We Got the INK: 3D Nano Printing

By Pranoti Kshirsagar /

Lisa McElwee-White’s group makes precursors, the “ink” used to deposit thin films and to 3D print structures on the nanoscale. Her collaborators use heat, light, electron beams or ion beams; her group are the chemists in the room. With the right precursor, an electron microscope can print a buckyball out of platinum, nanometres across.

About the guest

Lisa McElwee-White is the Crow Professor of Chemistry at the University of Florida and was chair of its chemistry department when we recorded this episode. She studied at the University of Kansas, did her PhD at Caltech and a postdoc at Stanford, where she joined the faculty before moving to Florida. Her research group develops precursor compounds for making thin films and nanostructures. She has since been elected president-elect of the American Chemical Society, serving as president in 2028.

Lisa McElwee-White curated the Real Scientists Nano Twitter account (@RealSci_Nano) from February 20 to February 26 2023. Read all of Lisa’s tweets from that week.

Key highlights in this episode

  • 02:22 The chemists in the room. Her group designs volatile precursor molecules for many deposition methods (heat, light, electron beams and ion beams), which almost no other group covers.
  • 05:54 3D printing with an electron beam. A focused electron beam switches on and off as it sweeps a pattern, depositing metal only where it hits the precursor gas, just like a 3D printer’s print head.
  • 09:50 From pre-med to tungsten nitride. She planned to become a doctor, fell for chemical research, and a chance question about tungsten nitride led to a 20-year collaboration on films for computer chips.
  • 18:50 Fixing chips at the nanoscale. Electron and ion beam writing repairs defective photolithography masks and edits prototype circuits. Her current industry work explores area-selective deposition as an alternative to lithography.
  • 30:25 When the student overtakes you. Her favourite moment is when a student’s ideas about their project become better than hers.
We Got the INK: 3D Nano Printing
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Why it matters

Before chemists like Lisa got involved, people doing electron beam deposition bought precursors designed for chemical vapor deposition. The standard platinum precursor carries nine carbons for every platinum atom, and an electron beam removes only one of them, so the result is mostly nanocrystalline platinum in a carbon matrix. Electrons don’t break molecules apart the way heat or ozone does, so Lisa’s group works out the actual mechanisms and designs precursors to match. Nanoscale metal writing is already used to repair photolithography masks and edit prototype chips, and her industry-funded work explores direct-write patterning as an alternative to the usual write, etch and polish steps. Even so, she is clear that a perfect metal deposit isn’t possible in a real microscope chamber.

Terms explained

In the guest’s own words, with a link to the moment they explain it.

  • Precursor: the “ink”: a compound that can be evaporated into the gas phase and moved to where deposition happens, then reacts to leave behind the element you want, such as ruthenium. (Lisa at 04:14)
  • Electron beam 3D printing: as a focused electron beam sweeps a pattern and switches on and off, the precursor either deposits or not, just like a 3D printer’s print head, but on the nanoscale. (Lisa at 06:36)
  • FEBID: focused electron beam induced deposition. It was discovered by accident, when people imaging samples noticed carbon building up from background hydrocarbons in the chamber. (Lisa at 27:57)
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Part of Nanofabrication & Advanced Manufacturing · Nanolithography & 3D nanoprinting

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