This chapter gives a necessarily brief overview of the techniques employed to create structures at the nanometer scale, and the tools used to examine matter down to that level. Entire books have been written about many of these topics. Here the emphasis will be broad exposure, and where possible explanations of the strengths and limitations of the various approaches.

Characterization

Characterizing materials at the nanoscale can be very challenging. It's easy to say what we want, as practitioners in this field. When presented with a sample or nanoscale structure, it would be wonderful if there were some tool or set of tools that could tell us, nondestructively, the position and composition of every atom in the sample, with atomic resolution. Unfortunately, this remains a fantasy. Over the years, however, a wide variety of experimental techniques have been brought to bear on the problem of materials characterization, applying different physical principles to acquire information about various aspects of the systems of interest. Some of these same techniques have been adapted or spun off into related approaches to nanoscale patterning and fabrication.

One can broadly divide the characterization techniques into two categories, bulk or global, and local. Bulk methods generally interrogate a volume or area of sample that is often much larger than the nanoscale, but nonetheless can reveal incredibly precise nanoscale information. Diffraction is the classic example. Local methods, in contrast, directly interrogate a nanoscale volume of sample, and somehow transduce those local interactions into macro scale signals.

X-ray techniques

Since their discovery in the late nineteenth century, x-rays have been incredibly useful for looking at the structure of materials. X-rays are electromagnetic radiation with photon energies in the keV to tens of keV range, and corresponding wavelengths down to subatomic scales. X-rays interact primarily with the inner electrons of atoms, and therefore their scattering is relatively greater for elements of higher atomic number.