Most miniature electronic, optical and micromechanical devices are made from expensive semiconductor or ceramic materials. For some applications like diagnostic lab-on-a-chip devices, thin-film polymers may provide a cheaper alternative, but the structure and properties of these materials—-often no more than a few nanometers (nm) thick—-are difficult to determine. In addition, defects in the thin polymer masking materials used to "print" integrated circuits can produce malfunctioning components. Consequently, researchers would like to have a non-invasive method for scanning polymer films for defects at high resolution.
Left: The crystal structure of a thin-film polymer "seaweed" crystal that is about four micrometers wide. Brighter areas indicate parts of the crystal with the greatest "strain." Center: The same crystal with lines superimposed showing the direction of strain between the crystals atoms. Right: Closeup of the upper left portion of the center image.
In the Aug. 23 issue of Applied Physics Letters,* researchers at the National Institute of Standards and Technology (NIST) report on an application of a new method for studying ultrathin polymers that makes it possible to visualize defects and structure in these materials and should help improve basic understanding of crystal formation in polymers.
Using a special form of near-field scanning optical microscopy, the NIST researchers were able to determine the structure of, and "strain" (stretching between atoms) in, thin-film crystals of polystyrene. Polystyrene is a ubiquitous plastic found in foam cups, CD cases and many other products.
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