Room-temperature formation of slant nanobelts and vertical wires on low-doped p-type (100) silicon via metal-assisted chemical etching

Abstract Despite its applications, metal-assisted chemical etching (MACE) is still not well understood. To elucidate its underlying mechanism, MACE with micron-sized gold mesh was systematically carried out across a wide range of volume ratio R of HF acid to H 2 O 2 solution. Slant wires were observed at room temperature over a broad range of parameters, which contradicts the well-established viewpoint that slantwise etching occurs only at elevated temperatures. Vertical wires form only in a narrow parameter space featuring a low R . The wide variation in observed slant angles indicates that the associated MACE processes do not exhibit a preferred etching direction. The observed R -dependent change of oxygen content in wires and of bubbling phenomena was explained by two competing mechanisms associated with direct and indirect Si dissolution. The high and low R regime is dominated by direct and indirect mechanism, respectively, whereas in the intermediate regime both mechanisms play an indispensable role. Slant wire formation is caused directly by the slantwise mesh movement. Although this movement is closely correlated with the direct mechanism, it cannot be fully explained by it. We hypothesize that hydrogen bubbling-induced flow has the potential to hydrodynamically drive the mesh slantwise and hence can be responsible directly for slant wire formation. To the best of our knowledge, this work not only reports a relatively novel phenomenon—slant wire formation by MACE at room temperature—but also provides, for the first time, a comprehensive understanding of its underlying complex mechanism.