Fast recovery rates of semiconductor gas sensors through the optimized use of laser irradiation

Abstract

Fast recovery rates of semiconductor gas sensors through the optimized use of laser irradiation: A new approach for a proven technology Semiconductor gas sensors have become an established technology for the detection of toxic industrial chemicals (=TICs) in CBRNe scenarios, owing to their high sensitivity, fast sensor response as well as attractive manufacturing costs. These sensors can detect a wide range of TICs and gases in the trace range while offering a rapid and cost-effective detection, making them a valuable tool for first responders and emergency management in CBRNe events. In addition to the above-mentioned advantages of these gas sensors, there are also disadvantages that can be compensated by a new research approach presented in this paper, in which the use of an additional technology is investigated. Once semiconductor gas sensors are exposed to a high gas concentration, they enter a saturated state that can last for minutes and during which the availability of the measuring system can no longer be guaranteed. During this time, important events might be overseen, which might have significant consequences, especially at critical TIC concentrations. In order to ensure consistently reliable detection by semiconductor gas sensors, its sensitive layer must be restored to its initial state as fast as possible after the exposure to an analyte, resulting in a faster recovery time. Therefore, the objective of our research is to demonstrate a regeneration method for the sensitive layer, using the principle of laser cleaning as the basis for our approach. The mechanisms underlying laser cleaning are diverse and depend on the effect to be achieved. For laser desorption, the laser beam is able to transfer enough energy to the sample to heat and vaporize the adsorbed molecules of the analyte. In addition to vaporization, ionization of the molecules or atoms may also occur. These ions can be expedited off the surface, removing the molecules from the sample. For laser ablation, the laser beam may be used to blast or ablate molecules from the surface. As opposed to laser desorption, the irradiated surface is hereby fragmented by the laser beam. To prevent this, the laser energy applied to the sample should be below the ablation threshold of the sensor surface. Optimal laser and irradiation parameters for effective cleaning of semiconductor gas sensors are investigated in this research study. For this purpose, commercially available semiconductor gas sensors are exposed to solvent vapors and irradiated with the assistance of a pulsed laser. The laser parameters, such as pulse frequency and fluence, are varied to determine the optimal cleaning conditions. The cleaning efficiency is evaluated by measuring the recovery time of the sensor to a target gas before, during, and after cleaning. The optimal laser and irradiation parameters determined in this study can be used to improve the performance of semiconductor gas sensors. Various application areas and target analytes can be considered. Further research is being undertaken to advance the miniaturization of the system.