R. Shashidhar

Raman Research Institute, Bengalūru, Karnātaka, India

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Publications (200)414.11 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: We report here the results of detailed density, dielectric and x-ray studies on three systems exhibiting different types of Smectic A-Smectic A transitions. It is found that although the layer spacing shows marked changes at the transitions, the corresponding density changes are extremely small. In every case studied, the dielectric anisotropy shows a pronounced decrease on going over to the lower temperature smectic A phase. This decrease can be correlated with the structural changes.
    Molecular Crystals and Liquid Crystals. 10/2011; 138(1):245-257.
  • D. Shenoy, A. Lavarello, J. Naciri, R. Shashidhar
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    ABSTRACT: The thickness dependence of ferroelectric polarization in a SmC* liquid crystal exhibiting a large value of polarization has been investigated. It is observed that the saturation value of the polarization shows no significant thickness dependence. This observation is in accordance with a recent theoretical framework developed by Galerne. It is shown that the wall thickness, where the polarization undergoes a reversal, and hence the self-screening effect, is insignificant in the material studied.
    Liquid Crystals 08/2010; 28(6):841-844. · 1.96 Impact Factor
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    S. MERY, D. LOTZSCH, G. HEPPKE, R. SHASHIDHAR
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    ABSTRACT: Novel liquid crystalline Low Molecular Mass (LMM) materials bearing two chiral lactate groups, as well as compounds of like structure to MHPOBC have been synthesized. All the LMM compounds exhibit the SmC*A (antiferroelectric) and/or SmC*gamma (ferrielectric) phases. The mesogens have been incorporated as pendant groups on polymer backbones of three different natures to prepare side chain liquid crystalline copolysiloxanes, homopolysiloxanes and homopolyacrylates. The investigation of the polymers by means of miscibility studies showed that the antiferro- and ferri-electric phases are strongly destabilized in the coposiloxanes and homopolysiloxanes, while in the homopolyacrylates a large temperature range mesophase is found to be miscible with the SmC*A phase. The physical properties of the mesophases and their stability, both for the LMM materials and the polymers, are presented and discussed.
    Liquid Crystals 06/2010; November 1(1997):629-644. · 1.96 Impact Factor
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    ABSTRACT: X-ray, electrical, electro-optical, and dielectric studies in the de Vries smectic A (SmA) phase of organosiloxane derivatives exhibit features surprisingly different from that of a conventional SmA phase. The switching data show a double peak profile, characteristic of an antiferroelectric (AF) structure. A model with the adjacent smectic layers having an AF-like arrangement and no global tilt correlation is proposed. Observed in molecules with differential interactions between the two termini, these findings have wide ramifications in understanding the minimum layer shrinkage of such systems.
    Physical Review Letters 05/2009; 102(14):147802. · 7.73 Impact Factor
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    ABSTRACT: A quantitative study of the structure and correlation of individual layer interfaces in a liquid-crystalline polymer multilayer film is reported. Off-specular and specular X-ray scattering data on successively deposited Langmuir-Blodgett films of the polymer show that the roughness of the first and subsequently deposited smectic layers is directly correlated with that of the chemisorbed hydrophobization layer and not correlated with the underlying silicon substrate.
    EPL (Europhysics Letters) 07/2007; 32(5):419. · 2.26 Impact Factor
  • R. Shashidhar, J. Naciri, B. R. Ratna
    03/2007: pages 51 - 76; , ISBN: 9780470141724
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    ABSTRACT: The study of charge transport through increasingly complex small molecules will benefit from a detailed understanding of how contaminants from the environment affect molecular conduction. This should provide a clearer picture of the electronic characteristics of molecules by eliminating interference from adsorbed species. Here we use magnetically assembled microsphere junctions incorporating thiol monolayers to provide insight into changing electron transport characteristics resulting from exposure to air. Using this technique, current-voltage analysis and inelastic electron tunnelling spectroscopy (IETS) demonstrate that the primary interaction affecting molecular conduction is rapid hydration at the gold-sulphur contacts. We use IETS to present evidence for changing mechanisms of charge transport as a result of this interaction. The detrimental effects on molecular conduction discussed here are important for understanding electron transport through gold-thiol molecular junctions once exposed to atmospheric conditions.
    Nature Material 12/2006; 5(11):901-8. · 35.75 Impact Factor
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    ABSTRACT: The correlation between molecular structure and electrooptic performance is studied for novel room temperature chiral smectic A liquid crystals. It is observed that slight modifications of the hydrocarbon chain connected to the chiral center result in dramatic differences in their electrooptic performance. If the hydrocarbon chain is shortened or if a double bond is localized at the end of the hydrocarbon chain, the tilt angle, electroclinic coefficient, and switching time are significantly suppressed.
    Molecular Crystals and Liquid Crystals - MOL CRYST LIQUID CRYST. 09/2006; 263(1):10.
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    ABSTRACT: An electro‐optical technique was used to measure the rotational viscosity of nematic liquid crystals, whose structures were chosen to investigate the effects of linking groups and lateral groups on rotational viscosity. These results are compared with the theory developed by Osipov and Terentjev. It is shown that the theory is useful in predicting rotational viscosity for specific molecular structures. The agreement between theory and experiment is found to be good for all the liquid crystals studied.
    Liquid Crystals 01/2006; 33(1):67-73. · 1.96 Impact Factor
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    ABSTRACT: Self-assembled monolayers (SAMs) of the isocyano derivative of 4,4'-di(phenylene-ethynylene)benzene (1), a member of the "OPE" family of "molecular wires" of current interest in molecular electronics, have been prepared on smooth, {111} textured films of Au and Pd. For assembly in oxygen-free environments with freshly deposited metal surfaces, infrared reflection spectroscopy (IRS) indicates the molecules assume a tilted structure with average tilt angles of 18-24 degrees from the surface normal. The combination of IRS, X-ray photoelectron spectroscopy, and density functional theory calculations all support a single sigma-type bond of the -NC group to the Au surface and a sigma/pi-type of bond to the Pd surface. Both SAMs show significant chemical instability when exposed to typical ambient conditions. In the case of the Au SAM, even a few hours storage in air results in significant oxidation of the -NC moieties to -NCO (isocyanate) with an accompanying decrease in surface chemical bonding, as evidenced by a significant increase in instability toward dissolution in solvent. In the case of the Pd SAM, similar air exposure does not result in incorporation of oxygen or loss of solvent resistance but rather results in a chemically altered interface which is attributed to polymerization of the -NC moieties to quasi-2D poly(imine) structures. Conductance probe atomic force microscope measurements show the conductance of the degraded Pd SAMs can diminish by approximately 2 orders of magnitude, an indication that the SAM-Pd electrical contact has severely degraded. These results underscore the importance of careful control of the assembly procedures for aromatic isocyanide SAMs, particularly for applications in molecular electronics where the molecule-electrode junction is critical to the operational characteristics of the device.
    Langmuir 12/2005; 21(24):11061-70. · 4.38 Impact Factor
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    ABSTRACT: Reported in this contribution are the synthesis, characterization, and charge transport properties of wire-like Ru2(ap)4(OPEn), where ap is 2-anilinopyridinate and OPE is -(CCC6H4)nSCH2CH2SiMe3 with n = 1 (1) and 2 (2). Scanning tunneling microscopy (STM) measurements of compound 2 inserted into a SAM of C11 thiol reveal that molecule 2 exhibits (i) the stochastic switching characteristic of wire molecules embedded in insulating SAMs and (ii) higher conductivity than the C11 thiol SAM. More importantly, analysis of the molecular electronic decay constant (beta) exhibits a decrease of at least 15% as compared to purely organic molecular analogues. Hence, the transport characteristics of molecules can be significantly improved for nanoscale electronics through the incorporation of a Ru2 fragment into conjugated backbone.
    Journal of the American Chemical Society 08/2005; 127(28):10010-1. · 10.68 Impact Factor
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    Small 08/2005; 1(7):702-6. · 7.82 Impact Factor
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    ABSTRACT: The second- and fourth-order apparent orientational order parameters of the core part of the molecule P2 (app) and P4 (app) , have been measured by polarized vibrational Raman spectroscopy for a homogeneously aligned ferroelectric smectic liquid crystal with three dimethyl siloxane groups in the achiral terminal chain, which shows de Vries-type phenomena, i.e., very large electroclinic effect in the smectic- A (Sm-A) phase and a negligible layer contraction at the phase transition between the Sm-A and Sm- C(*) phases. The apparent orientational order parameters of the rigid core part of the molecule are extremely small both with and without the external electric field in Sm-A . These results provide evidence for the existence of the de Vries Sm-A phase, where the local molecular director is tilted at a large angle.
    Physical Review E 05/2005; 71(4 Pt 1):041705. · 2.31 Impact Factor
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    ABSTRACT: Molecular electronics has been proposed as a pathway for high-density nanoelectronic devices. This pathway involves the development of a molecular memory device based on reversible switching of a molecule between two conducting states in response to a trigger, such as an applied voltage. Here we demonstrate that voltage-triggered switching is indeed a molecular phenomenon by carrying out studies on the same molecule using three different experimental configurations-scanning tunnelling microscopy, crossed-wire junction, and magnetic-bead junction. We also demonstrate that voltage-triggered switching is distinctly different from stochastic switching, essentially a transient (time-dependent) phenomenon that is independent of the applied voltage.
    Nature Material 03/2005; 4(2):167-72. · 35.75 Impact Factor
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    ABSTRACT: Reported herein are the synthesis, electrochemical and structural characterization of wire-like Ru2-alkynyl compounds, Ru2(ap)4(Ln)x, where ap is 2-anilinopyridinate, and Ln is –(CCC6H4)nSCH2CH2SiMe3 with n=1 (1) and 2 (2), and x can be 1 (a) and 2 (b). Reactions between Ru2(ap)4Cl and one equiv. of LiLn yielded the mono-alkynyl compound only, while the use of 4–5 equiv. of LiLn resulted in a mixture of both the mono and bis-alkynyl species. Single crystal X-ray diffraction studies of compounds 1a and 1b revealed structural similarities to Ru2(ap)4(C2Ph) and Ru2(ap)4(C2Ph)2, respectively. Magnetic, spectroscopic and voltammetric measurements also revealed a minimal perturbation on electronic structures due to the functionalization of OPE ligands with thiol-TMSE group (–SCH2CH2SiMe3). Most significantly, it can be estimated based on the structure of 1a that the Ru–OPE2–S– linkage in 2a is significantly longer than the depth of C11 thiol SAM and hence enables the insertion of 2a into the latter.
    Journal of Organometallic Chemistry - J ORGANOMET CHEM. 01/2005; 690(21):4734-4739.
  • Small 01/2005; 1(7):669-669. · 7.82 Impact Factor
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    ABSTRACT: The scaling of conductance across metal−molecule−metal junctions consisting of self-assembled monolayers of dithiol molecular wire candidates is demonstrated through current−voltage measurements carried out by two experimental techniques. We show that scanning tunneling microscopy measurements on single molecules are correlated with crossed-wire measurements of 103 molecules. This implies that the conductance through a group of parallel molecules is a linear superposition of the individual molecular conductance. Our results also indicate that intermolecular charge hopping does not strongly contribute to charge transport in a self-assembled monolayer, an important factor for the design of future molecular-based devices.
    Journal of Physical Chemistry B - J PHYS CHEM B. 11/2004; 108(47).
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    ABSTRACT: Coupling of photosynthetic reaction centers (RCs) with inorganic surfaces is attractive for the identification of the mechanisms of interprotein electron transfer (ET) and for possible applications in construction of photo- and chemosensors. Here we show that RCs from Rhodobacter sphaeroides can be immobilized on gold surfaces with the RC primary donor looking towards the substrate by using a genetically engineered poly-histidine tag (His(7)) at the C-terminal end of the M-subunit and a Ni-NTA terminated self-assembled monolayer (SAM). In the presence of an electron acceptor, ubiquinone-10, illumination of this RC electrode generates a cathodic photocurrent. The action spectrum of the photocurrent coincides with the absorption spectrum of RC and the photocurrent decreases in response to the herbicide, atrazine, confirming that the RC is the primary source of the photoresponse. Disruption of the Ni-NTA-RC bond by imidazole leads to about 80% reduction of the photocurrent indicating that most of the photoactive protein is specifically bound to the electrode through the linker.
    Biosensors and Bioelectronics 08/2004; 19(12):1649-55. · 5.44 Impact Factor
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    ABSTRACT: A detailed investigation of the processing parameters influencing the oxidative polymerization of 3,4-ethylenedioxythiophene (EDOT) and a methanol-substituted derivative (EDOT–CH2OH) was performed with the goal of maximizing the conductivity of the polymer. We show that the conductivity can be significantly enhanced by varying the monomer, oxidant (iron(III) p-toluenesulfonate (Fe(OTs)3)), weak base (imidazole (Im)), solvent (various alcohols), and solution concentrations. The effect of each variable on the final materials properties is investigated, and the parameters have been optimized to achieve conductivities as high as 900 S cm–1. Surface resistance below 150 Ω/□ for 80–90 nm thick films with visible-spectrum transparency exceeding 80 % is achieved. The combination of these properties makes the films highly suitable for numerous device applications.
    Advanced Functional Materials 06/2004; 14(6):615 - 622. · 10.44 Impact Factor
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    ABSTRACT: We demonstrate the ability to tune the current rectification in metal–molecule–metal junctions through control of the interaction strength of one of the two metal–molecule contacts. Current–voltage characteristics of thiolate bound molecular wires with a nitro or pyridine termination show that the extent of current rectification in a molecular junction correlates well with the extent of coupling between the chemical linker and metal electrode.
    Nanotechnology 06/2004; 15(7):S489. · 3.84 Impact Factor

Publication Stats

2k Citations
414.11 Total Impact Points

Institutions

  • 1976–2011
    • Raman Research Institute
      Bengalūru, Karnātaka, India
  • 2006
    • SAIC
      United States
  • 2002–2005
    • United States Naval Research Laboratory
      • Center for Biomolecular Science and Engineering
      Washington, D. C., DC, United States
  • 2003
    • Trinity College
      Hartford, Connecticut, United States
  • 1999–2003
    • The Catholic University of America
      • Department of Physics
      Washington, D. C., DC, United States
  • 1993
    • University of Florida
      • Department of Chemistry
      Gainesville, Florida, United States
  • 1989
    • Georgetown University
      Washington, Washington, D.C., United States
  • 1981–1982
    • Ruhr-Universität Bochum
      • Fachbereich Biochemie
      Bochum, North Rhine-Westphalia, Germany