a) FESEM image of aligned ZnO nanorods. b) TEM image of a single nanorod. c) HRTEM image taken
from the edge of the ZnO nanorod. Inset: Corresponding SAED pattern.
(Credit: Nanowerk.com. Reprinted with permission from Wiley-VCH Verlag)

Researchers in Taiwan have shown, for the first time, that they can directly grow vertically aligned, highly crystalline and defect-free single-crystalline zinc oxide nanorods and nanoneedles on paper.

Nanowerk.com has reported that researchers from the Department of Materials Science and Engineering at National Tsing Hua University have fabricated prototype hybrid junction diodes and UV photodetectors based on ZnO nanorod arrays on paper.

The team synthesized aligned ZnO nanowires on a piece of paper that predominantly contains cellulose and calcium carbonate. These surface modifications provide a conducting platform and also reduce surface roughness and damage occurring during synthesis, and they greatly enhance the alignment and uniformity of ZnO nanowires on the paper substrate.

According to the article:

In order to demonstrate the potential for organic/inorganic hybrid junction devices on paper substrates, the team fabricated p-n junction diodes with an average active junction of 1 cm × 1 cm using zinc oxide nanowires with 90 nm diameter and 1.5 µm length, grown on a 50 nm gold-coated paper substrate.

The researchers point out that stable electrical performance of hybrid devices at different bending or twisting positions is a critical challenge for flexible substrates. For this reason, they measured the electrical/mechanical fatigue properties of the diode at different bending positions across the junction area.

They found that there is only negligible difference in the turn-on voltage of the devices while the forward current at high voltage is slightly decreased with increase of bending angle. Repetitive bending of the diode affected the performance only marginally.

“The intrinsically rough nature of paper’s surface, its insulating properties, damage, and instability during the synthesis process are sizable inconveniences in realizing potential nanoelectronic devices on paper substrates” explains Lih-Juann Chen (PDF), who led the research. “In order to overcome these difficulties we have shown that the paper surface can be modified to different platforms such as conducting and semiconducting surfaces and can be protected from the external environment by being coated with a protective polymer layer.”

“We anticipate versatile applications for these zinc oxide nanostructures on paper in flexible, portable electronic gadgets and display devices as well as in biomedical applications—these are under investigation” says Chen. “We foresee a productive future for the direct growth of one-dimensional nanostructures on paper substrates, paving the way to low-cost, high-performance devices beyond the range of conventional technology. Innovative concepts and strategies are required to engineer materials and devices on such an exceptionally flexible platform.”

The findings were published in a recent issue of Advanced Materials.