Using Carbon Laser Patterning to Produce Flexible, Metal-Free Humidity Sensors

Simon Delacroix, Anna Zieleniewska, Andrew Ferguson, Jeffrey Blackburn, Sebastian Ronneberger, Felix Loeffler, Volker Strauss

Research output: Contribution to journalArticlepeer-review

10 Scopus Citations


A relative humidity sensor was produced by carbon laser patterning of a carbon precursor ink on a flexible substrate. Citric acid and urea, both inexpensive and naturally abundant molecules, are used as initial precursors to obtain a porous carbon foam after CO2 laser irradiation. The laser-patterned material is characterized by electron microscopy, Raman spectroscopy, and vertical scanning interferometry. An intrinsic p-type semiconducting behavior was confirmed by thermoelectric and Hall measurements. The resistance of this porous, metal-free material is sensitive to atmospheric variations, namely, temperature and relative humidity (≈5 Ω·%). Under dry atmosphere, the sensor acts as a thermometer with a linear relationship between temperature and relative variation of resistance (0.07%·K−1). The evolution of the sensor resistance at different relative humidities and temperatures is studied by electrical impedance measurements. The kinetic transitory regime of water desorption from the carbonaceous surface of the sensor is analyzed using Langmuir's model. The equilibrium constant of adsorption Kads has been determined, and the standard enthalpy of adsorption of water on the sensor surface is estimated at ΔadsH° = −42.6 kJ·mol−1. The simple and inexpensive production and its high, stable sensitivity make laser-patterned carbon interesting for humidity sensing applications, and the method allows for the large-scale production of printed sensor arrays.

Original languageAmerican English
Pages (from-to)4146-4154
Number of pages9
JournalACS Applied Electronic Materials
Issue number12
StatePublished - 2020

Bibliographical note

Publisher Copyright:
© 2020 American Chemical Society

NREL Publication Number

  • NREL/JA-5900-77856


  • Carbon laser patterning
  • Carbon semiconductor
  • Humidity sensor
  • Laser carbonization
  • Laser-induced graphene
  • Sensing


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