  Strain engineering provides an effective way of tailoring the electronic and
optoelectronic properties of semiconductor nanomaterials and nanodevices,
giving rise to novel functionalities. Here, we present direct experimental
evidence of strain-induced modifications of hole mobility in individual GaAs
nanowires, using in situ transmission electron microscopy (TEM). The
conductivity of the nanowires varied with applied uniaxial tensile stress,
showing an initial decrease of ~5-20% up to a stress of 1~ 2 GPa, subsequently
increasing up to the elastic limit of the nanowires. This is attributed to a
hole mobility variation due to changes in the valence band structure caused by
stress and strain. The corresponding lattice strain in the nanowires was
quantified by in situ 4D-scanning TEM (STEM) and showed a complex spatial
distribution at all stress levels. Meanwhile, a significant red shift of the
band gap induced by the stress and strain was unveiled by monochromated
electron energy loss spectroscopy.
