Strength measurement and calculations on silicon-based nanometric oscillators for scanning force microcopy operating in the gigahertz range

For an oscillator having a structure that can be modeled as a concentrated mass-spring model with constant Q factor, its minimum detectable force grad ient is proportional to (KM)(1/2), where M is the mass and K is the spring constant. Miniaturization of the oscillator acts favorably in increasing th e force resolution, since drastic decrease of the mass can then be achieved . With the aim of increasing the force and mass resolution of the oscillato r used for force detection in scanning force microscopy (SFM), we have deve loped a novel fabrication technique of nanometric oscillators by selective etching of laminated silicon substrates such as SOI (silicon on insulator) or SIMOX (separation by implanted oxygen). The oscillator has a tetrahedral or a conical tip supported by an elastic neck, and the tip serves as the m ass. Typical size of the oscillator lies in the range of 100-1000 nm. The o scillator could be tailored to have its natural frequency in the range of 0 .01-1 GHz, and a spring constant between 10(-1) and 10(2) N/m. The strength of the nanometric neck was 10(8) N/m(2) for both shear and normal forces, indicating that a neck 10 nm in diameter can withstand forces up to around 50 nN. Calculations on the different vibrational modes of the oscillator ga ve a better guideline to the design of the oscillators. (C) 2000 Elsevier S cience B.V. All rights reserved.