The ultimate goal to perform surface science studies under technologically relevant conditions includes wet-chemical methods to prepare
well-defined oxide surfaces [1]. The most widely practised approach
is hydrofluoric acid etching, even though this chemical poses serious
health risks and may inadvertently dope the surface with fluorine, an
efficient electron donor [2].
Here, we present a rational yet versatile wet-chemical alternative to
lengthy sputtering–annealing cycles in ultrahigh vacuum for preparing
single crystal oxide samples for surface science investigations. The method does not require hydrofluoric acid, is environmentally benign and
is demonstrated on rutile TiO2 (110), rutile TiO2 (011) and SrTiO3 (100),
but may have much wider application potential, also for surfaces that
are quickly destroyed by acids.
The procedure consists of (i) ultrasonication in the presence of a dispersing agent to remove polishing debris; (ii) thermal annealing to produce
equilibrium-shaped steps and terraces determined by the crystal
miscut; and (iii) oxidative cleaning in an alkaline mixture to remove
adsorbed organic contaminants from the surface. Each of the steps
is optimised based on AFM and characterisation in ultrahigh vacuum,
including by LEED and XPS. Following this wet-chemical preparation, we
demonstrate atomically resolved electrochemical scanning tunnelling
microscopy on TiO2 (110), on a sample that was never treated by sputtering–annealing.