(Nanowerk Spotlight) When scientists need to examine surface structures at the nanoscale, scanning electron microscopes offer one powerful approach among several advanced imaging technologies. These sophisticated instruments have transformed research in fields from microchip manufacturing to medical device development. Yet studying many important materials remained challenging because non-conductive samples, from biological tissues to advanced ceramics, accumulate electrical charges under the microscope’s electron beam. These charges create distorted images, much like static electricity disrupting a television signal.
Since the 1950s, scientists have worked around this problem by coating samples with a thin layer of gold before imaging. While this approach made electron microscopy possible for countless discoveries, it introduces significant compromises. Gold forms uneven coatings that leave vertical surfaces poorly covered. The gold layer also creates a grainy texture, with particles 10-12 nanometers wide that blur fine details researchers need to see. Applying these gold coatings requires expensive vacuum chambers, and controlling the coating thickness proves difficult – too thin fails to prevent charging, too thick masks important features.
Now researchers in Singapore have developed a simpler solution using a conductive polymer called PEDOT:PSS. This material can be applied like paint, forming smooth, continuous films that conform to every surface contour. The polymer consists of two components that work together – PEDOT conducts electricity while PSS helps create uniform coatings. The result is a layer just a few nanometers thick that conducts away electrical charges without obscuring sample details.
Deposition of thin conducting polymer films. a) Chemical structures of EG, DMSO, and PEDOT:PSS. b) Schematic illustration of the preparation of PEDT:PSS films by spin coating. c) Schematic illustration of Au deposition by sputtering. d–g) SEM images of etched glass samples (d) without a conductive layer, (e) coated with pristine PEDOT:PSS, (f) coated with PEDOT:PSS-EG, and (g) deposited with Au. h) Schematic illustration of uniform PEDOT:PSS and non-uniform Au films on nanostructured samples. The non-uniformity is indicated by the brightness. (Reprinted with permission by Wiley-VCH Verlag) (click on image to enlarge)
Testing on silicon computer chips demonstrated the method’s advantages. While gold-coated samples showed only surface patterns, the polymer coating revealed both surface features and underlying structures with unprecedented clarity. When examining wooden materials, the technique captured clear images inside microscopic pores, allowing researchers to analyze growth patterns in three dimensions. The polymer coating proved particularly valuable for studying ultra-light materials called aerogels, which have delicate networks of pores thousands of times thinner than a human hair. Traditional gold coating made these materials appear artificially grainy, but the polymer preserved their intricate structure.
The method also provided new insights into medical masks and filters by revealing their complete fiber network structure rather than just surface features. This capability could help manufacturers optimize filtration materials for better protection against viruses and particles. The polymer coating achieved conductivity of over 1000 Siemens per centimeter, exceeding the minimum needed for clear electron microscope imaging while maintaining transparency to the electron beam.
The technique does have limitations. The polymer solution’s acidic nature can damage some sensitive materials, though researchers found they could adjust its chemistry to protect samples. Coating thickness requires careful control between 5 and 20 nanometers – thicker layers risk filling in fine features while thinner ones may not conduct adequately.
The method’s simplicity makes it widely accessible since it requires only basic laboratory equipment rather than specialized vacuum systems. This new approach, which the researchers call “topographic SEM,” produces three-dimensional surface details that help scientists understand and improve materials ranging from energy storage devices to artificial tissue scaffolds. The technique achieves this by allowing the electron microscope to capture clear images not just of horizontal surfaces, but also along vertical walls and deep inside porous structures – areas that traditional gold coating methods often fail to reveal.
This advancement in microscopy technique opens new possibilities for materials science, semiconductor manufacturing, and biomedical research. By enabling detailed examination of complex three-dimensional structures at the nanoscale, topographic SEM could accelerate development of next-generation electronic devices, more efficient energy storage materials, and improved medical implants. The ability to clearly see structural details in all dimensions, combined with the method’s accessibility, provides scientists with a powerful new tool for pushing the boundaries of materials development and optimization.
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