Advances in atomic force microscopy

This article reviews the progress of atomic force microscopy (AFM) in ultra-high vacuum, starting with its invention and covering most of the recent developments. Today, dynamic force microscopy allows to image surfaces of conductors \emph{and} insulators in vacuum with atomic resolution. The mostly used technique for atomic resolution AFM in vacuum is frequency modulation AFM (FM-AFM). This technique, as well as other dynamic AFM methods, are explained in detail in this article. In the last few years many groups have expanded the empirical knowledge and deepened the theoretical understanding of FM-AFM. Consequently, the spatial resolution and ease of use have been increased dramatically. Vacuum AFM opens up new classes of experiments, ranging from imaging of insulators with true atomic resolution to the measurement of forces between individual atoms.Comment: In press (Reviews of Modern Physics, scheduled for July 2003), 86 pages, 44 figure

SmBaCuO films grown at low temperature and pressure

We have fabricated SmBaCuO thin films at 550-850°C and at oxygen pressures of 1.2-6.0×10-5 mbar in the presence of ozone. Various groups have reported on the existence of a solid solubility region in bulk Sm1+xBa2-xCu3Oy made at atmospheric oxygen pressure and 975°C. For these conditions, the superconducting transition temperature, Tc, is known to drop to zero as x is increased from 0 to 0.5. In contrast, we find hardly any decreases of Tc in our films in the range 0<x<1 and 750°C<Tgrowth<800°C, with Tc's about 90 K, from which we conclude that the solid solubility is strongly reduced or absent at low oxygen/ozone pressure in this growth temperature range. For this range of composition and growth temperature, we also observe no change in the c-axis lattice constant. The growth temperature that is needed to obtain a film with Tc,0 above 80 K equals 750°C, which is roughly 100°C higher than in the case of YBaCuO films grown under comparable conditions. These results are discussed using thermodynamic equilibrium data of RE1+xBa2-xCu3Oy (REY, Sm, La). At low temperature on a SrTiO3 substrate we observe an I-centered cubic phase