By combining a new generation of piezoelectric nanogenerators with two types of nanowire sensors, researchers have created what are believed to be the first self-powered nanometer-scale sensing devices that draw power from the conversion of mechanical energy. The new devices can measure the pH of liquids or detect the presence of ultraviolet light using electrical current produced from mechanical energy in the environment.
Based on arrays containing as many as 20,000 zinc oxide nanowires in each nanogenerator, the devices can produce up to 1.2 volts of output voltage, and are fabricated with a chemical process designed to facilitate low-cost manufacture on flexible substrates. Tests done with nearly one thousand nanogenerators – which have no mechanical moving parts – showed that they can be operated over time without loss of generating capacity.
Details of the improved nanogenerator and self-powered nanosensors were scheduled to be reported March 28 in the journal Nature Nanotechnology. The research was supported by the National Science Foundation, the Defense Advanced Research Projects Agency, and the U.S. Department of Energy.
In the paper, Wang and collaborators report on a new configuration for the nanowires that embeds both ends of the tiny structures in a polymer substrate. The wires can then generate current as they are compressed in a flexible nanogenerator enclosure, eliminating the contact with a metallic electrode that was required in earlier devices. Because the generators are completely enclosed, they can be used in a variety of environments.
"We can now grow the wires chemically on substrates that are foldable and flexible and the processing can now be done at substrate temperatures of less than 100 degrees Celsius – about the temperature of coffee," explained Wang. "That will allow lower cost fabrication and growth on just about any substrate."
The nanogenerators are produced using a multi-step process that includes fabrication of electrodes that provide both Ohmic and Shottky contacts for the nanowires. The arrays can be grown both vertically and laterally. To maximize current and voltage, the growth and assembly requires alignment of crystalline growth, as well as the synchronization of charging and discharging cycles.
Production of vertical nanogenerators begins with growing zinc oxide nanowires on a gold-coated surface using a wet chemical method. A layer of polymethyl-methacrylate is then spun-coated onto the nanowires, covering them from top to bottom. Oxygen plasma etching is then performed, leaving clean tips on which a piece of silicon wafer coated with platinum is placed. The coated silicon provides a Shottky barrier, which is essential for maintaining electrical current flow.
The alternating current output of the nanogenerators depends on the amount of strain applied. "At a strain rate of less than two percent per second, we can produce output voltage of 1.2 volts," said Wang. "The power output is matched with the external load."
Lateral nanogenerators integrating 700 rows of zinc oxide nanowires produced a peak voltage of 1.26 volts at a strain of 0.19 percent. In a separate nanogenerator, vertical integration of three layers of zinc oxide nanowire arrays produced a peak power density of 2.7 milliwatts per cubic centimeter.
Wang's team has so far produced two tiny sensors that are based on zinc oxide nanowires and powered by the nanogenerators. By measuring the amplitude of voltage changes across the device when exposed to different liquids, the pH sensor can measure the acidity of liquids. An ultraviolet nanosensor depends on similar voltage changes to detect when it is struck by ultraviolet light.
In addition to Wang, the team authoring the paper included Sheng Xu, Yong Qin, Chen Xu, Yaguang Wei, and Rusen Wang, all from Georgia Tech's School of Materials Science and Engineering.
The new generator and nanoscale sensors open new possibilities for very small sensing devices that can operate without batteries, powered by mechanical energy harvested from the environment. Energy sources could include the motion of tides, sonic waves, mechanical vibration, the flapping of a flag in the wind, pressure from shoes of a hiker or the movement of clothing.
"Building devices that are small isn't sufficient," Wang noted. "We must also be able to power them in a sustainable way that allows them to be mobile. Using our new nanogenerator, we can put these devices into the environment where they can work independently and sustainably without requiring a battery."
John Toon | EurekAlert!
Further reports about: > Ferchau Engineering > Materials Science > Science TV > energy sources > mechanical energy > mechanical vibration > nanometer-scale sensing devices > piezoelectric nanogenerators > sonic waves > technology roadmap > ultraviolet light > ultraviolet nanosensor > voltage changes > zinc oxide nanowires
An international team of physicists a coherent amplification effect in laser excited dielectrics
25.09.2017 | Universität Kassel
Highest-energy cosmic rays have extragalactic origin
25.09.2017 | CNRS
At the productronica trade fair in Munich this November, the Fraunhofer Institute for Laser Technology ILT will be presenting Laser-Based Tape-Automated Bonding, LaserTAB for short. The experts from Aachen will be demonstrating how new battery cells and power electronics can be micro-welded more efficiently and precisely than ever before thanks to new optics and robot support.
Fraunhofer ILT from Aachen relies on a clever combination of robotics and a laser scanner with new optics as well as process monitoring, which it has developed...
Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.
A warming planet
Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.
The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...
Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...
Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!
When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...
19.09.2017 | Event News
12.09.2017 | Event News
06.09.2017 | Event News
25.09.2017 | Power and Electrical Engineering
25.09.2017 | Health and Medicine
25.09.2017 | Physics and Astronomy