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 September 29, 2015

Contact printing with shape-memory polymers: Less expensive, more efficient

University researchers are developing a contact printing process, using shape-memory polymers, that would be less expensive and more energy efficient than other nanofabrication processes now in use. They believe the process could not only advance the nation's nanomanufacturing capabilities but, closer to home, contribute to Rochester's role as a national hub for next-generation integrated photonics.

Mitchell Anthamatten, Associate Professor of Chemical Engineering, along with co-PIs Alexander Shestopalov, Assistant Professor of Chemical Engineering, and John Lambropoulos, Chair and Professor of Mechanical Engineering, have received a $1.5 million NSF grant to further develop the process, then team up with an industrial partner to demonstrate its capability to produce high resolution organic light emitting diode (OLED) displays.  Beyond that, the researchers envision potential applications in a range of photonics, sensors and other devices.
    
Rochester was recently named the headquarters of a $625 million federal-, state- and industry-funded initiative to advance the nation's manufacturing capability of integrated photonics.  "The timing of this award is perfect," Anthamatten stated. "A  large group of optical applications could emerge, and this kind of nanomanufacturing could contribute to the AIM Photonics Initiative."  

Key to the NSF-funded project are the unique capabilities of shape-memory polymers.  As their name suggests, their shape or texture can be manipulated by a change in temperature or other variable.      

How would this work in contact printing?  
   
"Imagine a rubber stamp", Shestopalov explained, "made of a shape-memory polymer with features down to mere microns that could be used to transfer layers of organic or inorganic thin-film materials."
   
The stamping device is pressed down onto a desired thin-film material (an ink) which adheres to the stamp's pattern where contact is made. The stamping device, carrying the ink, is transferred to a target surface where it is heated.  The higher temperature causes the shape-memory polymer on the face of the stamping device to become curved, disrupting the adhesion between the stamp and the ink, and the ink is released onto the manufactured device, retaining the desired pattern.
      
"Basically it's a transfer process," Shestopalov explained.

The process has some key advantages over photolithography and masked shadow deposition, which are two of the most prevalent nanofabrication processes now used. Photolithography uses light to create high-resolution patterns but is relatively expensive and cannot be used with organic films.  Shadow mask deposition evaporates material through small holes, but that causes diffusion, which decreases resolution.
    
"We want to have a method that allows us to print different materials with higher resolution than shadow mask deposition and lower cost than photolithography," Shestopalov explained.  Moreover, the contact printing approach would not be limited to flat surfaces, because the stamping devices are flexible.

"So large photonic patterns that absorb certain wavelengths in the infrared region can be created with this technique," he said.

"The opportunity to collaborate between ChemE and MechE came about from the interaction of the three faculty via the Materials Science Program," Lambropoulos noted. "This is another benefit of having such a multidisciplinary program, such as MSC, in the College."
   
The research team will integrate their research into university courses for undergraduates including a team-taught course on nanomanufacturing that will "enhance manufacturing skills of students entering the workforce."

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