Researchers Peel And Stick Nanostructures To Various Materials

Engineers constantly tinker with nanoscale materials—building devices out of nanoparticles, nanowires, or two-dimensional sheets of materials—in hopes of optimizing desirable electrical or optical properties. Often, however, a nanostructure is most easily grown on one type of substrate, such as a silicon wafer, but needs to be transferred to another material for testing or use. That transfer process can be tricky and sometimes damages the structure. Now researchers have developed a simple and fast transfer method that works with a variety of nanomaterials and substrates, and causes no damage (ACS Nano 2014, DOI: 10.1021/nn501779y).

In the new method, Hua Zhang, a materials scientist at Nanyang Technological University, in Singapore, and colleagues deposit their nanostructures of choice on a silicon substrate coated with a 90-nm-thick layer of silicon dioxide. After spin-coating a polymer film over the substrate, they scratch away a 1-mm-wide strip of the film, exposing the SiO₂ at the edges of the substrate. Then they press down a thick layer of polydimethylsiloxane (PDMS) on top of the polymer film to keep the structure rigid during transfer.

To initiate the transfer, the team adds a small droplet of water to the exposed SiO₂. Because the SiO₂ is hydrophilic, but the polymer is hydrophobic, the water spreads easily across the substrate, separating the nanostructure from the silicon in seconds. The researchers then peel off the combination of PDMS, polymer, and nanostructure, and place it on a new substrate. Without the water to separate them, the nanostructure adheres strongly to the new substrate, making it relatively easy to lift off the PDMS—especially after heating the entire assembly on a hot plate to 50 °C, Zhang says. Finally, the researchers use dichloromethane at 50 °C to dissolve away the polymer film, leaving just the nanostructure.

Zhang’s team tested the method by transferring several types of nanostructures, including silver nanowires and sheets of MoS₂, to a variety of substrates, including glass and quartz. He hopes to adapt the method to transfer large areas of nanomaterials on the tens of centimeters or even wafer scale.