Using an atomic force microscope and a method called thermochemical nanolithography, scientists have painted the Mona Lisa on a surface about one-third the width of a human hair (30 microns).
The so-called Mini Lisa demonstrates a technique that could potentially be used to achieve nanomanufacturing of devices because the team was able to vary the surface concentration of molecules on such short-length scales.
Going pixel by pixel, the researchers positioned a heated cantilever at the substrate surface to create a series of confined nanoscale chemical reactions.
By varying only the heat at each location, they controlled the number of new molecules that were created. The greater the heat, the greater the local concentration. More heat produced the lighter shades of gray, as seen on the Mini Lisa’s forehead and hands. Less heat produced the darker shades in her dress and hair seen when the molecular canvas is visualized using fluorescent dye. Each pixel is spaced by 125 nanometers.
“By tuning the temperature, our team manipulated chemical reactions to yield variations in the molecular concentrations on the nanoscale,” explained Dr Jennifer Curtis of the Georgia Institute of Technology, lead author of a study published in the journal Langmuir.
“The spatial confinement of these reactions provides the precision required to generate complex chemical images like the Mini Lisa.”
Production of chemical concentration gradients and variations on the sub-micrometer scale are difficult to achieve with other techniques, despite a wide range of applications the process could allow.
The scientists produced chemical gradients of amine groups, but expect that the process could be extended for use with other materials. Another advantage is that atomic force microscopes are fairly common and the thermal control is relatively straightforward, making the approach accessible to both academic and industrial laboratories.
Bibliographic information: Carroll KM et al. Fabricating Nanoscale Chemical Gradients with ThermoChemical NanoLithography. Langmuir, 29 (27), pp. 8675–8682; doi: 10.1021/la400996w