Search Results (5 total)

Recent initial experiments in magnetic resonance force microscopy (MRFM) have detected the magnetic force exerted by electrons and nuclei in microscopic samples. The experiments generate a force signal by modulating the sample magnetization with standard magnetic resonance techniques. Sample sizes of a few nanograms generate readily detected force signals of order 10^-14 to 10^-16 Newtons. This article describes the present status of MRFM technology, with particular attention to the feasibility of detecting single-electron magnetic moments, and the possible applications of MRFM in biological imaging.

Detection of short-range interactions in combination with tunneling microscopy provides a means for characterizing the chemical nature of surfaces. Results are presented that demonstrate that carbon adsorbed on a rough, polycrystalline Ir surface can be detected on an atomic level.

We have used scanning tunneling microscopy to study self-assembled monolayers of mercaptohexadecanol in ultrahigh vacuum. In addition to tunneling, the interaction force gradient acting between tip and sample was measured. Analysis of the force-gradient data shows that the tip is in mechanical contact with the surface of the monolayer which, in turn, is elastically compressed. The lateral dimensions of the mechanical contact are substantially (approximately five times) larger than the width of the tunneling-current filament. The results suggest that the compression of the monolayer constitutes an integral part of tunneling through the molecules. This view is further supported by spectroscopic measurements showing that the density of states at the Fermi level as seen by tunneling depends on the initial tunneling voltage used to define the gap width.

The (001) surface of α-Ga single-crystal surfaces was investigated with the scanning tunneling microscope (STM) under ultra-high-vacuum conditions. The sputter-cleaned surface exhibits large, automatically flat terraces extending over distances of several 1000 Å. On the atomic scale, STM images reveal a 1×1 reconstruction of the surface lattice. The measured step height between the (001) terraces provides direct evidence for the existence of molecular Ga₂ dimers, a long-standing assumption that previously lacked clear experimental confirmation.

The interaction between an Ir tip and an Ir sample was investigated during normal tunneling operation of the scanning tunneling microscope. Force gradients compatible with metallic adhesion were observed within a range of 2 Å before making contact. Based on the theory of metallic adhesion, a scaling relation is derived which allows the tip geometry and the characteristics of the interaction to be accounted for in a systematic manner.