Theoretical and experimental investigation of optically driven nanoelectromechanical oscillators

The actuation of biologically functional micro- and nanomechanical structures using optical excitation is an emerging arena of research that couples the fields of optics, fluidics, electronics, and mechanics with potential for generating novel chemical and biological sensors. In our work, we fabricated nanomechanical structures from 200 and 250 nm thick silicon nitride and single crystal silicon layers with varying lengths and widths ranging from 4 to 12 μm and 200 nm to 1 μm, respectively. Using a modulated laser beam focused onto the device layer in close proximity to the clamped end of a cantilever beam, we concentrate and guide the impinging thermal energy along the device layer. Cantilever beams coupled to chains of thermally isolated links were used to experimentally investigate energy transport mechanisms in nanostructures. The nature of the excitation was studied through steady-periodic axisymmetric thermal analysis by considering a multilayered structure heated using a modulated laser source. Results were verified by finite element analysis, which was additionally implemented for the solution of steady-periodic and transient thermal, as well as steady thermoelastic problems. These theoretical investigations, coupled with our experimental results, reveal that the complex dynamics underpinning optical excitation mechanisms consists of two disparate spatial regimes. When the excitation source is focused in close proximity to the structure the response is primarily thermal. We show that as the source is placed farther from the clamped end of the structure, the thermal response progressively fades out, indicating the possibility of mechanical wave propagation. Understanding the excitation mechanisms may be useful for applications including compact integration of nanophotonic elements with functionalized nanomechanical sensors for ultrasensitive biochemical analysis.