A high-sensitivity fiber-optic displacement sensor for atomic force microscopy is described. The sensor is based on the optical interference occurring in the micron-sized cavity formed between the cleaved end of a single-mode optical fiber and the microscope cantilever. As a result of using a diode laser light source and all-fiber construction, the sensor is compact, mechanically robust, and exhibits good low-frequency noise behavior. Peak-to-peak noise in a dc to 1 kHz bandwidth is less than 0.1 Å. Images are presented demonstrating atomic resolution of graphite and magnetic force imaging of bits written on a magnetic disk.

This paper discusses the principles of magnetic force microscopy (MFM) and its application to magnetic recording studies. We use the ac detection method which senses the force gradient acting on a small magnetic tip due to fields emanating from the domain structure in the sample. Tip fabrication procedures are described for two types of magnetic tips: etched tungsten wires with a sputter-deposited magnetic coating and etched nickel wires. The etched nickel wires are shown to have an apex radius on the order of 30 nm and a taper half-angle of approximately 3°. Lorentz-mode transmission electron microscopy of the nickel tips reveals that the final 20 μm is essentially single domain with magnetization approximately parallel with the tip axis. Images of written bit transitions are presented for several types of magnetic media, including CoPtCr, CoSm, and CoCr thin films, as well as γ-Fe2O3 particulate media. In general, the written magnetization patterns are seen with high contrast and with resolution better than 100 nm. A number of magnetic recording applications are discussed, including the investigation of overwrite behavior and the writing characteristics in CoSm media at high data density. Computer calculations were performed to simulate the MFM response to written magnetic transitions. By including the extended geometry of the tip, the nonparallel orientation of the cantilever, and the finite width of the magnetic transitions, good agreement with experiment was obtained. The model calculations correctly predict the experimentally observed change in image contrast that occurs as a function of tip orientation. Computer calculations showing the dependence of resolution on tip geometry are also presented.

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We have demonstrated that a gold scanning tunneling microscope (STM) tip can be used as a miniature solid-state emission source for directly depositing nanometer-size gold structures. The process has been demonstrated in ultrahigh vacuum on gold substrates, and in air on gold and platinum substrates. Studies made in air suggest that the process is fast, repeatable, and field-induced. The emission mechanism is believed to be field evaporation of tip atoms, which is enhanced by the close proximity of the substrate. The technique has been used to write several thousand features with no apparent degradation of the tip’s ability to write. Elevated and room temperature studies show the written structures to be stable over periods of weeks, in contrast to some previous STM measurements of gold self-diffusion.

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