Getting 'Color' at the Nanoscale
We live in a world filled with color but for a long time we were not able to capture it with film and cameras. Eventually the technology was created and then perfected so we could enjoy the full spectrum at theaters and on televisions. Now researchers at Berkeley Lab have brought color imaging to the nanoscale realm where previously only spatial information was accessible.
To get the properties of a nanomaterial a researcher would typically be limited to an atomic force microscope, which runs a probe over the material, measuring the topography of the surface. Any chemical information was limited because the methods to study it, such as spectroscopy, cannot operate at such a small scale due to the diffraction limit of light. The researchers at Berkeley Lab have defeated that limit though by perfecting a device to convert near- and far-field light. Far-field light is what we experience every day and has a very long range, while near-field light decays quickly over short distances but can be used at lengths below the diffraction limit. The transducer the researchers developed to convert between the two forms of light has a tapered, four-sided tip, which can focus any frequency of light down to a few nanometers. By taking the tip and attaching it to an optical fiber on an atomic force microscope the researchers were able to get both spatial and optical data about whatever it is run over.
In this case it was an indium-phosphide nanowire, which is promising for solar power generation. The new probe made the unexpected discovery that in some regions of the nanowire the relationship between light and electricity was seven-times greater than others. Such a finding could greatly affect how the material may be used in the future.