Carving Nanopumpkins, Slicing Fingers, Cutting Water

This Halloween, put down the kitchen knives and the jack-o’-lantern kits because there’s a new pumpkin-carving technique in town: atomic-force-microscopy-biased lithography.

Kids attending the 25th annual Texas A&M University Chemistry Open House on Oct. 27 can pick out a spooky pattern and watch their very own “nanopumpkin” be formed on a silicon wafer in seconds.

“We found it to be a very engaging project for the kids,” says James D. Batteas, a chemistry professor at Texas A&M. “It’s a very simple chemical reaction that they’re watching happen in real time.”

The nanopumpkins measure about 5 µm wide—one-twentieth the thickness of a human hair. They’re made on a silicon wafer surface using a metallized atomic force microscope (AFM) tip to create a raised pattern that measures roughly 3 nm high. When a voltage is applied, oxidation occurs where the tip meets the silicon surface, forming a silicon oxide structure.

Although the actual lithography takes mere seconds, the programming of the pattern is time-consuming, explains Batteas’ graduate student Carrie Carpenter. The two are working on a Frankenstein design this year.

“The big learning curve is scripting the software to control the AFM to make the features exactly the way you want,” confirms Batteas. “You’re always at the mercy of the AFM tip. If the tip is blunt, you end up with big and fat pumpkins with very low resolution.”

No spare AFM tips ready for next week? Definitely pick the pumpkin-carving kit over the kitchen knife. Thanks to the folks at Improbable Research, the Newscripts gang got wind of a gruesome 2004 study that tested the safety of using different knives to carve pumpkins (Prev. Med., DOI: 10.1016/j.ypmed.2004.01.008). Medical researchers determined the forces required to cut and puncture a piece of pumpkin using pumpkin-carving tools and kitchen knives. They then used a machine to wield each weapon to see how badly it lacerated or punctured a human hand. Don’t worry, a cadaver hand.

They found that all utensils produced some injuries, but the ones that were a result of pumpkin-carving tools were “fewer and less severe” than those inflicted by serrated and smooth-edged kitchen knives.

Sharp knives certainly get a bad rap around Halloween, but they can be heroes in the lab. In search for ways to separate small molecules from a biological sample, a team led by Antonio A. García of Arizona State University devised a knife that can cut a drop of water without forming so-called satellite droplets (PLoS One, DOI: 10.1371/journal.pone.0045893).

To do so, they place the drop on a superhydrophobic surface made of either low-density polyethylene or Teflon-coated glass and tether the drop on either side by metal wire loops. Doctoral student Ryan Yanashima came up with the basis for the knife—a sharpened 0.02-inch-thick sheet of copper or zinc treated to be superhydrophobic—which is slowly lowered through the drop. (Watch the action at http://bit.ly/VpErqn.)

“The most exciting part of this was to show that water can be forced into acting like a solid,” García says. “The action of the knife is so slow that it looks like water is a soft solid or piece of Jell-O.”

The Newscripts gang wishes pumpkins were that easy to carve.