My roommate in university had a quirk that annoyed teachers no end: he had the smallest handwriting of anyone I’ve ever met. While I used big old Bic pens on wide-lined notebook paper, he was using fine-point mechanical drafting pencils on the narrowest-lined paper he could find, and still leaving lots of room for any corrections he might want to make.
Well, he must have really appreciated last week’s announcement in Science magazine that researchers at Northwestern University in Chicago have invented the world’s smallest pen. It works essentially the same as the 4,000-year-old dip pen (i.e., a pointy stick dipped in ink), but can draw a line only one molecule deep and only a few dozen molecules wide.
That’s because the “pointy stick” is an atomic force microscope, a commonplace laboratory instrument, while the “ink” is an oily, sulfur-containing compound called octadecanethiol. Their “paper” consists of granular gold particles fused to mica.
The pen was the happy result of someone looking at an annoyance and seeing instead an opportunity. An atomic force microscope uses an extremely fine stylus of silicon nitride to trace the contour of a surface, like a phonograph needle traces the shape of the groove on a record. By doing so, it renders a three-dimensional image of the surface so fine that the bumps caused by individual atoms can be seen.
But the atomic force microscope suffers from an annoying problem: water from the air tends to attach itself to the tip. The greater the relative humidity, the more water that collects. The Northwestern University researchers realized that, because this water is always moving from the tip of the microscope to the surface or vice versa, they could use it to float other molecules onto the surface–in other words, they could turn it into a kind of ink.
The “ink” and “paper” used in the initial experiments aren’t the best for drawing the finest possible lines; they were chosen because the lines produced would be easy to identify and measure. Even so, the scientists were able to draw lines as thin as 30 nanometers, or about one millionth of an inch.
One sample of their handiwork posted on the World Wide Web is a drawing of a cube just 1,000 nanometers on a side, with a pattern of parallel lines on the top, a pattern of dots on one side, and the letters NU (for Northwestern University, natch) on the other. (Researchers, like small boys, can’t seem to help using tools to carve their initials in unlikely places. In 1989, for example, IBM researchers dragged 35 individual atoms of xenon around on a copper plate, using a modified type of scanning electron microscope, and spelled the word IBM. This led to a sudden, urgent need on the part of other researchers all over the world to do things like write their own name with atoms, spell out the word “peace” in sulfur molecules, and draw sketches of Albert Einstein in a medium of mixed ions.)
Different “inks” and “papers” should allow for the creation of even finer lines. As well, the researchers hope to turn their dip pen into a fountain pen, one in which the “ink” flows continuously, which, in turn, will enable them to draw more complex patterns, because they won’t have to lift the pen and re-ink it after every stroke.
What are such tiny lines good for? Well, one possibility is that this tiny pin could be used to manufacture electronic circuitry a thousand times smaller than the smallest microcircuits that exist in computers today. And that, in turn, would mean computers enormously faster and more powerful than we have now.
In addition, the “dip-pen nanolithography,” which is what the researchers involve call it, is a great way to place molecules precisely where you want them. In a computer chip designed to test for the presence of certain chemicals, for instance, you could use the pen to other chemicals which would react to those you want to test for.
Further down the road, dip-pen nanolithography may help bring about nanotechnology, tiny machines able to manipulate single atoms, and thus able to build anything out of anything–in the process, eliminating poverty, pollution and hunger.
In the meantime, however, dip-pen lithography poses a serious threat to all those hobbyists around the world who do things like inscribing the Bible onto grains of rice.
Now that science has created a pen that can make lines only 30 billionths of a metre wide, the challenge is gone.
