In the second of this two-part series for the MRS Bulletin, we present the most commonly used tools for the quantitative determination of structure and chemistry in thin films. The physics of thin films is at a stage during which one encounters phenomena that have a fragile dependence on the structure and chemical properties of the interface; the field, therefore, is at a stage during which quantitiative structural and chemical determination at the atomic level is a must. It is the purpose of the December and January issues of the Bulletin to provide a start for researchers interested in the field. Of course, even during the writing of these articles new techniques are being invented and it is therefore impossible to provide a comprehensive review of all techniques being used these days.

The structure and morphology of a thin film is, apart from composition, probably its most significant feature. Again and again we find that electronic, chemical, mechanical, magnetic, optical, and superconducting properties depend on the arrangement of atoms and on disorder in this arrangement. As most thin films are created using some form of deposition technique in which atoms are brought together at a surface, it is at the surface that the first opportunity occurs for formation of a particular atomic structure and morphology. As deposition proceeds, a moving surface, the “growth front,” continues to serve as the template for structure formation. Various kinetic processes, such as atomic transport and the adsorption or desorption of atoms from already-formed structures, determine the final morphology of the film. Subsequent treatment can, of course, modify the structure and morphology, but clearly the initial events occurring at the surface influence, to a large measure, the final outcome.

Techniques sensitive to surface structure and morphology are therefore an important component in the toolbox of methods for the quantitative analysis of the properties of thin films. Electron diffraction techniques have been, and continue to be, the most powerful and versatile of these. Even though electron diffraction is also useful for the structural analysis of the bulk, when one speaks of electron diffraction in the context of thin films, one almost invariably refers to surface-sensitive diffraction. Other methods, in particular scanning probe microscopy, have recently become popular. In many cases, such methods serve to re-emphasize the value of electron diffraction for quantitative structural analysis of thin films.

Rutherford backscattering spectrometry (RBS) is probably one of the most frequently used techniques for quantitative analysis of composition, thickness, and depth profiles of thin solid films or solid samples near the surface region. It has evolved in the past few years from an obscure nuclear technique into a major materials characterization technique. This is primarily due to its simplicity, versatility, and the amount of information it can produce in a short time. Because of its quantitative feature, RBS analysis often serves as a standard for other techniques. The purpose of this article is to introduce the topic to a broad community of materials researchers. Readers who want a more rigorous treatment of the topic for utility purposes can refer to a monograph.

In the early 1960s, several of the low-energy atomic and nuclear physics laboratories started to use their accelerators to do research in solid-state physics. This activity opened up a fertile interdisciplinary area called ion-solid interaction, which impacts materials research significantly.

Atomic force microscopy (AFM) was invented in 1986 by Binnig, Quate, and Gerber as “a new type of microscope capable of investigating surfaces of insulators on an atomic scale.” Stemming from developments in scanning tunneling microscopy (STM), it became possible to image insulators, organic and biological molecules, salts, glasses, and metal oxides — some under a variety of conditions, e.g., ambient pressure, in aqueous or cryogenic liquids, etc. In 1987, Mate and co-workers introduced a new application for AFM where atomic-scale frictional forces could be measured. Likewise, in 1989, Burnham and Colton used the AFM to measure the surface forces and nano-mechanical properties of materials. Today, there are many examples of using AFM as a high-resolution profilometer, surface force probe, and nanoindentor. Several new imaging techniques have been introduced; each depending on the type of force measured, e.g., magnetic, electrostatic, and capacitative. Because of the diverse nature of the field and instrumentation, the names “scanned probe microscopy” and “XFM” (where X stands for the force being measured, e.g., MFM is magnetic force microscopy) have been adopted.