Nanoporous metals are fully-continuous, have high specific surface area, and are excellent electrical and thermal conductors. These properties make them well-suited to applications in (electro)catalysis, chemical sensing, and energy storage, amongst others [ 1]. Compared to the prototypical nanoporous Au [ 2], nanoporous Cu is comparatively under-studied despite being inexpensive, easily fabricated, and chemically stable [ 3]. Although its synthetic methods are relatively mature, there have been few high-resolution microscopic studies, particularly around the chemical nature of the nano-ligaments. Here we present a study into the microstructure, composition, and optical properties of nanoporous Cu.
Cu 0.3Mn 0.7 was prepared by induction melting and casting (as-cast, AC). A section was also heat-treated (HT) at 850°C for 24 h under flowing Ar, then quenched. Samples were dealloyed under free-corrosion conditions using 0.2 M HCl for 2 h [ 4]. Samples were analysed by scanning electron microscopy, X-ray spectroscopy (EDS), and electron back-scatter diffraction using a Zeiss Ultra+. Specimens for scanning transmission electron microscopy (STEM) were prepared by focused ion-beam (FIB) lift-out using a Thermofisher Helios G4 Xe plasma FIB. STEM and EDS were performed using a Thermofisher Spectra 300, operated at 300 kV, and electron energy-loss spectroscopy (EELS) was performed using a Gatan Quantum GIF attached to an FEI Themis 300, also operated at 300 kV.
Large (>200 μm) columnar grains contain a network Mn-rich dendrites due to coring on cooling [ 4], which is fully homogenized after heat-treatment. The dendritic structure is partially preserved after dealloying, which produces hierarchically meso-nano-porous Cu with ultimate ligament widths of 50–100 nm [ 5], shown in Fig. 1(a,b).
Fig. 1
(a) STEM-HAADF image of a large region of nanoporous Cu. Inset axes shows radially-integrated Fourier transform, showing feature sizes peaking between 50–100 nm [ 5]. (b) Higher-magnification STEM-HAADF image of nanoporous Cu, with rectangle indicating region analysed by EDS, shown in (c–e). (e) STEM-HAADF of a single ligament. Rectangle indicates region analysed by EELS, with L 2 (Cu, Mn) and K (O) intensities mapped in (f–h). Numbered rectangles indicate integration regions, with background-subtracted spectra colour-coded and shown in (j,k), and the arrowed rectangle indicates a composition profile shown in (i).
Smart Citations
