A new technique to probe nanoscale structures by depositing nanoparticles directly on top of features of interest has been developed by a scientist at the Jet Propulsion Lab in California. The method works because the nanoparticles locally enhance Raman scattering or infrared absorption. As well as imaging nanomaterials, it could be used to analyze fossils for submicron organic structures and even samples from other planets, like Mars.
"I am calling this new method 'targeted surface enhanced spectroscopy' (or TSES)", Mark Anderson told
nanotechweb.org.
TSES concept
Anderson used an atomic force microscope (AFM) to deposit nanoparticles (or their chemical precursors) directly on a nanoscale sample. The technique is similar to dip pen nanolithography (DPN), where liquid-dispersed materials are deposited from an AFM onto a surface. The nanoparticles are then illuminated with a spectrophotometer beam and locally guide and concentrate the light to small areas on the surface. "This provides a method to draw features to guide the enhanced fields and tailor the localized 'plasmonic' effect," explained Anderson.
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TSES is also an extension of tip enhanced Raman spectroscopy (TERS), which uses an AFM tip to locally enhance a Raman signal for sub-diffraction limit spectroscopy, he adds. "In fact, the new method simplifies integrating the AFM and spectrometer systems," said Anderson. "The TSES approach provides both surface enhanced Raman spectroscopy (SERS) and surface enhanced infrared absorption spectroscopy (SEIRA). It is also applicable to fluorescence spectroscopy as well."
The technique could be used to analyze nanoscale devices and materials. It might also be employed as a general method to make plasmonic device structures by exploiting DPN that allows liquid phase writing of colloidal particles or molecules on a surface with an AFM. In this way, structures with an optimal shape that can guide surface plasmons (surface excitations that involve billions of electrons) may be fabricated.
Analyzing ancient fossils and samples from Mars
Anderson says that his team is also planning to use the method to analyze ancient fossils for submicron structures. "This experience could then hopefully be applied to examining returned samples from future Mars missions," he explained. "NASA is planning Mars sample return missions for 2014 and 2016 that will robotically collect samples and return to Earth for extensive micro-analysis."
The work was supported by NASA's Planetary Instrument Development Program and is an outgrowth of earlier work that developed an AFM for Mars. "This will be fully realized on May 25 this year when the Phoenix spacecraft lands on Mars," said Anderson. "This mission has an AFM for analyzing Mars soil and dust and will carry the first nanotechnology-based instrument to land on another planet."
The results were reported in
Applied Physics Letters.
Source:
nanotechweb.org
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