Smarter Self-assembly Opens New Pathways for Nanotechnology


By Justin Eure

Aaron Stein enlarge

Brookhaven physicist Aaron Stein, lead author on the study, in the cleanroom at the Center for Functional Nanomaterials (CFN) at Brookhaven National Laboratory. Stein and his co-authors used the electron beam lithography writer in the background to etch templates that drive the self-assembly of block copolymers in precisely controllable ways.

UPTON, NY—To continue advancing, next-generation electronic devices must fully exploit the nanoscale, where materials span just billionths of a meter. But balancing complexity, precision, and manufacturing scalability on such fantastically small scales is inevitably difficult. Fortunately, some nanomaterials can be coaxed into snapping themselves into desired formations—a process called self-assembly.


self-assembling block copolymers enlarge

Electron beam lithography is used to adjust the spacing and thickness of line patterns etched onto a template (lower layer). These patterns drive a self-assembling block copolymer (top layer) to locally form different types of patterns, depending on the underlying template. Thus, a single material can be coaxed into forming distinct nanopatterns for example, lines or dots ‹ in close proximity. These mixed-configuration materials could lead to new applications in microelectronics.


Microchips, for example, use meticulously patterned templates to produce the nanoscale structures that process and store information. Through self-assembly, however, these structures can spontaneously form without that exhaustive preliminary patterning. And now, self-assembly can generate multiple distinct patterns—greatly increasing the complexity of nanostructures that can be formed in a single step.



Cooking up organized complexity

The collaboration used block copolymers—chains of two distinct molecules linked together—because of their intrinsic ability to self-assemble.


Gwen Wright and Aaron Stein enlarge

CFN researchers Gwen Wright and Aaron Stein at the electron beam lithography writer in the CFN cleanroom.

To guide self-assembly, scientists create precise but simple substrate templates. Using a method called electron beam lithography—Stein's specialty—they etch patterns thousands of times thinner than a human hair on the template surface. They then add a solution containing a set of block copolymers onto the template, spin the substrate to create a thin coating, and "bake" it all in an oven to kick the molecules into formation. Thermal energy drives interaction between the block copolymers and the template, setting the final configuration—in this instance, parallel lines or dots in a grid.


Brookhaven Lab physicists Aaron Stein and Kevin Yager discuss their directed self-assembly technique that enables different molecular patterns—in this case, parallel lines and dots—to coexist within a single nanostructure in specific arrangements. The ability to direct the self-assembly of materials into complex nanostructures could enable advances in microelectronics, sensing, and other applications.

Lines and dots, living together

This is a significant conceptual leap in self-assembly.

— Brookhaven Lab physicist Aaron Stein


"We had discovered an exciting phenomenon, but couldn't select which morphology would emerge," Yager said. But then the team found that tweaking the substrate changed the structures that emerged. By simply adjusting the spacing and thickness of the lithographic line patterns—easy to fabricate using modern tools—the self-assembling blocks can be locally converted into ultra-thin lines, or high-density arrays of nano-dots.

Kevin Yager enlarge

Study co-author Kevin Yager measuring the self-assembling thin film layers.



Gwen Wright, another CFN coauthor, added, "Many nano-fabrication labs should be able to do this tomorrow with their in-house tools—the trick was discovering it was even possible."

Greg Doerk

CFN co-author Greg Doerk



This work was funded by the DOE Office of Science.


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