When a linear dimension of a device or a theoretical subject of investigation is smaller than 1 ?m, it may be said that a one-dimensional nanoregime has been entered. In this sense the study of monomolecular and bimolecular layers and surface physics in general is now said to belong to nanoscience. More recently the study of surfaces has been enhanced by the techniques of nonlinear optical spectroscopy, by scanning tunneling spectroscopy and by atomic force microscopy.

The ancient use of submicron colloidal particles of gold and silver in glass to obtain colored window materials is an early example of three-dimensional nanotechnology. It is based on the range of plasmon-resonant frequencies in small metallic particles.

A small number of atomic layers of GaAs and GaAlAs or other semiconducting compounds have led to light-emitting diodes and lasers over a wide frequency range. Such layered structures have also created two-dimensional plasmas of conduction electrons which exhibit quantum Hall effects. Small semiconducting particles called quantum dots may function as versatile sub-microscopic light sources.

Biological and medical investigations have also focused increasingly on nanostructures during the past two decades. Genetics and neurophysiology are concerned with the detailed structure of individual molecules, including DNA, RNA and various enzymes and proteins on cell walls or other substrates.

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