Nanoscale Characterization of Materials
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-probe microscopy—have become tools of paramount importance in fundamental studies of surfaces. Furthermore, rapid progress in the development of new scanning-probe techniques and in the commercial availability of scanning-probe instrumentation has led to increasingly widespread application of these techniques to problems of both scientific and technological significance. Their growing importance is a natural consequence of the desire to design and fabricate ever smaller structures to improve performance or achieve new functionality in materials and devices, and of the limitations of more traditional experimental techniques in performing detailed and comprehensive characterization at the nanometer to atomic scale. An example of the extension of STM from fundamental surface studies to atomic-scale characterization of semiconductor heterostructures and devices is provided by Edward T. Yu in his article on cross-sectional STM studies of III-V semiconductor heterostructures. In this work, tunneling measurements performed on cross sections of epitaxial layers exposed by cleaving under ultrahigh vacuum provide detailed information about the atomic-scale structure of heterojunction interfaces and alloy layers. Correlation of information obtained from cross-sectional STM studies with epitaxial-growth conditions, complementary characterization studies, and device behavior then provides a comprehensive picture of the relationships among phenomena occurring during epitaxial growth, the resulting atomicscale morphology and electronic properties of heterostructures, and various aspects of device performance. Optical characterization of materials with spatial resolution in the sub-100 nm regime can be performed by combining
optical measurements with scanningprobe technology, as exemplified in the near-field scanning optical microscopy (NSOM) studies described by J.W.P. Hsu. Her article discusses the application of NSOM to the nanoscale characterization of defect structures in a variety of materials, with particular emphasis on the characterization of individual defects and the correlation of the optical and electronic activity associated with specific defects with structural features observable in topographic images. She presents as specific examples studies of strain-relaxed Sii_vGeA films and of perovskite oxide crystals and thin films, and also gives an overview of the application of NSOM to the characterization of optical and optoelectronic properties in a broad range of materials and device structures. R. Wiesendanger provides a description of the correlation among nanometerscale structural, electronic, and magnetic properties of thin magnetic films as elucidated in studies of ultrathin magnetic films using STM and scanning tunneling spectroscopy, spin-polarized scanning tunneling spectroscopy, and magneticforce microscopy. Scanning tunneling spectroscopy, in which the tunneling current is measured as a function of voltage, allows atomic-scale structure and local electronic properties to be correlated and, for Fe deposited o
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