Mechanically resonant nanostructures

Abstract

Electron beam lithography is used to make very small mechanical structures in single-crystal silicon. The structure may be a mesh having beam widths of less than 30 nm and suspended in a wafer, above a substrate. An rf drive voltage applied between the suspended structure and the underlying substrate produces vibration at or near the resonant frequency of the structure, and optical interference techniques are used to detect and measure the motion of the structure. The small dimensions of the structure provides a resonant frequency above 40 MHz. In one embodiment, the structure is a mesh formed of interconnected, very narrow, high aspect ratio parallel beams spaced about 315 nm apart. This results in a nanostructure having a low mass and a large relative surface area. The mesh is illuminated by laser light having a wavelength greater than the spacing between adjacent beams in the mesh so that small amplitude oscillations can be measured, with the detected change in optical reflection being proportional to the drive amplitude. The suboptical-wavelength features of the mesh provide a high measurement sensitivity, so that small changes in the mechanical properties of the mesh, resulting in corresponding small changes in the amplitude of the vibration, can be detected. A variable DC bias voltage applied to the vibrating structure allows adjustment of the motion of the structure and tuning of its vibration.