Nanoscience and Nanotechnology are emerging disciplines that seek to understand the nanoscale processes that govern a material’s behavior. While the bulk properties are well understood the properties of nanostructured materials can differ considerably from them. As devices get smaller and smaller the knoweldge of these properties becomes more important. This new direction of science is rather multi-disciplinary, spanning physics, chemistry, biology, medicine, and materials science, as well as many other fields.

Thin films in particular are the basis for a large number of technologies and are used for the preparation of novel materials. The use of the multitechnique approach to the growth and characterization of thin films is an important subject for basic as well as applied research [1]. Many examples exist in the literature and technology which prove that the important physical properties of thin film materials are strongly affected by their structure. To date many of these approaches were qualitative in nature or were very limited. In recent years, a general consensus has been emerging for the need of quantitative approaches to the structural characterizations and their correlation with physical property measurements. A large number of techniques such as High Resolution X-ray Diffraction and Neutron Scattering, Transmission and Scanning Electron Microscopy (TEM and SEM), Scanning Probe Microscopy (SPM), Nuclear Methods and a variety of surface techniques have been used for many years to characterize mostly qualitatively the chemistry and structure of thin films [1-2].

A number of physics problems are being intensively studied. These include the growth of a variety of metallic films, the physics of magnetic and superconducting films and studies of electrical transport and photoconductivity in complex materials. The new directions which are emerging include

• the preparation and study of novel micro- and nanostructures such as quantum dots and lines
• the growth of novel insulating magnetic materials,
• and exploration of new intermetallic systems.

The following will give a brief description of the various research problems being investigated:

Magnetic thin films have received renewed attention due to the discovery of unusual properties in the magnetotransport of magnetic superlattices [3-6]. These are also very important in a number of applications, such as sensors and media for magnetic recording, automotive and aerospace industries. These include: magnetic superlattices, exchange biased antiferromagnetic-ferromagnetic layers, single magnetic films, etc. One of the key ingredients in all these studies is understanding the connection between the chemistry and structure of the films and their physical properties. Considerable effort has been dedicated to these studies in all their aspects including growth, structural characterization and measurement of the physical properties. Recent highlights include the observation of large oscillations in the resistivity of Co/Ni superlattices, the correlation of interfacial roughness and Giant Magnetoresistance in MBE and sputtered Fe/Cr superlattices and a study of the dependence of exchange bias on the interfacial structure in ferromagnetic-antiferromagnetic bilayers.

Many of the applications in the field of superconductivity rely on the reliable and reproducible preparation of thin superconducting films with optimum properties [6-9]. Moreover, since these materials are invariably grown at high temperatures in proximity to other substances (substrates, buffers, etc.) the issue of interfacial structure is of great importance, particularly in this case because the relevant length scale which controls the physics is on the order of a few Angstroms. Recent highlights include a quantitative study of the structure of ceramic superlattices, the observation and detailed characterization of photosynthesis of superconductivity and the growth of phase spread alloys.

When the size of small structures becomes comparable to or smaller than the characteristic length of the physical phenomenon or interaction, new properties of these structures that are different from the properties of the bulk materials can be observed. For many physical phenomena, such as magnetism, capillary condensation, etc, this length scale is between 1 nm and 100 nm. For this reason, the interest to nanostructures has increased dramatically in the last decade. Various magnetic and nonmagnetic nanostructures are being fabricated and studied for their new, unusual physical properties. Understanding of these properties can lead to new and exciting applications: high-density recording devices, minituarized sensors, electronic gadgets, cancer treatment, and many others.

Bibliography:

[1] See for instance Epitaxial Growth. J. W. Matthews, ed., Academic Press, 1975, New York.
[2] For a review of structural and chemical determination of thin films see Materials Research Society Bulletin,Vol. XVII No. 12 and Vol. XVIII No. 1, I. K. Schuller and Y. Bruynseraede, eds., and references cited therein.
[3] For a comprehensive review of the field, see for instance, L. M. Falicov et al, Mater. Res. 5 , 1299 (1990).
[4] See for instance, Ultrathin Magnetic Structures, B. Heinrich and A. Bland, eds., Springer-Verlag, Berlin (in press).
[5] Ivan K. Schuller, S. Kim, and C. Leighton, Magnetic Superlattices and Multilayers, J. Mag. Mag. Mat. 200, 571 (1999).
[6] See for instance, Solid State Physics, Vol. 47, D. Turnbull and H. Ehrenreich, eds., Academic Press, 1994, San Diego, CA.
[7] See for instance, Metallic Multilayers, S. Maekawa, H. Fujimori, T. Shinjo and R. Yamamoto, eds. North Holland, 1993, Amsterdam.
[8] For a review of low T_c films, see for instance, B. Y. Jin and J. B. Ketterson, Adv. Phys. 38 , 189 (1989).
[9] For a review of high T_c films, see for instance, I. Bozovic et al., Jour. Super. 7 , 187 (1994).