  We investigate the tensile stress in freely suspended nanomechanical string
resonators, and observe a material-independent dependence on the resonator
length. We compare strongly stressed sting resonators fabricated from four
different material systems based on amorphous silicon nitride, crystalline
silicon carbide as well as crystalline indium gallium phosphide. The tensile
stress is found to increase by approximately 50% for shorter resonators. We
establish a simple elastic model to describe the observed length dependence of
the tensile stress. The model accurately describes our experimental data. This
opens a perspective for stress-engineering the mechanical quality factor of
nanomechanical string resonators.
