Combination study of electrochemical and RHEED experiments in vacuum is proposed.
Semiconductor characterizations of p-Si(1 1 1):H is electrochemically made in IL.
Specific adsorption of IL molecular ions scarcely occurs on p-Si(1 1 1):H.
The p-Si(1 1 1):H/IL interface is stable in vacuum.
The electric double layer capacitance of IL for p-Si(1 1 1):H is small.