Negative thermal expansion of nanoporous anodic aluminum oxide membranes

We have measured the thermal expansion of Ni nanowires (NWs) electrodeposited into self-organized nanoporous amorphous aluminum oxide (AAO) membranes without an Al substrate using X-ray diffraction between 110 K and 350 K. The results indicate an average thermal expansion of the Ni NWs-along the wire axis-of (alpha) over bar (NiNW) = -(1.6 +/- 1.5) x 10(-6) K-1. Assuming a bulk-like thermal expansion of the isolated Ni NWs, this result indicates that AAO also has a negative thermal expansion. We estimate the thermal expansion of nanoporous AAO to be alpha(AAO) = -(5 +/- 1) x 10(-6) K-1. We show that data obtained previously on the thermal expansion of metallic NWs grown in the nanoporous AAO may be interpreted as originating from a negative thermal expansion of the matrix. Published under license by AIP Publishing.