In a step towards realizing the concept of stretchable electronics and their applications, a team of researchers at the University have come up with the first coils of silicon nanowire that can be stretched to more than twice their original length.
“The industry of stretchable electronics is still in the infant stage,” Yong Zhu said. Zhu, assistant professor of mechanical and aerospace engineering, is part of the team that created the nanowire coils. “A major challenge is to keep the device functionality while being stretched, rolled, folded and distorted. This technology demonstrated a super stretchable architecture, i.e. a coil, using one-dimensional nanomaterials.”
Stretchable electronics have a wide range of applications such as surgical tools that naturally integrate with the human body, eyeball-like cameras with superior performance, and wearable electronics. Biomedical devices are among the most promising areas of application. The development is likely to impact small-scale biomedical applications, such as implantable health-monitoring devices.
“It’s exciting to imagine wearing electronically fabricated clothes that can sense what your body needs, and do all kinds of stuff – adjust fabric temperature according to your needs, change color, thickness, appearance or even adapt the color to match your background and create the effect of an invisibility cloak,” Lionel Edwin, a graduate student in Aerospace Engineering, said.
One dimensional nanomaterials, including nanowires, possess outstanding electrical, optical and sensing properties.
“Our technology paves the way for stretchable electronics and sensors based on one-dimensional nanomaterials,” Zhu said.
The team followed well-established techniques to create the coils – a technique called mechanical buckling. The silicon nanowires are placed on top of pre-strained a PDMS (polydimethylsiloxane) substrate. On release of the strain, the nanowires ‘buckle’ under the strain to form either a wavy or coiled shape.
Zhu and his team have made advancements in the process of buckling techniques.
“What’s unique in our research is that by carefully tailoring the surface properties of PDMS, we were able to achieve the wavy or coiled shape in a controlled fashion,” Zhu said.
“However, for a wavy structure, the maximum strains occur … at peaks and valleys, on the waves,” Zhu said. “As soon as the failure strain is reached at one of the localized positions, the entire structure fails. An ideal shape to accommodate large deformation would lead to a uniform strain distribution along the entire structure. A coil spring is one such ideal shape.”
The technology is still in its preliminary stages, and is yet to overcome certain challenges, according to Zhu.
“First, while mechanically the nanowire coils can be stretched over 100 percent, their electric performance cannot hold reliably to such a large range, possibly due to factors like contact resistance change or electrode failure,” Zhu said.
The next step is to produce the nanowires in bulk, as it is a tedious process.
“Fundamental understanding of the adhesion and friction between nanowires and PDMS is critical in order to achieve optimized nanowire assembly, alignment and transfer,” Zhu said.
While overcoming these challenges, the next stage in the research project will be working on a functioning model of a stretchable device. Zhu expressed interest in collaborating with other researchers on campus to develop stretchable devices and systems for diverse uses such as electronics, photonics and magnetics.
Ankita Upreti, a graduate student in electrical engineering, said, ”This technology will provide a springboard for further research efforts in bringing together mechanical and electronic components–[combining] them with our biomedical knowledge to enable conception of applications that will revolutionize the way we walk, talk and live.”
