/ Research / Christel Möller

Electron beam lithography also possible on uneven surfaces

Researchers from the SNI network have developed a new method for applying electron beam lithography to uneven surfaces. They are working with a floating resist that enables uniform coating. The work was recently published in the scientific journal AIP Advances.

Electron beam lithography can be used to produce structures on the nanometer scale. In this process, a precise electron beam chemically alters a coating, called a resist, so that it can dissolve locally. The resulting structure can then be transferred to other materials. However, it is problematic to apply the resist evenly on uneven surfaces.

Detour via the water bath
The team led by Dr. Floris Braakman in the group of Argovia professor Martino Poggio at the Department of Physics and Swiss Nanoscience Institute at the University of Basel has now developed a method that can be used to evenly coat uneven surfaces with a resist. "We need this because we want to place a quantum dot as a sensor on the tip of a cantilever," explains first author Luca Forrer, an SNI PhD student in the Poggio Lab. "However, conventional methods are not suitable for depositing the resist homogeneously even on the tiny tip."

The researchers solve the problem by first wetting a glass platelet with sugar solution, on which the resist can be evenly distributed. If this glass platelet is then carefully placed in water, the sugar solution diffuses into the surrounding water and the resist remains on the glass platelet. "From there, we let the resist slide into the water so that it then floats on the water surface," Luca Forrer describes. The researchers then immerse the tiny cantilever in the resist and carefully lift it off again with the resist attached. The cantilever is then evenly coated with the resist, including the tip, and only needs to be heated to remove the remaining water. The researchers can then lithograph the sample using the electron beam.

"This method will help us to place electrical contacts on the tip of an atomic force microscope cantilever and thus produce highly sensitive probes for studying electric and magnetic fields," Martino Poggio describes.