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The Atomic Force Microscope (AFM) has become a powerful apparatus for performing real-time, quantitative force measurements between materials. Recently the AFM has been used to measure adhesive interactions between probes placed on the AFM cantilever and sample surfaces. This article reviews progress in this area of adhesion measurement, and describes a new technique (Jump Mode) for obtaining adhesion maps of surfaces. Jump mode has the advantage of producing fast, quantitative adhesion maps with minimal memory usage.

The force needed to remove micrometer-size polystyrene particles from elastomeric substrates having Young's moduli of 3.8 and 320 MPa was measured using atomic force techniques. It was found that the removal force was approximately an order of magnitude less for the more rigid substrate than for the more compliant substrate. In both cases the removal force was independent of applied load. However, when the more compliant material was overcoated with the stiffer material, the particle removal force was found to increase with increasing pressure, with the limit at low pressure commensurate with the removal force observed for the stiffer substrate and commensurate with the more compliant material at higher pressures. The results are interpreted in terms of the penetration depth of particle asperities into the substrates.

A transform is described for analyzing scanning-probe-microscope images. This radial-histogram transform is shown to contain useful information for ascertaining the structure of an object in a scanning-probemicroscope image. The radial-histogram transform also allows quantitative assessment of tip dilation effects. The utility of the transform is illustrated by analyzing a noncontact atomic force microscope image of a nanometer size Au cluster supported on a mica substrate. Using the radial-histogram transform, detailed information about the faceting, structure, and orientation of the supported nanometer-size cluster is obtained. @S0163-1829~96!02819-7#

The surface force interactions between individual 8 μm diameter spheres and atomically flat substrates have been investigated using atomic force techniques. The lift-off force of glass, polystyrene, and tin particles from atomically smooth mica and highly oriented pyrolitic graphite substrates was determined as a function of the applied loading force in an inert nitrogen environment. While the relative magnitudes of the measured lift-off force were found to scale as expected between the various systems studied, the absolute values were a factor of ∼50 smaller than expected from the Johnson, Kendall, and Roberts theory. The surface topography of representative spheres was characterized with atomic force microscopy, allowing a quantitative assessment of the role that surface roughness plays in the adhesion of micrometer-size particles to substrates. Taking into account the radius of curvature of the asperities measured from the atomic force scans, agreement between the measured and theoretical estimates for...

We have analyzed the electron transport processes in Al/AlOx/Al junctions. The samples were produced by glow-discharge-assisted oxidation of the bottom electrode. The nonlinear I–V curves of 17 samples were measured at room temperature, being very well fitted using the Simmons’ equation with the insulating barrier thickness, barrier height, and the junction area as free parameters. An exponential growth of the area normalized electrical resistance with thickness is obtained, using just values from I–V curve simulations. The effective tunneling area corresponding to the “hot spots” can be quantified and is five orders of magnitude smaller than the physical area in the studied samples.

The surface force interactions between a single micrometer-size polystyrene sphere and a p-type silicon substrate were investigated using atomic force microscope techniques. The force of removal and the degree of deformation of the particle determined as a function of the applied loading force. The work of removal, estimated assuming a perfectly spherical particle and a smooth substrate, was also determined. The influence of surface contamination and the implications of the short contact times used in these experiments are discussed.

The surface topography of YBa2Cu3O7 thin films prepared by pulsed laser deposition is studied by atomic force microscopy and scanning tunneling microscopy. The possible contributions from observed structural features to the critical current density Jc are discussed. It is shown that the contribution of the screw dislocations associated with some structures can be either repulsive or attractive, depending on the dominant pinning mechanism. At low magnetic fields (to about 0.25 kOe) these dislocations can account for the observed critical current density values (Jc≳1011 A/m2) while for larger fields the higher‐density steplike growth structures can account for significant values of Jc. It is shown that the pinning strength associated with pinning at steps varies inversely with thickness.

An atomic force microscope tip is used as a vector positioner to manipulate nanometer‐size preformed Au clusters deposited on atomically smooth substrates. Using this technique, two‐dimensional cluster nanostructures can be assembled at room temperature.

An atomic force microscope has been used in the attractive (noncontact) force mode to image individual nanometer‐size Au clusters preformed in the gas phase and deposited on a variety of atomically flat substrates. Using this technique, it is possible to reliably image preformed clusters in their as‐deposited positions. This capability allows nanoindentation studies to measure the mechanical properties of individual nanometer‐size clusters supported on atomically flat substrates. We find that the elastic modulus of a 3.1‐nm Au cluster is 56−19+33 GPa. This should be compared to a bulk value of 80 GPa for polycrystalline Au and 120 GPa for crystalline Au in the [111] direction.

An atomic force microscope has been used in the attractive (noncontact) force mode to image individual nanometer-size Au clusters preformed in the gas phase and deposited on a wide variety of atomically flat substrates. Using this noncontact technique, it is possible to reliably image preformed clusters in their as-deposited positions. This capability allows nanoindentation studies to measure the mechanical properties of individual nanometer-size Au clusters supported on atomically flat substrates and permits a measure of the deformation of a nanometer-size cluster as a function of the applied load. Applying a compression model to the deformed clusters, an elastic modulus roughly 2/3 that of bulk Au is obtained for annealed clusters with sizes between 3 and 18 nm. If the clusters are unannealed, a significantly smaller elastic modulus is observed (approximately 1/6 that of bulk Au). As the applied load increases beyond \ensuremath{\sim}20 nN, the data suggest that the yield point of an annealed Au cluster can be exceeded and the atomic force microscope tip can fracture the cluster.

An atomic force microscope has been used in the attractive (noncontact) force mode to image individual nanometer-size Au clusters preformed in the gas phase and deposited on a wide variety of atomically flat substrates. Contact imaging modes are shown to provide sufficient lateral forces to dislodge the clusters. Using a noncontact technique, it is possible to reliably image preformed clusters in their as-deposited positions. This capability allows nanoindentation studies to measure the mechanical properties of individual nanometer-size Au clusters supported on highly oriented pyrolitic graphite and permits a measure of the deformation of a nanometer-size cluster as a function of the applied load.

Nanoindentation experiments on high quality Au films were performed in vacuum using an atomic force microscope. In these experiments, elastic behavior was observed until loading forces greater than ∼ 20 nN were applied. For loads larger than this, systematic changes in the jump-to-contact, loading/unloading and lift-off regions of the data occur. These observations are consistent with a transition from elastic to inelastic behavior during indentation.

We have made spin‐valve structures of Permalloy/Cu/Co by sputtering or electron‐beam deposition onto the antiferromagnetic oxide NiO. The oxides were made either by deposition of the metals and subsequent oxidation or by growing them in situ using reactive sputtering. The magnetic properties of the giant magnetoresistancestructures were studied by magnetoresistance, vibrating sample magnetometry, and ferromagnetic resonance methods. The oxides were characterized by x‐ray diffraction and atomic force microscopy. We studied surface roughness and structure as functions of thickness and oxidation temperature and correlated the oxide properties with the magnetic performance. We found that the metal layer roughened during the postdeposition oxidation process and that the resulting oxide layers were very effective in pinning the direction of the magnetic moment of adjacent metal films. Coercive fields over 500 Oe were obtained for Co overlayers on NiO films but the exchange bias field was generally less than 100 Oe and was not strongly dependent on the roughness. The beneficial effects of this strong pinning were offset to some degree by higher switching fields required in spin‐valve structuresdeposited over the Co. We also made reactively sputtered oxide antiferromagneticfilms which had smoother surfaces than those made by postdeposition oxidation.

A technique has been developed that allows a real-time measurement of the lift-off force required to remove a scanning force microscope tip from a substrate. Both topography and adhesion maps are obtained simultaneously, allowing the correlation between topography and adhesion properties to be studied. Quantitative values of important adhesion parameters can be extracted from these data. A number of examples are given which illustrate the utility of this technique.