Fig. 3: Experimental study on the formation mechanism of HEO films on Ga oxide layer and carbon substrate, respectively.

a Preparation and observation of a metal-nitrate mixed solution, wetted liquid Ga droplets attached TEM grid. b HAADF-EDS images of the liquid Ga droplet electroplated on a TEM grid after dropping a mixed metal salts solution. Scale bar is 0.5 μm. c, d TEM image of liquid Ga droplet after dropping mixed metal salts solution and enlarged view of the edge. The scale bars are 200 nm and 5 nm. e, f TEM image of Ga₂O₃@HEO after heating at 650 °C for 10 min and enlarged view of the edge. The scale bars are 100 nm and 5 nm. g, h TEM image of Ga₂O₃@HEO after heating at 650 °C for 30 min and enlarged view of the edge. d, f, h are the enlarged TEM images of the box area in (c, e, g), respectively. The scale bars are 100 nm and 5 nm.