SURFACTANT-INDUCED LAYER-BY-LAYER GROWTH OF CU ON RU(0001) AS REVEALED BY OSCILLATORY WORK FUNCTION CHANGES

Dynamical work function change measurements (DELTAphi), during the growth of thin heteroepitaxial films, have been performed using a special Kelvin probe. As a model system the deposition of thin Cu films on Ru(0001) and, especially, the influence of preadsorbed oxygen as a ''surfactant'' for layer-by-layer growth was studied in a wide range of temperature and oxygen precoverage (theta(O)). For appropriate conditions (T = 400 K, theta(O) almost-equal-to 0.4 ML) the DELTAphi-curves exhibit a remarkable oscillatory behavior of high amplitude which is clearly resolved up to at least 80 periods, the limiting fact being mainly an inhomogeneous deposition. Each period is demonstrated to correspond to the deposition of just one complete Cu layer clearly indicating a layer-by-layer growth mode. The origin of these oscillations is discussed in terms of existing models of growth mechanisms. Furthermore, it is emphasized that the so-called ''pendulum'' Kelvin probe is a very useful and inexpensive instrument for such in-situ film-growth investigations.