in magnetic tunnel junctions (MTJ). A magnetic tunnel junction consists of two ferromagnetic electrodes separated by a tunnel barrier. The resistance across this stack depends on the relative orientation of the magnetization of the ferromagnetic layers.

Since one can switch the relative orientation of the magnetization of the ferromagnetic layers by applying suitable magnetic field, this resistance can be altered by applying magnetic field giving rise to magneto-resistance. The MTJs will be fabricated using Pulsed Laser Deposition in an Ultra High Vacuum chamber. The main emphasis will be to tune the tunnel barrier properties and the right combination of the ferromagnetic electrodes.

The spin-polarization of the ferromagnetic electrodes will also be given emphasis. Other issues that will be addressed are the temperature stability of the TMR and the dependence of the TMR on bias voltage. Within this project, we expect to achieve fabrication of magnetic tunnel junctions with high TMR, good temperature stability for TMR and low biasing voltage. This study will address the fundamental physics involved in magnetic tunnel junctions.

Growth & Studies of CLBO & Related NLO CrystalsFunding Agency : DST (2004-2007)

This project deals with growth and studies of certain technologically important non-linear optical crystals. The crystals chosen for growth are materials of contemporary interest, used in ultra violet and visible regions of the optical spectrum, viz.

Cesium Lithium Borate (CLBO) and related borates as well as some new NLO crystals. Standard growth techniques like Czochralski pulling, flux method and TSSG are employed for this purpose.

CsLiB6O10 crystal has demonstrated 5% conversion efficiency in the 5th harmonic of Nd:YAG laser beam. It has relatively easy phase matching requirements, smaller walk off angle and higher damage threshold. Apart from post growth processing and characterization, non-linear optical studies such as measurement of SHG efficiency, laser damage threshold, etc. will be carried out. The problem related to hygroscopicity and consequent crystal cracking are to be combated with various doping and other physico-chemical processes. Growth of other new NLO borates is also envisaged.

Search for a permanent electric-dipole moment using laser-cooled 171Yb atomsFunding Agency : Swarnajayanti Fellowship, DST (2006-2010)

In this project, we plan to do an experiment to search for a permanent atomic electric-dipole moment (EDM) using laser-cooled 171Yb atoms launched in an atomic fountain. A uniform B field sets the quantization axis, and the Ramsey separated-oscillatory-fields method is used to measure the Zeeman precession frequency of the atoms.

Laser beams of appropriate polarization are used for preparation and detection in a given magnetic sublevel. The signature of an EDM is a shift in the Ramsey resonance correlated with application of a large E field. The precision is expected to be at least 20 times better than current limits because the use of a cold atomic beam allows application of E field 10 times larger than in a vapor cell, and the interaction time with the E field is 200 times larger compared to a thermal beam.

The leading source of systematic error in beam experiments, the E×v/c motional magnetic field, is reduced considerably because of the near-perfect reversal of velocity between up and down trajectories through the E-field region.

Development of high-precision frequency measurement techniquesFunding Agency : DAE-BRNS (2006-2008)

Measurements of the frequencies of atomic transitions can yield valuable information on hyperfine structure and isotope shifts in atoms. We have recently developed a technique to measure the absolute frequency of optical transitions with a relative precision of ~10-10. In this work, we propose to extend the technique to the measurement of transitions that are of interest to DAE programmes. We further plan to improve the precision by using a narrow two-photon transition in Rb as the frequency reference. For difference-frequency measurement of hyperfine structure and isotope shifts, we will use an acousto-optic modulator or rf modulation to shift the laser frequency, and then lock the frequency to the relevant frequency difference. This technique will be used to determine hyperfine structure in certain important isotopes with high accuracy. We will also develop the technique of linewidth narrowing of a tunable laser by locking its frequency to a high-finesse cavity.

Precision laser spectroscopy of atomsFunding Agency : DST (2005-2009)

In an earlier DST project, we have demonstrated our expertise in magneto-optic trapping of Rb and Yb atoms, use of coherent-control techniques for precision spectroscopy in multi-level atoms, and measurement of optical frequencies with 10-10 uncertainty. We have applied these techniques to the determination of hyperfine structure in Rb and Yb. In this project, we plan to measure the frequencies of D lines in alkali atoms such as Li, K, Rb and Cs. We have already trapped Yb atoms using a MOT on the 399nm line. The dominant trap loss mechanism is decay into low- lying metastable states. We will increase the trap lifetime by clearing these metastable states using diode lasers. By selectively blocking one of the clear-out lasers, we can optically pump atoms into the other metastable state, and trap them in the excited state. Alternately, we plan to cool and trap the atoms using the 556nm intercombination line, which has a much smaller Doppler cooling limit.

Experimental and Computational Studies on Neurobiological Systems (2005-2008) Inter-disciplinary

The project has following two goals:

  1. Setting up the multielectrode array facility for studying planar live neuronal network activities using electrophysiological and computational methods.
  2. Mechanisms for acquisition, reconstruction, analysis, and classification of brain images and neurobiological signal.

Three Dimensional and Four Dimensional Wavelet-based Loss-less Tomographic Image Coder: Algorithms and Architectures (2004-2006)

Medical images are normally huge in data size. With the emergence of 3-D medical images, uncompressed data requires considerable storage capacity and transmission bandwidth that may not be available in network of limited bandwidth.

Medical field can benefit tremendously from the technological advancements by sharing the knowledge by hosting huge databases of images and ECG and EEG spectra. Efficient data compression schemes (both at the algorithmic and architecture levels) are required for making this a reality.

The region-of-interest (ROI) is a scheme that allows efficient use of bandwidth for transmitting information. The study envisages to look at ROI problem, and develop appropriate algorithms.

Towards Doppler Imager and for Biomedical Impedance Imaging Equipment (2006-2009)

Visualization and Quantization of Breast Cancer Using Elastography and Magnetic Resonance Imaging

Early detection is one of the primary requirements of successful cancer treatment and this is more so in the case of breast cancer. It is well known that variation in tissue elastic properties are associated with the presence of cancer and forms the basis of clinical examination. Tissue stiffness, defined by Young’s modulus, can span a range of 1-100 kPa amongst various soft tissues in the body, with connection tissues and cartilages ranging from 100-1000 kPa. Studies have shown a significant variation in elastic properties between normal breast tissue and cancerous tissue. It has been shown a 15-fold increase in Youngs modulus of breast cancer tissue compared to normal tissue.

In soft tissues, the Young's modulus (E) is directly proportional to the shear modulus µ (E=3 µ). It explains the great interest of imaging the shear modulus distribution map that has influenced the development of numerous elastographic techniques. These techniques mainly differ by the kind of perturbation, which is applied to the medium, and by the imaging system used to estimate displacements within the medium.

 

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