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

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

Researchers at TMOS, the Australian Research Council’s Center of Excellence for Transformative Meta-Optical Systems, have developed a sensor made of nanowires one-fifth of a millimeter per side, meaning it can be easily attached to a silicon chip. .

In a study published in the latest issue Advanced materials, Ph.D. The center’s Australian National University team researcher and lead author Shiyu Wei describes the sensor as requiring no power source because it runs on its own solar-powered generator.

Wei says, “Because we integrate devices like this into the Internet of Things sensor network, the low power consumption is a huge advantage in terms of system size and cost. The sensor can be installed in your car with an alarm, and alerts will be sent to your phone if it detects a dangerous amount of nitrogen dioxide released from the exhaust.”

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

Current gas detectors are bulky, slow, and require a trained operator. Instead, the new device can quickly and easily measure less than 1 part in a billion, and the TMOS prototype used a USB interface to connect to a computer.

Nitrogen dioxide is one of the pollutants in the NOx category. In addition to contributing to acid rain, it is dangerous to humans even in small concentrations. It is a common pollutant from cars and is also produced indoors from gas stoves.

The key to the device is the PN junction – the motor of the solar cell – in the form of a nanowire (a small hexagonal pillar, about 100 nanometers in diameter, 3-4 microns in height) that sits on the substrate. The sensor was formed by an organized array of thousands of nanowire solar cells spaced approximately 600 nanometers apart.

The entire device was made of indium phosphide, the base of which was doped with zinc to form the P part and the N part at the tip of the nanowires, doped with silicon. The central part of each nanowire was undoped (inner part, I), separating the P and N parts.

Light hitting the device causes a small current to flow between the N and P parts. However, if any nitrogen dioxide, which is a strong oxidizer that sucks away electrons, touches the inner center of the PN junction, this will cause the current to drop.

The size of the immersion can be used to calculate the concentration of nitrogen dioxide in the air. Numerical modeling by EME postdoctoral researcher Dr. Zhe Li showed that the design and fabrication of the PN junction is critical to maximizing signal.

The properties of nitrogen dioxide – strong adsorption, strong oxidation – make indium phosphide easy to distinguish from other gases. The sensor could also be optimized to detect other gases by functionalizing the surface of the indium phosphide nanowire.

TMOS Principal Investigator Professor Lan Fu, head of the research team, says: “The ultimate goal is to detect multiple gases on a single small chip. In addition to environmental pollution, these sensors could be used for health care, for example, breath tests for biomarkers of disease.

“The small gas sensor is easily integrated and scalable. This, together with meta-optics, promises to produce multiplexing sensors with high performance and multiple functions, making them suitable for smart sensor networks. TMOS is a network of research groups in Australia committed to advancing this field.

“The technologies we develop will transform our lives and society in the coming years as Internet of Things technology is widely adopted for real-time data collection and autonomous response in applications such as air pollution monitoring, industrial chemical hazard detection, smart cities, and personal healthcare.”