Nano Focus: Millimeter-long GaN nanowires grow horizontally on sapphire substrate
- PDF / 910,124 Bytes
- 3 Pages / 585 x 783 pts Page_size
- 64 Downloads / 196 Views
ls and diodes, a temperature sensor, and electroencephalogram, electrocardiogram, and electromyogram sensors to monitor the brain, heart, and muscle signals, respectively. The circuit is attached to the skin by van der Waals forces only, so no adhesive is needed; the van der Waals forces are sufficient to maintain conformal contact with the skin, withstanding normal body movements over periods of hours without cracking or delamination. The researchers have also experimented with commercially available temporary transfer tattoos that could conceal the circuitry and provide greater adhesion if necessary. This technology is an outgrowth of the macroscale stretchable electronics that Rogers’s group and others have been investigating. Earlier versions were just too thick (a few mm to 1 cm), with elastic moduli a few orders of magnitude too high to match human skin. “We’ve extended some of those design concepts that we and others have been exploring in stretchable electronics to an extreme, in terms of design, filamentary shape, thinness, and modulus-matched substrate to enable this epidermal format,” Rogers said. “We view it as a different class of technology for that reason, but it has historical origins in flexible and, more recently, stretchable forms of electronics.” Tim Palucka
micrometer-length range, with limited control over their crystallographic orientation. Now, researchers at the Weizmann Institute of Science in Israel, led by Ernesto Joselevich, have reported in the August 19 issue of Science (DOI: 10.1126/science.1208455; p. 1003) the development of a process for producing millimeter-long GaN nanowires by guided growth on various crystallographic planes of a sapphire surface. The process allows the researchers to grow “very long and perfectly aligned horizontal nanowires with exquisite control of their crystallographic orientation,”
according to Joselevich. The research team, which included graduate student David Tsivion, postdoctoral fellow Mark Schvartzman, and staff scientists Ronit Popovitz-Biro and Palle von Huth, used chemical vapor deposition of GaN on eight different sapphire planes seeded with Ni catalysts to achieve these results. Analysis of the nanowires produced on these various planes revealed that those formed on surface steps and grooves were better aligned than those formed on a smooth plane. For instance, on a well-cut, smooth sapphire c-plane,
Bio Focus
Filamentary serpentine layout enables epidermal electronic “smart skin”
N
Nano Focus Millimeter-long GaN nanowires grow horizontally on sapphire substrate
M
ost nanowires are grown standing up, rising vertically from a substrate to reach heights in the range of tens of micrometers. They typically require post-fabrication processing to form aligned arrays of nanowires suitable for use in an electronic or optical device. Attempts to grow nanowires horizontally on a surface have had some success, but the resulting nanowires were still in the
734
MRS BULLETIN
•
VOLUME 36 • OCTOBER 2011
•
www.mrs.org/bulletin
ARM200F TEM with Col
Data Loading...
