Surface studies with scanning probe microscopy.

Abstract

Using scanning probe microscopy, several studies were carried out to characterize surface topographies and properties. First, utilizing scanning tunneling microscopy (STM), we characterized fullerenes deposited onto gold foils and highly oriented gold films. On gold foils, we found that C₆₀ packed in hexagonally ordered overlayers and that the images showed internal buckyball features that arose from electronic interactions between the molecule and the substrate. On gold films, with an ordered overlayer of methyl isobutyl ketone (MIBK), the isolated C₆₀ molecules showed internal features in a "doughnut" shape, different than those seen previously. We also imaged gold foils on which a significant number of larger fullerene molecules were deposited, and found only spherical molecules in our images. A theoretical analysis of the optical beam deflection atomic force microscope (AFM) predicted sufficient sensitivity to measure atomic corrugations greater than 1 A. This agreed with experimental results showing atomically resolvable images. Another theoretical investigation probe the relative magnitude of the forces between the tip, sample, and an adsorbed atom on a surface. Experimentally, we investigated cleaved multiple quantum wells ans showed surface corrugations with a period equal to the quantum well spacing. The third technique used was magnetic force microscopy (MFM). We analyzed a novel system that combined the tunneling aspects of STM with the force-sensing attributes of force microscopy, and provided the ability to simultaneously image surface features as well as magnetic domains with a sensitivity that depended on the spring constant of the tunneling tip. Experimentally, we used this system to image magnetic domains and reveal the surface roughness of magnetic recording media. The second MFM technique involved spin-coating a magnetic surface with a ferrofliud, then over-coating with gold, and finally imaging the surface with STM. The STM revealed raised ridges where the ferromagnetic particles clumped in regions of high magnetic field gradient. The finally MFM we utilized imaged magnetic fields using a beam deflection force microscope by modulating a magnetic disk head and detecting the vibration of the magnetic tip. We were able to image the fields of a floppy disk head.