• Murali Sastry

      Articles written in Bulletin of Materials Science

    • A note on the use of ellipsometry for studying the kinetics of formation of self-assembled monolayers

      Murali Sastry

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      Ellipsometry is currently one of the most important techniques for characterization of the deposition and growth mode of ultra thin organic films. However, it is well known that for thicknesses normally encountered in organic monolayer films, as would occur for example in self-assembled monolayers, ellipsometry cannot be used to simultaneously determine the thickness and refractive index of the monolayer film. Current practice is to assume a reasonable value for the film refractive index and calculate an effective ‘ellipsometric thickness’. This communication seeks to show that the alternative approach of assuming a thickness for the monolayer (determined by the length of the molecule) and calculating the effective film refractive index lends itself to easier and more meaningful physical interpretation. The Lorentz-Lorenz formula is then used to transform the effective refractive index into a surface coverage and hence to an effective mass coverage. The methodology advanced is applied to the kinetics of formation of a self-assembled monolayer of a well-studied molecule, octadecanethiol on Au.

    • On the morphology of SrCO3 crystals grown at the interface between two immiscible liquids

      Satyanarayana Reddy Debabrata Rautaray S R Sainkar Murali Sastry

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      In this paper we report on the growth of strontianite crystals at the interface between an aqueous solution of Sr2+ ions and organic solutions of chloroform and hexane containing fatty acid/fatty amine molecules by reaction with sodium carbonate. When fatty acid was used as an additive at the interface, the crystals grown were self-assembled needle shaped strontianite crystallites branching out from the seed crystal via secondary nucleation. Under identical conditions of supersaturation, the presence of fatty amine molecules at the liquid–liquid interface resulted in needle shaped strontianite crystals with spherical crystallites arranged around central needles. This clearly indicates that the functionality of the head group of the amphiphiles at the liquid–liquid interface affects the morphology of the strontium carbonate crystals formed. The use of interfacial effects such as dielectric discontinuity, polarity and finite solubility of the two solvents etc opens up exciting possibilities for tailoring the morphology of crystals at the liquid–liquid interface and is currently not possible in the more popular crystal growth with similar amphiphiles at the air–water interface.

    • Silver nanoparticles of variable morphology synthesized in aqueous foams as novel templates

      Saikat Mandal Sujatha K Arumugam Renu Pasricha Murali Sastry

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      In this paper, we describe the synthesis of silver nanocrystals within aqueous foams as a template. More specifically, we show that aqueous Ag+ ions may be electrostatically complexed with the anionic surfactants aerosol OT (sodium bis-2-ethylhexyl-sulfosuccinate, (AOT) and sodium dodecyl sulphate (SDS)) in a highly stable liquid foam. After drainage of the foam, the silver ions are reduced in situ by introducing sodium borohydride into the foam by capillary flow. This leads to the formation of silver nanoparticles of spherical, tape- and sheet-like morphology in the foam. The structure of the foam is extremely complex and presents reaction sites of different spatial extent. The differences in foam reaction–site geometry are believed to be responsible for the morphology variation in the silver nanoparticles observed. The silver nanoparticles are observed to be extremely stable in solution suggesting that the AOT or SDS molecules stabilize them. This approach appears promising for application in large-scale synthesis of nanoparticles and may be readily extended to other chemical compositions.

    • New approach towards imaging 𝜆-DNA using scanning tunneling microscopy/spectroscopy (STM/STS)

      Shirshendu Dey Sushama Pethkar Suguna D Adyanthaya Murali Sastry C V Dharmadhikari

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      A new methodology to anchor 𝜆-DNA to silanized 𝑛-Si(111) surface using Langmuir Blodget trough was developed. The 𝑛-Si (111) was silanized by treating it with low molecular weight octyltrichlorosilane in toluene. Scanning tunneling microscopy (STM) image of 𝜆-DNA on octyltrichlorosilane deposited Si substrate shows areas exhibiting arrayed structures of 700 nm length and 40 nm spacing. Scanning tunneling spectroscopy (STS) at different stages depict a broad distribution of defect states in the bandgap region of 𝑛-Si(111) which presumably facilitates tunneling through otherwise insulating DNA layer.

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