  Casimir forces in quantum electrodynamics emerge between microscopic metallic
objects because of the confinement of the vacuum electromagnetic fluctuations
occurring even at zero temperature. Their generalization at finite temperature
and in material media are referred to as Casimir--Lifshitz forces. These forces
are typically attractive, leading to the widespread problem of stiction between
the metallic parts of micro- and nanodevices. Recently, repulsive Casimir
forces have been experimentally realized but their reliance on specialized
materials prevents their dynamic control and thus limits their further
applicability. Here, we experimentally demonstrate that repulsive critical
Casimir forces, which emerge in a critical binary liquid mixture upon
approaching the critical temperature, can be used to actively control
microscopic and nanoscopic objects with nanometer precision. We demonstrate
this by using critical Casimir forces to prevent the stiction caused by the
Casimir--Lifshitz forces. We study a microscopic gold flake above a flat
gold-coated substrate immersed in a critical mixture. Far from the critical
temperature, stiction occurs because of dominant Casimir--Lifshitz forces. Upon
approaching the critical temperature, however, we observe the emergence of
repulsive critical Casimir forces that are sufficiently strong to counteract
stiction. This experimental demonstration can accelerate the development of
micro- and nanodevices by preventing stiction as well as providing active
control and precise tunability of the forces acting between their constituent
parts.
