Fig. 2
![Fig. 2](http://media.springernature.com/full/springer-static/image/art%3A10.1186%2Fs40494-019-0315-5/MediaObjects/40494_2019_315_Fig2_HTML.jpg)
Microscopic images of the silver box (a the surface morphology; b the cross cutting lines at the surface center; c the side view; d the internal morphology)
Microscopic images of the silver box (a the surface morphology; b the cross cutting lines at the surface center; c the side view; d the internal morphology)