Scanning near-field optical microscopy (SNOM or NSOM) is a form of scanning-probe microscopy (SPM) that provides light-based imaging of surfaces at better resolution than traditional light microscopy. With light microscopy, diffraction limits resolution to roughly 250 nm. SNOM instruments can have resolutions an order of magnitude greater, down to about 10 nm.

In SPM, piezoelectric motors control fine probes or cantilevered tips in or in near contact with a sample’s surface to analyze its topography, using light to probe the surface. In one form of SNOM, the probe, which has an optical aperture, is often a drawn-out optical fiber with a tip a few tens of nanometers across. The fiber, coated with metal to keep light confined within the tip, brings light waves in close proximity to the surface and, when in reflectance mode, transmits signal to the detector. In apertureless SNOM, which has developed rapidly over the past 10 years, the probe has a sharp metal SPM tip. Illumination from an external source is directed toward the interface between the tip and the surface. The tip creates electromagnetic interactions that enhance the coupling between the light and the sample, and the system collects and analyzes the scattered light from the sample.

SNOM can be used simply for optical imaging, but its use of light enables optical spectroscopy and thus chemical imaging of surfaces. This capability is one of SNOM’s major selling points. Depending on the tip used, other SPM imaging modes can also be supported by a SNOM system, and SPM and SNOM data can be correlated to provide a more complete picture of a surface

SNOM is used for materials-science research in academia and industry. Complex polymer surfaces are an important application, as SNOM can not only image a surface on the nanoscale, but its chemical-identification capabilities allow researchers to identify the components in blends of polymeric materials. SNOM can also be applied to metals, ceramics, semiconductor materials, thin films and advanced nanotechnology materials like graphene. Difficulties in using SNOM with “wet” samples have retarded greater usage of SNOM for chemical imaging in the life sciences.

In 2013, market demand for SNOM was about $20 million, though hard to gauge accurately, since most systems are sold as SPM systems, with SNOM one of many modes supported. There are relatively few market participants. Bruker, which acquired SPM leader Veeco in 2010 (see IBO 8/31/10), is the market leader and recently introduced the Inspire SPM system with apertureless SNOM optics. Other significant market participants include the German company WITec, the Israeli firm Nanonics and the Russian manufacturer NT-MDT. Neaspec is another company with a particular emphasis on SNOM. In February, a majority interest in Neaspec was acquired by Attocube Systems (see IBO 3/15/14). Other vendors include Park Systems, JPK and APE Research.

SNOM at a Glance:

Leading Suppliers

• Bruker

• WITec

• Nanonics

Largest Markets

• Academia

• Polymers

• Nanotechnology

Instrument Cost

• $100,000–$500,000