A variable-temperature homodyne reflectometry measurement technique for detecting nanoscale mechanical motion has recently been developed. We have extended this technique to make the first all-electrical measurements of an ensemble of as-grown, c-axis, single-crystal gallium nitride (GaN) nanowires. These nanowires are approximately 15 μm in length and 100 nm in diameter, and have fundamental resonance frequencies near 1 MHz, and mechanical quality factors, Q, (resonance frequency divided by resonance width) in excess of 104. These high-Q values are sensitive to surface conditions and offer the opportunity to study intrinsic damping mechanisms in the nanoscale resonators. The new microwave measurement technique has allowed us to study the ensemble behavior of nanowire resonances while varying extrinsic variables (e.g., temperature) and obtain statistics on nanowire resonance behavior. Our apparatus allows measurements to be made in either a two-phase lock-in mode, or in a power-spectrum mode, both of which have unique advantages. Our measurements demonstrate a position-spectral noise floor of 0.3 nm/ Hz, largely set by the dynamic range of our microwave readout system.

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