BITS Faculty Publications

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End date: 1999

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    Higher order elastic constants and generalized Gruneisen parameters of elastic waves and low temperature thermal expansion of gadolinium
    (Springer, 1996-12) Nair, Sindhu S.
    Expressions for the higher order elastic constants are derived using the sublattice displacements to the second degree in strains. These expressions are used to obtain the higher order elastic constants and their pressure derivatives in gadolinium. The higher order elastic constants are used to find out the generalized Gruneisen parameters of the elastic waves propagating in different directions in gadolinium. The Brugger gammas are evaluated and the low temperature limit of the Gruneisen gamma is obtained. The results are compared with the available reported values.
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    Fourth order nonlinear elastic coefficients of hexagonal close packed lattice
    (Elsevier, 1996-09) Nair, Sindhu S.
    The expressions for the fourth-order elastic constants of a hexagonal close packed lattice is derived using the sublattice displacements to the second order in strains. These expressions together with the expressions for the second- and third-order elastic constants have been used to obtain the higher order nonlinear elastic coefficients in some hexagonal metals. These expressions are used to find the second-order, third-order and fourth-order elastic constants of cadmium. The pressure derivatives of their elastic constants are also obtained. The results obtained are compared with the available experimental results.
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    Higher order elastic constants and second pressure derivatives of zirconium
    (IAEA, 1997) Nair, Sindhu S.
    Expressions for the higher order elastic constants are derived using the sublattice displacements to the second degree in strains. These expressions together with the expressions for the second and third order elastic constants have been used to obtain the higher order elastic constants and the pressure derivatives to second order elastic constants of hexagonal zirconium. The results obtained are compared with the reported values. The second pressure derivatives of zirconium are also reported
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    Higher Order Elastic Constants and Generalized Gruneisen Parameters of Elastic Waves and Low Temperature Thermal Expansion of Titanium
    (Elsevier, 1997-02) Nair, Sindhu S.
    The expressions for the 19 fourth order elastic constants, 10 third order elastic constants, and 6 second order elastic constants of a solid are derived using the method of homogenous deformation with interactions extending up to second neighbors using the sublattice displacements to the second degree in strains. These expressions are used to obtain the higher order elastic constants and their pressure derivatives in titanium. Titanium belongs to the hexagonal class of crystals. The higher order elastic constants are used to find the generalized Gruneisen parameters of the elastic waves propagating in different directions in titanium. The Brugger gammas are evaluated and the low temperature limit of the Gruneisen gamma is obtained. The results are compared with the available reported values.
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    Higher order elastic constants and generalised gruneisen parameters of elastic waves and low temperature thermal expansion of dysprosium
    (Elsevier, 1997-12) Nair, Sindhu S.
    The expressions for the 19 fourth order elastic constants, 10 third order elastic constants and six second order elastic constants are derived using the method of homogenous deformation with interactions extending up to second neighbours using the sublattice displacements to the second degree in strains. These expressions are used to obtain the higher order elastic constants and their pressure derivatives in dysprosium. Dysprosium belongs to the hexagonal class of crystals. The higher order elastic constants are used to find out the generalised Gruneisen parameters of the elastic waves propagating in different directions in dysprosium. The Brugger gammas are evaluated and the low temperature limit of the Gruneisen gamma is obtained. The results are compared with the available reported values.
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    Surface Structure Of Ale-grown Polycrystalline Calcium Sulfide Thin Films Studied By Afm
    (Materials Research Society of Korea, 1998) Dey, Srijata
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    Laser-Assisted Scanning Tunneling Microscopy Studies of Thin Ordered Molecular Layers
    (Springer, 1995) Dey, Srijata
    The irradiation of the junction of an STM with laser light may give access to the study of resonant effects. Since high laser intensities are required, an active compensation setup, designed to suppress the dominating nonresonant effects is used. Mixed films of the dye perylene-tetracarboxylic-dianhydride (PTCDA) and the liquid crystal octylcyanobiphenyl (8CB) were prepared on graphite and MoS2. STM measurements show small isolated domains of PTCDA embedded in 8CB. The islands could be imaged with high resolution even under the illumination with intense laser light. First experiments investigating the laser-induced contrast observed on the dye islands under active compensation of the nonresonant effects are discussed.
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    STM studies on dye molecules embedded in ordered liquid crystal structures and an approach for laser-assisted scanning tunneling microscopy
    (SPIE, 1993-06) Dey, Srijata
    Scanning tunneling microscopy, although capable of yielding very high resolution on periodic structures, very often provides only moderate resolution on singular features. Our work aims at the use of laser light to improve the identification of individual molecules. We report on scanning tunneling microscopy measurements performed on dye molecules dissolved in a liquid crystal and adsorbed onto highly oriented pyrolytic graphite. Either localized perturbations of the liquid crystal structure with the size of single molecules or more or less extended ordered domains of well resolved dye molecules were reproducibly imaged for several dyes. To study light-induced resonant effects the influence of non-resonant absorption leading to thermal expansion of tip and sample has to be suppressed. Therefore, an electro- optical system was realized using an ArPLU- and a dye laser of different wavelengths power-modulated with a relative phase shift of 180 degree(s). Preliminary results obtained with this setup are presented documenting the efficiency of the compensation.
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    An ultrahigh‐vacuum system for STM studies
    (AIP, 1994) Dey, Srijata
    An ultrahigh‐vacuum (UHV) system for STM studies is described where a home‐built STM is combined with a novel facility for in situ exchange of samples and tips. Technical details concerning the design of the sample and tip holders and the manipulation and storage equipment are given. For the preparation of organic films a compact evaporation source comprising two ovens with an excellent thermal insulation was constructed. First STM results of a coronene film on graphite and of tungsten diselenide are presented.
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    Scanning tunneling microscopy studies of diazo dye monolayers on HOPG
    (Elsevier, 1995-05) Dey, Srijata
    We report on scanning tunneling microscopy (STM) studies of monolayers of the diazo dye 4-[4-(N,N-dimethylamino)phenylazo]azobenzene (D2, summation formula C20H19N5) on the basal plane of highly oriented pyrolytic graphite (HOPG). Monolayers of the dye were prepared by vapour deposition or by dissolving the molecules in the liquid crystal octylcyanobiphenyl (8CB). The STM images show a double-row structure exhibiting different types of lattice defects and various domains. High-resolution images allow the identification of individual molecules and the observation of intramolecular contrast. The different orientations of the rows can be explained by a commensurate registry of the molecules with the substrate. A model for the unit cell is proposed.