Avoiding the need for molds, masks, and resists common to most lithographic processes, nanoscopic structures that self-assemble with functionality have been produced easily and cheaply from inkjet printers and lithographic pens by scientists at Sandia and the University of New Mexico.
The work, published in the May 4 issue of the journal Nature, reports researchers were able to use self-assembling inks to write patterns with both external form and internal function on multiple length scales and at multiple locations.
"Our ability to form arbitrary functional designs on arbitrary surfaces should be of practical importance for directly writing sensor arrays and fluidic or photonic systems," says Sandia project leader Jeff Brinker (1841).
The group’s rapid prototypes have already monitored the pH of fluids transported by capillary action, and formed structures that could act as wave-guides to direct laser light. By linking computer-aided design (commonly referred to as CAD) with an inkjet printer, it will be possible to create in seconds a functional nanostructure that was a drawing on a computer screen only moments before.
"We should be able to fabricate a substance that organizes itself to build a fluidic channel network instead of having to painstakingly design and cut one," says Jeff. "With positive ligands [active molecules that exhibit molecular recognition characteristics] in the mix to act upon incoming chemicals, we would have the equivalent of an analytical machine that built itself instead of needing construction."
He also envisions making a valve simply by creating molecular pores that change shape due to external input. "We could write structures that position pore pathways in a second, sensors included."
"People have used ink jet printers to print ceramic material into a substrate," says Jeff. "Here, inside each ink dot, the ink self-organizes into further function: pore networks, surface(s) decorated by organic functional ligands and mesoscopic pore channels. It’s a self-creating functional factory."
In effect, says Jeff, "we can combine thousands of different types of ink for different functionality. The process would work just the way color printers currently mix hundreds of different colored inks to get a blended result. With color-pattern software, we could make functioning materials with a variety of characteristics: say, strong, hard, and hydrophobic, with a low dielectric constant."
Ligands sprinkled into the ink could be used to sense light or heat, measure magnetic and electric fields, or filter gasses and liquids.
The work is an extension of previous achievements by the research group, also reported in Nature. These involved using simpler forms of the same technique to produce self-organized materials on the nanoscale. They were used to form sensitive nanoscale coatings (Lab News, Oct. 10, 1997), a nanoscale layering of materials that produced the structure and strength of seashells (Lab News, July 17, 1998), and nanospheres structured to selectively adsorb environmental molecules or dispense chemicals (Lab News, March 26, 1999).
The process, called evaporation-induced self-assembly, is based on the scientifically well-known tendency of two-sided detergent molecules composed of water-loving (hydrophilic) and water-hating (hydrophobic) portions to spontaneously form spherical molecular assemblies. By including organic and inorganic materials, detergent self-assembly can be harnessed to create organic and inorganic nanostructures. Continued mild heating polymerizes these nanostructures and bonds their interfaces. The Sandia/UNM process is promising because it does away with the tedious, sequential deposition of individual organic and inorganic layers, a much longer process when it is even possible.
Other members of the investigatory team are Hongyou Fan, Aaron Stump, Victor Perez-Luna, and Gabriel Lopez from the University of New Mexico Center for Micro-Engineered Materials and Department of Chemical and Nuclear Engineering. Participating Sandia researchers included Yunfeng Lu (former UNM student and Sandia postdoc in 1841, now at Applied Materials Inc. in Santa Clara, Calif.), Scott Reed (14192), Tom Baer, and Randy Schunk (both 9114). In addition to his position as senior scientist at Sandia, Brinker is also a professor at UNM.
The work continues to interest major research societies. "Hongyou Fan won a Materials Research Society Graduate Student Award silver medal for this work," says Jeff, "and Yunfeng Lu just indicated to me that for his work on self-assembly, he won the 31st Annual American Chemical Society’s Victor K. LaMer Graduate Award in Colloid and Surface Chemistry." The work was supported by Sandia’s Laboratory Directed Research and Development (LDRD) program, DOE , and DARPA.
Last modified: May 22, 2000