Reversible Molecular Adsorption and Detection Using Inelastic Electron Tunneling Spectroscopy in Monolithic Nanoscopic Tunnel Junctions

Monolithic nanoscopic tunnel junctions fabricated by atomic layer deposition are used to investigate the reversible adsorption and detection of a vapor phase molecule by inelastic electron tunneling spectroscopy. Molecular adsorption of acetic acid at room temperature is enhanced by a direct current electric field between the electrodes to attract and trap the molecules. Step-like features in current versus time plots are observed and assigned to discrete adsorption events. Inelastic electron tunneling spectra recorded at cryogenic temperatures match the signatures of acetic acid vibrational modes and indicate that the molecules are generally physisorbed in the junction. Annealing the tunnel junctions above room temperature desorbs molecules from the junction, and the removal of molecular features is verified by the tunneling spectra. Molecules are readsorbed in the same tunnel junctions at room temperature, which demonstrates reversible adsorption.