Electrochemical fabrication of ultralow noise metallic nanowires with hcp crystalline lattice

Abstract

We experimentally demonstrate that low-frequency electrical noise in silver nanowires is heavily suppressed when the crystal structure of the nanowires is hexagonal closed pack (hcp) rather than face centered cubic (fcc). Using a low-potential electrochemical method we have grown single crystalline silver nanowires with hcp crystal structure, in which the noise at room temperature is two to six orders of magnitude lower than that in the conventional fcc nanowires of the same diameter. We suggest that motion of dislocations is probably the primary source of electrical noise in metallic nanowires which is strongly diminished in hcp crystals.Metallic nanowires are integral components of several nanoscale electronic circuits, particularly in crossbar interconnect architectures. 1 Both experiments 2,3 and electrical modelling 4 have often addressed the effects of size on average electrical resistivity (ρ) of the nanowires, but very little is known about the low-frequency 1/f -type electrical noise in these systems which can seriously impede their application in nanoelectronics. 5,6 Moreover, recent experiments suggest that the magnitude of noise in nanowires can indeed be much larger than that generally observed in thin polycrystalline metal films. 7 Hence our objective here is to address two issues: (1) what is the microscopic origin of low-frequency electrical noise in nanowires, and (2) can the noise in nanowires be suppressed or reduced by appropriate engineering of growth and structural parameters.The power spectral density S R of low-frequency 1/f noise in resistance R is normalized as,where N e is the total number of electrons, and γ H is the phenomenological Hooge parameter that depends on the material properties, such as nature and kinetics of disorder, scattering cross-section of electrons, crystallinity, and so on. 8,9 In thin polycrystalline metallic films, γ H generally lies in the range ∼ 10 −3 −10 −5 , which is predominantly due to the migration of point defects along the grain boundaries. 10,11,12 Surprisingly though, the value of γ H , in electrochemically grown single crystalline fcc silver nanowires (AgNWs) (≈ 15 nm diameter ) was found to be very large (γ H ∼ 10 −1 − 10 −2 ), even when the grain boundaries are expected to be absent. Although an explanation based on Rayleigh-Platteau instability has been proposed for narrow nanowires 7 , the source of noise in wires of larger diameter (∼ 100 nm) is not clearly understood. Moreover, whether other defect kinetics, such as thermally activated movement of dislocations, 13 contribute to the observed noise still remains uncertain. * electronic mail:amrita@physics.iisc.ernet.inThe nature of crystallinity is known to have a profound influence on the kinetics of dislocations. 14 Since it is intimately connected to plasticity, a study of noise can also be relevant to understand the intrinsic structural aspects of the nanowires. Hence, to evaluate the role of defect kinetics on noise in nanowires, we have carried out detailed electrical characterization of si...

Morphology and composition controlled synthesis of flower-like silver nanostructures

“…To our knowledge, HCP crystal structures appear in silver nanowires prepared by electrochemical deposition [17-19] or by simply heating or evaporating FCC-Ag nanowires or nanoparticles [20,21]. Various metal nanostructures containing HCP structures with different morphologies including Ag belts [22], prisms [23], needles [24], rices [25], Au square sheets [26], and tadpoles [27] have been researched.…”

“…However, kinetic-controlled growth alone cannot interpret the occurrence of unusual and rare hexagonal close-packed (HCP) silver nanostructures apart from common FCC ones as noted in our previous report [ 15 ]. To our knowledge, HCP crystal structures appear in silver nanowires prepared by electrochemical deposition [ 17 - 19 ] or by simply heating or evaporating FCC-Ag nanowires or nanoparticles [ 20 , 21 ]. Various metal nanostructures containing HCP structures with different morphologies including Ag belts [ 22 ], prisms [ 23 ], needles [ 24 ], rices [ 25 ], Au square sheets [ 26 ], and tadpoles [ 27 ] have been researched.…”

Synthesis of Ultrathin Face‐Centered‐Cubic Au@Pt and Au@Pd Core–Shell Nanoplates from Hexagonal‐Close‐Packed Au Square Sheets

“…2, 3 More importantly, their functionalities are greatly affected by their crystal structures 4. For example, the hexagonal‐close‐packed (hcp) Ag nanowire exhibited low‐frequency electrical noise of two to six orders of magnitude lower than that of the conventional face‐centered‐cubic (fcc) Ag nanowire 4a. Therefore, control of the crystal structure is critically important during the synthesis of noble‐metal NCs.…”

Phase controlled synthesis and characterization of noble metal nanomaterials

“…In addition to the properties mentioned above, the structure transformation of noble metal naomaterials can also lead to the change of their electrical and magnetic properties 13,72 . For instance, the electrical noise in hcp Ag nanowires is far lower (up to several orders of magnitude) than that in the conventional fcc Ag nanowires 72 . Another study revealed that the 4H polytype of Ag nanowires demonstrates a relatively larger resistivity (19.9 μΩ cm) compared to that of the common fcc polytype (11.9 μΩ cm) 75 .…”

“…Moreover, their functional properties are also largely influenced by their crystal phases 18,72 . For instance, hexagonal close-packed (hcp) Ag nanowires demonstrated low-frequency electrical noise of two to six orders of magnitude lower in comparison with that of common face-centered cubic (fcc) Ag nanowires 72 . Thus the control over the crystal phase is of paramount importance in the preparation of noble metal NCs.…”