Lv150

The roughness and homogeneity of the epitaxial MoS₂ monolayer were measured by an atomic force microscope (NT-MDT Ntegra, Moscow, Russia). The MoS₂ MBE fabricated sample was characterized immediately after unsealing without any pollution at ambient conditions, and thus these defects demonstrated in AFM and SEM in Figure 1d–f are the result of an MBE fabrication procedure. These defects might be Mo nucleation sites. The surface images (2400 × 2400 pixels) of the MoS₂ samples were captured by an optical microscope (Nikon LV150, Tokyo, Japan) with a digital camera DS-Fi3. To investigate the MoS₂ surface morphology, we additionally used the scanning electron microscope using the acceleration voltage of 3 kV (JEOL JSM-7001F, Tokyo, Japan).

Condensation experiments were performed in a closed room with an area of 25 m² and a height of 3 m. The ambient temperature was controlled at 28 ± 1°C and the relative humidity (RH) was adjusted at 80 ± 2%. The surface superhydrophobilized aluminum foils with a size of 3 cm × 3 cm × 0.5 mm were placed on a horizontally orientated Peltier cooling stage with the hot side cooled by recirculating water. The sample surface was maintained at 0–1°C. The spontaneous motion of condensate droplets was observed and visualized by an optical microscope (Nikon LV 150) with a ×10 objective and charge-coupled device camera (CCD) at 25 fps. The phenomena were quantified by analyzing 2 min representative videos. Four short periods of time (only 1 s) spacing 30 s, all together 5 × 25 pieces of snapshots were used to quantify the average numbers of distinguishable drop location changes in 1 s videos (here named as “spontaneous motion frequency”) (Feng et al., 2012a (link); Feng et al., 2012b (link)).

The morphology of the ZnO nanostructures was observed by scanning electron microscopy (SEM) using a TESCAN LYRA 3 XMH instrument. Microwires were studied using an optical microscope (model D800; Nikon) equipped with a digital camera (model LV-150; Nikon). A white LED was used as the light source.