  Strain engineering is one of the most effective approaches to manipulate the
physical state of materials, control their electronic properties, and enable
crucial functionalities. Because of their rich phase diagrams arising from
competing ground states, quantum materials are an ideal playground for
on-demand material control, and can be used to develop emergent technologies,
such as adaptive electronics or neuromorphic computing. It was recently
suggested that complex oxides could bring unprecedented functionalities to the
field of nanomechanics, but the possibility of precisely controlling the stress
state of materials is so far lacking. Here we demonstrate the wide and
reversible manipulation of the stress state of single-crystal WO3 by strain
engineering controlled by catalytic hydrogenation. Progressive incorporation of
hydrogen in freestanding ultra-thin structures determines large variations of
their mechanical resonance frequencies and induces static deformation. Our
results demonstrate hydrogen doping as a new paradigm to reversibly manipulate
the mechanical properties of nanodevices based on materials control.
