Room Temperautre Hydrogen Detection with the Use of Engineered Nanostrutured Tinoxide Array

In the forefront of the challenges that are faced by the ensuing energy crisis; alternative fuel source such as hydrogen appear to be a viable substitute. All hydrogen gas related processes require accurate monitoring for leaks during storage and transportation.

The common problem that arises with the use of hydrogen is its inclination to leak along with its intrinsic capability of being highly flammable/explosive at 4 vol%. Precisely monitoring hydrogen during storage becomes imperative in industrial and general consumer applications in order to reduce the occurrence of accidents. The current sensor market includes the use of many different metal oxide sensors for use as hydrogen detectors. These chemical-resistors (chemi-resistors) function based upon the changes in conductivity due to gases chemical interaction with the sensing materials. The deficiency in most of the current metal oxide based chemi-resistors in use as detectors is that they are only applicable at elevated temperature (above 100 degree Celsius); this aids the sensor’s response kinetics by enhance kinetic interaction between gases and detector. This becomes both a safety concern due to its proximity to the highly explosive gas and also energetically inefficient. Therefore our research endeavor is to develop a low temperature, highly sensitive and robust hydrogen gas detector that operates at room temperature.

Thin film SnO₂ samples were deposited on SiO₂/Si substrates through a method of pulse laser deposition (PLD). Nano-architectured SnO₂ arrays were design with the use of nanosecond pulse laser interference irradiation of the thin films. The SnO₂ nanostructures fabricated were uniformly distributed along the surface of the substrate. Dimensions of the nanostructure were obtained through atomic force microscopy (AFM) and scanning electron microscopy (SEM). Results show that the nanoarray’s were ~8 nm in cross-sectional height and microns in length.

Tests of chemi-resistors were conducted at room temperature within the concentration limits of 300 to 9000 ppm under dynamic flow in order to simulate the actual environments that the device will experience. In comparison to SnO₂ thin film, SnO₂ nanostructured film illustrates a significantly larger drop in conductivity upon exposure to minimal concentrations such as 600 ppm. The nanostructured film exhibited (reduced resistances by 2 orders of magnitude) ~150 fold increase in electrical response (the ratio of resistance in hydrogen to the resistance in air). Calculations show that the increase is performance of the sensor is not proportional to the increase in surface area of the nanostructured array Theoretical calculation of the potential barrier generated through exposure to hydrogen enables the improved response by increasing the depth of the depletion layer. This depletion layer (volume of SnO₂ at which electrons have been strip from the conduction band) is increased in the nanostructured array hence generates larger electrical responses.

Nanostructured SnO₂’s incorporation into a microelectromechanical system platform has successfully produced a low temperature hydrogen gas sensor. The performance of the nano-architectured SnO₂ showed improved detection capability and promising applicability due to it fast response time, high electrical response and robustness. This research endeavor therefore combines aspect of interdisciplinary design and integration alongside the creation of microelectromechanical system that is capable of being applied to today’s market.