Scanning Probe Microscopy: Design and Applications

Doctoral thesis, 1993

A compact scanning tunneling microscope (STM) and a scanning ion-conductance microscope (SICM) has been constructed. The concentric microscope head was built around a commercial piezoelectric inchworm motor that was used for coarse positioning. The microscope has a high resonance frequency (9.6 kHz), low noise (0.01 nm/*Hz at 10 Hz), low thermal drift and high acoustical noise suppression. The distance dependence of the SICM-probe was found to be linear. A new kind of pipette with a nanometer sized aperture, intended for use in the SICM, was made by microfabrication methods. An STM-head for operation down to milli Kelvin temperatures has also been constructed. To increase the knowledge of the growth mechanisms and to identify possible flux pinning sites, STM topography was performed at room temperature on high quality laser deposited YBCO thin films. The films were grown at 710-760 °C, and the decreasing critical current density with higher deposition temperature could be related to a change in morphology of the surface. Titanium oxide is a successful biomaterial. However, the mechanism for the biocompatibility is not known. One influencing factor can be the topography at the nanometer scale. We performed STM experiments on three electropolished samples, one without further treatment, one was oxidized, and one was exposed to an argon glow discharge and then oxidized. The two first sample surfaces showed a granular structure, with a corrugation between 2 and 10 nm. At a larger scale, the glow discharge treated sample showed a more pronounced corrugation ~100 nm. A new method for studies of the spatial location of scattering centers in a mesoscopic sample has been invoked. A point contact is first formed between two metallic films by punctuating the insulating interlayer with the aid of an STM tip at liquid helium temperature. The influence on scattering centers in the vicinity of the point contact was studied by scanning the STM tip. Sharp switches in the resistance of the point contact were interpreted as due to spatial shifts or changes in the activity of scattering centers by the electric field around the tip.