The principle of nano tungsten oxide (WO₃) semiconductor sensors is based on the semiconductor properties of WO₃ and the interaction between its surface and gas molecules. Below is a detailed explanation:
- Semiconductor Properties of Tungsten Oxide
n-Type Semiconductor
Tungsten oxide is an n-type semiconductor with a higher concentration of free electrons than holes. This characteristic allows it to exhibit specific electrical properties when interacting with gas molecules.
Surface Defects and Oxygen Vacancies
Nano tungsten oxide materials often possess oxygen vacancies and surface defects, which enhance their ability to adsorb and desorb gas molecules. These features significantly improve the sensor’s sensitivity.
- Sensor Working Mechanism
Gas Adsorption and Resistance Changes
When the sensor is exposed to the target gas, gas molecules adsorb onto the surface of nano tungsten oxide. This adsorption alters the charge distribution on the semiconductor surface, leading to changes in its electrical resistance.
- Oxidizing Gases (e.g., O₂, NO₂):
These gases capture electrons from the semiconductor surface, forming negatively charged species. This reduces the number of free charge carriers, increasing the sensor’s resistance. - Reducing Gases (e.g., H₂, CH₄):
These gases donate electrons to the semiconductor, increasing the carrier density and decreasing resistance.
Heating Effect
To enhance sensitivity and response time, the sensor is typically heated to an optimal temperature.
- Heating accelerates gas molecule motion, facilitating adsorption and desorption on the semiconductor surface.
- It also removes impurities or residual gases on the surface, ensuring accurate measurements.
Signal Processing
The resistance change is converted into an electrical signal, which is then amplified, filtered, and processed. The processed signal can be used for display, recording, or control purposes.
- Applications and Advantages of Nano Tungsten Oxide Semiconductor Sensors
Advantages
- High Sensitivity:
The high surface-to-volume ratio and abundant surface defects enable the detection of extremely low gas concentrations. - Fast Response:
Nano-scale materials allow rapid changes in resistance, providing quick detection of gas concentration fluctuations. - Good Selectivity:
By optimizing the sensor’s structure and fabrication process, selective detection of specific gases can be achieved. - High Stability:
Nano tungsten oxide maintains good performance at high temperatures, making it suitable for demanding environments.
Conclusion
Nano tungsten oxide semiconductor sensors utilize the material’s semiconductor properties and surface interactions with gas molecules to detect gas concentrations sensitively and reliably. These sensors are widely used in environmental monitoring, industrial safety, and medical health applications, demonstrating significant potential in various fields.
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