Many different microscopic methods exist. Some have quite different underlying principles and, consequently, provide very different kinds of information. The ability to correlate the data and images from multiple modes on the same sample offers unique benefits for demanding applications. One combination of techniques that has been successful enough to result in the development of dedicated integrated systems is Raman-AFM, which combines Raman microscopes with atomic force microscopes (AFMs).

In Raman microscopy, a relatively standard optical microscope is used as the basis for carrying out Raman spectroscopy. The excitation laser and the Raman signal are carried through the microscope optics and, ultimately, to the spectrometer. Such an analysis provides information about the chemical composition of the sample. Raman microscopes typically have sub-micron spatial resolution. They can provide spectra at particular points of interest or develop a complete chemical map of the sample by scanning.

In contrast, an AFM makes a direct physical measurement of the sample by bringing a fine cantilever probe close to the sample’s surface. Different probe tips carry out various specific AFM modes that quantify the material, physical or electromagnetic properties of the sample directly at the point beneath the probe tip. By scanning the sample, a complete image map of the sample’s surface is obtained. AFMs also generally provide sub-micron spatial resolution.

The two techniques can be combined in different ways. Integrated Raman-AFM systems can switch between modes almost as easily as switching between different objective lenses in a microscope. More commonly, microscope vendors provide the means for coupling a Raman microscope with an AFM, so that the sample can be analyzed by both instruments without the need for relocating or reregistering the sample area. Another method is the use of specialized AFM tips that allow surface enhanced Raman spectroscopy to contribute to the Raman signal.

The combined Raman-AFM data provide both high-resolution chemical composition data and physical AFM data for the surface. This offers rich and complementary data about the sample for both materials science and life science research applications. Common sample types include living cells and tissues, semiconductor wafers and complex polymeric materials.

Because of the combined nature of the technology, the market participants are drawn from both the Raman and AFM markets. Few firms have the technical capability to provide both halves of the system. Bruker and WITec can provide both capabilities. WITec offers a truly integrated Raman-AFM system. Partnerships have formed to deliver integrated Raman-AFM platforms. One example is Renishaw and Bruker Nano’s InVia-Innova Raman-AFM. Other vendors include HORIBA for the Raman technology and NT-MDT, Agilent, Nanonics and Park Systems for the AFM systems.

Combined Raman-AFM Systems

at a Glance:

Leading Suppliers

• Bruker

• HORIBA

• Renishaw

Largest Markets

• Academia

• Pharmaceutical

• Polymers

Instrument Cost

• $250,000–$750,000