  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.
