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Focused MeV Proton Beams for 3D Nano-Lithography, DNA nanofluidics and Nanoimprint lithography: Outlook towards fast fabrication at sub 10 nanometer

Jeroen A. van Kan
Centre for Ion Beam Applications, Department of Physics, National University of Singapore


Microscopy has been an integral part of scientific development and has spurred development in many fields. Microscopy using fast protons has several advantages over other forms of microscopy. A fast incoming proton mainly interacts with substrate electrons, due to the mass mismatch between protons and electrons a proton beam practically follows a straight path through resist material. In proton-electron collisions most substrate electrons get enough energy to break bonds and typically have a short projected range (~nm). Proton Beam Writing (PBW) employs a focused MeV proton beam which is scanned in a predetermined pattern over a resist, which is subsequently chemically developed. PBW exhibits low proximity effect, coupled with the straight trajectory and even energy deposition along the path of the proton beam result in smooth sidewalls. The high penetration depth of the proton beam enables the production of high aspect ratio, high density 3D nano structures, ideal for high quality molds for nano-imprint-lithography. We can now1 focus proton beams down to 9.3 x 32 nm2, allowing high aspect ratio lithography down to 19 nm in HSQ. PBW is an ideal technique to fabricate lab-on-chip (LOC) devices with features at the micron as well as at the nano scale. An easy method is introduced allowing fast replication of nanofluidic LOC devices using accurately fabricated molds featuring cross-sections down to 60 nm in polydimethylsiloxane. These masters can be used more than 200 times to replicate nanofluidic devices capable of handling single DNA molecules. This method reduces fabrication and packaging complexity, allowing end-users to fabricate nanofluidic LOC devices. Using fluorescence microscopy the extensions of DNA molecules has been observed inside nano-channels, large scale DNA sequencing has also been demonstrated2. Progress towards fast PMMA LOC device replication, will be discussed as well.

The current limitation of proton focusing systems is the lack of user-friendly facilities. The main weak point in these microscopes is the source performance which is typically several million times less in brightness compared to electron beam sources. Recent tests with “on chip ion sources” have shown potential to improve the ion beam brightness by a million times3,4. This will allow us to develop a table top proton microscope capable of delivering sub 10 nm beam spot size for MeV protons. This new source will therefore enable many new application like:

  • Fast sub 10 nm 3D nanofabrication without “proximity effects”.
  • Sub 10 nm whole cell imaging, opening up new pathways to investigate the uptake of nanoparticles in drugs delivery.
  • Since 0.5 MeV protons will cause double stand breaks in DNA, this new system will provide an insight to improve cancer treatment in radiobiology using 200 MeV protons
  1. JA van Kan, P Malar, and AB de Vera, Rev. Sci. Instrum., 83, (2012) 02B902-1.
  2. C Zhang, A Hernandez-Garcia, K Jiang, Z Gong, D Guttula, SY Ng, PP Malar, JA van Kan, Liang Dai, PS Doyle, R de Vries, and JRC van der Maarel, Nucleic Acids Research, 41 (2013) e189
  3. N Liu, X Xu, R Pang, PS Raman, A Khursheed and JA van Kan, Rev. Sci. Instrum, 87 (2016) 02A903-1.
  4. D Jun and P Kruit, J. Vac. Sci. Technol. B, 29, (2011) 6.
Created November 1, 2016, Updated October 1, 2018