Nano electro mechanical systems (NEMS) [1], are being used extensively to study small displacements [2], mass sensing [3–6], spin-torque effect [7], charge sensing [8], Casimir force [9] and potential quantum mechanical devices [10, 11]. A variety of NEMS devices, fab- ricated using carbon nanotubes [12–16], graphene [17–19], nanowires (NWs) of silicon [20] and by micromachining bulk silicon [21], have been used to probe the underlying physics at nano scale. In this work we study the electromechanical properties of doubly clamped suspended n-type InAs NWs. In our suspended NW FET, the gate electrode serves three purposes: first, to modify the tension in the NW, second, to actuate the mechanical motion of the resonator and third, enabling us to systematically study the coupling of mechanical properties to the tunable electron density. As we will show, a tunable electron density leads to a variable screening length of the order of the nanowire’s cross sectional dimensions. Thus the electro-mechanical properties enter into a mesoscale regime. Such a variable electron density is not accessible in carbon nanotubes; the screening length cannot be tuned contin- uously – relative to the diameter of the carbon nanotube – as easily. However, the physics of charge screening in nanoscale capacitors [22] and ferroelectric devices [23] is intimately connected to that in our NEMS devices. Taken together, these observations suggest that a geometrical interpretation of capacitance is inadequate at the nano scale. Additionally, the gate allows us to tune the resonant frequency non-monotonically due to the competition between the electrostatic force and the mechanical stiffness ( ∼ 1 N/m) of the nanowire, a feature expected (but heretofore not studied in detail) for all electrostatically actuated NEMS. In this article, we demonstrate that the InAs semiconducting nanowire system man- ifests this transition from softening to hardening as the gate voltage is varied. In addition, mixing of the natural mechanical modes as a function of V DC g can be understood in terms of the structural asymmetries in the resonator. In the non-linear regime we study in de- tail hysteretic behavior as a function of V DC g (unlike the commonly studied response as a function of drive frequency) and we show that this can be understood by using the Duffing equation incorporating the effect of gate voltage. The observed hysteretic response with V DC g is an alternate knob for tuning the nonlinear response of our NEMS devices and can be used for charge detection [24]. Our work provides further understanding of the unique characteristics of NEMS devices operating at room temperature. The observed behavior can provide information on the nanomechanics of other systems whose electron density, stiffness or screening length cannot be so readily tuned. 

