Negative thermal expansion of nanoporous anodic aluminum oxide membranes

TL;DR

This study measures the negative thermal expansion of nanoporous anodic aluminum oxide membranes and Ni nanowires within them, revealing that both exhibit contraction upon heating between 110K and 350K.

Contribution

It provides the first direct measurement of negative thermal expansion in nanoporous AAO membranes and interprets previous nanowire data in this context.

Findings

Ni nanowires show negative thermal expansion along their axis.

Nanoporous AAO exhibits negative thermal expansion with a coefficient of approximately -5×10^{-6}/K.

Previous data on metallic nanowires can be explained by the negative expansion of the AAO matrix.

Abstract

We have measured the thermal expansion of Ni nanowires electrodeposited into self-organized nanoporous amorphous aluminum oxide (AAO) membranes without Al substrate using X-ray diffraction between 110K and 350K. The results indicate an average thermal expansion of the Ni nanowires -- along the wire axis -- of $\langle\alpha\rangle_{\rm NiNW}=-(1.6 \pm 1.5)\times 10^{-6}$/K. Assuming a bulk-like thermal expansion of the isolated Ni nanowires, this result indicates that AAO has also a negative thermal expansion. We estimate the thermal expansion of nanoporous AAO to be $\langle\alpha\rangle_{\rm AAO}=-(5 \pm 1) \times 10^{-6}$/K. We show that data obtained previously on the thermal expansion of metallic nanowires grown in the nanoporous AAO may be interpreted as originated in a negative thermal expansion of the matrix.