Tailoring of Structural Morphology of Silver Nanowires in Electrochemical Growth
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1058-JJ03-04
Tailoring of Structural Morphology of Silver Nanowires in Electrochemical Growth Amrita Singh1, Arindam Ghosh1, Amrita Singh2, and Amrita Singh2 1 Physics, Indian Institute of Science, C.V. Raman Avenue, Bangalore, 560012, India 2 Physics, Indian Institute of Science, Bangalore, 560012, India
ABSTRACT We demonstrate that commonly face centered cubic (fcc) metallic nanowires can be stabilized in hexagonal structure even when the surface energy contribution is relatively small. With a modified electrochemical growth process, we have grown purely single-crystalline 4H silver nanowires (AgNWs) of diameter as large as 100 nm within nanoporous anodic alumina and polycarbonate templates. The growth process is not limited by the Ag /Ag+ Nernst equilibrium potential, and time-resolved imaging with high-resolution transmission electron microscopy (TEM) indicates a kinematically new mechanism of nanowire growth. Most importantly, our experiments aim to separate the effects of confinement and growth conditions on the crystal structure of nanoscale systems.
INTRODUCTION Research on nanowires is continuously increasing because being a defect free nanoscale material it has potential applications in areas of plasmonics [1], nanoelectronics [2], superconductivity [3]. Moreover, nanowires can be used as interconnects in the nanoelectronics devices. Template synthesis has been proved to be a versatile and simple approach for the preparation of metal nanowires and nanotubes [3,4]. Anodic aluminum oxide (AAO) and polycarbonate (PC) are perfectly well suited for nanowire fabrication because they provide a well defined matrix with well defined pores. Normally metal such as Ag exists in an fcc crystal structure. However as the size of the material is decreased to nanometer length scales, a structural transformation from that of its bulk state can be expected with new atomic arrangements due to competition between internal packing and minimization of surface energy [5]. Existence of metastable phase of Ag and Au in hcp structure has been investigated by means of first principle total energy calculation [6]. However, the critical dimensions for surface energy-driven transformation of the fcc lattice in nano-systems remains uncertain, and have been predicted from fraction of a nanometer in computer simulation studies [5], up to ~ 25 nm by analytically balancing surface and bulk packing energy in AgNWs [7]. Uncertainty exists in experiment as well, particularly due to conflicting evidences of hexagonal crystal structure of nanowires and nanoparticles. Liu et al. reported observation of partial hcp phase coexisting with fcc AgNWs over a diameter range 10 − 75 nm [7], while earlier experiments reported only pure fcc phase over the similar diameter range [10,11]. Furthermore, pure fcc was observed in AgNWs of even sub-nanometer diameters confined within a nanotubes [8]. Consequently, it has been conjectured that the hcp phase in metallic nanowires results from diminishing size as well as appropriate growth mechanism, although no c
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