Introduction

Abstract

Scientific research into electronic systems was limited for a long period of time to naturally occurring isolated atoms or particles, metallic or semiconductor crystals, or beams of beta radiation. Most of these are three-dimensional systems, while an effective reduction of geometry to two or fewer dimensions — by a strong spatial localization to a plane, line, or point (i.e., confinement of an electron in at least one direction at the de Broglie wavelength) — occurs only in the case of atoms and electrons localized on crystal imperfections (e.g., on impurities).