Two-dimensional colloidal structures responsive to external fields

Introduction Well-characterized and extremely monodisperse colloidal particles have become model systems for various problems in statistical physics such as phase transitions or self-organization of colloids. The use of colloidal particles bears twO considerable advantages compared with atomic systems. First. the size of the particles in the micron range allows direct visualization by light microscopy with 'atomic' resolution. Second, because of friction with the surrounding solvent the dynamics of colloids is slowed down by more than six orders of magnitude when compared with atoms. The relaxation processes which appear almost instantaneous for the latter can therefore be resolved at all relevant time scales using colloidal particles. Past years have seen considerable advances in the development and investigations of colloidal model systems, in particular in restricted geometry such as quasi-two-dimensional layers of particles with or without lateral confinement. This is due to the great interest in packing phenomena and melting or glass-transition in finite systems or porous media. The scope of this review is to highlight the most recent experiments and related theoretical work on colloids in restricted geometry. Comparison of experimental data with computer simulations shows such striking agreement that certain colloidal systems come close to an analog computer. Other findings concern quantitative features of the classic Kosterlitz-Thouless two-dimensional melting, but also a two step-melting scenario of first order. Finally, a rccent study of Iight-induced melting in a colloidal system demonstrates the importance of fluctuations to stabilize a system of interacting particles.