Growth of isolated axial heterojunction nanowires by a solution phase growth process is reported. The dumb-bell shaped nanowires contain two silver telluride sections at the extremes joined by a tellurium section. Reaction of silver nitrate with tellurium NWs in aqueous solution at a molar ratio of 1:1 leads to the formation of amorphous partially silver reacted Te NWs. Low temperature (75°C) solution phase annealing of these silver deficient NWs results in phase segregation producing crystalline Ag2Te and Te phases with clear phase boundaries along the wire axis. Structural characterization of these dumb-bell shaped NWs was performed with different microscopic and spectroscopic tools. Solution phase silver concentration over the course of annealing indicated leaching of silver into the solution during the formation of biphasic NWs. Similar Ag:Te ratios were observed in both partially silver reacted Te NWs and phase segregated Ag2Te-Te-Ag 2Te NWs and this was attributed to redeposition of leached silver on the amorphous NW tips which eventually resulted in complete phase segregation. Successful integration of different chemical components in single NWs is expected to open up new application possibilities as physical and chemical properties of the heterostructure can be exploited. © 2012 The Royal Society of Chemistry.

Pradeep Thalappil

Department Of Chemistry

Heterojunctions

Leaching

Nanowires

Phase separation

Solutions

Tellurium

Tellurium compounds

Temperature

AXIAL HETEROJUNCTIONS

Chemical component

Low temperatures

Phase segregations

Physical and chemical properties

SILVER CONCENTRATION

SPECTROSCOPIC TOOL

Structural characterization

Silver compounds

Fulltext

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IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

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IIT Madras

Nanoscale

Hybrid A-B-A type nanowires (NWs) with Ag 5Te 3-HgTe- Ag 5Te 3 composition have been created by the reaction of Hg 2+ with Ag 2Te NWs. The NW morphology of Ag 2Te is preserved upon reaction with minor changes and the two separate phases formed are spatially separated within the same NW. The reaction of Hg 2+ with Ag 2Te NWs was monitored at different concentrations and the reactivity was attributed to cationic exchange depending on solubility products. Hybrid NWs were formed by partial cation exchange only at low concentrations (below 50 ppm) resulting in Ag 5Te 3 and HgTe within the same NW. However, at high concentrations (above 100 ppm), the HgTe phase alone was formed. These studies have been extended to other metal ions such as Pb 2+, Cd 2+, and Zn 2+ whose reactivity towards Ag 2Te NWs is different from that of Hg 2+. These ions form a passivating Te oxide layer upon reaction with other metal ions. The mechanism of reactivity of Hg 2+ is explained on the basis of free energy of formation of the ionic solid. Phase transition of Hg 2+-reacted NWs occurs at a lower temperature than the parent (Ag 2Te NWs) and other metal ions-reacted Ag 2Te NWs. Details of the process were elucidated using microscopic and spectroscopic investigations. The physical and chemical properties of the individual components within a NW are expected to provide a novel functionality to the metal chalcogenide systems. © 2011 The Royal Society of Chemistry.

Hybrid A-B-A type nanowires through cation exchange

A new approach for the synthesis of freely dispersible one-dimensional (1D) lanthanum telluride nanowires (La2Te3 NWs) in the solution phase is reported. The process involves a reaction between tellurium nanowires (Te NWs) and lanthanum nitrate (La(NO3)3) at roomerature. Te NWs act as templates for the formation of La2Te 3 NWs. The aspect ratio of the as prepared La2Te 3 NWs is the same as the parent Te NWs. Various microscopic and spectroscopic tools such as HRTEM, SEM, EDAX, XRD, XPS, Raman, UV?visible, and fluorescence were used for the characterization of the NWs. A new surface enhanced Raman active substrate was synthesized by doping silver in La 2Te3 NWs. Surface enhanced Raman spectra were studied using crystal violet (CV) as the analyte. Raman features have been observed up to a concentration of 10?8 M of CV. Different concentrations of Ag in Ag-doped La2Te3 NWs were investigated. The monodispersity, homogeneity, and Raman enhancement properties of the NWs, synthesized through a simple solution phase protocol, are expected to motivate further studies on this material. © 2010 American Chemical Society.

Journal of Physical Chemistry C

Lanthanum telluride nanowires: Formation, doping, and Raman studies

We have developed a room-temperature solution-phase route for the preparation of one-dimensional silver telluride nanowires (Ag2Te NWs). The Ag2Te NWs of 600 nm length and 20 nm diameter were synthesized by the reaction of tellurium nanowires (Te NWs) with silver nitrate (AgNO3) in water. We propose that Te NWs act as the template and the reducing agent simultaneously, enabling the formation of polycrystalline Ag 2Te NWs. Various microscopic and spectroscopic tools, such as HRTEM, SEM, EDAX, XRD, DSC, XPS, and Raman, were used for the characterization of Ag2Te NWs. The phase transition corresponding to the structural transition from the low-temperature monoclinic phase to the high-temperature face-centered cubic phase occurs at 417.7 K. We studied the electrical resistance and investigated the influence of temperature on the thermal emf. The Seebeck coefficient showed a maximum of ∼142 μV K-1, a value much higher than that of the bulk material and thin films (65-130 μV K -1). A surface-enhanced Raman scattering investigation of dispersed Ag2Te NWs showed them to be sensitive up to 10-7 M crystal violet. The monodispersity and the homogeneity of the NWs through a simple solution-phase protocol would pave the way for further studies and applications. © 2009 American Chemical Society.

Room-temperature chemical synthesis of silver telluride nanowires

ACS Nano

Lateral Etching of Core–Shell Au@Metal Nanorods to Metal-Tipped Au Nanorods with Improved Catalytic Activity

Nano Letters

Rational Synthesis of Ultrathin n-Type Bi2Te3Nanowires with Enhanced Thermoelectric Properties

Heterojunction double dumb-bell Ag2Te-Te-Ag2Te nanowires

Journal	Data powered by TypesetNanoscale
Publisher	Data powered by TypesetRoyal Society of Chemistry
ISSN	20403364
Open Access	No