Researchers at Nanjing University in China have developed a highly sensitive sensor that can detect mechanical strains more than an order of magnitude weaker than previously possible. The device, created by a team co-led by Feng Miao and Shi-Jun Liang, uses single-crystal vanadium oxide materials that undergo a transition from a conducting to an insulating phase when subjected to strain. This allows the sensor to produce large electrical signals in response to even tiny deformations.
The new device has potential applications in electronics engineering and materials science, and could be used to detect subtle changes such as those caused by microscopic water droplets moving on a surface or gentle airflows. The researchers demonstrated the sensor’s capabilities by using it to detect the slight mechanical pressure of a micron-sized piece of plastic and tiny vibrations produced by small water droplets.
The team’s work, published in Chinese Physics Letters, marks a significant breakthrough in strain detection technology and could pave the way for the development of ultra-sensitive quantum material sensing chips.
Quantum Materials for Strain Detection: A New Frontier
The detection of mechanical strains in materials has long been a challenge, particularly when it comes to weak deformations caused by minute changes in the environment. Traditional strain sensors based on metal and semiconductor compounds have limitations in detecting such weak strains due to their relatively stable resistances under strain. However, researchers at Nanjing University, China, have made a breakthrough by developing a sensor that can detect mechanical strains more than an order of magnitude weaker than previously reported devices.
The Flexible Mechanical Sensor
The new sensor is based on single-crystal vanadium oxide materials, specifically the bronze phase of vanadium oxide (VO2(B)), which undergoes a transition from a conducting to an insulating phase when subjected to strain. This phase transition produces a significant change in the material’s resistance, making it possible to generate large electrical signals that can be measured and used to quantify the strain.
The researchers initially chose to study VO2(B) to understand the mechanisms behind its temperature-induced phase transitions. However, they discovered that this material exhibits a unique response to strain, prompting them to shift their project’s focus to develop a sensor based on this quantum material.
Fabrication Challenges
Fabricating a sensor from VO2(B) was among the team’s biggest challenges due to the complex structure of vanadium oxide. To overcome this, they used a specially adapted hydrogen-assisted chemical vapor deposition micro-nano fabrication process to produce high-quality, smooth single crystals of the material. They characterized these crystals using a combination of electrical and spectroscopic techniques, including high-resolution transmission electron microscopy (HRTEM).
Measuring Strain-Induced Phase Transitions
The researchers loaded the polyimide substrate/VO2(B) into a customized strain setup and induced uniaxial tensile strain in the material by vertically pushing a nanopositioner-controlled needle through it. They then measured how the current-voltage characteristics of the mechanical sensor changed as they applied strain to it.
Under no strain, the channel current of the device registered 165 μA at a bias of 0.5 V, indicating that it is conducting. When the strain increased to 0.95%, however, the current dropped to just 0.50 μA, suggesting a shift into an insulating state. The researchers also measured the response of the device to intermediate strains and found that the resistance increased exponentially with applied strain.
Applications in Electronics Engineering and Materials Science
The new sensor has potential applications in electronics engineering as well as materials science. It can be used to detect slight mechanical deformations caused by placing small objects on it, monitor gentle airflows, and sense tiny vibrations produced when tiny water droplets move on flexible substrates.
According to Miao, “Our work shows that quantum materials like vanadium oxide show much potential for strain detection applications. This may motivate researchers in materials science and electronic engineering to study such compounds in this context.” Future studies will involve growing large-area samples and exploring how to integrate them into flexible devices, allowing for the creation of ultra-sensitive quantum material sensing chips.
This breakthrough demonstrates the potential of quantum materials for strain detection and opens up new avenues for research in this field.
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