Moving liquids with light: Photoelectrowetting on semiconductors

Liquid transport in microchip-based systems is important in many areas such as Laboratory-on-a-chip, Microfluidics and Optofluidics. Actuation of liquids in such systems is usually achieved using either mechanical displacement11 or via energy conversion e.g. electrowetting which modifies wetting. However, at the moment there is no clear way of actuating a liquid using light. Here, by linking semiconductor physics and wetting phenomenon a brand new effect "photoelectrowetting" is demonstrated for a droplet of conducting liquid resting on an insulator-semiconductor stack. Optical generation of carriers in the space-charge region of the underlying semiconductor alters the capacitance of the insulator-semiconductor stack; the result of this is a modification of the wetting contact angle of the droplet upon illumination. The effect is demonstrated using commercial silicon wafers, both n- and p-type having a doping range spanning four orders of magnitude (6\times1014-8\times1018 cm-3), coated with a commercial fluoropolymer insulating film (Teflon\textregistered). Impedance measurements confirm that the observations are semiconductor space-charge related effects. The impact of the work could lead to new silicon-based technologies in the above mentioned areas

PHÉNOMÈNES DE TRANSPORT EN SURFACE DANS LES SEMI-CONDUCTEURS

On montre que les propriétés de surface des semi-conducteurs massifs permettent de réaliser et d'étudier des situations équivalentes à celles rencontrées dans des couches minces semi-conductrices qui seraient monocristallines.It is shown that the surface properties of bulk semiconductors make possible the realisation and study of situations which are equivalent to the case of semiconducting thin layers which would be monocrystalline

LES ÉTATS DE SURFACE DANS LES SEMICONDUCTEURSMÉTHODES D'INVESTIGATION

L'existence de niveaux d'énergies à la surface des semiconducteurs, niveaux situés dans la bande interdite, bien que prévue théoriquement depuis longtemps est difficile à mettre en évidence expérimentalement. On examine les diverses méthodes utilisées et leurs principaux inconvénients. Une meilleure compréhension des phénomènes et les progrès de la technologie ont permis récemment d'élaborer des méthodes de mesures plus spécifiques des états de surface. On indique quels résultats ont été obtenus notamment dans l'étude de l'interface Silicium-Diélectrique.The theoretical existence of surface states in the forbidden gap of semiconductors has been demonstrated for a long time. Nevertheless, the experimental investigation is rather difficult. Many experimental methods include the presence of artefacts not necessarily correlated with the presence of surface states, even when producing similar effects. A better understanding of phenomena and the progress in technology have recently permitted the elaboration of specific methods of measurement. These are described and the principal results given