By Mark Dwortzan
One of the biggest obstacles on the road to mass-producing nanoscale devices ranging from integrated circuits to biosensors is a persistent inability to precisely manipulate nanomaterials to build reliable, functional products at a reasonable cost. The main challenge has been to pattern materials at precise locations in a repeatable manner over relatively large areas. Conventional approaches have proven inconsistent, wasteful and expensive.
To meet this challenge, Professor David Bishop (ECE, Physics, MSE) and collaborators at Boston University and Bell Laboratories have developed a low-cost, microelectromechanical system (MEMS)-based machine that directs atoms onto a surface through different-sized holes—each no more than 50 nanometers across—on silicon plates. These MEMS plates can move with nanometer precision to create exacting patterns over surfaces of more than 400 square microns, roughly the area of a human white blood cell. Shutters positioned a micrometer or so above each MEMS plate enable high-speed control of where and when atoms are deposited.
The researchers have produced lines, bridges, rings, infinity symbols, BU logos and many other nanoscale metal patterns by depositing gold and chromium atoms through the holes while moving the plates. The machine and the concept behind it are described in Nano Letters.
“We’ve figured out a way to directly write with small numbers of atoms, to do calligraphy with atoms,” said Bishop, who compared the new MEMS-based machine to a nano-spray painter. He envisions that the method could lead to a cost-effective, chip-based fabrication process for atomic-scale materials and devices that are initially designed in digital simulations, making possible everything from downsized electronics to more compact biosensors.
To come up with the idea to build a programmable device that could directly write with atoms, Bishop drew upon previous experiences working with MEMS technology and nanostencils, or stencils used to fabricate nanoscale patterns on a surface. The new method effectively uses MEMS technology to move a nanostencil over a silicon surface.
“People have devised a variety of techniques for moving atoms around that are expensive, complicated or not scalable,” said Bishop. “Our system avoids these drawbacks and provides programmability. It is fun technology to play with, we’re having a blast.”