Fig. 1. Schematic of the fabrication process of the micro-nano structured Cu film.

Fig. 2. Cross sectional and surface SEM images and AFM images: (a-c) a series of oblique Cu nanowire-array films with thicknesses varying from 4.7 μm (a1) to 16.4 μm (c1); (d) vertical Cu nanowire-array film perpendicular to the substrate with a thickness of 3.3 μm. Note that the contact angles (inset images) of the oblique nanowire-array film changed with varying thicknesses. SEM images of single nanowire: (e) and (f) oblique nanowires; (g) vertical nanowires. (h) Schematic of the contact state between water and nanowires in the nanogaps.

Fig. 3. Various micro-nano structured Cu films with low surface energy and hydrophobic wettability with a static contact angle of up to 133° were fabricated. The average diameter and density of the clusters depended largely on the film thickness and nano structure of the bone film, respectively. SEM images: (a) micro-nano structured oblique Cu nanowire-array film with a thickness of 19.1 μm; (b) Top of the cluster; (c) Micro-pit; (d) Detailed nanostructure of the micro-pit; (e) micro-nano structured oblique Cu nanowire-array film with a thickness of 4.5 μm; (f) micro-nano structured oblique Cu nanowire film with a thickness of 800 nm.

Fig. 4. The surface wettability of the Cu film was optimized by controlling its internal structure, thus, achieving extreme properties and contact angles from 6° to 152°. Surface and cross-sectional SEM images of Cu films: (a) Cu nanoparticle thin film (80 nm); (b) Cu nanoparticle thin film (50 nm); (c) Cu nanoparticle thin film (130 nm); (d) Cu foam film; (e) Cu nanowire-array films; (f) Micro-nano structured Cu films.

Fig. 5. Various micro-nano structured Cu films with low surface energy and hydrophobic wettability with a static contact angle of up to 152° were fabricated. The average diameter and density of the clusters depended significantly on the film thickness and nanostructure of the bone film, respectively. SEM images: (a) Micro-nano structured Cu nanoparticle film with a thickness of 2.8 μm; (b) cluster of micro-nano structured Cu nanoparticle film; (c) detailed nanostructure of top of cluster; (d) nanostructure of micro-pit; (e) micro-nano structured Cu dense-cluster film with a thickness of 500 nm; (f) Cu nanoparticle-clusters film with a thickness of 1.2 μm.

Fig. 6. Surface free energy of the Cu films.

Fig. 7. The surfaces of the Cu films were modified by Ni nanoparticles to investigate the effect of the nanogaps and nanowires aggregation on the wettability of the Cu films, which also indicated that the surface wettability of the Cu film was determined by the structure of the film rather than by the surface chemical state. Surface SEM images of the Cu nanowire-array films: (a1-d1) before modification; (a2-d2) after modification. The insets show the corresponding AFM images (top right corner) and contact angle pictures (bottom left corner). (e) Schematic of the contact state between water and the nanowires in the nanogaps. Scale bar: 500 nm.

Fig. 8. Cross-sectional SEM images of the Bi2Te3-Cu bilayer films: (a) Cu nanoparticle film with a diameter of 80 nm; (b) dense Cu nanoparticle film with a diameter of 50 nm; (c) Cu nanoparticle film with a diameter of 130 nm; (d) Cu nanowire-array film; (e) micro-nano structured Cu nanoparticle film; (f) micro-nano structured Cu nanowire-array film.