Imaging on the nanoscale
A team of researchers from FOM Institute AMOLF and Stanford University has developed a novel way to make three-dimensional images of extremely small objects. They combined two techniques to achieve this: cathodoluminescence and tomography. The new method could contribute to the development of solar cells, LEDs and lasers on a nanoscale. The researchers published their work in Nature Nanotechnology on 6 April 2015.
Step 1: cathodoluminescence
Lasers, LEDs and solar cells require control over light at the nanoscale. However, standard optical microscopy cannot be used to probe light at this scale. The standard imaging resolution is limited by a fundamental physical limit: the optical diffraction limit which is about 250 nanometers (a nanometer is a millionth of a millimeter). A new instrument, developed in Albert Polman's group at AMOLF, is able to make optical images at a resolution far below the diffraction limit. This so-called cathodoluminescence instrument makes a two two-dimensional image by using an electron beam to excite materials and detects the emitted light.
Step 2: tomography
The new study expands on this technique. The researchers used the cathodoluminescence instrument to fire electrons on small, crescent-shaped core-shell particles composed of a polystyrene core and a gold shell. These particles, with a diameter of 250 nanometer, serve as a model system in which multicolored light is concentrated in different nanoscale focal spots. The images obtained with this method were completed using a tomographic reconstruction: the measured sections were stacked onto each other to form three dimensional images. The AMOLF and Stanford team thus managed to make images of the coloured hotspots with a resolution far beyond the diffraction limit.
Polman: "We have worked with our Stanford colleagues for quite a while now, and this project is the crowning glory of that collaboration. We are now using the new method to design more efficient solar cells. There are also promising prospects to make novel LED technologies. On top of that, it might become possible to image biological systems with the technique."
Reference
Nanoscale optical tomography with cathodoluminescence spectroscopy
A. Atre, B.J.M. Brenny, T. Coenen, A. Polman and J.A. Dionne, Nature Nanotech. 10, 2015,
DOI: 10.1038/nnano.2015.39
Contact information
Albert Polman, +31 (0)20 754 71 00.