New nanowire sensors are the next step in the Internet of Things

A new, tiny nitrogen dioxide sensor could help protect the environment from compound pollutants that cause lung disease and acid rain.

Researchers from TMOS, the Australian Research Council’s Center of Excellence for Metamorphic Systems, have developed a sensor made from an array of nanowires, square one-fifth of a millimeter per side, which means it can be easily integrated into a silicon chip. .

In research published in the latest issue of Advanced materials, Ph.D. Australian National University team researcher at the Center and lead author Shiyu Wei describes the sensor as not requiring sensing power sourceIt runs on its own solar generator.

Says Wei, “As we integrate devices like this in sensor network for Internet of Things technology, after Low power consumption It is a huge benefit in terms of order size and costs. The sensor installed in your car can sound an alarm and alerts sent to your phone if it detects dangerous levels of nitrogen dioxide emitted from the exhaust.”

Co-lead author Dr Zhi Li says: “This device is just the beginning. It can also be adapted to detect other gases, such as acetone, which can be used as a non-invasive breath test for ketosis including diabetic ketosis, which could save countless lives.”

Current gas detectors are bulky, slow, and require a trained operator. In contrast, the new device could measure less than one part per billion quickly and easily, and the TMOS prototype used a USB interface to connect to a computer.

Nitrogen dioxide is a class of nitrogen oxides pollutants. In addition to contributing to acid rain, they are dangerous to humans even in small concentrations. It’s a common pollutant from cars, and it’s also created indoors by gas stoves.

The key to the device is a PN junction—a solar cell motor—in the form of a nanowire (a small hexagonal column about 100 nanometers in diameter, 3 to 4 microns in height) sitting on a base. An ordered array of thousands of nanowire solar cells, spaced about 600 nanometers apart, made up the sensor.

The whole machine is made of indium phosphide, with the base doped with zinc to form the P-part, and the N-section at the tip of the nanowire, doped with silicon. The middle part of each nanowire (intrinsic section, I) separating the P and N sections was unscrewed.

Light incident on the device causes a small current to flow between the N and P sections. However, if the intrinsic middle section of the PN junction is touched by any nitrogen dioxide, a strong oxidizer that absorbs electrons, it will cause the current to decrease.

The size of the drop allows the concentration of nitrogen dioxide in the air to be calculated. Numerical modeling by Dr. Zhi Li, postdoctoral fellow at EME, has shown that the design and fabrication of a PN junction are essential for signal maximization.

features Nitrogen dioxide– Strong adsorption, strong oxidation – make indium phosphide easy to distinguish from other gases. The sensor can also be improved to detect other gases by doping the surface of the nanowires with indium phosphide.

“The ultimate goal is to sense multiple gases on a single, small chip,” says Professor Lan Fu, TMOS Chief Investigator, head of the research group. In addition to environmental pollutants, these sensors could be deployed for healthcare, for example, for breath tests for vital signs of disease.

“The small gas sensor is easy to integrate and scalable. This, together with meta-optics, promises to achieve multiple sensors with high performance and multiple functions, which will enable them to be compatible with smart sensor networks. TMOS is a network of research groups across Australia dedicated to advancing this the field.

“The technologies we are developing will transform our lives and our society in the coming years, through the widespread implementation of IoT technology for real-time data collection and autonomous response in applications such as air pollution monitoring, industrial chemical hazard detection, smart cities and personal healthcare.”