Micromechanics: A toolbox for femtoscale science: "Towards a laboratory on a tip"

Abstract

Micromechanics and microscopy at the atomic scale became inseparably linked in 1986 with the invention of scanning force microscopy (SFM). The extreme sensitivity of these nanoscale science methods extends their use well beyond force detection. In principle, every signal domain such as magnetic, electrical, thermal, chemical, stress, and flow can be detected at ultimate limits of sensitivity, speed, and size through transduction into mechanical motion. We first pioneered the use of such SFM sensors as calorimeters enabling the detection of chemical reactions involving heat changes at the femtojoule level. These devices, which utilize the well-known "bimetallic strip" principle, have since been extended to a novel form of optical absorption spectrometer also capable of outperforming conventional techniques. Detection of stress induced in thin films on micromechamcal devices is also being actively pursued for electrochemical processes. Volume changes and heat having evolved during phase transitions have been separated successfully using a variation of the bimetallic method analogous to standard thermal analysis. The attachment of picoliter amounts of material at the apex of the cantilever device, the attachment of tiny zeolite crystals, and the fabrication of miniature shovels or thermocouples at the tip region will lead to the creation of a laboratory on a tip. The use of arrays extends the capabilities of these devices to applications such as artificial noses or for process control and has significant potential for sensor applications of all kinds. Progress so far indicates that a complete laboratory can be shrunk to the dimensions of the tip of a needle.