Ultrafast Photoacoustic Nanometrology of InAs Nanowires Mechanical Properties

InAs nanowires are emerging as go-to materials in a variety of applications ranging from optoelectronics to nanoelectronics, yet a consensus on their mechanical properties is still lacking. The mechanical properties of wurtzite InAs nanowires are here investigated via a multitechnique approach, exploiting electron microscopies, ultrafast photoacoustics, and finite element simulations. A benchmarked elastic matrix is provided and a Young modulus of 97 GPa is obtained, thus clarifying the debated issue of InAs NW elastic properties. The validity of the analytical approaches and approximations commonly adopted to retrieve the elastic properties from ultrafast spectroscopies is discussed. The mechanism triggering the oscillations is unveiled. Nanowire oscillations in this system arise from a sudden expansion of the supporting substrate rather than the nanowire itself. This mechanism constitutes a new paradigm, being at variance with respect to the excitation mechanisms so far identified in ultrafast experiments on nanowires and on a plethora of nanosystems. The present findings are relevant in view of applications involving InAs nanowires, knowledge of their mechanical properties being crucial for any device engineering beyond a trial-and-error approach. The results bear generality beyond the specific case, the launching mechanism potentially encompassing a variety of systems serving as nano-optomechanical resonators.