|
We report on the humidity-induced swelling behavior of thin film devices composed of 2D phosphatoantimonate
nanosheets and study their water uptake mechanism by means of ellipsometric porosimetry. Ambient humidity
changes cause significant swelling in thin films composed of turbostratically disordered H3Sb3P2O14 nanosheets
through water uptake between the nanosheet layers. This phenomenon is exploited to construct humidity
responsive colorimetric sensors based on 1D Photonic Crystals. We demonstrate the ultrahigh sensitivity of
H3Sb3P2O14/SiO2 Bragg stacks to ambient humidity, as well as reversible transparency switching as a
consequence of refractive index matching at high relative humidities. The Photonic Crystals show substantially
higher sensitivity to humidity as compared to ethanol vapor, reflecting the less favorable interaction of ethanol
with the nanosheet layers as compared to water. Based on their ultrahigh sensitivity to humidity,
phosphatoantimonate nanosheet based Bragg stacks can be used to track the motion of a finger by responding to
its humidity sheath, without the finger touching the sensor surface. The cycling stability of such optical touchless
positioning interfaces as well as the reversibility of the sensing event was demonstrated for more than 100
cycles. While the dew point presents an inherent lower limit to the sensor performance, the sensing ability
remains essentially unaffected at elevated temperatures up to 40 °C.
|
