Nanoelectromechanical Systems
  Nanoelectromechanical systems, or NEMS, are MEMS scaled to submicron dimensions. In this size regime, it is possible to attain extremely high fundamental frequencies while simultaneously preserving very high mechanical responsivity (small force constants). This powerful combination of attributes translates directly into high force sensitivity, operability at ultralow power, and the ability to induce usable nonlinearity with quite modest control forces. In this overview I shall provide an introduction to NEMS and will outline several of their exciting initial applications. However, a stiff entry fee exists at the threshold to this new domain: new engineering is crucial to realizing the full potential of NEMS. Certain mainstays in the methodology of MEMS will, simply, not scale usefully into the regime of NEMS. The most problematic of issues are the size of the devices compared to their embedding circuitry, their extreme surface-to-volume ratios, and their unconventional "characteristic range of operation". These give rise to some of the principal current challenges in developing NEMS. Most prominent among these are the need for: ultrasensitive, very high bandwidth displacement transducers; an unprecedented control of surface quality and adsorbates; novel modes of efficient actuation at the nanoscale, and precise, robust, and routinely reproducible new approaches to surface and bulk nanomachining. I survey each of these aspects in turn, and conclude by describing several of the exciting prospects in this new field. 
M.L. Roukes (Condensed Matter Physics, Caltech)