Zhu’s research team has created the first coils of silicon nanowire on a substrate that can be stretched to more than double their original length, moving us closer to developing stretchable electronic devices. Credit: North Carolina State Univ. |
Researchers at North Carolina State Univ. have created the first coils of
silicon nanowire on a substrate that can be stretched to more than double their
original length, moving us closer to incorporating stretchable electronic
devices into clothing, implantable health-monitoring devices, and a host of
other applications.
“In order to create stretchable electronics, you need to put electronics on
a stretchable substrate, but electronic materials themselves tend to be rigid
and fragile,” says Dr. Yong Zhu, one of the researchers who created the new
nanowire coils and an assistant professor of mechanical and aerospace
engineering at NC State. “Our idea was to create electronic materials that can
be tailored into coils to improve their stretchability without harming the
electric functionality of the materials.”
Other researchers have experimented with “buckling” electronic materials
into wavy shapes, which can stretch much like the bellows of an accordion.
However, Zhu says, the maximum strains for wavy structures occur at localized
positions—the peaks and valleys—on the waves. 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 length of the structure—a coil spring is
one such ideal shape,” Zhu says. “As a result, the wavy materials cannot come
close to the coils’ degree of stretchability.” Zhu notes that the coil shape is
energetically favorable only for one-dimensional structures, such as wires.
Zhu’s team put a rubber substrate under strain and used very specific levels
of ultraviolet radiation and ozone to change its mechanical properties, and
then placed silicon nanowires on top of the substrate. The nanowires formed
coils upon release of the strain. Other researchers have been able to create
coils using freestanding nanowires, but have so far been unable to directly
integrate those coils on a stretchable substrate.
While the new coils’ mechanical properties allow them to be stretched an
additional 104% beyond their original length, their electric performance cannot
hold reliably to such a large range, possibly due to factors like contact
resistance change or electrode failure, Zhu says. “We are working to improve
the reliability of the electrical performance when the coils are stretched to
the limit of their mechanical stretchability, which is likely well beyond 100%,
according to our analysis.”
A paper describing the research, “Controlled 3D Buckling of Silicon
Nanowires for Stretchable Electronics,” was published online Dec. 28 by ACS
Nano. The paper is co-authored by Zhu, NC State Ph.D. student Feng Xu and Wei Lu, an assistant
professor at the Univ.
of Michigan. The research
was funded by the National Science Foundation.
NC State’s Department of Mechanical and Aerospace Engineering is part of the
university’s College
of Engineering.
