Structural study on Ni nanowires in an anodic alumina membrane by usingin situheating extended x-ray absorption fine structure and x-ray diffraction techniques

Abstract

Polycrystalline Ni nanowires have been prepared by electrochemical deposition in an anodic alumina membrane template with a nanopore size of about 60 nm. In situ heating extended x-ray absorption fine structure and x-ray diffraction techniques are used to probe the atomic structures. The nanowires are identified as being mixtures of nanocrystallites and amorphous phase. The nanocrystallites have the same thermal expansion coefficient, of 1.7 × 10(-5) K(-1), as Ni bulk; however, the amorphous phase has a much larger thermal expansion coefficient of 3.5 × 10(-5) K(-1). Details of the Ni nanowire structures are discussed in this paper.

Negative thermal expansion of nanoporous anodic aluminum oxide membranes

“…A similar result was reported when studying Cu NWs electrodeposited into the AAO templates by Zhou et al [12]. Cai et al [13] studied Ni NWs by in-situ XRD and EXAFS. By XRD they measure a thermal expansion coefficient similar to that of bulk Ni, but EXAFS gave a larger value.…”

“…proposing the presence of a 50% of amorphous Ni in their NW. It should be remarked that in [13] the Ni NW were electrodeposited by DC.…”

Thermal expansion behaviors of hcp and fcc Co nanowire arrays

“…That is to say, there is no space between Co nanowires and pores of the PAAM. While, the thermal expansion of the PAAM results in the contraction of pores and produces a radial pressure on the nanowires [25]. In this case, the radial pressure can be released by the axial expansion.…”

Annealing Effects on the Metal and Semiconductor Nanowires Loaded Inside the Alumina Pores

“…Thus, at higher heating temperatures the alumina cell walls might produce a radial pressure on the nanowire. As reported (Cai et al 2008), the radial pressure can be relaxed by the axial expansion if the deposited nanowires are single crystalline demonstrating the complex thermal behavior during annealing in vacuum. In contrast, in the case of polycrystalline nanowires, there are enough of liquid-like spaces between nanocrystallites (Gleiter 2000) to release the stress from the lattice expansion and, thus, the thermal expansion coefficients of such nanowires are almost the same as that of the corresponding bulk.…”

“…Wang et al (2004) claimed that copper nanowires in alumina templates have a thermal expansion coefficient close to zero and this is attributed to the diffusion of vacancy defects from the body to the nanowire surface. The thermal expansion coefficient of Ni nanowires grown within the alumina pores (Ø pore ∼60 nm) at -2.0 V by direct current deposition was also studied in situ by specimen heating up to 600 ºC in vacuum (Cai et al 2008). These nanowires after deposition were found to be in the polycrystalline state with nanocrystallites up to 40 nm in size.…”