Measurements of the contact potential difference between different materials have been performed for the first time using scanning force microscopy. The instrument has a high resolution for both the contact potential difference (better than 0.1 mV) and the lateral dimension (<50 nm) and allows the simultaneous imaging of topography and contact potential difference. Images of gold, platinum, and palladium surfaces, taken in air, show a large contrast in the contact potential difference and demonstrate the basic concept.
The past six years has seen a tremendous growth in scanned probe microscopies of various sorts. In this letter, we add a new capability to this family−mapping of thermal conductivity variations on a nanometer scale. We show how our new probe technique can be used to measure thermal conductivity of conductors and thin insulating films deposited on top of conductors. Our results also demonstrate for the first time, the capability of the technique to image subsurface details of samples. As the thermal conductivities of different materials can vary by over three orders of magnitude, we suggest this as an important new contrast mechanism for studying materials on the nanometer scale.
Scanning force microscopy (SFM), operated in the attractive imaging mode, enables the precise measurement of the force between tip and sample over a tip–sample distance ranging from contact to tens of nanometers. The basic long range interactions (>1 nm: i.e., hydrodynamic, electrostatic, van der Waals, and capillary forces) between tip and sample have been measured and will be discussed. Each force leads to a different mode of operation in profiling samples. The most critical part of the SFM is the force sensor. Exact knowledge of the sensor properties is required for the interpretation of SFM measurements. We have used micromachined silicon sensors consisting of a monolithic silicon cantilever with integrated silicon tip and have performed a detailed characterization of the tip geometry and resonance properties. Examples of surface images on different samples (conductors, insulators and biological materials) and structures, ranging from atomic steps up to several microns high features, have been investigated to demonstrate capabilities and problems in SFM imaging.
SUMMARY
The protein surface layer of the bacterium Deinococcus radiodurans (HPI layer) was examined with an atomic force microscope (AFM). The measurements on the air‐dried, but still hydrated layer were performed in the attractive imaging mode in which the forces between tip and sample are much smaller than in AFM in the repulsive mode or in scanning tunnelling microscopy (STM). The results are compared with STM and transmission electron microscopy (TEM) data.
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