This brief article introduces the July 2004 issue of MRS Bulletin, focusing on Scanning Probe Microscopy in Materials Science.Those application areas of scanning probe microscopy (SPM) in which the most impact has been made in recent years are covered in the articles in this theme.They include polymers and semiconductors, where scanning force microscopy is now virtually a standard characterization method; magnetism, where magnetic force microscopy has served both as a routine analytical approach and a method for fundamental studies;tribology, where friction force microscopy has opened entirely new vistas of investigation;biological materials, where atomic force microscopy in an aqueous environment allows biosystems to be imaged and measured in a native (or near-native) state;and nanostructured materials, where SPM has often been the only approach capable of elucidating nanostructures.

The atomic force microscope (AFM) allows biomolecules to be observed and manipulated under native conditions. It produces images with an outstanding signal-to-noise ratio and addresses single molecules while the sample is in a buffer solution. Progress in sample preparation and instrumentation has led to topographs that reveal subnanometer details and the surface dynamics of biomolecules. Tethering single molecules between a support and a retracting AFM tip produces force–extension curves, giving information about the mechanical stability of secondary structural elements. For both imaging and force spectroscopy, the cantilever and its tip are critical:the mechanical properties of the cantilever dictate the force sensitivity and the scanning speed, whereas the tip shape determines the achievable lateral resolution.

Magnetic force microscopy (MFM) is a well-established technique for imaging the magnetic structures of small magnetic particles. In cooperation with external magnetic fields, MFM can be used to study the magnetization switching mechanism of submicrometer-sized magnetic particles. Various MFM techniques allow the measurement of a hysteresis curve of an individual particle, which can then be compared to ensemble measurements. The advantage of using MFM-constructed hysteresis loops is that one can in principle understand the origin of dispersion in switching fields. It is also possible to directly observe the correlation between magnetic particles through careful imaging and control of the external magnetic field. In all of these measurements, attention needs to be paid to avoid artifacts that result from the unavoidable magnetic tip stray field. Control can be achieved by optimizing the MFM operation mode as well as the tip parameters. It is even possible to use the tip stray field to locally and reproducibly manipulate the magnetic-moment state of small particles. In this article, we illustrate these concepts and issues by studying various lithographically patterned magnetic nanoparticles, thus demonstrating the versatility of MFM for imaging, manipulation, and spectroscopic measurements of small particles.

Atomic force microscopy (AFM) is now well established among the tools of choice for the analysis and characterization of materials.Applications of AFM span many industries including chemicals, plastics, pharmaceuticals, and semiconductors.Advancements in AFM instrumentation over the last five years have expanded the range of application of this technology to investigate thermal and mechanical properties of complex materials at high spatial resolution as well as structural and morphological characterization of materials subjected to thermal and mechanical stresses.In particular, this has been an enabling technology for an improved understanding of structure–property relationships in polymeric materials including homopolymers, blends, impact-modified polymer systems, porous polymer systems, and semicrystalline polymers.Practical examples illustrate applications of contact, tapping-mode, phase-imaging, hot-stage, and scanning thermal methods for the characterization of modern industrial polymer materials.

Scanning probe microscopy (SPM) was originally conceived as a method for measuring atomic-scale surface topography. Over the last two decades, it has blossomed into an array of techniques that can be used to obtain a rich variety of information about nanoscale material properties. With the exception of friction measurements, these techniques have traditionally depended on tip—sample interactions directed normal to the sample's surface. Recently, researchers have explored several effects arising from interactions parallel to surfaces, usually by deliberately applying a modulated lateral displacement. In fact, some parallel motion is ubiquitous to cantilever-based SPM, due to the tilt of the cantilever. Recent studies, performed in contact, noncontact, and intermittent-contact modes, provide new insights into properties such as structural anisotropy, lateral interactions with surface features, nanoscale shear stress and contact mechanics, and in-plane energy dissipation. The understanding gained from interpreting this behavior has consequences for all cantilever-based scanning probe microscopies.

This article describes the details of scanning probe microscopy measurements of interfacial friction from an experimental perspective. In such studies, the probe tip is taken as a model of a single asperity within a tribological contact, and interfacial forces are measured as a function of the sliding contact of the probe tip with the surface. With appropriate detection schemes, friction and load forces can be monitored simultaneously and used together to describe the frictional properties of the microscopic contact. This article provides a detailed description of the procedures and protocols of friction measurements performed with scanning probe microscopy, the relevant properties of probe tips, and the influence of environment on microscopic friction measurements. In addition, the article provides a brief overview of several categories of friction studies performed with scanning probe microscopy, highlighting the type of materials characterized in these studies as well as the importance and impact of the microscopic measurements.

Scanning tunneling microscopy and noncontact atomic force microscopy have been used to observe germanium growth on Si(001) and Si(111). The atomically resolved images provide invaluable information on heteroepitaxial film growth from the viewpoints of both industrial application and basic science. We briefly review the history of characterizing heteroepitaxial elemental semiconductor systems by means of scanning probe microscopy (SPM), where the Stranski–Krastanov growth mode can be observed on the atomic scale:the detailed phase transition from layer-by-layer growth to three-dimensional cluster growth was elucidated by the use of SPM. In addition, we comment on the potential of SPM for examining the spectroscopic aspects of heteroepitaxial film growth, through the use of SPM tips with well-defined facets.